SYLLABUS

A COURSE OF LECTURES

PHYSIOLOGY

J. BURDON-SANDERSON, M.D., LL.D., F.R.S.

JODRELL PROFESSOR OF PHYSIOLOGY IN UNIVERSITY COLLEGE, LONDON

SECOND EDITION
I

LONDON
H. K. LEWIS, 136 GOWER STREET, W.C.

i879

LONDON t

PRINTED BY H. K. LEWI'S,
136 GOWER STREET.

J>

PREFACE.

IN the new edition of the Syllabus of my Lectures on
Physiology, I have followed the same arrangement as in
the last, with the exception that in the chemical part the
descriptions of immediate principles, which were before
printed separately, have now been incorporated in the
text. The whole has been revised, and some parts have
been much extended. Under the title " Practical Exer-
cises," I have added to the Syllabus instructions for labo-
ratory work relating to the chemical properties of the
animal liquids, and of the most important foodstuffs ; and
to the physiological endowments of living tissues and
organs. The experiments I have selected are of so simple
a character that, with the directions given and such aid
as he will readily obtain in the laboratory, every man who
takes pains will find it easy to carry them out successfully.
The chemical series already form part of the Course of
Practical Physiology. The others, which relate chiefly to
the properties of the excitable and contractile tissues, have
been hitherto omitted ; not because they are regarded as
of less importance, but for want of space — a difficulty
which will be removed as soon as our new laboratories are
completed. I cannot too strongly recommend their use
to all who desire to acquire a serviceable knowledge of
the elementary facts of physiology. They will also fulfil
another but less important purpose, that of aiding candi-

IV PREFACE.

dates in their preparation for the higher examinations in
physiology, of the University.

To the " Practical Exercises " I have added a series of
" Demonstrations." Under this heading I have given an
account of experiments which, although they are of such
fundamental importance that every student ought to wit-
ness them, cannot be advantageously repeated. These
are given during the winder session, all students who
have already attended the summer practical course being
invited to attend them.

CONTENTS.

PART I.

PAGE

THE CHEMICAL PROCESSES —

IMMEDIATE PRINCIPLES OF FOOD . . ,/'... . 2

DIGESTION 7

INTESTINAL ABSORPTION 16

BLOOD . 17

THE SPLEEN 22

LYMPH. . . . . . . . . 23

CHEMICAL PROCESS OF RESPIRATION 23

URINE .26

MUSCULAR TISSUE 31

NERVOUS TISSUE 32

EXCHANGE OF MATERIAL 33

PRODUCTION OF HEAT' ....... 41

PRACTICAL EXERCISES RELATING TO FOOD STUFFS ... 44

,, ,, ,, ANIMAL LIQUIDS . . 48

PART II.

MECHANICAL PROCESSES —
MUSCULAR CONTRACTION
CIRCULATION
THE HEART
RESPIRATION
BODILY MOTION .
VOICE AND SPEECH

55
59
66
68
70
72

vi CONTENTS.

PART III.

PAGE

FUNCTIONS OF NERVOUS SYSTEM —

NERVES 74

FUNCTIONS OF NERVE CENTRES 78

„ „ ROOTS OF SPINAL NERVES .... 80

„ „ WHITE COLUMN OF SPINAL CORD 81

CENTRES OF MEDULLA OBLONGATA 82

DEATH BY ASPHYXIA 9°

REFLEX OF SWALLOWING 91

REGULATION OF PERISTALTIC ACTION 92
INFLUENCE OF NERVOUS SYSTEM ON PROCESSES OF

SECRETION 94

REGULATION OF LOCOMOTION 97

,, ,, MOTIONS OF THE EYEBALLS ... 98

FUNCTIONS OF THE BRAIN 100

SENSATIONS AND PERCEPTIONS 103

TACTILE SENSATION ........ 104

MUSCULAR „ 105

VISION 105

HEARING 115

TASTE 119

SMELL 121

PRACTICAL EXERCISES RELATING TO THE PHYSIOLOGICAL
PROPERTIES OF THE ORGANS AND TISSUES OF THE NERVOUS

AND MUSCULAR SYSTEMS 123

DEMONSTRATIONS 139

N.B. — Before using the Syllabus the Student must make the
following corrections : —

P. 2, 1. 12 from bottom, for "when boiled" read "at temperatures above
73° C."

P. 3, 1. 4, for " bases " read "basis."

P. 3, 1. 4 from bottom, for "by the prolonged" read " by prolonged."

P. 9, 1. 22, for "dried gastric mucous membrane and hydrochloric acid"
read " expressed juice of gastric mucous membrane dried at a low tem-
perature. "

P. 10, 1. $,for "bases, by" read "by basic."

P. 12, 1. ii from bottom, for " stercobolin " read "stercobilin."

P. 14, 1. 5 from bottom, omit "having."

P. 15, 1. i, for " C6" read "C8," line n,for " H50" read "H5."

P. 12, 1. 25, for " solubility " read "insolubility."

P. 42, in the table, for "9069" read "9-069," and for "230" read "5-230."

P. 43, in the table, for "at 582 " read "X 0-582."

SYLLABUS OF A COURSE OF LECTURES

ON

PHYSIOLOGY.

PART I.
THE CHEMICAL PROCESSES.

ANIMAL life, as observed in man and the higher animals,
is an aggregate of chemical processes for which food and
oxygen afford materials, the products being heat, muscular
action, carbonic anhydride, water and ammonia. Food
essentially consists of albuminous bodies, carbonic hydrates
and fat, all of which undergo chemical disintegration in
the animal body, in addition to water and certain inorganic
salts. The fats and carbonic hydrates are the sources
from which the organism derives the material for muscular
action and the production of heat. Their carbon and
hydrogen leave the body as CO2 and H2O. Of the proteid
material used by the body, a part is represented in the
discharges by bodies of known chemical constitution con-
taining nitrogen (nitrogenous "metabolites"): theremainder
eventually leaves the organism as CO2 and H2O, but may,
in the meantime, take part in the production of fat, or of
other non-nitrogenous immediate principles.

Vegetable life is also a chemical process. Green plants
build up their tissues out of carbonic anhydride, ammonia
and certain inorganic salts. Colourless plants do not dis-
sociate carbonic anhydride, but derive their carbon entirely
from the soil on which they grow. The most important

B

2 IMMEDIATE PRINCIPLES

constituents of the tissues of plants are albuminous bodies,
and carbonic hydrates; for these exist in all plants. The
characteristic property of a plant is its power of forming
its tissues out of inorganic materials.

The term protoplasm is used to denote the apparently,
but not really, homogeneous substance which forms the
active parts of the tissues of plants and animals. It con-
sists chiefly of albuminous bodies, and exhibits in itself all
the essential phenomena of life : for in it, not only the
general actions which belong to the organism as a whole,
but the specific actions of particular parts, such as those of
muscle, nerve and gland, have their seat.

IMMEDIATE PRINCIPLES OF FOOD.

* ^ The term " immediate principle" or " proximate principle" (<rrot%stav) is
applied to any ' ' substance, " in the chemical sense, which exists as snch in
living organisms. It is tmderstood to be applicable to bodies which are met with
in the secreted liquids, as well as to the constituents of the blood and tissues.

ALBUMINOUS BODIES (PROTEIDS).

Proteids are non-crystallizable bodies of unknown constitution, of which
the centesimal composition is about Carbon 53, Hydrogen 7*5, Nitrogen
1 5 '5, Oxygen 23, Sulphur I *o. They are soluble, or capable of imbibition
with water, insoluble in alcohol or ether. They are all stained yellow by
nitric acid, and then disintegrated, leaving a yellow precipitate which dissolves
orange red in ammonia.

Aqueous solutions of proteids are Isevo-rotatory. When a solution is sepa-
rated from water by a septum of colloid membrane, the proteid diffuses with
extreme slowness into the water.

They occur in the tissues or fluids of plants and animals under two prin-
cipal forms, distinguished from each other according as they are coagulated or
remain in solution when boiled.

The coagulable proteids comprise the albumins proper, which are soluble in
water, and the globulins, which are insoluble, but are readily held in solution
in presence of neutral salts, particularly NaCl. From these (often called
native albumins) the mass of the proteid material of animal and vegetable
tissues is formed,

The albuminatcs are soluble in aqueous liquids, only when these are acid
or alkaline : they are precipitated by neutralization. They must be regarded
as derivates from the others ; for bodies which correspond entirely in their
characters with those albuminates which exist in the tissues of plants and
animals can be obtained by the prolonged action of alkalies or acids on
coagulable proteids.

OF FOOD. 3

Albuminoids. — There exist in the animal body several substances which,
although close allied to the proteids, are separated from them by several well-
marked differences. One of these, Collagen, is of great importance, as yield-
ing Gelatin. It constitutes the "organic bases " of bone, and is the most
important constituent of the connective tissues generally. Gelatin is the pro-
duct of boiling "collagen." It swells in cold water, but does not dissolve ;
its solution in hot water "gelatinizes" on cooling. It is precipitated by
tannin and corrosive sublimate, not by acetic acid and potassic ferrocyanide.
Chondrin, a similar product obtained from cartilage, is distinguished from
gelatin by being precipitated by acetic acid.

CARBOHYDRATES.

Cellulose. — The material of the outer membrane of the plant-cell is un-
affected by dilute acids or alkalies, but is converted by strong sulphuric acid
into a body which is coloured blue by iodine.

Starch is the chief constituent of the " Starch grains " contained in the cells
of plants ; in these grains it is enclosed in concentric envelopes of an insoluble
body resembling cellulose ; it is soluble in water, the solution being opalescent ;
it is coloured blue by iodine ; the blue colour disappears on heating, but re-
appears on cooling, unless the heating has been long continued. Starch is
converted by prolonged action of weak acids into Dextrin (a body which is
coloured red by iodine), and eventually into grape sugar. It is converted in
presence of diastatic ferments, e.g., those of the salivary glands, pancreas, and
liver into grape sugar.

Grape Sugar or Dextrose or Starch Sugar (C6 H12 O6) occurs in extremely
small quantity in blood, muscle, and other tissues, and (according to Briicke)
in normal urine. It is distinguished by its power of reducing certain metallic
salts, by its dextro-rotatory action, by its splitting, when subjected to the
action of the yeast-plant at a suitable temperature, into alcohol and carbonic
acid, and by its yielding lactic acid in presence of albuminous bodies in process
of putrefaction. It is soluble in \\ parts of cold water, and to any extent in
boiling water. From its solution in boiling alcohol, it readily crystallizes.
On the power of reduction possessed by grape sugar depends the important
test known as "Trommer's Test," which consists in adding solution of
potassic hydrate to the liquid supposed to contain sugar, and then weak
solution of cupric sulphate, so long as the precipitate of cupric hydrate first
formed redissolves on agitation. On gently heating, a yellow precipitate is
formed of cuprous hydrate, or a deposit of cuprous oxide (see Practical Part,
Section II.)

Milk Sugar or Lactose constitutes about 15 percent, of the solids of milk :
it can be obtained directly from whey, after separation of albuminous com-
pounds, by crystallization in rhombic prisms (CI2 H22 On -f- H2 O) : it is con-
verted by the prolonged boiling with weak acids into fermentescible sugars
(galactose and dextrose) ; it is transformed very readily into lactic acids
under the influence of a ferment usually present in milk.

Cane Sugar does not occur in the animal body, but is an important con-

B 2

4 IMMEDIATE PRINCIPLES

stituent of food. When boiled with dilute acids, cane sugar is converted into
dextrose and levulose. A similar change takes place in gastric digestion.

FATS.

Palmitin (C3 H5 (C16 H31 O)3 O3) and Stearin (C3 H5 (CI8 HM O)3 O3),
which in solution in olein constitute animal fat, are insoluble in water, soluble
iri hot alcohol, ether, chloroform, benzole, &c. Under the influence of super-
heated steam they are decomposed, taking up water and yielding glycerine
and Palmitic and Stearic acids respectively. (C3 H5 (C,6 H3, O)3 O3 -f 3 H2 O
= C3 H5 (H3) O3 + 3 Ci6 H32 O2.) A similar change takes place more
gradually under the influence of pancreatic secretion in the intestine, as well
as in presence of albuminous bodies in putrefaction. Alkaline palmitates and
stearates (Soaps) are obtained when fat is dissolved in potash or soda with the
aid of heat ; such soaps exist in bile. When fat becomes rancid, it not only
undergoes transformation into acids and glycerine, but takes up oxygen, in
consequence of which volatile and pungent acids belonging to the same series
(Cn H2n O2), but containing less carbon, are formed.

Palmitin fuses at 40° C., Stearine at about 60° C. According to the pro-
portion in which they exist in different kinds of fat, the fusing points of such
fats vary. Thus, \vhile beef fat fuses at 37° C., and contains three parts of
Stearin and Palmitin to one part of olein, human fat, which contains less
Stearin and relatively more olein, fuses at 25° C. Olein (C3 H5 (C18 H33 O)3
O3), is the fluid fat in which stearin and palmitin are dissolved. Olein solidifies
a few degrees above freezing point, and is more soluble than the other fats in
ether. Palmitic Acid (C16 H32 O2) and Stearic Acid (C18 H3G O2) are crystalline
bodies, chiefly distinguished from each other by their relation to heat, the
former fusing at 62° C., the latter at 70° C. Their relations to solvents cor-
respond with those of the fats. Palmitic acid crystallizes from its solution in
hot alcohol in bunches of fine needles ; stearin in shining plates. Oleic Acid
(C18 H34 O2), which belongs to the series Cu H2n _ 2 O2, fluid at ordinary
temperatures, is decomposed by strong potash, potassic palmitate and acetate
being produced.

Butyrine (Ca H5 (C4 H7 O) O3) and the corresponding glycerides of other
volatile acids (capronic, caprylic, and myristinic) occur in small proportion in
butter.

FOOD.

F/esfrowes its nutritive value to its albuminous and colla-
genous constituents, its fat and its salts. Lean meat (beef)
contains about 25 per cent, of solids, of which 18 percent,
is albumin, and yields about 2 per cent, of gelatin to
boiling water. Flesh of young animals (veal) yields 5 to
10 per cent. The interstitial fat of meat varies in quantity
from 4 to 1 5 per cent.

OF FOOD.

5

Meat yields to warm water at 60° C. about 3 per cent, of
albuminous material and nearly as much extractive. On
boiling the aqueous extract, the albumin coagulates (as
scum), but when the boiling is long continued some of it
redissolves (Mulder). Consequently the quantity of albu-
minous material contained in bouillon, always small, varies
according to the mode of preparation. It may be increased
by the addition of a trace of hydrochloric acid to the
water used. Bouillon, beef tea, and other similar products
owe their value, partly to the gelatin, but chiefly to the salts
and extractive which they contain. "Liebig's Extract"
contains neither proteid nor gelatin.

Meat, when roasted, retains its juice, which, from the
comparatively low temperature of the internal parts (indi-
cated by the colour) does not coagulate. The tenderness
which meat acquires by keeping is due to conversion of
some of its myosin into albummate. Cooking is useful,
not only as preparatory to digestion, but as destructive of
parasites and of morbid and septic products.

Milk. — All of the constituents of milk are of nutritive
value. Cream consists chiefly of casein and butter; Butter
contains, in addition to the ordinary fats (Palmitin, Stearin,
and Olein), about 2 per cent, of the glycerides of the
volatile acids; Biitter milk consists of sugar, casein and
salts ; Whey of sugar and salts; Cheese of casein with
variable quantities of butter, and of the products of de-
composition of both. Human milk contains less than 4 per
cent, of casein, between 3 and 4 per cent, of butter, and
from 4 to 5 per cent, of sugar. In Colostrum the casein is
partly replaced by serum albumin. Cows' milk contains
much more casein than human milk, but no more sugar :
consequently, when the former is diluted, as a substitute for
the latter, milk sugar (which as crystallized from whey
always contains calcic and potassic phosphates) must be
added. Cows' milk always contains a small percentage of
albumin.

6 FOOD STUFFS.

Eggs. — Eggs contain about 73 per cent, of water, 15 of
albumin, and 12 of fat. Yolk of egg yields lecithin (see
" Nervous Tissue ") in considerable quantity, and vitellin,
a proteid body analogous to paraglobulin (see "Blood").

' Vitellin is obtained when yolk of egg, which has been previously extracted
with ether, is treated with solution of common salt. It is precipitated on the
addition of water.

Cereals, Pulses and other Vegetable Foods. — Wheat flour
derives its alimentary value from its large percentage of
proteids (13 per cent.) and starch (73 per cent), but chiefly
from its containing gluten, and its consequent adaptedness
for bread-making. In the fermentation of dough, grape-
sugar splits into alcohol and carbonic acid under the
influence of the yeast-plant. By this means the dough is
raised. In baking, the dough is subjected to a very high
temperature (i 50° C. to 200° C.). Most of the starch becomes
soluble, and much of it is converted, especially in the crust,
into dextrin. Notwithstanding the destruction of sugar
in fermentation, a loaf weighs about a quarter more than
the flour used to make it. Rye flour, nearly as rich in
proteids and starch as wheat, is also used for bread-making,
but yields a less perfect product. It contains more cellu-
lose and less albuminous substances. Barley and Oatmeal
cannot be so used, as they yield no gluten. They also
contain less proteids (5 to 10 per cent.) Barley owes its
importance to its being a source of diastase and grape-
sugar. Maize, although poor in albuminous bodies, is rich
in starch, but in both these respects it is exceeded by rice.
Rye and maize are severally liable to a parasitic disease
which renders the grain morbific. The Pulses owe their
value to the legumin they contain, and to their large per-
centage of proteid (23 to 25 per cent.) Potato contains
75 per cent, of water. In the dry state it contains about
8 per cent, of proteid and 70 per cent, of starch. Its
cellulose becomes gelatinous by boiling, and is thus soluble

DIGESTION. 7

in the digestive liquids. Fruits and succulent vegetables
owe their nutritive value to the sugar and to the organic
acids and the salts which they contain. Their percentage
of albuminous material is very small.

Inorganic Salts of Food. — Beef yields, when dry, about
4 per cent, of ash, potash constituting more than two-thirds
of the total bases. The most important potassium salts are
phosphate and chloride. The proportion of sodium salts
is very small. In boiling meat, nearly the whole of its
alkaline salts pass into the bouillon. Wheat flour contains
about 2 per cent, of ash, of which one-third is reckoned as
potash and nearly half as phosphoric anhydride. The
constitution of the ash of potatoes and other juicy vege-
tables is similar, but the yield of phosphoric acid is relatively
less ; the percentage of potash is about four times as great
as that of all the other bases together. Milk yields about
2*5 per thousand of ash, of which about I per thousand
is reckoned as potash, 0*25 as soda, and about o'4 as lime.

In an adequate diet comprising 250 grammes of meat,
and 400 grammes of bread, the former would yield 1*5
gramme of potash, the latter r6. An adequate diet of
milk (two and a half litres) would yield about 3 grammes.

DIGESTION,

including the Physiology of the Liver and Pancreas.

Human saliva, the mixed secretion of the submaxillary,
parotid, and sublingual glands, and of the mucous glands
of the mouth, is a tenacious, slightly turbid, and slightly
alkaline liquid ; it contains about half per cent, of solids,
of which about half is inorganic. The organic constituents
are albumin, globulin, mucin, and a diastatic ferment ; the
salts are those of the blood, but the proportion of earthy
bases is larger. Ferric salts colour saliva blood-red : this
reaction is due to sulphocyanate of potassium, which it

S DIGESTION

derives from the parotid. Its mucin is derived from the
submaxillary, and its ferment chiefly from the same
source. Its turbidity is due to salivary corpuscles, and
epithelial elements. The salivary secretion of the dog
(submaxillary) contains no ferment, and no sulphocyanate.
It yields a very large proportion of CO2 to the mercurial
vacuum.

Saliva owes its value in digestion chiefly to its diastatic
ferment, but it is also of use as a solvent and lubricant.

Digestion in tJie Stomach.

The relative importance of gastric as compared with
salivary digestion varies in different classes of animals
according to the nature of their food. In the carnivora
the food enters the stomach unchanged, and remains there
for many hours. The stomach is of relatively large size,
and its whole surface is provided with peptic glands. In
the herbivora, as, e.g., in the horse, the thoroughly masti-
cated and insalivated food is retained only for a very short
time in the stomach. The organ is accordingly very
small, and only a part of its mucous lining is digestive.

Human gastric juice is a colourless transparent liquid
of very low specific gravity (1005). It contains neither
albumin nor mucin, and may be regarded as a solution of
pepsin, hydrochloric acid, chloride of sodium, and other
salts. It is secreted by the peptic cells of the glands of
which the digestive part of the mucous membrane chiefly
consists. The secretion takes place in answer to mechan-
ical or chemical stimulation of the mucous surface ; the
act is attended with increased circulation of blood in the
mucous membrane.

The process of gastric digestion consists in the trans-
formation of the albuminous bodies of the food into acid-
albumin and peptone (parapeptone), under the combined
influence of pepsin and of a free acid. In the dog, the

IN THE STOMACH. 9

gastric juice can be proved to contain free hydrochloric
acid, for the quantity of chlorine in it is considerably more
than sufficient to combine with all the metals present.
As regards human gastric juice the proof is less complete.
Lactic acid is present in chyme whenever carbohydrates
are being digested. It has been found that hydrochloric
acid can be replaced by phosphoric acid, as well as by
acetic and other acids of the same series.

Pepsin, although resembling the albuminous bodies in
chemical composition, exhibits none of their distinctive
characters. It exists in gastric juice in a state of imperfect
solution, so that it can be removed from it by mechanical
means ; on this fact Briicke's method of preparing pure
pepsin is founded. It is capable cf taking part in the
digestion of albuminous substances, even in the smallest
quantity, provided that the liquid is not too dilute, and
that it does not contain too large a proportion of the
product of digestion — peptone. In the process, the pep-
sin neither increases, diminishes, nor undergoes any loss of
activity.

The substance commercially known as pepsin consists
of dried gastric mucous membrane, and hydrochloric acid.
A solution of pepsin which possesses its digestive proper-
ties is obtained by extracting fresh mucous membrane
with glycerine.

In animals that die during digestion, the stomach
digests itself after death. During life such digestion is
prevented by the alkalinity of the tissues. Chyme, as
it leaves the stomach, contains remains of animal and
vegetable structure, unaltered starch grains, fat particles,
and (after milk diet) curd particles. It does not normally
contain bile. It yields a mixture of gases in which there
is much less oxygen than in common air, and a larger
proportion of CO2.

Peptone differs from proteids in the readiness with which it diffuses
through animal membranes. It resembles them in chemical composition

10 SECRETION OF BILE.

(approximate composition of gastric peptone in 100 parts — Carbon 49,
Hydrogen 7, Nitrogen 15, Oxygen 28, Sulphur i). It is soluble in water in
all proportions ; insoluble in alcohol or ether. Its solution diffuses readily :
it is unaffected by heat ; and, when acidulated with acetic acid, is not pre-
cipitated by ferrocyanide of potassium. It is precipitated by tannin bases, by
lead acetate, and by solution of Hg I2 in iodide of potassium.

Secretion of Bile.

Human bile contains 10 per cent, of solids, of which
about 4 per cent, is bilin, i^ per cent, fat, 2 per cent,
mucus and colouring matter, i to 2 per cent, alkaline
soaps, i per cent, salts. It is believed that about two
pounds of bile are secreted daily. The density of bile
differs according to the mode of collection and the time
of secretion. Bilin and fat originate, along with other
bodies, from proteid in the living substance of the liver
cells. The colouring matter is derived from that of the
blood. The mucin is secreted by the mucous membrane
of the gall bladder. In the intestines the bilin is decom-
posed under the influence of septic ferment organisms:
glycin and taurin are absorbed, and either return to their
source, or may take part in the production of such bodies
as hippuric acid, and tauro-carbamic acid, which appear in
the urine ; cholalic acid is in great part lost in the faeces.
The fats and soaps are absorbed. The colouring matter is
transformed by reduction into a body having the char-
acters of hydrobilirubin.

In intestinal digestion the bile is antiseptic, and there
is reason to believe that it also promotes the absorption
of fat.

Nothing is as yet known as to the influence of the
nervous system on the secretion of bile.

BILIN.

Bilin (or Bile crystals], as obtained from ox bile, consists chiefly of sodic
glycocholate (CK H42 Na NO6), with a much smaller proportion of tauro-
cholate (C26 H44 Na NO7 S). Bilin of dogs' bile consists exclusively of
taurocholate. These soap-like bodies crystallize from the alcoholic solution

BILIN.

II

of the dry residue of ox bile on the addition of ether. The crystals are very
soluble in water and have the peculiar bitter sweetness of bile. The solution
is dextrorotatory. With concentrated sulphuric acid it becomes resinous and
yields after a time a yellow liquid having a green fluorescence. If, after
adding a trace of cane-sugar, a liquid containing bilin is mixed with sulphuric
acid and kept at a temperature between 50° C. and 600 C., a purplish violet
solution is obtained, which shows before the spectroscope an absorption band
at E and another near F. Solution of ox-bile crystals is precipitated by the
addition of neutral acetate of lead. The heavy precipitate consists of lead
glycocholate. By treating its solution in hot alcohol with sulphuretted
hydrogen, filtering and adding water to the filtrate, glycocholic acid (CK H43
NO6) is obtained as a resinous precipitate. Glycocholic acid is sparingly
soluble in water, readily in hot alcohol, from which it crystallizes. When it
is boiled with strong hydrochloric acid it is converted into a soluble com-
pound of hydrochloric acid and glycocoll, which is very soluble in water, and
a resinous product, often called bile-resin, consisting of cholalic acid and
dyslysin (see Cholalic Acid). When the liquid from which the lead glyco-
cholate has been precipitated is treated with basic lead acetate, with the
addition of ammonia, a second precipitate is obtained of lead taurocholate.
By suspending the lead precipitate of dogs' bile in alcohol, decomposing it
with HaS, filtering, concentrating the filtrate, taurocholic acid (C^ H4,5 NO7S)
is obtained in solution. On the addition of ether a syrupy precipitate is
formed, which afterwards crystallizes. It differs from glycocholic acid in being
excessively soluble in water, and splitting much more readily into cholalic
acid and taurin, than glycocholic acid does into cholalic acid and glycocoll.

Glycocoll, Glycin or Gelatin-sugar (C2 H5 NOa or (as Amido-acetic acid] C2
H3 (NH2) O2) is obtained from glycocholic acid by prolonged boiling with
strong hydrochloric acid. The firm resin which is formed consists of cholalic
acid and dyslysin (see Cholalic Acid); this having been separated, the
remaining liquid yields on evaporation glycocoll-hydrochlorate (C2 H5 NO2, H
Cl). From the aqueous solution of this substance glycocoll is obtained by
treating it with hydrate of lead oxide and then decomposing the soluble lead
glycocoll, after separating the chloride, with sulphuretted hydrogen. Glyco-
coll is soluble in five parts of cold water, and insoluble in absolute alcohol
and ether. It crystallizes from hot dilute alcohol in hard rhombohedral
crystals. Its solution in water has an acid reaction and sweetish taste.
It is called "gelatin-sugar" because, along with the body Leucin, it is a
product which is obtained when gelatin is acted on by sulphuric acid. Glyco-
coll has been obtained synthetically by the action of monochloracetic acid on
ammonia. (C2 H3 Cl O2 + NH3= HC1 + C2 H3 (NH8) O2.)

Taurin (C2 H7 NSO3) is best obtained from the bile of the dog, in which
the whole of the bilin consists of taurocholate. By boiling bilin with hydro-
chloric acid, separating the resin and evaporating the acid liquid, a residue
is obtained from which (after the glycocoll-hydrochlorate has been removed
by extracting it with absolute alcohol), taurin can be procured by treating it
with boiling water. Taurin is soluble in fifteen parts of cold, and very soluble
in hot water, sparingly in cold alcohol. It crystallizes very readily in large
4- or 6-sided shining prisms, each of which ends in a 4-sided pyramid. The

12 BILIN.

constitution of taurin can be best understood by remembering how it is
obtained synthetically, viz., by subjecting ammonic isethionate (NH4, C2 H5,
SO4) to a high temperature, in consequence of which it loses the elements of
a molecule of water. Neither the origin nor the destiny of Taurin in the
organism is known. It was, until lately, supposed that it was represented
in the urine by sulphates, and that its amide took part in the constitution of
urea ; but it has been recently proved experimentally that when dogs are
fed with Taurin, that body leaves the organism partly as such, but chiefly in
the form of Tauro-carbamic acid (C3 H8 Na O4).

Cholalic Add (C24 H40 O5) is insoluble in water, very soluble in alcohol,
sparingly in ether. It crystallizes from its solution in dilute alcohol, in
tetrahedra or octahedra, which, at first transparent, soon become opaque on
exposure. At high temperatures, it loses H2O and yields dyslysin (C24 HL6
O3) and undergoes a similar change when boiled with hydrochloric acid. It
is contained in decomposed bile as alkaline cholalate, and is precipitated
therefrom on the addition of acetic acid. From this precipitate it can be
extracted by alcohol.

Bilimbin (Cholepyrrhin C32 H36 N4 O6) can be obtained directly from human
bile, or from that of the dog by shaking it with chloroform. On separating
the solution thus obtained from the bile and then distilling off the chloroform,
a pitchy residue is left, which, after it has been exhausted by alcohol, is found
to contain crystals of bilirubin. The alcohol contains cholesterin and a brown
colouring matter which has been called bilifuscin. Bilirubin is a principal
constituent of biliary calculi ; powdered gall stone is first extracted with ether
to remove the cholesterin, and then treated with dilute hydrochloric acid and
washed : the residue yields, when treated with chloroform, a yellowish-brown
solution, from which bilirubin is precipitated on the addition of alcohol, or
crystallizes on evaporation, in red needles. It is insoluble in water, nearly
insoluble in boiling alcohol and in ether, more soluble in bisulphuret of carbon,
and most of all in chloroform. Its solution shows no absorption bands. It
further dissolves readily in potash or soda, and when the alkaline solution is
exposed to air, it gradually becomes green, and gives, when treated with
hydrochloric acid, a green precipitate (biliverdin), which is insoluble in chloro-
form but soluble in alcohol. Bilirubin, in dilute alkaline solution, when acted
on by sodium-amalgam, yields Maly's Hydro-bilirubin, a red body insoluble in
water, of which the solution in absolute alcohol shows before the spectroscope a
broad absorption band, between E and F. It is supposed by its discoverer to
be identical with the colouring matter of faeces (stercobolin) and with the
•urobilin of Jaffe, from both of which, however, it differs in some particulars.
The physiological origin and destiny of the colouring matter in the bile is
known. It has been observed that when crystalline haemoglobin in solution
is injected into the circulation, the rate at which colouring matter is secreted
by the liver increases enormously, and that bile pigment appears in the urine.
In the intestines most of the bilirubin secreted is converted into stercobilin
and discharged, but the chemical relations between it and the excreted colour-
ing matters are as yet uncertain. Liquids which contain bilirubin change
colour on the addition of nitric acid containing a trace of nitrous acid : at first
green, the colour passes through blue, violet and red, finally fading into

INTESTINAL DIGESTION. 13

yellow (see Practical Part, Section VI.). During the change the liquid
shows, when examined spectroscopically, first two absorption bands near the
line D, which are due to the blue colour (cholecyanin], and subsequently a
single band between b and F, referable to the yellowish red colour (Jaffa's
choletelin). Bilirubin, or a body ^distinguishable from it, occurs in tissues in
which blood has been extravasated in rhombohedral crystals (called Haema-
toidin).

Biliverdin (C32 H36 N4 O8) occurs along with bilirubin in the bile of man
and many animals, especially in those of which the bile is green. Its relative
quantity increases in inanition. Both colouring matters are met with in the
placenta of the bitch.

Intestinal Digestion.

Pancreatic juice is an alkaline liquid resembling saliva.
It is, however, of greater density, and probably contains no
globulin. It owes its activity to two ferments — a diastatic
and a peptic — both of which are contained in the precipi-
tate which is thrown down when pancreatic juice is treated
with alcohol. They can be extracted either from the
gland itself (Hiifner) or from the precipitate (v. Wittich)
by glycerine. From either extract a substance is precipi-
tated by alcohol, which, at the temperature of the body,
digests fibrin and other albuminous bodies in alkaline
liquids, and acts diastatically on starch. This substance is
called Pancreatin. It contains a proteid body, to which
the name Trypsin has been given by Kiihne, and to which
its peptic property appears to attach itself. From the
glycerine extract a substance containing the ferments is
precipitated by alcohol. Pancreatic juice emulsionizes and
decomposes neutral fats.

It has lately been proved (Heidenhain) that the cell-
substance of the living pancreas is inert, but acquires
peptic activity by keeping, and more rapidly when acted
on by dilute acids.

Proteids, subjected to pancreatic digestion, split into
two products, viz., a body having globulin properties,
and a peptone. The former passes into a peptone (called
by Kiihne antipeptone), which undergoes no further change

14 INTESTINAL DIGESTION.

in the intestine ; the latter is decomposed, yielding leucin
and tyrosin and other products.

Simultaneously with the changes which are due to the
action of the pancreatic ferments, others go on which are
associated with the development in the liquid of septic
organisms (bacteria), and with the disengagement of offen-
sive odours. These are the production of volatile bodies,
Indol and Skatol, the disengagement of CO2 and CH4
from "the decomposition of certain carbohydrates, of H
from butyric acid fermentation, &c. The products of
pancreatic digestion of proteids are also incidents of the
septic decomposition of the same bodies, but the former
process is distinguished from the latter by its great
rapidity.

The liquid which is obtained when raw fibrin is digested for a few hours,
or at the proper temperature with pancreatic juice or solution of pancreatin,
contains, after it has been freed from undissolved residue, besides common
albumin, alkali-albuminate and peptones, crystalline organic bodies, of which
the most important are Leucin and Tyrosin. To obtain them, the albumin is
first got rid of by slightly acidulating the liquid, boiling and filtering. The
filtrate is then reduced to a small bulk by evaporation, and heated with strong
alcohol to precipitate the peptone. On again filtering, an extract is obtained
in which, if left to itself, Leucin and Tyrosin crystallize.

Leucin (C6 HI3 NO2), when pure, crystallizes in colourless pearly scales,
which sublime in flocks at 170° C. like oxide of zinc. In impure solution it
forms spheroidal clumps, which, under the microscope, are seen to be made
up of round grains, each of which consists of fine needles radiating from a
centre. Tyrosin crystallizes, on cooling from its solution in boiling water, in
bunches or stellate groups of long slender needles ; it does not sublime when
heated.

Leucin is soluble in 27 parts of cold water and in hot alcohol. Tyrosin
requires 150 parts of hot water to dissolve it. In boiling alcohol Leucin
dissolves, Tyrosin remains, so that by means of it the two bodies can be sepa-
rated from each other. Leucin, when heated in a sealed tube with fuming
hydriodic acid, yields ammonic iodide and caproic acid, and is therefore
regarded as amido- caproic acid (C6 H13 NO2 -f 3HI = C6 H12 O2 -f NH4
I + 2l). Tyrosin (C9 Hn NO3), when acted on in the same way, yields a body
(C9 Hj0 O3) which may be regarded as oxyphenylpropionic acid, having
ammonic iodide and iodine. The physiological destiny of Leucin is unknown.
As regards Tyrosin, the recent researches of Kiissner have shown that when
it is introduced into the circulation it reappears in the urine as such : it cannot
therefore be regarded as a step in the production of urea.

GLYCOGEN. 15

Indol (CG H7 N) is obtained by digesting large quantities of albumin with
ox-pancreas and distilling the product. The distillate contains Indol, which
may be separated from it by agitating it with its bulk of ether. Indol fuses at
52° C. and boils at 245° C. It is soluble in water, and crystallizes from its
solution in shining plates. When introduced into the circulating blood or
alimentary canal, an "indigo-producing substance " appears in the urine. It
exists, under normal circumstances, in extremely small quantity in the in-
testinal contents.

Skatol, a crystallizable body of offensive odour, resembling Indol, has been
lately discovered by Brieger as a constituent of human faeces. It has also
been shown that Phenol (Carbolic Acid, C6 H5, OH) is constantly present in
fseces.

An alkaline liquid, called Succtis entericus, of low specific
gravity, is secreted by the mucous membrane of the small
intestine. Its digestive properties are as yet uncertain.

Glycogen.

Glycogen, or animal starch, is under normal conditions
always present in the living cell-substance of the liver ; in
inanition it gradually disappears ; it is present in the livers
of animals fed exclusively on flesh. The glycogen of the
liver increases after each period of digestion. Its quantity
is in general determined by the quantity of dextrose-pro-
ducing material or of lactose in the food, so that these
sugars are the normal but not the only source of glycogen.
The processes by which glycogen disappears from the liver
in inanition, and by which it is normally disintegrated in
the animal organism, are not known. After death, the
glycogen of the liver is converted into dextrose under the
influence of a diastatic ferment.

Glycogen or animal starch is soluble in water, yielding an opalescent solu-
tion. It is coloured brown or reddish-brown by iodine. Glycogen is ob-
tained in quantity, by throwing the rapidly comminuted liver of an animal
just killed, during the period of greatest digestive activity of the organ, into
boiling water slightly acidulated with acetic acid. ..From the pale yellow
filtered and concentrated extract, glycogen is precipitated by the addition of
alcohol.

16 INTESTINAL ABSORPTION.

In tes final A bsorption .

In intestinal absorption the dissolved constituents are
absorbed by the blood stream, the particulate by the
lacteals. The proteids of chyle are absorbed partly as
peptone, partly as alkali-albuminate. They enter the
circulation both by the veins and lacteals, but it cannot be
stated in what proportion. It is not known whether
coagulable albumin is absorbed or not.

There is reason to believe that most of the dextrose into
which all carbohydrates are converted in digestion is
absorbed by the veins, but direct evidence is wanting : the
remainder undergoes the lactic acid fermentation in the
intestine.

The fats are absorbed both as glycerides in the state of
emulsion, and as alkaline soaps and glycerine. The absorp-
tion of water, in consequence of which the intestinal content
becomes more and more concentrated as it advances,
takes place by the capillaries, and is mainly due to " diffu-
sion." Consequently it may be diminished or reversed by
the presence in the intestinal liquid of salts of high " osmo-
tic equivalent."

Faeces consist of insoluble residues of food and bile, and
of insoluble salts ; particularly calcic, magnesic, and am-
monio-magnesic phosphates. They yield certain gases,
viz., CO2, marsh gas and a trace of sulphuretted hydrogen.
In human excrement a crystalline body called excretin
occurs.

Diffusion of liquids. — When two liquids (of which one A is water, the other
B a solution) are separated by a membrane, an exchange takes place between
them through the membrane. So long as the two liquids remain unaltered
(as would be the case if the liquid on either side of the membrane were con.
tinually replaced by fresh of the same quality) the relation between the weight
of water which passes from A to B, and of the body in solution which passes
from B to A, is constant. This relation is called the osmotic equivalent. If
B holds NaCl in solution, the former is greater than the latter, and the
equivalent is said to be positive ; if HC1, it is less, and the equivalent is
said to be negative.

BLOOD. 17

BLOOD.

Blood is an opaque fluid mass, each cubic millimeter of
which contains some five millions of corpuscles floating in
an alkaline liquid. Of these about one in 400 are colour-
less. In circulating bloqd the corpuscles are equally
distributed. Out of the living body, blood coagulates, that
is, separates into clot and serum ; or, if coagulation is
prevented by a freezing temperature, into corpuscles and
plasma. If blood is agitated before coagulation, the fibrin
is collected on the agitating surfaces, and thus separated
from the cruor. The coagulum varies in character accord-
ing to the number of corpuscles, the time occupied, and
the form of the recipient. It consists essentially in the
concretion of the plasma into a felt-work of transparent
fibres, each of which is scarcely a micromillimeter in width,
and shortens immediately after it is formed. In the circu-
lating blood coagulation is prevented by the influence
upon it of the living tissues, with which it is in relation.
If blood is received into non-contaminated vessels, coagu-
lation is delayed or prevented. It is not dependent on the
access or escape of any gas or vapour. It is indefinitely
deferred at o° C, most accelerated at 40° C. By subsidence
at about 6° C. blood separates into plasma and corpuscles,
of which the weights in normal human blood are nearly
equal. It contains three albuminous substances, viz. : (i)
common albumin ; (2) a little alkali-albumin ; and (3) the
substance which becomes fibrin. Plasma coagulates at
ordinary temperatures, becoming gelatinous if diluted,
yielding a fim clot of fibrin if concentrated. The substance
which thus assumes the solid form is called, in its dissolved
state, plasmin, or the substratum of coagulation. It has
the properties of a globulin. Two kinds of globulin exist in
the plasma, one, named fibrinogen, in very small quantity
(0*3 per cent.), which disappears in the act of coagulation ;
the other, which is much more abundant, and may consti-

C

1 8 COAGULATION.

tute, according to recent researches, more than a third of
the total weight of proteid.

Serum albumin is soluble in water, and is not precipitated either by dilute
acids, by alkaline carbonates, or by NaCl. As it exists in the blood, it is pre-
cipitated by boiling or by addition of alcohol. It is Isevorotatory, and differs
from albumin of egg, in not being coagulated by ether, and in being more
soluble in HC1. Serum albumin can be separated from the soluble salts,
which are present in the serum, by prolonged diffusion with water. In this
state, however, its properties are altered ; it is neither coagulated by heat, nor
precipitated by alcohol.

Globiilins. — The globulins are distinguished from common serum albumin
by the fact that while insoluble in concentrated solutions of neutral salts,
particularly NaCl and MgSO4 and in distilled water, they are soluble in
weak solutions : they are also soluble in dilute alkalies. They are all
coagulable by heat, but at different temperatures.

Paraglobulin is the precipitate produced in serum by saturating it with
NaCl or MgSO4, or by diluting it and then neutralizing with acetic acid, or
by passing through it a current of CO2. This precipitate is soluble in one
per cent, solution of NaCl and coagulates at 73° C. It is contained, along
with serum albumin, in all the tissues and liquids of the body.

Fibrinogen is distinguished from paraglobulin by the greater difficulty with
which it is precipitated by dilution in neutral solution. It is contained in all
the coagulable liquids. Its solution in NaCl is coagulated by heat at 55° C.
(Hammarsten).

Fibrin differs from fibrinogen in its filamentous structure, and its solubility
in dilute NaCl solution. Like myosin, it is soluble in strong solutions of
NaCl, but with great difficulty : the solution coagulates at about 60° C.
It is convertible with difficulty by acids or by alkalies into albuminate.
Crude fibrin decomposes solution of H2O2 : it is converted by boiling into a
body resembling coagulated albumin.

The liquids contained in uninflamed serous cavities,
which coagulate imperfectly (pericardial fluid) or not at
all (hydrocele fluid), also contain both forms of globulin.
These liquids for the most part coagulate on the addition
of serum. Their percentage of fibrin-yielding material is,
however, small.

From blood which has been a short time withdrawn
from the circulation a ferment-like substance can be
prepared, the solution of which, although it contains no
globulin, promotes the coagulation of coagulable fluids.

In coagulation many of the colourless corpuscles of the

BLOOD-DISKS. 19

blood undergo disintegration : it is believed that they
take an important part in the process, and even contribute
the material out of which fibrin is formed. They appear
also to be the source of the ferment above mentioned, for
plasma filtered at a few degrees above o° C. loses its power
of coagulating at ordinary temperatures : this power is
restored to it by the addition of a ferment, but the quan-
tity of fibrin obtained is less than that yielded by unfil-
tered plasma.

The Plasma of blood contains about 0-5 per cent, of the
total blood-weight of soluble salts, of which between 0*3
and O'4 is sodic chloride, and about O'l sodic phosphate,
the remainder consisting chiefly of sodic carbonates. The
insoluble calcic and magnesic phosphates, of which plasma
contains about 0*04 per cent, of the blood-weight, are held
in solution by combination with albumin. Serum also
contains a trace of sulphates.

Serum, i.e., plasma which has been deprived of its
plasmin by coagulation, differs from plasma in the absence
of fibrinogen. It contains serum-albumin, paraglobulin,
and probably alkali-albuminate, besides salts and extrac-
tive. The whole of the proteid of serum (albumin and
globulin), with the exception of a trace of albuminate, is
separated by heat at about 73° C. It is also precipitated
by alcohol and by strong mineral acids.

Plasma contains oxygen and nitrogen in about the pro-
portion in which these gases are severally found in water.
It contains somewhat more free CO than the serum would
absorb if it were so much water.

! Blood-disks. — The coloured blood-corpuscles consist of
stroma and haemoglobin. They constitute about a third
of the weight of the blood, and contain about 43 per
cent, of solids, and 39 per cent, of haemoglobin. The
stroma is made up for the most part of substances soluble
in ether, viz., lecithin and cholesterin, and of globulins
resembling those of plasma. The blood-corpuscles also

C 2

20 HEMOGLOBIN.

contain inorganic salts, which differ from those of the
plasma, in the replacement of sodium by potassium.

The body of the corpuscles consists chiefly of globulins
associated with lecithin and cholesterin. The globulin is of
two kinds, the greater part resembling paraglobulin, the
remainder having the characters of myosin. The colour-
less corpuscles also contain glycogen, and are, like the
coloured corpuscles, relatively rich in potassic salts. The
nuclei contain a non-crystallizable nitrogenous body
(nuclein — not a proteid) which is insoluble in weak acids,
and hence in gastric juice, but dissolves very readily in
weak alkalies. The chemical relations of this substance
are as yet unknown. It is found in all nuclear structures,
e.g., in spermatozoids. The " protoplasm " of the colour-
less corpuscles consists chiefly of globulin associated with
lecithin and cholesterin. It contains glycogen.

In normal blood, haemoglobin exists only in the cor-
puscles, but in certain diseased states it is dissolved in the
plasma and is then crystallizable : the nature of the
change it undergoes is not known. A similar change is
produced artificially by repeated freezing and thawing, by
subjecting blood to a temperature of 60° C, or by the
action of ether or chloroform. The property which the
blood possesses of absorbing oxygen from the inspired air,
and of giving it up to the living tissues with which it is
brought into contact in the circulation, is due to its
haemoglobin.

Hamoglobin crystallizes from its solution, in forms which vary according to
the animal from which it is derived. The crystals are of the colour of
arterial blood, but become dark, without changing their form, when placed
in vacua at a low temperature. They then exhibit two colours, looking green
along the edges, purplish-red elsewhere : on the admission of air or oxygen,
the colour is restored.

Haemoglobin is very soluble in warm water, much less so in cold, but, in
this respect, crystals obtained from different animals differ : thus, the hgemo-
globin of the rat or guinea-pig is less soluble than that of man, and is much
more prone to crystallize.

BLOOD GASES. 21

Haemoglobin contains -g-J-§ of its weight of iron. Solution of hemoglobin
exhibits before the spectroscope characteristic absorption bands. Very dilute
solution shows one band to the blue side of the D line ; if the solution is
stronger, a second band appears to the red side of the E line ; by still more
concentrated liquids, the blue and violet rays are entirely absorbed, while
the two bands become confluent.

When blood is allowed to stand at ordinary temperatures, its haemoglobin
is soon decomposed, yielding haematin, a proteid body, and other products.
The same thing happens much more rapidly when solution of hasmoglobiu is
acted on by alkalies, in which case haematin and alkali-albuminates are
formed. In presence of weak acids, haemoglobin yields haematoin (so-called
"acid haematin ") and acid albuminate.

Hcematin (Caa H34 N4 Fe O5) is obtained when weak potash solution acts
on blood or solution of haemoglobin ivith access of air. On neutralizing, solid
haematin is precipitated. It is insoluble in water, alcohol, and ether, and
uncrystallizable.

The absorption spectrum of haematin presents a broad band to the red side
of the D line. After reduction by alkaline sulphides it shows two charac-
teristic bands, one in the yellow, the other in the green part of the spectrum.
When dried blood is warmed with glacial acetic acid, it yields crystals of
hcemin (haematin + HC1).

Solution of haemoglobin associates nitric oxide and carbonic oxide in the
same volume as oxygen. When oxygenated solution of haemoglobin or of
blood is acted on by carbonic oxide, its associated oxygen is replaced by that
gas. The solution acquires a colour which closely resembles that of arterial
blood, but is not affected by reducing agents.

The quantity of oxygen yielded to the barometer vacuum
by any quantity of aerated defibrinated blood is equal to
the quantity associated by the haemoglobin contained in
the blood,////^ the quantity absorbed by the plasma ; (hence
for every 5 centigrammes of iron i8'7 cubic centimeters
of oxygen at o° and 760 m.m.) In ordinary arterial blood
the yield of oxygen is a little less. Arterial blood at
40° yields about 40 per cent, of its volume of CO2, as
measured at o° and 760 m.m. The alkaline carbonates are
decomposed in the vacuum without the addition of an acid.

The human body contains about •£$ of its weight of
blood.

In the examination of blood for clinical purposes, it is
chiefly important to determine the percentage of haemo-
globin and the alkaline reaction.

22 THE SPLEEN.

Arterial blood becomes venous by contact with living
protoplasm. Venous blood is distinguished from arterial
by its crimson colour, its slight dichroistn, the less propor-
tion of oxygen which is associated with its haemoglobin, its
large proportion of combined CO2, its less proneness to
coagulation, and by containing fewer blood-corpuscles.
Venous blood differs somewhat in composition according to
its source. As compared with ordinary venous blood, that
of the hepatic vein contains less albumin and more ex-
tractives (e.g., urea and grape-sugar). In that of the splenic
vein, also, differences exist, which indicate that in this
organ the coloured blood-corpuscles are disintegrated, and
colourless corpuscles formed.

The Spleen.

The following are the facts best ascertained as to the
spleen-pulp, and the blood which flows from it : —

The spleen-pulp contains much haemoglobin, to which
the richness of its ash in iron is due (Malassez). The
aqueous extract of spleen-pulp contains uric acid, and the
allied body hypoxanthin, in quantities which, although
very small, are larger than those met with in any other
tissue (Strecker). The splenic blood contains fewer blood-
disks and more colourless corpuscles than the blood of any
other organ. There exist in the spleen structures which
are destined to become colourless corpuscles. It also con-
tains structures which are concerned in the breaking up of
blood-disks, and are the sources of the pigment with which
the pulp is provided. The enlargement of the spleen
which takes place a few hours after every considerable
meal, is chiefly if not entirely due to vascular dilatation
(Hosier).

CHEMICAL PROCESS OF RESPIRATION. 23

LYMPH.

Lymph or tissue juice resembles blood in being coagu-
lable and in containing colourless corpuscles. It differs
from it in being of lower specific gravity, in the tardiness
with which it coagulates, in the absence of blood-disks, and
consequently of haemoglobin, and in its containing rela-
tively to its weight less proteid, more urea and other
extractives, more sodic carbonates, and in yielding to the
mercurial vacuum more CO2. Its corpuscles are derived
partly from the tissues, but chiefly from the lymphatic
glands.

Chyle differs from lymph chiefly in respect of the larger
proportion of fat (about I per cent.) which is present in it.
Each of the minute granules to which chyle owes its
opacity consists of a fat particle enclosed in an envelope
of proteid.

CHEMICAL PROCESS OF RESPIRATION.

In respiration each quantity of air respired undergoes
the following changes : — Its oxygen is diminished by about
a quarter, viz., from 21 per cent, to 16 per cent. Its CO2
is increased a hundred-fold, viz., from about 0^04 per cent.
to over 4 per cent. It becomes nearly saturated with
moisture. It acquires nearly the temperature of the body.
It becomes more or less charged with organic impurity,
acquiring thereby a peculiar smell. Its volume is dimin-
ished by -g-J-o or thereabouts. Its weight is increased in
proportion to the weight of CO2 discharged.

The percentage of CO2 is dependent on the length of
time that the expired air has remained in the respiratory
cavity. (It can be increased by voluntary retention to 7*5
per cent.) Consequently, as the frequency of respiration
increases the percentage diminishes, though the total dis-
charge increases.

24 CHEMICAL PROCESS

Example : —

Frequency 6 24 48

Cubic centims of CO2 per minute 171 396 696

per respiration 28-5 16-5 14-5

(Vierordt).

The frequency remaining the same, the CO2 increases
with the amplitude of the respirations.
Example : —
Frequency — 12 respirations per minute.

Amplitude. CO, per min. (c.c.) Percentage.

3 Litres 162 5-4

6 „ 240 4-5

12 ,, 480 4-0

24 ,, 816 3-4 (Vierordt).

In the compressed air chamber the respirations become
more ample and the CO2 discharge increases.

Respiratory exchange of gases. — If a liquid is exposed to
a gas, the former absorbs the latter until equilibrium is
established. As soon as this is the case the tension of the
gas in the liquid is said to be equal to its tension outside of
it. If a liquid is exposed to a gaseous mixture, the ab-
sorption of each gas takes place as if there were no other.
If a very small volume of a gaseous mixture is exposed to
an indefinitely large volume of a liquid containing gases,
the latter will be absorbed from, or given off into the
former until the tension of each gas in the mixture is equal
to its tension in the liquid. When in this experiment the
liquid is the circulating blood, and the mixture atmospheric
air, the oxygen of the latter diminishes, for the tension of
oxygen in such blood scarcely amounts to 30 millimeters
(=^5- atmosphere), while the CO2 increases until its tension
amounts to about 40 millimeters.

The tension of carbonic acid in the air contained in the
air cells is so little inferior to that of ordinary venous
blood, that the discharge of CO2 would probably be in

OF RESPIRATION. 25

sufficient, unless the CO2 tension were greater in the
pulmonary capillaries than anywhere else in the circulation.
The nature of the agency by which this is brought about
is indicated by the fact that the addition of oxygenated
haemoglobin to serum in vacuo decomposes its carbonates,
setting free CO2, so that venous blood yields more CO2 to
oxygen than to the barometer vacuum. Consequently the
discharge of CO2 in pulmonary respiration is directly pro-
moted by the absorption of oxygen.

Respiration can be maintained without difficulty in an
atmosphere which contains much less than the normal pro-
portion of oxygen, so that an animal supplied with a limited
quantity of air continues to breathe in it until it has used
all but a fraction of the oxygen it contains.

The process by which the circulating blood gives oxygen
to the living protoplasm with which it comes into relation
in the capillary blood-vessels, and receives CO2, is often
called " internal respiration." The existence of such an
exchange of gases in the tissues is proved by the obser-
vation that venous blood differs, in the proportion of oxy-
gen and CO2 which it contains, according to the tissue
through which it has circulated.

The separation of CO2 by protoplasm, and the absorption
of oxygen, are distinct and independent processes, and do
not go on. pari passu. The former is variable ; its variations
are dependent on the functional activity of the tissue ; the
latter is constant and is associated with restitution. The
independence of the two processes is proved (i) as regards
muscular tissue, by the observation that muscle which has
been entirely deprived of oxygen can be thrown into
functional activity (i.e., contraction) without receiving any
supply, and that in contracting it gives off CO2 (Hermann) ;
and (2) as regards the entire organism, by the observation
that a frog, if kept at a low temperature, continues to dis-
charge CO2 at nearly the normal rate, in an atmosphere of
pure nitrogen (Pfluger).

26 URINE.

In the investigation of the chemical process of respiration
in man or the lower animals, three quantities are to be
determined, viz., the discharge of CO2, the absorption of
oxygen, and the discharge of water. In the most complete
methods (e.g., that of Regnault and Reiset) all three are
determined. In Pettenkofer's method, the CO2 and H2O
discharge only are determined ; but the method has the
advantage of being applicable to large animals and to man.

URINE.

The average daily discharge of urine of an adult male on
full diet is 1500 grammes, containing about 36 grammes of
urea, 07 gramme of uric acid, 16 grammes of sodic
chloride, and about 6 grammes of other inorganic salts,
besides colouring matter and other organic constituents.
Hence urine contains about 4*0 per cent, of solids, including
2-4 per cent, of urea. Its acidity is equal to that of a 0*2
per cent, solution of oxalic acid.

The salts of the urine are, common salt, potassic chloride,
sodic, calcic, and magnesic phosphates ; and sodic and
potassic sulphates. The discharge of sodic chloride varies
with the store of chlorine in the body. It is markedly
diminished by abnormal transudation of blood plasma.

The discharge of alkaline phosphates also varies with the
quantity stored in the blood plasma ; that of earthy phos-
phates with the disintegration of proteids of food. Hypo-
sulphites and sulphates occur in the urine as results of a
process of oxidation which has its seat in the kidneys, for
sulphates are met with only in traces in the blood or tissues.
Of the two alkaline bases about 8 grammes (reckoned as
potash and soda) are discharged daily, the soda constituting
a little more than half. In fever and all conditions attended
with increased disintegration of tissue or blood-corpuscles,
the proportion of potash is larger. If carbonates exist in
the urine they are derived from the oxidation of vegetable
acids used as food.

UREA. 27

Urine, if uncontaminated, may be kept for an indefinite
period without any change, excepting that its acidity and
colour increase slightly soon after it is passed (acid fermen-
tation). Under ordinary circumstances urine becomes
eventually alkaline when kept, in consequence of the pro-
duction of ammonic carbonate. This change takes place
rapidly in presence of a ferment which exists in the urine
in certain pathological conditions. The alkaline fermen-
tation is attended by the formation of triple phosphate.

It is by the discharge of urea that the rate at which
nitrogen is discharged from the organism is estimated.
Thus we learn that the discharge of nitrogen is subject to
regular diurnal variations ; that it is largest when food is
albuminous and abundant ; that it is diminished rapidly
by inanition, gradually by a diet containing a large
proportion of carbonic hydrates ; that it is increased by
ingestion of water, sodic chloride, and ammonium salts,
and that it is very slightly augmented by muscular exer-
cises.

Urea exists in all the animal liquids, and in most tissues,
excepting the muscular and nervous, in a proportion not
exceeding 0*03 per cent. This proportion is increased by
any interference with the renal excretion. Urea is a direct
product of the life of protoplasm. It is not as yet proved
that it is more actively produced in the liver than else-
where.

CRYSTALLINE ORGANIC BODIES OF THE URINE.

Urea or Carbamide (CO (NH2)2) exists as such in urine — so abundantly in
that of the carnivora, that it crystallizes therefrom on evaporation. In human
urine it can be crystallized from the alcoholic extract of the dry residue.
Urea (U) is excessively soluble in water, soluble in alcohol, insoluble in ether;
it is isomeric "with ammonic cyanate (NH4CNO) ; takes up water in contact
with certain ferments, and is transformed into normal ammonic carbonate
(CO (NH2)2+2H2O=CO3 (NH4)S). A corresponding change occurs when U
is acted on by alkalies or by strong sulphuric acid, ammonia being given off in
the former case, carbonic anhydride in the latter. On the addition of nitric
acid to strong solution of U, a snow-white precipitate is formed of Urea-nitrate
(U, NO3 H), consisting of rhombic plates having a characteristic imbricated

28 URIC ACID.

arrangement and mother-of-pearl lustre. Oxalic acid acts 'similarly, producing
Urea-oxalate (U, C2 H2 O4), but the crystals are not so characteristic. Both
bodies are quite insoluble in the acid liquids. An important compound (2U-f-
Hg (NO3)2+3Hg O) is obtained as a heavy amorphous white precipitate, when
a dilute solution of U is acted upon by dilute solution of mercuric nitrate in
excess. This body is insoluble in neutral or slightly acid liquids, but soluble
in nitric acid. On adding sodic carbonate to the solution it is precipitated.
Hence, if a solution of mercuric nitrate of known strength is added, drop by
drop, to a solution of U acidulated with nitric acid, and the mixture tested
from time to time by mixing a drop of it with a drop of sodic carbonate,
such mixture will be attended with the formation of an additional white
precipitate, so long as there remains any uncombined urea. The moment
that all has been used up, the test will indicate the presence of excess of
mercuric nitrate in the mixture, by the formation of a precipitate of basic
nitrate.

Uric acid exists in urine chiefly as an acid sodium salt
which is deposited in the cold. When this is decomposed
by a stronger acid the free acid crystallizes. Ammonium
urate occurs only in ammoniacal urine. Uric acid is
absent in the urine of herbivorous mammalia, but in that
of birds and reptiles it takes the place of urea as the
channel for the discharge of nitrogen. In man it is dis-
charged in relatively larger quantities in early infancy than
in adult life ; its relative proportion to urea is increased a
few hours after a full meal.

The daily discharge of uric acid is increased by certain
kinds of dyspepsia, in fever, and in certain chronic diseases.
It undergoes oxidation into urea and oxalic acid in the
body.

Uric Acid (C5 H4 N4 O3, also called lithic acid) being soluble in water only
in the proportion of one part to 14,000, exists as such in extremely small quan-
tities in urine. Uric acid crystallizes readily in urine to -which enough
hydrochloric acid has been added to decompose its urates. The most common
forms of crystals are the so-called whetstone crystals and the sheaf-like bundles
of flattened needles, which (as formed in urine) are always of an amber brown
colour. Acid sodic urate (C5 H2 N4 O3, HNa) is always present in normal
urine. In urine of which the urea has undergone transformation into ammonic
carbonate, ammonic urate (C5 H3 N4 O3, NH4) is deposited in needle-shaped
crystals which are often in stellate groups. In ordinary urine, when concen-
trated by evaporation and then cooled, an amorphous deposit falls, which
consists chiefly of sodic urate. The same body often occurs as a natural
subsidence in disease (lateritious sediment). Uric acid and urates reduce

HIPPURIC ACID. 29

cupric oxide and other metallic oxides and salts. When uric acid is moistened
with nitric acid, the excess of acid gently evaporated, and the residue after
cooling breathed on, and then held over strong ammonia, a bright red colour
is produced, which is due to the formation of murexide ; if potash or soda be
added instead of ammonia, the colour produced is violet.

Allantoin exists, along with uric acid and urea, in the
urine discharged during the first few days of life.

Hippuric acid, which in the urine of many herbivorous
mammalia replaces uric acid, also occurs in human urine
in very small proportion. It is of importance as affording
a channel for the discharge of glycin from the organism.
Taurin, in like manner, appears in the urine as Tauro-
carbamate. The body cystic oxide or cystin, which also
contains sulphur, occurs occasionally either as a crystalline
deposit or as a concretion. Its physiological relations are
unknown.

Hippuric acid (C9 H9 NO8) occurs in very small proportions (less than ofi
per cent. ) in human urine or in that of the carnivora, but so abundantly as
alkaline hippurates in that of herbivora, that on the addition of hydrochloric
acid it crystallizes out. It is obtained by boiling the urine of the horse or the
cow with milk of lime, filtering, concentrating the filtrate, and adding hydro-
chloric acid. It crystallizes in four-sided prisms, which have their edges bevelled
off at the ends. Hippuric acid is scarcely soluble in cold water, more readily
in hot, but its salts are very soluble. It appears in the urine of man and
other non-herbivorous animals, whenever benzoic acid (C7 H6 O2) enters the
organism, glycin being taken up and water given off. C7 H6 O2-|-C2 H3 (NH2)
O2=C9 H9 NO3+H2 O. On the other hand, it very readily undergoes decom-
position, yielding benzoic acid and glycin whenever urine containing it becomes
putrid. In the formation of hippuric acid from benzoic acid in the living
organism the glycin produced in the liver takes part, but it has not yet been
proved that the process by which it is normally produced in such large
quantity in herbivora is of the same kind ; it has, however, been shown
that sufficient sources of benzoyl exist in the food of such animals. As
regards the origin of hippuric acid in the carnivora and in man nothing is
known. In all animals of which the urine contains much hippuric acid (e.g.t
in the horse), " indigo-producing substance " is also present in relatively large
quantities.

The urine also contains an organic base, creatinin, the
percentage of which depends upon the quantity of creatin
taken as food.

30 COLOURING MATTER.

Creatinin is an alkaline body which exists in small quantity (about 0*1 per
cent. ) in urine. It is soluble in cold water, still more so in hot. From its
solution in boiling alcohol it crystallizes on cooling. On the addition of
syrupy solution of zinc chloride to its aqueous solution, characteristic warty
clumps are formed of the combination of zinc-chloride ((C4 H7 N3 O)2 Zn C12)
and creatinin, each of which is seen under the microscope to consist of
acicular crystals radiating from a centre (see Creatin, p. 32).

Human urine contains a soluble yellow colouring matter
(urochrome) which is precipitated from its solution by
acetate of lead ; it also usually contains a colourless chro-
mogenous substance, which when treated with hydro-
chloric acid yields indigo-blue. Grape-sugar exists
normally in urine, but in very small quantity. As, how-
ever, both uric acid and creatinin reduce cupric oxide, the
presence of sugar cannot be proved by the copper test
unless these bodies have been previously removed.

The yelloiv colouring matter of the urine is obtained by treating the liquid
with milk of lime, and allowing it to stand. After separation of the
deposit, the clear filtrate is precipitated by solution of plumbic acetate to
which ammonia has been added. The lead precipitate, having been treated
with just sufficient sulphuric acid to decompose it, yields a yellow solution,
which owes its colour to a body to which the name urochrome was given by
Thudichum. This body is soluble in water, insoluble in alcohol. Its solution
exhibits no absorption bands before the spectroscope. On boiling it for some
hours with sulphuric acid, various brown or black substances are formed, the
most characteristic of which (called uromelanine) is soluble in ammonia, and
is re-precipitated on neutralizing the solution with sulphuric acid. Of the
chemical relations of urochrome little is known.

Indigo -forming substance. — Urine (particularly that of the horse) when
mixed with half its volume of strong hydrochloric acid, becomes dark, and
after some hours exhibits a scum or sediment which contains indigo-blue
(C8 H5 NO). If this scum is collected on a filter and treated with ammonia,
a blackish substance with which it is mixed is dissolved and removed. If
after washing the filter with cold alcohol -(which dissolves out a red colour)
the filter and residue are boiled in the same solvent, a beautiful blue solution
is obtained, which, on cooling, deposits flocks of indigo-blue.

The materials which constitute urinary deposits and
concretions may be divided into those of acid and of
alkaline urine, the former comprising uric acid, urates, and
calcic oxalate, the latter the calcic and magnesic phos-
phates, triple phosphate, and calcic carbonate.

MUSCULAR TISSUE.

MUSCULAR TISSUE.

Muscular substance consists chiefly of a globulin named
myosin, which differs little from fibrinogen. This body is
fluid in living muscle, but coagulates when life ceases.
Frozen muscle carefully thawed, yields a juice which
coagulates (whether with the aid of a ferment is not
known) at ordinary temperature. The coagulum dissolves
readily in salt solution.

Muscle contains, in addition to myosin, serum-albumin
and other proteids which coagulate at lower temperatures.
The aqueous extract of dead, i.e. coagulated, muscle con-
tains a free acid (sarcolactic) which is not present during
life. The extract yields creatin by direct crystallization in
the proportion of about 0*2 per cent, of the weight of the
muscle employed. The glycogen which all muscle con-
tains in the perfectly fresh state is replaced by dextrose
in dead muscle. The extractive contains also Inosite,
Xanthin, Hypoxanthin, Taurin, and a trace of uric acid.

Myosin is obtained in quantity by thoroughly washing comminuted muscle
with water and then treating the insoluble residue with strong salt solution
(one part of brine to two of water), filtering the solution and then precipitating
by the addition of salt in substance. It is readily soluble in dilute HC1, or
alkalies, which soon convert it into acid or alkali-albumin. Its solution
coagulates in weak NaCl at 55° to 60° C.

Sarcolactic acid. — A body resembling lactic acid of milk, even in chemical
structure, but differing from it in being dextrorotatory, and in the solubility,
hydration and crystalline form of some of its salts. It is contained in the
alcoholic extract of the concentrated water extract of flesh from which the
creatin has been crystallized and separated. The syrupy mother liquor, after
treatment with sulphuric acid, is extracted with ether. The ether extract
leaves sarcolactic acid on evaporation.

Inosite or Muscle sugar exists sparingly in all muscle, and occurs patho-
logically in the urine in uraemia ; it is obtained in quantity from unripe beans.
It differs from grape-sugar in not affecting polarized light, in not reducing
metallic oxides, and in being incapable of alcoholic fermentation ; it, however,
yields sarcolactic acid by a process analogous to lactic fermentation. When
a solution of inosite is evaporated with nitric acid in a porcelain capsule, then
moistened with calcic chloride solution and again evaporated after the addi-
tion of a little ammonia, a bright rose-coloured patch remains (Scherer's test).

32 NERVOUS TISSUE.

When the aqueous extract of muscle from which the creatin has been crys-
tallized out (see Creatin) is precipitated by neutral lead acetate, a filtrate is
obtained from which inosite is precipitated by the addition of the basic acetate
test. It crystallizes from its solution in alcohol in rhombic plates or prisms
represented by the formula C6 H12 O6 + 2H2O.

Creatin (C4 II9 N3 O3) is obtained by direct crystallization from the water-
extract of meat. To prepare it, the extract must be first freed from albumin
by boiling, after which the phosphates and sulphates must be precipitated
by adding to the strained liquid a mixture of baryta water and baric nitrate.
The liquid having been filtered, the filtrate is evaporated over a water-bath
to a small bulk, when creatin separates in hard brilliant crystals. Creatin,
when treated with boiling solution of baryta, splits into Sarkosin (Methyl-
glycin) and Urea (C4 H9 N3 O2 + H2 O = C3 H7 NO2 -f CO (NH2)2).
When heated with acids, it loses water, and is converted into Creatinin
(C4 H7 N3 O).

Hypoxanthin (C5 H4 N4 O) (Sarkin of Strecker), occurs in the tissue of
the spleen and in muscle. It exists in the mother liquor of creatin, and can
be precipitated from it as an impure compound of argentic nitrate and
hypoxanthin by treating the extract with solution of nitrate of silver rendered
slightly alkaline by ammonia. Hypoxanthin, like xanthin, is soluble in
nitric and hydrochloric acids yielding crystalline compounds. Heated and
evaporated with fuming nitric acid, it gives the same yellow residue as
xanthin.

Xanthin (C5 H4 N4 O3) the xanthic oxide of Prout, exists in extremely
small quantity in urine, in the tissues of certain organs, and as an occasional
constituent of calculi. It is very insoluble in water, but soluble in hydro-
chloric and nitric acids, giving crystallizable compounds with both. When it
is heated with fuming nitric acid, and the product evaporated to dryness,
a pale yellow patch is left ; • from this circumstance it derives its name.
Xanthin can be prepared artificially by the action of oxidizing agents on
Hypoxanthin.

NERVOUS TISSUE.

Of the proteids of the brain little is known. The grey
substance is said to be acid, even when perfectly fresh.
All nervous tissue contains, in addition to Cholesterin and
Lecithin, which exist everywhere, a body called Cerebrin,
which is peculiar to the nerve fibres.

CRYSTALLINE PRODUCTS of the alcohol-ether extract of BRAIN.

Neurin or Cholin (N (C H3)3 (C2 H5 O) OH) is a strongly basic, colourless
syrupy fluid, which forms crystalline salts with acids. It is soluble in alcohol
and water, not' in ether. It is readily decomposed by heat, yielding trimethy-
lamine, ethylene oxide, glycol (C2 H4 (HO)2) and water. It is obtained by

EXCHANGE OF MATERIAL. 33

heating trimethylamine and ethylene oxide in aqueous solution (N (C H3)3 +
Ca H4 O + II., O = Neurin). Glycero-phosphoric acid (C3 H9 PO6 or
C3 H7 O3 PO (OH)2), the product which is obtained when phosphoric anhy-
dride or glacial phosphoric acid acts on glycerine, is a syrupy body, soluble in
water not in alcohol. Taking up H2O, it splits readily when warmed into
glycerine and phosphoric acid. Along with Neurin and a fatty acid, it is a
product of the decomposition of Lecithin, a body which may be regarded as
glycero-phosphoric acid in which H2O is replaced by Neurin, and 2 atoms of
H in the radical by 2 atoms of stearyl (C18 H^ O). Lecithin is consequently
called Neurin-distearyl-glycero-phosphate. Lecithin is an imperfectly crystal-
lizable body which fuses readily, is soluble in ether and swells out in water, like
starch, without dissolving. It is obtained by treating the ether alcohol
extract of yolk of egg, after first freeing it. from fats, with alcoholic solution
of platinic chloride. A chloride of platinum and of Lecithin separates, of
which the ethereal solution, when decomposed by sulphuretted hydrogen,
yields Lecithin hydrochlorate as a wax-like mass. The alcoholic solution of
this substance, when poured into boiling baryta water, splits into glycero-
phosphate, Neurin and stearate. Bodies of similar constitution in which the
radical of stearic acid is replaced by that of palmitic or of oleic acid are also
called Lecithins.

Cholesterin (C26 H^ O) crystallizes readily from ether-extract of powdered
gall-stones (of which it is usually the chief constituent) in rhombic plates,
which in mass have a mother-of-pearl lustre. These crystals contain a mol.
of H2 O, which they lose at 100° C. It fuses at 145° C., is insoluble in water,
soluble in alcohol, ether, chloroform, &c. When evaporated with nitric acid,
the residue on the addition of ammonia acquires a dull red colour. If sulphuric
acid is added to its volume of solution of cholesterin in chloroform, the solution
becomes first red then purplish, while the subjacent layer of acid acquires a
distinct green fluorescence. A body resembling Cholesterin (Excretin) has
been discovered by Marcet in human faeces, to which the formula C20 H36 O is
now attributed.

Cerebrin is a body of imperfectly known constitution, which is distinguished
from Lecithin with which it is associated by its solubility in boiling absolute
alcohol, its insolubility in cold alcohol, and its not being decomposed or acted
upon by boiling baryta water.

EXCHANGE OF MATERIAL.

The term "exchange of material" is used to denote the
results of the chemical processes (" functions"), which con-
stitute the life of the animal body, as they exhibit them-
selves in the entrance and discharge of material at its
surface. Its total amount is known by the direct or
indirect measurement of the quantities of carbon and

D

34 DISCHARGE OF CARBON.

nitrogen discharged, and of oxygen taken in daily, by
the organism, when the body-weight is constant.

The Discharge of Carbon.

' The influence of food on the rate of discharge of CO2 is
direct and immediate. The increase after each meal,
which may amount to 20 per cent, reaches its maximum
in about 2 hours. The effect is most marked when the
diet consists largely of carbohydrates.

About 95 per cent, of the carbon discharged leaves the
organism as CO2, and forms part of the "insensible loss,"
that is, the loss of weight of the body when no food is
taken and no liquid or solid excreta are discharged. The
insensible loss is made up of the sum of the CO2 and
water discharged, minus the weight of oxygen absorbed.
In man it amounts to about 25 grammes per 'hour.

Of the total hourly discharge of CO2 less than half per
cent is cutaneous. The hourly discharge of CO2 by
weight of an adult male when at rest, is about 32 grammes,
the weight of oxygen absorbed in the same time being
from 25 to 28 grammes. The hourly discharge of water
vapour is about 20 grammes.

As a volume of CO2 contains the same weight of O as
an equal volume of O, it is obvious that if all the inspired
O were discharged as CO2, the quotient (by volume) — called
the " Respiratory Quotient "— ^ would be = I. This,
however, is never the case. The volume of O absorbed
exceeds very considerably that of the CO2 discharge, the
ratio between them being determined by the composition
of the food. In animals which feed exclusively upon
carbohydrates, equality is approached. The excess of
oxygen is greatest when the diet consists largely of fats.

On a mixed diet comprising 100 grammes of proteid, 100 grammes of fat,
and 250 grammes of carbohydrates (see Table I. ), with a CO2 discharge of
770 grammes daily, the assumption of O by the organism amounts to 666

DISCHARGE OF NITROGEN. 35

grammes daily, of which 560 grammes are discharged as CO2, about 9
grammes in urea, 97 grammes in H2O, of which last 78 grammes are
formed at the expense of the hydrogen of the fat. Hence the quotient
-^-=o€84. In inanition, when (as in the case represented in Table II.
the proteids and fat of the organism take the place of food, and the CO,
discharge is reduced to 660 grammes daily, the assumption of O required is
649 grammes, of which 480 grammes are discharged in CO2, 4'5 in urea, and
164*5 in H2 O ; of this last 156 grammes are due to the oxidation of fat.

In the state of hibernation the respiratory quotient is
smaller than in any other known condition (often less than
0*5), for the hibernating animal lives almost entirely on
its own fat. In the similar state of inanition the excess
of the oxygen absorption is not so great, for here the
proteid constituents of the tissues waste in much larger
proportion.

The " insensible loss " is increased by muscular work ;
for, although the quantity of O absorbed is large during
exertion, this is far more than counterbalanced by the
greater increase of the CO2 discharge (diminution of the
respiratory quotient), and the still greater augmentation
of the evaporation of water from the pulmonary and cuta-
neous surfaces.

Diminution of the bodily temperature, however pro-
duced, determines increased CO2 discharge. In small
animals the CO2 discharge is greater in proportion to the
body-weight than in large ones.

The Discharge of Nitrogen.

The whole of the nitrogen which enters the circulating
blood by intestinal absorption (with the exception of so
much of the N of the faeces as is derived from unabsorbed
secretions) is discharged by the urine. The rate of dis-
charge is observed to vary according to the rate at which
nitrogen has been absorbed during the previous period, so
that under normal conditions the processes balance each
other. But in order to the establishment of this state of

D 2.

36 DISCHARGE OF NITROGEN.

" nitrogen equilibrium," it is necessary that the daily weight
of nitrogen absorbed should not fall below a certain limit,
determinable in respect of each species of animal by ex-
periment. In man the minimum daily allowance of N is
.about 1 5 grammes, or O'O2 per cent, of the body-weight ;
in the carnivora about O'l per cent. ; in the ox 0*005 per
cent. (Henneberg).

When the diet consists of proteid exclusively, a larger
quantity is required for the maintenance of the equi-
librium than when it also contains fat or carbohydrates.
Accordingly, in those animals or races of mankind whose
food consists largely of either of these constituents — par-
ticularly the latter — the nitrogen requirement is lower than
in others. The reason why this is so is not understood.

When the animal body is deprived of food, its " stored
proteid " rapidly disappears. During this process (the
first stage of inanition, and which lasts a few days only)
the nitrogen discharge as rapidly diminishes. During the
second stage it continues to diminish, but only in pro-
portion to the diminution of the total body-weight.

In an animal fed exclusively with flesh the nitrogen
discharge at first increases pari passu with the absorption
of proteid, the absorption of O being increased in exact
proportion to the increase which has taken place in the
quantity of material to be disintegrated, so that the
respiratory quotient remains nearly unaltered (Bidder and
Schmidt). Although, however, the overfed animal main-
tains its nitrogen equilibrium, it usually gains weight, and
therefore must " lay on " fat.

Relation of Muscular Work to the Discharge of Nitrogen
and Carbon. — The chemical changes on which the per-
formance of work by muscle depends, manifest themselves
in the production of CO2 and H2O. Consequently, in
muscular exertion both constituents of the "insensible
loss " are so augmented that (irrespectively of the
secondary effect produced on the skin) they more than

GELATINE AND FAT. 37

balance the increased absorption of oxygen (Pettenkofer).
The quantity of proteid required by the organism daily for
its maintenance is proportional to the weight of active
living material (protoplasm) that it contains, so that, in
general, those organisms are most vigorous which are
capable of producing the largest quantity of urea in pro-
portion to their weight ; but, in the case of muscle, the
proteid so used is not the source of the work done ; for
even if the whole of the proteid material which enters the
organism in a day, were devoted to this purpose, and em-
ployed in the most advantageous way, it would not afford
the material for a day's work.

The facts above stated are most easily understood on the
hypothesis that the disintegration of food proteid, i.e., the
production of urea and other " nitrogenous metabolites," is
exclusively a function of " living material," and that this
process is carried on in the organism with an activity which
is dependent on the activity of the living substance itself,
and on the quantity of material supplied to it. No
evidence at present exists in favour of a "luxus con-
sumption " of proteid.

Use of Gelatine. — In carnivorous animals on a diet of
flesh and fat, nitrogen equilibrium can be maintained with
a much smaller daily allowance of proteid with than with-
out gelatine. Hence gelatine is capable of partly replacing
proteid. But normal nutrition cannot be maintained either
with gelatine alone or with any mixture of gelatine and
fat, or of gelatine and proteid.

Relation of Fat to the Exchange of Material. — Fat is stored
for the purposes of nutrition in the adipose tissue, which,
without any disturbance of its histological integrity, gives
or receives fat according to the requirements of the or-
ganism. Tissue fat is not, however, as a rule, derived from
food fat of the same kind, for even when animals previously
starved receive fatty food, the fat " laid on " is not neces-
sarily chemically identical with that given. In the fattening

38 BALANCE OF

of herbivorous or omnivorous animals, the fat is largely
produced from carbohydrates. In lean carnivorous animals
it is deposited when they are well fed even with flesh
without fat. Hence it must be concluded that in such
animals the formation of fat from proteids is a normal
•process.

The Balance of Income and Discharge.

The relation between the income and expenditure of the
animal organism is best expressed in the form of balance
sheets, in which the quantities of proteid, fat and carbo-
hydrates of the food, are stated on one side, and CO2, urea,
and other excreta on the other, the value of each item
being computed according to the weight of C and N which
it contains. The income and discharge of H are left out
of account for the sake of simplicity.

This mode of statement is applicable to all the condi-
tions of nutrition which have been above referred to, viz.
(i) that in which the quantity and quality of the food taken
is sufficient, and not more than sufficient, for the mainte-
nance of the weight of the body without loss or gain, and
in which the diet is said to be adequate ; (2) the condition
of inanition in which the body, in the absence of food,
nourishes itself at its own expense ; (3) the condition in
which, in the absence of other heat-producing material,
proteid is necessarily employed for heat production, in
larger quantity than can be advantageously disposed of
by the organism.

These three cases are stated in the following Tables : —

INCOME AND DISCHARGE.

39

Albumin
Fat .
Carbohydrates

TABLE L*

Exchange of Material on Adequate Diet.
INCOME.

Nitrogen

100 grammes

100

250

15*5 grammes
o-o

0-0 ,,

15-5

Urea
Uric acid
Dejecta .
Respiration (CO2)

EXPENDITURE.

Nitrogen.
31-5 grammes |

o'S » J

14*4 grammes

o-o

15 '5

Carbon.

53 'o grammes

79'o

93 'o

225-0

Carbon.

6"i6 grammes

10-84
208-0

225-0

The quantities of albumin, fat, and carbohydrates in the Table represent a
diet consisting chiefly of meat and bread, with the addition of smaller
quantities of potato, butter, and eggs. It is seen that in man the discharge of
N per kilo, of body- weight is 0*21 grammes, and of carbon 3-03 grammes,
the quotient - being 14-5. In the carnivorous animal, which, according to
Bidder and Schmidt, uses 1*4 of N, and 6'2 of C per kilo, per diem, the ^
quotient is 4-4. In the human being on a flesh diet, the exchange of N
amounts to 0-83 per kilo, per diem, and the ^quotient is 5*2. Thus the
exchange of material of the human organism, when fed on flesh, is interme-
diate in character between the normal exchange and that of the carnivorous
animal.

TABLE II.

Exchange of Material on an exclusively Albuminous Diet.
INCOME.

Food.
Disintegration

Nitrogen.
62-3 grammes

Carbon.

279*6 grammes
45'9

* The data on which Tables L, II., and III. have been constructed have
been derived for the most part from the observations of Prof. Ranke on him-
self.

40 INANITION.

OUTCOME.

Discharged by Excretion 44*3 grammes 263*0 grammes

Retained in Store . 18*3 ,, 62*5 ,,

62-3 325-5

In the experiment referred to in this Table 1832 grammes of meat consumed
as food yielded 3*4 per cent, of Nitrogen, i.e., 62*3 grammes, and 12 '5
per cent, of Carbon, i.e., 229-3 grammes. Seventy grammes of fat also
consumed as food yielded 72 per cent, of Carbon, i.e., 50-3 grammes:
229-3 + 5°'3 = 279-6. During the same period 86-3 grammes of Urea were
discharged daily, containing 46*6 per cent, of Nitrogen, i.e., 40-4 grammes,
and 20 per cent, of Carbon, i.e., 17*3 grammes, to which must be added two
grammes of Uric Acid, containing 33 per cent, of Nitrogen, i.e., o-66 gramme,
and 35 per cent, of Carbon, i.e., 07 gramme. Further, 2*9 grammes of Nitro-
gen and 14 grammes of Carbon were discharged in the faeces, and 231 grammes
of Carbon were expired as CO2. Hence the total discharge of Nitrogen
(40-4 + o'66 + 2*9) was 43*96 grammes, and may therefore be stated as 44 :
and the total discharge of Carbon (17-3 + 07 + 14 + 231) as 263 grammes.
Deducting the quantity of Nitrogen discharged from that taken in, 18*3
grammes must have been retained in 108 grammes of Albumin, and conse-
quently 53 per cent, of that weight of Carbon, i.e., 62*5 grammes.

Comparing the quantity of Carbon disposed of in the 24 hours with the
quantity introduced as food, we find that the latter is in excess by 45-9
grammes, which must have been derived from the disintegration of the fat
of the body.

TABLE III.

Exchange of Material in Inanition.
DISINTEGRATION OF TISSUE.

Nitrogen. Carbon.

Albumin . . 50 grammes 7 '8 grammes 26-5 grammes
Fat • • • 199*6 „ I57'S

184-0

DISCHARGE OF NITROGEN AND CARBON.

Urea . . 17 grammes) rg mes 3.4grammes

Uric Acid . . 0-2 ., J

Respiration (CO,) . . . i8o'6 „

184-0

PRODUCTION OF HEAT. 41

This Table represents the exchange for a twenty-four hours' period, com-
mencing twenty-four hours after the last meal, and relating to the same person
as Table I. The discharge of N per kilo, of body-weight was reduced to
O'l, § being 23-5. In the carnivorous animal, in prolonged inanition, the
discharge of N per kilo, is 0*9 per diem per kilo, and ^ = 6 "6.

In fever the exchange of material resembles that of
inanition, but the disintegration of proteid is more rapid.

TABLE IV.*

Exchange of Material in Fever.
DISINTEGRATION OF TISSUE.

Nitrogen. Carbon.

Albumin . . 120 grammes 18 '6 grammes 63*6 grammes
Fat . . . 2057 „ 157-4

221'0

DISCHARGE OF NITROGEN AND CARBON.

Urea and Uric Acid 40 grammes 18*6 grammes 8*3 grammes
Respiration (CO2) 780 ,, 212-7 ,,

221'0

PRODUCTION OF HEAT.

Animal heat, like mechanical work, is a result of the
chemical process of the conversion of food into water,
CO2, urea, and other excreted products.

An approach to an experimental proof of this is obtained
by comparing the quantity of heat produced by a man or
an animal in a given time, with the quantity and physio-
logical "heat-value" of the different kinds of food con-
sumed during the same period.

Of these investigations the first is accomplished calori-
metrically ; the second by determining the quantity of

* The data for this Table are to be found in a paper in the Practitioner
for April, May, and June, 1876.

42 PRODUCTION OF HEAT.

heat produced by each substance used as food when com-
pletely burnt. The physiological heat-value of any sub-
stance is the quantity of heat produced by the chemical
disintegration which it actually undergoes in the animal
organism. Those substances which yield in the living
•body the same quantity of heat as by complete combus-
tion in the laboratory, have the same physiological as
physical heat-value ; but as regards substances containing
nitrogen, the result must be corrected by deducting from
it the heat produced by the combustion of the equivalent
weight of urea. Thus, albumin, which by complete com-
bustion yields 4998 units of heat, has a physiological
heat-value of only 4263 units. The results so obtained,
although only approximately correct in application, are
correct in principle ; for, however various may be the
chemical processes of animal life, their value as regards
the quantities of heat and work produced must be esti-
mated by the end-products.

Of the heat produced in the body, it is estimated by
Helmholtz that about 7 per cent, is represented by ex-
ternal mechanical work, and that of the remainder about
four-fifths is discharged by radiation and evaporation
from the surface, and one-fifth by the lungs and excreta.

The following Table exhibits the relation between the
production and discharge of heat in twenty-four hours in
the human organism at rest, estimated in kilogramme
units or calories : —

TABLE V.

PRODUCTION OF HEAT.

Consumption of Albumin . (loogrms.) . 100X4*263= 426 Cals.
„ „ Fat . . (loogrms.) . 100X9069= 907 ,,

„ „ Carbohydrates (223grms.) . 223 X 230 = 1167 „

2500 Cals.

PRODUCTION OF HEAT.

43

DISCHARGE OF HEAT.

(1) Warming Water in Food. . . . 2 '6 kilo. X 25° = 65'Cals.

(2) ,, Air .... 16 kilo. X 25° X o'26 = 104 ,,

(3) Evaporation in Lungs 630 at 582 = 367 ,,

(4) Radiation and Evaporation at Surface . . . . = 1964 ,,

2500 Cals.

The mean temperature of the body is remarkably con-
stant, but is higher in the central than in the superficial
parts. The uniformity of temperature is dependent on
the constant equilibrium of the two processes by which
severally heat is produced and discharged.

44

PRACTICAL EXERCISES

RELATING TO THE

FOOD STUFFS AND ANIMAL LIQUIDS.

I. — Starch, Dextrin, Dextrose, Fat.

!• Starch, is insoluble in cold water.

2. It dissolves imperfectly in hot water ; the liquid so obtained is opales-
cent.

3. It gives a blue colour with iodine, which vanishes when the liquid is
heated, but returns on cooling, if the heating has not been prolonged.

4- Dextrin is soluble in water.

5. The solution gives a red brown colour with iodine, which vanishes on
heating.

6. Dextrose (Grape-sugar) is crystalline and very soluble in water.

7. It reduces many metallic oxides.

8. The copper test. To a small quantity of ten per cent, solution of
cupric sulphate add about 5 c.c. of the liquid to be tested ; then solution of
caustic potash drop by drop until the solution is clear, and heat gradually. If
dextrose is present, the blue colour vanishes and a yellow precipitate appears
of cuprous hydrate, or a red precipitate of cuprous oxide.

9. Conversion of starch into dextrose. Boil about 50 c.c. of starch solution
in a flask with a drop of 25 per cent, sulphuric acid for five minutes. The
liquid becomes limpid. It contains in addition to dextrose much unconverted
soluble starch.

10. Fat. Lard is insoluble in water. By boiling with potash it yields a
solution of soap.

11. Decompose the solution by adding a few drops of dilute sulphuric acid.
On heating, a layer of fatty acid collects on the surface.

12. Microscopical preparations. Starch grains ; their disinte-
gration by hot water ; action of iodine on them. Crystalline forms of fatty
acids.

II.— Milk, Flour, Bread.

I. Milk has (in London) usually an acid reaction, and a specific gravity of
from 1025 to 1030. After removal of the cream, the specific gravity is higher.

FOOD STUFFS. 45

2. Milk contains fat, sugar, and proteids.

«• Proteids. Heat about 50 c.c. of milk in a flask to 50? C., add two
to six drops of dilute sulphuric acid (25 percent.) and shake ; the milk curdles ;
strain off the coagulated casein (curd) through muslin.

b. When milk is filtered under pressure through a porous disk, its casein,
being particulate, remains behind. The clear filtrate contains lactose
(milk-sugar) and salts.

c. The strained liquid from a (whey) contains lactose, which, like dextrose,
reduces metallic oxides. Apply the copper test (§ i, 8).

d. The coagulated casein contains much fat (butter) which can be extracted
by ether. The ether extract when evaporated on paper leaves a greasy stain.

e- Butter. Repeat § i, loandii. Butter yields a small percentage of
volatile acid.

3- Flour. Wash about a dessert-spoonful of sound flour in a muslin bag.

a. A milky liquid passes through containing much starch (§ i, 3) but no
sugar (§ i, 8).

b. After washing for some minutes, a sticky and tenacious material remains
on the muslin, which can be collected ; this after further washing forms an
elastic mass (gluten) which can be drawn out into threads, and on burning
gives off the smell of burnt feathers characteristic of a proteid.

4. Bread. Digest with warm water. The extract contains starch (§ i, 3)
and dextrose (§ i, 8). The residue consists principally of starch and gluten.

III. — Albumin and its Acid and Alkaline Modifications,

1. Albumin. White of egg (albumen) when diluted with water, strained
and filtered, yields a faintly opalescent liquid. This liquid contains a proteid
body, albumin, which diffuses through an animal membrane with great
difficulty (§ ix, 8).

2. Such a liquid, containing five per cent, of albumen, is to be used in the
following experiments. It coagulates on heating at about 70° C. if neutral.

3. To some of the liquid add a few drops of 0*1 per cent, solution of caustic
potash, and warm gently for two or three minutes. Boil. The liquid will no
longer coagulate, the albumin having been transformed into the alkaline modi-
fication (alkali-albumin or casein).

4. In a similar way treat another portion with a few drops of very dilute
sulphuric acid (o'l per cent.). Warm very gently for not less than five
minutes. On boiling no coagulation occurs, the albumin having passed into

its acid modification (acid-albumin, syntonin).

5. Cool some of the liquid obtained in 3. Colour it with litmus solution,
and add carefully very dilute acid. A precipitate falls on neutralization which
is soluble in excess of acid.

6. Make a similar experiment with the liquid obtained in 4, substituting
weak solution of potash for weak acid. A similar precipitate occurs on neu-
tralization, which is soluble in excess.

7. Take three portions, of 5 c.c. each, of the original liquid in three test-
tubes, and colour them with litmus. Dilute the O'l per cent, acid about 5

46 GASTRIC DIGESTION.

times, and add a drop of it to one of the portions ; to another add a drop of
potash solution similarly diluted. Heat all three tubes gradually, and note
the temperature at which each coagulates.

8. Make alkali-albumin solution as in 3. Divide it into two equal parts.
To one add two or three drops of ten per cent, ..solution of sodic phosphate.
Colour both with litmus and neutralize with weak acid. The portion without
sodic phosphate is precipitated. The other portion is not precipitated until
enough acid has been added to convert the sodic phosphate present into acid
sodic phosphate.

IV. — Characteristics of Proteids. Peptic Digestion.

1. Tests for proteid bodies in solution.

a. To some of the albuminous liquid referred to in § iii, 2, add strong
nitric acid. The precipitate obtained turns yellow on boiling.

b. Cool the liquid in a and add strong ammonia. The precipitate assumes

an orange tint (Xanthoprotein reaction).

c. To another portion add Millon's reagent. (Mercury is dissolved in
its own weight of strong nitric acid. The solution so obtained is diluted
with twice its volume of water. The decanted clear liquid is Millon's
reagent.) A precipitate is formed which turns dull red on boiling.

d. To a third portion add solution of potassic ferrocyanide, and a drop of
acetic acid. A white precipitate appears.

e. Introduce a fourth portion of the liquid into a test-tube containing one
drop of ten per cent, solution of cupric sulphate. On adding solution of
potash, a violet colour is obtained (compare § v, 2, b).

2. Paragloblllin (Fibrino-plastin).

a. Dilute five c.c. of serum with about seventy-five c.c. of water. Neu-
tralize carefully with a few drops of 0*1 per cent, sulphuric acid, and allow
the precipitate to settle.

This precipitate is soluble in excess.

b. Repeat a, passing a stream of CO2 through the liquid, instead of neu-
tralizing it with weak acid.

c. Repeat a and b without dilution. No precipitate is produced.

3. Peptic Digestion.

a. Introduce some fibrin into a test-tube and just cover it with 0*2 per cent,
solution of HC1. Allow it to stand for forty-five minutes in a water-bath at
from 35° to 38° C. At the end of this time the fibrin is swollen and trans-
parent, but has not dissolved.

b. Repeat a, using, instead of hydrochloric acid, water to which a drop of
glycerine extract of pepsin has been added.

The fibrin remains unaltered.

c. Repeat a, adding a drop of the same extract to the acid liquid. The
fibrin dissolves gradually.

d. Colour with litmus the liquid obtained in c. Neutralize carefully with
weak solution of caustic potash (§ iii, 6). The acid albumin formed during the
first stage of digestion is precipitated.

PANCREATIC DIGESTION. 47

V. — Pancreatic Digestion. Amylolytic Ferments. G'ycogen.

1. Pancreatic Digestion.

a. Introduce five c.c. of one per cent, solution of sodium carbonate, to which
a couple of drops of glycerine extract of pancreas have been added, into each
of two test-tubes. Boil one of them and allow it to cool. Add some boiled
fibrin to each, and place them both in the water-bath at 35° C. Compare
the changes produced with those observed in peptic digestion (§ iv, 3, c).

b. Examine the liquid product of a pancreatic digestion, previously pre-
pared by digesting albumin as in a. It is alkaline, and may have a charac-
teristic and offensive odour.

c. Boil some of this liquid after acidulating slightly. Albumin is coa-
gulated.

d. Colour another portion with litmus, and neutralize carefully (§ iii, 5) ;
alkali-albumin is precipitated.

e. In a liquid obtained by concentrating the product above referred to, after
having separated the greater part of the proteids contained in it, test for
Tyrosin by adding Millon's reagent and boiling. The presence of Tyrosin
is indicated by the reddish colour assumed by the liquid.

f. The liquid contains LeilCin in a crystalline form.

2. Peptones. A solution obtained either by pancreatic or peptic
digestion can be used.

a. The solution yields no precipitate either by boiling or by neutralization.

b. When treated as in § iv, I, e, it gives a red instead of a violet colour.
The liquid product of the slow putrefaction of proteids resembles in

most respects that of pancreatic digestion. To the latter, the presence of
septic organisms is not essential.

3- Amylolytic Ferments. Prepare some starch solution and
ascertain that it contains no dextrose, § i, 2 and 8. To another portion add
saliva, and place the tube containing the mixture in a water-bath at from
35° to 38° C. After a short time, the product will be found to contain
dextrose.

4- Glycogen.

a. To an extract of liver (prepared by extracting the perfectly fresh organ
with boiling water after washing) add a solution of iodine in potassic iodide.
The liquid assumes a red colour identical with that yielded under similar
circumstances by dextrine (see § i, 5).

b. On treating a slice of washed liver, hardened in alcohol, with iodine
solution, a similar colour is seen.

c. Repeat 3, substituting extract of liver for starch .paste, using the same
precautions.

1. Observe colour and reaction. The bile of carnivora is brownish-red
that of herbivora green. Neutralize and boil in a test-tube. Bile does not
contain albumin.

2. Acidify bile with acetic acid ; mucin is precipitated

48 BILE.

3. Prepare a solution of syntonin (§ iii, 4) by digesting albumin in water
containing O'2 per cent, of hydrochloric acid. On the addition of a drop of
bile, the mixture curdles en masse. If a large quantity of bile be added,
little or no precipitate may be formed, the liquid being rendered alkaline.

4. Boil bile with twice its bulk of strong hydrochloric acid for five minutes.
The bile is decomposed into bile-resin (cholic acid with colouring matter)
and glycin and taurin, the two last-mentioned substances remaining in
solution.

5- Pettenkofer's Test for CholiC acid. Spread a drop of bile
in a thin film on a white porcelain capsule. Mix with a drop of strong
solution of cane-sugar. Add concentrated sulphuric acid drop by drop, and,
if necessary, warm. A deep purplish-red colour appears.

6. Repeat the test with an alcoholic solution of bilin. The same colour
is produced.

7- Gmelin's Test for the colouring matter. Spread a drop of

bile in a thin film on a white porcelain capsule. Allow a drop of strong
nitric acid to fall into the middle of the film and observe the effect. The
drop becomes surrounded by rings of green, blue, red, and yellow, in the
order in which they have been named. Consequently the green, which is first
formed, is eventually farthest from the drop of acid. If, instead of allowing
the liquid to remain undisturbed, the acid be mixed with the bile, the liquid
passes through the same tints in the same order.

8. Warm a little nitric acid in a test-tube. Incline the tube and pour bile
down the side, so as to form a layer over the acid. The colours appear as in
7, at the line of contact of the two liquids.

9- Cholesterhl. Extract gall-stones with ether. The extract yields,
on evaporation, crystals of cholesterin, which, when dropped into warm
sulphuric acid, dissolve with a red colour. The residue, insoluble in ether,
consists of colouring matter and mucin.

10. Acidify 10 c.c. of bile in a flask with hydrochloric acid and add zinc.
Nearly close the flask with a cork to which acetate of lead paper is attached.
The taurin of the bile is decomposed, H2S being formed, which blackens the
lead paper.

Vll.— Urine.

1. Observe reaction and colour.

2. Determine the specific gravity, either by weighing or with the urine-
meter. Observe the effect of temperature.

3. Compare fresh with stale urine as regards appearance, smell, and re-
action.

4. Sulphates. Add baric chloride after acidifying with hydrochloric
acid. A white precipitate of baric sulphate is formed.

5- Chlorides. Add argentic nitrate after acidifying with nitric acid. A
white curdy precipitate of argentic chloride is produced.

6. Phosphates. Add ammonic molybdate to urine which has been
mixed with half its volume of nitric acid. Boil. A yellow crystalline pre-
cipitate falls.

URINE.

49

7- Urea. To urine evaporated to one-third, add a drop of nitric acid in a
watch-glass. Glistening scales of urea nitrate are abundantly formed in the liquid.

8. Uric Acid. To a hundred c.c. of urine add 5 c.c. of strong hydro-
chloric acid. Allow the liquid to stand for forty-eight hours. Dark red
crystals of uric acid separate from the liquid.

9- Urochrome. Precipitate about 50 c.c. with lead acetate and a drop
of ammonia. Filter. The filtrate is colourless. Scrape the precipitate from
the filter paper into a capsule. Mix with a few drops of strong sulphuric acid
and add to the pasty mass a little alcohol. Filter. The yellow filtrate on
boiling with excess of strong sulphuric acid turns black. Dilute the acid
liquid with a large quantity of water. The uromelanhie which separates
in flocks is characterized by its extreme solubility in ammonia. It can be
precipitated from its solution in ammonia by sulphuric acid.

10. IndigO. To 500 c.c. of urine add 250 c.c. of pure hydrochloric acid.
Allow the liquid to stand twenty-four hours. A coppery scum floats on the
surface. Filter. Treat the filter first with ammonia to extract the urome-
lanine, secondly with cold alcohol, which acquires thereby a red colour. On
boiling the residue in alcohol a blue solution is obtained, which exhibits the
absorption spectrum of indigo-blue.

N.B. — In consequence of the large quantities which must be used, this
experiment cannot be carried out by each student.

vin. — i. Quantitative determination of Urea. Urea

(CO N2H4) when decomposed by suitable oxidizing agents, yields CO2, H2O
and N. The most convenient reagent for effecting this decomposition is an
alkaline solution of sodic hypobromite. The CO2 is absorbed by caustic soda.
The nitrogen which is disengaged is collected and measured in a suitable
apparatus. Every 37^3 c.c. of nitrogen, at ordinary pressure and temperature,
corresponds to O'l grm. of urea. The hypobromite solution is prepared by
adding 25 c.c. of bromine to 250 c.c. of a solution containing 100 grm. of
caustic soda.

a. If Russell and West's apparatus is used, measure off in a
pipette 5 c.c. of urine and introduce carefully into the bottom of the "re-
action-tube." Rinse the sides of the tube with distilled water until the liquid
reaches the constriction. Plug with the caoutchouc stopper, avoiding the
introduction of air. Fill up the tube with the hypobromite solution and half fill
the trough with water. Fill the measuring tube with water and invert it in the
trough. Lift out the stopper, and, without loss of time, place the measuring
tube over the reaction-tube. Warm the bulb of the latter until the liquid just
boils, and read off the quantity of gas collected.

b. If Dupre'S apparatus be used, introduce 25 c.c. of hypobromite
into the flask c. Measure off 5 c. c. of urine into the test-tube, and close the
flask with the caoutchouc stopper to which the test-tube is attached. Open
the pinch-cock d and lower the measuring tube a, until the surface of the water
is at the zero point of the graduation. Close the pinch-cock and raise the
measuring tube. If the apparatus be tight, mix the urine gradually with hypo-
bromite solution by inclining the flask. Finally, tilt the flask so as to rinse out
the test-tube with the solution, and shake well for a few seconds. Immerse

50 UREA.

the flask in a vessel containing water at the same temperature as that in the jar.
At the same time lower the measuring tube. After two or three minutes,
raise the measuring tube again until the surfaces of the liquids inside and out
coincide. Read off the quantity of nitrogen which results from the de-
composition of the 5 c.c. of urine.

DUPRE'S UREA APPARATUS.

The stopper and te&t-tube represented in the upper left hand of the figure take the place
of the stopper, pipette and tube e f. The woodcut has been kindly lent by Dr. Dupre.

Phosphates. When solution of uranic nitrate or acetate is added in
successive quantities to a hot solution containing phosphates, previously
acidified with acetic acid, the whole of the uranium is precipitated so long as
any phosphate remains in solution as uranic phosphate. As soon as an excess

PLASMA AND SERUM. 51

of uranic salt is present, it can be detected by potassic ferrocyanide, which
gives a brown colour with uranic salts.

The standard uranic nitrate solution contains 35*5 grammes in a litre. One
c.c. corresponds to O'OO$ gramme P2O5.

To 50 c.c. of urine add 5 c.c. of a solution containing 100 grammes of sodic
acetate in 900 c.c. of water, to which 100 c.c. of glacial acetic acid have been
added. Heat the 55 c.c. to 80° C. Add the uranic nitrate solution, until a
drop of the mixture placed on a white porcelain slab gives a distinct brown
colour, with a drop of potassic ferrocyanide. Note the quantity of solution
used and calculate therefrom the percentage of P2O5 in the urine. *

IX. — Blood — Plasma and Serum.

*+* The experiments described in this section cannot be satisfactorily carried out in warm

weather.

1. Dilute about I c.c. of sodic sulphate plasma (obtained by collecting
blood in one-third of its volume of saturated solution of sodic sulphate) with 20
times its volume of water and place in a water-bath warmed to about 35° C. ; it
will probably coagulate in about 20 to 30 minutes.

2. To a second similarly diluted liquid add a drop or two of solution of
"blood-ferment " (prepared by precipitating serum with alcohol, collecting the
precipitate, drying in vacuo and extracting with water). The addition of this
solution promotes coagulation.

3. To 2-3 c.c. of pericardial fluid (from the horse) or hydrocele liquid add a
little serum and place the mixture in a warm bath ; it will coagulate.

4. Saturate about 5 c.c. of pericardial fluid with sodic chloride, by adding
finely-powdered salt, and shaking ; a proteid substance separates and forms a
thick scum on the surface. Pour off the liquid, dissolve the scum in water,
add a few drops of serum, and place in the warm bath ; the mixture will
coagulate.

5. Precipitate about 5 c.c. of sodic sulphate plasma as in 4, dissolve the
sticky precipitate in water and place in the warm bath ; the solution will
coagulate.

6. Acidify 5-10 c.c. of serum with a drop of acetic acid and boil, filter off
the albumin and evaporate the residue. Sodium chloride crystallizes in aggre-
gations of cubes.

7. Dilute i part of serum with 15 parts of water, add a drop or two of
dilute acid (o'l per cent.). Paraglobulin is precipitated (see § iv, 2, a).

* For details as to the hypobromite method, see Dupre's original paper in
the Journal of the Chemical Society, 1877, vol. i. p. 534.

The method for the determination of P2O5 is practised in this class as an
example of a volumetric process. For other methods relating to the urine
consult Handbook for the Physiological Laboratory, pp. 545-558. It is
important to remember, that in order to obtain trustworthy results, as
scrupulous care must be taken in the measurement and collection of the urine
passed during the period of observation as in the analytical procedures.

E 2

Aa B C

COLOURING MATTER
D E b F

OF BLOOD. 53

8. Tie up in a piece of bladder or other animal membrane some whipped
blood, and place the bag containing the blood in a beaker of distilled water.

The colouring matter and proteids exhibit but a slight tendency to pass
through the membrane ; the soluble salts pass through readily, and their
presence can be recognized in the water by the usual tests.

9. Pour over some fibrin contained in a watch-glass some solution of
peroxide of hydrogen. Bubbles of oxygen are given off. If some tincture of
guaiacum be added a blue colour is developed. Gluten, potato peelings, and
many other substances develop a blue colour under the same conditions.

X. — T/ie Colouring Matter of the Blood.

1. Observe the solar spectrum, noting the positions of the dark lines
D, E, b and F, in relation to the colours. Compare it with the spectrum of
a gas flame, which shows no dark lines.

2. Observe the spectrum of a flame coloured with sodic chloride, noting the
position of the bright yellow line.

3- Oxy-hgemoglobin. Introduce defibrinated blood into a test-tube,
and observe its opacity when undiluted.

a. Dilute by adding five to ten times its bulk of water. Place the test-tube
in front of the slit of the spectroscope, direct it to a gas flame. The only light
which passes through is that of the red end of the spectrum.

b. Add water until the green appears. Note the dark space (absorption
band.) between the red and green.

c. Dilute still further until the yellow-green light is distinguishable in the
middle of the dark space, dividing the single broad band into two.

d. After a further addition of water, note that the band nearest the D line
is somewhat more sharply defined than the other. The spectrum is still
shortened by the absorption of its violet end.

e. On diluting, until the solution is almost colourless, two faint bands ar
still visible.

f. Map on the diagram the appearances observed in 3, b and d.

4- Reduced Haemoglobin. To some blood diluted as in 3, dt add a
drop of solution of ammonic sulphide, and warm gently. The colour becomes
purplish. Place the tube in front of the slit as before, and observe the
change which has occurred. A single absorption band, with ill-defined edges,
takes the place of the two bands previously observed. Map its position on
the diagram.

5- Alkaline Hsematin. Add to solution of blood, rather stronger
than the last, a drop of solution of caustic potash. Warm gently; the colour
completely changes. Ah absorption band appears to the left of the line D,
and much of the blue end of the spectrum is cut off.

6. Reduced Alkaline Hsematin. To the solution obtained in 5
add a drop or two of ammonic sulphide and warm gently. Observe the
change of colour. Dilute if necessary. A strongly marked band is seen to the
right side of the line D, and a second less defined, which nearly coincides with
the line E.

54 COLOURING MATTER OF BLOOD.

7. CO-ll86IIlOglobill. Blood which has been acted upon by carbonic
oxide has a peculiar cherry-red colour. The two absorption bands have nearly
the same position as those of Oxy-haemoglobin, but no change is produced
when the liquid is treated with reducing agents, as in 4.

PART II.

THE MECHANICAL PROCESSES.
MUSCULAR CONTRACTION.

MUSCLE consists of parallel fibres, each of which is a
tube containing contractile living substance. This living
substance is of two kinds, which differ in their optical
properties, and are arranged in layers alternating with
each other. In contraction their absolute and relative
volumes alter. So long as the tissue is living, the con-
tractile substance can be squeezed out as juice (muscle-
plasma), but after death it solidifies and exhibits a tendency
to split, transversely and longitudinally. Muscle is neutral
when living, acid after death. Muscle-plasma coagulates
spontaneously at all temperatures above that of freezing.
At 40° C. coagulation is instantaneous : the promptitude
with which it occurs is the less, the lower the temperature.
The coagulum is myosin (see p. 31).

The chemical changes which constitute the life of muscle
manifest themselves in the production of CO2 and H2O,
which are disengaged in the proportions in which they
result from the combustion of carbohydrates. When the
tissue is inactive, these are formed in very inconsiderable
quantities ; but in muscular activity, the rate of discharge
is increased in proportion to the work done.

Living muscle is elastic, contractile and transparent.
As life ceases it stiffens, shortens, loses its contractility
and transparency, and the contents of its fasciculi become
solid. Death of muscle is promoted by defective blood
supply, high temperature or injury. It is slow and

56 MUSCULAR CONTRACTION.

gradual in the frog, rapid in man and mammalia. It is
associated with chemical changes which resemble those
which take place in contraction.

Partial rigor can be induced in living muscle by arrest, and removed by
restitution, of the circulation. Muscle becomes rigid at about 45° C. in
'frogs, 48° to 50° in mammals. Rigor occurs sooner after death in exhausted
muscles than in others : all rigid muscles are acid.

In doing work muscle shortens and thickens. Its vol-
ume diminishes very slightly and it becomes more exten-
sible. Every muscular contraction results from excitation
either extrinsic or intrinsic. An instantaneous extrinsic
excitation of a muscle by its nerve produces a single
contraction, called a twitch. The contraction begins a
certain time after the excitation (period of latent excita-
tion of du Bois-Reymond) ; it rapidly increases to a maxi-
mum and then gradually subsides. After contraction
has ceased the muscle is nearly as long as before, and
soon quite as long.

By the myographic method (see Practical Exercises)
a single contraction may be investigated with reference to
the time after excitation at which it begins, to its duration
and character, and to the modifications produced by
changes in its physiological condition, or in its temperature.
If two or more instantaneous excitations of a muscle
through its nerve follow each other, the effect is augmented
by each successive excitation; but the increment produced
by any single excitation is always less than that produced
by its predecessor. The effect of a series of equal exci-
tations following each other at very short intervals of
time, although apparently continuous, consists in reality
of a succession of instantaneous contractions, of which
the frequency is the same as that of the excitations. This
condition is called, in physiological language, Tetanus.
The number of single contractions per second of which a
tetanic or voluntary contraction is constituted may be
judged of by the " tone " heard in the contracting muscle.

MUSCULAR CONTRACTION. 5/

In ordinary voluntary contraction in man, the tone has a
vibration rate of from 38 to 40 per second.

Under the influence of the arrow poison (curare), the
end-organs of the muscular nerves become incapable of
performing their function, so that the muscles of animals
poisoned by this drug are virtually nerveless. The con-
traction produced by instantaneous excitation, at any
point of a " curarized " and extended muscle, progresses
from the point excited in the direction of the fibres. In
fresh muscles the rate of progress of the contraction wave
is from 3 to 4 metres per second ; the duration of the
contraction is about O'O/ second ; hence the wave length of
contraction is about a quarter of a metre. In exhausted
muscles and in muscles under the influence of cold, the
rate of progress is slower than in fresh muscle at the
ordinary temperature.

The above statements refer to the effects of single induction shocks, or of
successions of them. If a voltaic current is led for a moment through a
curarized muscle, the tissue is excited at the negative pole (cathode) at the
closure, and at the positive pole (anode) at the opening of the circuit. In
this case, the muscle remains contracted during the whole period that the
current is passing.

By the term " absolute force" is denoted the heaviest
weight a muscle is able just to lift, when contracting to
the utmost advantage under the influence of a sufficient
excitation. The weight which a muscle is able to lift
varies according to its extension, being greatest when it is
most extended — consequently greater at the beginning of
a tetanic or voluntary contraction than at the end. The
maximum quantity of work is done by a muscle when it
is nearly loaded to the utmost throughout the whole con-
traction. In order that this may be the case, the load and
the power of the muscle to lift it must diminish at the same
rate. If the load to be lifted remains constant, the muscle
acts most advantageously (i.e. does most work) when the

58 MUSCULAR CONTRACTION.

weight is considerably less than the maximum weight
which the muscle is able to lift. Muscle is elastic : a
muscle extended by a load recovers its original length
when the load is removed. When a loaded muscle is
extended by successive additions of equal weights to its
load, the increase of length, resulting from each addition,
becomes less and less as the extension proceeds, until no
further increase is observable. Of two muscles, of which
one is in tetanus, the other at rest, the former is more
extended by the same weight than the latter.

In contraction the temperature of muscle is slightly
raised : the greater the effort, and the less the work done,
the greater the rise.

In living muscles, differences of electrical tension are
usually observed 'between different parts of the natural
surface, which differences can be shown to be intimately
associated with the vital properties of the tissue, and
cease with the cessation of its life. The greatest differ-
ences (often amounting to several hundredths of a Volt)
present themselves when a sound surface is compared
with an injured one, the injured part being always
negative to the sound. In a muscle which is at rest,
all parts being in the same physiological condition, the
surface is -(according to Hermann) isoelectric or equi-
potential. Such a condition is rarely met with in the
voluntary muscles, for the slightest exposure or injury
produces electrical inequality, but is easily observed in
the resting heart. In voluntary muscles, separated from
the body, it is commonly observed that the end surfaces
are negative to the lateral surfaces. During the state
of excitation, which precedes contraction (period of
latent excitation) the electrical state of (uninjured) mus-
cular tissue undergoes a change which consists in its
becoming negative to the unexcited parts. In tetanus
this change precedes each single contraction (see p. 56).
In nerveless (curarized) muscles, the excitatory state

CIRCULATION. 59

is propagated along the fibres at a rate which agrees
with that of the propagation of the wave of contraction,
so that the latter is preceded in its progress by the
former. In nerved muscles, which are excited through
their nerves, the excitatory waves are similarly propa-
gated, but originate from nerve endings. In injured
muscle the electrical difference between injured and
uninjured surfaces is diminished during excitation.
This excitatory effect was therefore called by du Bois-
Reymond the "negative variation."

The excitatory disturbance is, in all cases, followed by
other changes, which correspond in time to the contrac-
tion, but have not yet been fully investigated.

All of the phenomena above described are comprised by du Bois-Reymond
in a theory, according to which every portion of living muscular fibre con-
tains electromotive particles, each of which has ends (poles), which are
directed towards the ends of the fibre, and are negative to the zonal surface,
which corresponds to the surface of the fibre. The effect of excitation is
to produce a momentary diminution of the electromotive force of these
particles. The particles being called by du Bois-Reymond * molecules, ' the
theory is known as the molecular theory of the muscle current.

In involuntary muscle the process of contraction is
similar, but much slower. It is attended with electrical
changes of the same nature as those observed in volun-
tary muscle.

CIRCULATION.

The Arterial Circulation. — The arterial system is an
elastic receptacle for blood, the form of which is dendritic.
At the ends of the ramifications, blood flows by in-
numerable capillary channels into the venous system.
Into the trunk, blood is injected at intervals by the
heart, each injection lasting from three to four-tenths of
a second. In the aorta the blood is squeezed by the
arterial wall with pressures which probably vary from

60 CIRCULATION.

6 to 10 inches (= 150 to 250 millimeters) of mercury
= J to | of an atmosphere = 3 to 5 Ibs. on the square
inch. It is this pressure which is the cause of the cir-
culation. Its maintenance is the function of the heart.
The sum of the lumina of the capillaries is much greater
than that of the aorta : the velocity of the capillary
blood-stream is in the same proportion less. Arterial
tissue recovers its length after stretching as perfectly as
muscle : it is however more extensible. In the living

o

body, its elastic properties are modified according to the
degree of contraction of the muscular elements it con-
tains.

The arterial blood-stream can be best understood by
reference to the schemata described below.

Schema I. As regards the relation of pressure to pro-
gressive motion, the arterial system is represented by a
tall cylindrical bottle from the bottom of which water
flows through a horizontal tube of equal width through-
out. In the arterial system, as in the schema, the lateral
pressure (supposing the velocity of the blood-stream to
be constant) is proportional to the sum of the resistances
in front. If such a bottle, having an aperture equal to the
lumen of the aorta, were substituted for the heart,
the height to which it would be necessary to fill it with
blood in order to carry on the circulation at the normal
rate, would represent the force required for that purpose.
That height multiplied by the weight of blood discharged
per second in grammes, would give in gramme-meters the
work done by the heart in the same time in maintaining
the circulation.

Schema 2. As regards wave motion, or pulsation, it is
represented by an elastic tube, ab, closed at both ends
and moderately distended with liquid, into which water is
suddenly and for a short time injected. The phenomena
observed remain unaltered, if, instead of closing the tube
at its ends, we imitate the conditions of the circulation by

CIRCULATION. 6l

injecting liquid into it at short intervals at a, allowing it
to flow out by a small opening at b. In the arterial system,
just as in this schema, the momentary distension produced
in the aorta by each injection of blood, is propagated to
other parts of the system at a rate which is dependent
on the previously existing pressure. Every such sudden
distension is followed sooner or later by a second, which
is called the second beat

By virtue of the elasticity of the arteries, part of the
motion which is communicated to the blood during each
ventricular systole is stored as arterial distension, to re-
appear as progressive motion during the diastolic interval.
If the arteries were not elastic, this motion would lose
itself in the shock of the blood against the rigid arterial
wall, whereby the arteries would be injuriously strained at
each injection of blood, and the effect of the heart's action
would be diminished.

Investigation of Arterial Pressure. — The haemadynamo-
meter is a mercurial manometer of which one limb can be
connected with an artery by a tube containing solution of
sodic bicarbonate. In order that the measurement may be
accurate, it is necessary (i) that the mean level of the
mercury surface in the proximal limb should be the same
as that of the arterial aperture ; and (2) that the tube
should enter the artery at right angles to its axis.

Any instrument by which the arterial pressure can be
measured, by inscribing its variations on a surface moving
horizontally by clockwork at a uniform rate, is called a
kymograph. A mercurial kymograph consists of three
parts — the clockwork and recording cylinder ; the mano-
meter and writer ; the tube and cannula by which the
manometer is connected with the artery. Its uses are
(i) to measure the mean arterial pressure and to record its
variations ; (2) to measure the duration of the pulsation
intervals. Its chief defect arises from the " proper
motion " of the mercurial column. The spring kymograph

62 CIRCULATION.

on Bourdon's principle is nearly free from " proper motion,"
and consequently enables us to measure the fine variations
of arterial pressure in the course of each pulse interval.

The pulse as felt by the finger indicates the moment of
greatest distension, i.e. that of greatest pressure in the
artery. The distinctness with which it is felt is propor-
tional to the shock communicated to the arteries by the
heart. Pulses are classified according to frequency, hard-
ness, duration and dicrotism. All of these characters may
be appreciated by the finger, but are studied more accu-
rately by the sphygmograph.

Three events may be distinguished in every pulse, viz.,
the beginning of the expansion, the collapse, and the
beginning of the second beat. Of these the first occurs
in the normal radial pulse about 0*15 second after the
beginning of the effective part of the systole of the left
ventricle. The second is synchronous with the end of
the systole, and hence immediately precedes the closure
of the sigmoid valves. The third is synchronous with, or
immediately after, the closure of the valves.

The graphical characters of the arterial pulse, e.g. the
radial, are determined by (a) the character of the diastolic
notch which, in the tracing, separates the first from the
second ascent, and (b) the relative height of the second
ascent. The notch is produced by the sudden cessation of
the flow of blood from the ventricle into the aorta. It
may be generally stated that the shorter the duration of
the systole and the less the vascular resistance, the deeper
is the notch.

The second beat is determined entirely by events which occur in the arteries
and capillaries. When any part of an artery is suddenly distended, all parts
of the arterial tree beyond pulsate after it ; but each pulsates at a different
moment, according to its distance from the par* primarily distended, and as
each attains its .maximum of distension, it sends back a return wave of expan-
sion. The moment at which the strongest return waves, and the greatest
number of them, arrive at the point of observation, is that at which the second
beat occurs.

CIRCULATION. 63

Unnatural frequency of pulse depends either on func-
tional disturbance of the cerebro-spinal centres or increased
bodily temperature (pyrexia). Unnatural celerity of pulse,
i.e. diminished duration of the period of expansion, is ob-
served either in association with increased frequency, or
in consequence of mechanical defect of the aortic valve.
The opposite condition (tardiness of pulse) occurs in
advanced age, and in collapse (e.g. in concussion), or under
the influence of certain drugs, particularly of opium and
digitalis.

Velocity of the Circulation. — The velocity of the blood-
stream is dependent on the relation of the effort made by
the heart to the resistance to be overcome in the vessels.
This resistance varies according to the condition of the
vascular nervous system.

It is believed that the velocity of the blood-stream in
the aorta is about a foot in a second ; in the capillaries
about i-5oth of an inch ; and that the circulation is
accomplished in the time occupied by about thirty pulsa-
tions of the heart.

Of the instruments used for investigating the progressive
movement of blood in the arteries, those by which the
quantity conveyed in a given time can be estimated are
called Dromometers (e.g. Volkmann's and Ludwig's), those
by which the rate of movement only is determined, Tacho-
meters. By the latter we learn that in the large arteries
the second beat or expansion is attended by a cessation or
even reversal of the blood-stream ; by the former, that the
rate at which blood is transmitted through an artery is
subject to great and often sudden variations, and that
these variations are independent of the rate at which blood
is discharged into the arterial system by the heart.

Capillary Circulation. — In studying the circulation in the
transparent parts of animals, we observe that the smallest
arteries are subject to great variations of diameter, and
often contract rhythmically ; that the progressive move-

64 CIRCULATION.

ment in arterioles is more rapid than in veins of corre-
sponding size ; that in the veins the coloured corpuscles are
carried along by the axial stream, the leucocytes tending
towards the vascular wall ; that when a tissue is injured
the capillaries begin first to widen and then to leak, the
plasma and leucocytes passing out in succession, and that
more intense injury produces stasis and extravasation of
the coloured disks.

Circulation in the Liver, Kidneys, and Spleen. — The dif-
ference between the pressure which exists in the trunk of
the portal vein and that of the hepatic vein probably does
not exceed half an inch. Consequently the blood-stream
through the liver is extremely slow. In the kidneys, the
blood enters the glomeruli at high pressure and with rapid
motion ; in the capillaries of the convoluted tubes the
motion is slow, and the pressure that of the venous system.
In the spleen, the quantity of blood contained in the
organ at one time, and, consequently, its bulk are subject
to very great variations ; these are mainly due to the
action of the muscular fibres contained in the capsule and
framework.

Venous Circulation. — The capacity of the venous system
much exceeds that of the arterial, and is sufficient for the
reception of the whole of the circulating blood. The mean
lateral pressure in the venous system, though much inferior
to that which exists in the arteries, is dependent on it and
varies with it. It is greater in the capillary veins than in
the venous trunks : this difference is the chief cause of the
venous blood-stream. It is greater during inspiration than
during expiration. This difference is more marked in the
intra-thoracic veins (where during inspiration the lateral
pressure sinks below that of the atmosphere) than in others :
it manifests itself in the respiratory movements of the brain,
and other similar phenomena. The venous blood-stream
is promoted by intermittent external pressure, hindered by
continuous pressure. The venous pressure, and, conse-

CIRCULATION. 65

quently, the quantity of blood in a limb, and the velocity
of the venous blood-stream, are much influenced by posi-
tion ; but this does not affect the quantity of blood .trans-
mitted through the part in a given time. A slight dimi-
nution of the pressure in the veins nearest to the heart
accompanies each pulsation : this is due to the diminution
of the volume of the heart, which occurs at the moment of
ventricular systole. When, from disease, the tricuspid
valve is incompetent, the opposite effect is produced, and
is called the venous pulse.

Veins are contractile, but there is no proof that their
contractility is of physiological importance in man. In
certain animals, the veins contract rhythmically.

The Lymph- Sir earn. — The progressive motion of the
lymph is dependent on the difference between the pressure
under which liquid exudes from the capillaries into the
tissue interstices from which the lymphatics spring, and
the pressure which exists in the lymphatic trunks. In all
muscular parts it is promoted by the alternate tension and
relaxation of the tendons and aponeuroses. In the visceral
cavities it is similarly aided by the respiratory variations
of external pressure to which the trunks are subjected, as
well as by the circumstance that the mean pressure in the
abdomen is greater than in the thorax. Solid particles,
if of sufficient minuteness, whether introduced into the
blood-stream or into the tissues, find their way into the
lymphatics, which can usually be " injected " by the intro-
duction of any particulate liquid into living tissue. It is
probable that such particles are for the most part arrested
in the lymph glands. The particulate constituents of
chyme are forwarded from the intestinal cavity into that
of the lacteals by the agency of the living protoplasm of
the epithelium and mucosa. The further progress of the
chyle in the mesentery is promoted by muscular action.

66 THE HEART.

THE HEART.

The heart consists, in its simplest form, of a muscular
dilatation provided with a valve or valves at either open-
ing, and a venous antechamber or reservoir, which in
the lower vertebrates is more perfect than in man and
mammalia. In the osseous fishes another dilatation
(the bulbus arteriosus) exists between the ventricle and
the branchial arteries, the function of which is to store up
energy during the ventricular systole, as the arteries do
in mammals. In the cartilaginous fishes the bulb is a
muscular organ in which energy originates, and it is often
provided with valves. These complications in the struc-
ture of the central organ are rendered necessary by the
simplicity of the circulation. In the batrachians the bulb
is less required, for only part of the blood-stream passes
through the respiratory apparatus, but the auricles are
still provided with valves. In the mammalian heart, the
mechanism of respiration renders the auricular valves
unnecessary.

Motions of the Heart and phenomena which accompany
them. — The form of the contracted human heart is that
of a cone, of which the base is elliptical and the apex
rounded off; in the relaxed state the heart assumes the
form of the wedge-shaped space in which it is contained.
It approaches the anterior wall of the chest in ex-
piration, and recedes in inspiration. In systole the ven-
tricles suddenly draw themselves together towards a part
of the septum which is about two-thirds of the way from
the auriculo-ventricular groove to the apex.

On grasping the contracting heart of an animal it is felt
to widen and become harder. The impulse is due to
these changes of form and consistency. It is felt most
strongly between the fifth and sixth cartilages.

Each heart period is divided into two parts, the period

THE HEART.

67

of repose and that of action. The period of rest com-
mences with the closure of . the sigmoid valve. Its
duration varies according to the frequency of the con-
tractions. During the whole of it, the cavities fill with
blood. The period of action, of which the duration in
man is rather more than four-tenths of a second, com-
mences with the auricular systole. About one-tenth of a
second later, the ventricular systole begins : thereupon
the auriculo-ventricular valves close and the blood is
suddenly ejected into the aorta and pulmonary artery.
At the end of the ventricular systole, which lasts about
three and a half tenths of a second, the ventricle sud-
denly relaxes.

The lateral pressure in the auricles is about equal to
that of the atmosphere. It rises, however, slightly in
auricular systole, attaining its maximum at the com-
mencement of ventricular systole. In the ventricles the
pressure sinks below that of the atmosphere immediately
after the sigmoid valves close ; at the moment of systole
it rises above the pressure in the aorta.

Each action of the heart is accompanied by two sounds.
The first is produced by two causes, the muscular con-
traction and the sudden tightening of the heart. The
second sound is due to the tightening of the aorta and
sigmoid valves.

The filling of the right ventricle may, in the normal
state, be attributed to the influence of the elasticity of
the lungs, and in its absence to the pressure in the
systemic venous system. The filling of the left ventricle
is mainly due to the pressure in the pulmonary veins,
and to the " aspirating power " of the ventricle itself. It
is supposed by Briicke to be aided by the^distension of
the coronary arteries.

It is probable that about 195 grammes of blood are
discharged by the left ventricle at each contraction.
If the lateral pressure in the aorta were equal to that of

F 2

68 RESPIRATION.

a column of blood two metres in height, the work done
by the left ventricle in each systole would amount to about
four-tenths of a kilogramme- meter, without counting any
work done within the heart itself.

RESPIRATION.

The alternating in-flow and out-flow of air, which con-
stitute respiration, result from the action of muscles which,
by changing the capacity of the chest, produce corre-
sponding, though not necessarily proportional, variations
of the capacity of the thoracic air cavity. In the state of
rest, that is when the chest is not acted on by contracting
muscles, its capacity is determined by the opposed trac-
tions of elastic structures in a state of tension — namely,
that of the lungs, which tends to diminish it, and those of
the ribs and cartilages, intercostal muscles, and diaphragm,
which tend to enlarge it. The capacity which the chest
possesses under this condition is called the capacity of
equilibrium. In ordinary tranquil breathing the chest is
expanded beyond its equilibrium capacity in inspiration,
but returns to it in expiration. The muscles by which
this is effected are the diaphragm and the scaleni, which
act by increasing the vertical diameter of the chest, and
the external intercostals, levatores, and intercartilaginous
internal intercostals, which increase its girth. When a
larger exchange of air is required by the organism
than can be thus secured, other inspiratory muscles
come into play, which, by their combined action, aid in
the expansion of the chest in inspiration, while in expir-
ation the whole visceral cavity is constricted by the
action of the muscles of the abdominal wall, of the lower
internal intercostals, of the serrati postici inferiores, and
of the sacro-lumbales — in consequence of which action the
chest acquires in expiration a capacity less than that of
equilibrium.

RESPIRATION. 69

In tranquil breathing the glottis is motionless, but in
the more active modes of respiration, the cords diverge in
inspiration, resuming their normal position in expiration.
In extreme dyspncea, inspiration is accompanied by dila-
tation of the nostrils.

The lungs, mechanically considered, may be regarded as
a collection of elastic and very distensible bags, all of which
communicate freely with each other as well as with the
atmosphere. The volume of each lung, when removed
from the chest, is much smaller than that of the cavity in
which it is contained, and which, in its normal state of
expansion, it completely fills ; consequently, when a pleural
cavity is opened, the lung collapses. When the closed
pleura is brought into communication with a mercurial
manometer, the column in the open limb falls, so that the
pressure to which any fluid in this cavity is exposed is less
than that of the atmosphere. As measured when the
chest is in the condition of equilibrium, the difference can
be shown to be about ifo of an atmosphere (7 millimeters
mercury). In natural inspiration it increases to 8 or 9
millimeters, and in full inspiration it may be increased to
30 millimeters. It is increased by any cause which de-
stroys the expansibility of any part of the lung.

As the organs contained in the chest are under the same
pressure as the fluid in the pleura, the flow of blood towards
the heart is aided by the elasticity of the lungs. The same
condition is also favourable to the diastolic filling of the
heart, which contracts with more effect after each inspira-
tion, so that the arterial pressure rises.

An adult male inspires from 25 to 30 cubic inches at
a time, and about 20 times per minute ; consequently,
from 500 to 600 cubic inches per minute. The greatest
volume of air which an individual is able to exchange
in a breath is called the "vital capacity." The mean
"vital capacity" of a man of ordinary height and build
(5 feet 7 inches, and 32 inches in girth) is 210 cubic

70 BODILY MOTION.

inches = 3480 cubic centimeters. A woman 5 feet 5 inches
in height and of average girth, has a vital capacity of
not more than 160 cubic inches. From observations
made on a large number of male adults of ordinary
heights, it has been found that on the whole the vital
capacity varies according to the height of the individual,
in such a way that a difference of I inch in height
makes a difference of 150 centimeters, i.e. about 9
cubic inches in vital capacity ; and further, that be-
tween two men of the same height, but different girth,
there will be a difference of about the same amount,
viz., 9 cubic inches for every inch difference in girth.
Similar laws have been found to hold good as regards
female adults. In individual instances this result is
much affected by the flexibility of the chest, the mus-
cularity of the individual, and other circumstances, the
influence of which it is difficult to estimate. After the
most complete expiration possible, a quantity of air re-
mains in the thorax, which is sometimes called " residual,"
and amounts to about 90 cubic inches. In the equilibrium
position the chest contains about 190 cubic inches ; when
fully expanded, about 300, of which 210 can be expelled.

Two sounds are heard in listening to the normal chest,
viz., the vesicular inspiration sound, and the bronchial
sound, which is chiefly expiratory. The former has its
seat in the infundibula, the latter in the rima glottidis. In
each case the production of the sound is dependent on the
sudden widening of the channel along which the air flows.

BODILY MOTION.

Action of Voluntary Muscles on the Skeleton. — With the
exception of those cases in which voluntary muscles act
peristaltically, the effect of muscular contraction in produc-
ing motions of the whole body, or of parts of it, is always

BODILY MOTION. /I

dependent on approximation of the ends of the muscles
concerned. The direction and extent of these motions are
regulated by the forms of the movable bones, and of the
symphyses or of the joints by which they are connected
with the rest of the skeleton. The term symphysis is appli-
cable to the connection of two bones by a perfectly elastic
material, in such a way that, after having been bent or
twisted on each other, they tend to recover their relative
normal position. The only example of this in the human
skeleton is that of the bodies of the vertebrae. The essen-
tial difference between the joint and the symphysis consists
in this — that in the former the bones have no normal
relation to each other, but assume with equal readiness
any among the infinite number of relative positions which
the structure of the joint allows.

Joints are divisible into those which have a single axis
of rotation (hinge joints) and those which have several
axes (ball-and-socket joints). It is essential to the efficient
working of a joint of either kind (i) that the two surfaces
should be kept in apposition ; and (2) that the movements
of the bones on each other should be restrained within
due limits ; accordingly contrivances exist in all joints for
these two purposes.

The efficiency of the action of a muscle in producing
motion about a joint depends on the mode of its attach-
ment to the bones. In all cases the effect produced is to
the force exerted, as the distance of the nearest point
of the straight line which connects the origin with the
insertion of the contracting muscle from the axis of
rotation of the joint is to the distance from the joint to the
insertion of the muscle.

The maintenance of the erect posture is dependent on
constant muscular exertion, for the line of gravity of the
head falls far in front of the condyles of the occipital bone,
that of the head and trunk together behind the line which
joins the hip joints, that of the whole body, in front of the

72 VOICE AND SPEECH.

ankle joint. As regards each of these parts, excepting the
head, the supporting muscles are aided by the forms of the
joints and the arrangement of the ligaments. In sitting,
the body if unsupported in front or behind is balanced on
the tubera isc/rii.

- In walking, the position of the advancing or acting limb
at the beginning of each step, is represented by the vertical
side, the following limb by the hypothenuse of a right-
angled triangle, of which the base is a step or pace, and
the apex is in the position of the hip-joint : at the same
moment the knee and ankle joints are flexed. Towards
the end of each step, both joints become strongly extended.
During each step the pressure of the foot upon the ground
increases towards the end : the pelvis oscillates once from
side to side and twice up and down, for every two paces, i.e.
in each period of progression. In walking there is no
interval during which the weight of the body is unsup-
ported : in running an interval exists, the relative length
of which increases as the pace quickens.

VOICE AND SPEECH.

The movements of the thyroid and arytenoid cartilages
by which the form of the glottis and the tension of the
cords are modified, are, (i) rotation of the thyroid on its
horizontal axis ; (2) rotation of each arytenoid on its
vertical axis ; and (3) rotation of each arytenoid on its
horizontal axis. The first produces tightening or relax-
ation of the cords, the second, opening or closure of the
vocal glottis. By the third, the arytenoid cartilages are
approximated to or withdrawn from each other so as
to vary the width of the space between them.

It is the principal function of the glottis to produce
those " compound musical tones " to which in physiology
we apply the term " voice." These, when modified by the

VOICE AND SPEECH. 73

mouth so as to become articulate, constitute "speech."
Articulation consists in the production of certain sounds
in the mouth and pharynx which are either associated
with voice (as in speaking aloud), or constitute all that is
heard (as in whispering). These sounds are distinguished
as vowels and consonants. Vowel sounds differ from con-
sonant sounds in possessing the characters of musical
tones, and may accordingly be distinguished by the rela-
tive vibration rates of the tones which constitute them.
Each vowel has its own pitch or tone. To produce any
vowel sound, such form must be given to the cavity of the
mouth and pharynx as to render it a " resonator " for the
tone which is characteristic of the vowel to be produced.
Consonants are modifications of the voice or whisper caused
by the passage of air through constricted or valvular parts
of the mouth or fauces. They derive their characters
from the duration and order of succession of the sounds
which constitute them. They are produced by the soft
palate, tongue or lips. They are divisible into four groups,
viz. (i) valve sounds, (2) blowing sounds, (3) nasal sounds,
(4) vibrating sounds. Of these groups each of the sounds
belonging to the first and second, presents itself in a soft
and a hard modification, of which the former cannot be
adequately produced in a whisper. This classification
does not include the aspirate H, which consists in the
production of an expiratory sound in the larynx, imme-
diately preceding that of the vowel sound aspirated.

PART III.
FUNCTIONS OF THE NERVOUS SYSTEM.

NERVES.

THE organs of the nervous system of which the functions
are known are (i) Reflex centres ; (2) End-organs ; and
(3) Conducting organs. The most important conducting
organs are nerves. A nerve is made up of fibres, each of
which consists of axis cylinder, medullary sheath and nu-
cleated sheath. The medullary sheath is divided into
lengths by septa at equal intervals, but the axis cylinder
is continuous. The axis cylinder consists chiefly of pro-
teid, the medullary sheath of material for the most part
soluble in ether.

Living nerve exhibits in itself three properties which
appear to be characteristic — (i) that when injured so as
to produce solution of continuity of its fibres, the injured
part is electrically negative to the uninjured, (2) that
when a nerve is excited, this electrical property is modified,
the modification thus produced characterising the state of
excitation, and (3) that this state can be propagated along
the fibre in both directions. With reference to the state
of excitation, two inferences are allowable, viz., (i) that the
electrical change exists in uninjured nerves, although it is
imperceptible, and (2) that it is associated with a chemical
change.

The state of excitation is capable of being propagated
from the nerve originally excited to excitable end-organs,
namely, in the case of efferent nerves, to muscle or gland,
and in the case of afferent nerves to centres. In this way

NERVES. 75

it manifests itself outside of the nerve, either in the produc-
tion of motions, secretions, reflexes, or states of conscious-
ness. The excitability of a nerve admits of being
measured by ascertaining the minimum excitation by
which the signs of the excitatory state can be evoked.
For this purpose the exciting agent used must be measur-
able. In the case of nerves of voluntary muscles, the
excitability can also be judged of by measuring the degree
of shortening of the muscle produced.

When the circulation ceases in a nerve or in the whole
body, its vital properties alter. Its excitability at first
increases, then gradually declines, until it is extinguished.
These changes take place in the same order in all nerves,
but occur earlier in parts nearest the centres (Ritter and
Valli) ; thus the intra-muscular parts of motor nerves
survive longest. Injury of a nerve produces increase of
excitability in the neighbourhood. The extinction of
excitability of a living nerve consequent on cessation of
circulation, is immediately followed by structural changes
affecting chiefly its medullary sheath.

In a similar manner loss of excitability and consequent
change of structure, are produced by severance of a nerve
from the cerebro-spinal centres. It is believed that they
may also result from want of exercise. Nerve is more
excitable and more vulnerable than muscle, but is less
affected by want of blood supply and less readily
exhausted by repeated excitation. The two last facts
indicate that its exchange of material is much less
active.

Influence of the voltaic citrrent on excitability. — (i.) Under
the influence of a constant current flowing along a nerve,
its excitability is increased near the negative pole (cathode),
decreased near the positive pole (anode), but the nerve is,
as a rule, not excited so long as the intensity does not vary.
(2.) Every variation of intensity of a current so directed
excites the nerve. Other things being equal, the degree

76 NERVES.

of effect produced is the greater, the shorter the time occu-
pied in the variation. No effect is produced if the current
is transverse. (3.) If the current is of moderate intensity,
the excitation occurs at make and break whatever its
direction — the make excitation starting from the cathode,
the break from the anode. (4.) If the current is strong,
the make excitation is suppressed when the current is from
the muscle ; the break excitation when it is towards the
muscle. (5.) If the current is weak, there is no excitation
excepting at make. The propositions 3, 4, and 5 constitute
the so-called " Law of contraction." (Pfliiger.) If the
current lasts long and is of great intensity, reversed 'after
effects manifest themselves on its cessation. Thus there is
increased excitability at the anode which may lead to
excitation and manifest itself in contraction (Ritter's
Tetanus). This contraction is increased by reclosing the
current in the opposite direction — annulled by reclosing it
in the same direction.

The above experimental facts constitute the basis of the doctrine of Elec-
trotonus. The contrast between the two opposite states (called Cathelec-
trotonus and Anelectrotonus) referred to in (i), is most easily observed in the
parts of the nerve which are immediately beyond the limits of the part through
which the current passes ; but it can also be studied in the intrapolar part.
Here it is found that the cathelectrotonic effect diminishes in extent, and that
the anelectrotonic increases as the current becomes stronger. The statement
(4) is satisfactorily explained on the ground that the propagation of the make
excitation which originates at the cathode, is hindered by the anelectrotonus
which exists at the anode, and that in like manner the break excitation is
interrupted in consequence of the after effect at the cathode. The fact re-
corded in (5) which occurs invariably, simply means that the cathodic excita-
tion is stronger than the anodic.

Methods and Processes of Excitation. — (i) A motor
nerve may be excited by the closing or opening of a vol-
taic current flowing along it ; (2) by any change in the
intensity of such a current ; (3) by the passage along it of
an induction current ; (4) by the passage of a succession
of induction currents in alternately opposite directions
(Faradization) ; (5) mechanically — either by a single per-

NERVES.

77

cussion or by a rapid succession of percussions (Heiden-
hain) ; (6) by chemical agents which either deprive the
nerve of water or disintegrate it.

In all measurable modes of excitation, the muscular
effect increases with the stimulus up to a certain limit,
beyond which there is no further augment. Excitations
just sufficient to produce the maximum effect are called
"maximal"; others "over maximal" or "minimal" as
the case may be. The effect of a minimal excitation is
increased when the seat of excitation is in cathelectrotonos ;
the effect of a maximal is diminished when it is in anelec-
trotonos.

Excitation of one or more of the constituent fibres of a
nerve is without effect on the others : it is incapable of
propagation from the excited fibre to any other struc-
ture excepting the end-organ in which it terminates.

The phenomena known as the " paradoxical twitch " and the " secondary
twitch from the nerve," which are apparent exceptions to the above statement,
are due to electrotonic variation.

If by the myograph or otherwise the time is measured
which elapses between an instantaneous excitation of a
motor nerve and the beginning of the contraction of the
muscle which it supplies, first with the seat of excitation
close to the muscle, and then with the seat of excitation
at 2 '6 centims. distant, it is found that there is a slight
difference amounting to about one-thousandth of a second
between the two measurements.

Living nerve is electromotive. The phenomena closely
agree with those of muscle. In an undivided nerve no
electrical differences manifest themselves either in the
normal state or during excitation. In a severed nerve,
the cut surface is found to be negative to the sound sur-
face ; the difference is, however, much less than in muscle.
An instantaneous excitation of any part of a severed
nerve produces a momentary diminution of the relative

78 NERVE-CENTRES.

negativity of the cut surfaces (negative variation). The
time at which this happens depends on the distance
between the seat of excitation and the section. The rate
of propagation of the negative variation as measured by
.the "rheotome" (Bernstein), agrees with that of the trans-
mission of the excitatory state in a motor nerve, as
measured by the myograph.

Electrotonic variation of the nerve current. — If during
the passage of the voltaic current through the central part
of a length of nerve, the extra-polar parts are investigated,
electrical differences show themselves which have the same
direction as those which are produced by the current in
the inter-polar tract.

FUNCTIONS OF NERVE-CENTRES.

By the term "centre" are designated certain parts of
the Brain or Spinal Cord, respecting each of which it is
known that it is concerned in the regulation or control of
some one of the chemical or mechanical processes of the
living organism. Our knowledge of the limits and topo-
graphical relations of these parts, and of the channels
by which they mutually influence each other, and the
.organs over which they preside, is derived almost exclu-
sively from experiments on living animals.

Nerve centres are excitable organs which owe their
physiological endowments to the nerve cells and reticulum
of which they consist, and to the connection of these
structures with afferent and efferent nerves. The excita-
tory state originates in them for the most part by pro-
pagation from afferent nerves, or from other centres, and
is propagated by them to other centres or to efferent
nerves.

This process is designated " reflex action ;" a term which
is applied to any case in which the function of a mus-

NERVE-CKNTRES. 79

cular, glandular, or other organ is called into activity or
arrested in consequence of the excitation of an afferent
nerve.

The most important reflex actions are muscular. These
are of two kinds, which may be called normal and
abnormal. Normal reflex processes spring from the
excitation of one or more peripheral sense-organs, by
usually feeble stimuli. They are characterized by the fact
that excitations of the same kind, originating from the
same end-organs always lead to the same results, that is,
occasion the same combinations or series of co-ordinated
muscular actions. This fact justifies the hypothesis that
in the centres there are channels of propagation, by which
the excitatory process is guided, notwithstanding that
our present knowledge of anatomy affords no clues by
which they may be traced. All normal reflex processes
are adapted to the accomplishment of useful purposes in
the animal economy.

Abnormal, incoordinate, or convulsive reflex processes,
do not occur in the healthy body, excepting in consequence
of injury. The excitatory state which here as in the other
case is communicated to the centre by an afferent nerve,
spreads from it to other centres by mere continuity of
structure, irrespectively of channels of propagation. Con-
sequently those centres which are nearest, are as a rule
first affected, and in their turn the motor nerves which
spring from them and the muscles to which such nerves are
distributed, without distinction of function. In the abnormal
state, whether induced by loss of blood, by interference
with respiration, by disease, or by poisons, incoordinate
reflexes may be excited by the action of ordinary stimuli
on sensory end-organs, but much more readily by injuries
of nerve trunks.

The time occupied by normal reflexes varies according
to their complexity, and to the remoteness of the centres
concerned, from a twentieth to a tenth of a second, or even

80 SPINAL NERVE-ROOTS.

more. Of this time, all but about a hundredth of a second
is occupied in the central process.

It is often observed that the muscular effect produced
by the excitation of one afferent nerve is hindered or
delayed by excitation of another. This phenomenon is
called inhibition. This may be attributed either to the
counteraction of two centres, or to the counteraction of
two excitations in the same centre.

Our knowledge of both kinds of reflex action is largely derived from the
observation of the phenomena exhibited by the body of the frog after the
animal has been killed by removing the brain. In preparations of this kind
it is seen (i) that definite series or groups of muscular actions adapted to
purposes, occur in response to excitation of particular spots of the cutaneous
surface ; (2) that slight excitations so applied, act by summation, i.e., do not
produce any effect until they have lasted for some time ; (3) that the excitation
of the central ends of nerve trunks produces irregular or convulsive reflexes,
the extent of which varies according to the intensity of the excitation ; (4)
that under the influence of strychnine, similar effects are produced, by ordinary
cutaneous stimuli ; (5) that by acting directly on the "convulsive centre" in
the medulla oblongata, or by faradization of the whole cord, general con-
vulsion is produced, similar to the partial effects above described (see
Practical Exercises).

Functions of the Roots of the spinal nerves and of their

Ganglia.

It was discovered by Charles Bell, in 1 8 1 1, that mechanical
irritation of the anterior roots of the spinal nerves, pro-
duced convulsive movements of the muscles to which they
were distributed. More than ten years later, Magendie
discovered that excitation of the posterior roots produced
pain, and occasioned reflex contractions of the muscles,
and that these were prevented by section of the anterior
roots : subsequently he discovered that in mammals after
severance of an anterior root, excitation of the peripheral
end influences the cord through the trunk and posterior
root of the same nerve. In the frog the anterior roots
are exclusively afferent.

Of the function of the ganglia of the posterior roots

THE SPINAL CORD.

8l

nothing is known, excepting that severance of a ganglion
from the nerve trunks to which it belongs, produces loss of
excitability and structural changes in afferent fibres of the
nerve. (Waller.)

Functions of the white columns of the Spinal Cord.

The most important anatomical facts relating to the channels by which
excitation is transmitted in the spinal cord, are (i) that the fibres of the
spinal nerves are not continued to the brain, but communicate with ganglionic
cells ; (2) that in the anterior roots this communication is direct, mediate in
the posterior, i.e. through the reticulum ; (3) that the anterior roots may be
traced through the anterior horns, to the anterior columns of the other side
by the white commissure, as well as to the anterior and lateral columns of the
same side ; (4) that the fibres of the posterior roots divide into two sets, of
which the smaller at once lose themselves in the substantia gelatinosa, the
larger division tending inwards towards the posterior columns, in which some
of the fibres appear to acquire a vertical direction ; (5) the sectional area of
the lateral columns of the spinal cord is, as measured at any part of its course,
proportional to the sum of the sectional areas of the nerves which enter it
below the section ; (6) the sectional area of the grey substance is proportional
to the sum of the sectional areas of the nerves which enter the cord in the
neighbourhood of the section.

The most important results of experimental investigation
as to the channels of propagation in the cord may be stated
as follows : — (i.) The fibres of the lateral columns are the
only channels of influence between the intra-cranial centres
and the lower limbs. (2.) The afferent fibres by which
excitation of either lower extremity influences the intra-
cranial centres, are contained in the lateral columns of the
opposite side. (3.) The fibres by which the intra-cranial
centres influence the muscles of either inferior extremity
are contained for the most part in the lateral column of
the same side. (4.) It is probable that the fibres of the
anterior and posterior columns serve as channels of com-
munication between neighbouring parts of the cord.
There is reason, however, for believing that in the lumbar
region, the posterior columns contain fibres by which
sensory impressions are transmitted upwards.

G

82 RESPIRATORY CENTRE.

The spinal cord is entirely insensible to mechanical
stimulation excepting in the immediate neighbourhood of
its motor roots. Its grey substance seems to be also
wholly insusceptible of electrical stimulation, but its fibres
can be excited either by single induction shocks or by
faradization.

Centres of the Medtdla Oblongata.

The central canal of the cord opens out into the rhomboidal space, or
fourth ventricle, the two grey columns (horns) thus becoming superficial, and
assuming such a position that what was before posterior lies outside. In the
stratum of grey substance thus exposed, are contained the regulatory centres
which preside over the most important functions of the body, namely those of
the heart, of the arteries, of the respiratory organs, of the organs of digestion,
of speech, of taste, and of locomotion. The origins of the nerves concerned
in the functions of these centres are in close relation with each other, but
nothing precise is known of their anatomical relations.

The regulatory centre for the heart is represented by two tracts of grey
substance on either side of the spinal canal, but nearer to the posterior sur-
face. At the cal. script, these diverge and become continuous with the vagal
tracts (alee cinerece) which are separated from each other by the nuclei of the
hypoglossal nerve. Each vagal tract is in relation at its upper end with the
nucleus of the glossopharyngeal nerve, which is close to the auditory striae.
Outside of each vagal tract are the internal and external nuclei of the auditory
nerve, which are respectively continued downwards into the grey tubercle of
Rolando and the restiform nucleus. Higher up, the internal auditory nucleus
becomes continuous with the origin of the sensory division of the trigeminus,
the motor division of which springs from the grey substance nearer the middle
line. The hypoglossal nucleus is continuous with those of the abducens and
facial, which lie underneath the eminentia teres of each side, and is in relation
externally with the origin of the motor root of the trigeminus. The same
motor tract is continuous upwards with the grey substance underneath the
floor of the aqueduct, from which the oculomotorius and trochlearis spring.

Influence of the Nervous System on respiration. — The
respiratory nervous system consists of (a) the regulatory
centre (vagal tracts) ; (b} the afferent fibres of the vagus ;
(c) motor fibres contained in the facial and recurrent, as
well as in the phrenic, intercostal, and other spinal nerves,
(i.) Destruction of the vagal tracts produces instant death
in mammalia ; destruction of the upper part only, arrests

RESPIRATORY CENTRE. 83

those respiratory movements which are dependent on the
facial nerve : destruction of the lower part only, arrests
the thoracic movements. (2.) The respiratory centre acts
automatically, i.e., is self-acting, but (3) its activity is affected
by the condition of the circulating blood, in such a way
that the more abundantly it is supplied with arterial blood
the less active are the respiratory movements, and the fewer
muscles take part in them. Accordingly saturation of the
haemoglobin of the blood with oxygen produces apncea,
i.e., suspension of respiratory effort, while defective arte-
rialization produces increased activity of both centres, i.e.,
hyperpncea, which, if prolonged and excessive (dyspnoea)
results in exhaustion. (See Asphyxia, p. 90.) (4.) The
centre receives through the vagus trunk two sets of nerve
fibres which act upon it antagonistically to each other. Of
these, one set are chiefly contained in the superior laryngeal,
the other probably exclusively in nerves distributed to the
bronchial tubes and lungs, of which some of the fibres are
also inhibitory. The influence of these fibres may be under-
stood by supposing either that the respiratory centre consists
of two parts, of which one is inspiratory, the other expiratory,
and that the second of these acts antagonistically to the
first, i.e. exercises an inhibitory influence over it, or that
there is one centre of which the action is affected in oppo-
site ways, according as one or the other set of fibres is ex-
cited. (5.) The condition which produces hyperpncea is
not excess of CO2 but defect of oxygen. (6.) The influence
of increase of the temperature of the blood on the respi-
ratory movements resembles that of defect of oxygen.

Experimental Proofs.— I. Destruction of the vagal tracts produces sudden
cessation of respiratory movements, without convulsion ; but severance of the
fascic. teretes above the striae stops only the respiratory movements of the
face, the laryngeal and thoracic movements continuing. 2. After section of
both vagi and of the cord above the third cervical vertebra, the animal dies of
asphyxia, but the respiratory movements of the facial muscles and those of
the sternomastoids continue. 3. Section of both vagi below the sup. laryng.
produces diminished frequency, increased amplitude and altered rhythm of
thoracic respiratory movements, with prolongation of each inspiratory act.

G 2

84 NERVOUS SYSTEM.

4. In artificial respiration the rhythmical action of the laryngeal and facial
muscles continues, and follows the rhythm of the artificial respirations, each
injection of air being followed by expiratory movements of the nares and
glottis. 5. Excitation of the central end of the divided sup. laryng. nerve
always produces transitory cessation of respiratoiy movements with relaxed
diaphragm. The same effect is produced by injection of air impregnated
•with NH3 gas into the larynx from below. 6. Excitation of the central end
of the divided vagus produces sometimes continuous or interrupted contraction
of the diaphragm, sometimes the effects described in 5. 7. Respiration of an
atmosphere containing excess of CO2 (20% or more) does not produce
dyspnoea if as much as 2OC/0 of O be present. 8. Dyspnoea is produced by
warming the blood which is supplied to the medulla oblongata, whether the
general temperature of the body be raised or not.

Reflex respiratory movements. — Co-ordinated respiratory
movements adapted for the exclusion or expulsion of
irritating substances from the respiratory cavities, are
determined either by mechanical or chemical excitation
of the nares (sneeze), of the mucous membrane below
and on either side of the epiglottis (closure of the glottis),
or of the vocal cords (cough), or of the bronchial mucous
membrane (paroxysm of cough by summation). In
coughing and sneezing, each reflex effect consists of three
acts, viz., a short inspiration, followed by a violent expul-
sive burst of air through a previously closed air-way, in
the production of which all the expiratory muscles, both
the constrictors of the abdominal cavity, and the depres-
sors of the lower ribs, take part. The closure, which is
the second phase in the process, takes place in cough at
the glottis, in the sneeze at the fauces. The afferent
channels concerned in these reflexes are contained in the
middle division of the trigeminus and the vagus. The
muscles are those of respiration and of the fauces and
soft palate.

The various abnormal modes of respiration which occur in disease, may be
referred either to altered rhythm of the centre (Cheyne Stokes breathing), to
excessive proneness to the production of reflex expiratory action (spasmodic
cough), to suspension of vagus action (true asthma), &c.

Influence of the Nervous System on the Heart. — i. The

OF THE HEART. 85

regulatory nervous system of the heart consists of (a) the
intra-cranial heart-centre (spinal accessory nuclei) ; (b) the
fibres of the spinal accessory and vagus, which are dis-
tributed to the heart, and (c) the accelerator nerves.
2. It was discovered by E. H. Weber in 1842 that through
the vagus the brain exercises an inhibitory influence on
the heart, i.e., that excitation of the cardiac fibres of the
vagus either arrests the heart in diastole, or, if less intense,
diminishes the frequency of its beats by prolonging each
diastolic interval, and thus diminishes the arterial pressure,
while it increases the amplitude of the arterial pulsation.
Between the excitation and the effect, a delay takes
place which (in the rabbit) amounts to £ second. 3. The
effect above described is produced reflexly by excita-
tion of various afferent nerves, e.g., in the mammal by
inhalation of irritant substances, in the frog by excitation
of the "rami mesenterici." 4. It is also produced by
direct excitation of the intra-cranial centre, by compres-
sion of the brain, by increase of arterial pressure in the
brain, or by the circulation in that organ of venous blood.
5. In most mammalia, particularly those in which, as in
the dog, the influence of the vagus centre on the heart is
constant, each inspiratory act is followed by increased
frequency of pulse. This may, with much probability, be
attributed to the inhibitory influence of the respiratory
centre on that of the heart.

In all of these instances, the experimental proof that the vagus is the
channel by which the heart is acted on, is obtained by observing that the effect
is no longer produced after both vagi have been divided.

6. In the frog, section of both vagi is almost without
effect on the rhythm of the heart, but in the dog, it is
followed by great increase of frequency and of arterial
pressure. Neither of these effects is obvious in the
rabbit.

7. Accelerator Nerves. — The increased frequency of the
heart-beats, which, in all animals, is produced along with

86 INTRA-CARDIAC GANGLIA.

increased arterial pressure by excitation of the cervical
part of the spinal cord, is attributable to direct excita-
tion of the accelerator fibres it contains. Accelerator
nerves, i.e., nerves of which the excitation induces increased
•frequency of action without in any other way affecting
the circulation, reach the heart from the spinal cord
through the sympathetic system. In the rabbit, they ap-
proach the heart through the inferior cervical ganglion ; in
the dog they are derived chiefly from the dorsal ganglia,
from the 1st to the 5th. In all cases there is a delay
of several seconds between the excitation and the effect.
When the inhibitory and accelerator nerves of the heart
are excited simultaneously, the effects balance each
other.

Infra-cardiac Ganglia and Nerves of the Heart. — The
nervous system of the heart of the frog consists of (i) a
plexus, which is situated in the septum between the
auricles, close to the opening by which the right auricle
communicates with the sinus venosus. This is con-
nected by nerve filaments with (2) smaller groups of
ganglion cells (Bidder's ganglia) in the neighbourhood of
the auriculo-ventricular furrow. Collections of ganglion
cells exist in other parts of the heart, but their arrange-
ment is imperfectly known. The phenomena relating to
the functions of the intra-cardiac ganglia may be studied
in the heart after its removal from the body, either in the
empty state or when supplied with blood or other nutrient
liquid in such a way as to enable it to fill and discharge
itself under natural conditions. The liquid used must
contain the salts of the blood, and a trace of proteid, but
need not contain haemoglobin. Mechanical or electrical
excitation of the dorsal surface of the right auricle
(inhibitory centre) arrests the heart in diastole. Accord-
ingly, if a tight ligature is placed round the heart in
this position, it loses the power of rhythmical contrac-
tion. If, thereupon, the auricles are cut off from the

VASCULAR NERVOUS SYSTEM. 8/

ventricle, the rhythmical action is resumed, provided that
the middle part of the base of the ventricle remains
intact. So soon as this part is cut off or destroyed, the
rhythmical contractions cease ; it is therefore believed to
contain the motor centre for the rhythmical motion of the
ventricle. After its removal, the ventricle responds to
each single or mechanical excitation by a single contrac-
tion, determined by the direct action of the excitant on
the muscular fibre. Similar motor centres are inferred to
exist in the sinus, auricles, and bulb. Application to
the beating heart of a trace of solution of the alkaloid
muscarine, stops it in diastole. The effect is promptly
counteracted by the application of solution of atropine in
similar manner and quantity. A heart so ' atropinized '
cannot be stopped in diastole, either by mechanical or
electrical excitation of its inhibitory centre.

Ganglia exist in the hearts of the higher animals, but
nothing is known of their functions.

Influence of the Nervotis System on the blood vessels
(Vascular Nervoits System}. — The principal vaso-con-
strictor centre is situated in the upper part of the floor
of the fourth ventricle ; subordinate centres exist in the
spinal cord, both in mammalia (Strieker) and in the frog.
The channels of the influence of these centres on the
arteries are contained in the lateral columns of the spinal
cord, from which they extend by the anterior roots and
rami communicantes to the ganglia and prsevertebral
plexuses of the sympathetic system, whence vaso con-
strictor nerves are distributed to the arteries.

The constrictor centres are in constant action ; their
activity varies with the CO2 tension of the blood, and is
consequently augmented by arrest of the circulation in the
brain. The centres are also influenced by excitation of
sensory nerves, of which the ordinary effect is to increase
their activity. But in the case of the afferent fibres which
reach the vagus from the heart (Depressor fibres), the

88 VASCULAR NERVOUS SYSTEM.

opposite effect is produced (see below). It cannot be
stated whether in this case the constrictor centres are
acted upon directly, or with the intervention of other
centres. I. Section of the spinal cord in the neck causes in
all animals vascular dilatation and consequent diminution
of the arterial pressure, and of the velocity of the circula-
tion. ' As the dilatation affects the vessels of the viscera
much more than those of the skin and of the muscles,
the distribution of the blood is altered. 2. Excitation of
any external sensory nerve produces contraction of the
blood vessels of the viscera, but dilatation of those dis-
tributed to the muscles and skin (Heidenhain, Bernstein).
In the normal animal the effect of these vascular changes
is to increase the velocity of the circulation and the
arterial pressure. In those animals in which the depres-
sor forms a separate nerve, excitation of the central end
of that nerve produces dilatation of the visceral blood
vessels, and consequent diminution of arterial pressure.
3. Severance of the constrictor nerves distributed to
external parts, or of spinal nerves, produces relaxation
of the arteries to which they are distributed, but after a
time the arterial tonus (see below) is restored, notwith-
standing that the communication between the arteries
and the central nervous system continues to be inter-
rupted. Excitation of the same nerves (peripheral ends
after section) determines, under normal conditions vas-
cular constriction, pallor, and diminished temperature, in
the parts to which they are distributed, and diminishes
the flow of blood in the veins which lead from those parts.
If, however, the nerves subjected to excitation are in a
state of partial degeneration, consequent on previous
severance, it often happens that the opposite effects are
produced. Again, if the temperature of the part is
already lower than the normal, the vessels dilate in
response to the excitation instead of contracting, even
though the nerve excited may have been divided imme-

VASCULAR NERVOUS SYSTEM. 89

diately before. 4. Excitation of the nerves distributed to
the abdominal viscera produces, under all circumstances,
vascular constriction. Section of the same nerves pro-
duces as invariably vascular dilatation. 5- In some
instances excitation of a cutaneous sensory nerve leads,
by reflex action, to vascular changes, limited to the area
of its distribution. These reflex effects vary according
to the mode of excitation. 6. Any nerve of which the
excitation (peripheral end after section) leads to vascular
dilatation and hyperaemia in the parts to which it is dis-
tributed, is called a vaso-inhibitory nerve. Fibres of this
kind are contained in the. lingual nerve, some of which
are distributed to the submaxillary gland, others to the
mucous membrane of the tongue. All erectile organs are
provided with vaso-inhibitory nerves, which are distributed
to their arterioles. On excitation of these nerves, whether
reflex or direct, the arterioles expand, in consequence of
which the venous system of the tissue becomes distended
with blood. 7. The normal state of contraction of the
arteries of a healthy part is called Tonus. The arterial
tonus is maintained by the constant activity of the vaso-
constrictor centres ; it is also influenced by conditions
which act independently of the vascular nervous system,
particularly by the temperature of the part (Mosso), by
the pressure under which blood flows into it (Heiden-
hain), by changes in the structure of the blood vessels
(Cohnheim), &c. It is subject to fluctuations which recur
at irregular intervals, and may either be limited to par-
ticular arteries or may affect so large a number simulta-
neously as to produce variations of the volume of the
organs supplied by them (Mosso), or fluctuations of arterial
pressure (Traube, Hering).

The regulation of the Circulation of the blood, i.e., the
maintenance of such a relation between the activity of
the heart and the resistance of the blood vessels as is most
advantageous, is effected by the combined action of the

9O ASPHYXIA,

cardiac and vascular centres. Overaction of the heart is
prevented by the influence of the resulting augmentation
of intra-cranial pressure on the heart centre in the medulla
oblongata ; over-constriction of the vessels by the influence
of the resulting increase of endocardial pressure through
the depressor fibres of the vagus on the vaso-motor
centre.

Death by Asphyxia. — When respiration is suddenly pre-
vented, either by complete occlusion of the air passages
or by submersion, the circulation of unarterialized blood
in the brain gives rise to disturbances of the actions of
the respiratory, cardiac, and vascular centres, which in a
few minutes bring respiration and circulation to an end.
The process is divisible into two stages. The first stage is
characterized by rapidly increasing hyperpncea, contraction
of the arteries, increased arterial pressure, and acceleration
of the circulation ; towards its close the expiratory move-
ments become more forcible than the inspiratory, and as
insensibility approaches, pass into " expiratory convul-
sions " of short duration. In the second stage the animal
is entirely unconscious ; the pupils are first contracted,
then dilated, while the convulsive expirations give place to
violent inspiratory gasps. After these have ceased the
heart continues to beat, at first slowly, then with increased
frequency but diminished effect, until at last the arterial
pressure has sunk to zero, and the whole of the blood has
collected in the venous system and in the cavities of the
heart. The duration of the process is mainly dependent
on the quantity of air contained in the respiratory cavity
at the moment of occlusion of the air passages, on the
relative quantity of blood which the animal possesses, on
its age, and on the activity of its chemical processes.

Influence of the nervous system on the Temperature of the
body. — The influence of the nervous system on the heat-
producing processes, by which the constancy of the tem-
perature of the body is maintained, is as yet unknown.

REFLEX OF SWALLOWING. 9 1

The discharge of heat is, in man, chiefly dependent on the
circulation of the blood in the skin and subcutaneous
tissues, and on the secretion of sweat. Both of these pro-
cesses are presided over by nervous mechanisms of such a
nature that their activity varies with the surface tempera-
ture of the body. In animals (particularly in the dog)
the increased activity of the respiratory movements, which
is produced by increase of bodily temperature (see Influ-
ence of Nervous system on respiration), also serves as an
efficient means of regulation.

The Reflex process of Swallowing. — In the accomplish-
ment of the act by which food is conveyed from the fauces
into the stomach, the following changes take place : —

The larynx is drawn upwards under the tongue and
nearer to the hyoid bone, the epiglottis applying its upper
surface to the base of the tongue, and its under surface to
the larynx ; the glottis is closed ; the palato-pharyngeal
arches tighten and approach each other, without quite
meeting. The soft palate with the uvula is drawn back-
wards (by the combined action of the levatores and palato-
pharyngei), while the posterior wall of the pharynx
advances to meet it, and thus completely shuts off the
nares from the pharynx. The morsel as it glides down-
wards between the nearly even surfaces offered by the
tongue, epiglottis and cricoid cartilages in "front, and the
palato-pharyngeal arches behind, is at once seized by the
constrictors and carried onwards by their successive con-
tractions into the oesophagus. By a mode of action which
is called "peristaltic," and which resembles that of the
intestine and other muscular tubes, the food is conveyed
as far as the closed sphincter of the stomach. As soon as
this happens, the sphincter opens to allow of its entrance
into the stomach, closing again immediately.

The centre which presides over this reflex process has its
seat in the medulla oblongata. It derives its most impor-
tant afferent influences from the mucous membrane of the

92 PERISTALTIC ACTION.

fauces. After section of the vagus, near its origin (vago-
accessorius), the muscles of the pharynx, as well as those
of the larynx and the cesophagus, are inactive, and the
reflex act of deglutition is prevented. The effect of
removal of the accessorius roots is scarcely different.
After section of both vagi in the neck, the first part of the
process is possible, but it cannot be completed. Food
collects in the relaxed cesophagus, being prevented from
entering the stomach by the permanently closed cardia ;
the glottis being inactive, portions of food are apt to enter
the trachea. The peristaltic action of the cesophagus
differs from that of the intestine in being much more
dependent on the intra-cranial centre which governs it.

Regidation of the peristaltic action of the Stomach and
Intestine. — Throughout the alimentary canal the motions
of its contents are produced by temporary constrictions of
its wall, which progress in the direction of its length. In
the intestine all that is observed is that the constriction
follows the mass in its progress and that, as a rule, every
peristaltic act begins at the pylorus and advances onwards.
In the stomach, the action is similar, but in consequence
of the form of the cavity, the effect is different ; for the
contents, instead of advancing, circulate along the smaller
curvature from pylorus to cardia, and along the larger, in
the opposite direction. In the inactive state, the stomach
is contracted and the pylorus closed, whereas the intestine
is (apparently) relaxed. When food is introduced into
the stomach its wall begins to relax and contract alter-
nately, each change beginning at the cardia. These
movements, at first feeble, become more and more
active towards the close of the process of gastric diges-
tion, the pylorus opening more and more at each relaxa-
tion, so as to allow of the gradual escape of chyme into
the duodenum.

The motions of the stomach are in large measure influ-
enced by the vagus, for after section of both vagi the

REFLEX OF VOMITING. 93

stomach is almost inactive, but can be brought into action
by exciting the nerve. In the frog, after section of both
vagi, the stomach is contracted. The function of the vagus
in relation to the stomach is therefore regarded as inhi-
bitory.

The peristaltic motion of the intestine is increased in
dyspnoea, arrested in apncea. Arrest of the circulation
usually increases its activity, but the effect varies according
to the previous state of the intestine. The splanchnic
nerves are the channels by which the influence of the
cerebro-spinal centres is conveyed to the intestines, but
nothing can be certainly stated as to the nature of that
influence. Inasmuch as the peristaltic motion can be
always suspended, if previously active, by excitation of
these nerves, an inhibitory function, like that of the vagus
in relation to the stomach, is attributed to them.

The Reflex of Vomiting. — Vomiting consists of three
acts, viz. (i) Descent of the diaphragm, (2) Relaxation of
the cardia and contraction of the longitudinal fibres of
the cardiac end of the oesophagus, (3) Closure of the
glottis and compression of the stomach between the
abdominal muscles and the still contracted diaphragm,
and discharge of its contents by a mode of action of the
muscles of the oesophagus and pharynx, which resembles
that of swallowing but is in reversed order. Usually the
process is preceded by increased secretion of saliva,
which is immediately swallowed. At the moment of the
discharge of the contents of the stomach the muscles of
the pharynx are brought into action, so as to give to
that cavity the same form as in swallowing, and prevent
the passage of vomited matters into the larynx or nares :
the neck is also extended. The centre for vomiting is
in the medulla oblongata, and is in close relation with
those which preside over the reflexes of coughing and
swallowing. It may be induced either reflexly or by
direct action on the centre. In the latter case, retching

94 INFLUENCE OF NERVOUS SYSTEM

may occur even after section of both vagi, but effectual
vomiting is impossible.

The Reflex of Defecation. — As defaecation is possible
after severance of the spinal cord in the dorsal region, pro-
vided that the lumbar part of the cord is in a normal state,
it must be essentially a reflex process, governed by a spinal
centre. When accomplished under these conditions, it
consists of two acts, namely, peristaltic contraction of the
rectum and relaxation of the sphincter externus. The
mode of action of the latter, although it consists of striped
fibres, resembles, when not controlled by the will, that of
the cardia and pylorus : in its ordinary state it is con-
tracted, but it is excited to rhythmical relaxation by the
presence of fsecal matter in the neighbouring part of the
rectum.

The Reflex of Micturition. — The retention and discharge
of urine are also reflex acts, not necessarily dependent on
the will. The mechanism of micturition resembles, so far
as the bladder is concerned, that of defaecation, urine being
discharged after severance of the spinal cord, at long inter-
vals, by the simultaneous contraction of the muscular wall
of the bladder and relaxation of the sphincter, this pri-
mary act being accompanied by other auxiliary movements
accomplished by striped muscles acting under the direction
of the same centre. In the normal animal, the anal and
vesical sphincters are so far under the control of the will
that their relaxation can be inhibited by voluntary effort.

Influence of the nervous system on the processes of Secre-
tion.— The processes of secretion which have been hitherto
investigated, are those of the salivary glands, the pancreas,
the gastric glands, the liver and the kidney.

The salivary glands are normally inactive, excepting
when excited by the presence of sapid substances in the
mouth. Hence the process is a reflex one. The centre
which governs it is in the medulla oblongata, and transmits
its influence to the submaxillary gland by the chorda

ON SECRETION. 95

tympani, and to the parotid by a nerve which springs
directly from the auriculo-temporal, ultimately, like the
chorda, from the facial. The submaxillary may be excited
to normal action by direct faradization of the chorda, in
which case it pours out its secretion in abundance, and
with such force, that if its duct is occluded, its internal
surface is exposed to a pressure which may exceed the
arterial. In addition to this, excitation of the chorda
produces dilatation of the arteries of the gland, in conse-
quence of which its supply of blood is largely increased.
It can, however, be shown that each of these two effects is
independent of the other. During excitation, the tem-
perature of the gland rises and the secreting cells undergo
important changes (in the dog, disappearance of the
" mucous cells " or discharge of their contents, multi-
plication or regeneration of the " protoplasm-cells ").
The submaxillary gland can also be made to secrete by
excitation of the vaso-constrictor nerves which accompany
its arteries ; the product so obtained is of high specific
gravity and contains much mucus. Severance of all the
nerves of the gland produces a continuous discharge of
watery liquid which continues for some time.

The pancreas. During the intervals of digestion the
pancreas is inactive. It begins to secrete immediately
after food is taken and attains its greatest activity towards
the end of gastric digestion. At this time it is red and
turgid, and is richest in the material to which its secretion
owes its digestive activity ; its cells are larger than before
and contain a granular material, which as secretion goes
on disappears, but is subsequently regenerated. Nothing
is known as to the channels by which the nervous system
influences the process. — The gastric glands are normally
brought into activity by the presence of food or of saliva
in the stomach. Their secretion ceases when the stomach
is empty, but can be readily excited by mechanical and
chemical stimuli, particularly by alkaline liquids. It is

96 [NERVES OF LIVER AND KIDNEY.

not dependent on integrity of the vagus nerves. Its
activity is associated with increased circulation of blood
in the mucous membrane, and with changes in the secret-
ing cells, comparable with those already described in
other glands. Nothing can, however, as yet be stated
with certainty as to the relation of these changes with
the process.

TJie liver. — The secretion of bile cannot be directly
excited by any mode of acting on the nervous system.
Excitation of the spinal cord, which at first increases the
discharge of bile, by producing constriction of the bile-
ducts, eventually diminishes it. The secretion of bile is
arrested by even very slight increase of pressure in the
bile ducts ; whenever this happens bilin and colouring
matter exist in the circulating blood (jaundice). The
power of the liver cells to store glycogen is annulled by
destruction either of the centre which controls its blood-
vessels or of the channels by which that control is exer-
cised ; in either case the urine becomes saccharine (glyco-
suria). A similar effect is produced by curare, carbonic
oxide and some other poisons, as well as by central exci-
tation of the vagus.

The kidneys possess no secreting nerves: the renal
nerves have no other function excepting that of constric-
tors of the arteries. The rate of secretion of urine is
directly influenced by the state of the circulation : thus,
it can be increased in animals by augmentation, and
diminished by reduction, of the pressure under which
blood enters the glomeruli. It can be diminished or even
arrested by increasing the pressure in the renal veins.
By destruction of the renal vascular centre in the floor of
the fourth ventricle, or of the renal nerves, the vascular
tone of the kidneys is annulled, in consequence of which
the urine flows abundantly (polyuria) and often contains
albumin (albuminuria), but is not necessarily saccharine.
Similar effects are observed after severance of the renal

MAINTENANCE OF BALANCE.

97

nerves ; excitation of the renal nerves arrests the secre-
tion.

Regulation of Locomotion (Maintenance of Balance}. —
The motions of the body in walking and other modes of
progression, although under the influence of the will, are
regulated by centres which act in obedience to impressions
of which the will takes no cognizance, received from the
retinae, from the semi-circular canals, and other sensory
end-organs. These impressions have to do chiefly either
with the relation of the head to the plummet line, or to
changes of speed or direction in the motions of the head
or body. With reference to impressions of the latter
class, it is to be noted, that all felt motions give rise, on
their cessation, to a subjective sensation of motion in the
opposite direction.

After injury of either of the crura-cerebri, animals have
a tendency to rotation of the body round an axis, which
usually lies on the side of the body opposite to that in-
jured. This tendency, when strong, manifests itself in
rolling ; when weaker, in manage motion. Similar effects
follow injury of the cerebellum, but in this case the axis
of rotation is often on the same side of the body as the
injury. After injury, or irritation of the semi-circular
canals, birds walk as if they had lost their balance, and
the head oscillates. The oscillation varies in direction
according as. the vertical or horizontal canals are inter-
fered with : if the former, the head moves backwards and
forwards ; if the latter, it is rotated from side to side. At
the same time, the head assumes an unnatural attitude,
and the body tends to fall backward or to the side. The
sensation of vertigo, in which the body of the affected
person seems to rotate round its vertical axis, is produced
by passive rotation in the opposite direction : when in-
tense, it expresses itself in actual rotation, the direction
of which is always opposed to that of the subjective
motion. Vertigo may be also produced by the passage

H

98 MOTIONS OF THE EYEBALLS.

of a voltaic current through the brain (cerebellum ?), in
which case the direction of the subjective rotation is
determined by that of the current. Both kinds of vertigo
are accompanied by nystagmus. In the frog, after
removal of the hemispheres, locomotion is as perfect as
in the normal animal, provided that the optic lobes and
cerebellum are present. A frog which possesses its cere-
bellum, but has no optic lobes, jumps normally, but fails
in maintaining its balance. In mammalia (the dog), loss
of the cerebellum is followed by disorders and perverted
action of the muscles of the trunk and limbs, in con-
sequence of which, neither voluntary nor reflex acts
can be accomplished in a manner adapted to their pur-
pose.

All of these phenomena may be understood on the
supposition that centres exist (in the cerebellum ?) of
of which it is the function (i) to receive impressions as
to the direction of the passive and active motions of the
body and of its parts ; and (2) to direct and regulate the
actions of the muscles of the trunk and limbs (indepen-
dently of consciousness) in obedience to those impres-
sions.

Regulation of the Motions of the Eyeballs and the
Actions of the Iris and Tensor of the Choroid. — These
actions are governed by centres which have their seat in
the floor of the aqueduct of Sylvius, and of the 3rd and
4th ventricles, the influence of which is conveyed to the
muscular structures, over which they preside, by the 3rd,
4th, and 6th nerves, as well as by channels which are con-
tained in the cervical portion of the spinal cord, and in
the corresponding part of the sympathetic system. They
have been localized by experiment as follows : — Excita-
tion of the floor of the aqueduct at its entrance into the
third ventricle, produces convergence of the visual axis,
and contraction of the pupil ; excitation of the anterior
tubercles of the corpora quadrigemina, or of the optic

ACTIONS OF THE IRIS. 99

thalami, occasions divergence and dilatation ; on excita-
tion of the outer part of either anterior tubercle, both
eyeballs are rotated to the opposite side.

The iris receives, in addition to sensory and vascular
nerves, constrictor nerves, which are distributed to the
sphincter pupillse, and dilatator fibres, which are believed
to terminate in muscular structures of corresponding
function. Every excitation of the retina by light is fol-
lowed, after an interval of about half a second, by con-
traction of the pupils. Both pupils respond to excitation
of one retina. In the frog, the iris continues to respond
to excitation of the retina, even after the eye has been
removed from the body. In accommodation for near
vision, the contraction of the tensor choroideae is normally
associated with convergence of the visual axes and nar-
rowing of the pupil. The dilatator nerves of the iris are
derived immediately from the trigeminus, ultimately from
the sympathetic system, for excitation of the upper cer-
vical ganglion produces dilatation, and destruction of it
narrowing of the pupil. Dilatation is also produced re-
flexly by excitation of any sensory nerve : in all cases it
is associated with vascular contraction (see Vascular Ner-
vous System), proptosis, widely-opened eyelids, and re-
traction of the membrana nictitans. These effects are
weakened, but not annulled, by extirpation of the upper
ganglion of the sympathetic. Corresponding phenomena
are observed in dyspnoea and during violent muscular
efforts. In deep sleep, the visual axes converge, and the
pupil is contracted. Certain alkaloids (called mydriatics)
produce lasting dilatation of the pupil, associated with
complete relaxation of the tensor of the choroid. Others
(called myotics) have the opposite effect ; in the former
case, the action is known to have its seat in the eyeball
itself. Convergence of the visual axes, and narrowing of
the pupil are so associated, that one of them cannot be
normally accomplished without the other. Accordingly,

H 2

TOO FUNCTIONS OF THE BRAIN.

accommodation for near vision is always accompanied by
contraction of the irides.

Regulation of the Movements of Expression. — On this
subject, information is derived from the observation of
disease. When the muscles of one side of the face
are rendered temporarily or permanently inactive by com-
pression or destruction of the portio dura in the Fallopian
canal, the affected side loses its expression, and is drawn
to the opposite side. The affected cheek is flabby, and
the eyelids cannot be closed (lagophthalmus paralyticus\
in consequence of which, tears flow over the cheek, while
the exposed eyeball is rotated upwards. If the lesion is
on the central side of the genu, these phenomena are
accompanied by asymmetry of the posterior arch of the
fauces, consequent on inactivity of the levator palati, as
well as by loss or impairment of hearing ; moreover, the
salivary glands of the affected side cannot be excited to
reflex secretion.

The Functions of the Brain — comprising those of the Cor-
tical Convolutions, Corpora Striata, and Optic ThalamL — A
frog which has been deprived of its hemispheres, acts in all
respects as a normal frog, excepting that it is incapable either
of interpreting its sensations, or of initiating voluntary acts.
The condition of the brainless mammalian animal is
analogous. It is subject to emotion, and acts in such a
way as to show that it is influenced both by impressions
received through the nerves of common sensation and
through those of sight and hearing, but it is incapable of
understanding, remembering, or willing. All of its acts
are of the kind described on p. 78. Any direct inter-
ference with the brain as, e.g., by compression of its sub-
stance, or by arrest, or great diminution of its circulation
(as in syncope), annuls consciousness. — Although at first
sight the development of the hemispheres seems in animals
to exhibit only a very general relation to that of the
mental faculties, it can be shown that the relation between

THE CONVOLUTIONS. IOI

the weight of the brain and intelligence is a very close
one, provided that the weight of the mesencephalon be
taken as the standard of comparison, not that of the
whole body.

The inference that is suggested by the anatomical rela-
tions of the corpora striata, viz., that they serve to bring
into connection the cortex of the hemispheres, particularly
of the " motor region," with the reflex motor centres of
the mid-brain, is supported by clinical observations, for
the almost constant result of lesions of these organs is
loss of voluntary control over the muscles of the opposite
side of the body (hemiplegia), a condition which is not,
as a rule, permanent. By experiment, we learn that the
part of the corpus striatum on which this effect depends,
is the nucleus lenticular -is ; for while destruction of this
part produces as complete hemiplegia as if the whole
hemisphere were removed, interference with the nucleus
caudatus is almost without effect.

There is, at present, no evidence either that the corpora
striata contain motor centres, or the contrary. As regards
the functions of the optic thalamus, no general statement
can at present be made.

The Convolutions. — It was formerly believed that all
parts of the cortex of the hemispheres have the same
function. It is now known that in certain regions each
part has physiological relations which are peculiar to
itself. The proof that this is so, lies in the observation
of two classes of phenomena, viz., (i) the effects of
electrical excitation of particular parts of the surface of
the hemispheres, and (2) the results of ablation of certain
parts.

As regards the effects of excitation, the best ascer-
tained facts are those which relate to the excitation of
the prse-frontal, post-frontal, and super-sylvian convolutions
of the dog ; corresponding in position to the convolutions
which surround the fissure of Rolando in the human

102 THE CONVOLUTIONS.

brain. These excitations severally induce co-ordinated
motions (varying in their character according to the pre-
cise part excited) of the head and neck, of the extremi-
ties, and of the muscles of the face, on the side of the
body opposite that on which the cerebral surface is ex-
cited. After removal or destruction of any of these parts
of the cortex, excitation of the white substance sub-
jacent to it produces the same effect as excitation of the
part of the cortex with which its fibres were previously
in relation, so that the cortical substance is not essential.
In all cases, a perceptible interval of time intervenes
between the excitation and the muscular action which
results from it.

The effects of ablation can only be studied after the
animal has entirely recovered from the immediate patho-
logical effects of the injury. From observations so made,
we learn (i) that absence of parts of the cortex, by the
excitation of which particular groups of muscles are
brought into action, is not associated with any impair-
ment of the function of the muscles, but only with loss or
impairment of the power of the animal to employ them
n the performance of certain combined motions ; (2) that
destruction of the whole or the greater part of the cortex
is attended with impairment of memory and perception.
If the lesion is on one side only, this impairment mani-
fests itself chiefly in relation to impressions received from
the opposite side of the body. According to recent
observations of Prof. H. Munk, visual perception is
localized in the occipital lobe. Thus (in the dog) ablation
of the posterior extremity of this lobe on one side, pro-
duces blindness of the middle and inner part of the retina
of the opposite side, and of the outer part of the retina
of the same side. In the ape, the same lesion produces
blindness of the inner half of the opposite retina, and of
the outer half of the retina of the same side. — It has
been long known clinically, that destruction (by disease)

FUNCTIONS OF SENSORY ORGANS. IO3

of the lower end of the ascending frontal convolution in
man (Broca's convolution), is associated with aphasia, a
condition in which the patient, though able to articulate,
and possessing the power of forming adequate concep-
tions which he remembers, is unable to word them. In
the vast majority of the cases in which this happens, the
lesion is on the left side of the brain.

COMMON AND SPECIAL SENSATION.
(Functions of Sensory end-organs^)

Sensations and Perceptions in general. — By the word
Sensation is meant in physiology the felt effect of an
excitation either of a sensory end-organ, or of a sensory
nerve. Sensations which originate from end-organs are
divided into those of common sensation, vision, hearing,
taste, &c., according to the end-organ affected. Sensations
which spring from direct irritation of sensory nerves, are
usually painful. Very feeble excitation of an end-organ
is not felt. As regards those excitations which from their
nature admit of measurement, it was found by E. H.
Weber that the degree of intensity which must be attained
by any excitation in order to be felt — the limen (Reiz-
schwelle) is constant in the same individual. As regards all
excitations of which the intensity exceeds the limen, it is
found that the " sensible increment " (i.e. the smallest
additional excitation that can be felt), is proportional to
the previous excitation. Hence, the sensation produced
by any given excitation varies inversely as the intensity of
the previous excitation. The ratio of the " sensible incre-
ment " to the " previous excitation " differs in different
cases. Thus as regards light, it is as I : 100, or there-
abouts ; as regards sound as i : 3, and so on.

104 TACTILE SENSATION.

Between an excitation of any end-organ and a voluntary
motion prompted by it, a time elapses, usually called the
" personal time," which is made up of the time required
for recognizing the sensation (perception) and the time
required for transforming it into muscular action (intention).
In the simplest possible case, that in which the person
under observation signifies his recognition of an expected
excitation by a preconcerted signal, the personal time is
about one-sixth of a second for sound, light, and touch.
By increasing the intensity of the excitation the time may
be somewhat diminished. If the sensation is of such a
character as to require interpretation or discrimination
before it is acted upon, the time is longer.

Tactile Sensation.

Tactile sensation is regarded as the function of the
so-called " tactile corpuscles " of the skin, and of analogous
end-organs which exist in the exposed mucous membranes.
According to the mode in which the end-organs are
affected, tactile sensation is divisible into that of Pressure,
that of Temperature, and that of Locality. As regards
pressure, Weber found that an increment of pressure on
the hand must amount to at least one-thirtieth of the
previous pressure to be felt. As regards temperature, the
degree of excitation is estimated by the difference between
the temperature of the object applied, and the actual
temperature of the skin. A difference of about one-eighth
of a degree can be felt. The sensation of locality may be
tested either by " interrogation," or by measuring the dis-
tance at which two points of excitation must be apart in
order that they may be felt as two. In relation to the
latter method, any area on the surface of the skin within
which two such points cannot be distinguished, is called a
"sensation area." The widths of sensation areas for

VISION. 105

different regions are, in millimeters, as follows : — Tongue I ;
finger-tip 2 ; lip 4 ; neck 20 ; back 60.

Muscular Sensation.

Muscular exertion is attended with a "sensation of
effort," the relation of which to the work done (e.g. the
weight lifted), according to Weber's experiments, is such,
that no difference less than a fortieth between two weights
lifted in succession can be appreciated. The sensation of
effort is therefore more delicate than the sensation of
pressure. The existence of sensory nerve-endings in the
sartorius muscle of the frog has lately been demonstrated ;
with this exception, channels of muscular sensation have
not hitherto been recognized.

Vision.

The Eye as an optical instrument. — To understand the
paths of luminous rays through the eye to the retina, it is
necessary to know the form of its three principal refracting
surfaces, and the refractive indices of its transparent
media. Of the normal eye the radii of curvature, indices
of refraction, and dimensions are approximately as follows :
— Radius of the corneal surface, 8 millimeters, radius of
the anterior surface of lens, 10 millimeters, of posterior
surface, 6 millimeters, these surfaces being severally 4
millimeters apart in the axis of the eye ; the distance from
the posterior surface to the retina is 13 millimeters. The
index of refraction of the aqueous or vitreous humour is
1-35, that of water being 1*336. The refraction-index of
the lens varies from 1-405 at the surface to 1-454 in the
centre.

An eye supposed to be constructed according to these
measurements is denoted by the term "schematic eye,"

106 THE REDUCED EYE.

which represents what the normal eye would be, if its
refracting surfaces were spherical, their centres in the same
axis, and its transparent media homogeneous.

The lensless or reduced Eye. — If it were not necessary that
the eye should be capable of being adjusted for the distinct
vision of objects of different distances, the lens would not
be required ; for an eye which consists of but one medium,
and has but one refracting surface, answers the dioptrical
purposes of the real eye in every respect, excepting that it
cannot be " accommodated." A schema of this kind is
called a " reduced eye." In such an eye, if the radius of
curvature of the cornea is 5'I2, and the index of refraction
about i "35, the conditions approach pretty closely to those
of the normal eye. In the reduced eye the straight line
which passes through the centre of the cornea and the
centre of its sphere of curvature is the axis. Rays which
are in the same line with a radius of the refracting surface
are not refracted : such rays are called principal rays. As
they all pass through the centre of the sphere of curvature
of the cornea, that centre is called the " crossing point."
In the normal eye this point lies immediately in front of
the posterior surface of the lens. Any number of rays
reaching the cornea from a luminous point (object) at
sufficient distance in the axis, are so refracted at the surface
that they converge to a point (image) on the other side.
Rays which emanate from a luminous point in a plane
including the first, which is vertical to the axis (object-
plane) converge to a point in the same vertical plane with
the image of the first point (image-plane). It thus happens
that (as regards flat surfaces of small extent which face
the cornea) every point of the object-plane is focussed in
the image-plane, forming there an inverted image. The
further the object-plane is from the refracting surface, the
nearer must be the image-plane. The point to which the
almost parallel rays which emanate from any very distant
point in ,the axis converge, is called the principal

THE LENS. ID/

focus. In the unaccommodated eye this point is in the
retina.*

The Lens. — When the tensor of the choroid is inactive,
the principal focus of the normal (emmetropic) eye lies in
the retina ; consequently those objects only are seen dis-
tinctly from which the eye receives parallel rays. The
process by which it is adjusted for vision of near objects,
is called "accommodation." Its accomplishment is the
purpose or function of the lens, and of the muscular and
fibrous structures by which its form is regulated, the
tensor of the choroid and the zonule of Zinn. The tensor
of the choroid consists, in man, of fibres of two kinds, viz.,
of annular fibres which encircle the border of the lens, and
of much more numerous meridional fibres which draw the
choroid towards the cornea. When (in the dog) this
muscle is thrown into action by excitation of the short
root of the lenticular ganglion, the anterior surface of the
lens becomes more convex and approaches to a shorter
distance from the posterior surface of the cornea.

The increase of convexity is due to the relaxation of
the zonule, by virtue of which the lens is left to its own
elasticity, and assumes a form approaching that which it
possesses after removal from the body. Under the influence
of atropin the tensor is completely paralysed ; in conse-
quence, the convexity of the lens is diminished ; for, in the
ordinary condition of the eye, the muscular fibres are not
entirely relaxed. The degree of accommodation of which
the eye is capable varies in different individuals at different
ages. Thus, in the normal emmetropic eye, which, when
entirely relaxed, sees distant objects distinctly, the lens can
in childhood be rendered convex enough to give well-defined
images of objects at a distance of 3 inches. As age advances,

* The statement above is simplified to the utmost by the substitution of the
hypothetical lensless eye for the schematic eye. All that has been said is
applicable to the real eye, but much is omitted. Those who desire to under-
stand in what way the formation of the image is modified by the presence of
the lens, will find it clearly explained in Hermann's Physiology, pp. 377-384.

108 ACCOMMODATION.

this distance (the " near limit " of vision) at first slowly, then
more rapidly lengthens, until at 50, nothing nearer than
1 2 inches ; at 60, nothing nearer then 24 inches can be
defined. Whence it results that, inasmuch as the form of
the lens when unaccommodated remains nearly the same,
the range of adjustment in advanced life is exceedingly
small. The term myopia is applied to the condition in
which the lens is too convex for parallel rays, even when
the eye is atropinized ; hypermetropia, to that in which it
does not become convex enough for parallel rays, even
when the tensor is in full action. In the former case the
defect must be compensated by concave, in the latter by
convex lenses.

The methods used for measuring the limit of near vision,
are founded on an experiment known as Scheiner's. A
diaphragm having two minute apertures at a distance
less than that of the width of the pupil, is placed immedi-
ately in front of the cornea, while the eye is kept fixed on
an object-point, at a sufficient distance to be distinctly
defined. If now the object is gradually brought nearer, it
is observed, that as soon as the " near limit " is passed, it is
seen double. The instrument used for making this experi-
ment with exactitude is called an optometer.

For all investigations relating to accommodation, it is of
importance to be able to determine in the living eye the
convexity of the anterior surface of the lens, under different
conditions. This is done by measuring the apparent
diameter of an object seen reflected in it. The instrument
used is called an ophthalmometer.

When the eye is contemplated by an observer so placed that the direction in
which he looks at it makes an angle of about 20° with the axis of the observed
eye, the image of any luminous object also placed in front of the eye, rays
from which form the same angle with the axis but on the opposite side, is seen
reflected in the middle of the cornea, and therefore, apparently, close to the
far border of the pupil. On the near side of this image a second appears
similar to it, but larger, feebler, and indistinct. When the observed eye is
accommodated, this image becomes smaller and a little more sharply defined.

THE RETINA. 1 09

Astigmatism. — This term is applied to a condition of the eyes in which the
curvature of the cornea is somewhat less in the vertical than in the horizontal
meridian. If such an eye is so accommodated that rays which lie in the
vertical meridian converge to the retina, while those in the horizontal meridian
converge beyond it, the point is seen as a horizontal bar.

Chromatism. — If the eye is fixed on a luminous point at a great distance, it
often appears as if it had a sharply defined red centre, surrounded by a luminous
fringe. This happens when the accommodation is such that the less refrangible
rays converge to the retina, the more refrangible in front of it. In the contrary
case, i.e. when the distance of the luminous point is less than that for which
the eye is accommodated, the centre is blue.

Entommatic vision. — Shadows of objects floating in the media of the eye
are distinguished by the retina, when the eye is illuminated from a point which
is so near the cornea that the rays in entering the eye become parallel. As
thus seen, objects behind the pupil may be distinguished from objects in front
of it, by the observation that they appear to move in the direction opposite to
that in which the source of light is moved.

Reflection of light in the Eyeball. — Light which reaches
the retina is partly absorbed, partly reflected. Every re-
flected ray returns approximately in the path of its incidence.
Consequently, although the cavity of the globe appears
under ordinary circumstances dark, it can be made to
appear luminous if illuminated by light which reaches it as
if it came from the eye of the observer. Thus, if a plate
of glass be so placed between the observing and the
observed eye that light emanating from a luminous source
is reflected by it into the observed eye, as if it came from
the other, the former appears bright ; and if it were possible
for both eyes to remain relaxed, that is accommodated for
extreme distance, a distinct image of the retina would be
seen by the observing eye. In the ophthalmoscope as
originally invented by Helmholtz, this is done by the
interposition of a concave correcting lens between the
observing eye and the mirror.

The Retina. — The retina is a sensory end-organ excited
by light. Its excitability has its exclusive seat in the
bacillary layer.

If a strong light is suddenly thrown, by a lens, on the outside of the eyeball
of a person in a dark room, an appearance of branching blood-vessels is seen
by him, of which the explanation is that the side light throws shadows of the

IIO THE RETINA.

retinal vessels on parts of the bacillary membrane, which are not accustomed
to receive them. If the source of light moves, the shadows move with it,
and in the same apparent direction. The motion of the retinal image (i) can
be measured ; that of the light (2) can also be measured, and the distance (3)
of the vessels from the bacillary membrane is known. If from 2 and 3, I be
calculated, it will be found to agree with the measurement.

The fovea centralis is more perfect structurally and func-
tionally than any other part of the retina. Accordingly, as it
lies approximately in the axis of the eyeball, objects which
lie in the prolongation of this axis (the visual line) i.e. those
on which the eye is fixed, are seen more distinctly than any
others. Thus, two objects so near together that the straight
lines leading from them to the crossing point of the eye,
meet each other at an angle of 60" or 70" (and of which con-
sequently the retinal images are at most 0*005 millimeter
from each other), can be distinguished as two. If the
images fall on the retina outside of the fovea, they must
be at least a millimeter apart, in order to be distinguished.
If the rays from two objects at the same apparent height
meet at 15°, and the eye is fixed on the one nearest the
middle plane of the body, the other (provided that its
retinal image does not measure more than 1*5 millimeter)
is not seen, for its image falls on the entrance of the optic
nerve, the so called " blind spot."

Retinal Purple. — The external layer of the bacillary membrane (outer joints
of the rods and cones) is infiltrated with a red colouring matter, which in the
eye removed from the body, remains unaltered so long as the retina is in the
dark, or is exposed only to yellow light. On exposure to ordinary or blue
light it disappears, but can be restored even after the cessation of the circula-
tion, by contact in the dark with the pigment epithelium. During life it is
alternately destroyed and reproduced according as the eye is exposed, or not
to light.

Excitability of the retina. — Process of excitation in the
retina. As with respect to other excitable structures, so in
the case of the retina, we may best distinguish between the
excitation and the physiological effect which it occasions
(sensation of light), by studying their time-relations. We
learn by observation, (i) that the sensation of light produced

SENSATIONS OF COLOUR. Ill

by an instantaneous excitation (say of -rj^") at first increases,
culminates about .j." after the excitation and then rapidly
diminishes ; (2) that of a succession of such excitations
following each other without intermission, all are at first
(during the first tenth of a second) equally effective, so
that the sensation occasioned by the series is equal to the
sum of the sensations which would have been produced by
all of the excitations had they occurred separately ; but
afterwards the excitations become less and less effective.
Hence it results, first, that in the case of illuminations of
the unexhausted retina of about Ty duration or less, the
sensation of light is proportional to the product of the
intensity and duration of the illumination ; and secondly,
that when the illumination is continued, the sensation of
light at first increases, then gradually diminishes. This
diminution of the excitability of the retina by previous
excitation is called " exhaustion." In consequence of it,
when we contemplate a bright object and then look else-
where, we see a dark image (called an after-image) of it.

When the retina is excited by homogeneous rays, i. e.,
by rays of which all are of the same refrangibility, the
effects follow each other in the same order, but it is
found that the colour-sensations occasioned by rays of
equal intensity, but different refrangibility, culminate at
different rates. The exhaustion produced by monochro-
matic light affects the excitability of the retina only in
respect of light of the same kind. Consequently, the
after-images of coloured objects are themselves coloured.

Colour sensations are said to be " blended " when the
rays which occasion them affect the retina, either simul-
taneously or in such rapid succession that their action is
simultaneous. If two kinds of light act simultaneously
on both retinae, they may also give rise to a blended
sensation.

Classification of colour-sensations : — The sensations oc-
casioned by monochromatic rays of different kinds admit

112 SENSATIONS OF COLOUR.

of being placed in linear series, in the order of the refran-
gibility of the rays which produce them. Those occasioned
by the simultaneous action of rays of different refrangi-
bilities are much more various, and cannot be arranged in
line. If, however, on a plane surface a central position is
assigned to the sensation " white," the other sensations may
be arranged round it in such a way, that the sensation
which results from the " blending " of any two or more
others has its place between them, at distances from each
which express their relative preponderances. In this
arrangement (called the colour circle) spectral colour sensa-
tions form an incomplete ring round white, between the red
and violet ends of which is placed purple. The relations
of colour sensations exhibited in the colour circle can be
most simply explained on the following hypothesis. (Young,
Helmholtz.) There are three fundamental colour-sensations,
viz. : red, green and indigo, from which all others are derived
by blending. Every element of the retina (every cone)
contains three terminal elements, one of which is most
excited by the less refrangible rays (red element), one by
the most refrangible (blue element), the other by those of
medium refrangibility (green element), but all more or less
by all.

The theory that red, green, and indigo, are the fundamental sensations is
supported by the following observations, among others: — I. If the spectrum
is contemplated while its colours are gradually weakened, until they cease to
be visible, the colours named are the last to disappear. (Briicke.) 2. If a
white surface is contemplated by a retina of which the excitability for a par-
ticular kind of homogeneous light has been weakened by excitation, it appears
to be coloured ; the colour sensation produced occupies a place in the colour
circle exactly opposite to that immediately occasioned by the excitation, and is
therefore said to be " complementary " to it. In like manner, if a coloured
surface is contemplated by a retina partially dulled by the same mode of
excitation, its hue is — provided that its colour is a blended one — altered, by the
weakening of one of its constituent sensations. But if after dulling the excit-
ability of the retina for red, an indigo surface is contemplated, its hue
remains unchanged, for inasmuch as, according to the theory, indigo rays
scarcely affect the red elements, the quality of the sensation is not affected by
their not taking part in its production ; if the experiment is repeated with a

MOTIONS OF THE EYEBALLS. 1 13

violet surface, the result is no longer the same. To the retina dulled for red it
appears bluer. Similar observations may be made as regards the other
primary colours. 3. The image seen in the dark after the eye has been
directed to the sun is at first bright, then fades away and becomes red. If
while the red image is observed white light is admitted, it becomes green.
The excitation of the red elements is more persistent than of the others, and
their consequent exhaustion more prolonged.

Colour-blindness. — In some persons (in consequence, it
may be supposed, of defective excitability of the green or
red elements of the cones), red, in others green is mistaken
for grey. About two in every hundred railway officials
examined by Bonders, were found to present one or other
of these conditions.

Motions (Rotations) of the Eyeballs. — I. The straight line
which connects the apex of the cornea with the fovca
centralis retince is called the " visual axis." The plane in
which the visual axes of both eyes lie is the " visual plane."
When the visual axes of both eyes are directed to the
horizon and are parallel to the middle plane of the body,
the eyes are in the " position of rest " (primary position).
2. The vertical plane in which the visual axis lies when the
eyes are in the position of rest, is called the " vertical
meridian " and the horizontal plane at right angles to it,
the "horizontal meridian" 3. All rotations of the eye-
balls take place round axes (called " axes of rotation ")
which cut the visual axis at right angles, about 17 millim.
behind its mid-point. (Listing and Bonders.) 4. Any
position into which the eyeballs can be brought by rotat-
ing them from the position of rest directly upwards (i.e.,
round horizontal and coincident axes of rotation), or directly
to the right or left (i.e., round vertical axes of rotation), is
called a secondary position. 5. In the position of rest
and in every secondary position, the horizontal meridians of
both eyes are in the visual plane. All other positions are
called " tertiary." In every tertiary position, the horizontal
meridians intersect the visual plane, at an angle which is
called the " angle of rotation." (See Exercises.)

I

114 MOTIONS OF THE EYEBALLS.

The muscles of the eyeball are divisible in respect of
their action, into two groups, of which one comprises
the rectus intermix and r. externus ; the other, the
obliquus inferior, and o. superior, which act in concert with
the rectus superior and r. inferior. The axis round which
any muscle rotates the eyeball is called its proper axis of
rotation. Those of the internal and external recti nearly
coincide with the vertical axis of the eyeball. Consequently
these muscles, acting antagonistically, rotate the eyes
directly to right or left (secondary positions). The com-
bined axis of the oblique muscles (the axes of the two
being approximately identical) is horizontal, but cuts the
equator of the eye at an angle of 60°. The combined axis
of the superior and inferior recti is neither horizontal nor
transverse, but has its inner end lower, as well as further
forwards than the outer. If, however, the rectus sup.
acts with the obliquus inf., they together rotate the eye
round an axis which lies between their own axes, and
nearly coincides with the horizontal axis of the eyeball :
the obliquus superior acts similarly in conjunction with the
rectus inferior. Thus rotations of the eyeball from the
rest position into secondary positions are performed, if to
right or left, by the internal and external recti, if upwards
and downwards, by the combined action of the other four
muscles.

When the eyes are so fixed on any point that it lies in
the visual axis of both of them, the point so contemplated
is seen singly and perfectly ; and all other points are seen
singly, but not perfectly, which are received by corre
spending points of the two retinae — that is by points which
would exactly cover each other if it were possible for both
eyes to occupy the same position, the vertical and horizon-
tal meridians respectively coinciding.

Mental Interpretations or Judgments of Visual Sensa-
tions.— I. Binocular blending of colours. When rays of two
colours enter the two retinse simultaneously, the sensation

HEARING. 1 1 5

is not always the same. Sometimes the two colours are
blended as completely as if both affected one retina : at
others there is a contest between the two, first one, then
the other predominating in the blending. 2. Judgment of
distance. We judge of the distance of any object, chiefly
by the degree of convergence of the visual axes, which we
find necessary in order to fix both eyes upon it. Conse-
quently, if one eye is shut and two or more objects of the
same form but of different sizes are placed before the other
at such distances that their retinal images cover equal
areas, their respective distances cannot be distinguished.
If both eyes are used a correct judgment can be formed
without difficulty. 3. Judgment of solidity. By explor-
ing an object with the eyes, i.e., by fixing them successively
on different points of its visible surface, we are able to
judge of the relative distances of these points, as well as
of their directions. It can, however, be shown that this
process is not ordinarily employed in judging of the form
and solidity of objects, but that the mind accomplishes this
instantaneously, by the blending of the two dissimilar
images which are received by the two retinae, whenever
both eyes are fixed on some point in a solid object at a
short distance from them. The point so contemplated is
of course seen single, others are for the most part seen
double : notwithstanding this, we are not conscious of any
confusion of images.

Hearing.

The process of hearing consists (i) in the production of
vibratory movements of the membrana tympani, which are
synchronous with the sound-vibrations of air in the
meatus ; (2) in the communication of these vibrations to
the liquid contained in the labyrinth ; and (3) in the pro-
duction of vibrations in all those parts of the lamina

I 2

Il6 HEARING.

spiralis of which the vibration-rate agrees with those of
vibrations existing in the liquid.

Sensations of sound are divided, according to the cha-
racter (form) of the air-vibrations which occasion them,
into non-musical sounds or noises, and musical sounds
or " tones." Of tones, simple and compound are distin-
guished. The former are heard when the air molecules
at the external surface of the membrana tympani are in
simple pendular vibration ; the latter when the vibrations
are compounded of vibrations of different rates of fre-
quency, of which the relations to each other may be 1:2,
1:3, 1:4, 1:5, and so on in the same order. The tones
which correspond to each of these simple constituent
vibrations, are called " partial tones." According to the
number, relative strength and relative frequency of the
simple tones into which they can be resolved, compound
tones differ in timbre or quality. Tones whether simple
or compound differ also in pitch : the pitch of a simple
tone is expressed by the number of its vibrations in a
second : that of a compound tone by the vibration-number
of its predominant partial-tone.

The middle ear. — The cavity of the tympanum across
which sonorous vibrations are transmitted by the ear
bones, communicates with the pharynx by the Eustachian
tube : the pharyngeal end of this tube is, however, usually
closed and can only be opened by bringing into action
the muscles of deglutition. The external wall of the
cavity is formed by the membrana tympani, which, by the
arrangement of the radiating and annular fibres which
compose its two layers, by the conical form of its internal
surface, and by the mode of attachment of the handle of
the malleus, is fitted for its function — the passive reception of
the motions communicated to it by the vibrating air parti-
cles at its surface. In the communication of the move-
ments of the membrana tympani to the foramen ovale, the
malleus and incus act as one piece ; for, so long as the mem-

HEARING. II/

brana tympani is tense, the tooth of the incus is kept locked
against the notch of the malleus. When in this con-
dition, the two bones rotate on an axis of which one
extremity is at the tip of the short process of the incus,
the other corresponding approximately to the attachment
of the ligamentum anterius of the malleus : hence the
axis of rotation nearly coincides with the upper border
of the tympanic ring. The two bones may be compared
when in action to a bell-crank lever of which one limb,
representing the handle of the malleus, is approximately
half as long again as the other (the long process of the
incus), and forms with it an acute angle. Consequently
every motion of the tympanic membrane which is trans-
mitted to the stapes is diminished by about a third.
When the membrana tympani is relaxed, the distance
between the tip of the long process of the incus and the
handle of the malleus slightly increases. Nothing can be
certainly stated as to the uses of the muscles of the
middle ear.

The internal ear. — The essential part of the organ of
hearing is the cochlea and particularly the organ of Corti.
The organ of Corti consists of a series of arches, about
3,000 in number, of extreme minuteness, the span of which
increases gradually from the base of the cochlea to the
helicotrema, and of epithelial elements (the hair-cells) in
relation with these arches, which are intimately connected
with the terminations of the cochlear nerve. These struc-
tures rest upon a ribbon-shaped fibrous membrane (the
lamina spiralis membranacea or membrana basilaris)
which is wide at the helicotrema, narrow at the base of
the cochlea. It is attached by its edges to bone, and con-
sists chiefly of fibres which run transversely to its length,
and are believed to be tense. Corti's organ is contained
in a spiral tube, triangular in section, the duct of the
cochlea, one side of which is formed by the membrana
basilaris, the other by the membrane of Reissner. •

Il8 HEARING.

With reference to the transmission of sound, the cavity
of the vestibule and cochlea may be regarded as divided
into two, that of the vestibule and scala vestibuli
which communicates with the lymph space surrounding
the vestibular sacs, and that of the scala tympani, which
is- closed by the membrane of the fenestra ovalis.
Although these two cavities communicate by a small
opening, they may be regarded as in so far separate that
any motion of the membrane of the foramen ovale must
be communicated to the membrane of Reissner, then to
the membrana basilaris and thereby to the organ of Corti.
From the structure of the organ of Corti it was inferred
by Helmholtz that it must be an organ for the perception
and discrimination of tones, and that the elements (nerve-
endings, Corti's arches and adjoining cells) serve in the
discrimination of the sonorous vibrations of the liquid in
which they are immersed — a function which is analogous
to that of the hypothetical red, blue, and green elements
of the retinal cones in regard to luminous vibrations.
Tones can be readily discriminated by the human ear of
which the vibration-rates range from 40 to 7,000 per second.
A skilled musical ear can distinguish more than 6,000
different tones within the range of these seven and a half
octaves ; consequently, as there are only 3,000 arches of
Corti, each must be capable of being excited by several
gradations of tone.

In the case of the elements of the cones of the retina
we can form no conception of the modes in which they
are acted upon by light, but the action of tones on the
organ of Corti can be satisfactorily explained by com-
paring that organ to a system of resonators. By a reso-
nator is meant anything which, by virtue of its form and
structure, is capable of being thrown into musical vibra-
tion. Every resonator produces when thus acted upon, a
tone which is peculiar to itself — its " proper tone," and is
readily excited by tones of the same vibration- rate when

TASTE.

119

communicated to it either through the air or otherwise.
Many resonators can be excited to vibration not only by
their "proper tones," but also by vibrations of approxi-
mately the same frequency, in a degree proportional to
the approximation. As there is reason to believe that the
resonators of the organ of Corti have this property, it
enables us to understand how it happens that the number
of distinguishable tones exceeds that of the elements
which serve to appreciate them. For a tone affects not
one, but two or more resonators, each in proportion to its
proximity to the tone by which it is excited, so that just
as every perception of colour is founded on impressions
received through at least three elements, every perception
of tone is occasioned by the simultaneous vibration of
several elements of the organ of Corti. The power of
distinguishing two tones which follow each other at very
short intervals of time, is known to vary with their rate
of vibration. Thus, whatever be the tone, it has been
found that the time intervening between one excitation
and its successor must be sufficient for about twenty-two
vibrations in order that they may be heard as two. Helm-
holtz explains this on the principle that the resonators of
the organ of Corti are very readily thrown into vibration,
and continue to vibrate only a short time after the excita-
tion has ceased.

Nothing can be stated with certainty as to the functions
of the end-organs of the vestibular sacs ; from their
analogy with the auditory vesicles of invertebrate animals
without cochleae it may be inferred that they have similar
functions. (With reference to the ampullae, see p. 97).

Taste.

Sensations of taste are occasioned by the access of
sapid substances to the tongue, either in the neighbour-
hood of the papillae vallatae, or of the papilla foliata of

120 TASTE.

either side, or to its upper surface close to the tip. Almost
all unmixed sensations of taste may be referred to one of
four fundamental kinds, viz., bitter, sweet, salty, and acid.
Those which cannot be so classified result for the most
part from the " blending " of gustatory with tactile or
olfactory impressions. Of the four fundamental tastes,
all can be appreciated by the papillae vallatae and the
papillae foliatae. The tasting power of the tip is im-
perfect, and in some persons wanting. When present,
it is in most persons confined to the appreciation of acid,
sweet and salty tastes. Taste sensations can be excited
by the passage of voltaic currents through the base of
the tongue, particularly when the anode is applied to
the neighbourhood of the papillae vallatae, or to the
papilla foliata of either side. Taste is believed to be
dependent on the excitation of certain end-organs, the
so-called taste buds, which are to be found in the struc-
tures above mentioned. As, after section of the glosso-
pharyngeal nerve in animals, these organs degenerate and
finally disappear, there can be little doubt that they con-
tain the gustatory terminations of that nerve. In judging
of their function it must remembered that they are met
with beyond the limits of the gustatory region, as, e.g.,
on the under surface of the epiglottis, in the larynx and
in the papillae fungiformes of parts of the tongue which
are not endowed with taste.

The taste region at the base of the tongue is supplied
by the glossopharyngeal nerve. The tip of the tongue
receives its supplies from the lingual, and has been found
in several instances in man to lose its tasting power after
destruction of that nerve. There is, however, reason for
believing that the gustatory fibres of the lingual are ulti-
mately derived from the glossopharyngeal nerve, through
the tympanic plexus. In animals, after section of the
glossopharyngeal nerves, near their origin, taste appears
to be entirely absent.

SMELL. 121

Smell.

Sensations of smell are occasioned when air containing
odorous substances in the state of vapour or gas is inspired
through the nostrils, but not when the cavity of the nares
is filled with their solution.

Smell is limited to the upper part of the septum, the
upper turbinated bone, and the upper part of the middle
turbinated bone. This region is characterized by its
yellow colour, by its slender columnar epithelial ele-
ments, and by the existence among them of the peculiar
spindle-shaped elements, which are believed to be the end-
organs of the nerve of smell. In inspiration, a large pro-
portion of the air inspired passes through the olfactory
region ; but, in consequence of the form of the channel
through which it passes, the expiratory current is almost
entirely diverted, so that odours of intrinsic origin are but
little perceived. The varieties of smell are more numerous
than those of taste, and appear to have little relation to
the chemical constitution of the gases or vapours which
occasion them.

123

PRACTICAL EXERCISES]

RELATING TO THE PHYSIOLOGICAL PROPERTIES OF THE

CONTRACTILE AND EXCITABLE
TISSUES.

I. — Modes of Excitation.

Electrical Excitation. — The requirements for the purpose are
Batteries (Grove's or Daniell's), an Induction coil, wires, two keys, and suit-
able Electrodes. The Induction apparatus used is that of Prof, du Bois-Rey-
mond. (See " Handbook," p. 351, fig. 298.) The key ordinarily used is also
that of du Bois-Reymond. The Electrodes are made as follows : — Cement
with sealing-wax two copper wires, each about three inches long and pointed
at one end, into two pieces of glass tube two inches long, just large enough to
contain the wires. The ends of the wires must project about half an inch
from the glass tubes, and must be coated on all sides, excepting one, with
yealing-wax. Bind the two glass tubes together with strong thread and
solder fine copper wires to the blunt ends of the electrodes.

I. Use Of th.6 Induction Coil. — a. For single induction shocks. —
Connect a Daniell cell by copper wires with the two upper screws which are
directly connected with the ends of the primary coil, interposing a key in the
circuit. Insert, the wires from the electrodes in the binding screws of the
secondary coil, and place the points of the electrodes against the tongue.
Withdraw the secondary coil from the primary and then gradually bring it
nearer, opening and closing the key after each approximation. The " break
shock" is first felt, and is throughout perceptibly stronger than the "make
shock." b. For faradization. — Connect the battery wires with the screws at
the bases of the brass pillars (C and A in fig. '293). If the platinum-pointed
screw (/) is properly adjusted, the hammer begins to vibrate on closing the
key, and a series, consisting alternately of " make" and "break" shocks, is felt,
which, as the secondary coil begins to cover the primary, becomes unbearable.
For many purposes it is desirable to avoid the great disparity which in the
ordinary arrangement exists between the opening and closing shocks. This is
accomplished by a contrivance known as Helmholtz' modification (see " Hand-
book," fig. 294) : — A side wire connects the outer pillar with the top screw of

124 ELECTRICAL EXCITATION.

the same side. The upper platinum-tipped screw is withdrawn and the under
platinum tip brought into contact with the vibrating hammer, at the moment
that it is drawn down by the temporary magnet. Compare the effects with
those previously felt, particularly when the primary coil is covered by the
secondary. It is convenient in all cases to interpose a key in the primary
circuit.

2. The Single Induction Shock.— Connect the primary coil of the
Induction apparatus with a Daniell cell, interposing a key. Arrange a rheo-
scopic preparation of the lower limbs of a pithed frog, by placing two slender
glass rods under the sacral plexuses, having first opened the visceral cavity and,
removed the viscera. Connect the electrodes with the terminals of the
secondary coil, and place them underneath the nerves thus separated from
other structures. The preparation should be supported in the vertical position
by a clamp. Remove the secondary from the primary coil until no response
occurs on closing or opening the key. Then bring the secondary coil gradually
nearer and observe that at a certain distance the preparation responds only to
the "break" shock, afterwards to both "make" and "break," but more
strongly to the latter, and finally with equal vigour to both.

3- The Extra Current.— To demonstrate Faraday's " extra current "
physiologically, introduce the exciting electrodes into the primary circuit of the
induction apparatus, removing the secondary coil. Connect the electrodes by a
couple of copper wires whose ends are united by a key, so that when the key is
closed the electrodes are in metallic connection by the wires and key as well as
by the coil and battery. Place the electrodes under the sacral plexus in the
preparation used in the previous experiment ; and observe that when the key
is opened the rheoscopic limbs respond strongly ; this is due to the extra
current, that is, to the induction current which is produced in the primary
coil in the same direction with the battery current, immediately after the
sudden diminution produced by the opening of the key.

4- Unipolar Excitation. — Connect one electrode with one terminal
of the induction coil and place it under the sacral nerves of the same pre-
paration, which for this purpose must be on a glass plate. No response takes
place either on making or breaking. Touch the preparation or otherwise
connect it with the earth, and it will be observed that it responds at break.

5- Faradization. — Arrange the coil for faradization and place the
electrodes under the sacral plexus in a similar preparation. The limbs are
extended and the muscles rigid. The spasm so produced persists, though
with gradually diminishing intensity, so long as the primary circuit remains
closed. This condition of tonic contraction is designated l^etanus.

6. Galvani's Experiment.— Take a clean bit of zinc wire, and coil
round one end of it a copper wire of the same length, so as to make a fork.
Pith a frog and lay it on its belly. Remove the skin from the back of the thigh,
separate with the finder and remove the narrow biceps femoris. Separate the
sciatic nerve which is thus brought into view, from the surrounding struc-
tures, and touch the nerve first with the copper wire, then with the zinc. It
will be observed that on closing the circuit thus formed, the gastrocnemitis muscle
contracts and the foot is extended. If it is moderately excitable, the same thing
happens also on opening it.

ELECTRICAL EXCITATION. 125

7. Excitation by Interruption of the Direct or Battery

Current. — For this purpose it is necessary to arrange the circuit so that its
intensity can be varied at will. This might be accomplished by the inter-
position of large resistances, but such a method would be so inconvenient as
to be impracticable. The method always used is to connect the poles of the
battery by a side wire, whose resistance can be varied at pleasure. As the
resistance of nerve and muscle is very high, the strength of the current in
the circuit varies approximately inversely as the resistance of the side wire.
A graduated side wire suitable for this purpose is called a rheochord. The
rheochord commonly used is that of du Bois-Reymond ("Handbook,"
fig. 298). Connect the two terminal binding screws of the rheochord with
the battery (a single Daniell's cell) interposing a key ; connect with the
same binding screws the two end screws of the reverser ("Handbook,"
figs. 299, 506), and finally insert the wires from the electrodes in the two
central screws (i & 2). Prepare the sacral plexus and rheoscopic limbs as
before, and arrange the electrodes. Diminish the resistance of the rheochord
to the utmost, and observe that on opening and closing the circuit, no
contraction takes place. Then gradually increase the resistance. At first
the muscles respond only to closure, subsequently to "make" and "break,"
whatever the direction of the current. On continuing the observation, par-
ticularly with stronger currents, it will be observed that the "make" and
" break " effects are in no instance equal, and that the nature of the inequality
is influenced by the direction of the current. The results are further modified
by exhaustion or injury of the nerve.

8. Excitation of a Motor Nerve by contact with a Con-
tracting Muscle. The Secondary Twitch.— After preparing the
sciatic nerve as above directed, expose the gastrocnemius as directed in 6.
Seize its tendon with the forceps and separate it from its attachments. Cut off
the tibia and femur, close to the knee on either side, along with the muscles
and other soft parts, taking care not to injure the nerve. A gastrocnemius
with its nerve as described, constitute a "nerve muscle preparation." Two
such preparations are required.

Place one of them, b, on a glass plate, and fix the other, a, along the edge
of a small piece of board. Then place the board on the glass plate in such a
position that the nerve of b can can be readily laid on the muscle of a.
Excite by a single induction shock passed through its nerve. At the same
moment that a contracts, b will contract. Then repeat the experiment, but
instead of passing single induction shocks, faradize the nerve. Tetanus is
produced in b, which lasts so long as a is tetanized. Ascertain that the effect
is not due to escape of current, by ligaturing the nerve and repeating the
experiment.

9- Mechanical Excitation. — Mechanical Tetanus. Connect a Grove
cell with the " Tetanometor," introducing a key into the circuit. The wire
from the zinc terminal of the battery must be inserted in the binding screw
marked Z, that from the platinum in K. Adjust the apparatus so that on
closing the key the ivory hammer vibrates so as to excite, without destroying,
a nerve placed on the ivory groove. The effect produced is identical with
tetanus by faradization.

126 THE MYOGRAPH.

10. Chemical Excitation.— Make a nerve-muscle preparation. Place
it on a card, having a hole in the middle just large enough to allow the nerve
to pass. Place the card, with the nerve hanging from it, over a beaker con-
taining ammonia. The muscle does not contract. Then cut off the nerve
and expose the muscle to the'gas. It contracts. Glycerine, on the other hand,
excites nerve readily, but scarcely acts on muscle.

11. Action of the Arrow Poison (Curare) on Muscle

and Nerve- — In a preparation of which the hemispheres have been
destroyed, pass a ligature under the sciatic nerve above one knee and tighten
it so as completely to arrest the circulation beyond. Inject a drop of a solu-
tion containing o'l per cent of curare under the skin and leave the preparation
in a moist chamber for an hour. Then test the condition of the muscles by
direct excitation and excite both sciatic nerves, comparing the effects. Although
both have been equally acted upon, it is on the ligatured side only that the
excitation is responded to. The experiment shows that the arrow poison acts
neither on nerve trunks nor on muscular tissue but only on the muscular
nerve-endings.

II.— The Myograph.

Any instrument by which a curve can be drawn which truly represents the
contraction of a muscle is called a myograph.

I. The most simple myograph is that of Marey, the construction of which
is as follows : — A pillar, supported by the horizontal triangular bar of the record-
ing apparatus (kymograph), carries a board seven inches long by two and a
half in width, which with the aid of a rack-and-pinion and adjusting screw,
can be moved either vertically or horizontally. At one end of the board is a
vertical pillar on which a writing lever is supported ; the point of the lever
can be brought into such a position as to inscribe its movements on the
revolving cylinder. The lever is centred on a horizontal axis, its motion being
resisted by a delicate spring. The upper surface of the board is covered to
within a short distance from the lever, with a thick plate of cork. (See
" Handbook," fig. 270 bis.)

Various muscles of the frog are used for myographic purposes ; the one
most easily prepared is the gastrocnemius. All that is required is to divide
the skin so as to expose the tendon, and to attach the latter to a strong liga-
ture thread. A strong needle must now be thrust through the end of the
femur without injuring other parts, so as to fix the femoral attachment of the
muscle to the cork plate in such a position that the ligature may be advan-
tageously fastened to the lever.

Arrange the apparatus for single induction shocks as directed in Section I., 2,
interposing in the primary circuit an additional key, which is so placed as to be
opened by the recording cylinder on arriving at a certain part of its revolution.

Cover the cylinder smoothly and tightly with glazed paper, taking care that
the edge of the crease does not catch the writing style. Smoke the surface
xiniformly with a paraffin lamp and put the cylinder on the middle axis.

Place the electrodes on the tongue and set the clock in motion, so as to
ascertain that the electrical apparatus is working properly.

THE MYOGRAPH. I2/

2. The Curve of a Single Contraction, or Twitch.— Pith a

frog and place it on its belly on the myograph plate. After preparing and
attaching the muscle as above directed, expose the sciatic nerve, and place the
electrodes under it. Adjust the style of the lever so as to touch the smoked
surface. Open the key of the primary circuit and set the clock in motion.
A line is drawn by the style — the abscissa of the future curve. As soon as
the fly has attained its maximum expansion, close both keys of the primary
circuit. At the moment the cylinder comes into contact with its key and
opens it, a curve is inscribed. Stop the clock and prepare for a second obser-
vation by giving a single or half turn to the pinion, and draw a second curve
similar to the first, and so on, until a series of parallel and similar curves has been
drawn. To observe the effect of exhaustion arrange the apparatus so that, while
the muscle is excited at each revolution, every tenth curve only is recorded.

3- Influence Of Veratrin. — Inject a drop of o-i per cent, solution
of Veratrin into the lymph sac of a brainless frog. After twenty minutes,
destroy the spinal cord and inscribe one or more muscle curves, and compare

hem with those previously obtained.

If in this, and in the preceding experiment, it be desired to employ the "nerve-
muscle preparation " rather than the entire pithed frog, the apparatus described
below may be substituted ; it can be made with simple materials, such as can
be procured anywhere. A thick brass wire is bent twice at right angles, in
the same plane. The middle part measures four inches, and each of the ends
two inches. On the middle part slides a cork bearing two centres, in which
an axis works. This axis bears a light lever about five inches long, which
moves in the plane of the two ends. The femur of the muscle-nerve prepara-
tion is attached by a wire to the upper end of the brass wire (called the
stretcher), and the tendon to the lever. A spiral spring, connecting the lower
end of the stretcher with the lever, serves to extend the muscle and opposes
its contraction. The nerve is enclosed in a tube provided with platinum elec-
trodes, which serves to protect it from evaporation. The whole apparatus is
supported as before (II, i), on an adjustable pillar, which is fixed to the
recording apparatus.

4- Influence Of Temperature on the Form of the Curve of Single
Contraction. — For studying this subject, the simple myograph just described
may be used. A spiral tube of metal of suitable form, must be prepared
and fixed to the stretcher so as to surround the muscle during the observation.
One end of the coil is connected by a flexible tube with a small reservoir of
water at a higher level, the other with a waste pipe. Make a muscle-nerve
preparation, pierce the femur with a fine awl, and pass a fine wire through
the hole and attach it to the upper arm of the stretcher. Secure the tendon
by a ligature to the lever and adjust the spiral spring, so that the lever is
parallel to the arms of the stretcher. With the aid of a fine silk thread
tied to its end, introduce the nerve with great care into the electrode tube and
close the latter with its cork. Adjust the writing lever.

Having made the same arrangement as in the last exercise, pass a stream of
water through the coil at the ordinary temperature and inscribe a succession of
curves. Then repeat the observation, passing water through at various tem-
peratures from 5° C. to 30° C., observing the successive alterations in the form
of the contraction curve.

128 THE MYOGRAPH.

5- The Curve Of TetanilS. — Arrange the apparatus (as directed in
Section I. 2) for single induction shocks. Introduce into the primary circuit
a reed which automatically makes and breaks the circuit twenty times in a
second. Prepare and fix the muscle according to either of the methods
described above. On closing the key of the primary circuit for ten seconds,
the muscle is tetanized and the curve inscribed on the cylinder (see p. 56).

Arrange the induction apparatus for faradization (see Section I. i,b), and
repeat the preceding observation.

6. The Time-Relations of a Muscular Contraction.—

I. By noting the time required for a sufficient number of revolutions of the
recording cylinder and accurately measuring its circumference, the rate of
movement of the recording surface may be determined, and thereby the
time-value of the records known. 2. A more direct method is to write
simultaneously under the tracing the oscillations of a tuning-fork of which
the vibration-rate is known. For this purpose the tuning-fork may be
made to inscribe its vibrations directly, or (more conveniently) it may
be introduced into a battery circuit, so as to interrupt it at each vibra-
tion. An electromagnetic writer (chronograph) is introduced into the same
circuit ; it vibrates synchronously with the fork, and reproduces its motions
on the cylinder. Record a curve of single contraction, using the " stretcher,"
and fix the recording cylinder on the quick axis. Mark the point of
excitation by bringing the trigger of the cylinder very slowly into
contact with the lever of the key. Measure the distances from the point,
— (i) to the beginning of the curve, (2) to its maximum, and (3) to its close,
and determine their value by either of the methods given above.

7. Measurement of the Period of Latent Stimulation and of

the Rate of Propagation in Nerve, by the Pendulum Myograph. —

Preparation of the Apparatus. Cover the glass plate smoothly with paper,
smoke its surface as before, and fix it to the pendulum. Arrange the
"trigger" and the "catch "so that the pendulum when detached from the
former just catches on the latter. Test the instrument by taking tracings
with a tuning-fork vibrating 100 times a second, on the smoked paper, when
the pendulum is moving at several different velocities (the velocity varying
with the positions of the trigger and catch). Arrange the electrical apparatus
for single shocks as in Sect. I. 2, including in the primary circuit one of the
keys of the myograph. Prepare the gastrocnemius as in Sect. II, I. Fix
the femur firmly to the cork table, pass the ligature round the pulley and
attach it to the lever, adjusting the spiral spring to a suitable strength. Take
great care that no part of the apparatus touches the glass plate, as the pen-
dulum swings. Arrange the lever very carefully, so that when it is brought
into position by the rotating handle it writes on the smoked surface. Observe
that the glass plate is so adjusted that the lever at first touches it lightly, but
presses more strongly as the plate swings past. Catch the pendulum with
the trigger, see that everything is in order — the keys closed, the lever in its
position, the electrodes under the nerve, etc. On liberating the pendulum, a
muscle curve is inscribed on the smoked surface. Withdraw the lever from
its writing position, bring the pendulum back past the key, close the latter,
keeping it closed by firm pressure of the finger, allow the pendulum to rest
against it, bring the lever into the writing position, and make a mark on the

THE FROG HEART. 129

surface, which indicates the moment of excitation. Take three or four similar
curves, depressing the table an equal distance after each observation (£ or £
turn) by the handle. Remove the muscle lever and take a tracing with a tuning-
fork, vibrating 100 times a second, carefully arranging the style of the fork in
the position previously occupied by the writing end of the muscle lever.
Remove the paper, varnish and measure the tracings. From the mean result
of the measurements, the latent stimulation may be computed.

8. Rate Of Propagation- — I. Prepare the muscle as in the last exercise.
Expose the sciatic nerve throughout its length. Place one pair of electrodes
under the nerve close to the muscle, and a second pair under the nerve near its
origin. Connect these two pairs of electrodes with a switch. To the middle
screws of the switch attach the wires from the secondary coil, so that by turn-
ing over the bridge of the switch, the near and the distant portion of the
nerve can be excited alternately without loss of time. The nerve should be
prepared with great care, and each exposed part should be protected by a flap
of muscle, except at the moment that it is being excited. Take tracings of
muscle curves in pairs, alternately exciting the near and distant portions of the
nerve. Take a tuning-fork tracing, varnish, measure the length of nerve
from one pair of electrodes to the other, and therefrom determine the rate of
propagation in the nerve (see p. 77).

III. — The Frog Heart.

1. Rhythmical Motions- — In a curarized preparation of which the
hemispheres have been destroyed, expose the sternum and cut across the
episternal cartilage. Then sever the sternum from its connections by a cut on
either side, and turn it down over the belly. The heart is seen still covered
by the pericardium. Expose the heart by carefully dividing the peri-
cardium. Note the condition of each of its cavities and the mode of its
rhythmical action.

2. The Inhibitory Centre.— For the purpose of observing the effect
of passing series of induction shocks through the inhibitory centre of the
heart, a fine ligature is attached to the frsenum (the thread-like ligament which
stretches from the dorsal aspect of the ventricle towards the lower part of the
pericardium). By means of the ligature the heart is raised out of its place
and turned upwards. The inhibitory centre is recognized by the whitish
crescent -shaped line which marks the junction of the wall of the sinus with
that of the right auricle. Faradize this spot for a second or less, placing the
points of the electrodes on the line, a couple of millims. distant from each
other. Observe the mode and order in which the cavities of the heart resume
their rhythmical action.

3. Destroy the spinal cord by pithing, and observe the changes thereby
produced in the state of the circulation, and particularly in the mode of action
of the heart.

4- The Cardiac VagUS Of the Prog.— a. Preliminary Dissection.—
Expose the trunk of the vagus nerve as it escapes from the cranium as follows : —
Remove the integument so as to bring into view the muscles of the back of

K

130 THE FROG HEART.

the neck on one side, avoiding injury to the cutaneous vessels. Then expose
the scapula, and sever with the scissors the cartilaginous from the bony
scapula ; remove the former, dividing the muscles attached to it, then expose
the sterno-mastoid muscle which connects the outer part of the petrous bone
and the posterior border of the cartilaginous ring of the membrana tympani
with the concave anterior border of the scapula. Remove or draw aside the
sterno-mastoid so as to expose the slender muscles (petrohyodei) which run from
the petrous bone to the posterior horn of the hyoid bone, embracing the
cavity of the pharynx. Parallel with these muscles, and in close relation with
them, are seen the carotid artery and several nerves, of which the two nearest
the cranium are the glosso-pharyngeal and the vagus.

b. Expose the vagus in a pithed preparation. Expose the heart as in III. I,
and introduce a small test tube into the gullet. Fix the preparation in such a
position on a cork, that the electrodes can be conveniently applied to the nerve,
at the same time that the motion of the heart can be observed.

5- The Stannius Heart. — Prepare a frog heart with fraenum ligature
as before. Then pass a thick ligature under the bifurcation of the aorta
between it and the venae cavae superiores. Then, seizing the fraenum ligature
with the forceps, turn the heart up. Carefully observe the position of the
"crescent," and loop the ends of the ligature so that when it is tightened it
may embrace the crescent. On tightening, the heart will stop in diastole.

In the heart so prepared, sever the ligatured parts from the rest of the pre-
paration with sharp scissors. The auricles and ventricle resume their normal
rhythmical action.

Cut off in a preparation which has been so treated, the remainder of the
auricles and the bulb, leaving the ventricle and auriculo-ventricular septum.
The heart continues to beat normally, or, if the beats cease, they are renewed
by a pinch, by an induction shock, or by bringing a hot wire into the neigh-
bourhood of the cut surface.

6. Localization Of the Motor Centres.— In one of two such pre-
parations (called ventricle preparations) which beat rhythmically, cut off the
whole of the auriculo-ventricular furrow with sharp scissors. The preparation so
obtained (the ventricle apex) does not contract spontaneously, but responds to a
single excitation, whether mechanical or electrical, by a single contraction, the
duration of which is dependent on the temperature. In the other preparation,
divide the ventricle by two parallel cuts into a middle and two lateral thirds. The
middle third includes the ventricular border of the interauricular septum, the
right lateral third contains the root of the bulb. The middle third beats
rhythmically, the lateral thirds respond to excitations by single contractions,
but do not beat of themselves.

7- Action Of MllSCarin and Atropin.— In an entire heart (a
heart removed by severing the vessels, for which purpose the organ should be
lifted out of the pericardium by a ligature tied to the fraenum), stop rhythmical
action by applying to it a drop of serum containing a trace of inuscarin.
Observe the relaxed and motionless condition of the ventricle. After a few
minutes apply (in serum) a drop of 0*2 percent, solution of atropin. Observe
the gradual restoration of rhythmical action in the atropinized heart. Observe
that faradization of the inhibitory centre is without effect.

THE FROG HEART. 13!

8. Action of the Constant Current on the Contractile

Substance Of the Heart. — For this purpose prepare electrodes as
directed in Exercise I. Fix a cork vertically on a sheet of lead about
an inch and a half square ; cover the top of the cork with wax mass, the
upper surface of which should be somewhat concave. Place the support
on a sheet of wet filtering paper and cover it with a beaker. Attach a fine
ligature to the frsenum, and remove the heart after severing the principal
vessels. Collect some blood and dilute it with as much 075 per cent, salt
solution, and place a few drops of it on the wax surface.

Make a "ventricle-apex preparation," as directed in 6. Having ascertained
that it does not beat rhythmically of itself, fix it in its place by the aid of
fine glass pins and replace the beaker.

Prepare and arrange two Grove's cells in circuit, interpose a key and a
pair of electrodes. Fix the electrodes, so that their points are in contact with
the apex and base respectively of the preparation. The passage through the
ventricle apex of a voltaic current in the direction of its axis produces
rhythmical action, which lasts as long as the current passes.

9- Study of the Ventricular Systole by the Graphical

Method. — Prepare a writing lever consisting of a glass rod about ^ inch
in thickness and five inches long, having at one end a knob of glass, and at
the other a writing point. This is thrust through a square bit of cork, which is
then pushed up to the knob. A fine steel needle passes through the cork at
right angles to the rod. The rod also bears, close to the needle, a vertical arm
of cork, by means of which it rests on the ventricle. The preparation lies on
a metal plate, which forms the upper end of a cylindrical brass box, through
which water, at any desired temperature, can be passed. This plate is furnished
with bearings in which the steel axis of the lever works. The metal box is
fixed to one of the adjustable supports of the recording apparatus.

a. The rhythmically contracting heart.

Expose the heart as before. Raise it from the pericardium by a ligature
attached to the severed froenum, and cut through the vessels. Place the heart
on the plate, adding a few drops of dilute serum, and arrange the lever so that
the cork arm rests on the ventricle, and the writing end inscribes its move-
ments on the blackened surface of the cylinder. The rate of motion should
be about 20 inches per minute.

Allow water at 12° C. to pass through the cylindrical box and record the
rhythmical contractions of the ventricle. Repeat the experiment, substituting
water at 17° and at 22°, and compare the tracings.

b. The curve of a single ventricular contraction.

Prepare finely pointed electrodes as in I. I, arranging for single induction
shocks. Fix the electrodes to an adjustable support, so that they can be
brought with precision into contact with the preparation. Prepare a Stannius'
heart and arrange it for recording as in a. Adjust the electrodes, taking care
not to interfere with the lever. Place the secondary coil at about 10 centimeters
distance from the primary, or nearer, if on trial it is found necessary to do so,
Then bring the point of the lever into contact with the blackened paper, so
as to write a base line or abscissa, and open the key. The rate of motion
of the recording surface should be about 2\ inches per second.

K 2

132 FUNCTIONS OF REFLEX CENTRES.

In order to obtain series of tracings which can be conveniently compared,
introduce into the primary circuit the self-acting key described in II. i. In
this way a number of curves may be drawn on the same abscissa, or on
parallel abscissae at convenient distances from each other. Having practised
one or other of these methods, proceed to make the following observa-
tions : —

, (i.) When a succession of ventricular curves are drawn at temperatures
varying from 12° to 18°, it is found that the duration of the systole is increased
by about o"'i for every degree of temperature.

(2.) When the ventricle is excited by single induction shocks, following each
other at about 10" intervals, each curve is observed to exceed its predecessor
in amplitude, the augments gradually diminishing from the beginning to the
end of the series.

(3.) In the muscular tissue of the heart, the period of latent stimulation is
much longer than in voluntary muscle. Its duration is about o"' 1 5. To measure
it, a vertical line must be drawn on the recording surface, indicating the position
of the writing point at the moment that the trigger of the cylinder comes into
contact with the lever of the self-acting key (see II. i).

IV. — Functions of the Spinal and other Reflex Centres of the Frog.

1. The preparation to be used in the following experiments is obtained by
severing the spinal cord immediately behind the medulla oblongata and intro-
ducing, by the opening made for this purpose, a wooden plug into the cranial
cavity, so as to destroy its contents. This having been done, it is placed on a
sheet of moist filter-paper, resting on its ventral surface with the hind limbs
extended, and covered with a bell jar. For a time it remains motionless, but
eventually assumes a position which differs but little from that of a living frog.
Observe the differences.

2. Prepare half-a-dozen pieces of filter-paper, each an eighth of an inch
square, and some strong acetic acid. Turn the preparation over, and after
observing that the natural position is not resumed, apply one of the squares,
after moistening it with acetic acid and drawing off excess by touching with
dry filter-paper, to the inside of the right thigh, and observe the result.
Repeat the experiment, holding the right foot. Next, attach the preparation
to a suitable holder in such a way that the trunk may be steadily supported
and the limbs may hang freely, and apply the squares in succession to different
parts of the surface, as e.g., to the skin on either side of the tendo Achillis, or
to either flank. Ol serve in each case that the muscular response which
results from excitation of the same part of the surface of the body is always
the same.

3. Arrange a second preparation as last described, using a holder so con-
structed that the limbs may be suspended at any desired height above the
table. Prepare several beakers of water acidulated respectively with I, 2, 3,
4 and 5 per thousand of sulphuric acid, and place some of each mixture in
a saucer. Beginning with the weakest of the acid liquids, bring down the
preparation with the rack and pinion, until the tip of the longest toe is

SENSATION AND PERCEPTION. 133

immersed. Repeat the experiment at intervals of three minutes with the
stronger liquids in order, carefully washing the foot after each excitation, by
dipping it into a beaker of water. Measure the time which intervenes
between the beginning of the excitation and the muscular response in each
case, with the aid of a metronome.

4. Observe carefully the attitude of a brainless frog when left to itself, and
its behaviour when placed on its back, on an inclined surface, or in water, as
well as when excited by cutaneous stimuli, comparing the phenomena observed
with those which exhibit themselves in the spinal cord preparation.

5. Proceed as in I, substituting a preparation in which, after destruction
of the brain, a couple of drops of a o'l per cent, solution of sulphate of strychnia
have been injected under the skin of the back. Observe that instead of
co-ordinate muscular responses, cutaneous excitation produces under the influ-
ence of strychnia, paroxysms of convulsion, in which the body and limbs
assume a characteristic attitude.

V. — Sensation and Perception.

1. Time Occupied in the Simplest Mental Processes

(see p. 104). — To measure the time required for responding to a signal (re-
action time or personal time), the simplest plan is to arrange a battery circuit
in such a way that it is closed by the same act by which the observer makes
the signal, and that it is opened by the response of the observed per-
son. Whatever be the nature of the signal, the requirements are: (i) Two
Grove's cells arranged in circuit; (2) a break key (a lever resembling in shape
a pianoforte key, which when touched breaks a mercurial contact) j (3) a
du Bois' key ; (4) an electro-magnet with a light lever attached to its arma-
ture ; (5) a chronograph ; (6) a recording surface, of which the rate of motion
is not less than I foot per second. The battery, two keys, electro-magnet
and chronograph, are arranged in circuit, and in such positions that the electro-
magnet lever may be in the neighbourhood of the observed person, and the
du Bois' key, cylinder and chronograph, in reach of the observer. On
closing the circuit, the lever is drawn towards the magnet and gives the signal.
The signal may be an induction shock through the tip of the tongue (in
which case an induction coil must be in circuit in addition to the instruments
above-mentioned), a touch on the hand given by the lever, a sound or a visible
signal, such as a white disk, letter or number, suddenly brought into view.

2. Tactile and Muscular Sensation.— in all the following

experiments two persons must take part : one of whom must vary the condi-
tions without the knowledge of the other, and note the results. In the experi-
ments relating to the sensations of pressure, locality, and muscular exertion,
the observed person must have his eyes shut.

The appreciation of Temperature must be tested by immersing the
same surface successively in water of slightly different temperatures. The
smallest differences can be detected when the temperatures of the liquids com-
pared approximate 30° C.

To test the sensation of Pressure, the hand or other part to be investi-

134 VISION.

gated must be entirely at rest, and supported on a horizontal surface. The
weights used must be moderate — from a pound to four or five pounds j in
which case it will be found that a difference between two weights of one-
thirtieth can be detected.

For testing the sensation of locality in any part of the surface of the
body, a pair of compasses is used, of which the points are provided with cork
sheaths, having smooth blunt ends. The points being at first at such a dis-
tance that when both touch the skin or mucous membrane of the tongue,
they are distinctly felt as two, they are gradually brought nearer until the two
impressions blend into one. The smaller the distance at which this happens,
the finer is the sensation of locality in the region investigated. Another
method is that of interrogation. The observer touches the skin, and asks the
observed person to designate the locality touched.

The sensation of muscular Exertion is tested by experiments,
each of which consists in lifting in succession two weights, of which one is
heavier than the other by a small but perceptible difference ; this difference is
diminished at each trial until it can no longer be appreciated. As it is essential
that sensation of pressure should be excluded, the weight to be estimated
must in each trial be enclosed in a handkerchief, of which the corners must
be held in the hand.

For the investigation of the sensation of taste and of the limits of the
gustatory region, four test liquids should be prepared, viz., saturated solution
of sulphate of quinine, 10 per cent, solution of common salt, 3 per cent,
solution of sugar, and o'l per cent, solution of citric acid. These liquids
represent the four fundamental sensations, each of which may be tested
separately, or two alternately. In each experiment a camel hair pencil is
dipped in the liquid, drained by touching it with filter paper, and applied for
a moment to the surface. To secure freedom from bias on the part of the
observed person, trials should be made in which tasteless liquids, or liquids
of different tastes are alternated in various orders, care being taken to irrigate
the surface between each trial and the following one, with water.

The voltaic sensations of taste are experienced when two zinc plates, which
form the terminals of a Grove's element, are applied respectively to the upper
and under surface of the tongue as far back as possible. As the effect differs
according to the direction of the current, a reversing key must be introduced
into the circuit.

VI.— Vision. *

I. The application of Schemer's experiment to the limitation of
the range of accommodation can be best understood if it is made as follows : —
Stretch a white thread from end to end along the blackened surface of a narrow
black board about a yard long. Fix at one end of the board a vertical screen

* The experiments and observations described under this heading are
arranged in the order in which the subjects they are intended to illustrate
happen to be referred to in the lectures.

VISION. 135

or diaphragm, having two vertical and parallel slits, about three millims.
apart, taking care that the slits are opposite the thread. When the thread is
contemplated through the slits, by a normal or myopic eye accommodated for
near vision, two white lines are seen, which converge towards the spot in the
thread, for the distinct vision of which the eye is accommodated, and, after
crossing, diverge. If the eye were hypermetropic, the lines would not con-
verge even if accommodated to the utmost.

2. Sanson'S or Purkinje's images.— The relative positions of the
observed and observing eye, and of the luminous object, which are most
advantageous for the observation of the image reflected by the anterior surface
of the lens, are stated on page 108. The experiment must be made in a dark
room. It is advantageous to substitute two lights, one above the other, for
the single luminous object referred to in the text.

3. Chromatism.— In order to see the effects described in the text
(p. 109) it is advantageous to place before the eye a purple glass, which, by
cutting off the rays of medium refrangibility, facilitates the perception of the
red and blue rays.

4- Reflection of light from the Retina (see p. 109).— To see

the eye of another person luminous, the simplest way is to interpose between
the observed and the observing eye a reflector, consisting of several glass
plates applied to each other by their surfaces, in such a position that the light
of a lamp placed en one side of the observed eye may be seen by it. The
moment that this is the case, the retina is illuminated ; and if the observed
eye is accommodated for distinct vision of the lamp flame, and a suitable
concave lens placed in front of the observing eye, a distinct image of the
flame is seen on the observed retina, the whole interior of the globe appearing
at the same time luminous.

5. The Fovea Centralis (see p. no). — (a) Fix a blackboard hori-
zontally at a level a little below that of the eyes. Mark a point a at one edge
of the board, and bring the right eye up to it, closing the other, and plant a
pin having a white bead for its head in the board at any distance at which it
can be distinctly defined. Draw on the board a semicircle having the point
a for its centre and passing through the pin, and plant along the circle a
number of similar pins, at an angular distance from each other of 5 degrees.
If the eye is fixed on any of these pins, it will be seen that its next neighbours
only are seen distinctly.

(l>) Draw two parallel lines in white, on a black ground, each £ millimetre
wide, and separated by an interval of the same width. Place the board
against a wall, and fix one eye on it at a distance of five feet (ij metre, and
consequently 100 times as far from the crossing point as the surface of the
retina). In a normal eye the two lines can be distinguished at that distance :
if not, lessen the distance until this is the case. If the eye is myopic, a cor-
recting lens must be used.

In those of the following experiments which depend on the blending of
retinal excitations which occurs when these follow each other in rapid succes-
sion, a circular brass plate which revolves on a central axis is used. It is
furnished with an arrangement by which its rate of revolution at any desired
moment can be measured.

136 VISION.

6. Duration and culmination of light sensations.— On a

black card draw two concentric circles, of which the respective diameters are
6 and 10 inches. Draw a straight line through the centre, so as to divide the
annular space between them into two equal parts. Cover one of these spaces
with white paper. Cut out the card along the outer circle and fix it to the
revolving disk.

If the rate of revolution is gradually increased, the moment can be deter-
, mined at which the sensations due to successive exposures of the white
sector become blended. It will be found that this happens when the rate
of revolution is such that the white is visible each revolution for from o"'i5
to o" '2 ; for the time required for the light given off by a white surface in
common daylight to produce its full sensational effect, is about a sixth of a
second. If the rate of revolution is further increased, the subjective lumi-
nosity diminishes, but finally becomes constant. Its brightness is then just
half of that of the white paper at rest.

7- Diminution of sensational effect in continued exci-
tation Of the Retina. — To prove that when the eye is exposed to the
light from a bright surface, the apparent luminousness of the surface after
culminating gradually diminishes, fix against a wall a black sheet of paper
with a small white square in the middle, and place beside it a white sheet of
similar size. Having fixed the eye steadily on the white square, suddenly
direct it to the adjoining white surface. A grey square is seen on a white
ground, of which the shade differs according to the number of seconds that the
white square has been contemplated.

. 8. Smallest perceptible difference.— Prepare a piece of black

paper," six centimeters in length, and varying in width from 2 millims. to
8 millims. Cut it transversely into six bits, and apply the smallest to a white
disk, half way between centre and circumference, with its long edge against
a diameter of the disk. Set the disk in rapid revolution and observe the
effect. Replace the bit of black paper by the one next it in width, and repeat
the observation. Proceed in this way until a faint grey ring is seen, when the
disk is in revolution. This happens when the width of the black surface is
about one hundredth of the circumference of the ring.

9. Visual perception Of Motion.— When a disk on which a num-
ber of concentric spirals at equal distances from each other are inscribed, is
contemplated in rapid revolution, radial motion is perceived, which is centri-
petal or centrifugal, according to the direction of rotation. If the eye is sud-
denly directed to a blank surface, radial motion is still for a time perceived,
but it is in the opposite direction. This experiment serves not only to illustrate
the principle enunciated on p. 97, but to prove that the subjective perception
is not due, as has been supposed in other similar cases, to felt motions of the
eyeballs.

For experiments relating to the blending of sensations of colour (p. 1 12),
disks are used, each of which has a radial cut extending from the circular hole
in the centre, to the circumference. Two or more of these cardboard disks
can be fixed to the brass disk, in such a way that a sector of each colour may
be exposed, and that their relative areas may be varied at will. For many
purposes of study, the following method of blending is more useful : —

VISION. 137

Fix a pane of plate glass vertically across the middle of a board about 16
inches long by 8 wide. On either side place a sheet of paper of the colours
•which it is desired to blend. Arrange the board so that the illumination of
each sheet may be varied, independently of that of the other, and that one
sheet is seen through the glass, the other by reflection.

10. The angle Of rotation (see p. 113). — Draw on a wall of a mode-
rately dark room, a horizontal line, at a height of a couple of feet above that
of the eyes. In a black card, cut out a cross, each bar of which should be
about a twentieth of an inch in width. Close one eye, and place the cross
between the other and a bright lamp, and fix the eye on the luminous cross for
several seconds. Then turn to the wall, which should be at a distance of
four or five feet, and direct the eye to a point exactly opposite it and at the
same level. If now the eye is fixed on a point in the horizontal line imme-
diately above the first (the position of the head being unaltered), it is seen
that the transverse bar of the bright image of the cross coincides with the
line. But if (the eye remaining fixed) the head is turned to the right,
the image gradually assumes an appearance of distortion, the upper end
of the upright bar seeming to incline to the left, and the outer end of the
horizontal bar to incline upwards. As in reality the horizontal bar coincides
with the horizontal meridian line of the retina, it is clear that the retinal
image of the horizontal line crosses the meridian line at an acute angle. This
angle is the angle of rotation for the particular (tertiary) position assumed by
the eye.

!!• Judgment Of Form. — For experiments on this subject pairs of
diagrams representing respectively the right and left aspects of characteristic
objects are used, of which the retinal images are blended by means of the
stereoscope. The most important observations are the following : — (a) If two
diagrams representing the right and left aspects of a pyramid are imaged on
the right and left retina, and the images blended by giving the eyes the degree
of convergence necessary to unite the apices, a solid pyramid is seen. If the
diagrams are transposed and the process repeated the pyramid appears
hollow, (b) If two similar diagrams are viewed stereoscopically, of which one
is represented white with black edges on a black ground, and the other black
with white edges on a white ground, the combined image is lustrous.

12. Judgment Of Distance. — If a number of balls of similar colour,
but differing in size, are allowed to fall one after another before one eye, the
the other being closed, at such distances that in each case their retinal images
are equal, and at such velocities that their images pass over the same retinal
distance in the same time, the observer is unable to form any judgment either
as to their size, distance, or rate of motion. All of these can be judged of at
once if the other eye is opened. For this experiment an apparatus is used.

139

DEMONSTRATIONS
RELATING TO THE FUNDAMENTAL PHENOMENA

OF

CIRCULATION AND RESPIRATION,

AND TO THE

ELECTROMOTIVE PROPERTIES OF MUSCLE.

I. — Mode of Measuring and Recording the Arterial Pressure. Use
of Recording Apparatus.

The instrument used is called a kymograph (see p. 61). The arterial
cannula is a T-shaped tube of glass. By its stem, it is connected with the
manometer (a U-shaped glass tube containing mercury). One branch of the
T is drawn out and bevelled so as to be easily introduced into the artery : to
the other is fitted a short piece of indiarubber tubing, guarded by a steel clip.
The stem of the cannula communicates with the proximal arm of the mano-
meter by an unyielding tube of lead or guttapercha. The proximal arm (that
connected with the cannula) also communicates by a long flexible tube with a
bottle containing solution of bicarbonate of sodium under pressure. The mano-
meter is fixed to the recording apparatus, so that its oscillations are inscribed on
the moving surface. This is effected by means of a style carried by a vulcanite
rod, which floats on the surface of the mercury in the distal (open) limb of the
manometer. The recording cylinder is driven by clockwork : it is either
covered with smoked glazed paper, or is fed by an endless roll of paper, in
which case a sable pencil, charged with coloured ink, is substituted for the
style. The paper surface in either case moves at a uniform] rate of 20 inches
per minute.

The artery used is the carotid of the rabbit. The distal end of the prepared
part of the vessel is ligatured. The proximal end is temporarily closed by a
spring-clip. The vessel having been opened near the ligature, the cannula
is introduced and secured in its place by a second ligature, its drawn-out
end being directed towards the heart. This done, the guttapercha tube of
the manometer is connected with the stem of the cannula, and the whole
system filled with solution of sodic bicarbonate under a pressure of about
four inches of mercury. On removing the clip on the artery, communi-
cation is established between the arterial system and the manometer,
which now records the variations of arterial pressure. The tracing exhibits
larger (respiratory) undulations, on each of which many smaller undulations
(cardiac pulsations) are inscribed. It shows (i) that each contraction of the

I4O DEMONSTRATIONS.

left ventricle produces a momentary increase of arterial pressure ; (2) that the
pressure increases after each inspiration, and sinks in the interval ; (3) that
during the rise of pressure, the pulsations are more frequent than during the

fall. Excitation of the Cardiac end of the divided Vagus,

by faradization, produces (if weak induction currents are used) diminution of
the frequency of the heart's pulsation and of the arterial pressure. If stronger
currents are used, the heart is arrested in diastole (see p. 85).

[N.B. In each of the Demonstrations I., II., III., and IV., a rabbit is
used, which is rendered completely insensible by a suitable anaesthetic, and is
killed before recovery.]

II. — The Normal Respiratory Movements. Influence of the Vagus Nerve
and of its Centre. Apncea and Dyspnoea.

The motions of a metal plate which is kept in constant contact with the
posterior surface of the central tendon of the diaphragm of the rabbit, by the
pressure of a spring are communicated by a long steel wire to the vertical arm
of a bell-crank lever. The horizontal arm of the lever is prolonged, and bears
a style by which an enlarged record of the respiratory motion of the diaphragm
is inscribed on the cylinder of the recording apparatus. The rate of movement
of the cylinder is the same as in the last demonstration.

The inspiratory contraction of the diaphragm is expressed by the descent
of the writing style, its relaxation by the ascent, which is at first rapid, but
afterwards more gradual.

Apnoea. When by excessive artificial respiration the circulating blood
becomes overcharged with oxygen, all respiratory movement ceases. On
discontinuing the injections of air, the respirations after a time begin again :
at first they are scarcely perceptible, but each exceeds its predecessor in
extent, until the normal is reached.

Dyspnoea. When nitrogen containing an inadequate percentage of
oxygen is respired, the opposite effect to that described above is produced.
The respirations become more ample and more frequent, and the auxiliary
muscles are brought into action. No such effect is produced by an atmosphere
containing as much as ten per cent, of CO2, provided that the supply of
oxygen is sufficient.

Excitation of the Superior Laryngeal Nerve.— Excitation

of the central end of the trunk of the superior laryngeal nerve, by faradization,
arrests the respiratory movements, the diaphragm becoming stationary in the
position of expiration. When extremely feeble currents are used, rhythmical
movements may continue at long intervals. Introduction of irritant gases or
vapours into the larynx produces similar effects.

Similar excitation of the central end of the divided vagus, below the cricoid
cartilage, produces effects which differ according to the strength of the induction
currents employed. When currents of moderate strength are used, the
diaphragm remains during the excitation in the position of inspiration, the
state of contraction being, however, usually interrupted by momentary relaxa-
tions at short intervals.

DEMONSTRATIONS. 141

III. — Influence of the Cardiac and Vasomotor Centres on the Circulation
and on the Motions of the Heart.

The atlanto-occipital membrane having been previously exposed, the
carotid is connected with the kymograph. A record is taken, and the mean
arterial pressure measured. On faradization of the spinal cord, at the level of
the third vertebra, mixed effects are observed, due partly to the excitation of
the vascular nerves, partly to escape of induction currents to the cardiac centre.
If both vagi have been previously divided, those due to the latter cause do not
appear. The cord is now severed above the seat of excitation, respiration
being continued artificially : the arterial pressure sinks to a third of the previous
mean. The excitation is repeated ; the pressure rises rapidly, the heart beating
with great frequency. On opening the thoracic cavity, the action of the heart
may be studied. It is seen that so long as artificial respiration is continued,
it beats regularly. If the injections of air are intermitted for a few moments, its
cavities become more distended and its action more vigorous than before, and
a similar effect is produced by excitation of the spinal cord.

IV. — Functions of Vascular Nerves.

Constricting Nerves. — Division of the trunk of the sympathetic
opposite the cricoid cartilage is followed by dilatation of the central artery of
the lobe of the ear on the same side, and increase of vascularity. On compar-
ing the temperature of the congested lobe with that of the other side, it is found
to be two or three degrees higher. The pupil of the same side is more
contracted than the opposite one. Excitation of the end next the superior
ganglion produces constriction of the central artery and abolishes the conges-
tion of the lobe.

Dilating Nerves. — Excitation of the central end of the great auricular
nerve (or of the posterior auricular) produces temporary vascular changes,
which are identical with those permanently produced by section of the sympa-
thetic.

Depressor Nerve.— Excitation of the central end of the divided
depressor occasions general diminution of arterial pressure (dependent on
dilatation of the blood-vessels supplied by the splanchnic nerves). If the
vagi have been previously divided, the diminution of pressure is not asso-
ciated with any change in the frequency of the contractions of the heart.

V. — Movements of Circulation and Respiration in Man.

i. The Cardiograph and Sphygmograph.— a. Two receiving

tympana (cardiographs) are used. One is applied to the seat of the cardiac
impulse, the other to the carotid artery. The two recording tympana with
which these are severally connected, inscribe the motion of the heart and that
of the artery respectively, on the same cylinder. The arterial expansion

142 DEMONSTRATIONS.

follows that of the heart at an interval of about eight-hundredths of a second.
The duration of the ventricular impulse is about three-tenths of a second.

b. The sphygmograph having been adjusted so as to record the radial pulse,
a receiving tympanum on the carotid is connected with a recording tympanum
attached to the frame of the sphygmograph, so that its lever writes on the
same surface as that of the sphygmograph. The interval of time between the
impulse of the carotid and that of the radial is about the same as that between
the carotid and the heart.

2. The StethOgraph. — The changes of form of the thorax in respira-
tion are investigated by the measurement of the diameters of the chest. The
most important diameters are the antero-posterior (from upper end of sternum
to third dorsal spine, 150 millims. and from lower end of sternum to eighth
spine, 200 millims. ) ; the transverse (at the eighth rib, about 230 millims. ).
These measurements refer to an adult male, as taken during the respiratory
pause. The first of these diameters increases about a millimeter, the second
about two millimeters, and the third about two and a half in ordinary tranquil
inspiration. These measurements, when recorded by the stethograph, yield
the " respiratory curve. "

VI.— The Heart of the Frog.

1. Rhythmical Motions of the Ventricle ; Influences
thereon of Temperature and other External Conditions.

2. The Cardiac Vagus, and the Intracardiac Inhibitory
Centre.

The experiments relating to these subjects are described in the Practical
Exercises. Such of them only as can be seen at a distance are shown.

VII. — Electromotive Phenomena of Mtisde.

The most important instrument used is a Thomson's Reflecting Galvanometer
of high resistance, the terminals of which are connected by insulated copper
wires with non-polarizable electrodes. These are in contact by their clay
plugs with the two surfaces to be compared.

To the needle of the galvanometer a light concave mirror is attached, on
which a beam of light falls and is focussed, after reflection, on a divided
screen. Thus the smallest deflection of the needle (by which any electrical
difference between the two contacts is indicated) can be exactly measured.
By means of a suitable shunt, either the whole, a tenth, or other decimal
fraction of any current flowing through the circuit can be led through the
galvanometer.

i. Electromotive Phenomena of Muscle.— The gastrocnemius

muscle of the frog is used. One of the electrodes is in contact with the convex
surface of the muscle near its upper end, the other with the expansion of the

DEMONSTRATIONS. 143

tendo Achillis. In this arrangement the surface of the tendon is negative to
that of the muscle.

2. On exciting the muscle by faradizing its nerve, a deflection takes place
in such a direction as to indicate that the electrical difference between the
two surfaces is diminished. After excitation the needle resumes its former
position.

3. The electrode in contact with the tendinous expansion is now brought
near to its fellow, so that both contacts are now muscular. They are nearly
isoelectrical. On injuring the lower of the two contacts mechanically or by
heat, it becomes at once strongly negative. On excitation of the nerve by
induced currents, the negativity diminishes as before.

4- Electromotive Phenomena of the Ventricle of the

Frog Heart. — A Stannius' Heart Preparation (see Practical Exercises) is
" led off" by contacts at its apex and base. If the heart is uninjured, these
surfaces will be found to be nearly isoelectrical. On injuring either surface it
becomes negative.

2. A normally contracting heart is led off by contacts similarly situated.
Each contraction is accompanied by a deflection of the needle, indicating that
the apex becomes first positive then negative. By injuring the apex, mechani-
cally or otherwise, the deflection becomes entirely positive.

3. A "ventricle preparation " is led off at apex and cut surface. During
contraction, the effect is similar, but the negative deflection is much larger.

4. A ventricle apex preparation (which does not contract spontaneously) is
led off as above. Its cut surface is at first strongly negative to the apex. On
excitation at the base by a single induction shock, the ventricle contracts, its
contraction being accompanied by a deflection indicating that the apex becomes
negative.

H. K. LEWIS, PRINTER, 136 GOWER STREET, LONDON.

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