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PHYSIOLOGY.

VOL. II.

LONDON

PRINTED RY S |M) T T I S W O O [) K AND CO.
NEW-STREKT SQUARE

» J

OUTLINES

OF

PHYSIOLOGY

HUMAN AND COMPARATIVE.

BY

JOHN MAKSHALL, F.R.S.

PROFESSOR OF SURGERY IN UNIVERSITY COLLEGE, LONDON :
SURGEON TO THE UNIVERSITY COLLEGE HOSPITAL.

k S

C 2S W

TRATED BY NUMEROUS M^OODCUTS.

>«*' r i

rC ,

IN TWO VOLUMES.

VOL. II.

r 't '■>'< '

■' ;

V

LONDON :

LONGMANS, GREEN, AND CO.

18C7.

i I

The right of trantlation in renerved.

Digitized by the Internet Archive
in 2015

https://archive.org/details/b21958580_0002

CONTEXTS

OF

THE SECOND VOLUME.

— ♦ —

SPECIAL PHYSIOLOGY—

THE VEGETATIVE FUNCTIONS.

PAGE

Digestion ........... 1

Sources, Varieties, and Nature of Human Food ... 2

Prehension and Preparation of Food 7

Mechanical Processes of Digestion . . . . .12

The Digestive Fluids ........ 53

Chemical Processes of Digestion 82

Summary of the Chemistry of Digestion .... 107

Circumstances which modify Digestion . . . .109

Eelative Value of different Foods . . . . .113

The Organs and Function of Digestion in Animals . .116

Absorption .151

The Absorbent Vessels and Glands 153

Endosmosis, Exosmosis, Osmosis, and Dialysis . . .100

General Absorption . . . . . . . .165

Absorption of the Food 174

Intrinsic Absorption . . . . . . . .182

The Absorbent System, and Absorption in Animals . . 186

CiBCniATION 187

The Heart and Blood vessels . . . . . .188

Course and Causes of the Circidation ..... 200

Action of the Heart 203

Motion of tlie Blood through the Arteries .... 222

VI

CONTENTS OF THE SECOND VOLUME.

The Pulse . . . . .

Motion of the Blood through the Capillaries
„ „ Veins

Period of a complete Circulation .

Quantity of Blood in the Body
The Uses of the Blood and its Circulation .

Organs and Fmiction of the Circulation in Animals

Nutrition

Nutrition of the Chyle

,, „ Blood

„ „ Organs and Tissues

Offices of the Blood and of its Constituents in Nutrition

Haimorrhage or Loss of Blood
Vitality of the Blood ....

The Coagulation of the Blood

Sanguification

The Blood Glands ....

The Liver considered as a Blood Gland
Glycogenic Function of the Liver
Sanguification and the Blood Glands in Animals

Secretion

Secretion in General
General Function of the Liver
The Mammary Glands and Lactation
Mucous Secretion and Mucus
Serous and Synovial Secretion

Excretion ......

The Renal Excretion .

„ „ in Animals .

Special Secretions and Excretions in A
The Skin and its Excretions
The Cutaneous Excretion in Animals

nimals

Respiration

The Organs of Respiration .

Mechanism of Respiration .

Changes of the Air in Respiration
Effects of Respiration on the Blood and Tissues
Conditions which modify the Chemical Processes
tion ........

Elfocts of Breathing other Gases than Air

of Respira

page

234

242

247

257

260

263

264

275

276

277

278
287
296

299

300

314

318

334

334

342

343
343
354
356

363

364

365
365
391
395
395
401

401

404

414?

435

444

463

469

CONTENTS OF THE SECOND VOLUME.

Asphyxia .....

Suspended Respiration and Animation
Effects of Breathing impure Air .

The Organs and Eunction of Respiration in Animals

AjtiMiL Heat, Light, and Electeicitt
Animal Heat ....

Effects of Cold on the Human Body
,, Heat ,, ,,

Theories of Animal Heat

Influence of the Nervous System on Animal Heat
Uses of Animal Heat
Hybernation
Spontaneous Combustion
Evolution of Light

„ Electricity

Statics and Dynajiics of the Human Body
Statics of the Human Body .

Specific Gravity of the Body
Height of the Body ....

W eight of the Body

Daily quantity of Food and its Composition
Relations between the Constituents of the Body and the
daily Food .......

Destination of the Food in the living Economy
Effects of Deprivation of Food
Dynamics of the Human Body ....

Measure of Heat, or Heat-Unit
Mechanical Coefficient, and Mcchiinical Equivalent of Heat
Quantities of Heat develoiied by Combustion
Cidorific Work of the Body
Daily Heat compared with the Quantity of Carbon and
Hydrogen oxidised
Mechanical Work of tho Body

Relations of the Kinds of Food to tho Modes of Work
Value of I'ood as a source of Motor Power
Transformation of Mechanical into Calorific Workin the Body
Nutritive or Assimilative Work
Electric Work
Nervous Force and Work

REPUODfCTION .....

Spontaneous Generation
VOL. II. a

vii

I’AOE

473

476

482

488

502

502

507

509

512

519

521

521

523

524
527

531

532

532

533
533

535

536
533
547
550

555

556

557

558

558

559
561
575

575

576

577
577

580

580

Vlll

CONTENTS OF THE SECOND TOLUME.

PAOE

Tli0 various Modes of Eeproduction 581

The Ovum generally 590

The Ovaries and Ova of Birds ...... 593

The Mammalian Ovaries and Ova ..... 597

The Ovaries and Ova of other Animals .... 600

Fertilization of the Ovum . . . . . . .601

Developjlent .......... 603

Changes in the 0\-um, and first formation of the Embryo . 603

General Development of the Embryo and its Appendages . 608

Development of the Organs . . . . . . .615

Development of the Tissues . . . . . . .641

Animal and Vegetable Cells 641

Development of the several Tissues ..... 646

Degeneration and Eeparation 661

Growth 664

Decay and Death 665

Index 671

SPECIAL PHYSIOLOGY.

SPECIAL PHYSIOLOGY.

THE YEGETATIVE FUNCTIONS.

The functions to be considered under this head, are the
nutritive and reproductive functions. The former include
digestion, absorption, chylification, circulation, nutrition, re-
paration, sanguification, secretion, excretion, and respiration,
together with the production of animal heat, mus9ular force,
light, and electricity.

Amongst other phenomena produced by the waste of the
solid constituents of the body, and the loss of the fluid, or watery,
part of the tissues, are the special sensations of hunger and
thir.st, which have their seat, like other sensations, in the
nervous system, and the phenomena of which have been ah-eady
explained (vol. i. p. 443 ). These sensations of appetite, excite
the desire to take food ; and by the process of digestion, the
food, thus taken, is prepared for absorption, and conversion
into blood. The term food includes all substances, received
into the alimentary canal, and used for the support of life, either
by supplying the waste constantly occurring in the living
animal tissues, or by affording materials for the maintenance
of the temperature of the body. Food, therefore, contains
substances which have a certain chemical relation to the
ti.ssues which it supports. These tissues, besides containing
water and s:iline substances, are composed of proximate or-
ganic principle.s, having a highly complex chemical constitu-
tion (vol. i. pp. 90 to 99). Food also consists, more or less, of
substances having already the same, or a similar, chemical
composition : for the animal body, so far as is known, has no
power of forming such proximate organic compounds out of

VOL. II. b

DIGESTION.

2

SPECIAL PHYSIOLOGY.

their component elements, or from the simpler combinations
of these.

Animals, indeed, are either carnivorous or herbivorous.
The carnivorous, or flesh-devouring species, obviously live
upon food possessing the same chemical composition as the
fluids and tissues of their own bodies ; and as regards the
herbivorous, or vegetable-feeding animals, their food also con-
tains proximate principles, closely resembling those which
exist in the animal body. Whatever the nature or source of
the food of Animals, its proximate principles are, therefore,
chemically similar ; and it is to the Vegetable Kingdom, that
we must attribute the power of chemically combining, under
the agency of solar light and heat, the elements derived trom the
simpler combinations of inorganic nature, into those complex
organic proximate principles which, thus elaborated in the
living tissues of vegetables, constitute the nutriment of Animals.
Hence, the Vegetable Kingdom derives its nourishment from,
and depends upon, the Mineral Kingdom ; the Animal Kingdom
derives its nourishment from, and depends upon, the Vegetable
Kingdom ; whilst the decaying portions of the Vegetable King-
dom which are unconsumed by animals, and the particles of
the bodies of animals which undergo change during life, or
decomposition after death, revert to the simpler chemical com-
pounds of inorganic nature, Avhich, again, under the influence
of the vito-chemical forces of the plant, are reintroduced into
the stream of organic existence.

Sources, Varieties, and Nature of Human Food.

The food of Man may be either solid or fluid. If solid,
it may be hard, so as to require to be broken by mastication,
or soft, so as merely to need subdivision, belbreit is swallowed.
Again, ibod may be derived from the inorganic or from the
organic world ; or it may be classified according to its source,
whether this be mineral, vegetable, or animal. Thus, the
alkaline and earthy salts, the traces of iron, sulphur, and
phosphorus, and the large quantity of water, are derived from
the mineral kingdom. Vegetable food includes the roots, stems,
leaves, Iruits, and seeds of plants; also certain products of
vinous decomposition, as the various alcoholic beverages,
and lastly, condiments, vegetable acids, and vinegar or the
product of the acetous lermentation. Animal food consists
of all the digestible parts of animals, in which is comprised

PROXIMATE CONSTITUENTS OF FOOE.

3

nearly every tissue, Avith the exception of the horny textures
and the hair, even the bones yielding nutriment on being
boiled. Besides this, eggs and roe, milk, butter, butter-milk,
curd, cheese, and whey, are comprehended in this category.

The chemical constitution of food, however, is the point to
which the greatest significance is to be attached ; and the
most useful classifications are founded on a consideration of the
different nutrient proximate chemical principles Avhich it
contains. Thus regarded, the multitudinous articles of diet
consumed by man, under his extremely varied conditions of
life, dependent on climate, social condition, national custom,
or individual habit, consist of a comparatively small number
of proximal e chemical con.stituents. The importance of these
chemical distinctions of the food, Avas clearly indicated by
Front, and has been since established by the researches of
Liebig, and many other chemists. Prout divided all nutrient
substances into albuminous bodies, such as the albumen, fibrin,
and casein of animals, and the gluten and legumin of plants \
oleaginous substances, including the animal and vegetable fats
and oils ; and sacc^a?'me matters, comprising the various kinds
of sugar. According to him, the typical form of animal food,
is that supplied, by nature, to the young of mammiferous
animals and man, viz. milk, in Avhich fluid, casein represents
the albiuninous kind of nutritive substances; butter, the
oleaginous kind; and sugar of milk, the saccharine kind.
Besides these, milk also supplies AA'ater, and the mineral matters
es.sential to the formation of the tissues.

A more exhaustive clas.sification of the nutritive substances
contained in food, is that Avhich folloAvs : —

1. A ZiMOTmoh/ substances. From the animal kingdom,
rnen, whether derived from the Avhite of eggs,from blood, or from
the muscular or nervous tissues ; syntonin, or the fibrinous ele-
ment of muscle, some of Avhich is contained in the expressed
juice of meat ; globulin, cruorin, and fibrin, from the blood ;
casein, derived from milk ; and the vitellin o\' t\\Q yolk of eggs.
The substance of the liver, pancreas, kidneys, and other glands,
is also, in great part, albuminoid, mixed, hoAveVer, especially
in the first organ, with fat. The brain substance is also highly
nutritive, containing both albuminoid and liitty matter. In
this group, must be included, not only cruorin, or the colour-
ing matter of the blood, butal.«o myochrome, or that of muscle,
both of which have an extraordinary allinity for oxygen. From
the vegetable kingdom, are obtained the albuminoid substance

u 2

4

SPECIAL PirrSIOLOGT.

gluten^ sometimes called vegetable albumen, which is chiefly
obtained from the seeds of the various kinds of corn, and other
grasses ; also legumin, which has been compared to animal
casein, and exists in large quantity in the seeds of peas, beans,
lentils, and other leguminous plants. Vegetable albumen
likewise exists, in small quantity, in the gi’owing or soft tissues
of the various succulent edible parts of vegetables and fruit,
such as the cabbage, cauliflower, turnip, apple, pear, and orange.

2. Gelatinoid substances. These, which are derived solely
from the animal kingdom, include jelhj of various kinds, ob-
tained from the gelatin-yielding tissues of animals, such as
isinglass, which is the dried sound, or air-bladder, of the
sturgeon, the areolar and fibrous tissues, tendons, and bones ;
also cliondrin, or the jelly obtained from cartilages. These
several tissues, however, are not supposed to contain gelatin or
chondrin, when in their raw or uncooked state. Gelatinoid
sub.stances are present in broths, jellies, and ivory bone-dust.
So far as their nutrient qualities are concerned, they must be
distinguished from the albuminoid substances.

3. Oleaginous substances. These comprehend the animal
fats and oils, stearin, margarin, 'pahnitin, and olein, the fatty
matters of the bile and of the brain, and those of the yolk of
eggs ; and also the fatty acids of butter, the butyric, capric, and
caproic. To these must be added, the vegetable oils, whether
solid or fluid, such as cocoa-nut oil, olive oil, and almond oil.

4. Amylaceous or starchy, gummy, and saccharine substances.
These comprehend the different varieties of starch, such as
potato starch, arrow-root, sago, tapioca, rice, and the starchy
portion of wheat and other grain. The gummy substances
include, besides all the natural gums and mucilages of fruits and
vegetables, the substance named dextrin, which results from the
transformation of starch, cellulose or lignin, and also pectin, a
constituent of succulent vegetables. The sugars are the com-
mon, or cane sugar, and grape sugar, derived, as such, from
vegetables, or produced by the transformation of starchy or
gummy substances. There are also the sugar of honey, which
is an animal prejiaration ; the glycogen, or animal starch, often
present in flesh, but chiefly found in the subsfimce of the liver ;
inosite, or sugar of muscle ; and lastly, the sugar of milk,
lactose, or lactin, which, though usually formed in the animal
economy, can also be artificially made, by acting upon starch
with certain acids, at a high temperature.

5. Stimulating substances. These consist of three classes :

PROXIMATE CONSTITUENTS OF FOOD.

5

viz. first, the various kinds of spices or condiments, the active
properties of wliich depend usually upon volatile or essential
oils; secondly, the parts of vegetobles, whether the leaves or
berries, which contain the alkaloids, thein, caffein, or theobro-
min, which are found in tea, cotfee, cocoa, and the Paraguay
tea. With these should probably be associated, the substances
named extractives, viz. cerehric acid, which exists in nervous
substance, and also in corn, especially in Indian corn ; creatin
and creatinin, which are found in the juice of meat, in the
brain, and in the blood, the former being converted in the
system into the latter; both of these act either as stimu-
lants, or by retarding chemical change and loss in the albu-
minoid tissues. The thein and allied bodies certainly stimu-
late the heart, muscles, and nervous system. Thirdly, there
are the various alcoholic beverages made by the fermentation
of saccharine substances, such as mead, beer, cider, wine, and
the stronger alcoholic fluids or spirits distilled from various
fermenting saccharine vegetable juices. These substances are
probably not immediately nutritive, or able to supply the
waste of material, but appear rather to act as stimuli to the
neiwous system, and also by preventing waste. To these may
be added, the several ethers formed in ripe fruits, and in wines,
from the action of the organic vegetable acids on alcohol. This
class may also include certain organic vegetable acids, such as
the acetic acid of vinegar, the tartaric, malic, racemic, oxalic,
and citric, derived respectively, from grapes or raisins, apples,
gooseberries, the esculent rhubarb, and the lemon, lime, and
orange ; and la.stly, the lactic acid existing in sauer-kraut, and
in fermented cucumbers or beans, all of which are iavourite
articles of diet with some nation.s. The prevalence of the de.sire
lor acids with the food, is remarkable. Lactic acid also exists
in sour milk, which is much consumed, and in the juice of
meat, together with paralactic and inosinic acids.

fi. Saline, earthy, and mineral substances. These, which
are, in certain proportions, essential articles of food, soda for
the blood, potash for the muscles, and lime for the bones,
consist of the chlorides of sodium and pota.ssium, the phos-
jihates of soda, potash, and of magnesia, perhaps the alka-
line suljihate.s, the j)hosphate and carbonate of lime, and
o.xide ol' iron. Minute traces of manganese and silica areakso
necessjiry, the latter being probalfly combined with fluorine.
Such substances as alumina and copper, are probably adventi-
tious ingredients, and of no essential importance as food.

(i

SPECIAL rnrSIOLOGY,

7. Water is the most abundant constituent of the animal
body, and is a most essential article of food. From the many
othces which it performs, dissolving the food, rendering it
capable of absorption and entrance into the circulation,
lacilitating all nutritive, secretive, and excretive processes,
and lastly, maintaining the diie elasticity and flexibility of the
tissues, and their susceptibility of vito-chemical change.s,
water may be regarded as a common vehicle, in which all
other articles of diet are conveyed into, through, and from the
animal economy.

The albuminoid and gelatinoid nutrient substances, resemble
each other very closely in composition ; in addition to car-
bon, hydrogen, oxygen, and sulphur, they contain nitrogen, and
have therefore been named, nib'ogenous or azotised food ; and,
as these substances are especially concerned in the formation of
the albuminoid and gelatiu-3uelding tissues of the body, which
indeed cannot be built up without them, they have been desig-
nated nutritive or plastic food. Moreover, as they supplj' the
waste which takes place in the muscular and other tissues, they
have been likewise called Jlesh-foi'niing, tissue- forming, or
hi sto genetic, food. On the other hand, the oleaginous and
saccharine substances are composed of carbon, hj’drogen,
and oxj-gen only, and are therefore named non-nitrogenous
or non-azotised ^oodi. The starchy, saccharine, and allied com-
pounds, form the carbhydrates ; whilst the fatty substances,
still richer in carbon, are named hydrocarbons. As neither of
these is ever supposed to be convertible, by the addition of
nitrogen, into nitrogenous, plastic, or fle.sh-forming food, but
rather, owing to their richness in carbon and hydrogen, and
their poverty in oxygen, to be ultimately used for the
j'urposes of maintaining the animal heat, either being first
stored up in the body as fiit, or being at once oxygenated
through the respiratory process, they have been classed to-
gether under the appellation of respiratory, calorific, or heat-
forming, food.

These distinctions, Avhich have been chiefly explained and
advocated by Liebig, undoubtedly represent a general truth ;
but they must be accepted with certain qualifications. In the
first place, albuminoid substances may, it would seem, undej'go
metamorphosis, in the living body, into fatty or evcTi starch-
like substances, and so may nourish non-nitrogenous, as well
as fleshy or nitrogenous, tissues. Moreover, the nitrogenous
tissues of the living bod}-, especially those of the muscles and

PREHENSION OF FOOD.

7

brain, themselves undergo a most active waste, i.e. a chemical
decomposition, of which the essential feature is oxidation ;
so that, to a certain extent, they too, in being decomposed, must
contribute to the evolution of heat, subserve the respiratory
process, and so far act as respiratory food.

Again, chemical analysis shows, that in the brain especially,
but also in muscular tissue, fatty matter is an important
constituent, essential, indeed, to the composition of those
tissues; moreover, starchy and saccharine matters exist in
certain organs, and are convertible, in the living economj'^, into
fat; hence the non-nitrogenous, oleaginous, and saccharine
substances must, also, be regarded as nutiitive or plastic food.
Even in young growing animal cells, fatty matter appears to be
an essential element. Again, as regards gelatin, and the
gelatin-yielding tissues, which, though they contain nitrogen,
have a lower chemical constitution than the albuminoid sub-
stances, it is not certain that they are convertible into, or
capable of being made use of as, nutriment for the living
tissues. It is now generally denied that they can be so
converted into, or assimilated by, tissues which, like muscle
and nerve, contain syntonin and albumen ; it is even doubted
whether they can be directly assimilated as nutriment, even by
the living gelatin-yielding tissues themselves, which, of course,
have an identical chemical composition. Such substances may,
therelbre, possess very limited or no nutritive or plastic
qualities ; and may merely be oxidised in the .system, like
the non-nitrogenous, respiratory food. The precise destination
of the several elements of food is, however, not completely
understood ; but neither of the two kinds of food, the nitro-
genou.s, or the non-nitrogenous, is alone adequate to support
animal or human life ; for perfect nutrition, the two must be
taken together in certain proportions.

The chemical composition of mo.st of the nitrogenous and
non-nitrogenous proximate constituents of animal substances
used as food, is given in the tables at pages i)G and 98, vol. i.
The closely similar composition of the nitrogenous and non-
nitrogenous proximate constituents of vegetable substances
used as food, is illustrated in the annexed table (p. 8).

Prehension and Preparation of Food.

In the lower animals, the important act of the prchen.sion
of food, is provided for, in every case, with the most admir-

8

SPECIAL PHYSIOLOGY.

Analysis of Vegetable Proximate Constituents.

G

0

9

9

U ^

0

'C

2

bo

>»

’§.'5 « i

0

H

S

C

Ph

Vegetable Albumen . . =

5o‘01

7-23

15'92

21-84

1 included
j with the
'■ oxygen

Vegetable Fibrin or Gluten . =

Legumin, a similar compo-i
sition, but not well deter- 1

64-6

7-2

15-81

22-29

mined . . . . >

Thein, Catfein (CgH,„NjOj) . =
Theobromin (C^HgN^O^) . =

49-4

5-2

28-9

16-0

46-7

4.4

31T

17-8

1

Vegetable Oils, chiefly Oleic

acid, and Glycerin (p. 96).

i

Starch. . .)

Dextrin or Gum . ^ ,

44-4

Cellulose and Dig- [ ^ ® lo 5I

6-2

49-4

1

uin . J

j

Cane Sugar (C,,H,.,0,,). .=

42T

6-4

51-5

1

Grape Sugar, Glu- 1 /p tt p \
cose, or Dextrose J ^ s 12 e) ~

40-

6-7

53-3

Alcohol (C^HjO) .

52-2

13-

34-8

i

Ether (C,H,„0) .

64'85

13-5

21-65

Vegetable Acids :

Citric (CgH,jO,) . . =

37-5

4-2

58-3

1

Malic (C^HgOj) . . =

3o-8

4-4

59-8

j

Tartaric (C^HgOg) . . =

32-

4-

64-

j

Alkaline and Earthy Salts and

Water, the same as in Ani-
mals ; but Land Plants con-

tain mostly Potash, and
Marine Plants mostly Soda.

1

able perfection of contrh'ance. In Man, however, the arm
and liand are so wonderfully organised for other, and higher,
pvirposes (vol i. p. 239), tliat their prehensile action, in the
gathering, or preparation, of food, and its conveyance to the
mouth, are, though essential, only subordinate offices of the
upper limb. 'J'he lips and tongue, Avhich, in the Mammalia,
are devoted, mainly at least, to the taking of food, are in Man
also so emjdoyed ; but higher services are demanded of these

PREPARATION OF FOOD.

0

parts, and we are accustomed to associate their meclianism more
especially with the faculty of speech. Lastly, the jaws and
teeth, although, in animals, they freqirently constitute the
most important, and, in the case of the lo\ver Vertebrata, the
sole organs of prehension, can hardly be said to fulfil, in Man,
in addition to their proper office of mastication, a jwehensile
office in reference to the food.

As regards the prehension of food, Man appears, indeed,
almost at a mechanical disadvantage, in comparison with the
animals beneath him, so far, at least, as concerns any special
adaptation of the parts of the organism, employed for that
purpose in animals. Nevertheless, he accomplishes this act
with facility.

In the choice and selection of food, Man, guided by his
intelligence, possesses enormous advantages over the lower
animals. lie ranges through the whole domain of the organic
kingdom, and by the arts of acclimatisation, breeding, cultiva-
tion, and agriculture, has improved many species, both animal
and vegetable, which, in their wild, and uncultivated condi-
tion, are much inferior as soimces of food. The improvement
of the cereal, or corn plants, of vegetables and fruits, and of
the ox, sheep, and pig, and also the acclimatisation of many
gallinaceous birds, and the more recent results of pisciculture,
and of attempts to breed the oyster, afford proofs of this
statement.

The use of fire for the preparation of food, is, like the
employment of fire in general, peculiar to Man, who has,
indeed, been designated a “ cooking animal.” The direct
application of fire heat to food, develops peculiar empyreu-
matic flavors and odours, in the cooked substance, whether
this be animal or vegetable ; but the more important action
of heat, whether applied directly, as in roasting or baking, or
indirectly, throTigh the agency of water, as in boiling, is to
change the molar and molecular condition of the cooked sub-
stances. Thus, the albuminoid bodies are more or less coagu-
lated ; the gelatin-yielding tissues become swollen and partially
gelatini.sed ; fat-cells are ruptured, and fiits are rendered more
tluid; the various kinds of starch have their granules jmlpi-
fied, and the cellulo.se and lignin of vegetable tissue, are
broken up, so as to liberate the contents of the cells. The
general result of cooking, is to disintegrate, and separate the
animal tissues into minuter portions, and to destroy the con-
tinuity of vegetable textures. Cooking, therefore, produces

10

SPECIAL PHYSIOLOGY.

hoth physical and chemical changes in the food, the tendency
of ■which is to facilitate mastication, and the subsequent action
of the digestive fluids, thus rendering them softer and more
digestible.

Man also has discovered and employed as drinks, numerous
beverages, obtained from the natural products of nearly every
climate, by the spontaneous, or the induced, alcoholic fer-
mentation of saccharine matter, whether this saccharine
matter exist ready formed, as in the juice of the gxape, or
other fruits, or ■whether it be artificially generated by the
transformation of starch into sugar, as happens when barley is
manufactured into malt. Besides consuming the immediate
products of fermentation, in the shape of wine, beer, and other
fermented liquors, distillation is had recourse to by Man, in
order to procure, in a more concentrated state, the spirit, or
alcohol, generated in that fermentation. Man, therefore, not
only employs the art of cooking, but also the chemical 2woce.sses
of fermentation and distillation, in the preparation of food,
using this term in its widest sense. The precise destination
of alcohol in the system will be hereafter discussed.

Other beverages are made by simple infusion or decoction,
so as to dissolve out certain nutrient or stimulating substances,
as from tea, roasted coffee, cocoa, and other vegetable jwoducts.
Sugar is used in solution, in the sweetening or preservation
of fruits, in cookery, and in ^^reparing various articles of con-
fectionery; it is a highly important and useful form of food.
Common salt, being contained in the blood and tissues, is an
essential article of food. Its use as a condiment, and also as a
preservative, especially of animal substances employed as food,
is very old and general. All animals are fond of s;ilt. Its
injurious influence on the quality of the food preserved in it,
has long been recognised, the continued use of such food, in
the form of salted provisions, favouring the production of
scorbutus or scurvy. Salt hardens the muscular and other
tissues jrreserved in it, by abstracting water from them ;
with this water, which appears in the brine, the soluble
potash and magne.sia salts, as well as the creatin and other ex-
tractives, are likewise absti-acted from the meat, and pass into
the preservative liquor, thus leaving the meat de.stitute of
many alimentary principles essential to health. Indirectly, this
may be the cau.se of .scurvv ; or that di.sease may jiartly de-
pend on the direct action of the common sjilt taken in exce.ss.

The employment of vinegar as a condiment, and the use of

THE DIGESTIVE PROCESSES.

II

vegetable acids, those universally favourite articles of diet,
aid in the solution of nitrogenous food, and possibly of the lime
salts, but they can scarcely be regarded as possessing positive
nutrient properties. Other condiments, and spices, serve to
stimulate the secretion of the digestive fluids, and excite the
movements of the alimentary canal.

In the artificial preparation of food, so as to render it
soluble, or more easy of solution, we assist the digestive
function itself, which, in adapting nutrient substances, by a
series of processes, for absorption into the tissues of the body,
has, for its immediate aim, the minute subdivision and the
solution of these substances.

The process of digestion, accordingly, includes certain
mechanical and chemical acts. The former have for their
object, to triturate and comminute the food, to mix it with
fluids and with the various secretions in the alimentary canal,
to move it within and onwards through the several portions
of that canal, and lastly, to expel from the body the un-
absorbed residue. The latter are accomplished by the aid of
the various digestive fluids poured into the alimentary canal.
Considered in the order in which they take place within the
body, the several processes necessary to digestion, are mastica-
tion, or the chewing of the food, and insalivation, or the
mixing it with saliva, which occur simultaneously in the
mouth ; deglutition, or swalloiuing, iu which the food is con-
veyed through the pharynx and oesophagus, into the stomach ;
gastric digestion, which takes place in the stomach, by aid of
the gastric juice, also called chymificalion, and sometimes,
though erroneously, digestion proper, for further true diges-
tive processes occur in the intestine ; and, lastlj'-, intestinal
digestion itself, accomplished by aid of the bile, pancreatic
juice, and intestinal juice, immediately preparatory to the
proper act of absorption of the digested materials, by the
lacteals, in which they appear as chyle. Absorption of certain
constituents of tlie food, however, likewise occurs, more or less,
through the capillaries of every part of the alimentary canal.
The residue of the food, or ingesta, together with the un-
absorbed secretions, form the egesta, the e.xpulsion of which,
constitutes the function of defecation.

The mechanical and chemical processes of digestion, require
separate, and lengthened, consideration.

12

SPECIAL PHYSIOLOGY.

MECHANICAL PROCESSES OF DIGESTION.

Mastication and Insalivation.

The parts concerned in mastication, are the teeth and jauis,
the jmiscles which move the lower jaw upon the upper one,
the imiscles of the cheeks, the Ups, the tongue, and jmlate.

The teeth in Man, as in all Mammalia, are developed in two
sets ; a Jh'st, less numerous, and smaller set, known as the milk,
temporary, or deciduous teeth, and a second set, larger and more
numerous, called the permanent teeth.

The milk teeth are twenty in number, ten in each jaw. The
five teeth, in either half of each jaAv, commencing at the middle
line, consist of two so-called incisor teeth, one canine, and two
molar teeth. The formula of these teeth is thus written, —

M2 Cl 14 Cl M2
M2 Cl 14 Cl M2'

When these teeth are shed, they are succeeded, at intervals,
by the permanent teeth, which are thirty-two in number,
sixteen in each jaw, eight in either half of each jaw ; viz.

Pig. 84.

Fig. 84 Human teeth, i, lower lateral incisor, seen from behind, c, lower
canine, seen from witliin. 6, second upper bicuspid, seen sideways. »«,
second lower molar, seen from without, i', section of an incisor tooth,
showing the pnlp cavity, extending from the point of the fang, the den-
tine, or tootli substance, the enamel on the crown, and the layer of
cement on the fang, rn', section of a molar tooth, showing the same
))arts, and the pulp cavity extending into each fang. (Blake.)

commencing at the middle line, two incisoi's, one canine, two
bicuspids, and three molars. The formula of these teeth is
therefore, —

M 3_P. 2 C 1_ I 4 _C 1_B 2_ j\[ 3
M3“B2~C1"I4 Cl B2 M3'

THE TEETH.

1.3

Each tooth, fig. 84, i to in, consists of an exposed part, called
the crown or bod>/, and of a part buried in the gum and jaw,
named the root ov fang ; at the junction of the crown and fang,
is the slightly constricted ceiwix or neck. The several kinds
of teeth differ in the form of their crowns, and in the number
of their fangs ; hence their different designations. The incisor
teeth, f, have wide, thin, crowns, slightly convex in front, and
smooth or marked with longitudinal furrows, but somewhat
concave, or bevelled off, on their hinder surface ; their edges,
which, at first, present three small prominent points, are, when
worn, long, narrow, and chisel-shaped, being well adapted for
cutting purposes ; hence their name. The fang is long, single,
and somewhat compressed from side to side. In the temporary
teeth, but much more markedly in the permanent set, the
upper incisors are larger, and occupy more space transversely,
than the lower ones ; in the upper jaw, the middle incisors are
larger than the lateral ones ; in the lower jaw, the reverse is
the case. The canine teeth, c, larger and thicker than the
incisors, are distinguished by the pointed character of their
crowns, which are very convex in front, and a little hollowed
behind, and also by the great size and length of their single
fang, which presents, on its sides, a slight longitudinal furrow.
The upper canines, popularly called the eye-teeth, are larger
and longer than the lower ones, and on their posterior surface,
close to the gum, is found a minute tubercle. The groove on
the fang, and this posterior tubercle, foreshadow the subdivided
fang and double crown of the bicuspid teeth. The canine
teeth are so named from their large size in the dog, though
they are still larger in the great feline animals ; in Man,
they are more uniform in size with the neighbouring teeth,
than in the larger Quadrumana and Carnivora. From their
single point or cusp, which wears down with use, these teeth
are sometimes called the cuspidate teeth. The bicuspid teeth,
b, sometimes called premolars, because they are placed before
tlie molar.s, and also named the small or false molars, have a
double crown furrii.shed with two pointed cusps or tubercles ;
viz. an outer higher, and an inner lower, one, between whicii
is an irregular depression. The summit of the crown is quad-
rangular, and compressed from side to side, contrasting Avitli
the pointed canines, and chisel-sliaped incisors. The fiina:,
in the lower bicuspids, is deeply grooved on each side, btit iii
the upper ones, is cleft for a certain distance at the jioint. The
molars or grinding teeth, m, arc the largest of the entire set ;

14

SPECIAL PHYSIOLOGY.

the first on each side of each jaw, are the largest, and the third,
or last molars, which are also named the wisdom teeth
( dentes sapientite), Ifoni their late appearance, are the smallest.
They have a large, nearly cuboid crown. In the upper
molars, this presents four cu.sps or tubercles, placed at the
angles of the upper surface, and separated by a crucial de-
pression ; the first and second of these teeth have the internal
anterior tubercle always the large.st ; in the last upper molars,
the two internal tubercles are blended. The crowns of the
lower molars are larger than those of the upper, and are dis-
tinguished by having a fifth small cusp or tubercle placed
between the outer and inner posterior cusps, rather nearer to
the former than to the latter ; this fifth cusp is best marked in
the last lower molar tooth. The grinding surface of the
lower molars is nearly square ; that of the upper, rhom-
boidal. In the lower jaw, the two anterior molars have two
iangs, but these are broad, grooved on their surface, and
sometimes subdivided at their points. In the upper jaw, the
fangs of the two anterior molars are three in number, two
outer and one inner fang, the latter being sometimes grooved or
even subdivided. The fangs of the upper molars are more
divergent than those of the lower ones. In the wisdom teeth,
or last molars of each jaw, the fangs are generally connate or
united into a mass, showing marks of subdivision into two
Iangs in the lower teeth, and three in the upper.

The row of teeth, in each jaw, forms what is called the
dental arch. In Man, it presents a broad, even curve, the
upper dental arch being larger than the lower, so that usually
it overlaps the latter when the teeth are closed, and thus siives
the edges of the incisor teeth from unnecessaiy wear. The
upper Ifont teeth are inclined slightly forwards, and the back
teeth, outwards; whilst the lower fi-ont teeth are vertical, and
the lateral teeth directed somewhat inwards, an arrangement
which corresponds with the greater size, and the overlapping
of the upper dental arch. In Man, the entire series of teeth
are characterised by being uninterrupted by any marked in-
terval, hiatus, or diastema, and by their nearly even height,
which however diminishes slightly Ifom before backwards.
In Mammiferous animals, the teeth are either of unequal height
at different parts of the jaw, or are interrupted by larger or
smaller intervals, or diastemata.

The temporary teeth, though of course, in each case, of
•smaller size, have forms like those of the ])ermanent teeth of

THE STEDCTCRE OF TUE TEETH.

15

the same name. The crowns of the incisors are chisel-shaped,
those of the canines pointed, and those of the molars square,
and provided with several cusps. The first upper molar, the
largest of all, has three cusps, and the second four; the first lower
molar four, and the second five. The fangs of the temporary
incisors and canines, are single ; those of the lower molars are
two in number ; those of the upper, three. In both jaws, they
are more divergent than those of the permanent teeth.

The hard mass of a tooth is hollowed out, so as to form a
cavity, called the jxulp cavity, because, diming life, it contains
a soft substance named the pulp. This pulp cavity, fig. 84,
i', m', varies in shape with that of the tooth ; it occupies the
base of the crown, and is prolonged down each fang, in the
form of a small canal, which opens at the point. The pulp
consists of areolar tissue, ^supplied with vessels and nerves,
which enter at the minute opening at the point of the fang ;
it is the remains of the vascular and neiwous papilla, upon
which the tooth is originally formed.

The hard portion of the tooth surrounding the pulp, is
composed of three substances; viz. the tooth substance, ivory,
or dentine, the enamel, and the crusta petrosa, or cement (see
fig. 84).

The dentine forms the greater part of the tooth, imme-
diately surrounds the pulp cavity, and corresponds, in form,
with the tooth itself. Its hardness is owing to the large
quantity of earthy matter which it contains, its chemical
compo.sition being 72 parts of earthy to 28 of animal matter ;
whilst ordinary bone shows a proportion of 66^ to 33-^. The
earthy salts contain G6'7 of phosphate of lime, 3’3 of carbonate
of lime, 1'8 of phosphate of magnesia and other salts, and
•some traces of fluoride of calcium. The animal substance is
converted into gelatin on being boiled.

The dentine consists of microscopic tubes, called the dental
tuhuli, which have hard walls, and are embedded in an
intermediate hard sub.stance. These tubuli, originally de-
scribed by Leeuwenhoek, commence by minute orifices on the
walls of the ptdp cavity, and proceed outwards in a slightly
wavy course, close together ; they soon divide dichotomously,
and reach the superficial portion of the dentine, near the sur-
face of which they terminate in fine branches, in loops, or
in minute dilatations from which still finer branches proceed,
or else in minute dentinal cells. The diameter of the inner
or larger ends of the tubes, is about the Tj^ogth of an inch ; their

16

SPECIAL PHYSIOLOGY.

terminations are immeasurably fine. These tubuli might be
compared to extremely minute Haversian canals, their finest
terminal ramifications to the canaliculi, and the minute den-
tinal cells to the corpuscles or lacunte of bone (vol. i. p. 47).
The dentine is, indeed, regarded as modified bone. In Man,
the dentinal cells are few in number, and very minute, so that
their similarity to the lacunas of bone is not so striking as it
is in the teeth of the horse and other animals, in which they
are larger and more numerous. In the recent state, the dental
tubuli are occupied by minute processes of the tooth pulp,
which serve the piu’poses of nutrition, and perhaps also
impai-t sensibility to the dentine. The substance of the walls
of the, tubuli, is comparatively thick; its structure is not
exactly known. The intermediate hard, or so-called inter-

Fig. 85.

Fig. 85. Section of a portion of the crown of a tooth, magnified about 300
diameters, d, the enamel, composed of wavy fibres, marked witli faint
cross lines ; the surface is bounded with a fine homogeneous layer. Be-
neath the enamel, is a portion of the tooth substance, showing the ends
of tlie tubercle of the dentine, and certain irregular spaces in it.
(After Kblliker.)

tubular substance, is slightly granular, and contains the
greater part of the earthy matter. AVhen this is removed by
an acid, the softened animal basis is said, by some, to consist of
fibres running parallel with the tubes, by others, of minute
corpuscles, arranged around the tubes, and, according to ano-
ther view, of fine lameUaj disposed concentrically around the
pulp cavity, across the direction of the tubules, which are
supposed to perforate the lamella;.

The enamel, the hardest of the dental substances, and, indeed,
of all known animal textures, is the dense white coverimr, which

THE STRUCTURE OF THE TEETH.

17

jiroteots the crowns of the teeth ; it is thickest on the edges of
the incisor and canine, and on the crown of the molar teeth,
and gradually becomes thinner towards the neck, wliere it
terminates. It contains more earthy matter than any other
animal tissue, viz. 96‘5 percent., of which 89‘8 are phosphate
of lime, with traces of fluoride of calcium, 4’4 carbonate of lime,
and 1'3 phosphate of magnesia and other salts. The animal
matter amounts to 3'5 per cent., the analysis shoAving a loss of
1 per cent. (Bibra). Berzelius estimated the animal matter at
the remarkably low proportion of 2 per cent.

The enamel, fig. 85, d, is composed entirely of microscopic
hexagonal prismatic fibres, or rods, arranged closely together
upon the dentine ; they are fixed, by one extremity, to minute
depressions on the surface of the dentine, and, following a
somewhat Avavy course, present, at their oirter ends, the
appearance of a hexagonal mosaic pattern, AA-here they form
the free surface of the enamel. On the croAvns of the teeth,
the enamel fibres are vertical ; on the sides, they become first
oblique, and then horizontal. Their diameter is of fii

inch. Near the surface of the dentine, minute interstices are
found betAveen the enamel fibres, supposed to be for the purpose
of nutritive permeation. In the groAving tooth, by the action
of an acid, the enamel may be separated into its microscopic
elements, viz. into delicate prismatic nucleated cells, the Avails
of Avhich coalesce, and which form moulds for the deposit of
the earthy matter. In the perfectly developed tooth, the thin
parietes of the cells become almost, or entirely, absorbed, and
the prismatic earthy casts are blended together as the enamel
fibres. On treating a groAving tooth Avith an acid, an exceed-
ingly delicate membrane or cuticle is found, covering the entire
surface, Avhich afterAvards, becoming calcified and coherent
Avith the ends of the subjacent fibres, forms an impenetrable
protective covering to it.

The ervstn petrosa, or cement, fig. 84, i', m', is a tliin layer
of true bone, Avhich coA'ers the fang, being thinnest next to
the enamel, and thickest along the grooves and near the
point ; it becomes thicker in advanced age, and sometimes
fills up the minute opening leading into the ptdp cavity. The
crusta petrosa contains lacuna; and canaliculi ; the latter, in
the deep layers, sometimes anastomose Avith the terminations
of the dental tubuli; in its thicker portions, it contains Haver-
sian canals, surrounded l)y concentric lamella;. Its outer
surface is firndy attached to a fibro-vascular and sensitive

A'OL. u. u

18

SPECIAL PHYSIOLOGY.

membrane, called the periodontal membrane^ 'which is analogous
to a periosteum, and serves to fasten the teeth in the alveoli or
sockets of the jaw, being itself united to the periosteal mem-
brane which lines the sockets.

The dentine gives strength and .solidity to the teeth, but
being penetrated by proce.sses of the sensitive pulp, and
doubtless subject to nutritive changes, it is liable,' Avhen
exposed, to suffer pain, and to undergo a process of decay
resembling caries, which may even be repaired by an exuda-
tion of dense iiTegular dentinal substance. The dentine,
though very hard, Avould not bear constant attrition ; hence
that singularly hard organised product, the enamel, is provided
as a covering to the exposed parts of the teeth. This enamel,
however, wears down, as is Avell seen in the incisor teeth, the
primitively sharp, wavy, ornotched edge of which, soon becomes
Avorn to an even chisel-like border. The enamel often exhibits
minute fissures, and in the depressions between the cusps of the
molar teeth, deep cracks, Avhich are the usual seats of com-
mencing caries in the subjacent dentine. As life advances, the
crusta petrosa often forms little knobs of bone upon the fangs
of the teeth ; and after a certain age, a deposit, partly resem-
bling dentine and partly bone, named osteo-dentine, or secondurij
dentine, is sometimes slowly formed in the tooth cavity, whilst
the pulp itself necessarily wastes. This deposit is produced by
a conversion of the pulp, and serves to strengthen and solidify
the tooth, as its croAvn is being Avorn aAvay ; in time, hoAv-
ever, this process ends by cutting oft’ the vascular suppljr of
the prdp, and leads to that final stage, in Avhich the remaining
parts of the teeth drop out, and leave the edentulous jaAV of
old age.

The teeth of Man, and of the Slammalia generally, are not
parts of the endo-skeleton, but appendages developed in the
mucous membrane of the mouth, Avhich, like the armour-
plates of the armadillo, the Ixiny scales of the crocodile, and
the scales and spines of fislies, all appendages of the skin,
belong to the exo-skeleton, or dermal skeleton.

The mode of development of the teeth, and the manner in
Avhich the milk teeth are shed, and the permanent teeth are cut,
Avill be described in the section on Development. The period
of the cutting or eruption ofthetemporaiy teeth is as follows : —

The milk teeth begin to appear at about the seventh month,
and are completed at the e.xpiration of the second year ; but
considerable difterence exists in regard to the precise periods

THE MILK TEETH.

19

of their eruption, frequently the first teeth appearing as early
as the fifth or sixth month, and some infants being born Math
teeth. The annexed diagram shows the usual order and average
time at which the milk teeth are cut, the numbers indicating
months.

I I
I

c

AI
M

24

The lower middle incisors appear first, and generally the
lower teeth are cut before the corresponding teeth of the
upper jaw. Before the cutting of the teeth, the edges of the
jaw, previously sharp, hard, and pale, become rounded and
swollen, and of a darker colour, and the apex of the future
tooth appears, like a white line or spot, through the gum.

The milk teeth, having, for a time, fulfilled the office of
mastication, fall out, and are succeeded by the permanent set,
destined to serve the same purpose through the remainder of
life. Teeth, once formed, cannot increase in size. The milk
teeth, though sufficiently large for the infantile jaws, and
strong enough to resi.st the action of the less powerful muscles
working them against the softer food consumed in the earlier
periods of life, would not be strong enough for the fully
developed jaws and muscles, and the harder food, of the
adult. Hence, they are removed to make way for a larger
set, which also, when once formed, undergo no change in
size. Their formation, and calcification, commence, indeed, at
very early periods of life, the ossification of the first perma-
nent teeth beginning at the age of six months, and that of the
last molars, or wi.sdom teeth, at about twelve years of age ;
yet their .size is proportionate to the dimensions of the future
alveoli and jaws, and to the future wants of the still unde-
veloped adult. The formation of the permanent teeth pre-
sents one of the clearest examjjles of anticipative design in the
animal economy ; for they are laid down, and their crowns
even arc fully formed, -whilst the jaw itself is still too small

7 '
9

18

12

M

M

20

SPECIAL PHYSIOLOGY.

for their proper accommodation, and their future alveoli do
not even exist.

The eruption of the permanent teeth corresponds, generally,
■with that of the milk set. Thus, the permanent incisors suc-
ceed to the temporary incisors, the canines of the one set, to
those of the other, and the two permanent bicuspids, to the
two temporary molars. The three permanent molars on each
side are cut, like the milk teeth, directly through the gums.

The cutting of the milk teeth, is doubtless, in many cases,
though not necessarily, a painfid process ; it may even pro-
duce reflex nervous irritation, which may affect the digestive,
circulatory, or muscular systems, causing diarrhoea, fever, con-

Fig. 86. Left side of lower jaw, at the age of five years, having the bony
substance partly removed, to show the second set of teeth, forming be-
neath the temijorary or milk teeth, i, temporary incisors, c, temporary
canine, m, first and second milk molar, and first permanent molar,
i', permanent incisors, forming in recesses or sacs within the jaw, below
the milk incisors, o', permanent canine, i', permanent bicuspids, com-
mencing below the two milk molars, which they reirlace. m', second
permanent molar, rising behind the first, which is already through the
gum. Above and behind this, is the sac of the wisdom tooth, or third
permanent molar.

vulsions, or paralysis. Lancing the gums of children, affords
relief in two ways; it removes the tension of the inflamed
gums, and also leads to the formation of a yielding and easily
absorbed cicatrix, in place of the firmer tis.sue of the gums.
The cutting of the ten anterior permanent teeth, is unattended
by pain, for the crown of each, passes through an opening in
the gum, left by the shedding of a milk tooth ; but the cutting
of the permanent molar teeth, which have no precursory tern-

THE PERMANENT TEETH.

21

porary teeth, is usually a painful process, more particularly
the cutting of the wisdom teeth, the jaw and gums being
frequently so cramped, that the tooth has not sufficient room
to rise.

At about the age of live years, immediately before the shed-
ding of any of tlie milk teeth, the jaw bone contains more
teeth than at any other period of life ; for, besides the milk
teeth, all the permanent ones, except the wisdom teeth, are
found in an advanced stage of growth embedded in the bone
(see fig. 86, and description). The rudiments of the wisdom
teeth first appear about the sixth year. The order and date
of the eruption of the permanent teeth, in the lower jaw, are
expressed in years, in the annexed diagram ; the corresponding
teeth in the upper jaw appear usually, in each case, somewhat
later.

I I

^ 5-7 *

c 7-9 ^

® 9-12 ^

® 8-10

^^10-12

M 5-7

12-14
17-25

In accordance with the increased number and size of the
permanent teeth, contemporaneous alterations take place in
both jaws. In youth, the alveolar border is almost semi-
circular, but in the adult, semi-elliptical ; it is, of cour.se,
shallow in the child, and deeper and broader in the adult ; its
hinder part e.specially, enlarges for the accommodation of the
permanent molars. At first, the wisdom teeth of the upper jaw,
lie behind and above the second molars; in the lower jaw,
these teeth are embedded in the base of the coronoid processes,
but descend to their proper position, as the jaw elongates. In
the infant, the angle Ibrmed behind by the lower jaw, is verv
obtu.se ; in the adult, it is nearly a right angle ; but in old
age, when the teeth have fallen out, it again becomes more

SPECIAL PHYSIOLOGY.

obtuse. The obtuseness of this tingle, favours the approxima-
tion of the edges of the jaws in the absence of teeth, both in
infancy and old age.

The use of the incisor teeth is to seize and divide, like
scissors, the softer portions of the food. The pointed canine
teeth, stronger, and situated at the sides of the dental arches,
also cut or pierce the ibod ; whilst the bicuspids, and especially
the molars, or grinders, are employed in bruising, crushing,
triturating, and grinding it. The harder parts of our food
are broken by the lateral, or posterior, teeth only. To ac-
complish these piu’poses, the lower jaw is made moveable upon
the upper one, which has no movement, except in conjunc-
tion with the skull itself. By two projections placed at the
summit of its back part, named condyles, the lower jaw ar-
ticulates with the hinder part of two depressions in the temporal
bones, named the glenoid fossce. The condyles of the lower
jaw are flattened before and behind, and widened trans-
versely; their long diameters are, however, not quite transverse,
but are inclined backwards and inwards, so that lines passing
through them, Avould meet at a point further back in the skull.
Each condyle has a loose hinge and gliding movement, in the
corresponding glenoid fossa ; but the two together form a firm
hinge-joint, admitting also of movements, in which both
condyles glide a little forwards and backwards, out of, and
into, the fossa;. Moreover, when this motion is limited to one
condyle, the lower jaw and teeth move sideways under the
upper ones, to the right hand or to the left, the point of the
chin being carried in the same direction. For the better
adaptation of the articular surfaces, and the gi-eater security of
the joint, a biconcave inter-articular cartilage, thin or per-
forated at its centre, and thicker at its margins, is interposed
betAveen the condyle and the glenoid fossa, and is earned
with the condyle, in all the movements of the jaiv, esiiecially
in the backward and forward movements, in the lateral move-
ments, and in extreme depression of the jaw, as in yawning.
This latter motion is checked by the jitery go-maxi I lary liga-
ment. Owing to the slight sliding movement of the cartilage,
the axis of motion of the lower jaw is not at the joint, but a
little below it, in a line Avith the grinding surfaces of the
teeth.

The force employed in moving the loAA'cr ujion the upper
jaAv, is muscular, and the agents immediately concerned, are
the muscles of mastication. In opening the mouth, the loAver

THE MUSCLES OF MASTICATION.

23

jaw partly descends by its own weight ; but it is also di-awn
downwards by that portion of the digastric muscle, which
ascends from the sides of the hyoid bone, and is inserted into
the hinder surface of the front part of the lower jaw. The
platysma myoides, a muscle of the neck, may also assist in
drawing the jaw down, and so likewise do the genio-hyoid
and mylo-hyoid muscles, which ascend to it Irom the hyoid
bone, this bone being fixed by the sterno-hyoid and omo-
hyoid muscles, which ascend to it from the sternum and the
scapulfc, and also by the stylo-hyoids and the hinder portion
of the digastrics, which descend to it from the styloid pro-
cesses, and the inner part of the mastoid processes of the tem-
poral bone. The external pterygoid muscles also draw the jaw
forwards, and so aid in its opening.

The closure of the jaw is accomplished by muscular effort
only, the muscles concerned being the nrost powerful of those
of the head and face. The chief of these are the temporal
muscles, which descend from the temporal fossa? at the sides
of the skull ; each arises from the frontal, parietal, temporal,
and sphenoid bones, passes beneath the zygomatic arch, and is
attached to the so-called coronoid process, at the upper and
anterior end of the ascending part of the lower jaw, about an
inch and a half in front of the condyle or joint. The leverage
with which the.se muscles act, is greater tlian if they had been
attached nearer to the condyles ; their action is like that of a
lever of the third order, in which strength is, to a certain
extent, sacrificed to rapidity of motion. Another muscle of
mastication, on eacli side, is the masseter, a very thick and
powerful muscle, which descends from the lower border of the
zygomatic arcli and neighbouring part of the malar bone, and
is inserted into the outer surfiice of the lower jaw, near its
angle, both on its ascending and liorizontal part. Eacli of
these muscles consists of a superficial part, the lilu'es of wliich
are directed downwards and backwards, and of a deep part,
tlie fibres of which descend obliquely forwards; whilst, there-
fore, the whole mu.scle closes the jaw, the superficial part can
draw this bone a little forwards, and the deeper part, slightly
backwards. On the inner side of each a.scending portion of the
jaw, between it and the cavities of the mouth and pharynx,
are two other strong muscles, named the external and intenatl
pterij(joi(h, which proceed from the .so-called jiterygoid pro-
ces.ses of the sf)henoid l)oncs, and from the palate bones, and
pass, the external one horizontally backwards and outwards.

24

SPECIAL PHYSIOLOGY.

to the inner surface of the neck of the condyle of the lower jaw,
and the internal one, obliquely backwards and downwards, to
the inner surface of the ascending part and angle of the jaw.
The latter muscles, on each side, co-operate with the temporals
and masseters, in raising the jaw, and assist a little in drawing
the bone forwards ; but the external pterygoids are the mui^cles
chiefly concerned in executing this latter movement, as in
protruding the chin. The backward movement is accomplished
by aid of the posterior fibres of the temporal, and by the
internal pterygoids. The external pterygoid of one side,
causes the lateral motion of the bone upon its opjwsite
condyle, and the lateral movement of the chin over to the
other side. To accomplish the forward gliding movement of
the interarticular cartilage, and, at the same time, to withdraw
the two synovial membranes, situated above and below it,
from the ri.sk of pressure, certain fibres of the external ptery-
goid mu.scle are fixed to the anterior edge of the interarticular
cartilage, and also to both synovial membranes. The move-
ments of tlie masticatory muscles accelerate the flow of saliva
and mucus into the mouth.

The chief movement, employed in dividing or lacerating
soft food, is a direct ascent of the lower jaw, accomplished by
the temporal, masseter, and internal pterygoid muscles. In
crushing harder food, or in the bad practice of cracking nuts
with the teeth, the same movemeirt occurs, the substance being
placed far back between the molar teeth, not only because
these teeth are broader and stronger than the rest, but becarrse
the muscular force is used with greater effect, the nearer to
the fulcrum it is exerted. The advantage of having the molar
teeth in the part of the jaw nearest to the fulcrum, is obvious.
A simple upward movement of the lower jaw is insufficient
for the purposes of mastication ; but the necessary bruising
and trituration of the food, are accomplished by its backward
and forward movements, and especially by the lateral move-
ment, combined Avith a slight backward and forward action,
which cause a rotatory or grinding motion of the lower teeth
upon the upper ones.

IMastication is extremely important in the case of all solid,
firm, or fibrous food, as Avell as of that Avhich is hard and dry,
pre])aring it, by comminution, for the action of the digestive
fluids ; when it is hurriedly or imperfectly performed,
dyspepsia often ensues.

lu the act of mastication, the saliva plays an important

Tine MUSCLES OF THE TONGUE.

2f)

mechanical part, as, indeed, it also does in the movements of
the tongue in speecli. Poni’ed into the mouth at various
points, especially from the inner side of the cheeks near the
molar teeth, it not only lubricates the mucous membrane,
thus facilitating the reciuisite and constant motion of the food
in the mouth, and moistens the teeth, so as to prevent the
adhesion of the food by the clogging of their grinding surfaces,
but, mixed with the food, it materially assists in softening it,
and converting it into a pulpy mass, fit to pass down through
the membranous gttllet. In mastication, the food is also
mixed with a small quantity of air. It has been observed
that in the mastication of dry food, such as crusts or biscuits,
a larger quantity of saliva is, for a time, secreted than in the
case of softer food ; this is probably, in part at least, due to
the more vigorous action of the muscles of mastication, excit-
ing a general determination of vascular and nervous energy
to the parts. It was found by Bernard, in experiments made
by opening the oesophagus of a horse, that the mass of food
swallowed, was usually mi.xed with about ten times its rveight
of saliva ; when the Whartonian ducts were tied, mastication
was performed much more slowly, and the food mass, taken
from the oesophagus, was drier, though covered with mucus, and
weighed only three and a half times its original Aveight.

Certain movements, which co-operate in mastication, are
performed, within the dental arches, by the tongue, and on the
outer side of these arches, by the buccinators, or cheek muscles,
which compress tlie cheeks. These movements serve to place,
and liold, the food betAveen the teeth, to turn it, so that fresh
portions may be subjected to the pressure of the teeth, and,
finally, Avhen it is fully masticated, to push or AvithdraAv it
from between the teeth, so that it may be SAvallowed. The
tongue also aids in crushing soft masses of food, and forming
them into .suital)le boluses to pass into the jdiarynx and gullet.

The toufiue is a muscular organ, composed of tAvo symme-
trical halves, separated from each other fiy a median fibrous
septum, and covered by mucous mend)rane and a submucous
fibnnis stratum. The muscles of this oi'ga7i are exim'nsic and
intrinsic. The former ]iass into the tongue, at its base and
under surface, and connect it Avith neighbouring ]>arts ; they are
four in number in each half of the tongue, viz. the hi/o-glossus,
the fienio-lri/o-filo.s.sus, the sl/ilo-r/lossus, and the palato-f/lossus,
so named from their respective bony attachments. A few
fibres of the superior constiuctor muscle of the pharynx, are

26

SPECIAL PHYSIOLOGY,

also connected with the side of the tongue. The wtrinsic, or
proper muscles of the tongue, are the superior longitudinal, the
inferior longitudinal or lingualis, and the transverse.

The ligo-glossus is a thin quadrilateral muscle, which, aris-
ing Irom the hyoid bone, passes upwards to the side of the
tongue, to be inserted between the stylo-glossus and the
lingualis. Beneath the hyo-glossus, is a flat triangular muscle,
the genio-hgo-glossits, the ajiex of which arises from the inner
surface of the anterior portion of the lower jaw, its base being
inserted into the hyoid bone, a small portion of the pharynx,
and the entire length of the under sirrface of the tongue. The
stglo-glossus arises from the styloid process of the temporal
bone, and divides into two portions on the side of the tongue,
one, longitudinal, blending with the lingualis, the other,
oblique, decussating with the hyo-glossus. The palato-glossus,
which, as previously mentioned, forms, on each side, the anterior
pillar of the soft palate, passes from the soft palate to the .side
and upper surface of the tongue, where it joins the fibres
of the stylo-glossus.

Of the intrinsic muscles, the superior longitudinal muscle
occupies the upper surface of the tongue, close beneath the
mucous membrane, extending from its apex to the hyoid
bone ; .some of the fibres are longitudinal, others oblique ;
many of them are branched or undergo subdivision, and
are connected, at intervals, with the submucous and glan-
dular structures. The inferior longitudinal, or lingualis,
muscle reaches from the apex to the base of the tongue, lying
between the hyo-glossus and the genio-hyo glossus, blending
iiuteriorlv with the fibres of the stylo-glossus. Between the
superior longitudinal and the lingualis, are placed the trans-
verse fibres ; internally, these are connected with the median
lilirous septum, and, pa.ssing outwards, they are inserted into
the dorsum and margins of the tongue, where they intersect
the other muscular fibres. These transverse fibres form the
greater portion of the substance of the organ ; they are inter-
mixed Avith a considerable quantity of fat.

From the varied course of its comjioncnt fibres, the tongue
possesses the porver of movement in all directions.

For the act of sucking, the tongue is especially important.
The lips of the infant being closely applied to the breast, the
tongue is drawn back, and the threatened A'acuum in the
mouth is filled with milk, forced in by the atmosjdieric
pressure on the breast, as well as b}^ the ela.sticity of the

THE FAUCES AND PALATE.

27

distended ducts of that organ. By means of the palate, uvula,
and posterior pillars of the fauces, the respiratory passages
through the nose and pharynx are shut off, so that air cannot
enter the mouth by that path, and, moreover, respiration is
not hindered, until the act of swallowing takes place. Drink-
ing, with the lips closed on the rim of any vessel, involves a
similar mechanism ; but the fluid is often allowed to enter the
mouth by its giaivity only. In sipping, the fluid is drawn in
by an inspiratory movement ; and, most commonly, the act of
drinking is performed partly by sipping, and partly by pour-
ing the fluid into the mouth. In drinking from a stream, the
lips are protruded and submerged, and a combination of suck-
ing with oral inspiration, takes place.

Deglutition.

Deglutition, or the act of sivalloiving, is that mechanical
process, by which the food is passed from the mouth, through
the opening called the fauces, into the pharynx, and thence
along the gullet, into the stomach. This act is usually de-
scribed as consisting of three stages : — first, that in which the
food is forced backwards from the mouth, through the fauces,
into the pharynx ; secondly, that in which it is made to
traverse the middle and lower part of the pharynx to the
gullet ; and thirdly, that in -which it descends along the gullet,
and enters the stomach.

The first stage of deglutition is performed by aid of the
tongue, the hinder part of the hard palate and the soft palate,
together Avith the so called pillars of the fauces. The hard
palate is formed by parts of the superior maxillary and palate
bones, covered by perio.steum and a dense mucous membrane.
The .soft palate descends, like an apron, from the posterior
border of the hard palate, and forms the upper margin and
sides of the opening, seen on looking into the mouth, called
the fauces. The arched border of this opening, forming the
isthmus of the fauces, jwesonts, in the middle line above, the
pendulous body, named the uvula. Two prominent ridges on
each side, are called the pillars of the fauces ; the anterior
pillars pa.ss down on the sides of the tongue, the posterior
pillars, on the sides of the pharynx ; between the two jhllars,
on each side, is a depression, in Avhich are lodged the soft, pro-
jecting, oval, or almond-shaped, somewhat rugose, glandular
bodies, named the amygdala; (almonds), or tonsils. The.se

SPECIAL PHYSIOLOGY.

2i

bodies present a number of follicular depressions, the sides of
which are surrounded by small closed spherical sacs, analogous
to those of the so-called Peyer’s patches in the intestines ;
they have thickish walls, lined by an epithelium, and contain
a tenacious greyish Avhite secretion ; sometimes they open on
the surface.

The mucous membrane of the under surface of the soft
palate, is covered with a squamous epithelium, and possesses
numerous compound racemose mucous glands. The mucous
membrane of the upper surface, turned towards the superior
])art of the pharynx, is continuous Avith that of the nasal
ibs.sEe, and, near the openings of the Eustachian tubes, has a
ciliated columnar epithelium. Between the two layers of
mucous membrane, which join at the free border of the soft
palate, are found, besides areolar tissue, bloodvessels, lym-
phatics, and nerves, a number of symmetrical muscles, by
means ol' Avhich, the soft, jAendent, valve-like palate, is
rapidly moved in Amrious directions. Thus, the palate and
uvida are raised by the levator a thin sheet of mus-

cular substance, Avhich descends from the petrous part of the
temporal bone and from the Eustachian tube, to the back ot
the soft palate ; moreover, two small auxiliary muscles descend
Avithin the uvula, constituting together the so-called azi/{/os
uvula muscle, Avhich elevates the uvula. Descending from the
pterygoid processes of the sphenoid bone, and from the Eusta-
chian tube, on each side, is a muscle, terminating beloAv, in a
little tendon, Avhich turns beneath the hamular, or hooked-like
end of the pterygoid process, and so, changing its direction,
spreads out toAvards the middle line Avithin the soft palate, and
unites Avith its felloAV of the ojjposite side. This muscle,
acting from its point of reflexion over the hamular process,
tightens and spreads out the soft palate, hence its name,
circiatijlexus, or tensor palati. The two pillars of the fauces,
on each side, likeAvise contiiin small muscles ; those Avithin the
anterior pillars, are named, from descending to the tongue, the
])aJato-glossi muscles ; and those Avithin the po.sterior pillars,
from passing to the sides of the phai'ynx, the palato-pliari/ngei
muscles. These muscles draw the soft palate doAviiAvards, and
either baclvAvards or forwards, in the direction of the tongue or
palate; by their joint action on the two aides, they also con-
tract the aperture of the fauces to a triangular fissure, Avhich
can then be conqiletcly closed by the uvula. By the variously
combined actions of the surrounding nuisclos, the fauces can

THE ntARYNX.

29

be closed, whether the palate be drawn upwards or downwards.
By the approximation of the posterior pillars to the uvula, and
by the simultaneous elevation of the palate, the middle part
of the pharynx can be shut off from its itpper part, so that
this latter, or the respiratory, portion, which communicates witli
the nasal fosste, is separated from the middle part, through
which the food has to descend.

In the first stage of deglutition, the lower jaw is raised, the
moitth is closed, and its cavity made smaller; the mass of food,
sufficiently masticated, and softened by the saliva, is placed
between the tongue and the hard palate, and is then pressed
backwards, by a movement of the tongue, beneath the slightly
sloping soft palate, which is rendered tense by the circitmfie.x
muscles. The anterior pillars of the fauces are separated, to
receive the mass, whilst the posterior pillars and the nvula, by
being elevated and approximated in the manner just described,
shitt off the upper part of the pharynx and the posterior nasal
openings. The tongue, becoming shorter and thicker, its pos-
terior part is rendered convex, and, by means of the mylohyoid
muscles, which form the muscular floor of the mouth, and also
by the digastrics, stylohyoids, and thyrohyoids, is then forced
upwards and backwards, and following the mass of food, propfds
it, through the fauces, into the middle portion of the pharynx ;
thus is completed the first stage in the act of deglutition.

The second stage of deglutition is performed through, and
by, the pharynx. This is a musculo-membranous sac, or bag,
about 4^ inches in length, and wider above than below,
which is suspended from the ba.se of the skull, in front of the
vertebral column, and behind the cavities of the nose, mouth,
and larynx, with all of which it communicates. It is through
the larynx, that the air passes to and from the lungs. On a
level with the lower border of the larynx, the pharynx be-
comes continuous with the oesophagus, or gullet. The pharynx,
fig. 87, has seven openings leading into it. At its upper part
in front, are the two posterior narcs, n, or nasal openings ; at
each side, are the apertures of the Eustachian tubes, which lead
to the tympanic cavities of the cars ; these four openings arc
above the level of the soft palate. Below the soft palate, p,
the pharynx opens, by the isthmus of the fauces, into the
mouth ; lower down, beyond tlie root of the tongue, is the
opening, e, into the larynx, I ; at its termination, is that
leading into the oesophagus, o. The walls of the pharynx
consist chiefly of three pairs of, so-called constrictor, muscles.

30

SPECIAL PHYSIOLOGY.

supported by areolar tissue, and lined throughout by a mucous
membrane, continuous with that of the nasal cavities, Eusta-
chian tubes, mouth, larynx, and gullet. The constrictor
muscles, named, from their relative positions, superior, middle,
and inferior, overlap each other from below, that is, in the
opposite direction to the slates of a roof, the inferior muscle
being external to the middle one, and the middle one external
to the upper one ; the superior muscle, which is open in front.

Fig. 87.

Pig. 87. Back view of tlie pharynx and part of tlio oesophagus, suspended
from the base of tlie skull, and laid open behind, n, openings of the
nasal cavities, called the posterior nares, separated by a median septum.
p, soft palate, with the uvula depending from it, in the centre. Below
this, the arches of the fauces, bounded by its posterior pillars : beneath
this arch, is seen the back of the tongue, e, the epiglottis, or valve
which protects the superior aperture of the larynx. I, the back of the
larynx, seen in the opened Jjart of the oesophagus, o, the oesophagus.
t, the trachea, or windpipe.

is, therefore, embraced, at its lower end, by the middle muscle,
whilst this again is embraced by the inferior constrictor.
Considered together, these constrictor muscles are attached,
above, to the ba.se of the skull ; in front and at the sides, to
various parts of the bones of the skull and face, and also to a.
fibrous band ])assing from the styloid process of the temporal
bone to the lower jaw; still lower down, to the side of the

SECOND STAGE OF DEGLUTITION’.

31

tongue, to tlie styloliyoid ligament, and the hyoid bone ; and,
lastly, to the thyroid and cricoid cartilages of the larynx.
Posteriorly, the fibres of the constrictor muscles, sweeping
backwards in a curved direction, meet at a raphe, or median
line, along the back of the pharynx. Spreading out on each
side of the pharynx, is the styio-pharyngeus muscle, which
descends from the styloid process, and also the 'palato-
jiharipujeus, which passes down in the posterior pillar of the
fauces. The upjier portion of the pharynx, above the level of
the soft palate, is exclusively respiratory, and its mucous
mendjrane is covered with a columnar ciliated epithelium ;
the middle portion, through which not only air, but food and
drink pass, and the lower portion below the laryngeal aper-
ture, which is devoted exclusively to the passage of food and
drink, are covered with a squamous non-ciliated epithelium.
Numerous simple and compound racemose mucous glands
open upon the pharyngeal mucous membrane, and moisten it
with their secretion.

In the second stage of deglutition, the softened mass of food,
forced, by the backward movement of the tongue, into the
middle portion of the pharynx, is compressed, in rapid succes-
sion, from above downwards, by the lower fibres of the supe-
rior constrictors, and more especially by those of the middle
and inferior constrictors, and thus is jwopelled ragridlg into
the upper end of the gullet. At the same time, the upper fibres
of the superior constrictors, and especially the fibres of the
stylo-pharyngei muscles, draw upwards, and somewhat out-
wards, the pharyngeal walls over the mass of food, as this is
forced downwards. The super-position of the constrictors,
one upon the other, from above downwards, facilitates the
propulsion of the food in that direction ; moreover, the food
itself meets with no obstruction from the edges of the two
lower constrictors, as would have been the case, had the im-
brication of the muscles been in the opposite direction. The
second stage of deglutition is rapidly performed, because re-
spiration is suspended during its occurrence. Provision must
also be made, during this .«tage of deglutition, for the safe
transit of drink and food through the pharyn.x into the gidlet,
without any drop or particle being forced upwards into the
nasal fossae, where it would excite irritation, or downwards
into the laryn.x, whence it would descend into the windjnpe,
and cause coughing, difficulty of breathing, or suffocation.
The posterior narcs are accordingly protected by the elevation

32

SPECIAL PHYSIOLOGY.

and tension of the soft palate above the middle portion of the
pharynx, in the mode already described (p. 29), so as to form
an inclined plane, beneath which the food glides into the
pharynx, as this ascends to I’eceive it. At the same time, the
opening into the larynx is protected by the epiglottis, a leaf-
like valve, situated at the root of the tongue (vol. i. p. 250),
fig. 87, e, fig. 9, e. This valve, in the ordinary condition of the
parts, stands erect, with its fi’ee margin directed upwards ; the
laryn.x then communicates with the middle portion of the
pharynx, and air can ]tass from the nose, and mouth, if that
be open, to and from the windpipe and lungs. When, how-
ever, the tongue is raised, and pressed backwards at the end
of the first stage of deglutition, the larynx is elevated, and the
mass of food, or the portion of liquid, then swallowed, presses
the previously erect ejnglottis downwards and backwards,
so as, together with certain folds of the mucous membrane
connected with its borders, completely to close the opening
into the larynx, whilst the food or drink is passing by it, into
the lower portion of the pharynx. The moment the solid or
fluid has thus passed down, the tongue resumes its previous
position, the epiglottis is again erected by the elastic Iblds
connecting it with the anterior part of the larynx and root of
the tongue, and the air passage is once more free for the
purposes of respiration.

The third stage of deglutition is performed by aid of the
muscular walls of the gullet or oesophagus. This musculo-
membranous tube is that portion of the alimentary' canal,
which extends fi-om the pharynx down to the stomach. It
mea.sures about nine inches in length, and is the narrowest
part of the alimentary canal, being itself narrowed at its lower,
but narrowest at its upper end. It descends through the
lower part of the neck and through the whole length of the
thorax, and then, perforating the diaphragm, opposite the
ninth dorsal vertebra, enters the abdominal cavity, and imme-
diately opens into the stomach. It is supported ujion the
vertel)ral column, being placed between the carotid arteries,
and behind the trachea, the heart, and the arch of the aorta ;
below the latter, it lies in the space between the two jdeura’, to
the right, and then in front, of the descending aorta ; it
traverses the diaphragm through a special opening, named
the oesophageal opening. The walls of the oesophagus are
composed ol‘ three coats, muscular, areolar, and mucous.

The muscular mat con.sists of an external layer of

TiriRD STAGE OF DEGLUTITION.

33

fibres, and an internal layer of circular fibres ; at the upper
end of the oesophagus, these fibres are chiefly striated, and
striated fibres are to be found in smaller numbers even down
to its lower end ; but the great mass of the muscular coat
consists of the plain, or unsti'iped, muscular fibres. The areolar
coat is a soft distensible tunic, which supports the mucous
coat. The mucous coat, reddish above, and pale below, is
thick, and when the oesophagus is closed, it is thrown into
numerous longitudinal plicae ; in this state, a section across the
tube presents no cavity, but, in its centre, a radiating or
branching cleft, formed by the meeting of the plicated folds.
The pharynx is permanently open, as far as the aperture lead-
ing into the larynx, but its lower portion, and the whole length
of the oesophagus, are habitually closed, their sides being always
in contact, excepting when solids, fluids, or gases are passing
through them ; they are examples of what are called jiotential
cavities. When, however, any solid or fluid is passing down
the oesophagus, the longitudinal plicae of its mucous coat are
obliterated. This membrane is beset with papillae, and covered
with a many-layered squamous epithelium, which, at the lower
end of the oesophagus, at the line of jmiction with the stomach,
abruptly changes its character, and presents a crenulated
border. The mucous membrane of the oesophagus is provided,
especially at its upper and lower ends, with small compound
mucous glands.

In the third and final stage of deglutition, the food, pressed
down by the muscles of the phaiynx, fir.st distends the walls
of the oe.sophagus, the muscidar coat of which, however, speedily
contracts above the morsel, and so urges it further downwards ;
the part thus dilated, then contracts above the mass of food,
which is thus driven on, and so, by a succession of similar
acts, is propelled, in separate portions, into the stomach. This
successive contraction of the muscular coat of the oesophagus,
from above downwards, is called vermicular ov peristaltic. Thci
circular fibres contract, in a wave-like manner, from above
downwards, and are the propulsive agents; whilst the longitu-
dinal fibres, drawing up and widening the walls of the oesopha-
gus, over the sides of the morsel of food, facilitate its descent.
Gravitation, though it may assist, has but little inlluencc on,
the downward movement of food or li([uids. The resistance to
be overcome, is slight, consisting only of the clastic pressure
of the walls of the ocsojdiagus and of the surrounding ])arts.
Solid substances, and even flnids, are habitually swallowed by
VOL. II. u

34

SPECIAL PHYSIOLOGY.

the horse and other animals, against the force of gravity; and
certain clowns can perform the feat of eating and even drink-
ing, whilst “ standing upon their lieads.” The rate of motion of
food through the cesophagus, is not so rapid as that through
the pharynx. Ordinarily, the movement causes only a alight
sensation at the upper end of the oesophagus ; but if the morsel
be too large, the act is painful, especially as the mass is passing
through the diaphragmatic oesophageal opening. As the oeso-
phagus receives fibres coming from the spinal accessory nerves,
but reaching it through the pneumogastrics, division of the
latter in the neck, paralyses the lower part of this tube, so that
the food remains in it, and distends it. It also receives sympa-
thetic nerve fibres.

The three stages of deglutition are distinguished from each
other in a remarkable manner, according to the mode in which
they are regulated, or governed, through the nervous system.
The_^rs< stage is voluntary, we place the food between the
tongue and the palate, and, by an effort of the Avill, pass
it backwards through the fauces, into the pharynx. E^^en
the accompanying movement of the soft j^alate, to shut ofl'
the nasal fossae, Avhich is an associated movement, so deter-
mined by habit as to be unconsciously performed, is neverthe-
less a voluntary movement, or at least one Avhich, by trifling
practice, may be voluntarily performed. The second stage is,
however, Avholly involuntary and automatic, and is performed
through the intervention of a reflex action, though it may be
partly imitoted by the Avill. No sooner has the food reached
a certain part of the fauces, than it excites afferent neiwes dis-
tributed to that part, the impressions on the fibres of AA’hich,
being conveyed to a certain neiwous centre, are reflected,
through efferent fibres of other nerves, to the Amrious and
numerous muscles required to contract ; and, by the simul-
taneous action of these, this stage of deglutition is rapidly
performed. Whilst, then, the first stage, Avhich inA'olves no
obstacle to respiration through the nose and pharjmx, is volun-
tary and deliberate, the second stage, during Avhich respi-
ration must be suspended, is involuntary and rapid, and, more-
over, is not entrusted to movements requiring practice, habit,
or attention, to ensure their perfect co-opei'ation, but is per-
formed as promptly, efficiently, and safely, the first time by the
neAV-born infant, as at any after period of life. The accidental
passage of food or drink into the air-passages, Avith its accom-
panying inconveniences, incidentally proves the advantage of

THE STOMACH.

35

the perfect performance of this movement. The afferent nerves
concerned in this important reflex act, are those supplying the
mucous membrane of the fauces and neighbouring joarts of the
pharynx, viz. the palatal branches of the fiftli pair, and, chiefly,
the pharyngeal branches of the glosso-pharyngeal and pneumo-
gastric nerves ; the efferent or motor fibres are contained, some
in the former, but mostly in the latter nerves, being, however,
derived partly from the spinal accessory nerves (vol. i. p. 336).
Some also belong to the hypoglossal, which governs the move-
ments of the tongue, and certain muscles of the neck ; to
the facial nerve, which supplies the digastric and stylohyoid
muscles ; and perhaps a few to the cervical spinal nerves. The
reflex nervous centre is situated in the medulla oblongata, and
upper part of the spinal cord. The f/iird stage of deglutition
is also entirely involuntary, and chiefly, if not wholly, reflex.
The afferent fibres concerned, are contained in the oesophageal
branches of the pneumo-gastric nerves, and the efferent fibres
are included in the same branches, derived partly, however,
from the spinal accessory nerves. It is supposed by many,
that the non-striated muscular fibres of the oesophagus, may be
directly stimulated by the substances swallowed, without the
intervention of any reflex nervous action.

Movements of the Stomach.

The stomach, figs. 13, 89, s,the dilated part of the alimentary
canal, into which the ccsophagus opens above, and Irom which
the small intestine leads below, is a musculo-membranous bag,
of a peculiar .shape, extending across the abdominal cavity,
from left to right, in front of the vertebral column, just below
the diaphragm and liver, immediately behind the anterior wall
of the abdomen, and above the transverse colon. It is some-
what pear-shaped, the wider end, fundus or cardiac end, fig.
89, 0, being turned to the left side, and the smaller ov pyloric
end, p, which ends in the small intestine, being turned to
the right .side. The oesophagus enters the stomach a little to
the riglit of the cardiac end. The upper border of the stomach
is concave, and is named the lesser curvature ; the lower
border, convex, is called the yreater curvature-, the left end ol'
the stomach, beyond the entrance of the oesophagus, is named
the (jreat cul-de-sac, and a slightly dilated part of the convex
border, towards the left end of the stomach, is called the lesser
cul-de-sac. After death, the human stomach sometimes has

SPECIAL PHYSIOLOGY.

.“IG

an hour-glass form, being constricted across its middle, or
somewhat nearer its pyloric end. The stomach has tAvo aper-
tures, one named the oesopharieal or cardiac opening ; and the
other the pyloric opening. It is attached, by its cesophageal
end, to the diaphragm, and, by its pyloric end, to the back of
the abdomen ; the lesser curvature is attached, by a double
fold of the peritoneum, or lining membrane of the abdomen, to
the under surface of the Ihmr ; the left end, or great cul-de-sac,
of the stomach, is connected, by a similar fold, Avlth the spleen,
and the greater cmwatiue is loosely attached, by like folds,
to the transverse colon. The greater curvature is the most
movable part of the organ, rvhich, rvhen empty, is flattened on
its anterior and posterior surfaces ; but, as its cavity is filled, it
is tilted forwards and upwards, so that its anterior and posterior
surfaces are then turned, respectively, oblicprely upwards and
forwards, and downwards and backwards, the oesophageal and
pyloric ends remaining almost stationary. The .stomach de-
scends with the diaphragm during inspiration, and ascends in
expiration ; its state of distension affects the cavity of the
chest, and, when over-distended, causes dyspnoea and palpitation
of the heart.

The capacity of the stomach is most A'ariable, ranging from
complete emptiness, with its walls in contact with each other,
to a condition of full distension, in which it may hold three
pints. When moderately full, it measures 12 inches in length,
by 4 in diameter. Its weight is about 44-ozs..

The membi'anous Avails of the stomach consist of four coats,
Auz. commencing from Avithout, the se?’0vs, muscular, areolar,
and mucous coats, all of Avhich are held together by a more
or less extensible areolar tissue. The serous coat, thin, trans-
parent, and smooth, is a part of the peritoneal lining of the
abdomen ; the anterior and posterior surfaces of the organ, are
covered by distinct layers of the peritoneum, Avhich, leaving
it along its greater and lesser curvatures, become applied to
each other, to form the double supporting folds named omenta,
by Avhich the stomach is held in connection Avith other parts.
The serous coat is elastic, and thus accommodates itself to the
variable state of distension of the organ, Avhich is also facilitated
by a loose inter-space bettveen the tAvo jtcritoneal layers along
its curvatures. The muscular coat, to Avhich the serous coat
adheres by fine areolar tissue, contains three layers of libre.s,
named, from their direction, longitudinal, circular, and oblique.
The longitudinal fibres, which are next beneath the serous coat.

THE COATS OF THE STOMACH.

37

are continuous with the longitudinal fibres of the oesophagus ;
they spread out over the stomach, being accumulated in gi-eat
numbers along the lesser curvature, in smaller numbers along
tlie greater curvature, and only thinly scattered upon the
anterior and posterior surfaces of the organ. At the oesopha-
geal opening, they form the so-called stellate and, at the

pylorus, they are again disposed in a uniform layer, and become
continuous with the longitudinal fibres of the small intestine.
The circular fibres, internal to the longitudinal ones, form
thin circular fasciculi at the great cul-de-sac, and surround the
whole extent of the stomach up to the pyloric end, Avhere they
are collected into a dense ring, Avdiich projects inwards, and
forms an annidar sphincter muscle. This projecting ring.

Fig. 88.

Fig. 8S. Vortical section through the pyloric end of the stomach, and the
curved part of the duodenum, to show the circular fold, or annular valve,
at the pylorus, s, small part of the stomach, d, part of the duodenum,
p, the pylorus, or pyloric opening of the stomach, with its annular
valves, a, ends of the common bile duct, and the hepatic duct, entering
tlie left side of the bend of the duodenum, to o])en internally by a
common orilico. Much reduced in size.

covered, on its interior, by the mucous membrane, constitutes
the pylorus or pyloric valve (ttuAj/, a gate)^ fig. 88, p, the
mu.scidar fibres of which can partially, or completely, close the
pyloric aperture of the stomach. The ohlujue muscular fibres
do not, like the longitudinal and circular set, to which they
are internal, extend over all parts of the stomach ; from
around the oesophageal opening, where they are continuous
Avith the circular fibres of the ocsoi>hagu.s, and form a sort of
sphincter, they may be followed lor a .short distance on the
great cul-de-sac of the stomach, s[)reading obli(|ucly down-
wards on its anterior and posterior surfaces. The muscular

38

SPECIAL PIIYSIOLOGT.

fibres of the stomach are pale, and, for the most part, non-
striated, tliough a few, in the longitudinal layer, present traces
of indistinct stride.

The areola?' coat of the stomach, sometimes called, from its
position, the submucous coat, consists of dense areolar tissue,
containing some fatty tissue, and a delicate layer of unstriped
muscular fibres. It supports the mucous coat, and, like it, is
of greater extent, and less expansible, than the muscular and
serous coats ; with the muscular coat, it is connected by very
loose areolar tissue, so that in the empty condition of the
stomach, it is thrown, together Avith the mucous membrane,
into numerous irregular, but chiefly longitudinal, folds, called
rugce. The bloodvessels, lymphatics, and nerves, belonging to
the mucous coat, subdivide in the areolar coat, before they
enter the mucous membrane. From the number of vessels
in it, the areolar tunic was formerly named the vascular
coat, and from its white colour, the nervous co;it; both terms,
hoAvever, are objectionable. Its muscular fibres are sup-
po.sed to assist, by their contraction, in the process of absorp-
tion.

The innermost, or mucous coat of the stomach, is a soft, pulpy,
smooth, membrane, of a pale straw colour, after death, but of
a pink, or bright red, hue during life, being much darker
during digestion. It is habitually moistened Avith mucus. It
adheres firmly to the areolar or submucous coat, and folloAvs
the folds or rufjee seen in the empty stomach, but Avhich are
completely obliterated, Avhen this organ is distended. The
mucous membrane is proAuded Avith multitudes of glands, to
be hereafter described, Avhich secrete the gastric juice. The
bloodvessels and lymphatics are numerous. The nerves of
the .stomach are derived, partly from the large terminal branches
of the pneumogastric or vagi nerve.s, Avhich are joined by the
splanchnic branches of the sympathetic, and partly also by
the sympathetic branches, proceeding along the arteries from
the cceliac or solar jilexus.

The stomach is a dilated portion, or diverticulum, of the
alimentary canal, intended for the reception and retention of
successive portions of fluid, and of masticated and insalivated
solid food, in order that Avhilst the Avatery and dissolved parts arc
absorbed, the solid substances may be subjected to the action
of the gastric juice. Besides the.se purposes, for Avhich itis fitted
by the extensibility of its serous and muscular coats, and by
the loose rugte of its less exjxinsible submucous and mucous

THE MOVEMENTS OF THE STOMACH.

3'J

tunics, the stomach also, by aid of its muscular fibres, im-
presses peculiar movements upon the food in its interior, and
urges onwards through the pylorus, into the small intestine,
those portions which are sufficiently softened and digested by
the gastric juice. In these movements, the longitudinal fibres
shorten the stomach ; the circular fibres lessen its diameter,
acting peristaltically from its cardiac onwards to its pyloric
end, whilst the oblique fibres draw the sides of the organ over
the alimentary mass. When the stomach is empty, the several
sets of fibres contract it in every direction, some narrowing it,
and others shortening it, and so reduce it to its smallest
])Ossible dimensions. The pyloric part diminishes relatively
less than the cardiac portion. When, however, the stomach
contains food, its internal surface is kept in close contact with
this, and the different fasciculi of each layer acting con-secu-
tively,give rise to complicated movements in certain directions.
The combined result of these, is a remarkable rotatory^ or
churning, motion, which urges the food Irom the great
cul-de-sac along the lower border of the stomach, towards
the pylorus, and thence back, along the upper border to the
great cul-de-sac again, and so on : such rotation is said to
occupy from one to three minutes (Beaumont). In order to
prevent regurgitation of the food into the oesophagus, espe-
cially during effort with the abdominal muscles, the cardiac
orifice is kept closed by the circular fibres of the lower end of
the oesophagus, aided by the edges of the opening in the
tliapliragm ; the pylorus is closed by its proper muscular ring.
As the outer layer of the alimentary mass becomes digested,
and converted into a pulp, it is pressed, by the peristaltic
action of the circidar fibres, tlirough the pylorus, and escapes
at intervals, into the duodenum. As this l)ulpy portion is
expelled, iresh layers of the food mass are brought into con-
tact with the gastric walls ; towards the end of digestion,
larger quantities pass the pylorus. Whilst the jiylorus per-
mits the f)a.ss<ige out oi‘ the stomacli, of the pulpy products
of gastric digestion, such solid substances as do not yield
lo the digestive proce.ss, are not allowed to pass, apparently
because they excite the contraction of the circular pyloric mus-
cular fibres. Such sub.stances, as well as fish bones, button.s,
[)lum .stones, or other bodies accidentally swallowed, remain in
the stomach for some time after tlic evacuation of ils digestible
contents; but after a certain delay, the ]>ylorus relaxes, and
allows them also to pass into the intestinal canal. The move-

•10

SPECIAL PHYSIOLOGY.

ments of the stomach are partly reflex, being excited through
the pneumogastric nerves, as is shomr by experiments on
animals ; but it would also seem probable that a direct stimu-
lation of its muscular fibres may co-operate. The sphincter
fibres at the cardiac end, appear to be under the government
of the sympathetic nerves. It is not known whether the con-
traction of the pylorus is a reflex act.

The gastric movements aid in the function of digestion, by
rotating the food in the stomach, thus exposing all parts of the
digesting mass to the action of the gasti-ic fluid, and by
continually removing the softer parts Ifom the surface, and
expelling them gradually through the pylorus, so that fresh
portions of that surface are then exposed. The pressure
exercised upon the contents of the stomach, may further assist
in the process of venous absorption. It is to be observed,
however, that portions of food, placed in perforated metal
tubes or balls, and introduced into the stomach, are neverthe-
less digested.

Movements of the Intestines.

The intestinal canal, fig. 89, d to r, or portion of the
alimentary canal extending from the stomach downwards, is
divided into a longer and narrower part, called the small in-
testine, d to i, and a wider and shorter part, named the lai-ge
intestine, c to r.

The small intestine extends from the pylorus^, to a valvular
opening leading into the large intestine, c; it measures about
20 feet in length, and becomes somewhat, though slightly,
narrower from above downwards. This long tube lies in coils,
or convolutions, occupying the middle and lower part of
the abdominal cavity, and the pelvis, fig. 13. It is supported
by a broad double fold of the peritoneum, named the mesentery,
Avhich is attached, by a shorter posterior margin, to the back
of the abdomen, but is connected by a longer anterior margin,
Avith the back of the small intestine, so that both it and the
intestine are throAvn into folds, Avhich are capable of constant
change in form and position. The layers of the mesentery are
prolonged over the intestine, and form its outer or serous coat ;
and between these two layers, are contained the bloodvessels,
lymphatics and lymj)hatic glands, and the nerves of the intes-
tine, all of Avhich help to support this part.

The small intestine commences on the right side of the
vertebral column, beneath the right lobe of the liver, and after

THE SMALL INTESTINE.

41

undergoing its numerous convolutions, terminates in the lower
part of the right side of the abdomen. For purposes of

Fig. 89.

Fig. 89. Diagram, showing the abdominal portion of the .alimentary canal,
its subdivisions, and the general position of these in the abdomen.
the stomach, o, the o3soi)hageal, or cardiac end. p, the pylorus, d, d,
the duodenum, or first portion of the small intestine, curving from right
to left, j, coils of the jejunum, or second part of the small intestine.
i,i, coils of the ileum, or third and last jiart of the small intestine,
c, the ciecum, or first part of the largo intestine, with its vermiform
appendi.x. co, co, co, ascending, transverse, and descending iiortions of
the colon, f, sigmoid llexure of the colon, r, straight intestine or
rectum. The small intestine is seen to occupy the middle of the abdo-
men, and to be surrounded on three sides by tho largo intestine.

description, it is said to be composed of three portions:
first, of a short portion named the duodenum, d, d {duodeiii,

42

SPECIAL PHYSIOLOGY.

twelve), because it corresponds in length to the width of
twelve lingers placed side by side ; secondly, of a longer portion
named the jejunum, j { jejunus, fasting), from its being usually
found empty after death ; and, lastly, of a still longer portion
named, from its numerous coils or convolutions, the ileum, i
{eiXttv, to coil).

The duodeninn, d, d, is about 8 or 10 inches long ; it is the
widest part of the small intestine, measuring from l-^ to 1^
inches in diameter; it is also the most fixed part, having no
mesentery, the peritoneum merely covering it in front, except
near the stomach. The duodenum de.scribes a horse-.shoe like
curve, the convexity of which is turned to the right ; first it

Fig. 90.

Pip. 90. Portion of the small intestine, dissected, to show the position
of its several coats, s, the outer, smooth, serous or peritoneal coat.
m, the muscular coat, composed of an outer layer of longitudinal fibres,
and an inner layer of circular fibres, c, the submucous and mucous
coats united together. Much reduced in size.

ascends, for about 2 inches, towai'ds the under .surface of the
liver and gall-bladder; then, it descends in front of the right
kidney ; next it passes from right to left, across the second
lumbar vertebra, the attachment of the diaphragm, the
ascending vena cava, and the aorta, and jias.sing slightly uji-
wards, joins the jejunum, opposite a line corre.sponding with
the superior mesenteric artery and vein. In the concavity of
the curve of the duodemim, is placed the right end or head of
the pancreas, which is here attached to the intestine. The
common bile duct and the pancreatic duct, open into the
duodenum.

The jejunum, j, forms about two-fifths, and the ileum, i, i,

THE VALA"UL-E CONNIVENTES.

43

the remaining three-fifths of the part of the small intestine
below the duodeiiem. The jejunum occupies the middle and
left regions of the abdomen ; whilst the ileum is placed in the
middle, lower, and right regions, and, occasionally, partly
descends into the pelvis. The termination of the ileum in
the large intestine, c, is situated in the right iliac fossa. The
jejunum has thicker and dark coloured coats, and is some-
what wider than the ileum, the average diameter of the
former being li inch, that of the latter 1 inch.

The membranous walls of the small intestine are composed,
like those of the stomach, of four coats ; viz. the serous,
muscular, areolar, and mucous coats. The seroMS coat, fig. 90,

Fig. 91.

P

Eig. 01. Portion of the small intestine, laid open to show the smooth
internal coat or mucous membrane, which is here thrown into numerous
transverse double folds or ridges, which are permanent. These are the
valvulse conniventes, v. A patch of theso-callcd Peyer’s glands, or glan-
dulm agminatfc, or aggregata;, with its little component round sacs, is
shown at p. The ohlong white jiiece of card, partly covering the patch
of Peyer, and marked with an asterisk, *, shows the relative size of the
piece of mucous membrance represented in Pig. 9S.

.1, derived from the peritoneum, is thin and elastic, to permit of
various degrees of distension ; whilst the smoothness and
moisture of its free surliice, facilitate the changes ol' form and
position of the intestinal convolutions upon each other, and
upon adjacent parts. 'J'hc rnusrular coat, consists, as else-
where, of an e.xternal layer of longitudinal, and an internal
layer of circular fibres. The longitudinal layer is thinner
than the circular layer, and is most distinct along the free
I border of the intestine; the circular fibres are arranged more
I closely together. 'I’he areolar or submucous coat, c, is loosely
I connected with the muscular coat, but more firmly with
9 the mucous meitdjrane, which it supports. Thin crescentic

44

SPECIAL PHYSIOLOGY.

extensions of this areolar coat project transversely, at intervals,
into the interior of nearly every part of the small intestine,
and, covered, on both sides and at their edges, by the closely
adherent raucous membi’ane, constitute the so-called valvulw
conniventes, fig. 91, v. These valves may be displayed by
opening the intestine, and immer.sing it in water. In a
portion of intestine inflated, dried, and laid open longitudinally,
they are seen as transverse crescentic folds or ridges, wider in
the middle, and tapering at either end. Each extends about
half or two-thirds around the interior of the tube ; the longest
are about two inches in length, and one-third of an inch wide
at their broadest part, but most of them are smaller ; the
larger and smaller ones alternate ; unlike the rugae of the
stomach, they are permanent, and not obliterated by distension ;
they do not contain any of the circidar muscular fibres, as the
pyloric valve does. They begin in the duodenum, about one
inch below the pyloras; in the lower part of the duodenum,
they are very large, and succeed each other closely ; about
the middle of the jejunum, they begin to get smaller and wider
apart ; in the lower half of the ileum, they become less dis-
tinct, and in the lowest part of that intestine, they are
altogether wanting. The mucous membrane of the small in-
testine, which also covers the valvulaj conniventes, is specially
characterised by being everywhere closely beset with an
immense number of minute thread-like processes, called villi ;
when immersed in water, these stand up and produce a
flocculent appearance, resembling the pile of velvet; hence
this mucous membrane has been termed villous. It also
contains the intestinal glands, to be presently described, and
other glands to be noticed, Avith the lacteals, in the section on
Absorption. The nerves of the small intestine are derived
immediately from the sympathetic system ; on their finest
branches in the submucous areolar tissue, are found multitudes
of the microscopic ganglia, elsewhere noticed (vol. i. p. 325) ;
others exist betAveen the circular aud longitudinal muscular
layers (Meissner, Auerbach).

The movements of the small intestine, depending on the
contraction of its longitudinal and circular fibres, alFord the
most perfect example of vermicula?' or peristaltic movements.
They consist, in the healthy state, of sloAv, successive, AAmve-
like contractions, chiefly of the circular fibres, from the upper
to the loAver part of the intestine. They are noticeable in
very emaciated persons dm-ing life, but are poAverfuUy ex-

THE LARGE INTESTINE.

45

cited by exposure of the intestines to the air, especially Avhen
the abdominal aorta has been tied ; they continue for a short
time after death, and even when the intestine is removed
from the body. By narrowing the small intestine, they urge
gently onwards from its upper to its lower end, the pulpy
mixture of the alimentary substances and digestive juices,
gently compressing these soft materials against the mucous
membrane, passing them on, over the numerous valvular con-
niventes, and so undoubtedly aiding in absorption. The
progressive contractions of the longitudinal fibres, open and
unfold the coils of the intestine, which otherwise might arrest
the progress of its contents.

The peristaltic movements of the intestines are influenced,
both through the cerebro-spinal and sympathetic neiwous
systems ; this is shown by experiments on animals, by irrita-
tion of the solar plexus, spinal cord, and brain, and also by
the peculiar effects of emotions on these movements ; they are
accelerated by moderate stimulation, and retarded, or arrested
or inhibited, by more powerful irritations. But, as they may
continue after the intestine is removed fi-om the body, it is
possible that they are usually excited, either by the direct
stimulation of the muscular fibres, or else, in a reflex manner,
through the intervention of the minute nervous uanglia found
in the submucous tissue, and in the circular and lono-itudinal
muscular layers. The stimuli which e.xcite these motions
are, in either case, the digested food, and the various digestive
fluids ; of the latter, the bile is the most stimulating, and its
importance as a regidator of the action of the alimentary canal
is well known. ’

Besides these intrin.sic movements, the small intestine is
acted upon jointly by the diaphragm and the abdominal
muscles, which subject it to various degrees of pressure, and
more or less alter its general position in the abdomen ; 'such
movements must aid in urging onwards the contents of the
intestine. It has been estimated that the time occupied in
the descent of the digested food along the small intestine is
about three hours. ’

The large inte.sthe, fig. 89, c to r, extends from the .small in-
testine to the termination of the alimentary canal. It mea-
sures usually about five or six feet, i.e. about one-fifth of the
whole length of the intestinal canal. Though much shorter
than the small intestine, it is considerably wider, measurimr
from U to 2t inches in width, being widest at its comineiice-

SPECIAL PHYSIOLOGY.

4G '

merit, and gradually narrowing as it descends. It pnr.snes a
remarkable cour.se ; commencing in the right iliac fossa, M'ljere
the small intestine opens into it, it ascends along the right
side to the under surface of the liver, then passes across,
between the umbilicus and the pit of the stomach, to the left
side of the abdomen, whence it descends to the left iliac fossa,
and, having described a double or sigmoid curve, enters the
pelvis, through Avhich it passes down, supported by the sacnim
and coccyx. The large intestine is more or less arbitrarilv
divided into three parts ; the first part named the ccEcum. c,
with its veiiniform ap^iendix ; the second part, the colon,
CO to CO, again subdivided into the ascending, transverse,
descending colon, and sigmoid flexure of the colon ; and the
third part, or terminal portion, named the rectum, r.

The ileum, i, enters the inner or left side of the large in-
testine, c, a short distance above the commencement of the
latter, which forms, below the point of entrance, a pouch-
like portion, about two inches in length, constituting the
ccecum, so named because it is a blind pouch or cul-de-sac,
fig. 92, c._

Projecting from the lower and back part of the CfEcum, is a
narrow, coiled, and tapering, tube, about 4 inches in length, and
about as thick as a worm, hence named the vemiiforni or worm-
like appendix, fig. 92, a. It commimicates with the CECcum
by an opening, protected by a membranous ridge ; its outer
end is closed- It may be regarded as a part of the ciEcuin
arrested in its growth, and is the homologue of the long
ca3cum found in Mammalia generally, the orang-outang, chim-
panzee, and wombat being, however, exceptions.

The cascum, and the ascending, transverse, and descending
colon, with its sigmoid flexure, are distinguished from the small
intestine, and also from the rectum, by their peculiar saccu-
lated form. The sacculi of these parts, are arranged in three
longitudinal rows, separated from each other by three inter-
mediate bands. Their presence depends upon a peculiar
arrangement of the coats of the inte.stine. These, as in
the small intestine, are four in number, viz. proceeding from
without inwards, the serous, the muscular, the areolar, and
the mucous coats. The serous or peritoneal coat, is complete
in only certain portions of the great intestine, viz. in the
transverse ])art of the colon, the sigmoid flexure, and the
upper part of the rectum ; whilst the catcum, the ascending
and descending colon, and the lower part of the rectum, are

THE LARGE INTESTINE.

47

closely fixed behind, and therefore receive only a partial
covering from the peritoneum. Tlie muscular coat consist.s, as
usual, of external longitudinal and internal circular fibres.
On the vermiform appendix, both sets of fibres form uniform
layers. On the sacculated pouch of the ctecum, and through-
out the whole length ol the colon, however, the longitudinal
fibres, thinly scattered over the sacculi, are chiefly collected into
three long bundles, which form the three longitudinal bands
between the sacculi. These bands, indeed, are shorter, fi-om
end to end, by nearly one-half, than the intermediate part of
the intestine, which accordingly is puckered, and projects
inwards in the form of sharp crescentic ridges between the
dilated parts which form the sacculi. These sacculi become
smaller and more scattered on the sigmoid flexure of the colon.
On the rectum, the longitudinal fibres speedily form a thick
stratum, evenly disfributed over the whole circumference of
the intestine, so that the sacculi disappear. The circular
fibres cover the whole surface, but are accumulated in greater
numbers on the ridges between the sacculi. Upon the rectum,
however, they soon form a thick and uniform layer ; the
lower portion of this is particularly Avell developed, con-
stituting the internal sphincter muscle, which constricts the
lower part of the bowel, and assists the external sphincter
muscle, situated beneath the skin, around the aperture of the
intestine, in keeping the bow^el closed. The areolar or sub-
mucous coat of the large inte.stine, is attached loosely to the
muscular coat, but more intimately to the mucous membrane j
it 13 sacculated, and helps to maintain the Ibrm of the intes-
tine ; it supports the tender mucous coat, and furnishes a
stratum, in Avhich the bloodvessels, lymphatics, and nerves,
ramify. The mucous coat, unlike that of the small intestine,
follows strictly the form of the intestinal canal itself; for it is
not throwm into proper folds, like the valvulai conniventes,
but only follows the concentric ridges between the sacculi.
Moreover, it differs from the mucous membrane of the small
intestine, in being somewhat thicker and jialer, and in being
perfectly smooth and entirely destitute of villi. In the ca;cum
and colon, it is of a greyish yellow colour, but in the rectum,
it is darker, thicker, more vascular, and more loosely con-
nected with the muscular coat. Its glands will be presentlv
described. The nerves belong to the sympathetic system ; in
the submucous coat, their fine branches present microscoj)ic
ganglia, which are also found outside the muscular coat. The

48

SPECIAL PHYSIOLOGY.

movements of the large intestine are not retarded by irritation
of the splanchnic nerves.

At the junction of the lower end of the ileum, fig. 92, i,
with the cajcum, c, and colon, co, there is found a very per-
fect valve, the ileo-cmcal valve, or valve of Tulp or Bauhin,
composed of two semi-lunar segments, having their free edges
directed towards the large intestine. The end of the ileum
is somewhat flattened on its upper and under aspects, and is
here inserted into the left side of the large intestine. The
flattened part of the small intestine, candes in, with it, the side
of the lai’ge intestine, and so forms the segments of the valve,

Pifr. 92.

Pig. 92. The ctecura, and the commencement of tlie ascending colon, laid
open in ft-ont, to show the ileo-coscal or ileo-colic valve, at the jum tion of
the small and large intestines, c, the cul-de-sac, named the cascum, or
blind intestine, a, vermiform appendix of the ca?cniu. co, part of the
ascending colon, i, A piece of the ileum, or small intestine, entering
the side of the largo intestine, between the cascuin and colon, by a hori-
zontal transverse fissure, bounded, above and below, by the crescentic
segments of the ileo-ciecal or ileo-colic valve. Much reduced in size.

which consist therefore of the coats of both intestines, ex-
cepting, however, the longitudinal muscular fibres and the
peritoneal tunic. If the latter be carefully divided where it
passes from one intestine to the other, the inserted part of the
small intestine, may be drawn out from the side of the large
intestine, when the two segments of the ileo-caical valve
disappear, and the small intestine seems to open widely into
tlie side of the large intestine. In the natural condition, the
segments of this valve are placed one above the other, and
leave, between their free edges, a narrow, nearly horizontal.

CONTENTS OF THE LARGE INTESTINE.

■45

slit, leading irom the small into the large intestine. Each
segment contains circular muscular fibres, areolar tissue, and
two layers of mucous membrane, continuous with each other
at the free edge of the segment. The mucous membrane of
the surface turned towards the ileum, is covei'ed with villi ;
whilst that turned towards the large intestine, is destitute of
those processes.

Notwithstanding the active absorption which takes place along
the whole length of the small intestine, its contents rediin a
pulpy consistence. By the peristaltic action of the circular
muscular fibres, they are pressed through the slit-like
opening between the segments of the ileo-cascal valve, having-
passed which, they are received into the pouch of the ctecum,
which now supports their weight, whilst the lateral position of
the valve relieves it from pressure. Once having passed the
valve, no force exerted upon the intestinal contents, can ever
return them into the small intestine, the valve-segments,
owing to the elasticity and muscularity of all the parts, meet-
ing closely together under every change of dimensions. Even
after death, when these parts are removed from the body, water,
poured into the colon, is, owing to the closure of the valve-seg-
ments, completely prevented from passing into the ileum. In
the ca2cum, the still pulpy residue of the processes of dige.stion
and absorption, undergoes further inspissation, perhaps also
fiirther digestion. By the combined and comparatively slow
peristaltic action of the longitudinal bands between the .sac-
culi, and of the circular fibres spread over the sacculi them-
selves, it is pres.sed upwards into the ascending colon, and, in
like manner, onwards from .sacculus to sacculus of the ascend-
ing, transverse, and descending colon, and, yet more slowly,
through the sigmoid flexure of the colon into the rectum, ac-
quiring, by gradual absorption, as it dc.scends, its final state of
inspissation, before it is expelled from the body. Undue pres-
sure, or weight, is prevented by the sigmoid curve of the intestine.
The e.xternal and internal .sphincters, which close the rectum
below, are kept contracted, in a reflex manner, by the action
of the spinal cord. In defaccation, these muscles are relaxed
whilst the intestine above contracts, the action being aided by
expulsive efforts on the part of the abdominal and expiratory
inu.scles generally, the dia])hragm being fixed after closure of
the glottis. The fibres .surrounding the cardiac opening of the
stomach, must also close that aperture simultaneous!}'.

VOL. u.

E

50

SPECIAL PHYSIOLOGY.

Vomiting.

In the ordinary exercise of their functions in the digestive
process, the oesophagus, the stomach, and the intestinal canal,
manifest, as we have seen, movements of the so-called peri-
staltic kind, due to successive wave-like contractions of their
muscular walls," excited, partly through the nervous system,
but also, especially in the case of the intestines, by the direct
stimulation of the food upon them. But, under certain con-
ditions, an undue local stimulation of the muscular fibres, or
some wider irritation, operating through the neiwous system,
excites these organs to reversed, or so-called anti-peristaltic,
action, often accompanied with powerful associated move-
ments of the abdominal muscles, and with certain peculiar states
of the diaphragm and muscles of respiration generally, so
producing the acts of eructation, regurgitation, retching, and
vomiting.

The eructation of gaseous matters, depends chiefly on the
contraction of the walls of the stomach and oesophagus, aided
slightly by that of the abdominal muscles and the diaphragm.

The act of vomiting is a more general, and powerful move-
ment, and often involves a contraction of the small intestines ;
but it depends essentially on a similar mechanism. Though
an exceptional phenomenon, and, in disease, often a serious or
fatal symptom, it is, in many instances, beneficial, relieving
the stomach of indige.stible, irritating, or poisonous substances,
expelling trom it morbid secretions, or even inducing a state
of exhaustion, in some way favourable to ultimate recovery.
Retching is imsuccessftd vomiting.

Regurgitation is performed by the same mechanism as
vomiting ; but its effect is limited to the expulsion of small
poi'tious only of the contents of the stomach. There are
persons who possess a sort of power of ruinination, swallowing
their food half chewed, and, after a time, returning it to the
mouth, where it is fully masticated, and then re-swallowed.

The actual contraction of the stomach, in vomiting, is
sometimes felt ; indeed, it has been Avitnessed. In a man, in
whom the entire stomach protruded through a Avound of the
abdomen, forcible and repeated contractions of this organ, Avere
observed to continue for half-an-hour, till it AAnis entirely
emptied of its contents (Lepine). As a preliminary con-
dition to the inverted action of the fibres of the stomach

ACTION OF THE MUSCLES IN VOMITING.

51

generally, the pyloric muscular ring contracts tightly, whilst
the oblique fibres surrounding the cardiac orifice are always,
and necessarily, relaxed ; otherwise the contents of the
stomach could not enter the oesophagus. The ineffectual
attempts to vomit, sometimes noticed, before the actual ex-
pulsion of the contents of the stomach, are due to the contrac-
tion of these cardiac fibres, which contraction ordinarily serves
to retain the contents of the stomach, during any violent effort
on the part of the abdominal muscles. The relaxation of
these fibres, in vomiting, is immediately followed by an anti-
peristaltic action of those of the oesophagus, movements which
have been observed in the horse, after the injection of tartar
emetic into its veins, and have been found to continue even
when the oesophagus is separated from the stomach. It has
been suggested, that the upward propulsion of the contents
of the stomach or intestines, and of matters rising in the
oesophagus, is due to a downward or peristaltic action meeting
with resistance, and producing a central, or so-called axial
current upwards (Brinton) ; but this explanation is not gene-
rally adopted, and antiperistaltic movements certainly occur in
animals.

The influence of the abdominal muscles in vomiting, is ob-
vious, and, indeed, Magendie suggested, that these muscles and
the diaphragm were alone concerned in this act, the stomach
being, as it were, passive, and merely compressed by the
descent of the diaphragm, and the backward movement of
the abdominal muscles. This view is supported by Bedard
and Budge. The administration of tartar emetic, to an
animal, or its injection into the veins, was said, by Magendie,
never to produce contraction of the stomach. He found that,
on drawing this organ out of the abdomen, no vomiting oc-
curred ; but, as soon as it was replaced in its normal situation,
the action of the abdominal muscles, or the pressure of the
hand, immediately produced vomiting; even after removal of
the abdominal muscles, so as to leave only the linea alba, or
the tendinous structure in the middle line of the abdominal
walls, the descent of the diaphragm, according to that
observer, still emptied the stomach. Moreover, on removing
the stomaeh, and supplying its place by a bladder attached to
the oesophagus, the contents of the former were forced up-
wards by the contraction of the abdominal muscles. It is,
however, generally believed, that these experiments merely
prove, that the abdominal muscles are powei'ful agents in

52

SPECIAL PHYSIOLOGY.

expelling the contents of the stomach into the oesophagus,
just as they assist, most materially, in the expulsion of the
contents of the other hollow viscera. They do not show a
completely passive condition of the stomach itself, which
organ, as just stated, has been seen to be able to empty its
own contents. In experiments on animals, when the abdomen
is opened, the movements of the stomach are frequently so
feeble and rapid, that they might escape observation.

It was supposed by Magendie, that the diaphragm is
actively concerned in vomiting, imdergoing a movement of
descent ; but, the associated acts necessary to vomiting, are
expiratory, and the descent of the diaphragm is an inspiratory
movement (Marshall Hall). At the moment of vomiting, the
diaphragm, though more or less contracted, is certainly /.recZ ;
for, previous to each act of vomiting, a poweiful inspiiatory
effort occurs, and the diaphragm of course descends ; but the
o-lottis is then closed, and any further movement, on the part
of the diaphragm, is thus prevented, so that it probably remains
passive in vomiting.

During vomiting, as in the second stage of deglutition, cer-
tain muscles draw the soft palate across the pharynx, and
Ill-event the vomited substances from passing into the posterior
nares ; but when the abdominal muscles act very powerfully,
these are sometimes ejected through the nose.

As elsewhere mentioned, vomiting is a reflex act, the
pneumogastric nerves being the afferent nerves, the medulla
oblongata and cord, the excitable centres, and the nerves of
the various muscles concerned, the efferent nerves, bometunes
it is excito-7notor, and induced by a local stimulus, applied to
the interior of the stomach itself, sucli as indigestible food,
medicines, poisons, or diseased secretions; it may also be due
to morbid irritability of this organ, ffoiii inflammation, ulcer-
ation or other disease; or the cause of irritation may be
distant, as in the intestines or some other part. In certain
cases, as in sickness produced by a blow on the eye-ball or
on the shin, by strangulation of the intestine, or by a calculus m
the kidney, the reflex act is sensori-motor, or accompanied by
sensations which are always of a painful kind, llie nausea
and vomiting caused by tickling the fauces, by disagreeable
tastes and odours, or by sickening sights, are likewise sensori-
motor in their character. Sea-sickness is also an example of
sensori-motor vomiting. Emotional causes may likewise excite
this act. Emetic medicines, which operate just as readily

TJIE DIGESTIVE FLUIDS.

53

Avlien injected into the veins, as -when introduced into the
stomach, probably act directly on the rellex nervous centres
concerned in vomiting; but they may operate on the extremities
of the afferent nerves of the stomach. These are the pneumo-
gastric nerves, irritation of which causes, amongst other results,
contraction of the muscles of the abdomen, and vomiting. In
the vomiting, named cerebral vomiting, which occurs after con-
cussion of the brain, and in certain diseases of that organ, the
cause of irritation is central. In some individuals, vomiting
can be performed voluntarily, this power being either natural,
or else accpiired by practice.

It is said that the act of vomiting hut seldom occurs in the horse ;
and it has been attempted to explain this, by reference to the structure
of the cardiac end of the stomach ; but it would seem rather to be due
to the very slight susceptibility of tlrat animal to the action of emetic
medicines.

THE DIGESTIVE FLUIDS.

The chemical processes concerned in the function of diges-
tion, consist ot peculiar reactions between the food and the
various secretions of the alimentary canal.

The dige.stive fluids, which are added to, and act chemically
on, the food in its progress through the alimentary canal, are
as follow: — first, the fluids of the mouth, 'consisting of the
mucus secreted by the mucous membrane and glands of that
cavity, and the saliva^ the product of the three pairs of salivary
glands, named the i:tarotid, suhmaxillarij, and sublingual glands ;
secondly, the secretion of the stomach, named the gastric juice ,
formed by minute gastric glands, or follicles, embedded in the
mucous membrane of that organ ; thirdly, the bile .secreted by
the liver, and poured into the duodenum ; fourthly, the g^an-
creatic juice secreted by the pancreas, and also added to the
food in the duodenum ; and lastly, the mucus and the intes-
tinal juices^ secreted by the mucous glands, and by the so-
called tubidi, which exist in vast numbers in the mucous
membrane of eveiy part of the small and large intestines.
Each of these fluids exercises a special transmutation on one or
more of the proximate constituents of the food, the tendenc}-
of such changes, being to convert tho.se constituents, from an
insoluble and unab.sorl)able condition, into a .state of solution,
or into a state in which they can be absorbed, that being the
ultimate object of the digestive process.

SPECIAL PHYSIOLOGY.

51

Sources and Comiiosition of the Buccal Mucus and Saliva.

The mucous (/lands of the month are named, according to
their position, labial, buccal, molar, /mlatcd, and linrjual.
These are chiefly compound racemose glands, forming rounded
masses beneath the mucous membrane, and opening into the
mouth by their proper ducts. At tlie base of the tongue, are
a few simple follicles, and some follicular depressions, having
little closed sacs in their walls, like the follicles of the tonsils.
The tonsils themselves probably also furnish some mucous
secretion. Beyond the mouth, the pharynx possesses inune-
rous simple follicles, and its upper part, compound racemose
glands. Their secretion lubricates the parts, and also the
suiface of the food. It may likewise aid the saliva in its
chemical action. Throughout the whole length of the oeso-
phagus, and especially in a circular group aroimd its lower
end, there are also mmierous compound mucous glands, which
perlbrm similar offices.

Of the three pairs of salivary glands, the parotid glands are
by far the largest, weighing fi-om 5 to 8 drachms each. They are
placed one on each side of the face, between the ear(7rapd, near,
ovc, (hroc, the ear) and the loAver jaw, which they overlap, being
there supported by their ducts and blood-vessels, and by a
strong fascia. The facial nerves pass through the glands. The
principal mass of each gland occupies the position above indi-
cated, and likewise penetrates amongst the muscles and vessels
of this region ; but a secondary or accessory portion, soda
parotidis, extends forwards along the excretory duct. This
canal, named the Stenonian duct, runs forward from the gland,
over the masseter muscle, passes obliquely through the
buccinator muscle, and, opposite the second upper molar
tooth, opens by a narrow orifice into the mouth. It is about

inches long, and about the diameter of a crow-quill, but its
orifice is very minute. The gland itself consists of numerous
compressed lobes, held together by the ramified ducts and
blood-vessels, and by areolar tissue. The lobes are again
divided into lobules, each of which is a minute racemose .
gland, the branched ducts of Avhich, terminate in vesicles, .
about 1-27777 ”ich in diameter, fig. 42, c., each being sur-
rounded by a network of capillaries. The sjiliva, scci’eted
Irom the blood into these vesicles, flows along the smaller f
bi'anches of the ducts, into the main canal or duct of Steno,
and is thence poured into the mouth at a place suitable for

THE SALIVAUT GLANDS.

55

moistening tlie dry food, and for being mixed with the
alimentary mass. The submaxillary glands are placed, one on
each side, beneath the horizontal part of the lower jaw,
attached by their ducts and blood-vessels, and supported by the
cervical fascia and certain muscles. Each gland is of a
roundish shape, and weighs from 2 to 2^ drachms; its struc-
tiwe resembles that of the parotid. Its chief duct, thinner
than that of the parotid, is named tlie Whartonian duct, and is
about 2 inches long ; it runs forwards between the muscles,
beneath the sublingual gland, to the side of the frasnum of the
tongue, where it opens upon a small eminence close to the
duct of the opposite side. These glands, therefore, discharge
their saliva, not outside the jaws, like the parotid glands, but in-
side the lower dental arch, their secretion being pressed up into
the mouth by the motions of the tongue. The sublingual glands,
the smallest of the salivary glands, are somewhat almond-shaped,
and weigh each about one drachm ; they form two narrow
oblong ridges, about 1-^ inch long, placed, one on each side,
beneath the tongue. Their structure resembles that of the
other salivary glands, but, instead of having a common duct,
the several lobules open into from eight to twenty ducts,
named the Rivinian ducts, some of which, including one large
duct named the duct of Bartholin, join the Whartonian duct,
as it runs for a certain distance immediately beneath the
gland. The saliva from the sublmgual glands, flows into the
mouth, beneath the tip and sides of the tongue.

The mechanical flow of the saliva into the morrth, is aided
by the contraction of the muscles of the tongue and jaw
engaged in mastication ; on opening the mouth before a look-
ing-glass, and then turning up, and stiffening, the tongue, the
.saliva is sometimes seen to be ejected a considerable distance,
from the orifices of the Whartonian ducts.

The salivary glands all receive branches from the sympa-
thetic nervous system ; the parotid glands are likewise
supplied by the fifth pair (its auriculo-temporal branch) ;
whilst the sublingual and .submaxillary glands receive nervous
filaments from the chorda-tympani branches of the facial
nerves. The saliva flows intermittently ; and its secretion is
excited through the nervous system, by the agency of which,
the quantity of this and other secretions, is cliiefly regulated
(Vol. I., p. 333). Thus, the presence of food, e.spocially of dry
food, in the mouth, and even the introduction of food into the
stomach through a gastric fistula, stimulates the How of .sahva;

5C

SrECIAL PIITSIOLOGY.

salt, vinegar, pepper, and other condiments, and particidarlj'
tobacco, and the root of the pellitory of Spain, have a still more
powerful effect ; these furnish examples of reflex stimulation
of the salivary secretion. The afferent nerves concerned, are
the gustatory branches of the fifth pair, and the glossopharyn-
geal nerves; the efferent nerve-fibres are contained in the
chorda-tympani branches of the facial nerves, or in the auri-
culo-temj)oral branches of the fifth pair. The neiwous centres
are the submaxillary ganglia, and the cerebro-spinal axis.
Besides this, the saliva is excited to flow by ideational or other
mental stimuli, such as the sight of food, or even the thought
of it. The act of speaking, and also that of vomiting, are
preceded by a flow of saliva. Fear diminishes or arrests it.
Irritation of the fourth ventricle, and the presence of certain
substances in the blood, esjDecially of mercury, likewise increase
the flow of this secretion. The effect of mercurialization in
exciting a flow of saliva, is specific.

The mode in wdiich the neiwous system influences the
secretion of saliva, has been elucidated by the interesting
experiments of M. Bernard. When the sublingual and sub-
maxillary glands, exposed in an animal, are at rest, little or no
saliva being formed, the veins are seen to contain a moderate
quantity of dark blood. On now stimulating the glands, in a
reflex manner, by the application of vinegar to the tongue, the
arteries supplying them dilate, the flow of blood through
these vessels becomes quicker, even the veins pulsate, the
venous blood is of a bright red colour, and there occurs a
copious flow of watery saliva. The afferent nerves concerned
in this reflex act, are obviously branches of the gustatory and
glossopharyngeal neiwes ; the efferent fibres are contained in
the chorda tympani ; for if either this or the facial, from which
it is derived, be cut, the active jDhenomena, above described,
all gradually cease, but they are again excited by indtation of
the distal ends of the divided nerves. If tlie facial nerve be
dra-wn out from the cranial cavity, irritation of the glosso-
pharyngeal no longer increases the flow of saliva. The efferent
nerves of the parotid glands, are said, by Eckhard, to proceed,
not from the chorda tympani or facial, but from the auriculo-
temporal branch of the fifth pair. As already stated (Vol. I.,
jD. 333), irritation of the S3'inpathetic branches supplying the
sublingual and submaxillarj'^ glands, has an opposite effect to
that of stimulating the fibres of the chorda tjunpani ; the
secretion from the glands, then becomes scanty and thick, the

THE SALIVA.

57

arteries small, the flow of blood through the gland diminished
and retarded, and the venous blood dark. To explain these
opposite phenomena, it is assumed that the sympathetic
nervous centres cause a contraction of the muscular coats of
the smaller arteries; whilst the cerebro-spinal centres inhibit
this power, and so induce a relaxed condition of the
arterial coats. The efferent effect, conveyed through the
chorda tympani nerve-fibres, is therefore not motor, but of
a special kind, controlling, or inhibiting, the action of the
sympathetic nerve-fibres and centres. This example Avill
suffice to illustrate the mode in which secretion generally, is
believed to be influenced through the nervous system. In-i-
tation of the sympathetic nerves does not alter the quality,
but only lessens the quantity, of the secretion of the jiarotid
glands. According to Eckhard, great numbers of mucous
corpuscles, exhibiting intrinsic movements, like those of the
Amoeba, are found in the viscid secretion of the sublingual
and submaxiUary glands, after irritation of their sympathetic
nerves ; such corpuscles, but in smaller number, exist, as we
shall see, in ordinary salma.

The chemical composition of the saliva is, according to Dr.
Wright, as follows : —

Water .

Ptyalin, or Salivin
Fatty matter
Albumen with Soda
Mucus .

Ashes .

Loss

98

81

18^

05

17

26

41

12^^

= 98-81

Solids . = 1’19

100-

100-

The saliva, thus constituted, is a transparent watery fluid,
destitute of smell ; its specific gi’avity varies from 1002 to
1008. Besides fine granular particles, mucous corpuscles,
derived, for the most part, from the lingual and tonsillar glands,
and epithelial cells detached from the mouth, the .saliva con-
tains the .so-called salivary corpuscles, spheroidal nucleated
cells, somewhat re.sembling the white blood corjrascle.s, Avhich
undergo Amoeba-like changes in form, and exhibit a molecular
movement in their interior.

The quantity of saliva secreted in twenty-four hours by all
the glands, has been estiitiated at from 1 to 3 lbs. : Imt it
differs according to the nature of the food, and the intervals
between the meals. Its flow is increased by mastication.

58

SPECIAL PHYSIOLOGY.

but is aiTested by tbe cessation of that movement. The saliva
from the parotid gland, is very thin and watery, and becomes
more abundant ditring mastication ; that from the .submaxillary,
and especially from the sublingual gland, is more viscid, and
flows more constantly, for jmrposes of speech. The parotid
glands, wdien active, are said to secrete from eight to ten times
their own weight in one houi'. When first secreted, and
especially during active secretion, the saliva is alkaline ; that
of the submaxillary gland is less so than that of the parotid.
In fasting, the moisture of the mouth is nearly neutral, or
even acid, at that time consisting probably almost entirely
of mucus. Tl]\e iityalin or salivin, the most important consti-
tuent of the saliva, is an albuminoid substance. Of the salts,
the tribasic phosphate of soda is probably the cause of the alka-
linity of the secretion ; besides this, there are found chlorides
of sodium and potassium, sulphate of soda, phosphates of lime
and magnesia, and oxide of iron. The tartar of the teeth is
formed by a deposit of these earthy salts, mixed with mucus,
and the remains of bacteria or vibrios ; it contains 20 per cent,
of animal matter. Urea has also been found in the fluids of
the mouth, and traces of ammonia, the results of decomposi-
tion. Thus far, the .salts of the healthy saliva resemble those
of the blood ; but it contains a peculiar and remarkable salt,
named the sulphocyanide of potassium, which strikes a deep
red colour, with a solution of a persalt of iron.

Source and composition of the Gastric Juice.

When the soft puljDy mucous membrane of the stomach is
examined under a moderate magnifying power, it presents a
delicate honeycomb appearance (fig. 93), caused by numerous,
shallow, hexagonal, or polygonal, depressions, named the cells
or alveoli of the stomach ; near the pylorus, these measure
T-J-yth of an inch in width, but elsewhere are smaller and less
distinct, measuring only -g-Jw^h to ^-gTjth of an inch. Between
the alveoli, are slightly elevated ridges, upon which, especially
near the pyloric end of the stomach, are minute processes,
which somewhat resemble villi, and are more distinct in the
infant. No lacteals, however, have been detected in them.
At the bottom of the alveoli are clusters of minute spots (fig.
93), which are the orifices of tubular follicles. These follicles,
called the yaslric glands or tubidi, secrete the gastric juice ;
they are arranged, side by side, in little groups (fig. 94), perpcn-

THE GASTRIC GLANDS.

dicularly to the surface of the membrane, and form almost its
entire substance. At the pyloric end of the stomach, where
the mucous membrane is thickest, the tubuli are the longest,
measiuing nearly -g^jjth of an inch in length ; towards the car-
diac end, where the mucous membrane is thinnest, they are
less thickly set, and become gradually shorter, measuring only
jdjyth of an inch in length ; their average diameter is about
jj^th to 5^th of an inch, the orifices, c, being somewhat
naiTOwer. Each follicle is somewhat dilated, or flask-shaped,
at its deeper or blind end ; the larger follicles are sometimes
convoluted or varicose, and sacculated at the blind end, or

Fig. 93. Minute portion of the surface of the mucous membrane of the
human stomach, showing the polygonal depressions or alveoli, with the
elevated ridges between them. At the bottom of the alveoli, arc seen the
open mouths of clusters of the tubuli of the stomach, or g.astric tubuli.
Magnified 60 diameters. (After Boyd.)

Fig. 91. Perpendicular section through a small piece of the mucous mem-
brane of the stomach, to show the clusters of the gastric tubuli. a, neck
of a single tubule, i, dilated end or fundus, filled with glandular epi-
thelial cells, c, orifices of the tubuli, at the bottom of the alveoli, m,
muscular bundles of the muscular coat. (After Kblliker.) Magnified
10 limes.

even .subdivided into two, or, sometimes, as in the pyloric por-
tion of the stomach, into as many as six or eight sliort saccu-
lated tubuli. These tubuli consi.st of extensions of the gastric
mucous membrane. The upjier third of each tubule, next 1o
its orifice, is lined by columnar epithelial cells (fig. 95, a),
arranged perpendicularly on the basement membrane. This
epithelium is continuous with that at the bottom of the
alveoli, and on the interalveolar ridges, and indeed is similar

Fig. 93

Fig. 94,

U

c

60

SPECIAL PHYSIOLOGY.

to that lining the stomach generally. In the lower two-thirds
of each tubule, the epithelium changes its character, being
composed of soft, romidish, oval, or compressed nucleated cells,
S, which, veiy much larger than the cylindrical epithelial
cells, and distended with granular matter, almost or completely
block up the cavity of the tubule. These soft epithelial cells
are named the peptic cells, because in, or by, them, the gastric
juice, or, at least, its characteristic animal substance, called
pepsin, appears to be formed. Some of these cells are present
as microscopic elements of the gastric juice. The tubuli,
which are said to number about five millions, are sometimes

Fig. 95.

Fig. 95. Single gastric tnbulns, or peptic glaml, more highly magnified.
a, neck of the tubule, lined with columnar epithelium. 5. dilated lower
end, or fundus, of the tubule, filled with oval nucleated glandular
epithelial cells, or peptic cells. Magnified 70 diameters.

named the peptic glands. They are .surrounded by a fine
capillary network; minute arteries and veins pass up and
down between them, and end in a capillary plexus on the
bottom of the alveoli, and on the interalveolar ridges. The
unstriped muscular fibres found in the submucous coat, are
placed immediately beneath these glands, and probably assist
in expelling their secretion.

Besides these proper gastric or peptic glands, there are found,
especially near the pylorus, clusters ot larger simple and com-
])ound nuicoits gland.s, which are lined throughout with cylin-
drical epithelium, and are supposed to secrete gastric mucus.

THE SECRETION OF THE GASTRIC JUICE.

GI

In certain conditions of the stomach, especially during and
alter digestion, and also in irritation and intlanimation of this
organ, and nearly always in the stomachs of infants, nume-
rous small, milky-white, elevated spots are seen scattered over
the mucous membrane. These consist of lenticular closed .sacs,
not opening on the surface; they are filled with a white, semi-
fiuid and finely granular substance. They resemble the closed
sacs of the tonsils, and of the so-called solitary and agminated
glands of the small intestine, to be hereafter noted ; like them,
they are now considered to be appendages of the absorbent
system. The lymphatics of the stomach form a fine net-vmrk
near the surface of the mucous membrane, and coarser plexuses
in the submucous coat, all intimately connected together.

The gastric juice, during the digestive process, or under the
excitement of condiments, small stones, and other irritant
bodies, exudes from every part of the mucous membrane of
the stomach, which then assumes a bright red hue. The
secretion pouring from the tubules, oozes from the alveoli in
minute drops, which speedily run together, and cover the whole
mucous membrane. This has been seen by Dr. Beaumont
and others, in the case of Alexis St. Martin, a Canadian voy-
ageur, the interior of whose stomach was exposed by a gun-
shot injury.

The condition of the stomach, and the formation of the
gastric juice, as of other secretions, are influenced by the
nervous sj'stem. It was shown, by Dr. John Keid, that the
division of both pneumogastric nerves, in the neck of a dog,
in the first instance, arrested dige.stion ; but that, if the animal
lived .sufficiently long, the process might be restored ; for then,
generally, the state of emaciation, which followed the ex-
periment, was removed, acid and partly digested food was
vomited, and absorption and chylification took place. This
restoration of function was not due to reunion of the divided
nerves, for portions of the nerves were removed, or care was
taken to keep the cut ends apart. Bernard also found, that,
on division ofthe.se nerves, the stomach became pale, its walls
relaxed, and the formation of gastric juice was instantly
arrested, digestion being thus stoi>i)cd. On the other hand,
galvanising these nerves increased tlie gastric secretion. Ac-
cording to Longet, however, the pneumogastric nerves are
rather the motor nerves of the stomach, their division, as he
believes, chiefly affecting the movements of that organ ; for
he found, that milk, introduced into the stomach one or two

G2

SPECIAL PHYSIOLOGY.

da5^s after the operation, always became coagulated; whilst,
although large portions of food were only acted upon on the
surface, owing to the paralysis of the muscular fibres, and the
necessary absence of the churning movements of the stomach,
yet small portions were actually digested. By Budge, it is
believed, that the very decided effect of division of these
pneumogastric nerves on digestion, noticed by Eeid and
Bernard, was owing to those nerves having been cut in the
neck, so as to interfere with respiration, and thus disturb the
whole economy ; for, he' observed that, on dividing them in the
rabbit, close to the cardiac orifice of the stomach, no interfer-
ence with the appetite, the gastric secretion, or digestion, oc-
curred. Although, therefore, the secretion of the gastric juice
appears to be influenced by the cerebro-spinal nervous system,
through the pneumogastric nerves, it cannot be said to be
dependent upon it. The effects of mental emotion, in arresting
digestion, sufficiently prove this influence.

It has been stated by Bernard, that galvanism applied to
the sympatlietic nerves of the stomach, causes an immediate
cessation of its secretion, this effect being the reverse of Avhat
happens, when the pneumogastric nerves are so stimulated.
If these two results are confirmed, they would correspond with
those already detailed (p. 56), as to the effects of stimulation
of the sympathetic nerves and the chorda tympani, on the
secretion of the sublingual and submaxillary glands. Neither
division of the splanchnic neiwes, nor section of the pneumo-
gastrics upon the stomach, that is to say, after the latter have
received the fibres from the former nerves, has appeared to
interfere much, or at all, with the gastric secretion (Schiff and
others) ; even the coeliac plexus, and the neighbouring ganglia,
have been removed without permanent effect (Budge). It would
seem impossible, however, in any such experiments, to remove,
or divide, all the sympathetic nerves of the stomach. Finally,
the influence of this part of the nervous system, on the gastric
secretion, is imcertain ; and it is not yet shown that the secre-
tion is either arrested by, or depends on, the sympathetic
system.

The quantity of the gastric juice secreted, appears to be
enormous. In dogs, the daily quantity has been calculated as
.nljjth (Corvisart), or (Lehmann), part of the weight of

the body ; the latter ratio Avould give 14 lbs., in a man of
140 lbs. weight, a quantity equal to rather more than 11 pints
daily. That this estimate, however large, is not extreme, is

THE GASTRIC JUICE.

63

shown by the feet that, in a case of gastric fistula, in a woman,
the estimated daily quantity was 30-i- lbs. av., the weight of
her body being 116 lbs. From observations on dogs, having
artificial gastric fistulas, the secretion appears to he less abun-
dantly excited by mechanical, than by chemical or special
irritants, such as salt or pepper ; acid food excites a less abundant
flow than food made slightly alkaline ; but allcali in the solid
state, induces an abundant secretion of mucus. Too powerful
mechanical irritation has a similar effect, lessening, or arresting,
the secretion of proper gastric juice, and, in both cases,
vomiting, and the passage of bile into the stomach, may take
place. Powerful chemical irritants arrest digestion, and cause
signs of inflammation. The effect of cold water, or ice, is,
after first causing the gastric membrane to be pale, ultimately
to increase the flow of blood to it, and to excite a very active
secretion; ice, in larger quantity, causes shivering, and delays
digestion. A high temperature, even a small quantity of
boiling water, produces collapse and death within four hours,
causing redness, turgescence, and ecchymosis of the mucous
membrane (Bernard). Dr. Beaumont found that, on injecting
into the human stomach only 2 ozs. of water at 50°, the tem-
perature of this organ was depressed to less than 70°, and
required more than half-an-hour to regain its normal standard,
viz. about 100°.

The specific gravity of the gastric juice, in Man, is 1002-5 ;
in the dog, 1005. The quantity of solids is about -5 per
cent. It is a colourless, or pale yellow, transparent, slightly
viscid, and strongly acid fluid, having a faint smell. It resists
putrefkction, and is rendered turbid on boiling. Its com-
position, mixed with a little saliva, is as follows (Schmidt) : —

Water

. 994-4

Pepsin, with other organic matter .

3-2

Salts .......

2-2

Free hydrochloric acid

-2

1000-

The gastric juice of the dog, contains ten times as much free
acid, and five times as much organic matter ; that of the sheep,
six times as much acid, and a little more organic matter ;
that of the horse, is somewhat more concentrated.

The .small quantity of solid matter in the gastric juice, is
remarkable, considering its extremely active ])owers. The
pepsin, its characteristic con.stituent, is a neutral, albuminoid,

64

SPECIAL PHYSIOLOGY.

substance, slightly soluble in water, forming, on evaporation, a
greyish viscid mass, and having a strong affinity for acids. It
is precipitated by tannin, acetate of lead, caustic alkalies,
alum, and alcohol. The saline matters consist chiefly of
alkaline and earthy chlorides and phosphates. A small amomit
of lactic acid exists in the gastric juice, but whether as a pro-
duct of secretion, or of decomposition, is not certain ; by
Bernard and others, it is even believed to be the special acid
of the gastric juice. Acetic, butyric, and other volatile acids
are certainly the j-esult of changes in the food. The presence
of free hydrochloric acid is undoubted, inasmuch as chlorine is
found in the gastric juice in larger quantity than the bases
which could combine with it ; and moreover, this acid has
been obtained by the method of dialysis, and therefore inde-
pendently of chemical decomposition (Graham). Its existence
affords a singular example of the liberation of a mineral acid
from its strongly combined base, by an organic process in the
living animal economy. The source of this acid is probably
chloride of sodium, or common salt ; and the seat of its de-
composition, like that of the formation of the pepsin, is pro-
bably the soft glandular epithelial cells, or peptic cells ; but it
has been suggested, that it may be secreted by the columnar
epithelial cells of the upper part of the tubuli and gastric
mucous membrane generally (Brinton). It is supjjosed by
Brlicke, that the pepsin is neutral when contained in the
peptic cells, and becomes acidified only after its escape from
these cells ; for the pepsin obtained fi'om the gastidc mucous
membrane of the animal, after its acidity has been removed by
washing, is neutral. It has also been shown by Bernard, that,
whereas the introduction of lactate of iron, and ferrocyanide
of potassium into the blood of a living animal, produces no
blue colour in the blood, ti.ssues, or secretions generally, nor
even in the gastric glands, yet the surface of the mucous
membrane of the stomach is stained blue. Other parts of the
body, moreover, become blue on the application of an acid.
This experiment, therefore, also favours the sujiposition that
the acid of the gastric juice is formed near, or at, the surface.
It is uncertain whether the separation of the hydrochloric *
acid, is a direct result of an act of secretion by secreting cells,
or whether it is a secondary product of a decomposition, in-
duced by the action of some other intermediately formed free
organic acid. The quantity of solid matter in the gastric
juice, and the relative amount of organic and saline consti-

r

THE LIVER.

C5

tURnts, differ in different animals. It is nniversally acid, but
the nature of the acid, as well as that of the organic peptic agent,
may vary in certain cases, according to the species, age, and
diet of the animal. When the stomach is at rest, its mucous
secretion is neutral or alkaline, semi-opaque, and more viscid
than the gastric juice.

4

Source and Composition of the Bile.

The liver is a solid organ of a dark reddi.sh brown colour,
measuring 10 or 12 inches from side to side, about 7 inches
from front to back, and about 3 inches in thickness at its
posterior margin, its anterior edge being, however, thin. Its
average bulk has been differently estimated at 88 or 100 cubic
inches ; its weight varies from 50 to GO ounces. It is the
largest secreting gland in the body, and, with the exception
of the lungs, occupies more space than any other organ. It
secretes the bile, the importance of which office is shown by
the fact, that the liver is found in all the Vertebrate, and in
most of the non-V ertebrate animals.

The substance of the liver has a sp. gr. of 1050 to 1060.
It has an acid re-action ; its composition, in Man, in 100 parts,
is said to be as follows (Beale). The extractive matters men-
tioned include the amyloid substance named glycogen, a
certain quantity of sugar, with traces ofiuosite, hypoxanthin,
xanthoglobulin, urea, and uric acid.

Wafer . . . . .

Fatty matters ....

3-82'

Albumen ....

4-67

Extractive matters .

fy-lQ

Alkaline salts ....

1-17

Earthy salts ....

•33

Vessels, &c., insoluble in water

10-03J

es-fts

31-42

100-

The liver is placed in the uy)per part of the abdomen,
beneath the diaphragm, reachiiig from back to front, and
from the right side partly over into the left. Its upper
surface is smooth and convex, and is ada])tcd closely to tin-
diaphragm. Its thick posterior boj-der rests on the pillars ol'
the diaphragm and on the vertebral column, being hollowed
out opposite the latter, and presenting also a deep notch for
the ascending vena cava. The thin anterior border is con-
cealed, in the recumbent posture, by the lower ribs and their
VOL. ti. K

66

SPECIAL PIITSIOLOGT.

cartilages, but descends a little below these parts, in standing,
especially during inspiration, when the diaphragm descends
(see fig. 13). This border is slightly notched, a little to the
left of the middle line. The right border of the liver, nearly
as thick as its posterior border, descends lower than the left,
and is in contact with the diaphragm ; the left border, thinner
even than the anterior margin, extends i;pwards to the cardiac
end of the stomach. The under surface, fig.* 90, is concave
and very uneven, presenting various slight depressions, where
it touches the stomach, the duodenum, the bend of the ascend-
ing and transverse colon, the right kidney, and its supra-
renal capsule ; this surface is also marked by special fossa; or
fissures for the lodgment of the gall-bladder, y, and for the
entrance and exit of bloodvessels, lymphatics, nerves, and
ducts.

The greater part of the surface of the liver, is covered by
the peritoneum, by which its slight changes of position in the
abdomen, are facilitated. At certain points, this serous mem-
brane passes, in the form of folds, to the abdominal Avails, and
thus aids in supporting or suspending the liver. These folds
constitute four of the five ligaments of the liAmr. The broad,
suspensory, or falciform, ligament is a triangular double fold,
attached by one border to the diaphragm, and to the anterior
Avail of tlie abdomen as far as the umbilicus, and by the other,
to the upper surface of the liver, as far as the notch in its
anterior margin ; the remaining border is free, and extends
from the notch in the liver, to the umbilicus. This latter
border contains a dense fibrous cord, named the round Iliiament,
llgamentum teres, fig. 96, a, Avhich is formed by the remains of
the umbilical vein, a structure Avhich becomes obliterated after
birth. A considerable portion of the thick posterior border
of the liver, is attached, by areolar tissue, to the diaphragm,
and is therefore not covered by peritoneum, AAdiich, instead,
passes from one part to the other, forms the so-called coronary
iiyument, and thus helps to suspend the liA'er to the diaphragm.
The right and left lateral ligaments are triangular peritoneal
folds, strengthened by intermediate fibrous tissue, Avhich pass
from each side of the liver to the diaphragm.

The liver is described as consisting of five lobes. Tims, it
is divided by the notch in its anterior margin, and by the line
of attachment of the suspensory ligament to its upper surface,
into a right, I, and left lobe, I', the former being quadrangular
in shape, and the latter someAvhat triangular, and constituting

THE LIVER.

67

only about one-fifth of the entire organ. A deep fissure on
the under surface, also marks the limit between these lobes.
On its under surface, the right lobe is further divided into the
Ibllowing smaller lobes : viz. the Spigelian lobe, a pyramidal

Fig. 96.

Fig. 90. View of tlic under siirfaee of tlie liver and stoinacli, lifted up, to
show the duodenum, pancreas, and spleen, and their mutual relations,
s, the under or posterior surface of the stomach, which is lifted up.
0, the msophagus. p, the pylorus, d, the horse-shoe curve of the duo-
denum. or first part of the small intestine. I, under side of the right
lobe of the liver. V, V, under side of the left lobe, the liver being turned
up. a, small piece of the round and suspensory ligament of the liver.
g, under side of the gall-bladder, ending below in the cystic duct: this
is joined by the hepatic duct, formed by the union of a right and loft
duct, from the two lobes of the liver. The common duct, resulting from
the union of the cystic and hepatic ducts, the ductus communis chole-
dochus, or common bile duct, passes down, as shown by the dotted lines,
behind the duodenum, to end with the pancreatic duct, also shown by
dotted lines, by a common orifice, on a papilla, in the duodenum, b, the
pancreas, attached to the curve of the duodenum ; it is i)artly di'sectod
to show its ci'ntral duct, with its branches, the end of it being indicated
by dotted hues, sis above described, m, the sisloen. attached ti) the left
end of the stomach and pancreas; its anterior notched border is seen.
The drawitsg indicates the dark colour of the sjslcon and liver, and the
white Colour of the isancreas.

mass situated near the liindcr border ; the caudate or tailed
lobe, jstissing forwards Irom the Spigelitm lobe; tiiid, histlv
the e<iuare or (/nadrale lobe, jslticed between the gall-b];idder
and the line of dcmtircation between the right and lell lobes.

e 2

68

SPECIAL PHTSIOLOGT.

The liver also presents, on its under surface, five fossa; or
fissures, in which are contained important vessels and ducts.
The longitudinal fissure passes, from before backAvards, be-
tween the right and left lobe.s, and is divided into two parts ;
the anterior part is named the umbilical fissure, w'hich con-
tains, before birth the umbilical vein, but afterwards, the round
ligament, the fibrous cord, left after the obliteration of that
vein ; the posterior part, called the fissure of the ductus venosus,
contains, before birth, the large vein so named, and subse-
quently the fibrous cord remaining after its closure. Thirdly,
extending nearly at right angles from the junction of the
umbilical fissm-e Avith the fissure of the ductus venosus, to
about the centre of the right lobe, is the transverse or portal
fissure, or porta, the gate, sometimes called the hilus of the
liver ; through this the chief bloodvessels, lymphatics, nerve.s,
and ducts of the liver pass in and out (see fig. 96). The
principal vessel Avhich enters here, is a large vein, the vena
porta; or 2^ortal vein. The fourth fissure is the notch on
the posterior border of the liver, Avhich joins the fissure for the
ductus venosus, and lodges the ascending vena cava and
the orifices of the so-called hepatic veins. The fifth fissure
receives the upper side of the gall-bladder.

The liA'er possesses three sets of bloodvessels, tAAm convey-
ing blood to it ; viz. the portal vein and the hejmtic artery,
and a third set, the hepatic veins, which carry the blood from
it. The liver in Man, and in the Vertebrata generally, is re-
markable for being supplied, partly by venous, and partly by
arterial, blood, for the portal vein, contrary to the usual office
of a vein, conveys blood into the liver. This portal A'ein, fig.
97, p, is formed by the union of the veins of the abdominal
organs of digestion and sanguification, excepting the liver
itself, viz. by those of the stomach, s, small intestine, i, large
intestine, co, except the lower tAvo-thirds of the rectum, r, of
the gall-bladder, pancreas, d, and spleen, m. The a" eins, from
these parts, unite to form the superior mesenteric and splenic
veins, which join to constitute the A’^ena porta;. The A^enous
trunk thus formed, p, is of great size, being more than half an
inch in diameter. It ascends to the imder surface of the lirmr,
and entering the portal fissure, there diAudes into a right and
left branch, for the corresponding lobes of the liver, in the
substance of which it ramifies like an artery. The hepatic
artery, which also conveys blood to the liver, i.s,a branch of
the ccdiac axis, a short trunk given off from the abdominal

Fig. 97.

/

\

Fig. 97. Diagram to show tho large vessels concerned in the so-called nortal j

circulation. The trunk, or body, is supposed to be divided down the I

middle line, so as to show the cavity of the thorax or che.st, above the I

arched diaphrag ii, and that of the abdomen below it. In the abdomen, !

I, is the liver ; s, tluf stomach ; d, a section of tin; duodenum, and pan-
creas; i, the small intestine; co, a part of the colon; r, the rectum;

TO, the lower end of the spleen; and Ic, the right kidne.v. Thu blood to
all these parts, is supplied thr.'Ugh art' ries which are branches of the
abdominal aorta, marked o. From the rectum, r, and the kidney, /c,
the blood is returned by veins, which end in thi' great ascending vein,
named the ascending vena l ava, marked c, which conveys the venous
blood directly through the diaphragm, and into the right side of the
heart, o. But the blood from the stomach, s ; spleen, to ; duodenum anil
pancreas, d ; small intestine, i; and largo intestine, co (excepting the
rectum, r), is collected by venous branches, which end in a large venous
trunk, named the vena portsc, or portal vein, p, by which this venous

blood is conveyed to, and distributed by branches through, the liver. l

From this organ, it is collected by other veins, which unite to form the i

hepatic veins, A, which then join the ascending vena cava, c, and so reach I

the right side of the heart. (

il

70

SPECIAL PHYSIOLOGY.

aorta, a; it enters the liver, by the side of the vena port®, at
the portal fissure, and, like that vein, divides into a right and
left branch for the coiTesponding lobes. The hepatic veins,
which convey the blood from the liver, converge from all
parts of the oi-gan, to the notch in its posterior border, where
they enter the ascending vena cava, by two or three main
trunks, and thus the blood from the liver, mixed Avith that
from the loAver half of the body, ascends to the heart.

The liver, like all secreting glands, is provided Avith ducts.
These, named the hepatic ducts, form, as they issue from the
gland, tAvo principal trunlcs, one fi-om the right, the other from
the left lobe. They emerge at the bottom of the portal fissure,
Avhere the tAvo chief divisions of the portal vein and hepatic
artery enter, and then unite to form a single duct named the
hepatic duct, ductus choledochvs, or hile duct. Having de-
scended for about tAvo inches, this joins another duct, proceed-
ing from the gall-bladder, fig. 96, g, named the cystic duct,
and so forms the ductus communis choledochus, or common
hile duct. This latter duct is about three inches long, and
tAvo or three lines Avide ; passing doAATi behind the duodenum,
d, it reaches the left or concave border of the intestine, AAdiere
it comes in contact Avith the pancreas, and soon after, Avith the
duct of that gland, or pancreatic duct, fig. 88, a, fig. 96. The
tAvo ducts then pass together, and obliquely, through the
Avails of the duodenum, for about three-quarters of an inch, and
finally, opposite the junction of the middle and lower parts of the
duodenum, about three inches below the pylorus, open upon a
slight eminence of the mucous membrane, by a common and
slightly constricted orifice, provided Avith a kind of sphincter.
Sometimes, hoAvever, the biliary and pancreatic ducts open
separately into the duodenum.

The lymphatics of tlie liver are either superficial or deep ;
the former ramify upon its siu’face, the latter emerge at tlie
]3ortal fissure. The nerves are comparatively feAv in number ;
they are derived chiefly from the sympathetic system, and, as
usual Avith those nerves, are supported on the ai-teries. The
pneumo-gastric nerves, especially the left, also supply a feAv
branches to the liv'er. The right phrenic nerves send filaments
to the peritoneal coat. Beneath the partial peritoneal invest-
ment, the liA'er possesses a proper areolar coat, Avliich covers
its Avhole surface, and, at the portal fissui'e, passes into the
interior of the organ, and becomes continuous Avith a loose
areolar tissue, named the capsule of Glisson, to be presently
descrilied.

THE HEPATIC LOBULES.

71

The proper substance of the liver, is firm, and presents, on a
section, a reddish-brown mottled asjiect. It is composed of
a multitude of compressed polyhedral masses, about the
size of a pin’s head, measiuang from -j^th to -jVth of an
inch in diameter, named the hepatic lobides ; they cause
the gi’anular appearance of the torn surface of the liver.
These little portions of gland substance, are held together
by the idtimate ramifications of the bloodvessels and ducts,
and also by a fine areolar tissue, occupying the inter-
lobular spaces, and named the interlobular tissue, which is
itself connected, on the smlace of the gland, with the areolar
coat. The hepatic lobrdes are closely arranged around cer-
tain canals, which commence at the portal fissure, branch
out in aU directions through the gland, becoming smaller
and smaller as they proceed, and ultimately lose them-
selves in tlie interlobular spaces. These are the p>ortal canals,
which contain not only the branches of the portal vein, but
also those of the hepatic artery, and hepatic ducts, the deep
lymphatics, and the nerves. Sm'rounding and supporting those
vessels, ducts, and nerves, is foimd the loose areolar tissue,
named Ghsson’s capsule, which, outside and beyond the portal
canal, is continuous with the interlobular tissue. A transverse
section through a portal canal, shows a roimdish space in the
gland-substance, occupied chiefly by a section of a portal vein,
with which, however, are associated one or two branches of
the hepatic artery, and hepatic duct, the whole being embedded
in the capsule of Glisson; the arteries are smaller than the duct ;
the canal also contains lymphatics, invisible, unless injected,
and nerves supported upon the arteries ; in the smallest portal
canals, the parts are not so distinct. The hepatic veins do not
lie in the portal canals, but pursue a separate course through
the liver, the branches of these being seen, on a section, passing
along through the gland, immediately surrounded by the lobules.
As the portal veins diverge from the portal fissure, whilst the
hepatic veins converge to the posterior border of the gland,
their branches cross each other ; moreover, tliey have very
different relations to the hepatic lobules.

Each minute lobule has one aspect, which is named its base,
whilst its other surfaces are called its sides. The bases of
all the lobules rest upon the so-called sublobular veins, which
are branches of the hepatic vein, the inner .surface of which,
as sliown when they arc opened, is marked by the ])olygonal
outlines of tlie bases of the lobules. When divitled trans-

SPECIAL PHYSIOLOGY.

72

versely, the lobules are polyhedral ; when cut longitudinally,
they present a foliated appearance, and are seen to be sup-
ported on the sublobular hepatic veins, like sessile leaves upon
a leaf-stalk.

The sides of the lobules are turned towards each other in the
interlobular spaces, towards the portal canals, or to the surface
of the liver. The portal veins, ramifying in the portal canals,
give off branches which enter the interlobular spaces, and are
hence named interlobidar veins] from these, still finer branches
penetrate the sides of the lobules, and end, within them, in the
so-called lobular venous plexus, or lobular capillary network.
From this network, proceeds a small vein, occupying the centre
of each lobule, named the intra-lobular vein, and belonging to
the hepatic venous system ; it opens by a minute orifice,
situated in the middle of the base of the lobule, into the cor-
responding sublobular vein.

It will thus be .seen, that the blood of the portal vein, is
conveyed, by the portal interlobular veins, to the sides of the
lobules, and thus reaches their internal vascular plexus, from
which it is collected by the hepatic intralobular veins, and
so passes out, at the bases of the lobides, into the sublobular
hepatic veins, by which it is ultimately conveyed away.

From the peculiar distribution of the branches of the portal
and hepatic venous systems, in each lobule, it follows that a con-
gested state of either, influences the mottled colom- of the liver
iu a characteristic manner. Thus Avhen the hepatic system is
congested, a rather frequent occurrence, the centre of each
lobule is dark, and the circumference paler ; whilst in portal
congestion, which is rare, and occurs chiefly in children, the
centre of each lobule is pale, and the marginal part dark.
From the great size of the portal vein, as compared with the
hepatic artery, it is evident that the liver is chiefly supplied
by venous blood. But even the arterial blood furnished to
this organ, by the hepatic artery, appears to become venous
and portal, before it reaches the plexus within the lobule. The
hejxitic artery is a nutrient vessel, supplying the framework,
and not the secreting tissue, of the liver ; its branches termi-
nate in a capillaiy network, in the coats of the bloodvessels
and ducts, in the areolar ti.ssue of the capsule of Glisson, the
interlobular tissue, and the areolar coat of the liver; from
these parts, the blood, now become venous, is believed to be
returned into the smaller porbil veins, and in this indirect
manner only, to reach the hepatic lobules. According to this

THE GALL BLADnEE.

73

view, amongst the sources of the portal blood, must be included,
not only the stomach, intestinal canal, pancreas, gall-bladder,
and spleen, but also the non-secreting part of the liver itself.

The secretinfj portion of the liver is composed, in each
lobule, first of the lobular capillary network or venous plexus,
already mentioned, as interposed between the termination of
the portal and the commencement of the hepatic venous
systems; secondly, of an intermediate gr/anfZ-si/Jshmce ov paren-
chyma, occupying the interstices of this capillary network; and,
thirdly, of the commencements of the hepatic or biliary ducts.
The gland-substance consists of roundish, or flattened, poly-
hedral, nucleated cells, having a delicate cell-wall, one or two
bright vesicular nuclei vdth nucleoli, and certain faintly
yellowish, semi-fluid, amorphous, granular contents, in which
are commonly found larger or smaller globules of oily matter.
These very peculiar cells, are named the hepatic cells ; they
vary from ™ diameter. They are

the true secreting gland-cells of the liver, their contents
closely resembling*the bile, which is secreted by them. The
relations of these cells to the finest commencements of the
biliary ducts, and the mode of commencement of those ducts,
are difficult points for investigation. The clusters of the
hepatic cells occupy the interstices of the lobular venous
plexus, and, whatever may be their relation to the finest com-
mencements of the ducts, or in whatever mode the bile, formed
within these cells, passes into the ducts, the hepatic cells
themselves lie outside the venous plexus, and this has no
direct communication with the ducts. The hepatic cells,
moreover, are aiTanged in lines or rows, which radiate,
among.st the bloodv'essels, fi’om the centre towards the circum-
ference of the lobule. By most anatomists, these rows of cells
are said to be supported on a thin basement membrane, which
is continuous with the walls of the commencing efferent biliary
tubes or ducts, so that the liver might be regarded as a com-
plex gland, having ramified anastomosing ducts (Beale and
Ketzius). According to another view, however, the hepatic
cells are merely aiTanged around the network of the lobular
ple.xus, and are unsupported by a proper basement membrane
(Kiilliker).

The (lall-bladder. — The hepatic, cy.stic, and common Vile
ducts, already described, are composed of a strong areolar
coat, containing a few muscular fibres, and lined by a mucous
membrane covered with a columnar epithelium ; in the finest

74

SPECIAL PHYSIOLOGY.

ducts, the epithelium is squamous. The walls of these ducts
present generally minute racenrose mucous glands, the ojjen-
ings of which, are arranged in rows within the ducts. The
cystic duct which leads to the gall-bladder, has, in its interior,
a series of oblique crescentic projecting ridges or folds, follow-
ing each other closely, so as to present the appearance of a
spiral valve.

The g all- bladder, fig. 9G, g, is a pear-shaped sac, Irom 3
to 4 inches long, about 1 inch across at its widest part,
and holding rather more than one fluid ounce. It is lodged
in a fossa on the mider surface of the liver ; its larger end or
fundus, projects beneath the anterior border of the gland ;
whilst its narrow end or neck, directed, beneath that organ,
upwards, backwards, and to the left, is continuous with the
cystic duct. Its upper surface is attached to the liver by
areolar tissue and bloodvessels ; the re.st is covered by the
peritoneum, which therefore furnishes it with a partial sei’ous
coat. Its proper walls are composed of interlacing bands of
white, flbrous, and areolar tissue, intermixed with elastic
flbres, and longitudinal and circular unstriped muscular fibres.
Within this areolar coat, is the mucous coat, which has a
pecifliar pitted or alveolar aspect, owing to the presence of
innumerable fine ridges, which bound polygonal dej^ressions
of various size and form ; at the bottom of the largest depres-
sions, there are seen, by aid of a lens, the orifices of fine
recesses resembhng mucous follicles. The mucous membrane
of the gall-bladder is usually of a deep yellow colour, and is
lined by a columnar epithelium.

The gall-bladder forms a sort of receptacle, or reservoir for
such bile as is not immediately required for the purposes of
digestion. It has been shown, in animals, in which artificial
openings, or fistulas, have been made into the hepatic duct, that
bile is being constantly secreted by the liver. In the intervals
between the process of digestion, the secretion is slow ; but,
during digestion, the bile is secreted very rapidly, and at once
passes along the hepatic duct, and common bile duct, into the
duodenum ; such bile is named hepatic bile. The joeriod of
most ra^iid secretion, in animals, has been variously stated to
be fi'om one or two hours, to ten or twelve hours after eating.
According to observations made by Dalton on a dog, the
quantity increases suddenly after eating, reaches its maximum
in an hour, and then gradually declines ; a far larger quantity
enters the intestine during the first hour, than in any other

THE BILE.

75

equal period. Abstinence lessens the quantity veiy much.
In the intervals between digestion, however, the bile being
secreted more scantily, has not sufficient force to pass through
the narrow orifice of the common duct, and thus more or less
of the secretion enters the gall-bladder ; there, it undergoes
inspissation, losing water, and receiving much mucus from the
gall-bladder, some having been already added to it, in the
ducts. It thus becomes darker, and more viscid, and, in this
condition, it is called cystic bile. The mechanical effect of the
spiral folds in the cystic duct, on the passage of the bile into,
or out of, the gall-bladder, is probably to favour its entrance,
and somewhat check its escape. During digestion, both
cystic and hepatic bile are believed to be employed, and it is
supposed that, at that period, the former is pressed out of the
gall-bladder, partly by the distended stomach, and partly by
the contraction of its own muscular fibres, stimulated in a
reflex manner, by the acid chyme passing over the orifice of
the common bile duct, the sphincter-like margin of which
may be at the same time relaxed.

The analyses of bile present some discrepancies which may
depend on the difference between the hepatic and the cystic
bile. Speaking generally, the bile is a yellowish, or yellowish-
green, viscid fluid, having a peculiar smell, and a bitter taste.
In carnivorous animals, its colour is brownish-yellow ; in
herbivorous animals, it is generally greenish. The quantity of
bile secreted by a man in tAventy-fom- hom-s, is uncertain. In
dogs, with artificial biliary fistula, the quantity secreted daily
is about oz. to every pound weight of the animal, or -^nd
part of its weight (Kblliker, H. Muller). Supposing the
weight of a man to be 140 lbs., this would give 70 ozs. or 4 lbs.
6 ozs. avoirdupois in a day, of which about -g^g-th, or nearly
3 ozs., would be solid matter. This estimate, however, appears
very high. Bidder and Schmidt calculate the daily quantity
secreted by man to be 5G ozs. ; Nasse and Platner’s observa-
tion on the dog, would give a total daily quantity for man of
ozs. ; whilst others again have estimated it at only from
17 to 24 ozs. The specific gravity of the cy.stic bile in man,
varies from 102G to 1032; that of hepatic bile is of course
less. The cystic bile of man, contains about 10 per cent, of
solid matter ; while the bile, from an artificial fistula in the
bile duct of an animal, i.e. hepatic bile, contains from 3 to 5
per cent. only.

76

SPECIAL PIiySIOLOGT.

The analysis of cystic ox gall by Berzelius, gives the follow-
ing percentage composition : —

Water ........ 90'44

Bilin, with fat and colouring matters . 8

The analyses by other chemists, show a similar composition,
but, according to Strecker, the bilin of Berzelius is a compound
substance. Its two characteristic constituents are the colour-
less conjugated fatty acids, named glycocholic or cholic, and tau-
rocholic ; the one formed by the combination of a nitrogenous
body, named glycocin, or glycocoll, and cholalic acid ; the other,
formed by the union of the same acid with another nitrogenous
body, which contains sulphur, named taurin. The chemical
relations of these substances may be seen, by comparing their
atomic compositions (Vol. I., p. 98).

Cholalic acid crystallises in Avhite tetrahedra ; dissolved in
sulphuric acid, with the addition of sugar, it yields a purple
violet colour, the reaction of the so-called Pettenkofer’s test
for bile. Glycocoll, obtainable also by the action of acids or
alkalies upon glue and some other animal substances, forms hard,
transparent, colourless, crystals, soluble in water, but nearly
insoluble in alcohol and ether. Taurin crystallises in white
hexagonal prisms, inodorous and almost ta.steless ; it contains
the large proportion of one-fourth its weight of sulphur ; it
leaves much sulphurous acid on being burnt, and gives otf
sulphuretted hydrogen Avhen decomposed. Both glycocoll and
taurin are neutral substances, having a tendency to unite with
acids, to form, as in the bile, conjugated acids. Glycocholic,
or cholic acid, consists of fine crystalline needles, soluble in
water and alcohol, but very slightly so in ether, having a bitter ’
sweet taste, and a strong acid reaction. Taurocholic acid has
not yet been obtained in a crystalline form. In the bile,
the glycocholic and taurocholic acids, which form from 4
to 7 per cent, of that secretion, are always united with soda,
as glycocholate and taurocholate of soda. The bile, however,
occasionally contains an excess of some base ; for, though
often neutral, it may be feebly alkaline. The substance of the
liver has, or rapidly acquires after death, an acid reaction.
The proportions of glycocholic and taurocholic acids, vary in
the bile of different animals, but are tolerably constant in each
species. In the dog, the glycocholic acid is scanty, and sometimes

Mucus, chiefly cystic .
Salts . . . .

1

9-56

100-00

THE CONSTITUENTS OF TUE BILE.

77

absent. In the pig, another allied acid is found, named
hi/ocholic, and a small quantity of an acid analogous to the
taurocholic. In the goose, a different allied acid exists, named
tauro-chenolic. Although varied in different animals, and
present in variable proportions, the characteristic constituent
of the bile is, in all cases, a soda salt of some fatty acid, resem-
bling the acids of fatty and resinous bodies. The sulphuretted
and nitrogenous body, taurin, is always present.

The next most characteristic constituent of the bile, is its
colouring matter, named by different chemists, cholepyrrhin,
bilipyrrhin, and biliphcvin. This fornis about 5 per cent, of
the secretion. According to Berzelius, two modifications of
colouring matter exist in bile. The one, a yellowish colouring
substance, was named by him bilifulvin ; it seems to coincide
with the cholepyrrhin and biliphtein of other writers. It is
uncrystallisable, insoluble in water, only slightly soluble or
insoluble (Brlicke) in alcohol, but especially so in caustic
alkalies, and in chloroform. It affords a peculiar reaction with
nitric acid or nitrates, which, when added in small quantities
to the yellow alkaline solution, first produce a green colour,
then blue, violet, and red, and finally yellow again, owing, it
is supposed, to the occurrence of different degrees of oxidation.
The other colouring matter of the bile, smaller in quantity, is
green, and hence was named by Berzelius, hiliverdin ; it was
supposed by him, though not proved so, to be identical with
chlorophyll. It is insoluble in chloroform, slightly so in alcohol,
and insoluble in water ; it appears to be a more highly oxi-
dised form of bilifulvin. These colouring matters are closely
allied to the hasmatin, or cruorin of the blood ; but neither
these, nor the fatty acids of the bile, pre-exist in the blood ;
they are formed in the liver by the hepatic cells.

In addition to these, its essential constituents, bile contains
about 1 per cent, of ordinary fats, margarin and olein, or
alkaline margarates and oleates. It also presents traces of
clwlesterin, the fatty or resinoid body, which likewise exists
in nervous substance, in the blood, and in certain diseased
exudations. Cholestorin crystallises in brilliant colourless
plates, insoluble in water, soluble in boiling alcohol and in
ether, and absolutely resisting saponification. In the living
body, it is probably held in solution by fluid fats. The bile
contains about 1 per cent, of salts, its ashes yielding, besides
soda in large proportion, traces of potash, magnesia, and lime,
in combination with phosphoric acid and chlorine. The

78

SPECIAL PHYSIOLOGY.

mucus found in bile, indicated by the presence of mucous
and epithelial cells, is an adventitious substance, derived from
the walls and follicles of the bile ducts or gall-bladder.

Besides being engaged in the formation of biliary substances,
partly intended for use in the digestive process, and partly
destined, as we shall hereafter explain, to be thrown out of the
body as excrementitious matters, the liver has recently been
discovered to perform another most remarkable office in the
economy, viz. that of sejiarating from the blood by its cells, a
substance named ghjcogen, or animal starch, which has the
property of being rapidly transformed into glucose, or grape
sugar. This sugar is .supposed to enter the hepatic blood, to
proceed with it to the heart, and thence to the lungs, to be
oxidised in the respiratory process, and aid in the develop-
ment of heat. This glycogenic or sugar-forming function
of the liver, will be more fully noticed in the section on
Secretion.

Sources and Composition of the Pancreatic Juice.

The pancrens {-Kav rpeac, all flesh), or abdominal sweetbread,
is a long, narrow, pinkish, gland, flattened before and behind,
having its right, larger end lodged in the concavity of the
duodenum ; whilst its left, pointed exfremity, touches the spleen.
Its shape has been compared to that of a dog’s tongue, or of a
hammer. It crosses over the front of the first lumbar vertebra,
behind the lower border of the stomach, and is held in place
by its attachment to the duodenum, by its bloodvessels,
nerves, lymphatics, and ducts, by areolar tissue, connecting it
with adjacent parts, and by a peritoneal layer. It is about 6
or 8 inches long, 1^ inch broad, and from an inch to
1 inch thick, being thicker at its larger end. It rrsually
Aveighs between 2^ and 3^ ozs , but sometimes as much as
G ozs.

In structure, the pancreas resembles the salivary glands,
and has been termed the abdominal salh'ary gland. Its
numerous lobes and lobules are compressed, and are held
together l)y the Amssels, ducts, and interlobular areolar tissue.
Each lobule, like those of the parotid gland, fig. 42, c, consists
of a branched duct, ending in rounded A^esicles, surrounded
by networks of capillaries. The ducts fi'om the numerous
lobes, join a jtrincipal duct, Avhich runs through the gland
from left to right. This duct, the pancreatic duct, or canal of
Wirsung, who discovered it in the human body, in 1G42, is

THE PANCREATIC JUICE.

79

about tlie size of a small quill ; it emerges from the larger
end of the gland, and, accompanied by the common bile duct,
passes, with it, obliquely through the walls of the duodenum,
and, about 3 inches below the pylorus, opens into the intestine
by a common orifice with the bile duct, or sometimes by a
separate aperture. Occasionally there exists a supplementary
pancreatic duct, which enters the duodenum about an inch
from the chief duct.

The secretion from the pancrea.s, or the pancreatic juice, is
a somewhat viscid, transparent, colourless, and inodorous fluid.
The quantity secreted daily, in animals, varies, according to
different observers, from 1.5 to 35 grains per hour for each
pound weight of the body ; so that in a man Aveighing 140
pounds, the quantity secreted would be from 4^ ozs. to 11
ozs. per hour. The secretion is probably not continuous, and
its quantity increases as digestion goes on, the activity of the
process being, by some, referred to the absorption of albu-
minoid substances already digested. From these fluctuations,
it is impossible to estimate correctly the quantity formed
daily ; AV'hich has been differently estimated at fi-om 7 ozs. to
1 lbs. Statements, almost as discrepant, have been made
concerning the gastric juice and bile, correct results, as regards
these internal secretions, not being so attainable as in the
case of the saliva. The collection of these fluids, by aid of
artificial fistulas, in animals, is open to the objection, that the
conditions, especially of the nerves, Avhich govern the quantity
of the secretion, are not liealthy. The total quantity of the
digestive fluids poured into the alimentary canal, after taking
food, is, however, much greater than Avas formerly supposed,
and, in comparison Avith the blood circidating in the body, is
very great.

The solid con.stituents of the pancreatic juice, as e.stimated
from cases of artificial fistulas in animals, vary from 1 -5 to fi,
or even 1 0 per cent. ; the more rapid the secretion, the less
.solid matter it contains. Its most peculiar constituent is an
albuminoid substance n.amed pancreatin, tlie special composi-
tion of Avhich is not yet determined. Like salivin, this sub-
stance is soluble in Avater, coagulable by heat, and precipikible
by alcohol, but may again lie dissolved in Avater; unlike
albumen, it is precipitated by sulphate of magnesia. To the
pancreatin, are attributed the peculiar digestive properties of
the pancreatic juice, Avhich differ, in one re.spect most remark-
ably, from those of the saliva. The pancreas, indeed, resembles

80

SPECIAL PHYSIOLOGY.

the salivary glands anatomically, but not physiologically ; for
its secretion is much more viscid, is coagulated by strong
mineral acids, and does not contain sulpho-cyanide of potas-
sium. Its salts, about '5 to !• per cent., are chiefly chloride
of sodium and phosphate of lime and magnesia. Like the saliva,
it is alkaline, but more strongly so ; as digestion proceeds,
it becomes more alkaline, but less viscid and coagulable. On
standing, it speedily becomes neutral and then acid ; it soon
puti-efie.s, but may be preserved for a few days, at a tempera-
ture of 45° ; its properties are destroyed by a heat slightly
above that of the body. It contains the debris of a few
nucleated cells.

Sources and Composition of the Intestinal Juices.

The mucous membrane of the small intestine, is provided
with two kinds of secreting glands, named respectively, after
their discoverers, the glands o f Brunner and the glands, follicles,
or crypts of Lieherlcuhn. The secreted products of all these
glands, constitute the succus entericas.

Brunner s glands are found in the duodenum, being most
abundant near the pylorus, and disappearing lower down,
very few being present at the commencement of the jejunum.
They are compound racemose glands, like the buccal and labial
glands, and appear to bear the same relation to the pancreas
as those glands do to the salivary glands. They secrete a
viscid alkaline mucus.

1\\e follicles or crypts of Lieherlcuhn are found throughout
the small and large intestines. They consist of multitudes of
minute tubuli, closed at their deep extremities, but opening
on to the surface of the mucous membrane, perpendicularly to
which they are arranged, more or less closely together. In the
small intestine, they measure from -/(yth to ^\yth of an inch in
length, and about ^,y^th of an inch in diameter. Their orifices
are seen, fig. 98, by aid of a lens, in all parts of the small in-
testine, even on the valvulte conniventes, between the villi, and
also in little circlets, around the closed sacs of the so-called
agminated glands. Their total number has been estimated
at several millions. They are sometimes flask-shaped, but
never sulidivided, like the gastric glands; they are liimd
with a columnar epithelium, fig. 99, and are surrounded bv
capillaries.

They contain a transparent granular fluid, the intestinal

THE INTESTINAL TDBULI AND JUICE.

81

juice 2^1'oper] sometimes they are distended with opaque
mucus, and desquamated epithelial cells destitute of fat. The
composition of the intestinal juice, is not well known; it pro-
bably ditf'ers from ordinary mucus, and has special jaroperties ;
it is colourless and viscid, and is usually described as being
strongly alkaline, but, according to others, it is acid in a great
imrt of the small intestine ; it contains from 2 to 3'5 per cent,
of solid matter, in which is included an organic substance,
jwecipitable by alcohol and resoluble in water, but forming
insoluble precipitates with metallic salts.

Attempts have been made to collect it, from animals, by liga-
turing previously emptied portions of intestine, or by forming

Fig. 98. Fig. 99.

Fig. 9S. Portion of the border of a Peyer’s patch, inagiiified about twelve
diameters. It shows the minute pointed processes named the villi of
the small intestine, found both on the general surface, and also on the
lighter part or Peyer’s patch. On this latter, are seen the rounded or
oval sacs, constituting the agminatod glands, with the villi between, not
upon, them. Around the borders of those, are circlets of the orifices of
the intestinal tubuli, or crypts of Lieberkiihu, others of which are seen,
scattered over the general surface between the villi. (After Boehm.)

Fig. 99. Diagrammatic vertical section of one sac, and a part of another,
from a patch of Peyer, with the surrounding iiarts. g, the sac with its
granular contents. /, one of the intestinal tubuli, crypts, or follicles
of Liebcrkiihn, of which three others are seen, on the other side of the
sac. V, the intestinal villi, on the surface of the mucous membrane,
covering the patch, m, cut ends of the circular muscular fibres j be-
neath these, the longitudinal fibres, and the serous or peritoneal cover-
ing of the intestine. (After Kolliker.) Magnified forty diameters.

artificial intestinal fistulse ; but tlio fluid so obtained, must
differ from the normal secretion, 'flic quantity daily secreted
in Man is uncertain, but is doubtless considerable, especially
after meals,

VOL. II,

G

82

SPECIAL PHYSIOLOGY.

The tubuli or crypts of Lieberklihn of the large intestine,
are longer, Avider, more nnnierona, and moi'e closely arranged
than tliose of the small intestine. The entire surface presents,
Avhen examined with a lens, a cribriform aspect, due to the
numerous orifices, Avhich, in the loAver ]tart of the intestine,
are almost visible to the naked eye; they are lined Avitli
columnar epithelium. Besides these crypts, thei-e are found,
scattered over the raucous membrane of the large intestine,
small depressions, resembling saccular glands; they Avcre
formerly desci-ibed as solitary glands, but they are lined Avith
a columnar epithelium only, and are ]>laced over certain closed
sacs, exactly similar to those of the so-called solitaiy glands of
the stomach and small intestine, and of the agminated glands
of the latter.

The inte.stinal juice of the large intestine, resembles, so far
as is known, that of the small intestine, being composed partly
of mucus, but chiefly of a sjiecitd secretion, Avhich is .said to be
alkaline, though, in the catcum, the intestinal contents are acid.

CHEMICAL PROCESSES OF DIGESTION. ACTION OF THE DIGESTIVE
FLUIDS, WITH HEAT.

As already stated, the purpose of the digestive process in
the animal economy, is the reduction of alimentary substances
into a soluble and absorbtible condition, a state of solution, or
of exceedingly minute subdivision and suspension in a fluid,
being an essential condition, antecedent to the absorption of
any nutrient substance into the living tis.sues. Food, as Ave
have seen, considered chemically, consists of Avater, alkaline
and earthy salts, and certain important organic proximate
constituents, Avhich are clas.sitied into non-nitrogenous and
nitrogenous substances.

Of these, the Avater, the natural medium of solution or
suspension of the solid alimentary substances, and likcAvise the
saline substances, both alkaline and earthy, Avhich are mostly
dissolved in it, correspond Avith the A\ater Avhich forms three-
fourths of the soft tissues of the bodj', and with the Avater and
salts of the blood : they tire directly ab.sorbcd Avithout any
digestive change. The organic constituents, Avhcther non-
nitrogenous or nitrogenous, tire some of them soluble, and
some insoluble in water at the temperature of the interior of
the body, viz. about 102°. The soluble uou-uitrogenous bodies

PROBLEMS OF DIGESTION.

83

are pectin, gum, dextrin, sugars, alcoliol, organic acids, and
ethers. The soluble nitrogenous substances are certain forms of
albumen, fibrin, casein, gelatin, and chondrin ; the albuminoid
principles of the digestive fluids, viz. salivin, pepsin and pan-
creatin, which are probably in a state of solution in the living
body; creatin and creatinin; cerebricacid; andthein, caffeinand
theobromin. Many of these also are possibly directly absorbed.
The insoluble organic constituents are the uon-nitrogenous
cellulose, starch, and fatty matters ; and the nitrogenous solid
forms of albumen, syntonin, casein, fibrin, gluten and legumin,
and the gelatin and chondrin-yielding tissues. AH these, how-
ever soft or minutely divided, must be dissolved, before they
can be absorbed. They are the most abundant constituents of
our ibod : in all kinds of bread, and biscuit, in cooked potatoes,
rice, sago or tapioca, the quantity of insoluble starch is greater
than that of soluble starch, gum, dextrin, or sugar ; in cooked
meat, poultry, fish, and eggs, and also in cheese, the albuminoid
constituents are all solidified ; the vegetable gluten and legumin
are either solid, or are coagulated by cooking ; and even the
fluid or finely granular casein of milk, is first precipitated or
curdled in the stomach, by the action of the acid gastric juice.
Indeed, undissolved, though minute, granides of amyloid,
insoluble oleoid, and soliditled albuminoid substances, con-
stitute the most nutritive forms of food.

In a chemical sense, these substances are instable com-
pounds; they have a high atomic constitution, and are easily
broken up by powerful chemical agents, by elevated tempera-
tures, fermentation, or putrefaction. Nevertheless, under ordi-
nary circumstances, they are insoluble in water at the heat of
the body, and are decornpo.sable,or rendei'ed soluble, only by the
action of agents and temperatiii'es, which would be desti'uctivo
to living animal tissues. 'I'hus, starch is rendered mucilaginous
only at the temperature of 1(!0° ; it is changed into dextrin at
a still more elevated temperature ; and it is convertible into a
sugar, by the highly corrosive sulphuric acid. Of the fats, mar-
garin and stearin become fluid only at temperatures higher than
that of the body, viz. 114°, and 118°; none of them are easily
miscible with, or can be kept suspended, in minute particles,
in watery fluids; and to reiulcr any of these soluble in water,
they mii.st be .saponified by the action of cau.stic alkalies, which
are destructive to living tissue.s. The solid albuminoid prin-
ciple.s, so far from being soluble even in boiling water, have
their component jtarticles knit .still more firmly together, by

84

SPECIAL PIITSIOLOGT.

being boiled; and putrefaction alone will dissolve them, — a
condition inconsistent Avith their retention of nutritive pro-
perties, and, indeed, converting them into noxious products.

The first problem of digestion, howcA'er, is to render such
substances, Avhich, in this point of view, are refractory, soluble
at a temperature, and by means of agents, compatible with the
life and integrity of the digestive organs themselves. But,
secondly, starch, even when dissolved, so as to form a soluble
mucilage, and also albumen, Avhen perfectly soluble as in the
white of egg, are too tenacious to pass readily through moist
membranes, and belong to the so-called colloid bodies, Avhich
have a feeble permeating power, in comparison Avith the so-
called crystalloid substances (Graham) ; whilst oil, likeAAUse,
passes through moist membranes, only under considerable
pres.sure. Accordingly, in the process of digestion, starch is
not only dissolved, but is converted into the crystalloid,
and highly permeating substance, sugar ; albuminoid bodies
are converted into a substance named albuminose, Avhich,
though not shoAvn to be crystallisable, nevertheless, permeates
moist membranes Avith great facility ; AAdiilst fatty matters are
either emulsified, decomposed, or dissolved. These transmu-
tations are daily accomplished, within the body, at its proper
temperature, in modes at present only hypothetically explained,
by the re.spective actions of the salivin, pepsin, pancreatin,
and conjugated fatty acids, of the saliva, gastric juice, pancreas,
and bile.

Action of the Saliva and other Fluids of the j\[oidh.

The saliva, the chief fluid poured into the moAAth, acts first,
by its Avatery basis, as a solvent, contributing thus also, to the
perfection of the sense of taste. It di.ssolves saline substances,
the organic acids, alcohols, and ethers, gum, sugar, and tin;
soluble albuminoid and gelatinoid bodies. Secondly, and most
importantly, the saliva changes the starch granules, first into dex-
trin, and then into soluble and crystalloid dextrose, glucose or
grape-siAgar, ready for absorption. Dextrin has the same atomic
constitution as starch, CftllioGj) Avhilst grape sugar, C6H|;06,
appears to be produced from it, by the taking up of 1 atom of
Avater H2O. No evolution of gas takes place, as occurs in alco-
holic fermentation. Tlie change is more rapid than fermenta-
tion. On adding some saliva to a AA'cak solution of boiled starch,
and immediately testing it Avith iodine, the blue colour of

ACTION OF THE GASTRIC SECRETIONS.

85

iodide of starch fails to appear ; or, on mixing saliva with a
small quantity of cooked starch, already rendered blue by
iodine, the colour is discharged. (Vintschgau.) These facts
prove that the starch is changed ; its conversion into sugar, is
shown by examination with a polariscope, or by boiling the
fluid, after adding a slightly alkaline solution of tartrate of
cojiper, when a yellomsh red precipitate of oxide of copper
is thrown down, indicating the presence of grape-sugar
(Trommer’s test).

The parotid saliva is, by itself, able to convert starch into
sugar ; that of the submaxillary and sublingual glands accom-
plishes the change, when combined with the mucus of the mouth,
which, indeed, has, by some, been regarded as the sole agent in
this transformation. A mixture of all the fluids of the mouth
appears, however, to form the most active combination for this
pimpose. Besides the saliva and buccal fluids, the pancreatic
juice possesses this property in great perfection ; but the
gastric juice and the bile do not. Most animal membranes
also, such as the mucous membrane of the mouth, intestines,
and even the bladder, particularly if they are in a state of
commencing decomposition, exhibit this power.

The constituent of the saliva, to which this peculiar power of
transmutation is due, is the salivin or ptyalin, which is said to
actcatalytically,or bypreserece,or contact; forif this albuminoid
substance be precipitated by alcohol, collected on a filter, and
re-dissolved in water, it will stiU effect the transformation very
rapidly, and will convert 2,000 times its own weight of starch
into sugar. Neither dilute alcohol or acids, nor, it is said,
even a boiling heat, arrest altogether the action of salivin.
Finally, although the action of saliva is more rapid and com-
plete on cooked starch, yet grains of raw starch, masticated
and mixed with saliva in the mouth, and then maintained at a
temperature of 100°, at length break down, and are converted
into sugar, d’he saliva has no specific action on gum, pectin,
cellulose or fatty matters, unless it may, to a slight degree, emul-
.sify the latter, nor yet on albuminoid or gelatinoid substances.

Action of the Gastric Jvice, and Mucus of the Stomach,

It is the gastric juice, secreted by the peptic glands, which
accomplishes the act of gastric digestion ; the secretion of the
racemose glands, lined with columnar epithelium, found near
the pyloric end of the stomach, is supposed not to participate

86

SPECIAL PHYSIOLOGY.

in this office, but it may act in the further conversion of
starch into sugar. In tliis stage of digestion, albuminoid
and gelatinoid sub.stances are .specially acted upon, and are
reduced to a pulpy mixture, containing the so-called albumi-
nose or peptone. The solid or insoluble forms, .such as coagu-
lated albumen, syntonin, and librin, are slowly dissolved ;
certain of the soluble forms, as the casein in milk, and the
albumen in vegetable juices, are first precipitated, and then
di.ssolved ; whereas fluid albumen, as the raw white of egg,
remains in solution whilst it is being converted into albumi-
nose. Albuminose resembles the albuminoid bodies in chemi-
cal composition, though differences will probably hereafter be
detected in it. Whatever the peculiarity of the albuminoid
body, whether it be albumen, syntonin, fibrin, or casein, gluten
or legumin, it is tran.sformed into an almost identical albumi-
nose. Moreover, this albuminose, or peptone, possesses pro-
perties which distinguish it from the albuminoids. Thus, it
is no longer coagulable by heat, nor by the action of nitric
acid, though still precipitable by tannic acid, metallic salts,
and strong alcohol ; it is soluble in all proportions in water,
so much so, that the act of digestion of the albuminoids, or
their conv'ersion into albuminose, has been referred hypotheti-
cally to a kind of hydration of the albuminoids, or a taking uji
by them, of certiiin atoms of water, just as the hydration of
starch or dextrin, appears to be a ste]> in their conversion into
sugar. Gelatin, and the gelatin-yielding tissues, furnish a
special kind of peptone, a viscid fluid, which does not, accord-
ing to some, gelatinize or stiffen in the cold. The transforma-
tion of albuminoid and gelatinoid std)stances into the idtimate
albumen and gelatin-peptones, is not sudden, but is charac-
terised by intermediate stages, in which less soluble forms of
these substances appear, nanred parapeptones. Parapeptone
is precipitated, in thefoini of flocculi, from the peptone, when
their mixed acid .solution is neutrali.sed bj^ an alkali ; it is
insoluble in water, though gradually dissolved by M'eak acid
and alkaline solutions. Tlie peptone', as already said, is
highly soluble in water, and precnpitable by tannic acid,
alcohol, and metallic salts. When a solution of peptone is
injected into the blood of an animal, it does not appear in
the renal exerotion ; but when albumen, dissolved in very'-
weak hydrochloric acid, is employed in a similar manner,
albumen is lound in the urine. These facts indicate that a
true metamorphosis is elfected in the albuminoid constituents

AUTIFICIAL DIGESTION.

87

of food. The peptone ultimately produced, is not only freely
soluble in wafer, bun most I'eadily permeates moist animal
membranes, and hence is a substance admirably fitted for ab-
sorption.

The gastric juice has no peptic action upon either the
amyiaceous or oleaginous constituents of food.

The agent by which the gastric juice dissolves, or excites
the solution of, albuminoid and gelatinoid substances, is the
peculiar animal substance, itself albuminoid, the /)epsm ; but
the free acid contained in it, is also essential to the digestive
process. Dilirte hydrochloric, or other acid, of the sti'ength
of that present in the gastric juice, possesses by itself no
digestive property, though it renders the tissues semi-trans-
parent, and dissolves out earthy matter from bones. Again,
pepsin alone, obtained pure by precipitation from the gastric
juice by means of alcohol, filtraiion, and re-solution in water,
also possesses no digestive power ; nor does pure gastiic juice,
provided that its acid be carefully neutralised ; for small
pieces of meat, or albumen, placed in such solutions, do not
digest, but alter a time putrefy.

The.se, and many other, facts concerning the rapidity and
results of digestion, have been established by experiments,
amongst the most interesting in I^hysiology, on artijicial clirjes-
tionii.e., by subjecting different substances to the action of
different digestive fluids, under exactly like conditions. The
temperature employed may vary from !)G° to 102°. During
natural digestion, the temperature of the stomach of Alexis
St. Martin, was Jbund to be from 100° to 101° F.; whilst
during fasting, it was 08° or 00°. (Dr. P. Smith )

An artificial digestive fluid may be obtained directly from
the human or animal stomach, by first exciting the How of
gastric juice, and then cati.sing vomiting; or it may be
collected from artificial gastric fistula; in animals. A digestive
fluid may, however, be more conveniently, and less cruelly,
obtained from tlie gastric mucous membrane of the recently
killed sheep, calf, o.x, or pig, especially if the animal be
slaughtered whilst digestion is going on in the stomach.
Finely cut portioti.s, or scrapings, of the mucous membrane, are
to be macerated in 20 times tlicir weight o\' cold water for 24
hours, with frecpicnt agitation of the mixture. A temperature
as low as a0° is desirable, to prevent the pejisin, extracted from
the membrane, from exhtiusling itself, more or less, in the
digestion of that membrane itself. The Ifagments of the mu-

88

SPECIAL PHYSIOLOGT.

cous membrane being allowed to subside, the supernatant fluid
is poured off, forming a solution of pepsin extracted from
the pejjtic cells, but containing only a slight and insuffi-
cient quantity of free acid ; for the pepsin is stored up in the
peptic cells, so that it may be extracted by water after death,
whilst the acid of the gastric juice is probably secreted only
when required, perhaps by the columnar epithelial cells; it
therefore ceases on the death of the animal. Hence the solution
of pepsin as above prepared, requires an addition of hydro-
chloric acid, to make it digest actively. Too little, or too much,
acid diminishes its peptic properties. Ten minims, i.e. about
13 drops of the pure hydrochloric acid of commerce, to every
ounce of the digestive fluid, is said to be the best proportion.

The inefficiency of the acid, and of the solution of pepsin,
separately employed, and the powerful eftect of the two
together, may be thus strikingly illu.strated. Three fluids are
to be jDrepared, one, of hydrochloric acid and water, in the
proportion of 13 drops to the ounce; a second, of the above
described solution of ^^epsin, exactly neittralised by carbonate
of soda; and a third, of the same solution, acidified with hydro-
chloric acid, in the proper proportions. In equal quantities of
these fluids, contained in glass jars of the same size, are'
suspended the legs of fowls, or the fore-limbs of rabbits, either
cooked or uncooked, one in each jar ; the jars are then placed in
a water-bath, and maintained at a temperature ranging between
9G° and 102°, for 24 hours. At the end of that period, the limb
suspended in the hydrochloric acid and water, is found to be
slightly swollen, pale and semi-transparent, whilst the solution,
itself of a yellowish tint, is quite clear, and free from depo.«it.
The limb submitted to the action of the neittralized solution
of pej^sin, which is itself slightly turbid, appears sodden, but
its surface is nowhere dissolved ; the fluid itself is darker, but
not more turbid. In the acid solution of pepsin, however,
all the soft parts of the digested limb are, as it wei-e, eaten aivai/
and pulpijied, or dissolved ; the tendons disappear first, then
the muscles, next the ligaments, and lastl}', even the bones
and cartilages are more or le.ss attacked, the slight residual
mass contrasting strongly with the undissolvcd and swollen
limbs in the other two solutions; moreover, the fluid itself has a
brownish colour, and presents a soft flocculent or jmlpy grumous
sediment, several inches deep, which, on the slightest agitation,
mixes easily Avith the fluid above, and resembles the digested
contents of the stomach, after taking animal food.

GASTRIC DIGESTION.

89

Phosphoric, sulphuric, and even nitric acid maybe employed
in the artificial digestive fluid, but they are not so suitable as
hydrochloric. Very strong acids, metallic salts, caustic alkalies,
alum, tannin, and strong alcohol, destroy its digestive proper-
tie.s, and so does a temperature of 120°. A strongly acid artificial
gastric juice is better suited for the digestion of some sub-
stances, such as coagulated albumen, the solid syntonin of
cooked muscle, and legumin ; whilst fibrin is more quickly
dissolved in a feebly acid juice, even 1 drop to 1 oz. of
fluid. (Briicke.) The strongly acid natural gastric juice of
the Carnivora, acts most quickly on the firmer animal albumen,
but the less acid secretion of the Herbivora, most quickly on
the softer vegetable gluten. The human gastric juice has a
feebler power even than that of the herbivora ; its acidity
declares itself immediately on the introduction of food into
the stomach, and increases, for a time, as digestion goes on,
when the less digestible food requires to be attacked ; when
the stomach is empty, the acidity quite disappears.

The power of the ga.stric juice to dissolve animal substances,
is well illustrated by the softening or digestion of the coats of
the stomach by its own secretion, after death, often noticed
both in men and animals dying whilst digestion is going
on : all the coats of the stomach may be thus perforated ; in
the human body, the effects may simulate the action of a
corrosive poison.

The immunity of the living gastric mucous membrane,
or its power of resisting the solvent action of its own secretion,
has been variously explained. According to one view, the
epithelium and mucus constitute a sufficient protection ; for
when the former is detached, the subjacent tissue is said to be
attacked, in the living stomach, as well as after death. The
‘vitality’ of the mucous membrane (the sum of its vital actions),
has been supposed. to enable it to resist solution ; and this resist-
ance necessarily ceases on the death of the part. A more recent
view, founded on many experiments, attributes the non-solution
of the living mucous membrane, to the protecting influence of
the blood in the capillaries, which is snpj)osed to maintain, so
long as the circulation continues, the alkalinity of the tissues, a
chemical condition incompatible, as we have seen, with j^eptic
digestion. (Pavy.)

The digestive action of the fluids of the living stomach was
shown long ago by Spallanzani, Stevens, Tiedemann, Gmelin,
and others, who induced dogs to swallow pieces of sponge

90

SPECIAL PHYSIOLOGY.

fastened to strings, and afterwards withdrawing them, obtained
a quantity of fresh gastric juice, which slowly dissolved food,
kept in it at a temperature of 100°. But the most direct
evidence of the solvent power of gastric juice, is that obtained
by Dr. Beaumont, who employed the fluid collected from the
stomach of the Canadian voyageur, Alexis St. Martin. With
that fluid, the pjrocess of solution was very rapid. Three
di’achms of boiled beef ])laced in an ounce of fluid, main-
tained at a temperature o( 100°, began to digest in 40 minutes ;
in 60 minutes, a pulpy deposit began to form ; in 2 hours, the
areolar tissue was digested, leaving the muscular fibres dis-
connected or loosened ; in G hours, these were nearly all
digested; and in 10 hours, the meat was completely dis.solved ;
the gastric juice, from being transparent, was now the colour of
whey, and contained a meat-coloured sediment. Digestion
was still more rapidly accomplished, when a similar piece of
beef, attached to a thread, was placed in Alexis St Martin’s
stomach ; for, although at the end of one horn-, its condition
appeared much the same as that of the piece of beef digested
ill the gastric fluid out of the body, at the expiration of two
hours, it was completely dissolved.

From these and other experiments, it is evident, that, with
the exception of the rapidity of the two processes?, artificial
and natural digestion are identical in character. The rapidity
of natural, as compared with artificial digestion, may probably
be explained, partly by the more powerful action of a con-
tinuously fresh supply of gastric juice, and partly by the
constant removal of the outer pulpificd layer of the nutrient
mass, by the incessant pressure and motion of this mass
by means of the muscular coats of the stomach. Artificial
digestion is much accelerated by occasional agitation.

The mere qutintity of fluid em]Dloyed in natural digestion,
must also be very important. It has been shown, from
experiments on the gastric juice of the dog, that 2U ozs. of
fluid are needed for the digestion of 1 oz. of albumen. The
dailjr quantity of gastric juice secreted by a man, 140 lbs. in
weight, has been estimated at 14 lbs. or 11 jiints inqierial. A
pint of saliva, which is a moderate estimate, and 2 pints of
water consumed as beverage, would make a total of 14 pints
of fluid, employed in the gastric digestion of the daily
.solid food; beyond the stomach, 2.V pints of bile, 14 pint
ol pancreatic juice, and one pint of intestinal juice are
added. The total (quantity of fluid employed in the digestive

THE TROPEUTIES OF PEFSIN.

91

process in 24 hours, certainly exceeds the qirantity of blood
in the body, wliicli, taken at y'^th part of the weight of the
latter, would be, lor a Man weighing 140 lbs., less than
1 1 lbs., or 9 ]iints. It is evident, therefcn-e, that the large
quantities of fluid, daily secreted I'or the jiiirposes ol diges-
tion, can only be supplied by a circular movement of the same
aqueous particles, in succe.^sive acts of secretion, ab.^orption,
re-secretion, and re-absorpiion. The water which leaves the
blood, to form part of the digestive juices, re-enters the blood
with the absorbed food, once more leaves it in the newly
formed digestive juices, and is again re-absorbed, until diges-
tion is complete. This continued irrigation of the food, com-
bined with the activity of the freshly formed gastric juice,
must greatly contribute to the rapidity of natural digestion.

That the pepsin of the gastric juice, is the special agent in
the gastric digestion of albuminoid and gelatinoid substances,
is easily shown. By evapewating the natural gastric juice, or
the artificial solution of pepsin, to a viscid consistence, and
adding strong alcohol to it, the pepsin is precipitated in
whitish docculi, which may then be separated by filtration,
from the other constituents ol' the gastric juice, dried at
a low temperature, and preserved lor months. The dried
pepsin thus obtained, foims a firm, greyish, mass, or powder ;
it is easily soluble in, or miscible with, water, and 1 grain
dissolved in so large a quantity as 00,000 grains, i. e. 6^ pints
of acidified water, still possesses digestive properties. Pepsin,
whether dry or dissolved, as in natural or artificial gastric
juice, loses its dige.stive power, if it be subjected to a tempe-
rature a little above that of the body, for example, a heat
even of 120°. It is likewise rendered inactive, by strong
chemical reagents It is remarkable that alcohol, which pre-
cipitates it, and temporai ily suspetids its dige.stive properties,
does not destroy them ; for on .sufficient dilution with water,
it is redi.ssolved, and again becomes active. The energy of
pepsin, like that of .salivin, in converting starch into sugar, is
catalytic. The action of conl.ict or pressure, exhibited by both
the.se substances, differs from that of the yetist ferment in the
alcoholic fcrmimtations, in not ctiusingthe evolution of any gas,
and in not being contitnially re|)roduced. It is said, how-
ever, by some, that the j)ei)sin does not itself undergo wa.ste in
the process of digestion ; but the power of a given quantity
is certainly limited. Salivin and pepsin have been retiarded
as albuminoid bodies in a state of cluuxje, and capable of

92

SPECIAL PHYSIOLOGY.

inducing changes in otlier albuminoids, with which they are
brought into contact. Putrescent albuminoid substances, as is
Avell known, can propagate putrescent changes to fresh albu-
minoid substances, and can also convert starch into sugar, or
one form of sugar into another. But pepsin is not a putrescent
body, nor is the peptone, produced by its action on albumen,
putrefied. On the contrary, it has been shown by experiment,
that fresh gastric juice, applied to putrid meat, first arrests
putrefaction, removing its signs, and then digests the meat.
Like fermentation and putrefaction, however, digestion is
retarded by low temperatures, altogether arrested at a tem-
perature of 34°, and is stopped by high temperatures, by the
action of absolute alcohol, strong acids, alkalies, and metallic
salts.

The action of the gastric juice varies, according to the
character of the food, its state of comminution or subdivision,
and its condition of dryness or moisture. In order to deter-
mine the time requii'ed for the solution of different nutritive
substances, these have been introduced, inclosed in perforated
tubes of metal or glass, into the stomachs of animals, and then
have been withdrawn ; or, animals have been fed with such
substances, and afterwards killed at certain intervals. The
most important observations, however, are those made by
Dr. Beaumont in the human subject. In the stomach of
Alexis St. Martin, a mixed meal of animal and vegetable food,
was nearly all dissolved into a pulp, within an hour ; and the
stomach was completely emptied in 24 hours. A breakfast,
consisting of three hard boiled eggs, some pancakes with coffee,
being taken at 8 o’clock, the stomach was empty at 10T5.
Two roasted eggs and three apples, eaten at 1 1 o’clock on the
same day, had disappeared at 12T5. Boast pig and vegetables,
afterwards eaten at 2 P.Ji., were half dissolved at 3, and had
disappeared at 4’30. It was further observed, that a meal,
consisting of boiled dried cod-fish, potatoes, parsnips, bread
and butter, eaten at 3 o’clock, was about half digested at 3'30,
the bread and parsnips having disiippcared, the fish being
sejiarated into threads, and the potatoes being lea.st altered ;
at 4 o'clock, very few pieces of the fibre of the fish were
found, but some of the potato was still perceptible ; at 44U)
all was completely pulpified ; and at 5 o’clock, the stomach
Avas empty. Again it was found, that rice and tripe Avere
digested in 1 hour; that eggs, salmon, trout, apples, and
venison, took 14 hour; tapioca, barley, milk, liver, and fish.

CIIYMIFICATION.

93

2 luurs; turkey, lamb, potatoes, pork, 2^- hours; beef,
mutton, and poultry, from 3 to 3-i- hours ; and A'eal a little
longer. The order in which each separate article of food
is mentioned above, indicates its relative digestibility, at least,
in the stomach of Alexis St. Martin.

As a rule, animal substances are more rapidly digested than
vegetable substances. 'J'he rate of digestion of different sub-
stances corresponds with the relative necessity for their being
acted on by the gastric juice. Thus, those Avhich require the
most digestion by that fluid, necessarily remain the longest,
whilst those which are merely liberated, but are not dissolved
in it, pass out sootier ; and fluids, Avith their soluble ingi-edients,
disappear the most quickly. In cases of fistulous openings in
the dog, and in Man, it has been found that fibrin is digested
in half an hour, casein in 1^ hour, gelatin in 2 hours, coagu-
lated albumen in G hours, and tendons in 10 hours.

During gastric digestion, the muscular tissue breaks up
first into its fasciculi, and then into fibres, the striai of Avhich
gi-adually disappear, the sarcolemma, as Avell as its sarcous
contents, being dissolved ; fragments of the fibres, however,
pass into the intestine, and there undergo further, though, it
may be, incomplete, digestion. Yellow elastic tissue appears to
resist the action of the gastric juice ; tendinous fibres dissolve
slowly; white areolar fibres are totally dissolved. The cor-
puscles of cartilage are not digested, but the inter-cellular
substance undergoes solution. The areolar fibres of adipose
tissue disappear, and frequently also the walls of the fat-cells ;
but their fiitty contents are commonly said to resist the action
of the gastric juice ; fat, however, may begin to be broken up
into the fatty acids. (Marcet.) Of vegetable tissues, the
cellulose or lignin of the cell-walls, including the dotted,
annular, and spiral ducts, for the most part resist the action of
the gastric fluid, which is also inoperative upon .starch grain.s,
though it does not interfere with, or totally aiTest, the action
of the swallowed saliva, and of the mucus of the stomach, upon
.starch. Chloi'ophyll, the green colouring matter of plants,
appears to resist digestion ; but the jiectinous and albuminoid
contents of vegetable cells, are completely dis.solved.

ChijmiJicalion and Chyme.

The general product of digestion in the stomach, resulting
from the combined admixture with the food, and the action

04

SPECIAL PHYSIOLOGY.

upon it, of the saliva, tlie mucus of the mouth and stomach, and
the gastric juice itself, is called the chyme ; the process of its
formation is named chymificution. The chyme is a thick, pulpy,
grumous, fluid, containing the food thus tiir digested, together
with partially digested, and indigestible, matters; it hasa strong
sour smell and taste, and an acid reaction. The degree of
acidity of the chyme varies, however, according to the quantity
of acid, such as lactic or acetic acid, in the food, and also ac-
cording to the relative quantities of saliva and gastric juice con-
tained in it, much gastric juice rendering it more acid, and an
excess of saliva less so. The colour of the chyme depends on the
food, being whitish in an infant fed on milk and farinaceous
food, but of a brownish hue when meat is eaten, or greenish
after vegetable diet; sometimes also, it is tinged with bile, which
has ascended into the stomach. The presence of saliva, mucus,
and gastric juice, is indicated by characteristic microscopic
nucleated cells. The composition of chyme, like its colour,
also varies with the nature of the food. With ordinary diet,
it consists of a mixture of the saline, amylaceous, saccharine,
albuminoid, gelatinoid, and fatty matters of the food, in different
conditions of conversion or solution. The starch, partly changed
into dextrin and sugar in the mouth, continues to undergo
transformation in the stomach, even more rapidly, because the
vegetable cells are loosened or dissolved, so as to set free the
starch grains. The conversion of starch into sugar in the
stomach, is due to the saliva swallowed with it, tor, in an
animal, ligature of the oesophagus, which prevents the continued
entrance of saliva into the stomach, arrests this transforma-
tion. A good deal of starch always pa.sses from the stomach,
undissolved. The albuminoid and gelatinoid substances are
represented in the chyme, by albuminose or the albumen and
gelatin-peptones ; whilst the fatty matters of animal tissues,
perhaps to a small extent decomposed, are loosened from the
lilt cells, and, as well as the liitty matter of butter or cheese,
are reduced to minute particles, intermixed with the rest of
the chyme.

The characters of the chyme depend, however, not only on
solvent actions, but also on the process of absorption, which
begins in the stomach, as soon as that oi-gan contains fluid or
dissolved matters. Owing to the esctipe of chyme into the inte.s-
tine, the quantity actually in the stomach, ;it any one time, is
small; and, owdng to absorption, the quantity which passes into
the duodenum, is much less than the quantity of fluid swallowed

USES OF THE BILE.

95

and secreted for the purposes of gastric digestion. Even the
soluble constituents of the chyme, are constantly being removed
by absorption. The soluble constituents of our solid and fluid
food, such as saline matters, .sugar, alcohol, and thein, and
ahso the soluble products of digestion, such as sugar, and the
albumen and gelatin-peptones, mixed with some solivin and
pepsin, are greedily absorbed, with the water of the chyme, by
tlie blood-vessels of tlie mucous membrane of the stomach, and
are then conveyed through the portal vein, into the liver.

The chyme itself, therefore, at any one moment, does not
represent the simple product of the digestion of food, but the
joint product of the double process of digestion and absoi'ption.
In comparison with the food taken, it necessarily contains a
larger proportion of fatty matter, than of saline, siiccharine,
amylaceous, albuminoid, or gelatinoid substances ; for the fatty
substances luive undergone little, or no, chemical change, and
no absorption from the stomach, whereas the others have been
more or less dissolved, altered, and absorbed.

The semi-fluid product is, moreover, constantly being forced
forwards, drop by drop, through the pylorus into the duodenum,
where it undergoes further changes, now to be considered.

Action of the Bile.

The bile performs a most important part in the intestinal
digestive process; but its action does not depend on the presence
of an albuminoid substance, like salivin, pepsin, or pancreatin.
Its importance is shown by its highly complex composition,
and by its containing sub.stances which, unlike the itrea and
uric acid of the renal excretion, do not pre-exist in the blood,
but are formed in the hepatic cells. Secondly, the bile, as
already stated, (pp. 74-5), is much more abundantly secreted
during the jwocess of digestion than at any other period ; and
although this may be due to the accompanying activity of the
portal circulation, yet the general adaptation of means to ends
in the animal economy, suggests the conclusion that the .secre-
tion is most required at that juirticular time. Lastly, the
situation at which the bile is di.scharged into the alimentary
canal, immediately below the stomach, and therefore very higli
up in the intestine, seems to indicate its special adaptation to
the further digestion of some important constituent of the
chyme. JMcvertheless, as we shall hereafter see, a large portion
of the solid constituents of the bile, is removed from tlie body.

96

SPECIAL PHYSIOLOGY.

and this fluid must, to a gi-eat extent, be regarded as an ex-
crementitious fluid, serving to eliminate carbon, hydrogen,
and sulphur. The bile also sei’ves certain supplementary non-
chemical uses. Thus, it excites the mucous membrane of the
intestine, and so probably cau.ses an increased secretion of
mucus and intestinal juice. It moreover, stimulates, either
directly, or through the nerves, the contractile fibre-ceUs of the
mucous membrane and its villi, as Avell as those of the muscular
coat of the intestine ; the former action, probably, promotes ab-
sorption by the villi ; whilst the latter excites the intestinal
peristaltic action, and so aids in the onward movement of the
intestinal contents. It is weU-known that a scanty supply of
bile may lead to constipation, whilst an excess of that fluid
induces diarrhoea : hence, it may be inferred, that a proper
quantity helps to maintain the healthy action of the intestines.
The insjDissated bile of the ox is used as an aperient medicine.

As regards the chemical action of the bile, experiments,
made outside the body, by digesting various constituents of
food in that fluid, at a temperature of 100°, show that it has
an exceedingly feeble action in changing starch into sugar ;
cane sugar is slowly converted by it into lactic acid ; it neither
dissolves albuminoid substances, nor saponifies or dissolves fat.
Albuminoid and gelatinoid bodies, although stained, are other-
wise unaltered ; fatty matters, agitated with bile, form an im-
perfect opaque emulsion, but after a time, if left undi.sturbed,
separate themselves entirely from that fluid, unchanged. Bile
is said to arrest the actions of saliva and ga.stric juice, even
when these have already commenced, upon starch and albumi-
noid substances. Indeed, the bile and the gastric juice de-
compose each other, when mixed out of the body ; but this
does not seem to be the case, when the gastric juice is alread}’-
combined with peptone. In living animals, in which biliary
flstulte have been established, so that the bile, prevented from
entering the intestinal canal, escapes at the surface of the body,
amylaceous, albuminoid, and gelatinoid substances are still
completely digested. With regard to fatty matter.s, however,
the bile, appears, in some way, to assist in, or to determine,
their absorption. It has been assumed that the bile is a sapo-
naceous compound, and that it dissolves fiitty mattei's directly,
like an ordinary soap; but soaps contain more or less free
alkali, which assists in dissolving additional fat, whilst the
alkaline reaction of bile, even when present, depends pro-
bably on phosphate of soda. Experiment shows, however,

USES OF THE BILE.

97

that the bile is highly important for the proper digestion of
iatty matters. In animals with biliary fistulaj, the chyle col-
lected from thelacteals, or absorbents of the intestines, contains
but a small quantity of fat ; half, or even more, of the fat taken
with their food, passes unchanged from the alimentaiy canal ;
;md, as a consequence of this, tlie bodies of such animals
are very lean. According to the observations of Blondlot and
others, animals thus treated, may live even as long as five
years. Again, after ligature of the biliary duct in an animal,
which prevents the descent of bile into the intestine, the
fiuid in the lacteals is clear and deficient in fat, instead of
presenting its characteristic milky-white colour, and fatty
molecular contents. In what mode the bile contributes to the
absorption of fat, is not yet known. It certainly does not
appear to act chemically, by decomposing or dissolving
neutral fats ; nor does it make, with oily matters, a permanent
emulsion. It probably co-operates with the pancreatic juice.
It has also been shown, that fatty matters permeate moist animal
membranes more readily tlian usual, if they be first wetted
with bile, or with an alkaline solution. Since provision is
made in the saliva and gastric juice, for the complete digestion
of amyloid, gelatinoid, and albuminoid substances, and, as we
shall presently show, in describing the action of the pancreatic
juice, of fatty matters also, the bile may be supposed to possess
no exclusive digestive power, but rather to be superadded,
in order to complete some particular part of the digestive
process.

As the contents of the upper part of the duodenum, like
those of the stomach, are strongly acid, whilst those of the
.small intestine generally, become gradually alkaline in their
descent, it was formerly thought that the bile, then regarded
as a very alkaline fluid, was concerned in neutralising the acid
of the chyme; but it is now known that the bile is but feebly
alkaline, or sometimes even neutral, and the alkalinity gi-adu-
ally acquired by the contents of tlie small intestine, is attri-
buted ])artly to the pancreatic and intestinal juice.s, and partly
to the evolution of ammonia, fiom slow decomjjosition.

The bile not only imparts a bright yellow colour to the
chyme in the duodenum, but it further appears to exercise an
anti-putrescent action, thus preventing, or retarding, a fetid
decomposition of the contents of the intestine; for, in ‘the
absence of bile fi-om the alimentary canal, these frequently
become decomposed, causing flatulence and diarrhoea. In

VOL. II. u

98

SPECIAL rilTSIOLOGT.

experiments made ■with bile, out of the body, it is found that
various fermenting processes are arrested by that fluid.

The colouring matter, ■with the cholesterin, and a certain
portion of the other constituents of the bile, are found, more
or less altered, in the residue of digestion ; but by far the
larger portion of its characteristic, conjugated glycocholic and
taurocholic acids, is absorbed by the mucous membrane of
the intestine. These acids, when boiled Avith hydrochloric
or other acids, are decomposed into cholalic acid, on the one
hand, and glycocoll and taurin, on the other. The cholalic
acid is then changed into choloidinic acid, and this again into
a resinoid substance, soluble in ether, but insoluble in Avater,
called di/slijsin. These decompositions, due, atomically, to loss
of certain atoms of Avater, are .shoAvn beloAv : —

Cholalic acid ....

Choloidinic acid, and 1 Avater . . CoiHjgO^ + HjO

Dyslysin, and 2 Avater . . . . C.^iH^gOj +

Similar decompositions appear to occur in the living body ;
for, in the small intestine, the acids of the bile are set free
from their soda salts, by the hydrochloric and other acids in
the chyme. At the commencement of the ileum, they are
already half decompo.sed, and partially absorbed : at the end
of the 'ileum, they are Avholly decomposed; Avhilst, in the
contents of the large intestine, only dyslysin is present.

Action of the Pancreatic Juice.

The pancreatic juice ^ or so-called abdominal .saliva, possesses,
like that fluid, in a remarkable degree, the poAver of converting
starch into dextrin and grape sugar. The fresh juice is capa-
ble of so converting more than four times its Aveight of starch ;
the substance of the gland, macerated in Avater, also exhibits
this poAver. Hence, probably, it aids in the metamorphosis of
the starch, Avhich has escaped the action of the siiliva. Thi.s,
hoAvever, is a secondary use of the pancreatic fluid ; for the
mucus of the stomach and intestine, and the intestinal juice,
also subserve this purpose ; moreover, the pancreas is as large
in carnivorous mammalia, the natural food of Avhich confriius
no .starchy matter, as it is in the herbivorous species.

The action of the pancreatic juice on gelatinoid substauce.s,
has not been specially studied ; but opinions differ as to its
poAver over albuminoid bodies. It is by most authorities
maintained, that it does not digest these substances, because it

ACTION OF THE PANCREATIC JUICE.

99

does not dissolve them in experiments out of the body. When
the pancreatic juice, or the iniiision of the gland substance
employed, has undergone a kind of putrefaction, such solu-
tion may occur ; but this is a condition not present in the
living body. Moreover, any albuminoid substances mace-
rated in water, will putrefy and slowly dissolve, and such
putrefied soluble matter rapidly sets up similar changes in
fresh albuminoid substances. Corvisart and Meissner believe,
however, that the pancreatic juice is able to peptonise
albuminoid substances, but that it only possesses this pro-
perty when they have been previously mixed with gastric
juice and bile, or when they are slightly acidified ; or, as
Bernard supposes, only after a certain quantity of the digested
food has already pa.ssed into the circidation, so as to supply
the blood with materials suitable for the secretion of some
special product, needed for a very powerful pancreatic juice.

E.xtirpation of the pancreas affords no certain information
concerning the use of its secretion. According to some, the
removal of the gland is followed by the absence of white chyle
in the lacteals, and the presence of undigested fat in the contents
of the large intestine ; at the same time, emaciation occurs.
According to others, when this gland is extirpated, neither a
total arrest of nutrition, nor death by starvation, necessarily
follow, every constituent of the food still undergoing more or
less perfect digestion, the office of the pancreatic juice being
fulfilled by other secretions. Complete degeneration of the
pancreas in Man, the liver and other organs remaining healthy,
does not necessaiily interfere with the digestive process ; but,
in certain diseases of this gland, fatty matter has been observed
to pass undigested through the alimentary canal. The use of
the pancreatic juice, seems, indeed, to be subsidiary, or comjde-
meutary, to the other digestive fluids; for it aids tlie saliva in
the conversion of starch into sugar. It is siiid by some to be
able, with the gastric juice, to dissolve albuminoid matters,
and if, as is generally believed, its chief office is to digest fatty
inatter.s, it must co-operate, in some manner, with the bile.

The effects of the pancreatic juice, on fatty matters, have
been shown by experiments out of the body, and by observa-
tions on living animals. If either the fluid, obtained fresh
from pancreatic fi.stulie in animals, or a Avatory infusiou of the
substance of the gland just taken from an animal killed during
the digestive process, be agitated with a neutral fat, and the
mixture be maintained at a temperature of 100°, the fatty

u 2

100

SPECIAL PnySIOLOGY.

substance is most perfectly emulsified, the action being much
more complete and durable than if saliva, bile, intestinal juice,
or any other animal fluid, had been employed. The emulsion
lasts as long as eighteen hours, after which the fat sepa-
rates. It is found, however, that a portion of the olein, mar-
garin, and stearin, is now decomposed, having been rapidly
separated into the corresponding fatty acids and glycerin.
These effects are most marked when the pancreatic juice is
collected a short time after digestion has begun, all the
characters of the secretion being then most evident.

This remarkable decomposition is usually attributed to the
pancreatin, combined with the operation of the free alkali of the
fluid, just as pepsin with an acid, effects the transformation of
albuminoid substances. The pancreatic juice no longer pos-
sesses this ]30wer of decomposing neutral fats into their fatty
acids and glycerin, in the presence of ordinary acids, which
destroy its alkalinity ; hence it has been urged, that the acidity
of the chyme must prevent this peculiar decomposition. But
the pancreatic fluid and the intestinal juice are strongly alka-
line, and moreover, the bile may here interpose, and, by
means of the soda present in combination with its conjugated
acids, may neutralise the acids of the chyme, and so permit
the decomposition of the neutral fats of the food by pancreatic
juice ; for this process may not be interfered with by the
acids of the bile, which are themselves fatty. That the action
of the pancreatic juice is, in some important way, aided by
the bile, and conversely, that the action of the bile is seconded
by that of the pancreatic juice, is highly probable, from the
fact that they are discharged into the intestinal canal so near
together, generally, indeed, at a common orifice.

It happens, however, that in the rabbit, the chief pan-
creatic duct enters the small intestine rather more than twelve
inches below the bile duct, which opens asmsual a little belotv
the pylorus ; another smaller duct also exists, but it is almost
impermeable. This arrangement has been taken advantage
of, ill physiological experiments on the use of the pancreatic
fluid. The most interesting and imjiortant of these, is one
originall}'^ performed by Bernard, and since repeated by others.
A rabbit is crammed with fat, or its stomach is injected with
oily matter, and it is afterwards killed, whilst digestion is
going on ; it is then found that the fatty matters in the intes-
tine, above the entrance of the pancreatic duct, though mixed
with the bile, are yet unchanged ; ivhilst below that jioiut they

ACTION OF THE FANCKEATIC JUICE.

101

begin to be emulsified ; moreover, the lacteals, or absorbent
vessels of’ the intestine, above the point of entrance of the
pancreatic duct, although bile is there mixed with the food,
are filled only with a clear transparent fluid, and, indeed, are
mostly invisible ; whilst, at a point immediately below the
entrance of the pancreatic duct, those vessels are charged with
their characteristic milk-white fluid, containing fatty particles.
To this apparently precise and unexceptionable experiment, it
has been objected, by those who dispute the influence of the
pancreatic juice in the digestion of fatty matters, that the
difference in the contents of the lacteals, above, and be-
low, the entrance of the pancreatic duct, depends upon the
time that has elapsed before the animal is killed, after being
fed with fat. When this is done within two hours, it is
said, that the lacteals given off above the pancreatic duct,
are found filled with white chyle ; but if the animal be killed
from four to six hours after, the lacteals below the pan-
creatic duct are alone filled. These results are not in
accordance with the experience of most observers, who fully
confirm those obtained by Bernard. It is further stated
by that e.xperimenter, that ligature of the pancreatic duct,
arrests the emulsification and absorption of fat, but this,
again, is disputed by others. The opposite conditions observed
by them, are explained by Bernard, on the supposition, either
that the smaller pancreatic duct escaped ligature, or that
certain minute glands of the duodenum, in part supplied the
place of the pancreas. It has been a.sserted, that if the small
intestine be tied, in cats and puppies, below the entrance of
the pancreatic duct, and oil, mixed with milk, be injected into
the bowel below the ligature, the lacteals, after a time, become
filled with white chyle (Frerichs). It is also said, that after
the formation of a pancreatic fistula in a cow, chyle collected
from a fistula, subsequently made in the thoracic duct, con-
tains almost as much fat as that of other cows in which no
pancreatic fistula has been established (Colin and Lasaigne).
Furthermore it is objected, that no large amount of saponified
fat, is found either in the contents of the intestine, or in the
chyle itself, as might be expected, if the pancreatic juice
decomposed the neutral fats, and so rendered them absorbable
(Bidder and Schmidt).

To conclude : first, the pancreatic juice e.xercises a po.sitivc
yiower of converting starch into sugar, and so may aid in
digestion. Secondly, its digestive power over albuminoid

102

SPECIAL PHYSIOLOGY.

and gelatinoid bodies, when it is fresh, is very slight, but more
marked when it is acidified, or Avhen it co-operates with the
gastric juice. Thirdly, it possesses a remarkable power of
emulsifying fat, and rendering it absorbable, more marked even
than that of the bile. Lastly, whilst, out of the body, it not
only emulsifies, but also decomposes the neutral fats into their
fatty acids and glycerin, it is uncertain whether this decompo-
sition actually takes place Avithin the body.

A case has been recorded, in Avhich a calfs pancreas, taken
internally, aided the a.ssimilation of fat ; and, quite recently,
preparations of pancreatin made from animals, like those of
pepsin long employed, have been administered medicinally.

Action of the Intestinal Juices.

OAving to the mixture of secretions in the intestinal canal,
it is dillicult to determine the digestive pi'operties of the
intestinal juices. Portions of food, enclosed in perforated
tubes, have been introduced through artificial openings, into
the small intestine, the duodenum being first tied, in order to
prevent the saliva, gastric juice, bile, and pancreatic juice,
from passing doAvn. Other experiments haA'e been made, by
isolating portions of the small intestine and its contents, by
including them between two ligatures. Vaifious kinds of food
have also been subjected to artificial digestion, outside the body,
at a proper temperature, in the juices of the small or large in-
testine, or Avith portions of the mucous membrane macerated in
Avater. From such experiments, several conclusions are obvious.
The strongly alkaline intestinal juice certainly conA'erts starch
into sugar, many believing that this change is chiefly accom-
plished in the small intestine ; .sugar itself here also passes
into lactic and butyric acids ; it acts still more poAverfully in
the solution of albuminoid substances. Lastly, it is also more
or less capable of forming an emulsion Avith i’at, and so of aiding
the pancreatic juice, or even of suppl)dng its place. It Avonld
seem, therefore, that the intestinal juice operates as an auxiliary
dige.stive agent upon the three principal constituents of our
food. Its effects do not appear to be interfered Avith I)y tho.so
of the other digestive fluids. The action of the secretion of
Brunner’s glands, and that of the intestinal juice, sejxarately,
are quite unknoAvn.

CHANGES OF FOOD IN THE INTESTINES.

103

Changes of the Food in the Small and Large Intestine.

Contents of those Intestines.

In considering tlie changes in the food, which occur in any-
given part of the intestine, it must be remembered, that the
tliiids, poured into the alimentary canal higher up, are still
present, in greater or less quantity, in the intestinal contents
lower down, and doubtless exercise some digestive influence.
Thus, gastric juice, and even saliva, must be present in the
upper part of the duodenum, and more or less pancreatic juice
and bile, in the lower part of the small intestine. The venous
pulpy chyme, poured from the stomach into the small intestine,
is acid, and brownish or variously coioured; but, on its admix-
ture with the bile and pancreatic juice, it assumes a bright
yellowish colour and becomes much more opaque, owing to
the addition of the biliary colouring substances, the decompo-
sition of the acids by the bile, and the gradual emulsification
of the fatty substances by the pancreatic juice. The contents
of the upper part of the small intestine are still acid, partly
from the acid of the gastric juice, and partly from the acids of
the bile, which are set free by the former ; but their acidity is
gradually diminished, not only by the alkaline pancreatic juice,
but also, and chiefly, by the even more powerfully alkaline intes-
tinal juice. The hydrochloric acid of the gastric juice, is
probably soon neutralised, and is then absorbed into the blood,
as chloride of sodium or common salt. At the lower end of
the ileum, the reaction of the residual intestinal contents, is
generally stated to be alkaline ; but near that point, in a case
of accidental fistula in the human subject, it has been found
acid, notwith.standing the alkaline condition of the mucous
membrane. The contents of the cajcum are said to be acid ;
but those of the large intestine generally, to be alkaline.
Much, however, depends on the nature of the food ; for, from
the formation of acetic or lactic acid, during the use of an
excess of vegetable diet, the contents of the whole intestinal
canal may be acid. In carnivora, the contents of the ctccum,
from the presence of ammonia, c.xhibit an alkaline reaction,
whilst in the herbivora, they are always acid, from the pre-
sence of lactic acid.

The chemical composition of the contents of the small
intestine, is dependent on the nature of the food taken. It
miust also vary at dilferent parts of the canal, according to the

]04

SPECIAL PHYSIOLOGY.

composition and quantity of the secretions mixed with it, and
according to the reiative quantity and nature of the substances
which have been absorbed from it. Thus, the contents of the
first part of the duodenum, consist of the acid chyme, with
bile and pancreatic juice, i. e., of a mixture of the food taken,
whether this be bread, milk, meat, or eggs, together with
saliva, gastric juice, bile, pancreatic juice, and mucus, minus a
certain amount of the water and dissolved substances, which
have already been absorbed. These substances, which are
almost exclusively absorbed bj'^ the blood vessels, con.sist of
saline matters, linaltered starch, sugar, Avhether pre-existing
in the food, or produced by conversion of starch, dissolved
albuminoid and gelatinoid substances, in the shape of albu-
minose and gelatin-peptone, salivin, pepsin, creatin and
other extractive matters, and lastly, traces of alcoholic, etherial,
acid, and various sapid, substances. The sugar found here, is
said, by some, to be grape sugar, the conversion of cane sugar
into grape sugar being chiefly accomplished, in this part of the
alimentary canal, by the agency of the intestinal juice. No
fatty matter is yet absorbed, but it all remains in the contents of
the upper part of the duodenum. Even after the admixture of
the bile and pancreatic juice, all the substance!?, just enume-
rated, still continue to undergo solution and absorption, and the
fatty matters, also now emulsified and rendered absorbable, are
gradually taken up, together with some of the fatty acids of
the bile. The contents of the small intestine are thus pro-
gressively robbed of all their dissolved or emulsified nutrient
substances, in which they become by degrees poorer. Finally,
passing into the large intestine, they acquire a greater con-
sistence and a darker hue.

The contents of the large inte.stine have been .supposed to
undergo an imperfect secondary digestion in the cscum ; and
there are reasons for believing, that such a process, due to the
action of lactic or other acids and of the intestinal juices, may,
especially after heavy meals, be continued along the rest of the
intestine. This may explain the digestion and absorption of
the nutrient substances in enemas, by means of which the
system, as is well known, may be for a long time supported.
Whether starch is changed, or fat emulsified, is uncertain. The
final residue consists chiefly of the insoluble or undigested
portions of the food, broken down into .small fragments. In it
are found, particles of vegeUible matter, such as unaltered
starch-grains, woody fibre, remains of vegetable epidermic,

CONTENTS OF THE LAHGE INTESTINE.

105

and other cells, with portions of spiral and annular ducts. Of
animal substances, tliere are present, portions of yellow elastic
tissue, cartilage cells, unchanged lat, epidermoid, and epithelial
cells, unchanged iragments of fibrous tissue, such as portions
of tendon or fascia, and muscular fibres more or less altered,
though having escaped complete digestion ; besides this, there
are certain earthy salts, especially the ammonio-magnesian-
pho.sphate, with the phosphates of magnesia and of lime.
The neutral salts of the vegetable acids, such as the citrates,
tartrates, malates, and benzoates of potash or soda, appear
partially in the contents of the lower part of the large intestine,
as carbonates, the rest having been absorbed, also, it is said,
chiefly in the form of carbonates. Furthermore, the ftecal
mass contains colouring matters and other substances left from
the almost completely changed or decomposed bile, such as
cholalic and choloidinic acids, traces of cholesterin, and
especially the substance named dyslysin, also a crystaUisable
sul)stance containing sidphur, named exci'etine (Marcet), traces
of stearic, margaric, and a peculiar fatty acid called excreteric
(Marcet"), with some animal matter, probably the residue of
the pancreatic and the mucous secretions, especially of those of
the larger intestine. It appears certain, indeed, that the
glandular apparatus of the intestines, serves to excrete, and
thus eliminate from the blood, products of the decomposition
of the tissues, which would be injurious if retained in it;
these must be present in the fiecal substance, and may in
great part explain its odour. The .small intestine, with its
villous mucous membrane, is adapted to the function of absorp-
tion ; but the non-villous mucous coat of the large intestine
appears better adapted for excretory purposes. The percentage
composition of the ashes of the daily cjuantity of fieculent matter
removed from the body, varie.s, according to the food, from
2 to 10 oz. ; the average quantity is about 6 oz., of which
three-fourths are water. The percentage composition of the
ashes, alter burning, is as follows : —

Cliloride of sodium, alkaline sulphates, and pliosphato

of soda (or potash) ...... 4

Phosphate of lime and phosphate of magnesia . 815

Sidphatn of limo ....... 4-5

Phosphate of iron 2

Silica 8

100-

The contents of the stomach invariably include a certain

106

SPECIAL PHYSIOLOGY,

quantity of atmosplieric air (4 nitrogen to 1 oxygen), which
has been mixed with the food and saliva in the month, and
swallowed with them. The decomposition of the amylaceou.s
and saccharine food, into lactic and butyric acid, may cause
the evolution of carbonic acid and hydrogen. The oxygen,
and especially the carbonic acid, being more soluble in water,
would be more easily absorbed than the nitrogen and hydro-
gen ; but the nitrogen may also pass into the blood. An
interchange of the other gases with carbonic acid from the
blood, may take place, by what might be termed intestinal
respiration. In the small intestine, the carbonic acid and
hydrogen relatively increase in quantity, the nitrogen remain-
ing about the same ; whilst the oxj^gen disappears. On
including a loop of the small intestine of a living animal,
between ligatures at two different points, the gases of the
blood, oxygen, carbonic acid, and nitrogen, have been found to
pass into the interior of the intestine ; so that these gases
may be both absorbed from, and excreted into, the intestinal
canal. In the large intestine, besides carbonic acid-, as the
principal gas, carburetted liydrogen may appear, owing to the
slow decomposition of its contents; nitrogen abounds after a
flesh diet, and hydrogen after a milk diet ; lastly, though, it
would seem, but seldom, as a consequence of the decomposition
of the albuminoid substances containing sulphur, or of the
taurin of the bile so rich in that element, or possibly from
the de-oxidation of sulphates, small quantities of sulphiu-etted
hj'drogen gas are evolved. These two last-mentioned gases
may also be absorbed into the blood ; indeed, it has been
shown experimentally, that animals may be quickly poisoned
by injecting sulphuretted hydrogen into the large intestine.

The time taken by different articles of diet to descend
through the alimentary canal, varies. Laxative medicines may
pass in four hours, carbonate of iron in twelve hours, the
coloui-ing matter of spinach and other vegetables in eighteen
hours, and grape-pips and cherry-stones in from three to four
days. It has been shown that it is useless, and perhaps
imprudent, to administer purgatives immediately offer the
accidental swallowing of buttons, coins, or .stones ; it is better
to administer thick tenacious food for a day or two, and then
give a dose of castor oil.

SUMMARY OF THE DIGESTIVE CHANGES.

107

Stanmar^ of the Chemistri/ of Digestion.

We have seen that the digestible and absorbable parts of
food, consist chiefly of the carbliydrates, or the amylaceous,
gummy, and saccharine substances; of hydrocarbons, or fats
and oils ; of nitrogenous gelatinoid and albuminoid substances,
and extractive matters ; of hydrocarbonaceous alcohol and
organic acids ; of saline substances, and of water.

Part of the starch is converted, by the saliva in the mouth,
into glucose or grape sugar ; this change still goes on in the
stomach, even in the presence of the gastric juice ; it is com-
pleted, or, according, to some, chiefly accomplished, in the
interior of the small intestine, by the continued action of the
saliva and by the superadded agency of the pancreatic and
intestinal juices. Cooked starch is changed more rapidly than
raw starch, the cells of Avhich sometimes escape digestion ; the
emptied envelopes of the starch grains commonly remain
undigested. Cane sugar (Bouchardat), and milk-.sugar (Leh-
mann), are for the most part converted into grape sugar,
in the stomach, moi-e particularly in the intestine; small
quantities of cane sugar are said to be absorbed without
change (Bernard). The grape sugar, thus formed from starch
and other sugars, or that which may be contained in the food,
is principally absorbed as such by the blood vessels; but it
appears partially to be changed, especially when abundantly
taken, within the alimentary canal, into lactic acid, and this
again into butyric acid, with an accompanying separation
of carbonic acid and hydrogen. Thus ; —

1 Grape sugar = 2 Lactic acid

Cell, A =

2 C,II,0,

1 1 Butyric acid
1 2 Carbonic acid
(,4 Hydrogen

c,ir,o,

2 CO.,

4 II

The albuminoid bodies begin to bo digested in the stomach,
by the gastric juice; whilst their solution is continued, and
completed, in the small inte.stine, by the additional action of
the intestinal juice. Fluid albumen, and especially vegetable
albumen, and coagulated fibrin, are easily digested ; coagulated
albumen, casein, gluten, and Icguinin, more slowly. Casein
is first precipitated in a llocculent form, and then dissolved.

108

SPECIAL PHYSIOLOGY.

All albuminoid substances are converted at once into albumi-
nose or albumen-peptone. Gelatin and gelatin-yielding tissues
are converted into gelatin-peptone. The.se peptones, and also
the saliva, pep.sin, and pancreatin, are absorbed from the
stomach, as well as from the small intestine, and chiefly by the
blood vessels.

Fats, whether pure, and merely melted by the heat of the
stomach, or whether forming part of an organised tissue, and
set free by the digestion of the enveloping areolar tissue and
walls of the adipose cells, coalesce, into small drops, in the
stomach and upper part of the duodenum. In the small
intestine, so long as its contents remain acid, the fats are
merely emulsified by the pancreatic juice, aided possibly by
the bile ; in the lower portion of the small intestine, however,
where the intestinal contents become more or less alka-
line, certain quantities of the fat are probably decomposed
into their fatty acids and glycerin, by the further action of
the pancreatic juice, and may even be saponified by the
strongly alkaline intestinal juice. Thus emulsified, decom-
posed, or saponified, all but a small residue of the fatty
matters are absorbed by the lacteals of the intestines.

Alcohol, in all its forms, ethers, and other soluble acid and
sapid bodies are absorbed unchanged, along the whole surface
of the alimentary canal, chiefly, if not entirel}'', by the blood
vessels. This absorption begins even in the mouth, otherwise
these substances would prodirce no flavour. The organic acids
pi'obably decomposed into carbonates.

The extractive matters, creatin and creatinin, the cerebric
acid, those which are uncrystallisable, and perhaps some of the
cruorin and myochrome, are also probably ab.sorbed without
change, by the blood vessels.

The saline constituents of the food are chiefly absorbed
without alteration ; the soluble ones, from the mouth, .stomach,
and intestinal canal generally ; Avhilst the less soluble phos-
phates of magnesia and lime, appear rather to be dissolved in
the large intestine. Any carbonates contained in the food or
drink, must be decomposed by the acids of the gastric juice,
by the lactic acid of the food, and by the acids resulting from
the decomposition of saccharine matters. The salts formed
by such organic acids with soda or potash, are either absorbed
into the blood, and there converted into carbonates, or they
are thus changed in the intestinal canal.

atcr remains undecomposed, and is absorbed freely during

HOW DIGESTION IS INFLDENCED.

109

tlie digestive process, constituting the natural menstruum,
in which the different soluble substances are dissolved, and in
which the latry matters are suspended.

or substances, the digestion of which is doubtful, may be
mentioned vegetable mucus, gums, pectin, and cellulose. The
three former, though soft and tender substances, miscible
but probably not actually soluble in water, are said, by some,
indeed, neither to be capable of being absorbed, nor yet to
be so chemically changed, as to become so. The softer kinds
of cellulose, such as that contained in the growing tissues
of green vegetables, in the tuber of the potato, and in the
pulp of fruits, are supposed to be dissolved in small quantity, if
not for nutrient purposes, yet in order to set free their starchy,
gummy, saccharine, and albuminoid contents. lierbivorous
animals, however, certainly digest large quantities of cellulose
and vegetable pectin, by changing them into sugar. Chloro-
phyll, speaking generally, is indigestible. Though putrescent
meat, such as high game, may be first sweetened, and then
digested by the gastric juice, yet certain decomposing sub-
stances, like poisonous or fermenting sausages, cannot be
corrected by the juices of the stomach, but excite vomiting
and diarrhoea, and, when absorbed, often prove fatal.

Circumstances winch modify Digestion.

The rate of gastric digestion of certain articles of diet, has
already been mentioned (p. 92). It pai’tly depends on the
relative solubility of the various proximate constituents of the
food ; but it may also be greatly modified by other circum-
stances, such as the quantity, consistence, and peculiar mix-
tures of the food, its condition of subdivision, its absolute
fpiantity, the relative quantity of its different constituents, the
absence or presence of stimulating substances, the conditions
f)f the nervous system, the state of sleeping or waking, the
condition of the body as regards health, habit, individual
peculiarities, bodily fatigue, and oven the condition of the
mind. Ile.st and exercise also affect the digestive process.

The more rapidly and jierlectly the constituents of any
given kind of food, are capaltle of being dissolved, the more
easily such food is dige.sted, .and vice versa. As a rule, bread
not too new, nearly :dl kinds of metit, poultry and white fish

eggs, milk, jelly,and the gelatin-forming ti.ssues, and well-boiled
potatoes, are easy of digestion ; whilst new bread and potatoes,

no

SPECIAL PinSIOLOGY.

liitty meats, fat, tendons, cartilage, cheese, and green A'^egetables
are more difficult of digestion. Hard-boiled eggs are, of course,
more difficult to digest than the line coagulum of albumen
formed in a custard, or in the gravy of meat, owing obviously
to the difference of consistence and degree of subdivision in
the two cases. Mashed potatoes and finely grated cheese, and
soft cream- and milk- cheeses, are more easily and rapidly
digested than plain boiled potatoes or hard cheese. Again, all
vegetable substances too much matured, and therefore com-
posed of cells having harder cell walls, are more difficult to
digest, and hence require much cooking, and artificial sub-
division, to burst and break down the cells, and permit the
digestive juices to enter their interior, and act on their con-
tents. Carrots, turnips, cabbages, celery, artichokes, aspara-
gus, and onions, may be classed in this category. Even the
cooking of flour, and of all other amylaceous articles of diet,
helps digestion in an extraordinary degree, by bursting or
swelling the fecula or starch grains. Large quantities of adi-
pose tissiie, intermixed with muscular tissue, probably impede
the penetration of the gastric juice, and so render too liit meats,
such as pork, and also oily fish, as, for example, salmon, com-
paratively indigestible. It has been found that the flesh of
animals living in a wild state, is more digestible than that of
the allied tame species, probabl}'^ owing to the more fatty
muscular tissues of the latter. A large quantity of fat, in the
shape of fatty tissue, taken with other food, may have the same
effect of interfering with digestion ; but such fatty tissue is
far preferable to fat itself, and more easy of digestion, because
it is contained in areolar ti.ssue, and is divided into minute
spherules within the fine adipose cells, so that the gastric
juice percolates it ivith comparative facility. lienee suet and
cooked fat are more digestible than the melted fat derived
from them, and swimming on the surlace of gravy. Pizre solid
fats having a gramilated te.xture, esjiecially cold butter, the
particles of which adhere togethei’, as it were, only by certain
points of contact, are more easily digested than the same fats
taken in a melted condition, such as oiled butter, in which,
the oleaginous particles have completely coalesced. It is pos-
sible, also, that the heating of fatty matters determines slight
chemical changes, inconsistent with easy digestion. But per-
haps the most objectionable effect of fat, is that which occurs
in certain processes of cooking, in vdiich it .saturates heated or
dried albuminoid, gelatiuoid, or amylaceous substances, and

now DIGESTION IS INFLUENCED.

Ill

SO preoccupies their interstices, as to render them extremely
difficult of penetration by the gastric juice, -which is aqueous,
as in the case of buttered toast, or greasy hot dishes of any
kind. Moreover, owing to the high temperature in roasting
or baking, the substances above mentioned, as well as the fats
themselves, sometimes undergo peculiar chemical changes,
by which acrolein, or other pyrogenic compounds are per-
haps developed. These latter conditions are met with in the
burnt parts of roasted joints, in over-roasted, baked, or fi-ied
parts of the skin of poultry or of fish, and especially in greasy
and burnt pie-crust.

It would seem that animal albuminoid substances, held in
solution, as in soups and broths, are not more easily digested
than the same substances in a solid form ; for the water
requires to be almost entirely absorbed, before the nutrient
principles can be converted into peptones. Hence, solid food,
even in the case of many invalids, is more suitable than
bulky fluid food. It is said that dextrin, introduced into the
system, favours the digestion of albumen (SchifF) ; this affords
an illustration of the advantage of mixed diets.

Too large a quantity of food, at any one meal, also renders
digestion proportionally difficult. When the digestive powers
are weak, the bad effect of quantity is much more obvious.
It is believed that the secretion of the gastric juice especially,
is regulated, as to quantity, more by the demands of the
body, than by the amount of food taken ; hence, an excess of
food, not only remains undigested, but acts as an irritant to
the stomach itself, lessening its further secreting power, and, if
passed on into the duodenum, causing more or less disturbance
to the system. At the same time, some solid substance is
essential or favourable to digestion ; hence, perhaps, the habit
of certain nations, mixing, with their scanty food, some indi-
gestible material, such as saw-dust or earth, which can only
increase its bidk. Alter a very heavy me.al has been digested,
the stomach secretes but a very weak gastric juice (Schiff).

The effects of cold water, or ice, in repressing the secretion
of the ga.stric juice, and so retarding the digestive process,
have been already mentioned ; the reduction of the tempera-
ture of tlie stomach, and the retardation of the capillary cir-
culation, aflbrd an explanation of tlie.se facts ; taken in large
([uantities, with or after Ibod, ices and iced beverages must
suspend dige.stion. On the other hand, digestion is un-
doubtedly favoured by moderate quantities of alcohol, also by

SPECIAL PHYSIOLOGY.

1 12

salt, vinegar, lemon juice, pickles, sauces, and spices, these
substances acting as stimulants to the secreting processes
necessary for digestion, especially to that of the gastric juice ;
vinegar, moreover, contributes, by its acidity, to swell and
pulpif}'^ albuminoid substances. Lemon juice yields, in addi-
tion, potash salts to the blood. AVines and beers also contain
potash, magnesia, and lime ; the red wines especially, yield
small quantities of tannin, and traces of iron.

Severe exercise of the body, or active employment of the
mind, too soon after a meal, hinders digestion ; even moderate
exertion of the body is not desirable immediately after a full
meal, rest being found decidedly to favour digestion ; but
persons of sedentary habits digest slowly. Sleep is said to
I'etard this proce.ss, but otherwise does not interfere with it.
Mental emotion may arrest digestion, perhaps, by putting a stop
to the secretion of gastric juice. Digestion, as already men-
tioned, requires, for its due performance, the secretion of large
quantities of the digestive fluids, and this can only be accom-
plished by an incresed supply of blood to the organs concerned
in this function ; hence, any acts which determine the blood
strongly to the brain or muscles, interfere with it.

Habit has an extraordinary effect in modifying the digestive
power in particular instances ; thus, infants or invalids, who
have been habitually fed on fluid and easily digested food, are
inconvenienced, or injured, by the use of hard food difficult of
digestion, and can only by degrees acquire, or regain, a stronger
digestive power. Those persons, even, who are accustomed
to take food of a dry and hard nature, and requiring strong
digestive powers, have their digestive organs deranged by the
use of soft and succulent food, which they can only properly
digest after a kind of education. A certain effort in the di-
gestive act, is probably beneficial, as it is natural to the system.

Custom, and differences of climate, explain the well known
national peculiarities of diet, and akso the fact that, as a rule,
a foreign dietary, unless modified, or gradually adopted, is less
adapted to the digestive powers of individuals of different
nations and climates.

Finally, the effects of individual differences, or, as they are
called, idinaj/ncracies, are truly remarkable in the case of the
digestive functions. In cei-tain instances, particular, and per-
haps not otherwise difficultly digestible, substances invariably
produce the most serious pain and disorder; whilst substances
ordinarily indigestible, may perhaps be readily dige.sted.

VALUE OF DIFFERENT FOODS,

113

Tims, for example, oysters, lobster's, crabs, and salmon, -will each
produce, in different persons, severe attacks of indigestion,
and even give rise to eruptions on the skin. In some persons,
strawberries are known to produce a similar efiect ; and to
others, cucumber is almost a certain poison.

Relative Value of different Foods.

The following Table, chiefly from Vierordt, exhibits the com-
posifion of a few of the great variety of articles of food consumed
by Man. It shows the total amount of solids, and the propor-
tions of organic proximate constituents, salts, and water, in each
article of diet ; also the relative amount of its nitrogenous and
non-nitrogenous constituents, and, as regards the latter, the
respective quantities of oleaginous, amylaceous, and saccharine
matters. The relative value of different articles of diet, for
plastic or tissue-forming purposes, for calorific or respiratory
purposes, or for maintaining the proper saline constitution of
the blood, is thus shown, so far as their chemical composition
is concerned ; but this alone affords no sufficient indication
for the practical choice of diet in individual cases, so much
depending on the physical characters and mode of prepar-
ation of food, as well as on the age and idiosyncracies of the
individual.

The total quantity of solids, shown in the first column of the
following Table, reveals the highly nuh'itive quality of legu-
minous and cereal food, butter, cheese, and eggs, in compari.son
with meat ; but sixch general comparisons are ine.xact, for the
proportions of non-nitrogenous and nitrogenous substances, in
each kind of food, are not taken into account. As regards the
latter, cheese is the most nutritious diet, then the leguminous
seeds, next meat, and then, in order, the yolk of egg, flour, the
white of egg, and bread. As regards fiit, the order of nuti-itive
value is, butter, yolk of egg, and cheese. Starch and sugar are
most abundant in wheat, next in the Icguminosa and the in-
ferior cereals, less so in potatoes, and least in the succulent
vegetables and fruits.

Ghee.se is an extraordinarily concentrated diet; the legu-
minosa are highly nutritious, especially those grown in hot
countries, but they ref[uire a thorough preparation and good
cooking ; the great merit of bread, is its solt, porous, permeable,
and well-cooked substance ; the advantage of meat consi.sts
in its concentrated, yet succulent, tender, and easily digested

VOL. II. I

114

SPECIAL PHYSIOLOGY.

substance, and in its containing the very elements of the tissues
and the blood, even fat, creatin, and the potash salts. Potatoes
are a weak food, one ]50und being only equal to about six
ounces of bread, and four ounces and a half of lentils ; they are
not much more nutritious tlian the succulent vegetables,
but, like these and fruits, they contain, which bread does
not, potasli, so essential to the muscles ; hence, perhaps, their
utility in preventing and curing scurvy.

A well selected vegetarian diet is quite equal to the main-
tenance of life and health ; the Japanese, the Hindoos, and
the lazarroni of Naples, subsist chiefly on a vegetable diet. The
macaronis and vermicellis are composed of ghrten, with but a
small proportion of starch. Indian corn, and also wheat, though
not in such quantity, contain cerebric acid, a remarkable
nitrogenous compound, found in the nervous substance, of very
high atomic constitution. Broth is a very weak nutriment,
even when some strong farinaceous element is added to it ; so
is beef tea, if improperly prepared. Meat contains prin-
ciples which may be extracted, some better by cold water,
others by warm water, and others, again, by boiling ; it should,
therefore, be cut into small pieces, be submitted for three
hours each time, in succession, to half its weight of cold, of
warm, and of hoilincj water ; the fluids, strained off from the
first and second macerations, are to be mixed with that strained
off hot from the third or boiling process, and the mixture shoidd
be just brought to a boiling heat to cook it ; the fat .should be
skimmed off ; a few drops of some acid, with salt, will increase
the flavour. Thus prepared, beef-tea contains albumen,
tracesof syntonin, fibrin, cruorin, and myochrome,in aflocculent
state ; and gelatin, creatin, cerebric acid, perhaps glycogen,
inosite, paralactic, lactic, and ino.sinic acids, and salts of pofiish,
soda, and magnesia, in a state of solution ; nearly all the
syntonin remains in the shrunken meat; the fat is never
absolutely removed. Beef-tea, if good, is a light, nutritious,
easily assimilated, conservative, and stimulating food. The
now much used extractum carnis or extract of meat, is the in-
spissated juice of meat, and resembles a viscid beef-tea; but it
contains no gelatin, and no glycogen or sugar ; to be truly
nourishing, it reqirires the addition of some albuminoid and
amylaceous materials. Malt liquors are more nutritious than
weak beef-tea. Alcohol stimulates, and develops heat; it
seems to be partly digested and oxidised, though a great
j)ortion escapes unchanged by the lungs, skin, and kidneys.

TABLE OF ANALYSES OF FOOD.

1 15

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La. Lactin.

116

SPECIAL PHYSIOLOGY.

THE ORGANS AND FUNCTION OF DIGESTION IN ANIMALS.

The process of digestion, by which food is dissolved and rendered
absorbable by the living body, is almost universally performed by ani-
mals ; and a digestive apparatus is found in nearly all animals, a few
Entozoa and most Protozoa excepted.

The general idea of such an apparatus, is an internal digestive cavitj-,
communicating with the exterior. The plan of construction of this
internal receptacle, presents a general resemblance in each separate
Sub-kingdom, but in each, it offers further modifications. These are the
most varied and detailed in the Vertebrata, but they exist also in the
Mollusca and Annulosa, and may be traced in the Molluscoida, Anuu-
loida, and even in the Ccelenterata. In the Vertebrata, the plan is not
only modified in each Class, but, in the Mammalia esj^ecially, it presents
peculiar adaptations, suiting it to the carnivorous, insectivorous, frugivo-
rous, herbivorous, omnivorous, and marine habits of the animals com-
posing its several Orders. The digestive apparatus becomes, indeed,
like the rest of the economy, more complex as we ascend in the animal
scale ; and its diversities of form and structure become most obvious in
the highest groups.

The digestive cavity usually takes the form of an alimentary canal,
which, in its perfect condition, presents two orifices, an inlet, and an
outlet. It is usually divisible into an oesophagus or gullet, a stomach,
and an intestine. Its relative length and capacity, and the complication
of its superadded parts in any given case, have reference chiefly to the
nature of the food. Thus the vegetable-feeding species of any group, be
it Order, Class, orSub-kingdom, have a longer, more capacious, and more
complicated apparatus, than their congeners which live upon animal food.
This fact is illustrated by comparing the snail with the oyster, most
insects with spiders, the caterpillar with the perfect insect, the tadpole
with the perfect frog, the vegetable-feeding tm-tles and tortoises with
the carnivorous fishes, the granivorous with the carnivorous birds, and
the herbivorous with the carnivorous quadrupeds.

It is said that the intestine of the domestic cat, is longer than that of
the wild cat, and even that the same is the case with the vegetarian
races of men, as compared with men generally. The greater length and
complication of the alimentary canal in vegetable feeders, are owing to
their food requiring more prolonged digestion than an animal diet; its
increased capacity is due to the fact, that to obtain a given quantity of
nutriment capable of supporting life, a gi-eater bulk of vegetable food is
required than of animal food, particularly so, when that consists, not of
fruit and seeds, but of grasses, or the green parts of herbs and trees,
as is the case with the food of the Euminants, Solipeds, and Pachyderms.

The digestive apparatus is also modified to suit the physical condi-
tion of hardness or softness of the food, and the various modes in
which the animal must seize, crop, and masticate it; hence the existence
of modifications in the jjrehensile and masticatory apparatus, the mouth,
teeth, and gizzard. Furthermore, the periods of feeding influence the
form of the digestive organs; animals of the same order, Euminants
for oxamjfle, which feed constantly, having a simpler construction of the
stomach than those which, by instinct or necessity, take food or drink at

PREHENSION OF FOOD IN ANIMALS.

n

longer intervals ; hence the great capacity of the stomach and large intes-
tine in the Ruminants, Solipeds, and Pachyderms generally, theexistence
of water-cells in the paunch of the camel, and the presence of large
crops in many granivorous birds. In the Class of Birds generally, an
example is met with of a modification dependent on the plan of the
Class itself; for a heavy external masticating apparatus, connected with
the head, being inconsistent with the organic aim of construction for
flight, an internal crushing apparatus, or gizzard, is present where the
food requires it.

Prehension of Food in Animals.

Mammalia. — The prehensile limbs of the Quadimmana seize the food,
and transfer it to the mouth. In the feline tribe, the paws serve to cap-
ture living prey, but do not convey it to the mouth, this being accom-
plished by movements of the head and jaws. lu many Rodents, as in
the squirrel, rat, mouse, and guinea-pig, and also in the kangaroo, and
other Marsupials, the two anterior limbs are often used together for
holding food, and approximating it to the mouth. In most Mammalia,
however, the anterior limbs are organised for locomotion, and the jaws
and teeth are the instruments used for capturing or cropping the food, and
for its introduction into the mouth. In all cases, the lips are employed.
The act of sucking, characteristic of all young Mammalia, and that of
drinking in the adult, is performed by the lips, cheeks, and tongue, and
the lapping of the Carnivora, by the latter organ only.

Special contrivances for the seizure of the food, are noticed in the
snout of the tapir, the proboscis of the elephant, the long tongue of the
giraffe, and the extensible viscid tongue of the ant-eaters. The marine
and piscine Cetacea, have either rudimentary or no limbs ; some, like the
dolphin and porpoise, seize their prey by means of their many-toothed
jaws ; the whale-bone whale opens its huge mouth, as it moves through
tlie water, which, entering that cavity, filters through the numerous
whale-bone plates, descending from the upper jaw and fringing the
sides of the mouth, and so leaves multitudes of soft marine creatures,
Pteropods and others, in the interior of the mouth, ready to be swal-
lowed; lastly, the vegetable-feeding dugong employs its lips and jaws.
The ornitliorhynchus takes its food by its duck-bill horny mandibles. In
a few Mammalia, as in certain Quadrumana, Bats, and Rodents, cheek-
pouches exist for the temporary reception of food ; these are very large
in the hamster and opossum.

liirds. —The raptorial species, and also the parrots, use the foot pre-
hensively, as well as the jaws. In most binls, however, the bill is the
substitute for the tooth-bearing jaws and fleshy lips of the Mammalia,
and the shape of this most characteristic part in Birds, is variously
modifled to suit the character of the food. Thus, it is short and strong
in the granivorous sparrows and linnets ; long and tender in the small
insectivorous warblers and fly-catchers ; notched in other insectivorous
birds, as in the shrikes ; short and gaping in the swallows and night-
jars, which catch their prey upon the wing ; strong and hooked in tho
rapacious eagles and vultures, which tear up their food ; long, conical,
and of great strength, in the digging rook, and in tho wood-peckers,
which pierce tho bark of trees ; short, curved, and of great depth in tho

118

SPECIAL PHYSIOLOGY.

piirrot tribe, which can crush hard nuts ; exceedingly delicate and taper-
ing in the humming birds, to enable them to penetrate the tubular
corollas of flowers ; ponderous and ungainly in shape, in the toucan
and the adjutant; long, strong, and pointed, for the catching of fish, in
the herons, storks, and kingfishers ; elongated and suctorial, in the
snipes and sandpipers, which seek their food in bogs or sands; flattened,
grooved, and sensitive, in the ducks, geese, swans, and spoonbills ; or
it presents still other forms, for holding fish, as in the pelicans, pilgrims,
albatross, penguins, and auks. In the cross-bills, the mandibles, when
closed, pass by each other so as to present the appearance of a deformity,
but this peculiar conformation enables them to extract, with gi’eat
facility, the seeds from the fir cones. The young pigeon is fed on the
regurgitated contents of the crop of the mother-bird. This is accom-
plished, not, as is usually stated, by the mother placing its bill in the
mouth of the young bird, but by the very opposite manoeuvre. The lower
mandible of the young pigeon, is elongated and boat-shaped, and, for a
time, of disproportionate size as compared with the upper mandible:
hence it forms a sort of spoon for the reception of the food taken from
the gullet of its parent ; as the pigeon grows, the lower mandible becomes
relatively smaller (Tegetmeier). In the parrots and woodpeckers, the
tongue is prehensile.

Reptiles. — These, like birds, have no lips. They capture their prey
with the jaws, which are horny in the Chelonians, have small teeth in
the Ophidians, powerful teeth in the larger Saurians, and delicate and
even complex teeth in the small insectivorous species. The limbless
serpents crush their prey in their coils, before swallowing it. The pre-
hensile tongue of the chameleon is well known.

Ampliihia. — In these animals, the soft lips and jaws are sometimes
provided with minute prehensile teeth ; the food is taken by a snapping
movement. The tongue of the toad has been already referred to
(Vol. I. p. 246).

Fishes. — By these, the food is invariably seized by the jaw.s, which
are usually provided with numerous sharp recurved teeth ; though, in
some species, the mouth is suctorial, and the teeth are few, or even
wanting. In the amphioxus, the oral orifice is guarded with soft cirrhi,
whilst the mucous membrane of the mouth is provided with ciliated pro-
cesses ; the food is perhaps conveyed into the mouth by ciliary action.

Mollusca and Molluscoida. — The so-called feet of the Cephalopods
serve to convey food to the mouth : but the tentacula generally present in
Molluscs, are sensory rather than prehensile, the food being seized by the
mouth, as in the terrestrial and in certain aquatic trasteropods, or brought
thither by currents of water caused by movements of the mantle, or by
cilia, as in the LameUibranchiata. In the molluscoid Polyzoa, the ciliated
tentacles around the oral aperture produce a vortex, by which minute
organisms in the water are hurried into the pharynx. In the Tunicata,
the cilia lining the fore-part of the alimentary canal, accomplish a
similar purpose.

Annulosa and Annnloida. — Most Annulosa have distinct buccal appen-
dag<>s, consisting of two pairs of jaws ; the first pair are the mavdih/e.s,
or pincers; the second are the which support the prtfp/. By

these parts, the food is seized, examined, or even divided. In many
Insects and Crustacea, and in Spiders, one or more pairs of the limbs are

THE TEETH IN ANIMALS.

119

also employed in conveying food to the mouth ; sometimes, as in the
crabs and lobsters, such limbs are enormously developed, the. pincers on
one side of the body being smooth, and on the other, knobbed. In cer-
tain perfect insects, the food being viscid or fluid, the mandibular
appendages are specially modified, as, c.g., in the butterflies and moths,
in which they form a long tube or canal named the grohoscis, which can
be unfolded from its spiral coils, and protruded into flowers; a suck-
ing proboscis also exists in certain flies and gnats. In the fleas and bugs,
the mandibles are penetrating and suctorial. Amongst the Annelides,
the sand-worms have soft feeble tentacles ; but the earth-worms and
leeches have the mouth either simply suctorial, or cutting and suctorial.
In some worms, a retractile proboscis exists, developed from the lining
membrane of the pharynx, and not from the cephalic segments of the
exo-skeleton, like the jaws of the higher Anmdosa. The Annuloid Entozoa
either have a special suctorial apparatus, or live by general imbibition.
The marine worm-like forms are suctorial, whilst the Eotifera have a
ciliated disc, which creates a vortex in the water. In the starfishes and
echini, there are no prehensile tentacula ; in the Crinoida, the arms may
act prehensively ; in the holothiirida or sea-cucumbers, large labial
appendages or tentacula exist.

Codmterata. — These exclusively aquatic animals have contractile non-
ciliated tentacles, sometimes few and simple, or divided, as in the hydra,
sometimes very numerous, as in the sea-anemones, and often of great
length and of irregular form, as in the medusse and others. These are
always prehensile ; but food may also be drawn into the body, by the
alternate expansion and contraction of its muscular walls. In the
Physograda, the mouth is developed into depending tubular suctorial
processes or cirrhi.

Protozoa. — In the Infusoria, the cilia draw the water and food into
the buccal orifice, and there is no other prehensile apparatus. In the
lowly-organised Rhizopods and Amoebae, the soft body is merely applied
to the substance serving as food. In the Sponglda, etu-rents of water are
drawn through numerous in-cuiTent or inhalent orifices, into the interior
of the porous mass, whilst ex-current or exhalent orifices, fewer in
number, serve for their expulsion. This process not only assists in re-
spiration, but also in entangling food against their sarcodous substance.
Finally, the parasitic Gregarinida live by direct imbibition.

The Teeth and Mastication in Animals.

True teeth, or calcified organs, belonging to the exo-.sk(deton, and
composed of dentine, or of this with enamel and cement, are peculiar
to the Vertebrata ; for the so-called teeth or denticles of certain
Mollusca, Annulosa, and Annuloida, have no such structure.

Teeth are entirely absent in Birds ; but they are generally, though
not universally, present, in Fishes, Amphibia, Reptiles, and Mam-
malia. In the last-named Class alone, are the characteristic milk
teeth met with, that first temporary and deciduous set, which falls out
and is succeeded by the permanent teeth. With the exception of a
few fishes, and the vegotablo-fooding iguanas amongst reptiles, which
have grinding teeth, these organs in Fishes, Amphibia, and Reptiles, are

120

SPECIAL PHYSIOLOGY.

essentirtlly prehensile, or incisive, being used for seizing, and holding
the prey, or for dividing it into portions small enough to be swallowed ;
but it is in the Mammalia, that mastication proper, performed by
teeth set in movable jaws, is most perfect, the food being, in many
of them, not only seized, but afterwards gnawed or chewed.

In the different classes of the Vertebrata, the teeth differ remarkably
in number, shape, position, and mode of insertion.

Mammalia. — Amongst these, the Monotremata are almost edentulous,
or destitute of teeth, for the echidna has no such organs, but merely
horny processes on the tongue and palate, whilst the ornithorhynchus
has horny teeth. In the Cetacea, two genera have calcified teeth before
birth only, the upper jaw afterwards supporting the whale-bone plates.
In the manis, or pangolin, and in the true ant-eaters, or m3-rmeco-
phaga, amongst the so-called Edentata, there are likewise no teeth. All
other Mammalia possess them.

The number of the teeth in the Mammalia, in conjunction with other
differences in shape or kind, furnishes an important means of zoological
distinction. It ranges from 2 in the narwhal, to as many as 190 in the
dolphins. In the elephant, there are at most 10, usually only 6, viz. one
entire molar, or sometimes parts of two, on each side of both jaws, toge-
ther with the two tusks of the ujjper jaw. In the Eodents, the ordinary
number is 20, but there are sometimes only 12, and in the hare and
rabbit 28. In the Ruminants, in the apes of the Old AVorld, and com-
monly throughout the Mammalia, as in Man, there are 32, but 44 is said
to be the typical number. (Owen.) In one of the armadilloes, as an
exception to the rule in that genus, there are 98 teeth. Amongst the
Cetacea, the narwhal, just mentioned, and some other species, have
only 2 teeth ; the cachalot has more than 60, the common porpoise
between 80 and 90, and the true dolphins from 100 to 190.

The form of the teeth presents greater variety in the Mammalia than
in any other Class. AVhen numerous, they are usually prehensile, small,
pointed, and of nearly equal size throughout the jaw; sometimes slightly
recurved, and sometimes variously flattened or compressed. AVhen
the teeth are in moderate number, some are devoted to one purpose
and some to another, and they are usually’ modified into incisor, canine,
premolar, and molar teeth. The incisors, as in Man, are flat, chisel-
shaped, and cutting or gnawing ; the canines are larger and conical, to
bite, hold, and tear ; the premolars and molars are variously cusped or
tuberculated, and either flattened at the sides for cutting, or broad at
the summit for grinding the food. The incisor teeth are smallest in the
insectivorous, larger in the carnivorous and frugivorous species, of great
strength in the croppingHerblvora, but especially strong in the gnawing
Eodentia. The canine teeth, prominent in the carnivorous dogs and
cats, are also large in many non-carnivorous animals, as the ape, boar,
musk-deer, elephant, and others, in which they are used for offence or
defence. The carnivorous molars are generally flat, narrow, ridged and
tuberculated, the anterior ones being often very diminutive. The
herbivorous molars are flat-crowned, quadrangular, or lozenge-shaped,
and provided with tubercles, as in the Quadrumana, or marked with
crescenticor transverse ridges and furrows, as in theEuminants, Solipeds,
Pachj’dermata, and Eodents. In animals living on mixed diet, the
crowns of the molar teeth are furnished with blunt tubercles. The tusks

THE TEETH IN MAMMALIA.

121

of the elephant are huge canine teeth ; those of the walrus are also
canine. The single tusk of the male narwhal or Monodon, several feet
in length, is also an upper canine tooth ; it springs on one side of the
median lino, from the superior maxillary hone ; hut an immature tooth
is foimd concealed in the hone of the oppositeside ; in the female narwhal,
both tusks remain undeveloped, one in each upper jaw-hone. The curved
canine tu.sks of the Bahyroussa are also remarkable ; those of the upper
jaw are larger and longer than those of the lower jaw, and sometimes
perforate the upper lips.

The teeth in Mammalia are limited to the jaws. They are confined
to the inferior maxilla in the cachalot, to the premaxillary hones in the
upper jaw in the narwhal, and to the superior and inferior maxillary
bones, being wanting in the premaxillary hones, in most Ruminants. But
usually, teeth are found in all three of these hones. However varied
in number and in form, mammalian teeth are always arranged, in
each jaw, in a single row or dental arch, in which, where dilferent kinds
of teeth exist, one or more gaps occur, named diastemata. When a
diastema is absent, the teeth are of equal length. In the human jaw,
as already mentioned, there is no diastema, hut this is also the case in
certain extinct quadrupeds.

The mammalian teeth are usually fitted closely into sockets in the
jaws, each tooth and each fang, if these he multiple, having its own
socket, lined by a periosteum which fixes it. In certain Cetacea, the
sockets are wide and shallow, and the teeth ai'e attached to the gum,
rather than fixed in the jaw. Each tooth generally has a constricted
part or neck, between the crown and fang, to which the gum is fixed ; but
no neck is seen in the numerous small teeth of the dolphin, in the tusks
of the narwhal, elephant, and walrus, or in the incisors of the Rodentia.

The teeth of most Mammalia, like those of Alan, consist chiefly of
dentine, the crown being protected by enamel, and the fang being
covered by the cement, which sometimes passes over the crown also.
The microscopic structure of these tissues, however, presents certain
minute pecidiarities. The tusks of the narwhal, walrus, and elephant,
are destitute of enamel, and consist almost wholly of the modification of
dentine known as ivorij, the .surface being at first covered by a thin
layer of cement, which becomes worn by use. No enamel exists on the
molars of the dugong and cachalot, nor on the teeth of the Edentata.
In the Quadrumana, and in the Carnivora generally, as in Alan, the
cement is so thin over the enamel of the crown, as to be almost inap-
preciable ; but it is thick jn Ilerbivora, and especially so on the molars
of the elephant, sloth, dugong, walrus, and cachalot. In the Ruminants,
in most Rodentia, and in the Pachydermata, the enamel and the cement
are arranged, within the crowns of the molar teeth, in double vortical
plates or folds, between corresponding processes of the dentine, the
variations in which, form a means of classification in the Rodentia and
Pachydermata.

When one of these compound teeth, such as a molar of the ox, deer,
sheep, horse, or the still more complex grinder of the elephant, first cuts
through the gum, the crown is covered with a thick layer of cement,
which dips in between folds of enamel, which, in their turn, conceal
variously-disposed plates of dentine. In the course of time, the cement on
the grinding surface is worn down, and the folds of the subjacent enamel

]22

SPECIAL PHYSIOLOGY.

become visible. With further attrition, the cement between the folds
of enamel wears away faster than the enamel itself, and hence the broad
surface presents ridges corresponding with the harder enamel, and
furrows corresponding with the softer cement, an arrangement well
adapted, like the roughened surface of a mill-stone, for the grinding of
hard grain, woody fibre, or roots. As the process of wear extends, the
summits or bent parts of the folds of enamel are also worn through,
and the concealed plate of dentine is exposed ; in this case, the most
complex markings appear on the grinding surface, produced by the
alternating and often tortuous bands of dentine, enamel, and cement.

When the mammalian teeth, whether simple or complex, are worn
down to the fang, they generally, as in Man, loosen and fall out ; for
their growth is completed at a certain period, after which their pulps
shrink, they become subject to wear or decay, and undergo little or no
repair. A remarkable provision exists, however, for the presennition
of the cutting edge of the chisel-like incisor teeth, characteristic of, and
necessary to, the gnawing Kodentia. These teeth show a persistent
growth ; the fang is deeply implanted in the jaw, and remains hollow
and open at the base, into which the persistent pulp extends. The so-
called enamel organ, on the anterior wall of the socket, is also persi.s-
tent. Fresh dentine is constantly being formed witbin, upon the pulp,
and fresh enamel upon the anterior surface, by the enamel organ ;
whilst the unequal wear of the hard coating of enamel in front, and of
the dentine behind, preserves, dmnng the whole of life, the chisel-like
edge. From the persistent growth of these peculiar teeth, it happens,
that if one of them be drawn or accidentally lost, the opposing tooth being
no longer worn down by use, continues to elongate, and, following its
natural cuiwe, attains an abnormal size and shape, and its point turns
round, and even penetrates the oppo.sife lip. The teeth of the arma-
dilloes and sloths also grow continuously, on persistent pulps.

In many Mammalia, sex exercises a remarkable influence on the de-
velopment of certain teeth. Thus, in the Quadrumana, especially in
the anthropoid apes, the upper canine teeth, in the male, are more than
twice the size of the same teeth in the female ; the tusks of the boar
and of the male elephant, and musk-deer, are larger than those of the
female animals. In the dugong, which, an exception in Cetacea, has
both temporary and permanent incisor teeth in the two jaws, the upper
permanent incisors project beyond the gum, in the male ; but in the
female, the permanent incisors in both jaws remain concealed throughout
life, their growth being arrested before they cut the gum. The asym-
metrical tusk, the rudimentary and, concealed condition of the opposite
tooth of the male narwhal, and the hidden rudiments of both teeth in
the female, already mentioned, also show the influence of sex.

This rudimentary condition of certain teeth is, however, sometimes
independent of sex, but characterises groups of animals. Thus in the
ox tribe, altliough the temporary incisors appear above the gum in both
jaws, the permanent incisors are not developed in the upjjer jaw, but
remain in a rudimentary condition within the bone.

The four canine teeth also exist, in a rudimentary state, in all young
Riiminants, though they never rise above the gum. In both jaws of the
young whale-bone whale, rudiments of teeth exist, which are never
lurthor developed.

THE TEETH IN HEHTILES.

123

Jiirds. — In Birds, the Iiorny coating of the edentulous jaws, is deve-
loped, in successive lamiine, from the tegumentary membrane covering
those bones. In the parrots, this horny coat is thick, and is formed
and supported upon papillce. The absence of teeth in birds, is associated
with the existence of a muscular stomach, or gizzard.

Reptiles. — Of these animals, the Saurians exhibit the most perfect
dentition, then the Ophidians, whilst the Chelonia are edentulous, their
jaws being covered with a thick and dense horn, variously modelled,
so as to act in bruising or dividing the food, the jaws of the vegetable
feeders being thick, and those of the carnivorous species sharp on their
edges.

In the Reptiles which possess teeth, the number varies, but in exist-
ing species, it is never very small, being 30 in certain monitor lizards,
and 29, the lowest known number, in the Ophidian amphis-
beeua. The number is not so determinate, nor are individual teeth so
specially characterised, as in the Mammalia. In the crocodiles, and in
many lizards, the teeth are limited to the jaw-bones ; but they exist also
on the pterygoid bones in the roof of the mouth, in the iguana, and on
the palatine and pterygoid bones, in most Ophidia. In many of the latter,
teeth are absent from tlie inter-maxillary bones. The jaw-teeth form
single arches, excepting only in the caecilia or blind-worm, in which
the lower front teeth are arranged in a double row.

The typical form of the reptilian tooth is conical, but in a few
species this is departed from. These conical teeth vary greatly in size
from the minute teeth of the blind-worm, to the powerful canine-like
teeth of the crocodile. They are sometimes cylindrical, but more fre-
quently compressed, or much flattened and blade-like, having sharply
trenchant, or even serrated, margins. The surface is either smooth and
polished, or longitudinally striated. In the iguanas, the crowns of the
teeth are widely expanded, and their sides and margins curiously
notched. The teeth are relatively longest in Serpents, and in the case
of the poison-teeth or fangs, present a remarkable structure. These
poison-fangs are strongly recurved, and contain a canal, opening at both
ends on the anterior or convex aspect of the tooth, above, close to the gum,
and below, a short distance from the point of the tooth. The secretion
of the poison-gland, found at the side of the head, is convej'edby a duct,
to the opening of the poison-canal near the base of the tooth. Into this,
the poi.son is forced by muscles which tighten the gland capsule and
compress the gland ; and thence it is conveyed, through the opening in
front of the point of the tooth, into any wound. The poison-fangs aro
anchylosed, or fixed by osseous union, to the superior maxillary bones ;
but since, in the poisonous serpents, these bones are movable, the poison-
teeth can either, as when at rest, lie flat upon the gum, or they can be
brought into a vertical position, in the act of striking.

The teeth of Reptiles have a short undivided root, which is, for the
most part, anchylosed to the bone on which it rests. In the crocodiles,
however, the teeth are separate, and are lodged in deep sockets ; in the
black alligator, the front teeth are embedded in sockets, whilst the
hinder ones are fitted into a continuous groove. In the serpents and
geckos, the anchylosed teeth aro fixed to the sides of shallow sockets,
but in the chameleons and most lizards, to the inner surface of a single
alveolar plate.

124

SPECIAL PHYSIOLOGY.

Reptilian teetli always contain dentine and cement, sometimes also
enamel and true bone. In most Saurians, the enamel exists as a thin
coating orer the crowns. The presence in certain teeth, of bone, besides
the cement covering the dentine, depends on the conversion of the
base of the pulp into bone, as the tooth becomes anchylosed to the jaw.
The microscopic structure of the dentine, differs slightly from that of
the dentine in Mammalia, its substance being traversed by canals com-
municating with the pulp cavity. In the iguana, the dentine is singularly
inflected on its surface. In the poison-fang of the serpent, the dentine is
folded on itself, in front of the pulp-cavity, so as to form the poison-groove
or canal ; a longitudinal section of the tooth, shows the tapering pulp-
ca\’ity behind the poison-canal ; whilst a transverse section shows this
canal surrounded by the dentine, coalescing in front of it, the pulp-
cavity forming a crescentic fissure behind it.

As the teeth of Reptiles wear out and fall away, an almost unlimited
succession of new ones replaces them throughout life, a process entirely
different from the simple succession of temporary and permanent teeth
in the Mammalia. The new tooth usually appears at the inner side of
the base of the old one ; but the poison-fangs of the serpents are replaced
by new teeth, formed behind the old ones.

When, as is usual, the teeth are anchylosed to the jaw, the new tooth
simply grows up on a papilla, and replaces the falling one ; but in the
alligators and crocodiles, in which the teeth are lodged in sockets, the
new tooth, also formed on a papilla, gains access, by a process of absorp-
tion, to the interior of the old one, penetrates its pulp, grows up within
> it, raises it, and finally throws it off from its own summit. By this time,
as seen in the gavial, another rudimentary tooth is formed, and proceeds
to grow, in like manner, into its predecessor. The process of absorption
resembles that of the fangs of the milk teeth, in Mammalia ; and like
that, it has been incorrectly attributed to mechanical pressure ; for the
growing tooth is softer than the old one, which is being absorbed.

Amphibia. — Fine prehensile teeth are found on the upper jaw and
palate bones of the frogs and salamanders, more seldom on the lower
jaw also. In the toads, only palatal teeth are present. Teeth are ab-
sent in the proteus and siren.

Fishes. — The teeth of Fishes present extraordinary varieties, greater
than those of any other Class. Their number is almost countless in the
silurus, its allies, and in the pike ; but they become fewer or wholly
absent, in the lower orders of fishes. The chimserte have two teeth in
the lower, and four in the upper jaw; the lepidosiren has only a single
dental plate in each jaw, and two small teeth on the nasal bones ; the
tench has one tooth on the occiput, besides some on the pharyngeal
bones ; whilst the myxine and m}'xinoid fishes have a single, tooth on
the palate, meeting two dental plates upon the tongue. Lastly, in the
syngnathus or pipe-fish, in the hippocampus, in the Lophobranchiate
fishes, in the sturgeon, ammocete, and amphioxus, no teeth exist.

The shape of the teeth in fishes, differs much. They are usually simple
and conical ; they are minute, numerous, and viUiform in the perch ;
longer, ciliiform or setiform, often bifid or trifld; and rasp-like or
mdidiform, on the back of the vomer in the pike. They are commonly
cylindrical, but sometimes flattened into a lancet-like blade, either
straight, curved, bent sideways, or even barbed. The base may be broad.

THE TEETH IN FISHES.

125

as in the larger teeth of the pike, the lophius, and certain sharks ; the
edge is sometimes finely serrated, as in the sharks generally, or is
notched, so as to divide the tooth into from two to five lobes. In other
less known fishes, they are short and blunt, cubical, or prismatic, with from
four to six sides, and closely arranged in a sort of mosaic work, showing
their convex or flattened summits over broad surfaces. These surfaces
are well calculated for grinding seaweeds, and crushing shell-fish or
corallines, as seen in the teeth of the seams or wolf-fish, and the cunei-
form dental plates of the parrot-fish, which truly masticate their food.

The teeth of Fishes, as already indicated, are by no means limited to
the premaxillary and premandibular bones of the upper and lower
jaws. In the sharks and rays, they are thus confined to the fore-part
of the mouth ; but in the carp, all the teeth are at the back of the mouth,
supported on the pharyngeal and basi-occipital bones. The parrot-fish
has teeth, botlr at the front and back of the mouth, i.e. on the premaxil-
lary and premandibular bones, and on the upper and lower pharyngeals.
In most fishes, there are teeth, not only on the above-named bones, but
also on other bones around the middle part of the mouth, as on the
palate bones, vomer, hyoid bones, and branchial arches, sometimes on
the pterygoid, sphenoid and nasal bones, and, though rarely, on the true
superior maxillse. Teeth are found in the median line, on the palate of
the myxines, and even, in a few cases, on the symphysis of the jaw, a
position not observed in any other Vertebrata. In the lampreys, most
of the teeth are placed on the lips.

The teeth of Fishes are usually anchylosed to the bone on which they
rest, the dental and osseous tissues being blended ; occasionally it is
the side of the tooth, and not the base, which is thus fixed. In certain
Cartilaginous fishes, some of the teeth are divided at their base, and are
so attached by ligaments, as to allow the teeth to be bent backward in
the mouth, by casual pressure ; but when this is removed, the teeth
spring up again. Even the anchylosed teeth arc first attached by liga-
ment only. A few examples are met with of the teeth being embedded
in sockets ; but then also anchylosis exists. The short strong teeth,
which almost pave the mouth of the wolf-fish, are anchylosed to special
eminences.

The teeth of Fishes are almost invariably composed of some kind of
dentine only, the enamel and cement being absent. In certain cases,
as in the carp, the tooth substance is brown and semi-transparent; in
the Cyclostomata, it has been differently described as dense, albuminoid,
or horny ; the labial teeth of certain goniodonts and ebrntodonts are
flexible and elastic. The true dentine of fishes’ teeth, is very compact,
especially on the .surface of the tooth, whore it occupies the place of
enamel; this superficial layer has been called vitro dentine. Another
modification of dentine, commonly found in fishes’ teeth, is named o&teo-
dentine, because it contains vascular canals, resembling the Haversian
canals of bone, between which are dentinal tubuli, no longer minute and
parallel, but large, divided, and ramified. The so-called vaso-dintine
is also found in the teeth of fishes, and, though more rarely, the 'plici-
dentine, lahi/rmtho-dintine, and dendro-d<ntine, so called from the
vjavi/, or dendritic appearances seen in them on sections. Although
teeth consisting of dentine alone, are only found in fishes, yet the most
complex known teeth are met with in this Class. Thus, in the wolf-

126

SPECIAL PHYSIOLOGY.

fishes, and diodons, the teeth contain dentine, osteo-dentine, enamel, and
cement ; and in the parrot-fishes, each pharyngeal tooth is composed of
non-vascular dentine, covered by an enamel, anchylosed to the bone by
vaso- or osteo-dentine, and fixed to the neighbouring teeth, in the same
row, by intermediate cement.

The teeth of Tishes, besides being liable to be accidentally torn off at
their bases, are shed not merely once, as in Mammalia, but many
times during life. In the pike and other common fishes, and in the Car-
tilaginous fishes, as the sharks, the formidable teeth are renewed and
coutinually advance into place from behind, as the old ones break, or fall
out. A few quite exceptional examples of strictly permanent teeth are
met with, as in the lepidosiren and chimera.*^

The Jaws and their Muscles.

The oral aperture of the Vertebrata, is a transverse opening, provided
with jaws, one or both of which move vertically. In the Cyclostome
fishes, the mouth, however, is circular-, and, in the amphioxus, oval
and longitudinal.

The form and strength of the jaws, the mode of articulation and mo-
tions of the lower jaw, or of both jaws, and the corresponding muscular
apparatus, vary with the habits and food of the different Vertebrata.

In all the Mammalia, as in Man, the upper jaw is fixed to the bones
above and behind it, and has no independent motion ; whilst the lower
jaw is movably articulated to the under side of the temporal bones, and
is raised, moved horizontally, or depressed, by muscles exactly similar
to those found in the human body.

In the large Carnivorous mammalia, however, the glenoid fossae are
not shallow, as in Man, but deep, narrow, and form long channels
running from side to side, and inclining backwards and inwards towards
each other. As the condyles of the lower jaw are equally narrow and
elongated transversely, the motions of the jaw are limited to an up and
down motion, in which not only is a general, firm hold secured, but the
notched edges of the laterally compressed molars pass close by each
other, like those of the blades of scissors. In Insectivorous mammalia
the motions of the jaws are almost equally limited. In the Kodentia,
besides shutting powerfully in gnawing, the jaw executes rapid backward
and forward movements, across the ridges of their molar teeth, so as
easily to grind tough vegetable substances. In the Herbivora, the lower
jaw is not limited to an up and down movement only, as in the Car-
nivora, nor to that, and a superadded backward and forward movement,
as in the Eodentia, but it is also capable of great lateral play. To per-
mit tliis, the glenoid fossm are wide and shallow, the condyles of the
lower jaw are short, obtuse, and scarcely prominent, and the pterj’goid
muscles, which chiefly execute the lateral motions, are very large. The
lower jaw is carried, during mastication, in a sort of circular sweep,
beneath the upper jaw, first forward, and to one side, and then back-

* See the article ‘ Teeth,’ by Professor Owen, Cyclop. Anat. and
Phys., from which the preceding account of the teeth in the Vertebrata
is chiefly derived.

DENTICLES OF THE LOWER ANIMALS.

127

ward and to the other, and so on, as may be readily noticed in the cow,
when chewing the cud ; the broad molar teeth, with their unequal
ridges and furrows of enamel and cement, are thus most effectually em-
ployed. In the edentulous ant-eater and ornithorhynchus, the condyles
of the jaws, and the glenoid fosste, are only slightly developed, and the
movements are comparatively simple, and feeble.

In Birds, the actions of the jaws are prehensile and not masticatory,
excepting perhaps in the parrots, in which there is a lateral motion.
For the most part, the motion is hinge-like, and not very powerful,
excepting in the strong-billed birds, such as the finches, rooks, toucans,
and Kaptores, which latter hold and tear their food by movements of
the head and neck.

In Reptiles, whether they live on animal or vegetable food, the jaws
are also prehensile, or incisive, rather than masticatory, except in the
herbivorous iguanas, the molar teeth of which are large and tuber-
culated. In Amphibia, the jaws are weak, and snapping or suctorial.

In Fishes, the movements of the jaws are, likewise, for the most part,
simply of a snapping and prehensile or incisive character ; but the
pharyngeal and other dentigerous bones within the mouth, are also
movable, and these bones, as well as the jaws, especially in the parrot-
and wolf-fishes, are provided with strong masticating muscles, which
make them act powerfully against each other.

Denticles of the Non- Vertebrate Animals.

As already stated, true teeth are found only in the Vertebrata, but
denticular organs are met with in some of the other Sub-kingdoms.
Amongst the Mollusca, the Cephalopods are provided w’ith horny jaws,
which open and shut vertically. Some Gasteropods, also, have similar,
but smaller, jaws moving laterally ; but nearly all of them are pro-
vided with a peculiar strap-shaped band, beset with rows of minute horny
denticles situated in the mouth, and often spoken of as the tongue.
This organ, named by Huxley the odontophore, is placed not on the floor,
but on the roof, of the mouth. It is moved backwards and forwards
by appropriate muscles, and thus files or rasps very hard substances ;
as its anterior part is worn away, the odontophore, with its horny den-
ticles, is renewed within a special sac, seen at its hinder end.

Amongst the Annulosa, the Arthropoda have mandibles, always
found at the sides of the mouth, and provided with strong muscles,
which give them a horizontal, not a vertical motion ; they are composed
of calcareous or chitinous substance, and differ remarkably in shape, in
different species, being usually curved and pointed, and having serrated
or dontated edges ; tliey are strong in the actively feeding Inrvm, and also
in most perfect Insects, as in wasps and beetles. In the Crustacea, the
mandibles are verj' strong, and in certain species, as in the lobster,
liard gastric luberclcs, worked by powerful muscles, exist at the entrance
of the stomach. Even amongst the soft Annelids, a denticular apparatus
exists, as seen in the leech, which, by means of throe minute denticles,
inflicts a tri-radiate wound.

Amongst the Anntdoida, many of the minute Rotifora possess complex
denticulated plates, which are worked transversely across the oral orifice.
In the hard-shoUed Echinodermata, a singular masticatory apparatus

128

SPECIAL PHYSIOLOGY.

is found which, in its perfect form, consists of five large flattened, calci-
fied denticles^ having their free edges smTounding the oral aperture ;
the outer borders of these denticles, voiy peculiar in form, are received
into a frame-work, the whole structure, in its entire state, forming the
lantern of Aristotle ; powerful muscles act upon those denticles, which
comminute, or triturate, the food.

No denticles exist in the Coelenterata ; minute denticular organs are
seen in some of the stomatode Infusoria, but they are, of course, absent
in the astomatous Protozoa.

The Salivary Glands, and Insalivation, in Animals.

Salivary glands, or glands opening into the mouth, exist in most
animals. In the Mammalia, they are nearly always jiresent, but differ
much in number and size. In the higher Mammalia, they resemble the
glands in Man, except that the submaxillary is unusually large, and, in
the seals and cats, the sublingual gland appears to be wanting. In
Herbivorous, the salivary glands are larger than in Carnivorous Mam-
malia, in harmony with the more bvdky, often drier, and amylaceous
character of the food. In the Euminants, all the glands, but especially
the parotids, are very large, and even supernumerary glands are found, as
in the ox. In the ant-eater, the salivary apparatus is enormously de-
veloped ; the glands cover the fore-part of the neck, and, even reach
to the chest; a special reservoir, or A/atfrfcr, exists beneath the

mouth, in which the saliva is probably detained ; when rendered
viscid, by absorption of its fluid, it lubricates the tongue, and assists in
catching ants. In the Cetacea generally, the salivary, like the lachrymal,
glands are wanting, the fluid medium in which they live, and the animal
natm’e of their diet, rendering saliva unnecessary ; in the herbivorous
dugong, however, the parotid glands exist, but not the sublingual.

In Birch, the salivary glands are small in the wading and web-footed
species, which live upon soft animal food ; whilst they are proportionally
larger in the rapacious and granivorous species. The saliva of birds
is chiefly used to lubricate their food. In the woodpeckers, these glands
are large, and the viscid sahva assists the tongue in entangling insects.
In the Chinese swallow, which builds the edible nests, the parotid gland
is largely developed, and its secretion is used in making the nests.

Amongst Itepiiles, large salivary or buccal glands, found in the Ophidia
generally, but not in all species, beneath the gum, along the margins of
both jaws, serve to lubricate their prey before it is swallowed. The
poison-glands of the venomous species, may perhaps be regarded as
extraordinarily modified salivary or buccal glands. In the Chelonian
and Saurian I'eptiles, the salivary apparatus consists chiefly of lingual
glands. In the chameleon these are found in the enlarged extremity
of its singularly formed insect-catching tongue, and secrete the shm}'
mucus with which it is covered.

In the Amphibia, similar glands are found, which, in the toad, serve
a like office.

In Fishes, no salivary glands exist.

In the Mullusca, glands opening into the mouth, or into the commence-
ment of the gullet, and therefore i^resumably salivary, exist in nearly all

THE PHARYNX IN ANIMAT.?.

129

Cephalopods, Pteropods, and Gasteropods, vai-j'ing in form and size,
according to the construction of the mouth, and tho nature of the
food.

Amongst the Annidosa, glands, always regarded as salivary, exist in
well-marked, but most variable forms, sometimes opening into tho mouth,
at the base of the mandibles, or beneath the proboscis, and sometimes
further down, near the stomach. These glands are, of course, minute,
and simple in structure, forming, either short follicles, vesicles, blunt-
ended tubes, long twisted tubes, as in all butterflies, and most beetle.s,
or even branched tubes, as in Blaps. In the Mjmiapods, similar glands
exist. In the Cirrhopods, they are of considerable size, and form the
cement gland.

In the Annuloid Echinodermata elongated caical tubes surround the
(Esophagus, and secrete a -viscid fluid, which mixes -with the food. Salivary
tubuli have even been described in tho Entozoa and Eotifera. No such
glandular structures exist in the Ccelenterata, or Infusorial Protozoa.

The Pharynx and Gullet, and Deglutition in Animals.

The parts concerned in deglutition and the act itself, are similar in
all the air-breathing Vertebrata, but both become gradually simplified.
The uvula is absent, excepting in the higher Quadrumaua. The soft
palate is very large in the elephant and the Cetacea. Tonsils are
always present. In all cases, from the highest Mammalia down to the
Amphibia, the pharynx communicates with the cavities of the mouth,
larynx, and oesophagus, and also, on each side, with the tympanum. In
Mammalia, the structure of its walls resembles that in Man, and in the
second stage of deglutition, it rapidly and safely transmits the food and
drink into the oesophagus, over the laryngeal opening, whilst the third
or oesophageal stage of deglutition is also, as in Man, performed more
slowly by waves of peristidtic contraction, even against gravity, as is
seen in the horse, when drinking. In Birds and licytiles, the phaiynx
is of simpler construction and action, being in the Serpents enormously
dilatable. In the Amphibia, it approaches the less defined character
which it presents in Fishes.

In Fishes, which re.spire, in tho water, by gills, the pharynx has no
communication with the nasal fossse, and, moreover, the larynx and air-
breathing apparatus are absent, except, in some cases, the air-bladder ;
hence the pharynx forms a mere infundibular passage, leading from
the mouth into tho shut eesophagus ; but its sides are supported by
the cartilaginous or bony framework of the branchial arches, between
which are the branchial openings ; besides this, there are special
pharyngeal bones, which, as already mentioned, often bear prehensile
or even masticatory teeth.

In the Molluscous, Annuloso, and still lower Classes, a special pharynx
is seldom distinguishable ; but tlio buccal cavity usually pa.sses directly
into the oesophagus. In the Molluscoida, however, a part called tho
pharynx, exi.sts between the mouth and tho oesophagus.

A true pharynx is, indeed, characteristic of the Vertebrata, and is
•specially developed in those which respire air, and in which the food
has to be swallowed, without entering the sensitive air-passages, and

VOL. II. K

130

SPECIAL PHYSIOLOGY.

but a momentary interruption to the breath. In the cold-blooded
Serpents, however, which swallow animals entire, deglutition is painfully
slow, and causes a certain interference with respiration. In the young
kangaroo, whilst it is still retained in the marsupium or abdominal
pouch, the upper part of the larynx is elongated, and projects, as in the
Cetacea, into the posterior nares, so that the milk passes down on each
side, without risk of entering the air-passage, and without interference
with the act of breathing.

The Stomach and Intestines in Animals.

Mammalia. — In the Quadrumana, the stomach often resembles that
of Man, but it is sometimes globular or elongated, sacculated, constricted,
or bent on itself ; a cardiac and a pyloric portion are alwaj's recognisable.
In the Carnivora, the stomach also presents the human shape, but the
cardiac pouch is large. In the insectivorous Cheiroptera, it is globular ;
in the vampyres, it is long and conical, the cardiac end being the larger ;
in the frugivorous species it is still longer, the cardiac pouch is con-
stricted in its middle, and the pyloric portion is bent. In the proper
Insectivora, this organ is elongated. In the Edentata, it is, usually
simple ; but in the genus Manis, the cardiac and pyloric portions are
marked off by an intern.al fold, and, in one species, a long sac extends
from the pyloric portion. In the sloths, the stomach is first divided
into a cardiac pouch and a pyloric portion ; the former has a dense
epithelium, and is again subdivided into two parts, one ending in a
blind canal ; the pyloric portion has thick walls, and a soft mucous
membrane, and is subdi^nded into two parts, which might be compared
with the third and fourth stomachs of the Euminants. In the ant-
eaters, the cardiac part of the stomach constitutes a kind of crop, whilst
a second chamber, having thick walls and a hard gristly lining, some-
what resembles the gizzard of the bird, and, compensating for the want
of teeth, crushes the ants, by aid of the sand swallowed with them.

It is in the Ruminants, however, which are all vegetable-feeders, that
the stomach presents the most remarkable complication, being divided
into four distinct cavities ; first, the paiinch, rumen, ingluvies, or pa7ise-,
secondly, the honey-comb, water-hag, reticulum, or bonnet ; thirdly, the
omasum, manypUes, psalterium, or feuillet ; and, fourthly, the abomasum,
reed, rennet, or caillet. The fii'st stomach, or paunch, is the largest,
sometimes attaining enormous dimensions ; it forms a bag, constricted at
one point, and placed to the left of the (Esophagus, which opens into its
right upper end; its mucous membrane is papillated, and covered with a
dense white squamous epithelium. In the camel tribe, two clusters of
diverticula, or cells, exist, one on each side of the paunch. In the drome-
dary, each cluster is eighteen inches long and six inches broad. The
component cells, quadrangular, and arranged in rows, are, when dis-
tended, about three inches wide and deep ; their orifices are closed by
membrano-muscular folds ; some are subdivided by membranous ridges
into secondary cells. These water-cells of the paunch are intended for
storing up water, which is found only at long distances in arid countries.
They arc emptied by the action of their muscular walls.

The second stomach, or honey-comb, much smaller than the paunch,
forms a simple bug beneath the (Esophagus, between the paunch and the

THE EEMINANT STOMACIL

]31

third stomach or manyplies. Along the inner surface of its upper
concave border, is a peculiar demi-canal or groove, named the xsopJmgcal
(/roove, which runs from the right half of the cesophagus, of which it
seems a continuation, on into the manyplies ; its borders, composed of
the muscular, submucous, and mucoiis coats, are much elevated, and can
be brought together, so as to form a tube leading directly from the oeso-
phagus, past the paunch and honey-comb, into the manyplies. The in-
terior of the honey-comb is characterised by a cell-like or reticular
structure, being developed into numerous polygonal cells, which are
shallow in the reindeer and giraffe, deeper in the ox and sheep, and
stiU more capacious in the llamas and camels. The mucous membrane,
in the horned species, is papillated, especially on the inter-alveolar
ridges. The cells of the honey-comb or water-bag retain water, which
during digestion is mixed with the food. They are not proper water
reservoirs, like the cells of the camel's paunch ; for, unlike these, they
have no marginal covering folds, are always open, are more sub-divided
internally, and do not, when filled, bulge on the outer surface. Moreover,
the cells of the honey-comb are present in all Ruminants, whilst those of
the paunch exist only in the camels, dromedaries, and llamas.

The third stomach, or manyplies, is usually the smallest cavity of the
complex ruminant stomach ; but in the camels it is larger than the honey-
comb. It forms a sac, placed between the honey-comb and the fourth
stomach, or rennet-bag ; it communicates with the former, by a narrow
passage, but opens quite freely into the latter. Its inner surface is re-
markably increased by numerous longitudinal laminae or folds, having
their free edges turned towards the cavity, varying alternately in depth,
and numbering from forty, in the sheep, to twice that number, in the ox ;
their resemblance to the leaves of a book, has given rise to the appellations
manyplies, psalterium (psalter), and feuillet. The mucous membrane
of the manyplies is viUous.

The fourth stomach, or rennet-hag, from which, in the calf, the rennet
is procured for curdling milk in the manufacture of cheese, is about one-
third of the size of the paunch ; it is elongated and conical in form,
being wider at the left end next to the manyplies, and gradually narrow-
ing towards the pylorus, near which the muscular coat is thickened, and
where a circular pyloric valve exists. The mucous membrane, thrown
into loose, irregular, longitudinal rugte, connected by smaller transverse
ones, is soft, destitute, of villi, and highly vascular. It is chiefly com-
posed of the countless gastric follicles, which open upon its surface.
The rennet- bag is the true digestive stomach, being the only part of
the compound ruminant stomach which secretes gastric juice.

The ruminant animal, cropping its herbaceous food, first partially
masticates and insalivates it, and then swallows it. Afterwards, the
animal being at rest, the food, so swallowed, is returned into the
mouth, where it is now remasticated and once more swallowed. This
constitutes the act of rumination, characteristic of these animals. The
crude food, when first swallowed, descends in largish masses, which
force open the borders of the oesophageiil groove, and so escape into the
paunch. Water, doubtless, is conducted along that groove into the
lioney-comb, or so-called water-bag, but it also partly escapes between
the margins of the groove, and so enters the paunch, wliero, in the camel
tribe, it is received into the system of water-cells there situated.

K 2

SPECIAL PHYSIOLOGY.

ia2

The food, partially masticated and insalivated, lubricated with mucus,
and mixed with water and the juices of the paimch, undergoes macera-
tion in that cavity, and also probably enters the honey-comb, in which
it is further watered. Now, moulded by muscular action into small
masses or pellets, either in the cells of the honey-comb bag, or by the
cesojDhageal groove itself, it is propelled into the oesophagus, and thence,
by an anti-peristaltic action, into the mouth. The soft and small pellet
is there deliberately remasticated and insalivated, and is thus reduced to
a semi-fluid pulp, which again passes down the oesophagns, and the
margins of the oesophageal groove being now closed by muscular con-
traction, so as to form a complete tube, the semi-fluid mass is this time
transmitted into the third stomach, or manyplies, from which it cannot
retnrn. Here it is brought into contact with a large surface of mucous
membrane, loses much fluid and soluble saccharine and other substances,
and is then passed on to the rennet-bag, for the digestion of the albu-
minoid matters.

The precise mode of action of the borders of the cesophageal groove
and other parts, is not known. Some suppose that the animal conveys
the food or drink, instinctively or voluntarily, either into the first or
second stomach, or else into the third. But according to another view,
the process is partly a reflex act, and partly mechanical. In every act
of deglutition, the borders of the oesophageal groove are believed to be
approximated by a co-ordinated muscular act. When the food or fluid
swallowed, is large in mass or quantity, it is supposed to overcome the
muscular action, and so to pass, if solid, into the paunch, and, if fluid,
partly also into the honey-comb ; but if the material swallowed be semi-
fluid or fluid, and in moderate quantity, it is suggested that it may be
conveyed along the temporary tube into the manyplies (Fiourens). In
the act of sucking, the milk is said to pass at once into this cavity, on ac-
count of the small quantity swallowed at a time. It is not certain whether
the regurgitated pellets are moulded in the cells of the honey-comb bag
itself, or in the oesophageal groove ; nor whether the pellet is inti-oduced
into the lower end of the oesophagus, by the contraction of the sides of
the groove, or by that of the reticulum itself. Though reflex, and pro-
bably excited by the food as a stimulus, and therefore not volitional,
these movements of the ruminant stomach and oesophagus may be in some
extent controllable by the will.

In the Pachydermata, the stomach is more simple. Thus, it is elon-
gated, and possesses a long cardiac pouch in the elephant and rhinoceros,
but in the former, it presents numerous internal transverse folds. The
hippopotamus has two cardiac pouches, opening widely into the rest of
the stomach ; in the tapir and hyrax, this organ forms two cavities. In
the pig, the stomach resembles externally that of Man, though the car-
diac end is more projecting, and a considerable extent of the lining
membrane, near the oesophageal opening, is covered with a thick epithe-
lium. In the peccary, still more of the cardiac portion is lined b}' a
dense epithelium.

In the Solipeds, the stomach is rounder, the oesophageal and pyloric
openings are near to each other, and the cardiac portion of the organ is
lined by a thick epithelium, which terminates by a dentated margin.

In the Rodentia, the stoihach is also marked oflF into a cardiac and
pyloric portion, often indicated by an external constriction ; the cardiac

LENGTH OF INTESTINE IN MAMMALS.

133

part is lined by a thick epithelium, and the pjdoric end by a soft glandu-
lar mucous membrane. In the beavers, and some other species, the
stomach has glandular crj-pts and cmca, the use of which is not known.

The Marsupials, whether carnivorous or herbivorous, have usually a
simple somewhat elongated stomach, sometimes provided, like that of the
beaver, with numerous crypts. In the kangaroo, the stomach is of
remarkable length, being as long as the body ; its middle portion is
sacculated, and marked by three longitudinal muscular bands, somewhat
like the colon ; it has three compartments, two being cardiac pouches,
and also three rows of large crypts along the bands.

It is remarkable that the carnivorous Cetacea have a more complex
stomach than the herbivorous species. In the dugong, amongst the
latter, this organ is elongated, and marked off into a cardiac and a
pyloric portion, by a constriction, from near which two blind pouches
proceed ; the cardiac pouch presents a large glandular surface. The
carnivorous cetacean stomach possesses from tlu-ee to seven cavities,
the first of which has a thicker epithelium than the rest.

On taking a general view of the above described modifications of the
mammalian stomach, it would seem that, in its simplest form, it is a
specially dilated part of the alimentary canal, distinguished by its abun-
dant glandular tubules ; this becomes elongated and narrower at a cer-
tain part, next constricted, and then partially subdivided within, bj'
internal folds. These subdivisions in the complex stomach become still
more pronounced, and associated with important differences of structure
in the various coats, especially in the lining membrane. The pyloric
portion of even the simplest stomach has larger gastric glands than the
cardiac portion ; and, in the compound stomachs, this part alone presents
gastric tubuli, and secretes gastric juice. The cardiac end, variously
subdivided and modified, is often lined by a thicker epithelium, and has
been regarded as a dilatation of the oesophagus.

The inicstinal canal is, in all Mammalia, marked off from the stomach,
by a circular muscular rim or pyloric vah'e. It presents even greater
varieties than the gastric cavity, and these are more immediately refer-
able to the nature of the food.

The most noticeable difference is in the relative length of the intestines,
from the pylorus downwards, which are nearly always shorter in the
flesh-feeding, and longer in the vegetable-feeding species, in every Order.
The following Table illustrates both the rule and the exceptions : — •

Flesh-Feeders.
Carnivora —

Cat, dog
Bear, hyaena
Seal

Insectivora
Cheiroptera — ■
Insectivorous bats

. 6 to 1

9 or 8 to I
. O') to 1
6 or 3 to 1

. 2 to 1

Vegetable-Feeders.
Ruminantia —

yhcep . . . 30 to 1

Solipeds —

Horse . . 20 or 15 to 1

Cheiroptera —

h’ rugivorous pteropus 7 to 1

Quad rum ana —

Omnivorous . 8 or 3 to 1

Excepting in the Cetacea, .and a few Edentata and Cheiroptera, the sub-
division into a small and largo intestine, prevails throughout. Accord-
ing to its length, the small intestine is more or less convoluted; it
usually has internal valvula; conniveiites, and a villous mucous mem-

i34

SPECIAL PHTSIOLOGT.

brane; villi are always wanting in the large intestine. At the junction
of the small with the large intestine, a more or less perfect ileo-csecal
valve is found, except in the Monotremata, Cetacea, and certain Edentata
and Cheiroptera.

The colon is usually sacculated. A csecum nearly always exists, its
presence and size corresponding closely with the nature of the food,
being either absent or small in flesh-feeders, and highly developed in
vegetable-feeders. It is absent in all Insectivora and Cheiroptera, in
some of the Edentata, and in certain Cetacea. In the Carnivora, ge-
nerally, it is short and narrow, and is absent in the bears and weazels.
It is present, and of variable length, in the Qnadrumana. In all Rumi-
nants, it is capacious, but it is still larger in the Solipeds, being, in the
horse, three times as largo as the stomach, and measuring two feet in
length. In the Pachyderms, it is somewhat smaller, but the hyi-ax
has two caeca. Amongst the Rodentia, the caecum is absent in the in-
sectivorous dormouse, short and small in the omnivorous rat ; but it
attains its greatest size, and is even marked by circular or spiral folds,
in the herbivorous genera, as in the rabbit and hare, being, in the
latter, eight times as capacious as the stomach. In the carnivorous
Cetacea, there is usually no cajcum, but the balajna has a small one ; in
the herbivorous species, this part exists, being sometimes very large, but
sometimes short and bifid. The carnivorous Marsupials have no
caecum, and the insectivorous species a small one ; in the frugivorous
specie.s, it is wide, and twice as long as the body, and in the herbivorous
species three times as long.

The narrow part of the crecum, the vermiform appendix, present in
Man, exists in the apes and gibbons, and in the marsupial wombat,
but in no other mammalian animal.

In the Monotremata, a small caecum alone indicates the place of
junction of the small and large intestine ; the intestinal canal is narrow,
but widens below, and ends in a cloaca, as in birds.

Birds. — The digestive canal in Birds is nsuall}’’ complex, the oeso-
phagus being more or less dilated near its lower end, to form the cro^;,
or ingluvics, to which succeeds the •provcntricidiis, or proper secreting
stomach, and beyond this, is a third cavity, forming the.gic^ard. In the
pelican, the floor of the mouth, and in some other birds, the sides of the
fauces, are dilated into receptacles for food.

The (esophagus varies in length according to that of the neck. In
the storks, herons, and pelicans, which swallow their prey whole, it is
very wide, and in the cormorant, it forms a large pouch. It communicates
freely with the proventriculus, and its longitudinallj’ plicated mucous
membrane has numerous follicles, which secrete a mucus to moisten the
food, and aid in deglutition. The crop, or dilated portion of the mso-
phagus, is not distinct in the toucans and hornbills, or in frugivorous
and insectivorous birds, or in most of the waders. It is even wanting,
amongst the swimming birds, in the swans and geese, but is small in the
ducks. The largo birds of prey have a small crop, lodged in front of the
furcular bone or merrythought, at the root of the neck. The crop i.s
most developed in the grain-eating gallinacea, forming a dependent bag,
connected with one side of the oesophagus, as in the fowl, or, as in tho
pigeons, consi.sting oven of two lateral oval sacs. Wliere a crop exists,
tho short portion of tho oesophagus below it, is named the second or

THE CHOP AND GIZZARD OF BIRDS.

1.35

lower oesopliagus ; it gradually dilates into the proventriculus, which
has no constricted cardiac orifice.

The proventriculus, also called the ventriculus succmturiatus, the true
glandular stomach, varies in form and size in different birds, being
sometimes wide and straight, and sometimes round. In the rasorial birds,
it is wider than the oesophagus, but smaller than the gizzard ; in the
birds of prey, it is about the same size as the gizzard ; in the parrots
and storks, it is larger than the gizzard, and in the ostrich, four or
five times as large. Its mucous membrane is thicker and more vas-
cular than that of the msopbagus or even of the crop, and, as in the
mammalian stomach, is provided with numerous gastric glands arranged
perpendicularly to the surface, sometimes simply tubular, as in the carni-
vorous eagle and sea-gull, the insectivorous swallow, and the granivorous
pigeon, and often sacculated, or even expanded into compound follicles,
as in other grain-eaters, viz. the fowl, turkey, rhea, and ostrich. The
disposition of these glands on the interior of the proventriculus, differs
in different Orders, and even in different genera of the same Order.
Thus, they may be diffused over the whole surface, or may form a single
oval, elongated, or triangular cluster, two oval lateral clusters, or four
arranged in a circular manner, or they may form a zone or belt.

The gizzard, gigerium or ventriculus bulbosus, the third, last, or muscular
stomach of birds, is a more or less flattened, ovoid receptacle, having
two neighbouring apertures at its upper part ; one, into which the. pro-
ventriculus opens, and the other leading into the intestine. Between
and below, as it were, these apertures, the gizzard forms a cul-de-sac,
varying in size, and having walls of variable thickness in different
species. In the birds of prey, the muscular coat is thin, and its fibres
radiate from two lateral tendinous centres. It is in the rasorial and
flat-billed swimming birds, as exemplified in the fowl and swan, that the
gizzard is most developed ; the deep red muscular fibres here form foiu'
very thick masses, two of which, named the muscxdi laterales, constitute
the sides of the gizzard, whilst two smaller ones, the musculi intermedii,
are placed at one end ; they all radiate from, and towards, two very strong
anterior and posterior tendons. The cavity of the gizzard is compara-
tively small, and is bounded by two flat surfaces, covered by a very
thick, cuticular, horny, or even tuberculated lining membrane, supported
on a dense, fibrous, submucous coat. The lining membrane is hardest
in the granivorous birds, especially in those species in which the food is
most solid ; its density increases at the points where the pressure and
friction are greatest. In the petrel, it presents a layer of small square
tubercles, suggesting a likeness to the gastric denticles of certain Gas-
teropods. Hunter observed that in a sea-gull fed on barley, the muscles
and cuticle of the gizzard became thicker than natural.

A pyloric valve usually exists in Birds ; it is placed, in most species, a
little below the gizzard, so that there is a short pyloric portion of
the stomach intervening between the gizzard and the duodenum.
The pyloric valve is very strong in some birds ; it is double in tlio
gannet, and, in the ostrich, forms six or seven ridges, which close the
pylorus like a grating, permitting only small stones to pass.

The uses of the crop, proventriculus, and gizzard of Birds, are obvious.
The crop, absent or small in birds living on fruit, insects, small aquatic
animals, or flesh, but reaching its utmost development in those which

136

SPECIAL PHYSIOLOGY.

feed on grain and other seeds, forms, like the ruminant paunch, a cavity
for the retention and maceration, dm’ing several hours, of hard and
dry food, so as to prepare it for the solvent action of the proper gas-
tric juice of the proventriculus, and the grinding force of the gizzard.
Seeds soften and swell under the influence of the scanty saliva, and of the
more copious secretion of the crop. Pigeons will sometimes devour so
many dry peas, as to be almost suflTocated when these swell in the crop.
The crop has been compared to the hopper of a mill, and the gizzard to
the millstones, the former and larger cavity receiving the food, and de-
livering it, in successive suitable quantities, into the latter, which is so
much smaller. Whilst rearing its young, the mucous membrane of the
double crop of the pigeon becomes thicker and more vascular, its
glands enlarge, and secrete a milkj^ looking fluid, wdiich mixes tvith the
softened grain in the crop, and is then, by an antiperistaltic action, regur-
gitated into the mouth, from which, in the manner above-described (p.
118), it is taken by the young pigeon, serving the same purpose as the
lacteal secretion of the Mammalia. The proventriculus of Birds has
been compared with the cardiac, and the gizzard, with the pyloric, por-
tion of the mammalian stomach. The secretion of the proventriculus has
the same digestive properties as those of the gastric juice of Mammalia.
The gizzard, which, when it exists, forms an internal masticatory or^an,
supplying the want of a masticatory apparatus in the head, has evi-
dently a mechanical office. By the aid of pebbles, gravel, or sand,
swallowed especially by granivorous birds, it triturates the food. Such
birds do not thrive, without a supply of pebbles or gravel ; and pigeons
have been known to carry these to their young. Grains of barley,
enclosed in strong perforated tubes, pass through the alimentary canal
of the bird undigested, whilst meat, similarly enclosed, is dissolved.
Unbruised corn, Avith its hard silicious coat unbroken, is not soluble in
gastric or intestinal juice. The gizzard of the ostrich can flatten metal
tubes, pulverise glass balls, and break or blunt the points of needles and
lancets, without injury to its hard internal coat. The grinding of the
stones in a bird’s gizzard, may beheardby the stethoscope.- The movements
of the walls of this cavity, are supposed to be slightly rotatory. In the
membranous gizzard of the cuckoo, as I, as wmll as others, have
found, the hairs of caterpillars are sometimes impacted in a regular
spiral manner, as if felted by a continuous movement of partial rotation ;
balls of hairs spirally disposed have also been seen. These facts have,
been often quoted, in support of the view that, in all animals, intrinsic
movements of the walls of the stomach may occur.

The intestine of Birds generally, is, relatively to the body, shorter than
that of Mammalia, but longer than that of Eeptilos. It varies in length
and width, as well as in the arrangement of the com'olutions, and in the
relative development of the cmca. In the birds of prey generally, the
intestine is not more than twice as long as the body, including the bill,
but in the osprey it is eight times as long. It is longer in frngivorous and
granivorous birds, and shorter in the flesh-eating species. The duodenum
ahvays forms a long loop, embracing the pancreas. The remaining por-
tion of the small intestine, isA-ariously folded in different birds, the con-
volutions being cither spiral, concentric, or irregular. The mucous
membrane is usually plicated. The distinction between small and large
intestine now becomes less marked, there being no ileo-caecal valve, and

THE STOMACH IN HEETILES.

137

villi being found on the mucous membrane of both. Their place of
junction is, however, frequently indicated by the presence of a crecum,
or rather of two cseca, for this diverticulum is most commonly double.
The cieca are wanting in some vultiu-es, in the cormorant, wryneck,
and toucan, and in many carnivorous, insectivorous, and frugivorous
birds ; they are small and short in other vultures, in the eagles, and in
the solan-goose, and also, w'hen they exist, in the Insessorial tribes.
They are longer in the noctmmal than in the diurnal birds of prey.
Amongst the Easores, they are short in the pigeons, but very long in the
grouse, each measiu’ing three feet, or thrice the length of the body, their
internal surface being increased by eight longitudinal folds ; in other
Easores, they are of moderate length. In the Cm-sorial birds, the intes-
tinal canal, as well as other parts, approaches more nearly the mamma-
lian character. The cteca, however, are absent in the cassowary, which
obtains a constant supply of succulent vegetable food; whilst in the
ostrich, which lives upon dry and scarce food, they are wide, about
two feet long, and have an internal spiral fold, like that of the hare.
In Birds generally, as in Mammalia, the caeca are absent, or small, when
the food is concentrated and easily digestible ; but when it is slower of
digestion, or is taken in larger quantity, and at longer intervals, these
appendages are most developed.

The large intestine beyond the caeca, is long and mammalian-like in the
ostrich, but usually is relatively short, straight, and not verj' wide ; it
terminates by an imperfectly valved circular opening in the dilated cavity
called the cloaca, into which also the ureters and the duct or ducts of
file reproductive organs, open. In the hinder wall of the cloaca, is situated
the glandular organ known as the bursa Fahricii.

Lastly, there exists in many birds a short, narrow, blind diverticulum,
connected with the small intestine ; this is the vestige of the vitelline
duct, which, in the embryo and young bird, connocts the yolk sac with
the intestine. It is called the vitelline emeum ; it has no special digestive
function. A similar diverticulum is occasionally found in Mammalia,
and even in Marr.

Reptiles. — The alimentary canal in this Class, is more simple than
in Birds, to which, however, it approaches more nearly than to that
of Fishes. The oesophagus varies in length, according to that of the
neck ; it is wide, plicated, and dilatable in the Ophidia ; as in Birds, it
joins the stomach without any constriction or cardiac orifice ; but the
mucous membrane suddenly ceases to have a dense epithelium, and be-
comes soft, smooth, and glandular. In the larger Saurians, the first part
of the stomach has the form and structure of a gizzard, presenting thick
muscular walls, the fibres of which radiate from two opposite central
tendons ; the pyloric part, more decidedly glandular, corresponds with the
short portion sometimes found between the gizzard and the duodenum in
Birds. In the Serpents, the cardiac part of the stomach is long, slightly
saccular, and highly dilatable, whilst the pyloric portion is nairower and
very muscular, being the only part like a gizzard. In the Cholonians,
the stomach is curved, and larger at the cardiac than at the pyloric end.
The pyloric valve is usually present in Eeptilcs, though not very dis-
tinct, and sometimes is scarcely recognisable.

The intestine in Eeptilcs is shorter and wider than in Birds. In the
Saurians, there is mostly an ileo-colic valve ; the crocodiles have no

138

SPECIAL PHYSIOLOGY.

csecum. In the Chelonians, the intestine is long and muscular ; an ileo-
csecal valve usually exists, and also frequently a csecum. In Serpents,
the small intestine especially, is elongated ; the ileo-colic valve is indis-
tinct, or its place is indicated only by a change in the size of the canal ;
the lars:e intestine sometimes has transverse folds in its interior, analo-
gous with the spiral valve in the same part in Cartilaginous fishes. As
shown by the fonn of certain reptilian coprolitcs. these folds must have
been well developed in some extinct Saurians. The mucous membrane
of the large, as well as of the small, intestine is plicated and villous.
The lower end of the larger intestine, forms a cloaca, receiving the ducts
of the urinary and reproductive organs. The presence of a csecum in
certain Chelonia, furnishes an additional example of the association of
this organ with the use of a vegetable diet. The existence of a gizzard
in some Reptiles, is one of the indications of the relations of this Class
with Birds.

Amphibia. — The oesophagus of the Amphibia is short, dilatable and
muscular. The stomach is fish-like, being tubular, wider at the cardiac
than at the pyloric end, and placed transversely, or curved upon itself.
The intestine in the toad and frog, is readily distinguishable into small
and large, the former opening into the side of the latter; the ileo-c»cal
valve is indistinct or absent. In the more fish-like Batrachia, the division
into small and large intestine, is imperceptible. The latter ends in a
cloaca, which receives the ducts of the urinary and reproductive organs.
The relation between the length of the intestinal canal and the nature
of the food, is illustrated in the long and coiled intestine of the young
vegetable-feeding tadpole, as compared with the short intestine of the
insectivorous adult frog and toad.

Fishes. — In Fishes, the alimentary canal presents its most simple verte-
brate form, being wide, and, in relation to the body, short. The cesophagus,
short, wide, and muscular, sometimes passes so evenly into the stomach
that the structure of the mucous membrane alone distinguishes them ; in
the former, it is pale and longitudinally plicated ; in the latter, it is softer,
redder, and full of gastric tubuli. In the Cyclostomata, it forms only a
dilated portion of the neaidy straight canal. In the Osseous fishes es-
pecially, it varies in size, but is usually tubular, bent once upon itself,
and narrower towards the pylorus; sometimes, b}- protrusion of the con-
vex border, and shortening of the concave border, it becomes fiask-shaped
or globular, with its cardiac and pyloric openings placed near together.
The cardiac orifice, large, and sometimes provided with a valvular fold,
not only readily permits the swallowing of the prey whole, but some-
times allows of regurgitation and rumination, the food being remasticated
by the teeth, or by the pharyngeal bones, as seen in the carp. The pyloric
part is sometimes so muscular as to resemble an imperfectly developed
gizzard, having thick walls and a dense squamous epithelial lining.
A pyloric valve nearly always exists.

The intestine is relatively short and wide, of nearly uniform diameter
throughout, has few convolutions, and is distinguished into a large and
small intestine, by a slight constriction only ; there is no distinct ileo-
colic valve, but sometimes a short crncum exists. The small intestine
has usually connected with it, immediately below the pylorus, the so-
called appendices pylorica;, which have been compared with the pancreas.
The largo intestine is often, as in the sharks, provided with internal folds

THE STOMACH IN MOLLUSCA.

139

or a spiral valve, by which its surface is much increased. It is also
generally thrown into rugse, which augment its surface. In some species,
the intestine is unusually long ; it is rarely supported upon a mesentery,
excepting at a few points. The peritoneal cavity presents the unusual
condition of opening directly on the exterior. In the singular am
phioxus, the alimentary canal is short and nearly straight, the stomach
being scarcely dilated ; the intestine, as well as the mouth and sides of
the pharynx, is provided throughout with cilia, which assist in moving
on the fluids in the alimentary canal.

Mollitsca. — In these animals, the alimentary canal, though simpler
than in the Vertebrata, presents, as in them, many gradations, from a
very complex form in the Cephalopods, to that of a slightly convoluted
canal, with a simple dilatation for the stomach in the Lamellibranchiata.
No distinction exists into small and large intestine.

In the Cephalopods, the oesophagus, which perforates the cephalic
cartilage, is long, very dilatable, and ends in a strong gizzard, roundish
or elongated in shape, lined with a hard epithelium, provided with two
digastric muscles radiating from two lateral tendons, and having its
cardiac and pyloric orifices near together. Sometimes, before entering
the gizzard, the oesophagus expands into a crop. Below the pyloras,
the intestine dilates to form a spherical, triangular’, elongated, or spiral
cavity, having a follicular mucous membrane ; this has also been re-
garded as a stomach, but the ducts of the liver enter it through a sort
of sac. Lower down, the intestine forms a simple, more or less curved,
tube, which bends up, and opens into the branchial chamber, at the base
of the mantle, not far from the mouth. The ink-bag is situated close to
the lower portion of the intestine, and opens near it.

In the Pteropods, there are also, sometimes, found a crop and a distinct
gizzard; the intestine presents three or four bends, surrounded by the
liver.

In the Pulmo- and Branchio-gasteropods, the oesophagus is long, and
frequently expands into a crop ; the stomach itself often consists of two
or more cavities; the first is usually lined with a thick epithelium, and
is sometimes provided with hard internal laminse or denticles, consti-
tuting a sort of gizzard, which is most developed when the buccal
masticating organs are least so ; the second has softer walls, and forms
the true digestive stomach. The relative position of these triturating and
digestive cavities, is the reverse of that metwith in birds. The intestine,
more or less coiled, larger and more tortuous in the vegetable-feeders, and
usually embedded in the liver, receives the hepatic ducts, bends once or
twice, turns forwards, and ends near the fore part of the body, usually
on the right side, but sometimes on the left, or even on the back. It is
lined with a ciliated epithelium.

In the Lamellibranchiata, the transverse mouth is concealed in the
mantle, the oesophagus is short, the stomach forms a simple dilatation,
and the intestine is relatively simple, describing a few turns, and ending
by a straight portion, opening at the hinder part of the mantle ; its con-
volutions are embedded in the substance of the liver, and its terminal
part is sometimes embraced by, or perforates, the heart. As already
stated (Vol. I. p. 127), the direction of the principal bend of the intestine,
whether to the dor.sal or h.'cmal, or to the ventral or neural surface of
the body, is characteristic in each Molluscous Class (Huxley).

140

SPECIAL PirySIOLOGT,

Molluscoida. — In the Asciclioida and Brachiopoda, the alimentary
canal is very simple, consisting either of a convoluted, or of a short re-
curved tube, merely dilated at the stomach, and having its terminal
orifice approximated more or less, to the often wide and valved mouth.
In the Salpida, the outlet of the intestine is at the hinder end of the
body. In some Brachiopoda, the intestine ends in a bUnd-sac, having no
inferior aperture or outlet.

In the Polyzoa, the mouth, situated in the centre of the circlet of cili-
ated tentacles, leads into a wide pharynx, and short oesophagus, which
terminates in a muscular stomach ; from this, the intestine bends up-
wards again, and opens near the side of the oesophagus, close to the
outer border of the tentacular circle. In some species, the stomach is
muscular or gizzard-like. These creatures present one of the lowest
types of animals possessed of a true alimentary canal, distinct from the
walls of the body, shut off from the peri-visceral cavity, and having a
distinct and permanent inlet and outlet.

Anmdosa. — The alimentary canal here also presents marked degrees
of complexity, from the highly developed apiparatus found in certain
Insects, to the simple straight tube seen in the lowest Worms. The
oral aperture or mouth, and the anal aperture or outlet, are always at
opposite ends of the body. As a rule, the carnivorous kinds have a
short intestine, and the vegetable-feeders a longer and even tortuous
intestinal canal.

In the Insects, the alimentary canal varies with the stage of meta-
morphosis. In the vermiform larva, it is a straight tube, passing from
one end of the body to the other; sooner or later, a dilatation appears,
forming the stomach, which sometimes becomes divided transversely,
and the oesophagus may also be further dilated into an ingluvies or
crop. The intestinal canal presents caeca, and therefore a sort of dis-
tinction into small and large intestine. In the mandibulate Insects, as in
tlie wasps and beetles, the crop is often glandular; tlie gizzard, wliich,
unlike what occurs in Birds, is placed above the digesting stomach, lias
very muscular walls and a chitinous lining membrane, provided fre-
quently with prqi’ections, laminae, hairs, or denticles, but sometimes this
part is indicated only by being a little more muscular. The true
stomach has soft delicate walls, usually provided with numerous gastric
follicles. Sometimes the stomach has no follicles, but its interior is
laminated, or developed into cells, or into a few short caecal tubes ;
sometimes it is quite smooth. The intestine is generallj' narrow, more or
less convoluted, and seldom supported by a mesentery, but rather by the
tracheae; it sometimes presents dilatations or di\'isions, so as to imitate,
perhaps in form only, the subdivision into a small and largo intestine.
Certain fine caecal tubes communicating with it, are probably glandular
structures rather than diverticula of the intestine. The first part is un-
doubtedly fitted for absorption, whilst the lower end is more excretory.
It presents a terminal dilatation or cloaca, into which the reproductive
organs open.

In the Myriapods, the alimentary canal is narrow and nearly straight,
and is either, as in the carnivorous species, merely slightly dilated, to
form a stomach, or, as in the vegetable-feeders, complicated by pairs
of saccular projections, which have been regarded as crops, or gizzards,
but may be merely glandular recesses. The intestine is straight, vide.

THE STOMACH IN ANNULOIDA.

141

plicated, and sometimes sacculated. Ctecal tubuli open into various parts
of the alimentary canal.

In the Arachnida, the digestive tube is straight, very short, and com-
paratively simple. The stomach, scarcely dilated, has sometimes four
appended sacculi, and sometimes csecal prolongations, reaching into the
bases of the palpi and legs. The intestine sometimes presents a globular
dilatation, before it finally narrows.

Amongst the Crustacea, the higher forms, such as crabs and lobster.s,
possess a short wide sac, provided with internal hard calcareous, or
chitinous denticles, which serve at once the purpose of a gullet, a
masticatory apparatus, a stomach, and a gizzard. The denticles, ar-
ranged symmetrically around the canal, are worked by powerful muscles,
and are shed when the animal changes its shell; besides the larger
denticles, there are often stiff hairs, bristles, and horny ridges. The in-
testine, marked ofFhy a constriction from this denticulated stomach, is
short, nearly straight, and simple ; it is sometimes subdivided by an im-
perfect valve, and, though seldom, has one or two cteca. In the lower
parasitic Crustaceans, the alimentary canal is, however, straight and
simple, becoming narrower as it passes backwards.

The shortness and simplicity of the alimentary canal, in the Spiders,
Scorpions, and Crustacea, which live, some upon the juices of other
animals, and some on crushed animal food, compared with the length
and complexity of the digestive tube in vegetable-eating insect larvae,
or in the perfect beetles, further illustrates the modifications already
noticed in the digestive canal of the higher animals, according to the
nature of their food.

In the Annelida, the alimentary canal never presents any convolutions
or bendings, and the mouth and outlet are always at opposite ends of
the body. It has no mesentery. It is either quite simple, not even pre-
senting a gastric dilatation, as in the lower marine species, or it is deve-
loped into simple tubuli, or subdivided pouches, or it may be regularly
sacculated, as in the leeches, the blood sucked by those animals being
retained, and slowly digested in the sacs. In the earth-worm, these sacs
are represented by simple constrictions ; it also has a sort of gizzard,
and, within the intestine, a tubular ctecal organ, named the typhlosole,
the use of which is not known.

Annuloida. — In the Eotiferous animalcules, the alimentary canal
presents a pharyngeal dilatation, or crop, sometimes regarded as the
stomach ; the intestine is narrow and simple, opening sometimes at once
on the surface, sometimes after forming a sort of cloaca ; the orifice is
usually near the hinder end of the body, on its dorsal aspect. In the
Turbcllaria, minute marine and fresh- water worms, an alimentary canal
is present, which is either simple, sacculated, or most remarkably ramified
or dendritic ; with few exceptions, such as tlieNemertis and Microstoma,
it has but one aperture, viz. a mouth, which is often provided with a
disc-like sucker, for holding on to surfaces ; the pharynx also has a
proboscis, for sucking or boring purposes. Of the parasitic Scolecida,
the Nematoida, or thread-worms, have an alimentary canal, with both
inlet and outlet, a pharyngeal dilatation, .and a simple intestinal tube,
sometimes, however, dilated, so as to form a sort of stomach, and some-
times a second dilatation lower down. In the Trematoda or flukes,
such as the distoma, tristoma, and others, there exists either a double

142

SPECIAL PHYSIOLOGY.

or a ramified canal, ■with a common pharynx, but no anal aperture. In
the Gordiacea, or hair-worms, there is likewise no such outlet. The
organisation of all parasites, to whatever class they belong, is more or
less aberrant.

In the Toeniada or tape-worms, and in the Acanthocephala, repre-
sented by the echinorhynchus and echinococcus, also parasites living in
tlie interior of other animals, there is no alimentary canal, nutriment
being absorbed by them directly, through the integuments, from the
digested food, or from the juices of the animal in which they live. In the
tape-worms, straight tubes, with transverse or even radiating branches,
exist, which are doubtless concerned in the nutritive processes, rather
as circulatory and respiratory, than as digestive organs.

In the Echinodermata, the alimentary canal is well developed, distinct
from the walls of the body, provided, in most cases, with openings at
both extremities, and even supported by a mesenteric fold. In the
Crinoida, the stomach and intestine are situated in the central part of
the body, the latter opening at one side. Below the complex masticatory
apparatus, elsewhere described (p. 128), the intestine of the Echinida,
at first narrow, widens out, and presents a crecal dilatation, beyond
which the intestine coils twice round within the shell, reversing its
direction in the latterhalf. In the Star-fishes, and also in the Ophiurida,
the alimentary canal is very short, and gives off two ramified diverticula
into each ray ; the intestine opens by a minute orifice on the back ; un-
digested matters are frequently discharged by the mouth. In the holo-
thurida, the intestine describes a zig-zag course; the outlet is placed at
the hinder end of the body.

Cmlenterata. — In this well defined aquatic Sub-kingdom, there is no
longer an alimentary canal, separate from the walls of the body, and pro-
vided vuth an oral and anal aperture. The digestive canal is very short
and wide, and has but one external opening, the mouth, which, however,
serves both for the ingestion of food, and the egestion of residual matters,
and excretions ; at its inner end, the digestive canal opens widely into
the general cavity of the body. From this latter, numerous canaliculi
are prolonged, in the medusse, into the disc, some of them opening by
pores in its margins. In certain ctenophorous forms, as in beroe, cydippe,
and cfestum, the body cavity also opens, by one or two orifices or pores,
at a point opposite to the oral aperture, but these are not intestinal or
anal openings.

In the Actinozoa, the digestive canal projects a certain distance
into the body cavity, which forms, outside that canal, the perivisceral
cavity. In the Hydrozoa, the digestive canal becomes continuous, bj' a
very wide opening, with the body cavity, without any portion of it pro-
jecting into that chamber; hence there is no surrounding or perivisceral
chamber, and the outer surface of the continuous digestive and body
cavities, itreboth in contact with the water. The hydra niaj’be inverted,
like the finger of a glove, and its outer surface, now become internal,
will digest its food equally well.

In the compound Hj-drozoa, the lower end of the body cavity of each
polyp communicates, b}' a tubular process, with a common channel ex-
tending through the entire stem, a circulation of fluid, often containing
granular particles, taking place through the whole colony. In the com-
pound Actinozoa, the digestive cavities of the individual animals also

THE LIVER IN ANIMALS.

U3

open into a chamber in the common fleshy basis, the aperture being
radiate in shape, and capable of being closed by muscular contraction.

Protozoa. — Of these, the higher Infusoria alone possess any represent-
ative of an alimentary canal. In the paramecium, for example, a de-
pression exists on the surface of the body, bordered by cilia, and leading
to an aperture called the mouth, from which a short blind tube, named
the gullet, dips into the sarcodous body. This is the last imperfect
trace of a digestive canal, seen in the Animal Kingdom. Temporary
cavities, formed by movements in the sarcodo, into which food, or
colouring matters may penetrate, appear like stomachs, whence the name
poti/ffastric applied to some of those microscopic creatures ; but as these
cavities may be seen slowly to move within the sarcode, up one side,
■and down the other, they are no longer regarded as stomachs. The
undigested food, after thus circulating through the sarcode, is expelled
at a particular point, either near the mouth, or near the hinder end of
the bod}’’, which point is only then recognisable.

In the Sponges, Rhizopods, and Gregarinida, no trace of an alimentary
canal exists. The system of canals with incurrent and excurrent aper-
tures, seen in the Spongida, is not digestive more than it is respiratory
or reproductive, but depends on the plan of construction of Spouges,
which are composed of an open framework, supporting aggregations of
astomatous amoebiform masses of sarcode, each of which directly assimi-
lates food. In the solitary amoeba, and its allies, the proteiform con-
tractile sarcode applies itself to nutrient substances, and completely
encloses them ; digestion and assimilation take place within it, and
the undigested portions are extruded at some indiflferent point. The
Rhizopods are noiu-ished in a similar manner. The microscopic parasitic
Gregarinida, appear like the tsenia and echinococci, to imbibe nutrient
matter directly by their surface, from the fluids of the intestine, peri-
visceral cavity, or other chambers or tissues of the animal, in which they
live.

The Abdominal Digestive Glands.

Gastric Glands. — Gastric tubuli exist in the secreting portion of the
stomachs of all the Vertebrata, becoming short and simple in the frogs
and fishes. In the higher Mollusca and Annulosa, as in the Cephalopods,
Pteropods, and perfect Insects, the stomach also has numerous follicles,
probably analogous to gastric tubuli ; but in the lower Mollusca and
Annulosa, and in the Molluscoida and Annuloida, the walls of the gastric
cavities are often destitute of distinct glands. This is the case also
with the walla of the digestive canal in the Coelenterata.

Liucr.— This important organ, or some representative of it, is more
widely distributed amongst animals than any other secreting or excret-
ing gland. It is present as a well-defined organ, not only in all the
Vertebrata, the amphioxus only excepted, but also in all the Mollusca
and Molluscoida, and is represented in the Annulosa by tubular creca or
follicles, which are found even in the Annelida, and likewise in the
Rotifora and Echinodermata amongst the Annuloida. No correspond-
ing part, however, exists in those Annuloida which are destitute of a
distinct alimentary canal, such as the Trematoda, Tmniada. and Acan-
thocephala, nor yet in the Ccclenterata, much loss in the Protozoa.

144

SPECIAL PHTSIOLOGT.

Amongst the Vertebrata, the liver, proportionally to the body, becomes
progressively larger in passing from the Mammal to the Fish. Its
general form corresponds with that of the abdominal cavity ; thus, it is
broad in the apes and the Carnivora, longer in the larger Ruminant and
long-bodied animals ; of moderate length in Birds; broader in the com-
paratively short Chelouia and Sauria, but long in the elongated Ophidia ;
broad and short in the frogs and toads, but long in the newts ; stretch-
ing widely into the abdomen of the broad-shaped skates and rays, but
lengthened out in the eel. Its position is usually symmetrical, but in
the Mammalia with large compound stomachs, it is placed more towards
the right side, as is also the case in the anthropoid apes : in Fishes,
generally, it lies more on the left side of the body. In Birds, in w'hich
the diaphragm is complete, the liver is notched for the reception of the
heart and pericardium ; in Reptiles, Amphibia, and Fishes, which have no
diaphragm, the liver also reaches up to the pericardium, except when the
body is very long, as in the serpents and eels.

The liver in the Mammalia generally, is nearly simple, its lobes being
only slightly marked. In the Ruminants, it is subdivided into three
lobes ; in the Rodentia and Carnivora, there are from three to five lobes,
viz. a central one, and one or two on each side ; sometimes, it is further
subdivided into small and irregular secondary lobules. In the llama,
amongst Ruminants, the under surface, and in the capromys, a Rodent ani-
mal, the whole surface, is divided by deep fissures into angular masses,
resembling those of the kidneys of the bear. In Birds, the lobes are tu o,
and symmetrical ; in Reptiles and Amphibia, the lobes are also generally
two, but the liver is undivided in the Ophidia ; in Fishes, the liver is often
more subdivided. The microscopic structure of this gland, in all the
Vertebrata, resembles that of the human liver. In the curious amphioxus,
a long cfEcal appendage from the intestinal canal, having a layer of
greenish cells lining its interior, is regarded as a rudimentary liver, no
distinct organ otherwise existing.

In the Mollmca, the liver is a large, symmetrical, solid, and lobulated
organ, having two ducts. Its great development in these animals, and
also, it may be added, in the cold-blooded Vertebrata, may be_ connected
with the function of storing up fatty matter, as the adipose tissue does
in the higher Mammalia. The nucleated hepatic cells in the Non-
vertebrate animals, aird also in the cold-blooded Vertebrata, contain
much more simple oleaginous matter than they do in the warm-blooded
Vertebrata, in w'hich latter, the proper biliary fatty acids chiefly occupy the
cells ; in Birds, the cells contain less ordinary fat than in Mammals.
Sometimes, as in the Cephalopods and Lamellibranchiata, the liver is
subdivided into minute lobules, composed of branching ducts, ending in
dilatations. In the Gasteropods, the ramified ducts and terminal
follicles are more distinct, so as to form a loose compound racemose
gland. The chief ducts are ciliated internally.

Amongst the Molluscoida, the Brachiopoda have a large, minutely
lobulated liver, composed of ramified tubuli. As some of the earliest
fossils yet discovered belong to this Class, a hepatic organ yielding
bile, and, therefore, digestive processes corresponding with those,
known to us in the present day, must have existed in most remote
periods of the earth’s history. In the Aseidioida, the liver presents
interesting gradations; for, in different cases, it may consist of a small

THE GALL-BLADDER IN ANIJIALS.

145

gliind, a duster of follides, a single follido, or simple lacunre or lamiiue
on the inner side of the intestine ; it is represented only by a yellowisli,
orange-coloured, or broumish glandular spot, on hrjiutic portion of the
walls of the intestine. In the Polyzoa, the sides of the intestine below the
stomach, are marked with brown hepatic tubes, follicles, or spots.

Amongst the Annulosa, the Crustacean liver is of a yellowish colour,
large, and complex. In some kinds, as in squilla, it is symmetrical,
lobulated, and sublobulated, each sublobule consisting of clusters of
round follicles conuecte.d with a central duct. In the crabs and lobsters,
the follicles of the liver are innumerable, much branched, and separated
from each other. In the river crab, the follicles are less ramified. In
the lowest Crustaceans, such as the parasitic argulus, the hepatic follicles
are still more simple, or this organ consists only of a mass of nucleated
cells.

In the highest Insects, and in the Myriapods, the liver is represented
by hepatic tubuli, connected with the intestine ; these are short and
numerous in dytiscus, only two, but elongated, in blaps, or even single, as
in the grasshoppers ; sometimes they are mere vesicles. In no case is
the liver massive, but always tubular. In the Spiders, the hepatic
follicles are either short and simple, or they end in compact clusters
of vesicles. In the Annelids, the liver is represented by gland cells,
situated either in ramified tubes, as in Arenicola, or in tubuli ending
in an oval sac, as in Aphrodita, or in numerous follicles, as in the leech.

Amongst the Annuloida, a single long follicle in the Trematode
w onus, represents the simplest form of rudimentary liver ; in the
parasitic Tteniada and Echinococci, the liver, as indeed the intestine
itself, is unrepresented. In certain Echinodermata, as in asterias,
coloured cells are found in the walls of the radiating prolongations of
the gastric cavity, which perhaps secrete biliary matter.

In the Ccelenterata, no separate hepatic organ exists in connection
with the simple digestive cavity ; but the walls of this, as in velella,
sometimes present a mass of gland cells, which may form bile. No such
product has yet been found in any part of the unicellular Protozoa.

Blood-Vessels of the Liver. — In all the Vortebrata, the liver receives
blood both from the hepatic artery and the portal vein. In the Mam-
malia, this vein, as in Man, has only a few communications with the
lumbar and pelvic systemic veins. In Birds and Reptiles, the connection
between the pelvic and portal veins is such, that a part of the blood from
the lower extremities, and from thetail, joins the portal blood, and passes
into the liver. In Fishes, the caudal veins, and sometimes those from the
reproductive organs and the air-bladder, are connected with the portal
system. In the Mollusca, the liver is supplied solely with arterial
blood ; the same is the case also in the Annulosa and Crustacea, indeed,
in all Non-vertebrated animals which have blood-vessels.

(iall-Blmhler. — In Mammalia, a gall-bladder is sometimes present, and
sometimes absent. Amongst the herbivorous kinds, it is present in nearly
all Ruminants, as in oxen, sheep, goats, and antelopes, but not in the
camels and stags. It is also absent in Holipcds and in most Pachyder-
mata, as in the horse, tapir, peccary, and elephant, but not in the pig.
In the elephant, the hei)atic duct is dilated and thickened, and has a
spiral fold within. The gall-bladder is wanting, in the mice and ham-
sters, amongst Rodentia ; also in the sloths, amongst the I'ldentata. and
VOL. II. L

U6

SPECIAL PHYSIOLOGY,

in the true Cetacea. In the carnivorous and insectivorous kinds, tiie
gall-bladder is present. In the cat and a few other animals, it is some-
times double. When the gall-bladder is present, a cystic, hepatic, and
common bile-duct exist.

In Birds, the gall-bladder is generally present, but is wanting in cer-
tain species of a particular genus, without obvious relation to its habits
or food ; it is absent in the ostrich, pigeons, toucans, and manj’ parrots.
Proceeding from the liver, in Birds, are two ducts, one hepatic, to the
duodenum, the other to the gall-bladder, from which a cystic duct runs
on to the duodenum ; there is, therefore, no common bile-duct. When
the gall-bladder is wanting, the two hepatic ducts open separately into
the intestine.

In Eeptiles, a gall-bladder always exists, but it varies in form. It is
placed at a distance from the liver and has a long cystic duct, in the
Ophidians ; but it is imbedded in the substance of that gland in the
Chelonians. There either is a common bile-duct, or the cystic and
hepatic ducts open separately into the duodenum.

The gall-bladder invariably exists in Amphibia.

In Fishes, this receptacle is usually present, though it is absent in
many genera, being then replaced by a dilatation upon one of the
hepatic ducts, which are here usually numerous.

in the Mollusca and Molluscoida, in which the liver is massive, no
gall-bladder is found ; nor coidd such a receptacle exist in connection
with the hepatic tubuli of the Annulosa and Annuloida.

Pancreas. — This gland, or some representative of it, is present only
in the Vertebrata, and in the higher Mollusca. It is not so widely dis-
tributed amongst animals as the liver ; and, moreover, it much sooner
assumes a rudimentary form, in the descending series, viz. in the Fishes.

In Mammalia, Birds, and Eeptiles, the pancreas occupies the concavity
of the constantly present curvature of the duodenum. In Mammalia,
when the duodenal mesentery is short or absent, as in the Quadrumana,
Carnivora, Euminants, and Solipeds, the pancreas is compact and elon-
gated, with a portion extending towards the spleen, so that it may seem
bilobed, as in Carnivora and Euminantia, or even trilobed, ns in the horse,
the splenic portion being double ; when, however, the duodenum has a
wide mesenter}', as in Eodentia, the pancreas forms an arborescent mass
between the two layers of the mesentery, as seen in the rabbit and rat.

The typical number of pancreatic ducts, in the Mammalia, appears to
be two, as indeed is the case in the early condition in Man, the upper
and larger duct alone persisting. In the horse and dog, there are also
two duets, the lower one being the larger ; in the dog, this latter opens
separately into the duoden\im, but the upper one enters it close to the
bile-duct. lu the lion, two ducts join the bile-duct, and enter the
duodenum by a common orifice. In the rabbit, the upper duct is very
minute, and the chief duct opens from 9 to 12 inches below the pylorus.
In all cases, how'ever, the pancreatic fiuid is discharged into the duo-
denum. In certain Carnivora, as in the seal, and sometimes in the cat,
the chief duct dilates into a reservoir, previously to entering the in-
testine.

In Birds, the pancreas is proportionally larger than in other Verte-
brata, in part, perhaps, owing to the deficiencies in the salivary glands.
It usually consists of from two to six elongated portions, attached, as

THE TYLOIUC ArPENDAGES.

147

usual, to tlio much bent duodenum. Each portion of tlie gland lias a
duct, generally opening separately into the intestine. There are six ducts
in the vulture, fowl, heron, and grebe, three in the crow, pigeon,
gnnise, and duck, but only one in the eagle, quail, ostrich, and stork.
In the stork alone, the single pancreatic duct opens, by a common orifice,
with a single hepatic duct. Usually, one at least of the pancreatic ducts,
in Birds, opens above the bile-duct, but this is not constant; when
several pancreatic ducts exist, they usually open alternately with other
hepatic or cystic ducts ; the cystic duct generally oiiens lowest. The
bile and pancreatic juice must be speedily, and almost simultaneously,
mixed with the food. In the ostrich, however, these secretions are
mixed with the food at some distance apart, the bile escaping through
the single hepatic duet, close to the pylorus, and the pancreatic juice
also by a single duct, 3 feet lower down.

In Reptiles, the pancreas is usually large. It is larger in the herbi-
vorous than in the carnivorous Saurians, being largest in the iguanas. In
the Chelonians, this gland is even ramified, as it is in the Rodents. In
the Ophidians, it is either long and bifid, pyramidal, or round. The
duct is nearly always single, and generally enters the duodenum sepa-
rately, but sometimes with the bile-duct. In the Serpents, the pancreas
is joined to the spleen, and has even been confounded with it.

In the Amphibia, the pancreas is found in the mesentery, between the
stomach and duodenum ; it is smallest in the purely aquatic species, such
as the tritons. In the frog, the bile-duct perforates the pancreas, and, it
is believed, receives small pancreatic ducts in its course. In the lowest
Amphibia, as in the siren, the pancreas is much subdivided, so as to
approximate to the form of the pyloric appendages in the Fishes ; its
ducts are no longer united into one, or into a few principal trunks, but
form numerous parallel canals, opening separately into the duodenum.

In many Fishes, there are found, opening into the duodenum, near the
pylorus, certain simple tubular or ramified follicular prolongations of the
coats of the intestine, lined by a glandular membrane, nametl t\\e pyloric
appnu/fi(/(.‘f. The food does not enter them, and, from their position and
glandular character, they have usually been regarded as the homologues
of the {Kincreas, but they are somewhat anomalous organs. In the
stuigeon, these appendages are so numerous as not to have been counted ;
the cod and whiting have about 120, the salmon 60, averaging 6T
inches in length, the sprat 9, the perch 3, the turbot 2, and tho ammodytes
and polypterus only 1. They are entirely absent in many Orders.
When few in number, they open separately into the intestine; but when
numerous, they combine into clusters, each opening by a single orifice.
Thus, oO caeca, in the pilchard, open by 30, and in the tunny by
only 0 orifict'S ; in the swordfish, there are only two openings, and, in
the sturgeon, the multitudinous c«eca open by a single short duct. They
arc largest and most numerous in fishes of active digestion and rapid
growth, and, on the whole, most developed in tlio more voracious tribes.
They are more commonly few and large in the Osseous fishes, whilst in
the Cartilaginous group they are usually smaller and numerous. When
absent, the mucous membrane of tho intestine below tho pylorus, is,
sometimes, as in the eel, thick, vascular, and glandular, and yields, on
pressure, a copious secretion.

The pyloric appendages are certainly glandular organs and not in-

1, 2

148

SPECIAL PIITSIOLOGT.

tcstinal diverticula, intended for purposes of absorption ; but it has been
suggested that they are special glands, and that the true representative
of the pancreas in hishes, is a small gland sometimes found attached to
the liver. Such an organ exists in the carp, pike, silurus, sturgeon, and
ray, in which hsh it is large and has a duct opening near the bile-duets,
and in many other species. In some instances, it would seem to bo a
detached portion of the liver, but in other cases, its pancreatic structure
is undeniable. Certain fish, as, for example, the trout, possess this
organ as well as the pyloric appendages ; in others, it is very small ; in
some, itis 7iot found, but may then be represented by glandrdar structures
in the walls of the intestine. Bernard, who doubts the pancreatic cha-
racter of the pyloric appendages, asserting that their secretion is acid
and viscid, like the intestinal juice, and not alkaline and diffluent, like the
pancreatic juice, states that a watery emulsion of the 'profer pancreas of
the ray, converts starch into sugar, and decomposes fatty matters into
their proper fatty acids and glycerin, like the secretion or substance of
the pancreas of the higher Yertebrata.

In certain Cephalopods, a laminated and follicidated sac, connected
with the two hepatic ducts, in other Cephalopods, a spiral appendage,
and, in many Branchio-gasteropods, as in aplysia and doris, a long
CEeoal glandular tube, which communicates with the intestinal canal
below the stomach, may represent a molluscan pancreas.

In the Amudosa, the Insects and some others, have tubuli, connected
with the upper part of the intestines, which may bo pancreatic. Similar
rudimentary parts exist in the Eotifera, amongst the Annuloida. In
cases in which such tubuli are not present, gland cells are sometimes
found in patches upon the lining membrane of the intestine. Sometimes
even these are not distinguishable.

Ivtestmal Glands. — In all the Yertebrata, besides structures resem-
bling the closed sacs of the solitary and agminated glands, the intestinal
tubiili or crypts of Lieberkiihn exist. In Mammalia and Birds, and
probably in Eejjtiles, Amphibia, and the higher Eishes, racemose mucous
glands are found in the duodenum.

The tubular or saccular appendages, the short cseca, or the minute
patches of glandidar epithelial cells, distinguished by their colour and
contents, which are found in the Molluscous, Anmdose, and lower allied
forms, are probably not representatives of the intestinal tubuli in the
higher animals, but rather of the liver and pancreas. Indeed, the in-
testinal canal is itself so minute in many of these lower animals, that
its lining membrane is almost of necessity simple, smooth, and covered
throughout with a delicate epithelium only.

The Chemical Processes of Digestion in Animals.

In Studying the action of the digestive fluids, physiologists have em-
ployed not only tho human secretions, but also, and sometimes exclu-
siv(dy, those collected from fistulaj in animals, and likewise artificial
fluids made by macerating the glands in water. The properties of these
several secretions having been established experimentally, in regard to
certain vertebrate animals, it is reasonable to conclude that, whei-cver
these partieular glands exist, the respective secretions possess similar, if
not identical, properties.

DIGESTION IN ANIMALS.

HO

The stilira is most abundant in herbivorous and granivorous animals,
in which the quantity of food to be moistened is greater, and the special
action of this tluid on starchy matter is most required ; in carnivorous
and insectivorous creatures, this action is not necessary, and the secretion
is less plentiful, being used rather for purposes of lubrication ; or, as in
Fishes, it may even be wanting. Nevertheless, the saliva of the dog,
taken fnim the mouth, converts starch into sugar, though somewhat
slowly! It is said, however, that the secretions of the parotid and sub-
nnaxillary glands in the dog, and oven of the parotid only, in the horse,
are by themselves, and unmixed with the mucus of the mouth, incapable
of effecting this transformation.

In those. Mollusca, Annulo.sa, and Annuloida, in which, as in Cepha-
lopoda, Insecta, Myriapoda, and Eotifera, glands, called salivary, exist,
the exact properties of the secretion, and its chemical action on the food,
have not yet been determined; but it is usual to regard those glands,
whether tubular or follicular, which open into the upper part of the ali-
mentary canal, as salivary glands. On similar grounds, gland structures
opening into the stomach are considered as gastric glands ; those con-
nected with the upper part of the intestine, as hepatic, or liepatic and
pancreatic; and, lastly, those emptying themselves into the lower part of
the intestine, as excretory, and probably renal.

As albuminoid substances are essential to the formation of all animal
tissues, the gastric juice, which acts upon them, would appear to bo
likewise an essential solvent in the digestive function of evei-y animal.
Hence, it is probably present in all animals, certainly in the lowest
whieli posses a stomach, and even in the Coelenterata. AVhen no distinct
gastric tubuli exist, the peptic agent is secreted by the colls of the
lining membrane of the digestive cavity.

The stomachs of Fishes, after death, are often rapidly digested by their
own gastric juice ; whereas this occurrence is much less frequent in
Man and Mammalia. This has been referred to the small difference of
temperature which takes place after death, in a fish, as compared with
a warm-blooded animal. The gastric juice of fishes habitually acts at
a low temperature ; whilst that of the warm-blooded animal operates
at a much higher temperature. It is said that the gastric juice of fishes
loses its peptic properties at the ordinary temperature of a warm-
blooded animal, and inversely, that the gastric juice of the warm-blooded
animal acts slowly, or not at all, at tho temperature of the fish ; and,
moreover, that the solvent powers of the gastric juice of a Mammal aro
not lost, until it has been heated to 120°; whilst in the case of the fish,
they aro lost at 80° (Brinton). If this be confirmed, it shows a remark-
able modiflcjition of tho properties of the same secretion, in different
animals having particular conditions of existence. It would bo interest-
ing to note whether post-mortem digestion of the gastric cavity of tho
non-vertobrated animals ever takes place.

From its peculiar colour, tho hile can be easily recognised. It may thus
be detected in those Annnlo.se and Annuloid animals, even in the minute
Botifora, in which tho liver is not massive, us it is in the Vortebrata,
Mollu-sca, and higher Molluscoida, being reiiresented only by hepatic
tubuli ; coloured secretions aro also detected in tho gland cells of still
•lower animals. Tho office of the bilo must bo similar in all animals in
which it is found.

150

SPECIAL PHYSIOLOGY.

The peculiar property of the 'pancreatic juice, that of emulsifying and
decomposing fat, has been shown by Bernard, to exist not onlj’ in Mam-
malia, but also in Birds, Beptiles, Amphibia, and Fishes, as, for example,
in the goose, turtle, frog, salamander, and ray. Moreover, he asserts
that, when the pure saliva, in any animal, is incapable of converting
starch into sugar, the pancreatic fluid possesses this property.

The action of the intestinal juice upon food, has been shown to be in the
higher animals, as in Man, supplementary to that of the other secretions.
In the lower animal forms, in which the intestinal tubuli come to repre-
sent important glands, an analogous blending of function may prevail.

The organic food of all animals, whether derived from other animals
or from plants, consists of similar proximate chemical substances ; and
the solution of these is probably accomplished, in all cases, by pro-
cesses of a similar nature. But our knowledge of the specific chemical
differences, and modes of action, of the digestive fluids in different ani-
mals, is yet imperfect. In the Mammalia, and perhaps in all Vertebrata,
the composition and action of the fluids resemble those obseiwedin man.
The gastric juice of the herbivorous sheep and calf dissolves animal food,
as readily as that of the omnivorous pig and carnivorous dog. But many
modifications, yet undiscriminated by the chemist, doubtless exist, as
illustrated by the ascertained varieties in the acids of the gastric juice
and the bile, in certain Mammalia and Birds (pp. 65, 77). Still more
important differences in composition and power may exist, especially in
the lower tribes, in some or all of the digestive secretions, adapting
them to the solution of substances, ordinarily indigestible. Thus cel-
lulose, lignin, and even resinoid bodies from the vegetable kingdom, and
yellow elastic tissue, cartilage, and the horny, chitinous, and coriaceous
integuments from the animal kingdom, are eaten and probably partially
digested by certain insects and other creatures, though usually those
substances resist digestion.

In the complex alimentary canal and glandular appendages of the
Vertebrata, Mollusca, and Anuulosa, in the more simple digestive system
of a polyzoon, or of a rotiferous animalcule, and even in the digestive
cavity of the hydra, with its single external opening, its communication
with the caidty of the body, and its want of distinct glandular appen-
dages, the digestive secretions are always produced by glandular epi-
thelial cells, whence they are discharged into the alimentary canal, at
suitable points, to act upon the food. In the absence of massive or
tubular glands, or of clusters of special cells, it is even possible that
adjacent cells, nearly or quite similar under the microscope, may per-
form the office of different glands. Digestion, in the hydra, may bo as
complex a process, regard being had to the chemical composition of its
food, as in the highest Vertebrata. So long, indeed, as we recognise in
any animal a distinct digestive cavity, wo may reasonably infer the
occurrence of a digestive process, rendering diflerent nutrient substances
soluble and absorbable. The starchy, albuminoid, fatty, and the less
digestible substances iised as food, must require their peculiar trans-
muting, liquefying, or enndsifying solvents, produced in infinitesimal
quantity, but acting with characteristic power. It is observable, how-
ever, that of these fluids, the peptic and emulsifying agents are the
most essential, specific, and universal : for in the cold-blooded aquatic
animals, whether vertebrate or non-vertebrate, such as the voracious

ABSOIU’TIOX.

151

Fishes, and the carnivorous Mollusca and Coelenterata, there is little or
no necessity for a salivary Iluid capable of transmuting starch ; whilst
even in the lowest animals, fatty and albuminoid substances are essential
eoustitueuts alike of the bodies and of the food. The low temperature
of these animals, and the higher temperature of the starch-feeders
generally, are interesting facts, in connection with the heat-producing
power of amylaceous diet.

In the unicelhdar Protozoa, whether, as in the Infusoria, there exist
a short tube leading into their interior, or, as in the Sponges and Khizo-
lX)ds, no digestive cavity at all, solid food must also be dissolved by
some action of the animal, before it is absorbed; though these uni-
vei-sally aquatic creatures may be partly nourished by materials already
dissolved in the surrounding medium.

In the case of the parasitic Glregarinida, and even of certain of the an-
nuloid Entozoa found in the alimentary canal of other animals, the
nutrient substances absorbed are probably those whicli have already been
digested, and so prepared for absorption by the gastric and other secre-
tions of those animals, a sort of vicarious digestion being here employed.
In those Entozoa, however, which infest other organs or tissues, such
as the air-tubes, muscles, brain, and interior of the eyeball or blood-
vessels, probably, little or no digestive change of the nutrient materials
is required ; the nutritive function consists merely of imbibition and
a.ssimilation, observed in the ultimate nutritive processes in the higher
animals, and digestion is merged in nutritive absoqjtion.

ABSORPTION.

By the process of digestion, the food is reduced to a com-
pound alimentary basis, composed of aqueous, saline, extractive,
mucilaginous, saccharine, amylaceous, oleaginous, and albu-
minous matters, sometimes mi.xed with alcoholic, ethereal, acid,
pungent, odoriferous, and colouring substances. The mate-
rials of this comple.x pabulum, whilst retained within the
digestive cavity, remain, strictly speaking, external to the
living frame ; but a process immediately ensues, by whicli they
are, sooner or later, taken up into, and enter, the living tissues ;
this is termed Absorption. The chief object of this process
of the absorption of food., is the introduction of new material,
for the repair of the continuous waste of the living body.

Absorption, however, considered as a physiological func-
tion, consists of more than the mere taking up of nutrient
materials from the interior of an alimentary canal, or of a
simple digestive cavity, or at the surface of a unicellular
animal organism. It includes that general process by which
all external soluble substances, whether solid, fluid, or gaseous.

152

SPECIAL PHYSIOLOGy.

r‘

Eii,'. 100. General view of the principal absorl>ent or J „,„i

Klancls. The superlicial lyn.plmtics are al.own on
on tlio left limbs ; the deep lyinpbatics on tbo rig

THE ABSORBENT SYSTEM.

15.3

beneficial or poisonous, nutrient, stimulant, or respiratory, are
introduced into the tissues of the body, through any natural
or artificial surface tvhatever. jMoreover, it comprehends, in
part at least, another process, by means of Avhich j^ortions of
the livinar tissues are themselves removed, or absorbed, Avithin
the body. The former of these tAvo processes is sometimes
named _7t'/iera^ absorption, and the latter, intrinsic or interstitial
absorption. Intrinsic absorption is essentially a nutritive
]>rocess. The term extrinsic may be applied both to general
absorption and to the absorption of food.

The Absorbent Vessels and Glands.

In ilan, and the Vertebx’ata generally, two sets of vessels are
engaged in the proce.sses of absorption, viz. first, certain blood-
vessels, especially the venous capillaries, and the smaller veins ;
and, .secondly, the absorbent vessels proper.

The absorbents of the body generally, Avliich ahvays convey
the transparent hpnph, and are named the hjmpliatics, com-
mence, by netAvmrks, near the various membranous surfaces,
and in the interior of certain tissues and organs. Their num-
ber, in any part, seems to be proportionate to the quantity of
areolar tissue Avhich it contains, rather than to the number of
its bloodvessels, or the activity of its functions; thus, lym-
phatics haA'e not been found in the brain and spinal cord, and
only a feAV in the muscles ; but in the subcutaneous areolar
tissue, and in the intercellular spaces, they are very abundant.
They are numerous in the serous and synovial membranes, but
.still more so on the mucous membranes and skin. The trunks
from the commencing lymphatic netAvorks (fig. 100), either
proceed in company Avith the bloodvessels, thus forming the
deep Ijpnpliatics, or else run on the surface of organs, or in the
.subcutaneous cellular tissue of the body and limbs, so forming
the superficial Ijjmphatics. From all parts of the body, they

phatic jtlands aro seen in the nock ami axilla;, at tho elbow, in the
(troins, pelvis, and abdomen; a part of tho small intestine, i, shows its
chief lymphatic or lacteal trunks, passing on to the mo.sontery, through
the mesenteric glands, to the upper and back part of tho abdomen.
a, the chief trunk of tho absorbent system, named tho tlioracic duct,
commencing below, in a dilatation, named the receptnculum cliyli, and
curving down in tho neck at c, to end in tlio groat veins at tho root of the
neck, where the jugular and subclavian veins join to form tbc left inno-
minate vein, V. On tbo right side of tho nock, smaller lymphatic trunks
aro seen entering the groat veins.

154

SPECIAL PHYSIOLOGY.

run towards the root of the neck, where they end in the venous
system. More numerous than the bloodvessels, they pur.sue
an irregular course, often unite and again divide, and present,
in certain situations, as especially seen in young subjects, small
retia mirabilia or lymphatic networks, enclosed in a thin areolar
investment. They, moreover, pass through the bodies known
as lymphatic ylands, which may be regarded as more highly
and specially developed retia (p. GG). Ultimately, the lym-
phatics of the lower limbs, of the lower half of the trunk, of
the left side of the head and neck, and of the left, upper limb,
join the great trunk of the lymphatic system, the thoracic duct, a.
Those from the right side of the head and neck, and right

Fig. 101.

Fig. 101. Superficial lymphatics upon the heart, situated beneath the
serous coat or visceral part of the pericardium. The figure also serves
to show the shape, position, and subdivisions of the heart. 1, the left,

2, the right auricle ; 3, the left, 4, the right ventricle ; 5, the descend-
ing part of the arch of the aorta.

njjper limb, unite to form a small separate timnk, named the
right lymphatic duct. This enters the venous system at the
point of junction of the right jugular and subclavian veins,
its oi’ifice being guarded b}’ a double valve. A few separate
and smaller lymphatic trunks are also said to enter the veins
oi' the neck at dift'erent points. All the organs of the thoracic
and abdominal cavities, hai'e superficial as well as deep lym-
phatics belonging to them, figs. 100, 101. The lymphatics

THE AUSORBExNT VESSELS.

155

were first described by Fallopius (15G1), but afterwards much
more fully, by lludbeck and Bartholin ; the thoracic duct was
i detected by Eustachius (obiit. 1570).

' The thoracic duct (fig. 100 a), begins below by a dilatation,
i named the receptaculum cli>/li, usually placed upon the second
lumbar vertebra. From this i^oint, the duct ascends, somewhat
tortuously, in front of the vertebral column, into, and through,
the thorax. Placed, at first, a little to the right of the aorta, it
passes, opposite the third dorsal vertebra, behind the arch of
that vessel, crosses over the oesophagus, and ascends on its
left side to the root of the neck, c, where it curves downwards
and outwards, behind the great bloodvessels, and finally opens
into the angle of junction of the left internal jugular and
subclavian veins, the entrance being guarded by a strong
double valve. The thoracic duct measures from eighteen to
twenty inches in length, and from two to three lines in width ;
it is somewhat varicose, or constricted at intervals, owing to
the presence within it of numerorrs double semi-lunar valves,
which have their free margins directed upwards, so that they
are closed by downward pressure, and support the weight of
the column of fluid contained in the di;ct. At the root of the
neck, the contents of the absorbent system are poured into the
venous system, and are mixed with the venous blood flowing
towards the heart, regurgitation ifom the veins to the ab-
sorbent trunks being prevented by the valves placed at the
opening of the latter into the veins.

d'he coats of the l}miphatics, as elsewhere explained, are
remarkably thin, and therefore highly permeable to fluids.
The trunks themselves are very difficult to find, and even the
thoracic duct eludes an ordinary dissection.

Lymphatic r/lands are found (fig. 100) in the arm-pits and
groins, and a tew at the bend of tlie elbow, and in the ham,
where they are named respectively axillary, inguinal, anti-
brachial, and popliteal glands ; chains of glands, on each side
of the neck, are named the cervical or concatenated glands ; in
the thoraxj numerous glands, placed around the great air-
tubes or bronchi, and usually containing a black deposit, are
named bronchial glands ; lastly, in the pelvis and abdomen,
are the iliac, lumbar, and mesenteric glands.

Like general absorption, the absorption of food from the
alimentary canal, is perfoi'rned by the agency not only of the
bloodvessels but also of the (d>sorbents ]>roper ; those of the
small intestines, which occasionally — that is, during digestion

1.56

SPECIAL PIIYSI0L0G5L

convey the milky white lluicl, chjjle, are named the lacteals, or
chi/liferous vessels.

The arteries of the intestine, chiefly derived from the
mesenteric arteries, subdivide and inosculate in the mesentery,
forming numerous vascular arches before they reach the
attaclied border of the intestine; entering and ramifying in
tlie submucous coat, their branches penetrate, and further
subdivide in, the mucous membrane, in which they end in
close networks of capillaries, near the mucous surface, around
tlie intestinal tubuli and glands, and within the countless villi.
From the capillary network.s, the minutest venules proceed,
and soon join to form larger veins, running to the attached
border of the intestine ; beyond this, the veins unite in the
mesentery into still larger trunks ; these, with the veins of tlie
stomach, pancrea.s, and sj^leen, ultimately ibrm the portal
vein, which enters, and subdivides in, the liver. The veins
from the lower part of the large intestine, however, do not
enter this portal system, but join the veins from the lower
half of the body ; so, too, the veins proceeding from the
mouth, pharynx, and gullet, enter the general venous system.

The lacteals, which may be said to be limited to the small
intestine, below the entrance of the bile-duct and pancreatic
duct, resemble the lymphatics of the stomach, large intes-
tine, and other parts of the body, and, like them, convey,
when not engaged in absorbing food, only a transparent
lymph. The lacteals were discovered by xVselli (1(122);
their connection with the thoracic duct was shown by
Pecquet (1G51). In the mucous membrane of the stomach
and large intestine, the absorbents probably arise by networks,
like those of other membranes. In the small intestine, how-
ever, Avhich is the proper seat of lacteal absorption, besides a
network near the general mucous surface, absorbent vessels,
which form, as it were, the radicles or absorbent extremities of
the lacteal system, commence within the villi which specially
characterise this part of the intestinal canal. These villi,
during digestion, project into the pulpy digested food, as the
rootlets of a plant, with their absorbing spongioles, depend in
water or penetrate the soil.

The lacteals commence within the villi by closed extre-
mities, and not by open mouths (fig. 102, 1). By some
anatomists they are siiid to arise by a plexiform network,
which, at the base of the villus, pa.sses into larger vessels.
According to others, a single lacteal vessel occupies the centre

THE LACTEALS.

157

of each villuf?, commencing near tlie apex Vjy a simple closed
extremity, by a dilated ampulla, or by a loop, which may be
part of a network, and ending in the general network at its
base. The diameter of the lacteals in the villi, is from to

of an inch. The network at their base, consists of a liner
and a coarser layer, in the latter of which the vessels possess

Fig. 102. Fig. 103.

Fip. 102. Two intestinal villi Iii.^lily ina.inified, .showing the two suppo.sed
modes of commencement of the lacteals, i, in their interior j one mode,
l).v a dilated ampulla, Urn other by a network. The columnar epithelial’
cells. 2. covering the villi, arc a'.so shown ; and likewise a portion of the
cainllary network, :i, lying oiitsiiie the lacteal vessel. The larger lacteals
at the base of the villi are indicated.

Fig. 103. The artery, capillary network, and vein of an intestinal villus
artificially injected. The liglit-colounal vessel represents the minute
artery which conveys the blood into the villus; the dark vessel is the
vein along which the blood returns ; the intermediate capillary network
is marked 2.

Viilvfs. (Teichniann.) Tlie villi tire al.so very vascular, each
containing a minute artoritil tind venous twig, with a close
capillary network outside tlie lacteal vessels (tig. 102, 3, and
fig. 103). The substance of the villus consists of a delicate
e.Klension of the mucous membrane, composed of a mixed soft
areolar and granular tissue, containing fatty particles; further'

158

SPECIAL PHYSIOLOGY.

each villus contains, around the central lacteal, a few unstriped
muscular fibres, by the contraction of which the villus may be
sliortened, and its substance thrown into transverse folds ;
lastly, the epithelial covering of the villus, which measures
only about -prVtr thickness, is composed, like

that of the intestine generally, of a single layer of columnar
nucleated cells, pointed at their attached end, but wider, flat-
tened, and more or less polygonal at their free extremity.
This part of the cell has been described as being ciliated, but
the appearance is generally attributed to the existence of fine
lines passing from the free end to the interior of each cell, and
regarded by some as pores. In animals killed while lacteal
absorption is going on, these epithelial cells are/requently found
to be distended with fatty matter, the villi having a swollen
and tuberculated aspect. At this time also, the central lacteals
of each villus, and also the subjacent vessels, are found dis-
tended with whitish or bluish chyle. Upon the surface of
the small intestine (fig. 104, 1), running beneath the peritoneal
coat towards its attached border, are seen larger chyliferous
vessels, proceeding between the layers of the mesentery, 2, 2 ;
thence others, passing through the mesenteric glands, 3, con-
verge to the back of the abdomen, where they end in the
receptaculum chyli, or dilated part of the thoracic duct
(fig. 100, a). If this duct be tied immediately after death, in
an animal killed during digestion, it, as well as the chyliferous
vessels generally, becomes much distended, and either of these
vessels may burst, and the chyle may be extravasated at many
points.

Beneath the mucous membrane in various parts of the ali-
mentary «inal, as in certain recesses at the root of the tongue
(p. 54), and in the tonsils (p. 27), or scattered singly over the
internal surface of the stomach, small intestine, and large intes-
tine, and, lastly, collected in patches in the small intestine,
there exist peculiar saccular bodies, called glands, which,
however, do not appear to belong to the secreting gland
system, but perhaps rather to the absorbent system. They
are neither racemose glands, like the glands of Brunner, nor
open follicles, nor tubuli, like the gastric glands and the
crypts of Lieberkiihn, but dosed sacs, not communicating
with the interior of the intestine, unless under some excep-
tional conditions. In the stomach and intestine, these bodies
exist in two forms. First, as the so-called solitary glands of the
stomach (p. Gl), small intestine (p. 82), and large intestine

THE CLOSED INTESTINAL GLANDS.

159

(p. 82), scattered over the mucous surface, as small soft
whitish bodies, somewhat prominent, and about one line in
diameter, or the size of a millet-seed when they are fully dis-
tended. Each sac consists of a thickish soft capsule, composed
of an indistinctly formed areolar tissue, mixed with nuclei,
and encloses a semi-opacjue, adherent, and semi-fluid granular
matter, containing mixed fatty and albuminous molecules.

Fig. 104.

Fig. 101. Portion of the small intestine, 1, 1, with its mesentery; 2,2,
showing the superficial lacteal vessels in the intestine and mesentery.

The mesenteric glands are also seen at 3, and elsewhere.

nuclei, and cells, amongst which loops of capillary vessels are
Siiid to penetrate from all sides. The mucous membrane passtis
completely over those sties, find usually even a few villi tire
placed upon them. In the large intestine, they are situated at
the bottom of a wide recess, having a narrow orifice, which has
been erroneously regarded as an opening into the .s;ic. Secondly,
clusters of these sacs, the agininated r/lands, or Peyer’s glands
(Peyer, 1077), are found in the small intestine only. The.“o
Peyer's patches, twenty to thirty in number, :ire cither rounded

160

SPECIAL PHl'SIOLOGr.

or oval, being from half an inch to three or more inches in
length, and about hall’ an inch or more in width ; they are
placed at intervals, longitudinally along the free border of the
intestine (Fig. 91). Commencing, of small size, in the lower
part of the duodenum, they gradually become nujre frequent
and larger in the jejunum and upper part of the ileum, but
are largest and most numerous in the lower part of the ileum.
Their component sacs (Figs. 98, 99) exactl}'^ resemble in struc-
ture the single sacs of the so-called solitary glands. When
distended, as occurs during the absorption of food, the patches
of Peyer’s glands present a whitish speckled appearance, and,
if moderately magnified, each sac is seen to be surrounded by
a little zone of darki.sh points, which are the mouths of the
crypts of Lieberkiihn, thrust outwards by the filling of the sac.
The mucous membrane over the sacs, is entire. A^illi are
seen in the intervals between them and sometimes, as is the
case with the solitary glands, even iipon them. 0[ipo.site
the.se patches, the submucous coat of the intestine is more vas-
cular than elsewhere, and especially aboimds in lymphatics,
which, however, have not been traced into the sacs, but here
form plexuses of large and easily injected vessels.

The sacs of both the solitary and the agmiuated glands are
sometimes found open, as if by rupture through distension ;
but from their normally closed condition, the tatty and albu-
minoid nature of their contents, the abundance of lymphatics
in their neighbourhood, and from the special distension of
these, as well as of the sacs themselves, during the process of
intestinal ab.sorption, it is with much reason inferred, that
both the solitary and agminated glands are concerned, in some
way, in this last-named function ; the mode in which they
act, and the precise nature of their office, are, however, not
yet understood.

Endosimsis, Exosmosis, Os7nosis, Liquid Diffusion, and

Dialysis.

The ahsorpiion of liquids, or of substances in a state of solution, by
the living animal body, is either a simple filtrating process, connected
with the fiwa jMTOsiti/ of the tissues; or it partakes of the character of
diedysu, or the penetration of liquid or dissolved substances through a
moist membrane permeable to such bodies, without being direetly
porous, like a filter; or, lastly, it may be connected with special
•selective or rcpeJlcnt actions in the living tissues. Even in the last case,
the process may be physical, i.e., either filtrating or dialytie. The pene-
tration of dissolved substances through the tissues, occurs, not only in

ENDOSMOSIS AND EXOSMOSIS.

161

general absorption and the absorption of food, but also in intrinsic ab-
sorption, in all acts of nutrition, in the reabsorption of the disintegrated
materials of the body itself, likewise in the various acts of secretion and
excretion, in certain processes of the function of respiration, and of those
of taste and smell.

L'nclosmosis. — The action of the living tissues, in these several func-
tions, has, since the researches of Dutrochet (1827), been in part referred
to the physical processes of so-called endosmosis and exosmosis, or the
passage of fluids in opposite directions through dead animal membranes
(fvSov, endon, within ; wcrix6s, osmos, impulse). It was first pointed out
by Parrot, of St. Petersbiu’g(1803), that, if two liquids of imequal density
are separated by a pemieable organic membrane, a mutual but unequal
interchange takes place between them ; but Dutrochet more fully in-
vestigated the subject. His endosniometer consists of a bell-shaped glass,
covered at its mouth with a thin animal membrane, and fitted at its
upper end with a graduated tube ; a coloured solution of sugar, gum, or
some saline substance, being introduced into the glass, the covered
mouth is then immersed in water, when it is found that the solution
rises in the graduated tube, to a considerable height above the level
of the water around it. This phenomenon Dutrochet named endosmose.
During its occurrence, however, some of the dissolved substance con-
tained in the tube, passes into the water outside, and this process he
named exosmose. The more rapid flow, however, usually takes place
from the rarer to the denser fluid ; and hence, if the endosmometer be
filled with water, and be dipped in the solution, the more active, or so-
called endosmotic current, really passes outwards through the mem-
brane. Dutrochet pointed out that the force of endosmosis bears a
certain ratio to the density of the inner fluid, and that the quantity of
fluid which passes, depends also on the extent of the membrane. To avoid
the effects of gravity, he from time to time adjusted the endosmometer,
so that the fluids inside and outside, were kept on a level. He showed
that capillarity, or capillary ascension, does not account for the pheno-
mena, which, he admitted, cannot be satisfactorily explained. He supposed
that endosmosis and exosmosis are peculiar to organic membranes, and
that they explain the rise of the sap in plants, many processes of the
animal body, and probably also the motions of various vegetable and
animal fibres and cells.

More recently, these physical phenomena have been studied by
Bedard, Matteucci, Graham, and others. The direction of the current
through an animal membrane, is not always found to be from the lighter
to the denser fluid ; for water passes more rapidly into alcohol, than
alcohol into water. The great endosmotic temlency of water has been
attributed to its high specific heat, which is higher than that of any
other fluid. (Bedard.) But the properties and qualities of the various
fluid, or saline and other soluble, substances, are also found to influence
the result. The phenomena are favoured by moderately high tempera-
tures, by pressure, by the saturation of the membrane with acids or
alkalis, by special relations between the membrane and one of the
fluids, and by the constant removal of the ondosmosing fluid by motion
or by evaporation.

Professor Graham has examined st^parately, first, the tendency of
different liquids or solutions to mix with each other directly, and,

VOL. II. -\I

162

SPECIAL PHYSIOLOGY.

secondly, tlie influence of a permeable membrane interposed between
them. The former phenomena constitute liquid diffusion, and the latter
osmosis, or dicdysis.

Liquid Diffusion. — A phial, with ojDen month, is filled, nearly to the
top, with a given solution, and is tlien placed in a larger vessel, into
which water is carefully poiu-ed, so as to stand considerably above the
level of the mouth of the phial ; or a graduated jar is filled, up to the
highest mark but one, with water, and then, by means of a pipette, the
solution to be tried is pom-ed in at the bottom of the jar, so as to
elevate the water to the top of the scale. On leaving phials or jars, so
prejiared, standing, without agitation, or change of tcmperatm-e, the
substance in solution ascends in the water, against the influence of
gravity, as if it were volatile. In other words, it diffuses ; hence
the term liquid diffusion. All soluble substances diffuse in this way,
but they are not equally diflfiisible. Thus, in phial experiments, the
relative quantities of the following substances, diffused through the
water above, from solutions of like concentration, in the same time, are
as follow, chloride of sodium 58, nitrate of soda 57, sulphate of soda 27,
cane sugar 26, gum 13, and albumen 3. In jar experiments, the relative
times of diffusion of equal quantities of different substances are these;
hydrochloric acid, the most diffiisible substance hitherto tried, 1 ;
ciiloride of sodium 2'3 ; sugar 7 ; sulphate of magnesia 7 ; albumen 49 ;
and caramel, or burnt sugar, 98. The rate of diffusion of different
substances is, therefore, remarkably different, being very high for hydro-
chloric acid and chloride of sodium, but low for gum, albumen, and
caramel. So distinct and constant is the diffusive power of different
sub.stances, that, from mixed solutions of these, chloride of potassium
ascends more rapidly than common salt, and this, faster than sulphate
of soda ; with salt and albumen, the difference is still more marked.
Weak chemical compounds may even be decomposed through the differ-
ent diffusive power of their constituents ; thus, alum, a double sulphate
of alumina and potash, is decomposed, in a phial diffusion experiment,
by some of the sulphate of potash rising away from its associated sul-
phate of alumina.

The rate of diffusion, in proportion to the quantity of the substance
diffused, is greater when the solution is weak ; but the absolute quan-
tity diffused is greater with strong solutions. Heat increases the rate
of diffusion, common salt, e. g. diffusing 2i times more rapidly at 120°
than at 60°.

From various points of contrast, including their behaviour as diffu-
sible bodies, chemical substances are arranged by Graham into crystal-
loids and colloids.

Crystalloid bodies are hard, rigid, and quicklj'- .soluble ; their solutions
are never viscous ; they are always more or less sapid ; their chemical
reactions are quick and energetic, but in a molecular souse, they are, if
left to themselves, static, or little liable to molecular changes. This class
includes every crystallisablo body, and evoi’y substance capable of
entering into the formation of a crystalline body.

Colloid substances do not crystallise, but are amorphous ; they have,
when dry, a vitreous structure, and instead of being hard and
brittle, are soft or tough; they dissolve freely but slowly, their
solutions being more or less viscous, and they gelatinise on cooling, or

DIALYSIS.

163

Ly concentration. Ilence they are named colloids, from collin or gela-
tin, and sometimes poctoids, from their gummy character ; they are
tasteless or insipid, but they may give rise to sapid crystalloids ; their
combining equivalents are high, and their molecules accordingly heavy;
as acids, or bases, they are chemically inert, but they are liable to
remarkable molecular changes, and, in this sense, exhibit great dynami-
cal activity ; they have a weak affinity for water, and are easily thrown
down from their solution in it. They readily undergo metastasis, passing
from a state of solution into the gelatinous, pectous, or solid condition,
and, tvith time, even into the crystalloid .state, either spontaneous!}-,
or by the slightest contact with extremely minute }3ortions of other
substances ; thus a solution of silicic acid is gelatinised by part
of an alkaline or earthy carbonate. Lastly, in their soft condition, they
form, like water, media for liquid diffusion, a crystalloid body diffusing
itself through a jelly, almost as readily as through water itself. Colloid
substances include gelatinised starch, dextrin, gum, caromel, gelatin,
albuminoid bodies, vegetable and animal bodies, extractives, and a num-
ber of soluble hydrated mineral substances, as, for example, silicic acid
and peroxide of iron.

Of the two great classes of substances thus distinguished, crystal-
loids are highly diffusible, whilst colloids are of low diffusibility.

Finally, liquid diffusion is to be regarded, not as a purely iffiysical
process, like the diffiision of gases, which depends on a tendency of those
elastic fluids to intermix in inverse proportions to their density; nor is
it to be explained by capillarity ; for the diffusion of different sub-
stances does not coincide with their ascension in capillary tubes ; but
this process appears rather to depend on chemical action. The high dif-
fusibility of crystalloids is explained by their powerfid attraction for
their solvent, the mobility or volatility of which is determined by their
presence ; whilst the low diffusibility of colloids is referred to their
feeble combination with their solvent, on the volatility of which they
accordingly have little effect.

Bialysis. — The phenomena of the diffusion of liquids into each other
are rendered more definite by the interposition of permeable mem-
branes between them. If a gutta-percha hoop be closed on one side with
vegetable parchment, the tray thus formed will not allow water to pass
through it by filtration. By supporting, or suspending, such a tr.ay in
a large vessel of water, and pouring a thin layer of the fluid or solution
to 1)0 experimented upon, into it, dialysis, or diffusion through the per-
nieable membrane, tiikos j)lace. Crystalloid bodies, in solution, pass
through the membrane, or dialyse, into the water, with groat raj)idity;
whilst colloid bodies are almost absolutely prevented from passing.
Thus, in equal times, the pro[)ortion of common salt which dialyses
is 7’6, of cane sugar LG, and of gum '029; or, again, the quantity
of salt which dialyses being iy'2, that of dextrin is '034, of gum -013
of caramel -009, and of alljumen -OOG; whilst gelatin, extract of meat, and
boiled stiirch, do not dialyse at all. The rate of dialysis is influenced
by the depth of the fluid in the tray, by the area of the membrane, by
the strength of the solution, and, to a certain degree, though loss than
liqtiid diffusion, by tetnperature. The process is not mechanical, btit
chemical, the resttlfs being more definite than those of liquid diffusion.
Lialysis depends on the affinity of the substance experimented upon, for

164

SPECIAL PHYSIOLOGY.

the water in the moist permeable membrane. CrystaUoicls, which
dialyse rapidly, have an affinity for, or unite with, the water of the sep-
tum, and, by successive combinations of their molecules with the water
in that membrane, they pass through to the water outside it, and thus a
movement, otherwise invisible, becomes apparent. On the other hand,
colloids have little or no affinity for the water of the septum, and,
therefore, do not make their way tlu’ough it. The membranous septum
is itself colloidal ; its molecules have, therefore, only a slight affinity
for water, and pei-mit the stronger affinity of the crystalloids, suc-
cessively to displace them, and so to pass through ; whilst colloids
generally, are too feeble to accomplish this displacement. Thin layers
of any colloidal substance, such as films of gelatinised starch, albumen,
jelly, gum, and miicus, also act as dialysers.

Dialysis has been employed for the artificial separation of crystalloids
and colloids. Saline and earthy matters, rendered soluble by acetic or
hydrochloric acids, may be dialysed from albumen, or lime from solu-
tions of gum, pure albumen or gummic acid remaining. Morphia,
strychnia, and other crystallisable alkaloids, have been separated from
organic fluids ; and even part of arsenious acid, mixed with

porter, milk, defibrinated blood, or pieces of intestine, has yielded 80 or
90 per cent, of that minute quantity, by dialysis, in 24 hours. These
dialytic actions also explain more completely, the long known phenomena
of endosmosis and exosmosis. The force concerned in liquid diflTusion
was at first named, by Graham, osmotic force; and endosmosis and
exosmosis were regarded, by him, as due to the action of this force in
opposite directions, or to a positive and negative osmosis ; the direction
of the chief visible current appears to be always towards any sub-
stance having the properties of a base, water flowing towards a salt, and
from an acid. Subsequently, however, Graham distinguished liquid
diffiision from diffusion through membranes, or dialysis.

Dialysis must take place in the living body, in which compound and
simple permeable and colloidal membranes abound, such as the base-
ment membranes, capillary walls, and cell walls, all of which are subject
to the constant action of solutions of crystalloid and colloid bodies,
either acids, alkalis, and salts, or albuminoid and extractive substances.
The process of absorption most obviously suggests diffiisive and dialytic
actions ; but so also do those of nutrition, secretion, and excretion, and
even the interchange of the gases of the blood and air, in respiration,
for these gases are dissolved at the moment of interchange. Moreover,
the sapidity of ci-ystalloids and the insipidity of colloids are associated
respectively, with a high and a low diffusibility. It has even been sug-
gested, as indeed was hinted by Dutrochet, that rapid dialytic action
may take place, not only in vegetable movements, but also in the inti-
mate changes of condition of the muscular fibres, in the states of con-
traction and relaxation, and that it may thus form a link in the trans-
formation of chemical into mechanical force, which is realised in animal
motion. Lastly, organisation and living action are indissolubly asso-
ciated with the existence of one at least of these two great classes of
substances, discriminated by their different dialytic power ; for all the,
tissues of plants, and animals, from those of the seed or germ, upwards,
we colloidal in their nature.

GENERAL ABSORPTION.

165

General Absorption.

The chief natural absorbing surface is the mucous mem-
brane of the alimentary canal. Thus, it takes up the greater
part of the food ; moreover, saline, colouring, odorous, sapid,
and other substances, may be detected, soon after having
been swallowed, not merely in the blood, but in the secretions
of distant glands ; and, lastly, specific effects, medicinal or
poisonous, may be produced upon remote parts of the s}^stem,
e.g. upon the brain and spinal cord, as Avhen prussic acid is
applied to the tongue, strychnine is taken by the stomach, or
nicotine is administered in enemas.

The mucous membrane lining the air-passages and air-
cells of the lungs, is also absorbent, that of the air-cells espe-
cially taking up gases iu a state of solution. Water, various
other fluids, and saline solutions, accidentally introduced into
the air-passages, are also partly absorbed. From certain cases
of increase in the weight of the body, beyond that of the food
and beverage taken, it has been inferred, though this is doubt-
ful, that the pulmonary mucous membrane may even absorb
the vajjour of water from the air, instead of exhaling it, as it
usually does. Many substances, of a more or less volatile or
soluble character, may be introduced into the sy.stem through
the air we breathe, either iii a vaporous state, as in the case of
carburetted, sidphuretted, phosphuretted, and arseniuretted
hydrogen, cyanogen, alcohol, ether, chloroform, mercury, phos-
phorus, and miasmatic and contagious exhalations, or in the con-
dition of fine particles, as e. g. arsenic. The general ana2sthesia
produced by chloroform, depends on its absorption by the pul-
monary capillaries. Mercury and phosphorus, employed by
the looking-glass manufacturers and lucifer-match makers, are
taken up, partly by the mouth, but also probably by the lungs ;
and numerous cases of poisoning by arsenic, in which the health
has been serioinsly deranged, have been observed amongst
manufacturers of artificial flowers and green loaper-hangings,
from the ar.senite of copper, or Scheele’s green, employed by
them. Such papers are unfit for dwelling rooms.

The conjunctiva is also ab.sorbent, as is shown by the
poisonous effects of prussic acid, dropped into the eye of a
rabbit. Other mucous membranes likewi.so ab.sorb fluids and
di.s3olved substances; the bile, for example, becomes more
or less inspissated in the gall-bladder.

166

SPECIAL PHYSIOLOGY.

Absorption by the skin also takes place, especially when a
substance is kept in prolonged contact with it, as in the case
of painters who do not cleanse their hands from white lead,
and are attacked with the dropped UTist or paralysis of the ex-
tensor muscles of the fore-arm. In the thin and moist skinned
Amphibia, absorption by the integument is very active ; lor
if kept in a condition of drought, these animals become ex-
tremely attenuated; whilst they rapidly swell out, if then
placed in a moist atmosphere, or upon damp earth, thus
proving that their skin is both absorbent and exhalant. A
dog placed in an air-tight ves.sel, with its head unenclosed,
has been killed by the vapour of the oil of bitter almonds
absorbed only through the skin. In regard to Man, absorp-
tion through the skin, if this be whole, is not very active ;
indeed, it has been, though erroneously, denied. The non-
vascular cuticle impedes this process, and, in this way, is of
great importance, e.specially in the practice of certain arts, in
which the body is subject to contact with deleterious agents.
Nevertheless, water may be absorbed by the whole skin, for
the weight of the body is increased after the use of Avarm
baths. (Madden.) Shipwrecked sailors, destitute of Aesh
water, find that, by immersion in the sea, or by Avetting the
clothes in sea-Avater, thirst is relieved ; this may be partly
attributable to a diminution of the exhalation of Avater from
the blood through the skin, oAving to the preA^ention of
evaporation, but it is doubtless partly ahso clue to direct
absorption. In the use of very hot baths, above the tempera-
ture of the blood, more Avater is lost, by perspiration and
pulmonary exhalation, than is absorbed, so that the body is
lighter after such a bath ; in a bath of 90°, the processes of
absorption and exhalation are balanced, no change taking
place in the body Aveight ; in tepid and cold baths, cutaneous
absorption exceeds exhalation, and the body gains in Aveight.
Saline substances, such as iodide of potassium, cyanide of
potas.sium, nitrate of potash, or chloride of ammonium, dis-
.solved in baths, do not, according to some, enter the system ;
but others allege that they may be found in the blood and
urine. The use of medicinal baths is based on the supposi-
tion that they are so absorbed ; and the discrepancies betAveen
the re.sults of ditferent experiments, may, in part, depend on
the employment of baths at ditferent temperatures, AAdiich, as
just stated, produce difierent results. A condition of e.xhaus-
tiou favours cutaneous absorption. The softening of the cuticle

GENERAL ABSORPTION.

167

greatly fecilitatcs the process: thus, an onion crushed and
worn in the shoe, will cause the breath to smell; garlic-
poultices applied to the arm, and lint dipped in turpentine to
the body, produce characteristic odours in the ludne; jalap
poultices may have an aperient etFect; whilst applications of bel-
ladonna to the skin have been followed by dryness of the throat,
dimness of sight, and by alarming, sometimes fatal, symptoms
of poisoning. The introduction of foreign substances through
the skin is greatly aided by the thinness of the cuticle and
by friction, as is illustrated by the effects on the system of
mercurial inunction, and also by the rubbing in and conse-
quent absorption of cod-liver oil ; but both these substances
are absorbable even without friction.

The importance of the non-vascular cuticle as a protective
covering, antagonistic to absorption, is shown indirectly by
the effects of its removal ; thus, the surface of the true skin,
exposed in blisters, absorbs with great fiicility and rapidity :
the unprotected and highly vascular surface of the cutis is no
longer able to resist the entrance of the most deleterioirs sub-
stances ; and even the cantharidin, or active principle of the
Spanish-fly, used for producing the blister, is itself, sometimes,
in this way absorbed. It has been stated that the lymphatics
of the skin, which are very numerous and large, and have
very thin walls, absorb adventitious substances, perhaps, more
readily than the bloodvessels; the reverse, however, is the
case with the lacteals.

The serous and synovial membranes also absorb, sometimes
even very rapidly. Poisons injected into the pleural and peri-
toneal cavities, in living animals, are found to be most quickly
taken up. Moreover, the serous exudations which occur in
inflammation of these membranes, into the pericardial, pleural,
and peritoneal cavities, are more or less rapidly removed by the
curative pjroce.ss of resorplion ; the fluids poured out into the
joints, in cases of rheumatic or other inflammation, and even
blood extravasated into those cavitie.s, are also, though more
slowly, absorbed. The rapid absorption of the cerebro-spinal
fluid (vol. i. p. 29.5) affords another instance of the facility of
absorption from an internal cavity ; so likewise does the
absorption of blood and other effused matters, and even that of
the broken and non-dissolved cataractous lens from the interior
of the eyeljall.

Absorption from the areolar connective tissue is proved by
the taking up, from its interspaces, of dropsical fluids, or effused

1G8

SPECIAL PHYSIOLOGY.

blood ; also by the poisonous effects of agents introduced ex-
perimentally into the areolar tissue in animals; and lastly,
by the effects of tlie hypodermic or subcutaneous injection of
solutions of morphia, or other medicinal agents, into the living
human body, for the relief of neuralgic pain, and of the suffer-
ing after severe operations, or for the piu’pose of inducing
sleep, or of relieA’ing obstinate cough, or other irritation.

Lastly, absorption from the artificial sm-faces of ulcers and
wounds, is shown by the taking up of medicinal or poisonous
substances, such as mercuiy, arsenic, morphia, ati’opine,
conium, and other substances, applied to granulating sores.

The vessels concerned in general absorption in the vascular
tissues, are the bloodvessels and lymphatics ; but in the non-
vascular tissues, as well as in non-vascular animals, absorption
must take place by direct permeation into the cells or other
tissue elements.

Absorption by the veins, or venous absorption, is proved
by cutting across the limb of air animal, excepting its chief
artery and vein, and then applying strychnine below the place
of section, Avhen the poison will still act, being conveyed in
the blood of the undivided vein. Poisoning still takes place, if
the artery and vein be also divided, and then rejoined by
pieces of quill, so that the jioison cannot be imbibed and con-
veyed by the coats of the vessels, but' can only pass along the
venous blood current. To show that the poisoning does not
take jilace through the nerves, all parts of a limb may be
divided, excepting the chief nerve, when poison, applied to it,
does not affect the animal. Absorption by the veins generally,
has also been proved by blistering the skin, applying a solution
of feiTO-cyanide of potassium, and, after a time, examining the
blood in the veins, ivhen that salt has been detected in it.
Absorption also occurs through the portal veins. The pul-
monary veins likewise absorb ; for prussiate of potash, in solu-
tion, introduced into the trachea, appears sooner in the left
cavities of the heart, to rvhich the blood returns from the
lungs, than in the right cavities, to which the blood returns
from the body generally. Absorption by the pulmonary
vessels also takes place in the passage of dissolved oxygen
into the blood during respiration.

In absorj)tion by the bloodvessels, the dissolved substance
passes through the thin walls of the capillaries, or finest
venules, and so enters the circulation ; but as these vessels
are always covered by tissue, sometimes exceedingly thin, as

VENOUS ABSOEPTION.

169

in the air-cells, and sometimes thicker, as in the cntis, the
absorbed substances not only pass through the coats of the
vessels, but must also permeate this overlying tissue. This part
of the absorptive process, corresj^onds with that form of absorp-
tion which occurs in the non-vascular tissues and in animals
destitute of vessels. Absorption never takes place through the
open mouths of vessels, as was formerly supposed ; but, instead, a
process of permeation occurs through the living tissues, physic-
ally identical with that of dialysis through dead animal and
other moist permeable membranes, out of the body. This
permeation is determined generally, first, by the tendency of
different solutions to mix together, or of certain substances
contained in the fiuid on one side of the membrane, to pass
into the fiuid on the other side, which does not contain them ;
and, secondly, by certain chemical rekitions between the
mendjrane and the srtbstances applied to it, so that the mem-
brane will permit some things to pass through it more readily
than others. The rapid dialysis of acids, salt, sugar, and
other substances, as proved by their quick production of
ffavour in the mouth, and the equally rapid passage of saline
and metallic poisons, especially of the vegetable alkaloid.",
cyanide of potassium, prussic acid, and many other foreign
and noxious substances, into the blood, corresponds Avith their
crystalloid character ; Avhilst the inert colloidal gum, and
albumen, are slowly absorbed, and are almost tasteless. The
removal of the dialysed material, from beyond the septum,
increases the rapidity of the process; and thus also, the
natural process of absorption is more rapid, the quicker the
circulation in a part; lor the constant renewal of the blood
keeps up the required difference between that fluid and the
• solution of the foreign material, and the quicker the cir-
culation the more rapid and complete is the renewal of the
blood.

Absorption by the bloodvessels is necessarily favoured by
the thinness of the layer of tissue Avhich covers them, and is
opposed by a tliicker and denser covering ; thus, ab.sorption is
very rapid from the lungs and jieritoneum, quick also from the
gastric and intestinal mucous membrane, not quite so quick
from the exposed surface of the cutis, Avhilst it is almost
entirely arrested, when this is covered by the cuticle. It is
very rapid from the subcutaneous cellular ti.ssue, where solu-
tions injected artificially, come into almost immediate contact
with the walls of the capillaries and venules. Absorption takes

170

SPECIAL PHYSIOLOGY.

place, though slowly, through the coats of even the larger
veins, as has been shown, by exposing and insulating such a
vein in an animal, and placing poison upon it, when death
has followed. Absorption is favoiu-ed by moderate tempera-
tures, but is retarded by temperatures much higher, or much
lower, than that of the blood.

The rate of absorption of certain substances is very rapid ;
ferro-cyanide of potassium introduced into the stomach, has
been found in the urinary excretion after the short space of
GO seconds ; but when the stomach is more or less full, the
absorption is retarded accordingly. (Erichsen.) The rapid
passage of saline substances into tlie saliva, has been shown by
Bernard. Alcohol is absorbed so quickly, that its effects on
the brain, when injected into the stomach of dogs, are almost
immediate, death occurring in about two minutes, the stomach
being then fimnd to be empty, and the blood to contain large
quantities of alcohol. (Percy.)

Substances once introduced into the veins, by absorption,
are carried with the blood to the heart, and thence, along the
arteries to every part of tlie body. The condition of the cir-
culation materially affects the rapidity of absorption. If the
vessels be full of blood, or even if they be artificially injected
with water, it is found that water introduced into the pleura is
absorbed more slowly (Magendie) ; if the vessels be emptied by
previous venesection, absorption takes place more rapidly. Ab-
sorption is also more active, when the water of the body has been
diminished, by abstinence from fluids, or by imusual excretion.
It is often suggested, that persons about to expose themselves
to contagion or malaria, should previously take food, so as to
diminish the chances of absorption, which is believed to be
more likely to occur when the bloodvessels are in a compara-
tively empty state, or Avhen the system is imperfectly
nourished. The supposed immunity may be due to the le.ss
exhausted condition of the nervous system, or to some other
unrecognized power of resisting diseased indueuces.

The process of absorption by the bloodvessels, is so dependent
upon the movement of the blood, that if a ligature be placed
on those vessels in the limb of an animal, or entirely around
the limb, either, in the former case, absorption takes place
slowly through the lymphatic vessels ouly, or, in the latter
case, it does not occur at all. Thus, if a poi.son be inserted
under the .skin of an animal’s foot, and a tight bandage be
applied round the limb, no symptoms of general poisoning

LYiMrilATIC ABSORPTION.

171

ensue ; but if the bandage be then removed, and the circula-
tion through the limb be restored by gentle friction, poisoning,
or even death will occur. Hence, the immediate ligature of a
limb above a wound inflicted by a poisonous serpent, Avill
arrest the fm’ther entrance of the venom into the circulation.
The application of cupping glasses to a poisoned wound,
operate.s, not merely by drawing out portions of the poison,
owing to the removal of atmospheric pressure from the part,
but also by stagnating the circulation in the injured and
adjacent parts ; sucking a poisoned wound acts in a similar
manner. In a certain degree, the destruction of the part by
caustic or the actual cautery also operates thus, but also by
the simultaneous destruction of the poison itself. The prompt
removal of the poisoned tissues also arrests further absorption.

The process of absorption is influenced by the nervous
system, for, after division of the sciatic nerve in the hind
limb of a guinea-pig, aconite, which was not previously taken
up through the skin, has been found to be absorbed ; this has
been attributed to the dilatation of the smaller arteries, Avhich
follows section of the vasi-motor nerves. (Waller.) Certain
stimulating agents, such as chloroform and turpentine, Avhich
favour absorption, may do so, by producing dilatation of the
bloodvessels, as is indicated by the increased redness of the
surface to which they are applied. It has been supposed that
galvanism promotes absorption, but the contrary seems to be
the case. Heat, friction, and moistiu'e, as well as exercise of
a part, obviously favour absorption ; whilst the opposite con-
ditions of cold, rest, and absolute drynes.s, disqualify a part
from performing this function.

The share of the process of general absorption, due to the
absorbent vessels, i.e. to lijnipliatic absorption, is small. When
the cuticle of an animal is removed by bli.stering, and a solu-
tion of ferro-cyanide of potas.sium is applied to the denuded
cutis, though tlie poison may be found in the veins, it has not
been detected in the thoracic duct. Neverthele.ss, even when
the abdominal aorta and inferior vena cava of an animal have
been tied, to prevent the circulation of the blood through the
hinder limbs, and Avhen, in addition to this, the internal iliac
veins have also been tied, to cut off the collateral circulation
through the veins of the pelvi.s,cyanideof potassium, and .strych-
nine, in.serted beneath the .skin of the feet, even after the limbs
have become rigid, have been detected above the seat of the
ligatures, and have produced characteristic symptoms of poison-

172

SPECIAL PHYSIOLOGY.

ing ; the lymphatic vessels nuist here have been the channels
of absorption. In certain instances, morbid products are con- ^
veyed through lymjjhatic vessels, as, e.g. decomposed animal
fluids, pus, simple or specific, and also cancerous matter ; but
the extension of disease along the course of the lymphatics, 1
and througli the lymphatic glands, may be sometimes due to
the propagation of a morbid process in the coats of the lym-
jdiatics. The colouring matter of the bile has been seen in
the lymphatics of the gall-bladder, after ligature of the gall- ^
duct, and consequent retention of the bile in its receptacle. )
The subcutaneous lymphatics near tatooed portions of the t
skin, are sometimes found charged with colouring matter, form- I
ing characteristic ramified lines, differing in coiirse from that ^
of the bloodvessels. Moreover, the identity of structure be-
tAveen the l}'mphatics and the lacteals, and the undoubted
absorbent function of the latter, favour the conclusion that the ' !'
former vessels likewi.se absorb. The termination of all the , f
lymphatics in the venous system, and the direction of the »
valves in their interior, not only support this vieAv, but enable !
us to determine the course and destination of their contents. ,

The Jjjmpli, elsewhere described (vol. i. jd. G7), re.sembles
chyle deprived of its molecular basis, and of nearly all its fatty
matter ; but its clear, colourless, and limpid character, so
unlike the milky opalescent aspectof the chyle, renders it difficult
of detection in its vessels during life. Distended transparent
l}unphatics have, however, been seen on the surface of the
liver in recently killed animals, and the lymph itself has been
observed flowing from the cut surface of that oi'gan, and also
from lymphatic fistulaj, the result of disease in man, and
from artifrcial openings established in the lymphatics of a
horse’s leg.

The constituents of the chyle are derived essentially from
the digested food, but the precise source of the lymph con-
tained in the lymphatics, and also in the lacteals, during the
intervals between digestion, is not perfectly understood. In
part, the lymph would seem, from its similarity in composition,
to be derived from the nutritive plasma, which permeates all
the living tissues. This plasma, itself derived from the liquor
sanguinis, consists chiefly of that part of the nutrient liuid
poured out through the walls of the capillaries, which is not
enqdoyed for the nutrition of the tissues. The surplus of
nutrient materials, together with sufficient water, is sup])osed
to pass into the lymphatics in the form of lymph, and so to be

FORMATION OF THE LYMriI.

173

iiltimately returned to the blood. It is also supposed that the
tissues, themselves undergoing nutrient changes, yield products
which may, in part, be fitted to enter the commencing lym-
jihatics; but these, no doubt, chieliy find their way into the
capillaries and minute venules, and thus entering the blood,
are subsequently cast off as excretory products. Whatever
be its source, the fluid and dissolved constituents of the lymph
find their way into the commencing lymphatics, through the
delicate coats of these vessels, which form closed tubes, having
no open mouths, and no direct communication with the capil-
lary or other bloodvessels. It has, however, been recently
maintained, that the commencing lymphatics communicate
witli, or originate in, lacunar spaces, situated in the areolar
tissue which peiwades the whole body, and that they com-
mence in fine hollow processes in the ramified nuclear fibre
cells of that tissue, which are also supposed to be hollow. But
these views have not been confirmed.

As the commencing lymphatics are generally most abun-
d.ant in tissues in which the nutritive changes are not very
active, and least abimdant, or not detected, in organs which
undergo very rapid metamorphosis, it is probable that
the waste products of nutrition are chiefly, or, in the case of
the nenmus centres, entirely, returned into the circulation,
through the capillaries and minute veins. It is probably cor-
rect to infer that the lymphatics do not remove wasted and
excrementitious materials, unfit for the further use of the sys-
tem, as Hunter formerly .supposed, but rather that they take
up matters which may be again employed in the blood, for the
purposes of nutrition. The fibrin of the lymph, which en-
ables that fluid to form a slight coagulum, though not in the
vessels, as occurs with the blood, and also the lymph-cor-
puscles, which so closely resemble the white corpuscles of the
blood, are present before the lymph has passed the lymphatic
glands, but they increa.se in quantity beyond those glands. The
fibrin may be partly derived from that portion of the nutri-
tive pla.sma effused through the walls of the capillaries, which
is ab.sorbed by the commencing lymphatics ; its gradual in-
crease in quantity in the larger lymphatics may depend on
inspi.s.sation, or enrichment, taking place within the glands,
which are very va.scidar ; additional Jihrin or fibrinorjen.! from
which the fibrin is fonned, may even be elaborated in these
glands. Tlie lymph corpuscles may also be, in some way, more
abundantly dcvelojied witliin the glands, which must, more or

174

SPECIAL PHTSIOLOGT.

less, retard the rate of motion of the lymph. The outer areolar
spaces of the glands, which receive the lymph as it enters, ‘
contain numerous corpuscles and granules, some of which are ’
probably added to the moving .stream of Ijmiph. But .such >
corpuscles are undoubtedly formed, though in smaller number, j
independently of the glands ; for they may be detected in
both the lymphatic and lacteal vessels, before these have
passed through glands ; also in the lymphatic vessels of the .
hind limbs of birds, on which no lymphatic glands are found ; ;

and likev'ise, in the lymph of Eeptiles, Amphibia, and Fishes,
although in these animals no lyurphatic glands exist at all, but ,
only complex or simple lymphatic plexuses. The destination i
of the lymph corpuscles is the blood ; they probably consti-
tute in the Vertebrate, after birth, the chief, if not the only !
source of the white corpuscles of the blood, as will again be ••
mentioned in the Section on Sanguification. ji

I

Absorption of the Food.

The absorption of the digested food is only a special ex-
ample of the general absorj)tive function. It has been main-
tained by some, that the nutritive constituents of the food, are
absorbed fi'om the alimentary canal by the lacteals only ; by
othei's, that this absorption is accomplished by the minute blood-
vessels alone ; but both sets of vessels are concerned in this
function, each apjiarently performing special otEces. j

That the bloodvessels of the alimentary canal absorb, has >
been thus proved. Strychnine has been introduced, in a
living animal, into a portion of intestine, included between
two ligatures, and separated from the mesentery, excepting by
its arteries and veins ; so long as the circidation through the
intestine is arrested by compression of the bloodvessels, no I
symptoms of poisoning occur, but when the blood is allowed I
to How through the vesseLs, the animal is speedily poisoned. I
Moreover, certain alimentary substances, such as albumiuose, I
dextrin, sugar, and lactic .acid, have been found in the I
blood of the mesenteric veins ; many chemical substances, I
especially metallic salts, and those which easily j^enetrate I

animal membranes, as e.g. the ferro-cyanide of potassium, when I

taken with the food, have been detected in the venous blood, I ^
and even in the secretions; so also odorous substances, such as I ^
musk, camphor and garlic, alcohol, and soluble colouring mat- I j
tors, as e.g. cochineal and madder, taken into the stomach, I

LACTEAL ABSORPTION.

175

have been found in the blood. Even insoluhle .substances,
such as charcoal, sulphur, and, it is said, starch, taken inter-
nally, in a state of minute subdivision, have been detected in
the mesenteric veins. .

The entrance of nutrient and other matters from the intes-
tinal canal into the lacteals, is proved by the distension of
those vessels with white chyle, during digestion, especially
after listature of the thoracic duct. The chemical composition of
the chyle (vol. i. p. 92), shows that, besides absorbing the water
of the food, the lacteals take up small quantities of .saline sub-
stances and extractives, a certain quantity of the albuminose
products of digestion, and, in particular, a very large amount
of tatty matter. With regard to non-nutrient substances,
however, the absorptive power of the lacteals, is much more
limited than that of the veins. First, with regard to poisons ;
iir experiments, the opposite of that just recorded, the arteries
and veins of a piece of intestine, isolated by two ligatures,
have been tied, whilst the rest of the mesentery, containing
the lacteal vessels, has been left t;ntouched ; poison then in-
troduced into the intestine, is not absorbed, so as to destroy
the animal, until, by loosening the threads on the bloodvessels,
blood is again allowed to flow' through them. (Magendie and
Segalas.) To such experiments it has been objected, that
tying the bloodvessels suspends the iimctions of the lacteals,
which may lose their absorbing power, when the capillary
circulation around them is stopped. The experiment has,
therefore, been varied, so as to permit the local circulation to
continue ; thus, the vein fl-om the part of the intestine into
which the poison is introduced, is first compressed, and then
opened below the point of compression, so that the blood
returning along it, escapes, and does not enter the general cir-
culation, although the local circulation in the intestine still
goes on. Under these conditions, no poisoning takes jdace,
but this speedily happens when the pi-essure on the vein is
removed, and the blood returning by it, enters the general
circulation. Nevertheless, poisons are slightly and slowly
absorhalile by the lacteals, especially poi.sonous salts in a state
of solution. The lacteals also absorb innocuous sidine matters,
sugar, and extractive matters, but not so easily as the veins;
neither do they so readily take uj) odorous substances; with
regard to soluble colouring matters, turmeric is taken up
by them, whilst other dissolved colouring substances, such as
madder-lake, indigo, gamboge, and rhubarb, are said not to

176

SPECIAL PHYSIOLOGY.

be absorbed. (Tiedemann and Gmelin.) Substances in a state
of extremely minute subdivision, such as charcoal, sulphur,
and even particles of indigo, have also been found in the lactesil
vessels, as Avell as in the bloodvessels, having probably pene-
trated into those vessels in the villi.

From the preceding facts, it would seem that the absorbing
power of the veins is general, whilst that of the lacteals is
select. The veins permit the entrance into them indifferently,
of probably all kinds of soluble substances, which do not
actually alter or destroy the texture of their coats, but the
lacteals have a sort of selective power, by Avhich they take
up certain substances in preference to others, nearly, or com-
pletely, rejecting some. Both kinds of vessels, but especially
the lacteals, appear to allow, in some way or other, the
entrance into them of exceedingly minute particles of insoluble
substances, not by a process of dialysis, but by porous diffu-
sion, the pores being, however, invisible in the walls of the
capillaries or lacteals, though specially di.scernible, according
to some, in the epithelial cells upon the villi. The direct
penetration of the walls of the capillaries and lacteals, has been
compared with that of a needle entering a larger vessel. A
certain hardness of the penetrating particles is necessary, for
lamp-black, which is finer and softer than charcoal, does not
enter the vessels. Penetration of the soft tissues, by minute
bodies, withotit serious injury to the former, is illustrated by
the wandering movements of the smaller Entozoa, through and
amongst the living tissiies.

By lar the larger quantity of the water of the food and drink,
and of the saliva and gastric juice, is token ujj by the veins.
This process begins immediately, and goes on rapidly, in the
stomach ; it regulates the consistence of the gastric contents, and
the strength and acidity of the gastric juice ; more water, in-'
eluding some of that belonging to the biliary, pancreatic, and
intestinal secretions, is taken up by the veins of the intestines ;
but much is here absorbed by the lacteals, to form the fluid part
of the chyle. The saline con.stitrtents of the food are absorbed
directly, in chief part, by the veins, these substances, such as
chloride of sodium and phosphate of soda, requiring, like
water, no digestion ; minute traces of them, however, also
enter the lacteals. Sugar and extractive matters likewise
enter chietly by the veins, and but slightly through the lac-
teals. The organic acids, and their sjdts, are converted into
carbonates, and undergo venous absorption. Alcohol also

ABSOKPTION OF FOOD BY VEINS.

177

passes in cliiefly, if not entirely, by the veins, and so likewise
do the ethereal, odorous, sapid, and colonring matters of the
food, and probably also most medicinal and poisonous sub-
stances. Venous absorption even begins in the mouth, as may
be inferred from the occurrence of taste ; but it is much more
active in the stomach and intestines. Soluble albuminoid
substances, if not converted into albuminose, may be absorbed
directly by the veins of the stomach and small intestine, and
certainly by those of the large intestine, as is exemplified in the
restorative effects of nutrient enemas. The soluble albuminose,
the product of digested albuminoid bodies, must also be in
part absorbed by the veins ; for the quantity of albumen taken
up into the chyle, is scarcely equal to that contained in the food.
The gelatin-peptone probably enters the veins. Lastly, fatty
matters have not been directly proved to be taken up by the
veins, though, if in a saponified condition, they may be so, and
the capillary network has been seen to assume a turbid ap-
pearance, as if containing fat. (Briicke.) Besides this, in cases
of disease, not only the colouring substances, but the fatty
matters of the bile, enter the circulation through the venous
system. The chief channels of entrance of the fatty matters
emulsified during the process of digestion, are, however, the
lacteal vessels, as is proved by the large proportion of fat in
the chyle.

The veins, thus, absorb most of the Avater, and of the saline,

I saccharine, extractive, acid, alcoholic, odorous, sapid, and colour-
ing sub.stances, together Avith some albumen or albuminose,
probably the gelatin peptone, and possibly saponified fatty
matters. On the other hand, the lacteals absorb the rest of the
. Avater, small quantities of the saline, saccharine, and extrac-
1 th'e substances, a considerable proportion of the albuminose
' bodies, and nearly all the fat. In the Intervals betAveen the
absorption of food, the lacteals of the small intestine, like the
lymphatics of other parts of the body, contain only a transpa-
rent lymph, and then perform, for the tissues of the intestine,
the office of the lymphatics generally. The same is true, at all
times, of the lymphatics of the stomach and of the large intes-
tine, Avhich never contain chyle, but always lym])h.

It may be presumed, that the absorption Avhich takes place
from the stomach, is chiefly performed by means of the blood-
vessels, because the gastric mucous membrane is destitute of
villi, and, therefore, of proper lacteal ve.ssels ; nevertheless,
nutrient and other substances, prevented from entering the

VOL. II. N

178

SPECIAL PIIYSIOLOGT.

intestine, by ligature of the pylorus, have been shown to be
absorbed by the gastric lymphatics. Tlie process by which
certain parts of the food are absorbed by the bloodvessels of tlie
alimentary canal, must be identical with that of the general
absorption of soluble substances from other vascular surfaces,
or tissues, of the body. Like the latter, it partakes of the
nature of the physical processes of liquid diffusion and
dialysis. Water, and substances dissolved in it, such as
soluble salts, sugar, extractive matters, and solul)le albumen
or alburainose, permeate the epithelial and subjacent layers of
the mucous membrane, and also the thin coats of the capillaries
and smallest venules, not merely of the villi, but of the general
surface of the intestinal canal, in the same manner, pro-
bably, as a similar solution would pass through moist dead
animal membranes. The tetaperature of the interior of the
body, greatly favoru’S the osmotic process. The ])enetration
of the water with its dissolved contents, is a dialytic pheno-
menon ; and by a similar action, the entrance of certain sub-
.stances is probably permitted more readily than that of others,
the crystalloid substances, such as the salts and sugar, with
the creatin and creatinin of the extractive matters, and also
the albuminose and gelatin peptones, entering more readily
than the colloid substances, such as dissolved starch, mucilage,
albumen, gelatin,' and the non-crystallisable extractive matters.
But dissolved colloidal starch is converted by the salivin, into
the crystalloid sugar; and albumen and gelatin, when di-
gested by the acid pepsin, are changed into albumino.se and
gelatin peptones, which, though not true crystalloid.s, are much
more dialysable than the albuminoid and gelatinoid substances
contained in oirr food. The molecular metastases, or changes
in ((uestion, may be in some way connected with a process of
lujdration. It has also been suggested that a colloid body may
be formed by groups of crystalloids, and so its temporary-
metastasis from one condition to another, may be explained.
It is possible also that there may be special reactions between
alimentary substances and the living mucous membrane and
walls of the vessels, favouring or resisting the passage of some
or other of those substances. But this is uiicei-tain ; and
the act of ab.sorption by the bloodvessels, is so ea.sy, rapid,
and general, in the case of non-nutrient, and even of manj^
poisonous substances, that their walls can pos.sess but little if
any power of selection or exclusion. Fatty matters, however,
unless in a state of saponification, do not readily, or at all.

ABSOnrTION OF POISONS.

179

enter the bloodvessels. Experiment has shoAvn that even
when finely divided, as they exist, for example, in the yolk of
the egg, and in milk, they may be made, under moderate
pressure, to j^ermeate moist membranes (Heidenhain) ; and
lurther, that the natural repugnance between oil and wetted
membranes, is much overcome, if these latter are saturated in
alkaline solutions or in bile. (Wistinghausen.) A temperature
of 100°, or that of the interior of the body, facilitates this
permeation of fat. Though acids generally, and esjDecially
the hydrochloric acid, which exists in gastric juice, are rapid
dialysers, and so penetrate very quickly the colloidal albumi-
noids of the food, which they help to dissolve, yet acidity
appears to be opposed to the absorption not only of fat, but of
actually dissolved substances ; whilst, a neutral or alkaline con-
dition favours their absorption. In certain cases, especially in
regard to organic substances of an extraneous, medicinal or
poisonous, character, it appears that the digestive fluids not
only dissolve, but also alter, the properties of substances taken
into the stomach. Thus, there are two substances found to-
gether in the bitter almond, named aimjgdalin and emulsin, the
former of which is decomposed by a catalytic action of the
latter, and gives rise to the formation of prus.sic acid. Now,
it has been found by Bernard, that amygdalin, introduced by
itself into the stomach of any animal, is digested, dissolved,
and absorbed, without giving rise to poisonous symptoms.
Again, emulsin alone taken into the stomach, produces no ill
effects. If, however, after the absorption of the dissolved
amygdalin from the stomach, emulsin be directly injected into
a vein, death speedily ensues, from the formation of prussic acid
in the blood or ti.ssues, by the decomposition of the dissolved
amygdalin under the influence of the emulsin, thus intro-
duced into the circulation, and brought into relation Avith it.
But on the other hand, if the emulsin be introduced into the
stomach, and the amygdalin be injected into the bloodvessels,
poisoning does not ensue, showing either that the emulsin is
not absorbed from the alimentary canal, or that its properties
are destroyed. The latter is, probably, the case, for emulsin
is easily soluble, and Avhen it and the amygdalin are intro-
duced together into a vein, or even into distant parts of the
circulation, their meeting in the blood is immediately followed
by the characteristic decomposition of the one under the
influence of the other, prussic acid being evolved, and the
animal being killed.

180

SPECIAL Pin'SIOLOGY.

After the absorbed materials have entered through the
capillary walls, their onward progress depends upon the forces
concerned in the circulation of the blood.

The process of absorption by the lucteals, is of a more
special nature than that by the bloodvessels ; for though they
admit the entrance, probably by simple dialysis, of watei’,
with traces of saline, saccharine, and extractive substances,
that is, of the crystalloid bodies, and also take up in certain
proj^ortion, the dialysable albuminose, yet they are specially
characterised by absorbing fatty matters, which, though
crystalloid, are insoluble in water, and non-dialysable, unless
they are actually saponified. In the alimentary canal, how-
ever, they are merely liquefied, or emirlsified, i.e. reduced to a
state of extreme molecular subdivision, or they are decom-
posed into their fatty acids and glycerin. The special power
of the lacteals, of absorbing fatty matters, has not yet been
fully exjfiained. Some have supposed that the fats pass
through the epithelial substance of the villi, into the lacteals,
in a state of saponification and solution, and then reappear as
neuti'al fats in the chyle. The action of the bile and of the
alkaline pancreatic and intestinal juices, as already explained,
undoubtedly prejiares the fatty matters for more easy pene-
tration into the lacteals. The epithelial cells of the villi, which
are often formd distended with drops of fat during the digestive
process, are probably specially concerned in the absorption of
fat by the lacteals. It has been sirpposed that these cells
teed, as it were, upon the fatty matters contained in the intestine,
and, having become distended, discharge their fatty contents
into the commencing lacteals. A nutritive process is imagined
to take place, similar to that which occurs in the epithelial
cells lining the commencing ducts of the secreting glands,
but in a reverse direction ; that is to say, not by the assimi-
lation of materials from the blood into these secreting cells,
to be discharged at the sm-face, but by the assimilation of
materials from the surface inwards, to be discharged into the
lacteals. This fatty matter must enter the epithelial cells
covering the villi, in the form of exceedingly minute molecules,
by porous diffusion or transmission ; and the fine vertical lines
or streaks, noticed by certain observers in these cells (p. 158),
are supposed, by some to be minute pores or channels, through
which the highly sirbdivided fatty matters, or even fine solid
particles of charcoal, enter the interior of the cells, and so
proceed into the lacteals. How the fat particles pass from the

MOTION OF THE CHYLE.

181

colls into the commencing lacteals, is not known. By some it
is said that the inner pointed ends of the epithelial cells,
terminate in caudate areolar tissue cells, which, in their turn,
communicate with the lacteals. But this is more than doubt-
ful ; and the actual transmission is probably by porous dif-
fusion, through true but invisible pores.

The onward motion of the chyle, from the commencing
lacteals in the villi, into and through the larger absorbent
vessels on the walls of the intestine, and along the mesentery,
to the thoracic duct, depends on several agencies. First, the
chief cause is probably the vis a tei'go, or foixe from behind,
originating in the continuous nature of the absorptive process
at the commencement of the lacteals. The existence of this
force, is proved by the distension of the whole system of
vessels, including the thoracic duct, even to the occurrence
of ruptrrre, when that duct is tied in an animal a short time
after it has been fed. This pressure from behind, produces a
motion of the fluid in the larger absorbents, just as the con-
tinuous absorption of fluid by the spongioles at the extremities
of the roots of trees, causes the rising of the sap. Even in
simple dialysis, in purely physical experiments, as Avith the
endosmometer of Dutrochet, there is an ascending motion of the
fluid in the graduated tube, due to the energy at work in the
moist membrane. Secondly, the contraction of the non-striated
muscular fibres of the villi, which, Avhen stimulated by galva-
nism, in living animals, have been observed to shorten those
processes, must compress the central lacteal of each villus, and
so urge on its contents into the general netAvork of absorbents.
The bile may help to excite this muscular act. Thirdly, the
contraction of the scattered muscular fibres in the submucous
coat, and also the peristaltic movements of the proper muscular
coat of the intestine, likeAvise e.xcited by the food and by the
bile, Avill serve to empty the intestinal lacteals into those of
the mesentery. Fourthly, the lacteals and the lymphatics, as
Avell as the thoracic duct, have muscular fibres in their coats,
the contraction of Avhich moves onwards their contents, and
also empties them on their being exposed to the air, in animals
recently fed; this explains the collap.scd state of these vessels
after death. There are also muscular fibres in the inter-
alveolar septa of the lymphatic glands. Fifthly, the semilunar
valves found in pairs in the interior of the larger lacteals,
both in the Avails of the intestine and in the mesentery, must
determine the movement of the contained chyle, always in the

182

SPECIAL PHYSIOLOGY,

same direction, by whatever force such movement may be
induced. In this way, even the pressure of the abdominal
walls and viscera, must assist the onward flow of the chyle. Its
direction necessarily coincides ■with that of the fi’ee margins of
the v.alves, viz., towards the thoracic duct, all retrogression of
the chyle in the direction of the intestine, being effectually
prevented. Lastly, the quick motion of the blood in the great
veins at the root of the neck, into which the thoracic duct
opens, and the effects of inspiration, are also causes of a cer-
tain vis a f route, ov force from before, which draws the lymph
or chyle from that duct into the veins. The descent of the
diaphragm in inspiration, acts not only by removing pressure
from the great veins in the thorax, but also by increasing the
pressure on the abdominal lymphatics and the lower end of the
thoracic duct.

The quantity of mixed lymph and chyle poured into the
blood in twenty-four hours, has been estimated, from experi-
ments in animals, to be, in an adult man, nearly 29 lbs., of
which the smaller proportion is chyle, the rest being lymph.
(Bidder and Schmidt.) It has been ingeniously suggested by
Vierordt, that, if the absorption of fat be supposed to take
place exclusively by the lacteals, and the composition of the
chyle be assumed to be uniform, the daily quantity of chyle
may be calculated from the daily quantity of fat taken in the
food. Thus, the quantity of fat consumed in the day, being
taken to be 3 oz., and the chyle, to contain three per cent, of
fatty matters, the quantity of this fluid formed daily would be
about 100 oz. or 6^ lbs. The chyle is a highly nutrient fluid.
It adds not only fatty matter, but, like the lymph, a certain
amount of flbrin or fibrinogen, albumen, extractives, and salts,
and also a number of granules and proper corpuscles, to the blood.
The gradual entrance of these into the blood, is of some im-
portance in the maintenance of the proper composition of that
fluid, and, accordingly, nutrient substances are absorbed rather
more slowly than those which are not nutrient. The more
concentrated the products of digestion, however, the more
rapid is their absorption ; at least this is true of sugar and
albumino.se. (Becker, Funke.)

Intrinsic Absorption.

The special process, by which the fluid or solid parts of the
living body, are interstitially removed, the so-called intrinsic

I.NTKINSIC ABSORPTION.

183

absorption, is usually described with the simpler phenomenon
of general absorption. But it is a different and more complex
process, implying a previous liquefaction, or fine disintegration,
of the solid particles of the absorbed tissues, before these can
enter the lymphatics or bloodvessels concerned in their
removal. It is in part, therefore, a nutritive or denutritive
process.

Intrinsic absorption is sometimes simply interstitiid, accom-
plishing the removal of tissues, molecule by molecule, without
any solution of continuity, or breach of substance, in them,
the part affected becoming merely smaller, and not necessarily
undergoing any special change of fonn. During simple in-
terstitial absorption, nutritive changes, involving the deposi-
tion of fresh material, must still go on, but the process of ab-
sorption is relatively more active than that of the deposition of
new matter. This kind of interstitial absorption is illustrated
in the ivasting Avhich takes place as the result of hunger or
starvation, and also in the disease known as atrophy.

Another form of intrinsic absorption, known as progressive
absorption, involves more or less solution of continuity, or
breach of substance. It is often apparently caused by pressure
interfering with the nutrition of a part ; it is exemplified in
certain morbid processes, as when an aneurismal, or other deep-
seated tumour, in approaching the surface, induces absorption
of the interposed structures, even the bones being absorbed
under the effects of constant pressure. Abscesses also tend to
the surface of the body or of internal mucous cavities, by a
similar progressive absorption. Another form of this process
is named disjunctive absorption ; in this, the living part of a
tissue, in immediate connection with a dead portion, is re-
moved by absorption, and so the dead part is detached ; such
a process occurs in the separation of a slough from a soft
tissue, or of a necrosed or dead portion of a bone, from a living
part, and also in the throwing off of a portion of the entire
limb, as in the case of gangrene of the foot.

Certain tissues also undergo intrin.sic absorption much more
readily than others. Bone, one of the harde.«t tissues in the
body, is very readily absorbed ; its numerous Haversian canals,
and cancelli,and even its general medullaiy cavitie.s, are chan-
nels or spaces produced, during its growth, by an absorptive
excavation of a previously solid os.seous tissue ; such changes
occur in it, even when it is fully developed ; and, as just now
stated, it is very easily absorbed under abnormal pressure.

184

SPECIAL PHYSIOLCGT.

The fangs of the temporary or milk teeth, which are composed
of dentine, a substance more compact than bone itself, under-
go progressive absorption under the influence of pressure from
the summits of the rising permanent teeth, and, in this way,
are loosened, and finally drop away from the gum. Cartilage
is less easily absorbed than bone, but, nevertheless, it does
yield to that process. The fascia?, areolar tissue, skin, and
mucous membranes, also give way irnder the progressive
absorption caused by abscesses rvliich are advancing to the
surface ; the epidermis and epithelium, however, burst me-
chanically. Vascularity is necessary for the occurrence of
true intrinsic or progressive absorption. Cartilage is probably
absorbed by closely adjacent vessels. All vascular organs and
tissues are liable to progressive absorption under pressure,
and all may undergo waste or atrophy.

In the progress of development, in Man and animals, many
instances occur of the disappearance of parts not permanently
needed, such as the temporary gills of the higher Amphibia,
the tails of the tadpoles of the anourous species, and also cer-
tain large bloodvessels which are no longer required in more
advanced conditions of development. The removal of the
membrane which closes the pupil of the eye, when it is no longer
needed for the vascular sirpply of the lens, is another instance
of intrinsic absorption ; so also are the many changes which
take place in the jaws, during the formation of the sockets for
the teeth, and their filling up when these are lost. Sometimes
an entire organ of complex structure, with its proper paren-
chyma, bloodvessels, lymphatics, and nerves, becomes atro-
phied by interstitial absorption. Thus, the thymus body,
a ductless gland, which exists in the fore part of the
neck and thorax, in the young of Man, and the Mammalia
generally, disappears as life advances. In the human body,
the thymus exists only as a mere vestige, after the age of
twelve years.

By the process of resorption, blood, lymph, drop.sical effu-
sions, pus, and other fluids are easily taken up fi-om the areolar
tissue in which they are extravasated or effu.sed. From the
serous cavities, and especially from the joints, they are less
ea.sily resorbed. It is probable that the solid albuminoid con-
stituents of such effused products, undergo a chemical change
of degeneration, becoming converted into fatty matter, and
some nitrogenous, perhaps ammouiacal, compound, both of
which are absorbable. It has been found that a piece of

USES OF ABSORPTION.

185

muscle introduced into the cavity of the peritoneum, first loses
its water, and then gradually undergoes a fatty change.

When injlammation reaches a certain height, besides the
exudation of plastic matter from the bloodvessels, and the
formation of cells, which may end in the production of pus, or
of new-formed tissue, the nutrition of the pre-existing tissue
itself may suffer, and it may become slowly disintegrated, or
undergo molecular death. It then falls away imperceptibly,
and a chasm is left, called an iilcev, the process itself being
named ulceration. Both the vascular and non-vascular tissues
are liable to become ulcerated. It was once supposed that
the formation of an ulcer, or the ulcerative process, began and
continued by the interstitial absorption of an inflamed tissue,
this form of absorption being named ulcerative absorption ;
but although a true absorptive process may occur in some
forms of ulcer, there is little doubt that, generally speaking,
the erosion of a living tissue, known as ulceration, is due to
the molecular death and melting away of the tissues. Ulcers
always occur on surfaces, whether in vascular parts, such as
the skin, mucous membranes, and bones, or in non-vascular
parts, such as the cornea and the articular cartilages.

There is reason to believe that both the li/mphatics and the
bloodvessels are concerned in the various forms of intrinsic
absorption or resorption. The agency of the lymphatics is
rather inferred from analogy, than demonstrated by facts. It
is impossible to doubt that the bloodvessels are also concerned
in it, for the phenomena may take place in parts in which
lymphatics are not believed to exist, as, for example, in the
brain ; but the process is here undoubtedly much slower.

Intrinsic absorption is favoirred by continued moderate
pressure, as by the use of surgical bandages, which, however,
may also act by restraining the supply of blood and the nutri-
tion of a part. It is also favoured by an elevated position, by
friction, and by stimulating applications. It serves important
uses in the economy, enabling the whole system to be main-
tained, for a time, upon itself, and, by the absorption of fatty
matter stored up in the adipose tissues, supporting the respira-
tory function, even in the ab.sence of food. In the removal
and casting out of diseased products, or dead parts, it also
exerci.ses a u.seful and conservative office.

In conclusion, it may be repeated that, in addition to
these important uses, the function of absorption generally,
ministers to the nutritive function, by the conveyance into

186

SPECIAL PHYSIOLOGY.

the circulating system, not only of the materials of the food, but
also of the residual part of the plasma of the blood, not imme-
diately ertrployed in the nirtrition of the tissues amongst which
it is poured out ; and, lastly, that it assists in the elaboration
of those essential organised elements of the blood, its white
and its red corpuscles.

The Absorbent System, and Absorption in Animals.

A lymphatic and lacteal apparatus exists only in the Vertebrate Suh-
kingdom. In all cases, the finest vessels commence by blind extremities,
and the absorbent trunks empty themselves ultimately into the veins,
forming, as it were, a closed system superadded to, or constituting an
offset from, the blood system, with which, in the lower Vertebrata, it
communicates at a groat number of points, not only in the neck, but also
in the abdomen and pelvis.

In Mammalia generally, as in Man, well-developed lymphatic glands
are found ; in the Carnivora, owing probably to the shortness of the in-
testine, the mesenteric glands are so closely aggregated, as to appear
like a large conglomerate gland. In Birds, lymphatic glands are also
found, especially in the fore part of the body, but they are less perfectly
developed, and, in other parts, are replaced by elaborate plexuses of lym-
phatic vessels ; in accordance with the general lateral symmetry of these
animals, there are two thoracic ducts, each with its receptaculum chyli ;
in certain birds, as in the goose, dilatations of the pelvic lyunphatics are
met with, the coats of which are provided with unstriped muscular fibres,
which do not contract periodically or rhythmically ; the lympliatics of
the hinder part of the body communicate very frequently with the veins.
In Eeptiles, the lymphatic glands are absent, but their place is apparently
supplied by the great size and abundance of the absorbents themselves,
and by numerous plexuses of closely-packed vessels ; the valves are either
imperfect, or are found only in the larger tninks ; commimications with
the veins, exist in the lower limbs. In this Class, as well as in the
Amphibia and Fishes, there occur, connected with the lymphatic sys-
tem, those remarkable rhythmically contractile sacs, known as lym-
pliatic hearts ; they have been found in the neck of certain Ophidia, and
in the pelvis of the tiu'tle and crocodile. In the iAmphibia, the lym-
phatics are relatively large, but few in number ; neither valves nor
lymphatic glands exist ; the lymphatic hearts, usually four in number,
have walls composed of striated muscular fibres : in the frog, two of
these hearts are situated, one on each side of the neck, opposite to the
third cervical vertebra, and two posteriorly in the pelvic region. It is
in Fishes that the absorbents are fewest in number ; they are delicate
transparent vessels, destitute of valves, excepting at the points of en-
trance into the veins, which are here very frequent : the lacteals appear
almost destitute of distinct walls. In the tail of the eel, and in many
fishes, behind the cranium, outside the jugular veins, there are found pairs
of lymphatic hearts, or dilatations of a similar nature to the true lym-
phatic hearts of the Amphibia. No lymphatics have been obsen'cd in
the amphioxus.

CIRCULATION.

isr

The chyle varies in colour and opacity in different animals ; thus, it is
very milky-looking in the carnivorous, but almost colourless in the
herbivorous Mammalia ; it is also more transparent in the cold than in
the warm-blooded Vertebrata.

It is usually considered that no vessels homologous in character and
office, with the lymphatics and laeteals of the Vertebrata exist in Non-
vertebrate animals ; but it has been suggested that the so-called blood-
system of the Mollusca and higher Annulosa, with its usually colourless
contents, including corpuscles much more like the white than the red
blood corpuscles of the Vertebrata, may possibly be the homologues of
the vertebrate lymphatic system. Be this as it may, these vessels are
undoubtedly concerned, not only in the function of circulation, but also
in that of absorption ; for absorbed materials not only pass into the
perivisceral cavity, and penetrate the soft tissues of the body, immedi-
ately and directly, but they also enter the interior of these so-called
bloodvessels, mingle with the circulating fluid, and thus are conveyed
to the most distant parts of the frame. Such vessels must be con-
cerned both in the absorption of the food, and in all the phenomena
of general extrinsic and intrinsic absorption. In those Non-vertebrate
l animals, which, as the Annuloida, possess the so-called water vascular
system, or some analogous vessels, general absorption may be assisted
by them. In the Ccelenterata, all of which are destitute of proper
vessels, the fine tubular extensions of the body cavity into the soft disc,
must aid in this process ; but in the simple hydra, absorption must be
accomplished by direct imbibition through the cells lining the digestive
cavity, and by general percolation through the soft intercellular spaces.
In the Protozoa, it must occur through the sarcodous cell-substance, of
which those animals consist.

Whilst, therefore, in the lowest non-vascular animals, nutrient matters
at once permeate the tissues which they have to nourish, and whilst, in
all animals possessed of vessels, whether absorbent or circulating, or
: fulfilling both functions, a similar permeation of nutrient matter takes
; place through the lining membrane of the digestive cavdty, yet, in the
latter case, it has no immediate nutrient action on the solid tissues, but
speedily passes into the bloodvessels or absorbents, .and thus directly
or indirectly enters the circulating fluid or blood. Mixed with this, it
I probably undergoes further elaboration, before it again transudes through
the walls of the fine vessels, into the solid tissues, which are ultimately
: nourished by it.

CIRCULATION.

We have seen that tlie tib.sorbent vessels end in the gre.at
veins at the root of the neck, .and that there, the lymph and
chyle are poured into the blood. The blond is not permitted
to remain stationary in any part of the living body ; but in
order to fulfil its oflices in the general functions of nutrition,

188

SPECIAL PHYSIOLOGY.

secretion, and excretion, and its special office of stimulation in
regard to the nervous and muscular systems, and in order that
it may be constantly purified by the respiratory process, it is
kept in continual motion throughout the vdiole of life.
This motion of the blood takes place, in Man and in most
animals, in distinct cavities and channels, viz., through the
heart and bloodvessels, the arteries, capillaries, and veins.
The movement itself is named, from its definitely recurrent
course, the circulation of the blood.

The general distribution of the arteries, capillaries, and
veins of the body, and the structure of these vessels, have
already been explained (vol. i. pp. 18 and 57). The heart,
or central organ of the circulation, requires now to be
described.

The Heaut.

The Heart and Bloodvessels.

The heart, enclosed in its sac, or pericardium, is placed
obliquely in the thorax, between the lungs (fig. 13), occup)'-
ing a space about 4 inches in width. It is of a conical shape.
Its base, connected with the large bloodvessels, is directed
upwards, backwards, and to the right, corresponding with the
middle of the dorsal region ; its apex turned downwards, for-
wards, and to the left, points to the left of the sternum,
opposite the interspace between the fifth and sixth ribs, two
inches below and one to the sternal side of, the left nij^ple.

Its anterior surface, turned slightly upwards, is convex ; its
posterior surface, directed downwards, and supported by the
diaphragm, is flattened. This organ is about the size of the
closed fist. In the adult male it weighs from 10 to 12 oz.,
but from 8 to 10 oz. only in the female. Its proportion to the
body, in the former sex, is as 1 to 169 ; in the latter, as
1 to 149. It measures about 5 inches in length, 3-| in width,
and 2^ in thickness. It increases in weight, and enlarges in
all its dimensions, as life advances.

The heart is a hollow muscle, its cavity being completely
divided internally, by a longitudinal septum, into a right and
a left lateral chamber. Each chamber consists of two cavities,
one called an auricle, the other a ventricle, marked off from
each other by a transverse constriction, which forms on the
surface the auriculo-ventricidar groove. The auidcle and
ventricle of the same side open into each other, but those of

DESCIlirTION OF THE HEART.

189

the opposite sides do not communicate. The tAvo auricles are
placed at the base of the heart ; their Avails are thin ; they are
separated from each other by the median septum, and receive
blood from large veins. The tAvo ventricles lie beloAv the
auricles, have AA'alls of considerable thickness, and form the
most solid part of the organ ; each is connected with a large
artery. Tavo longitudinal furroAvs, one anterior, the other
posterior and less defined, correspond Avith the position of the
median partition which separates the tAvo ventricles Avithin.
The right ventricle occupies more of the anterior, and the left
vmntricle more of the posterior, surface of the heart ; the left
ventricle reaches loAver than the right, and so forms alone the
apex of the heart, the longitudinal furroAvs and septum termi-
nating a little to the right of the apex. Each of the four
cardiac cavities requires fiu'ther description.

The right auricle (fig. 105, .3) consists of a larger part, named
the sinus, and a smaller part leading from it in front, named
the appendix auricidce or j)i'oper auricle, so called on account
of its resemblance to a dog’s ear. The margins of the appen-
dix are notched, and its walls, instead of being thin and
smooth, like those of the sinus, are thick, and marked inter-
nally by prominent lleshy bands, the musculi pectinati. Into
this auricle the systemic veins open, viz., the superior vena
cava, 1, at the upper and forepart of the sinus; the inferior
vena cava, '>, at its lowest part ; and, lastly, the large coronarp
vein at the back, its orifice being protected by a thin mem-
branous valve, the coronary valve, or valve of Thehesius ; besides
this, there are numerous apertures of small veins belonging
to the heart, and certain recesses in the auricular Avails. Upon
the septum, betAveen this and the left auricle, is an oval
depression, the fossa ovalis, bounded above, and at the sides,
by a margin named the annulus ovalis. The fossa ovalis is
the vestige of an opening, the foramen ovale, Avhich exists
before birth, then permitting the blood to pass from the right
into the left auricle : sometimes the foramen ovale is not
entirely obliterated, in that case, a small valved aperture leading
obliquely, Iteneath the annulus ovalis, into the left auricle.
Attached to the anterior margin of the orifice of the inferior
vena cava, is a thin membranous semi-lunar fold, called the
Eustachian valve (fig. 105), the free concave border of Avhich
is turned upwards and to the left ; it is often small, freqtiently
perforated, and sometimes Avanting. Before birth, it is large,
and of great importance in directing the course of the blood.

190

SPECIAL rilYSIOLOGT.

Lastly, in front and to the left of the opening of the inferior
cava, is the large apei'ture leading into the right ventiucle,
named the right miriculo-veutricular opening.

The right vent7-icle, 4, forms a somewhat conical cavity,

Fig. 10.5. ’

I'ig. lf)3. Diagram of the heart and great bloodve.ssels. Tlie right cavities
of the heart, or right auricle and ventricle, and the pulmonarj' ai tery,
are supposed to be laid open. 1, the superior vena cavaj 2, inferior
vena cava; 3, right auricle laid open, showing the orillce of the superior
and inferior cavse, the latter guarded by the Eustachian valve ; 4, right
ventricle laid open, showing the anterior segment of the tricuspid
valve, its chorda; tendinese, and musculi papillares. The thin walls of
the auricle, and the thicker walls of the ventricle, arc seen 07i their
sections ; 6, pulmonary artery laid open, to show parts of two of its
semilunar valves * ; 7, part of the left auricle : the pulmonary veins are
not represented, being concealed at the back of the heart ; 8, the left
ventricle ; 9, the aorta, giving off branches to the head and upper limbs,
and arching down to form the abdominal artery, which supplies
branches to the rest of the body. The arrows show the course of the
blood from the veins, 1, 2, to the right auricle; 3, through the auriculo-
ventricular opening into the right ventricle, 4, and thence along the
imhnonary artery, 6.

shut off from the left ventricle by the thick interventricular
septum. At it.s base, i.s the opening from the .auricle just
mentioned, whilst above, .and in front of this, is the aperture
leading into the ])ulmona7-g artery. That portion of the ven-

DESCRIPTION OF THE HEART.

191

triclc conducting to the artery, forms a conical prolongation,
named the infundibulum or conus arteriosus. Both of these
openings are guarded by remarkable valves. Tlie auriculo-
ventricular opening corresponds with the middle of the
sternum, on a level with the third intercostal spaces and fourth
costal cartilages. It is somewhat oval, and measures about
1-^ inch in diameter, in the male. It is surrounded by a strong
fibrous ring, and its valve, being composed of three pointed
segments, is hence called the tricuspid valve. These segments,
of a trapezoidal shape, are formed by a doubling of the lining
membrane of the heart, enclosing bands of fibrous tissue, and,
it is sjiid, a few muscular fibres ; the segments are continuous
at their base, and are there fixed to the fibrous ring around
the opening into the auricle (fig. lOG a, 2). Of the three seg-
ments, one corresponds to the front of the ventricle, another to
its posterior wall, and the third, the largest, lies between the
auriculo-veutricular opening and the pulmonary artery. Each
segment is thicker at its centre ; whilst its margins are thinner,
more transparent, and indented. To the margins, and also
to the venti'icular surfaces of the segments, are attached
numerous fine tendinous cords, the chorda; tendinea; (fig. 105),
the other ends of which are connected either with certain
muscular columns, to be presently described, projecting from
the walls of the ventricle, or with the inner surface of that
cavity, especially with the septum. The chordas tendineaj,
proceeding from the adjacent margins of any two segments of
the valve, are connected with the same muscular column. Some
of .(he cords are inserted into the base of the segments, others
are connected with its central thicker part, Avhilst the finest
and most numerous are inserted into its thin marginal portion.

The muscular bands just mentioned, named the columnee
carnecB, are found in nearly every part of the inner surface of
the ventricle. They are of three kinds : first, some which
form merely irregular, and frequently reticulated, prominences
on the sides of the cavity ; a second kind are adherent at
each end, though free in the middle ; lastly, a third kind, con-
siderably larger than the others, and named the musculi papil-
lares, form three or four lumdles, which jirojcct upwards
from the walls of the ventricle, and are connected wi(;h some
of the chordee tendinea: of the tricuspid valve. 'The internal
surface of the infundibulum is smooth.

The orifice of the jmlmonary artery, fig. 105, 5, corrc.sponds
with the upper border of the third left costal cartilage, and

192

SPECIAL PHYSIOLOGY.

second intercostal space, close to the stennnn. It is circular,
and measures, in the male, a full inch in diameter. Its pro-
tecting valves consist of three semi-circular membranous folds,
named semi-lunar valves (fig. 105*, fig. 106, 4), attached, by
their convex margins, to the sides of the pulmonary artery at
its line of junction Avith the ventricle, but free at their straight
borders, Avhich are turned upAvards in the direction of the
artery. In the middle of the free border of each A'alve, is

Fig. 106.

6 a

Fig. 106. Three views of tlie base of the heart, after removal of the
auricles; the coimncncements of the pulmonary artery ai.d the aorta
are left, in order to show the valves of the heart and their altered
positions at different moments of the heart’s action, a, 1, interior
of part of the right auricle; 2, right auriculo-ventricular, or tri-
cuspid valve ; 3, right ventricle ; 4, pulmonary artery and its semilunar
valves ; 6, interior of part of the left auricle ; 0, left auriculo-ventri-
cular, bicuspid, or mitral valve; 7, left ventricle; 8, aorta, and its
semilunar valves. In this view, alt the v'alves have their segments a
little apart, b, shows the auriculo.vcntricular apertures open, and
their valves apart; the arterial orilices are closed, and their valves
in contact : condition during diastole of the ventricles, c. shows the
opposite conditions of the valves ; condition during systole of the ven-
tricles.

a small fibro-cartilaginous nodide, the corpus Arantii, When
stretched across the vessel, the borders meet each other, form-
ing lines diverging from the centre at angles of 120°. The
free and attached margins of each A'alve contain tendinous
fibres ; tendinous fibres also radiate acro.ss the valve, from the
corpus Arantii to its attached margins, so that tAvo thin semi-

DESCRIPTION OF THE HEART.

193

liiiuir portions, called lumdce, are left, one on either side of the
nodule. Behind the segments, the pulmonary artery presents,
at its base, three slight dilatations or pouches, the sinuses of
Valsalva.

The left auricle (fig. 105, 7), somewhat smaller than the
right, has thicker walls, measuring, on an average, 1-^ line in
thickness, whilst those of the right auricle measure only
1 line. Like the latter, it consists of a sinus and an appendix.
The sinus is placed behind the aorta and pulmonary artery.
The appendix, projecting forwards and to the left side, is nar-
rower, and more curved and notched, than the right one ; its
musculi pectinati are smaller and less numei’ous. At the back
of the auricle are the openings of the lour pidmonari/ veins,
two on each side, their orifices being destitute of valves. On
the septum, between this and the right auricle, is a lunated
depression, bounded below by a crescentic ridge, the vestige of
the foramen ovale. At the lower part of the auricle, is the
opening into the left ventricle, or left auriculo-ventricidar
opening.

The left ventricle, 8, is longer, and more conical in shape,
than the right ventricle ; it has much thicker walls, the pro-
poi-tion being as 3 to 1. The walls are thickest opposite the
middle of the cavity, and thinnest at the apex, whilst the
light ventricle is thickest near its base. The average thick-
ness, in lines, of the walls of the two ventricles in the male, in
whom they are somewhat thicker than in the female, are, for the
left ventricle, at the base, middle, and apex, 4^, 5^, and 3^ ;
and for the right, 1|^, 1§, and l^g-^^. (Bizot). The left ventricle
increases in thickness as life advances ; but the right remains
unaltered after the period of full development.

At the left and hinder part of the base of this ventricle, is the
oval opening from the left auricle ; in front and to the right
of this, is the circular aperture of the aorta. These open-
ings are, after death, .smaller than the corresponding orifices
on the right side of the heart. The annexed Table shows the
circumference of all four apertures, in the adult male and
female (Peacock) : —

Male. Female.

Inches Linos Inches Lines

4 6 4 0

3 7 3 10

3 4 3 3

3 0 2 10

VOL. II.

0

194

SPECIAL PHYSIOLOGY.

The left auriculo-ventriculai- opening corresponds to the
centre of the sternum, reaching upwards a little to the left.
It is guarded by a valve, resembling the tricuspid valve, but
formed of two segments instead of three, and hence called the
bicuspid or mitral valve (fig. 106, 6). The two segments are
named, from their relative position, anterior and posterior ;
the former is somewhat the larger. The segments are pro-
vided with cJiordo} tendinece, fewer in number than those of
the tricuspid valve, but having similar attachments ; all
these structures are stronger and thicker than those of the
right ventricle. The internal surface of the left ventricle gene-
rally, like that of the right, is provided with three kinds of
columnce cai'nece, which, however, are relatively small and
numerous ; there are only two musctdi papillares.

The round orifice of the aorta lies behind the junction of
the third left costal cartilage with the sternum. It is sepa-
rated from the auriculo-ventricular opening, by the base of the
anterior segment of the bicuspid valve, here joined to the aortic
fibrous ring. The aortic orifice is protected by three semi-
lunar valves (fig. 106, 8, fig. 107, b, 2), resembling those of the
right side in form, in their mode of attachment to the sides of
the great bloodvessel, and in the peculiar direction of their
free edges towards the artery ; but they are thicker and
stronger, have their corpora Arantii larger, and their lunular
margins more developed. The pouches, or sinuses of Val-
salva, at the base of the aorta, are also larger than those of the
pulmonary arteries. The two coronary arteries, or nutrient
arteries of the heart, arise from the bottom of two of these
pouches, close behind the corresponding semilunar valves.

The cavities of the heart are lined by a very fine serous
membrane, named the endocardium, which is continuous Avith
the lining membrane of the large vessels; it is someAvhat
thicker in the auricles than in the ventricles, and thicker in
the left than in the right cavities ; the Amlves of the heart
consist essentially of folds of this membrane, enclosing fibrous
tissue. It is difficult to determine the capacity of the cavities
of a muscular oi-gan like the heart ; the estimates given of the
capacity of the left ventricle, vary from 4 to 6'3 oz. ; the right
ventricular cavity is usually said to be a little larger. The
capacity of each auricle corresponds Avith, or is a little smaller
than, that of the respective ventricle.

The muscular fibres of the heart. — The substance of the
heart is almost entirely composed of muscular fibres, arranged

THE AORTA AND ITS BRANCHES

195

Fig. 107.

a.

Fig. 107. a, the aorta detached from the heart and from the body. 1,
ascending aorta, showing the enlargements or pouches at its commence-
ment, known as the sinuses of Valsalva; 1', 1", de.scending aorta, thoracic
and abdominal ; 2,3,3,2, branches from the arch of the aorta, which supply
the head and upper limbs ; 4, coeliac axis, or artery, which divides into
three branches to supply the stomach, liver, and spleen ; 5, renal
arteries for the kidneys ; 6, superior, and 7, inferior mesenteric arteries
which supply the small and large intestine; 8, 8, iliac arterie.s, which
give off branches to the pelvis and lower limbs ; 9, 9', intercostal and
lumbar arteries, which supply the walls of the thorax and abdomen, b,
portion of the left ventricle, and the commencement of the aorta, laid
open, to show the aortic .semilunar valves; 1, portion of the aorta, with
the orifices of the coronary arteries, or nutrient arteries, of the heart ;
2, the three valve segments ; 3, portion <jf the loft ventricle, c, diagrams,
to show the action of the valves in the veins ; 1, the valves open, so that
the blood can pass on; 2, valves closed, so that the backward flow of the
blood is arrested.

o 2

196

SPECIAL PHYSIOLOGY.

in layers, covered externally by a reflection of the serous
membrane of the pericardium, and lined, within the cavities,
by the endocardium. Four fibrous rings also exist, viz. those
around the two auriculo-ventricular openings and the orifices
of the pulmonary artery and aorta. Besides this, the heart
possesses jjroper arteries, capillaries, and veins, deep and super-
ficial lymphatic vessels, and numerous nerves and nervous
ganglia.

The fibrous rings of the left side of the heart, are, like
the valves, stronger than those of the right side. Those of the
auriculo-ventricular orifices give attachment to the segments
of their respective valves, and also to a few of the muscular
fibres of the auricles and ventricles. The rings surroimding
the orifices of the pulmonary artery and aorta, present a smooth
ventricular border, attached to the muscular substance of
the ventricles ; and a deeply-notched arterial border, with
which the pouches of Valsalva are connected. When the
heart of an animal is boiled, so as to harden its muscular, and
to gelatinise its fibrous, portions, the auricles and great blood-
vessels may be easily separated fi’om the ventricles; three
apertures only are then seen in the muscular substance of the
base of the ventricles ; viz. one for the left auriculo-ventricular
opening, another for the orifice of the pulmonary artery, and a
third, the largest, common to the left auriculo-ventricular
opening and the aortic orifice ; for the fibrous rings around
these two latter are conjoined at one point. Behind the aortic
orifice, and between the two aiuiculo-ventricular openings, is
a piece of fibro-cartilage, which, when ossified, forms the hone
o f the heart.

The heart, though an involuntary muscle, has dark red
fibres, marked with transverse stria?, like those of the voluntary
muscles; but they differ, in being often branched and joined
together again, and in having their fasciculi interlaced ; more-
over, the fibres are somewhat smaller, less distinctly striated,
sometimes marked by faint longitudinal streaks, and, for the
most part, are not attached to tendinous structures : the sar-
colemma of each fibre is not easily seen, excepting in fatty
degeneration of the fibres. There is scarcely any areolar
tissue between the fibres, hence the characteristic firmness oi’
the contracted heart.

The arrangement of the muscular fibres of the heart, is
one of the most difiicnlt subjects of investigation. Vesalius,
Albinus, and even Haller, were unable to follow them ; and

FIBKES OF THE VENTRICLES.

197

very difFerent and complicated descriptions of the fibres have
been given by Lower, Winslow, Senac, Wolff, Gerdy, Drmcan,
Reid, Budge, and, more recently, by Pettigi-ew.

Alter long boiling or maceration in pure alcohol, the fibres
of the auricles, but especially those of the ventricles, may
be stripped off, and unwound in flat bands or layers. The
auricular and ventricular fibres are quite independent, the
auriculo-ventricular fibrous rings, with the pericardium and
endocardium, forming the sole bond of union betAveen them.

The fibres of the auricles, consist of a superficial and deep
layer. The superficial layer is thin, incomplete, and common
to both auricles ; its fibres are transverse, and chiefly found
oil the front of the auricles ; a few enter the septum. Tlie
deep layer consists of looped and annular fibres proper to each
auricle ; the locped fibres are fixed, by both ends, to the cor-
responding fibrous ring, and pass, in various directions, over the
surface of the auricle ; the annidar fibres embrace the auri-
cular appendages, and also surround the large venous open-
ings in each auricle, extending both over the auricle and the
veins.

The fibres of the ventricles, first studied by Lower (1669),
present a far more complex arrangement. They present
numerous, and somewhat easily separable, layers, having a
general spiral arrangement around those cavities. The super-
ficial fibres pass, more or less obliquely, dowiiAvards from right
to left, on the front of the ventricles, and, in the opposite
direction, i.e. upivards from right to left, at the back of the
ventricles. A fetv of these fibres are almost vertical. On the pos-
terior or under surface of the heart, many of the superficial fibres
are common to both ventricles, pa.ssing from one to the other,
over the line of the septum, the surface being flattened, and
the two ventricles blended together. On the upper surface, or
in front, however, a great number of the superficial fibres dip
in at the line of the septum, decussating with each other, so
that the ventricles are here more distinct ; nevertheless, some
of these fibres pass from one ventricle to the other. Wlien
these are removed, the deeper fibres are found to be chiefly
proper to each ventricle ; so that, as said by Winslow, the
ventricular portion of the heart seems to be composed of .two
hearts, enveloped in a third. As the fibres become deeper,
they are less and less oblique, until, at last, they are nearly
transverse, excepting such as ascend on the inside of the
ventricles. According to their mode of dissection, difl'erent

198

SPECIAL PHYSIOLOGY.

anatomists make different numbers of layers, and some divide
these into numerous component bands. According to Petti-
grew, the latest authority, there are seven layers, three outer
ones, the fibres of which become successively less and less
oblique downwards from right to left, a central transverse
layer, and three inner ones, the fibres of which become more
and more oblique in the opposite direction.

The ventricular fibres, whether superficial or deep, have
long been known to form spirals, at and near the apex of the
heart, the superficial fibres forming a completely closed spiral,
and each succeeding layer a more open one. Hence, on look-
ing directly at the apex of the heart, a remarkable whorl, or
vortex, of fibres is seen, in which these appear, in turn, to sinlc
towards the interior of the ventricles ; if the fibres of each
layer be now raised up and removed, the vortex becomes
more and more open, and at length the cavities of the ven-
tricles are exposed.

It was believed by Lower, Gerdy, Eeid, and other anato-
mists, that the ventricular fibres chiefly, if not entirely, arise
from the auriculo-veuti'icular fibrous rings, and that, after pass-
ing spirally round the heart, they turn upon themselves at the
apex, there forming, as indicated especially by Lower and Gerdy,
twisted continuous loops, and then pass up directly through
the walls or septum of the ventricles, back to the fibrous rings
again, or reach them indirectly, through the musculi papil-
laresand chords tendineai of the tricuspid and bicuspid valves.
In short, the fibres of the ventricles were described as forming
loops, open towards the base of the heart, but closed, and
twisted into a vortex, at the apex. However, according to
Duncan, the fibres form loops in the direction of the base, as
well as in that of the apex ; and Pettigrew affirms that none,
or almost none, are attached to the fibrous rings, but pass by
them, in the form of loops. Moreover, the elaborate dissec-
tions of the last-named anatomist, show, that just as, at the apex,
the superficial fibres penetrate, to become, as has been long
known, the deep-seated fibres, so, at the base, the superficial
fibres are likewise continuous with the deepest fibres.

In the left ventricle, which Pettigrew regards as the typical
ventricle, the first, or superficial layer, passes, both at the
apex and base, into the innermost or seventh layer, the second
into the sixth, and the third into the fifth ; the foitrth layer is
central, and forms a transverse layer situated between the
third and the fifth. Each successive double layer encloses the

BLOODVESSELS OF THE IIEAKT.

199

next in order, and the necessary limitation of the central layer,
and its absence at the apex and base, account lor the greater
thickness of the walls of the left ventricle, across its middle.
The spiral fibres, which may be traced from the front of the
auriculo-ventricular opening, pass over the anterior surface of
the ventricle, and, alter describing one turn and a half, dip into
the apex posteriorly ; whilst those coming from the back of
that opening, pass over the hinder surface of the ventricle,
wind forward, and enter the apex anteriorly ; after dipping
inwards, the former end in the anterior musculi papillares
and column£e carnese, and the latter, in the posterior musculi
papillares and column® came®. The spiral and interwoven
arrangement of all these layers, must assist the powerful and
simultaneous contraction of the ventricular w'alls, and may
perhaps explain the rotatory movement of the heart during
each beat, to be hereafter noticed.

The structure of the right ventricle is similar, but less
complete. Internal to the fourth layer, the fibres of the one
ventricle are altogether independent of those of the other.
The layers of the right ventricle, are continued into each
other, not at the apex only, as in the case of the left ventricle,
but also along the whole length of the septum. The right ven-
tricle is regarded, by Pettigrew, as a sort of segment of the
left one, and he refers to the shape and perfection of structure
of the latter, and also to the position, and the mode of develop-
ment, of the septum, from a protrusion of the anterior wall of
the single ventricle of the primitive heart, as according with
this view.

The ventricular fibres, in the hearts of the Mammalia generally, seem
to be arranged on the same plan as that of the human heart ; and a cor-
respondence is observed in the di.sposition of these fibres in the Bird,
Reptile, and Fish.

The nutrient arteries of the heart, are the two coronarij
arleries, the first branches given off from the aorta ; they
arise just beyond the semilunar valves, wind round the
auriculo-ventricular groove, and give off two chief branches
which run along the furrows between the ventricles. The
cardiac veins end chiefly in a .short trunk, named the cardiac
sinus, which opens into the back of the right auricle, and is
I)rotected by the valve of Thebesius, already deseribed ; this
sinus is interesting, as being the persistent portion of the lower
end of the left descending vena cava of the early embryo, the
remainder of which closes from the root of the neck down to this

200

SPECIAL PHYSIOLOGY.

sinus, leaving only certain vestiges behind. Numerous small
cardiac veins enter the right auricle by separate openings. It
has been supposed by some, that the blood may pass directly
from the cavities into interstices in the tissue of the heart,
and this appears to be the case in the heart of the frog and ol’
certain Fishes, in which only one ventricle exists, containing a
uniform fluid ; but this could hardly occur in the hearts of the
warm-blooded Birds and Mammalia, in which there are two
separate ventricles, one containing dark or impure blood. In
these, ample provision exists, in proper arteries, capillaries,
and veins, for a special nutrient circulation. The lymphatics
are superficial (fig. 101) and deep. The nerves of the heart
are derived, on each side, from the pneumogastric nerves, and
from the symjDathetic system. The former give off cardiac
branches fl-om their trunks, and also from their recurrent laryn-
geal branches; whilst the latter give off sympathetic cardiac
branches from the cervical ganglia. The phrenic nerves send
offsets to the pericardium, and possibly a few fibres to tlie
heart itself. The sympathetic and pneumogastric branches
unite to form the cardiac plexuses, from which small plexuses
and branches proceed along the coronary arteries. Certain
important ganglia exist upon the heart ; the ganglion of
Wrisherg lies beneath the arch of the aorta, and in animals,
as in the calf and frog (Remak), others are found about the
base of the ventricles. In the course of the cardiac nerves,
certain enlargements have been described as microscopic
ganglia (Leej ; but, according to other anatomi.sts, these are
thickenings of the sheaths of the nerves. The lining mem-
brane of the sinus of the right ventricle, is most abundantly
supplied with nerves.

Course and Causes of the Circulation.

In moving through the human body, the blood takes the,
following definite twofold course, the circulation in Man, like the
heart itself, being double. Proceeding from the left side of the
heart through the aorta (fig. 108, 9, 9), and its various branches
called the systemic arteries, the blood is distributed to every
part of the fi-ame, reaching the capillary vessels throughout
the body generally ; from these capillaries, it pas.ses into the
minute venules, and, collected into larger and larger veins, 1,
2, finds its way back to the right side of the heart, 3, 4 : this
part of the circulation is called the greater or syste7iiic circula-

COURSE OF THE BLOOD.

201

tion. From the right side of the heart, 3, 4, the blood issues
through X\iQpuhnonarn artery, 5, and by its brandies is conveyed
to the lungs, passes through the pulmonary capillaries, is col-
lected by the pulmonary veins, 6, and so returns once more
to the lell side of the heart, 7, 8 : this part of the circulation,
is called the lesser or pulmonary circulation. In the systemic
circulation, therefore, the blood leaves the left side of the
heart, and returns to the right side ; in the pulmonary circula-
tion, the blood leaves the right side and returns to the left.
'I'he left side of this organ, is sometimes called the systemic,
and the right side the pulmonary, heart. The greater circula-
tion being performed through the body generally, and the
lesser circulation through the lungs, the two are continuous, at
the heart, with each other, a given portion of blood passing
first through the one, then through the other, afterwards
through the former again, and so on. The portal circulation,
already described (p. 68), is a special offset of the systemic
circulation.

The history of the discovery of the Circulation, affords a good
illustration of the slow and laboured steps, by which man arrives
at true knowledge. By Hippocrates, 400 b.c., the veins and
arteries were confounded under one name, (pXeijig, phlebes, the
word, artery, being applied by him to the trachea or windpipe.
Aristotle distinguished the arteries from the veins, and noticed
that the fonner were usually found empty of blood, contain-
ing only air : the heart, however, was known by him to be in
connection with the veins, and these were suppo.sed to convey
the blood into the body. Galen tvas the first to maintain that
the arteries contained blood as well as air. Vesalius pointed
out that the two sides of the heart have no direct communica-
tion. Servetus demonstrated the passage of the blood through
the lungs. The term ‘ circulation ’ first occurs in the writings
of Cffisalpinus, who had access to a treatise by Servetus. At
length, in 1628, William Harvey published, in his work, ‘He
motu cordis et sanguinis ’ — on the motion of the heart and
blood — an account of his great discovery, or demonstration of
the real course of the blood, or of the Circulation. He founded
his conclu.sions, fir.st, on the anatomical connections and con-
tinuity of the heart, arteries, and veins; secondly, on the facts,
that on dividing an artery, blood issues from that end which
is still connected with the licart, whilst on dividing a vein, the
blood comes from the end furthest from the heart ; thirdly, on
the fact that a vein, when tied, swells on the side of the liga-

202

SPECIAL PHYSIOLOGY.

ture furthest from the heart; and lastly, on the direction of
the valves in the veins, and of those situated in the heart itself.
Afterwards, the mode in which the blood passes from the

Pip. 108. Diagram of the cavities on the two sides of the heart, to show
the course of the blood through it. 1, Vena cava superior ; 2, vena cava
inferior; 3, right auricle ; 4, right ventricle ; 5, pulmonary artery ; 6, 6,
pulmonary veins, right and left ; 7, left auricle ; 8, left ventricle ; 9.
aorta ; 10, hepatic veins. The dark parts are those which contain venous
blood ; the light parts contain arterial blood. The arrows indicate the
course of the blood within the heart, and tlirough the lungs and the
body. Thus, the dark blood returns from the upper half of the body
by the superior vena cava, 1, and from the lower half of the body by the
inferior vena cava, 2, joined by the hepatic veins, 10 ; it enters the right
auricle, 3, passes into the right ventricle, 4, and then through the pul-
monary ai'tery, 5, and it branches through the capillaries of both lungs.
Here, it is changed into red blood; gathered then into the pulmonary
veins, 6. 6, it enters the left auricle, 7, passes into the left ventricle, 8,
and thence through the aorta, 9, and its branches, into the capillaries of
all parts of the body. Here it again becomes dark, and is once more
returned by the venm cavce, 1, 2, to the right side of the heart. It is
seen that the right and left sides of the heart do not communicate. The
one always contains dark, the other red blood.

arteries into the veins, not quite understood by Harvey, was?
explained by Malpighi’s discovery of the capillary vessels, ini
the frotr’s foot, in 1061.

Fig. 108.

•I

ACTION OF THE HEART.

203

The proofs of the circulation of the blood, now usually ad-
vanced, are identical with those just mentioned, viz. the
anatomical connection and continuity of the heart, arteries,
capillaries, and veins ; the different direction in which the blood
escapes from a cut artery and a cut vein ; the effect of ligature
upon the veins ; the special direction of the valves of the
heart and veins ; and lastly, the actual observation of the
blood moving in the capillary vessels of the transparent parts
of animals, such as the translucent bodies of the larvte, or
young, of Amphibia and Fishes, the gills of the tadpole, the
web of the frog’s foot, the mesentery of the mouse, the wing
of the bat, and even the retinre of our own eyes.

The chief cause of the motion of the blood, is the con-
traction of the muscular walls of the heart upon its fluid
contents. But the movement of the blood, is modified by
the elasticity and muscular contractility of the coats of the
arteries; it is aided by the pressure of the muscles of the
body upon the veins, and likewise, to a certain degree, by the
movements of the walls of the chest in respiration. Perhaps
also the changes incidental to nutrition, secretion, excretion,
and respiration, which occur in the blood, in the systemic and
pulmonary capillaries, may influence its motion through them.
The direction of the blood-current, is primarily determined by
the valves within the heart, and is aided by those within the
veins.

Action of the Heart.

The heart, the great agent concerned in the circulation,
propels the blood from its interior, into the body and lungs, by
means of successive contractions of its ventricular walls. The
contractility of its muscular tissue, is the immediate source of
the motor power which impels the blood through the body.
The suspension of the heart within the smooth pericardium,
facilitates its movements; whilst the equally smooth endo-
cardium diminishes the friction of the blood against the walls
of its cavities. The heart has been likened to a force-pump,
but this is a rude comparison ; for a pump is a passive appara-
tus, through which some extrinsic force operates ; whereas the
heart, alternately dilating and contracting, first receives the
blood from the veins, and then drives it into the arteries, by
means of a force resident in its own walls. In this action,
the right and left auricles dilate and contract together ; and
the right and left ventricles also dilate and contract together.

204

SPECIAL PHYSIOLOGY.

The contraction of the two ventricles, always takes place im- ]
mediately after that of the two auricles ; and when theventricles
have contracted, an interval, or pause, occurs, before another
contraction of the aui'icles takes place, and during this pause,
both sets of cavities are gradually dilating. The contraction
of the auricles and ventricles, is named their systole, whilst
their dilatation is called their diastole ; the order of the suc-
cessive dilatation and contraction of these parts, was compared
by Harvey to the successive movements of deglutition. Thus,
when the auricles are dilating, they receive blood from their
respective veins, and when they contract, they force the blood
into the ventricles, which are then dilating to receive it ; Avhen
the ventricles are filled, they in turn contract, and propel the
blood into the great arteries. But the right auricle receives
the blood from the body generally, and the right ventricle
propels it into the lungs ; whilst, of the left cavities of the
heart, parted off completely from the corresponding cavities of '
the right side, the left auricle receives the blood from the
lungs, and the left ventricle propels it into the body. As the
auricles merely propel the blood into the ventricles, their
walls are comparatively thin, whilst the thicker walled ventri-
cles have relation to the greater work they have to perform.
The proportionately greater thickness of the walls of the left
ventricle, and the greater strength of the mitral and aortic
semilunar valves, as compared with the tricuspid and pulmo-
nary semilunar valves on the right side of the heart, have
relerence to the greater force needed to distribute the blood
through the body, than through the lungs.

On tracing the course of the blood, through the body and the
fom- cavities of the heart, it is foimd that, proceeding from the
left ventricle (fig. 108, 8), the blood passes, through the aorta
and arterial system, into the capillaries of the whole body, and
thence back by the systemic veins, l, 2, into the right amdcle,

.3 ; from the right auricle it passes into the right ventricle, 4,
and thence proceeds through the pulmonary ai-teries, 5, capil-
laries, and veins, 6, 6, of the lungs, into the left auricle, 7, £
from which it passes into the left ventricle, 8, and thence is '■
propelled, as before, through the aorta, 9, into the arteries ofl'B
the body. I

The mechanism and details of these movements, are very*
complex. As the auricles dilate, the blood enters and dis--B
tends them, that filling the right auricle, coming from the two fr
vence cavse and the nutrient veins of the heart itself, that filling.B

MOVEMENTS OF THE HEART.

2C5

the lelt auricle, from the four pulmonary veins. As the auricles
are filling, some of the blood passes through them, into the
corresponding ventricles, but the instant the auricles are fully
distended, they contract, and discharge nearly the whole of
their contents into the ventricles, which, at this period, are
dilating to receive the blood. The backward flow of the blood
from the auricles into the veins, is checked, more or less com-
pletely, by the contraction of the muscular fibres suiToitnding the
orifices of the vente cavte and pidmonary veins, and, as regards
the right auricle, by the Eustachian and Thebesian valves, at
the mouths of the inferior vena cava and cardiac sinu.s, and bv
those in the great veins at the root of the neck. The blood passes
from the auricles into the ventricles, through the right and left
auriculo-ventricular openings; the tricuspid and mitral valves,
placed respectively at those openings, having the fi-ee borders
of their segments directed towards the ventricles, offer no
opposition to this movement of the blood ; but the gradual
filling of the ventricles, and especially their complete disten-
sion, are accompanied by a closure of the segments of the
valves, the blood getting behind them, or between them and
the walls of the distended ventricles. The ventricles now
contract, and propel the blood into the great arterial trunks
proceeding from them, i. e. the right ventricle into the pulmo-
nary artery, and through the lungs, and the left ventricle into
the aorta, and through the body. The reflux of the blood
towards the respective auricles, is now prevented by the
sudden closure of the tricuspid and mitral valves, the seg-
ments of which are, moreover, prevented from being forced
back into the auricles, by the chorda? tendinea? respectively
attached to them. The blood, driven from the ventricles into
the pulmonary artery and the aorta, opens the segments of
the semilunar valves situated at the commencement of each
of those vessels, and displaces onwards the column of blood
contained within them, which, however, is not cjuite stationary.
Four effects ensue : first, a vibratory impulse to the blood
columns in the pulmonary artery and aorta, and in their
branches ; secondly, an increased velocity of the blood column ;
thirdly, an increa.sed pressure within the arteries; and,
fourthly, owing to the resistance offered by the blood in
front, a distension of the elastic walls of the arteries them-
selves. But the ventricles, having contracted, after a short
pause begin to dilate again, and then the columns of blood
in the two great arteries, reacted upon by the recoil of the

206

SrECIAL PirYSIOLOGY.

distended and elongated coats of those vessels, would flow back
towards the ventricles, if the segments of the semilunar
valves did not speedily open out across the mouths of those
vessels. The blood first getting into the pouches, or sinuses,
of Valsalva behind the valves, an action which is facilitated
by the projecting corpora Arantii, then presses on the whole
arterial surface of the segments, and so regurgitation into the
ventricles is prevented. The force which thus acts upon the
two columns of blood, to close the semilunar valve.s, is the re-
silience of the coats of the previously distended arteries ; but it
is itself derived from the heart’s action, ■which has caused dis-
tension of the vessels. As the muscular walls of the ventricles
relax, and their cavities dilate, the tricuspid and mitral valves
reopen, and blood passing from the auricles, begins to All
them again. In the meantime, the auricles themselves have
been dilating to the point of distension, and again, at that
moment, the actions of the heart necessaiy to the circulation
recommence, viz., the rapid conti’action of the auricles, the
complete distension of the ventricles, and the sudden con-
traction of these cavities.

A complete action of the heart, consists of a single systole
and diastole of its auricles and ventricles. The period occu-
pied in such an action, commences with the systole of the auri-
cles, includes the systole of the ventricles, and terminates at
the perfect diastole of the auricles, Avhen these cavities are
fully distended, and ready to perform their systole again.
During this period of a complete cardiac act, the auricles con-
tract quickly, whilst the ventricles contract a little mm-e slowly ;
but the auricles dilate slowl^q whilst the /ventricles dilate
more quickly. Hence, (see the Table at p. 212,) the systole
and diastole of the two sets of cavities, occupy different
parts of the entire period of a single cardiac action or beat.

The diastole of both the auricles and ventricles, has been
supposed to depend on an active contraction of particular sets
of their muscular fibres ; but it is now generally regarded as
a passive phenomenon of dilatation, dependent on the rest or
relaxation of all their fibres.

The systole of the auricles, consists of a progressive contrac-
tion, which spreads from the orifices of the great veins towards <1
the auriculo-ventricular openings, the auricidar appendices il
acting last; the auricles, therefore, contract towards the base J
of the ventricles. The .systole of the ventricles is not only I
.somewhat slower, but is more imiibrm than that of the auricles, ,|

ACTION OF THE VALVES.

207

being simultaneous through every part of their walls, the total
result being likewise to draw them towards their base, i.e. to-
wards the orifices of the great arterial trunks. By this action, the
ventricular portion of the heart is shortened, rendered thicker
from back to front, and more convex on its anterior surface ;
it is also widened a little posteriorly (Budge) ; at the same time,
it becomes very firm and hard, like any other contracted mus-
cular mass. Owing to the elongation of the great arterial
trunks, at the moment of their distension by the blood, the
base of the heart descends within the thorax ; moreover, the
apex is tilted upwards, and lifted a little towards the left ;
whilst the entire heart, owing, perhaps, to the obliquity of its
muscular bands, rotates slightly on its axis, and undergoes a
screw-like motion to the right. The base of the heart appears
to move to a greater extent than the apex, because the down-
ward movement of the entire heart lessens the change of posi-
tion upwards, caused by the contraction of the ventricles.
Some even maintain that the apex is moA’-ed a little down-
Avards and to the left.

These changes in the form and position of the heart, bring
its anterior surface, a little above the apex, up to the walls of
the chest, the pericardium, hoAvever, intervening, and pro-
duce a slight concussion against them. This, well knoAvn as
the impulse of the heart, is felt most distinctly opposite a point
a little beloAv the middle of the ventricles, betAveen the fifth
and sixth ribs of the left side, 2 inches from the sternum.
The impulse coincides with the systole of the ventricles.

The auriculo-ventricular valves, and the semilunar valves,
are open and shut alternately at different moments of the
heart’s action ; for the auriculo-ventricular valves are open,
and the semilunar valves closed, during the diastole of the
ventricles ; Avhilst the former are shut, and the latter open,
during the systole of those cavities. Their joint action is
remarkable, for they determine, like the Auilves of a force-
pump, the direction of the blood through the tAvo sides of the
heart, and lienee the course of the circulation generally. The
segments of the auriculo-ventricular valves, connected by the
chordse tendinea; Avith the sides, or with the musculi papil-
lares, of the corresponding ventricles, are first opened by the
torrent of blood rushing from the auricle into the Amotricle; then
they are gradually raised from the sides of the ventricle, and
suddenly closed, as is now generally maintained, by the action
of the blood itself, during the ventricular diastole ; although

208

SPECIAL PHYSIOLOGY.

Haller, from observations on a living animal, believed that
their closure was in part due to the action of the papillary
muscles. Immediately the ventricles begin to contract, so
as to change the form and size of the cavities and auriculo-
ventricular orifices, and press forcibly upon the contained
blood, the valve-segnients, as already stated, are prevented
irom being driven back into the auricle, by the chorda3 tendi-
nea;, which are kept tense by the musculi papillares contract-
ing simultaneously with the walls of the ventricles. Were it
not for the existence of the papillary muscles, the chordte ten-
dinea3 would be relaxed, and the segments of the valves would
be more or less forced into the auricular cavities. The tricuspid
valve is said to close less perfectly than the mitral (Himter) ;
thus a certain quantity of blood is driven back into the right
auricle, and also beyond it, upon the blood in the great veins,
producing a slight regurgitant flow, as far as the valves of the
jugular veins, and causing a venous pulse, synchronous with
the pulse in the carotid arteries. The reflux thus permitted
from the right ventricle, is probably important, preventing the
over-distension of that cavity by any temporary obstruction
to the circulation through the lungs, from muscular eflbrt, or
cold ; it has been found experimentally, that when the heart is
forcibly distended, its pulsations are immediately arrested, a
condition which is thus guarded against. It is certain that
the quantity of blood delivered by the right auricle into
the right ventricle, is subject to variation ; whilst that pro-
pelled from the left auricle into the left ventricle, is probably
uniform ; on that side of the heart, the mitral valves close
accurately, and no regurgitation takes place. Vierordt, how-
ever, doubts the normal occurrence of any reflux, even on the
right side, because no such regurgitation takes place during
the auricular systole, nor yet any backward pressm-e in the
venous trunks.

The semilunar valves at the orifices of the pulmonary artery
and aorta, have no chorda; tendinea;, but they meet accurately
across the orifices of those vessels, the little corpora Arantii
assisting in the complete closure of the three segments in the
centre. These valves, opened by the blood projected firom the
ventricles, would be closely applied to the walls of the arteries,
were it not for the presence of the pouches of Valsalva behind
them ; but the blood retained in those pouches, facilitates the
separation of the valves from the sides of the vessels, and their
subsequent opening out across those vessels, by the pressure of

SOUNDS OF THE HEART.

209

the blood acted upon by the distended and resilient arteries.
The shock of the columns of blood in the arteries, is sustained
mainly by the stronger and more tendinous part of the valves,
their thinner marginal lunules, being applied against each
other, so as to form three lines radiating from the centre of
the vessel between the contiguous borders of the valves. The
greater the resilient force of the arteries, the more accurate
and close is the apposition of the valves.

The closure of the auriculo-ventricular and the semi-limar
valves, is necessarily accompanied by a tightening out of
their respective segments ; this is the chief cause of certain
•sounds, which, on listening over the region of the heart, are
heard, at stated intervals, in the period of each single cardiac
beat. The.se sounds of the heart are tivo in number, in
each beat. They are audible to the ear placed on the thorax ;
but they are commonly examined by the tubular instrument,
named the stethoscope. In certain circumstances, they may
be heard by the individual himself. The two sounds occur
in quick succession, after which there is a period of silence,
often named the pause. The first sound is deep, dull, and
long ; the second is higher in tone, sharp, and short. The first
closely precedes the pulse at the wrist, and coincides nearly
with the impidse of the heart ; the second follows immediately
after the pulse. Supposing the entire period of the heart’s
beat, to be divided into eight equal parts, the first sound and
the brief period which elapses between it and the second, have
been said to occupy four parts ; the second sound, to take rather
le.ss than two ; and the silent interval, or pause, between it
and the recurrence of the first sound of the next beat, to
occupy rather more than two parts (Laennec) ; hence the period
of the sounds would be to the period of silence, as 3 to 1. But
the proportions have been perhaps more correctly, stated to be
2 to 1 (Williams), or nearly 1 to 1. (Volckmann.)

From observations on living animals, it has been found that
the first sound coincides with the systole of the ventricles, the
closure of the auriculo-ventricular valves, the opening of the
semilunar valves, and the entrance of the blood into the great
arteries. At this period, the auricles are beginning to dilate.
Moreover, the first sound is speedily followed by the pulse,
that in the lacial artery occurring about ■jVth of a second, and
that in the radial artery at the wrist ^th of a second, after-
wards. The second sound coincides with the closure of the
semilunar valves, and the opening of the auriculo-ventricular
VOL. u. !•

\

210

SPECIAL PHYSIOLOGY.

valves; whilst, at this period, the ventricles begin to dilate,
and the auricles continue their already commenced diastole.
The pause of silence, which succeeds to the second sound,
coincides with the full dilatation, and the subsequent contrac-
tion, of the auricle, and also with the completed dilatation of
the ventricles ; during this pause, the semilunar valves are
closed, and the auriculo-ventricular valves are open.

The causes of the heart’s sounds, have been very closely
investigated, owing to the changes which they undergo in
disease, and to the peculiai’ity of the sounds which are then
developed. The Jb'st sound is usually referred to the closure
of the auriculo-ventricular Amlves, either, directly and solely, as
being dependent on the sudden tension of their segments, or,
partially and indirectly, as due also to the muscular sound
of the contracting ventricular walls, the sudden passage of the
blood into the great arterial trunks, and the imjDulse of the
heart itself against the side of the chest. Unless these valves
were closed, the walls of the ventricles would not act so
forcibly as they do; neither would the blood rush into the
great arteries, nor Avould the impulse of the heart be so
decided. Whilst, therefore, as is commonly believed, the
tension and vibration of the tissue of the closed auriculo-
ventricular valves may be really the chief cause of this sound,
yet the three other accessory causes, viz. the muscular sound
of the ventricles, the sound of the moving blood, and its
friction against the orifices of the arteries, and, lastly, the
impulse of the heart against the chest, may contribute to the
production of the sound as actually heard. But the importance
of these causes has probably been overrated. That the muscular
sound is not essential, is shown by the fact, ascertained experi-
mentally, that the sounds are not heard, if the great veins
be compressed, so that no blood enters the heart, although its
contractions may continue ; the production of any sound by
the internal movement of the blood, or its rushing through
the ai'terial openings, is doubtful; and ordinary muscular con-
traction does not give rise to any loud or sudden sound. The
cause of the second sound appears to be better determined ; it
is attributed almost entirely to the tension of the suddenly
closed semilunar valves, across the orih'ces of the aorta and
pulmonary artery. The tension of the membranous substiince
of the valves, is sufficient to cause a loud sound ; but, by
many authorities, the collision of the columns of blood in the
great arteries, against themselves, and against the valves,

SOUNDS OF THE HEART.

211

SO as to produce that tension, is regarded as a conjoint
cause of the actual sound heard in the heart. When, in
living animals, one segment of each of these valves, is held
back by a hooked needle, so that it cannot close, the second
sound of the heart ceases. This sound has also been imitated
in dead animals, by injecting fluid into the aorta, against the
valves. The occurrence of changes in, and the occasional
cessation of, the second sound, in cases of disease of the semi-
lunar valves, also favour this explanation ; so, likewise, does
the fact that the second sound is so short, and occurs at the
instant of the tightening out of these valves, and not during
their subsequent and quiet closure. Lastly, there is no other
simulteneous condition, or action, of any part of the heart
which could produce a sound ; the ventricles and auricles are,
at this time, both quietly dilating, and the resilience of the
great arterial trunks, forcing the blood back upon the semi-
lunar valves, is the only mechanical action then capable of
causing a sound.

The contraction of the auricles, which occurs in the latter
part of the pause in the heart’s beat, produces no audible
sound, unless the heart be exposed, and the stethoscope be
placed upon it.

It is usually held to be confirmatory of the preceding views,
as to the causes of the two sounds of the heart, that the first
sound is more distinctly heard opposite the fifth intercostal
space of the left side, below the left nipple, i.e. over the region
of the apex of the ventricles, where these approach nearest to
the walls of the chest, to which they communicate the sound ;
whilst the second sound is heard most clearly in the third lelt
intercostal space, close to the sternum, i.e. over the base of the
ventricles, and the commencement of the great arteries, where
these approach nearest to the thoracic walls.

The difference in the pitch and character of the two sounds,
is partly explicable thus : the deep and dull tone of the first
sound, may depend on the greater size and deeper position of
the auriculo-ventricular valves, on their thicker attachments,
and on the quantity of muscular substance which overlies them ;
the higlier and sharper tone of the second sound, may be con-
nected with the thinner structure and attachments, and with
the less covered position of the semilunar valves.

The following Table shows the order and duration of the
complicated actions of the different parts of the heart during
each complete beat, and also their relations, in point of time,

a 2

Sounc?s and Movcmmts of the Heart.

212

SPECIAL PHYSIOLOGY.

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'TJ

o

p

CArACITT OF THE HEART.

213

to the two sounds of the heart, to the subsequent pause or
interval of silence, and to the occurrence ol' the pulse at the
wrist. The diiration of the events is given after Laennec.

It is seen that the first sound occupies ^ of the entire beat,
the second nearly ^ of the beat, and the period of silence
rather more than the remaining The Table likewise ex-
hibits the alternation of the systole and diastole of the auricles
and ventricles, as well as the relative duration of their respec-
tive systolic and diastolic conditions. Thus the rapid systole
of the auricles, occupies only .^th of the whole period, and their
diastole |ths ; whilst the slower systole of the ventricles occu-
pies J-, and their diastole the other ^ of tlie whole period or
beat. According to Vierordt, the period of diastole of the
auricle, is really shorter, being only f ths or .^ths of the whole
period ; the remaining ^ths or |^ths of that time, usually
regarded as the period of diastole, must, in that case, be viewed
as representing a distended, or continued dilated, condition of
the auricle. In the Table, the systole of the auricles and
ventricles together, is seen to occupy -|ths, and the interval
between the contraction of the ventricles and the commence-
ment of the next beat, .|ths of the whole period. According
to Cheveau, however, the A'entricular systole in the horse,
occupies only a little more than Ttn of the entire beat ; San-
derson’s researches coincide with this statement as to the great
rapidity of that event.

At each beat of the heart, the ventricles are supposed to be
almost completely, if not entirely, emptied ; the left ventricle
is often found in that state after death, especially if examined
during the period of the rigor mortis. On a section, the walls
of that ventricle are then seen to be so thick, from their contrac-
tion,as tohave been frequently described asbeing hypertrophied.
Although the right ventricle, as already mentioned, allows a
little blood to escape back into its corresponding auricle, yet
both ventricles are supposed to throw practically, equal quan-
tities of blood ; for, unless this were so, the left ventricle
would receive either too little or too much blood from the
synchronous action of the right ventricle, the quantity of water
lost, as vapour, from the blood, in its course from one ventricle
to the other, through the lungs, being insignificant, amounting
to less than ^th of a grain, during each beat of the heart. The
quantity of blood thrown at each .sy.stole, by the ventricles, was
formerly said to be, in the adult, about 4 oz., which was
described as the normal capacity of each of those cavities ;

214

SPECIAL PHTSIOLOGV.

but the most recent researches have led to higher estimates,
viz. 5'3 oz. (Valentin), 6'2 oz. (Volkmann), and even G'3 oz.
(Vierordt.) Positive mea.surements are impossible ; the results
obtained, rest on various calculations in haemadynamics, to be
hereafter mentioned. The capacity of the auricles is said to be
rather less than that of the ventricles, but the quantity of
blood Avhich they contain, is sufficient to distend the ventricles,
as these are partly filled by blood flowing through the auricles
into them, before the occurrence of the auricular systole.

The fo7'ce of the aui'icular contractions cannot be measured.
Prom observations on the blood-pressure in the arteries., the
force of the left ventricle, is estimated to be equal to about
^t^th part of the weight of the entire body ; whilst that of the
7’iglit ventricle, is supposed to be less than half that force.
The difference in the average thickness of the walls of the tAvo
ventricles, Avhich is about as 3 to 1, affords one ground for
estimating the difference in their power.

The dilatation of all the cavities of the heart, is, at least
chiefly, an intrinsic or spontaneous act, and not simply a
passive distension, caused by the blood flowing from the veins
into the auricles, or by that forced by the auricles into the
A'entricles ; for when the heart of an anijnal is removed from
the body, or even when its auricles are separated from the
ventricles, both sets of cavities not only contract, but dilate.
In neither of these conditions, how'ever, does any internal
pressure, or dilating force, act upon their interior, like the
blood in the living state ; the cavities of the heart mu.st
therefore dilate spontaneously, OAAung, as already mentioned,
to the relaxation of their previously contracted muscular walls.
This dilatation assists the entrance of blood into them, by
diminishing the resistance to the passage of that fluid ; it
thus saves the Avaste Avhich Avould occur in the employment
of a special dilating force.

The heart in Man, as obserA'ed in the case of beheaded
criminals, beats only a feAV minutes after their e.xecution ; this
is also true of the Avarm-blooded animals. Its contractions
continue much longer, after systemic death, in cold-blooded
and hybernating creatures. The actions of the heart become
sIoAver and irregular, ceasing last in the right auricle, the
so-called vltinmm nioriens. They are stimulated by heat, the
injection of fre.sh blood, the action of oxygen, and by galvanism;
they are arrested by carbonic acid, sulphuretted hydrogen, the
vapour of chloroform, and also, after a time, in a complete
vacuum.

RHYTHM OF THE HEART’S ACTION.

215

The beats of the heart, recurring at more or less regular
intervals, exhibit an example of so-called rhythmic action ; their
rhythm, like that of the respiratory movements, is, indeed, very
remarkable. The cause of this rhythm was, at one time, sup-
posed to be the stimulation of the inner surface of the cavities
of the heart by the blood, and it was further imagined that
some relation might exist between the special irritability of the
right side of the heart, and the qualities of the dark or venous
blood returning from the body, and also between that of the left
side of the heart, and the qualities of the red or arterial blood
entering them from the lungs. Moreover, the ventricles,
stimulated to contract by their contents, w'ere supposed, after
forcing the blood through the body and lungs resjsectively,
to accomplish the filling of the auricles; the contraction of
these, excited, in a similar manner, by their contents, was sup-
posed once more to fill the ventricles, and so on. The mus-
cular walls of the heart, undoubtedly possess great irritability,
even in a warm-blooded animal ; the inner surface of the
auricles and ventricles, is also both sensitive and excitable, and
is certainly more rapidly acted on by poisons than their outer
surface. (Henry.) But the heart, or even a separate portion
of that organ, taken from a hybernating warm-blooded, or from
any cold-blooded Vertebrate animal, may not only retain its
general irritability for days, but may continue, for a time, to
perform rhythmic contractions and dilatations, even if removed
from the body, though no blood is left in it, and though
freed fi-om the stimulus of oxygen, as when placed in a vacuum.
The frog’s heart will beat thus for twelve hours. Although,
therefore, the rhythmic motions of the heart in the living
animal, may be partly due to the stimulus of the blood enter-
ing its cavities, yet this cannot, under all circumstances, be
the cause of such rhythmic actions.

Through the pneumogastric nerves, the cerehro-spinal
nervous centres, as .shown by experiment and by observation
in disease, greatly influence the heart’s action, under some cir-
cumstances, increasing, and, under others, lowering or inhibiting
it (vol. i. p. .38!)) ; but there is no evidence of their being the
cau.se of the rhythmic character of its movements. The action
of the heart is influenced by the emotions and passions, and, ac-
cording to some, even by the will. In the celebrated case of
Colonel Townsend, recorded by Chcyne, the breath could be
held, and thus the movements of the heart could be controlled
by an act of the will. The heart is excited or de])ressed by
various diseases of the brain, as by cerebral inflammation on

216

SPECIAL PHYSIOLOGY.

the one hand, and by apoplexy on the other ; and its action is
disturbed, or even abruptly suspended, by severe injury or
destruction of the brain or spinal cord, or of these two parts of
the nervous centres together. These and other phenomena of
a similar kind are due to excitement or shock, and their effects
are often more or less ti-ansitory. The sympathetic neiwous
centres, and the cervical parts of the spinal cord with which they
are connected, also influence the movements of the heart, as is
shown by experiments, and by the effects of blows on the abdo-
men, or of other injury, or disease (vol. i. p. 391). But if the
injury, either to the cerebro-spinal' or sympathetic system, be
gradually inflicted, the heart’s movements will continue, even
although the brain and spinal cord be removed, particularly
if artificial respiration be performed. From these facts, and
especially from the circumstance that the rhythmic movements
continue after the removal of the heart, it is evident that the
regulating agent of these movements, is not in the great
nervous centres, but somewhere in, or upon, the heart itself.
It is now admitted, indeed, that the numerous sympathetic
ganglia, connected with the nerves upon the heart, are the
sources of the stimulus or force which excites the rhythmic
contractions of its muscular fibres. In the hearts of the frog
and tortoise, these ganglia are chiefly found near the junction
of the auricles and ventricles, in the neighbourhood of the
auriculo-ventricular openings. If the heart of one of these
animals, be removed from the body, and be divided longitu-
dinally into its right and left halves, the auricle and ventricle in
each half will still continue to contract and dilate rhythmically ;
if, however, the heart be divided ti-ansversely, below the base
of the ventricles, so that a larger or smaller portion of the
ventricles is detached from the rest of the heart, the auricles
and the base of the ventricles which are connected, continue
to contract rhythmically. But the separated piece of the
ventricles, no longer does so, although isolated and spreading
contractions may still be excited in it, by the application of a
mechanical or other stimulus. By yet further sections, the re-
gulating agent of the rhythmic action, is shown to be confined
to the immediate neighbourhood of the auriculo-A'entricular
orifices, or to the line of junction between the auricles and ven-
tricles, in which part the chief ganglia are found. The syn-
chronous combination of the auricular and ventricular motions
on the two sides, may be due to connections between the .several
ganglia. These local cardiac ganglia must be regarded as

FnEQDE.NCY OF THE HEAUX’s BEATS.

217

nervous centres, which originate a co-ordinate and rhyth-
mically exerted energy, stimulating the muscular fibres of the
auricles and ventricles to perform their characteristic move-
ments, in regular and periodic succession. It has been sug-
gested that these nervous centres exert, or discharge, such
energy rhythmically, or at periodic intervals, owing to a
periodicity in their nutritive processes, by which they alter-
nately accumulate and discharge the nerve force necessary to
excite the muscular substance of the heart (Paget). Why
this periodicity of nutrition occurs, is still unexplained.

It has been supposed that the condition of the blood dis-
tributed to the substance of the heart itself, may, in some way,
determine its rhythmic actions, either the presence of dark
venous blood in its capillaries directly stimulating the mus-
cular contractility (Brown-Sequard), or the absence of oxy-
gen acting in a similar manner (Radcliffe).

When the heart of a cold-blooded animal is removed, irri-
tation of any part of it, is propagated to the rest, and rhythmic
contractions are set up ; but if the heart be partially divided, the
effects of the irritation may be still conducted along muscular
parts, but not along the tendinous structures. In the entire
heart, Avhen removed, the auricular contractions always begin
at the sinus ; this fact, and also the successive actions of the
auricles and ventricles, justify the comparison of tl:^ese move-
ments, to the progressive peristaltic motions of the oesophagus
and intestines. When a ligature is applied around the
entrance of the venee cavae into the right auricle, the auricles
and ventricles remain for a time distended, but the sinus con-
tinues to contract.

frequency of the beats of the heart, as indicated by the
impulse against the left side, and by the pulse, averages, in a
healthy adult, about 70 in a minute; but in the male, it is
below, and in the female, above that number. The frequency
of the heart’s beats, and therefore of the pulse, is modified,
however, by many circumstances. It is affected by the
stature, being slower in tall, and quicker in short persons. The
influence of se.x just indicated, may possibly be due to the
accompanying difference in stature ; the difference in the sexes
ranges from 10 to 14 per minute. Age has a still more
remarkable effect. Thus the pulse is quicker before birth
than after. In infancy it is very rapid, and it gradually
diminishes in frequency as life advances. It is .said, however,
to be somewhat slower in infants under six months of age.

218

SPECIAL PHYSIOLOGY.

thiin after tliat period, and also to become quicker again
in extreme old age : —

Frequency of the Pulse at different Periods of Life.

No. of Beats per

Periods of Life Minute

before birth
At birth .

Fir.st year .

Second ,,

Third „ .

Seventh ,,

Fourteenth ,,

Adult life

Old age (above 70)

. 150

. 140 to

130

. 130 „

115

• 115 „

100

100 „

90

. 90 „

85

• 85 „

80

75 „

65

• 80 „

75

Temperament and idiosyncrasy modify the number of the
heart’s beats, which are fewer in phlegmatic, and quicker in
sanguine and nervous persons. Tlte heart beats more slowly
in sleep, and more quickly during excited states of the mind
or body ; the depressing passions lower the number of its
beats, or even aiTest its movements altogether. Disease some-
times, as in fever and inflammation, increases the frequency
of the heart’s action, or, as in compression of the brain and
in apoplexy, diminishes it. Loss of blood, when gradual and
moderate, diminishes the frequency of the heart’s beats ;
whilst sudden or excessive hemorrhage increases them. The
effect of taking food, is to accelerate the heart’s action, animal
food producing a more immediate effect, and vegetable food a
more lasting one : Avarm food acts more quickly than cold.
The effect of alcoholic and other stimulants is Avell known,
and is indicated by their title. It is alleged, that the pulse is
more accelerated after breakfast than after dinner. Absti-
nence and starvation lower its frequency, so also does the
pi'olonged use of a A-egetable diet, or the drinking copiously of
water. Muscular exertion increases the number of the heart’s
beats, an alternate contraction and relaxation <'f the muscles,
luiA'ing a greater effect than a continuoits contraction ; it also
increases the respiration. Posture, has a i-emarkable influence,
evidently dependent on the muscular effort expended in main-
taining different positions of the body ; thus, the beats of the
heart are slowest in the recumbent, somewhat quicker in the
sitting, and most freqmmt in the standing, posture. The in-
crease per minute, produced by the change from the recum-
bent to the sitting jjosition, is (!, and from the latter to the
standing posture ii more, i.c. a difference ol' 15 occurs between

FREQUENCY OF THE HEAKt’s BEATS.

219

the lying and standing positions. The effect of posture is
greater in the morning than in the evening, and it is greater
also when the pulse is quick than when it is slow, the differ-
ence resulting from the change between lying down and
standing being 9 only, when the pulse is 60, 15 when the
pulse is 80, and 27 when the pulse is already 100 (Guy). That
the increase in the heart’s beats, from change of posture, is due
to muscular effort, is shown by placing a person in the recum-
bent position on three chairs, and then removing the central
one, when the pulse immediately rises, although the horizontal
po.sition is still maintained ; whereas, in a person fastened to
a revolving board, and moved into the erect posture, without
effort of his own, no such elevation of the pulse takes place.
The frequency of the heart’s action undergoes changes coinci-
dent with the seasons, being greater in spring and summer
than in autumn or winter. The rapidity of the heart’s action,
is also influenced by the hour of the day, being always quicker
in the morning, and somewhat retarded towards evening, other
conditions as to health, food, and the state of the body being
equal ; this difference depends, doubtless, on the gradual ex-
haustion of the powers of the system during the day’s Avork,
and on the recovery of poAver by the rest obtained at night ; it
may partly explain, Avhy the pulse is more accelerated after
breakfast than after dinner. During fasting, the pulse exhibits
three periods of increased rapidity, and three periods of
descent in the tAventy-four hours ; thus, it rises from midnight
to 2 A.Ji., from 10 to 11 a.m., and from 2 to 6 p.m. ; whilst it
falls from 3 to 4 a.m., from 1 to 2 p.m., and from 6 to 8 p.ai.
The joint effect of the time of day and of food, is illustrated by
the fact that the pulse, though progressively decreasing from
tAvo hours after breakfast to from 3 to 5 in the morning,
exhibits fluctuations after each meal, so that four maximum,
and four minimum, points are noticeable daily. The difference
between the highest and lowest points, varies from fourteen to
thirty-four pulsations. The minimum points are all observed
before meals, the maximum points about two hours after-
Avards, the greatest increase being after breakfast. Ex-
ternal temperature and its concomitant effects on the body,
also influence the beats of the heart most materially, an eleva-
tion of temperature increasing, and a gradual lowering of the
temperature diminishing, their frequency, as is illu.strated by
the exciting effect of a Avarm bath, and by the influence of long
continued exposure to cold ; but tlie sudden and brief appli-

220

SPECIAL PHYSIOLOGY.

cation of cold, accelerates the beats of the heart. Elevation
above the level of the sea — in other words, a diminution of
the atmospheric pressitre — is found to increase the beats of
the heart ; thus. Dr. Frankland, whose natui-al pulse is 60,
found that after six hours’ sleep on the summit of Mont Blanc,
thus excluding the effects of recent muscular effort, his pulse
was 120 per minute; on reaching, in the descent, the so-
called Comdor, it was 108; at the Grand Mulet it was 88 ;
and at Chamounix it was 56. As one effect of high elevation,
is to increase the frequency of the respiration, in conse-
quence of the greater tenuity of the atmosphere, and, as a
relation exists between the frequency of the heart’s action and
the respiratory movements, the increased rapidity of the pulse
in elevated positions, may thus be partly explained. An in-
crease in the density of the atmosphere, such as takes place in
a submerged diving-bell, is said to lower the frequency of the
pulse, and also the movements of respiration. An increase of '
barometric pressure of ^th of the normal pressure, lowers the
pulse, on an average, ten beats per minute, whilst the respira-
tions are simultaneously lessened by two. (Vivenot.)

The normal relation between the number of respirations and
the heart’s beats, is, on an average, 1 to 4 ; in diseased con-
ditions, this ratio is often interfered with, but it is preserved in
those accelerations or retardations of the breath and pulse,
which take place in the healthy state, such as those due to exer-
cise, change of posture, food, stimulants, and emotion, or to the
opposite conditions of rest, abstinence, or depressing influences.
Thus, if the normal respirations were 16 per minute, the
pulse would be about 64 ; and if the former were increased to
18 or 20, the latter would be raised to 72 or 80. Expiration
diminishes, and inspiration increases, the frequency of the
pulse.

A certain relation appears to exist between the facility or
the difficulty of the capillary circulation, and the rapidity or
slowness of the heartls action ; and this may explain some of
the preceding phenomena. Thus, the application of cold to
the surface of the skin, limiting or checking the circulation
through the systemic capillaries, by contracting the small
arteries, is accompanied by a retardation of the heart’s beats ;
a state of repose acts, but less powerfully, in the same way.

A feeble and slow respiration, lessening the capillary circula-
tion through the lungs, has a similar effect ; so also has hold-
ing the breath. On the other hand, exercise and heat

DISEASED ACTIONS OF THE HEAET. 221

quicken the systemic capillary circulation, and also increase the
Irequency of the ventricular systoles, and so does a quickened
and active condition of the respiration. Any obstacle to
the flow of blood through the vessels, and thereby to the
action of the ventricles, appears therefore to be sympathised
with, and a reduction of the heart’s beats is the result ; whilst
the removal of such obstacle is followed, in like manner, by
the greater rapidity of the beats. Exercise, excitement, and
food, probably, also act on the heart, by producing a greater
flow of blood to that organ.

Not only the frequency, but the force of the heart’s beats,
may be modified by external or internal circumstances. This
force is increased by all those conditions which may be charac-
terised as stimulating or strengthening, such as exercise, food,
stimulants, repose, and so on; whilst depressing and weaken-
ing conditions, on the other hand, lessen its force. Stimulating
medicines, such as ammonia, ether, and alcoholic preparations,
increase the force and frequency of the heart’s beats ; whilst
sedatives, and especially digitalis, diminish their frequency, the
latter drug not lessening the force. The impulse of the heart,
generall}' proportional to the strength of the body, is affected
by various conditions ; it is least felt in the recumbent posi-
tion, on the back or on the right side, and most distinctly in
the prone position, or when lying on the left side ; in the up-
right posture it is moderately strong. The impulse of the
heart is less manifest in stout persons, but much more evident
in thin ones ; it is also more perceptible during a forcible
expiration, and less so during a powerful inspiration, because,
in the latter case, the heart is overlapped by the inflated lung,
whilst in the former, it approximates closely to the walls of
the chest. It is also increased by e.xciting causes, such as ex-
ercise, food, stimulants, and certain emotions which produce
the so-called perceptible impulses constituting palpitation of
the heart. As already mentioned, the rhythm of the heart may
be interfered with by causes acting through the nervous system,
in which case, it may even become irregular, so that successive
beats of the heart take place at unequal intervals of time, or
certain beats may altogether intermit.

Lastly, the force, rhythm, impulse, and likewise the sounds of
the heart, are variously modified by morbid conditions of that
organ and the adjacent parts, as by thickening or hypertrophy,
thinning or atrophy, of its walls, thickening and imperfect
closure of, or irregular growths on its valves, adhesion of the

V

n

\ 222 SPECIAL PTIYSIOLOGY.

I,

pericarcliiim to the heart, or the presence of membranous
de|DOsits or fluid between it and that organ. The impulse and
/ sounds may even be altered by affections of the lungs, pleura,

or thoracic walls. The morbid changes in the sounds of the

* heart, are distinguished by terms descriptive of their character,

' position, cause, or period of occurrence. Thus, there are

• murmurs blowing or rasping, and friction sounds ; mitral or
tricuspid sounds ; aortic or pulmonary ; regurgitant or constric-

^ tive ; diastolic or systolic. The most marked and frequent

murmurs are the mitral regurgitant, from imperfect closure of
the mitral valve, and the aortic constrictive, from narrowing of
the orifice of the aorta. General enlargement of the heart, in-
creases the area of local dulness on percussion of the chest,
due to the contrast between the solid heart and the inflated
' lung. Fluid effused into the pericardium, also increases the

dulness ; but, moreover, it weakens or gives a distant charac-
ter to the heart’s sounds. Drier and solid effusions, as of '
'i lymph, cause a peculiar pericardial friction sound, or even

tremors wliich may be felt in the thoracic parietes, dependent
on a rubbing together of the surfaces of the heart and its peri-
cardial sac. j

Motion of the Blood through the Arteries^ and influence of those
Vessels on the Circulation.

The phenomena of the circulation of the blood through the
arteries, have been studied exclusively in the sy.stemic arterial
vessels; for the pulmonary arteries and their branches are
removed from direct observation and experiment. The
' structure and distribution of the arteries, the properties of their

coats, and their mode of subdivision and anastomoses, already
described (vol. i. pp. 18, and hT), have important influences on
the motion of the blood through them. The very smooth, glassy
surface of the internal coat, serves, like that of tlie endocardium
of the heart, to diminish the friction between the blood and
the sides of the bloodvessels.

The remarkable physical property of elasticity, possessed by
the middle arterial coat, is of extreme importance ; it exists in a
more striking degree in the larger arteries, especially in those
near to the heart ; it is manifested not only on stretching the
vessel in a lateral, but also in a longitudinal direction. Two
purposes are served by this elasticity ; first, it protects the
artci-ies against the force of the heart, to which they yield, !

CONTRACTILITY OF THE ARTERIES.

instead of offering a rigid resistance ; and, secondly, it enables
them to recoil, alter they have thus yielded, and to react upon
the column of blood within them. It is this recoil which
gradually converts the intermittent force of the heart, into a
continuous pressure in the small vessels. Moreover, tlie
elasticity of the arteries enables them to bear occasional
increase in the quantity of blood forced into them from the
ventricles, as in conditions of e.xcitement; or a more permanent
addition to the normal quantity, as in plethora. Lastly, it
prevents their compression by the ordinary muscular move-
ments, and jiermits them to bend and elongate, and so to
accommodate themselves to changes of position in the trunk
and limb.s.

d'he vital contractiliiij of the involuntary muscular arte-
rial walls, is of equal importance. Contrary to Avhat is the
case with their elasticity, this contractility is feebly manifested
by the larger arteries, but is very active in the smaller ones.
This property of the arteries, is shown by their slow contrac-
tion after death, owing to which, when no longer distended by
the force of the heart, they contract, and are usually emptied
of blood ; also by their contraction under the influence of
cold, heat, and mechanical, chemical, and electrical stimuli,
applied either to themselves, or to their nerves. Like the
contractility of the other muscular fibres of organic life, that
of the arteries is slow in its manifestation. Different stimuli,
however, act differently in exciting it. Some are said to cause
slow conti'action, and others, a more rapid contraction, with
subsequent slow return to the natural state ; some speedily
produce marked dilatation, and others, a dilatation, followed
slowly by a persistent condition of contraction. The stronger
the stimulus, the more likely is it to produce this latter effect.
The tonic contraction of an artery is powerfully excited by
cold ; whilst warmth rela.xes it ; but a cau.stic heat causes the
most durable contraction, which may, in part, explain the effect
of the actual cautery in arresting hatmorrhage. John Hunter
demonstrated the exi.stencc of this contractility in portions of the
moderate-sized arteries, which, he showed, went on contracting,
for a time, after death, by a sort of rif]or mortis, and then dilated
again, owing to the resiliencyof the elastic coat. Poiseuille found
that, after .subjection to an equal distending force, an artery,
which still retained its vital contractility, contracted more than
a perfectly dead one ; he also observed that when a living artery
was injected with a certain force, it recoiled with a ijreaicr

224

SPECIAL PHYSIOLOGY.

iorce, a result implying more than the reaction of mere elas-
ticity, which could only be equal to the original force. The
vital contractility of the smaller arteries, has been demonstrated
in the mesenteric arteries of toads and frogs, by means of
cold (Schwann), by the application of magneto-electricity to
the frog’s web (Weber and Kdlliker), and in stiU smaller
vessels in the mouse, bat, and frog, by various chemical, irri-
tant, and mechanical stimuli (Wharton Jones, Lister, and many
others). Weber found that minute arteries begin to contract
in two or three seconds after stimulation ; in five to ten seconds,
they are diminished to half their original area, and, the
stimulus being continued, become completely closed, after
which, the electrical cuiTent being removed, they slowly
dilate again to their original size. The vital contractility of
the arteries, may be excited through the nervous system, either
directly, or in a reflex manner ; for they undergo changes in dia-
meter, tlu’ough the contraction or relaxation of their muscular
coat, induced by divi.sion or irritation of the v'asi-motor nerves
or nervous centres (vol. i.p. 389). Two purposes are fulfilled by
this vital contractility of the arteries; first, that of slowly adapt-
ing the capacity of the entire arterial system, to the quantity of
blood circulating through it; and, secondly, under the control
of the nervous system, that of modifying the relative quantity
permitted to flow to any given organ. Moreover, if, during
life, a small artery be cut quite across, its contractility closes
its orifice, and so arrests further htemorrhage. This fact, in-
deed, is quoted as a proof of its contractility ; lor the elas-
ticity of the arterial walls is insufficient to account for the
perfect contraction of a wounded vessel, and -would rather
tend to keep it partly open, as Ave see hapjrens in a dead
artery.

It has been supposed that the contractility of the arteries
might serve, as well as their elasticity, to adapt them to the
intermittent and variable pressure of the blood projected into
them by the heart ; but there is no evidence of this, and
the characteristic slowness of action of organic muscular fibres,
renders it doubtful Avhether the ai’teries could alternately relax
and contract, concurrently Avith the rapid action of the
heart.

The so-called tone of the arterial system, seems to depend on
a healthy contraction of the muscular coat — the so-called pro-
I>erty of tonicitu being a continued exercise of muscular con-
tractility. This tonicity is shoAvn by the contraction Avhich

CnAKACTERS OF ARTERIAL CURRENT.

225

takes place in the portion of an artery included between two
ligatures, when it is punctured to allow of the escape of its
contained blood ; also by the gradual emptying of an arterial
trunk beyond any point at which it has been tied — a contrac-
tion much more complete than elasticity can explain ; and,
again, by the almost complete obliteration of the canal of a
portion of artery removed from a living animal, and subjected
to continued cold. The elasticity of the artery, is, however,
also, incessantly at play in the natural state of the vessel,
which is always in a condition of moderate and constant
tension, permitting and explaining its slight contraction and
retraction into its sheath, when it is divided.

As already stated, by the successive contractions of the ven-
tricles, and by the closure of the auriculo-ventricular valves, the
blood is not only directed from the heart into the great arterial
trunks, but is also projected into them by successive jerks. If
the arteries had rigid inelastic walls, this intermittent motion
of the blood in them, would be propagated even to the capillary
system. Owing, however, to their elasticity, and to the suc-
cessive closure of the semilunar valves across the mouths of
those vessels, the separate impulses caused by the ventricular
contractions, are gradually rendered less distinct, and, finally,
before the stream of blood enters the capillary vessels, its
motion becomes continuous. The elastic coats of the aorta,
near the heart, having been distended by the force of the left
ventricle, recoil on the contained blood ; this fluid being
practically incompressible, transmits the pressure on itselfj
backwards, so as to close the semilunar valves, and forwards,
so as also to urge onward the column of blood in the systemic
arteries. But the intermittent effect of the heart’s strokes, is
propagated onwards through all the main arteries of the body,
in which it is manife.sted by the pulse, and by the escape
of the blood per .saltum, or in jets, from any of those vessels
when they are wounded. The motion of the blood from
the ventricle, is truly intermittent — that is, it ceases abso-
lutely at intervals ; the jet from a large artery, when wounded,
is not quite intermittent ; that from the smaller arteries,
though the stream is jerking, is distinctly remittent, i.e. the
jet never ceases altogether, but is alternately .stronger and
weaker ; finally, in the smallest or microscopic arteries, the
flow of the blood, under ordinary circumstances, loses even
the remittent character, and becomes perfectly equable and
continuous, and remains so in the capillary vessels. This

VOL. II. q

226

SPECIAL PHTSIOLOGT.

effect of the elastic recoil of the previously distended arterial
walls, may be illustrated by the action of a vulcanised india-
rubber tube, which, if of sufficient length, changes the jerk-
ing flow of water, forced into it by a syringe or pump, into
a flowing stream. The force of the ventricle, transmitted
through the column of blood, acts most powerfully on the
vessels nearest to the heart, in which the elastic tissue is
most abundant; whilst the effect of the ventricular force is
gradually weakened in the more distant vessels, the elastic
coat of which becomes proportionally thinner. On the con-
trary, as already mentioned, the muscular fibres are relatively
least abundant in the largest, and most so in the smallest
arteries ; and it is improbable that their contractility is called
into play, to resist the distending effect of the heart’s force.
Although the arteries, by their resilience, at length convert
the intermittent stroke of the heart into a uniform propulsive
force, yet the heart itself is still the moving agent of the
arterial blood ; for the recoiling force exercised by the arteries,
is itself due to their previous distension by the force exerted
by the heart. When, indeed, this force is too weak to distend
the arteries as usual, the remittent flow, or jerking escape of
the blood, is observed in the most remote arteries, not only in
those next to the capillar}'- vessels, but even in the capillaries
themselves. The elasticity of the arteries engenders no new
force in the circulation, but utilises that of the heart. With-
out it, the force of this organ would probably rupture the
microscopic arteries, or the capillaries, of many delicate struc-
tures, and so give rise to internal hajmorrhages or apoplexies;
such accidents, indeed, occur when the coats of the arteries
are converted, by disease or degeneration, into more or less
rigid tubes. Besides acting in the distension of the coats of
the arteries, a certain part of the heart’s force is lost, being
propagated, by disturbance of those vessels, to the neighbour-
ing hard or soft tissues.

The frequent branchings and bendings, and especially the
anastomoses of the arteries, or their communications with one
another, as they approach the organs to which they are distri-
buted, as well as in the interior of those organs, serve to dimi-
nish, as well as to equalise, the force of the heart’s action. The
multiplication of the smallest arteries, and, therefore, of their
points of entrance into certain delicate organs, as . seen in the
ciliary arteries of the eyeball, and in tJie pia-mater of the
brain, must also lessen the pressure upon each of them.

BATE OF MOTION OF ARTERIAL CURRENT. 2L*7

Moreover, the frequent anastomoses of the arteries, as in the
vicinity of the joints in the limbs, and especially at the base of
the brain, serve to secure a due and constant supply of blood
to a given part through certain vessels, when others are
temporarily obstructed by external or internal pressure, or
permanently intemrpted by aneurisms, tumours, or acci-
dental division of the ligature of an arterial trunk. Anasto-
mosing branches given off above and below the seat of ligature,
gradually, or even rapidly, enlarge, forming large collateral
vessels, through which the so-called collateral circulation is
carried on. Such enlargement of an artery is due, not to a
mere relaxation of its coats, and consequent dilatation, but to
an increased nutrition of its walls, by which it undergoes a
positive enlargement ; in like maimer, arteries which are no
longer traversed by blood, though, in the first instance, they
merely contract, afterwards become reduced in size, by a
positive atrophy or absoption of their coats.

The supply of blood to a given organ, depends primarily
upon the size of the main artery distributed to it ; but
secondarily also, upon the rate of motion of the blood through
those vessels, which varies, as we shall see, according to many
circumstances. But, as previously mentioned, the calibre of
the arteries, especially of the smaller ones, is not constant ;
for it undergoes changes in accordance with the state of relaxa-
tion or contraction of their muscular coat, being sometimes of
normal size, and sometimes larger or smaller than usual. The
increased redness of the cheeks in blushing, or that of irritated
and inflamed parts, depends partly upon a temporary change,
in the calibre of the smallest arteries, which are then mani-
festly dilated. Hence the supply of blood to a part or organ,
may also be regulated by the contractility of its arteries,
which is itself controlled by the nervous system.

The rate of motion of the blood in the arteries, has been
calculated from observations made upon animals. Two kinds
of instruments have been employed in such observations. One,
the hamadromometer of Volkmann, consists of a bent U-shaped
glass tube, having its ends fitted into a short, straight, hollow
metallic mounting, placed at right angles to it. By means of
stopcocks, a free passage can be maintained, either through the
straight portion of the apparatus only, or through the bent
U-shaped part. When the two ends of the straight portion
of this instrument, arc fastened into the cut ends of the divided
carotid artery of a dog, the arterial blood-current may either

228

SPECIAL PHYSIOLOGY.

be .allowed to flow through the straight portion, or it may be
suddenly diverted, by changes in the stopcocks, through the
bent or U-shaj^ed part. The rate of motion of the blood
through the latter, being observed, and the length of this tube
being known, the velocity of the blood-current is ascertained.
Another instrument, the hcematocliometer of Vierordt, is com-
posed of a small square box or cell, made with glass sides, filled
with water, and having an aperttire of entrance and one of
exit, each fitted with a tube ; to these tubes, the cut ends of a
divided artery are att.ached. Within the box, is a fine pendu-
lum, carrying, in order to aid the observation of its movements,
a disc of silver, which, when the pendulum is at rest, h.angs
close to the aperture of entrance. A citrved graduated scale
is m.arked on the side of the vessel. When the arterial blood
is permitted to flow into this box, it raises the pendulum with
a velocity corresponding wuth that of its owm motion, and
which is at once measured by the graduated scale. According
to Vierordt, the mean velocity of the blood in the carotid
of a horse is 11'7 inches, of the dog 10 inches, and of the
calf 9 inches per second ; the calculated velocity in the aorta
of the horse, is 12‘5 inches, and in the human carotid, rather
more than 10 inches per second. According to Volkmann,
the velocities for the carotid artery in these anim.als, are
a little higher ; but in the metatarsal artery of the horse,
only 2'2 inches per second. By means of the tachometer of
Chauveau, a modification of Yierordt’s instrument, it is shown
that a great difference in the velocity of the blood-current,
exists during the systole and diastole of the left ventricle ;
for during the systole, in the horse, the velocity is about
20^ inches, and during the diastole only 8^ inches per second.
The velocity of the blood in the arteries, is, moreover, dimi-
nished during inspiration, and increased during expiration.

From the preceding figures, it appears that the rate of
motion of the blood in the arteries, is quickest ne.ar the heart,
gradually becoming slower in the more distant vessels. First,
the effect of the heart’s action is diminished by the resist-
ance offered, by friction and adhesion, to the passage of the
blood through the arteries and capillary vessels; this iric-
tional resistance, though rendered as slight as possible by the
smooth lining membrane of the arteries, is increased by the
curvature, by the angular bending, and by the frequent sub-
division, of the arteries, by an unusual rigidity of the walls
of the arteries, and by any alteration in the viscidity of

U JiM AD YN AMOMETE R.

229

tlie blood, or in its nutritive attractions for, or relations with,
the capillary walls and the tissues beyond them. All these
conditions, therefore, tend to retard the velocity of the blood-
current, by an increase of resistance and friction. Secondly,
the force of the heart, and therefore, the rate of motion of the
blood, is Avasted by the slight loss from fi-iction between the
particles of the elastic coat of the vessels, occurring in their
di.stension and recoil, and likewise by the disturbance of the
artery and the surrounding tissues. Lastly, an efficient cause
of retardation in the arterial blood-current, is the obvious
increase in the total capacity of the branches of the arteries,
as compared Avith that of the trunks from which they arise ;
for not only do the united diameters of tAvo or more branches,
exceed the diameter of the parent trunk, but, though of course
in a much less degree, the combined areas of tAvo or more
branches, are usually larger than the area of the parent trunk.
The combined areas of the tAvo iliac arteries, into Avhich the
abdominal aorta divides, are, hoAvever, larger than that of the
aorta itself. Opening an artery, Avhich not only causes hemor-
rhage, but also diminishes the resistance in the artei-ies, in-
creases the velocity of the blood in the opened vessel : this
result may be exhibited by experiments with artificial tubes
injected Avith water, and then opened.

The force of the heart, or the blood pressure, in the arteries,
has been frequently investigated, both by the earlier and
later physiologists. Stephen Hales found that, on fitting a
long tube containing Avater, into the crural artery of horses,
the force of the blood-current Avas sufficient to elevate the
Avater in the tube, to heights varying, in different cases,
from 8 feet 3 inches to 9 feet 8 inches. From these and
other experiments, he inferred that the pressure of the blood
in the large arteries of the human body, would support a
column of blood 90 inches, or 7 feet 6 inches, high, or a
Aveight of 3 pounds 7 ounces per square inch. More recently,
Poiseuille invented the hcenuuhjnamometer, a much more con-
venient instrument, in Avhich a short column of mercury is
substituted for the longer column of Avater in Hales’s apparatus.
This instrument, as noAV improved, and named a manometer,
consists of a U-shaped glass tube, having one of its stems or
legs longer than the other; the shorter leg is bent horizontally,
and provided at its end Avith a stopcock, and Avith a piece of
clastic tube, so that it can readily be adapted to the cut end
of a divided artery in a living animal. The loAver curved

230

SPECIAL PIIYSIOLOGY.

part, and 3 or 4 inches of both legs of the U-shaped tube, are
filled with mercmy, and the space in the short leg, between
the surface of the mercury and the stopcock against which
the artery is fixed, is occupied with a solution of common
salt, sulphate of soda or Glauber’s salt, or carbonate of soda,
so as to prevent the coagulation of the blood when it enters
the apparatus. At the back of the tube, is fixed a graduated
scale, the zero of which corresponds with the level of the
mercury when at rest in both legs. When the horizontal part
of the short leg of this instrument, is connected with an artery,
and the stopcock is opened, the apparatus being maintained
in a vertical position, the force of the blood-current depresses
the mercury in the shorter, and raises it in the longer leg.
The difference between the level of the mercury in the two
legs, gives the height of the mercurial column supported by
the blood pressure. But the level of the mercurial column
in the longer leg, is very inconstant ; for it is raised at each
ventricular systole, and lowered at each diastole : the highest
point indicates the full power of the heart, overcoming the
resistance of the column of blood, and distending the arterial
walls; whilst the lowest point shows that force, reacting
through the resilience of the arteries only. The mean height
between the two levels, is usually recorded as the average
blood pres.sure. Hales had already noticed, in his apparatus, a
descent of 1 inch in the blood column, between each pulsation.
To determine the exact force in pounds weight, the difference
between the sectional area of the artery experimented upon,
and that of the tube containing the mercuiy, must be noted, and
the weight of a mercurial column of the indicated height, but
of the same area as the artery, must be determined by calcula-
tion. Should any blood descend into the tube, its weight must
be reckoned, thoirgh it is only weight of mercury.

By means of a simple haamadynamometer, Poiseuille foimd
that the blood pressure varied little in different sized arteries,
and in different sized animals; and he concluded that 6’3
inches of mercury was, in all cases, the average equivalent of
pressure. This general result corresponds nearly with that
calculated by Hales for Man ; thus mercury being 13'G times
heavier than water, 6'3 inches of the former would be equal
to 85'68 inches of the latter, Hales’s estimate giving 90 inches
of blood, which ai’e equal to 95 of water. Again, 6'3 inches
of mercury on the square inch, would be equal to 3 lb. 2 oz.
pressure, Hales’s estimate being equal to 3 lb. 7 oz.

ARTERIAL BLOOD PRESSURE.

231

The force of the left ventricle itself, can only be estimated
from that observed in the arteries nearest to the heart ; taking
the blood pressure in the aorta, at 6’3 inches of mercury, then
the force of the left ventricle is found by multiplying that
number by the square inches contained on the internal surface
of that cavity.

The uniformity of pressure believed by Poiseuille, to exist
in arteries, both near to and distant from the heart, which
was thought to equalise the force of the circulation in every
part, and so to render congestion or deficiency of blood, ordi-
narily impossible, does not appear to prevail. In a system of
rigid tubes, the pressui'e would be uniform, unless these were
of very great length, and then only from friction. In curved
and resilient tubes, however, branching into vessels of rather
larger area than the trunks, some loss of force must be sus-
tained. Neither is it true, as Poiseuille supposed, that, in a
series of animals of different size, the blood pressure in the
arteries is nearly uniform, because, as he alleged, it is regu-
lated by a relation between the force of the ventricle, and the
size of the aortic orifice.

An adaptation of the htemadynamometer, named the Jcyino-
graphion, which yields A'ery accurate results, has enabled
more recent experimenters, to correct the observations and
conclusions of Poiseuille. Upon the surface of the mercury
in the longer leg of the ordinary instrument, there rests a float,
which is made to carry a vertical rod ; on the upper end of
this, is fixed a horizontal pencil, having its point resting on
a drum capable of revolving upon a vertical axis. When the
instrument is in use, the drum is made to turn at a given rate,
by clockwork, and the pencil, moved by the mercury, de-
scribes a waved line corresponding with the variations in the
blood pressure. In this way, the pressure is shown by Ludwig,
Volkmann, and other.s, to vary in animals of different size, and,
in the same animal, in arteries at different distances from the
heart, as well as according to different states of the circulation,
respiration, and nervous system. Thus, in the horse the average
blood pressure was nearly 1 1 inches ; in the dog, nearly
6 inches ; in the rabbit, as a mean, rather more than 1 inch ;
and in the frog, rather less than 1 inch. Again, in the carotid
of the calf, the pressure was equal to 4^ inchf^s of mercury ;
but in the metatarsal artery to only inches. Lastly, in
medium-sized animals, the blood pressure varies from Jth to
-fiths of an inch in the larger vessels. According to other

232

SPECIAL PHTSIOLOGT.

authorities, it differs much more than this, even in the same
artery. Moreover, there are slight fluctuations, due to the state
of the respiration, to hsemorrhage, starvation, muscular effort,
and other causes, implying variations in the force of the
heart, either increase or diminution. The pressure is weaker
in yotmger animals. In the pulmonary arteries, the pressure
is only equal to from ^ to 1 inch of mercury ; but the abnor-
mal disturbing effects of opening the thorax cannot be accu-
rately estimated (Ludwig).

The force of the blood-current in the arteries, or the blood
pressure, not only varies between each ventricluar systole, and
according to the strength of the heart’s action in different cir-
cumstances ; but it is increased by an addition to the quantity
of blood already contained in the system, as when blood is
artificially injected into the veins ; whilst, on the other hand,
it is lessened by a diminution in the quantity of blood in the
body, as in cases of htemorrhage.

The influence of the respiratory movements on the pressure
of the blood in the arteries, is very complex. Inspiration, or
breathing in, is usually said to produce a diminution in the
arterial pressure, and expiration,- ov breathing out, to cause
an increase in that pressure. In explanation of this view, it
is stated, that, during the act of inspiration, the blood enters
the thorax more readily, and thus relieves the whole vascular
system of tension ; whilst during expiration, the difficulty
offered to the entrance of blood into the chest, increases the
tension in the vessels, in the arteries as well as in the veins.
According to Vierordt, however, in inspiration, the readier en-
trance of the blood into the thorax, causes the right side of tlie
heart, and soon, also, the left side of that organ, to become more
distended, and the arterial pulse, accordingly, increases in
fulness, owing to increased arterial blood pressure, during the
course of inspiration ; on the other hand, in expiration, from
the resistance offered to the flow of blood into the chest, the
right side of the heart, and soon, also, the left side, receive
less blood, so that the arterial pidse, owing to diminished
arterial pressure, becomes, in the further progress of expira-
tion, smaller. With regard to the blood pressure in the
arteries, Vierordt, referring to the effbcts of inspiration and
expiration, in filling the heart with blood, states that, in the
former act, the blood pressure, though at first lessened, after-
wards increases, reaching its maximum at the beginning of
expiration, after which it diminishes. These views are fui-ther

DIFFERENTIAL MANOMETER.

233

modified Jay the researches of Dr. Sanderson, who states
that the rise in the arterial pressure begins with the act
of inspiration, and continues to increase during exjairation
hloreover, by these researches, in which a very large hama-
dynamometer and kymographion wer^ used, the respiratory
act is shown to consist of a period of action occupy inn-
two-fifths, and of a period of repose occupying three-fifths’
of the entire act; of the former period, two-thirds are taken
up by inspiration, and one-third by expiration. The arterial
pressm-e begins to increase at the commencement of inspira-
tion, and continues to rise during expiration, at the end of
which, and during the pause, it gradually sudsides. In
violent expiration, the vascular tension is increased ; but also
in the prolonged inspiratory efforts of dyspnoea.

The increased pressure from expiration, is illusfrated in the
tension, and occasional rupture, of bloodvessels in the act of
coughing. It has already been mentioned that the velocity of
the blood in the arteries, is slightly increased during expira-
tion, and diminished during inspiration, contrary to what hap-
pens in regard to the blood pressure. Indeed all the conditions
connected with increased resistance by friction, which dimi-
msh the velocity, increase the blood pressure ; whilst those'
■which lessen the friction and resistance, diminish the pressure
and increase the velocity. ^All variations in the arterial blood
pressure, are less marked, when the pulse is more frequent
and also as the arteries become smaller. ’

A double hiemadynamometer, or differential manometer, has
been devised by Bernard, by means of which the different de-
grees of pressure in different arteries, or in the same artery
on the two sides of the body, under different conditions, or tlm
different pressure in the arteries and veins, can be very con-
veniently determined. It consists of a U-shaped tube, the
bend of which is occupied by mercury, with a solution of
carbonate of soda, above it, in each leg : to the two extremi-
ties, the bloodvessels to be experimented on, are attached by
suitable pipes provided with stopcocks. When these are
opened, if the pressure in the two attached bloodves.sels is
equal, the level of the mercury in each side of the bend
remains unaltered ; but when it is urfequal, the mercuiy fiills
in the leg connected with that vessel, which has the gi'^atest
pressure on its contents. For example, in the two carotids
or two facial arteries, of a horse, the pressure is equal ; but if
the instrument be connected with one artery near the heart

%

234

SPECIAL PHYSIOLOGY.

and witli another more remote, it is unequal. Moreover,
when this instrument is connected with the same artery on
the two sides of the body, division of the sympathetic nerves
on one side, is followed by an elevation of the mercury on
that side, indicating a loss of tension in the coats of the corre-
sponding vessel. ,

The Pulse.

The pulse is the well-known beat of an artery, sometimes
visible to the eye, if the artery be superficial, but more
commonly felt by the finger placed upon the beating vessel.
Sometimes the pulse is perceptible to the individual himself,
being either felt as a throbbing sensation, or heard, as a noise,
when near the ear. The remote cause of the pulse, is the force
of the heart, for its beats correspond in number with the con-
tractions of the left ventricle. Its immediate cause, however,
is the momentary distension and recoU of the coats of the
artery, propagated ^ along the vessel from the heart onwards,
after the manner of a wave-motion, and produced by the
propulsion of successive quantities of blood into the arterial
system by the left ventricle ; and commencing at the instant
of closure of the mitral valve. The force transferred to these
successive quantities of blood, is partly exhausted, in urging
on the blood already in the vessels ; but the resistance thus
met with, as we have seen, diverts the force partly on to the
elastic sides of the arteries, and so distends them.

This distension of the arteries occurs first in the aorta, close
to the heart, but rapidly follows along the entire arterial
system. It consists, not only of a lateral dilatation of the
vessels, but also of an elongation. The former change is but
slight in arteries which can be subjected to examination, and
is too quick to be followed readily by the eye ; whilst the latter
is much more evident, as in the case of superficial and tortuous
arteries, such as the temporals, which may be seen to become
more curved during the passage of the pulse-wave along them.

The total amount of dilatation observed dm-ing the passage
of a pulse- wave along a given length of the carotid artery of
a dog, has been measured, by placing the artery in a tube
filled with water, and having another fine upright glass tube
fitted into it ; the elevation of the water in the latter, at each
pulse, shows an increase of -jVid of the bulk of the piece of
artery so enclosed (Poiseuille). According to Vierordt, the
increase is as much as The mechanical effect of this

THEORY OF THE PULSE.

235

combined dilatation and elongation, but especially of the
elongation, of a living artery, and of its subsequent contrac-
tion and slrortening, and particularly of the latter, is a move-
ment of the vessel in its bed, a motion -which is visible in
superficial arteries, especially in thin and aged persons, and
•which can be rendered more perceptible by placing a small
bristle across it. It is this change of place, or locomotion, of
the artery, which is the chief cause of the jDulse felt on placing
the finger upon the vessel. The blood itself being practi-
cally incompressible, the shock of the heart’s stroke irpon
it, is communicated, almost instantly, throughout the whole
blood in the arterial system ; but the effect of the disten-
sion, or distension wave, which begins in the aorta, near
the heart, apparently takes a certain time to be continued
onwards, for reasons to be presently explained; hence there
is a certain measurable rate in the propagation of the pulse
to the distant arteries. This is the theory of Marey. But
the rate of motion of the distending pulse-wave, is much more
rapid than the motion of the blood particles themselves within
the vessels, being about 30 feet per second ; whilst, as already
stated, the velocity of the blood is only about 10^ inches per
second in the carotid, and about inches per second in the
distant arteries. This comparison will serve to impress on
the mind, the fact, that the pulse-wave is not caused by the
onward motion of the blood, but by a wave-motion induced
in the entire column of blood, which operates in its passage,
laterally, as well as longitudinally, on the coats of the arteries.

The impulse of the heart nearly coincides with the systole
of the ventricles, or, rather, it happens somewhat later than
the commencement of the ventricular contraction. Now, the
pulse-wave passes along the larger arteries, at the termination
of the ventricular contraction, i.e. after the impulse of the
heart is felt on the side of the chest ; and it takes ^th of a
second to reach the radial artery at the wrist. Nevertheless,
the pulse is felt even in the most distant parts of the arterial
system, before the second sound of the heart is heard, whilst
the cause of this sound, is the sudden closure of the semi-
lunar valves across the mouth of the aorta and the pulmonary
artery. This fact, as first pointed out by Colt, refutes the fol-
lowing theory of Weber, once so generally adopted, as to the
cause of the propagation of the pulse-wave. That physiologist
supposed that the aortic semilunar valves, being closed by
the backward movement of the blood near them, owing to

256

SPECIAL PHYSIOLOGY.

the recoil of the walls of the aorta nearest to the heart, acted
as a fulcrum, from which the blood was propelled onwards by
the yet unused resilient force of the aorta, into more and more
distant portions of the arterial system, so as to produce the
successive wave- like distension of their coats.

This theory of Weber assumes a minor cause, in place of the
greater and true one, viz. only a residual portion of the force
originating in the ventricular stroke, instead of the whole
ventricular impulse. The closure of the aortic valves is not
essential to the phenomenon of the pulse, which occurs before
the second sound, when these valves are open. But if the
pulse-wave be essentially due to the direct force of the heart,
communicated through the arterial blood column acting at
ihe closure of the mit7'al-valve, so the closure of the aortic semi-
lunar valves is not without effect on that blood column, and
on the arteries which contain it. When the pulse is very
accurately examined, a subsidiary wave occurs after the prin-
cipal one, producing the phenomena named dichrotism or the
dichrotal pulse, and this, as will be soon explained, has been
referred by some, to the effects of the closure of these valves.

For the investigation of this and other phenomena of the
pulse, instruments named sphygmogra2}hs have been devised.
The original apparatus of Vieroi’dt, consists of a long, slender,
well-balanced, horizontal lever, or measuring rod, supported,
near one end, on a proper fulcrum, and having a short vertical
stem projecting downwards from near the fulcrmn, and ending
in a little button which rests upon the arteiy. To some part
of the lever, near the button, are attached certain contrivances;,
to secure a true vertical motion, and, at its free end, it carries
a short pencil, the point of which rests against an upright
cylinder or drum covered with paper. To this cylinder, when
the instrument is in action, a known rate of motion is imparted
by clockwork ; at each pulsation of the artery against the
button, the lever rises and falls, and so the pencil describes an
up and down line on the revolving drum of paper. In tliis
way, a series of pulsations are recorded by an up and down
waved line of a peculiar character. In Marcy’s improved in-
strument, and in other still later ones, the delicacy of record is
more perfect, the lever is longer and lighter, its motions are
steadied by the addition of a slight spring, and the pencil
leaves its tracings upon a piece of smoked glass which is moved
forwards by clockwork, or upon a coil of paper which is con-
stantly being unwound.

THE SrHTGMOGRAPH.

237

Tlie wared lines traced by such an instrument, show, by the
number of the undulations in a given space, the frequency
of the pulse. ; by the length of the up and down strokes, the
amplitude of the pulse movement, or the force of the pulse ;
and by the greater or less inclination of these strokes from the
perpendicular, or the horizontal distance between the points
of commencement of the upward strokes, the duration of the
pulse-waves. Besides this, certain variations in the lines
indicate other characters, such as firmness, or tremulousness,
and so forth. There is, however, one character of the pulse
recogni.sable by the finger, concerning which, the sphygmo-
gi-aph gives information Avhich may be delusive, viz. the
volume of the pulse, wdiich may be full in very different condi-
tions of the sy.stem. A fidl pulse is usually slow and strong,
but it may be quick ; on the other hand, a small pulse is gene-
rally quick and feeble, but not necessarily so. The pulse is
"wiry, thready, or small, in haemorrhage, or on approaching
death. In recording the pulse movements, this instrument also
indirectly measures the force and duration of the systole of the
left ventricle, and the duration^ of the respiratory movements.

The sphygmogi-aph has been'ingeniously employed by Marey
to assist in determining the cause of the pulse itself. An india-
rubber cylinder, provided with internal valves, is fitted at one
end, to a short, and at the other to a long, elastic tube. By
alternately relaxing and compressing the cylinder, water, under
the direction of the valves, is drawn in through the short tube,
and pumped intermittently through the longer one. Thi.s
latter tube is disposed in three loose horizontal coils, each of
which is brought in contact with a sepai-ate sphygmographic
lever, the pencils of all of which, rest upon a paper, previously
ruled with vertical and horizontal lines, and which revolves upon
one drum, common to the three pencils. The sphygmographic
pencils being placed, at starting, exactly under one another,
and the drum being made to revolve, three horizontal lines
are first simultaneously traced ; but when the india-rubber
cylinder is repeatedly compressed, so as to inject water by
separate impulses into the long tube, thus imitating the ven-
tricular propulsion of the blood into the arteries, undulations,
resembling the pul.se- waves, travel along the coils of the tube’
and move thethree sphygmogi-aphic levers, the pencils of which
record the moment of commencement, the extent, and the du-
ration of the movements occurring at three diflerent points
of the tube, by up and down lines of corres])onding character

238

SPECIAL PHYSIOLOGY.

and form. In the first place, the line corresponding with the
point nearest to the propulsive cylinder, shows a greater am-
plitude in its undulations, owing to the greater force of the
lateral pressure on the walls of the tube at that point ; whilst,
in the other two lines, a progressive diminution in the vertical
depth of the undulating lines, shows a gradual diminution in
the pressure, in proportion to the distance from the agent of
propulsion. But what is of more interest in relation to the
cause of the pidse-wave, is the fact, that though the com-
mencement of the wave, at each of the three points tested by
the sphygmographs, is simultaneous, the nearer Avave reaches
its highest point, before the others, which reach theirs at pro-
gressively later times. This is believed by Marey to happen
in the living body, and to explain the apparent retardation of
the pulse movement, or distension effect, Avhich is indicated i
by the pulse itself being felt ;^th of a second later in the
Avrist than close to the heart, although, from the practical
incompressibility of the blood, the shock imparted to it by the
left ventricle, must be instantly propagated through the Avhole
of that fluid, in the arteries, just as that of the india-rubber
cylinder is through the equally incompressible AAmter.

The phenomenon known as the dichrotous pulse, is also
detected and studied by the sphygmograph. Formerly, it AAns
supposed to be absolutely the result of disease, or of some
grave irregularity ; but Avith more delicate instruments, its
presence is often detected even in healthy conditions. It is
represented by a slight secondary undulation in the doAvn-
stroke of the chief or primary pulse-line. It sometimes occurs, I
in health, during walking, and is noticeable also in the healthy I
pulse, Avhenever, OAving to the diminished tonicity of tlie I
arteries, and their defective distension, they are in a condition I
to obey slighter impulses communicated to the blood. In the I
opposite conditions of a highly tonic or distended state of the I
arteries, this subsidiary wave motion of the dichrotous pulse, I ,
is not perceptible. In abnormal conditions, it is a sign of a I ^
relaxed state of the arterial system, or of a loss of blood. .1 ‘
According to Naumann, the cause of this dichrotism, is the ’■ ,
.shock communicated to the blood, at the instant of closure of I '
the aortic semilunar valves, Avhich, like the sudden arrest of ill
a fluid by the closure of a tap, produces a shock or jar, Avhich il '
is transmitted back through the Avhole column. The timedlj
of occurrence of the dichrotous pulse, corresponds Avell Avith jl J'
this hypothesis; for AA'hilst the primary pulse movement is I.

THE DICHROTOUS PULSE.

239

felt before the second sound of the heart, the dichrotous
■wave immediately follows it. It is, however, suggested by
Marey, that this dichrotism may be due to the primary wave
being checked at the lower end of the abdominal aorta, where
that vessel divides into the common iliacs, owing to the tact,
elsewhere referred to, that the two iliac arteries are smaller
than the aorta fi-onr which they proceed, contrary to the gene-
ral rule, that the area of the branches exceeds that of the
parent trunk. At this point, the primary pulse-wave is sup-
posed by Marey, to rebound, and to produce a back wave,
which causes the dichrotous pulsation. In support of this
explanation, it is alleged, that whilst the pulse is dichrotous in
aU the arteries arising from the arch of the aorta, it is not so
in the femoral arteries and arteries of the lower limbs, along
which the primary pulse-wave only travels. But Naumann
asserts that the dichrotous pulse-wave diminishes in force, as it
recedes from the heart — a fact which would support his view,
but be opposed to Marey’s ; for, in the former case, the wave
is supposed to travel outwards from the heart, but in the latter,
towards the heart, i.e. from the lower end of the abdominal
aorta. Another suggestion has been made, viz. that whilst a
primary wave occurs in the blood, a secondary wave follows it
in the coats of the vessels ; this opinion rests upon an experi-
ment, in which it was shown that the simple injection of a
fluid intermittently into an elastic tube, produces such a double
wave.

An ordinary vigorous pulse-line, as marked on the .sphyg-
mographic paper, consists of a series of up and down strokes,
which succeed each other at regular intervals, without any di-
chrotous wave-line in the down-stroke. But the pulse, as is
well known, presents, owing to various causes, many modifica-
tions in character, each of which is recorded by the sphygmo-
graph. Thus, by increased frequency of the heart’s action,
the pulse is rendered more rapid, as in the quick pulse, and
then the up and down strokes of the sphygmographic line
become more crowded in a given horizontal space. Again,
the pulse may be augmented in force, as in the strong or
hounding pulse, caused by a more powei ftd action of the heart,
as under the effects of stimuli or mental excitement, and then
the length of the up and down strokes is increased. The
pulse is sometimes hard, as when the tension of the arterial
walls is increased, whether from exalted tonicity, from exti'eme
fulness of the vascular system, or from obstruction in the

240

SPECIAL PHTSIOLOGT.

capillaries, causing an obstacle to the flow of the arterial
blood. This may happen either from inflammation of a part,
or from the brief application of cold to the surlace of the body;
the coats of the arteries being already much distended, or
their tonic contraction being excessive, the pulse-wave scarcely
distends them further ; hence the up-stroke is short, nearlv
vertical, and occupies but little space, whilst the line of
descent is gradual and prolonged, marking the slow and difli-
cult recoil of the vessel. Lastly, the soft pulse, which is met
with in relaxed conditions of the system, or may be pro-
duced by hot air or water-baths, depends on a deficiency in
the quantity of blood in the arteries, or on a defective state
of the tonic contraction. With such a pulse, the up-stroke
is long, owing to a greater freedom of play of the elastic ar-
terial walls ; the down-stroke is much prolonged, and exhibits
a small secondary wave, constituting the dichrotal piilse.
IVIoreover, the horizontal space betAveen the commencement of ,
each up-stroke, is diminished, indicating a greater frequency of
the heart’s beats, whilst, in the hard pulse, the opposite is the
case ; for, as already mentioned, a sympathy exists betAveen
the action of the heart and the state of the circulation ; the
number of its beats being diminished, but their force in-
creased, when the capillary system is obstructed, Avhilst the
two opposite states occur, when that system permits the easy
transmission of the blood. When a hard pulse depends upon
a local cause, such as inflammation, it may be accompanied
by an increase in the number of beats ; but Avhen upon a
general cause, such as the application of cold to the AA’hole
body, by a diminution in the number of pulsations.

The absolute duration of each pulse, as measui-ed in time by
the number of beats in a minute, is indicated on the sphygrao-
graphic paper, by the horizontal distance betAveen the com-
mencement of two adjoining up-strokes. This duration may I
vary as much as 37 per cent, in a series of beats. It varies I
most in the sIoav pulse ; for the more frequent the pulse, the I
more equal are its beats in duration ; it is very remarkable in I
the sloAv pulse produced by poisoning Avith digitalis. On I
comparing the up Avith the doAvn stroke of each pulse-line, it .1
is seen that, usually, the former has a less horizontal pi'ogres- I
sion than the latter, indicating that the distension or dilatation I
of the arteries, Avhich is related to the ventricular systole, takes -I
place in a shorter time than the recoil or contraction of the tl ^
vessel, Avhich is related to the diastole. It Avas formerly said il j

.1

TAXATIONS IN THE PULSE. ^41

that the ratio between them was as 1 to 2 ; but, in health, the
proportion seems to be, in an average pulse, only as 100 to
106 ; in a quick pulse, the ratio is as 100 to 136 ; in the
slow pulse, as 100 to 80 (Vierorclt). The period of dilatation
varies more than that of contraction.

The influence of the respiratory movements on the ptdse,
so far as its force is concerned, has already been indicated, in
describing the arterial blood pressure (p. 232). The volume
of the pulse during inspiration, as compared with its volume
during expiration, is said by Vierordt to be as 218 to 191. It
is now established, by aid of the sphygmograph, that the force
of the pulse is gradually increased during inspiration, and
reaches its maximum during expiration, this fact being indi-
cated by the gradual ascent of the line of mean pressure,
drawn through the middle of a series of up and down strokes.
The tension of the artery, on which the fiilness of the pulse
inversely depends, is increased during inspiration and up to
the end of expiration, the pulse becoming harder and tinner, and
the length of the up and down strokes shortened ; whilst,
after expiration, in the pause, the tension of the vessels is
lessened, the pulse becomes softer and fuller, and the up and
down strokes of the curves are longer. Lastly, the frequency
of the pulse is modified during inspiration, not, as is some-
times stated, then becoming slower, but, as shown by Vierordt,
increasing in frequency, owing to the more easy supply of blood
to the heart ; this view is confirmed by Sanderson, who,
moreover, points out that this increase of frequency continues
up to the end of expiration, as is indicated by the greater
closeness of the up and down strokes in the horizontal space
representing the period of the inspiratory and expiratory acts,
as compared with those registered in the space representing the
pause at the end of the latter. The duration of each pulse is
longer in inspiration than in expiration.

The pulse being ultimately dependent on the heart’s action,
is necessarily modified in frequency, strength, and rhythm, by
all those conditions which influence the number, strength,
and rhythm of the heart’s beats, such as age, sex, stature,
position of the body, atmospheric pressure, state of nutrition,
stimulation, and excitement, as already detailed (p. 217).
When the heart’s action is very feeble, the pulse is said to
1 become more evident in the smallest arteries, being propa-
! gated to a greater distance from the heart, even to the capil-
. lary vessels. This apparently anomalous result is explained
VOL. II. K

U

2+2

SPECIAL PHYSIOLOGY.

by the heart’s action being then too Aveak to distend the
larger vessels to such a degree as, by their subsequent recoil,
to convert the intermittent flow of the blood, into a uniform
and equable motion. Want of rhythm in the heart, causes
irregularity of the pulse. The so-called intermittent pulse in-
dicates an ineffective ventricular systole, which is too Aveak to
act on the arterial blood column. It may depend on a defi-
cient supply of blood to the left side of the heart, as Avell as on
debility of that organ. It occurs after long fasting, and is also
common at puberty, in old age, and in various diseases. In
healthy persons, its duration is somewhat longer than that of a
single beat of the heart.

Motion of the Blood through the Capillaries.

The tissues in Avhich capillary bloodvessels are found, and
those in which they are absent, their number and size in the
various ti.ssues and organs, the varieties in the arrangement of
the capillary network, and the structure of their delicate Avails,
are elsewhere detailed (vol. i. p. 60). The form of the capil-
lary netAvmrk in different parts, has no relation to the functions
of those parts, otherwise than so far as these depend on the forms
and disposition of the structural elements, betAveen — not into —
which the vessels penetrate. But the closeness of the network,
and the consequent number of the capillary vessels in a given
space, are proportional to the actiAuty and importance of those
functions.

The capillaries form the intermediate blood channels be-
tween the finest arteries and veins. When examined in the
transparent part of a living animal, they are seen to be of dif-
ferent sizes, some conveying two or more rows, and others
only a single row, of blood corpuscles. Moreover, Avhen
watched sufficiently long, they are observed to undergo slow
changes in diameter, so that vessels, at one time capable of
conveying several roAvs of blood corpuscles, shrink, and no
longer convey more than a single roAv, or even become tempo-
rarily incapable of admitting any corpuscles, so that they
merely convey the liquor sanguinis. It Avas at one time sup-
posed that vessels, named vasa serosa, or serous vessels, con-
stantly so small as only to admit the fluid portion of the blood,
existed in all or many parts of the body ; but their presence
generally, which was purely conjectural, has not been confirmed.
By some authorities, however, it is at least suggested that, in

THE CAPILLARY CIRCULATION.

243

the cornea, capillaries may exist, which habitually convey only
the liquor sanguinis (Kolliker, Hyrtl).

In watching the capillary circulation, it is seen that svich
vessels as have ceased for a time to convey blood particles,
again dilate and admit them, and, from this alternate contrac-
tion and dilatation, a vital contractility has been attributed to
the coats of these vessels. The structure of their delicate
walls, however, which are composed of homogeneous membrane
containing nuclei but destitute of muscular fibre-cells, negatives
the idea of their possessing a vital contractility ; and, more-
over, it has been found that no contraction, or other change, of
these walls, occurs on the direct application of the electric
stimrdus to them. Their walls are, however, elastic, and the
changes in diameter of the vessels, are probably due, either to
distirrbed conditions in the neighbouring small arteries, owing
to the contraction or relaxation of their muscular coat, or to
movements in the tissues in which the capillaries are distii-
buted, and in which organic muscular fibres, fibre-cells, or
other contractile elements, such as pigment-cells, are frequently
present. The capillaries do not, therefore, seem to exercise
any mechanical influence on the circulation of the blood
through them, by virtue of an active contractile force, resident
in their walls ; but they may adapt themselves, by their elas-
ticity, to the varying quantities of blood, distributed to any
particular part. Such conditions must occur in the opposite
states of blushing and pallor of the skin ; in the conditions of
fulness or emptiness of the capillaries of a gland or membrane,
according as it is secreting or not; and in the condition of
health and inflammation, in any vascular part, such as the
conjunctiva of the eyeball.

The real propulsive cause of the motion of the blood in the
capillaries, is the same as that of the arterial circulation, viz. the
ventricular systole, modified, in its effects, by the resilience of
the elastic coat of the arteries themselves. Indeed, in a living
animal, if the force of the left ventricle, communicated to the
blood in the arteries, be arrested by pressure on, or ligature of,
those vessels, the stream of blood in the capillaries soon almost
entirely stagnates, and the venous current beyond them is
stopped, whilst the tension or blood pre.ssure in the arteries also
ceases. Moreover, in the fish, as we shall hereafter find, the force
of the single ventricle of the heart, is sufficient to propel the
blood first through the gills, and then through the arteries of the
body. It has been supposed that certain mutual attractions and

K 2

2-14

SPECIAL PHYSIOLOGY,

repulsions between tlie blood and the tissues lying outside the
systemic capillaries, or betAveen the blood and the air in the
lungs, may influence tlm movement of the blood through the
capillaries, and even constitute a moving power in the capil-
lary circulation. But this implies an attractive force in regard
to the blood in the arterial half of the capillary network, and
a repulsive force in regard to the blood in the venous half of
that network, an hypothesis complex, and yet unproved.

The supposition of the existence of a local attractive and
propulsive force, exerted on the blood passing through the
capillaries, is held to be supported by the folloAving facts : —
The gradual emptying of the arteries after death ; the main-
tenance of the circulation in the portal system ; the periodic
and local changes in the circulation during secretion, or in
other conditions, such as fainting and fright, or in diseases
such as congestion and inflammation ; the obstructive changes
w'hich occur in the pulmonary circulation during asphyxia ;
the great activity of this circulation, when the respiratory
changes are rapid ; and lastly, the fact of a circulation of blood
occuiTing in the embryo of animals before the development of
the heart (Draper). It has been further pointed out, that of
.two fluids contained in a capillary tube, that which has the
greatest affinity for the sides of the tube, will flow along it
quicker than the other, owing to mere physical action.

On the other hand, it is alleged that, although a healthy
condition of the walls of the cajAillaries and of the tissues
beyond them, and a healthy performance of their functions,
are necessaiy to an unimpeded floAV of the blood through these
vessels, and although a stasis or stagnation of the blood, and
a dilatation of the capillaries, accompany a state of inflammation,
imperfect secretion, or defective respiration ; yet such facts do
not prove the existence of a special jjropulsive force, resident
in the walls of the healthy capillaries, or dependent upon the
healthy nutritive, secernent, or respiratory function ; they
may merely shoAv that the capillary circulation, though
dependent upon the action of the heart and arteries, may be
retarded or arrested by abnormal relations between the blood
and the tissues, or air, outside the capillary Avails. The en-
largement of the capillaries, Avhich accompanies such stagna-
tion of the blood in them, and also the shrinking of these
vessels, as the part recovers, imply an exercise of elasticity
by tl'.eir Avails ; but this cannot be, under any circum-
stances, a moving force in the circulation, but rather a means

THE CAPILLARY CIRCULATION.

245

of adapting the size of the capillaries, to variations in their
contents.

The motion of the blood in the capillaries, when observed
under the microscope, in animals not too much disturbed in
the experiment, is constant, equable, and regular; but the
character of the movement, may be modified by the dilatation
or contraction of the neighbouring small arteries under the
action of cold or other stimuli, by obstructions in the veins,
and by the condition of the heart itself. When, as already
mentioned, the heart’s systole is weak, the motion of the
blood in the capillaries, may, from the non-development of a
perfect recoil in the arteries, become pulsatory ; and when the
heart is still more enfeebled, the blood in the capillaries may
merely oscillate, or be completely arrested, or a backward
current may even take place in it. These and many similar
disturbances, even under the microscope, have been often
erroneously referred to active influences in the coats of the
capillaries, or in the surrounding tissues.

The motion of the blood in the capillaries, is more rapid in
the centre of each little stream, and slower at its surface, near
the walls of the vessel. The existence of corpuscles in the
living blood, affords the means of determining this fact ; for the
red corpuscles may be seen to move, comparatively swiftly,
along the centre of the vessel, whilst the white corpuscles
travel, much more leisurely, along the sides, the ratio of their
respective movements being as 9, or even 17, to 1 (Weber).
The outer, thin, more slowly moving film, in contact with the
inner surface oi the capillaries, measures, under different cir-
cumstances, from 1th to only g-th of the diameter of the vessel.
It forms the still layer or space of Poiseuille, in which the
white corpuscles move slowly along, as if some special attrac-
tion retained them against the sides of the vessel, whilst the
red corpuscles are hurried along the centre. This striking
phenomenon may have, in part, a physical explanation ; for a
retardation always occurs in the movement of that portion of
a fluid which is in contact with the walls of a tube, as com-
pared with the rate of motion along its axis, this effect being
due to friction in large tubes, and also to capillary attraction
in small tubes. In the living animal economy, the retardation
of the circumferential layer of blood in the capillaries, must
have an important influence on the nutritive, secretive, and
respiratory processes, all of which arc accomplished within a
certain range of the capillary circulation ; it may merely

246

SPECIAL rnrSIOLOGT.

facilitate the withdrawal from the blood, and the escape through
the capillary walls, of certain necessary materials ; or it may
be itself an indication of nutritive, or other, attractions from
without, operating on the stratum of fluid lying next to the
thin capillary walls. Some such attraction may prevail between
the pale corpuscles and the walls of the vessels themselves,
but the existence of this has not been established. These cor-
puscles, however, appear to be naturally much more adhesive
than the red corpuscles, as is shown by their clinging to a
glass slide or cover, as seen when a minute drop of blood is
spread out and examined under the microscope.

The actual rate of motion of the blood in the capillaries,
as watched and measured by aid of the micrometer in the
field of the microscope, in the case of individual blood parti-
cles, has been found by various observers to be, in the frog’s
web, rather more than 1 inch per minute, in other word.s, about
.j^Lth of an inch per second (Hales, Valentin, Weber). As to
the warm-blooded animals, the rate of motion is higher, being,
according to Volkmann, 1'8 inches per minute in the dog;
whilst the observations of Ludwig and Vierordt on the
entoptical retinal image, or image of Purkinje, give a velocitj',
in the retinal capillaries of their own eyes, of from about
1-^th inch to rather more than inch per minute. The
average velocity in Man, might therefore fairly be estimated at
about 2 inches per minute, or ^^^th of an inch per second, i.e.
twice the velocity in the frog. The apparent rate of motion
of the blood, in the capillaries of either a warm or cold-blooded
animal, as seen under the microscope, is so high, that the
observer is apt to be misled with regard to its actual velocity ;
and, deceived by the apparent motion, to doubt that the real
velocity is only 1 inch per minute in the cold-blooded animal,
and 2 inches per minute in the warm-blooded animal. But
the area of observation being enormously magnified, the appa-
rent or angular motion of the blood before the eye of tlie
observer, is increased in the same proportion ; so that in the
field of a microscope magnifying 180 diameters, the rate of
motion of the capillary blood, appears to be, in the frog, 180
inches per minute, or 3 inches per second, and in the warm-
blooded animal, to equal twice that velocity. The actual slow
rate of motion of the blood through the capillaries, is remark-
able and important, in connection with the nutritive, secernent,
and respiratory functions, giving ample time, as it Avere, for
the important interchanges between the blood and the tissues

TilE VENOUS CIRCULATION.

247

or the air, which take place in them, especially for those of
deoxygenation and oxygenation, which occur, the former in
the systemic, the latter in the pulmonary, capillaries.

The slow rate of motion of the blood in the capillaries, is
even more striking, when it is compared with the rate of
motion in the ai’teries, which, as already mentioned, is esti-
mated at about 10 inches per second, or GOO inches per
minute, in the human carotid, so that the velocity of the blood
in the systemic arteries, is 300 times greater than that in the
systemic capillaries. It has been calculated that in the pul-
monary capillaries, the rate of motion of the blood is five times
greater than the average rate in the systemic capillaries, i.e.,
10 inches per minute, or the ^th of an inch per second.

This remarkable retardation of the blood in the capillary
vessels, as compared with its velocity in the arteries, is doubtless,
in part due to increased friction, dependent on the vast increase
in the number of channels through which the blood now has
to pass ; but its chief cause is the very great increase in the
capacity of the capillary, as compared with that of the arterial
system. It has already been stated that the combined sectional
areas of the firat and second degrees of arterial branches, as a
rule, slightly exceed the sectional area of their common trunk.
In the smallest arteries this is doubtless much more marked ;
and on aiTiving at the capillaries, the increase in the total sec-
tional area of the bloodvessels, or, as it is otherwise expressed,
in the capacity of the capillary system, is sudden and immense.
A fluid moving from a small into a wider tube or channel, has
its motion retarded accordingly ; and the change of capacity,
in passing from the arterial to the capillary system, has been
compared to that which would take place in a very short cone.
The relative areas of the two systems of vessels, are usually,
indeed, estimated, as bearing an inverse ratio to the measured
velocity of the blood in them. Hence, according to the pre-
ceding data, the sectional area of all the capillaries in the
human body, would be at least 300 times greater than that of
the chief arterial trunks. It has also been calculated to be
about 400 (Volkmann), 500 (Bonders), and even more than
300 times (Vierordt), greater than the area of the aorta.

Motion of the Blood through the Veins.

The position and structure of the veins, and of their valves,
have been described in vol. i. pp. 18 and 58. Their walls,

248

SPECIAL PHYSIOLOGY.

though thinner, and more easily compressible, than those of
the arteries, and less elastic and contractile, are very strong,
the vena cava having been found to require a greater force to
burst it, than the aorta. Collecting the blood from the capil-
laries by minute venous radicles, the sy.stemic veins convey
the dark blood, from all parts of the body, back to the right
auricle of the heart. In the limbs, the superficial veins lying
beneath the skin are not subjected to the pressiu’e of muscles;
whereas the muscles must press upon the sides of the deep
veins. The pulmonary veins, which convey bright blood
from the lungs to the left auricle, are peculiarly circum-
stanced, being, like the pulmonary arteries, situated entirely
within the chest.

The blood in the veins, as indicated by opening a vein in
the living body, moves by an even flow, destitute of any pul-
satory or jerking movement ; for the rhythmic character of the
heart’s action, is already lost in the capillaries, and the equable
flow of blood in them, necessitates a corresponding equability in
the motion of the venous blood. But the primary force which
urges on the blood in the veins, is still the heart’s action,
modified by the resilience of the arteries, which, after having
nearly exhausted itself, in propelling the blood through the
capillaries, is still adequate to move on the blood in the veins.
The chief resistance in the circulation of the blood, takes
place in the capillaries, where, doubtless, it is very great;
indeed, the force of the blood in the veins, as measured by
h£emadynamometers fitted into those vessels, varies from -j^uth
to ^th of that of the blood in the corresponding arteries
(Poiseuille). In the dog, the blood pressure in the jugular
vein, is fi’om to ^th of that in the carotid artery (Valen-
tin) ; but the blood pressure diminishes, in proceeding from
the branches to the larger veins, and in the great veins close
to the heart, the pre.ssure is scarcely appreciable. But certain
facts seem, nevertheless, to show that this force is really the
residue of that of the left ventricle, which is therefore an ade-
quate cause, and probably the true cause, of the motion of the
blood in the veins, towards the right auricle. First, pressure
upon all the arteries of a given part, arrests the flow of blood
from a wounded vein belonging to the same jrart. Secondly,
if the venous circrdation from a given part, be entirely
arrested, by pressure on, or ligature of, the veins, the blood-
pressme in them is said to rise, so as even to be equal to that
in the corresponding arteries (Magendie). Thirdly, as already

CAUSES OF THE VENOUS CURRENT. 24'J

stated, when the heart’s action is weakened, its rhythmic force
is propagated into the capillaries, giving a pulsjitory movement
to the blood contained in them, and so establishing the fact that
the heart’s action extends to that part of the circidation ; but,
besides this, under certain conditions, oscillations occur in the
blood-pressitre in the veins, as indicated by the hEemadynamo-
meter. Fourthly, water injected into the arteries, with a
force less than that of the heart, returns through the veins.
Lastly, it has been shown by Dr. Sharpey, that defibrinated
ox’s blood injected into the thoracic aorta of a dog, passes
freely back by the veins of the lower limbs ; also, that if tlie
aorta be tied in the abdomen, below the origin of the arteries
of the stomach and intestines, the blood still returns along the
inferior vena cava. In the former case, the blood passes
through a single capillary system, namely, that of the lower
limbs, whilst, in the latter, it is propelled through two sets of
capillary vessels, viz. through those of the alimentary canal,
into the portal venous system, onwards through the capillary
plexuses of the hepatic lobules, and then through the hepatic
veins into the vena cava inferior. The pressure employed in
these experiments, as measured by the haemadynamometer,
was maintained at about 6 inches of mercury, which is known
to agi-ee with the force of the left ventricle in the living dog.
To propel the blood through the pulmonary arteries, capil-
laries, and veins, a less force was sufficient. From the
preceding considerations and experiments, the adequacy of
the heart’s force, to complete the circulation of the blood
back to itself, may therefore be considered as established.
The position of this organ in the centre of the circulatory
system, its large muscular mass, and the proportionate thick-
ness of the right and left ventricles to the work which each
has to perform, likewise favour the conclusion that the heart,
when present, is the real agent in the circulation of the
blood. A circulation also takes place, however, in so-called
acardiac embryos, in which the heart is absent, though, in
some of these, the movement of the blood may depend on the
action of the heart of a conjoined embryo. Again, in the
early embryo of the chick, a movement of tlie blood in the
so-called vascular area, is noticeable before the heart begins
to pulsate ; but this movement is irregular, and takes place
from the vascular area towards the embryo. Moreover, as we
shall hereafter see, a true circulation takes jdace, in contractile
I ^vessels, in certain of the lower animals, which arc destitute of

250

SPECIAL PHYSIOLOGY.

a lieart. Lastly, in plants, examples are met with of a circu-
lation independent even of contractile vessels or cells. The
advocates of the existence of a force, originating in the capil-
laries or their neighbourhood, relying on these and other facts
already mentioned, of course suppose it to be superadded to
that of the heart in the venous circulation.

The motion of the blood in the veins, and its consequent
return, through them, to the heart, are aided, in Man and the
higher animals, by certain secondary or so-called adjuvant
causes, such as the pressure of the muscles, and the thoracic
respiratory movements.

In a few exceptional cases, the veins themselves possess a power of
rhythmic contraction ; the veins in the delicate ears of the rabbit, have
been seen to pulsate ; in the bat’s wings, the veins contract from 8 to
10 times in a minute (Wharton Jones). The caudal vein of the eel,
the portal veins of the myxine, and some of the abdominal veins of the
amphioxus, are also pulsatile at certain points.

The effects of muscular pressure, considered as an aid to the
circulation, are entirely due to the presence and direction of the
valves in the interior of the veins. These are found chiefly in
the veins of the limbs, especially in the superficial veins, and
also in the large veins at the root of the neck. Firrthermore,
the free edges of the valve-segments being turned towards the
heart, in the direction of the venous blood- ciu-rent, the valves
allow the return of blood to the heart, but are speedily closed,
when any obstacle to the onward flow of the blood occurs, as
when a vein is compressed between a valve and the heart.
Under such circumstances, the reflux of the blood in the
veins, from its trunk to its branches, is checked, and on any
additional pressure, the blood contained in the veins, isurged on
towards the heart. Moreover, owing to the frequent anasto-
moses between neighbouring veins, some of the blood may also
be pressed into collateral channels, which are not subjected to
pressure, and so be aided in its progress to the heai't. This is
exemplified by the increased quantity of blood forced into the
superficial veins of the limbs, during muscular efforts which
compress the deep-seated veins. In the actions of different
muscles in the various movements of the body, sometimes one
set of veins, sometimes another, must be compressed ; and the
varying degrees of compression to which the deep-seated veins
especially are subjected, must assist or hasten the return of
blood to the heart. But this is not an essential cause of the
venous circulation, for that is perfectly performed dmung the

AIDS TO THE YENODS CDBBENT.

251

most complete rest of the muscles of the limbs, as in the state of
repose, sleep, and paralysis ; moreover the circulation through
the brain is performed altogether independently of muscular
pressure, and of the presence of valves in its veins. When,
owing to muscular exertion, a larger quantity of blood is re-
turned to the heart in a given time, the frequency of the
heart’s beats is always increased, a mutual adaptation being
thus evidenced, between the rapidity with which the blood is
returned to the heart, and that with which the heart endeavours
to tran.smit it onwards.

The respiratory movements have been long believed to aid
in the systemic circulation of the blood. Unlike the pulmo-
nary circulation, the systemic circulation is partly performed
within, but partly, and chiefly, without, the thorax ; hence
different portions of it, are unequally affected or disturbed by
the thoracic movements. It has already been stated that
during, and almost to the end of expiration, the blood pressure
in the systemic arteries is increased ; the effects of this increased
pressure have even been recognised beyond the capillaries, in
the veins; for the flow of blood from a divided vein becomes
stronger at each expiration. But expiration, though it aids
the arterial current, must, when the continuity of the veins is
perfect, retard the venous cun-ent ; for the chest walls must
then compress the contents of that cavity, including the right
auricle and great venous trunks, and so hinder or check the flow
of blood into them. This is shown by the accumulation of blood
in those veins, by the congestion of the face, and by the dis-
tension of the veins of the neck and forehead, during expiratory
efforts, such as coughing or sneezing, and holding the breath,
with or without some other accompanying effort. The ex-
piratory thoracic movements cannot, therefore, be regarded as
contributing to the venous circulation, the effect on the blood
in the arteries, being more or less counterbalanced by that on
the blood in the veins. The inspiratory movements increase
the arterial blood pressure, without otherwise affecting the
blood-current in the arteries ; because the semilunar valves
prevent regurgitation towards the thoracic space. But the
absence of similar valves at the entrance of the vena; cava; into
the right auricle, so far permits the influence of insj)iration on
the blood in the great veins, as to facilitate its entrance into
the thorax, i. e. into the gi’eat venous trunks and the right
auricle of the heart.

If a bent tube be inserted into the jugirlar vein of an

252

SPECIAL PETSIOLOGT.

animal, and its lower end be dipped into fluid, the latter will be |
found to rise within the tube, at each inspiration, sinking again, |
even a little below its original level, during expiration (Sir D.
Barry). The blood pressure, as measured by the hasmadynamo- •
meter, has also been shown to be less, by from 3 to 7| inches, in I
the veins duringinspiration, especially in those near to the chest; I
in the sciatic vein, on the other hand, it is no longer observed.

If the veins had rigid walls, the eifect of inspiration in draw- .
ing the venous blood into the thorax, would be considerable ; |

but the collapsible character of their coats, and their yielding
on pressure, prevent this exhausting process. At the root of the
neck, the great veins are more or less supported by, or attached |
to, the bones or other parts, and so may be partially maintained |
in a pervious condition. The effect of inspiration is, indeed,
limited to the large veins close to the thorax ; for, as we have
seen, the blood pressure in the more distant veins of the limbs ,
is not increased during inspiration. It is this suction force |
towards the chest, during inspiration, which has been named,
in regard to its effect on the circulation, the vis a fronts^ in
contradistinction to the vis a tergo, derived mainly from the
heart, modified by the arteries, possibly aided by the nutritive I
and respiratory work accomplished through the capillaries, and
certainly assisted by muscular pressure. The existence of this I
suction force towards the thorax, and its influence on the !
venous blood-current, are illustrated by theaccidents which have
sometimes occurred in surgical operations in the region of the j
neck, when air has been drawn in through wounded and
patulous veins, and has occasionally caused death. Horses
have been often killed by blowing air down the jugular vein.
The right side of the heart is, in such cases, found filled with
frothy blood. The cause of death is probably due, not to )
paralysis of the muscular fibres of the heart, but to the me-
chanical impossibility of the passage of frothy blood through
the capillaries of the lungs.

The presence of valves in the veins near the heart, also con-
tributes to the intermittent aid given to the venous circulation
by the respiratory movements; for, whilst they permit, during ■
inspiration, the influx of blood through the large veins into
the chest, they prevent the reflux of the blood in them during jj
expiration, so that the balance of advantage is in fiivour of the f
return of the venous blood. The valves of the jugular veins i
not only serve this purpose, but also prevent the regurgitation «
of the blood towards the brain, during coughing, or other ||

EFFECTS OF GRAVITY ON THE CIRCULATION.

253

efforts accompanied by violent expiration or compression of
the chest. This reflux motion of the blood in the great veins
of the neck, is shown by alternating conditions of fulness and
emptiness of those vessels, synchronous with expiration and
inspiration, producing the so-called respiratory pulse. In cases
in which portions of the skidl have been removed in the living
body, and in which the veins within the cranium, protected
from atmospheric pressure at their sides, may be compared to
the tube in Sir D. Barry’s experiment, an alternate rising and
sinking of the brain have been observed, corresponding respec-
tively with the movements of expiration and inspiration. These
movements must be distinguished from the slighter pulsatory
movements coincident with the heart’s action, and dependent
on the pulse of the cerebral arteries. In constrictive disease
of the valved orifices of the heart, the return of blood into
that organ from the veins, is impeded, and those vessels,
accordingly, become permanently distended near the heart.
Such disease almost always affects the orifices on the left side
of the heart, and its effect on the great systemic veins, is com-
municated backwards, indirectly, through the pulmonarj^ cir-
culation. Even in the healthy condition, the imperfect closure
I of the tricu-spid valve causes a venous pulse at each ventricular
systole, the shock being conveyed through the blood in the right
auricle, and thence into the veins of the neck, as far as the
: first set of valves.

The effects of gravity on the venous circulation, or rather
I on certain parts of it, have been sometimes erroneously esti-
; mated ; for it was imagined that the upward current through
! the veins in the lower part of the body, i.e. below the heart,

■ was resisted by the weight of the column of blood below that
organ ; whilst the venous circulation in the upper half of the

i body, i.e. above the heart, was thought to be aided by the

■ weight of the corresponding column of venous blood. But
' the circulation of the blood being performed in a closed system
i of vessels, consisting, as it were, half of arteries and half of
1 vein.s, which meet in the capillaries, the weight of the venous
i blood in the lower limbs, is counterbalanced by that of the
^ arterial blood. Hence, the gravity of the venous blood does not,

t per se, offer, such an obstacle to the circulation, as requires to be
' overcome by the force of the heart; for the two columns of blood
I balance each other haemostatically, like columns of water in a
U-shaped tube. With regard to the vessels above the heart, they
also form a double closed system, and the advantage of gravity

U54

SPECIAL PHYSIOLOGY.

on the venous side, is, so far as the heart’s action is concerned,
counterbalanced by the disadvantage on the arterial side.

Gravity, however, does actually affect the circulation, through
its influence on the circulatory organs, especially on the
capillaries and veins ; for these vessels are not rigid, like a
U-.shaped tube, but yielding. The weight of the entire
column of venous blood, for example, is supported by the
coats of the veins, those of the lower limbs having more
weight to bear than the veins of the trunk, and these again
more than the veins of the upper limbs, neck, and head.
Hence the coats of the veins, in the lower limbs, especially
those of the less supported subcutaneous veins, are propor-
tionally thicker than those in the upper parts of the body, the
coats of the jugular vein being very thin, and those of the
saphenous vein very thick, in proportion to their size. Hence,
too, the valves are more numerous, and of greater strength,
in the veins of the lower limbs than in those of the upper
limbs ; whilst in the neck, they exist only in the neighbour-
hood of the chest. The mechanical effect of these valves, is to
save the entire length of the vein from the total pressure of
the venous column, and to divide it into shorter subordinate
columns, into which, however, weight is still transmitted by
the collateral veins. When the valves of the veins of the
lower limbs, are weakened, and no longer close perfectly, those
vessels become distended, and varicose. If the tonicity and
elasticity of the smaller veins be impaired, or overcome, by
prolonged over-distension, from obstructions to the return of
blood from them, or by general debility, the fluid part of the
blood is liable to escape through the coats of the capillaries
and minute veins, so as to cause dropsy.

The rate o f motion of the blood in the veins, is much quicker
than that in the capillaries ; but not so quick as in the arteries.
In the jugular vein of a dog, the rate of motion has been
estimated at 6|^th inches per second (Volkmann). Considered
generally, the average velocity of the blood in the veins, is
said to be from to ^ of that of the blood in the correspond-
ing arteries ; this estimate is founded on the supposed relative
capacity of the venous, as compared with the arterial, system,
Avhich .is believed to be as 2 or 3 to 1. As the velocity of
the arterial blood diminishes in the smaller arteries, partly in
consequence of friction, but also owing to the increased
capacity of the branches in comparison A\dth the trunks, so
inversely, as the veins diminish in capacity from their

rECULIAEITIES IN THE TENOUS CIRCULATION.

255

branches to their trunks, the velocity of the blood in them
increases as it approaches nearer and nearer to the heart, and,
in the larger veins, becomes equal to about f, or more, of the
velocity in the corresponding arteries. The form of the
entire vascular system has indeed been likened to two bent
cones, joined at their apices in the heart, and at their bases
in the capillary system. The quantity of blood received by
the right auricle, closely agrees with that thrown from the left
ventricle ; hence, therefore, the velocity of the venous current,
as it enters the right auricle, must be less than that of the
arterial blood passing through the aortic orifice ; for the com-
bined areas of the two vente cavs, are greater than the area of
the aorta.

The rate of motion of the blood in the veins, is more subject
to disturbing causes, whether of acceleration or retardation,
than in any other part of the circulation. Thus, the effects of
muscular pressure, though, on the whole, favourable to the
onward flow of the blood in the veins, are necessarily inter-
mittent, according or not as the muscles are at play. Again,
the opposite influences of expiration and inspiration, though
felt only within a certain distance of the thorax, and so affect-
ing the rate of motion of the blood in the large veins only, are
themselves liable to great variations, according to the activity,
violence, or depth of the inspiratory or expiratory movements.
Such variations occur constantly during life, and incess;mtly
alter the rate of motion of the venous blood-current. In ex-
periments on animals not subjected to the continued and
uniform influence of chloroform, the struggles, and the respira-
tory efforts of the creature, greatly disturb the velocity of the
venoirs current, sometimes checking, sometimes accelerating,
it. Individual’estimates of the velocity of the blood in the
veins, must therefore be accepted, with some reservation.

There are certain peculiarities in the venous circulation of
particular parts of the body. Thus, the portal circulation is
peculiar, from the fact that the blood pa.sses in it, through
a second capillary network, before it returns to the heart;
for the blood which circulates thus through the liver, has
already been driven through the capillary vessels of the
other abdominal organs of digestion. There are no valves
in the portal or hepatic veins ; but the latter are retained con-
stantly in a pervious state, by their adhesion to the substance
of the liver, a condition favourable to the pa.ssage of the
blood from that organ. Again, the circulation within the

25G

SPECIAL PHYSIOLOGY.

cranium, presents peculiarities; the arterial trunks which
enter it, four in number, are of large size, traverse bony
passages in their way to the cranial cavit}^, and unite by ana-
stomoses in the interior of the skull, at the base of the brain,
all which arrangements are calculated to secure a full and
free supply of blood to the brain, under various conditions of
external pressure, or other impeding causes. Besides this,
the proper arteries of the brain, ramiiy, in an unusuallj’-
tortuous manner, upon its complex surface, and at last divide,
in the pia-mater, into a close web of numberless branches sup-
ported by a delicate cellular tissue ; from these, long slender
minute vessels enter the brain at all points, ensuring a perfect
supply of blood, and its even and gentle entrance into the
delicate cerebral substance. The veins within the cranium
present special modifications; first, they have no valves;
moreover, the largest venous channels consist of passages
between layers of the dura-mater, the fibrous membrane
which immediately lines the skull ; hence, they are not sub-
jected to accidental pressure, such as might interfere with the
blood-current within them. Lastly, as the cranium itself has
unyielding walls, the circulation of the blood through the
brain, is carried on under very peculiar conditions, as compared
with that of other organs, which are subject to atmospheric,
and perhaps muscular, pressure also. The brain and the blood
being incompressible, the quantity of blood within the cranium,
must either be always the same, or else some special provision
must exist for its increase or diminution in quantity. It has
been suggested, that the quantity of blood in the cranium is
absolutely unalterable, and that the only changes -which can
take place in the cerebral circulation, are various compensatory
displacements of the blood, in the interior of the arteries, veins,
and capillaries ; but experiments have shown that the brain of
an animal may be rendered pallid, i.e. may be deprived of the
blood in its vessels, by extreme venesection. Moreover, the
presence of the cerehro-spinal fluid (vol. i. p. 295), and the
known rapidity with which the secretion and absorption of so
diffluent a fluid, may take place, afford a feasible explanation
of the mode in which variations in the quantity of blood in
the vessels within the cranium, may be rapidly counter-
balanced.

The pulmonary circulation presents many peculiarities. Its
arteries convey dark or deoxygenated, and its veins bright or
oxygenated, blood. Neither its veins or arteries anastomose,

PERIOD OF COMPLETE CIRCULATION.

257

except in their very finest ramifications ; its veins have no
valves, either in their course, or at their entrance into the
left auricle; its capillaries are large, most numerous, and
very short between the arteries and veins. As every part of the
pirlmonary circulation is carried on within the thorax, the
flow of blood from the right ventricle, through the pulmonary
vessels, to the left auricle, is, unlike the systemic circulation,
equally influenced in every part, at each moment, by the
varying conditions of thoracic pressure. Lastly, the loops of
the pulmonary circulation are much shorter than those of the
systemic vessels, and the blood takes much less time in passing
through them. The velocity of the blood is greater, and the
blood pressure much less.

Period of a complete Circulation.

It has been seen that the chief cause of the circulation of
the blood in Man, and in animals possessing a heart, is un-
doubtedly the muscular force of that otgan ; that the relative
velocity of the blood-current in its several parts, is quickest in
the arteries, slower in the veins, and slowest, by many degrees,
in the capillaries, the actual rate in the large arteries being
about 10 inches per second, in the small arteries probably
about 2'2 inches per second, in the capillaries about -j\yth of
an inch per second, and in the medium-sized veins from about
^ to ^ of the rate in the corresponding arteries ; and lastly, that
the rate of movement through the pulmonary circulation, is five
times more rapid thqn that through the systemic circulation.
There remains yet to enquire, in what period of time the
complete circulation is performed, that is to say, in what
time, a given minute portion of blood, thrown from the left
ventricle, or passing any other given point of the circulation,
will flow through the body and lungs, back to the same point.
The conclusion arrived at on this subject, based on many
experiments in animals, is, that, in Man, a complete circulation
of a given particle of the blood, may be performed within
a much less time than one minute. A solution of ferro-
cyanide of potassium (selected for the facility with which it
may be detected by appropriate chemical tests), being injected
into the right jugular vein of a horse, successive portions of
blood are drawn from the oppo.site jugular vein, and subse-
quently tested; the presence ofthe salt has been detected in the
portion of blood so drawn, at the expiration of 30 or even of 20

VOL. ir. s

258

SPECIAL PHYSIOLOGY.

seconds (Hering). In such an experiment, the ferrocyanide of
potassium could not have passed through the tissues across
the neck, from one vein to the other, but must have proceeded
with the blood along the right jugiilar vein, to the right
side of the heart, thence, through the pulmonary vessels, to
the lei't side of that organ, next through the aorta, carotid
arteries, and capillaries of the head and neck, and thence
along the veins into the left jugular ; in other words, it must
have performed, with the blood, a complete circuit through the
lesser circulation in the lungs, and through that part of the
greater circulation which belongs to the head and neck. The
passage of the ferrocyanide of potassium, from the jugular
vein, through the lungs, and thence, through the hinder limbs
of the horse, to the great saphenous vein of the thigh, takes
place in 20 seconds ; and, from the same vein, to various arteries
of the body, in still shorter times, viz. to one of the facial
arteries in 10 seconds, but to more distant arteries, as e.g.
to the metatarsal in the hind limb, in from 20 to 40 seconds
(Hering).

Similar experiments have been made, but on an improved
method, by arranging a series of small cups on a rotating
apparatus, so that they can be quickly moved in succession,
before an aperture in a vein ; in this way, the blood is collected
at very short and exact intervals. The time occupied in a
complete circulation of the blood, can thus be determined even
in small animals. In them, speaking generally, the passage of
poisonous substances injected into the veins, takes place more
quickly than in the horse. In the dog, the time is found to be
16'7 seconds; in the rabbit, nearly 7‘79 seconds; in the
cat, 6‘69 seconds, and in the squirrel, 4‘39 seconds; in the
horse, it is 31‘5 seconds (Vierordt). Allowing for the obvious
effect of size, and consequent length of the bloodvessels, it must
be concluded that the blood in the human body, performs
the complete roimd of the circulation, in even less than half a
minute.

Viorordt has pointed out a remarkable relation between the freqaiency
of the pulse, that is, of the heart’s beats, in different Mammalia and Birds,
and the ascertained average period of the complete circulation in them.
The frequency of the pulse in these animals, increases, generally, as their
■size diminishes, being, for example, in the horse, dog, cat, rabbit, and
squitTel, respectively, 66, 96, 240,, 220, and 320 in the minute, or 60
• seconds. But, as we have seen, the times of a complete circulation in
them are, 31'6, 107, 6'69, 779, and 4'39 seconds. Prom such data,
it is shown, that a complete circulation, in these several animals, is

PERIODS OF PARTS OF THE CIRCULATION.

259

performed during the following numbers of heart’s beats; viz. 28-8,
26'7, 26-8, 28'5, 23'7. Thus, in the horse, for example, as 60 sec. ;
55 beats: : 31-5 sec.: 28 8 beats. In the larger Birds, nearly the same
proportion prevails ; and the mean relation is found to be about 27
heart’s beats for each complete circulation.

In Man, Vierorclt calculates that, with the pulse at 72
per minute, the heart’s beats are 27'7 for each complete
circulation, which is accordingly performed in 23’1 seconds, or
less than half a minute. Thus as 72 : 60 : : 27'7 : 23T.

Every portion of the blood does not complete its circulation
in exactly the same time. As regards the pulmonary circula-
tion, but little difference can occur, whether a given portion of
blood passes through the right or the left lung, or through this
or that portion of either lung, on its way from the right to
the loft cavities of the heart; but even here, certain differences
in the length of the route pursued by different portions of
blood, must exist. In the systemic circulation, however, the
differences are much more marked ; the shortest route through
which a poition of the blood has to pass from the left to the right
cavities of the heart, is that through the nutrient vessels of
the heart itself, and the longest route, that through the vessels
of the lower limbs. Different portions of the blood have, in-
deed, to circulate through arches of varying length, and hence
the time which they take to traverse different parts of the
body, must be somewhat different.

The slow rate of motion of the blood through the capil-
laries, only 2 inches per minute in warm-blooded animals,
appears, at first sight, to be opposed to the above-mentioned
conclusion as regards the high rate of velocity of a complete
circulation ; for in that circulation, the blood passes through
two sets of capillary vessels, pulmonary and systemic, besides
traversing the arteries and veins of those two circulations, as
well as both sides of the heart. But it has been estimated
that the systemic capillaries of any given organ or tissue of
the body, numberless as they are, cannot measure, from the
finest arteries to the finest veins, more than about yjyth of an
inch in length ; the pulmonary capillaries must be still shorter.
According to Vierordt, the systemic capillaries do not measure,
on an average, more than 7;’(jth of an inch in length, although
these limits are not well defined. The blood may therefore pass
through both the systemic a7ul pulmonary capillaries, in a period
of about 3^ seconds only (viz. in 3 seconds through the former,
and in ^ a second through the latter-named vessels). Assuming

260

SPECIAL PHYSIOLOGY.

with Vierordt, the total period of a circulation at about 28
seconds, in a man of average height, this would leave a balance
of 24^ seconds for the passage of the blood through the arterial
and venous channels and the heart. Supposing the mean
length of the arteries and veins to be, in a man of average
stature, 30 inches, and the average velocity of the blood in the
arteries to be 6 inches per second (the extremes being 10 and
2j inches), the time requii’ed for the passage of the blood
through the arteries, would be 5 seconds, and through the
corresponding veins, the velocity in which is estimated as being
^ to ^rd that of the arteries, the time would be 12^ seconds,
making in all 17-g- seconds, for the circidation through the
systemic arteries and veins. To this must be added a period
of 3.^ seconds, for the pas.«age of the blood through the pulmo-
nary arteries and veins (the rate of motion in them being said
to be five times more rapid than in the systemic arteries and
veins), making a total of 21 seconds. This, with the 3J seconds
above mentioned as required for the pulmonary and systemic
capillary circulations, equals 24^ seconds, or rather more than
the 23T seconds allowed for the complete circulation. These
numbers, though only approximating to the truth, still show
that the slow rate of the blood in the capillary poi-tion of the
circulation, or in the area of nutritive and respiratory inter-
changes, is quite consistent with the ascertained rapidity of the
circulation, considered as a whole.

The circulation of the blood is said to be generally, but not
always, accelerated by an increased frequency of the heart’s
action. As life advances, it becomes slower.

Quantity of Blood in the Body.

The total quantity of blood in the body, has been the sub-
ject of much investigation and discussion. The estimates of the
older authors, for tlie most part, were too high, Avhilst some of
those of later Avriters, probably err in the oppo.site direction.
The actual quantity, in a man of average height and weight,
has been supposed, by some, to be 26 or 30 lbs., and by others
only 12 lbs. The ratio betAveen the Aveight of the blood and
the weight of the body, the blood included, has been estimated,
by some authors, as 1 to 4^, and, by others, as 1 to 13;
according to tlie.se proportions, Avhich differ so Avidely, the
total quantity of blood in the body of a man Aveighing 150 lbs.,
would be either upwards of 33 lbs., or only about 11^- lbs.

TOTAL QUANTITY OF BLOOD.

2G1

Observations on the quantity of blood lost in hajmorrhages,
are not considered trustworthy, since in slow bleedings, large
quantities of liuid are absorbed from the tissues, to refill the
emptying vessels, and so add largely to the amount of blood
that may be drawn. The quantity of blood escaping from the
vessels in decapitated criminals, added to that which may bo
subsequently expelled from the vessels, by cautious injections
of water, gives a more accurate result. But careful experi-
ments on animals, are of most value. The method of Herbst,
Avhich consists in quick bleeding from many vessels opened
simultaneously, gives the proportionate weight of the blood to
that of the body, as from 1 to 12 in the ox, 1 to 16 in the dog,
and 1 to 24 in the rabbit; hence, it would appear that the larger
the animal, the greater is the proportion of blood to the body.
Valentin compared the specific gravity of the blood drawn from
a living animal, before, aird after, the injection into its blood-
vessels of a given weight of water, the diminution of the
specific gravity of the blood, by that quantity of water, serving
as a factor in the calculation ; this method gives about 1 to 4^
as the ratio to the body in the dog. Chemical substances easy of
detection, having been injected into the blood, in known amounts,
and the quantity, in a certain portion of the blood drawn fi’om
the vessels, having been determined, data have been obtained for
calculating the total quantity of the blood ; this method shows
a ratio of 1 to 8 or (Blake). AVelcker’s chromatic method
is so called, because he estimates the amount of blood left in
the body after bleeding, by means of the colouring matter.
A set of standard colom^ed solutions is first prepared, by
mixing a certain known quantity of the blood of an animal,
with different known quantities of water. The creature is
then bled rapidly to death, and the blood so drawn is weighed.
The residual blood in the vessels, is then estimated in the fol-
lowing manner ; — the vessels are wa.shed out with free injec-
tions of water ; the whole body of the animal is likewise
divided into small pieces, and macerated, so as to extract all
the cruorin in it; these aqueous solutions are then mixed
together, and measured, and the tint of the mixture is compared
with the standard solutions, and thus the quantity of blood
in it is determined. In this way, the proportion of blood
to the body, in the dog, is estimated at about 1 to 12.

The quantity of blood in the body, has been calculated by
Vierordt, by multiplying the quantity supposed to be expelled
I’roin the left ventricle at each systole, by the number of times

262

SPECIAL PHYSIOLOGY.

tlie heart contracts during a complete circulation of the blood
through the system. The mode in which the latter datum is
obtained, has already been explained (p. 258-9) ; the former is
thus arrived at. The average velocity of the blood in the
human carotid artery, is assumed to be equal to that in the
carotid of a dog, and the sectional area of the vessel being
known, it is easy to determine, by multiplying one into the
other, the quantity of blood which passes through any part of
that artery in a second. Thus 261 millimetres, the velocity
of the current in the carotid per second, x '63 square centi-
metres, the sectional area of that vessel, = 16'4 cubic centi-
metres, the quantity which passes through a certain part of the
vessel in one second. The quantities passing per second, in
the innominate, left subclavian, arch of the aorta, and coro-
nary arteries of the heart, are then estimated in the same
way, the rate of motion of the blood in the aorta being
assumed to be ;jth faster than it is in the carotid. By these
steps, Vierordt arrives at the conclusion that the quantity of
blood projected through the orifice of the aorta from the left
ventricle, every second, is 207 cubic centimetres, or 219
grammes in weight, or nearly oz. av. But as the heart beats
72 times in a minute or 60 seconds, there occur l^th systoles
in each second of time ; hence, the quantity of blood thrown
into the aorta at each systole, is about 180 grammes, or rather
more than 6'3 oz. (p. 213).

As all the blood in the body, must pass once through the
aorta, in every complete circulation of that fluid, and as this
requires 2 7 ‘7 systole ; to accomplish it, the quantity thrown
at each systole, or 180 grammes, x 27'7, the number of
heart’s beats, gives, for the total quantity of blood in the body,
4,986, or, in round numbers, 5,000 grammes, which are equal
to about 11 lbs. av. ; this, compared with the average weight
of the body, taken by Vierordt at 140 lbs., is about as 1 to
12'6. The jDi’oportion finally adopted by Vierordt, as pre-
vailing throughout the warm-blooded Vertebrato, is 1 to 13.
Assuming the average weight of the adult male to be 150 lbs.,
the usual estimate of English writers, the total quantity of
blood in the body, would be about 11-^ lbs. av. It has been
found that on bleeding an animal soon after feeding, nearly
double the quantity of blood is obtained, as compared with the
result of bleeding a similarly sized animal in a state of lasting.
This circumstance may partly explain the great differences in
the estimates above recorded ; it also justifies the conclusion

USES OF THE BLOOD.

263

that, in certain conditions of the body, the quantity of blood
in tlie human adult of average weight, may be even as much
as 14 lbs.

The quantity of blood thrown into the aorta at each systole,
which is likewise the measure of the capacity of the left ven^
tricle, is equal to about •g-bjjth part of the weight of the body.
It would further seem that, in warm-blooded animals gene-
rally, the quantity of blood flowing through an equal weight
of the body in a given time, is proportional to the frequency
of the heart’s beats. Thus, in GO seconds, the quantities of
blood which pass through 1,000 parts in weight of the body,
in the horse, in Man, in the dog, rabbit, and squirrel, are,
respectively, 152, 207, 272, 620, and 892 parts, the fre-
quency of the pulse in them being 55, 72, 96, 220, and 320.
The ratios, accoi'diugly, are all about as 3 to 1, The more rapid
the heart’s action, therefore, the quicker must be the nutritive
changes in the tissues of the body ; moreover, as there is no
evidence of the capillaries being relatively more numerous in
the smaller and quick-pirlsed animals, the circulation through
their vessels must be relatively qiricker.

The Uses of the Blood and of its Circulation.

The blood itself is a highly complex fluid, renewed from,
though not altogether formed out of, the lymph and chyle,
and perfected, as we shall hereafter see, by the aid of the vas-
cular glands and the respiratory organs. One of its offices is
evidently that of providing an exceedingly elaborate material
for the nutrition of every part of the body, and for the pro-
duction of the various secretions which are used in the
organism. The fluid character of the blood, fits it for trans-
mi.ssion through a vascular or circulatory apparatus, even
through the finest vessels ; and in this circulation through the
body, by means of such an apparatus, its proper nutrient
materials are conveyed to all the organa and tissues of the
frame, into which a fluid plasma passes through the coats of
the capillaries. But, secondly, besides furnishing a constant
stream of nutrient material, the blood receives, by absorption
into its own current, refuse and effete matters from the whole
system, and subsequently tran.sports them to proper excreting
organs, by which they are thrown out of the body. Lastly,
the dark venous blood receives, through the respiratory organs,
a quantity of oxygen from the air inhaled into the lungs, and

264

SPECIAL PltTSIOLOGY.

transports this oxygen in the red and arterial blood, to every
part of the frame, either for its special stimulation, or for
combination with its proximate chemical constituents, in the
exercise of the functions of those parts ; the returning venous
blood brings back, amongst other oxidised materials, carbonic
acid, and conveys this to its proper excreting apparatus, the
lungs-, whence it is thrown off. The circulating organs in
animals ate, therefore, modified, in accordance with the cha-
racters of their respiratory organs.

ORGANS AND FUNCTION OF CIRCULATION IN ANIMALS.

Vertehrata.—^Tsi& Vertebra ta generally, like Man, have not only a
perfectly formed blood, containing coloured and colourless corpuscles,
but they also possess a central heart placed in a pericardium, and con-
nected with a completely closed system of bloodvessels, consisting of
arteries, capillaries, and veins. In the Amphioxus alone, there are no
coloured corpuscles, and the heart has no pericardium. As we have
seen, the Vertebrata only, have a system of absorbent vessels, which
empty themselves into the bloodvessels. The size of the red corpuscles
in several animals is given in a Table at p. 77-8, vol. i.

But important peculiarities exist in the vascular systems of some of
the Vertebrata, dependent upon the structure of their respiratory organs.
Thus, in Mammalia, Birds, Eeptiles, and Amphibia, respiration is
performed by means of lungs, and hence they are called pulmonated or
air-hreathing Vertebrata. These consist of two divisions, one including
Mammalia and Birds, in which the temperature of the blood is high, and
another, including Eeptiles and the perfect Amphibia, in which the
temperature of the blood is low ; the former are the warm-blooded, pid-
monated or air-breathing, Vertebrata, and the latter, the cold-blooded,
pulmonated Vertebrata. Again, Fishes breathe by means of gills or
branchiae, and constitute the branehiated or water-breathing Vertebrata ;
they are still more decidedly cold blooded. In each of these divisions,
special modifications of the circidatory apparatus are met with, dependent
On differences in the degree, or kind, of their respiration. The Class
Amphibia, contains animals which commence life as aquatic branehiated
creatures, but whichj in the adult state, become pulmonated ; their circu-
latory organs are accordingly modified during life, and in a few,, which
retain, in the adult condition, both gills and lungs, the organs of circu-
lation present a composite form. In all cases, a ported circulation is
present.

In the warm-blooded, pulmonated Vertebrata, which include the
Mammalia and Birds, the heart, as in Man, consists of four cavities, two
auricles, and two ventricles, a right auricle and ventricle constituting
the right side, and a left auricle and ventricle forming the left side, of
the heart, the two sides being separated by a perfect intervening septum.
The general distribution of the vessels is also the same. All the blood
which returns from the body to the right auricle, is sent through the
lungs, by the right ventricle, and on into the left auricle, before it is

THE CIRCDLATIOX IN REPTILES.

265

agiiin distributed to the body by the loft ventricle. As in the human
body, there is ii perfect douhle circulation.

Certain minor peculiarities are mot with. Thus, the position of tho
heart is usually median, except in tho orang-outang, and perhaps in
other Anthropoid apes, in whicli it inclines to the left side, as in Man.
In many Kuiuinants, a bony structure, the bone of the heart, strengthens
the base of the ventricular septum. In tho dugong, the apex of tlio
heart is deeply notched, tho ventricles being there separate; in tho
manatee, it is less notched.

In Man, and tho higher Mammalia, the chief arteries spring from the
arch of the aorta, unsymmetrically — an arrangement said to favour tlio
distribution of blood to the riglit fore limbs, rather than to the left ; but
in the lower Mammalia, tho branches arise symmetrically. In the hind
part of tho tail of the whale, the caudal artery runs, for purposes of
protection, through tho base of the echelon bones, on the under side of
the vertebriB. In many climbing lemurs, in the lion, and other largo
Carnivora, the brachial artery of the arm passes through an opening in
the humerus, and thus is protected from muscular pressure: so also
does tho iirtery of tho coffin bone, or hoof bone, in the horse.

A cluster of closely ramified arterial vessels, which frequently anas-
tomose together, and again coalesce into a single trunk, is named a rctc
mirahUe. Examples of such retia mirabiUa occur in the carotid arteries
within the cranium of tho Ruminants, the effect of which may be to
chock the too rapid flow of blood to the brain, during grazing. Similar
structures are found in the fore limbs of tho climbing sloths, and lemurs.
In diving animals, such as tho Cetacea, large retia mirabiUa exist in the
thorax, the object of which is probably to allow the prolonged sus-
pension of respiration during the submergence of those animals.

In tho higher Mammalia, as in Man, there is but one superior vena
cava; but in the Pachydermata and Kodentia, there are two superior
venm cavm, and sometimes a cross branch between them, in the neck.
Suppose an enlargement of this cross branch, so as to form a left inno-
minate vein, the blood from the left side of the head and neck and the
left upper limb, would pass over to tho right side, whilst the trunk of
the loft vena cava might then be obliterated, as far as the heart. In
certiiin diving Mammalia, venous ‘plcxitses, or venous retia mirabilia, exist,
in which tho impure blood is for a time retained. The portal system, in
the Mammalia, is entirely unconnected with tho I'onal veins ; sometimes
tho portal veins have valves.

In Birds, the heart is very strong, and lies exactly in tho middle lino ;
moreover, the chief branches from tho arch of tho aorta, are also sym-
metrical, in accordance with the equal bilateral development, so important
and typical in Birds. Tho veins in Birds, have relatively fewer valves ;
tho portal system communicates, by a few branches, with tho renal veins;
moHiover, the veins of tho pelvis and lower limbs, likewise contribute
branches to it.

In \\\%cold-hloodrd,‘jndmonated. Vcrtebrata,yi\\\Q\\ comprise the Reptiles,
and tho perfect Amphibia, tho heart is reduced to throe cavities; viz.
two auricles and one ventricle. One auricle, tho right and larger one,
receives blood from the system ; tho olhor, tho loft, usually smaller,
receives blood from tho lungs ; both discharge their contents into the
common ventricle, which thus receives a mixture of dark venous blood

266

SPECIAL PHYSIOLOGY.

from tho system, and bright arterial blood from the lungs. From the
single ventricle, there proceed, in the Reptilia, a distinct aortic and
pulmonary trunk, but in the Amphibia, only a single arterial trunk
exists, from which the pulmonary arteries take their origin; in either
case, a part of the mixed ventricular blood again passes through the
lungs, whilst most of it is propelled through the body. The blood is no
longer entirely sent through the lungs, before it is distributed to the
body again, as happens in the warm-blooded Birds and Mammals, which
possess a perfect double circulation ; on the contrary, a more or less
mixed blood goes to the lungs, and a more or less mixed blood to the
body. The pulmonary and systemic circulations are not wholly distinct,
but meet in the common ventricle ; the circulation is not completely
double. In the highest Repitiles, the Saurians, wdiich approach the Birds
in so many parts of their organisation, there exists, however, a partial
ventricular septum, which, in the crocodiles, is said sometimes to be even
complete. The outwardly single ventricle always gives off two arterial
trunks, and the. internal septum is so placed, that it serves to direct the
dark systemic venous blood entering from the right auricle, chiefly into the
pulmonary arterial trunk, whilst it turns the current of red arterialised
blood coming through the left auricle from the lungs, towards the aortic
or systemic arterial trunk. In these animals, then, the circulation
approaches closely to the character of the double circulation in Birds and
Mammals ; but the impei-fect structure of the ventricular septum may
permit a certain amount of intermixture of the two kinds of blood in
that cavity. The right or anterior portion of the ventricle, which is
connected with the pulmonary artery, has thinner walls than the left
or posterior portion, which is connected with the aorta. In the Chelonia
and Ophidia, a less perfect septum also exists, but it gradually becomes
smaller, and therefore less able to separate the two currents of blood, or
to guide these in special directions. In the perfect adult Amphibia, the
.single ventricle has either only slight traces of a septum, or, more com-
monly, no septum whatever ; the single arterial trunk, proceeding from
it, is sometimes named the arterial bulb, or bulbus arteriosus. Even
the auricular septum is imperfect in the Proteus.

The arrangement of the branches of the aorta, in these cold-blooded
pulmonated Vertebrata, is also peculiar. In Man and Mammalia, the
single aortic arch bends over the root of the left lung, and continues on
as the abdominal aorta. In Birds, the ai-ch of the. aorta turns down over
the root of the right lung, to become the abdominal aorta. In the higher
Reptiles, two aortic arches exist, one on each side, forming a right and
left aortic arch, which descend over the roots of the corresponding lungs,
and join together, somewhere in front of the vertebral column, to form
the abdominal aorta. Of these, the right aortic arch, the only one
present in Birds, is larger than the left, and evidently forms the proper
systemic artery; for it gives off the arteries to the head, neck, and upper
limbs, which parts accordingly receive almost entirely red blood, which is
directed into the aorta, as already mentioned, by the ventricular septum.
On the other hand, the left aortic arch is small, is joinetl by a short trunk
to the pulmonary artery, which springs from the. other side of the septum,
and from it receives dark blood ; hence it follows that the abdominal
aorta, formed by the coalescence of the right and left aortic arches,
carries mixed blood to the posterior part of the trunk, and the hind limbs.

THE CIRCULATION IN FISHES.

267

In the lower Eeptiles, three aortic arches exist on each side; the upper
pair give off the vessels of the head and neck, the lower pair give origin
to the pulmonary arteries, and all combine, by short branches, into two
descending trunks, which unite to form the abdominal aorta. Here,
also, a more perfectly oxygenated blood is provided for the anterior, or
more important part of the animal, a less perfectly oxygenated blood, for
the hinder part.

A portal circulation exists in both Reptiles and Amphibia ; it is con-
nected with the renal veins, which also exhibit a renal portal system;
i.e. a set of veins, which convey blood into the kidneys for distribution in
their interior. The condition of the organs of circulation in the young
or immature Amphibia, will be best understood after that of Fishes has
been described.

The cold-blooded, branchiafcd Vertebrata, or Fishes, have no lungs ;
those organs being represented, however, in a few species, by the so-called
air-bladder, an appendage, usually, of the pharyngeal part of the ali-
mentju’y canal. The heart is now simplified by the suppression of the left
auricle, there being no pulmonary veins to end in it; the ventricle also is
single, as in the Amphibia and Reptiles, but it never presents any trace
of an internal septum. There remain, therefore, but a single auricle
and a single ventricle. The auricle, like the right auricle in other cases,
receives the dark venous blood from the body, and transmits it, through
an orifice provided with valves, into the ventricle. This is very mus-
ctilar, and propels the blood, not into the lungs, for there are none, nor
directly into a systemic arterial trunk, or aorta, for immediate distri-
bution through the body generally ; but, on the contrary, the single
ventricle sends it into a short trunk, called the arterial hidb, which
has valves at its root, and, in a few examples, is even partially divided
into two. From this bulb, a series of arched vessels, usually five, some-
times four, in number, proceed upwards, supported on the cartilaginous
branchial arches, and convey tho blood, through the branchial arteries,
into tho gills, in which it passes through capillary vessels, and is then
collected by the branchial veins ; these running towards the vertebral
column, unite together on tho dorsal aspect of the alimentary canal, to
form a single systemic arterial trunk, which corresponds, in function, with
tho aorta of the higher Vertebrata. From this, branches are given off to
all parts of the body, excepting tho gills and generally, if not always,
certain parts of tho head, which are, singularly enough, supplied by special
branches proceeding at once from the branchial veins. From tho body
generally, tho blood is brought back, by tho systemic veins, to tho single
auricle. In tho Fish, therefore, all the blood which returns Horn tho body
to the heart, is sent first through tho respiratory or oxygenating organs,
before it re-enters tho system ; the respiratory apparatus is so interposed
that it forms a part of the general circulation, tho branchial circulation
being continued on to the systemic circulation, without tho blood coming
back to tho heart between them. Ileiico the circulation in tho br.an-
chiated Fish, is said to bo einc/le, as distinguished from tho imperfectly
I doxdile circulation of tho cold-blooded, and tho compldely double circula-
tion of tho warm-blooded, pulmonatod Vertebrata. Tho heart of tho
' Fish, is also said to bo a branchial and not a xystemic heart, bocauso its
immediate work is to force tho blood into tho branchiie or gills. No
special contractile apparatus exists beyond tho gills, to accomplish tho

268

SPECIAL PHYSIOLOGY.

circulation through the body — a fact which has already been adduced
(p. 24:3), to show that the heart’s action is adequate to drive the blood
through the systemic circulation of Man, and the pulmonated Mammalia.
In the caudal veins of tlie eel, however, as already mentioned, there
exists a pulsating portion, named a venous heart, which undoubtedly
assists in the return of the venous blood to the distant •proper heart.
Its presence may be connected with the unusual length of the systemic
vessels in this part of the eel ; but even here, the heart propels the
blood through the vessels of the gills, and afterwards through the
systemic arteries and capillaries. Pulsating dilatations are likewise
found in the arteries of the pectoral fins of the torpedo and chimsera,
and in the portal vein of the myxine.

In Fishes, as in other Vertebrata, a portal system of veins exists;
it is composed not only of the veins from the digestive organs, but
also of those from the other viscera in the posterior part of the abdomen,
and likewise of some of those from the liinder part of the body. The
venous trunks thus formed, conduct blood to the kidnej^s as well as to
the liver, so that, in Fishes, both these glands receive venous blood.
After being distributed through them, the blood is returned to the heart,
by proper hepatic and renal veins, which open into the vena cava in-
ferior. Ketia mirabilia, both arterial and venous, exist in certain
Fishes, on the swimming bladder, in the eyes, and in the neighboiirhood
of the gills and the intestines.

Since all the blood of Fishes, after its return from the body, passes
through the respiratory organs, before it again proceeds to the body, it
might be inferred that the respiration must be more complete in them
than in the Keptiles, in which only a portion of the venous blood is
transmitted to the respiratory organs, whilst some is distributed to the
body again. But in Fishes, the respiratory process itself is less active
than it is in Beptiles, being aquatic, instead of aerial. As the heart in
the Fish, is a branchial or respiratory heart, its single auricle and ven-
tricle have been supposed to be homologous with the right auricle and
ventricle, or respiratory heart, of the Bird and Mammal. This view, how-
ever, is only partially correct ; for though the auricle in the Fish’s heart,
is homologous with the right auricle of the more perfectly formed lilam-
malian or Avian heart, and therefore respiratory, the single ventricle
represents both ventricles of the heart of the warm-blooded Vertebrata,
and, indeed, rather the left than the right ventricle. In the Fish, the
branchial vessels given off from the arches, which proceed from the bulbus
arteriosus, end in the systemic arterial trunk, and thobranchiseand their
vessels, may therefore bo regarded as organs interposed in the systemic
circulation. In the pulmonated Vertebrata, on the contrary, the pul-
monary arteries enter the lungs, from which the blood is returned through
pulmonary veins, and those latter do not unite to form an artery, but i
re-enter the auricular portion of the heart ; so that the pulmonary system !
is not, like the branchial system, continuous with, or a portion of, the
systemic, but altogether a special circulation.

The Amphibia begin life as aquatic branchiatod animals, but most of
them, in their mature state, lose their gills and acquire lungs, so as to
become pulmonated, and air-breathing. In this metamorphosis, not
only transitions occur in the respiratory organs from the Piscine tx) the
lieptiiian condition, but also simultaneous adaptations of the circidating

THE CIRCULATION IN AMRHIBIA.

i>69

system. The clifFerences in the mode of respiration, and in the character
of the circulation, which are observed between two great Classes of the
Vertebrata, viz. Fishes and Eeptiles, are exactly paralleled by the differ-
ences mot with in the immature and mature respiratory and circulatoi'y
organs, in an individual Amphibian ; and the progressive steps which
lead from one state to the other, can be seen in the evolution of a single
animal. Those changes maybe traced in the frog, or in the salamander.
In the tadpole of the former, external branched gills first appear, but
soon become absorbed, and are succeeded by internal laminated gills,
resembling those of the Fish. In this condition, the heart, composed of a
single auricle and ventricle, receives the blood from the body, and pro-
pels it into a bulbus arteriosus, and thence, by three lateral symmetrical
branches, or branchial arterial arches, into the gills ; after passing through
capillary vessels, it is collected by the branchial veins, from the foremost
of which the arteries of the head are given off; these veins, but chiefly
the second and third, combine to form the systemic artery or descending
aorta, which conveys the blood into the rest of the body, whence it is
again returned by the veins, to the single auricle. This form of circula-
tion is truly Fish-like ; but at the base of each branchial lamina, a minute
vessel runs directly from each branchial arterial arch, to the com-
mencement of the descending aorta ; as development goes on, more
blood passes through these communicating vessels, directly from the
bulb into the descending aorta, without traversing the vessels of the
, gills ; still later, the gills themselves diminish, and more and more
blood passes through these little arched vessels at their base ; finally,
the gills and their vessels, being the one atrophied, and the other
• obliterated, the whole of the blood proceeding from the ventricle through
the arterial bulb, traverses these enlarged symmetrical communicating
vascular arches, and so reaches the descending aorta. In the meantime,

; from the lowermost vascular arch, on each side, there has been de-

■ veloped a little vessel, which ramifies on the walls of a small sac, or
1 rudimentary lung ; and as these organs are gradually enlarged, the vessels
i in question grow, and form the pulmonary arteries. liy these, one por-
I tion of the blood from the single ventricle, is carried to the newly evolved
I respiratory organs, the air-breathing lungs ; whilst the rest is conveyed
t through the remaining vascular arches, now reduced to two in number
' on each side, partly into the arteries of the head and nock, but chiefly
. into the aorta, and the body generally. Lastly, the blood returning

from the lungs, enters a small superadded auricle, or left auricle, which
; becomes parted off from the right; whilst the blood which returns from

■ the bo<ly, enters the ordinary right auricle. Thus is established
I an incomplete double circulation, precisely the form met with in

the lower Reptiles. In passing to the higher Reptiles, the essential
change consists in the gradual rising up of a septum within the single
' ventricular cavity, by which it becomes more and more completely
1 divided into two chambers, as seen in the Saurians, and especially in the
crocodile. This change, when quite complete, and constant, produces
1 the perfectly divided ventricles, with their entirely separate pulmonary
i and systemic arterial trunks, as found in the heart of the Bird and
^Mammal. Thus are formed the four-chambered heart and the completely
( double circulation.

Similar changes, in the heart and great vessels, occur in the young

270

SPECIAL PHYSIOLOGY.

newt or water salamander ; but the external gills not being transitory,
or giving place to internal gills, as in the tadpole of the frog, remain
throughout the larval condition, becoming, at one time, very large and
plumose. Like the internal gills of the hidpole, tliey receive vessels
from the bulbus arteriosus, and, as in them, their disappearance is asso-
ciated with the same clianges in the future distribution of the blood,
which is henceforth sent partly to the lungs, but chiefly to the body.

Certain of the Amphibia possess, in their mature condition, both kinds
of respiratory organs, viz. external gills and lungs, and are hence named
Perenni-hrunchiata. In these, as in the Proteus, the condition of the
circulation corresponds with that found in the intermediate stages of the
larval condition of the newt. Three anterior arches from the bulb,
supply the branchial arteries, and a fourth gives a vessel, which becomes
the pulmonary artery of its O'wn side ; the pulmonary veins end in a
rudimentary left auricle, and the systemic veins in a right auricle ; the
ventricle is single, and gives off the bulbus arteriosus, from which arise
the vascular arches just mentioned.

In the somewhat anomalous Fish, the Lepidosiren, or mud-fi.sh of the
Gambia, a remarkable approximation is shown towai’ds the perenni-
branchiate amphibian form of respiration and circulation. It has six
pairs of branchial vascular arches; of these, the first, fourth, fifth, and sixth
supply the branchiae, which are. filamentous, but not external, like the
permanent gills of the lower Amphibia. The second and third pairs,
pass as simple channels into the descending aorta, and also give off
branches which unite to form a single pulmonary artery, distributed to
the largely developed cellulated air-bladder. The single pulmonary
vein ends in the sinus of the inferior vena cava.

The preceding descriptions indicate a unity of plan in the circulating
organs of the Vertebrate series of animals, as marked as that which
may be traced in their skeleton and nervous system — gradual modifica-
tions of this plan being manifested in ascending from the lower to the
higher animals.

In the Amphioxus, the loudest Fish, and therefore the lowest Vertebrate
animal, the circulating system retains its Vertebrate type in the
arrangement of the principal vessels ; but it presents the singular ano-
maly of not having a single central heart, but possessing instead,
numerous contractile cavities situated in the course of the chief blood-
vessels. Beneath the complex branchial chamber, is a conti-actile vessel,
or bulb, performing the office of a ventricle ; from this, as many as
fifty pairs of branchial arterial arches arise, at the root of each of which,
is a contractile dilatation. These numerous branchial arteries, of which
the anterior ones are themselves contractile, end, as usual, in the branchial
veins, which are equally numerous, and combine together to form the
proper descending aorta, -which is placed immediately beneath the chorda
dorsalis. The foremost vascular arch, the duct of Botal, joins the aortji,
without supplying branches to a branchial fringe. The aorta distributes -
branches to ail parts of the body, the veins from which ultimately unite
to form two venous trunks, one a portal vein, a part of which is dilated
and contractile, and another which represents the vena cava inferior, on
■ft'hich is found a contractile sinus, jiulsating rhythmically, and propelling
the blood forwards into the rudimentary ventricle already described.
The great number and wide distribution of rhythmically contractile

•«(

THE CIRCULATION IN NON-VERTEBRATA.

271

cavities in the circulatinu system of tlio Amphioxus, suggest a com-
parison with the multiple hearts, or pulsating chambers, seen in certain
Molluscous and Annulose animals. Its blood also contains only colour-
less corpuscles.

In the Non-vertebrate animals, the blood, and the organs of its circu-
lation, whore they exist, are peculiar, and distinguished from the same
parts in the VortobiMta. The blood, in the higher forms of those animals,
is corpusculated, but its corpuscles are not smooth and colom-ed with
cruorin, like the red corpuscles of the Vertebrata, but, even when the
blood itself is tinged, they are usually colourless and granular, like the
white blood corpuscles and lymph corpuscles of the Vertebrata. Some-
times, however, they ai'e flattened, discoid, or even angular ; and occa-
sionally they have a bluish or greenish tint. In the simplest of these
animals, the blood contains only gi-anules.

This common nutritive fluid, or blood, has, indeed, been regarded by some
as corresponding rather with the lymph, and the vessels, in which it cir-
culates, as homologous rather with the lymphatic system of the Verte-
brata. It is certain that no other vessels corresponding with lympha-
tics, exist in the Non-vertebrate animals ; and no lymphatics have been
detected in the Amphioxus, which has only colourless corpuscles. The
vessels in which it circulates, present this great peculiarity as contrasted
with the circulating apparatus of the Vertebrata, that they no longer
form a continuous series of well-defined tubes, or time bloodvessels ;
but, even in the highest forms, and, to a still greater degree, in the lowest
forms, the blood passes from such definite vessels into spaces lying, as
it were, between the viscera and tissues of the body, furnished doubtless
with a lining membrane, but not having otherwise distinct walls or
coats. In the higher of these animals, these spaces form spongy recesses,
sinuses, or lacuna, and in the lower forms, merely feri-visceral or inter-
visceral spaces.

Connected with the true vessels, in many of the higher forms, there
are found one or more rhythmically pulsating contractile cavities, which
are therefore called hearts ; sometimes these are unilocular or ventricidar,
sometimes bilocular, or auricular and ventricular ; sometimes they are
multilocular. One of these hearts only can bo regarded as homologous
with the heart of the Vertebrata, in some of which animals, as in the bat,
the eel, torpedo, myxino, and amphioxus, for example, portions of the
venous system are also pulsatile. Pulsating cavities also exist, as wo
have seen, in certain Koptiles, Amphibia, and Fishes, in connection with
the lymphatic system, viz. the lymphatic hearts.

When the heart in a Non- vertebrate animal is single, it is, as a rule,
placed on the dorsal aspect of the body, i.e. on the surface opposite to
the one upon which the nervous axis is found ; it is, moreover, systemic,
or sends the blood to the various parts of the body, including the liver,
and not to the respiratory organs, which only receive the blood as it is
returning from the body to the heart. This is the reverse of the arrange-
ment met with in Fishes, in which the heart is respiratonj. In the Fish,
the heart receives and transmits dcoxygenated blood, whilst in the Nou-
vortobrate animal it receives and transmits an o.xygonatod fluid. When
the heart is bilocular, it is constricted externally, and presents a delicate
projecting border or valve between the uiu’icle and ventricle. When the

272

SPECIAL rnTSIOLOGT.

heart is multiple, the supernumerary ones are always simple or respi-
ratory, and are placed upon the veins near the respiratory organs, any
modifications of which, as in the Vertebrata, necessitate changes in the
arrangements of the vascular system. Aportal venous system never exists,
the liver being always supplied by the S3'stemic arteries. The vessels
are named arteries and veins, according to the direction of the current
within them, and not from their structure ; for distinct coats, like those
of the arteries in the Vertebrata, are not recognisable. Though extremelj'
delicate valves are present in the heart, they are not found so regular!}'
disposed in the veins, as in the Vertebrata. Sometimes, a pericardium
exists. True capillaries, provided with distinct walls, and intermediate
between the finest arteries and the finest veins, have not been demon-
strated, and in most instances are certainly absent ; but, the arteries
pour out the circulating coi'pusculated fluid, into lacunae, or interstices,
between the organs or elements of the tissues, from which it is collected
into venous sinuses and trunks.

Mollusca. — The most perfect condition of the circulatory system, in
the Non-vertebrate animals, is met with in this Sub-kingdom, and in the
Class Cephalopods. In the cuttle-fish, for example, there is found a
systemic ventricular heart, provided with valves at its orifice ; it is
usually rounded, has strong mu.scular walls, and even internal columnae
carneee. Arteries proceed from it to all parts of the body, excepting to
the branchiae or gills, the liver even receiving branches. The blood is
returned into a large vein, or venous sinus, which is surrounded by a
remarkable cellular organ filled with blood, and from which symmetrical
lateral branches, two or foiu' in number, according to the number of the
gills, proceed to those organs, each presenting, as it enters the giU, a
pulsating dilatation, or so-called branchial heart, which helps to propel
the blood through the gills. From the gills, the blood is returned into
large venous sinuses, which, being contractile, act as auricles, and thence
passes into the ventricular systemic heart already described. In the
Ptoropods and in the Gasteropods, there is but a single heart, which is
always systemic, distributing its contents by one arterial trunk and
numerous branches, to the body and liver, from which, having passed
through lacunm or spaces, it is again collected by veins, and by them
conveyed to the respiratory organs ; from these, it is collected by other
canals, the branchio-cai'diac veins, and is so brought to the heart again.
In the terrestrial Pulmogasteropods, as in Helix, the venous blood from
the body, passes through small vessels on the walls of the pulmonary
air sac, and is then collected into a lai-ger vessel, which conveys it to
the heart; whilst in the aquatic Branchiogasteropods, as in Doris, the
blood returning from the body, is carried, by special vessels, into the
gills, and is then conveyed, by other vessels, back to the heart. In both
kinds of Gasteropods, the heart consists of an auriele and ventricle,
between which there is found a distinct but minute valve, which serves
accurately to direct the course of the circulating fluid. In the Lamelli-
branchiata, the heart, usually single, but sometimes double, in correspon-
dence with the bilateral arrangement of the parts of the body of these
animals, and often perforated by the intestine, is placed in a pericardium,
situated near the adductor muscle, which closes the shell ; when single,
it has sometimes one and sometimes two auricles, connected with its
simple ventricle; when the heart is double, each has only one auriele.

CIRCULATION IN ANNULOSA.

273

Molhtscoida. — In these animals, the circulatory organs become still
more simple, or even disappear. Thus, in the Ascidioida or Tunicata,
although the bloodvessels, or blood sinuses, are very complex on the
walls of the peculiar respiratory atrium, the heart itself has no valves
between its dilated parts or chambers, and the blood is propelled by
opposite peristaltic actions, separated by an interval or pause, first in
one direction and then in the other ; hence the heart is sometimes
systemic and sometimes respiratory, and each chamber is sometimes
auricular and sometimes ventricular in function. In the compound
Ascidioida, it is stated that the vessels of one animal, are connected
through the footstalk or common “ stolon,” with those of the others
belonging to the same cluster. In the Brachiopoda, there is still a
proper simple heart, sometimes, it is said, two ; but the circulating
system is considerably reduced in extent : the numerous contractile
cavities found in these animals, have not been proved to have any con-
nection with the blood system, but rather to be comparable with the
atrium of the Tunicata. Lastly, in the Polyzoa, neither a contractile
heart, nor even vessels, have yet been detected ; in these soft delicate
animals, the nutritive fluids are supposed to permeate the walls of the
alimentary canal into the perivisceral spaces, and thence to penetrate
every part of the body.

Annulosa. —In the largest animals of this Sub-kingdom, the circulatory
apparatus presents the greatest simplification. Thus, amongst the Crus-
taceans, a single, well developed, muscular, systemic, dorsal, heart is found
in the lobster ; it is placed in the median lino, beneath the hinder border
of the thoracic part of the shell, and is enclosed in a delicate sac, which,
from its resemblance to the pericardium in the Vertebrata, has been so
named, but which is, in reality, a venous sinus. From the heart, six
systemic arteries are given off to the head, stomach, liver, and caudal
extremity ; from the lacunae or spaces between the tissues and organs,
the circulating fluid is collected by veins, which end in sinuses placed
above the ventral surfiice; from those, it is conveyed, by distinct vessels,
into the gills, there being sometimes contractile dilatations at the base
of those organs ; having passed through the gills or branchiae, it is then
returned, by the so-called hranchio-cardiac veins, to the largo venous
sinus enclosing the contractile heart, into which it enters through valved
apertures, and is then propelled into the systemic arteries already de-
scribed. No cilia ever exist in the interior of any part of the circulating
system of the highest or Arthropodous Annulosa. In most other
Crustacea, the plan of the circrilating apparatus, is the same as in the
lobster; but in certain of the lowest forms, the simple heart is replaced
by an elongated, and sometimes by a segmented, contractile vessel, or
dorsal vessel, provided with lateral valved openings, by which the blood
enters from an enclosing venous space or sinus. In Insects, the circu-
latory system presents, as has already been seen in so many instances,
modifications adapting it to special forms of the respiratory apparatus.
In them, there no longer exist cither lungs or gills, but tracheal
respiratory tubes ramified through every part of the body. The heart
is replaced by a numerously segmented dorsal vessel, provided with
valves between each segment, contracting rhythmically from behind
fonvards, and having numerous lateral valved openings, through wliich
the circulating fluid, returned from all parts of the body, enters from

VOL. II. T

274

SPECIAL PHYSIOLOGY.

an enclosing so-called pericardial, but really venous, space- or sinus.
The corpusculated fluid or blood, propelled from the anterior ex-
tremity of the dorsal vessel, passes, however, not so much into distinct
vessels, as into channels, lacunae, or spaces, in and between the
various organs and tissues of the body, and so comes into relation
with the universally ditfused tracheal tubes, and then again finds its
way back to the pericardial venous sinuses. The chief modification
of this system, seen in the Myriapoda and Spiders, consists in the com-
parative length or shortness, the equal development, and the more or
less frequent segmentation of the valvcd dorsal vessel, in accordance
with the consolidation or multiplication of the segments. Thus, in
the Geophilida, the number of contractile segments, is upwards of L50;
in lulida, as many as 75 ; in Scolopendrida, 15 to 21 : all are separated
by well-formed valves. A small ventral trunk also exists in some
Myriapoda. In the Arachnida, the dorsal vessel sometimes consists of
only four or five closely packed chambers. These segments, with their
interposed valves, are found only in the body of the perfect Insect, and
usually uTimber eight or less ; in the thorax, the dorsal vessel has no
valves, and, in front, it ends in a fine vessel, from which a few branches
have been traced. In the microscopic Arachnida, such as the acari,
there are no proper vessels, but the nutritive fluid contained in the
perivisceral chamber, is moved by means of contractions of the muscles
of the intestines and the skin. The scorpion presents the unusual
condition of possessing a distinct abdominal vein, proceeding from the
tail, and giving branches to the pulmonary sacs.

In the Annelida, the best anatomists agree in doubting the existence
of either a contractile chamber or heart, or of a contractile dorsal vessel ;
the only cavities possessed by them, analogous to the more perfectly
developed circidatory apparatus of the Arthropodous Insects, Myriapods,
Spiders, and Crustacea, are the perivisceral spaces,lacun8e, and channels,
in which a slightly corpusculated fluid has been found. It is in this
Class, including the various marine and terrestrial Worms and the Leeches,
that those remarkable ramified vessels are met with, extending into every
segment and portion of the body, named the 2}scudo-h(Bmal vessels, which
contain, sometimes a colourless, though usually a red coloured fluid,
often corpusculated, but the colour of which is not dependent on the
corpuscles. These vessels are, at one or many parts, dilated and con-
tractile, and, at certain parts, lined with oil ia. They always communicate,
at some point, by a tubular stem with the exterior ; a principal trunk on
the dorsal aspect of the body, has beeu regarded as the representative of
the true dorsal vessel of the higher Aunulosa ; but their homologies
are believed to be rather with the so-called water-vessels of the still
more lowly organised Annuloida, than with the non-ciliated vascular
apparatus of the Arthropodous Aninilosa.

Annuloida. — In these animals, nothing analogous to a blood system
e.xists, there being neither blood nor true bloodvessels, or lacunar blood
spaces. The water-vessels of the Kotifera or Wheel-animalcules, of the
marine Turbellarian Worms, the Trematodo Flukes, the Nematode Thread-
worms, and the tape-like Tmnia and its allies, the Acanthocephali, are
ciliated canals, which comimuiicate, at some point, with tlie exterior, and
are, by some, regarded rather as re.sqiiratory organs. Neither a heart,
nor a dorsal vessel has boon found in them. The extensive system of

NUTRITION GENERALLY.

275

umhidacral and other vessels, possessed by the Eehinodermata, also
coinmxinicates with the exterior, and is, apparently, partly respiratory,
and partly locomotive. No heart or bloodvessels have been detected in
tlieso animals.

Ccelmterata. — These are also destitute of blood, cardiac apparatus,
and proper circidatory vessels. In the Aotinozoa and Hydrozoa, the
digestive cavity communicates with the perivisceral or general cavity of
the body, from which ramificatious, sometimes very fine and numerous,
proceed through the disc and other more developed parts. In this way,
nutritive fiuids get access to all parts of the body, without a circulation
of blood.

Protozoa. — The singidar, characteristic, slowly pulsating vesicles,
which alternately contract and dilate within the soft sarcodous sub-
stance of the Infusoria, and Ehizopoda, although they sometimes present
radiating ramifications, as in certain Infusoria, are probably respiratory
rather than circulatory. In the sarcode of the Sponges, and in the
unicellular Gregarinida, there are not even contractile vesicles ; and no
trace whatever of internal vessels. The clrculatiou of external fluid
through tlie porous substance of a sponge, has, of course, no affinity to
a true internal circulation.

NUTRITION.

The general process, by which the microscopic elements of
the tissues and organs of the body, are maintained in a healthy
condition, and are renovated after disintegration and waste in
use, constitutes the function of Nutrition.

Nutrition proper, consists in the maintenance of a living
part, without any important change of form or size. Growth
implies a more active nutritive process, resulting in an increase
of dimensions. Development, besides nutrition and growth,
requires evolution, or changes of form. Reparation is a
nutritive act, which has for its object, the healing of a wound
or loss of sitbstance, or the more perfect restoration of an in-
jured or lost part, licproduction of a lost part, is an extreme
example of reparation. The act of secretion is a nutritive
process, in which the products of nutrition are incessantly
thrown out from the system. The reproduction of the indii
vidual, is a special nutritive phenomenon.

In Man and the higher animals, the blood is the common
source of the nutrient material lor the solid parts of the fi-ame,
and, in its ra[)id circulation through the body, it passes, wliilst
in the capillaries, within a very minute distance of the ele-

T 2

276

SPECIAL PHYSIOLOGY.

mentary constituents of the various tissues and organs. In
yielding this mitrient material, the blood itself is necessarily
impoverished, and accordingly is, in its turn, renewed, or
nourished, chiefly from the lymph and chyle, both of Avhich
are likewise constantly being reformed or renewed. All three
fluids, the lymph, the chyle, and the blood, are, however,
more or less organised, or at least, the products of organisa-
tion. They are, indeed, tissues, or fluid jiarts of tissues,
being the moveable contents of vessels or tuljes formed by the
coalescence of hollow elongated nucleated cells. Like the
more solid tissues, they are subject to nutritive waste and
renovation. In its widest sense, nutrition includes, therefore,
the renewal of the lymph and chyle, the renewal of the blood,
and the maintenance, or renewal, of the solid tissues and
organs of the body.

In each of these processes, there is one common character,
viz. that the renewed fluid, or solid, assumes some portion of
a nutrient pabulum, dilferent from itself, and converts it into
a likeness of itself. Hence the term assimilation is employed
to indicate the assumption of necessary material into itself, by
a fluid or solid tissue. The nutrition of the chyle and blood,
or the 231'ocesses of cliyliflcation and sanguification, are espe-
cially included under the term primary assimilation, whilst
the nutrition of the solid tissues and organs, from the blood, is
described as secondary assimilation.

Nutrition of the Chyle.

The composition of this fluid, its relations to the food, and
the share which the process of absorption has in its formation,
have already been described. The nutritive character of that
part of the process of cliyliflcation, which consists in the
absorption of tatty matters, has likewise been indicated. The
fatty particles of the chyle within the lacteals, certainly differ
from the emulsionised fat found on the surfiice of the intes-
tinal mucous membrane, and the albuminose of the intestinal
canal appears as albumen and fibrin in the chyle. Accord-
ingly, these last-named substances, and perhaj)s also the fat,
undergo true assimilative changes, and not a mere absoi'ption,
as they enter the chylifetous vessels. Moreover, the cor-
puscles which appear, as the fluid advances through the lym-
phatic plexuses and glands, afford distinct evidence of evolu-
tion, organisation, and, therefore, of a.ssiinilative power. The

1'

NUnUTION OF THE BLOOD. 277

columnar epithelial cells upon the villi, and also the cells of the

absorbentvessels and the alveolar spaces of the lymphatic glands,

which are themselves developed by the coalescence of hollow

nucleated cells, the parietes of which continue to be endowed ,

with special properties of an elective and, therefore, assimila- j'

tive nature, participate in this process. K, as previously

alluded to (p. 180), the process be regarded as secernent, the j

moveable contents of the lacteals, form a secretion, and the j,

entire lymphatic system constitutes a large gland, the secreting !

tubuli of which begin either amidst the tissues of the body, as t

lymphatic plexuses, or in the villi of the small intestine, as ;

the commencements of the lacteals ; whereas the terminal ducts, i

of which the chief one is the thoracic duct, open into the great !

veins at the root of the neck. The vascularity of the septa

within the lymphatic glands, favours the near proximity of

the fresh chyle or lymph, to the capillary bloodves.sels ; in this

way, these fluids may be inspissated by venous absorption, and,

moreover, by the action of the ai'terial blood, the fibrinous

matter may acquire the increase which is noticed beyond the

lymphatic glands.

Nutrition of the Blood.

The most obvious evidence of organisation in the blood, is
the existence of its white and red corpuscles. The very special
characters of the latter, which are found only in the blood of
the Vertebrata, and which, as we shall see, undergo evolution
and decay, afford proof of a farther assimilative action, than
that which takes place in the formation of the lymph and
chyle. The blood, however, owes the maintenance of its
extremely composite nature, to other processes than to those
of a self-assimilative character : viz. to its losses in the nutri-
tion of the solid tissues of the body, and in the formation of
the various secretions ; to the changes which it incessantly
undergoes, by the entrance into it of new matter, by venous ab-
sorption on the one hand, and to the passage from it of effete
matter, by excretion on the other ; and lastly, to tiie profound
alterations in its character, effected by the action of o.xygen in
the respiratory process. For these reasons, the subject of the
formation of the blood, or Sanguification, will be more con-
veniently considered hereafter.

I

278

SPECIAL PHYSIOLOGY.

Nutrition of the Organs and Tissues.

The nutrition of the various solid parts of the body, nutrition
lirogger.! or secondary assimilation, consists of the folloAving
ste])s or stages.

First, a nutritive fluid or plasma, exudes fi-om the blood,
through the coats of the capillaries, into all the interstices of
the tissues. This process may be partly due to porous diffu-
sion, under the influence of the pressure of the blood in the
bloodvessels, but partly also to a dialytic movement, regu-
lated by the chemical relations between the liquor sanguinis
and the walls of the capillary vessels. As these vessels are
eAmrywhere developed in the same manner, from coalesced
nucleated cells, the structure, chemical composition, and pro-
perties of their Avails, are probably the same in every tissue
and organ. Hence Ave may infer that the nature of the exuded
fluid plasma, is the same in every part of the body, and,
accordingly, that a imiform material derived from the blood, is
provided for the nutrition of every part of the system. This
nutritive plasma is sometimes supposed to be identical Avith
the liquor sanguinis ; but this is doubtful. Fluids eflused
into various parts of the body, Avhen present in sufficient qiian-
tity to be examined, are found to undergo coagulation after they
are removed from the influence of the Ihung tissues; thej’^
therefore contain a certain quantity of fibrin or fibrinogen, and so
far resemble the liquor sanguinis ; but they appear generally to
possess less albumen and saline matter. Moreover, the liquor
sanguinis contains all the ingredients of the blood, Avhether
nutrith'-e or effete, excepting the Avhite and red corpuscles ;
Avhilst it is more jArobable that the exuded plasma, destined
for the nuti-ition of the tissues, consists of a purer nuti'ient
material. Whatever its precise nature, the exuded plasma
passes into the finest interstices of the vascular tissues, betAA'een
the capillary networks, and bathes all the elementaiy parts of
those tissues. Moreover, it penetrates, bejmnd the vascular
parts, all the moist non-Amscular tissues, such as the car-
tilage.s, the cornea, the capsule and the substance of the
crystalline lens, and, likeAvise, probably even reaches the in-
tervals between the cells of epithelial and epidermoid tissues.
The essential difference between a Avascular and a non-vascular
tissue, consists in the rehitiA'e distance of their microscopic
elements from the nearest cajiillary vessels, and, therefore, in
the space through Avhich the plasma has to ]iass from those

THE NUTRITIVE ATTRACTIONS.

279

vessels, before it penetrates the tissue. All the tissues, indeed,
whether vasctilar or non-vascular, whether penetrated by
capillaries or not, are, strictly speaking, extra-vaficular^ that
is to say, their elementary parts are outside the walls of the
corpuscles. The existence of serous or white vessels smaller
than, but continuous with, the capillaries, is not generally
admitted ; but in certain tissues, secondary nutritive channels
may exist, as, for example, the lacunas and canalicTili of bone,
and the tubuli of the dentine, by aid of which the nutritive
tiuid may be still fiu-ther distributed. The tubular structui’e
of the connective tissue corpuscles and their processes, and
the connection of these with the lymphatics, are not admitted.

The second stage of the nutritive process, consists in the
exercise of a certain selective act, or so-called elective affinity,
by the elementary parts of the tissues and organs, by which
they assimilate to themselves such portions of the nutritive
fluid as are suitable, either without or with further change, to
renew, molecule by molecule, their disintegrating substance.
The nucleated cells of the epidermis and epithelium, the cor-
puscles of the grey matter of the brain, the tubular fibres of
the white nervous tis.«ues, the complex fibres of the striated
muscles, the simple fibrous forms of the contractile fibres or
fibre-cells of the organic muscular tissue, and of the fibrous and
areolar tissues, and lastly, the consolidated intercellular sub-
stance with the remnants of cells imbedded in it, as in car-
tilage and bone, each derives from the e.xnded plasma of the
blood, and assimilates, its required chemical constituents. The
more rapid the waste, the more active is the renovation, both
processes being most marked in the muscular and nervous
ti-ssues, which produce and regulate all animal movement.
This assimilative power of the tissue elements, is the j>er-
sistent, primitive, nutritive force, inherited from the gerrn-cell.
It is probably alike po.sse.ssed by every cell, however remote
in its descent from the parent cell, and however modified,
so as to form parts of a composite animal or ti.ssue, just
as it undoubtedly is when a single cell constitutes the entire
animal. This germ force, or germinal force, is the essential
cause of all nutritive jdienomena, as it is of all organisation,
whether animal or vcgetaltle. By it, the cellular yeast plant
grows and maintains itself in fermenting saccharine solutions,
the larg(!i- fungi feed themselves upon juices derived from
decaying organic matter in the soil, the various (i-isues of the
more complex flowering plants are formed and sujiported out

SPECIAL PHYSIOLOGY.

of a common pabulum, the sap ; and, in the Animal Kingdom,
the unicellular Gregarina, the sarcodous llhizopod, the protei-
form Amoeba, the soft-bodied Cmlenterata, with their ectoderm,
endoderm, and intermediate tissue, and, lastly, all the complex
tissues and various organs of animals higher in the scale,
and of Man, are duly nourished. By this, the nerve tissue
attracts from the plasma outside the capillaries, its e.ssential
latty and other constituents, the muscular fibre assumes the
materials for fresh syntonin, the cartilage those for its chondrin,
the bones, their peculiar animal and earthy materials, and so
on, of every other tissue of the body. The act of nutritive
assimilation, is said to imply a metabolic effort, operating in
regard to the substance of the tissues, whilst in development,
or evolution, this is associated Avith a metaniorphic effort,
which determines their form. Both kinds of nutritive pheno-
mena are manifest chiefly, probably exclusively, in certain
areas around the nuclei, or corpuscles, of the cells, the so-
called germinal centres^ Avhich are therefore knoAvn as areas
and centres of nutrition. The few cases in Avhich, as in elastic
ligaments, the nuclei or corpuscles are said to be absorbed,
may only be apparent exceptions to the rule. Certain con-
ditions of the blood, and of the temperature of the body, are
essential to the occurrence of nutritAe actions. They are
most active at the commencement of the life of any animal, and
gradually decline as that advances, until the power tomaintoin
the bod}', is overcome by the forces which lead to its degenera-
tion and decay.

In reference to the act of assimilation, and, indeed, of original organi-
sation, it is remarked by Graham, that colloidal substances may not
only be regarded as forming the essential plastic elements of the body,
capable like all colloids, of existing both in the liquid and in the pec-
tous condition ; but that, in the organising and assimilating process,
these colloidal bodies do pass from the liquid into the pectous state, as
they assume the form and cliaracters of tissues and organs. The slow
rate of these colloidal changes, harmonises with the gratlual and pericalic
natiu-e of the processes of growth and disintegration, with which allA'ital
phenomena, Avhether of vegetative or animal life, are connected. The
KXERGiA, or force, peculiar to colloids, may be, indeed, the primarj- source
of the physical force appearing in the phenomena of vitality (Graham).

Thirdhj, the result of tlie act of assimilation by the various
tissues, is to leave a residual fluid in the interspaces of the
tissue-elements, otttside the capillary vessels. The nature of
this interstitiiil fltiid, uidike the common plasma of Avhich
it is a residue, must differ in the different tissues, as, for

THE EFFECTS OF UE-NUTRITION.

281

example, in muscle, brain, liver, and connective tissue. This
residual portion of the nutritive jdasma not being effete, but
merely defective in composition, is supposed to enter the
commencing lymphatics, and thus to be returned to the blood
through the absorbent system. Probably, as already indicated,
this is accomplished by true assimilative acts, on the 2:>art of
the lymphatic vessels and glands, owing to which, certain
appropriate constituents only of the residual portion of the
plasma, enter the commencing lymphatics. It is remarkable
that these vessels are most abundant in the connective tissue,
in which the residual part of the plasma is least altered, and
few or absent in muscle and brain, where the greatest modifi-
cations are effected in it, and where, accordingly, it is less
fitted to form fresh lymph. It might be conceived, without
adopting Virchow’s and Ilecklinghauser’s views as. to the
origin of the lymphatics in the connective tissue corpuscles,
that the areolar tissue in, and between, all the organs of the
body, acts as a sort of spongy bed or matrix, into which the
residual part of the nutritive plasma escapes, and so may be
more easily taken up by the lymphatics which abound in it.

Fourthly, the final residue of the exuded plasma, which is
neither used by the tissues of the body, nor absorbed by the
intruded lymphatic vessels, remains to be accounted for.
This must be conveyed, probably, by simple and unavoidable
dialysis, without power of selection or rejection, into the
venous half of the capillary network, and the minute venules
immediately adjoining. No other destination can be assigned
to it, and unless it were carried off, dropsical accuimdations,
or effusions, would take place in the tissues. From this, it
would aj)pear, that whilst the still serviceable parts of the
residual plasma, left after the nutrition of the other tissues, are
restored indirectly to the blood, by lymphatic absorption and
assimilation, the unserviceable, or final, and no longer nutritious,
residuum, passes into the circulation directly, by means of
venous absorption.

Lastly, with this final residuum of the nutritive plasma,
there are nece.«sarily mingled the products of the disintegration
of the tissues, ^ivhich always accompanies their action. With-
out waste there is no use, and without use there is no life.
It is the lo.ss which living and acting tissues undergo, which
nece.ssitatcs their nutrition; and whilst new pabulum is
brought by the arferitd blood, which yields a nutritive plasma
through the walls of the arterial half of the ca|)illary network,

2S2

SPECIAL PHYSIOLOGY.

from wliich plasma all tlie tissues receive respectively their
requisite materials, the products of their waste would seem
first to become dissolved in the ultimate residuum of the
plasma, and with it, to enter the venous blood, through the walls
of the venoris half of the capillaries and of the minute veins.
These products of waste are really effete, and no longer fit for the
pm'poses of initrition ; physiologically, they are the result of
a process of de-nutrition, and, chemically considered, of a pro-
cess of oxidation, of the tissue substance. It is these which
impart to the blood,, its positive venous characters. Thus,
venous blood is more watery; it contains less nutritive matter ;
it is also rendered impure by containing the waste products of
the tissues, the chief of which are carbonic acid, lactic acid,
and urea. The former of these, as we shall hereafter see, is
replaced by oxygen in the lungs, and so a negative defect in
venous blood, the want of that stimulating agent, is supplied.
Here, also, the carbonic acid is given off ; whilst the lactic
acid, phosphates, and urea, are eliminated, or cast out of the
blood, by the excretory glands, especially by the skin and
kidneys.

The five stages of the nutritive process, though here sepa-
rately described, viz. the exudation of the nutritive plasma
from the blood, the assimilation of parts of this by the tissues
under repair, the absorption and assimilation of other portions
by the lymphatics, and lastljq the reabsorption of the final
residue, together with that of the waste products of the tissues,
by the venous capillaries and veins, are, of course, in the
living body, simultaneously and continuously performed, and
in the healthy condition, Avith a perfect balance of action.
Especially must the removal of the Avaste products, be inces-
sant, or they Avould taint the nutritive plasma, and cause
inflammation, as in reality occurs in rheumatism and gout.

In the embryo, and in the growing animal, nutrition not
only repairs the constant Avaste of the tissues, but, as already
stated, conti'ibutes to the formation of neAv morphological ele-
ments, in the processes of development and groAvth. Bnt,
after the body has attained its maturity, groAvth ceases in
most, though not in all, of the tissues. Hence two kinds of
nutritive processes are notice.able in the adult.

Ill one, not only are the already existing cell-elements, and
their secondary intra- or intercellular products, supplied Avith
materials for their special nutrition, until they have passed
through all the metamorphoses peculiar to them; but neiv cell-

FORMS OF NUTRITION.

2S3

elements, or germinal centres, are constantly being reproduced
and developed, for the purpose of supplying the place of those
Avhich are cast off ; these new cells are, in turn, succeeded
by others. This process, named continuous fp'oivth, occurs in
the epidennis, nails, and hair, in the epithelial tissues of the
mucous membranes and secreting glands, and probably also in
the grey nervous substance. Moreover, from the active in-
ternal changes of absorption and deposition constantly going on
in bone, as indicated by observations on the bones of animals
fed with madder, it would seem that new cells are continually
being formed in that tissue, and, if so, perhaps in cartilage
also. In the nutrition of the blood, there occurs not merely a
continued renovation of pre-existing red corpuscle.s, but also
the death and disappearance of a certain proportion of these,
together with the reproduction of new ones. In the othei’
mode of nutrition, when once a tissue has attained maturity,
no new morphological elements are added to it ; such is sup-
po.sed to be the case, with the areolar and fibrous ti.ssues, and
with the muscular and nervous fibres. In these tissues, the
nutritive process consists merely in interstitial disintegration
and deposition, aflTecting the elements of the perfectlj'^ formed
tissue, molecule by molecule, so as effectually to preserve the
shape and size of a part or organ, as long as the normal or
healthy standard of nutrition is maintained. According to
this view, even the enlargement of a muscle from exercise, is
owing to an increase in the size of the fibrillas in each fibre,
and not to the formation of new fibres, or even of new fibrilla; ;
whilst muscular emaciation is due merely to a diminution
in the .size of those elements. It is, however, supposed by
some, that, as in bone, .so in muscle, new centres of growth,
or nuclei, are developed from time to time, and give rise to
new fibres, amongst the pre-existing ones, some of which are,
on the other hand, constantly undergoing retrograde changes,
and disappearing.

In the mode of nutrition by the continuous growth of new
cells on the surface, the old elements are cast off directly at the
surface of the body, or of some one of its internal mend)ranes ;
parts of them, however, are .sometimes reabsorbed as secretions.
In theinter.stitial mode of nutrition, the products of disintegra-
tion, arising from nutritive changes in the substance of tlie
tissue, are taken up, if not by the absorbents, at all events by
the bloodvessels, and .so enter the blood.

The phenomena of nutrition are necessarily affected.

284

SPECIAL PHYSIOLOGY.

through the blood, by the quantity and quality of the food, by
all the changes which occur in the blood itself, by what is
called the general condition of the health, by exercise or the
reverse, and by external conditions, such as temperature, me-
chanical causes, pressiu'e or violence, or chemical agents.

Nutrition is also aifected, and modified, by the state of the
nenmus system, as exemplified by the effect of emotions and
other causes, probably in the main, through the action of the
vasi-motor nerves regulating the diameter of the small arteries
of a part. Perversions of the condition of the nerves or
nervous centres, may induce a perverted state of the nutritive
processes, both general and local. The formative and nutri-
tive energy is, however, not derived from the nervous system;
for it is manifested not only in animals destitute, so far as is
known, of any nervous system, but even in plants. Moreover,
it begins to act in the ovvtm, previous to the existence of a
nervous system, which system, indeed, is developed by its
agency. Of the numerous instances usually adduced, to prove
that the nervous system may directly guide, or modify, the
nutritive changes in the tissues, independently of its action
on the bloodvessels, none are satisfactory, if adduced in the
case of animals jwssessing bloodvessels; for it is impossible,
in such cases, to exclude the action of the nerves upon these
vessels. But there are animals, low in the scale, such as the
Beroe and other Coelenterata, in which a nervous system
exists, without bloodvessels ; and, in these cases, any action
of the foi’iner, upon the nutritive processes, must be direct, and
not through the agency of vessels. The increased ntttrition
or secretion from a part in such an animal, due to a stimulus
acting on its nerves, furnishes, unless this is influenced by the
contraction of the tissues themselves, the requisite example of
such direct action. If so, by analogy, it might also occur in the
vascular animals, and in Man.

Certain muscular organs, stimulated through the nerves,
such as the gravid itterus of the Mammalia, and the muscles
of the frog after the season of hybernation, undergo normal
periodic enlargements. In this form of over-nutrition, both
the jn’oeesses first mentioned, usually occur, viz. an increase
in the size of the pre-existing elements, or hfipertrophy, and
also an increase in their number, or hjiperplasia. Budge has
actually observed this latter mode of increase, in the muscles
of the frog, new fibres being developed from nuclei arising
from the old ones within the sarcolemma of the pre-existing

MORBID FORMS OF NUTRITION.

285

fibres. In such cases, a corresponding increase takes place in
the nerves, and new nerve fibres also appear to be develoj^ed
by aid of the nuclei of the old ones (Klilme). The blood-
vessels of such parts must also enlarge — a change not due to
simple dilatation, but to a coincident interstitial hyperti-ophy
of the tissue elements of their walls.

Various deviations from the normal standard of nutrition, are met
with in the body; they are fertile sources of organic disease, giving rise
to the morbid conditions known as hypertrophy and hyperplasia, neoplasia,
atrophy, softening, induration, degeneration, and injlammation, with its
consequences.

Hypertrophy and hyperplasia, already defined, are usually attributed,
either to an over-abimdanee of certain materials in the blood, suitable
to tlie development of some particular tissue, or to excessive supply of
blood, to over-exercise of a part, or to some not understood tendency to
an increase of size or growth, by excessive enlargement or multiplication
of the tissue-elements. Muscular hypertrophy and hyperplasia, are more
common in the involuntaiy than in the voluntary muscles.

Neoplasia, or the formation of new growths, is referred to a perverted
nutrition. Its cause is unknown ; though it is attributed, with some
probability, to the accumulation in the blood of some similar nutritive
material or pabulum, fitted to stimulate their formation, and support
their growth and nutrition. The resulting tumours are sometimes
homoplastic or homologous, that is, they exhibit a structure similar to
that of some normal tissue ; or they are heterologous or heteroplastic,
their structure being entirely unlike any healthy texture. Fatty, fibrous,
cartilaginous, and bony tumoui-s belong to the former, and tubercle,
fibroplastic sarcomas, and cancers, to the latter variety of new formations.
These, when once formed, are the seat of continued nutritive changes,
more or less perfect and proper to themselves, and maintaining, in the
midst of interstitial changes, the character of the abnormal tissue-
elements of each growth.

Atrophy, or the gradual or rapid wasting of a part or tissue, depends
on general defective nutritive activity, an unhealthy condition or deficient
stipply of blood, want of exercise in a part, or loss of intrinsic nutritive
power. Atrophy may be general, as that which follows deficiency of
food or actual starvation, or partial and local, as that wdiich occiu-s in
the fatty tissue, when no fatty, amylaceous, or saccharine food is eaten,
and the blood is destitute of fatty matter.

Softening, induration, and degeneration, imply not only defective, but
more or less altered, nutrition. The first consists in a liquefaction of
the tissue-elements ; the second and third, in depositions, in or about
them, of albuminoid or amyloi<l substance, or in an actual conversion of
the proper albuminoid or gelatin-forming material of the tissue, into
fatty matter — a change not unfrequontly seen in muscular tissues, espe-
cially in tlurse who indulge in alcoholic beverages. In certain cases, fatty
degeneration prepares a tissue, or some morbid deposit, the result of
inflammatory or perverted hypertrophic or hyperplastic tictiou, for more
easy absorption and removal from the body ; sometimes this and other
changes destroy tumours, and so lead to exhaustion and death.

Injlammation is essentially an abnormal or altered nutritive process.

2S6

SPECIAL PIIYSIOLOGT.

It commences in some altered relation between the nutritive qualities
and reactions of a tissue, and of the blood, or its exuded plasma ; the
normal nutritive changes are arrested; the rinuscd plasma soon becomes
excessive in quantity ; new products are stimulated into gro\vth, includ-
ing, essentially, cells formed by multiplication of the pre-existing connec-
tive tissue corpuscles. Moreover, the condition of the blood, and of the
capillaries, very soon becomes changed ; the blood becomes less fluid, and
the vessels distended and enlarged, causing a state of congestion ; the red
corptiscles of the blood in the part, cohere, and at last become motionless
or stagnate, stasis being produced ; the -white corpuscles increase in
number in the blood generally, owing it is supposed, to over-activity of
the commencing lymphatics of the inflamed part. Lastly, the nerves
of the part are excited by these changes, and by the disturbance in their
own nutrition. The chief obvious results and evidences of inflammation,
are swelling, redness, heat, and pain ; but these are etfects, and not even
essential characters, for one or more of them may be, under certain
circumstances, absent.

Inflammation may end favourably in resolution, which consists in the
absorption of the exuded material, and of the new products stimulated
to growth by it. These may, however, undergo rapid increase, and form
solid and morbi<l j^lustic deposits, or fluid jms, abounding in corpuscles
like the white blood corpuscles, and so give rise to induration, inflam-
matory thickening, or suppuration. Collections of pus, surrounded by
plastic deposit, constitute abscesses ; these, by progressive absorption of
their coverings, may reach the surface, and bm-st. A further result of
inflammation, is idccration, which consists in the molecular death, and
gradual softening and falling away, of a highly inflamed part of the
surface of a tissue or organ, causing a loss of substance, or sore known
as an ulcer. Gangrene, or mortification, is the complete molar death of a
part, dependent, sometimes, on excessive inflammation, causing obstruc-
tion or occlusion of the larger or smaller bloodvessels, or an actual
destruction by violence, heat, cold, or chemical agents. The body may
also be wounded, or parts even completely detached from it.

As inflammation and its consequences, are essentially derangements of
the nutritive process, so, on the other hand, all the rc^mrafi ye phenomena
seen in the living animal body, which tend to preserve life, consist in
most remarkable and energetic manifestations of modifled development,
growth, and nutrition. Thus, the cavity of an abscess, is chiefly closed
by the. collapse of its sides; but, also, by a new and very vascular, soft,
red formation, in its interior, known as granulations, which are developed
from new cell-elements, partly metamorphosed into connective tissue,
and partly into bloodvessels, whilst certain of the cells escape as pus;
idtimately, these granulations cohere, and the orifice being closed up. is
covered by new epidermis, or by cicatrisation. An ulcer, or a wound is
filled up, and healed, in a similar manner, by granulation, suppuration,
and cicatrisation, the resulting mark being named a scar, or cicatrix.
The temporary covering, or natimil dressing of an ulcer, known as a
scab, consists of dried exuded materials and pus. Gangrenous parts
are detached, separated, and thrown off, by a remarkable ulcerative pro-
cess, or molecular decay, occurring, not in the dead parts, but in the living
parts in immediate proximity to tluun ; when these aro detached, the
raw surface is healed by granulation, supipuration, and cicatrisation.

USE OE THE BLOOD IN NUTUITION.

287

n The healinc) of actual wounds, differs according to tlio extent, depth, and
* * relative proximity of the surfaces, and the degree of their exposiu’e to the
air. It may sometimes occur by immediate ov direct union, as iii the healing
of subcutaneous wounds, without any manifest intlammation, and, it is
I said, even without any observable exudation of intermediate or uniting
' plastic matter. Sometimes this may also occur in the healing of external

' cut surfaces, which have quite ceased to bleed, and can be maintained

ill accurate aud immoveable apposition, and from between which air can
I be totally excluded. Most frequently, however, healing is accompanied by
; more or less inflammatory action, and the formation of a new uniting
. ' substance ; this constitutes union by adhesive injlammation, or by the
first intention. In this mode of union, plastic matter is exuded, new
1 cells are fomied and converted into connective and capillary tissue, and

I so the divided, but apposed surfaces, are joined. When the wound is

1 deep, or the loss of substance is great, or the apposition of the surfaces

i impossible, or when, from any other cause, the adhesive inflammation does

: not happen, then the surftices granulate and suppurate, like those of an

I ulcer or abscess, and when these have closed up the cavity, cicatrisation

I ensues. The extent and mode of reparation in each tissue, and in va-

: rious animals, will bo explained in the Section on Develoj)ment. In all

> cicatrices, or other repaired parts, nutritive changes afterwards go on,

1 resulting, as in the healthy tissues, in the maintenance of the form and

I characters of the newly developed tissue or scar.

Offices of the Blood and of its several Constituents in
Nutrition.

1

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I

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I

f.,

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The general fact, already indicated, that the blood is the
source of all the nutrient material for the solid tissues of the
body, is illustrated in many ways. Thus, the activity of the
nutritive process, is coincident with the quantity and quality
of the blood supplied to a particular part or organ. Unless
it be constantly supplied, through the absorbent system, with
fresh nutriment from food, it becomes itself impoverished,
showing the demand made upon it, by the nutritive wants of
the solid tissues. Ligatitre of the arteries of a part, is followed
by a diminution in its size, owing to defective nutrition ; and
not only does complete closure of the arteries accomplish this,
but even their compression. There are instances in which an
increased supply of blood, through enlargement of the arteries,
occurs as a natural phenomenon in the living body, and, in
such cases, this determination of blood, as it is called, is ac-
companied by an increased growth in the part or organ supplied,
as e.xernplified in the annual development of the antlers of
the stag, and in the periodic enlargement of the mammary
glands in the Mammalia, for the suj)ply of their young with

288

SPECIAL PHYSIOLOGY.

milk. Again, the falling of the antlem, and the disappearance
of portions of healthy bone, in the ordinary nutrition of that
texture, are always preceded, or accompanied, by a gi-adnal
shrinking and final closure of the vessels which nourish them,
by the filling up of the Haversian canals of the bony tissue ;
thus, nuti'ition is arrested, as the supply of blood is cut off.
Lastly, hasmorrhages, or bleedings, are followed eventually, by
diminished nutrition of the body. But the immediate effects
of severe luemorrhage, are most remarkable. The functional
activity of the muscular and nervous systems, the exercise of
which also demands rapid nutritive changes, is either enfeebled,
suspended, or lost. Every sensation, perception, emotion, or
volition, and every movement, is accompanied by disinte-
gration of nervous or muscular tissue, or of both ; these tis.sttes
are maintained in a fit state for action, by a due supply
of oxygenated blood and nutritive plasma, and the several
changes Avhich occur in them and in the blood, are retro-
gi’e.ssive chemical decompositions, accomplished through the
agency of the oxygen conveyed in the latter. Accordingly,
a loss of blood from hasmorrhage, a diminution of that fluid
from pressure on the vessels, or an arrest of the circulation
from ligature, or other causes, is followed by a diminution,
suspension, or annihilation of the functions of a muscle or
nervous centre. Similar results ensue fi'om serious alterations
in the quality of the blood, as when the proportion of oxygen
in it, is deficient, or Avhen cai'bonic acid is in excess, as is seen in
the immediate loss of consciousness and muscular power, which
follows the arrest of the decarbonising and oxygenating pro-
cesses of respiration. The nutrition of the body generally,
also becomes defective, from a continually diminished supply
of pure air, owing to the blood not being then duly oxygenated
and purified. Finally, the influence of the blood, in stimu-
lating and nourishing the tissues, is directly proved by the
remarkable resuscitating effects of injecting that fluid into
the veins of persons or animals, previously deprived of blood
by accidental or intentional ha3inorrhage, the powers of the
whole sj'stem which have previously been suspended, being,
in this way, almost instantaneously restored.

The nutritive, stimulating, and resuscitating powers of the
blood, depend on the chemical constitution of the liquor san-
guinis, and on the number, composition, and properties of the
cor])uscles which it contains ; and the special offices of the
dill’erent parts of this fluid, for the processes of nutidtion, may

USE OF TUE RED CORPUSCLES.

289

be referred both to its nrorpliological .and chemical constituents,
which lun-e already been described (Vol. I. pp. 62, 90).

The white corpuscles appear to serve, at all periods .after
birth, for the renovation of the red or coloured ones. They
are very abund.ant in sickly and ill-fed persons ; also in antemia,
in inflammations, and in certain diseases of the spleen, probably
because they do not then undergo the usual change into red
coi-puscles, and so relatively accumulate in number.

The red corpuscles, by virtue, as it would seem, of the
colouring matter, or cruorin, are the great carriers into the
system of oxygen, which displaces carbonic acid from the
blood during respiration, as will be explained in the section
on that subject. The substance usually known as hasmatin,
is a product of the decomposition of cruorin, by the action
of acids or caustic alkalies. The hasmatin of Lecanu is a
highly coloured albuminoid substance, containing iron ; its
chemical relations with themyochrome of muscles, thej^igment
of the choroid and ii'is, of the hairs and skin, in both the dark
and fair races of mankind, and also with the colomdng matters
of the bile, the urine, and the supra-renal bodies, may indicate
some nutritive relations between it and them ; it may perhaps
be formed in the spleen, or in the lungs, and may be dissolved,
in minute qaiantity, in the nutritive plasma, and so find its way
chieflv to the mu.scles and hairs, in the colouring matter of
both of which, iron is also found. The red corpuscles also
probably furni.sh, by their solution, continuous supjjlies of
albuminoid matter to the liquor sanguinis, the globulin of
the corpuscles having a close resemblance to albumen and
syntonin. The fact, however, that the red corpuscles contain
most of the potash, whikst the liquor sanguinis contains most
of the soda, of the blood, may indic.ate that the muscular tissue
which akso abounds in potash, may receive special nourish-
ment from these ; and, as they also contain a phosphorised fatty
matter, they may have special nutritive relations, direct or
indirect, with the nervous substance. The quantity of the
red corpuscles in the blood, is certainly greatest in healthy and
vigorous persons. These corpuscles are also most abundant
in the hot-blooded Birds, not (juite so numerous in the Mam-
malia, the temperature of which is not sohigh,and muchfewer in
the cold-blooded Reptiles, Amphibia, and Fi.shcs. Their pro-
portion in the blood, is in direct relation, not only with the
temperature of the body, but also with the general activity
.and energ}.'of the muscular and nervous apparatus. From this

VOL. II. u

290

SPECIAL PHYSIOLOGY.

cause, the ratio of the general solids to the Avater of the blood,
shoAvs similar proportions in the different Vertebrate Classes.

The special nutritive office of the liquor siinguinis, must be
explained by its composite chemical constitution. Its peculiar
physical character of smooth viscosity, due to the albumen,
and particularly, it is said, to the fluid fibrin Avhich it contains,
is highly favourable to the easy passage of the blood along
minute channels like the capillaries, Avithout its exuding too
freely through their Avails, and perhaps also to the uniform
suspension of the red particles in it. A tendency to exude
in undue quantity through the coats of the vessels, is probably
fiivoured by a diminution in the amount of fibrin, as AveU as
by like changes in the proportions of the albumen and the .salts.

The uses of the particular chemical constituents of the blood,
as a Avhole, require further consideration. The albuminoid
principles of the blood, its most abundant constituents, include
the globulin of the red corpuscles, the albumen of the Avhite
corpuscles, and that held in solution in the liquor sanguinis ;
this latter is said to be chiefly derived from, or prepared by,
the blood corpuscles, the globulin of Avhich is believed to escape
into the liquor sanguinis, either through their thin envelopes,
or after their solution. These albuminoid substances are of
the highest nutritive value ; for they, or their derivatives, are
found, in larger or smaller quantity, in aU the tissues and
organs of the body, both in the microscopic cell elements
and the intercellular substance, appearing as albumen or
syntonin in the nervous tissues, as syntoniu in the muscles,
much changed, as a gelatin-, or chondrin-, yielding sub-
stance in the fibrous and areolar tissues, bone, and cartilage,
and as elastin in the yelloAV ligaments and other elastic
tissues. Gelatin is not found in the blood itself; but Avhen
digested, it is converted into a gelatin-peptone, and so be-
comes absorbed as Ave have seen, but in Avhat state, is not yet
knoAvn ; nor is its destination in the nutritiAm processes of the
body certain. Either it may serAm for the direct nutrition of
the gelatin-yielding tissues ; or, and this is very probable, itmay,
by itself undergoing oxidation, conserve other more important
tissues, and, at the same time, maintain the temperature of the
body. Its efficacy as administered in jellies, beef-tea, and
broth, in cases of sickness, e.specially indicates its importance
as an article of diet. Eurtliermore, the albuminoid substances
such as salivin, pepsin, pancreatin and casein, found in many
most important secretions, must be derived from the albumen

USES OF THE FIBRIN.

291

of the blood. The quantity of these formed in the day,
i.s considerable, but those contained in the digestive fluids,
are quickly absorbed into the blood again. Thougli so highly
nutritive, and absolutely essential to the economy, albumen,
considered as an organisable substance, has no metamorphic
power ; though it affords a fit material for metamorphic
action.

The fibrin of the blood, was formerly supposed to be specially
intended for the nutrition of the muscles, their albuminoid
constituent, syntonin, being considered to be identical with the
fibrin of the blood. It is now believed that the fibrin is not so
essential for nutiative purposes as the albumen, and the small
proportionate quantity in the blood, as compared with other
albuminoid bodies, viz. about 1 to 90, is in accordance with
this idea. Fibrin is more highly oxidated, or contains
more oxygen, than albumen ; hence it may be a degraded form
or condition of albumen, exhibiting a retrogressive change into
some still lower compounds. As ah-eady mentioned, it may
assist in maintaining some essential physical characters of the
blood ; and, lastly, it plays a highly important part, in
causing the coagulation of this fluid. To this change in
the blood, the character and causes of which will be here-
after discussed, the first closure of the orifices of bleeding
arteries and veins is often due, and further hasmorrhage is
thus arrested. Moreover, in most acts, especially in the union
of divided parts, and in the healing of sores, the fibrin con-
tained in the exuded plasma, coagulates, forming the first bond
of union, and a matrix in which nuclei or nucleated cells are
developed ; further reparative changes then ensue, according to
the tissue wliich is the seat of reparation. But the coagulation of
exuded fibrin in the living animal economy, though often bene-
ficial, sometimes induces injurious consequences to the system,
as, for example, in adhesive inflammation of the peritonamm,
by which the intestines and other organs become adherent, or
constricted by bands of newly-formed tissue, which interfere
with, or altogether hinder, their proper movements and
actions, in similar adhesions between the lungs and the side
of the chest, between the heart and the pericardium, and also,
and still more strikingly, in the attachment of the iris to the
capside of the lens, or other jiarts within the eyeball, even
causing blindness by the conqilete closure of the pupil. Not
only fibrinous exudations from the vessels, but even extrava-
sated blood itself, may coagulate within tlie tissues ; by some,

292

SPECIAL PHTSIOLOGT.

it is maintained that it may itself become the seat of subse-
quent organisation.

The fatty matter of the blood, -which is of varioirs kinds, is
highly nutritive, scarcely any tissue being altogether destitute
of fat in larger or smaller quantity. Phosphorised fats espe-
cially abound in the nervous substance, and exist in the red
corpuscles of the blood. Fat is always present in newly-
forming tissues and newly -forming cells, the nuclei of which
often contain fatty particles suiTOunded by an albuminous
deposit. Fatty matter is found, too, not only in the fluid parts
of the blood, but also in the organised morphological elements,
the blood corpuscles, especially in the red ones. It was ob-
served bv Ascherson, that when oleaginous substances are
agitated wdth albmninous solutions, the fatty matter breaks
up into minute particles, sun-oimded by a film of albu-
men ; and he believed that some such physical combina-
tion of oleaginous and albuminoids matter, might explain
the formation of the low'est morphological elements, such as
granules, and even of certain nuclei, though not the origin and
growth of cells themselves. Without adopting this view, it
may be admitted that fatty matter is essential to all nuclear
and cell growth, and to every process of tissue foimation, even
to the assimilation of albuminous matter ; for fat globules are
always present in the ovum or germ-cell of every animal. Fat
is necessary to the fonnation of certain secretions, as of the bile,
milk, and sebaceous matters of the skin. The bile contains a
very large quantity of fatty acids. It is possible that tift itself
may be derived from other constituents, as from albuminoid,
amyloid, or saccharine matter. The great value of oleoids,
especially of such as are easily digested, absorbed, and assimi-
lated, is exemplified in the beneficial action of cod-liver oil
in tuberculous diseases. Besides its use as a nutritive sub-
stance, the fat of the blood is probably also constantly subject
to oxidation, for the production of animal energy and heat.
But there are other substances in the blood, Avhich are pro-
bably even more easily oxidated than its fats.

Arterial blood does not contain any amyloid substance ; but
traces of s^tgar are present in it. This is formed in the liver,
but also, it would seem, in the muscles, and probably in
other parts; it is also taken up from the food. Nevertheless,
the quantity present is small ; it is, perhaps, less concerned in
nutrition than in the production of heat and motion by its
rapid oxidation. It may, however, take part in the formation

USES OF THE SALTS OF THE BLOOD.

233

of milk. The inosite, lactic acid, creatin, and creatinin, and
other extractives, are probably not so much directly nutritive,
as stimulating, or excretive ; they all represent stages of
chemical retrogression, from less to more oxidised compounds,
and may, by their further oxidation, assist in the evolution of
heat. As completely effete and non-iiutritious, or even
poisonous, must be classed, the urea, detectable, in minute
traces in the blood, as well as the ammonia which escapes fi-om
it when it is drawn, and the uric acid, all of which are ex^
cretory substances.

The salts of the blood are said to prevent its decomposition,
and also to regulate its chemical characters and its specific
gravity or density, so as to adapt it to the healthy condition of
the liquor sanguinis and blood corpuscles floating in it. It is
well kno^vn that certain salts are preservative, and, likewise,
that if the blood corpuscles be suspended in a fluid of too low
a specific gravity, they immediately become distended, a pro-
cess of endosmosis going on into them ; whereas, if the fluid be
of too high a specific gravity, they shrink by exosmosis. But
neither of these supposed irses, explains the great variety of
the saline constituents of the blood ; for one saline substance
alone, say common salt, would have sufficed for both these
jiurposes. Several uses are probably served by this variety.
Thus, some salts, perhaps, are necessary for the maintenance
of the properties of blood ; others are destined for the nutrition
of certain tissues, or the formation of certain secretions ; whilst
others again appear to be the result of the disintegrating and
oxidating processes going on in the tissues and organs of the
body, during the e.xercise of their respective functions.

Thus, common salt, or chloride of sodium, appears to be pre-
sent in the blood of all animals, and in every tissue. Its great
importance is evidenced by the tenacity with which it is hcdd in
the bodies of animals, and accumulates in their blood and tissues,
even when, as in the case of the herbivorous species, the food
which they consume, contains conq)aratively minute traces of it.
The strong necessity and appetite lor s;dt, felt by the herbivorous
Mammalia, is shown by their licking lumps of that subsbmce,
or boiled bones, .scattered about their ])a.stures; and also by
the periodical migrations of herds of cattle to the sidt districts
in South America — facts which indicate that s;dt is indispens-
able for the healthy condition of the blood, and of the tissues
which are nourisluid from it. It would seem, indeed, that
chloride of sodium is associated with every important act of

294

SPECIAL PHTSIOLOGY.

tissue fonufition and change. Of the secretions, all exhibit
minute traces of salt ; but the gastric juice, in particular, con-
tains an acid — the hydrochloric — derivable only from the salt
of the blood ; for the quantity of chloride of potas.sium, as
compared with the chloride of sodium, in the blood, is so small,
that it may be inferred that the latter is the source of this
acid of the gastric juice. The large quantity of soda present
in the bile, in combination Avith its fatty acids, is probably
also derived from the common salt in the blood ; the separation
of the chlorine from this, for the formation of the hydrochloric
acid of the gastric juice, maybe accompanied by the transference
of the sodium, in the shape of soda, to the hepatic cells, for
combination Avith the biliary acids. Again, the lime salts in
the blood, chiefly the phosphate of lime Avith carbonate, held in
solution in lactic and carbonic acids, are highly important
nutritive stibstances, being found in all growing tissues ; as
is Avell hnoAvn, they are especially deposited, as a consoli-
dating material essential to the formation of the skeleton, and
of the dentine and enamel of the teeth. Of these tissues,
although the enamel undergoes no nutritive change after it
has been formed, and the dentine very little, the bones are
constantly exhibiting A^ery active metamorphoses. Carbonate
of lime, phosphate of magne.sia, and silicates and fluorides, are
usually a.ssociated Avith the phosphate of lime.

But there are other salts, such as the phosphates and sul-
phates, both of potash and soda, Avhich, probably, are derived
from the oxidation of the phosphorus and sidphur contained
in the phosphorised fatty matters found in the red corpuscles,
and especially in the nervous tissues, and in the sulphuretted
albuminoid substances existing in mirscle and brain. The
phosphorus and sulphur in these compounds, are either directly
oxidised, and combined Avith soda or potash, or else they pass
first into intermediate substances, such as the highly sul-
iduAretted .substance, the taurin of the bile. If carbonates of
soda or potash exist in the blood, they also are probably not
nutrient, but represent the resrdts of chemical retrogressive
metamorphoses in the blood and tissues. MoreoA^er, the phos-
phate of soda, A'/hich has an alkaline reaction, and auy carbo-
nate of soda Avhich may be present in the blood, serve very
important and .special u.ses in that fluid, helping to dissoh’e
the albumen, to favour the chemical oxidation of many sub-
stance.s in the blood, the absorjjtion of gases, and the pas-
sage of the nutrient plasma through the Avails of the capillaries.

USES OF THE GASES OF THE BLOOD.

295

The salts of potash are, it avouIcI seem, absolutely necessary to
the nutrithm changes Avhich occur in muscular tissue. Tlie
importance of potash especially, in preserving the healthy con-
dition of the blood, perhaps by determining or aiding the chemi-
cal actions necessary for that end, is illustrated in the beneficial
efi'ects of fresh vegetables and li-uits, as articles of food. They
especially abound in neutral or acid salts of potash ; and a diet
from Avhich they are absent, if long irsed, induces that condi-
tion of the blood, Avhich causes scurvy or scorbutus. The
employment of neutral salts of potash, aids, at least, in the cure
of this disease ; but it is more effectiially remedied by the use
of lime juice, potatoes, or fresh vegetables themselves. Hence,
perhaps, a vegetable diet operates on the blood and tissues, in
some other mode than by the potash in Avhich it abounds.

Of the gases contained in the blood, the nitrogen is pro-
bably indifferent, and Avithout special office, its relative
proportion constantly varying, both in arterial and venous
blood. On the other hand, the oxygen must be regarded as
an agent of the highest importance. It purifies the blood,
and, dissolved in, or combined Avith, the cruorin of the red cor-
pirscles, is by them carried through the system, and operates
on all the tissues. Its action is not so much to contribute to
the formation of tissue, by being combined Avith, or fixed in, the
ti.ssues in the act of morphosis, as to stimulate the tissue ele-
ments, especially those of the nervous and muscular tissues, to
their proper functions, causing chemical changes or oxidations of
their .substance, or of the blood pa.ssing through them, essential
to their action, and more or less destructive of their substance.
So essential is oxygen for this purjiose, that the deprivation of
it, for but a feAv minutes, is fatal to the life of these tAvo tissues.
As to the carbonic acid gas of the blood, not only is it neither
nutrient nor stimulant, but it is the chief ultimate jToduct of
the oxidation of the tis.sues, being probably derived, hoAVCAmr,
from the oxidation of intermediate compounds, into Avhich
the materials of the used-up blood and tissues break doAvn. It
is the ultimate effete form in Avhich most of the decomposed
carbonaceous substances are eliminated from the body. It is
an impurity in the blood, Avhich requires to be incessantly ex-
pelled from it, and, indeed, is so displaced by the aid of the
oxygen in res[)iration. Under its influence, the scarlet colour
and the other properties of arterial blood, are changed, and the
blood becomes dark and venous. It is .so detrimental to the
life of both the nervous and muscular tissues, that, in cases of

296

SPECIAL PHYSIOLOGY.

asphyxia, in which it ceases to be eliminated by the lungs,
death seems rather to take place from the poisonous nature of
the accumulated carbonic acid, than from the mere absence of
the nutritive, or stimulating and vivifying, oxygen.

The nuti'itive properties of the blood, differ according to
many circumstances, being influenced by the character of that
fluid, the age, sex, temperament, habits as to exercise and occu-
pation, the constitutional state, and the nature of the food.
Thus arterial blood is more nutritive and stimulating than
venous blood, which will not long support life, especially that
of the nervo-muscular apparatus. Arterial blood not only
contains more oxygen, and less carbonic acid; but its liquor
sanguinis is richer in fibrin, and its corpuscles contain more
cruorin and saline substances, and much less fat — their total
.solid matter being less than that of the corpuscles in venous
blood. The fluid part of arterial blood, also contains less fat,
but more saccharine and e.xtractive matters. Auaiu, the blood
is less rich in childhood than before birth ; its corpuscles in-
crease, however, at puberty, but, after fifty years of age, again
diminish. The blood is richer in solid contents, especially in
red corpuscles, in men than in women ; the same is true of
plethoric and sanguine persons, as compared with those of
lymphatic or serous constitution. The quantity of the fatty
matter, is more influenced by the diet, than that of the other
organic proximate constituents. Exercise in the open air,
purifies and oxygenates the blood. This fluid is, of coui'se,
profoundly modified in disease.

Ilcemorrliacje or Loss of Blood.

The escape of blood from its vessels into the surrounding
tissues, is named extravasation ; if into one of the ciivities of
the body, or externally, it is named haemorrhage. The loss
of fi'om four to six pounds of blood, from one or more of the
great vessels, Avill generally prove fatal to an adult ; but if
the htemori-hage be slower, much larger quantities may be
drawn from the blood-ve.ssels, without a directly fatal issue.
Death from sudden haemorrhage, is caused by the want of
sufficient blood to siqjply the nervous centres, so that fattd
sjjncope, i.e. fainting, takes place ; when death occurs from
prolonged hajmorrhage, it is not from a defective supply of
nutriment to tire tissues generally, but from a slow exhaustion
of the nervous and muscidar power, aflcctiug the brain, spinal

ILEJIORRIIAGE.

297

cord, and heart, due to a deficient supply of nutriment and of
oxygen to them, in consequence of the diminution in the
number of the red corpuscles.

Everyone should bo acquainted with the various forms of accidental
hiemorrhage, and their impromptu treatment. If it be general oozing
from small vessels, which is easily recognised, and if it proceed from a
part to which pressure can be applied, a handkerchief closely folded into
the form of a pad, and tirmly boimd over the spot by another handker-
chief, will generally suffice to staunch the bleeding for a time ; the part
should then bo kept elevated and at rest. In haunorrhage from a vein,
the blood is dark, and the stream flows continuously, welling up over
the surface. Moreover, pressiu’e with the finger on the side of the
wound further /ro/n the heart, will ahnost entirely arrest the bleeding;
whilst if pressure be applied on the side of the wound next to the heart,
the flow of blood becomes more copious. To arrest venous huemorrhage,
a small thick pad should be applied upon the wound, so as to extend a
little to the side fiu’ther from the heart ; this should be firmly seciu’ed by
a handkerchief or bandage ; the chief pressure must be made on the
side of the wound away from the heart, because that is the direction
from which the blood flows. Arterial h;emorrhage is known by the
blood being bright, and projected in a jet from the wound, sometimes
to a considerable distance, usually by jerks, though, if the artery be
very small, there are merely slight intermissions in the force of the jet,
and, in wounds of very minute arteries, the jet is continuous. Moreover,
pressure on the side of the wound further from the heart, has no effect
on the stream ; but pressure on the side nearer the heart, stops it. To
arrest arterial hsemorrhage from a small artery, therefore, a pad of
suitable size should be applied upon the wound, and extend also on
the side next to the heart; it must be, not merely firmly, but tightly
bound by a handkerchief or suitable bandage. If the artery be large
and deep seated, very forcible pressure becomes necessary, and in order
to communicate this specially to the artery itself, a small thick and un-
yielding kind of pad is necessary. This should bo made, not by folding
a hankerchief, but by rolling it up as tightly as possible, with, or with-
out, some firm substance enclosed within it. Beneath the handkerchief
used as a bandage, a short stick may bo inserted on the side of the limb
opposite to the wound, and then be twisted round, so as to increase the
pressure.

These directions apply to veins and arteries situated in the limbs.
Upon the head, simple pressure with the thumb or finger, will suffice to
stop bleeding from either kind of vessel, because the bones of the
cranium affortl a perfect means of counter-pressure. Wounds of the
largo vessels of the nock, roqiuro very special management; but, as a
general rule, direct pressure with a pad, maintained in its place by the
thumb, is the best means to have recourse to, until proper assistance, by
forceps and ligatm-e, can bo afl’ordod.

In ca.se.s of sudden and great lof3s of blood, living blood,
drawn from the veins of another per.son, has been injected
into the veins of those suffering from the htemorrhage. This

298

SPECIAL PHYSIOLOGY.

is known as the transfusion of blood. Two hundred years
ago, Lower (1665) suggested this operation, having found
that animals, apparently dead from lia'inorrhage, were quickly
revived, when blood, taken from another animal, Avas imme-
diately injected into the veins. As an operation upon the
human subject, transfusion was perfected by Dr. Blundell.
The blood received into a Avarmed funnel connected Avith a
proper syringe, is immediately transferred to the veins of the
patient, no time being permitted for the occurrence of coagu-
lation. The records of fifteen cases of the saAuug of life by
this operation, have been collected by Bedard. In experi-
ments on animals, it is better to defibrinate the blood, so as to
prevent coagulation ; the process of Avhipping the blood, al.so,
to a certain extent, oxygenates the blood. It has been sup-
posed that the fibrin itself is injurious; but the better
oxygenation of the beaten defibrinated blood, may account for
its apparent superiority. Arterial blood has been shoA\m to
have a greater restorative or stimidating effect, than Amnous.
The serum of the blood is useless for the purposes of trans-
fusion. Water has also no effect, unless it be used Avarm ; it is
useful when the blood is loaded Avith carbonic acid, as in as-
phyxia, or cold and already thick or tarry, OAving to loss of Avater,
as in cholera. Solutions of common salt, or of salts selected
so as to imitate those of the blood, yield surprising, but only
temporary, restorative re.sults. The blood of one Mammalian
species, may be injected, Avith impunity, into the Amins of an-
other species ; and, contrary to Avhat Avas formerly supposed,
blood possessing oval red corpuscles, such as the blood of
Birds, does not jArove fatal Avhen injected into the veins of
hlammals, in AAdiich the red corpuscles are circidar, provided
the injected blood be arterial, and not venous, nor previously
agitated Avith carbonic acid (Bischoff). Blood taken from a
starving animal, is highly injurious, if injected into the Amins
of another, causing peculiar symptoms, apparently referrible
to the effects of decayed or decomposed animal matter (Ber-
nard). Hence the animal, or person, subjected to transfusion-
experiment, or ojieration, should be in good health, and re-
cently Avell fed ; for then, not only Avill the loss of blood be
bettor supported, but the blood itself Avill be noAvly derived
from the food ; moreover, OAving to the more Avatery character
of the chyle, as compared Avith the blood, the fibrin in the
latter Avill be diluted, and any injurious influence Avhich this
substance might produce, Avill be diminished.

VITALITY OF THE BLOOD.

20!)

The accidental injection of air with the blood, into the veins,
has probably been the cause of the fatal results in some ti'ans-
fusion experiments. Air so injected, or introduced by wounds
of the veins in the neck, when it reaches the heart, is speedily
tatal, either by mechanically interfering with the functions of
the valves, or by chemically failing to excite contraction, likc^
pure blood ; or it may induce coagulation, or obstruct the
pulmonary capillaries, after it has been driven with the blood,
in the state of froth, through the prdmonary arteries.

Vitality of the Blood.

The blood, as it exists in the vessels of a living animal, is
not a mere physical and chemical mixture of certain substances
adapted to the nutritive wants of the rest of the body ; but,
with or without the enclosing capillaries, it is an organised fluid
tissue, possessing vitality like the solid tissues. Its corpuscles
are evolved and disintegrated, like the other structural elements
of the body. As we shall hereafter see, these bodies are ori-
ginally developed simultaneously with the earliest vessels of
the embryo, and the loss to which they are subject during life,
is repaired by corpuscles newly formed in the system. The
physiological endowments of these corpuscles, especially of
the red ones, are quite peculiar, and are as characteristic as
those of any of the structural elements of the solid tissues.
With regard to the liquor sanguinis, in which the corpuscles
float, it also has vitality, and must be regarded as the liquid,
inter-cellular, or inter-nuclear, matrix of a fluid tissue ; for it
is originally elaborated, with the corpuscles, in the interior of
conjoined nucleated cells. The vitality of the liquor san-
guinis, is, probably, however, like that of the infra-, or inter-
cellular parts of the solid tissues, dependent upon its corpuscles,
gymnoplasts, or nuclei, which are its real centres of growth ;
just as the semi-fluid nervous substance, the somewhat firmer
sarcous elements, the areolar fibi'es, and the yet denser mati'ix
of cartilage, or the solid deposit of osseous tissue, appear to
be dependent upon the nuclei proper to those tissues respec-
tively.

Tlie vitality of the blood, is merely a vegetative life, its
inherent vital properties being strictly nutritive, and including
neither contractility nor sensibility. The fluidity of the
liquor sanguini.s, is an indispensable condition to the life of
the whole body, and such vitality as it or the corpuscles

300

SPECIAL PHYSIOLOGY.

possess, must be constantly exercised in the maintenance of
that condition. So, reciprocally, the persistence of the vital
properties of the blood, implies, within certain limits, the
maintenance of its peculiar fluid state and chemical constitu-
tion. Yet, as Ave shall immediately see, the remarkable change
which takes place in one constituent of the liquor sanguinis —
viz. : in th.Q fibrinogen, or fibrin, Avhich, Avhen blood is drawn
from the body, solidifies into delicate fibrils, and, entangling
the corpuscles, gives rise to the phenomenon known as the
coagulation of the blood — is, by many eminent physiologists,
regarded as a vital act.

The Coagulation of the Blood.

This phenomenon, already elsewhere noticed (Vol. I. p. G5),
does not consist of a solidification of all the elements of the
blood, but of that of the fibrin alone, of which on an average not
above 3 parts exist in 1000 of blood. The effects of this change
in so small a quantity of fibrin, are very remarkable. A few
minutes after blood is drawn from a vein or artery, it appears
to set, or stiffen, into a red jelly-like mass or clot-, from the
sm’face of this, yellowish transparent drops of fluid very soon
exude, which then run together in little pools ; the red mass
slowly shrinks, forces more and more of the transparent fluid
from it, becomes more and more solid, and, at the end of from
twenty-four to forty-eight hours, constitutes a clot equal in
bulk to about one-third of the total Amlume of the blood, the
rest now consisting of the yelloAV fluid, Avhich is named the
serum. This serum contains most of the Avater, besides the
albumen, salts, and extractives of the blood ; Avhilst the clot,
coaguluin, or crassamentum, is composed of the fibrin, together
Avith the red and Avhite corpuscles. The clot still contains,
however, some serum, and, in order to remoA^e this, it is neces-
sary to lift it from that fluid, cut it in pieces, and drain it
upon a proper filter.

The composition of the clot and serum, may be inferred
from the facts stated in p. DO, Vol. I. When portion.s of the
clot are examined under the microscope, the solidified fibrin
is seen in the form of exceedingly minute fibrilla;, not more
than the -3-0-0-515 of an inch in diameter, nearly
straight, subdividing dichotomously, and sometimes assuming
the appearance of rows of minute particles. These fibrillaj
are most perfect, Avhen the blood coagulates sloAvly. The red

COAGULATION OF THE BLOOD.

301

corpuscles in the clot, are no longer separate from each other,
so as to be freely mobile, as in the circulating blood, but have
run together in adherent masses or columns, which have been
compared to overlapping rows or piles of coins ; the white
corpuscles are also entangled, but not in groups, though, under
certain circumstances, they collect more abundantly in the
upper part of the clot.

As freshly drawn blood coagulates, it gives off a vapour
known as the halitus of the blood. A minute quantity of
ammonia escaping in this halitus, is also evolved (Kichardson).
No carbonic acid escapes, as was once suppo.sed. An odour,
often characteristic in the case of different animals, is likewise
perceptible, not so much during the coagulation of the blood,
as before that event takes place, when the blood is hottest.
Diming coagulation, no heat is evolved, the temperature of
the blood, indeed, being already lowered, more or less, before
this phenomenon begins.

The coagulation of the blood is influenced by many cir-
cumstances, wdiich determine its rapidity, and modify the
characters of the clot itself, as to form, colour, and consistence.

The external conditions which accelerate the formation of
the clot, are rest, or, on the contrary, very active stirring,
moderate increase of heat, exposure of the blood to air, its
slow escape from an artery or vein, its reception into shallow
vessels, and contact with rough or multiplied sui-faces, or with
foreign solid bodies, and, in certain cases, its slight dilution
with water. Within the body, the circumstances which
favour the coagulation of the blood, are certain enfeebled
states of the system, fr-equent bleedings, laceration of the
ve.ssels from which the blood escapes, inflammation of the
coats of the vessels, or of the lining membrane of the heart,
and so called atheromatous, or other deposits, upon the vessels
or upon the valves.

On the other hand, coagulation is retarded, or intemipted,
by movement, cold, heat beyond a certain temperature, the
exclusion of air, as by covering the blood with a stratum of
oil, its rapid escape from a vein or artery, its reception into
deep vessels, its contact with .smooth surtaces, its exemption
from the intrusion of foreign solid bodies, and also by the
addition of strong solutions of neutral alkaline salts, or
of minute quantities of ammonia. Moreover, it is retarded
by the admixture of certain vegetable substances containing
narcotic and sedative alkaloids, such as opium, hyoscyamus,

302

SPECIAL PHYSIOLOGY.

belladonna, aconite, and digitalis, and even by strong infusions
of tea and coffee. In the case of the addition of strong solu-
tions of neutral salts, and of many other substances, subse-
quent dilution of the mixed blood, by adding water to it, is
followed by a feeble coagulation. The internal conditions
which retard coagulation, are certain inflammatory states of
the system, perfect smoothness of the interior of the heart and
bloodvessels, and, above all, a healthy condition of their lining
membrane.

Althouah rest, as when drawn blood is set aside, is favoim-
able to coagulation, and moderate agitation, as when the blood
is gently shaken in a bottle, delays this act, it is remarkable
that stirring blood rapidly with a rod, or ivhipping it with a
bundle of sticks or wires, causes the fibrin quickly to coagu-
late in thready masses on the rod ; this is the usual method
of defibrinating blood, which afterwards remains fluid, or
forms but a very soft imperfect second coagulum. The effect
of whipping, depends on the rapid and frequent contact of
the multiplied surfaces of the wires with the blood. Again, a
temperature varying from 100°, or the natural temperature of
the blood, up to 120°, accelerates coagulation, but a greater
heat retards it; at 150° this property of the fibrin, is said to
be permanently destroyed, whilst, above that temperature, the
albumen of the blood itself coagulates. When blood is allowed
to cool, its coagulation is retarded in proportion to the degree
of cold to which it is subjected; at 27-^°, or 4^° below the
ireezing point of water, it solidifies; and if it has not been
previously allowed to coagulate, and the freezing process is
rapidly completed, it will coagulate on being thawed. The
coagulating property is, therefore, proportionally, sooner de-
stroyed by an elevation than by a lowering of the temperatiu-e
of the blood ; moreover, fi-ozen blood may be preserved for a
long time, and yet retain its power of coagulating when thawed.
The influence of exposure to air, in accelerating the coagula-
tion of the blood, probably explains the corresponding effects
of the slow escape of the blood from the vessels, and of its
reception into shallow basins. These conditions do not act
by lowering the temperature, for that would retard coagula-
tion, nor by the escape of the halitus merely ; but it has been
suggested that they operate by favouring the escape of am-
monia from the blood. All conditions which ficilitate the
escape of vapour or gas from the blood, certainly favour its
coagulation. Thus, coagulation occurs in a vacuum, a fact

COAGULATION OF THE BLOOD.

S03

which shows that the presence of air is not necessary, a con-
dition too whicli would favour the escape of ammonia ; but it
also occurs, and even more quickly, Avhen the blood is sub-
jected to increased atmospheric pressure. Complete exclusion
from air, though it retards, does not prevent coagulation, as
blood will at last coagulate in closed vessels, and even within
the dead body shut up from the air. The rapid escape of
blood from its vessels, and its reception into deep glasses or
basins, are supposed to retai'd coagulation, by alfording less
opportunity of exposure of the blood to the air. Of all the
circumstances wdiich hasten the formation of the clot, the
multiplication of the points of contact with solid bodies seems
to be the most potent ; the smallest particle of thread suffices
to induce rapid coagulation, where, in the absence of any
foreign body, a much slower process of clotting would have
occurred. Blood received into metal or earthenware utensils,
is said to coagulate sooner than when received into glass
vessels, perhaps owing to differences of roughness of the
surface. The accelerating effect of slight dilution and the
retarding influence of the addition of saline solutions, are not
well explained ; they may operate, simply by altering the
specific gravity, and also the viscosity of the blood. The re-
tardation, or prevention, of coagulation, by the addition of
ammonia, even if tiansmitted through the blood, in the form
of vapour, the occurrence of coagulation in such blood when
the ammonia escapes, and its resumption of the fluid state
on the introduction of fresh ammoniacal vapour — phenomena
which can be reproduced several times over, in the same
blood — are the chief facts addirced, together with the known
presence of ammonia in the halitus of the blood, in favour of
the hypothesis of Dr. Richardson, that the ammonia is the
cause of the fluidity of the blood in the body, and its escape,
the immediate occasion of coagulation in drawn blood.

The mode of action of narcotic and sedative poisons, is not
understood. The more rapid coagulation of the blood in
feeble states of the sj/stem, does not depend upon an increased
quantity of the fibrin or coagulating substance, but rather on
the dilute or watery condition of the blood. On the other hand,
the more slowly coagulating blood of the inflammatory state,
is accompanied by an actual increase in the quantity of fibrin,
though there apj)ears, possibly from the high specific gravity
and richness of the blood, to be a greater resistance to the act
of coagulation. The necessity for perfect smoothness of the

304

SPECIAL PEYSIOLOGY.

interior of the heart and bloodvessels, in order to prevent
coagulation, may be infeired from the highly polished cha-
racter of their epithelial lining ; the influence of rough surfaces
in their interior, in determining coagulation of the blood, is
shown by the small cf>agula formed ujDon excrescences of the
valves of the heart, and by the flakes of fibrin, which collect
on atheromatous or calcified portions of vessels, in the rough
interior of aneurisms, and at the openings of lacerated vessels,
which are so much sooner closed by coagula, than those
which are cleanly cut. Coagrda have been induced ex-
perimentally in animals, in the interior of large vessels, by
the passfige of needles, wires, or threads into such vessels;
when formed in an artery, the coagulum is firm and elongated
in the direction of the blood cui’rent, whilst, in the veins, the
clots are loose and massive. In certain cases, during life,
especial ly during the last hours of life, such coagrda may form
in the living blood, especially when rough excre.scences exist on
the valves of the heart. The influence of an inflamed con-
dition of the coats of the bloodvessels, in causing coagrdation
of the fibrin, has been referred to the partial loss of vi^ity, or
to the interruption of the vital proce.sses, in the inflamed tissue,
by which it is, so far, approximated to the state of inanimate
matter. The injection of pus, the pulpy substance of the brain,
and other semi-solid matters, into the bloodvessels of an animal,
rapidly coagulates the blood, a result probably attributable
to the effects of contact witlr the multiplied surfaces of non-
living matter.

Blood confined in a living vein between two ligatures, retains
its fluidity for a long time, beginning to coagulate commonly,
after from 3 to 5 hoiri-s, and sometimes even being only im-
perfectly clotted at the end of 24 hours, though such blood will
coagulate in a few minutes when withdrawn from the living
vein. If the vein be dead, although the blood is equally well
excluded from the air, coagulation takes place within a quarter
of an hour. Experience shows that blood may be retained in
occluded vessels, and yet continue fluid for a considerable time,
or that blood may be extravasated in the midst of tlie living
tissues, and yet jireserve its fluidity for many days, though it
will soon coagulate when afterwards withdrawn from the body.
From the.se and other facts, it has been inferred that the living
tissues possess some .special projicrty, by which they Tuaintain,
or preserve, the fluidity of the blood ; according to one view,
they actively prevent its coagulation ; according to another.

CirARACTEBS OF THE COLOUR.

305

they operate negatively, by not determining that process, us
dead matter would, whether it were an inorganic solid, or u
dead animal substance, such as brain substance, dead muscle,
or pus. The poisons and the. modes of death, which influence the
coagulation of the blood, for the most part retard or prevent
it. Sudden destruction of the substance of the brain or spinal
cord in an animal, causes coagulation of the blood even in the
living vessels, in which clots are found after a few minutes.
The poison of venomous serpents, appears altogether to destroy
the coagulating property of the blood ; narcotic poisons, and
prussic acid, have the .same effect ; asphyxia or suffocation,
whether from hanging, drowning, or the action of gases unfit
to support respiration, also cause the blood to remain fluid
after death. In cases of death by lightning, by electric
shocks, by blows on the epigastrium, or after a severe chase,
the blood has been said not to undergo coagulation ; but this
seems to be untrue, the blood being often, though not always,
foimd fluid, but after a time undergoing coagulation. In cholera,
the coagulation is also postponed.

The foiin, consistence, and colour of the clot, exhibit many
varieties. From healthy blood, the clot is flat or slightlv
concave on the upper surface, especially if the blood has been
received in a shallow basin, when the clot is soft, and very
little serum exudes from it. When an upright vessel is used,
the surface of the clot is a little more concave. The consist-
ence of a healthy clot, is firm and uniform ; its colour is bright
red ou the top, from exposure to the air, but dark in its lower
portions. In inflammatory diseases, especially in pneumonia
or inflammation of the lungs, the blood is very rich in fibrin,
containing, instead of 3, above 5, often 7, and even as many
as 13 parts in 1,U00 ; nevertheless it coagulates slowly, and
the coagulum presents a remarkable peculiarity known as
the huffy coat. Such a coagulum shrinks more than usual,
is exceedingly firm, and very concave on its upper surface,
forming what is called the “ cup,” which presents a thick layer
of a nearly colourless, yellowi.sh, or greenish yellow hue, the
so-called huff or huffy coat. This coat, and the cupped form,
are more marked when the blood is received into a narrow and
deep basin, than into a shallow one ; in the former case, the
coagulation is slower, and in the latter quicker, as with healthy
blood. 'I'he buffy coat is very firm and tough, and, when ex-
amined under the microscope, is found to consist of fibril-
lated fibrin, intermixed with many white corpuscles ; from

VOL. II.

306

SPECIAL PHYSIOLOGY.

some cause, the red corpuscles partly subside before tlie
commencement of coagidation, and so escape being entangled
in the upper portion of the clot. It was formerly supposed
that the slower rate of coagulation of inflammatory blood, ac-
coimted for this subsidence of the red corpuscles from the
upper strata of the fluid, before coagulation took place ; and
this view is supported by the fact that the corpuscles, which
are heavier than the liquor sanguinis, do subside in blood,
the coagulation of which is intentionally retarded by the ad-
dition of strong solutions of sulphate of soda or of common salt.
But other circumstances probably cooperate to increase the
tendency of the corpuscles to settle down. The disposition of
the red corpuscles to run together in columns and masses, in
blood drawn from the body and left at rest, is increased in the in-
flammatory state, the corpuscles then running into larger clusters,
clinging more firmly together, and even losing their circuljur
form, and becoming elongated. The aggregation of the cor-
puscles into larger masses, perhaps causes them to subside more
rapidly than if they adhered in the usual minute piles or
columns ; and this, together with the retardation of the coagu-
lating process, may account for the formation of the buffy
coat. This unusual aggregation of the corpuscles, also occurs
in certain- low constitutional states, and, it is said, in plethora;
it likewise happens, when the coagulation of the blood is re-
tarded intentionally in experiments. A tendency of the cor-
puscles to fall to the lower part of a living vein enclosed by
ligatures, has been seen in animals. The nature and cause of
this tendency of the corpuscles to run together, remains, how-
ever, yet unexplained. Their apparent mutual attraction is
diminished by the addition of weak saline solutions, and the
bully coat, if the blood be inflammatory, is less distinctly
developed, although the period of coagulation is delayed. The
addition of any mateiual, Avhich, like mucilage, increases the
aggregation of the corpuscles, accelerates the subsidence of the
corpuscles, and increases the bully coat.

Contrasting with the firm, fibrinous, and contracted clot of
the blood in inflammation, are the loose, soft coagula, cha-
racteristic of the blood of weak, cachectic, and ana?mic persons,
even though the clot is formed more rapidly. A deficiency of
fibrin causes the clot to be soft. During bleeding, the power
of coagulation of the blood is gradually modified as the blood
flows, the last quantity drawn setting more rapidly, but form-
ing a softer clot. Fragile, almost semi-fluid clots arc found in

IS COAGULATION A VITAL ACT?

307

the blood of those who have died of cholera, from strokes of
liglitning, or from asphj'^xia.

That the immediate cause of the coagulation of the blood, is the
solidification of the fluid fibrin of the liquor sanguinis, is shown
by the existence of the fibrinous fibrillse, in clotted, but not
in fluid blood ; by the formation of the buffy coat without any
admixture of the red corpuscles, the upper and firmest part of
this coat, being nearly pure fibrin ; and lastly, by the fact that
whipping the blood, which removes the fibrin, prevents any
further coagidation, the corpuscles themselves not possessing
this power, then remaining free and suspended, or subsiding in
the serum, Avhich is likewise no longer coagulable. Experi-
ments also demonstrate this property of the fibrin. Thus,
if the coagulation of the blood be retarded, by the addition of
solutions of neutral salts, the red and white corpuscles have
time to subside, and the upper clear fluid, which still contains
its fibrin, then undergoes coagulation, the delicate colourless
clot exhibiting the characteristic microscopic fibrillae. Again,
by adding a solution of salt or of sugar, to a quantity of frog’s
blood, the corpuscles of which are very large, the fluid part of
the blood, or liquor sanguinis, may be actually filtered from'
the corpuscles, and will afterwards undergo coagulation.

The cause of the solidification of the fibrin, has been the
subject of much speculation and difference of opinion, and is
still not satisfactorily understood.

Many living physiologists, agreeing with Harvey, Hunter, and
others, maintain, as already stated, that the coagulation of the
blood, is a manifestation of vital power in that fluid. Harvey
said of the blood, that it was the primum vivens and the nl-
timum moriens of the body ; whilst Himter considered the
coagulation of the blood as its last act of life. An analogy
has been dra-\vn, somewhat vaguely, between the solidification
of the fibrin of the blood and muscular contr-action, and, per-
haps with more justice, between it and the rigor mortis, or
rigidity of the muscular tissue after death. Several modern
authorities perceive in the fibrillation of the solidifying fibrin,
the evidence of an organising plastic })roce.ss, the feeble efforts
of a formative vital energy. Moreover, it is urged that
effusions, undoubtedly fibrinous, upon the surfaces of serous
membranes, in the interior of the eyeball, between the ends
of tendons or other cut surfaces divided subcutaneously, and
in other situations, become organised and vascular, and are
converted into a low form of areolar or fibrous tissue ; and

3U8

SPECIAL PHYSIOLOGY.

that not merely fibrin, but even blood clots in the interior
of vessels, as in cases of ligature of arteries, or blood extrava-
sated in the midst of the tissues, may also become, under certain
circumstances, vascularised, and converted into a definite tissue,
in the same way as infiammatory fibrinous exudations are,
the blood corpuscles not assisting in the process, but rather
delaying it (Huntei’, Zwicky, Paget, Hewett).

Notwithstanding the support given to the idea of the coagula-
tion of the blood being a vital act, and of the possession of a vital
property of solidification by the fibrin of that fluid, it may be
doubted whether this doctrine is correct. There is no real
analogy between muscular contractility, which requires pecu-
liarities of structure, and complex statical and dynamical elec-
tric conditions, and the simple change of the fibrin of the blood
from a fluid to a solid state. If its comparison with the rigor
mortis be more exact, the tendency of modern opinion is to
regard this phenomenon not as a vital act, but truly as a rigidity
of death, dependent on chemical changes then ensuing. Again,
there is no true resemblance between the minute fibrillEe of
solidified fibrin, and any fibrous or other tissue of the body ;
the former are homogeneous, the latter, indeed, always present
differences of ]>arts. Fibrinous deposits or effusions may be-
come the seat of positive organisation, so as ultimately to give
rise to a tissue ; hut then nuclei, or centres of growth, arranged
in methodical order, and even cells, appear within it, for the
formation of the future tissue elements and the new capillary
vessels ; these nuclei and cells are supposed to have their origin
not in the fibrin, but from the corresponding parts of the sur-
rounding tissues. In cases of so-called organisation of the
ooagula formed in ligatured arteries, in the interior of in-
flamed veins, or in other situations amidst the living tissues,
it is the surface of the clots next in contact with those living
tissues, which first presents appearances of organisation and
vasoularisation. This suggests the possibility that, subsequently
to the eli'usion of blood, a true plastic exudation may take
jflace around the clot, and may penetrate between the columns
of its aggregated corpuscles; in this way, the apparent organisa-
tion and vasoularisation of a clot, may rdtimately be the f^ime
]>rocess as that -of a fibrinous effusion, depending on formative
acts on the part of the surrounding cell elements, which give rise
to nuclei, cells, or intercellular substance. According to this
view, the coagulum of the blood constitutes a sort of nidus
for future developmental processes, but is not itself converted

IS COAGULATION A rilYSICAL ACT?

309

into tissue. The fibrilhe of the coagulated fibrin, may support
the effused mass, divide it into areola? or spaces, and thus
favour the penetration of exuded plastic matter, and the
penetration of nuclear growths through it. The plastic lymph,
though a fibrinous material, may not be identical with the
solidified fibrin of the blood, but may be a true protoplasm,
more distinctly and positively possessed of organisable tenden-
cies, and thus of a real though low form of nutritive life. If this
be so, the strongest argument in favour of the vital character
of the coagulation of the fibrin of the blood, is nullified.

IMoreover, many facts appear irreconcileable with such a
doctrine. Thus, the blood of a horse has been kept in a fluid
state, by means of nitre for fifty-seven weeks, and yet speedily
coagulated, when sufficiently diluted with water (Gulliver).
Frozen blood, as already stated, will coagulate wdien thawed.
If, therefore, coagulation is a vital act, the life of the blood
must be admitted to be capable of being “ pickled ” and
“ frozen ” (Gulliver). It is replied by the vitalists, that the
vitality of the fibrin is simply preserved in a dormant condi-
tion, by the prevention of spontaneous change or decomposi-
tion; just as the dormant vitality of seeds and ova, endures
for years, and as that of infusorial animalcules, and even of the
highly organised llotifera, may be restored, after considerable
elevation or lowering of the temperature, or may be sus-
pended, and so conserved, by desiccation. But the recovery
of animalcules after freezing, is, probably, only apparent, a
minute drop of surrounding unfrozen water perhaps defending
them from actual congelation ; whilst in blood thoroughly
frozen, the fibrinous fibrillse, undergoing no nutritive changes,
could hardly escape that event. Furthermore, there is no
example of the recovery of life, by any of those minute orga-
nised beings, after immersion in so potent a substance as a
solution of nitre, which is a well-known solvent of fresh
fibrin.

On the supposition that the coagulation of the fibrin, is not
a vital, but a physical process, it has been maintained that the
fibrin is held in a fluid state, in the living blood, by a minute
rpiantity of ammonia, and that the escape of this ammonia is
the immediate cause of its coagulation — at least when blood is
drawn from the liody. The celebrated Robert Boyle (I (184)
considered that the blood gave out a spirit, and observed that
it could be maintained in a fluid .state by a salt of ammonia,
and that clotting occurred after the removal of this. It was

310

SPECIAL PHYSIOLOGY.

proved by Haller, that the halitns of the blood is alkaline.
Albumen, it is known, is rendered soluble by the fixed alkali,
soda, but may be precipitated by the addition of an acid.
Lastly, it has been shown, by Richardson, that ammonia is
really given off fi’om blood, microscopic crystals of hydrochlo-
rate of ammonia being formed on a piece of glass moistened
with a trace of hydrochloric acid, and held over freshly-drawn
blood ; also that, by the transmission of the ammoniacal vapour
from Iresh blood, through other fresh blood, the latter may be
kept fluid for an unusual time ; that air containing the vapour
of ammonia, has the same effect, and will, even after coagula-
tion has taken place, restore the condition of fluidity — the
clotted and fluid conditions being alternately producible, ac-
cording as the ammoniacal vapour is passed into the blood, or is
permitted to escape from it. The minute proportion of 1 part
of ammonia to 3000 of blood, is sufficient to maintain the
fluidity of the latter. Finally, nearly all the conditions Avhich
appear to favour, or accelerate, the coagulation of freshly-
drawn blood, are such as would also facilitate the escape of the
volatile alkali from it (Richardson).

Other considerations and tacts appear, however, to show
that the escape of the ammonia from the blood, which un-
doubtedly occurs, is not the cause of the solidification of the
fibrin, but merely an accompaniment of that change. In the
liquefaction of solid fibrin by ammonia, and its alternate re-
coagulation and liquefaction by the subsequent subtraction
and addition of ammonia, it is not certain whether the fibrin
of these secondary and tertiary solidifications, is identical with
the fibrin of the primary clot. Many experiments and obser-
vations further show that freshly-drawn blood may be placed
in such conditions, that its ammonia cannot well escape, and
yet coagulation will occur ; e.g., when blood is received into a
bottle which is quickly stoppered, or when blood rendered
fluid by ammonia, coagulates, though tardily, if kept in air-
tight vessels (Zimmerman); or, again, when blood, subjected
to increased barometric pressure, which would check or pre-
vent the escape of ammonia, is found to coagulate even quicker
than usual (Colin). Moreover, blood drawn from an animal,
and exposed to the air for fifteen minutes, at a temperature of
32°, even though its ammonia had probably escaped, has been
found to remain fluid for upwards of five hours, when intro-
duced into the freshly removed heart (Briicke). The blood in
a dead body, is usually Ibund coagulated in the heart and the

FIBRIN A COLLOID BODY.

311

larger arteries and veins, but fluid in the smaller vessels,
although ammonia could apparently escape, or transude, moi'e
easily from the latter. This coagulation in the heart and larger
vessels, is partly due to post-mortem changes, but, sometimes
at least, the clots begin to form during the last moments of
life. Again, blood confined between two ligatures in a living
vein, retains its fluidity for many hours ; but if a piece of
glass tube be introduced between the blood and the walls of
the vein, coagulation very speedily occurs (Briicke). So,
too, when needles, wires, or threads are passed through living
vessels, the blood will coagulate in the vessels, though the
ammonia could not, by any possibility, escape from the moving
blood (Simon and Lister). The coagula thus formed in veins,
are large, soft, and dark ; whilst those formed in pierced
arteries, are small, compact, and pale. In both kinds of vessels,
the broadest or attached part, or base of the clot, is directed
towards the heart. No escape of ammonia can take place
when a clot forms in a ligatured artery, nor in that coagula-
tion of the blood dmring life, which occurs from the sudden
destruction, in animals, of the substance of the nervous centres.
Nor can this explain the coagulation produced by the injection
of dead brain substance, or of ptis, into the blood, nor the fact,
that blood enclosed between two ligatures, in a dead vein,
speedily coagulates ; whilst blood similarly enclosed in a living
vein, remains fluid, the facility for the escape of ammonia
being apparently, in either case, the same (Astley Cooper,
Briicke, Lister).

Indeed, this last-mentioned experiment, added to the well-
known circumstances, that blood, extravasated amidst the
living healthy tissues, remains for a long time fluid, whilst if in
contact with inflamed vessels or tissues deficient in vitality,
or with the lining membrane of vessels containing morbid
deposits, or with dead animal substances out of the body, it
quickly coagulates, indicates a striking contrast between the
effect of contact of living and dead animal tissues on the
blood, the former, in some way, retarding or antagonising the
coagulation of that fluid, the latter, in some way, accelerating
or determining it (Lister.)

It has been suggested that the immediate cause of the
coagulation of the fibrin, may have .some relation to the dis-
tinction between the crystalloid and the colloid condition of
matter (Graham). Fibrin, like all albuminoid bodies, is a

colloid substance ; and one of the properties of these, is a

312

SPECIAL PHYSIOLOGY.

proneness to molecular or molar metastases, by -wbich they
pass, not only from a pectous to a liquid, but also from a liquid
to a pectous state (p. 163). Albumen undergoes this latter
change, on the application of heat; casein, on the addition of
acid pepsin, or of an acid with heat, and fibrin, still more readily
than either, becoming, when left to itself, solidified at mode-
rate temperatures, and, more rapidly, at somewhat higher tem-
peratures. The coagulation of fibrin not being due to any
external apparent cause, has been designated spontaneous.
But this more ready assumption by fibrin, of the pectous con-
dition, can hardly be spontaneous, in the usual sense of that
term ; unless, indeed, we suppose the vital endowments of
this remarkable substance, to be higher even than Hunter
believed. Crystallisation is as much spontaneous, in one
sense, as coagulation. The latter probably depends upon
some definite molecular or molar changes, strictly physical,
like any other less rapid efifect of colloidal energy, and occur-
ring when the fluid fibrin is removed from the ordinary in-
fluence of processes going on in the living vessels and tissues
within the body, or when it is sitbjected to other influences
exerted upon it by the dead tissues, or by foreign bodies
generally. *

The action of these latter may be catalytic, or due to con-
tact, and the fact, that rough or multiplied surfaces accelerate
coagulation, favours this view. It has been suggested that
dead matter may induce a reaction between the solid and
fluid constituents of the blood, in which the former, that is the
corpuscles, impart to the fibrin of the liquor sanguinis a dis-
position to coagulate. When, however, no foreign substance
is introduced into the blood, the catalytic action has been sup-
posed to be due to the corpuscles themselves, which, as it
were, ceasing to undergo their characteristic vital changes,
and so, in effect, becoming dead, determine, like other dead
•animal matter, the solidification of the fibrin (Lister). The
influence of the red corpuscles, in producing or accelerating
coagirlation, is well established ; the upper colourless stratum
of either inflammatory or diluted blood, in which the cor-
puscles have subsided, coagulates more slowly than the lower
part, in which the corpuscles are present (Gulliver). Chyle, to
which a minute portion of blood is added, will coagulate in two
or three minutes, though the same, when pure, takes from
twenty-five to ninety minutes to coagulate (Schmidt). The
fluids of ascites, pleurisy, and pericarditis, that of blisters, and

COAGULATION IS A Pin'SICAL PROCESS.

313

of other so-called serous exudations, readily coarrulate after the
addition of a minute quantity of blood, even, it is said, of a few
red corpuscles; whilst other portions of those Huids, kept apart,
do not. The same effect is produced, however, on the admix-
ture of two such fluid exudations. Fragments of the crystal-
line lens, the composition of which resembles, or is identical
with, the globulin of the red blood corpuscles, and even the
crystals of hiemato-globulin obtained from those corpuscles,
also induce the formation of a coagulum in these fluids.
Hence Schmidt, to whom these latter observations are chiefly
due, believes that, within the blood cells, there exists a fibrino-
jplastic substance, and in the liquor sanguinis a Jibrino-genous
substance, and that by the escape of the former and its union
with the latter, the act of solidification is effected. But, since
dead animal tissrres of all kinds, and even clots, or solidified fibrin
itself, either fresh, or dried and powdered, produce the same
effect, it may be that the action of the corpuscles, in causing
coagulation of the fibrin, is not a vital process ; and that if, as
supposed, their contained globulin escapes, by exosmosis,
through their envelopes, into the liquor sanguinis, this is, in
reality, a post-mortem event.

Finally, therefore, it is submitted that, out of the body, the
solidification of the fibrin, which is the sole cause of the coasu-
lation of drawn blood, is due to a mere physical, molecular or
molar change, resulting in its transformation from a liquid to
a pectous state, as is common to colloidal bodies ; that this
change is permitted, after the life of the blood, or the inces-
sant nutritive mutations which occur in living blood, cease ;
that it is accelerated, or induced, by the contact of dead matter,
either proper, or extraneous, to that fluid, and that it is to be
regarded, not as a token of life, but as a sign of death. When
coagulation occurs within the body, it is still under conditions
indicative of the diminution or cessation of the ordinary vital
interchanges of the blood, and so may be equally regarded
as a physical process, or, at least, as one of those e.xamples in
which the essential cause is physical, though sometimes it
may be utilised, and directed to certain formative ends. Lastly,
if this view be maintained, the fibrinous fibrillas of clots formed
in the living bloodvessels, or extravasated amongst the tissues,
cannot be supposed themselves to be converted, any more than
the red corpuscles, into organised tissue elements ; but, by their
trabecular arrangement, they may facilitate the penetration
into such clots, of an organisable blastema, with nuclei or

314

SPECIAL physiology.

nucleated gymnoplastic cells, and intercellular substance, for
the production of newly formed tissue.

The formation of an external clot at the mouth of a wounded or
divided vessel, is the first step taken by nature, in the eifort to close the
vessel ; to this, succeeds the fomiation of an internal clot, the base of
which, in a divided vessel, corresponds with the wound, the apex ex-
tending towards the heart, as far as the nearest branch of any size.
From the divided edge of the vessel, a nutritive plasma, or bla.stema, is
pom-ed out, in which nuclei and nucleated cells, probably derived from the
surrounding cell elements, appear, and form the future areolar tissue,
with its eapillai-y network, which closes the aperture in the vessel. In
the case of a completely divided artery, the muscular coat of the vessel
contracts, and retracts within the sheath, and so helps its closure; a
lacerated or twisted artery retracts even more securely than one cut
cleanly across. When an artery is tied, as in surgical operations, its
middle and internal coats are cut through by the thread, whilst the
outer one is enclosed in the knot ; the two former tunics contract, and
turn in towards the area of the vessel, and it is upon their cut edges
that the primary clot first forms, and from them, that the new tissue,
which closes the vessel, is produced ; the constricted part of the outer
coat, sloughs, and permits the ligature to come away. The artery is
closed, and slirinks up to the nearest branch, the primary clot being
absorbed : the collateral vessels are greatly increased in diameter, to
carry on the circulation beyond the point of ligature. Pressure, by aid
of a needle passed through the soft parts upon the side of a divided
artery of moderate size, enables its cut end to close : this is now some-
times employed after operations, and is known as acupressure (Simp-
son and others).

SANGUIFICATION.

The occurrence of this process in the economy of the higher
animals and of Man, is implied in the popular expression of
snaking blood. The corpuscles, both red and white, waste, or
become worn out, from the nutritive changes which occur in
the solid tissues, and in the blood itself. Tlieir number, espe-
cially that of the red ones, certainly increases with a high
rate of living, and materially diminishes from htemorrhage,
starvation, or disease. This waste, and loss of number in the
corpuscles, must be repaired.

The ivhite corpuscles are supposed to be derived from the
lymph and chyle corpuscles which enter the blood, and are
identical Avitli its white corpuscles, in size, form, stnicture,
and chemical composition. The large number of white

FORMATION OF RED BLOOD CORPUSCLES.

315

corpuscles ftiund in the blood, three or four hours after com-
plete digestion, their greater abundance in the veins than in
the arteries, and especially in the left innominate vein as com-
pared Avith other veins in the body, are facts Avhich favour
this view. No other ordinary source for the production of the
white corpuscles of the blood, has been suggested, although it
has been supposed that, under certain circumstances, as in local
inflammation or excitement, they might possibly arise within
the capillaries, by subdivision and growth of the nuclei in the
walls of those vessels, and then, becoming detached, be moved
on with the blood. Some may also arise within the spleen.

The mode of formation of the blood corpuscles, both white
and coloured, in the embryo and its membranes, is peculiar, and
will be described in the Section on Development. After birth,
the red corpuscles, it is generally believed, are developed from
the white ones, however these latter may arise. Many tran-
sitional forms have been traced in the blood. In the progress
of change in the Mammal, as described by some (Funke,
Paget, Kblliker), the contents of the white corpuscle become
more fluid and homogeneous, the compound nucleus disappears,
the surface becomes smooth, the size diminished, the shape
flattened, disc-like and then biconcave, an exceedingly thin
envelope forms around them, and they acquire a red colour in
their interior. According to others (Wharton Jones, Busk,
Huxley), this is true, as regards the nucleated coloured cor-
puscles of Birds, Reptiles, Amphibia, and Fishes ; but in the
Mammalian non-nucleated coloured corpuscle, it is the nu-
clear portion only, of the white corpuscle, which is converted,
by the necessary changes, into a red corpuscle. By some, it is
thought that the smaller white corpuscles, or the larger ones
after subdivision, undergo this transformation, by flattening,
disappearance of the nucleus, and acquisition of cruorin ; others
regard the smaller pale bodies often described in the blood, as
if they were wasting, not growing, red corpuscles.

In the Oviparous Vortebrata, therefore, the red-blootlod corpuscle is a
transformed pale corpuscle ; but in the Viviparous Mammalia, including
Man , the red corpuscle is the homologue of the nucleus only of the Oviparous
blood corpuscle. In both cases, the pale corpuscle is perhaps a naked cell
orgymnoplast; but a distinct, though delicate, envelope or cell wall, after-
wards appears. The difference between them appears to bo, that in
the Mammalian red corpuscle, the envelope touches the nucleus, around
which there are no cell-contents, or the nucleus disappears in these ;
whilst in the other Vertebrata, the envelope is at a distance from tho
nucleus, the cell-contents being abundant. Tho importance of tho
nucleus, as a centre of activity, is thus well illustrated.

316

SPECIAL PirySIOLOGY.

The chemical changes in the corpuscles, are no less remark-
able than those which affect their form. Their globulin
acquires phosphorus and iron, the former element a.ssociated
with fat, and the latter with the colouring matter or cruorin.
They now also manifest a singular affinity for oxygen. It is
not quite certain, in what part of the circulation the change of
white into red corpuscles takes place ; but it is supposed that
this is completed during the passage of the venous blood, in
which the white corpuscles aboimd, through the capillaries
of the lungs; they are fewer in the arterial blood. The
remarkable effects of the respiratory process on the blood, and
the strong affinity of the red corpuscles themselves, when fully
formed, for oxygen, prove that the oxygenation of the blood,
which takes place in the lungs, is accompanied by changes of
deep importance in its corpuscles, and favour the idea that it
may even be concerned in the conversion of the white cor-
pitscles into red ones.

It has been already stated, that the red corpuscles, after
enduring or living a certain time, waste or die. Many writers
have supposed that they accumulate in the spleen, becoming
impacted, as it were, in the venous sinuses of that organ, and
then shrinking and disappearing. By others, again, it is
believed that the cruorin, or red colouring matter, is added to
the young corpuscles in this organ, perhaps even from the
debris of those red corpuscles which become stagnated and
disintegrated in it.

Besides the corpuscles, however, the intercellular fluid
matrix of the blood, or liquor sanguinis, is, as we have seen,
constantly undergoing loss, in supplying the materials neces-
sary for the maintenance and formation of the great variety of
tissues and secretions. Every act of nutrition, like those of
secretion, must remove something from, and so far impoverish,
the blood. The albumen of the liquor sangiiinis, is constantly
replenished from that of the lymph and chyle, and, by venous
absorption, from the digested food ; but it may also contain
certain more highly elaborated albuminoid materials, derived
from the corpuscles. Some of the substances employed in
nutrition, such as the salts and earthy matters, may belong
properly to, and proceed from, the liquor sanguinis itself; so
also may certain albuminoid matters. But others may merely
traverse that fluid, on their way from the blood corpuscles,
in which they are finally completed, to the tissues, escaping,
through the envelopes of the corpuscles, by dialysis or e.xos-

FOltMATlON OF LIQUOR SANGUINIS.

317

mosis, passing across the liquor sanguinis, by liquid dilFusion,
and then permeating the capillary walls, by dialytic or porous
diffusion : so likewise of the fatty matters, which must be
immediately added to the blood from the nutrient chyle.
Some substances, of a more special kind, may be formed by
changes in the corpuscles, and may ai’terwards traverse the
liquor s;vnguinis to reach the tissues. The elaborative office
of the corjmscles, and their influence on the composition anti
formation of the liquor sanguinis, are undoubted.

The flbrin of the blood, is believed to be derived from the
albumen, of which it is said to be a modified, degraded, or
more oxidised condition. It has been stated that, on passing a
galvanic current through a solution of albumen, a concretion
of a substance resembling fibrin, becomes attached to the posi-
tive pole (Smee) ; but this deposit may not be identical with
fibrin.

The blood of the hepatic and renal veins, contains only a
small quantity of fibrin, and coagulates but imperfectly ;
hence it has been conjectured that fibrin may be destroyed, or
o.xidised, in the liver and kidneys. On the other hand, the
blood of the splenic vein contains much fibrin, coagidates very
firmly, and, ewen when defibrinated by whipping, will pro-
duce a second clot, after long exposure to the air. It is
thought also, by some, that the action of the muscles may give
rise to an appearance of fibrin in the blood ; for on injecting
defibrinated blood into the arteries of a recently detached
animal’s limb, the blood, returning by the veins, is found to
contain fibrin, whenever the muscles have been excited to
repeated contractions by galvanism.

The amyloid and saccharine matters are probably added to
the blood, chiefly from the bver, the inosite from the muscles.
The nitrogenous creatin and creatinin, are probably products
of the decomposition of albuminoid matter. The colouring
matter is possibly, in part, newly formed in the lungs ; but
previously existing oruorin may perhaps be used again.

The nutritive changes, whether of waste or renovation, in
the homogeneous or formless licjuor sanguinis, added to those
which take jilace in the organised elements or blood corpuscles,
imply a more special, and more complicated, nutritive movement
than that which occurs in any one of the tissues or glands ; for
they reciprocate with the metamorphoses of all the tissues
and glands. 'Ihc variety of nutritive and secernent changes to
which the blood ministers, and in which it itself undergoes

318

SPECIAL PHYSIOLOGY.

incessant corresponding alterations, is very great, and yet its
highly complex, but essential, constitution remains, within
certain limits, the same.

The constitution of the blood, is also continually changed,
on the one hand, by the accumulation, within it, of its o-wn effete
materials, and its reception of those of the disintegrated solid
tissues, and, on the other, by its constantly casting out of itself
the various products of that decay. In this way, its creatin,
creatinin, and urea, and its lactic and carbonic acids, enter, and
then escape through the agency of the renal, cutaneous, and
re.spiratory excretions. The quantities of effete extractives
and of urea are small, for they are always being canned off ; if
they accumulate, mischief ensues. Considering that the blood
is constantly drawn upon for the supply of nutriment to the rest
of the body, that it is intermittently and variously renewed,
that it is itself subject to decay in its essential structural and
fluid elements, and the seat of constant additions and subtrac-
tions, its composition retains a remarkable rmity. The com-
plexity of the mutual relations between the blood and the
tissues and glands, its renovation from the lymph and chyle,
and the rapidity of its purification from the poisonous or
injurious chemical products of the disintegration of tissue, by
the excretory processes, are very surprising. When imperfectly
elaborated, or purified, by the formative, nutritive, and secre-
tory or excretory processes, it becomes unhealthy, and a pos-
sible source of disease. Emotional and other distimbances of
the nervous centres, may, through their influence over these
processes, also render the blood unhealthy or even poisonous.
General disorder ensues, and the functions, especially those of
the liver, alimentary mucous membranes, kidneys, skin, and
mammary glands, are vitiated. Cutaneous and other local
diseases arise. Further, the blood may become the vehicle of
miasmatic and malarious poisons, or the seat of ;?)unotic de-
compositions, and so fevers, simple, exanthematous, intermit-
tent or remittent, typhoid or choleraic, may ensue.

THE BLOOD GLANDS.

In Nutrition, certain materials are attracted to, and assimi-
lated by the tissues, from the common nutrient plasma of the
blood, and the materials so attracted, are removed from the
blood. In the act of secretion, as, for e.xainple, in that of sivliva
and bile by the salivary glands and the liver, various other

THE DUCTLESS GLANDS.

319

materials are sepai'ated from the blood. Nutrition and secre-
tion are, indeed, intimately allied, the former being a secre-
tive process, and the latter a nutritive process; hence nutrition is
sometimes termed nutrient secretion. Diminished or increased
activity, or arrest, of the nutritive processes in certain tissues,
such as the nervous or muscular systems, may affect the blood
quite as seriously as errors in the secreting processes ; and the
healthy balance of both functions, is necessary for the preserva-
tion of the normal constitution of the blood.

All secreting glands, however, possess special channels,
called ducts, which open either upon the exterior of the body,
as in the case of the cutaneous and mammary glands, or into
some internal cavity, as e.g. the salivary and gastric glands, and
by which the materials separated from the blood, are conveyed
away, though some of them may be more or less completely
reabsorbed. But in the nutrition of tissues, such as muscle
or nerve, the materials separated from the blood, are not
carried away by ducts, but remain, for a time, as part of the
body, and are only reabsorbed, when they have performed
their proper fimctions, and, in doing so, have undergone
further change.

Now, there exist in the Vertebrata generally, and in Man,
certain peculiar organs, Avhich, from their compact form, gene-
ral appearance and relations, and highly vascular character,
have been called glands ; but they have no secreting orifices,
channels, or ducts proceeding from them, to open on the sur-
face, or into the cavities, of the body. These organs include the
spleen, the supra-renal bodies, the anterior portion of the
pituitary body, the thyroid body, and the thymus. From
being destitute of ducts, they are named the ductless glands ;
from their obvious connection with the process of sanguifica-
tion, they are called blood glands ; and, lastly, from their
influence on the blood, being entirely exerted on that fluid
within its vessels, they have been termed vascida?- glands. By
some, the closed sacs already described (p. 1 58), as being found
in the mucous membrane of the alimenfeiry canal, if not classi-
fied as mere dependencies of the lymphatic system, are ar-
ranged with the ductless glands.

The organic proce.sses proper to these ductless glands, par-
take both of the characters of nutrition and secretion. Their
substance is nourished like that of a muscle, but each, acting
like a gland, separates from the blood something very special.
On the other hand, although, like a muscle, and unlike a

320

SPECIAL PHYSIOLOGY.

gland, they do not yield up their products directly by a duct,
yet they doubtless impart to the blood, not merely the effete
materials from their waste, but the substances formed by their
special elaborative or assimilating power — substances essential
to the constitution of the blood itself. They might be termed
nutritive or assimilative glands.

21ie Spleen. — This organ is a soft, dark, bluish body, attached
to the cardiac end of the stomach ; it is placed beneath the
diaidiragm, and is nearly or quite covered by the lower ribs.
Its shape is a flattened oval, convex and smooth on its left
sm'face, and concave on the right surface, which is applied
to the great cul-de-sac of the stomach. Along this surface
is a vertical fissure, named the hilus, sometimes notched in
front, at which the bloodvessels, lymphatics, and nerves pass
in or out. By these last-named pai’ts, by a peritonaeal dupli-
cature, named the gastro-splenic omentum, and by a reflection
of the peritonaeum from the spleen on to the diaphragm,
named the suspensory ligament, this organ is held in its
place.

The size and weight of the spleen, vary more than those of
any other solid orgain in the body, not only in different per-
sons, but at different times in the same individual. This is
chiefly owing to changes in the quantity of blood it contains.
It u.sually measures about 5 inches in length, 3|- from front to
back, and l-l- from side to side ; its average weight is about
G oimces, but it may vary from 4 to 10 ounces. Up to the
age of forty, its proportionate weight to that of the body, is as
1 to 350 ; after that age, the ratio diminishes gradually to
1 to 700. In ague and other fevers, the spleen becomes en-
larged by increase of substance, as well as by distension with
blood, sometimes weighing 20 lbs. In certain diseased condi-
tions of this organ, it has weighed 40 lbs. ; on the other hand,
it has been reduced to of an ounce in weight. Its specific
gravity is about 1060.

Within the peritona?al serous covering, the spleen has a
proper, strong, fibro-elastic coat, which is j)rolonged, at the
hilus, into the interior of the organ, forming elastic sheaths
around the bloodvessels, lymphatics, and nerves. Cro.ssing
in every direction between these sheaths and the inner surface
of the elastic coat, are numerous slender elastic bands, named
trabecula; {ti-abs, :i beam). In the spaces, or loculi, formed
between these trabecula;, outside ihe vessels, is contained the
so-called splenic pulp. This is a soft, bluish-red or brownish

STEUCTURE OF THE SPLEEN.

321

mass, which may be pressed out from the intertrabecular
spaces, and which becomes of a brighter red when exposed to
the air.

The proper coat, the sheaths of the vessels, and the ti-abe-
culte, consist of white fibrous and areolar tissues, mixed with
elastic fibres, and contain, especially in animals, pale, fusiform,
unstriped muscular fibre-cells. The splenic pulp consists of
a colourless, granular parenchyma, mixed Avith numerous
coloured cells, with red blood corpuscles of various size, shape,
and state of aggregation. The colourless parenchyma is com-
posed of round, oval, and fusiform nucleated cells, of nuclei,
and of a granular matrix; it somewhat resembles the con-
tents of the sacs of the solitary and agniinated intestinal
glands. The coloured cells, or altered red blood corpuscles of
the splenic pulp, are peculiar to this organ. Some closely re-
semble the ordinary red blood corpuscles ; others, however, are
smaller, and of a bright golden colour, broAvn, or black ; some-
times their contained pigment is gathered into a rod-shaped
mass, or into some crystalline form, or is broken up into
minute granules. Frequently they present the unique condi-
tion of agglomeration into little clusters or heaps, Avhich are
sometimes free, but sometimes enclosed in a delicate membrane,
or encysted, so as to appear like large compound cells, containing
from two or three, to as many as twenty altered blood corpuscles.

Embedded in the splenic pulp, are numerous whitish vesi-
cular bodies, measuring from |th to ^rd of a line in width,
named the Malpighian co?yuscles of the spleen ; they are
attached, in clusters, to the small arteries, and are supported on
the trabeculjE, so as to appear like sessile buds or fruit upon a
stem. Their envelope is partly derived from the fibrous coat
of the artery, and partly from the outer harder layers of their
contents. Their cavities have no communication Avith the
bloodvessels on Avhich they rest. Smaller bodies found in
the spleen, are said to be Malpighian corpuscles in an im-
mature state. They are composed of an extremely delicate,
imperfectly fibrous, envelope, enclosing granular, nuclear,
and nucleated-cell elements, like those of the splenic
itself.

The splenic arteries, entering at the hilus, ramify through
the spleen by rapid subdivisions, Avithout anastomoses, after the
manner of the branches of a tree ; many (juickly divide into a
coarse capillarg network, Avhich as speedily ends in the minute
veins. The capillaries are most abundant in the splenic pulp,

VOL. II. Y

322

SPECIAL PHA'SIOLOGY.

and also on the surface, and in the interior, of the Malpighian
corpuscles. The smallest veins chiefly end, almost imme-
diately, in larger ones, Avhiih form close plexu.ses and venous
diverticula between the trabecula;. Eecent researches show,
that Avhilst some of the arteries end in capillaries, from which
veins arise in the usual manner, other of these vessels end in
veins which suddenly enlarge, and, lastly, others even termi-
nate in lacunce, or spaces destitute of distinct Avails, but
bounded only by the elements of the pnlp (Gray, Billroth).
The interior of some of the veins, presents a closely dotted
appearance, from the numerous openings of little venules or
diverticula around them. In the blood of the veins, splenic cells,
altered blood corpuscles, and clustered blood corpuscles, are
sometimes found, as from mutual extra- and intra-A'asation.
The blood of the splenic veins contains, hoAvever, fcAver red
corpuscles, but more fibrin, than other venous blood. On
escaping from the hilus, the venous trunks unite to form the
splenic A'ein, Avhich, like the other tributaries of the portal
system, is destitute of valves ; some of the veins of the spleen
pass on to the stomach, and join Avith its veins. The lipnpJia-
tics of the spleen, divided, as usual, into a superficial and deep
set, are by no means numerous. The mode of origin of the
deep set, is unknoAvn. It has been supposed that the caAuties
of the Malpighian bodies, commimicate directly Avith the lym-
phatics, but this has not been proved. The spleen is supplied
Avith comparatively few nerves, Avhich are derived from the
sympathetic system.

The splenic pulp, with its granules, mrclei, and nucleated
cells, must be the seat of rapid nutritive and formative pro-
cesses. The bulk of this organ, increases in a marked man-
ner during, and especially toAvards the end of, the process
of digestion ; an enlargement due, not only to an increase in
the quantity of blood contained in the splenic A^essels at that
period, but also to a simultaneous increase in the quantity of
all the microscopic elements of the pulp itself. Even the INIal-
pighian corpuscles increase in size, and, it is said, in number,
after the digestive process is completed. Their diminution in
both respects, in states of exhaustion and innutrition preceding
death, may account for their existence in ]\Ian having been
denied. In starving animals, the Malpighian bodies are cer-
tainly feAv and small, or they may even disappear ; Avhereas
they become larger and more abundant, in those Avhich are Avell
fed. The coloured cells, or altered red blood corpuscles, are

USES OF niE SPLEEN.

323

likewise increased in niimber in highly nourished conditions
of the body.

Since the colomdess nuclei and nucleated cells of the spleen,
bear some resemblance to lymph-corpuscles in an early stage
of development, and since, in certain conditions, such cor-
puscles, then considered as nascent Avlnte blood corpuscles, are
found in larse numbers in the blood of the minute veins and
larger venous trunks, the spleen has been regarded, by
Hewson and others, as one of the seats of formation of the
white corpuscles of the blood, probably by the successive sub-
division of old cells, thus acting, as it tvere, as a large lymph-
(jland, directly connected with the venous system. In certain
cases of enlargement of the spleen, white corpuscles are Ibund
in extraordinary number in the blood of the splenic vein, so as
even to alter its colour, and the number of these white cor-
puscles in the blood, generally increases to such an extent, that
their proportion to the red corpuscles, may be as high as 1 to 10.
This condition has been named leucceniia or leucocythcemia,
meaning white blood.

It has also been siipposed (KoUiker, Funke, Billroth) that the
spleen may be the seat of formation, in some yet undetermined
way, of commencing red corpuscles. The small bright yellow
corpuscles, enclosed in larger cells, may undoubtedly be traced
in the spleen, through a series of intermediate phases, into the
ordinary flattened disc-like red corpuscle ; but that these
appearances indicate an upward develoj^ment, is doubtful. On
the contrary, it is suggested that the red blood corpuscles,
having for a time performed their functions in the circulation,
and having lived, as it were, their natural life, may really
undergo disintegration and destruction in the spleen (Kblliker).
This hypothesis requires another mode of interpreting the
microscopic appearances just described, as to the alteration,
agglomeration, and encystment of the red blood corpuscles in
this organ. Since clusters of altered red corpuscles, are found
in the splenic veins, it has been inferred that they proceed
from the interior of the ve.ssels, and are extravasated into the
pulp when sections are made of this organ ; but if the unde-
fined spaces or lacuna?, de.scribed by Gray and Billroth, exist,
the presence of these altered blood cells in both the pulp and
the veins, and likewise the passage of the white nuclear and
nucleated elements of the splenic pulp into the veins, would
be easily explained. In support of the view that the red cor-
puscles decay in the spleen, it is said that when the spleen is

324

SPECIAL PHYSIOLOGY.

removed in frogs, these corpuscles become heaped or agglome-
rated in the blood itself (Moleschott). hloreover, as the
quantity of fibrin in the blood of the splenic vein, is greater
than in any other part of the venous system, it has been sug-
gested that this excess of fibrin, is derived from the partial
oxidation of the globulin of the red corpuscles, -which are rela-
tively diminished in number in the splenic vein. The oxygen
necessary for this change, is that belonging to the corpuscles
(Bedard).

Active and important chemical changes, however, must occur
in the capillaries and in the pulp of the spleen ; but these are
not yet understood. The chemical composition of the pulp,
which resembles closely that of the blood, is very complex. In
every 1000 parts, there are 750 of water, 242 of organic, and 8
of saline and earthy matters. The organic substances consist
chiefly of albumen, or some albuminoid body; besides this, there
are traces of fat, and certain quantities of pigment like that of
the blood, -with smaller quantities of inosite, sarcin, leucin,
tyrosin, xanthin, and even of uric acid. Soda and iron are the
chief inorganic substances.

The variable size of the spleen under different conditions in
the same person, has attracted much notice. It reaches its
largest dimensions, five hours after a meal, t'.e., near the
termination of the process of chymification ; seven hours later,
provided no food has been taken, it is reduced to its smallest
size, and is then also most deficient in blood. The elasticity
of the whole fibrous framework of the spleen, including its
proper coat, the sheaths of the vessels and the trabeculaj, and
also the large size of its veins and the absence of valves in
them, facilitate the distension of this organ with blood during
the turgid condition of the vascular system, which results from
the venous and lacteal absorption of the products of digestion.
The resiliency of those elastic tissues, will also favour the
diminution of the organ in an opposite condition of the sys-
tem. But the pale muscular fibres of the spleen, Avhich exist
in abundance in the larger animals, and in smaller number in
Man, may, by alternate conditions of relaxation and contrac-
tion under the influence of tlie sympathetic system, or of some
direct stimulus, materially assist in these remarkable changes
of size. Electrical ciuTents passed through the spleen, cause
that organ to contract. It has long been supposed that the
alternate enlargement and diminution of the spleen, serve a
mechanical purpose, and that this organ acts as a diverticulum

THE SDPEA-RENAL BODIES.

325

to tlie entire portal venous system, or to the vessels of the
stomach and duodenum, in connection with certain changes in
the circulation, dependent on digestion. The small size of the
spleen during that process, is attributed to the bloodvessels of
the stomach and duodenum, being at that period distended ;
Avhilst, when digestion is completed, those vessels diminish in
size, and the spleen enlarges. The spleen is certainly quickly
reduced in size, when the portal venous system is unloaded
by haemorrhage or by pirrgatives, and it becomes enlarged in
obstructive diseases of the liver and heart ; but the idea of its
serving .specially as a diverticulum, is too mechanical, and but
partially expresses its true fimction. A mere plexus of blood-
vessels wordd have sufficed for such a purpose, without the
co-operation of a peculiar parenchyma, like the splenic pulp ;
moreover, as already stated, not merely are the bloodvessels
of the spleen, distended during its periodic enlargement, but
the splenic pulp itself, and even the little Malpighian bodies,
are obviously increased in volume.

Notwithstanding much that is obscure in the history of this
organ, it would seem, from the abundance and character of
its microscopic elements, its chemical composition, its large
supply of bloodvessels, and the peculiar relation of these to
the pulp, that the spleen probably has for its office, as an
assimilative or nutritive gland, the elaboration of the albu-
minoid constituents of the blood, and perhaps, as Hewson
long ago suggested, the formation, like the lymphatic glands,
of the germs of the white and red blood corpuscles. The sirp-
position that it is also the seat of a degeneration of the red
corpuscles, is no contradiction to such a view. Some of the
materials of the old corpuscles, as, e.g.^ the pigment, may be
used up again in the formation of new ones ; for, like all duct-
less glands, the spleen, whilst, on the one hand, it abstracts
materials from the blood, by special nutritive processes, on
the other, it returns to that fluid, in some altered condition, all
that it has so attracted from it.

The supra-rened bodies or capsules. — These organs, two in
number, one on each side of the body, are small, Hat, trian-
gular, yellowi.sh masses, placed on the summit of the corre-
sponding kidneys, which they surmount like a cocked hat.
Each measures about 1-^ inch in width and 2 or 3 lines in thick-
ness, and weighs nearly 2 drachms. They consist of an outer
deep-yellow, lirrn, cortical portion, and of an inner dark, soft,
medullary part, the whole organ being invested by a proper

326

SPECIAL PHYSIOLOGY.

areolar coat, -whicli sends prolongations into its interior. The
cortical part presents numerous oval loculi, or spaces, in the
areolar framework, placed end to end in little rows or columns,
and arranged perpendicularly to the surface. These loculi were
formerly thought to be oval or tubular closed vesicles, with
distinct walls ; but they are merely interspaces in the areolar
framework of the organ. They contain a granular plasma,
composed of an abundance of granules, with few or many fat
particles, nuclei, and nucleated cells ; towards the centre of the
organ, the cells are larger, and less regularly arranged, so that
the columnar appearance is there lost. The medullary, or
softer central portion, is composed of a delicate filamentous
tissue, connected with the areolar tunic and framework of the
cortical substance, and having in its interspaces also, besides
bloodvessels, a granular plasma, containing nuclei and certain
cells, the latter resembling the ganglionic cells of grey nervous
substance (Leydig, Kolliker). The arteries, numerous and
small, reach the supra-renal bodies at many points of their sur-
face, and ramify between the rows of loculi, ending in capillary
networks around them. The veins, also numerous, are col-
lected into a plexus in the centre of the organ, where a venous
sinus, sometimes taken for a gland cavity, is found. The
lymphatics are said- to be not very numerous. The nerves,
lioweAmr, are very large, and are derived chiefly from the sym-
pathetic, but also in part from fibres of the pneumo-gastric
and phrenic nerves.

From the quantity of blood received by the supra-renal
bodies, and from the number and character of their microscopic
elements, it is evident that the nutritive processes Avhich take
place within them, are Amry active. Probably, like the spleen,
they modify the blood passing through them, by subtracting
from it, and returning to it, certain materials in an altered form ;
but their precise function is unknoAvn, Avhether this be entirely
elaborative, or partly destructive. A curious bronzed colour
of parts of the skin, has been frequently seen in disease of the
supra-renal capsules (Addison, Hutchinson) ; but cases of
similar cutaneous bronzing, haAm been noted, in Avhich the
capsules Avere healthy (Pai'kes, Harley); moreover, these
organs have been found diseased Avithout bronzing of the skin
(Kirkes, Day, Ilutchinson). From the numerous cells, like
ganglionic cells, in the medullary portion of these bodies, it has
been suggested that this j)art may constitute a nervous ap-
paratus, or be nutritively connected Avith the nervous system.

THE THYROID BODY.

327

The Pituitary Body. — The posterior lobe of this body
(vol. i. p. 305) consists of true nervous substance ; but its
anterior lobe is composed of an areolar framework, forming
loculi or spaces, which contain a granular plasma, nuclei, and
nucleated cells of various forms, a structure somewhat, though
not precisely, like that of the cortical part of the supra-renal
capsules, or the vesicles of the thyroid body. It may, there-
fore, be temporarily classified Avith the ductless glands, though
not from any established identity or similarity of function,
Avhich is Avholly unknown.

The Thyroid Body. — This body, commonly named the thy-
roid gland, is a soft, reddish-brotvn, vascular organ, placed upon
the front and sides of the upper part of the trachea, and reach-
ing upwards to the sides of the larynx, to tvhich it is sus-
pended. It is formed of ttvo lateral, somewhat pyriform lohes,
joined together, at their lower and larger ends, by a transverse
part, named the isthmus. The lobes are about 2 inches long,
and measure ^ of an inch in their thickest part. The thyroid
body varies in tveight from 1 to 2 ounces ; it is larger in the
female than in the male.

The thyroid body differs in structure from the other ductless
glands, inasmuch as its proper tunic and fr-amework of areolar
tissue, forms loculi, in which are embedded multitudes of
rounded closed vesicles, bounded by a distinct membrana
propria, and lined by an epithelium. The vesicles, Avhich mea-
sure from ft 0 0 (jth to -g^gth of an inch in diameter, contain a
viscid, clear, albuminous fluid, in which are found nuclei
and cells resembling the uniform epithelial-like layer. The
arteries, four in number, and of considerable size, end, between
and upon the walls of the vesicles, in a close capillary net-
work, which empties itself into the veins. The lymphatics are
numerous and large ; their relations to the structural elements
of the thyroid body, are unknown ; but it is supposed, from
their relative size and abundance, that they are more con-
cerned in returning the contents of the thyroid vesicles to the
blood, than the lymphatics of the supra-renal bodies, or spleen,
are, in regard to those organs.

Enlargement of the thyroid body constitutes the disease
known as yoitre, in which the condition of Avhite blood, leuco-
cythaemia, or leucaemia, is often induced. In such cases, the
nucleated cells of the thyroid body, and their contained
nuclei, are smaller than usual, and, a fact of much interest,
the white corpuscles of the blood are not only more numerous

328

SPECIAL PHYSIOLOGY.

than in health, but are also unusually small. This so far
favours the view, that the thyroid body may aid in the forma-
tion of the morphological constituents of the blood.

The thyroid body may also influence, like the other duct-
less glands, the chemical composition of the circulating fluid.
The chief constituent of the glairy fluid of the thyroid r^esicles,
is of an albuminoid nature ; but, unlike the splenic pulp, it con-
tains a noticeable quantity of fatty matter. Its extractives and
salts differ in no important particular, from those of the blood.

Some physiologists have supposed that the thyi-oid body
acts mechanically, as an occasional diverticulum for the blood
concerned in the cerebral circulation ; but the evidence of
this, is even less than that adduced on behalf of a similar
hypothesis concerning the spleen and the portal circulation.

The goitrous enlargement of the thyroid body, which produces such
unsightly disfigurement of the neck, is most frequently met with in
females. It prevails in particular countries, and in particular districts
of those countries. Thus, it is met wdth chiefly in the north of Italy,
and in certain cantons of Switzerland, most markedly in the canton of
the Valais. In other European countries, it is met with much less fre-
quently ; but still asserts a preference for particular districts. In Eng-
land, it is most common in Derbyshire, and hence its popidar name, the
Derbyshire neck ; but it is observed in many other scattered localities.
In spite of careful investigations, involving researches into the climate,
solar influence, atmospheric peculiarities, rain-faU, soil, and drinking-
water of those districts, and into the manifold conditions of existence of
the people, the true cause of goitre has not yet been inductively ascer-
tained. It is more common in the coiintry than in towns, and is almost
entirely confined to hilly and mountainous districts, being more particu-
larly observed in the valleys of those districts ; but it is not prevalent
in all elevated or mountainous regions. It has been variously attributed
to the. deficiency of oxj’gen in the higher levels of the atmosphere ; to the
want of solar light in valleys, especially since, as is alleged, it prevails
more on the southern, and comparatively sunless, sides of such valleys ;
to the habitual use of drinking water derived from the melting of glaciers
or of snow, and therefore almost entirely destitute of saline and earthy
salts ; and, again, on the contrary, to the presence of lime, but particu-
larly of magnesia, in such water, derived from the limestone or mag-
nesian limestone, often found in districts in which goitre is common.
Lastly, its special prevalence amongst females, has been assigned to the
custom, in hilly districts, of carrying water, or other heavy substances, on
the head, by wliich it is alleged that the muscles of the neck compress
the veins, and so cause congestion, and ultimate enlargement of the
thyroid body.

In the canton of the Valais, whore goitre prevails in its most intense
form, it is often associated with an arrest of development of the whole
frame, especially of the skull and brain, which constitutes the condition
known as Cretinism. The Crdtin may, indeed, be said to be a small

THE THYMUS GLAND.

329

idiotic human being, distinguished from ordinary idiots, by the thyroid
body being enlarged or goitrous. But in the Cretin districts, persons of
full stature, of duly proportioned cranial and cerebral development, and
of ordinary intellectual capacity, are seen with goitres larger even than
those found in Cretins themselves.

The thymus body, or thymus gland. — This ductless gland
is a temporary organ in the animal economy. Present in the
embryo, it attains its largest relative size to the body in the
infant, and seems to be most active in function a short time
jifter birth, growing up to that period even faster than the body.
It then continues to gi’ow, so as to keep pace with the rest of
the body, up to the age of two years ; but soon, it no longer
increa.ses with the body, and, at about twelve years of age, is
usually changed into a fatty mass; according to Friedleben,
it may grow a little after the second year, and not become
fatty until after puberty. Finally, especially in thin per.sons,
it gradually wastes, so as to leave nothing but a mere vestige
behind.

In its most complete condition, it forms a double organ,
composed of two lateral irregular lobes, joined by a central
raa.ss, and situated partly in the lower region of the neck and
partly in the thorax, lying upon the trachea and the gi’eat
bloodvessels. It measures, at birth, about 2 inches in length,
and weighs half an ounce. It is a soft, pinkish-grey body,
consisting on each side of a string of compressed lobules, con-
nected together by an elongated part, like a cord. A strong
areolar coat encloses, and connects, the various lobules, and
sends intervening coverings between their ultimate subdivi-
sions. The lobules, or acini, are composed of a soft milk-white
parenchyma, consisting of granular matter, nuclei, and nu-
cleated cells ; the central part of each lobule, is so soft or fluid,
that, when opened, a cavity is found, which extends into the
secondary lobules, of which the primary ones are composed.
The cord which connects the lobules together, contains the
same parenchymatous substance, and is likewi.se soft or fluid
in the centre, so as to form a cavity, called the reservoir of the
thymus ; this communicates with the soft cavities of all the
lobules, and also with certain small sacculi situated in its
walls. Each lateral half of the thymus, has its proper reser-
voir, the two sometimes communicating tlirough the central
transverse mass. The cavities within the lobules and con-
necting cord, are not lined by a distinct limitary membrane
and epithelium ; the fluid within them, is milky white, and

330

SPECIAL PHYSIOLOGY.

resembles chyle. It contains nuclei and nucleated cells, simi-
lar to those of the white parenchyma itself. Many of these
closely resemble the developing lymph-corpuscles found in the
loculi of the lymphatic glands, and, therefore, also the white
corpuscles of the blood. No minute fatty molecules, similar to
those forming the “ molecular ba.sis” of the chyle, are foimd,
however, in the white fluid of the thymus. To chemical ana-
lysis, this body yields about 20 per cent, of solid matter, chief!}’’
albumen, some gelatin, only a little fatty matter, and traces
of sugar, leucin, sarcin, xanthin, salts of formic, acetic, succinic,
and lactic acids, chloride of potassium, and alkaline and earthy
phosphates. The bloodvessels of the thymus are large and
numerous ; the arteries penetrate to the central cavity, and
thence ramify towards the surface of the lobules ; the capil-
laries travei’se the soft white parenchyma in all directions, the
chief terminal plexuses being near the surface of the lobules ;
the veins are large and, Avhat is unusual, do not accompany
the arteries. The lymphatics are also numerous and of great
size, terminating, some in the thoracic duct, others in the
right lymphatic duct, and others directly in the neighbouring
large veins. It is supposed that the lymphatics assist in con-
veying the contents of the cavities of the thymus into the
blood ; but their direct communication Avith those cavities has
not been demonstrated. The nerves are small, and are de-
rived fi’om the pneumogastric nerve, and the sjnnpathetic
system.

The office of the thymus, would seem to be, to prepare an
albuminoid pabulum, fitted for the formation and maintenance
of the blood, exactly at that period of life when growth is rela-
tively most rapid, f.e., in the earliest years of infancy. It is
possible, moreover, that its nuclei and nucleated cells, espe-
cially those Avhich resemble the lymph-corpuscles, are the germs
of future Avhite blood corpuscles, a view especially urged
by Hewson. The almost complete absence of fatty matter,
hydrocarbons, or carbhydrates, from the thymus, as Avell as
fi’om the thyroid body and spleen, Avould seem opposed to the
idea, that any of these organs stored up such substances for the
direct purposes of combustion. Yet it has been conjectured
that the fluid of the thymus, forms a reseinm of material suited
for oxidatiou in the respiratory process, at a time Avhen such
matters, derivable from the Avaste of muscular tissue, are by no
means abundant (Simon). Later, hoAvever, in fully nouri.shed
children, the thymus becomes (juite fatty, its nucleated cells

THE DUCTLESS GLANDS GENERALLY.

331

being converted into adipose cells, -whicli might then yield
their fiitty combustible matter to the blood. In the hyberna-
ting INIammalia also, this organ continues to grow more rapidly
than the body, up to the adult period of life, and, when thus
persistent, contains much adipose matter. This is also said to
be the case in most Reptiles. It was at one time held, that the
thymus body acted as a diverticulum, in regard to the pulmo-
nary circulation, in the child.

The closed sacs of the tongue, tonsils, fliarynx, stomach,
and intestinal canal. — These, as elsewhere described (p. 158),
whether solitary or clustered, may be regarded as minute
representatives of the larger ductless glands, to which in their
closed form, their vascularity, and their albuminoid, granidar,
nuclear, and nucleated cell-contents they bear a certain
generic resemblance. They might, indeed, be compared to
the Malpighian bodies of the spleen ; but they diifer from the
vesicles of the thyroid body, in having no distinct cavity lined
by an epithelium. They might be said to stand in the same
relation to the larger ductless glands, that the small and simple
tubular glands of the stomach and intestine, do to the large
secreting glands, with extensive excretory ducts.

The ductless or vascular glands considered generally. — ■
Before the structure of these organs was less understood than
it is at present, they were sometimes supposed to possess parts
analogous to the terminal acini, vesicles, or dilated ends of the
ducts of true secreting glands ; and the absence of the ducts
themselves, was said to form the most marked distinction be-
tween them and these glands. But the thyroid body alone has
distinct vesicles, limited by a membrana propria and an epithe-
lium, and so far approximating to the characters exhibited by
the commencing ducts of a secreting gland. In the spleen,
and even in the .supra-renal bodies, the inter-trabecular
areolae, and the columnar loculi, are not so surrounded, but
are mere interspaces in an areolar framework. The minute
encapsulcd Malpighian bodies of the spleen, and likewise the
closed sacs of the alimentary canal, have no lining epithelium
or true basement membrane. The branching sacculated
canals, and secondary cavities, or acini of the thymus, caunot
be compared to true glandular structures, for they also are
destitute of a lining membrane and epithelium. Indeed these
ductless glands, instead of resembling the secreting glands
with ducts, possess characters approximating them rather to
the lymphatic glands, with their numerous loculi and albu-

332

SPECIAL PHYSIOLOGY.

Tninoid corpuscular contents ; but they differ in this, that
their cavities do not open directly into the lymphatic vessels.

Considered generally, their proper parenchyma, with its
granular plasma, nuclei, and nucleated cells in various stages
of growth, constitiites their most important and characteristic
anatomical element. The rest of their structure, is either the
frameAvork of the organ, or consists of the bloodvessels, lym-
phatics, and nerves.

The physiological influence of these organs in the economy,
must be exercised on the blood, and must be exerted, especially
through a nutritive process, by the nuclear and nucleated
cell-like constituents. The blood entering such an organ,
yields to it, by exudation through the walls of the capillaries,
a common plasma, from which, by a nutritive process depen-
dent on the special attractive, selective, and assimilative
powers of the microscopic elements, certain special materials
are separated. The residue of the plasma, re-enters the circu-
lation, either directly through venous, or indirectly through
lymphatic absorption, as in every instance of simple nutrition.
Hence, in the first place, the blood which passes through these
organs, must be modified, as in all nutrition, by the abstrac-
tion of certain of its constituents ; and the effect is peculiar
in each organ.

But, secondly, the proper substance of these ductless glands,
cannot remain unchanged and inactive, subject to no further
metamorphoses, and productive of no special influence upon,
or service in, the economy. On the contrary, it would seem
certain, that something must also be added, by their agency, to
the blood as it passes through them. The materials attracted
from the blood by their proper substance, and elaborated
within them by a sort of nutrient secretive act, are returned,
more or less altered, into the blood current. This may chiefly be
accomplished by solution and venous absorption in the spleen,
supra-renal bodies, and thyroid body, or by ljunphatic ab-
sorption in the thymus and closed sacs of the alimentaiy
mucous membrane, or by occasional opening of the loculi into
the veins, as in the spleen, or into the lymphatics, as conjec-
tured by some to be the case in the thymus.

By both subtraction and addition of material, the blood
must be specially modified, as it passes through those organs,
which, from their various actions, contribute, therefore, to the
elaboration and maintenance of the complex chemical constitu-
tion of the blood. It is for the jireparation of the albuminoid

THE DUCTLESS GLANDS GENERALLY.

333

constituents of the blood, that these organs are destined, and not
for the formation of fatty matter, which is so scanty in their
composition. Their action upon the colouring matters, Avhich are
also albuminoid, may be, in the case of the spleen andsupra-renal
bodies, to decompose or re-compo.se those peculiar substances.
Moreover, from the resemblance of the microscopical ele-
ments of their abundant and characteristic parenchyma, to
the white blood corpuscles, they are probably concerned in the
formation of those bodies, and therefore of the future red cor-
puscles, assimilating the nutrient plasma of the blood into
distinct morphological elements, just as the lymphatic glands
and vessels develop a corpusculated fluid in their interior.
Hence, both chemically and morphologically, the blood glands
are believed to contribute to the important process of sanguifi-
cation. The products of nutrient secretion, formed by these
organs, all enter the systemic veins, excepting those elaborated
by the spleen, Avhich first enter the portal blood, and so pass
through the liAmr, before they reach the right side of the heart,
to be sent to the lungs.

It is remarkable that all the large ductless glands are pre-
sent and active during embryonic life, and also in the most
active period of growth after birth. The supra-renal bodies,
at first, in the embryo, much larger than the kidneys, are, in
the adult, only ^^th part of the weight of those glands. The
thymus especially ceases, after birth, to grow in proportion to
the rest of the body, and then gradually wastes ; a positive
relation has been observed, in young animals, between its size
and the state of their nutrition. The thyroid body and the
pituitary body are also larger proportionally in the embryo
and the infant, than in the adult ; but they continue to be
present throughout life. At birth, the weight of the thyroid
body, as compared Avith that of the body generally, is as
1 to 2.50 or 1 to 400 : but it .soon ceases to enlarge Avith the
body, for, after three weeks, the proportions are as 1 to IIGG,
and in the adult only as 1 to 1800 (Krause). The spleen,
hoAvever, enlarges Avith the body, and maintains its propor-
tionate size ; but it is undoubtedly largest in the most active
period of life, about early manhood. As to the closed sacs of
the tonsils, tongue, pharynx, and solitary and agminated
glands of the stomach and intestine, they exhibit a continuous
development Avith the rest of the body, and are permanent
structures.

Finally, it wmxld seem, that, Avhatevcr may be the general or

334

SPECIAL PHYSIOLOGY.

special uses of the ductless glands, some of them, at least, are
not absolutely essential to life. The thymus, though very
large in the early period of development and growth, ulti-
mately disappears as a distinct organ. The thyroid body may
be totally altered by disease, becoming cystic, indurated, or
filled with earthy deposits, without serious detriment to the
health. The spleen has been extirpated from animals, with-
out any obvious ill consequences, and, it is .said, in a few
cases, even from the human body. In certain animals, the
spleen is multiple, minute detached spleens, named splenculi,
existing near the principal organ. When the latter is re-
moved, the splenculi become enlarged, and so supply, ph}'sio-
logically, the. jDlace of the extirpated spleen. In other cases,
the lymphatic glands of the neck and axilla, have become in-
creased in size ; and, on the whole, the result of such experi-
ments, would seem to show, not the want of importance of the
spleen, but that its functions may be performed, as it were
vicariously, by other organs of the body; The same may be
time in cases in which the thyroid body is diseased. It is
said, however, that in animals, after removal of the spleen, the
quantity of iron in the blood, is diminished, and that the appetite
becomes voracious, and the temper fierce. Eemoval of the
supra-renal bodies is fatal ; according' to some, directly, owing
to the retention of some poisonous substance in the blood ;
according to others, indirectly, as a consequence of the inci-
dental injury to the nerves and other neighbouring parts
(Harley).

THE LIVER CONSIDERED AS A BLOOD GLAND. GLYCOGENIC
FUNCTION OF THE LIVER.

The action of the ductless or nutritive glands, viz. that of
extracting material from the blood, elaborating it, and, in-
stead of eliminating it by ducts, returning it into the blood,
by means of venous or lymphatic absorption, is, to a certain
extent, imitated by the liver, the largest secreting gland in the
body. In the embryo, the liver is, indeed, a true blood gland,
blood corpuscles even being developed in its capillary net-
work. But probably then, and certainly after birth, the
hepatic nucleated cells, which secrete the bile, like the special
parenchyma of the ductless glands, attract and assimilate
material from the blood, and form a peculiar substance, which
is not discharged by the bileducts, but enters the blood either

GLYCOGENIC FUNCTION OF THE LIVER.

335

through the veins or the lymphatics; most probably, how-
ever, through tlie former. But this substance, is not albu-
minoid, like the supposed products of the assimilative action
of the ductless glands; it is amyloid, forming an animal
starch, closely resembling the amylaceous substances developed
so abundantly in the Vegetable Kingdom. By Claude Ber-
nard, its discoverer, it was named ghjcogene, from its yielding
sugar when mixed witli ferments ; it has also been called
hrpatine (Pavy), and zo-amyline (Eouget). It is obtained
by bruising the substance of the liver in water, boiling the
fluid to coagulate the albumen, filtering through animal char-
coal, and then precipitating the substance sought for, by
means of pure acetic acid, or alcohol. It is white, taste-
less, flocculent, and readily soluble in pure water ; with iodine,
it forms a reddish violet compound, the colour of which dis-
appears at a temperature of 176°, but returns on cooling. It
does not reduce the salts of copper. Minute granules, ajrpa-
rently covered with an albuminous fibrin, are found in the
hepatic cells ; the.se are not fatty, being insoluble in ether, birt
they behave with re-agents in such a manner, as probably to be
particles of this substance. Its atomic composition is identical
with that of starch, dextrin, and grape sugar, Cg Hjg O5,
but its general properties are intermediate between those
of starch and dextrin. Like dextrin, when dissolved in
water, glycogen is immediately transformed into gi-ape sugar
by albuminoid ferments, as is proved by the solution then
decomposing the salts of copper, and turning the rays of
polarised light to the right hand, and also by its readily
p.assing into the alcoholic, or the lactic acid, fermentation.

An amyloid or cellulo.«e substance was long ago found in
the Tunicated animals (Schmidt), and amyloid bodies have
since been observed in other Non-vertebrate animals (Carter).
In a peculiar degeneration of various tissues and organs of the
human body, as of the nervous substance, muscles, liver,
spleen, kidneys, prostate, and other parts, amyloid bodies, or
so-called corpora amylacea, have been frequently met with
(Virchow, Mekel, Kouget). Bernard himself detected a
glycogenic substance in the placenta, and in various embry-
onic tissues, especially in the muscles, though he thought it
disappeared from them in after life. Amyloid substance is
sometimes certainly present in healthy muscle ; it has been
found in the muscles of the horse a few hours after feeding,
though, in the lasting condition, none is present. The occur-

336

SPECIAL PHYSIOLOGY.

rence of a starchy substance, is, therefore, as Rouget believes,
by no means confined to the tissues of vegetables, nor even to
the liver amongst the animal organs, but this substance may,
tmder certain conditions, be a product of the nutritive action of
nearly all the tissues.

The glycogenic function of the liver is, however, most
remarkable, and constitutes a special assimilative office, super-
added to its ordinary use of secreting bile. Since neither
glycogen nor sugar is found in the bile, it is obvious that, if
this animal starch be employed in the economy, it, or some
product of it, must enter the blood, either directly through the
veins, or indirectly through the lymphatics. It is now knotra
that, not the glycogen itself, but the sugar resulting from its
transformation, is absorbed by the hepatic veins. The detec-
tion of considerable quantities of sugar in the blood of the
hepatic veins and of the right auricle of the heart, led, indeed, to
the discovery of the glycogenic function of the liver. At first
it was supposed by Bernard, that the sugar itself Avas formed by
that organ. That this is not derived directly from starch or
sugar in the food, is shoAvn by its occurrence in animals
killed after being fed, for at least a month, on meat alone.
That the sugar comes from the liver, is shown by the fact, that
after injecting Avater into the portal vein, until the fluid
escaping from the hepatic veins, is colourless and free from
sugar, it is possible, after Avaiting a certain number of hours, to
obtain, by injecting more Avater, a further supply of sugar.
Hence Bernard concludes, not merely that the sugar is pro-
duced in the liver, but that it must be formed by a sIoav,
chemical, and not necessarily vital, change of an amyloid sub-
stance within the liver. By treating the liver substance in
the mode already mentioned, the glycogen is then obtained
separately.

The transformation of starch into sugar, by salivin, sug-
gested the idea that this glycogen of the liver, also requires a
special ferment to induce its metamorphosis. It Avas thought
that, if not the salivin or pancreatin, this ferment might be some
albuminoid product of one of the ductless glands; but extirpation
of the salivary glands or pancreas, of the spleen, su^wa-renal
bodies, thyroid, or thymus, in a series of experiments on animals,
threAv no light on the question (Schifi’). The albuminoid
substance is probably formed in the liver itself ; for, Avhereas
glycogen, like starch or dextrin, is not easily transmissible
through the coats of the hejAatic vessels, it is probably con-

QUANTITY OF HEPATIC GLYCOGEN.

337

verted into the readily dialysable sugar, before it is taken
up by those veins. The fibrin and albumen of the blood,
whether arterial or portal, will also convert dissolved gly-
cogen into sugar. A boiling temperature destroys the power
of the ferment, whatever this may be.

It has been suggested by Pavy that, although an amyloid
substance abounds in the liver during life, no sugar, or but
A'^ery small traces of it, are then present in this organ ; and
that, except in disease, transformation of the hepatin into sugar
is, for the most part, a post-mortem resiilt. This observer
found no great difference in the quantity of sugar in the various
large bloodvessels, either in the arteries, or in the hepatic or
portal veins ; the quantity detected was very small, averaging
about y^th of a grain in 100 grains of blood. In the liver
substance itself, macerated, instantly after death, in caustic
potash or in very cold water, no sugar could be detected,
though the hepatin or glycogen was then extracted. Most
physiologists, however, coincide with Bernard, in believing
that the formation of sugar in the liver, is constantly taking
place during life ; and that the accompanying decomposition
of the glycogen into sugar, may explain the relative higher
temperature of the blood, which has been observed in the
hepatic veins.

The average quantity of sugar obtainable from the liver of
the horse and calf, varies from 4 to 2 per cent. ; in the rabbit’s
liver, it is about 2-5 per cent., and in Man, as noticed in healthy,
recently executed criminals, about 2 per cent (Bernard). By
others, sugar has been found in the liver of Birds, Reptiles,
and Fishes, though in the cold-blooded animals the quantity is
small ; it has even been detected in the liver of the Mollusca
(Bernard). It is more easily obtained from the veins than
from the substance of the organ. The relative proportion
found in the portal blood, in the systemic venous blood, and
in the arterial blood of animals fasting, or fed only on llesh, is
about -OG parts in 100; whereas, in the hepatic blood, the
quantity is usually about 1 per cent. In fully fed animals,
especially after a meal conPiining starch, the quantity in each
kind of blood is increased. In one experiment on a well-
fed horse, killed soon after digestion, the proportion of sugar
found in the liver, was nearly 2'fi per cent. ; whilst that in the
hepatic vein, was about IT, in the lymph -44, in the chyle '22,
and in the blood generally ‘00.5 (Poiseuille and Lelbrt).

The glycogen of the liver, being admitted to be the source

VOL. II. z

.338

SPECIAL PHYSIOLOGY.

of the sugar found in the hepatic blood, the origin of tlie
glycogen itself is yet undecided. Some have questioned the
power of animal tissues, to form an amyloid subshince, and
have suggested that the glycogen of the liver is derived
from the starchy matter of the food, which might be supposed,
in Herbivorous animals, to be partly accumulated, in a modi-
fied form, in the hepatic cells or elsewhere, hlore sugar cer-
tainly, is obtainable from the livers of Herbivorous, than from
those of Carnivorous animals, and more irom Herbivorous
animals recently fed on amylaceous food ; but glycogen con-
tinues to be formed in the livers of fasting or actually starved
animals, and of animals fed for a month, or more, exclusively on
flesh. In such instances, the glycogenic substance found in the
liver, cannot be derived directly from food, but is formed by
some action of the hepatic cells, in which, as already men-
tioned, minute grains, apparently of an amyloid nature, have
been detected. The constituents of the flesh used as food, <
which can be thus metamorphosed by the hepatic cells, are fat
and albmniuoid substances ; for the small quantities of amyloid
matter sometimes found in flesh, and of inosite or muscle-sugar
always present in it, which is incapable of the alcoholic
fermentation and does not turn the rays of polarised light, are
not sufficient to produce it. By some, it has been suppo.sed that
the hepatic cells have the power of decomposing the neutral
fats of the food, into glycerin and the fatty acids, stearic and
oleic; furthermore, that the former is the source of the
glycogen, and that the latter assist in the formation of the fatty
acids of the bile: thus, 2 of glycerin, i.e., 2 (CjPIgOg)^- 2
of oxygen (Oj), are equal to 1 ofglycogen(C6H,Q05)-f-3 of water
3 (HgO). It has been objected to this, that the formation of
sugar and of bile in the snail, has been obseiwed to be an
alternately performed function (Bernard). Another mode of
origin of 'the glycogen fi-om fatty matter, supposes that the
conjugated fatty acids of the bile, tauro-cholic, and glyco-cholic
acids, are first formed, that they are then re-absorbed from
the intestinal canal by the portal vein, and are decomposed
into glycogen and a nitrogenous product, which is ultimately
converted into urea, and eliminated by the kidneys ; for dogs
with biliary fistulaj, appear to have no glycogen in the liver, and
other dog.s, after long fasting, if fed with taurin, show an
abundance of glycogen in that organ. By some, again, albu-
minoid principles arc suj)posed to be decomposed in the hepatic
cells ; according to one view, the products are glycogen and

USE OF THE HEPATIC GLYCOGEN.

339

the two conjugated biliary acids, one of which contains nitrogen,
and the other, in addition, sulphur : according to another view,
they are glycogen, and various nitrogenous bodies, such as
creatin, creatinin, and other substances, which are ultimately
excreted as urea. The continuous formation of sugar in the
eggs of birds, during incubation, shows that glycogen may be
formed independently of amylaceous food, and its origin from
albuminoid matter, is rendered probable from the fact, that in
animals fed on fat or oleaginous food alone, or even on pure
starch, as distinguished from vegetable food containing starch
mixed with other constituents, the glycogen is much dimi-
nished in quantity (Stokvis); whereas, in those fed on gelatin, it
is almost normal in quantity, and attains its maximum in animals
led on highly albuminous diet (Bernard and Schmidt). The
experiments of Dr. Pavy alone give opposite results, showing
the greatest amount of sugar in animals fed on vegetable food
only ; but the increase of sugar then observed by him, might
be partly owing to sugar formed from the food itself. He
found, in the livers of dogs, the proportion to be about 7 per-
cent. with a pure animal diet, 14'5 per cent, with meat and
sugar, and 17 per cent, with a purely vegetable diet. It is
believed that the glycogen found so abundantly in the muscles
of the embryo, the inosite formed in the nruscles after birth,
and the small quantity of glycogen which they contain after
the liver has commenced its glycogenic office, are also derived
from the decomposition of albuminoid substance into gly-
cogen, and some oxidisable nitrogenous body, such as creatin
or creatinin.

The use of the glycogenic function of the liver, is .suppo.sed to
be that of continuously supplying an easily oxidisable ma-
terial for the purposes of maintaining animal heat and motion.
Sugar is a very unstable element in the presence of oxygen
with albuminoid .substances, such as are found in the blood.
As already stated, the quantity of sugar found in arterial
blood, that is in the blood which has passed through the lungs,
is much smaller than that in the hepatic venous blood.
Besides undergoing oxidation, like the sugar of the food, so as
to form carbonic acid and water, the liver-sugar may also be
capable of transformation, through the assimilative force of
some of the animal tissues or organs, into fatty matter, or some
other substances necessary to the living economy.

The sugar may likewise act as a solvent of the carbonate and
phospate of lime in the blood. It has also been said to aid in

z 2

340

SPECIAL PHTSIOLOGT.

the decomposition of albuminoid, into oleaginous or other com-
pounds.

Wlien animals are covered with varnish, which arrests the
cutaneous transpiration, and interferes with the respiratory
changes and the development of animal heat, both the sugar
of the hepatic blood, and the glycogen of the liver, soon dis-
appear ; but, by then employing artificial warmth, they may be
again formed. In hybernating animals, in which the respira-
tory process is also reduced to a minimum, the .formation of
sugar continues, but its oxidation, after it pa.sses into the
circulation, is imperfectly carried on, or entirely ceases, so
that it accumulates in the blood, and even appears in the urine.
So too, in the disease known as diabetes mellitus, the sugar
fomid in that excretion, is supposed to depend upon the ac-
cumulation of sugar, probably of liver sugar, in the blood ; for,
in such cases, other secretions and excretions also exhibit traces
of that substance. That the sugar excreted by the kidneys in
diabetes, is not formed in those organs, is certain ; and it has
been noticed, that if the blood contain of a grain of sugar
in 100 grains, this substance is no longer completely consumed,
or oxidised, in the combustive processes of the economy, but
appears in the various secretions and excretions, most abun-
dantly in that from the kidneys. In the diabetic condition,
not only may the sugar formed in normal quantity, accumulate,
from not vindergoing decomposition, but the liver may generate
more sugar than usual.

A temporary and remediable diabetes may occur from the
undue ingestion of sugar, or sugar-forming substances, with the
food. Moreover, many medicinal agents appear to determine
an increased activity of the glycogenic function of the liver,
producing an artificial diabetes ; such are, morphia, strychnia,
and phosphoric acid in large quantities (Pavy). Asparagus hasa
.similar effect ; so likewise has the injection of various stimulat-
ing fluids into the portal vein (Harley), and the inhalation of
acetone and benzine. Caustic potash and carbonate of soda
check the formation of sugar (Pavy).

An experiment, first made by Bernard, in which an artificial
diabetes is produced, shows that certain parts of the nervous
system influence the sugar-forming function (vol. i. pp. 35(5,
394). It illusti'ates the power of the nervous system over the
nutritive and assimilative processes, and may explain certain
cases of ordinary diabetes. By passing a needle through the
back of the occipital bone in the rabbit, and irritating with

INFLUENCE OF THE NERVES ON THE LIVER.

341

its point, the floor of the fonrtli ventricle, from near which the
deep roots of the pnenmogastric nerves spring, he produced an
artiticial diabetes mellitus. Moreover, irritation of the cerebro-
spinal axis, from the cerebral peduncles down to the roots of tlie
pnenmogastric nerves on the sides of the medulla oblongata,
increases the Ibrmation of sugar in the blood, and gives rise
to temporary diabetes. On the contrary, division of the
pnenmogastric nerves in the neck, that is, above the point
where their branches to the lungs are given off, appears to
restrain the formation of sugar in the system ; section of the
spinal cord below the origin of the phrenic nerves, has appa-
rently a similar effect.

It has been suggested that these effects are not direct upon
the liver it.self, but that, in the normal condition, a certain
stimulus, perhaps associated with the demand created by the
process of oxidation going on in the lungs, proceeds from
those organs, through the pnenmogastric nerves to the medulla
oblongata, and is thence reflected through other nerves, to the
liver, where it excites or regulates the glycogenic action. On
interrupting the continuity of this nervous chain, by division
of the pnenmogastric nerves, the formation of sugar is checked.
Disturbances in the respiratory function, induced through the
nervous system or otherwise, may favour the formation of sugar
and its accumulation in the blood, and so produce diabetes.
It is said, furthermore, that division of the great splanchnic
neiwes, or of the sympathetic nerves in the neck, increases
the formation of sugar in the liver ; this may depend, not on
an increased formation of glycogen, but on the increased
cpiantity of blood then admitted to the liver, owing to dilata-
tion, through the action of the vasimotor nerves, of the
small arteries of the abdominal viscera generally. The larger
flow of blood through the portal system and liver, may change
the glycogen already formed, into sugar, more quickly than
usual, and thus favour its more rapid escape from the hepatic
cells. This explanation may al.so apply to the effect of irritation
of the back of the medulla ol)longata, in the floor of the fourth
ventricle ; for the vasimotor sympathetic nerve fibres of the
viscera of the abdomen, have been proved to pass down, in
that part of the medulla, from the cerebral peduncles and optic
thalami (Schiff).

The formation of glycogen by the liver, its conversion into
sugar, and the entrance of this into the blood by the veins,
establish the importance of this gland in the process of Sangui-

342

SPECIAL rnrSIOLOGY.

fication. These facts also suggest the possible occurrence of
some similar, but yet unknoAvn, actions in other secreting
glands, and also in such tissues as muscle and nerve, as well as
in the ductless glands.

Sanguification and the Blood Glands in Animals.

In the Vertebra ta generally, the processes concerned in the formation
of the white and red corpuscles, and the fluid matrix of the blood, are
similar to those which occur in Man. Besides an absorbent system, the
blood-glands, or ductless glands, are found in all the Vertebrate Classes,
but they do not all exist in every Class. The spleen is almost univer-
sally present; the supra-renal capsules disappear earlier in the descend-
ing scale, the thyroid body and the thymus still sooner.

The spleen is present in all cases, excepting in the myxine fishes.
It always possesses its peculiar structure and characteristic dark red
colour; it varies much in shape, even in Mammalia, being, in diflTerent
cases, round, oval, much elongated, lobulated, or even multiple. The
latter condition is seen in the dolphin. The existence of supernumerary
spleens, or splencidi, in dogs, cats, and other animals, has been already
mentioned. In Birds, the spleen is small, and either round, oval, fusi-
form, or flat ; in Reptiles, Amphibia, and Fishes, it is of variable size,
and differs in form according to the general shape of the body. In
Birds and Reptiles, this organ is usually attached to the pancreas ; in
Reptiles and Fishes, it is rather connected with the intestine than with
the stomach, as in Mammalia. The existence of the Malpighian bodies,
is doubtful in the Amphibia, and denied in Fishes; but the large
aggregated blood-cells exist in all Vertebrata.

The supra-renal bodies are present in all Mammalia, Birds, Reptiles,
in most, if not all. Amphibia, and in all but the lowest Fishes. They are
always of a yellowish, ochreous, or golden hue. In Mammalia, they are of
various forms, commonly three-sided, but often elongated, cylindrical,
oval, round, or even crescentic. They are sometimes a little removed
in position from the kidneys, as in the elephant and seal. They are large
in Rodentia, and small in Carnivora, especially in the seal ; their size,
as compared with the kidney, is, in the guinea-pig, as 1 to 4 ; but in
the seal, only as 1 to 150. In the Cetacea, they are lobulated, and super-
numerary supra-renal bodies are met with in many animals. In Birds,
these organs are small, and often lobulated. In Reptiles, they are usu-
ally placed on the renal veins, or vena cava inferior; in the Ophidia,
the right one is the larger. In Batrachia, they are very small, broken
up, or often indistinct, and embedded in different parts of the kidney.
In Fishes, too, when present, they are usually small and nndtiple, and
often found even at the back of the kidney ; in the sturgeon and the
Cyclostomatous fishes, their existence is doubtful.

The thyrofi, body is attached to the larynx in the Mammalia only.
In Birds and Reptiles, it is placed low down in the neck, or even in
the cliest, near the inferior larynx. Its position seems to be regulated
rather by its vascular connections, than by any peculiar relation to the
proper larynx. In Reptiles also, it is in the tlioracic cavity, close above
the heart. As to Fishes, it has been supposed that the va-<cular organs

SECRETION GENERALLY.

343

known as pseud o-hranchi<s, attached to the branchial apparatus, are the
homologues of the thyroid body ; but the balance of evidence is opposed
to this view, and if tlie thyroid body exist at all, it is only occasion-
ally, as a small isolated mass, lying on the bulbus arteriosus.

The thi/mus gland is well marked in the Mammalia, being either con-
fined to the thorax, as in the Carnivora, Insectivora, and Marsupialia,
or having also shorter or longer cervical cornua, or extensions upwards
into the neck, as in Quadrumana, Bats, Eodents, Solipeds, and espe-
cially in the Ruminants. In the ox tribe, its cervical part extends up
to the lower jaw, forming the neck siucetbread, and, from the calf, is the
part sold as the best sweetbread. This organ is a conjoined bilateral
mass ; its structure is lobulated and sacculated, as in Man. It is largest
in the young animal, and disappears later in life. It is said to become
larger in hybernating animals. In Birds it is represented, but only in
the chick and young bird, by a small tube, having slight dilatations
upon it; but it is sometimes divided off into sacs. In young Reptiles, it
has also been found, and likewise in the tadpoles of most Amphibia ;
but not, it is said, in the siren or proteus, in which the lungs are the
least developed. In Fishes, the thymus is absent.

In the Amphioxus, none of those ductless glands are found, not even
the spleen ; in this animal, no coloured blood-corpuscles exist.

In the Non- vert ebrata, these glands and coloured blood corpuscles are
equally absent ; nor is any organ recognised in them, as being specially
concerned in the process of sanguification. The liver, however, is al-
most universally present, and its glycogenic function has been detected
in the snail ; and as it is a blood gland, forming blood corpuscles in the
Vertebrate embryo, it may suffice for the wants of the Non-vertebrate
organism, in reference to the formation of blood. Such organs as the
spongy masses around the great veins in the Cephalopods, may, per-
haps, be concerned in sanguification.

SECRETION.

.SECRETION IN GENEU.tL.

Secretion (secernerc, to separ<ate) is the separation, by a
gland or membrane, of certain materials, in a more or less fluid
state, from the blood, and their escape, by means of proper
ducts or openings, or from a smooth membrane, on to the
surface, or into the interior, of the body. This general process
is, however, divisible into secretion 2>roper imd excretion. In
secretion proper, xhe products a.ve formed by a nutritiue process,
the result of a specitd attractive, selective, or as.similative
power, possessed by some epithelial structure ; and moreover,
after being discharged from the months or ducts of the glands,
or from the surface of membranes, tliey are used for certain
I)urposes in the living economy. In excretion, the educts are

344

SPECIAL PHYSIOLOGY.

ra.i\\Qv elimiyialed from the blood through the agency of special
structures, also epithelial ; and they are henceforth cast out
from the body as elFete, useless, or even injurious substances.

Secretion may be performed by glands, or by membranes ;
but excretion is always effected through the agency of glands.

The secreting glands are the liver, pancreas, the salivary, and
lachrymal glands, the true mucous glands of the nose, mouth,
fauces, pharynx, oesophagus, and duodenum, the simple tubular
glands of the stomach and intestines, other minute glands
associated with the ducts of some of the larger glands, the
sebaceous and meibomian glands, and lastly the mammary
glands. The secreting membranes are the mucous, serous, and
synovial membranes. The excreting or excretory glands are
the kidneys, and the sweat glands of the skin ; to a certain extent,
the liver, and perhaps the intestinal tubuli, especially those
of the great intestine ; perhaps, also, the sebaceous cutaneous
glands; and, lastly, the lungs, which may be viewed as excret-
ing glandular organs, destined to eliminate carbonic acid from
the blood.

In certain forms of secretion, the separated products closely
resemble those contained in the blood itself, such as the albumen
of the serous and synovial fluids. Thus, the serous and syn-
ovial secretions consist of little more than the transuded
materials of the plasma of the blood, unaltered in chemical
character, but modified in their relative proportions. The
casein of milk, is also merely a modified form of albumen. In
other more special secreting processes, there are formed, not as
mere transudations, but as the result of peculiar assimilative
actions, substances not present in the blood itself, but, neverthe-
less, little removed in chemical character from its albuminoid
constituents ; such, e.g., as the pepsin, pancreatin, and salivin of
the gastric juice, pancreatic fluid and saliva, and the mucin of
the mucous glands. The three former substances are, by
some, regarded as examples of an albuminoid compound under-
going retrograde chemical changes, or in peculiar states of
hydration. In other cases, the substances formed by secreting
glands, though more remote in chemical constitution from
that of the materials of the blood, and not pre-existent in it,
are of a higly complex nature, and are only partially reduced
or oxidised substances, such as the tauro- and glyco-cholic
acids of the bile, the butyrin of the milk, and the fat of the
sebaceous secretion. Extreme examples of special .«ecretive
power, by which compounds not existing in the blood, are

SECRETION AND EXCRETION COMPARED.

345

Ibrmed from it, are afforcled by the appearance of sidplio-
cyanogen in the saliva, and of hydrochloric acid in the gastric
juice. So, also, soda is withdraum troni the normal soda salts
of the blood, by the agency of the liver, to combine with the
fatty acids of the bile.

In the case of the excretions, hoAvever, the characteristic
substances eliminated from the blood, pre-exist in that fluid,
as the result of decomposition, and, are always much more
chemically reduced by oxidation, than any product of secretion,
or they are even completely oxidised. They usually exhibit a
comparatively simple atomic constitution, are often crystalli-
sable, and frequently take the form of bases or acids, such as the
lactic and uric acids, and the urea, formed in the urine, together
with the sulphates and phosphates resulting from the oxidation
of the albuminoid constituents of the body ; such also as the
lactate of ammonia, and the acetic and formic acids of the cu-
taneous excretion ; and lastly, the perfectly oxidised carbonic
acid, given off in small quantities by the skin, but forming the
characteristic product excreted by the lungs. Such substances
are manifestly incapable of animal organisation. They are even,
if retained in the system, noxious, or fatal. The purpose of ex-
cretion, is, indeed, to rid the body of the compounds which are
formed during the action of the living tissues, by the oxidation
of their substance, or of the blood passing through them.
The successive stages of oxidation, render such compounds
more and more removed from an organisable character, and
necessitate their removal.

In all the .secretions, if one e.xcepts the peculiar albuminoid
substances, the saline substances and other special com-
pounds, are either crystallisable, such as the sulphocyanide of
potassium in the saliva, the soda salts of the biliary acids,
and the lactin or sugar of the milk, or crystalloid, such as the
hydrochloric acid, and other acids in the gastric juice. All
these would freely dialyse from the blood, or from the secreting
cells. As to the modified albuminoid substances, which are
colloidal, such as salivin, pepsin, panci'eatin, and casein, it is
possible that the secreting cells may themselves burst, and
yield up their albuminoid contents ; or the secretion of such
substances from the blood, may ])re.sent us with examples of the
metastasis of colloidal substances from the pectousto the licjuid,
or from the litpiid to the pectous state, as occasion may require.

In the process of excretion, it is, as already mentionecl, the
highly dill'u.siblo crystalloids alone, which escape from the

346

SPECIAL PHYSIOLOGY.

blood, so that it may more readily be referred to a pure
dialysis, the one condition necessary, say, in the secretion of
urea, e.g., being a special chemical relation between the dia-
lysing epithelial cells and the dialysable urea, which serves to
locate the excretion of that substance in the kidney.

In the formation of living vegetable tissues, crystalloids,
such as ammonia, cai’bonic acid, and water, are converted into
colloids, and the further .processes of organisation, up to the
final and highest nutritive stage, require various metastases
of these colloids. In the downward step of disintegration
and disorganisation, materials are formed, which are to be
e.xcreted, and then the crystalloid condition of matter again
prevails, as in the irrea and uric acid thrown off by the
kidneys, which easily pass into ammonia, and the carbonic
acid and water of the cutaneous and pulmonary exhalations.

The general forms of the secreting and excreting glands,
and the mode in Avhich those forms may be derived from the
involution of a simple secreting membrane, have already been
described (vol. i. p. 70). In all cases, there is invariably
found, even in the ultimate ramifications of the gland ducts, a
limiting or basement membrane covered by a stratum of
epithelial cells. All glands are, moreover, very vascular, and
receive large quantities of blood. The special secretions and
excretions are the products or educts of special organs. The '

most essential modifications of the anatomical gland-elements, I

are those which relate to the epithelial cells. In secretion
proper, these important elements are frequently dissolved or
ruptured, and their contents, if not their envelopes, escape as
part, perhaps an essential part, of the secretion itself, as in the
case of the saliva, pancreatic fluid, gastric juice, and milk,
and of the sebaceous and the mucous secretions, and also,
perhaps, of the bile. But in the case of the lachrymal secretion,
and in the excretory processes generally, this is not so ; for
the epithelial cells in the ducts of the kidney, the lachrymal
gland, and the sweat glands, and also, it may be added, in the
air-cells of the lungs, merely Avithdraw, as it were, by a ^
special attraction, certain products already pre-existing in the ^
blood, and part with them again, into the ducts or canals, Avhich
convey them out from the body, Avithout themselves undergoing
any necessary dissolution or decay.

The liver receives a peculiar venous blood, loaded Avith the
jirodncts of the venous absorption of the food, and Avith those
which enter the blood of the spleen ; but, Avith this exception.

USE OF THE EFITIIELIUM IN SECRETION.

347

the cause of the differences between the several secretions,
cannot depend on the character of the blood distributed to the
respective glands, which is uniformly pure arterial blood.
Neither can it depend upon the number or arrangement of
the capillary vessels, for these peculiarities can only determine
the quantity, not the quality, of a given seci'etion. Nor is there
any evidence to show that the walls of the capillaries differ
in different glands, nor even the basement or limiting mem-
brane, which always presents a glass-like, structureless, appear-
ance. Again, the relative simplicity, or complexity, of a gland
cannot be supposed, in any way, to determine the character
of its secretion ; for, though differently formed glands, sup-
plied by the same blood, often yield different secretions, yet
there are cases, in which very similarly formed glands produce
different secretions, as, for example, the salivary, pancreatic,
and mammary glands. Moreover, on regarding the Animal
Kingdom generally, it is found that similar secretions, as, e.rj.,
the bile, the gastric secretion, and indeed nearly all the secre-
tions, are formed, in different cases, by glands of variable
structure, sometimes complex, sometimes simple, according
to the position of the animal in the scale of organisation.
There is one component, however, of all secreting and excreting
organs, whether membranous .or glandular, viz., the epithelial
layer, which appears to be essential to specific secretion, and
to be the seat of the selective assimilative power of the true
secreting glands, and of the selective eliminative power in the
excretory glands. The epithelial cells of different membranes
and glands, most frequently present differences of structure and
arrangement, suggestive of the po.ssession of different pro-
perties. The peptic and hepatic cells, the columnar cells of
the intestinal tubuli, and the cells of the sebaceous cutaneous
glands, are totally different from each other. Even in the
simplest glands in animals, as in the so-called hepatic tubuli,
special epithelial cells are discernible. Epithelial cells are
components of the solid texture of the body, sttbject to the
ordinary proces.ses of development, growth, and nutrition ;
but they are distinguished by a pectiliar destiny or purpose
in the economy, and to them we must refer that special
form of nutrition, which, instead of resulting in the de-
velopment or maintenance of a tissue, destined for certain
mechanical or vital purposes in the animal framework, is
employed for the formation, or separatio)i, of more or less
liquid products, intended for digestive or other uses, or

343

SPECIAL PIIYSIOLOGT.

destined to be eliminated, and entirely discharged, from the
system.

Most frequently, the gland-cells effect changes in the
materials which are presented to them by the blood ; but, at
other times, they attract from that fluid, compounds which
pre-exist in it. In either case, it is these cells which attract
or separate the products or educts, from the circulating fluid.

The general conditions which influence the functions of
secretion and excretion, are the quantity of blood supplied to
the respective glands, the quality of that blood, the presence of
external stimuli, acting directly or indirectly on the nerves,
and perhaps some governing influence of the nervous system
itself.

As a rule, an increased quantity of blood supplied to a
gland, determines an increase in the amount of its secretion,
as is illustrated by the increased redness of the gastric mucous
membrane observed, in the case of the Canadian voyageur,
Alexis St. Martin, during the active secretion of the gastric
juice, and by the increased vascular tiu’gescence of the mam-
mary gland during lactation. As in ordinary nutrition, however,
the secretive demand, implied by an increased secretive act,
precedes the actual flow of additional blood to a given
gland.

The influence of quality in the blood, is perhaps greater in
regard to the excreting than to the secreting glands, as might
indeed be expected. The presence of a greater or less quantity
of the special materials to be separated and eliminated from
the blood, must have a direct effect. An excess of urea or
uric acid in the blood, whatever may be its cause, deterinines
an increased elimination of those products from the kidneys,
and an increased consumption of water, augments the quantity
of the renal excretion. A temporaiy increase of carbonic
acid in the blood, owing to the rapid oxidation of combustible
substances, is followed by an increased evolution of that gas
from the lungs; whilst the drinking of water augments the pul-
monary exhalation and the cutaneous transpiration. The various
secretions are also modified in quantity, by the amount of
fluid absorbed from the stomach ; and the relative amount of
their characteristic ingredients, is deiiendent on the existence
of certain proportions of particular blood constituents from
which they are derived, as seen in the production of the fatty
acids of the bile, and of the sugar, and the peculiar fatty acids
of the milk.

INFLUENCE OF THE NERVES ON SECRETION.

349

The effects of stimnli, are chiefly to be noticed as influencing
tlie quantity of a given secretion, as in the case of a flow of
tears, induced by a foreign body irritating the conjunctiva, or
of saliva, from the action of vinegar, mustard, or salt. Stimuli
act probably through the intermediation of the vasimotor nerves,
either directly, or else by reflex action, through other nerves
and nervous centres with which the vasimotor nerves are
connected. The general effect of such stimuli, is to dilate
the small arteries of the gland ; a corresponding increase
tlien occurs in the flow of blood to it, and is the proximate
cause of an increased secretion or excretion. This increase
may, as in the case of the saliva, augment the quantity but not
improve the quality of the secretion, which becomes more
watery than usual.

There are many facts which show an intimate relation
between the nervous system, and the secreting activity of the
several glands. Thus, the emotions often determine increased
secretion, as e.y. from the lachrymal glands, the skin, the ali-
mentary mucous membrane, and the kidneys. The sight, or
even the idea of food, will excite the flow of saliva. Extreme
passion or grief has been known to modify, or even render
p(usonous, the mammary secretion. Direct experiments also
show most remarkable effects produced upon the secretive
process, through the nervous system, as illustrated in regard
to the sahvary glands (vol. i. p. 333 ; vol. ii. p. 56), the
gastric glands (vol. ii. p. 61), and the liver (vol. ii. p. 340).

All glands are provided with sympathetic nerves, and
many, if not all, po.ssess others derived from the cerebro-.spinal
nervous system. The e.xperiments just referred to, show that
the quantity of a secretion is differently affected by the section,
or irritation, of these two sets of nerves. Thus, irritation of
the pneumogastric nerves, increases the quantity of the gastric
juice, whilst irritation of the sympathetic nerves, diminishes
or arrests it. Again, divi.sion of the sympathetic nerves of
the submaxillary gland, increases the flow of saliva, but irrita-
tion of the di.stal cut portion of the nerve, dimini.shes it ; on
the other hand, section of the cerebral nerve, diminishes, whilst
irritation of the di.stal cut end, augments it. Even simple
irritation of tlie undivided sympathetic nerves, causes diminu-
tion, whilst a similar irritation of the undivided cerebral
nerve, causes an increase of the secretion. Since, in the
former case, the small arteries of the gland contract, and the
supply of blood is diminished, whilst in the latter, those

350

SPECIAL PHYSIOLOGY.

vessels dilate, and more blood is distributed to the gland, the
diminution or augmentation of the secretion, accords, in either
case, with differences in the quantity of blood conveyed to the
gland, and the influence of the nervous system in regulating
the quantity of the secretion, is indirectly manifested by the
dilatation or contraction of the coats of the small arteries.

With regard to the influence of the nerves on the quality
of a secretion, it is found that when the arteries are con-
tracted, and the supply of arterial blood lessened, not only is
the quantity of saliva diminished, but the colour- of the venous
blood returning from the gland, is, as usual, dark ; whereas,
when the arteries are dilated, the supply of blood is increased,
and the amount of secretion augmented, then the colour of
the returning venous blood, is bright. In the foi-mer case,
the passage of the blood through the gland, seems to be suffi-
ciently deliberate, to permit of the proper nutritive or secre-
tive interchanges between it and the epithelial cells ; whilst in
the latter case, the blood flows so rapidly through the glands
as not to undergo these changes. It is not proved that the
sympathetic nerve determines, or even increases, the secreting
power of the gland.

By controlling the quantity and velocity of blood passing
through a gland, the sympathetic nerves may, therefore, not
directly, but indirectly, by permitting the characteristic func-
tion of the gland, preserve the essential qualities of its secre-
tion ; whilst, on the other hand, the cerebro-spinal nerves, by
determining an increased supply and quicker motion of the
blood, must, by partially interfering with, or ovei-Avhelming,
the special actions of the secreting cells, increase the fluid in
the secretion, but so dilute and lower its qualities.

^Wiilst it is not yet proved that either the sympathetic, or
the cerebro-spinal, nervous system has any power over the
chemical acts of secretion, independently of their goAmming
influence over the bloodvessels, it must be added that this is
a point on Avhich opinions are at variance. As already re-
marked (p. 284), if, as it seems scarcely possible to doubt, the
nervous system iuiluences the secreting processes in such of
the loAver animals as are unprovided Avith bloodvessels, and
yet possess nerves, it is difficult to deny the existence of some
such direct inlluence in the higher Avascular animals and in
Man, however unintelligible the nature of such a controlling
process may be.

Whatever the influence of the nervous s}'stem upon secre-

YICAKIODS SECEETION.

351

tion, it may be centric, or peripheral, and either simple or
reflex, according to the part in which the stimulus originates,
or to which it is applied. Tears are shed, and saliva flows,
under the centric stimulation of painful or joyous emotions,
and on the occurrence of ideas relating to food ; whilst the
same secretive acts are performed under reflex action, from
neuralgia of the fifth cerebral nerve, or from local irritation
of the conjunctiva or of the mouth.

When, either from disease of the glands, or from an over-
accumulation, in the blood, of the materials to be excreted,
these are no longer eliminated through the usual organs, they
are sometimes vicariously eliminated through some other
gland or membrane. Thus, urea has been found in almost
every secretion and excretion of the body, in the gastric and
intestinal discharges, in the lachrymal and salivary fluids, in
the nasal mucus, in the synovial and serous fluids, the per-
spiration and even in the milk. The pigment of the bile,
which is probably more of an excretory than a secretory
product, occasionally appears in the renal excretion and in
other fluids of the body. The.se are instances of real vicarious
excretion, but in regard to the secretions proper, no such
metastasis, or transference, of secreting power has been ob-
served, no authentic example of milk secreted by the liver or
kidneys, or of saliva formed by the mammary gland, having
yet been met with. The presence of the colouring matter of
the bile in various true secretions, as in the pancreatic juice,
the milk, the mucus of the bronchial glands and membrane,
and even in the serous and synovial fluids, is perhaps only an
apparent example of vicarious secretion ; for, in these cases,
the colouring matter of the bile is probably re-absorbed into
the blood, and then is simply exuded into all parts of the body
with the common nutrient plasma, and so tinges the various
solid tis.sues, organs, glands, and secretions. There is, more-
over, no evidence that, even in these cases, the more abun-
dant and truly secretory products of the hepatic cell action,
viz. the soda salts of the biliary acids, accompany the bile
pigment in its passage through the body, or into the secretions
of other glands. The biliary pigment probably represents an
excretory part of the bile, and, if not preformed in the blood,
is easily di.ssolved and taken up by it, and thus it may obey
a true metastasis like other excretory substances. It certainly
appears very readily in the urine, and also sometimes in the
persjtiration.

352

SPECIAL PHYSIOLOGY.

Certain excretions are complementary to each other, as, for
example, those of the lungs and the liver. The more abundant
the excretion of carbon in its perfectly oxidised form of car-
bonic acid gas from the lungs, the smaller is the amount
of cai'bonaceous compounds excreted in the bile ; whilst, on
the other hand, when the respiratory changes are diminished
through heat of climate, or defective exercise, the biliary
products are increased. The excretions of the skin and the
kidneys, are also, to a certain extent, complementaiy to each
other, not only as regards their aqueous constituents, in respect
of which, each is, moreover, supplemented by the lungs, which
give off more or less vapour according to the relative degree
of moisture of the air, but also in regard to some of the jjro-
ducts of oxidation of the albuminoid tissues, viz., urea, am-
monia, and carbonic acid.

Different secretions and excretions differ as to the time at
which they are prepared. Some are constantly or continuously
formed, whilst others are secreted, or excreted, intermittently,
or remittently. Secretions are more commonly intermittent or
remittent, seiwing occasional purposes in the economy, as, e.g.,
the gastric juice, the secretion of which is probably limited
to the period of digestion, and the lachiymal, salivary, hepatic,
pancreatic, and mammary secretions, which are always being
secreted in small quantities, but are, from time to time, as
required, produced in much larger amounts. On the other
hand, the excretions being injurious, and requiring to be
eliminated, as rapidly as possible, from the blood, are charac-
terised by theii’ constant separation both day and night, the pro-
cess varying in activity, however, according to circumstances.

The force by which the secretions are urged along the
ducts, is probably the vis a tergo, dependent upon the pre.ssure
of continuously fi’esh-formed portions of fluid secreted in the
commencing ducts. The movement in the larger ducts, is
aided by the slow contraction of the organic muscular fibres
in the walls of the ducts. In some cases, as in the bile and pan-
creatic ducts, and the ureters, rhythmic movements have been
seen, and in others, peristaltic movements. The pressure on
the fluid in the ducts, is sometimes considerable, as is seen by
the occasional ejaculation of the saliva, and the expulsion of
the milk. The action of the surrounding muscles, must, here
and elsewhere, also be taken into account. In certain cases,
the larger ducts are dilated near their mouths, into temporary
receptacles for the secretion, as is seen in the parotid and

NUTRITION AND SECRETION COMPARED.

353

lactiferous ducts. Still more special developments of the
excretory apparatus, are met with in the shajDe of reser-
voirs or bladders, with contractile walls, when, as in tlie case
of the bile, the secretion is abundant and used intermittently,
or when, for other reasons, an excretion requires to be re-
tained, and only occasionally expelled.

The daily quantities of the various secretions and excretions,
as stated elsewhere in the account of each, differ remarkably
in different individuals, and in the same individual under
different circumstances. The quantities of the excretions, in
health, conform to the quantity of water taken in the solid
and fluid food, one of the objects of this elimination of water,
being to maintain the due characters of the blood. In the
formation of the extraordinary quantities of the secretions
employed in the digestive process, the water concerned is, as
already mentioned, separated from the blood, used in dissolving
the food, re-absorbed, and re-secreted many times over.

The preceding facts and considerations, illustrate the general
resemblances and differences between nutrition and secretion.
In both processes, the blood yields a common plasma to certain
organs ; from this plasma, in both, materials are attracted by
a selective property possessed by pre-existing tissue elements;
and, in both,- the residual and altered plasma re-enters the
blood. But this difference arises : in the one, the separated
materials form an intrinsic part of a solid and more or less
permanent tissue, and enter into the coherent framework of
the body ; whereas, in the other, whilst a part thus remains to
form the gland-tissue itself, the essential products are dis-
charged, in the fluid state, by ducts, and are applied extrinsi-
cally, to special functions of the economy, sometimes, however,
being then re-ab.sorbed into the blood. Both the nutritive
and the secretive process yield various results, according to
the tissue in which they occur ; nutrition forms nerve, muscle,
or bone, and secretion, saliva, pancreatic juice, or milk,
according to the nature of the tissue elements which select, or
determine, the separation of the nutrient or secreted materials,
from the blood plasma. Both nutrition and secretion are modi-
fied by the quantity and quality of the blood, and by the re-
actions of the vasimotor nerves. The nutritive and secretive
processes may both be either continuous or intermittent, the
former being illustrated by the continuous formation of the
epidermis and of mucus, and the latter by the intermittent
nutrition of the muscular and nervous tissues and the forma-

VOL. II. A A

354

SPECIAL PHTSIOLOGT.

tion of the gastric juice. Lastly, the two processes resemble
each other, in being more active in some parts than in others,
being more so, in the heart, the nervous centres, and the
salivary glands and sweat glands, than in the tendons, carti-
lages, bones, and the mucous and sebaceous glands.

SPECIAL SECRETIONS.

Most of the secreting glands and their products, have already
been considered, viz. the lacluynial glands and the tears, ivith
the appendages of the eyes; the nasal glands, with tire organ
of smell ; the ceruminous glands, with the ear ; the sebaceous
glands, with the skin ; and, lastly, the mucous glands of the
mouth, fauces, pharynx, oesophagus, stomach, and duodenum,
the saliva and salivary glands, the gastric and intestinal
tubuli and their secretions, the liver and pancreas and their
respective products — with the organs and ftmction of Diges-
tion. The tracheal and broncliial mucous glands will be men-
tioned hereafter, in the Section on Eespiration. There remain,
however, certain general considerations concerning the liver
and its offices, which may be here noticed ; whilst the mam-
mary glands with the function of lactation, and the mucous,
serous, and synovial secretions also requii’e description.

Secreting Function of the Liver.

The source of the bile secreted by the hepatic cells, is the
exuded plasma of the portal blood, which, however, is joined
by the blood from the nutrient capillaries of the liver, derived
from the hepatic arteries. That the portal blood is essential,
and the arterial blood non-essential as such, to the formation
of bile, is proved by the facts, that when the portal vein is
compressed, the quantity of bile is diminished, and that when
it is tied, bile is no longer secreted ; whereas, if the hepatic
arteries be tied, its secretion is not necessarily arrested
(Schiff). In certain cases of malformation, the portal vein
has been found to open into the inferior vena cava, and yet
bile has been secreted. Hence the portal blood has been held
to be non-essential to the formation of bile ; but, in such
cases, the umbilical vein is permeable, and sends branches
through the liver ; moreover, the blood of the hepatic arteries,
having first become venous, may enter the lobular plexuses,
and so secrete the bile.

FUNCTIONS OF THE LIVER.

355

That the biliary acids are not preformed in the blood, but
are elaborated in the hepatic cells, is shown by extirpating the
liver in frogs ; these animals then survive for some days, and
yet no trace of the fiitty acids of the bile is found in the
blood, which would be the case, if the bile were preformed in,
and merely separated as an educt from, that fluid. The green
colouring matter, and also cholesterin, may, however, pre-exist
in the blood. The cholic acid may be derived from the fats
of the blood, whilst the taurin and glycocoll, which are conju-
gated with it, the former containing both sulphur and nitrogen,
and the latter only nitrogen, probably arise from the decom-
position of albuminoid substances. The colouring principles
may he formed from the cruorin, or colouring matter of
the blood, which they closely resemble. Animals fed on fat,
have been said to secrete proportionally more bile ; but this
is denied, and the quantity of albuminoid food consumed,
seems rather to regulate the amount of this secretion.

Besides its office in digesting fat, and stimulating the mus-
cular acts concerned in digestion and absorption, the bile has
other uses. The fatty acids, largely reabsorbed, may become
converted, in the circulation, into carbonic acid and water, for
respiratory, motor, and calorific purposes. The glycocoll, taurin,
and the colouring matters are apparently excreted. The glyco-
coll is probably thrown off by the kidneys as urea, for when
it is administered as food, more urea is then eliminated ; the
colouring matters, altered from a yellow to a greenish, and then
to a dark-brown hue, some taurin, and likewise a small portion of
the cholic acid, converted into dyslysin, are found amongst the
excreta. The excremeutitious character of the bile, is fiirther
indicated by the size and activity of the liver before birth,
when no digestion is going on. Moreover, by its glycogenic
function, the liver performs a highly important nutritive
office, affording to the body respiratory food. Lastly, it
may be said to act as a purifying agent on the venous blood
returning from the alimentary canal, partly by its direct power
of assimilating albuminoid, oleaginous, saccharine, and colour-
ing substances, but also partly as a sort of filtering organ, in
which foreign bodies, such as metallic salts and other sub-
stances, are detained, and prevented from entering too sud-
denly into the general circulation.

Irritation, or division, of the pneumogastric nerves, below
the diaphragm, appears to produce no effect on the quantity
of the bile accreted in a given tim6 ; but injury to both, or even

A A 2

SPECIAL PHYSIOLOGY.

sne

to one of those nerves higlier up, interferes with the biliary
secretion, perhaps by its effect on the circulation and respi-
ration.

When the bile is not eliminated from the system, or when
it is reabsorbed, symptoms of nervous prostration ensue, with
headache and jarmdice, often followed by death. The con-
stituents of the blood, out of which the bile is formed, when
retained, or the bile itself when taken up, appear, therefore,
to be noxious, or even jDoisonous.

The combined assimilative, secreting, excreting, and puri-
fying actions of the liver, are consistent with its large size, its
general presence in nearly all animals, its marked vascularity,
the peculiar source of its blood, the high temperature of its
tissue and of the hepatic blood returning from it, and the
singular variety of the metamorphic changes which take place
in it. So long as its office was supposed to be merely to
secrete 2 oz. of solid biliary 7natter daily, whilst the lungs
excrete 8 oz. of carbon in the same time, the size and other
characters of this gland, were not fully explained, espe-
cially in its embryo state ; but its gl^^cogenic ftmction, and
its influence in the process of sanguification, sufficiently ac-
count for its pre-eniinenee amongst all the glandular organs of
the body.

The Mammary Glands and Lactation.

The human infant, and the young of all Mammalia, are
supplied with suitable nutriment for the first months of their
existence, in the well-known fluid named milk, secreted by the
mammary glands. It is in the female only, that these glands
yield milk, the proce.ss being termed lactation. In the males
of mammiferous animals, these glands exist, but their j^arts are
very small.

The mammary gland, in woman, is a large organ, composed
of numerous lobes, arranged, in a more or less radiating man-
ner, ai'ound the projecting part, named the mammilla, or
nipple. The lobes, which may be moved slightly upon each
other, are separated by fibrous septa, and are held together
by a general investment, stronger on the under side of the
gland, where it rests upon the pectoral muscle. Each lobe
consists of a number of lobules, possessing the structure of a
compound racemose gland, closely resembling that of the
parotid gland (fig. 42, c). The terminal ducts end in clusters of
short follicles, or vesicles, about Tj^th of an inch in diameter,

CnABACTERS OF THE 31 ILK.

357

•which, -ivhen filled, are just visible to the naked eye, and the
walls of which are lined with a layer of soft glandular epithelial
cells. From these follicles, the smallest lactiferous ducts unite
into one or more larger ducts for each lobule, and these join into
still larger tubes called galactoplierous ducts, one or more for
each lobe. These large ducts, about fifteen in number, i-un to
the centre of the gland, and generally dilate, so as to form tem-
porary receptacles for the milk. The walls of these ducts are
composed of a fibrous coat, containing unstriped muscular
fibres, and lined by a mucous membrane continuous with the
skin. They open at the summit of the nipple, by separate
small round orifices, seen at the bottom of little depressions in
the skin. The arteries of the mammary gland are numerous,
and proceed from many sources ; they present a good example
of the enlargement of bloodvessels supplying a part, in Avhich
increased activity of function occiu’s. Numerous capillaries
surround the terminal vesicles of the gland. The veins and
lymphatics are also numerous. So likewise are the nerves,
partly spinal, and partly sympathetic, the latter reaching the
gland along the arteries.

The first secretion of milk is preceded by an enlargement
of these glands, which causes a certain hardness and tenderness
of the part, and a febrile disturbance of the system, known as
milk fever. The first milk secreted, much thicker and darker
than the sub.sequent secretion, is named the colostrum. After
lactation is established, the secretion is not imiform, but
remittent, proceeding slowly during the intervals of suckling,
so as not usually to accumulate and cause suffering, but sud-
denly increasing, in accordance with the great afflux of blood
to the glands, during the act of nursing. The fulness and
increased secretion experienced at this time, constitute the
phenomenon called the draught. From each di.stended gland,
the quantity obtainable by pressure, is about two ounces; but
the daily (juantity secreted by both, fluctuates according to so
many circumstances, that no correct avei’age is attainable.
The composition of the milk, also varies exceedingly. Its
specific gravity ranges from 1,030, or le.ss, to 1,035. The
colour of human milk, is blui.sh-whitc, owing to its greater
transparency as compared with cow’s milk. It is opalescent,
and perhaps fluorescent. It contains from 8G0 to 910 parts
of water in 1,000, the solid matter varying accordingly, from 14
to 9 per cent. ; its average composition is 89 parts ol‘ water to
1 1 of solid constituents. These latter consist of 4‘5 of lactin or

358

SPECIAL PHYSIOLOGY.

sugar of milk, 3‘5 of casein, 2'5 of fatty matters or butter, '3
of extractives, and '2 of alkaline and earthy salts, together
with traces of iron. Milk likewise contains, like the blood,
carbonic acid gas, nitrogen, and oxygen, the total amount of
these gases being about 3 per cent, of its volume ; more than
half of this is carbonic acid gas, and only -g^j-th part oxygen,
the remainder being nitrogen.

The milk is a true secretion, formed out of the materials
of the exuded plasma of the blood, by the agency of the
ejnthelial cells of the terminal vesicles of the gland. It is
composed of a slightly turbid fluid, containing suspended in it,
a vast number of minute, more or less spherical, particles
named the milk globules-, these are composed of an oily matter,
surrounded by a thin fihn or pellicle of albuminoid substance,
probably of casein, for neither ether nor an alkali, which
Avould dissolve fatty matter, attacks them, unless they are first
acted on by acetic acid, or are strongly agitated, so as to
di.ssolve or break the albuminoid film, which does not appear
to be organised. These milk globules vary from i aoootd to
g-^t^-Qth of an inch in diameter; other and much smaller
spherical particles, manifesting the molecular movement, exist
in the fluid, and probably cause its turbidity ; some of these
may consist of casein, but they are chiefiy fatty, and readily
dissolve in ether. The milk also contains a few epithelial
cells from the ducts. Owing to the thin pellicle around the
milk globules, these do not at once run together, but only
coalesce, after a time, in the formation of the cream. In the
colostrum the milk globules are very minute, but there also
exist in it, peculiar large, yellowish, closely and finely granular
fatty corpuscles, which resemble the so-called exudation cells,
or compound inflammation cells ; these appear to result from
, the fatty degeneration or transformation of the glandular epi-
thelial cells. The colostrum contains albmneu, or at least it
coagulates on boiling ; it also has a larger projDortion of sugar
and saline constituents. It exercises an aperient effect upon
the ne^v-born infant. The colostric condition sometimes persists
for too long a period, and then the milk is less suitable for food.

As long ago remarked by Prout, milk presents us with
a type, or pattern of food, for it contains, in definite and
duly balanced proportions, nitrogenous and non-uitrogenous
nutrient suljstances, albuminoid, fatty and saccharine, fitted
for both plastic and respiratory purposes, and, besides these,
suitable salts for the blood and tissues. JNIilk, as we have

CONSTITUENTS OE THE MILK.

359

seen, is composed of water, which holds in solution lactin or
milk-sugar, casein or the albuminoid substance characteristic
of this secretion, certain extractive matters, and salts ; whilst
it contains, in suspension, fatty with albuminoid matter.
\Vlien set aside in quantity, a natimal analysis of milk takes
place ; first the oily matter, being of light specific gravity,
together with a certain amount of casein, and even sugar and
saline substances, rises as cream, the globules of which, by
agitation, as in the process of churning, combine to form
butter, leaving most of the casein, the sugar, and other sub-
stances, extractives, and salts, in the butter-milk. After a
time, some of the sugar in this butter-milk, undergoes a
peculiar fermentation, perhaps excited by the casein, and is
changed into lactic acid ; this immediately precipitates the
casein in minute flocculi, which combine to form the so-called
curd. The residiral fluid, called the whey, now contains most of
the lactin or sugar of milk, with lactic acid, extractives, and salts.

The fatty matter of the cream, consists chiefly of olein, but
it also contains stearin, and, in particular, a peculiar fat, named
butyrin, Avhich is a compound of butyric acid and gljmerin,
and imparts to butter its characteristic taste and smell. It
yields, when acted on by alkalies, and also when spontaneously
decomposed at high temperp,tures, besides butyric, small
quantities of caproic and capric acids. The casein of human
milk, is not so eassily precipitated by acids or by rennet, as
the casein of cow’s milk; in this respect, and also as regards
its smaller quantity of casein, human milk resembles more
closely the milk of the ass. The lactin or sugar of milk,
which may be separated by crystallisation from inspissated
whey, is convertible into grape-sugar, by dilute mineral, or
by vegetable, acids ; it is very prone to enter into the lactic
fermentation, and even to form butyric acid by decomposition ;
but it is difficult to transform it into alcohol. The extrac-
tives of milk have not been well examined. The salts
resemble those of the blood ; but they present curiously a
larger relative amount of the earthy pho.sphates of lime and
magnesia, which are combined with, and rendered soluble by,
the casein. Chlorides of .sodiiun and potassium, and taices of
phosphate of iron, are met with. Human milk may be either
neutral, alkaline, or acid ; but the milk of most animals
usually, and that of the Carnivora always, at the time of its
examination, is acid, from the ])rcsence of free lactic acid.

The casein is probably I'ormod, by the secreting porver of

360

SPECIAL PHrSIOLOGT.

the mammary gland cells, from the albuminoid principles of
the blood ; but, according to some, it is preformed in the blood
itself, during the period of lactation. It supplies materials to
the infant, for the re-formation of albuminoid compounds. The
oily matters derived from the animal fats, or from sugar, and
the sugar itself, the .source of -which is yet unknown, are not only
directly adapted for respiratory purposes, and the production
of animal motion and heat, in the infant, but also, as -well as
the casein, are doubtless employed, in part, in various important
nutritive and secretive processes. The salts of the milk are
also those -ndiich are essential to the formation of blood, salts
of potassiimi and iron for the corpuscles, and salts of soda,
calcium, and magnesium for the liquor sanguinis. , The phos-
phates of lime and magnesia are absolutely neces.sary for the
growth of the young skeleton. Of all the secretions, milk is
especially nutritive, and most closely resembles blood in com-
position, its chief distinction from that fluid, being the large
quantity of sugar in it. Milk alone contains albuminoid, fatty,
and saccharine elements combined. Its secretion is not essential
to the system, being, ordinarily, limited to one sex, and, in
that, being temporary or periodic. From its general resem-
blance to blood, the arrest of its secretion, is not so pernicious
as the non-secretion of the bile ; nevertheless, its retention
within the gland, besides causing obstruction of the ducts,
inflammation of the organ, and its consequences, may likewise,
perhaps, prove injurious through re -absorption, especially of
the crystalloids, lactin, and lactic acid. It has been supposed
that its constituents may be retained in the blood, and so
account for the constitutional disturbance which follows the
sudden arrest of the secretion ; but the proper constituents of
the milk are probably not, normally, pre-existent in the
blood, though they may, like those of other secretions, be
reabsorbed. Cases of vicarious secretion of milk, which are
very numerous, may depend on reabsorption, and distant
exudation, of the absorbed constituents. A case has been
recorded of the expectoration of milk following sudden arrest
of the secretion. Instances of so-called vicarious secretion of
milk from the inguinal region, have been supposed to be due
to the presence of supernumerary mammary glands in that
position. This would correspond with the normal situation
of these glands in some of the lower animals, and, rudiments
of more than one pair of mammary glands, are sometimes met
with in the human body.

EFFECT OF THE NERVES ON THE 3IILK.

361

The quantity and quality of the human milk, vary accord-
ing to many circumstances. Thus, it is not only most
abundant, but most nutritious, in nursing women, from the
age of 15 to 20, whilst it is least so, in those from 35 to 40.
The constitution also greatly influences the character and
nutritive qualities of the milk ; hence the necessity for the-
selection of healthy wet-nurses. In the early periods of
lactation, the casein is at first relatively small in quantity,
but afterwards becomes increased and attains a determinate
ratio ; whilst the sugar is at first abundant, but afterwards
reduced in proportion. From experiments on the cow, the
fatty matters seem to vary most, chiefly according to the
nature and quantity of the food, the temperature in which
the animal lives, and the amount of exercise it is permitted
to take. Thus, warmth and rest, increase the quantity of
oily matter, whilst cold and exercise diminish it (Playfair).
Exercise, however, increases the relative amount of casein.
Both in the human subject and in animals, the nature of the
food, and the quantity of water taken in, or with, it, must
directly influence the specific gravity, the amount of solid
matter, and the relative quantities of the several ingredients
of the milk. It has been observed in the cow, that the last
milk drawn, at any one time of milking, is richer than the first.

The influence of the nervous system in modifying the
quantity and quality of the milk, is most important, and
imiver.sally recognised. Irritation of the nipple increases, by
a reflex influence, the flow of milk ; this is probably one
cause of the rapid flow of the secretion during the act of
suckling. Continued local irritation, combined with a strong
desire for the occurrence of lactation, and a fixed attention
towards the mammary glands, have been known to produce
this secretion in women not recently mothers, to protract its
flow for many years, to excite it in aged Avomen and in girls,
and even, it is said, in individuals of the male sex. In that
sex, usually, hoAvever, the rudimentary glands yield only
occasionally a thin clear fluid, the composition of which is
uncertain. The influence of the nervous system, as affected
by mental states, upon the secretion of the milk, is further
evinced by the abundant flow, the so-called draught, often
excited by the sight, or even by thinking of the infant.
Tranquil and pleasing emotions favour the normal secretion ;
but anger, anxiety, grief, and terror may produce serious
modifications in the quality of the milk, or may even suspend

I

362 SPECIAL PKYSIOLOGT.

its formation. Violent passion may induce such changes in
this secretion, as to cause it to be poisonous, and even
immediately latal, to the infant. This probably arises from
some modification in the blood (p. 318).

To secure the healthy performance of the function of lacta-
tion, an ample amount of nutritious food, moderate exercise,
tranquillity of mind, and regular habits, are necessary condi-
tions ; a defective or excessive diet, fatigue, and irregularities
and excesses of all kinds, are unfavourable. The influence of
alcoholic stimulants, in moderation, is, by promoting digestion
indirectly, favomable to the supply of milk. Medicinal agents,
especially those of a powerful kind, should be avoided ; many
of them enter the milk, and may thus affect the child.
Mineral and saline substances, and the alkaloids, such as
quinine and morphia, pass more readily into the mUk than
vegetable aperients.

The peculiarities in the milk of the cow and other animals, as com-
pared with human milk, are interesting in a dietetic and economic point
of wew : — •

Woman

Cow

Goat

Sheep

Ass

Mare

(Simon)

(Simon) (Chevalier) (Chevalier) (Simon)

(Luiscius)

Water . . .

. 890

860

868

856

907

888

Solid matters

. 110

140

132

144

95

112

Butter . . .

. 25

38

33

42

12

8

Casein . . .

. 35

68

40

45

16

16

Sugar, with ex-
tractives

1 48

30

53

50 1

65

88

Salts . . .

2

6

6

7j

According to this Table, the milk of the goat, more closely resembles,
in chemical composition, the human milk than does that of any other
animal ; but it has been found that, besides having a peculiar odour,
its ciu’d is remarkably compact. The milk of the sheep, differs a little |

more from human milk. That of the mare and of the ass, are charac- ;

terised by the small quantity of butter and casein, and the large quantity
of sugar, which they coutiiiu. The milk of the mare, is most remarkable i

for its enormous proportion of sugar ; this may explain its disposition 1

to undergo the alcoholic fc.rmentiition, a fact turned to account by many j

Tartar tribes, in order to make an intoxicating drink. The milk of the ^

ass, notvvithstanding its difference from human milk, is, perhaps from the i

difficulty with which its casein is precipitated, and from the delicacy of f

its curd, the most easily digested by the human infant. Cow’s milk, f

which is the great source of milk for human food and the great substi-- •!

tute for human milk in the ease of infants, contains more casein and 1
more butter than human milk, but only about 3-6ths of the quantity of li
sugar. The specific gravity of good milk is about 1030, that of the li

cream being 1024, and that of the skimmed milk about 1035; by ^

means of a proper lactometer, the quality of milk may bo determined ti

THE MUCOUS SECRETIONS.

363

approximately by every householder. Considered as infant food, the
milk of the cow, is too rich in casein and butter, and too poor in sugar;
hence it should be diluted and sweetened, either with common white
sugar or, what is better, with sugar of milk. Half a pint (imperial) of
good fresh cow’s milk, with half an ounce of milk-sugar and half a pint
of water, will form a tolerably near approximation to ordinary human
milk, but it is deficient in the due proportion of saline, earthy, and
ferruginous salts. As an infant advances in age, the sugar and water
may be diminished, and farinaceous food may be added. It is well
known that the milk of certain breeds of cattle, is richer than that of
others. Authorities differ as to the relative richness of the milk of
cows fed in town dairies or in country pastures, but country milk must
be more natural, and better as food, than the artificially forced produc-
tion of the town-fed animal, other circumstances being equal.

The mammary glands, as is well known, differ in arrangement and
position in different orders of Mammalia ; sometimes, as in the Carni-
vora and in the pig, they are divided into numerous portions, disposed
along nearly the whole length of the under side of the trunk, each
symmetrical mass having its own nipple ; sometimes, as in the Rumi-
nants, and in the genus Equus, they are post-abdominal ; in the
Cetacea, they are situated even stiU fm-ther back; in the Quadrumana,
as in Man, they are found in the pectoral or thoracic region only. The
microscopic structure resembles that of the human gland, excepting in
the lowly organised Monotrematous ornithorynchus, in which the milk
glands consist merely of clusters of simple blind follicles, opening in a
group on the skin. This simple structure suggests an homologous rela-
tion between the mammary and the cutaneous glands.

Mucous Secretion and Mucus.

i\Iucu.s is the clear, or slightly turbid, colourless, viscid
fluid found on mucous membranes. It is partly secreted by
the epithelial cells of the compound racemose glands, but in
part, also, by those of the surlace of such membranes. It is
a special secretion from the plasma of the blood, and difiers
from it chemically. IMucus is commonly alkaline, but often
speedily becomes acid; normally, perhaps, it is neutral. It
is composed chiefly of water, holding in it from 4 to G per
cent, of solids. It contains desquamated epithelial cells,
mucous corpuscles which closely resemble the Avhite blood
corj)Uscles, and pus corpuscles, and also certain nucleated cells
intermediate between the true mucous cells and epithelial
cells. Its chief constituent is a special albuminoid substance,
called mucin, which, precipitable by alcohol, acetic, and other
acids, but not by boiling, swells up, rather than dissolves, in
water, and is the cause of its natural viscidity ; besides this,
it contains a small amount of extractives, and salts hke those
of the blood. It is sometimes very thin, as when secreted from

364

SPECIAL PHYSIOLOGY.

the nose during a cold ; in other situations, it is much more
viscid, as the intestinal or vesical mucus, and the nasal mu-
cus ; that from the air passages in cases of cold, is very viscid,
and contains albumen. The use of mucus, is chiefly me-
chanical, assisting in the acts of mastication, deglutition, or
speech, or, as in certain animals, in the capture of prey. It
aids in taste and smell, preserving the moisture of the parts,
and acting also as a solvent. It is likewise protective, both me-
chanically and chemically, by offering resistance to the action
of the digestive fluids, which do not easily dissolve it. Some-
times it behaves as a ferment, possibly assisting the salivin,
pepsin, and pancreatin, though not possessing very active
powers. It, or something mixed with it, imdoubtedly deter-
mines the retrograde decomposition of the renal excretion, wlien
this is retained longer than usual in the body. Mucin, not
being readily soluble or digestible, cannot, strictly speaking,
be nutritive or absorbable.

Serous and Synovial Secretions.

These fluids, Avhich cover and moisten the surface of the
serous and synovial membranes, differ so little in composition,
from the plasma of the blood, that their formation has, by
some, been regarded, not as a process of secretion but as one
of transudation through those membranes. A certain modi-
fication of the plasma of tlie blood, as it is exuded fi'om the
capillaries, is here accomplished, howeAmr, by the action of the
epithelial cells, which, in a single layer, cover these membranes.
These fluids may sometimes contain, in certain morbid con-
ditions, excretory materials, such as urea, lactate of soda,
sugar, and traces of bile pigment, aU of Avhich are manifest
transudations.

The serous fluids, which must not be confounded with the
serum of the blood, contain as much as. 99 per cent, of
Avater, a feAv salts, some albumen, and a substance slightly
soluble in alcohol. They are thin and scanty in normal con-
tions, in the cavities of pleura, pericardium, peritonteum, and
arachnoid spaces, their use being merely to prevent friction.
The aqueous humour of the eyeball, may be regarded as a
serous secretion, adapted, by its locality, to a Amry special
pm-pose. When accumulated in abnormal quantity, from in-
flammation, serous fluids cause internal dropsies, and, in that
case, generally contain traces of fibrin, AA'hich Avill sloAA'ly co-
agulate alter removal Irora the body.

EXCRETION

365

Tlie si/novial fluid, or synovia, is much more viscid than the
serous fluid ; it contains nearly 6’5 per cent, of albumen,
together -with flitty matter, salts resembling those of the blood,
epithelial cells, corpuscles like the pale corpuscles of the blood,
and, it is said by some, a substance closely resembling mucin.
The use of this fluid, found alike in joints, in the so-called
bursai mucosa, and in the sheaths of tendons, whether these
move in grooves on the bones lined with cartilage, or in soft
parts only, is chiefly mechanical, to prevent the effects of fric-
tion ; but in the joints, it may act nutritively on the cartilages.

EXCEETION.

The characters which distinguish excretion from secretion
proper, have already been detailed (pp. 343-5). Its products,
like those of secretion, are fluid or gaseous, at least in the human
body, although semi-solid, or solid, urine occurs in Birds and
Keptiles. The term excreta, is also commonly applied to the
solid materials ejected from the intestinal canal, as the resi-
duum of the digestive process. These, however, are only
partly excreted substances, such as unabsorbed biliary and
other products more or less changed, substances thrown out
by the intestinal glands, and undigested mucus and epithe-
lium. The greater portion of the mass, however, consists of
undigested food, such as elastic tissue, sarcolemma, the walls
of vegetable cells, spiral ducts, and woody fibre.

The fluid excretions are those eliminated by the kidneys and
the skin, the former excretion being the more complex. The
exlialation of carbonic acid from the lungs, is an excretory
process more immediately nece.ssary to life than any other.
The lungs may be regarded as excretory glands, and the car-
bonic acid e.xpelled from them, as a gaseous excretion ; but
the .speciality of this process, its association with the absorption
of oxygen, and its peculiar mechanism, render it necessaiy to
consider the entire function separately, under the head of
Kespiration.

Renal Excretion,

The urine, excreted by the kidneys, is the most perfect ex-
ample of a fluid excretion given off by the animal economy ; its

3G6

SPECIAL PHYSIOLOGY.

various constituents exist preformed in the blood ; they are,
moreover, highly oxidised nitrogenous products of the decom-
position of the albuminoid tissues, and of the albuminoid con-
stituents of the blood. They are destitute of organisation,
and incapable of it; neither can they be made, in animals, to
undergo an ascensive chemical metamorphosis fitting them for
nutrient purposes ; they are of no further use in the organism,
and, indeed, if retained, are highly injurious to it. Hence
they are destined to be, once for all, separated, or excreted
from it, and to be, as soon as possible, entirely discharged from
the body. It facilitates this end, that they are chiefly crystal-
loid bodies, and therefore easily dialysable. It is proAuded,
moreover, that a very large proportion of the blood should
pass through the organs by which these substances are elimi-
nated, for the quantity sent through them in twenty-four hours
amounts to nearly 2000 lbs. (BroAvn-Sequard) ; so that all the
blood in the body, may pass through them 150 times in that
period. Lastly, the excretion of urine is continuous or in-
cessant.

The Kidneys.

The kidneys are two dense, firm, dark-red, solid, but fragile
glandular organs, situated at the back part of the abdominal
cavity, in the lumbar region, one at each side of the vertebral
column, on a level Avith the last dorsal and the tAA'o or three
upper lumbar vertebra?, and reaching from the eleventh rib
to near the crest of the hip bone. The right kidney, owing
to the proximity of the liver on that side, is about a rib’s
breadth loAver than th^ left. The kidneys are placed behind
the peritona?um, and are held in position by their bloodA'essels,
nerves, and the excretory ducts, called the nreters ; they are
likewise srrrrounded by an areolar tissue, Tisually loaded Avith
fat, forming the so-called adipose coat, Avhich, being a bad
conductor of heat, serves to preserve the temperature of these
organs. The shape of the kidney, is Avell known and charac-
teristic. Each is about 4 inches long, 2 AAude, and 1 thick ;
the left one is rather longer and thinner than the right. In
the male, each AA'eighs from d-s- to 5i ounces ; in the female, .
about ^ oz. less. The left kidney is generally about ^ oz.
heavier than the right. The AA'eight of the two glands together,
in proportion to that of the bodjq is about as 1 to 240. The
specific gravity of the kidney substance is 1050. Its chemical
composition is 7G per cent, of AA’ater, 15 of albuminoid sub-

k

1

STRUCTURE OF THE KIDNEYS.

367

stance, only 1 of fatty or resinous matter, which is chiefly
cholesterin, together with certain extractives, including inosite,
cystin, taurin, and xanthin.

If one kidney be atrophied or destroyed by disease, the
other one usually enlarges. In certain cases, the kidneys are
joined by a t:-ansverse portion of gland substance, the upper
border of which is generally concave, the resulting mass form-
ing the so-called horseshoe kidney. The two conjoined
kidneys are sometimes found on one or other side of the lum-
bar region, or even in the pelvic cavity. A few instances are on
record, of the presence of three kidneys, the third gland,
usirally called a movable or Jloating kidney, being placed
either on one side of the vertebral column, or in front of it, or
else in the pelvis.

The upper end of each kidney is surmounted by the cor-
responding supra-renal body. Its internal concave border
presents towards its middle, a deep longitudinal fissure, called
the hilns, which leads into a cavity within the organ, named

Fig. 109.

Fi(r. 109. Diagram of a longitudinal section of the kidney. 1. Cortical
substance. 2. A pyramid. 2'. Mammilla or papilla of a pyramid, lying
in its opened calyx. 3. Portion of ureter expanding above into the
pelvis of the kidney, then dividing into the infundibula, and afterwards
into the calyces.

the sinus. This gives exit and entrance to the bloodvessels,
absorbents, and nerves, and also to the ureter ; the renal or
emulgent veins hero lie in front, the ureter behind, and the
renal arteries between them.

3CS

SPECIAL PHYSIOLOGY.

The kidney is everywhere closely invested by a proper firm,
smooth, fibrous coat, which may be readily torn off; it is,
however, connected Avith the gland substance, by numerous fine
fibrous processes and vessels ; it passes in at the hilus, lines
the cavity of the sinus, and is even reflected on to the ureter
and bloodvessels.

On making a longitudinal section of the kidney through
the hilus, the solid gland substance is found to consist of an
outer cortical portion, and of a deep-seated medullary portion.
The cortical substance is continuous over the whole organ,
and dips in betAveen the different parts of the medullary
portion, Avhich is disjDOsed in a series of conical masses. The
cortical substance is about 2 lines in thickness, and forms about
^ of the entire gland. It is of a reddish colour, soft, granular,
and friable, and contains a number of little round dark-red
spots, Avhich indicate the position of certain minute bodies,
named the Malpighian corpuscles of the kidney. The conical
masses of the medullary substance, from fifteen to tAventy in
number, form the so-called pyramids (Malpighi). Their bases,
turned toAvards the surface of the kidneys, and also their sides,
are encompassed by the cortical substance ; but their apices
are turned toAvards the sinus, in the interior of the organ,
where they form little eminences, called the papillae or
mammillae. The substance of the pyramids, is firmer and
darker than the cortical substance, and, as seen on a section, is
striated from apex to base, the latter part being much darker
than the former.

Outside the hilus, the iireter presents a funnel-shaped dila-
tation, or membranous cavity, called the pelvis of the kidney,
which, as it passes into the sinus, divides into three tubes,
named the infundibula', these again subdivide into from seAmn to
thirteen smaller, also funnel-shaped, tubes, called the calyces,
Avhich surround, or embrace, the papillie. One calyx often
includes tAvo, or even three, papiUtn, so that they are usually
feAver in irumber than the latter.

The cortical and medullary substances are both composed
of minute closely packed tubules or ducts, the tubuli uriniferi,
Avith bloodvessels, absorbents, and nerves, held together by a
soft material of ill-defined structure. The latter is described
as consisting of a very fine, scarcely recognisable, areolar tissue
or stroma, more evident in the medullary portion, but forming,
at the surface of the kidney, a thin layer beneath the fibrous
coat ; a parenchyma is also described by some. The different

THE MALPIGHIAN CORPUSCLES.

369

appearance of the cortical and mednllaiy substances, de-
pends on the different aiTangement of their ducts and blood-
vessels.

In the cortical portion, the tubuli uriniferi are very nu-
merous, much convoluted, and inosculate freely with each
other ; they are, on an average, about -g^th of an inch in
diameter, and are kno^vn as the tubes of Ferrein. They gene-
rally commence by free closed extremities ; sometimes, how-
ever, they anastomose together, forming loops ; many are said
to begin as minute purse-like dilatations, which form little
partial capsules around the Malpighian corpuscles (Bowman) ;
nearly all are somewhere connected Avith these capsules.
In the pyramids or medullary substance, the tubuli quickly
unite together many times, dichotomously or by twos, and,
becoming larger and straight, constitute the so-called ducts of
Bellini ; these form tapering bundles, directed to the papillae,
or apices, of the pyramids, on which they open by minute
round orifices. It has been estimated that there are as many
as two millions of tubuli in each kidney ; that the number of
orifices in a square line of a papilla, are 100 ; and that there
are from 300 to 500 on the surface of a single papilla (Krause)
The straight tubuli are widest near their orifices, measuring
from -^-sTyth to :j-^th of an inch ; they caitse the striated
appearance of the pyramids. The uriniferous tubules are
composed of a transparent basement membrane, lined with a
thick polygonal, or spheroidal, glandular epithelium, Avhich
occupies about two-thirds of the diameter of the membranous
tube. The epithelial cells have very delicate walls, a roundish
nucleus, fine granular albuminoid contents, and occasional fat,
pigment, and other particles. This epithelial layer is con-
tinuous with that covering the free surface of the papillo3. In
the coldblooded Vertebrata, it is, in parts, provided with cilia.

The Malpighian corpuscles of the cortical substance, are
placed either at the free closed extremities of the convoluted
tubuli, or in the course of the loops Avhich these occasionally
form. These little l)odies, the glomeruli of Kuysch (IGGO), are
spheroidal, and measure about -j-^th of an inch in diameter.
Each is composed of a rounded, close coil of minute vessels,
which projects, like a little ball, into one of the capsules of the
tubrdi. It appears that a minute branch of the renal artery,
named an afferent vessel, reaches each Malpighian body, and,
dividing into superficial coiled branches, forms a globular
network ; from the centre of this, an efferent vessel arises, and

VOL. II. II II

370

SPECIAL PHYSIOLOGY.

leaving the corpuscle, forms, with the efferent vessels from
neighbouring corpuscles, a dense vascvalar plexus, which sur-
rounds the contiguous tubuli. According as the capsule of
the Malpighian corpuscle, is formed at the commencement, or
on the side, of a tubule, it is said to be lateral or terminal.
At the mouth of the capsule, the spheroidal epithelium of the
tubule loses its character; for within the capsule, the epithelium
is squamous and remarkably thin. It is said by some, to be
continued over the surface of the Malpighian corpuscle which
projects into the capsule (Gerlach, Isaacs). But according
to Bowman, the corpuscle lies naked in the capsule, ■without
any such covering, the afferent and efferent vessels being
supposed to perforate the capsule. These vessels enter and
pass out at nearly the same part of the corpuscle, which is
there attached to its capsule. According to some observers,
the efferent vessel is alvvaj^s narrower than the afferent one,
and hence has arisen the idea that the blood is checked, or
held back, in the coiled vessels of the corpuscle. The central
vessels of the corpuscle, are, by some physiologists, regarded as
capillaries, and the efferent vessel as a vein, which then breaks
up to form the fine plexus around the adjoining tubule — an
arrangement supposed to represent, on a veiy minute scale, a
renal portal system. But all the coiled vessels, and even the
efferent vessel of the Malpighian corpuscles, are, by others,
considered to be arterial, the whole forming a microscopic rete
mirabile, which ultimately, by the efferent vessel, ends in a
true capillary network around the tubules.

The renal or emulgent arteries, right and left, spring fi'om
the sides of the aorta ; they are short, and very large for the
size of the kidneys, being out of proportion to the mere
nutritive necessities of these organs. They soon divide into
four or five branches, Avhich pass between the pyramids, and
are partly distributed, in the form of nutrient vessels, to the
cortical and medullary substances, and to the common coat of
the kidney ; but they chiefly terminate in the Malpighian
corpuscles, or in the fine vascular network which surrounds
the tubuli. The veins accompany the arteries, and end, for
each kidney, in a single large renal or emulgent vein, which
joins the ascending vena cava. The lymphatics are numerous,
and consist of a superficial and deep set. The renal nerves
are small but numerous, and may be traced even on to the
afferent arteries of the Malpighian corpuscles ; but their mode
of termination is unknown. They are derived from the sym-

ACTION OF THE KIDNEYS.

371

j)athetic nerves found on the renal artery, and from the lesser
splanchnic nerve.

The ureter, its pelvis and calyces, are composed of an ex-
ternal fibro-elastic coat, continuous with the proper capsule of
the kidney ; of a muscular layer, which consists of external
longitudinal and internal circular fibres ; and o-f a mucous coat,
continued on to the papilliE, and lined with a spheroidal
epithelium. The ureters, in animals, contract slowly on the
application of galvanism or other stimuli ; sometimes they
act rhythmically. Their lower ends enter, at each side, the
Hindus or base of the urinary bladder, penetrating its coats
obliquely, and opening into it, by a narrow elongated orifice,
so guarded by muscular bundles, that the reflux of urine into
them is prevented.

Action of the Kidneys.

The purpose of the enormous number of uriniferous tubes,
is, as in glands generally, to increase the extent of secreting
or excreting surface, within a given space. It has been calcu-
lated that the total amount of smrface in the coiled tubes in
each kidney, exceeds forty-four square feet ; and to this must
be added, the excreting surface of the straight tubidi as well
(Vierordt). The Malpighian bodies are quite pecidiar to the
kidneys, these little vascular coils, projecting into a duct,
having no resemblance to the solid sacs which bear the same
name in the ductle.ss gland, the spleen. So special a structure
has doubtless some special office. Since these bodies have been
shown to project into the tubuli, at or near their commence-
ment, it has been conjectured that they separate from the
blood the greater part of the water of the urine, and that then,
the inspissated blood which passes from them by the efferent
vessel, enters the vascular plexus around the tubuli, and yields
to the spheroidal epithelium, the proper solid constituents of
the urine, which are thence excreted into the tubules them-
selves, and are washed away out of those canals, by the watery
exudation descending from the Malpighian corpuscles. The
naked condition of the glomerulus, and the squamous character
of its epithelium, are fitted for a simple process of transudation ;
whilst the spheroidal epithelium of the tubuli is adapted to a
true excreting office, though the walls of the tubuli niu.st like-
wise excrete a little water. It is impo.ssiblo to deny, more-
over, that the glomeruli have also a true excreting office. It
is now believed to be certain, that all the blood of the renal

II u 2

372

SPECIAL nrXSIOLOGY.

arteries, goes through these Malpighian corpuscles, before it
reaches the tubules, and if it then becomes inspissated, the
blood which circulates around the tubules, may be compared
to the portal blood of the liver, being, as it were, venous blood
highly charged with materials destined to be sepai-ated from it.
In support of the view that the Malpighian corpuscles separate
the Avater, it has been urged that in Birds and Eeptiles, in
which the urine is partly, or almost entirely, solid — though in
the Amphibia and Fishes, loAver in the scale, it is again fluid —
these bodies, though numerous, are remarkably small. l\Iore-
over, the analogy of the minute vascular arrangements Avithiu
the kidney, Avith a portal system, is thought to be faA'oured
by the fact that, in Reptiles, a branch from the hepatic portal
vein is distribirted to the kidney.

That some, at least, of the peculiar constituents of the urine,
of Avhich urea, uric acid, creatin, and creatinin are the chief,
exist preformed in the blood, is certain ; for the tAVO latter
are found in it, in considerable quantity, urea in smaller
quantity, and uric acid perhaps only as an exceptional ingre-
dient. It has been suggested that the urea and the other
crystalloids present in the inspissated blood, may pass, by SAvilt
dialysis, into the aqueous contents of the tubuli ; but though
these substances, and urea especially, are highly dialysable,
yet such a physical exjjlanation of their separation from the
blood, Avould not account for their special appearance in the
renal excretion, rather than in any other, or, for the quan-
tity eliminated from the system in a given time, considei-ing
hoAV minute is the normal proportion of urea, and hoAV much
less that of uric acid, in the blood. It is, indeed, impos-
sible to deny that the spheroidal epithelial cells of the tubes,
have a special affinity for the proper urinary constituents ; or,
and this may be of more moment in explaining their appear-
ance in the urine, that some of these substances are formed by
the special metamorphoses of other materials Avithin these cells.
In the former case, the cells would merely select the urinary
constituents fi'om the blood, and transmit them into the tubuli ;
in the latter, they Avould, in addition, be the seat of special
chemical decompositions. In the first case, for e.xainple, they
might be sujAposed to sejiarate pre-existing Tii-ea from the
blood, but, in the latter, to metamorphose creatin or creatinin
into urea. Indeed, after extirpation of the kidneys — an
operation Avhich animals Avill outlive a fcAV days — the blood is
not found to contain much urea, but to be rich in nitrogenous

KATE OF THE RENAL EXCRETION.

373

extractive matters, which include creatin and creatinin. More-
over, if the ureters be tied, so tliat tlie escape of the urine
from tlie excreting structure of the kidneys, is at first hindered,
and at last prevented, urea is found in great abundance in the
blood, as if its formation had gone on in the spheroidal epithe-
lial cells, and it had been duly excreted, but then reabsorbed,
or else had been absorbed from those cells directly into the
blood.

It is further supposed that the smaller relative diameter of
the efferent vessels of the glomeruli, and the unusual blood
pressure in the renal arteries, may have an influence in the
excretory work of the renal apparatus. By some, it is
thouglit, that a selective or metamorphic power of the cells, is
indicated by the fact, that uric acid salts are actually seen, in
the cells lining the straight tubuli, in the kidneys of Birds.
Wliilst the products of the decomposition of the tissues, are
passing from the inspissated blood of the vascular ple.xus upon
the tubules, into the epithelial cells, some of the thin watery
fluid witliin the tubes, is reabsorbed by those vessels, and thus
the renal blood partly regains its fluidity, whilst the urine
becomes more concentrated.

Under e.xcessive pressure in the arterial blood-columns of
the kidneys, as, e.g. when the aorta is tied below the points
of origin of the renal arteries, albumen appears in the urine.
The same event happens from obstruction of the renal ducts or
vessels, or from the pressure of tumours upon them. This is
not a dialytic process, albumen being a colloid substance, and
difficult to dialyse; but it is probably an example of simple
porous diffusion or filtration. In acute inflammatory condi-
tions, fibrinous exudations from the blood, form in the tubuli,
and appear in the urine, as minute coagula or casts.

The urine excreted into the tubuli, urged on by the vis a
tergo of a constant process of excretion, escapes from their
orifices into the calyces. From these, it descends along the
infundibula, the pelves of the kidneys, and the ureter.s, into the
bladder, partly by gravity, and jwobably partly propelled by
tlie rhythmic peristaltic actions ofthemuscularcoatoftho.se
canals. Accumulated in the bladder, it becomes further con-
centrated by ab.sorption of water, and is mixed with mucus
from the ducts and from that viscus.

The constaneg and the great rapidifg of the excretion of
urine, have been observed in cases of malformation, known as
inversion of the bladder, in which the lower part of the ab-

3T4

SPECIAL PEYSIOLOGT.

domen and the anterior portion of the urinary bladder are
defective, so that the fundus of this organ, into which the
ureters open, is exposed. Under ordinary circumstances, the
urine is seen to flow in drops, from the mouths of the ureters ;
but, after drinking freely, it runs in little streams.

The urinary excretion is affected, both in quantity and
quality, by the nervous system. Thus, it is increased in
quantity, and lowered in quality, by hysteria, fear, and other
mental emotions, this effect being probably due to dilatation
of the renal arteries. Injury of the spinal cord, affects the
urine, chiefly causing a great development of carbonate of am-
monia and the precipitation of phosphates, owing, it appears, to
congestion and inflammation of the bladder, with an increased
secretion of mucus from it. Complete removal of the brain
and spinal cord, in animals, does not much affect this excre-
tion.

The walls of the bladder chiefly consist of layers of un-
striped muscular fibres, collected into bundles, arranged like
figures of 8, on- the iront, back, and sides of the organ. Some
of these, surrounding the neck, act like a sphincter ; the others
form detrusor, or expellent muscles. The act of emptying the
bladder, requires the simultaneous relaxation of the one, and
the contraction of the other set. These are usually reflex acts,
excited directly by the accumulated fluid, or by some irritation
of the nervous system. The act of expulsion is aided by the
contraction of the abdominal walls.

The Urine.

The daily quantity of fluid excreted by the kidneys of an
adult healthy man, varies from 30 oz. to 80 oz. ; but, on an
average, it has been estimated at about 50 oz. This quantity
varies according to the amount of fluid taken in the food and
as beverage, the activity of exhalation by the skin and lungs,
and the amount excreted by the intestinal canal. More fluid
is excreted by the kidneys in winter than in summer, the
skin being less active in the former, and more so in the latter,
season. The quantity is said to be increased under higher
barometric pressure. The specific gravity of the urine, differs
much, not merely according to the different proj^ortions, but
also according to the different nature of its solid constituents;
in health, it may range from 1015 to 1030; usualljq however,
it deviates only slightly from 1020. The urine excreted after

CONSTITUTION OF THE URINE.

375

drinking much water, and taking little or no food, which is
named urina potus, is of course of low specific gi-avity ; that
after eating a full meal, is of high specific gravity, and is called
urina cibi vel chjli\ Avhilst after complete abstinence from both
food and drink, as in the morning, it is most completely satu-
rated with solid constituents, and is therefore at its highest
specific gravity ; it is then called urina sanguinis. The
amount of solid constituents, is irrespective of that of the
fluid, and depends on the activity of the metamorphosis of the
tissues, and of the superabundant food. Its usual bright amber
colour varies, according to its density, from that of a colourless
fluid to a deep yellowish brown. In disease, the colour and
specific gravity, present important variations ; thus, in Bright’s
disease of the kidneys, th-e specific gravity may be as low as
1003, being little higher than that of water ; its proper con-
stituents are then deficient, whilst albumen, derived from the
plasma of the blood, is present ; on the other hand, in diabetes
mellitus, in which the urine contains sugar, the specific gravity
may be as high as 10.50. The peculiar odour of the urine, is
strongly developed by a heat sufficient to produce evaporation.
The natural reaction of this fluid, is acid, but after digestion,
and especially after a vegetable diet, it may become aUcaline ;
in herbivorous animals, this is its normal character. The
cause of its acidity, will be discussed after its chemical compo-
sition has been described. From a particular kind of decom-
position, kno%vn as the acid fermentation, its acidity may be
increased, after it has been excreted ; on the other hand, by a
decomposition of the urea, in which carbonate of ammonia is
generated, it may acquire a strong alkaline reaction a few
hours after its excretion, or even, in certain diseases, whilst it
is yet retained in the bladder. In such a condition, an ab-
normal deposit of phosphates takes place.

Normal urine consists of water, holding a very variable
quantity — viz. from 2 to 7 per cent. — of solid substances, of
which urea is the chief; besides this, there are uric and hip-
puric acid.s, free carbonic acid, often, lactic acid, occasionally
oxalic acid, extractive nitrogenous matters, partly crystallisable,
such as creatin and creatinin, xanthin, phenylic, carbolic, ben-
zoic and other acids, uncrystallisable extractives of uncertain
composition, small qirantities of special pigments, traces of
fatty matter, numerous salts, such as sulphates, phosphates and
chlorides of potash, soda, lime, and magnesia, with silica,
nuicus, and epithelium. The relative proportions of its various

376

SPECIAL PHYSIOLOGY.

solid constituents in 100 parts, and the daily average quantity
of each, excreted for every 1 lb. weight of the body, in a
man weighing 145 lbs. avoirduj^ois, are shown in the annexed
Tables.

Daily quantity for \lb. weight of body substance, in a Man of I45Ws.

weight (Parkes).

Water

. 2'9 drachms.

Urea .......

. 3'53 grains.

Uric acid ......

. -059

>>

Hippuric acid ......

. -237

))

Creatin .......

. -032

))

Creatinin ......

. -048

))

Colouring matter, and other extractives .

. 1-062

))

Sulphuric acid .....

•214

Phosphoric acid .....

. -336

>»

Chlorine .......

. -875

>♦

Composition of 100 parts of the Solid Constituents (Lehmann).

Urea .......

. 49-68

Uric acid ......

. 1-61 grains.

Extractives ; Creatin, Creatinin, Hippuric

1 28-95

acid. Salts of Ammonia, Chloride of Sodium

>>

Alkaline sulphates .....

. 11-58

Alkaline phosphates ....

. 5-96

Phosphates of lime and magnesia

. 1-97

ii

The water of the daily urine, equals about one-half of that
taken into the stomach ; supposing the total quantity of the
excretion to be from 30 to 50 oz., the water Avould be from
28 oz. to 47 oz. The solid constituents amount to from 2 oz.
to 3 oz. in the twenty-fonr hours.

The urea is by far the most important and characteristic
substance, amounting to upwards of an ounce, or half the solid
constituents, in 24 hours, or, according to some estimates, to as
much as 500 grains. Its atomic composition, CH^N,0, corre-
sponds with that of carbamide, COII4N2, and also Avith that
of 1 atom of hydric cyanate of ammonia, viz. CNOH-f-NHg.
It is readily transmutable, by the absorption of the elements
^ of two atoms of Avater, into carbonate of ammonia, one atom
of Avhich contains C05-1-2(N1I^). Urea is thus obtained:
evaporate cautiously a considerable quantity of Airine to the
consistence of syrup ; to this, add sloAvdy its bulk of nitric
acid, AAdien certain crystals are throAvn doAvn, Avhich are nitrate
of urea ; dry these upon a filter, decolorise them by dis-
solving them in Avater, and boiling Avith animal charcoal, and
recrystallise ; once more dissolve tlie crystals, and noAV sepa-

SOURCES OF THE UREA.

377

rate the nitric acid, by means of carbonate of baryta. On
evaporating the solution, a pasty substance is left, from which
alcohol dissolves out the urea, and the filtered solution yields,
on evaporation, pure crystals of this substance. These cry-
stals are long, colourless, four-sided prisms, extremely soluble
in hot, and even in cold, water ; hence urea never enters into
the composition of ui’inary sediments or calculi. It dialyses
most actively. It is neutral in its reaction to test paper ; but
it acts as a base, combining with acids to form definite salts.
As hydric cyanate of ammonia is identical in composition,
crystalline form, and chemical properties, with urea, and as
the former substance can be made in the laboratory, it affords
an example of the imitation of an organic compound, by
artificial means (Wohler). Urea contains 46'7 per cent, of
nitrogen, together with 20 per cent, of carbon. One ounce,
taken as the ordinary daily excretion, contains about 220
grains of nitrogen.

The sources of the urea, are evidently nitrogenous organic
compounds, which have undergone decomposition by partial
oxidation. It constitutes the highest product of oxidation of
the albuminoid and gelatinoid substances in the body. It
is derived, partly from the tissues, but partly from the food,
merely assimilated into blood ; not, as was at one time sup-
posed, from the tissues only. This is proved by many facts.
Thu.s, the urea is always increased after meals, especially about
three or four hours after the food is taken. In animals fed on
too httle nitrogenous food to counterbalance the waste of the
albuminoid tissues, more urea is given off than the nitrogen
in the food would form ; when the waste is just compensated
for, then the urea is erjual to the nitrogen in the food ; lastly,
when an excess of nitrogenous food is given, the weight of
the animal increases, and, after a time, an excess of urea is
eliminated. Urea is still excreted, even in starving animals,
though in smaller quantity than usual ; it is increased by
feeding them on a vegetable diet containing nitrogen, espe-
cially on bread and beans; its quantity is still greater, on a
mixed vegetable and animal diet, but it is greatest of all, on an
exclusively animal diet. In a dog weighing 30 kilogrammes,
the daily excretion of urea, with a pure animal diet, varied
from 150 to 180 grammes — that is, it equalled ij J^th or x'j^th
of the weight of the body. In Man, with an exclusively animal
diet, the daily riuantity excreted was found by Lehmann to be
about 820 grains, with a mixed diet 500 grains, with a vege-

378

SPECIAL PHYSIOLOGY.

table diet 347 grains, and with a completely non-nitrogenous
diet 237 grains. The researches of Dr. E. Smith, confirm
these results, and further show that an animal diet increases
the excretion of carbonic acid from the lungs. In other ex-
periments, the quantity excreted daily, on a superabundant
animal diet, was‘ found to be nearly .3 pz. ; on a moderately
animal diet continued for ten days, from If to 2 oz. ; and
after a diet of sugar, prolonged for four days, the daily quan-
tity of urea was rather less than oz. Not only, then, is
urea formed largely from the food, but chiefly so, the quan-
tity derived from the tissues, as above shoAvn, when a non-
nitrogenous saccharine diet was taken, being less than half the
ordinary daily amount. Sometimes even more is eliminated
during a total abstinence fr’om food, as if, in the latter condi-
tion, an animal maintained its temperature by waste of its
nitrogenous tissues.

In the female, from her smaller frame, her less active
nutrient metamorphoses, and the smaller quantity of food
consumed, the daily quantity excreted is about f of an oz.
Proportionally to the weight of the body, it is less abundantly
formed in women ; but children up to seven years old, excrete
about twice as much urea, proportionally, as adults, and in-
fants more than children ; in old age, the relative amount is
diminished. The effect of age, depends upon the diminished
activity of the nutritive functions, and the smaller quantity of
the food. Exercise was formerly believed to increase the
quantity of urea, and rest to have the opposite effect ; but re-
cent observations show that the immediate effect of exercise
is to diminish the excretion of tuea, though towards the end
of labour, and especially in the period of re.st afterwards, it
is greatly increased. Gelatin, which seems never to be di-
rectly assimilated by the tissues, but rather to save them from
oxidation, is readily, perhaps directly, converted into urea.
Water, especially if taken with food, causes au increase in the
ureal excretion, and also in that of the saline constituents of
the urine. Diminished temperature and increased barometric
pressure, are said to increase the quantity of urea. In most
cases, the urea is not eliminated xmtil some hours after its
actual formation in the system, or until the determining cause
of its increase, has taken eflect. The quantity excreted is
greater during the day than in the night. Common salt, phos-
phoric acid, theobromine, urea itself, uric acid, and cantha-
rides, are found to increase the amount of urea excreted, whilst

UltIC ACID.

373

tea, but especially coffee, alcohol, turpentine, and digitalis,
diminish it. It is remarkable that such large quantities of
nitrogen and carbon, are eliminated from the .system in the
form of ui’ea — a comparatively inactive chemical substance ;
whereas carbonate of ammonia, a compound readily produced
from the elements of urea, and an extremely irritating and
noxious substance, is not formed in quantity, in the ani-
mal economy. In certain diseases of the kidneys, the urea
is not excreted, but, the blood becoming vitiated, uraemic
poisoning occurs, characterised by symptoms, such as convul-
sions and coma, referrible to the nervous centres, and often
fatal. It was formerly supposed that the urea itself is the
toxic agent, but possibly it is the carbonate of ammonia de-
rived from the decomposition of the urea. In these cases,
ammonia is found in the breath, and, after death, in the
blood ; the injection of that substance into the veins of an
animal, also causes similar symptoms. A dilute solution of
urea, to which a small quantity of mucus or other animal
substance is added, readily ferments, and, evolving a pungent
odour, forms carbonate of ammonia ; this kind of fermentation
may take place very rapidly, even within the bladder. The
amount of irrea increases in all those diseases which are ac-
companied by an increase of tissue change, such as active
inflammation of the lungs, or of the membranes of the bi-ain,
and in fevers generally, even though less food and exercise are
taken than in health. In fever, the quantity has been found
to be double the ordinary amount, viz. 1065 grains daily ; in
pyEemia, it has reached 1235 grains (Vogel and Warnecke).
During recovery, the quantity excreted falls for a time, al-
though more food and exercise are taken.

U ric acid is found not only in the imine, but also in the blood,
and in mo.st organs of the body. It contains 33'3 per cent,
of nitrogen, and has the following composition : CgH^N^Og;
it is therefore regarded as resulting from a less complete oxida-
tion of the nitrogenous compounds of the food and of the body,
than that which produces urea. The formation of urea in the
system, is supposed, by some, to be normally preceded by that
of uric acid. The former may be easily produced from the
latter, by processes in wdiich oxidation forms a part ; when an
I alkaline urate is digested with portions of liver, at a certain

I temperature, urea is formed at the expense of the uric acid.
Animals to which uric acid is administered with the food,
excrete an unusually large quantity of urea. Some of the

380

SPECIAL PHTSIOLOGY.

products of the metamorphosis of the muscular tissue, such
as creatin, xanthin, and sarcin, have affinities with uric acid.
Lastly, in a state of rest, the quantity of uric acid excreted,
increases, whilst the urea ultimately diminishes, the reverse
being the case from exercise.

The quantity of rn-ic acid excreted daily, has been esti-
mated at from 8-^ to 15 grains ; but this, like the quantity of
urea, varies very much, most markedly according to tlie amount
of nitrogenous food which is taken, and less so according to
the age and sex. Its quantity is lessened by exercise. With
animal diet, its quantity is said to be 4'5 grains, and Avith
vegetable diet, only about 1'5 grain daily (Haughton.) In
the urine, it is either combined Avith soda, forming the urate
of soda Avhich is held in solution, or else it is dissolved
by the alkaline phosphate of soda. Being less soluble than
its salts, uric acid is quickly precipitated by acids, and more-
over, being itself less soluble in cold than in Avarm Avater, it
is commonly precipitated from normal urine after cooling.
This may be partly from the diminished solvent power of the
cooler Iluid, and partly from the occurrence of the lactic acid
fermentation. Uric acid is then precipitated and deposited,
either in an amorphous poAvder, or in fine crystals of pecu-
liar forms, often tinged with colouring matter. Tlie crystals
are sometimes little flattened rhomboids, sometimes they
resemble a coffin or a barrel, and sometimes they are almost
spherical. It forms the most common urinary sediment, and
tlie most frequent kind of renal or vesical calculus or stone
in the kidney or bladder. Hence it is also named lithic acid
{\iOoQ, a stone). Urate of soda constitutes the solid urinary
excretion of Serpents, and is also present, in large quantity, in
the Avhite pasty portions of the dejecta of the flesh and .fish-
eating Birds, such as the haA\drs and oavIs, the penguins and
other sea-birds. Hence it exists in large quantity in guano.
It may be obtained pure from human calculi, or from the solid
excretion of the serpent, by dissolving the urate in those sub-
stances, in a hot solution of caustic potash, and reprecipitating
it irom the filtered fluid, by means of another acid. The pre-
cipitate is a white poAvder, composed of colourless rhomboidal
scales; it is almost insoluble in cold Avater, and only slightly so
in hot, and is absolutely insoluble in alcohol and ether ; it is
soluble in alkaline solutions, and very readily in solutions of
lithia. Fi-om all these solutions, it is immediately repreci-
pitatcd, even by feeble acids. Heated nearly to dryness Avith

HirrURIC ACID.

381

nitric acid, uric acid turns red, and, on the addition of auuuo-
nia, a beautiful purple substance, named murexkl. is formed, a
reaction Avhich constitutes a test for uric acid. The fact that
uric acid is a less perfectly oxidised compound than urea, ex-
plains, perhaps, its formation in excess under certain conditions,
as, e. g. udien the quantity of tissue metamorphosed, or the
quantity of food taken, is greater than the supply of oxygen can
convert into urea, as, e.g. in acute inflammations, rheumatis^m,
and gout, in all Avhich diseases, large quantities of uric acid
deposits, or of urates, are thrown down from the urine, which
is loaded at critical periods, after the climax of the attack. At
the onset of the gout, the uric acid sometimes nearly, or en-
tirely, disappears from the urine ; it may then be detected in
the blood. The gouty concretions, known as chalk-stones, are
composed of urate of soda, with ti-aces of urate of lime. When
in acute inflammatory di.sease, the uric acid is increased, the
urea is simultaneously diminished. In diseases of debility, this
acid is usually diminished in quantity ; it may also be reduced
by a spare diet, the avoidance of acids, the use of large quan-
tities of water, open-air exercise, so as to ensure the perfect
oxygenation of the blood, and by all measures tending to
increase the action of the skin, such as exertion, friction, baths,
especially hot-air and water baths, and warm climates. The
use of tobacco augments its excretion, whilst quinine and
alcohol lessen it. Alkalies assist in its excretion.

Ilippuric acid {'imroc, a horse), first detected in the urine of
the hor.se, is also constantly present in human urine, sometimes
amounting to as much as 15 grains in twenty-four hours; it
has often been overlooked (Liebig). It crystallises in four-sided
prisms, and has the atomic composition, C9II9NO3, so that it
is neither so nitrogenous nor so completely an oxidised body
as urea or uric acid, but contains a larger proportion of car-
bon than either substance. Benzoic acid and other benzoyl
compounds, also oil of bitter almonds, and succinic and other
allied acids, when taken internally, cause an excess of hip-
puric acid in the urine (Ure). To explain thi.s, it has been
suggested that benzoic acid, C7II6O2, combined with the bile
product, glycocoll, C2lI,9N02, is equal to one atom of hippuric
acid, and one atom of water. The source of the hippuric acid
ordinarily present, is not yet known. Its quantity is influenced
by the character of the diet, and by the amount of exercise;
it is increased by a purely vegetable diet, is lessened by a
mixed diet, and is dimini.shed still more remarkably in

382

SPECIAL PHYSIOLOGY.

those who are living on animal food only. According to some,
it is absent in persons who abstain from spices ; also in infants
at the breast, and in Herbivorous animals deprived of food.
In the last two cases, uric acid alone is produced, in the one
case, from the milk, and in the other, from the tissues of the
animal itself (Ranke). Hippuric acid is not only found in
large quantities in the horse, but also in other Herbivorous
animals ; and most of these consume grasses, in many species
of which, certain aromatic principles exist. In the Carnivora,
it exists in minute quantities. Although, most probably,
hippuric acid is commonly derived from certain aromatic
substances, yet it has been shown that its formation from
albuminoid bodies, is quite possible (Stiideler).

Very minute quantities of benzoic acid, and xanthin or
xanthic oxide, also exist in the urine, with traces of certain
volatile acids, phenylic, carbolic and taurilic, on which the
odour of this fluid may depend.

The creatin and creatinin found in the urine, are both
crystallisable nitrogenous bodies. The former exists in small
quantities, the latter amounts to about 1 5 grains a day. Crea-
tinin C4H7N3O + 2(HO), differs from creatin C^flgNgOo by
one atom of water. They are obtained by precipitation with
salts of zinc, and by the subsequent decomposition of the
zinc compounds. Creatin is a neutral substance, incapable
of combining either with acids or alkalies ; but creatinin
is a powerful base, having a sti'ong alkaline reaction, and
forming ciystallisable salts with acids. Creatin exists in large
quantities in the juice of muscle, from which it was first pre-
pared by Liebig. Creatinin is present only in small quantity
in the juice of flesh, but is readily formed by the action of
strong acids upon creatin. Creatin appears to be, with succinic
acid, a product of the decomposition of sjmtonin, whilst crea-
tinin results from still further decomposition ; from its basic
nature, it approaches in character to urea, into which sub-
stance, and sarcosin, it is decomposed by the action of baryta
at the boiling-point. Albumen may be broken up artificially,
by the action of powerful acids or alkalies, into glycocoll,
tyrosin, and leucin, nitrogenous bodies intermediate between
it and urea. By the action of caustic alkalies on creatin, urea
is formed, whether through the previous formation of creatinin
is not certain. Albumen, creatin, creatinin, and urea, form,
therefore, a descending series of nitrogenous bodies. Both
creatin and creatinin are more abundant in exercised muscles,

ACIDS OF THE URINE.

383

and, therefore, would seem to be products of muscular action ;
both substances are present, in small proportions, in healthy
blood, from which they are excreted, also in small quantit}',
by the kidneys. They are supposed to be transformed cliiefly
into urea, probably through the agency of the epithelial cells
of the uriniferous tubes, and, thus changed, finally enter the
urine. Creatin and creatinin, therefore, are compounds pro-
bably preformed in the body, i.e. in the muscles, thence enter-
ing the blood by venous absorption ; they are excreted from
it, in minute quantity, in their proper form, but chiefly after
conversion into urea. They are the principal immediate
soiurce of the last-named substance, which is even associated
with them, in the juice of the flesh of certain Cartilaginous
Fishes (Frerichs and Stiideler).

The colouring substance of the urine, urinary pigment or
uro-hffimatin, contains iron, and is separable into red, blue, and
yellow colouring matters, named uro-rhodin, uro-glaucin, and
uro-xanthin. Their nature is not well understood ; they
exist but in small quantity, and are very prone to decom-
position. According to some, these pigments are allied to
indigo, and its derivatives, indigo-red, indigo-blue, and in di-
can. The blue pigment, or uro-cyanide, is named the indigo
of urine.

The non-crystallisable extractive matters of the urine, exist
in large quantities, and require further investigation ; they
are nitrogenous bodies, some even containing sulphur and
phosphorus, probably derived from the albuminoid tissues;
they are liable to decompose, and are abundant in certain
diseased conditions.

Traces of mucus and epithelium, either of the spheroidal
glandular kind from the tubuli, or of the squamous kind from
the interior of the bladder, also occur, as cloudy deposits, in
this excretion.

There are also several non -nitrogenous, hydro-carbona-
ceous, or carbonaceous substances in urine. Thus, lactic acid,
CgllgOg, occurs occasionally, as, e.g. when that acid, or some
of its salts, are present in large quantity in the blood, owing to
feeble conditions of the respiratory process, or to defective
oxidating processes in the blood. By Lehmann, lactic acid
is sfiid to be constantly present, and to be the cause of the
acidity of the urine; but, by others, this is supposed to depend
upon free j)ho.sphoric acid, or, on an acid phosphate of soda,
or perhaps upon this acid, together with a minute quantity

SPECIAL PHYSIOLOGY.

381

of dissolved uric acid ; for it is difficult to suppose the exist-
ence of free lactic acid, so long as any alkaline urates are
present, and these latter salts may always be obtained by the
quick evaporation, in vacuo, of perfectly fresh urine. The
acidity of the urine, gradually diminishes for from three to
five hours after a meal, and sometimes the excretion becomes
actually alkaline. This effect occiU'S simultaneously with the
development of the large quantity of acid in the gastric juice
poured out for the digestion of the food ; whilst the return of
the irrine to its acid condition during fasting, corresponds
with the cessation of the formation of acid in the stomach.
This temporary diminution in the acidity of the urine, or its
positive alkalinity, is most marked when animal food is taken,
which requires more acid to digest it ; with vegetable food, it
is less so ; with mixed diet, the effects are intermediate
(Roberts). The alkalinity of the urine after a vegetable diet,
and of that of the Herbivora generally, is not opposed to these
observations, and has another explanation. In such diet,
large quantities of neutral alkaline salts of the vegetable acids
are met with, which are converted in the alimentary canal, or
in the blood, into carbonates; the quantity of albuminoid
food or tissue metamorphosed, is so small, as not to yield enough
sulphuric and phosphoric acid, to neutralise this alkali. The
urine is also often alkaline in gastric disorder. In the Carni-
vora, ammonia acts the part of a base to the acids of the urine,
instead of the fixed alkalies.

Oxalic acid, C2O3-I-H2O, also occurs in the urine, especially
after eating fruit, which contains organic acids, also after drink-
ing fluids containing free carbonic acid, and lastly, when the.
respiratory process is seriously disturbed. Any condition
which tends to overload the blood with carbonic acid, favours
the appearance of oxalic acid in the urine ; in children, it is
a frequent constituent, and, in combination with lime, forms
the comparatively common mulberry calculus. Lastljq car-
bonic acid itself is found in a state of solution, in the quite
recently discharged urine of both IMan and animals. Besides
this, the urine contains nitrogen, with traces of oxygen, and,
but only as a product of decomposition, sulphuretted hydrogen.

Minute traces of certain Jats, such as olein and stearin,
occur in urine. In certain cases, a fatty substance, probably
a mixture of ordinary fats, named keistin, appears as a scum
upon it ; and, in altered conditions of the kidneys, large quan-
tities of oily matter, rise up to the surface.

URINARY DEPOSITS.

385

The salts found in the urine, average about 1-8 part per
cent, of that fluid, though they vary extremely according to
the character of the food, and the amount of fluid ingesta ;
the latter increase their quantity. Of 100 parts of these salts,
the sulphates form 45 parts, the phosphates 24, and the chlo-
rides 23, the residue consisting of the salts of the organic acids.
The chief base is soda, next in order potash, then ammonia,
magnesia, lime, and lastly, in minute quantities, iron and
silica. Whilst most of these salts are derived directly from
the materials of the food, others undoubtedly proceed from the
metamorphoses of the tissues ; but even these are, of course,
ultimately derived from the food. The sulphates and phos-
phates of the alkalies, originate in the oxidation of the sulphur
and phosphorus belonging to the albuminoid substances found
especially in the muscular and nervous tissues ; the quantity
of these salts, is increased by exercise, which conduces .to
changes in those tissues. The earthy phosphates must also be
ultimately derived from the food, either directly, or through
tissue changes ; their quantity appears to increase, on the ad-
ministration of chloride of sodium. The chloride of sodium
itself varies in quantity, according to the amount consumed
with the food ; one office of the kidneys, is to regulate the
quantity of that salt retained in the blood. The ammonia of
healthy urine, occurs chiefly in the triple pliosphate of ammo-
nia and magnesia ; it is an ultimate product of the decom-
position of albuminoid substances, the creatin, creatinin and
urea being probably intermediate stages.

Under certain circumstances, amorphous or crystallised de-
posits, or sediments, are formed in the urine ; and sometimes,
even solid concretions, named urinary calculi or stones, occur
in it even within the body.

The most common sediment is of a yellowish or reddish
hue, and consists of mixed urates and uric acid, with some of
the colouring principles ; these, being less soluble in cold than
in hot fluids, may be precipitated from urine, clear at the time
of its discharge from the body. When turbidity exists at the
moment of discharge, or subsequently, though the urine be
maintained at the temperature of the interior of the body, the
condition must bo regarded as one deviating from health. But
a uric acid .sediment may be caused by an acid fermentation
of the urine, often a.ssociated with the growth of penicillium.
The acid then formed, usually lactic acid, decomposes the
urates in solution, and uniting with their base, whether soda

VOL. II. c c

I

386

SPECIAL PHYSIOLOGY.

or ammonia, precipitates the less soluble uric acid. The
coloured extractive matters may, through changes produced
in them by atmospheric action, increase the solvent power of
the fluid for the urates, and so prevent their precipitation in
tlie process of cooling. The quantity of uric acid sediment,
therefore, does not necessarily correspond Avith that in the
urine itself, for sometimes it may be precipitated, though ex-
isting in small proportion, and sometimes be suspended, though
present in larger quantity. If the uric acid compounds be
in excess, the temperature lowered, and a free acid be formed,
a deposit is sure to take place. In hot climates, the cutaneous
excretion is very active, a quantity of acid is thus remoAmd
from the system, and deposits of lithic acid are accordingly
rare. Phosphatic sediments are also occasionally met Avith,
owing to peculiar decompositions or fermentations, affecting
the urea, Avhich is then converted into carbonate of ammonia ;
by this, the earthy phosphates are precipitated, as ammoniacal
magnesian phosphate, or as phosphate of lime. This alkaline
fermentation occurs sooner or later, at certain temperatures ;
but in those diseases, in Avhich the urine is too long retained
in that viscus, and also in inflammation of the urinary mucous
membrane, it sometimes happens in the. bladder itself. This
form of alkalinity is to be distinguished fi-om that Avhich
depends on the presence of potash or soda ; in the latter case,
the blue colour given to litmus paper, is permanent ; whilst
Avith ammoniacal urine, it is fugitive, OAving to the volatility
of ammonia. The alkaline fermentation is probably induced
by the pus, or by the excess of mucus. The acid fermentation
is also believed to be excited by the mucus of the bladder. The
abundant sediments formed in the critical stages of fevers and
gout, are of the uric acid type. The fine iridescent film, fre-
quently seen on the surface of the urine, in dyspeptic and
neiwous diseases, consists of crystals of the triple phospate of
ammonia and magnesia. Prolonged mental effort is said to
cause an increase in the amount of phosphates ; but this is not
established by observation, although this condition does occur
in diseases of the nervous centres. The knoAvn existence of
phosphorus in the fatty matter of the brain, has doubtless
suggested this idea. Other morbid sediments consist of pus
and blood.

The concrete deposits named calculi, commence by the col-
lection of some crystallisable substance, around accidental
fibrinous or other masses Avhich may be minute, and ultimately

PASSAGE OF SEBSTANCES INTO THE URINE. 387

almost, or entirely, disappear. Upon such a centre of forma-
tion or nucleus^ successive layers of crystallised substance are
deposited in laminte or crusts, cemented together by traces of
mucus. The first layers deposited, often differ from those
■which follow, and sometimes the layers alternate, constituting
a composite calculus. The simplest calculi are those consisting
of a mixture of uric acid with rrrates, forming the uric or
lithic acid group ; they are generally oval, somewhat flattened,
smooth, or slightly rough, yellowish, and hard. The oxalate
of lime or mulberry calculi are, as their name implies, roughly
tuberculated, and brownish or black in colour ; they are very
hard. They contain some colouring substance derived from
the blood. The phosphatic calculi are either smooth on the
surface, opaque-Avhite, or white and semi-transparent, or else
finely crystalline, light and soft, so as, indeed, to be easily worn
by attrition, when two or more coexist in the bladder ; they
offer but little resistance to crushing instruments. They are
composed of the triple phosphate of ammonia and magnesia,
combined with some phosphate of lime. Other and rarer
forms of urinary concretions, are the carbonate of lime, cystic
oxide, and xanthic oxide calculi.

Many articles of diet, and medicinal agents, pass into the
urine entirely unchanged ; such are the alkaline chlorides,
phosphates, sulphates, and nitrates. Of these salts, chloride
of sodium acts especially as a stimulant to all the processes of
tissue metamorphosis, and herein may be found one of the
chief uses of this universal constituent in the fluids of all
animals. The carbonates of the alkalies, and the caustic
alkalies, produce, however, still more powerful effects. The
vegetable alkaloids, as qitinine, morphia, and strychnia, cer-
tain vegetable colouring substances, such as saffron and
rhubarb, and many odorous substances, as turpentine, garlic,
assafcetida, and valerian, likewise pass unchanged. Nitric,
phosphoric, and sulphuric acids also escape, combined with
appropriate bases derived from the blood ; sulphuric acid dis-
places phosphoric, and this latter acid, the feebler inorganic and
organic acids. Most substances, however, undergo a change
before they enter the urine. Thus, the organic acids, such
as lactic, but especially tartaric, citric, malic, racemic, and also
acetic acid, and their salts, do not reach the urine as such, but,
united with soda or potash, they are converted in the system,
into carbonates, whicli enter the urine. Hence, the alkaline
condition of this fluid, caused by succulent vegetable diet, and

c c 2

388

SPECIAL PHYSIOLOGY.

the alkaline urine of the Plerbivora. Again, as already men-
tioned, benzoic acid and the allied cinnamic acid, are first
converted into hippuric acid. Organic compounds containing
sulplnrr, produce sulphates in the urine. A great number of
substances, on being taken into the stomach, do not reappear
in the urine, such as ether, thein, calfein, theobromin, as-
paragin, amygdalin, musk, camphor, and certain colouring
matters, such as cochineal and chlorophyll. Alcohol, though
chiefly decomposed in the system, may partly appear in the
urine. Of the metallic salts, such as arsenic and antimony,
the bases of which can, of course, undergo no change in the
body, some appear with great facility in the urine; whilst others
enter that fluid with difficulty, or only in minute traces even t
after long periods of administration; such are gold, silver,
mercury, lead, bismuth, zinc, and iron. Alumina is absorbed
with difficulty, or not at all, hence it does not appear in the '
urine.

Water is eliminated with great rapidity from the kidneys. |
In large quantities, as already stated, it causes, by stimulating :
the excreting power of the uriniferous tubes, an absolute in-
crease in the amount of urea separated from the body ; though
relatively, owing to its dilution, a given quantity of urine
contains dess urea. The diminution in the quantity of urea
and uric acid excreted by the kidneys, caused by many agents,
such as coffee, tea, alcohol, . and tobacco, articles so Avidely
and instinctively adopted by mankind as dietetic substances,
has been explained, by supposing that they interfere Avith, or ''
retard, the metamorphoses of the albuminoid and fatty tissues,
and so preserve them from Avaste. In this Avay, Avhen taken |
in moderation, they conseiwe the strength. The action of !
creatin and creatinin, so abundant in beef-tea and beef-juice, ;
may be similar. Thein and caffein resemble those substances
very closely in composition.

The rapidity with which Avater and substances soluble in it,
pass into the urine, after being taken into the stomach, for-
led to the idea, that direct channels of communication,
passagesf or ducts, existed betAveen the stomach and the
Ifld-iieyel.or some other part of the urinary apparatus. !Many
ihvestigatjoha Avere undertaken, some even Avith pretended
sp.ccess,, for'j|l>ft.pi«:pQse of discovering such passiiges. No sucli
cjommunicatioijs)i Itawmea', exist. Soluble substances pass from
the stomach into the cincuiation, by venous absorjjtion, and
are then, after ti‘aversiug'»the lungs, convej’ed by the renal

* # #

BILE, SUGAB, AND ALBUMEN IN DIUNE.

389

arteries to the kidneys, in which, by porous diffusion or
dialysis, they enter the uriniferous tubules, and so reacli the
urinary passages. The rate at which this circuitous route
thi’ough the vascular system, from the stomach to the kidneys,
occurs, is adduced as one proof of the rapidity of the circulation
of the blood (p. 170). When the stomach is empty, after long
abstinence, the time is 1 minute; 4 hours after a meal, it is
2 minutes; 1-^ hoim after, 6^ minutes; 1 hour after, 14
minutes; and 25 minutes after, 16 minutes. If the test sub-
stance be taken with the food, it requires 40 minutes for it to
appear in the urine (Erichsen).

The affinity of certain sub.stances for the living tissues,
influences the rate of their passage from the stomach to the
kidneys, saline substances, for example, passing more rapidly
tlian colouring matters. The relative diffusibility of the sub-
stances, may also modify the result. Pigments pass but
slowly, indigo and madder requiring fifteen minutes, rhubarb
and biliary pigments twenty minutes, logwood and other
colouring matters, twenty-five minutes.

It has been seen that many substances, Avhich are formed
in, or belong to, the body, are liable to enter the urine, viz.
pus, fatty matters, certain biliary products, sugar, inosite,
leucin, allantoin, tyrosin, sarcin, htematin, fibrin, and albumen.
If bile be no longer separated from the blood in the liver,
or if its discharge by the alimentary canal, be prevented, it
may appear in the urine, as it will in any other secretion or
excretion ; this happens in certain organic diseases of the liver.
But, in the more common form of jaundice, the bile pigments
only pass into the urine, giving it a dark colour. The sugar
which appears in the urine in diabetes (p. 340), is not produced
in the kidneys, nor does its presence in the urine necessarily
imply disease of those organs ; a larger quantity than usual
being present in the blood, it escapes through the excreting
structure of the kidneys. Its increased amount in the blood,
depends on an abnormal action of the liver, or on the imperfect
oxidation of the sugar in the blood, through some defect in the
respiratory process. The transitory appearance of sugar in
the urine, is not of much consequence ; but its persistence in
diabetes, is serious. A minute trace constantly occurs in
healtliy urine, though it escapes ordinary te.sts (Brlicke).
Tlie presence of albumen in the urine, is important, especially

390

SPECIAL PHYSIOLOGY.

blood in the renal arteries. Thus, drinking enormous quan-
tities of water, has been known to produce temporary albu-
minuria or albuminous urine ; on the other hand, albumen is
sometimes met with in this fluid, after indulgence in very full
meals, or in cases where the heart’s action is materially
increased, or again, where the aorta is compressed below the
renal arteries, or from renal congestion or inflammation pro-
duced either by cold applied to the skin, or by the undue use
of diiiretics or irritants, such as the Spani.sh fly ; possibly, also,
by division of the renal sympathetic nerves (Krimer). The
occurrence of albuminoid matter after full meals, may be
accormted for, by the jmobable introduction into the blood,
under those circumstances, of more or less albuminose, which
has a higher osmotic tendency than albumen itself ; when in-
jected into the veins, it, indeed, appears in the urine. Again,
hgature of the aorta below the renal arteries, in animals,
or the forcible injection of blood through those vessels,
causes an artificial albuminuria. Persistent albuminous urine
indicates some degeneration of the excreting tissues of the
kidneys, usually consisting of the so-called granular de-
generation, or “ Bright’s disease,” the result of interstitial de-
posits of an albuminoid, fatty, or amyloid nature. In such
cases, the lateral pressure of the blood in the capillary vessels
of the kidneys, is increased, either by the obstruction of the
circulation through them, or as a result of the non-performance
of the ordinary excreting process. Besides the albmnen of
the blood, even the plastic fibrinous substance may exude
into the uriniferous tubules, and, becoming coagulated in their
interior, form, together with altered epithelial cells, or with
fatty matter, uric acid, blood or pus corpuscles, little cylindri-
cal masses, known as casts, which are washed out of the
tubes, and are easily detected in the urine by the microscope.
Sometimes, the casts consist only of basement membrane.
Bright’s disease may, however, exist without the presence of
albumen, in the urine.

To detect bile in the urine, Pettenkofer’s test is used
(p. 76). Sugar is detected by Tromuier’s cojDper test (p. 85),
or by boiling with liquor potassaa, which causes a deep brown
colour when sugar is present. Albumen is detected by boiling
the urine, and adding a few drops of nitric acid, to make sure
that the urine is not alkaline ; certiiin precipitates, caused by
heat, are then dissolved, but an albuminous precipitate remains,
as whitish or yellowish flocculi of coagulated albumen. After

THE KIDNEYS IN ANIMALS.

391

the continued administration of certain metallic poisons, such
as arsenic and antimony, their detection in the kidneys or liver,
may furnish the means of discovering crime.

As the blood is the most complex fluid proper to the body,
being the source of noirrishment to the tissues, and also the
medium through which the products of their metamorphoses
reach the excreting glands, so the urine is by far the most
complex of the animal excretions. Its peculiar ingredients
display important relations to the gelatinoid and albuminoid
principles of the body and of the food, the metamorphoses of
which, during the nutrition of the muscular and nervous sys-
tems, constitute, with those of the hydrocarbons and carbhy-
drates consumed in respiration and motion, the characteristic
chemical phenomena of animal life. They especially eliminate
nitrogen, but also a large amount of carbon, and some hydrogen.
The excretion of effete nitrogenous matters by the kidneys, may
be assisted by the liver ; but most of the nitrogenous fatty acids
of the bile, are reabsorbed. It is by the kidneys, that these
nitrogenous products of metamorphosis, are constantly being
removed ; and if their function be arrested, grave mischief
ensues. Ligature of the ureters is followed by an accumulation
of urea in the blood ; removal of the kidneys, by an increase of
the creatin and creatinin in the blood, and also, though to a
less extent, of urea, which is found in the serum ; a urinous
odour appears in many of the secretions. In the urfemic
poisoning, which depends on disease of the kidneys, the urea,
ceasing to be excreted through them, is detectible, in large
quantities, in the perspiration, and also in the vomited matters.
The urea itself, or the carbonate of ammonia resulting from its
decomposition, then easily detected in the breath, circulates
through the brain and spinal cord, and causes imperfect respira-
tion, convulsions, coma, and death.

The Kidneys and the Urine in Animals.

These important glands, so essential to the animal economy, are well
developed in all the Vortebrata, forming, as in Man, two symmetrical
organs situated at the back of the abdomen. In Mammalia, as in Man,
the kidneys are composed of an external cortical substance, consisting
chiefly of convoluted tubuli, and of an internal medullary substance in
' which the tubuli are straight. The kidneys of many Mammalia exhibit
the typical bean shape, but they are often more rounded than in Man, as in
the sheep, pig, and dog. They are sometimes more or less lobulated.
In the ox, the kidney is suldobulatcd, being marked by fissures between
the pyramids, which form the lobules, remaining, however, united beneath

392

SPECIAL PHYSIOLOGY.

the divided cortical portion. In certain Carnivora, as in otters, seals, and
bears, the pyramids, each covered by its own cortical layer, are separated
by deeper fissures, into which even the capsule of the kidney penetrates,
so that the lobules form clusters of distinct polyhedral masses attached to
the separate infundibula of a much ramified ureter. The kidney is most
deeply lobulated in the Cetacea. In the early embryonic condition of
this organ in all Mammalia, the lobulated character is present ; in the
Cetacea and certain Carnivora, it persists, and forms the so-called com-
pound kidney ; in other animals, as in the ox, the lobules partly coalesce ;
lastly, in the sheep, dog, and Man, they completely unite, as develop-
ment advances. Indeed, a lobulated or ramified condition seems to be,
a less developed form of many glands than the massive shape, as is
illustrated by the liver, jsancreas, spleen, and thymus in animals. Lobu-
lation of the lung, however, is a sign of higher development. Subordinate
peculiarities exist as to the mode in which the papillae of the kidneys,
are connected with a simple or much subdivided ureter.

In Birds, the kidneys no longer present an obvious distinction into a
cortical and medullary substance, and the gland tissue is much less firm
than in the Mammalia. In Birds, these organs are of considerable
length, occasionally blended together, in places, across the middle line ;
they extend from the posterior border of the lungs, down to the lower end
of the rectum, and are moulded into recesses in the bones of the lower
part of the spinal column. The kidneys of Birds are, therefore, slightly
lobulated. The uriniferous tubuli of each lobule, are arranged in bundles
or tufts, which end in the outer or superficial part, by dichotomous tubes ;
the symmetrical ureters proceed from the abdominal surface of the
glands, receiving the uriniferous tubules directly, without the formation
of infundibula, or of a pelvis. They open below, in the upper and back
part of a dilatation found at the lower end of the alimentary canal,
named the cloaca, where there is a sort of recess, which has been re-
garded as representing an imperfect bladder.

In Reptiles, the kidneys are very large, occupy the same general
position as in Birds, and are usually of great lengtli. In the turtles,
tortoises, and lizards, they are symmetrical, and fixed to the lumbar and
pelvic regions ; but in Serpents, the right kidney is placed higher than
the left, as if for convenience ; they extend along the greater part of
their elongated and flexible spine. The kidneys present no distinction
of cortical and medullary substance ; but they are deeply lobulated,
and loosely connected with the surrounding parts. The ureters are long
and narrow, and end in a sort of cloaca. The tuhuli uriniferi are
reduced to convoluted, or even short straight, csecal tubes, arranged in
converging bundles, or placed transversely. In the crocodile, the con-
voluted tubuli are so distinct as to appear like a cortical layer.

In Amphibia, the kidneys are flat and broad at their hinder end, but
become very narrow at their anterior part, and thus show an approxi-
mation to their form in Fishes. Numerous ducts proceed from their
inner border, to a long slender ureter, which opens into the cloaca.

In Fishes, the kidneys are proportionally large ; they varj' in sliape
in different species, but, as a rule, are narrow and of extreme length, being
attached beneath the bodies of the vertebra?, along the whole or the
greater part of the abdominal cavity, above the air-bladder when that
organ exists. There is no distinction of cortical and medullary sub-

THE RENAL VESSELS IN ANIMALS.

393

stance, and tufts of slightly tortuous urinary tubuli, or completely
straight csecal tubes, end at once in narrow elongated ureters, which
usually open, on each side, into the cloacal portion of the rectum, but
which sometimes first coalesce. In the low Myxinoid fishes, the upper
portion of the kidneys is much attenuated, and presents a complete
unfolding of the gland structure ; the tubtili, instead of being long and
aggregated, are short, distinct, and commence by little dilatations, into
which the Malpighian glomeruli project. In the amphioxus, the kidney
has not been distinctly made out, though it is probably represented by
a narrow gland-like mass placed near the abdominal pore.

The kidneys in Birds, Reptiles, Amphibia, and Fishes, may be con-
sidered as composed entirely of cortical substance ; they invariably con-
tain Malpighian corpuscles, or arterial glomeruli, which are usually
scattered through the gland, and, as usual, project into dilatations of the
uriniferous tubuli. These bodies vary in size, apparently in accordance
with the size of the animal, as well as in different Classes. Thus they fire
larger, i and ^ of an inch in the lion and horse, than in Man,
they are much smaller in the guinea-pig, cat, and mouse, 5^ atn
inch ; they are small in Fishes, 5^, and Amphibia, 5^, but smallest of
all in Reptiles, ^ to 5^. In the pointed renal lobules of the boa,
they are smaller in the narrow than in the wider portions of each lobule.
In the simpler kidneys of Fishes, they are represented by small vascular
plexuses. Cilia are found in the uriniferous tubuli in the Cold-blooded
^'ertebrata ; they commence at the neck of the capsules into which the
Malpighian bodies project, and extend for a short distance along the
tubuli, sometimes throughout their whole length. The current which
they produce, as seen after death, is towards the orifices of the tubules.
Cilia have not yet been distinctly seen in Birds or Mammalia.

In Birds, Reptiles, Amphibia, and Fishes, the renal arteries, instead
of being two in number as in Mammalia, are numerous, and are derived
from adjacent branches of the aorta, or from the aorta itself. Besides
this, the kidneys in these Classes, receive more or less venous blood from
the hinder limbs in Birds and the four-footed Reptiles and Ampliibia,
and from the hinder parts of the body in Ophidia, and in Fishes. The
rest of the blood from the hinder portion of the body, usually passes
partly to the vena cava, and partly to the vena porUe ; in Reptiles,
Amphibia, and most Fishes, it goes chiefly to the latter; in a few Fishes
all the blood from the hinder part of the body, proceeds to the kidneys.

The fact, that the kidneys in Birds, Reptiles, Amphibia, and Fishes,
receive a supply of venous blood, was first noticed by Bojanus, but the
detailed arrangement of tho afferent veins was fully investigated by
Jacobson. These renal portal veins become more numerous in tho lower
Vertebrata. After entering tho kidneys, they quickly subdivide, and end
in tho vascular plexuses which surround the uriniferous tubuli. Tho
Malpighian bodies still receive arterial vessels only, but give off efferent
vessels which join the plexuses around tho tubuli. In tho lower Verte-
brata, accordingly, tho .special urinary products, like tho bite products,
are, in all oases, excreted from venous blood ; and the small quantity of
arterial blood which enters tho kidneys, first passes through the vascular
tufts of the Malpighian bodies, and so becomes modified, before it
reaches the plexuses armind the proper excreting tubuli, in tho same
manner that the hepatic arterial blood becomes venous, before it roaches

394

SPECIAL PHYSIOLOGY.

the intra-lobular plexuses of the liver. As already stated, the existence
of this portal arrangement of the vessels in the kidneys of Birds, Reptiles,
Amphibia, and Fishes, supports the view, that in Mammalia, also, the
renal arterial blood becomes venous in traversing the vessels of the
glomeruli, before it serves for the excretion of urinary constituents.
The pasty or solid character of the urine in Serpents, may depend, not
only on the small size of the glomeruli, but also on the fact, that
these animals swallow little or no water.

Excretory glandular organs, having the function of kidneys, exist at
least in the higher Non-vertebrate animals ; but owing to the different
plans of construction in these Sub-kingdoms, it is impossible to recognise
much, if any, resemblance of position or structure, between them and
the renal organs even of the lowest Fishes. But the unity of the vito-
ehemical processes of animal life, is proved by the detection of urinary
products in some of these excretory organs in tlie Mollusca, Annulosa,
and Ccelenterata. Uric acid has been found in the two former Classes,
and guanin in the last.

In t)ie Mollusca, the organs which represent kidneys, are not connected
by ducts, with the alimentary canal. In the Cephalopods, remarkable
spongy masses of follicles, exist around the large branchial veins, and
■discharge themselves, by numerous apertures, into the branchial cavity ;
these are supposed to act as renal emunctory organs, their excreted fluid
•containing uric acid. In the Gasteropods, a smaller follicular organ,
also containing that acid, is usually found in the neighbourhood of the
heart, and its ducts open near the intestinal orifice, generally into the
branchial cavity. In the Lamellibranchiata, a similar organ, but, in
most cases, less distinct, is also found near the heart, close to the lower
end of the intestine, opening into the cavity of the mantle. In the
Molluscoida, distinct renal organs have not yet been recognised. Amongst
the Annulosa, the Insecta, Myriapoda, and Arachnida, have excretory
organs believed to be renal, consisting of long- tubes, often beginning
by clusters or tufts of vesicles ; they are sometimes few, as in Alyriapoda,
sometimes very numerous, as in the higher Insects. As in the Vertebrata,
they open into the lower part of the intestine, or even close to its
orifice ; sometimes the principal duct is dilated near its lower end, as if
to form a urinary bladder. The coloured fluid discharged by the lepi-
doptera, on their emerging from the chrysalis, proceeds from these
vessels, and contains uric acid. No such renal organs are found in the
Crustacea, which are aquatic. In the Annuhida, in which they are
likewise absent, the water-vessels may have some excretory function,
and eliminate urinary products.

In certain of the Ccalcnterata, small clusters of cells projecting into the
body cavity, and containing guanin, are regarded as renal organs ; but
in the simplest forms of these animals, the excretion of the products of
the decomposition of albuminoid substance, is probably accomplished by
the external and internal surfaces of their hollow bodies.

Lastly, in the minute Vrotozea, such products must also be eliminated
by the general surface.

THE SEBACEOUS GLANDS.

.395

Special Secretions in Animals.

Certain secretions or excretions, in animals, may perhaps be regarded,
not merely as serving a peculiar purpose in the economy, but also as
fulfilling an emunctory office, eliminating from the system, substances
which might be as injurious to animal life, as urea and uric acid.
Amongst such, may be mentioned, the castor of the beaver, the musk of
the musk-deer, the peculiar secretion of the civet-cat, and those of
other Mammalia, also the venom of Serpents, the acrid secretion of the
skin of the toad, the ink of the cuttle-fish, which yields the sepia
colour used by painters, the poisons of the stings of the bee and the
wasp, the sugar secreted by aphides, the odoriferous excretions of the
bugs and many other beetles, the poison in the tail of the scorpion and
the mandibles of the spider, the odoriferous exudations of the lumbrici,
and even the threads of the sea-nettles. Examples of special secretion,
are also met with in those glands which, in many caterpillars, supply
the silk used in progression or for the cocoons, in the spinneret glands
of the Spiders, the cement gland of the Cirrhopods, and the glandular
structures which secrete the byssus of certain Lamellibranchiata.

However different and specialised may be the actions of the various
glandular organs in the Animal Kingdom, which yield such widely different
products, they are aU based on a common plan of structure and function.
Even in the highest animals, and in Man, their physiological relationship
is evidenced by an occasional tendency to a vicarious action, in which
one gland or several glands take on the suspended function of another.

THE SKIN AND ITS EXCRETIONS.

By means of its sebaceous and sudoriferous glands, the skin
secretes and excretes fatty matter, and the perspiration or
sweat. Besides this, it exhales water from its surface, and
throws off certain quantities of carbonic acid gas.

The sebaceous or oily matter, formed by the so-called seba-
ceous glands (vol. i. p. 459 ; fig. 69, a), consists of a mixture of
olein, saponified fat, cholesterin, a small quantity of an umramed
albuminoid substance, and a few epidermic cells. Its ashes
abound in earthy phosphates. The fat is either derived from
the fatty matter of the plasma of the blood, or more pro-
bably from the metamorphosis of the albuminoid contents of
the epidermic cells of the sebaceous glands. It is poured out,
partly on the surface of the skin, but more commonly into the
interior of the hair follicles, even into the most minute ones.
In contributes to soften and render flexible both the hairs and
the skin, and, by protecting the latter from the action of water
or a([ueous solutions, it renders the skin more effectual as
a defensive organ. The so-called cera/mVioas and ilfeiio/zncm

396

SPECIAL PHYSIOLOGY.

glands of the ear and eyelids, may be regarded as special
modifications of sebaceous follicles.

In all Quadrupeds which possess hairs, sebaceous or oil glands exist ;
the glandulai JJropygii, or caudal glands, of Birds, supplying the fatty
secretion with which they anoint their feathers, are highly developed
sebaceous glands.

The epidermic tissues generally, viz. the cuticle, nails, and
hairs, have been viewed as solid excreted substances. "When
worn, cut, shed, or desquamated, they undoubtedly rid the
economy of a large amount of nitrogenous, sulphimous, and fer-
ruginous matter. The continual loosening of epithelial cells,
irom the gastro-pulmonary cavities, must serve a similar office.

The sudoriferous, sudoriparous, or sweat glands are pre-
sent, in larger or smaller numbers, in all parts of the skin.
They are small, rounded, pinkish bodies, placed immediately
beneath the true skin, and average about ^ of a line in
diameter. Each sweat gland consists of a fine tube, clo.sed and
coiled up into a ball at its deeper end, from which a straight
part of the tube, or duct, passes up through the cutis and
cuticle, and opens by a somewhat widened orifice on the
surface. When the cuticle is thick, as in the palms and .soles,
this tube passes through it in a spiral manner (fig. 66, 5, 6).
The whole tube, when unrolled, measm-es about ^ of an
inch in length, and about .5.^^ of an inch in width. This
tube consists of an outer vascular coat, prolonged from
the cutis, and of an epidermoid lining, continuous with the
cuticle ; the spiral portion is composed of the latter only. Two
coiled tubes may unite into one duct. When a sweat gland is
destroyed, it is not reproduced. In some situations, the sweat
glands are of large size, as in the axillas, where they
measure nearly two lines in diameter, are of a darker red colour,
are composed of branched tubes, and secrete a thick, exceed-
ingly acrid, and odorous fluid. In the palms and soles, the
openings of the sweat glands, the so-called pores of the skin, are
tbund on the papillary ridges ; in other parts, they are scattered
over the surface. They are most numerous on the palm of the
hand, where 2,800 orifices are found on a square inch ; they
are fewest on the back of the neck and trunk. Non-striated
muscular fibres, arranged longitudinally, exist in the vascular
coat ol'the ducts of the larger sweat glands (Kolliker).

The perspiration, or sweat, which is e.xcreted by the sudori-
fei'ous or sudatory glands, is not the only water}^ exhalation
from the skin ; for water is undoubtedly e.xhaled from the in-

THE PERSPIRATION.

397

tegument generally, as well as from the sweat glands. The
perspiration is said to be insensible, when no visible moisture is
discernible on the skin, and sensible, when it is so discernible ;
but there is no real difference between them; in the former
case, the fluid part evaporates as fast as it exudes from the
orifices of the sweat glands, whilst, in the latter, it remains
for a moment or so, in minute transparent colourless drops.

The sweat usually contains about 97 ’5 of water and 2 5
of solid matter, but sometimes less than 1 per cent, of the
latter. The organic constituents are little more than half of
this, and are composed chiefly of fat, which is probably almost
entirely derived from an admixture of the secretion of the
sebaceous glands ; but the palms of the hands and the soles of
the feet, are more or less greasy, although no sebaceous follicles
exist in that part of the skin. Besides this, the organic matters
of the perspiration, contain an albuminoid substance, the
nature of which is unknown, and acids, which give it an acid
reaction, by some supposed to be lactic acid, but now usually-
regarded as a mixture of a peculiar nitrogenous acid, named
sudoric, with the volatile acetic, metacetonic, formic, and
butyric acids, together with the fatty caprylic and caproic
acids. Some of these acids are combined with alkalies. Al-
most one-fourth of the solid matter, is urea, the total daily
quantity having been estimated at about 150 grains, which
would yield about seventy grains of nitrogen. This urea is
easily decomposed, and gives rise to amnioniacal salts, such as
were described by Berzelius, for no ammonia is found in per-
fectly fresh perspiration. The inorganic matters are chiefly com-
mon salt and chloride of potassium, phosphate of soda, and traces
of earthy phosphates, and iron. On burning the total solids,
some sulphates are formed, indicating the presence of sulphur
in some combination, probably with the organic matter. A
certain quantity of epidermic cells and extraneous substances,
also occur in the residue. The odour of the perspiration,
depends partly on the volatile acetic, formic, and various fatty
acids, but also perhaps on special, but unknown, volatile odorous
substances. Some of the odour may be due to decomposing
urea. In certain diseases, in which the excretion from the
kidneys is seriou.sly diminished, or altogether suppressed, as
in Bright’s disease and cholera, when the urea and uric acid
are retained in the blood, large quantities are frequently ex-
creted by the skin, probably chiefly by the .sudoriferous glands.
Besides the above-named substances, alcohol in small quantity.

398

SPECIAL PHYSIOLOGY.

.sugar, albumen, biliary matters, and other substances, have
been found in the perspiration.

The uses of the perspiration are two-fold ; first, to get rid
of a certain quantity of water from the system ; and secondly,
to eliminate from the body, certain special products of chemical
metamorphosis.

Many attempts have been made to determine the average
quantity of fluid exhaled by the skin, under ordinary circum-
stances, in twenty-four hours, and the variable quantities
which are given off under different conditions. In the earlier
experiments, the losses, by exhalation both from the skin and
tlie lungs, were confounded, the body being weighed together
with the food and drink taken in twenty-four hours ; at the
end of that time, the weight of the body was again taken, and
also that of the intestinal and renal excreta ; the difference in
these two totals, gave, for the amount of cutaneous and pul-
monary exhalation together, -f of the total loss of weight of
the body (Santorini). By enveloping the body in an im-
permeable oil-silk bag, so as to condense and retain the water
of the cutaneous exhalation, it was found that, in an adult,
about 30 oz. are daily exhaled by the skin, whilst at the
same time, 15 oz. are given off by the lungs, making a total
daily loss, by both skin and lungs, of 45 oz. (Seguin). The
total loss has, however, been estimated at 454 oz. in the
autumn, 44 oz. in summer, and 37 oz. in spring, in a person
under the average size (Dr. Dalton). Other estimates give
an average total loss of 57 oz., 51 oz. in the winter, and 63 oz.
in the summer.

The quantity of perspiration exhaled by different parts of
the body, differs widely. Its general quantity is influenced
both by intrinsic and extrinsic conditions ; thus it is augmented
by increased vascularity of the skin, by a higher temperature of
the body, by a quicker circulation, and therefore by exercise
and effort generally. Perspiration may also be induced by
additions to the clothing or covering of the body, and likewise
by breathing in a confined space; it is also increased by
peculiar conditions of the nervous system, as by certain de-
pressing emotions, and syncope, all of which tend to relax the
skin and its bloodvessels. It is, on the other hand, diminished
or almost entirely arrested, in febrile conditions and certain
forms of excitement, and, it is said, also by the use of coffee.
It is increased by taking food generally, but more particularly
after dinner. The secretion is stated to be most active about

I

QUANTITY OF THE PERSPIEATION.

399

noon, and least so in early morning. It is also augmented
during sleep.

Of the external conditions which modify the quantity of
the perspiration, by far the most important are the tempera-
ture and hygrometric condition of the atmosphere. Thus in
warm air, which increases the activity of the cutaneous circu-
lation, the perspiration is increased, whilst cold air has the
opposite effect ; again, dry air increases the perspiration,
whilst damp air diminishes it. Simple warmth acts by in-
creasing the vascular action through the skin ; whilst dry-
ness operates by maintaining a constant evaporation from
the cutaneous surface ; on the other hand, cold diminishes the
vascrdarity of the. skin, and dampness of the air impedes
evaporation. The combination of moisture with heat, how-
ever, increases the exhalation by the skin, which then appears
in large drops. Motion in the air, whether warm or cold, dry
or moist, increases the relative amount of perspiration, by
carrying it off more quickly. The perspiration is said to
be diminished by increased atmospheric pressure. This ex-
cretion is also augmented by large quantities of drinks,
especially when taken warm ; by so-caUed sudorific medi-
cines, such as nitre, Dover’s powder, and vinegar ; by elec-
tricity ; and also by hot baths, whether water-baths, vapour-
baths, or hot-air baths, especially when, as in the Turkish
and Roman baths, friction and shampooing are superadded.
Certain curious local sweatings have been noticed, affect-
ing the head alone, or the feet and hands, or even one side of
the face only, phenomena which probably are due to some loss
of poM'er in the vasi-motor nerves of the arteries of those parts,
giving rise to dilatation of the vessels, increased vascularity,
and increased secretion. Suppression of the cutaneous exha-
lation and excretion, is more or less dangerous, causing either
local internal congestion or inflammation, or general poison-
ing of the blood and fever, from the retention of effete matters
in the system. Hence the ill effects of sudden cold, or chill to
the surface, especially after previous overheating of the body
to the point of fatigue, and with the accumulation of effete
substances of waste in it. The chief use of this copious ex-
halation of water from the skin, as will be explained in the
Section on Animal Heat, is that of regulating the temperature
of the body, under variations of external temperature.

The mutual balance between the respective quantities of
the renal and cutaneous exhalations, under different jdiysical

400

SPECIAL PHYSIOLOGY.

conditions, chiefly those relating to the temperature and hygro-
metric condition of the air, is shown by the facts, that in cold
weather the skin exhales less, and the kidneys excrete more
fluid, whilst in warm weather the skin eliminates more and
the kidneys less. The skin is sometimes said to regulate the
quantity of fluid given off by the kidneys, and the quantity
of fluid left, in reserve, in the blood and the soft tissues gene-
rally ; but the kidneys should rather be regarded as the true
regulators in this matter. The skin and also the lungs are ex-
posed to external influences of temperature, and to the relative
hygrometric state of the air, which must affect the quantity of
their exhalations ; but the kidneys, being placed in uniform
conditions, are sensitive self-acting regulators, operating
through stimulation of the vasi-motor nerves, which govern
the state of the arteries and vessels of the glomeruli, and de-
termine the supply of blood. In certain conditions, moreover,
the renal and cutaneous excretions, instead of being vicarious
as to quantity, are simultaneously increased or diminished.

The office of the perspiration, in removing effete matter from
the blood, is, in the first place, evident, from the composition of
its solid constituents, although these are comparatively scanty.
Supposing 30 oz. of perspiration to be the daily quantity ex-
creted, the amount of urea and of other peculiar solids thus
eliminated, Avould be about ^ oz. ; whilst the daily quantity of
solid urinary products amounts to from 2 oz. to 3^ oz.

As an organ of excretion, however, the skin further elimi-
nates carbonic acid gas. The skin, indeed, is to a slight extent,
even in Man, a respiratory membrane, giving off carbonic
acid, and actually absorbing oxygen. The quantity of carbonic
acid gas exhaled by the comparatively dry cutaneous surface
of the human body, is, of course, relatively to that given off
by the lungs, very much less, and has been variously esti-
mated at from ^ to -gig- (Scharling), at (Scharling and
Hannover), and at -yws (Edward Smith), of that given off by
the proper respiratory organs, the lungs. It is stated that in
regard to the skin, a little more carbonic acid is given off thaujf
oxygen is absorbed, which is the reverse of what happens in
the lungs ; but the. estimation of the quantity of oxygen ab-
sorbed, is extremely difficult. The same remark applies to
the nitrogen, a minute trace of which is siiid also to be taken
up by the skin. The activity of this cutaneous respiratory
process, as it must be called, is considerably increased by
exercise. The quantity of nitrogenous matter daily removed in

RESniiATION.

401

the sliapo of desquamated epidermic cells, is said to bo about
11 grains. A partial interference with the excretor}'- function
of the skin, causes headache, lassitude, and febrile reaction ; a
more serious disturbance, by OA'er-exciting the kidneys, will
bring on temporary albuminuria.

The preceding facts sufficiently exjdain the high importance
of cleanliness of the skin, for the preservation, not only of
comfort, but of health. Daily ablutions by sponging, and the
occasional use of the tepid bath, are of great efficacy in the
maintenance of a pure condition of the blood.

The Cutaneous Excretion in Animals.

The sudoriferous glands of the higher Vertebrata, and the cutaneous
glandular organs of the lower Vertebrate, and Kon-vertebrate animals,
have been already described (vol. i. p. 473).

When the skin of a rabbit is shaved, and the body subsequently
coated over with varnish impenetrable to water and gases, death ensues
from asphyxia in from six to twelve hours, a condition which has been
named cutaneous asj>hyxia. The symptoms are depression, difficulty
of breathing, lowering of the temperature, congestion of the tissues and
organs with dark blood, and ultimate death. The arrest of cutaneous
respiration may partly account for this form of death, with accumulation
of carbonic acid in the blood ; but doubtless also, it depends on the
shutting in of peculiar cutaneous products. The fatal result can scarcely
be referred to the non-exhalation of water. In the soft-skinned Am-
phibia, the entire cutaneous surface exhales carbonic acid, and absorbs
oxygen ; in the frog, for example, after removal of the lungs, 4 cubic
inch of carbonic acid gas has been excreted from the skin, in eight
hours (Bischoff). This experiment is performed by putting the animal,
after deprivation of its lungs, under a glass receiver filled with air, and
'placed over mercury ; the carbonic acid is absorbed by lime water, and
so measured. The skin of the frog, w-hich is moist and full of capillary
vessels, presents conditions favourable to the solution and diffusion of
gases in contact with it, by a mechanism to be explained in the next
Section. Probably nearly as mucli carbonic acid is eliminated by the frog,
from its cutaneous surface, as from its comparatively simple lungs.

In the soft-skinned, aquatic, Non-vertebrato animals, the integument
is often an adjuvant, or the chief, or solo, respiratory surface, being for
that purpose frequently ciliated.

KESPIllATION.

Tlie arterial blood in juissing tlirongli tlic systemic capil-
laries, serves the ])Ui]ioses ot nutrition, slinuilation, secretion,
and excretion, and the blood, :is it leaves tliose capillaries,
VOL. II. P L>

402

SPECIAL PHYSIOLOGY.

is tainted by the products of venous absorption. In llie
various changes Avhich it undergoes, the arterial blood both
loses and acquires certain substances, and so becomes venous.
Thus changed, it returns to the heart, and, being now con-
veyed through the pulmonary capillaries, is there rapidly
restored to its arterial condition. This conversion of venous
into arterial blood, is the immediate object of ihe respiratory
process. In it, oxygen is absorbed by the blood, whilst car-
bonic acid, together with some Avatery vapour, is given off.
The source of the oxygen is the atmosphere; the carbon of
the carbonic acid is derived from the blood and tissues,
themselves supplied by the food. The chemical union of the
oxygen with carbon, and also Avith hydrogen, in tlie system,
maintains the movements and the temperature of the body,
and is the source of its nervous poAver and electricity.

The function respiration, therefore, has for its immediate
effect, the purification of the blood, and for its ultimate uses,
the production of Animal Heat, Motion, and Nervous Energy.

In plants, as elsewhere mentioned, the respirator}' process is re-
versed. Under the action of light, the carbonic acid and water taken
Aip, partly by the leaves, but chiefly by the roots, are decomposed in the
leaves; the oxygen is liberated, Avhilst the carbon and hydrogen, with
the hydrogen and nitrogen from ammonia, together with sulphur and
phosphorus, combine to form the proximate constituents necessary for
the food and fuel, which nourish animals, and support their respinitory
and other vital processes.

We have just seen that the .skin is the seat of a feeble
respiratory process, consisting of an interchange of oxygen and
carbonic acid. A small amount of oxygen may also be ;ib-
sorbed, and of carbonic gas exhaled, at the mucous surfaces
of the stomach and intestines ; for atmospheric ;iir is SAvalloAved,
mixed Avith the saliva and food, and dissolved in the drink.
But in animals generally, excejAting in the very lowest, special
respiratory organs, often consi.sting of a very comj)licated ap-
paratus, are pi-esent.

The respiration of animals is performed, sometimes in air
and sometimes in Avater, the former being termed uih-ial, and
the latter aquatic, respiration. The IMammalia, including
Man, all Birds, Reptiles, and Amphibia, amongst the "Verte-
brata, the Pulmo-gasteroj)ods belonging to the Mollusca, and
the Insecta, Arachnida, and jMyriapoda amongst the Annulosii,
are aerial breathers, and are pia)A'ided either Avith comjilex
holloAv organs named lungs, Avith simpler air sacs, or else Avith

PHENOMENA OF RESPIKATION.

403

minute air- tubes, or trachea;, all these organs communicating
directly with the atmosphere. A certain numl^er of the
Amphibia, all the Fishes, the Mollusca generally, except the
puhnonated Gasteropods, all the Molluscoida, the Crustacea
amongst the Annulosa, and all the Annuloida, Coelenterata, and
Protozoa are aquatic breathers, and are provided either with
projecting organs named branchke or giUs, sometimes external,
but more commonly concealed, orwdth internal ciliated sacs or
canals, or with external ciliated processes, discs, or sxirfaces,
always in contact with ivuter.

In aerial respiration, the source of the oxygen taken into
the body, is the atmosphere, into which the ctirbonic acid is
given off. In aquatic respiration, although the breathing is
subaqueous, so that the oxygen is taken up Ifom, and the
carbonic acid given off into, the water, still the ultimate source
of the oxygen, is the atmospheric air dissolved in that medium.
The solvent power of water for air, is very great, and owing
to the greater solubility of oxygen than of nitrogen in water,
the air held in solution in this Iluid, contains an unusual pro-
portion of oxygen.

The gr(;at importance of the function of respiration to
animal life, is shown by the fact that its interruption, by me-
chanical or chemical interlereiice with the respiratory organs,
is speedily followed by death. Air-breathing animals are
(piickly suffocated by strangulation, by immersion in water,
by placing them under the receiver of an air-pump and then
exhausting it, by giving them only a limited supply of air,
or by making them breathe gases not containing free oxygen.
Aquatic breathers are as quickly destroyed, if the fluid by
which t'ley are surrounded, has been deprived of air by boiling,
or by placing it under the receiver of an air-pump, and then
e.vhausting it.

In studying the respiration of Man, and the Mammalia
generally, we have to consider the structure of the organs of
respiration, i.e. of the thora.x and its muscles, the air-passages,
and the lungs ; the mechanism of re.spiration, or the respiratory
movements by which air is alternately drawn into, and expelled
Irom, the body ; the movement of the air in respiration, and
the capacity of the lungs; the changes which the air undergoes
during resjiiration ; the changes produced by this process upon
the blood and the tissues; the circumstances which modify
the rc.spiratory interchanges, including the phenomena of
asphyxia, and the effects of breathing b;id air; and lastly, the

1)D 2

404

SPECIAL PHYSIOLOGY.

organs and functions of respiration in animals. Afterwards it
Avill be necessary to consider the phenomena of Animal Heat,
Light, and Electricity ; and to discuss, in a separate Section,
the interesting questions relating to the Dynamics of the
Animal Economy.

THE ORGANS OF RESPIRATION.

The Thorax.

The thorax (vol. i. p. 27 ; figs. 10, 13, 14) is an osseo-
cartilatrinous framework filled in with soft tissues, which
contains and protects the central organs of respiration and
circulation. It corresponds with the dorsal region ol' the spine.
In front, it is formed by the sternum and the cartilages and
anterior parts of the ribs; behind, by the dorsal vertebrie and
posterior portions of the ribs ; and, at the sides, by the re-
mainder of the ribs. Between these solid parts, are the inter-
costal muscles, which are overlaid, in parts, by other muscles.

The cavity of the thorax is conical, being naiTow above and
broad below. Its upper opening, enclosed between the first
dorsal vertebra, the first ribs, and the top of the sternum, is
Avider transA'^ersely than from front to back ; its plane inclines
doAvnwards and forwards. The lower opening, hounded by the
ensiform cartilage, the last dorsal A'-ertebra, and the loAver ribs
or their cartilages, is much larger than the upper one. It is
also Avider fi’om side to side than from front to back, but its
plane inclines doAvnAvards and liackAA’-ards, so that the thoracic
caAuty is much deeper behind than in front.

The upper opening transmits — besides certain muscles of
the neck, the large bloodvessels of the head and upper limbs,
numerous nerves and lymphatics, the thoracic duct, and the
oesophagus — the princqAal air-tube, the trachea, or Avindpipe,
Avhich leads to the lungs ; the summits of the tAS'o lungs, ascend
beyond this opening. The loAver opening is closed by the mus-
cuio-tendinous, movable structure, named the diaphraam, -which
is itself arched, and reaches higher up on the right side ; this
o])ening transmits the oesophagus, the great vessels, the thoracic
duct, and the vagi and certain sympathetic nerves.

The Air Passages.

The nose, pharynx, and larynx haA’e already been described.
The trachea, or Avindpipe, placed in the middle line, descends

THE AIR PASSAGES.

405

from the larynx, on a level with the fifth cervical vertebra, to
opposite the third dorsal vertebra, where it divides into two
smaller air-tubes, named the bronchi, one for each lung. The
trachea (fig. 110, l) is about 4^ inches in length, and from ^ to
1 inch in width ; it is wider in the male than in the female.
Its anterior surface and sides are convex ; its posterior surface
is flattened. It is overlapped at its upper part, in front and at
the sides, by the isthmus and lobes of the thyroid body ; it

Fig. 110. Air-tubes of the human lungs, dissected out, and seen from the
front. 1, trachea or windpipe. 2, the right and left bronchi, the right
being the wider, the left the longer of the two. 3, outline of the left
lung collapsed. 4, bronchia, or bronchial tubes in the lung, cut short.
a. transverse section of a portion of the trachea, showing the incomplete
C-shaped rings, with the Hat membranous part behind.

is also covered by certain muscles and vessels of the neck, and
is concealed, lower down, by the upper part of the sternum
and by the remains of the thymus gland. In the thorax, the
large bloodvessels are in front of it, but in the neck, it is
placed between them. Behind, its flattened surface rests on
the oesophagus, by which it is separated from the spinal column.
Its lower thoracic portion is placed in the space known as the
posterior mediastinum, situated between the lungs.

40G

SPECIAL PHYSIOLOGT.

The trachea is composed of from sixteen to twenty indepen-
dent, transverse, incomplete hoops or rings of cartilage, held
together by an intermediate tibrons coat, within which are
mnsciilar and elastic fibres and a mucous lining membrane.

The cartilages are flattened bands, incomplete behind, each
being shaped like the letter C (fig. JIO, 5), with its open part
turned backwards. The first cartilage, which is suspended to
the cricoid cartilage of the larynx, is the broadest ; the last
cartilage is V-shaped. The fibrous coat not only connects the
cartilages together, but covers both their outer and inner sur-
faces; behind, where the cartilages are absent, this membrane
is continuous. An external laj’cr of longitudinal unstriped
muscular fibres, is found connected with the fibrous membrane
and Avith the cartilages; Avhilstan inner transverse set extends
between the ends of the cartilages. Bundles of elastic fibres
are placed immediately beneath the mucous membrane ; at
the posterior flat membranous part of the tube, they are seen
as jmllow longitudinal bmids. The mucous membrane, con-
tinuous with that of the larynx and bronchi, has a columnar
cilitated epithelium. Numerous tracheal mucous glands are
found embedded in the Avails of the tube, e.«pecially at its
back part. Its nerves are derived from the pneumo-gastrics
and the .sympathetic.

The right hronchua measures about 1 inch in length; it is
Avider, and has a more horizontal direction, than the left
bronchus ; it enters the root of the right lung, opposite the
fourth dor.sal vertebra. The left hronchus is about t\A'ice as
long as the right one ; it is, hoAvever, narroAver, and passes
obliquely doAvnAvard beneath the arch of the aorta, and in front
of the (Esophagus, thoracic duct and descending aorta, to enter
the root of the left lung, opposite the fifth dorsal A'ertebra.

The structure of the bronchi is similar to that of the trachea:
in front and at the sides, they are conve.x, and strengthened
Avith incomplete hoops of cartilage, but behind, they are flat,
membranous, and muscular. The cartilages are narroAver and
shorter than those of the trachea ; in the right bronchus, there
are from six to eight, and in the left, from nine to tAA'elve.

The Lungs.

The lungs, fig. 13, I, I, are tAA’oin number, and occupjq co7n-
pletelg and accurateh/, the lateral oi" pleural chambers of the
thorax, one on each side of the pericardium and heart, h. Each

THE LUNGS.

407

lung is tree in all directions, except at a part of its inner
surtiice, which is connected, by means of the bronchi and the
pulmonary arteries and veins, ■with the trachea and the heart,
tig. 111.

The lungs are porous, spongy organs, thetis.sue of which is so
elastic, that, although they till the closed pleural chambers, they
collapse more or less, when the thorax is laid open. If scpieezed,
they give rise to a peculiar sensation called crepitation, owing
to the air which is contained in them. Their size and weight
present great variations, depending on their state of inflation,
and the cpiantity of blood in their ves.sels, or of serum in their
tissue. The average -weight of the two lungs togedier, is, how-
ever, abotrt 42 ounces, the right lung being about 2 ounces
heavier than the left; they are larger in the male than in the
lemale ; they are moreover heavier, their proportion to the
body being as 1 to 37 in the former, and as 1 to 43 in the
latter. Otving to the air in the lungs, they float entirely, or
even in portions, in water; the speciflc gravity of their sub-
stance, ranges from 345 to 746, water being 1,000. The coto/r
of the lungs, varies at different periods of life ; in the newly
born infant, they are of a pinkish white ; in the adult, they are
darker, and become mottled Avith deep slate-coloured spots,
patches, or lines, which increase in number and assume a
deeper line, as life advances, becoming, in some individuals,
even black.

The surface of each lung, is invested by a thin, smooth, trans-
parent, elastic serous membrane, named xhe jiJeitra, Avhich passes
into certain fissures upon the surface of the lungs ; at the root
of the bangs, it is reflected upon the inner surface of the corre-
sponding pleural chamber of the thorax, the whole of which it
line.s, forming a closed sac (.see vol. i. p. 27). The parietal
portion of this itiembrane, ptirtly lines the sides of the thorax,
where it forms the costal pleura-, but, in the middle line, it
covers a portion of the pericardium and other parts, and
touches the o])posite ]ileura ; above, it closes in the upper
opening of the thorax, reaching higher than the fir.st ril) ; below,
it lines the diaphragm. A triangular du])licaturc, forming the
broad ligament of tlie lung, passes down from the root of the
lung to the diaphriigm, and .serves to retain the lower portion
of the btng in position. The free and moist surfitces of the
l)ariebd and pidmonary portions of the pleura, touch each
other. If serous fluid, blood, pus, or air should collect betAveen
them, the cavH'/ of the pleiini becomes evident, and the diseases

408

SPECIAL PHYSIOLOGY,

known as liydrothorax, hemothorax, empyema, or pneu-
mothorax are developed. The right and left pleure are quite
distinct from each other. The place Avhere they come into
contact, is just above the middle of the sternum ; here they
are connected together by areolar ti.ssue, but in other parts
of the middle line, they are separated from each other by an
interval, called the mediastinum, in Avhich all the parts con-
tained in the thorax, except the lungs, are lodged. The right
pleural chamber is shorter and wider than the left.

Each lung, as well as the pleural chamber into which it
accurately tits, is of a conical shape, and presents an apex, a
base, an outer and inner surface, and an anterior and po.sterior
border. The apex is blunt, and projects into the neck, from an
inch to nearly an inch and a half above the first rib. The base is
broad and concave, and rests on the convexity of the dia-
phragm ; its margin is thin, and passes between that muscle
and the wall of the chest ; it reaches much lower down at the
outer side and behind than it does in front. The outer surface,
smooth and convex, is in contact with the walls of the thora.x,
and is of greater depth behind, than in front. The inner sur-
face is concave, being adapted to tlie pericardium and heart,
behind which it presents a depres.sion, called the hilits,
where the bronchi and pulmonary vessels forming the root
of the lung, pass in and out. The anterior borders of the lungs
are thin, and partly overlap the ])ericardium, that of the right
lung reaching to the middle of the Avhole length of the ster-
num, that of the left lung doing ,so only as low as the fourth
costal cartilage. Above this point, the anterior borders of the
two lungs, are merely separated from each other by their
])leural membranes ; but below it, the anterior border of the
left lung forms, over the pericardium and apex of the heart, a
V-shaped notch, the base of Avhich is turned to the middle
line (fig. 13j. The posterior border of each lung, much longer
than the anterior, is broad and rounded, and occupies the deep
groove on either side of the vertebral column, reaching below,
between the ribs and the diaphragm.

Each lung is divided, by a deep fissure, into an upper and
lower lobe. This princijial Jissnre extends from the jiosterior
border of the lung near the ape.x, obliquely downwards and
forwards, to the anterior border near the base. The upper
lobe, on each .side, is smaller than the lower one, and resembles
a cone having an oblique btise ; the lower lobe has a some-
what quadrilateral .shape. The upper lobe of the right lung.

LOBULES OF THE LUXGS.

409

is subdivided by :i second fissure, wliich, passing forwards and
upwards from the oblique fissure to the anterior border, cuts
off a sniallei’ triangular lobe, named the' middle or third lobe
of that lung. A rudimentary third lobe is sometimes present
in tlie left lung. In the right lung, there are sometimes four
lobes. 'J'he right lung is about an inch shorter than the left,
and the concavity of its base is more jwonounced ; this cor-
responds with the higher position, and greater convexity of
the right half of the diaphragm, over the right lobe of the
liver. The right lung is also wider than the left, the breadth
of the latter being diminished by the projection of the heart
into the left half of the thorax.

The root of each lung, which is found on the inner surface
somewhat above the middle, and much nearer the posterior
than the anterior border, contains, as already stated, the
bronchus, the pulmonary artery, and the two pulmonary veins ;
it also includes the nutrient vessels or bronchial arteries and
vein.s, lymphatics and lymphatic glands, nerves, and areolar
tissue, all being surrounded by a tubular rellection of the
pleura. In the root of the lung, the pulmonary artery is
])laced behind the pulmonary veins, but in front of the bron-
chus, bronchial vessels, and lymphatic glands. The relative
position of the bronchus and artery from above downwards,
differs on the two sides; on the right side, the bronchus lies
above the artery; but on the left side, the bronchus (fig.
Ill, 4), descending lower, to pass beneath the aortic arch, is
placed below the artery, 6. The pulmonary veins, 7, 8, on
both sides, are situated below the other structures.

The air tube, bloodvessels, lymphatics, and nerves found in
the root of the lung, enter it, and, dividing and subdividing,
penetrate not only its lobes, but reach certain much smaller por-
tions of the lung substance, named the lobules. These lobules,
which constitute the proper pulmoiian/ substance, or parenchij-
ma, are small compressed ma.sses, which might be regarded as
little independent lungs, or lunglets ; they fit accurately against
each other; they vary in .shape and size, being, on the surface
of the organ, large and ])yramidal, with their base directed
outwards, whilst in the interior, they are small and of irregular
polyhedral shape. Each lobule is composed of a terminal
branch of an air-tube, surrounded by a clu.stor of air-c6lls com-
municating with it; also of pulmonary and bronchial vessels,

I lymphatics, and nerves, with a fine interstitial areolar tissue.

1 The lobules are supported on the terminal air-tubes, as if 011

410

SPECIAL PHYSIOLOGY.

stalks, but they are likewise held togeiher by the vessels, and
by an interlobular areolar tissue, which attaches their sides
together, and is itself connected with a general covering of
areolar tissue, found upon the surface of the lung, beneath the
pleura, named the subpleural or stibserous coat. Both the in-
terlobular and subserous tissues, contain many elastic fibres.

Fig. 111.

1

Fir', in. Baok view of the lungs and hea' t, with the air-tuhes and groat
bloodvessels attached. 1, trachea or wiiulpipo. 2, 2, lungs; the left one
part^' dissected, to show the bronchial tubes and the pulmonary
arteries and veins branching in it. 3, heart. 4. left bronchus, entering
at the root of the lung, beneath the arch of the aorta, which is seen cut
across, fi, left pulmonary artery. 7. 8, lei t pulmonary veins, entering,

5, the left auricle; beneath the right pulmonary veins, is the inferior ,
vena cava, cut across. 9, back or under surface of the left ventricle of
the heart.

On entering the lung, each bronchus divides into an upper
and lower branch, one for e;ich lobe; but, on the right side,
the lower branch gives off a smaller one, which passes into the
middle or third lobe of that lung. In.side the hmg, the bron-
chi continue to subdivide, at obtuse angles, into smaller and
smaller tubes, called brnncliuf, these never coalesce again, but
continue separate, after the manner of the primary ducts of a

AIR TDBES OF THE LUNGS.

411

gland, or of the branches of a tree. Tliese tubes generally divide
dichotonionsly, or in twos, but sometimes three bronchia pro-
ceed from a common trunk, or small lateral bronchia are given
off. The finest bronchia, forming the lobular bronchial tubes,
end in the lobules, as ■will presently be described. The com-
bined sectional area of tlie smaller bronchia, is very much
greater than that of the larger bronchia or the trachea.

Within the lung, the bronchia are round, and not flattened
posteriorly, like the ti'achea and its primary divisions in the
root of the lung. Their constituent elements are similar to
those of the trachea, but these are here much modified. Thus, the
cartilages, instead of being aiTanged in regular transverse slips,
assume the form of angular or polygonal plates of proportionate
size, placed on all sides of the tubes. At the angles of bifur-
cation of the tubes, spur-shaped pieces of cartilage iisually sup-
port them ; minute flakes are found even in the smaller bronchia.
But the cartilages are absent in bronchia, the diameter of
which is less than a cjuarter of a line ; the walls of such tubes
are entirely membranous. A fibrous coat and longitudinal
elastic fibres, are present in all the tubes, down to the very
smallest. The muscular fibres, of the unstriped kind, are no
longer limited to the posterior portion of the tube, but, ar-
ranged in circular bundles, form a layer external to the car-
tilages; they extend to the smallest ramifications of the
bronchia. The mucous membrane lining the bronchia, is
thinner than that of the bronchi and trachea, with which it is
continuous ; it is covered with a ciliated columnar epithelium.
The walls of the bronchi and larger bronchia, are provided
with mucous glands.

The terminal bronchial offsets distributed to the lobules, or
the lobular bronchial tubes, divide within the lobules, from four
to nine times, according to the size of the lobule. The branches
thus formed, become gradually smaller, being at length re-
duced to diameter. They

finally terminate in the so-called intercellular passages, or
air sacs, which offer a marked contrast, both in form and
structure, to the tubes; for instead of a cylindi-ical form, they
appear like irregular passages, traversing the substance of the
lobide at various angles, and communicating freely with each
other; at the same time, they no longer present either longitu-
dinal, elastic, or circular muscular fibres. Moreover, the
diameter of the intercellular pass;iges, is somewhat greater
than that of the fine.st bronchial tubes from which they proceed.

412

SPECIAL PHYSIOLOGY.

and it increases a little at each division, whilst the tubes, in
this respect, as already mentioned, diminish in size as they
divide. Finally, the sides of the intercellular passages, at
first smooth, like those of the lobular bronchial tubes, soon
become recessed by numerous closely-set, sharply-defined,
cup-shaped depressions ; these are the so-called air-vesicles
or air-cells. An intercellular passage may, indeed, be re-
garded as a space between the air-cells, which surround it
on all sides.

Fig. 112.

Pig. 112. Magnified diagrammatic view of groups or clusters of air-cells, '
one being laid open. 1, small bronchial tube, dividing into others which iL '■
are membranous. 2, vesicular portion of lobule, with air-cells on its \ r
surface. 3, the same, laid open, to show the recesses or air-cells in its j

interior. ],

I

The air-cells or air-vcsicles (fig. 112, 2, 3), the ultimate re- *
cesses to which the minutely subdivided air gains access, ‘
measure from Tj-g-jjth to ^Vth of an inch in diameter. They
are smaller in the interior of the lungs, larger on the surface,
and largest at the apices and thin edges of those orgau.s. They ^

are larger in the male than in the female, and gradually ’

increase in size .as life advances. Those cells whicli occupy i **

the central portion of a lobule, .appear like polyhedral alveoli, j

separated from each other by delicate septa. By some, it is •

THE AIR CELLS AND CAPILLARIES.

•;i3

said that the sides of the cells are frequently perforated or
deficient, so that neighbouring cells communicate with each
other (Waters) ; but this is not universally admitted, at least
as regards the hitman lung. The cells situated beneath the
pleura, are four or six sided. No direct communication exists
between the air-cells of adjacent lobules. The number of air
cells in both lungs, has been calculated to be about 6,000,000.
The walls of the air-cells, are thin and transparent, and are
composed of areolar, mixed with fine elastic, tissue, lined by an
exceedingly delicate mucous membrane, consisting of a thin
transparent basement membrane, covered with a polygonal
squamous non-ciliated epithelium.

The pulmonary arteiies and veins are the functional, or
respiratory, vessels of the lungs. The ]mlmonary arteries,

Fig. 113.

a

Fifr. 11.3. Sirmll portion of tlie inner surface of the air-cells, with the caoil-
iary network iujectrclj the pulmonary caiiillaries are seen to be wider
than the meshes between them.

unlike the systemic arteries, convey venous blood from the
right ventricle of the heart to tlie lungs. The trunk of the
pulmonary artery, having passed obliquely upwards and to the
left, for about '2 inches, reaches the concavity of the aortic
arch, and there divides into the right and left pulmonary
arteries ; each of these enters the corresponding lung, and
divides into as many primary branches as there are lobes ;
these branches ra])idly subdivide in company with the bronchia,
and finally end in the 'jmlnionari/ capillaries. These last-
named vessels, placed beneath the mucous membrane of the air-
cells and intercellular ]>assagcs, form a delicate and close net-
work composed of a single layer of small vessels, having exceed-
ingly thin walls ; their width varies from to Toirirt'' of

an inch ; that of the meshes between them, is much less ; at the

414

SPECIAL PHYSIOLOGY.

sides of adjoining cells, the capillury network is placed between
their adjacent walls, so that it is acted on by tlie air on both
sides. The venules which arise from the capillary network,
quickly join to form larger trunks, which generally pursue a
different route to that of the arteries ; they finally end in four
pulmonary veins, two Ifora each lung, which convey the arterial-
ised blood to the left auricle of the heart. The pulmonary veins
are destitute of valves ; their capacity is said to be about equal
to, or even less than, that of the juilmonary arteries. Within
the lungs the pulmonary arteries are usually situated above
the bronchial tubes, and the prdmonaiy veins below. The
Ironchial arteries are the nutritive A^essels of the Inns: : thev
are given off from the aorta, or from an intercostal artery, and
are distributed to the Avails of the bronchia and pulmonary
vessels, to the interlobular areolar tissue and other neighbour-
ing parts ; they usually end in the bronchial veins, but the
branches Avhich supply the smallest bronchia end in the
pulmonary capillary network. The lymphatics are superficial
and deep, and terminate in the bronchial glands at the root of
the lung. The nerves are derived from the vagus and sympa-
thetic; connected Avith the latter, are nmnerous minute ganglia
(Kemak).

Mechanism of Respiration.

The respiratory movements are of two kinds — viz. those
Avhich draAV air into the breathing organs, or the movements of
inspiration, and those Avhich exjiel the air from those organ.s,
or the movements of expiration. A complete respiration
therefore consists of an inspiratory and an e.rpiratory act.
Inspiration reejuires a greater effort than expiration. At the
commencement of the indejtendent existence of air-breathing
animals, the former act precedes the latter, the lungs being
then filled, before air can be expired from them ; on the other ■
hand, the final respiratory act consists of an expiration, and
to expire is synonymous Avith to die.

Inspiration. — The thorax is a closed cavit3’, with movable
Avails, the available space in Avhich, beyond that occupied by
the heart and bloodvessel.s, ocsophagu.s, thoracic duct, lym-
phatic glands and nerves, is accurately filled by the two
lungs. The interior of these spongy organs, however, com-
municates Avith the outward atmosphere through the nose,
mouth, pharynx, larynx, trachea, bronchi, and broiu-hial tubes,
ilence any enlargement of the thoracic cavity, from expansion

MECHANISJI OF I-NSriKATION.

415

of its Avails, is immediately accompanied by tlie entrance of
air, tlirongh the air-passages just mentioned, into the interior
of the Inngs, and by the inllation of those elastic organs, as
they Ibllow the expanding Avails of the chest. In describing
the inspiratory act, it is sometimes said that a virtual vacuvm is
formed in the thorax, Avhich the air fills, by entering throngh the
only pass;iges by Avhich it can reach its interior. But the vacuum
in question, is only threatened or impending, none being really
formed. The equilibrium betAveen the atmospheric pressure
on the surface of the lungs, acting through the Avails of the
thorax, and that on their interior, ojAerating through the open
air-passages, being disturbed by the active expansion of the
thoracic parietes through the agency of the inspiratory muscles,
the air outers the air -passages simultaneously, in exact and
instant correspondence Avith the amount of expansion, and the
lungs as instantly become inflated, and folloAv the inner surface
of the expanding thoracic Avails.

In this inspiratory movement, the thorax is enlarged in
each of its three dimensions : in depth from belbre backwards,
in Avidth from side to side, and in length or height from above
doAvnAvards (see fig. 11-1). The enlargement in depth, fioni
the spine to the sternum, is accompli.shed by the eleAuition of
the ribs, Avhich being movably articidated Avith the vertebral
column behind, and continued on, by their cartilages, to the
sternum in front, and having, moreover, an obli(jue direction
from their posterior to near their anterior extremities, neces-
sarily cause an elevation and jArojection fonvai-ds of the
sternum, Avhen they are slightly lilted upon their posterior
points of attachment, to a less oblique position. The jAoint
of support or fulcrum ol'ciich rib, is the vertebral cohnnn;
Avhilst the connection of the upper ten ribs in front, directly
or indirectly, Avith the steiTUun, enables them to elevate and
push fbnvard that bone, and thus, to incia.-ase the antero-
posterior diiimeter of the chest. The enlargement of the
tliora.x in width, is likewise accomjilished by the elevation of
' the curved and ol)lif[uely attached ribs ; for by such a move-
ment, as may be illustrated on the skeleton, or on an apparatus
consisting of jiicccs ol' hoops attached obliciuely to a common
upright support, the ribs, in becoming more hoilzontal, are
not merely lifted, but slightly rotated on their hinder attached
extremities ; their sides are thus carried outward.s, their outer
surfaces being turned .somewhat iqtAvard.s, iind their inner .stir-
faces dowiiAvards. 'I'he totiil result, as it iill'ccts all the ribs.

41C

SPECIAL PHYSIOLOGY

is to expand the thorax in its transverse diameter. Lastly,
the increase in the vertical diameter or height of the thoiax,

Fig. 114.

Pig. 114. Diagrammatic view of an antero-posterii r section of the cavities
of the thoiax and abdomen, 'with tlie diaphragm intervening, to show tlie
ciianges in the position of this septnin, and of the walls of the chest and
abdomen, in respiration; a, abdominal cavity; t, thorax ; t’, v, vertebral
cohniin ; d, diaphragm. The dark lines show the position of the parts
after inspiration, the dotted lines after expiration, s, section of the
sacrum, and p, of the symphysis pnbi', forming the posterior and an-
terior boundaries of the pelvic cavity, which communicates above with
the abdomen.

which, in its costal portion, is diminished by the antero-
posterior and transverse expansion, is accomplished by the

EXPANSION OE THE TIIOEAX.

417

action of the arched or vaulted diaphragm, fig. 14, d, which
I'orms the base of the thorax. The central tendinous expan-
sion, the diaphragm, is drawn down by the contraction of its
circumferential muscular parts ; and this movement, named
the descent of the diaphragm, causes an important elongation
of tlie thoracic space.

Of these three modes of enlargement of the thoracic cavity,
its elongation from above downwards, by the descent of the
diaphragm, is by tiir the most considerable. In ordinary re-
spiration, it constitittes in men, and, it is said, particularly in
children, the principal respiratory movement; but it is ac-
companied-by a slight lifting of the walls of the thorax, in front,
at the sides, and especially at the lower part of the chest. When
the diaphragm thus de.sceuds, the abdominal viscera do so like-
wise, and the abdominal walls, their muscles probably relaxing,
become prominent ; whilst in expiration, when, as may be
supposed, the diaphragm ascends, the abdominal viscera are
carried upwards, and the abdominal walls, slightly reacting,
fall in. Hence, respiration performed, chiefly or entirely, by
means of the diaphragm, is termed abdominal, diaphragmatic,
or inferior costa I respiration; it is the typical form of respiration
in the male and in children. When breathing is mainly per-
formed by the movements of the ribs, it is termed pectoral or
superior costal respiration, and this is the characteristic form
of breathing in the female, a fact which has been, by some,
attributed to the habitual use of stays, but which may be a
provision against the occasional impediment to abdominal re-
spiration, which occurs in that sex. Over-distension of the
abdomen, from any cause, as fiom gaseous or solid accumula-
tions in the large intestine, tumours, or dropsical effusions,
hinders abdominal re.spiration, the embarrassment to which is
shown by the special efforts made to perlbrm costal respiration.
If the diaphragm contracted by itself, it woidd not only draw
down its own tendinous vaidt, but would also pull the lower
ribs downwards and backwards towards the vertebral column,
and so diminish the lateral and antero-posterior dimensions of
the lower part of the chest; but, in ordinary, and in deep in-
spiration, this tendency is counteracted by a proper adjust-
ment of the force which raises the ribs.

The elevation of the ribs in inspiration, is accomplished, in
ordinary breathing, by the coojjcration of a number of small
muscles placed dee])ly between, and upon the ribs. First, more
especially concerned, are the external intercostal muscles. These

VOL. II. E E

418

SPECIAL PIITSIOI.OGY.

occujiy the interspaces between all the ribs, extending, in each
intercostal space, from close to the vertebral column to the
neighbourhood of the costal cartilages ; their fibres pass down-
wards and fonvards, fi-om one rib to another (see fig. 4). It
was at one time supposed that these muscles, being placed be-
tween adjacent rib.s, could not elevate tho.se bones, unless the
uppermost rib was first fixed, but that then each intercostal
muscle could raise the rib below it. It has been shown, how-
ever, by observations on living animals, that the action of these
muscles in elevating the ribs, does not require the previous
fixing of the first rib. The mechanical principle on which
this apparently singular re.sult depends, may be illustrated by
a simple apparatus, consisting of an upright support of Avood,
to which two bars are so attached at one end, by means of pins,
as to be capable of being elevated or depressed; the bars them-
selves being held horizontall}q a piece of Amlcanised india-rubber
is fixed tensely, and obliquely downwards and forAvards from
the upright support, betAveen the bars — i.e. in the sjime direc-
tion as the fibres of the external intercostal muscles. When,
now, the bars are drawn doAvn, the india-rubber is stretched,
and on being left fi-ee to act, immediately eleA^ates both bars
again, and supports them even in an oblique direction upAvards.
'The explanation of this result is as folloAvs: — the elastic force
tends to approximate the ends of the piece of vidcanised india-
rubber ; this can only be accomplished by such a motion of
the movable bars as Avill bring the points, to Avhich the ends
of the india-rubber are fixed, as near together, i.e. as nearly
vertical to each other, as possible ; and this results in the joint
elevation of both bars. In the living body, the A'ertebral
column represents the upright support, and the rilis the bars ;
but the eftect is here modified by the someAA'hat fixed con-
dition of the cartilages of the ribs to the .sternum, Avhich bone
is, accordingly, moAmd upwards and forAA’ards. Secondly,
there are found at the back ol‘ the chest, near the spine, and
descending fi’om the several dorsal vertebr® to the subjacent
ribs, muscles knoAvn as the long and short levators of the ribs.
These not only assist in eleAmting Uie hinder parts of the ribs,
but also slightly rotate them, so as to CA^ert their lower borders.
This slight rotation of the ribs, Avhich acconqianies their ele-
vation, inci’eases the diameter of the chest, and also AA'idens
each intercostal space along the sides of the thorax, AA’here
the ribs are more movable than at their anterior and posterior
extremities. The elasticity of the costal cartilages, is highly

DEEP INSPIKATION.

419

iavourable to this elevation and rotation of the ribs, rendering
both movements easier of execution, than if the costal frame-
work were entirely composed of bone. Thirdly^ besides the
simpler action of the levators of the ribs, and the more com-
plex movements of the external intercostals, it is certain that
a portion of the so-called internal intercostals may, as will
again be mentioned, also aid in elevating these bones and the
sternum.

In deep inspiration, many more muscles come into play
than in ordinary breathing. Thus, the anterior and posterior
scaleni muscles, which descend, on each side, from the cervical
vertebrte to the first and second ribs, aid powerfully in eleva-
ting those ribs, and, through them, perhaps all the others. The
posterior superior serrati muscles, situated deeply, one on each
side of the back of the chest, must also raise certain of the
ribs. The cervicales ascendentes muscles will have a similar
action. If the scapula, or shoulder bone, and the clavicle, or
collar bone, are previously fixed by the muscles which descend
to them from the head and neck, viz. by the trapezius (fig. 5, 2),
sterno-mastoid, levator of the angle of the scapula, and greater
and lesser rhomboid muscles on either side, then a very large
and important muscle, the great serratus (fig. 4, 5), which
passes from the base of each scapula, over the sides of the
chest, to the eight upper ribs, must also assist powerfully in ex-
panding the chest, by raising and drawing the ribs outwards.
So, likewise, in front of the thorax, the subclavius muscle,
which passes from the collar-bone to the first rib, and the
lesser pectoral muscle, which descends from the scapula to the
third, fourth, and fifth ribs, on each side, will then serve to
elevate the ribs. In still more forced inspiration, when even
the arms are fixed, by holding on to some external object of sup-
port, the great pectoral muscles in front (fig. 4, 2), and the
latissivii dorsi behind (fig. 5, 3), both of which, besides other
attachments, are connected, on the one hand, with the humerus,
and, on the other, with certain of the ribs, may then cooperate
in tlie elevation and outward rotation of these latter bones, and
thus assist in inspiration. All the muscles just mentioned,
are named auxiliary muscles of inspiration ; but a few of them
only, those first described, are ordinarily employed in deep
inspiration. In very extreme cases, however, nearly every
muscle of the body may assist in inspiration, by fixing certain
parts, and thus affording more efficient points of action to the
proper respiratory muscles.

li £ 2

420

SPECIAL PHYSIOLOGY.

The chief work performed in the act of inspiration, consists
in overcoming the elastic resistance of the costal cartilages, and
lifting the weight of the ribs. The lungs themselves are pas-
sive, or rather their elasticity has to be overcome. These organs,
becoming inflated in every direction from their roots, as they
follow the thoracic walls, are necessarily enlarged in all direc-
tions, antero-posteriorly, transversely, and vertically. The
elastic fibres of the air-tubes, yield both in a longitudinal and
a circular direction. The elastic walls of the air-cells, are ex-
tended generally ; so also are the interlobular and subserous
areolar tissue, and the pulmonary and costal pleurte. To faci-
litate the ingress of air, the air-passages, from the nose and
mouth down to the interior of the lungs, are supported either
by bones or cartilages, as, for example, by the cartilaginous
alee of the nostrils, the bones of the nasal cavities, the car-
tilages of the larynx, the incomplete cartilaginous hoops of the
trachea and primary bi'onchi, and lastly, by the less regular,
but well-adapted plates of cartilage of the secondary bronchi
and the bronchia. As especially fitted to maintain the pervi-
ousness of the bronchia, the cartilaginous spurs placed at the
angles of bifurcation of those tubes, deserve particular men-
tion. Through simple, membranous tubes, however firm, the
free and instant entrance of the air necessary to proper inspira-
tion, would have been impracticable ; and, moreover, such tubes
would have quickly collapsed during expiration. At the
larynx, the narrow triangular glottis has musculo-membrauous
margins ; but the state of this aperture, is regulated by the
nervous system, which exercises a special control over it, and
though it may be voluntarily or involuntarily closed, it is
habitually open.

Mechanical obstructions in any part of the air-passages, by
excluding the air, may prove fatal. The forcible closure of
the mouth and nose for criminal purposes, the wilful filling of
the fauces with a handkerchief or cloth, the compression of
the windpipe, the accidental impaction of pieces of food or of
some foreign body in the glottis, closure of this aperture from
spasm, or from swelling of the surrounding mucous membrane,
a condition known as oedema of the glottis, the lodgment of
masses of food, too large to be swallowed, in the oesophagus,
and, lastly, the introduction of fluid in any quantity, as in
drowning, operate in this Avay.

When the thoracic Avails are so injured, that an opening
exists through them ijito the pleural chamber, their expansion

MKCIIANISM OF EXPIRATION.

421

is no longer followed by the proper inflation of the lungs ; but
the air passing in through the artificial opening, to supply the
threatened Auacuura, the lung is subjected to equal atmospheric
pressure both on its pleural surface and within its air- passages
and air-cells, and owing to the elasticity of its component struc-
tures, it collapses to a greater or less extent. If the opening be
oblique or valved, as in certain punctured or gunshot womids,
some air may still enter the lung by the trachea. As the two
pleurre form distinct chambers, when one only is punctured,
the corresponding lung alone becomes collapsed, and though
respiration is embarrassed, death does not necessarily ensue.
If, however, both pleuraj are simultaneously wounded, both
lungs collapse, and death follows from asphyxia or suffocation.

Expiration. — The movement by which the air, having
entered the lungs by an inspiratory effort, is again driven
from them, is more passive in its character than that of in-
spiration, depending less upon muscular action, but more on
the relaxation of the inspiratory muscles and on the elastic
resilience of the organs and tissues concerned.

As the muscles of inspiration cease to act, the tendinous
part of the diaphragm, the chief of those muscles, ascends into
the thorax, followed by the abdominal viscera, Avhich are
supported in their upward movement by the cooperation of
the mu.scles of the abdominal walls. At the same time, the
ribs, and the sternum, which were elevated, descend, and fall
back, whilst the effects of the rotation of the ribs, are counter-
acted by the elastic recoil of the costal cartilages. Lastly, the
elasticity of the limgs themselves, plays a most important part,
acting like an extended spring let loose, and serving to expel
the air from the air- tubes and air-cells. The longitudinal and
circular fibres of the bronchi and bronchia, shorten and narrow
those tubes ; the elastic walls of the air-cells, diminish their
size, and the interlobular, and especially the subpleural elastic
tissues, aid powerfully in compressing every portion of the
lung.

The importance of the elasticity of the component structures
of the lungs, as an exjjiratory force, is shown by an experi-
ment, which also illustrates the mode in which a lung expands
by the removal of atmospheric pressure from its outer surface,
and by the concurrent entrance of air, under its ordinary pres-
sure, into the Vjronchial tubes. A bell-shaped glass jar, hav-
ing a wide mouth below, and a strong open neck at its upper
end, has the latter opening fitted with a peribi'ated cork tightly

1

■122

SPECIAL PirrSIOLOGT.

cemented in. The lower end of a glass-tube, about ^ inch
wide and 1 foot long, is closely secured into the bronchus
of a sheep’s lung ; the upper end of this tube is then pas-sed
up into the bell-shaped glass jar, and pushed through the hole
in the cork, until the lung is suspended high up in the jar ;
the tube is then hermetically cemented to the orifice in the
cork, its upper end being lelt free and open. A piece of moist-
ened bladder, in the centre of which a stop-cock is closely tied,
so as to project outwards, is now placed loosely over the
mouth of the jar, and is tightly secured to its rim, by cord.
When the apparatus is held upright, the glass-tube repre-
sents the trachea, and the bell-shaped jar may be compared to
the thorax, with this difference, however, that its sides are not
movable, and are not in contact with the lung; lastly, the
loosely extended moist sheet of bladder occupies the position of
the diaphragm, the upward vaulted form of which may now be
imitated, by opening the stop-cock in the centre of the bladder,
thrusting this latter up into the bell-jar, and then closing the
stop-cock. In this position, the bladder is supported by the
atmospheric pressure, and the suspended lung is quiescent. On
now pulling the stop-cock dotvnwards, the bladder descends, •
imitating the descent of the diaphragm, the atmospheric pres-
sure on the surface of the suspended lung is removed, and, in
anticipation of the threatened vacuum, air enters through the
glass tube into the interior of the lung, which, as may be seen
through the jar, immediately becomes inflated. In this con-
dition, the elastic tissues of the lung are put ttpon the stretch.
But if the stop-cock be let go, the elastic resilience of this
organ, causes the lung once more to contract, and the artificial
diaphragm of moist bladder again ascends into the jar, until
the atmospheric equilibrium inside and outside the lung, is re-
established. The experiment may be repeated again and again,
the accidental entrance of an excess of air between the sides of
the jar and the surface of the lung, being remedied by open-
ing the stop-cock, thrusting the bladder well up into the jar,
and then closing it again. If desired, a manometer may be
adapted, by a separate opening, to the top of the jar, so as to
measure the expanding force used in distending the lung, as
the bladder is drawn down. The two lungs of a dog, con-
nected with the trachea, answer for this experiment as well
as the sheep’s lung ; but the elasticity of the lung of the seal
or the lion, is much greater. The clastic force of the human
lung, has been calculated at 8 oz. per square inch of surlace,

CONTUACTION OF TKE THORAX.

423

being equal to about 150 lbs. in the male, aud about 12-1 lbs.
in the female (Hutchinson).

It has been shown experimentally, that the conti-actility of
the unstripecl muscular fibres of the air-tubes, is excited by
electricity, as well as by chemical and mechanical stimuli; and
it has been suggested that they may assist in expelling air
from the lungs ; but the slow action of organic muscular fibres,
renders it unlikely that they cooperate in movements so rapid
as those of respiration ; it is more probable that they regulate
the diameter of the air-tubes, and perhaps aid in expelling
mucus, or other secretions, from the smaller tubes. The cilia,
which exist throughout the air-tubes, from the entrance of the
air-cells upwards beyond the larynx, not only as.sist in the diffu-
sion of moisture over the interior of these tubes, but perhaps
also in retaining particles of dust which abound in the air, and
so preventing their reaching the air-cells, and likewise in im-
pelling upwards towards the glottis, mucus and entangled
particles of matter. The current produced by these cilia,
always sets in the upward direction.

Ordinary expiration is undoubtedly aided by certain proper
expiratory muscles, especially by the internal intercostals.
These muscles occupy only the anterior three-fourths of the
intercostal spaces, being absent at the back part of the chest;
they are placed inside the external iuterco.stals. Their fibres
pass, in each space, from above, downwards and backiuards, or in
the oppo.site direction to the fibres of the external intercostals.
As already alluded to, the forepart of these muscles near the
sternum, especially of the four or five upper ones, is said to
assist in elevating the ribs in inspiration ; but, elsewhere,
these muscles depress the ribs, invert their loAver edges, and
diminish the Avidth of the intercostal spaces, thus acting as
expiratory muscles, diminishing the capacity of the thorax
both from before backAvards, and in Avidth. Within the internal
intercostals are situated the infracostals, small muscular
bundles, having the same direction as the internal intercostals,
but reaching over tAVO or three spaces; they are also expira-
tory muscles. The triancjulares sterni, small thin mu-scles,
found on the internal surface of the sternum and cartilages of
the true ribs, likeAvi.se cooperate in e.xpiration ; some main-
tain, hoAvever, that a portion of these tniiscles is inspiratory.
The auxiliar}! muscles of expiration, are the Aipper jiart of the
serratns mac/nus, Avhen the .scapula is previously fixed ; the
posterior inferior serrati, Avhich pass from certain dorsal and

424

SPECIAL PHYSIOLOGY.

luml:)ar vertebra upwards to the last four ribs ; the qnadrati
lumborum muscles, which ascend from the pelvis and lumbar
vertebras to the lower ribs; certain portions of the long
muscles of the back, known as the erectores spinw, and, lastly,
the abdominal muscles which are concerned in drawing the
lower ribs downwards and inwards, such as the extei-nal and
internal ohliqui, the transver sales, the recti, and pyramidales
muscles. The abdominal muscles assist, even in ordinary
expiration, by supporting or raising upwards and backwai'ds
the abdominal viscera, when the relaxation of the diaphragm
causes these to ascend. In extremely forcible expiration, as in
powerful inspiration, all the muscles of the body may be brought
into some action. It is remarkable that a single small muscle,
the arytenoid (vol. i. p. 258), which closes the aperture of the
glottis, may, by an act of the will, be made to counteract
the poweriul efforts of tlie ordinary and auxiliary muscles of
expiration. Under this condition, the walls of the thorax are
rendered tense and firm, so as to form a solid base of support
for the forcible use of the upper limbs. So also in voluntary or
involuntary abdominal expulsive efforts, the chest is usually first
filled by an inspiratory act, in which the diaphragm descends,
and then, the glottis being closed, the diaphragm is fixed,
and the abdominal and auxiliary expiratory muscles come
into action, so as to compress the abdominal contents.

The movements of inspiration and expiration which con-
stitute a complete respiratory act, succeed each other alter-
nately, from the moment of birth until that of death ; and
this character of succession is named the rhythm of the respi-
ratory acts.

The number of complete respirations in a given time, varies
according to many conditions. In the adult, the respirations
vary from 14 to 18 per minute; in childhood, at about
five years of age, they are said to be about 2G per minute;
whilst at birth, they are as many as 40 to 50; in extreme age,
the frequency of the respirations is again increased. Persons
of small stature, breathe more quickly, but less deeply, than
taller people. The resjhrations are less frequent, but deeper
in the male, than in the female. The number of resjiirations
is increased by exei’cise and work, by food, stimulants, and
moderate cold, and at great altitudes ; whilst it is diminished
in sleep, by moderate heat, by increased barometric pressure
(see p. 220), by slaivation, and by depressing influences and
agents generally. It is curious that if the attention be

KESriRATDRT MOVEMENTS AND PAUSE.

425

directed to the breathing, the number of respiratory acts
is usually diminished. In quick walking, the respirations
may be 30 in a minute ; in running, 7 0 ; and in violent
efforts, as many as 100 per minute. In sleep, the respira-
tions are slow, because the interval between expiration and
inspiration, is unusually prolonged. As elsewhere noticed,
there is a certain ratio, in health, between the number of the
respirations, and that of the beats of the heart, the proportion
between them being in the adult, usually aboirt 1 to 4.
In childhood, the respirations are relatively quicker, their
proportion to the pulse, being from 1 to 3 or 3^. The
ordinary ratio between the respirations and the pulse, is
maintained in the daily and seasonal variations of the latter.
But in certain diseases, it is seriously disturbed, and forms
an important guide in medical practice ; thus in pneu-
monia or inflammation of the lungs, the respirations are
so quickened, through embarrassed function from congestion
of the vessels, that the ratio may even be as 1 to 2. In
hysteria, the respirations are also much increased in proportion
to the pulse. In typhoid states, and in narcotic poisoning,
the respirations become so slow, owing to some influence on
the nervous centres, that their ratio to the pulse may be as
1 to 8.

The whole period occupied by a complete respiration, is
divisible into three stages — viz. an inspiratory and an expira-
tory stage, followed by a pause, or stage of rest. According
to some, there is also a pause between inspiration and expira-
tion, but this can very seldom be recognised or measured.
The total period of a respiration, being represented by 10,
the in.spiratory movement occupies 5 parts, the expiratory 4,
and the recognisable pause between this and the succeeding
respiratory act, 1. The period of motion, to that of rest, is
therefore as 9 to 1 (Walshe). According to Vierordt, the
period of inspiration being equal to 10, that of expiration, to-
gether with the pause, is, in deep respirations, 14; in quick
breathings, 24. As he estimates the pause at one-fifth of the
whole period, the numbers repre.senting the inspiration, the
expiration, and the pause, would, in the former case, be 10, 9,
and 5, and in the latter 10, 17, and 7. According to recent
observations with the sphygmograph and kymogi'aphion, the
whole re.spiration ])criod being 15, insj)iration occu])ics 4,
expiration 2, and the pau.se 9 parts ; the ratio of the move-
ment to the pause, is as 2 to 3 (Sanderson). In the disease

42G

SPECIAL PniSIOLOGY.

called emphysema, which consists in a dilatation of the air-
cells, the periods of expiration and inspiration are equal, or
the former is even longer than the latter. In cases of tuber-
cidar deposit, the expiration is also prolonged.

The force exercised by the inspiratory muscles in ordinary
respiration, in an adult man, varies from about 1'5 inch to
4'5 inches of mercury ; but, in exceptional cases, it may rise
to even 7 inches. This force increases more rapidly than the
actual amount of expansion of the chest, for when, in the same
body, 70, 90, 190, and 200 cubic inches of air were injected
into the lungs, the pressure Avas found to be Iq 1'5, 3’25, and
4'5 inches of mercury. The expiratory force is, on an average,
about one-third or one-fourth stronger than the inspiratory
force, varying from 2’ to 5'8 inches of mercury, and rising
even, in certain cases, to 10’ inches (Hutchinson). This is
due to the cooperation of the elasticity of the lungs, and the
resilience of the chest walls, with the muscular effort. The
force of the inspiration, is, therefore, the severer test of the
strength of the body. The expiratory power is said to be
greater in men of 5 feet 7 or 5 feet 8 inches in height, than in
those either above or below that stature.

The entrance and escape of the air into, and out of, the air-
tubes and air-cells, during inspiration and expiration, produce
certain sounds named respiratory murmurs, Avhich may be
heard by the ear placed on the chest or by aid of the stetho-
scope. In health, the inspiratory and expiratory murmurs,
named the bronchial or tubular sounds, which depend on the
movement of the air through the air-tubes, are heard oA^er
the site of the larger bronchia, between the scapulte, and over
and near the upper part of the sternum. They are distinct
and characterised by a .soft bloAving noise; those of inspiration
and expiration, are of nearly equal duration. The vesicular
respiratory murmurs, dependent upon the entrance and escape
of the air in, and out of, the air-cells, are only faintly audible,
like a gentle breezy noise ; the expiratory vesicular murmur
is Aveaker, and three or four times shorter, than the inspira-
tory murmur. The duration of the sounds, is altered by the
same causes as those Avhich modify the length of the move-
ments of inspiration and cxiAiration.

Accumulations of mucus or other secretions in the air-tubes, pro-
duce abnorniiil sounils, Avhicli are named rhovchi, or rules. These vary
in character, according to tlio seat, quantity, and nature of the secreted
matters. Thus, a fine crepitant rhouchus is produced by fluid exudation-

RHYTHM OF RESPIRATION.

42’/

in the air-cells, in pneumonia; a sub-crepitant rhonclius arises from the
bubbling of air through fluid in the smaller air-tubes ; a sonorous rhon-
chus, with its snoring, rasping, and cooing varieties, depeni's on obstruc-
tions in the larger air-tubes; a sibilant, or whistling, rhonchus is caused
by mucous accumulations in the air-passages ; and, lastly, a cavernous
rhonchus is produced in cavities, or caverns, in the lung, formed in the
destructive stage of phthisis. Peculiar, harsh, rubbing, or grating noises,
named friction sounds, frequently heard in inflammation of the pleura,
are caused by the rubbing of rough exudations of lymph eifiised on
the pulmonary or costal pleura. Again, the relative amount of air and
tissue in ditferent parts of the thorax, causes differences in the sounds
produced by percussion with the Angers, or otherwise, at different
points of the thoracic surface. The percussion sound over the lungs, is
more hollow, or, as it is termed, resonant, than over the heart, or great
bloodvessels ; the ascent of the convex liver into the concave base of
the right lung, the two being of course separated by the diaphragm,
alters the percussion sound, by diminishing the resonance at the base of
the right side of the chest. The chest is more resonant over the great
bronchi, than at other parts of the lungs. The resonance is everywhere
greater in thin persons. Various changes in the lungs, produce great
alterations in the resonance of the corresponding parts of the chest ;
congestions, thickenings, consolidations, accumulations of fluid as in
hydro- or hsemo-thorax, or empyema, and the presence of tumours,
cause dulness in the percussion sounds ; whilst an abnormal amount
of air, either in dilated or ruptured air-cells, as in emphysema, or in
the cavities excavated in the lung-substance, as in phthisis, or in the
pleural chamber, as in pneumo-thorax, cause an increased degree of re-
sonance on percussion. Lastly, the term vocal resonance is applied to
the sound heard on the surface of the chest, whilst the person is speak-
ing; it is also modified by various internal conditions. A vibration
felt on the walls of the chest, during speaking, is called the vocal fre-
mitus.

The rhythmic movements of respiration, are governed by a
special part of the nervous centres, cooperating with certain
nerves. The rhythmic movements of the heart, not yet fully
e.xplained, are performed by a muscular organ, itself entirely
uninfluenced by the will. But the mitscles of respiration are
1 truly subject to the will. We can increase or dimini.sh the

i rapidity and force of these movements, according to our plea-
P sure ; we may imitate them, and can interrupt or arrest them at
I any chosen point of the respiratory act. This latter power is,
however, of limited duration. Very prolonged interruption
1 of the respiration, produces convulsions. But, even after a
i period of from twenty to thirty seconds, there arises, when
I the breath is held, a feeling so distressing, that it overcomes
I the most powerful volition. This feeling, termed want of
breath, at last irresistibly compels the resuinjition of the respi-
ratory acts. Like other sensations, it has its seat in some

42S

SPECIAL PIITSIOLOGT.

portion of the grey substance of the nervous centres, and
these being irritated, excite the motor nerves of the muscles
of inspiration, which are then thrown into involuntary action.
The ordinary respiratory movements are also involuntary ;
they continue to be regularly performed during the pro-
foundest sleep, in a state of coma, in deformed infants in
which the cerebrum is deficient, and, for a time, even in ani-
mals after the head has been removed.

The respiratory movements are, indeed, the most striking
examples of reflex movements in the body. Their nature has
already been generally discussed (vol. i. p. 346). The afferent
or excitor nerves of inspiration are the pulmonary branches
of the pneumo-gastric and sympathetic nerves, which latter
contain fibres derived from the spinal cord ; also the cutane-
ous nerves of the face belonging to the fifth cranial pair, and
the cutaneous nerves of the body generally. The nasal nerves
and the laryngeal branches of the pneumo-gastric, excite expi-
ratory movements, as in sneezing and coughing. The nervous
centre which governs the respiratory movements, is a limited
portion of the grey matter of the medulla oblongata opposite
the roots of the pneumo-gastric nerves, as has been proved
e.xperimentally (vol. i. p. 354-5). The so-called vital knot, at
the back of the medulla, corresponds with the interval between
the occipital bone and the arch of the axis ; in this space, an
animal may be suddenly killed by introducing a sharp, strong
knife, so as to pith it, or divide the medulla. The efferent or
motor resjDiratory nerves are : the phrenic nerves, which supply
the diaphragm ; the intercostal nerves, which supply, amongst
others, the muscles of that name ; the lon(j thoracic, or so-called
external respiratory nerves of Bell, which are distributed to
the serrati muscles ; the spinal accessory nerves, which supply
the trapezii muscles ; and the facial nerves. In extreme
respiratory efforts, other motor nerves, are of course con-
cerned. The reflected stimulus is conveyed to the roots of
these nerves, along a particular tract of the spinal cord, situ-
ated behind the anterior roots of the spinal nerves, and descend-
ing along the lateral columns of the cord, from between the
olivary and restiform bodies ; this is the resjnratoi'y tract of
Sir C. Bell, but, except as a path of special conduction, it has
no respiratory influence. It is remarkable that the phrenic
nerves which supply the diaphragm, the most active muscle in
inspiration, arise from the cervical plexus, and therefore
from a jiart of the cord much higher than the roots of the

INFLUE>’CE OF NERVES ON RESPIRATION.

429

highest intercostal nerves. Hence it happens that in certain
injuries or diseases of the spinal cord, when the scat of these is
above the origins of the intercostal, but below those of the
phrenic nerves, costal respiration may be entirely abolished,
whilst diaphragmatic breathing goes on. In such cases, how-
ever, death ultimately occurs from asphyxia, caused by the
slow exudation of fluid into the lungs.

The respiratory movements being regarded as reflex or
excito-motor, the first act of inspiration performed at birth,
is said to be induced by the stimulus of cold acting on the
excitable extremities of the fifth cranial nerves, which supply
the nasal fosste and the skin of the face, and also on those of
the cutaneous nerves of the whole body. Cold, or a smart
blow applied to the surface of the body of an apparently still-
born infant, will .sometimes excite inspiration ; and, moreover,
if the face of an infant be protected by warm covering, the
first inspiratory act may be postponed (Marshall Hall). Once
established, the reflex respiratory movements are believed to
be excited by a peculiar stimulus, accompanying the sum of
disagreeable sensations included in the feeling of want of
breath. By some, it is supposed that the venous blood, de-
prived of oxygen, and loaded with carbonic acid gas and other
effete matters, owing to the periodic interruption to the process
of oxygenation, may be the cause of some of those disagTeeable
feelings, and may periodically stimulate the medulla and
spinal cord, and so rhythmically excite the motor nerves of
inspiration ; according to others, it is rather the want of
oxygen, which excites the movements, for an excess of that
element enfeebles them.

The division of one vagus nerve in an animal, as a rule,
lowers the frequency of, and embarrasses, the respiration, and
the lungs become sometimes, but not alway.s, the seat of ex-
travasations of blood. Division of both vagi nerves in the
neck, immediately diminishes the frequency of the respirations
to one-half, and later to one-third, or even one-fourth, of the
normal number ; the insj)irations become not only slower, but
deeper, embarra.ssed, and puffing, or spasmodic ; the expira-
tions, on the other hand, are shorter; whilst the pause
between the ex[)iration and the succeeding ins])iriition, be-
comes more and more prolonged, which accounts for the
diminished number of resj)iratory acts in a given time. Death
usually takes [ilace after from two to six days; the blood first
becomes darker, as indicated by blueness of the lips, the tern-

430

SPECIAL PHYSIOLOGY.

perature sinks, and the animal dies of asphyxia. Congestion
of the pulmonary vessels, extravasations of blood, and exuda-
tions of frothy sanguineous serum and mucus, are found in
the air-cells and bronchial tubes, and partial solidification of
the lung tissue occurs. Sometimes, however, death appears
to ensue from disturbance of the digestive functions ; but if
these be recovered from, the animals may then live for many
days. The continuance of the respiratory rnoA’^ernents, for a
time, after division of the pneumo -gastric nerves, depends on
the excitability of the other afferent nerves of the body, espe-
cially of those of the skin. It seems doubtful whether the
unstriped muscular fibres of the bronchial tubes, can be excited
through the pneumo-gastric nerves. Their contractility is
soon exhausted by stimuli directly applied to them; moreover,
it is lessened by certain narcotics, especially by belladonna
and stramonium ; hence the use of such remedies in asthma,
in relieving the paroxysms of dy.spnoea, which are supposed to
be due to a spasmodic contraction of these organic muscular
fibres.

The respiratory apparatus is employed, either voluntarily
or involuntarily, in many other acts necessary to the economy,
or conducive to its comfort. In these, the movements of
respiration are sometimes accelerated or strengthened, and
sometimes diminished or checked.

Thus, speaking, singing, shouting, and whistling, are voli-
tional movements, recpiiring special voluntary efforts of ex-
piration, often modified and graduated in the most varied yet
e.xact manner, and supported by inspirations performed at
stated and suitable times. The act of spitting consists of a
sudden expiration, accompanied by a peculiar position of the
tongue, lips, teeth, and cheeks, having for its object the expul-
sion of saliva or other accumulations, from the mouth.

The semi-voluntary or involuntary acts which necessitate
the cooperation of the respiratory apparatus, are much more
varied. Thus, coughing is a sudden, strong expiration, ac-
companied by a peculiar noise, following a closure of the
glottis and of the upper opening of the larynx, and usually
preceded by a deep inspiration, to give effect to the cough. A
column of air, suddenly driven from the air-tubes, as suddenly
opens the glottis, and, being forced through the mouth, moves
on accumulations or foreign bodies, and expels them from the
bronchi, trachea, and larynx. Sneezing consists of a quick

APPLIED RESPIRATORY MOVEMENTS.

431

noisy expiration, following a decided, sudden, and deep in-
spiration ; but the glottis is not closed, as in coughing, and
the column of air is not driven through the mouth, but is
directed, by the closure of the lances, into, and through, the
nasal fossre. The irritation which causes sneezing, has its seat
in those fossaj, whilst that which induces coughing, as is well
known, resides in the fauces, the larynx, especially at the glottis,
or in the air-tubes. The stimuli which excite coughing, are
cold air, irritating gases, fluids or solids, and diseased secre-
tions. The noise of sneezing, is produced in the nose ; whilst
that of coughing, originates at the glottis. Snoring is produced
by the resonance of the air passing, in or out, through the
nasal cavities and the throat, owing to some irregular vibra-
tions of the soft palate and uvula ; it is sometimes dependent
on narrowing of the fauces by enlargement of the tonsils, or on
other peculiarities of conformation. In snoring, there is no
special modification of the respiratoiy movements themselves,
either as to force, frequency, or quickness. Yawning consists
of a deep prolonged inspiration, the air being drawn in through
the mouth, which is widely opened, by a consentaneous spas-
modic action of the muscles of the lower jaw ; this is then
followed by a slow expiration, accompanied usually by a lifting
of the soft palate, and sometimes by a prolonged characteristic
sound. It may be accomplished by the will, and is often the
result of involuntary imitation. Sighing also consists of a
slow, deep inspiration, mostly accomplished through the mouth,
and followed by a prolonged expiration, likewise associated
with a peculiar sound ; it often occurs after the attention has
been strongly fixed ; it is usually emotional. Sobbing is pro-
duced by rapid convulsive contractions of the diaphragm,
associated with closure of the glottis. In the movements

resemble those of laughter, to be next described, although they
are excited by very different emotions. Laughing consists of
a series of sudden, short expirations, quickly succeeding each
other, and divided, as it were, by intermediate closures of the
glottis, giving rise to peculiar interrvqited sounds. Laughter
luniishes an excellent example of a reflex respiratory move-
ment, excited either by sensori-motor imju-essions acting
through cei'tain cutaneous nerves, as when it is caused by
tickling; or by emotional stimuli, as when it is the result of
joy ; or by a volitional stimulii.s, as when it is imitated by the
actor. Lastly, hiccup is a short, sudden inspiration, produced
by a sharp, convulsive contraction of the diaphragm, at the

432

SPECIAL PHYSIOLOGY.

end of which the glottis is suddenly and spasmodically closed,
so that the air strikes it from below. Of these varied move-
ments, some, such as sighing and yawning, may be induced by
certain conditions of the respiratory organs themselves, whilst
others, such as laughing and crying, are never so excited.

Movement of the Air in Respiration and Capacity of the Lungs.
— After the lungs have been once inflated, as in the new-born
infant, they are never, except from disease, entirely emptied
of air. The most forcible expiration tails to accomplish this,
and the quantity of air then retained in their tissue, is termed
the residual air. The quantity, above thi.s, held in the lungs
after an ordinary expiration, but which may be expelled by a
voluntary forced expiration, is called the reserve air, or some-
times the supplemental nYr. The quantity inspired and expired
at each ordinary respiratory act, is called the breathing or tidal
air ; and the still further quantity, which can be drawn in by
a forcible inspiration, is termed the complemental air (Julius
Jeffreys). The total quantity which, after the deepest inspira-
tion, can be expelled by the fullest expiration, is considered
the measure of the so-called vital capacity of the chest or of
the individual, because it shoAvs the volume of air which is
commanded by the vital movements of the thoracic Avails. It
is the extreme differential capacity of the chest, minus the
space occupied by the residual air, Avhich cannot be expelled ;
it represents the total difference betAveen the fidlest inspiration
and the fullest expiration. This vital capacity in any indivi-
dual, is of great importance, as indicating the extreme poAver of
breathing in exercise or effort : and it ftirnishes highlv signi-
ficant information in certain diseases, esjDecially in those of the
lungs themselves (Hutchinson).

The determination of the actual quantities of air, AA’hich are
the measures of the residual, resexwe, breathing, and comple-
mental air, and that of the total respiratoiy poAver or vital
capacity of the chest, is extremely difficult. The elaborate
and .successful researches of Hutchinson, Avere made by means
of his .so-called spirometer. This apparatus is really a minia-
ture gasometer ; it consists of an inner cylinder, closed at its
upper end, but open beloAv, Avhere it dips into AA-ater contained
in an outer larger cylinder, Avhich is closed beloAV and ojien
aboAm ; and it has a scale, by Avhich its a.«cent and descent
can be measured. The inner cylinder is accurately balanced, .
by Aveights attached to cords passing over pidleys affixed to
the OAxter cylindex-. The inner cyliixder being dejxx'essed, aixd :

THE VITAL CAPACITY.

433

allowed to fill with water, the person experimented on, blows
air into it, by a tube which passes beneath its open mouth.
The cylinder is raised, and when the expiratory effort is com-
plete, the tube is closed by a stop-cock, so as to retain the air
in the spirometer, and its quantity is read off upon the scale.

The residual air has been variously estimated at from 40 to
260 cubic inches; but, according to Hutchinson, it ranges trom
75 to 100 cubic inche.s. It is most difficult to measure; for,
after death, the lungs are not so empty of air, as they are
after forced expiration dm-ing life, and it is not easy to esti-
mate the difference. Besides, althoitgh the amount of residixal
air, corresponds generally with the size of the chest, it is influ-
enced also by the relative mobility or stiffness of the Avails, so
that age, imparting rigidity to the costal cartilages, increases
the residual, at the expense of the re.serve or supplemental air.
The residual and reserve air together, are taken, in the adult
male, to be from 150 to 200 cubic inches (Hutchinson).

Accurate estimates of the so-called breathing air, and vital
capacity, are of great importance. The breathing air has been
differently calculated, from 10 to 92 cubic inches; but, accord-
ing to the most recent observers, it ranges, in the adult male,
from 16 to 20 cubic inches (Hutchinson), from 17 to 33
(Vierordt), from 16 to 25 (Coathupe), and from 30 to 39 cubic
inches, in persons whose stature varies from 5 feet 7^ inches
to 6 feet (Dr. E. Smith). A fair estimate for a person of
mean height, 5 feet 6-^ inches, would be about 20 cubic inches,
for the average of the day and night respirations. The vital
capacity in an adult male, of the stature of 5 feet 7 inches, is,
on an average, about 230 cubic inches, the air being sujAposed
to be at a temperature of 60°. The complemental air Avould
therefore be 120 cubic inches.

The following are the estimated quantities, in cubic inches,
calculated for the daily and nightly average, in a man of the
stature of 5 feet 6^ inches: —

Eesidual Air .
Eeserve Air
Breathing Air .
Complemental Air

Cubic Inches
90

90 I Total displaceable Air,
20 lor VOtal Capacity =

. 120 j 230 cubic inches.

Total Air after deepest Inspiration 320

These numbers cannot be regarded as absolutely accurate,
but they illustrate the general proportions. The depth of tin

VOL. II. F F

434

SPECIAL PHYSIOLOGY.

ordinary inspiration, as measured by the breathing air, and the
total displacement of air in forced respirations, indicating the
vital capacity, differ much, according to the size of the body,
but even in persons of the same age, height, and weight, they
are liable to variation ; for they do not merely depend on the
size of the thorax, but necessarily on the mohility of its walls, and
on the extent to which they are actually moved in the several
inspiratory and expiratory acts. This may partly account for
the great diversity in the estimates of the breathing air. The
vital capacity has been shown to differ according to the stature ;
the variation in persons between the heights of 5 and 6 feet,
follows a sort of law, every additional inch of height being
accompanied by an average increase of 8 cubic inches in the
vital capacity. Thus the capacity at 5 feet 6^ inches being 230
cubic inches, that at 5 feet would be about 174, whilst that at
6 feet would be about 270 cubic inches. The vital capacity
in Avomen, is much smaller than in men, the proportion being
almost as 1 to 2. It increases, in both sexes, from 15 to 35
years of age, at the rate of about 5 cubic inches per annum ;
Avhilst from 35 to G5, it diminishes by 1-^ cubic inch in a like
period. The greatest capacity met Avith by Hutchinson, A\'as in
a giant 7 feet high, who Aveighed 308 lbs. ; his capacity w'as
464 cubic inches. The minimum was 46 cubic inches, and
occurred in a dAvarf measuring 29 inches in height, and weigh-
ing only 40 lbs. Modern dress impedes respiration, for a man
Avho could only expire 130 cubic inches Avhen his clothes
Avere on, accomplished 190 cubic inches Avheu unclothed. The
posture of the body modifies the vital capacity ; for if, in the
attitude of standing, it be 260 cubic inches, in the sitting
posture it is 235, in the recumbent position 230, and in lying
on the face 220. The degree of distension of the stomach,
likeAvise influences the vital capacity of the chest. Corpulency,
in persons Aveighing more than 160 lbs., diminishes the Autal
capacity, at the rate of 1 cubic inch for CAmry additional
pound up to 196 lbs. or 14 stone AA'eight. Practice Avith the
spirometer, increases the poAver of forcing up the inner cylinder,
Avhilst nervousness and aAvkAvardness operate the other A\’ay.
Hence, in the use of this apparatus, alloAvance must be made
for all the above-mentioned disturbing influences ; and, it is
certain, that the so-called vital capacity is not strictly related
to the muscular poAver of the individual. Nevertheless, it is
a A'aluable addition to our means of diagnosis, as to the con-
dition of the lungs; the ob.structed state of those organs in the

VITAL CAPACITY OF THE CHEST.

435

earlier stages of phthisis, and the deficient respirator}^ movement
dependent upon this condition, cause a serious diminution in
the vital capacity, as compared with the normal standard in
persons of the same sex, age, and stature. A diminution of
16 per cent, in the normal capacity, is said to indicate a disea.sed
condition (Hutchinson) ; but care must be taken to allow for
the eflfects of congestion, and of abdominal disease.

If in a person 5 feet Gi inches in height, the breathing air
averages, during the twenty-four hours of work, rest, and
sleep, 20 cubic inches at each inspiration, and the number of
respirations joer minute for the day and night, be taken at
18, the quantity of air inspired and expired by an adult man
of mean stature, in one minute woidd be 360 cubic inches.
This would give 518,400 cubic inches or 300 cubic feet, for
the twenty-lbur hours. This amount is less than the total
daily quantity as estimated by Valentin, Avhich is 688,348
cubic inches ; less also than the quantity, viz. 686,000 cirbic
inches, found by Edward Smith to be the average in four
adults, of a mean height of 5 feet 10^ inches, during a state
of rest. During ordinary exercise, the estimates of the last-
named observer, give 804,780 cubic inches; in the case of
the actively employed labourer, 1,568,390 ; and during a day’s
work, including twelve hours of Alpine exercise, 1,764,000
cubic inches. Vierordt’s estimate for the twenty-four hours,
is 732,000 cubic inches; but that author assumes the quan-
tity of air inspired per minute, to be 450 cubic inches.
Edward Smith found it to average 500 cubic inches in the
day, and 400 during the night, in four persons of the mean
.stature of 5 feet 1 0^ inches.

It has been estimated that, with a vital capacity of 200
cubic inches, the force employed in making the necessary full
inspiration, is equal to the raising of 300 lbs. weight upon the
surface of the chest ; but in forcible expiration, the power
exerted is much greater. In ordinary breathing, supposing
the quantity of air inspired to be 20 cubic inches, the resist-
ance overcome by the inspiratory muscles, is equal to a weight
of 200 lbs.

Chanrjes in the Air from Respiration..

The air expired from the chest, differs in three respects
from that which is inspired. It is increased in temperature,
except of course when the inspired air is already hotter tlian
the body itself. It contains, as a rule, more moisture, unle-ss

F K 2

436

SPECIAL PHYSIOLOGY.

when it is previously, and exceptionally, saturated vdth watery
vapour. Lastly, it undergoes important changes of compo-
sition, the chief of which consist in a loss of oxygen and an
addition of carbonic acid.

The increase of temperature in the expired air, is regulated
by the temperatm’e of the air taken into the lungs. "\^Tien
the surrounding air is cold, the increase is not quite so great
as when its temperatm-e is nearer that of the body ; but the
difference is less than might be supposed. With the thermo-
meter at from 50° to 68°, the expired air has a temperature of
95° to 100° ; whilst if the external temperature be 32° or
freezing-point, then the expired air is not more than 86°.
According to Valentin, however, in ordinary breathing, the
temperature of the expired air in the winter, is only 1° less
than that of the air expired iu summer. In tranquil respira-
tion, the expired air becomes comparatively warmer than in
rapid breathing, as if, in the latter case, sufficient time 'was
not allowed for the air to gain warmth. The increased
warmth of the expired air, necessarily causes an increase of
volume, but this is partly neutralised by a small loss of air in
respiration, owing, as we shall see, to the absorption of more
atmospheric oxygen by the lungs, than is equal to the car-
bonic acid exhaled. The actual volumes of the inspired and
the expired air, are as 97'2 to 99’5 ; but, after the equalisation
of their temperature, the volume of the exph-ed air, is
so reduced, that it becomes less, by the amoimt of ox}'geii
absorbed in excess of that of the carbonic acid given out.

The surplus of watery vapour in the expired air, as com-
pared with that in the inspired air, depending on the hygro-
metric condition of the air before it is breathed, it becomes
difficult to estimate tlie daily quantity of water actually
exhaled from the hmgs. This has, however, been variously
calculated at from 11 to 16 oz., or, as an approximate average,
at 15 oz. per diem ; but the quantity, according to modifying
circumstances, ranges from 6 to 27 oz. The source of this
vapour, is the water of the blood, and thus, like the aqueous
basis of the secretions and excretions, it must assist in regu-
lating the degree of fluidity of the blood. Some of the vapour
of the breath, comes from the fauces, mouth, and nose, but the
greater part, from the air-cells and air-tubes. It would seem
that a small quantity of hydrogen is converted into water in
the resjiiratory process, and may also come to be thus expelled.
After taking food, or alcohol, the pulmoniu'}' e.xhalation is said

CHANGES OF COMPOSITION IN EESPIEED AIK.

437

to be increased, bnt it is lessened during fasting. As a rule,
the expired air is almost comjDletelj’^ saturated with vapour,
holding as much as it can dissolve, according to its tempe-
ratm-e ; but this is true only of calm respiration ; for in
hurried breathing, neither can the air be elevated to its
highest temperature, nor can it be completely saturated with
moisture. The more calmly air is breathed, the greater the
loss of water by the lungs. Lastly, the drier the inspired air,
the greater must be the amount of pulmonary exhalation ; ibr,
in breathing air already perfectly saturated, only such further
quantity of water can be added to it, as its increase of tem-
peratiue in the lungs, will enable it to dissolve. The inhala-
tion of actual vapour, stops the pulmonary exhalation. So, too,
when the temperature of the surrounding air, is 100° or 102°,
and it is already satruated, the temperature of the blood itself
being about the same, no further exhalation of water from the
lungs, is possible ; nor can the skin then give off more watery
vapour. Under such circumstances, the kidneys, and perhaps
also, though to a slight extent, the mucous membrane of the
intestines, excrete more actively. The pulmonary exhalation
contains, besides Avater, traces of carbonic acid, ammonia,
chlorides, urates, and even some albuminoid substance, and
it readily undergoes decomposition.

The changes in the composition of the expired air, are regu-
lated by that of the inspired air. The composition of the
atmosphere, in fi-ee space, is singularly uniform in different
localities, and at different altitudes. By Aveight, supposing it
to be dry, it contains nearly 77 parts of nitrogen, and 2‘6 of
oxygen. Besides these, its essential constituents, it contains a
small percentage of carbonic acid, disengaged into it by ter-
restrial agencies, partly physical, such as volcanoes and springs,
partly chemical, as the decomposition of carbonaceous matter,
but chiefly organic, as from the respiration of plants; the
atmo.sphere also presents minute traces of nitric acid, ammonia,
and carburetted hydrogen, from the decomposition of animal
and vegetable substances. In towns, it often contains sul-
phuretted hydrogen and sulphurous acid, from the combustion
of coal ; in the neighbourhood of chemical works, it may also
be charged Avith chlorine, mineral acids and metallic sub-
stances. Under certain circumstances, a very pure air contains
the important substance known as ozone, Avhich is now usually
regarded as a modification of oxygen. It is most abundant in
sea air, in early morning, and, in England, Avith south-Avest

438

SPECIAL PHYSIOLOGY.

or west winds; it is almost absent with east Avinds, and is quite
so in tire centre of large towns, and in the atmosphere of
dwellings.

By volume, dry air consists, in round numbers, of 80
volumes of nitrogen, and 20 of oxygen, or of 4 Amlumes of
the former to 1 of the latter. A closer analysis gives, 79
volumes of nitrogen to 21 of oxygen. The quantity of car-
bonic acid gas averages ‘04 volumes per cent., or, as it is
commonly exjDressed, 4 parts in 10,000.

The effect of a single resjnration on the composition of the
air breathed, is first, to remove from 100 volumes of air, about
5 volumes of oxygen, i.e. about ^th its normal quantity of
that gas; and, secondly, to add to it, about 4 volumes per
cent, of carbonic acid gas. Besides this, hoAvever, the quantity
of nitrogen is slightly increased ; and ammonia, carbm’etted
hydrogen, certain salts, organic matter, and various imdeter-
mined volatile substances, are added to the air in the respira-
tory process.

The annexed Table, from Vierordt, shoAvs the percentage
composition, in volumes, of air, before, and after, it has been
once breathed ; the air being, in both cases, supposed to be
perfectly dry. The minute trace of carbonic acid gas iu un-
breathed air, only '04 per cent., is here neglected.

Atmospheric Air Air once breathed

Nitrogen .... 79'2 . . . 79’3

Oxygen 20-8 . . . loA

Carbonic Acid . . . — . . . 4’3

Loss — . . .1

100 100

During a single respiration, therefore, 5'4 parts of oxygen
disappear, being absorbed by the lungs ; Avhilst only 4‘3 jxirts
of carbonic acid are exhaled from those organs. IMoreover, a
minute quantity of nitrogen appears to be given off into the
expired air. Lastly, oAving to the excess of oxygen absorbed,
over the carbonic acid exhaled, there is a loss of 1 per cent, of
the air inspired. These results are founded on nearly 600
observtitions ; but, as Ave shall hereafter see, individual expe-
riments exhibit remarkable deviations, according to numerous
circumstances.

Absorption of Oxygen. — The qtiantity of ox)'gen absorbed
in respiration, is determined by careful examination of the
quantity left in the expired air. This is done by using pyro-
gallic acid, Avhich greedily attracts it, to take it up, or by com-

ELIMINATION OF CARBONIC ACID.

43a

billing it with hydrogen, by means of the electric spark. There
is no doubt that the greater portion of the oxygen absorbed,
which in a single respiration is about |-th the total quantity
in the air, combines somewhere, and in some ivay, with car-
bon, to Ibrm the carbonic acid which is exhaled. But as the
carbonic acid produced, exactly equals in volume the oxygen
concerned in its jiroduction, the surplus of oxygen absorbed
over the carbonic acid exhaled, must remain in the system, and
is probably therein combined with hydrogen, or with the sul-
phur and phosphorus of the albuminoid constituents of the
body. In Man, from ithto ^th of the total amount of oxygen
absorbed, does not reappear in the carbonic acid, but remains
to be combined with other o.xidisable substances. In dogs fed
upon carbhydrates, such as starch or sugar, or even upon
milk, -^ths of the oxygen absorbed, are returned as carbonic
acid, only remaining in the system ; if large quantities of
flesh are eaten, more of the oxygen, i.e. -1th, is retained ;
lastly, when fat alone is consumed, ^^ths are retained, as if a
pure fat diet stimulated the oxidation of the nitrogenous
tissues (Regnault and Reiset). Again, in Herbivorous animals,
■which consume many carbhydrates in their food, the pro]iortion
of oxygen retained in the system, is exceedingly small ; whereas,
in Carnivorous animals, the food of which is chiefly' nitrogenous,
but also fatty, a very large proportion is retained (Dulong and
Despretz). In starving animals, also, which practically live
carnivorously, ix. on their ovvn tissues, a large proportion of
the oxygen is retained, amoimting even to fths of the total
quantity absorbed.

Elimination of Carbonic Acid. — The fact of the elimination
of this gas from the lungs, may be shown by blowing slowly
through a tube into lime water, which soon becomes turbid
from the formation of carbonate of lime, more especially as the
last quantities of air are being expelled from the chest. The
determination of the quantity of carbonic acid gas given off
in respiration, is extremely difficult, notwithstanding the in-
genuity of the methods enq)loyed for this purpose.

The simj)lest method, used by Prout, Dumas, Vierordt, and
others, consists in causing a person to inspire air through the
nose, and expire it through a tube, held in the mouth, into a
closed bag or receiver ; and then in analysing the e.xpired air,
by agitation with lime-water or with a solution of caustic
potash, either of these subskinces absorbing the carbonic acid,
which can thus bo measured. The oxygen has, at the same

SPECIAL PHYSIOLOGY.

.(■10

time, been estimated, by means of pyrogallic acid, or by de-
flagration with hydrogen, by means of the electric spark
(Vierordt). Such a method, excellent for individual trials, is
not adapted for general or comparative experiments ; because
the same person does not, under such conditions, breathe
equally, at all times, even after considerable practice ; nor can
different persons breathe equally, in regard to each other, differ-
ences in the depth and duration of the respirations, rendering
a comparison of the results fallacious.

For these reasons, observations have been made on men and
animals, placed in suitable hermetically closed chambers, and
able to breathe with less, or even no restraint. The hrealhing-
chamber communicates with the air by means of a small
supply tube on one side, and on the other, is connected, by a
tube, with an asph'ato?', i.e. a second closed chamber filled
with Avater ; according as this w'ater is permitted to flow
from the aspirator, air is Avithdrawn irom the breathing- cham-
ber, Avhilst fresh air enters by the supply tube. To ensure the
absence of carbonic acid irom the air employed, the supply
tube has a bend in it, containing a solution of caustic potash.
The tube connecting the breathing-chamber Avith the aspirator,
has also a bend containing asbestos, moistened Avith concen-
trated sulphuric acid, for the absorption of the exhaled Avater;
besides this, it is fitted Avith a Liebig’s potash-tube, for fixing
and Aveighing the carbonic acid formed in respiration, and
also Avith another bent tube, for a£jain desiccating the remain-
ing air. By such an apparatus, the quantity of air passing
through the air-chamber, and the quantity of carbonic acid
produced in any given time, can be determined (Dulong and
Despretz’s experiments on animals). In observations on men,
the body has been enclosed in a second smaller box, so that the
head alone projected into the air-chamber ; the products of
cutaneous respiration and exhalation, are thus separatedfrom the
pulmonary respiration and exhalation, the gases and vapour
given off by the skin being retained in the smaller box, and
those given off by the lungs being discharged into the breath-
ing-chamber (Scharling’s and Hannover’s experiments on
IMan). By others, the face alone has been covered Avith a
tight-fitting mask, through A\diich a stream of air enters by
tAvo A'alved openings, and from Avliich it is draAAm off through
a tube into a receiver, by means of an air-jAump (Andral and
Gavarret). Instead of supplying the breathing-chamber, in
Avhich animals have been placed, AA-ith pure atmosjAheric air,

ELIMINATION OF CARBONIC ACID.

441

known quantities of oxygen, proportioned to the quantity of
carbonic acid formed, have been introduced. Tlie arrange-
ments necessary for the gi’adual absorjDtion of the carbonic
acid and the introduction of fresh oxygen, render this apparatus
somewhat complex, but interesting results have been obtained
by it (Eegnault and Reiset). In long-continued experiments,
however, the quantity of nitrogen in the chamber, gradually
increases by exhalation from the animal’s lungs ; hence the
atmosphere breathed by it, is no longer normal, and the
respiration is modified accordingly.

The experiments of Pettenkofer and Voit, undertaken with
the pecuniary assistance of the late King of Bavaria, are still
more elaborate, costly, and complete. A large closed breathing-
chamber is provided, in which the person experimented upon,
can live and breathe for many hours as easily as in an ordinary
apartment ; and through it, copious streams of air, as much
as 75 cubic metres per hoiu, are drawn, by means of a double
pimip worked by a small steam-engine, the total quantity
passed through, being accurately registered, after desiccation,
by a gas-meter interposed between the chamber and the pump.
Atmospheric air is admitted to the chamber by proper aper-
ttmes, and the amount of carbonic acid gas and water already
contained in it, is accurately determined. The contaminated
air leaves the chamber by two tubes, one passing from near
the ceiling, and the other Irom near the floor, which then join
a common tube ; this tube leads into a desiccating box, from
which the dried air passes through the gas-meter to the
cylinders of the double air-pump. To absorb and measure
the whole of the carbonic acid gas contained in this large
stream of air, the total product of the respiration of the
person living in the chamber, would be an inconvenient
proce.ss ; accordingly, a small portion of the contaminated air is
diverted for that purpose, through an analysing apparatus,
into which this portion of the air is drawn by a peculiar
suction- and pressure-pump, moved by the steam-engine which
works the larger pump. This portion of air passes in suc-
cession, through an apparatus which ab.sorbs and measures, first
the water, and then the carbonic acid contained in it, and after-
wards through a desiccating box and small gas-meter,by which it
is ultimately measured. Its (juantity, compared with the larger
quantity drawn through the main tube, furnishes the means
of calculating the total quantity of carbonic acid eliminated
by the person confined in the breatliing-chamber, in a given

442

SPECIAL PHYSIOLOGY.

time. The quantities of carbonic acid gas and water, formed
by the combustion of a stearin candle in the chamber, may be
determined by this apparatus, as correctly as by the ordinary
process of organic analysis.

Dr. E. Smith has employed a small mask, which fits tightly
over the mouth and nostrils, and is provided with a valved inlet
and outlet. The air is inspired through, and measured by, a
spirometer consisting of a delicate gas-meter. The expired air
passes through a desiccator, containing sulphuric acid to absorb
watery vapjour ; then through a gutta percha box, divided
into many chambers and cells, containing caustic jDotash, and
offering a surface of 700 square inches, so as to abstract the
carbonic acid ; and, lastly, through a second desiccator to
retain any moisture carried off and lost, from the p^otash box.
The increase in weight of the mask, with the connecting-tube
and first desiccator, shows the amount of vapour exhaled from
the lungs ; whilst the addition to the joint weight of the potash
box and the second desiccator, gives the weight of the carbonic
acid expired.

Eegnault and Eeiset, Pettenkofer and Voit, and Dr. Edward
Smith, have endeavomnd to determine not merely the amount
of carbonic acid eliminated, in ordinary breathing, but also
the influence of those conditions which modify that amount,
and likewise have attempted to obtain data for comparing the
quantity of carbonic acid formed and of oxygen taken in, with
the animal heat evolved.

Some only of the results obtained by various observers, can
here be quoted. Dumas, calculating that by an adidt male, of
average size, 320 cubic inches of air are respired in one
minute, and that this contains on expiration, 4 per cent, of
carbonic acid, concluded that about 13 cubic inches of car-
bonic acid are exhaled per minute, which would be equal to
a total of 5|- oz, av. of carbon thrown off by the lungs in
twenty-four hours. The calculations of Valentin and Brunner,
Davy, Allen, Pepys, and Lavoisier, agree closely, yielding, as a
general result, 8 oz. of cai’bon exci'eted by the lungs in twenty-
four hours. Andral and Gavarret estimated the daily quantity
at 9 oz. ; Vierordt says that it varies from 5 to 8 oz. Dr. E.
Smith found, as an average of eight exp^eriinents, the daily
quantity, in a state of rest, in four men, whose meiui height
was 5 feet 9| inches, to be 7T44 oz. ; the extremes were
5'G oz. and 7’85 oz. With an ordinary amount of exercise.

I

ELIMINATION OF NITROGEN.

443

he estimates the quantity at about 8^ oz., and in a working
man I'ully engaged in labour, at rather more than 11^ oz.

Adopting as a basis of calculation, the estimate already given
at ddS, viz. of 300 cubic feet, or 518,400 cubic inches, as
the total quantity of air respired in twenty-fom- hours, by an
average-sized adrdt male, 5 feet inches in height, allowing
ibr the effects of work in the day and the inffuence of repose at
night, and, moreover, calculating that the average quantity
of carbonic acid in the air when expired is 4 per cent., then
20,730 cubic inches of carbonic acid would be given off in
the twenty-four hours. As 100 cubic inches of carbonic acid
gas, weigh 47 ‘2 G grains, this quantity would weigh about
9,800 grains, Avhich would contain 2>G72 grains, or rather
more than G oz. av. of carbon. This is perhaps a fair calcu-
lation for a man of medium size, not engaged in any special
exercise, or labour.

Elimination o f Nitrogen. — The nitrogen of the atmosphere,
which serves to dilute the oxygen, is, to a slight extent, absorbed
by the blood, for that ffuid always contains nitrogen in a
state of solution. Nitrogen, however, is also given off from
the blood through the breath ; and the balance appears to be
rather in favour of the process of elimination. The quantity
thus thrown off by Avarm-blooded animals, is so minute as
never to exceed consumed ( Vierordt) ;

sometimes it is less than y^th part (Regnault and Keiset).
The source of this small excess in the nitrogen exhaled, was
at one time supposed to be the nitrogenous aliments, the
quantity of nitrogen excreted by the kidneys, skin, and intes-
tines, being supposed to be less than that taken in the food.
The quantity of nitrogen not accounted lor in the renal, cu-
taneous, and intestinal excretions, has been said to be equal to
yjth of the oxygen consumed in an adult, which nearly agrees
with the estimate of Kegnault and Keiset above mentioned.
But, according to Voit and others, however, all the nitrogen of
the food which is actually subjected to metamorphosis in the
blood, is accounted lor in the nitrogenous constituents of the
urine. The minute and unimportant excess in the exjjired
air, may, therefore, be derived frona the atmospheric air,
which is swallowed with the saliva, food, and drink, and is
taken iq> by venous absorption ; its oxygen being utilised in
the blood, tlie nitrogen escapes through the walls of the pul-
monary capillaries and the air-cells, into the breath. In favour

SPECIAL PHYSIOLOGY.

441

of this view, it may be added, that the decomposition of nitro-
genous substances in the system, so as to yield free nitrogen,
is unkno%Tn ; that in starving animals, which probably swallow
less air, nitrogen is not given off in excess, but some of it seems
rather to be absorbed ; and lastly, that whilst the quantities
of oxygen and carbonic acid in arterial and venous blood,
dilFer in a constant manner, the quantity of nitrogen follows
no such rule, and even varies in both kinds of blood.

Other Substances Eliminated in the Breath. — Chloride of
sodium, hydrochlorate of ammonia, uric acid, and urates of
soda and ammonia, have been found in expired air. The car-
bonate of ammonia, frequently present, is sometimes partly
derived from decaying animal matter between, or belonging
to, the teeth ; but some of it is believed, by certain physio-
logists, to come from the blood. The carburetted hydrogen
occasionally found in the breath, proceeds from the blood, into
which it enters by absorption from the alimentary canal. The
presence of organic matter in the breath, is detected by passing
the expired air through strong sulphuric acid, which, in a
prolonged experiment, becomes broAvn. According to recent
enquiries, this organic substance is albuminoid, and Avhen col-
lected and alloAved to putrefy, becomes- extremely offensiAm ;
Avhen accumulated in small and over-croAA’ded rooms, it has a
foetid, repugnant odour. It may possibly be the medium, or
vehicle, of certain contagions throAvn off by the breath ; it is
not to be confounded Avith the bad smell from carious teeth, or
from idcers in the mouth, pharynx,, or air-passages. IMany
odorous substances may exist in the breath, derfred from
food, drink, or medicines, such as cheese, alcohol, or perhaps
aldehyde, given off after the use of alcoholic beverages, the
volatile principles of garlic, onions, and spices, ethers, chloro-
form, camphor, musk, and many other medicinal substances.
Phosphorus dissolved in oil, and injected into the A'eins of an
auim.al, is given off by the lungs in some imperfectly oxidised
state, so that the breatli is luminous as it passes from the
nostrils.

Effects of Respiration on the Blood and Tissues.

Changes in the Colour of the Blood. — The most obA'ious
change effected in tlie blood, as it passes through the lungs, is
that fi-om the dark purple venous, to the bright scarlet arterial,
tint. A similar change of colour takes idIucc on agitating dark

CnANGES IN TEE COLOUR OF THE BLOOD.

4J5

venous blood with air, and, still more quicklj', with oxygen ;
it also occurs when venous blood is introduced into a moistened
bladder, and suspended in air or in oxygen gas. The causes
of this change of colour, have been the subject of much enquiry.

It is found that on adding water to bright arterial blood, it
becomes of a dark hue ; whilst strong solutions of common salt,
saltpeti-e, or bicarbonate of potash, when added to venous
blood, immediately brighten its colour ; this effect has been
attributed, either to the direct action of the saline substances,
or else to the change which they produce in the specific gravity
of the blood. It has been supposed that the red corpuscles,
by exosmosis of fluid into the denser solution of the saline
substance, shrink, and thus, from being slightly biconcave,
become deeply so. On the other hand, the addition of water,
has the effect of producing an endosmosis of fluid iuto the
corpuscles, and so causes tliem to swell, and assume a flat or
even biconvex form.

These opposite changes of shape have been supposed to
modify the power of the corpuscles to absorb coloured light,
more being absorbed when they are swollen, and less Avhen
they are shrunk. But, according to Professor Stokes, this
explanation is inconsistent with optical principles, and the
change of colour is due to a modification in the refractive
poAver of the corpuscles; in the shrunken state, their refractive
poAver is increased, and, accordingly, a larger amount of reflec-
tion takes place from the surfaces of contact of the corpuscles
Avith the surrounding fluid ; Avhilst in the distended state, their
refractive poAver is diminished, and less reflection takes place
from their surfaces. But, although the brilliant coloirr, pro-
duced by the addition of strong saline solutions to the blood,
and the dark hue occa.sioned by diluting it Avith Avater, may be
thus satisfactorily explained, the natural alterations of colour
produced in the blood, by the respiratory changes, cannot be
so accounted for ; though venous blood is of someAvhat less spe-
cific gravity than arterial, yet there is no evidence of its con-
taining fewer salts ; moreover, direct observation has failed to
detect any difference in form, betAveen the corpuscles of the
two kinds of blood ; and lastly, the inadecjuacy of such a
purely physical expjlanation, is proved by the fact that, even
Avhen the red corpuscles are entirely dissolved, or Avhen pure
Solutions of criAorin or the colouring substance of the blood,
are employed, precisely similar changes in colour ensue,
from alternately agitating them Avith o.xygcn and carbonic

446

SPKCIAL PHYSIOLOGY.

acid, in the former case, the colour being brightened, and in
the latter rendered dark. The nature of the changes thus in-
duced in the cruorin of the blood, has been revealed by the
photo-chemical discoveries of Hoppe and Stokes, in which the
so-called spectmin analysis is employed, to detect most recon-
dite changes in the cruorin.

The formation of the prismatic solar spectrum, by passing a beam of
simligbt through a prism, has already been explained (toI. i. p. 546). In
this spectmm, when sufficiently magnified, it has long been observed,
that numerous, fine, dark lines exist, the lines of Frauenhofer; these are
owing partly to the presence of vapour in the air, which refracts some of I
the light, but chiefly to the absence, in the light examined, of luminous
rays of certain degrees of refrangibility ; the consequence of which is, that
some parts of the spectrum are left unoccupied by any light whatever.

In the solar spectrum, Frauenhofer described 80 dark hands or lines ; but
2000 are now recognised. Light obtained from different sources, as by
the combustion of different substances, or ordinary light first passed '
through transparent bodies, solutions, or even through the vapours of
volatile substances, or proper gases, either colourless or coMired, and after-
wards transmitted through a prism, also forms a spectrum ; but on com-
paring the magnified spectra of different substances, it is found, in
many of them, that the dark bands differ in number, position, width, and
intensity ; and, moreover, that in the case of certain lights, which are
coloured, colour bands of different position, number; width, and inten-
sity, make their appearance. The yellow colour band of sodium, is a
remarkable example of this.

The dark bands, sometimes called absorption hands, and the colour
hands, being characteristic and constant, for certain substances, they
constitute most delicate means of detecting, and discriminating between,
such substances. This is done by the spectroscope, an instrument con-
sisting essentially of a tube with a slit at one end, a prism at the other,
and a small magnifying glass with which to magnify the spectrum.
This method is the so-called spectrum analysis, by which, not only have
new substances been detected in chemical processes upon the earth, but
some at least of the constituents of the luminous atmosplieres of distant
stars, have been determined. It has also been emp]o}’ed to follow the
entrance of peculiar substances, such as lithium and emsium. into the
blood and tissues of living animals, to measure their rate of absorp-
tion, their preference for particular tissues, and their periods of excre-
tion from the body (Bence Jones). To the same observer, we owe very
interesting rese, arches, in which the jluorescent property of quinine
(vol. i. p. 547) is made use of, to follow that substance into, and out of,
the living economy, by its presence or absence in the crystalline lens of '
the eye. It, moreover, appears that a peculiar animal substance, also ■
fluorescent, and therefore named by Dr. Jones, quhioidin, is constantly j
present in the animal body. i|.

Amongst otlier results of the spectrum analysis of coloured solutions, . ■.
it was discovered by Hoppe, that dilute solutions of blood, produce itco
peculiar dark absorption bands of great beauty and distinctness, situated

SPECTRUM ANALYSIS OF BLOOD.

447

in the spectrum, between the D and E lines of Frauenhofer, and having
a remarkably bright intermediate colour band. He showed that this
speetmm was formed by the coloured blood of animals generally; that
the red colouring substance seemed to remain unchanged by the action
of alkaline carbonates and caustic ammonia, for its spectrum remained
unaltered ; but that it was instantly decomposed by acids, and more
slowly by caustic alkalies, a substance being then produced, which
causes different absorption bands, and corresponds with the htematin
of Lecauu.

This subject has since been further investigated by Professor Stokes.
To examine the natural blood spectrum, he placed a small portion of
blood well diluted with water, or a watery extract of the clot, in a test-
tube ; this being held up to the light, behind a fine slit in a piece of
black card or a metal plate, and looked at through a prism, the two
characteristic, sharply-defined, dark absorption bands, with the in-
termediate bright streak, were readily seen. On adding to the coloured
solution, a reagent capable of abstracting oxygen from it, a remark-
able change occurred in the spectrum. First, it became a little darker ;
but, besides this, instead of the two dark bands with their intermediate
bright streak, a single, broader, and less defined band was now seen,
situated nearly opposite the place of the bright band in the spectrum
of the simple solution. Since the solution of blood is alkaline, and
since acids, as just mentioned, decompose its colouring substance, it
was necessary to employ a peculiar deoxygenating agent ; the one
selected, was a solution of protosulphate of iron, containing a small
quantity of tartaric acid, which prevents the precipitation of the iron by
alkalies ; this was rendered slightly alkaline, by a little soda. On next
exposing the deoxygenated and altered coloured solution to the air in a
shallow vessel, or on agitating it with air, by shaking it in a long tube,
it was found that the colour again became brighter, and that, on examina-
tion with the prism, the characteristic dark bands, with the interme-
diate bright one, again appeared. These changes were evidently attri-
butable to the reoxygenation of the colouring substance by the oxygen
of the air. This beautiful experiment realised the supposition pre-
viously entertained by Stokes, that he might imitate, and possibly ex-
plain, the change of colour of arterial into venous, and of venous into
arterial, blood. That the single band of the altered solution, does not
belong to the reagent, is shown by examining that separately ; and
that it is not produced by a compound of the reagent with the colour-
ing substance, but simply by deoxygenation of the latter, is proved
by the same effects being produced by other deoxidising agents, such as
protochloride of tin, and hydrosulphuret of ammonia, and also by the
ordinary and well-known displacement of oxygen, by means of carbonic
acid. Moreover, these reagents have themselves no power to produce
the newly-observed colour band.

From the.se experiments, it is concluded by Stokes?, that there
exists in the blood, a natural colouring matter, which might
be named cruorin, capable, like the colouring matter of indigo,
of a.ssuming, by alternate ab-straction and reintroduction of
oxygen, two states of oxidation, in which it differs in colour

44S

SPECIAL PHYSIOLOGY.

and in its action on the spectrum. The hfematin of Lecanu is
an artificial compormd, produced by the decomposition of this
cruorin by powerful acids, and is named by Stokes, hrowu
hcematin, to distinguish it from red heematin, formed by the
oxidation of the brown variety, both of which show different
absorption bands to those of cruorin.

The cruorin in its bright condition, is named scarlet cruorin,
and in its dark condition, ci'uorin ; the former gives the

spectrum Avith two dark bands and an intermediate light one, and
the latter, that Avith a single dark band. The purple cruorin,
or deoxygenated kind, is supposed to exist in venous blood,
and the scarlet, or oxygenated kind, in arterial blood. The
eAudent attraction of cruorin for oxygen, is supposed to account
for the absorption and combination of that gas Avith the blood ;
and thus also tor the special attraction, or affinity, of the red
corpuscles for oxygen, of Avhich, indeed, they have been often
named the carriers.

As apparently opposed to these conclusions, it is found that
ordinary venous blood exhibits the spectrum of the scarlet
cruorin, and not that of the purple cruorin ; but this, as
observed by Stokes, may merely shoAv that most of the cruorui
in venous blood, is still scarlet cruorin, the colouring substance
being only partially converted into the purple condition.
Venous blood, indeed, like arterial blood, still contains oxygen
as Avell as carbonic acid, though in different proportions; and,
althoiAgh it is unequal to the perfect maintenance of the
functions of the muscular and nervous substance, it is still
better than no blood at all (BroAvn-Sequard). INIoreover,
e.xtensive hemorrhage is not necessarily fatal ; and persons
affected Avith chlorosis, exhale carbonic acid as freely as those
in health. It is possible, also, that carbonic acid may act less
poAverfully, Avhen the blood is undiluted than AA'hen, as in ex-
periments, it is mixed with AA^ater.

The cruorin of the blood being supposed, in the act of
I’espiration, to undergo oxygenation as it assmnes its scarlet
colour, its deoxygenation, or reduction, may be effected by
substances contained in the blood, AA’hich themselves undergo
oxidation at its expense. Such a change certainly takes place
in blood diluted and put aside, before putrefaction takes place, .
the spectrum being distinctly altered to that of purple cruorin,
and being changed back again to that of scarlet cruorin, by
agitation As'ith air. A temperature as high as tliat of the blood
in the body, facilitates these changes.

AFFINITY OF CRUORIN FOR OXYGEN.

44 9

The possible mode of occurrence of such alternate changes in tlie
blood in the systemic and the pulmonary capillaries, is illustrated by
Stokes, by first reducing, or deoxygenating, a solution of scarlet cruorin,
by means of a slightly alkaline solution of the protoxide of tin in tar-
taric acid, and then re-oxygenating it, by -agitation of the altered coloui-ed
solution with air. If the mixtiu-e be now allowed to stand for two or
three minutes, the colouring matter is again slowly deoxidised; by agi-
tation it is once more oxidised ; and so on for a number of times. In
this experiment, the purple cruorin absorbs oxygen more readily than
the salt of tin does ; but afterwards, it slowly parts with oxygen to that
salt.

In the same way, the purple cruorin, as it passes througli
the lungs, absorbs oxygen by a special affinity, and then in
circulating through the systemic capillaries, it is partially
deoxygenated, to supply the tvants of the disintegrating tissues,
by a so-called parenchymatous respiration] on returning to
the lungs, it is once more reoxygeuated.

The various alterations in the colour of the blood, noticed
in different conditions, accord with this conclusion. Thus the
blood is unusually dark as it returns from the muscles, and
the depth of its colour is in exact proportion to the activity of
those muscles, when, as we shall see, it also contains the most
carbonic acid. On the other hand, the venous blood returning
from glands in a state of active secretion, is of a bright scarlet
hue ; whereas, when the glands are inactive, it is dark (vol.
i. p. 333 ; vol. ii. pp. 5G, 350). In the latter case, the quantity
of blood passing through the gland, is .small ; nutrition proper
is going on, and a proportional quantity of carbonic acid is
formed and taken up ; whereas for active secretion, the condi-
tions existing are, a larger supply of blood, with a proportion-
ally less amount of deo.xygenation. Again, it has been noticed
that, at high temperatures, there is much less difference in the
colour of the arterial and venous blood-current, and also a
less amount of resjiiratory interchange ; whereas, at low tem-
peratures, the difference of colour is greater, and so likewise
is the activity of the respiratory iwocess. In anmmia, in the
•state of hybernation, and also in sleep, the venous blood has
the same colour as the arterial ; and both the pulmonary and
the parenchymatous respiration are imperfectly performed.
Lastly, in asphyxia and in cholera, the blood is exceedingly
dark, and, in both diseases, contains unusually large quantities
of carbonic acid.

A further result of these researches, is to show that the
oxygen carried through the body by the blood, is, to a largo

VOL. It. 0 a

450

SPECIAL PHYSIOLOGY.

extent, actually chemically combined with it, i. e. with the
cruorin of the red corpuscles, though some must be merely
dissolved in the liquor sanguinis, and all must pass through
that fluid, to enter and escape from the corpuscles. But that
a certain proportion of the oxygen is retained in the liquor
sanguinis, is shown by the fact, that the clot of dark venous
blood assumes a bright hue when placed in the serum of arterial
blood, or even of the scarlet venous blood returning from an
actively secreting gland. It is uncertain whether any of the car-
bonic acid is specially attached to the red corpuscles ; it would
rather seem not. The coagulum of the scarlet venous blood
from a gland, as well as that of arterial blood, becomes dark-
ened, when placed in the serum of dark venous blood ; so that
carbonic acid certainly exists in the liquor sanguinis of venous
blood. It appears to be partly dissolved in the serum, and
is partly, perhaps, in a state of loose chemical combination.

Changes in the Fibrin of the Blood.

During the aeration of the blood in the lungs, and perhaps as
a special result of the action of oxygen ab.sorbed from the air,
the amount of fibrin is increased in arteilal, as compared with
that in venous blood ; a difference also exists in the coagu-
lating power of the arterial fibrin, which forms a firmer clot
than that of venous blood. The influence of oxygen, in in-
creasing the amount of fibrin, has been shown, by causing
rabbits to breathe pure oxygen for a short time, and also by
inducing an unusual activity of the respiratory movements by
means of electricity applied to the spine and chest. In these
experiments, the quantity of fibrin in the arterial blood was
increased respectively to 2 4 and 2’9 parts in 1000 of blood;
whereas in the ordinary arterial blood, the proportion found was
only 1’65 (Gardner). The fibrin is, of course, produced at the
expense of some other albuminoid body, either globulin or
albumen. Even out of the body, a subsUmce somewhat like
fibrin, though not positively determined to be fibrin, has been
produced by transmitting o.xygen gas (A. II. Since), or ozone
(Gorup-Besanez), through a solution of albumen.

Change in the Temperature of the Blood.

Numerous attempts have been made, to determine whether

re be any diflerence, and if so, what difference, between

I

CHANGES IN THE GASES OF THE BLOOD. 451

the temperature of the blood, before and after it has passed
through the lungs. The older physiologists, and also some
recent observers (Harley and Savory), have maintained that
the blood in the left ventricle, is warmer, by from 1° to 2° than
that in the right ventricle ; and, in accordance with this, it
has often been supposed that the oxygen combined directly with
certain constituents of the blood in the lungs, to produce the
whole of the carbonic acid given off in respiration. But it is
now known that this latter supposition is incorrect. Many
observers, moreover, have found that the blood in the left side of
the heart, is not so warm as that in the right cavities, owing,
as they maintain, to a cooling process, caused by the entrance
into the lungs of air of a lower temperature than the blood,
and by the evaporation of moisture from the internal pulmonary
sm-faces. This does not affect the general conclusion, that the
venous blood returning from the limbs, is cooler than the
arterial blood of the same parts. We shall revert to this sub-
ject in the Section on Animal Heat.

Changes in the Gases of the Blood.

It has been elsewhere noticed (pp. 165, 168), that the vapour
of water, and also many volatile substances and gases, are readily
absorbed into the blood by the lungs ; and, indeed, one of the
two chief phenomena of respiration, viz. the entrance of o.xygen
into the blood, illustiatcs the absorptive power of the pulmonary
mucous membrane.

This absorption of oxygen from the inspired air, by the
venous blood brought to tlie pulmonary capillaries, is associ-
ated with the evolution of carbonic acid, which escapes from
that venous blood, and is added to the air about to be expired.
These two joint interchanges of the gaseous elements of
the air and of the blood, are essential steps in the conversion
of venous into arterial blood. That the blood participates in
these changes, is shown l)y the fact that venous blood contains
less oxygen and more carbonic acid than arterial blood, which,
on the other hand, contains more oxygen and less carbonic
acid, as shown by the following table (Magnus).

Oxygen Carbonic acid

100 vols. of Venous Wood . . 5 vols. 26 vols.

100 vols. of Arterial blood . .10 vols. 20 vols.

It has also been found that the proportions of oxygen and

0 o 2

I

T

l(

[

{

I.

1

452

SPECIAL PHYSIOLOGY,

carbonic acid in venous blood returning fi-om muscles at rest,
are 7'5 and 31, and from muscles in action, 1-2G5 and 34-4;
whilst in arterial blood the proportions are 17'3 of oxygen
and 24'2 of carbonic acid (Sczelkow). According to Magnus,
arterial blood contains twice as much oxygen as venous blood
generally, whilst, in the special case of the blood from muscles,
the proportion is at least as 2'3 to 1. Again, ordinary venous
blood contains ^ more carbonic acid than arterial, and that
from muscles at rest, about \ more.

The interchanges of oxygen and carbonic acid between the
air and the blood, which characterise respiration, have, through
the researches of Dalton, Draper and Graham, received a partly
physical and a partly chemical explanation. The elimination of
urea and uric acid, by the kidneys, and of certain excretory
ingredients of the bile, is accomplished by organic vito-chemical
processes performed by certain special epithelial cells ; but the
absorjition of oxygen by, and the elimination of carbonic acid
from, the lungs, or other respiratory organ, are purely phy-
sical and chemical processes. These may, indeed, be imitated
artificially out of the body ; for, as already mentioned, if a
moist bladder be filled with venous blood, and be supended in
atmospheric air or oxj'gen, the surface of the blood in contact
with the bladder, soon becomes scarlet, and, during that
change, oxygen is absorbed, and carbonic acid is given out
from it, throiTgh the moistened bladder. It is remarkable that
a function of the animal economy, so immediately and con-
stantly necessary to life, is removed from the contingencies
surrounding a purely organic process, and is brought into the
sphere of physical and chemical actions. It is also worthy of
remark, that the physical processes which accomplish the
escape of the deleterious carbonic acid gas from the blood, and
mix it with the air, also aid in the entrance of the essential
purifying and stimulating oxygen from the air, into that fluid.
The processes in question, are the diffusion of gases, or the ten-
dency of dry gases to diffuse into each other, and their mutual
diffusion when in a dissolved condition.

It was shown by Dalton, tliat, even when a light gas, such as hy-
drogen, is poured into a glass jar, on to the surface of a heavy one,
such as carbonic acid, or when a bottle full of tlie light gas, is inverted
over anotlicr bottle containing a heavy gas, with their mouths applied
to each other, the giscs do not remain stationary, but are mutually
transported into each other against gravity until they have intermixed
in certain definite proportions. The facility with which they intermix

DIFFUSION OF GASES IN THE LUNGS.

453

is such, <as to have been expressed by the phrase that each gas offers no
more resistance to the other, than would an actual vacuum. This simple
intermixtm-e is called the diffusion of gases-, it takes place with a defi-
nite energy, irresistible and invariable, when the conditions exist for
its exercise. The force with which it takes place, and its extent, in any
particular instance, are said by Dalton to be, generally, inversely as the
densities or weights of the two gases respectively. Subsequent experi-
ments on a most extended scale, enabled Graham to determine the true
numerical expression, or law, of this diffusive power or energy of gases,
viz. that the rate of diffusion of any gas, if dry and pure, is inversely
as the square root of its density or specific gravity. Graham showed
moreover, that this diffusion takes place through narrow tubes, and
through porous substances, according to the same law, provided that
the gases be dry and chemically indifferent to each other, and to the
substance of the porous septum. On the other hand, when films of india-
rubber or of shell-lac, moist animal membranes, or even soap-bubbles,
are employed as the septa interposed between any two gases, diffusion
still takes place, but then, not according to the above mentioned law,
but under modifications dependent on the relative solubility of either
gas, in the intexqiosed septum. Lastly, experiments made by Draper,
on gases in a state of solution, show that these still manifest mutually
diffusive tendencies, although not according to Graham’s law of their
simple diffusion in a dry state. This moist diffusion of gases, has
been tenned false gaseous diffusion.

Both simple and spurious difliision occur in aerial respiration
performed by lungs or air sacs, but the latter only, in aquatic
respiration, performed by gills or moist surfaces.

The breathing air in calm respiration, about 20 cubic inches,
amounts to only .Jth of the reserve and residual air together, 180
cubic inches, which are ordinarily retained in the lungs (see p.
433). Even in active respiration, it wotdd only amount to about
ith, viz. 4.5 cubic inches. Hence, so small a displacement of the
air in the lungs, at each inspiration and expiration, cannot di-
rectly influence the air contained in the remote air-cells, espe-
cially as the bronchial tubes constantly increase in their total
capacity, from the trachea to the air sacs. The simple diffusion
of gases here comes into play ; for since, as we shall presently
see, the last portion of air expelled in a long expiration, is
richer in carbonic acid than the first portion, it is probable
that the residual air, which is never expelled from the lungs,
becomes increasingly richer in carbonic acid gas, and therefore
poorer in o.xygen, in the direction of the air-cells; hence, the
diffusion of o.xygen must take place from the larger bronchi,
to which the pure air gains access, towards the air-cells ; whilst
carbonic acid diffuses itself in the opposite direction, from the
air-cells towards the larger air-tubes. The re.spiratory move-

454

SPECIAL PHYSIOLOGY.

ments doubtless continually change the air in the lungs, and, as
it were, partially ventilate the air-passages ; but the energy' and
rapidity of the diffusive process, and its incessant operation,
supplement their effects. The diffusion-process is accelerated by
differences of temperature between any two gases, a condition
constantly operating in respiration. Moreover, the pulmonary
exhalation, which, in the air-ceUs and smaller air-tubes, exi.sts
in the form of vapour, likewise has a similar tendency to dif-
fuse into the drier air in the larger passages. That this
diffusion of carbonic acid gas, actually occurs in the lungs, may
be shown, by steadily holding the breath, with the open mouth
kept in comnn;nication with a bag, or other reservoir, holding
a known volume of atmospheric air, when this latter is soon
found to contain a readily appreciable quantity of carbonic acid.
In apparent death or trance, when the respiratory movements are
suspended, a minimum respiratory interchange of gases may
thus take place, just sufficient to prevent the extinction of
life. In the deepest stages of hybernation in animals, this
also must be the mode of respiration. Under ordinary cir-
circumstances, however, the necessity for air, cannot thus be
relieved ; but successive respiratory movements are excited
through the nervous system, in order to satisfy it.

But the entrance of oxygen into, and the escape of carbonic
acid from, the blood of the pulmonary capillaries, from and into
the air in the air-cells, is not explicable by simple diffu.sion; for
this double process is one of moist or false gaseous diffusion.
Both gases must be dissolved, as they pass in, or out of, the pul-
monary tis.sues and capillaries ; and the actual diffusion result
depends first, on the relative solubility of the diffusing gases in
the fluid of the natural moist septum through which thej' pass,
and, secondly, on the special chemical affinities of those gases
for the blood. The simple diffusion volumes of dry oxygen
and carbonic acid, are in the proportion of 1174 to 1000, the
oxygen, or lighter gas, having a higher diffusion volume than
the carbonic acid or heavier one. But this proportion does not
agree with the ratio of the oxygen absorbed to the carbonic
acid evolved in respiration, which, according to the Table in
p. 438, is as 1255 to 1000. The quantity of oxygen absorbed,
is, therefore, not only greater than that of the carbonic acid
evolved, but greater than that which the law of the diffusion
of dry gases would account for. Again, the relative solubility
of tliese gases in the ivaier of the walls of the air-cells and
cajjillaries, and in that of the blood, will not explain the differ-

AFFINITY OF THE BLOOD FOR OXYGEN.

455

cnce ; for carbonic acid is nearly 30 times more soluble in
water, than oxygen, and, accordingly, it exhibits a liir greater
difiusibility through a dead moist membrane, instead of a less
diffusibility, as occiu'S in actual respiration. It has been shown
that recent blood, even at a temperature of 32°, retains from
IG’8 to 19 ‘8 volumes per cent, of oxygen ; whilst water, at
00°, dissolves not quite 3 volumes. Furthermore, Iresh blood
deprived of its fibrin, at a temperature of 48°, absorbs 178
volumes of carbonic acid ; whilst water takes up about 90
volumes. Hence, the proportion between the oxygen absorbed,
and the carbonic acid exhaled from the blood in respiration,
does not depend on the relative solvent power of the blood
for those two gases, Avhich is about as 1 to 10.

The remarkable affinity of blood for oxygen, is also shown
by another calculation. The absolute quantity of carbonic
acid, which is taken up by the blood, is larger than that of the
oxygen. But in comparison mth Avater, the special affinity of
blood for oxygen, is much stronger than that for carbonic acid ;
for the quantity of oxygen absorbed by the blood, in comparison
with that absorbed by water, is about as 18 to 3, or 6 to 1,
whilst the quantity of carbonic acid absorbed by the blood, in
proportion to that taken up by Avater, is only about as 178 to
90, or le.ss than 2 to 1.

The total quantity of all the gases nonnally contained in
100 volumes of blood, amounts to someAvhat less than 50
volumes, t.e. about half its OAvn volume. This is less than it
is capable of dissolving mider artificial pressure, or through
other means. Of these 50 volumes, about 12’5 are oxygen,
34‘5 carbonic acid, and 3 nitrogen. Of 100 Amlumes of these
mixed gases, the mean of several observations, hoAvever, gives
28'2 oxygen, G4‘7 carbonic acid, and 7T nitrogen. Nitrogen,
therefore, is also absorbed by blood in larger proportion than
by Avater, Avhich can only take up 1'5 volume.s, whilst blood
can be made to absoil) 5 volumes, per cent.

It is plain, that both oxygen and carbonic acid are held in
the blood, not merely by its solvent poAver, as Avas supposed
from the experiments of Magnus, because he obtained those
gases from the blood, by placing it under an air-pump, or by
displacing them with streams of hydrogen ; but that it is in
part, and in great part, held in it by special chemical affinities.
It is, moreover, evident that the absor])tion of oxygen by the
blood, depends on one kind of chemical affinity, and that of
carbonic acid, on another.

456

SPECIAL PHYSIOLOGT.

Tlie oxycjen is supposed almost entirely to enter into chemical
combination, essentially with some constituent of the red cor-
puscles; for although, as shown by its relative effects on dark
clots, the serum may contain variable quantities of oxygen, yet
neither it nor the liquor sanguinis, can absorb more oxygen
than prtre water (Berzelius). That the oxygen is chemically
combined is, moreover, inferred from the fact, that pyrogallic
acid, which has an extraordinary affinity for this gas, does not
withdraw it, when injected in solution into the blood, but ap-
pears unaltered in the urine. The extreme affinity of blood
for carbonic acid, though partly due to the solubility of that
gas in water, may be partly owing to some special absorptive
power in the albuminoid or other organic constituents ; but it
is in a marked degree dependent on the carbonate, or perhaps
rather on the phosphate of soda, which exists in considerable
quantities in the liquor sanguinis.

The special affinity of the red corpuscles for oxygen, has
been atti-ibuted to the iron contained in them, that element
being supposed to be in the condition of a sesquioxide in the
corpirscles of arterial blood, and of a carbonate of a protoxide
in those of venous blood, the oxygen, it is said, being di.splaced
by the’ carbonic acid, which preponderates in venous blood,
and is the source of the carbonate above mentioned (Liebig).
It has, indeed, been alleged that the fibrin is concerned in this
transportation of the oxj'gen through the circulation, it having
been supposed to be in a higher state of oxidation in arterial
than in venous blood. But the spectrum analysis of the blood,
proving that oxygen produces such remarkable changes in the
relations of the cruorin to luminous rays, would lead to the con-
clusion, that it is this colouring substance of the red corpuscles,
Avhich is the real carrier of oxygen through the blood. FiU'ther-
more, it has been shown that the blood corpuscles even absorb
ozone, which is oxygen in a peculiar condition, with great
avidity, and yield it up to oxidisable substances when brought
into contact with them ; the cruorin is also specially con-
cerned in this reaction. In animals provided with a distinct cir-
culation and red blood, the activity of the respiratory function
is closely related to the number and dimensions of the coloured
corpuscles in the blood ; for these are few and large in the
Cold-blooded, whilst they are gi-eatly increased in number and
diminished in size in the Warm-blooded Verte.brata. The
latter arrangement provides for an enormous multiplication of
the surfaces of the corpuscles.

SEAT OF THE OXIDATION FHOCESS.

457

The entrance of oxygen into the blood, being thus due to the
joint action of false gaseous diffusion and chemical affinity, the
escape of carbonic acid gas from the blood, is perhaps dependent
on diffusion only. The accumulation of this gas in the venous
blood, owing to chemical processes to be presently mentioned,
produces a greater tension in the carbonic acid in the blood, than
in that present in the air of the air-cells ; for it is proportion-
ally much more abundant in the former than in the latter.
Hence, an outward diffusion of the carbonic acid dissolved in
the venous blood, through the moist walls of the pulmonary
capillaries and air-cells, and its escape into the residual air, at
the surface of the lining membrane of the cells. The carbonic
acid thus dissolved in the blood, is chiefly contained in a state of
solution in the liquor sanguinis, the red corpuscles having no
special affinity for it. The absorption and evolution of nitro-
gen in the respiratory process, are accomplished also by moist
diffusion.

Two points yet remain for consideration, viz. ; — In what part
of the circulation, and at the expense of ivhat constituents of
the blood and tissues, does the o.xygen ab.sorbed in respiration,
become united with carbon, to produce the carbonic acid given
off? The answer to these questions, constitutes an important
part of the theory of respiration. Previously to the discovery
of oxygen, nitrogen, and carbonic acid, all explanations of the
respiratory process were necessarily vague. The earlier phy-
siologists believed that the air — the source, as they deemed it,
of the animal spirits — found its way through the lungs, and
obtained an entrance, as such, into the so-called arteries.

Oxygen, or phlogiston, was discovered by Priestly and
Scheele, in 1774. Black had already described what he called
fixed air, and Kutherford had determined the existence, in air
respired by an animal, of a peculiar gas incapable of support-
ing further respiration or combustion. Lavoisier named the
gas first discovered by Priestly and Scheele, oxygen ; by him
also, the gas described by Rutherford, now more commonly
known by the name of nitrogen, given to it by Chaptal, from
its being contained in nitre, was named azote {a, not, and zoe,
life), from its inability to support life, in respiration ; lastly,
Lavoisier demonstrated that the fixed air of Black, now shown
to be produced alike by the action of acids on limestone, by
combustion, fermentation, and respii'ation, contains the element
carbon. These great discoveries were indeed the commence-
ment of the modern science of Chemistry, and the foundation

458

SPECIAL PHYSIOLOGY.

of all true chemical theory ; and Lavoisier himself, in com-
bining and adding to the knowledge of his predecessors, at once
applied the results to explain the respiratory process of animal
life, and offered to science the first theory of respiration.

Lavoisier saw that the oxygen absorbed in respiration, united,
in some way and somewhere, with carbon, to produce the car-
bonic acid evolved ; he regarded the process as a sort of com-
bustion, and supposed that the combination took place in the
lungs, i.e. in the pulmonary capillaries, in which the obvious
change from venous to arterial blood, occurs ; the oxygen was
thought to be there immediately transformed into carbonic acid,
and then as immediately given off. But later inquiries have
shown that this view must undergo modification. It was
not known to Lavoisier, that both venous and arterial blood
contain these two gases, and that both, therefore, circulate in
the two kinds of blood ; nor was he aware, that frogs made to '
respire nitrogen or lij'^drogen, that is, an atmosphere destitute
of oxygen, continue for a time to exhale carbonic acid. The
existence of both carbonic acid and oxygen, in solution, in the
entire blood, shows that the combination of oxygen with some <
carbonaceous compound in the venous blood derived from the j
disintegrated tissues, does not take place in the lungs only ; f
but that this union must occur in some other part of the body. 1
hloreover, if this moist combustion took place entirely in the j
lungs, those organs should be very much warmer than any other t
part of the system ; but, thougli some authorities, as already !
mentioned, maintain that the blood in the left ventricle, just^
retmmed from the lungs, is Avarmer than the blood in the right t
ventricle, the alleged increase of temperature has never been i
stated to be more than 2° ; Avhilst eqirally competent observers «
testify to an exactly opposite condition, as regards the tern- •# ,
jierature of the venous and arterial blood, before, aud after, it t
has passed through the lungs.

According to another and more plausible vieAV, the oxygen i
in the aerated blood, partly dissolved in the serum, but chiefly •'
in loose chemical combination with the coloured substance of :
the red corpuscles, and perhaps Avith the fibrin, is conveyed in
the arterial blood, to the systemic capillaries, Avhere a certain r, .
loss of oxygen, and a nearly proportionate addition of carbonic . .
acid, occur, the blood then becoming Amnous. On this suppo-
sition, the process of oxidation, or respiratory^ combustion, takes
]ilace not in the lungs, nor in the pulmonary capillaries, but in
the system, in or near the systemic capillaries. This opinion is 1

SEAT OF THE OXIDATION FROCESS.

459

in harmony with the fact, that the arterial blood once having
acquired, in passing through the pulmonary capillaries,its special
cliaracters, amongst others, its bright colour, retains that colour,
and, by jiresumption, its other qualities also, along the whole
arterial system, only losing them, as it passes through the
systemic capillaries. It is also consistent with other facts,
already mentioned, viz. that, whereas arterial blood contains
more oxygen than Amnous blood, venous blood contains more
carbonic acid. If, as is asserted, the sugar found in the venous
I)lood in the right side of the heart, is absent in the arterial
blood in the left side of that organ, then a small portion of the
oxygen absorbed in the lungs, or else some of that previously
contained in the blood, must have united with that carb-
hydrate, and so have given rise to a certain amount of carbonic
acid; but by far the larger proportion of the oxygen, probably
passes on unchanged, in the arterial blood-current.

How much of the sy.stemic process of oxidation Avhich then
takes place, occurs in the blood of the systemic capillaries, or
in the tissues traversed by those vessels, is yet unknown. But
there is reason to believe, that it happens in both situations.
In the fimctional activity of all the tissues and glands, both
secreting and ductless, but especially of the muscular and
nervous tissues, constant nutritive changes are in progress; their
life never stands still. Disintegration and renewal are tm-
ceasing; and the former always implies retrograde chemical
metamorphoses, of Avhich jjartial or complete oxidation is a
characteristic phenomenon. The production of carbonic acid
is one of the ultimate results. It is supposed by some, that
here a repetition of the false or moist diffusion proces.s, may
take place, oxygen passing from the blood in the capillaries
to the substance of the ti.s.sues and glands, Avhilst carbonic acid
passes from them back into the blood. This interchange of
the two gases at the systemic capillary circulation, constitutes
the parenclu/niatous respiration, which, so far as the blood is
concerned, is exactly the reverse of the pulmonai’y respii-ation;
i'or in the former, the blood loses oxygen and gains carbonic acid,
Avhilst in the latter, it loses carbonic acid and gains oxygen.
This consumption of oxygen, e.spccially by the nervous and
muscular tissues, and its combination with their sub.stance,
are said to explain the .so-called stimulating effect of oxygen
upon those tissues, when they are actively engaged in their
special offices in the living economy. The (juantity of oxygen
consumed, and of carbonic acid evolved, in any given case, are

4G0

SPECIAL PHTSIOLOGT.

found to be proportioned to the degree of activity of tlie ner-
vous and muscular structures. The muscles especially, require
a large supply of oxygen for their nutrition, but more for their
effective action ; the blood returning from a mu-scle at rest,
as we have seen, contains 7'5 vols. per cent, of oxygen, but
when in exercise, only 1'25 vols.; whereas arterial blood con-
tains 17 vols. The prepared muscles of a frog, of course
deprived of circulating blood, continue to absorb oxygen, and
to give off carbonic acid, so long as their contractility is mani-
fested (G. Liebig). Whether during life, this de-nutritive
o.xidation is entirely completed in the tissues, and the resulting
carbonic acid is then transmitted from them, to the returning
systemic blood, or whether some intermediate products of dis-
integration enter the blood, and are oxidated therein, or, lastly,
Avhether both varieties of this combustive process take place
during the ordinary nutritive changes in the tissues, is not Avell
known. That substances properly belonging to the blood, are
also oxidated within the systemic capillaries, cannot be denied;
they are probably fatty matters and carbhydrates, or their
derivatives, introduced into the blood from the food, constituting
the so-called respiratory food \ but it has hitherto been sup-
posed that these are quite as actively oxidised in the lungs,
and in the arterial blood-current generally, as in the systemic
capillaries. But many have believed, and recent researches
appear to shoAv, that although the nutritive processes of the
muscular tissue demand oxygen for the removal of disinte-
grated albuminoid and other materials, jmt that in the active
contraction of muscle, or in the development of animal motion, it
is not, as was supposed, the muscular substance which Avastes,
by being more actively oxidised, but, rather, that some com-
bustible substances in the blood, of the nature of respiratory food,
either fatty matters or carbhydrates, then undergo oxidation,
that this chemical action yields the cai'bonic acid foimied in the
blood of muscles, and that it is at once the source of tlie
motive poAver exercised by the muscles, and of the heat
evolved in the .system. (See the Section on Animal Dynamics.)

In conclusion, then, it appears that the oxygen taken in
during re.spiration, combines first, Avith the tissues during
their action and nutrition, especially Avith the neiwous and
mu.scular tissues ; secondly, Avith the partially effete matters of
the blood, and, lastly, Avith the materials of the respiratoiy food.
Hence, the carbonic acid, Avhich is one of the ultimate pro-
ducts of these changes, is deriAmd partly from the disintegrated

THE SDBSTANCES OXIDISED.

461

sul'stance of the tissues, especially the nervous and muscular
tissues, and partly from substances merely assimilated into the
blood from the Ibod. The oxidation of the respiratory food,
appears to take place in the blood itself, partly in the lungs,
but chiefly in the arterial blood-current, and, during muscular
action, largely in the capillaries of the muscles. The oxida-
tion of the substance of the tissues, may occur, partly, in the
tissues themselves, outside the walls of the systemic capillaries,
but partly, also, in the blood itself, into which certain inter-
mediate eliete products of disintegration may enter, and there
tmdergo further oxidation, after the manner of the respiratory
food.

The second point above suggested for consideration, viz.
the nature of the substances immediately oxidised, must re-
main at pre.sent in obscurity. That they contain carbon is,
however, certain. Some of this united with oxygen, forms the
carbonic acid given off in respiration. They also contain hy-
drogen, frequently in excess of the quantity of oxygen atomi-
cally present in them ; and then, by oxidation of this hydrogen,
water must be formed in the system. But some carbon and
some hydrogen escape perfect oxidation, appearing, combined
with nitrogen and a little oxygen, in the urea, uric, and
hippuric acids, and other nitrogenous excretory compounds.
The sulphur contained in the albuminoid bodies, and the phos-
phorus present more especially in the phosphuretted fats of
the red blood coipuscles and in the grey nervous substance, are
likewise oxidised, at the cost of the oxygen taken in by the
respiratory process, so as to form sulphuric and phosphoric
acids, which appear in combination with alkalies or earthy
matters, in the urine. The sulphur may be partly traced in
the intermediate formation of taurin in the bile. With i-egard
to the nitrogen contained in the so-called nitrogenous tissues,
it is, as already mentioned, almost entirely accounted for, by
the urea and uric acid — passing, probably, through interme-
diate chemical forms, such as creatin, creatinin, sarcin, glycin,
allantoin, and otheis. Minute quantities appear to escape
from the blood, as ammonia. The nitrogen exhaled from the
lungs, and the small loss of that substance from the epidermis
and the intestinal excreta, a’-e not mctamorphic, the former
being derived from the air swallowed with the ingestaand the
saliva, and the latter being contained in non-metamorphosed
organised matter, ('liolosterin is also a scarcely oxidised ex-
cretory hydro-carbon.

462

SPECIAL PHYSIOLOGY.

The great object, therefore, of the respiratory function, is to
introduce oxygen into the living animal economy ; this oxy-
gen, by giving rise to numerous and incessant chemical changes,
stimulates the animal tissues, combines with their substance
and with the products of their disintegration, and ultimately
converts them, either into crystalloid products, Avhich can be
readily excreted from the kidneys or skin, or into a gas — very
soluble in water and in the blood — which can be readily dis-
placed from the latter fluid, in the lungs or in other respi-
ratory organs, by the stronger affinity of oxygen itself for a
certain constituent of the blood. In accomplishing this, it
also combines with certain constituents of the blood, assimi-
lated to it from the respiratory food, and thus forms more of
the same displaceable gas.

As an important collateral result, this process of oxidation,
due to the respiratory fonction, produces animal motion and
animal heat. In the Cold-blooded animals, in which respiration
is comparatively feeble, and which consume but a small quan-
tity of the carbhydrates, the quantity of force and heat en-
gendered is relatively small; but in the Warm-blooded Verte-
brata, much heat and force are manifested, and the quantity
of respiratory food consumed, and the activity of the respira-
tion are very great. The quantities of oxygen absorbed and
of carbonic acid evolved, are much larger in the latter than
in the former animals.

In animals provided with distinct blood and a comjdete cir-
culation, the immediate effects of the respiratory process take
place in that fluid, which is thus purified and rendered fit to
maintain life. But the ultimate effect is still largely exerted on
the tissues, the blood acting as a vehicle for the respiratory agent
and its products. In the lowest members of the animal scale,
respiration is equally necessary, and has similar ultimate re-
sults ; but its effects are direct or immediate upon the tissues.

The relation between the chemical actions of the body and
the amount of force and heat develoj^ed in it, also the mani-
festation of nervous power, and the evolution of electricity
and light in animals, phenomena in which oxidation, at the
expense of the oxygen absorbed in respiration, is likewise
necessary, will hereafter require further consideration.

MODIFICATIONS OF RESPIRATION.

4C3

CONDITIONS WHICH MODIFY THE CHEMICAL PROCESSES OP
RESPIRATION.

The quantity of oxygen absorbed, and of carbonic acid
eliminated, in the respiratory process, is modified by the fre-
quency of the respirations, the number of times the same air
is breathed over again, the temperature of the air, its degree
of moisture, and its density ; also by the conditions of age, sex,
exercise, repose, or sleep, by the character and quantity of the
food or drink, the period of the day or season, the state of
health or disease, and by the use of remedial agents.

In rapid breatlimg, less oxygen is absorbed, and less car-
bonic acid is given off, at each respiratory movement, as if
sufficient time were not allowed for the usual rate of mutual
interchange of the two gases. With six respirations per mi-
nute, 5'5 per cent, of the expired air has been found to be
carbonic acid ; with 24 respirations, 3'3 per cent. ; and with
96 respirations per minute, only 2'6 per cent (Vierordt).
But although in slow breathing, more oxygen is absorbed, and
more carbonic acid is exhaled at each respiration, yet, in a
given time, as shown by multiplying the quantity exhaled by
the number of respirations, the absolute quantity of the gases
absorbed and exhaled, is increased by rapid breathing. In
deep inspirations, the interchange of gases is said to be propor-
tionally less, when compared with the quantity of air ; but the
total amount of interchange is greater, because the volume of
air inspired and expired, is so much larger. The last portion
of air expired, in all cases, contains less oxygen and more
carbonic acid, than the first portion ; the former, no doubt,
containing air coming from the finest air-tubes, close to the
air-cells, in which the actual absorption and exhalation occur.

The relative purity or impurity of the air, likewise affects
the result ; as when the same air is breathed over and over
again, and so becomes more or less charged with carbonic acid.
Thus, in an experiment in which 300 cubic inches of air were
repeatedly breathed for a period of three minutes, only 9'5
per cent, of carbonic acid was found in it; the total quantity
being 28'5 cubic inche.«, or 9'5 cubic inches per minute. In
the same person, with fresh air at each inspiration, the quan-
tity was 32 cubic inches per minute. However often the same air
was re.spired, it was never found to contain more than 10 per

464

SPECIAL PHYSIOLOGY.

cent, of carbonic acid (Allen and Pepys). These results are
caused by the increasing difficulty offered by the accumulation
of carbonic acid in the air of the air-passages, to the escape by
moist diffusion, of the carbonic acid from the blood into the
air-cells, and to its simple diffusion through the air of the air-
passages.

The effect of an increased temperature of the air, is to dimi-
nish, and that of a lower temperature, is to increase, the quan-
tity of carbonic acid exhaled by the lungs. Between the
temperature of 47° and 67°, i.e. with a difference of 20° in
the external temperatui'e, a variation has been obsen^ed in
the quantity of carbonic acid exhaled, of 2'5 cubic inches per
minute (^Vierordt). At very low temperatures, the quantity of
carbonic acid exhaled, may even be more than twice as great
as that given off at very high temperatures. A sudden in-
crease of temperature, produces a marked immediate effect,
viz. a decrease of 2’75 cubic inches per minute, for 16° of
elevation of temperature, but this is not subsequently so regu-
larly maintained (Dr. E. Smith). The absorption of oxygen
is, of course, inversely affected.

The density of the air, also influences the chemical changes
dependent on respiration, their activity being increased Avhen
the density of the air is diminished.

A moist atmosphere, the temperature being the same, greatly
favours in animals, the exhalation of carbonic acid ; more-
over, the influence of moisture is so great, as to neutralise, at
high temperatures, the effect of such temperatures in dimi-
nishing the exhalation of that gas (Lehmann). The exact
hygrometric state of the air, ought always, therefore, to be token
into account, in experiments on the composition of expired
air. The great influence of moisture, may account for some
of the discrepancies between the results of different observers.

As regards age, the quantity of oxygen absorbed and of car-
bonic acid exhaled, increases generally, in both sexes, to about
the thirtieth, and then remains stationary to the fortieth year,
after which it diminishes, so that at seventy, the amount only
slightly exceeds that proper to the age of ten years. The in-
fluence of sex, as might be expected from the greater .size and .1
activity of men, is, after the eighth year, shown in the 2'>i'opor-
tionally larger amount of oxygen absorbed, and of carbonic acid ;|
exhaled, in that sex. In the male also, the increase due to
age, continues progrcs.sively up to the thirtieth year, at which
period, it is stationary ; whereas in the female, the gradual

t-

|-t'

Jh:

m

N

EFFECTS OF EXERCISE ON THE CARBONIC ACID. 4 65

increase stops at the age of puberty, and the quantity remains
stationary until about forty, when it once more increases for a
time, before the diminution dependent on old age, begins. The
smaller absolute quantity of carbonic acid exhaled in child-
hood, is, nevertheless, very large, in proportion to the weight of
the body, in accordance with the high activity of the nutritive
function, and with the large consumption of food at that period.
The size of the body, in different adults, produces a corre-
spondent result on the total quantity of carbonic acid exhaled.
The development of the muscular system, however, produces ’
a greater effect, than that which depends on the mere height or
weight of the body, or on the dimensions of the thorax.

Exercise, as might be expected, increases the quantity of
carbonic acid exhaled, not only whilst it is being taken, but
also for a short time afterwards. The increase may equal one-
third of the amount exhaled during rest, and this may con-
tinue for one hour after the cessation of exertion. This residt
depends both on a greater quantity of air being breathed, and
on an increased percentage of carbonic acid in the expired air
(Vierordt). Other observations show even a greater relative
increase, for in walking two and three miles per hour, the
quantities, 1ST grs. and 25'8 grs., were about two or two
and a half times as great as the normal amount in the sitting
posture; at tlie tread-wheel, the quantity fluctuated between
42'9 grs. and 48‘G grs., that is, from about four and a half to
five times as great, the pulse and the respiration being, of
course, greatly accelerated (E. Smith). Prolonged exertion
producing fatigue, diminishes the exhalation. Much less car-
bonic acid is exhaled during the night than in the day. During
sleep, the amount given off is considerably diminished, in cor-
respondence with the more superficial and slower character of
the respiratory movements of the chest, with the cessation
of the ordinary actions of the muscular and nervous tissues
and of the usual metamorphoses of the re.spiratoiy food, and
with the smaller loss and production of heat. In experiments
performed in air-tight chambers, the diminution per hour
in sleep, was about one-third of the normal quantity (Schar-
ling). According to other e.stimates, the quantity exhaled, in
a given time, during profound sleep, is about one-half that of
the average quantity in the same time during the day.

The period of the day, influences the quantity of carbonic
acid exhaled, quite independently of the condition of sleep or
wakefulness. The ratio in a like time of the night and day,

VOL. II. H II

4G6

SPECIAL PHYSIOLOGY.

being as 1 to 1'25 (Scharling), or as 1 to 1'8 (E. Smith).
Taking the whole day of 24 hours, the smallest quantity is
exhaled in the middle of the night, and the largest in the
middle of the day ; a slight increase occurs at sunrise, and a
prolonged and constant diminution after 9 o’clock in the even-
ing (B. Smith). The difficulty of resisting the effects of severe
cold, between midnight and sunrise, is well known. A sea-
sonal influence on the products of respiration, has also been
noticed ; the maximum product occurs in spring (April and
l\Iay), and the minimum at the end of summer (September),
a gradual increase occurring in early winter (October, No-
vember, and December), and a gradual decrease in early
summer (June, July, and August). Hence, heat, as the result
of seasonal changes, equally with artificial heat, diminishes
the quantity of carbonic acid exhaled, and climatic cold in-
creases it ; moreover, it Was found by Barral, that the daily
quantity of carbon exhaled by the skin and lung.«, was, in
winter, upwards of 5,000 grains, and in summer only about
3,700 grains. But neither temperature alone, nor this, added
to the effects of atmospheric pressure, account for the seasonal
changes (E. Smith). It may be remarked, however, that the
hygrometric condition of the air in the above researches, was
not taken into account, but this, as shown by Lehmann, is of
the highest importance ; the period of increase corresponded
with the wet months, and that of decrease with the diy months
of the year.

Food generally increases the absolute quantity of carbonic
acid given off from the lungs, whilst fasting has the opposite
effect, the proportion of carbonic acid in a given quantity of the
expired air, being, however, greater during starvation. Thus,
in a person six feet high, in whom the average quantity of
carbon exhaled, when at rest, with ordinary diet, was 7 '85 oz.,
the daily quantity exhaled whilst fasting, was 5’9 oz. ; the di-
minution produced by fasting for the 24 hours, being rather
more than one-fourth the usual quantity exhaled when taking
food (E. Smith). The quantity exhaled in fasting, sinks to a
certain line, which has been named the basal line, below which,
in health, it does not descend ; but prolonged starvation ulti-
mately diminishes it. The influence of food has been shown,
by an increase after breakfast of one-fourth the previous quan-
tity, and after dinner of about-two thirds (Scharling); the
chief increase noted by Dr. Smith, was after brealdast and tea,.

and not after early dinner. Thus, the

quantity of

EFFECTS OF FOOD ON THE CARBONIC ACID.

467

carbonic acid exhaled, by a certain person, being 20 '6 cubic
inches (9'77 grs.) per minute, the quantity during continuous
fasting being about 14 cubic inches (6'61 grs.), and the
maximum and minimum quantities in the working day with
food, 22 cubic inches (10-43 grs.) and 14'2 cubic inches
(6'74 gi’s.), the increased exhalation after breakfast and tea was
from 4-2 to G-3 cubic inches (from 2 to 3 grains), and after early
dinner only from 2'1 to 4’2 cubic inches (from 1 to 2 grains).
The different effect of ditferent kinds of food and drink, as
observed by Dr. Smith, is, in some respects, remarkable ; all
nitrogenous foods increase the exhalation of carbonic acid ; and
so does any mixture of nitrogenous matters with the carb-
hydrates, such as is found in bread, oatmeal, and milk ; but pure
starch has scarcely any effect ; pure fat seems even to diminish
the quantity of carbonic acid evolved, though pure sugar in-
creases it. Tea, coffee, and cocoa cause an increase more sud-
den and marked than that produced by any other substances
experimented with ; pure alcohol also increases the quantity ;
but of the spirits ordinarily in use, rum increases the quan-
tity, brandy and gin diminish it, whilst whisky varies in its
effects ; wine and ale increase it, whilst the volatile or aro-
matic ingredients of both spirits and wine, seem to le.s.sen the
quantity exhaled. Distilled water has been found to dimini.sh
the exhalation of carbonic acid. The opposite effects of dif-
ferent alcoholic fluids, such e.g. as rum and brandy, are
referred by Dr. Smith to the separate action of the alcohol,
sugar, aromatic srrbstances, and nitrogenous bodies in each of
those fluids respectively; and the different effects of rveak
alcoholic liquors, and of pure alcohol, have been explained by
suppo.sing, that in the former case, the alcohol may act chiefly
by stimulating the respiratory changes ; whilst in the latter,
it may interfere with the oxidation of the ordinary consti-
tuents of the body. Habitual drinkers, usually, accumulate
fat.

From the preceding facts, it would appear that the constitu-
ents of food, do not act in proportion to the quantity of carbon
they contain ; but that some specifically excite the re.spiratory
interchanges,apparently by increasing the processes of oxidation
in the body, and by augmenting the depth of the respirations,
or the quantity of air inspired. Two substances, identical in
composition, sugar and starch, act differently; the former ex-
citing rcspiratoi-y interchange, the latter not doing so. Milk,
especially when new, is a more powerful excitant even than a

H II 2

SPECIAL PHYSIOLOGY.

4r,8

purely albuminoid substance. The nitrogenous foods increase
the quantity fi-om 1 to 2T cubic inches (from to 1 gr.), mixed
nitrogenous and hydro-carbonaceous foods give an increase of
about 4‘2 cubic inches (2 grs.) per minute ; milk, a perfect
mixed diet, 4 cubic inches (nearly 2 grs.) per minute ; spirits
of wine 2T cubic inches (1 gr.) ; rum 3 cubic inches (about
I's S^‘) ) stout 2T cubic inches (1 gr.); whilst tea, cof-

fee, and cocoa increase the evolution of carbonic acid from 3 to
6 3 cubic inches (1|- to 3 grs.) per minute (E. Smith). Certain
substances, such as sugar, alcoholic fluids, tea, and coffee, pro-
duce their effect very quickly, reaching their maximum within
half an hour ; whilst flesh, bread, oatmeal, and milk act later,
their influence enduring as long as two hours and a half
(E. Smith). Lastly, the effect of a high diet on one day, may
affect the respiratory changes, as well as the excretion of
urea, on the followng day, imparting, as it were, a somewhat
durable stimulus to the system.

The amount of carbonic acid exhaled, is dimini.shed in all
chronic and organic diseases of the lungs, in hectic con-
ditions, and in cholera ; whilst it is increased in chlorosis, in
which the number of the red corpuscles is diminished. The
proportion of carbonic acid in a given amomit of expired air,
is increased in certain exanthematous diseases, as in measles,
and especially in smallpox, in which it is nearly doubled ;
whilst, on the other hand, it is reduced about one-half, in
typhus fever. The absolute quantities exhaled in these and
other diseases, have not been sufficiently investigated.

The effects of remedial agents, generally, on the absorption
of oxygen and exhalation of carbonic acid, have likewise yet
to be scientifically determined. The inhalation of the vapour
of chloroform and ether, diminishes remarkably die escape of
carbonic acid from the blood; and this constitutes an accessory
cause affecting the nervous system. In the treatment of diseases
by change of climate, the increased respiratory interchange
which is induced by cold, and the diminished oxidation wliich
takes place in higher temperatures, should be considered, as well
as the great influence of atmospheric moisture, in increasing the
exhalation of carbonic acid, and of a dry air, in diminishing it.
It is pos.sible that, in some, degree, the hygienic value of a dry
climate, such as Egypt, in the treatment of diseases of ex-
haustion, may deiiend upon the comparatively limited amount
of waste and oxidation of the tissues generally.

In hybernating animals, the quantity of oxygen absorbed

EFFECTS OF FOREIGN GASES.

409

and carbonic acid evolved, is, like the respiratory movements
themselves, reduced to a minimum, or, it is said, the respira-
tory interchanges are even absolutely arrested.

Effects of Breathing other Gases than Air.

As already mentioned, many gases and vapours of volatile
substances, are introduced into the system, by absorption fi-om
the pulmonary mucous membrane. Chloroform, ether, cam-
phor, and turpentine, thus produce their characteristic activi!
results on the system ; so likewise do tobacco smoke, the smoke
of the datura stramonium, and the vapour of mercury. The
gaseous combinations of hydrogen with other elements, such as
arseniuretted, phosphuretted, sulphuretted, and carburetted
hydrogen, are especially and directly poisonous. The arseniu-
retted hydrogen is the most powerful, less than one-tenth of a
grain, when inhaled, having proved fatal to Man. Sulphm-etted
hydrogen stands next in potency, air containing from one to
three per cent, having been respired without much incon-
venience to Man, though much less destroys animals. Car-
buretted hydrogen, or marsh gas, the fire-damp found in
coal mines, is still less active as a poison, but destroys life
when present in large proportions. The vapours of nitric,
nitrous, sulphurous, and hydrochloric acids, as well as those of
ammonia, which are compound bodies, and those of bromine,
iodine, and chlorine, which are simple bodies, are likewise
positively injurious when inhaled into the lungs, causing
direct irritation of the mucous membrane, and producing
decompositions of a special kind when taken into the blood.
Besides causing an increase of the mucous secretion, intense
bronchorrhoea, serous inflammation, and often permanent
cough, they frequently produce, through reflex nervous action,
violent spasm of the glottis, and so may cause asphyxia or
death from suffocation, without entering the air-tubes ; some-
times death results from oedema of the glottis. There is one
I gas, a compound of nitrogen with oxygen, the nitric oxide, or
I laughing-gas, which, when inhaled for some minutes, produces
i a state of temporary intoxication, and, at the same time, main-
jl tains respiratory chemical changes, at the expense of the
! oxygen contained in it, the products of respiration being, in
! such a case, carbonic acid with a large excess of nitrogen.

! By a long continuance of the experiment, insensibility, and,

470

SPECIAL PHYSIOLOGY.

as has been shown on animals, actual suffocation, probably
from the carbonic acid, may be produced.

Besides these directly irritant and poisonous gases, there
are some which are only indirectly injurious, being in them-
selves inert and innocuous. Thus, snails have been kept in pure
liijclrogen for a long time, and frogs as long as fourteen hours,
without any injurious effects; and nitrogen is equally harm-
less to frogs (Collard de Marti gny, Muller, Bergmann). In the
experiments on frogs, carbonic acid is exhaled, for a time, in
as great, or even greater, quantity than if the animals had
breathed atmospheric air ; more is excreted in hydrogen than
in nitrogen. The total quantity of carbonic acid, so given
off, is, however, limited, doubtless because no more oxygen
can be absorbed ; the lungs of the frog have been usually
emptied of air, by compression or the use of the air-pump,
and the only oxygen left in the animal, was that in the blood
or the tissues. Some of the hydrogen and nitrogen seems to be
absorbed, but only in small quantity. The exhalation of car-
bonic acid in these cases, must be owing to the successive moist
and dry diffusion taking place into the hydrogen or nitrogen ;
and the diffusive force, in the former gas especially, would be
much greater than that into air. In the case of Warm-blooded
animals, only the newly-born or very young can support such
an experiment, without the rapid extinction of life ; but they
may live a short time, and yield carbonic acid to the artificial
atmosphere of hydrogen or nitrogen. Fully-grown Birds and
Mammalia, expire rapidly in pure hydrogen or nitrogen ; the
.symptoms being instantaneous difficulty of respiration, gasping,
loss of muscular power, and, at the end of two or three minutes,
cessation of the heart’s action ; the lungs are found engorged
with venous blood. The animals, indeed, are asphyxiated
from the deprivation of oxygen, of which they require a larger
and more constant supply, in comparison with the 3'oung of the
same species, or with Cold-blooded animals. That the nitro-
gen is not in itself injurious, is obvious from the large propor-
tion of it — about four-fifths — in ordinary atmospheric air ; and
that the same is true of hydrogen, is shown by the fact that, if
this gas be mixed with oxygen, in the same proportions as
nitrogen and oxygen exist in the air, animals live and breathe
in such a mi.xtiire, without the least inconvenience.

From all that has preceded, it is evident that of the two gases
in the atmospliero, the oxygen is the active ingredient in respira-
tion ; for nitrogen alone, as we have seen, causes suftbeation.

EFFECTS OF CARBON GASES.

471

Hence oxygen has been named vital air. Considered in
reference to its office, it is a supporter of life, or of the proper
animal functions ; but, as regards the body itself, it is a de-
structive, not a constructive, agent, operating constantly in its
disintegi'ation and oxidation, in the various processes of animal
life. The proper medium for healthy respiration, is pure at-
mospheric air, which contains, besides a minirte trace of carbonic
acid, four-fifths of nitrogen, and only one-fifth of oxygen. But
an addition to the normal quantity of oxygen, is of more or
less importance. Twice or three times the usual quantity in
air, at first causes no apparent inconvenience, and no special
change in the products of respiration ; but it is probable that,
after a time, certain injurious consequences would ensue,
though experiments are wanting to determine the point. Pure
oxygen, however, is highly injurious; the vital functions are
stimidated as if by a fever ; the pulse and respiration are in-
creased in frequency ; after an hour, insensibility gradually
comes on, complete coma then ensues, and death occurs in from
six to twelve hours. On examination of the animal, the heart is
found pidsating violently, although the motion of the diaphragm
is arrested. The blood, after death, is of a bright colour
in the veins, as well as in the arteries ; the mucous membranes
are red ; the blood coagulates quickly ; oxygen has evidently
been absorbed in large quantity ; the blood in the systemic
capillaries is no longer properly changed to venous blood ; and,
on the other hand, the presence of over-oxygenated blood in the
nervous centres which govern respiration, lessens their activity,
which is called into play apparently by the stimulus of a certain
quantity ofcarbonic acid in the blood. The symptoms produced
by breathing oxygen, are rapidly alleviated by respiration in
atmospheric air.

Of the three compound gases containing carbon, viz. car-
buretted hydrogen C II.), carbonic oxide C O, and carbonic acid
C O2, carbonic oxide is the most poisonous. This gas, which
is produced by the imperfect combustion of carbon, is given
off, together with carbonic acid, in the fumes of burning coke
or charcoal. The addition of 5 per cent, of this gas to
air, is sufficient to make it irrespirable, and to cause death,
and it is this gas, rather than the carbonic acid, which pro-
duces fatal results, in suicide by charcoal fumes. In these
fumes, however, besides the carbonic acid and the carbonic
oxide, there arc ammoniacal salts, an empyreumatic oil, some-
times sulphurous acid, watery vapour, nitrogen, and traces of

472

SPECIAL PHYSIOLOGY.

free ox; gen. The symptoms produced by smaller quantities
of carbonic oxide in air, are, giddine.ss, faintness, headache,
convulsions, and irregularity of the pulse ; the freest in.spira-
tions, or insufflations of pure air, or of diluted oxygen, are
essential for recovery at such a crisis. When death ensues from
the breathing of carbonic oxide, the blood is not found dark, as
in asphyxia from carbonic acid, but even the venous blood is
of a bright red hue, and the jiroperties of the corpuscles are
permanently modified ; for they exhibit no further changes on
exposure to oxygen or to carbonic acid.

Carbonic acid being a natural product of the respiratory
jfrocess, its injurious effects upon animal life, possess an inte-
rest greater than that which attaches to those of other gases.
The quantity of this gas in ordinary air, is about 4 parts in
10,000, -g-s^d-o^th part, or '04 per cent. In air once breathed,
the proportion rises to about 4 j^er cent, i. e. part, or

400 parts in 10,000, a corresponding quantity of oxygen being
simultaneously removed. If this air be respired a second time,
a much smaller portion of carbonic acid is added to it, and
still less, at each subsequent respiration. When air contains
about 10 per cent, or yV^h its volume, of carbonic acid,Avhen
one-half of the normal quantity of oxygen, has likewise dis-
appeared, it is irrespirable, and fatal to man. Warm-blooded
animals have been found to die in an atmosphere containing
from 12 to 18 per cent. The symptoms of poisoning, may be
said to begin with even a much smaller proportion in the air,
even Avith as little as one-third per cent. For a time, no marked
symptoms are observed, but after a certain interA'al, there
occur headache, sense of fulness in the temples and occiput,
giddiness, muscular prostration, oppression of the chest, difficult
respiration, palpitation of the heart, subjective, disturbed sen-
sations, such as singing noises in the ears and flashes of light,
faintness, delirium, then droAvsiness, unconsciousness, convul-
sions, coma, and death. Sometimes A’omiting occurs, and oc-
casionally death ensues from apoplexy. On examination after
death, the cerebral Amssels are found congested, and serous
exudations to be present in the ventricles and at the base of
the brain ; sometimes clots of blood are found in the sub-
stance of the brain. Carbonic acid is the choke-damp of mines.

PHENOMENA OF ASPHYXIA.

473

AspJnjxia.

Wlien a person is completely immersed in an atmosphere
of almost pure carbonic acid, as in brewers’ vats, in cellars in
which wine is fermented, or in caverns, such as the Grotto del
Cane, death occurs much more rapidly ; the glottis is some-
times spasmodically closed, and respiration is as completely
arrested by this impediment to the passage of air, as it is in
strangulation, or in any other mechanical form of suffocation.
Even if the glottis should remain patent, the entire absence
of oxygen from such an atmosphere, wordd produce suffocation
almost as speedily ; for twenty seconds is the extreme time
during which the breath can be held by voluntary effort ; so
tlrat suffocation might be said to commence at the expiration
of that brief period. In any case, the form of death, which so
rapidly ensues, is that by asphyxia, the essential characters
of which, are, loss of muscular power and consciousness, cessa-
tion of the movements of the chest, and then of the pulsations
of the heart, with accumulation of blood in the right side of
that organ, and in the whole venous system, so that even the
skin becomes livid. The blood remains a long time fluid.

The mode in which death occurs from asphyxia, whether
caused by compre.ssion of the chest and abdomen, by direct
suffocation from external strangulation, internal choking, or
spasmodic closure of the glottis, or whether produced indi-
rectly by immersion in some irrespirable gas, or in water, by
paralysis of the respiratory nervous centres, or by narcotic
poisonings, is somewhat complicated. The respiratory inter-
changes of carbonic acid and oxygen, between the blood in the
pulmonary capillaries and the air in the air-cells, diminish or
cease ; the venous blood, reaching the lungs, no longer gives off
its carbonic acid, and the pulmonary capillary circulation is
more or less quickly stopped. The forward effects of this,
are, that the left side of the heart receives, at first, imperfectly
aerated blood, and then little or no blood at ;ill, so that the
functions of the brain and nen/ous centres, of the muscu-
lar system, and of the heart itself, all of which require, for
their maintenance, a due supply of arterial blood, gradually or
rapidly cease ; ultimately, the left side of the heart and the
arteries, accommodating themselves by their muscular con-
tractility and elasticity, are nearly or entirely emptied, or con-
tain but very small quantities of dark non-aerated blood. On

474

SPECIAL PnrSIOLOGT.

the other hand, the backward effects of the arrested circulation
in the pulmonary capillaries, are ultimately, to distend the right
side of the heart, and the entire venous system, with very dark
blood. The stagnation of the blood in the pulmonary capil-
laries, which is the first stage of the fatal process, has been
attributed to some direct influence of the carbonic acid on the
blood corpuscles ; for the circulation in the transparent parts of
animals, may be arrested, by subjecting the capillaries to the
action of carbonic acid ; moreover, as the red corpuscles of
the blood undergo enlargement when acted upon by this gas,
it has been supposed that these bodies may then obstruct the
capillaries mechanically (Wharton Jones). It has also been sug-
gested that there exist, in the healthy state, certain local attrac-
tions and repulsions between the walls of the pulmonary ca-
pillaries and the currents of the non-aerated and the aerated
blood respectively, connected with the respiratory interchanges
of the carbonic acid and oxygen, which are essential to the
onward movement of the blood-cuiTent.

In the slower forms of asphyxia, indicated by the more
gradually-developed cerebral symptoms, the stagnation of the
blood in the pulmonary capillaries, is preceded by a simple
retardation of the blood-current in them ; but the entire blood
is defectively aerated. Hence this fluid, owing to its ab-
normal condition, passes imperfectly through the systemic
capillaries; the arteries and the left ventricle become some-
what distended, and the heart for a time beats more powerfully
and more frequently, as if to overcome this resistance. But
the activity of the nervous centres and muscular system is
soon diminished, in proportion as the blood becomes less and
less aerated ; at length, both are completely paralysed, the
senses fail, consciousness is lost, the respiratory nervous centres
lose their power, respiration becomes laboured and much in-
terrupted, general convulsions ensue, and respiration ceases.
The contractile power of the heart itself, becoming diminished,
it beats more slowly, and at length ceases to contract. The
left ventricle not only no longer receives its appropriate stimu-
lating blood, but even loses its power of rhythmic contraction,
owing to the poisoning of the blood in the nutrient vessels of
the heart and its nervous ganglia ; whilst the cessation of the
action of the right ventricle, is chiefiy the result of over-dis-
tension, for venous blood is its proper stimulus, and the con-
tractility of that side of the heart is retained, for more or less
time, after it has ceased to beat sjmntaneously. If, indeed,

CARBONIC ACID IS A BOISOX.

•)75

the state of over-distension be relieved by puncturing the
right auricle, or the great veins, the right ventricle will again
begin to contract ; whilst the left venti'icle may be once more
excited by duly arterialised blood. By some, it has been sup-
posed that the obstruction to the pulmonary capillary circula-
tion, is due to the mechanical non-expansion of the lungs, but
it also occurs in asphyxia produced in animals made to respire
nitrogen, in which case, the kmgs are not contracted. More-
over, the vascular pulmonary obstruction, which is caused by
asphyxia, is relieved by the inhalation of oxygen very rapidly,
as compared with the gradual dilatation of the arterial system,
when any mechanical obstruction to the circulation of the
blood in them, has to be removed. The question has arisen,
whether in asjihyxia from the inhalation of carbonic acid,
the result is due to the diminished supply of oxygen, or to a
directly poisonous eftect of the carbonic acid itself. The
latter conclusion is supported by the fact that when animals
are made to breathe an atmosphere consisting of carbonic acid,
mixed with oxygen in the same proportion as exists in air,
or even in much greater proportion, they are still quickly de-
stroyed by asphyxia. It has been found, moreover, that a
diminution in the proportion of oxygen, increases the poison-
ous effects of the ct.rbonic acid ; wJiere the quantity of oxygen
is reduced to 16 or 10-^ per cent., death speedily ensues, even
though the carbonic acid is constantly being removed ; but if
the oxygen be maintained at its ordinary proportion of 21 per
cent., the ill effects of carbonic acid are not manifested more
rapidly, even though as much as 20 per cent, of that gas be
pre.sent in the respired air. A still more positive proof of the
directly poisonous influence of carbonic acid, is furnished by
the following singular experiment. One bronchus of a tor-
toise was tied, and the animal lived apparently without incon-
venience ; the respiration, accomplished by one lung, being
temporarily sufficient. But if, by special arrangements, ordi-
nary air was allowed to enter one lung, and carbonic acid the
other, through their respective bronchi, the animal soon died,
the introduction of carbonic acid into the system, being the
sole difference in the two conditions. This experiment also
proves that carbonic acid may, in certain conditions, not only
not escape from the lungs, but may actually bo absorbed by
them (Rolando).

476

SPECIAL PHYSIOLOGY.

Suspended Respiration and Animation.

The length of time which different animals, or Man, can sur-
vive without resjiiration, varies, according to many conditions,
chiefly referable to the relative degree of activity of the ani-
mal functions in any given case, but sometimes also to special
provisions. The more active the nirtritive and respiratory
processes, and the greater the development of heat, the sooner
does death by suffocation ensue. Thus, cold-blooded animals,
with the feebler activity of all their functions, have less need
for air than warm-blooded animals, the water-newt, e.g. fre-
quently remaining, even in its active summer life, a quarter
of an hour or more under water ; whilst frogs and lizards
have been kept, in experiments, for years without food, en-
closed in porous stones, or buried in earth ; but when they are
hermetically enclosed, they sooner or later die. Warm-blooded
animals and Man, on the other hand, are rapidly asphyxiated.
Hybernating Mammalia are able to live, in their peculiar tor-
pid condition, with a supply of air so defective, that they would
die asphyxiated in it, during their active summer condition.
Newly-born animals, being less dependent on the perfect state
of respiration, survive submersion for much longer periods,
especially when their temperature is low ; rabbits, under such
circumstances, having survived as long as 26 minutes, and
puppies even 50 minutes ; young guinea-pigs, however, do
not seem to possess this immunity. Even full-grown animals
resist the injurious effects of submersion in water, for a longer
time than usual, when their temperature has been previously re-
duced as low as 64°, but not lower ( Brown- Sequard). Again,
it has been observed, that full-grown warm-blooded animals die
sooner from drowning, than from simple apnoea caused by im-
mersion in nitrogen or hydrogen, by choking, or by strangvda-
tion, the more rapid fatal result in drowning, being due, not only
to the deprivation of air, but to the partial filling of the air-
passages and air-cells with water, and to the poisonous effects
of carbonic acid. Thus, the average time in which rabbits,
suddenly deprived of air, cease apparently to live, has been
found to be 3 min. 25 sec. ; in the case of dogs, the time is 4
min. 5 sec. ; the action of the heart, however, was maintained
for 7 min. 10 sec. ; moreover, the animals thus deprived of
ail', could be restored to life ailcr 3 min. 50 sec. On the
other hand, an immersion iii water for only 1|- or 2 minutes,

HOLDING THE BREATH,

477

usually rendered recovery impossible. La-stly, if the trachea
of an animal be divided and plugged, so that the water may
be excluded from the air-passages, and it be then submerged,
even for four minutes, it may recover its respiratory power
(Kep. Med. Chir. Soc.). Animals subjected to a diminished
atmospheric pressure under the receiver of an air-pump, are
asphyxiated, sometimes, perhaps, owing to the liberation of
gases in the blood of the small pulmonary bloodvessels.

Li a few Warm-blooded Mammalia, destined for an aquatic
life, as, e.g. in the Cetacea, there exist special provisions in the
presence of arterial and venous pleuxuses or diverticula, in
which the blood may accumitlate dtrring their submergence.
The retia mirabilia, or Avonderful networks of the arteries,
contain a supply of oxygenated blood, which is employed, as-
requii-ed, by the submerged animal ; whilst the large venous
plexuses receive a like quantity of deoxygenated blood. Whales
can remain upwards of an hour beneath the water. Certain
diving birds possess similar diverticula of both arteries and
veins.

In Man, under ordinary circumstances, the breath can be
held for about 20 seconds ; but after an ordinary inspiration,
the period of endurance without air, may be prolonged to 25
seconds. If, hoAvever, a single forcible expiration be made,
and then a deep inspiration be taken, the period may be ex-
tended to about 33 seconds. If five or six deep expirations
and inspirations be made, one after the other, so as to clear
the lungs as completely as possible of used-up air, and then a
deep inspiration be taken, from one and a half to tAvo minutes
may be alloAved to pa.ss Avithout inconvenience from Avant of air,
Avith the exception of slight giddiness at first. This fact it is
useful to remember in passing through rooms filled Avith
smoke or on fire, or on entering such rooms, or descending
a vat, or diving in water to save the life of another. In en-
tering an apartment on fire, or filled Avith smoke, it is better
to stoop or creep along the floor, as the air in that situation is
cooler and less pungent; but in the ca.se of Avells, brcAvers’
'vats, or sewers, the entrance of Avhich, for a time, is mo.st
i hazardous, there is no great elevation of temperature, and the
loAver strata of air arc the most poisonous. By practice, persons
[may accustom themselves to an interruption of the respiratory
[process for three or four mimrtes, without loss of consciousness,
I or other serious consequences, three minutes being the ordinary
rlimit attained by the skilled pearl-divers of Ceylon.

47S

SPECIAL PHYSIOLOGY.

Some of these divers use a small spring-clip, made of horn,
which they slip over the end of the nose, the instant before
they enter the water. This, on the one hand, prevents the
escape of air from the thorax through the nose, and, on the
other, the entrance of water through the same passage ; without
this contrivance, the diver must hold the nose with one hand,
which would limit his powers of search and prehension at
the bottom of the sea ; moreover, if the nosti-ils are not closed,
the muscles of the glottis and of inspiration must be kept
incessantly strained, or an irresistible expiratory effort would
take place, and expel some air from the chest. With this
protection on the nose, however, the diver has only to keep
the mouth closed ; the inspiratory muscles are not required
to act, and the contents of the chest are mechanically retained.

Persons who have been submerged for four or five minutes,
are rarely restored to life, and sometimes, often owing, doubt-
lessly, to the entrance of water into the air-passages, persons who
have been submerged scarcely a minute, cannot be resuscitated.

A submergence of five minutes, is almost certainly fatal to
hlan, still recoveries have occasionally taken place after much
longer j^eriods, even a quarter of an hour, and it is said after half
an hour or more. In such cases, however, it is believed that just
before, or at the moment of immersion, syncope, from some
cause or other, has taken place. In this condition, or in a state
of trance, the heart beats feebly, or scarcely at all, the respi-
rations are weak and shallow, and life may be said to be
interrupted, or so feebly maintained, that it may be continued
as well under the water, as above it ; venous blood is not
propelled through the system, so that the nervous centres are
not poisoned by carbonic acid; and, unless the temperature of
the water be very low, the vitality of the respiratory nervous
centres, of the muscles of respiration, and especially of the
heart, may be suspended, but not altogether destroyed. Such
a condition of syncope or fainting, may be produced, either by a
severe blow causing concussion of the brain, by other plij^sical
shocks to the body, by sudden fright, or violent passion. For
these reasons, attempts at the resuscitation of apparently
drowned persons, should always be resolutely’’ persevered in, .
even under most unfavourable circum.stjvnces.

Certain methodical rules have been laid down, by means of
so-called artificial respiration, for the recovery of drowned
persons; and, with the exception of such parts of those rules, as
relate to the removal of water from the mouth and nostrils, and

ArvTIFICIAL EESPIRATION.

479

the replacing of cold and wet, by warm dry clothing, similar
instructions would apply to the recovery of persons suffocated
in brewers’ vats, wells, and sewers, and also to those asphyx-
iated in the administration of ether or chloroform. In the
case of persons mechanically strangled or choked, the external
or internal cause of obstruction in the air-passages, must of
course be first removed. The earlier rules, published by the
Koyal Humane Society, for the recovery of drowning persons,
were improved by Dr. Marshall Hall ; but the most simple
and convenient are those of Dr. Silvester, which have been
incorporated with the present rules of that Society.

Euxes of the Eotal Humane Society.

Treatment to restore Natural Breathing.

Eule 1. — To maintain a Free Entrance of Air into the Windpipe.

Cleanse the mouth and nostrils ; open the mouth ; draw forward the
patient’s tongue, and keep it forward : an elastic band over the tongue
and under the chin will answer this purpose. Eemove all tight
clothing from about the neck and chest.

Eule 2. — To adjust the Patient’s Position. — Place the patient on his
hack on a flat surface, inclined a little from the feet upwards ; raise
and support the head and shoulders on a small Arm cushion or folded
article of dress placed under the shoulder-blades.

Eule 3.— To imitate the Movements of Breathing. — Grasp the patient’s
arms just above the elbows, and draw the arms gently and steadily
upwards, until they meet above the head (this is for the purpose of
drawing air into the lungs) ; and keep the arms in that position for
two seconds. Then turn down the patient’s arms, and press them
gently and firmly for two seconds against the sides of the chest (this
is with the object of pressing air out of the lungs. Pressure on the
breast-bone will aid this). (The Silvester method.)

Eepeat these measures alternately, deliberately, and perseveringly,
fifteen times in a minute, until a spontaneous effort to respire is
perceived, immediately upon which cease to imitate the move-
ments of breathing, and proceed to Induce Cihculation and
Warmth.

Should a warm bath bo procurable, the body may bo placed in it up
to the neck, continuing to imitate the movements of breathing. Eaise
the body in twenty seconds in a sitting position, and dash cold water
against the chest and face, and pass ammonia under the nose. The
Patient should not bo kept in the warm bath longer than five or sis
minutes.

Rule 4. — To r.rcite Inspiration.— Tturing the employment of the above
method excite the nostrils with snuff or smelling-salts, or tickle the
throat with a feather. Eub the chest and face briskly, and dash cold
and hot water alternately on them.

480

SPECIAL PIITSIOLOGT.

Treatment after Natural Breathing has been restored.

Eule 5. — To induce Circulation and Warmth. — Wrap the patient in
dry blankets and commence rubbing the limbs upwards, firmly and
energetically. The friction must be continued under the blankets or
over the dry clothing.

Promote the warmth of the body by the application of hot fiannels,
bottles or bladders of hot water, heated bricks, &c., to the pit of the
stomach, the armpits, between the thighs, and to the soles of the
feet. Warm clothing may generally be obtained from by-standers.

On the restoration of life, when the power of swallowing has returned,
a teaspoonful of warm water, small quantities of wine, warm brandy
and water, or coffee, should be given. The patient should be kept
in bed, and a disposition to sleep encouraged. During reaction large
mustard plasters to the chest and below the shoulders will greatly
relieve the distressed breathing.

In the recovery from drowning, or from other forms of
asphyxia, the various phenomena which characterise the pro-
duction of that state, are, as it were, reversed or rmdone,
beginning at the re-establishment of the flow of blood through
the pulmonary capillaries. On the introduction of air into the
lungs, by the artificial imitation of the respiratory movements,
oxygen is once more absorbed by, and carbonic acid given off
from, the venous blood reaching those organs ; these renewed
chemical changes in the blood, induce again its onward motion
through the capillaries into the pulmonary veins; thence it
flows on, more or less oxygenated, into the left side of the
heart, which resumes contractions of sufficient strength to
propel this oxygenated blood into the nutrient arteries of tlie
heart and its ganglia, as well as into the muscular and nervous
systems generally. In this way, the rhythmic power of the heart
itself, and the excitability of the respiratory nerves, the nervous
centres, and muscles, are restored, and, subsequently, conscious ‘

sensation, perception, and volition. In the meantime, more-

over, the restoration of the capillary circulation in the lungs,
liberates the blood previously pent-up in the right cavities of
the heart, gradually unloads those cavities, facilitotes, more
and more, at each moment, their free action, and so by degrees
empties the over-distended venous system. The freer return
of the blood from the systemic capillaries, being thus permitted,
that part of the circulation also is relieved, the lividity and
coldness of the surface of the body, are removed, and simul-
taneously, the vigour of the left side of the heart being in-
creased, the flow of properly oxygenated blood, throughout the

1*1

k

h

f-t!

I

rirt

ARTIFICIAL CIRCULATION.

4S1

whole system, and life itself is restored. The action of the air
upon the blood in the capillaries of the skin, may slightly assist
in these favourable changes ; for the lividity of the skin some-
times diminishes, even when life is not restored.

It has been found by Dr. Eichardson, that artificial respira-
tion, by direct inflation of the lungs of animals, tails to restore
the pulmonary capillary circulation, if the beats of the heart
have actually ceased, an event which usually occurs alter five
minutes. Insufflation of tlie lungs with hot air, is more stimu-
lating to the heart, but yet not adequate to restore the pirlmo-
nary blood-current. The employment even of oxygen or
ozone, mixed wdth the air, is useless, unless the heart is still
acting. Galvanism will revive the respiratory movements,
but, unless the heart is still beating, it fails to re-establish the
motion of the blood through the lungs. In short, if once the
blood-ci;rrent in the pulmonary arteiy and its branches, be in-
terrupted, the blood corpuscles in the small vessels speedily
coalesce, and then the increasingly feebler contractions of the
heart, merely propel blood into the trunk of the pulmonary
artery, but not through the lungs. Artificial respiration by
insufflation, or even by Silvester’s method, must not be at-
tempted, or continued, when the feeblest natiu-al respiratory
movements are discernible. The introduction of air into the
lungs must then be veiy gentle ; the temperature of the air
should, if possible, be as high as 120°, and never below 60°.
Galvanism, being exhaustive of, as well as stimulating to the
respiratory muscles, should either be emploj^ed for a limited
time, or should be perha])s avoided. Certain experiments, on
what Dr. Richardson terms artijicial circulation, encourage him
to hope, that means may ultimately be found of restoring life,
if the blood is not actually coagulated, an event which does not
usually take place before twenty minutes, and may not do so
within an hour, in unopened and unexposed bloodvessels. In-
jections of oxygen into the circulation, or of peroxide of hydro-
gen into the trachea, may excite the heart or muscidar system
generally, but they do not restore the circulation through the
lungs. The injection of vapour, and of hot water at the tempera-
ture of 1 20°, into the veins, excites the action of the heart in an
extraordinary manner ; wliilst that of wanu delibrinated and
deoxygenated blood has no effect. Galvanism, applied to the
heart jointly with artificial respiration, excites both sides of
that organ, and, for a time, restores the pulmonary circulation.
The forcible injection of blood into the jugular vein, with

VOL. II. II

4S2

SPECIAL PHYSIOLOGY

the view of overcoming the resistance to the motion of the
blood in the lungs, entirely fails in its object. On the other
hand, suction of the blood, by aid of a syringe introduced into a
large artery, draws soTiie of that fluid through the pulmonary
capillaries, in an oxygenated state, and on its being reinjected
into the artery, so as to reach, amongst other parts, the walls
of the heart through the coronaiy arteries, effectually re-es-
tablishes the pulmonary circulation, and all the functions of
the body. The injection of the blood back into the arterj", in
a pidsatory or inteiTupted manner, revives the action of the
heart most completely from its quiescent, cold, and partly
I’igid state, even one hour and five minutes after death. These
interesting experiments, though not yet of practical applica-
tion in the treatment of asphyxiated persons, serve to corro-
borate the generally-received opinion, that an essential fact in
asphyxia, is the retardation, and subsequent arrest, of the move-
ment of the blood through the pulmonary capillaries, and point
to the reliefer removal of that condition, as the turning-point
of success in all attempts at resuscitation.

Effects oj- Breathing Impure Air.

Instances have occurred, in which the carbonic acid exhaled
by large numbers of persons crowded together in .small a]3art-
ments, has been most destructive to human life. The Black
Hole of Calcutta was a room only 18 feet square, having two
small windows; into this apartment, 146 prisoners were
literally crammed, and, during one night, 123 of them perished.
'I'he cruelty of an enemy, in 1756, was scarcely more disastrous
than the ignorance of the captain of an Irish passenger steamer,
in 1848, Avho, during a storm, confined under closed hatches,
in a small crowded cabin, 150 passengers, of whom 70 died in
the night.

But carbonic acid produces injurious effects, even when it
exists, in the air, in quantities too small to cause asphyxia; as,
for exampile, when not more than one per cent, is pre.sent. Thus,
in ill-ventilated apartments, the presence of an excess of car-
bonic acid in the atmosphere, interferes with the proper oxy-
genation of the blood ; for, as already mentioned, less and less^ 1
carbonic acid is exhaled, as the proportion of that gas increases » j
in the inspired air. Headache, oppression of the senses, lassi--’
tude of the muscles, and languor of the mind, are the results ; *
the oxidation of the eflete matters of the blood, is imperfectly

AIR AND AIR SPACE FOR ROOMS.

483

performed or prevented, and they accordingly accumulate in
tliat fluid ; the pulmonary and cutaneous exhalations become
still more loaded with such substances, and, together with the
carbonic acid itself, and the ordinary exhalations from the skin
jind lungs — with which the air in such confined apartments, is
already infected — produce still more depressing effects upon,
and ultimate injurious consequences to, the system.

During each minute, an ordinary adult inspires and expires
f)60 cubic inches of air, exhales 14’4 cubic inches of carbonic
acid, and absorbs at least 15 cubic inches of oxygen ; this
renders 150 cubic inches of air totally irrespirable ; for, as
already mentioned, this condition is arrived at, when half the
normal quantity of oxygen (30 parts in 150) is replaced by
carbonic acid. But in order that the air of any room, should
be fit for continuous respiration, a much greater change must
be effected in it, than that of merely replacing, minute by
minute, the 360 cubic inches of air breathed in that time.
For the 4 per cent, of carbonic acid contained in it, is sufficient,
with the concitiTent loss of oxygen, to deteriorate a much
larger quantity of air. It is 100 times more than tliat wdiich
is present in common air, for this is only '04 per cent. ; and
therefore, even when diluted with 100 times its volume of
ordinary air, the mixture would still contain twice the normal
quantity of carbonic acid, viz., '08 per cent., or 8 parts in
10,000 ; this is about the average quantity in the air of certain
large manufacturing towns. For such a dilution, 36,000 cubic
inches, or more than 20 cubic feet of air would be required.
Owing, however, to the rapid, spontaneous, dry diffusion of the
carbonic acid, a less degree of actual dilution is sufficient for
the purposes of healthy respiration ; and it has been variously
computed, that from 4 to l() cubic feet of air per minute, which
last-named quantity, with the respired air, would yield an
atmosphere containing 12 parts of carbonic acid in 10,000,
are needed for each person, in sleeping or sitting apartments,
schools, courts, theatres, workshops, factories, barracks, work-
liouses, or prisons. Hospitals, especially for surgical cases or
lever.s, refiuire at least double that quantity. Much depends
on the temperature of the air, for a higher temperature requires
a more rapid change. Moreover, besides the removal of car-
bonic acid and the renewal of oxygen, it is of the utmost
moment that other pulmonary and cutaneous exhalations,
whicb contain volatile organic matter and ainmoniacal salts
should be diluted, oxidated, or removed. If the i^roducts of

1 1 2

■484

SPECIAL PHTSIOLOGT.

tlie combustion of artificial lights, especially of gas, enter the
air of the room, a still further allowance of fresh air is ne-
cessary.

Were it not for the law of diffusion of gases, the evils arising
from overcrowded and ill-ventilated rooms, would be much
greater. In the air of a very close room, which had been
occupied by 500 people, and in which fifty candles had been
burning. Dr. Dalton found, after it had been shut up for two
hours, one per cent, of carbonic acid. But Dr. Roscoe has
shown that in theatres, the percentage is usually ’0321, and in
schoolrooms '331 ; indeed, in no rooms did he ever find more
than ‘5 per cent., owing, as he remarks, to the constant diffu-
sion and interchange of air through the crevices and openings
at the doors, windows, and fire-place. Furthermore, in proof
of the rapidity and importance of the diffusion of carbonic acid
in the air, he found that the percentage of carbonic acid was
nearly uniform in every part of an occupied room, at the same
time. Nevertheless, this accidental diffusion is insufficient for
the proper change of the air in a crowded room. The escape
and entrance of quantities of air, are indispensable for the re-
moval of the noxious products thrown off from the living body,
and for the renovation of the atmosphere. This is to be ac-
complished, consistently with warmth and comfort, by artificial
ventilation.

Besides this motion of the respired air, and its replacement
by fresh air, a certain actual breathing space should be allowed
for each person occupying private sleeping apartments, or for
those attached to barracks, workhouses, prisons, and, e.specially,
to hospitals. The day rooms being more or less constantly
opened may be smaller. The practice of architects and build-
ers, up to a recent date, was to allow not less than 800 cubic
feet of space for each person ; but this is too little, especially
in infirmaries and ho.spitals, in which 1,200 cubic feet per head
are not considered too much, and for military hospitals in warm
climates, as much as 2,500 cubic feet per head have been recom-
mended. The importance of sufficiency of breathing space
and of ventilation, in sleeping apartments, can hardly he over-
rated, especially when we reflect that, even in health, the bed-
room is occupied, ft’om first to last, nearly 8 hours out of the
24, or nearly one-third of our existence. In ho.spitals and
infirmaries, the same room is too frequently occupied both
day and night.

The deterioration of health, from neglecting to sleep in a

EFFECTS OF BAD AIR.

485

pure air, is shown in many ways. Many competent authorities
attribute the deposition of tubercle in the lungs, i.e., the early
stage of phthisis, partly to inadequate respiration, and to im-
perfect oxidation of the constituents of the blood and tissues.
Consumption appears to have been engendered in the Quadru-
mana coiTfined in the small overcrowded monkey -houses of the
London and Parisian Zoological Gardens ; but after increased
accommodation and proper ventilation were secured to those
animals, tubercular disease almost disappeared from amongst
them. The small, close, sometimes doubly-glazed houses in
\Yales, contrast with the open dwellings of the inhabitants of
Skye, and so does the prevalence of consumption in the former,
with its rarity in the latter, districts. At an infant school at
Norwood, a great mortality occun’ed amongst the children,
clearly dependent on imperfect ventilation. Similar experience
might be derived from every large town in the kingdom, pro-
vided facts w'ere always duly i-ecorded and understood. In
the infant hospital at Dublin, 2,944 children died dmdng four
years, under a system in which ventilation had been utterly
neglected ; whilst in a similar period, during which many
improvements in this respect, were made, the mortality fell to
279. Sometimes the injury may consist in a lowering of the
strength of the system, which exposes it to the attacks of im-
pending epidemic or zymotic diseases. The effete matters
retained in the blood, must deteriorate the fluids of the body,
or escaping into the air, they may form an organic nidus for
the development of some diseases, or they may ferment, be-
come. putrescent, and so favour the multiplication and spread of
poisonous fomites. Such effete matters may even undergo
decomposition within the body. The lowered condition of
health thus induced, favoims the continuance of the evil prac-
tice of breathing impure air ; for in this depressed sbite of the
respiratory and other functions, the need for fresh air is less
felt, and habit reconciles the senses, and dulls the perception,
to the effects of the suicidal practice of inhaling an atmosphere
poisoned by oneself. Persons accustomed to hot, close, unven-
tilated rooms, loaded with a vitiated atmosphere, do not recog-
nise either by smell, or by the sensations of enfeebled bodily
health and infirmity, the effects of the impurities which they
breathe. Moreover, they often believe themselves, and are re-
garded by others, to be in an average state of health ; but the
onset of an e])idcrnic, or of a contagious disease, reveals their
want of power to resist morbid iuiluences. As a most serious

48G

SPECIAL PIITSIOLOGT.

predisposing cause of disease and mortality, during such visita-
tions, the overcrowding of rooms, whether large or small,
public or private, is fully recognised.

The overcrowding of the population in parts of towns or villages, is
also very inimical to health. This is doubtless partly to be explained by
the fact, that it is the poorer classes, less well provided for, in every way,
which occupy' such neighbourhoods ; it is also partly due to the closer
proximity of the inhabitants to each other, and to their increased lia-
bility, from this circumstance, to communicate diseases to one another.
But the increased accumulation, within a limited space, as in towns,
or in the immediate neighbourhood of dwellings, as in villages, of the
excreta, and of the waste animal and vegetable matters of the food,
which constitute, when undergoing decomposition, sources of contami-
nation to the air, cannot be here disregarded. Indeed, it has been
shown that whereas, in the open coimtry near Manchester, the quantity'
of organic matter in the air, is only 1 grain in 200,000 cubic inches,
in the confined and overcrowded districts within that city, the pro-
portion is, 25 grains in the same quantity of air.

The open ditches for drainage, and the heaps of garbage and refuse,
in villages, and the uncleansed sewers, defective drains, and untrapped
water-closets and sinks, in cities and towns, by admitting the escape of
foul air into the environs, the lanes, the streets, or the houses them-
selves, are serious causes of insecurity to health. Sewer-atmosphere
usually contains sulphuret of ammonium, or ammonia and sulphuretted
hydrogen, frequently carburetted hydrogen, and besides these, it is
loaded with organic matter, decomposing or putrescent, mixed with
the spores of fungi, and with the minute living organisms known as
bacteria, or, at any rate, with the organisable material in which these are
generated. A house into which such an atmosphere is conducted, by an un-
trapped sink, or other defect, resembles, when closed at night, an inverted
beli-jar over an open gas-pipe, or a receiver specially connected with the
sewer, which acts as a retort for the evolution of poisonous vapours. It is
necessary to exclude such chances of contamination of the air inside a
dwelling-house ; and to prevent also the contamination of the atmos-
phere in the immediate vicinity of the dwelling, from which tlie internal
supply for ventilation is derived. This is the immediate sanitary purpose
of a perfect system of sewerage and drainage. Water is, for large cities
certainly, and perhaps also, wherever available, the most cleanly, and
convenient vehicle for carrying away the excretory products of the inhabi-
tants ; the sewers should themselves be ventilated. Great care is needed
to prevent the sewage matter from contaminating wells, or other sources
of drinking-water ; for water is, thus, as easily, and much more insidi-
ously, contaminated than air. Earth closets are suitable for the country.

It seems probable, though but little is certainly known on these sub-
jects, that zymotic diseases, whether contagious or epidemic, spread them-
solvo.s, at least to a groat extent, through the air, and enter the body
through tlio lungs ; moreover, it is possible that the agents which cause
them, have, if not an org-amc germinating, at least a cheTuical self-mul-
tiplying property, and Unit impurities, whether in solid bodies, in water,
or in air, may form a nidus for such increase, or growtli.

The mortality from epidemic and contagious diseases, both local and

PURE WATER.

•187

general, has been repeatedly demonstrated to be proportional to the
impure condition of the atmosphere of houses or localities. On the
other hand, a decrease in the amount and severity, of zymotic diseases,
and in the rate of mortality induced by them, has been shown to follow
sanitary improvements in clifFereut towns. In the city of Salisbury, the
annual average mortality during eight years previous to the complete
drainage of Jhe city, was 27 in 1,000 ; whilst in the succeeding eight
years, it was reduced to 2 1 in 1,000. In the city of Ely, with a population
of 6,176 persons, living in 1,200 houses, the average annual death rate,
in the seven years from 1843 to 1849 inclusive, was 26 per 1,000 ; in
the year 1851, public sanitary works were brought into operation, and,
in the seven years from 1851 to 1857, the death rate was reduced to
20^, whilst in the last of those years, it was only 19 in the 1,000.
Besides securing a larger supply of better water, 4,000 cubic yards
of cesspools were filled in, and trapped water-closets were substituted ;
but, in 1857, 200 houses were yet unconnected with the public drainage,
and the pigsties were left, as being too sacred to be touched. It is notice-
able, that, whilst the death rate in this city, was reduced, subsequent to
the sanitary improvements from 26 to 19, the annual death rate in
the surrounding country was still 21, in 1857 (William Marshall). The
annual mortality at Pau, one of the healthiest places in Franco, varie.s
from 28 to 23 per 1,000; the highest actual mortality in England
is 45, the lowest is 11, and the average, 22, per 1,000. A comparison
with these figures, indicates the sanitary position of the city of Ely.
The death rate of 11 per 1,000, is regarded as representing the inevit-
able annual mortality oi this country; the additional deaths beyond that,
constitute the ^reyew^iWe dependent almost entirely on zymotic

diseases, the ravages of which might be more or less controlled by
sanitary improvements. It has been quite recently shown, that one im-
portant and unexpected result of public sanitary improvements, is a
marked diminution in the number of deaths from phthisis ; this is pro-
bably due to the better system of drainage, and to a general elevation of
the health of the inhabitants (Dr. G. Buchanan).

A supply of pure water to a town, is of immense sanitary as well as
economical importance. It facilitates the cleansing and purification of
both dwelling-houses and streets, and thus assists in the improvement
of the air. It substitutes a wholesome beverage, for that contained in
unclean tanks or butts, or for the water of surface wells, which from
the soakage of filth, from pigsties, stables, or cesspools, is frequently
converted into a deleterious, or even directly poisonous, drink. Impure
water may act, by slowly introducing into the system, organic matter
undergoing more or less change, and probably, capable of deteriorating
directly, or indirectly, the composition of the blood, and thus ultimately
lowering the health, and rendering the body more subject to the in-
fluence of zymotic agents. At otlicr times, the water may act as the
receptacle, the nidus, and the vehicle, of such zymotic poisons. The
evidence collected first by Dr. Snow, in the epidemics of cholera in
Lambeth, and afterwards by the Bov. H. Whitehead, in St. James’s, West-
I minster, and by others, at Epping, and elsewhoro, concerning the influ-
ence of water in intensifying, or probably in communicating cholera, is
too strong to be resisted, though it has met with but a tardy acceptance.
I The use of water, free, if possible, from organic impurities derived

488

SPECIAL rilYSIOLOGA*.

from dwellings, or from other sources, is as essential to good health as
pure air. Filtering and depositing heds fairly purify water, on a largo
scale ; but in private houses, if any doubt exist as to the character of the
drinking water, special filtration through animal charcoal, or through
the magnetic oxide, or the carbide of iron, or if this be too expensive,
boiling, and subsequent agitation or exposure to a pure air, are desirable
precautions. ‘

In regard to public improvements, sanitary science consists in the
perfection of cleanliness of the town, the house, the water, and the
atmos-phere. The cost of such improvements, and the great question of
the utilisation of sewage, have also an economical aspect. For the national
welfare, it is essential that sanitary work should be done ; but it is not
necessary that it should be directly profitable, or even free from cost.

THE ORGANS AND FUNCTION OF RESPIRATION IN ANIMALS.

As already stated, respiration is usually either aerial, or aquatic,
according to the medium in which an animal is fitted to live ; but, in a
few cases, both kinds of respiration are possible, as in the true Am-
phibia. Examples of aerial, and of aquatic breathers, are met with
in the Vertebrate, Molluscous, and Articulate Sub-Kingdoms ; but in
the MoUufecoida and Annuloida, as well as in the Coelenterata and
Protozoa, the respiration is, in all cases, purely aquatic. The respiratory
organs afford no grounds for classification.

Aerial Respiration.

The general principles, physical and chemical, on which this kind of
respiration is performed in animals, are the same as those which govern
the respiratory process in Man ; but the organs concerned, vary accord-
ing to the animal, and exhibit wide departures from the form and
structure of the apparatus in Man, as we descend in the scale.

Vertebrata. — In all Mammalia, the respiratory apparatus is similar
in plan, and even in detail, to that of the human body. There is a
complete thorax with movable walls, separated from the abdominal
cavity by a perfect diaphragm, and containing lungs suspended freely
in pleural chambers, resembling, in all essential particulars, those of
Man. The respiratory movements are performed in the same manner ;
their frequency also has a general relation to that of the pulse. The
respirations are fewer, like the beats of the heart, in the larger Mam-
malia than in the smaller ones, these latter requiring relatively, more
frequent changes of air in the lungs, to maintain sufficient respiratory
action for the development of heat, and for other purposes in their eco-
nomy. In the Carnivora, the lungs are relativel}’ much larger than in
the ITorbivora. The right lung is usually the larger. In the horse,
and elephant, and in most Cetacea, they are .simple in form ; but more
commonly they are divided into lobes; usually on the left side, these
do not exceed three, and, on the right, five lobes.

In Birds, besides a typical symmetrical arrangement, as to position
and size, important peculiarities in the respiratoryapparatusaremetwith.
The thorax and abdomen form but a single cavity, there being usually
a rudimentary diaphragm only, which is spread out upon the base of
the lungs, as in some llcptiles. In the ostrich tribe, however, the

THE LUNGS OF BIRDS.

4S9

diaphragm approaches, by its greater clevelopmont, the Mammalian cha-
racter, and in the Apteryx, this musculo-tendinous partition is quite
perfect. The thoracic walls are constructed on a modified plan. The
sternum, here expanded into the largo breastbone, which gives attach-
ment to the muscles of flight, forms the greater part of these walls, and
even supports the abdominal viscera ; whilst the ribs, which have a
peculiar angular joint between their sternal and vertebral portions,
occupy proportionally a smaller part. The absence of the diaphragm,
and the difficulty of expanding a thorax thus constructed, by any active
inspiratory movement, have led, as it were, to a complete reversal of the
meclianism by which the air is drawn into, and expelled from, the chest.
In Mammalia, and in Man, inspiration is an active, whilst expiration
is, to a large extent, a passive movement ; but in Birds, expiration is
active, whilst inspiration is chiefly, if not entirely, passive. In expi-
ration, the large sternum is drawn towards the vertebral column by
muscular effort; the ribs are approximated, and bent at the above-men-
tioned angles, and so the thoracic part of the thoracico-abdominal cavity
and therefore its contained lungs, are compressed, and air is driven from
them. The expiratory muscles now cease to act, and the sternum,
chiefly by the elastic resilience of the bent ribs, being drawn from the
vertebral column, pressure is removed from the surface of the lungs, and
air is inspired ; the expansion of the lungs, is probably favoured by the
contraction of the incomplete diaphragm, which is attached to their
base. The condition of the thorax and lungs when at rest, corresponds
with the state of distension, whilst active breathing begins by an eflfort
to force air from the chest, and not to draw it in, as is the case in
Mammalia. The luvgs of Birds, are somewhat flattened, and fixed to
the back of the thorax ; they are relatively smaller than in Mammalia ;
their lobules are very distinct, each having its own bronchial tube and
bloodvessels. Their interior is extremely subdivided, or celhdar ; the
sacculi or cells thus formed, are at first supported by delicate cartilagi-
nous trabeculce ; but some open into the ultimate air-cells. These cells
are small ; whilst the capillaries upon them are exceedingly numerous,
and their network very close, and owing to the frequent communications
between neighbouring clusters of air-cells, and to other minute arrange-
ments, come into relation with the air on both sides. These capillaries
when injected, seem to bo varicose, and even to project into the air-cells,
in such a manner as to appear naked, or not covered by mucous mem-
brane ; this view is adopted by some, though, more probably, an exceed-
ingly delicate membrane exists upon them.

The high temperature, the active habits, and the rapid waste of tissue
in Birds, are associated with a corresponding activity of the respiratory
function. These animals absorb a larger amount of oxygon, and exhale
more carbonic acid, in relation to their weight, than the Mammalia ;
they are al.so much more dependent on a due supply of pure air, than
the latter, and are much more quickly asphyxiated. Two supplementary
anatomical conditions, peculiar to Birds, must more or loss aid in their
active respiration. First, there are usually found in the neck, thorax,
and abdomen, and even in the limbs, membranous bags, named air-sacs,
into which the air gains acce.ss by extensions from certain bronchial
tubes, which roach to the surface of the lungs, and there communicate
with the thoracic or pleural air-sacs, from which other communications

490

SPECIAL PIIYSIOLOGT.

extend to the abdominal, and remaining air-ca\'ities. These air-sacs are
highly elastic, have a few plain muscular fibres in their walls, and are
lined by a fine, moderately vascular, and partially ciliated mucous mem-
brane. Secondly, in many Birds, most of the hones are hollow and ai'e
filled with air. In certain Mammalia, some of the bones of the face and
cranium, contain air ; but, in most Birds, besides these bones, the vertebne
and sternum, and even the long bones, which, in Mammalia, and in the
early condition of the Bird, contain marrow, such as the clavicle, humerus,
and femm-, and even the merry thought and shoulder bones, are in the full-
grown Bird, occupied with air, which finds access to their interior, by
special membranous canals leading from the adjacent air-sacs. AATien the
trachea is tied, respiration may be performed for a time through an aper-
ture made in the arm-bone. These cavities in the bones, are lined with
a membrane which, as compared with that of the air-sacs, is highly vas-
cular. In Birds, killed suddenly, or destroyed slowly by drowning, the
air in the air-sacs and bones, is often charged with from 8 to even 15
per cent of carbonic acid (Dr. Davy) ; respiratory interchanges of ox3'gen
and carbonic acid, probably therefore here take place between the air
and the blood, and these cavities must be regarded, not so much as sup-
plementary, as sub-respiratory chambers, for the increase of the surface of
absorption and exhalation. But their importance, in this respect, has
perhaps been exaggerated. An equal extension of respiratory surface,
if that only were needed in the economy of the Bird, might have been
obtained by a trifling enlargement of the lungs themselves ; the mem-
brane lining the cavities of the bones, is not so vascular as a respiratory
membrane usually is, whilst that of the capacious air-sacs, is still less
so ; moreover, there are some Birds which have no air in the long bones,
or even in other bones ; such exceptions occur in various Orders,
chiefly, however, amongst the smaller Birds, and some aquatic species ;
lastly, the Apteryx has no air in any of its bones, and is even destitute
of air-sacs, excepting the pleural chambers, in this respect being quite
singular.

The high temperature of Birds, has probably some other explanation
than the presence of these sub-respiratory air-chambers. As already
mentioned, vol. i. p. 236, these air-sacs, and the air-cavities in the bones,
ainnot much diminish the weight of a Bird in the air, by the relative
temperature of their contents, but they may aid in flight, by their dis-
tending, and giving fixity to the thorax, which is the base of action for
the wings; they may also, by the different pressure which is exercised
upon them dui’ing flight, act as a sort of pneumatic apparatus for the
movement of air through the lungs, at a time when ordinar}’ expiration
is necessarily interfered with.

In Reptiles, the highest of the Cold-blooded animals, the respirator}'
apparatus is well developed ; but in comparison with the hlammalia and
Birds, the lungs, though even larger in proportion to the size of the
body, are not nearly so minutely subdivided in their interior, as in the
Warm-blooded Vertobrata. Besides this, neither the arrangements of the
heart and large bloodvessels, nor the structure of the thorax, are so well
adapted for the perfect distribution of the blood to the lungs, and for
the coutinuous introduction of fresh air into the air-cells ; lastl}’, the
pulmonary capillaries are not so numerous.

The greatest diversity is met with in these animals, as regards the

THE LUNGS OF EEUTILES,

•J91

structure and the mobility of the thoracic walls. In the Saurians, as
in the Crocodiles and Lizards, the thorax is constructed somewhat after
the Mammalian type, with movable ribs and a small imperfect sternum ;
in the Chelonia or Turtles and Tortoises, the walls of the thorax are
completely immovable, being fused, as it were, into the carapace and
plastron ; whilst, in the Ophidians or Serpents, the thoracico-abdominal
cavity is very capacious and expansible ; the exceedingly numerous ribs
are disconnected in front, owing to the complete absence of a sternum ;
they are extremely movable, and have powerful muscles attached to
them. In the higher Saurians only, is any trace of a diaphragm found ;
no such structure exists in the Chelonia, or Ophidia. The act of respi-
ration is never performed in these animals, by an inhaling movement.
In this respect they resemble Birds ; but they ditfer from these even
more remarkably, for they all force air into the chest, by an act some-
what similar to that of deglutition. Air being drawn into the pharynx,
by the depression of the hyoid apparatus and its attached soft parts,
the posterior nares are then closed, and, by an elevation of the same
parts, the air is forced down through the glottis into the trachea. Expi-
ration depends chiefly on the elasticity of the lungs, indeed, almost en-
tirely so in the Chelonian Eeptiles, being assisted only by the abdo-
minal muscles ; whereas, in the Saurians and Ophidians, it is aided by
the intercostal muscles and the resiliency of the walls of the chest. The
lungs of Eeptiles, fig. 116, are large in proportion to their bodies, and in
the Chelonia, are attached to the sides of the chest. They are sometimes
cellular, and sometimes saccidar. When they are cellular, as in the Sau-
rians, and the Chelonians, 3, the cells are few, and form large alveolar
spaces, presenting, on a section, a spongy structure, the bronchial tubes
being soon lost in the wide cellules which communicate freely with ono
another. In certain Saurians, the two lungs are unequally developed ;
and, in the lower forms, the lungs become much elongated, and smoother
in their interior. In the Ophidians and snake-like Saurians, it is the
rule to find only a single, long, cylindrical, sac-like lung, in a fully
developed state, viz. the right one ; the left lung is either slightly,
or not at all, developed. The single lung, when distended, reaches
through the greater part of the cavity of the body, and is saccular; the
portion nearest to the trachea, however, has its sides marked with nu-
merous alveolar depression.s or imperfect cellules, supported by a carti-
laginous framework, and having vascular walls ; the larger portion of
the sac has smooth and slightly vascular membranous parietos, fig. 1 15, i .
Even in the Crocodiles and Turtles, owing to the large size of the cel-
lules, and to their slightly subdivided form, the pulmonary mucous
surfiice for the capillary network, is comparatively small ; in the Serpents,
it is even proportionally less. Besides this condition, the less perfect
nature of the inspiratory mechanism, the small quantities of air slowly
and feebly impelled into the lungs, and the arrangements of the vascular
system, imply a less active respiration, in accordance with their usually
r slower life and habits. In the aquatic Ophidia, the buoyancy of tho
body, is greatly aided by tho size of the lungs, especially in the Turtles,
the shell of which is of great weight.

In the Amphibia, which include the Frogs, Toads, Newts, Sirens,
Proteus, and others, the anterior walls of tho thorax are defective, and
there is no diaphragm. The air, as in Eeptiles, is drawn through tho

492

SPECIAL PHYSIOLOGY.

nostrils into the pharynx, by the depression of the hyoid apparatus and
floor of the throat, and is propelled through the glottis, by the subse-
quent elevation of the same parts. The lungs of the Frog, fig. 1 15, ^2, may
be described as subcellular ; the internal subdivision of their surface into
cells, is more simple than that of the Saurian Reptiles, though more
complex than the alveolar structure of the Ophidian lung. The corre-
sponding bronchus opens at once into this subcellular lung, the alveoli

Fig. 115.

Fig. 115. 1, Lungs of a serpent; the right one onl.v is fully developed; it
is of such length, that the upper and lower portions alone are repre-
sented ; the upper end is trahoculatcd and sacculated. 2, Lungs of the
frog, showing their simple cellular character. 3. Portion of the lung
of a turtle, showing its compound cellular structure.

at the upper part of which, are supported by fine cartilaginous trabe-
culte; it has been aptly compared to a single ultimate lobule of the
lung of the Bird ; but the layer of capillaries is single, and is exposed
to the air on one side only. The respiration of the Amphibia, is com-
paratively imperfect, and their blood is cold ; moreover, it is ixirtly

THE AIR-BLADDER OF FISHES.

403

performed by the surface of their moist skin, as lias been proved by
their continuing to exhalo carbonic acid, after the removal of both
lungs, an operation which they, for a time, survive. Even, in temperate
climates, the Amphibia hybernate beneath the water ; and, in that state,
they respire solely by the skin ; but in summer, simultaneously with
a greater general energy, their respiration becomes more active, and then
they breathe by the lungs also. The necessity for respiration, increases
in these and in other cold-blooded animals, with the elevation of the
temperature of the surrounding medium, which excites them to greater
activity of body. In the Siren, and Amphiuma, the interior of the
lungs is only slightly alveolar, presenting the last traces of a structure
like air-cells ; in the Proteus, the lungs are smooth on their internal
surface, like the air-sacs of the Fish ; the trachea is membranous, and
the glottis is a simple cleft.

In the early larval, or tadpole, state, all the Amphibia breathe aqua-
tically, and some species retain the means of so doing, in the adult
condition ; but all of them then have lungs, however simple.

To Fishes, the aquatic form of respiration is proper ; but, as the ho-
mologuo of the limgs of the other Vertebrata, the air-bladder of certain
species requires mention. The air-bladder of the Fish, is a simple mem-
branous sac or bag, placed beneath the spine, sometimes elongated,
cylindrical, or fusiform, sometimes pyriform, sometimes provided with
simple diverticula, more rarely with short branched tubuli ; sometimes
it is double, one part being longer than the other, thus resembling
the asjrmmetrical lung of the Serpents. The air-bladder always contains
some air. It is usually a closed sac; but, in many cases, as in the pike,
carp, salmon, and herring, it communicates, by means of a short open
duct, the ductus pneumatieics, with the oesophagus, near the stomach or
higher up ; in the Lepidosiren, it communicates with the pharynx, and even
opens into it by a slit like a glottis ; it is also bifid, and slightly alveolar,
closely resembling, therefore, a simple saccular lung ; it sometimes pre-
sents vascular projections in its interior. The idea, that the air-bladder
is the homologue of the lungs, is supported by the fact, that in the
embryoos of the so-called pulmonated Vertebrata, the primitive lungs
originate as little buds developed from the sides of the upper part of
the oesophagus, which afterwards become hollowed out and branched.
There is no homology between the gills and lungs in the Vertebrate series
of animals ; they have analogous functions, but they are totally distinct
parts of the organism.

Certain fishes, as the Loach, can swallow air which probably enters
the air-bladder ; but, in other cases, and especially when this organ forms
a closed sac, air must be alternately excreted from the blood and ab-
sorbed by it, according as the bladder is full or empty. In the Am-
phioxus, the alimentary canal aids in tho respiratoi-y process. The
analysis of tho air in the air-bladder, sometimes shows a largo propor-
tion of carbonic acid, and sometimes little more than nitrogen. In a
few species, in which it is of great size, and communicates freely with tho
pharynx, tho air-bladder may be regarded as a feeble sub-ro.spiratory
organ. In the great majority of cases, however, it is a rudimentary
part, exercising little or no respiratory function ; it is largo in tho
Flying fishes, and in some others capable of energetic and sustained ex-
ertion. As elsewhere mentioned (vol. i. p. 232), when distended, it

494

SPECIAL PHYSIOLOGY.

diminishes the specific gravity of a Fish supported in water, and also
alters the centre of gravity of the animal. It is usually absent in
what are called ground-fishes, which live in deep water; but its pre-
sence or absence appears to follow no precise rule, either as regards the
habits, size, or generic position of the Fishes in which it exists or is
wanting.

Mollusca. — The Pidmogasteropods offer examples of Non-Vertebrated
aerial breathers; they are terrestrial in their habits. In the Snails,
for example, a large sac communicating with the external air, by an aper-
ture situated on the left side of the neck, is found in the shelled varie-
ties, beneath the back part of the mantle, in that portion of the body
which occupies the smaller coils of the shell. It has numerous blood-
vessels ramifying upon its walls, and is usually lined with cilia. This
simple sac may be taken to represent the primitive idea of a lung, that is
to say, a sac, formed by an inversion of the surface of the body, lined by
a thin moist membrane, communicating with the air, and possessing,
distributed upon its walls, bloodvessels, which have thin coats and a con-
stantly moving blood-current in them. Such an organ becomes perfected
by increase of size, by multiplication of its parts, so as to constitute a
multilobular lung, by subdivision of its internal surface into saccules or
air-cells, and by the penetration of air-tubes into its numerous lobules.
The remaining Gasteropods, and, indeed, all other Mollusca and MoUus-
coida, breathe aquatically.

Annulosa. — Numerous instances of air-breathing animals, occur in this
Sub-kingdom. Entire Classes without exceptions, such as the Myriapoda,
the Arachnida, and the extensive and most important Class of Insects,
breathe in this way. Of the Annelida, a few only are terrestrial and respire
air; these, such as the earth-worms, have pairs of small sacculi opening
on the sides of the body, in each segment ; but they are usually filled
w'ith mucus. Similar structures exist in the leech. The air-breathing
Annulosa, generally, however, do not breathe by soft membranous com-
pound sacs like lungs, or by soft air-bladders, or even by simple soft
sacculi like those of the land-snails ; but they have internal air-chambers,
suiTounded by stiff walls, so that they are kept constantly patent, and
are not easily compressed.

In the Myriapoda, these chambers are saccular, a pair of sj-mnietrioal
sacs existing in each of the many segments of the body ; they commu-
nicate by short membranous tubes, the walls of which exhibit spiral
lines, with little apertiu'es on the sides of the segments, named spiracles or
stigmata. From these sacs, in one species, forming a step towards the
condition of Insects, other short twigs ramify into tlie body, or laige
.symmetrical lateral timnks connect them all together. In this wa}’, air is
conveyed into close proximity with the nutrient fluids, and respiratory
interchanges are accomplished.

In the Arachnida, air-sacs exist in the spiders, communicating im-
mediately with spiracles or stigmata on the surface of the body, and
frequently having their internal membrane plicated, sons to increase the
surface for exposure to air, for the aeration of the fluids of the body.
This plicated structure is associated with a more perfect condition of the
circulation, and compensates for the comparatively limited distribution
of the air, in those active and powerful animals. In other Ai-achnida, the
air-chambers are tubular, constituting trachea;, as found in the mites.

respiration in insects.

40 r>

The Insects possess in greatest perfection, this particular modification
of an aerial respiratory apparatus, viz. a series of almost incompressible
canals or tubes, instead of sacs. In these exceedingly active and ener-
getic animals, most of which are organised for flight, the respiratory
apparatus consists, first of tubuli, which commence at the sjnracles or
stigmata found on each side of certain segments of the body, and, after
a short course, lead into two longitudinal lateral tubes, extending from one
end of the animal to the other. From those principal tubes, branches
are given off for each segment; these branch again and again, until the
finest ramifications penetrate the substance of every organ, especially
the muscles, and even the ganglionic nervous centres, and the complex
eyes. These tubuli, large and small, constitute the well-known trachea;
of Insects. They are recognised under the microscope, by the beautiful
structure of their walls, which are composed of coherent spiral fibres
arranged in the most regular manner, and maintaining by their elasticity,
the whole tracheal system in a patent sta*^e, resisting the pressure to
which they are subjected during muscular effort. By these open canals,
air is freely introduced into every portion of the Insect. In many
perfect Insects, especially in those of powerful flight, the body or abdomen
is made to perform active movements, by w'hich air is drawn in and out
through the spiracles. Closure of the spiracles, or the filling of the tra-
cheae with oil, speedily asphj'xiates these animals. Although, therefore,
the circulatory apparatus is limited to a dorsal vessel, with largo venous
sinuses and interstitial lacimae, without capillary vessels, yet the respira-
tory apparatus is diffiised through every organ and portion of the bodj-,
and the aeration of the blood is most complete. The respiratory function
of these, the most perfectly developed examples of the Annulose animals,
is, in the majority of species, extremely active, in harmony with their
general energy and comparatively high temperature. In the largest
Insects, and in those which, though of smaller size, possess remarkable
powers of sustained flight, as the Bee-tribe, the longitudinal tracheal
trunks are dilated in certain segments, so as to form air-sacs with rigid
walls. The size of these, presents considerable variation, being largest
in species possessing the greatest powers of flight. The wings of the
perfect Insect have no homology with the true limbs, for they spring from
the dorsal and not from the abdominal surface; in their structure and
mode of evolution, they are more like respiratory organs, being filled
with ramified trachea;.

The trachea; and their dilatations in the flying Insects, sometimes de-
signated the Birds of the Non- vertebrate Creation, have been supposed,
like the membranous and osseous air-cavities in Birds, to diminish
the specific gravity of the body during flight, by tlio warmer air in
them ; but any such effect must bo immea,surablo. Their hollow, stiff
structure, however, utilises the material employed in the most admirable
manner, and so relatively diminishes weight ; wliilst the large dilatations
or sacs met with, especially in Insects of flight, may serve as store-
chambers for air, the spiracles being perhaps more or lo.ss closed during
that act.

Insects absorb, and convert into carbonic acid, a relatively largo quan-
tity of oxygen, even during rest; but the respiratory interchanges aro
much more active during locomotion. A bee will perform during the ex-
citement immediately following its capture, as many as 125 respiratory

49f.

special rnTSIOLOGT.

movements of its body per minute ; but after an hour and a half, these
may decline to forty-six per miinito. In the first hour of an excited
respiration, one-third of a cubic inch of carbonic acid has been found to
be generated, a larger quantity than -was produced in twenty-fours by
a bee in its quiescent state, and far more than is given off by the
lungs of a Man, in proportion to his weight (Newport). In the larval
condition, as exhibited in caterpillars and grubs. Insects are also pro-
vided with stigmata, lateral tubes, and tracheae ; and so is the pupa or
chrysalis of those insects, which pass through the perfect stages of
metamorphosis. But the respiratory process in the pupa, is less active
than in the perfect Insect, and in the chrysalis, less active than in
the larva. It is curious that the larva? of certain insects, as of
the gnats and Ephemerte or day-flies, and the dragon-flies, are purely
aquatic in their habits ; but still for the most part, they also breathe by
tracheae, the spiracles of which exist only in the hinder portion of the
animal ; these they protrude above the surface of the water, for respi-
ratory purposes. In the larva of the gnat, one of the spiracles of the
tail segment, is provided with a tubular prolongation, the mouth of
which, beset with fine setae which retain vesicles of air, is made to reach
the surface of the water, so that the creature can breathe whilst the rest
of the body is submerged, and the head turned downwards, in order to
watch for its prey. The larvae of the Ephemera?, still more curiouslj',
breathe by external tuft-like or leaf-like thoracic or abdominal gills, con-
nected with the tracheae or by similar organs situated in the intestinal
canal ; but in the perfect state, like other Insects, they breathe by tra-
cheae. Aquatic beetles come to the surface to breathe, or carry globrdes
of air below the water. The same habit prevails among certain Arach-
nida, some of the water-spiders even building nests beneath the water,
and carrying down air to them, which they can afterwards respire.

Aquatic Respiration.

In this form of breathing, the physical process concerned, is simply
that of the moist or false difmion of gases in a state of solution, those of
the blood or nutritive fluids of the animal interchanging with those of
the water, which, whether fresh, brackish, or marine, is the universal
medium of aquatic respiration. That water contains air, is .shown by
placing it under the air-pump, or by boiling it, which processes abstract
or expel the air, and render it unfit to support aquatic animal life. The
quantity of free oxygen contained in water, is, of course, much less,
volume for volume, than it is in air, inasmuch as the source of the
oxygen, is the air itself, held in solution. But the air, dissolved in
water, is somewhat richer in oxygon than the ordinary atmosphere ;
this is explained by the fact that oxygen is twice as soluble as nitrogen,
in that fluid. Nevertheless, the gaseous interchanges in aquatic respira-
tion, are necessarily slower and less energetic than in aerial breathing.
The temperature of aquatic breathers is low ; they maintain a heat very
little raised above that of the surrounding medium, which is also a much
belter conductor of heat than air. and so robs them quickly of their
caloric ; tlicir movements and otlier vital acts, arc comparatively sluggish
and slight ; their life is more vegetative, and even those whicli have a
perfect circulation, arc characterised by possessing cold blood. The

RKSriRATION IN AMPHIBIA.

497

Mfimm.alian aquatic species, such as seals, porpoises, and whales, though
chiefly or entirely inhabiting the water, are yet air-breathing animals
provided with lungs, and warm-blooded.

In water-breathing animals, in which a distinct circulation of blood
exists, a special respiratory organ is always present, connected with the
circulatory apparatus. With the exception of Insects, this is true like-
wise of air-breathing animals. The more perfect the circulation, the
more carefully must respiration be provided for ; otherwise, carbonic
acid, accumulating in the blood, woidd be speedily conveyed to the
nervous centres, and produce rapid poisoning. Such an event is more
imminent in the warm-blooded air-breathing, than in the cold-blooded
water-breathing animals.

The most perfect breathing apparatus, for aquatic respiration, consists
of exceedingly vascular projecting membranous processes of various
forms and complexity. In the lower animals, such processes are more
simple, and in the absence of a distinct circulation, they are ciliated
upon their surface. These projections are named hranchia or gills ;
they differ in structure, as much as the lungs of the air-breathing
animals. Again, in certain forms of aquatic animals, and in some
Entozoa, there are found, with or without gill-like projecting organs,
remarkable internal ramified tubes or vessels, communicating, by an
opening, with the surface of the body, and partially ciliated in their in-
terior : these are the so-called water-vessels or water-vascular system ;
they appear to have a respiratory office. In still lower aquatic animals,
destitute altogether of vessels, certain hollow ciliated portions of the sur-
face, or interior, of the body, exist, named ciliated sacs ; in others, ciliated
discs are present ; often the cilia are methodically arranged on the surface,
or in the interior of the body ; lastly, in tbe lowest forms, these micro-
scopic moving organs cover a portion or every part of the minute or-
ganism, and so are auxiliary to respiration.

Vertebrata. — The highest of this Class which have gills, are the Ani-
philria. In the larval or tadpole condition, all these animals have
minute gills, and frequently even two sets of these organs. The first set
are called the external gills, and consist of soft processes slightly
branched, or very much subdivided, or even plumose ; they are attached
to the side of the neck and project freely into the water. In the larva
of the higher or tail-less Amphibia, the frogs and toads, the external
gills remain only for a fewdays ; but in the tailed salamanders or newts,
they exist for a longer period, and in the lowest Amphibia, they persist
throughout life. They are, at least when newly developed, always
covered with cilia, and each minute subdivision or branch contains a
looped capillary vessel, one side of which convoys outwards, the de-
oxygenatod venous blood, and the other inwards, the oxygenated or arte-
rial blood. The second sot of gills, found in certain Amphibia only,
are named the internal gills-, these appear in frogs and toads after the
wasting of the external gills; they consist of niinulo fringes of vascular
processes attached to tho cartilaginous branchial arches of the hyoid appa-
ratus, and are protected by a fold of tho skin of tho nock, so as to lio in
a sort o( branchial chamber, which comrminicates with tho pharynx; tho
opening on tho right side of the nock, very early becomes closed. Water
reaches these internal gills, by flowing in through tho month or nose, and
then out through a small orifice on tho loft side of tho nock, tho movement

VOL. 11. K K

49S

SPECIAL PHYSIOLOGT.

of the water being caused by an act resembling that of deglutition. It is
these internal gills, found in some of the Amphibia, which are the repre-
sentatives or homologues of the gills of Fishes ; they are not developed
in Menobranehus and Amphiuma. In the frogs, toads, and true sala-
manders, both sets of gills disappear; hence these are named Caduci-
branchiate Amphibia ; they afterwards breathe by the lungs and skin only.
In the salamandroid Amphibia, including the .-Axolotl,

Menobranehus, Siren and Proteus, the gills are persistent ; they are
really the external gills, though the)' may become attached, as in the
Ajcolotl, to the first branchial arch of the hyoid apparatus.

In Fishes, the branchise or gills, which are always internal or covered,
attain their highest development and most complex forms. They usually
consist of numerous comb-like processes, supported, like single or double
fringes, on the branchial arches of the hyoid apparatus, and forming four
or five laminse on each side of the pharynx. They are, in some cases, as in
the Cartilaginous Fishes, concealed by the integuments ; but in others, as
in the Osseous Fi.shes, by a moveable osseous and cutaneous covering,
named the opcrmhiiyi. In the latter case, only one external gill opening
exists on each side, the operculum overlapping all the branchial arches ;
but internally the gill-chamber opens into the pharynx, by separate
clefts or apertures between the branchial arches. In the former case,
however, the gill chamber is completely divided into passages, vaiying
from three to seven in number, each having a separate internal and
external aperture, corresponding with the clefts or spaces between the
branchial arches. In some of the lowest forms, the gills are mere folds
of membrane, lining distinct sacs. In the Myxine, the branchial outlets
unite into a single canal, which nms backwards, and opens on the
under surface of the fish, at a sort of abdominal pore.

The extent of surface obtained by the comb-like fringes of the gills
of Fishes for exposure to water, is very large, especially in the rays
and skates. The water drawn into the opened mouth, is forced, at
intervals, by the hyoid and pharyngeal muscles, between and over the
gills, in the direction of their fringes, and is rapidly expelled at the
sides of the neck, the action, as seen in an ordinary fish, being ac-
companied by regular movements of deglutition, and by a characteristic
opening and shutting of the opercula. In the Cartilaginous Fishes,
the water passes in streams from the lateral openings, which are
sometimes more or less valved. Drawing a fish rapidly backwards
in the water, may asphyxiate it, by bending up the branchial fringes,
if the opercula be open, or by exclusion of water, if these be closed.
Each fringe-like process of a gill-plate, is supplied by a brancli of
the branchial artenj, which brings dark or venous blood from the
heart and bulbus arteriosus ; this divides into minute vessels, which
end in the branchial capillaries; from these again, the r’eins
arise, which pass back to the base of the gill, and all combine to form
the aorbi. In passing through the gills, the blood is oxygenated. As
the heart of the Fish is branchial, all the blood returned from the body,
is propelled through the gills, before it is again distributed to the body ;
nevortholoss the respiration of fishes, being aquatic, is feeble, and their
temperature is cold. The gills of fishes, are not ciliated on their surface ;
but it is necessary that they should continue moist, or the usual respira-
tory interclianges between the blood, and the air dissolved in the water,

RESPIRATION IN MOLLUSC A.

499

would soon cease. Eespiration will, however, go on for a short time
in the air, provided that the gills remain moist. Certain fishes, as the
eel and others, leave the water for a time. The Anabas of Ceylon,
is said even to climb up trees and bushes after food ; on the sides of
its head, just above the gills, the pharyngeal bones are convoluted, and
the anterior branchial arches support chambers with laminated walls,
for holding quantities of water. Fishes are necessarily suffocated when
removed from the water, the gills becoming first clogged and then dry,
circulation and respiration in them being both arrested. They are also
asphyxiated in water, which no longer contains oxygen in solution, or
even when foreign substances are dissolved in it ; sugar speedily destroys
them. In that exceptionally organised marine animal, the Amphioxus,
the mouth is provided with ciliated lobes, which, by ciliary action, propel
the water into the pharynx. This cavity is dilated, has its sides sup-
ported by a complex lattice work of branchial cartilages, upon which
the branchial vessels are placed ; its sides are perforated by numerous
slits, upwards of 100 in number, the edges of w'hich are ciliated,
and which lead into the perivisceral cavity of the abdomen. The water
used for respiratory purposes, is expelled from this cavity, by an opening
named the abdominal 'pnre. Moreover, the entire alimentary canal is
ciliated internally, and the water which passes through it, may also be
employed in the aeration of the blood.

On comparing the entire series of the Vertebrata, as regards their
mode of respiration, it is seen, that in the adult state, the Mammalia,
Birds, Eeptiles, and Caducibranchiate Amphibia breathe by lungs ; that
the Perennibranchiato Amphibia and the tadpoles of the Caducibran-
cliiate kinds, breathe both by lungs and gills ; and lastly, if we disregard
the sub-respiratorj- air-bladder occasionally present, that Fishes breathe
entirely by gills. The respiratory process in these animals, is, however,
much more active than in the aquatic Non-vertebrata, which we have
next to describe. This is due to the comparatively greater size of the
gills, to their more perfect and complex stnicture, to the special contri-
vances for moving the water over their surfaces, and to the proximity
of the heart to these organs.

Mollusca. — Of these chiefly aquatic animals, the most highly developed
gills exist in the highest Class, the Ceplialopods, in which the branchi®,
being very largo but non-ciliated, consist of foliated laminte, united
by a common stem, which supports the branches of the branchial arteries
and veins. The gills are lodged, one or two on each side, in the cavity of
the non-ciliated mantle, which has two orifices, one by the side of the nock,
at which the water outers, and another placed at the extremity of the
tubular process called the funnel, from which the water passes out. The
movement of the water is accomplished by the alternate dilatation and
contraction of the muscular walls of the mantle. In the Ptoropods, the
branchite arc also laminated, being placed sometimes within, and some-
times without, the mantle, and being always ciliated. In the naked
species of Branchio-gastoropods, the gills consist of ciliated, fringed,
sometimes tubular processes, projecting into the water (Niidibranchi-
ata), and arranged either along the sides of the body in tufts (Tritonia),
or else in a circular disc-like manner on the dorsal region (Dorsibran-
chiata), or around the lower opening of the alimentary canal (Doris);
sometimes a fold of the mantle partially or completely covers them. In

K K 2

500

SPECIAL PIITSIOLCGY.

those kinds which have univalved shells, the gills consist of ciliated pli-
cated fringes, lodged in the last spire of the shell, the water gaining access
to the cavity in which they are contained, sometimes by a long tube, and
sometimes by a wide opening. Amongst the lowest Branchio-gastero-
pods, are some species allied to the Nudibranchiate group, which have
no branchite, but are believed to respire by means of their surface only,
or by that, aided by certain ciliated extensions of the digestive cavity.
A few genera, such as Onchidium, possess, besides arborescent branchia*,
distinct air-sacs, showing a transition between the branchiate and pul-
monate divisions of the Gasteropoda. In the bivalved Lammellibran-
chiata, mussels, oysters, and others, the gills consist, as their name
implies, of two pairs of flat laminae, composed of a double layer of mem-
branous rods, covered with fine cilia, and supporting the bloodvessels.
In some genera, these branchiae are freely exposed, when the valves of
the shell are open (oyster) ; in others, they are enclosed by the ciliated
lobes of the mantle, at each end of which, an aperture exists for the
entrance and exit of the water, which is driven through, by ciliarj' action.

MoUuscoida. — Amongst these, which are all aquatic, the Ascidioida.
possess, in the anterior part of the body, large respiratory atria or
chambers, or branchial sacs, lined with cilia, and communicating with
the exterior. These atria are formed by an expansion of the part for-
merly named the pharynx, which is supported by a rod, called the
endostyle, the sides of which are, in some species, cleft by numerous
.slits, through which water passes into an interval between the branchial
atrium and the proper walls of the body, and then escapes at the opening
of the mantle. In the Brachiopoda, the cavity of the mantle itself, is
the chief respiratory chamber; it presents vesicular dilatations covered
wth vessels, which probably act as gills. In the Polyzoa, the peri-
visceral cavity, which contains nutrient fluid, is prolonged into the
numerous, delicate, tentacular processes, arranged around the oral
aperture, which are covered with rows of beautiful cilia ; hence the
fluid in their interior, is aerated by the currents of water on their
surface.

Annulosa. — The aquatic Annulosa are represented only by the Crus-
taceans, and the Tardigrade Arachnida. In the larger Crustacea, the
gills or branchiiB present the form of flattened laminm, which, in the
higher forms, such as the lobsters and crabs, are enclosed in proper bran-
chial cavities within the shell ; in the lobster, there are twenty-two
branchim on each side. Through tlmse cavities, copious streams of
water are propelled by the continual movements of special flapping organs,
consisting of the last joints of some, or all, of the abdominal limbs,
which are flattened out for that purpose.

In the hind crabs, which are drowned if kept in water, but which
remain on hind a long time, the gills are moistened by the watery con-
tents or secretion of a spongy or laminated organ, situated, witli the gills,
in the gill-chamber. In still lower and smaller Crustaeea, the branchial
consist of delicate foliaeeous or flabcllar organs, attfvehed tothe under side
of the segments of the bo iy, which project into the water, and are usually
kept in a constant state of motion. In the Crustacean Onisci or wood-
lice, and allied forms, which inhabit moist places, there exist near the
covered gills, networks of air-tubes, or even air-sacs, thus ap]iroaching
the Insects. In some of the lowest aquatic Arachnida, us the P3'cnogo-

USE OF CILIA IN EESPIRATION.

501

nida, no special respiratory organs have been detected. No cilia exist
in any of the aquatic Arthropodous Anniilosa. It has already been
mentioned, that the larvfe of certain Insects, which live in water,
breathe by gill-like appendages connected with the abdomen, or with the
intestituil canal. The Annelida or worms are generally hranchiatod ; the
gills are composed of a highly-divided delicate membrane, either branched
or tufted, and usually ciliated ; they are sometimes external and situated
either on the back, on every segment of the body, as in Nereis and
Eunice, or around the head only, as in Serpula ; sometimes they are
internal or covered, as in Polynoe ; or they are represented merely by
ciliated sacs, as in the leech.

Anmdoida. — These are, also, either aquatic, or parasitic in the interior
of other animals. Such as have soft integuments, probably respire
through the skin. None ever possess branchiae ; but special provisions
for the respiratory function are met with. Thus, in all tire worm-
shaped Scolecida, there exist peculiar ramified contractile vessels, the
trunks of which open on the surface of the body, and are in part ciliated
in their interior; these are the so-called wafer-uessefe, which are supposed
to be subservient to the respiratory process. In the Rotiferous animal-
cules, ciliated disc# of the most varied shape, perform this function. In
the Echinodermata, respiration seems also to be performed, partly by the
sides of the perivisceral cavity which communicates generally with the
exterior, admits the sea-water, and is lined with cilia; and partly by the
contractile ambulacral vessels, which can also be distended with fluid.
In the Holothurida, the perivisceral cavity is closed ; the ambidacral
system is reduced to its lowest condition, but important ramified tubular
organs, communicating by a trunk with the cloaca, and projecting into
the perivisceral cavity, are regarded as respiratory organs; they aro
contractile and are lined with cilia.

Cmlenterata. — All of these are aquatic. They possess no distinct
circulatory organs, and accordingly no separate respiratory apparatus ;
respiration seems to be accomplished by the interchange of oxygon and
carbonic acid, indifferently through any part of the external surface, or
specially perhaps at certain ciliated portions of the internal surface of
their body cavities, and withi n the numerous ciliated tubular prolongations
of that cavity, which ramify in the soft disc of some of those animals.

Protozoa. — These universally aquatic animals, exhibit the same want
of distinct respiratory organs, unless the contractile vesicles bo of this
character. In the Infusoria, more or less of the surface of the body is
ciliated. In the Sponges, the tubular passages through the body, form
respiratory surfaco.s, being in many species provided, at certain points,
with cilia. L;tstly, in the Rhizopods, or Eoraminifera, and in the still
humbler Grcgarinida, not oven cilia aro present ; but the almost
structureless or simple c.oll-like body of those animals, must bo stimu-
lated, disintegrated and purified, by direct absorption of oxygon, and
exhalation of carbonic acid, so fir as is necessary for their sim|)lo life.

The presence of vihratile cilia, on the respiratory surfic.es of the lower
forms of most aquatic animals, is a noticeable anatomical fact ; they
often occur in the embryonic, if not in the adult condition. They
servo, when pnisent, to change continually the stratum of water in im-
mediate conbict with the breathing sui-faces ; and, acconling to some,
their motion is even to bo attributed to the active chemical changes

502

SPECIAL PHYSIOLOGY.

which take place on those surfaces. They are not, liowevcr, essential, for
they are not always present. Their absence from the branchiae of the
Cephalopods amongst Mollusca, and of the Crustacea, amongst Annii-
losa, form the most striking exceptions. Amongst the aquatic Vertebrata,
they are not found on the gills of fishes, unless upon the branchial ap-
paratus of the singular Amphioxus ; they exist on the temporary gills of
the Amphibia, but probably not on the permanent gills of the Perenni-
branchiate forms. Amongst air-breathing animals, they are wholly
absent in the sacs or trachese of the higher Annulosa. In the lowest
air-breathing Vertebrata, viz. the Amphibia, they exist in the lungs as
well as in the respiratory passages ; but, in all other instances, they
appear to be confined to the air-passages and air-tubes, not extending to
the air-cells. It must also be remembered that they are found on other
organs, besides those concerned in respiration.

ANLALUj heat, light, and electricity.

ANIMAL HEAT.

Inorganic bodies have a constant tendency, by losing or
gaining heat, to adapt themselves to the temperature of sur-
rounding media or objects. They may also be artificially
cooled, or artificially heated, to all possible degrees. The
same is true of dead organised bodies, within the limits of
combustion, as of a dead tree, or of a dead human body.
Living plants and animals also receive, or give off, heat
physically, but they have, besides, a common power of re-
si.sting external temperatures ; with plants, this power is very
feeble, but with animals it is more marked. In the higher
animals especially, there is an inherent power of maintaining
a temperature differing from that of the surrounding media,
which are in general cooler, but may be warmer, than their own
bodies. Moreover, each kind of animal is able to maintain,
within a certain range, a temperatiue proper to itself; but,
since even living animals, like dead ones and inorganic bodies,
exhibit the same physical phenomena of absorption, conduc-
tion, and radiation of heat, they undergo constant changes,
usually in the direction of a loss of heat. Hence, there must
exist within them, a power of constant renewal, or production,
of fresh heat. The standard temperature of an animal is
understood to express its proper heat ; Avhilst the form of heat
produced in its body, for the maintenance of this temperature,
is known as Aiiimal Heat.

TEMPERATURE OF ANIMALS.

6l'3

This function of producing heat, is universal in the Animal Kingdom,
and all the processes of animal life are influenced by it.

Animals have been dmded, according to their temperature, into the
Cold-blooded and the Warm-bloodtd animals, the former being under-
stood to include all the Non-vertebrate animals, and, amongst the Verte-
brata, the Fishes, Amphibia, and Eeptiles ; whilst the Warm-blooded
animals consist of the Birds and Mammalia, including Man. Amongst
the Non-vertebrate Classes, the Protozoa and Ccelenterata, having no
proper blood system, can hardly be designated cold-blooded ; yet they
have a close relationship, as regards the phenomena of temperature, with'
that division of animals. It has been proposed to name the Cold-
blooded animals, animals of variable temperature, and the Warm-blooded
creatures, animals of constant temperaiure ; because the former have
their actual temperature greatly influenced by, that is to say, elevated or
lowered, according to corresponding changes in the temperature of the
media in which they live ; whilst, on the other hand, the latter exhibit
nearly a uniform temperature, under important alterations in that of
the surrounding media (Bergmann).

In regard to the Protozoa, it has been shown, that when water con-
taining Infusoria, is frozen, these minute creatures are not always neces-
sarily destroyed by being likewise frozen, but each siu-vives for a
certain time, surrounded by a little uncongealed watery space ; this can
only be accounted for, on the supposition that the animalcule continues
to produce a minute quantity of proper or individual heat. In tlie
aquatic Non-vertebrate animals generally, a similar power of resisting
cold exists ; though there are but few obseiwations on the heat-producing
powers of those animals. The temperature of a number of earth worms,
leeches, slugs, or snails, collected in heaps, has been found to be from
to 2° higher than the air. In the air-breathing Insects, the heat
evolved in the larval or caterpillar stage, is sufficient to maintain the
body from to 2° in the Lopidoptera, and from 2° to 4° in the Ilymen-
optora, above that of the surrounding medium. In the chrysalis stage,
the temperature is nearly that of the surrounding medium, very little
heat being evolved. In the perfect Insect, the temperature may vary in
the bee from 3° to 10°, and in the butterflies from 5° to 9°, above that
of the air. The temperature of bees, in numbers, as in a hive, may be
as high as 16° above that of the air. The nursing bees sometimes reach
a temperature of 22J° above that of the atmosphere. Insects, there-
fore, under certain circumstances possess a heat-producing power nearly
equal to that of the warm-blooded animals. The temperature of bees is
raised by exercise and excitement, and diminished by rest, sleep,
hybernation, and want of food.

In Fishes, the temperature of the blood, is usually from to 1°
warmer than the surrounding water at moan temperatures. In other
instances, it is 2° to 3° higher, and in a few exceptional cases, in which
the muscles and the blood are darker, the heart is larger, and the gills
provided with enormous nerves, as in the tunny and bonito, the teinpo-
peraturo is still higher; tluit of the bonito has been found to bo 99°,
or 18^°above the tomj)oraturo of the sea (Davy). In the frog, when
the external medium has a temperature of about 60°, the animal is
from 20 fo Ii° warmer than it; but when the external temperature
is lowered to about 43°, thou the animal is from 2° to 3^° warmer.

504

SPECIAL PHYSIOLOGY.

The edible frog, enclosed in ice at 21°, has exhibited a temperature
of 37^°.

In ileptiles, the temperature of the body is still higher, though j*et
it is dependent on the external temperature. The turtles produce
less heat than the serpents, crocodiles, and lizards ; the temperature of
some of the latter has been found to bo 86°, that is, 16° higher than
that of the surrounding air. These facts show that in the cold-blooded
animals, the temperature is greatly dependent on, and regulated by, that
of the surrounding medium, but also that there is a moderate individual
heat-producing power even in them. This power, moreover, absolutely
increases, like the functions of the animal generally, at still higher
temperatures ; but yet not so as to enable the animal to reach that
temperature.

In the Warm-blooded, animals, the temperature is high and constant,
and, as already mentioned, is, within certain limits, plainly independent
of the external temperature, owing to special powers exercised within
their bodies. Amongst the Mammalia, the average temperature of the
body, is lower than that of Birds, which present the highest temperature
of any animals, although their general organisation places them in a
lower rank than the Mammals. The ordinary range in the Mammaba, is
from 97° to 104°; in Birds, it varies from 100° to 108°, or even 111°.
In the sheep, the temperature has been found to be from 103° to 105°, in
the pig, 106° ; but in the arctic fox, it has been found to be 107°, the
air being only 14°. In sea-birds, as in the guUs, the temperature is
lower than in other birds, varying from 100° to 105° ; in the common
fowl it ranges from 107° to 110°, according to the climate and season,
and in the swallow, it is even 111^° (J. Davy).

The temperature of the tissues of the human body, speaking
generally, ranges between 98° and 100°; but that of the blood,
which is the hottest part of the organism, ranges from 100° to
102°. The blood varies in temperature in different parts,
being hottest in the hepatic veins, which bring the blood from
the liver ; this blood is somewhat warmer than that of the
vena portce, and even 1° higher than the blood of the aorta
(Bernard). Directly opposite statements have been made as
to the temperature of the blood, before, and after, it has passed
through the lungs ; but the most recent researches favour the
conclusion that the blood in the left side of the heart, is nearly
•^° lower than in the right side of that organ ; a slight cooling
process is supposed to occur in the lungs from the air admitted
into them. The blood of the superficial veins of the limbs,
coming from the exposed skin is naturally cooler, from the
influence of the atmosphere, than that of the arteries, which
lie deeper ; the temperature of tlue blood in the deep veins, as in
the femoral vein, is also said to be about 1° cooler than that
in the femoral artery (Becquerel and Breschet). The relative
warmth of the o}’gaus and tissues, ahvays less than that of the

VARIATIONS IN THE HEAT OF THE BODY.

505

blood, depends on their vascularity, their distance from the
central part of the body, or their proximity to the surface, and
on the degree to which they are protected by external covering.
Thus, whilst the temperature in the abdomen (in the bladder),
has been found to be nearly 102°, even higher than that ol the
thorax, the temperature under the tongue is about 98° ; and
in the axilla 96°; that of the hands and feet may ordinarily be
from 9° to 12° cooler than the central parts, i.e. from 90° to 93°.

Various conditions modify the temperature of the human
body ; neither age nor sex produce any remarkable difference'.
The temperature of infants and of old persons, is about normal,
so long as they are placed under favourable conditions of pro-
tection. But the power of infants and very young children,
as well as of the aged, to resist the lowering effects of cold, is
less than in the adult. Experiments on the young of Mammalia
and Birds, show this ; their small bodies, and also those of the
human infant, will cool comparatively more rapidly by radi-
ation and conduction, than those of adult animals and Man ;
their calorific power may be as great, but they cool more
quickly. Hence the greater necessity for the protection of
clothing, and for artificial warmth.

The influence of race is also slight or ineffective. In hot
climates, and in hot seasons, the mean temperature of the body
is somewhat higher than in cold climates and seasons, the dif-
ference being more marked in animals than in Man. The
difference, however, usually amounts to not more than from
1° to 2°, showing how slight is the influence of climate, and
proving the independence of the temperature of warm-blooded
creatures of external changes. According to Dr. I. Davy,
however, in a long series of observations, whilst the external
temperature varied as much as 22° Fahr., i.e. from 60° to 82°,
that of the body fluctuated 5'5° Fahr., i.e. from 96'5 to 102°.
The power ofMan to resi.st, and accommodate himself to,climatic
variations of temperature, is greatly aided by shelter, clothe.s,
fire, means of cooling the air, and peculiar selection of food ;
he can create an artificial climate, and protect himself against
its hostile influences. Sleep lowers the temperature of the body
from 1° to 2°, all the organic functions, even circulation and
respiration, being at that time likewise less active. No constant
diurnal variations of the temperature of tlie body, iu Man, have
been observed ; but, in Birds, the highest temperature seems to
be attained at noon, and the lowest about midnight (Chossat).
Exercise increases not only the sensation of warmth iu the

506

SPECIAL PHYSIO LOGY.

body, but actuall3^ raises the average temperature ; the effects,
however, being by far most evident in the extremities. Thus,
the general temperature after quick running, may become
nearly 2° warmer ; after walking, the deep-seated parts show
little or no change, Avhilst the feet and hands are raised many
degrees, the action of the heart and lungs being quickened, as
well as that of the muscular system generally, so that more
rapid metamorphoses take place (pp. 425, 465). Deficient _/boii
and positive abstinence, lower the temperature, wh}', will be
explained hereafter ; on the other hand, abundance of food
and the use of stimulants, ultimately increase it ; but the
immediate effect of a meal, or of taking wine, is said to be
temporarily to lower the animal heat. The depression of the
temperatiu'e, observed in animals, in Avhich the skin is covered
with an impermeable varnish, has already been mentioned
(p. 401). According to Becquerel and Breschet, in rabbits so
treated, the temperature falls speedily from 100° to about 75°,
before death takes jDlace. The change in the colour of the fur
or feathers, to white as winter approaches, in the case of Arctic
mammalia and birds, retards radiation, and so conserves their
animal heat. In disease, the temperature of the human body,
has been found to rise or fall many degrees above, or below,
the normal temperature. Thus, in fevers with acceleration of
the pulse and respiration, in active phthisis, in pyaemia, and
other diseases, temperatures of 104°, 106°, and 108-|'°, have been
noted, and in tetanus of 110f°, i.e. nearly 10° higher than the
normal standard. On the other hand, in asthma and in
cyanosis, or the so-caUed blue disease, in which, owing to a
communication between the right and left auricles of tlie heart,
the blood is imperfectly oxygenated in the lungs, the tempe-
rature of the body is unnaturally low ; this is also the case in
syncope, apparent death, and cholera, in which last disease, the
blood becomes so thickened as scarcely to circulate. In the
stage of collapse in cholera, the temperature of the surface of
the body may be, according to different authorities, as low as
from 80° to 67°, i.e. from 15° to 28° below the ordinary tem-
]3erature of the exposed skin. The sensation of heat, or the
opposite one of cold, experienced by a person in disease, does
not always correspond with the actual temperature of the body ;
ibr in the cold stage of ague, though the feeling of cold is
extreme, the temperature of the body may be actually raised
(vol. i. p. 470). On the approach of death, generally, with a
feebler jjulse and respiratory action, combined frequently with

EFFECTS OF EXTREME COLD.

507

the evaporation of profuse perspiration, the tenpierature is
gradually lowered : first, in the hands and feet, then in the
forehead, ears and nose, and afterwards in the j^arts nearer to
the centre of the body. It has been observed, not only in
cholera, in which the temperature of the body is lowered from
the disease during life, but also in yellow fever, in which the
body is hotter than natural, that the temperature after death
undergoes an actual elevation ; this is probably to be accounted
for, by the conduction of heat from the central parts, together
with the cessation of the cooling influence of the evaporation
of the cutaneous exhalation.

After death, the cooling process goes on, in accordance with
the physical laws which regulate the temperature of inorganic
moist bodies, the rate at which this cooling takes place, de-
pending chiefly on the external temperature and relative
motion of the air, on the degree of exposure of the body, its
condition of emaciation or obesity, — fat being a bad conductor
— and on the conducting power of the clothes, or other objects
in immediate contact with the corpse.

Effects of Cold on the Human Body.

The power possessed by the human body, of maintaining its
proper temperature, independently of external conditions, is
limited within certain ranges; conditions of cold or heat are
met with, which not only produce great inconvenience, but
which, in the absence of special protection, may exercise a
fatal influence. It has been shown experimentally, that, when
a Mammalian animal has lost about 20° to 21°, or about ;|th
of its normal heat, it suffers so greatly, that a further loss of
heat is fatal to it, death ensuing from debility or congelation.
On the other hand, an addition to the temperature of the body
of a Mammiferous animal, of about 13°, is equally serious, con-
stituting a limit beyond which death .speedily occurs. Hence
in Mammalia generally, an artificial elevation of the temperature
of the body, is sooner fatal than an artificial lowering of that
temperature. The same is probably true of Man, a greater
range of temperature, in disease, having been observed previous
to death, in the descending than in the ascending scale of
warmth. The relative degi’ees of external heat and cold, which
are endurable by Man, with proper precautions, in the different
climates of the world, also prove that he can sustain, without
injury, a greater diminution than an elevation of the external

508

SPECIAL PHYSIOLOGr.

temperature. In the arctic regions, the thermometer has been
recorded at temperatures as low as from — 55°to — 7 0°, the latter
temperature being no less than 170° below the normal tem-
perature of the blood ; whilst in tlie other direction the highest
temperature registered in the tropics, is about 130° in the
shade, viz. about 30° above the blood heat. Man is much
more readily inured to cold than to heat; and the inhabitants
of temperate regions, when they remove to the tropics, require
to be more specially acclimatised, and can scarcely avoid be-
coming ill ; whilst, in removing to colder latitudes, with due
precautions, health may be more easily preserved. Nevertheless,
cold, to the I’eeble and aged, is the great enemy of animal
life, and the chief remote cause of human mortality.

When the living human body is exposed to the prolonged
action of extreme cold, without protection, a gradual benumbing
of the sensibility, a lowering of the circulation and respiration,
and a general torpidity of the system, are produced. These
effects occur more readily in children, and in infirm, ill-fed, or
starved persons, and also in aged persons ; and lastly, in those
Avho are previously overcome by fatigue, or by the narcotic
effects of alcohol. The nervous system is specially subjected
to the influence of cold ; the senses frequently act irregularly,
giving rise to noises in the ears, and spectral visions ; delirium
often supervenes, and, finally, an irresistible tendency to, and
desire for sleep, takes complete possession of the frame. Further
exposure to cold, then produces a fatal coma. Isolated examples
of death from this cause, happen in the experience of civilised
life ; but large numbers of troops, and even entire armies, es-
pecially Avhen ill-fed, clad, and protected, have been lost from
the injurious effects of extreme cold. The effect of cold is
most marked, when the body itself is motionless. Its evil or
fatal effects occur more rapidly, however, Avhen the atmosphere
itself is in motion ; because, then, fresh quantities of cold air
are brought continually in contact with the body, and so
conduct away its heat more rapidly. A moist atmosphere is
also detrimental, on account of its being a better conductor than
dry air.

The local effects of extreme cold are usually manifested, first
upon parts unprotected by covering, or most distimt from the
centre of the body, such as the feet, hands, face, or ears, and
especially the nose. In such case, the skin first becomes red,
from congestion of the dilated small arteries and capillaries;
next it becomes blue, from arrest of the circulation ; and after-

EFFECTS OF EXTREME HEAT.

509

•wards of a tallowy Avliite, from the extreme constriction of tlie
arteries suj)plying the part, so that the circulation is fii'st
retarded, and then entirely arrested. In perfect congelation,
minute particles of ice actually form in the tissues. The
congealed tis.sues may sometimes be restoi’ed to their normal
state, provided that the return to a higher temperature, be
gradual, as is often and best accomplished, in extreme ca.«es
oi frost-bite^ by triction with snow or ice-cold water. By
warming the frozen parts too rapidly, the gases of the blood
and tissues, set tree at the moment of congelation of the water,
are expanded in the interior of the capillaries, or amongst the
fine structural elements of the tissues, bursting the Ibrmer
or destroying the latter, and so inducing gavgrene. In fatal
cases of exposure to cold, the body may not, or may, be com-
pletely frozen, for the process of congelation of the water in
the tissues may penetrate through the whole dead body ; but
death long precedes such a result, owing, on the one hand, to
the fatal benumbing influence of cold on the nervous system,
and, on the other, to the retention of some of the proper heat
of the bodj', after actual death.

Effects of Heat on the Human Body.

These are also of great interest. In resisting moderately
high temperatures, the problem to be solved, is that of main-
taining the temjierature of the body, within ‘2°, oi- at most 5°,
of its ordinary standard, at a time when it is not only pro-
ducing heat within itself by its vito-chemical actions, but is
also, like any other material mass, receiving heat from a
surrounding medium, hotter than it.-^elf. Thus, the mean
daily temperature of the air, in the tropics, during the six
summer months, ranges as high as from 80° to 90°, in the
shade, the highest daily temperature in the shade, varying
from 104° to 118°, Jiud the lowest nocturnal temperature,
ranging from G0° to GG°, the heat thus exhibiting a vtiriation of
from 44° to to .G2° in the cour.se of 12 hours. In e.xceptiontd
seasons, the highest temperature rises to I.‘iO°. Again, in the
direct rays of tlie sun, the heat is, of cour.se, still greater. The
elTect on the system, is aggnivatcd by motion ol the hot air.
The adaptibility of Man to extrenics of temperature, enables
him, however, to live in .such a climate.

The chief means of maintaining the normal temperature of
the body, in hot climates, consists in a large increase in the

510

SPECIAL PHYSIOLOGY.

amount of tlie water exhaled from the surface of the lungs
and of the skin, especially, however, from the latter. The
skin becomes bathed with fluid, the evaporation of Avhich,
at the high temperature of the surface and of the surrounding
air, occasions a loss of heat and a reduction in the temperature
of the evaporating surface. In this way chiefly, the heat of the
body is lowered, and maintained nearly at its normal standard.
The effect in reducing the tempei’ature of the body, is greater,
if the atmosphere be dry as well as warm, and then, also, if it
be in motion ; these conditions favour cutaneous exhalation
and evaporation.

It has been shown, by an ingenious experiment, that the evaporation
from the surface of the skin of the living frog subjected to high tem-
peratures, is sufficient to maintain the temperature of the animal at a
stationary point, after it has reached a certain height ; whereas moist
mushrooms, .subjected simultaneously to the same conditions, soon
obey the temperature of the surrounding air. The frog and the
mushrooms were placed in a chamber filled with dry air, heated from
122° to 140° ; at the end of a quarter of an hour, both the frog and the
mushrooms were nearly at an equal temperature, viz. from 62° to 72°,
each having, by simultaneous evaporation into the hot air, maintained
a comparative coolness. As the experiment proceeded, the temperature
of both rose to about 100°, at which point, the frog’s temperature
remained stationary, whilst that of the fungi, no longer able to undergo
further evaporation, continued to rise. The continuous exlialation from
the moist skin of the frog, was the only cause which could explain the
non-occiu’rence of a further rise in its temperature (De la Eoche and
Berger).

The effect of evaporation, in reducing the temperature of the
living body, may also be illustrated by the results of experi-
ments made on sponges wetted, and porous vessels filled with
hot water, and placed in a dry oven, in which the air was still
hotter ; these bodies actually lose heat at first, evidently owing
to temporary evaporation.

It has been supposed that the living animal body may possess
some special means of resistance to external heat, but of this
there is no proof whatever. It may be entirely exjflained by
the effects of evaporation.

Thus, when the surrounding air is warm or hot, e.specially
if it be dry, the evaporation from the skin is increased, and so
the temperature of the body is lowered ; whereas, in colder
air, especially if this be also moist, the diminished amount oi
evaporation, tends so fiir, to conserve the animal heat. The
increased perspiration excited by the great heat of the skin,
furnishes, lor a certain time, suflicient material for evaporation.

EFFECTS OF EXTREME HEAT,

51 1

There is a limit, however, to the amount of this excretion, and
also to its rapidity of evaporation ; for when the surrounding air
becomes moist, a check being put to the evaporation, the body
is no longer thus defended, and its temperature begins to rise.
Thus, in a room, the temperature of which was 260°, and the
air dry, it was found possible to remain for 8 minutes, by which
time, the body was not much elevated in temperature, although
the clothes, and other articles in the room, became very hot
(Blagden and Banks). A case is on record of a person re-
maining 10 minutes in a dry hot air-bath at 284°; whilst
Chabert, the so-called fire-king, went into ovens heated from
400° to 600° ; but of course, for a much shorter period. Many
workmen employed in foundries or glass works, also withstand
veiy high temperatures, the skin being profusely bathed with
perspiration ; these men of necessity drink large quantities of
fluid. When, however, the air is moist as well as hot, the
temperature that can be endured is much less ; for, in a vapour
bath, at a temperature of only 120°, the body rapidly gains heat,
as much as 70° in 10 minutes, and a feeling of great and in-
supportable discomfort is experienced (Berger and DelaKoche).
It issjiid, however, that, from habit, the Finns can withstand,
for upwards of half-an-hour, moist air or vapour baths gradu-
ally raised to 158°, or even to 167°. Animals surrounded by
air heated gradually to 200°, speedily die, their temperature
being then raised about 13° above their natural standard (The
same Authorities). This seems, accordingly, to be the extreme
limit of heat endurable by a warm-blooded animal. Most
cold-blooded animals are killed by a temperature of about 75°.

In civil life, even in temperate climates, direct exposure to the
rays of the sun, is often fatal, producing some profound disturb-
ance of the nervous centres, caused either by congestion of the
vessels of the brain, owing to quickening of the circulation,
or, as some have supposed, by expansion of the blood, from
■ the heat acting on the contents of the skull, the capacity of
which is unchangeable. This coup de soled occurs still more
• frequently in the tropics, amongst troops on the march, or
I amongst coolies or slaves working on railways or plantations.

[ In Pekin, during about ten days in July 1743, the thermometer
[stood at the extreme height of 104° in the shade, and in that
1 period 11,400 people died. Under extreme elevations of
i temperature, the only safety consi.st« in retiring to the pro-
j' tection of houses, and in reducing the tenijjerature of the
1 atmosphere in them by artiticial methods, such as by the use of

512

SPECIAL PHYSIOLOGY.

large fans or punkahs, wet hangings, and other means. Habit
accustoms the Chinese, negroes, and others, to bear a greater
heat than the natives of temperate climates can support.

Theories of Animal Heat.

Previously to the time of Lavoisier, the heat of the body
was more or less vaguely referred to friction, the organic
processes of nutrition, the influence of nervous action, and
generally to what Avas understood as the action of the so-
called vital force.

In consolidating the discoveries of his predecessors, in
regard to the chemical nature of carbonic acid, oxygen, and
nitrogen, and in explaining therefrom, the chemical processes
and products of respiration, Lavoisier propounded, for the
first time, a distinct scientific theory of the production of
animal heat. This, now known as the chemical theory of
animal heat., regards this heat as the result of an oxidation or
combustion process, affecting the animal frame. Carbon,
when heated in the presence of oxygen, unites with that gas,
forms carbonic acid, and evolves heat. In like manner,
Lavoisier argued, that the formation of carbonic acid in the
blood, as the result of respiration in living animals, must be
accompanied by an evolution of heat.

Though Lavoisier was Avrong in supposing that this union
of oxygen with carbon, takes place in the pulmonary capillaries,
nevertheless, his chemical theoiy of respiration is, Avith certain
modifications and extensions, accepted as the true theory of
animal heat.

To found this theory of respiration, it Avas necessary to
compare the amount of heat evolved, during the direct com-
bination of a certain quantity of oxygen and carbon out of
the body, Avith the amount of heat given off from a living
animal during its consumption of a similar quantity of oxygen.
This enquiry Avas surrounded by many difficulties.

To obtain data for these purposes, Lavoisier made the first
step in the science of calorimetry, by burning given quantities
of carbon and hydrogen, in his so-called ice calorimeter.
This Avas a closed metal case Avith double side.s, between
Avhich ice Avas packed ; the source of heat to be subjected to
experiment, Avas placed in the interior of the case, and the
fiuantity of heat given off, Avas e.stimated by the quantity of
ice Avhicli Avas melted. The tcaler calorimeter of Count

CHEMICAL THEORY OP ANIMAL HEAT.

513

Ivumford is constructed on a similar plan, but is filled with
distilled water of a known temperature, and measures the
quantity of heat given out in the experiment, by the ele-
vation of temperature of a known quantity of water.

In the first accurate experiments on animals, which were
made by Dulong and Despretz, a water calorimeter was em-
ployed. The animal was placed in a metal chamber, which
was sniTounded by a given quantity of water enclosed in a
still larger vessel ; air was conducted to the internal chamber
by one tube, whilst a second long spiral tube passing through
the water, like the condensing tube of a still, conveyed away
the warm air, which, before it escaped, gave up its heat to
that fiuid. The stream of air was rendered uniform by an
apparatus known as an aspirator, a large closed vessel filled
with water, and connected with the tree end of the coiled air-
tube, so that on the gradual escape of the water from the
aspirator, through a stop-cock, air was drawn through the
apparatus at a uniform rate. In the water of the calorimeter
itself, a moving fan agitated the fiuid, so that its temperature
was kept uniform duting the experiment. Lastly, the air, as
altered by the respiration of the animal, or a part of it, the
rest then being measirred, was analysed, in order to determine
the quantity of carbonic acid produced. It was, at that time,
erroneously supposed that this corresponded exactly with the
quantity of oxygen consumed. Rabbits or dogs were subjected
to experiments, varying from an hour and a half to two hours’
duration ; and the results obtained by Dulong and Despretz,
showed that the amormt of heat given off, was from to ^ more
than the quantity of carbonic acid produced would account
for. In subsequent experiments, made by Despretz alone, it
was found that from j to of the heat was thus imaccounted
for.

The excess in the heat actually produced by the animals
experimented on, was supposed to be accoimted for, by the
friction of the heart and the muscles, by that of the blood in
the vessels, by the di.sengagement of heat taking place in the con-
version of fiuid into .solid matter in the nutrition of the tissues,
and by some possible action of the nerves. It has, indeed,
since been shown, that heat is really given out in muscular
contraction. Neverthele.ss, these supj)osed causes of animal
heat are not primary, but secondary, causes. The heat given
off in muscular contraction, is itself engendered by oxidation
in the blood of a muscle, or in the muscle itself, during the

VOL. II. L L

514

SPECIAL PHYSIOLOGY.

so-called parenchymatous respiration. The heat produced by
mere friction in the body, must have its source in muscular con-
traction, and this, as we have just said, is due to chemical
change or oxidation. The conversion of fluid into solid sub-
stance, in the nutrition of the tissues, is, as will be presently
explained, an apparent, and not a real, cause of internal heat ;
and lastly, any influence of the nervous system is indirect,
operating only by exciting organic processes, themselves in-
volving oxidation.

The deficiency of heat-producing power in the quantity of
carbonic acid given off by the animals experimented upon by
D along and Despretz, in comparison with the heat Avhich they
simultaneously evolved, may be otherwise accounted for. Iii
the first place, these observers did not determine the tem-
perature of the animals, before and after each experiment,
which might have shown some retention of heat. But other
points are of more moment. The modern researches of Favre
and Silbermann, prove that the heat evolved by carbon in its
combustion, is greater than that estimated by Dulong and
Despretz. It is now known, that more oxygen is absorbed in
respiration than is returned in the form of carbonic acid, and
this oxj'gen doubtless is also combined in the system, partly
with hydrogen, and partly Avith sulphur and phosphorus, in
either case evohnng a certain amount of the heat of chemical
combination. The hydrogen of the carbhydrates, being
already associated Avith oxygen in the proportions to form
Avater, is not supposed to be able to give out further heat ;
but some of that contained in the fat and albuminoid bodies,
must be oxidised in the system, as Avas first suggested by
Barral, though much of the hydrogen of the lAitrogenous sub-
stances, appears in the urea. The larger part of the heat is,
hoAvever, due to the oxidation of carbon in the system. The
nitrogen is neA’^er oxidised, but passes out almost entirely in
the form of urea, and supplies no animal heat. Experiments
have shoAvn that carbon, in different states of aggregation, yields
slightly different quantities of heat in being burnt, Avood
charcoal giAung out more heat than the more compact coke.

The combination of carbon and hydi'ogcn, in the animal
economy, is not like that Avhich occurs in artificial combustion, I
simple and direct, but complex, and marked b}' intermediate de- '
compositions, and most varied products. By many, it has been
supposed that these conditions might modify, in some Avay, the
quantity of heat evolved ; but it seems more probable, that no

CHEMICAL THEORY OF ANIMAL HEAT.

515

number of intermediate stages of decomposition, can alter the
total quantity of lieat given out ; and that, according to the
degree of oxidation which occurs, the same amount of heat is
evolved, whether this be direct and rapid, or complex and slow.
Such decompositions in the body, may affect the amount of
heat evolved in particular organs or parts of the system, as
in the liver, kidneys, or the muscles when in action ; but
they cannot modify the ultimate or total heat product. It has
even been conjectured that the oxygen of the atmosphere used
in respiration, being partly ozonised, might evolve a larger
amount of heat than in ordinary combustion ; but the same
air is employed in both cases.

The idea entertained by Dulong and Despretz, that a balance
of heat might be evolved in the conversion of fluid into solid
substances during the act of nutrition, has been mentioned as
fallacious. If, indeed, new nutrient matter be solidified in the
act of deposition, the process of disintegration of tissue, which
precedes or accompanies this, implies a precisely similar amount
of liquefaction, which would involve a disappearance of heat. In
the digestive and secretory processes, too, the numerous acts of
liquefaction imply absorption of heat. Bertholet has recently
advocated the view, that molecular as well as chemical changes
in the body, may give rise to heat. The mode in which a par-
ticular, complex, organic compound splits up, may influence
the amount of heat which it gives off, and, localUp this would
affect the temperatiu’e ; but there is a balance in these actions,
and the total result is that of simple change Certain pro-
cesses of hi/dration, or the assumption and Jixation of consti-
tutional water., which are supposed by Bertholet to be con-
stantly occurring in the system, and to be the actual cause of
animal heat, may likewi.se produce local evolutions of heat.
The formation from starch, of sugar, lactic acid, and oxalic
acid, imply successive acts of hydration, and so perhaps also
do the changes of albumen into gelatin, glycocoll, creatin,
creatinin, and urea. But a certain •quantity of o.xygen
actually disappears in the body, and two of the chief ultimate
products of excretion, carbonic acid and water, are oxidated,
not simply hydrated. Urea alone can be considered such
a product, being of course imperfectly oxidised. The sup-
position, that hydration will explain the formation of all the
animal heat, overlooks the far larger amount of heat evolved
in the ultimate oxidation of the carbon and hydrogen, which
leave the body as carbonic acid and water ; nor does it ex-

1. L 2

516

SPECIAL PHYSIOLOGY.

plain the higher temperature of those animals ^vhich consume
a large quantity of carbon and hydrogen in their food.

With regard to the human body, the estimates of Despretz
were made on the supposition that a Man, according to his
weight, expired seven times as much carbonic acid as the dog
experimented on by him. The quantity thus arrived at, i.s
much less than that computed by all subsequent experimenters,
being only equivalent to 5^ oz. of carbon in the 24 hours.
Other observers have estimated the daily excretion of carbon,
in the form of carbonic acid, as 8 or 9 oz. The size and weight
of these persons, have not been recorded. Vierordt’s estimate,
in a number of individuals of different heights, ranges from
5 to 8 oz. In men of a mean height of 5 feet 9^ inches. Dr.
Edward Smith estimates the quantity at upwards of 7 oz.
The calculations hereafter given, for a person 5 feet 6^ inches,
yield a quantity somewhat exceeding 6 oz. of carbon per day.
These results are obtained by direct experiments on the
absolute quantity of carbonic acid expired by animals or Man.
Liebig’s estimate is still higher : thus, the quantity of carbon in
the daily food, being determined on the one hand, and that
contained in the urine and intestinal excretions, on the other,
the difference, which was taken to represent the amount given
off by the lungs and the skin together, amounted to 13'9 Hessian
ounces, or to upwards of 15 oz. av., of Avhich ^ oz. might be
exhaled Ifom the skin, and 14-g- oz. from the lungs. This large
quantity was found in vigorous soldiers, actively exercised in
the open air, and supplied with abundant food. In other ex-
amples, viz. in prisoners compelled to labour, the quantity was
about 11-^ oz. av. ; whilst in a prison, where no forced labom’
was practised, it was about 9^ oz. av. Similarly estimated, the
carbon expired daily by sailors in the Danish Navy, was found
to be about 10-^ oz. av. (Scharling). These results, taken
generally, so tar confirm the chemical theory of animal heat,
that they nearly explain the deficiency of ^ or ^ left by the
daily combustion of 5^ oz. of carbon, calculated to be elimi-
nated by Despretz ; the excess of oxygen absorbed, which
unites Avith hydrogen, and to a small e.xtent with sulphur and
phosphorus, may explain the rest.

The chemical theory of the production of animal heat by
oxidation, is in harmony Avith the fact, that increased respira-
tion increases the amount of chemical decomj)osition in the
body, and simultaneously, the amount of heat produced.
Thus, all the conditions connected Avith mje, sex, period of the

TEJirERATURE OF ANIMALS.

517

day and season, as well as those relating to food, whether in
excess or deficiency, or whether absolutely Avithdrawn, as in
starvation, and to exercise (pp. 4G3-9), Avhich increase the
activity of the respiration and the amount of carbonic acid
given off, raise the temperature of the body ; whereas all
those which diminish the respiratory actions and their chemi-
cal products, lower that temperature. The relations, as to
respiration and temperature, in the lower animals, confirm
this vieAV. It has been objected, that not only the respiratory
function, but all the other functions of the body, are similarly
modified under the above-named conditions ; and that, there-
fore, the variations of temperature may be referable to other
processes, as Avell as to the respiratory interchanges. But
since no fimction of the body Avhatever, whether it be that of
sensation, the guidance of motion, motion itself, nutrition,
secretion, or any other function, can be performed without
concomitant changes in the chemical molecules of the ti.ssues
or organs concerned, and as all these changes are but steps
or stages towards a more or less complete oxidation, so any
production of heat by them, must ultimately be referred to
this chemical action. According to any other view, the heat
would be produced from nothing, or without that accom-
panying conversion or change in the condition of force and
matter, Avhich we now know is necessary for its production.

The Cold-blooded animals expire but small quantities of
carbonic acid, and their respiration is feeble ; whilst opposite
conditions are noticeable in the Warm-blooded animals. The
most active of these latter, give off more carbonic acid, and
manifest a higher temperature, the Carnivorous Mammalia
being, in both these respects, above the Herbivorous, the
smaller quadrupeds above the larger ones, and, as a Class, the
Birds above the Mammals. The relative complexity of the
pulmonary organs, the extent of the respiratory surface for the
exposure of the blood in the capillaries, and the contrivances
for the more frequent reneAval of air in the air-cells, keep pace
Avith the increase of temperature in the animals themselves.
In the hottest animals knoAvn, viz. Birds, special peculiarities
exist in the air-cells, and the air-cavities in the bones,
Avith which are associated great force of the heart, gi’eat
rapidity of its action, a high rate of motion of the blood through
the capillaries, a large number of red blood corpusclo.s, a small
amount of evaporation from the skin, and a solid condition of
the urinary excretion, involving less loss of heat in its pro-

518

SPECIAL PHYSIOLOGY.

duction than if it were fluid. The urinary products of Birds,
are, moreover, chiefly composed of urate of ammonia, which
contains less oxygen than urea, so that more of that element
passes olF as carbonic acid (J. Davy).

The importance of the relation between the quantity of the
red corpuscles in the blood, and the temperature of the body, is
illustrated by the following numbers, which show the quantity
of dried solids of the clot, in 1,000 parts of blood, in a series of
animals belonging to the several Classes of the Vertebrata.
The hen, 157T; the dog, 123'8; the tortoise, 80; the frog, 69;
and the eel, 60 parts in 1,000 (Prevost, Dumas, J. Marshall).

Animal heat being regarded as the re.sult of a process of
oxidation, the small amount generated by the Cold-blooded
animals, may be supposed to be derived from the metamor-
phosis of their OAvn tissiies or blood. The same may be true
as regards the large Carnivorous animals, the active habits
of which, in high external temperatures, may furnish sufScient
oxidisable material in the metamorphosed blood and mus-
cular and nervous tissues, to maintain the temperature of their
bodies ; but Carnivorous animals consume also large quantities
of fat, proportionate, it may be remarked, to the coldness of the
climate in which they live. In warm climates, Man also might
thus sustain his temperature ; but in colder regions, Avhere
the loss of heat from the body is more rapid, Man, like the
Herbivora, Avhose habits are inactive, must rely upon food also,
as one source of oxidisable material; and like them, upon food
containing more carbon and hydrogen, and proportionally less
nitrogen. In different persons, and in different seasons and
climates, the extent to which carbonaceous and hydrogenous
food is relied on, as a source of combustible material, may
vary. An elevation of the external temperature, will lessen
the amount of oxidised food ; whilst the opposite condition
increases it. The excess of carbonic acid exhaled in cold
seasons, can only be accounted for, by its proceeding from the
greater quantity of food then consumed. On these principles
may be explained the fact, that no one dietary is economically
adapted to all constitutions, occupations, habits, races, seasons,
or climates ; hence the labourer recjuires a different diet to the
sedentary student, and the native of the tropics different food
to the Laplander.

NERYODS SYSTEM AUD ANIMAL HEAT.

519

Influence of the Nervous System in the production of Animal

Heat.

This was formerly greatly exaggerated, and was attributed
to some direct action of the so-called nervous force. Many
researches upon animals, have shown that injuries to the brain,
whether by sections, or by the administration of narcotics,
are followed by a lowering of the temperature of the body
(Brodie, Legallois, Wilson Philip, Hastings, C. Williams, and
Chossat).

In paralysis from cerebral disease in Man, the paralysed
limbs are usually of lower temperature than the sound limbs,
the difference sometimes being as much as 7°. On the other
hand, an elevation of temperature in certain regions, may
follow local injuries of the nervous system. Thus, Avhen the
spinal cord is divided in the middle of the back, in a Warm-
blooded animal, the loAver half of the body may become
Avarmer, and remain so for some time. In complete paralysis
of the lower half of the body, in Man, from injury of the
cord, a similar increase of heat has been observed in the
groin, viz. 111° (Brodie). Besides these facts, there are
many which shoAv, that general depressing causes acting on
the nervous system, lower the temperature, whilst excited
conditions of that system are accompanied by increased
animal heat, for example, exhaustion or fear on the one hand,
and strength or passion on the other. In the last instances,
the influence of the nervoits system is plainly indirect, and
mu.st be attributed to a corresponding diminution or increase
of the pulse and respiratory acts. The rdtimate influence of
alcohol, in raising the temperature of the body, may also be
partly due to its specific stimulating effect on the nervous
system, and through it, on the heart and respiratory organs ;
but it may also yield a ready fuel or combustible substance,
easily absorbed into the system, and easily oxidised in it ;
these two last-named qualities may account for its great use
in cases of exhaustion from fevers. Again, Avhen the sympa-
thetic nerve is divided in the neck of an animal, or its chief
cervical ganglion is removed, the temperature of the Avhole of
that side of the face, may rise even as high as 11° above its
normal standard ; and this may continue for mouths with
increa.sed sensibility, and increased colour from vascular
congestion. In such a case, when the distal end of the cut
nerve is galvanised, the temperature for a time liills (Bernard).

520

SPECIAL PHYSIOLOGY.

The elevation of local temperature, is also believed to be an
indirect effect, and to depend on an increase in the flow of
blood to the part, consequent upon a relaxation of the walls of
the smaller arteries, owing to the loss of controlling power on
the part of the vasi-motor nerves (vol. i. p. 389). Serious
injuiy or disease of the spinal cord, may act in the same way,
because the sympathetic system has connections with, or
origins in, it (vol. i. p. 391). The lowering of the temperature
after destruction of the brain, which continues in spite of
artificial respiration, — not performed too rapidly, so as to cool
the animal by that very process (Brodie), but more slowly
(Wilson Philip and Williams), — has also been, of late, most
frequently attributed to the loss of some indirect influ-
ence of the nervous system, over the strictly chemical heat-
producing changes in the system, whether of respiration, nutri-
tion, or secretion. Lastly, it has been suggested that heat may
be directly produced in the nervous substance itself, owing
to the rapid metamorphoses to which it seems liable, in its
healthy and active condition, or else to some transformation or
passage of its ordinary force or mode of action, into a calorific
action producing heat, in the same manner as, in the electric
fish, it may be converted into electricity (Carpenter). The
nervous substance must be decomposed in all cases in which
it is in action, especially during exercise, when it contr-ols the
muscular movements ; much movement always produces heat.
In such instances, and also in psychical acts, the nervous
substance is directly oxidated ; so that ultimately, the animal
heat evolved, is the result of chemical action.

That the nervous .system is not essential to the production
of heat in living oi-ganisms, seems to be shown by the facts,
that in many of the lower animals, no traces of a nervous
system have yet been discovered, and, tlmt in certain pro-
cesses of vegetable life, as in the fertilisation of the ovide and
in the commencing stages of germination, heat is also evolved.
When, however, in animals, that system is present, it is en-
dowed with such power of control over all the functions gene-
rally, and exhibits such innate activity, that it determines and
excites wa.ste in other tissues, and undergoes waste in its ovm,
thus indirectly or directly contributing to the production of
animal heat.

HYBERNATION.

521

Uses of Animal Heat.

The modes in which the heat of the body, is expended, are
several. First, it supplies the constant loss of heat from the body,
by radiation and conduction to the clothes or other surround-
ing objects or media, when, as is usual, these are cooler than the
body. It also llirnishes the heat necessary to vaporise the
water of the cutaneous and pulmonary exhalations; it warms
the air expired from the lungs ; it heats the secretions as well
as the body itself; and, lastly, it warms the food and drink
taken into the body, when these are cooler than the internal
organs, and aids in the solution of digestible substances, and
in their metamorphosis for the purposes of absorption. Of
100 parts of heat given off by the body, 72'9 are lost by
radiation from the surface, 14'5 by evaporation from the skin,
7'2 by evaporation from the lungs, 3’5 from warming the air
used in respiration, and 1'8 by the urine and solid excreta.

As the standard of temperature remains constant within 2°
or .3°, between hot and cold seasons, and tropical and arctic
climates, the quantity produced in the body, depends on the
external temperature, and must be greater in cold climates, in
which the loss is greater, than in warm climates. The amount
required to be produced, is also modified by the degree of pro-
tection of the body, either by shelter or clothing.

Hphernation.

Amongst the most remarkable phenomena preseaitod by animal life,
in the temperate and cold regions of the earth, are those which are
known under the name of hphernation. During the winter season, a
few Mammalia retire into burrows or other shelter, and there, either
under the influence of the low temperature, or guided by au inherent
instinct or an acquired feeling, pass into a condition of torpor much
more profound than ordinary sleep. The marmot, dormouse, and hedge-
hog, arc the most familiar examples of this hybernation in the Mam-
malia. It is remarkable that no Birch are known to bybornate, the
belief once prevalent that swallows retired to the bottom of ponds to
hybernato, being erroneous. Amongst Reptiles, both serpents and snakes,
as well as land-tortoises, bybernate ; and in the Amjehibia, the frogs and
newts. Both serpents and frogs have been kept in this condition, by
artificial cold, for three years. Hybernation in Fishes, is not known, unless
it bo compulsory from freezing of the water. Of the Non-vertebrate
animals, only terrestrial Species are known properly to bybornate, such
as the land-snails and slugs amongst tlio MolJusca, and (bo clirysalides of
certain Insects, which pass through a winter, before they change into the
imago state. Even in the Protozoa, examples are met with, of a winter
state or condition, in which those animals undergo the process known as

522

SPECIAL PIIYSIOLOGY.

cncystation, so called because in it, they surround themselves with a
protective cyst, in which they remain dormant, until the return of warmth
induces peculiar changes in them, for the reproduction of new animals.

The condition of partial hybernation manifested by certain animals,
which collect a store of winter food, such as the beaver and others, is
named spurious hybernation. In this state, the circulation and respira-
tion are not so diminished in activity, nor the temperature so reduced, as
in true hybernation ; for though the animals sleep much, they, from time
to time, arouse themselves to take food.

In the true hybernating Warm-blooded animal, not only the nervous
and muscular systems are quiescent, but digestion entirely ceases, no
food being taken. The circulation is very slow ; the respiratory move-
ments are almost, or according to some, completely, arrested ; the
interchange of oxygen and carbonic acid in the air-passages, can take
place by diflFusion only ; the absorption of oxj'gen and the evolution of
carbonic acid, are very slight, and the animal heat accordingly sinks ; so
that, without protection from the cold of the winter season, the animal
would die. The respiration which continues, is supported by a store of
fat, which serves as fuel during the dormant state ; when the creature is
roused from this condition, by any irritation, by heat, or by great cold,
distinct respiratory movements take place, the heart’s beats are quick-
ened, and it manifests increased activity. If the animal be arotised by
extreme cold, it soon becomes still more torpid, and may even die if the
low temperature be long continued. If excited too completely by warmth,
it is also apt to die, unless provided with suitable food, and carefully
maintained at a moderate temperature. The suspension of animation
in Reptiles and Amphibia, is still more complete ; but probably even here
some vital action goes on. In many instances, in the lower Non-verte-
brate animals, it is probable that all the organic processes are. for a time,
completely suspended, as, e.g. when they are almost frozen, or first dried
and then frozen.

In the Animal Kingdom, considered generally, we observe that a high
temperature of the body, not only increases the activity of the various
functions, but that this very activity produces, in its turn, a demand for
increased respiration, and so engenders an increased amount of animal
heat. In the case of Cold-blooded animals, also, an elevation of the tem-
perature of their bodies, by external heat, increases their activity and
their demand for increased respiration ; and, accordingly, it is found that
in Reptiles more carbonic acid is given otf in high temperatures, a result
opposite to that which takes place in Warm-blooded animals, and in Man.
The respiration of Warm-blooded and Cold-blooded animals is said also
to differ, if not absolutely, at least relatively, in this particular; that it
is only in the Warm-blooded creatures, that some portion of the food,
when absorbed into the blood, is devoted at ouce to respiratory pur-
poses, forming, as it were, fuel immediately destined for the production of
heat by oxidation, without having previously entered into the tissues ;
whereas in the Cold-blooded animals, the tissiies only, and not the food
merely assimilated into the blood, except perhaps in exceptional cases,
and then in a far lower degree, are oxidated, and so produce a small
amount of animal heat. In the Warm-blooded animals the blood cor-
puscles are much more, numerous, and the quantity of carbonic acid
excreted is much greater, than in the Cold-blooded species.

SPONTANEOUS COMBUSTION.

523

Spontaneous Comhustion.

The highest natural temperature attained, in the healthy-
state, by any animal, is that noticed in the swallow, about 111° ;
the highest temperatm-e observed in the healthy hitman body,
is 102°; and in disease, 111°. Moreover, experiments have
shown that an increase of 13° in the temperature of the body
of one of the Mammalia, is fatal. It is obvious that the highest
of these temperatures, is entirely inadequate to set on fire the
animal tissues ; it is even insufficient to inflame the vapour of
alcohol. It is, therefore, impossible to believe that the body of a
drunkard, whose blood and tissues may even be supposed to be
saturated with alcohol, or with some of the products of its de-
composition, coidd spontaneously burn ; for the temperature of
ignition of the tissues, or of such compounds, is much higher.

Of the so-called cases of spontaneous combustion, not one
has actually been seen to happen. Natimally, no eye-witness
is present, but the more or less consumed body is found ; and
such occurrences usually take place in persons addicted, dur-
ing their life, to habits of intoxication. The event is rendered
marvellous by the supposition of a spontaneous process of
combustion. Of the possibility of burning the dead body with
a due amount of heat, or even of parts of the body before life
in the remainder of it, is entirely extinct, there is no doubt,
the sensibility being supposed to be deadened by excessive
alcoholism. But the heat, necessary for this combustion, is far
greater than is generally suppo.sed. It is extremely difficult
to bum a dead body. That the presence of alcohol in the
blood and tissues, would increase the inflammability of the
dead or dying body, is possible. The commencement of the
combustion, is clearly to be looked for in external, not in
internal, causes. In all recorded instance.s, these ca.ses have
happened either in the night, or at other times when fire,
(I candles, or matches were present, or might be supposed to be
k present ; for frequently the evidence of this may be destroyed
f by the spread of the combustion itself. On the whole, it is
fi rational to conclude, more e.specially as habitual drunkanls are
i incapable of exercising care in regard to these sources of
I danger, that they have themselves, in a state of intoxication,
N set hre, in falling or otherwise, to their clothes or other com-
V bustible materials, or that they have been reached by flames
jij otherwise occasioned by the falling of candles, or by the
■ emission of .sparks from the fire. It is significant that no case
p of spontaneous combustion, has ever happened in an animal.

524

SPECIAL PirrSIOLOGT.

EVOLUTION OF LIGHT.

A few examples are on record, of the evolution of light from
certain excretions or discharges from the living human body ;
but most of these instances have been observed in diseased
and dying persons. The perspiration after violent exercise,
in one case, and the urinary excretion in several instances, have
been seen to display a decided luminosity ; in the former ca.se,
the luminous matter being even transferable to the clothing. In
three instances of persons in the last stage of phthisis, a light,
owing apparently to luminous breath, has been noticed playing
about the features; the surface of a cancerous ulcer is also said
to have exhibited a similar appearance. In these cases, the
light is supposed to proceed from the slow oxidation of phos-
phorus or of some phosphuretted compound, resulting fi-om the
incipient decompo.sition of the excretions, or from their contain-
ing some imperfectly oxidised compound of phosphorus, which
had accumulated in the blood, and become eliminated in those
fluids, but which would ordinarily be thronm off, in the shape
of alkaline or earthy pho.sphates. Phosphorus dissolved in oil,
injected into the veins of a dog (p. 444), produces a luminous
condition of the breath ; and a luminous state of the urine has
been observed in men who have taken phosphorus medi-
cinally. It has been suggested that, as a large number of the
cases of luminous breath in men, have occuiTed in persons
addicted to excessive drinking, certain bodies, derived from the
decomposition of alcohol, may impede the proper oxidation of
the phosphuretted compounds, which then escape in the breath
or other excretions. It is even presumed that the presence of
such compounds in the blood, may impart an unusual degree of
combustibility to the body. But the knovm compounds deri-
vable from alcohol, even aldehyde, are not so readily oxidisable
as the imperfectly oxidised compounds of phosphorus. This
explanation is therefore speculative ; and the so-called cases
of spontaneous combustion of the bodies of intemperate per-
sons, as just stated, are unfounded, and capable of exjilanation
on other and simpler grounds.

Dead animal matter is frequently luminovs or phosphoresce/it.
The surfaces of the muscles and other soft parts of bodies
undergoing dissection in anatomical schools, have sometimes
been seen to emit a brilliant light ; and luminous exhalations
from graveyards, e.specially from the recently exposed soil,
have not unfrequently been observed. The remains of de-
caying animal matter generall}', may also become phosjihores-

LUMINOSITY IN ANIMALS.

525

cent ; but this more particularly happens in the case of
marine Fishes and the marine Mollusca, Crustacea, and Cmlente-
rata. This is also at present attributed to a true phosphores-
cence, sotneimperf'ectly oxidised phosphuretted ccmipound being
supposed to be the result of an incipient stage of decomposition.
It disappears on the occurrence of actual putrefaction.

The warm-blooded Vertebrata apparently possess even less power than
Man, of evohnng light from the living body, or authentic eases of such an
event, woidd have been recorded. The light seen in the eyes of the cat
, and other creatures, in the dark, is merely a reflection from the iridescent
portion of the choroid coat within the eyeball. Amongst the cold-
I'looded Vertebrata, the gi’ey lizard is said to deposit eggs which are
sometimes luminous ; and a species of frog in Surinam, is described as
emitting light, especially from the mouth. Certain cases of luminosity
amongst marine Fishes, may be owing to the agitation and percussion of
smaller luminous animals in the water ; but a marine species of Scopelus,
allied to the Salnionida, is said to emit stars of light from the body
and head ; it is in one of these fishes, that Leuckart has recently described
scattered organs, containing lens-like bodies, which are regarded by him
as eyes (vol. i. p. 60-1). These may be light-reflecting organs.

The most remarkable and characteristic examples of the omission of
light from the living animal body, occur amongst the Non-vertebrate
creatures. Some of these are met with in air-breathing animals. Thus
amongst the Anmdosa, two families of Coleopterous insects or beetles,
vdz., the Elaterida and Lampyrida, furnish us with the well-known
examples of the fire-flies and glow-worms. The fire-flies proper to hot
climates, give out a very brilliant light from two spots, one on each side
of the thorax, and from a third on the under side of the same part ; the
light is present in both sexes. In the glow-worms, however, the light
is softer, and though observed in the male, and, even more feebly, in the
chrysalis, in the larvae, and in the egg, it is decidedly more striking in
the female ; it is also chiefly obseiwod at particular seasons. It proceeds
from the under side of the three last segments of the abdomen. Exa-
mined under high magnifying powers, the luminous patches are seen to
consist of little sacs, containing a yellowish granular matter, which is
the luminous substance. These sacs are closed by horny lids, having
peculiar flat surfaces, suited to the diffusion of tlio light ; the granular
matter and sacs are traversed by numeroTis air-tubes, or tracheae. The
light is given out, even after the segments arc removed from the rest
of the body, and luminous streaks may be produced by rubbing the
yellow matter between the fingers. There seems no douljt that the
cause of the luminosity, is the feeble combustion of some organic com-
pound excreted by the animal. It is said, however, not to contain phos-
phorus in any appreciable quantity, and the product of its combustion
is carbonic acid (Mattcucci). Other alleged instances of luminous
winged Insects, are doubtful. Amongst the Annulosa, .some Centipedes,
and, under certain circumstances, the common earth-wonu, also present
examples of luminosity. Amongst the Mollusca, there are luminous
air-breathing Gasteropods.

I5y far the larger number of luminous Non- vertebra to animals, is

526

SPECIAL PHYSIOLOGY.

found amongst the aquatic Ijreathers, and exclusively, perhaps, amongst
the marine species. Of the Molluscous marine animals, the Cephalo-
dopous Octopus, the Pteropodous Cleodora, and the Lamellibranchiate
Pholas, exhibit luminosity. Many Molluscoid animals, but especially the
Tunicated Salpida and Pyrosomida, are eminently distinguished for this
property. Again, many minute marine Crustacea appear like little lumi-
nous specks in glasses of sea-water, especially when this is agitated ; and
they are even discernible in the stomachs of larger Mollmscoid animals,
which feed upon them. Some of the marine Annelida are distinguished
by being able to emit sudden scintillations of light along the body,
which may be repeatedly excited by mechanical irritation. It has been
suggested that, in those cases, the light may be excited through nervous
agency, which may possibly undergo conversion into light (Carpenter).
Amongst the Annuloid animals, certain Star-fishes are said to be lumi-
nous. But the Ccelenterata yield the largest number of luminous
marine creatures, especially the Acalephae and the Hydroid Polyps, such
as Pennatula and others. Lastly, a minute jelly-like creature, formerly
assigned to the group Acalophse, amongst the Ccelenterata, but now
classed amongst the Protozoa, by some as a Ehizopod, but by others as
a pecTiliar and gigantic Infusorial animalcule (Huxley), the Noetiluca
miliaris, is the most common of all light-giving creatures in the tem-
perate oceans, and is the chief cause of the luminous nocturnal appear-
ance in our Northern Seas. In the Tropics, the phenomenon is much
more striking and brilliant, and depends upon a greater variety of
animals, especially upon the Medusas and the Hydroid Polyps.

The luminosity of these various marine animals, is said to depend
upon a mucous secretion from their integument, which will even impart
luminosity to water or milk, with which it is mixed. The so-c;illed
phosphorescence is always more marked in warm than in cold climates ;
it is increased by moderate elevation of the temperature of the water,
and, most remarkably, by brisk agitation of the fluid, either because the
secretion is detached from the animals, or simply owing to their excite-
ment. The light is extinguished b}"^ extremes of either heat or cold; it
disappears in vacuo, and is restored on renewed exposure to air ; it is
rendered more vivid by various stimulating substances, if moderately
used, and also by electricity ; but it is extinguished by the excessive
employment of these, and especially by such vapours as those of ether
and chloroform, whicli would interfere with oxygenation. Oxygen
increases and maintains the phosphorescence ; carbonic acid first excites,
and then destroys the luminous property ; sulphuretted hydrogen almost
instantly ari’osts it. The luminosity may continue for a time after
death, unless this has been produced by some specially poisonous sub-
stance. It entirely ceases as soon as putrefaction begins.

Prom the preceding facts, it is obvious that the luminosity of animals
is owing to some living action, and not to decomposition.

Its use is by no means understood. The supposition that it solves
occasionally to guide one sex to the other, affords a very partial explana-
tion of the facts ; for it does not apply to the cases of the multitudes of
hermaphrodite marine luminous animals. It may conduce to their de-
struction, by assisting other animals in seeking Ihomas food ; or it may
serve to illuminate deep waters. But this curious phenomenon aft'ords a
good e.xample of the imj'orfeetion of our knowledge o( final causes.

ANIMAL ELECiraCITY.

527

In the glow-worm, it appears not to be phosphorus, but some earbon-
compound, which produces the light. Even in the case of the numerous
marine luminous animals, it is not proved that the light is owing to the
slow oxidation of a phosphuretted substance. This, however, seems
more probable in the case of animals living in water, in which the
luminous oxidation of a phosphuretted body, is more conceivable than
that of a hydro-carbonaceous substance. It is possible that some, at
least, of the feeble light exhibited in these phenomena, or its intensi-
fication, is due to fluorescence developed in a high degree ; fluorescent
substances certainly exist in living animals. The term phosphorescence
must be regarded as descriptive and provisional only, for the light may
not depend, in any case, upon the oxidation of a phosphuretted compound.

The evolution of light from these animals, as a normal phenomenon,
and that from the human body, as an occasional or morbid occm-rence,
must be accompanied by chemical change, in which the chemical energy
passes into the form of light. The photic work of the animal body, must
therefore depend on the chemical energy evolved by it. But the
quantity of matter subjected to change in its production, is very small.

EVOLUTION OF ELECTRICITY.

•

' The electric cuiTents constantly present in the living nervous
and muscular tissues, and the common electric current present
in the entire human body, and in the bodies of the lower animals
generally, especially noticeable in the frog, have been else-
where mentioned (vol. i. pp. 106, 281). This common current
usually passes from the lower extremities to the head of an
animal ; but in the upper limbs of the human body, it is said to
be directed from the shoulder to the fingers. Electric cuixents
have also been detected upon different secreting surfaces and
glands, and even between a secreting membrane and the veins
returning from it. These phenomena cease Avith the life of
the animal experimented upon. The direction of these cur-
rents, is shown by delicate galvanometers. Thus, currents pass
from the venous blood, which is positive, to the gland or se-
creting surface, which is negative; no current passes between a
gland and the arterial blood. Arterial blood is said to be positive,
as compared Avith venous blood (Scoutetten). Between the
coiTesponding points of the two sides of the body, or of opposite
limbs, no electric currents are ordinarily found; but they occur
betAveen non-correspondent points, and even betAveen corre-
sponding points, if there is a difference Avith respect to their
nutritive activity, as when one limb is at rest, and the other in
motion, or as Avhen one limb is more or less inflamed (Matteucci,
Du Bois-lieymond). The electricity of the human body under
ordinary circumstance.s, is rapidly conducted from it, and thus

528

SPECIAL PHYSIOLOGY.

an equilibrium is maintained with respect to surrounding media.
But when the body is insulated, its proper electric state is
speedily manifested, either when it is brought into contact with
non-insulated bodies, the galvanometer intervening, or Avhen
two insulated persons are connected with the galvanometer, or
touch each other. Thus examined, the electric condition of
men is usually positive, that of women is said more frequently
to be negative. Sanguine and irritable persons exhibit a more
active electric condition, than others. It is Avell known that
electricity is sometimes developed in the body, bj'^ friction, or
by the rapid removal of stockings, e.specially silk ones, or of
other articles of dress which fit closely to the skin. This phe-
nomenon is accompanied by slight crackling noises, and even
by sparks, especially in dry rveather, dry air being a better
non-conductor than moist, and so preventing the escape of the
electricity of the body. Remarkable and exceptional instances
of the accumulation of electricity in the human body, are on
record, in which, if the per.son were only moderately insulated,
sparks could readily be drawn from any part of the body.

The total quantity of electricity developed in the body, must
be very large ; but owing to the quantity of water in the
tissues, to the high conducting power of that fluid, and to the
absence of aiTangements calculated to insulate the electric
currents, the electricity passes as soon as it is generated, into a
state of equilibrium. Moreover, this animal electricity speedily
acc[uires a condition of equilibrium, as regards neighboiudng
objects and media ; and it is only rvhen the body is more or
less perfectly insulated, that other than static currents can be
detected in it.

a

t

Similar electric currents exist in all Warm-blooded Vertobrata, and
are probably universal in the Cold-blooded Vertebrata. In the frog,
they are remarkably strong, and the animal itself, so lar as its muscular
■system is concerned, and probably also as regards its nervous system, is
peculiarly susceptible to electric influences.

It is amongst the Cold-blooded Vertebrata only, and in the lowest Class
of these, wz., in Fishes, that the singular power exists, of generating
and accumulating, within certain organs, a largo amount of electricity
which can be discharged from tho body, in the form of a shock, either in-
voluntarily or, apparcntl}' also, at tho will of tho animal. Eleetilc fishes
are found in almost all climates ; but they belong to different genera.
There are eight species known at present to possess this power. Of
these, five are marine ; three of these are Torpedoes, belonging to the
Ray-family ; they inhabit tho iMediterrauean and tho Atlantic, and are
sometimes even used as food. Tho fourth is tho Trichiurus, or Sword-fish
of tho Indian Seas. Tho fifth marine species is the Tetraodon, found
amongst the Comora Islands. Tho frcish-water or river species of electric

ELECTRIC FISHES.

529

fishes are the Sihmis or Malapteriirus, a salmon-like fish of the Nile,
Niger, and Senegal, rivers of Africa; the Momyrus, or Nile Pike, and
lastly, the celebrated Gymnotus, or Electric Eel, found only in the Amazon
and other largo rivers of South America.

In the Torpedoes, which are true flat fishes, the electric organs con-
sist of two compressed oval masses, lying ono on each side of the head,
and reaching from between the gills into the body ; they are supported
in front and externally, by a cartilaginoiis border. They consist of a
strong membranous investment, enclosing a soft pulpy structure, divided
by septa, into hexagonal columns, which have their ends directed towards
the upper and under surface of the fish. Each column is subdivided, by
delicate and extremely vascular partitions, into numerous separate cells,
and each cell is filled with a clear fluid, of which ^th part is albumen,
with traces of common salt. Owing to the large proportion of water in
them, the specific gravity of the electric organs, is only 1026, wliilst that
of the body of the fish, is 1060. These remarkable organs are supplied
with very large nerves, larger than any other nerves in the body, and
larger than any nerve in animals of the same size. The nerves arise
from a special nervous ganglion, called the electric lobe, connected with
the medulla oblongata, immediately behind the cerebellum ; at their
roots, these neixes have apparent connections with the fifth and eighth
pairs ; their finest branches end in close plexuses, tipou the delicate jiar-
titions between the cells of the columnar portions of the electric organ.
The electric organs of the Gymnotus, are four in number, arranged in
two pairs, one larger than the other ; they form ono third of the entire
bulk of the animal, and extend nearly its whole length. Their structure
is similar to that just described in the Torpedo ; but the prismatic
columns of cells are larger, fewer in nmnber, and of greater length, for
they are placed lengthwise in the electric organ and body of the Eish.
The nerves are derived, it is said, from the spinal cord only, and are up-
wards of 200 on each side of the body. Some of its nerves proceed from
the fifth cranial nerve, but most of them, it is asserted, from the spinal
cord.

In the Silurus, there is no such distinct electric organ ; but a dense
fibrous tissue, having albuminous substance contained in its interstices,
surrounds the whole body, and is regarded as the homologue of the
more perfect organs of the Gymnotus and Torpedo.

The power of the Torpedo to give shocks, is comparatively small, but
these excite much pain. The sliock of the Sihu-us, and of the largest
Gymnoti, which measure twenty feet in length, is sulliciont to kill small
animals, and to paralyse men and horses, both as regards sensation and
motion. The electric power depends upon the integrity of the nerves
connected with the electric organs, as is proved by the results of par-
tial or complete division of tlioso nerves. Small portions of the organ,
connected with the body by no other part than a nerve, still retain their
electric power. Destruction of (he electric loijo in the Torpedo, com-
pletely destroys the electric power. The discharge of electricity in the
Gymnotus, may be caused, by touching different points on the same side
of the body, or different points on opposite sides of the body; in the
Torpedo, it is excited by touching the upper and under surface of the
animal. But it is said, that when exactly corresponding points on the two

VOL. II. M M

530

SPECIAL PHYSIOLOGY.

sides, or on the same surface of the body, are touched, no shock occurs,
and that not even a ciirrent passes through a galvanometer. Contact -Buth
one point only, induces no shock, and a Gymnotus instinctively endea-
vours to bring a second point into near relation Bith anything which
touches it. The back of the Torpedo, is electrically positive ; the ventral
surface is negative ; the strongest currents are obtained immediately over
the electric organ. In the Gymnotus, however, the most powerful shocks
are obtained, by touching the two extremities of the body, which here
present opposite electric states, the head being positive, and the tail
negative.

The electric discharge from these Fishes, not only produces shock to the
living nerves of one individual, or even of a chain of persons touching
each other’s hands, but it affects the galvanometer, magnetizes needles,
accomplishes chemical decompositions, and even produces a spark in a
properly devised circuit (Faraday). There can be no doubt, therefore, of
its perfect identity 'with the electricity developed by physical means.

The energy of the electric discharge, depends on the size and strength
of the animal. It is exhausted by too frequent use ; sometimes a
powerful discharge precedes death. Torpedoes, in which the electric
nerves have been divided, appear to live longer than those the electric
organs of which are subject to repeated irritation. The electric
energy, like that of the ■vital processes generally, is greater, and less
easily exhatisted, in young Torpedoes than in older ones, and shocks
have been felt even from the foetal Fish, as it has been extracted from
the abdomen of the parent. Just as the embryo of the Snapping Turtle,
has been seen to snap its jaws whilst still in the egg, so the foetal Tor-
pedo has been seen to try and bring its surfaces in proper contact with
foreign bodies, so as to pass the shock through them. The electric power
is first excited, and then destroyed, by strychnia and morphia. A tem-
perature of 32° suspends the power, which is again restored by immer-
sion of the Fish in water at a temperature of from 58° to 68° ; at 86°,
rapid and strong discharges take place, and the Torpedo soon dies.

The use of this remarkable power, beyond that of serving for protec-
tion, or for obtaining food, is not evident; indeed allied Species, ex-
posed to the same enemies, and living on the same food, flourish ■without
such organs. Moreover, the Gymnotus kills many more fishes than it
eats, and Torpedoes, kept in confinement, have been found to destroy
small fishes -without eating them. The electric discharge has been sup-
posed to assist indirectly in the digestive process, inasmuch as animal
substances subjected to powerful electric currents, undergo ready de-
composition ; the intestine of the Toi'pedo is very short, but so also is
the digestive canal of the allied Species. It has also been imagined that
oxygen may be supplied to the gills, by decomposition of the water near
tliem by those organs ; but this is improbable. Lastly, it has been thought
that they may rendertheFish galvanometric,and thus enable it to recognise
changes in the electric condition of the surrounding medium. The chief
use, however, must surely be protective. It has been said, that certain
Molluscs and Insects are able toemit feeble shocks of electricity; but this
is doubtful. The Cmlonterata, as the Sea-Anemones and others, irritate
and destroy their prey by stinging organs, which act suddenly, but are
not really electric.

STATICS AND DYNAMICS OF THE BODY.

511

The great size of the nerves distributed to the electric, organs, the
special distribution of the extremities of the nei-vos upon the mem-
branous u-alls of the cells, the results of division of those nerves, and. of
destruction of the so-called electric lobe, the excitement of the organs by-
irritation of the brain, and lastly, the apparent subjection of the -svhole
apparatus to the -n-ill of the animal, sho-\v, that in some -u'ay, the elec-
tric phenomena developed in these living galvanic batteries, are largely
dependent on the nervous system. According to one -view, the electric
force may be developed and accumulated in the electric organ, and
may be merely discharged under the influence of the nerves. But it is
diflflcult to understand, ho-sv this could happen in an organ apparently un-
insulated, for its membranous envelope is as good a conductor as moist
tissues or -water. Another theory supposes, that static electric currents,
similar to those which are detected in muscidar tissue, but of a far more
powerful kind, are constantly circulating through these organs ; and that
the equilibrium of such currents being disturbed by some action of the
nervous system, a discharge of the electric force then takes place. In
accordance -with this view, the organs themselves, with their vascular
cell-walls, seem constructed for a special purpose, being unlike any
other known animal organ ; after repeated discharges, time must be
allowed for the restoration of the power of giving shocks ; and lastly,
the electric force is precisely proportioned to the general activity of
the nutritive functions. Moreover, a difference has been observed in
the character of the discharge or shock, between the Torpedo and the
Gymnotus, a difference connected with peculiarities in the structure of
their electric organs. The shock is more powerful in the Gymnotus,
the piles of cells of the organ being extremely long ; whereas in the
Torpedo, the shock is less powerful, and the piles of cells are sliorter.
It has been supposed, by some, that the so-called nerve-force is directly
converted, in these organs, into electric force ; and the fui’ther inference
has been drawn, that the two forces are hereby shown to be identical.
The former hypothesis may be correct, but the latter opinion is not so
(vol. i. p. 291). The two forces are so far related, that either most
easily excites the other. The ultimate source of the electric power, is
chemical action, most probably oxidation. •

STATICS AND DYNAMICS OF THE HUMAN BODY.

Physiology is not sufficiently positive or perfect, as a science,
to have its exact constants. But we may here collect certain
numerical expression.s, concerning the specific gi'avity, height,
and weight of the body; the weights of its various organs;
the relative quantities of its chief proximate chemical con-
stituents ; also, concerning the weight of the daily food, and its
proportion to the weight of the body ; its proximate consti-

II M 2

532

SPECIAL PHYSIOLOGY'.

tuents, and the relations of these to the proximate constituents
of the body ; their destination in the economy ; and the effects
of deprivation of food.

Besides this, we may examine, in a general manner, the
chemical work performed within the body; and endeavour to
estimate, numerically, its vito-chemical processes, and their
relation, on the one hand, to the food, drink, and air, and, on
the other, to the mechanical and calorific work, performed in,
and by, the system. The nutritive, electric, and nervous work,
may also be here again noticed.

STATICS OF THE HUMAN BODY

Specific Gravity of the Body.]

The specific gravity of the body, depends upon that of its
various tissues and organs. Essentially, all the materials of
the body, with the exception of the fatty substances, are heavier
than water, and the mean specific gravity of all the tissues, is
higher than that of water. But the air retained in the lungs
during life, even the residual and reserve air, is just suffi-
cient to counterbalance the higher specific gravity of the body
generally, and so enables it to float (vol. i. p. 227).

The specific gi-avities of the chief tissues are given in vol. i.
p. 78; that of the principal organs, is mentioned in their
description. The specific gravity of the entire body, with
air in the lungs, is usually stated to be from 1060 to 1070.
As bone is the heaviest, and fat the lightest, of the tissues, the
specific gi’avity of the entire body, is influenced by the relative
proportions of these two tissues ; hence it is gi-eater in thin
bony persons, but less than the average in children and women,
who are generally fatter than men, and, also, in corpulent
persons of either sex. But the practical buoyancy of the body
in water, is, of course, chiefly determined by the size of the
chest and lungs, the freedom of the latter from congestion or
deposits, and their condition of inflation. On the least in-
spiratory and expiratory movement, the body rises or sinks
in Avater. Necessarily, the body is more buoyant in the sea,
than in fi-esh water. The effect of clothing, or of any kind
of Aveight, is, of course, adverse to buoyancy.

WEIGHTS OF ORGANS OF THE BODY.

533

Height of the Body.

The human body continues to grow, at least up to the age
of twenty -live (Quetelet), and, as it woirld seem, even up to
the age of thirty years (Dansonp The mean height of tlie male
in Belgium, at tweuty-hve years of age, is 66 T inches, or
168 centimetres* (Quetelet). The mean height of males, at
twenty-one years, in Germany, is found to be 68T inches,
or 173 centimetres (Zeising). Measurements of 4,800 cri-
minals, in England, give a mean height in the male, from
twenty-five to thirty years, of 66‘5 inches, or nearly 169 cen-
timetres (Danson). The extreme divergence of the German
measurements, must be exceptional, and due probably to too
limited a number of observations. The English stature is
nearer to a mean. The height of the full-grown female, at
thirty years of age, is 62’2 inches, or 158 centimetres
(Quetelet). The mean difference between the height of the
sexes, is about 4 inches.

Weight of the Body.

The estimated average weight of the body in the male, is also
rather less, according to Quetelet, than acording to other ob-
servers. From thirty to forty years of age, it is 140 lbs., or
63'66 kilogrammes.^ From twenty-five to thirty years of age,
the mean weight of the male, according to Danson, is 143' 1
lbs., or 65 kil. Vierordt adopts the result of one observation
on a powerful male, aged forty-two, whose weight was about
143’5 lbs., or 65’25 kil. The weight of the female, at thirty,
is 121 lbs., or 55 kil., i.e. about 22 lbs. le.ss than that of the
male ; but the weight increases in women up to the age of
fifty, when it is about 123’2 lbs., or 56 kil.

ifrom the preceding numbers, a mean height of 5 feet 6-^
inches, and a weight of 144 lbs. avoirdupois, may be as-
sumed, for the average full-grown male. In the calculations
made by English writers, on the working power of a man,
150 lbs. is, however, usually taken as his weight.

Weights of different Parts and Organs of the Body.

These are taken from Duroy and Krause, the weights given
by them, having been converted into lbs. and ozs. avoir-
dupois : —

* A centimotro = '3937 inch,
t A kilograinnio = 2'2 lbs. avoirdupois.

53-t

SPECIAL PHYSIOLOGY.

The recent skeleton ....

lbs. oz.
21 8

OZ.

344

Muscles and tendons

77 8

1240

Skin and subcutaneous fat

16 5

261

Brain ......

3 2^

60'5

Spinal cord .....

H

1-25

Eyes ......

1

•5

Tongue and hyoid bone

3

3

OEsophagus .....

If

1-75

Stomach ......

7

7

Small intestine .....

1 lU

27'5

Large intestine .....

1 1

17

Salivary glands ....

2-5

Liver

4 4

65'5

Pancreas . . . . . ' .

3

3

Spleen

8-0

Thyroid body and remains of thymus

1

4

■75

Blood = -jL weight of body

11 0

176

Heart ......

104

10-25

Eight and left kidneys

104

10-25

Larynx, trachea, and larger bronchi .

03

2 lo|

2-75

Lungs ......

42-25

Unweighed parts ....

1 44

20-75

Total

143 8

2296

Proportions of the Proximate Constituents of the Body.

All the constituents of the body, belong to five chief cate-
gories ; viz. albuminoid substances and those immediately
derived fi-om them, fats, salts, extractives, and water. The
following Table shows the quantities of these substances in a
body supposed to weigh 1.50 lbs. ; and also the proportions
of each in 1,000 parts (Moleschott) : —

Quantities
in the body
in lbs.

Proportions
in 1000 parts

Albuminoid substances and their deriva- ?
tives j

30

201

Fatty matters

4

25

Salts .......

14

92

Extractives ......

1

6

Total solids ......

49

324

Water .......

101

676

150

1000

DAILY QUANTITY OF FOOD.

535

Daily Quantity of the Food, and its Composition.

It has been stated that a daily consumption of 2 lbs. of
bread, with 12 oz. of meat, which contain 11'6 oz. of carbon,
and •? oz. of nitrogen, will support a fully-exercised adult,
(Bedard). According to another estimate, 1 lb. of meat,

1 lb. 3 oz. of bread, 3|- oz. of fat, and about 2^ imperial pints
of water, are needed by a healthy, actively-employed man
(Dalton). Vierordt’s estimate, as we shall see, assigns 4 oz.
of dry albuminoid matter, 3 oz. of fat, 11-j of starchy food,
and 1 oz. of salts. An ordinary English labourer is said to
consume daily, a diet containing 12 oz. of carbon and 5 of
nitrogen, and a dietary containing only 10-4 oz. of carbon,
and '42 of niti'ogen, is stated to be insufficient to preserve his
health (Ed. Smith). Cases, however, are on record, such as
that of Louis Comaro, in which a much lower diet has served
to maintain life and health for very long periods. The diet of
men engaged to run, walk, or row, and also that of jockeys,
has occupied special attention in England; and though entirely
the result of empiricism, the rules laid down, correspond gene-
rally with the suggestions of science. They usually include
an excess of meat diet, a spare allowance of amylaceous and
saccharine food, and a more or less strict abstinence from
alcoholic beverages, tea, coffee, and tobacco. Very active
exercise, sweating, sponging, early rising and retirement to
rest, are also enjoined.

The daily food may be classified under four chief cate-
gories ; viz. the albuminoid substances, the fatty and
starchy substances, the saline or mineral substances, and
the water. According to Vierorclt, a healthy adult is suffi-
ciently nourished, by consuming daily, 4'2 oz. av. of dried
albuminoid substances, 3T of fatty matter, 1T5 of amyla-
ceous food, and IT of sfdine substances. Playfair has e.sti-
mated that the daily diet of an active adult man is about 4'2 oz.
of dry albuminoid substances, 1'8 of fats, 18‘7 of starch, and
•9 of mineral substances. The difference between these diets,
the former preponderating in fatty matters, and the latter
in starchy substances, is doubtless owing to differences of
national habit. To these .solid substances, viz. 19'9 oz. in the
former, and 25T) oz. in the latter diet, must bo added 93 oz. of
water, which, according to Vicrordt, includes tliat taken both
in the food and drink, making a total of 112'9 oz. in the first

5S6

SPECIAL PHYSIOLOGY.

diet, and 118'6 in the second diet. The daily amount of new
material taken into the body, will, in the former case, be about
■^tjth, and in the second, about of the total weight of the

body. In the diet indicated by Vierordt, the proportion of
non-nitrogenous to nitrogenous food, is as 3-|- to 1 ; whilst in
that allowed by Playfair, it is as 4| to 1. But a compen-
sation exists in the fact, that the fatty matters, in excess in the
German diet, are much richer in carbon than starch; for,
adopting the so-called starch equivalent for fat. which is as
2 '4 to 1, and expressing the fatty matters, in both diets, as if
tliey were starch, the disparity between them is lessened.
The starch equivalent in the former diet, would then be 19,
and in the latter 23, which, as compared with the amount of
nitrogenous matter identical in both diets, viz. 4'2 oz., would
give a ratio between the non-nitrogenous, or hydro- carbona-
ceous elements, and the nitrogenous, of about 4^ to 1 in the
diet of Vierordt, and of about 5^ to 1 in that of Playfair.

The annexed Table shows these facts more clearly.

Daily food of an adult man, in oss. avoirdupois : —

Playfair

Vierordt

Proportions
in inOO parts
(Vierordt)

Albuminoid substances .

4-2

4-2

37

Fatty matters

1-8

31

28

Salts .....

•9

1-1

8

Starch .....

18-7

11-0

103

1

Total solids .

2o-6

19-9

176 j

Water ....

90

93

824

116-6

112-9

1000 j

Relations between the Coiistituents of the Body and those
of the Daily Food.

Having determined the proportions of the different proxi-
mate constituents of the body, in 1000 parts, and the same
proportions in regard to the proximate constituents of the food,
and knowing that the total weight of the daily food is about
■o’fjth of the total weight of the body, it is easy to ascertain
approximately, the I'atio between the daily quantity of each of
those proximate constituents of the food, and the quantity of

COJISTITUEMTS OF THE BODY AND THE FOOD.

537

the same, or similar substances, present in the body. The
results are shown in the annexed lable.

1

1

In 1000
parts of
the body

In 1000
parts of
food

In 50 parts
of food, i. e,
^the
•weight of
the body

Proportion per
cent, of consti-
tuents of food,
to similar consti-
tuents in body

Albuminoids

201

37

1-85

•9

Fats ....

25

28

1-4

6-6

Salts ....

92

8

•4

■4

Carbhydrates, viz., I

starch, sugar, ex- 1

6

103

5-15

86

tractives J

Water ....

676

824

41-2

61

Totals

1000

1000

60

From this comparison, it appears that, in round numbers, the
daily supply of albuminoid substances in the food, is rather less
than 1 for every 100 parts of albuminoid materials in the body;
that the supply of fat, is parts for every 100 in the body; that
of salts, less than a part ; and of water, G parts only for every 1 00.
On the other hand, the proportion of the carbbydrates in the
Ibod, as compared with the small quantity of substances of simi-
lar composition in the body, is as much as 86 per cent. This
obviously suggests that the amyloid and saccharine substances
are not largely employed for conversion into tissue, but have
.some other function in the economy, one of which, there
is reasoir to believe, is to supply fuel for the purposes of
generating chemical force, to be transformed into animal
motion and heat. These, indeed, are the so-called calorific
substances, heat-givers, or respirator jj food, as distinguished
from the albuminoid substances, plastic food, or flesh- fanner s.
From the small percentage of these latter bodies, daily supplied
to the system, it is evident that not more than part of

such sub.stances in the body, can, on an average, be replaced by
nutritive metamorphoses in one day. Hence, we arrive at the
conclusion, that 100 days, at least, are necessary, supposing
waste and supply to be equal, for the complete transformation
of a// the albuminoid, and their derived constituents, in the living
body. But the actual rate of metamorphosis is so different in
-^he several albuminoid tissues, as e.g. in muscular, as compared
with tendinous, tissues, and moreover, .so inconstant, that no safe

53S

SPECIAL PIIYSIOLOGT.

conclusions can be arrived at upon such general data. The
fatty matters of the body, are possibly changed in much less
time.

It is difficult to estimate the ordinary daily waste of the
human body. It has been shown, however, that the daily
quantity of food, necessary to maintain an animal at its normal
weight, is more than twice the weight of the daily loss Avhich
it undergoes, when deprived of all food. When the weight of
the food, is only equal to the loss during temporary starvation,
the animal continues to lose Aveight, and the egesta given off
by the alimentary canal, the kidneys, the skin, and the lungs,
weigh more than the quantity of food taken. This has been
attributed to the requirements of the processes of digestion,
Avhich demand the formation of copious secretions containing
much solid matter ; but as most of them are reabsorbed, it is
more probably to be explained by the fact that, in a starving
animal, the Avaste is reduced to a minimum, and that the effect
of insufficient food, is to excite the system to an unaccustomed
activity, and to loss by metamorphosis. Nevertheless, during
health, Avith sufficient food, and in a sufficiently long period,
there must be an actual balance betAveen the loss and the
supply.

Destination of the Food in the Living Economy.

This subj ect includes tAvo points of investigation — viz. the
intermediate, and the idtimate, chemical changes or meta-
morphoses of the different proximate constituents of the food.
The latter point may be first examined.

In order to arrive at the ultimate destination of the proxi-
mate constituents of the food, after these have compensated
for the Avaste of tissue, or have been consumed in furnishing
force for imparting motion and heat, it is necessary to deter-
mine the intrinsic composition of those constituents, and that
of the various excreted mattei’s. The chemical constitution
of the ingesta Avhich pass into the body, must be compared
Avith that of the egesta Avhich pass from it — tAVO terms of an
equation, Avhich, if our means of experiment, and our knowledge,
Avere exact, should be shoAvu precisely to correspond. This
comparison has been attempted by Vierordt, as shoAvn in the
following Tables, in Avhich the quantities, giAmn by him in
grammes, have been reduced to ozs. avoirdupois : —

DAILY INGESTA AND EGESTA.

533

A. Ingesta during 24 hours, in ozs.

Food, drink,
and air

Quantities

consumed

H.,0 of
starch, and
water

C

H

N

0

Salts

Albumen

4-23

2-29

-28

-66

1

Fat

3T7

2-47

-36

-34

Salts

M3

1-13

Starch

11-63

6-46

5-17

Water

93

93

Oxygen j
of air J

26-24

26-24

Totals

139-4

99-46

9-93

-64

-66

27-68

1-13

B. Egesta during 24 hours, in ozs.

Excretions

Quanti-
ties ex-
creted

Water

C

H

N

0

Salts

Breath ; Carbonic acid
and Water . . .

Perspiration ; do. do.
r Urea

Urine -J Water

(_ Extractives
Solid excreta . . .

Water formed in the
system ....

43-4

23-62

62-31

6-07

(4.

11-66

23‘3

59-98

4-52

8-79

-09

{:f

-71

f-07

b-03

-1

•44

?

-56

-1

22-95

-23

-41

-43
f -27
I 3-29

-92

-21

,4

139-4

99-46

9-93

-64

-66

27-58

1-13

In Table A, the quantities of the various constituents of the
daily food, solid and fluid, are the same as those quoted in
p. 535. The daily amount of oxygen introduced into the system,
is calculated from the quantity known to be given off, in that
period, as carbonic acid from the lungs and skin. The quan-
tities of hydrogen and o.xygen which exist in the carbhydrates,
in the proportions to form water, are set down as water.

In Table B, the ultimate destination of all the chemical
elements of the constituents of the ibod, is traced. The totals
under each head in the two Tables, correspond, the decimals
having been, in some cases, slightly altered in the reduction

540

SPECIAL PHYSIOLOGY.

of grammes into ounces. The upper row of the figures which
reter to the urine, re])resents the elements of the urea ; tlie
lower row, those of the non-nitrogenous urinaiy constituents.
Above two thirds of the hydrogen of the food, are converted
in the body, into water, partly by uniting with oxygen already
in the food, biit chiefly by combination Avith oxygen from the
air. The remainder of the oxygen, unites Avith carbon, to form
the carbonic acid of the pulmonary and cutaneous exhalations.
Of the entire excreta, 32 per cent, pass oiF by the breath, 17
by the skin, 46’5 by the kidneys, and 4'5 by the alimentary
canal. The ultimate products of the chemical metamorphoses
of the food within the living body, are regarded essentially
as urea, carbonic acid, salts, and ivater. The small residue
consists chiefly of nitrogenous and other matters in the faces,
and of epithelial, and epidermoid, losses.

The intermediate stages of metamorphosis, which occur as
the food is assimilated into blood, or solid tissue, and the fur-
ther exceedingly complex, and only imperfectly knoAvn, changes
Avhich these undergo, have been fblloAved, more or less com-
pletely, in describing the composition and use of the different
kinds of food (p. 2-7), the modes of their assimilation (p. 174),
the office of the several constituents of the blood (p. 287), and
the sources of the biliary and urinaiy pulmonary excretions
(pp. 354, 377). A summary or general view of these meta-
morphoses, may now be given.

Water appears to undergo no decomposition into oxygen
and hydrogen ; rather it is increased by additional Avater set
free, or actually produced, by the union of oxygen and hydro-
gen, in the body itself. It is probably concerned in processes
of hydration and dehydration, thus effecting changes in the
more complex elements of the body.

The saline substances of the food, pass, for the most part, un-
changed through the body, and reappear again in the excre-
tions, especially in the urine ; but the chlorides must undergo
temporary decomposition for the formation of the hydrochloric
acid of the gastric juice, the chlorine, hoAvever, again meeting
Avith appropriate bases. Additional sahne matters appear in
the excreta, besides those in the food, chiefly alkaline sul-
phates, formed by the oxidation of the sulphur in the albumi-
noid compounds of the body, and magnesian phosphates, re-
sulting from the oxidation of the phosphuretted fats of the
blood corpuscles and the brain. The ammonia in the breath,
in the perspiration, and in the urine, and also the urea, uric

DESTINATION OF OLEOIDS.

541

acid, and hippnric acid, are saline substances, the products of
decomposition of one or more nitrogenous matters in the body.

The carbhydrates, starch, and sugar, are changed, the first
into sugar, and both, probably after transitional mutations,
into lactic, oxalic, or other acids. Their elements are ulti-
mately traceable, the carbon, in the carbonic acid of the breath
and perspiration, and the hydrogen and oxygen, in water.
Sometimes starch or sugar may give rise, apparently by an
upward metamorphosis, to biliary or other ftitty acids, and
thus to fat, which may then be deposited in the tissues as fat,
or they may protect and thus spare the fat already in the body.
Sugar and starch given with meat or albuminoid food, produce
obesity ; they are even more fattening than fat itself, as they
are more easily oxidised, and act more effectually as protectors
to the other constituents of the body. Ultimately, their ele-
ments are, in any case, subjected to the same oxidising processes,
yielding carbonic acid and luater. Their upward transforma-
tion is probably exceptional, because they are more easily
oxidisable than fat.

The fattjj matters, or hydro-carbons, are usually decomposed
into their fatty acids and glycerin, before they enter the chyle,
and are probably recomposed there, or in the blood ; possibly, also,
they are again decomposed, under the influence of the alkaline
constituents of the blood, on the eve of being oxidised. This
oxidation may be direct or immediate, into carbonic acid and
water ; but the fat may be first employed, perhaps in the forma-
tion of the choleic acid of the bile, or of the volatile fatty acids
of the milk, butyric, capric, and caproic ; or it may be still fur-
ther resolved into propionic, formic, or acetic acids, and so pass
to the ultimate condition of carbonic acid and water. The
hydrogen of fat, being in excess of its oxygen, and not in the
proportions to form water, as in the carbhydrates, this ele-
ment and the carbon, which also exists in exces.s, demand, for
their reduction, a much larger relative supply of oxygen from
the air. Hence, in regard to vito-chemical calculations, the
fats may be represented by a starch equivcdent, 1 part of fat
being erpial to 2'4 parts of starch. A minute portion of fat may
remain almost unoxidiscd, in the form of cholesterin. Fat,
like the carbhydrates, also saves the metamoqihosis of the
albuminoid tissues and food; for if an animal be fed on insuffi-
cient animal diet, to w'hich .sotne fat is added, there is less
waste, and a smaller consumption, of nitrogenous matter than
if it be fed on a scanty meat diet without lat. A normal pro-

542

SPECIAL PHTSIOLOGT.

portion of fat in the food, also saves the consumption of meat ;
for the Aveight of an animal is then maintained wth one third
or one fourth less meat, than when it is fed on meat alone.
An excess of fat in the diet, however, has, as its chief result,
an increase of weight, by accumulation of adipose tissue.
The most siiccessful plan of fattening animals, is not to with-
draw the albuminoid foods, but to allow these to remain the
same in quantity, and to increase the hydrocarbons and carbhy-
drates. The researches of Lawes and Gilbert, show that in the
fattening of animals, much more fat is produced than there is
flit in the food, only ^-th, or ^rd being contained in the food, and
therefore, from f rds to f ths being produced from other sources,
largely from the carbhydrates, but also from any excess of
nitrogenous food, after the albuminoid tissues are supplied.
This is especially the case, if the non-nitrogenous food be
defective, or if an animal be fed on flesh only (Voit.)

Alcohol, which may be considered as one type of hydrocar-
bonaceous food, has been said, by some, to escape wholly un-
changed, by the breath and the excretions; but it is generally
believed to be, at least, partly oxidised, either with or without
previous conversion into aldehyde, acetic acid, or some other in-
termediate substance or substances. It is not supposed to contri-
bute directly to the formation of tissue, not even of fat. It is not
essential as an article of diet ; it may even be detrimental, by
its chemical action on albuminoid substances, hardening and
precipitating them, or by its physiological action, stimulating
or even poisoning the nervous system, or producing slow and
insidious changes in the blood, the tissues, and the secreting
and excreting organs, which render the system unable to resist
injury or disease ; it may even lay the foundation for irre-
mediable organic changes in the brain, heart, bloodvessels,
liver, and kidneys. In smaller and more moderate quantities,
alcohol, however, is probably oxidised in the blood, and so
serves for the development of motion and heat. It restores a
feeble pulse, quickens the vascular action, and so raises, for a
time, the vital activity of all the functions, vegetative as well as
animal. Much diflerence of opinion exists as to the claim of
alcohol to be regarded as an aliment, of course of the non-
nitrogenous class. Alcohol certainly enters the circulation;
but its eflect on the blood is not understood, though it has been
supposed to I'ender that fluid thicker, and tlie blood plasma
less fit for penetrating the tis.sues. Persons have been known
to live long periods on alcoholic beverages, but not on pime

DESTINATION OF ALCOHOL.

.543

alcohol, unless this was accompanied by small quantities of
bread or other food. So also persons who drink much beer
become fat, but spirit drinkers do not. It has been supposed to
be possibly nutrient to the nervous system, but this is not es-
tablished, and its plastic properties may be doubted. Whether
it may act by saving tissue, through its own oxidation, or
whether it may senm as respiratory or calorific food, depends
on its ability to undergo oxidation in the system. Accord-
ing to Lallemand, Perrin, and Duroy, it leaves the body en-
tirely, and unchanged; this view is also, in some measure,
supported by Dr. E. Smith. By these authors, alcohol has
been found 'unchanged in the blood, in the various organs,
especially in the liver and the cerebro-spinal nervous centres,
and also in the breath, the perspiration, and the urine; more-
over, they have not formd aldehyde, nor acetic or oxalic
acids, into which alcohol has been said to be changed in the
body. It has also been shown that aldeh}fde, if administered,
is itself unstable in the system, and appears as acetic acid.
But the quantities of alcohol found in the excretions, do not
appear to have been accurately compared, by those observers,
with the quantity actually taken into the stomach. Baudot and
Thudicum have shown that when this is done, the quantities
eliminated are proportionally small. Even in theresults obtained
by Lallemand, Perrin, and Duroy, only ;|^th of the alcohol taken,
is thus accounted lor (Gingeot). In these cases, and also in those
in which enormous quantities have been given in disease, more
or less alcohol must therefore be appropriated, or assimilated, by
the tissues, be retained in them, or be oxidised. The adminis-
tration of alcohol does not increase, but diminishes, the tempe-
rature (Perrin, Dumeril, Demarquay, Ringer, and Rickards),
and also the quantity of carbonic acid gas evolved (Lehmann,
Vierordt, Hammond, Bdcker, Lallemand, and Dr. E. Smith).
The quantity of urea excreted, is likewise diminished. Duchek
and Mialhe supposed, that this was owing to the formation of
aldehyde, or some other compound not so perfectly oxidised as
carbonic acid; but this is hypothetical. The efl'ect seems rather
to be due to its lowering, in some manner, all those organic
proce.sses, which lead to the formation of carbonic acid by the
disintegration of blood and tissue (Moleschott, Carpenter); in
this way, alcohol may retard waste, and conserve power. It
may also favour the ibrmation of new tissue, and save the
combustion of fatty matter (Hammond).

Albuminoid bodies, the most complex substances in the animal

544

SPECIAL PIIYSIOLOGr.

economy, undergo, as might he supposed, the most compli-
cated intermediate changes, before they are ultimately resolved
into their simplest excretory products. Albumen itself, con-
stituting the pabulum of the tissues, does not undergo any
upward chemical metamorphosis ; all its changes are nece.s-
sarily retrograde. Slight modifications, perhaps of hydra-
tion, convert it into albuminose, pepsin, salivin, and pan-
creatin. Equally slight oxygenation probably changes it into
globulin, fibrin, syntonin and casein ; this, together with a loss
or total deprivation, of sulj^hur, is concerned in the produc-
tion from it of keratin, chondrin, and gelatin ; the disappear-
ance of the sulphur, must be an essential step in the nutrition of
the gelatin-yielding tissues. The substitution of iron, perhaps,
for hydrogen or carbon, with a loss of oxygen, is possibly the
mode of derivation of the cruorin, or blood pigment, from albu-
minoid matter ; whilst the other pigments, pulmonary, cuta-
neous, biliary, and urinary, e.specially abound in carbon, and
may be formed by processes of dehydration. The nitrogenous
acid of the nervous substance, cerebric acid, is probably derived,
directly or indirectly, from some breaking up of albumen, but
this peculiar acid, which contains phosphorus, exists in Indian
corn and other food ; the glycocoll and taurin of the glyco-
cholic and tauro-cholic acids of the bile, also, perhaps, proceed
from the dissolution of albuminoid substances ; and it is more
than probable that glycogen, or animal starch, and taurin, are
formed in the liver, likewise, by the splitting up of albumen.

In this case, the glycogen contains the carbon, with hydro-
gen and oxygen in the proportions of water, whilst the choleic
acid, with the glycocoll and taurin, contain, besides those ele-
ments, the nitrogen and sulphur. The formation of gelatinoid
substances from albiunen, which must happen in nutrition, libe-
rates sulphur, which may either be oxidated, or find its escape
in the taurin of the bile. Albumen may even be a source of
common fat ; for the biliary acids might ea.sily give ri.se to
oleic and other fatt}’’ acids. During the changes due to the
development of the eggs of the limna3us or water snail, the
percentage of albumen in the ova, alter drying, is said to be
diminished from 95‘2 to 91'8, whilst that of tlie fatty matter
is increased from ‘G to 2'2 ; the percentage of sitlts is.increased
from 4 to G (Burdach.) It is further alleged that albumen is
resolvable into glycogen and urea, a change which is supposed
to be the origin of the sugar formed in the system in diabetes,
at least when no skirch or sugar is taken in the food (llaugh-

DESTINATION OF ALBUMEN.

5J5

ton). In this case, the albuminoid mattei- is supposed only to
have been assimilated into the blood, not to have entered into
the formation of tissue.

If albumen be broken up in the liver, then its non-nitro-
genous products are resolved into carbonic acid and water ;
the sulphur appears in the alkaline sulphates, except Avhen
it passes off as dyslysin in the solid excreta, whilst the nitro-
genous bodies ultimately reach the chemical condition of urea.
But the more obvious metamorphosis of the albuminoid bodies,
is that which consists of a series of retrograde chemical changes
into more oxidised nitrogenous bodies, such as creatin, crea-
tinin, leucin, tyrosin, inosinic acid, sarcin, xanthin, hippuric
acid, and uric acid, by which path they ultimately reach the
condition of urea, a substance identical with cyanate of am-
monia, and wdiich has also been regarded as a carbamide or a
carbide of amidogen, which contains cai’bon, hydrogen, nitro-
gen and oxygen. The ammonia found amongst the saline con-
stituents, is probably always derived from a further breaking up
of urea.

Albumen may be artificially decomposed, by acids or alkalies,
or by spontaneous changes, into leucin, tyrosin, and gly-
cocoll, all which nitrogenous compounds are found in the
body, especially in venous blood, and in the liver and spleen ;
whilst creatin, creatinin, and inosinic acid, are found in actively
exercised muscles, and in the blood. Creatinin is, of all these
substances, the nearest to urea, and is readily converted into
it, by assumption of the elements of water. Urea itself has
been found in the muscles of certain fishes. Gelatin and the
gelatinoid substances, behave in their downward metamorphoses
like albuminoid bodies, yielding especially urea, but no sul-
phur compounds. It is doubtful whether they ever undergo
an upward metamorphosis into albumen ; but they may spare
the waste of this, and may save, and even nourish, the gelatin-
yielding ti.s.sues. Large cjuantities alone are useful for this
purpose ; when much gelatin is taken in the food, the urea is
increased in the urine, the specific gravity of which has been
known to rise to 1034.

One important inference from our ])resent knowledge con-
cerning the chemistry of the food in the body, is this : that all
food may be either oxidised after being merely absorbed, or as-
similated into the blood, as well as after its constituents have
been converted into tissue. This is sufficiently obvious as
regards carbonaceous and hydrogenous food, or the resparatory

VOL. II. N N

546

SPECIAL PIIYSIOLOGA'.

food ; but it is eqi;ally true of the plastic albuminoid and
gelatinoid substances. The excretion of urea is not so much
increased by muscular exertion, as was once supposed, but it
i.s largely augmented by an excess of nitrogen in the food (E.
Smith, Voit, Lehmann, Fick and Wiscileuus, and others).
The excess of any substance in the food, beyond that wliich is
necessary for the ti.ssues and for respiration,' is known as the
luxus consumption, or diet of hixury ; it reappears in an in-
creased excretion of urea, carbonic acid, and rvater.

Interesting deductions may be drawn, Irom comparing the
destination of the food in the Herbivorous and Carnivorous
animals. In the Ilerbivora, a very large proportion of the
carbon, hydrogen, and nitrogen, of the food, passes off undigested
from the alimentary canal; whilst in the Carnivora, nearly all
the food constituents are absorbed into the chyle or blood Of
the carbon which thus enters the blood, the ratio of that given
off by the lungs and skin, to that excreted by the kidneys, is,
in the Ilerbivora, about as 30 to 1, whilst in the Carnivora, the
proportion is only a< 10 to 1. Of the hydrogen absorbed, a
gTeater relative proportion is also found in the cutaneous and
pulmonary excretions, in the Ilerbivora, viz. 25 to 1, as com-
pared with the urine ; but in the Carnivora, the proportions in
the urine, as compared with the breath, are reversed, being as
3‘25 to 1. The nitrogen, in the Carnivora, passes almost ex-
clusively into the urine, the proportion to that in the skin and
lungs, being as 99 to 1 ; in the Ilerbivora, the ratio is only as
1'5 to 1. The excreta in a Carnivorous animal, represent also
the excreta of an animal fed on a pure flesh diet ; but those of
an Herbivorous animal, exhibit tlie results of an e.xcess in the
proportion of the carbhydrates, viz. an increased activity of
the pulmonary and cutaneous exhalations.

It must further be observed that the quantities of the al-
buminoid substances, or their derivatives, removed in a solid
form from the body, in the mucus and unused secretions of
the digestive canal, in the epithelium from other mucous mem-
branes, and with the epidermis, nails, and hair, are very .small,
and escape all active metamoiqdiosis.

Finally, the sum of all the chemical changes in the body,
is oxidation. The carbon of all the carbhydrates and hydro-
carbons, appears as carbonic acid, and their hydrogen and
oxygen, as luater. A portion of the carbon, hydrogen, and
oxygen, of the deconi2)Oscd albuminoid bodies, also appears in
the excreUi, as carbonic acid and water ; but a considerable

DEPRIVATION OF FOOD.

547

portion of these elements, witli the nitrogen, is discharged in
the Ibrm oiurea. The sulphur and phosphorus produce their
respective oxygen acids. For these changes, a larger amount
of oxygen, beyond that contained in the body, is needed ; and
this is supjdied by the atmosphere in respiration. It has been
computed, that 100 parts of dried meat require 1G7 parts, by
weight, of oxygen, for their disintegration in the body. The
results appear as 182 parts of carbonic acid, 52 of Avater, and
31 of urinary products; Avhilst only 2 parts escape unchanged
Iroin the alimentary canal. No pure carbon, hydrogen, or
nitrogen, is evolved from the body, but only cliemical combi-
nations of these elements, Avith oxygen, or Avith each other.
Ammonia is one of these. The minute quantities of carburetted
and sulphuretted hydrogen, sometimes disengaged, are jArobably
direct products of the decomposition of the food, and not the
results of vito-chemical processes. Of the carbon, 8‘8 oz. are
evolved as carbonic acid from the lungs, nearly OT oz. Irom the
skin; 0'34 oz. escape by the i;rine, and 0'71 oz. by the solid
excreta. All the nitrogen appears in the two latter excretions,
0’56 oz. in the former, and OT oz. in the latter.

The so-called respiratory, calorific, or heat-giving, elements
of the food, chiefly enter the blood, and there undergo oxi-
dation ; Avhilst the plastic, histo -genetic, or tissue-forming
elements, unless taken in excess, first build up the blood
corpuscles and the solid tissues, and then undergo oxidation ;
but these latter in reality contain fat and often sugar, Avhich
may be immediately oxidised in the blood ; and so even an
albuminoid diet, may in that case, act as respiratory food. This
must be the case in starving men and animals, in animals fed
on a pure flesh diet freed from fat, and, to a certain extent, in all
Carnivora. On the other hand, the carbhydrates are probable
sources of fat ; and fatty matter is essential to plastic or histo-
genetic processes. The distinction of the tAvo classes of food
is therefore, as previously sttitcd, inexact ; even the respinitory
food is more or less assimilated, as it enters the chyle and the
blood, and both the blood and the chyle are fluid parts of a
tissue. Hence even respiratory food is plastic, as regards
those fluids.

Ejfects of Deprivation of Food.

When an animal is entirely deprived of food, or Avhen the
quantity supplied is insuflicient to compenstite for the Avaste of

N N 2

548

SPECIAL PHYSIOLOGY.

the tissues, the weight of its body gradually diminishes, and it
ultimately dies of inanition or stai'vation.

The phenomena attending this condition, have been best
studied by Chossat.

The surface of the animal’s body, looks paler and withered, and the
skin seems wi-inkled, owing to the disappearance of adipose tissue.
The secretions become more scanty and concentrated, hence the mouth is
parched, and the digestive fluids wanting ; but the gall-bladder becomes
distended with thick tenacious bile. From the first, the m-ine is scanty
and strongly acid. The fieces are much reduced in quantity, are com-
posed almost entirely of greenish biliary matter, and, shortly before
death, contain an excess both of water and salts.

Nutrition is interrupted or arrested. A warm-blooded animal becomes,
after a time, restless and excited, and continues so till the last day of
life ; a sudden fall in its temperature then occurs, and it passes into a
state of almost complete insensibility. Birds, in this condition, no longer
attempt to fiy ; they sometimes gaze at surrounding objects, sometimes
seem to be asleep. The pulse and the respiration become gradually
slower, and the limbs cold. The general debility increases, until at
length, being unable to stand, the animal falls over on one side, and
does not again move. Diarrhoea always comes on during the last
twenty-four or forty-eight hours of life, and is attended with a peculiar
foetid odour of the body, a sign that decomposition is commencing. The
condition of stupor gradually becomes more profound, dilatation of the
pupil ensues, and the animal dies, death being sometimes ushered in by
violent contractions of the muscles of the back, so that the bod}' is
drawn backwards, a condition known as opisthotonos.

All the organs of the body suffer loss both in volume and weight,
though in very different degrees. Death usually occurs when the
animal has lost about ^ of its weight. In many cases, however, the
loss of weight is equal to more than i and in others to only i of that
of the body. This appears to be almost entirely dependent on the
quantity of fatty tissue contained in the body, before food is withheld,
the loss of weight being greater, the larger the amount of fat p>reviously
in the system.

In animals which had lost ^ of their weight, it was found that A
of the fat had disappeared, A of the spleen, — of the liver and pancreas,
^ of the heart, muscles, and alimentary canal — the latter at the same
time having undergone considerable shortening — A of the kidneys, A of
the respiratory organs, 1 of the bones, A of the eyes, and only A of the
nervous substance. Of the adipose tissue, the fat cells remain, the con-
tents alone being re-absorbed. The diminution in the quantity of the
blood, is very great, about 2 of it disappearing. Young and thin animals
suffer much less loss of weight, but they die sooner.

The duration of life appears to be but little affected, whether the
animal be allowed to drink, or whether it bo totally deprived of water.
It has, however, been shown that, if a dog bo kept without water, the
tissues and organs lose weight, almost in the same proportion as if it
had been deprived of solid food, with one exception, for there is little
diminution in the adipose tissue. Every tissue becomes drier ; but the

STARVATION.

549

glandular organs and the hrain do not suffer so much as the other parts.
There can ho no doidjt that the drinking of water in starvation, prolongs
animal life. The smaller Mammalia, and Birds, if tliey are at the same
time deprived of drink, usually die in nine days. Cold-blooded animals
live a long time witiiout food; frogs have been known to survive nine
mouths.

As shomi by experiments on Birds, the effect of starvation, is to
diminish the average temperature for the first few days slightly, but as
death approaclies, very rapidly, the fall being, in the last twenty-four
hours, about 25°. The greatest waste of tissue occurs in the fat, whilst
the nervous system scarcely experiences any loss ; so that the lowering
of the temperatm-e, and the fatal result, seem to be due to the loss of
oxidisable material, and not to a destructive waste of the nervous energy.
The fatty nervous substance may support itself at the expense of the
adipose tissue ; and this may, in part, account for the great waste of the
latter. The effects of exhaustion in long continued fevers, may be
similarly explained. The use of fat, as a restorative in the case of
starving animals, seems to be, that it interposes an easily oxidisable
substance, and so diverts the process of oxidation from the albuminoid
tissues ; and, in ordinary cases, it preserves the fat already stored up in
the body.

In tlie human subject, death from starvation is, though rarely,
but too frequently observed. At first, tliere is acute violent
pain over tlie region of the stomach, which is relieved by pres-
sure. In the course of ttventy-four or forty-eight hours, this
passes off, and is followed by a sensation of weakness and sink-
ing, which is principally felt over the same part. The mouth
becomes dry and parched, the breath is hot, the eyes are wild,
staring, and glistening, and there is sometimes a distressing
feeling of cold over the whole body. One of the most cha-
racteristic symptoms of starvation, is the intense thirst, which
now supervenes. The entire body becomes reduced to a
skeleton, the jtrominences of the bones are visible ; the face is
pale and corpse-like ; there is sinking of the eyes and cheeks.
A state of extreme debility ensues, so that the individual, in
attempting to walk, totters like a drunken man. He is unable
to make ;my efibrt, and sometimes has been observed to whine
and bur.st into tears. The voice gradually becomes feebler.
The weakness increases in intensity, and delirium supervenes.
A peculiar fetid odour emanates from the body, the suriace of
which becomes covered with a browni.sh offensAe e.xcretion.
Occasionally, the mucous membranes of the different ojionings
of the body, become red and inflamed. "The p.sychical functions
arc variously affected; .sometimes imbecility, at others idiocy,
is iuduced. During the fimine in Ireland in 1847, mania,
which, according to Jlo.shui, forms a prominent symptom in

550

SPECIAL PHYSIOLOGY.

starvation, was never observed (Donovan). A fit of maniacal
delirinin, or an attack of violent convulsions, Irequently, and,
indeed, commonly, precedes death.

The bodies of persons who have died from starvation, pre.sent
siojns of great emaciation, with dryness of the skin, all the fat
of the adipose tissue, and so much fluid, having been ab.sorbed.
The stomach and intestines are emjjty, and, like the other large
viscera, contracted and reduced in size ; their mucous mem-
brane is occasionally found ulcerated. The coats of the small
intestine, become ver}^ thin and almost tran.sparent, a condition
considered, by some, as quite characteristic of death from star-
vation. All the organs, except the brain, are almost destitute
of blood. The large vessels connected with the heart and lungs,
are collapsed and empty. The gall-bladder is distended Avith
bile, and the neighbouring parts are much coloured Avith this
fluid, from post-mortem transudation. In some cases, the
eyes are open, and exhibit an intense red colour, as if they had
been highly inflamed, resembling Avhat is sometimes seen in
persons Avho haAm died from exposure to cold. Decomposition
of the AA’hole body, quickly takes place.

The time that a Man can live Avithout food, has been vari-
ously estimated. It is generally supposed that a healthy person,
dejAi’ived of both solid and liquid food, Avould die in from seA'en
to ten days. Cases, hoAvever, are on record of men AAdio haAm
lived moie than three Aveeks, Avithout touching solid food.

DYNAMICS OF THE HUMAN PODY.

The chemical processes continually occurring in the nutri-
tion and Avaste cf the living animal body, throAv light upon
many other phenomena Avhich take place in it. Besides these
vito-chemical processes, it exhibits Auirions (hpiamic acts, viz.
pia'eli/ dipiamic, as in the performance of certain internal and
external mechanical Avork, by nervo-muscular action ; thermic^
as in the evolution of animal heat ; electric, as exemplified in
the currerts of electricity AA'hich constantly play through all
living nervous and muscular substance, and in the more
poAverful discharges of the electric fishes ; and lastly, ;)/(0G‘c,
illustrated by the evolution of light in the loAver animals.
The living animal body is, according to this A’iew, a machine,
in, and by, Avhich certain physical teerk is performed.

In the Inorganic Avorld, chemical, dynamic, thermic, electric,
and photic phenomena, are also continually occurring. They

ORGANIC AND INORGANIC FORCES.

r,51

are ahvays manifested in connection -with certain changes in
the condition of a material substratum, or matter^ and modern
physicists have arrived at the conclusion, that, however differ-
ent these phenomena may be from each other in their outward
manifestation, they may be referred, not to a different force in
each case, but to correlated forces, or to one force, or energy,
capal le of acting in many convertible modes. Each mode of
manifestation of force, has been experimentally'- shown to be
capable of giving rise to the others, or rather of changing into
them ; for it disappears in so doing, and equivalent quantities
of those other modes of action, are then called into play. Thus,
for example, aiTested mechanical motion, or friction, produces a
proportionate quantity of heat ; whilst heat, in the expansion
of water into steam, gives rise to motion. Chemical action, in
the explosion of gunpowder, produces motion, heat, and light,
and doubtless also electrical phenoniena, whilst the moving
cannon-ball develops heat as it strikes the target. Electricity
also will give rise to chemical action, motion, heat, and light,
and so on. Heat and all these other actions, are modes of
motion, either of the masses or of the molecules of matter. In
the various conversions of one into the other, there is neither
loss nor production, but merely a transmutation of force.

In the Organic world, similar manifestations of force occur :
chemical, dynamic, thennic, electric, and photic. The mate-
rial substratum concerned, consists of carbon, hynlrogen, ni-
trogen, sulphur, phosphorus, oxy'gen, and so forth, all being
elements which exist in the inorganic world. The ])heuomena
are invariably prodirced, only in connection with certain
changes in the condition of these elements and their com-
pounds. Hence, it seems probable, first, that these organic
manifestations of force, are likewise correlated within them-
selves ; and, further, that they are also correlated with the cor-
responding manifestations of force display’^ed in the inorganic
world ; that they' are the same both in degree and kind ; and
that they' are botli derived from a common cosmical energy,
the organic modes being, tor a time, operative in a special
sphere of action, but returnable again to the inorganic store.

By including, in one view, the Vegetable and Animal King-
doms of the Organic rvorld, the conversion of inorganic mate-
rials into organised matter, and its restoration back to the
inorganic world, may be readily traced. Ifiie carbonic ac’d,
the ammonia represented in the urea, and the water, wliich,
with certain .salts, are the ultimate products of the vito-chcuiical

552

SPECIAL PHTSIOLOGT.

processes of animal life, are the very substances needed for the
nutrition of plants. They are themselves actually unor-
ganised, or inorganic ; they are assimilated and deoxidised by
growing plants, under the influence of solar light and the for-
mative agencies of the vegetable cells, and, besides building up
those cells, they are combined into all the higher chemical pro-
ducts necessary for the food of animals, whether amyloid, oleoid,
or albuminoid. The Herbivorous animals, supported by these
products, transfer them to the Omnivorous and Carnivorous
animals, including Man himself. By animals, as we have
seen, these various products, oxidised by the air, once more
revert to the same simple chemical compounds destitute of
organisation. Now, the elementary substances, which enter
into the ascending or j;?’ogi'essive metamorphoses in plants, pass
out, after their ?’et?’ogressive metamorphoses in animals, with
all their properties and qualities unchanged. Engaged in the
organic vortex, vegetable and animal, they still retain their
nature. However freqirently subjected to this temporarj^ di-
version from the inorganic state, they are unchanged. It is dif-
ficult to suppose that in their condition as parts of organised
bodies, vegetable or animal, they manifest mere similitudes of
their inorganic forces, which they afterwards lay aside ; but
it is easy to comprehend, that they may carry vuth them, into
their new position, all their properties and energies, and exer-
cise them in the manifestation of those phenomena, which are
identical in both Departments of Nature.

The methods and reasoning employed in physical research,
in the examination of the various external natural phenomena,
may be applied to the study of the corresponding phenomena
in physiological science. As physico-chemical action, in the
inorganic world, is correlated with mechanical work, heat, elec-
tricity, and light, so, in the organic world, vito-chemical changes
may equally be associated with nervo-muscular or dynamic,
thermic, electric, and photic phenomena, and eA’eu with the
actions usually referred to the so-called nervous force. Thus, a
chemical change of blood or tissue, or of both, is es,sential to
muscular and nervous action, to the development, of animal
heat, to the electrical phenomena of living bodies, and to the
evolution of light in animals. So, too, certain mechanical Avork,
performed exclusively within the animal body, must, when
completed, pass into heat, as the result of arrest, concussion,
or friction. Heat, again, is necessjiry for the solvent processes
accompanying the digestion :md absorption of the food ; and

ORGANIC AND INOEGANIC FOECE?.

553

it exercises a -well-known influence upon, and often deter-
mines, the quantity of the chemical change and dynamic work
performed in the body.

In the Inorganic world considered exclusively, gravitation
and solar heat are the chief modes in which force is manifested.
The evaporation of water from the surface of the earth, its
conversion into clouds, its descent in the form of fogs, rain,
snow, or hail, the formation of glaciers, mountain-streams, and
rivers ; and the production of ascending, descending, and hori-
zontal currents in the atmosphere, are the evidences of these
forms of energy. Oxidation and other chemical changes,
though not absent, are comparatively inactive in the present
condition of the inorganic world.

In the Organic world, however, in plants and animals,
chemical change constitutes the most essential modes or forms
of force, and the source of the other forms of force manifested
by them. Under the influence of certain of the solar I'ays, dif-
tering from the simply heating raj'^s, viz. the luminous and the
actinic I’ays, the deoxidation and fixation of certain elements,
take place in plants; and iu these elements so fixed and
combined, a force, derived from the solar rays, is then stored
up. In animals, again, oxidation is the essential phenomenon,
an opposite chemical change occurs, the force stored up in the
animal blood or ti.ssues, which is but a transfer of that of the
vegetable constituents of thefood,is, together with the force pro-
per to the oxygen of the air, then liberated, and, by the special
organic apparatus of the animal body, is changed, as retjuired,
into other modes of action, Tnuscular, nervous, thermic, diges-
tive, or excretory, necessary for the maintenance of animal
existence. In supplementing the mechanical forces of nature
dependent on gravitation or solar heat, such as wind- and water-
power, Man has had recourse to chemical change, as a source
for the production of lieat and mechanical force. The carbon
and hydrogen of coal are made to unite with oxygen; from
this combination, heat is evolved; by this, water is converted
into steam ; and, by the expansive force of the latter, the re-
quisite motion is oljtained. An obvious comparison is here
suggested between a machine and the body, between the force
obtained by the combustion of dead matter and the oxidation
of the living tissues; and, la.stly, between the working of a
steam engine and the muscular movements.

In general j)hysics, restdts, to be of .scientific value, must
be expressed numerically. The quantity of fuel and o.xygen

554

SPECIAL PHYSIOLOGY.

undergoing change in combustion, is accurately determined by
weight or volume ; the relatii'e amount of heat evolved, is
ascertained and recoixled ; and if the heat be applied, as by ex-
pansion for mechanical purposes, the value of the work it per-
forms is exactly measured. By such means, the amount of each
kind of force manil'ested, is expressed in numbers, so that their
mutual eqirivalents, when they are transformed one into the
other, can be determined. The introduction of this method into
the domain of phj^siology, necessitates the determination of the
quantity of matter undergoing change by oxidation, and of
the work performed by it, in the living body. The results,
however incomplete, are full of interest and promise.

In comparing the animal body with a machine having its
source of poAver in combustion or chemical changes, it is usual
to make this distinction : in the latter, the force is entirely j
derived from the combvxstion of substances introduced into the
machine, and acts ujjon parts of the machine, them.selves
passive in the work ; whereas in the former, the parts of the
machine not only perform the work, but, to a certain extent,
their very matter undergoes the changes by which the force is
produced. In the steam engine, the heat and the mechanical
work are produced by the direct transformation of fuel distinct
from the machine itself; in the animal frame, the warmth and
motor force are evolved fr-om the direct transformation of the
iluids and solids of the living apparatus. As will be here- .
after seen, the quantity of work accompli.shed, in proportion to
the amount of chemical change which takes place, is far greater
in the animal body than in the most economical steam engine.

But, although the solids or fluids of the animal machine
undergo chemical metamorphoses, as the indisjDensable con-
dition of its action, the waste occasioned by those changes, is,
necessarity, ultimately supplied from the food. If food be
taken in e.xce.ss, as in the luxus consumption, it undergoes
oxidation in the blood, without passing into tissue ; if the
(juantity be normal, it enters both the blood and the tissues,
and then becomes oxidised ; lastly, if food be withheld, the
blood and the tis.sues undergo oxidation, they having been
themselves derived from previous!}'’ assimilated food. The
food is, in the last resort, the source and measure of the jwwcr
engendered, as a consequence of oxidation in the body. Ac-
cordingly, exact numerical estimates of the work accomplished
in the human body, must refer both to the amount of com-
bustible or oxidi.sable material in the food, and to that of the
products of its o.xidation found in the exci'ctions.

HEAT-UNITS.

555

The two most obvious forms of work performed in tlie living
bumun body, are the proper dynamic or mechanical work, and
the calorific woi'k. Besides these, however, there are the nutri-
tire work, and the mental work. The mechanical work isnervo-
muscnlar, and is associated Avith electric work. Some of it
is internal, siwh as that of the respiratory muscular ap^Aaratus,
especially of the diaphragm and intercostal muscles, of the organs
of circulation, the heart and arteries, and that of the pha-
rynx, cesophagus, stomach, intestines, and other internal mus-
cular organs. Other internal mechanical Avork is that per-
formed by the muscles Avhich maintain the position of the
body, by themu.scles of mastication, and by those of the organs
of speech and sense, and also the tonic contraction of the Avhole
muscular system. A very large part of the mechanical Avork
is, howcA'^er, ordinarily external, such as is manifested in the
movements of locomotion and labour. The proportion of the
internal to the external Avork, in a labouring man, is as 2 to
1. The calorific AS'ork relates to the formation of heat; this
is generated, as Ave shall see, either, in part, directly through
the oxidation of respiratory food, and, in part, indirectly from
the idtimate transiiirmation of the mechanical Avork of the
body into heat; or, according to some, it is entirely derived from
the latter source. The nutritive Avork is the digestive, absorp-
tive, assimilative, and secretive Avork, liquefacient or solidi-
lacient, often dialytic, attractive, or repellent. The mental
Avork is that Avhich is involved in the operations of the brain,
acting as the bodily organ of sen.sation, emotion, and thought.
The volitional Avork of the brain, and the non-volitional Avork
of the spinal cord and ganglia, in controlling the voluntary
and involuntary uiusclcs, cannot be separated from the exter-
nal and internal mechanical work perlbnued by those muscles.
Besides the electric Avork in Man and in animals generally,
special electric Avork is performed by many animals, and photic
phenoniena are manifested by a fcAv.

In considering the relations between the.se forms of Avork in ,
the human body, and the source of the ])OAver in the o.xidation
of the food, the following data, belonging to physical science,
are usually emj)loyed, the calculations being expres.sed in the
French metrical system, Avhich so readily adapts itself to such
u.ses.

Mcanurc of Heat, or Ikat-Uiiit.

The thermomrtrr morely .slioAv.s tlio tempcraturo of solid, fluid,

or giuseoiis sub-stancus. Tho actual <pianlitics of heat, necessary to pro-

556

SPECIAL PITTSIOLOGT.

duce changes of temperature, arc determined by the apparatus knoT\m as
a calorimeter ; and the quantity needed to impart, to a definite portion of
water, a definite warmth, is taken as a quautitatire standard. Thus a ‘
quantity of heat which will raise the temperature of 1 gramme (1 cubic
centimetre, or 15'543235 grains) of water, 1° centigi-ade (1’8° Fah-
renheit), is named a heat-unit, or calorie. Ten sucli heat-units will
raise the temperature of 10 grammes of water also by 1° C. ; but, acting
on smaller quantities of water, they will raise their temperatm’es pro-
portionally, as, for example, 6 grammes by 2° C., and 10 grammes by
1° C., and so on, of lOO’s or 1,000’s of heat-units.

Mechanical Coefficient, and Mechanical Equivalent of Heat.

Heat may produce work which is internal and direct, as in the lique- i
faction of solids, o.g. in the melting of metals, and the turning of ice into I
water, or in the conrorsion of fluids into vapour, as of water into steam, ■ j
or in the mere expansion of fluids or gases, as of mercury or air ; but heat J
may, also, act externally and indirectly, as occurs in the emploj-ment of
the expansive force of steam in machines or engines of various kinds. The '
quantity of work performable by heat, is very remarkable. Thus, starting
from the heat-unit previously determined, it has been shown liy ^Jlayer,
Joule, Clausius, and others, that such a heat-uuit, viz. the quantity of heat
which will raise the temperature of 1 gramme of water bj' 1° centigrade,
if utilised by being converted into mechanical work, is equal to the
lifting of the same weight of water, viz. 1 gramme, to a height variously
estimated at, from 421 to 433 metres, 424 metres being the number
usually adopted. Convoi’sely, the same force will lift 424 grammes, 1
metre high ; or twice that number, viz. 848 grammes, half a metre ; or 1
half that number of grammes, viz. 212, to a height of 2 metres, or 106 J
grammes, 4 metres, and so on for other quantities, larger or smaller. 'l
The mechanical coefficient of heat, is therefore 424, and the mechanical j
equivalent of 1 heat-unit, is expressed as 424 metre-i/rammes. For larger *
weights, mctre-ldlogranmies are tised ; and it is here that the decimal
notation of the metrical system, is so useful. Thus 1 kilogramme of
water (1,000 grammes) requires 1,000 heat-units, to raise its temperature,

1° centigrade; and these 1,000 heat-units will lift the same weight
of water, viz. 1 kilogramme, 424 metres high ; or, conversely, 424 kilo-
grammes, 1 metre high ; 212 kilogrammes, 2 metres: or 106 kilogrammes,

4 metres high, and so on. The mechanical equivalent of 1.000 heat-
units is expressed, therefore, as 424 metre-Zr/fogrammes (met. kils.).

In English works, the scale of temperature employed is that of Fah-
* renheit, of which 18° are equal to 1° cent. ; the weight is the lb. av.,
of which 2-2 are equal to 1 kilogramme, and the measure of height is
1 foot, of which 3'28 are equal to 1 metre. The mechanical equivalent
of a given quantity of boat, is expressed in foot -pound a. Thus the heat
which will raise the temperature of 1 lb. of wafer, l°Fahr., will lift that
weight, viz. 1 lb., to a height of 772 feet, or 772 lbs. to a height of 1 foot,
and so on ; hence the mechanical coefficient of heat, in this system, is
772, and its mechanical equivalent is expressed as 772 foot-pounds
(ft. lbs.). To reduce the English ft. lbs. into the French met. kils.. divide
the former by 7'216, which is the number obtained by multiplying the

CHEMICAL FORCE AND HEAT,

5j7

number of pounds in a kilogramme, by the number of feet in a metre,
viz. 2"2 X 3‘28. On the other hand, met. kils. multiplied by 7’216, are
changed into ft. lbs.

Not only is heat convertible into mechanical work, but mechanical
work may bo reconverted into heat, and the same equivalents, as before,
express the ratio between them. Thus a mechanical force equal to
lifting 1 kilogramme of water 42-1 metres high, will, when employed in
friction, blows, or otherwise, develop a temperature equal to 1,000 heat-
units, or will raise the temperature of 1,000 grammes, i.e. of 1 kilo-
gramme of water, 1° cent. In friction, for example, according to the
phj'sical theory, so ablj' expounded by Tyndall, that heat is a vibratory
motion amongst the molocides of matter, the resistance arrests, to a
certain degree, the motion of matsses of matter rubbed against each
other; but the visible motion so disappearing, is transferred to the mole-
cules, and so causes the invisible motion known to us as heat. The
frequency of these vibrations, increases in proportion to the sensible heat
produced.

Quantities of Heat developed bp the Chemical Process of Combustion.

In order to be able to determine the relation between chemical force
and mechanical work, it remains to be ascertained, what is the amount of
heat evolved by the combination of proportional quantities, or atomic
weights, of two or more elementary substances. The heat evolved in the
combustion of charcoal with oxygen, is thus measured, the heat itself
being supposed to be the result of an almost infinitely rapid motion of the
combining molecules, through almost infinitely minute distances. Ex-
periments made on the amount of heat imparted to water in a calori-
meter, have established the fact, that very different amounts of heat are
given off by burning equal weights of different combustible bodies. The
mode of estimating these varying quantities, is, by moasru’ing the
heating effects pi-nduced by the combustion in oxygen, of 1 gramme
weiglit of each substance, upon the standard gramme of water employed
in the calculation of the heat-units (Favre and Silbormann). In this
way, 1 gramme of carbon, in combining with oxygen in the act of perfect
combustion, to form carbonic acid, evolves as much heat as will raise
the temperature of 8,080 grammes of water, 1° cent. ; in other words,
it evolves 8,080 heat-units. Again, 1 gramme of hydrogen, in uniting
with o.xygen to form water, evolves 34,462 heat-units. Now, carlmn
and hydrogen are the two chief combustible or oxidisablo elements of
the food, the blood, and the solid tissues ; the nitrogen passes out of the
body unoxidised, but combined in the urea. Most of the carbon and
hydrogen escape from the system, completely oxidised, as carbonic acid
and water ; but some of each of those elements, especially of the carbon,
appear combined with a little oxygon, and also with the nitrogen in the
urea. Moreover, the quantity of heat given out by combustible bodies,
appears to be the same, wliether they are oxidised slowly or rapidly.
The physical data just explained, may tliereforo bo applied to the quanti-
tative examination of the relations between the ehomical changes occur-
ring in the human body, and the amount of mechanical and calorific
work performed in it.

558

SPECIAL PnrSIOLOGT.

Calorific Work of the Body.

The number of heat-imits given off by a dog in 24 hours,
having been ascertained to be 393,000, the number evolved,
in the same time, by a Man weighing seven times as much as
the dog, would lie 2,751,000 heat-units (Despretz). From
calculations ot the number of heat-units given off by the
body in various ways — by radiation, b)^ evaporation of water,
and by the warming of the respired air and excreta — it has
also been estimated that the daily loss, and therefore the daily
production of heat by it, amoimts to 2,700,000 heat-units
(Helmholz).

Com])cirison of the Baity Amount of the Animal Beat, with the Quantity of
Carbon and Hydrogen o.vidised in 24 Hours.

Now, the quantity of carbon in the daily food, according to Table A
at p. 539, is 9 93oz. or 281'2 grammes; the quantity of hj’drogeu, not
already combined with its due proportion of oxj-geu in the carbhydratps,.
is 0-64 oz. or 18'86 grammes. Deducting from these, the quantities
of those elements contained in the itrine and solid excreta, Table B,
viz. 106 oz. or 29'8 grammes of carbon, and 0'2 oz. or 6'3 grammes of
hydrogen, there remains a residue of 251 '4 grammes of carbon, and of
12'56 grammes of hydrogen, free for conversion into carbonic acid and
water. The 25P4 grammes of carbon, multiplied by its heat coefficient
8,080, produce 2,031,312 heat -units ; whilst 12’56 grammes of Imlrogen,
multiplied by its heat coefficient 34,462, give 432,842 heat-units, the
total being 2,464,154 heat-units (Vierordt). This calculation shows a
deficit in the heat, derivable from the combustion of the daily food, as
compared with that given off daily by the body, of about 286,800 heat-
units, or about ^ only of the total estimated qtiantity of heat given
off in the day. It has been supposed that the heat evolved by the
sulphur and phosphorus oxidised in the body, would go far to meet this
deficit. But iu 120 grammes of albumen, the supposed daily supply,
there are only 1'4 grammes of sulphur; and, as the heat coefficient of
this element, is 2,307, the heat from that source, pirovided all the sulphur
were oxidised, which is not the case, would only amount to about
32,300 heat-units ; the phosphorus would yield a somewhat smaller
number. Moreover, there are considerations which would appear to
make the deficit still worse. Thus, although the hvdrogen of the starchj'
food, is excluded by Vierordt, because, being present with oxygen in the
]iroport,ions to form water, it is probably already so combined, and
therefore unaldo to evolve any further heat of combustion, vet no
deduction is made for such hydrogen as may be balanced by the oxygen
in the fatty and albuminous food. In this fat and albumen, besides the
oxygen which passes out with the urea and the solid excreta, sufficient
exi.sts to unite tvith, and so neutralise about, 2 grammes of hydrogen ;
and if it be so combined, a loss of heat power must bo admitted, of about
68,900 heat-units. A small qtiantity of the carbon and hj’drogen of the
food, also disappears unoxidised as earburetted hydrogen. It is, fm'ther-

MECHANICAL WORK OF THE BODY.

559

more, usually maintained, that a certain quantity of chemical action is
transformed into external mochanical work, without being converted
into heat in the body ; and this quantity has been estimated as liigh as

235.000 heat-units. From these circumstances, the total deficit in
the heat-units of the food, ns compared with those supposed to be given
off from the body, would be 500,000, i.e. between i and i of the daily
heat.

This discrepanc}' may, however, be fully explained, by possible errors
in the larger data. Thus, the estimated weight of the human body, and
therefore the number of heat-units producible by it, in proportion to the
particular dog experimented upon by Despretz, may be too large ; or the
dilily supply of ctirbon and hydrogen in the food, may be underrated
for a man of the estimated weight. Vierordt himself elsewhere assumes
only 2,500,000 heat-units as the average daily quantity evolved by an
adult ; and the same number has been accepted by Carpenter as the pro-
bable number for a man weighing 180 lbs., i.e. much above the average
standard. The adoption of this number, would reduce the deficit to

300.000 heat-units, which would be provided for, by a daily addition of
37 grammes of carbon in tlio food, a quantity which would bo contained
in3oz. of starch, or liyoz. of fat. According to Playfair’s Tables (p.
563), such an additional quantity is actually consumed. The results of
improved methods of research and calculation, therefore, quite support
Lavoisier’s chemical theory of animal heat.

Mechanical Work of the Body.

The daily working power of a Man, and the actual mechanical work
done, according to his individual strength, must vary greatly according to
the exercise or labour he undergoes. It is said that a Man can raise
100 lbs., 1 foot in a second, for 8 or 10 hours in the day ; that, on level
ground, ho can draw 640 lbs. weight ; that he can lift 286 lbs. with both
hands, and support on his shoulders, 330 lbs. The daily work of a Man,
is said to be between i and l of that of a horse. More exact compu-
tations show, that with severe labour, the daily work of a Man is equal
to 207,871 met. kils. or 1,500,000 ft. lbs. (Kanken) ; with moderate
labour, it is not more than 66,518 met. kils. or 480,000 ft. lbs. (llanken).
The work performed by pedestrians, has been estimated at 109,570 met.
kils. or 790.720 ft. lbs. (llaughton). In marching, a soldier exercises
a tractive force equal to A, of the weight of his body, arms, and
accoutrements. The coefficient of traction, is therefore expressed as
being of the weight to bo moved ; hence a soldier weighing 150

lbs. with 60 lbs. of weight to carry, and marching 14 miles per day,
performs work equal to 107,560 met. kils. or 776,160 ft. lbs. (Playfair).

Thus, 150 + 60 -^ 20 lbs. x 14 x 5,280 feet= 776,160 ft. lbs.

The mean of 9 estimates of laborious work, according to various au-
thorities, is 105,605 met. kils. or 762,048 ft. lbs. This reprcscnls the
daily external mechanical work of the body. Of the internal mechanical
work, a large portion, which is usually referred to the external work, is
that which poises the body and supports it. Ni'xt to this, is the true
internal work, of which the most is performed by the heart, which has
been estimated by one authority at 37,871 met. kils. or 273,280 ft. lbs.

560

SPECIAL PHYSIOLOGY.

(Haugliton) ; and by another at 70,000 met. kils. or 492,520 ft. lbs. in
24 hours ; the daily work of the left ventricle alone, is estimated at
46,000 metre-kilogrammes (Vierordt). Another estimate gives 43,000
met. kils. for the left ventricle, and 21,000, for the right ventricle,
making a total of 64,000 (Bonders). According to the lowest estimate,
the work of the heart, which is always beating, is equal to more than
i, and, according to the highest, to nearly f, of the total daily external
work. Taking the, highest estimate of the heart’s work, and adding it to
the mean labour-work of Han, as above estimated, we arrive at the sum
of about 175,600 met. kils. To this must also be conjoined, the work of
respiration, i.e. of the diaphragm and the intercostal muscles, 63,000
met. kils. (Bonders), the work of the digestive organs, and other in-
ternal mechanical work, which will probably raise the total daily
mechanical work, external and internal, performed by a man engaged in
active employment, to the sum of 250,000 met. kils. From other
calculations, Vierordt adopts 200,000 met. kils. but exclusive, as it
would seem, of the internal work. Again, the actual mechanical elFort,
or work accomplished by a muscle, is equal to the product of the weight
lifted, mriltiplied by the height to which it is lifted. Thus, with a
frog’s muscle, Weber found that 5 grammes were lifted 27’6 millimetres,
15 grammes 25'1 mm., 25 grammes ll’45mm., and 35 grammes 6’3
mm. The products of these numbers, showing the work accomplished in
each case, are respectively 138, 376, 286, and 220 gramme-millimetres.
Hence, although the work effected, at first Increases with the load, it
soon reaches a maximum, and then diminishes. Since even' muscle
becomes exhausted by work, and requires intenals of rest for repai-ation,
it is necessary, in order to determine the actual mechanical work accom-
plished by a Man or animal, to take into account the element of time.
in this way, it has been estimated that the mechanical work of a Man, is
represented by 7 met. kils. per second, and that of a horse, by from 60
to 70 met. kils. Allowing 8 hours workout of the 24, the daily work of
a Man would be 201,600 met. kils. (Eedtenbacher). The average work
per second, throughout the day, would bo 2'3 met. kils.

In the steam engine, the amount of heat evolved by the fuel con-
sumed, is sometimes 30 times, and, in the most economical engines, 20
times, greater than the quantity converted into useful mechanical work :
theoretically, the utmost available mechanical power is only -A j>art of
that producible by the heat of the coal consumed. But in the human
body, the economy of combustible material is much gi'cater. The total
amount of heat given off from the body, in 24 hours, has been sho^vn to
be from 2,500,000 to 2,750,000 heat-xinits. Tlie former or smaller
quantity would lift a corresponding number of gi'ammes, or 2,500 kilo-
grammes, to a height of 424 metres ; and would therefore yield a me-
chanical equivalent of about 1,060,000 met. kils. or about 5 times as
much as that which is requisite for the total daily work, viz. 250,000
met. kils. Whilst, therefore, in an engine, A part only of the fuel con-
sumed is utilised as mechanical power, i of the food absorbed by iMan
is so appropriated. This latter proportion agrees with Ilclmholz's
calculations.

SOURCES OF HEAT AND WORK.

561

Relations of the Kinds of Food, to the Modes of Work.

The calorific and mechanical work of the body, being thus
understood to have their immediate source in the power stored
up in the food and in the oxygen of the air, and which is set
free on the occurrence of chemical combination between them,
after such food is assimilated into blood or tissue, — it may be
admitted that, allowing for certain errors of calculation and de-
ficiencies of knowledge, the numerical or quantitative method
shows that sufficient matter is oxidised in the body, to account
for both those modes of work. It must, however, next be en-
quired, what are the relations of the different kinds of food to
these two different modes of work.

It has long been observed, that the carbon in the carb-
hydrates and hydrocarbons, or amyloids and oleoids of the
daily food, greatly exceeds that contained in the nitrogenous
or albuminoid food. In Table A, p. 539, the ratio is shown
to be 7'64 to 2'29, or rather more than 3 to 1 ; the number of
heat-units developed by the former, would of course be pro-
portionally large. If to this carbon, be added the hydrogen
not united witli oxygen, this portion of the food seems to be
the obvious source of calorific power in the body. Vierordt
remarks, indeed, that, if from the carbon and hyclrogen of the
nitrogenous food, enough of those elements be deducted to form
the urea excreted by the kidneys, a quantity remains, totally
insufficient to develop the heat-units neces.sary for the calorific
work ; for then only 57‘3 grammes of carbon and 6'3 grammes
of hydrogen, will be left, which, multiplied by their heat co-
efficients 8,080 and 34,4G0, yield a total number of 680,082
heat-units, Avhich is only about ^ of the required daily
amount, viz. 2,500,000. The non-nitrogenous ibod, in ac-
cordance with the general opinion, is, therefore, regarded as the
essential source of the aninud, heat. Indeed, 22 oz. of starch
alone, not an unusual quantity in certain daily dietaries. Tables,
p. 563, wotild yield 2,187,000 heat-units.

As regards the mechanical work, it is well-known that this,
whether internal or external, involuntary or volunttuy, is per-
formed through ncrvo-mu.scular action ; that this implies
fatigue and waste of the muscular .-.md nervous substance ; that
so long as muscular contractility lasts, so long do oxidation
changes go on in a muscle ((r. hiebig) ; that a due supply of
oxygenated blood is necessary lor the continuance of this con-

VOL. II. 0 0

552

SPECIAL PHYSIOLOGY.

tractility ; and that the quantity of carbonic acid contained in
the venous bloodreturning from muscles, is in direct proportion
to their activity. It is further certain that the muscular and
nervous tissues must be largely siq^plied by the nitrogenous
or albuminoid portion of the food. From these liicts, it might
Avell be inferred, that the mechanical or nervo-muscidar work
of the body, has its immediate source in the transformation
and oxidation of the muscle itself, and, therefore, in the so-
called histogenetic, plastic, or Hesh-forming nitrogenous food.
The opinions and practice of agriculturists, railway contrac-
tors, and trainers of men destined for athletic sports, further
indicate, that a proportional increase in the quantity of Hesh-
fonning food, is believed to be necessary for animals or men
engaged in severe or protracted labour.

The teaching of Liebig, on these points, is indeed very precise and
decided. According to him, the hydrocarbons and carbhydrates are the
exclusive hoat-fomiers ; whilst the sole source of mechanical power, is
the oxidation of the nitrogenous substance of the muscles and nerves,
built up again by the albuminoid or plastic constituents of the food.
These views have been very generally accepted, and liave been especially
supported, amongst others, by Eanke, Draper, Playfair, and Odling.
Draper says of muscular contraction, that it may be supposed to be due
to disintegration of the sarcous particles, and that the transformation
of muscle by oxidation, may be tlie condition of muscular action. Odling
regards the combustion of the carbon and hydrogen of fat, as liberating
a force exhibited solely in the form of heat ; whilst the combustion of
an equal quantity of the carbon and hydrogen of voluntary muscle, is
' expressed chiefly in the form of motion.

Playfair has endeavoured to show, on numerical grounds, that although
the chemical combination of the carbon and hydrogen of the albuminoid
food, with oxygen, is insuflflcient to account for the calorific work, yet it
is adequate to produce the mechanical work of the body. Hence he con-
cludes that it is the ultimate magazine of force, for the production of its
dynamical operations. The following are the jJrincipal facts and argu-
ments to which he directs attention.

From numerous English and foreign sources, he has collected a series
of dietaries actually in use, under various conditions of rest or work, of
which the annexed Table A, gives only the mean results. The starch
equivalent includes the actual starch of the food, together with the carbon
and hydrogen of the fat, expressed as starchy matter, 1 part of fat being
considered equal to 2A parts of starch. The siihsisfcnce diet, is that
which is considered neccs.sary to support life in a condition of rest, or the
diet necessary for the vital mechanical work of the body ; it is illustrated
by the convalescent diet of hospitals, and by the low diets of ill-fed
persons. The diet needful for active emplo^-iucnt in health, is repre-
sented by the diet of soldiers during peace. An improved diet necessary
tor more arduous work, is that given to soldiers during war. The diet of
active labourers, is exemplified in that of the corps of Hoyal Engineers

SUBSISTENCE AND OTnEK DIETS.

563

engaged in civil employment. Lastly, a still fuller diet, is that of
labourers and others employed in yet more continuous and heavy work.

A. Mean results of Dietaries hi oz. avoirdupois.

1

1

1

tn

u

o

a

«s

J3
So S

1 equi-
lent

B

c 0

n and
givers

fl

0

3=1

0

1

1

%

o

•55
a “

''0 C5

tn

0

f-g

9.^

'eS

0

b,

03

03

03

Subsistence diet

2-33

■84

11-69

13-68

_

7-469

Soldiers’ diet
during peace j

4-215

1-847

18-69

22-059

•714

2-267

9-72

11-987^

1 Do. during war

5-41

2-41

17-92

23-48

■68

2-9

9-81

12-71

j Do. in civil "1
1 work j

[ Diets of la- '(
bourers /

5-08

2-91

22-22

29-38

■93

2-73

12-113

14-844

5-64

2-34

20-41

25-97

—

—

—

13-89

1

B. Average Quantities in oz. of different Food Constituents, consumed
under different conditions of rest and work {Playfair').

Food Constituents

Sub-

sistence

diet

Diet in
quietude

Diet of
healthy
adult

Diet of
active
labourers

Diet of
hard-
worked
labourers

Addition
required
for active
labourer

Flesh-formers

2-0

2-5

4-2

5-5

6-5

3-5

Fat .

O'D

1-0

1-8

2o

2-5

2-

Starch .

12-0

12-0

18-7

20-0

20-0

8-

Starch equivalent.

13-2

14-4

22-0

26-0

26-0

12-8

Carbon

6-7

7*4

11-9

13-7

14-3

7- 1

The subsistence diet in Table B, is supposed to show, amongst other
facts, the quantity of albuminoid food consumed in the performance of
the absolutely essential internal mechanical work of the body, when at
complete rest. Taking this as a datum quantity, the additional amounts
consumed in quietude, in full health, in active labour, and in hard
labour, arc ’o, 2'2, 3'5, and 4‘5 oz. In extreme labour, the quantity
of flesh-formers, is, therefore, more than trebled, as compared with the
subsistence diet. The starch equivalent is also increased, being, how-
ever, only doubled. This increase, Playfair considers as coincident with
the additional animal heat given off in increased exertion, during which
all the functions, digestive, assimilative, circulatory, and respiratory, are
much excited. An increased consumption of non-nitrogonous food, is not
only demanded by an increased waste of the nitrogenous tissues, but it
may even cause the latter, by exciting the animal functions. As, for
an active labourer, 3-5 oz. seems to bo the additional amount of albu-
minoid food needed beyond the subsistence diet, so a horse, when at work,

564

SPECIAL PHYSIOLOGY.

is said, by Playfair, to consume 27 cz. more nitrogenous food than
when at rest. The proportion between these superadded quantities, iu
the Man and the horse, is about 1 to 7^, and, as already mentioned, the
horse’s daily work is estimated as being equal to that of 7 or 8 men. It
is further stated, that the work of a horse, is to the work of an ox, as
1-43 to 1 ; whilst the total albuminoid food consumed by those two
animals, when engaged in labour, is as L46 to 1. In animals fed exclu-
sively upon a flesh-diet, allowance being made, when necessary, for the
fat contained in it, Bischoff, Pettenkofer, and Voit, found that the carbon
excreted in the urea, is about ^th of the quantity given off iu the form of
carbonic acid ; hence Playfair supposes that 1 part of albumen, if oxi-
dised by 100 parts of oxygen, may be transformed into3T, or about 3
parts, of urea, which would contain 3 of carbon, into 21 parts of carbonic
acid, which would contain 21 of carbon, and into 13 parts of water. The
carbon in the urea and carbonic acid, is, here also, as 1 to 7. Urea itself
is regarded as a compound of carbonic oxide and ammonia, and its carbon,
as being only partially oxidised. Of the h}’drogen, three-fourths are
deducted, as being either already combined with oxygen, or as belonging
to the ammonia. The heat-units are accordingly calculated for so much
carbonic acid, carbonic oxide, and water, and also for sulphuric acid formed
by the sulphur of the albumen. One ounce of albumen, 437'o grains,
or 28'35 grammes, if thus decomposed, would yield 126,500 heat-units,
the mechanical equivalent of which, is 53,762 met. kils. Hence the 2 oz.
of flesh-formers iu the subsistence diet, would afford 107,524 met. kils.
of work, which exceeds the essential vital work performed in the body
in the condition of convalescence, the, work of the heart representing
the largest item of the internal mechanical or vital work, being taken
at 37,781 met. kils., which, however, is too small an estimate. -Again,
the 3i oz. of additional albuminoid food consumed by the active labourer,
are mechanically equivalent to 188,167 met. kils.; whilst the mean
amount of laborious work, is only equal to 105,605 mot. kils. Lastly,
the 6^ oz. of albuminoid food consumed by the active labourer, jdeld
295.691 met. kils.; whereas his total mechanical work, external and
internal, is, as we have seen, only 250,000 met. kils Even if each of
the above-mentioned mechanical equivalents of the albuminoid food, be
reduced by one-twelfth, for that which passes off in the solid excreta with-
out undergoing combustive change, still, in each case, enough power re-
mains, derived from the oxidation of the albuminoid food, to execute
the mechanical work, whether internal or external, performed by the
body.

It is maintained by Playfair, that the blood cannot bo the source of
the motor power, but this opinion is open to question. The quantity of
fat in muscular tissue, only 2 per cent., is .too small to accomplish it.
The fat in the heart, could only yield 10,157 met. kils., whilst the work
of the heart is estimated as equal, at least, to 37,780 met. kils. In 4 oz.
of dried flesh, there would be 150 grains of fat, which would yield 36,888
met. kils., whilst that amount of muscular substance itself, would yield
214,544 met. kils. The fat of muscle being therefore wholly inadequate
to produce the mechanical work, it is pri'sumed, by Playfair, that tlie
larger quantity yielded by the muscle itself, must be reg-arded as its
source. Moreover, the fatty substances, ns we know, are wanted for
heat-giving purposes. They are required, we may add, to supply the

UREA AS A MEASURE OF WORK.

56.5

waste of the nervous substance in muscular action ; and tlie ftit in the
muscles, may protect them from oxidation, when no movement is taking
place; but fat alone cannot act vicariously as a substitute for albumi-
noid food. In starving animals, the fat wastes gradually day by day,
undei-going oxidation at an equal daily rate, whilst the muscle wastes
irregularly, at first slowly, then more uniformly, but, at the approach of
death, very slowly indeed, the mechanical work, external and internal,
being reduced to a minimum.

The amount of albumen allowed in the dietary of Vierordt (p. 539),
after deducting the urea, and ^th for loss by the solid excreta, would
yield 680,000 heat-units, or a mechanical equivalent of 261,152 met.
kils., a quantity closely corresponding with the amount obtained by
Playfair’s calculations, and likewise exceeding the estimated total daily
mechanical work of 250,000 met. kils.

The small balance of unemployed force, is regarded by Playfair as
proving the extreme economy of the operations of the living body. If,
indeed, the mechanical work derived from the chemical energy developed
in the oxidation of 3^oz. of excess of albuminoid food, viz. 188,167 met.
kils., be compared with the external mechanical work of an actively em-
ployed labourer, 105,605 met. kils., the proportion of actual work to the
total producible energy is about as 1 to If. In comparing the total work
performed, 250,000 met. kils., with the total heat produced from aU the
food, 295,691 met. kils., more than |thof the chemical energy developed
are utilised, instead of ith, as estimated by Hehmholz, and others, and
instead of ^th, as is the ease in the best steam-engines. Every particle
of energy developed in the body, is probably, in some way, usefully
employed.

The researches of the Rev. Dr. Haughton on excreted pro-
ducts, taken as the measure of work, bear on this question
of the source of motor power in the body. By determining
the quantities of urea excreted by the kidneys, under different
circumstances of rest and labour, he endeavours to ascertain
the potential energy represented by the urea, considered as a
product of the decom[>osition of the albuminoid tissues. The
work of th.e body, is classified, by him, into vital, mental, and
mechanical. These he supposes to be represented resjiectively,
by the daily excretion of 297, 217, and IdG’h grain.s, making
a total of 050'5 grains of urea: the total daily amount e.x-
creted by a person engaged in very active bodily and mental
work, is, therefore, 050’5 grains. In routine labour, he infers
that -loo grains of urea are sufficient to represent the vital and
mechanical work ; but, in higher work, he allows 5313 grains
of urea; and regards 575 grains, as the average for a healthy
actively engaged adult. As 1 part of urea repre.sents 3T parts
of dried albumen, this daily average quantity of urea, viz. 575
grains, represents 3‘!) oz. of dry albuminoid food ; 400 grains,
2-8 oz. ; and 050 grains, 4'3 oz. This quantity is thus ap-

566

SPECIAL PHYSIOLOGY.

portioned by Haugbton ; for the vital work, 297 grains, repre-
senting 2 oz. of albumen; for the mental work, 217 grains,
representing 1’4 oz. ; and for the mechanical work, 136-5 grains,
]-epresenting -9 oz. To raise these quantities into the actual
quantities of allniminoid food consumed, T-Vtli more must be
added, in each case, for the albumen eliminated, luichanged, in
the solid excreta. Then it will be seen that the quantity of
urea taken to represent the vital work, is more than equal to
the desh-formers in the subsistence diet of Playfair. But the
quantity said to correspond with the external mechanical work,
is insufficient, rejrresenting, even with an addition of yVth, less
than 1 oz. of albuminoid food ; whilst the mechanical work of
an active healthy adult, demand.s, according to Playfair, an
extra quantity of 2'2 oz. of flesh-formers, beyond the sub-
sistence diet. The large qmintity allotted to mental work, is
perhaps excessive, and may supply the deficiency ; for the
quantity of albumen corresponding with the total amoimt of
urea, is 4'4 oz. ; this, with its superadded j^th, would more
than equal the full diet of Playfair, though it would not ap-
proach the 5'5 oz. diet of the active, much less the 6'5 oz. of
the hard worked, labourer.

But the estimates of Ilaughton, as to the quantity of urea
excreted daily under conditions of labour, are less than the
quantities which have been observed by others. The quantity
in convalescence, and in cases of starvation or hunger-cure,
ranges from 263 to 300 grains; the average qirantity in health,
appears to vary from 560 to 580 gi-ains; and the quantity
excreted daily, by hard-worked labourers, has been found to
differ, according to their work and food, from 600 to 700. or
800 grains. In Hammond’s e.xperiments on himself, whilst
without exercise, the quantity of urea excreted daily, was 487
grains, and of uric acid 24’9 grains, — the quantities of those two
substances excreted in moderate e.xercise, were 682 ’1 grains,
and 13'7 grains ; and, in hard exercise, as much as 865 grain.s,
and 8 -2 grains. The quantity of urea which corresponds with
5-5 oz. of albuminoid food, the active labourer’s diet, is 735
gi-ains. The estimates of Ilaughton are evidently low ; if
augmented, in accordance with the ob.servations of others, as
to the increase in the urea excreted during I’ull exercise, and
'with a full diet, they might, at iirst, ajipear to harmonise with
the view, that the chemical energy developed by the o.xida-
tion of the albuminoid food, is the source of all the mechanical
work performed in the bodv. The production of the urea, is

DREA NOT A MEASURE OF WORK,

567

not supposed, by itself, to develop the energy recpiired; bnt
this substance is an index to the quantity of albuminoid sub-
stance oxidated, in the body, into urea, carbonic acid, water,
and sulphuric acid. This urea can be easily separated and
weighed ; but the carbonic acid and w'ater, derived from the
partial oxidation of the albuminoid food, mixing with the
much larger quantities derived from the carbhydrates and
hydrocarbons, completely escape measurement.

But the theory of Liebig (1842-51), as to the special soiuce of the
motor power of the system, thus illustrated by arguments and calcu-
lations, derived from an advanced state of knowledge concerning the re-
lations between chemical action, heat, and motion, is opposed by many
authorities, especially by Mayer, Traube, Donders, Heidenhain, more re-
cently by Pick and Wislicenus, and, in England, by Lawes and Gilbert,
and by Frankland. The experiments of Lehmann, Ed. Smith, Voit,
BischofF, Speck, and Dr. Parkes, have assisted much to elucidate this
subject.

It was long ago maintained by Mayow, of Bath (1681), that, for the
occurrence of muscular action, combustible material, fat, must be con-
veyed by the blood to the muscles, together with some principle derived
from the air in respiration. According to Mayer, of Bonn (1845), an
early obsen^er in the field of quantitative research as regards heat and its
relations to other forms of force, a muscle is not the material by the
chemical change of which, mechanical work is produced ; but an appa-
ratus by means of which, the transformation of force is accomplished.
If the former were true, he argues that the heart woidd be completely
oxidised, in doing its own work, in 8 days. He believes the capillaries
of the muscle, to bo the seat of the actual changes, and the blood to
be the fuel consumed. Traube also has distinctly taught, that the sub-
stances, by the burning of which, force is generated in the muscles, are
not the albuminoid constituents of those tissues, but non-nitrogenous
substances, either fats or carbhydrates. Bonders and Heidenhain coin-
cide in these views.

It has, moreover, been found that the amount of urea excreted, is regu-
lated, not so much by the exorcise taken, as liy the quantity of albuminoid
food which is consumed. Hence much of this substance must be formed
independently of the metamorphosis of muscle; and therefore Haughton’s
estimates of it, as a measure of work, become seriously invalidated.
Lastly, much uncertainty prevails, as to the accuracy of the data em-
ployed for the calculations of the heat given off in the oxidation of
albuminoid food, and, therefore, as to the correctness of the deductions
from them, made by Viorordt, Playfair, and others. Thus, Lawes and
Gilbert (1852) obscn'cd, that of two pigs fed, one on lentils, which
contain 4 per cent, of nitrogen, and the other on barley, which con-
tains only 2 per cent., the excreta of the former yielded twice as
much nitrogen as those of the Latter; from which they infer that the
quantity of urea excreted, fie. of albuminoid substance decomposed, is no
guide to the amount of work done, the o.xorcise taken having been the
same in each case, but that it depends on the quantity of nitrogenous

568

SPECIAL PHYSIOLOGY.

food consumed. They, moreover, conclude that some of the muscular
power depends on the oxidation of non-nitrogenous substances. Again,
the researches of Edw. Smith, Voit, Lehmann, Bischoff, and Parkes,
indicate that the urea excreted, bears no definite relation to the labour
performed ; and that in prolonged exercise, the increase of urea is very
small. The cfiFects of treadwheel labour, serve only to increase the quan-
tity of urea, by 19 grains in 24 hours, as compared with that eliminated in
easy labour’ (Smith). In fasting animals, the effects of increased exertion
are also very slight as regards the urea, and seem to be regulated by
the periods of ingestion of water, and by the increased respiration and
circulation, rather than by the direct waste of the voluntary muscles
(Voit, Bischoff).

Lastly, the exqreriments of Dr. Edw. Smith prove, on the other
hand, that the production of carbonic acid does increase, strictly in
accordance with the exercise taken. During sleep, the quantity exhaled
in an hour was, in his own case, 19 grammes ; whilst lying down before
sleep, 23 ; in a sitting postiu-e, 29 ; whilst walking two miles an hour,
70’5 ; in walking throe miles an hour, 100'6 ; and upon the treadwheel,
lifting his body, 28’65 feet in a minute, as much as 189’6 grammes per
hour.

The recent observations of Fick and Wislicenus, on the results
of a certain amount of work performed by themselves, also point to
the conclusion, that muscular eflbrt, on a non-nitrogenous diet, does not
increase the quantity of urea excreted from the body ; moreover, they
conchide that the oxidation of the quantity of albuminoid substiince, or
plastic nitrogenous material, w’hieh would correspond with the urea and
other nitrogenous compounds then excreted, does not yield sufficient
potential energy to perform the work accomplished. The mechanical
work undertaken by them, was the ascent of the Faulhorn, a mountain
in the Bernese Oberland. From the middle of the day before, until the
ascent was completed, no albuminoid food was taken, so that no excess,
or luxiis consumidion, might interfere with the experiment. Diu’ing 11
hours of the night previous to the ascent, the quantities of urea excreted
by them respectively, were by Fick, 12’5, and by Wislicenus, 11 ’75
grammes. During the 7 hoiu’s and 40 seconds occupied in the ascent,
or work-hours, i.o. from 10 min. past 5 a.m. to 20 min. past 1 p.m., the
quantities were 7' and 6'7 grammes. During the next 5 horirs and 40
min. of rest, or after work, in which an abundant meal of meat was con-
sumed, the quantities were O’ and o’l grammes. The quantity of urea
excreted per hoiu’ was, therefore, increased during exercise on a non-
nitrogenous diet. In determining the relation between the quantity of
albuminoid substance decomposed, and the mechanic;il work pcrforincd,
tlioy take into account not only the urea, but tlie whole nitrogen eliminated
in a more or loss oxidised form, and they find that this, during the actual
period of work, would represent in F. 22’098, and in W. 20’89 grammes
of albumen. The minute trace of nitrogen given off from the skin, is
neglected, and so is the larger quantity contained in the fieces,
because it passes off in almo.st unoxidi.sed compounds. The possible
retention in the system, of some partially oxidised albuminoid sub-
stances, such as creatin, is admitted ; but to compensate for this, they
adil a quantity of albumen, equal to the nitrogen excreted in the period
of after work, making the respective totals, 37’17 and 37’ grammes of

REAL SOURCE OF MOTOR ROWER.

5C9

albumen oxidised. The heat given out by the oxidation of these quan-
tities in the body, is unknown ; but from avowedly imperfect data, and
making the fullest possible allowance, they conclude that the energy
obtainable from its oxidation, might bo for F. 250,000, and for W.
249,000 heat-units ; giving respectively 106,250, and 105,825 met. kils.
of mechanical power. Now the chief work actually performed by them,
was lifting the weights of their bodies, as clothed, through the lieight of
the mountain ; this is measurable by nndtiplying the former by the latter.
Thus F. exerted a force of 66 kil. x 1,956 metres= 129,096 met. kils.,
and W. a force of 76 kil. x 1,956 metres = 148,696 met. kils. ; if to this,
bo added the internal work of respiration and circvdation, the totals
are for F. 159,637, and for W. 184,287 met. kils. These results show,
therefore, that the moan work performed, in proportion to the power
derivable from the oxidised albumen, was as 3 to 2. It is well known,
however, that much other work is performed in the exercised body,
which does not contribute directly to the external work performed ; and
Heidenhain has computed that only one half of the energy of the force-
generating processes, is really used as work. Hence, double the amount
of work was actually performed in the bodies of F. and W., or 319,274 and
368,574 met. kils. ; in other words, the ratio of work performed, to the
power derivable from the consumption of albuminoid substances in the
body, was as 3 to 1. Since, therefore, it is impossible for the oxidised
albumen, to be the sole and exclusive source of the power manifested in
the work of the body, to which it can contribute so little, they conclude
that the oxidation of non-uitrogenous substance, must yield, at least,
the larger proportion of the force required, not only for the production
of heat, but also of mechanical motion. Moreover, since it is improbable,
that, in so delicately an organised apparatus as the muscular tissue, two
sorts of decomposition should occur, for the purpose of liberating the
same force, they believe that, as non-nitrogenous substances are decom-
posed for that ‘purpose, those only are decomposed. The nitrogenous sub-
stances of the muscle, however, simultaneously undergo waste or wear,
and thus yield urea. In conclusion, they show that the resemblance of the
living animal body to a steam-engine, is more close than is usually
admitted; the muscle is an apparatus for burning its appropriate fuel,
the hydro-carbons and carbhydrates, in the same manner as an engine
burns its proper fuel, coal or coke; in action, the muscle does not
specially oxidise itself, any more than the engine is burnt ; but in action,
both the muscle and the engine undergo wear. In use, the wear, in
either case, is not much increased, but the consumption of fuel is
decidedly greater. It is possible, they remark, either that non-nitrogenous
substances in the muscle, act as the combustibles, or that they pass
through the muscle in a rapid stream, their particles being immedititely
oxidised, and then carried away. ,

The general conclusions of Fick and Wisliconus, are strongthoned by
the subsequent researches of Dr. Frankhuul, who has also suppliedmore
secure data, for estimating the heat-units produced by the oxidation of
albuminoid substances in the body. It was admitted by the German
physiologists, that these could not Ijo equal to the heat-units evolved by
the combustion of the separate elements of allmmon out of the body,
although they allowed that quantity in their calculat ions. Hy mixing a
certain quantity of musek deprived of fat, albumen, and urea, all dried at

570

SPECIAL PIIYSIOLOGT,

212° F., with chlorate of potash, deflagrating the compounds, and measur-
ing the heat evolved, by its effect in raising the temperature of water, Dr.
Frankland shows that 1 gramme of each of these substances respectively
evolves, 5,103, 4,998, and 2,206 heat-units. Now, as the muscular sub-
stance is imperfectly oxidised in the body, forming urea, or some still less
completely oxidised material, it can only yield the above-mentioned
number of heat-units, minus the number producible by the quantity of
the imperfectly oxidised nitrogenous substances into which it is converted
in the system. Albuminoid bodies, in undergoing decomposition, yield
about |rd their weight of urea. Hence, using the above given data, 1
gramme of dried muscle oxidised in the body, would yield 5103 —
or 6103 — 735 heat-units = 4368 heat-units, or 1848 met. kils. of mecha-
nical power; for 1 gramme of pure albumen, the results are 4263 heat-
imits, or 1805 met. kils. of force. Applying these datato Fickand "Wisli-
cenus’ experiments, it will be found that, as they eliminated resjiectively,
nitrogen equal to 37'17 grammes, and 37 grammes of albuminoid sub-
stance, the available energy they produced would bo only 08.690, and
68,376 met. kils. ; whilst their computed work was 319,274 and 368,574
met. kils. The mean ratio of the work performed, to the power derivable
from the oxidation in the body of the nitrogenous substance of muscle,
was, therefore, less than they had supposed, viz. as 5 to 1 .

Again, if the method devised by Frankland. for measui-ing the
energy derivable from the oxidation of albuminoid substances in tho
body, he correct, then the determinations of Haughton and Playfair are
inadmissible. Moreover, applying the same data to the observations
of Edw. Sinitli on prisoners working on the treadwheel, to those of
Haughton on men engaged at sliot drill, and to those of Playfair on
fully employed labourers, Frankland found that the work accomplished
was, in the first case, nearly 2 to 1, in the second case, more than 2 to 1 ,
and in the last case, P3 to 1, in proportion to tlie force indicated by
the excreted nitrogen ; and yet, in each of these cases, unlike the experi-
ments of Fick and Wislicenus on themselves, the food contained a largo
amount of nitrogenous substances, which increased tho quantity of
nitrogen eliminated. Fick and AVislicenus intentionally cousmued a
non-nitrogenous diet.

Dr. Franklaml agrees with the previous conclusions, that the trans-
formation of muscle tissue, is almost entirely independent of tho amouvi of
work performed ; that, in Man, non-nitrogenous substances must be the
chief soiu'co of tho energy which is transformed into muscular work ;
that the muscle is an apparatus in wliich tliis energy is evolved, at tho
expense of lij^lro-carbonaceous fuel, or a machine for converting jmtential
energy into mechanical force, and that it docs not undergo much more
waste when in action, than when at comparative rest. Besides this, he
believes that tho oxidisalilo material does not rciiuire to be previously
organised or mailo part of tho muscle, but only to bo digesti'd and
assimilated into tho blood, of which it forms a part. Ho conceives that
tho materials of the food, together with oxygen, circulate in the blood
going through tho muscle, and that when tho latter is quiescent, no
chemical action takes ]fiace ; but that when a muselo is excited to act
by a nerve, the nerve force determines the oxidation of non-nitrogenous
matters in the blood, and so sets free jiotential energy, partly acting as
heat, and partly as motion. Dr. Frankland admits, however, that

REAL SOURCE OF MOTOR POWER.

571

nitrogenous matters may also bo employed for this purpose, as is
illustrated by the work performed by men and animals fed on tlesh
diet. But ordinary flesh contains much fatty matter.

Dr. Parkes has observed the effects of exercise and rest, under dif-
ferent diets, on the excretion of imea, over longer periods than those
noticed by Pick and Wislicenus. His results likewise show, that on a
«o«-nitrogenous diet, exercise produces no increase in the excretion of
nitrogen ; that less lu-ea is excreted diu’ing the period of actual work ;
and that, the elimination of nitrogen, is regulated, rather by the character
of the diet than by the amount of exercise. The subjects of observation
were two healthy soldiers, whose normal daily standard of excretion of
nitrogen, was first ascertained diu-ing a period of six days, in winch they
took their ordinary food and exercise. For two days, they consumed
non-nitrogenous food, and rested ; the urea, and the total nitrogen ex-
creted, then fell to a mean of less than one-half the normal quantity,
and yet the men lost weight. They next returned for four days, to their
ordinary diet and occupation ; the nitrogen excreted, as imea and other-
wise, immediately increased from day to day, but did not, on the last day,
reach its normal standard ; and the total quantity excreted in the four
days, was less than half of that eliminated in four of the first six days ;
some nitrogenous food was apparently retained for the nutrition of the
tissues, or to supply the nitrogenous blood-material expended in the two
days of non-nitrogenous diet. For the next two days, the men again took
a non-nitrogenous food, but instead of resting, they underwent full
exercise, walking, on the first day, 23'76, and on the second, 32'78
miles ; the food satisfied the sense of hunger which was felt ; much
fatigue was experienced, especially on the second day ; the excretion of
nitrogen decreased during the first thirty-six hours, but in the succeeding
twelve hours, which were hours of rest, it showed a marked increase ;
the pulmonary and cutaneous excretions increased, the former 100, and
the latter 50 per cent. ; the men lost weight. Finally, being allowed
their usual diet, with ordinary exercise, the quantity of urea again rose
daily, and at last surpa.ssed the normal quantity. The chief difference
in these results, as compared ^vith those of Fick and Wislicenus, whose
observations were not sufficiently prolonged, is in the increased excretion
of nitrogen, during the hours of rest, after severe exercise on a non-nitro-
genous diet. This may merely show that the effects of the changes taking
place in the muscles during exercise, arc slow to manifest themselves in
the excreta. The diminution in the nitrogenous excretions, during actual
work, on a non-nitrogenous diet, may, as Parkes suggests, bo owing to
nitrogen being then retained and used, and not to the entire absence of
decomposition in the muscular tissues.

In subsequent experiments on this subject. Dr. Parkes found that,
upon an ordinary mixed diet, containing a daily quantity of about 19 G
grammes of nitrogen, rather less of that element was excreted during the
early periods of exorcise, and during actual exercise, than during rest,
especially during the rest immediately after work, when the quantity rose,
so as to be excessive. Ho suggests a now explanation of the facts, viz.
that a muscle increases in size when in action, then appropriating more
nitrogen than it loses ; but that, when it is at rest, it lessons in bulk,
losing more nitrogen than it api)ropriatos. Muscular movement is re-
garded as duo to a process oi J'ormuiiun, and repose as accompanied

572

SPECIAL PIIYSIOLOGT.

by disintegration. The non-nitrogenous substances surrounding the
ultimate muscular elements, undergo change during the action of the
muscle ; the effete products, chiefly of those non-nitrogenous substances,
as Eanke and others have supposed, arrest the muscular contraction ;
a period of rest follows, in which the effete products are removed, and
nitrogen is eliminated ; and the muscle is once more fit for action. This
view explains most of the facts very well ; it is also in accordance with
experience, as to the necessity of nitrogenous food for persons engaged
in prolonged muscular work ; and yet it admits that the changes in the
nitrogenous elements of muscle, are inadequate to produce the move-
ment, and refers these to the chemical energy evolved by some neigh-
bouring non-nitrogenous substances.

The views of Liebig, as to the separate and exclusive sources
of heat and motion in tlie animal economy, are, therefore,
controverted by more recent knowledge ; it is certainly dis-
proved, that the disintegration of mu-scular substance, is the
only source of muscular power ; and it is equally proved that,
in Man, and probably in Omnivorous animals, the oxidation
of non-nitrogenous materials is its chief source. But the
chemical powers of the living animal economy, have perhaps
been underrated ; and a priori theories may, in both direc-
tions, limit too much our notions resj^ecting them. Carnivorous
animals, as Avould ajDpear from the observations of Lawes and
Gilbert on fattening animal.s, of Savory and others, upon rats
and dogs fed on a flesh diet exclusively, have the j^ower of
splitting up albuminoid bodies into fats and certain nitrogenous
compounds. If so, this fat on being oxidised, may become the
source of motor power. Besides, as albuminoid bodies are un-
doubtedly oxidised in the body, they must furnish potential
energy transformable either into heat or motion. It seems
impossible to believe, with Dr. Frankland, that the blood o>dp,
and not the nervo-muscular substance also, is oxidised in the
production of muscular force ; or to deny that nitrogenous
substances may also yield force, as well as heat. Work is well
performed, for a short time, on a non-nitrogenous diet, but
fatigue is at last felt, and nitrogenous matter must be Avasted ;
otherwise it would not be retained in unusual quantity, when
nitrogenous food is again taken, after a temporary abstinence
from it. Nitrogenous food must therefore be supplied, pro-
bably, in accordance with the amount of work done (Parkes).
A muscle may be a machine, and the blood circulating through
it, the fuel ; but being a living tissue, it, and its nerves and
controlling nervous centres, waste, or they would not become
fatigued arid exhausted by work. A muscle probably wastes

IMrOUTANCE OF NON->’ITI{OGENOUS FOOD.

573

more than a machine -wears. This waste may depend largely
on the loss of the hydrocarbons, and carbhydrates, in the
muscle, and the nerves, yet the more abundant nitrogenous
substances in them must likewise participate in the exhaustive
process. Before, too, we accept Dr. Parkes’ view as to mus-
cular action being accompanied by an absorption of nitrogenous
substance, and by growth, it becomes necessary to determine
the amount of brain-, spinal-cord-, and nerve-substance, which
is consumed, or changed, in all motor acts. This is probably
considerable, and possibly largely affects the fatty matter of
those organs. Might not this oxidation, together with the
nutritive changes accompanying it, explain, in part, the in-
creased evolution of carbonic acid during exercise ? By oc-
cupying the oxygen in the blood, it might also account for
there being less to act upon the muscular tissue. Yet, we know
nothing of the amount of change in the nervous substance
considered separately.

The exact destination of the potential energy, liberated by
the double process of oxidation of nitrogenous and non-
nitrogenous materials, which undoubtedly takes place in mus-
cular motion, cannot at present be precisely pointed out. In
Man, the latter substances undergo far more abundant decom-
position than the former, and, as remarked by Frankland,
whilst the nitrogenous materials are only partially oxidised,
being discharged as urea, and retaining about ^th of their
potential energy unexpended, the non-nitrogenous sub.stances
yield all their energy in the body, being oxidised perfectly as
carbonic acid and water.

There are many facts Avhich indicate the necessity for large
amounts of non-nitrogenous food, for the due performance of
muscular work. It is in the larval stage, that Insects gene-
rally consume the most albuminoid food, and perform the least
amount of work, whilst, in the perfect condition, as in bee.s,
butterflies, and moths, their muscular activity is remarkable,
although their food is almost purely saccharine or non-nitro-
genous (Verloren). The goat, chamois, gazelle, and many other
Ruminants, are singularly swift and active creatures ; their
food, however, is not highly nitrogenous, but chiefly consists
of carbhydrates. It is not probable that the mu.scidar Avork
in any of the.se cases, is performed by the oxidation of albu-
minoid matters only ; for, in that event, the mnscle.s, especially
the minute ones of Insects, Avonld soon be entirely oxidised,
and could not be restored by the scanty supply of nitrogen in

574

SPECIAL PHYSIOLOGY.

the food. The remarkable provisions for digesting tlie carb-
hydrates and rendering them absorbable, appear therefore to
have reference, not only to their nse as heat-givers, but also as
sources of motor power. The production of sugar from starch,
is a imiversal action of the saliva of all animals, and long-
continued digestion in the Euminant stomach, will even change
the cellulose. It has been remarked, that the chief food-manu-
factures are concerned with non-nitrogenous articles of diet ;
that eggs contain, Avhen dried, 40 per cent, of fatty matter ;
that fat is always present in meat ; that the poor consume
much bacon-fat ; and the rich, who eat most albuminoid food,
likewise take more butter, sugar, and alcohol (Lawes and
Gilbert). The use of bacon by the agricultural labourer,
has given rise to a familiar epithet for him. The chamois-
hunters prefer a store of bacon-fat and sugar, to any other
provisions, on a hunting expedition ; and Fick and Wislicenus
ascended the Faulhorn on non-nitrogenous diet, without special
fatigue. But, on the other hand, Parkes found, that on the
second day of severe exercise, on a non-nitrogenous diet,
healthy soldiers complained of unusual fatigue. Practically,
it would seem that sufficient nitrogenous food being supplied
for the nutrition of the muscular and nervous system, then the
most effective diet for a labourer, is that which contains a large
proportion of non-nitrogenous substances. Athletes should
train on meat, but enter into their contests, uj^on amylaceous,
saccharine, or fatty food.

Dr. Frankland has extended his method of determinin'! the
heat-units by deflagration with chlorate of potash, to various
articles of diet, in order to test, in this way, their mechanical
ecjuivalents, or motor values. The actiral energy of a given
Aveight, 1 gramme, of each substance, when burnt out of the
body, is ascertained by experiment; and, in the case of
albuminoid bodies, the energy Avhich would be developed from
them, Avhen oxidised, in the body, is calculated, by deducting
the energy remaining in a corresponding quantity of urea.
The following Table gives some of the results :

According to this mode of estimating the A’alue of food, as
compared Avith that Avhich regards its composition only (p. 1 15),
cheese still retains a very high position, being inferior only to
oils, fats, butter, and cocoa nibs. It appears, moreover, that
•55 parts of fat are equal to 1'15 of cheese, to I'.'l of pea meal,
to 3‘5 of lean beef, and to 5 parts of potatoes.

TRAxNSFOEMATION OF WORK.

575

Value of Food as a Source of Motor Pozvcr {FranMand).

Article of Food
in

natural condition

Met. Kils. of Force,
from 1 Gramme
oxidised in the
body

Weight in ozs.
required daily, to
support the move-
ments of respiration
and circulation

Cod Liver Oil

3,857

1-5

Beef fat (dry)

3,841

1-5

Butter .....

3,077

1-8

Cocoa nibs ....

2,902

1-9

Isinglass (dry)

1,914

—

Cheese (Cheshire) .

1,846

3-

Oatmeal .....

1,665

3-4

Arrowroot ....

1,657

3-4

Flotir .....

1,627

3-5

Peameal ....

1,598

3-5

Bice .....

1,591

3-6

Gelatin (dry) ....

1,550

3-6

Sugar .....

1,418

3-9

Egg (yolk) ....

1,400

3-9

„ (hard-boiled) .

966

5-8

Bread-crumb ....

910

6-4

Ham, lean (boiled) .

711

7-9

Mackerel ....

683

8-3

Beef (lean) ....

604

9-3

Veal (lean) ....

496

11-4

Stout .....

455

—

Potatoes .....

422

13-4

Whiting. ....

335

16-8

Bass’s Ale ....

328

—

Apples .....

273

20-7

Milk

266

21-2

Egg (white) ....

244

23-1

Carrots .....

220

25-6

Cabbage .....

178

31-8

Transformation of iMechanicxd into Calorific Work in the

Bodij.

Every kind of internal work, wlietlicr vital, mental, nervo-
muscular or meclianical, electric or nutritive, excepting the
solvent processes, ultimately passes into heat witliin tlie body.
The purely external mechanical work is thought by some, how-
ever, to be an exception ; but this is nut entirely so ; it is only
the case, when motion is communicated to external matter. At

576

SPECIAL PHYSIOLOGY.

the moment of action of a muscle, indeed, an inverse proportion
exists between the Avork accomplished and the heat produced.
A muscle develops more heat, when it cannot shorten itself, so as
to produce external movement or Avork ; as, for example, A\'hen
a person attempts to move an overwhelming Aveight, or over-
come an unyielding resistance, as compared Avith the effect of
free action in lifting a movable Aveight. Any effort or motion
Avhich is stopped or resisted, or Avhich disappears in any Avaj^,
passes necessarily into heat ; even the electric currents in
muscles and nerves, Avhen they are lessened by disturbance, or
rest, contribute, hoAVCA^er slightly, to raise the temperature of
an acting muscle, and therefore of the body. In fever, the
muscles may become as hot as 105° Fahr., and in tetanus,
111° Fahr. (Ludwig) ; they are then hotter even than the blood
(Fick) ; but this happens Avhen most of their chemical energy
of decomposition can pass into heat, none being required lor
Avork. During muscular action, the chemical energy pas.ses
into that perceptible motion, Avhich Ave call contraction or
shortening ; during arrested effort, it appears in the invisible
motion, Avhich joroduces heat.

On the supposition, that the muscular force is deriAmd fi-om
the oxidation of albuminoid substances, the greater part or the
Avhole of it, is ultimately transformed into heat, and is added to
the avoAvedly larger store derived from the non-nitrogenous
food. But thetlieory Avhich regards animal motion, as chiefly,
or entirely, derived from the energy supplied by the non-
nitrogenous materials of the blood or tis.sues, and therefore from
the non-nitrogenous food, is not inconsi.stent Avith the A-iew,
that these latter are the calorific or heat-forming materials ;
for they then serve both offices. The transformation of po-
tential energy into muscular poAver, Avhether exerted inter-
nally or externally, is necessarily accompanied by the iiltimate
production of heat Avithin the body ; and this is the chief, and
probably the only, source of animal heat (Frankland).

Nutritive or Assimilative Work.

The assimilative Avork performed in the body,isalso chemical,
being partly liquefacient, ]:artly dialytic, and partly solidifa-
cient. It must be performed at the expense of chemical energy,
developed during the many transformations of the nutritiA-e
materials, as these are, in turn, digested, hydrated, dissolved,
absorbed, and converted into tissue. The amount of force

NEllYOUS FOECE AND WOEK.

577

employed in digestion, is small, as compared with the other
great demands of the system. Playfair suggests that it is
measurable, by the amount of nitrogen of the nitrogenous sub-
.stances tcmnd in tlie solid excreta ; and that it may, as he
thought of the mechanical work, be ultimately referable to the
energy of the albuminoid food. The quantity of nitrogen which
escapes by the lungs and skin, is quite unimportant ; with
ordinary diet, the urea includes -|4ths of that contained in the
food, -whilst the solid excreta yield about (Kanke). This
small quantity is the residue of the mucus, salivin, pepsin,
pancreatin, glycocoll, and taurin of the digestive fluids, the
solid constituents of all of which, in a Man, weighing 150 lbs.,
would be upwards of 8 oz. per diem. Playfair supposes that,
whilst most of the substances are reabsorbed, a certain portion
of each undergoes chemical change, being, as it were, degraded,
and becoming unfit for entering the circulation. This remains,
therefore, as a quantitative expression of the force which has
been employed in (he processes of primary assimilation. It
may be a residual index of such actions, but not a source ot
power itself, for it escapes unoxidised. All nutritive work,
implying solidification of material, likewise ultimately passes
into heat.

Electrical Work.

The currents of electricity developed in the body generally,
those found between arterial and venous blood, in muscle and in
nerve, in secreting and in special electric organs, are developed
through chemical action, involving waste by oxidation of the
blood or tissues, and indirectly therefore of the food, whether
of the nitrogenous or non-nil rogenous food, or of both, is not
yet determined. They do not appear to be derived from
friction, changes of temperature, or magnetism, as in the in-
organic world. The chemical energv of the body, thus
diverted to electric work, cannot, however, be expressed in
numbers. Unless it passes off to surrounding objects or
media, it is converted into heat, or into motion and heat,
within the frame, and so assists in the calorific work.

Nervous Force aud Work.

As ehsewhere mentioned (vol. i. p. 284), there exists in
nervous substance, a peculiar electro-polar condition of the
nervous molecules, which is altered, not merely by the passage

VOL. II. r p

578

SPECIAL PHYSIOLOGY.

of an ordinary electric cun'ent through a whole nerve, as is the
case with the muscular current, but also when that current,
or any other stimirlus, traverses a small portion of the nerve.
The existence of nervous STibstance, is essential to the mani-
festation of this peculiar condition ; the force concerned in its
production, may be itself what is called the nerve-force, or it
may be transfoiaued into that force, serving, in either ca.se, to
excite the contraction of a muscle, on the one hand, or the refle.x
or sensitive excitability of a nervous centre, on the other. The
reaction of a reflex nervous centre, may also require, or depend
upon, such molecular polarity. Even sensation, and the higher
and purely mental processes, are associated with, and rest
upon, similar molecular conditions and properties. The special
condition of the nervous matter, which accompanies sensation,
emotion, thought, consciousness, and will, is unlcnoAvn to us ;
but the molecular polarity of the nerve-substance, is, as much
as the nervous substance itselfi a part of the constitution of the
living animal body. The polar condition of the nervous
molecules, represents a portion of the vito-physical woi’k of the
system ; and variations in it, are associated with changes in the
nervous matter itself. These changes are chemical, and imply
Avaste, oxidation, and renovation. All nervous action, or work,
requires both food and air, containing stores of force, Avhich,
exhibiting itself first in chemical combination, is transformed
into the electro-polarity proper to, and manifested only by
the nervous substance built up within the bodies of animals,
and capable of being excited by appropriate stimuli.

The portion of nervous Avork, performed in the control of the
various inrAScular acts, voluntary or involuntary, and belonging
to the animal or vegetative functions, cannot, at present, be dis-
sociated, in any calculations, from the muscular Avork itself. As
to the nervous Avork connected Avith sensiition and other psychical
actions and reactions unaccompanied by motor results, it is
impossible, at present, to measure them, and Haughton’s allot-
ment of the so-called mental work of the body, to a certain
proportion of the urea, is purely conjectural. It is not even
knoAvn hoAV far it may be due to changes in nitrogenous or non-
nitrogenous matter; it probably depends upon both. Possibly
some estimate of its amount, might be made, by studying the
amount and the sources of the phosphates formed in the system.
Ui-ea is probably produced by the decomposition of nerAmus
substance, especially of the albuminoid a.xial fibres, and uon-
medullated terminal portions of the motor nerves; urea has

FORMATIVE FORCE.

579

been found in the muscles of certain Fishes. The phosphates of
the juice of muscle, and the phosphorus in the red corpuscles of
the blood, may be a source of phosphates in the urine ; but
the cerebric acid of the grey nervous substance, is especially
characterised by containing phosphorus, probably unoxidised;
and over-activity and disease of the nervous system, are said to
increase the amount of phosphates so excreted. The oxida-
tion of phosphorus, or of phosphuretted fat, may be one source
of electro-polar nerve-force. In any case, such molecular
polarity is ultimately transformed into heat within the body,
and affords another example of the economy with which the
various forms of vito-physical force engendered in the animal
system, are employed within it. The energy of every sub-
stance oxidised in the body, into whatever form of force it may
be transmuted, is doubtless applied Avith the least possible loss.

In conclusion, it may be observed that, although the results
of the application of the principles of physical research, to the
explanation of the ph}"siological phenomena discussed in this
Section, are at present incomplete, yet, considering the extreme
complexity of the phenomena exhibited by living animals,
and the difficulty, even in regard to Man alone, of obtaining
coiTect average numerical data, enough has been determined to
render it certain, that all the strictly physical processes Avithin
the body, Avhether ' chemical, mechanical, thermic, electric, or
photic, are performed by modifications of the common force
Avhich produces similar phenomena in the inorganic world
around us.

There e.xists, hoAvever, in the living animal, as in the living
vegetable organism, a special formative or organising energy,
evolving the perfect animal or plant from the primitive ovum
or ovule, developing its various tissues and organs, and con-
seiwing these from the commencement to the termination of
its individual exi.stence. The influence of this force, moi-eover,
extends from the parent to the offspring, generation after
generation. Its relations to the vito-physical and vito-
chemical forms of force Avorking in the body, arc entirely
unknown. Its truly marvellous results are con.sidered in the
following Section on Ileproduction Development.

580

SPECIAL PIirSIOLOGT.

PvEPEODUCTION.

Spontaneous Generation.

The life of individual organisms, whether vegetable or animal,
is limited, death, at last, ensuing from accident, disease, or
natural causes. The maintenance of the species, by the repro-
duction of new individuals, is accomplished in different modes
in different animals.

All animals, so far as is known, even the very lowest, are
produced from parents. The occurrence of the original genera-
tion of an animal, without the intervention of a parent, or the
so-called equivocal or spontaneous generation, is not believed
in by the best authorities. All cases of supposed spontaneous
generation, cited before the introduction of good mici’oscopes,
may be set aside as valueless. The present condition of the
question, is fully illustrated in the recent controversy between
MM. Pouchet and Pasteur. It is admitted by both those ob-
servers, that only the lowest Protozoic forms of animal life
are concerned in this question, the assertions of Crosse and
others, as to the spontaneous development of a complete
Annulose animal, being unworthy of serious consideration.

With regard to the Infusoria, however, it is alleged by
Pouchet, that, if impure water be boiled, so as to destroy all
organic life in it, and then be absolutely excluded Irom the air ;
or if air only be admitted which has previou.sly passed through
red-hot tubes ; or, again, if water be boiled in flasks which are
then hermetically sealed — organisms, belonging to the simplest
forms of Infusorial life, will make their appearance; and that
these will even be followed by the subsequent appearance of
higher ciliated Infusoria. It is strongly asserted that, in .such
experiments, absolute care has been taken to prevent the acci-
dental intrusion ol' germs, however minute, into the water or air.
By Pasteur, on the other hand, it is affirmed that, if sufficient
precaution be taken, no manifestation of life occurs in the fluid
experimented upon, or, at least, so exceiitionally, that it may
well be attributed to the accidental entrance of floating germs.

The following experiments have been devised by Pasteur,
to illustrate this subject. Small flasks of boiled water, luive
been closely fitted, at the mouth, with tubes, into a bend or
bulb of which, cotton-wool is inti’oduced ; this intercejits
floating germs, but yet allows the interchanges jwoper to

THE MODES OF REPRODUCTION.

581

gaseous cliffiision : in such experiments, no organisms are
developed in tlie water. On the other hand, with the same
fluid boiled, and placed in a flask, fitted with a similar tube
without the cotton-wool, multitudes of Infusoria are de-
veloped. In other experiments, instead of cotton-wool, gun-
cotton was employed, and placed so as to intercept the
germs in the air ; this gun-cotton being afterwards dissolved
in ether, ova, and germ-forms were collected in the residue,
and recognised under the microscope. Moreover, portions of
the cotton-wool or gun-cotton charged with the germs, pro-
duced, in water or in vegetable infusions, the same kinds of
Infusoria as appeared in the liquids unprotected by the gun-
cotton.

It would seem, however, that in boiled vegetable infusions,
hermetically sealed with a certain quantity of air, also pre-
viously heated to a red heat, those singidar organisms, named
bacteria, wdiich are probably vegetable, may, after several
months, appear (Child).

The position of the advocates of the doctrine of spontaneous
generation, is a difficult one. An apparently positive result, in
an experiment with hermetically-closed vessels, is attributed
by their opponents, to want of care in the preparation of the
water or the infusion, or to the accidental intrusion of germs.
The position of the opponents of the doctrine, is also difficult,
because they seek only to establish a negative. A sufficient
number of negative re.sults, obtained by conscientious ob-
servers, is all the evidence that can possibly be advanced in
such a ca.se. The onus probundi is thrown upon the supporters
of the doctrine.

The Varums Modes of Reproduction.

In the Vegetable Kingdom, two modes of reproduction are observed,
viz. the 7wn, sexual and the sexual. The former presents several varieties,
viz. (/emmation, or the formation of buds, as in ordinary plants, or in
special eases, of bulbs which are detached buds, or sHbdwision or fission,
as in the micro.scopic algre, and perhaps in the lower fungi. The sexual
mode is by true spores or seeds, wliich require fertilisation. The two
modes commonly occur in all plants.

The mode of propagation by buds, or by cuttings, sonms to prolong a
variely, cr a species, merely by multiplying the individual; but tlio
sexual mode alone will render ponnanont an accidental variety, or will
perpetuate, for a length of time, a specific form. In tlic fungi, and in
the lower algaceous forms, it seems probable that an alternate form of
generation may occur, such as will presently bo described, in the case of

582

SrECIAL PHYSIOLOGY

certain animals : that is to say, the two forms of reproduction, sexual
and nonsexual, may alternate in different generations ; in other words,
spores may produce intermediate forms, which, in their turn, may
directly reproduce the parent form.

The reproduction of animals from parents, also presents
the nonsexual and the sexual modes.

The nonsexual mode of reproduction, may either consist in a
simple cleavage or division called fission, or in the formation of
hucls, known as gemmation or budding. Both these forms occur
only in the lower Classes of animals. Fission, or fissiparous
rejjroduction, consists of a constriction, once or several times
repeated, in the soft body of an animal, followed by its com-
plete division into two or more parts, each of which is then
developed into an individual as complete, in every respect, as the
parent animal. This form of reproduction is noticed as one
mode of development in the Infusorial animalcules, the process
being sometimes, as in Paramecium, extraordinarily rapid. It
also occurs in the formation of the segments in some vermiform
intestinal Entozoa, but not amongst animals higher in the
scale. In artificial fission, as performed upon the Hydra, a
similar ju-ocess is imitated. If, for example, a Hydra be cut,
lengthwise or transversely, into several parts, each portion will
complete itself. Some of the Annelida, or Woi'ms, on being cut
across, develop a new head to the lower half, and a new tail
to the upper portion, of the divided body.

Gemmation, or gemmiparous reproduction, consists in the
formation of an offshoot or hud, from the body of the parent
animal, which either continues to grow in connection with the
parent, so that composite animals are jrroduced, as the many-
chambered Ilhizopods ; or aggregates or colonies of animals are
formed, attached by a common stem, or stolon, as in the case
of the Yorticellaj, amongst the Infusoria. This is, also, the
ordinary mode of propagation of the Hj'dra, amongst the
Coelenterata ; of the compound coralline Polyps, of the com-
pound Ascidioida, and of Nais, amongst the Annelida. Geinma3
may also, after a time, detach themselves from the parent stem,
move away, and develop as independent animals, which may
themselves gemmate, and form a new colony, as in the com-
poimd Poly])s and the compound Tunicata, or become new in-
dependent animals, as in the IMedusns. Sponges are thus re-
produced by detached bodies, known as geminules, Avhich, at
first ciliated and free-moving, afterwards become smooth and
fixed, and then grow into a new sponge.

SEXUAL llErBODUCTION.

583

As representing a special form of internal gemmiparoiis re-
production, may perhaps be included tliose remarkable cases,
in which groups of minute cell-like bodies, sometimes named
pseudova, to distinguish them from true ova or eggs, are de-
veloped somewhere in the interior of the body of the parent
animal, and, after a time, undergo successive stages of develop-
ment, sometimes into forms externally resembling that of the
parent animal, though not possessing rejn'oductive organs, but
much more commoidy into forms not resembling the parent
animal. By detachment, protrusion, or rupture of the parent,
these new animals then become independent beings. This
form of reproduction is observed in the Aphides only, among
Insects, and in the Daphnia, among the smaller Crustacea.
Light and heat are important agents in determining the oc-
curi-ence of this process.

The larger reproductive bodies foimd in the Sponges, and
developed as cold weather approaches, called capsules, have
by some, been regarded as of the nature oi pseudova, but they
may be sexual products. The so-called germ-cells of the
Hydra, which, towards winter, are sometimes developed in the
walls of the gastric cavity in one individual, whilst a spenn-
cell appears in that of another, though sometimes both kinds of
cells are developed in the same Polyp, have likewise been
referred to this class of bodies ; but their sexual character
is more probable.

In the sexual mode of reproduction, known as oviparous re-
production, which is a higher form of propagation, an ovum, or
germ-cell, and a fertilising cell, or sperm-cell, are ahvays neces-
sary, and co-operative, in other words, a female and a male
product, according to the distinction oi sex.

In some animals, as in the Ccelenterata, in certain Scolecida,
as in trematode Entozoa, in many Gasteropods, and in a few
branchiated Annelida, the male and I'emale products are de-
veloped in one individual, wliich is then said to be monvecious
or hermaphrodite. In the Medusa’, and in the Entozoa, the
germ-cells are fertilised by the sperm-cells of tlie same animal ;
but in the Snails, and other Pulmo-gasterf)]iods, there is an
intercliange of office, one individual I'ertilising the ova of
another, and liaving its own ova fertilised in return.

In the remaining animals re])roduced by true ova, viz. the
higher Annuloida and tlie Annulosa, the Molluscoida, Mollusca,
and Vertebrata, the re[)roductivc elements are Jbund in sepa-
rate individiuils belonging to opposite sexes. Sucli animals

584

SPECIAL PHYSIOLOGY.

are named dioecious. The ovum is then, in some cases, as in
Fishes and Amphibia, I'ei-tilised without, but in other cases, as
in Reptiles, Birds, and Mammalia, within, the body of the
female or ovigerous parent. In this ovum, when fertilised, the
embryo is developed, undergoing a scries of important changes,
which constitute the process of evolution or transformation.

Some curious examples of the coexistence in the same in-
dividual, but at different setisons, of a sexual with an appa-
rently nonsexual mode of reproduction, have been met with, in
the lower Classes of animals. This presents us with the various
forms of parthenogenesis, or development by .so-called unferti-
lised ova. This mode of reproduction, is illustrated in the
Aphis, amongst Insects, in the female of which, one act of fer-
tilisation is sufficient for a long succession of distinct repro-
ductive acts. Another most striking example is exhibited by
the Bee, as was first observed by Dzierson, and afterwards by
Siebold, Berlebach, Leuckart, Owen, and others. The ova of
the Queen-bee are deposited by her, in the cells of the comb,
and in that act, according to the size and form of the cell, .she
either fertilises the ovum, or not. This is accomplished by
her pwinitting, or preventing, the escape of a small quantity of
liuid from a sac in the interior of her body, named the
spermotheca, which has been previously charged, by the act of
the male bee, with fertilising liuid, during flight in the air. If
the ovum be fertilised, it produces a working-bee, i.e. an tm-
developed female, any one of which, by abundance of feeding,
may beco.me a queen-bee. But if the ovum be not fertilised
by the fluid of the spermotheca, it jwoduces only a drone, or
male. This latter result may be brought about experimentally,
either by interruption of the communication between the
spermotheca and the oviduct, or by the effects of a temjjerature
low enough to destroy the properties of the fertilising fluid.
So also, if the wings of the queen-bee be cut, she remains
with the sac uncharged with the fertilising fluid, and her eggs,
which she will then deposit all the same, produce only drones.
jMoreov’er, a working bee, not fed up to the condition of a
queen-bee, may deposit eggs, which, not having been fertilised
in the ordinary way, produce only drones. In the Bee, there-
fore, the phenomenon occurs, of an ovum undergoing develop-
ment, wiihout obvious direct iertilisjition. Hence the name
parthenogenesis. Similar phenomena have now been observed
in many other Insects.

In certain remarkable cases, a sexual generation by true

ALTERNATE GENERATION.

as5

}

fertilised ova, or germ-cells, may occur, togetlier with repro-
duction, b}' apparently unfertilised pseudova, ov germinal cells.
This happens, for example, in certain Entozoa, and also in the
Aphis, or plant-louse. Sometimes these two modes of re-
production alternate, in dqferent generations, more or less
regularl3^ In such cases, the form of the animals produced
from the true ova, or the first generation, differs, in some
respects, from that of the parent, especially in being nonsexual ;
whilst the offspring of these, or the second generation, derived
from pseudova, may either resemble the original parents, or
may produce, nonsexually, a third generation, or several gene-
rations, the last of these producing animals, which are sexual
and resemble the parents. This is named propagation by
alternate generation. In it, a female parent animal produces
ova, wliich are duly fertilised. The embryoes, or larvce, de-
veloped from these, are, at no time, like the mother ; they
grow, and then develop, in their interior, either a single in-
dividual, which becomes like the parent; or they may, by
external division, or external or internal gemmation, produce
many such ; or they may Ibrm, either at once, or in succession,
a series of young, derived from unfertilised pseudova, which
at once, or after two, three, or even more generations, ulti-
mately produce animals similar to the first parents. These
again, like those parents, propagate sexually. The inter-
mediate generation, or generations, of nonsexual proliferous
larva;, have been called, by Steenstrup, nurses, to distinguish
them from tmie mothers.

This development by alternate generation, never occurs in
the Vertebrata, and only rarely in the higher Non-vertebrata.
Amongst the Mollusca, no proper examj)le of alternate genera-
tion has yet been met with ; but it is almost constant in the
Molluscoida. Amongst the Arthropodous Ammlosu, it has
been ob.served in but one Crustacean, Daphnia, and in only a
few Insects, such as tlie Aphides, but not in the Arachnida or
Myriapoda. The vVphides pi-esent a remarkable cxfvmple of
this alternation : in the hot season, they multiply i-apidly, by
successions of internal generations of pseudova ; but as the
temperature is lowered in the autumn, males and females
appear, and dcvclo[)ment by ova ensues. In early spring,
these ova again produce vivij)arous individuals, whicli multiply
by pseudova, and, alter many generations, towards the ap-
proach of winter, sexual ^Vphides once more afipear. This
I alternate generation likewise occurs in many Annelida, its

586

SPECIAL PHYSIOLOGY.

asexual phase then constituting the so-called fission, as in
Nemertes, Nais, and others. It is common also, and occurs
in all degrees, in the Annuloida, as in the Scolecide, the Tre-
matode, and the Cestode parasitic worms, in the Eotifera,’ and
the Echinodermata, and also, generally, in the Coelenterata,
and in many Protozoa. Amongst the Ccelenterata, and others,
the form which is evolved from the fertilised ovrun, is named
a scolex ; the compound forms arising from the budding or fis-
sion of the scolex, are named strobila, and the perfect animals,
again exhibiting true reproductive organs, are named “profiot-
tides. In the Sponges, sexual reproductive organs have been
seen, giving rise to bodies like ova, in which a spongilla is
developed. These alternate with the gemmules. In the uni-
cellular Protozoon, besides fission, the so-called nucleus and
nucleolus, or double nuclei, are believed re.^jDectivety to repre-
sent the male and female jDroducts, not germ- and sperm-cells,
but germ- and sperm-nuclei.

This mode of reproduction by alternate generation, often
presents oi genetically-related animal forms, exhibit-

ing not only a nonsexual character, but a totally different
.shape and organisation, as comjDared with the parents. The
ovum of certain Echinodermata, of the Echinida and Ophiurida
for example, develops into a free-swimming ciliated embryo,
which becomes converted into a medusa-like larva, known as
the pluteus, a form which has quite a Coelenterate type; but in
the body of this, near the digestive cavity, close upon the re-
maining substance of the original ovum, or yolk -mass, a young
Echinus appears, in the form of a circular disc, rvhich gradually
assumes a quinary radiated form, and ultimately becomes a
perfect Echinoderm. In the same way, the ova of the Tamia?,
or Tapeworms, taken by animals which live upon oflal, or
swallowed by Man in water, pa.ss into the alimentary canal,
and there develop into Echinococci, or Cysticei'ci, which pene-
trate, whilst ver}'^ minute, the surrounding tissues, by a process
of boring, and so find their way into all jxarts of the body,
and there grow as Cysticerci or Echinococci. The tissues ot
an edible animal (as a pig, for example), thus infested, being
then eaten, the Echinococci, if not destroyed by the cooking,
attach themselves to the intestinal mucous membrane of the
person ivho eats them, and form the head of a tamia, which
then, by succe.ssive fission, produces its long segmented body,*
each section of which, now named a proglottis, is really inde-
pendent of the rest, and is provided with true re^moductive

jMETAMOnrilOSIS.

587

organs, sperm-cells, and ova. The Trichina is not, as was once
supposed, an intermediate ibrm, by alternate generation.

Lastly, ill the interior of certain Trematode worms, such as
the Planariie, and Distoinata, a succession of nonsexual larvEe
is developed, each producing others within them, until, at last,
sexual forms appear resembling the original parent. Thus a
Distoiiia, lor example, which is found as an entozoary parasite
in the Limnams, a fi-eshwater snail, develops ova, which are
evolved into elongated larval of veiT simple oi-ganisation ;
these larval are composed simply of nucleated cells, which gi-ow
into ciliated organisms, and then burst through the skin of
the larva, attach themselves to a Limnams, and, having become
metamorphosed into a true Distoma, perforate the tissues of
the snail.

In these cases of alternate generation, there occurs, there-
fore, a sort of metamorphosis, because the cycle of evolution
is at last always completed, by a return to the parent form ;
but the stages of the metamorphosis supervene in different gene-
rations, and not in the same individual. So likewise, in all
cases of nonsexual reproduction, whether by so-called fission,
by gemmation, external or internal, or by recognised pseud-
ova, a return, at last, takes place to sexual development, by
true ova which require fertili.sation. Hence the latter mode
of reproduction appears the more important i'unction, to
which is assigned the continuance of the specific forms of
animal life.

In the Molluscoid Tunicata, hoAvever, and in Insects,
Crustacea, and certain Fishes, and also in Amphibia, a true
metamorphosis occurs in each single individual — i.e., a transs-
formation takes place not in the embryo in ovo, but after the
escape of the young from the ovum as an independent being.
In such instances, the young animal, on emerging from a
fertilised ovum, has at first no resemblance to the parent, but
exhibits a provisional form and organi.sation, suited to its
conditions of life. After a time, however, it undergoes changes ;
some organs or ]>arts disappear, whilst others begin to bo
formed, and, finally, it assumes a .state of mature existence,
resembling its parent, and exhibiting one or other form of sex.
Thus the larva, or wormlike caterpillar, of tlie Insect, pro-
ceeds from the egg. Consuming large (piantities of food, it
grows, and then changes into the pupa, or chrysalis ; in this
condition, no food being taken, remarkable changes occur, of
which the formation of wings is the most obvious. From

588

SPECIAL PHTSIOLOGT.

this, finally, it emerges as the imago or perfect insect. The
relative degree or extent of the metamorpliosis, differs in
different Orders and Families of Insects. Tlie suspension or
arrest of the ordinary 23liases of this metamorphosis, occa-
sionally gives rise to monstrosities, such as butterflies with
caterpillars’ heads, and other curious forms.

Metamorphosis may also be said to occur in some of the
lowest Fishes, certain forms of Ammocete having been shown
to be the larvte of the lamprey, Avhich after^^'ards undergo
coinparatively slight changes in the buccal and branchial ap-
paratus.

In the Amphibia, the tadpoles of the frogs and others, as
developed from the egg, present a fishlike form, and possess
at first external and then internal gills; but ultimately, in the
higher forms, they assume the perfect Batrachian conformation,
lose their gills, and breathe by lungs. The extent of cluinge
is most marked in the anourous or tail-less Amphibia. In the
salamanders, however, no internal gills are developed, like
those of the frog; and the tail, instead of undergoing inter-
stitial absorption, is retained. The suspension of the meta-
morphic process, at certa n early stages, leads to the formation
of the Perennibranchiate Amphibia, in which lungs also exist,
such as the Proteus, Siren, Axolotl, and Menubranchus.

The preceding cases are instances of progressive metamor-
phoses. But metamorphosis may be, as far as general organi-
.«ation is concerned, retrograde, animals being, in the larval
stage, actively locomotive, and, in the perfect stage, fixed or
•sessile. 'I'hus, the young of the Ascidioida are free-swimming,
tailed, and ciliated animals, whilst in their perfect condition
they are fixed. In the Crmstacea, the larvaa exhibit progressive
mettimorphoses of a remarkable character. In the Cirrhopods,
the larvte are active, move freely in the water, and possess
eyes, but, afterwards, they become se.ssile, fixed by the head,
and lose those organs. They present an example of retrograde
or recurrent metamorphosis. In the parasitical Crustacean
Lerneada, which attach themselves to fishes, and even in the
Laniellibranchiate jMollusca, the perfect animal is less highly
endowed than when in its larval condition.

The phenranena of individual metamorphosis, so obvious in
the Insects and the Am[)hibia, after their escape from the egg,
are, in reality, not singidar; \'ov phases of evolution, or Irans-
formation, occur in the development of the embryoes of all
animals, even of the highest A'^ertebrata ; but these are often-

OITY OF THE REPRODUCTIVE PROCESS.

589

times rapid, and occur in such an early stage of embiyonic
life, as not to be so obvious.

Ova and Pseudova. — A true ovum, the product of a female
organ or ovary, is a nucleated cell, jjossessing a delicate cell-
■\vall, a contained nucleus, within wliich is a nucleolus, and,
besides that, certain cell- contents. It is a proper and special
germ-cell, set apart for the reproduction of a new individual.

The male product, or fertilising element, the product of the
so-called sperm-cells, formed in the testes, is a fluid containing
micro.scopic bodies named spermatozoa ; these are endowed
with the power of active movement, which lasts, in the Warm-
blooded Vertebrata, for a few minutes, in the Cold-blooded
Fishes, for days, and in certain Mollusca and Anmdo.sa, even
for months, when received into the special receptacle, or sper-
molheca. From their mode of development, from the character
of their movements, and from the effects of reagents upon them,
they may be regarded as ciliated gymuopla.sts, or ciliated
nuclei, which may be compared to single particles of ciliated
epithelium. The sperm-cell in which they have their origin,
and from which they escape, by rupture of the cell- wall, is the
homologue of the germ-cell, or ovum.

In true sexual reproduction, the product of the sperm-cell
enters and fertilises the germ-cell, and imparts to it the power
of specific reproduction, just as the pollen of the anther of a
flowering plant, fertilises the vegetalile ovule.

The unfertilised ovinn of a qne. n or female bee, and also
the pseudova of the A])his, and of other animals prouagated by
alternate generation, are also nucleated cells, portions of the
parent animal, set apart for particular purposes, and retaining
special ]>owers of further evolution; they are, therefore, also
germ-cells, or rather germinal cells. They may be viewed as
undeveloped, or ametamorpho.«ed, j)ortions of a itreviously fer-
tilised blastema, which has itself resulted from the first stages
of evolution of a true ovum ; they are, however, retained
i in connection with some portion, usually internal, of the
l nonse.Kual, and only indirectly fertilised, offspring, waiting
i for their opportunity of individuid evolution. They have, in
’ truth, been fer ilised. According to this view, every individual
animal form, whether the result of direct sc.xual evolution,
or of parthenogenesis, or of any sttige of alternate generation,
is produced from a primitive coll, which, having been directly
or indirectly fertilised, undergoes multiplication and differen-
tiation, so as to evolve the future animal. The simjtlest forms

590

SPECIAL PHYSIOLOGY.

of reproduction, by gemmation or by cleavage, are but ex-
tensions of individual animals, themselves traceable to the
evolution of two primitive, sexually developed, fertilising, and
fertilised cells. Even in the lowest Protozoa, evolutions of
new beings, from time to time, occur by the conjugation of
two nuclear particles in their interior, which, at least, imitate
a sexual process.

Whatever variety the reproductive process of animals may
present, the primitive cell, Avhether it be a fertilised ovum, an
unfertilised ovum, a or the commencement of a

bud, is, in all known cases, a part or product of a pre-existing
parent. No satisfactory proof has yet been adduced, of the
spontaneous origin of such a cell. Hence the doctrine of
spontaneous generation, collapses from failure of proof.

The Ovum considered generally.

The parts seen in an unfertilised animal ovum, as already
stated, are the cell- wall, the contents, the nucleus, and the con-
tained nucleolu^, fig. 116. The delicate cell-wall constitutes the
vitelline membrane, or yolk-sac. The more or less transparent,
granular, or coloured contents, constitute the yolk. The nu-
cleus is a transparent, solid, or vesicular body, here named the
germinal vesicle, or vesicle of Purkinje. Lastly, the nucleolus
within it, is a fine granular or vesicular corpuscle, called the
germinal spot. The germinal vesicle and spot are the essential
parts, or active centres of growth, of the ovum.

As to the Vegetable Kingdom, in the higher plants, which are produced
from seeds, a part exists in the seed, known as tlie ovule ; within this,
which is a vegetable cell, is found the gcrm-vesicle, a structiu’e homologous
with the germinal vesicle of the animal ovum. Like it, its future de-
velopment requires the co-operation of a fertilising agent, which is here
derived from the pollen-cells. In the lower or flcwerless plants, the
spores are usually fertilised by moveable filaments named zoosperms, or
by simpler elements.

The size of the ovum of difierent animals, differs very much,
not in accordance with the size of the parent animal, but
rather with the course and conditions of development of the
future embryo. The dilference in size, depends almost entirely
upon the quantity of the yolk or cell-contents. The cha-
racter of this yolk also varies ; sometimes it is so finely
granular and colourless, as to appear clear ; whilst, in other
cases, it is so distinctly granular and colotired, as to contain
large granules and even vesicles, with oil-globules, to be

MEROBLASTIC AND IIOLOBLASTIC OVA.

501

more or loss opaque, and to present a pale or deep yellowish
hue.

The j/olk is a most important constituent of the ovum. In all
cases, it \s formative, yielding material for the first formation of
the embryo; sometimes it is also nutritive, or provides nourish-
ment for it, during a considerable period of its growth.

In one series of animals, oviparous, the development of the
embryo within the ovum, occurs entirely after the latter has
been deposited by the parent animal ; whereas, in another
series, often viviparous, the embryo is more or less developed
within the parent. In the first case, niitrient material must
be specially provided in the ovum, for the future embryo, the
various organs of which are developed at the expense of the
yolk-contents, mitil the young animal has reached a phase of
development, in which it can take external materials for its
future nourishment. In such cases, the yolk is comparatively
larcje in quantity, and rich in oi-ganic granular contents, opaque,
and coloured ; it is chiefly nutritive, and, in small part only,
fomnative. Such ova are named merob/ustic (/itprr, a part,
fiXuarbc, a germ) ; they include the eggs of the higher Crus-
tacea and Arachnida, those of the Cephalopods, and those of
the Os.seous and Plagiostomatous Fishes, of Reptiles and Bh-ds,
and of the Monotrematous order of the Mammalia. The ova
of the Amphibia, are imperfectly meroblastic. In the second
case, either a very slight part, or no portion, of the yolk is
nutritive, but all, or almost all, is directly formative ; the yolk
is comparatively small, frequently clear, and less rich in gra-
nular organic contents. These ova are called Jioloblastic (oAoe,
the whole). They are met with in the eggs of the Echino-
dermata and of the Annelid.s, in those of the simplest Crus-
tacea and Arachnida, in those of Insects, and of the Mollusca
generally (excepting the Ce]dialopods), in the Cyclostomatous
Fishes, and, lastly, in the Mammalia, including Man.

The Jioloblastic ovum (tig. IK!) consists of a tran.sparent,
homogeneous, or sfructurclesa vitelline me7nbrane, which, to-
gether with a clear outer stratum of the yolk, sometimes of
considerable proportionate thickness, constitutes the zona pcllu-
cida. Within this, and completely filling it, is the limpid, or
faintly granular, gertn-yolk, or formative yolk, with its germinal
vesicle, and spot. The meroblastic ovum (fig. 1 1 9) consists, ex-
ternally, of the vitelline or vitcllary membrane, which is thin,
and often also homogeneous or .structureless, but, in some cases,
slightly granular, or, in parts, indistinctly fibrous. There is

592

SPECIAL PIIYSIOLOGT.

no zona pellucicla, hut the interior of the vitelline membrane
is lined with a stratum of polygonal nucleated cells, knoAvn as
the epithelial layer . Within this, is the distinctly granidar, nu-
tritive yolk, a, which may either be whitish or yellowish. On
one part of the surface of the nutritive yoUv, is a small circular
disc, known as the cicatricula, or germinal disc. This is, in
fact, the germ-yollc, or formative yolk, spi-ead out, in the mero-
blastic ovum, upon a small part of the surface of the nutritive
or food-yolk, instead of being spherical, and occupying the
entire vitelline cavity, as in the holoblastic ovum. Lying, at
one time, in the midst of the formative or germ-yolk, or ger-
ininal disc, are found, as in the other ova, the germinal vesicle
and spot (fig. 117).

Fig. 116.

Fig. 116. Holoblastic ovum or germ-cell, of a Mammalian animal, unferti-
lised (Allen Thomson), n, vitelline membrane or envelope, thick, and
clear, aftiTwards forming the zona pelhcciila ; within it, is the granular
yolk, or cell-contents ; in this, the germinal vesicle, or nucleus; and in
this, the germinal spot, or nucleolus, b, the ovum, or germ-cell, burst,
part of the granular yolk, with the germinal vesicle and its contained
germinal spot, having escaped, c, the germinal vesicle surrounded by
a little granular matter. — Magnilied 80 diameters.

lit the Mammalia, the yolk is so small in quantity, as tjuickly
to become insufficient for the nourishment of tlie embryo, and
special structures are very early formed, to enable it lo derive
support from the nutrient fluids of the parent. These are
imperfectly developed in the linplacental, but are more com-
plete in the Placental, I\Iammalia. Of the meroblastic ova,
tho.se of lleptiles and Bird.s, but particularly the latter, ]ire-
seiit by fill- the most tibundant nutritive yolk. Prom the
size of the egg, and from the occurrence of all the sbiges of
development cluring an external incubating j^focess, which

THE OTCM OF THE BIIU).

593

may be carried on by artificial meanf!, tlie egg of llie Bird es-
pecially presents the most lavonrable opportunity ofwatcliing,
from honr to hour, tlie stages of development of the Vertebrate
embryo, within the ovum.

The Ovaries and Ova of the Bird.

The ecjri of the common fowl is first formed within the
body of the hen, in the organ named tlie ovarjj, which is
attached to the back of the abdominal cavity, in the lumbar
region. In the female embryo of all Birds, two ovaries exist,
but almost universally the left one only is present in the
mature Bird ; the Dorking fowl is an exception, having both
ovaries persistent. This is also the case in certain of the birds
of prey. The ovary itself consists of a cluster of small spherical
bodies, closely invested by membranous ovisues, and named
the ova. These are at first destitute of the white, and consi.st
only of minute yolks invested with the vitelline membrane.
The ovi.sacs are all held together by a loose areolar stroma
and bloodvessels, so as to form a bunch or raceme, and are
invested by the peritouffium. To the lower part of the ovary,
is attached the wide funnel-shaped opening, or infundibulum,
of a long tortuous tube, named the oviduct, which is also
single, being present only on the left side ; it opens below
into the cloaca, or common outlet of the alimentary, urinary,
and reproductive organs in the Bird. In the ovaiy, each yolk
is enclosed in its ovisac, the narrow suspensory part of which
is named the pedicle. The yolks are of all sizes, fi-om that of
a pin’s head, or smaller, to the completely-formed yolk. In
structure, the minute ova at first resemble the holoblastic

I ovum ; but as they grow, they become meroblastic, and the
cicatricnla, or disc (fig. 117) oit\\G (jerni-yolk, or formative yolk,
is very early recognised upon the rapidly inercasing formative
yolk ; it is nearly always at that part of the yolk whicii cor-
re.sponds with the pedicle of the ovisac. It is now that the ger-
minal vesicle, c,//, with its contained .spot, or macula (jerminativa
of Purkinje, are distinctly seen ; but no juicleated cells exist.
The vesicle and spot disap])ear as the yelk descends along the
oviduct, whether the egg be fertilised or not; they are not found
when the egg is laid, fig. 1 1 8, but the cicatrietda has then become
subdivided into two layers, thcdeej)er one containing nucleated
cells, many of which are also seen in the central parts of the
yolh. As each yolk eidargc.s, its ovisac increases in vascularity,

! and, when the yolk approaches maturity, a non-vascular band,

I VOL. II. Q y

I

594

SPECIAL PIITSIOLOGY.

or zone, forms aronncl it, in wliich, at a part named the stifpna,
a rupture occurs, and the yolk escapes into the infundibulum
of the oviduct. The remainder of the ruptured ovi.sac, with
its coverings, is cup-shaped, and Ibrms the calyx, which
gi-adually shrinks, appearing for a time as a cup-.shai)ed body.
As the yolk descends along the oviduct, the mucous membrane
of this canal, which is vascular and glandular, secretes the
albumen, or ^ullite ; this is now added to the surface of the yolk,
being deposited in spirally-arranged layers, owing to the rota-
tion of the ovum during its descent, in which it is guided by
numerous spiral folds of the mucous membrane. The first or
inner layers of the white, are the densest, and at each end or

Tig. 117.

Pig. 117. Part of the yolk of the hen’s egg. suiiposccl to be taken from the
ovarium (Allen Thomsoii). A, ijortioii of the sui face of llic yolk, show-
ing the cicatricula, vitelline disc, or germ-yolk, with the germinal
vesicle, still present in its centre. (Magnified 6 diameters.) B, side view
of cicatricula. C, vertical sectional plan of cicatricula; m, vitelline
membraoe; i/, granular substance of disc; g, germinal vesicle.

polo, are denser and semi-opaque, twisted portions of the
Avhite, named the chalazce-, the turns of these are in opposite
directions, and are also produced by the spiral movements of
the yolk, in its descent. Towards the lower part of the oviduct,
the egg, now composed of the J’^olk and white, enters a dilated
portion known as the isthmus of the oviduct, which is lined by
a thick mucous membrane, provided with innumerable villi ;
it is here that the egg acquires a covering, which corresponds
with the chorion of the Mammalian ovum, and becomes partly
calcified to form the shell. The inner part forms the shell-
membrane, and the outer part, becoming calcified, is the shell.
These being secreted and deposited outside the Avhite, the egg
is completed, and then passes through the cloaca to be dejiosited.
Birds are called oinparous animals.

THE hen’s egg.

595

The shell of the perfect egg (fig. 119, e) is composed of 9(?
jiarts of earbouiite of lime, 2 of phosphate oflime, and 2 of animal
matter. The earthymatter is deposited in minute ci’ystalline par-
ticles, embedded in a delicate animal basis ; the shell is porous,
admitting the evaporation of fluid from Avithin, and the passage
of gaseous matters in both directions. The shell-membrane, d,
next within the shell, has the appearance of tissue-paper, and
consists of scA^eral layers of fine matted fibres, runnmg spirally,

Fig. 118.

Eiff. IIS. Cicatrioula of the hen’s cfrp, after it has been iaicl (Allen
Thoinsoii). A, eicatrieiila, or f:onn-yolk in a fertilised egg; it shows a
transparent central area, looking dark, and a few halones or haloes near
the cireninfcriniee. J!, vertical sectional plan of the cicatricula and ad-
jacent part of yolk, in a fertilised laid egg; a, vitelline membrane; 5, 5,
thick part of cicatricula or germ-yolk, with thin part or area in the
centre; c, group of gr.anules, occupying the iiosition of the former germinal
vesicle, which has disappeared in the progress of evolution ; rf, the canal
containing white yolk, leading to the lalebra; ce, the .vellow, or nutri-
tive yolk. C, (acatricula of an nnfrrlilised egg; it has no germinal
vesicle, and no trausjiarent area, but only irregular blotches.

and compo.sed, it is said, of .solidified allmmcn. At tlic larger
end of tiic egg, the shell-membrane separato.s, ;ifter a lime, into
two layers, between which, from the tvasting of the iluid of
the egr, air finds its way from without through the shell ; the
interval is named the air-space, /'; it increases with the length
of time that the egg is kept ; it is not essential to, though it

0 Q 2

59G

SPECIAL PHYSIOLOGY,

may assist in, tlie respiration of the embryo-chick. The albu-
men, or ivhite of the egg, is more fluid next to the shell-
membrane, but becomes denser in its deeper parts, next to
the yolk; it consists of 11'5 per cent, of albumen, 1 to
2 of fat, '5 of saline matters, chiefly chloride of sodium, 2 of
extractives, and about 84 per cent, of water. Within the white,
the large yolk is held in its place, or moored, by the two coiled
elastic threads, named the chulazce, c c, and, being lighter than
the white, floats in it. Moreover, owing to the chalazae being
attached below the centre, or horizontal axis, of the yolk, a

Fig. 119.

Fig. 119. Section of the hen’s egg (Allen Thomson), a, meroblastic yolk,
enclosed by the vitelline menibiane. 6, inner dense part of albumen.
b', outer thinner or more fluid part, c, c, the chalazm. d, double shell-
membrane. e, the shell. /, the air-space between the two layers of the
shell-membrane. The section of the yolk shows the halones, or concen-
tric layers, also the central cavity or latebra, and the canal leading up
from this to the cicatricula or disc at its summit.

Itarticular portion of the .surface of the latter, is always upper-
most when the egg is laid upon its side ; during incubation,
tlierefore, it is next to tlie hen's body, and more accessible to
air and light. The^o//r, a, enclosed within its proper vitelline,
or vitellari/ membrane, is of a ptile-yellow colour, and even
ol' a lighter specifle giavit}^ than water ; it is composed of
2‘.) per cent, of fatty oi- oily matter, 17 of albumen, triices of
phosphorised iatty matter, of cerebric acid, and of salt.s, amount-
ing in all to 2 per cent., and of 52 per cent, of water. It presents
a fluid basis, com^wsed of albumen in solution, mixed with fine

THE MAMMALIAN OVUM.

597

graimles ; in this, are contained larger granules, and also larger
bodies, called yolk-vesicles. These latter are not true cells, lor
they contain no nuclei ; they vary from :f-i',7yth to -jr^jjth of an
inch in diameter, and are composed chielly of fot particles
atrcrrcffated together, but having no distinct cell-membrane or
envelope around them, though they may be covered by an
indistinct tilm of firmer albuminous substance. The outer
parts of the yolk, as may be seen when it is boiled, are lamin-
ated or stratified, the several concentric layers being called
halones or haloes, fig. 119; in its centre, is a cavity, known as the
central cavity or latehra, fig. 119, in Avhich the yolk is more fiuid
and contains true nucleated cells, mixed with free oil-globules
of different sizes, floating in an albuminous fluid, and forming
what is called the ivhite yolk. This is an extension of the
germ-yolk. Leading from this central cavity to that surface
of the yolk which always floats uppermost, is a channel also
filled with white yolk. At the upper end of this channel,
is the pale, circular spot, or disc, known as the cicatricula or
germinal disc, figs. IIG, 117. This, which is the essential part of
the germ-yolk, consi.sts, even before the commencement of in-
cubation, of two distinctly separable layers : the upper layer
consists of firm and clear sub.«tance ; the under layer, Avhich
is larger, is more opaque, and is composed of nucleated cells.

The Manmalian Ovaries and Ovum.

In the Mammalia, the organs in which the ova are formed,
the so-called ovaries, are alwa)ns double, one on each side.
They are solid and not racemose, as in the Bird, and are of
.small proportionate size, corre.sponding with the smaller size
of the holoblastic ova. Tiiey consist of a firm, indistinctly
fibrous, vascular stroma, containing numerous vesicles, dis-
tended with a clear fluid, and named the Graafian vesicles or
follicles, homologous with the ovisacs of Birds. These vary
in size, from that of a pin’s head to that of a pea, according to
the stage of their maturity. The walls of each Graafian vesicle,
consist of an enclosing vascidar stroma, within which is a
memhrana propria, and, within that an epithelial layer or layers,
forming the memhrana granulosa. Embedded in a part of this
latter, n.'imcd the proligerous disc, is the minute holoblastic
ovum, averaging about yiV(7th of an inch in diameter. The
size of the Human ovum, varies fi-nm Trijith to i-jjth of an
inch, that of the germinal vesicle, from -T-^^yth to of :in

598

SPECIAL PHYSIOLOGY.

inch in diameter. In the Mammalian ovary, the ovisac, or
Avail of the Graafian vesicle, is not everyAvhere in close contact
with the ovum, as in Birds.

At a certain period, a Graafian follicle bursts, not by a fis-
sure, but by a small opening, and the ovum, Avith some of the
nucleated cells of the membrana granulo.sji, a fcAv of Avhich
have noAV acquired a club-shape and cling to the ovum in
stellate masses, enters the funnel-shaped end of the so-called
Fallo])ian tube, Avhich corresponds Avith the oviduct in the
Bird. DoAvn this tube, the ovum descends by peristaltic
action, perhajAS aided by the movements of ciha, into the cavity
ofthe or Avomb, Avithin Avhich it undergoes its futme

dcA^elopment. Each ovary has its OAvn Fallopian tube.

The emptied Graafian follicle, the Avails of Avhich have pre-
viously become thickened and Amscular, is first filled Avith
effused blood, Avhich becomes absorbed. A yelloAv substance
is then deposited in its coats, and, becoming plicated, forms
the so-called corpus luteuni] this is vascular, and consists of
cells arranged in a columnar manner, mixed with soft fibres,
and a yelloAvish fat. It gradually disappears.

In the meantime, the lining-membrane of the irterus, Avith
its columnar ciliated epithelium, has become thickened and
more vascular, and certain glands Avithin it are highly deve-
loped, so as to form perpendicular tubuli. The intertubular
substance also undergoes hypertrophy, soon containing many
ncAv cells, Avith much fluid and fatty matter, thus forming
a soft nutrient matrix, from Avhich, by mere imbibition, the
early ovum may be nourished. The sxiperjicial stratum of
the altered mucous membrane, thus modified, becomes
changed into the soft, pulpy, opaque membrane, knoAvn as the
decidua, because it is throAvn off Avith the embryo at birth.
This membrane consists, after a time, of two layers, knoAvn as
the decidua vera, and the decidua rejiexa. The decidua Amra is
cribriform, being perforated by little orifices corresponding Avith
the enlarged uterine glands ; it lines the uterus, but is Avanting
at the orifice, and also at the openings of the tAvo FallojAian tubes.
It contains tortuous arteries proceeding from the uterus, together
Avith large veins and venous sinuses, fine areolar ti.ssue, nu-
cleated cells, and soft granular matter. As this structure
groAvs, it ultimately forms the maternal portion of the pla-
centa, Avith its arteries, and venous sinuses or lacuncv, AAdiich
is intended to convey nourishment to the future embi'yo, and
to accomplisli the respiratory changes in its blood. To some

THE CHORION AND ITS CHANGES.

5!)!)

part of tlie deciclua vera, the ovum soon becomes adherent,
wliilst the decidua rejlexa, as its name implies, covers in tlie
ovum, either owing to a sinking-in of that little body, or to a
rising-up of the decidual membraue. Ultimately the two portions
of the decidua, coalesce, or the reflected part disappears. At the
same time that the decidua generally, is becoming converted
into the maternal portion of the placenta, the ovum itself, having
been fertilised, grows rapidly, and undergoes remarkable
changes in its interior — some relating to the formation of the
embryo itself, others referring to the coats or membranes,
which constitute its means of protection and of attachment to
the maternal placenta. The outer vitelline membrane, which,
from its thick and transparent albuminoid character, is named
the zona pellucida, having lost the club-shaped adlierent cells of
the membrana granulosa, has developed around it, a thin but
strong, whitish membrane, named the chorion, corresponding
with the shell-membrane of the Bird’s egg. The chorion is a
fibrous membrane, having a layer of tesselated cells outside it.
At first, smooth on its outer surface, it speedily becomes covered
over with minute, soft, scattered knobs, which soon enlarge
and form simple villi. These, composed of nucleated cells
only, like the outer tesselated layer of the chorion itself, grow
rapidly, and form swollen or club-shaped ends, which embed
themselves in the soft structure of the early decidua vera, from
which they doubtless actively absorb nourishment for the
ovum. Afterwards, these primitive villi are replaced by other
branched or tufted villi, which form the so-called sliagg/j or
villous chorion. These latter villi, after the others have dis-
appeared, continue to cnlaige, receive bloodvessels proceeding
from the embryo now forming within the ovum, and so pro-
duce vascular processes or tufts, which project, or depend, into
the venous sinuses or lacunaj of the maternal portion of the
placenta. They constitute the embryonal ov faiUd portion of the
placenta, and, coining into close relation with the maternal
blood, are the organs by which the nutrition and respiration
of the embryo are henceforth carried on.

The cliorion itself soon becomes lined with another membrane,
named the amnion, which, as will afterwards be described, is
derived Irom tlie embryo, and contains a fluid, the liquor
amnii, which serves to protect the foetus in v,tero\ until the
moment of its birth. TTie Mammalia are called viviparous
animals.

600

SPECIAL PHYSIOLOGY.

The Ovaries and Ova of other Animals.

The description of the o^m of Mammalia and Birds, applies, in most
respects, to the ova of the other Vertebrata ; bxit there are certain pecu-
liarities in some of these, and in the ovaries in 'which they are formed.
The same parts in the Non-vertebrate animals, also require notice.

liepiilia. — In the Reptiles, which like Birds are oxiparous, the ovary
is also, as in them, racemose, and, as a ride, single. The yolk is large,
and covered with an abundant white, enclosed in a shell ; but this is
soft, instead of being firml}' calcitied. When the yolk is formed, the
ova escape, by dehiscence, into the abdominal cavity, and arc afterwards
received into the oviduct, which is placed at a considerable distance
higher up. By these, as in Birds, they are discharged into the cloaca,
and thence are generally deposited externally, or oviparously. In the
A'ipcr, the slow-worm, and green lizard, however, the development of the
omlu-yo takes place partially within the body of the parent ; hence such
reptiles are said to be ovovivvparous.

Amphihia. — In the Amphihia, the ovaries are double, and the ova are
no longer, as in the Mammalia, Birds, and Reptiles, brought to matm'it v
in sMccessioJz, but simultaneously, being received into the oviducts, thej’
are conveyed to the cloaca, and are then deposited in the water, either
singly, in chains, or in masses. They are surrounded by a soft, mucous,
areolar tissue, which swells up in the water, keeps the ova apart, allows
light and aerated water to got between them, and supplies temporary food
to the young tadpoles.

Fishes. — In Fishes, the ovaries are also double and symmetrical, and
are chiefly remarkable for the enormous number of ova developed in
them. The number of ova in a codfish, has been found to be upwards
of 3,500,000, in a flounder 1,300,000, and in a mackerel more than
500,000. They are usually matured and deposited simultaneously, but
in the case of migratory sea-fishes, like the herring, probably at suc-
cessive periods. In certain Fishes which are' ovoviviparous. the ova
are few in number, and are deposited at short intervals. iMost com-
monly, the ovaries have an excretory duct, continuous with them, like
the duct of a gland, by moans of which the ova are discharged into
the water. The Cartilaginous, and a small number of Osseou.s Fishes,
however, have no such excretory duct, but the ova pass into the peri-
toiueal cavit}'', from which they escape, in the Cyclostomata, by an orifice
on the under-side of the hinder part of that cavity, named the abdo-
minal pore. In the sharks, a short tube, or rudimentary oviduct, first
receives the ovum. In a sort of chamber, connected with this, the
peculiarly-.shaped, horny, protective case is secreted, like a chorion,.in
which the ovum is discharged.

In the Non-vertobrated animals, the ovaries are neither solid and
parenchymatous as in hlammalia, nor racemose as in Birds, Reptiles,
Annihibia, and Fishes. In the higher forms, they consist of sacs, cecca,
or tubuli, which may he simple or ramified, and which, like a gland,
have an attached or connected duct, named the oviduct, which, however,
is not sopara® from the ovary, as in most Vertebrata. In the lowest
forms, the ova are developed, sometimes in a loose filamentous tissue, or
in membranous plicm, or upon stalks or processes in the interior of the

FERTILISATION OF THE OVUJI.

601

body, as in the Cadonterata, oi’ are actually embedded in its substance,
as in the Protozoa.

MoUusca and Molhtscoida. — In tlie Cephalopods, the ovaries are sac-
cular. The ova are developed upon short processes in these sacs, and.
when detached, leave a part behind, somewhat resembling a calyx. They
are received into a special chamber, in which a protective covering i.s
superadded to them. In the other Mollusca, the ovaries are found either
arranged in strings, or in masses in the body-cavity. In the Lamelli-
branchiata, the ovaries are follicular. In the Molluscoida, the ova, de-
veloped in follicles, are discharged by the oral cavity.

Anntilosa and Annuloida. — In Insects, the eggs are generally nume-
rous ; the ovaries are crecal, like the follicles of glands ; they are double
and symmetrical, but have a common outlet, in a sort of cloaca ; fre-
quently, the eggs are laid by aid of an ovipositor. The females of many
Insects, have a reservoir, known as the spermotheca, like the bee. In
the Crustacea, the ovaries are also double, each having its own outlet;
they form caeca, usually branched, but in the lower forms, simple. The
oviducts are often provided with a spermotheca. The Arachnida h;lve
clongateil vesicular ovaries. In the Myriapoda, they are like those of
Insects. In the Annelids, the ovaries have no omducts, but the ova are
set free in the perivisceral cavity. Amongst the Annuloida, in the
vermiform Scolecida, the ovaries are either simple, or, more commoidj',
consist of much-ramified tubuli. The ova are numerous, and arc dis-
charged from a p>roper outlet, or from the anal orifice. In the Tienia,
the ovaries are multiple, like the body; each segment has its ramified
canals ; in one species, the total number of eggs, in all the segments, is
said to be 64,000,000. In the Rotifera, the ovary is single and saccu-
lar ; the young are sometimes developed, more or less completely, within
the parent animal. In the Echinodormata, the ovaries are ramified
tubes, modified according to the shape of the body of the animal, there
being usually a pair in each arm or segment; but in the Holothurida,
they are single, have terminal clusters of emea, and open near the
mouth.

Ccslmterata. — In .some of these, as in the Physograde and Cirrhigrade
forms, the ova are developed in clusters on the base of the cirrhi. In
the Pnlmogrado forms, they are developed in sacs in the body-cavity.
In the Actinozoa, they adhere to plicated folds of membrane, in that
cavity. There are no oviducts, and the ova are discharged from the oral
aperture.

Protozoa. — In these animals, the germ-coils, scarcely appear like true
ova ; they form on, or in, the substance of the parent.

From the jircceding account, it is evident that the ovaries are homo-
logous with glands ; so that the germ-cells, or ova, may, as well as the
spcrm-cells, bo regarded us the products of a special nutrient secre-
tive act.

The Feriilisation of the Ovum.

The fertili.sa.tion of tlie ovum, Avhetlier it occur -within, or
without, the body of tlie ovigerou.s parent, requires tlie con-
tact of the male fertilising agent, whicli, in many cases, has

602

SPECIAL PHYSIOLOGY.

been recognised nnd(3r the microscope, by the actual presence
of sj)ermatozoa upon, or even witliin, the zona pellucida of
the Mammalian ova, or upon, or within, the vitelline mem-
brane in other ova.

In the IMammalia, fertilisation occurs in the Fallopian tube,
or in the uterus. In Birds and Reptiles, and in the higher Car-
tilaginous and a few Osseous Fishes, which are ovoviviparous,
it takes place as the yolk enters the oviduct, before it receives
its coating of albumen. In Amphibia, it happens at the time
of dejDOsit of the ova, and in Fishes, with the exception of a
few, immediately after. In the hlollusca and Molluscoida,
Annulosa and Annuloida, and Coelenterata, fertili.sation occurs
within the body, whether the sexes be distinct, or whether

Pip;. 120. a, spermatozoa of the squirrel, h, spermatozoa of the ilosr, still
enclosed in the sperm-cells. Three spermatozoa arc shown free, above.
Very highly magnified (Wagner, Leuckhardt).

hermaphrodite individuals contain both ovaries and fertilising
organs. Even in the Protozoa, separate nuclear bodies exist,
which combine or conjugate, jireviously to the reproduction
of new individuals.

In the Mammalian ovum, it is said that the germinal vesicle
approaches one side of the germ-cell, and even has its
germinal spot turned in the same direction — that is, towards the
side directed to the place of rupture in the Graafian follicle.
Such a movement would certainly facilitate the access of the
fertilising agent to the germinal vesicle and .spot, that i.s, to
the nucleus and nucleolus of this primitive cell.

Fig. 120.

(

CLEAVAGE OF THE YOLK.

G03

In tlie Frog’s spawn, the spermatozoa have been seen in the
jelly-like envelopes of the ova, and also within the ovum. In
certain Osseous Fishes, a minute, lim nel-shaped aperture, named
the microjii/le, forms, at one period, in the vitelline membrane,
and admits the entrance of the spermatozoa. A micropyle has
also been seen in the ova of the Lamellibranchiate MoUusca,
of certain Insects, and of some Echinodermata. In these cases,
the vitelline membrane is relatively thick. No micropyle has
been seen in any of the Vertebrata, excepting in Osseous
Fishes.

DEVELOPiVIENT.

CHANGES IN THE OVUJI. FIRST FORMATION OF THE EMBRYO,
AND ITS APPENDAGES.

The first essential change which occurs in the fertilised
ovum, is the so-called cleavage or segmentation of the yolk.
In the holoblastic Mammalian ovum, the yolk is seen to be
agitated by a peculiar movement — to elongate, contract itself
in the middle, and then to divide into two. Each half rapidly
undergoes further movement, contraction, and division, so that
it now consi.sts of form parts. By subsecjuent subdivision, these
next form eight, sixteen, thirty-two parts, and so forth. The
frst effect of this cleavage, is to transform the yolk into a
mulberry-looking mass ; but, after repeated subdivision, the
surface again becomes smooth, and uniform or granular, and
is composed entirely of an immense number of polyhe-
dral nucleated cells, which form a layer within the vitelline
membrane, and constitute the so-called germ-sac of Coste, or
blastodermic vesicle of Bischoff. The central fluid part be-
comes clear. The segmentation of the entire yolk, has been
observed in all cases of development from holoblastic ova, even
in Non-vertebrate animals. In the eggs of certain Branchio-
gasteropods, a remarkable revolution of the yolk takes place,
subsequently to the period of its segmentation, the yolk turn-
ing first in one way and then in another, within the vitelline
membrane ; tliis is said to depend on ciliary movements.
In the meroblastic ova of the Cephalopods, certain Fishes, Bop-
tiles, and Birds, only a jiart of the yolk, viz. the germ-yolk:,
in the neighbourhood of the germinal vesicle, undergoes this

604

SPECIAL PHYSIOLOGY.

segmentation, the result being the formation of tlie riennimtl
disc or cicatricula, already mentioned, from -which, however,

Fig. 121.

Fig. 121. Changes in the ovum of a Mammalian animal, after fertilisation
(.\llen Tliomson). a to e, successive .stages in the segmentation or
cleavage of the yolk, a, yolk still undivided; 6, cleft into two masses,
each surrounding a nucleus; c, divided into four; </, non-divided; e,
mulberry-like stage of subdivision, to form the blastoderm. The small
nucleated yolk-masses have no distinct envelopes. The ovum has ac-
quired a thicker coat, or chorion. After this, the surface of the yolk
again becomes smooth, and composed of nucleated cells, having true
envelopes. The diagram / shows the relations of the embryo and its so-
(aalled appendages. The dark curved body is the embryo ; beneath it, is
the open part, h ading by the vitelline duct, to the yolk-sac, or future
umbilical vesicle. Immediately surrounding the embryo, above it, and
at each end, is the sac of the amnion, or true amnion ; the dotted line
shows the false amnion. Outside this, is the chorion, cho, with its ru-
dimentary villi. The bladder-like organ, i)rojecting from the h.uder end
of the embryo, is the allantois.

mi extension of a single layer of cells, proceeds over the un-
segmented portion of the yolk, forming the so-called ger-
minal sac.

THE GERMINAL DISC.

605

This yolk-cleavage is a phenomenon of ceU-diiision. It is
stated by iMliller, Gegenbauer, and Leydig, that the germinal
vesicle, or nucleus of the cell of the ovum, and the germinal
spot, or nucleolus of that cell, are directly concerned in this
process. The nucleolus and nucleus are said to divide suc-
cessively into two, four, and many nuclei ; around which, the
yolk, apparently governed by these successive subdivisions of
the nucleus, gathers for the development of the nucleated cells.
In the last generation, these cells acquire distinct cell-walls.
According to others, in certain animals, the germinal vesicle
and germinal spot, the primitive nucleus and nucleolus, dis-
appear completely, immediately after fertilisation occurs, and
their future destiny cannot be traced ; but a fresh cell or
nucleus is supposed to be formed, around which the yolk
gathers, and by the repeated subdivision of this, into two, four,
eight, and so forth, the cleavage of the yolk is accomplished.
The first cell from which these arise, has been named the eiii-
hr/jo cell. According to the former view, the cells which
appear on the surface of the yolk, and out of a part of which, as
we shall immediately see, the embryo itself begins to be
evolved, are derived directlij from a nucleus, once forming a
part of the maternal organism. According to the latter view,
they, and therefore the embryo, are developed indirectln, or
independently, after the solution and diflusion of the jmmitive
germinal vesicle and spot, with the fertilising agent, in the
substance of the yolk. In the fiowering plants, also, the nucleus
or germ-vesicle of the ovule, or ovum-cell, is said, by some,
not to participate in the formation of the cells from which
the embryo plant is developed. Whichever of the j:)receding
views be adopted, the cleavage of the yolk is attributed, how-
ever, to the formative force, known as the (jerm- force, resident
in the first-formed nucleus and nucleolus, and continued in
all their successive subdivisions. The germinal vesicle and
spot, as already stated, arc said to disappear even in uni'ertilised
Bird’s ova.

The formation of the layer of nucleated cells which constitute
the fjerni-sac of the holoblastic, or the (jermiiud disc of the mc-
roblastic, ovum, as a result of the cleavage of the yolk, is alto-
gether preliminary to the formation of the embryo, whidi
cannot yet be recognised. In the Nou-vertebi-ate holohlastic
ovum, as, for e.xample, in the Nematoid Ascarides, these cells
soon aggregate into a more or less coiled ojiacpie mass, which
as.-.umes the shape of the embryo, and then, by further develop-

606

srECiAL rnrsiOLOGT.

ment, actuiilly forms the young animal. Tljis is also the case
in the Echinoclermata, the smalle)- Crustacea, and Arachnida,
the Insecta, and the Mollusca, except the Ce]dialopods. But in
the higher animals, with holohlastic ova, such as the Cyclo-
stomatous Fishes, the Amphibia, and the Mammalia, the
cleavage-cells form, at a certain ]>art of the germ-sac, a small
opaque hemispherical mass, which soon spreads out into a
disc-like layer, and constitutes the so-called fjei'ininal disc
or area, area (jei'ininativa, embri/o-spof, or hlastodemi. It is
the central part of this, which is directly concerned in the
iormation of the embryo. In the Molluscous, and other animals
just enumerated, no such germinal area is found. In all the
meroblastic ova, Avhether of Non-vertebrate or Vertebrate type,
as is well seen in the hen’s egg, the cicatricula, or germinal
disc, already described, constitutes this germinal area or em-
bryo-spot.

In this area, as in that of the higher holohlastic ova, the
first traces of the embryo are formed. Amongst the Non-ver-
tebrate types, those of the higher Arachnida, and Crustacea,
appear as a certain number of opaque spots, having a beautiful
symmetrical arrangement, whilst in the Cephalopods, they
commence by a small number of primitive masses. In the
Vertebrate holohlastic or meroblastic ova, the commencement
of the embryo is always indicated, amongst other things, by
the appearance of a linear qjrimitive streak. This is quite
characteristic of the Vertebrate type of ovum, not occurring
even in the elongated Annulose type. The evolution of the
Vertebrate embryo, can alone occupy our attention here. That
of the chick in ovo, will be generally followed ; but the pecu-
liarities ol'the ovum of the Mammalia, will also be indicated.

When first formed, the appearance of the blastoderm, or
blastodermic layer of the germinal tirca, is nearly or quite
unilbrm, all its nucleated cells being tiliko, and the result of a
homogeneous evolution. But soon, a heterogeneous develop-
ment ensues, cells of difierent character, and collected in
peculiar situations, iippear, and, by more special aggregations,
and wider dift'erentiiitions, the various parts which ibrm the
embryo, its organs, tissues, and aiipendages, are evolved.

First, the germinal area or disc incri'ases in size or thicknes.s,
by the Iormation of new cells; as already mentioned, it veiy
early consists of two layers, named the upper, external, or
serous, and the lower, internal, or mucous germinal lamina, or
jdate-, between these, a middle germinal layer, lamina, or
[)late, is .soon formed, but rather in cinncction with the serous

THE THREE GERMINAL LAYERS.

6U7

layer. The internal layer, epithelial in structure, is soon pro-
longed over the germinal sac, -which covers the yolk ; the outer
layer also extends itself, but the middle layer does not pass be-
yond the limits of the embryo-spot. As the germinal area
enlarges, it presents a central transparent region, kno-wn as the
transparent, area, or area pellucida, around -\vhich is a denser
portion, named the opaque area, or area opaca-, beyond this,
is the vitelline area. The transparent area is at first circular,
but soon oval, and aftenvards pear-shaped ; in it, the first
rudiments of the embryo appear, in the form of a linear
oblong mark, or streak, called the primitive trace, or groove.
This consists of a median or axial fuiTow, bounded by t-wo
lateral longitudinal plates, named the laniinoi dorsales, -which
enlarge and elongate, as the area itself becomes larger and
j)yriform in outline. Beneath this groove, immediately below
its floor, appears a delicate, semi-opaque thread, at first cel-
lular, but soon becoming cartilaginous, named the chorda dor-
S(dis or notochord, which part, so characteristic of the Vertebrate
type, is recognisable in the chick, as early as 18 horn's after
incubation. These ar'e the rudimentary parts of the embryo,
one end giving origin to the head, and the other corresponding
with the tail. The position of these rudiments is remarkaltly
constant in the hen’s egg, always lying trau.sversely to the
long axis of the egg ; as the embryo-chick develops, it turns
upon its side, so that the forepart of the head usually faces
the narrow end of the egg.

In the rudimentary stage just described, a vertical section
across the embryonal line of the germinal area, would show the
edges of the three germinal lagers of the blastoderm, Avith the
])rimitive groove or furrow in the centre, and the cross-section
of the chorda dor.salis beneath it.

From these three layers, the parts of the future embryo are
tlius evolved. From the upper external or serous layer, also
njinied the sensorial layer, are developed, along its axial pcu'tion,
the cerebro-spinal nervous axis, and the organs of the senses ;
and, from its lateral portions, the cuticle or ouior skin, with
its epidermic appendages, the feathers, bill, jind claws, and in
Mammalia, the nails and hairs; lastly, the sebaceous and sitdo-
riferous cutaneous glands and the Meibomian, certuninous, and
mammary glands. From the middle layer, also called the
motorio-sexual layer, are developed, by coinpliciited metamor-
phoses of its substance, the bones, the muscular system, the
peripheral spinal nerves, the sympathetic ucrve.s, the heart,
blood ves.sels, and lymphatic .system, the so-called ductless

G08

SrECIAL PHYSIOLOGY.

glands, and the reproductive organs; also, next to the external
layer, the time skin, and, next to the internal layer, the nuis-
cidar and submucous coats of the alimentary canal. Lastly,
from the internal layer, also called the mucous or intestinal
layei', are developed, the epithelial lining of the alimentary
canal, and all its glandular extensions, such as the mucous,
gastric, and intestinal glands, the pancreas and the livei", also
the lungs and respiratory passages, and the urinary apparatus,
including the bladder, ureters, and kidneys.

Whilst, therefore, the middle layer gives rise, by very strik-
ing differentiations, to a great variety of tissues, the upper
and lower layers, except that part of the former which gives
origin to the brain and spinal cord, produce textures com-
posed of simpler forms of cell-tissue.

These layers also contribute, in a manner to be presently
described, to the formation of three parts or appendages ex-
ternal to the body of the embryo — viz., the amnion, the yolk-
sac or umbilical vesicle, and the allantois.

GENERAL DEVELORJfENT OF THE EMBRYO AND ITS APPENDAGES.

The borders of the primitive or vertebral groove, including
parts of the external and middle layer (the former named the
medullary plate, and the latter the vertebral plate), rkse up on
each side, and ultimately unite along the middle line, to form a
canal, containing the rudiments of the future brain and spinal
cord ; the anterior part or cejdmlic end of this canal, becomes
more expanded than the rest, whilst the posterior part tapers
to a point. In this way, the. so-called neural cavity (vol. !.■
p. 134) of the future animal, is formed above the chorda dor-
sal i.s, traces of which are, lor a time, found jrassing through
the bodies of the growing vertebra;. Soon, from the vertebral
])lates, where these tuni upwards, the external and middle
layers extend sideways, constituting the so-called lateral plates,
which, growing downwards, and bending inwards, IbiTu the
walls of the abdomen, and enclose a cavity which is placed
Inaieath the chorda dorsalis, immediately in contact with the
yolk ; this ultimately constitutes the lia’inal or tlioracico-
abduminal cavity of the I'uture animal; it soon contains the
heart and great bloodves.sels, and the rudiments of the alimen-
tary canal, which is eom]ileted by a corre.spondiiig fblding-in
ol'the internal bla.stodermic layer which lies immediately upon
the yolk.

THE AMNION.

C09

>•>

The embryo, by the bending in of its sides, next appears to
be raised from the yolk, and partially shut off' from it, by a
sort of constriction which takes place, first beneath the head
and the caudal extremity, and afterwards at each side. Ulti-
mately, this constriction shuts off the body of the embryo
from the yolk-sac, which then communicates only by a narrow
passage, the ductus vitelli, or vitelline duct, with the central
space in the interior of the embryo, now the rudimentary
alimentary canal, lying in the ha;mal cavity. The yolk-sac
thus cut off', shrinks, and forms the umbilical vesicle. The
head of the embryo, now free, bends down towards the yolk,
and forms the cephalic flexure. At the same time, a delicate
transparent membranous fold, derived from the external germi-
nal layer of the blastodenn, rises, like a hood, over that part of
the embryo; a similar, but smaller, fold rises over the free
caudal extremity, and, on each side, Avhere the lateral plates
bend in to form the constriction just described, corresponding
folds arise. These folds are double ; they gi'ow, and at length
meet over the back of the embryo, and coalesce so as to form,
by their innermost layer, a complete, but delicate, closed sac,
called the amnion, Avhich, in the chick, is perfected as early as
the third day of incubation. This is at first close to the em-
bryo, but it soon expands, and carries with it the outer layer of
the same folds, which afterwards reaches the shell membrane
in the Bird, but in the Mammalian ovum, becomes attached to
the inner surface of the chorion, and so forms the flalse amnion.
The .°ac of the amnion surrounds the vitelline duct, in a sort
of sheath, and thence becomes continuous with the skin cover-
ing the body of the embryo (see fig. 121).

The amnion is, thin, transparent, and non-vascular. It
consists, at first, of a .stiatctureless basement membrane, lined
with a delicate sf[uarnous epithelium ; afterwards it contains
fusiform cells, and a fine areolar tis-sue, and, in Birds, even non-
striated muscidar fibres. Its fluid contents, the litivor amnii,
usually alkaline, consist of water, having in solution from 1
to 3 per cent, of solid matter: this is composed of a little albu-
men, traces of urea and uric acid, allantoin and other extrac-
tives, salts, such as lactate of soda and sul])hate and j)ho.sphate
of lime, and lastly, sebaceous matter, epidermoid scales, and
minute hairs thrown off from the embryo.

The amnion, considered as an appendage of the embryo, is
chiefly j>rotectivc, but may be re.s])iratory or eTiuinctory. It
is present not only around the embryo of the Bird, but also

VOL. II. I! u

610

SPECIAL PHTSIOLOGT.

around that of Mammalia and Reptiles. The embryoes of the
Amphibia and the Fish, however, which are developed in, and
surrounded by, water, are destitute of an amnion, no such
covering being formed, and no folding over of the external
blastodermic layer taking place, as in the ovum of the Reptile,
Bird, and ISIammal.

The umbilical vesicle or yolk-sac already mentioned, may also
be regarded as another appendage of the embryo. It is formed,
as just described, by the lower part of the yolk-sac, sur-
rounded by an extension of the innermost germinal layer, and
connected Avith the intestinal canal of the embryo, by the con-
stricted passage named the vitelline duct (fig. 121). It is not
only external to the body of the embryo, but also outside the
cavity of the amnion. Very early, certain bloodvessels are deve-
loped in the middle germinal layer of the embryo, and, spread-
ing into a netAvoi'k of vessels, they extend upon the surface of
the yolk, and form the so-called vascular area. Two special
branches, named the omphalo-mesenteric arteries, convey blood
from the embryo thi'ough this area, and a vascular membrane
is thus formed, which gradually covers the umbilical vesicle or
yolk-sac, and also extends itself, at least in the Birds’ and Rep-
tiles’ eggs, by numerous projecting folds, into the substance of
the yolk. From the substance of the yolk, these bloodvessels
absor’o dissolved nutrient material ; and, for a time, the blood
contained in them, is aerated by interchanges of carbonic acid
and oxygen between it and the other fluids of the egg or ovum.
In the Bird, the yolk-sac is very large ; it is gradually drawn
into the abdomen of the chick, and may be found in that cavity
after the chick is hatched. In time, its contents are gradiuilly
absorbed, and its remains are frequently traceable as a short
blind sac or stem, the vitelline ccecum, connected Avith some
part of the small intestine. Sitaiilar changes are observed in
Reptiles. In the Plagiostoinatous Fishes, as in the sharks, the
yolk-sac remains, for a long time, suspended to the abdomen of
the young fish. In the Osseous Fishes, the yolk, being smaller,
sooner disapjAears. In the Cyclostomatous Fishes, and in the
Amphibia Avhich have holoblastic ova, the yolk-sac is still
smaller and more ti-ansitory. Lastly, in the Mammalia, it is
very minute, but undergoes slight groAvth, especially in the
Carnivora and Rodentia. It is found, after a time, as a circular,
pale-yelloAv disc, attached to the amnion, and having no further
function ; sometimes, as in Ruminantia, it is completely ab-
sorbed.

THE ALLANTOIS AND ITS CHANGES.

611

Besides the amnion and the yolk-sac, another most import-
ant appendage of the embryo in Birds, Beptiles, and Mam-
malia, remains to be described. This is the so-called allantois.
In the Bird’s egg, it appears as a small eminence, at first con-
sisting of nucleated cells, but soon becoming vascular, situated
on the under-side of the embryo, close to its caudal end. It is
derived from portions of the internal and middle germinal layers,
which, in this situation, ibrm the intestinal part of the alimentary
canal. The allantois soon becomes a hollow protrusion of the
intestinal wall, growing out, in the form of a sac or bladder, be-
yond the body of the embryo, and being placed, like the um-
bilical vesicle, outside the sac of tlie amnion (fig. 121). It
carries out with it, numerous bloodve.ssels, which are developed
in the middle germinal layer, and are connected with the great
vascular trunks of the hinder part of the embryo. It cjuickly
extends itself, tiU it reaches the inner surface of the shell-
membrane of the egg, over the interior of which it spreads,
with its walls closely applied to each other, so as to ibrm a
double membrane, the outer layer of which, in contact with
the shell-membrane, retains its bloodvessels, whilst those of
the inner layer, next to the white of the egg, become shrunken.
The hollow stalk or stem of the allantois, which is situated
within the embryo, opens into a small cavity, developed in
connection with the lower end of the intestine, named the
urogenital sinus, which fonns the rudimentary Mrmnry iZacZtZer.
Between this cavity and the opening in the walls of the embryo,
through which the vitelline duct passes to the umbilical sac,
hence called the umbilical opening, the allantoid canal closes,
and is converted into the urachus, or superior ligament of the
bladder. Outside the umbilical opening, the bloodvessels of
the allantois, now named the umbilical vessels, ramify in
the outer layer of the allantois, next to the sheU-mem-
brane, forming a densely vascular structure applied to the
inner surface of the whole shell, separated fi’om it only by
the shell-membrane. In an early stage of development, the
allantois of the Bird, is contractile, and acts as a sort of
urinary bladder, its fluid containing urea, allantoin, sugar,
certain salts corresponding with those of the blood, Avith slight
traces of albumen. It receives, indeed, the secretions of certain
organs known as the Wolffian bodies, or primordial kidne//s,
and also tho.se of the rudimentary kidneys themselves. Its
superficial vascular layer next to the shell-membrane, Avhich
lias been named the endochorion, is the active respiratory

jt u 2

612

SPECIAL PHYSIOLOGY.

organ of the embryo bird, after the vessels upon the yolk-sac
have ceased to be sulRcient for this jmrpose. The blood to
be aerated, passes from the embryo through the umbilical
arteries on to the allantois, and retm-ns to the embiyo by the
umbilical vein. As the period of hatching approaches, the
vessels of the allantois and this membrane itself, become par-
tially dried ; the young bird chips the egg, and begins to
breathe by its lungs. By the time it escapes fi-om the shell,
the allantois and its vessels are quite desiccated.

The allantois is present also in Reptiles, the shell of the eggs
of which is soft and thin, and the oxygenation of the blood
easily performed. In Amjdiibia and Fishes, there is no allan-
tois, the respiration of their embryoes, which are entirely
aquatic, being at once accomplished by means of giUs, so that
no allantois is needed.

In the Mammalia, however, the allantois is invariably pre-
sent, and fulfils a most important office ; for it is the means of
conveying outAvards, from the embryo to the maternal struc-
ttmes, the A'essels Avhich connect the two, and ser\'e in the func-
tions of nutrition and respiration. Its inner part forms, as
usual, the urachus, and joins the apex of the future urinary
bladder ; and its outer part, for a time, constitutes the so-called
allantoid sac. This outer part extends itself, till it reaches the
inner surface of the chorion. As already described, this last-
named structure is formed upon the altered vitelline membrane,
and soon becomes coAmred, on its outer surface, Avith little
knobs ; these are developed into temporary A-illous processes,
composed entirely of nucleated cells, and employed in absorbing
nourishment for the early mammalian embryo. After a time,
these simple Aulli disappear, being, as it Avere, obliterated by
the groAvth and distension of the chorion. But then, the cho-
rion itself, and the outer Imjer of the amnion, ox false amnion,
AV’hich is noAV in close relation Avith the chorion, becomes the
seat of development of other processes, Avhich, Avith a thin
covering of cells from the chorion itself, form the ramified
tufted villi of the so-called s/mf//7// c/m/7(>«. As the allantoid
sac of the Mammalia, Avith its contained bloodvessels, groAvs,
it reaches the inner surface of the chorion, and, its ve.ssels
entering the villous processes of the latter, form loops in their
interior. These proce.sses, noAv vniscular, and constituting the
embryonal or fwtal portion of the placentiv, jjonetrate, through
the decidua, into the maternal portion of the placenta, pro-
jecting into its venous sinuses and lacuiue, and form the so-

THE TLACENTA.

613

called fatal villi. These are covered by their own epithelium
and basement membrane, and also by a loose layer belonging
to the lining-membrane of the maternal venoirs sinuses. The
blood of the Mammalian embryo, passing along the umbilical
arteries, upon the allantois, circulates through these fcetal villi,
which are themselves bathed with the maternal blood. The
two bloods come into close relation, being separated only by
the most delicate tissues, but they do not intermingle. In
this way, nutriment is absorbed fi’om the maternal blood, for
the maintenance of the growth of the embryo ; and possi-
bly effete matters are especially eliminated from the em-
bryonal blood. This latter blood is oxygenated by a respi-
ratory process, consisting of an interchange of carbonic acid
and oxygen between the embryonal and maternal blood, jirst
as occurs in the gills of the Amphibian tadpole, and of the
Fish, which are bathed in water. The blood in the umbilical
arteries of the embryo, is, as we shall see, nearly all dark or
venoirs blood ; that in the maternal venous sinuses, is really
arterial, for the maternal portion of the placenta contains no
capillaries, the branches of the uterine arteries which enter it,
terminating at once in the venous lacmiEe, from which the
time uterine veins pass oblicprely. Having been properly
purified and nourished, the embryonal blood returns from the
placenta, enters the umbilical veins, and through them, reaches
the embryo again. In the Reptile and Bird, the respiration
of the embryo takes place between the embryonal blood in
the vessels of the allantois, and the atmospheric air in the
fluids of the egg, or outside the shell-membrane : in neither
Class, do the ves.sels of the allantois or the branches of the
umbilical vessels, penetrsite the outer coverings of the ovum,
as occurs in the Mammalia generally.

The exact relations of the allantoid sac and its vessels, with
the chorion, and especially the extent to Avhich it covers the
interior of that coat, vary in the different Orders of Mammalia.
In the Monotremata and Marsupialia, for example, the allantois
i.s small and pear-shaped ; its vessels are merely arborescent,
and do not penetrate the chorion. Hence there is no special
organ, or placenta, intermediate between the embiyo and the
uterine walls, and these animals are therefore named Impla-
cental Mammalia.

In the porpoise, the pig, the horse, and, it is said, in the
camel tribe also, every part of the chorion and the allantoid
endochorion, which are coextensive, is covered with va.scular

614

SPECIAL PHYSIOLOGY.

processes ; these enter the hypertrophied uterine membrane
at all points, and form the so-called diffused placenta. In the
Euminants, with the possible exception of the camels, the
vascular endochorion, or developed allantois, is also coex-
tensive with the chorion ; the vascular processes project, and
attaching themselves to the uterus at certain definite scattered
points of the surface, form the embryonal cotyledons ; these
consist of clusters of ramified villi, which fit into coivespond-
ing ramified canals, arranged in cup-shaped depressions of the
uterus, called the maternal cotyledons. No decidua exists, in
these cases, between the embryonal and the maternal tissues,
and they are easily detached from each other. The blood in
both, is brought into close proximity, but the vessels of each
are independent, and the two bloods do not intermingle. In the
dog, cat, and Carnivora generally, the ovum, at first round, after-
wards becomes oval, fusiform, or elongated, and occupies a com-
partment in the elongated uterus. The endochorion, or allan-
toid sac, is very extensive ; but the villous processes, absent from
the ends of the ovum, form a broad zone around its middle.
A true decidua exists, and the combined structures constitute
the zonular placenta. In the Eodentia, as is well seen in the
rabbit, the allantoid sac reaches a small part only of the inner
siu-face of the chorion ; at this point alone, permanent vascular
processes are developed, which, entering the hypertrophied
uterine membrane, part of which forms a decidua, constitute
a discoid placenta.

In the formation of the discoid human placenta, it is noticed
that the allantois is very small, appears early, and soon wastes;
it reaches the chorion at only one point, not spreading out
coextensively with it; and it conveys outwards, as usual,
the umbilical arteries, the branches of which enter the jier-
manent villous processes of the shaggy chorion, or fa?tal villi ;
these are limited to one part of the ovum, penetrate the
decidual and hypertrophied portion of the uterine walls, and
enter the maternal venous sinuses.

The tivo umbilical arteries and one umbilical vein, are
supported upon the remains of the now impervious allantois,
which grows into a soil mucous connective tissue ; with these
parts also are ibund the Avasted ve.stiges of the v'itelline duct,
with its atrophied ornphalo-mesenteric artery and veins; these
structures becoming elongated, and surrounded with a tubular
process of the amnion, form the umbilical cord or navel-string.
This cord is, therefore, connected with the jdacenta at one end.

DEVELOrMENT OF TEE SKELETON.

615

and Avith the naA'el of tlie embryo at the other. Its Amssels
are ahvays more or less spirally twisted.

At the birth of the Mammalian embryo — an event Avhich,
with the human infant, happens at the end of the fortieth week
— the foetus and its membranes are detached fi-om the inner
surface of the uterus. The embryonal vascular portion of these
membranes, Avhether it be a diffused, cotyledonous, zonular, or
discoid placenta, is always detached. In the case of the zonu-
lar and discoid forms of placenta, Avhere a true decidua is
developed, a part of the maternal tissues is also separated at
the same time. Where there is no decidua, as in the diffuse
and cotyledonoirs forms, the foetal villi are merely detached
from the surfaces or recesses into Avhich they fit. In the latter
cases, parts of the maternal tissues, especially of the veins and
venous lacunae, come away. Hemorrhage is ordinarily quickly
aiTested, owing to the obliquity of the passages leading into
the deeper uterine veins, and to the firm contraction of the
uterine walls. If these become relaxed, arterial, but not venous,
hemorrhage may occur.

DEVELOPMENT OF TEE ORGANS.

The share taken by each of the three germinal layers of the
blastoderm, in the formation of the several systems of organs,
having been described, their special development may now be
considered.

The Skeleton, 3Iuscles, and Integuments of the Body.

The vertebral column is developed from the vertebral plates
of the middle germinal layer, found on each side of the verte-
bral groove and chorda donsalis. As the vertebral groove
clo.ses along the back of the embryo, first opposite the cervical
and dor.sal regions, small sriuare masses ai'e seen on each side
of the median line, in the inner thicker portion of ihe Amrtebral
plates. These were formerly considei’ed to be the rudiments
of the bodies of the vertebim only, and were named the 2n‘imi-
tive or p)'imordial vertebree ; but they are better named the
dors(d segments, for other structure.s, besides the vcrtebim, are
developed from them. In the thoracic region, the posterior
ends of the rilis, and, throughout the whole length of the ver-
tebral column, the roots of the sjfinal nerve.s, together Avith the
ganglia on the posterior roots, Avhich are of great proportional
size, the spinal muscles, and the cutis covering these parts,

616

SPECIAL PHYSIOLOGY.

are thus formed ; a small portion only, therefore, is developed
into the future vertebras. The part which forms the skin and
spinal muscles, is named the dorsal plate or division, whilst the
rest is called the ventral plate or division. The innermost por-
tion of this latter, which is called the vertebral plate, grows in-
wards, and surrounds the chorda dorsalis, so as to enclose it in
a thick, continuous, membranous sheath ; this divides anew,
transversely, into annular portions, corresponding with the
bodies of the future cervical, dorsal, lumbar, sacral, and coc-
cygeal vertebrte, into which they are developed, by passing
first into a cartilaginous, and then into an osseous, state. The
body of the atlas joins the axis, to form its odontoid proces.s.
The remains of the chorda dorsalis are traceable, for a long
time, through the centre of the bodies of the vertebrae, but
ultimately they become absorbed. In the lowest or Myxinoid
Fishes, however, the chorda dorsalis is recognisable through-
out life. Between the vertebras thus formed, an intermediate soft
tissue becomes developed into the intervertebral substances, in
which the notochord persists, as the softer fibrocartilaginous
centre. Whilst the bodies of the vertebrse are thus produced,
another portion of the dorsal division of the vertebral plates,
ascends towards the back of the embryo, grows around the
vertebral groove, and then forms the arches and sjnnous pro-
cesses of the vertebrae, so completing the vertebral column.
These cartilaginous arches first close in the dorsal part of
the column, and then meet everywhere, except opposite the
coccyx, and sometimes at the lower end of the sacrum ; the
non-formation or non-union of these arches, constitutes spina
bifida.

At the anterior or cephalic end of the embryo, as ah-eady
mentioned, the sides of the vertebral groove, composed of the
medullary and vertebral plates of the external and middle
germinal layers, expand, and, meeting above in the middle line,
enclose a space which forms the rudiment of the cranium
and its contents. This is soon marked off into three pairs of
symmetrical sacs or dilatations, named the cerebral vesicles,
which, bending down towards the yolk, form the cephalic
flexure, or bend of the neck. In that part of the walls of these
vesicles, which corresponds with the middle germinal layer,
the cephalic capsule or primordial shill is formed ; this is at
first memlu-anous, then partly cartilaginous, and ultimately
bony. Into the iloor of this cavity, the anterior extremity
of the cartilaginous notochord, or chorda dorsidis, penetrates

DEVELOPMENT OF THE LIMBS.

617

only a short distance, reaching, in the middle line, as far for-
Avards as the future sella tiu’cica in the sphenoid bone, which
lodges the pituitary body. The base only of the primordial
skull, becomes cartilaginous, like the bodies of the primitive
vertebra) ; the sides and upjjer part of the cephalic capsule
remain membranous. The primordial skull does not divide
into transverse segments, lilce the rudimentary annular verte-
bra). Its cartilaginous portion is developed into the base and
sides of the occipital bones or basi- and ex-occipitals, the
ala) majores of the s^Dhenoid or ali-sphenoids, and the pre-
sphenoids and orbito-sphenoids or ala) minores, also into the
turbinate bones, the median po)-tion of the ethmoid bone, and
the cartilaginous nasal septum. The vo7iier, however, is
formed from a membrane, below the septum. The upper
part of the occipital bone or supra-occipitals, the
bones, the squamous part of the temporal bones, the frontal
bones, and the nasal bones, are developed as distinct opercular
bones, directly from special centres of ossification in mem-
brane, and not from cartilage. The petrous and mastoid parts
of the temporal bone, and the floor of the tympanum, are
developed from osseous centres in the basal cartilage ; the tym-
panic ring arises from a fibro-cartilage, specially connected with
the ear. The bones of the /ace, including the upper and lower
jaios, also the ossicles of the ear, the styloid process of the tem-
poral bone, and likewise the hyoid bony apparatus, are deve-
loped from the so-called visceral or branchial arches, which
are formed, as will be hereafter described, from the lateral
A'entral plates of the cephalic portion of the embryo.

Opposite the trunk or body of the embryo, the outer or
lateral part of the ventral plates, extends downAvards fi-om the
vertebral plates, to surround the ha)mal cavity or future thora-
cico-abdominal chamber of the embryo. Within these plates,
in the thoracic region, opaque lines appear, Avhich ultimately
form the ribs ; Avhere they close below in the middle line, the
rudiments of the separate pieces of the sternum are developed ;
these may remain ununited in the middle line, constituting
a rare and remarkable deformity — -fissura sterni. In a similar
manner, the pelvic or innominate bones, the ilmm, ischium, and
pubes, arc formed near the hinder part of the body; and the
scapular arch, consisting of the scapula and clavicle, at the
fore-part of the trunk.

A little later, the rudiments of the limbs appear, like small
knobs, on e;ich side of the trunk. In the centre of these, Avhich

G18

SPECIAL PHYSIOLOGY.

consist of extensions of the middle germinal layer, the rudi-
ments of the bones are soon seen, and ultimately become dis-
tinguishable as the bones of the arm, forearm, and hand, or
of the thigh, leg, and foot. As the dorsal segments give origin,
not only to the vertebraj, but also to the neighbouring muscles
and to the covering of the cutis, so the lateral plates, -which
produce the ribs and sternum, and the scapular and j^elvic
arches, and also the extensions of those plates which form the
future limbs, not only give origin to the bones of those parts,
but also to the corresponding muscles and cutis. The epider-
mis or cuticle covering all these parts, and, indeed, that of the
whole body, is formed upon them, by the common external
germinal layer.

At first, the future skeletal parts are soft, and composed of
cells but slightly differentiated from the rest of the cells of
the germinal layer or blastoderm ; by degrees, these parts
become cartilaginous or membranous, and -ultimately they
undergo ossification. The process of ossification, with its order
and times of occurrence, will be hereafter noticed.

Not only are all the muscles, and also the true skin thus deve-
loped, as well as the bones, ligaments, and joints, but likewise
their re.spective vessels and lymphatics, and the nerves, both
motor and sensory, tvhich constitute the peripheral part of the
spinal and cranial nerves, excepting those of special sense. The
first muscles to be developed are those of the vertebral grooves,
next the muscles of the neck, then those of the abdomen, after-
wards those of the limbs, and lastly the facial muscles. The limbs
are at first like simple buds, derived from tlie lateral plates;
but they soon show divisions into their respective segments,
and expand and flatten at their extremities ; these next exhibit
indentations corresponding with the future toes or finger-s,
which, for a time, are webbed. The itpper limb is usually
developed before, and more quickly than, the lower one. The
limbs are at fir.st simple masses of blastema, which gradually
change into cartilage, bone, muscle and skin. On the surface of
the body and limbs, a layer of polygonal epidermic cells is
very early traceable ; this is the commencement of the cuticle.
The papillaj of the skin, the rudiments of the hairs, feathers,
nails or claws, and also of the cutaneous glands, afterwards
appear.

The mamnarj/ rjlands, when first formed, resemble the cu-
taneous glands, consisting of solid processes derived from the
epidermic layer, and penetrating tlie cutis ; these afterwards

DEVELOPMENT OF THE BRAIN.

619

branch out, and ultimately become hollowed, to form the mam
mary ducts and vesicles.

The Brain and Spinal Cord.

The sides of the vertebral groove are lined on their surface,
by a special layer of blastema, known as the medullarij plates,
derived from the external germinal layer. When the groove
and its cephalic expansion are closed, first in the neck, and
then along the middle line of the back of the embryo, a me-
dullan/ canal with a cephalic enlargement, is formed; and the
medullary plates, becoming thicker and growing from below
upwards, are converted, subsequently to the appearance of car-
tilages in the rudimentary vertebraj, into a tube of primitive
nervous substance, the anterior part of which is expanded
into three vesicles, placed at first one behind the other, but
afterwards bent with the head and neck of the embryo, and
named the anterior, middle, and posterior, primary cerebral
vesicles ; of these, the middle one is much the largest. From
them are developed, respectively, the prosencephalon, the hinder
part of which has been named the diencephalon, the mesence-
phalon, and the epencephcdon, of which latter the hinder part
is called the metencephcdon. The tubular portion of this me-
dullary canal, forms the spinal cord, which at first consists of
numerous cells having a radiated arrangement around a cen-
tral canal, and for a long time retains its hollow condition.
Even in the perfectly-formed state, it presents a rudiment of
this cavity, in the .so-called central canal of the spinal cord,
(vol. i. p. 313). The cells ne.xt to the canal, form its epithelial
lining, or ependyma, whilst the outer ones are developed into
the nervous substance. The cord at first extends throughout
the entire vertebral canal, but afterwards it gi-ows in lengtli less
rapidly than the vertebral column, and the cauda equina is gra-
dually formed. The .substance of the embryonic spinal cord, is
composed of simple nucleated cells, which are developed chiefly
into the grey sirbstance of the cord, but partly also into fine
connective tissue and bloodves.sels. The white substance of
the cord is .subsequently formed. The peripheral part of the
sjjinal nervous .system, as already mentioned, is developed,
with the framework of the head, trunk, and limbs, from the
middle germinal layer.

Fr< in the posterior cerebral vesicle, at fir.st smaller, but
soon larger, than the middle one, is evolved, in the metence-
phalon next to the spinal cord, the medulla oblongata. At

620

SPECIAL PHYSIOLOGY.

this point, the nervous substance, developed from tlie primitive
medullary plates, does not form a complete canal, as in the
spinal cord, but remains open behind, constituting the fourth
ventricle, and is marked on its floor by the calamus scriptorius,
which leads into the canal of the spinal cord. Anterior to the
medulla, but still in the posterior cerebral vesicle or epencepha-
lon, appear the pons and the rudimentary cei'ehellum, an angular
projection forwards marking the line between them. At first,
the cerebellum consists of a thin transverse plate of nervous
substance ; then it enlarges, and becomes laminated ; the cen-
tral part, or venniform jn’ocess, is recognised before the lateral
parts, or hemispheres ; the grey matter gradually becomes
thicker on the surface, and the corpora dentata are formed
within ; the pons Varolii and the superior and inferior pedun-
cles also gradually enlarge. Owing to the bend which occurs '
between the cephalic and cervical portion of the embryo, a
posterior projecting angle is formed between the spinal cord
iind the posterior cerebral vesicle ; this corresponds with the
cervical tuberosity of the embryo.

The middle cerebral vesicle, or mesencephalon, slightlj’^ bent
forwards and downwards across its middle, is, at first, the largest,
bnt grows relatively slower than the others. After a time, it
is developed, on its dorsal aspect, into the corpora quadrigeinina,
which form proportionally large masses, and are at first hollow
— a condition which is permanent in Birds, bitt not in I\Iam-
malia. On the under-side, the peduncles of the cerebrum are
formed ; between these parts, a cavity remains, tvhich ultimately ,
shrinks into the small canal connecting the fourth ventricle with |
the middle ventricles of the brain, named the aqueduct of
Sylvius.

The anterior cerebral vesicle is, at first, more prominent later-
ally, though smaller, than themiddleone ; it isalsoatfirstsmooth,
but soon exhibits a median sulcus, and gi'ows far more rapidly
than the others, being destined to form the cerebritm. It soon
bends directly downwards. The portion immediately in front ;
of the middle vesicle, named the diencephalon, forms the two ,
optic thalami, which originally consist of a single hollow mass,
but afterwards become solid ; they are divided by a fissure,
Avhich remains as the third ventricle, and communicates behind
with the Sylvian aqueduct. The pineal gland is either an off-
shoot from the thalami, or it is derived from the pia mater.
The optic nerve also originates in a part of this vesicle.
The pituitary body, or hypojdiysis cerebri, in both its nervous

DEVELOPMENT OF THE BRAIN.

621

part, and its posterior thyroid-like portion, is said to arise from
the base of the brain, or to be in part developed from tlie pia
mater. The prosenaephalon, or portion of the anterior vesicle in
ifont of the optic thalami, gives origin to the corpora striata,
upon which the cerebral hemispheres, with the corpus cal-
losum, the fornix, and the ventricles, are rapidly evolved.
The corpora striata, and the hemispheres, are, it is said, at first
separated by a slight constidction.

The hemispheres are developed from before backwards,
leaving between them the cavity of the third and lateral ven-
tricles, which, for a time, open freely into the yet hollow corpora
quadrigemina. Gradually the hemispheres overlap the ojitic
thalami, and then, in the higher Vertebrata, thecorpoi’a quad-
rigemina, and, lastly, even the cerebellum. At first smooth on
the surface, and composed of thin walls enclo.sing a large cavity,
the hemispheres, by degree.®, become thicker, and marked on
the surface with the primarij grooves or fissures, which subdi-
vide them into frontal, parietal, occipital, temporal, and central
lobes, and afterwards with the secondary sulci between the con-
volutions— the grey matter on the surface also gradually becom-
ing thicker. The cerebral hemispheres, develojred on each side
of the middle line, are first connected only at their base and
anterior part, by rudimentary commissural structures of
nervous substance : these are the commencing peduncles,
which may be traced, as white bands, upwards from the cord,
the anterior commissure, and the rudimentary transverse com-
missure or corpus callosum. But, as the hemispheres grow
backwards, the transverse commissural fibres of the latter,
extend in the .same direction, and thus the future corpus cal-
losum is formed with the fornix, composed of longitudinal fibres,
beneath it, and the septum lucidum, enclosing the cavity of
the fifth ventricle, between them. From the under-.surfiice of
the anterior part or frontal lobe of each hemisphere, a hollow
process extends forward, forming the future olfactory lobes, the
central cavities in which, in some animals, remain, in commu-
nication with the ventricles of the hemi.sphercs, but, in others,
are obliterated. From the hinder and lateral part of the an-
terior cerebral vesicle, the primary optic or ocular vesicle, or
rudimentary eye, is developed, forming connections with the
optic thalamus and corpus quadrigeminum. From both these
latter j)art.s, which are then hollow, two tubular processes of
nervous substance, extend forward to the optic vesicles, and
are ultimately developed into the optic tracts and optic

622

SPECIAL PHYSIOLOGY.

nerves. Farther back, on the sides of the future medulla
oblongata, are the primary auditory sacs or vesicles, which are
not developed, like the ocular vesicles, as outgrowths of the
cerebral vesicles, but commence on the surface of the embryo,
as will be immediately described.

The membranes of the brain and cord, are formed between
the nervous centres and the walls of the cranial and spinal
cavities. The pia mater is first recognisable.

The sympathetic nervous system is said to be developed from
the middle germinal layer.

The Organs of the Senses.

The Nose. — As the olfactory lobes become consolidated, the
nasal ca.vities, with the olfactory lining-membrane, are de-
veloped as inversions of the integument of the face, in the
so-called primary olfactory groove. This, remaining open,
becomes subdivided, to form the two nasal passages or
fosste. At one time, these fossa? are closed at the bottom, a
condition Avhich is permanent in Fishes ; afteiuvards they com-
municate, in fi-ont of the palate, with the mouth, as in certain
Amphibia ; 'finally, they open only into the pharynx, as in
Eeptiles, Birds, and Mammals.

The Eye. — The primary ocular or optic vesicles commence,
as already mentioned, as flask-shaped outgrowths of the first
cerebral vesicle, with which they soon appear connected by a
hollow stalk, the future optic tract and nerve. The interior
of each optic vesicle, quickly becomes lined with nervous sub-
stance. At the same time, the surface of the common integu-
ment covering the vesicle, presents air inversion of the epidermic
layer, which, becoming constricted at its orifice, closes and
forms a sac; this is ultimately converted into the capsule of
the lens, within which the lens-fibres are gradually developed,
from radiating, epidermoid, nucleated cells. This growth, with
other deeper tissue.s, pushes, as it were, the anterior and lower
part of the nervous layer of the primary optic vesicle, upwards
and inwards, against the posterior and ujtper part, giving rise
to a cup-shaped nervous expansion, open below, named the
secondary optic vesicle, wdthin which the vitreous humour is
developed, this being also, like the lens, an integumentarj' struc-
ture. The sides of this secondary vesicle, consist of two layers,
which subsequently blend, and their edges, at first sejxirated
below, close in that situation, include the central artery of the

DEVELOPMENT OF THE EAE.

623

retina, and form the anterior part of the optic nerve and the
retinal expansion. The anterior part of this secondary vesicle,
corresponds with the pars ciliari.s of the retina, and gives origin
to no nervous elements. The yellow spot does not appear until
alter birth. The outer coats of the eyeball, or the sclerotic and
cornea, are partly growths of the secondary vesicle.s, and partly
derived from the neighbouring cutis. The choroid coat, also
derived from the secondary vesicle, is at first adherent to the
retina ; the iris, growing at a later peidod from the margin
of the choroid, forms an imperforate curtain, the central part
of which, or memhrana pupillaris, becomes transparent, then
gradually loses its vessels, and finally disappears. The capsule
of the lens is, for a time, invested by a vascular membrane,
supplied by the central artery of the retina, and connected with
the pupillary membrane and margin of the iris. The aqueous
humour is secreted very late, the parts in front of the lens, pre-
viously touching each other. For a time, the eyeball is simply
covered with the integument, but this rises up, above and
below, into small crescentic folds , which become the future eye-
lids ; these, for a time, cohere at their edges, and then separate.

The Ear. — The auditory sacs are not developed, like the optic
vesicles, from the cerebral vesicles, but, like the lens and its
capstde, from inversions of the common integument. They
commence by a little pit or depres.sion, which afterwards be-
comes completely shut off from the surface, and, receding, is
eventually attached to the side of the medulla. This primitive
auditory sac forms the sac of the labyrinth, with Avhich the
auditory nerve, an independent formation from the medulla
oblongata, is soon connected. From the sac of the labyu'inth,
are gradually developed, the membranous semicircular canals,
and the winding cochlea, with the fluids in those cavities. All
the.se parts are at first straight processes, but afterwards
become curved or .spiral. The cavity of the tympanum, with its
ossicles, tlie tympanic bone, and the auricle, are formed ex-
ternally to the deeper jiarts, in connection with the pharynx
and Eu.stachian tube, as will bo described with the development
of the face. 'I'he osseous walls, which afterwards invest the
labyrinth, are formed from the primitive cartilage of the base
of the cranium. The mastoid proce.ss is not holloAved out into
large air-cells until after puberty. The external meatus and
the auricle are outgrowths of the annular fibro-cartilage,
which forms the tympanic bone. The auditory grey neiwous
centre arises, near the posterior j)yramid and restiferm body

624

SPECIAL PHYSIOLOGY.

of the medulla oblongata, as two masses, the outer one of
which gradually moves backwards into the cerebellum itself
The auditory nerve consists of two portions, both of which
become connected with these masses ; but the anterior portion
of the nerve, also joins the superior peduncle of the cerebellum,
and even reaches the interior vermiform process (L. Clarke).

The Parts of the Face.

The extension doAvnwards of the lateral ventral plates of
the embryo, rvliich, opposite the trunk, fornr the sides of the
harmal cavity, occurs also beneath the cephalic part. Here,
however, where the future face is developed, the liEemal cavity
is imperfectly closed in at the sides ; for these plates, ndth their
coveiiirg and lining membranes from the external and inter-
nal, or epidermic and intestinal germinal layers, split, on each
side, into four processes or lohes^ with little clefts between them,
forming the so-called visceral or hranchial arches, and the
visceral or branchial clefts. The term branchial is applied to
these arches, becartse the permanent gills or branchite of the
Fish, and the corresponding temporary gills of the Amphibia, are
developed from homologous parts ; but in the embryoes of the
Ileptile, Bird, and Mammal, these arclies give rise, through very
early metamorphoses, to other organs. Within theiii, minute,
but impoi-tant vessels, as will be hereafter seen, are teinpo-
rai'ily present. Gills are never developed on them, and they
never exercise a respiratoiy function. In these three last-named
Classes, the allantois, a part not present in Amjihibia and
Fi.shes, is the embryonic respiratory organ.

The first branchial cleft, above the first arch, sometimes
named the maxillary cleft, forms the cavities of the mouth and
nose; these are originally conjoined, but subsequently become
separated, by the growth of the upper jaw, from the substance
of the first arch, between the na.sjil cavities above, and the mouth
below. The nasjil walls and septum grow downwards from
the cranium, Avhilst the upper jaw and palate are developed
transversely from the face, to meet them. From the posterior ,
part of the second hranchial cleft, between the first and second ‘
branchial arches, are formed, the cavity of the tympanum, ^
which at first contains soft connective tissue, the Eustachian
tube, which is also at first filled with a similar tissue, the
membrana tym]iani, and the extern.al auditory meatus and its
ajqiendages. The auricle commences as a little ring around

DEVELOPMENT OF THE FACE.

625

the margin of the meatus. Tlie third and fourth branchial
clefts completely close up, and disappear very early.

Within the branchial arches, little cartilaginous plates are
soon developed. From the upper edge of the first of these
arches, a process is formed, named the maxillary lobe, from
■which the upper jaw is developed, together with the whole
side of the lace, including the internal pterygoid process and
the palate-bone. The malar bones and lachrymal bones are
tbrmed as opercular bones. The first arch also gives origin,
by another process, to the rudimentary lower jaw, and likewise,
it is said, to the tongue. From the cranimn, a median process,
known as the frontal process, descends in the middle line of the
liice; and with this, an external and internal nasal process are
also connected. These, by their junctions, form the walls and
partition of the nasal fossa;, and the centre of the upper lip.
In this latter part, the intermaxillary bones, which carry the
upper incisor-teeth, are independent ibrmations. The lachry-
mal duct is a fissure which remains partly open, between the
external cranial nasal process and the facial maxillary lobe.
Sometimes these parts are arrested in development, and fail
to unite properly, giving rise to the conditions of harelip and
cleft palate. Certain other congenital defects, connected chiefly
with the apertures of the body, as well as with the back of
the head and spine, are explained by similar arrests of normal
adhesive processes of development.

From the middle part of the first branchial arch, to Avhich
we now return, the incus of the tympanum is developed.
From it, also, a remarkable cartilaginous process, named
Meckel's process, or Meckel's cartilaye, arises, which gives
origin to the malleus, and also extends forwards from that bone
to the rudimentary lower jaw, which is developed indepen-
dently upon it, after the manner of the opercular bones of the
cranium, which rest upon the basal bones. Afterwards,
iVIeckel’s process wastes, e.xccpt a part, which forms the j^co-
cessus f/racilis of the malleus. From the second branchial arch,
are developed the stapes, from a minute cartilage, and also the
stapedius muscle, with its bony canal ; these belong to the
tympanic cavity. In the neck, the second arch forms the
.styloid process, the stylohyoid ligament, and the little cornu
of the hyoid bone, which early unites with the tongue. The
cartilage of the third branchial arch, gives origin to the yreat
cornu and body of the hyoid bone; but the arytenoid cartilage,
and the epiglottis, are develoi)cd from the first arch. The

VOL. II. s s

G26

SPECIAL PHYSIOLOfiT.

fourth branchial arch soon coalesces with the side of the neck.
All tliese changes occur very early in the jjulmonated Verte-
brata.

The, Alimentary Canal.

The digestive canal is at first merely the interior of the body-
cavity, which is formed by the folding downwards and inwards
of the lateral ventral plates, and which, originally, communicate.s
Avidely with the yolk-sac, by the open vitelline duct. The Avails
of this common body-cavity, are derived principally from the
middle germinal layer, but they are lined by the inner or in-
testinal germinal layer. It is a short straight chamber, closed
at both the cephalic and the caudal end of the embryo. Its
innermost part soon separates from the sides of the embryo, and
forms a tube, in Avhich an abrupt bend occirrs opposite the um-
bilical opening, and for a time projects through it, being there
connected Avith the vitelline duct. In the Bird, this duct con-
tinues open, even after the chick is hatched ; but in the Mam-
mahan embryo, it soon becomes closed, and, attached to the
jArimary bend of the alimentary canal, fonns the slender jjedicle
of the yolk-sac or umbilical vesicle. The part of the canal, or
tube, above the bend, forms the pharynx, oesophagus, stomach,
and a portion of the small intestine ; the part beloAV the bend,
the remainder of the small intestine, and the large intestine : the
distinction betAveen these, is soon indicated by the appearance
of a cajcum, a little loAA^er doAvn than the bend. The closed
upper end of this alimentary tube, extends to the base of the
cranium, corresponding Avith the pharynx, the oesophagus being
continuous Avith it beloAv. The lower closed eud corresponds
Avith the loAver portion of the rectum. At a certain time, there
is neither an oral nor an anal aperture. The buccal orifice is
originally formed by a depression above the first branchial
arch, and then opens into the pharynx, the tongue being already
developed in its interior. At the lower end of the rectum, the
anal orifice appears as a depression, Avhich uhimately opens
into the boAvel. The stomach proper is, at first, a longitudinal
dilatation of the alimentary tube, Avhich gradually as.sumes an
oblicjue, and then a transverse, position. The primitiA’e ali-
mentary tube is closely attached to the vertebral column, and
is coAmred by the peritoiucum formed upon it and upon the
Avails of the cavity of the body, as it sejiarates from the latter.
But after the stomach has changed its position, the coiiA'olutions
of the small intestine, and the remarkable bend of the large

DEVELOKMENT OF THE TEETH.

627

intestine around them, occur. These changes are owing to a
greater development of the intestine, than of the mesentery.
Tliis latter structime and the omenta are now fully formed.
The small intestine is, for a time, wider than the large intes-
tine. The vermiform appendix of the cascum is, as it were, an
incompletely developed, yet growing, part of the large intestine.
The valvula3 conniveutes of the small intestine and the sacculi
of the colon, appear afterwards. Fringed villi, at first, exist
throughout the embryonic alimentary canal, but they are
permanent only in the small intestine.

The Teeth.

In the cavity of the mouth, the middle and internal germinal
layers give origin to the buccal papilla; and also to the teeth,
which are themselves formed, partly by the corium, and partly
by the epithelium of the buccal mucous membrane. At first,
the rudimentary ripper and lower jawbones of Man, have no
alveoli, and the membrane which covers their horse-shoe
shaped borders, is quite smooth. After a time, however, a
groove appears on the margin of each maxillary bone, which
gradually deepens and widens, and becomes separated by thin
osseous septa, into rudimentary alveoli.

In the meantime, according to one authority (Goodsir), the
mucous membrane over the margin of the jaws, also presents
a groove, called the primitive dental groove, from the bottom
of which minute imjnlla; arise, in the human jaw ten in num-
ber, above and below. These are the rudimentary pulps of the
future milk teeth. Those of the upper jaw appear first. In each,
the order of their appearance, is as follows : — the first molar, the
canine, the central incisor, the lateral incisor, and the second
molar. Tliis is the papillary stage, which is soon converted
into the follicidar stage, by the rising up of membranous folds,
between and around the papillae. By this time, each papilla
has enlarged, and asstimod the form of the crown of the future
tooth ; whilst small inembTanous lids, or opercula, corre.spond-
ing, in number and shajic, to the surfaces of each tooth, overlap
the papilla. Sub.sequeutly these follicles become deeper, and
are closed by the adhesion of their opercula and by the union
of the borders of the dental groove, and, at their iqiper jiart, a
thicker jiortimi is .seen, which comstitutos the enmnel organ.
The .so-called dental sacs are thus formed, and the saccular
stage is conqiletcd.

According to Kiillikcr and other.s, however, the dental

628

SrKCIAL PHYSIOLOGY.

papilla;, follicles, and sacs, are formed entirely beneatli the epi-
thelium over the jaw. The enamel organ is the part first de-
veloped, as a thickening of the deeper layers of the epithelium,
Avhich grows down into a flask-shaped depression, formed in
the vascular layer or corium of the mucous membrane ; the
papilla then rises up as an extension trom this membrane.
By renioving the epithelium, the dental groove, follicles, and
opercula, of Goodsir, are seen.

The form of the summit of the beingcompleted within

the sac, a thin cap of dentine appears on it, which gradually
increases at its edges, and becomes thickened on its inner sur-
face ; whilst the papilla, at first groAving Avider, but then con-
tracting at its base to form the cervix of the tooth, continues to
grow longer, and commences to form the fang, Avhich shortly
acquires its covering of crusta petrosa. In the meantime, by a
separate proce.ss, the surface of the cap of dentine, on the
croAvn, becomes covered by the groAving enamel, formed from
the enamel organ. At last, by the gradual gi-oAvth of the
fang, the tooth is pressed against the gum, Avhich, becoming
absorbed, the finished surface of the enamel is exposed, and
the tooth is cut. The fang is noAv completed to its point, and
the papilla, noAv called thejsi^Zp, remains asavascular and nervous
mass, occupying the pulp cavity, and receiving its vessels and
nerves through an orifice left at the apex. In the meantime,
the alveolus in the bone, has closely adapted itself, to the fang.

In the groAvtli of a tooth having several cusps and fangs, a
separate shell of dentine and enamel forms on each cusp, the
Avhole afterAvards uniting ; Avhilst the dentine shoots in at
opposite points of the base of the pulp, AA'here this begins to
divide to form the separate fangs.

Behind the groAving milk teeth, in each jaAv, recesses are
formed in the corium of the mucous membrane, Avhich
also become filled Avith epithelium, out of Avhich future
enamel organs are developed. Moreover, a Avascular papilla arises
from the bottom of these llask-.shaped depressions or cavities of
reserve (Goodsir), Avhich finally close, and become the sacs of
a like number of the permanent teeth. These sacs are at first
oval, and adliere to the back of the sacs of the correspond-
ing milk teeth, but aftenvards they become more elongated,
and recede from the gum, to Avhich they are only attiiched by
a fine cord or pedicle, found behind the necks of the other
teeth. In thisAA'ay, in Man, the ten anterior permanent teeth in
each JaAV, are develojjed. But the sacs for the three additional

DEVELOPMENT OF THE TEETH.

62<J

or superadclecl permanent teeth, on each side of the two jaws,
viz., the sacs of the permanent molars, are Ibrmed by little
2)ostenor cavities of reserve, which appear on the edges of the
jaws, behind the other teeth. These latter teeth are cut like
the milk teeth. But the anterior permanent teeth emerge dif-
ferently. Between the fang of the temporary tooth and the sac
of the corresponding permanent tooth, there is a thin layer of
cancellated osseous tissue ; and in this bone, is a little canal,
which lodges the pedicle of the sac. The crown of a permanent
tooth, being completed within its sac, it.s fang or fangs begin to
be formed ; the crown is pressed against the bony partition
separating it from the fang of the milk tooth, and, when this is
ab.sorbed, against the fang itself. A peculiar, thick, pulpy,
vascular areolar ti.ssue intervenes between them, and tippears
to accomplish a gradual absorption, first of the cntsta petrosa,
afterwards of the dentine, and even of the lo^ver part of the
enamel of the milk tooth. Sometimes this process of absoi-ption,
which is not due merely to pressure, is temporarily interrupted,
a renewed deposition of dentine taking place. At length, the
side of the socket, the fang, neck, and even part of the crown
of the milk tooth, having been ab.sorbed, the tooth is loosened,
hangs for a time by the gum, and finally drops out. The per-
manent tooth rises in its place ; the crown appears above the
gum, whilst the fang, closely followed by a consentaneous
development and modelling of the osseous tissue of the jaw,
becomes firmly fixed in its socket. The giving way and dis-
appearance of the bone in one place, and its growth in other
directions, by inter.stitial absorption and deposition, are re-
markable examples of the plastic endowments of the osseous
tissue.

The development of the teeth in the Mammalia, conforms
generally, to the process above described.

Tho dentition of the Marsupial ia, however, has lately been shown to
be very peculiar. The only tooth which is succcssional, is the last
jrromolar, on each side of both jaws ; it alone is preceded by a temporary
tooth, which lias a molar shape. Tho other teeth of the Mansupial jaw,
not having any predecessors, might perhaps bo regarded as themselves
belonging to tho first set, though not falling out ; but this view seems
contrary to the homologies of these teeth, which show them to bo
permanent, rorhaps in a very early stage of development, transitory
nuliments of other temporary teeth, may bn met with in the fore part of
the jaw of the Marsupials (Flower). Tlio milk premolars of tho guinea-
pig, are .shed even before birth ; the milk teeth of tho Hats, Insectivora,
and seals are very simple and temporary; tho lirst incisors of the

6.30

SPECIAL PHYSIOLOGY.

elephant are very small, and the large incisors of tho Eodents, do not
appear to have temporary predecessors.

The teeth are always parts of the cxo- or dermo-sheleton. The re-
placement of the deeiduous, by permanent teeth, occurs only once. But
in the carnivorous Cetacea, the Edentata, and the Monotremata, there is
no succession of teeth. Such animals are called Monophyodonts, the
ordinary Mammalia being named Diphyodonts. The teeth of Eeptiles
and Fishes, are also developed upon papillae, and are mostly enclosed in
sacs, or follicles, in certain cases, provided with an enamel organ ; in the
parrot fish, the rudiments of the teeth sink into alveoli ; in the pike,
they sink only into sacs or follicles; in the sharks and rays, they
remain as papillae on the surface, thus representing the papillary,
follicular, saccular, and alveolar stages of development of the teeth of
Mammalia.

The Digestive Glands, the Lungs, and the Spleen.

The mucous glands of the mouth, the salivary glands, the
mucous glands and sjtecial tubular glands of the stomach and
intestine, the liver and pancreas, and even the lung.s, are
developed from the middle and innermost germinal layers,
the latter forming the epithelial lining of the several glandular
organa. They usually commence bj'' processes of epithelium,
which sink into the corium, penetrate into numerous bud-like
projections, con-esponding with the future lobes and lobules of
the gland, and are subsequently hollowed out, to form the ducts.

Thus, the lungs commence by two solid cellular processes,
from the fi’ont of the oesophagus, which soon become hollow.
These processes branch out into numerous, at first solid,
but afterwards hollow, ramifications, which become lined by
a cilicited epithelium, and form the bronchi, bronchia and
air-cells. The primitive lungs open separately into the
pharynx, but afterwards by a common trachea. The
trachea and larynx are produced by a lengthening out and
excavation of a primitive peduncle, derived from the oeso-
phageal walls : the larynx is developed from two lateral
symmetrical masses of blastema, connected in front. Until
the lungs are inflated at birth, they resemble a solid gland
containing ducts Avith terminal acini ; they then lie close to
the back of the thcrax.

The liver first appears, as two small conical projections of
the corium and epithelial tissue, on the side of the intestine,
below the stomach. These soon become holloAv, and from
them, numerous, solid, cylindrical branches extend into the
groAving matrix. Continuing to extend, these ramified masses
of cells, ultimately unite in a terminal netAvork, and, becoming

DEVELOriilENT OF THE EIUNAET ORGANS.

631

hollowed out, form the bile-ducts, The liver rapidly acrpiires
a relatively large size, and is lobed ; it soon even begins to
secrete bile, or, at least, the colouring substance of the V)ile,
for the biliary acids are said to be absent. This imperfect
hepatic secretion enters the intestine of the embryo, forming
the so-called meconimn.

Tlhe pancreas is developed, in a similar manner, close to the
.spleen, by the formation of a small mass of cells li’om the
epithelial layer on the left .side of the intestine, Avhich after-
wards grows, and becomes canaliculated to form the pancreatic
ducts.

The spleen commences near the great curvature of the
•stomach, but probably from a distinct blastodermic mass. The
thyroid body appears as a similar small mass, in contact with
the oesophageal lining .membrane, in close connection with the
commencing larynx. The thymus is said to originate separately,
in iront of the great vessels of the neck, as a delicate closed
tube, which becomes diverticulated at the sides, and filled
with nucleated cells and fluid.

The Urinary and Reproductive Organs.

The bladder, as already stated, is a part of the urogenital
sinus, and is connected at its apex with the urachus, or
obliterated abdominal portion of the allantois. It is developed
originally, as a small pouch, connected with the lower end of
the large intestine. The part of the intestine, below the
primitive communication with the bladder, forms a true
cloaca, into which the digestive, urinary, and reproductive
canals all open. The anterior part is soon separated from the
proper intestinal portion, by a septum which corresponds
with the future perinajura. It is this anterior part, which
forms, for a time, the sinus uro-genitalis, the common outlet of
the urinary and reproductive pa.ssages, and which becomes
ultimately modified according to the sex.

Very early in embryo life, two remarkable symmetrical
organs appear, at first as two linear elevations, one on each
side of the primitive vertebrae, forming proportionally Amry
large reddish masse.s, and reaching from o])j)0.sito the heart to
the lower end of the verteliral column. Originally, they consist
of two symmetrical longitudinal canals, in the walls of which
slight caecal depres.sions speedily form. When fidly developed,
they consist of numerous comb-like, blind, hollow processes,
lined with ciliated epithelium, very vascular, and communi-

632

SPECIAL PHYSIOLOGY.

eating each with a long duct, Avhich runs doAvmvards, and
opens into the genito-urinary sinus. IMalpighian bodies, or
ai-terial tufts, have been detected in them. The.se organs
are the Wolffian bodies, or primordial kidneys, so called
because their secretion contains, amongst other products, uric
acid ; in Fishes, they are said to become the future kidneys.
In the Warm-blooded Vertebrata, they are in no Avay connected
with the development of the kidneys, but rather Avith the first
formation of the reproductive organs. Their secretion finds
its Avay, through the genito-rudnary sinus, into the allantois, or
future urinary bladder. They are proportionally larger in
the lower Vertebrata, and persist for a longer time. At first,
highly vascular, they attenvards almost entirely disappear, as
the proper kidneys ax’e formed. The kidneys themselves,
commence as thick, smooth, or lobulated opaque masses, or
processes of cells, arising from the sides of the cloaca, behind
the Wolffian bodies; as these latter diminish, the kidneys
enlarge, and gradually receding from the urogenital sinus and
cloaca, assume their future normal position. They continue
to be connected Avith the urogenital sinus, by a duct which
forms the future ureter, pelvis, and calyces. The renal matidx
at first contains bundles of solid processes, Avhich aftenvards
become hollowed out, to form the tubuli uidniferi ; these are
said not to open originally into the pelvis of the kidney. The
kidneys soon become lobulated, but aftenvards smooth. Mal-
pighian bodies appear in them very early. The supra-renal
bodies are independent formations.

On the inner side, and somcAAdiat behind each Wolffian body,
appears, rather early, a little opaque mass, AAdiich is ultimately'
changed, according to the sex, into the ovary or the spermatic
gland. Tavo ducts, the ducts of ]\fuller, ajxpear simultiineously',
connected at their loAver ends Avith the sinus uro-genitalis, but
terminating at their upper ends, at first, -;n blind extremities.
In the male, these become connected Avith the spermatic gland,
at the back of Avhich, even in the adult condition, they’- some-
times present a long diverticulum. In this .situation, too,
vestiges of the Wolffian bodies may'- still be traced (Giraldcs).
In the female, these ducts do not coalesce Avith the ovaries, but
remain separate and form the oviducts of Fi.shes, Amphibia,
Reptiles, and Birds, the left one only’ usually persi.sting in the
adult condition, in the two last-named Classes. In the IMammalia,
they constitute the free part of the Fallopian tube; betAA'een it
and the ovary, are found, in the adult, A’estiges of the Wolffian

DEVELOPMENT OF THE VASCULAR SYSTEM.

633

bodies (Kosenmliller). From the lower end of these tubes,
and from the portion of the genito-urinary sinus into which
these ducts open, the futtire uterus, or the prostate gland, is
developed. In the Monotreinata, an intermediate condition
exists, approaching to the birdlike structure of the parts ; for
the two Fallopian tubes open separately into the rtro-genital
sinus. In the Marsupials, and some Rodents, they combine
before they open, forming a double uterus. In the Slarsupials,
remarkable pouches, the so-called marsitpia, supported by
special bones, are found in connection with the pelvic organs ;
they receive the young, which are born in an immature state.
In other Rodents, the uterus is cleft. In the Cetacea, Solipeds,
and Ruminants, the uterine chamber is double, or two-horned ;
in the Carnivora, Insectivora, and Cheiroptera, the horns of
the itterus are conqmratively short. In the apes, this organ
is but slightly notched. The human uterus forms a simple
triangular chamber.

The Heart, Bloodvessels, and Blood.

The first appearance of bloodvessels in the embryo and its
appendages, can be best observed in the incubated hen’s egg.
In the middle germinal layer, where it extends over the yolk,
linear clusters of nucleated cells appear, and arrange themselves
in streaks, which soon iinite in a retiform manner ; these
speedily become distinguished, by special processes of differen-
tiation or development, into an external firmer part, or wall,
which forms a future bloodvessel, and an internal softer
part, which remains fluid, and I'urther separates into liquor
sanguinis and blood corpuscles, some of which are colourless,
whilst others soon accpiire the characteristic red colouring
matter. The fluid central part of these red streaks, is blood ; it
soon exhibits movement, and, as the vessels become connected,
it forms continuous streams. These earliest vessels on the
surface, of the yolk, constitute the so-called vascular area ; they
I terminate in a marginal bloodve.ssel, known as the sinus ter-
[ mimdis\ this, extending beyond the embryo, both in front

[and behind, divides into vessels which run towards each ex-
tremity of the embryo. In the meantime, in front of or
beneath the chorda dorsalis, near the cej)halic end of the cm-
J bryo, within the middle germinal layer, a solid mass of cells
II appears, connected with certain branching streaks; the outer
q part of this becomes converted into an elongated sac or
f dilated tube, the judmitive heart, and tho interior into the

634

SPECIAL PHYSIOLOGY,

liquor sanguinis and blood corpuscles ; whilst from the con-
nected streaks, are developed, an arterial trunk which divides
into two branches, at the anterior end of the now tubular heart,
and a venous trunk communicating with its hinder end. These
rudiments of a propulsive organ or heart, Anth its embryonic
arterial and venous channels, are, moreover, soon connected
with the vessels already mentioned as being formed outside the
embryo, in the vascular area upon the yolk, and thus a deter-
minate direction is given to the blood circulating through the
embryo and the surroiinding vascular area. At this time, there
are no capillaries in the embryo ; all the vessels are either
arterial or venous. The blood appears to pass out fi-om the sides
of the embryo, and to reach the terminal sinus, by which it is
conveyed back in the direction of the cephalic end of the embryo.
The heart, which originates very early — after the commence-
ment of the second day in the chick — in a group of cells con-
nected with the intestinal portion of the middle blastodermic
laj'er, soon forms a straight longitudinal utricle, or sac, from
the anterior end of which a short arterial trunk arises, the
bnlbus arteriosus. This speedily divides into two branches,
which give off two anterior and two posterior vertebral arteries;
the former supply the cephalic part of the embryo, and the latter
soon unite, to form the descending aorta. The primitive aorta
is very early connected Avith two small arteries, named the
omphalo-mesenteric or meseraic arteries, Avhich pass laterally
on to the yolk-sac, hence they are also named vitelline arteries,
and branch out into the vascular area ; they coiiAmy the blood
from the heart and body of the embryo, over the yolk-sac.
After a time, one of these arteries disajApears, the left usually
remaining. From the vascular area, the blood is returned
to the embiyo, by the anterior recurved ends of the terminal
sinus, which appears to have the function of a rmin. But from
the hinder part of the A’ascular area, other veins proceed, and
end in posterior branches, which join the recurved ends of the
terminal sinus to form the two omphalo-mesenteric veins-, these
enter the embryo, and become connected Avith the posterior
extremity of the still sti'aight, sac-like, heart. After a time, the
right omphalo-mesenteric vein shrinks, the left one remaining
pervious.

In the Bird, the Amssels of the Avascular area become A'ery
large, and form the vitelline vessels-, they send A'ascular pro-
cesses into the substance of the yolk, and thus food is absorbed
by, and supplied to, the embryo. The yolk-sac is the temporary

DEVELOrMENT OF THE HEART,

635

aliinentary chamber of the embryo, and, in certain lower
animals, it remains so; its vessels are represented by the ab-
dominal veins in the Non-vertebrate forms. The vessels of the
yolk persist in the Bird up to the period of hatching, and for
some time afterwards, until the contents of the yolk sac are com-
pletely absorbed. But in the Mammalian ovum, the ornphalo-
me.senteric artery and vein continue very small, and soon
become obliterated. The circulation through the vascular area
to the terminal sinus, in them, is probably chiefly respiratoiy.
But now a change takes place in the circulation outside the
embryo, both in the Bird and in the Mammal. The allantois
grows, and two arteries, proceeding from the posterior verte-
brals, named the hypogastric or umbilical arteries, proceed out
upon it ; whilst two veins, returning upon it, also named
umbilical, join the common trunk of the omphalo-mesenteric
veins. The right umbilical vein then disappears, and the left
one, enlarging, as the .single left omjflialo-mesenteric vein
diminishes, soon appears as the chief median vein, carrying
the blood from the allantois, or its modification, the placenta,
back to the heart of the embryo. It now passes through or
beneath the liver. When the vitelline vessels, in the Mam-
malian embryo, have .shrunk, the proximal part of the left
omphalo-mesenteric vein, forms the trunk of the portal vein,
and the part beyond this, after joining with the umbilical A^eiu,
constitutes the ductus venosus, with which vessels the liver
and its veins are now seen to be connected.

iVs the embryo develops, the heart itself undergoes a process
of bending or curvaature, like an italic letter S. At the .same
time, it enlarges, and acrpiires thicker walls; the anterior or
arterial part, which gives off the bulbus arteriosus, is now
placed nearer to the under side of the embryo, whilst the pos-
terior or venous part, which receives the conjoined veins, is
turned backwards towards the vertebral column. The saccular
! heart is now marked off, by two constrictions, into three
I chambers, of which the first, or the one netirest the veins, soon
i e.xhibiting two superficial bulgings, corresponds with the future
auricles ; the .second, also quickly showing an external line of
I subdivision, or notch, forms the ventricles, :ind the third, lying
in front of and above the others, forms the bulbus arteriosus.
Each of thc.se quickly becomes subdivided. Thus, a septum,
I commencing on the anterior part, opposite to an external
t groove in its ventriculiir portion, grows upwards and back-
1 wards from the apex to the base of the heart, and ultimately

636

SPECIAL PHYSIOLOGY.

divides it into the right and left ventricles. Some time after
this, the septum between tlie auricles begins to appear, growing
both from above and below, like two folds with crescentic
margins ; the edge of the upper fold, as it grows, keeps to the
right side of the lowei- fold, so that the passage from one auricle
to the other, named the foramen ovale, is more or less oblique.
The septum is completed at the period of hatching of the chick,
and of the birth of the Mammalian embryo. Lastly, the bulbus
arteriosus becomes subdivided longitudinally, into the pulmo-
nary artery and the aorta, each remaining connected with its
respective ventricle. The primitive heart, whilst it is still
merely a straight tube, already manifests its jumper function, its
walls containing sarcous cells of round, oval, and fusiform shape,
and distinctly contractile, the conti'actions soon being seen to
proceed, in regular succession, from the hinder, or venous, to ,
the anterior, or arterial end. Then, and even much later,
when the heart is beginning to acqttire its characteristic shape,
its contractile walls present no distinct muscular fibres, but
only large contractile nucleated cells, which are at first round-
ish, but afterwards become developed into spindle-shaped, or
even forked, contractile fibre cells. The valves are developed,
in their re.spective positions, from the inner surface of the
heart, commencing very early.

The arterial system of the entbryo, is dcA^eloped by the for-
mation, and subsequent metamorjDhoses, of five arches on each
side, which are formed in succession fi-om the original arterial
trunk at the anterior end of the heart, all, however, not being
present at the .same time. The arch first formed, consisting of
the two branches into which the primitive arterial trunk diA'ides,
and Avhich, curling backwards, unite along a part of their course j
to form the descending aorta, has already been described. I
Behind this first arch, a second, third, fourth, and fifth arte-
rial arch are formed on each side, the first arch being obli-
terated before the last one appears ; all in turn coale.sce as
they pa.ss backAvards, like the returning part of the first pair,
to assist in forming the descending aorta. This is the condi-
tion Avhich persists in Fishes, by Avhich the trunks of their
characteristic branchial A'essels are formed (ji. 2G7). In the
higher Vertebrata, this state is very rapidly changed, and its
several phases of deA^elopmcnt correspond Avith the adult con-
dition of the Amphibia, and, in some respects, of Ifeptiles and
Birds as Avell. These changes fully explain the mode oi origin
of all these varieties, from a common Vertebrate embryonal

DEYELOrjrENT OF THE VEINS.

G37

type. The upper primitive arterial ai'ches, or primary arches,
are said to occupy the third branchial or vi.sceral arches or
lobes, already described as appearing in the facial and
cervical regions of the embryo. These arterial arches are
thus modified : — The fifth, or posterio?- arch, the last one
formed, di.-<appears on the right side ; whilst, on the left, it con-
stitutes the trunk of the future pulmonary artery, and joins the
fourth arch. This fourth arch, on the left side, forms the left
aortic arch, wdiich, joining with the first, then descends and
unites, in the Bird, with the con’esponding or fourth arch of
the right side, to form the aorta ; but in the Mammal, the fourth
arch, on the right side, does not form a right aortic arch, but
remains pervious, as the innominate and the commencement of
the right subclavian arteries, from which the vertebral and axil-
lary arteries are given off. On the left side, the subclavian
is given off directly from the fourth, or left aortic, arch. The
commencement or inner ends of the third arches, form the
corresponding common carotids, whilst the third arches them-
selves remain as the internal carotids. The commencement or
inner ends of the first and second arches, become the external
carotids, the transverse parts of the last-named arches, en-
tirely disappearing (Kathke).

The veins of the embryo, consist, at first, of four symmetrical
! cardinal veins, two anterior and two po.sterior, one on each side.

I The anterior and posterior vein of each side, join to form the
: so-called right and left ducts of Cuvier ; these again unite in
! the middle line, into a very short trunk, which, at an early
period, opens into the single auricle, and, except in Fishes,
ultimately forms part of that cavity ; hence the two ducts of
Cuvier open independently, as two superior veme cavae, into the
auricle. This condition remains permanent in Birds and some
of the lower Mammalia, which possess both a right and a left
vena cava superior, opening separately into the right auricle.

I Instances are occasionally met with, from arrest of deve-
i lopment, of two such veins in the Imman body. The anterior
1 cardinal veins remain on each side, as the internal jugular vein.
I Between them, across the root of the neck, a transver.se branch
I is very early formed, below the future subclavian veins. This
t cross branch, becoming enlarged, at the same time that the part
t of the left cardinal vein, extending below it down to the
I coronary veins on the back of the heart, is obliterated, con-
I veys the blood from the left side of the head and upper limb,
' over to the venous trunk of the right side, and forms the future

638

SPECIAL PHYSIOLOGY.

left innominate vein, the persistent venous trunk of the right
side becoming the vena cava superior. The posterior cardinal
veins originally return the blood from the WoltSan bodies, and
from the hinder part of the embryo. These afterwards become
the azygos veins, of which, hoAvever, the right one only re-
mains in Man and the higher Mammalia, the left vein disap-
pearing up to the back of the heart. Here, however, traces of
the left cardinal trunk., or left vena cava superior, remain as
the cardiac sinus, or the short dilated terminal portion of the
great cardiac or coronary vein. Sometimes a smaller azygos
vein, on the left side, ascending to the innominate, represents
another portion of the primitive cardinal A'ein ; from this
point, however, down to the cardiac sinus, at the back of
the heart, vestiges of the course of the primitive vein, may be
found throughout life. The left superior vena cava, when it
exists, pursues the same coru'se. The inferior vena cava is
developed as a median vein accompanying the aorta, altogether
independently of the posterior later cd cardinal veins. It is
chiefly formed by the upper part of the omphalo-mesenteric
trunk, which is joined by the umbilical vein, forming the
ductus venosus ; it also receives the common trunk of the
future iliac veins. It terminates, at first, in the left half
of the common auricle, but is soon shut off from that, by the
lower fold of the inter-auricular septum. The mode iu which
the pulmonary veins are formed, and brought into relation with
the left auricle, is not known.

Embryonal and Foetal Circidations.

The circulation established Ijetween the early embiyo and the
vascular area upon the yolk, has been called the first emhryonal
circulation ; it is intended for nutrient and respiratory pur-
poses. In the ovum of aU the Vertebrata, it soou ceases to be
sufficient as a respiratory circulation. Thus, in the Fish and
Amphibia, the branchial arclies give origin to external or
internal gills, which carry on the embryonic resjflration ; Imt
in the lieptile. Bird, and IMammal, the allantoid s;ic is de-
veloped, the bloodvessels of which convey blood outwards
from the body of the embryo, in order that it may be aerated, ,
and then return it to the embryo again, thus assisting in the
res|flratory frmetiou. hloreover, in the Mammalian ovum, iu
which the yolk is so minute, the allantois and its vessels, as
we have seen, assist in the formation of the which is

not only a respfratory, but a uutrieut organ. This allantoid

THE E(ETAL CIRCULATION.

639

or placental circulation constitutes what has been called
the second emhvyonal circulation. It is thus carried on : —
ironi the iliac arteries of the embiyo, the two hppogastric
or umbilical arteries proceed outwards along the allantoid
sac, and, in the eggs of the lieptile and Bird, rainily in
the outer layer of the allantois, immediately beneath the
permeable shell and shell-membrane. In the Mammalian
embryo, the blood enters the membranous or villous placenta,
and is returned by the single umbilical vein, which runs be-
neath the liver and joins the inferior vena cava, just below the
heart. In passing beneath the liver, the umbilical vein com-
municates freely with the jwrtal vein. The blood brought
back by the umbilical vein, is arterialised ; it partly enters the
liver through its portal veins, and is thence returned by the
hepatic veins, to the inferior vena cava, but it is partly con-
ducted on directly to this-last named vein, the portion of the
venous trunk which so conducts the blood, being named the
ductus venosus. In the vena cava inferior, this mixed hepatic
and arterial blood becomes further mingled tvith the venous
blood from the hinder part of the embryo, and the combined
stream then enters the right auricle, and here, guided by the
Eustachian valve, is chieHy, and, in the early stages of de-
velopment, entirely, conveyed, through the foramen ovale in the
auricular septum, directly into the left auricle. On the other
hand, the purely venous blood returned from the anterior half
of the embryo by the superior vena c;iva, separated by the
same valve, remains in the right auricle. The contents of the
auricles being, by their contraction, driven into the corre-
sponding ventricles, it follows tliat the partially arterialised
blood in the left auricle, enters the left ventricle, and from it,
is propelled into the aorta and its branches, whilst the venous
: blood in the right auricle, enters the right ventricle, and from
it, is propelled into the jmhnomuy artery. The pulmonary
artery is, in the embryo, connected by a short arterial trunk,

I named the ductus arteriosus, with the under side of the arch
I of the aorta. Hence the blood in the descending aorta below
that point, is mixed with the venous blood collected in the
right auricle, whilst the arch of the aorta contains the arte-
rialised blood collected in the left auricle. This latter blood
is therefore conveyed by the great branches given oil' from the
arch of the aorta, to the anterior ])art of the embryo, i.e. to
the head, neck, and upper limbs; whilst the former, or non-
i arterialised blood, ju'oceeds, in very small (|utintity, through the

640

SPECIAL PnYSIOLOGT.

still narrow pulmonary artery, into the collapsed lungs, but
almost entirely through the descending aorta, iliac arteries and
their branches, to the posterior part of the trunk of the embryo
and the hinder limbs. A portion of it, however, is also conveyed,
along the hypogastric or umbilical arteries, to the allantois or
placenta, to be once more renovated; from these parts it is
then returned to the embryo, by the umbilical vein, as arte-
rialised blood, and pursues the course already described, over
again. The foetal circulation is, therefore, largely accomplished
by the action of the right ventricle, and the walls of this cavity,
before birth, are of equal thickness with those of the lelt
ventricle. The right auricle is then also larger and thicker
than the left.

It is probable that, from the admixtime of the venous blood
of the embryo, at several points, with the arterialised blood
brought from the allantois or placenta, no portion of the em-
bryo is supplied with pure arterial blood, especially whilst the
foramen ovale, between the auricles, is very patent. Never-
theless, the head and upper limbs always receive blood more
perfectly oxygenated than that distributed to the lower half
of the body. This difference is associated with the more
rapid development of the important parts situated in the
anterior half of the embryo. Thus, the head, the ence-
phalon and the organs of the senses, exhibit a far greater
activity of development, than the hinder portion of the embryo
and the corresponding part of the nervous axis. The anterior
limbs also show a greater relative development than the poste-
rior. These conditions have even been regarded as having
the relation of cause and effect ; but probably they are merely
associated coirditions. As the heart approaches its perfect
state, and the foramen ovale becomes smaller, and its
course through the auricular septum more oblique, the arte-
rialised blood is jn’obably more completely conducted into the
left auricle, and so, through the left ventricle, aorta, and great
arteries, reaches more esjiecially the anterior part of the body.

Change in the Circulation at Birth.

At the period when the young Eeptile escapes from its egg,
when the young Bird first chips the shell, and when the young
Mammal is born, each begins to respire by the lungs. A modi-
fication of the circulation then becomes necessiiry, to connect
it with, and adapt it to the newly- employed respiratory organs:
the allantoid or placental circulations become aiuested ; the

DEYELOPMENT OF THE TISSUES.

641

allantois is withered, and the placenta is first detached from
the maternal system, and afterwards from the young animal,
near the umbilicirs or navel. From the umbilicus inwards,
the umbilical vein shrinks on its coagulated contents, as far as
the portal vein, and forms the future round ligament of the
liver. From the portal vein to the inferior vena cava, the
venous channel, called the ductus venosus, likewise contracts on
its coagulated blood, and is then obliterated, remaining only
as a fibrous cord. The foramen ovale in the auricular septum,
becomes completely closed. The ductus arteriosus, connecting
the pulmonary artery with the arch of the aorta, the primitive
ductus jBotalli, also contracts on its coagulated contents,
and is soon converted into a fibrous cord ; whilst the I'ight
and left divisions of the pidmonary artery leading to the lungs,
become enlarged, and convey a far larger quantity of blood than
before ; the pulmonary veins, which bring back the blood from
the lungs to the left auricle, are, at the same time, propor-
tionally enlarged. Lastly, the portions of the hypogastric arteries
which pass upwards by the sides of the bladder and urachus,
to issue at the umbilicus as the umbilical arteries, likewise
shrink and become obliterated. By these changes, which are
accomplished within three or four days, the circulation
acquires its permanent condition, or what is called the
complete double circulation', the venous blood, retm-ned from
the whole body, is propelled by the right auricle, exclusively
into the right ventricle, and fi’om thence, through the pulmo-
nary artery and its right and left branches, entirely into
the lungs. From these, it is returned, arterialised, to the left
auricle, is exclusively delivered into the left ventricle, and is
thence propelled through the ascending and descending aorta
and their branches, on to every part of the body. To com-
plete these changes, the left ventricle, which now performs
the whole wmrk of the systemic circulation, speedily acquires
a greater thickness of its walls than the right ventricle.

DEVItLOPMENT OF THE TISSUES.

Animal and Vegetable Cells.

Whilst the forms and relations of the organs, are evolved in
the manner just detailed, their component tissues are under-
going development. Tliese tissues, with their comj)lox struc-
ture and composition, are gradually produced from simple, and
originally identical, anatomical elements. They commence,

VOL. II. T T

642

SPECIAL PIITSIOLOGT.

like the organs which they build up, in the early periods of the
formation of the embryo, originating directly from, or through
the agency of, nucleated cells of the blastoderm, held toge-
ther by an intermediate matrix or blastema (/3\aoroc, blastos,
a germ). These cells are themselves the internal offspring
of the contents of two cells — the germ cell and the spenn cell.
The former, or nidal cell, fertilised by the latter, produces a
brood of uniform cells, from which, by further midti plication
and differentiation, all the tissues are evolved. These two
cells are, originally, elementary histological parts of the tissues
of parent animals, evolved by special developmental processes.

It is supposed by Schleiden, Schwann, and their followers,
that all organised tissues, whether animal or vegetable, are
produced directly from cells ; but, though this is proved con-
cerning the vegetable tissues, there are certain animal struc-
tures, which, it would seem, are not formed out of such cells
themselves, but are developed, for example, fj-om the inter-
cellular matrix or substance. Hence the so-called cell theory
is regarded, by many, as exploded, so far as animal organisms
are concerned. But if the definition of the term cell, be
extended, these discrepancies of view, may be generally re-
conciled.

In a perfect vegetable cell, figs. 46, 47, as seen detached in the vesicle
of a microscopic ftmgus, or aggregated in the section of an onion, there
is found, a wall ov periplast always composed of cellulose or lignin, with a
contained or cndoplust, the outer part of which is often firmer

than the interior, and is named the primordial utricle ; in the endoplast,
is a nucleus, and in that, often, a nucleolus-, aroimd the nucleus, is col-
lected a soft, granular, germinal matter. In becoming altered, so as to
constitute a vegetable tissue, these cells enlarge, change their shape, the
nature of their walls or contents, and their connections or modes of
junction, forming flat polygonal cells, polyhedral cells, elongated, fusi-
form, tubular, or reticular tubular tissue, plain, dotted, or spiral ducts,
woody fibre, spores, zoosperms, pollen, or ovules. The intercellular
substance is always scanty. For the formation of the tissue of a growing
plant, such cells must also multiply ; and this is effected by division of
the cells, or by the formation of buds, or offshoots, which is much the
same process, and re.semblcs the fission or gemmation of non-scxual
reproduction ; but they can also multiply, ns in the spore cases of fungi,
by internal or endogenous formation, which more resembles the sexual
mode of reproduction. In the vegetable cell, the essential punctum or
point, the centre of nutritive or developing force, is the nucleus, or the
nucleolus. It is this which appears to attract materials for the forma-
tion of the germinal matter around it, for the maintenance of the
endoplast, and for the deposition of the periplast.

lu animal cells, far greater variety of form and plasticity

ANIMAL CELLS.

643

of function, are observed. When in their most complete con-
dition, as in the ovum, they consist, like a vegetable cell, of a
cell -wall or envelope, i\\Q i^eriplaat, of fluid or semifluid contents,
the endoplast, of a nucleus, and usually of one, two, or more
nucleoli. The cell wall is a thin, delicate, homogeneous, trans-
parent membrane ; but this is absent in many cells, such as
ihe primary embryonic cells, and the white corpuscles of the
blood, lymph, and chyle. The outer part of the endoplast, is
said sometimes to be firmer than the rest, and to constitute a
special investment, like the primordial utricle of the vege-
table cell (Huxley). In less perfect cells, there is often merely
found a nucleus enveloped in a soft granular mass, as in the
fusiform, unstriped muscle cell. The perfect cells may be
called cystoplasts ; the imperfect cells, gymnoplasts. The cell
contents of the former, or the cell substance of the latter, pre-
sent, in certain cases, as in the primitive embryonic cells and
in all newly-formed cells, besides fat particles, a peculiar semi-
fluid, transparent, tenacious, albuminoid substance, called the
protoplasm, which contains very minute molecules, and oleoid,
and often amyloid matter. This protoplasm frequently presents
movements, seen also in vegetable cells, which may depend on a
contractility in the protoplasm, for it has been observed to be
excited by electrical currents (vol. i. p. 182). This proto-
plasm usually diminishes, becomes altered, or di.?appears as
the cell grows ; but sometimes it is retained during its whole
existence. It is very easily colom-ed by carmine, and is thus
made evident in microscopic investigations. The soft substance
which gathers especially around the nucleus, corresponds with
the germinal matter of Beale, which he regards as the formative
matter of the cell, as distinguished from the special contents, or
investments, which he names formed matter. The nucleus is
a vesicular body, which, in a growing cell, is round or oval ;
its nucleolus is also, by some, said to be vesicular, but it may
be, for a time at least, solid. These two structures are the
essential parts, the essential puncta of the cell, the so-called
germinal centres, or centres of cell-nutrition and cell-life.

It is supposed by Schwann, that an animal cell may arise in
the soft, clear sub.stance known as blastema, a sort of germinal
matter ; that in this, by the development and collection of a
number of minute molecules, a nucleus, called by him a cyto-
blast, is formed ; and, lastly, that upon this, a fine membrane
grows, and gradtially .separating itself from the nucleus, forms
the cell wall, with its intermediate cell contents. This mode

T T 2

644

SPECIAL PHYSIOLOGY,

of origin is also supposed by Schwann, to be the one by which
new cells continue to be formed during the whole of life ; but
it is more commonly believed, that the nuclei of new cells,
proceed from the division or midtiplication of pre-existing
cells, and that all are the direct descendants of those originally
formed in the ovum. The hypothesis of the free formation of
cells, is, as regards tissue life, the analogue of spontaneous
generation, as regards animals themselves.

The formation of new animal cells from pre-existing cells,
may take place in several ways. Thus the old or parent cell
may divide into two cells ; in this case, the nucleus first sepa-
rates into two, and the cell itself then presents an indentation
across its centre, which, gradually increasing, divides it into
two cells, each containing its proper nucleus ; or sometimes
the nucleus, instead of dividing into two, may divide into
three, four, or, as has been noticed in the embryo of the frog,
even into six nuclei, the cell itself then separating into a cor-
responding number of cells. This has been named the fissi-
parotis mode of development. In the so-called gemmiparovs
development, new cells are described as being formed by the
evolirtion, and subsequent detachment, of buds from the side of
a cell. Instances occur, as in the soft medullary tissue in the
interior of bones, and also, it is said, in the spleen, of the for-
mation, by repeated subdivision, of many nuclei in the interior
of a single parent cell. In bone, these multiple nuclei of the
cells, remain as nuclei ; but in the spleen, they may develop
into an ordinary nucleated cell. Fi'ee nuclei are those which
are found in a blastema or matrix, in very actively growing
parts, or in morbid new growths ; they originate from, or by
the influence of, the old or pre-existing nuclei of the surround-
ing tissues, themselves the progeny of still anterior cells.
They may appear to be evolved, in some way, from aggrega-
tions of protoplasm, but still, it is submitted, always under the
influence of preformed nuclei or nucleoli. In the so-called
exogenous development, rupture of the wall of the old cell
occurs, the nuclei escape, and a new cell is developed from
each (Bennett). The endogenous mode of formation consists
in an increase in size of the old cell, a cleavage of the nucleus
into two, and the development of two cells Avithin the original
cell wall;

Animal cells undergo various changes in size and form
(fig. 122). 'J'heir nuclei, for example, may increase in size and
alter in shape, but not to such an extent as the cells them-

ANIMAL CELLS.

645

selves ; in many cells, they become obscure ; and in some
cells, as in those of elastic tissue, they finally disappear.
Their envelopes may expand and burst, or they may shrivel
up and dry. The cells may dissolve and disappear, or become

Kg. 122.

Eig. 122. Forms of animal nucleated cells, o, flat and round cell of red
and white blood corpuscle, h, ramified cell of grey nervous matter,
c, cells, multiplying by binary division of nucleus and cell, and em-
bedded in a solid matrix of cartilage, d, cells of areolar connective tissue,
showing their splitting into flbrillm. e, elastic fibre cells. /, ramified
pigment cell, g, muscular fibres, ft, capillary vessel.

the seat of special deposits. Sometimes the substance of a cell
undergoes but little apparent change ; but usually, their con-
tents are modified according to the tissue which they form, or
the secretion which they prepare, a, h. Thus, some cells, as
those of bone, dentine, and enamel, become loaded with earthy
matter ; others, as the red corpuscles, with iron in combination,
and colouring substance ; others, as those of adipose tissue,
with fat ; some with mucus or horny matter. Their relations
to each other, may undergo many modifications. In the fluids
of the body, as, e.g. the blood, the cells remain separate. In
the solid tissues, they may be simply connected together by a
minute quantity of intercellular substance, as in the epithe-
lium and epidermis. Sometimes they elongate, and form fibres
in various ways, d ; or, after lengthening, they may subsequently
join with similar cells, and give rise to the formation of
tubes. The septa between these may be ab.sorbed, and the
coalesced .and arborescent branches of different hollowed cells,
may lead to the production of ca pillary, /q or lymphatic plexuses.
Moreover, animal cells seem to exercise a singular power over
the intercelluLar substance, blastema or matrix, which often

646

SPECIAL PHYSIOLOGY.

appears very large in quantity, in proportion to tlie cells them-
selves, as, tor example, in cartilage, c. This matrix may be
watery, soft and gelatinous, firmer and tenacious, still more
solid and hyaline, or hard and opaque. It presents great
varieties in chemical composition. It may be structureless,
striated, fibrillated, fibrous, distinctly granular, or organically
crystalline. Lastly, cells may undergo atrophy, or degenerate,
become the seat of morbid deposits, especially of fat, and may
finally die.

In contrasting the animal with the vegetable cell, it may
be said that each vegetable cell, always a cystoplast, retains
its own cell wall, and is, in a certain sense, independent of
the rest. The intermediate substance is either absent or in-
visible, or it takes the form of a separate periplast for every %
cell. Each cell is encased anatomically, and isolated physio-
logically. They cohere rather than co-operate.

As to the animal cells, they are sometimes cystoplasts, often
gj-ranoplasts. The presence of a separate periplast, is not
universal ; the endoplast probably has not even a primordial
utricle; the outlying region of the cell, is not specially protected,
but the intermediate matrix, which may be a common peri-
plast, is most abundant, and often curiously specialised in
structure and composition. The cells are fused together
rather than coherent, and they manifest great dependence on
each other, less individual isolation of function, and more
marked physiological co-operation.

Nevertheless, both animal and vegetable cells are organic
bodies, living by the properties operating in their centres of
growth and nutrition, the nucleus or nucleolus. The vegetable
cell feeds upon inorganic materials, the animal cell on a pabu-
lum of organic origin, but not on an organised pabulum.
Organisation only exists when, under the influence of nuclear,
nucleolar, or cell action, the nutrient pabulum forms part of
a living cell or its contents.

Development of the several Tissues.

Connective Tissue, and its varieties, areolar, fibrous, and

jelly-like.

The embryonal connective tissue is a jelly-like substance, consisting
of a transparent, soft amorphous matrix, in which numerous nucleated
cell-elements are found. According to one view, some of these cells
elongate in the soft matrix, become fusiform, unite into long wavy bands,
and thou split into the fibrilla; of the fibrous or areolar forms of connective

DEYELOrMENT OF THE ADIPOSE TISSUE.

647

tissue, their nuclei being ultimately lost sight of. According to another
explanation, the elongated cells and the matrix, blend together into a
homogeneous mass, which then becomes fibrillated, fig. 122, In any
case, the nuclei remain as connective tissue corpuscles. In many situations,
softish and nearly homogeneous tissues are met with, which are evidently
modifications or arrested developments of connective tissue, as in the
coats of small vessels, in the soft neurilemma of the smallest branches
of nerves, in the submucous coat and villi of the small intestine, in the
papillm of the skin, and elsewhere. The cornea presents a peculiar form
of fibrous connective tissue ; whilst the -\dtreous humour is an imper-
fectly developed areolar tissue, in which the cells have gradually dis-
appeared, or exist only at the sm’face, whilst the matrix has become
deliquescent. The soft embryonal connective tissue and the vitreous
humour, contain no gelatin, but merely albumen and mucin. The chemical
change into gelatin, occurs only with the perfect development of this
tissue. The cornea contains chondrin and not gelatin.

Elastic 2'issue.

In the development of this tissue, which is nearly always associated,
or intermixed, with the connective, some of the cells of the embryonal
tissue pass through the changes just described as proper to connective
tissue cells, whilst others subsequently become much elongated and at-
tenuated, branch out into fine ramifications, which unite with those of
adjacent cells, undergoing similar changes, and preserve their nuclei
in their central or thickest part. Sometimes these nuclei are ramified,
at other times, they are fusiform. In many situations, as in fibrous
membranes, ligaments, and tendons, in the true skin, in the cornea of
the eye, and elsewhere, these ramified and united cells remain in the
above described condition, their nuclei forming the connective tissue
corpuscles. It has been said, that they are hollow, and that their fine
ramifications convey a nutrient plasma tlu'ough the dense fibrous tissues
in which they lie, and hence these have also been called plasm-cells.
Lastly, they have been said to form the commencements of the lym-
phatics ; but this is not proved. According to some, the intercellular
substance becomes fibrillated, and appears to be a sort of deposit from,
or an excretion upon, the nuclei or cells.

In other situations, as in the loose areolar connective tissue, these
fine fibres appear darker, and form networks of elastic fibres. ThoEO
reticular fibres, becoming thickened by a deposit on their outer surface,
form the stronger varieties of elastic tissue ; by being joined or
further thickened in parallel planes, they give rise to the elastic fibrous
networks of the air-tubes, or to flat fenestrated elastic membranes, as
in the arteries. The true elastic fibres are said to lose their nuclei ;
but they may bo merely covered in and hidden.

Adipose Tissue.

The ve.siclos of this tissue, however small or large, are obviously
nucleated cells, in which fatty matter has accumulalod; their nuclei
become obscured, or oven di.sappcar. The fat colls have been traced in
all stages of development, from minute cells lying in the embryonal con-
nective tissue, at first containing only an albuminous fluid, thou a few

648

SPECIAL PHYSIOLOGY.

scattered oil-di’ops, and finally attaining tlioir fully distended condition.
Other cells adjacent to them, become changed into areolar connective
tissue, bloodvessels, or lymphatics, which hold the fat cells together, and
minister to their nutrition. Often, when the fatty matter is absorbed
from the cells, in emaciation, the nuclei again become visible. In
the marrow of bones, the nucleated cell structure is very clearly and
beautifully seen. The reddish parts of the marrow, also contain smaller
cells, and often compound nuclear cells, not fatty, called the meduUary
cells ; these are very numerous in growing bone.

Cartilage, Fihro-Cartilage, and Yellow Cartilage.

The development of cartilage, is more easily traceable than that of any
other tissue, from nucleated cells which are the immediate descendants
of the primitive embryonal cells. In the simplest form of cartilage, as
in the chorda dorsalis, and in certain other embryonal curtilages, the cells
have very delicate walls, which are closely applied together, grow into a
polyhedral shape, and present at first no apijreciable intermediate matrix.
More commonly, as in the cartilaginous pieces which precede the for-
mation of the bones, and in articular cartilage, the original delicate cell-
walls acquire an outer deposit or secondary cell-wall, which goes on
thickening, blends with that of other cells, and also with a surround-
ing intermediate matrix. This is partly formed by the secondary
membranes, but partly, it is said, in the blastema between the cells. This
matrix either remains transparent, or becomes granular, or even more
or less fibrillated. The cells themselves enlarge, and new ones arise
within them, by successive endogenous binary subdivisions of the
nucleus, accompanied by corresponding constrictions of the cell itself.
Moreover, secondary capsules are formed around each new cell, whilst
the caiDsule of the parent cell is fused with the intercellular matrix,
and so disappears, fig. 122, c. The secondary capsules of the new cells,
in their turn, blend with the matrix, and cease to be visible, whilst fresh
formations of still newer cells, arise by division of their nuclei. The
matrix thus formed, is apparently homogeneous, but exhibits faint striae
on the application of reagents. Sometimes a nucleus, instead of dividing,
and each new one forming a separate capsule, becomes invested by a series
of concentric capsules, developed one within the other. Sometimes no
secondary capsules are formed, the primary one only persisting. The
contents of the growing cells, become clearer, and the nucleus plainer.
Amyloid substance has been found in young cartilage cells.

In ^('jro-cartilage, the intermediate matrix, with some of the cells,
becomes changed into connective tissue, whilst other colls remain in the
form of cartilage cells. In the yellow cartilages, intermediate elastic
tissue filires are developed between the cells, the rest of the matrix
preserving its cartilaginous character.

Osseous Tissue, and the Bones.

Tlio mode of formation of perfect bone, is exceedingly complex. It
is never developed direotlj% l)ut by the intervention either of cartilage,
or of an imperfectly formed fibrous connective tissue, the precursory
tissues, as they are called, in which ossification takes place.

In the intra-carlilagiiioiis mode of origin of bone, the cartilage cells

DEVELOPMENT OF DONE,

64<J

first rapitlly multiply, by the formation of new cells within the old ones,
giving rise to clusters of softish nucleated cells in a clear matrix. In
a long bone, these cells are largest in the centre, and have their long
diameter across the axis of the bone; as they grow, the matrix Usually
becomes faintly tibrillated. Wherever ossification is about to begin,
there appear in the cartilage-substance, certain soft ramified spots,
which consist of masses of smaller nucleated cells, out of which the
bloodvessels and blood are formed, these ramified soft spots coa-
lescing, form canals, whilst the contained bloodvessels, establishing
coiuimmications with previously existing ones, supply blood to the
cartilage about to undergo ossification. The c.artilage cells are first
grouped into elongated clusters, separated by a clear matrix ; a deposi-
tion of earthy matter then takes place in this matrix between the cells,
in the form of opaque granules, by which process, the matrix becomes
darker by transmitted light, and is soon calcified. This calcifying
process partially affects the outer walls or secondary membranes of the
cells, but not their contents.

The cartilage which is thus changed into bone, is called cartilage
of ossification, ossi/ging cartilage, or precursory cartilage. The bony
tissue into which it is converted, is called the primary bone ; for it is no
sooner formed than, as a general rule, it begins to be the seat of further
important changes, during which it is almost entirely, or entirely, ab-
sorbed, to make way for the development of the secondary bone, or per-
fect osseous tissue. This last alone possesses lacunoe and canaliculi,
concentric laminae, Haversian canals, and theii- contained bloodvessels,
cancelli, and in the case of the long bones, a central medullary cavity,
with its vascular and medullary contents.

The change is thus accomplished. The primary bone is comparatively
compact and opaque. In it, softer spots, or areola, appear, the second-
ary cavities, or medullary spaces (Muller), quite distinct from the ramified
vascular canals in the precursory cartilage. These spaces appear to be
formed by the junction of the adjacent clusters of cartilage cells, now
disappearing, in consequence of the solution and absorption of the in-
termediate, dark, granular and calcified matrix. These areolaj contain,
at first, a softish ossifying blastema, in which there very soon appear
certain fresh nucleated cells, smaller than cartilage cells, and resembling
medullary cells ; besides these, there are developed, an imperfectly formed
fibrous connective tissue and, likewise, many newly evolved bloodvessels.
The adjacent areolae being opened into each other, by the progressive
absorption of the primary bone, their vessels become connected ; and in
their thinned walls, the secondary or perfect bone is deposited, in suc-
cessive layers, by the transformation of corrosjionding strata of the soft
ossifying blastema and its contained colts. Hence the explanation of
the concentric laminae of the perfect bone. The indi.stiuctly fibrous
matrix of the ossifying blastema, idso becomes saturated with coalescing
osseous granules, so as to appear perfectly transparent and liomogoncous,
instead of opaque and granular, like the primary bone. Tho entangled
nucleated cells, tho walls of which also become calcified, are believed to bo
converted into stellate cavities, by tho partial intrusion of tho calcifying
process into them, and so to form the greater part of, or all, tho bone
lacuna, whilst their radiating branches, multiplying, become very lino,

650

SPECIAL PHYSIOLOGY.

and joining those of adjacent cells, form the canalicuK. The primary
opaque granular bone contains no lacunse. Some of the areolae, or spots
of solution, absorption, and new deposit, reduced in size by the succes-
sive formation of concentric laminae of secondary bone around them,
ultimately constitute certain of the Haversian canals ; whilst others,
even after they are lined by secondary bone, continue to widen by
further solution and absorption of the surrormding bone, whether pri-
mary or secondary, and so form the larger nutrient foramina and canals,
the small and large cancelli, and even the chief meduUarj^ cavity of
a long bone. Indeed, so long as the bones themselves continue to
grow, and even, but less evidently, throughout life, such processes of solu-
tion, absorption and re-deposit are repeated, in the secondary bone, over
and over again, as it is modified, by age, in size, form, and structure.

In the intra-memhranous mode of origin of bone, there first appears,
in connection with some previously developed fibrous membrane or pre-
cursory membrane, which afterwards forms the fibrous periosteum, a soft
matrix, or blastema, which contains largish nucleated granular corpuscles,
and soon puts on an indistinctly fibrous aspect; it resembles, indeed, imper-
fectly developed fibrous connective tissue. This fibrous matrix and the
walls of its included cells, become opaque by graniilar calcification. This
occurring in successive strata, forms the bone tissue ; whilst the cavities
of the cells, becoming stellate, with fine radiating and communicating
branches, constitute the lacunce and canaliculi. This process of calcifica-
tion occurs from the first, in a reticular manner. The fine spicula of the
network, increase in thickness, by the formation around them, of a soft
transparent osteogenic substance (Miiller), which ultimately becomes
bone. The granular corpuscles, or osteoblasts, are embedded in the
new-formed bone. The interspaces, meshes, or areolse, form softer spots,
the constituent cells of which develop into blood-cells, bloodvessels, i
and areolar tissue, and, after changes in their parietes, such as those
already described in speaking of the secondary bone tissue of bones |
preceded by precursory cartilage and primary bone, constitute the j
canals of Havers, the larger vascular foramina and canals, and the
cancelli of the cancellated bony tissue.

Although, therefore, the iutra-cartilaginous and intra-memhranous
modes of formation of bone, differ from each other, the development of
the secondary bone which goes on, passu, with the absorption of the
primary cartilage-formed bone, is analogous to the intra-membranous
mode of ossification. The soft ossifying blastema, in the one case, and
the precursory membrane in tho otlier, alike resemble an imperfectly
formed fibrous connective tissue, and undergo similar changes. Che-
mical considerations also support this analogy, for, on removing the
earthy matter from primar}' bone, its organic substance 3’ields chondrin,
whilst the animal basis of tho secondary bone, and of the intra-mem-
branous-formed bone, gives gelatin on being boiled.

The intra-membranous mode of ossification, is solely concerned in the
formation of the bones of the face, and of those of the upper part and
sides of the cranium. The upper and lower jaw bones, the palate bones
and vomer, tlie malar, nasal and lachrymal bones, are included in this
category ; so also are tho frontals and parietals, the squamous part of
tho temporals, the part of the occipital above the occipital eminence,

DEVELOPMENT OF BONE.

651

and certain slight portions of the sphenoid. In the case of some of
the cranial bones thus formed, the precursory membrane is developed
outside a corresponding primordial cartilage, which is said to be after-
wards absorbed. The cranial bones begin by one or more flat radiat-
ing centres of ossification, which spread out as the membrane advances,
and go on increasing in thickness, until, at length, they meet at the dif-
ferent sutures ; after this, they still continue to grow at their edges, imtil
the cranium has reached its full size — an arrangement needed to suit
the rapid growth of the brain. The clavicle is likewise in part formed
from membrane, but afterwards in cartilage also.

The intra-cartilaginous mode of formation of bone, occurs in the basal .
portions of the cranium, ^nz. in the ethmoid, in nearly the whole of the
sphenoid, in the petrous and mastoid parts of the temporals, and in the
occipital bone below the occipital eminence. It also occurs in all the
rest of the skeleton, excepting only the clavicles. For each bone there
is developed a sep>arate precursory cartilage, which is enclosed in a definite
perichontlrium, and is at first small and rudimentary in form, but gra-
dually acquires, as it grows, the general shape of the bone which is to
be developed from it. Practically, therefore, the skeleton is, at first, and
for a long time, more or less cartilaginous.

Certain centres of ossification, one, two, three, or even more, accor-
ding to the size and form of the future bone, appear at definite spots in
the cartilage, and extend into it as the latter increases in size. The
cartilage continues to grow in the direction of the articular surfaces of
the joints, and also in that of the various processes, until the develop-
ment of the bone is complete. The bony tissue also goes on growing in
the same direction, by the successive fonnation of the primary and
secondary osseous tissue. But in other directions, and especially towards
the sides of the bones, the precursory cartilages, sooner or later, cease to
grow, and then the further increase in such directions, is accomplished
by intra-membranous ossification beneath the soft and growing peri-
osteum.

Suppose in a long bone, for example, a single ossific centre to fonn in
the middle of the precursory cartilaginous shaft, as, indeed, is always the
case. Then, separate ossific centres subsequently appear at the ends,
constituting what are termed epiphyses (etti epi, and 4ivu> phuo, I grow),
and in the larger bones, other smaller pieces are developed at the apices
of the more remarkable projections or processes. The precursory car-
tilage of the bone, at last, ceases to grow in width, and, henceforth, the
shaft of the growing bone is steadily increased in diameter, by successive
subperiosteal intra-membranous deposits on its outer surface. At the
same time, the medullary cavity is formed by a continuous absorption
going on within. A platinum wire, placed around the growing humerus
or femur of a young pigeon, is found, after a time, enclosed in the sub-
stance of the bone, or, if examined a little later, in the hollow of the
bone itself. But tlie precursory cartilage continues to grow in length
long after, and the bony shaft, and the epiphyses developed at the ends,
ultimately meet, but do not coalesce by osseous tis.suo, until the full
length of the bone has been atbiincd. This is evidently a provision for
securing a progressive elongation of the bone during many years, toge-
ther with a proper development of the articular ends of the bones, all

C52

SPECIAL PHYSIOLOGY.

that time. At the ends of the bones, very thin layers of the precursory
cartilage, remain permanently unossified, and form the articular cartilages
of the joints. Immediately beneath this articular cartilage, is a thin
stratum of ossified cartilage or frimary bone, recognisable by being
smoother and more compact than the rest. This is the only part of the
primary bone which is permanent. The rest of this, and, indeed, the
earliest formed, and many succeeding portions of the secondary bone,
and also the subperiosteal intra-membranous bone, must be completely
absorbed, before any long bone has completed its growth ; for the young
bone would easily lie in what becomes, by continuous absorption, the
medullary cavity of the full-grown bone. The mode of increase in long
bones, is well shown by giving, at stated inteirals, to young pigs or other
animals, madder mixed with the food. The colouring matter of this
root, has an affinity for the salts of lime, and when it is being taken in
the food, the bone then formed has a reddish tinge, whilst the bone
deposited at other times, is yellowish white. By this means, it is proved
that successive additions are made at the surface and ends of the grow- i
ing bone, and that absorption of the bone is continually taking place in
its interior. Again, the distance between two holes made, one above the
other, in a young bone, is not increased by its subsequent growth (Hales,
Hunter, Duhamel) ; whereas a ring of wire placed closely aroimd a
growing bone, is soon foimd to be embedded in its substance, and at
later periods, even in the medullary cavity (Duhamel and others).

Most of the smaller bones have but one ossific centre. In the large
hip-bones, tliree primary ossific centres are formed, one each for the ilium,
ischium, and os pubis ; these grow and finally coalesce around, and at the
bottom of, the acetabulum. In the vertebrse generally, three primary
ossific centres appear, and then join around the vertebral ring, the bone
being afterwards completed by five epiphyses. In both these instances,
and also in the case of the occipital foramen, and the cranial cavity, the
arrangement described, facilitates the expansion of the cavity or canal,
around which the bones are destined to grow. The sternum is formed by
the coalescence of many pieces. The cartilages of the ribs, and of the
nose, are the unossified parts of the preciu’sory costal and nasal carti-
lages. Sometimes the number of ossific centres, has reference to the
homological relations of the bone.

The order in which the ossific process begins in the various bones of
the skeleton, is very singular, not always coinciding with that in which
the cartilaginous rudiments of the bones appear. The clavicles are the first
bones to show ossific centres, and then the lower jaw, which has one in
each lateral half. Next in order, are the vertebrre, the humerus, the femur,
the ribs, and the lower and larger portion of the occipital bone. Then,
the upper jaw bones, the frontal bone, the scapula, the radius, and ulna,
and the tibia and fibula. After that, most of the other cranial and facial
bones ; the iliac bones, the metacarpus, the metatarsus, and the pha-
langes of the fingers and toes ; the ethmoid, and turbinated bones, the
sternum, the ischium and the os pubis ; the os calcis, and another of the
tarsal bones, named the astragalus, and then the hyoid bone. At birth,
and for sometime afterwards, all the carpal bones, the five smaller tarsal
bones, the last pieces of the cocej^x, the patella, and the sesamoid bones,
are still entirely cartilaginous, having no ossific centres in them. By

STRUCTCEE OF THE VERTEBRATE SKELETON.

653

the end of the fifth year, all these, except the scaphoid, trapezoid,
and pisiform carpal bones, are ossifying, the last-named bone not show-
ing any ossific deposit until the twelfth year. The various epi23hyses of
the long and other bones, are not all finally joined by osseous union to
their respective shafts or chief masses, until after the completion of the
full period of growth of the body, or about the twentieth or twenty-first
year.

The Vertebrate Skeleton generally. — In examining the skeleton of the
Vertebrate series of animals, progressive stages of development, from a
cartilaginous to a more and more osseous condition, may be recognised.
Low in the scale, as in the amphioxus, the skeletal framework is com-
posed of a hyaline substance, containing nucleated cells, between which
are very fine fibres. In the Myxinoid fishes, it is composed of very
distinct fibres, with cartilage cells intermixed. In the Chimsera, it con-
sists, in some parts, of fibro-cartilage, and, in others, of cartilage. The
vertebral column of the stiu’geon, is a mixture of cartilage, fibro-cartilage,
and bone. In the skates and sharks, the cartilaginous skeleton is
covered in parts, or entirely, with a crust of ossific matter. In the
Lophius, the bones are fibrous and osseous. Lastly, in the so-called
Osseous Fishes, the skeleton is entirely bony.

In the ossified parts of the skeleton of the Cartilaginous Fishes, the bony
matter consists either of an irregular granular deposit, between and within
the cartilage cells, or of polyhedral bone cells, or of ramified bony laminae.
In the less perfectly formed bone, neither lacrmse, canaliculi, laminae,
nor Haversian canals exist. In the more complete bone of the Osseous
Fishes, those elements are introduced by degrees. The Haversian canals,
in some cases, appear as a few long channels, from which simple
canaliculi are given off. In a still higher structure, lacunte, of a
peculiar form, are introduced, of moderate size, tapering form, and
sending out very short wide canaliculi. Frequently, the lacunse of diffe-
rent layers of Fishes’ bone, cross each other at acute angles ; but more
commonly, they are arranged in parallel lines. Sometimes no Haversian
canals exist ; but usually they are jmesent, though small. In rare in-
stances, fine concentric lines are visible around these canals, representing
rudimentary laminae. In the lepidosiren, the lacunae are very large,
and the canaliculi much branched; they thus approach the characters
1 of bone in Ampliibia.

I In Amphibia, the skeleton is entirely osseous ; the bony tissue pre-
I sents largo and wide lacunae, very complex and ramified canaliculi,
f concentric laminae, and Haversian canals. In a few situations, the
lacunte cross each other at acute angles.

In the Reptiles, and also in Amphibia and Fishes, the bones are solid,
or contain but a few recesses filled with fat. The Haversian canals in
Reptilian bone are small, the concentric laminae irregular and wavy, the
lacun;e of medium size and shorter than in the Fish, and the canaliculi
very fine. Some lacunae cross at acute angles, as in crocodiles.

In Birds, the lacunae are smaller than in Reptiles, but Airgor than in
Mammalia. In the latter animals, the bony structure resembles that of
Man.

«>

654

SPECIAL PHYSIOLOGY.

Muscular Tissue.

The fibres of both the smooth and the striped varieties of this tissue,
have been traced in their development, from nucleated cells, derived im-
mediately from the embryonal cells.

In the case of the smooth fibres, the nucleated cells, at first roundish,
become elongated and fusiform ; their cell walls and their contents blend
into one mass, which assumes, by degrees, the sarcous character ; in the
meantime, the nucleus of each fusiform cell, becomes much elongated.
Many such fusiform cells produce, by their cohesion, a smooth mus-
cular band.

The striped muscular fibres have been described, by some, as arising,
each from the coalescence of rows of nucleated cells (Schwann). But
by other and more recent aiithorities, they are regarded as being each
developed by the extreme growth of a single cell (Eemak, Fox). It has
also been maintained that they originate wdthout the intervention of true
cells, through the agency of rows of nuclei, lying in a blastema, which
afterwards gives rise to the fibre, by a series of changes occurring in it
(Savoi’y). These differences of opinion are probabl}^ as much due to the
different interpretation of the same appearances by different observers,
as to differences in the observations themselves. They illustrate the
difficulties of microscopic research. If the primitive animal cell which
fonns a muscular fibre, be regarded as a gj'mnoplast, easily fused with
its neighbours, the discrepancy of opinion may, perhaps, be reconciled.

Supposing rows of nucleated cells to coalesce, to form a single fibre, it
is believed that the coalescing parts of the cell walls, are absorbed, and
that thus a long tube is fonned, which ultimately becomes the sarcolemma ;
the contents of the united cells, at first finely granular, are said to grow
and become sarcous, their elements arranging themselves into linear and
transverse series, first on the outer surface next to the sarcolemma, and
then more centrally, so as to form the transversely marked fibrillae. In
the meantime, as the cells grow in length, the nuclei separate from each
other, and become obscured, but are never lost. If, however, only one
long cell forms each fibre, the wall of such an elongated cell, is believed to
constitute the sarcolemma, and the contents, originally granular, are said
to be gi’adually increased and differentiated into the tibrillte, first becom-
ing marked by longitudinal lines, and afterwards by transverse stripe.
The nuclei multiply by successive subdivisions, and remain surrounded
by granular matter. By many, it is thought that the original cell wall, or
cell walls, do not form the sarcolemma, but that this is the result of a
subsequent deposit of homogeneous membrane around the nearly per-
fectly formed bundle of fibrillae.

Whatever their precise mode of origin may be, the muscular fibres seem,
when first recognisable, like very fine bands, sometimes not more than
one-tenth of the diameter of the fully formed fibre, and having bulging
nuclei in them at intervals. When composed of such fibres, the young
muscles resemble their tendons. As the fibres gradually increase in
width, they assume the adult characters, and become uniform in diameter,
so that the nuclei are no longer so easily visible (fig. 122, g). At birth,
all the muscles are said already to contain their full number of fibres, so
that their future growth consists only in an increase of length and width

DEVELOPMENT OF NERVOUS TISSUE.

655

of the pre-existing fibres. At, birth, the fibres are about one-fifth of
their ultimate dimensions. The fibrilltE of each fibre, may during growth
become a little wider ; but it is thought rather that they increase in
number. In other words, the individual sarcoiis elements retain their
size, but they are accumulated in a greater number of longitudinal rows.
In the enlargement of the muscles, which takes place from exercise, in
all probability the fibres do not increase in number, but in size, and
contain either more or larger fibriUse. In the opposite condition of the
wasting of a muscle, the fibres remain the same in number, but become
smaller, owing to a diminution of their contents ; the fibrillse also
decrease in number, grow indistinct, or even disappear altogether. In a
wholly paralysed, unused, or diseased muscle, fatty matter is substituted
for the characteristic sarcous elements.

It is obvious that such striped muscular fibres as, like those of the
heart, are but indistinctly striated, may bo regarded as less perfectly
developed fibres. Certain of the smooth fibres, in which the sarcous ele-
ments are very distinctly granular, or dotted, also approach in character
and development, to the higher or striated form of fibre. The fusiform
fibre cells, and last of all, the elongated, spindle-shaped, oval, or round
contractile cells of the heart of the embryo, are the lowest form of all.
There is thus a gradual transition from the simplest to the most com-
plex form of muscle cells.

In the case of the ramified form of the striated muscular fibre, noticed
in the tongue, lips, and face, and of the reticular form observed in the
walls of the adult heart, the primitive nucleated cells, out of which they
are developed, either simply ramify, or ramify and coalesce with the
branches of other cells, and then acquire their sarcous contents.

Nervous Tissue.

The ganglionic cells, fig. 122, h, are derived from metamoi’phosed
embryo-cells, and from the direct descendants of those cells, by ordinary
modes of multiplication. The rounded ganglionic cells are formed by a
simple enlargement, and a gradual alteration of their contents ; the nuclei
persist, and are very distinct ; the branched cells are formed by the out-
growth of one or more of the peculiar processes with which they are
provided. The envelope is prolonged on to the processes, and becomes
connected with the homogeneous tubules of the nerve fibres ; the processes
contain nervous substance. The very small roimdod colls, and the freo
nuclei, found in some parts of the grey substance of the nervous centres,
may be early stages of future ganglionic cells.

The grey or gelatinous fibres, found chiefly in the sympathetic system,
whether they be regarded as true nervous elements, or ns a peculiar form
of connective tissue cells, appear to be produced by the coalescence of
elongating fusiform nucleated cells, the contents of which, as the cells
enlarge, become soft and finely granular, whilst the nuclei appear
wider and wider apart. Even in the most highly developed of these
fibres, there is but little evidence of a tubular character or wall. The
medullary sheath or fatty layer is absent. They have been compared,
by some writers, to the non-medullated portions of the white nerve
fibres, or to the axis cylinder or ceniral band only of those fibres, which,
however, have a tubular sheath. The most perfect grey fibres cer-

656

SPECIAL PirrSIOLOGY.

tainly resemble a transitory condition of the fibres out of which the
white or tubular nerve fibres are developed.

The white dark-bordered, or double contoured tubular fibres, are
themselves derived from fusiform nucleated cells, which are embryo
cells, or their descendants. By coalescing, they first form grey granular
fibres, with elongated nuclei at intervals, and, in that stage, resemble the
grey or gelatinous fibres of the sympathetic system. But the grejdsh con-
tents of these fibres, soon become opaque, and white, and resolve themselves
into the central albuminoid band or axis cylinder, and then acquire the
surrounding fatty layer or medullary sheath; whilst the walls of the
coalesced cells, are said to unite, to form the outer tubular membranous
sheath of the perfect fibre. Instead of imagining many cells to coalesce,
a single cell may be supposed to go on dividing, to form a nerve fibre.

The branched terminations of the nerves, according to what has been
seen in the tadpole, originate in the junction of ramified formative cells,
which keep on joining those already fimther developed.

Sometimes more than one white tubular fibre has been seen forming
in a single embryonic, or less developed, one — a fact which would show
that the tubular membranous sheath might be developed otherwise than
by the cell walls of coalesced formative cells.

Bloodvessels,

The arteries and veins, excepting the very finest, are, as already men-
tioned, not so much tissues as compound structures, built up of several
tissues. They are developed in two very different ways.

In the first place, the principal vascular trunks, or the arteries and veins,
of the germinal membrane of the embryo generalljq and of its commenc-
ing organs, and indeed the heart itself, appear primitively as solid cords,
composed of multitudes of embryonic nucleated cells. After a time,
the innermost part or axis of these cords, becomes changed into blood,
the soft spaces coalescing and forming a system of canals ; whilst the
outermost cells are then gradually metamorphosed, in the ordinary man-
ner, into the epithelial, elastic, muscular, and connective tissues which
compose the coats of the vessels. This mode of formation is apparently
limited to the early and principal vessels ; for subsequently, the arteries
and veins, which are continuously being added, as the bodj- grows, are
developed in another manner— viz. by the transformation of previously
constructed large-sized capillaries, the calibre of which is increased,
whilst the coats are gradually thickened, by the formation of additional
tissues developed in the ordinary way.

The capillary vessels originate in two modes, according to their size. ,
The larger capillaries are formed by the coalescence of linear series of
nucleated colls, and the subsequent absorption of their attached ends, so
that a homogeneous tube is produced, recently shown to bo lined with a
fusiform epithelium, the nuclei of which seem to bo attached to the walls
of the vessels. These soon become connected with previously existing
vessels, and the blood then enters them. Tlic finer vessels, or those of
the actual capillary networks, originate in nucleated formative cells,
lying amongst the elements of a newly growing tissue; tliese become
ramified or stellate, by sending out fine processes or branches, which
run towards, meet, and coalesce with, other fine processes growing from

DEVELOPEMENT OF THE BLOOD.

G57

the larger capillaries just described ; afterwards they coalesce with pro-
cesses of other ramifying cells which appear in succession. These coa-
lesced processes and the cells themselves, become progressively enlarged
and hollowed out, so that a tubular or vascular network is produced,
the component vessels of which, though, at first, so fine as to convey
only the liquor sanguinis or plasma of tho blood, become idtimately
wide enough to carry the blood corpuscles also (fig. 122, It), New ca-
pillaries may also be developed within tho meshes formed by the older
ones. The walls of the coalesced ramified cells, constitute the homo-
geneous membrane- of the coats of the capillaries, in which the nuclei of
the formative cells, and especially those of the epithelial lining after-
wards formed, c.in be recognised. The more numerous and closely set
the stellate formative cells, tho closer is the capillary network developed
from them.

Blood. ■

This important fluid is primitively developed, as already mentioned,
in the interior of tho newly forming heart and principal vascular
trunks. At first, its structural elements — the hloocl-cdh or corpuscles,
are colourless cells with faintly gi'anular contents and a distinct nucleus,
in all rc.spects identical with tho embryonic cells. They soon become
loosened, and then separated from each other, by the formation of an
intermediate fluid plasma, the new liquor sanguinis) their contents be-
come less granular, and coloured by tho formation of colom-ing matter in
their interior, but their nucleus remains. They are now red blood-cor-
puscles; but as compared with those of tho fully formed blood, they
are mucli larger, spherical instead of discoid, darker in colour, and
nucleated, instead of being destitute of a nucleus. Once formed, they"
speedily enlarge, elongate, or assume a somewhat flattened and elliptical
figure, somewhat resembling the shape of tho blood corpuscles of tho
Amphibia ; the nucleus soon divides into two, or oven into tlireo or four
portions, or young nuclei ; tho walls of tho so altered cells, then become
constricted between these young nuclei, and, ultimately, the cells divide
into as many new colls as there were nuclei ; this process, it is supposed,
may bo repeated over and over again.

After a time, corrc.sponding with the date at which tho liver begins to
grow, this process of subdivision of the primitive nucleated red-cor-
puscles ceases, and then multitudes of colourless nucleated cells appear,
especially in tho blood of tho liver .and of tho spleen, and also in tho
lymph.atic system ; and either without, or with, previous multiplicaf ion
by subdivision of their nuclei, constriction of tho cell w.all, and actual
partition, they acquire, oven within tho spleen and liver, some red
colouring matter, and .are changed into nucleated red-corpuscles.

Both sets of those spherical, nucleated red-corpuscles, are ultimatelv
converted, by a slight diminution of size, by a flattening of two opposite
sides, and by the gradmil wiisl ing and final disappeanuicc of the nucleus,
into the typical non-nucleated disc-like rod-corpuselcs of tho fully formed
1 blood. This condition exists at, or even a considorablc lime before.

I birth. After birth, during tlio growth of tho body, and in tho adult, the
red-corpuscles of tho lilood are developed from tho colourless ones, as
already els(ovhere described (ji. 315).

The white blood-corpuscles are evidently the unaltered, colourless,
VOL. II. U U

G58

SPECIAL PHYSIOLOGY.

nucleated cells, derived, at first, from the blood itself, afterwards from
the liver, and permanently from the spleen and the lymphatic system.
Under certain circumstances, as in inflammation, colourless blood cor-
puscles may perliaps originate in the blood itself, within the general
capillary system.

Th.0 2)lcisma of the blood, at first the product of the liquefaction of the
intermediate blastema or matrix, probably effected under the agency of
the formative cells, is afterwards the complex result of various acts not
only of a formative, but also of an absorptive and excretory kind.

Lymphatics or Ahsorhents.

The mode of formation of the principal absorbent trunk, the thoracic
duct, is probably like tliat of the primitive bloodvessels.

The small lymphatics, according to observations made in the tadpole’s
tail, originate by the junction of nucleated cells, in the same way as
the large capillaries ; but they are said to anastomose much less fre-
quently. The extension of the absorbents into newl}' growing tissues, is
effected, as in the case of the capillary network, by the formation in the
new tissue, of peculiar cells, which Ijranch out, and join certain very fine
processes, given off from tlie lymphatics already developed. These
stellate cells are said to be more jugged in their outline, than those of
the capillaries.

The lymphatic glands are believed to be developed from clusters of
lymphatic vessels, which give out projections, afterwards converted into
the alveoli or cells of the cortical portion of those glands.

The chief microscopic structural elements of the lymph and chyle, the
small and large nucleated corpuscles, most probably originate in the
lymphatic vessels and glands, by subdivision of pre-existing corpuscles,
and perhaps multiply by subdivision. Probably also some of those
seen in the chyle and intestinal lymph, before it reaches the mesenteric
glands, originate in the solitary or agminated glands. They also seem
to be formed in the spleen, thyroid, and thymus glands, or even in the
interior of the commencing lymphatics. At first, these cells are minute,
and their envelope closely surrounds the nucleus. In this form, they
constitute the small lymph corpuscles. They grow into the larger ones,
by the deposition of soft granular matter between the exterior and the
nucleus. They also multiply by elongation, subdivision of the nucleus,
constriction of the delicate cell-substance, and partition into two new
cells, each having its own nucleus.

The molecular base of the chyle, is apparently the result of a process
of aggi’cgation of the simplest kind, whiUt the fluid part of the lymph
and chyle, may be regarded as an extremely diffluent blastema or fluid
matrix.

Vascular or Ductless Glands.

The several organs thus grouped together, arise from masses of
primitive embryonic cells and blastema, which appear in the situations
already described with their development as organs. The closed sacs
of the lingual, tonsillar, pharyngeal, gastric, and solitary and agmi-
natod intestinal glands, and also the closed sacs or Malpighian corpuscles

DEVELOrMENT OF EriTHELIAL TISSUES.

659

of the spleen, are deyelopod by the multiplication of cells or cell-nuclei,
of which the outer ones form a membranous envelope, and the inner ones
the special pulp, with its traversing bloodvessels. The cells of the
thyroid body, and those of the supra-ronal body, originate also by cell-
growth, which is most readily observed in these peculiar organs. The
new colls of the thyroid are said to be formed by a process of budding
or protrusion, and subsequent constriction and separation. The pa-
renchyma of the spleen, the thick walls of the recesses of the thymus,
as well as its fluid contents, and lastly the pituitary body, are formed
of gyninoplasts, nuclei, and a matrix.

Secreting Membranes and Glands.

The subcutaneous synovial bursse, mere interspaces in the subcuta-
neous connective tissue, probably arise, at first, by a process of softening
and absorption of that tissue, and afterwards by an extension of their
walls. In the true synovial membranes, in the serous membranes, and
in the mucous membranes, the defined limiting or basement membrane
is developed from very fine, almost homogeneous, connective tissue ; but
in the glands, the well-defined glassy basement membrane is supposed to
be a sort of excretion from the epithelial cells which cover the surface.
The origin of the glands, as organs, has already been described. They
commence as masses of nucleated cells, evidently destined to be epithe-
lial ; these project into, and fill up, recesses in the corium beneath. They
either remain simple, as in the case of the gastric tubuli, or they may
extend so as to develop the most complex gland, like the liver or kidney.
The cavities of the ducts, which are at first solid, are formed by a
softening of the intercellular matrix, along certain special lines of cells.

Epithelial and Epidermoid Tissues.

These arise, generally, from the multiplication and metamorphosis of
the embryonic cells of the outer and inner germinal layers of the
embryo. In the case of the serous membranes and of the synovial mem-
branes of the joints, they also originate from cells in deeper portions of
the embryonic structure.

The modifications which these cells undergo, however various, always
permit them to retain their nucleated-cell character throughout their
whole existence. The changes of shape, structure, and contents, neces-
sary to transform them into the various kinds of epithelial and epidt r-
nwid structures, can be understood by perusing the description of them in
vol. i., p. 72. Pigmentary deposits may occur either in simple epithe-
lial cells (fig. 43), or in ramified cells (lig. 122, f ).

In the many-layered cpithelia, these changes maybe seen at one view,
all occurring simultaneously (fig. 44). The cuticle at first cannot bo dis-
tinguished from the cutis. All the epithelia, as well as the epidermis,
exhibit a continuous growth. The glandular cpithelia show the witlest
departure from the primitive cell-type, especially as regards the chemical
composition of their contents. The mode in which cilia are developed
on the ciliated epithelia, is not exactly known. It may be by outgrowths
of the cell-wall, inchaling jirocosscs of the cell-contents, or by a fission
of tho substance of the coll.

The nails are developed, not on tho surface, but beneath a thin epi-

c V 2

660

SPECIAL PHYSIOLOGY.

dormic covering; tlie young nail consists of compressed and easily
separable cells.

The hairs appear as little black specks under the cuticle ; these are
clusters of coloured epidermic cells of the Malpighian layer, fitting into
depressions in the cutis, which are lined by a basement membrane. This
rudimentary follicle enlarges, and acquires its fla.sk-shaped character; its
walls are formed by the thickened basement membrane, and by a layer of
colls, belonging to the corium, outside it. The outer epidermic cells form
the root-sheaths, and the central ones, resting upon a little vascular
papilla, develop into the hair. This increases in diameter and length,
and then pierces the cuticle, beneath which it is really formed, sometimes
by its point, and sometimes in a bent position. The first hairs are very
fine, and form the down or lanugo. All new hairs, when old ones are to
be shed, commence by a cluster of epidermic cells, formed at the bottom
of the hair-follicle, upon the side of the old papilla ; as these grow, they
detach the old and falling hairs.

Dental Tissues.

The dentine is a dermoid hone, formed by the gradual transformation
and ossification of the superficial portion of the dental papillae or pulps,
and not by a mere excretion or deposit on their surface. The pulp is
chiefly composed of rounded nucleated cells, in a clear matrix, but con-
tains also a few areolar fibres, and many bloodvessels. The outer cells
become lengthened, like colmnnar epithelial cells. Bysome, it is thought
that a single layer of these cells, may, by elongation and other modifica-
tions, develop into the whole length of a dentinal tubule. It is more
commonly sripposed, that successive layers of pulp-cells are developed,
coalesce with each other, undergo metamorphosis, and become ossified,
in order to complete a tubule. Lastly, it has been suggested, that rows
of secondary cells developed within one primary cell, and subsequently
coalescing, are so transformed. There are dififercnces of statement,
as to the mode in which this occurs. The nuclei of these sccondarj"
cells, are supposed to coalesce, and, remaining hollow, to form the den-
tinal tubuli. All the other parts of the cells, and of the intermediate
matrix, become calcified, and constitute the walls of the tubuli and the
intcrtubular dentinal substance. The fine bifurcated ends of the tubuli,
are formed by branching and anastomosing processes of the cells. Uj on
the surface of the growing dentine, next to the enamel, is seen a fine base-
ment membrane, named the f reformative numlranc ; it is supposed to
be the seat of commencing calcification, to bo very early converted
into the more compact supei'ficial dentine, and to assist in connecting
this with the enamel.

The enamel organ (p. 625) consi.sts of a soft pellucid tissue, entirely
epithelial in its utiture. It is composed, on its inner or deeper as] ect. of
a layer of columnar epithelial cells, which are tippilied to the preforma-
tivo membrane of the dentine. Outside these, is a thick stratum, com-
posed of stellate colls, forming a network of fibres, enclosing multang-
ular aroolio, filled with transparent substance, and having brilliant
spots at the junctions of the fibres. Its outer part consists of epithelial
cells, arranged in masses, between projections of the enclosing vascular
mucous membrane. These masses are sometimes so large and prominent.

REPARATION OF THE TISSUES.

661

as to appear like wliite bodies beneath tho gum, and have been
erroneously regarded as glands — tho dental glands (Sorres). It is
usually stated that the colls of tho enamel organ, become elongated, and
calcified, with gradual absorption of their animal substance — at first
forming a soft cretaceous mass, but afterwards becoming hard, and being
firmly fixed to the surface of the preformativo membrane (Schwann,
Kolliker, and others). Their nuclei disappear, or leave only a fine
linear trace. It has been supposed that tho enamel-cells are
developed beneath the prefomiative membrane (Huxley); but this view
is not generally entertained. It is variously imagined that a single
prismatic cell serves to form a single enamel prism, running through
tho whole thickness of that structure ; or that several secondary cells
combine to form each prism. As the enamel organ terminates at the
cervix of the tooth, the formation of enamel is limited to the crown.
The crusta petrosa is developed upon tho fang, probably by intra-
membranous ossification. ,

REPARATION.

The process by which injured or lost parts of the body, are
repaired or reproduced, so tliat similar tissues are, after a time,
developed in their place, is known as regentration or reparation.
The formative power is here the .same as that by which the
embryo is first developed, and the developmental processes
concerned, are but extensions of those retained in mature
life. This process of regeneration is most active during the
earlier periods of existence. Thus, in cases of so-called spon-
taneous amputation occurring to the foetus in utero from con-
striction by the umbilical cord, fingers have been afterwards
developed on the remaining portion of the limb. Instances, too,
have been recorded, in which almo.st as remarkable re-forma-
tions of lost parts, have occurred in infants, and even in children.
In the same manner, the capacity of repair gradually diminishes
as life advances, lost parts which, in early life, are regenerated,
being afterwards imperfectly and incompletely re-formed.
Hence, in a child, tho reparation of an injury may ea.sily take
place ; whereas in old age, a similar lesion will remain unre-
paired. Experiments have shown that the vigour and celerity
of the repair of I'ractures, and the union of tendons in IMammalia,
are in an inverse proportion to the age of the tinimal (Paget).

Amongst tho lowest iinimiils, tlio process of reparation after injury, is
identical witli the process of reproduction by gemmation or fission. If
tho hydra bo cut up into a number of small pioces, each of these becomes
developed into a perfect hydra, and this process can bo repeated, over
and over again, with a similar result. The Annuloida likewise possess very
great reparative powers ; thus it has been noticed that tho holothnrida,
when pulled about or injured, expel tho wholo of their viscora; after a

662

SPECIAL PHYSIOLOGY.

few months these are regenerated. Amongst the higher Nonvertehrate
animals, however, in which reproduction by gemmation or fission does not
occur, the power of reproducing a perfect body from a fragment does not
e.xist. The Crustacea and Arachnida can, when fully developed, reproduce
limbs and antennse. In the Myriupoda, on the other hand, the reparative
power ceases when they have reached their full development ; whereas,
previously to this, antennae and limbs may be reproduced. The larvae
of Insects are endowed with like powers of reproduction ; but the perfect
Insects, at least the higher ones, have no such regenerative power,
lienee it appears that the amormt of reparative power, is in an inverse
ratio to that of the development tlmough which the animal has passed
in its attainment of perfection (Paget). The reproductive power of the
Mollusca has not been much investigated ; it is said that the common
snail can reproduce the head, if the cerebral ganglion be preserved.
Amongst the Vertebrata, the Amphibia possess very great reparative
jjower. After excision of an eye fipm the triton, or newt, a new one, it is
said, may be developed in its place, and the reproduction of an entire
limb, or of the tail, occurs readily in them.

But in Man and the Warm-blooded animals, the true repara-
tive process is much more limited, being confined strictly to
the reproduction of certain tissues.

In the first place, there are several parts, such as the epi-
dermoid and epithelial tissues, and also the red corpuscles of
the blood, which are naturally undergoing constant reparation
or decay, and are as constantly being reproduced, by what has
been termed continuous growth, or nutritive repetition.

Secondly, certain tissues of comparatively simple structure
and chemical composition, and of low vital endowments,
appear to be capable of regeneration. Such are the ai'eolar
and fibrous tissues, elastic tissue, and bone, which fulfil me-
chanical uses in the body, serving to connect and support its
various parts.

Lastly, bloodvessels, lymphatics, and nerves, tissires which
penetrate other parts or organs, are likewise endowed with
this poAver.

Other tissties and organs of a special kind, Avdiich ha^m a
complex structure, higher chemical constitution, or peculiar
properties or functions — such as true cartilage, muscle, the
grey substance of the nervous centres, the essential parts of
the organs of special sensation, the cutis and its glands, the
secreting and excreting glands, and the ductless glands — are not
regenerated alter injury or destruction.

The regeneration of particular tissues, is accomplished by
the multiplication and evolution of previously formed cell-
elements, whether these be gymnoplasts, nuclei, or nucleoli ;
and by the modification of the intercellular or internuclear

REPARATION OF THE TISSUE.?.

CG3

dements, or matrix, -^vithin the splicre of action of those nutri-
tive centres. In tliis way, the epidermis and epithelium are
speedily reproduced. The mode of formation of new Ipmph-
corpuscles and blood-corpuscles, already described (p. G57),
is to be explained in a similar way. The connective, mem-
branous, fibrous, or tendinous areolar tissues, and the elastic
tissues, are regenerated in the same manner as that in Avhich
they are developed. Connective tissue is the chief medium of
restoration or repair in wounds or ulcers of tissues or parts,
which, like muscles, glands, and the cutis, are not repro-
duced. In its growth, it becomes penetrated by new capil-
laries and lymphatics, which are developed after the manner
already described as their original mode of formation. The
development of new vessels, in the meshes of effused ljunph or
blood, in the restoration of the lost tail or limbs of the Amphi-
bia, and also in tumours, is accomplished in the same Avay.
Curtilage if removed by accident, or softened and ab.sorbed in
disease, is not regenerated, but cup-shaped caAuties are left,
which may Avear smooth ; if it be rent or broken across, it
does not unite, but the separated parts become connected by
strong fibrous or osseous belts. Nbav cartilage is produced in
certain tumours. Bong tissue is regenerated Avith remarkable
facility ; the process ahvays takes place by the intra-mem-
branous form of ossification. The iutra-cartilaginous form,
hoAvever, occurs in tumours. Injury to a muscle, such as divi-
sion of its fibres, provided that the cut ends haAm not retracted
too far from each other, is repaired by a uniting hand of
dense connective tissue, Avhich re-establishes the continuity and
office of the mti.scle ; but Avhen a Avhole mu.scle is torn across,
it may retract, and form altogether ncAV connections, or it may
cease to be used, and then undergo fatty degeneration. A
divided nerve is quickly united by connective tissue; in the
cicatri.x, nerve-fibres :ire aftenvards funned, Avhich join the
divided fibres, and completely restore their functions, tvhether
these be reflex, sensory, or motor. The nerve-fibres beyond
the line of section, tisuall}'- lose their medulla, ry sul)sfance or
sheath, Avhich previously undergoes :i granular and liitty dege-
neration ; but the tubuliir .sheath, the axis-fibn', and the
nuclei remain. When the ends of the nerve are once more
united, the medullary sheath of the fibres is reformed, the
reproductive process beginning at the cicatrix and extending
downwards. In young animals, the medullary substance may
be restored before the nerve is united.

GC4

SPECIAL PIITSIOLOGT.

GRO'WTII.

Tlie human infant, especial!}’, exhibits an imperfect and
feeble condition at birtli, and many clianges, besides mere in-
crease of size, take place in it, before it reaches the conditions
of puberty and maturity. At birth, the average Aveight of
the male infant is about 71bs., and of the female infant about
G-jlbs. The lengths, in the two sexes, are about 18|- inches
and 18 inches. The nutritive vegetative functions alone ex-
hibit a special activity, those of animal life proper being com-
paratively quiescent. The new-born child takes food, and
sleeps ; at hrst, it passes upwards of twenty hours out of the
twenty-four, in a state of slumber ; and during the first year, it
requires from twelve to fifteen hours’ repose. The respiration,
circulation, and development of heat are relatiA’ely more active
than in the adult ; but the power of re.sisting cold is feeble,
and hence protecthm clothing is necessary.

The general groAvth of the body, is at first rapid, but affer-
Avards much more gradual. Half the adult height is reached
by about the end of the third year, Avhilst to attain the re-
maining half, fifteen or eighteen years more are required. At
20 years of age, a Man is rather more than 3^ times his height,
and about 20 times his Aveight, at birth. This groAvth is not
equal in all parts of the body, the lower extremities, Avhich
Avere less developed in the embryo, noAV becoming proportion-
ally more developed : on the other hand, not only the head, but
also many internal organs, such as the liver, kidneys, and
supra-renal bodies, Avhich are proportionally large at birth,
aftenvards gTOAv relatively more sloAvly ; the thymus gland
even shrinks. The muscular system and the volitional poAver
Avhich commands it, are simultaneously developed and strength-
ened. At the end of the third month, the infant easily supports
the Aveight of its head ; at the fourth month, it is able to sit
upright; at the ninth month, it craAvls on the ground ; before
the end of a year, it can, Avith assistance, step ; and at A'arious
times, from one to two years or more, it can .stand, and begin
to run alone. At six months, it can lisp, and, before the end
of the year, can imitate a few definite articulate sounds of one
or two syllables. The senses and the mind are gradually
bi'ought into exerci.se, hearing, as indicated by the effect
of noises, before sight, as shown by the attractiveness of light
or of bright-coloured objects. The development of sight, as a
source of definite knoAvledge, under the education of touch, has

DECAY AKD DEATH.

665

been already fully explained. Of the other senses, perhaps,'
taste is tlie next to be developed, and after that, smell and
touch. Tlie order of appearance of the milk and permanent
teeth, has already been detailed. The food of the infant, before
it acquires teeth, is fluid, and the entrance of this into the
stomach, distends that organ, and completes its transverse
direction ; after the teeth appear, the food may be increased in
density, from semifluid to more or less solid nutrient sub-
stances.

Life has been divided into periods, rvhich may be physiolo-
gically thus distinguished. From birth to the appearance of
the first tooth, the child or infant may be called a sucHing •,
fi'om thence to the time when the milk-teeth begin to fall out,
is the period of childhood ; thence to the period of puberty, is
the age of boyhood or girlhood ; from this to the final com-
pletion of the statru-e, is the epoch of youth or maidenhood',
after that, is the period of maturity. Beyond this, comes the
decline of life, and afterwards old age.

Puberty occurs in the male, at the age of from fifteen to
eighteen, according to the climate, and in the female, from
twelve to fifteen. After the full stature has been attained, a
certain development still goes on. the skeleton especially
strengthening and solidifying itself, even up to the age of 25
in women, and 28 or more in men. At this period, also,
the intellectual powers attain perfection, and the balance
betrveeu assimilation and waste, is fully established.

DECAY AND DEATH.

The life of every organi.sed being, depends ultimately on the
due and persistent performance of the tissue-changes. These
are not only constantly wasting and undergoing repair, through
the whole organism, by which means the life of the individual
is maintained, but they degenerate and decay. Their inrtritive
energy becomes enfeebled ; they are no longer renewed or re-
paired ; their further development is arrested ; the organs no
longer perform their various functions; and then natural
decline, decay, and finally death ensue.

Death may affect a tissue, or :i part, or an organ only, of the
body ; it is accordingly .said to be molecular, or jmrtial, tis
the case maybe; this is illustrated in ulceration, 'mv\ gan-
grene or mortijicution, of the soft ti.ssues, or caries, or necrosis,
of bone. General death, also called somatic death ( coi/ni, the
body), affects the entire system. I’artial or molecular death is

666

SPECIAL PUTSIOLOGT.

only followed by general or somatic death, when it interferes
with the processes of organic life. Somatic death is the result
of a permanent arrest of the circulation. Besides this natural
mode of death, or death from old age, or climacleric death,
there are unnatural, premature, or accidental modes of death,
which may occur at any period or moment. The immediate
causes of accidental or unnatural somatic death, are syncope,
asjjhyxia and coma-, these occur from injury or disease. Old
age is the cause of natural somatic death. Coma and syncope
have, been alluded to in the Section on the Nervous System,
vol. i. pp. 296, 355 ; and a.sph}’xia is described at length under
Ilespiration, vol. ii. p. 473. They may here be again briefly
noticed.

In syncope, death begins at the heart, this organ either losing
its irritability and power of contractility, or being affected
with a tonic spasm. In the former case, it is found, after death,
flabby and flaccid, with its cavities either filled with blood, or
empty ; in the latter case, it is firm and contracted, and almost
or entirely empty. Death by syncope, may be occasioned by
widely difterent causes. Thus, it may take place through the
nervous system, as when a violent shock or concussion is com-
municated to the body ; it is in this mode, that strong mental
emotion, as intense fear, joy, or grief, or sunstroke, lightning,
extensive burns of the surface of the body, and sedative poi-
sons, are fatal to life. The effects of many sedative poisons —
as, e.g. of aconite, digitalis, and tobacco — are produced by the
passage of the deleterious substance into the blood, and by the
action of the blood, thus vitiated, on the nerves of the heart. |
Again, death by syncope may proceed from an enfeebled con- (
dition of the heart's substance, so that its contractile power
gradually fails, a mode of death which is exceedingly common, j
It occurs in persons affected with disease of the tissues of the
heart, especially in cases of frxtty degeneration of this organ.
Starvation (p. 549), exhausting diseases, and long-continued
violent e.xertion, are further causes of death from feebleness of
the heart’s action. Lastly, this mode of death may occur from
sudden and profuse hemorrhage, the circulation being arrested, ^
not from loss of the contractile power of the heart, but owing to^
the insuflicient quantity of blood which passes into its cavities. ■
It takes place when a large bloodvessel is wounded, or wheni j
it is ruptured owing to disca.se of its coats, and in cases of pro- ;
fuse internal hemorrhage, as when an aneurism bursts.

Death by asphyxia, or suffocation, occurs when the move- '

DECAY AND DEATH.

667

menta of respiration, or the access of oxygen to the lungs, ai'e
arrested, the flow of blood through the jndmonary capillaries
then ceasing. This mode of death occurs in cases of disease
affecting the heart and lungs, and, though more rapidly, in chok-
ing, strangulation, and drowning. The breathing ef cai'bonic
acid and other poisonous gases, also kills by asphyxia ; but this
fatal result is due both to the absence of free oxygen and to
the deleterious properties of the gas. The simple privation of
atmospheric air, acts only indirectly on the heart ; for the move-
ments of this organ, and, indeed, even the pulsation of the
smaller arteries, continue for a time, although all other signs
of vitality have disappeared. The blood, as it traverses the
pulmonary capillaries, now no longer undergoes the chemical
changes es.sential to respiration, for it is non-aerated or venous,
and cannot therefore sustain the functions of the various parts
to which it is distributed. At first, it passes freely through
the pulmonary veins to the left side of the heart, whence it is
distributed through the arteries, to the different parts of the
body. Its noxious action on the brain, is quickly shown, by
the rapid suspension of its sensorial functions, unconsciousne.ss,
and convulsions. The circulation in the pulmonary capillaries
is at first gradually retarded, and at length totally arrested ; so
that the lungs are gorged, and the right side of the heart over-
distended with venous blood, which passes into the left cavities
of the heart, in smaller and smaller quantities. Owing to this
diminution in the supply of blood, and to its vitiated quality,
the contractions of the heart become gradually more feeble, and
finally all the vital actions are arrested. In the fir.st stage of
asphyxia, the face is livid, although voluntary, or instinctive
and conscious, efforts are made to breathe, but without success.
In the second stage, volition and even consciousnc.ss are lost,
though convuLsive movements are performed. In the third
stage, all outward and respiratory movements have cea.sed, but
the heart still beats. In an asphyxiated animal, the heart will
beat for seven minutes, or three minutes after the arrest of
external movements.

In comn, death begins at the brain, the sensorial functions
being those which are fir.st suspended. This mode of death
occurs in fevers, in certain diseases of the brain, and in injuries
of this organ, when these do not kill by shock or concussion.
Thu.s, a person may receive a violent blow on Ihe head, giving
rise to symptoms of syncope ; and after a time, although the
heart regains its power, and respiration and circulation still

6G8

SPECIAL PIITSIOLOGY.

continue, a state of profound stupor sets in, and death occurs
in a comatose condition. Narcotic poisons, such as opium, bella-
donna, and chloroform, also produce death by inducing coma.

Death, however, frequently occurs in all these three modes.
Thus, pressure on the brain, may not only induce coma, but also
asphyxia and syncope, by paralysing the medulla oblongata,
froiii which the pneumogastric nerves, supplying the heart and
lungs, arise. The fatal effects of chloi’oform, on the other
hand, may depend on asphyxia, coma, or cardiac syncope.

Death from old age, or the gradual decay of nature, the
natural mode of dying, is much less common than death from
unnatural causes. Towards the decline of life, the formative
power becomes defective ; the processes of nutrition, growth,
and development of the tissue elements, no longer keep pace
with the individual waste and death of these ; so that the
various organs of the body suffer a marked and gradually in-
creasing structural deterioration or degeneration, and their
functional powers are consequently diminished. These dete-
riorations or degenerations constitute senile atrophy, and are as
natural and normal to the living organism as nutrition itself.
The body either wastes and dries, or it grows fat, the indi-
vidual either becoming emaciated or else corpulent. The coats
of the arteries undergo fatty changes, the cornea exliibits the
arcus senilis, and there is an increased quantity of fat in all
the tissues and organs. The arteries become the seat of cal-
careoirs deposits, the bones contain an increased quantity of
earthy salts, and the cartilages undergo ossification. The walla
of the bloodvessels and other structures become thickened ;
the mucous membrane of the alimentary canal frequently
presents an ash-coloured appearance, and the lungs, even early,
exhibit deposits ( f black pigment. Lastly, if disease or injury
in no way interferes Avith the ordinary duration of life, the
activity of all the functions slowly dimirishes, until the vitality
of the eirtire organism gradually becomes extinct.

The ordinary external appearances Avhich indicate death,
are, the cessation of breathing, the absence of pulse, a half-*
closed state of the eyelids with dilatation of the pupils,
clenching of the jaws Avith slight protrusion of the tongue,
and partial contraction of the fingers. The skin is cold an'’
pale, or, if livid, is becoming paler. After a feAV days, a
deceptive increase of colour of the skin, is sometimes noticed,
oAving to the blood being forced, by the cAmlution of gases from
the larger central vessels, into the small vessels of the skin.

DECAY AND DEATH.

669

The only positive signs of actual death are those which
depend on inolecidar change or death, viz. rigkliti/ of the mus-
;cles of the whole body, and putrefaction of tlie tissues. These
are most marked in organs and tissues, the vital functions
of which are the most active. They supervene more rapidly
:in Warm- than in Cold-blooded animals. The action of the
1 heart and the movements of respiration, may be so muclt
I reduced, as to be altogether imperceptible, so that the i'unctions
of circulation and respiration, ajipear to be arrested. This is
[Occasionally observed in temporary syncope, in which a person,
:to all appearances dead, has, after a time, regained conscious-
mess, and recovered. The peculiar condition of the nervous
: system called catalepsy, and the state of trance, are likewi.se
! further examples of so-called apparent death. But, as previ-
lously stated (vol. i. p. 1G3), on the occurrence of actual death,
I the irritability of the mu.scles, by degree.s, disappears, elec-
t tricity no longer excites their contraction, and then cadaveric
rigidity sets in. The time at which this comes on, its duration,
and many other points connected with it, have also been there
[mentioned. The commencement of putrefaction is first in-
dicated by the appearance of a bluish-green patch on the
: surface of the abdomen or thorax ; this goes on increasing in
: size, and becomes brownish, the margins by which it spreads,
■retaining, however, the primitive colour. Putrefiiction then
i shows itself in other parts of the body. The rapidity of this
I process, j)resents great differences, the tissues being much
■ more prone to putrefy after certain diseases; the temi’.eroture
of the surrounding air, also influences, considerably, the quick-
mess with which the dead body is finally decomposed.

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INDEX

ABD

ALB

A BDOiTEN, cavity of, i. 31

Abdominal glands in animals, ii. 143 ;

— pore of Amphioxiis, ii. 499
Abdncent nerve, i. 315, 333
Aberration, spherical, i. BO'J, 536
Abomasum of Ruminants, ii. 130
A bscess, ii. 986

Absorbent glands, i. 66, 111; ii. 155;

— vessels, i. 65; ii. 153, 658. Lymphatics,
i. 66 ; ii. 153, 658. Lacteals, i. 67 ; ii.
156

Absorbents, i. 33

. Absoiution, i. Ill ; ii. 151. General, ii.
153, 163 ; by alimentary canal, ii. 165 ;

— vessels of , ii. 174; — Inngs.ii. 165,438,
439; — conjunctiva, ii. 165; — serous and
synovial membranes, ii. 167 ; — skin, ii.
166; — areolar connective tisspe, ii. 167 ;

— ulcers and wounds, ii. 168. Venous, ii.
16S, 171; cii'cnmstancos which indu-
ence, ii. 169, 171, 177, 179. In non-
va-scular parts, ii. 168. Lymphatic,
ii. 171. Lacteal, ii. 175, IbO, 181.
Rato of, ii. 170. Inlluence of nervous
system on, ii. 171. Venous and hicteal,
contrasted, ii. 176. Of food, ii. 174 ;

— sugar, ii. 176 ; — saline substances, ii.
176 ; — albuminoid substances, ii. 177 ;

— fatty matters, ii. 177, 178, 179, 180. In-
trinsic, ii. 153, 182-185; interstitial, ii.
183 ; progressive, ii. 183 ; disjunctive, ii.

183 ; uses of, ii. 185 ; rapidity of, ii. 183,

184 ; e.v.nmples of, ii. 184; ulcerative, ii.

185. Uses of, ii. 185. In animals, ii.

186, 187. Of oxygen in respiration, ii.
438, 439 ; by stomach and intestines, ii.
402

Abstraction, faculty of, i. 378
Accessory nerve, i. 316, 335
Acervnlus cerebri, i. 305
Achromatic lenses, i. 552
. Achromatopsy or colour-blindness, i. 593
. Acm.s of the Body (proxiinalo constitu-
ents!), i. 85, 86. Acetic, i, 86. Butyric,
i. 86. Caproic, i. 86. Cerobric, i. 85,
Cnolalic, i. 85, Cholic or glycocholic,
i. 85. Formic, i. 86. Glyccro-phos-

phoric, i. 86. Hippuric, i. 85. Lactic,
i. 86. Lithio, i. 85. Oleic, i. 86. Oleo-
phosiphoric. i. 86. O.xalic, i. 86. Pal-
mitic, i. 86. Propionic, i. 86. Stearic,

i. 86. Tnurocholio, i. 85. Uric, i. 85
Acotyledons, i. 140

Acrogens, i. 140

Actinic or chemical rays, i. .548

Actinozoa, iserivisccral cavity of, ii. 142

Adam’s apple, or pomum Adami, i. 250

Adipose tissue, i. 45 ; ii. 647

Adult age, ii. 665

Aerial breather.s, ii. 402 ; — respiration,

ii. 402, 488-496

.aisthesodic substance of Spinal Cord, i.
342

JEsthesiometer, i. 463
Atterent nerve fibres, i. 277, 328, 349
After-sensations, i. 431, 465, 482, 495, 521,
583

Ago, effect of, on pulse, ii. 217 ; on quan-
tity of o.vygcn absorbed and carbonic
acid clirninated, in respiration, ii. 465 ;
on quantity of urea excreted, ii. 378 ;
on aninuil heiit, ii. 595
Air, ii. 437. Air-.sjKice for rooms, ii. 4S3 ;
for individuals, ii. 484. Changes of, in
respiration, ii. 435-4 14. Effect of a single
respiratioti on the composition of, ii.
438. Quantity of, respired in one
minute, ii. 435
Air-bladder of Fi.shes, ii. 493
Air-cells or air-sacs of lungs, ii. 411-
413

Air-i!aBSago.s, ii. 404-406.

Air-sacs in Birds, ii. 489, 490
Albmneu, i. 81 ; ii. 3, 8. Vegetable, ii.
4, 8

Albuminoid substances. Do.stination of, in
body, ii. 543. Jlctamorpho.sis of, in
body, ii. 543. In the blood, ii. 299.
U.ses of, ii. 290. In liaily fo(jd, ii. 536.
Decomposition, artificial of, ii. .545. In
body, ii. 534. Action of gastric jnico
on.’ii. 86; of ])ancrc.atio juice on, ii.
98, 99 ; of intestinal juices on, ii. 102.
— Excreta, uuoxidised, ii. 546

672

INDEX.

ALB

Albutninose, ii. 84, 86. DistinpiiiBlicd
from Albuminoids, ii. 86. Formed from
gelatiu, ii. 86
Albummiiri.r. ii. 389, 390
Alcohol, destination of, in body, ii. 542.
U.se of, in body, ii. 543. An aliment, ii.
542

Alcoholic beverages, ii. 5
Aldehyde, destination in body, ii. 54.3
Alimentary canal, i. 31, lie. Length and
capacity of, in reference to food, ii. 116.
In animals, ii. 129

Allantois, ii. 611.612. Growth and desti-
nation of, ii. 612, 635

Alveoli of teeth, ii. 16. Development of,
ii. 629

Ambulacral vessels of Eohinodemiata, ii.
275

Amnion, ii. 599, 609. Fluid of, ii. 609
Aniphiarthroses, or nii.xed joints, i. 188
Amphibia. Prehension of food, ii. 118.
Progression on solids, i. 225 ; in fluids,

i. 230. Teeth, ii. 124. Jaws, ii. 127.
Salivary glands, ii. 128. Pharynx, ii.
129. Alimentary canal, ii. 138. Integu-
ment of, i. 473. Cloaca, ii. 138. Liver,

ii. 144. Gall-bladder, ii. 146. Pancrea.s,

ii. 147. Lymph, atic hearts, ii. 186.

Portal circulation, ii. 267. He.art, ii.
26.5, 266. Circulation, ii, 266. Renal-
portal system, ii, 267, Spleen, ii, 342,
Supia-renal bodies, ii. 342. Thymus
gband, ii. 343. Kidneys, ii. 392. Thorax,
ii.491. Respiration by lungs, ii. 492 ; by
gills, ii. 497, 498. Touch, i. 472, 474.
Taste, i. 483, 484. Smell, i. 498. Hear-
ing, i. 523. Sight, i. 601. Locomotion
on solids, i. 225 ; in fluids, i. 230. A’oice,

i. 271. Cerebrum, i. 407.408.411,413.
Cerebellum. 1. 413. 414. Tongue, i. 484.
Ova of, ii. 600. Heat of, ii. 503

Amphioxus. or Lancelet, i. 125. Alimen-
tiu-y canal, ciliated, ii. 139. Blood cor-
puscles of, ii. 264, 271. Circulation in,

ii. 270. Blood-glands absent, ii. 343.
Absorbents absent, ii. 187. Nervous
system, i. 41 6. Sight, i. 601. Smell, i.
499. Resiuration, ii. 499. Chorda dor-
salis. ii. 653. Heart is not simple, ii. 270

AmygdaliC, ii. 27
Amyliu. i. 86 {see Starch)

Amyloid substance. In Tunicata, ii. 335.
In healthy muscle, ii. 335 ; — degene-
ration of tissues and organs, ii. 335
Analogies in animals, i. 137
Auelcctrotouus, i. 285
Animal, Dissection of, i. .34
Animal cells, i. 75 ; ii. 641. — Functions,
general view, i. 107 ; table, i. 117 ; special
])hysioIogy of, i. 155. — Heat, ii. 502, 521
(.wlleat). — Electricity, ii. 527-531 (see
lilectricity). — Light, ii. 524-527 (see
Light). — Kingdom, Cuvier's arrange-
ment, i. 120; modern arrangement, i.
122; outlines of. i. 120. — Magnetism,
i. 402. — Sub-kingdoms, i. 124
Animals, Classilicatiou of, i. 120-122.

AQU

Expression and gesture in, i. 247. Com-
pared with plants, i. 145. Hearing,
organs and sense, i. 522. Locomotion
in air, i. 234 ; in fluids, i. 228 ; on solids,
i. 218. Nervous system and its functions,
i. 403. Organs and function of sight in,

i. 597. Ovaries and ova of, ii. GltO. Posi-
tion of man amongst, i. 132. Prehension
and Manipulation, i. 244. Reproduction
of, ii. 380. Smell, organs and sense, i.
496. Special senses, i. 439. .Skin, i. 473.
Taste, organs and sen.se, i. 4S3. Tonch,
its sense and organs, i.471. Voice, i.
269. Cold-bloodetl. ii. 503, 517, 522.
■W,arm-bloodetl.ii..503, 504, 517, .522. Car-
nivorous, ii. 517 , 518. .546. Herbivorous,

ii. 517, 518, 546. Hybernation of, ii.
521

Ankle, adaptation to erect posture, i.
209

Annelida. Digestive organs and glands,
ii. 141.145. Pseiulo-hmmal vessels, ii.
274. Respiration, ii. 494, 501 . Touch.!.
472,474. Hearing, i. 525. Sight, i. 606.
Locomotion, i. 226. Nervous system, i.
128. Reproduction of, ii. 582, 586. Lu-
minosity in, ii. .526

Asnuloida. General characters and
classes, i. 129. Locomotion in water, i.
233; on solids.!. 226. Nervous system and
actions, i. 423. Prehension, i. 246 ; ii.
118. Denticles, ii. 127. Salivary tiibnli,
ii. 129. Alimentary canal, ii. 141, 142.
Gastric glands, ii. 143. Liver, ii. 14-5.
Pancreatic tiibnli. ii. 148. Circulation,
ii. 274. Respiration, ii. 50] . Hearing,

i. .525. Sight, i. 607. Touch, L 472.
Smell, 499

Annulosa. Eyes of, i. 604. Development,

ii. 585, 606. General characters and ,
cLisses, i. 128. Luminosity. ii. .52.5. Ner-
vous system and actions, i. 420. Ova. ii.
601. Prehension, i. 246 ; of food, ii. 118.
Mandibles mid m.vxill.T. ii. US. Pro-
boscis. ii. 119. Salivary glands, ii. 129.
Alimentary canal, ii. 140. Liver, ii.
145. Circulation, ii. 27:1. 274. Renal
organs, ii. 394. Respiration, ii. 491-496,
.500, 501. Touch, i. 472. 474. Smell, i.
499. Hearing, i. .521, .525. Sight, i.
604-607. Locomotion on solids, i. 226 ;
in fluids, i. 233 ; in air, i. 235. Voice, i.
271, 272

Ant-eaters, salivary glands in, ii. 128
Antiperistaliic action, ii. .50
Antlers of stag, development of, ii. 287 ;
falling of, ii. 2,88

Aorta, i. 29, 31 . In Reptiles and Amphibia,
ii. 266. Primitive, ii. 634. 636. 637. 641
Aortic arch in Man and Mamm.alia. ii.
266. In Birds, ii. 267. — Arches in
Reptiles, ii. 266. 267
Aphides, reproduction of, ii. 583, 585
Apnn n, i. .147
Appetite, i. I l l

Aiinatic breathers, ii. 403. — Respiration,
ii. 463, 496-502

INDEX,

673

AQU

Aqnoous humour, i. M2, .'344, n55 ; ii. G23
Auacii-Sida. Digestive organa and glands,
ii. 141, 145. Circulation, ii. 274. Renal
organs, ii. 304. Respiration, ii. 494, .5()U.
Touch, i. 472, 474. Hearing, i. 525.
Sight, i. ()0fi. Locomotion, i. 226. Ner-
vou.s system, i. 421, 422
Arachnoid membrane, i. 21, 295
Arantii, corpus, ii. 192, 194
Arbor vitas, or tree of life, i. 307
Arches, arterial, ii. 636. Branchial, or
visceral, ii. 624
Arcus senilis, ii. 668

Area, germinal, ii. 606. Opaca, ii. 607.
Pellucida, ii. t07. Vitelline, ii. 607.
Vascular, ii. 610, 633

Areolar tissue, i. 13, 43. Intermuscular,
ii. 646, 663

Aristotle, lantern of. ii. 128.

Arm, adaptations of, i. 239
Arterial arches, ii. 636. — blood (see

Blood). — bulb of fishes, ii. 267.
Arteries, i. 18, 111. Development of, ii.
656. Influence of, on circulation, ii. 222.
Elasticity, ii. 222, 223, 225. 226. Vital
contractility, ii. 223, 224. Tone, ii. 224,
225. Character of cuiTent in, ii. 225.
Branchings, bendings, and anastomoses,
ii, 226, 227. Rate of motion of blood in
different, ii. 228 ; slower in more distant
arteries, ii. 228, 229. Blood pressure, ii.
229-234. Modified by respiration, ii. 232,
233. Effect of division of sympathetic,
on, ii. 234. Pulse, ii. 235, 242. Ratio
between dilation and contraotion of, ii.
240, 241. In Mammalia, ii. 265. Struc-
ture of, i. 57. Omphalo-mesenterio, ii.
610, 634. Umbilical, ii. 614, 635, 639.
Vitelline, ii. 634. Primitive, ii. 636. Hy-
pogastric, ii. 635, 639. Mode of closure,
ii. 314

Arthrodia, or planiforra joints, i. 190
Articnlata, General characters, i. 121,128
Articulations, i. 187

Artificial circulation, ii. 481. — respira-
tion, ii. 478-481

Arytenoid cartilages, i. 250. — muscles,!.
252, 258 ; ii. 424

A.«!CiDioti)A. Digestive glands and organs,
ii. 140, 144. Circulation, ii. 273. Re-
spiration, ii. .500. Hearing, i. 524. Sight,

i. 604. Locomotion, i. 233. Nervous
system, i. 420. llcproilnction, ii. 582.

Asphyxia, ii. 473. Essential characters,

ii. 473. Death from, ii. 473-475, 66il.
Recovery from, ii. 480. Treatment of,
ii. 479, 480, 481. Cutaneous, ii. 401

Aspirator, ii. 513

A.s.similatiom Primary, ii. 276. Secondary,
ii. 276. Nutritive, a metabolic effort,
ii. 280

Assimilative glands, ii. 320
Asthma, ii. 430
As'igmatism, i. 565

Atmosphere, Composition of, ii. 437. 438
Atrophy, ii. 285. Senile, ii. 668. Of Muscle,

1. 162

BIB

Attention, i. 376
Automatic acts, i. 347, 385
Auditory organs (see Hearing). — nerve,
i. 315, 508, 521. — vi sides, ii. 622
Auricle, or pinna, i. 500, 512
Auricles of heart, ii. 189_, 193
Automatic movements, i. 385
Awaking, causes of, i. 393
Axile bodies, or tactile corpuscles, i. 454
Axis-cylinder of nerve, i. 54
Azote, ii.457 (see Nitrogen)

Azotised constituents of the body,!. SI, 97

T3ABYROUSSA, tusk of, ii. 121
Bacteria, ii. 581

Balance of body maintained, i. 212
Bartholin, duct of, ii. 55
Basement membrane, i. 68, ii. 659
Basis of support of body, i. 197
Batrachia (see Amphibia)

Bat, flight of, i. 234
Bauhin, valve of, ii. 48
Beef-tea, preparation and contents of, ii.
114

Bellini, tnbe.s of, ii. 369
Beverages, ii. 10

Bilateral action of the nervous system, i.
395

Bile, i. 111. Non-elimination, ii. 356.
Source and composition, ii. 65, 354. Se-
cretion, constant, ii. 74 : effect of injury
of vagus nerve on, ii, 355, 356. Hepatic,
ii. 74. Cystic, ii. 75. Constituents of,
75, 76, 77. Pettenkofer’s test for, ii. 76.
Uses of, ii. 356. Action of, ii. 95-97 ;
anti-putrescent, ii. 97 ; excreraentitious,
ii. 96, 355 ; on fat, ii. 96, 97. Supple-
mentary non-chemical uses, ii. 96.
Scanty and excessive supply, ii. 96.
Present in lower part of small intestine,
ii. 103. Specific gnivity, ii. 75. De-
composition, in intestines, ii. 98. Portal
blood essential to formation, ii. 3.54. Not
preformed in blood, ii. 355. Source of
acids and colouring matters, ii. 355
Bilifulvin, i. 83, ii. 77
Bilin, ii. 76
Biliphatin, ii. 77
Bilipyrrhin, ii. 77 _

Biliverdin, i. 83 ; ii. 77
Bill, different shape of, in Birds, ii. 117, 118
Binocular parallax, i. 580
Birds. Prehension of food, ii. 117. Bills,
ii. 117. .laws, ii. 127. Salivary glands,
ii. 128. Pharynx, ii. 129. Crop, or in-
gluvies, ii. 1.34,135,136. Proventrlculus.
ventriculussuccenturiatus, or true glan-
dular stomach, ii. 135, 136. Gizzard,
gigerimn, vcnlricnlusbulbosus, third or
muscular stomach, ii. 135, 186. Pyloric
valve, il. 135. Heat of, ii, 504. Intes-
tines, ii. 135, 136. Integuments, i. 473.
Ilco-cmcal valve, abscnt,li. 135. Ciccum,
usually douhle, ii. 137 ; — vitelline, ii.
137,610. Crcca sometimes wanting, ii,
137. Cloaca, ii. 137. Bursa Pnbrlcii,

VOL. II.

X X

674

IKDEX.

BU

1S7. Esophagus, ii. 134. Liver, ii. 144.
Gall-bladder, ii. 14G. Pancreas, ii. 14G,
147. Lymphatic system, ii. 186. Portal
circulation, ii. 2G5. Heart, ii. 264, 265.
Aortic arch, ii. 26G. Spleen, ii. 342,
Supra-renal bodies, ii. 342. Thyroid
body, ii. 342. Thymus gland, il. 343.
Kidneys, ii. 392. Thorax, ii. 488, 489,
Lungs and respiration, ii. 489. Air-sacs,
ii. 489, 490. Bones, air-cavities in, ii.
490. Temperature of, ii. 504. Touch, i,
471,472. Taste, i. 483. Smell, i. 49».
Hearing, i. -522. Sight, i. ,599, GOO. Lo-
comotion on solids, i. 222-224 ; in fluids,

i. 228,229 ; in air, i. 2.3-5-239. Voice,!.
269-271. Perching, i. 223. Prehension,
1. 245, 24G. Encephalon, i. 40.5, 406.
Cerebrum, i. 407, 408, 411, 412, 413.
Corpora qu.adrigemina, i. 412. Cerebel-
lum, i. 413, 414. Spinal cord, i. 415.
Hypoglossal nerve, i. 416

Bladder, urinai-y, i. 31. Inversion of, ii,
373, 374. Walls of, ii. 374
Blastema or matrix, i. 76 ; ii. 642. G43
Blastoderm, and its three layers, ii. 60S
Blastodermic vesicle, ii. G03
Blind spot of the eye, i. 568, 570
Blood, i. 62. Affinity for oxygen, ii. 4.55,
4.56. Arterial, characters of, ii. 402,
444 ; uses of, ii. 288. Buffy coat. ii. 30-5,
306. Changes in quality, ii. 288 ; in
fibi'in, ii. 4-50 ; in gases, ii, 451-462 ; in
temperature, ii. 450, 461 ; in colour, li.
444 ; — ■ cause of, ii. 445-449. Clot, forms
of, ii. 30.5-307. Coagulation of, i. 65 ;

ii. 300-314 ; accelerated, retarded, or
Interrupted, ii. 301, 302, 303, 304,305;
Induced in animals, ii. 304 ; cause of, ii.
307 ; a vital act, ii. 807, 308, 309 ; a
physical process dependent on escape of
ammonia, ii. 309, 310 ; dependent on the
colloidal action of fibrin, ii. 311, 312;
dependent on reaction between fluid and
solid constituents, ii. 312 ; dependent
on catalytic action of corpuscles, ii. 312 ;
dependent on influence of red corpus-
cles,ii. 312,313; dependent on reaction
of fibrino-genous and fihrlno-plttstic
substances, ii. 313. Colouring matter,
source of, li. 317, 51-t ; offcctof different
substances on, ii. 415. Composition of,

I. 911. Constituents ijroximate, i. 90 ;
continually changed, ii. 318; uses of
particular constituents of : — albumi-
noid. 11.290 ; extractives, ii. 293 ; fatty,

II. 292; fibrin, ii. 291 ; ga«es, ii. 29.5;
salts, ii. 293, 295; sugar, ii. 292. Ef-
fete matters in, ii. 293. Corpuscles, 1.
62. Ued corpuscle.s, 1. 63 ; affinity for
oxygen, ii. 466; origin of, afterbirth,
ii. 316 ; origin of, in embryo, ii. 667 ;
decay of, ii. 316; function of, ii. 289;
chemical changes in, ii. 316; collected
In spleen, ii. 316 ; quantity in animal.s,
li. 289,518 ; absent in Amphioxiis, ii.
261; absent in non-Vertebrnta, 271.
White corpuscles, i, 63 ; origin of, ii. 314,

BOD

315; changedintored,ii,31C; in goitre,
ii. 327, 328; function of, ii. 2»U; in
lencremia, ii. 323 ; development of, ii.
657 ; regeneration of, ii. 663 ; size of, i.
77 ; stasis of in inflammation, ii. 280.
Cruorin, where added to corpuscles, ii.
316; changes in colour during respira-
tion, dependent on oxidation of,ii. 447 ;
scarlet, ii. 448 ; purple, ii. 448 ; affinity
for oxygen, ii. 449; ctxygen chemically
combined svith, il. 450. Determination
of,ii.287. Develo))ment of, ii. 633. Ex-
tractives.!. 91 ; ii.295. Extravasation of,
li. 296. Fibrin, i. .90; office. li. 291 ; coa-
gulation is sometimes injurious, ii. 291 ;
changes in, during respiration, ii. 450 ;
artificially formed, ii. 4-50 ; source of, ii.
317, 544 ; oxidised in liver and kidneys,
ii. 317 ; splenic vein contains much. ii.
317. Gases In 100 volumes, ii, 4-55,
Hmmatin of, i. 83 ; production, ii. 289;
destination, ii. 289. Halitus, ii. 301.
Heat or temperature, ii. 504. Impure,
action of, ii. 318. Liquor sanguinis, 1. 62;
fluidity of, essential to life, ii. 299, office
of, ii. 290, source of its albumen, ii.

316, amyloid and saccharine matters, ii.

317, creatin and creatinin, ii. 317. fatty
matters, li, 317, fibrin, il. 317, salts and
earthy matters, ii. 316. Loss, orlnemor-
rhage, ii. 296 ; effects of, ii. 2SS. Micro-
scopic elements, i, 62. Nutrition, ii.
277. Nutritive properties, how affected,
ii. 296. Odour, ii. 30 1 , Quantity in body,
ii. 260-263 ; — projected through aorta
per second, ii. 262 ; — at each systole,
ii. 262 ; — sent through kidneys, ii. 366.
Hatio between blood and body in Man,
ii. 260, 262 ; in animals, ii. 261. Respi-
ratory changes, ii. 111-150. Spectrum
analysis, ii. 447. Transfusion, il. 297.
Uses of, and of its circulation, ii. 263,
264 ; in nutrition, ii. 27.5, 287. Venous,
characters of, i. 90 ; ii. 282.402, 444. Of
animals, ii, 289, 518 ; of Amphioxus, ii.
264.271; of Non-vertebrata. ii. 271 ; cor-
puscles, coloureil, i. 63 ; white, i. 64 ;
red (size of), i. 77.

Blood-glands absent in Non-vertebrata, ii.

343 (see Ductless Glands).

Bloodvessels of Non-vertebrata, ii. 271 . Of
liver, in animals, ii. 145. Regeneration
of, ii. 663. Development of, ii. 633, 656.
Structure of, i. 57 ; arteries, i. 57 ; veins,
I. 58 ; capillaries, i. 59.

Bony, Human. Effects of cold on. ii. .507-
509 ; of heat on, ii. 509—512. Electricity,
ii. .527. Heat, ii. .504—521. Luminous-
ness, ii, 524. Statics. ii.5:)2. Dynamics,
ii. 550. Stature, ii. .533. Weight, ii.

533. Temix'raturo, ii. .504— 521. Spccifio
gravity, ii. 532. Height, ii. 5;i;i. Pro-
portions of jiroximate constituents, ii.

534. Transformation, substance of, ii-
537. Cliemicul clianges, sum of, in. ii-
546. Compand with a machine, ii.

560. Growth of, ii. 664. Decay of, ii-

INDEX,

BON

6G5, Height of, at birth, ii. 6G4. Weight
of. at birth, ii. GG4

Bone, i. 40, 18o. Composition of, i. 88.
Primai-y, ii. 049 , 052. Secondar.v, ii.
649. Development of, ii. 048. Kepara-
tion of, ii. 003

Bones, i. 108. Adaptation to purposes
served by them, i, 185. Air-cavities of,
in Birds, i. 230 ; ii. 490. Long bones,
development of, ii. 05i
Bonnet, of Ruiniuants, ii. 130
Botal, duct of, ii. 270, 041
Brachiopoda, digestive organs of, ii. 140.
Digestive glands, ii. 144, Circulation,
ii. 273. Respiration, ii. 500
Brain, i. 23, 108 , 294. Mode of ascertain-
ing composition of white substance, i,
87. Parts of, i. 297. (See those parts.)
Size and weight of, i. 290. Develop-
ment of, ii. 010, 020. Supply of blood,
to, i. 296, ii. 250

Branchite, ii. 403, 497. Of Amphibia, ii.
497. — Fishes, ii. 498. — Mollusca, ii.
499. — Annulosa, ii. 500, 501
Branchial arche.s, ii. 024. — clefts, ii. 624.
— arteriesof Fish, ii. 207. — vessels sup-
plying gills of Fish, ii. 498. — arterial
arches of Amphibia, . — sacs. Mol lus-
coida, ii. 500. — heart of Fish, ii. 207
Branchiated or water-breathing Vertc-
brata, ii. 264

Bright’s disease, urine in, ii. 375, 390
Breath {see Re.spiration)

Breathing air, ii. 432, 433
Bronchi, i. 29 ; ii. 405, 406
Bronchia, or bronchial tubes, 1. 29 ; ii. 410
Bronchial sounds, ii. 420. — vessels, ii.
414

Brunner’s glands, ii. 80
Buds, animal, ii. 582
Buffy coat, ii. 305

Bulbus arteriosus, development of, ii. 634

Butter-milk, ii. 359

Butyric acid, i. 86

Byssus of Lamellibranchiata, ii. 395

^ADAVERIC rigidity, i. 175 ; ii. 609
Caducibrancli late Amphibia, respira-
tion in, ii. 498, 499

Omcnra, i. 33 ; ii. 40. Absent in certain
Mammalia, ii. 134. XJsually prosout
and double in Birds, ii. 137. Absent in
Crocodile, ii. 137. Sometimes present
in Fishes, ii. 138. — vitelline, ii. 010
Caillet of Ruminants, ii. 130
Calamus scriptorius, i. 309
Calculi, urinary, ii. 380, 387
Calorescence, i. 548
Calories, ii. 550

Calorific food, ii. 0, 537, 517, 501. — rays,
i. 548. — work of body, ii. 555, 508
Calorimetry, ii. 512
Calorimeters, ii. 512, 513
Calyces of kidney, ii. 308
Calyx of ovary, ii 591
Camel, water-cells of, ii. 1-30

CT5

CAV

Camera ohscura, i. 553
Canal of Wirsung, ii. 78
Canals, portal, ii. 71. — semi-circular, i.
500

Can.aliculi of bone, i. 47 ; ii. 650
Cancer, ii. 285

Capillaries, structure of, i. 59. Length
of systemic, ii. 259. Development of,
ii.'GSO

Capillary circulation, ii. 242-247. Cause,
li. 243. Theories, ii. 243, 244. Pheno-
mena, ii. 245. Still layer of, ii. 245.
Rate of motion of blood in systemic, ii,
240 ; in pulmonary, ii. 247. Retardation
of blood in, ii. 247, Resistance in, ii. 248
Caproic acid, i, 86
Capsules of the kidney, ii. 396
Garbhydrates, ii. 6. Destination of, ii,
541. In relation to heat, ii. 501 ; to
work, ii, 501. Necessity for in work,
ii. 573

Carbon, a source of animal heat, ii. 514.
Daily excretion of, ii. 516, Relation of
to animal heat, ii. 558
Carbonic acid, i. 115. Quantity in atmo-
sphere, ii. 438 ; in venous and arterial
blood, ii. 451,452. Daily e.xcretion of,
ii. 516, 517. Eliminated in respiration,
ii. 439^43. Qu.antity determined, ii.
439-442 ; — modified, ii, 463-469, 517,
Destructive to lifOj ii. 482. Injurious in
small quantities, ii. 482. Diffuses from
blood, ii. 457. Effects of breathing it,
ii. 472 ; appearances after death, ii. 473
Caries, ii, 065

Carnivora, Digestive organs, ii. 116, 130,
134. Digestive glands, ii. 144, 140.
Supra-renal bodies, ii. 342. Mammary
glands, ii. 303, Kidneys, ii. 392. Re-
spiration, ii. 488. Touch, i. 471. Taste,

i. 483. Smell, i. 497. Sight, i. 598,599.
Locomotion, i. 222. Prehension, i.
244, 245. Cerebrum, i. 407, 409, 410,
411. Cerebellum, i. 414. Corpora
quadrigemina, i. 412

Carnivorous Animals, digestive organs of,

ii. 110. Destination of food in, ii. 540,
Respiration in, ii. 518. Oxygen ab-
sorbed by, ii. 439

Cartilage, i. 12, 45 : ii. 048, 663. Compo-
sition, i. 88. Precursory, ii, 049. Ossi-
fying, ii. 049
Caruncle, i. 528 _

Casein, i. 83. Formation and use, ii. 300,
544

Castor of the beaver, ii. 395
Casta in urine, ii. 373, 390
Catalepsy, ii. 009
Caterpillar, ii. 587
Cathclcctrotoiius, i. 285
Cauda cquiua, i. 320 ; ii. 619
Cavities of tlie Body and contalhed organs,
i. 19. Abdomen, i. 31. Cheat, i. 27.
Skull and spinal column, i. 19. Face,
i. 20. — of reserve (teeth), ii. 028, 209,
llieinal, i. 134 ; ii. 008, Nclual, i,
134 i li. 008.

X X

0

676

INDEX,

CEL

Oell. Germ-, ii. 5S3 589,642. Sperm-, il.
.583,589,642. — theory, ii. 642. — nuclei
and nucleoli, ii. 643. — force, ii. 643,

646. — life, ii. 643. — development and
STOWth, ii. 643, 644. — division, ii. 604,
644

Cells, Animal, ii. 641 ; structure of, ii.
643 ; origin and development of, ii. 643 ;
by various modes, ii. 644 ; metamor-
phosis of, ii. 644 ; compared -\vith vege-
table, ii. 646. Vegetable, structure of,
ii. 642

Cellular tissue, i. 43
Cement, ii. 17

Central canal of spinal cord, i. 313. — grey
commissure of spinal cord, i. 312.

Centre of gravity of the body, i. 197
Cephalopoda. Digestive organs, ii. 139.
Digestive glands, ii. 129, 144. Circula-
tion, ii. 272. Renal organs, ii. 394. Re-
spiration, ii. 499. Touch, i. 472. Taste,
i. 484. Smell, i. 499. Hearing, i. 524.
Sight, i. 603. Locomotion, 1. 233
Cerebellum, i. 23, 297. 307. Parts of,l. 307.
Fibres of, i. 308. Functions of, i. 363.
Of Mammalia, i. 413,414. Birds, i. 413,
414; experiments on, i. 363. Reptiles,
i. 413,414. Amphibia, i. 413,414. Fishes,
i. 413, 414

Cerebral hemispheres, i. 299. Develop-
ment of, ii. 621. — lobes in Fishes, i.
408,412. — peduncles, i. 297; functions
of, i. 358. — vesicles, ii. 616, 619
Cerebric acid, i. 85 ; ii. 114
Cerebro-spinal axis, i. 294 ; effects of irri-
tation of, ii.341. — nerves, i. 313; func-
tions of, i. 327. — nervous system, i. 294;
summary of functions, i. 380
Cerebnmi, i. 23, 297, 29k Convolutions,
i. 301, Cortical substance, i, 302, 367,
Fibres, i, 303, Fissures, i, 299, 300,
Hemispheres, i, 24, 292, 372. Lobes, i.
300. Medullary substance, i. 303. Pe-
dmicles, i. 297, 357. Ventricles, i. 299,
306. Action on the muscles, i. 375.
Experiments on, i. 370. Functions, i.
167. In MainmaUa, i. 406^08, 408-411,
412, 413; Birds, i. 407, 408, 411,412,
413 ; ReptUes, i. 407, 408, 411, 412, 413 ;
Amphibia, i. 407,408, 411, 413; Fishes,

i. 407, 408, 411, 412, 413. Development
of, ii. 620, 621

Cerumen, or ear-wax, i. 501
CuTACKA. Digestive organs, ii. 133, 134.
Digestive glands, ii. 128, 146. Supra-
renal bodies, ii. 342. Mammary glands,

ii. 363. Kidneys, ii. 392. Respiration,
ii. 488. Touch, i. 471. Taste, i. 483.
Smell, i. 497. Hearing, i. 522, Sight, i.
598,599, L/Ocomotion, 1. 222, 228. Voice,
i. 269. Cerebrum, i. 410. Retia mira-
hilia, in, ii. 477

Chiila7.!u, ii. 594 , 596
Clialk-stoncs in gout, ii. 381
Cheeks, ii. 25

CiiKiiioiTEiuv. Digestive organs, ii. 1.30,
133, 1;14. Sight, i, 598. Locomotion,!,
222, 234. Corebrum, i . 407

CLA

Chemical changes in body, sum of, ii.
546. Relation of, to heat ii. 558. — of
air, in respiration, ii. 435, 444. — of

blood, ii. 451-462. — force, relation to
heat and work, ii. 556-8. —composition
of the body, i. 80 ; of constituents of
(see Constituents). — processes of diges-
tion, ii. 82 ; in animals, ii. 148
Childhood, ii. 665
Cholalic Acid, i. 85 ; ii. 76
Cholepyrrhin, ii. 77
Cholesterin, i. 86
Cholic or Glycocholic Acid, i. 85
Chondrin, i. 82 ; ii. 544
Chorda dorsalis, ii. 607, 648 ; changes in,
ii. 616

Chorion, ii. 594, 599, 612
Choroid, i, 531, 537
Chromatic aberration, i. 552, 556
Chrysalis, ii. 587

Chyle, i. 67, 111 ; 11. 156, 182. Composi-
tion of, i. 92. Molecular basis of, i. 68.
Causes of Motion of, ii. 181, 182. In
animals, 11.187
Chylification, i. Ill ; ii. 276
Chyme, i. Ill ; ii. 93-95 ; a product of
digestion and absorption, ii. 95
Chymification. i. Ill ; ii. 93, 94
Cicatricula, ii. 592, 593, 597, 604, 606
Cicatrisation, ii. 286

Cilia, i. 73, 177,178. Movementsof, 1. 179 ;
velocity, i. 179 ; effects, i. 179 ; con-
tinuance of, i. 180 ; occurrence in man,
i.177; • — in animals, i. 178. Size, i. 178.
Uses, general, i. 181 ; in air-tubes, ii.
423 ; in aquatic respiration, ii. 501, 502 ;
in tubuR uriniferi of cold-blooded Ver-
tebrata, ii. 393

Ciliary ligament, i. 537. — muscle, i. 538.

— processes, i. 538
Circles of dissipation, i. 5.52
Circulation, i. Ill, ii. 187. Course and
causes of, ii. 200-203, 204. Pulmonary,

i. 112; ii. 201. Systemic, i. 112; ii.

200. Portal, ii. 69. Discovery of. ii.

201. Through heart, ii. 204, 205 ; arte-
ries, il. 222-234 ; capillaries, il. 242-247 ;
veins, ii. 247-257. Effect of pavity on,

ii. 2-54. Peculiarities, portal, ii. 255; cra-
nial, ii. 256; pulmonary, ii. 256, 257.
Period of a complete, ii. 257-260. Re-
lation between frequency of pulse and
period of circulation, ii. 258, 259 ; — in
Man, ii. 259 ; in Mammalia, ii. 264 , 265 ;
in Birds, ii. 265 ; in Reptiles, il. 26,5-267;
in Amphibia, immature, ii. 26.8--270 ;
in Perennibranchiata, ii.270; in Fishes,
ii. 267, 271 ; in Ainphioxus, ii. 270;_in
Lopidosiren, ii. 270; in Mollusca, ii. 272 ;
Jlolluscoida, ii. 273 ; Annulosa, ii. 273,
274; Annuloida. ii. 274; Coclenterata, ii.
275 ; Protozoa, ii. 275. Embryonal, first,
ii. 638; second, ii. 639. Allantoid or pla-
cental, ii. 6,639. Foetal, ii. 638. Change
in, at birth, ii. 640. Double, completed,
ii. (ill. Artificial, ii. 481.

Clairvoyance, i, 403

INDEX.

6T7

CLA

Classification of Animals, changes in, i.
122

Cleavage of yolk, ii. 603,

Cleft palate, 11. 625
Clefts, branchial or visceral, ii. 624
Clicking sounds in speech, i. 26S
Climate, effects of, on animal heat, ii.
505

Cioaca, ii. 59.3. In Birds, ii. 137 ; in In-
sect.s, ii. 1-10 ; in Reptiles, ii. 138 ; in
Amphibia, ii. 138 ; in Monotremata, ii.
134

Clot, or Coagnlum, of blood, i. 65 (see
Blood)

Coagulation of blood, i. 65 (see Blood)
Coagnlum of blood, i. 65 (see Blood)
Cochlea, i. 506, 519. Functions of, i. 519.

Development, ii. 623
Coefficient (mechanical) of heat, ii. 556
Ccelentehat.v. Reproduction of, ii. 582.
Ova of, ii. 601. General characters and
classes, i. 129. Nervous system and
nervous actions, i. 424. Luminosity, ii.
526. Digestive canal, ii. 142. Formation
of bile in, ii. 145. Circulation, ii. 275.
Renal organs, ii.394. Respiration, ii. 501.
Hearing, i. 525. Sight, i. 607. Touch,

i. 473, 474. Locomotion in fluids, i. 233.
Prehension, i. 246 ; — of food, ii. 119

Cold, eflfects of, on ifan,ii. 507 509. Power
of resisting, ii. 508
Cold-blooded Animals (see Animals)
Colloid bodies, ii. 84. 162. Energia pecu-
liar to, U. 163, Effects of, in nutrition,

ii. 280

Colon, i. 43 ; ii. 46

Colostrum, ii. 357. Corpu=cles of, ii. 358.

Chemical composition, ii. 358
Colour-blindne.s.«, i. 595
Colour- top, i. 588

Colouring matter of blood (see Blood)
Colours, i. .548
Coma, death by, ii. 667
Combustion, spontaneous, ii. 523. — of

respiration, ii. 457-161.

Complemental air, ii. 432, 433
Complementary colours, i, 548
Conductility of nerve-fibres, i. 102, 272
Conduction of sounds, i.

Congelation, effects of, ii. 509
Conjunctiva, i. 527

Connective tissue, i. 42; ii. 646, 663.
Areolar form, i. 42. Fibrous form, i.
43. Composition, i. 88. Corpuscles of,
ii. 647 “

Consensual or Sensori-motor actions, i.
382

Con.sonants. i. 267
Constants, physiological, ii. 531
Consciousness, i. 376; — is ino.xplicahle, i.
425

Constituents of the body, i. 80. Proxi-
mate composition of, i. 95,96. Ultimate
composition of, 1. 94, 100
Continuous growth, ii. 283, 662
Contraction, idio muscular, 1. 157. — neu-
romuscular, 1. 157. — of muscle, condi-

CYS

tions of, i. 161 ; force of, i. 161 ; pheno-
mena of, i. 158 ; peculiarities of, i. 160
Convolutions of the cerebrum, i. 301
Coprolites, reptilian, ii. 138
Corium, i. 451

Cornea, i. 531, 537, 555, Supposed vessels
of, ii. 243

Cornua of lateral ventricles, i. 306
Corpora amylacea, ii. 335. — dentata of
cerebellum, i. 307 ; of medulla oblong-
ata, ii. 310. — geniculata, i. 305 ; func-
tions of, i. 359. — olivaria, ii. 309 ; —
development of, i. 305 ; ii. 620 ; f unotioms
of, i. 358

Corpus Aran tii, ii. 192, 194., — oalUrsum, i.
299, 303 ; ii. 621. — luteum, ii. 598.

— striatum,!. 304 ; ii.621; functions of,

i. 360

Corpuscles. Blood, i. 62 (see Blood).

. Bone, i. 47. Lymph, i. 07. Nervous
matter, i. 52. Pacinian, i. 455. Tac-
tile, i. 57, 454. Salivary, ii. 57
Correlation of forces, i. 438; ii. 551, 552,
579

Cortical substance of cerebellum, i. 307 ;

of cerebrum, i. 302 ; of kidney, ii. 368
Cotyledons, ii. 614
Cotyloid cavities, i. 191
Coughing, 1. 382 ; ii. 430
Coup-de-soleil, ii. 511
Cranial vertebraj. i. 21. — nerves (see

Nerves) ; — of Vertebrata, i. 416
Craniology, 1. 369

Cranium and its bones, i. 7, 19. Circula-
tion in, ii. 256
Cream, ii. 359

Creatin, i. 85, 98. — of urine, ii. 382
Creatinin, 1. 85. 98. — of urine, ii. 382
Crepitation of lung, ii. 407
Cretinism, ii. 328

Crop in Birds, ii. 134 ; use of, ii. 135, 136
Cruorin, i. 83 (see Blood)

Crusta petrosa, ii. 17 ; ii. 628
CnnSTACEA. Digestive organs, ii. 141.
Digestive glands, ii. 145. Circulation,

ii. 273. Respiration, ii. 500. Touch, i.
472, 474. Smell, i. 499. Hearing, i. .52.5.
Sight, i. 606. Locomotion, i. 226, 233.
Reproduction of, ii. 583, 585

Crying, ii. 431

Cry-talline lens, i. .542, 555 ; ii. 622
Crystalloid bodies, ii. 81,162. — converted
into colloids in vegetables, ii. 346.

— escape in excretions, ii. 345
Crystals from blood, 1. 83
Curd, ii. 359

Cutaneous asphyxia, ii.401. — glands and
excretion (see Skin and Perspiration).

— excretion in animals, ii. 401
Cuticle, i. 449

Cutis vera or true skin, i. 419. Structure
of. i. 451

Cuvier, ducts of, ii. 637
Cystic duct, ii. 70. Mechanical effect of
spiral folds in, ii. 75
Cysticcrci, 11. 586
Cystoplasts, i. 75; ii. 043
1

C78

INDEX,

DAL

DEC

TAALTONISM, or Colour-blindness, i. 595
Daphnia, reproduction of, ii. 583
Dazzling, i. 589

Death, i. 105 ; ii. G64, GGo. Somatic, ii.
G().5. Molecular, ii. 28G, GG5. Climac-
teric, ii. G6G. From syncope, ii. G6G ;
asphyxia, ii. 6GG ; coma, ii. GG7 ; old
age, ii. 6G8. Signs of, external, ii. GG8 ;
positive, ii. G69. Apparent, ii. G69.
Eifect of on animal heat, ii. 50G, GOT
Decay, ii. 665, 6G8
Decidua vera and reflexa, ii. 598
Decussation of pyramids of medulla ob-
longata, i. 309. — of optic nerves, i.

306, 3T4, 579
Defascation, ii. 11
Degeneration, ii. 285

Deglutition, i. 110 ; ii. 27-35. First stage,
ii. 27-29 ; second stage, in 29—82 ; third
stage, ii. 32-34. Stages regulated by
nervous system, ii. 34, 35. In animals,
ii. 129, 130

Dendro-dentine, ii. 125
Dental arch, ii. 14; — pulps, ii. 15. — sacs,
ii. G27. — groove, ii. 627. — papillae, ii.
627. — follicles, ii. 627. ■ — glands, ii.
661. — tissues, i. 15 ; ii. 628, 660
Denticles of the Non-vertebrate animals,
ii. 127

Dentine, ii. 15, 628, GGO
Determination of blood, ii. 287
Development, i. 117 ; ii. 275 , 603. Meta-
bolic and metamorphic, ii. 280. — of
tissues generally, ii. 641, separately, ii.
646. Adipose, ii. 647. Bone, ii. 648.
Cartilage, ii. 848 ; articular, ii. 652.
Connective, ii. 646. Dental, ii. 660.
Elastic, ii. 647. Epidermoid, ii. 659.
Epithelial, ii. 659. Fibro-cartilage, ii.
648. Glandular, ii. 659. Muscular, ii.
654. Nervous, ii. 655. Bloodvessels,
ii. 633. Blood, ii. 633, 657. Primitive
arteries, ii. 636. Primitive veins, ii.
637. Ductless glands, ii. 658. Lymph,
ii. 658. Lymphatics or absorbents, ii.
658. Thyroid boiiy, ii. 631, 658. Tliy-
nms, ii. 631, 658. Epidermis, ii. 659.
Hairs, ii. 660. Nails, ii. 659. The Em-
bryo, general, ii. 60S; the appendages
of, 60S ; organs of, ii. 615. Skeleton, u.
615. Brain, ii. 616. Heart, ii. 633, 635.
Skull, ii. 616. Limbs, ii. 617. Muscles,
it. 615, 618. Nerves, ii. 615, 618. Skin,
ii. 618. Nervous system, ii. 619. Spinal
cord, ii. 619. Medulla oblongata, ii.
6 1 9. Cerebrum and its ports, ii. 620, 621 .
Cerebellum, ii. 620. Organs of Senses,
ii. 622. Nose, ii. 622. Eye, ii. 622. Ear,
ii. 623. Face, ii. 624. Tympanum, ii.
624. Tympanic bones, ii. 624, 625. Ali-
mentary canal, ii. 626. The Teeth, ii.
627 ; in Mnmumlia, ii. 629. Digestive
glands, ii. 630. Lungs, ii. 630, Liver,
if. 630. Pancreas, ii. 631. Spleen, ii.
631,6.58, Urinary organs, ii. 631. Ile-
))rodiictive organs, ii. 631. Circulatorv
organa in Amphibia, ii. 2Gs, 270

Dextrose or dextrin, i. 86 ; — produced by
action of saliva on starch, ii. 84
Diabetes mellitus (see Sugar)

Dialysis, ii. 160, 163, 164. Separates
crystalloids and colloids, ii. 164. Occurs
in absorption, ii. 176 ; in excretion, ii.
346

Diaijhragm, i. 27. Action of, ii. 417 ; — in
Mammalia, ii. 488 ; in Birds, ii. 488,489-;
in Reptiles, ii. 491 . Absent in Amphi-
bia, ii. 491

Diartbroses, or movable joints, i. 190
Diastema, ii. 14, 121
Dichromism, i. 596
Diebrotism, or dichrotal pnise, ii. 236
Dicotyledons, or Exogens, i. 139
Diencephalon, ii. 619,620
Diet, tables of, ii. 563. Daily, 5.536
Diffusion, of ga.ses, ii. 452, 453. Law of,
ii. 453. Simple and spurious, ii. 453
DiGE.s'noN, i. 116 ; u. 1 ; — in animals, u.
149-1 51 . Mechanical processes of, ii. 11.
Chemical processes, ii. 82-109. Artificial,
ii. 87-93. Summary of chemistry of, ii.
107-109. Circumstances which modify,
ii. 109-113. Time occupied by, ii. 92, 93.
Intestinal, ii. 102-104. Gastric, ii. 85-
95. Organs of, in animals, ii. 116-148 ;
chemical processes in, ii. 148-151
Digestive fluids, u. 53. Action of, u. 82,
84. Artificial, ii. 87, 88
Diphyodonts, ii. 630
Dicecious animals, ii. 584
Disc, germinal, ii. 593, 597, 604. — proli-
gerous, ii. 597
Disdiaclasts, i. 51

Disease, effect of on Animal heat, ii. 506
Distance, knowledge of i. 583
Distoraa, reproduction of, if. 587
Diving and divers, ii. 477, 478
Dorsal plates, ii. 616. — segments, ii. 615
Double consciousness, 1. 402
Drainage, importance of, ii. 486, 4S7
Draught, iu lactation, ii. 357
Dreaming, i. 400

Drinking, ii. 27. In Mammalia, U. 117
Dropsy, ii. 254

Drowning, recovery from, ii. 479
Drum of the ear, i. 501
Duct, cystic and hepatic, ii. 70. Panr-
creatic, ii. 78. Stcuonian, ii. 54. Rivi-
nian, ii. 55, Wbartoniau, ii. 55. Of
Bartholin, ii. 55. Common bile, ii. 70.
Thoracic, ii. 154. Galactophorous, ii.
.357. Pneumatic, of fishes, ii. 493
Ductless glands, i. 74 ; ii. 319. Actions of,
ii. 319, 320. Development, ii. 6.58. Con-
sidered generally, ii. 331-334. Prepare
.albuminoid constituents of blood, ii.
.3,32, .333. Form white blood corpuscles,
ii. 333. Active iu enihryouic life, iL
,333. Not essential to life, ii. 3,34 _
Duetns communis chehdochus, ii. 70.
Vitelli, ii. 609, 610. Arteriosus, ii. 639,
611. Botalli, ii. 270, 641. MUlleri. it.
632. Cuviori. ii. 637. Ycuosus, develop-
ment of, ii. 635, 641

IKDE5

679

DUL

Dtilong arid Dcsprotz, Animal heat, il. 513
Uumlmess, i. 3(iS

Duodenum,!. 33; ii. -1?. Contentsof, ii. 104

Dura mater, i. ‘Jl. 304

Dynamics of Human Body, ii. 532, 500-537

Dyslysin, iu 98. 545

Dyspua’a, i. 447

T7AB, Ossiclcsof, i. 501. Musclesof,i. 504,
517. E.\ternal. i. 500. Intcrunl, or laby-
rinth, L 505, Middle, or tympanum, i.
501. Development of, ii. 023, 024
Echinococcu Reproduction of, ii. 580
Echi.n'odkr.mata. Digestive organs, ii. 142.
Dige.stive glands, in 129, 143, 145. Am-
bniacral ves-sels, ii. 275. Respiration, ii.
501. Sight, i. 007. Touch, i. 472. Lo-
comotion, i. 220, 2S3. Reproduction,
ii. 580. Nervous system, i. 424
EDENTAT.t. Digtstive organs, ii. 130,133,
134. Digestive glands, ii. 145. Sight, i.
•5.99. Locomotion, i. 222
Efferent nerve-fibres, i. 328, 349
Egesta, ii. 11. Daily qu-iutity, ii. 539
Eggs, or ova, ii. 583. Of Bird, ii. 592, 593;
shell of, ii. .595 ; albumen, ii. 590 ; yolk,
ii. 590. Of Fishes, ii. 000. Of Amphibia,
ii. OOn. Of Reptiles, ii. 009
Elastic tissue, i. 44 ; ii. 047
Elastin, i. 88

Electric organs in Fishes, ii. 529-.531.
— work, of body, ii. 555, 577. — ctir-
rejits of the body, i. 1 70. — phenomena
in nerves, i. 280. — relations of mus-

cular tis.siie, i. 100

Electricity, protiuction by respiration, i.
115; by oxidation, iL .577. Animal, ii.

527- 531 ; in Man, ii. 527 ; in Fishes, ii.

528- 531

Electro-polarity of nerves, i. 283 ; ii. 577
Elcotrotonieity of nerves, i. 283
Elephant, trunk of, i. 245 ; ii. 117. Tusks
of, ii. 120, 121

Embryo, evolution of, iL .581. — cell, ii.
0O.5. — spot, ii. 000. Position of, in egg,
ii. 007. (ieneral evolution of, ii. 008.
Appendages of, ii. 008. Respiration of,
in Bird.s. ii. 012; in Mammals, ii. 013,
039. Nutrition of, in Mammal, i. 013,
039 ; in Birds, ii. 010. Birth of, ii. 015.
Circulation in, first, ii. 038 ; second,
ii. 039

Emotion, i. 307, 371, 380, .381, 392
Emotional movements, i. 381
Enamel, ii. 10, 17. Development of, ii.

028, 600. — organ, ii. 028, 000.
Enarthrodia, or tiall and socket joints, i. 1 9 1
Encephalon, i. 290. In Vertebrata, i. 405
Endochorion, il. Oil
Endogens or .Monocotyledons, i. 139
Endogenous growth of cells, ii. 044
Endosmometer. ii. 101
Endosmoshs, il. 100. 101
Endnplast. 11. 012, 013
Entoptical images, i. 592
Ependyma, ii. 019

EYE

Epcnceplialon, ii. 019, 020
Epidermic tis.sue,i. 72 ; ii. 059,003. Com-
position of, i. 82
Eiiidermis, structure of, i. 449
Epiglottis, i. 20, 248. Use of, in degluti-
tion, ii. 32

Epiphyses, development of, ii. 051
Epithelial cells, forms of, i. 72. Use of, iu
glands, ii. 347, 348

Epithelial tissue, i. 72; ii. 059,003. Com-
position of, i. 92
Equivocal generation, ii. 5.80
Equivalent, mechanical, of lieat, ii. 550
Erect posture, adaptation of laxly to, i
207

Eructation, ii. 50

Eustachian tube, i. 502 , 510 ; development
of, ii. 024. — valve, ii. 189
Evolution, c.Tcle of, ii. 587. Phases of. ii.
.588. — or transformation of euibryc
ii. 584

Excitability, property of nervous tissues,

i. 102, 272

Excito-motor acts, i. 347, 382
Excreta, ii. 305. In Herbivora. ii. 540;

Carnivora, ii. 540. Daily, ii. 540
Excretine, ii. 105

ExciiF.riox, and Excretions, i. 114 ; ii.
343. Organs of, ii. 344. Crystalloids
escape in, in 34.5, 340. Influence of
epithelium on, ii. 347. Conditions which
influence, ii. 348-351. Effect of nervous
system on, ii. 349-351, Vicarious, ii. 351,
Complementary, ii. 352. Con.stant, in-
termittent, or remittent, ii. 352. Move-
ment of along the ducts, ii. 3.52. Renal,

ii. 30-5, 374-391. Cutaneous, 39.5-401.
Cutaneous and renal, balanced, ii. 399,
400 ; in animals, in401. — of carbonic
acid by stomach and intestines, ii. 402.
Intestinal, ii. 104, 105,30.5. Pulmonai'y,
430-144

Exercise, effect of, on carbonic acid ex-
lialed in respiration, ii. 40.5. Effect of
on animal heat, ii. 50-5 ; on exhalation,
cutaneous, and pulrnon.iry, ii. 398, 430
Exogens or Dicotyledons, i. 139
Exogenous growtli of cells, ii. 0 14
Exosmosis, ii. 100, 101
Expiration, ii. 421-124. Eln-sticity of
lungs, in, ii. 421. Muscles of, ii, 42:i,
424. Force of, ii. 420. In Birds, active,
ii. 4S9

Expression and gesture in Animals, i. 247.
iu Man, i. 24 0

Extractive matters, i. 81 (see Blood and
various organs)

Extrnctum caruis, ii, 114
Eye and its appeudiiges, i. 520-514. Ad-
juslmoiit to distance, i. 557 ; — affected
by modicine. i. 501. Refraction ofliglit
iu, i. 5.54. Convergence of, i. 573. Func-
tion of (see Sight). Ill animals (see
Kiglit). Duvnlopmciit of. ii. 022
Eyeball, coats of, i. 530. lUovemouts of,
i. 534. Muscles of, i. 533. Nerves of,
i. 530, Parts of, i. 531-544

680

INDEX

EYE

Eyebrows, i. 52G, 530
Eyelashes, or cilia, i. 528
Eyelids, or pali)ebra3, i. 52G, 530. Deve-
loiiment of, ii. G23

"PACE, i. 7. Bonesof, i. 24. Development
of, ii. G24

Facial nerve, i. 31 G, 333

Pieces, composition of ashes of, ii. 105

Fallopian tube, ii. 598

Falsetto voice, i. 2G3

Fal.v, i. 21

Fat, absorption of, by veins, ii. 177. 17S,
179 ; by lactoala, ii. 177, ISO. Action of
bile on, ii. 9G ; of pancreatic fluid on,ii.
99 ; of intestinal juices on, ii. 102.
Fattening animals, ii. 542
Patty degeneration, ii. 2S5
Fatty matters, i. 85. In daily food,
ii. 536. Of body, quantity of, ii. 584.
Destination of, in body, ii. 541. Source
of, in body, ii. 541, ,544. Essential to
nuclear and cell growth, and tissue
formation, ii. 292. Fatty tissue, i. 46.
Development of, ii. G47
Fauces, i. 2G, 1 10,474. ii. 27
FavTB and Silbermaun on Heat Units, ii.
514

Fenestra ovalis, i. 503. — rotunda, i. 504
Ferrein, tubes of, ii. 3G9
Fercili.satiou of ovuie, ii. 590. — of ovum,
ii. 601

Feuiilet of Buminants, ii. 130
Fibre-cells, i. 49

Fibres of cerebellum, i. 308. — of cere-
brum, i. 303. — of muscle, i. 48-50
Fibrillm of muscles, i. 50
Fibrin, i. 82. — of blood (see Blond)
Fibrinogen, ii. 313. Fibriuo-plastic sub-
stance, ii. 313

Fibro -cartilage, i. 46 ; ii. G48
Fibrous tissue, i. 43 ; ii. C4G,GC3
Fire-flies, ii. 525

Fishes. Prehension of food, ii. 11 8. Teeth
and jaws, ii. 124-126, 127. Pharynx,
ii. 129. CEsnpbngus, ii. 1.38. Stomach,
ii. 138. Intestine, ii. 138. A))pendices
])yloric!E, ii. 138. Spiral valve in
rectum, ii. 139. Peritoneal cavity, ii.
139. Liver, ii. 144. Gall-bladder, ii.
146. Pyloric appendages, ii. 147. Pan-
creas, ii. 148. Lymphatic hearts, ii.
186. Portal circulation, ii. 268. Heart,
ii. 267. Arterial bulb, ii. 267. Branchim,
ii. 403, 498. Branchial artery, ii. 267.
Air-bladder, ii. 267, 493. Bennl portal
circulation, ii. 268. Spleen, ii. 342.
Siipra-renal bodies, ii. 342 Thyroid
body, ii, 342, 343. Kidneys, ii. 392,
393. Gills, ii. 403, 498. Touch, i. 472,
473. Taste, i. 484. Smell, i. 49,8.
Hearing, i. 523. Sight, i. 601, 602. 603.
Locomotion on solids, i. 225 ; in fluids,
i. 230-233 ; in air, i. 234, 235. Sounds
nnido by, i. 271. Enoepbalon, i. 405.
Cerebrum, i. .107, 408, 411, 412, 413.

TOO

Cerebellum, i. 413, 414. Corpora bi-
gem ina or optic lobes, i. 412. Medulla
oblongata and spinal cord, i. 415. Hy im-
glossal nerve, i. 416. Ova, ii. 600.
Heat, ii. 503. Integuments, i. 473. Fly-
ing fishes, i. 235. Electrical fishes, ii.
528-531

Fission of animals, or fissiparous repro-
duction, ii. 582-586 ; of animal cells,
ii. 644

Fissura Stemi, ii. 617
Fissures of brain, i. 299, 301
Flesh, or muscles, i. 13
Flesh-formers, ii. 537, 547, 561
Flight, i. 205. — in animals, i. 234
Fluorescence, i. 547 ; ii. 526
Fcetal placenta, ii. 599, 612, 638. — circu-
lation, ii. 639

Follicles, i. 70. Graafian, ii. 597. Of
Lieberkiihn, ii. 80-82
Food, ii. 1. Nature, sources, .and varieties,
ii. 2. Classification, ii. 3. Chemical
constitution, ii. 3 ; albuminoid, ii. 3 ;
gelatinoid, oleaginous, amylaceous, or
starchy, gummy, and saccharine, ii. 4 ;
stimulating, ii. 4 ; saline, earthy, and
mineral, ii. 5 ; water of, ii. 6. Prehen-
sion of, ii. 7. Preparation of, ii. 9.
Salt in, ii. 10. Besidue of, in largo
intestine, ii. 104, 105. Changes in mouth,
ii. 84, 8.5 ; in stomach, ii. 85-95 ; in
small and large intestine, ii. 103, 104.
Constituents, proximate, animal, ii.
3-6 ; vegetable, ii. 8 ; organic, ii. 82. 83.
Use, ii. 6, 7. Action of heat on, ii. 9.
Time occupied in digestion, ii. 92, 93.
Prehension of, in Animals, ii. 117-119.
Belative value of dilferent, ii. 113,114.
Effect of, on elimination of carbonic
acid gas from lungs, ii. 466-468. — of
warm-blooded animals, ii. 522; cold-
blooded animals, ii. 522. Daily quantity
of, ii. 535 ; relation of, to constituents
of body, ii. 537. Bespimtory, calorific,
or heat-forming, ii. 6, 537, 547. Plastic,
histo-genetic, or tissue-forming, ii. 6,
537, 547. Waste of, ii. 538. Destination
of, ii. 538. Changes of, ultimate, ii.
538 ; intermediate, ii. 540. Nitrogenous,
or albuminoid, ii. 3 ; in relation to
work, ii. 562 ; do.stination of, ii. 543,
562. Non-nitrogenous, or hydrocarbons
and carbliydrates, ii. 6 ; in relation to
work, ii. 562 ; in relation to heat, ii.
561 ; to work, ii. 561 ; necessity for, in
work, ii. 573. Kinds of, in relation to
heat and work, ii. 561. Value of, ns
source cf motor power, ii. 575. Ingesta
and cge.sta, daily, ii. 539. Jlelnmor-
pliosis of, intermediate, ii. 540 ; ultimate,
ii. 538 (see also separate Constituents
of Food). Lu.xus consumption of, ii.
546. Destination of, in Herhivora, ii.
546 : in Carnivora, ii. 546. Deprivation
of. ii. .547 ; in Animals, ii. .548 ; in Man.
ii. 549. — is fuel. ii. 554. — is nltimato
source of force, ii. 554. Liebig's views

INDKX,

681

FOO

on, ii. 5G'2 ; opposed, ii. 5G7. Effects of
on animal heat, ii. GOG
Foot, adaptation of, to support weight, i.
•J07

Foot pounds, ii. RoG
Foramen ovale, ii. 1S9, GIG
Foraminifera (see Protozoa)

Force, formative or organising, i. 102 ;
ii. 579. Germ-, i. 107 ; ii. U05, 601.
Sperm-, ii. .589. Muscuiar-, i. IGl.
Nerv'o-, i. 291. Vital, i. 105
Forces of Organic World, ii. 551-553.
Corrclarion of, ii. 552, 579. . — of Inor-
ganic World, ii. 550, 553. Correlation
of, i. 438 ; ii. 551.

Form in .Animals, Laws of, i. 135
Formative projierty of tissues, i. 102 ; ii. 597
Formic acid, i. 8G
Forms of i)rogression, i. 203
Fornix, i. 303 ; ii. G21
Fossa ovalis, ii. 189
Fovea centralis, i. 540, 5G8
Frankland, on source of motor power, ii.
5G9

Friction, sounds of, pleural, ii. 427 ; in
heart disease, ii. 222
Frost-bite, ii. 509

Functions, Animal, i. 108, 155. Vegetative
i. 110. Nutritive, i. 110. Reproductive,
1.117

/^ALACTOPnOROUS ducts, ii. 357

Gall-bliulder, i. 31 ; ii. 73, 74. — in

Vertobrata. ii. 145, 146. — in Nou-

vertebrata, ii. 1 46
Galvanoscopic limb of a frog, i. 290
Ganglia, i. 108, 294. — of sympathetic

system, i. 322

Ganglion of po.storior root of spinal nerve,
i. 319

Ganglionic corpuscles, i. 52 ; ii. 055
Gangrene, ii. 280, 509, G05
Gases (see Respiration)

Ga.'s.serian ganglion, i. 315
OA.STEnoi>oi).s. Digestive organs, ii. 139.
Digestive glands, ii. 129, 144. Circula-
tion, ii. 272. Renal organs, ii. 394.
Respiration, ii. 494, 499, 500. Touch, i.
472. Taste, i. 484. Smell i. 499. Hear-
ing, i. 524. Sight, 1. 004. Locomotion,

1. 225,233. Nervous system, i. 127,419
Gastric digestion, ii. 8.5-95. Glands, ii.

.59 : in animals, ii. 143
Gastric juic(!, i. Ill ; ii. 01-G5. Artificial,
ii. 87. Action of, ii. 85, Infiuence of
nervous system on, ii. (i|. Quanti y, ii.

02, 03, 90 ; effect of different stimuli on,
ii. 03. Siwciflc gravity, ii. 03. Com-
position, ii. 03. Source of hydrochloric
acid in, ii. 01. No action on starch or
fats, ii. 87. Arrests putrefaction, ii. 92.
Present in duodenum, ii. 103. Inflnencc
of section of vagus on, ii. 01. Action
of, on albuminoid and gclatinoid bodies,
ii. 80

Gelatin, i. 82 ; ii. 544. — not found in

GLA

blood, ii. 290. Use of, ii. 290. Motamo-
phosis of in body, ii. .545
Gemmation, intemal, ii. 583 ; or Gemmi-
parous reproduction, ii. 582 ; in animal
cells, ii. 044
Gemmules, ii. 582

Generation, i. 1 17 ; ii. 580 (ice Reprodne-
tion). Spontaneous or equivocal, ii.
580, 590. Alternate, ii. 585, 589
Genetic relations of Animals, i. 138
Genetically related different forms, ii.
580

Germ-cells, ii. 5,83, 589, G42. — sac, ii. 003,
G05. — force, i. 107 ; ii. G05, GUI ; is nu-
tritive force, ii. 279 ; is reparative force,
ii. (161

Germinal matter, ii. 042,643. — cells, ii.
585, 589. — centres, i. 280. — sac, ii.
604. — vesicle, ii, 590, 592, 593 ; desti-
nation of, 605. — spot, ii. 590, 592.

— disc, ii. 692, G05. — area, ii. fiOG
Gesture, in Animals, i. 247. In Man, i.
246

Gidd ness, i. 442

Gigerium, or gizzard, in Birds, ii. 135
Gills (see Branchim)

Gizzard in Birds, ii. 135, 13G. — in other
animals, ii. 138. 139, 140, 141
Glaxd.s. Forms of, i. 70 ; simple, i. 70 ;
compound, i. 71. Ductless, vascular, or
blood glands, i. 74 ; ii. 318,334 ; spleen,

i. 33, 74, 113 ; ii. 320, G31 ; suprarenal
bodies, i. 33, 74, 113 ; ii. 325, 632 ; thy-
mus gland, i. 74, 1 13 ; ii. 329, 631 ; thy-
roid body, i. 74, 113; ii. 327, 631 ; pitui-
tary body, i. 305 ; ii. 327, 621 ; closed
sacs of alimentary canal, ii. 61, 82,
158, 160, in animals, ii. 342. Excreting
glands, i. 114, ii. 34 ; kidney’s, i. 31,

ii. 366, 632, in animals, ii. 391 ; lungs,

i. 27, 114, 115, ii.406, 630, in animiils,

ii. 488 ; sudoriferous or sweat glands,

i. 69, 114, 459, ii. 618, 659. Secreting
glands, in general, ii. 344 ; Brunner’s,

ii. 80 ; c.audal of Birds, ii. 396 ; ceru-
minons, i. 501 ; lachrymal, i. 26, 114,
529; liver, i. 31, 111 ; ii. 65, 334, 630,
in animals, ii. 143 ; mamm.ary, i. 69,
114, ii. 356, 618, in animals, ii. 3G3 ;
Meibomian, i. 459, 527 ; mucous, ii.
363; iianorcas, i. 33, 111 ; ii. 78, 631,
in animals, ii. 146; salivary, i. 26, 110 ;
ii. .54 ; parotid, i. 26, ii. .54, sulilingual,

i. 26, ii. .55, submaxillary. i. 26, ii. 55 ;
in animals, ii. 128 ; sebaceous, i, 69,
459, ii. 659 ; tubular, i. 70 ; tubular of
stomach or gastric, ii. 5.8-60, 158. of
intestines, or Licberklllm's follicles,

ii. 80

Gl.AXIW, An.snnnKXT, i. 33, 66, 111, ii.1.54.
Closed glands, ii. 158, 160; agmiimtcd,
or I’t'yer's, ii. 81, 159, 160, solitary, ii.
61, 82, 1.58, 159; in Vertobrata, ii. 148.
l.aoteal, i. 33, 66, 171 ; mc.senteric, ii.
155. Lymphatlo, i. 66. 112; ii. 154, 1.55,
058 ; in Mammalia, ii. 186; Birds, ii.
186 ; absent in Reptiles, ii. 18G ; absent

082

INDKX,

GLA

In Amphibia and Pishes, ii. 18G ; absent
in Invertebrata, ii. 187.

Gland-cells, office of, ii. 348
Glenoid cavities, i. 191
Glisson, capsule of, ii. 70, 71
Globulin, i. 81. Action in co.agnlation of
blood, ii. 313. Use of in nutrition, ii. 290
Glomeruli of Ruysch, ii. 309
Glosso-pharvngeal nerve, i. 310, 3.34, 477
Glottis, i. 20, 2,31. Vocal, i. 207. Re-
spiratory, i. 257
Glow-worm, ii. 525
Glucose, i. 80
Gluten, ii. 4
Glycerin, i. 80

Glycero-phosphoric acid, i, SO

Glycocholic acid, ii. 70

Glycogen, i. 80 ; ii. 78, 335. Source, ii.

337, 339, 544. Destination, ii. 339
Glycocoll, or glycocin, i. 85 ; ii. 70
Goitre, ii. 327, 328
Gomphosis, i. 188

Goose's skin, or horripilation, i. 459
Graafian follicles or vesicles, ii. 597
Granulations, ii. 280
Grape-sngar, i. 80

Growth, i. 117 ; ii. 275, 004. —of cells, ii.
041. — of tissues (see Development

and Reparation). Continuous, ii. 283,
002

Gullet or CEsophagus, i. 27, 29, 110 ; ii, 32
Gustatory nerve (see Trigeminal)
Gyninoplasts, i. 75 ; ii. 043
Gy'mnotus, or Electrical Eel, ii. 528, 531

TT^JIADROMOMETER, ii. 227
HiEinadynamnmeter, ii. 229
Hn?mal cavity, ii. 008
Hiematin, or Hannin, i. S3 (see Blood)
Hiematochometer, ii. 228
Hmmato-globiilin, i. 83
Hiematoidin, i. S3

Eiemorrhage, or loss of blood, ii. 290.
Death from, ii. 290, 297. Tre.atmeut of ,
ii. 297. Arterial and venous, ii. 297.
Effects of, ii. 288

Hairs, structure of, i. 450. Development
of, ii. 000

Hair-follicle or sac, i. 457
Halitus of blood, ii. 301
Halones of egg, ii. 597
Hand in apes aud monkeys, i. 244. — in
Mau, adaptations and charaoteristics, i.
213. The tactile organ, i. 400
Harelip, ii. 025
Harmouia. i. 1,88
ITaversiau caual.s, i. 47, 1.85
Head, i. 7. Adaptation to erect posture in
Man, i. 21 1

Healing of wounds, ii. 287
Hearing, acuteno.ss of, i. 521. Organs of,
1. 500. Organs aud sense in animals, i,
522 525. Sense of, i. 50(1, 511. Subjec-
tive sensations of, i. .521
Heaut, i. 29. 111. Structure of, ii. 188,
200 ; auricle, left, ii. 193, right, ii. 189 ;

HEA

auricles, fibres of, ii. 197 ; bloodvessels,
of. ii. 199, 200 ; chordai tendinete, ii.
191, 194; columna; cameie, ii. 191,
194; endocardium, ii. 194; fibrous
rings, ii. 190 ; lymphatics, ii. 200 ; mus-
cuhir fibres of, i. -52 ; ii. 194 199 ; mu.s-
culi papillares, ii. 191, 194; nerves, ii.
200 ; ventricle, left, ii. 193, right, ii.
190; ventricles, fibres of, ii. 197-199 ;
valve, mitral, ii. 194, tricuspid, ii. 191 ;
valves, semilunar, ii. 192, 194. Deve-
lopment of, ii. 033, 034, 035. Action of,
ii. 20.3-222; frequency of, ii. 217, cir-
cumstances which modify, ii. 217-221 ;
at different ages, ii. 217,218 ; period of a
complete action, ii. 200; cardiac ganglia,
nervous centres, source of force, ii. 210;
contractions endure longer in cold-
blooded and hybernating animals, ii.
214 ; corpora Arantii, use of. ii. 208 ;
diastole, li. 204, cause of, ii. 200 ; dila-
tation of cavities spontaneous, ii. 214 ;
disease or injury, iufluenee of, on, ii,
215, 216; diseased actions of, ii. 221,
222; emotions and passions, induence
of, on, li. 215; force of beats, circum-
stances which modify, ii. 221 ; impulse
of, ii. 207, how affected, ii. 221 ; move-
ments of, ii. 205 ; nervous system, in-
fluence of, on, ii. 215, 210 ; palpitation,
ii. 221; pause, ii. 209; pouches of
Valsalva, use of, ii. 208 ; ratio between
beats of, and respir.ation. ii.220; rhythm-
ic action, causes of, ii. 215, condition of
blood in substance of, said to determine
it, ii. 217 ; right auricle, the ultimnm
moriens, ii. 214; sounds of. ii. 209-213,
causes of, ii. 210, 21 Realise of difference
of the two, ii. 211, characters of, ii. 209,
condition of cavities and valves during,
ii. 209, 210, relative duration of, ii. 213,
where most distinctly heard on .surface
of cliest, ii. 211 ; systole of, ii. 204. cause
of auricular, ii. 200, cause of ventricular,
ii. 200, 207 ; effect of. on shape of ven-
tricular portion of heart, ii. 207 ; systoliO
and diastolic conditions of cavities, re-
lative duration of. ii. 213; valves of,
action of. ii. 207 209 ; ventricles, capa-
city of, ii. 213, relative thickness of, ii.
214; ventricular eou tractions, foi'ce of,
ii. 214. In A'ertebrata, ii. 204-271.
Sfammalia, ii. 204 ; Birds, ii. 205 ; Rep-
tiles. ii. 205, 200 ; Amphibia, ii. 205, 200 ;
I'ishes. ii. 207 ; Non-vertchrata. ii. 271-
274. Mollusca, ii. 272 ; Molluscoida, ii.
273 ; Auiitilosn, ii. 273, 274

Hearts, lympbntic, in Reptiles, ii. ISO; in
Amphibia, ii. ISO ; in Eishes, ii. ISO

Heartburn, i. 440

Heat, meetiauicnl eoefficient of. ii. 556,
equivalent of, ii. 550 ; of combustion, ii.
557 ; of cheiniral change, ii. 557 ; a mode
of motion, ii. 551 , 557 ; of body. compsrM
with chemical changes in it, ii. 5.58; in
relation to food, ii. 501 ; sensibility to,
I. 408 ; produced in muscular action, i.

INDEX

683

HEA

104 : power of resisting, ii. 509-511.
Hent-fonners, ii. G, 637, 547, 5G1. ■ — units
in physics, ii. 555, of body, ii. 558

Animal, i. 115 ; ii. 502-521 ; in
Non-vertcbrata, ii. 503 ; in Vertebrata,
ii. 503 ; in cold-blomled animals, ii. 503,
517 ; in warm-blooded animals, ii. 504,
617 ; in Man, ii. 504, 521, how modified,
li. 505-507, effects of, on body, ii. 509-
612 ; how regulated, ii. 510 ; theories of,
ii. 512-518 ; Lavoisier's views, ii. 512-
61G ; Dulong and Despretz, ii. 513 ; car-
bon, a source of, ii. 512, 513 ; hydrogen,
a source of, ii. 513 ; local, ii. 504, 515 ;
hydration, a cause of, ii. 615 ; molecular
change, a cause of, ii. 515 ; in Carnivora,
I li. 517, 518; in Herbivora, ii. 517, 518 ;
relation to red corpuscles, ii. 518 ; ner-
vous system, influence of on, ii. 519;
uses of, ii. 521 ; how expended, ii. 521
■ Height of body, ii. 533. — at birth, ii. GG4
: Hemispheres of cerebrum, i. 24, 299.
Functions of, i. 373. Development of,
ii. 621

! Hepatic artery, ii. 68. A nutrient vessel,
ii. 72. Terminations of, ii. 72
Hepatic celLs, ii. 73
Hepatic ducts, ii. 70

Hepatic lobules, ii. 71. Colour of, ii. 72
Hepatic veins, ii. 70, 71
Hepatin, i. 86 ; ii. 335
Herbivora, Digestive organs of, ii. 116.
Destination of food in. ii. 546. Ilespira-
tion of, ii. 518. Oxygen absorbed by,
ii. 439. Corpora quadrigemina, ii. 412
Hermaphrodite Animals, ii. 583
Heterologous or heteroplastic tumours, ii.
285

Hiccup, ii. 431

Hip-joint, evidences of special adaptation,

i. 210

Hippocampus major, i. 306. Minor, i.
806

Hippuric acid, i. 85 ; ii. 381, 382
Histogenetic food, ii. 6, 537, 547, 501
Homologies in Animals, i. 136
Homologous or homoplastic tumours, ii.
285

Honey-comb of Ruminants, ii. 130
Horopter, i. 580

Horripilation orgoose's .skin, i. 459
Horse, daily work of, ii. 559, 564
Humours of the eye, i. 531, .542
Hunger, i. 444

Hybernation, ii. .521, 522. Respiration in,

ii. 454

Hydra, reproduction of, ii. 582, 583
Hydration, a sourco of Animal Jfent, ii.
515. — in the prwluction of albumi-
nose, ii. 86 ; — of sugar, ii. 84
Hydrogen, effect of breathing, ii. 470. A
source of Animal Heat, ii. 514. Rela-
tion of to Animal Heat, ii. 558
Hydrocarbons, ii. 6. Destination of, ii.
541. — in relation to heat, ii. 501 ; — to
work, ii. 561
Hyocholic acid, ii. 77

INS

Hyoid bone, i. 26 ; ii. 25. 625
Hypencsthesia, 1. 341
Hypermetropia, i. 565
Hyperplasia, ii. 285

Hypertrophy, ii. 285. — of muscle, i. 162
Hypnotism, or magnetic sleep, i. 402
Hypoglossal nerve, i. 317, 336, 477
Hypophysis cerebri, i. 305

TDEAS and Ideation, i. 367, 373, 374, 376,

-L 380, ,381, 382

Ideo-motor acts, i. 381

Idiots, brain of, i. 296

Ileo-caical valve, ii. 48, 49

Ileum, intestine, i. 33 ; ii. 42, 43

Image of Purkinje, i. 593

Images, entoptioal, i. 592

Im.ago, ii. 587

Incubus, or night-mare, i. 400
Incus, i. 502 ; ii. 625
Induration, ii. 285

Infant, weight and length of, ii. 664
Infancy, ii. 605
Infants, milk for, ii. 363
Inflammation, ii. 285, 286
Infundibula of kidney, ii. 368
Infundibulum of oviduct, ii. 693. — of
Fallopian tube, ii. 598
Ingesta, daily, ii. 539

Infusoria, rejiroduction of, ii. 580, 582,
586 (see Protozoa)

Ingluvies in Birds, ii. 134. — of Rumi-
nants, ii. 130

Ink-bag of Cephalopods, ii. 139, 395
Inhibition of effect of stimuli ou motor
nerves, i. 286

Inorganic bodies, characters, i. 148
Inorganic proximate constituents of the
body, i. 80, 95
Inosite, i. 86 ; ii. 293

Insnlivation, i. 1 10 ; ii.25. — in Animals,
ii. 128

iN.SECTTVoiu. Digestive organs, ii. 130,
134. Locomotion, i. 222
INSECTA. Digestive organs, ii. 140. Di-
gestive glands, ii. 143, 145, 148. Circu-
lation, ii. 273. 274. Heat, ii. 60;i.
Renal organs, ii. 394. itesiuration, ii.
495,496; — of certain larviu, ii.501 , Ln-
minosity of. ii. 525. Touch, i. 472, 474,
Smell, i. 499. Hearing, i. 524. Sight,
i. 604-606. Locomotion, i. 226, 235.
Sounds inmlo by, i. 271. Nervous Sys-
tem, i. 420—122.

Inspiration, ii, 414-420. Enlargement of
thorax in, ii. 415-417. Alusclcs of, ii.
417-419. Force e.xerted in, ii. 426. — in
Birds is passive, ii. 489. Quantity of
air taken in, at each, ii. 432 ; quantity
breathed in twenty-four hours, ii. 435.
Snpplementary nses of, ii. 430-432. In-
gress of air in, how facilitated, ii. 420,
First inspiration at birth, ii. 429. Cir-
cumstances wliich modify tho number
of, ii. 424, 425.

684

INDEX,

INS

Instincts of Animals, i. 378, 418. — of
Man, i. 378, 379, 392
Intellect, i. 377, 380
Intermuscular septa, i. 13
Intervertebral substances, development of.
ii. G16

Intestinal canal (see Intestine). — diges-
tion, ii, 102-104. — glands of Vertebrata,
ii- \48. — juice, i. Ill ; sources and com-
position of, ii. 80-82; action of, ii. 102;
action of in animals, ii. 1.00
Intestines, i. 33, 111. Length of, in ani-
mals, ii. 133. Development of, ii. 627.
Small, ii. 40—43; coats, ii. 43,44; vilii,
ii. 44; structure of villi, ii. 1.57, 108 ;
vermicular or peristaltic movements, ii.
44, 40. Large, ii. 45, 46 ; structure of,
ii. 46-49 ; coatsof, ii. 46, 47. Passage of
foodalong.ii. 45,49. Contents of , ii. 103-
106. Descent of substances through, ii.
106. Digestion in, ii. 102-104. Juices
of, 80-82. Glands, Brunner’s, ii. 80 ;
Lieberkiihn’s follicles, ii. 82 ; Peyer’s
patches, ii. 81, 109, 160 ; solitary, ii. 82,
331 ; agminated, ii. 81, 159, 160, 331.
Changes of food in, ii. 103, 104. Action
of juices of, ii. 102. Gases contained
in, ii. 106. Valvulfe conniventes, ii.
44. Contents of small, alkaline, ii. 97.
In Vertebrata, ii. 133-139; Mollusca, ii.
139 ; Molluscoida, ii. 140 ; Annulosa, ii.
140, 141 ; Annuloida, ii. 141, 142 ; Coelen-
terata, ii. 142 ; Protozoa, ii. 143
Intrinsic forces of Animal mechanism, i.
203

Inveutebrata. Alimentary canal, ii.
139-143. Gastric glands, ii. 143. Liver,
ii- 143, 144, 145. Pancreas, ii. 148.
IBood, ii. 271. Bloodvessels, ii. 271,
272. Nervous system, i. 419-425.
Touch, i. 472, 474. Taste, i. 484.
Smell, i. 499. Hearing, i. 624-526.
Sight, i. 603-607. Locomotion on solids,

i. 226, 227 ; in fluids, I. 233; in air, i.
235. Voice, i. 271, 272. Prehension, i.
246. Heat of, ii. 503. Digestive organs,

ii. 139-143. Digestive glands, ii. 128, 129,
143, 144, 145, 146, 148. Circulation, ii.
271-275. Renal organs, ii. 394. Respi-
raiion, ii. 494-496 ; 497, 499-502. Pre-
hension of food, ii. 118, 119. Denticles,
ii. 127. 128, Salivary glands, ii. 128,
129. Pharynx, ii. 129

Involuntary movements, i. 381
Iris, i. .531, 538, 556, 557. Governmeutof,
i. 567, Development of, ii. 023
Isthmus of fauces, ii. 27
Ivory, ii. 121

JACOB'S membrane, i. .540

Jaws, i. 110; ii. 21. — in animals, ii.
126, 127

Jaw, lower, develo])ment of, ii. 624,
Upper, dovelopjnent of, ii. 625
Jejunum, i. 33 ; ii. 42. 43
Joiut-oil, or synovia, i. 12, 189

LAM

Joints, i. 11, 108, 187. Immovable, 1. 188
Mixed, i. 188. Movable, i. 189; Bah
and socket, i. 191 ; Hinge or gingljTorm:
i. 190 ; Planiform, i. 190 ; Special formaj
i. 192

Judgment, i. 367

X^EISTIN, ii. 384.
Keratin, i. 83 ; ii.

584.

KinxEYS, i. 31, 114. Description of, ii,
360-371. Chemical composition, ii. 366.-
Atrophy or disease of one,ii. .367. Horse-
shoe, ii. 367. Movable or floating, ii„

367. Hilus, ii. 367. Sinus, ii. 367. Cor^ Ux—
tical substance, ii. 368. Medullary snbt Uu'saj
stance, ii. 368. Malpighian corpuscles, ii.
368,369,370. Pyramids (Malpighi), ii.

308. Papillm or mammillm, il. 368.'
Pelvis, ii. 308, 371. Infundibula, ii.i

368. Calyces, ii. 368, 371. Tnbuli
nriniferi, ii. 368. Tubes of Ferrein, ii.

369. Capsules, ii. 309. Ducts of Bellini,
ii. 369. Cilia in, of cold-blooded Ver-r
tebrata, ii. 369. Bloodvessels of Jlal-
pigliian bodies, ii. 369, 370 ; portal cha-i
racter of, ii. 370. Arteries, ii. 370.

Veins, ii. 370. Lymphatics, ii. 370.
Nerves, ii. 370, 371. Function of, iiJla!,:..^
371. Office of Malpigliian corpuscles,!

ii. 371 ; of spheroidal epithelium o^ Itie't-j
tubuli, ii. 371, 372, 373. Effect on
blood, of extirpation of, ii. 372 ; of
ligature of ureters, ii. 372. Bright's
disease, or granular degeneration, ii.

390. Renal organs in animals, ii. 391-
394. Primordi .1, ii. 611,631. Develop-:
ment. ii. 632. Ureter, ii. 366, 371
Kinesodic substance (in spinal cord), i. i
344

Kissing, sound of, i. 268
Knee-joint, con.structive adaptation
erect posture, i. 2u9
Kymographiou, ii. 231, 279

to;

J ABTRINTH or internal ear, i. 505
Labyrintho-dentine, ii. 125
Laclirymal canals or caualicnli, i. .529. —
glands, i. 26. 114, 526, 529. — lake, 1.
628. — papilla;, i. 528. — piincta, i. 529. >
— .sac and groove, i. 530
Lactation, ii. 356 ; how influenced, ii.
362

Lncte.als, i. 33, 67, 111 ; ii. L56, 1.57. Com-
mencemeut in villi, ii. 156. Absorption ^
by. ii. 175

Lactic acid, i. 86 ; ii. 64. 383
Lactin, i. 86 ; ii. 357. .359
Lncunm of hone. i. 47
Lamei.i.iuraxchl\ta. Dige-stive organa,
ii. 139. Digestive glands, ii. 144. Cir-
culation, ii. 272. Roual organs, ii. 394.
Respiration, ii. 500. Touch, i. 4'2-
Sight, i. 604. Locomotiou, i. 225, ‘233.
Nervous System, i. 127, 419

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INDEX,

f)85

XAil

1 Lamina spiralis, i. S06. — cribrosa, I. 537.

— fusca, i. 537. — of cerebellum, i. 307.

— dorsalis, ii. G07. Sensorial-, ii. G07.
Motorio-sexual-, ii. G07. Mucous-, ii. 6u8

i Lanugo, ii. GGO
^ Lai'TOj, ii. 5S5, 587

I Laryngeal movements, i. 257. — nerves,
functions of, i. 2G5. — muscles, action
of, i. 257,258. — sac, i. 251
[Laryngoscope, i. 25G

[Larynx, i. 2G, 115, 248. Cartilages,!. 249.
Mucous membrane, i. 252. Muscles,
1. 252. Nerves, i. 252. Ventricle, i. 251.
Functions of, i. 255
[ Latebra of egg, ii. 597
:Laughing, ii. 431. — gas, ii. 470
[Lavoisier's theory of Animal Heat, ii.
512-18

[Leaping, i. 217. Combined with running,

i. 217

[Lecithin, i. SG

, Lens, crystalline, i. 542. Development of,

ii. G22

Lenses, errors of artificial, i. 651. Ee-
fraction of light by, i. 550
[Lepidosiren, circulation in, ii. 270. Ko-
spiration in, ii. 493
Lencmmia, ii. 323
Leuciu, i, 85
Leucocythsemia, ii. 323
Levers employed in the body, 1. 198
lieberkUhn’s follicles, ii. 80-82. — present
in all Vertebrata. ii. 148
Life, or vital action, i. 105. Periods of,
ii. GG5

Ligaments, i. 7, 11, 189. Elastic, i. 193
Ligamenta subflava, i. 194
Ligamentum denticulatum, i. 295. —
teres, i. 191

Light, i. 545. Absorption of,i. .548. Effects

Ion the eye, i. 589. Evolution of, by Man,
Ii. 524 ; — by Animals, ii. 525—527 ;
— cause of, ii. 52G. Refraction of, i.
549 , 554

Imbs, development of, ii. G17
ingu.al nerve (see Trigeminal)
ips, absent in Birds, ii. 117 ; in Reptiles,
ii. 118

iqnid diffusion, ii. 1G0, 1C2. Rate of, with
different substances, ii. 102
iquor amnii, ii. 009. — lymphrn, i. C7.
— sanguinis, i. 02 (see Blood)
isping, i. 208.

ithic acid, i. 85 ; ii. 380, 387. — calculi,
ii. 387

rvKii, i. 31, 111. Description, ii. G5,
Ligaments, ii. GO. Lolws. ii. CO, G7.
11 Lobules, ii. 71, 72. Fissures, ii. 08.
n Bloodves.sels, ii. 08, 70. I.ymphatics,
|{ ii. 70. I’roiier substance, ii. 71. Nerves,
|l ii.70. Interlobular tissue, ii. 71. Secret-
>1' Ing portion, ii. 73. In embryo, a true
•' bIoo<I-glami, ii. 334. Functions, ii. 3,54.
[[ Glycogenic olllcc, ii. 78, 33,1-342 ; sugar
i from, ii. 3.30 ; quantity of sugar, ii. 337 ;
e nse of, ii. 339 ; modified, ii. 340 ; in snail,
[4' 843. Becreting oQlcu, ii. 354. Con-

MAL

sidered as a blood-gland, ii. 334-342. In
animals, ii. 143-145. Development of,
ii. 030

Lobe, electric, of torpedo, ii. 529
Lobes of cerebellum, i. 307 ; laminee of,
i. 307. — of the cerebrum, i. 300. Olfac-
tory, i. 305 ; ii. G21
Lobular plexus of liver, ii. 72
Locomotion of Animals in air, 1. 234; in
fluids,!. 228 ; on solids, i. 218. — of Man
in air, i. 234 ; in fluids, i. 227 ; on solids,
i. 20G. In Mammalia, i. 218-222, 228,

234. Birds, i. 222-224, 228, 229, 235-239.
Reptiles, i. 224, 225, 229, 230. 234, 235.
Amphibia, i. 225, 230. Fishes, i. 225,
230-233, 234, 235. Annulosa, i. 226,233,

235. Annuloida, 1. 226, 233. Mollusca,
i. 225, 233. Molluscoida, i. 233. Coelen-
terata, i. 233. Protozoa, i. 227, 233

Locomotive organs in Man. i. 185. Bones,

i. 185. Joints, i. 187. Muscles, i. 194
Lumino.sity, Animal, ii. 525 (see Light)
Lungs, i. 27, 114,115; ii. 40G. Develop-
ment of, ii. 630. Description of, ii. 406.
Mediastinum, ii. 408. Pleural covering,

ii. 407. Lobes, ii. 408, 409. Lobules,
ii. 409. Parenchyma of, ii. 409. In-
terlobular tissue, ii. 410. Subpleural
coat, ii. 410. Bronchia, ii. 410. Lobu-
lar bronchial tubes, ii. 411. Intercel-
lular passages or air-sacs, ii. 411. Air-
cells, ii. 412, 413. Pulmonary arteries,
ii. 413; veins, ii. 414. Bronchial arte-
ries, ii. 414 ; veins, ii. 414. Lymphatics,
ii. 414. Nerves, ii. 414. Elastic force
of human, ii. 422, 423. Passive in in-
spiration. ii. 420. Elasticity in expira-
tion, ii. 421, 422. Capacity, ii. 432—435.
In Mammalia, ii. 488. In Birds, ii. 489.
In Reptiles, ii. 490, 491. In Amphibia,
ii. 492. Homologue of, in certain Fishes,
ii. 493 ; in Mollusca, ii. 494, 495 ; in
Annulosa, ii. 494-496. Absent in Fishes,
ii. 267

Lunula of nail, 1. 455
Luxus consumption of food, ii. 546
Lymph, i. 67, 112. Composition, i. 92.
Corpuscles, i. 67 ; ii. 658. Source, ii.
172. Formation, ii. 173, 174, 658.
Quantity poured into blood in 24 hours
ii. 182

Lymphatic absorption (see Absorption);

— ghinils or ganglia, i. 66; ii. 164;
— .(lovelopmencof, ii. 658. —in animals,
ii. 186. — hearts in animals, ii. ISG ;

— networks or plexuses, ii. 1.54
Lymphatics, i. 112. Deep and superficial,

ii. 153. Develoitment, ii. 6.58. Abun-
dant in connective tissue, ii. 281. Few
or absent in muscle and brain, ii. 281

IVL ACULA Germinativa, ii. 590, 592 593 •
— lutca of eye, i. 54U ; ii. 623 ’

Magnetic slee]i, i. 402
JliignetLm, Animal, i. 402
Malpighii, Pyramids of, ii. 368

G8G

INDEX.

MAL

Malpighian corpuscles of spleen, 11. 321,
322. — of kidneys, ii. 3G.S. 3(il), 370 ; small
in Birds and Ueptiles, ii. 372
Malleus, i. 502 ; ii. (i25
Mammalia. Classification, 1. 12G. Im-
placental, i. 120; ii. 013. Placental
non-deciduate, 1, 120 ; ii. 013 ; deciduate,
1. 120 ; ii. 014. Prehension of food, ii.
117. Cheek pouches in some, ii. 117.
Teeth, ii. 120-122. Jaws, ii. 126. Sali-
vary glands, ii. 128, Pharynx, ii, 129.
Stomach, ii. 130-133. Intestinal canal,
ii. 133,134. Liver, ii. 144. Gall-bladder,
ii. 14-5. Pancreas, ii. 140. Lymphatic
glands, ii, 180. Portal circulation, ii.
265. Heart, ii. 204, 20.5. Aortic arch,
ii. 200. Spleen, ii. 342. Supra-reual
bodies, ii. 342. Thyroid gland, ii, 342.
Thymns gland, ii. 343. Mammary glands,
ii. 363. Kidneys, ii. 391, 392, Thorax,
ii. 488. Lungs, ii. 488. Touch, i. 471,
473. Taste, i. 483, Smell, i. 490, Hear-
ing. i. 522. Sight, i. 698, 699. Loco-
motion on solids, i. 218-222 ; in fluids,

i. 228 ; in air, i, 234, Voice, i. 269. Pre-
hension in, i. 244,245. Enceplialou, i. 405,
400. Cerebrum, i. 400-408,408-411 ,412,
413. Cerebellum, i. 413,414. Medulla
oblongata, i. 415. Spinal cord, i. 415.
Corpora quadrigemina, i. 412. Embryo
of, ii. 608-015. Ileatof.ii. 504, Ovaries
and ova of, ii. 592. Reproduction of,

ii. 003-641

Mammary glands, 1. 69, 114; ii. 3-50.
Structure of, ii. 356. Function of, ii.
357. Periodic enlargement of, ii. 287.
In animals, ii, 303
Mammilla, ii. 350
Mammillie of kidney, ii. 368
Man. Doily work of, ii. 559. — compared
with horse, ii. 559. Position in Animal
Series, i. 132

Mandibles of Annulosa, ii. 1 18, 119
Manipulation in Animals, i. 244. — in
Man, i. 239

Manometer, ii. 220 ; differential, ii, 233
Manjqilies of Ruminants, ii. 131
Margaric acid, i. 90
Maigarin, i. 86
Marrow, i. 45 ; ii. 040
MAiisupi.tLiA. Digestive organs, Ii. 133,
134. Locomotion, i. 222. Voice, i. 209.
Cerebrum, i. 408, 409, 411, 413
Marsupial pouches, ii. 633
Mastication, i. 110. Parts concerned in, ii.
12. Muscles, ii. 22-24. Movements, ii.
24. Use of saliva in, ii. 25 ; of tongue, ii.
25 ; of cheeks, ii, 25. In Vertebrafa, ii.
119-127. In Nonvertebrata, ii. 127, 128
Matrix, of cells, ii. 042
Maxillru of Annulosa. ii. 118
Meiusuro of beat, ii. 555
Meatus, external auditory, 1. 500, 513 ; in-
ternal, i. 508

Mechanical work of body, ii, 555, 559,501 ;

traiisformeil into heat, ii. 575
Mechanics of the body, i. 197

MOD

Meckel’s process, ii. 025
Slediastinum, i. 27 ; ii, 408
Mednlla oblongata, i. 297, 309 ; ii. 01
Fibres, i. 310. Pyramids, i. 309. D,
velopment, ii. 019. Functions, i. 35.
Reflex functions, i. 353. Of Vertebrati.

i. 414

Medullary plates, ii. 008, 019. — tissui
cells of, i. 45 ; ii. 049. — sub.stance i
cerebeUum, i. 307 ; of cerebrum, i. .303
of kidney, ii, 308
Mental work of body, ii. 555, 578
Meibomian glands, 1. 459, 527
Membrana nictitans, i. 529. — tympam
1. 501, 514

Membranous tongues, vibrations of, i. 25

Memory, 1. 307, 371, 377, 380

Mental faculties of Man, i. 370 {see Psy.

chical faculties)

Mesencephalon, ii. 619

Mesenteric glands, ii. 155. — in Camivorai

ii. ISO.

Mesenteries, i. 34 ; ii. 40
Mesmerism, i. 402
Metabolic energy, ii. 280.

Metamorphic force, ii. 280.
Metamorphosis, cycle of, ii. 587. Tme. ii
587. — of Insects, ii. 587. — of Am.
phibia, ii. 588. Progressive and retro
grade, ii. 588. — of Animal cells, ii. 044
Jfetencephalon, ii. 010
Micropyle, ii. 003
Metre-kilogrammes, il. 656
Milk-fever, ii. 357

Milk, Human, ii. 357. Colostrnm, ii. 357.1
Corpuscles of, ii. 358. Chemical com'
position, ii. 357, 358, 3.59. Globules, ii.
858. A type of food, ii. 358. Butter of,
ii. 359. Lactin or sugar, and lactic acid, ,
ii. 359, 300. Curd and whey, ii. 359.
Casein of, how formed, ii. 290, 360, 544 ;
its use, ii. 300. Oily matter, ii. 360.
Salts, ii. 300. Resembles blood, ii. 300.
Retention of, ii. 300. Vicarious score-:
tion, ii. 300. Quantity and quality
modified, il. 361 . Influence of nervous:
system on, ii. 301, 302. Chemical com-
position of, in M'oman and Animals, ii.
362. Of cow, for infants, il. 363
Milk-teeth, ii. 12, 18, 19. Development,
of, Ii. 028

Minerals, relations to Animals and Plants, -
i. 148

Molar death, ii. 286

Molecular changes, a source of Animal :
Heat, ii. 515, — death, ii. 280. — move-
ments, i. 155

Moli.u.sca. Characters and CIa.«scs, i.
121, 120. Prehension of food. ii. US-
Salivary glands, ii. 128. Alimeiitaiy
canal, ii. 139. Nervous system, i. 419.
Liver in, ii. 144. Circulation, ii. 272.
Renal organs, ii. 394. Respiration, ii-
494. 499, 500. Touch, i. 472, 474. Taste,
i. 484. Smell, i. 499. Hearing, i. 524.
Sight, i. 603. Locomotion on solids, i.
225 ; in fluids, i. 233. Prehension, i.

INDEX,

087

MOL

SO'i. Luminosity, ii. 526. Ovaries and
nvii, ii. (iOO. Development of, ii. 58U,
fiili). Heat of, ii. 51)3

Mou.usuoiija. Cliiu-acters and Classes, 1.
127, Prehension of food in, ii. Il8.
Pharynx ill, ii. 129. Alimentary canal
In, ii. UO. Liver, ii. 11-4. Circulation,

■ li. 273. llesiiiration, ii. 500. 'J'oiicli, i.
472, 474. Smell, i. 499. Ileariug, 1.
524. Sight, i. (!o4. Locomotion in
fluids, i. 233. Prehension, i. 24fi. Lu-
minosity, ii. 520. Nervous system, i.
420

llonocotyledon.s, or Endogena, i. 130
lloncccioiifi AnlrnaU, ii. .583
llonophyodonts, ii. 1130
lio.soTliK.MATA. Digestive organa, ii. 1.34.
Jlammary glands, ii. 3U3. Siglit, i. .599.
Cerelirum,i.408, 409,411. Implaceutal,
ii. 613

1 Mortality from epidemics and contagious
I dise.a,-.ea, ii. 4,86, 487
I MortiBcation, ii. 286

MrrnoN’, i. 108,153,381. Ciliary, i. 177.
Muscnlar, i. 156. Sarcodous, i. 182. Of
blood through the arteries, ii. 222-234 ;
through the capillaries, ii. 242-247 ;
through the veins, ii. 247-257. In vege-
tables, i. 184. Passive organs of, i. 108.
Active organs of. i. 108. Production of,
1. ILl. Knowledge of, i. 585.

Motor fibres of nerves, i. 277 ; — oculi
nerves, i. 314, 332

Motor power, source of, ii. 555—559, 561-
575

Motorial centre, i. .361. — stimulns, path
of, in spinal cord, i. 342
Mouth, ii. 25. Mucous gland.a of, ii. 54.
MovrmenTS, automatic, i. 385 ; con.scn-
sual or aenaori-motor, 1. 381, 382 ; emo-
tional, i. 381, 3.84; Ideational or ideo-
motor, i. 381, 384 ; instinctive, i. 381,
382 ; involuntary, i. 381 ; reflex or excite
motor, i. 381-383 ; aenaori-motor, i. 331,
3.82 ; voluntary, i. 381 ; rhythmic, i.
385. Of Animal sarcode and protoplasm,

i. 1H2. Of Man and Animals, i. 184,
Regulation of, i. 108, 272, 293

Mucin, i. 83 ; ii. 363

Mucous mcmhranca, i. 69 ; ii. 659. Action
of, ii. 363

Mucus, i. 69; ii. 363. Chemical composi-
tion, ii. 363. Use, ii. 364. Acta as a
ferment, ii. .364, 379, 386
Muller, ducts of, ii. 632
Miirexid, ii. 381

Murmurs, respiratory, ii. 426. — cardiac,

ii. 222

Mitscm volitantca, i. 592
MuKcr.KS, i. 13, 108. Development of, ii.
61.5,618. Enlarged l)y exercise, ii. 28.3.
Fixation of, i. 5 1 . IT, so of in locomotion ,

i. 194. Elasticity of, i. 161. Heat of,
I ii. .504. .Structure of, i. 51. Of mastica-
tion, ii. 22-21; clicck, ii. 25; tongue,

ii. 25, 26 ; soft palate, ii. 28; pharynx,
ii. 29, 30, 31 ; inspiration, it. . 17-419 ;

NER

e.xrpiration, ii. 42.3, 424 ; eyeball, i. 533 ;
middle ear, i. 504. 517 ; lai-yux, i. 252
Muscular contractility, i. 160' ; cause of, i.
172 ; duration of, i. 163. — contractiou,
phenomena of, i. 158 ; heat proiUiced
by, i. 164; phenomena accompanying,
1. 164. — currents of electricity, L 166 ;
determined by galvanometer, i. 166.

— fibres, phain or unstriped, i. 48 ; ii.
654 ; striped or striated, i. 49 ; ii. (154.

— irritability, i. 101, 156. —sensations,

the sixth sense, i. 433. — sense, i. 162,

362, 366. 441. — sound, i. 164. — tissue,
1. 48 ; ii. 651, 663 ; composition of, i. 89.

— tonicity, i. 162, 351
Musk of the musk-deer, ii. 395
Myopia, 1. 565

Mvm.u'ODA. Digestive organs, Ii. 140.
Digestive glands, il. 129, 145. Circula-
tion, ii. 274. Renal organs, ii. 394. Re-
spiration, ii. 494. Touch, i. 472, 474.
Sight, i. (i06. Locomotion, i, 226

TNJAILS, structure of, i. 455. Develop-
ment of, ii. 6-59
Narwhal, tusk of, ii. 121
Nasal duct, i. 530. — cavities, i. 26
Nausea, i. 445
Necrosis, ii. 665
Neoplasia, ii. 285

Nerve-cells, i. 62, 291 ; ii. 655. — cords, i.
294. — currents, electrical, i. 280. —

fibres, afferent, efferent, and reflex, i
277 ; motor and sensory, i. 277 ; grey or
gel.atinous, i. 53 ; ii. 666 ; white or
tubular, i. .54 ; ii. 056
Ncrve-force. i. 291
Nerve-root, i. 56
Norve-triink, i. 56
Nerves of respiration, i. 334 ; ii. 428
Neiive.8, i. 24, 108. Of the internal senses,
i. 301. Action on muscles, i. 287. Elec-
trotonicity, i. 283. Electropiilai'ity, ii,
577. Functions, i. 273. Mode of action,
i. 289. Modes of termination, i. 56.
Connection with centres of sensation,
i. 336. Rate of conduction in, i. 279.
Respiratory, i. 334 ; ii. 428

Cranial, i. 313. First pair, or

olfactory, i. 313, 331, 4H7, Hccond pair,
or optic, i. 314, 331, 531. Third pair, or
motoros oculi, i. 314, 332. Fourth pair,
patiietic, or trochlear, 1. 314, 332, Fifth
])air. trigeminal, or trifacial, 1. 314,332.
Eixth pair, abducent, i. 3L5, 333. Seventh
l)nir: portio mollis, or auditory, i. 310,
508,521 ; iiortio dura, or facial, i. 316,
333. Eighth jmir : glosso-pharyngcul,
i. 316, 334, *117 ; jmeuinogastric or
vagus. L 316, 33-1 ; spinal accessory, i.
316,33.5. Ninth iiair, or hypo-glossal,
i, 317, 336, 4 17. J''niicUona of, i. 331,
Niimhor of llhres in each. i. 317

Spinal, i. 317. Cervical, 1, 317,

319. Cocc.tgoal, i. 317, 320. Dorsal, i.
317,319. Lumbar, 1. 317, 319. .Sacral,

6S8

INDEX,

NER

OSS

i. 317, 319. Functions, i. 328. Roots,
1.320. Anterior roots, i. 318. Posterior
roots, i. 318, 339

Nervous force, ii. 577. — ])lexuses, i. 5C,
320. — substance, composition of, i. 83 ;
properties of, i. 273. — sy.stem aud its
functions in animals, i. 403 ; bilateral
or double action of, i. 395 ; cerebro-
spinal, i. 294 ; sj’mpathetic, i. 294 ; de-
velopment of, ii. G19 ; effect of on Ani-
mal Heat, ii. 519 ; its functions, i. 29.3;
its strncture, i. 294 ; functions of dijffer-
ent parts, i. 32G. — influence on absorp-
tion, ii. 171 ; on heart’s action, ii. 215,
21G, 217; on nutrition, i. 394, 395; ii.
284 ; on sugar forming function of liver,

i. .35G, 394 ; ii. 340, 341 ; on secretion, i.
894,395; ii. 349-351 ; on secretion of sa-
liva, i. 333 ; ii. 5G, 57 ; of tears, i. 392,
395 ; of gastric juice, ii. G1 ; on excretion

ii. 349-351 ; on excretion of urine, ii. 374 ;
on respiration, ii.427. — psychical func-
tions, i. 37G

Nervous tissues, i. 52 ; ii. G55, GG3
Nervous work, ii. 577
Nervomuscular work, ii. 555, 578
Neural cavity, i. 133 ; ii. 608
Neurilemma, i. 5G
Neurility, i. 102, 273
Nightmare or incubus, i. 400
Nipple, ii. 356

Nitrogen, effect of breathing, ii. 470.
Elimination from lungs, ii. 443 ; from
skin, ii. 400

Nitrogenous food (see Food). Constituents
of body, i. 81, 97

Nodes or Nodal points of vibrating bodies,
1. 253

Noeud, vital, i. 3.54 ; ii. 428
Non-azotised constituents of the body, i.
85, 99

Non-nitrogenous food (see Food). Con-
stituents of body, i. 85, 97
Nou-vascular tissues, i. 62
Nose, structure of, i. 486. Development
of, ii. 622, 624

Notochord, ii. 697 ; changes of. ii. 616
Nucleated cells, i. 75 ; ii. 643-646
Nucleus aud nucleolus of animal cell, ii.

643 ; of vegetable cell, ii. 642
Nutrition, i. 112; ii. 275. Definition,
ii. 275, 276. Chyle, ii. 276, 277. Blood,
ii. 277 (see Blood). Organs and tissue.s,
ii. 278. Areas and centres of, ii. 280.
Conditions essential to, ii, 280 ; modify-
ing it, ii. 283, 284. 'When most active,
ii. 280 Essential cause of, ii. 279 ;
stage first, ii. 278 ; second, ii. 279
third, ii 280; fourth, ii. 281 ; fifth, ii.
281, 282. Continuous growth, ii. 2.82,
283, 662. Interstitial disintegration and
deposition, ii. 282, 283. Influence of
nervous system on, i. 394 ; ii. 284. Not
dependent on nervous system, ii. 284.
Periodic, hypertrophic, and liyperpl.as-
tic, ii. 284, 285. PervtTsions of. ii. 285.
Dopondeut on blood, ii. 287. Effect of

ligature of arteries, ii. 287. Effect of
determination of blood, ii. 287. Effect
of haemorrhage, ii. 288. Office of white
corpuscles of blood, ii. 289; of red, ii.
289 ; of albuminoid principles of blood,
ii. 290 ; of fibrin of blood, ii, 291 ; of
fatty matter of blood, ii. 292; of sugar
of blood, ii. 292 ; of extractivesof blood,
ii. 293 ; of salts of blood, ii. 293-295;
of gases of blood, ii. 295. Of the em-
bryo, ii. 610, 613, 639, 640
Nutritive glands, il. 320 (see Ductless
Glands)

Nutritive repetition, ii. 283, 662
Nutritive work of body, ii. 555, 576.

QBJECTIVE sensory stimuli, i. 426
Oblique muscles of eyeball, i. 533
Occipital foramen, i. 21 ; ii. 652
Ocular spectra, i. 590
Odontophore, ii. 127
Odours, i. 489

Oidema of the glottis, ii. 420
aH.sopnAons, i. 27, 110 ; ii. 32, 33. Action
in deglutition, ii. 33. In Vertebrata,
ii. 134-138. In Jlollusca, ii. 139. In
Molluscoida, ii. 140. In Annulosa, li.
140

CEsophageal groove in Ruminants, ii. 131.

Action of, ii. 132
Old age, ii. 065, 668
Oleic acid, i. 86
Olein, i. 85

Oleophosphoric acid, i. 86
Olf.actory cells, i. 487. — lobes, i. 305, 487 ;
ii. 621 ; in animals, i. 408, 412 ; develop-
ment of, ii. 621. — nerves, i. 313, 331,
487

Olivary bodies, i. 309, 356
Omasum of Ruminants, ii. 130
Omenta, i. 34 ; ii. 36

Omphalo-mcsenterio arteries, ii. 610, 634.

— veins, ii. 634
Operculum of Fishes, ii. 498
Ophthalmometer, i. 559
Ophthalmoscope, i. 597

Optic axes, i. 532, 534. — commissure, i.

532. — tracts, i. 532. — centre of the eye,

i. 556. — lobes in animals, i. 408, 412.

— nerve, i. 314, 331, .531. — pore. i. .537.

— thalamus, i. 304 ; ii. 620 ; functions, i.
359. — vesicles, ii. 62 1 , 622 ; secondary,

ii. 622

Optometers, i. 564
Orbits of the eye.'-', i. 526
Organs of the Body, weight of, ii. 534
Organic bodies. Cliaracters. i. 148
Organic proximate constituents of the
liody, i. 80. 96. Azotised or nitrogenised,
i. 80, SI, 97. Non-n7.oti.=ed, i. 81, 85, 99
Organic constituents of food. li. 82, S3.

— mat' or in the breath, ii. 444
Organisation, i. 152 ; ii. 646
Osmazome, i. 89

Osmosis, ii. 160

Osseous tissue (see Bone and Tissue)

INDEX,

689

OSS

Ossicles of the ear, i. S03, 514 ; il. G25
Ossiticatiou, from cartilage, ii. 649 ; from
membrane, ii. 650. Intra-cartilaginous,
li. 64S ; where it occurs, ii. 651. Mem-
branous, ii. 650 ; where found, ii. 650.
Centres of, ii. 651. Order of process, ii.
, 652

Osteodentine, ii. 18, 125
Osteoblasts, ii. 650
Osteogenic substance, ii. 650
Otoliths or otoconia, i. 507, 520
Ovary. Of Bird, ii. 593. Mammal, ii. 597.
Reptiles, ii. GOO. Amphibia, ii. 600.
Fishes, ii. 600. MoUusca, ii. 601. An-
nulosa.ii. 601. Coelenterata, ii. 601. — is
a gland, ii. 601. Development of, ii. 632
Oviduct of Bird, ii. 593
Ovipositor, ii. 601
Ovisac, ii. 593
Ovule, Vegetable, ii. 590
Ovum, ii. 583. Compared with pseudo-
vum, ii. 589. Unfertilised, ii. 589.
Origin of, from parent, ii. 590. General
account of,ii. 590. Meroblastic, il. 591.
Holoblastic, ii. 591. Sizes of, ii. 590,
597. Mammalian, li. 592, 597. Of Bird
and Reptile, il. 592, 593. Of Reptiles,
ii. 600. Amphibia, li. 600. Fishes, ii.

600. MoUusca, ii. 601. Annulosa, ii.

601. Cmlenterata, ii. 601. Fertilisa-
tion of, ii. 601. Micropyle of, ii. 603.
Changes in, ii. 603

Ox, daily work of, ii. 564
Oxalate of lime calculi, ii. 384.

Oxalic acid, i. 86 ; ii. 384
Oxidation of body, ii. 546. — of food, the
source of force, ii. 554. — processes in
body, ii. 457^61. — of muscle, ii, 561
Oxygen, i. 115. Combines with red cor-
puscles, ii. 456. Effect of breathing, ii.
471. Discovery of, ii. 457. Affinity of
cruorin for, ii. 449. Combines with
cruorin, ii. 449, 4.50. In liquor sanguinis,
ii. 450. Absorption of, in respiration,
ii. 438, 439. Contained in venous and
arterial blood, ii. 451,452. Conditions
which modify quantity of, absorbed in
respiration, ii. 463, 464, 465
Ozone, ii. 437, 438

■pACnYDERMATA Digestive organs,
■*- ii. 132, 134. Digestive glands, ii. 145.
Sight, i. 598, 599. Locomotion, i. 220,
221. Cerebrum, i. 407, 409, 410, 411
Pacinian corjniBclcs, i. 455
Pain, i. .110,447

Palate, i. 474 ; ii. 27, 28. Cleft — , ii. 625.

Hard and soft, ii. 27, 28
Palpebrai or eyelids, i. 526
Palpebral lis.sure, i. 528
Palpitation of the heart, i. 446
Palmitic acid, i. 86
I’almitin, i. 86

1’AN'cnKA.s, i. 33, 68, 111. Description and
structure of, ii. 78. In animals, ii. 146-
148. Development of, ii. 631.

VOL. II.

PIT

Pancreatic juice, i. Ill ; ii. 79. Secretion
not continuous, ii. 79. Composition, ii.
79, 80. Action, ii. 98-102. In animals, ii,
150. Present in small intestine, ii. 103
Pancreatin, i. 84 ; ii. 79
Pause of Ruminants, ii. 130
PapiUte of cutis, i. 453. — of teeth, ii. 627,
660. — of kidney, ii, 368. — of tongue, i.
475

Parapeptone, ii. 86

Parenchyma of Organs (ace those Organs)
Parotid glands, i. 26 ; ii. 54
Parthenogenesis, ii. 584, 589
Pathetic nerve, i. 314, 333
Paunch of Ruminants, ii. 130
Pedmioles of cerebeUum, i. 307. — of cere-
brum, i. 297

Pelvis, points of adaptation, i. 210. — of
kidney, ii. 368

Pepsin, i. 84 ; ii. 63, 64, 87. Special action
of, ii. 91. Properties of, ii. 91. Source
of, ii. 544
Peptone, ii. 86
Perception, i. 367, 380
Percussion of chest, ii. 427
Perenni-branchiate Amphibia, ii. 270.
Circulation, ii. 270. Respiration, ii.
498, 499

Pericardium, i. 29 ; ii. 188. — absent in
Ampliioxus, ii. 264
Perichondrium, i. 46
Perimysium, i. 61
Periodontal membrane, ii. 1 8
Periplast, ii. 642, 643

Peristaltic or vermicular contraction, i.
160; ii. 44,45

PeritoniEum, i. 34 ; ii. 36, 42, 626
Perivisceral cavity of Actinozoa, ii. 142
Perspiration, ii. 396. Insensible, ii. 397,
Sensible, ii. 397. Chemical composition,
ii. 397. Uses, ii. 398, 399. Average quan-
tity exhaled in 24 hours, ii. 398. Quan-
tity influenced, ii. 398, 399. Suppression
of, ii. 399. Use of in regulating heat of
body, ii. 510

Pottenkofer's test for bile, ii. 390
Peyor’s glands, 1. 75, 113; ii. 81, 159, 160
Pharynx, i. 110, 115; ii. 29-31. Action
on "deglutition, ii. 31. Closed sacs, ii.
331. In animals, ii. 129
Phosphates, elimination of, ii. 579
Phosi)hatic calculi, ii_. 387
PhosphOnes, i. 571, 577, 594
Phosphorence of animals, ii. 525
Photic work, ii. 527. — of body, ii. 566
Photometers, i. 589
Phrenic nerve, i. 319
Phrenology, i. 369

Phthisis and imiicrfect ventilation, ii. 485
Physics, methods of research in, ii. 552,
553

I'liysiology, General, i. 101. Sliecial, i. 155

Pin Mater, i. 24, 295

Pigeon, mode of feeding young, ii. 118

Pigment cells, i. 73, 83 ; il. 659

Pineal gland or body, i. 305, 358 ; li. 620

Pitch of a sound, i. 253

y y

690

INDEX.

PIT

Pituita, i. 48G

Pituitary body, i. 305, 356 ; ii. 327. —

membrane, i. 486

Placenta, origin of, ii. 598. Structure and
uses, ii. 613. Maternal, ii. 598, 612.
Detachment of part of, ii. 615. Fcetal
part of, ii. 599,612. Diffused, ii. 614.
Cotyledonous, ii. 614. Discoid, ii. 614.
Zonular, ii. 614

Plants, classification, i. 139. Resemblances
between them and animals, i. 144. Dif-
ferences between them and animals, 1.
145. Respiration in, i. 141 ; ii. 402.
Structure and functions, i. 140. Tissues
of, i. 141 ; ii. 642

Plasma of the blood, i. 62, 112 ; ii. 278
Plastic deposits, ii. 286. — food, ii. 6, 537,
647, 561

Plem-a, i. 27 ; ii. 407. Costal, ii. 407.
Cavity of, ii. 407

Pleural chamber of thorax, ii. 407
Plexuses of vessels {see Capillaries and
Lymphatics) . — of spinal nerves, 1. 319.

— of sympathetic nervous system, i. 322
Plioi-dentine, li. 125

Pluteus, 11. 586

Pneumo-gastrlc nerves, 1. 316. Punction
ofi 1. 3.34. Influence on biliary secretion,
ii. 355, 356. Effect of division of, ii. 429,
430 ; on glycogenic function , ii. 341
Poison fangs in serpents, ii. 123
Pollen cells, ii. 590

PoLYZOA. Digestive organs, ii. 140. Di-
gestive gl.ands, ii. 145. Circulation, ii.
273. Respiration, ii. 500. Touch, i. 472
Pons Varoli, i. 297. Fibres of, i. 308.
Functions of, i. 356. Development of,
ii. 620. In Vertebrata, i. 414
Portal canals, ii. 71

Portal blood is source of bile, ii. 3.54. Cir-
culation, ii. 69. In animals, ii. 265, 267,
268

Portal vein, ii. 08

Portio dura, or facial nerve, 1. 315, 333.

— mollis, or auditory nerve, i. 315, 331,
508, 621

Posture, erect, i. 207. — recumbent, and
mode of rising, 1. 206. — sitting, and
mode of rising, i. 206. Effect of on the
pulse, ii. 218

Precursory cartilage, ii. 649. — membrane,
ii. 6.50

Preformative membrane, ii. 660
PrchensOe limbs of quadruped Mammalia,
i. 222

Prehension and manipulation in animals,

i. 244. — in Jlan, i. 239. — of food in
animals, ii. 117-119

Presbyopia, 1. 565
Pressure, sensibility to, i. 464
Primitive streak or trace, ii. 606. Optic
vesicles, ii. 621, 622. Dental groove,

ii. 627

Primordial vertebrnj, ii. 615. — kidnej's,
ii. 615

Proboscis of Annulosa. ii. 119. — of Ele-
phant, i. 215; ii. 117

PUR

Process, Meckel’s, ii. 625
Proglottis, ii. 586

Progression upon solids, i. 203, 206. —
. under water, 1. 204. — upon a fluid, i.
204. In water, i. 204, 227. — through
the air or flight, i. 205
Pronation, i. 242
Propagation of sound, i. 509
Propionic acid, i. 86
Prosencephalon, ii. 619, 621
Protein, i. 97

Proteus, circulation, ii. 270. Respiration,
ii. 492, 498

Protoplasm, i. 75 ; ii. 642, 643. Move-
ments of, i. 182

PnoTOZO.t, general characters and classes,

i. 130. Reproduction, ii. 580, 583. Heat,

ii. 503. Luniinosity in, ii. 526. Pre-
hension of food, ii. 119. Alimentary
cavity in higher, ii. 143. Circulation, ii.
275. Contractile vesicles, ii. 275. Re-
spiration in, ii. 501. Sight, possible, i.
607. Locomotion on solids, i. 227 ; in
fluids, i. 233. Nervous system and
action, 1. 424

Proventriculus in Birds, ii. 135. Use of,
ii. 136

Proximate constituents of the body, i. 80.
Inorganic, i. 80, 95. Organic, i. SO, 96,
100. Proportions of, ii. 534 ; relative to
daily food, ii. 536
Psalterium of Ruminants, ii. 130
Pseudo-branchite of Fishes, ii. 343
Pseudo-hajmal vessels of Annelida, ii. 274
Pseudoscope, 1. 583
Pseudova, ii. 583, 585, 589
Psychical functions of nervous system, i.

108,272, 293, 361, 376, 380
Pteropods. Digestive organs, ii. 139.'
Digestive glands, ii. 129. Circulation,
ii. 272. Respiration, ii. 499. Sight,!.
604. Locomotion, i. 233
Ptyalin or saliviu, i. 84 ; ii. 58
Puberty, ii. 665

Pulmonary artery, i. 29 ; ii. 413, 414.

— veins, i. 29 ; ii. 413, 414
Pulmonated or air-breathing Vertebrata,
warm and cold-blooded, ii. 264
Pulp of tooth, ii. 15

Pulse, ii. 234-242. Frequency of, ii. 218.
Modifie<l by many cause.s, ii. 217-221.
Cause, immediate, ii. 234 ; remote, u.
234. Locomotion of artery in, ii. 23.5.
Tlieories of, ii. 235, 2-36. Pulse-wave,
rate of, ii. 235. Character.sof,ii.237, 239,.
240. Dichrotal, ii. 236 ; cause of, ii.
238, 239. Absolute duration, ii. 240.
Volume of, ii. 237. Intiuence of re.'pi-
ratory movements on, ii. 241. Modified
by lieart’.s action, ii. 241. Irregular, ii.
242. Intennittont, ii. 242. Respiratory,
ii. 253. Venous, ii. 208
Piilse-respiraiion ratio, ii. 220, 425. Effect
of disease on, ii. 425
Pupa, ii. 587

Pupil of the eye, i. 538, 566 ; ii. 623
Purkiuje, imago of, i. 593

INDEX

691

PUS

RES

Pus, ii. 2SG
Putrefaction, ii. GG9
Pyloric appemingeii, ii. 147, 148
Pylorus or pyloric valve, ii. 37
Pyramids of -Malpighi, kidney, ii. 3GS. Of
the medulla oblongata, i. .3UG ; decussa-
tion of, i. 309

QUADRUMANA. Digestive organs, ii.
130, 134. Digestive glands, ii. 146.
jMammary glands, ii. 3G3. Touch, i.
471. Sight, i. .398, 599. Locomotion on
solids, i. 218-220. Voice, i. 2G9. Pre-
hension, i. 244, 245. Cerebrum, i. 40G,
408, 409, 410, 413. Cerebellum, i. 413,
414

Quadrupeds, mode of standing and loco-
motion, i. 219. Adaptation for swim-
ming, i. 228
Quinoidin, ii. 44G

■pADIATA. General characters, i. 121.

Rales, ii. 42G, 427
Reason, i. 3G7, 379

Receptaculum chyli, ii. 155 ; in Birdstwo,
ii. 18G

Reciprocation of sounds, i. 2G4
Recollection, i. 377
Recti muscles of eyeball, i. 533
Rectum, i. 33 ; ii. 4G
Reed of Ruminants, ii. 130
Reflocuon ot light, i. 545, 54G; sound,
i. 51 1

Refie.v action of spinal cord, i. 34G. — acts,
i. 277, 382. — movements, i. 347, 382 ; re-
spiratory, i. 34G ; ii. 428, 429 ; sympa-
thetic, i. 393

Refraction of light, i. 549, 5.50
Regeneration of the tis.sues, ii. GG3
Regurgitation of food, ii. 50. Contents of
crop by pigeon, ii. 13G
Relations between Organic and Inorganic
Kingdoms, i. 148. Between Animals,
and Plants, and llineraU, i. 148. Be-
tween Animal and Vegetable Kingdoms,

i. 139. Of Man with Animals, i. 118.
Of Man and Animals with Plants, i.
139. Of Man with e.xtcrnal nature, i.
IbS

Renal arteries, ii. 370, — veins, ii. 370.
— vessels in animals, ii. 393. — excre-
tion, ii. 3G5

Renal portal system in animals, ii. 2G7,
2G8. 393

Rennet-bag of Ruminants, ii. 131
Reparation, i. 112; ii. 275. — of the

tissues generally, ii. GGl ; — in animals,

ii. GGl. Separate tissues in man, ii. GG2,
GG3

Reparative force, ii. GGl. Phenomena, ii.
28G

RniM»mrrT[ox of the individual, ii, 275,
580. — of Vegctables,ii. 581,590, — of

Animals, ii. 582. Equivoc.al or spon-
taneous, ii. 580, 589. — of Vertebrata,
ii. .583. — Mammalia, ii. 597. — Bii-ds,
ii.593. — Reptiles, ii. GOO. — Amphibia,
ii. GOO. Fishes, ii. GOO. Mollusca, ii. .583.
Molluscoida, ii. .583, 685, .587. Annu-
losa, ii. 583, 585, .58G. Annuloida, ii.
583, 8(1. Ccnlenterata, ii. .582, 583, 586.
Pi-otozoa, ii. 580, 582, 583-58G. Insecta,
ii. 584, 587, Crustacea, ii. 583, 585.
Entozoa, ii. 58G, 587. Echinodermata,
ii. 58G. Infusoria, ii. 580-583, 58G.
Bee, ii, 584. Aphides, ii. 583, 585.
Tienia, ii. 586. Non-sexual, ii. .582.
Sexual, ii. 583. Fissiparous, nr by divi-
sion, ii. 582, 586, .589. Genimiparous,
or by buds, ii. 582, 589. Oviparous, ii.
583,591. Hermapln'odite, ii. 583. Par-
thenogenetio, ii. 5.84-589. Alternate,
ii. 585, 589. Ovoviviparous, ii. 600. Vi-
5'iparous, ii. 591. Of a lost part, ii. 275.
Reotilia. Prehension of food, ii. 118.
Teeth, ii. 123, 124. Jaws, ii. 127. S.ali-
vary glands, ii. 128. Pharynx, ii. 129.
CEsophagus, ii. 137. Stomach, ii. 137.
lutegnments of, i. 473. Intestines, ii.
137.138. Cloaca, ii. 138. Liver, ii. 144.
Gall-bladder, ii. 146. Pancreas, ii. 147.
Lymphatic hearts, ii. 186. Portal cir-
culation, ii. 2G7. Heart, ii. 265, 266.
Aortic arches, ii. 266, 2G7. Pulmonary
and systemic circulations, ii, 266. Renal
portal system, ii. 267. Respiration, ii.
490, 491. Spleen, ii. 342. Supra-reual
bodies, ii. 342. Thyroid body, ii. 342.
Thymus gland, ii. 343. Kidneys, ii.
392. Thorax, ii. 490, 491. Lungs, ii.
490, 491. Tongue, i. 483. Touch, i.
472. Taste, i. 483. Smell, i. 498.
Hearing, i. 522, 523. Sight, i. 601. Heat,
ii. 504. Ova of, ii. 600. Locomotion on
solids, i. 224, 225 ; in fluids, i. 229, 230 ;
in air, i. 234, 235. Voice, i. 271. En-
cephalon, i. 405, Cerebrum, i. 407, 408,
•111, 412, 413. Cerebellum, i. 413, 411.
Spinal cord, i. 415. Vagus nerve, i.416.
Corpora bigemina, i. 412. Reproduc-
tion of, ii. GUO
Reserve air, ii. '132, 433
Residual air, ii. 432, 433
Resonance of sounds, i. 2G2
Resorption, ii, 1<84

Resimhatiox, Organs of, ii. 404. Air-
passages, ii. 404; — ciliated, ii. 423.
Bronchi, ii. 405, 406. Lungs, ii. 406-
414; air-cells, ii. 412, 413; air-sacs, ii.
411, 412; arteries, bronchial, ii. 414,
pulmonary, ii. 413; bronchia, ii. 410;
intercellular passages, ii.41 1,412 ; lobes,
ii. 408,409; lobules, ii. 409 : lymphatics,
ii. 414 ; nerves, ii. 4 14 ; parenchyma, ii.
409 ; jileura, ii. 407, 408 ; veins, bron-
chial,ii. 414, pulmonary, ii. 1 14. Thorax,
ii. 404 ; cavity of, ii. 404 ; framework
of, ii. 404 ; openings of, ii. 404. Trachea,'
ii. -lOI-lOG

function of, i. 114; ii. 401. Ao-

Y V 2

692

INDEX,

RES

ti-i-ity of. related to mmiber and size of
red L'orpuscles, ii. 4,n(;. Air. clmnges of
ill, ii. 435 ; in coniporition, ii 43G, 438,
in moisture, ii. 435, 430, 437, in tem-
periiture, ii. 435. 436 ; complemental, ii.
43'i, 433 ; composition of dry, ii. 438 ;
effect ot a single respiration on, ii. 438 ;
ingress of, facilitated, ii. 420 ; resi rve,
ii. 432, 433 ; residual, ii. 432, 433 ; sup-
plemental, ii. 432. 433 ; tidal, ii. 432,
433 ; quantity of, inspired and expired
in 24 hours, ii. 436. Artificial respira-
tion. ii. 478, 479, 480, 4.81. Breatliing-
air, ii. 432, 433. Carbonic acid, elmiina-
tinn ot, ii. 439-443 ; e.xperimeuts on
quantity given off, ii. 439-442 ; quantity
given off in 24 hour-s, ii. 443 ; how modi-
fied, ii. 403-469. Capacity of chest, ex-
treme dtlterenlial, ii. 432. Chemical
processes, how modified, ii. 403-469.
Cilia, use of in, ii. 423. Disorders of, ii.
420, 430 ; from injury to thoracic walla,
ii. 420, 421. Effects of, on the blood and
tissues, ii. 444-402 ; on colour of the blood,
ii. 444, causes of, ii. 445-4.50 ; on fibrin of
the blood, ii. 450 ; — gases of the blood,
ii. 451-402 ; — temperature of the blood,
ii. 450, 451 ; of other gases than air on,
ii. 469-473 ; of impure air in, ii. 482-487.
Elastic force of lung in, ii. 422, 423. Em-
bryonic, ii. 012, 013, 039. Gases, dif-
fusion of, in, ii, 4.53-4.57. Immediate
effect of, ii. 402. Importance of, ii. 403.
Nervous system, influence of, on, ii.
427-430. Nitrogen, elimination of, ii.
443. Organic matter, elimination of,
ii. 444. Oxidation process, object of,
ii. 402; seat of, ii. 457-401. Oxygen,
absorption of, ii. 438, 439 ; explanation
of interclianges of gases in, ii. 452-402 ;
source of, ii. 403 ; quantity modified, ii.
463-465. Period ot a, consists of three
stages, ii. 425. Pulse-respiration ratio,
li. 425 ; in disease, ii. 425. Varieties of,
abdominal, ii. 417, how hindered, ii. 417;
diapliragiuatic, ii. 417 ; costal inferior,
ii. 417, superior, ii. 417 ; mimher of per
minute, at different ages, ii. 424 ; num-
ber of circumstances wliicli modify the,
ii. 424, 425 ; pectoral, ii. 417. Khythm
of, ii. 424 ; atfected by nervous system,
ii. 427—430. Soimds ot, various, ii. 420,
427. Spirometer, a measure of, ii. 432.
Intestinal, ii. 100. Mechanism of, ii.
414. Movements of, reflex, ii. 428 ;
Movements ot expiration, ii. 421^24 ;
jiartly piu«sivo, ii. 421 ; elasticity of lung
in, ii. 421, 422; muscles concerned in,
ii. 423, 424 ; wallsof air-cells, Used in, ii.
•■23 ; in Birds, active, ii. 489 ; force of,
ii. 42(i. Movements ot inspiration, ii.
414-420; first, at birth, ii. 429; chief
work of, ii. 420 ; enlargement of thorax
in, ii. 415-417 ; force of, ii. 420, in full,
ii. 435 ; ingress of air, how facilitated,
ii. 420; imisclcs concerned in, ii. 417-
419 ; supplementary uses of, ii. 431-432.

RUN

Nerves, afferent and efferent of, ii. 428,
429; effect of division of, ii. 429, 430.
Nervous centre, le noeud vital, or vital
knot, i.354, 35,5 ; ii. 428,429. Substances
oxidised in,natirreof, ii. 461. Temporary
suspension of, ii. 470-478. Ultimate
uses of, ii. 402. \ ital capacity of chest,
ii. 432, 433, 434,435 ; how influenced, ii.
434, 435. Want of breath, feeling of. ii.
427, 428. In animals, ii. 488-502 ; aerial,
ii. 402, 488—196 ; aquatic, ii. 403, 490-
502 ; in warm-blooded animals, ii. 522 ;
in cold-blooded animals, ii. 522 ; in
Mammalia, ii. 488 ; Birds, ii. 488-490 ;
Reptiles, ii. 490,491, 522 ; Amphibia, ii,
491-493, 497, 498; Fishes, ii. 493, 494,
498, 499 : Mollu.sca, ii. 494, 499, 500 ;
Molluscoida, ii. 500 ; Annulosa, ii. 494-
490. 500, 501 ; Annuloida, ii. 501 ; CcE-
lenterata, ii. 501 ; Protozoa, ii. 501 ; in
Insects, ii. 495, 490 ; in Plants, ii. 402.
Resuiratoi-y food, ii. 6, 537, 547, 561 ; — dis-
turbances produce diabetes, ii. 341, 589 ;

— tract, ii. 428.

Restiform bodies, i. 309, 310
Retching, ii. .50

Rete mucosum, i. 449
Retia mirabilia in animals, ii. 205, 208
Reticulum of Ruminants, ii. 130
Retina, i. 531, 539; ii. 622. Action of,
i. 509. Corre,sponding parts of, i. 577
Retinal elements, i. 540. — images, extra-
retinal, i. 692; intra-retinal, i. 693.

- - impressions, i. 586
Rheoscopic limb of a frog, i. 289
Rhonchi, ii. 426, 427

Rhythm of the heart, ii. 215. — of respira-
tory acts, ii. 424
Rhythmic contraction, i. 160
Ribs, i. 10 ; li. 617

Rigidity of death, or rigor mortis, i. 173,
175 ; ii, 009. Probable causes of, i. 170.
Time of occurrence, i. 175
Rivinian duct, ii. 55
Rods of Corti. i. 508, 519
Rodextia. Digestive organs, ii. 132, 134.
Digestive glands, ii. 144, 145, 140.
!suprn-rennl boilies, ii. :)42. Touch, i.
471. Sight, i. 698. Locumotion, i. 222.
Cerebrum, i. 407, 408, 409, 411, 413.
Cerebellum, i. 414

RoTiKEiiA. Disrestive organs, ii. 141.
Digestive glands, ii. 129, 143, 148.
Water-vessels, ii. 274. Re.<i)iration, ii.
601. TottcU, i. 472. Hearing, i. 625.
Sight, i. 007. Locomotion, i. 233
Rumen ot lUiminauts, ii. 130
Rumlxa.ntia. Digestive organs, ii. 130,
131,134. Digestive glands, ii. 128,144,
145, 140. Bone of heart, ii. 205. Mam-
mary glands, ii. 363. Smell,!. 497. Sight,
i. .598, 599. Locomotion, i. 220, 221,
222. Cerobrum, i. 407," 409, 410, 411.
Ccrebcllnm, i. 414

Rumination, ii. 131, 132. Reflex charac-
ter of, ii. 132
Running, act of, i. 216

INDEX,

693

SAL

C ALIYA, i. UO. Flow of, aided by miis-
^ color contraction, ii. flo. Influence
of nervous system on secretion of, ii. .5.i,
56, 57. Effect of mercury on flow of,
ii. 56. Chemical composition of, ii. 57.
Corpuscles of, ii. 57. Cause of alkalinity
of, ii. 5S. Action of, ii. 84, 85. Sulpho-
cyanide of potas.sium in, ii. 58. Present
in upper part of duodenum, ii. 106
Salivary bladder in Ant-eater, ii. 128
Salivary glands, i. 26, 110; ii. 54. Sub-
lingual, i. 26 ; ii. 55. Parotid, i. 26 ; ii. 54 ;
Submaxillary, i. 26 ; ii. 65. In animals,
ii. 128, 129

Salivin, or ptyalin, i. 84 ; ii. 85
Salts, absorption of, ii. 176. Of urine, ii.
385. Of blood, i. 91 ; ii. 293. Use of in
body, ii. 293, 540. Destination of in
body, ii. 540

Sanguification, i. 113 ; ii. 276, 277, 314.

In animals, ii. 342, 343
Sapidity, i. 481
Sarcin or Sarcosin, i. 85
Sarcode, movements of, i. 182
Sarcolemma, i. 49

Sarcous elements of musc'e, i. 43, 50
Satiety, sensation of, i. 445
Scalte of cochlea, i. 506
Schneiderian membrane, i. 485
Sclerotic, i. 531. 536

ScOLECin.t. Digestive organs, ii. 141. Re-
spiration, ii. 501. Locomotion, i. 233
Scole.x, ii. 586

Scorbutus, or Scurvy, ii. 295
Sebaceous glands, i. 69, 459
Sebaceous matter, ii. 395
Secretion, i. 113; ii. 343. Definition,
ii. 275, .343. Performed by glands or
membranes, ii. 344. Products of, like
or different to those in blood, ii. 344.
Products of, usually crystalloid, ii. 345.
Influenced by epithelial cells, ii. 316 ;
by various conditions, ii. 348 ; by quan-
tity of blood, ii. 348 ; by <iuality of
blood, ii. 348 ; by external stimuli, ii.
349 ; by nervous system on, i. 394 ; ii.
849-351. Cause of different secretions,
ii. 346 , 317. Epithelial cells essential to,
ii. 347. Con.stant, intermittent, or re-
mittent, ii. .352. Special, in animals,
ii. 395. Movement of, along ducts, ii.
352. Comparefl with nutrition, ii. 353,
3'd; — with excretion, ii. 345, 316
Secretions, particular (nee those .Secretions)
Secreting membranes and glands, i. 68, 69
Sediments, urinary, ii. 385, 386
Segmentation of yolk, ii. 6113
Segmeutsof body, mode of balancing, i.212
Segments, dorsal, ii. 615
Semicircular canals of ear, i. .506, 520 ; ii.
623

Semilunar cartilages, 1. 193
Sensation, i. I08, 272, 293, 380. Centres
of, i. .337. Conditions of, 1. 426. Defini-
tion of, i. 425. Effect of repetition, i.
431. In general, i. 425. Laws of, i. 419.
Paths of In spinal cord, 1. 339. Special,

SOB

i. 433. Suspension of, i. 432. Velocity
of impressions, i. 430

Sensations. Aftereffects, i. 4 31. Associ-
ated, i. 431. Connected with circulating
sy’stem, i. 446. Connected with respira-
tory organs, i. 446. Duration of, i. 430.
Effect of alternating, i. 432. Internal
or corporeal, i. 441 ; nervous, i. 441 ;
muscular, i. 441. Outward projection
of, i. 429. Peculiaritiesof, i. 432. Radia-
tion of, i. .345. Transference of, i. 345.
Variety of, i. 433
Senses of animals, special, i. 439
Senses, i. 425. Varietiesof, i. 433. Organs
of (see Separate Senses)

Sensibility, property of nervous tissues, i.
101, 272, 293

Sensori-motor acts, i. 348, 382
Sen-nrium, common, i. 360. True, i. 3o9,
361

Sensory fibres of nerves, i. 277. Stimuli,
i. 426 ; objective, i. 426 ; subjective, i.
427

Septum of auricles, ii. 636. — of ventricles,
ii 636

Serous membranes, i. 68
Serous secretions, ii. 364. Chemical com-
position, ii. 364
Serum of blood, i. 65
Shell and shell-membraue of egg, ii. 595
Shouting, ii. 4311
Sighing, i. 266 ; ii. 431
Sight, i. .526-554. lu animals, i. 597-007.
Information given by .sense of. i. .574,
583. Loug and short, i. 563. Org.ansof,
i. 526

Sigmoid flexure, ii. 40
Singing, i. 260 ; ii. 430
Single vision with two eyes, i. 576
Sinus urogmiitalis, ii. 611, 631. — ter-

minalis, ii. 634

Sinuses of Valsalva, ii. 193, 194. — of au-
ricles, ii. 189, 193
Sipping, ii. 27
Skeleton, i. 7

Skeleton, development of, ii. 615. A'er-
tebrate, development of, ii. 653
Skin, i. 13, 449 ; ii. 395. In animals, i. 473.
Development of, ii. 618. Fatty secre-
tion, ii. 395. Perspiration, ii. 396-400.
Exhalation of water by, ii. 396 ; of car-
bonic acid, ii. 401). Absorption of oxygen
by, ii. 400; of nitrogen, ii. 400. In-
torru))ted action of, ii. 401
Skull and spinal column, cavity of, i. 19.
Skull, development of, ii. 616
Sleep, i. 396, 432. Amount requiri'd, i.
399. Causes of, i. 398. Effect on animal
heat, ii. 505

Smell, i. -191 . Acuteness of, i. 495. After
sensations of, i. 495. Conditions of. i.
492. Organs of, i. 4.84. Organs and
sense In animals, i. 496. Sense of, i. 484.
Snapiiing turtle, ii. 539
Sneezing, ii. 130, 431
Snoring, ii. 431
Sobbing, ii. 431

694

INDEX

soc

Socket or cavity of joints, i. 191
Softening, ii.

SoLll’EDS. Digestive organs, ii. 132, 134.
Digestive glands, ii. 14fl, 14G. Sight, i.
.")9.S, 599. Locomotion, i. 220
Solitary glands of intestinal canal, i. 113 ;
ii. 158

Somatic death, ii. 065
Somnambulism, i. 491
Sound and its propagation, i. .599. —

colours, i. 51 1 , 529. Communication and
excit.ation of, i. i>10

Sounds, pitch of, i. 253. Strength or in-
tensity of, i. 2-53. Tone or timbre of, i.
253. Their production and modification,

i. 2-52. Of heart, ii. 209-213 ; ch.aracters
of, ii. 209 ; causes of, ii. 210, 211

Speaking, i. 260 ; ii. 430
Species, reproduction of, ii. 580, ,587
.Specific gravity of Human Body, ii. 532.
Of organs (given with the Organs). Of
animal fluids and tissues, i. 78 (Table)
Spectra, i. 590
Spectroscope, ii. 440

Spectrum, solar, i. 540. Absorption or
dark bands of, ii. 440. Colour b.ands of,

ii. 446. — analysis, ii. 440 ; — of blood,
ii. 447

Speech, i. 200. Imperfections of, i. 208
Sperm-cell, ii. 583, 589, 042 ; — force, ii, 001
Sijermatozoa, ii. .589, 602
Spertnotheca, ii. .584, 001
Spherical aberr.ation, i. 552, 550
Sphincters, ii. 49
Sphygmogr.aph, ii. 230-238
Spigelian lobe, ii. 07
Spina bifida, ii. 010

Spinal canal, i. 21. Column,!. 7. Acces-
sory nervo, i. 317, 335. Cord, i. 24, 108,
294,297, 311; eentral canal of, i. 313;
central gi'ey commissure of, i. 312;
columns of, i. 311 ; enlargements of, i.

31 1 ; functions of, i. 338 ; reflex action
of, i. 340; of .Tertebrata, i. 415; efTcct
of injury of, on respiration, ii, 429 ;
efl'ect of in glycogenic function, ii. 341 ;
Development of, cord, ii. 010, 019. —
nerves {nee Nerves)

Spirometer, ii. 432
Spitting, ii. 430

Splanchnic nerves, influence on glycogenic
function, ii. 341

SlT.unx, i. 33, 71, 113 ; ii. 320. Dc.scription
of, ii. 320. Coats of. ii. 321. Trabeculiu
of, ii. 320, 321. Parenchyma or pulp, |
ii. 320, 321. Coloured cells of, ii. 321. <

lUalpighian coriniscles, ii. 321. Arte-
ries, ii. 321. Veins, ii. 322. Capillaries,
ii. 321. Lymph.atics. ii, 322. Nerves,
ii. 322. AVhlte blood corpuscles formed
in. ii. 323. Corpuscles formed in, ii. 323.
Bed eor))U.scles di.sintegrated in, ii. 323.
tliemical composition, ii. 321. Variable
size. ii. 321. I’rohablo ollice, ii. 324. In
nuiinals, ii. 312. Development of, ii.
031, 058

Sponyida, reproduction of, ii. 582, 583, 580

STR

.Spongilla, ii. .580

Spontaneous amputation, ii. 001. — com-
bustion, ii. 523. — generation, ii. 580
Squint, i. 534
Stammering, i. 208

Standing, i. 213. — at ease, i. 213. — on
one leg, i. 213
Stapes, i. 593 ; ii. 025

Starch, vegetable, i. 80. Action of saliva
on, ii. 84, 85 ; of bile on, ii. 90 ; of pan-
creatic juice on, ii. 98; of intestinal
juices on, ii. 102. Destination of, in
body, ii. 541. — eiinivnlent, ii. .541. In
daily food, ii. 536

Starch, animal, ii. 78. Formed by hepatic
cells, ii. 335

Starvation, i. 445; ii. 549. In Animals,
ii. 548

Stasis of red corpuscles of blood in inflam-
mation, ii. 280

Starics of H uman Body. ii. 532—550

Stature of Human Body, ii. 533

Steam Engine, IVoi'k of, ii. 5.54, 500.

Compared to work of body, ii. 554, 500
Stearic acid. i. SO
Stearin, i. 80
Stenonian duct, ii. 54
Stcreomonoscope, i. 582
Stereoscope, i. 581
Sterni flssura, ii. 017
Sternum, i. 10 ; ii. 017
Stethoscope, ii. 209
Stigma, ii. 594

Stimuli, action on the nerves, i. 273.
Exciting muscular contractility, i. 150.
Of nervous excitability, i. 272. Of the
retina, i. 594. Of sensation, i. 420. Of
vital projxirties of animal tissues, i. 103,
150 ; external stimuli, i. 103 ; internal
stimuli, i. 104 ; mental stimuli, i. 104.
Of vital properties, action of, i. 103,
104

Stolon, in animals, ii. 582
Stomach, i. 31. 110. Description and
structure of, ii. 35-38. Digestion seen
in, ii. 92, 93. Function of. ii. 3,8.
Jiovenients of. ii. 39. Alveoli of, ii. 58.
Tnbuli or glands of. ii. 5,8-oo. Peptic
cells of, ii. 00. Solitary glands of. ii. 01.
Post-mortem digestion of. ii. 89. 140.
Of Saint Martin, ii. 01 , 87, 90-93. Gases
contained in, ii. 105, 100. Juice of, ii.
01. Coats of, ii. 30. Temperature of,
ii. 87. In Mammalia, ii. 130-133. In
linminantia dividial into four distinct
cavities, ii. 130, 131. In Birds, ii. 134,
135. In lloptilos, ii. 137. In Amphibia,
ii. 138. In Fishes, ii. 138. In Mollusca,
ii. 139. In Jlollnsooida, ii. 140. In
Annulosa, ii. 140, 141. In Anmiloida,
ii. I ll, 142. Closed sacs of. ii. 331. In
animals, ii. 130-142. Development of,
ii. 025

Strabismus, i. 534
Stridnlation, i. 271
StringcHl instruments, i. 253
Strohila, ii. 580

INDEX,

695

STU

Stuttering, i. 2fiS
Subarachnoid fluid, i, 205
Subcutaneous areolar tiis.-uc, i, 13
Subjective sensory stimuli, i, 427, 4fiC, 470,
4,S2, 405, 521 , 595, — “ Ego,” i, 378
Sublingual glands, i, 20 ; ii, .55
Submnxillary glands, i, 2G ; ii, 55
Submergence, effect of, in syncope, ii, 478
Succus entericus, ii, SO
Sucking, il, 2(i, In Mammalia, ii, 117
Sudoric acid, ii, 397

Sudoriferous or sudoriparous gl.ands, ii, 39G
SUG.VK, 1, 8(1, Grape, glucose, or dextrose,

i, 8G, Inosite, 1, SG, Lactin, or sugar
of milk, i, SG, Absorption of, by veins,

ii, 17G : by lacteals, ii. 17G. From tran.s-
formation of glycogen, absorbed by he-
patic veins, ii. 33G. Average cinantity
in liver of man and animals, ii. 337.
Found in liver of iinimals, ii. 337. Pro-
portion in different kinds of blood, ii.
337. Trommer's test for, ii. 85. Effect
of covering animals with varnish on
formation of, ii. 340. Accumulates for
hybernation, ii. .340. In diabetes, ii.
340, 389, 544. In urine, ii. 375,389. In-
creased or diminished by medicines, ii.
340. Increased by section of splanchnic
nerves, or of sympathetic in neck, ii,
341 : by disturb^ respiratory functions,
ii. .141 , 5Sil ; by irritating floor of fourth
ventricle, i. 35G, 394 ; ii. 340, 341 ; by-
certain portion of the cerebro-spinal
axi.s, ii. 341. Ite.^-trained by section of
vagu.s nerves, or of cord, below origin of
phrenic nerves, ii. 341. Destination of
in body, ii. .541,

Sulci of cerebellum, i. 307. — of cerebrum,
1. 300

Sulphocyanirte of potassium, of saliva ,ii. 58
Sun-stroke, ii. 51 1
Supination, i. 242.

Supplemental air, ii. 432, 433
Suppuration, ii. 28G

Suprarenal bodies, i. 31, 74. 113 ; ii. 325.
Description of, ii. 325. Structure of,
ii. 325, 32G. Functions of, ii. 32G. In
animals, ii. 342

Suspended respiration and animation, ii.
47G

Sutures, i. 21, 188. Dentate or serrated,
i. 188. I.imbou.s, i. 188. Sfiuamons, i.
188. Fal.se. i. 188

Stvallowing, ii. 27-35 (.we Deglutition)
Sweat, ii. 39G (see Perspiration)

Sweat glands, i. G9, 114; 11. 3I)G
Swimming of animals, i. 228. — of man,
i. 227

Sympathetic Ganglia and Nerves, func-
tion.? of, i. 38G. Nerves, i. 31 , 3.f ; action
on vessels, i. 391 ; section increases
glycogenic function, ii. 341
Sympathetic ner\ons system, i. 294, 322.
In animals, i. 41G. Influence of, on se-
cretion and excretion, ii. 349-351. In
Vertelwata, i. 41G
Synopta, 1. 424

TAD

Synarthroses, or immovable joints, i. 188
Syncope, death by, ii. CGG
Synovia, or joint-oil, i. 12, 189 ; ii. 3G5
Synovial capsule, i. 189. — membranes, i.
12, G8

Syntouin, or fibrin of muscle, i. 82. Origin
of, ii. 290, 544

Systole of ventricles, ii. 204 (see Heart)

gtABLES showing : —

(1) Analysis of 1000 parts of blood, i.
90. (2) Animal functions, i. 117. (3)
Cranial nerves and their functions, i.
331. (4) Analysis of azotised substances,
i. 98. (5) Analysis of organic proxi-
mate constituents, i. 9G. (G) Measure-
ments of eyeball, i. 544. (7) Quantities

of water, chloride of sodium, and phos-
phate of lime contained in 1000 parts of
certain tissues, fluids, Ac., of the body,

i. 94. (8) Senses, i. 437. (9) Size of

red blood corpuscles in animals, i. 77.
(10) Size of structural elements of tis-
sues, i. 77. (11) Specific gravity of

certain animal fluids and tissues, i. 78.
(12) Ultimate chemical elements of
body, 1. 100. (13) An.alysis of organic
proximate constituents of vegetable food,

ii. 8. (14) Analyses of food, ii. 115.

(15) Length of intestines in different
animals, ii. 133. (IG) Circumference of
auriculo-ventricular and arterial open-
ings, ii. 193. (17) Sounds and move-

ments of the heart, ii. 212. (IS) Com-
position of milk in woman, the cow,
goat, sheep, ass, and mare,li. 3G2. (19)
Daily quantity of constituents of urine
for lib. weight of body substance in a
man of 1451bs. weight (Parkes), u. 37G.
(20) Composition of 109 parts of solid
constituents of urine (Lehmann), ii.
37G. (21) Air used in respiration, ii.

433. (22) Percentage comimsition, in

volumes of air, before and after it has
been once breathed, ii.438. (23) Oxygen
and Carbonic acid in venous and arterial
blood, ii. 451. (24) Weights of the va-

rious parts and organs of the body, ii.
633. (25) Proportions of proximate

con.stitueuts of body, ii. 534. (2G)

Daily food of adult man in ounces, ii.
63G. (27) llelations between proximato
con.stituents of food and those of body,
ii. 537. (28) Daily Ingosta and their

compo.sition, ii. 539. (29) Daily Egessta

and their composition, ii. 539. (3U)

Various daily dietaries (Playfair), il.
5G3. (31) Dietaries iinderdilVercntcon-

ditions of rest and e.xercise (Playfair),
ii. 5G3. (32) Valno of food, as n sonreo

of motor power (Frankland), ii. 575

Tachometer, ii. 228

Tactile corpuscles or nxilo bodies, 1. 4.54.

Tadpole of frog, circnlntiou in, ii. 2G9.
— newt, circnlation in, 11. 2GU, 270 ;
respiration in, ii. 497

696

INDEX,

TiE

Tajuia, reproduction of, ii. 580. Ova of,
li. 601

Tartar of teeth, ii. 58
Taste, after impressions, i. 482. Charac-
ter of sense of, i. 479. Conditions of
exercise of sense of , i.478, 481. Organ of,

i. 474. Nerves of, i. 315, 310, 477, 478.
Sense of, 1. 474, 477. Subjective impres-
sions, i. 482. Without sapidity, i. 481.
In animals, i. 483, 484.

Taurin, i. 85 ; ii. 70.

Tauro-chenollc acid, ii. 77.

Taurocholic acid, i. 85 ; ii. 76.

Tears, i. 530.

Teeth, i. 110. Formulse of milk and per-
manent. ii. 12. Description of, ii. 13-
16. Milk, ii. 12, 14. 15; peculiar do
Mammalia, ii. 119. Permanent, ii. 12-
14. Structure of. ii. 1.5-18. Period of
eruption of, ii. 1.8-21. Use of the dif-
ferent, ii. 22. Canine, ii. 13. Incisor,

ii. 13. Bicuspid ii. 13. Molar, ii. 13.
Pulp of, ii. 15. Peculiar to Vertehrata,
ii. 119. Of Mammalia, ii. 119, 120 ; de-
velopment of, 11. 629; influence of sex
on size of, ii. 122. In Beptiles, ii. 123,
124. Amphibia, ii. 124. Fishes, ii. 124-

126. Denticles of Non-vertebrata, ii.

127, 128. Absent in Manis and the
Myrmecophaga, ii. 120 ; in Eoliidnn, ii.
120 ; in Birds, ii. 119, 123. Dovelopmeut
of, ii. 627, 629. Tissues, development
ii. 660

Temperature, sense of, i. 459, 467. Of
body, &c. {see Heat) Of animals, ii.
503 {see Heat)

Tendons, i. 13
Tentorium, i, 21

Testis, ii. 589. Development of, ii. 632
Tetanus, i. 157

Textures in the tongue and larynx of a
sheep, i. 39. Of the body, i. 38
Thalamus opticus, i. 304
Thallogens, i. 140
Thaumatrope or stroljoscope, i. 588
Thebesius, valve of, ii. 189
Thermal sensations, i. 467
Tliirst, i. 443

Thoracic duct, i. 31 , 111. Description of,
ii. 1-54, 155. In Birds, two, ii. 186
Thorax, i. 27. Capacity of. ii. 432. In
Mammalia, ii. 488. Birds, ii. 488, 489.
Reptiles, ii. 491. Amphibia, ii. 491
Thymus gland, i. 74, 113. Description,
ii. 329. Function, ii. 330, 331. In
animals, ii. 343. Development of, ii.
631, 6.58

Thyroid body, i. 74, 113. Description of,
ii. 327. Goitrous enlargement, ii. 327,
328. Function, ii. 328. In animals, ii.
342. Development of, ii. 631, 658
Thyroid cartilage, i. 250
Tidal air, ii. 432, 433
Timbales, i, 271

Tis.sub.s. Chemical composition of, i. 87.
Microscopio structure, i. 42 ; absorbent,
i. 65 ; ii. 658 ; adipose or fat, i. 45 ; ii.

TUB

647 ; areolar, i. 42 ; ii. 646, 663; blood, .

i. 62 ; ii. 657 ; bloodvessels, i. .57 ; ii. 6.56, .
663; cartilage, i. 45; ii. 648 , 6.52 , 663;:
connective,!. 42 ; ii. 646, 663 ; dental, ii. .
15, 16, 17, 628, 660 ; elastic, i. 44; ii. .
647 ; epidermic, i. 72; ii. 659. 663 ; epi-
thelial, i. 72; ii. 6-59, 663; fibre.s, plain
muscle, i. 48 ; ii. 654, 663 ; fibres, strijad .
muscle, i. 49 ; ii. C-54, 663 ; fibro-carti-
lage, i. 45 ; ii. 648 ; fibrous tissue, i. 43 ;
glands, i. 68 ; ii. 659 ; Isicteals, i. 67 ;
lymphatics, i. 66 ; ii. 0-58; marrow, i. 45;

ii. 649 ; mucous membranes, i. 69 ; mus-
cular tissue, i. 48 ; ii. 654, 663 ; nervous
tissue, i. 52 ; ii. 655, 663 ; non-va.scnlar
tissues, i, 62, 72 ; osseous tissue or bone,
i. 46 ; ii. 6-18, 663 ; secreting membranes,
i. 68 ; skin, i. 68 ; ii. 618 ; serous mem-
branes, i. 68 ; synovial membranes, i.

68 ; yellow cartilage, i. 45 ; ii. 648. ,
Physical properties, i. 79 ; development
of {see Development) ; rei)aration of {see
Reparation). Size of structural elements
of, i. 76 (Table). Specific gravity of, i.

78. Structural elements of, i. 75. Blas-
tema or matrix, crystals, granules,
liomogeneous or structureless mem-
brane, nuclei, nucleated cells, simple
fibres, nucleated fibres, compound fibres,
tubes, vesicles, protoplasm, i. 75. Vital
properties,!. 101. All are e.vtra-vascu-
lar, ii. 279.

Tone of voice, nasal, i. 262. — veiled, i.
263

Toxgue, nerves of, i. 477. Papilla; of,

i. 475. Parts of, i. 474. Structure of, ,

ii. 25, 26. Use of, in mastication, ii. 25 ;
in deglutition, ii. 29. Closed sacs of, ii. i
331. InBirds, i. 245, 246. In Gasterojxrda, '
ii. 127

Tongued instruments, i. 253-255
Tonicity of muscle, i. 162. 351 i

Tonsils, i. 26 ; ii. 27. Present in Mam-
malia, ii. 129. Clo.scd sacs of, ii. 331
Tor]«does, electrical, ii. 528—531
Touch, as the tactile sense, i. 459. After .
sensations of, i. 465. Delicacy in differ-
ent parts of the body. i. 461. Education *
of, i. 466. Hallucinations connected
with, i. 467. In ormation conveyed by '
the sense of. i. 459, 465. Organ of. i. |
449. Sensation exciteii by internal J
causes, i. 466. Sense of, i. 449. Sense 1
and organs in Anim.ils. i. 471—174
Trachea, i. 26 ; ii. 404-406. Of Insects, *
ii. 403, 495
Trance, ii. 669

Transformation {see Metamorphosis)
Transfusion of blood, ii. 298
Tri :eminal or trifacial nerve, i. 314. 332.
Third division, lingual or gustatory
nerve, i. 315, 316, 477, 478
Trochlear joints, i, 190. Nerve, i. 314, 332
Trommer’s test for sugar, ii. 390
Trunk, i. 7

Tube, Eustacliian, ii. 502, 516. Fallopian,
ii. 598

INDEX

697

TUB

Tuhuli uriniferi, ii. 3(iS. In animals, ii.

Tulp, valve of. ii. 48
Tumours, ii. -’8.5

Tunicata. amyloid substance in, ii. 335
Tympanum or middle ear. i. 501. Muscles
of, i. 504, 517. Ossicles of, i. 602. — and

its bone.', development of, ii. B24, 625
■ Types of form in animal series, i. 133.
Annuloid type, i. 135. Aunulose type,
i. 133. Cielenterate type, i. 135. ilol-
luscoid ty pe. i. 13-5. Molluscous type. i.
133. Pp-tozoic type, i. 135. Verte-
brate type, i. 133
Typlilosole of Annelida, ii. 141
TyrubUi, i. 85

T’LCF.R, ii. 286

Ulceration, ii. 185, 286
intimate chemical con.stituents of the
I boily, i. 94. Table of elements, i. 100
I Uliimum moriens, i. 163 ; — and primum

1 viveus, ii. 307

I Umbilical vesicle, ii. 609, 610, 626. Arteries,
ii. (ill, 614, 63-5, 639. Opening, ii. 611.
Cord, ii. 614. Vessels, ii. 611. Vein, ii.

, 614, 635, 639

f Unity in variety in animals, i. 1-38
I Upper limb of man, adaptations, i. 239.

Stnicture of, i. 240
I Urachus, ii. 611., 631

; Urmmic poisoning, ii. 379

Un a, i. 85 ; ii. 376, 377. Mode in which it is
obtained, ii.376, 377. Source.s of, ii. 377,
378. Effect of retention of, ii. 379.

! Quantity e.vcreted, ii. 377, 378, 379.

E.xcretion of, increased, ii. 379. As a
measure of work, ii. 565. Not dependent
on exercise, ii. 568, 571. Dependent on
food, ii. 568, 571. Source of, ii. 544, -545.
Increased by food more than by exercise,
ii. 546. Relation to mental work,ii. 566,
678

Ureters, i. 31 ; ii. 366. Effect of ligature
of, on blood, ii. 373

Uric acid, i. 85; ii. 379. How obtained,
ii. 3,80. Quantity diminished, ii. 381 ;
e.xcretcd, ii. 380, 381. Quantity increasd,
ii. 381. E.xcreted by Keptiles, ii. 380;
by Birds, ii. 380 ; by Mollusca and An-
nulosa, ii. 394 ; in chalk stones, ii. 381 .
Calculi, ii. 387

Urina potfis, ii. 375. — cibi vel chyli, ii.
375. — sanguinis, ii. 375
-1 Urinary bladder, inversion of, ii. 373, 374.
i htrueture of, ii. 374
I Urinary organs. Development of, ii. 631
1 Urine, ii. 371. Casts in, ii. 373. Albu-
minous, M, 373, 389, 390. Passage of,
from kidneys to bladder, ii. 373, 371.
E.xcretion of, rapid and constant, il. 373,

374. Influence of nervous system on ex-
cretion of, ii. 374. Dally (piantity ex-
creted,ii. 374. Partly solid in Birds and
Keptile.s, ii. 372. In Bright's disease, ii.

375. In diabetes mellitus, ii. 375. lle-

VEI

action of, ii. 375, 383, 384. Composition
of, ii. 375, 376. Water of, ii. 376. Urea
(see Urea). Uric acid (see Uric acid).
Hippuric acid, ii. 381, 382. Creatin and
creatinin, ii. 382, 383. Uro-h;ematin or
colouring substance, ii. 383. Extractive
matters, ii. 3,83. Lactic acid. ii. 383.
O.xalic acid, ii. 384. Salts, ii. 385. Sedi-
ments, ii. 385, 386. Calculi, ii. 386, 387.
Substances which enter it unchanged,
ii. 387. Alkaline in llerbivora, ii. 387,
388. Most substances enter it changed,
ii. 387. Rapidity with which .soluble
substances pass into, ii. 389. Bile in,
ii. 389. Sugar in, ii. 389. Albumen in,
ii. 389, 390 ; how produced, ii. 390 ; in
Bright’s disease, ii. 390; how detected,
ii.390. The most complex animal ex-
cretion, ii. 391

Urn-genital sinus, ii. 611, 631
Uro-luematin, li. 383
Ui'opygii glanduliE, of Birds, ii. 396
Uterus, ii. 598. Venous sinuses of, ii. 615.

Various lorms of, ii. 633
Utricle, primordial, ii. 642
Uvula, i. 26 ; ii. 27. Absent in animals,
except in higher Quadrumana, ii. 129

■yAGI nerves (see Pneumogastric nerves)

' Valsalva, Sinuses of, ii. 193, 194
Valve of Thebesius, ii. 189. Eustachian,
ii. 189. Tricuspid, ii. 191. Semi-lunar,
ii. 192, 194. Mitral or bicuspid, ii. 194.
lleo-ctecal, ii. 48. Absent in Monotre-
niata, ii. 134 ; — some Edentata, ii. 134;
— certain Cheiroptera, it. 134 ; — Ce-
tacea, ii. 134; — Birds, ii. 136. Indis-
tinct or absent in Amphibia, ii. 138. No
distinct, in Fishes, ii. 138. Of 'Pulp or
Bauhin, ii. 48. Of veins (see Veins).
Of lymphatics (see Lymphatics)

VAlvulai conniventes, ii. 44

Varicose veins, ii. 2-54

Vasa serosa, ii. 242. — vasorum of arteries,

i. 68 ; — of veins, i. 59
Viiscular glands (see Ductles.s glands)
Vasi-motor nerves, inlluence of, i. 389
Vaso-dentine in tlio Fish, ii. 125
Vegetable albumen, i.4, 8. — cells,!. 141 ;

ii. 64l. — Kingdom, general outlines, i.
139. — motion, i. 183. — textures, i. 14 1.

Vegetative functions, i. lib ; ii. 1 ; nutri-
tive, i. 11b ; reproductive, i. 117.

Vhixs, i. 18, 1 1 1. Circulation through, ii.
247-257 ; systemic, ii. 248 ; pulmonary,
ii. 248; causes of, ii. 248-2511; muscular
)ire.ssurc aids, ii. 250, 251 ; respiratory
movements aid, ii. 251,252; valves, ii.
•2-')b, 252, 253. Diverticular action of, ii.
25b. llhythmio contractions in, il. 25b.
Effects of gravity on circulation in, ii.
253 , 2.54. Varicose, ii. 2,54. Rate of
motion of blood in, ii. 254 ; increases
near the heart, ii. 254, 255. Disturbing
causes of, 11.255. Valves of, i, 59; ab-
sent in portal, ii. 2-:<5 ; and in hepatic.

INDEX,

69 S

YEN

ii. 255 ; in cranium, ii. 255 ; in lungs, ii.
257. In Birds, ii. 2(i5. In Pishes, ii.
2BS. Introduction of air into, fatal, ii.
222. Structure of, i. 5S. Development
of, ii. 65C. Cardinal or primitive, ii.
6it7. Umbilical, ii. 614, 6-35, 6.32. In-
terlobular, ii. 72. Sublobuhar, ii. 72.
Intralobular, ii. 72

Vena cava, superior i. 29 ; ii. 265 ; double
in some animals, ii. 265. Inferior, i. 29, 31
Venaportie, ii. 69. Development of, ii. 635
Venous absorption, ii. 168-171. — blood,
i. 90 (see Blood). — heart in eel, ii. 268
Ventricle of cerebellum, i. 308. Irritation
of floor of fourth, produces diabetes, i.
356, 394 ; ii. 340, 341

Ventricles of the cerebrum, i. 299, 306.

— of heart, ii. 190, 193
Ventriculus bulbosus in Birds, ii. 135.

— succeuturiatus in Birds, ii. 135
Ventriloquism, i. 268

Vermicular or peristaltio contraction, i.
160 ; ii. 44, 45

Vermiform appendix, i. 33 ; ii. 46. Exists
in the ape, gibbon, and wombat, ii. 134
Vermiform processes of cerebellum, i. 307
Vertebne, i. 21. Development of, ii. 615
Vertebral column, i. 7. Adaptations to
erect posture, i. 211
Vertebral gi'oove, ii. 606, 608
Vertebral plates, ii. 608
Vertecbata. Characters and Classes, i.
121, 124. Placental, ii. 613. Impla-
Cf-ntal, ii. 613. Warm-blooded, i. 125.
Cold-blooded, i. 125. Abranchiate, i.
125. Branchiate, i. 125. Pulmouated
or air-breathing, ii. 264. Warm-
blooded, ii. 264. Cold-blooded, ii. 264.
Branchiated or water-bi'eathing, ii.
264. Touch, i. 471—174. Taste, i. 483,
484. Smell, i. 496. Hearing, i. 522-
524. Sight, i. 597-603. Locomotion
on solids, i. 218-225 ; in fluids, i. 228-
233 ; in air, i. 234-239. Voice, i. 269-
271. Encephalon, i. 405, 406. Cere-
brum, i. 406-413. Cerebellum, i. 413,
414. Pons Varol, i. 414. Medull.a
oblongata, i. 414. Spinal cord, i. 415.
Cranial and spinal nerves, i. 416. Sym-
pathetic nervous system, i. 416. I’re-
hensiou, i. 244-246. Nervous actions, i.
417—119, Cerebral lobes, 1, 412. Olfac-
tory lobes, i. 412. Optic lobes, i. 412,
Blood glands, ii. 342. Integument, i.
47.3. Nervous system, i. 403—119. Cir-
culation, ii. 264-271. Kidneys, ii. 391-
391. Blood corpuscles, quantity of, ii.
518. Oi'gans of digestion, ii. i30-139.
Digestive glands, ii. 128, 143, 144, 14.5-
148. Uospiratiou in, ii. 488-191, 497-
499. Pharynx, ii., 129, 130. Stomach and
intestines, ii. 130-139. Gastric glands,
ii. 143. Livor,ii. 143, 144. Call-bladder,
ii. 145, 146. Pancreas, ii, 146, 147,
Ih'ehcusion of food, ii. 117,118. Teeth,
ii. 119-126. .Taws, ii, 126, 127. Sali-
vary glands, ii. 128

WAR

Vertebrate skeleton, development of, il.
653

Vertigo, i. 442

Vesicle, germinal of Purkinje, ii. .590, .592,
593. Bhustodermic, ii. 603. Umbilical,
ii. 609, 610. Auditor}', ii. 622. Gr.aa-
fian, ii. 597. Optic or ocular, il. 621,
Cerebral, ii. 616, 619
Vesicular re.spiratory murmurs, ii. 426
Vessels and Nerves, General position of,

i. 18

Vessels (see Bloodvessels and Lymphatics)
Vestibule of labjTinth of ear, i. 506, 519
Vibrations of solid bodies, i. 252
Villi, intestinal, ii. 44. Structure of, ii,
157, 1.58. In both small and large in-
testines in Birds, ii. 137. — of chorion,

ii. 599, 612

Visinsita, i. 101, 156, 173. — musculosa,i,
101, 156, 173. — nervosa, i. 102, 291
Visceral plates, arches, and clefts, ii. 6'24
Vision, double, i. 576, 577. Field of. i.
572. Of objects in erect position, i. 571.
Range of, i. 663. Single, i. 579. With
two eyes, i. 575. In animals, i. 598-
607 '

Vital action or Life, i. 105. — capacity of
the chest, ii. 432-435 ; how modified, ii.-
434,435. — force, i. 105, 291. — knot, i.
354 ; ii. 428. — properties of tissues, i.
101; contractility, i. 101, 156; sensi-
bility, i. 101; formative pro])erty, i.
102 ; uses of, i. 1 05. ■ — stimuli, i. 104, 157.
— contractility, i. 101
Vitality, i. 105. — of the blood, ii. 299
Vitellin, i. 81

Vitelline membrane, ii. 590, 596. Duct,
ii. 609, 610. -Arteries and veins, ii. 634.
Ca'cmn, ii. 610
Vitellus, or yolk, ii. 590
Vitreous humour, i, 542, 555 ; ii. 622
Vitro-dentiue, ii. 125

Vocal apparatus in man, i. 259. Cords, i.
25il ; sui)erior or false, i. 250 ; true. i. 251.
Vibratory action of. i. 255. Fremitus,
ii. 427. Resonance, ii. 427
Voice and Speech, i. 248. In Man, organs
of, i. 248. Modification of. i. 261. Per-
sonal quality, i. 262. Quality or timbre,
1. 260. Strength, i. 261. Varieties, i.
260. Production and characters, i. 255.
In animals, i. 269-272
Volition, seat of, i. 339
Voluntary motion, i. 381
Vomiting, ii. 50-53. An antiperistaltio
act, ii. 50. Contraction of stomach in,
ii. 50. Anti])eristnltic action of msopha-
gus in. ii. 51. Influence of abdominal
muscles in, ii. 51, 52. A rclie-x act, ii.
52. Cerebral, ii. 53. From emotional
causes, ii. 52
Vowel sounds, i. 266

' ' Want of breath, i. 446 ; ii. 427
Warm-blooded Animals (see Animals)

INDEX.

699

WAT

Water, use of in system, ii. 515. Destina-
tion of in body, ii. 540. Constitutional,
ii. 015. Formation of in body, ii. 514.
A.S a constituent of the body, i. 94.
Importance of pure, ii. 487, 4SS
Water-bag of Ruminants, ii. 130
Water-cells of paunch in camel tribe, ii.
130

Water-vessels of Eutozoa, ii. 497. — of
Rotitera, ii. 274. — of Scolecida, i. 129
Weight of body, ii. 533. At birth, ii. 694.
— of Organs of the body, ii. 534 ; effect
of starvation on, ii. -548
Whartonian duct, ii. 55
Whey, ii. 359
Whispering, i. 266
IVhistling, i. 268 ; ii. 430
White substance of brain, composition of,
i. 87.

Will, i. .367, 37 1 , 374, 375, 379, 380
Wind-instruments, i. 2.53
Wind-pi[)e, i. 26, 115 ; ii. 404-406
Winking, i. 530
Wirsung, canal of, ii. 78
Wolffian bodies, ii. 611, 631
Work, daily of man, ii. 559 ; of horse, ii.
559, 564 ; of ox, ii. 564 ; compared with
ste.am-engine, ii. 560. Modes of, in re-
lation to food, ii. 561. Electric, ii. 555,
577. Photic, ii. 555. Nutritive or as-

ZOO

similative, ii. 555, 576. Mental, ii. 555,
578. Mechanical, ii. -555, 559, 561 ;
transformed into heat, ii. 575. Nervo-
musoular, ii. 555, .578. Calorific, ii.
5.55, 558, 561.; Varieties of in body, ii.
555

Worms, heat of, ii. 503
Wounds, healing of, ii. 287

^ANTHIN, i. 85

yawning, i. 383 ; ii. 431

Yellow cartilage, i. 46 ; development
of, ii. 648

Yellow spot of the eye, i. 54ff ; ii. 623
Yolk, ii. 590, 593. — sac, ii. 590,626 ; of

birds, ii. OKI. Cleavage or segmenta-
tion of, ii. 003. Formative and nutri-
tive, ii. 591, 593. Germ- and food-, ii.
592, 693, 597. — vesicles, ii. 597.

70-AMYLINE, ii. 3.35
' ^ Zona pellucida, ii. 591, 599
Zoological Anatomy, objects of, i. 118.

Physiology, objects of, i. 118
Zoo-sperms, ii. 590

THE END.

I.OXDOX

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