CORNELL UNIVERSITY.
THE
Bostncll P» ^lotocr Cibrarg
THE GIFT OF
ROSWELL P. FLOWER
FOR THE USE OF
THE N. Y. STATE VETERINARY COLLEGE.
1897
Cornell University Library
QP 34.A82 1893
Notes on physiology,
3 1924 001 040 207
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Library
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PHYSIOLOGY
LIBRARY.
NOTES %. ^
ON
PHYSIOLOGY
HENRY ASHBY, M.D. Lond., F.R.C.P.
THYSICIAN TO THE GENERAL HOSPITAL FOR SICK CHILDREN, MANCHESTER
LECTURER ON DISEASES OF CHILDREN, FORMERLY LECTURER ON
ANIMAL PHYSIOLOGY, OWENS COLLEGE ; DEMONSTRATOR
OF PHYSIOLOGY, LIVERPOOL SCHOOL OF MEDICINE
§i*ijr (Sbiiion, xltasiraiefr
LONDON
LONGMANS, GREEN, AND CO.
AND NEW YORK : 15 EAST 16'" STREET
1893
ft
Ale rights reserved
PREFACE
TO
THE SIXTH EDITION
In preparing the sixth edition, the text has been
thoroughly revised and many chapters re-written.
Seven new woodcuts have been added.
H. A.
St. John Street, Manchester :
March 1893.
PREFACE TO THE FIRST EDITION
These Notes were originally compiled for the use of
students of the Liverpool School of Medicine, when
preparing for the primary examination of the College
of Surgeons. They now appear in print, in the
hope that they may prove useful to a wider class of
students. The information they contain is founded,
to a large extent, on Quain's 'Anatomy' (8th ed.),
Gray's 'Anatomy,' and Foster's 'Text-Book of
Physiology,' to which works the student is referred
for his general reading. Fifty questions, taken for
the most part from the Calendar of the College of
Surgeons, are added.
H. A.
Manchester :
Sept. 1878.
CONTENTS
CHAPTER I
PHYSIOLOGICAL CHEMISTRY
PAGE
Inorganic salts — Organic crystalline bodies — Carbo-
hydrates — Fats — Proteids— Albuminoids . . i-
CHAPTER II
PHYSIOLOGICAL HISTOLOGY
Epithelium — Pigment ...... 19-28
CHAPTER III
THE CONNECTIVE TISSUES
Connective tissue— Retiform tissue — Adipose tissue . 28-35
CHAPTER IV
CARTILAGE AND BONE
Hyaline cartilage — White fibro-cartilage —Yellow elastic
cartilage — Structureof bone— Development ofbone 35-48
CHAPTER V
MUSCLE
Striated muscle — Muscular fibre of heart — Non-striated
muscular fibre — Chemistry of muscle — Physical pro-
perties of muscle — Effects of muscular exercise — Stand-
ing — Sitting — Walking ..... 48-64
viii Physiology
CHAPTER VI
SKIN
PAGE
The epidermis— The dermis— Sweat-glands —Hairs —The
perspiration ....... 64-71
CHAPTER VII
THE BLOOD
Red corpuscles— Haemoglobin — White corpuscles — Liq.
sanguinis — Serum— Gases of the blood — Coagulation
of the blood -Quantity in the body . . . 72-86
CHAPTER VIII
THE CIRCULATION
The heart —A cardiac revolution —Cardiac impulse— Work
done by heart— Frequency of pulsations —Endocardial
pressure — Innervation of the, heart — Ganglia — Action
of vagus — The arteries — Arterial pressure — The pulse —
The capillaries —The veins — Innervation of the blood-
vessels —Action of poisons on the circulation . 87-116
CHAPTER IX
LYMPHATIC SYSTEM
Modes of origin -Lymphatic vessels —Thoracic duct -
Lymph —Chyle —Movements of lymph — Lymphatic
glands 117-124
CHAPTER X
RESPIRATION
Trachea and bronchi — Infundibula— Air-cells - Mechanism
of respiration— Vital capacity —Changes of the air in
respiration— Dyspnoea— Nervous mechanism of respira-
tion —Coughing — Effects of respiration on the circula-
tion 124-143
Contents ix
CHAPTER XI
ANIMAL HEAT
PAGE
Cold- and warm-blooded animals — Gain and loss of heat to
the body — Heat generated in the body— Distribution of
heat— Regulation of heat ..... 143-147
CHAPTER XII
FOOD
Nitrogenous food — Meat — Eggs — Cheese — Destiny of
nitrogenous food — Dynamic value of proteids — Fats —
Destiny of fats — Amyloids — Inorganic materials —
Dietetics — Diets — Effects of insufficient diet— Effects
of starvation ....... 147-163
CHAPTER XIII'
DIGESTION
Teeth — Structure of teeth— Chemical composition — De-
velopment — The tongue — The mouth — Papilla —
Tonsils — Mastication — Salivary glands — Saliva — In-
nervation of salivary glands — Deglutition — The oeso-
phagus — Stomach — Gastric glands — Gastric juice-
Chyme — Vomiting — Structure of small intestine— Bile
— Pancreas — Pancreatic juice — Large intestine — De-
fecation . . . . . . . . 163-200
CHAPTER XIV
ABSORPTION AND NUTRITION
Albuminous foods — Starches — Fats .... 200-203
CHAPTER XV
THE LIVER
Fissures — Lobes— Lobules — Vessels — Functions of liver —
Glycogen — Secretion of bile .... 203-210
Physiology
CHAPTER XVI
THE KIDNEYS
PAGE
Structure— Malpighian bodies — Convoluted tubes— Blood-
vessels — Urine — Estimation of urea — Secretion of
urine— The bladder— Micturition . . . 211-228
CHAPTER XVII
THE DUCTLESS GLANDS
Spleen — Supra-renals — Thyroid — Thymus . 229-236
CHAPTER XVIII
NERVOUS SYSTEM
Nerves — Terminal end-organs — Structure of grey matter
— Ganglia — Functions of nerves — Electrical pheno-
mena of nerves — Classification of nerves — Nerve
centres — Automatic actions — Reflex actions — Spinal
cord — Functions of the cord — Medulla oblongata —
Pons Varolii — Mesencephalon — Corpora quadrigemina
— Crura cerebri — Cerebellum — Thalamencephalon —
Corpus striatum — Cerebrum — Speech centre — Cranial
nerves— Sympathetic ...... 237-306
CHAPTER XIX
THE SENSES
Smell — Taste — Tactile impressions — Feeling — The eye —
The ear 306-333
CHAPTER XX
MECHANISM OF SPEECH
The larynx— Articulate sounds . .... 333-340
Contents xi
CHAPTER XXI
ORGANS OF GENERATION
PAGE
Uterus — Ovaries— Ovum — Impregnation — Chorion — Yolk-
sac — Amnion — Allantois — The placenta — Foetal circula-
tion — The mammary glands — Secretion of milk— The
testes — The spermatozoa ..... 341-363
CHAPTER XXII
THE PHASES OF LIFE
Infancy— Childhood— Youth— Adult age— Old age . 363-364
APPENDIX
Metric System 365
Questions on Physiology 366
Index 375
CHAPTER I
PHYSIOLOGICAL CHEMISTRY
The ultimate constituents of the human body com-
prise some fifteen or sixteen of the elements. They
are — •
Oxygen Sulphur Sodium Silicon
Hydrogen Phosphorus Potassium Fluorine
Carbon Chlorine Magnesium Lithium
Nitrogen Calcium Iron Manganese
Only three of the above elements occur in the body
in their free state ; viz. Oxygen, which enters through
the lungs and is found in all the fluids of the body,
either in solution or loosely combined ; Nitrogen, also
found dissolved in the fluids of the body ; Hydrogen,
which occurs as a product of decomposition in the
alimentary canal.
These sixteen elements are combined in various
proportions, to form the compounds which exist in the
tissues of the body. The simpler bodies are crystal-
line in form, as chloride of sodium and urea ; the more
complex, as albumin, are amorphous. The former,
being crystalloids, readily pass out of the body through
the excretory organs ; the latter, being colloids, are
better suited to form part of its tissues.
2 Physiological Chemistry
These bodies may be divided into the following
classes : —
I. Inorganic Compounds.
II. Organic Crystalline Salts, or the Urea
Group.
III. Carbo-hydrates, or Sugars.
IV. Hydro-carbons, or Fats and their Allies.
V. Albuminous, or Proteid Compounds.
VI. Albuminoid, or Gelatinous Compounds.
I. The Inorganic Compounds include water,
acids, bases, and salts.
Water, H 2 0, forms about 70. per cent, of the
whole body ; it is one of the chief constituents of the
juices and tissues, and is a general solvent, by means
of which various materials may be taken in as food,
or excreted from the body. The various organs or
liquids contain variable quantities ; thus, enamel con-
tains 2 per cent. ; saliva, 99-5 per cent.
Acids consist of —
Hydrochloric, which exists free in the gastric
juice and in combination with bases in all
the tissues and fluids.
Carbonic, with bases in blood, teeth, and bones.
Phosphoric, in combination with bases, in the
bones, teeth, corpuscles, brain, &c.
Sulphuric, with bases in blood, serum, and
secretions.
Hydrofluoric, with bases in bones and teeth.
Silicic, with bases in hair, epidermis.
Bases —
Sodium, in all tissues and fluids.
Potassium, in the muscles, red blood corpuscles,
nervous tissues, secretions.
Ammonium, sparely in the gastric juice, urine,
saliva.
Urea 3
Calcium, in bones and teeth and fluids.
Magnesium accompanies lime.
II. The Organic Crystalline Bodies are very
numerous ; for the most part they are the result of
the disintegration of albuminous material, and nearly
all contain nitrogen. The principal members of this
group are urea, uric acid, xanthin, hypoxanthin, hippu-
ric acid, kreatin, kreatinin, lactic acid, lecithin, neurin,
cerebrin, leucin, tyrosin, and cholesterin.
Urea, CH 4 N 2 or CO(NH 2 ) 2 , forms the chief-
constituent of the solid portions of the urine of man
and the carnivorous animals ; it is also found, but
less freely, in the urine of herbivorous animals, rep-
tiles, and birds. It exists in minute quantities in the
blood, lymph, and liver. It is found in larger quan-
tities in all the fluids of the body in advanced Bright's
disease.
Preparation — artificially. — By heating a mixture
of potassic ferrocyanide and manganic dioxide on an
iron sheet, potassic cyanate is formed, and is dissolved
out with water. The potassic cyanate is treated with
ammonium sulphate, ammonium cyanate and potassic
sulphate being formed ; the potassic salt is removed
by crystallisation, and the mother liquor, on evapora-
tion to dryness, and extraction of the dried residue
with alcohol, yields urea.
It can also be made artificially by heating ammo-
nium cyanate, a rearrangement of atoms taking place.
NH 4 CNO = (NH 2 ) 2 CO
Ammonium cyanate = Urea.
From urine. — The urine is evaporated to a thin
syrup, and its own volume of colourless nitric acid
added ; nitrate of urea is formed and readily crystal-
lises. The nitrate is dissolved in water, decolorised
by animal charcoal and recrystallised. To obtain
the urea pure, the nitrate is decomposed by barium
4 Physiological Chemistry
carbonate, the barium nitrate which is formed is
allowed to crystallise out, and the liquor containing
urea evaporated to dryness and extracted with alcohol.
Properties. — Urea crystallises from water in long
thin colourless needles. If formed slowly the crystals
are four-sided, and have
pyramidal ends. It is
a colourless substance
of saline taste, soluble
in water and alcohol,
insoluble in ether.
Urea is closely related
(being isomeric) with
ammonium cyanate,
NH 4 CNO, and carba-
mide, (NH 2 ) 2 CO.
Amides are com-
pounds in which hy-
Fig. i.-Crystals of nitrate of urea. drOXyl HO is replaced
by NH 2 . Thus, if in
the molecule of carbonic acid, CO(HO) 2 , we replace
one HO we get monamide or carbamic acid ; if we
replace both we get carbamide or urea.
CO HO
Carbonic acid.
CO HO
Monamide.
co NH 2
Carbamide, or urea.
Characteristic reactions and tests. — (i) Pure nitric
acid gives in a strong solution of urea a crystalline
precipitate of urea nitrate. These crystals are colour-
less six-sided prisms, and are sparingly soluble in
alcohol (fig. i).
(2) Mercuric nitrate gives a white precipitate in
the absence of chlorides.
(3) Nitrous and hypobromous acids decompose
urea, nitrogen and carbonic acid being
liberated.
Uric Acid
CO(NH 2 ) 2 + 3 HBrO = C0 2 + N 2 + 2 H 2 + 3 HBr
Urea + Hypo- =Carbonic + Nitro- + Water + Hydro-
bromous acid acid gen bromic
acid.
(4) Fused with caustic potass, or treated with con-
centrated sulphuric acid, urea is resolved
into ammonia and carbonic acid. The same
change takes place in the presence of decom-
posing animal matters as in stale urine, the
urine becoming ammoniacal : —
CO(H 2 N) 2 + 2 H 2
Urea + Aq.
= (NH 4 ) 2 C0 3 .
= Ammonium carbonate.
Uric Acid, C 5 H 4 N 4 03, is present in small
quantities in the urine of man and the carnivora, in
smaller quantities in
that of the herbivora.
It never occurs in the
free state in normal
urine, but in com-
bination with soda,
potash, or ammonia.
It is present in the
spleen, liver, and also
in the blood in gout ;
and 'urinary calculi
are often composed
of it. It forms about
90 per cent, of the
solid residue of the
urine of snakes, and
is present in large proportion in the urine of birds.
In birds and reptiles uric acid is the medium by which
nitrogen escapes from the system, thus taking the
place of urea.
Preparation.— -It is best obtained from the ex-
crement of snakes, by boiling with caustic potass
until the urate of ammonium of which it consists is
Fig. 2. — Crystals of uric acid from urine.
6 Physiological Chemistry
decomposed, the ammonia being driven off. The uric
acid is precipitated in an impure state by adding hydro-
chloric acid. The precipitate is re-dissolved in potass
and re-precipitated by acid.
From urine. — By acidulating with hydrochloric
acid, and allowing to stand for twenty-four hours,
reddish crystals of impure uric acid being precipitated
(fig. 2).
Properties. — Pure uric acid is a white crystalline
powder, almost insoluble in cold water, insoluble in
alcohol and ether. The crystals vary in shape, but
are for the most part of a rhombic form. It is di-
basic, and combines with bases to form soluble salts,
as the urates of ammonium, potassium, and sodium.
By oxidation, uric acid yields, in the presence of
acids, alloxan and urea ; in the presence of alkalies,
allantoine and carbonic acid. Uric acid can be
prepared by heating urea and glycin together.
Tests — Murexide test. — A small portion of uric
acid is moistened with strong nitric acid, and
evaporated at a gentle heat. It effervesces,
and leaves a reddish coloration, which on
adding ammonia becomes purple.
Schifs test. — Uric acid is dissolved in a solution
of sodium carbonate ; and dropped on paper
moistened with silver nitrate a brown stain
is formed.
Hippuric Acid, C 9 H 9 N0 3 , occurs in small quan-
tities in the urine of man and carnivora, but abun-
dantly in the urine of herbivora ; in the latter it is the
chief means of passing nitrogen out of the body. It
is precipitated by iron salts. Heated in a test-tube, it
is decomposed into benzoic acid and ammonic ben-
zoate, which condense on the sides of the tube, and
an oily substance remains behind. Most of its other
Kreatinin 7
salts are soluble. It crystallises in fine needles
(see fig. 3). _
Kreatin, C 4 H D N 3 02, exists in the muscles, and
can be obtained from extract of meat. It occurs in
colourless oblique rhombic prisms ; soluble in hot,
Fig. 3.— Crystals of hippuric acid (Landois and Stirling).
sparingly soluble in cold water. It has a neutral re-
action, and when boiled with baryta water, splits up
into urea and sarcosin.
Kreatinin, C 4 H 7 N 3 0, is an alkaline body which
exists in small quantities in muscle-extract and in
urine. It crystallises in colourless prisms. Kreatin,
on boiling with HC1, loses H 2 and forms krea-
tinin. It can be separated from the urine by pre-
cipitating with mercuric chloride. It unites with zinc
chloride, forming crystals, which help to identify it
(see fig. 4)-
8 Physiological Chemistry
Xanthin, C 5 H 4 N 4 2 , exists in small quantities in
urine, in the spleen, and muscles. It is insoluble in
water, soluble in nitric and hydrochloric acid. When
heated with nitric acid and evaporated, a yellow resi-
due is left. It occurs in some calculi.
Hypoxanthin, C 5 H 4 N 4 0, occurs in the tissues of
the spleen and muscles, and has been noticed in the
urine of leukaemia ; when oxidised it forms xanthin.
Fig. 4. — Kreatinin, zinc chloride, a, in balls with radiating lines ;
£, crystallised from water ; c, from alcohol (Landois and Stirling).'
Lactic Acid, C 3 H 6 3 , is the acid formed during
lactic fermentation, and is found in sour milk and in
the alimentary canal. Sarco-lactic acid has the same
composition as lactic, but differs from it in the solu-
bility and crystalline form of its zinc and calcium
salts. It is found in the muscles, and can be obtained
from muscle-extract.
Leucin g
Indican, C 8 H 7 NS0 4 , is a substance derived from
indol, the basis of indigo, formed in the intestine as
a product of digestion ; it is present in variable quan-
tities in the urine ; when treated with an equal quantity
of HC1 and a drop of solution of chloride of lime,
indigo blue is formed.
Lecithin, C 44 H 90 NPO 9 , occurs in the brain, yolk
of egg, pus, and in smaller quantities in the blood and
bile. It is a white crystalline substance, soluble in
hot alcohol and ether.
Cerebrin and Neurin are two substances which
occur in the brain, and the latter also in yolk of egg.
Leucin, C 6 H 13 N0 2 , in conjunction with tyrosin,
is found in many of the organs and fluids of the body,
Fig. 5.— Crystals ofleucin and tyrosin (Salkowski and Leube).
in the pancreas, liver, spleen, in the peptones of the
alimentary canal, and in the urine in acute yellow
atrophy and other diseases of the liver. These
substances are formed during the decomposition of
io Physiological Chemistry
albuminous substances. They may be prepared by
the artificial decomposition of albumin, fibrin, casein,
gelatin, &c, but are most readily obtained by boiling
horn-chips in dilute sulphuric acid. Leucin can also
be obtained synthetically. Impure leucin appears
under the microscope in the form of oily lumps clus-
tering together (fig. 5) ; when pure it forms white flat
crystals. It is soluble in water and alkalies, less so
in alcohol.
Scherer's test. — Place a small portion on platinum
foil with a drop of nitric acid and evaporate
gently. A colourless residue will be left, which,
on the addition of liq. potassse, will become
yellow and form an oily drop.
Tyrosin, C 9 H u N0 3 , is generally found in con-
nection with leucin, and consists of minute colour-
less microscopic needles of a silky lustre (fig. 5). It is
less soluble in water than leucin, and is insoluble in
alcohol, but soluble in liq. potassse and dilute acids.
Ifoff)?iann's test. — Add mercuric nitrate and boil ;
the liquid will become rose-coloured and de-
posit a red precipitate.
Piria's test. — Add a few drops of concentrated
sulphuric acid, warm, neutralise with chalk,
filter, and add ferric chloride ; the liquid will
become of a violet colour.
Cholesterin, C 26 H 44 0, cannot be said to belong
to the Urea group, for chemically it is an alcohol, and
is the only member of the alcohols present in the
system. It occurs in small quantities in the blood,
bile, and nervous tissues. It is insoluble in water
and cold alcohol ; soluble in ether, chloroform, and
boiling alcohol. It occurs in white crystals, for the
most part in rhombic plates (fig. 6). It is generally
prepared from gall-stones by boiling with alcohol,
filtering, and allowing to crystallise. With strong
Grape Sugar
1 1
H 2 S0 4 and a trace of iodine it becomes of a violet
colour, which afterwards changes to green and then
red.
III. Carbo-Hydrates. — The principal carbo-
hydrates found in the animal body are : i. Grape
sugar. 2. Maltose. 3. Milk sugar. 4. Inosit.
5. Glycogen. 6. Dextrin.
1 . Grape Sugar or Dextrose, C 6 H , 2 6 , occurs
in small quantities in the blood and urine, and in
larger quantities in
the contents of the
alimentary canal.
When pure it forms
four-sided prisms, but
is generally seen in
irregular warty lumps.
It is soluble in water
and alcohol. It un-
dergoes decomposi-
tion in the presence
of certain ferments.
It is precipitated by
acetate of lead and
ammonia.
(a) Alcoholic fer-
mentation takes place under the influence of yeast ;
alcohol and carbonic acid are formed : —
C 6 H l2 6 = 2 C 2 H 6 + 2C0 2 .
(0) Lactic fermentation. — Under the influence of
the bacilli found in decomposing animal matters,
lactic acid is formed in the first instance, and after-
wards butyric acid, carbonic acid and hydrogen.
1st stage, C 6 H 12 6 =2C 3 H 6 3 .
2nd stage, 2C 3 H 6 3 =C 4 H 8 2 + 2C0 2 + 2H 2 .
The acidity of the contents of the large intestine is
due to the presence of lactic acid.
Fig. 6. — Crystals of cholesterin.
1 2 Physiological Chemistry
Trommel's test. — Boil the solution with a few
drops of solution of cupric sulphate and excess
of caustic potass ; if dextrose is present an
abundant reddish-yellow precipitate of cuprous
oxide will fall.
Moore's test. — Boil with caustic potass ; if sugar
is present the liquid will become first light
yellow and afterwards brown.
Fermentation test. — Add a small quantity of
yeast, and leave in a warm place for 24 hours ;
a considerable quantity of carbonic acid will
be evolved, which can be collected in a suitable
apparatus. Alcohol will be present in the liquid.
2. Maltose, C^H^On + H 2 0, is the form of
sugar which is mainly produced by the action of
diastase such as ptyalin on starch. It possesses more
rotatory power ( + 150) over polarised light than dex-
trose ( + 58)- Its reducing power over cupric oxide
is less than that exercised by dextrose. Maltose is
converted into dextrose under the influence of some
of the intestinal ferments, and by boiling with dilute
acids, but not by the action of malt diastase.
3. Milk Sugar or Lactose, C 12 H 2i O n , is
found in milk. It differs from dextrose in being more
insoluble in -water, and not readily undergoing the
alcoholic fermentation. It readily undergoes the lac-
tic fermentation. It precipitates cuprous oxide from
alkaline solutions in the same manner as dextrose.
It is insoluble in alcohol.
4. Inosit, C 6 H 12 6 , occurs in small quantities in
the spleen, liver, and brain, and appears in the urine
in uraemia. It undergoes the lactic but not the
alcoholic fermentation.
5. Glycogen, C 6 H, O 6 , is found in considerable
quantities in the livers of well-fed animals, in smaller
quantities in the white corpuscles of the blood,
Dextrin 1 3
placenta, and foetal tissues. It is an amorphous,
white, tasteless powder, soluble in water, insoluble in
alcohol. Its aqueous solution is opalescent.
Preparation. — Kill a well-fed rabbit shortly after
a meal, quickly remove the liver, and after cutting
it in slices, throw it into boiling water without loss of
time. After boiling for a short time (to prevent the
ordinary post-mortem change which glycogen under-
goes into grape sugar) pound the liver, boil again and
filter. The filtrate contains the glycogen, and certain
albuminous substances which must be removed. The
latter are precipitated with potassio-mercuric iodide in
the presence of hydrochloric acid. The glycogen is
then precipitated by adding alcohol.
Tests. — Dilute mineral acids (except nitric) con-
vert it into grape sugar. Iodine gives a red
coloration, which disappears on warming and
reappears on cooling. (Starch gives blue with
iodine, dextrin red, which disappears on warm-
ing, and does not reappear on cooling.)
6. Dextrin, C 6 H 10 O 5 . — Starch is converted into
dextrin by the action of ferments, the dextrin formed
being in turn converted into maltose if the action of
the ferment is continuous. Dextrin is found in the
alimentary canal and also in the blood. It becomes
of a red colour on addition of iodine ; the colour
disappears on warming, and does not, as in the case
of glycogen, reappear on cooling.
IV. Hydro-Carbons, or Fats.— The principal
fats present in the animal body are : —
•i
Stearine ,£ h r\\ f O
( ( -18 J:1 35 < J)3 J
Palmitin^ 3i0)3 }0 3
01ein (CAO)J '
1 4 Physiological Chemistry
These neutral fats, when submitted to the action of
superheated steam, or heated with lead oxide, com-
bine with water, and form glycerine and a fatty acid.
Palmitin Glycerine Palmitic acid
C3H.5 ) n H) n _C 3 H 6 l r . C 16 H 31 o
(C 16 H 31 0)3f 03 + 3 Hl - H 3 I° 3+3 H U -
Stearin is best obtained from beef or mutton
suet. It is the hardest of the fats, and crystallises
in white shining plates. It has the highest melting-
point (60° C.)
Palmitin is best prepared from palm oil ; it
crystallises in needles and has a lower melting-point
than stearin (40 C.)
Olein is prepared from olive oil, and is fluid at
ordinary temperatures.
Glycerine, C,^* } 0,, or C 3 H 5 (OH) 3 , is a
syrupy fluid with sweet taste and a neutral reaction ;
it is soluble in water and alcohol, but not in ether.
It dissolves many metallic oxides, and on heating
decomposes, acrolein being formed.
V. The Albuminous Bodies or Proteids occur
,in almost all the tissues and fluids of the body. They
^derive their name from the white of egg, which is
taken as a type of the group. They will not crystal-
lise, and are obtained pure with difficulty. They are
insoluble in alcohol and ether, soluble in strong acids
and alkalies, undergoing decomposition in the process.
They are not formed in the animal body, but enter
the body in the form of food derived from the vege-
table kingdom. Urea is the chief product of their
oxidationjwithin the body, carrying away all their N ;
C0 2 and H 2 are also formed. They have the
following average percentage composition :
Albumin
15
O
H
C
N
S
2 1 per cent.
7-5
54
16
1
All proteids in solution give the following reac-
tions : —
1. Xantlwprotein Reaction. — Heat with strong
nitric acid, cool, and add ammonia. An
orange colour is produced.
2. Milton's Reaction. — Add some Millon's reagent
(Hg(N0 3 ) 2 + HgN0 3 ) and heat ; the fluid will
become red, and if sufficient albumen is pre-
sent, a precipitate will fall.
3. Biuret Reaction. — Add some liq. potassae and a
drop or two of solution of cupric sulphate ;
heat : a violet colour is produced.
The proteids include several groups : —
1. Albumins. 4. Fibrin.
2. Derived albumins. 5. Coagulated proteids.
3. Globulins. 6. Albumoses.
7. Peptones.
1. Albumins. — The albumins are soluble in
water, insoluble in alcohol and ether. They are
coagulated at a temperature of 70° C. If dried at a
lower temperature, they form a tasteless yellow mass.
The albumins are precipitated in the following
ways : —
(a) By boiling and acidulating with nitric acid.
\p) By concentrated nitric acid in the cold.
(c) By the addition of acetic acid and potassic
ferrocyanide.
(d) Boiling with acetic acid and strong solution of
sodium sulphate. „.7^t'
1 6 Physiological Chemistry
The two different forms of albumin are serum-
albumin and egg-albumin.
They differ in that —
(a) Egg-albumin is coagulated by ether, serum-
albumin is not.
(b) Coagulated serum-albumin is soluble in strong
nitric acid, egg-albumin is not.
(c) Serum-albumin injected beneath the skin does
not appear in the urine, egg-albumin does.
2. Derived Albumins.— (a) Alkali Albumin.
— If albumin in solution is treated with dilute caustic
potash and gently warmed, some of its properties
undergo change. The alkaline solution will no longer
be precipitated by boiling. It is precipitated on
neutralisation with acids, and is soluble in excess of
the acid. It is not precipitated on neutralisation in
presence of the alkaline phosphates. (6) Casein. —
This substance closely resembles alkali albuminate, but
differs from it in containing sulphur. It can readily
be prepared from milk by saturating with magnesium
sulphate, or by acidifying and gently warming ; it is-
precipitated when milk comes in contact with the walls
of the stomach, (c) Acid Albumin. — If albumin in
solution is treated with HC1 or other acids, it under-
goes a change in its properties. It is no longer
coagulated by heat. It is precipitated on neutralisa-
tion with an alkali, and is redissolved by excess ; its
precipitation is not prevented by alkaline phosphates.
It is precipitated on boiling with lime-water. If
muscle be dissolved in dilute HC1, a body termed
syntonin, closely resembling, if not identical with, acid
albumin, is formed.
3. Globulins. — These bodies differ from the
albumins in being insoluble in water, precipitated by
C0 2 , or on saturating their solutions with NaCl.
They are converted into acid albumen by HC1. They
The Proteids 17
are soluble in dilute solutions of NaCl, the solution
being precipitated by heat. '
They include (a) globulin, (b) paraglobulin, (c)
fibrinogen, (d) myosin, (e) vitellin. (a) Globulin
exists in the crystalline lens, and closely resembles
paraglobulin in its properties, but differs from it in
not assisting to form fibrin, (b) Paraglobulin
occurs in blood and serum, and in -smaller quantities
in some of the tissues. It gives rise to fibrin when
mixed with any fluid, as hydrocele fluid, containing
fibrinogen, (c) Fibrinogen exists in blood, peri-
cardial, pleural, and hydrocele fluids. It closely
resembles paraglobulin, but when thrown down by
C0 2 it is less flocculent and more viscous, (d)
Myosin is present in dead muscle. It is not so
soluble as fibrinogen. It is converted into syntonin
by dissolving in HC1. (e) Vitellin exists in yolk of
egg ; it is soluble in dilute NaCl solutions, but differs
from other members of the group in not being precipi-
tated by saturating with NaCl.
4. Fibrin is obtained by whipping freshly-drawn
blood. It forms tough, white strings, which are
insoluble in water and dilute NaCl solution ; is con-
verted into syntonin by digestion with HC1.
5. Coagulated Proteids. — When solutions of
the albumens or globulins are heated to 70 C, they
are coagulated. In this condition they are insoluble
in water and saline solutions, but soluble in strong
acids or alkalies. They are dissolved during gastric
and pancreatic digestion, peptones being formed.
6. Albumoses. — When proteids are acted on by
ferments (such as pepsin or trypsin) in the presence
of an acid, they are dissolved and certain bodies
termed albumoses and peptones are formed. The
albumoses are the first products, and later pep-
tones are formed. Three albumoses have been de-
scribed, froto-, hetero-, and deutero-albutnose. They are
C
1 8 Physiological Chemistry
distinguished from the peptones by being precipitated
from their solutions by saturating with ammonium
sulphate. Some of the albumoses are virulent poisons
if injected into the blood.
7. Peptones. — The peptones are soluble in water,
they readily diffuse through animal membranes, are
not precipitated by boiling, acids, or by potass-fero-
cyanide and acetic acid ; thus differing from other
proteids. They are precipitated by tannin, iodine,
and acetate of lead. A trace of copper sulphate with
excess of caustic soda produces a rose colour (pink
biuret reaction).
Summary of the Distinguishing Tests of the principal Proteids
( Waller)
/"egg-albumin . . . ether ppt.
CCi boiHn| SOn -^ serum-albumin . . . no ether ppt. No MgSO,
ppt.
\ globulins .... MgSO, ppt.
.acid and alkali albumins . ppt. on neutralisation
No coagulation J ^bumoses .... HNO^ppt. in cold, soluble
on 01 ing I pe p tones .... p; n k biuret reaction of fil-
1 trate after saturation with
* Am 2 SO,
VI. The Albuminoids or Gelatinous Bodies.
These substances, which occur as the principal con-
stituents of many tissues, resemble the albuminous
bodies in their composition, but differ from them in
many of their reactions.
They include — •
1. Mucin. 3. Chondrin.
2. Gelatin. 4. Elastin.
1. Mucin is found in fcetal connective tissue and
in tendons. It occurs also in the mucous secretions,
saliva, bile, gastric juice, &c, giving them their ropy
consistence. It is not coagulated by boiling. It is
Histology 1 9
precipitated by acetic acid. It gives the proteid
action with Millon's reagent and nitric acid, but not
with sulphate of copper and liq. potass.
2. Gelatin. — Bones, connective tissues, tendons
yield gelatin on boiling. When dry it is a colourless,
transparent body ; it swells up in cold and dissolves
in hot water ; the solution, on cooling, forms a jelly.
It is precipitated by tannic acid and mercuric chloride,
not by acetic acid. It does not yield the proteid
reactions with nitric acid, Millon's reagent, or copper
sulphate.
3. Chondrin forms the bulk of the matrix of
cartilage, and can be prepared by boiling cartilaginous
substances in water, the solutions forming a jelly
on cooling. It is precipitated by acetic acid and lead
acetate.
4. Elastin. — The yellow elastic fibres present in
the lig. subflava, and other parts of the body, consist
of elastin. It does not dissolve in boiling water, but
is soluble in boiling caustic potass.
CHAPTER II
HISTOLOGY
The animal tissues, when examined by the aid of the
higher powers of the microscope, are seen to consist
of certain (1) structural elements, embedded in or sur-
rounded by (2) an intercellular substance or matrix.
The structural elements are either cellular in form,
or consist of various forms of fibres which have
originally been derived from cells. The intercellular
substance consists of a finely granular or homogeneous
substance in which the cells are embedded, or it may be
c 2
20 Histology
present only in small quantities, acting as a sort of
cement to connect the cells together. When in small
quantities, as between epithelial cells, it is invisible
unless stained by silver nitrate.
THE ANIMAL CELL
The cells found in the animal body vary from ^
to -g-^ inch in diameter, and consist of two parts,
(i) The protoplasm, or chief substance of the cell.
(2) The nucleus, a small dark body situated near the
centre of the cell, and which takes up colouring
matters more readily than the protoplasm. In some
cells an external membrane may be distinguished, but
it is not universally present.
I. Protoplasm. — By means of the higher powers
of the microscope, and aided by chemical reagents, it
has been demonstrated that the protoplasm — in some
cells at least — is not homogeneous, but consists of a
fine network of fibres resembling a sponge, and has
hence received the name of the spongioplasm, or
reticulum, and a hyaline substance occupying the
meshes known as the hyaloplasm (enchylemd). In
some cells the outer layer of protoplasm becomes
hardened'so as to form a sort of enclosing membrane
or capsule. The protoplasm in some of the cells is
so soft that various minute bodies, such as oil globuleSj
starch granules, and water globules, may be found
embedded in its substance. These matters may be
taken up by the cells, as in the case of the epithelial
cells lining the villi of the intestines, or they may be
formed in the protoplasm of the cells, as in the cells
which line the acini of the mammary gland.
The chief proteid present in protoplasm is plastin,
a muco-globulin containing phosphorus ; lime is also
present,
Protoplasm 2 1
Protoplasm in an active state is able to effect im-
portant changes in the blood or lymph with which
it comes in contact. Thus all forms of protoplasm
(1) absorb O from the lymph and give up C0 2 , heat
and other forms of energy being produced. (2) The
protoplasm of some cells, as, for instance, those of the
mammary gland form milk, and those lining the peptic
glands, pepsine. (3) Under some circumstances
protoplasm is able to select certain substances from
the blood ; thus, the epithelium of the kidney selects
urea.
The term metabolism is applied to all the changes
which go on in protoplasm.
Under some circumstances protoplasm is capable
of certain movements ; these are best seen in the white
blood corpuscle. If a white blood corpuscle is ob-
served under suitable conditions, it will be seen that
a portion of the protoplasm is protruded, so that the
corpuscle is no longer of a rounded shape, but has
become more or less elongated ; the protruded portion
may be withdrawn and other processes protruded.
These movements, which resemble those of an inde-
pendent animal, are termed amoeboid. By means of
these movements the corpuscle is able to change its
position, and to find its way through the walls of the
minute blood-vessels and capillaries, and wander in
the surrounding tissues. These movements also enable
the corpuscles to take minute particles into their
interior, such as minute granules of colouring matter.
These amoeboid movements are dependent upon
a supply of oxygen, as the movements cease after
awhile if oxygen is withdrawn ; in warm-blooded
animals the movements cease if the temperature falls
to 10° C. ; a few degrees of temperature above that of
the normal temperature of the body increases the
activity of the movements, while a still higher tem-
perature arrests them.
22
Histology
II. Nucleus. — The nucleus is usually a small
rounded body situated near the centre of the cell. In
some cases, as in some nerve cells, the nucleus occu-
pies nearly the whole of the cell. In typical cases the
nucleus is bounded by a wall or capsule. Examined
by a high power the nucleus is seen to consist of (i)
a network of fibres connected with the nucleus wall,
termed the chromoplasm or nuchoplas7ii ; (2) a homo-
geneous substance occupying the interstices of the
chromoplasm, termed the nuclear matrix. The chromo-
plasm differs from protoplasm in that it is more readily
stained by logwood, carmine, and gentian violet. One
or more small rounded bodies, the nucleoli, may be
present in the nucleus.
During life new cells are constantly being formed
to take the place of those which are worn out. New
cells are formed by the division of existing cells. A
cell divides either by what is called ' direct ' or ' in-
direct ' division. In the former case, which appears
to take place rarely, there is a simple fission of the
nucleus followed by a division of the cell. In ' in-
direct ' division (Karyokinesis) the process of fission
is preceded by some peculiar changes in the chromo-
plasm of the nucleus. These changes, which are very
complicated, have been observed in the cells of living
animals, the time of complete fission lasting from half
an hour to three hours.
EPITHELIUM
The various free surfaces of the body— as, for ex-
ample, the external surface of the skin, the mucous
membranes, the internal membrane of the arteries,
and the serous sacs— are lined by cells of different
characters, which form the epithelium or endothelium.
The latter term is applied by some to the flattened
Epithelium 23
cells which line the serous sacs, blood-vessels, and
lymphatics.
The epithelial cells differ very considerably in
shape and size, but they agree in possessing nuclei
and finely granular cell contents. Epithelial cells are
connected together by a small quantity of a homo-
geneous albuminous substance, termed the intercellular
cement ; it is stained of a dark brown colour by silver
nitrate. Blood-vessels do not penetrate between the
cells, the latter being nourished by the exuded plasma.
On the other hand, numerous nerve fibres may be
distinguished between the epithelial cells.
Epithelium may be divided into the following
varieties : —
1. Tesselated or pavement epithelium
2. Stratified epithelium
3. Columnar ,,
4. Transitional ,,
5. Glandular „
6. Ciliated „
1. Tesselated or Pavement Epithelium.— A
single layer of epithelium is found lining the pleura,
pericardium, peritoneum, arachnoid, arteries, veins,
capillaries, lymphatic vessels, acini of the lungs,
anterior and posterior aqueous chambers of the eye,
and looped tubes of Henle in the kidney. The cells
consist of a thin plate with an oval nucleus, but differ
considerably in shape; those lining the serous sacs
being polyhedral or nearly circular (fig. 7) ; the cells
lining the arteries and capillaries being elongated, and
the lymphatics having epithelium, with an irregular or
wavy border. The outline of these cells is readily
shown by staining their intercellular cement with
silver nitrate.
2. Stratified Epithelium.— In this variety there
are several layers of cells ; it covers surfaces which
24 Histology
ire especially liable to friction. It covers the true
;kin, forming the epidermis (fig. 8) ; it forms the
superficial layer of the mucous membrane of the
;avity of the mouth, tongue, oesophagus, conjunctiva,
ind vocal cords, vagina, external aperture and fossa
lavicularis of the urethra. The deeper cells of the
iermis are more or less round, though the deepest are
Fig. 7.— Pavement epithelium Fig. 8.— Skin of negro, vertical section
from a serous membrane ; (Quain's Anatomy). _ a, a, papilla? ;
magnified 410 diameters £, layer containing pigment ; c. Mal-
(Quain's Anatomy), a, cell- pighian layer or rete mucosum ; d, horny
body ; b, nucleus ; c, nucleoli. layer of flattened cells.
columnar, and form the rete mucosum ; the superficial
cells are flattened, overlap at their edges, and form
the horny layer or stratum corneum, which covers the
soles of the feet and palms of the hand. The deeper
cells are not closely applied to one another at their
edges, but are separated from one another b"y minute
spikes or prickles, the spaces between the spikes
Epithelium 2 5
forming channels. When the cells are isolated they
appear to be surrounded by the spikes, and are called
'■prickle-cells'
3. Columnar (fig. 9). — This
variety consists of cylindrical or club-
shaped nucleated cells, the thick
ends being towards the free surface.
Their sides are often more or less
flattened from mutual pressure, or
more or less irregular from the pre-
sence of lymphoid cells situated
between adjoining epithelial cells.
The protoplasm of the cell is granu-
lar from the presence of minute
vacuoles ; it may also contain mucin
and fatty globules. At times the
outer ends of the cells are distended
by mucus, forming the so-called
'goblet' cells (fig. 10). There is
always a nucleus containing a fine network. The free
border of the cell is more refractile than the rest
(G. 9. — Columnar cells
from the rabbit's
intestine (Quain's
Anatomy). **, an ir-
regular projection ;
«, nucleus with its
network ; str, the
fine striated border ;
a fat-globule is visible
in the left-hand cell.
Fig. 10— Goblet cells, highly magnified (Quain s Anatomy). The right-
hand cell shows distinctly the intra-nuclear network, which radiates in
the lower part of the cell, and also into the mucus-containing part.
of the protoplasm of the cell, and is finely striated.
Columnar cells are found lining the alimentary canal
from the oesophageal end of the stomach to the anus,
26 Histology
lining the ducts of glands and the olfactory region of
the nose.
4. Transitional. — This variety consists of flat-
tened cells on the surface, a middle layer of pear-
shaped cells, their rounded ends fitting into the under
surface of the flattened cells, and an inferior layer of
rounded or pyriform cells fitting between the thin
ends of the middle layer. The bladder, ureters, pelvis
of kidney are lined by transitional epithelium, and also
the larynx and pharynx, where the columnar and flat-
tened cells come in contact.
5. Glandular. — The acini of the various glands
of the body, as the convoluted tubes of the kidney,
the salivary and peptic glands, are lined by spheroidal
or cubical cells. These cells are nucleated ; their
protoplasm performs the important work of separating
or elaborating from the blood the materials which
form the secretion of the gland.
6. Ciliated. — In some parts of the body the epi-
thelial' cells are provided with minute rods which are
constantly in motion, and serve to propel mucus or
any minute particles in contact with them towards
the orifice of the chamber or tubes whose walls they
line. They vibrate at the rate of about 700 per
minute. These minute rods are probably prolongations
of the intra-cellular network, and their movements
are independent of any nervous mechanism. Chloro-
form vapour and carbonic acid gas arrest their move-
ments. Weak acids or alkalies and moderate electric
currents stimulate them. Ciliated epithelium is for
the most part columnar in shape (fig. n).
They are present in man —
(a) Lining the mucous membrane of the air-
passages. Commencing near the nostrils, they line
the nasal cavity (except the olfactory region), the
antrum, ethmoidal and frontal sinuses, the nasal and
lachrymal ducts, the upper part of the pharynx, the
Pigment 2 7
Eustachian tube, tympanic cavity, larynx, except the
vocal cords, trachea, and bronchi till they enter the
infundibula of the lungs.
{b) Lining the mucous membrane of the uterus,
commencing at the middle of the cervix and con-
tinuing along the Fallopian tubes
to their fimbriated extremities.
(c) Lining the vasa efferentia,
coni vasculosi, and upper part
of the globus major of the testis.
(d) Lining the lateral ven-
tricles of the brain and central
canal of the spinal cord in the
child.
Many of the animalcula and
algae, as the paramecia, rotifera,
vorticella, volvox, are provided
with cilia as a means of locomotion, or for producing
currents in the water, so as to carry their prey within
their reach. Cilia are also found in the gills of the
oyster and salt-water mussel, and doubtless serve to
bring a fresh supply of oxygenated water in contact
with the capillaries of their gills. In man, they
probably prevent the accumulation of mucus or
foreign particles on the surfaces they line, and possibly
in the testicle help forward the immature spermatozoa.
They are most readily obtained for the microscope
by snipping a small piece from the gills of the mussel,
and covering with thin glass ; they will continue to
work for hours if evaporation be prevented.
Fie. 11.— Columnar ciliated
epithelium from nasal
mucous membrane x 300
(Quain's Anatomy).
PIGMENT
Pigment is met with in various parts of the body,
for the most part in epithelium and connective tissue
cells. It is met with in epithelium cells in the external
layer of the retina and posterior surface of the iris ;
28 The Connective Tissues
in the deep layers of the cuticle in the dark races
(fig. 8, b), the membranous labyrinth of the ear, and
olfactory region. In connective tissue cells which are ir-
regularly branched, it is found in the outer layer of the
choroid coat, in the iris and pia mater. It also occurs
in some nerve-cells. The pigment itself consists
of minute brown particles, which when they escape
from the cells exhibit the ' Brownian ' movements.
Pigment occurs in some pathological states, as in the
rete mucosum in Addison's disease and in melanotic
tumours. The pigment of the choroid is evidently
of use in absorbing any redundant light which enters
the eye. Chemically it is characterised by the large
percentage (nearly 60 per cent.) of carbon which it
contains.
CHAPTER III
THE CONNECTIVE TISSUES
Connective or Areolar Tissue is present almost
universally throughout the body, serving to connect
the various organs with one another, as well as to bind
together the parts of which an organ consists. The
muscles are surrounded by a connective tissue sheath,
which penetrates into their substance, binding to-
gether the fasciculi and fibres. The same tissue is
present beneath the skin and mucous membranes,
and forms a sheath for the arteries, veins, and nerves.
It is plentifully supplied with blood-vessels and lymph-
atics, and many nerves pass through its substance.
Microscopically, four different elements may be seen —
1. Connective tissue cells or corpuscles.
2. White fibrous tissue.
3. Yellow elastic tissue.
4. Ground substance.
Connective Tissue Cells 29
1. Connective Tissue Cells (fig. 12).— On
examining the connective tissue of young animals,
various cells will be seen with fine granular contents
and nuclei lying in spaces in the ground substance.
Some are branched, others flattened or rounded.
Three kinds of cells may be distinguished, these are
\h& flattened or lamellar, the granular, and vacuolated
or plasma cells.
The flattened cells, as their name implies, are more
or less flat in shape, resembling epithelium. They
Fig. 12. — Connective tissue from a young guinea-pig (Quain's Anatomy).
c, flattened cell ; d, branched corpuscle ; g t granular corpuscle ; /, leu-
cocyte.
are often branched (fig. 12, d), their branches joining
together to form a kind of network, as in the cornea.
The cells in the fibrous tissue of tendons are square
or oblong, and form continuous rows, as seen when
the tendon is viewed longitudinally ; when viewed in
transverse section they appear irregularly branched,
sending their branches between the bundles of the
tendon. The granular cells (fig. 12, g) are mostly
rounded in form, and are coarsely granular. The
30 The Connective Tissues
plasma cells are mostly elongated in shape, and are
distinguished from the others by their containing
vacuoles in their protoplasm.
2. White Fibrous Tissue.— When areolar or
fibrous tissue is examined with a high power, it will
be seen that it is principally composed of fine, wavy,
parallel fibres ; these are united in bundles by a very
small amount of the ground substance (fig. 13).
Fig. 13. — White fibrous tissue x 400 (Quain's Anatomy).
Acetic acid causes the fibres to swell up and become
indistinct. On boiling they yield gelatine.
3. Yellow Elastic Tissue forms a variable
proportion of connective tissue, being especially
abundant beneath the skin, mucous and serous mem-
branes. Microscopically, it consists of yellow, elastic,
curling, branching fibres, of a larger size than the
fibres of white fibrous tissue. It is unchanged by
Distribtition of Connective Tissue 3 1
acetic acid and the weaker alkalies. Chemically it
yields elastin (fig. 14).
4. Ground Substance. — The intercellular ma-
terial present in connective tissue consists of a homo-
geneous material, surrounding the cells and fibres,
cementing them together.
It is stained by silver ni-
trate like the intercellular
cement of epithelium.
Distribution of
White Fibrous Tis-
sue. — Those connecting
tissues of the body which
require to be inelastic,
tough, unyielding, are
formed of pure white
fibrous tissue without ad-
mixture of yellow. Such
are the tendons, fasciae,
aponeuroses, most liga-
ments, the periosteum,
the dura mater, pericar-
dium, &c. They are white
in colour, and will not
readily stretch. Besides
the ordinary wavy fibres, they contain connective tissue
corpuscles.
Distribution of Yellow Elastic Tissue.— In
some parts of the body an elastic material is required
to connect bones together or to form the walls of blood-
vessels. Yellow elastic tissue enters largely into the
following structures : —
1. Ligamenta subflava of the vertebras.
2. The stylo-hyoid, thyro-hyoid, crico-thyroid
ligaments, the vocal cords, and calcaneo-
scaphoid ligament.
3. The middle coat of the larger arteries and veins
Fig. 14. — Elastic fibres from the lig.
subflava x 200 (Quain's Anatomy).
32 The Connective Tissues
4. It is present beneath the mucous membrane
of the trachea, and forms the walls of the
infundibula.
5. The capsule and trabecule of the spleen,
lymphatic glands, and erectile tissues.
6. Forming the ligamentum nuchse of horse
and ox.
RETIFORM TISSUE
Retiform or Adenoid Tissue consists of a
delicate network formed by connective tissue cor-
puscles joining their branches together. In some
parts the corpuscles and their nuclei are very apparent,
Fig. 15.— Thin section from the cortical part of a lymphatic gland (Quain's
Anatomy), a, b, network uf fine trabecular ; c, lymph corpuscles still
remaining in the meshes.
whilst elsewhere but little can be seen of nuclei at the
intersections of the fibres. Retiform tissue forms the
stroma or framework of lymphoid tissue.
In lymphoid tissue, the spaces in the network are
occupied by leucocytes. It is found in lymphatic
glands, solitary glands of the intestine, tonsils, spleen,
&c.
Adipose Tissue 33
ADIPOSE TISSUE
Adipose Tissue is present in many parts of the
body. It forms a layer beneath the skin, in the sub-
cutaneous connective tissues, except beneath the skin
of the eyelids and penis ; it forms a layer of con-
siderable thickness covering the buttocks, thighs, and
abdomen, in well-nourished subjects. In the internal
organs it is collected around the kidneys, heart, in the
joints, and folds of the omentum, but it is absent from
the cranium and lungs.
Structure. — Fat, to the naked eye, has a coarse or
finely granular appearance from the presence of large
or small lobes ; these are again made up of lobules ;
each lobule has its afferent arteriole, meshwork of
capillaries, efferent vein, and fat cells. The tubes and
lobules are bound together by areolar tissue.
Fat Cells. — When examined microscopically .the
vesicles or cells are, in well-nourished bodies, round
or oval in shape, 3^ to -^-n mcn in diameter (fig. 16).
They are derived from ordinary connective tissue cells,
and consist of a delicate envelope, m, the remains of
the original protoplasm of the cell, which includes
a nucleus more or less flattened, n, and fat globule
distending the cell, fg. After death a bunch of crystals
may be seen within the cell, cr. Under favourable con-
ditions of nutrition, connective tissue cells may be
seen to contain oil globules in their protoplasm, others
in which, the globules are fused together and are com-
mencing to push the nucleus to one side, distending
the cell and converting it into a fat vesicle. In
starvation the reverse takes place, the oil globules are
absorbed, serous fluid takes their place, and finally
these may disappear and a small branched connective
tissue cell be left. The contents of the vesicles in
the human body consist of olein, palmitin, and stearin.
34
The Connective Tissues
Uses.— i. Adipose tissue serves as a convenient
packing material, which fits in between the tissues and
organs, and from its fatty nature it serves to diminish
friction. For example, the subcutaneous fat covering
the buttock forms a soft pad, and allows the skin to
work smoothly over subjacent structures.
2. Adipose tissue is an excellent non-conductor,
and "serves to retain the heat of the body.
Fin. 16.— Fat cells, highly magnified (Quain's Anatomy), fg, fat globule
distending a cell ; «, nucleus ; nl, membranous envelope ; cr, bunch of
crystals ; c, capillary ; v, vein ; c t, connective tissue cell.
3. Adipose tissue serves to store up for future
use a substance rich in carbon and hydrogen. The
destiny of fat is eventually to be converted into C0 2
and H 2 0, its oxidation serving to maintain the heat
of the body and give rise to muscular energy. Hy-
Cartilage 35
bernating animals fatten during the autumn on starchy
foods, the stored fat serving to maintain them during
their winter sleep.
CHAPTER IV
CARTILAGE AND BONE
Cartilage is a bluish or yellowish -white semi-trans-
lucent elastic substance, without vessels or nerves,
and surrounded by a fibrous membrane, the peri-
chondrium. This membrane is richly supplied with
blood-vessels, lymphatics, and nerves. It is absent on
the articular surfaces. Cartilage, on boiling for some
hours, yields an albuminoid called chondrin, which,
like gelatine, sets into a jelly on cooling, but differs
from gelatine in being thrown down by tannic acid
Cartilage may be divided into —
(Temporary
1. Hyaline . . \ Costal
(Articular
„., ,.., (White
2. Fibro-cartilage . | Ye]low
1. Hyaline Cartilage (fig. 17) is present in
many parts of the body. In the foetus it forms a
firm, elastic material for the skeleton, prior to the
deposition of lime salts and consolidation of the
bones. In the adult it supplies an elastic material as .
the costal cartilages, to assist in forming the walls of
the chest, its elasticity aiding in an important manner
the expiratory act. It caps the ends of bones at the
joints, and helps to diminish friction and lessen
shock. It forms in large measure the walls of the
trachea and bronchi, serving to maintain their rigidity
D 2
36
Cartilage and Bone
and prevent collapse. It also forms the septum and
lateral cartilages of the nose, the thyroid and cricoid
cartilages in the larynx.
Structure. — The matrix or ground substance is
finely granular and transparent, and, like the matrix
m&L
— 9
m
'<&.:
, :
«';
Fig
k*
w
e (Quain's Anatomy), a, group of two cells
/», group of four ; //, protoplasm of cell ; g t fatty granules ;
, nucle
of connective tissue, is stained brown by silver
nitrate. By long maceration the matrix can be broken
up into fine fibres.
The cells occupy special cavities in the matrix,
called the cartilage lacuna;. Each cavity is lined by
Cartilage 37
a membrane, the capsule, which in growing cartilage
is thickened by the addition of a layer of the hyaline
matrix, distinct from the rest. The cells consist of
round, oval, or elongated little masses of protoplasm
with one or two nuclei : under a high power fine fibres
and minute granules can be distinguished in the
protoplasm. The nuclei are finely granular in appear-
ance, but under a high power this granular appearance
is seen to be caused by a fine network of chromoplasm.
Each lacuna generally contains one cell, but it may
contain 2-8 cells ; in the latter case, cell-division is
proceeding more rapidly than the formation of the
ground substance.
Hyaline cartilage is modified in different situa-
tions : —
(a) Temporary. — Cartilage forms a support for
the fcetus, and a bed for the deposition of the lime
salts. The cells are small, for the most part angular,
provided with tails, and uniformly scattered through
the matrix, except where ossification is proceeding,
when they arrange themselves in columns. The
matrix is very finely granular.
(b) Costal. — The cells are large and collected
into groups, and contain oil globules ; near the ex-
terior surface the cells are flattened and lie parallel
with the surface. The matrix exhibits a tendency to
the deposition of lime salts, beginning from the cir-
cumference of the cells, though no true bone is formed.
The matrix contains some scattered fibres.
The cartilages of the nose, thyroid, cricoid, trachea,
and bronchi resemble costal, though for the most part
no fibres are to be seen in the matrix.
(c) Articular. — In the layer near the bone the
cells are arranged in columns, though irregularly dis-
tributed near the surface. The matrix is not prone to
calcify, like rib-cartilage. Near the articular surface
the cells resemble the connective tissue cells of syno-
vial membrane.
3S
Cartilage and Bone
FIBRO-CARTILAGE
i. White fibro-cartilage
2. Yellow fibro-cartilage
White Fibro-cartilage differs from hyaline in
having the matrix occupied by
fibres of white fibrous tissue.
It is consequently tougher and
less elastic. Its microscopic
characters resemble white
fibrous tissue rather than car-
tilage, consisting of parallel
wavy fibres with a few cartilage
cells (fig. 1 8). It is distributed
in the following manner : —
i. Inter-articular fibro-car-
tilagesform small pads occupy-
ing a movable joint, their
surfaces being free and lined
by synovial membrane. They
greatly assist in deadening the
effects of shock. They are
present in the temporo-maxil-
lary, sterno-clavicular,acromio-
clavicular, inferior radioulnar
a; articulations, and also in the
£ knee-joint.
"\ 2. Circumferential, serving
, bright stripe ; c, row of clots in bright stripe which are
enlargements of the intercolumnar septa or sarcoplasm. These septa are
represented by the longitudinal lines d. The continuity of these lines
through the bright stripe is difficult to see in the fresh fibre, but is distinct
after treatment with acid. The columns between the longitudinal lines
are the fibrillar or sarcostyles.
these lines are, in reality, the sarcoplasm or interstitial
substance which unites the fibrillar together, and which
appear dark (fig. 27, d) ; seen in cross section the sarco-
plasm appears as a fine network, as it is seen here
surrounding the fibrillar These longitudinal lines
Cardiac Muscular Fibre
exhibit enlargements at regular intervals, the
being situated in or near the clear transverse
(fig. 27, c). A fine membrane
(Krause's membrane) can be
demonstrated running across
each light stripe.
Cardiac Muscular Fibre
differs from ordinary striated
muscle in having very faint cross
stripes and no sarcolemma ; the
fibres are also branched. If the
fibres are acted on by osmic
acid, they are seen to consist (in
mammals') of oblong nucleated
cells, some being forked at
their extremities, and joined end
to end (fig. 28).
Fig. 28.— Muscular fibre cells from heart
* 4 2 5 (Quain's Anatomy). «. 'ine °f junc-
tion between two cells ; b, c, branching
cells.
53
latter
stripe
s =
54 Muscle
II. Non-Striated Muscular Fibre is pale in
colour, is not under voluntary control, and consists of
bundles of contractile cells (fig. 29). It is found in
many parts of the body — walls of stomach and in-
testines, blood-vessels, trachea, oesophagus, ducts, iris,
&c. The cells are elongated or spindle-shaped, with
an oblong rod-shaped nucleus, and are surrounded
by a very delicate homogeneous sheath. The proto-
plasm of the cells exhibits faint longitudinal striation
(fig. 29 a) ; the nucleus shows a fine network similar
to the nucleus of epithelial and other cells. They
vary in length, and are ttiVo i ncn t0 Woo i ncn in
breadth. The cells are held together by a transparent
semi-fluid cement substance.
Chemistry of Muscle
Muscle when removed from the body, or shortly
after general death takes place, enters into the con-
dition of rigor mortis. The chemical features of dead
muscle, or muscle in a condition of rigor mortis, differ
considerably from living muscle.
Dead Muscle is acid in reaction, contains
myosin, various albumins, sugar, extractive bodies, as
kreatin, sarco-lactic acid, xanthin, hypoxanthin, inosit,
salts, &c. (solids, 25 per cent.). Its acidity is due to
the presence of sarco-lactic acid. Potassium salts
and phosphates are especially abundant.
Living Muscle is faintly alkaline, contains no
myosin, but a substance or substances from which
myosin is formed on coagulation of the muscle-
plasma, no sarco-lactic acid, glycogen instead of sugar,
various albumins and extractives, as in dead muscle.
The chemical changes taking place in muscle when
passing into a condition of rigor mortis consist in the
formation of myosin and sarco-lactic acid, change of
Physical Properties of Muscle 5 5
glycogen into sugar ; carbonic acid is set free. Healthy
living muscle even while at rest absorbs O and gives
out C0 2 . The exchange of gases is greatly augmented
during contraction.
Muscle Plasma can be prepared from the
muscles of cold-blooded animals by pounding the
minced muscle with a 1 per cent, solution of salt, kept
at a temperature of 0° C, The filtered fluid {muscle
plasma) is fluid at 0° C, but clots if the temperature
is raised. Muscle plasma is faintly alkaline, but
becomes acid on coagulation, due to the formation of
sarco-lactic acid. The body which separates from
the muscle plasma on coagulation is myosin, the fluid
which remains is muscle serum.
Myosin may be prepared by allowing muscle
plasma to fall, drop by drop, into water ; little balls
of myosin are formed.
Physical Properties of Muscular Tissue
The most important properties of muscles are
extensibility, elasticity, contractility.
Extensibility. — Living muscle is extensile, i.e.
capable of being extended or stretched ; this is
necessary, inasmuch as when one set of opposing
muscles as the extensors of the fingers contract, the
opposing flexors are stretched. The muscles of the
body are always in a state of extension, i.e. always
slightly stretched. Dead muscle is less extensile, and
its elasticity is less perfect than living muscle.
Elasticity. — Muscle possesses but little elas-
ticity ; a small weight will stretch it, but that little is
very perfect, as it returns rapidly and perfectly to its
original length.
Contractility. — Both muscle and nerve in a
living state are irritable, that is, they respond when
a stimulus is applied. The muscle responds by con-
56 Mtiscle
trading, the nerve by transmitting the stimulus to its
termination. This contractility is the characteristic
property of muscle. If a muscle of a recently killed
frog be laid bare, and any form of stimulus applied,
such as the electrodes of a battery or coil, a hot wire,
a chemical substance, or a mechanical injury, it will
be thrown into a state of contraction. The stimulus
may be applied to muscle itself, or to a nerve in con-
nection with the muscle.
Rigor Mortis. — This term is applied to the
stiffening which muscle undergoes at death. In the
human subject rigor mortis is complete in four to six
hours after death, and lasts twenty-four hours to
several days. In exhaustion of muscular power prior
to death, as in animals hunted to death, or in soldiers
killed on the field of battle, it sets in very rapidly,
and is well marked- On the other hand, in wasted
bedridden patients it is ill-developed, and soon passes
off. It commences in the muscles of the jaw, then
affects those of the neck and trunk, next the lower
and finally the upper limbs. The cause of rigor
mortis is the coagulation of the myosin ; the stiffening
is arrested by the injection of a 10 per cent, solution
of common salt. Muscle in this condition is thicker,
shorter, and firmer than living muscle ; it cannot be
excited by any stimuli, it is acid in reaction, from the
formation of lactic acid. It is opaque, and the electric
currents have disappeared.
Idio-muscular Contractions. — If in a patient
suffering from phthisis or some wasting disease, a
superficial muscle, as the pectoralis major, be smartly
tapped, a local contraction, or wheal, is produced
which slowly travels along the muscle in the form of a
wave. This phenomenon is only observed in exhausted
muscle or muscles in which the nutrition is impaired.
Fibrillar contractions may also be seen in wasted
muscles, as in progressive muscular atrophy. These
Muscular Contraction 57
consist in the quivering of local muscular fibres, with-
out any external stimulus being applied.
Phenomena of Muscular Contraction
• 1. Change in Form. — When a muscle contracts
it shortens -that is, its ends come nearer together,
while the muscle itself becomes thicker ; but there is
no change of bulk : what it loses in length it gains in
thickness ; according to Landois the volume is slightly
diminished.
2. Chemical Changes during Contraction.
(a) Oxygen is used up. Living muscle is constantly
consuming oxygen, but more carbonic acid appears
than can be accounted for by the oxygen used, (b)
Carbonic acid is set free, not accompanied by a cor-
responding consumption of oxygen. Probably some
complex body splits up, producing these two acids.
(c) Muscle is normally neutral or faintly alkaline ;
when it contracts it becomes acid, the acidity being
due to the formation of sarco-lactic acid. Other
changes doubtless take place, of which little is
known.
3. Negative Variation of Muscle Current.
Whenever a muscle contracts, a change takes place
in its electrical current. If a muscle when at rest,
arranged so as to show its normal current, be made
to contract or enter into a state of tetanus, the normal
current will undergo diminution during the contrac-
tion. By refined methods it has been shown that the
negative variation occurs during the ' latent period '
of stimulation.
4. Production of Heat during Contraction.
Venous blood coming from an active muscle is
warmer than blood from muscle in a state of rest. The
gastrocnemius of the frog shows an increase of about
one-tenth of a degree C. for each contraction. The
58
Muscle
heat developed depends to some extent on the work
done.
5. Production of Sound during Contrac-
tion. — A sound is emitted from a muscle during
contraction. By placing the ear over a contracting
muscle a deep-toned sound will be heard.
6. Phenomena of a single Muscular Con-
traction. — If the sciatic nerve of a frog while still
attached to the gastrocnemius, and recently removed
Fig. 30. — Muscle curve obtained by pendulum myograph (Foster). A,
moment when the shock is sent into the nerve ; v. the commencement, c the
maximum, n the close of the contraction ; E, curve made by chronograph.
from the animal, be placed upon the electrodes of
an induction apparatus, and a single shock, either
making or breaking, be made, the muscle gives a
short, sharp contraction. If the muscle nerve pre-
paration be arranged in connection with a pendulum
myograph, in which the tendon of the muscle is
attached to a lever recording its movements on a
moving surface, the lever rising during contraction
and falling during relaxation, a curve similar to fig. 30
will be produced. The time occupied in tracing the
curve is marked by the vibrations of a tuning-fork,
recording on the same surface ; the apparatus also
marks the exact moment when the induction-shock is
Mttscular Contraction
59
sent into the nerve. By this means three facts will
be demonstrated : — ■
(a) There is a latent period (A to B, fig. 30), that
is, a short time elapses after the entrance of the shock
into the nerve before the contraction of the muscle
commences. This latent period is occupied by (1)
the passage of the impulse along the nerve, and (2)
certain changes taking place in the muscle itself before
it begins to contract.
(b) There is a period of ascent or contraction (B to C).
This is slow at first, then more rapid, and slower again
A B B'
Fig. 31. — Diagrammatic muscle curves representing electrodes placed on
nerve (producing curve with dotted line) and on muscle (continuous
line) (Foster). A — vj, represents whole latent period, including the
time occupied by nerve impulse in travelling along the nerve, and
changes in the muscle ; R - s' represents time occupied by impulse along
nerve ; A — B represents latent period of muscle.
before the ascent is gained. The rapidity or slowness
of the ascent at the various stages depends upon the
weight to be raised and the exhaustion of the muscle.
(c) A period of descent or relaxation (C to D). This
is more prolonged than the ascent ; it is more rapid
at first than towards the end of relaxation. Exhausted
muscles relax slowly.
If instead of placing the electrodes on the nerve
they are placed upon the muscle itself, a muscle-curve
(fig. 31) will be produced ; the latent period A to B
will be shorter than A to B', in consequence of the
6o
Muscle
time occupied by the impulse travelling down the
nerve being eliminated, the latent period in this case
representing preparatory changes in the muscle itself.
Nerve-impulses in the frog travel at the rate of about
28 metres per second ; in man 33 metres per second.
The latent period of a frog's muscle varies from -pini-th
to o fryth of a second. It is shorter when the muscle is
fresh and when under the influence of strychnia ; it is
prolonged when the muscle is heavily weighted, and
in poisoning with curare.
7. Tetanus. — If single induction shocks are
made to follow each other slowly, a succession of
Fig. 32.— Curve of Incomplete tetanus or clonus (Hermann^. The stimula-
tions succeed each other sufficiently rapidly to conceal the influence of
each stimulation. Had they been more frequent an unbroken curve
would have been produced.
curves are produced. But if they follow more rapidly,
so that there is not time between the shocks for the
muscle to relax, a condition of constant spasm is pro-
duced, known as tetanus. If the tetanus be in-
complete, as in fig. 32, the waves produced by
successive shocks are still perceptible. This is
sometimes termed clonus. In complete tetanus, as
produced by the magnetic interrupter in an induction
machine, these are fused into one continuous curve.
In the gastrocnemius of the. frog twenty-seven shocks
Muscular Exercise 6 1
per second, and rorty per second in man, are re-
quired to throw the muscle into a state of complete
tetanus.
8. Action of Poison on Muscle.— Curare
paralyses the terminations of the motor nerves, so that
stimulation of the nerve produces no contraction, while
direct stimulation of the muscle produces contraction.
The sensory nerves are unaffected. It produces death
by paralysing the respiratory muscles. Veratria causes
an excessive prolongation of the muscular contraction.
9. Fatigue. — Tired muscles are sluggish in their
movements, and their contractions are weaker than
normal muscles. At first the contractions increase in
height and duration ; then they increase in duration,
but diminish in height. Rest refreshes the muscles,
the blood in the meantime bringing it nutrient
materials and carrying away fatigue products. Serum-
albumin, if injected into the blood, acts as a refresher,
Egg-albumin, albumose, and peptones are non-
nutritive, and the latter two are poisonous.
10. Properties of Non-striated Muscle.—
When any stimulus is applied directly to an involuntary
muscle, or to a nerve in connection with it, it contracts.
The latent period is longer than in striated muscle ;
the contraction takes place more slowly, but lasts
longer. The force exerted, as in the uterus in
parturition, or the bladder in expelling urine, may be
very great.
Effects of Muscular Exercise
1. On the Lungs. — Elimination of Carbon.
The most important effect of muscular exercise is to
increase the number of the respirations, and thereby
the quantity of air passing in and out of the lungs,
leading to an increased absorption of oxygen, and
elimination of carbonic acid. An adult, under ordinary
62 Muscle
circumstances, during inspiration draws in 480 cu. in.
per minute ; if he walk four miles an hour, he draws
in five times as much, or 2,400 cu. in. ; if he walk six
miles an hour, he draws in seven times as much, or
3,360 cu. in. Probably the excessive absorption of
oxygen and formation of carbonic acid takes place in
the muscles. For the effects of exercise on carbonic
acid given off during respiration, see p. 137.
2. On the Circulation. — The increased work
performed by the muscles requires increased activity
on the part of the heart, to keep up the supply of
arterial blood. The amount of increase is usually
from 10 to 30 beats during exercise. After exercise
the heart's action becomes slower. Excessive exertion
may lead to hypertrophy of the left ventricle.
3. On the Skin. — The minute arteries of the
skin become dilated, the perspiration is increased,
more water, salts, and acids pass off from the system.
The amount of perspiration may be more than double
the usual amount. The evaporation reduces the tem-
perature of the body, which would tend to rise. There
is danger of a chill after the exertion is over, the skin
still remaining wet while the heat of the body has
declined.
4. On the Voluntary Muscles. — The muscles
grow and become firmer in substance. If, however,
the exercise be excessive, after growing to a certain
extent, they will waste.
5. On the Digestive System.— The appetite
increases with exercise, especially for meat and fats ;
this is doubtless the result of the wear and tear of
the muscles and the increased elimination of carbon.
Digestion is more perfectly performed, and the cir-
culation through the liver and portal system quickened.
6. On the Kidneys.— The water of the urine
and the salts are probably lessened in consequence
of the increased perspiration. It has been shown by
Muscular Movements 63
various observers, including Parkes, that during active
exercise the urea in the urine is not increased, but
active exercise is followed by an increased appearance
of urea. It appears, therefore, that to a certain extent
muscular exercise increases the elimination of urea,
the urea making its appearance in the period of rest
succeeding the exercise.
7- On the Temperature.— The temperature will
not be increased ; the extra consumption of oxygen
and the friction of the muscles tend to raise the
temperature, but the evaporation from the surface of-
the skin prevents much increased heat of body.
Various Muscular Movements
Standing. — In standing the muscles fix all the
joints of the vertebras and lower extremities so as to
form a rigid column ; any disturbance of equilibrium,
i.e. any tendency to fall, is counteracted by muscular
action. The head is fixed upon the vertebral column
by the muscles of the neck ; the vertebral column is
maintained in a state of rigidity by the erector spina?
and other muscles ; the hip, knee, ankle, and tarsal
joints are fixed by the rigid contraction of their exten-
sors and flexors.
Sitting. — In sitting, the body is supported on the
tuber ischii, whilst the head and spine are fixed by
their muscles, the muscles of the legs are relaxed and
therefore at rest ; in leaning back on a support, the
muscles of the back are also in part relaxed.
Walking. — In walking the legs move alternately,
the movements being divided into two acts : —
1. One leg, the active one, is vertical and slightly
flexed at the knee and supports the weight of the
body ; the passive leg is extended, being behind the
other, and touching the ground with the tip of the
great toe.
64 Skin
2. For the forward movement of the body, the
active leg is inclined forward and the knee straight-
ened out (extended), the heel being lifted off the
ground, so that only the tips of the toes touch the
ground ; in the meantime the passive leg leaves the
ground and swings with a ' pendulum-like movement '
forward, touching the ground in front. The passive
leg now becomes the active one, and act 1 is re-
peated.
Running. — In running the active leg as it is
forcibly extended gives the impetus forward, and only
one leg touches the ground at a time.
CHAPTER AT
SKIN
Consists of —
1. Epidermis or cuticle.
2. 1 )crmis, corium or cutis vera.
3. Sweat glands, nails, hair, and sebaceous glands.
1. The Epidermis forms a protective covering
over the whole surface of the body. It varies in
thickness in different parts, being especially thick on
the palms of the hands and soles of the feet, and
wherever the skin is exposed to friction. It is moulded
over the surface of the corium, covering the ridges,
the depressions and the papilte. It is made up of
three principal layers : (a) the horny layer, or stratum
corneum, is the most superficial, and consists of layers
of flattened cells, which are dry and horny, without
any nucleus ; (b) the stratum lucidum, composed of
several layers of nucleated cells, which are more or
less indistinct, and in section appear as an almost
homogeneous layer ; (c) the rete mucosa m or Malpighian
The Dermis 65
layer contains, in its upper part, layers of ' prickle '
cells, and its inferior layer consists of a single stratum
of columnar cells. Pigment is principally found in
the lowest layer (fig. 8, b). According to Ranvier,
fine varicose nerve-fibrils penetrate into the Mal-
pighian layer, and end in knob-like swellings.
L..M
H
-6
-c/
Fig. 33. — Vertical section of skin and subcutaneous tissue x 20 (Quain's
Anatomy), a, horny ; b, Malpighian layer : c, corium ; e, papillae ;
f, fat clusters ; £•, sweat glands ; h, ducts ; z, their openings.
2. The Dermis, or true skin, is made up of an
interlacing network of connective tissue, formed of
white fibrous tissue, yellow elastic tissue, corpuscles,
vessels, and nerves. In some parts of the body, as
F
66 Skin
in the skin of the scrotum, perineum, penis, the cutis
vera contains unstriated muscular fibres. There are
also small muscular fibres in connection with the hair-
follicles. Beneath the skin the subcutaneous tissues
contain abundant adipose tissue. Numerous fine
ridges are seen on the surface of the skin of the palm
of the hand, and sole of the foot. The ridges are
caused by rows of little elevations of the cutis vera,
termed papilla. These little eminences are more or
less conical, or sometimes club-shaped ; they may be
Fig. 34.— Section of a sweat gland (distal end) (Quain's Anatomy).
a, basement membrane ; b, lining cells ; c, lumen of tube.
compound, and contain a capillary loop, nerve, and
touch-corpuscle ; they project into the epidermis, and
by raising it up as it were, form a ridge on the surface
of the skin. They serve to increase the sensitiveness
of the part, lodging a touch-corpuscle in a favourable
position for receiving sensations of touch (fig. 8).
3. Sweat Glands are situated in the subcu-
taneous tissue, and consist of a fine tube which forms
the duct, continuous with a blind extremity which is
coiled up into a ball of -^ inch in diam., and is sur-
rounded by a plexus of capillaries to form the gland
(fig. 33). The distal part of the gland— namely,
Nails 67
some three-fourths of the coiled-up tube nearest the
blind extremity — is of greater diameter than the rest,
and is formed of a single layer of columnar cells, while
between this and the limiting membrane is a layer
of non-striated muscular cells (Klein) ; the lower fourth
of the coil and also the sudoriferous canal as far as the
rete mucosum consists of several layers of polyhedral
cells, an external limiting membrane and also an
internal limiting membrane ; the epithelium of the
duct is at its mouth continuous with the epithelium
of the epidermis. The largest number of sweat glands
are present in the palm of the hand ; next, in the sole
of the foot.
Nails. — The nail consists of a root and body.
The root is that part of the nail which is covered by
the skin, the body the external part which ends in the
free edge. The lunula is the whitish portion of the
body near the root, where the skin beneath is less
vascular.
Structure. — The nail closely resembles the epider-
mis, and is, in fact, a modification of that structure,
consisting of hard and thin layers of cells on the sur-
face and round moist cells beneath, corresponding
to the rete mucosum. Posteriorly the nail fits into a
groove which lodges its root. The part of the cutis
vera to which the root is attached is called the matrix,
and is provided with large papillae. The part to which
the body of the nail is attached is called the nail-bed.
Hairs consist of a shaft and root. The shaft
of the hair is cylindrical, and covered with a layer of
imbricated scales, arranged with their edges upwards.
The substance of the hair consists of fibres, or elon-
gated fusiform cells, in which nuclei may be dis-
covered. There are also present in some hairs small
air-spaces, or lacuna?. In the coarser hair of the
body there is the medulla, or pith, which is occupied
by small angular cells and fine fat-granules.
68
Skin
The root of the hair swells out into a knob, and
fits into a -recess in the skin, called a hair follicle.
The follicle consists of two coats, an outer, or dermic
coat, continuous with the corium, and an inner, con-
tinuous with the epidermis, and called the root-sheath
(figs. 35 and 36). The outer, or dermic, consists of
three layers : (a) formed of connective tissue, blood-
vessels and nerves ;
(b) principally of
corpuscles and a
fibrous matrix ; (c)
inner coat consists
of a homogeneous
membrane. The
inner, or epidermic
coat, comes away
when the hair is
pulled out, and
hence is called the
root-sheath. It is
made up of two
layers, the outer
root-sheath and
inner root-sheath.
The outer root-sheath
corresponds with
the rete mucosum,
and is thicker than
the inner, and is
composed of large
rounded cells. The
inner root-sheath corresponds with the horny layer. It is
composed of flattened cells. The deeper cells of the
inner root-sheath form what is called Huxley's layer.
The bulbous root of the hair fits on to a papilla,
which is very large in the tactile nasal hairs of the cat.
Small bundles of involuntary muscular fibres connect
Fig. 35. — Magnified view of a hair-follicle
- (Quain's Anatomy). a, hair showing
medulla, fibrous substance, and cuticle ;
b, inner, and c t outer root-sheath ; d,
dermic or external coat ; e, imbricated
scales forming a cortical layer on the
surface of the hair.
Functions of the Skin
69
the corium with the root of the hair, so that in con-
tracting they elevate the hair.
The Sebaceous Glands consist of a small duct,
which opens into the hair follicle, and is connected
by its other end with a cluster of saccules lined with
epithelium, which secrete fatty matters.
Functions of the Skin. — 1. The skin every-
where clothes the external surface of the body, pro-
tecting the underlying
parts from injury. 2. It
affords support and pro-
tection to the termina-
tions of the sensory
nerves, which render it
an important sense
organ. 3. It is a bad
conductor of heat, and
thus serves to preserve
the heat of the body.
4. It is supplied with a
large extent of capillary
blood-vessels, and thus
by its means a large sur-
face of blood is exposed
to the cooling influence
of surrounding bodies.
The dilatation or con-
traction of the blood-
vessels supplying the
skin will help to regu-
late the heat of the
body. 5. The sweat-
glands which it contains
make it an important excretory organ. 6. It plays a
subsidiary part as an organ of respiration. 7. Under
exceptional circumstances, absorption takes place from
its surface.
Fig. 36. — Section of hair follicle
(Quain's Anatomy). I, dermic
coat ; a, outer layer of dermic
coat ; bb, blood-vessels ; c, middle
layer ; d, inner or hyaline layer :
2, epidermic coat or root-sheath ;
e, outer root-sheath ; fg, inner
root-sheath ; k, cuticle of root-
sheath ; i, hair.
7 tne mus k deer the
smallest, ^j T inch. They are oval in the camel tribe.
In birds, reptiles, amphibians, and fishes the coloured
corpuscles are elliptical discs, the proteus having the
largest, ^^ inch by -j^ inch ; they have also a pro-
minent central nucleus. The red corpuscles are soft,
elastic, and while pressure changes their shape, they
readily regain it. When examined shortly after being
drawn from the vessels, they adhere together by their
surfaces, and appear like rolls of coins.
Number.— There are about 5,000,000 red cor-
puscles per cubic millimetre in the body in health.
This number is diminished after haemorrhages and in
anaemia from whatever cause ; in one case of anaemia
recorded by Gowers there were only 1,290,000 per
cub. mill, present in the blood. The estimation of
the number for clinical purposes is made by means of
the haemacytometer of Gowers. This apparatus pro-
vides the means of mixing five cub. mill, of blood with
995 cub. mill, of a solution of sodium acetate of
s.g. 1025 ; a drop of this solution is then placed in a
cell in the centre of a glass slip such as are used for
microscopic purposes, the floor of which is divided
into squares, each being ^ mill, square ; the cor-
puscles settle on to these squares, and when placed
under a microscope the number in each square can
be counted and the total number thus calculated.
Structure. — The red blood-corpuscles consist of
(1) the stroma, i.e. a transparent soft framework of
protoplasm ; (2) haemoglobin, a crystalline colouring
matter which pervades the stroma.
Effects of Reagents.— Water.— Salt Solu-
tion. — According to Schafer the red blood-corpuscles
consist of an envelope or membrane with fluid coloured
o
Effects of Reagents 75
contents. The effect of water on the corpuscles
appears to favour this view, as they gradually imbibe
the water and swell out (fig. 38). On the other hand,
a three-quarter per cent, salt solution, or any fluid of
greater density than the blood plasma, causes them
to shrink by exosmosis and become crenated or horse-
chestnut-shaped (fig. 38, /).
Carbonic Acid.— If the horse-chestnut-shaped
corpuscles be treated with carbonic acid gas, they
again become smooth, , j
though they do not regain
their original biconcave
form, but are more or less
concavo-convex. 1,
Tannic Acid.— If the •-£$' ^Q|
horse-chestnut-shaped cor- ^*
puscles are treated with F ^^ ™ H *=£££ °-
2 per Cent, tannic acid, "•, corpuscle seen edgeways,
, t . , 1 l • slightly swollen ; b-c, one of the
their haemoglobin Sepa-, sides bulged out; d, spherical
rates itself from the stroma *°™ ; ": decolorised stroma;
_ , . . _/, horse-chestnut-shaped effect of
Ot the COrpUSCleS, and IS salt solution ; g, action of tannin
extruded in drop-like «p°n a red corpuscle,
masses. From this experiment it has been stated that
the corpuscles are formed of a colourless stroma con-
taining hemoglobin (fig. 38, g).
Boracic Acid. — In newt's blood, treated with
2 per cent, boracic acid, the nucleus becomes of
deeper colour at the expense of the disc, and a fine
network of fibrils is displayed, which pervades both
disc and nucleus. This fine network is occupied
normally by haemoglobin, and a homogeneous inter-
stitial substance.
Chemical Constituents of Red Corpuscles.
1. Haemoglobin. 3. Salts.
2. Globulin. 4. Gases.
5. Water.
7 6
The Blood
i. Haemoglobin contains C.H.O.N.S.Fe., and
forms 90 per cent, of (dried) red corpuscles. It is
soluble in water and serum, crystallising in man and
many mammals in elongated rhombic prisms, octa-
hedral in the guinea-pig, and hexagonal in the squirrel.
It can be obtained in crystals from the guinea-pig,
Fig. 39. — Blood-crystals, magnified. 1, human blood ; 2, guinea-pig ;
3, squirrel ; 4, hamsler.
dog, rat, or mouse, but with difficulty from the blood
of sheep, ox, or pig (fig. 39).
Preparatioti. — The haemoglobin is made to leave
the corpuscles by shaking with ether or by alternately
freezing and thawing the blood. The blood is thus
rendered translucent or ' laky ' ; one quarter of its
bulk of alcohol is added, and it is placed in a tem-
perature of 0° C. to crystallise.
Hsemoglobin exists in the human blood in two
forms, one in loose combination with oxygen — oxy-
Hcemoglobin
hemoglobin— and the other as reduced haemoglobin.
During the circulation of the blood, the O in combina-
Red. Orange
Blue.
Reduced
Hsematin
bo
A a b C Eh F
Fig. 40.— Spectra of haemoglobin and its compounds.
tion with haemoglobin is very readily given up to the
tissues. If oxy "hemoglobin be acted upon in solu-
tion with a reducing agent, as a solution of ferrous
78 The Blood
sulphate and tartaric acid with excess of ammonia, it
is reduced and becomes of a purplish red colour.
Oxy-haemoglobin gives in the spectrum two narrow
dark bands in the yellow and green, reduced haemo-
globin a single broad dark band intermediate in posi-
tion between the two (fig. 40). Haemoglobin readily
decomposes, forming haematin and globulin. Haemo-
globin gives a characteristic blue colour when treated
with tr. guaiaci and solution of peroxide of hydrogen.
Methaemoglobin is found in old blood-stains
and in bloody urine ; it gives four bands in the spec-
trum (fig. 40, 5.).
CO-Haemoglobin is a more stable compound
than oxy-haemoglobin, and is formed in the body
when CO is inhaled, carbonic oxide displacing the
oxygen in the haemoglobin, the animal quickly dying.
CO-haemoglobin is of a florid red colour, and gives
two absorption bands in the spectrum very like- those
of oxy-haemoglobin, but they are nearer the violet
end of the spectrum and somewhat nearer together.
These bands may be seen in the examination of the
blood of persons poisoned by coke or charcoal fumes
(fig. 40, 3).
Haematin is a black amorphous body containing
iron, and is formed when haemoglobin is decomposed ;
it is insoluble in water but soluble in dilute acids or
alkalies ; acid haematin gives four absorption bands
in the spectrum, alkaline haematin gives one absorp-
tion band, and reduced alkali-hsematin gives two
(fig. 40, 6, 7).
Hajmin. — Haematin forms with HC1 a com-
pound called hasmin, which crystallises in minute
rhombic prisms. Haemin crystals are prepared by
adding a small crystal of common salt to dried blood
on a slide, and an excess of acetic acid : on gently
heating and allowing to cool, the crystals form. The
presence of these crystals is used as a test for blood.
Origin of the Red Corpuscles 79
Haematoidin. — Crystals of hasmatoidin are found
where haemoglobin has decomposed, as in old clots of
blood in the body. It is supposed to be identical with
bilirubin.
2. Globulin or Paraglobulin. See Coagulation.
3. Salts. — These amount to 1 per cent, of the
dried solids, the principal salts being those of potas-
sium and phosphates.
4. Gases. — Oxygen loosely combines with the
haemoglobin. Nitrogen in small quantity. The
amount of carbonic acid gas in the corpuscles is un-
certain ; by far the greater part exists in the serum
(see p. 83).
5- Water forms 56-5 per cent, of the corpuscles.
Origin of the Nucleated Red Blood-cor-
puscles in the Embryo. — From cells in the vas-
cular area of the mesoblast. These mesoblastic cells
become branched, and their processes join together,
so that an irregular network of granular corpuscles is
formed. The nuclei multiply, some form corpuscles
which acquire a reddish colour, others remain to form
the epithelium of the capillaries. The first formed
red corpuscles are nucleated cells, exhibit amceboid
movements, and multiply by division. In the human
embryo up to the end of the first month all the red
corpuscles are nucleated. These primary nucleated cor-
puscles are gradually succeeded by ordinary red cor-
puscles, and before the end of intra-uterine life the
nucleated ones have disappeared.
Origin of the Red Blood-discs in the
Adult. — 1. From the nucleated corpuscles in the red
marrow of bone (Neuman's cells). Peculiar cells are
seen in the marrow filling the spaces of the cancellous
tissue of the ribs, flat bones, and the ends of the
long bones, which are apparently intermediate forms
between marrow cells and red blood-corpuscles.
They closely resemble the nucleated red corpuscles
80 The Blood
of the embryo. 2. From the leucocytes or white blood-
corpuscles. 3. From the blood-platelets.
Fate of Red Corpuscles. — Probably broken
up in spleen and liver. Haemoglobin probably forms
bile-pigments.
White Corpuscles or Leucocytes
The white corpuscles in human blood are
spheroidal, finely granular masses of g-gVo inch, in
diameter. In a cubic millimetre of human blood
there are about 10,000 white corpuscles. Some of
them are of less size, being smaller than the red cor-
puscles. They have a lower specific gravity than the
red. They have no cell-wall, and their substance
consists of protoplasm. According to Heitzmann,
their granular appearance is due to a fine intercellular
network, having small dots at the intersections of the
network. In the meshes of the network there is a
hyaline substance. They possess one or two nuclei,
which are readily brought out by acetic acid. When
examined in a fresh state, especially if placed on a
warm stage, they exhibit spontaneous change of shape
like the amoebae, these movements being termed
amoeboid. The movements consist in a protrusion of
processes of protoplasm, which are retracted and other
processes protruded.
Both in human and newt's blood there are some
colourless corpuscles which contain coarser granules
than others ; these are called granular corpuscles.
The white corpuscles will take up coloured foreign
particles, as vermilion. They are found in various
tissues of the body, as in the meshes of the retiform
tissue of lymphatic glands, tonsils, solitary glands, &c.
In inflammation they pass through the walls of the
capillaries into the tissues. They are present in the
blood in the proportion of 1 per 300 red corpuscles
White Corpuscles 81
after a meal, and i per 800 during fasting ; they are
much more numerous in some diseases, as in leuco-
cythaemia.
Composition :—
1. Several albuminous substances.
2. Lecithin and glycogen.
3. Salts, mainly potassium and phosphates.
4. Water.
Origin. — Probably from the lymphoid tissues of
the body, i.e. lymphatic glands, solitary glands, spleen,
&c, by division of the leucocytes existing there. The
thoracic duct and lymphatics are constantly pouring
white cells into the blood, derived from the mesenteric
and other lymphatic glands.
Fate. — They are possibly converted into red cor-
puscles. During inflammation they pass through the
capillary walls, and are converted into pus cells ; it is
also probable they are utilised in other ways than in
forming pus, possibly being converted into the cell-
elements of new tissues, or taking the place of worn-
out cells throughout the body. They seem to play a
part in the formation of fibrin ferment.
Blood-platelets. — These are colourless, oval
discs, found in the blood, and named blood-platelets,
by Bizzozero. They are best seen in the blood of the I
guinea-pig.
Liq. Sanguinis is a clear yellow alkaline fluid in
which the corpuscles float. It may be obtained by
allowing the slowly coagulable blood of the horse to
stand in a tall vessel surrounded by ice. The tem-
perature of o° C. prevents coagulation, the corpuscles
subside, and the clear fluid may be removed by pipette.
Its Composition may be described as blood minus the
blood corpuscles.
Serum. — When blood has coagulated, and the
G
82
The Blood
clot separated, a thin yellow transparent alkaline fluid
is left, of specific gravity 1028.
Human serum consists of —
I.
Albumin
4-5 per cent
2.
Paraglobulin .
3'i
3-
Extractives .
■2 „
4-
Fatty matters
•2 ,,
5-
Salts .
■85 „
6.
Water and gases .
9i-
1. Albumin exists in combination with the so-
dium as an albuminate. It is in the form of serum-
albumen, differing from egg-albumen in not being
coagulated by ether. On boiling the serum, the
albumen coagulates ; the fluid, after being deprived
of its albumen, is called serosity.
2. Paraglobulin (serum-globulin), one of the
fibrin factors, is present, all the fibrinogen disappearing
during coagulation.
3. Extractives include kreatin, kreatinin, urea,
uric acid, and traces of grape sugar.
4. Fatty Matters in minute division, and com-
bined with sodium as soaps.
5. Salts, principally sodium salts, in combination
with CI and C0 2 , smaller quantities of potassium and
calcium phosphates and sulphates.
6. Gases. — C0. 2 , partly free, and partly in com-
bination with the sodium.
Gases of the Blood
In human blood it has been calculated that 100
vols, of blood contain : —
o co =
Arterial blood 20 vols. 39 vols.
Venous blood 8-12 „ 46 „ 1-2
measured at o° C. and 760 mm.
N
1-2 VOls.
Gases of the Blood 83
Oxygen is present in arterial blood in the pro-
portion of 20 per cent. ; in venous blood the amount
necessarily varies according to whether the blood has
passed through an organ in a state of activity or in a
state of rest. In asphyxia oxygen may be entirely
absent from the blood. Nearly the whole of the oxy-
gen is in loose chemical combination with the hemo-
globin of the corpuscles. The oxygen of the blood
can be expelled from it by means of the mercurial air-
pump ; no oxygen escapes till the pressure is reduced
to 125 mm., or about -j=th of the ordinary atmospheric
pressure ; the gas is then rapidly given off and the
blood becomes dark. The oxygen can also be ex-
pelled by passing other gases, CO, NO, N or H,
through the blood. It can also be extracted by reduc-
ing agents, as ammonium sulphide and Stokes's fluid
(sulphate of iron, tartaric acid with excess of ammonia).
Carbonic Acid.— This gas is present in arterial
blood in the proportion of about 39 per cent. ; in
venous in variable amount, according to the vein from
which it is taken and the activity of the organ yielding
it ; it averages 46-50 per cent. C0 2 is present in the
liq. sanguinis in combination with sodium ; a part,
the ' loose ' C0 2 , so called on account of its being
readily given off in the mercurial air-pump, is in com-
bination with sodium as the hydro-sodic carbonate
(NaHC0 3 ) ; and part also as 'fixed' C0 2 , as it can
only be expelled by an acid, being in the form of
sodic carbonate, Na 2 C0 3 . When hydro-sodic car-
bonate is exposed to diminished pressure in the air-
pump, C0 2 is given off as follows : —
2 NaHC0 3 =C0 2 + Na 2 C0 3 + H 2 0.
Carbonic acid -is also present in small quantities in
the red corpuscles in loose chemical combination
(Ludwig).
Nitrogen exists simply dissolved in the blood.
84 The Blood
Coagulation of the Blood
Blood drawn from a living animal into a beaker
first becomes viscid and then is converted into a jelly.
This jelly is of the same bulk as the previous blood.
Finally, the jelly contracts, forming the clot, and a
yellow clear liquid, the serum, oozes out. In man
blood becomes viscid in two or three minutes, forms
a jelly in five or six minutes later, and a few minutes
later still the serum begins to appear. In the horse
coagulation goes on more slowly, so that the cor-
puscles have time to sink before the jelly stage is
reached ; so that a yellowish stratum is formed on the
top, free from red, but containing white corpuscles,
called the ' buffy coat.' This buffy coat appears in
human blood in certain inflammatory conditions.
Many circumstances favour or postpone the co-
agulation of the blood. The principal are —
Circumstances favouring Coagulation
1. Contact with foreign matter.
2. Moderate temperature, ioo c to 120° F.
3. Stasis of blood in the vessels, or injury to or
inflammation of the lining membrane.
Circumstances retarding Coagulation
1. Contact with lining membrane of the blood-
vessels.
2. Cold (o° C.) indefinitely postpones.
3. Addition of neutral salts, or the caustic alkalis.
Contact with foreign matter quickly determines
coagulation, while contact with the endothelium of
the blood-vessels exercises a restraining influence. If
the jugular vein of a horse be ligatured at both ends
Coagulation of the Blood 85
and cut out, the blood will remain fluid, apparently
indefinitely or until decomposition sets in, but will
clot on being withdrawn. Blood will remain fluid
for several days in the excised heart of the turtle.
Horse's blood allowed to stand surrounded by ice will
remain fluid indefinitely. Blood drawn into a saturated
solution of sodic phosphate will remain fluid, but will
clot if diluted.
The immediate cause of coagulation is the forma-
tion of fibrin, of which blood yields about -2 per cent.
According to A. Schmidt, fibrin is formed by the
union of two albuminous bodies present in the blood
— paraglobulin and fibrinogen ; a third body, of the
nature of a ferment, is essential, or at any rate favours
the process. The ferment is derived from the white
blood-corpuscles. According to Hammarsten coagu-
lation is brought about by the conversion of fibrinogen
into fibrin, under the influence of fibrin-ferment.
Paraglobulin playing only a minor part in that, it
leads to a more abundant clot when present. Injec-
tion of albumose into the blood-vessels of a dog
prevents coagulation, as blood drawn shortly after fails
to clot. In some diseases, such as diphtheria, albu-
moses are formed in the blood and tissues, and act
as virulent poisons, profoundly altering the blood, and
giving rise to a non-coagulation of the blood and a
tendency to haemorrhage.
Fibrin. — This substance may be obtained by
stirring some freshly- drawn blood with a stick or
bundle of twigs. It is a white stringy body, insoluble
in water or alcohol, soluble in alkalies, lactic, phos-
phoric, and acetic acids. HC1 converts it into
syntonin.
Paraglobulin (Serum-globulin) may be ob-
tained from serum by passing through it a stream of
C0 2 , or saturating it with NaCl or MgS0 4 . It is
thrown down as a granular white precipitate.
86
The Blood
Fibrinogen may be obtained in a similar manner
by passing C0 2 through hydrocele or pericardial fluid,
or saturating with NaCl. These fluids, however, are
not constant in their compositions, and sometimes they
contain no fibrinogen.
The Ferment is obtained by adding defibrinated
blood to twenty times its bulk of alcohol ; a precipitate
of albuminous bodies with the ferment is thrown down.
Distilled water dissolves out the latter, and if added
to a solution containing fibrinogen and paraglobulin,
coagulation quickly ensues. It has not been isolated
as a solid substance.
Amount of Blood in Body. — Probably about
■yzth. of the body-weight as estimated by the hemo-
globin of the blood. By calculating the amount of
blood escaping from the body of a decapitated criminal,
by weighing the solid residue, after the addition of
the blood washed out of the blood-vessels by injection
of water, Lehmann estimated the amount of blood as
being i in 8.
In a new-born child it is i in 19.
Quantitative Composition of Human
Blood as a whole : —
Water .
. 790 parts
Fibrin .
2 „
Haemoglobin
• 140 »
Albumen, &c.
• 60 „
Salts .
■ 8 „
The Circulation 87
CHAPTER VIII
THE CIRCULATION
The circulation is carried ori by means of the —
1. Heart, beating about seventy per minute,
alternately receiving blood from the venous system,
and discharging it into the pulmonary artery and
aorta.
2. Arteries, with elastic and muscular walls, form-
ing channels for the blood to the system, assisting the
heart in maintaining the circulation, and regulating the
supply of blood to different parts.
3. Capillaries. — Canals of minute calibre, with
thin permeable elastic walls, allowing both liq. san-
guinis and white corpuscles to pass through their
walls into the surrounding tissues.
4. Veins, forming channels back to the heart,
provided with muscular walls and valves, and being
sufficiently capacious to hold the total blood of the
body.
THE HEART
The heart consists of four chambers with con-
tractile walls, situated in the chest, and surrounded
by a fibro-serous sac — the pericardium — in which it
works.
The Pericardium. — This membranous sac is
attached below to the diaphragm, while its upper and
narrower part surrounds and is attached to the great
vessels connected with the base of the heart. ' It
consists of an external fibrous layer, and an internal
serous sac. The fibrous layer is a tough, dense
88 The Circulation
membrane, attached below to the central tendon and
muscular fibres of the diaphragm ; above it is at-
tached to the great vessels, and is continuous with
their external coats. The serous covering consists of
a parietal layer, which is united to the inner surface
of the fibrous layer, and a visceral, which is reflected
round the great vessels enclosing the aorta and pul-
monary artery in a common sheath. In structure the
serous layer resembles other serous membranes.
General Description of the Heart. — In
form, the heart resembles a cone, its base being
directed upwards, backwards, and to the right, its
apex downwards, forwards, and to the left. In part it
is covered by the lungs, especially during inspiration.
Its apex-hesX is felt at the fifth intercostal space, two
inches below the nipple, and one to the inner side of
the left nipple line. In order to map the outline of
the heart on the chest-wall, define the base by drawing
a transverse line across the sternum corresponding
with the upper border of the third costal cartilages,
continuing it i inch to right of sternum, and i inch
to left. Loiver border. — Draw a line from the apex-
beat through the sterno-xiphoid articulation to the
right edge of sternum. Right border. — Continue last
line with an outward curve to join the right end of
the base line. Left border. — Draw a line curving to
left (inside nipple) from the apex-beat to the left end
of the base line.
Cavities of Heart. — The heart contains four
chambers, two auricles and two ventricles.
The Right Auricle receives the blood from
the superior and inferior venae cavse at its upper and
lower posterior angles. The septum between the two
auricles forms the posterior wall, and presents the
fossa ova/is (fig. 41, 3'), the remains of the foramen
ovale, which is surrounded by a border (except below),
the annulus ovalis. Between the two orifices of the
Cavities of the Heart
89
venae cavse is the tubercle of Lower (fig. 41, 3), and in
front of the opening of the inferior vena cava is the
m_S:
Fig. 41. — The right auricle and ventricle opened and part of the wall
removed so as to show their interior (Quain's Anatomy), i, superior
vena cava ; 2, inferior vena at the place where it passes through the
diaphragm ; 2', the hepatic veins cut short ; 3, tubercle of Lower ; j, fossa
ovalis, the Eustachian valve is just below ; 3", opening of the great
coronary vein and valve ; 4, 4, right ventricle ; 4', large anterior columnar
cornea ; 5, the anterior ; 5', the inferior ; 5", septal segment of the tri-
cuspid valve; 6, interior of the pulmonary artery; 7, 8, aorta; 9, inno-
minate and left carotid artery; 10, left auricular appendix; n, 11, left
ventricle,
90 The Circulation
Eustachian valve. The coronary vein opens into the
auricle between the inferior cava and auriculo-ven-
tricular opening, and is guarded by the valve of
Thebesius (fig. 41, 3"). The auricular appendix is a
tongue- shaped appendage, which projects from the
anterior angle, and covers the root of the aorta. The
cavity of the auricle is smooth, except that of the
auricular appendix, which presents the muscular bands
called musculi pectinati. The openings into the right
auricle are the following : (1) Openings of vena?
cavae ; (2) auriculo-ventricular opening ; (3) orifice of
coronary sinus ; (4) openings of one or two small
veins of right ventricle ; (5) foramina Thebesii, which
are small depressions, some of them transmitting
minute veins.
The Right Ventricle forms the right border and
chief part of the anterior surface of the heart. At its
base are two orifices guarded by valves, the auriculo-
ventricular and the pulmonary artery. The inner
surface presents muscular elevations termed columna
carnea, some of which are attached by their ex-
tremities to the wall of the ventricle, others are at-
tached along their whole length, while a third set are
connected by their bases to the ventricular wall, and
are connected by their other extremities to the seg-
ments of the tricuspid valves, by means of the chordce
tendinece (see fig. 41).
The Left Auricle is situated at the posterior
part of the base of the heart. It receives two pul-
monary veins on each side, and opens into the left
ventricle through the mitral valve. The interior of
the left auricle is smooth like the right, its appendix
presenting musculi pectinati.
The Left Ventricle forms the left margin of
the heart, the greater part of the posterior, and a small
part of the anterior surface. Its walls are some three
times as thick as the right ventricle, its musculi papil-
Valves of the Heart 91
lares are larger, and the chordae stronger. Like the
right ventricle, it has two orifices, auriculo-ventricular,
guarded by the mitral, and the aortic, guarded by the
semilzttiar valves.
Endocardium. — The internal membrane lining
the heart closely resembles the lining membrane of
the arteries. It consists of a single layer of tesselated
epithelium, with a connective-tissue layer beneath.
Valves of Heart. — The mitral and tricuspid
valves are situated at the auriculo-ventricular orifices,
and prevent the passage of blood into the auricles
during the ventricular systole. They consist of flaps
or cusps, two in the mitral, and three in the tricuspid,
connected by their bases to the auriculo-ventricular
orifices ; their free margins and lower surfaces give
attachment to the chordae tendineEe which connect
them with the musculi papillares. They are formed
of a duplicature of the lining membrane of the heart,
strengthened by connective tissue. During the ven-
tricular systole, the pressure of the blood in the
ventricles presses their free edges, or rather their
marginal surfaces, together, the musculi papillares
regulating the tension of the chords and preventing
the valves from becoming retroverted into the au-
ricles.
The semilunar valves guard the aortic and pul-
monary openings. They consist of three semicircular
folds attached by their convex margin to the wall of
the artery at its junction with the ventricle, and are
formed by a reduplication of the lining membrane
strengthened by fibrous tissue. In the centre of each
free margin is a little nodule, the corpus Arantii,
the three meeting in the centre when the valves are
closed. On each side of the corpora Arantii is a thin
semilunar marginal surface, where the fibrous tissue
is absent, called the lunula ; these surfaces come in
contact when the valves close. After the systole of
92 The Circulation
the ventricles, the tension of blood in the aorta and
pulmonary artery closes the valves by distending them
and pressing the marginal surfaces together. The
semilunar valves during the ventricular systole are
pressed back against the walls of the aorta, and hence,
according to Briicke, prevent the filling of the coronary
arteries which arise from the sinus of Valsalva during
the ventricular systole, the coronary arteries being
filled after the closure of the valves and during the
diastole of the ventricle.
Sounds of the Heart. — First sound. — Best
heard at the apex-beat. It is synchronous with the
ventricular systole, commencing immediately the
ventricle begins to contract, but ceases before its
completion (see fig. 42, outer ring). It is louder,
longer, duller, than the second sound. Various
explanations have been given as to its cause ; none
of them are entirely satisfactory. It has been
ascribed to : —
(1) Closure of auriculo-ventricular valves ; (2)
muscular sound of contraction of ventricles ; (3) car-
diac impulse against chest-wall.
The closure of the auriculo-ventricular valves
seems the most probable cause, as when these valves
are diseased the normal first sound is replaced by a
murmur. The last explanation (3) is improbable.
A systolic murmur or blowing sound is heard at the
apex of the heart when the mitral valve is imperfect
and allows of regurgitation. In ' button-hole ' mitral
— that is, when the passage between the mitral valves
is narrow so as to resemble a small button-hole — a
presystolic murmur is heard, the murmur in this case
being synchronous with the auricular systole.
The second sound is short and sharp ; it is heard
best at the junction of the third right costal cartilage
with sternum, and corresponds to the closure of the
semilunar valves, Between the first and second
Sounds of the Heart
93
sounds the pause is very short, but between the
second and succeeding first the pause is longer, and
is about equal in duration to the time occupied by
the first and second sounds together (fig. 42). In
certain abnormal conditions of the aortic valves, when
the valves fit together imperfectly and allow of re-
gurgitation, ' double ' murmurs are heard at the base
of the heart, replacing the first and second sounds.
Fig. 42. — Diagram illustrating sequence of events in a cardiac revolution.
The roughened valves both obstruct the blood-current
and allow also of regurgitation, and thus an abnormal
sound is produced during both systole and diastole.
Doubling, or reduplication of the first or second sound,
is produced by the two sides of the heart not acting at
the same moment ; this condition is sometimes present-
in Bright's disease, when the tension is abnormally high
in the arterial system. Normally the aortic valves close
£ s to ¥ V sec. before the pulmonary valves, on account
94
The Circulation
of the greater tension in the aorta (see p. 97). Accord-
ing to Potain, normally there is a reduplication of the
second sound at the end of inspiration and beginning
of expiration.
The sounds have been likened to the pronuncia-
tion of the syllables lubb, dup.
A Cardiac Revolution.— A complete cardiac
cycle includes : (1) systole of the auricles ; (2) sys-
tole of the ventricles ; and (3) a passive interval
(see fig. 42).
(1) The auricular systole commences in the
muscular fibres surrounding the great veins, the
contraction running through
vessels and auricles in a peristaltic
wave, emptying the contents of
the vessels into the auricle, and
then emptying the auricle itself,
the appendix being the last part
to contract, the ventricles be-
coming filled. Regurgitation into
the great veins is ^hindered by
(a) Peristaltic contraction of the
muscular walls of the veins, their
mouths becoming narrowed ; (b)
Aspirating power of thorax during
inspiration ; (c) Valves at junc-
tion of subclavian and internal
jugular veins. Regurgitation
into the coronary sinus is pre-
vented by the valve of Thebesius.
(2) Then follows immediately the systole of the
ventricles. The ventricles become tense and hard,
change from a rounded to a more conical form ; the
heart twists on its long axis from left to right, and
ejects the ventricular contents — 5 to 6 oz. of blood —
into the aorta or pulmonary artery ; the auriculo-
ventricular valves close at the commencement of the
Fig. 43. — Transverse sec-
tion through the middle
of the ventricles of a
dog's heart in diastole
and in systole (Ludwig.)
A Cardiac Revolution
95
ventricular systole, while the semilunar valves open.
The ventricular systole is not so simple as it at first
sight appears ; the first stage or act consists in the
sudden hardening of the ventricular walls at the com-
mencement of their contraction ; the second is the
forcible ejection of their contents, followed by closure
of the semilunar valves ; thirdly, there succeeds a
quiescent period, when they remain empty and con-
tracted. The first stage, which is synchronous with
the ' cardiac impulse,' is registered on the cardio-
a le & a' h'
Fie. 44. — Tracing obtained by a cardiograph placed directly on the ventricle
of a cat's heart (Foster), a — b, corresponds to the distension of the ven-
tricle, during the auricular sj'Stole ; b — c, the time during which the ven-
tricles change their shape from a flattened to a rounded form ; e, marks the
closure of the auriculo-ventricular and opening of the semilunar valves ;
c — d, the expulsion of the ventricular contents, and time during which
the ventricle remains contracted ; d — a', relaxation of the ventricles.
The semilunar valves probably close atyC
graphic tracing (fig. 44) by the sudden rise of the
lever, b e ; the other two are included in that part of
the tracing between e and f. The semilunar valves
open and the auriculo-ventricular close at e, at the
commencement of the active contraction, and the
semilunar valves close and the auriculo-ventricular
open at f, at the end of the systole. The time oc-
cupied by a complete beat is about "8 sec. It will be
96 The Circulation
divided in the following manner, supposing that the
heart is beating at 60 per minute : —
Contraction of auricles = -!- sec.
Dilatation of auricles = f- sec.
Contraction of ventricles = -f sec.
Dilatation of ventricles = f sec.
or,
Auricular systole = \ sec.
Ventricular systole = % sec.
Pause = -f sec.
(See fig. 42.)
Some observers make the auricular systole occupy
•j' v sec. instead of i. Thus : —
Auricular systole = T V sec.
Auricular diastole = T 9 a sec.
Ventricular systole = x 4 - sec.
Ventricular diastole = -^ sec.
(3) The passive interval which follows the
ventricular systole corresponds with the auricular
diastole, blood pouring from the great veins into the
auricle.
Cardiac Impulse. — The impulse of the heart
may be both seen and felt in the fifth intercostal space,
midway between the left edge of the sternum and a
line drawn vertically through the nipple. It is most
marked during expiration, and disappears or diminishes
at the end of inspiration, inasmuch as the heart's apex
is separated from the chest-wall by lung. It is caused
by the sudden hardening of the left ventricle during
the systole, and probably also in part by the heart
twisting slightly on its axis, the apex being brought
more forward.
A tracing can be obtained from the cardiac im-
pulse in a man by means of a cardiograph. Fig. 45
shows the curve registered by the impulse of the
Work done by Heart
97
heart of a healthy man ; a b corresponds to the auri-
cular systole, the ventricles being filled with blood ;
b c, c e, correspond
with the apex-beat
and ventricular sys-
tole ; d and e mark
the closure of the
aortic and pulmonary
valves, the aortic
closing J n sec. before
the pulmonary ; e /
marks the diastole of
the ventricles.
Work done by
the Heart. — It has
been calculated that
the daily work of the
right ventricle, is
equal to 15,000 kilo-
gramme-metres ; the
left ventricle is equal to 60,000, so that the total work
of the heart in twenty-four hours may be estimated
at 7 5, 000 kilogramme-metres, or about one-fifth of
the total work performed by the body. This is about
the amount of work performed by a man in the
ascent of Snowdon (Foster).
Frequency of Cardiac Pulsations.— In the
adult, 65-75 (average 72) per minute. In the foetus,
150-200. At birth it is 140 ; end of second year,
no; end of fifth, 100 ; end of fourteenth, 86 ; at
twenty-one, 75. It is affected by position, being five
beats more when sitting than lying down, and ten
more in standing than sitting, a result due to the
greater number of muscles brought into a state of
contraction. The number of beats is increased by
active exercise, during digestion, and by excitement.
Increased resistance to the flow of blood at first in-
H
Fig. 45.— Tracing obtained by cardiograph
from apex-beat of a healthy man. ad,
contraction of the auricles ; b c, contrac-
tion of ventricles ; d, closure of the
aortic ; e } closure of pulmonary valves ;
cf, diastole of ventricles. (Landoisand
Stirling.)
98 The Circulation
creases, then, if continued, diminishes the number of
beats. Diminished pressure, as in a large hemorrhage,
increases the number of beats.
When the heart beats faster the duration of both
systole and dgistole is diminished, but the diminution
is most marked in the diastole. Normally the systole
or working time of the ventricles is equal to about
nine hours out of the twenty-four, and the rest is
equal to fifteen hours. When the heart-beats are
increased in number, as in the fevers, the total systole
or work of the heart in twenty-four hours is increased as
compared with the total resting time. Thus, if the
heart beat 100 times per minute, the systole will
amount to nearly eleven hours and the diastole to
thirteen hours (Waller).
Endocardial Pressure.— Goltz and Gaule
found the maximum pressure in the left ventricle of
a dog amount to 140 mm. of mercury, 60 mm. in the
right ventricle, and 20 mm. in right auricle. Imme-
diately after the systole a negative pressure of — 52 to
— 20 mm. was observed in the left ventricle, in the
right ventricle about —17 mm., and in the right
auricle —12 to — 7 mm. While to some extent this
negative pressure is due to the aspirating power of the
thorax during inspiration ; yet, as a considerable nega-
tive pressure is observed after the chest is opened, it
would appear that the suction-power or active dilata-
tion of the ventricles, and in a lesser degree the
auricles, is of considerable service in carrying on the
venous circulation.
Innervation of the Heart
The nervous mechanism of the heart consists of —
i. Intra-cardiac ganglia.
2. Extra- cardiac — (a) inhibitory centre, (b) accele-
rating centre.
Cardiac Ganglia 99
3. Inhibitory nerves, i.e. vagi.
4. Accelerator nerves, i.e. sympathetic.
1. Intra-cardiac Ganglia —Automatic Ac-
tion. — If the heart of a mammal be removed from the
living body it will continue to pulsate for a few mo-
ments, but the movements quickly cease, though they
can be prolonged for a short time if some arrangement
be made for supplying it with arterial blood. If a frog's
heart be removed from the body it will continue to beat
for hours, or even days, if it is kept moist, or, better
still, supplied with a fluid containing O and also some
nutrient fluid, as serum-albumin. It has been as-
sumed that this automatic action of the heart is the
result of the motor ganglia which the heart contains.
Left auricle and pulmo- v, Superior venae cava; and
nary veins i ) {\ . J vagi nerves
Aortic bulb ~\^-*/ J_^^£^_^/ Sinus venosus and Re-
V \^ZF^ /~~ mak's ganglia
7 * *V^ ( Inferior
Bidder's ganglia ? ^^\ \ J interior vena cava
Ventricle \ /
Fig. 46. — Diagram of the frog's heart.
This, however, is not universally true, as when a liga-
ture is placed between the sinus venosus and the rest
of the heart (auricles and ventricle), the latter part
ceases to beat, although it contains Bidder's ganglia
(see figs. 46 and 47). Moreover, parts of the heart,
such as the venae cavas and upper part of the sinus
venosus will pulsate when separated from the rest of
the heart, though no ganglia have been demonstrated
in them ; and the heart of the snail contains no nervous
elements, yet it beats rhythmically. It would seem
that the property of rhythmical contraction is an
attribute of heart muscle. While it is unsafe, in the
present state of our knowledge, to make any dogmatic
statement about the functions of the cardiac ganglia,
loo The Circulation
it would seem they are capable of originating
rhythmical pulsations and retaining this power after
the muscular fibres themselves have ceased to con-
tract automatically. The ganglia appear also to be
more sensitive to outside stimuli than the muscular
fibres. The principal facts known concerning the
cardiac ganglia have been studied in the frog's heart.
The frog's heart consists of two auricles above and a
single ventricle below ; the latter is continuous in front
with the aortic bulb, which divides into two aortas —
right and left. Pos-
teriorly the right auri-
cle receives the sinus
venosus, a small cham-
ber formed by the
junction of the two
r , . superior venae cava;
Jig. 47. Scheme of nerves or frogs x , . r
heart (Landois and Stirling), r, Re- and inferior vena cava.
maf S) and b, Bidder's ganglia ; s v, Thecardiac branches
sinus venosus; A, auricles; V, ven-
tricle;. IS A, bulbus arteriosus; Vag, of the Vagi paSS to the
vagi; I V C, inferior vena cava; .:_„,. ..„,.„,,,, whprp
S V C, superior vena cava. SlnUS \ UIOSUS, Wliere
they are connected with
some nerve-cells which form Remak's ganglia; branches
proceed along the auricular septum to two ganglia
situated in the auriculo-ventricular groove, called
Bidder's ganglia (see figs. 46 and 47).
The most important experiments in connection with
the ganglia of the frog's heart are the following : —
Stannius's Experiment.— If the sinus venosus
be separated from the auricles by tying a ligature
round the line of junction between the two (see
fig. 48, 1), the sinus venosus and veins continue to
beat, while the auricles and ventricles stand still in
diastole. If an incision be made at the auricular-
ventricular groove, so as to separate the ventricle from
the auricles, Bidder's ganglia being included with the
ventricle, the ventricle commences to pulsate again.
Extra-cardiac Centres 101
Thus the sinus venosus and ventricle are pulsating,
though with a different rhythm, while the auricles are
motionless (see fig. 48, 2). This experiment has
been thought to prove that both Bidder's and Remak's
ganglia are motor in
function, while the
auricles contain in-
hibitory ganglia.
Section of the
Heart— If the ven- Y Vw^
tricle be Separated Fir.. 4 S.— Stannius's expeiiment (Landois
frnm the- nnrir]pu Vw a,Hi Stirling). A. auricle ; V, ventricle ;
irom tne auriCleb Dy sv , s i„ us venosus; the zigzag lines in-
meanS Of SCisSOrS, the dicate which part continues to beat ; in
, i • j 7 7 2 the ventricle beats at a different rate.
cut being made below
the auriculo-ventricular groove, so that the upper part
of the ventricle goes with the auricles, Bidder's ganglia
being included, the auricles will continue to beat
rhythmically, while the lower part of the ventricle is
motionless. If the heart be divided longitudinally, each
half — an auricle and half- a ventricle — will pulsate.
2. Extra-cardiac Centres. — The inhibitory
(vagus) centre is situated in the medulla, and is con-
stantly in action. It is capable of being influenced by
the excitation of various sensory nerves. The accele-
rating centre is also in the medulla ; it is not constantly
in action. These centres are largely influenced by
afferent nerves from various parts of the body. Thus
a ghastly sight, good news, an inflamed pericardium or
peritoneum, may profoundly influence the pulsations of
the heart through its regulating centres in the medulla.
3. Inhibitory Action of Vagus —If the vagus
of a frog or rabbit be excited by an interrupted
current, the heart's action will become slower, and the
blood-pressure in the arteries will be diminished ; or
if the current be strong, it will be arrested in diastole.
The researches of Roy and Adami show that even
weak excitation of the vagus reduces considerably the
102
The Circulation
amount of blood passing through the heart, by
reducing the force and frequency of the cardiac beats.
A strong excitation will stop the contraction of the
auricles and keep them quiescent ; it will temporarily
arrest the ventricles, but the ventricles will recom-
mence their contractions in spite of the continued
excitation of the vagus. Section of the vagi is
VACUS CENTRE
ACCELERANS
CENTRE
/NH/BITORY
CA/VCL/ON,
ACCELERATING
GANGLION
Fig. 49.— Diagram illustrating the connexions of the inhibitory and
accelerator} 7 nerves of the heart.
followed by an acceleration of the cardiac beats. If
atropin be injected, even a strong current passed
along the vagi will not diminish the cardiac beats.
Reflex Inhibition. — If the intestines of a frog
be struck sharply, or the mesenteric nerves stimulated,
the heart is brought to a standstill in diastole. If the
The Arteries
103
vagi are divided, or the medulla destroyed, this effect
will not take place. The stimulus ascends to the
medulla along the mesenteric nerves, and descends
to the cardiac ganglia along the vagi. Irritation of
other sensory nerves, as the posterior auricular, will
have a similar effect.
4. Accelerator Nerves. — The sympathetic
nerves which pass from the cervical cord to the last
cervical and first dorsal ganglia, and from thence to
the heart, are called the accelerator nerves. Stimu-
lation of these nerves with the interrupted current
causes quickening of the heart's action, and causes it to
beat with greater force. The output of blood is also
increased. The accelerator nerves exert no influence
on the heart if the cardiac branches of the 'vagus
have been paralysed by section or by atropine.
It would thus appear as if the accelerator nerves
act as a check on the vagus (Roy and Adami).
Passing along with the accelerators are some branches
which are vaso-constrictors for the coronary arteries.
THE ARTERIES
Structure. — The arteries have three coats —
I Epithelial.
t. Internal j Sub-epithelial.
1 Elastic.
,,.,-,, I Muscular.
2. M.ddle |E]astic _
3. External — Connective tissue.
1. Internal (fig. 51, a, I?).— This coat may be
readily stripped off the inner surface of the artery as a
transparent, colourless, elastic and brittle membrane.
It is formed of —
(a) An epithelial layer, consisting of a single
layer of thin, elongated cells, with nuclei (fig. 50).
io4
The Circulation
(b) Sub-epithelial layer, composed of branching
corpuscles lying in cell-spaces of homogeneous con-
nective tissue,
(c) Elastic layer, consisting of a fine membrane
marked with interlacing network of fibres and per-
forated with round openings, and termed fenestrated
membrane of Henle (fig. 5 1 b).
2. Middle or Muscular (fig, 51, c)— In the small
and medium-sized arteries the middle coat consists of
pure non -striated muscular fibre, arranged transversely
round the artery with only a slight
admixture of elastic tissue. In the
larger arteries yellow elastic fibre
predominates, and, indeed, the aorta
consists of nearly pure yellow elastic
tissue.
3. External coat, or tunica
adventitia (fig. 51, d), consists ot
fine connective tissue, with a vari-
able amount of elastic tissue ar-
ranged longitudinally.
Circulation in the Arteries.
The arteries are elastic and con-
tractile tubes which convey the
blood from the heart to the capil-
laries. The larger arteries are ex-
ceedingly elastic, but feebly con-
tractile ; the small arteries are
contractile on account of the mus-
cular tissue in their walls, while
they are less yielding and elastic
than the larger arteries. Their
elasticity allows them to dilate
during the systole of the heart,
thus diminishing any risk of rupture, and their elastic
recoil during the diastole, when the aortic valves are
closed, assists in maintaining the circulation, and con-
Fig. 50. — Epithelial
layer lining the pos-
terior tibial artery of
man x 250 (Qnain's
Anatomy).
The Arteries 105
verts what would be an intermittent supply of blood
to the capillaries into a constant stream. The contractile
power possessed by the smaller arteries is of great
importance (1) in regulating the supply of blood to an
organ. Thus during digestion the minute gastric
arteries dilate and supply the peptic glands with a
larger supply of blood than during fasting. The
arterial muscular tissue is regulated by the vaso-motor
nerves. (2) It assists in arresting haemorrhage, when
an artery is completely divided, by occlusion of the
Fig. 51.— Transverse section of part of the wall of the posterior tibial artery
x 75 (Quain's Anatomy). a, epithelial and sub-epithelial layers ;
b, elastic layer of inner coat ; c, muscular layer ; d, outer coat, consisting
of connective-tissue bundles.
divided ends. (3) It enables the arterial system to
accommodate itself to the amount of blood in the
body. At each ventricular systole some 5 oz. of blood
are forced into an already overfilled aorta and arterial
system ; the effect of this being (1) to increase the
tension in the arterial system and distend the elastic
walls of the aorta and large arteries, (2) to send a
wave-impulse along the blood in the arteries, which is
gradually lost before reaching the capillaries, and
which can be felt in the radial as the pulse. If the
arteries were rigid tubes, the intermittent action of the
heart would cause an intermittent flow of blood from
the arteries to the capillaries. The effect of the ven-
tricular systole is to distend the walls of the aorta, to
store up force during the systole to be utilised in
io6
The Circulation
continuing the circulation during diastole, the recoil
of the elastic walls assisting to convert the intermittent
blood-stream into a continuous one. If a large vessel,
as the carotid, is divided, an intermittent stream of
blood flows out, but a
wound of a small artery
yields a steady stream.
Arterial Pres-
sure. — The pressure
of blood in the arteries
is measured by con-
necting the carotid
artery of a rabbit or
dog with a |j -shaped
tube containing mer-
cury. If afloat on- the
mercury be made to
carry a small camel's-
hair brush or pen, the
oscillations of the mer-
cury caused by the
varying tension in the
blood-vessels can be
recorded by the brush
or pen writing on a re-
volving surface. Such
an arrangement is
called a kymograph.
The pressure in the
arteries undergoes vari -
ations which correspond — (i) with each systole of the
left ventricle, (2) with the movements of" respiration
(see p. 141).
The mean pressure in the carotid of man probably
amounts to about 150-200 mm. (6-8 in.), in the aorta
250 mm. (9-8 in.), and in the brachial 1 10-120 mm.
(4-3-47 in.) of mercury.
Fig. 52.- Transverse section through a
small artery and vein (Gray's Anatomy).
A, artery ; V, vein ; e, epithelial lining ;
111, circular muscular fibres with nuclei ;
«, external or connective tissue coat.
The Arteries 107
The arterial pressure or tension decreases in pass-
ing from the larger to the smaller arteries, in spite of
the increased friction which results from the blood
travelling through smaller channels. The reason for
this decrease in pressure is to be found in the fact
that the total sectional area of the smaller arteries is
greater than the trunk from which they were derived,
and the blood is therefore travelling as it were through
a wider stream. The blood-pressure varies under
different circumstances, depending upon three factors :
(1) the force and frequency of the heart's contrac-
tions, (2) the elasticity and tone of the arteries, (3)
the resistance in the capillaries. The force of the
heart and tonus of the arteries may vary to suit
altered conditions of the circulation. Thus, ligature
of the large arteries or an injection of saline fluid into
the circulation (when the pressure is normal) leads
to only a transitory rise in the pressure, the pressure
quickly falling to normal. The injection of a greater
volume of fluid than is equal to the volume of the
blood in the body leads to high pressure and death.
A moderate haemorrhage, less than 3 per cent, of
the weight of the body, does not lower the pressure ;
more than this leads to a lowering, and perhaps
death.
Velocity of the Flow. — The rate of movement
of the blood in the arteries has been measured prin-
cipally in the carotids of the horse, dog, and rabbit.
In the horse Volkmann found the velocity to be
300 mm. per sec. in the carotid, 165 mm. in the
maxillary, and 56 mm. in the metatarsal. Various
instruments are employed for this purpose, the
Stromuhr of Ludwig and the Hamatachometer of
Vierordt being the principal. In order to measure
the time occupied by the circulation of any portion
of blood, ferrocyanide of potassium is injected into
the jugular vein, and the blood from the peripheral
io8
The Circulation
end of the same vein tested from time to time. In
this way a complete circulation has been found to
take place in 15 sees, in the dog, and 23 sees, in the
human subject {Hermann).
The Pulse. — The impulse or shock caused by
the overfilling of the aorta during the ventricular
systole is the cause of the pulse. This pulse-wave
travels at the rate of 5-10 metres (15-3° ft.) per
second along the arteries, and is lost at the capillaries.
This pulse-wave must be carefully distinguished from
the blood-current, the latter travelling only some
300 mm. (12 in.) per second; the former stands in
the same relation to the moving blood as does a wave
on the surface to the cur-
rent of a slowly flowing
river. The duration of
the ventricular systole
being fths second, before
the end of the systole the
pulse-wave would have
travelled about 12 ft., if
that were possible, so that
the beginning of each
wave is lost at the peri-
phery before the end of
it has left the ventricle.
The more rigid the arteries
the faster the wave travels ;
the more distensible the
more slowly it travels. If
the finger be applied to the radial artery, the artery
will be felt to expand beneath the finger some 75
times a minute ; under some circumstances the pulse-
wave will feel to be double or dicrotic. This di-
crotism is shown by the sphygmograph to be constant
in health, but is more marked when the tension in the
arteries is low, and the arterial walls more dis-
Fig. 53. — A normal pulse-trace mag-
nified, a li c, primary wave ;
c d e, predicrotic wave; efg, di-
crotic wave ; e, aortic notch ; a— e,
systole ; /— a', diastole of the
ventricles.
Pulse
109
/
Fig. 54. — Tracing of a dicrotic pulse
(fever).
tensible than usual, as in febrile conditions of the
system.
In a sphygmographic tracing, fig. 53, the up-stroke
a — b is caused by the pulse-wave as it travels along
distending the artery and raising up the lever of the
sphymograph. The down-stroke b—a' is more gradual
than the up-stroke, and
is caused by the descent
of the lever consequent
on the artery regaining
its normal calibre. The
descent is marked by
several minor waves. The
largest of these, efg, is
called the dicrotic wave,
and is due to a wave or vibration sent along the
arteries by the sudden closure of the aortic valves.
The cause of the other minor waves, the pre- and
post-dicrotic, is uncertain. The character of the
pulse as regards frequency, tension, &c, is modified
by changes occurring (1) in the beat of the heart,
(2) or changes taking
place in the arterial
walls or capillaries.
Thus in the low ten-
sion of some fevers,
due to a relaxed con-
dition of the arterial
system, there is a
sharp, short ventricular
contraction, giving a
straight up-stroke (fig.
54, a — b) to the primary
wave, and a prominent dicrotic wave, efg. The same
result occurs after a warm bath, the arteries relaxing
and the tension becoming low. In Bright's disease
the tension is high and the ascent of the primary
Fig. 55.
-Yortic regurgitation (Landois
and Stirling).
1 1 o The Circulation
wave is gradual, and the secondary waves small. The
same effect is produced by a cold bath.
In aortic regurgitation (fig 55) the up-stroke is
sudden and high, in consequence of the dilatation and
hypertrophy of the left ventricle, a larger volume of
blood than usual being propelled into the arteries ; the
down-stroke is abrupt and the dicrotic wave very
slightly marked on account of the imperfect closure
of the aortic valves.
The characters of the pulse which are of most
importance clinically are (1) frequency, (2) compressi-
bility, (3) rhythm. The terms large or small, strong
or weak, are also used, but are of less importance
and apt to be misleading. The pulse-rate is easily
ascertained with the finger on the radial artery and
watch in hand. The relative compressibility may be
ascertained by pressing the finger on the artery ; the
pulse may be felt to be liard or soft. A hard, slow
pulse signifies high arterial tension, as in Bright's
disease ; a soft, quick pulse, low tension, as in fevers.
In such cases the pulse is usually markedly dicrotic.
The rhythm may be altered so that the beats are
irregular or are intermittent.
Pulse-rate. — In health the normal pulse-rate in
an adult is 70 in a male and 80 in a female ; in the
newly-born it is 130-140 ; at three years of age it has
fallen to 100 ; at ten years of age to 90 ; at twenty-
one years to 70 ; after middle-life it is slightly higher.
THE CAPILLARIES
Structure. — The smaller arteries end in a fine
network of vessels, which differ in structure from the
arteries and veins, in that their walls contain no
muscular elements, but consist of a single layer of
elongated epithelium continuous with that of the
arteries ; the epithelium is rendered apparent by
The Capillaries
1 1 1
injection of solution of silver nitrate, and exposing to
light, the reagent darkening the intercellular material
and rendering the outline of the cell apparent (fig.
56). The nuclei can be stained with logwood. In
the vessels slightly larger than the capillaries a layer
of elongated muscular fibre cells is added.
Size. — Their average size in the human body is
about -joVoth of an inch, but they differ in different
parts of the body. They are comparatively large in
the marrow of bone, skin, and mucous membrane ;
small in lung, muscle,
and brain. The net-
work is close in lung
and muscle.
Circulation in
Capillaries. — The
velocity of the blood
in the capillaries is
very much less than
in arteries or veins,
being about '57 mm.
to 75 mm. per second
( 1 '4-1 - 8 inches per
minute). But a very
small portion of the
capillary system is tra-
versed by any one
blood-corpuscle. The
flow is constant, not
intermittent, as in the larger arteries. Under some
abnormal circumstances, as in hypertrophy of the left
ventricle and a rigid condition of the arteries, an in-
termittent flow or pulse may occur in the capillaries.
This may be demonstrated by pressing the finger on
the forehead ; alternations of redness and pallor are
noted lit the border of the pressure-mark. The red
blood-corpuscles, for the most part, travel in the
Fig. 56. - Capillary vessels from the
bladder of a cat (Chrzonszczewsky).
1 1 2 The Circulation
mid-stream, the white corpuscles moving more slowly
along the side. The thin capillary walls allow the
liq. sanguinis readily to pass through, and so bring
the blood in direct contact with the tissues, and also
nourish parts by irrigation in which there are no
capillaries, as cartilage and the cornea. Under
certain circumstances, as in inflammation, when the
capillaries are distended, the white corpuscles push
through the capillary wall into the tissues passing
through the intercellular substance between the en-
dothelial plates. This is termed Diapedesis. The
capillary circulation can be readily seen when the web
of a frog's foot is spread out beneath the microscope.
It may also be seen, suitable precautions being taken,
in the mesentery of some of the smaller mammals.
The capillary walls, though they contain no muscular
element, are apparently contractile. The calibre of
the capillary channels is distended when a large
supply of blood reaches the part, and the channels
shrink when the supply is less. It appears that some-
times they can change their form independently of
any engorgement with blood, the endothelial cells
which form their walls being apparently slightly con-
tractile. The movement of blood in the capillaries
is dependent upon the action of the heart, modified
by the arteries.
Veins
Distribution.— The veins carry the blood from
the capillaries to the heart. They ramify through the
body like the arteries, but they are more numerous,
anastomose more freely, and are of greater capacity.
They usually accompany the arteries ; but there are
exceptions, as the hepatic, sinuses of the skull, and
veins of spinal cord.
Structure. — The veins have thinner walls than
the arteries. They have the following coats :—
The Veins
ii3
1. Internal. — This coat closely resembles the
inner coat of the arteries (fig. 57).
2. Middle.— This coat is thinner and less mus-
cular and contains more white fibrous tissue than the
middle coat of the arteries. The muscularity of the
middle coat is best marked in the splenic and portal,
and least marked in the hepatic part of the inferior
vena cava and subclavian veins (fig. 57).
3. External. — This coat consists of connective
tissue and elastic fibres. In certain veins this coat
contains a considerable quantity of muscular tissue,
as in the abdominal cava, iliac and renal. The
FlG.57. — Transverse section of part of the wall of one of the posterior tibial
veins (Schafer). a, epithelial and subepithelial layers ; b, elastic layer
of inner coat ; c, middle coat of muscular and connective tissue ; d, con-
nective-tissue coat.
striated muscular fibre of the heart is prolonged for
some distance on the walls of the pulmonary veins
and venae cavse. Muscular tissue is wanting in most
of the veins of the brain and pia mater, retina,
venous sinuses of dura mater, and cancellous veins of
bone.
Valves. — The valves consist of semilunar folds
of lining membrane, strengthened by including con-
nective tissue. They consist for the most part of two
flaps or pockets, which come in contact by their
free margins, and prevent reflux of blood towards the
capillaries. The veins of the extremities, neck, and
1
1 1 4 The Circulation
scalp have, numerous valves, while they are absent
for the most part in the deep veins of the abdomen,
chest, and cranium. Many other veins are destitute
of valves. Such are the vena? cavse, portal, hepatic,
renal, uterine, pulmonary, and sinuses of skull. There
are a few in the intercostal and azygos.
The forces which propel the blood in the
veins are —
i. Vis a tergo — heart's action.
2. Vis a fronte — aspiration of the thorax.
3. Muscular contraction.
(1) The vis a tergo or force exerted by the heart
in assisting the flow of blood in the venous system is
probably not great, the velocity of the blood in the
small veins being small.
(2) The vis a fronte or force supplied by the
suction action of the chest during inspiration is much
more considerable. When an ordinary inspiration is
taken, not only is air drawn into the air-passages by
the expanding chest, but the blood in the great veins
external to the chest is sucked towards the right
auricle. The effect is more powerful if a deep in-
spiration is taken. During an ordinary expiration the
sucking action becomes nil, while during a powerful
expiration, as in blowing or coughing, the expiratory
effort obstructs the flow of blood into the chest and
causes congestion of the venous system.
(3) During muscular exercise the veins are com-
pressed by the contracting muscles, the effect being
to drive the blood towards the heart, the valves pre-
venting its return towards the capillaries.
The velocity of the blood in the venous system
is small when compared with the arteries, though
greater in- the large veins near the heart than in the
smaller veins. It is about 200 mm. per sec. (7 to 8
inches) in the jugular vein of the dog. The pressure
Vaso-motor Centres 115
in the crural vein of the sheep has been shown to be
1 1 "4 mm. of mercury (-4 inches), while in the sub-
clavian it was —1 mm. to —5 mm. during inspiration,
the mean pressure being — -i mm.
Venous Pulse.— The flow of blood in the veins
is, unlike the flow in the arteries, continuous and not
intermittent. In the large veins, however, the aspi-
rating power of the thorax draws the blood to the
chest during inspiration, and thus leads to more or
less intermittency. In case of regurgitation through
the tricuspid valve, there is a ' back-stroke ' seen in
the veins of the neck, sometimes called a 'venous
pulse.'
Innervation of the Blood-vessels
1. Vaso-motor centres — medulla, cord, ganglia.
2. Vaso-motor nerves, i.e. (a) vaso -constrictor,
(b) vaso-dilator.
Vaso-motor Centres.— The principal vaso-
motor centre is situated in the medulla. Nothing is
known of this centre anatomically, its position having
been determined by experiment. Excitation with the
interrupted current of the medulla of a frog will cause
the vessels in the web of the foot (when seen beneath
the microscope) to contract. The same result can be
witnessed in the rabbit by exposing a small artery.
Section of the cord below the medulla causes the
vessels to dilate. The latter experiment shows that
the muscular fibre of the arteries is in a continual
state of contraction or tonus. Various subsidiary
vaso-motor centres are situated in the spinal cord.
Besides the vaso-motor, or rather vasoconstrictor
nerves, there are vaso-inhibitory or vaso-dilators.
Such are the chorda tympani to vessels of the submaxil-
lary glands, and the nervi erigentes to the arteries of
the erectile tissue of the penis. The vaso-motor centre
1 2
1 1 6 The Circulation
can also be influenced by various afferent nerves :
this may occur through the higher nerve-centres, as
in blushing ; excitation of the central end of various
sensory nerves will bring about contraction of arteries ;
while the vagus contains, especially in the superior
laryngeal branch, fibres which excite and also fibres
which, when stimulated, lead to inhibition of the
vaso-motor centre.
Action of Poisons on the Heart and
Circulation
Muscarin, an alkaloid extracted from a poisonous
mushroom, injected into the circulation, slows the
heart and finally arrests it in diastole. It is assumed
to stimulate the inhibitory ganglia of the heart.
Pilocarpin has the same effect.
Atropine increases the frequency of the heart-beats,
and appears to paralyse the inhibitory ganglia, thus
antagonising muscarin. Excitation of the vagus has
no effect.
Nicotine, like atropine, paralyses the inhibitory
ganglia.
Physostigmin, or Eserin, in small doses increases the
effect of stimulation of the vagus, and to this extent
antagonises atropine.
Digi/alin. — The first effect is to slow the heart and
give increased strength to the systole. In the second
stage the heart becomes irregular in action and in-
creased in frequency ; finally the heart is arrested in
systole.
Aconitin and Veratrin slow the heart by exciting
the vagus.
Alcohol and Etlier in small doses stimulate the
heart, so that it beats more strongly and more
quickly.
Origin of Lymphatics 1 1 7
CHAPTER IX
LYMPHATIC SYSTEM
Distribution. - The lymphatic vessels may be
said to take their origin in every tissue of the body
supplied with blood ; they carry back into the vas-
cular system any excess of the plasma of the blood
which has transuded from the capillaries, and which is
not required for the nutrition of the tissues. The
lymphatics or lacteals which originate in the mucous
membrane of the alimentary canal, perform the im-
portant office of taking up certain of the products of
digestion and conveying them into the vascular system
after their passage through the mesenteric glands.
The lymphatic capillaries commence in various ways
in the tissues ; by their junction they form the
larger lymph-vessels ; these finally join either the
left or right thoracic duct, and by their means the
contents of the lymphatic vessels enter the subclavian
veins.
Modes of Origin. — The lymphatics have varied
modes of origin — (1) in plexuses or networks of
capillaries ; (2) in lacuna or clefts in connective
tissue ; (3) in lymph spaces or cavities. 1. Plexi-
form. — Networks of capillary lymph-vessels are pre-
sent beneath the skin, and mucous membrane of the
stomach and intestines, some of the plexuses being
joined by small blind vessels, as in the villi.
2. Lacunar. — Various spaces or interstices in the
connective tissue of various organs are connected
with the lymph capillaries. These clefts are generally
without a complete endothelial lining, but the endo-
thelial cells forming the wall of the lymph capillaries
are directly continuous with the connective-tissue
1 1 8 Lymphatic System
cells in the clefts or lacuna?. 3. Lymph spaces
or cavities. — In some parts the lymphatic capillaries
commence in spaces or sinuses lined by a single layer
of squamous epithelium, or rather, endothelium, with
sinuous outlines, similar to the endothelium lining
the lymph vessels. Such are found beneath the skin
and mucous membranes, in the diaphragm, lungs,
liver, &c. Resembling these, only very much larger,
are the serous sacs, such as the pleural, pericardial, and
peritoneal cavities ; also the synovial cavities and the
subdural and subarachnoid spaces. The cavities are
directly connected with the lymphatics by minute
holes — the stomata surrounded by a layer of poly-
hedral cells. By means of these openings fluids and
solid matters can enter the lymphatics.
Lymphatic capillaries. — These consist of
channels, for the most part larger than the capillaries
of the vascular system, their walls consisting of a
single layer of flattened nucleated epithelium, with
sinuous outlines. Sometimes a small artery is com-
pletely surrounded or ensheathed in a lymphatic
capillary ; the space surrounding the artery is termed
the perivascular lymph space.
Lymphatic vessels. — The capillaries empty
themselves into vessels which closely resemble veins.
These are lined by a single layer of elongated nucleated
flattened cells with sinuous outlines ; outside the
epithelial coat is a thin layer of longitudinal elastic
tissue, the middle coat consists of muscular tissue,
and the external of a mixture of connective and mus-
cular tissue. They are provided with valves so closely
approximated as to give them a beaded appearance.
The valves resemble those described with the veins.
Thoracic duct. — All the lymphatics of the body,
except those of the right side of the head, right
thorax, right upper extremity, and right side of the
heart, empty themselves into the thoracic duct. The
Lymph 1 1 9
thoracic duct commences opposite the second lum-
bar vertebra, this part being dilated and termed the
receptaculum chyli, and terminates in the subclavian
in the neck near its junction with the jugular.
Functions.— Liq. sanguinis exudes from the
capillary blood-vessels to supply the tissues with
materials for their nutrition. The excess of liq.
sanguinis thus supplied enters the lymphatic capil-
laries, passes through the lymph glands into the
thoracic duct, and thence into the venous circulation.
The liq. sanguinis that has passed out of the capil-
laries accumulates in the connective-tissue spaces, or
lacunae, from which the lymphatics arise.
The lymphatics which arise in the villi of the
small intestines are termed lacteals, and during
digestion absorb fatty matters, and to a smaller extent
soluble matters and albumen from the contents of the
intestine. During the digestion of food, the columnar
epithelium covering the villi may be seen to be dis-
tended with oil globules (though some observers
assert the oil globules pass between the cells), these
globules passing from the epithelium into the retiform
tissue, and thence into the fine lacteal present in the
villus.
Lymph has been described as blood minus the
red corpuscles. It is a yellow alkaline fluid of sp. gr.
1045 and 6-7 per cent, of solids.
It consists of —
White corpuscles. Extractives.
Elements of fibrin. Salts.
Albumen. Water.
It has been obtained for examination from the
thoracic duct during a fasting period, or from some
large lymphatic vessel. The white corpuscles are
more numerous in lymph which has passed through
lymph glands. They vary in size ; the larger con-
120 Lymphatic System
tain two or three nuclei and show more active
amoeboid movements than the smaller ones.
Chyle may be described as lymph plus fatty
matters. It may be obtained from the thoracic duct
during a period of digestion. It is an opaque milky
fluid which clots when drawn from the duct : the clot
exhibits a pink colour. It contains 8-9 per cent, of
solids.
It consists of —
White corpuscles.
Albumen.
Immature red.
Extractives.
Fatty matters.
Salts.
Elements of fibrin.
Water.
Examined miscropically, white corpuscles are
seen in abundance in chyle drawn from the upper
part of the thoracic duct. Many of these white
corpuscles are of a reddish colour, and are probably
in process of being converted into red.
The fatty matters consist of oil globules of various
sizes and finely divided matter of a granular appear-
ance, which forms the molecular basis of chyle.
Chyle undergoes changes in its passage from the villi
to the thoracic duct ; these changes are effected
through the agency of the mesenteric glands. They
consist in a diminution of the molecular basis and
an increase of the white corpuscles and elements of
fibrin. Some of the white corpuscles appear to be of
a reddish colour.
Movements of the Lymph
1. Vis a tergo. Pressure of blood in the blood-
vessels.
2. Contraction of muscular fibres in their walls
and in the villi.
Lymphatic Glands 121
3. Compression by muscular action of voluntary
muscles.
4. Vis a f route. Aspiration of thorax.
1. If a ligature be applied to the thoracic duct,
the chyle will tend to accumulate behind it, or if a
tumour compress it the lacteals will become dilated
and tortuous. This shows the existence of some vis
a tergo. The liq. sanguinis leaves the capillaries under
considerable pressure, and accumulating in the spaces
of the tissues readily passes into the lymphatic vessels.
Increase of pressure in the arteries causes increased
tension in the lymphatics.
2. The muscular fibres in the walls of the lym-
phatic vessels act after the manner of the lymph-
hearts in the frog. The contraction of the muscular
fibres of the villi assists in emptying the contents of
the contained lacteal.
3. Contraction of the voluntary muscles com-
presses the lymphatic vessels in the same way as the
veins, driving the lymph forwards, the valves prevent-
ing reflux.
4. The enlargement of the chest during inspiration
sucks the blood in the large veins towards the heart ;
the rapid motion of the blood in the subclavian over
the orifice of the thoracic duct will tend to make the
contents of the duct discharge into the vein, thus sup-
plying the vis a fronte.
Lymphatic Glands.— The basis of all lymph-
glands is the so-called lymphoid tissue, which consists
of retiform or adenoid tissue with lymph corpuscles
occupying the meshes of the network (fig 58). Lym-
phoid tissue therefore consists of (a) a network of fine
fibres ; (b) small nucleated cells at the intersections
of the network, which may be separated from the
fibrils of the network ; (c) lymph-corpuscles occupying
the meshes. Some of the corpuscles are small with
122
Lymphatic System
a large nucleus, and are probably the newest formed ;
others are larger and probably older, with two or
three nuclei, and exhibit more lively movements on
the warm stage than the smaller ones.
Lymphoid tissue, according to Klein, occurs in
the body in the following ways — (i) Diffuse lymphoid
Fig. 58. — Diagrammatic section of lymphatic gland (Sharpey). a i, afferent,
c /, efferent lymphatics ; C, cortical substance ; M, reticulating cords of
medullary substance ; Is, lymph-sinus ; c, fibrous coat sending trabeculse
/ r into the substance of the gland ; Ik, lymphoid tissue.
tissue, which is found extensively beneath the epithe-
lium of mucous membranes, notably of the trachea,
soft palate, tonsils, root of tongue, pharynx, small
and large intestines. (2) Cords, cylinders, or patches in
Lymphatic Glands
12 •
the pleura and spleen. (3) Lymph follicles, being
oval or spherical masses, in the tonsils, root of tongue,
upper part of pharynx, stomach, intestines (solitary
glands), nasal and tracheal mucous membranes. In
the Malpighian corpuscles of the spleen.
Compound Lymphatic Glands.— These are
the commop lymph-glands, which are small rounded
bodies placed in the course of the lymphatic and
Fig. 59. - Thin section from the cortical part of a lymphatic gland (Hi;.).
ad, network of fine trabecular, formed by retiform tissue, from the
meshes of which the lymph-corpuscles have been washed out, except at
c, where they are left.
lacteal vessels, and through which the lymph and
chyle pass on their way to the thoracic duct. They
are collected in groups, such as the mesenteric,
portal, bronchial, splenic, cervical, lumbar and inguinal
glands. The afferent lymphatics enter the glands on
its outer or convex surface, and emerge as the efferent
lymph-vessels at the hilum. Each gland is surrounded
by a fibrous capsule which passes into the interior as
the trabeculce or septa.
The trabecular pass one-third or one-fourth of the
way into the gland (the cortex), dividing it into oval
compartments (fig. 58, tr), whilst in the central portion
124 Lymphatic System
they join together and form small compartments of an
irregular shape (medullary portion). The capsule and
trabecular are formed of fibrous tissue and non-striped
muscular tissue, and carry the vessels which enter the
gland, and are distributed to the lymphoid tissue of
the gland. The compartments of the cortex contain
oval masses of lymphoid tissue which do not com-
pletely fill them, and which form the lymph follicles of
the cortex ; the medullary portion contains .irregularly
shaped or elongated masses called the medullary
cylinders (fig. -58, C, M). The space left free between
the lymph follicles and the cortical trabecular, and
between the medullary cylinders and the trabecular,
forms the lymph sinus (Is). The lymph path or sinus
is occupied by coarse retiform tissue. The afferent
lymphatic vessels, having entered at the cortex at the
external surface, open into the lymph sinuses of the
cortex, then the lymph passes into the lymph sinuses
of the medulla, and leaves the gland by the efferent
lymphatics at the hilum. The passage of the lymph
through the sinuses is delayed by the reticulum, and
any foreign bodies or inflammatory products may be
arrested in the passage.
CHAPTER X
RESPIRATION
TRACHEA AND BRONCHI
The walls of the trachea and two bronchi consist of
several constituents —
1. Connective tissue. 3. Muscular.
2. Cartilages. 4. Submucous.
5. Mucous membrane.
Trachea
125
1. The Connective Tissue coat forms an ex-
ternal sheath for the trachea, surrounding and joining
together the cartilages (fig. 60, /).
2. The Cartilaginous Rings are incomplete
behind, being C-shaped, are 16-20 in number, consist
Fig 60 —Longitudinal section of the human trachea (Klein), a, ciliated
epithelium ; />, basement membrane ; c, superficial part of the mucous
membrane, containing capillary vessels and lymphoid tissue ; d, deeper
layer of mucous membrane, consisting mainly of elastic, fibres ; e sub-
mucous tissue containing the larger blood-vessels, mucous glands and
fat ;/, fibrous tissue, investing cartilages ; g, fat-cells ; A, cartilage.
of hyaline cartilage, and serve to maintain a certain
amount of rigidity in the walls.
126 Respiration
3. The Muscular Layer is present behind,
connecting the tips of the cartilages together, and
is also present behind in the intervals between the
rings. Its fibres belong to the unstriated variety, and
serve by their contraction to diminish the diameter
of the tube.
4. The Submucous Coat (fig. 60, e) consists of
loose connective tissue containing mucous glands,
blood-vessels, and adipose tissue, and serves to con-
nect the mucous membrane with the cartilages and
their sheath.
5. The Mucous Membrane consists of from
within outwards (fig 60) — (a) a single layer of
columnar ciliated epithelium cells, with a few ' goblet
cells ' ; {/>) a basement membrane ; (c) a layer of
lymphoid tissue, with a network of capillary blood-
vessels ; (d) a layer of longitudinal elastic fibres,
collected into bundles, which are readily seen as
longitudinal striae on slitting up the trachea.
The bronchi external to the lungs exactly resemble
the trachea in structure, the right having 6 to 8, the
left 6 to 12 incomplete cartilaginous rings.
Lungs (weight — right, 24 oz., left, 21 oz.)
The lungs are surrounded by the pleurae, the
smooth surfaces of the latter diminishing friction
during the movements of respiration. In shape they
are conical, the apex projecting into the root of the
neck, the base resting upon the arch of the diaphragm ;
the inner surface being flattened where the bronchi
and vessels enter.
The lungs consist of —
1. Lobes ; 2. lobules ; 3. bronchi ; 4. terminal
bronchioles, alveolar passages and infundubila ; 5.
air-sacs : 6. blood-vessels and nerves.
Lungs
127
1. The Lobes are the primary divisions, the right
having three, the left two.
2. Lobules. — The lobes are divided into lobules
of various sizes, their outline being most readily seen
on the cut surface of foetal lungs ; they are separated
by fine connective tissue. In structure they resemble
a lung in miniature, having a terminal bronchiole,
and a branch of the pulmonary artery and vein.
3. The Bronchi, on entering the lung, divide
and redivide, each of the smaller divisions entering
a lobule. In structure they resemble the trachea,
with some, modifications. The cartilages in the larger
tubes form more or less
complete rings, but as
the tubes get smaller
the cartilages form in-
complete rings, consist-
ing of small plates in
the walls arranged in a
circular manner, and
finally are wanting al-
together in tubes of
1 mm. in diameter. The
muscular fibres entirely
surround the tubes,
and may be traced into
the finest ramifications. The elastic fibres extend to
tubes of the smallest size, and become continuous
with the elastic fibres forming the walls of the infun-
dibula. The ciliated epithelium ceases before their
entrance into the infundibula.
4. Terminal Bronchioles and Infundibula.
After repeated sub-divisions, the bronchial tube, when
reduced to 1 mm., is called a terminal, lobular, or
respiratory bronchiole. Each terminal bronchiole ends
in one or more enlarged passages called the alveolar
passages or ducts, from which are given off blind
Fir,
61. — Diagrammatic representation
of a terminal bronchiole, alveolar pas-
sages, and infundibula (Schafer).
128 Respiration
dilatations, the infundibula or end-sacs. The walls of
the terminal bronchioles are in part, and the walls of
the alveolar passages and infundibula are completely,
beset with a number of air-cells or alveoli, which open
into them by wide apertures (fig. 61).
In the terminal bronchioles the cartilages have
disappeared, and the cylindrical ciliated epithelium is
being replaced by a layer of small polyhedral granular
cells, so that their walls consist of (a) a layer of
granular cells ; (b) a muscular coat of non-striated
fibres ; (c) a thin layer of elastic fibres, {a) The
granular cells are gradually replaced by flat, trans-
parent, nucleated cells, as the alveolar passages open
into the infundibula ; these flattened cells also line
the air-vesicles ; (b) the muscular coat is continued
into the alveolar passages and infundibula, but does
not surround the air-cells ; (c) the elastic fibres
forming the outer coat of the terminal bronchioles
are continued on to the air-cells, and form their walls
(fig. 62).
5. Air-cells (fig 62) are about -25 mm. ( T ^„ in.)
in diameter ; they are lined internally by flattened,
transparent nucleated cells, continuous with those of
the infundibula, and their walls are formed by the
elastic fibres continuous with the elastic tissue of the
bronchi and its divisions. According to Klein, the
walls of the air-cells contain connective-tissue cells,
the spaces which they occupy being continuous with
the lymphatic capillaries.
6. Pulmonary Vessels and Lymphatics. —
The pulmonary arteries accompany the bronchial
tubes, and, like them, do not anastomose. Their
terminal arterial branches, '025 mm. (-fuVo m -) m
diameter, lie between the air-sacs, and send a net-
work of capillaries over them. The bronchial arteries,
two or three in number, arise from the aorta, are dis-
tributed to the bronchi, lymphatic glands, connective
Lungs 129
tissue, and mucous membrane. The right bronchial
vein enters the vena-azygos, and the left the superior
intercostal vein. The deep lymphatics arise from the
Fig. 62.— Section of cat's lung, highly magnified, stained with nitrate of
silver (Klein). In the centre is seen an infundibulum in cross section,
lin. d with flattened epithelium, groups of polyhedral cells are seen on
one side ; the alveoli are lined by flattened cells and here and there a
polyhedral cell.
lacunae or spaces occupied by the connective-tissue
cells in the elastic tissue around the air-sacs. They
K
1 30 Respiration
empty themselves into the perivascular lymphatics.
The superficial lymphatics enter the subpleural lym-
phatics, and all eventually enter the bronchial lymph-
glands.
Pleurae. — The lungs are surrounded by a serous
membrane which adheres to the pulmonary surface
and is also reflected on to, and lines the inner surface
of, the thoracic cavity. The pulmonary and costal
pleural surfaces are always in contact under normal
conditions, so that there is no pleural cavity, and the
smooth moist surfaces prevent friction. When the
pleura is inflamed the pleural surfaces become
roughened by the exudation of lymph, a ' friction
sound ' or ' rub ' is heard, being caused by the rough
surfaces rubbing together. Sometimes serum is
effused, and then the pleural and costal surfaces are
separated from one another by the effused fluid
(pleuritic effusion).
Mechanism of Respiration
The lungs are compound elastic bags communi-
cating with the outside air by means of the bronchi
and trachea and suspended in a semi-distended state
in an air-tight cavity with movable walls. When the
cavity of the thorax is enlarged by the contraction of
certain muscles, the lungs become distended by draw-
ing in air through the trachea. When the muscles
relax, the lungs tend to collapse, expelling most of
their contained air — a result due in part to the -con-
traction of the elastic tissue they contain, and also to
the recoil of the elastic rib cartilages.
If an opening is made (as the result of accident or
disease) either through the chest wall from outside or
through the lung so that a bronchus communicates
with a pleural cavity, the lung collapses, and air enters
the pleural cavity {pneumo- thorax). If there is a
Inspiration
m
wound on both sides, death immediately follows as
neither lung can become inflated.
Inspiration. — The chest enlarges in three direc-
tions, viz., downwards, forwards, and laterally. The
enlargement downwards is effected by the contraction
of the diaphragm. At rest the diaphragm presents a
convex surface to the thorax ; in contracting this sur-
face becomes flatter, the floor of the chest is conse-
quently lowered and the cavity of the thorax enlarged,
and air enters to distend the lungs. The contraction
of the diaphragm tends to press the abdominal viscera
downwards and causes the walls of the abdomen to
project during inspiration.
The antero-lateral enlargement is effected by
raising the ribs. A vertebro-sternal rib has two
movable joints, the posterior where the head articu-
lates with the sides of the bodies of the vertebne, and
the anterior at the junction of the costal cartilage with
the sternum. The anterior end occupies a lower
position than the posterior, so that the rib is in more
or less of an oblique position. When the anterior
ends are raised the sternum will be pushed forward,
and the antero-posterior diameter of the chest en-
larged. In normal inspiration the antero-posterior
diameter is increased 5 mill., in a deep inspiration
about 30 mill. When the ribs are raised by the ex-
ternal intercostal muscles, the angles which they make
with the sternum become more obtuse, and the chest
enlarged in the tranverse diameter.
Muscles in action in easy inspiration :
t. Diaphragm, enlarges the chest downwards.
2. Scaleni, fix the upper two ribs.
3. External intercostals J , , , '
4. Levatores costarum 1 , ° ,,
1 3 2 Respiration
Muscles which may be brought into action
in laboured inspiration :
i. Serratus posticus superior, raise 2nd, 3rd, 4th,
and 5th ribs.
2. Sterno-mastoid, raise the clavicle.
I raise the ribs, the
scapula and arm
being fixed.
3. Serratus magnus
4. Pedoralis major tres.
Hydro-Carbons, or Fats. — These are neutral
bodies derived from both animal and vegetable foods.
They consist of olein, palmitin, and stearin. Olein and
palmitin are met with both in animal and vegetable
products ; olein is fluid at ordinary temperatures ;
palmitin has a semi-fluid consistence. Stearin is a
solid fat, is found only in animal products, and exists
largely in suet. They all have glycerine for a base in
combination with the corresponding fatty acids, oleic,
palmitic, and stearic. The fats are remarkable for the
small quantity of O they contain ; thus in palmitic acid
C| , H 32 , O, the amount of O is about 12 per cent, of
its weight, leaving from 80 to 90 per cent, available
for force-production.
Digestion of Fats. — The gastric juice dissolves
the connective tissue binding together the fat -vesicles
and sets free the fat. The fatty matters are emulsified
in the small intestine by the action of the pancreatic
juice, and in a lesser degree by the other secretions,
and for the most part enter the lacteals, though a
certain proportion, which has possibly become saponi-
fied, enters the portal vein.
Destiny of Fats. — The fats are utilised in the
body for force- production, either immediately, or are
stored as adipose tissue to be used when required.
They therefore serve for the maintenance of heat and
1 54 Food
performance of muscular work. The capacity of a
material for force-production depends upon the amount
of unoxidised C and H it contains, and of all alimen-
tary substances fats take the highest place. Experi-
mentally, Frankland has shown that the actual heat
developed by the various alimentary substances when
burnt in O is as follows : —
i gramme beef fat . 9,069 gramme-degrees,
butter . 7,264 „
„ beef muscle 5,103 ,, ,,
,, arrowroot . 3,912 „ „
That is to say, 1 gramme of fat, when burnt, will give
off heat sufficient to raise 9,069 grammes of water
i°C, whereas the same amount of arrowroot would,
when burnt, only raise 3,912 grammes of water i°C.
It is found that the inhabitants of arctic regions
readily devour all kinds of fat, while in the tropics the
foods of the inhabitants consist largely of farinaceous
and saccharine matters. The force generated by the
oxidation of the hydro-carbons is available for muscular
work. A large amount of muscular work can be
performed on a fatty or starchy diet. During muscular
exercise the amount of C0 2 given off by the lungs
varies according to the work done : thus, 5 grains per
minute during sleep, and 25 grains per minute walking
at the rate of three miles an hour.
The amount of mechanical work obtainable from
the oxidation of —
1 gramme beef fat = 3,841 kilogramme-metres,
butter = 3,077
,, beef muscle = 2,161 „ ,,
„ arrowroot = 1,657 ,, „
that is, the force derivable from the oxidation of
1 gramme of fat is sufficient to raise 3,841 kilo-
Starches , 155
grammes one metre. (1 kilogramme-metre = 7^32
foot-pounds.)
The products of the combustion of fat are H 2
and C0 2 . Animal life cannot long be maintained on
a non- nitrogenous diet. Dogs fed on fat, or fat and
starches, emaciate and die. Nitrogenous food is re-
quired to renew the tissues, which become wasted and
worn during the processes of life.
Carbo-Hydrates or Amyloids
These comprise starch, cane sugar, grape sugar,
milk sugar, glycogen. Chemically these bodies differ
from the fats in containing a smaller quantity of
uncombined carbon and hydrogen, the O existing
in sufficient quantity to form water with all the
H present, as in starch (C H| O.-,), grape sugar
(C H, 2 O fi ).
Starch is met with in vegetable products. It is
prepared for absorption by being converted into grape
sugar in the mouth and small intestine. Cane sugar
and glycogen are converted into grape sugar in the
stomach and intestines. Milk sugar (C] 2 H. 22 M +
H 2 0) and grape sugar (C 6 H l2 6 + H 2 0) are readily
absorbed by the portal vein and submitted to the
action of the liver. Here some change takes place.
Sugar injected into the jugular vein rapidly appears
in the urine ; injected into the portal, it does not,
unless in large quantity. The grape sugar is con-
verted in the liver into glycogen (C (i H l2 6 - H 2 0— -
C (i H, O s ), and probably also into fat.
It is uncertain whether the glycogen is reconverted
into sugar and oxidised in the system, or whether it
enters the system as glycogen or some similar body.
In any case it is oxidised, being converted into C0 2
and H 2 0, and giving rise to heat, and supplying force
for the performance of work.
156 Food
INORGANIC MATERIALS
Various salts exist in the body in combination with
the organic materials that form the tissues. The chief
salts consist of calcium, sodium, potassium, magnesium,
and iron, in combination with chlorine, and phosphoric,
carbonic, and sulphuric acids.
The various salts form an essential part of the
food, inasmuch as they exist in every tissue of the
body. They exist in most forms of food consumed,
both animal and vegetable, in milk, in drinking-
water. Water is an important element in the food ;
it forms nearly 60 per cent, of the body-weight, and
is constantly being lost to the body through the lungs,
kidneys, and skin.
DIETETICS
Experience proves that a mixed diet is the best
to maintain the body in health. Dogs will not live
on hydro-carbons or carbo-hydrates alone. Too much
nitrogenous food leads to an excessive amount of urea
and uric acid, and throws increased work on the
excretory organs.
Milk, the food of early life, may be taken as a
typical illustration of a natural combination of the
various foods. Milk contains —
Water ....
Solids ....
Nitrogenous matters (casein-
Woman
87-88
12-13
Cow
86-87
ogen and albumen) .
Milk sugar , . . .
Fat . " .
Ash
1
7
4-
-2
■5
"2
4
4"
4-
-s
-5
'7
Cow's milk differs from woman's milk in that it
contains a larger amount of caseinogen, it curdles
more quickly, and the precipitated casein is heavier
Dietetics 1 5 7
and more solid than the casein of woman's milk.
There is less sugar in cow's milk than woman's milk.
In comparing cow's milk with the diet of an adult
given below, it will be noted that starches take the
place of some of the fat. If cow's milk were substi-
tuted for the diet given for moderate work, some eight
pints would have to be taken daily. The amount of
water taken would be an objection. Milk is, however,
an easily digested food, and is much used as a food in
illness.
Diet for Moderate Work. — The normal diet
for a man in health can only be arrived at by experi-
ence. Taking the average of a large number of
healthy persons, it has been found that the following
diet will suffice : —
Albuminous matter .
ozs. avoir.
• 4'5
gramme
I30
Fatty matter
Carbo-hydrates
Salts
• 3'°
I4'2
I'O
3 4
404
3°
Thus about 23 ozs. of dry solid food are contained
in this standard diet, about ith of which is nitrogenous.
If we reckon that 50 per cent, of ordinary food is
water, these 23 ozs. will correspond to 46 ozs. of
ordinary solid food. In addition about 50-80 ozs. of
water are taken. The force -producing value of this
standard diet is nearly 4,000 foot-tons.
The standard diet will necessarily be altered under
different conditions. It is said that an Esquimaux eats
about 20 lbs. of flesh and oil daily, and men working
heavily necessarily require more than when at rest.
Diet for Idleness. —
ozs. • grammes
Albuminous matter . . . 2-5 77
Fats i'o 28
Carbo-hydrates. . . . 12-0 340
Salts 0-5 14
158 Food
This diet will keep a man alive, but is not sufficient
if he performs any work.
Hard Work Diet. — The average dietary of a
labourer performing hard work has been calculated
at—
Nitrogenous matter .
ozs.
5'°
grammes
142
Fat
Carbo-hydrates .
Mineral ....
3'°
22'2
I'O
84
630
3°
Dynamic value, 5,232 foot-tons.
Taking the model diet for ordinary men
N.
c.
OZS.
grains
grains
Nitrogenous matter .
• 4'S
316
I,o68
Fat .
• 3'°
1,024
Carbo-hydrates
• 14*25
2,768
316 4,860
It appears, therefore, that a man on ordinary diet
and doing an ordinary amount of work requires 300
grains of N and 4,800 grains of C. (N 20 grammes
and C 320 grammes.)
The ratio of the quantities is 1 : 15. In albumen
the ratio is 1 : 3'5. Hence, if albumen alone were
used, and the 300 grains of N were supplied, there
would be a deficiency of C, and if the 4,800 grains
of C were supplied, there would be more N than
required. In bread the ratio is as 1 : 30 ; so that if
bread alone were used there would be a superfluity
or deficiency of either N or C. Two pounds of bread
and three-quarters of a pound of meat will fulfil the
above conditions, though they will do so better if 1-2
ozs. of butter be added. Or the following more varied
diet may be adopted : —
Dietaries
159
1 1 lb. bread
Foundation j i lb. meat
1 1 lb. fat .
1 1 lb. potatoes
. ■ U pint milk
Accessories -\ f ii
I t lb - eggs .
-L lb. cheese
c
grammes
117
34
84
45
20
J5
20
335
N
grammes
5'5
7'5
''3
2
3
21
Table showing amount of different constituents in
some foods
In 100 parts
Articles
Water
Albu-
minates
Fats
Carbo-
hydrates
Salts
Beef and mutton .
75
IS
8-4
1-6
Bacon .
15
8-8
73'3
—
2-9
Salt beef
49-1
29-6
•2
—
211
White fish
78
i8-i
2-9
—
1
Flour .
IS
11
2
70-3
17
Bread .
40
8
i-5
49 '2
i - 3
Rice
10
5
•8
83-2
•5
Oatmeal
IS
126
5-6
63
3
Peas (dry)
is
22
2
S3
2-4
Potatoes
74
i-5
■1
23-4
1
Eggs •
73"5
i3'5
n-6
—
1 •
Cheese .
36-8
33'5
24-3
—
5'4
Milk .
867
4
37
5
•6
Butter .
6
•3
9i
27
Sugar .
3
96'S
•5
(After Parkes)
Dietaries. — Infancy. — The newly-born infant is
generally put to the breast a few hours after birth, but
a few days generally elapse before the flow of the
breast-milk is thoroughly established, especially in the
1 60 Food
case of women who are mothers for the first time.
The infant at first takes the breast every two hours
during the day, and every four to six hours during
the night for the first six weeks or two months. After
this the infant takes more at a meal, and only takes
the breast every four hours during the day, and
sleeps most of the night. The infant is to be nursed
entirely from the breast for the first six or seven
months.
If artificially fed for the first month, it should take
10 ozs. of good cow's milk, diluted with an equal
quantity of barley-water or freshly-made whey ; 2 ozs.
being given every two or three hours during the day,
and every four hours at night.
This amount should be gradually increased so
that at three months of age 20 ozs. of milk diluted with
10 ozs. of barley-water or whey may be given every
four or five hours.
This amount should be again increased so that
when the infant is six months of age it is taking 30 ozs.
of undiluted milk.
From six months to twelve months. — From 30 ozs.
to 40 ozs. of milk should be taken, the milk being
thickened at some of the meals with some starchy
form of food, as rusks, biscuit powder, &c. As the
salivary and pancreatic secretions are not thoroughly
established before the age of six months, it is unwise
to give children any starchy foods before that date.
From one to two years. — At a year old, thicker
food, taken with a spoon instead of through a bottle,
may be given.
First meal, 7.30 a.m. — 8 to 10 ozs. of milk, with
finely crumbled bread or porridge.
Second meal, 11 a.m. — 6 to 8 ozs. of milk and
water.
Third meal, 1.30 p.m. — Some gravy or beef-tea,
with sopped bread-crumbs ; or a tablespoonful of
Diets 161
finely minced mutton chop and bread-crumbs. Light
pudding.
Fourth meal, 6 p.m. — Same as th,e first.
Diet for Children :
Breakfast. — Bread and butter, or porridge, 5 ozs. ;
milk, 10 ozs. or ad lib., may be diluted with weak tea
and sugar added.
Dinner. — Cooked meat, 3 ozs. ; vegetables. 2 ozs. ;
light pudding, 4 ozs.
Tea. — Bread and butter, 5 ozs, ; milk, 10 ozs. or
ad lib.
Diet for Adults: — {Full Hospital Diet) —
Breakfast. — Bread, 10 ozs. ; butter, § oz. ; coffee
or tea, with milk and sugar, 15 ozs.
Dinner. — Cooked meat, 6 ozs. ; potatoes, 8 ozs. ;
light pudding, 8 ozs.
Tea. — Bread, 10 ozs. ; butter, \ oz. ; coffee or tea,
15 ozs.
Supper. — Milk or bread and milk, 10 ozs.
An examination of the gains and losses of an
adult man in twenty-four hours, as estimated by direct
experiment when the body-weight was remaining
nearly stationary, showed that the gains in the form
of food, &c, roughly amounted to 20 grammes of N,
315 grammes of C, 2,000 grammes of water, and
24 grammes of salts ; 709 grammes of O in
respiration ; these being equal to about v.'nth the
weight of the body. His losses by the urine, feces,
and expired products amounted to 20 grammes of N,
274 of C, 248 of H, mostly in form of water, 2,630
of O in the form of C0 2 or H 2 and 24 of salts ;
leaving him 145 grammes heavier than before.
Effects of an Insufficient or Improper
Diet. — Infants or adults supplied with insufficient
M
1 62 Food
food become pale, emaciated and weak, and often die
of some intercurrent disease, to which their weak
state predisposes, as diarrhoea or dysentery. The
effects of an improper diet are especially seen in
infants when fed on thick starchy foods. They suffer
from indigestion, flatulence, constipation or diarrhoea,
are fretful and sleepless, become wasted, suffer from
skin eruptions, and are frequently convulsed before
death.
Effects of Food in Excess— One of the
principal effects of an excess of proteid food is to
throw extra work on the excretory organs, as • the
liver and kidneys : this result is especially marked
when little exercise is taken. Gout, lithaemia with
disordered liver and kidneys, and indigestion are apt
to follow. The effects of an excessive amount of
fatty or starchy matters in the food is sometimes
shown in the excessive formation of adipose tissue,
and often in indigestion.
Effects of Starvation. — The most prominent
symptoms are, first, pain in the epigastrium, relieved
by pressure ; this subsides in a day or two, and is
succeeded by a feeling of weakness and of intense
thirst. The countenance becomes pale, the body
exhales a peculiar fcetor, and the bodily strength
rapidly fails. The temperature is lower than normal.
The mental powers exhibit similar weakness, first
stupidity, then imbecility, which sometimes is suc-
ceeded by maniacal delirium. Life terminates by
gradually increasing torpidity, or, occasionally, by a
convulsive paroxysm.
With entire abstinence from food and drink, death
occurs in from eight to ten days. The Welsh fasting
girl lived eight days. This time may be prolonged if
water can be obtained, or if surrounded by a warm
damp medium.
The loss during starvation falls most heavily on
Digestion
163
the fat, next the glandular organs, then the muscles,
the heart and brain being affected least The post-
mortem examination shows extreme emaciation and
complete absence of fat. All the organs, with per-
haps the exception of the brain, are bloodless ; the
coats of the intestines are thin and empty of contents ;
the gall-bladder full, the bile staining the surrounding
parts. The body rapidly passes into decomposition.
The percentage of dry solid matter lost during
thirteen days by the most important tissues of a cat
was as follows :—
Adipose
tissue
97 "o per cent
Spleen
63'i V
Liver .
56-6 „
Muscles
3°' 2 »
Blood
17-6 „
Brain and cord
o'o „
CHAPTER
XIII
DIGI
iSl
'ION
Teeth.
Two sets of teeth make their appearance during the
life of man :—
I. The temporary or milk teeth (20).
II. The permanent set (32).
I. The Temporary Set appear during the first
two years of life. They consist of two incisors, one
canine, and two molars in each half-jaw, making
twenty in all.
They make their appearance through the gums in
M 2
164 Teeth
five groups, in the following order (though exceptions
occur even in healthy children) : —
First group — Two lower central
incisors .... 6th- 8th months.
Second group — Four upper in-
cisors ..... 8th-ioth „
Third group — Two lateral lower
incisors and first four molars . i2th-i4th ,,
Fourth group — Four canines . i8th-2oth „
Fifth group — Four back molars . 2oth~3oth „
II. The Permanent Set. — The first six months
of life arc passed without any teeth ; by the end of
the second year or middle of the third the milk teeth
have all appeared, and these begin to be replaced by
the permanent set at the sixth year, and are completely
replaced by them at the twelfth or thirteenth year ; the
teeth being completed by the eruption of the wisdom
teeth at the age of about twenty-one. When com-
plete there are thirty-two, there being two incisors, one
canine, two bicuspids, and and three molars, in the
half of either jaw.
The molars of the temporary set are replaced by
the permanent bicuspids ; the three permanent molars
appear in the jaw behind the molars of the milk teeth.
The permanent teeth appear in the following
order : —
6th year
First molars.
7th „
Two central incisors
8th .,
Two lateral incisors.
9th „
First bicuspids.
10th ,,.
Second bicuspids.
nth-i2th years
Canines.
i2th-i3th ,,
. Second molars.
i7th-2ist ,,
Wisdom teeth.
The Incisors (8) are arranged side by side in the
Structure of the Teeth 165
front of the jaws. They have a single long conical fang,
and a sharp chisel-shaped edge, for dividing the food.
The Canines (4) are placed singly next to the
lateral incisors. Their fangs are single, large, and
conical, compressed laterally, and cause a prominent
ridge on the alveolus of the jaw. The crown is more
pointed than in the incisors.
The Bicuspids (8) are arranged four in each
jaw. The fangs are bifid at their apices, more marked
in the upper and second bicuspids, and are grooved
laterally. The crown is compressed from before back-
wards, and is surmounted by two tubercles, or cusps,
separated by a groove.
The Molars (12) are arranged three in each jaw,
behind the bicuspids. They have from two to three
fangs. In the two anterior molars of the upper jaw
there are three in number, two external and one
internal. The two anterior molars of the lower jaw-
have two fangs, one anterior and one posterior. In
the third molar, or wisdom tooth, the fang is irregular
and single. The crowns of the molar teeth are
cuboidal in form, rounded on each lateral surface, and
flattened in front and behind. The upper molars
have four cusps at the angles of the grinding surface,
separated by a crucial depression ; the lower molars
have five cusps. The molars, from the great breadth
of their crowns, are suitable for grinding and pound-
ing the food.
Structure. — Minute anatomy : A tooth consists
of a croiifn, which projects from the gum ; a root, or
fangs, which are fixed in a socket in the bone ; and a
short intermediate ?ieck. Each is supplied with an
artery and nerve, and has a central cavity filled with a
soft vascular sensitive substance, the pulp. On ver-
tical section a tooth shows —
1. Pulp. 3. Dentine.
2. Crusta petrosa. 4. Enamel.
1 66
Teeth
i. The Pulp .occupies the central cavity of the
tooth, and consists of fine connective tissue, nucle-
ated cells, blood-vessels, and nerves, The cells, or
Fig. 67.— Vertical section of the upper part of an incisor tooth (IColliker).
«, the pulp cavity ; £, dentine ; c, arched incremental fibres ; d, cement :
c, enamel with bands indicating the direction of the range of fibres ',/,
coloured lines of the enamel.
odontoblasts, form a stratum on the surface of the
pulp, and send fine processes into the dentine tubules.
The arteries are derived from the internal maxillary,
and the nerves from the fifth pair.
Development of the Teeth 167
2. The Crusta petrosa, or cement, covers the
fang of the tooth, its place being taken below by the
enamel which covers the crown. In structure it re-
sembles bone, containing lacunas and canaliculi, but
they are larger and more irregular.
3. The Dentine forms the principal mass of the
teeth ; it is protected by the crusta petrosa and enamel,
and hollowed out in the centre to form the pulp-
cavity. It is somewhat harder than bone, and differs
from it in structure. It is penetrated by numerous
fine tubes, giving it a striated appearance beneath the
microscope, the tubes appearing dark and the matrix
in which they lie transparent. The tubules open into
the pulp-cavity, and radiate to the periphery, giving
off small branches. They are 5 ,-,'„„■ in. in breadth,
and have a distinct wall, the dental sheath. As the
dentine is sensitive, it is possible they may convey
nerve-fibres as well as prolongations' of the cells of
the pulp-cavity. The matrix is homogeneous.
4. The Enamel is very hard and covers the crown.
It is made up of microscopic prisms arranged side
by side ; these prisms are six-sided and -50V0 m> m
diameter, and are marked at intervals by transverse
lines.
Chemical Composition. — The hard tissues of
the teeth, like bone, consist of animal and mineral
matter : the former yields gelatin on boiling, and
exists in different amounts in the tissues —
Bone . . 33 per cent, animal matter.
Crusta petrosa 30 ,, „ ,,
Dentine . . 28 ,, ,, ,,
Enamel . . 3-5 „ „ „
The mineral matter consists of calcic phosphate
and carbonate, magnesic phosphate and calcic fluo-
ride.
Development.- At the seventh week of intra-
i68
Teeth
uterine life a groove appears on the surface of the
jaws, which involves the soft embryonic tissues of the
jaw as well as the Malpighian layer of the epithelium.
It was called by Goodsir the primitive dental groove.
This down-growth of epithelium forms the common
enamel-germ (fig. 68, /), and from it the enamel is
developed. From the bottom of this groove, which
has become flask-shaped in section, papilla;, ten in
number, arise. These
papillae, as they grow up-
wards, push before them
and become surrounded
by the enamel-germ, and
the portion of the primi-
tive groove in which each
is situated becomes cut
off from the rest, so that
now the papilla has be-
come enclosed in a
cavity. In the meantime
the cavity containing the
papilla becomes sur-
rounded by a vascular
membrane, the dental
sac. The papilla now acquires more and more the
shape of the future tooth (fig. 69/). By the end of the
fourth month of foetal life, thin caps of dentine are
formed on the papillae of all the temporary set. At
the time of birth, the crowns of the anterior milk
teeth are fully formed (see fig. 70). After birth de-
velopment proceeds, the fangs being formed, so that
they are ready to be cut in the order given (p. 164).
The sacs in which the ten permanent teeth which
replace the temporary are formed are derived from
the neck of the enamel-germ (fig. 69 B,/p), and these
form the enamel-germs of the future teeth. The pos-
terior permanent teeth (the three molars) arise from
Fig. 68.— Section across the upper jaw
of a fecial sheep (Waldeyer). c c',
epithelium of mouth ; j\ neck ; _/"',
body of special enamel genu.
Development of the Teeth 169
Fig. 69.— Sections at later stages than fig. 68, the papilla having become
formed (KLolliker). c, epithelium of the gum ;/ t neck of enamel germ ;
f\ enamel organ ; e, its deeper columnar cells ; p, papilla ; s, dental sac ;
B,y^*, enamel germ of permanent tooth.
170
Digestion
sacs formed by an extension backwards of the original
groove.
At birth only one of the permanent set, namely,
the first molar, has its cap of dentine already formed
though this is not constant ; the calcification of the
incisors commences a month or so after birth, the
"ig. 70. — The dental sac exposed in the jaw of a child at birth (Quain's
Anatomy). ) sympathetic from the cervical
sympathetic.
Deglutition
Deglutition is a complicated act by means of
which food passes from the mouth into the oesophagus
without any part of it being allowed to enter the
nasal cavity or the larynx. It is usually divided into
three acts : —
i. The passage of food to the back of the mouth.
2. Its passage across the orifice of the larynx.
3. Its seizure by the constrictors and its passage
through the oesophagus to the stomach.
1. The bolus having been prepared, the tongue
carries it back through the anterior pillars of the
fauces, the movement being effected through the
agency of the stylo-glossus and intrinsic muscles of
the tongue.
2. The soft palate is raised by the action of its
muscles, and, assisted by the contraction of the upper
part of the superior constrictor, shuts off the cavity of
(Esophagus 1 8 1
the nose from the pharynx. The larynx is raised
behind the hyoid bone by the action of the stylo-
pharyngeus and thyro-hyoid, the vocal chords are
approximated, and the epiglottis closely fitted over
the rima glottidis by the action of the depressor.
The passages both into the nares and larynx being
closed, the descending bolus passes over the root of
tongue, the epiglottis, and beneath a roof formed by
the contraction and approximation of the palato-
pharyngeal muscle, is seized by the constrictors, and
propelled into the cesophagus.
The first stage in which the tongue passes the
bolus to the isthmus faucium is a voluntary act. The
second and third are purely reflex, and can take place
independently of the will and during sleep, or in a
state of coma. Patients who are unconscious will
swallow if partly raised up and liquids out of a
' feeder ' be allowed slowly to trickle over the back of
the tongue. In profound coma swallowing becomes
impossible. The respiration centre is lower in the
medulla than the deglutition centre, and may continue
in action when the former will not.
Deglutition is a reflex act. The afferent nerves are
the glosso-pharyngeal and branches of the 5th. The
nerve centre is in the medulla. The efferent nerves are
the pharyngeal branch of vagus, hypo-glossal, glosso-
pharyngeal, and facial.
The (Esophagus
The cesophagus is the muscular tube extending
from the pharynx to the stomach. It consists of
three coats : —
1. External, or muscular.
2. Middle, or submucous.
3. Internal, or mucous.
1 82 Digestion
i. The External consists of an outer layer of
longitudinal and an inner layer of circular muscular
fibres. The muscular fibres in the upper part are
striated, but are gradually replaced by non-striated in
the lower half.
2. The Submucous coat consists of connective
tissue, and contains some mucous glands.
3. The Mucous coat is pale in colour, and when
the oesophagus is contracted is thrown into longitu-
dinal folds. In structure it resembles the skin, having
a cutis, papilte, rete mucosum, lined by stratified
flattened cells.
The food is propelled along the oesophagus by the
peristaltic action of its muscular walls. It is a reflex
act ; the afferent and efferent nerves are supplied by
the vagus. The centre is in the medulla. Food ac-
cumulates in the oesophagus of an animal in which
the vagus is divided below the pharyngeal branches,
the animal being able to swallow the food, but the
oesophagus fails to pass it on into the stomach, from
paralysis of its muscular walls.
Stomach
The stomach is a somewhat conical or pyriform-
shaped sac, the left extremity or cardiac end being the
larger, the right or pyloric extremity being the smaller.
It has two orifices, the cardiac, where the oesophagus
enters, and the pyloric orifice, at the entrance into the
duodenum. When moderately distended it measures
10 to 12 inches in length, and from 4 to 5 inches in
breadth.
Structure. — Four coats :
1. Serous. 3. Submucous.
2. Muscular. 4. Mucous.
1. The Serous is divided from the peritoneum ;
it invests the whole organ, except at the curvatures.
Stomach 183
2. The Muscular contains fibres of the non-
striated variety. Longitudinal , best marked along the
curvatures and near the pylorus. Circular, forming
a complete layer over the whole extent of stomach,
becoming thick and strong at the pylorus, and form-
ing the sphincter. Oblique, scattered over surface
and continuous with circular of cesophagus.
3. The Submucous consists of a layer of con-
nective tissue between the muscular and mucous.
4. The Mucous is a smooth pink membrane,
which is loosely attached to the tissue beneath, and
when the stomach is empty is thrown into ruga;. The
mucous membrane contains a fine layer of muscular
tissue, the muscularis mucosa, internal to which are
the tubular glands.
The epithelium of the surface consists of a layer
of columnar cells extending into the mouths or ducts
of the gastric glands.
Gastric Glands. — On examining a section of
stomach stained with logwood or aniline, rendered
transparent with glycerine, the gastric glands are seen
parallel to one another and closely crowded together
with their blind extremities towards the muscularis
mucosa?, and opening on the surface of the mucous
membrane. Their length varies from -£$ to -^ in.,
and diameter ^^ to -g^ v in. in breadth. Two different
kinds of glands are distinguished ; some in larger
numbers near the pyloric orifice are lined throughout
with columnar epithelium, and are supposed to secrete
mucus, and are called pyloric glands. The cardiac
glands, so named from the portion of the stomach
where they occur most numerously, have columnar
epithelium at their mouths only, the rest of the gland
being lined by two different sets of cells ; those at
the circumference of the tubule resting on the base-
ment membrane, being oval in shape, are called ovoid
ox parietal, and another set, occupying a more central
1 84
Digestion
position, are cubical or columnar in shape, and are
termed central cells. These
cells are finely granular,
and contain an oval nucleus.
They are occupied by num-
erous granules during fast-
ing, but which, like the
granules in the cells of the
salivary glands, mostly dis-
appear during a period of
activity. Delicate lymphoid
tissue may be seen in places
in the mucous membrane,
resembling the solitary
glands of the intestine.
The Gastric Juice is
a thin colourless acid fluid
of specific gravity iooi to
ioio, containing | to i
per cent, of solids in man.
The daily amount varies,
an average being 10 to 12
pints (7 to 8 litres). It
contains —
1. Pepsin.
2. A curdling ferment.
3. Hydrochloric acid
(free).
4. Mucin.
5. Salts and water.
About two-thirds of the
solid matter consists of
peptones and pepsin, and
one-third of salts. Amount
of free HC1='2 per cent.
Artificial Gastric Juice is best prepared by
dissecting off the mucous membrane of the stomach
Fie. 75. — A cardiac gland from
the bat's slomach (Langley).
c, columnar epithelium of the
surface ; n, neck of the gland
with central and parietal cells ;
/, base or fundus, occupied only
hy principal or central cells,
which exhibit the granules ac-
cumulated near the lumen of the
gland.
Gastric Juice 185
of a pig, cutting it into small pieces, and digesting it
in glycerine for a few days, filtering and adding fresh
mucous membrane. This may be repeated several
times. Each time the glycerine will take up a fresh
quantity. A little of the glycerine extract added to
•2 per cent, solution of HC1 will form an active arti-
ficial-gastric juice.
Action of Gastric Juice on Proteids.— The
characteristic action of gastric juice is its action on
albuminous compounds, converting them into the
peptones. If shreds of fibrin be placed in artificial
gastric juice and kept at a temperature of 38 C, the
shreds first swell up and become transparent, then
gradually dissolve, leaving only some slight fiocculent
remains. If thin slices of white of egg be similarly
treated, the edges become translucent, and finally
they completely disappear. This completes the first
stage of the process, the proteid being converted into
acid-albumen or syntonin. As the digestion proceeds,
first albuminose and finally peptone is formed. Both
albuminose and peptone are present in the final pro-
duct. The presence of these three bodies can be de-
monstrated in the following way : — (1) by neutralising
a portion of the fluid with sodium carbonate, a pre-
cipitate of acid-albumen occurs ; (2) on adding HN0 3
to another portion, a precipitate of albuminose occurs,
which disappears on warming and reappears on cooling;
(3) a third portion of the fluid is shaken with amnion,
sulphate, filtered, and the filtrate tested for peptone by
adding NaHO and a trace of copper sulphate, a rose
colour indicates that peptone is present (see p. 18).
Action on various Foods. — Cooking renders
meat more digestible by separating and breaking down
the fibres. When exposed to the action of gastric
juice the connective tissue is dissolved, and the fibres
set free ; the transverse striae become well-marked, the
fibres show a tendency to transverse cleavage, and
1 86 Digestion
finally become broken up and disappear. The fatty
matters are set free from their envelopes. Fish and
eggs are digested in the stomach in about one hour
and a half ; beef, mutton, and fowls in two and a half
to three hours. The gluten of bread is dissolved and
converted, like albumen, into peptone, the starch
being set free. Milk is quickly coagulated by gastric
juice, the casein being precipitated ; this is apparently
brought about by the action of a curdling ferment.
The coagulated casein is quickly redissolved and con-
verted into peptone.
Gastric juice has no action upon elastic tissue,
cellulose, starch, or mucus.
The part that pepsin plays in digestion is that of
a ferment resembling the action of ptyalin in the
saliva. Pepsin is not destroyed in the act of diges-
tion ; its digestive power appears to be infinite. Yet, if
more and more fibrin be added to artificial gastric
juice, it will at last remain undissolved, the arrest of
digestion being due to an accumulation of the pep-
tones and want of acid. For, if the liquid be diluted
and more acid added, digestion will recommence.
The activity of the pepsin is greatest at a temperature
of 3o°-so° C. (9o°-ii2° F.). It is completely de-
stroyed by boiling.
Gastric juice contains a distinct ferment which has
the property of curdling milk (W. Roberts).
Chyme. — The grumous acid fluid, resulting from
the digestion of the food in the stomach, is termed
chyme. It contains (i) peptones resulting from the
conversion of various proteid substances — albumen,
fibrin, casein, gelatin, &c. ; (2) various partly-digested
proteids, as muscular fibre, connective tissue ; (3) cer-
tain substances which are not digested in the stomach,
as fat, cellulose, elastic tissue, starch, &c. ; (4) various
salts and sugar in solution.
Digestion of the Stomach. — If a quantity of
Stomach
187
milk be introduced into the stomach of a rabbit and
the animal killed an hour after and laid in a warm
place for twenty four hours, the walls of the stomach
I it
111 ! ■■; ^ ,
■ / - " .
-' ■■
%dlar
Frc 76. — Diagram of the abdominal part of the alimentary canal (Brinton).
c, the cardiac ; p, pyloric end of the stomach ; d, the duodenum ; J, 1,
convolutions of the small intestine ; cc, csecum ; AC, ascending colon ;
tc, transverse, and nc, descending colon ;sf, sigmoid flexure ; r, rectum ;
A, anus,
will probably be found digested. If a portion of the
stomach of a dog be ligatured, the wounded stomach
188 Digestion
<•>'
sewn up, and the dog allowed to live a few hours, the
portion included in the ligature will be digested. The
stomach itself is not digested during life, in conse-
quence of the circulation through its walls of alkaline
blood.
Secretion of Gastric Juice. — The stomach
has two secretions, one thick, tenacious, and alkaline
— the gastric mucus ; the other, thin, acid, and watery
— the gastric juice proper. The former is secreted
during fasting, while the latter is only secreted when
food or fluid enters the stomach. Saliva or alkalies,
pepper, alcohol, excite the secretion of gastric juice.
Their action is reflex : the vagus is probably the
afferent nerve, which acting on the medulla, inhibits
the sympathetic and dilates the blood-vessels supply-
ing the glands ; the efferent impulses descending
along the splanchnics.
Movements of the Stomach.— Food during
digestion in the stomach is kept in motion by the
peristaltic action of its walls. By the contraction of
its muscular fibres currents are set up in its contents,
the food travelling along the large curvature and re-
turning by the lesser, while as digestion proceeds
certain portions are passed through the pylorus into
the duodenum.
Vomiting is a reflex act by which the contents
of the stomach are expelled through the oesophagus
and mouth. Very different circumstances may give
rise to vomiting : —
i. Irritation of the terminal fibres of the vagus
from the presence in the stomach of certain sub-
stances, as ipecacuanha, or a catarrhal state of the
mucous membrane.
2. Irritation of the terminal fibres of different
branches of the vagus or sympathetic, as in tickling
the fauces, an inflamed peritoneum, an enlargement
of the uterus, as in the vomiting of pregnancy.
Small Intestine 189
»
3. Direct irritation of the nervous centres, as in
tumour of the brain, or circulation through the nerve-
centres of certain substances, as apomorphia.
4. Vomiting may also be induced by disgusting
smells, sights, or tastes. The afferent nerves depend
upon the cause ; they may be the vagus, sympathetic,
first, second, &c. The nerve centre is probably in the
medulla. The efferent nerves are the phrenics and
nerves to the abdominal muscles.
Mechanism of Vomiting.— Peristaltic waves
run from the pylorus to the cardiac end of the
stomach, the cardiac aperture being firmly closed.
Then, a deep breath having been taken, the diaphragm
fixed, and glottis closed, the cardiac sphincter is sud-
denly opened by fibres continuous with the longitu-
dinal fibres of the oesophagus, the abdominal muscles
contract, and, the stomach being fixed by the dia
phragm, its contents are expelled.
Structure of Small Intestine. — The small
intestine commences at the pylorus and empties itself
into the caecum, and is about 20 ft. in length. It is
divided into three portions, the duodenum, occupying
the first 10 or 12 inches, the upper two-fifths of the
remainder being jejunum, and the lower three-fifths
ileum.
It has four coats, serous, muscular, submucous,
mucous. The Serous entirely surrounds the gut,
except where the vessels enter. The Muscular con-
sists of two layers, external longitudinal and internal
circular. The Submucous is a loose connective
tissue layer between the mucous and muscular. The
Mucous lines the intestine, and in the upper part of
the jejunum is thrown into numerous transverse folds
called the valvules conniventes, which are permanent
and extend about two-thirds of the way round the in-
testine. They increase the absorbing surface and help
to delay the contents of the intestine. The mucous
190
Digestion
coat is separated from the areolar by a thin layer of
muscular fibres, the muscularis mucosa, and like the
stomach, is lined by columnar epithelium. It is pro-
vided with —
i. Villi.
2. Brunner's glands.
3. Crypts of Lieberkuhn.
4. Solitary glands.
5. Peyer's glands.
6. Lymphoid tissue and vessels.
1. The Villi are small processes of mucous mem-
brane which extend from the pylorus to the ileo-csecal
Fig. 77. — Transverse section of a villus of the cat's intestine (Schafer).
c, columnar epithelium ; g, goblet cell ; /, lymph corpuscles between
epithelium ; 6, basement membrane ; c, blood capillaries ; ;«, section of
muscular fibre ; ci, central lacteal.
valve, and give the inner surface of the intestine a
velvety appearance. They are about ¥ ] „ to J a inch in
length, and are closely set together. They consist of
an external layer of columnar epithelium, a basement
membrane, a plexus of capillary vessels, a lacteal
Small Intestin
ne
191
vessel, a few muscular fibre cells prolonged from the
muscularis mucosae, and lymphoid tissue-(fig. 77).
2. Brunner's Glands are small compound
glands existing in the duodenum. They consist of
clusters of acini in connection with a minute duct,
which opens on the surface.
3. The Crypts of Lieberkuhn are minute
blind tubes which exist in every part of the intestine
Fig. 78.— Vertical section of a portion of a patch of Peyer's glands, with
lacteal vessels injected (Frey). a, villi ; 6, tubular glands ; c, muscular
layer of the'mucous membrane ; it, cupola or projecting part of a lymphoid
gland ; e, their central part ; /", g, g', lacteal vessels.
opening between the villi. They are lined by co-
lumnar epithelium, and are T \- s inch to 3-^ inch in
length (fig. 78 b).
4. The Solitary Glands are small white bodies
about the size of millet seeds scattered through the
192 Digestion
intestine. They consist of lymphoid tissue surrounded
by a plexus of capillaries.
5. Peyer's Glands are a group of glands re-
sembling the solitary glands in structure (fig 78).
They are situated for the most part in the lower
portion of the ileum. The groups are oblong, and
placed lengthways in the intestine opposite to the
attachment of the mesentery.
6. Lymphoid tissue is found in various places
in the submucous tissue, in addition to that of the
solitary and Peyer's glands.
Secretions poured into the Intestine
Bile is an alkaline, golden-yellow fluid of a bitter
taste and specific gravity 10 18, and containing about
14 per cent, solid matter. If it remain long in the
gall-bladder it becomes viscid, from the presence of
mucus. From 30 to 40 ozs., or 1000-1500 grammes,
are secreted in 24 hours.
Composition : —
Per cent.
I.
Mucin |
2.
Bile-pigments . . J
2 ~3
3*
Sodium salts of bile-acids .
9-10
4-
Cholesterin . . 1
5-
Lecithin 1
' 2_- 3
6.
Salts
■5-i
7-
Water ....
85-86
Bile-pigments. — The yellow colour of the bile ot
man and the carnivora is due to Bilirubin ; the green
colour of herbivora and that of man after oxidation
is due to Biliverdin. A small quantity of Biliprasin
may be present.
Gmeliris Test.— When strong yellow nitric acid
is added to bilirubin or human bile on a white plate,
Bile 193
a succession of colours is produced in the order of
the colours of the spectrum — green, blue, violet,
indigo, and red. If biliverdin be used the same
result occurs, the first colour being blue. In apply-
ing the test to urine, care must be taken to notice
the colours succeed one another in their right order,
as the presence of indican may cause green, blue,
and yellow colours.
Bilirubin may be prepared from dog's bile by
acidulating with acetic acid and shaking with chloro-
form ; the chloroform dissolves the bilirubin, and on
evaporation leaves the pigment of a red colour.
Biliverdin may be obtained by allowing an
alkaline solution of bile to become green by exposure
to the air. The bilirubin is oxidised and biliverdin
formed ; it may be separated by precipitating by
HC1, dissolving in alcohol and evaporating. Bili-
rubin is believed to be derived from haemoglobin
during its passage through the liver. It seems to
be identical with the haematoidin found in old blood-
clots.
The Bile-acids are taurocholic and glycocholic
acids. These acids are composed of cholic acid in
combination with taurin and glycocine.
Pettenkofer 's Test. — A small quantity of dilute bile
is mixed with a few drops of sugar (cane sugar) and
strong H a S0 4 added ; the solution becomes first
cherry red, then of a purple colour. Some other
organic substances give a similar colour, but may be
distinguished by the spectroscope.
Preparation. — Bile is rubbed up with animal char-
coal and dried at steam heat ; it is thus rendered
colourless. The bile-acids are then dissolved out by
absolute alcohol and precipitated by ether, as silky
needles which readily take up moisture and form a
syrupy fluid.
Cholesterin can be obtained best from gall-stones
1 94 Digestion
by boiling with alcohol and filtering while warm ;
white rhombic crystals of cholesterin form (fig. 6).
Uses of Bile
i. Slight action in converting starch into sugar
2. Assists in emulsifying and saponifying fats.
3. Assists in the absorption of fats.
4. Increases peristaltic action.
5. Prevents putrefactive changes in intestines.
The action that bile exerts in converting starch
into sugar and in emulsifying fat is slight. Mucous
membrane wetted with bile allows minute globules
of fat to pass readily through it, and in this way it
aids the absorption of fat. It increases the peri-
staltic action of the intestine, thus aiding in the
propulsion forwards of the contents of the intestine.
It stimulates the contraction of muscular fibres of
the villi, emptying the lacteal, and forcing onwards
its contents. It checks putrefactive changes. In
jaundice, where the bile is prevented from flowing
into the intestine, there is a tendency to constipation
and flatulence.
Bile is being constantly secreted, and accumulates
till required in the gall-bladder. When the acid con-
tents of the' stomach enter the duodenum a reflex
action is set up, leading to the contraction of the gall-
bladder, and pouring out of bile into the intestine.
Pancreas
The pancreas is an elongated lobulated gland,
which lies across the abdomen, behind the stomach,
and in front of the first lumbar vertebra. It is 6 to 8
inches long, 1 !, inches average thickness, and weighs
from -2.\ to 3?? ounces.
Pancreas
195
The cells lining the alveoli are columnar or pyra-
midal in shape, with a spherical nucleus. Their
protoplasm is finely granular near the lumen, and
transparent near the basement membrane (fig. 79).
After a period of activity, nearly the whole cell be-
comes clear.
Structure. — The pancreas belongs to the class
of compound racemose glands, and closely resembles
IK
H&iafofifii
Fig. 79.— Section of the pancreas of the dog (Klein), a, termination of
duct in the tubular alveoli, a.
the salivary glands, though of somewhat looser texture
the lobules being separated by more connective
tissue.
Pancreatic Juice is a clear, viscid, alkaline fluid
resembling saliva, but of greater specific gravity, and
containing from 2 to 5 per cent, of solid matter.
About 12 to 16 ounces are secreted in 24 hours.
It contains : —
1. Four ferments :
(a) Trypsin, changes proteids into peptones.
1 96 Digestion
(b) Pancreatic diastase, changes starch into
dextrin and maltose.
(c) Curdling ferment, precipitates the casein of
milk.
(d) Emulsive ferment, emulsifies and saponifies
fats.
2. Albumen. 3. Mucin 4. Salts and water.
Action
i. It changes proteids into peptones in alkaline or
neutral solutions, afterwards decomposing them into
leucine and tyrosine.
2. It converts starch into dextrin and sugar.
3. It emulsifies and saponifies fats.
On Proteids. — Pancreatic juice artificially prepared
from pancreas acts in a somewhat similar manner on
proteids as gastric juice, but can go further and break
up peptone into leucine and tyrosine. It acts ener-
getically on some proteids, as the casein of milk, pro-
vided the solution is alkaline, but is less active than
artificial gastric juice on white of egg. Its solutions
require to be alkaline, equivalent to one per cent, of
sodium carbonate. Its activity depends upon a ferment
called trypsin.
Pancreatic digestion of proteids differs from gastric
in that (1) it requires an alkaline instead of acid
medium ; (2) the proteids are dissolved without the
preliminary swelling ; (3) leucin, tyrosin, and similar
bodies are formed.
On Starch. — Pancreatic juice acts with great
energy on raw or cooked starch, quickly converting it
into dextrin and maltose. It is more energetic than
saliva.
On Fats. — Pancreatic juice, when shaken up with
fats and oils, reduces the oily matters to a state of fine
Large Intestine 197
division and suspends them, forming a milky fluid. It
also splits up fats into glycerine and their respective
acids.
An artificial pancreatic juice can be made by
pounding up fresh pig's pancreas with powdered glass,
and adding dilute spirit or glycerine.
If artificial pancreatic juice be added to milk,
coagulation takes place ; if the milk is rendered alka-
line by carbonate of soda, before the addition of the
pancreatic fluid, no curdling takes place ; and at a
temperature of about 35° C. the casein is gradually
converted into peptone.
Succus Entericus. — This is the secretion of
the intestinal glands. It appears to act in a similar
way to pancreatic juice. It also contains a ferment
which converts cane sugar into invert sugar.
Large Intestine
The large intestine consists of caecum, colon,
rectum.
Structure —resembles the small intestine, with
some modifications.
The Serous coat completely surrounds the in-
testine in the transverse colon ; is incomplete else-
where.
The Muscular coat consists of two layers, the
longitudinal being arranged in three flat bands, except
at the rectum. One band is posterior, another an-
terior, and a third lateral or inferior in the transverse
colon ; along the latter the appendices epiploicae are
attached. These longitudinal fibres, by being shorter
than the intestine, throw it into sacculi, which are
marked off from one another by constrictions where
the circular fibres are most marked. The circular
fibres form a thin layer over the intestine, and are
best marked at the constrictions.
198 Digestion
The Mucous membrane is lined with columnar
epithelium, and is destitute of villi. It has numerous
glands of Lieberkuhn and solitary glands, also retiform
tissue.
The junction of the small and large, intestine is
guarded by a valve, and the termination of the rectum
by the sphincter. But little, if any, digestive action
goes on in the large intestine ; the principal work
done is absorption ; the contents of the intestine be-
come firmer and harder as they approach the rectum.
The contents of the large intestines are acid, from the
acid fermentations going on in the faecal matters.
Movements of the Intestines
If the abdomen of a recently killed animal be
opened, the muscular fibres of the intestines will be
seen alternately contracting and relaxing, but working
down the intestine in waves so as to propel the con-
tents downwards. This peristaltic action is increased
by the presence of food or bile, or by irritation of
the vagus nerve. It is checked by irritation of the
splanchnic. The exact nervous mechanism is un-
known, but it is probably automatic, like the action
of the heart. The movements of the large intestine
resemble those of the small ; the feces are lodged in
the sacculi during the relaxation of the intestine.
Defecation.— The sphincter is normally con-
tracted under the influence of a nervous centre in the
cord. The sigmoid flexure prevents the feces from
pressing too heavily on the rectum. The act of
defecation consists in an inhibition of the nervous
centre in the cord which governs the sphincter, re-
laxation of the sphincter taking place. At the same
time a deep breath is taken, the glottis is closed, the
diaphragm and abdominal muscles contract, press
Summary
199
upon the descending colon, and eject the contents of
the rectum, the sigmoid flexure having previously
become filled by peristaltic action.
Summary of Digestive Changes
The essential work of digestion is performed by
a singular group of bodies termed ferments. These
bodies are found in nearly all the secretions poured
into the alimentary canal, and play an exceedingly
important part in dissolving the food. These fer-
ments are soluble in water, and differ in this respect
Table of the digestive juices and their
ferments (Roberts).
Pancreatic
juice
Intestinal
juice
Digestive fluid
Saliva .
Gastric juice .
Ptyalin or
Diastase
; a. Pepsin
b. Curdling
1 ferment
a. Trypsin .
b. Curdling
I ferment
1. Diastase .
\d. Emulsive
» ferment
Invertin .
Action
Changes starch into dex-
trin and sugar
Changes proteids into al-
bumose-peptone in the
acid solution
Curdles casein of milk
Changes proteids into pep-
tone in alkaline solu-
tions
Curdles the casein of milk
Changes starch into sugar
Emulsifies and partly sa-
ponifies fat
Changes cane sugar into
invert sugar
2oo Digestion
6
from the organised insoluble forms, as the yeast plant.
They diffuse through animal membranes, though with
difficulty ; they are rendered inert by a heat of 70° C.
(160 F.), and they are precipated by strong alcohol.
Mouth. — The food is crushed, mixed with saliva
and reduced to a pulp ; a certain amount of starch
converted into maltose and rendered slightly alkaline.
Fats and proteids unaltered.
Stomach. — Contents rendered acid, conversion
of starch into sugar ceases, connective tissue of fats
dissolved, and fats set free. Proteids dissolved and
peptones formed. The albuminous foods are dis-
solved for the most part, and a grumous mixture of
peptones, liquid fats, and starches is formed, which is
termed chyme, and is gradually passed through the
pylorus into the intestine.
In the Intestine. — The chyme mixes with the
bile, pancreatic and intestinal juices, becomes alkaline,
conversion of starch into sugar recommences, emul-
sifying of fat begins, and the undissolved proteids
are converted into peptones. The diffusible peptones
and salts enter the portal vein, the fat in a fine state
of division entering the lacteals. In the large intes-
tine the liquid chyme becomes more and more solid,
is rendered acid by fermentative changes, and acquires
the odour of fasces.
CHAPTER XIV
ABSORPTION AND NUTRITION
The food must be acted upon by the various secre-
tions of the alimentary canal before it can enter the
blood-vessels or lacteals with which the walls of the
stomach and intestines are well supplied.
Absorption 201
The Albuminous Foods are crushed and re-
duced to pulp in the mouth, and converted into the
peptones by the action of the gastric, pancreatic, and
intestinal juices. By far the greater part of the pep-
tones thus formed enter the capillary blood-vessels
of the stomach and villi. Being diffusible through
animal membranes, they pass through the walls of the
capillaries by osmosis, enter the portal vein, and are
conveyed to the liver. In the liver they are either
split up into more oxidised bodies, as glycogen, urea,
or kreatin, or are reconverted into albumen to assist
in the nutrition of the tissues.
In the present state of our knowledge it seems
uncertain where or how peptones undergo change,
whether before reaching the liver or in their passage
through the liver. Some observers have failed to find
peptones in the portal vein.
The Starches are converted into dextrin and
sugar by the action of the saliva, pancreatic, and
intestinal juices, and being thus rendered diffusible
enter the portal vein, and are conveyed to the liver.
The liver probably converts the sugar into glycogen,
and stores it up till required to be oxidised for the
production of heat and muscular energy. A variable
amount of sugar appears to be converted into lactic
acid in the intestines.
The Fats are crushed and reduced to pulp in the
mouth, and their fibrous tissue and vesicular envelopes
dissolved in the stomach, so that the oily matters are
set free. In the small intestine they undergo two
different changes, which are effected by the secretions
of the small intestine : —
1. They are emulsified.
2. They are saponified.
The emulsification consists in reducing the fat
into fine particles, small enough to readily enter the
202 Absorption and Nutrition
lacteals. The saponification consists in the formation
of soaps : thus olein is decomposed, the glycerine
being set free, and the oleic acid forming an oleate
with sodium or potassium for a base.
Small quantities of the fatty matters find their way
into the portal vein, but by far the major quantity
enters the lacteals of the villi. The particles of fat
enter the protoplasm of the columnar cells surround-
ing the villi, so that if these cells be examined during
a period of digestion they are seen to be distended
with fat particles. They next pass into the retiform
tissue of the villi, and thence into the lacteal, which
commences in the villus. Finally, the fatty matters
forming the chyle pass through the mesenteric glands
and into the receptaculum chyli and thoracic duct.
The exact forces in operation which determine the
entrance of fat into the lacteals are not thoroughly
understood. Animal membranes Wetted with bile
much more readily allow fatty matters to pass through
them than membranes not so treated. The cells
surrounding the villi, perhaps, exercise some selective
power, as the glandular epithelium does in the con-
voluted tubes of the kidney. The fat, once within a
villus, is driven onwards by the contraction of the mus-
cular fibres present in the villi, compressing the lacteal
and forcing onwards its contents, the aspirating power
of the thorax supplying the vis a fronte. The fatty
matters and albuminous materials present in the chyle
are gradually, in part, converted during its passage
through the mesenteric glands into the elements of
fibrin and white blood-corpuscles.
The food that has entered the body in the form of
meat, starch, sugar, fats, after being digested passes
into the blood-vessels in the form of peptones, fatty
matters, and sugar. What processes must they un-
dergo before they become formed tissue, such as
muscle, nerve, tissue, or gland ? But very little is
The Liver
203
known of such changes. Some of the albuminous
and fatty matters are converted into white corpuscles
and fibrin, probably through the action of the blood-
glands, i.e. spleen, lymphatic, lenticular, tonsils, thy-
mus glands ; the white corpuscles passing into red or
exuding into the tissues to become transformed into
the actual cells or fibres of the various tissues.
The albumen, fats, and sugars absorbed from the
alimentary canal pass out of the body at the kidneys
and lungs as urea, salts, and C0 3 . About the inter-
mediate stages our knowledge is scanty.
Summary
Peptones (major part)
Sugar
The portal vein
absorl is
Salt
Soaps ,,
Fats (trace)
^ Water (major part)
The lacteals ab- _
sorb
Fats (major part)
Soaps (small part)
Peptones ,,
Sugar (trace)
Salts „
MVater (small part)
CHAPTER XV
TH
E LIVER
The liver is the largest gland in the body, and weighs
50 to 60 ozs. In the foetus and child it is larger in
proportion to the body-weight than in the adult, being
1 in 20 to 30 in the child and 1 in 40 in the adult.
204 The Liver
The liver receives the blood of the portal vein and
hepatic artery, the hepatic veins carrying away the
blood from trie organ. Its under surface is divided
into lobes by five fissures.
The Fissures are the transverse, where the vessels
and nerves enter ; the longitudinal, situated between
the right and left lobes, is divided into two by the
transverse fissure, the anterior part forming the um-
bilical fissure and containing the round ligament, and
the posterior the fissure of the ductus venosus, con-
taining the obliterated remains of the ductus venosus
of the foetus. The fissure of the gall-bladder, or rather
fossa, makes the fifth.
The Lobes are, right and left, separated by the
longitudinal fissure. The lobulus quadratus situated
between the gall-bladder and longitudinal fissure.
The lobulus Spigelii, between the fissure for the ductus
venosus and inf. vena cava. The lobulus caudatus
forms a sort of ridge extending from the base of the
Spigelian lobe to the under surface of the right lobe.
Structure. — The liver has two coverings, the serous
and fibrous coats.
The Serous is derived from the peritoneum, and
is reflected round the organ, except where the vessels
enter, and at the posterior border.
The Fibrous or Connective Tissue coat in-
vests the whole gland, and at the transverse fissure
becomes continuous with the fibrous tissue which
accompanies the blood-vessels into the substance of
the liver, and forms the capsule of Glisson.
Hepatic Lobules.— On section of the liver its
substance will be seen to be composed of closely-
packed bodies of rounded outline and of about i to
2 mm. (j\j to „ J | T inch) in diameter. These lobules
for the most part have a darkish-red centre and
lighter circumference, and in some animals, at least,
are separated by a small quantity of connective tissue
Hepatic Cells 205
The centre of the lobule is occupied by an intralobular
vein, which collects the blood from the capillaries of
the lobule and empties itself into the sublobular ; the
latter opens into the hepatic veins. The circum-
ference of the lobule is surrounded by the interlobular
veins, which are branches of the portal system ; capil-
laries passing from the circumference to the centre
of the lobule connect the interlobular veins with the
intralobular.
The Hepatic Artery enters the liver at the
transverse fissure, accompanies the portal vein and
Fig. 80. — Section of a portal canal (Schafer). a, branch of hepatic artery;
v, branch of portal vein ; d, bile duct; //, lymphatics.
ducts, and supplies the connective tissue of the liver
(fig. 80, a).
The Hepatic Cells are packed in between the
network of capillaries in the lobule. They are of
rounded or polyhedral form, ¥ J- U - to T -^ v - ff inch in dia-
meter. They have a yellow granular appearance
and a well-marked prominent nucleus. Whilst in a
206 The Liver
quiescent state the liver-cells are larger and more
granular than after action. On examining the cells
by a high power, they may be seen to contain a fine
network which extends into the nucleus. They are
joined together by an albuminous cement, which
contains fine channels for the bile-capillaries ; during
digestion they contain minute oil-globules and gly-
cogen.
The Biliary Ducts commence by a fine plexus
of capillaries which run between and surround the
cells (fig. 81). In a very thin section minute openings
may be seen between the cells, which are the aper-
tures of the capillary ducts. The larger bile-ducts are
lined with columnar epithelium, their coats being
formed of fibrous and elastic tissue, with a mixture of
unstriated muscular fibre.
The branches of the portal vein, artery, and duct
accompany one another through the liver, the hepatic
veins travelling by themselves (fig. 80).
Functions of the Liver
The portal vein carries the blood which has circu-
lated through the walls of the stomach and intestines,
pancreas, and spleen. It is loaded with material
absorbed from the contents of the stomach and in-
testines. This blood is submitted to the liver before
entering the general circulation. In its circulation
through the liver it enters the interlobular plexus,
travels through the capillaries of the lobule, coming
into close relation with the hepatic cells, enters the
intralobular veins, and finally the hepatic veins convey
it to the inferior vena cava.
The liver in the adult has at least three func-
tions : —
1. Formation of glycogen. ? Conversion of gly-
cogen into sugar.
Glycogen
207
2. Action on albuminous substances.
3. Secretion of bile.
4. In the foetus it appears to give origin to white
blood-corpuscles.
1. Glycogen, or Amyloid Substance (C 6 H 10
O s ), is present in the cells of the healthy liver. The
liver contains from 1^ to 2\ per cent. When pure
Fig. 81.— Section of rabbit's liver with the intercellular network of bile-
canaliculi injected (Hering). Two or three layers of cells are represented.
I?, capillaries.
it is a white, tasteless, inodorous powder, insoluble in
alcohol, soluble in water, forming a white opalescent
solution. It closely resembles starch in appearance,
but differs from it in being stained reddish-brown by
iodine. Like starch, it is readily converted into sugar
by the action of dilute acids or ferments. Besides
208 The Liver
being present in the liver it is found in living muscle,
white corpuscles of the blood, brain, placenta, and
most tissues of the fcetus.
Preparation. — Fresh liver is boiled with strong
solution of KHO, which dissolves the liver-tissue and
the glyclogen, and on pouring it into alcohol the gly-
cogen is precipitated tolerably pure. Another method
consists in making a decoction of liver, precipitating
the albuminous matters with potassic hydrarg. iodide
and HC1, and afterwards precipitating the glycogen
with alcohol (see p. 13).
Origin. — Glycogen is principally formed in the
liver from the saccharine elements of the food.
C 6 H 12 O b -H 2 O=C 6 H I0 O 5
Grape sugar - Water = Glycogen,
Dogs fed on starch or sugar rapidly accumulate
large quantities of glycogen in the liver ; when fed on
a purely animal diet very much smaller quantities are
found. This appears to show that while glycogen is
formed in small quantities from albumen, yet by far
the major part originates from the saccharine elements
of the food. In badly nourished or half-starved
animals no glycogen is found. Fatty foods do not
increase the amount.
Destiny of Glycogen. — The fate of glycogen is un-
certain. There can be no doubt it serves to store up
material rich in C and H ; but the exact manner in
which it is utilised is not fully understood. Bernard
maintained that it is gradually reconverted into sugar
as required, and oxidised in the capillaries of the body
to maintain the heat or to supply muscular energy.
He based this view on his analysis of the blood,
which showed that a larger quantity of sugar existed
in the hepatic than in the portal vein. He also found
a greater quantity in the arteries than in the veins,
which seemed to suggest that sugar disappeared in
Functions of Liver 209
the capillaries. Pavy maintains that the hepatic veins
during life only contain a trace of sugar, and the
arteries contain no more than the veins. He argues
that the large quantities of sugar found in the hepatic
veins after death are due to a post-mortem change of
glycogen into sugar, and that during life only traces
are to be found. He does not believe that glycogen
is reconverted into sugar during life, and that if it
were in any quantity, it would run off at the kidneys,
as in diabetes. The question is still subjudice. Recent
analyses, however, show that the amount of sugar
in portal blood is 1 per 1,000, in the blood of the
hepatic veins 2 per 1,000 : this certainly suggests that
glycogen is converted into sugar in the liver, and that
glycogen is stored in the liver as a sort of carbohydrate
reserve.
It is probable that the sugar in the blood is con-
sumed by active muscle, and is discharged as CO, and
H 2 0.
Diabetes is a disease characterised by an abnor-
mal quantity of sugar in the urine. Its immediate
cause is a rapid conversion of glycogen into sugar
in the liver, depending probably on some disturbed
innervation of the blood-vessels. It can be induced
artificially in animals by puncture with a needle of
the vaso-motor centre of the medulla. This leads to
dilatation of the blood-vessels of the liver, an in-
creased supply of arterial blood, and an increased
conversion of glycogen into sugar, which makes its
appearance in the urine.
2. Action on Albuminous Substances. —
(a) Preparation of the "peptones for assimilation.
(6) Splitting up of various bodies into urea, &c.
(a) The portal vein contains the peptones which
have been absorbed from the alimentary canal. These
bodies disappear during their passage through the
liver, being probably converted into serum-albumen.
p
210 The Liver
(b) The liver probably splits up various substances,
as albumen, kreatin, leucin, and tyrosin, the products
being glycogen, urea, and uric acid. In certain
diseases, as acute yellow atrophy of the liver, the
urea in the urine is lessened, and tyrosin and leucin
appear to take its place.
3. Secretion of Bile. — In all probability the
pigments and biliary acids are formed in the liver,
and not merely separated from the blood. No trace
of either of them has been found in frogs whose livers
have been extirpated. To what extent the secretion
of bile gets rid of effete matters from the system is
uncertain. The biliary acids are in large part re-
absorbed after having taken part in the digestion of
the contents of the small intestine.
4. Foetus. — The relative size of the liver in early
fcetal life is about half the body-weight ; at full time
it is about 1 in 18. It receives blood from two
sources — (a) the umbilical vein, a portion of which
escapes through the ductus venosus directly into the
inf. vena cava ; (b) the portal vein, which carries
venous blood resembling that of the body generally.
The functions of the fcetal liver differ from those of
the adult principally in its being a blood-making
organ. After the formation of the placenta the um-
bilical vein brings various nutritive materials from
the maternal system ; the liver seems, out of these
materials, to produce numerous colourless nucleated
corpuscles which are poured into the blood. Probably
before birth it ceases to do so, the spleen and lymphatic
glands taking its place.
The biliary secretion (meconium) of the foetus is
purely excrementitious in character.
The Kidneys 2 r 1
CHAPTER XVI
THE KIDNEYS
The kidneys are situated in the lumbar region,
opposite the last dorsal and two or three upper lumbar
vertebrae. They are about 4 inches in length, and
weigh 4 to 5 oz. each.
Structure. — The kidneys are invested by a thin
fibrous capsule, which is attached by connective tissue
and blood-vessels. It is easily stripped off. On
making a longitudinal section through a kidney the
glandular structure will appear to be divided into two
portions : (1) the outer or cortical portion, for the
most part occupying the surface, except at the hilus ;
(2) the medullary portion, consisting of a number of
pyramids separated from one another by cortical sub-
stance.
1. The Cortical Substance occupies the greater
part of the gland, being ^ to \ inch . in depth at the
surface, and extends into the centre of the gland
between the pyramids ; the cortical portion between
the pyramids being termed the columns of Bertini.
It is of a light red colour, and more or less dis-
tinctly striated in appearance, the striations being due
to the interlobular vessels and bundles of straight
tubes which pass from the base of the pyramids to
the capsule. The Malpighian bodies may be seen
as reddish points, or sometimes standing out from
the surface like grains of sand. The bundles of
straight tubes are called the medullary rays (fig.
82, m),
2. The Medullary Portion occupies the centre
of the gland, and consists of eight to twelve of
the pyramids of Malpighi. These pyramids are sur-
p 2
212
The Kidneys
rounded at their bases and sides by cortical sub-
stance, while their apices project into the dilated
portion of the ureter at the hilus, which forms the
pelvis. The pyramids are divided by Ludwig into
two layers or zones — the boundary layer (fig. 82, g),
and the. papillary layer
(p). The boundary layer
has well-marked stria-
tions, this appearance
being due to the vasa
recta (fig. 84, ab, vb), and
to the bundles of tubules
(fig. 82, h) passing down
the pyramid towards the
papilla. The papillary
layer is of a more uniform
dull red colour.
The Malpighian
Bodies are about ,-Jj
inch in diameter, and are
situated in the cortical
portion between the
fig. 8=.-Sectioii through part of medullary rays. They
the dog's kidney (I.udwig). r, cor- consist of a tllft of capil-
tical layer ;g, boundary layer ;fi, pa- , . *•
pillary layer ; /;, bundles of tubules lary vessels in a Capsule
in the boundary layer prolonged f orme( i Dy tne dilated end
into the cortex as the medullary ; J
rays, m ; i, spaces containing vasa of a Urinary tubule. The
recta (not represented in the figure) ; f r ■ terme( l j-Ug a-/ ome _
c, portion of cortex between the luu ls tciuicu tltc gtumt
medullary rays containing inter- rulltS, the membranous
lobular vessels, glomeruli, and con- ^ t> ) x
voiuted tubes. envelope Joowmans cap-
sule. The glomerulus
receives an arterial twig from an interlobular artery,
and its efferent vein joins a plexus which surrounds
the convoluted tube before joining an interlobular
vein. Bowman's capsule consists of a homogeneous
membrane, lined by flattened epithelium, and joins a
convoluted tube by a constricted neck.
Urina ry Tub ules
213
The Convoluted Tubes (fig. 83) commence as
capsules in the cortex, twist upon themselves several
times, then, on joining a medullary ray, take nearly a
CURBED
COLLECTING
TUBULE
PROXIMAL)
CONVOLUTED?'
TUBULEj
STRAIGHT - *
COLLECTING-)-
TUBE/
DESCENDING L1MB\
OF HENLE'S LOOP/
1
Fig. 83.— Diagram of the course of the uriniferous tubules (G
Anatomy).
■rays
214 The Kidneys
straight course. They have a distinct lumen, and are
lined by short columnar cells, narrower at the lumen
than at the basement membrane. The outer part of
the cell is distinctly striated ; their inner part is
granular. They have a well-marked nucleus. The
convoluted tubule passes into a spiral tubule of
Schachowa, which is situated in the medullary rays ;
these are more or less spirally arranged : the epithelium
is the same as in the convoluted tubes. The spiral
tubule on entering the boundary layer becomes
narrower, and forms the descending loop-tube of Henle ;
the epithelium is 'here flattened, with a prominent
nucleus. The ascending loop-tube, which has re-
entered the boundary layer, is wider than the descend-
ing, and is lined by a layer of polyhedral fibrillated
cells. It next enters the cortex, is somewhat narrower
and wavy, and passes upwards in a medullary ray. It
then leaves the medullary ray and forms an irregular
tubule. Its shape is irregular, its lumen small, and its
epithelium consists of short, columnar, fibrillated cells.
The irregular tubule passes into the second convoluted
tube, closely resembling the "first convoluted tube.
It then passes into a more or less wavy collecting tube
before it joins a straight collecting tube. The collect-
ing tubes commence in the cortex and pass through
the boundary layer into the papillary layer, are lined
by columnar or cubical epithelium, and have a distinct
lumen.
Blood-vessels. — The renal artery, on entering
the kidney, breaks up into numerous primary branches,
which travel along. the columns of Bertini, and are
called the arteria propria renales. These divide at
the base of the pyramids and form arches with their
neighbours ; these arches give off (i) branches into
the cortex termed the interlobular arteries, from
which the afferent vessels to the Malpighian tuft arise
(fig. 84) ; the efferent vein from the glomerulus breaks
Fig. 84.— Diagram of the
distribution of the blood-
vessels in the kidney (Lud-
wig), ai, ai, interlobular
arteries ; vr\ vz } interlobu-
lar veins; g, glomerulus;
vs, stellate vein ; ar, vr-,
artenae et venee rectce
forming bundles, ab and
vb\ vp } venous plexus in
the papillae.
216 The Kidneys
up into a capillary network which ramifies on the
urinary tubules in the cortex, and after an extended
course joins the interlobular veins ; the efferent
vessels of the lowermost glomeruli break up into
capillaries, which pass straight down into the boundary
layer, and surround the straight tubules : (2) branches
downwards into the pyramids running between the
bundles of collecting tubes, and termed the vasa recta
or arterice recta.
The Renal Veins. — The vence iiiterlobulares cor-
respond with the arteries, and receive some veins
termed stellate from beneath the capsule, and also the
small veins which receive the blood from the minute
plexus surrounding the convoluted tubes.
The vence rectce run along the pyramids accom-
panying the corresponding arteries.
The vence proprice renales pass along the columns
of Bertini after having been joined by the vena? inter-
lobulares and vena? recta?.
Pelvis and Ureter. — The ureters convey the
urine to the bladder, the upper dilated portion form-
ing the pelvis. The pelvis is divided into two or
three primary divisions, and these again divide into
shorter ones termed calicesox infundibula, which receive
the papilla? or apices of the pyramids of Malpighi.
The collecting tubes open at the papilla? and discharge
their contents into the pelvis. The pelvis and ureters
are lined by transitional epithelium.
Urine
The urine is a clear yellow fluid of specific gravity
1020, of peculiar odour and acid reaction. It is con-
stantly being secreted by the kidneys, and is collected
in the bladder. On an average 52 ozs. (1,500 c.c.) are
passed per diem. The solids amount to about 4 per
Urine 217
cent. The principal constituents are the following,
with their amounts in 24 hours : —
Urea . . 500 grs., or 33 grammes=2 - 2 per cent.
Uric acid . 7-8 „ -5 gramme = '03 „
Kreatinin . 14 „ "9 „
Hippuric acid 6 ., -4 ,,
Chlorides . 105 „ 7 „
Sulphates
Phosphates
Sodium
Potassium \ Smaller quantities.
Ammonia
Earthy salts
Pigment, &c.
Urea. — Properties, tests, &c. (see p. 3).
Quantity of the Urine. — The average quantity
of the urine amounts to about 50 ozs., or 1,500 c.c.
The amount varies at different ages and under dif-
ferent circumstances. In infants the amount passed
is about 10 ozs. in the 24 hours. In children gene-
rally the amount passed is less than in adults. The
temperature and moisture of the surrounding atmo-
sphere by their action on the skin greatly influence the
secretion of urine. In a Turkish bath, or in summer,
where the skin is acting freely, small quantities of
concentrated urine are passed, while, on the other
hand, exposure to a dry east wind causes the secretion
of large quantities of pale limpid urine. The amount
of fluid ingested, as well as an increased or decreased
blood-pressure, influences the amount of the urine.
Colour of the Urine. — The colour varies
according to the degree of concentration of the urine.
The pale golden yellow colour is caused by the
presence of a pigment, urobilin, derived from the
haemoglobin of the blood. In some conditions of
anaemia the urine is pale though its solid contents
218 The Kidneys
may not be low. In children it is paler than in
adults.
Specific Gravity. — The average specific gravity
is 1020, though it may vary from 1002 to 1040, ac-
cording to the amount of fluid ingested as well as the
amount of perspiration taking place. In infants the
specific gravity is 1003 to 1006.
Acidity.— Normal urine is slightly acid. This
acidity is not due to the presence of free acid, but to
the presence of acid phosphates. This acidity is in-
creased after muscular exercise and much animal food.
After much vegetable food, or organic acids, as tar-
trates and citrates or alkalies, the urine becomes neutral
or alkaline.
Sources of Urea. — The greater part of the effete
nitrogen of the body passes out of the system in the
form of urea, a much smaller quantity in the uric acid,
kreatinin, hippuric acid, and other minor constituents.
The stages of the process by which proteid matters
are converted into urea are not well understood. It
is probable that leucin, tyrosin, kreatin, glycin, uric
acid, hippuric acid, which are nitrogenous bodies less
complex than proteid, and more complex than urea,
may be intermediate stages between proteid and
urea. It must not be supposed that all the urea
secreted passes through all these stages. The two
most probable sources of urea are (1) from kreatin ;
(2) from leucin and tyrosin.
1. Kreatin is found in the blood, and in most ot
the tissues of the body — muscle contains from -2 to
•4 per cent. ; while urea does not exist in muscle, and
only to a very small extent in the various organs. It
is possible that kreatin represents the waste product of
the albumen of the tissues ; that, in consequence of
the changes necessitated by life, there is a constant
formation of kreatin in all the tissues of the body,
and that this kreatin passes into urea in the blood,
Urea 2 1 9
the liver, or in the kidneys. The small increase of
urea in the urine after active exertion would, on this
view, represent an increased wear and tear, leading to
an increased formation of kreatin and urea.
2. If the amount of nitrogenous food be increased
in quantity, the amount of urea excreted in the urine
is also increased. This would indicate that a certain
part of the albumen of the food is split up into urea,
&c, without its having taken part in the formation of
any tissue. Leucin and tyrosin are found in the small
intestine, and are formed when pancreatic juice acts
upon albuminous foods. It is probable that the
leucin and tyrosin enter the portal veins, and are con-
verted into urea in the liver. This is rendered the
more probable from the fact already mentioned, that
in acute yellow atrophy of the liver, leucin and tyrosin
replace urea in the urine.
Amount of Urea — About 500 grains of urea
escape through the kidneys during 24 hours ; but
this amount varies according to circumstances, the
amount being increased after large quantities of
animal food, slightly after exercise, and also during
fevers. The urea is diminished after vegetable food
or fasting, and in certain forms of kidney disease.
Urzemia. — In certain conditions of the body,
such as Bright's disease, and in fevers, there is a
greater accumulation of effete material in the body
than can be carried off by the kidneys. Certain
toxic effects, such as convulsions and coma, result.
This is probably, though not certainly, due to the
accumulation of urea in the blood.
Estimation of Urea. — There are two methods :
(1) Liebig's ; (2) Russell and West's.
1. Liebig's method depends upon the fact that
urea forms an insoluble precipitate with mercuric
nitrate. Before the estimation can be made, the sul-
phates and phosphates present are precipitated by
220 The Kidneys
baryta water, and the liquid filtered. A certain quan-
tity of the filtrate is taken, and a solution of mercuric
nitrate of known strength (10 c.c. = 'i gramme of
urea) is dropped into the urine with frequent agitation ;
a white precipitate falls. From time to time, as the
mercuric solution is added, a drop of the liquid is
tested on a white slab with a drop of solution of sodic
carbonate ; when all the urea is precipitated and free
mercuric nitrate present in the solution, a yellow
precipitate occurs with the sodic carbonate. The
amount of mercuric solution added is read off, and
the corresponding amount of urea estimated. If
great accuracy is required, the amount of CI present
must be estimated, and an allowance made in esti-
mating the urea, as no precipitate of urea occurs
until all the chlorine present has combined with the
mercury.
2. Russell and West's method depends upon the
fact that urea is decomposed by hypobromous acid
into C0 2) N, H. 2 0. The C0 2 is absorbed in passing
through a solution of NaHO and the N measured in
a graduated tube (see fig. 85). The amount of N
given off indicates the amount of urea present in the
urine (see p. 5).
Uric Acid.— Some 7 to 8 grains of uric acid are
excreted daily in the urine, for the most part in the
form of urates of potassium, sodium, or ammonium.
The amount varies, being increased after animal diet,
and in certain diseases, as gout. Its source is uncer-
tain, being, like urea, a waste product formed from
the breaking up of nitrogenous compounds. It is
probable that in certain derangements of the liver
uric acid is formed instead of urea. It represents a
less oxidised form than urea (see p. 5).
Kreatinin. — Some 14 grains daily of kreatinin
escape by the kidneys. Probably the greater portion
of kreatin formed in the body has been converted
Hippuric Acid
2 2 1
the
into urea, a small amount being converted into
kreatinin which escapes with the urine (see p. 7).
Hippuric Acid.— Only about 6 grains of hip-
Fig. 85. — Gerrard's apparatus for estimating the amount of urea in urine.
a is a wide-mouthed bottle connected to b by means of a flexible tube
and T-shaped glass tube ; b is a cylindrical vessel graduated so as to
measure the amount of gas given off from a ; c is a vessel connected to
b by a flexible tube below, and arranged to slide up and down. To use
the apparatus both c and b are nearly filled with water, and c is raised or
lowered so that the water stands at a level marked o on b ; 25 c.c, of a
solution of hypobromite of soda is placed in the bottle «, and 5 c.c. of
urine in a test-tube, the latter being placed without spilling, by means of
forceps, in a, and the india-rubber stopper placed in the bottle. On shaking
the latter so as to mix the urine and hypobromite solution, nitrogen gas
is evolved, the carbonic acid being absorbed by the excess of soda
present. The gas collects in the graduated cylinder, and the amount is
indicated by the marks on the side. The reservoir c is lowered so that
the water in both stands at the same height before being read off. The
hypobromite solution is made by adding 25 c.c, of bromine to 250 c.c. of
a 40 per cent, solution of NaHO.
222 The Kiditeys
puric acid are secreted daily in man, though a very
much larger amount is present in the urine of the
herbivora (see p. 6).
Pigments. — The yellow colour of the urine is
due to several pigments, urobilin, urochrome, urorubin,
the nature of which is ill understood. Indican also
occurs in the urine in variable quantities ; it is known
by the presence of a blue colour, due to the formation
of indigo, when strong acids are added to the urine
(see p. 9).
Inorganic Salts. — These are numerous, the
most abundant being sodium chloride, smaller quan-
tities of potassium, magnesium, calcium in the form
of phosphates, sulphates, chlorides, and carbonates.
The amount and variety of the salts in the urine
differ according to the food taken, the alkalies being
increased during a vegetable diet, the urine becoming
alkaline, the earthy salts being increased when animal
food is taken.-
Secretion of Urine
The Malpighian bodies, and that portion of the
urinary tubules known as the convoluted tubes, are
both engaged in the separation of the urine from trie
blood. The Malpighian bodies, as before explained,
consist of a tuft of capillaries fitting inside a capsule
communicating with the convoluted tubes, and are
probably engaged in secreting the greater part of the
water and inorganic salts of the urine, the process
depending to some extent upon the pressure in the
capillary tuft.
The convoluted tubes are lined by glandular
epithelium, and are surrounded by a plexus of ca-
pillaries. The epithelium lining them appears to
exercise a certain selective influence in secreting the
urea and uric acid and pigment. These substances,
Secretion of Urine 223
having been separated from the blood and entered
the urinary tubules, are washed down by the water and
salines transuding through the capillary tufts into the
capsule above.
Secretion of Urine by the Glomerulus. —
The amount and character of the urine largely
depend upon the blood-pressure in the glomeruli
of the kidney. If the pressure be increased, larger
quantities of water will be passed, and under certain
circumstances,- as in nephritis, albumen and blood.
The passage, however, of fluid from the capillary
tuft is not a mere filtration, inasmuch as the urine
must pass through the wall of the 'capillary and
through the epithelium covering it. Injury to, or an
alteration in, the epithelium may possibly allow albu-
men or other constituents of the blood to pass.
The experiments of Roy have shown that the
volume of the kidney readily undergoes change, the
dilatation of the arteries causes increase, and the con-
traction of the arteries decrease, of volume. If this
alteration in volume be registered by a suitable
apparatus on a moving surface, a curve will be pro-
duced resembling the blood- pressure curve, both
respiratory undulations and pulse being well marked.
The arteries of the kidney are supplied with vaso-
motor nerves, and thus the blood-supply to the
kidney and the blood-pressure in the glomeruli are
regulated.
As the amount of urine depends so largely on the
blood-pressure in the glomeruli, it will be well to state
concisely the conditions upon which this depends.
According to Foster the blood-pressure in the glome-
ruli is increased —
1. By an increase of the general blood-pressure,
brought about (a) by an increased force of the heart's
beat ; (b) by the constriction of the arteries supplying
the skin or other part.
224 The Kidneys
2. By a relaxation of the renal artery.
It may be diminished —
i. By a lowering of the general blood-pressure
(a) by diminished force of the heart's beat ; (b) by a
dilatation of the arteries of the skin or other areas.
2. By a constriction of the renal artery.
Section of the renal nerves causes a dilatation of
the renal arteries and a copious secretion of watery
urine. Stimulation of the renal nerves has an oppo-
site effect.
Section of the splanchnic nerves is followed by an
increased flow. Stimulation arrests the flow.
Stimulation of a sensory nerve produces constric-
tion of the renal vessels and diminished urine.
Section of the cord, below the medulla, leads to a
general dilatation of the arteries of the body, lowers
the general blood-pressure, and arrests the secretion
of urine.
Stimulation of the cord produces a similar effect
by constricting the renal arteries. The rise in general
blood-pressure is not sufficient to overcome the re-
sistance offered by the constricted renals.
Injection of urea into the blood causes first a con-
striction, and then a dilatation, of the renal arteries,
followed by an increased flow of urine.
Some diuretics, as sodium acetate, cause a dilata-
tion of the vessels and an increased flow at once.
These diuretics appear to act directly on the vessels,
as they increase the urine after the nerves are
divided.
Secretion by the Renal Epithelium. — Whilst
the secretion of the watery and saline constituents of
the urine takes place at the glomerulus, and is largely
dependent upon blood- pressure, the urea, uric acid,
and other substances present in the blood are ap-
parently secreted or separated from the blood through
the agency of the epithelium lining the convoluted
Secretion of Urine 225
tubes. Even after the medulla has been divided, and
the urine, in consequence, has ceased to flow, the in-
jection of urea, sodium acetate, and some other bodies,
is followed by a free secretion of urine. Blood con-
tains about '02 per cent, of urea in health, and as much
as '2 in the urasmia of nephritis, while urine contains
2 per cent. It is evident that the epithelium of the
kidneys is actively employed in selecting the urea in
the blood and passing it into the urine.
Heidenhain's experiment with indigo-carmine also
shows this. The spinal cord of a rabbit is divided so
as to lower the blood-pressure, a solution of indigo-
carmine is injected into the blood, and the rabbit is
killed an hour later. The cortical layer of the kidneys
is found blue in colour, which is due to the presence
of blue granules in the epithelium and in the lumen of
the convoluted tubes and the ascending lines of
Henle's loop ;- the capsules of the glomeruli are free
from the blue granules.
From these facts it appears probable that the
secretion of urine takes place both through the
medium of the glomerulus and through the capillary
plexus and the epithelium lining the convoluted
tubes. The primary work carried on by the former
is to discharge water from the blood, and flush, as it
were, the convoluted tubes, the amount of urine se-
creted being dependent upon blood-pressure. The
primary office of the epithelium lining the convoluted
tubes is to select certain substances circulating in the
blood, and secondarily a secretion of sufficient water
to enable them to pass through the epithelium and
tubes.
The pressure under which urine is secreted has
been determined in the dog by placing a manometer
in the ureter. It amounted to 60 mm. of mercury,
the pressure in the aorta at the same time being
100 mm.
The Kidneys
The Urinary Bladder
The bladder has an average capacity of about
20 ozs., but is capable of becoming distended to a
much greater extent. It is situated in the pelvis, its
base or fundus being seated on the rectum or vagina
in the female. When completely distended its apex
rises out of the pelvic cavity.
Structure of the Bladder. — The bladder is com-
posed of a serous, muscular, submucous, and mucous
coat.
The Serous coat only partly invests it, covering
the upper half or more of the posterior wall, and
being reflected from the sides and apex to the sur-
rounding parts.
The Muscular consists of unstriated fibres ar-
ranged in three layers. The external or longitudinal
is most distinctly marked on the anterior and posterior
surfaces of the organ. This layer forms what is
sometimes called the detrusor urince, muscle. The
circular or middle layer surrounds the bladder in a
more or less oblique direction ; it is more circular in
direction towards the base and around the neck ; it
consists of a dense layer of fibres, which forms the
sphincter vesica. The internal layer is thin and more
or less longitudinal in direction.
The Submucous coat is formed of connective
tissue and blood-vessels.
The Mucous Membrane is pink and smooth ;
it is thrown into wrinkles or rugae, except at the
trigone, where it is adherent to the muscular layer
beneath.
It is lined by transitional epithelium (p. 26) re-
sembling that of the ureters, and consisting of three
layers, the most superficial being cubical ; the second
Micturition 227
more or less pear-shaped, fitting into the layer above ;
the deepest more or less rounded or oval, sending
processes into the mucous membrane beneath.
Micturition
The urine trickles drop by drop down the ureters,
into the bladder, where it collects and gradually dis-
tends it. The exit from the bladder is opposed by
the sphincter vesicae, or, as some believe, by the
elastic and muscular fibres of the urethra. The urine
is expelled by the contraction of the walls of the
bladder, more especially by the detrusor vesicas, and
is assisted when much distended by the contraction
of the abdominal walls. Micturition is a reflex act,
but one which (with the exception of infants) is
under the influence, if not under the control, of the
will.
The mechanism appears to consist of an automatic
centre in the lumbar part of the cord, maintaining the
constant contraction of the sphincter (fig. 86, m s), a
second centre, which when stimulated excites con-
traction in the detrusor u d. These centres are anta-
gonistic, so that an afferent impulse from the bladder s
excites the detrusor centre, at the same time inhibiting
the sphincter centre.
These centres are normally under the control of
the will, so that although an afferent impulse may
ascend from the bladder to the centres of the cord
and up to the sensorium, yet by an effort of will the
sphincter centre may be assisted and the detrusor
inhibited, or vice versa. Thus when the bladder
becomes distended an afferent impulse from the blad-
der reaches both lumbar centre s and brain ; if the
opportunity is favourable for micturition the controlling
Q 2
228
The Kidneys
influence of the will is removed, the reflex contraction
of the detrusor taking
place, assisted perhaps
by the voluntary abdo-
minal muscles.
In animals when
the cord is divided, or
in man injured above
the lumbar centre, so
that the controlling in-
fluence of the will is
cut off, an involuntary
emptying of the bladder
takes place. In chil-
dren, when sleeping
heavily, or when the
spinal centres are un-
duly irritable, a dis-
tended bladder or the
irritation of worms in
the bladder or rectum
will cause incontinence
of urine. In animals
Fig. 86. —Diagram showing probable
plan of the centre for micturition
(after Gowers). M T, motor tract ;
s t, sensory tract in the spinal cord ;
MS, centre, and ms, motor nerve Or man, when the luill-
for sphincter ; M D, centre, and md, U„ r r p n (- rpt . arp i n ii, rP H
motor nerve for detrusor; s, afferent Udf i ( - Lncres *« injured
nerve from mucous membrane to s,
sensory portion of centre;?, bladder;
at r the condition during rest is
indicated, the sphincter centre in
action, the detrusor centre not .
acting ; at a the condition during quence Ot relaxation 01
action is indicated the sphincter the sphincter. At other
centre inhibited, the detrusor act- . r
ing. times urine accumu-
lates, distends the blad-
der, and then escapes in drops, from failure of the
detrusor to act.
or destroyed, the urine
may dribble away as it
is formed, in conse-
The Ductless Glands 229
CHAPTER XVII
THE DUCTLESS GLANDS
The spleen, lymphatic glands (including lenticular
glands of alimentary canal and tonsils'), supra-renals,
thymus and thyroid, form the ductless glands. The
pituitary, peneal, and coccygeal bodies are not in any
sense glands, nor have they probably any analogous
function to them.
Spleen
The spleen is the largest and most import ant of
the ductless glands. It is a soft, red, vascular organ,
situated at the cardiac end of the stomach beneath
the diaphragm. It has two coats, a serous and fibro-
elastic.
The Serous closely invests its surface except at
the hilus and at the spot where it is reflected to the
stomach and diaphragm.
The Fibro-elastic or Tunica propria is a
strong capsule surrounding the organ, and, passing
into its substance at the hilus, forms a sheath for the
vessels and trabecule, which divide the gland into
spaces occupied by the pulp. It consists of white
and yellow fibrous tissue, and non-striated muscular
fibre, the latter well marked in the pig and dog, but
more scanty in man. The capsule is highly elastic,
and capable of great distension.
The Spleen Pulp occupies the spaces between
the trabeculae, is of a dark-red colour, and semi-solid
consistence. The pulp, when examined in thin section
beneath the microscope, is seen to consist of a network
of branched connective tissue corpuscles (fig. 87, p) —
230
The Ductless Glands
the supporting cells of the pulp — the branches joining
one another, and forming a fine retiform tissue. Many
of these connective tissue corpuscles contain a clear
oval nucleus, and some contain yellowish pigment
granules, possibly derived from the blood-corpuscles,
The spaces between these branched cells contain (i)
red corpuscles, (2) white corpuscles of various sizes
and more or less granular, (3) transitional forms
between red and white corpuscles, (4) cells containing
red corpuscles, (5) pigment granules.
Fir,. 87. — Thin section of spleen pulp, showing the origin of a small vein
(Quain's Anatomy). 7<, vein filled with blood corpuscles, which are in
continuity with others, />l, filling up the interstices of the retiform tissue
of the pulp. At / the blood corpuscles have been omitted from the
figure, and the branched cells are better seen ; w, wall of the vein.
The Splenic Artery enters the spleen by divid-
ing into six or more branches, which ramify in the
interior, supported by the trabecular, and break up in
the pulp into fine branches. The small arteries ter-
minate in capillaries, the walls of which eventually are
lost, their cells becoming gradually transformed into
the connective tissue corpuscles of the pulp, and
their contained blood wanders freely through the
Spleen 2 3 1
retiform tissue of the pulp. The minute veins arise
in a manner similar to that in which the arteries
terminate and eventually empty themselves into the
splenic vein. Thus the blood in its course through
the spleen, after leaving the arteries, wanders freely
through the pulp before entering the veins (fig. 87).
The terminal arterial branches do not anastomose
with one another.
The Malpighian Corpuscles are small bodies,
about tjV in. in diameter, and may readily be seen in
the child's spleen as small white dots scattered thickly
over the cut surface. They are seated upon the small
arteries, their sheath being continuous with that of the
arteries, though in man the sheath is not very distinct,
and the tissue of the Malpighian body is continuous
with that of the spleen pulp. In structure they con-
sist of lymphoid tissue, the leucocytes being densely
packed in a fine network. A small artery enters their
substance.
Functions. — The exact functions performed by
the spleen in the animal economy are ill understood ;
the most certain are the following : —
(1) During digestion the spleen becomes con-
gested, the arteries and trabeculae being relaxed, the
elastic tissue yielding, and the organ containing more
blood. This has been attributed, by some, to the
necessity of having an excessive quantity of blood in
the portal system during digestion, the spleen acting
as a reservoir, but more probably it is connected with
important changes going on in the spleen pulp. Rapid
contraction of the spleen takes place when the vagus
or splanchnics are stimulated ; it also contracts on
galvanising the medulla. Rhythmical contractions of
the spleen have been noted in the cat and dog.
(2) The spleen is a source of white blood-cor-
puscles to the blood, the splenic vein containing 1
white to 60 red, whereas in ordinary blood it is 1 to
232 The Ductless Glands
400. The blood in passing through the pulp conies
into close relation with the lymphoid tissue, and new
corpuscles are formed.
(3) Red corpuscles are probably broken up and
disintegrated in the spleen. The spleen pulp shows
yellowish granular matter, which may be derived from
the haemoglobin of the red corpuscles. This colour-
ing matter may be converted into pigment in the
liver.
(4) The conversion of white corpuscles into red
has been attributed to the spleen, but this is very
uncertain.
(5) The spleen has been successfully removed
from a dog, and no great change has been noted in
the animal. In some cases the lymphatic glands have
become enlarged after the removal of the spleen.
The human spleen has been removed successfully.
(6) The spleen is apt to be enlarged in some
morbid conditions, as anaemia, leucocythagmia, ague,
and some fevers.
Lymphatic Glands
Have already been referred to (p 122).
Supra-renals
The supra-renals are two small bodies of a
somewhat triangular shape which surmount the
kidneys.
They are about \\ in. in height and \\ in. in
width. They weigh 1 to 2 drms. each.
Structure.— -They are invested by a fibrous coat
which surrounds each organ. On section they arc
seen to consist of a cortical portion, forming the
greater part of the organ, of firm consistence and
yellow colour, and a medullary portion, which is soft
and pulpy, and of a brownish black colour.
Sttpra-renals
23:
The Cortical portion consists of a fibrous
stroma, in the meshes of which are cells arranged in
columns which radiate from the centre of the gland.
Fig. 88. —Vertical seclion of supra-renal body (Eberth). 1, cortical sub-
stance ; 2, meduilary substance, a, capsule ; //, zona glomernlosa ; c,
zona fasciculata ; d, zona reticularis ; e, groups of medullary cells ; /,
section of a vein.
234 The Ductless Glands
The cells are granular, yellow, and nucleated, and are
about T7 -nro in- in diameter, and contain minute oil-
globules. Small arteries run between the columns.
The Medullary part is separated from the cor-
tical by a layer of connective tissue, and is best
marked in the supra-renals of young animals. It
consists of a stroma, in the meshes of which are en-
closed groups of cells which are coarsely granular,
have no oil-globules, and some of them are branched.
Nerves. — Bundles of nerves run through the
cortex, and form a network in the medullary part.
Function. — Nothing is known for certain re-
garding the function of these bodies. The most
interesting point is their connection with Addison's
disease, in which tuberculosis of the supra -renal
capsules is accompanied by a bronze tint on the
skin, vomiting, and progressive emaciation. Some
maintain that, like the spleen, they exercise some in-
fluence on the elaboration of nutritive material in the
blood. Others believe them to be connected with the
nervous system, and the cells of the medullary portion
to be nerve-cells.
Thyroid Gland
The thyroid gland consists of two lateral lobes
situated on either side of the trachea and larynx, and
joined by an isthmus which crosses in front of the
trachea at the third and fourth rings. It is soft, of
a reddish colour, and weighs from i to 2 oz., and is
larger in the female than in the male.
Structure— It is invested by a layer of fibrous
tissue which connects it with the surrounding parts.
It is composed of a number of closed vesicles, which
are from w },u i n - i' 1 diameter to the size of a millet-
seed. Each vesicle is surrounded by a plexus of
capillaries, and lined by a single layer of epithelium.
Thyroid Gland
235
They normally contain a clear yellow viscid fluid, and
sometimes white corpuscles and degenerated red cor-
puscles. The organ is very vascular, receiving a large
blood-supply (fig. 89).
Function. — But little is known concerning the
function of the thyroid body. It has been supposed
that, like the spleen, it pours white corpuscles into the
blood. It is enlarged in certain diseases, as in goitre,
which is common in Derbyshire and the valleys of
Fig. 89. — Section of the thyroid gland of a child (Quain's Anatomy). Two
complete vesicles are seen. In the middle of one of the spaces a blood-
vessel is seen. Between the epithelium there are small cells like lymph
corpuscles.
Switzerland, and seems to be connected with the
constant use of water impregnated with magnesian
limestone ; and in exophthalmic goitre, a disease
characterised by enlarged thyroid, prominence of the
eyeballs, and irregular action of the heart. Horsley's
experiment in removing the thyroid in monkeys and
dogs produces tremors of the muscles ; a diminution
of the red blood corpuscles, so that profound anaemia
results ; the white blood corpuscles are increased in
236 The Ductless Glands
number ; the subcutaneous tissues and the salivary
glands become distended with mucin. The symptoms
produced resemble myxoedema as seen in the human
subject.
Thymus Gland
The thymus gland reaches its full development at
the end of the second year of life, and then gradually
dwindles away. When examined in an infant it is
seen to be an elongated, soft, pinkish body lying
behind the sternum, and in front of the pericardium
and great vessels : it extends into the neck some
distance, being covered in by the sterno-hyoid and
thyroid muscles. It consists of a capsule of fibrous
tissue, sending trabecular into the gland, dividing it
into lobes and lobules. These lobules are again
divided into follicles. These follicles are irregular in
shape, and contain a central portion or medulla and
an external cortical portion. The follicle consists of
lymphoid tissue in some respects resembling a solitary
gland ; in the cortex there is a retiform network, the
meshes being filled with lymphoid cells. In the
medulla the retiform tissue is coarser and the cells
fewer, but it contains peculiar bodies, known as the
concentric corpuscles of Hassall. The thymus is pro-
bably a lymph-gland.
Nervous System 237
CHAPTER XVIII
NERVOUS SYSTEM
The nervous system is divided into —
1. The Cerebro-spinal system.
2. The Sympathetic system.
1. The Cerebro-spinal includes the brain, spinal
cord, certain ganglia, motor and sensory nerves. The
motor nerves are supplied to the striated or voluntary
muscles ; the sensory are distributed to the organs of
sense, skin, and other parts endowed with sensibility.
The nerve-fibres are mostly of the medullated kind.
. 2. The Sympathetic consists of a series of gan-
glia and nerves, which supply the involuntary mus-
cular fibre of the uterus, stomach, intestines, ducts,
and blood-vessels. The sympathetic system has a
less symmetrical arrangement than the cerebro-spinal ;
the nerves are of a reddish colour, and are com-
posed, for the most part, of non-medullated or grey
fibres.
These two sections of the nervous system are
intimately connected with each other — indeed, they
can hardly be regarded as distinct systems ; the
sympathetic may be regarded as that portion of the
nervous system which supplies the internal organs and
blood-vessels.
Structure of the Nervous Mechanism : —
I. Purely conducting organs, nerves.
II. Terminal end organs.
III. Central organs, as brain, cord, ganglia.
2 3 8
Nervous System.
I. Nerves
The nerves consist of bundles of nerve-fibres
bound together by a common tissue sheath. This
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sheath, which is called the epineurium, surrounds the
whole nerve and binds its bundles or fasciculi to-
gether. It contains blood-vessels, lymphatics, con-
Medullated Nerves 239
nective-tissue cells, and adipose tissue. Each nerve-
bundle or funiculus is surrounded by a special sheath
of its own, termed the perineurium (fig. 90, p). Be-
tween the lamella? of the perineurium there are dis-
tinct lymph spaces. The nerve-fibres are separated
from one another by a delicate connective tissue
called the endoneurium, which contains many connec-
tive-tissue cells (fig. 90).
Nerve-fibres are of two kinds : —
(a) Medullated. (b) Non-medullated.
(a) The Medullated Nerve-fibres are present,
for the most part, in the cerebro-spinal system. They
vary very much in size, being from -,o',ro to Tl ,J„ s in.
in diameter. When examined shortly after death,
they appear as translucent, glistening threads, with a
dark border. On addition of various reagents it can
be made out that a medullated nerve consists of :
(1) Primitive nerve-sheath.
(2) Medullary sheath.
(3) Axis cylinder.
(1) The. primitive nerve-sheath or neurolemma is a
thin hyaline membrane which surrounds the nerve-
tubule. In this sheath annular constrictions may be
seen at intervals, which project into the nerve tubule
as far as the axis cylinder ; these constrictions are
called the nodes of Ranvier. On the inner surface of
the sheath are nuclei surrounded by finely granular
protoplasm ; these nuclei do not belong to the neuro-
lemma. The neurolemma is absent in the nerves
which form the white substance of the brain and cord,
optic and acoustic nerves. Many of such nerve-
fibres are varicose, owing to small accumulations of
fluid between the axis cylinder and medullary sheath.
(2) The medullary sheath, or white substance of
Schwann, is semi-fluid during life, but coagulates after
>40
Nervous System
n
death. It consists of fatty matters, soluble in ether,
which when squeezed out of the primitive sheath
appear like bright drops with a dim contour. When
c the white substance has coagu-
lated, the nerve, which imme-
diately after death appears to
have a single outline, becomes
dark-bordered. According to
Klebs, the axis cylinder and
medullary sheath are separated
by a narrow space, called the
periaxial space, containing a
cement substance. The me-
dullary sheath is stained black
by osmic acid. It is absent at
the nodes of Ranvier (fig. 91).
(3) The Axis cylinder is
a narrow thread which runs
through the centre of the nerve.
It is albuminous in nature, is
continuous with the poles of
nerve-cells, and stains with car-
mine, logwood, chloride of gold,
or, better than all, aniline blue-
node with nucleus: c, axis bi ac k. In places it can be seen
cylinder, projecting at the , ... L . £>.,,.,
broken end ; /, primitive to be distinctly fibnllated.
sheath within which the Medullated nerves when
medullary sheath, which is
stained dark by osmic acid, coming near their terminations
is somewhat refracted. ^ thdr meduUary sheatn .
Some medullated nerves, especially in the optic nerve,
possess more or less regular varicose enlargements.
(<5) Non-medullated Nerves consist of—
(1) Primitive nerve-sheath.
(2) Axis cylinder.
They closely resemble the medullated nerves, but
the white substance of Schwann is wanting. They
Fig. 91.
-Two portions of me
dullaled nerve-fibres, afte
treatment with osmic acid,
showing the axis cylinder
and the medullary and pri-
mitive sheaths (Quain's
Anatomy). A, node of Ran-
vier ; b, middle of inter-
.Nerve Endings 241
vary in size from ^-^ to - ff J i)tF in. in diameter. They
are present for the most part in the nerves of the
sympathetic system, but they are also present in the
cerebro-spinal nerves.
II. Terminal End Organs
(A) Sensory Nerves end in —
1. Networks or plexuses.
I (a) Pacinian bodies.
(b) End bulbs..
(c) Touch corpuscles.
(d) Rods and cones,' taste-buds,
&c. &c.
2. Special Organs
(B) Motor Nerves end in —
1. Non-striated. 2. Striated muscle.
1. Sensory Networks or Plexuses. — The
nerve-bundles as they approach their terminations
divide and re-divide till the branches consist of only
one or two tubules. In the skin and mucous membrane,
when the nerves are approaching the surface epithe-
lium, they lose their medullary sheath, join together,
and form the subepithelial plexus. From this plexus
fine fibrils are given off, which, according to Klein,
pierce the rete mucosum, and end beneath the cells
of the horny layer, or, according to some, in the
epithelial cells themselves.
In the cornea there are two terminal plexuses,
superficial and deep. The superficial forms a sub-
epithelial plexus, which gives off minute fibrils, which
end in the interstitial substance between the epithelial
cells on the surface. The deep plexus is situated in
the substance of the cornea ; some of the fine fibrils
are said to end in the corneal corpuscles.
R
242
Nervous System
lip
2. Special Organs— («) Pacinian Bodies
are ovoid in shape, about T V to ^ in. in diameter-,
and are found attached to
the digital, plantar, pudic,
infra-orbital nerves, and
mesenteric nerves' of cat.
These bodies consist of a
number of concentric
membranes placed inside
each other, enclosing a
clear space in the centre,
which contains the termina-
tion of a nerve. Each cap-
sule consists of a hyaline
membrane marked with
fine transverse fibres, and
lined on its inner surface
by a layer of endothelial
cells. There is no fluid
between the layers, as
sometimes described. The
central clear mass contains
a hyaline matrix and an
axis cylinder, the sheath and white substance of
Schwann being lost before the nerve enters the clear
space. Besides the nerve a minute artery enters the
Pacinian body, and distributes capillaries between the
capsules.
{b) End Bulbs exist in man in the conjunctiva,
lips, mucous membrane of mouth, soft palate, genital
organs. They are about ^ m in. in diameter, and
consist of an ovoid corpuscle, in which a medul-
lated nerve-fibre terminates. They are surrounded
by a capsule continuous with the perineurium sur-
rounding the nerve. The matrix is a granular mass
containing oval nuclei. The nerve loses its medullary
sheath and after branching ends in bud-like processes.
Fig. 92. — Tactile corpuscle within
a papilla of the skin of the
hand, stained with chloride of
gold (Quain's AnatomyX -£>,
epidermis. The convolutions of
the nerve-fibres within the cor-
puscle are well seen.
Nerve Endings
243
(c) Touch Corpuscles or Tactile Corpuscles
occur in the papilla; of the corium of the volar side of
the hands and feet in man (fig. 92). They are about
-^ in. long. They are connected with one or two
medullated nerve-fibres. The nerve-fibre winds round
the corpuscles several times, then loses its medullary
sheath and penetrates into its substance where the
axis cylinder divides, is more or less coiled, and ends
in slight enlargements, (d) Other end organs, as the
a b
ii, ," :->- f) i
- .y —
FlG. 93.— Nerve ending in muscular fibre of a lizard (Quain's Anatomy).
In a, the end-plate is seen edgeways ; b, from the surface ; s s, sar-
colemma ; pp, expansion of axis cylinder. In b the expansion of the
axis cylinder appears as a clear network.
rods and cones, taste-buds, organ of Corti, will be
described in connection with sight, taste, &c.
(B) Terminations in Muscles. — 1. Non-stri-
ated muscles are supplied with non-medullated nerves,
which form plexuses ; these plexuses give off the
primitive fibrils which run in the interstitial substance
between the cells ; and, according to some, give off
fine branchlets, which enter the nuclei of the cells
themselves.
244
Nervous System
2. Striated Muscle. — Nerves surrounded by
their perineurium run in the connective tissue forming
the sheath of the muscle. Branches are given off
which form a plexus ; other branches containing two
or three nerve tubules form an intermediate plexus
for the supply of the smaller bundles of fibres. The
nerve-tubules enter the muscular fibres, the primitive
sheath becomes fused with the sarcolemma, while the
axis cylinder loses its medullary sheath and passes
through the sarcolemma ; the axis cylinder ends on
the surface of the muscle substance, becoming im-
bedded in a flat granular mass, the end-plate of Kiihne.
The end-plates viewed in profile form Doyere's promi-
nences (fig. 93).
III. Structure of the Central Organs
The Grey Matter is present on the surface of
the convolutions of the cerebrum, cerebellum, in the
Fig. 94. — Two nerve cells from the cortical grey matter .of the cerebellum
(Quain's Anatomy).
central parts of the spinal cord, corpora striata, optic
thalamus, corpora quadrigemina, ganglia, &c.
Nerve Cells 245
It consists of : 1. Nerve-cells. 2. Nerve-tubules.
3. Pigment. 4. Blood-vessels. 5. Neuroglia.
White Substance consists of : 1. Nerve-tubules.
2. Blood-vessels. 3. Neuroglia.
1. Nerve Cells are small rounded or branched
bodies, destitute of a cell wall, formed of finely granu-
lar, protoplasm, in reality consisting of a fine network
of fibrils. Each cell contains a nucleus, having a
well-defined capsule, fine network, and a nucleolus.
They sometimes contain pigment. The cells are
surrounded by a perivascular space. In shape they
are apolar, unipolar, bipolar, or multipolar, according to
the number of processes they possess. Each process is
continuous with the axis cylinder of a nerve (fig. 94).
Neuroglia. — This name is given to the frame-
work of the grey and white matter of the cerebrum,
cerebellum, and cord. It con-
sists of branching nucleated cells
(glia-cells), the branches passing
between and supporting the nerve
* fibres and cells. In some parts
of the nervous centres, as, for
instance, the grey matter of the
cerebrum, the supporting sub-
stance appears to be finely granu-
lar, but this appearance is really fig. 55. -Part of resi-
due to the fine nerve tubules and $£?*■ °Anatlmy). cord
branches of the glia-cells seen in
section. The glia-cells are fibrillated, the fine fibres
passing through the body of the cell.
The White Matter is distributed in various
places in the brain and cord, connecting the grey
matter of different parts. The nerve-fibres are
medullated, but have no primitive sheath. They vary
in size, often possess varicose swellings, due to an
accumulation of fluid between axis cylinder and
medullary sheath.
246
Nervous System
Ganglia. — These consist of rounded or elongated
bodies found in various situations in connection with
nerves. They are present in the following places : —
1. Cerebro-spinal. — On the posterior roots of
the spinal nerves ; on the roots of the fifth (Gasserian),
Nerve Ganglia
>47
facial, vagus, glossopharyngeal ; in several other situa-
tions, as the ophthalmic, Meckel's, the otic, and sub-
FlG. 97. — Two nerve-cells from a spinal ^an^lion (Quain's Anatomy), s/t,
nucleated sheath : «, «, nuclei of primitive nerve-sheath. From each
cell a nerve-fibre arises, and after a convoluted course bifurcates opposite
d, from which point they separate.
maxillary. These ganglia are surrounded by a fibrous
sheath continuous with the nerve with which they are
248
Nervous System
connected ; from this sheath prolongations are sent
into the substance of the ganglion. On examining a
section under a low power (fig. 96) the nerve-fibres
will be seen entering the ganglion at a, and leaving
at b, the principal mass of nerve-cells being present
at the periphery, but they are also present in the more
central parts. Some nerve-fibres apparently pass
through the ganglion without being connected with
any cell ; all the cells are, however, connected with
a nerve-fibre. The cells differ in size, are unipolar,
Fig. c
-A group of ganglion cells interposed in a bundle of sympathetic
nerve-fibres from the bladder of a rabbit (Klein).
rounded or pyriform in shape, are surrounded by a
sheath, and have a large oval nucleus and nucleoli.
The single nerve-fibre with which they are con-
nected (fig. 97) divides after leaving the cell, and
passes in opposite directions. This bifurcation is
often T-shaped. The nerve-cells are not all unipolar
in the cerebro-spinal ganglia, for in the otic, spheno-
palatine, submaxillary, and ophthalmic there are multi-
polar cells.
2. Sympathetic. — There are numerous ganglia
in connection with the sympathetic system, some of
which, as the semilunar, are of considerable size ;
others, as those situated in the walls of the bladder
Functions of Nerves 249
or heart, are microscopic. The principal set are (a)
forming a chain by the side of the vertebral column ;
(b) in numerous places in the walls of the heart,
intestines, uterus, and in connection with the plexus.
In these ganglia the cells may be unipolar, bipolar,
or multipolar. They are mostly oval or pyriform,
with a sheath, nucleus, nucleoli (see fig. 98).
PROPERTIES AND FUNCTIONS OF NERVES.
i. Nutrition. — Nervous matter receives a rich
supply of blood ; the network of capillaries in the
grey matter is closer than in the white. The nerve-
cells receive their nourishment from liq. sanguinis
which has exuded from the vessels. Active nerve-
cells absorb O and eliminate C0 2 . Some nerve-
centres exercise an important influence over the nutri-
tion of certain nerves ; thus, if a motor nerve of the
spinal cord is cut off from the grey matter in the
anterior cornua, it undergoes fatty degeneration, and
the muscle it supplies becomes atrophic. If a sensory
nerve is divided, the part attached to the posterior
ganglion remains normal ; that part which has been
separated from the ganglion degenerates.
When a nerve is cut in a mammal, the ends often
reunite in a few weeks.
2. Nervous Excitability and Conductivity.
Nerves, like muscles, are irritable or excitable. If
one end of a nerve is irritated by the application of a
stimulus, such as the application of heat, the. elec-
trodes of a battery, or by other means, the irritation
or excitation is conveyed along the nerve to its farthest
extremity. If the nerve is attached to muscular fibre,
a contraction is produced ; if the nerve ends in a
sensory centre, a sensation is produced, or the secre-
tion of a gland poured out if the nerve terminates
there. The nerves receive impressions through the
medium of certain terminal organs, as the touch
250 Nervous System
corpuscles, rods and cones of retina, and convey the
impression produced to a certain sensory centre, and
a sensation is felt ; or they receive an impulse from
certain motor centres, and convey the impulse to their
termination in the end plates of the muscles, and a
muscular contraction ensues.
If the nerves are too frequently excited they
become fatigued, and a certain amount of repose is
necessary for them again to conduct impressions.
There are several methods of measuring the
velocity of the nerve-current. The ordinary method
in motor nerves of frog consists in applying the elec-
trodes directly to the muscle, and measuring the time
that elapses before the contraction, the contracting
muscle recording its movements by means of a lever
on a revolving drum (a chronograph marking time) ;
then, if the electrodes be applied to the nerve, at
some distance from the muscle, and the time again
measured, it is evident that the difference between
the two will be the time that the nerve-current took to
travel through the nerve (fig. 31).
The velocity of the nerve current has been cal-
culated to be about 80 ft. per sec. in the frog, and 100
to 120 ft. per sec. in man, though some have placed it
at 200. Sensory impressions in man have been mea-
sured in the following way : — Arrangements are made
for a person to give a signal — the moment he feels a
prick, say, on his great toe — and the time noted
between the prick being administered and the signal
given. Another experiment is made in the same way
by pricking a point nearer the brain, say the knee,
and the time measured. The difference between the
two will be the time the impression takes to travel
from toe to knee. It has been found that the velocity
is about the same as in motor nerves — no to 120 ft.
per sec. This method is, however, open to many
objections.
Electrotonus 2 5 1
3. Electrical Phenomena of Nerves. — Elec-
trical currents are present in living nerves. If a
piece of a'nerve be cut out and placed upon the elec-
trodes of a galvanometer, so that the surface of the
nerve touches one electrode and the cut end the
other, a current will be observed to pass from the
surface through the galvanometer to the cut end.
The nerve-currents exactly resemble the muscle-
currents. When the nerve is excited there is a dimi-
nution or negative variation of the normal current.
Electrotonus. — If a constant current be passed
along a nerve, the nerve is thrown into a peculiar
state termed electrotonus. If the current travel in
the direction of the natural nerve-current, the latter is
increased ; if in the contrary direction, it is diminished.
While a portion of nerve is traversed by the con-
stant current, its properties are to some extent
altered ; the portion in the neighbourhood of the
positive pole is said to be in an aneledrotonic state,
while the portion of nerve in the neighbourhood of the
negative is in a cathelectrotonic state. The position of
the neutral point between the two varies with the
strength of the current passing through the nerve.
With a current of medium intensity, the neutral point
is midway between the poles ; with a weak current the
neutral point is nearer to the positive than the nega-
tive ; with a strong current the neutral point is nearer
the negative than the positive. When a nerve is in
theanelectrotonic state, its natural nerve-currents are
increased, but its excitability and conductivity are
diminished ; when in the cathelectrotonic, its natural
nerve-current is diminished, but its conductivity and
excitability are increased.
Pfliiger's Law of Contraction. — When a
constant current of medium strength is passed along a
motor nerve, no effect is produced upon the muscle,
except on opening and closing the current. The con-
252 Nervous System
traction of the muscle is influenced (1) by the direction,
(2) by the strength of the current— that is, the strength
of the contraction on making and breaking contact
varies not only according to the strength of the
current applied, but also to the direction, whether the
current is passed downwards in a direction from the
spinal cord to the muscle, or in an upward direction
from the muscle to the cord. The following is a brief
statement of the facts : —
Stren
-;Lh of Current
Descending
1
Make ! Break
Ascending
Make
Break
Very weak
Weak .
Medium
Strong .
'. '. '. 1
C R
C R
C C
C R
R— rest.
R
C
C
R
R
R
c
C
C — contraction
From this' table it will be seen that, if either a
weak or a strong current is passed along a motor nerve
in a downward direction, there will be a contraction at
making only. With a strong ascending current there
is a contraction on breaking only.
Pfltiger's law also holds good in the case of man,
but the conditions are necessarily different as the elec-
trodes are applied to the skin and not directly to the
nerves or muscles. It is usual to apply one electrode
over a nerve or muscle and another at some distant
part, as for instance, the back of the neck. If the anode
(4) be placed at the back of the neck, and the
kathode ( — ) over the nerve, the current will be a de-
scending one, and vice versa. When the kathode is
applied over the nerve and the current is closed or
opened, we have a kathodic closure contraction or a
Functions of Nerves
2 53
kathodic opening contraction ; if the anode is applied,
we have an anodal closure or opening contraction. The
following formula expresses what occurs normally.
Weak currents
Medium currents .
Strong currents
KCC
KCC
KCC
nil
ACC
ACC
nil
AOC
AOC
nil
. nil
ICOC
In disease, as for instance in ' infantile paralysis,'
this does not hold good, there being what is termed
the reaction of degeneration ; normally KCC appears
with a weaker current than ACC, but in the reaction
of degeneration ACC appears with a weaker current
than KCC, or with a current of the same strength.
Moreover, excitability to the induced current is
diminished or lost, the excitability to the continuous
current being exaggerated.
Functions and Classification of Nerves
Nerves may be divided into :
I. Efferent or Cen-
trifugal nerves
Motor, supplying the vo-
luntary or involuntary
muscles.
Vaso-motor, supplying the
muscular fibres of the
blood-vessels.
< 3 Secretory, supplying glan-
dular epithelium.
Inhibitory, which modify
the action of nerve-
centres.
5. Trophic, regulating the
nutrition of a part.
254 Nervous System
1 1. Nerves of common sensa-
tion, pain, touch, &c.
II. Afferent or Cen-12. Nerves of special sense.
tripetal nerves. 1 3. Nerves taking part in re-
flex actions, and which
cause no sensation.
/i. Connecting motor cen-
III. Intercentral J tres.
nerves. ] 2. Connecting sensory cen-
( tres.
1. Motor Nerves. — Each muscle in the body
has its ' nerve-supply,' or its nerve which connects it
with motor centres on the surface of the brain.
Stimulation of the nerve evokes a muscular contrac-
tion.
2. Vaso-motor Nerves. — These nerves are
divided into vaso-constrictor and vaso-dilator or
vaso-inhibitory. Stimulation of the cervical sympa-
thetic produces contraction of the arteries supplied to
the ear and face ; stimulation of the splanchnic, con-
traction of the arteries of the kidneys : such nerves
are vaso-constrictor. Stimulation of the chorda-
tympani causes dilatation of the vessels supplied to
the submaxillary gland ; stimulation of the nerves
supplied to the arteries of corpora cavernosa causes
dilatation of the vessels and turgescence of the erectile
tissue : such nerves are termed vaso-dilator or vaso-
inhibitory.
3. Secretory Nerves. — The chorda-tympani is
not only a vaso-inhibitory nerve, but also contains
fibres which stimulate the glandular epithelium of the
submaxillary gland. There are also nerves supplying
the mammary and lachrymal glands, which, when
stimulated, increase secretion.
4. Inhibitory Nerves. -Certain centres in the
brain or medulla exercise a depressing or hindering
Functions of Nerves 255
action on other centres. The nerves which connect
these centres are called inhibitory nerves. The brain
exercises an inhibiting or controlling influence over
the centres for defaecation and micturition in the
cord. The vagus is the inhibitory nerve supplying
the heart, inasmuch as when stimulated the heart's
action is slowed, and if the stimulus be sufficiently
strong it stops in diastole.
5. Trophic Nerves. — The nutrition of the
body is dependent, to a certain extent, upon the ner-
vous system. Thus in certain diseases of the spinal
cord bedsores very rapidly form over the sacrum.
While the nervous system exercises an important
influence over the nutrition of a part, it is doubtful if
there are any nerves whose sole office consists in
regulating the nutrition of a part.
Sensory Nerves. — Many divisions may be
made in this group. Thus there are nerves which
convey sensations of pain, touch, temperature, or of
special sense. The nerves of common sensation con-
nected with the spinal cord pass through the posterior
roots, and have a ganglion situated in their course,
just outside the cord. If sensory nerves are divided,
a sensation of pain is experienced if the central end is
irritated.
Eccentric Reference of Sensations. — The
mind refers the origin of every sensation that reaches
it through a sensory fibre to the end organ of that
fibre, even though stimulation has been applied to the
trunk of the nerve. Thus, persons whose arms or
legs have been amputated often feel sensations which
they refer to their ringers or toes. Any stimulation of
the optic nerve, mechanical or electrical, the mind
refers to the action of light upon the retina.
Functions of Terminal Organs. — Probably
all nerves end at their peripheral distribution in
some form of terminal organ. The optic nerves are
256 Nervous System
connected with the rods and cones of the retina, and
other sensory nerves are connected with taste-bulbs,
olfactory corpuscles, tactile corpuscles, or epithelium.
Motor nerves end in end-plates inside the sarcolemma.
Light will not affect the optic nerves, except through
the medium of the rods and cones ; sensations of
touch will not be received at the brain if the skin is
stripped off the fingers. The terminal organs seem
to play the part of receivers of impressions, and
awaken an excitation in the nerves connected with
them.
Functions of Nerve Centres
Groups of nerve-cells, which form the nerve-
centres, are arranged in the body in two systems, the
cerebro-spinal and the sympathetic system consisting
of ganglia scattered through the body. The centres
may be classified in various
ways, according to their
functions ; thus, on the sur-
face of the brain there are
motor or discharging centres,
centres of special sensations,
as of sight touch ; in the
Fig. go.-Di ag ra m n-presejiting a medulla there are inhibitory
simple reflex act. M, muscle ; Nc, -*
nerve-centre ; s, sensory surface, and accelerating Centres.
They all, however, fall into
two great divisions, though it is not always easy to say
to which class they belong ; these are automatic centres
and reflex centres.
Automatic Actions are actions which are
evoked in the absence of any influence external to the
nerve-centre. The brain is the seat of the higher
automatic centres, those connected with volition and
intelligence. In the medulla the respiratory centres,
cardiac centres, vaso-motor centres, are in a certain
sense automatic. So are also the intrinsic ganglia of
Reflex Actions 257
the heart, and the small ganglia found in the walls of
the intestines. At the same time it must be remem-
bered that many of the centres enumerated above are
influenced by sensory or -afferent impulses, and are
reflex as well as automatic ; indeed, some would deny
them their automatism, and believe that no motor im-
' pulses can be generated in the absence of all eccentric
influences.
Reflex Actions. — For reflex action the follow-
ing apparatus is required : —
1. A sensory surface in connection with an afferent
nerve (fig 99, s).
2. A nerve-centre, nc.
3. An efferent nerve connected at its central end
with the nerve-centre and by its peripheral end with
some muscle, or muscular tissue, or gland, m. The
sentient surface or end organ being excited, the im-
pulse travels along the afferent nerve to the centre,
and is reflected from the centre along the efferent
nerve to the muscle.
The stimulus may be of various kinds ; it may be
a simple tickling of the skin, or a bright light, or a
hair in the glottis. Some reflex actions are performed
without one being conscious of them, as the contrac-
tion of the pupil or the changes in the calibre of the
arteries. Others, as winking or swallowing, are
attended with consciousness. Some reflex acts can
be influenced or controlled by the will, as micturition
or coughing ; others are entirely beyond the control
of the will, as the second and third acts of swallowing.
The excitability of the centres in the cord is increased
by severance from the centres in the brain. Thus,
reflex movements are more active during sleep, or in a
decapitated frog than in an uninjured one. Strychnine
in toxic doses increases the irritability of the centres
of the cord, while the bromides, chloral, and atropine
diminish their excitability.
258 Nervous System
In some cases the reflex act seems to be adapted
to a purpose, as in the efforts made by a decapitated
frog to wipe away a drop of acetic acid placed on its
back.
The following instances of reflex acts may be
taken as examples : —
(1) Contraction of iris : aff. nerv., the optic ; '
nerv. centr., the corpora quadrigemina ; eff. nerv.,
third.
(2) Winking : aff. nerv., the fifth or optic ;
nerv. centr., the corpora quadrigemina ; eff. nerv.,
seventh.
(3) The first respiration after birth from impres-
sion of cold on the skin ; aff. nerv., the sensory of
skin ; nerv. centr., the medulla ; eff. nerv., phrenics,
intercostals, &c.
(4) Vomiting from tickling fauces : aff. nerv.,
the glossopharyngeal, fifth ; nerv. centr., the medulla ;
eff. nerve., phrenics, nerves to abdominal muscles,
vagi.
(5) Sneezing from a draught of cold air; aff.
nerv., the nasal branches of fifth ; nerv. centr., the
medulla ; eff. nerv., intercostals, nerves to abdominal
muscles, phrenics, &c.
(6) The secretion of saliva is a good example of a
reflex act in which a more complicated mechanism is
brought into action than in some of the examples
given. In the secretion of saliva from the submax-
illary salivary gland, the afferent nerves capable of
stimulating the nerve-centre are as follows : — (1) The
nerves of taste ; (2) the sensory branches of the fifth
nerve supplied to the mucous membrane of the
mouth ; (3) nerves of smell ; (4) optic nerves ; (5)
gastric branches of the vagus. The nerve-centre for
secretion of saliva is situated in the medulla. The
efferent nerve is the chorda tympani, which contains
two sets of fibres, vaso-dilato and secretory fibres ;
Spinal Cord 259
so that when this nerve is stimulated reflexly or
directly, the artery supplying the gland dilates and
the cells of the gland are stimulated to secrete (fig.
100).
Reflex actions are also seen in various forms of
disease or abnormal conditions, such as vomiting
ARTERY
CLAND
VASO -DILATOR
NERVE
SECRETING/ NER¥E
NERVE/ CENTRE
&
M £MBRAA/E
Fig. 100. — Diagram illustrating innervation of salivary glands.
from cerebral tumour, vomiting of pregnancy, grind-
ing of teeth from irritation of worms, palpitation of
heart, &c.
Time occupied in Reflex Acts.— The rapidity
with which a reflex act is performed varies from -05-
•06 second. The stronger the stimulus applied the
shorter will be the time.'
Spinal Cord
The spinal cord has its upper limit at the margin
of the occipital foramen, and extends downwards to
the lower border of the first lumbar vertebra. It is
fifteen to eighteen inches in length, and presents
s 2
26o
Nervous System
two enlargements, the cervical arid lumbar. It ends
below in the cauda equina, which consists of a bundle
of nervous cords.
Structure. — The cord consists of —
i. The grey matter in the centre.
2. The white substance externally.
1. The Grey Matter appears in the form of two
irregularly shaped crescents, joined to one another by
a commissure, in the centre of which is the central
Post, median col.
Post, septum
Post. ex. col.
Am.
cornu
. Cells of
ant. cornu
Central canal^
Subs, gelat. cart.''
Post, commissure'/
Ant. commissure
Ant. root
Ant. fissure Direct pyramidal tract
Fig. ioi. — Diagrammatic transverse section of the spinal cord x 6, on z
level with the eighth thoracic nerve (after Schwalbe).
canal. The anterior cornu (fig. ioi), or horn of the
crescents, is broad and rounded ; the posterior
cornu is long and narrow, tapering towards
Spinal Cord
261
the external surface
of the cord at the
post. lat. fissure ; near
its tip it has a pe-
culiar semi-transpa-
rent appearance — the
substantia gelatinosa.
Near the outer sur-
face of each crescent
the grey matter is less
sharply marked off
from the white than
elsewhere, its pro-
longations forming a
sort of network —
the processus reticu-
laris. A somewhat
pointed projection of
the grey matter in
the lateral region is
called the inter -me-
diolateral cornu. The
grey crescents vary
in shape in different
parts of the cord,
being narrow in the
dorsal ; the ant. cor-
nua are large and
broad in the cervical
and lumbar regions.
The nerve-cells of
the grey matter are
collected into four
groups or rather co-
lumnar tracts. (1)
Vesicular column of
the anterior cornu
Fig._ ioia. — Diagrammatic sections of the
spinal cord at different parts to show the
chief localised tracts of fibres in the
white substance (Quain's Anatomy). /.,
at the level of the sixth cervical nerve ;
//., of the third dorsal; ///., of the
sixth dorsal ; IV., of the twelfth dorsal ;
V. t of the fourth lumbar, d.p.t., direct
pyramidal tract ; cj.t., crossed or lateral
tract ; c.t., direct cerebellar tract ;g, post-
median column.
262 Nervous System
(fig. 1 01). These, for the most part, are multipolar, and
vary in size from ^ Tl - in. to ¥ 'n, in. They are directly
connected by their processes with the motor nerve-
fibres. They are best marked in the cervical and
lumbar enlargements. (2) Posterior vesicular column
of Clarke (fig. 101), reaches from the eighth cervical to
the third lumbar. The cells are large and fusiform,
with their long axes parallel to the cord. (3) Column
of the intermedio-lateral tract, ox posterior -lateral group
(fig. ior), confined to the dorsal and upper part of the
lumbar spinal cord Consists of small spindle-shaped
cells. (4) A small group of multipolar cells in the
posterior horn.
2. The White Matter is divided into two halves
by the anterior median and posterior fissures. Each
lateral half is again divided by two lateral fissures,
which are merely grooves along the line of attachment
of the anterior and posterior branches into an anterior,
lateral, and posterior column. The white substance
on section, and examination by a high power, displays
the cut ends of the nerve-fibres, presenting small rings
with a dot in the centre, the dot representing the axis
cylinder, and the surrounding space the white sub-
stance of Schwann.
Course of the Nerve-Fibres in the Cord.—
By various methods of research, especially by study-
ing the development of the cord, and certain patho-
logical changes occurring as the result of injury or
disease, the following tracts have been distinguished
in the cord : —
A. Descending Tracts.— (1) The direct pyra-
midal tract, or column of Turk (fig. ioia, d.p.t.), is
traced down from the anterior pyramid of the medulla
of the same side, and, therefore, has not decussated.
Probably the decussation of these fibres goes on along
their whole course. This tract cannot be traced
farther than the middle of the dorsal region.
Spinal Nerves 263
(2) Tlie lateral or crossed pyramidal tract (c.p.t.)
can be traced down, diminishing as it goes, to the
third or fourth sacral nerves.
B. Ascending Tracts. — (1.) The direct lateral
cerebellar tract (c.t.) lies between the lat. pyramid,
tract and the outer surface of the cord. It disappears
at the second or third lumbar nerves. The remainder
of the antero-lateral column has not been mapped
out ; it is, probably, commissural.
(2) The post-median column, or tract of Goll (g),
only extends downwards as far as the middle of the
dorsal region.
(3) The posterior external column is sometimes
called Burdock's column, ox fasciculus cuneatus.
(4) The anterior division of the lateral column is
called the anterior radicular zone.
Spinal Nerves. —Thirty-two pair of nerves arise
from the cord, each nerve arising by two roots, an
anterior and a posterior. The anterior arises by
several bundles from the antero-lateral region of the
cord ; the posterior arises by a single bundle from the
posterior horn of grey matter. The two roots join to
form the trunk of the spinal nerve ; there is a ganglion
on the posterior.root. Section of the anterior root is
followed by paralysis of the muscles supplied by the
nerve ; excitation of the peripheral end gives rise to
contraction of the muscles ; irritation of central end
has no effect. Section of the posterior root causes loss
of sensation in the area of its distribution ; stimula-
tion of its central end causes cries of pain ; stimula-
tion of its peripheral end has no effect. If the anterior
root be divided, the whole peripheral part of the
fibres degenerates, so that in a section of a mixed nerve
the degenerated motor fibres can be identified. If
the posterior root be divided between the ganglion
and its junction with the anterior root, all the sen-
sory fibres in the mixed nerve below the junction
264 Nervous System
degenerate. If it be divided between the ganglion and
the cord, the sensory fibres in the mixed nerve remain
intact, but the central parts of the fibres degenerate
up through the cord to the medulla.
Functions of the Cord
1. As a conductor of impressions and impulses.
2. As a series of nerve-centres.
The Cord as a Conductor
1. The spinal cord forms a channel of communi-
cation between the brain and nerves, passing to the
periphery of the body. The exact path of the motor
and sensory nerves is not satisfactorily settled, as
there are discrepancies between the results obtained
by different observers.
Motor Path. — Motor impulses travelling from
the brain to the anterior pyramid of the medulla, for
the most part decussate in the medulla, crossing to
the crossed pyramidal tract of the opposite side. A
minor portion travelling along the direct pyramidal
tract (fig. ioia, d.p.t.) decussates by crossing to the
crossed pyramidal tract in the cervical and upper
dorsal region. Decussation is therefore going on not
only in the medulla but in the cervical and upper
dorsal regions. The motor impulses pass from the
lateral columns into the anterior cornua, become con-
nected with the ganglionic cells there, and leave the
cord by the anterior root.
Sensory Path. — According to the experiments
of Gotch and Horsley, the fibres of the posterior roots
divide into two classes ; first, those that run straight up
the cord in the posterior column without becoming
connected with any nerve-cells until they reach the
Functions of the Cord 265
medulla ; and secondly, those which enter the grey
substance and become connected nerve-cells. 80 per
cent, of the afferent impulses travel up the same side
of the cord ; this 80 per cent, is made up of 60 per
cent, which travel up the posterior column and 20 per
cent, up the lateral column ; while of the remainder
some 1 5 per cent, pass up the posterior column on the
opposite side, and a few up the lateral column of that
side.
Reflex Functions of the Spinal Cord
2. Frog. — If the spinal cord of a frog be
divided immediately below the occipital foramen, the
frog will retain its usual sitting attitude, with the ex-
ception of sinking down into a somewhat less erect
position, the fore limbs being more spread out. It
will exhibit no respiratory movements. If one of the
hind legs be pulled out straight and let go, it will be
drawn up again to its normal position. If the skin of
one flank be tickled, the muscle beneath will contract.
Pinch the same spot, or apply a drop of acetic acid,
and the leg of the same side will make a sweeping
movement to clear away the source of irritation ; if
the leg of the same side be held or cut off, the leg
of the other side will repeat the movement. Place
the frog on its back, it will make no effort to regain
its position. The above actions of the brainless
frog are complicated, co-ordinated, purposeful in
character ; but, however stimulated, the animal never
leaps.
In the Mammal.— For some days after the
division of the cord in a dog, very feeble reactions
are given by the nervous mechanism of the cord.
After some weeks movements of a varied character
are evoked by tickling or pinching the toes.
In man, when the cord is crushed from the effects
266 Nervous System
of accident or disease, the legs will start up on tickling
the soles or in passing water. In the normal condition
it is generally possible to evoke reflex actions of the
cord by gentle stimulation of the skin by a touch or
light stroke. Tickling the soles of the feet, more
particularly during sleep, will cause a slight with-
drawing movement of the muscles of the foot, called
the ' plantar reflex,' The centre for this movement
is situated in the lower part of the lumbar enlarge-
ment. Irritation of the skin of the buttock will often
produce a contraction of the glutei (gluteal reflex),
the nerve-centre being situated at the origin of the
fourth or fifth lumbar nerves. Irritation of the inner
side of the thigh will cause a contraction of the
cremaster (cremasteric reflex), drawing up the testicles,
the centre being connected with the first and second
lumbar nerves. There is also an abdominal reflex
and an epigastric reflex, which may be produced by
stroking the side of the abdomen and side of the
chest respectively. The ' patellar reflex ' is obtained
by allowing the knee to swing freely, and then sharply
tapping the patellar tendon, the leg jerking forward ;
this movement is probably due to the stimulus
reaching the muscle direct, the time occupied being
too short for a reflex act, but it nevertheless depends
upon the integrity of a nerve-centre situated in the
upper part of the lumbar enlargement of the cord.
Action of Strychnia.-— Strychnia gives rise to
an excessive excitability of the spinal cord. An animal
having received a poisonous dose, dies in a condition of
tetanus, the movements of respiration being arrested.
A frog does not readily die, as respiration is con-
tinued through the skin ; the Contracted condition
of the muscles is abolished by destroying the spinal
cord.
In a frog under the influence of strychnine, the
slightest stimulus of the skin evokes a reflex action,
Centres in the Cord 267
the slightest touch sending all the muscles into pro-
longed tetanus.
Inhibition of Reflex Actions. — The brain
exercises a powerful influence in restraining or in-
hibiting reflex actions. A brainless frog exhibits re-
flex actions better than one with brain intact. If the
experiment be tried of suspending a frog with cerebral
hemispheres only removed, with its toes dipping in
dilute acid, and the time which elapses before their
withdrawal noticed, and the same experiment repeated,
stimulating the optic lobes at the same time, the time
elapsing before the withdrawal will be prolonged,
showing the optic lobes have inhibited the reflex
centres.
Man, by an effort of will, can prevent the with-
drawal of his feet if the soles are tickled.
Special Centres in the Spinal Cord.
1. Centre for maintaining tonus of the muscles.
2. Centre for sphincter of bladder.
3. Centre for sphincter of rectum.
4. Centre for contractions of uterus.
5. Centre for erection of genital organs.
6. Cilio-spinal centre.
1. The muscles of the body are kept in a constant
state of contraction or tonus ; this effect is due, pro-
bably, not to an automatic but to a reflex mechanism
constantly in action.
2, 3. The centres for micturition and defsecation
appear to exist in the lumbar region of the spinal
cord.
4, 5. The centres that govern the movements of
the uterus and erectile tissues are situated in the
lumbar region of the cord.
The above centres are to be considered reflex
rather than automatic.
268
Nervous System
The Medulla Oblongata
The medulla is bounded above by the lower
border of the pons Varolii, and is continuous below
with the spinal cord at a level with the foramen
magnum.
Structure. — The medulla is divided on the surface
by fissures into short columns, which have received
Hypoglossal n.
N. gracilis
N. cuneatus
F. solitanus
F. gracilis
i F. cuneatus
Restiform body
Subs, gelat. R.
Root of 5th
Fig. 102. — Diagrammatic transverse section of the spinal bulb at about the
middle of the olivary body, to illustrate the principal nuclei and tracts at
that level ; x 3 (after Schwalbe).
different names ; each lateral half having from before
backwards : —
Anterior pyramid.
Lateral tract and olivary body.
Restiform body.
fasciculus cuneatus.
Posterior pyramid
fasciculus gracilis.
Medulla 269
White Matter of the Medulla.— The ana-
tomical connections of the cord and medulla are very
complicated.
Tracing upwards the different columns of the cord,
we find that the anterior column {direct pyramidal tract)
is continuous with the anterior pyramid of the same
side. The lateral pyramidal tract joins the anterior
pyramid of the opposite side. These two are motor,
and are continuous with the crusta.
The antero-lateral (exclusive of the above) is sen-
sory, and probably passes up through the front part of
the restiform body, through the superior peduncles of
the cerebellum to the superior lobe.
The direct cerebellar tract joins the restiform body
and forms the inferior peduncles of the cerebellum.
The posterior medium column joins the posterior
pyramid and ends in the nucleus gracilis ; fas. posterior
external column is continuous with the funiculus
cuneatus and ends in the nucleus cuneatus. It is
probable that both the latter are continuous with the
tegmentum of the opposite side, decussating above the
pyramids.
Grey Substance of the Medulla. — The
medulla contains various nuclei ; two masses of grey
matter which 1 receive the posterior pyramids and
funiculus cuneatus, called the nucleus gracilis and
nucleus cuneatus. The anterior lateral nucleus. The
lower part of the fourth ventricle contains the nuclei
of the hypo-glossal, spinal accessory, vagus, glosso-
pharyngeal, and auditory (figs. 102 and 118).
Functions of the Medulla
(a) Conductor of impulses and impressions.
(b) As a collection of nerve-centres.
270 Nervous System
(a) The Medulla as a Conductor
The Motor impulses travel through the anterior
pyramids, decussating to the lateral column of the
opposite side of the cord.
The Sensory path is not so well known, it pro-
bably passes along the posterior pyramids, decussating
above the anterior pyramids (see above).
(6) Nerve Centres in the Medulla
(1) Respiratory centres.
(2) Vaso-motor centre.
(3) Cardiac centres.
(4) Centres for deglutition.
(5) Centre for voice.
(6) Centre for mastication
(7) Centre for expression.
(8) Centre for salivary secretion.
(1) The Respiratory Centres consist of an
inspiratory and expiratory centre, and are both reflex
and automatic. Ordinary respiration is a reflex act ;
a venous condition, i.e. a want of O in the blood
circulating through the capillaries of the lungs, stimu-
lates the terminal fibres of the vagus, ths vagus trans-
mits the impression to the medulla, it is reflected
along the phrenics, intercostals, &c, to the muscles of
inspiration, and a fresh supply of air is drawn into the
lungs. The more venous the blood the more vigor-
ously are the terminal fibres of the vagus excited, and
the more muscles brought into play. If the vagi are
divided the number of respirations sink to at least
one -third, but they are still continued, and the animal
does not die of asphyxia. It is probable that the
venous blood supplied to the medullary centre itself
Pons 2 7 1
excites it, or, like the intracardiac ganglia, it acts in
an automatic manner.
(2) The Vaso-motor Centre is the centre of
the sympathetic system supplied to the muscular fibre
of the blood-vessels, intestines, ducts, &c. If stimu-
lated, the vessels all over the body contract, and the
arterial tension is raised ; if paralysed or inhibited
they dilate, and arterial tension is lowered. The vaso-
motor centre keeps the blood-vessels of the body in a
state of tonic contraction ; it acts reflexly, and any
influence which inhibits it will dilate the vessels.
(3) Cardiac Centres. — The rhythmical con-
traction of the heart is caused by the action of its own
intrinsic ganglia, but its action is regulated by ganglia
situated in the medulla. There are two extracardiac
ganglia, one accelerating, acting on the heart through
the sympathetic, and the other inhibitory, associated
with the vagus. (See page 102 and fig. 49).
The presence of the above ganglia renders the
medulla of vital importance to the living mammal.
Death immediately results by destroying it. This
can readily be accomplished by ' pithing,' i.e. by
thrusting an awl-shaped instrument into the medulla,
passing it between the occiput and atlas, and breaking
up the nervous substance.
Pons Varolii
The pons shows, on traverse section, (1) super-
ficial and deep transverse fibres, derived from middle
peduncles of cerebellum ; (2) longitudinal fibres con-
tinuous with the ant. pyramids ; (3) longitudinal
fibres of the formatio reticularis, continuous with the
medulla ; (4) grey matter of upper part of 4th ven-
tricle, containing nuclei of facial, motor of 5th, sensory
of 5th, auditory, and 6th.
272 Nervous System
Mesencephalon
The mesencephalon is developed from the middle
vesicle of the brain, and represents the optic lobes of
fishes and birds. It includes the nuclei around the
aqueductus Sylvii, the corpora quadrigemina, and
crura cerebri.
The Aqueduct of Sylvius (fig. 103) is a closed
canal between the third and fourth ventricles. The
grey matter of the aqueduct is a prolongation from
the floor of the fourth ventricle, and contains the
nuclei of the third and fourth nerves, and the upper
nucleus of the fifth. The tegmenta lie below the
aqueduct.
The Corpora Quadrigemina (fig. 103) are four
rounded eminences seated over the aqueductus Sylvii.
Each of these bodies is covered with a layer of
white matter ; the lower or posterior pair contain a
grey nucleus, and are separated by a band of white
matter, the fillet, from the grey matter of the aqueduct.
The superior pair have a layer of grey matter beneath
the white layer on the surface, and underneath the
former is a longitudinal tract of fibres— the stratum
opticum.
The Crura Cerebri (fig. 103) lie beneath the
corpora quadrigemina, and consist of (1) an inferior
or anterior layer of longitudinal fibres called the
erusta (cr.), and is a direct prolongation upwards of
the pyramid bundles of the pons, and passes upwards
to the internal capsule ; (2) the substantia nigra
consists of a centre nucleus of grey matter, the cells
containing pigment (s.n.) ; (3) superior or posterior
longitudinal bundles of nerve-fibres, interspersed with
transverse ones, called the tegmenta (t) ; it is a direct
prolongation upwards of fibres probably derived from
Cerebellum
273
the posterior columns of the cord (see p. 269), and
passes upwards to the optic thalamus.
The Cerebellum is situated at the posterior part
of the brain, and consists of peduncles, various lobes
and processes. The peduncles are three in number,
the superior, middle, and inferior ; they serve to con-
nect the cerebellum with the cerebrum, pons, and
medulla respectively.
The cortical portion consists of grey matter, and
the central portion of white substance with a nucleus
of grey, the corpus dentatum.
Fig. 103.- Outline of Lwo sections across the mesencephalon (Quain's
Anatomy). A, through the middle of the inferior corpora quadrigemina ;
B, through the middle of the superior corpora quadrigemina. cr. t crusta ;
s.fi., substantia nigra ; t, tegmentum ; s, Sylvian aqueduct, and surround-
ing grey matter; s.c.p., superior cerebellar peduncle; J", fillet, c.q.,
corpora quadrigemina ; ///. 3rd nerve ; d. V., descending root 5th nerve.
The cortical substance has three layers (fig. 104) —
(1) External. — Consists of small cells sparingly
distributed, some rounded, others irregular in shape,
with various processes ; fibres which are for the most
part^processes of the large cells of the middle layer,
and run at right angles to the surface (b\
(2) Middle. — Consists of cells of Purkinje ar-
ranged in a single layer. They are pyriform in shape,
nucleated, and have long processes running into the
external layer, and are -sT^th to nrWrh inch in dia-
meter (c).
(3) Inner or granule layer. — Consists of small
round granular corpuscles, about the size of white
274
Nervous System
Fl ^'=i.^ 4 '7 S '? CU ' r , e , 0f corte '; of cereM1 ™ (Quain's Anatomy), a, pia
™ f, ,'. ?' ?"f nal k , y " ; f > la 5' er of corpuscles of Pmkinie ; rf, inner or
granule layer ; ?, medullary' centre.
Functions of Brain - 275
blood-corpuscles, arranged in dense masses, which
in stained specimens form a well-marked coloured
layer (d).
Phenomena Exhibited after Removal of
Cerebral Hemispheres
Frog. — After the removal of the cerebral hemi-
spheres the animal main-tains its normal attitude. If
laid on its back, it will turn over and regain its feet.
Voluntary motion lost.
Cannot direct movements.
Cannot jump.
Cannot recover position if-{
aid on back.
Olfactory lobes.
Cerebral lobes.
Fig. 105. — Diagram illustrating higher nerve-centres of the frog (after
Lauder Brunton).
If its foot is pinched, it will hop away. If thrown
into water, it will swim, reach the edge, clamber up,
and sit perfectly still. If its back is stroked, it will
croak. If placed in water and the temperature raised,
it will make efforts to escape. If it jump away after
a stimulus has been applied, it will avoid any object
in its path. It will never move without some stimulus
being applied. All spontaneous action has departed.
276 Nervous System
It will not feed itself, but will sit still till it decom-
poses (fig. 105).
Fish exhibit similar phenomena : they swim about
in the water ; the movements are not voluntary, but
result from the stimulus of the water in contact with
the body.
Pigeon with cerebral hemispheres removed sits on
its perch and balances itself perfectly. When thrown
in the air it flies, when pinched it moves forward. If
not meddled with it appears to be in a profound
sleep, though occasionally it will dress its feathers or
yawn. Its pupils contract normally. It resists any
efforts made to open its beak, but swallows when food
is placed in its mouth. It makes no spontaneous
movements ; the yawning and dressing itself are pro-
bably the result of the irritation of the wound.
Rabbit. — When the cerebral hemispheres are re-
moved the animal is at first prostrate ; after a while
it can use its legs, though the fore ones are weak. If
pinched it springs forward ; but, unlike frogs in a
similar condition, will strike itself blindly against any
obstacles in its path. When pinched severely it utters
cries.
In higher animals, as cats and dogs, motor paralysis
is so marked after the removal of the hemispheres
that no conclusions concerning equilibrium and co-
ordinated movements can be drawn.
At first sight it would appear that consciousness
was necessary for the performance of complicated
movements and the avoidance of objects in the path ;
the cries elicited on pinching would appear to indi-
cate the sensation of pain. Probably they are the
result of a reflex mechanism, and are similar to walk-
ing during sleep, or the cries elicited from patients
when under chloroform. The medulla contains
centres for reflex actions more complicated than the
cord, and the corpora quadrigemina and cerebellum
Functions of Cerebellum 277
contain centres for still more complex acts, as the
reflex expression of emotion, the avoidance of an
object when leaping, or the co-ordination of many
contracting muscles.
Functions of Corpora Quadrigemina
In man they contain {nates or subjacent struc-
tures') —
(1) Centres for co-ordination of the movements
of the eyeballs.
(2) Centre for the contraction of the pupils.
In some of the lower animals they contain —
(3) Centres for co-ordination of retinal impres-
sions with certain muscular movements.
(4) Centre for maintenance of equilibrium.
Ferrier found, on applying a weak interrupted
current to the surface of the nates in the monkey,
that irritation of one side caused the opposite pupil
to become widely dilated, followed by dilatation of
the pupil of same side. The eyeballs are directed
upwards and to the opposite side, and the ears
retracted. The legs become extended, the jaws re-
tracted, and angles of mouth retracted. Irritation of
the testes produces similar results, but in addition cries
are elicited.
Functions of the Cerebellum
Removal of the cerebellum in a pigeon renders
co-ordinated movements, such as walking, flying,
turning round, imperfectly performed. There is no
loss of muscular power or of sensation ; the bird
struggles to get on to its legs and flaps its wings in its
endeavour to fly, but its movements are awkward and '
irregular. Injury or a tumour of the middle lobe of
the cerebellum in man gives rise to a staggering gait,
not unlike that of a drunken man ; there is a difficulty
278
Nervous System
in maintaining the equilibrium, especially when the
eyes are closed, and in turning sharply round.
Section of the middle lobe of the cerebellum in
monkeys gives rise to difficulty in maintaining the
equilibrium ; injury of the anterior extremity of the
middle lobe causes the animal to tumble forwards,
while when the posterior end is injured there is a
tendency to fall backwards.
Fig. 106. —Transverse section through the brain (Quain's Anatomy), cc,
corpus callosum ; L V, lateral ventricle ; th thalamus ; str, lenticular
nucleus of the corpus striatum ; c, caudate nucleus of the same ; between
th and str is the internal capsule; outside sir is a thin gray band, the
claustrum ; outside this is the fissure of Sylvius, and island of Reil ;
sit, v, vessels on the surface : /, pineal gland ; B, basilar process.
From these observations it would appear that in
man the middle lobe of the cerebellum is in some
way or another connected with the co-ordination
of muscular movements, especially with those move-
Basal Ganglia 279
merits which maintain the equilibrium of the body.
Paralysis and muscular contractures often are present
in cerebellar tumours, but these are probably due to
the cerebellum compressing the mot.or tracts in the
pons, or giving rise to distension of the lateral ven-
tricles in consequence of pressing on the vena galeni.
The functions of the lateral lobes of the cere-
bellum are unknown ; they are connected by means
of the fibres of the superior and inferior with the
cortex of the hemispheres, and according to Gowers
they are in some way connected with mental pro-
cesses.
Basal or Central Ganglia
These consist of the corpus striatum and optic
thalamus ; passing in close relation with them is the
internal capsule (fig. 106).
The corpus Striatum consists of two parts —
an intra-ventricular portion, projecting into the lateral
ventricle of the same side as an elongated grey body
called the caudate nucleus (fig. 106 and fig. 107),
and an extra-ventricular portion, the lenticular
nucleus, more deeply placed, and is separated
from the optic thalamus (see fig. 107) by the internal
capsule. On its outer side it is in close proximity to
the island of Reil, the claustrum intervening (see
fig. 106 and fig. 107). It consists of three parts. It
is uncertain if the corpus striatum has any connection
with the cortex, but fibres coming from it enter the
internal capsule. It consists of grey matter, and con-
tains many nerve-cells.
The optic thalamus is more or less oval-shaped ;
it consists of grey matter, containing many nerve-
cells ; it has a superficial layer of white fibres. On the
inner side it projects into the lateral ventricle, being
placed posteriorly to the caudate nucleus ; on its outer
28o
Nervous System
side is the internal capsule. It is connected with the
cortex, optic tracts, and with the tegmentum of the
cms.
Fig. 107. — Transverse (vertical) section of a cerebral hemisphere, made in
front of the optic thalamus (Landois and Stirling). CCa, corpus callo-
sum ; N(J, caudate nucleus (the letters themselves are placed in the
lateral ventricle); NL, lenticular nucleus; IC, internal capsule; CA,
internal carotid ; a SL, lenticular striate artery (' artery of haemor-
rhage ') ; F, A, L, T, motor centres governing movements of face, arm,
leg, and trunk, the fibres of which converge to pass along the internal
capsule.
The internal capsule is a broad band of fibres
which connects the cortex of the brain with the cms,
and in which lie both the motor and sensory paths.
Cerebrum 281
The anterior limb separates the caudate and lenticular
nuclei (see fig. 107), the posterior limb lies between the
latter and optic thalamus. It is best seen in horizontal
section of the brain ; the two limbs are seen to join at
an acute angle called ' the knee.'
The functions of the corpus striatum and optic
thalamus are not known with certainty. As they lie
deeply, and any injury involving either almost certainly
injures the internal capsule also, it is very difficult to
ascertain their functions. The optic thalamus has been
supposed to be in some way related to the sense of
sight. According to the older view, the office of the
basal ganglia was the co-ordination of muscular move-
ments in the performance of complex acts : thus,
to quote Broadbent, 'the corpus striatum translates
volition into action or puts in execution the com-
mands of the intellect ; that is, selects, so to speak,
the motor nerve-nuclei in the medulla and cord
appropriate for the performance of the desired action,
and sends down the impulses which sets them in
motion.'
As already stated, the internal capsule contains the
motor and sensory paths from and to the cortex, the
motor path occupying the anterior two-thirds (fig. 107),
and the sensory the posterior third of the hind limb.
The Cerebrum
The cerebral hemispheres form two ovoid masses
of grey and white matter, with convolutions on their
surface. The grey matter is mostly present on the
surface, and forms a layer from \ to \ inch in depth,
the amount being greatly increased by the convolu-
tions. The white matter is arranged in various ways :
longitudinal fibres, as the fornix ; transverse fibres, as
the corpus callosum ; peduncular fibres, connecting
282 Nervous System
the grey matter on the surface with the corpora
striata (corona radiata), and the latter with the pons
(crura).
The grey matter of the cerebrum resembles the
grey matter elsewhere, though the number and shape
of the nerve-cells undergo considerable variation.
Five or more layers have been described, but they
blend imperceptibly into one another : —
(1) The most external layer is composed mostly
of neuroglia, and contains a few small cells with fine
processes.
(2) Contains a large number of small pyramidal
or arrow-head cells.
(3) Is of greater thickness, and contains large
pyramidal or arrow-head cells, with their points to the
surface of the convolutions. They are separated by
bundles of nerve-fibres running towards the surface.
(4) A narrow layer of irregular- shaped cells with
fine processes.
(5) Wider than the last, and composed of fusiform
and irregular cells, mostly extending parallel to the
surface.
The large pyramidal cells present in the third and
fourth layers are especially well-developed in the
motor centres in the ascending frontal convolution.
In the occipital lobes, and about the calcarine fissure,
the large cells are very scanty.
Functions of the Convolutions.— The grey
matter on the surface is the seat of the higher pro-
cesses of mind, including volition, memory, intellect,
and the emotions. It also contains perceptive centres
of special sense, as sight, hearing, touch, smell, taste.
Special motor areas or centres have been localised by
Ferrier in the parietal regions, and various perceptive
centres in the temporo-sphenoidal lobes. The cere-
Convolutions
283
bral cortex appears to contain a collection of centres,
towards which incoming sensations converge from all
parts of the body ; here they come into relation with
one another, and give rise to motor impulses which
pass to the corpora striata, and thence to the muscles.
Ferrier considers the frontal lobes are connected with
the intellectual faculties, and the posterior lobes with
the appetites. Reference to fig. 108 will show the
motor centres, stimulation of which by a weak Faradic
current causes movement in the corresponding group
Fig. 108. — Lateral view of left half of brain. Motor areas shaded ; dotted
area indicates the speech centre (Landois and Stirling).
of muscles, or destruction of which causes paralysis.
The perceptive centres of vision and hearing are also
mapped out ; those of touch, smell, and taste are
situated in the convolution on the inner side of the
temporo-sphenoidal lobe.
Motor Areas. — It is from the motor centres
situated at the cortex of the brain that fibres arise
which pass through the white substance in the centre
of the brain, along the internal capsule to the anterior
pyramids of the medulla, and on to the pyramidal
284 Nervous System
tracts of the cord. Injury to these centres causes,
first, paralysis, and afterwards descending degeneration
along the motor path takes place.
The leg-centre (fig. 108) occupies the highest part
of the ascending frontal and parietal convolutions on
each side of the fissure of Rolando ; it also occupies
the paracentral lobule on the inner surface.
The arm-centre occupies the middle third of the
above convolutions (fig. 108).
The face-centre occupies the lower third of the
ascending frontal and parietal convolutions ; the lips
and tongue have their centre at the lowest part of the
ascending frontal.
The trunk-centre is apparently situated on the
inner surface in the longitudinal fissure in front of the
leg-centre.
Sensory Centres. — The position of the centre
for sensation of the limbs and trunk has not certainly
been defined. According to Flechsig, the fibres of
the sensory path of the internal capsule pass upwards
to the central convolutions, i.e. ascending frontal and
parietal convolutions and parietal lobe. If this view
is correct, this region contains both motor and sensory
centres. Ferrier localised the centre of tactile sensa-
tion in the hippocampal region. In cases of injury to
the brain followed by loss of motor power and loss of
sensation, if recovery takes place sensation returns
sooner or later, though the parts paralysed may never
regain their power. This return of sensation is, no
doubt, due to other parts of the brain taking on the
functions of the part destroyed.
Smell. — The olfactory centre is probably situated
at the anterior extremity of the uncinate convolution.
The experiments of Ferrier, as also anatomical and
pathological researches, would seem to indicate this.
Vision. — The visual area is seated in the occipital
lobes ; but the exact spot has not certainly been
Speech Centre 285
determined. According to Ferrier's experiments on
monkeys, destruction of the angular gyri and occipital
lobes cause total and permanent blindness. In man,
disease of one occipital lobe causes hemianopia—thsX
is, blindness of the lateral halves of both retinae
corresponding to the side of the lesion.
Auditory Centre, — The centre for hearing in man
is situated in the first temporo-sphenoidal convolution.
Destruction of this region has been followed by loss
of hearing on the opposite side, though this was not
permanent (Gowers). This convolution has been
found atrophied in cases of congenital deafness.
Speech Centre. — The centres connected with
speech are in the posterior extremity of the inferior
(3rd) frontal convolution of the left hemisphere ; the
island of Reil is apparently also concerned. Damage
to this centre is followed by the loss of the faculty of
speech — a condition to which the term aphasia is
applied. The patient may have perfect control over
his lips, tongue, &c, and may be able to utter articu-
late sounds, but he cannot combine the sounds so as
to form words by which he can express his thoughts.
He can neither express himself in writing, nor can
he read. In some cases the patient can express his
thoughts in writing when he cannot by speech.
Rapidity of Cerebral Operations. — Mental
operations occupy a longer period than simple reflex
actions. By means of a suitable apparatus and a
system of signalling this period can be approximately
measured. A stimulus is applied, as an induction
shock ; and the person experimented on gives a signal
the instant he feels it, both being recorded on a moving
surface. The interval is called ' the reaction period.'
This period includes the time occupied by the im-
pression in travelling along the nerve to the centre,
its perception by the mind, and the time occupied by
the motor impulse travelling to the muscles giving rise
286 Nervous System
to muscular contraction. The reaction period for
feeling is 1 sec, hearing \ sec, and sight -!- sec. But
these figures are likely to vary in different persons.
Course of the Motor Fibres. — The course of
the motor path, or pyramidal tract, as it is called, from
the parietal convolutions to the muscles is better
known than the. course of the sensory path. The
fibres forming the motor path on leaving the cortical
centres pass through the white ' centrum ovale,' and
converge to the internal capsule (fig. 107), where they
occupy the anterior two- thirds or more of the posterior
limb ; entering the crus cerebri, they pass along the
crusta, occupying the middle two- fifths, extending
from the surface below to the substantia nigra above
(fig. 103) ; passing on to the pons, the fibres separate
into bundles lying between the superficial and deep
transverse layers, and being surrounded by much grey
matter ; entering the medulla, the motor fibres rejoin
one another, forming the anterior pyramids ; at the
lower part of the medulla about three-fourths of the
fibres decussate, passing to the opposite side to form
the lateral or crossed pyramidal tract of the cord ;
those which do not decussate pass down their own
side of the cord, forming the ante?'ior or direct pyra-
midal tract (fig. 109).
Hemiplegia. — Damage to the motor centres at
the cortex, or to any part of the motor path, is followed
by paralysis of the face, arm, and leg of the opposite
side. In a severe case the face is paralysed, chiefly
the lower half ; the tongue when protruded points
towards the paralysed side, and the arm and leg are
completely powerless. For the most part, the muscles
of mastication, respiration, and the trunk muscles
escape ; these muscles, being associated in their action
with those of the opposite side, are probably excited
to act by the nervv-centres which supply their fellows.
The commonest cause of hemiplegia is a rupture of the
Sensory Fibres
AO,
INTERNAL CAPSULE
lenticulo-striate artery and a consequent destruction
of the internal capsule (fig. 109).
In some forms of hemiplegia
the 3rd, 4th, 6th, or other cranial
nerves may be involved.
Course of the Sensory
Fibres. — Less is known con-
cerning the path of the sensory
than the motor fibres. The
fibres which enter the cord from
the sensory nerves mostly pass up
the posterior and lateral columns
of the same side and decussate in
the medulla. A few pass at once
on entering to the posterio-lateral
column of the opposite side. In
the medulla and pons, the
sensory path is believed to lie
in the formatio reticularis, from
which it passes along the tegmen-
tum of the cms and enters the
internal capsilk, occupying the
posterior third of the hind limb.
From the internal capsule the
path lies through the central
white substance to the cortex,
being distributed to that part
of the cortex which lies be-
neath the parietal bone (Flech-
sig), or, according to Ferrier, to
the hippocampal region. In
the upper part of the pons the
path is joined by the sensory
fibres from the face (5th nerve),
so that the posterior part of
the internal capsule contains
sensory fibres from the whole tra?a,/couK?ofraotSrpath-
288 Nervous System
of the opposite side of the body. Apparently, also,
the fibres from the special organs of sense, taste, hear-
ing, smell, vision, pass through the internal capsule.
Hemianesthesia. — Destruction of the posterior
portion of the internal capsule gives rise to loss of
sensation to touch, pain, and temperature of the oppo-
site side of the body ; the organs of special sense are
also involved. If the sensory path is destroyed below
the pons, the parts supplied by the 5 th nerve escape.
In many cases of hemiplegia there is also more or
less loss of sensation.
Functions of the Cranial Nerves
First, or Olfactory. — The olfactory nerve arises
from the under surface of the frontal lobe in front of
the anterior perforated space by three roots, the ex-
ternal, middle, and internal. It lies on the orbital
surface of the frontal lobe, lodged in a sulcus, and
swells out into an enlargement, the olfactory bulb.
The branches or true olfactory nerves, some twenty
in. number, pass through the cribriform plate, and
ramify upon the upper part of the septum, and the
superior and middle turbinated processes. The olfac-
tory bulb or lobe consists of grey substance ; the
peripheral nerves consist of nerve-fibres, which are
non-medullated. The mucous membrane, over which
the olfactory nerve is distributed, is softer and more
pulpy than the respiratory region. It is of a yellow
colour. The epithelial cells are modified so as to
form terminal organs for the olfactory nerves. The
columnar cells are continued downwards in a root-
like process, and between the cells there are fine
threads or rods, connected at their inner extremities
with spindle-shaped olfactory cells, the cells being
apparently connected with filaments of the olfactory
Optic Nerve
289
nerves. The olfactory nerves do not decussate, and
are unlike all other nerves in this respect.
Optic Nerve. — Each optic tract arises from the
posterior part of the optic thalamus and the corpora
geniculata. Leaving this attachment, it winds forward,
Fig. no.— Cells and terminal nerve-fibres of the olfactory region. 1, from
the frog ; 2, from man. a, epithelial cell, extending into a root-like pro-
cess ; b, olfactory cells ; c t peripheral rods ; d, their central filaments.
3, olfactory nerve fibre in dog. a, division into fine fibrillse. Irritation
of the olfactory terminal organs gives rise to a sensation of smell.
crosses the crura cerebri as a flattened band ; then,
becoming more cylindrical, it passes forwards, joining
its fellow of the opposite side to form the commissure,
In front of the commissure the optic nerves, as they
u
290 Nervous System
are now called, receive a sheath from the dura mater
and arachnoid, and pierce the back of the eyeball.
Decussation takes place at the commissure, but this
decussation is a peculiar one.
According to Charcot, the decussation of the optic
tracts takes place as represented in fig. 111, there
being not only a crossing at the chiasma, but also
Fig. hi.- -Scheme of decussation of optic tracts (Charcot), le and RE,
le t and right eyes ; c, commissure ; LG and k g, left and right geniculate
bojies ; Q, corpora quadrigemina : L H and R H, left and right cerebral
c: lire of vision ; b and a, nerve-fibres from left and right sides respec-
tively of left eye ; b' and a\ corresponding fibres from right eye.
at the corpora quadrigemina. According to this
view a lesion at c would intercept the fibres from
both nerve-centres going to the inner side of each
retina, and cause blindness of each inner half of the
retina, a condition to which the term double temporal
hemianopia is applied. A lesion in the optic tract
behind the chiasma would intercept the fibres going to
each lateral half of the retina of the same side — lateral
Third Nerve 291
hemianopia. A lesion of the cortical centre (angular
gyrus) would, according to this view, produce total
blindness in the opposite eye.
Gowers dissents from Charcot's views, and does not
believe that a second crossing takes place in the
corpora quadrigemina. In man, as shown by patho-
logical observations, a lesion of the chiasma gives
rise to double temporal hemianopia ; a lesion of the
optic tract and between the chiasma and the occipital
cortex gives rise to lateral hemianopia; a lesion of the
cortex itself at the angular gyrus causes partial loss of
vision of the opposite eye, the central portion round
the yellow spot remaining sensitive to light. This
condition is called crossed amblyopia.
Stimulation of the optic nerve produces sensations
of light ; thus flashes of light are seen when the elec-
trodes of a galvanic battery are placed on the temples,
and the current slowly interrupted. The optic nerve
is also the afferent nerve in the reflex contraction of
the pupil, in the closure of the eyelids, when a bright
light falls on the retina.
Third, or Oculo-motor. — This nerve takes its
deep origin in a cluster of cells, situated in the floor
of the aqueduct of Sylvius ; its nucleus is joined in-
feriorly by the nucleus of the fourth nerve (fig. 118).
From this nucleus the fibres pass through the crus to
its inner side. The third nerve is purely motor, being
distributed to all the muscles of the eyeball, except
the superior oblique and external rectus ; it also sup-
plies the circular fibres of the iris and the ciliary
muscle. Paralysis of this nerve gives rise to (1) ptosis,
or drooping of the eyelid in consequence of the un-
opposed action of the orbicularis ; (2) the eyeball is
turned outwards and downwards by the ext. rectus
and sup. oblique ; (3) the pupil is dilated and fixed ;
(4) the eye cannot be accommodated to near objects ;
(5) there is also double vision.
(12
292 Nervous System
Fourth Nerve. — This nerve arises from a nu-
cleus immediately below that of the third in the floor
of the aqueduct. The fibres pass downwards and
backwards, emerge at the upper part of the valve of
Vieussens, and wind round the cms to the base of the
brain. It is purely motor, and supplies the superior
oblique. Paralysis of the fourth nerve causes squint,
Fie. 112.— Nerves of the orbit from the outer side (Quain's Anatomy). The
external rectus has been cut and turned down ; 1, optic nerve ; 2, the
trunk of the third nerve; 3, its upper division passing to the levator
palpebral and superior rectus ; 4, its long lower branch to the inferior
oblique muscle ; 5, the sixth nerve ; 6, the Gasserian ganglion ; 7, the
ophthalmic nerve ; 8, its nasal branch ; 9, the ophthalmic ganglion ; 10,
its short or motor root ; n, long sensory root from the nasal nerve ;
12, sympathetic from the carotid ; 13, ciliary nerves ; 14, frontal branch
of ophthalmic.
the eye being directed upwards and inwards, and
double vision.
Fifth or Trigeminal Nerve. — This nerve
emerges from the side of the pons Varolii, and con-
sists of two roots, the smaller being the motor. The
motor root arises from a nucleus (fig. 118, V,) imme-
diately in advance of the 7th nucleus. The sensory
root arises from two nuclei, the middle (V 2 ) and inferior
(V 3 ) of the 5 th. The fibres pass through the pons,
Fifth Nerve 293
and appear at the surface. The sensory root becomes
connected with the Gasserian ganglion* from the fore
part of which the three primary divisions proceed.
They are (a) Ophthalmic, purely sensory to the eye
and forehead, eyelids, conjunctiva, tip of nose ;
secreto-motor branches to the lachrymal gland (fig. 113).
Injury to this nerve causes ulceration and sloughing
of the cornea. (b) Superior maxillary or second
division (fig. 113) is purely sensory to skin of face,
mucous membrane of the nose, and teeth of upper
jaw. Pungent odours, as of ammonia, are perceived
through this nerve, (c) Inferior or third division
(fig. 113) is sensory to the tongue, mouth, teeth, and
skin covering lower jaw. It confers tactile sensibility
on the tongue, and through it pungent and acid
tastes, as of pepper, vinegar, and mustard, are per-
ceived. Motor filaments are supplied from its an-
terior division to the muscles of mastication, including
the buccinator, anterior belly of digastric and mylo-
hyoid.
There are four ganglia in connection with the fifth
nerve : —
1. The ophthalmic or lachrymal ganglion
(fig. 112). Motor root from inferior division, third;
sensory . from nasal ; sympatetic from carotid. It
gives off sensory motor and vaso-motor branches to
the eye.
2. The spheno-palatine or Meckel's gan-
glion (fig. 113). Motor root from the facial through
the greater superficial petrosal ; sensory root from
second division of the fifth ; sympathetic root from
carotid. It gives off motor fibres to the levator palati
and azygos uvulae ; sensory fibres to the mucous mem-
brane of the nose and palate.
3. The otic ganglion (figs. 1 13 and 1 14). Motor
root from inferior division of the fifth ; sensory root
from the glosso-pharnygeal through lesser superficial
2 94 Nervous* System
petrosal ; sympathetic root from the middle meningeal
artery. It gives off motor fibres to the tensor tympani
Fifth N.
Facial N,
Mylo-hyoid
Fig. 113.— Diagram of the fifth nerve, its connections and branches, od,
ophthalmic division ; c, frontal ; e, lachrymal ; d, nasal, s m, superior
maxillary : 2, terminal branches, nasal, labial, and palpebral ; 2, recur-
rent ; 3, orbital ; 4, dental ; 5, to Meckel's ganglion, 1 d, Inferior divi-
sion : a, motor division joining anterior division, mostly motor, terminal
branch to the mucous membrane of mouth : posterior division ; at, auri-
culotemporal ; lingual to tongue ; inferior dental ; mylo-hyoid branch to
digastric and mylo-hyoid.
and tensor palati ; secretory fibres to the parotid
gland.
4. Thesubmaxillaryganglion(rlg. 113). Motor
Sixth Nerve
295
root from the facial through the chorda tympani ;
sensory root from lingual of the fifth ; sympathetic root
from facial artery. It gives off vaso-inhibitory fibres
from the chorda tympani to the submaxillary gland ;
secretory fibres also from the same source to the
glands.
Fifth N,
Facial N.
Meckel's G.
Fig. 114. — Diagram of the facial nerve and its connections (after Young).
Facial nerve ; r, geniculate ganglion ; gs.p., great superficial petrosal
passing to Meckel's ganglion ; s.s.p., small superficial petrosal passing to
the middle meningeal ; 2, chorda tympani, joining lingual ; 3, nerve to
the stapedius ; 4, communicating branch with ganglion of the root of the
vagus; 5, posterior auricular nerve ; 6, branch to stylo-hyoid and digas-
tric. M M, middle meningeal artery ; I M, internal maxillary artery ;
at, auriculotemporal nerve ; I, lingual ; id, inferior dental.
Sixth or Abducent Nerve.— This nerve arises
from a nucleus in the floor of the pons (fig. 118, VI.),
close to the nuclei of the seventh and motor of the
fifth ; it emerges between the medulla and pons. It
supplies the external rectus. When this muscle is
paralysed there is well-marked internal squint.
296 Nervous System
Seventh or Facial. — The nucleus of the facial
is in close relation (fig. 118, VII.) with the nucleus of
the sixth. It emerges from the medulla between the
restiform and olivary bodies. The auditory arises
from three nuclei, one of which forms a convex promi-
nence in the outer part of the lower half of the fourth
ventricle.
The facial is motor, and supplies the muscles
of the face, lips, stylo-hyoid, digastric, soft palate
(through the spheno-palatine ganglion), tensor palati
and tensor tympani (through the otic ganglion),
stapedius, external muscles of the ear, and supplies
vaso-inhibitory and secretory fibres to the submaxillary
and sublingual glands. It is the special muscle of
expression : when injured the corresponding side
of the face becomes a blank, the mouth is oblique,
being dragged towards the sound side. The eye is
wide open and cannot be closed, and tears run down
the cheek ; food accumulates between the gum and
cheek, and the pronunciation of labial consonants is
rendered difficult, and movements of the nostril
cease. Should injury to the nerve occur above the
origin of the chorda tympani and petrosal nerves
(fig. 114), there will be an interference with the
sense of hearing, through paralysis of the stape-
dius and tensor tympani ; dryness of one side of
the tongue, owing to the implication of the chorda
and submaxillary glands ; and relaxation of the soft
palate and pointing of the uvula to the sound side,
in consequence of paralysis of the azygos and soft
palate.
The auditory nerve passes into the internal audi-
tory meatus, and divides into two branches ; one is
distributed to the cochlea, the other to the vestibule.
It fulfils two functions : it is the nerve of hearing, and
also conveys, by means of the fibres distributed to
the semicircular canals, information to the sensorium,
Glosso-pharyngeal
297
Carotid
Fig. 115.— Diagram of the glosso-pharyngeal and its connection and branches
(after Young). Glosso-pharyngeal ; jg, jugular ganglion ; pg, petrosal
ganglion: 1, tympanic branch ; 2, filaments to the carotid; 3, to Eusta-
chian tube ; 4, to fenestra rotunda ; 5, to fenestra ovalis ; 6 and 7, to small
and great superficial petrosal ; 8, pharyngeal branches ; o, to stylopha-
ryngeal and constrictors ; 10 and it, tonsillitic and terminal. Vagus
branches from ganglion of root : s, superior cervical ganglion.
298 Nervous System
which assists in maintaining the equilibrium of the
body.
The Glosso-pharyngeal.— This nerve arises
from a nucleus in close contact with that of the vagus
(fig. 118, IX.), and is in part overlapped by the audi-
tory nucleus. The fibres emerge from the lateral
tract of the medulla below the auditory. This nerve
(fig. 115) is the special nerve of taste for the back of
the tongue ; it supplies the root of the tongue, soft
palate, pharynx, and tympanum with common sensa-
tion. It supplies motor fibres to the stylo-pharyngeus,
middle constrictor, azygos uvulae, levator palati. It is
probable, however, that the last two are supplied by
the facial.
The Vagus or Pneumogastric. — The nucleus
of the vagus (fig. 118, X.) is situated immediately
below the nucleus of the glosso-pharyngeal, and is
continuous with it. It arises from the medulla, im-
mediately below the glosso-pharyngeal. It contains
both sensory and motor fibres, though part of the
latter are derived from the spinal accessory. The
vagus is distributed to three different sets of organs
(fig. 116) — (a) the lungs and respiratory passages;
(b) the heart ; (c) the pharynx, cesophagus, and
stomach.
(a) The superior laryngeal is the nerve of sensa-
tion to the mucous membrane of the larynx, and
supplies one muscle — the crico-thyroid. Paralysis of
this nerve causes loss of sensation in the larynx, and
interferes with the utterance of high notes from
paralysis of the crico-thyroid. The inferior laryngeal
is the' motor nerve to the intrinsic muscles of the
larynx, except the crico-thyroid. Stimulation of the
central end of the superior laryngeal causes a flaccid
state of the diaphragm, and excites contractions of
the expiratory muscles. The vagus supplies several
different sets of fibres to the lungs, motor to the
Glosso-Pharyng.
Ganglion of trunk
Pharyngeal branches
Vagus
Ganglion of root
Hypoglossal
r°^ RT^i. Spinal accessory
Hepatic
Gastric Splenic
Fig. ii6.— Diagram of vagus, its branches and connections.
300 Nervous System
muscular fibre of the bronchi, ordinary sensory fibres,
and fibres which, when stimulated, excite the contrac-
tion of the inspiratory muscles.
(b) The vagus contains fibres which inhibit the
action of the heart, by antagonising the activity of
the intracardiac ganglia. Also sensory fibres which
convey the sensations of pain, as in angina pectoris.
(