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A MANUAL OF PHYSIOLOGY.
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MANUAL OF PHYSIOLOGY
WITH PRACTICAL EXERCISES.
UY
G. N. STEWART, iM.A., D.Sc, M.D. Edin., D.P.H, Camb.,
I'KOFESSOR OF PHVSIOLOGV IN THE WKSIERN RESERVE UNIVERSITY, CLEVELAND ;
FORMERLY GEORGE HENRY LEWES STUDENT ;
EXAMINER IN I'HVSIOLOGY IN THE UNIVERSITY OF ABERDEEN ;
SENIOR DEMONSTRATOR OF FHYSIOLOGY IN THE OWENS COLLEGE, VICTORIA UNIVERSITY,
ETC.
WITH NUMEROUS ILLUSTRATIONS, INCLUDING
FIVE COLOURED PLATES.
THIRD EDITION.
PHILADELPHIA :
W. B. SAUNDERS,
925 WALxNUT STREET.
LONDON,
bailliere;, tinoall & cox.
FROM THE PREFACE TO THE FH^ST EDITION.
In this book an attempt has been made to interweave formal
exposition with practical work, in the way my experience at
the Harvard Medical School and the Western Reserve
University has shown to be best suited to the needs and the
opportunities of the American student. An arrangement of
the Practical Exercises with reference to the systematic
course has this great advantage — that by a little care it is
possible to secure that the student shall be actually working
at a given subject at the time it is being lectured on.
Cross-reference from lecture-room to laboratory, and from
laboratory to lecture-room, from the detailed discussion of
the relations of a phenomenon to the living fact itself, is
thus rendered easy, natural, and fruitful.
As some teachers may wish to know how a course such as
that described in the Practical Exercises may be conducted
for a fairly large class, a .few words on the method we have
followed may not be out of place. It is obvious that many
of the exercises require more than one person for their per-
formance ; and it may be said that, except in the case of
the simpler experiments and the chemical work as a whole,
which each student does for himself, it has been found
convenient to divide the class into groups of four, each
group remaining together throughout the session. It is
possible that some may find a group of four too large a unit,
and it is certain that three, or perhaps even two, would be
better ; but in a large school so minute a subdivision is
6 FROM Tlir: PREFACE TO THE FIRST EDITIOX
hardly possible, without entailing excessive labour on the
teachers.
The systematic portion of the book is so arranged that it
cah equally well be used independently of the practical
work, and aims at being in itself a complete exposition of
the subject, adapted to the requirements of the student of
medicine.
As to the matter of the text, it is hardly necessary to say
that this book does not aspire to the dubious distinction
of originality ; and it is literally impossible to acknowledge
all the sources from which information has been derived.
In many cases names have been quoted, but names no less
worthy of mention have often been of necessity omitted.
G. N. STEWART.
Cami!RID(;e, September^ 1895.
PREFACE TO THE THIRD EDITION.
The first edition was quickly exhausted, and the second was
simply a reprint. In the present edition the book has been
revised, and in parts rewritten. A considerable amount of
new matter has been added, especially in the Practical
Exercises. These additions, however, have in part been
balanced by the omission of some passages and the abridg-
ment of others, and the bulk of the volume is only a little
increased. I am indebted to my friend Dr. Arthur Clarkson
for Fig. 112 and all the coloured drawings, except Plate I.,
11-13, taken from a paper by Dr. Kanthack and Mr. Hardy,
and Plates III., 4, and IV., 4, supplied by my former pupil.
Dr. Kelly. Figs. 2, 94-98, 106, 116, 119, 120, 152, 174, 234,
264, and 277, have been borrowed from Beaunis' ' Physiologic.'
Messrs. Jung and Zeiss have lent me several electrotypes of
instruments.
G. N. STEWART.
Ca.muridge, August 15, 1898.
CONTENTS.
I'AGE
INIRODUCTION - - - - - - I?
CHAPTER I.
The Circulating Liquids of the Body - - - 25
Blood-corpuscles - - - - - 26
Life-history of the corpuscles - - - -31
Coagulation of blood - - - - - 36
Chemical composition of blood - - "45
Haemoglobin and its derivatives - - - 46
Quantity of blood - - - - - 5^
Lymph and chyle - - - - -52
Functions of blood and lymph - - "54
CHAPTER IL
The Circulation of the Blood and Lymph - - 67
Flow of a liquid through tubes - - - 71
The beat of the heart - - - - 74
The sounds of the heart - - - -77
The cardiac impulse - - - - -79
Endocardiac pressure - - - - 81
The pulse - - - - - - 88
Arterial blood-pressure - - - - 99
Velocity of the blood .... 105
The volume-pulse ■ - - - -116
The circulation in the capillaries - ' - - Ii7
The circulation in the veins . - - - 120
The circulation-time . . . - - 122
The relation of the nervous system to the circulation - 127
Intrinsic nerves of the heart - - - - 128
Extrinsic nerves of the heart - - - - '33
Vaso-motor nerves ----- 148
The lymphatic circulation . . - - 166
CHAPTER HL
Respiration - - - - - . . 194
Mechanical phenomena of respiration - - - I97
Types of respiration ----- 202
Frequency of respiration - - - - 206
CONTENTS
VM.V.
CHAPTER VI.
Excretion
Excretion by the kidneys
Chemistry of urine
The urine in disease -
Secretion of urine
R v.sv\KM:\os—conlinued
\ital capacity ..... 208
Intra-thoracic pressure .... 209
Respiratory pressure - - - - - 2ro
Relation of respiration to the nervous system - - 211
Chemistry of respiration .... 223
Solution and pressure of gases - - - 229
The gases of the blood .... 234
Seats of oxidation ..... 243
Respiration of muscle .... 245
Influence of respiration on blood-pressure - - 249
Effects of breathing condensed and rarefied air - - 255
\'oice and speech . - . . . 259
CHAPTER IV.
DlC.ESTION ...... 279
Mechanical phenomena of digestion - - - 283
V^omiting --...- 292
Chemistry of the digestive juices - - - 294
Saliva ..... 295
Gastric juice - - - . . 300
Pancreatic juice .... -505
Bile ----.- 309
Succus entericus - - - 3' 5
Secretion of the digestive juices - - - 317
Changes in pancreas and p.irotid during secretion - 319
Changes in gastric glands during secretion - - 320
Changes in mucous glands during secretion - 322
Mode of formation of the digestive juices - - 326
Why the stomach does not digest itself - - 330
Influence of the nervous system on the salivary glands - 332
Influence of the nervous system on the gastric glands ■ 342
Influence of the nervous system on the pancreas - 344
Influence of the nervous system on the secretion of bile - 345
Influence of the nervous system on the secretion of intestinal
juice - - - - - - 347
Secretion of the digestive juices (summary) - - 348
Digestion as a whole .... ^^g
Bactericidal function of the gastric juice - - - 355
CHAPTER V.
.A.BSORPHON ...... 360
Diffusion and osmosis .... ^60
Absorption of the food .... ^63
Formation of lymph .... ^68
.Absorption of fat - - - - ■ 370
.Absorption of water, salts, and sugar - - 37'
.Absorption of proteids .... yjz
384
385
385
391
395
CONTENTS
Excretion— ((^////^///(v/
Influence of the circulation on the secretion of urine - 405
Micturition - - - - - - 4 10
.Excretion by the skin - ■ ■ 4'2
CHAPTER \I1.
Metaboi-ism, Nutrition and Dii.tktics - - 430
Metabolism of proteids - - - 43^
Formation of urea . . - - 432
Metabolism of carbo-hydrates— glycogen - 439
Diabetes ------ 444
Metabolism of fat ... - - 446
Income and expenditure of the body - - - 45°
Nitrogenous equilibrium - - - - 45^
Laws of nitrogenous metabolism - - - 457
Carbon equilibrium - - - - 461
Dietetics ------ 464
Internal secretion - - - - - 47i
CHAPTER VIII.
Animal Heat ------ 477
Calorimetry . - . - - 479
Heat-loss ------ 482
Heat-production . . . - - 484
Thermotaxis - ... - 491
Fever - - - - - 501
Distribution of heat ----- 505
Temperature topography . - - - 507
CHAPTER IX.
Muscle - - - - - - 517
Physical introduction - - - - 5^7
Physical properties of muscle - - - - 53J
Stimulation of muscle . . - - 533
The muscular contraction . - - . 537
Optical phenomena of (and structure of muscle) - 53^
Mechanical phenomena of - - - 54'
Influence of fatigue on - - - - 549
Thermal phenomena of - - - - 559
Chemical phenomena of - - - 5^-
Source of the energy of muscular contraction - - 5^4
Rigor mortis . . . . - 563
CHAPTER X.
Nerve ------- 570
The nerve-impulse ; its initiation and conduction - - 57i
Stimulation of nerve ----- 572
Electrotonus . . - - - 574
Conduction in the nerve . - - - 579
Velocity of the nerve-impulse - - - - 581
Nutrition of nerve ----- 584
Trophic nerves ----- 587
Classification of nerves . - . - 589
CONTENTS
CHAPTER XI.
I-A(,K
Electro-Physiolocy - . . . . 605
Currents of rest and action . . . . 606
Polarization of muscle and neive - - - 615
Electrotonic currents .... 616
Heart-currents - - - - - 621
Glandular currents ----- 623
Eye currents ..... 624
Electric fishes . . - . . 624
CHAPTER XII.
The Central Nervous Systkm - - - - 635
Structure .---■- 636
Development ... - - 637
Histology - - - ■ - -638
General arrangement of grey and white matter in the central
nervous system ... - - 644
Arrangement of grey and white matter in the spinal cord - 646
Arrangement of grey and white matter in the upper part of
the cerebro-spinal axis • - - - 651
Functions of the central nervous system ■ - 663
Functions of the spinal cord . - . - 665
Decussation of impulses in the cord - - - 670
Reflex action . . - - - 674
Automatism of the spinal cord . - - - 681
The cranial nerves ----- 685
The functions of the brain - - - - 692
Functions of the cerebellum . - - - 694
Co-ordination of movements - - - - 700
Functions of the cerebral cortex - - - 7°3
Motor areas . - - - - 707
Sensory areas - - - - - 7 1 1
CHAPTER XIII.
The Senses - - - - - -73^
Vision ...... 734
Physical introduction - - - - 734
Structure of the eye - . . - 742
Refraction in the eye - - - - 743
Accommodation - - . . 747
Iris - - - - - - 750
Defects of the eye - - - - 755
Ophthalmoscope . - - - 761
Diplopia .... - 765
Rods and cones in vision - - • 773
Blind spot - - - - -77^
Talbot's law - - - - - 780
Colour vision - - - - - 7^1
Hearing - - - - - - 797
Smell and taste ... - - 806
Tactile senses ----- 809
Muscular sense - - - - - 812
CONTENTS 13
CHAPTER XIV.
I-AOK
RliPRODUCTION ------ 822
Regeneration of tissues .... 822
Reproduction in the higher animals - - - 823
Menstruation .... - 824
Develo|MTient of the ovum ... - 824
Physiology of the embryo .... 827
Index ..----- 835
PRACTICAL EXERCISES.
INTRODUCTION.
1. General reactions of proteids - - - - 20
2. Special reactions of groups of proteids - - - 21
3. Carbo-hydrates - - - - -23
4. Fats - - - - - - 24
CHAPTER I.
1. Reaction of blood - - - - - 57
2. Specific gravity of blood - - - - 57
3. Coagulation of blood - - - - " 5^
4. Preparation of fibrin-ferment - - - - 60
5. Serum - - - - - - 60
6. Enumeration of the corpuscles - - - - 61
7. Opacity of blood - - - - - 61
8. Laking of blood - - - - - 61
9. Globulicidal action of serum - - - - 62
10. Blood-pigment - - - - - 62
(i) Preparation of haemoglobin crystals - - 62
(2) Spectroscopic examination of haemoglobin and its
derivatives - - - - 62-64.
(3) Guaiacum test for blood - - - - 64
(4) Quantitative estimation of haemoglobin - - 65
(5) Hgemin test for blood-pigment - - - 66
CHAPTER II.
1. Microscopic examination of the circulating blood - - 168
2. Anatomy of the frog's heart - - . - 168
3. The beat of the heart - - - - - 168
4. Apex of the heart . - . . - 169
5. Heart-tracings - - - - - 169
6. Dissection of vagus and cardiac sympathetic in frog - - 171
7. Stimulation of the vagus in the frog - - - I73
8. Stimulation of the junction of the sinus and auricles - -174
9. Action of muscarine and atropia on the heart - - I74
10. Stannius' experiment - - ■ - - '75
11. Stimulation of cardiac sympathetic in frog - - -175
12. The action of the mammalian heart - - - 176
13. Action of the valves of the heart - - - 179
14. Sounds of the heart ----- 182
15. Cardiogram - - - - - - 182
16. Sphygmographic tracings .... 182
17. Plethysmographic tracings - - - - 183
14 CONTENTS
1 8. Pulse rale - - - 184
19. Hluod-pressuie tracinj^ ----- 185
20. Influence of position of tlie body on blood-pressure ■ - r87
21. Klfects of JKL'inorrliaj^e and transfusion on blood-pressure - 188
23. The influence of albuinoses on the blood-pressure - - 188
23. Effect of suprarenal extract on the blood-pressure - - 189
24. Section and stimulation of cervical sympathetic in rabbit - 189
25. Stimulation of the depressor nerve - 190
26. Determination of the circulation-time - - 192
CHAPTER 111.
1. Tiacing of the respiratory movements - - - 272
2. Heat-dys])n(La ..... 272
3. Measurement of volume of air inspired and expired - 274
4. Measurement of the respiratory pressure - - - 274
5. Determination of carbon di(jxide and oxygen in inspired and
expired air - - - - - - 275
6. Estimation of carbon dioxide and water yiven off by an animal - 276
7. .Section of both vagi - . . . . 278
CHAPTERS IV. AND V.
1. Chemistry and digestive action of saliva - - 374
2. .Stimulation of the chorda tympani - - - 375
3. Effect of drugs on the secretion of saliva - - - 376
4. Digestive action of gastric juice - - - - 376
5. To obtain chyme and gastric juice - - 378
6. Digestive action of pancreatic juice - - - 378
7. To obtain pancreatic juice .... ^79
8. Chemistry of bile . - . . . 380
9. Microscopical examination of f;rces - - - 381
10. Absorption of fat - - - - - 381
1 1. Time required for digestion and absorption of food substances - 381
12. Quantity of cane-sugar inverted and absorbed in a given time - 382
13. Auto-digestion of the stomach - . . . 383
14. Time recjuired for food to pass through alimentary canal - 383
CHAP IE R Vl.
1. .Specific gravity of urine - - - - 416
2. Reaction of urine ----- 416
3. Chlorides in urine - - - - - 416
4. Phosphates in urine - - - - - 4' 7
5. Sulphates in urine - - - - - 418
6. Indoxyl in urine . . - . - 418
7. Urea ...... 419
8. Total nitrogen in urine - - - - - 421
9. Uric acid ------ 422
10. Kreatinin ..---- 424
11. Hippuric acid - . . - . - 424
12. Proteids in urine ... - - 424
13. .Sugar in urine ----- 426
14. Catheterism - - - - - - 4-9
CONTENTS 1 5
( IIAI'IERS VII. AND VIII.
I'Al.K
1. (ilycogen - - - - - - 5''
2. Experimental glycosuria - - - ■ 5'2
(i) Injection of suj^ar into the blood - - - 512
(2) Phloridzin diabetes - - • - 5'^
(3) Puncture diabetes - - - - 5 '3
(4) Alimentary glycosuria - - - - 5 '3
3. Measurement of the lieat given off in respiration - - 5 '3
4. Excretion of urea and proteids in food - - ■ 5'5
5. Thyroidectomy - - - - - 5' 5
6. Thyroidectomy with thyroid feeding - - - 516
CHAPTERS I.\. AND X.
1. Difterence of make and break induction shocks - - 590
2. Stimulation by the voltaic current- - - - 59^
3. Mechanical stimulation ----- 593
4. Thermal stimulation . . - - - 593
5. Chemical stimulation ----- 593
6. Ciliary motion . - . . . 593
7. Direct excitability of muscle— curara - - - 593
8. Graphic record of ' twitch' ... - 594
9. Intluence of temperature on the muscle-curve - - 594
10. Influence of load on the muscle-curve - - - SQ'^
11. Influence of fatigue on the muscle-curve - - - 596
12. Seat of exhaustion in fatigue of the muscle-nerve preparation - 596
13. Seat of exhaustion in fatigue for voluntary contraction - 597
14. Influence of veratria on muscular contraction - - 598
15. Measurement of the latent period - - - 59^
16. Summation of stimuli ----- 599
17. Superposition of contractions - - - - 599
18. Composition of tetanus ----- 599
19. Velocity of the nerve-impulse . - - - 600
20. Chemistry of muscle ----- 601
21. Reaction of muscle in rest, activity and rigor - - 603
22. Action of suprarenal extract . - - - 603
CHAPTER XI.
1 . Galvani's experiment ----- 627
2. Contraction without metals ... - 627
3. Stimulation of a nerve by its own demarcation current - 627
4. Secondary contraction ----- 627
5. Demarcation and action currents with capillary electrometer - 628
6. Ac-tion-current of the heart - - - - 629
7. Electrotonus ------ 629
8. Paradoxical contraction - - - ■ " '^3°
9. Alterations in excitability and conductivity produced in nerve by
a voltaic current ----- 630
10. Formula of contraction ----- 632
11. Ritter's tetanus ----- 633
12. Positive polarization ----- 633
13. Galvanotropism . . - - - 634
1 6 CONTENTS
CHAPTER XII.
I'AOK
1. Hemisection of the spinal cord . - - - 728
2. Section and stimulation of nerve-roots - - 729
3. Reflex action ----- - 729
4. Action of strychnia .... 729
5. Excision of cerebral hemispheres (frog) - - - 729
6. Excision of cerebral hemispheres fpigeon) - - - 730
7. Stimulation of the motor areas in the dog - - - 730
8. Removal of the motor areas in the dog - - -731
CHAPTER XIII.
1. Formation of inverted image on retina - - - 815
2. Phakoscope - - - - - - 815
3. Scheiner's experiment ----- 816
4. Kuhne's artificial eye - - - - - 817
5. Mapping the blind spot ----- 819
6. Ophthalmoscope ----- 819
7. Pupillo-dilator and constrictor fibres - - - 820
8. Colour-mixing - - - - - 821
9. Talbot's law - - - - - - 821
10. Purkinje's figures - - . . - 821
11. Relation of pitch and vibration frequency - - - 821
12. Beats - - - - - - 821
13. Acuity of touch ..... 821
A MANUAL OF PHYSIOLOGY.
INTRODUCTION.
' Life is a power superadded to matter ; organization arises
from, and depends on, life, and is the condition of vital action ;
but life never can arise out of, or depend on, organization.' —
John Hunter.
Living matter, whether it is studied in plants or in animals,
has certain peculiarities of chemical composition and struc-
ture, but especially certain peculiarities of action or function
which mark it off from the unorganized material of the dead
world around it.
Chemical Composition of Living Matter. — Although we cannot
analyze the living substance as such, we can to a certain,
but limited, extent reconstruct it, so to speak, from its ruins.
When subjected to analytical processes, which necessarily
kill it, living matter invariably yields bodies of the class of
protcids, which have approximately the following composition:
Carbon, 5i'5 to 5^*5 per cent.; oxygen, 20*9 to 23*5 per
cent. ; nitrogen, I5"2 to 17 per cent. ; hydrogen, 6"g to y^
per cent., with small quantities of sulphur and generally of
phosphorus. Nuclco - protcids, which are compounds of
proteid with nucleins, a series of bodies very rich in phos-
phorus, are also constantly met with. Certain carbo-hydrates,
composed of carbon, hydrogen, and oxygen (the last two in
the proportions necessary to form water), of which glycogen
(CfiHioOs) may be taken as a type, appear to be always
present. Fats, which consist of carbon, hydrogen, and
oxygen, and of which tristearin, a compound of stearic acid
with glycerine, of the formula C:;H5, 3(CisH350o), may be
2
i8 A MANUAL OF PHYSIOLOGY
^iven as an example, are often, but perhaps not always,
found. Finally, water and certain inorganic salts, such as
the chlorides and phosphates of sodium, potassium, and
calcium, are constantly present.
Structure of Living Matter The Cell. — The investigations of the
last few years have shown that protoplasm, the primitive living
substance, when examined with sufficiently high powers, is by no
means the ' homogeneous, structureless material ' it was at one time
believed to be. It is rather a substance of porous or reticulated
structure, a spongework or network, holding a fluid in its meshes.
And in all probability the network is the true living machinery, the
liquid in its interstices being perhaps pabulum, from which the
waste of the living framework is made good, or material upon which
it works, and which it is its business to transform. So that in build-
ing up our typical cell we start with a piece of protoplasm of reticular
structure, the network in which is called the intracellular network.
Somewhere in the midst of this cell-substance we find a body which,
if not absolutely different in kind from the protoplasm of the cell, is
yet marked off from it by very definite morphological and chemical
characters. This is the nucleus, generally of round or oval shape,
and bounded by an envelope. Within the envelope lies a second
network, which, when the nucleus is about to divide in the manner
known as indirect division, or karyokinesis, becomes converted into
one or more coiled filaments or skeins. Both the network and the
filaments are made up of rows of highly refractive particles, embedded
in a homogeneous matri.x. These particles possess the property of
staining readily and deeply with dyes, and have, therefore, been
described as consisting of cJiroiuatin : and there is a certain amount
of evidence that this chromatin is either made up of nucleins
(substances composed of a sulphur-free organic acid, nucleic acid,
combined in various proportions with proteids), or yields nucleins by
its decomposition (Zacharias). In any case, it is believed that it is
to the presence of nucleic acid that the chromatic material owes its
affinity for such basic dyes as methyl-green. The meshes of the
nuclear reticulum contain a semi-fluid material, which does not
readily stain.
When we carry back the analysis of an organized body as
far as we can. we find that every organ of it is made up of
cells, which upon the whole conform to the type we have
been describing, although there are many differences in
details. Some organisms there are, low down in the scale,
whose whole activity is confined within the narrow limits of
a single cell. The Amoeba sets up in life as a cell split off
from its parent. It divides in its turn, and each half is a
complete .\mceba. When we come a little higher than the
INTRODUCTION 19
Amceba, we find organisms which consist of several cells,
and * specialization of function ' begins to appear. Thus
the Hydra, the ' common fresh-water Polyp ' of our ponds
and marshes, has an outer set of cells, the ectoderm, and an
inner set, the endoderm. Through the superficial portions
of the former it learns what is going on in the world ; by
the contraction of their deeply-placed processes it shapes its
life to its environment. As we mount in the animal scale,
specialization of structure and of function are found con-
tinually advancing, and the various kinds of cells are grouped
together into colonies or organs.
The Functions of Living Matter. — The peculiar functions of
living matter as exhibited in the animal body will form the
subject of the main portion of this book; and we need only say
here (i) that in all living organisms certain chemical changes go
on, the sum total of which constitutes the metabolism of the
body. These may be divided into (a) integrative or anabolic
changes, by which complex substances (including the living
matter itself) are built up from simpler materials ; and
(b) disintegrative or katabolic changes, in which complex sub-
stances (including the living substance) are broken down
into comparatively simple products. In plants, upon the
whole, it is integration which predominates ; from sub-
stances so simple as the carbon dioxide of the air and the
nitrates of the soil the plant builds up its carbo-hydrates and
its proteids. In animals the main drift of the metabolic
current is from the complex to the simple ; no animal can
construct its own protoplasm from the inorganic materials
that lie around it ; it must have ready-made proteid in its
food. But in all plants there is some disintegration ; in all
animals there is some synthesis. (2) The living substance is
excitable — that is, it responds to certain external impressions,
or stimuli, by actions peculiar to each kind of cell. (3) The
living substance reproduces itself. All the manifold activities
included under these three heads have but one source, the
transformation of the energy of the food. It is not, however,
upon the whole, peculiarities in food, but in molecular
structure, that underlie the peculiarities of function of
different living cells. A locomotive is fed with coal ; a
2 — 2
20 A MAXl'AL Of /'//YSIOLOGY
stcam-piimp is fed with coal. The one carries the mail,
and the other keeps a mine from beinj^ Hooded. Wherein
lies the difference of action? Clearly in the build, the
structure of the mechanism, which determines the manner
in which enerf^y shall be transformed within it, not in any
difference in the source of the energy. So one animal cell,
when it is stimulated, shortens or contracts ; another, fed
perhaps with the same food, selects certain constituents
from the blood or lymph and passes them through its sub-
stance, changing them, it may be, on the way ; and a third
sets up impulses which, when transmitted to the other two,
initiate the contraction or secretion. In the living body the
cell is the machine ; the transformation of the energy of the
food is the process which * runs ' it. The structure and
arrangement of cells and the steps by which energy is trans-
formed within them sum up the whole of biology.
PRACTICAL EXERCISES.
Reactions of Proteids.
I. General Reactions of Proteids. — Egg-albumin may ho. taken as
a type. Prepare a solution of it. In breaking the egg, take care
ihat none of the yolk gets mixed with the white. Snip the white up
with scissors in a large capsule, then add ten or fifteen times its
volume of distilled water. The solution becomes turbid from the
precipitation of traces of globulin, since globulins are insoluble in
distilled water. Stir thoroughly, strain through several layers of
muslin, and then filter through paper.
(i) Add to a little of the solution in a test-tube a few drops of
strong nitric acid. A precipitate is thrown down, which becomes
yellow on boiling. Cool, and add strong ammonia : the colour
changes to orange (xantlio-proteic rcactioji).
(2) Acidify another portion strongly with acetic acid, and add a
few drops of a solution of potassium ferrocyanide. A white [)re-
cipitate is obtained. Peptones do not give this reaction.
(3) To a third i)ortion add a drop or two of very dilute cupric
sulphate and e.xcess of sodium or potassium hydrate ; a violet colour
appears. Peptones and proteoses (albumoses) give a pink {biuret
reactiflii).* See p. 377.
(4) To another portion add Millon's reagent ;t a precipitate comes
* The reaction is also given, although more faintly, with the hydrates
of lithium, strontium, and barium.
f Millon's reagent consists of a mixture of the nitrates of mercury with
nitric acid in excess, and some nitrous acid. To make it, dissolve mercury
PR A cr/c. I /. Exr.Rc 7 .sv;.s- 2 1
down, which is turned reddish on boiling. If only traces of proteid
are present, no precipitate is caused, but the licjuid takes on a red tinge.
(5) Heat a portion to 30" C on a water-bath. Saturate with
crystals of ammonium sulphate ; the albumin is precipitated. Filter,
and test the filtrate for proteids by (3). None, or only slight traces,
will be found. The sodium hydrate must be added in more than
sutiticient quantity to decompose all the ammonium sulphate. It
will be best to add a piece of the solid hydrate. Peptones are not
[irecipitated by ammonium siil[)hate, Init all other proteids are.
2. Special Reactions of Groups of Proteids— (i) Coagulable Pro-
teids : {a) Native Albumins.— (a) Heat a little of the solution of
ei^g-a/l'u/iiin in a test-tube ; it coagulates. With another sample
determine the temperature of coagulation, first slightly acidulating
with dilute acetic acid — a drop or two of a 2 per cent, solution.
To determine the Temperature of Coagulation. — Support a beaker
by a ring which just grips it at the rim. Nearly fill the beaker with
water, and slide the ring on the stand till the lower part of the beaker
is immersed in a small water-bath (a tin can will do quite well). In
this beaker place a test-tube, and in the test-tube a thermometer,
both supported by rings or clamps attached to the same stand. Put
into the test-tube at least enough of the albumin solution to com-
pletely cover the bulb of the thermometer, and heat the bath, stirring
the water in the beaker occasionally with a feather, or a splinter of
wood, or a glass rod, the end of which is guarded with a piece of
indiarubber tubing. Note the temperature at which the solution
becomes turbid, and then the temperature at which a distinct coagu-
lum or precipitate is formed.
{ft) A similar experiment may be performed with serum- albumin^
obtained as on p. 60.
{b) Globulins. — Use serum-globulin (p. 60), or myosin (p. 602).
Fibrinogen is also a globulin, but cannot easily be obtained in
quantity. Verify the following properties of globulins :
(a) They coagulate on heating.
{ft) They are insoluble in distilled water (p. 60).
(y) They are precipitated by saturation with magnesium sulphate
or sodium chloride (p. 60).
They give the general proteid tests (i) to (5).
(2) Derived Albumins or Albuminates— («) Acid-albumin. — To
a solution of egg-albumin add a little -2 per cent, hydrochloric acid,
and heat to about body temperature — say 40° C. — for a few minutes.
Acid-albumin is formed. It can be produced from all albumins and
globulins by the action of dilute acid. Make the following tests :
(a) Add to a portion of the solution in a test-tube a few drops of
a solution of litmus ; the colour becomes red. Now add drop by
drop sodium carbonate or dilute sodium hydrate solution till the
tint just begins to change to blue. A precipitate of acid-albumin is
in its own weight of strong nitric acid, and add to the solution thus
obtained twice its volume of water. Let it stand for a short time, and
then decant the clear liquid, which is the reagent.
22 A .)/./.\Y/.I/. OF rilYSlOLOGY
thrown down. Add a little more of the alkali, and the precipitate is
redissolved. It can be again brought down by neutralizing with acid.
(/i) Heat a portion of the solution to boiling ; no precipitate is
formed.
(y) Add strong nitric acid; a precipitate appears, which dissolves
on heating, and the liquid becomes yellow.
(/>; Alkali-albumin. — To a solution of egg-albumin add a little
sodium hydrate, and heat gently for a few minutes. Alkali-albumin
is jiroduced. It can also be derived by similar treatment from any
albumin or globulin.
{u.) Neutralize, after colouring with litnms solution, by the addition
of dilute hydrochloric or acetic acid. Alkali-albumin is precipitated
when neutralization has been reached. It is redissolved in excess of
the acid.
(/i) To another portion of the solution of alkali-albumin add a few
drops of sodium phosphate solution, then litmus, and then dilute acid
till the alkali-albumin is precipitated. More of the dilute acid should
now be required to precipitate the alkali-albumin, since the sodium
phosphate must first be changed into acid sodium phosphate.
iy) On heating the solution of alkali-albumin there is no coagu-
lation.
(3) Proteoses ( Albumoses) . — For preparation and reactions, see
P- 377- They differ from group (1; in not being coagulated by heat,
and from group (2) in not being precipitated by neutralization.
They are soluble (with the exception of hetero- and dys-albumose),
in distilled water, and are not precipitated by saturation of their
solutions with magnesium sulphate or sodium chloride. Saturation
with ammonium sulphate precipitates them. AVith a solution of
commercial ' peptone,' which consists chiefly of albumoses, and
contains only a little true peptone, perform the following tests :
(a) Boil the solution ; there is no coagulation.
(/?) Biuret reaction, (3) p. 20.
(7) .Add to a little of the solution a drop of strong nitric acid by
means of a glass rod or small pipette ; a precipitate is formed, which
dissolves on heating, and reappears on cooling.
(4) Peptones. — For preparation and tests, see p. 377. They differ
from groups (i) and (2) in the same way as albumoses, and they
differ from albumoses in not being precipitated by ammonium
sulphate. Saturate the solution of commercial * peptone ' with
ammonium sulphate ; the albumoses are precipitated. Filter ; the
peptones are contained in the filtrate. On it perform the biuret
test, as described in (5), p. 21 ; and note that the pink colour is the
same as that given by albumoses.
(5) Coagulated Proteids. — These are divided into two classes :
{a) Proteids coagulated by heat, such as boiled white of egg.
{b) Proteids whose coagulation is determined by the action of
ferments. Of these, fibrin is a type. Both classes give such of the
general proteid tests, (i), (3), (4), p. 20, as with suitable modifica-
tions can be instituted on solid substances. Thus, in performing
(3), a flake of fibrin or a small piece of the boiled egg-white should
PRACTICAL EXERCISES 23
be soaked for a few minutes in a dilute solution of cupric sulphate.
Then the excess of the cupric sulphate should be poured off, and
sodium hydrate added, when the coagulated proteid will become
violet. Heat-coagulated proteids are insoluble in water, weak acids
and alkalies, and saline solutions, but fibrin is slightly soluble in the
latter.
Carbo-hydrates.
1. Glucose or Dextrose. — Make a solution of dextrose in water^
and apply to it Trommer's test for reducing sugar. Put some of
the dextrose solution in a test-tube, then a few drops of cupric
sulphate, and then excess of sodium or potassium hydrate. The
blue precipitate of cupric hydrate which is first thrown down is
immediately dissolved in the presence of dextrose and many other
organic substances. Now boil the blue liquid, and a yellow or red
precipitate (cuprous hydrate or oxide) is formed.
2. Cane-sugar. — Perform Trommer's test with a sample of a solu-
tion. A blue liquid is obtained, which is not changed on boiling.
Now put the rest of the solution in a flask. Add rr^gth of its bulk of
strong hydrochloric acid, and boil for a quarter of an hour. Again
perform Trommer's test. It shows that much reducing sugar is now
present. The cane-sugar has been ' inverted,' i.e., changed into a
mixture of dextrose and levulose.
3. Starch. — (i) Cut a slice from a well-washed potato; take a
scraping from it with a knife, and examine with the microscope.
Note the starch granules with their concentric markings, using a
small diaphragm. Run a drop of dilute iodine solution under the
cover-slip, and observe that the granules become bluish. Examine
also with a polarization microscope. (2) Rub up a little starch in a
mortar with cold water, then add boiling water and stir thoroughly.
Decant into a capsule or beaker, and boil for a few minutes. After
the liquid has cooled, perform the following experiments :
{a) Add a few drops of iodine solution to a little of the thin starch
mucilage in a test-tube. A blue colour is produced, which disappears
on heating, returns on cooling, is bleached by the addition of a little
sodium hydrate, and restored by dilute acid.
{b) Test the starch solution for reducing sugar by Trommer's
test. If none is found, boil some of the mucilage with a little
dilute sulphuric acid in a flask for twenty minutes, and again
perform Trommer's test. Abundance of reducing sugar will now be
present.
4. Dextrin.^ — Dissolve some dextrin in boiling water. Cool. Add
iodine solution to a portion ; a reddish-brown (port-wine) colour
results, which disappears on heating and returns on cooling. The
colour is also bleached by alkali, restored by acid. If too little
iodine has been added there may be no restoration of the colour by
the acid. The addition of a little more iodine to the acid solution
will then cause the port-wine colour to return, and this may be again
bleached by alkali, and will now be restored by acid.
5. Glycogen. — See p. 511.
24 A MANUAL OF rilYSIOLUGY
Fats.
(a) Take a little lard or olive-oil, and observe that fat is soluble in
ether or warm alcohol, but not in water. Put a drop of the ethereal
solution of fat on a piece of paper, and note that it leaves a greasy
stain.
(/i) Boil a little lard with potassium hydrate in a capsule. The
fat is broken up into glycerine and fatty acid, and the latter unites
with the alkali to form a soap. Add a small quantity of a 20 per
cent, solution of sulphuric acid, and heat. The fatty acids are set
free and collect on the surface.
(7) Emulsification. — Put in one watch-glass a few drops of neutral
(fresh) olive-oil, and in another a few drops of a rancid oil containing
fatty acids. Add a dilute solution (o"25 per cent.) of sodium
carbonate to each. An emulsion will be formed in the second
watch-glass, but not in the first. Examine it under the microscope,
and note the globules of oil of various sizes.
Or the watch-glasses may first be filled with the sodium carbonate
solution, and a drop of fresh oil then placed on the surface of the
solution in one and of rancid oil in the other, by means of a small
pipette. A creamy white ring will soon spread out from the rancid
oil, and cover the sodium carbonate solution.
CHAPTER I.
THE CIRCULATING LIQUIDS OF THE BODY.
In the living cells of the animal body chemical changes are
constantly going on ; energy, on the whole, is running
down; complex substances are being broken up into simpler
combinations. So long as life lasts, food must be brought
to the tissues, and waste products carried away from them.
In lowly forms like the amoeba, these functions are per-
formed by interchange at the surface of the animal without
any special mechanism ; but in all complex organisms they
are the business of special liquids, which circulate in finely
branching channels, and are brought into close relation at
various parts of their course with absorbing organs, with
eliminating organs, and with the tissue elements in general.
In the higher animals three circulating liquids have been
distinguished : blood, lymph, and chyle. But it is to be
remarked that chyle is only lymph derived from the walls
of the alimentar}- canal, and therefore, during digestion,
containing certain freshly - absorbed constituents of the
food ; while both ordinary lymph and chyle ultimately find
their way into the blood, and are in their turn recruited
from it. The blood contains at one time or another every-
thing which is about to become part of the tissues, and
everything which has ceased to belong to them. It is at
once the scavenger and the food-provider of the cell. But
no bloodvessel enters any cell ; and if we could unravel the
complex mass of tissue elements which essentially constitute
what we call an organ, we should see a sheet of cells, with
capillaries in very close relation to them, but everywhere
26 A MANUAL OF PHYSIOLOGY
separated from them by a thin hiycr of l}mph. And to
describe in a word the circulation of the food substances, we
ma}- say thai the blood feeds tlie lymph . and the lymph feeds the cell.
Morphology of the Blood.
The blood consists essentiall\- of a liquid part, the plasma,
in which are suspended cellular elements, the corpuscles.
When the circulation in a frog's web or lung or in the tail
of a tadpole is examined under the microscope, the blood-
vessels are seen to be crowded with o\al bodies — of a
yellowish tinge in a thin layer, but in thick layers crimson —
which move with varying velocity, now in single file, now
jostling each other two or three abreast, as they are borne
along in the axis of an apparently scanty stream of trans-
parent liquid. Nearer the walls of the vessels, sometimes
cHnging to them for a little and then being washed away
again, may be seen, especially as the blood-flow slackens, a
few comparatively small, round, colourless cells. The oval
bodies are the red or coloured corpuscles : the colourless
elements are the white blood-corpuscles or leucocytes ; the
liquid in which they float is the plasma (' Practical Exercises,'
p. 1 68).
The Red Blood-corpuscles differ in shape and size and in
other respects in different animal groups. In amphibians,
such as the frog and the newt, they are flattened ellipsoids
containing a nucleus, and the same is true of nearly all the
other vertebrates, except mammals. In mammals they are
discs, hollowed out on both the flat surfaces, or biconcave,
and possess no nucleus. But the red corpuscles of the
llama and the camel, although non-nucleated, are ellipsoidal
in shape like those of the lower vertebrates. As to size, the
average diameter in man is between 7 and 8 ^.* In the
frog the long diameter is about 22 fi, while in Proteus it is as
much as 60 /j-, and in Amphiuma, the corpuscles of which
can be seen with the naked eye, nearly 80 fx (Plate I., i).
As regards the structure of the red corpuscles two views
are held : (i) That they are hollow vesicles or globules,
bounded by a delicate but resistant envelope, perhaps of
* A micro-millimetre, represented by symbol /», is j^'m, millimetre.
THE CIRCULATIM; Ll()UinS OF THE no/))' 27
fatty nature (Schafer) ; (2) that they are solid bodies, with
a spongy and elastic framework, denser at the surface of the
corpuscle than in its centre, but continuous throughout its
whole mass (Rollett).
Envelope and spongework are sometimes spoken of as the
stroma of the corpuscle, in contradistinction to its most
important constituent, a highly complex pigment, the
haemoglobin, which, either in solution as such, or in
solution as a compound with some other unknown sub-
stance, or bound in some solid or semi-solid combination
to the stroma, fills up the whole space within the envelope,
or all the interstices of the spongework. To the physical
properties of the stroma it is usual to attribute the great
elasticity of the corpuscles — that is, the power of recovering
x^_:>f
EU/thant'
■0 09Umm
Man
■0011
/ //O^^^^V
\- Cat
■0 065
1 /////^Yn
Sheen
•0 050
1 III ) rl "1 —
Goat ,
•0 04i^
v^
J Mu sk -deer
■002s
u;. I. — Diagram showinc; Relative Size ok Red Coki-usci.e.s ok Various
Animals.
their original shape after distortion — for their elasticity is no
wise impaired by the removal of the haemoglobin.
When blood with disc-shaped corpuscles is shed, there is
a great tendency for the corpuscles to run together into
groups resembling rouleaux, or piles of coin. No satisfactory
explanation of this curious fact has yet been given.
Creiiation of the corpuscles, a condition in which they
become studded with fine projections, is caused by the
addition of moderately strong salt solution, by the passage
of shocks of electricity at high potential, as from a Leyden
jar, by simple exposure to the air, and in poisoning with
Calabar bean. Concentrated saline solutions, which abstract
water from the corpuscles and cause them to shrink, make
the colour of blood a brighter red, because more light is
now reflected from the crumpled surfaces. On the other
38
A MANUAL OF I'J/YS/OLOiJY
hand, the addition of water renders the corpuscles spheri-
cal ; more of the light passes through them, less is reflected,
and the colour becomes dark crimson (Plate !.)•
The White Blood-corpuscles, or Leucocytes. — The red cor-
puscles are peculiar to blood. The white corpuscles may
be looked upon as peripatetic portions of the mesoblast (see
Chap. XIV.), and some of them ought not in strictness to be
called blood-corpuscles. They are more truly body cor-
puscles. Similar cells are found in many situations, and
wander everywhere in the spaces of the connective tissue.
They pass into the bloodvessels with the lymph, and may
pass out of them again in virtue of their amoeboid power.
They consist of undifferentiated living substance or ' proto-
FlG. 2. — AMfEBOni MOVKMENT.
A, B, C, D, successive changes in the form of an amoeba.
plasm,' and under the microscope appear as granular,
colourless, transparent bodies, spherical in form when at
rest, and containing a nucleus, often tri- or multi-lobed.
Many of the leucocytes of frog's blood at the ordinary
temperature, and of mammalian blood when artificiall}'
heated on the warm stage, may be seen to undergo slow
changes of form. Processes called pseudopodia are pushed
out at one portion of the surface, retracted at another, and
thus the corpuscle gradually moves or * flows ' from place to
place, and envelops or eats up substances, such as grains of
carmine, which come in its way. This kind of motion was
first observed in the amoeba, and is therefore called amoeboid.
The leucocytes of human blood are not all of the same size,
THE CIRCULATING IJOl'IDS OF THE IIODY 29
and differ also in other respects. They may be classified
(i) according to the presence or absence of granules in their
protoplasm, and the fineness or coarseness of the granules ;
(2) according to the chemical nature of the dyes with
which the granules stain. The most important recent
work on this subject is that of Kanthack and Hardy. They
find that Ehrlich's ' neutrophile ' cells are in reality oxyphile
— that is, their granules do not stain with neutral dyes,
such as fuchsin or methyl green, but do stain with acid
dyes like eosin (Plate I., 2). They classify the wandering
cells of the blood into five varieties, as follows :
r{i) Coarselygranular(eosino-
^ ,-, 1 . • phile cell of Ehrlich) - 10- ii /; in diam.
Oxyphile torranules stain- , ' r- , i / ^ '
.^'^ ■, ^ ■ . - (2 Finely ^ranular neutro-
mg with eosin). ^ , ., ^^ ,^., — ■ Z;, .,.
phile and amphophile cells
of Ehrlich) - - - 8-9 // „
Basophile (granules stain- j (3) Finely granular (tri-lobed
ingwith methylene blue). I nucleus) - - - -7/' „
(4) Hyaline cells, free from
granules (one nucleus,
generally spherical) - - 8"5-io// „
(5) Lymphocytes, possessing
a single large nucleus with
comparatively little proto-
plasm around it - - 6 // „
In human blood the finely granular oxyphile cells make
up 60 to 80 per cent, of the whole number of leucocytes, the
lymphocytes (and hyaline cells) 20 to 30 per cent., and the
coarsely granular oxyphile cells less than 5 per cent. ; but
these proportions are far from being constant.
Blood-plates. — When blood is examined immediately after
being shed, small colourless bodies (0*5 to 5 ^i in diameter)
of various shapes — sometimes flat and of nearly circular
outline, sometimes irregular — may be seen. These are the
blood-plates or platelets. They can be best studied when
the blood is run directly into some fixing solution.* Their
significance is unknown ; but they are not produced by the
breaking up of other elements of the shed blood, for they
have been observed within the freshly excised and therefore
still living capillaries — in the mesentery of the guinea-pig
and rat (Osier).
* Such as Hayem's solution (sodium chloride, i grm. ; sodium sulphate,
5 grm. ; mercuric chloride, 05 grm. ; water, 200 grm.).
30
A MAxrAL OF p//ys/oLO(;y
Enumeration of the Blood-corpuscles. — This is done by
taking a measured ciuantity of blood, diluting it to a known
extent with a Hcjuid which docs not destroy the corpuscles,
and counting the number in a given volume of the diluted
blood (p. 6i).
The average number of red corpuscles in a cubic milli-
metre of blood is about 5,000,000 in a healthy man, and
about 4,500,000 in a healthy woman, but a variation of
1,000,000 up or down can hardly be considered abnormal.
In persons suffering from profound ansemia the number
may sink to 1,000,000 per cubic millimetre, or even less,
while in new-born children and in the inhabitants of high
plateaus or mountains it may rise to 8,000,000, or even
more. In the latter instance a residence of a fortnight in
■saaai
Fig. 3. — Curve showing the
Number ok Red Corpuscles
AT Different Ages (after
SoRENSEx's Estimations).
The figures along the horizontal axis
are years of age, those along the
vertical axis millions of corpuscles
per cub. mm. of blood.
the rarefied air is sufficient to bring about the increase, and
a subsequent residence of a fortnight in the lowlands to
annul it.*
The number of white blood-corpuscles is on the average
about 10,000 per cubic millimetre of blood, or one leucocyte
for every 500 red blood -corpuscles. In leukaemia the
number of white corpuscles is enormously increased — it may
be in extreme cases to 500,000 per cubic millimetre — while
at the same time the number of the red corpuscles is
diminished ; and the ratio of white to red may approach
I : 4. An increase has also been observed in certain infec-
tive diseases as part of the inflammatory reaction. There
are also physiological variations, even within short periods
of time ; for exairiple, the number of lymphocytes is in-
* In 86 apparently healthy students (male) the average number of red
corpuscles was 5,145,000 per cubic millimetre. In 79 of these, the number
ranged from 4.000,000 to 6,400.000 : in 49 (or 57 per cent, of the whole),
from 4,500.000 to 5,400,000; in 3, from 3,500,000 to 3,900,000 ; in 3, from
6,500,000 to 6.900.000. In one observation the number reached 7.300.000.
THE C/A'CULATIXG IJ()17/)S OF THE liOnV 31
creased when dij^estion is soins ^n- The number of blood-
plates is about j()o,()oo to the cubic millimetre of blood.
Life-history of the Corpuscles. — The corpuscles of the blood,
like the body itself, fulfil the allotted round of life, and then
die. They arise, perform their functions for a time, and
disappear. But although the place and mode of their origin,
the seat of their destruction or decay, and the average
length of their life, have been the subject of active research
and still more active discussion for many years, much yet
remains unsettled.
In the embryo the red corpuscles, even of those forms
(mammals) which have non-nucleated corpuscles in adult
Hfe, are at first possessed of nuclei. In the human fcetus,
at the fourth week all the red corpuscles are nucleated.
Fic;. 4.— CUKVE SHOWING PROrORTION OI WillTE CORPUSCLES TO RED AT
DiFKERENT TlMES OK THE DaY (AKTER THE RESULTS OF HiRT).
At I the morning meal was taken; at II the mid-day meal; at III the evening
meal. During active digestion the number of lymphocytes in the blood is greatly
increased, both absolutely and relatively to the number of the other leucocytes.
Later on the nucleated corpuscles gradually diminish in
number, and at birth they have almost or altogether dis-
appeared, some of them, at least, having been converted by
a shrivelling of the nucleus into the ordinary non-nucleated
form. In the newly-born rat, which comes into the world
in a comparatively immature state, many of the red
corpuscles may be seen to be still nucleated. The first
corpuscles formed in embryonic life are developed outside of
the embryo altogether (in the guinea-pig). Even before the
heart has as yet begun to beat, certain cells of the mesoblast
(see Chap. XIV.) in a zone ('vascular area") around the
growing embryo begin to sprout into long, anastomosing
processes, which afterwards become hollowed out to form
32 A MAX UAL OF PHYSIOLOGY
capillary bloodvessels. At the same time clumps of nuclei,
formed b}- division of the original nuclei of the cells, gather
at the nodes of the network. Around each nucleus clings a
little lump of protoplasm, which soon develops haemoglobin
in its substance ; and the new-made corpuscles float away
within the new-made vessels. In later embryonic life the
nucleated corpuscles seem in part to be developed in the
liver, spleen, red bone-marrow, and the blood itself by
division of previously existing nucleated corpuscles, in part
to be formed endogenously within special cells in the liver,
spleen, and perhaps the lymphatic glands.
In the mammal in extra-uterine life the chief seat of
formation of the red blood-corpuscles seems to be the red
marrow of the bones of the skull and trunk, and of the ends
of the long bones of the limbs. For a short time, however,
after birth the formation of non-nucleated corpuscles may
still go on in other situations, as in certain cells in the
omentum of the rabbit (Ranvier), and in the subcutaneous
connective-tissue corpuscles (Schiifer) ; while at any time the
spleen (Bizzozero and Salvioli) in dogs and guinea-pigs, and
probably other organs, may in emergency — for instance,
when the number of blood-corpuscles has been seriously
diminished by haemorrhage — take on a blood-forming func-
tion. In the red marrow special nucleated, feebly amoeboid
cells, originally colourless or nearly so, multiply by karyo-
kinesis or indirect division, and are transformed by various
stages into the ordinary non-nucleated red corpuscles, which
are washed away in the blood-stream. These blood-forming
cells have received the name of erythroblasts or haemato-
blasts.
A constant destruction of red blood-corpuscles must go
on, for the bile-pigment and the pigments of the urine are
derived from blood-pigment. The bile-pigment is formed in
the liver. It contains no iron ; but the liver-cells are rich
in iron, and on treatment with hydrochloric acid and
potassium ferrocyanide, a section of liver is coloured by
Prussian blue. Iron must, therefore, be removed by the
liver from the blood-pigment or from one of its derivatives ;
and there is other evidence that the liver is one of the places
THK CIRCULATING LinUIDS OF THE JlODV 33
in which red corpuscles are actuall}' destrojed. Destruction
of the corpuscles also seems to take place in the spleen and
hone-marrow. Although the statement that free blood-
pigment exists in the plasma of the splenic vein is incorrect,
red corpuscles have been seen in various stages of decom-
position within large amceboid cells in the splenic pulp ; and
deposits containing iron have been found there and in the
red bone-marrow in certain pathological conditions. It is
not unlikely that the coloured corpuscles may break up also
in other localities, and even to some extent in the blood itself.
The lymphocytes are undoubtedh', the coarsely granular
oxyphile cells probably, and the hyaline cells possibly, derived
from the lymph. The lymphocytes are probabl}' identical
with the small lymph-corpuscles, and have little, if any, power
of amceboid movement. They are formed largely in the
lymphatic glands, for the lymph coming to the glands is
much poorer in corpuscles than that which leaves them.
The lymphatic glands, however, are not the only seat of
formation of leucocytes, for lymph contains some corpuscles
before it has passed through any gland; and although a certain
number of these may have found their way b}- diapedesis
from the blood, others are formed in the diffuse adenoid
tissue, or in special collections of it, such as the tonsils, the
Peyer's patches and solitary follicles of the intestine, and
the splenic corpuscles. To a very small extent white blood-
corpuscles may multiply by karyokinesis in the blood.
The fate of the leucocytes is even less known than that
of the red corpuscles, for they contain no characteristic
substance, like the blood-pigment, by which their destruction
may be traced. That they are constantly breaking down is
certain, for they are constantly being produced. But we do
not know whether, under normal conditions, this process
takes place exclusively in the blood-plasma or in particular
organs or tissues.
Physical and Chemical Properties of the Blood.
Fresh blood varies in colour, from scarlet in the arteries
to purple-red in the veins. It is a somewhat viscid liquid,
with a saline taste and a peculiar odour. Its reaction is
3
34 .1 .U.LXr.l/. ()/■' /'//VS/OLOGV
alkaline to litmus-paper, chietly owin^' to the presence of
di-sodium phosphate (Na.jHPO^) and sodium carbonate.
The alkalinity is not constant ; it is increased during
digestion, when the acid of the gastric juice is being
formed ; it is lowest in the morning, and highest in the
afternoon. It is diminished by muscular exertion, owing
to the formation of lactic acid ; and since acid substances
seem to be produced in all active tissues, the alkalinity of
venous is less than that of arterial blood. In herbivorous
animals the alkalinity of the blood is easily lessened by the
administration of acids, but in carnivora and in man it is
much more difficult to bring about such a change, the acid
being neutralized by ammonia, which is split off from the
proteids. In many diseases, however, and particularly in
those accompanied by fever, this protective mechanism
breaks down, the alkalinity of the blood becomes seriously
reduced, or even, as has sometimes been observed in
diabetic coma, gives place to an acid reaction. The
average alkalinity of human blood, as estimated by titra-
tion with a standard acid after the corpuscles have been
broken up, is that of a '4 per cent, solution of sodium
hydrate (Loewy).
The average specific gravity of blood is about 1066 at
birth. It falls during infancy to about 1050 in the third
year, then rises till puberty is reached to about 1058 in
males (at the seventeenth year), and 1055 in females (at the
fourteenth year). It remains at this level during middle life
in males, but falls somewhat in females. In chlorotic
anaemia of young women it may be as low as 1030 or 1035.
It rises in starvation. Sleep and regular exercise increase
it (Lloyd Jones).*
The Electrical Conductivity of Blood. — The liciuid portion of the
blood conducts the current entirely by means of the electrolytes dis-
solved in it, the most important of these being the inorganic salts ;
* In 136 students (male) tlie average specific gravity of the blood, as
determined by Hammerschlag's method (p. 57) was io53'8. In 121 of
these the variation was from 1050 to 1065 ; in 70 (or ^\'4 per cent, of the
whole), from 1054 to 1060 ; in 4, from 1046 to 1049 ; in 9, from 1066 to
1070. In 2 the specific gravity was only 1040.
THE CIRCULATING IJOr/DS OF Till: 1U)1)V 35
and the conductivity of the serum varies, in different specimens of
blood, within a comparatively narrow range. The conductivity of entire
(defibrinated) blood, on the contrary, varies within wide limits ; and the
most influential factor which governs this variation is the number of
the corpuscles suspended in it. When the blood is relatively rich in
corpuscles and poor in serum, its conductivity is low ; when it is
poor in corpuscles and rich in serum, its conductivity is high. The
(.'vplanation is that the intact red corpuscles have an electrical con-
ductivity so many times less than that of serum, that they may, in
com[)arison, be looked upon as non-conductors. 'I'his must be either
because the envelope of the corpuscle refuses passage to the dis-
sociated molecules (the ions), which, in virtue of their electrical
charges, render a liquid like blood a conductor, or permits them
only to pass very slowly, or because substances (salts, f.,^,^) which would
otherwise act as electrolytes within the corpuscles are united to non-
conducting substances (proteids or hemoglobin) in such a way that
they are never dissociated into their ions, and therefore do not
conduct (p. ^(^2).
The Relative Volume of Corpuscles and Plasma in Unclotted
Blood, or, what can be converted into this by a small correction,
the relative volume of corpuscles and serum in defibrinated
blood, can be easily determined, with approximate accuracy, by
comparing the electrical conductivity of entire blood with that of its
serum. Another simple method is to centrifugalize a small quantity
of blood, after mixing it with a known amount of a 2^^ per cent,
solution of potassium bichromate, in a glass tube of narrow bore
(hsematocrite) until the corpuscles have been collected into a solid
' thread ' at the outer extremity of the tube. Their volume and that
of the clear liquid which has been separated from them are then read
off on an adjacent scale. By these and other methods too elaborate
for description here, it has been shown that the plasma or serum
makes up about two-thirds, and the corpuscles about one-third, of the
blood. But this proportion is, of course, liable to the same variations
as the number of corpuscles in a cubic millimetre of blood. It
depends, further, the number of corpuscles being given, on the
average volume of each corpuscle. For instance, when the molecular
concentration, and therefore the osmotic pressure (p. 360), of the
plasma is reduced, as by the addition of water or the abstraction of
salts, water passes into the corpuscles and they swell ; when the
molecular concentration of the plasma is increased, by the abstraction
of water or the addition of salts, water passes out of the corpuscles,
and they shrink.
Laking of Blood. — Even in thin layers blood is opaque, owing to
reflection of the light by the red corpuscles. It becomes trans-
parent or 'laky' when by any means the pigment is brought out of
the corpuscles and goes into true solution. Repeated freezing and
thawing of the blood, the addition of water, the passage of electrical
currents, constant and induced, putrefaction, heating the blood to
60° C., and many chemical agents (as bile-salts, ether, saponin), cause
this change. The blood-serum of certain animals breaks up the
36 A A/ANC/AL OF PHYSIOLOGY
coloured corpuscles of others, and sets free their i)igment — for
example, the serum of the dog destroys the corpuscles of the rabbit.
It has been customary to speak of ' laking' as if in every case the
process was essentially the same. Hut this is far from being the
fact. For instance, when defibrinated blood is laked by freezing and
thawing, its electrical conductivity and its molecular concentration
(as shown by a determination of its freezing-point, p. 361) are practic-
ally unaltered ; the haemoglobin has made its way into the serum, but
the electrolytes of the corpuscles remain in their original seat or in
their original combinations. The same is true at first, when the laking
is accomplished by the action of putrefactive bacteria, although
later on both the conductivity and the molecular concentration are
markedly increased. On the other hand, when the laking is
brought about by the addition of water, such alterations take place
in the conductivity and freezing-point as indicate that the electro-
lytes of the corpuscles have been liberated and have passed into
solution in the serum along with the haemoglobin.
Since changes begin in the blood as soon as it is shed,
having for their outcome clotting or coagulation, we have to
gather from the composition of the stable factors of clotted
blood, or of blood which has been artificially prevented
from clotting, some notion of the composition of the un-
altered fluid as it circulates within the vessels. The first
step, therefore, in the study of the chemistry of blood is the
study of coagulation.
Coagulation of the Blood. — When blood is shed, its viscidity
soon begins to increase, and after an interval, varying with
the kind of blood, the temperature of the air, and other
conditions, but in man seldom exceeding ten, or falling
below three, minutes, it sets into a firm jelly. This jelly
gradually shrinks and squeezes out a straw-coloured liquid,
the serum. Under the microscope the serum is seen to
contain few or no red corpuscles ; these are nearly all in the
clot, entangled in the meshes of a kind of network of fine
fibrils composed of fibrin. In uncoagulated blood no such
fibrils are present ; they have accordingly been formed by a
change in some constituent or constituents of the normal
blood. Now, it has been shown that there exists in the
plasma — the liquid portion of unclotted blood — a substance
from which fibrin can be derived, while no such substance
is present in the corpuscles. In various ways coagulation
can be prevented or delayed, and the plasma separated from
THE CIRCULATINC. L/OUIDS Of THE IIODY 37
the corpuscles. For example, the blood of the horse clots
very slowly, and a low temperature lessens the rapidity of
coagulation of every kind of blood. If horse's blood is run
into a vessel surrounded by ice and allowed to stand, the
corpuscles, being of greater specific gravity than the plasma,
gradually sink to the bottom, and the clear straw-yellow
plasma can be pipetted off. Or, again, the addition of
neutral salts to blood may be used to delay coagulation,
the blood being run direct from the animal into, say, a
third of its volume of saturated magnesium sulphate
solution. The plasma may then be conveniently separated
from the corpuscles by means of a centrifugal machine.
Again, two ligatures may be placed on a large bloodvessel,
so that a portion of it can be excised full of blood and
suspended vertically ; coagulation is long delayed, and the
corpuscles sink to the lower end. In these and many other
ways plasma free from corpuscles can be got ; and it is found
that when the conditions which restrain coagulation are
removed — when, for instance, the temperature of the horse's
plasma is allowed to rise, or the magnesium sulphate plasma
is diluted with several times its bulk of water — clotting takes
place, with formation of fibrin in all respects similar to that
of ordinary blood-clot. The corpuscles themselves cannot
form a clot. From this we conclude that the essential
process in coagulation of the blood is the formation of
fibrin from some constituent of the plasma, and that the
presence of corpuscles in ordinary blood-clot is accidental.
In accordance with this conclusion, we find that lymph
entirely free from red corpuscles clots spontaneously, with
formation of fibrin ; and when fibrin is removed from newly-
shed blood by whipping it with a bundle of twigs or a piece
of wood, it will no longer coagulate, although all the cor-
puscles are still there.
What, now, is the substance in the plasma which is
changed into fibrin when blood coagulates ? If plasma,
obtained in any of the ways described above, be saturated
with sodium chloride, a precipitate is thrown down. The
filtrate separated from this precipitate does not coagulate
on dilution with water ; but the precipitate itself — the so-
38 A MANUAL OF PI{YSIOLO(,Y
called plasmine of Denis — on bein^ dissolved in a little water,
does form a clot. Fibrin is therefore derived from some-
thing in this precipitate. Now, 'plasmine' contains two
proteid bodies — fibrinogen, which coagulates by heat at
about 56" C, and serum-globulin, which coagulates at about
75" C, and it was at one time believed that both of these
entered into the formation of fibrin (Schmidt). Hammer-
sten, however, has shown that fibrinogen alone is a precursor
of fibrin ; pure serum-globulin neither helps nor hinders
its formation. This observer isolated fibrinogen from blood-
plasma by adding sodium chloride till about 13 per cent,
was present. With this amount the fibrinogen is precipi-
tated, while serum-globulin is not precipitated till 20 per
cent, of salt is reached. After precipitation of the fibrinogen
the plasma no longer coagulates ; and a solution of pure
fibrinogen can be made to clot and to form fibrin, while a
solution of serum-globulin cannot. Blood-serum, too, which
contains abundance of serum-globulin, but no fibrinogen,
will not coagulate.
So far, then, we have reached the conclusion \h2X fihvin is
formed by a chaui^c in a substance, fibrinogen, which can be
obtained by certain methods from blood-plasma. It may
be added that there is evidence that fibrinogen exists as
such in the circulating blood ; for if unclotted blood be
suddenly heated to about 56 , the temperature of heat-
coagulation of fibrinogen, the blood loses its power of
clotting. Since fibrinogen is readily soluble in dilute saline
solutions and fibrin only soluble with great difficulty, we
may say that in coagulation of the blood a substance soluble
in the plasma passes into an insoluble form. But this is
not a mere physical change, for it seems to be initiated by a
splitting up of the fibrinogen into two proteid bodies —
thrombosin and fibrinoglobulin — only the former of which
is transformed into fibrin, while the latter remains in solution.
How is this change determined when blood is shed ? We
have said that a solution of pure fibrinogen can be made to
coagulate, but it does not coagulate of itself. The addition
of another substance in extremely minute quantity is neces-
sary. This other substance is fibrin ferment, which can be
THE CIRCULATI.XG LKjUIDS OF THE BODY 39
obtainetl by precipitatin;^^ blood-serum, or defibrinated blood,
with fifteen to twenty times its bulk of alcohol, letting the
whole stand for a month or more, and then extracting the
precipitate with water (Schmidt). All the ordinary proteids
of the blood having been rendered insoluble by the alcohol,
the fibrin-ferment passes into solution in the water, and the
addition of a trace of the extract to a solution of fibrinogen
causes coagulation. The active substance itself does not
seem to be used up in the process, nor to enter bodily into
the fibrin formed ; a small quantity of it can cause an
indefinitely large amount of fibrinogen to clot ; its power is
abolished by boihng. For these reasons it is considered to
be a ferment.
This action of the fibrin-ferment on fibrinogen helps to
Fig. 5. — Diagram of Clot wuh Biffy Coat.
V, Lower portion of clot with red corpuscles : w, white corpuscles in upper layer
of clot ; c, cupped upper surface of clot ; s, serum.
explain many experiments in coagulation. Thus, transuda-
tions like hydrocele fluid do not clot spontaneously, although
they contain fibrinogen, which can be precipitated from
them by a stream of carbon dioxide or by sodium chloride.
But the addition of a little fibrin-ferment causes hydrocele
fluid to coagulate. So does the addition of serum, not
because of the serum-globulin which it contains, as was
once believed, but because of the fibrin-ferment in it. The
addition of blood-clot, either before or after the corpuscles
have been washed away, or of serum -globulin obtained
from serum, also causes coagulation of hydrocele fluid, and
for a similar reason, the fibrin-ferment having a tendency to
cling to everything derived from a liquid containing it. On
the other hand, serum, which does not of itself clot, although
40 A MANUAL OF PHYSIOLOGY
fibrin-ferment is present in it, because the fibrinop^en has all
been changed into fibrin ciurinp; coagulation of the blood,
can be made to coagulate by the addition of hydrocele fluid,
which contains fibrinogen. We have thus arrived a step
farther in our attempt to explain the coagulation of the
blood : // h essentially due to the formation of fibrin from the
fibvino^cn of the plasma under the influence of fibrin -ferment.
What is the nature of the fibrin-ferment, and what is its
source ? There seems good reason for believing that it
has very close relations with a substance or substances
belonging to the group of nucleo-proteids, for nucleo-proteid
can be obtained from solutions of fibrin-ferment, and, by
appropriate treatment and in the presence of proper con-
ditions, solutions of nucleo-proteid can either be made to
yield fibrin-ferment or to develop that influence on coagula-
tion which is the characteristic test by which we recognise
it. Nucleo-proteids are contained in the nuclei and proto-
plasm of cells, and have been prepared from the thymus,
testis, kidney, lymphatic glands, and other organs, by pre-
cipitating their watery extracts with dilute acetic acid
(Wooldridge), or by extracting with sodium chloride and
then precipitating with excess of water (Halliburton). The
precipitated nucleo - proteid can be dissolved in dilute
sodium carbonate solution. When it is injected slowly or
in small amount into the veins of an animal, it abolishes for
a time the power of coagulation of the blood ; and when this
' negative phase,' as it is called, has been once established,
even a very large and rapid injection produces no further
effect. If, however, a considerable quantit\- of the solution has
been injected at the first, the result is very different : exten-
sive intravascular clotting instantly ensues ; the animal dies
in a few minutes ; and the right side of the heart, the venas
cava?, the portal vein, and perhaps the pulmonary arteries,
may be found choked with thrombi. Curiously enough, no
such effects are produced in albino rabbits or in Norway hares
in their albino condition (Pickering). A solution of fibrin-
ferment prepared by Schmidt's method behaves, when in-
jected into the blood-stream, like a weak solution of nucleo-
proteid, readily producing the negative phase, but causing
THE CIRCULATING LIQUIDS 01' THE BODY 41
with difficulty intravascular coagulation. On the other
hand, while fibrin-ferment favours, in a high degree, the
clotting of blood-plasma after it has been shed, nucleo-
proteid is a much less efficient coagulant outside than
inside the vessels. There are other facts, to which we
shall immediately refer, which show that fibrin-ferment is
not precisely identical with nucleo-proteid, although it is
derived from it.
Our discussion of the nature and relationships of the
fibrin-ferment throws light upon its source. It exists
only in small amount in the circulating blood ; for when
blood is received into alcohol direct from an artery, but
little ferment is found in it. In shed and clotting blood
the only possible sources of nucleo-proteid, so far as we
know, are the corpuscles and the blood-plates. The red
corpuscles we may at once dismiss, for although they con-
tain a small amount of nucleo-proteid, not only do they
remain intact under ordinary circumstances during coagula-
tion, but there is the strongest evidence, as has already
been pointed out, that they do not make any essential
contribution to the process. We have left over the leuco-
cytes and the platelets. The latter are said, and the former
are known, to yield nucleo-proteids when they are broken
up in the laboratory : and it is highly probable that from
both, but especially from the white corpuscles, nucleo-
proteid is liberated in the first moments after blood is shed,
and that this nucleo-proteid is then changed into actual
fibrin-ferment. This surmise is strengthened by the fact
that in freshly-shed blood destruction of leucocytes and
blood-plates takes place ; and Hardy has shown that the
blood of the crayfish, which coagulates with extreme rapidity,
contains certain colourless corpuscles which, immediately
it is shed, break up with explosive suddenness, and that
substances which hinder the breaking up of these corpuscles
restrain coagulation. Further, the white layer or ' buffy
coat ' which tops the tardily-formed clot of horse's blood
(Fig. 5), and consists of the lighter, and therefore more
slowly sinking, white corpuscles, causes clotting in other-
wise incoagulable liquids like hydrocele fiuid, much more
42 A MA.XUAL UF PHYSIOLOGY
readily than the red portion lA the clot, and yields far more
fibrin-ferment on treatment with alcohol.
But when we have traced the fibrin-ferment to the nucleo-
proteid of the leucocytes, and the fibrinogen to the plasma,
and have seen that the interaction of the two causes, first a
splitting up of the fibrinogen, and then the formation of
fibrin from its thrombosin constituent, we have not yet got
to the bottom of coagulation. We have still to ask what it
is that happens to the inert nucleo-proteid in the first
moments after the blood has been shed and converts it into
active fibrin-ferment. The researches of late years have
shown that a third factor is involved : calcium is present in
some form or other wherever coagulation occurs. The following
facts illustrate the role of the calcium : A solution of
fibrinogen free from calcium will not coagulate on the
addition of calcium-free nucleo-proteid, but will coagulate
if a soluble calcium salt be also added. The addition of
a soluble oxalate to blood {'2 or '3 per cent, potassium
oxalate) prevents coagulation by precipitating the calcium
as insoluble calcium oxalate. From plasma prepared in this
way a nucleo-proteid ma}- be separated which contains little
or no calcium and does not cause coagulation, but which on
treatment with a calcium salt acquires the properties of
fibrin-ferment. The same is true of the nucleo-proteid
which can be extracted from so many organs by Wool-
dridge's method. And the most probable explanation of the
intravascular coagulation caused by the injection of nucleo-
proteid is that in the presence of the calcium salts of the
plasma it produces fibrin-ferment, although it has not as yet
been conclusively shown that the amount of fibrin-ferment
obtainable from the blood is increased after injection of
nucleo-proteid. In the curious hereditary disease known as
hamophilia, a deficienc}' of calcium seems occasionally to
be responsible for the diminished coagulability of the blood ;
and the internal administration of a solution of calcium
chloride has sometimes been thought to lessen the tendency
to hccmorrhage, or its local application to cut short an
actual attack. Injection of commercial peptone into the
veins of a dog, though not of a rabbit, deprives the blood
THE CIRCULATISC. LI or IDS OF THE liODY 43
for a time of its power of coa^^'ulation, apparcntl}' in j)art b)-
reason of the attinit}' of peptone for calcium salts, for its
action can be prevented by injection of calcium chloride
(Fekelharin<^), and imitated by injection of potassium oxalate,
\vhile the peptone plasma outside of the body can sometimes,
though not invariabl}-, be caused to clot by the addition of
a soluble salt of calcium. (Hut see p. 45.) Soaps hinder
coaf^^ulation in the same way. The precise action of the
calcium has not yet been made clear. Pekelharing supposes
that active fibrin-ferment is a compound of calcium with
nucleo-proteid, and that in coagulation calcium is handed
over to the fibrinogen by the fibrin-ferment. Lilienfeld
imagines that the nucleo-proteid first acts on the fibrinogen,
causing it to split up into thrombosin and fibrinoglobulin,
and that the thrombosin then unites with calcium to form
fibrin. To sum up, wc may say that there is a general agreement
that the presence of calcium is essential to the formation of fibrin,
and a preponderance of opinion that the fibrin is formed by the
union of calcium with fibrinogen {or thrombosin) under the
influence of fibrin-ferment {or nucleo-proteid).
To a certain extent the action of nucleo-proteid in coagulation can
be imitated by other substances of animal origin, such as the
albumoses of snake venom (Martin), and even by certain artificial
products of the laboratory, the synthesized colloids of Grimaux,
which, when injected into the blood, produce the same phenomena
of intravascular coagulation down to the finest detail, and including
the negative phase. It is not known whether these substances act
on the leucocytes or other cells, and thus cause an increased pro-
duction or an increased liberation of nucleo-proteid, or whether they
actually take its place
So far we have been considering the problem of coagulation as if
all the data for its solution could be obtained by a study of the blood
itself In other words, our main business up to this point has been
the explanation of coagulation in the shed blood ; it has been only
incidentally, and with the object of casting light on the question of
extravascular clotting, that we have touched on the coagulation of
the blood within the living vessels. It is not possible here to
adequately discuss, nor even to define, the differences between the
two problems. All we can do is to warn the student, and to
emphasize our warning by one or two illustrations, that valuable as is
the knowledge derived from experiments on extravascular coagula-
tion, it would be totally misleading if applied without modification
to the circulating blood, i'or instance, we have recognised in the
leucocytes an important source of the nucleo-proteid which plays so
44 A MANUAL OF /'//YS/OLOCY
great a part in the clotting of shed blood ; l)ut we know that
leucocytes are constantly breaking down in the lymph and the
blood, and wc have to inquire how it is that coagulation docs not
occur, e\cei)t in disease, within the vessels. Calcium is not wanting
to the circulating i)l;isma, fibrinogen is not wanting, and it has already
been mentioned (p. 41) that a small amount of fibrin-fermcnt can
be obtained from the perfectly fresh and, as we might almost say,
still living blood. Why, then, does it not coagulate? Some have
said that the quantity of fibrin-ferment is too small ; but if any is
present, some coagulation ought to occur if the conditions were
exactly the same as in a test-tube. Others have said that coagulation
is ' restrained ' by the contact of the living walls of the bloodvessels ;
but although it is certain that the contact of foreign matter, and all
dead matter is foreign to living cells, does hasten the destruction of
leucocytes, and therefore the liberation of fibrin-ferment, it is
evident that it is just this 'restraining' influence of the vessels
which has to be explained. Schmidt has attempted a chemical
exjilanation. He starts with the assunijition that some ready-made
fibrin-ferment, or its precursor, exists not only in the circulating
blood, but in the circulating plasma, for he finds that the blood-
plasma of the horse, entirely freed from formed elements by
filtration through several folds of filter-paper at a temperature
of o" to 0-5° C, remains fluid at the ordinary temperature of the
air for hours, but eventually coagulates. On this and other evidence
he bases the view that substances formed by the breaking down
of white blood-corpuscles in shed blood are not the only cause
of coagulation, although they undoubtedly greatly accelerate it.
According to Schmidt, a precursor, or mother-substance of fibrin-
ferment, is produced in the body from all, or most, proto-
plasmic Cells, from white blood-corpuscles among the rest, but not
exclusively, nor even pre-eminently, from them. This substance
passes continually into the blood, and fibrin-ferment is continually
formed from it, but is always being neutralized by other chemical
processes. So that living blood within the living vessels may be said
to be acted upon by two sets of influences, one tending to coagula-
tion, the other opposing it. Under normal conditions, the processes
that make for coagulation never obtain the upper hand ; but any-
thing which interrupts the circulation, and consequently the free
interchange between blood and tissues, interferes with the entrance
of the sui)stances that render the fibrin-ferment inactive. In the
clotting of extravascular plasma, free from corpuscles, Schmidt sees
the continuation, under modified conditions, of a normal jirocess
always going on within the bloodvessels. In the lungs it would
seem that the forces which favour coagulation are feeble, or the
forces that resist it strong, for blood, after passing many times
through the pulmonary circulation without being allowed to enter
the systemic vessels, loses its power of clotting (Ludwig and Pawlow).
The liver is another organ whose relations to the coagulation of
the blood are peculiar. We have already mentioned that the injection
of proteoses ('peptone') into the blood of dogs causes it to lose its
THE circulatim: L/or/ns of tin: isonv
45
coagulability. The effect gradually passes away, till after some hours
the original [lower of coagulation is restored (p. 1X9). 'I'he liver is
known to l)e intimately concerned in the production of this remarkable
result, for if the circulation through it be interrupted, the injection of
l^roteose is ineffective, l-'urther, if a solution of proteose is artificially
circulated through an excised liver, a substance is formed which is
capable of suspending the coagulation of blood outside of the body, a
property which proteoses themselves do not possess. It is not believed
that the proteose is actually changed into this anticoagulant substance,
but rather that the liver cells [jroduce it as a ' reaction ' to the
presence of the foreign substance, being perhaps stimulated in some
way by the circulating proteose. Under certain conditions, some of
which are known and others not, the injection of proteose causes not
retardation, but hastening, of coagulation ; and if this has been the
result of a first injection, a second is equally unsuccessful. It is
possible that by an effort of the organism to restore the normal
coagulability of the blood, on which its very existence depends, a
second substance with fibrinoplastic powers is produced, and that
the result of an injection of proteose is determined by the relative
amount of coagulant and anticoagulant secreted in a given time.
Fk;. 6. — DiAt.KA.M Miowi.xc Rkla in !■; (^)rANrirv ok Soi.ms and Watkk
IN RkD CORl'USCI.ICS AND I'l.ASMA.
The Chemical Composition of Blood.
The serum of coagulated blood represents the plasma
luiiius fibrinogen (or its thronibosin element) ; the clot repre-
sents the corpuscles //»,s fibrin. Thus :
Plasma — Fibrin (ogen) = Serum.
CorpKscles + Fibrin = Clot.
I'lasma+Corpuscies = Serum + Clot = Blood.
Bulky as the clot is, the quantity of fibrin is trifling ("2 to
•4 per cent, in human blood). The plasma contains about
10 per cent, of solids, the red corpuscles about 40 per cent.,
the entire blood about 20 per cent.
Serum contains 8 to g per cent, of proteids, about "8 per
cent, of inorganic salts, and small quantities of neutral fats,
urea, kreatin, grape-sugar, lactic acid, and other substances.
The proteids are scnmi-nlbnuiin and scrnui-globuliii. In the
rabbit the former, in the horse the latter, is the more
abundant ; in man they exist in not far from equal amount.
46 .1 M. L\L \1 L OF I'll YSI OL 0(J Y
In cold blooded animals the serum-albumin is scantier than in
mammals, the globulin relatively more {plentiful.
Serum-alhumin belongs to the class of native albumins. It has
been obtained in a crystalline form from the scrum of horse's blood.
It is soluble in distilled water, and is not precipitated by saturating
its solutions with certain neutral salts. Heated in neutral or slightly
acid solution, it coagulates first at 73 , then at 77', then at 84' C.
But this is not sufficient ])roof that it consists of a mixture of three
proteids, as has been held.
Sennit-giobuiin belongs to the globulin group of proteids. It is
insoluble in distilled water, and is precipitated in saturated solutions
of neutral salts. When heated, it coagulates at 75" C. (p. 60).
Of the inorganic salts of serum, the most important are
sodium chloride and sodium carbonate. Small amounts of
Fig. 7. — Dia<;ram or Spkctroscopk.
A, source of light ; B, layer of blood ; C, collimator for rendering rays parallel ;
D, prism ; E, telescope.
potassium, calcium, and magnesium, united with phosphoric
acid or chlorine, and a trace of a fluoride, are also present.
The Red Corpuscles consist of rather less than 60 per cent,
of water and rather more than 40 per cent, of solids. Of
the solids the pigment haemoglobin makes up about go per
cent. ; the proteids and nucleo-proteid of the stroma about
8 per cent. ; lecithin and cholesterin less than i per cent. ;
inorganic salts (which vary greatly in their relative propor-
tions in different animals, but in man consist chiefly of phos-
phates and chloride of potassium, with a much smaller
amount of sodium chloride) 1*5 per cent.
Hemoglobin. — Of all the solid constituents of the blood haemo-
globin is present in greatest amount, constituting, as it does, no less
than 13 per cent., by weight, of that liquid. It is an exceedingly
complex body, containing carbon, hydrogen, nitrogen, and oxygen in
much the same proportions in which they exist in proteids (p. 17).
Iron is also present to the extent of almost exactly one-third
THE CIRCVLATING LKJC/DS OF Till: IIODY 47
of I per cent., and there is also a little sulphur, the amount of
which stands in a very simple relation to the quantity of iron (i atom
of iron to 3 of sulphur in dog's haemoglobin, and i atom of iron to
z of sulphur in the hi^moglobin of the horse, ox, and pig). Haemo-
globin appears to be made up of a proteid element which contains
all the sulphur, and a pigment which contains all the iron, the proteid
constituting by far the larger portion of the gigantic molecule, whose
weight has been estimated at more than 16,000 times that of a
molecule of hydrogen. Since its percentage composition is still
undetermined with absolute precision, it is impossible to give an
empirical formula that is more than approximately correct. For
dog's haemoglobin Jaquet gives C7-,sH^i-2o:i^i;i.-;,^:;l'^^-^L'is) which would
make the molecular weight 16,669.
The most remarkable property of haemoglobin is its power
of combining loosely with oxygen when exposed to an
atmosphere containing it, and of again giving it up in the
presence of oxidizable substances or in an atmosphere in
which the partial pressure of oxygen (pp. 231, 236), has been
reduced below a certain limit. It is this property that
enables haemoglobin to perform the part of an oxygen-
carrier to the tissues, a function of the first importance,
which will be more minutely considered when we come to
deal with respiration.
The bright-red colour of blood drawn from an artery or
of venous blood after free exposure to air is due to the fact
that the haemoglobin is in the oxidized state — in the state of
oxyhaemoglobin, as it is called. If the oxygen is removed
by means of reducing agents, such as ammonium sulphide,
or by exposure to the vacuum of an air-pump, the colour
darkens, the blood-pigment being now in the form of reduced
haemoglobin. In ordinary venous blood a large proportion
of the pigment is^ in this condition, but there is always
oxyhaemoglobin present as well. In asphyxia (p. 217), how-
ever, the whole of the oxyhaemoglobin may disappear.
Crystallization of Hceinoglobin. — In the circulating blood the
haemoglobin is related in such a way to the stroma of the corpuscles
that, although the latter are suspended in a liquid readily capable of
dissolving the pigment, it yet remains under ordinary circumstances
strictly within them. In a few invertebrates, however, it is normally
in solution in the circulating liquid. As a rare occurrence hemo-
globin may form crystals inside the corpuscles. When it is in any
v^•ay brought into solution outside the body, it shows in many animals,
4S
.1 MANUAL OF rUYSlULOL,y
but not in the same degree in all, a tendency to crystallization ; and
the ease with which crystallization can be induced is in inverse pro-
portion to the solubility of the haemoglobin. Thus, it is far more
dititicult to obtain crystals of oxyh;emogloi)in from human blood than
from the blood of the rat, guinea-pig, or dog, whose blood-pigment
is less soluble than that of man, and for a like reason the o.\yha;mo-
globin of the bird, the rabbit, or the frog crystallizes still less readily
than that of human blood.
As to the form of the crystals, in the vast majority of animals they
()\vh;LMinigloliiii
Ki (liKed ha;nio2liil)U»
t ' > mic oxide
hemoglobin
Ml th»:niOKlobin (in
;; id solution)
Ac I'i-h.tmatin (in
■ llic-rcal Mihition).
All;aiine-li;eni.'itin
llciiiochromogen
Ha;niatoporphyrin
(in acid solution)
Haematoporphyrin
(in alkaline solu-
tion)
B C D E ^ F
FlC. S. -TaIUK OI Sl'IX-lRA Ol H.KMOCLOIilN AND US DKRIVATI VES.
B, oxygen line; D. sodium line; C and F, hydrogen lines; b, magnesium line.
are rhombic prisms or needles, but in the guinea-pig they are tetra-
hedra belonging to the rhombic system, and in the squirrel si.\-sided
plates of the hexagonal system.
Reduced haemoglobin can also be caused to crystallize, though
with more difficulty than o.xyha-moglobin, since it is more soluble.
Crystals of reduced hii:moglobin were first prepared from human
blood by Hiifner, who allowed it to putrefy in sealed tubes for
several weeks.
THE CIRCULATING LIOUIDS OF THE BODY
49
When a solution of oxyha;moglobin of moderate strength
is examined with the spectroscope, two well-marked absorp-
tion bands are seen, one a little to the right of Fraunhofer's
line 1), and the other a little to the left of E. A third band
exists in the extreme violet between G and H. It cannot
be detected with an ordinary spectroscope, but has been
studied by the aid of a fluorescent eye-piece (Soret), by
projecting the spectrum on a fluorescent screen, and by
photographing the spectrum (Gamgee). The addition of a
reducing agent, such as ammonium sul-
phide, causes the bands in the visible
spectrum to disappear, and they are
replaced by a less sharply-defined band,
of which the centre is about equidistant
from D and E. This is the charac-
teristic band of reduced haemoglobin.
The spectrum of ordinary venous blood
shows the bands of oxyhaemoglobin.
KiG. 9. — Crystals <jf
OXY-H.^;MOGLOBI N.
a, human ; /', squirrel ;
c, guinea-pig.
Carbonic oxide hicmoglobin is a representa-
tive of a class of huemoglobin compounds
analogous to oxyhaemoglobin, in which the
loosely-combined oxygen has been replaced
by other gases (carbon monoxide, nitric
oxide) in firmer union. Its spectrum shows
two bands very like those of oxyhaemoglobin, but a little nearer the
violet end. Carbonic oxide haemoglobin is formed in poisoning
with coal gas. Owing to the great stability of the compound, the
haemoglobin can no longer be oxidized in the lungs, and death may
take place from asphyxia. It is, however, gradually broken up, and
this is an indication that artificial respiration may sometimes be of
use in such cases.
Methaemoglobin is a derivative of oxyhemoglobin which can be
formed from it in various ways, e.g., by the addition of ferricyanide
of potassium or nitrite of aniyl (Gamgee), or by electrolysis (in the
neighbourhood of the anode). It very often appears in an oxyhaemo-
globin solution which is exposed to the air. It has been found in
the urine in cases of haemoglobinuria, in the fluid of ovarian cysts,
and in hasmatoceles. The strongest band in its spectrum is in the
red, between C and D, but nearer C, nearly in the same position as
the band of acid-h?ematin. Reducing agents, such as ammonium
sulphide, change methaemoglobin first into oxyhcemoglobin and then
into reduced hiemoglobin. It has by some been regarded as a more
highly oxidized hremoglobin than oxyhemoglobin. Rebutting
evidence has, however, been offered to the effect that the same
4
50
.1 MANUAL OF rilYSIOlAMiV
quantity of oxygen is required to saturate both pigments, and this
evidence appears to be sound. The difference seems to he rather in
the manner in which the oxygen is united to the haemoglobin
in the methiL'nioglol)in molecule than in the (juantity of oxygen
which it contains. For methicmoglobin, unlike oxyhcemoglobin parts
with no oxygen to the vacuum, while, on the other hand, in the
j)resence of reducing agents it yields up its oxygen even more readily
than oxyhiemoglobin does (Haldane).
By the action of acids or alkalies oxyh;x;moglobin is split into
ha.matin and proteid bodies, of which the exact nature is little known.
When the hiximoglobin is acted on by acids in the absence of oxygen,
hiiimochromogen is first formed, which then gradually loses its iron
and is changed iiuo hcematoporphyrin. If oxygen be present,
ha:?matin is the final product. By the action of alkalies reduced
0\tjHb
Carbcntcfxi_iJthb. \ Iwc
HotinC(/i rcniri/fn btma
Htnmattiftcriihifrm (acid)
_ Mctlia'in c i^lebtn ^
' ficiJ Hatmatin V^!!'.
Alkaline Harmahn \t'%
Reduced Hb. V"'"^
Fig. io.— Diagram to show the Ciiii:i Ciiakactkristics by which
haemoglobin and some of its derivatives may be recognised
Spectroscopically. The Position of the Middle of each Band
is indicaiei) roighly by a vertical llne.
haemoglobin yields /icEinochro/iiogefi, which is stable in alkaline solu-
tion, and gives a beautiful spectrum with two bands, bearing some
resemblance to those of oxyha^moglobin, but placed nearer the violet
end. The band next the red end of the spectrum is much sharper
than the other.
Hctmathi, the most frequent result of the splitting up of haemo-
globin, is generally obtained as an amorphous substance with a bluish-
black colour and a metallic lustre, insoluble in water, but soluble in
dilute alkalies and acids, or in alcohol containing them. In addition
to the iron of the hivmoglobin, ha^matin contains the four chief
elements of i)roteid bodies, carbon, hydrogen, nitrogen and oxygen.
Hicinatoporphyriu^ or iron-free hx^matin, may be obtained from
blood or haemoglobin by the action of strong sulphuric acid. Its
spectrum in acid solution shows two bands, one just to the left of D,
the other about midway between I) and K. Like oxyha.Mnoglobin, re-
duced haemoglobin, carbonic oxide hivmoglobin, methaemoglobin and
other derivatives of haemoglobin, it also has a band in the ultra-violet.
H(T-miu is a compound of hiematin and hydrochloric acid, which
THE CIRCULATIM; LiqUIDS OI- THE liODY 51
crystalli/.cs in tlie form of small rhombic plates, of a brownish or
brownish-black colour, 'i'hey are insoluble in water, but readily
soluble in dilute alkalies (see Practical I-'.xercises, p. 66).
Chemistry of the White Blood Corpuscles. — The composition of
pus-cells and the leucocytes of lymphatic glands has alone been
investigated. The chief constituents of the latter are a globulin
coagulating by heat at 48° to 50" C. ; a nucleo-proteid coagulating in
5 per cent, magnesium sulphate solution at 75° C, and causing
coagulation of the blood on injection into the veins of rabbits ; an
albumin coagulating at 73° C. ; and a ferment with powers like the
pepsin of the gastric juice. In pus-cells glycogen has been found.
The Quantity of Blood. — The quantity of blood in an animal
is best determined by the method of Welcker, The animal
is bled from the carotid into a weighed flask. When blood
Liver 29-3 ^^P''^
11/ ^'^"■^clcs 29 2
hrecUve%%i/sHe artklungs 2 21
Jnti sttne skc/tnital oiqans 6 3
Skin ^ 11
Ktdneys 16
Ntrft Centres tZ
SjiUon OZ I
Fig. II. — Diagram to illustrate the Distriiuhton ok thk Blood i.n
THE Various OrgaxNs of a Rabbit (after Ranke's Measurements).
The numbers are percentages of the total blood.
has ceased to flow, the vessels are washed out with water
or normal saline solution, and the last traces of blood are
removed by chopping up the body, after the intestinal
contents have been cleared away, and extracting it with
water. The extract and washings are mixed and weighed ;
a given quantity of the mixture is placed in a haematino-
meter (a glass trough with parallel sides, e.g.), and a weighed
quantity of the unmixed blood diluted in a similar vessel
till the tint is the same in both. From the amount of
dilution required, the quantity of blood in the watery solu-
tion can be calculated. This is added to the amount of
unmixed blood directly determined.
Many other methods have been devised on the principle
of injecting a known quantity of some substance into the
circulating blood, and then, after an interval has been
allowed for mixture, determining the change produced in a
4—2
2 A MANUAL OF PHYSIOLOGY
sample. Thus, the specific gravity of a drop of blood having
been measured, a certain quantity of normal saline (a '5 to
"7 per cent, solution of sodium chloride) may be injected
into a vein, and the specific gravity again determined. Or
the electrical resistance of a small sample of blood may
be measured before and after injection of a given quantity
of a substance, such as sodium chloride, which reduces it.
Or the total solids may be determined in a specimen before
and after injection of a known weight of distilled water.
Or an animal may be caused to inspire carbonic oxide
for a given time ; from the quantity taken in, and the
quantity fixed by a known weight of blood withdrawn from
the animal, the weight of the whole blood maybe calculated.
The quantity of blood in the body was greatly over-
estimated by the ancient physicians. Avicenna put it at
25 lb., and many loose statements are on record of as
much as 20 lb. being lost by a patient without causing
death. The proportion of blood to body-weight has been
found by accurate experiments to be in man and the dog
I : 13, new-born child i : ig, cat i : 14, horse i : 15, frog
I : 17, rabbit i : ig. Fig. 11 illustrates the distribution of
the blood in the various organs of a rabbit. The liver and
skeletal muscles each contain rather more than one-fourth ;
the heart, lungs, and great vessels rather less than one-
fourth ; and the rest of the body about one-fifth, of the total
blood. The kidney and spleen of the rabbit each contain
one-eighth of their own weight of blood, the liver between
one-third and one-fourth of its weight, the muscles only
one-twentieth of their weight.
Lymph and Chyle.
Lymph has been defined as blood without its red cor-
puscles (Johannes Miiller) ; it is, in fact, a dilute blood-
plasma, containing leucocytes, some of which (lymphocytes)
are common to lymph and blood, others (coarsely granular
basophile cells) are absent from the blood. The reason of
this similarity appears when it is recognised that the plasma
of lymph is derived from the plasma of blood by a process
of physiological filtration (or secretion) through the walls of
THE CIRCULATING LI Oil IDS OF THE BODY 53
the capillaries into the lymph-spaces that everywhere occupy
the interstices of areolar tissue. Lymph, as obtained from
one of the large lymphatic vessels of the limbs, or from the
thoracic duct of a fasting animal, is a colourless or some-
times slightly yellowish liquid of alkaline reaction. Its
specific gravity is much less than that of the blood (1015 to
1030). It coagulates spontaneously, but the clot is always
less firm and less bulky than that of blood. The plasma
contains fibrinogen, from which the fibrin of the clot is
derived. Serum-albumin and serum-globulin are present in
much the same relative proportion as in blood, although in
smaller absolute amount. Neutral fats, urea, and sugar are
also found in small quantities. The inorganic salts are the
same as those of the blood-serum, and exist in about the
same amount, sodium preponderating among the bases, as
it does in serum. The following table shows the results of
analyses of lymph from man and the horse (Munk) :
Horse.
Man.
Water
/ Fibrin
' Other proteids
Solids Fat
Extractives* -
.Salts
95-0 p.c.
o-i \
4-1 1
trace 5*0
0-3
0-5 )
95-8 p.c.
trace -4"2
-J
Chyle is merely the name given to the lymph coming from
the alimentary canal. The fat of the food is absorbed by
the lymphatics, and during digestion the chyle is crowded
with fine fatty globules, which give it a milky appearance.
There may also be in chyle a few red blood-corpuscles,
carried into the thoracic duct by a back-flow from the
veins into which it opens. Chyle clots like ordinary lymph.
The following is the composition of a sample analyzed by
Paton, and obtained from a fistula of the thoracic duct in
a man :
* The term 'extractives' is somewhat loosely applied to organic
substances which exist in so small an amount, or have such indefinite
chemical characters that they cannot be separately estimated.
54 A MANUAL OF PHYSIOLOGY
Water - - - ■ 'j53'4
Solids .... 466
Inorganic - - - 6*5
Organic - - - 401
Proteids - - - '37
Fats . - - . 2406
Cholesterin - - - 06
Lecithin - - - o'36
The quantity of chyle flowing from the fistula was esti-
mated at as much as 3 to 4 kilos per twenty-four hours, or
nearly as much as the whole of the blood. The flow has
been calculated in various animals at one-eighteenth to one-
seventh of the body-weight in the twenty-four hours. The
quantity of lymph in the body is unknown, but it must be
very great — perhaps two or three times that of the blood.
The gases of the blood and lymph will be treated of in
Chapter III.
The Functions of Blood and L3nnph.
We have already said that these liquids provide the
tissues with the materials they require, and carry away from
them materials which have served their turn and are done
with. These materials are gaseous, liquid, and solid. Oxygen
is brought to the tissues in the red corpuscles ; carbon dio.xide
is carried away from them chiefly in the plasma of the blood
and lymph. The water and solids which the cells of the
body take in and give out are also, at one time or another,
constituents of the plasma. The heat produced in the
tissues, too, is, to a large extent, conducted into the blood
and distributed by it throughout the body. It is not known
whether the leucocytes play any part in the normal nutrition
of other cells, although it is probable that they exercise an
influence on the plasma in which they live ; but they have
important functions of another kind, to which it is necessary
to refer briefly here.
Phagocytosis. — Certain of the amoeboid cells of blood and
lymph, and the cells of the splenic pulp, are able to include
or 'eat up' foreign bodies with which they come in contact, in
the same way as the amceba takes in its food. Such cells are
THE CIRCULATINC. LIQUIDS OF TI/E BODY 55
called phagocytes ; and it is to be remarked that this term
neither comprises all leucocytes nor excludes all other cells,
for some fixed cells, such as those of the endothelial lining
of bloodvessels, are phagocytes in virtue of their power of
sending out protoplasmic processes, while the small, im-
mobile, uninuclear leucocyte, or lymphocyte, is not a phago-
cyte.
Although it is not at present possible to assign a physio-
logical value to all the phenomena of phagocytosis, either as
regards the phagocytes themselves or as regards the
organism of which they form a part, there seems little doubt
that under certain circumstances the process is connected
with the removal of structures which in the course of
development have become obsolete, or with the neutraliza-
tion or elimination of harmful substances introduced from
without, or formed by the activity of bacteria within the
tissues. During the metamorphosis of some larvae, groups of
cilia and muscle-fibres may be absorbed and eaten up by the
leucocytes. In the metamorphosis of maggots, for example,
the muscular fibres of the abdominal wall, which are absent
from the adult form, are removed in this way. At the time
when the tail of the tadpole disappears, multitudes of leuco-
cytes swarm into it, and some of them may be seen with
fragments of muscle or nerve inside them.
But the behaviour of phagocytes towards pathogenic
micro-organisms is of even greater interest and importance.
Metschnikoff laid the foundation of our knowledge of this
subject by his researches on Daphnia, a small crustacean
with transparent tissues, which can be observed under the
microscope. When this creature is fed with a fungus,
Monospora, the spores of the latter find their way into the
body-cavity. Here they are at once attacked by the leuco-
cytes, ingested, and destroyed. But after a time so many
spores get through that the leucocytes are unable to deal
with them all ; some of them develop into the first or
* conidium ' stage of the fungus ; the conidia poison the
leucocytes, instead of being destroyed by them, and the
animal generally dies. Occasionally, however, the leuco-
cytes are able to destroy all the spores, and the life of the
56 A MAXUAL OF PnYSlOU)i,Y
Daphnia is preserved. This battle, endinpj sometimes in
victory, sometimes in defeat, is believed by Metschnik(jff to
be typical of the struggle which the phagocytes of higher
animals and of man seem to engage in when the germs of
disease are introduced into the organism. He supposes
that the immunity to certain diseases possessed naturally
by some animals, and which ma}- be conferred on others by
vaccination with various protective substances,* is, to a
large extent, due to the early and complete success of the
phagocytes in the fight with the bacteria ; and that in
rapidl3'-fatal diseases — such as chicken-cholera in birds and
rabbits, and anthrax in mice — the absence of any effective
phagocytosis is the factor which determines the result.
Others have laid stress on the action of protective sub-
stances supposed to exist in the living plasma itself, although
only as yet demonstrated in the serum. It is possible that
such substances are manufactured by the leucocytes, and
either given off by them to the plasma by a process of
'excretion,' or liberated by their complete solution. And it
may be that it is only when the bacteria have been crippled
by contact with these defensive ' alexins ' that the leucocytes
are able to ingest them and complete their destruction.
Diapcdesis. — The fact that leucocytes can pass out of the
bloodvessels into the tissues (Waller, Cohnheim) has a very
important bearing on the subject of phagocytosis. The
phenomenon is called diapedesis, and is best seen when a
transparent part, such as the mesentery of the frog, is
* The most recent invebtigations go to show that MetsrhnikofTs
phagocytic theory of immunity requires modification in the case of the
higher animals and man, although the brilliant biological observations on
which it was originally built retain all their value. He su|)posed that
in the immunizing process the leucocytes underwent certain changes,
acquired, so to speak, a sort of 'education ' that enabled them to cope
with bacteria against which they were i)reviously |)owerless. It seems
more probal)le that in the presence of the substances that confer immunity,
not only the leucocytes, but other cells, are stimulated to produce bodies
which cut short the life, or at least inhibit the growth, of the bacteria. It
may be, however, that the leucocytes take the lead in this reaction. And
the voracious and almost undiscriminating a|)petite displayed by cells
which englobe with equal avidity a granule of carmine or a particle of
proteid, a globule of fat or a fragment of ( arbon, renders it dititicult to
believe that they do not also act, to some extent, directly as phagocytes
in the jiresence of pathogenic organisms.
THE ClRCUl.ATlNi'. IJOUIDS OF Till: IIODY 57
irritated. Tlic first effect of irritation is an increase in the
flow of blood through the affected region. If the irritation
continues, or if it was originally severe, the current soon
begins to slacken, the corpuscles stagnate in the vessels, and
inflammator}' stasis is produced. The leucocytes adhere in
large numbers to the walls of the capillaries, and particularly
of the small veins, and then begin to pass slowly through
them by amceboid movements, the passage taking place at
the junctions between, or it may be through the substance
of, the endothelial cells. Plasma is also poured out into the
tissues, the whole forming an inflammatory exudation.
Even red blood-corpuscles may pass out of the vessels in
small numbers. The exudation maybe gradually reabsorbed,
or destruction of tissue may ensue, and a collection of pus
be formed. The cells of pus are largely, if not entirely, emi-
grated leucocytes.
PRACTICAL EXERCISES ON CHAPTER I.
N.B. — /// the following exercises all experifueiits on animals which
would cause pain are to be done under complete ancesthesia.
1. Reaction of Blood. — With a clean suture-needle prick one of the
fingers behind the nail. Bandaging the finger with a handkerchief
from above downwards, so as to render its tip congested, will often
facilitate the getting of a good-sized drop. Put a drop of blood on
a piece of glazed neutral litmus paper; wash off in 10 to 30 seconds
with distilled water. .\ blue stain will be left, showing that fresh
blood is alkaline.
2. Specific Gravity of Blood— (i) Ilammerschlag's Method.— V\x\. a
mixture of chloroform and benzol of specific gravity x-o6o into a small
glass cylinder. Obtain a drop of blood as in i. Put it in the mixture
by means of a small pipette. If it sinks, add chloroform, if it rises, add
benzol, till it just remains suspended when the liquid has been well
stirred. Then with a small hydrometer measure the specific gravity
of the mixture, which is now equal to that of the blood Eiltt-r the
liquid to free it from blood, and put it back into the stock-bottle.
This is a convenient method, but some prefer —
{2) Rofs Method.— Tdikt 25 small bottles containing mixtures of
glycerine and water of specific gravity ro27, t'o29 . . . 1070.
Begin with bottle 1-059. Pour a little of the liquid into a small
vessel. Then prick the finger with a sharp, clean suture-needle, and
suck up a small drop of blood into the horizontal limb of a capillary
tube with a rectangular elbow. Immerse the horizontal part of the
tube in the glycerine mixture, and gently blow the drop of blood into
58 A MANUAL or /W/VS/OLOCV
it. If it neither rises nor sinks, the specific gravity of the blood
is I 059. If it sinks, the experiment must be repeated with a
mixture of higher specific gravity, say ro6i ; if it rises, with a
mixture of lower specific gravity, say i '057, and so on. If the drop of
blood rises in mixture 1061 and sinks in mixture 1059, the specific
gravity is between those two figures, and may be taken as 1 "060.
3. Coagulation of Blood. — (i) Take two tumblers or beakers,
label them " and /:(, and measure into each 100 c.c. of water.
Mark the level of the water by strips of gummed pa|)er, and pour it
out. (If a sufficient number of graduated cylinders is available, they
may of course be used, and this measurement avoided ) Into a put
25 c.c. of a saturated solution of magnesium sulphate, and into
ft 25 c.c. of a I per cent, solution of potassium oxalate in normal
saline solution (-6 per cent, solution of sodium chloride). If the
dog provided is a large one, these quantities may be all doubled.
(2) Insert a cannula into the central end of the carotid artery of a
dog anesthetized with morphia* and ether.
To put a Cannula into an Artery. — Select a glass cannula of
suitable size, feel for the artery, make an incision in its course
through the skin, then isolate about an inch of it with forceps or a
blunt needle, carefully clearing away the fascia, or connective tissue.
Next pass a small pair of forceps under the artery, and draw two
ligatures through below it. If the cannula is to be inserted into the
central end of the artery, tie the ligature which is farthest from the
heart, and cut one end short. Then between the heart and the other
ligature compress the artery with a small clamp (often spoken of as
' bulldog ' forceps). Now lift the artery by the distal ligature, make a
transverse slit in it with a pair of fine scissors, insert the cannula, and
tie the ligature over its neck. Cut the ends of the ligatures short.
If the cannula is to be put into the distal end of the artery, both
ligatures must be between the clamp and the heart, and the bulldog
must be put on before the first ligature (the one nearest the heart)
is tied, so that the piece of bloodvessel between it and the ligature
may be full of blood, as this facilitates the opening of the artery.
(3) Run into a and ft enough blood to fill them to the mark.
(4) Take a small thin copper or brass vessel, and place it in a
freezing mixture of ice and salt. Run into it some of the blood from
the artery. It soon freezes to a hard mass. Now take the vessel
out of the freezing mixture and allow the blood to thaw. It will be
seen that it remains liquid for a short time and then clots.
(5) Run some of the blood into a porcelain capsule, stirring it
vigorously with a glass rod. The fibrin collects on the rod ; the
blood is defibrinated and will no longer clot.
(6) Now let the dog l)leed to death, and collect the whole of the
blood in a jar. Observe that the flow of blood is temporarily
* One to two centigrammes of morphia liydrochiorate per kilogramme
of body-weight should be injected subcutaneously about half an hour
before the operation. It is convenient to use a 2 per cent, solution, and
10 c.c. of this is sufficient for a dog of good size. Note that diarrheea and
salivation are caused by sucii a dose.
PR A CTICA L EXERCISES
59
increased by pressure on the abdominal walls, which sijueezes it
towards the heart, by passive pumping movements of the hind-legs,
and also during the convulsions of asphyxia, which soon appear.
Notice that the blood begins to clot in a few minutes, and that
very soon the vessel can be tilted without spilling the blood. Set it
aside in a cool place, and observe next day that some clear yellow
serum has separated from the clot.
(7) Observe that the blood in a and /3 has not coagulated. Label
four test-tubes A, B, C, D,
and put into each about 5 c.c.
of the oxalated blood. Add
to A and B 5 or 6 drops of a
2 per cent, solution of calcium
chloride, to C 12 drops, and
to D as much as there is of
the blood. Leave A at the
ordinary temperature, put the
other test-tubes in a water-
bath at 40' C, and note when
clotting occurs.
(8) By means of a centri-
fuge (Fig. 12) separate the
plasma from the corpuscles in
a and (i. (With Jung's hand
centrifuge fairly clear oxalated
plasma may generally be ob-
tained in about twenty
minutes. Magnesium sulphate
[' salted '] plasma usually takes
a little longer to separate.)
With the decalcified plasma
from (3 repeat the observations
in (7).
With the plasma from a
perform the following experi-
ments : {a) Put a small quan-
tity of the plasma into eight
test-tubes, labelling them E,
F, G, H, I, K, L, and M.
Dilute E and F with ten times,
and G and H with live times,
as much distilled water as was taken of plasma ; dilute the plastiia
in I and K with ten times, and in L and M with five times, its
volume of a solution of fibrin-ferment containing some calcium
chloride. Put E, G, I, and L in the bath at 40° C, and leave the
rest of the test-tubes at room temperature. Observe in which of the
test-tubes, if any, coagulation occurs, and the time of its occurrence,
and report the result.
If no centrifuge is available, the decalcified and salted blood must
be left standing in a cool place for twenty-four hours or more till the
Fig. 12.— Centrifui^.e (Jung).
The four cylinders shown at the top of
the figure are so swung that they become
horizontal as soon as speed is got up.
6o
A MANUAL OF PHYSIOLOGY
corpuscles settle. The plasma can then be siphoned or pipetted off.
Instead of dog's blood, the blood of an ox or pig may be obtained at
the slaughter-house.
4. Preparation of Fibrin -Ferment. — Precipitate blood-serum with
ten times its volume of alcohol. Let it stand for several weeks, then
e.xtract the precipitate with water. The water dissolves out the
fibrin-ferment, but not the other coagulated proteids.
5. Serum. — Test the reaction, and determine, both by the hydro-
meter and the pycnometer.or specific gravity bottle, the specific gravity
of the serum provided, or of the serum obtained in experiment 3.
Seruvi Prottids. — (i) Saturate serum with magnesium sulphate
crystals at 30' C. The serum-globulin is precipitated. Filter off.
5^/,'' ' i-J, 'l^'' 1
FlC. 13. — ThOMA-ZEI,-3 H.KMOt VluMEl tK.
M, mouth-piece of tube G, by which blood is sucked into 5 ; E, bead for mixing ;
a, view of slide from above: b. in section ; c, squares in middle of B. as seen under
microscope.
Wash the precipitate on the filter with a saturated solution of mag-
nesium sulphate. Dissolve the precipitate by the addition of a
little distilled water, and perform the following tests for globulins :
{a) Saturate with magnesium sulphate. A precipitate is obtained.
{b) Drop into a large quantity of water, and a flocculent precipitate
falls down, (c) Heat. Coagulation occurs. Determine the tempera-
ture of coagulation (p. 21).
(2) To a portion of the filtrate from (i) add sodium sulphate to
saturation. The serum-albumin is precipitated. (Neither magnesium
sulphate nor sodium sulphate precipitates serum-albumin alone, but
the double salt sodio-magnesium sulphate precipitates it. and this is
formed when sodium sulphate is added to magnesium sulphate.)
(3) Dilute another portion of the filtrate from (i) with its own
bulk of water. Slightly acidulate with dilute acetic acid, and determine
the temperature of heat coagulation.
(4) Precipitate the serum-globulin from another portion of serum
by adding to it an equal volume of saturated solution of ammonium
PRACTICAL EXERCISES 61
sulphate. Filter. Precipitate the serum-albumin from the filtrate by
saturating with ammonium sulphate crystals.
(5) Dilute serum with ten to twenty times its volume of distilled
water, and pass through it a stream of carbon dio.xide. The serum-
globulin is partially precipitated. This is the starting-point of a
method said to be the best for obtaining pure serum-globulin.
(6) Acidulate some scrum with dilute acetic acid and boil. Filter
off the coagulum, and to the filtrate add silver nitrate. .\ non-
proteid precipitate insoluble in nitric acid but soluble in ammonia
indicates the presence of chlorides.
6. Enumeration of the Blood corpuscles. — Use the Thoma-Zeiss
apparatus (lig. 13). I'rick the finger to obtain a drop of blood.
Suck the blood up into the capillary tube S to the mark i.* Wipe
off any blood which may adhere to the end of the tube. Then fill
it with Hayem's solution (p. 29) or 3 per cent, sodium chloride to
the mark loi. This represents a dilution of 100 times. Mi.x the
blood and solution thoroughly, then blow out a drop or two of the
liquid to remove all the solution which remains in the capillary tube.
Now fill the shallow cell B with the blood mixture. .Slide the cover-
glass on, taking care that it does not float on the liquid, but that the
cell is exactly filled. Put the slide under the microscope (say Leitz"s
oc. III., obj 5), and count the number of red corpuscles in not less
than ten to twenty squares. The greater the number of squares
counted, the nearer will be the approximation to the truth. Now
take the average number in a square. The depth of the cell is
,\) mm., the area of each square ^Jo sq. mm. The volume of the
column of liquid standing upon a square is 4,h5ij cub. mm. One
cub. mm. of the diluted blood would therefore contain 4,000 times
as many corpuscles as one square. But the blood has been diluted
100 times, therefore i cub. mm. of the undiluted blood would con-
tain 400,000 times the number of corpuscles in one square. Suppose
the average for a square is found to be 13. This would correspond
to 5,200,000 corpuscles in 1 cub. mm. of blood.
7. Opacity of Blood. — Smear a little fresh blood on a glass slide,
and lay the slide on some printed matter. It will not be possible to
read it, because the light is reflected from the corpuscles in all
directions, and little of it passes through.
8. Laking of Blood. — (i) Put a little fresh blood in three test-
tubes, A B and C. Dilute A with an equal volume, B with two
volumes, and C with three volumes, of distilled water, and repeat
experiment 7. The print can now be read probably through a
layer of A, but certainly through B and C, since the haemoglobin is
dissolved out of the corpuscles by the water and goes into solution,
the blood becoming transparent or laked. That the difference is
not due merely to dilution can be shown by putting an equal quantity
of blood in two test-tubes, and gradually diluting one with distilled
water and the other with a 0*9 per cent, solution of sodium chloride,
which does not dissolve out the haemoglobin. Print can be read
* If the tube has not been properly filled, blow the blood out immediately.
On no account permit it to clot in the capillary tube.
62 A MANUAL OF PHYSIOLOGY
through the first with a smaller degree of dilution than through the
second. Examine the laked blood with the microscope for the
' ghosts,' or shadows of the red corpuscles. The addition of a drop
or two of methylene blue will render them somewhat more distinct.
(2) Put some blood in a test-tube, or flask ; cork up, and let stand
till it begins to putrefy. It becomes laked.
9. Globulicidal Action of Serum. — (i) To a small quantity of
rabbit's blood add an equal volume of dog's serum. Mix and let
stand for fifteen or twenty minutes. The colour of the blood is now
darker than before, and it can be seen to be laked. Examine
microscopically.
(2) Place a small drop of rabl^it's blood and a somewhat larger
drop of the dog's serum on a slide, near, but not quite in contact
with, each other. Now put on a cover-slip, so that the drops just
come together, and examine at once with the microscope with a
moderately high power. Where the two drops mingle, the red
corpuscles will be seen to fade out, leaving only their ' ghosts.' A
few of the corpuscles which come into contact with the, as yet,
undiluted serum may be entirely dissolved.
(3) Heat some of the dog's serum to 60 C. for ten minutes, and
repeat (i) and (2). No effect will now be produced on the rabbit's
corpuscles.
(4) Repeat (i) and (2) with dog's blood and rabbit's serum. The
blood will not be hiked.
10. Blood-pigment — (i) Preparation of Haemoglobin Crystals.—
{a) Heat some dog's blood to 60 or 65 C in a water-bath for about
ten minutes, taking care that the latter temperature is not exceeded.
Cool, and examine the oxyha^moglobin crystals with the microscope.
They form long rhombic prisms and needles.
{b) Adda little crude saponin to dog's blood in a test-tube. Shake
up well, and allow it to stand till the colour becomes dark. Then
shake vigorously, and a mass of hcemoglobin crystals will be lormed.
{c) Put a small drop of guinea-pig's blood on a slide. Mix with a
drop of Canada balsam and cover. Tetrahedral crystals of oxy-
ha^mogloijin will soon form. The slide may l)e kept.
(2) Spectroscopic Examination of Haemoglobin and its Derivatives.
— (<?) With a small, direct-vision spectroscope look first at a bright
part of the sky. Focus by pulling out or pushing in the eyepiece
until the numerous tine dark lines (Fraunhofer's lines), running
vertically across the spectrum, are seen. Narrow the slit by moving
the milled edge till the lines are as sharp as they can be made. Note
especially the line D in the orange, the lines E and /' in the green
and F in the blue. Always hold the spectroscope so that the red is
at the left of the field. Now dip an iron or platinum wire with a loop
on the end of it into water, and then into some common salt or sodium
carbonate, and fasten or hold it in the flame of a fishtail burner. On
examining the flame with the spectroscope, a bright yellow line will be
seen occupying the position of the dark line D in the solar spectrum.
This is a convenient line of reference in the spectrum, and in
studying the spectra of hcemoglobin and its derivatives, the position
PR A cTiL A L j:xi:a'cises
63
of the absorption bands with regard to the 1) line should always 1)6
noted. The dark lines in the solar spectrum are due to the absorp-
tion of light of a definite range of wave-lengths by metals in a state
of vapour in the sun's atmosi)here, and of course no dark lines arc
seen in the spectrum of a gas-llame. Now arrange the spectroscope,
test-tube and gas-flame on a stand as in Fig. 14. Half fill the test-
tube with defibrinatcd blood. Nothing can be seen with the spectro-
scope till the blood is diluted. Pour a little of the blood into
another test-tube, and go on diluting till, on focussing, two />ands of
o.whamoglolnii are seen in the position indicated in Fig. S. Draw
the spectrum ; then dilute still more, and observe which of the bands
Imc. 14.— Sl'ECTROSrtM'IC EXAMINATIIJN OF BLOOD-P IGMEN'T.
first disappears. Now put 5 c.c. of the blood into another test-tube,
and dilute it with four times its volume of water. Take 5 c.c. of this
dilution, and again add four times as much water, and so on till the
solution is only faintly coloured. Note with what degree of dilution
the bands disappear. Then examine each of the solutions with the
spectroscope and draw its spectrum.
(b) Make a solution of blood which shows the oxyhitmoglobin
bands sharply. Add a drop or two of ammonium sulphide solution
to reduce the oxyhiemoglobin. Heat gently to about body-tempera-
ture. A single, ill-defined band now appears, occupying a position
midway between the oxyheemoglobin bands, and the latter disappear.
This is the band of reduced hccmoglobin (Fig. 8).
(c) Carbonic Oxide Hccmoglobin.— Vdiss coal-gas through blood for
64 .1 MAXL'AL OF rilYSIOLOCY
a considerable tune. Examine some of the blood (after dilution)
with the spectroscope. Two bands, almost in the position of the
oxyh;emoglobin bands, are seen ; but no change is caused by the
addition of ammonium sulphide, since carbonic oxide hcX^moglobin
is a more stable compound than oxyhivmoglobin.
{d) Metlucnun^lobin. — Put some blood into a test-tube, add a few
drops of a solution of ferricyanide of potassium, and heat gently. On
diluting, a well-marked band will be seen in the red. On addition
of ammonium sulphide this band disappears ; the oxyha;moglobin
bands are seen for a moment, and then give place to the band of
reduced haemoglobin (Fig. 8).
U) Acid Hdinatin. —To a little diluted blood add strong acetic
acid and heat gently. The colour becomes brownish. The spectrum
shows a band in the red between (" and I ), not far from the position
of the band of methnemoglobin. The addition of a drop or two of
ammonium sulphide causes no change in the spectrum, and this is a
means of distinguishing acid-htematin from methcemoglobin. If
more ammonium sulphide be added, hi^matin will be precipitated
when the acid solution has been rendered neutral, and a further
addition of ammonium sulphide or sodium hydrate will cause the
hcTematin to be again dissolved, a solution of alkaline hrematin being
formed. This in its turn may be reduced by an excess of ammonium
sulphide, and the spectrum of ha^mochromogen may be obtained
(Fig. 8).
(/) Alkaliiie Hicmatin. — To diluted blood add strong acetic acid
and warm gently for a few minutes. Then, when the spectroscopic
examination of a sample shows that acid-hitmatin has been formed,
neutralize with sodium hydrate. A brownish precipitate of haematin
is thrown down, which dissolves in an excess of sodium hydrate,
giving a solution of alkaline haematin.
Or add sodium hydrate to blood directly, and warm for a couple
of minutes after the colour has changed decidedly to brownish-
black. The spectrum of alkaline ha^matin is a broad but ill-defined
band just overlapping the J) line, and situated chiefly to the red side
of it (Fig. 8).
{g) /J(rnioc/iroiii();^en. — To a solution of alkaline h.ematin add a
drop or two of ammonium sulphide. The band near I) disappears,
and two bands make their appearance in the green (Fig. 8).
(//) Hiematoporphyrin. — Put some strong sulphuric acid in a test-
tube. .Add a few drops of blood, agitate the test-tube till the blood
dissolves, and examine the purple licjuid, diluting it, if necessary, with
sulphuric acid. Its spectrum shows two well-marked bands, one just
to the left of D, and the other midway between I) and K (Fig. 8).
(3) Guaiacum Test for Blood. A test for blood — much used in
hospitals, and, indeed, a delicate one, but not always trustworthy
unless certain precautions be taken — is the guaiacum test. A drop
of freshly-prepared tincture of guaiacum is added to the licjuid to be
tested, and then ozonic ether (peroxide of hydrogen). If blood be
present, the guaiacum strikes a blue colour. The decomposition of
the peroxide by the blood seems to be due to the stroma of the cor-
PR A CTR \ 1 /. EXERCISES
65
puscles rather than to the pigment, and other ' oxygen carriers ' —
^.if., fresh vegetable protoplasm-will cause the same colour.
(4) Quantitative Estimation of Haemoglobin— (<0 By FleischPs
Hicmoiiu'ier ( Kig. 15). — I'ill with distilled water that compartment a
of the small cylinder (above the stage) which is over the tinted wedge.
Put a little distilled water into the other compartment a. Now prick
the finger and fill one of the small cajiillary tubes with blood. See
that none of the l)lood is smeared on the outside of the tube. Then
wash all the blood into the water in compartment a, and fill it to the
brim with distilled water. By means of the milled head /"move the
Fig. 15. — Fi.eischl's H.^mometer.
tinted wedge K till the depth of colour is the same in the two com-
partments. The percentage of the normal quantity of haemoglobin
is given by the graduated scale P. For example, if the reading is
90, the blood contains 90 per cent, of the normal amount ; if 100, it
contains the normal quantity. The observations should be made in
a dark room, the white surface, S, arranged below the compartments
a and a , being illuminated by a lamp. Or the instrument may be
placed in a small box, lighted by a candle. It is best that each result
should be the mean of two readings, one just too large and the
other just too small.
{b) Hoppe-Seyler's Method. — Two parallel-sided glass troughs are
used. In one is put a standard solution of oxy-hajmoglobin of known
strength, in the other a measured quantity of the blood to be tested.
The latter is diluted with water until its tint appears the same as that
of the standard solution, when the troughs are placed side by side
on white paper. From the quantity of water added it is easy to
calculate the proportion of hcemoglobin in the undiluted blood.
66 A MANUAL OF PHYSIOLOGY
Greater accuracy is said to be obtained if the haemoglobin in the
standard solution and that of the blood are converted into carbonic
oxide haemoglobin by passing a stream of coal-gas through them.
(5) Microscopic Test for Blood-pigment. — Put a drop of blood on
a slide. Allow the blood to dry or heat it gently over a flame, so as
to evaporate the water. Add a drop of glacial acetic acid ; put on a
cover-glass, and again heat slowly till the liquid just begins to boil.
Take the slide away from the flame for a few seconds, then heat it
again for a moment ; and repeat this process two or three times.
Now let the slide cool, and examine with the microscope (high power).
The small black, or brownish-black, crystals of hsemin will be seen
(Plate I., 3). This is an important test where only a minute trace of
blood is to be examined, as in some medico-legal cases. If a blood-
stain is old, a minute crystal of sodium chloride should be added
along with the glacial acetic acid. Fresh blood contains enough
sodium chloride.
A blood-stain on a piece of cloth may first of all be soaked in a
small quantity of distilled water, and the liquid examined with the
spectroscope or the micro-spectroscope (a microscope in which a
small spectroscope is substituted for the eye-piece). Then evapo-
rate the liquid to dryness on a water-bath, and apply the haemin
test. Or perform the hasmin test directly on the piece of cloth. In
a fresh stain the blood-corpuscles might be recognised under the
microscope, after the cloth had been soaked and kneaded in a little
glycerine.
CHAPTER II.
THE CIRCULATION OF THE BLOOD AND LYMPH.
The blood can only fulfil its functions by continual move-
ment. This movement implies a constant transformation
of energy ; and in the animal body the transformation of
energy into mechanical work is almost entirely allotted to
a special form of tissue, muscle. In most animals there
exist one or more rhythmically contractile muscular organs,
or hearts, upon which the chief share of the work of keeping
up the circulation falls.
Comparative. — In Echinus a contractile tube connects the two
vascular rings that surround the beginning and end of the alimentary
canal, and plays the part of a heart. In the lower Crustacea and
in insects the heart is sirnply the contractile and generally sacculated
dorsal bloodvessel ; in the higher Crustacea, such as the lobster, it is
a well-defined muscular sac situated dorsally. A closed vascular
system is the exception among invertebrates. In most of them the
blood passes from the arteries into irregular spaces or lacunae in the
tissues, and thence finds its way back to the heart. Amphioxus,
the lowest vertebrate, has a primitive lacunar vascular system ; a
contractile dorsal bloodvessel serves as arterial or systemic heart, a
contractile ventral vessel as venous or respiratory heart. From the
latter, vessels go to the gills. Fishes possess only a respiratory heart,
consisting of a venous sinus, auricle, and ventricle. This drives the
blood to the gills, from which it is gathered into the aorta ; it has
thence to find its way without further propulsion through the systemic
vessels. Amphibians have two auricles and a single ventricle ;
reptiles, two auricles and two incompletely-separated ventricles. In
birds and mammals the respiratory and systemic hearts are com-
pletely separated. The former, consisting of the right auricle and
ventricle, propels the blood through the lungs ; the latter, consisting
of the left auricle and ventricle, receives it from the pulmonary veins,
and sends it through the systemic vessels.
General View of the Circulation in Man. — The whole circuit
5—2
68
A MAXL'AL OF PHYSIOLOGY
of the blood is divided into two portions, verj- distinct
from each other, both anatomically and functionally — the
respiratory or lesser circulation, and the systemic or greater
circulation. Starting from the left ventricle, the blood passes
along the systemic vessels — arteries, capillaries, veins — and,
on returning to the heart, is poured into the right auricle,
and thence into the right ventricle. From the latter it is
driven through the pulmonary artery to the lungs, passes
Fig. i6. — Diagram oi ihi: Genkkal Col-rsf. of tiu. Circulation.
RA, LA, right and left auricles ; RV, LV, right and left ventricles.
through the capillaries of these organs, and returns through
the pulmonary veins to the left auricle and ventricle. The
portal system, which gathers up the blood from the in-
testines, forms a kind of loop on the systemic circulation.
The lymph-current is also in a sense a slow and stagnant
side-stream of the blood circulation ; for substances are con-
stantly passing from the bloodvessels into the lymph-spaces,
and returning, although after a comparatively long interval,
into the blood by the great lymphatic trunks.
Physiological Anatomy of the Vascular System. — The heart is
to be looked upon as a portion of a bloodvessel which has
THE CIRCULATION OF THE BLOOD AND LYMPH 69
been modified to act as a pump for driving the blood in a
definite direction. Morphologically it is a bloodvessel ; and
the physiological property of rhythmical contraction which
belongs to the muscle of the heart in so eminent a degree
is, as has been mentioned (p. 67), an endowment of blood-
vessels in many animals that possess no localized heart.
Even in some mammals contractile bloodvessels occur; the
veins of the bat's wing, for example, beat with a regular
rhythm, and perform the function of accessory hearts.
The whole vascular system is lined with a single layer
of endothelial cells. In the capillaries nothing else is
present ; the endothelial layer forms the whole thickness of
the wall. In young animals, at any rate, the endothelial
cells of the capillaries are capable of contracting when
stimulated ; and changes in the calibre of these vessels can
be brought about in this way. The walls of the arteries and
veins are chiefly made up of two kinds of tissue, which
render them distensible and elastic : non-striped muscular
fibres and yellow elastic fibres. The muscular fibres are
mainly arranged as a circular middle coat, which, especially
in the smaller arteries, is relatively thick. One conspicuous
layer of elastic fibres marks the boundary between the middle
and inner coats. In the larger arteries elastic laminae are
also scattered freely among the muscular fibres of the middle
coat. The outer coat is composed chiefly of ordinary con-
nective tissue. The veins differ from the arteries in having
thinner walls, with the layers less distinctly marked, and
containing a smaller proportion of non-striped muscle and
elastic tissue ; although in some veins, those of the pregnant
uterus, for instance, and the cardiac ends of the large
thoracic veins, there is a great development of muscular
tissue. Further, and this is of prime physiological import-
ance, valves are present in many veins. These are semilunar
folds of the internal coat projecting into the lumen in such a
direction as to favour the flow of blood towards the heart,
but to check its return. In some veins, as the venae cavae,
the pulmonary veins, the veins of most internal organs, and
of bone, there are no valves ; in the portal system they are
rudimentary in man and the great majority of mammals.
70 A MA A' UAL OF PHYSIOLOGY
The valves are especially well marked in the lower limbs,
where the venous circulation is uphill. When a valve
ceases to perform its function of supporting the column of
blood between it and the valve next above, the foundation
of varicose veins is laid ; the valve immediately below the
incompetent one, having to bear up too great a weight of
blood, tends to yield in its turn, and so the condition spreads.
The smallest veins, or venules, are very like the smallest
arteries, or arterioles, but somewhat wider and less muscular.
The transition from the capillaries to the arterioles and
venules is not abrupt, but may be considered as marked by
the appearance of the non-striped muscular fibres, at first
scattered singly, but gradually becoming closer and more
numerous as we pass away from the capillaries, until at
length they form a complete layer.
In the heart the muscular element is greatly developed
and differentiated. Both histologically and physiologically
the fibres seem to stand between the striated skeletal muscle
and the smooth muscle. In the mammal the cardiac
muscular fibres are made up of short oblong cells, devoid of
a sarcolemma, often branched, and arranged in anastomosing
rows. Each cell has a single nucleus in the middle of it.
The fibres are transversely striated, but the striae are not so
distinct as in skeletal muscle. Many fibres pass from one
auricle to the other, and from one ventricle to the other.
The auricles and ventricles are also, in some mammals at
least, connected in early life by muscular tissue; and even in
the adult traces of this connection may persist (Plate I., 4).
In the frog's heart the muscular fibres are spindle-shaped,
like those of smooth muscle, but transversely striated, like
those of skeletal muscle. From the sinus to the apex of the
ventricle there is a continuous sheet of muscular tissue.
The problems of the circulation are partly physical, partly
vital. Some of the phenomena observed in the blood-stream
of a living animal can be reproduced on an artificial model ;
and they may justly be called the physical phenomena of the
circulation. Others are essentially bound up with the pro-
perties of living tissues ; and these may be classified as the
vital or physiological phenomena of the circulation. The
THE CIRCULATIOX OF THE BLOOD AND LYMPH 71
distinction, although by no means sharp and absolute, is a
convenient one — at least, for purposes of description; and as
such we shall use it. But it must not be forgotten that the
physiological factors play into the sphere of the physical,
and the physical factors modify the physiological. Con-
sidered in its physical relations, the circulation of the blood
is the flow of a liquid along a system of elastic tubes, the
bloodvessels, under the influence of an intermittent pressure
produced by the action of a central pump, the heart. But
the branch of dynamics which treats of the movement of
liquids, or hydrodynamics, is one of the most difficult parts
of physics, and, in spite of the labours of many eminent
men, is as yet so little advanced that even in the physical
portion of our subject we are forced to rely chiefly on
empirical methods. It would, therefore, not be profitable to
enter here into mathematical theory, but it may be well to
recall to the mind of the reader one or two of the simplest
data connected with the flow of liquids through tubes :
Torricelli's Theorem. — Suppose a vessel filled with water, the level
of which is kept constant ; the velocity with which the water will
escape from a hole in the side of the vessel at a vertical depth h
below the surface will be v = s/'^-gh, where g is the acceleration pro-
duced by gravity.* In other words, the velocity is that which the
water would have acquired in falling in vacuo through the distance h.
This formula was deduced experimentally by Torricelli, and holds
only when the resistance to the outflow is so small as to be negligable.
The reason of this restriction will be easily seen, if we consider that
when a mass m of water has flowed out of the opening, and an equal
mass ;// has flowed in at the top to maintain the old level, everything
is the same as before, except that energy of position equal to that
possessed by a mass /// at a height h has disappeared. If this has
all been changed into kinetic energy E, in the form of visible motion
of the escaping water, then Yj = hmv- =^ fngh, i.e., v= ^2gh. If,
however, there has been any sensible resistance to the outflow, any
sensible friction, some of the potential energy (energy of position),
will have been spent in overcoming this, and will have ultimately
been transformed into the kinetic energy of molecular motion, or heat.
Flow of a Liquid through Tubes. — Next let a horizontal tube of
uniform cross-section be fitted on to the orifice. The velocity of
outflow will be diminished, for resistances now come into play. When
the liquid flowing through a tube wets it, the layer next the wall of the
tube is prevented by adhesion from moving on. The particles next
* Le., the amount added per second to the velocity of a falling body
Cr=32 feet).
72
A MANUAL OF PHYSIOLOGY
this stationary layer rub on it, so to speak, and are retarded, although
not stopped altogether. The next layer rubs on the comparatively
slowly moving particles outside it, and is also delayed, although not
so much as that in contact with the immovable layer on the walls of
the tube. In this way it comes about that every particle of the liquid
is hindered by its friction against others — those in the axis of the tube
least, those near the periphery most — and part of the energy of position
of the water in the reservoir is used up in overcoming this resistance,
only the remainder being transformed into the visible kinetic energy
of the liquid escaping from the open end of the tube.
If vertical tubes be inserted at different points of the horizontal
tube, it will be found that the water stands at continually decreasing
heights as we pass away from the reservoir towards the open end of the
tube. The height of the liquid in any of the vertical tubes indicates
the lateral pressure at the point at which it is inserted ; in other
words, the excess of potential energy, or energy of position, which at
that point the liquid possesses as compared with the water at the free
end, where the pressure is zero. If the centre of the cross-section of
Fig. 17.-
-DlAGRAM TO ILLLMRATE Fl.OW OK WaTER ALO.NG A HORIZONTAL
Tlbe conne( ted with a Reservoir.
the free end of the tube be joined to the centres of all the menisci, it
will be found that the line is a straight line. The lateral pressure at
any point of the tube is therefore proportional to its distance from the
free end. Since the same quantity of water must pass through each
cross-section of the horizontal tube in a given time as flows out at the
open end, the kinetic energy of the liquid at every cross-section must
be constant and equal to \mv-, where v is the mean velocity (the
quantity which escapes in unit of time divided by the cross-section)
of the water at the free end.
Just inside the orifice the total energy of a mass m of water is mgh ;
just beyond it at the first vertical tube, mgh -vlmi^, where //' is the
lateral pressure. On the assumption that between the inside of the
orifice and the first tube, no energy has been transformed into heat (an
assumption the more nearly correct the smaller the distance between
it and the inside of the orifice is made), we have ;//i;// = nigh + ^wt'-,
i.e., hmv- = mg{h -//). In other words, the portion of the energy of
position of the water in the reservoir which is transformed into the
kinetic energy of the water flowing along the horizontal tube is
measured by the difference between the height of the level of the
THE CIRCULATION OF Till- BLOOD AND LYMPH 73
reservoir and the lateral pressure at the beginning of the horizontal
tube — that is, the height at which the straight line joining the
menisci of the vertical tubes intersects the column of water in the
reservoir. Let H represent the height corresponding to that part of
the energy of position which is transformed into the kinetic energy
of the flowing water. H is easily calculated when the mean velocity
of efflux is known. For v= s/2gVl by Torricelli's theorem (since
none of the energy corresponding to H is supposed to be used up in
overcoming friction), or H = ^" At the second tube the lateral
pressure is only //'. The sum of the visible kinetic and potential
energy here is therefore h/iv- + »igk". A quantity of energy mg {H - H')
must have been transformed into heat owing to the resistance caused
by fluid friction in the portion of the horizontal tube between the
first two vertical tubes. In general the energy of position repre-
sented by the lateral pressure at any point is equal to the energy
used up in overcoming the resistance of the portion of the path
beyond this point.
Velocity of Outflow. — It has been found by experiment that v^ the
mean velocity of outflow, when the tube is not of very small calibre,
varies directly as the diameter, and therefore the volume of outflow
as the cube of the diameter. In fine capillary tubes the mean velocity
is proportional to the square, and the volume of outflow to the fourth
power of the diameter (Poiseuille). If, for example, the linear velocity
of the blood in a capillary of 10 /x in diameter is \ mm. per sec, it will
be four times as great (or 2 mm. per sec.) in a capillary of 20 /^
diameter, and one-fourth as great (or \ mm. per sec.) in a capillary
of 5 ,a diameter, the pressure being supposed equal in all. The
volume of outflow per second is obtained by multiplying the cross-
section by the linear velocity. The cross-section of a circular capillary,
10 ^ in diameter, is tt (5 x TTTTni)' = > say, y ^io 0 SQ- mm. The outflow
will be Ti^Toir X i = ITS ^Tj 0 cub. mm. per sec. The outflow from the
capillary of 20 ,a diameter would be sixteen times as much, from
the 5 /x capillary only one-sixteenth as much. Some idea of the
extremely minute scale on which the blood-flow through a single
capillary takes place, may be obtained if we consider that for the
capillary of 10 /a diameter a flow of 0-^00 cub. mm. per sec. would
scarcely amount to i cub. mm. in six hours, or to i cc. in 250 days.
When the initial energy is obtained in any other way than by
means of a ' head ' of water in a reservoir — say, by the descent of a
piston which keeps up a constant pressure in a cylinder filled with
liquid — the results are exactly the same. Even when the horizontal
tube is distensible and elastic, there is no difference when once the
tube has taken up its position of equilibrium for any given pressure,
and that pressure does not vary.
Flow with Intermittent Pressure. — When this acts on a rigid
tube, everything is the same as before. When the pressure
alters, the flow at once comes to correspond with the new pressure.
Water thrown by a force-pump into a system of rigid tubes escapes
74 A MANUAL OF PHYSIOLOGY
at ever>' stroke of the pump in exactly the quantity in which it enters,
for water is practically incompressible, and the total quantity present
at one time in the system cannot be sensibly altered. In the
intervals between the strokes the flow ceases ; in other words, it is
intermittent. It is very different with a system of distensible and
elastic tubes. During each stroke the tubes expand, and make
room for a portion of the extra liquid thrown into them, so that a
smaller quantity flows out than passes in. In the intervals between
the strokes the distended tubes, in virtue of their elasticity, tend to
regain their original calibre. Pressure is thus exerted upon the
liquid, and it continues to be forced out, so that when the strokes of
the pump succeed each other with sufficient rapidity, the outflow
becomes continuous. This is the state of aftairs in the vascular
system. The intermittent action of the heart is toned down in the
elastic vessels to a continuous steady flow.
The Beat of the Heart. — In the frog's heart the contraction
can be seen to begin about the mouths of the great veins
which open into the sinus venosus. Thence it spreads in
succession over the sinus and auricles, hesitates for a
moment at the auriculo-ventricular junction, and then with
a certain suddenness invades the ventricle. In all prob-
ability the contraction wave is propagated without the
intervention of nerves, from fibre to fibre of the muscular
tissue, which, although presenting certain variations in its
character in the different divisions of the heart and at their
junctions, forms a more or less continuous sheet over the
whole of the organ. This conclusion rests in part upon the
observation that the delay of the wave at the auriculo-
ventricular groove is much greater than it ought to be if the
excitation were transmitted by nerves, since the velocity of the
nerve-impulse is exceedingly great (p. 5S2) ; and the further
observation that, when the ventricle is caused to contract
by artificial stimulation of the auricle, this delay is appre-
ciably greater when the stimulus is applied as far from the
ventricle as possible than when it is applied as near to it as
possible. In the mammalian heart the starting-point of the
contraction is likewise the mouths of the veins opening into
the auricles, which are richly provided with muscular fibres
akin to those of the heart. But the wave advances so
rapidly that it is difficult, if not impossible, to trace in its
course a regular progress from base to apex, although the
ventricular beat undoubtedly follows that of the auricle, and
THE CIRCULATION OF THE BLOOD AND LYMPH 75
the capillary electrometer indicates that, in a heart beating
normally, the negative change associated with contraction
begins at the base and then reaches the apex (p. 622). It is
not definitely known how in the mammal the beat of the
ventricle is co-ordinated with that of the auricle. The
alleged absence of muscular connection has led to a very
general belief that the link is of a nervous nature ; and
certainly there is no dearth of nerves running between the
auricles and the ventricles that might serve as such a bridge.
But recent work makes it possible that, at least in some
animals, the contraction wave may spread, as in the frog's
heart, along fibres, apparently muscular, which, in the form
of slender strands, interpenetrate the ring of fibrous tissue
between the auricles and ventricles (Kent).
The most conspicuous events in the beat of the heart, in
their normal sequence, are : (i) the auricular contraction or
systole ; (2) the ventricular contraction or systole ; (3) the
pause or diastole. The auricles, into which, and beyond
which into the ventricles, blood has been flowing during the
pause from the great thoracic veins, contract sharply. The
contraction begins in the muscular rings that surround the
orifices of the veins, so that these, destitute of valves as they
are, are sealed up for an instant, and regurgitation of blood
into them is prevented. The filling of the ventricles is
thus completed ; their contraction begins either simul-
taneously with the relaxation of the auricles or a little
before it. The mitral and tricuspid valves, whose strong but
delicate curtains have during the diastole been hanging
down into the ventricles and swinging freely in the entering
current of blood, are floated up as the intraventricular
pressure begins to rise, so that, in the first moment of the
sudden and powerful ventricular systole, the free edges of
their segments come together, and the auriculo-ventricular
orifices are completely closed (Fig. 68, p. 181). In the
measure in which the pressure in the contracting ventricle
increases, the contact of the valvular segments becomes
closer and more extensive ; and their tendency to belly into
the auricle is opposed by the pull of the chordae tendineae,
whose slender cords, inserted into the valves from border to
76 A MANUAL OF PHYSIOLOGY
base, are kept taut, in spite of the shortening of the ventricle
by the contraction of the papillary muscles. During the
systole, the ventricles change their shape in such a way that
their combined cross-section — which in the relaxed state is a
rough ellipse with the major axis from right to left — becomes
approximately circular, and they then form a right circular
cone. As soon as the pressure of the blood within the con-
tracting ventricles exceeds that in the aorta and pulmonary
artery respectively, the semilunar valves, which at the begin-
ning of the ventricular systole are closed, yield to the pressure,
and blood is driven from the ventricles into these arteries.
The ventricles are more or less completely emptied during
the contraction, which seems still to be maintained for a
short time after the blood has ceased to pass out. The
contraction is followed by sudden relaxation. The intra-
ventricular pressure falls. The lunules of the semilunar
valves slap together under the weight of the blood as it
attempts to regurgitate, the corpora Arantii seal up the
central chink, and the aorta and pulmonary artery are thus
cut off from the heart. Then follows an interval during
which the whole heart is at rest, namely, the interval
between the end of the relaxation of the ventricles and the
beginning of the systole of the auricles. This constitutes the
pause. The whole series of events is called a cardiac cycle
or revolution (see Practical Exercises, p. 176).
It will be easily understood that the time occupied by any
one of the events of the cardiac cycle is not constant, for
the rate of the heart is variable. If we take about 70 beats
a minute as the average normal rate in a man, the ventricular
systole will occupy about '3 second; the ventricular diastole,
including the relaxation, about '5 second. The systole of
the auricle is one-third as long as that of the ventricle.
This rhythmical beat of the heart is the ground phe-
nomenon of the circulation. It reveals itself by certain
tokens — sounds, surface-movements or pulsations, alterations
of the pressure and velocity of the blood, changes of volume
in parts — all periodic phenomena, continually recurring
with the same period as the heart-beat, and all funda-
mentally connected together. And if we hold fast the idea
THE CIRCULATION OF THE BLOOD AND LYMP// -j-j
that when we take a pulse-tracing, or a blood-pressure curve,
or a plethysmographic record, we are really investigating the
same fact from different sides, we shall be able, by following
the cardiac rhythm and its consequences as far as we can
trace them, to hang upon a single thread many of the most
important of the physical phenomena of the circulation.
The Sounds of the Heart. — When the ear is applied to the
chest, or to a stethoscope placed over the cardiac region,
two sounds are heard with every beat of the heart ; they
follow each other closely, and are succeeded by a period of
silence. The dull booming 'first sound' is heard loudest in
a region which we shall afterwards have to speak of as that
of the 'cardiac impulse' (p. 79); the short, sharp, 'second
sound' over the junction of the second right costal cartilage
with the sternum.
There has been much discussion as to the cause of the
first sound. That a sound corresponding with it in time
is heard in an excised bloodless heart when it contracts, is
certain ; and therefore the first sound cannot be exclusively
due, as some have asserted, to vibrations of the auriculo-
ventricular valves when they are suddenly rendered tense
by the contraction of the ventricles, for, of course, in a
bloodless heart the valves are not stretched. Part of the
sound must accordingly be associated with the muscular
contraction, as such. As we shall see (p. 557)5 the sound
caused by a contracting muscle is probably, in part at
least, a resonance tone of the ear. This lessens the
difficulty of understanding how a simple non-tetanic con-
traction like that of the heart should give rise to a
* muscular ' sound of definite pitch. Further, the fact
that the first sound is heard during the whole, or nearly the
whole, of the ventricular systole is against the idea that it is
exclusively due to the vibrations of membranes like the
valves, which would speedily be damped by the blood and
rendered inaudible. But there is undoubtedly a valvular
as well as a muscular factor involved ; and, indeed, there is
reason to believe that the valvular note is the essential
part of the sound, which perhaps acquires its peculiar
booming character from the resonance tones of the ear, and
78 A MAXUAL OF PHYSIOLOGY
possibly of the chest-wall, set up by the muscular contrac-
tion. Some observers have been able to distinguish in
the first sound the valvular and the muscular elements,
the former being higher in pitch than the latter, but a
minor third below the second sound. Further, when the
mitral valve is prevented from closing by experimental
division of the chordae tendineae, or by pathological lesions,
the first sound of the heart is altered or replaced by a
* murmur.' This evidence is not only important as regards
the physiological question, but of great practical interest
from its bearing on the diagnosis of cardiac disease. It
may be added that the point of the chest-wall at which the
first sound is most easily recognised is also the point at
which a changed sound or murmur connected with disease
of the mitral valve is most distinctly heard. The sound is,
therefore, best conducted from the mitral valve along the
heart to the point at which it comes in contact with the wall
of the chest. Changes in the first sound connected with
disease of the tricuspid valve are heard best, in the com-
paratively rare cases where they can be distinctly recognised,
in the third to the fifth interspace, a little to the right of
the sternum.
Sir Richard Quain has recently revived the theory that the first
sound is due, not to the vibrations of the auriculo-ventricular valves,
nor to the muscle-sound of the contracting ventricles, but to the impact
of the ventricular blood on the semilunar valves at the moment of
systole, and the resistance which it encounters as it passes through
the orifices of the aorta and pulmonary artery. But although some
of the facts which he cites seem to favour such a view, there are many
difficulties in the way of its acceptance.
The second sound is caused by the vibrations of the semi-
lunar valves when suddenly closed, ' the recoiling blood
forcing them back, as one unfurls an umbrella, and with an
audible check as they tighten ' (Watson). The sharpness
of its note is lost, and nothing but a rushing noise or bruit
can be heard, when the valves are hooked back and pre-
vented from closing. It is altered, or replaced by a murmur
when the valves are diseased. As there is a mitral and a
tricuspid factor in the first sound, so there is an aortic and
a pulmonary factor in the second. The place where the
second sound is best heard (over the junction of the second
THE CIRCULATION OF THE BLOOD AND LYMI'II 79
right costal cartilage and sternum) is that at which any
change produced by disease of the aortic valves is most
easily recognised. The sound is conducted up from the
valves along the aorta, which comes nearest to the surface
at this point. Changes connected
with disease of the pulmonary
valves are most readily detected
over the second left intercostal
space near the edge of the
sternum, for here the pulmonary fk;. i8.--Dia(.kam ok Makky's
artery most nearly approaches Cari)io<;raph.
■^^ •''■'■ A, knob attached to flexible mem-
the chest-wall. brane tied over end of metal box—
-TV. Hi. J • < i. T ' the knob is placed over the apex-
The first sound is 'systolic — ^^^^^ . ^ j^ the folded edge of the
that is, it occurs during the ven- membrane; B is the tubecommuni-
' " _ catmg with a recordmg tambour.
tricular systole ; the second is
' diastolic,' beginning at the commencement of the diastole.
The Cardiac Impulse. — A surface-movement is seen, or an
impulse felt, at every cardiac contraction in various situa-
tions where the heart or arteries approach the surface. The
pulsation, or impulse, of the heart, often styled the apex-
beat, is usually most distinct to sight and touch in a small
area lying in the fifth left intercostal space, between the
mammary and the parasternal line,* and generally, in an
adult, about an inch and a half to the sternal side of the
former. It is due to the systolic hardening of the ventricles,
which are here in contact with the chest-wall, the contact
being at the same time rendered closer by their change of
shape, and by a slight movement of rotation of the heart
from left to right during the contraction (Practical Exer-
cises, p. 182). Even in health the position of the impulse
varies somewhat wdth the position of the body and the res-
piratory movements. In children it is usually situated in the
fourth intercostal space. In disease its displacement is an
important diagnostic sign, and may be very marked, especi-
ally in cases of effusion of fluid into the pleural cavity.
Various instruments, called cardiographs, have been devised
* The mammary line is an imaginary vertical line supposed to be
drawn on the chest through the middle point of the clavicle. It usually,
but not necessarily, passes through the nipple. The parasternal line is the
vertical line lying midway between the mammary line and the corre-
sponding border of the sternum.
8o
A MANUAL OF PHYSIOLOGY
:. 19. -Cakdiocram taki:n wnii
Marev's Cardiograph.
A, auricular systole ; V, ventricular systole ;
D, diastole. The arrow shows the direction in
which the tracing is to be read.
for magnifying and recording the movements produced by
the cardiac impulse. Marey's cardiograph consists essenti-
ally of a small chamber, or tambour, filled with air, and
closed at one end by a flexible membrane carrying a button,
which can be adjusted to
the wall of the chest.
This recciviui:^ tambour is
connected by a tube with
a recording- tambour, the
flexible plate of which acts
upon a lever writing on a
travelling surface — a uni-
formly-rotating drum, for
example — covered with
smoked paper. Any move-
ment communicated to
the button forces in the
end of the tambour to which it is attached, and thus raises
the pressure of the air in it and in the recording tambour;
the flexible plate of the latter moves in response, and the
lever transfers the movement to the paper. The tracing,
or cardiogram, obtained in this way shows a small elevation
corresponding to the auricular systole, succeeded by a large
abrupt rise corresponding to the beginning of the first
sound, and caused by the ventricular systole. The rise is
maintained, with small secondary oscillations, for about
•3 of a second in a tracing from a normal man, then gives
way to a sudden descent, that marks the relaxation of the
ventricles, the beginning of the second sound, and the closure
of the semilunar valves. An interval of about "5 second
elapses before the curve begins again to rise at the next
auricular contraction.
Such was the interpretation which Marey put upon his tracings, and
although neither his results nor his deductions from them have
escaped the criticism of succeeding investigators, it is doubtful
whether any adequate reason has been brought forward for dis-
carding them. The difficulties that beset the subject are great, for
the cardiogram is a record of a complex series of events. The very
rapid variation of pressure within the ventricles, the change of shape
of the heart, the sliglit change of position of its apex, if such occurs,
must all leave their mark upon the curve, which is besides distorted
THE CIRCULATION OF THE BLOOD AND LYM/'If 8i
by the resistance of the elastic chest wall, the inertia of the recording
lever, and the compression of the air in the connecting tubes. It is
only by comparing in animals the cardiographic record with the
changes of blood- pressure in the heart and arteries that even our
present degree of knowledge of the human cardiogram has been
attained.
Endocardiac Pressure.— The function of the heart is to
maintain an excess of pressure in the aorta and pulmonary
artery sufficient to overcome the friction of the whole
vascular channel, and to keep up the flow of blood. So
long as the semilunar valves are closed, most of the work
Fig. 20. — Curves of Endocardiac Pressure taken with Cardiac Sounds.
Aur., auricular curve ; Ve/i/., ventricular curve ; AS, period of auricular systole ;
VS, of ventricular systole ; D, diastole.
of the contracting ventricles is expended in raising the
pressure of the blood within them. At the moment when
blood begins to pass into the arteries, nearly all the energy
of this blood is potential ; it is the energy of a liquid under
pressure. During a cardiac cycle the pressure in the cavities
of the heart, or the endocardiac pressure, varies from
moment to moment, and its variations afford important data
for the study of the mechanics of the circulation.
For the study of the endocardiac pressure, the ordinary mercurial
manometer (p. 99) is unsuitable, since, owing to the relatively great
amount of work required to produce a given displacement of the
6
82
A MAX UAL OF PHYSIOLOGY
mercury, it does not readily follow rapid changes of i)ressure, and
the mercurial column, once displaced, continues for a time to
execute vibrations of its own, which are compounded with the true
oscillations of blood-pressure. Hut by introducing in the connection
between the manometer and the heart a valve so arranged as to
oppose the passage of blood towards the heart, while it favours its
passage towards the manometer, the maximum pressure attained in
the cardiac cavities during the cycle may be measured with con-
siderable accuracy. When the valve is reversed the apparatus
becomes a minimum manometer. In this way it has been found
that in large dogs the pressure in the left ventricle may rise as high
as 230 to 240 mm. of mercury, and sink as low as — 30 to —40 mm. ;
while in the right ventricle it may be as much as 70 mm., and
Fir., 21. — Dia(;ram of Fn k's C-si'rim; Manometer.
A, hollow spring filled with alcohol. Its open end R is covered with a membrane and
is fixed to the upright F ; the other end C is free to move, and is connected with a
system of levers, which move the writing point D ; E is the cannula, which is connected
with the bloodvessel. When the pressure in the spring is increased it tends to straighten
itself. ,
as little as - 25 mm. In the right auricle a maximum pressure of
20 mm. of mercury has been recorded.
Our knowledge of the maximum and minimum pressure attained
in the cavities of the heart, even if it were far more precise than it
actually is, would only carry us a little way in the study of the endo-
cardiac pressure-curve, for it would merely tell us how far above the
base-line of atmospheric pressure the curve ascends, and how far
below the base-line it sinks. To exhaust the problem, we require to
have tracings of the exact form of the curve for each of the cavities
of the heart, and to know the time-relations of the curves so as to
be able to compare them with each other, and with the pressure-
THE LIRCULATIOS OF THE liEOOD AND LYMl'll 83
curves of the great arteries and great veins. To obtain satisfactory
tracings of the swiftly-changing endocardiac pressure is a task of the
highest technical difficulty, and it is only in very recent years that
it has been accomplished with any approach to accuracy l)y the
use of elastic manometers, in which the blood-pressure is counter-
balanced, not by the weight of a column of licjuid, as in the mercurial
manometer, but by the tension of an elastic disc or of a spring.
One of the earliest of these was the now perhaps somewhat obsolete
C-spring manometer of Fick (an adaptation of Hourdon's pressure-
gauge), of which a diagram is given in Fig. 21. Probably the most
perfect elastic manometers of the modern type are the improved
instrument of Fick (Fig. 22), with the various modifications it has
undergone in the hands of v. Frey and others, and especially the
manometers of Hiirthle.
Hiirthle's spring manometer consists of a small drum covered
with an indiarubber membrane, loosely arranged so as not to vibrate
with a period of its own. The drum is connected with the heart or
with a vessel, and the blood-pressure is transmitted to a steel spring
Flu. 22.— Pick's Elasiic Manometer.
i7 a is a metal piece tunnelled by a narrow canal of about i mm. in diameter, which
enlarges below to a shallow saucer-shaped space b. The wide opening of b is covered
by a thin piece of indiarubber c, to the centre of which an ivory button d is attached.
The button presses on a strong steel spring/; which is attached at one end to the brass
frame ee, and at the other, by means of an intermediate piece ^, 10 the lever h\ b'\%
filled with a few drops of water, but the canal a contains only air. When a is con-
nected with the interior of the heart or of an artery, the changes of pressure are trans-
mitted to the spring, and recorded by the writing-point of the lever.
by means of a light metal disc fastened on the membrane. The spring
acts on a writing lever. The instrument is so constructed that for a
given change of pressure the quantity of liquid displaced is as small
as possible, and it is on this that its capacity to follow sudden
variations of pressure chiefly depends. The manometer is connected
with the cavity of the heart by an appropriately-curved cannula of
metal or glass, which, after being filled with some liquid that
prevents coagulation (Practical Exercises, p. 185), is pushed through
the jugular vein into the right auricle or ventricle, or through the
carotid artery and aorta into the left ventricle. Some observers fill
only the cannula with licjuid, and leave the capsule of the elastic
manometer and as much of the connections as possible full of air.
Others fill the whole system with liquid. And around the question
of the relative merits of 'transmission ' by liquid and by air has raged
6—2
84
.1 J/.L\Y/JZ OF I'HYSIOLOCY
a controversy which does not even yet show signs of coming to an
end, for there is reason to sup[)ose that the character of the curves
obtained is to some extent modified by the manner in which the
pressure is transmitted.
Thus, the pressure-curve of the ventricle, according tc
Hiirthle and those who, like him, have employed manometers
with licjuid transmission (Fig. 23), remains after the first
abrupt rise, which undoubtedly corresponds to the ventricular
systole, almost parallel to the abscissa line for a consider-
able time, and then descends somewhat less suddenly than
it rose. This S} stolic ' plateau,' although usually broken by
minor heights and hollows, perhaps due to inertia oscilla-
tions of the liquid or the recording apparatus, would indicate
that the ventricular pressure, after reaching its maximum,
Fig. 23. — SiMUi.TANKors Record ok Prkssire in Lkit Vkntrici.k (v) and
Aorta (a). (Hurthi.k.)
The tracings were taken with elastic manometers : o indicates a point just before the
closure of the mitral valve ; i, the opening of the semilunar valve ; 3, the closure of
the semilunar valve ; 4, the opening of the mitral valve. The ventricular curve shows
a ' plateau.'
maintained itself there throughout the greater part of the
systole. The tracings yielded by the best manometers with
air transmission (Fig. 24) show the same suddenness in the
first part of the upstroke and the last part of the descent —
that is, the same abruptness in the beginning of the con-
traction and the end of the relaxation. But they differ
totally in the intermediate portion of the curve, which,
climbing ever more gradually as it nears its apex, remains
THE CIRCULATION OF THE BLOOD AND LYMPH 8,'
but a moment at the maximum, then immediately descendinf,'
forms a ' peak,' and not a plateau.
While perhaps it is hardly possible at present to decide
finally between the plateau and the peak, yet the bulk of the
evidence goes to show that the former is not, as the advocates
of the peak have claimed, an artificial phenomenon, but
does in reality correspond to that continuation of the systole
of the ventricle, that dogged grip, if we may so phrase it,
which it seems to maintain upon the blood after the greater
Fit;. 24. — CoMrAKisoN of Presstke-Curves of Left Auricle, Left Ven-
tricle, AND Aorta, (v. Frey.)
Recorded by elastic manometers with air transmission. The ventricular curve shows
a ■ peak.'
portion of it has been expelled. This conclusion is essentially
in accordance with the results of Chauveau and Marey,
obtained long ago by means of their ' cardiac sound,' which
was in principle an elastic manometer, though of somewhat
faulty pattern (Fig. 25).
It consisted of an ampulla of indiarubber, supported on a frame-
work, and communicating with a long tube, which was connected
with a recordmg tambour. The ampulla was introduced into the
heart through the jugular vein or carotid artery in the way already
86 A MAXUAL OF PHYSIOLOGY
described. Sometimes a double sound was employed, 'armed with
two ampulhe, plac ed at such a distance from each other that when
one was in the right ventricle the other was in the auricle of the same
side. Each ampulla communicated by a separate tube in the
common stem of the instrument with a recording tambour, and the
writing points of the two tambours were arranged in the same vertical
line. When any change in the blood-pressure takes place, the
degree of compression of the ampullar is altered, and the change is
transmitted along the air-tight connections to the recording tambours.
Simultaneous records of the changes in the blood-pressure in the
right auricle and ventricle obtained in this way indicate a sudden
rise of the auricular pressure corresponding with the auricular systole,
followed by a sudden fall ( Fig. 20). This is rei)resented on the ventri-
cular curve by a smaller elevation, which shows that the pressure in the
ventricle has been raised somewhat by the blood driven into it from
the auricle. Then follows immediately a great and abrupt increase
of ventricular pressure, the result of the systole of the -ventricle.
FiG. 25. — Diagram ok Cardiac Sound kor Simui/ianeous Rkglstration
OK Endocardiac Pressure in Auricle and Ventricle.
A, elastic ampulla for auricle ; V for ventricle ; T, tubes connected with recording
tambours.
This elevation remains for some time at the maximum, and then the
curve suddenly sinks as the ventricle relaxes. Near the bottom of
the descent there is a slight elevation, due, as Marey su[)posed, to
the closure of the semilunar valves, which causes a t)etter-marked
and simultaneous elevation in the curve of aortic pressure when this
is registered by means of a sound passed into the aorta through the
carotid artery. Both the auricular and ventricular curves now begin
again to rise slowly, showing a gradual increase of pressure as the
blood flows from the great veins into the auricle, and through the
tricuspid orifice into the ventricle. This slow rise continues till the
next auricular systole.
It is probable, however, that some of the smaller elevations
on the curves of Chauveau and Mare}-, and particularly that
which they associated with the closure of the semilunar
valves, were due to the oscillations of their apparatus. For
it is a remarkable fact that on most of the endocardiac
pressure tracings of the best modern manometers, whether
THE CIRCULATIOX OF THE BLOOD AND LYMPH 87
the curves belong to the type of the peak or of the plateau,
no sudden change of curvature, no nick, or crease, or undu-
lation reveals the moment of opening or closure of any
valve. But by experimentally graduating a pair of elastic
manometers, and obtaining with them simultaneous records
of the pressure in auricle and ventricle, we can calculate at
what points of the ventricular curve the pressure is just
greater than and just less than the pressure in the auricle.
The first point, it is evident, will correspond to the instant at
which the mitral or tricuspid valve, as the case may be, is
closed, and the second to the instant at which it is opened.
And in like manner, by comparing the pressure-curve of the
aorta with that of the left ventricle, the moment of opening
and closure of the semilunar valves may be determined
(Figs. 2}^ and 24). According to the best observations, the
closure of the semilunar valves takes place at a time corre-
sponding to a point on the upper portion of the descending
limb of the intraventricular curve.
The study of the curves of endocardiac pressure enables
us to add precision in certain points to the description of
the events of the cardiac cycle which we have already given,
and, as regards the ventricles, to divide the cycle into four
periods :
(i) A period during which the pressure is lower in the ventricles
than either in the auricles or the arteries, and the auriculo-
ventrictdar valves are consequently open, and the semilunar valves
closed. This is the period of ' filling ' of the heart.
(2) A period, beginning with the ventricular systole, during
which the pressure is rising abruptly in the ventricles, while they
arc as yet completely cut off from the auricles on the one hand
and the arteries on the other by the closure of both sets of valves.
This is the period during ichich the ventricles are, to use a homely
but expressive phrase, ^getting up steam.'
(3) A period during which the pressure in the ventricles overtops
that in the arteries, and the semilunar valves are open, while the
auriculo-ventricnlar valves remain shut. This is the period of
' discharge.'
(4) A period during ichich the pressure in the ventricles is again
less than the arterial, while it still exceeds the auricular pressure,
88 A MAAUAL OF PHYSIOLOGY
and both sets of valves are closed. This is the period of rapid
relaxation.
Of the four periods, the second and fourth are exceedingly
brief. The third is relatively long and constant, being but
slightly dependent on either the pulse-rate or the pressure
in the arteries. The duration of the first period varies in-
versely as the frequency of the heart : with the ordinary
pulse-rate it is the longest of all.
We have already said that a negative pressure may be detected in
the cardiac cavities by means of a special form of mercurial mano-
meter. This is confirmed by an examination of the tracings written
by good elastic manometers, for the curves of both ventricles may
often descend below the line of atmospheric pressure. The cause of
this negative pressure has been much discussed. In part it may be
ascribed to the aspiration of the thoracic cage when it expands
during inspiration (p. 209). But since the pressure in a vigorously-
beating heart may still become negative, though not to the same
extent as before, when the thorax has been opened, and the influence
of the respiratory movements eliminated, we must conclude that the
recoil of the somewhat narrowed, or at least distorted, auriculo-
ventricular rings, and of elastic structures in the walls of the ventricles,
exerts of itself a certain feeble suction upon the blood.
The Pulse. — At each contraction of the heart a quantity of
blood, probably varying within rather wide limits (p. 127),
is forced into the already-full aorta. If the walls of the
bloodvessels were rigid, it is evident (p. 74) that exactly
the same quantity would pass at once from the veins into
the right auricle. The work of the ventricle would all be
spent within the time of the systole, and only while blood
was being pumped out of the heart would any enter it.
Since, however, the vessels are extensible, some of the blood
forced into the aorta during the systole is heaped up in the
arteries, beyond which, in the capillary tract, with its rela-
tively great surface, the chief resistance to the blood-flow
lies. The arteries are accordingly distended to a greater
extent than before the systole, and, being elastic, they
keep contracting upon their contents until the next systole
over-distends them again. In this way, during the pause
the walls of the arteries are executing a kind of elastic
systole, and driving the blood on into the capillaries. The
work done by the ventricle is, in fact, partly stored up as
THE CIRCULATION OF THE BLOOD AND LYMPH 89
potential enerp^y in the tense arterial wall, and this energy
is being continually transformed into work upon the blood
during the pause, the heart continuing, as it were, to con-
tract by proxy during its diastole. Thus, the blood pro-
gresses along the arteries in a series of waves, to which the
name of ' blood-waves ' or ' pulse-waves ' may be given.
Wherever the pulse-wave spreads it manifests itself in
various ways — by an increase of blood-pressure, an increase
in the mean velocity of the blood-flow, an increase in the
volume of organs, and by the visible and palpable signs to
which the name of pulse is commonly given in a restricted
sense. The intermittence in the flow with which the pulse-
wave is necessarily associated is at its height at the begin-
ning of the aorta. In middle-sized arteries, such as the
radial, it is still well marked, but it dies away as the capil-
laries are reached, and only under special conditions passes
on into the veins.
The pulse was well known to the Greek physicians, and
used bvthem to a certain extent as an indication in practical
medicine. Harvey demonstrated with some clearness the
relation of the pulse to the contraction of the heart, but
Thomas Young was the first to form a proper conception of
it as the outward token of a wave propagated from heart to
periphery.
When the finger is placed over a superficial artery like the
carotid, the radial or the temporal, a throb or beat is felt,
which, without measurement, seems to be exactly coinci-
dent with the cardiac impulse. In certain situations the
pulse can be seen as a distinct rhythmical rise and fall of
the skin over the vessel. The throbbing of the carotid,
especially after exertion, is familiar to everyone, and the
beat of the ulnar artery can be easily rendered visible by
extending the hand sharply on the wrist. When the pulse
is felt by the finger, it is not the expansion, but the
hardening of the wall of the vessel, due to the increase of
arterial pressure, that is perceived ; and even a superficial
artery when embedded in soft tissues so that it cannot be
compressed, gives no token of its presence to the sense of
touch. Sometimes an artery is longitudinally extended by
90 A MANUAL OF PIIYSIOLOl'.Y
the pulse-wave, and this extension may be far more con-
spicuous than the lateral dilatation. This is particularly
seen when one point of the vessel is fixed and a more distal
point offers some obstruction to the blood-flow, as at a
bifurcation, or in an artery which has been ligatured and
divided.
By means of the sphygmograph, the lateral movements of
the arterial wall, or, rather, in man, the movements of the
skin and other tissues lying over the bloodvessel, can be
magnified and recorded. It would be very unprofitable to
enumerate all the sphygmographs which ingenuity has in-
vented and found names for. The first rude attempt to
magnify the movements of the pulse was made by loosely
Fic. 26. — Scheme of Marey's Spiiv(;mo(jrai'h.
A, Toothed wheel connected with axle H, and gearing into toothed upright B ;
C, ivory pad which rests over bloodvessel and is pressed on it by moving G, a screw
passing through the spring J ; E, writing-lever attached to axle H, and moved by its
rotation ; E writes on U, a travelling surface moved by clockwork F.
attaching a thin fibre of glass or wax to the skin with a
little lard, in order to demonstrate the venous pulse which
appears under certain conditions. \'ierordt improved on
this by using a counterpoised lever writing on a blackened
surface. But the inertia of the lever was so great that the
finer features of the pulse were obscured. In all modern
sphygmographs there is a part, usually button-shaped, which
is pressed over the artery by means of a spring, as in Marey's
and Dudgeon's sphygmographs, or by a weight, or by a
column of liquid. In Marej's instrument, the button acts
upon a toothed rod gearing into a toothed wheel, to which
a lever, or a system of levers, is attached. The lever has
a writing-point which records the movement on a smoked
plate, or a plate covered with smoked paper, drawn uni-
formly along by clockwork. Brondgeest's pansphygmograph
is a particular application of Marey's tambours, for receiving
THE CIRCVLATIOX OF THE BLOOD AM) LYMPH 91
and ref^istering the movement of the pulse, as is Marey's
own ' sphygmograph of transmission.' (Practical Exer-
cises, p. 182.)
In a normal pulse-tracing (Fig. 27) the ascent is abrupt
and unbroken ; the descent is more gradual, and is inter-
rupted by one, two, or even three or more, secondary
wavelets. The most important and constant of these is the
one marked 3, which has received the name of the dicrotic
wave. Usually less marked, and sometimes absent, is the
wavelet 2 between the dicrotic elevation and the apex of
YiG. 27. — Pulse Tracings.
1, Primary elevation ; 2, predicrotic or first tidal wave ; 3, dicrotic wave. The
depression between 2 and 3 is the dicrotic or aortic notch ; 3 is better marked in B
than in A. C, dicrotic pulse with low arterial pressure ; D, pulse with high arterial
pressure — summit of primary elevation in the form of an ascending plateau. E, systolic
anacrotic pulse ; the secondary wavelet a occurs during the upstroke corresponding to
the ventricular systole. F, presystolic anacrotic pulse ; a occurs just before the systole
of the ventricle. In this rarer form of anacrotism. a may sometimes be due to the
auricular systole when the aortic valves are incompetent.
the curve. It is generally termed the predicrotic wave.
Following the dicrotic wave are sometimes seen one or more
ripples, which have been called by some elastic elevations.
In the explanation of the pulse-tracing, a fundamental fact to be
borne in mind is the elasticity of the vessels. When a wave of
increased pressure passes along a rigid tube with open ends, it dies
away at the ends, and is followed by no secondary waves. But when
the tube is elastic, the primary wave is necessarily followed by
secondary waves, the whole system passing through a series of
vibrations to regain its original position. When an incompressible
fluid like water is injected by an intermittent pump into one end of
an elastic tube a wave is set up, which is transmitted to the other
end of the tube. It is a positive wave — that is, it causes an increase
92 A MAXUAL OF PIIYSIOLOi.Y
of pressure and an expansion of the tube wherever it arrives ; and if
a series of levers l)e i)laced in contact with the tube, they will rise
and sink in succession as the wave passes tliem. If the tube is a
very long one, the wave, by the time it has reached the further end,
may have become extinguished by the friction ; but if the tube is
not long enough for this to happen, it will be there reflected, and
run towards the central end as a centripetal wave. Here it may
again undergo reflexion, and pass out once more as a centrifugal,
twice-reflected wave.
When the licjuid ceases to enter the tube at the end of the
stroke, a wave of diminished j)ressure — a negative wave — is generated
at the central end, and is propagated to the distal end, where it may
be reflected just like the positive wave.
Although under certain conditions the dicrotic wave is so
marked that the double beat of the pulse was discovered
and named by physicians long before the invention of any
sphygmograph, perhaps no physiological question has been
more discussed or is less understood than the mechanism of
its production. Two points, however, seem to be clear :
(i) That it is a centrifugal, and not a centripetal, wave —
that is to sa}', it travels away from, and not towards, the
heart ; (2) that the aortic semilunar valves have something
to do with its origin.
It is not a centripetal wave, for when tracings are taken
simultaneously from arteries at different distances from the
heart (say, from the carotid and the radial), the dicrotic
wave is always separated by the same interval of time from
the primary elevation. This can only be explained by
supposing that it has the same point of origin, and travels
with the same velocity and in the same direction as the
primary wave. It is not, then, a wave reflected directly
from the peripheral distribution of the artery from which the
pulse-tracing is taken. Nor does the contention of v. Frey
and V. Kries, that it is a twice-reflected wave, seem more
likely, although they have indeed by experiments on newly-
killed animals been able to detect the traces of such waves,
which, reflected first, as they suppose, from the small arteries
in general, run towards the heart, and are then again re-
flected outwards from the semilunar vahes.
Perhaps the explanation that best takes account of the
facts and renders most clear the role of the semilunar valves
THE CIRCULATIOy Ol' THE BLOOD AM) LYMl'Il 93
is somewhat as follows: When the systole abruptly comes
to ati end and the outflow from the ventricle ceases, the
column of blood in the aorta tends still to move on in virtue
of its inertia, and a diminution of pressure, accompanied by
a corresponding contraction of the aorta, takes place behind
it, just as a nej^ative wave is set up in the central end of the
elastic tube when the stroke of the pump is over. At the
same moment, and while the semilunar valves are still for
an instant incompletely closed, the diminution of pressure
in the beginning of the aorta is intensified by the aspiration
of the relaxing ventricle, which sucks the blood back against
the valves, and drawls them a little wa}- into its cavity.
A negative wave, therefore — a wave of diminished pressure,
represented in the pulse-curve by the ' aortic notch ' — travels
out towards the periphery. The diminution of pressure is
quickly followed by a rebound, as always happens in an
elastic system, the recoiling blood meets the closed semi-
lunar valves, the aorta expands again, and the expansion is
propagated once more along the arteries as the dicrotic
elevation.
Of the origin and significance of the predicrotic wave we
know so little that it would not be profitable to discuss it.
It seems, however, to be a secondary wave of oscillation. The
so-called elastic oscillations (Landois) are probably due, in
large part at least, to vibrations of the recording apparatus.
When the semilunar valve becomes incompetent in disease, or is
rendered insufficient in animals by the artificial rupture of one or
more of its segments, the dicrotic wave, as will be readily understood
from the manner in which it is produced, either disappears
altogether or is markedly enfeebled. But apart from any anatomical
lesion or functional defect in the aortic valves, the prominence
of the wave varies with a great number of circumstances, some of
which are in a measure understood, while others remain obscure.
It varies in particular with the abruptness of discharge of the
ventricle and the extensibility of the arteries. The conditions are
usually favourable when the arterial pressure is low, for the blood then
passes quickly from the ventricle into the arteries, which, already
only moderately tense, are easily dilated by the primary wave, then
sharply collapse, and are again abruptly distended when the dicrotic
wave arrives. And, in fact, an exaggeration of the dicrotic wavelet
may be artificially produced by nitrite of amyl (Fig. 70, p. 183),
a drug which lessens the blood-pffessure by dilating the small
94 A MANUAL OF I'UYSIOLOi'.Y
arteries, or by muscular exercise (Fig. 69, p. 183), running, for
instance, wliich is supposed to lower the arterial pressure, partly by
dilatation of the muscular and cutaneous arterioles, and partly by
accelerating the venous flow (p. 121). The increase in the pulse-
rate may also have something to do in this case with the exaggeration
of the dicrotism, which is very frequently, although by no means
invariably, associated with a rapidly-beating heart, and therefore is
often seen in fever. On the other hand, in certain diseases asso-
ciated with a high arterial pressure the dicrotic elevation almost
disappears. Atheromatous arteries, being very inextensible, do not
allow a dicrotic pulse.
Since the pulse represents a periodical increase and diminution in
the amount of distension of an artery at any point, the line joining
all the minima of the pulse-curve will vary in its height above the
base-line, or line of no pressure, according to the amount of per-
manent distension, i.e., permanent blood-pressure, which the heart in
any given circumstances is able to maintain. Any circumstance
that tends to lessen the permanent distension will cause a fall of the
line of minima, and any circumstance tending to increase the
distension will cause that line to rise. If, for example, the arm be
raised while a pulse-tracing is being taken from the wrist, the line of
minima falls because the permanent pressure in the radial artery is
diminished.
The form of the pulse-curve varies in the different arteries,
and therefore in making comparisons the same artery should
be used. When the wave of blood only enters an artery
slowly, the ascending part of the curve will be oblique.
This is normally the case in a pulse-curve of a distant artery,
such as the posterior tibial. The height of the wave is also
less than in an artery nearer the heart, such as the carotid,
or even the axillary, where the primary elevation is rela-
tively abrupt (Fig. 71, p. 183).
Anacrotic Pulse. — As a rule, the ascent of the tracing is
unbroken by secondary waves, but in certain circumstances
these may appear on it. This condition, which, when well
marked at any rate, may be considered pathological, is
called anacrotism (Fig. 27). It is seen when the discharge
of the left ventricle into the aorta is slow and difficult — e.g.,
in old people whose arteries have been rendered less
extensible by the deposit of lime-salts in their walls
(atheroma), and in cases where the orifice of the aorta has
been narrowed from disease of the semilunar valves (aortic
stenosis). Since these conditions are in general associated
THE CIRCrLATION OF THE liLOOI) A A'/) LYMPH 95
with hypertrophy and dihitation of the left ventricle, the
slow emptying; of the ventricle is, perhaps, partly due to the
}j;reater quantity of blood which it contains.
In whatever way the delay in the emptying' of the ventricle
is brought about, the most probable explanation of the
anacrotic pulse is that the delay affords time for one or
more secondary waves to be developed in the arterial system
before the summit of the curve has been reached, and that
these are superposed upon the long-drawn primary elevation.
In aortic insufficiency, where the left side of the heart is
never cut off entirely from the aorta, the auricular impulse
is sometimes marked on the pulse-curve as a distinct
elevation ; and this gives rise to a peculiar kind of anacrotic
pulse, especially in the arteries nearest the heart (Fig. 27, F).
Frequency of the Pulse, — In health, the working of the
cardiac pump is so smooth and apparently so self-directed,
that it needs a certain degree of attention to perceive that
the rate of the stroke is not absolutely constant. It is, in
reality, affected by many internal conditions and external
influences.
At the end of fcetal life the rate is given as 144-133 ; from
birth till the end of the first year, 140-123 ; from 10 to 15
years, 91-76 ; from 20 to 25 years, 73-69. It remains at this
till 60 years, and increases again somewhat in old age.* At
all ages the pulse is somewhat quicker in the female than in
the male, the excess amounting to about 8 beats a minute.
So that if we take the average rate for a man (in the sitting
position) as 72, the average for a woman will be 80. The
difference is partly due to the fact that the average man
is taller than the average woman ; and it is known that in
persons of the same sex and age the pulse-rate has an
inverse relation to the stature. But there may be, in
* It must be remembered that these numbers are merely averages.
Some heahhy individuals have a much slower pulse-rate than 72 per
minute, and some a rate considerably greater. Thus, while the average
pulse-rate (taken in the sitting position) of 74 healthy (male) students,
whose ages ranged from 18 to 36 years, was 'j'})^ the extreme variation was
from 54 to 98. In the standing position the average was 80, and the varia-
tions 64 to 105. In the supine position, average 69, and variations 48 to
98. After a short spell of muscular exercise (generally running up and
down some flights of stairs) the average in the standing position was 1 19,
the variations 75 to 164, and the average increase 32.
96 A MANUAL OF I'llYSIOLOGY
addition, a real sexual difference. The position of the body
exercises a small, but relatively constant, influence on the
rate, which is greater in the standing than in the sitting
posture, and greater in the latter than in the recumbent
position. And this is true even when muscular action is as
far as possible eliminated by fastening the person to a board.
The pulse is further affected by the respiratory movements,
especially when they are exaggerated in forced breathing,
being accelerated during each inspiration (p. 249). It is
also increased by the taking of food, and especially of
alcoholic stimulants, by muscular exercise, in fever and
many other pathological conditions, and by a high external
temperature. ^ A warm bath, for example, causes a very
distinct acceleration of the heart ; and Delaroche found that
in air at the temperature of 65' C. his pulse went up to 160.
A cold bath may depress the pulse-rate to 60, or even less.
During sleep it may fall to 50. It is greatly influenced by
psychical events, and that in the direction either of an
increase or a decrease. Finally, it ought to be remembered
as of some practical importance that the pulse-rate in women
and children, but particularly in the latter, is less steady
than in men, and more apt to be affected by trivial causes.
And it is a good general rule to let a short interval elapse
after the flnger is laid on the artery before beginning to
count the pulse, so that the acceleration due to the agitation
of the patient may have time to subside.
Various Characters of the Pulse. — Certain terms which have
come down from the older medicine, and are still used clinically to
describe various conditions of the circulation as investigated by
feeling the pulse, must here be briefly touched on :
' Hard ' pulse {pulsus durus). Here the mean blood-pressure is
high, the vessels are considerably distended, and the pulse therefore
feels hard. With a ' soft ' pulse {pulsus mollis) the mean blood-
pressure is low.
With a ' quick ' pulse {pulsus celer) the artery is rapidly distended
by the pulse-wave. With a ' slow ' pulse {pulsus tardus) the disten-
sion is slow.
The terms ' strong ' pulse {pulsus foriis) and ' weak ' pulse {pulsus
debilis) refer to the amount by which the pulse- wave increases the
blood-pressure at the point.
' Large ' pulse {pulsus inagnus) and ' small ' or ' thready ' pulse
THE CIRCULATION OF THE BLOOD AND LYMI'H 97
{pulsus parvus) refer to the increase in the (juantity of blood which
every i)ulse-\vave causes in the vessel.
The ' force of the pulse ' is a phrase which is often ambiguously
used, sometimes apparently as synonymous with ' strength,' and
sometimes with ' size,' as above defined. In fact, the quantitative
information obtained by feeling the pulse with the finger, although
more valuable for clinical purposes than anything that can be
deduced from an ordinary sphygmographic record, is far inferior in
precision to the (lualitative notion which that time-honoured pro-
ceeding affords. The ' force of the pulse ' does not necessarily
correspond with the force of the heart. It depends partly on the
suddenness with which the pulse-wave distends the artery, partly on
the amount of this distension in relation to the previous permanent
distension, and to some extent on the calibre of the vessel. Other
things being ecjual, the pulse in a large vessel will feel stronger than
that in a smaller vessel. This last factor accounts for the inequality
in the force of the pulse which is not infrecjuently found between the
two radials even of a healthy person.
Rate of Propagation of the Pulse-wave. — When pulse-tracings
are taken simultaneously at two points of the arterial system
unequally distant from the heart, by two sphygmographs
whose writing-points move in the same vertical straight line,
it is found that the ascent of the curve begins later at the
more distant, than at the nearer point. Since waves like
the pulse-wave travel with approximately the same velocity
in different parts of an elastic system like the arterial ' tree,'
this ' delay ' must be due to the difference in the length of
the two paths. The difference in length can be measured ;
the time-value of the ' delay ' can be deduced from the rate
of movement of the recording surface ; dividing the length
by the time, we arrive at the rate of propagation of the
pulse-wave. This rate has been found to be about 8"5 metres
per second in man in the arteries of the upper limb, and
9'5 metres in those of the lower limb, the difference being
due to the smaller distensibility of the latter. The mean
velocity of the pulse-wave would correspond to not much
less than 500 miles in twenty-four hours, or about the same
as the speed of a fast Atlantic liner or of a wave of the sea
in a strong gale. The velocity of the pulse-wave must
not be confounded with that of the blood-stream itself,
which is not one-thirtieth as great. A ripple passes over
the surface of a river at its own rate — a rate that is
7
98 A MAiXUAL Of PlIYSfOLOGY
independent of the velocity of the current. The passage
of the ripple is not a bodily transference of the particles
of water of which at any given moment the wave is com-
posed, but the propagation of a change of relative position
of the particles. The mere fact that the ripple can pass up
stream as well as down is sufficient to illustrate this. The
pulse-wave does not, however, correspond in every respect
to a ripple on a stream, for the bodily transfer of the blood
depends upon the series of blood-waves which the heart
sets travelling along the arteries. Every particle of blood
is advanced, on the whole, by a certain distance with every
pulse-wave in which for the time it takes its place. But
no particle continues in the front of the pulse-wave from
beginning to end of the arterial system. The ' delay ' or
' retardation ' of the pulse (the interval, say, between the
beginning of the ascent of the carotid and radial curves) is
practically constant in the same individual, not only in
health, but also in most diseases. But the retardation is
markedly increased when the pulse-wave has to pass
through a portion of an artery whose lumen is either greatly
widened (aneurism), or greatly constricted (endarteritis
obliterans).
The velocity of the pulse-wave has sometimes been de-
duced by comparing a tracing of the cardiac impulse with
a pulse-tracing taken at the same time from a distant artery.
But, as we have seen in dealing with the action of the heart,
the ventricle does not at the very beginning of its contraction
acquire sufficient force to cause the opening of the semi-
lunar valves. The pulse, therefore, even in the aorta, must
lag behind the ventricular pulse ; and the amount of this
' lag ' must be subtracted from the total retardation. But
since the aortic * lag,' unlike the retardation between two
arteries, varies greatly even in health, depending as it does
on the arterial blood-pressure, this method of determining
the velocity of the pulse-wave is not satisfactory.
The Blood-pressure Pulse. — In man it is only possible to
trace the pulse-wave along the arteries by movements of
the walls of the vessels transmitted through the overlying
tissues. In animals the changes of pressure that occur in
THE CIRCULATION OF THE BLOOD AND LYM/'If
99
the blood itself can be directly registered, and these changes
may be spoken of as the blood-pressure pulse. At bottom,
as already pointed out, the phenomenon is exactly the same
as that we have been dealing with in our study of the
external pulse. We are only now to follow, b}- a more
direct, and in some respects a more perfect method, the
same wave of blood along the same channel.
Measurement of the Blood-pressure, — Hales was the first to
measure the blood-pressure. This he did by connecting a
Fig. 28. — Dia(;ram of Mercurial Kymograph.
The record is taken on the endless strip of paper E, which is made to revolve at a
uniform rate, or on an ordinary drum ; D is a float carrying a writing point ; C is the
m;inometer, the ditference of level of the mercury [Hg] in the two limbs of which
measures the blood-pressure ; A is a pressure bottle filled with sodium carbonate or
magnesium sulphate solution and connected by the flexible tube B with the manometer ;
F is the bloodvessel ; G, the connecting cannula.
tall glass tube with the crural artery of a horse. The height
to which the blood rose in the tube indicated the pressure
in the vessel. Poiseuille, nearly half a century later, applied
the mercury manometer, which had already been used in
physics, to the measurement of blood-pressure. Ludwig
and others improved this method by making the manometer
self-registering by means of a float in the open limb, sup-
porting a style which writes on a revolving drum, the whole
arrangement being called a kymograph. (For the method
of taking a blood-pressure tracing, see p. 185.)
7—2
loo A AfANUAL OF PHYSIOLOGY
For reasons already nientioneil the mercurial manometer
is better suited for measuring the mean blood-pressure, or
for recording changes in the pressure which last for some
time, than for following the rapid variations of the pulse-
wave. For the latter purpose, one of the class of elastic
manometers is required (p. 82).
A blood-pressure tracing taken from an artery with a
.manometer of this sort yields the truest picture of the
pulse-wave which it is possible to obtain, because the re-
production of it is the most direct. The fact that such a
tracing shows a close agreement with the trace of a good
Fig. 29.— Curves ok Bi.ood-I'Rkssurk iakkn wiiii a Sikinc Manomkikr
I- ROM THE CAROTH) ARTERY OI- A Doi". (Hi RTHLE).
When I was taken the blood -pressure was high ; 2 corresponds to a medium, 3 to a
low, and 4 to a very low blood-pressure ; / is the primary elevation — this and the
succeeding elevations between / and a are called systolic waves ; the systolic waves are
followed by a marked elevation d, which corresponds to the dicrotic pulse-wave.
sphygmograph applied to the corresponding artery on the
other side, is a striking proof of the general accuracy of the
sphygmographic method for physiological purposes, and
enables us to guide ourselves in transferring to man, in
whom, of course, the sphygmograph can alone be used, the
information derived from direct manometric observations in
animals.
For the same reason it is unnecessary to discuss the
manometric tracings, as regards the pulsatory phenomena,
in all their details. It will be sufficient to say that while
the form of the blood-pressure pulse-curve varies with the
Tin: ciRcrLATios OF Tin: iiLoon axu lymph ioi
mean blood-pressure, the dicrotic \va\e is always marked on
it, preceded b}- one or more oscillations falling within the
period of the systole, and followed b}- one or more within the
period of the diastole. When the blood-pressure is low, the
first or primary elevation is the highest of the whole curve
(Fig. _'()). When the blood-pressure is high, the maximum
falls later, coinciding with one of the secondary systolic
waves, but always preceding the dicrotic wave ; and the
curve assumes an anacrotic character.
That all the secondary oscillations, including the dicrotic
wavelet, are of central, and not of peripheral origin, may
be shown, just as in the sphygmographic method, by re-
cording the blood-pressure simultaneously at two points of
the arterial system at different distances from the heart —
e.g^., in the crural and carotid arteries. The secondary
waves are found, by measuring the tracings, to reach the
more distal point later than the more central.
The increase of pressure during the systole, as indicated by the
height of the primary elevation, is always very large, much larger
than it appears in a tracing taken with a mercury manometer. In
the rabbit this pulsatory variation is one-third to one-fourth of the
minimum pressure. In the dog it is still greater, owing to the slower
rate of the heart, and oftens amounts to 50 mm. of mercury, while
under favourable conditions (low minimum pressure and slowly beat-
ing heart) the systolic increase of pressure may be actually more than
double the minimum (Hilrthle). Fick found also, by means of his
spring manometer, that the pulsatory variations of blood-pressure
were greater than the respiratory variations (p. 249), although in the
records of the mercury manometer the reverse appears often to be
the case. Landois, too, in the course of experiments in which a
divided artery was allowed to spout against a moving surface, and
to trace on it a sort of pulse-curve painted in blood (a haemautogram
as it is called), observed that the rate of escape of the blood was
nearly 50 per cent, greater during the systole, than during the diastole,
of the heart. The existence of the dicrotic wave on this tracing
was long looked on as the best proof that it was not an artificial
phenomenon.
The wave of increased pressure, as it runs along the
arterial system, carries with it wherever it arrives an
increase of potential energy. But this excess of potential
energy is continually being worn down, owing to the friction
of the vascular bed ; and although in the comparatively
I02 .1 MAXi'AL OF r/IYSI()IJ)(;Y
large arteries the loss of energy is not great, it rapidly
increases as the arteries approach their termination, and
begin to branch. For not only is the total surface, and
therefore the friction, increased with every bifurcation, but
the mere change of direction and division of the wave cannot
take place without loss of energy. For this reason the
fluctuations of blood-pressure are greater in the large
arteries near the heart than in arteries smaller and more
remote. In the wide and much-branched capillary bed the
pulse-wave disappears altogether, and the blood-pressure
becomes relatively constant or permanent. And it is for
some purposes convenient to look upon the blood-pressure
in the arteries as made up of a permanent element, with
pulsatory oscillations superposed on it. Since no portion of
the arterial system is more than partially emptied in the
Vu:. 30. — Blood-pressure Tracing.
The horizontal straight line intersecting the curves is tlie line of mean pressure.
interval between two blood-waves, the minimum or perma-
nent pressure is ahvays positive — i.e., always above that of
the atmosphere. The only reason for this is that the beats
of the heart succeed each other so rapidly that the succes-
sive waves overlap or ' interfere,' and are onl}' separated at
their crests.
If the heart is stopped while a blood-pressure tracing is
being taken— and we shall see later on how this can be done
(p. 134) — the minimum line of the tracing goes on falling
towards the zero-line. When the heart begins beating again,
the pressure-curve rises, not by a continuous ascent, but by
successive leaps, each corresponding to a beat of the heart,
and each overtopping its predecessor, till the old line of
minimum or of mean pressure is again reached.
The mean arterial blood-pressure is the permanent pressure
plus one-half of the average pulsatory oscillation. In a
blood-pressure tracing the line of permanent pressure joins
rUE CIRCriATION OF THE BLOOD AND LYMI'lI 103
all the minima ; the line of maximum pressure joins all the
maxima ; the line of mean pressure is drawn between them
in such a way that of the area included between it and the
blood-pressure curve as much lies above as below it (Fig. 30).
As has been said, a tracing taken with a mercury manometer
gives approximately the mean blood-pressure. Each beat
of the heart is represented on it by a single elevation of no
great size, sometimes not amounting to more than one-
twentieth of the height of the curve above the line of zero
or atmospheric pressure. The small oscillations due to the
heart-beat are superposed upon much longer, and often, as
registered in this way, larger waves, caused by the move-
ments of respiration. The line of mean pressure intersects
the respiratory waves midway between crest and trough
(Fig. JO).
So much having been said by way of definition, we have
now to consider the amount of the mean arterial pressure,
the variations which it undergoes, and the factors on which
its maintenance depends.
As to its amount, it will be sufficiently accurate to say
that in the systemic arteries of warm-blooded animals in
general (including birds), and of man in particular, the
mean pressure does not, under ordinary conditions, descend
much below 100 mm. of mercury, nor rise much above 200
mm. ; while in cold-blooded animals it seldom exceeds 50
mm., and may fall as low as 20 mm.
It does not seem possible, at least with our present data, to further
subdivide these two great groups ; nor do we know precisely whether
the distinction depends mainly on morphological or mainly on
physiological differences, whether, that is to say, the warm-blooded
animal has a higher blood-pressure than the cold-blooded chiefly
because its vascular system (and especially its heart) is anatomically
more perfect, or because its heart beats faster and works harder. It
may be that it is for both of these reasons that the birds, which in
certain other respects are more nearly related to the reptiles than
to the mammals, mount, as regards the pressure of the blood, into
the mammalian class, and that a manometer in the carotid of a goose
will rise as high, or almost as high, as in the carotid of a horse, a
sheep, or a dog, while the pressure in the aorta of a tortoise is no
higher than in the aorta of a frog. But we know that the mere
average rate of the heart has of itself comparatively little influence
on the blood-pressure within either group, for the heart of a rabbit
104 A MAXUAL 01- PHYSIOLOGY
beats, on the average, ver)' much faster than the heart of a dog, and
yet the arterial pressure in the dog is certainly at least as great as
in the rabbit. Nor does the size of the body seem to have any
definite relation to the mean pressure, even in animals of the same
species ; and there is no reason to suppose that the pressure is less
in the radial artery of a dwarf than in the radial artery of a giant.
In man the blood-pressure has been estimated by adjust-
ing over an artery an instrument known as a sphygmo-
manometer, which, in its most modern form, consists
essentially of a hollow rubber pad containing liquid or
air, and connected with a metallic (spring) manometer,
graduated beforehand by comparison with a mercurial
manometer. The pad is pressed down over the artery till
the pulse beyond it is just felt to disappear under the finger.
The reading of the manometer is then taken as approxi-
mately equal to the maximum blood-pressure. A slight
deduction must, however, be made on account of the
resistance to compression of the artery itself and the tissues
over it. In the radial artery of a healthy man the blood-
pressure may, perhaps, average 150 mm. of mercury. In
the anterior tibial artery of a boy whose leg was to be
amputated the blood-pressure, measured by means of a
manometer connected directly with the artery, was found
to var}- from 100 to 160 mm., according to the position of
the body and other circumstances.
In a woman sixty years old, in good health, the following
readings were obtained with the sphygmomanometer :
June 28 - - - 126 — 130 mm. of mercury.
„ 29 - - - 126 — 136 „
Aug. 3 - - - 132—144
„ 7 - - - 134-140
„ 12 - - - 136—144 „ (Zadek.)
Such measurements on man, so far as they can be trusted,
show that the mean blood-pressure in one and the same
artery may vary for a considerable time only within com-
paratively narrow limits.
This relative constancy of the general arterial pressure is the result
of a delicate adjustment between the work of the heart, the resistance
of the vessels, and the volume of the circulating liquid. The
quantity of the blood is tolerably steady in health, and considerable
changes may be artificially produced in it (p. 165) without affecting
the pressure in any great degree. On the other hand, the work of
THE CIRCULATIO.X OF THE BLOOI) AND LYMl'll 105
the heart and the jjeripheral resistance are highly variable and vastly
influential. A narrowing of the arterioles throughout the body or in
some extensive vascular tract increases the peripheral re>istance ;
and if the heart continues to beat as before, the pressure must rise.
If the arterioles are widened, while the heart's action remains un-
changed, the pressure must fall. In like manner an increase or a
decrease in the activity of the heart, in the absence of any change in
the peripheral resistance, will cause a rise or a fall in the blood-
pressure. But if a slowing of the heart is accompanied by an increase
in the peripheral resistance, or a dilatation of the arterioles by an
increase in the activity of the heart, the one change may be partially
or completely balanced by the other, and the pressure may vary
within narrow limits or not at all.
Not only is the mean pressure, as measured in a large artery,
tolerably constant, but if recorded simultaneously in two arteries at
different distances from the heart, it is seen to decrease very
gradually so long as the arteries remain large enough to hold a
cannula. It is nearly as high, for instance, in the crural artery of a
dog as in the carotid. It is easy to see that this must be so, for
the resistance of the arteries between the point where the arterioles
are given off and the heart is only a small fraction of the total
resistance of the vascular path ; and we have said (p. 73) that the
lateral pressure at any cross section of a system of tubes through
which liquid is flowing is proportional to the resistance still to be
overcome. This is also the reason why the pressure is always much
lower in the pulmonary arter\- and right ventricle than in the aorta
and left ventricle (only one-third to one-sixth as great), for the total
resistance of the vascular path through the lungs is much less than
that of the systemic circuit.
The Velocity-pulse. — We have seen that the blood is pro-
pelled through the arteries in a series of waves that travel
from the heart towards the periphery. The particles in the
front of the pulse-wave are constantly changing, but since
every section of the arterial tree is successively distended,
every section contains more blood while the pulse-wave is
passing over it than it contained immediatel}- before. And
since there is always a fairly free passage for this blood
towards the periphery, there is a bodily transfer on the
whole of a certain quantity with every wave.
The translation of the blood, instead of being entirely inter-
mittent, as it would be in a rigid tube or in an elastic system
with a slow action of the central pump, is to some extent
constantly going on ; for a portion of a blood-wave is always
passing through every section of the arterial channel. Thus,
we arrive at the same distinction as to the onward move-
io6 A MAXCAL OF PHYSIOLOGY
ment of the blood itself as we previously reached in regard
to the blood-pressure, the distinction between the constant
or permanent factor of the velocity and the periodical factor,
which we may call the velocity-pulse.
The Velocity of the Blood. — By the velocity or rate of flow
of a river we should mean, if the flow were uniform through-
out the whole cross-section, the rate of movement of any
given portion or particle of the water. If we could identify
a portion of the water, we could determine the velocity by
measuring the distance travelled over by that portion in a
given time. If the velocity was uniform over the channel,
we could predict the actual time which would be re-
quired to traverse any fractional part of the measured
distance. If, however, the velocity of the current changed
from point to point, then we could only deduce from our
observation the mean rate of the river for the measured
distance. To determine the actual rate for any given
portion of this distance over which the rate was uniform,
we should have to make a separate observation for this
portion alone.
But as soon as we pass from an ideal frictionless river to
an actual stream, in which the water at the bottom and near
the banks flows more slowly than that in the middle and on
the surface, we are in every case restricted to the notion of
mean velocity. We may distinguish between the velocity of
different parts of the current, between that of the mid-stream
and the side current, the bottom and the surface layers ; but
when we consider the river as a whole, we take cognizance
only of the mean or average velocity. And at any cross-
section this may be defined as the volume of water passing
per hour, or whatever the unit of time may be, divided by
the cross-section of the current. It is evident that this
does not enable us to determine the actual velocity of any
given particle of the water at any given moment within a
measured interval : nor does it tell us whether or not the
average velocity of the current has itself undergone varia-
tions within the period of observation.
We have dwelt upon this point because the measurement
of the velocity of the blood, to which we must now turn.
Tin: CIRCULATION OF THE BLOOD AND TV M I'll 107
involves the same considerations. Within the smaller
arteries, as the microscope shows us, and as we should in an\
case expect from what we know of fluid motion, the blood-
current, apart from the periodical variations in its velocity,
due to the action of the heart, varies in speed from point
to point of the same cross-section. The layer next the
periphery of the vessel, the so-called peripheral plasma-
layer or Poiseuille's space, moves more slowly than the
central portion, the axial stream. In fact, we must suppose
that in the large as well as in the small vessels the layer just
in contact with the vessel-wall is at rest, while the stratum
internal to this slides on it and has its velocity diminished
by the friction. The next layer again slides on the last, but
since this is already in motion, its velocity is not so much
diminished, and so on. The velocity must therefore in-
crease as we pass towards the axis of the bloodvessel, and
reach its maximum there (p. 168).
Again, the velocity must be altered wherever an alteration
occurs in the width of the bed, that is, in the total cross-
section of the vascular system ; for since as much blood
comes back in a given time to the right side of the heart
as leaves the left side, the same quantity must pass in a
given time through every cross-section of the circulation.
Wherever the total section of the vascular tree increases,
the blood-current must slacken ; wherever it diminishes, the
current must become more rapid. Now the total section
increases as we pass from the heart along the branching
arteries, and reaches its maximum in the capillary region. It
gradually diminishes again along the veins, but never becomes
so small as in the arterial tract. W^e must, therefore, expect
the mean velocity to be greatest in the large arteries, less
in the veins, and least in the arterioles, capillaries and
venules. Although in strictness we are only at present con-
cerned with the arteries, it will be well to consider here what
a change of velocity at any part of the vascular channel really
implies. To say that when the channel widens the velocity
diminishes, is not to explain the meaning of this diminution,
A diminution of velocity implies a diminution of kinetic
energy, and it is necessary to know what becomes of the
io8 A MAXUAL OF PHYSIOLOGY
energy that disappears. The stock of energy imparted by
the contraction of the heart to a given mass of blood con-
stantly diminishes as it passes round from the aorta to the
right side of the heart, for friction is constantly being over-
come and heat generated. This energy, as we have seen,
exists in a moving liquid in two forms, potential and kinetic,
the former being measured by the lateral pressure, the latter
varying directly as the square of the velocity. Whenever
the velocity, and therefore the kinetic energy, of a given mass
of the blood is diminished without a corresponding increase
in the potential energy, some of the total stock of energy
must have been used up to overcome resistance (p. 'j^.
In a uniform, rigid, horizontal tube, as has been already remarked,
the velocity (and consequently the kinetic energy) is the same at
every cross-section of the tube, while the potential energy, represented
by the lateral pressure, diminishes regularly along the tube. When
the calibre of the tube varies, it is different. Suppose, for instance,
that the liquid passes from a narrower to a wider part, the velocity
must diminish in the latter. The kinetic energy of visible motion
which has disappeared must have left something in its room. Here
there are three possibilities: (i) The kinetic energy that has dis-
appeared may be just enough to overcome the extra friction in the
wider part of the tube due to eddies and consequent change of
direction of the lines of flow ; in this case the potential energy of a
given mass of the liquid will be the same at the beginning of the
wider part as in the narrower part. The lost kinetic energy will
have been transformed into heat. (2) The kinetic energy which has
disappeared may be greater than is enough to overcome the extra
resistance ; a portion of it must, therefore, have gone to increase the
potential energy, and the lateral pressure will be greater in the wide
than in the narrow part. (3) The lost kinetic energy may be less
than enough to overcome the extra resistance ; in this case both the
lateral pressure and the velocity will be less in the wide than in the
narrow part. It has been experimentally shown that when a narrow
portion of a tube is succeeded by a considerably wider portion,
and this again by a narrow part, case (2) holds : and the liquid may,
under these conditions, actually flow from a place of lower to a place
of higher lateral pressure, t
In the vascular system the conditions are not the same.
The widening of the bed which takes place as we proceed in
the direction of the arterial current is not due to the widen-
ing of a single trunk, but to the branching of the channel
into smaller and smaller tubes. In the larger arteries the
increase of resistance is so gradual that both the potential
THE CIRCULATION OF THE BLOOD AND LVM/'H 109
and the kinetic energy diminish only slowly, and the lateral
pressure and velocity are not much less in the femoral artery
than in the aorta or carotid. But in the capillary region
the friction increases so much that althouf,'h the velocity,
and therefore the kinetic ener^^y, is j[:[reatly less than in the
arteries, the amount of kinetic enerj:^y lost is not upon the
whole equivalent to the energy consumed in overcoming the
extra resistance ; the potential energy of the blood is also
drawn upon, and the lateral pressure falls sharply in the capil-
lary region, as well as the velocity. Where the capillaries
open into the veins, the lateral pressure again sinks abruptly,
while the velocity begins to increase, till in the largest veins
it is probably about half as great as in the aorta.
Where does the extra kinetic energy of the blood in the
veins come from ? To say that the vascular channel again
contracts as the blood passes from the capillaries into the
veins, and that, since the same quantity must flow through
every cross-section of the channel, the velocity must neces-
sarily be greater in the narrower than in the wider part, does
not answer the question. The greater portion of the kinetic
energy of the arterial blood is, as we have seen, destroyed,
or, rather, changed into an unavailable form, into heat, in
the capillary region. The mean velocity of the blood in the
capillaries is not more than --^ to tt^^ of the velocity in the
aorta ; the kinetic energy of a given mass of blood in the
capillaries cannot therefore be more than (o^^)-, or xo^tfit of
its kinetic energy in the aorta. In the veins, taking the
velocity at half the arterial velocity, the kinetic energy of the
mass would be one-fourth of that in the aorta, or at least
10,000 times as great as in the capillary region. This extra
kinetic energ>' comes partly from the transformation of some
of the potential energy of the blood. The resistance in the
veins is very small compared with that in the capillaries ; less
of the potential energy represented by the lateral pressure
at the end of the capillary tract is required to overcome this
resistance, and some of it is converted into the kinetic
energy of visible motion, the lateral pressure at the same
time falling somewhat abruptly. Contributory sources of
kinetic energy in the veins are the aspiration caused by the
A MANUAL OF I'HYSIOLOGY
respiratory movements and the pressure caused by muscular
contraction in general, which, thanks to the valves, always
aids the flow towards the heart. From these two sources
new energy is supplied, to rein-
force the remnant due to the
cardiac systole (p. 121).
Measurement of the Velocity of
the Blood. — i. Direct Obsenatioti. —
\a) This method can be applied to
transparent parts by observing the rate
of flow of the corpuscles under the
microscope. But it is only where the
blood moves slowly, as in the capil-
laries, that the method is of use.
(^) Part of the path of the blood
through a large vessel may be arti-
ficially rendered transparent by the
introduction of a glass tube, of ap
proximately the same bore as the vessel
(Volkmann). The tube is filled with
salt solution, and the blood admitted
by means of a stop-cock at the moment
of observation. The time which the
blood takes to pass from one end of
A, B, glass bulbs : ,i, a metal disc, the tube to the Other is noted, and the
whrch tn'i^^1.t^trd :"the dtc^"1 length divided by the time gives the
E, F, cannula- attached to b. and velocity of the blood in the tube. If
connected with the peripheral and the calibre of the tube is the Same as
central ends of a divided bloodvessel. ^i ^ r .u .. ..u- i »u
At the beginning of the experiment, that of the artery, this IS also the
A and the junction between A and B velocity in the vessel ; but if the Calibre
are filled with oil ; Bis filled with jg different, a correction would have
normal salme or dehbrmated blood : , , ™, , ,
a being turned into the position to be made. 1 he method IS not a
shown in the figure, the blood passes good One, for the reason, among others,
through F and u into A, and the oil ^j^ ^ ^j^ j j^be introduces an extra
IS forced mto B. As soon as the °
blood has reached the mark w, the resistance.
disc a. with the bulbs, is rapidly 2. Ludxvig S Strotnu/ir. — This instfU-
rotated, so that C is now opposite » „ „, tu^ ^., t-u . „f ui^^j
F. The blood now passes into B, ^ent measures the quantity of blood
and the oil is again driven into A. which passes in a given time through
When the oil has reached D. reversal ^hg vessel at the croSS-section where it
is agam made, and so on. .. jt^ -^.^ttl j
IS inserted. It consists of a U-shaped
tube, with the limbs widened into
bulbs, but narrow at the free ends, which are connected with a
metal disc. By rotating the instrument, these ends can be placed
alternately in communication with a cannula in the central, and
another in the peripheral portion of a divided artery ; or they can
be placed so that none of the blood passes throug;h the bulbs,
but all goes by a short-cut. One limb of the instrument is
Fig.
;i. — Siko.MUHR OF
WIG AND Dog 1 EL.
Lui>
THE CIRCULATION OF THE BLOOD AX/) I.YMI'U n,
filled with oil, and the other with defibrinated blood. The limb con-
taining the oil is first put into communication with the central end,
and that containing the blood with the peripheral end of the artery.
The blood from the artery rushes in and displaces the oil into the
other limb, the defibrinated blood passing on into the circulation. As
soon as the blood has reached a certain height, indicated by a mark,
the instrument is reversed, and the oil is again displaced into the
limb it originally occupied. This process is repeated again and again,
the time from beginning to end of an experiment being carefully
noted. The number of times the blood has filled a bulb in that
period, the capacity of the bulb and the cross-section of the vessel
l)eing known, all the data required for calculating the velocity of the
blood in the vessel have been obtained.
Suppose, for example, that the capacity of the bulb up to the mark
is 5 c.c, and that it is filled twelve times in a minute, the quantity
flowing through the cross-section of the artery is i c.c, or i,ooo cub.
mm. per second. Let the diameter of the vessel be 3 mm., then its
, . /3\" 3'i4 X Q
sectional area is ttx /-j =^ =7-06 sq. mm. The velocity is
1000 J
= 141 mm. per second
7 •06
Various improvements in this method have been made, such as
graphic registration of the reversals of the stromuhr.
3. A tube or box, in which swings a small pendulum, is inserted
in the course of the vessel. The pendulum is deflected by the blood,
and the amount of the deflection bears a relation to the velocity
of the stream (Vierordt's hcBmatacho meter : Chauveau and Lortet's
much more perfect dromograph) (Fig. 33).
4. PitoTs Tubes. — If two vertical tubes, a and /', of the form
shown in Fig. 32, be inserted into a horizontal tube in which liquid
is flowing in the direction of the arrow, the level will be higher in a
than would be the case in an ordinary side-tube without an elbow ;
in b it will be lower. For the moving liquid will exert a push on the
column in a, and a pull on that in b. The amount of this push and
pull will vary with the velocity, so that a change in the latter will
correspond to an alteration in the difference of level in the two tubes.
Instruments on this principle have been constructed by Marey and
Cybulbki, the former registering the movements of the two columns
of blood by connecting the tubes to tambours provided with writing
levers, the latter by photography (Fig. 36).
5. The electrical method., described on p. 123, for the measurement
of the circulation time, can also be applied to the estimation of the
mean velocity of the blood between two cross-sections of the arterial
path which are separated by a sufficient distance. For example, salt
solution can be injected into the left ventricle or the beginning of
the aorta, and the interval which it takes to reach a pair of electrodes
in contact with, say, the femoral artery, determined. Knowing the
distance between the point of injection and the electrodes, we can
then calculate the mean velocity.
A MA.\i'AL or PHYSIOLOGY
2.— PnoT's Tubes.
Of these methods, 3 and 4 are alone suited for the study
of the velocity-pulse, that is. the change of velocity occurring
with every beat of the heart.
The curves obtained by
Chauveau'sdromograph show
a general agreement with
blood-pressure tracings taken
by a spring manometer, and
with records of the external
pulse obtained by a sphygmo-
graph. There is a primary in-
crease of velocity correspond-
ing with the ventricular systole, and a secondary increase
corresponding with the dicrotic wave (Fig. 37). Like all
the other pulsatory phenomena,
the velocity-pulse disappears in
the capillaries, and is only
present under exceptional cir-
cumstances in the veins.
Fick, from a comparison of
sphygmographic and plethys-
mographic tracings (p. 116),
taken simultaneously from the
radial artery and the hand, has
demonstrated that in man the
velocity-pulse exhibits the same
general characters as in animals
(Figs. 34 and 35). And v. Kries
has confirmed Fick's conclu-
sions by actual records of the
velocity-pulse obtained by means
of an arrangement called a gas
tachograph (Fig. 38).
This consists of a plethysmo-
graph connected with the tube
of a gas-burner. W^hen the
part enclosed in the plethys-
mograph expands, air issues
from the connecting tube, and
Dk«j.mo-
A, tube connected with bloodvessel ;
B, metal cylinder in communication
with A. The upper end of B has a
hole in the centre, which is covered by
a membrane, m, through which a lever,
C, passes ; C has a small disc/, at its
end, which projects into the lumen of
A, and is deflected in the direction of
the blood-siream through A. The de-
flection is registered by a recording
tambour in communication by the tube
E with a tambour D, the flexible
membrane of which is connected with
the lever or p-.-nduluni C.
THE CIRCULATION OF THE BLOOD AM) LY.Uril 113
causes an increase in the height of the llame. When thu
part shrinks during diastole, air is drawn in from the flame,
which is depressed. Since the speed of the blood in the
iMC. 34.
1' !'■■ 35-
KiG. 34. — The highest of the three curves is a plethysniographic record taken from
the hand ; the second curve is a sphygmogram taken simultaneously from the corre-
sponding radial artery ; the lowest (interrupted) curve is the curve of velocity deduced
from a comparison of the first two. (Fick.
Fig. 35. — Simultaneous plethysniographic and sphygmographic tracings.
Fh;. 36. — Cybui.ski's Arrangement kor Recording Variations in iiik
Vei.ocity ok the Blood.
.\, tube connected with central, B with peripheral end of divided bloodvessel. The
blood stands higher in the tube C than in D. A beam of light passing through the
meniscus in both tubes is focussed by the lens L on the travelling photographic
plate E. The velocity at any moment is deduced from the height of the meniscus in
the two tubes C and D.
veins may be considered constant during the time of an
experiment, the rate at which the volume of the part alters
114
A MANUAL OF PHYSIOLOGY
at any moment is a measure of the pulsatory change of
velocity in the arteries of the part. And by photographing
the movements of the flame on a travelling sensitive surface,
the velocity-pulse is directly recorded.
l-ii;. 37. — SiMULTANKOus Tracin(;s ok thk \'Ei,ocn y (Uri'KR Curve) and
Pressurk (Lower Curve). (Lortet.)
Tlie tracings were taken from the carotid artery of a horse. The curve of velocity
\v;is obtained by the droinograph. The dicrotic wave is marked on it. The slightly
curved ordinates drawn through the curves indicate corresponding points.
The mean velocity, like the mean blood-pressure, is^more
variable in the large arteries near the heart than in the
smaller and more distant arteries. Dogiel found in measure-
ments taken with the stromuhr (a good instrument for the
Fio. 38. — Photographic Record oe the Velocitv-i>ui.se ohiained rv ^\\\■.
Gas Tachograph (v. Kries).
The upper curve is the photographic representation of the movements of the flame,
and corresponds to the curve of velocity.
estimation of mean speed), within a period of two minutes,
velocities ranging from over 200 mm. to under 100 mm. per
THE CIRCULATfON OF THE liLOOD AND LYM/'/f 115
second in the carotid of the rabbit, and from over 500 mm.
to less than 250 mm. in the carotid of the dog. Chauveau,
with the dromoj^'raph, found the velocity in the carotid of a
horse to be 520 mm. per second during systole, 150 mm.
during diastole, 220 mm. during the period of the dicrotic
wave.
It is probable, however, that if these numbers are at all
accurate for bloodvessels in the immediate neighbourhood
of the heart, there must be a rapid diminution in the
velocity even while the arteries are still of considerable
calibre. For it has been found by the electrical method
that, in anaesthetized dogs at any rate, as is shown in the
following table, the mean velocity between the origin of the
aorta and the crural artery in the middle of the thigh is
usually less than 100 mm. per second.
No. of
Body- i
Distance between
point of injection
and electrodes,
in miliime'res.
Average time be-
tween injection
Average
Average
velocity
Average
distance
experi-
weight
and arrival of the
pulse-rate
per second,
traversed per
ment.
in kflos.
salt solution,
in seconds.
per minute.
in milli-
metres.
heart-beat,
in mm.
I.
34-55
420
4-62
105
909
51-9
II.
17-5
495
yi
69
86-8
75-4
III.
1499 1
400
5-0
102
80
47
IV.
10-32 1
470
7-12
74-5
72-9
587
\'.
7165;
330
7-83
46-3
(weak beat)
42-1
54-5
In I. the injecting cannula was in the descending part of the
thoracic aorta, in V. at the very origin of the aorta, and in II., III.
and IV. in the left ventricle.
As to the speed of the blood in the arteries of man, our
data are insufficient for more than a loose estimate. But it
does not seem likely that the mean velocity of a particle of
blood in moving from the heart to the femoral artery can
exceed 150 mm. per second for the whole of its path. This
would correspond to rather more than a third of a mile per
hour. In the arch of the aorta the average speed may be
twice as great. ' The rivers of the blood ' are, even at their
fastest, no more rapid than a sluggish stream. A red
corpuscle, even if it continued to move with the velocity
with which it set out through the aorta, would only cover
8—2
Il6 A MANUAL OF PIIYSIOLOC.Y
about 15 miles in twenty-four hours, and would require five
years to go round the world.
The Volume -pulse. — When the pulse-wave reaches'a part it
distends its arteries, increases its volume, and gives rise
to what may be called the volume-pulse. This may be
readily recorded by means of a plethysmograph, an instru-
ment consisting essentially of a chamber with rigid walls
which enclose the organ, the intervening space being filled
up with liquid (Fig. 39). The movements of the liquid are
transmitted either through a tube filled with air to a record-
ing tambour, or directly to a piston or float acting" upon a
writing lever. Special names have been given to plethys-
Ku;. 39. — I'LEl llYSMOGKAl'll KOR ArM.
F, float attached by A to a lever which records variations of level of the water in H,
and therefore variations in the volume of the arm in the glass vessel C. Or the
plethysmograph may be connected to a recording tambour. The tubulure at the
upper part of C is closed when the tracing is being taken.
mographs adapted to particular organs ; for example, Roy's
oncometer for the kidney. The method has been successfully
applied to the investigation of circulatory changes in man,
a finger, a hand or an entire limb being enclosed in the
plethysmograph. With a fairly sensitive arrangement, every
beat of the heart is represented on the tracing by a primary
elevation and a dicrotic wave. The general appearance of
the curve is very similar to that of an ordinary pulse-tracing,
though there are some differences of detail, especially in
the time relations. A volume-pulse has been actually ob-
served not only in limbs and portions of limbs, but also (in
animals) in the spleen, kidney and brain, and other organs,
and in the orbit. In the soft tissues of the mouth and
THE CIRCULATION OF THE BLOOD AND LYMril 117
pharynx, too, a volume-pulse (the so-called cardio-pneumatic
movement) can[[bc detected by chanj^es in the pressure of
the air in the respiratory passages, which may even reveal
themselves by a variation with each beat of the heart in the
intensity of a note prolonged in singing, especially after
fatigue has set in (Practical Exercises, p. 183).
Doubtless the weight of an organ would also show a pulse cor-
responding to the beat of the heart, if it could be isolated from the
surrounding tissues (except for its vascular connections), and attached
to a recording balance, as could probably be done with a kidney.
Further, it is possible that the temperature, at least of the super-
ficial parts, is altered with every beat of the heart. For the amount
of heat given off by the blood to the skin increases with its mean
velocity, and, therefore, although the difference may not in general
be measureable, more heat is presumably given off during the
Fig. 40. — PLETHYSMOGRArn Tracing from Arm.
The tracing was taken by means of a tambour connected with the plethysmograph.
The dicrotic wave is distinctly marked.
systolic increase of velocity than during the diastolic slackening.
In fact, with a very sensitive instrument (bolometer, or resistance
thermometer, p. 479) applied directly to an exposed artery, indi-
cations of a change of temperature of the vessel-wall with each
beat of the heart have been observed. And this, along with other
considerations, suggests that, at any rate in certain situations and
under certain conditions, there may even be a pulse of chemical
change ; that is, a slight and as yet doubtless inappreciable ebb and
flow of metabolism corresponding to the rhythm of the heart.
The Circulation in the Capillaries. — From the arteries the
blood passes into a network of narrow and thin- walled
vessels, the capillaries, which in their turn are connected
with the finest rootlets of the veins. Physiologically, the
arterioles and venules must for many purposes be included
in the capillary tract, but the great anatomical difference—
ii8
A MANUAL OF PHYSIOLOGY
the presence of circularly-arranged muscular fibres in the
arterioles, their absence in the capillaries — has its physio-
logical correlative. The calibre of the arterioles can be
altered by contraction of these fibres under nervous in-
fluences ; the calibre of the capillaries, although it varies
passively with the blood-pressure, and is possibly to some
extent affected by active contraction of the endothelial cells,
cannot be under the control of vaso-motor nerves acting on
muscular fibres.
Harvey had deduced from his observations the existence
of channels between the arteries and the veins. Malpighi
was the first to observe the capillary blood-stream with the
Fig. 41.
-Diagram to Illustrate ihe .Sloik ok I're^sure along
THE Vascular System.
A, arterial ; C, capillary ; V, venous tract. The interrupted line represents the line
of mean pressure in the arteries, the wavy line indicating that the pressure varies with
each heart-beat. The line passes below the abscissa a.\is (line of zero or atmospheric
pressure) in the veins, indicating that at the end of the venous system the pressure
becomes negative.
microscope, and thus to give ocular demonstration of the
truth of Harvey's brilliant reasoning. He used the lungs,
mesentery and bladder of the frog. The web of the frog,
the tail of the tadpole, the wing of the bat, the mesentery of
the rabbit and rat, and other transparent parts, have also
been frequently employed for such investigations. From
the apparent velocity of the corpuscles and the degree of
magnification, it is easy to calculate the velocity of the
capillary blood-stream. It has been estimated at from
•2 to "8 mm. per second in different parts and different
animals.
The comparative slowness of the current and the dis-
THE CIRCULATIOX OF THE BLOOD AXD LYMPH 119
appearance of the pulse are the chief characteristics of
the capillary circulation. The explanation we have already
found in the great resistance of the narrow and much-
branched vessels. Although the average diameter of a
capillary is only about 10 /u, (5 to 20 ix in different parts of
the body), the number of branches is so prodigious that the
total cross-section of the systemic capillary tract has been
estimated at 500 to 700 times that of the aorta.
The total cross-section of the vascular channel gradually
widens as it passes away from the left ventricle. In the
capillary region it undergoes a great and sudden increase.
At the venous end of this region the cross-section is again'
somewhat abruptly contracted, and then gradually lessens as
the right side of the heart is approached ; but the united
sectional area of the large thoracic veins is greater than that
of the aorta.
The blood-pressure in the capillaries has been measurud by
weighting a small plate of glass laid on the back of one of the
fingers behind the nail, until the capillaries are just emptied, as
shown by the paling of the skin (v. Kries), or by observing the
height of a column of lic^uid that just stops the circulation in a
transparent part (Roy and Graham Brown). The last-named
observers found that a pressure of 100 to 150 mm. of water (about
7 to II mm. of Hg) was needed to bring the blood to a standstill in
the capillaries and veins of the frog's web ; that is, about a third of
the blood-pressure in the frog's aorta. The pressure in the capil-
laries at the root of the nail in man varies from 30 to 50 mm. of
mercury.
Under certain conditions the pulse-wave may pass into
the capillaries and appear beyond them as a venous pulse.
Thus, we shall see that when the small arteries of the
submaxillary gland are widened, and the vascular resistance
lessened, by the stimulation of the chorda tympani nerve,
the pulse passes through to the veins. And, normally, a
pulse may be seen in the wide capillaries of the nail-bed
— especially when they are partially emptied by pressure —
as a flicker of pink that comes and goes with every beat of
the heart.
We have seen that the lateral pressure at any point of a
uniform rigid tube through which water is flowing is propor-
tional to the amount of resistance in the portion of the tube
I20 A MAXl'AL OF ri/YS/OLOGY
between this point and the outlet. In any system of tubes
the sum of the potential and kinetic energy must diminish
in the direction of the How; and although the problem is
complicated in the vascular system by the branching of the
channel and the variation in the total cross-section, yet
theory and experiment agree that in the larger arteries the
lateral pressure diminishes but slowly from the heart to
the periphery, the resistance being small compared with the
resistance of the whole circuit. In the capillary region the
vascular resistance abruptly increases ; the velocity (and
therefore the kinetic energy) abruptly diminishes, and the
Fig. 42. — Relation ok BLOOui'REbsUKE, VEi.ocny. and Cross-section.
The curves P, V and S represent the blood-pressure, velocity of blood, and total
cross-section respectively in the arteries A, capillaries C, and veins \'.
lateral pressure falls much more steeply between the begin-
ning and the end of this region than between the heart and
its commencement. In the veins only a small remnant of
resistance remains to be overcome, and the lateral pressure
must sink again rather suddenly about the end of the capil-
lary tract. Fig. ^2 shows by a rough diagram the manner
in which the pressure, velocity and cross-section probably
change from part to part of the vascular system.
The Circulation in the Veins. — The slope of pressure, as we
have just explained, must fall rather suddenly near the
beginning and near the end of the capillary tract. It con-
tinues falling as we pass along the veins, till the heart is
again reached. In the right heart, and in the thoracic
portions of the great veins which enter it, the pressure may
be negative — that is, less than the atmospheric pressure.
THE CIRCULATIOS OF THE liLOOD AN/) LYMPH 121
And since nowhere in the venous system is the pressure
more than a small fraction of that in the arteries, its
measurement in the veins is correspond in/:(l}' difficult, because
any obstruction to the normal flow is apt to artificially raise
the pressure. A manometer containing some lighter liquid
than mercury, such as water or a solution of magnesium
sulphate, is usually employed, in order that the difference of
level may be as great as possible. In the sheep the pressure
was found to be 3 mm. of mercury in the brachial, and
about II mm. in the crural vein; in the dog's portal vein
about 10 mm.
The venous pressure being so low, or, in other words, the potential
energy which the systole of the heart imparts to the blood being so
greatly exhausted before it reaches the veins, other influences begin
here appreciably to affect the blood-stream :
1. Contraction of the Muscles. — This compresses the neighbouring
veins, and since the blood is compelled by the valves, it it moves
at all, to move towards the heart, the venous circulation is in this
way helped.
2. Aspiration of the Thorax. — In inspiration the intrathoracic
pressure, and therefore the pressure in the great thoracic veins, is
diminished, and blood is drawn from the more peripheral parts of the
venous system into the right heart (p. 250).
3. Aspiratiofi of the Heart. — When the heart, after its contraction,
suddenly relaxes, the endocardiac pressure becomes negative, and
blood is sucked into it, just as when the indiarubber ball of a
syringe is compressed and then allowed to expand. But we cannot
attribute any great importance to this ; and, of course, it is only the
relaxation of the right ventricle which could directly affect the venous
circulation.
4. Every change of position of the limbs, as in walking, aids
the venous circulation (Braune), and this independently of the
muscular contraction. When the thigh of a dead body is rotated
outwards, and at the same time extended, a manometer connected
with the femoral vein shows a negative pressure of 5 to 10 mm. of
water. When the opposite movements are made, the pressure
becomes positive.
It follows from the number of casually-acting influences
which affect the blood-flow in the veins that it cannot be
very regular or constant. We have seen that in the great
arteries there is a considerable variation of velocity and of
pressure with every beat of the heart ; and although this
variation is absent from the veins, since normally the pulse
does not penetrate into them, the venous flow is, never-
t22 A MANUAL 01- PHYSIOLOGY
theless, as a matter of fact, more irregular than the arterial.
So that if it is difficult to give a useful definition of the
term ' velocity of the blood ' in the case of the arteries,
it is still more difficult to do so in the case of the veins.
Where voluntary movement is prevented, one potent cause
of variation in the venous flow is eliminated ; and in
curarized animals certain observers have found but little
difference between the mean velocity in the veins and in the
corresponding arteries. Others have found the velocity in
the veins considerably less, which is indeed what we should
expect from the fact that the average cross-section of the
venous system is greater than that of the arterial system.
To sum up, we may conclude that, upon the \,hole, the
blood passes with gradually-diminishing velocity from the
left ventricle along the arteries ; it is greatly and somewhat
suddenly slowed in the broad and branching capillary bed ;
but the stream gathers force again as it becomes more and
more narrowed in the venous channel, although it never
acquires the speed which it has in the aorta.
To complete the account of the circulation in the veins, it
must be added that in some healthy persons, but more fre-
quently and more distinctly in cases of incompetence of the
tricuspid valve, a venous pulse may be seen in the jugular
vein ; but this pulse travels from the heart against the blood-
stream, not with it.
The Circulation-time. — Hering was the first who attempted
to measure the time required by the blood, or by a blood-
corpuscle, to complete the circuit of the vascular system.
He injected a solution of potassium ferrocyanide into a vein
(generally the jugular), and collected blood at intervals from
the corresponding vein of the opposite side. After the
blood had clotted, he tested for the ferrocyanide by addition
of ferric chloride to the serum. The first of the samples
that gave the Prussian blue reaction corresponded to the
time when the injected salt had just completed the circula-
tion.
This method was improved by \'ierordt, who arranged a number
of cups on a revolving disc below the vein from which the blood was
to be taken. In these cups samples of the blood were received,
and the rate of rotation of the disc being known, it was possible to
THE CIRCULATION OF THE BLOOD AND LYMl'II 123
measure ihe intLrval between the injection and appearance of the
salt with considerable accuracy. Hermann made a further advance
by allowing the blood to play upon a revolving drum covered with a
paper soaked in ferric chloride, and by using the less poisonous
sodium ferrocyanide for injection.
Even as thus modified, the method laboured under serious defects.
It was not possible to make more than a single observation on one
animal, at least without allowing a considerable interval for the
elimination of the ferrocyanide, and, further, the method was unsuited
for the estimation of the circulation time in individual organs. In
both of these respects the more recently introduced electrical method
presents considerable advantages ; for by its aid we can not only
obtain satisfactory measurements of the circulation time in such
organs as the lungs, liver, kidney, etc., but we can repeat them an
indefinite number of times on the same animal.
A cannula, connected with a burette (or a Mariotte's bottle, or a
syringe), containing a solution of sodium chloride (usually a i"5 to
2 per cent, solution), is tied into a vessel — say, the jugular vein.
Suppose that the time of the circulation from the jugular to the
carotid is required — that is, practically the time of the lesser or
pulmonary circulation. A small portion of one carotid artery is
isolated, and laid on a pair of hook-shaped platinum electrodes,*
covered, except on the concave side of the hook, with a layer of
insulating varnish. To further secure insulation, a bit of very thin
sheet-indiarubber is slipped between the artery and the tissues.
By means of the electrodes the piece of artery lying between them,
with the blood that flows in it, is connected up as one of the
resistances in a Wheatstone's bridge (p. 519). The secondary coil
of a small inductorium, arranged for giving an interrupted current,
and with a single Daniell cell in its primary, is substituted
for the battery, and a telephone for the galvanometer, according to
Kohlrausch's well-known method for the measurement of the re-
sistance of electrolytes. It is well to have the induction machine
set up in a separate room and connected to the resistance-box by
long wires so that the noise of the Neefs hammer may be inaudible.
The bridge is balanced by adjusting the resistances until the sound
heard in the telephone is at its minimum intensity, the secondary coil
being placed at such a distance from the primary that there is no
sign of stimulation of muscles or nerves in the neighbourhood of
the electrodes when the current is closed. A definite, small quantity
of the salt solution is now allowed to run into the vein by turning
the stop-cock of the burette. It moves on with the velocity of the
blood, and reaching the artery on the electrodes causes a diminution
of its electrical resistance (p. 34). This disturbs the balance of the
bridge, and the sound in the telephone becomes louder. The time
from the beginning of the injection to the alteration in the sound is
* The electrodes can easily be made by beating out one end of a piece
of thick platinum wire to a breadth of 5 or 6 mm., and then bending the
flattened part into a hook.
124 A MANUAL 01' PHYSIOLOGY
the circulation-time between jugular and carotid, and it can be easily
read off by a stop-watch. Instead of the telephone a galvanometer
may be used, the eciual and oppositely directed induction shocks
being replaced by a weak voltaic current and the platinum by un-
polarizable electrodes (p. 526). But this is somewhat less convenient,
and in general not more accurate.
The circulation-time of an organ like the kidney can be measured
by adjusting a pair of electrodes under the renal artery and another
under the renal vein, and reading off the interval recjuired by the
salt solution to pass from the point of injection first to the artery
and then to the vein. The difference is the circulation-time through
the kidney.
For certain purposes, and particularly for measurements on small
animals like the rabbit, or on organs whose vessels are too delicate
to be placed on electrodes without the risk of serious interference
with the circulation, another method may be employed with ad
vantage. It depends on the injection of a i)igment, like methylene
blue, which at first overpowers the colour of the blood and shows
through the walls of the bloodvessels, but is soon reduced to a
colourless substance, methylene white. The details of the method
are given in the Practical Exercises (p. 192).
It may be said in general terms that in one and the same
animal the time of the lesser circulation is short as compared with
the total circulation - time, relatively constant, and but little
affected by changes of temperature. In animals of the same
species it increases with the size, but more slowly, and rather in
proportion to the increase of surface than to the increase of weight.
Thus a dog weighing 2 kilogrammes had an average pulmonary
circulation - time of 4-05 seconds, while that of a dog weighing
1 1 "8 kilos was 87 seconds, and that of a dog with a body-weight of
1 8" 2 kilos only io'4 seconds. It is probable that in a man the
pulmonary circulation-time is not usually much less than 1 2 seconds,
nor much more than 15 seconds.
The circulation time in the kidney, spleen and liver is
relatively long and much more variable than that of the
lungs, being easily affected b)- exposure and changes of
temperature (increased by cold, diminished by warmth).
In a dog of 13*3 kilos weight the average circulation-time
of the spleen was i0"95 seconds; kidney, i3"3 seconds;
lungs, 8*4 seconds. The circulation-time of the stomach and
intestines is (in the rabbit) comparatively short, not exceed-
ing very greatly that of the lungs, but it is lengthened by
exposure. The circulation-time of the retina and that of the
heart (coronary circulation) are the shortest of all.
THE CIRCULATION OF THE liLOOD A.VIJ LYMPH 125
The total circulation-time is pro[)erly the time required for the
whole of the blood to complete the round of the pulmonary and
systemic circulation. But there are many routes open to any given
particle of blood in making its systemic circuit. If it passes from
the aorta through the coronary circulation it takes an exceedingly
short route. If it passes through the intestines and liver, or through
the kidney, or through the lower limbs, it takes a long route. So
that to determine the total circulation-time by direct measurement
Fig 43.— Measurement of the Pulmon.^ry Circulation-time in
Rabbit by Injection ok Methylene Blue.
we must know (i) the quantity of blood that passes on the average
by each path in a given time, and (2) the average circulation-time of
each path If the average weight of blood in each organ be repre-
sented by «v 7.',, iv.„ etc.; and the average circulation - times
by ^, t-2, h-> e'<^- ' ^"^ * ^^ ^^^ ^°^^^ systemic circulation-tirne ; then
w t w,-, w^L, etc., will represent the quantity of blood passing
through each organ in / seconds, since in the average circulation-
126 A MAXUAL 01- rilYSIOLOGY
time of an organ the whole of the blood in it at the beginning of
the period of observation will have been exchanged for fresh blood.
But the whole of the blood in the body, which we may call
W, passes once round the systemic circulation in / seconds. There-
fore, 7i\- + 7C'.,- + 7C'.,-, etc., = W . In this equation everything can be
determined by experiment except /, and therefore / can be calculated.
Adding / to the pulmonary circulation-time, we arrive at the total
circulation-time.
Although our experimental data are as yet too meagre to make the
calculation more than a rough approximation, it appears probable
that in certain animals the total circulation-time is five or six times
as great as the pulmonary circulation-time. If the same ratio holds
good in man, the total circulation-time is unlikely to be much less
than a minute or much greater than a minute and a quarter. We
shall see directly that this estimate is confirmed by data derived
from a different source. In the meantime, we may use it provisionally
to calculate the work done by the heart. Let us take for simplicity
the total circulation-time as i minute in a 70-kilo man, the cjuantity
of blood as 5^ kilos, and the mean pressure in the aorta as 200 mm.
of mercury. Up to the time when the semilunar valves are opened,
the work done by the left ventricle is spent in raising the intra-
ventricular i^ressure till it is sufticient to overcome the pressure in
the aorta. If a vertical tube were connected with the left ventricle,
the blood would rise till the column was of the same weight as a
column of mercury of equal section and 200 mm. high. This column
of blood would be about 2-56 metres in height. If a reservoir were
placed in communication with the tul)e at this height, a (juantity of
blood C(iual to that ejected from the ventricle would at each systole
pass into the reservoir ; and the work which the blood thus collected
would be capable of doing, if it were allowed to fall to the level of
the heart, would be equal to the work expended by the heart in
forcing it up. Thus, in i minute the work of the left ventricle would
be equal to that done in raising 5^ kilos of blood to a height of
2"56 metres — that is, about 14 kilogramme-metres; in 24 hours it
would be, say, 20,000 kilogramme-metres. Taking the mean pressure
in the pulmonary artery at one third of the aortic pressure (the
estimates of different observers vary from one-third to one-sixth in
different animals), we get for the daily work of the right ventricle
about 7,000 kilogramme-metres. The work of the two ventricles is
thus about 27.000 kilogramme-metres, which is enough to raise a
weight of half a stone from the bottom of the deepest mine in the
world to the top of its highest mountain, or to raise the man himself
to more than twice the height of the spire of Strasburg Cathedral.
By friction in the bloodvessels this work is almost all changed into
its equivalent of heat, namely, about 63,000 small calories (p. 479).
Further, since the contraction of the heart is always maximal (p. 131),
and there is reason to believe that the quantity of blood ejected at a
single systole by the left ventricle (being dependent upon the inflow
THE CIRCULATIOS OF THE BLOOD AM) LY .)//>// 127
from tlie i)iilmonary veins, and therefore upon the inllow into the
right side of the heart from the systemic veins) varies widely, some
of the mechanical effect of tlie contraction must he wasted when
the (juantily is less than the ventricle is capable of expelling.
Output of the Heart. — If 5^ kilos of blood pass through the heart
in I minute with the average pulse-rate of 72 per minute, the quantity
ccoo
ejected by either ventricle with every systole will be =-- 76 grm.,
72
or about 72 c.c. This is much less than the amount assigned by
Vierordt, which has gained the greatest vogue in physiological text-
books, but all recent observers who have directly measured the out-
put are agreed that Vierordt's estimate is too high. Thus, in a series
of experiments on more than 20 dogs, ranging in weight from 5 to
nearly 35 kilos, it has been shown that the output, or contraction
volume, as it is sometimes called, of the left ventricle per kilo of
body-weight diminishes as the size of the animal increases ; and the
relation between body-weight and output is such that in a man
weighing 70 kilos we can hardly suppose that the ventricle discharges
more than 105 grm. of blood per second, or 87 grm. (80 c.c ) per
heart-beat with a pulse-rate of 72. Putting this result along with
that deduced from the circulation-time, we can pretty safely conclude
that the average amount of blood thrown out by each ventricle at
each beat is not more than 70 or 80 c.c. Zuntz, from the quantity
of oxygen absorbed by the blood in the lungs, has estimated the
output at 60 c.c. But according to him this may be doubled during
severe muscular work, when, as a matter of fact, by the aid of the
X-rays or by percussion of the chest, the volume of the heart may
be shown to be considerably increased. In the middle of last
century, Passavant calculated the output at 46-5 grm., which is almost
certainly too low.
The Relation of the Nervous System to the Circulation.
So far we have been considering the circulation as a purely
physical problem. We have spoken of the action of the
heart as that of a force-pump, and perhaps to a small extent
that of a suction-pump too. We have spoken of the blood-
vessels as a system of more or less elastic tubes through
which the blood is propelled. We have spoken of the re-
sistance which the blood experiences and the pressure which
it exerts in this system of tubes, and we have considered
the causes of this resistance, the interpretation of this
pressure, and the physical changes in the vascular system
that may lead to variations of both. But so far we have
not at all, or only incidentally and very briefly, dealt with
128 .1 MANUAL OF PHYSIOLOGY
the physiolop^ical mechanism through which the physical
changes are brought about. We have now to see that
although the heart is a pump, it is a hving pump ; that
although the vascular system is an arrangement of tubes,
these tubes are alive ; and that both ht-art an(J vessels are
kept constantly in the most delicate poise and balance by
impulses passing from the central nervous system along the
nerves.
In many respects, and notably as regards the influence of
nerves on it, we may look upon the heart as an expanded,
thickened and rhythmically-contractile bloodvessel, so that
an account of its innervation may fitly precede the descrip-
tion of vaso-motor action in general.
The Relation of the Heart to the Nervous System. — A very
simple experiment is sufficient to prove that the beat of the
heart does not depend on its connection with the central
nervous system, for an excised frog's heart may, under
favourable conditions, of which the most important are a
moderately low temperature, the presence of oxygen and the
prevention of evaporation, continue to beat for days. The
mammalian heart also, after removal from the body, beats
for a time, and indeed, if defibrinated blood be artificially
circulated through the coronary vessels, for several hours.
But although this proves that the heart can beat when
separated from the central nervous system, it does not
prove that nervous influence is not essential to its action,
for in the cardiac substance nervous elements, both cells and
fibres, are to be found.
The Intrinsic Nerves of the Heart. — In the heart of the frog
numerous nerve-cells are found in the sinus venosus, espe-
cially near its junction with the right auricle (Remak's
ganglion). A branch from each vagus, or rather from each
vago-sympathctic nerve (for in the frog the vagus is joined a
little below its exit from the skull by the sympathetic),
enters the heart along the superior vena cava (pp. 173, 174).
Running through the sinus, with whose ganglion cells the true
vagus fibres, or some of them, are believed to make physiological
junction (p. 141), the nerves i)ursue their course to the auricular
septum. Here they form an intricate plexus, studded with ganglion
cells. From the plexus nerve fibres issue in two main bundles,
riiE CI RcrLA rioN of rini blood axd lymi'ii 129
which pass down the anterior and posterior borders of tin se[)turn
to end in two clumps of nerve cells (Bidder's ganglia), situated at
the auriculo-ventricular groove. These ganglia in turn give off
fine nerve-bundles to the ventricle, which form three plexuses, one
under the pericardium, another under the endocardium, and a third
in the muscular wall itself, or myocardium. From the last of these
plexuses numerous non-medullated fibres run in among the muscular
fibres and end in close relation with them. Similar jilexuses of nerve-
fibres exist in the mammalian ventricle. F>ut while a few scattered
ganglion cells arc found in the upper part of the ventricular wall,^
neither in the mammal nor in the frog have any been as yet demon-
strated in the a|)ical half.
Cause of the Rhythmical Beat of the Heart. — It was long sup-
posed that the presence of ganglion cells was the clue to the
explanation of the automatic contraction of the heart, and
by some they are still looked upon as centres from which
impulses are sent out at regular intervals to the cardiac
muscular fibres. Nor on a superficial view are arguments
wanting in support of this opinion. We divide, in the frog,
the sinus which contains ganglion cells from the lower
portion of the heart, and it continues to pulsate. We cut
off the apex, which contains no ganglion cells and it remains
obstinately at rest. Further, if, without actually cutting off
the apex, we dissever it physiologically from the heart by
crushing a narrow zone of tissue midway between it and the
auriculo-ventricular groove, we appear to abolish for ever its
power of rhythmical contraction. The frog may live for
many weeks, but in general the apex remains in permanent
diastole. It can be caused to contract by an artificial
stimulus, but it neither takes part in the spontaneous con-
traction of the rest of the heart, nor does it start an in-
dependent beat of its own. What can be simpler than to
suppose that the sinus beats because it has ganghon cells in
its walls, and that the apex refuses to beat because it has
none ? But if we pursue our investigations a little farther,
we shall find that the matter is more complex. Let us
inquire, for instance, what happens to the auricles and
ventricle of the frog's heart when the sinus is cut off. The
answer is that, as a rule, while the sinus goes on beating,
the rest of the heart comes to a standstill, in spite of the
numerous ganglion cells in the auricular septum and the
9
I30 A MAM'.ir or rHYSlOLOi^Y
auriculo-ventricular groove. Not only so, but if the ventricle
be now severed from the auricles by a section carried through
the groove, it is the former, poor in nerve-cells though it
be, which will usually first begin to beat. We shall again
have to discuss this experiment (p. 142). It, at any rate,
proves this, that the presence of ganglion cells is not the
only condition on which the power of automatic rhythmical
contraction depends. For a portion of the heart rich in
ganglion cells ma}-, under certain circumstances, refuse to
beat. The converse is also true : rhythmical contraction,
either spontaneous or artificially induced, may be observed
in many organs that are free from nerve-cells, or in which,
at least, no nerve-cells have ever been discovered. The
embryonic heart, for instance, beats with a regular rhythm
at a time when as yet no ganglion cells have grown into its
walls. The isolated bulbus aorta; in the frog, which seems to
contain no ganglion cells, and even the tiniest microscopic
fragments of it, will pulsate spontaneously. A portion of
the apex of a cat's ventricle, presumably ganglion-free, con-
tinues for a considerable time to beat with a rhythm of its
own when connected with the rest of the heart by nothing
but its bloodvessels. We know, further, that the ganglion-
free apex of the frog's heart, lifeless as it seems when left
to itself, can be caused to execute a long and regular series
of pulsations when its cavity is distended with defibrinated
blood, or serum, or certain artificial nutritive fluids, or even
normal saline solution ; that strips of the ventricle of the
tortoise, also free from ganglia, can be made to beat rhythmi-
cally; that the rhythmical contraction of the smooth muscle
of the ureter of the rabbit and dog is aft'ected by distension
much as that of the cardiac muscle is ; and, finally, that
even ordinary skeletal muscle can contract in a rhythmical
manner under the stimulus of a certain tension and in
certain saline solutions.
We can hardly doubt, in view of such facts — and others of
like significance might easily be added — that the power of
automatic rhythmical contraction possessed by the heart is
essentially a property of the cardiac muscle, a property
which belongs also, though in much smaller degree, to
THE CIRCULATIOX OF THE BLOOD AND LYMPH 131
muscular tissue in other parts of the vascular system, ^.^'.,
in the central artery of the rabbit's ear, and the veins of the
bat's wing. At the same time it must be remembered that
full and formal proof of the myogenic origin of the cardiac
beat has not yet been given. It is probable, but not proven.
We have seen that there is a normal order or sequence in
which the different parts of the heart contract, the contrac-
tion beginning both in the frog and in the mammal at the
base, and travelling more or less rapidly towards the apex.
It would seem that the muscular tissue of the part of the
heart in which the beat begins has a higher rhythmical power
than the rest of the cardiac muscle, and that normally the
contraction is only propagated, not originated, by the lower
portion of the heart. But under certain conditions the
normal sequence can be reversed. In the heart of the
skate, it is easy by stimulating the bulbus arteriosus to
cause a contraction passing from bulbus to sinus. Not only
may the normal sequence be changed in the entire heart,
but any part of the heart may apparently have its rhythmical
power exalted by appropriate means, so that it can be
brought to beat rhythmically when isolated from the rest of
the heart. On the other hand, the power of propagating the
contraction may be artificially interfered with — increased by
heat, diminished by cold, aboHshed by pressure or fatigue.
If, e.g., a frog's heart is supported hy a clamp fixed in the
auriculo-ventricular groove, and the clamp is tightened or
the ventricle cooled, while the auricle is at the ordinary tem-
perature, or if the auricle is heated while the ventricle is
at the ordinary temperature, only every second or third
auricular beat will be followed by a ventricular beat (p. 172).
In addition to its marked power of rhythmical contraction,
the cardiac muscle is distinguished from ordinary skeletal
muscle by other peculiarities. The most striking of these is
that * it is everything or nothing with the heart ' ; in other
words, the heart muscle, when it contracts, makes the best
effort of which it is capable at the time ; a weak stmiulus, if
it can just produce a beat, causes as great a contraction as
a strong stimulus. Another peculiarity is that a true tetanus
of the cardiac muscle cannot be obtained at all, or only under
9—2
132 A MANUAL OF PHYSIOLOGY
very special conditions. When the ventricle of a nonnally
beating frog's heart is stimulated by a rapid series of induction
shocks, its rate is generally increased, but there is no definite
relation between the number of stimuli and the number of
beats. Many of the stimuli are ineffective. In the same
way a portion of the heart, such as the apex of the ventricle,
when stimulated in the quiescent condition by an interrupted
current, responds by a rhythmical series of beats, and not by
a tetanus. It is evident that the cardiac muscle, like ordinary
striped muscle, is for some time after excitation incapable
of responding to a fresh stimulus, i.e., there is a refractory
period. But this is immensely longer in cardiac than in
skeletal muscle. When the phenomenon is analyzed, it is
found that a stimulus falling into the heart muscle between
the moment at which the contraction begins and the
moment at which it reaches its maximum, produces no effect
— is, so to speak, ignored. When the stimulus is thrown in
at any point between the maximum of the systole and the
beginning of the next contraction, it causes what is called
an extra contraction. The extra contraction is followed by
a longer pause than usual — a so-called compensatory pause
— which just restores the rhythm, so that the succeeding
systole falls in the curve where it would have fallen had there
been no extra contraction (Fig. 44). The refractory period
is shorter for strong than for weak stimuli, and is markedly
diminished by raising the temperature of the heart. So
that stimulation of the heated heart with a series of strong
induction shocks may cause a tetaniform condition, if not a
typical tetanus. The contraction of the normally beating
heart is really a simple contraction, and not a tetanus. The
capillary electrometer shows only the electrical changes
corresponding to a single contraction (p. 622) ; and when
the nerve of a nerve-muscle preparation is laid on the heart,
the muscle responds to each beat by a simple twitch, and
not by tetanus (p. 179).
Like ordinary skeletal muscle, the cardiac muscle is at first
benefited by contraction, so that when the apex is stimulated
at regular intervals, each contraction is somewhat stronger
than the preceding one. To this phenomenon the name of
THE CIRCULATION OF THE BLOOD AM) LYMPH 133
the staircase or * treppe ' has been given from the appearance
of the tracings (p. 548).
The Extrinsic Nervous Mechanism of the Heart. — While, as
we have seen, the essential cause of the rhythmical beat of
the heart resides in the tissue of the heart itself, it is con-
stantly affected by impulses that reach it from the central
nervous system. These impulses are of two kinds, or, rather,
produce two distinct effects : inhibition, or diminution in the
rate or force of the heart-beat, and augmentation, or increase
in the rate or force. Both the inhibitory and the augmentor
impulses arise in the medulla oblongata, and perhaps a
A frog's heart
was stimulated at
a point correspond-
ing to the nick in
the horizontal line
below each curve.
In I and 2 there
was no response ;
in 3 and 4 there
was an extra con-
traction, succeeded
by a compensatory
pause.
FlU. 44.-REi-RACTORY VEKH'V AM- C 'M I'EN > A K 'K V PaUSE (MAKEY).
narrow zone of the neighbouring portion of the cord ; and
they can be artificially excited by stimulation in this
region. They pursue their course to the heart by fibres
which may in certain animals be mingled together, but are
anatomically distinct. We may, therefore, divide the ex-
trinsic or external nervous mechanism of the heart mto a
cardio-inhibitory centre with its efferent inhibitory nerve-
fibres, and a cardio-augmentor centre with its efferent
augmentor nerve-fibres. Both of those centres, as we shall
see, have also extensive relations with afterent nerve-fibres
from all parts of the body, including the heart itself.
It was in the vagus of the frog that inhibitory nerves were
first discovered by the brothers Weber more than fifty years
'34
A MAMAL OF I'liYSIOLOGY
a^o, and even now our knowledge of the cardiac nervous
mechanism is more complete in this animal than in any
other. We shall, therefore, first describe the phenomena of
inhibition and augmentation as we see them in the heart of
the frog, and then pass on to the mammal.
In the frog the inhibitory fibres leave the medulla oi)!ongata in the
vagus nerve. The augmentor fibres come off from the upper part of
the spinal cord by a branch from the
third nerve to the third sympathetic
ganglion, and thence find their way
along the symialheiic cord to its
junction with the vagus, in \vhi< h they
run, mingled with the inhihitory fibres,
down to the heart.
When the vago-sympathetic in
the frog or toad is cut, and its
peripheral end stimulated, the
heart in the vast majority of cases
is stopped or slowed, or its beat
is distinctly weakened without, it
may be, any marked slowing. In
other words, the rate at which the
heart was working, before the
stimulation, is greatly diminished,
or reduced to zero. Such an
effect, a diminution of the rate of
working, we call Inhibition. What
precise form the inhibition shall
take, whether the stoppage shall
be complete or partial, appears to
depend partly upon the strength of the stimulus used, and
partly upon the state of the heart itself. Some hearts it may
be impossible to stop with weak stimulation, although other
signs of inhibition may be distinct, while they are readily
stopped by stronger stimulation. In other cases the
strongest stimulation may not produce complete standstill.
Again, a heated heart may be more readily brought to
standstill by stimulation of the vagus than a heart at the
ordinary temperature or a cooled heart.
But there are other points of importance to be noted in
Fir,. 45 (after Foster).—
Diagram ok Extri.nsic
Nerves of Frog's Heart.
Ill, 3rd spinal nerve ; AV,
annulus of V'ieussens ; X, roots
of vagus ; IX, glosso-pharyngeal
nerve ; VS, combined vagus and
sympaiheiic ; i. 2, and 3, the ist,
2nd, and 3rd sympathetic ganglia.
The dark line indicates the course
of the sympathetic fibres. The
arrows show the direction of the
augmentor impulses.
THE ClRCrLATION Of Tllli BLOOD AM) LYMl'll 135
regard to this inhibition: (i) It docs not begin for a httle
time after stimulation has begun. In other words, there is
a distinct latent period ; and the length of this latent period
is related to the phase of the heart's contraction at which
the stimulus is thrown in, and to the rate at which the heart
is beating. As a general rule, the heart makes at least one
beat before it stops.
(2) The inhibition does not continue indetiniteiy, even if
stimulation of the nerve is kept up. Sooner or later, and
Fi«.. 4D.— Tkacin'. from Frog's Heart.
A auricular V ventricular tracing. Sinus stimulated (primary coil 70 mm. from
secondary). Heart at temperature 11-2° C. Complete standstill. The tune tracing
between the curves marks intervals of two seconds.
usually, in fact, after an interval of a few seconds, the heart
begins again to beat if it has been completely stopped, or to
quicken its beat if it has only been slowed, or to strengthen
it if the inhibition has only weakened the contraction,
and it soon regains its old rate of working. Not only
so, but very often there follows a longer or shorter period
during which the heart works at a greater rate than it did
before the inhibition, and this greater rate of working may
be manifested by increased frequency of beat, or increased
i>6
J MA.\(/AL Ol- I'HYSlOLOi.Y
strength of beat, or by both. When the temperature of the
heart is low, increased frequency; when it is high, increased
strength, is generally seen during this period of sccondaiy
ajignioitafiv)!.' The cause of this secondary augmentation,
and of the primary augmentation sometimes seen in fresh
preparations and often in hearts that have been long
exposed (F"ig. 49), excited much speculation before it was
known that sympathetic fibres existed in the vagus. There
is no longer any doubt that it is due to the stimulation of
these accelerator or, as it is better to call them (since mere
acceleration is not the onl)- consequence of their stimula-
Fii;. 47. — hKoi.'s Hkaki. \ai.is S i iml'i.aii- h.
Temperature of heart 3' C, 78 mm. between the coils. Diminution in force of auricle
and ventricle, but not complete standstill. Time tracing shows two-second intervals.
tion), anginenU'V fibres in the mixed nerve. For (i) excita-
tion of the roots of the vagus proper within the skull, and
therefore above the junction of the sympathetic fibres,
causes no secondary augmentation, or very little, and the
inhibition lasts far longer than when the mixed trunk is
stimulated.
(2) Excitation of the upper or cephalic end of the sym-
pathetic cord before it has joined the vagus causes, after a
* Augmentation is termed 'secondary' wlien it is i)receded by inhibi-
tion, 'primary' when it is not so preceded.
TItl-: CIRCULATIO.X OF TUIi liLOOD AM) l.YMl'H ij7
relatively long latent period, marked augmentation. And if
the contractions of the heart are registered, the tracing bears
a close resemblance to the curve of secondary augmentation
following excitation of the mixed nerve on the other side
with an equally strong stimulus and for an e(iual time.
(3) When the vago-sympathetic is stimulated weakly there
is little or no secondary augmentation. Now, it is known
that the augmentor fibres require
a comparatively strong stimulus
to cause any effect when they are
separately excited, whereas a weak
stimulus will excite the inhibitor)
fibres.
The question arises at this point,
why it is that, when the inhibitor}
and augmentor fibres are stimu-
lated together in the mixed nerve
(and the same is true when the
sympathetic on one side and the
vagus on the other are stimulated
at the same time), the inhibitors-
effect always comes first, when
there is any inhibitor} effect, while
the augmentation always has to
follow. The answer has some-
times been given, that the latent
period of the augmentor fibres is
longer than that of the inhibitors-
fibres. But although this is cer-
tainly the case, the answer is in-
sufficient. For the period of post-
ponement may be much greater than the latent period of
the sympathetic fibres when stimulated by themselves. The
inhibition apparently runs its course without being affected
by the simultaneous augmentor effect, which, lying latent
until the end of the inhibition, then bursts out and com-
pletes its own curve. It is not like the passing of two waves
through each other, but rather like the stopping of one wave
until the other has passed by. It seems as if augmenta-
A is a curve representing in
an experiment the rate of the
heart before stimulation of the
sympathetic, and B the maxinuim
rale after stimulation, the number
of beats per ico" being laid off
along the vertical, the temperature
of the hearth along the horizontal
axis. C is a curve showing theratio
of the frequency after, to that
before stimulation of the sym-
pathetic. D shows the absolute
amount of acceleration at the
various temperatures, the ordi-
nates being the excess of the rate
after, over that before stimulation.
•3S
A A/AAr.lL OF PHYSIOLOGY
tion cannot develop itself in the presence of inhibition — at
least, until the latter is nearly spent. In the frog, at any
rate, the two processes can hardly be considered as
antagonistic, in the sense that a definite amount of
augmentor excitation can overcome a definite amount of
inhibitory excitation. Nor is it the case that when the
heart is played upon at the same time by impulses of both
Fit;. 49.— Fko. . - Heak'.
A, auricular; V, ventricular tracing. \'eniricle beating very feebly. Vagus stimu-
lated (60 mm. between coils). Marked augmentatioti of ventricular beat.
kinds, it pits them against each other and strikes the
balance accurately between them. It is possible, however,
that when the inhibitory fibres are very weakly, and the
aiigmentory fibres very strongly stimulated, the amount of
inhibition may be somewhat diminished. In mammals, on
the other hand, a true antagonism seems to exist; and
stimulation of the inhibitory nerves is less effective when
the augmentors are excited at the same time.
■mt ( IRCILATION or Tim liLOOD AND LYMPH 139
In mammals (and in what follows wc shall restrict ourselvt-s to the
dog, cat and rabbit, as it is in these animals that the subject has Ixen
chiefly studied) the inliibiioiy fibres run down the vagus in the neck
and reach the heart by its cardiac branches. Tiiey are not, however,
generally believed to be derived from the roots of the vagus itself, but
from the inner branch of the spinal accessory, which joins the vagus.
'y\\t.an^)ihnior fibres leave the spinal cord in the anterior roots of the
second and third thoracic nerves, and
possibly to some extent by the fourth
and fifth. Through the corresponding
white rami communicantes they reach
the sympathetic cord, and running
up through the stellate ganglion (first
thoracic), and the annulus of Vieussens,
which surrounds the subclavian artery,
to the inferior cjrvical ganglion, they
pass off to the heart by separate ' ac-
celerator' branches, taking origin either
from the annulus or from the inferior
cervical ganglion.
In the dog the vagus and cervical
sympathetic are, in the great majority
of cases, contained in a strong common
sheath, and pass together through the
inferior cervical ganglion. After open-
ing this sheath they may with care be
separated, the fibres running in distinct
strands, and not mixed together as in
the vagosympathetic of the frog. For
some distance below the superior
cervical ganglion the cervical sympa-
thetic is not connected with the vagus,
and here the nerves may be separately
stimulated without any artificial isola-
tion, but the electrodes must be very
well insulated, as the available length
of nerve is small.
In the rabbit, cat, horse, and some
other mammals, the vagus and sympa-
thetic run a separate course in the
neck.
OK CaR-
111 E Dog
FjO. 50. — DlACKA.M
1)1 AC Nkrves in
(after Foster).
II, III, second and third dorsal
nerves; .SA, subclavian artery;
AV, annulus of Vieussens ; ICG,
inferior cervical ganglion ; CS,
cervical sympathetic ; i, first
thoracic or stellate ganglion of the
sympathetic ; 2, second thoracic
ganglion ; Ac, accelerator or
augmentor fibres passing oft' to-
wards the heart ; X, roots of vagus;
XI, roots of spinal accessory ; JG,
jugular ganglion ; G TV, ganglion
trunci vagi; In., inhibitory fibres
passing off towards the heart.
The effects of stimulation of the vagus or vago-sym-
pathetic in the mammal are very much the same as in the
frog, except that secondary augmentation is far less marked
or altogether absent, and that in the mammal the inhibitory
fibres have no direct action on the ventricle. It indeed
beats more slowly when the auricle is slowed, but this is
I40
,1 MA.xuAL or rifvsior.oi'.Y
only because in the normally beating' heart the ventricle
takes the time from the auricle. The strength of the ven-
tricular contractions is not at all diminished, even when the
auricle is beating very feebly during inhibition. When the
auricle is completely stopped, which does not occur so
readily as in* the frog, the ventricle also stops for a short
time, but soon begins to beat again with an independent
rhythm of its own. In the frog the ventricle is directly
affected by stimulation of the vagus, and the force of its
beats is diminished
independently of
the inhibitor}'
effects in the
auricles (Practical
Mxercises, pp. 178,
179)-
Stimulation of
the accelerator
nerves in the dog
causes an increase
in the force of both
the auricular and
ventricular con-
traction, and, as a
rule, in addition,
some increase in
the rate of the
beat.
As to the nature
of the physiological linkage between the cardiac nerves and the
muscular tissue of the heart we know but little. It has
been supposed that within the heart itself there may exist
peripheral nervous mechanisms which mediate between the
nerves and the muscle. We have already given reasons
for denying to the gangli(jn cells any important share in
the maintenance of the rhythmical beat, but we have not
assigned them any function. It has been suggested that
the ganglia may act as local inhibitory, or even as local
augmentor, centres. Others, however, have inclined to the
G. 51. — JiLOOU-l'Kh.'^.'iUkK TRACING (RaBBII).
Vagus stimulated at i. Stimulus stronger in B than
in A (Hiirthle's spring manometer).
THE CIRCULATION OF THE EI.OOD AND LYMPH \\\
view that the cells on the course of nerve-fibres in the heart
are rather stations where the fibres lose their medulla, and
where possibly other anatomical changes and rearrangements
occur, than important intermediate mechanisms which
essentially modify the physiological impulses falling into
them, and shape the visible results that follow those im-
pulses. In the discussions that have arisen over this
question, appeal has frequently been made to the action of
certain poisons on the heart.
Thus, after nicotine has been injected subcutaneously, or
painted directly on the heart of a frog, stimulation of the
vago-sympathetic causes no inhibition ; it may cause aug-
mentation. But stimulation of the junction of the sinus
and auricle still causes inhibition, as in the normal heart.
Curara, conine, and other drugs, resemble nicotine in this
respect.
Atropia and its allies, such as daturinc, not only abolish
the inhibitory effect of stimulation of the vagus trunk, but
also that of stimulation of the junction of sinus and auricle.
Muscarine, a poison contained in certain mushrooms
(p. 174), causes diastolic arrest of the heart, which, when
the circulation is intact, becomes swollen and engorged
with blood. This action takes place in a heart already
poisoned with nicotine or one of its congeners, but not in a
heart under the influence of atropia or its allies. And a heart
brought to standstill by muscarine can be made to beat again
by the application of atropia, although not by nicotine.
These facts may be explained as follows : Nicotine
paralyzes not the very ends of the vagus, but the ganglia
through which its fibres pass. Stimulation of the sinus,
which is practically stimulation of the vagus fibres between
the ganglion cells and the muscular fibres, is therefore
effective, although stimulation of the nerve-trunk is not
(Langley). On the other hand, the atropia group paralyzes
the nerve-endings themselves, so that neither stimulation
of the sinus nor of the nerve-trunk can cause inhibition.
Muscarine, on the contrary, stimulates the vagus fibres
between the nerve-cells and the muscle, or the actual nerve-
endings, or some other local nervous mechanism, and thus
142 A MANUAL OF PIIYSIOI.OC.Y
keeps the heart in a state of permanent inhibition, which is
removed when atropia cuts out the nerve-endin{:(s. It is
quite in accordance with this, that muscarine has no effect
on a heart whose vagus nerves, as occasionally happens,
have no inhibitory power.
Some observers have supposed that although muscarine and pilo-
carpine in large doses do act on the nervous structures of the sinus,
their primary and chief effect is to depress the rhythmical power of
the muscle, which atropia, on the other hand, increases (Gaskell).
And this view gains a certain amount of support from the facts that
muscarine and atropia act very much in the same way on the heart of
the mammalian embryo (rat, rabbit, etc.) before and after the develop-
ment of its intrinsic nervous system, and thai the passage of an
interrupted current through the heart of very young embryos causes
distinct inhibition. But, on the other hand, muscarine fails to affect
the heart in many invertebrate animals — for instance, in the Daphnia
(Pickiring). So that the only conclusion to which it is possible to
come is that we do not as yet thoroughly understand either the mode
of action of these su!)stanc cs or their point of attack.
Stannius' Experiment. Nor can much more be said of another
series of phenomena that are intimately related to our present subject,
and have excited, since they were first made known by Stannius, an
enormous amount of discussion. The chief facts of this classical
experiment we have already mentioned (p. 130), and they are also
described in the 'Practical Exercises' (p. 175). They are easy to
verify, but difficult to interpret. To (iaskell and his followers the
most probable explanation of the standstill caused by the first ligature
is that the lower portion of the heart, when cut off from the sinus in
which the beat normally originates, needs some time for the develop-
ment of its rhythmical power to the point at which an independent
rhythm can be maintained. Jor in the heart of the tortoise, in which
a similar temi)0rary standstill of the auricles and ventricle occurs
when the former are detached from the sinus, the circulation of a
blood solution through the coronary vessels or the application of
atropia, both of which, according to C.askell, increase the rhythmical
power of the cardiac muscle, prevents or removes the standstill. The
effects following the second Stannius ligature are supposed to be due
to stimulation of the muscular tissue by the ligature. But it is not
easy to explain why the second ligature should stimulate the ventricle
in preference to the auricles, and why the first ligature should
apparently not stimulate the muscular tissue at all. Nor does the
explanation become easier if we suppose, as is sometimes done, that
it is the Bidder's ganglia which are stimulated by the ligature or by the
knife, for there is no real evidence that they have motor functions.
Another view is that the first ligature stimulates the inhibitory
mechanism (vagus fibres) at the junction of the sinus and right auricle,
a position in which it is specially sensitive to stimuli. This causes
inhibition of the whole of the heart below the ligature. The second
TIIK CIKCVI.ATlOy OI Till. lil.OOl) AM) l.VMl'll 143
ligature cuts off tlu- ventricle from the inhibitory ini[)ulses, while
leaving the aurirle -^tiU under their intluence.
Nature of Inhibition and Augmentation. — So far we have been
discussing the phenomena of inhibition and augmentation as ultimate
facts. We have not attempted to go behind them, nor to ask what it
is that really happens when inhibitory impulses fall into a heart, which
from the first days of embryonic life has gone on beating with a regular
rhythm, and in the space of a second or two bring it to a standstill.
The question cannot fail to press itself upon the mind of anyone who
has ever witnessed this most beautiful of physiological experiments ;
but as yet there is no answer except ingenious s[)eculations. 'I"he
most plausible of these
is the trophic theory ot
Ciaskell, who sees in the
vagus a nerve which so
acts upon the chemical
changes going on in the
heart as to give them a
trophic, or anabolic, or
constructive turn, and
thus to lessen for the
time the destructive
changes underlying the
muscular contraction.
The augmentor nerves,
on the other hand, are
supposed to exert a
katabolic influence, and
to favour these destruc-
tivechanges. And while,
according to Oaskell,
the natural consequence . .
r\( 'nViiKitir.!-! ic i tfnfr Temperaiure 12". Marked increase in force. Onlv
01 mniouion is a ^W&t; auricular tracing reproduced. Time trace, two-second
of increased efficiency intervals.
and working power when
the inhibition has passed away, the natural complement of augmenta-
tion is a temporary exhaustion.
But it must be remembered that this distinction is not as yet based
upon any very solid foundation of actually observed and easily-
interpreted facts, while to some of the facts brought forward in its
favour undue importance has been given. For instance, a positive
electrical variation has been seen in the quiescent auricle of the
tortoise on stimulating the vagus, and a negative variation in the
quiescent frog's ventricle on stimulating the cardiac sympathetic,
neither of these variations apparently being accompanied with any
sensible mechanical change. It has been argued from this (on the
assumption that the negative variation observed when most excitable
tissues, muscle and nerve, for example, are stimulated, is the ex-
pression of destructive metabolic changes or katabolism), that the
vagus has the power of causing constructive (anabolic) changes, and
Fig. 52. — Frog's Heart.
Sympathetic stimulated (30 mm. between the coils).
144 A MANUAL OF rilYSlOLOGY
the augmentor nerves the power of causing destructive (kataboUc)
changes, a[)art from mechanical effects. Hut all that we really know
is that electri( al changes and chemical changes can Ijoth be evoked
in living tissues. We are (juite ignorant of the relation between
the two.
The Normal Excitation of the Cardiac Nervous Mechanism.
— We have now to inquire how this elaborate nervous
mechanism is normally set into action. And we may say at
once that, strikinj; as are the effects of experimental stimula-
tion of the vagus trunk or the nervi accelerantes in their
course, it is only under exceptional circumstances that the
efferent nerve-tibres, at any rate before they have entered the
heart, can be directly excited in the intact body. In certain
cases the pressure of a tumour or an aneurism on the nerve-
trunks, or, in the case of the accelerators, the progress cf
a pathological change in the sympathetic ganglia through
which the fibres pass, has been thought to bring about by
direct stimulation a slowing or a quickening of the pulse. In
some individuals the vagus may be excited by compressing
it against the vertebral column or against a bony tumour in
the neck. But it is from the cardio-inhibitory and cardio-
augmentor centres in the medulla oblongata that the im-
pulses which regulate the activity of the heart are normally
discharged. Inhibitory impulses seem to be constantly
passing out from the medulla, for section of both vagi
causes almost invariably an increase in the rate of the
heart, at least in mammals, although the increase is less
conspicuous in animals like the rabbit, whose normal pulse-
rate is high, than in animals like the dog, whose pulse-rate is
comparatively low. Section of one vagus usually causes only
a comparatively slight increase, for the other is able of itself
to control the heart. It is not known whether the augmentor
centre in like manner discharges a continuous stream of im-
pulses, or is only roused to occasional activity by special
stimuli. For the results of section of the nervi accelerantes,
or the extirpation of the inferior cervical and stellate ganglia,
are dubious and conflicting. But if it does exert a tonic
influence on the heart, this is far feebler than the tone of
the inhibitory centre. As to the nature of this inhibitory
tone, and the manner in which it is maintained, we know
THE CIRCULATIOX OF THE liLOO/) AX/) LYMril 145
but little. It may be that the chemical changes in the
nerve-cells of the inhibitory centre lead of themselves to the
discharge of impulses along the inhibitory nerves. But
there is some evidence that, in the complete absence of
stimulation from without, the activity of the centre would
languish, and perhaps be ultimately extinguished. I'or
when the greater number of the afferent impulses have been
cut off from the medulla oblongata by a transverse section
carried through its lower border, division of the vagi pro-
duces little effect on the rate of the heart. Be this as it
may, we know that the activity of the inhibitory centre is
profoundly influenced — and that both in the direction of an
increase and of a diminution — by impulses that fall into it
through afferent nerves and by stimuli directly applied to
it. And we may assume that the same is true of the
augmentor centre. When, for instance, the central end of
one vagus is stimulated, the other being intact, the usual
result is a slowing or weakening of the heart, which, how-
ever, is generally less marked than when the stimulation is
applied to the peripheral end of the nerve. But sometimes
the heart is accelerated without any trace of a preceding
inhibition.
The depressor nerve, a branch of the vagus, which is
easily found in the rabbit as a slender nerve running quite
close to the sympathetic in the neck, and a little to its inner
side, falls into the same category with the vagus itself as
regards its reflex action on the heart, to which it bears a most
important relation. Stimulation of its peripheral end has
no effect, for the cardiac fibres which it carries are afferent,
not efferent. But excitation of its central end causes a
marked fall of blood-pressure (p. 161), accompanied bv, but
not essentially due to, a distinct slowing of the heart. If
the animal is not under the influence of an anaesthetic, there
may also be signs of pain, and for this reason the depressor
has sometimes been spoken of, somewhat loosely, as the
sensory nerve of the heart. The abdominal sympathetic
(of the frog) also contains afferent fibres, through which
reflex inhibition of the heart can be produced when they
are excited mechanically by a rapid succession of light
10
146 A MANUAL OF PHYSIOLOGY
Strokes on the abdomen with the handle of a scalpel
(Goltz).
On the other hand, when the central end of an ordinary
peripheral nerve like the sciatic is excited, the common
effect is pure augmentation, which sometimes perhaps
develops itself with greater suddenness than when the
accelerator nerves are directly stimulated. Occasionally,
however, the augmentation is abruptly followed by a typical
vagus action. Here the reflex inhibitory effect seems to
break in upon and cut short the reflex augmentor effect.
These examples show that certain afferent nerves are
especially related to the cardio-inhibitory, and others to the
cardio-augmentor, centre, or at least that the central con-
nections of some nerves are such that inhibition is the
usual effect of their reflex excitation, while the opposite is
the case with other nerves. But it is improbable that the
effect of a stream of afferent imp)ulses reaching the cardiac
centres by any given nerve is determined solely by anato-
mical relations. The intensity and the nature of the
stimulus seems also to have something to do with the result.
For when ordinary sensory nerves are weakly stimulated,
augmentation is said to be more common than inhibition,
and the opposite when they are strongly stimulated. And
while a chemical stimulus, like the inhaled vapour of
chloroform or ammonia, causes in the rabbit reflex inhibi-
tion of the heart through the fibres of the trigeminus that
confer common sensation on the mucous membrane of the
nose, the mechanical excitation of the sensory nerves of the
pharynx and oesophagus when water is slowly sipped causes
acceleration.* The stimulation of the nerves of special
sense is followed sometimes by the one effect and some-
times by the other. To complete the catalogue of the
nervous channels by which impulses may reach the cardiac
centres in the medulla, we may add that there must be an
extensive connection between them and the cerebral cortex,
since every passing emotion leaves its trace upon the curve
of cardiac action. It is a remarkable fact, too, and one
* In 78 healthy students the average pulse-rate (\x\ the sitting position)
was increased from 73 to 85 per minute by sipping water.
rilE CIRCL'LATIOS OF THE BLOOD AM) LYMl'J/ 147
that can onh' be explained by such a connection, that
althoiijijh in the \ast majority of individuals the will has no
influence whatever on the rate or force of the heart, except,
perhaps, indirectly through the respiration, some persons
have the power, by a voluntary effort, of markedly accelerat-
ing the pulse. In one case of this kind it was noticed that
perspiration broke out on the hands and other parts of the
body when the heart was voluntarily accelerated. A rise of
blood-pressure due to constriction of the vessels has also
been observed. The effort cannot be kept up for more than
a short time, and the pulse-rate quickly goes back to normal.
It has been recently asserted that this peculiar power is
more common than has been supposed, and that where it is
present in rudiment, it can be cultivated, although it is a
dangerous acquisition (Van de Velde).
As an example of the direct action of a chemical stimulus
on a cardiac centre, we may cite the marked inhibition pro-
duced by injection of an extract of the suprarenal capsule
into a vein (p. 475), and as an instance of the direct action
of a physical change, the slowing of the heart in asphyxia as
the blood-pressure rises (p. 163). The variation in the pulse-
rate associated with changes in the position of the body,
to which we have already referred (p. 96), has been attri-
buted to direct stimulation of the inhibitory centre by the
increase of blood-pressure in the medulla oblongata when a
person who has been standing assumes the supine, or even
the sitting, posture. But it may also be due in part to
changes in the amount of muscular contraction.
Theoretically, quickening of the heart might be caused
either by a diminution in the inhibitory tone or by an
increase in the activity of the augmentor centre ; and
slowing of the heart might be due either to a diminution in
the augmentor tone, if such exists, or to an increase in the
activity of the inhibitory centre. So that it is not always
easy to interpret such results as we have quoted above.
But it would appear that under ordinary conditions the rate
of the heart is mainly regulated by the inhibitory centre,
which, within a considerable range, can produce variations
in either direction. The augmentor mechanism is perhaps
10 — 2
1 48 A M. 1 XUA L OF I'H YSIOL OG Y
merely auxiliary to the inhibitory, being called into action
only in emerj^encies.
Vaso-motor Nerves. — Just as the muscular walls of the heart
are governed by two sets of nerve-fibres, a set which keeps
down the rate of working and a set which may increase it,
the muscular walls of the vessels are under the control of
nerves which have the power of diminishing their calibre
(vaso-constrictor), and of nerves which have the power of
increasing it ivaso-dilaior). All nerves that affect the calibre
of the vessels, whether vaso-constrictor or vaso-dilator. are
included under the general name vaso-motor. These vaso-
motor nerves, like the augmentor and inhibitory fibres of
the heart, are connected with a centre or centres, which in
turn are in relation with numerous afferent nerves. So far
as we know at present, vaso-motor nerves influence chiefly
the small arteries. Although nerve-fibres have been seen
surrounding capillaries, nothing is known of any change of
lumen occurring in these vessels as a direct result of the
action of nerves going to them. Xor has the existence of
vaso-motor nerves for veins, except the portal system, been
proved up to this time by any clear and unambiguous ex-
periment, although there are grounds on which it has been
argued that in some animals, at least, the nervous system
does govern the calibre or ' tone ' of the whole venous tract.
These grounds will be mentioned in the proper place.
Meanwhile, before describing the distribution of the best-
known tracts of vaso-motor fibres and defining the position
of the vaso-motor centres, we must first glance at the
principal methods by which our knowledge of this subject
has been attained.
(i) In superficial and translucent parts inspection is sufficient.
Paling of the part indicates constriction : flushing, dilatation of the
small vessels. This method has been much used, sometimes in con-
junction with (2) in such parts as the balls of the toes of dogs or cats
(when there is little or no pigment present), the ear of the rabbit, the
conjunctiva, the mucous membrane of the mouth and gums, the web
of the frog, the wing of the bat, the intestines, uterus, and other
internal organs.
(2) Observation of changes in the temperature of parts. This
method has been chiefly employed in investigating the vaso-motor
nerves of the limbs, the thermometer bulb being ti.xed between the
THE CIRCULATION Of THE BLOOD AXD LYMPH 149
toes. In such peripheral parts the temperature of the blood is
normally less than that of the blood in the internal organs, because
the opportunities ot cooling arc greater. The effect of a freer cir-
culation of i^lood (dilatation of the arteries) is to raise the tempera-
ture ; of a more restricted circulation (constriction of the arteries), to
lower it.
(3) Measurement of the blood-pressure. If we measure the
arterial blood-pressure at one point, and find that stimulation of
certain nerves increases it without affecting the action of the heart,
we can conclude that upon the whole the tone of the small vessels
has been increased. But we cannot tell in what region or regions
the increase has taken place ; nor can we tell whether it has not been
accompanied by diminution of tone in other tracts.
But if we measure simultaneously the blood-pressure in the chief
artery and chief vein of a part such as a limb, we can tell from the
changes caused by section or stimulation of nerves whether, and in
what sense, the tone of the small vessels within this area has been
altered, for example, if we found that the lateral pressure in the
artery was diminished, while at the same time it was increased in the
vein, we should know that the ' resistance ' between artery and vein
had been lessened, and that the blood now found its way more
readily from the artery into the vein. If, on the other hand, the
venous pressure was diminished, and the arterial pressure simul-
taneously increased, we should have to conclude that the vascular
resistance in the part was greater than before. If the pressure both
in artery and vein was increased, we could not come to any conclu-
sion as to local changes of resistance without knowing how the
general blood-pressure had varied.
It is also sufficient to nieasure the blood-pressure simultaneously
at two points of the arterial path by which blood reaches the part,
provided that there is a distinct difference in the pressure at the two
points. The ratio of the two pressures will not be altered by any
general change of blood-pressure due to changes in the action of the
heart ; any alteration in the ratio will indicate a change in the peri-
pheral vascular resistance in the part beyond the more distal of the
two manometers.
On this principle, Hiirthle has studied the changes in the circula-
tion of the brain by inserting manometers into the central end of the
divided common carotid and the peripheral end of the internal
carotid. The former shows the lateral pressure in the aorta, the
latter that in the circle of Willis.
(4) The measurement of the velocity of the blood in the vessels
of the part. This may be done by the stromuhr or dromograph, or
by allowing the blood to escape from a small vein and measuring the
outflow in a given time, or, without opening the vessels, by estimating
the circulation time (p. 123). When changes in the general arterial
pressure are eliminated, slowing of the blood-stream through a part
corresponds to increase of vascular resistance in it ; increase in the
rate of flow implies diminished vascular resistance. Sometimes the
red colour of the blood issuing from a cut vein, and the visible pulse
ISO A MANi'AL OF PI/YSIOLOCY
in the stream, indicate with certainty that the vessels of the organ
have been dilated.
(5; Alterations in the volume of an organ or limb are often taken
as indications of changes in the calibre of the small vessels in it.
^^'e have already seen how these alterations are recorded by means
of a plethysmograph (p. 1 16). The brain is enclosed in the skull as
in a natural plethysmograph. and changes in its volume may be
registered by connecting a recording apparatus with a trephine hole.
(6) For the separation of the effects of stimulation of vaso-
constrictor and vasodilator fibres when they are mingled together, as
is the case in many nerves, advantage is taken of certain differences
between them. For example, the vasoconstrictors degenerate sooner
than the vaso dilators when cut off from the nerve-cells to which they
belong. So that if a nerve is divided, and some days allowed to
Fig. 53. — Pl.KlHV.■^.MOGkAM^ JIlM' LiMB Ol Ca 1 ).
To be read from right to left. On the left hand is shown the effect of slow stimula-
tion of the sciatic (i per second) ; on the right hand the effect of rapid stimulation
(64 per second ).
elapse before stimulation, only the dilators will be excited. The
vaso-dilators are more sensitive to weak stimuli repeated at long
intervals than to strong and frecjuent stimuli, and the opposite is true
of the constrictors. AVhen a nerve containing both kinds of fibres is
heated, the excitability of the vasoconstrictors is mcreased in a
greater degree than that of the dilators ; when the nerve is cooled,
the dilators preserve their excitability at a temperature at which the
constrictors have ceased to respond to stimulation (Fig. 53).
The Chief Vaso-motor Nerves. — The first discovery of vaso-
motor nerves was made in the cervical sywpathciic. When
this nerve is cut, the corresponding side of the head, and
especial!}- the ear, become ^'reatly injected owing to the
dilatation of the vessels. This experiment can be very
readily performed on the rabbit, and the changes are most
THE CIRCULATIOX OF THE liLOOD AM) LYMl'II 151
easily followed in an albino. The ear on the side of the cut
nerve is redder and hotter than the other ; the main arteries
and veins are swollen with blood, and many vessels formerly
invisible come into view. The slow rhythmical changes of
calibre, which in the normal rabbit are very characteristically
seen in the middle artery of the ear, disappear for a time after
section of the sympathetic, although they ultimately again
become visible (Practical Exercises, p. 189).
Stimulation of the cephalic end of the cut sympathetic
causes a marked constriction of the vessels and a fall of
temperature on the same side of the head. From these
facts we know that the cervical sympathetic in mammals
contains vaso-constrictor fibres for the side of the head and
ear, and that these fibres are constantly in action. Certain
parts of the eye, and the salivary glands, larynx, oesophagus,
and thyroid gland, are also supplied with vaso-motor (con-
strictor) nerves from the cervical sympathetic.
It has been asserted that the cervical sympathetic con-
tains vaso-constrictor fibres for the corresponding half of the
brain and its membranes, although fibres of this kind also
reach it by other routes ; but this has been disputed, and
some observers have even gone so far as to deny that the
vessels of the brain have any vaso-motor nerves (Roy and
Sherrington). To say the least, their existence must still be
regarded as ' not proven,' although nerve-fibres may be seen
in and around the walls of the cerebral bloodvessels (Huber),
and it is difficult to believe that these have not a vaso-motor
function. That the nerve contains some dilator fibres seems
proved by the fact that stimulation of the cephalic end in
the dog causes flushing of the mucous membrane of the
mouth on the same side. The vaso-motor fibres of the head
run up in the cervical sympathetic, and then pass into various
cerebral nerves, of which the fifth or trigeminus is the most
important.
The tyigcuii)iHs nerve contains vaso-constrictor nerves for
various parts of the eye (conjunctiva, sclerotic, iris), and for
the mucous membrane of the nose and gums, and section of
it is followed by dilatation of the vessels of these regions.
The lingual branch of the trigeminus supplies vaso-motor
152 A MANUAL OF I'l/YS/OLOGY
fibres to the tongue, and apparently both vaso-constrictor
and vaso-dilator.
In some animals, the rabbit for instance, the ear derives
part of its vaso-motc^r supply directl)' from the cerebro-
spinal system, through the great auricular nerve, as well as
through the cervical sympathetic.
Another great vaso-motor tract, the most influential in
the body, is contained in the splaiichuic nerves, which govern
the vessels of many of the abdominal organs. Section of
these nerves causes an immediate and sharp fall of arterial
pressure. The intestinal vessels are dilated and overfilled
with blood. As a necessary consequence of their immense
capacity, the rest of the vascular system is underfilled, and
the blood-pressure falls accordingly. Stimulation of the
peripheral end of the splanchnic nerves causes a great rise
of blood-pressure, owing to the constriction of vessels in
the intestinal area. We therefore conclude that in the
splanchnics there are vaso-motor fibres of the constrictor
type, and that impulses are constantly passing down them
to maintain the normal tone of the vascular tract which
they command. The presence of dilator fibres (for the
intestines and the kidney, for example) has also been
demonstrated in the splanchnic nerves, although the con-
strictors predominate, and special methods have to be
employed for the detection of the dilators.
The same is true of the nerves of the extremities, which
certainly contain vaso-dilator fibres in addition to vaso-
constrictors, although the difficulty of demonstrating the
presence of the former is fully as great as it is in the
splanchnics. For the investigation is complicated by the
fact that such nerves as the sciatic suppl}- with vaso-motor
fibres two leading tissues — skin and muscle ; and these are
not necessarily affected in the same direction or to the same
extent by stimulation of their vaso-motor fibres. The vaso-
constrictors under ordinary conditions preponderate, so that
section of the sciatic or the brachial is generally followed by
flushing of the balls of the toes and rise of temperature,
stimulation by paling and fall of temperature. By taking
advantage, however, of the unequal excitability of dilators
THE CIRCULATION OF THE liLOOD AM) LYMI'II 153
and constrictors in a degenerating nerve, and of the differ-
ences between the two kinds of fibres in their reaction to
electrical stimuli (p. 150), it has been shown that vaso-
dilators are also present, and come to the front when
the conditions are rendered favourable for them and un-
favourable for the constrictors.
The vaso-motor fibres for the fore-limb (dog) issue from the cord
in the anterior roots of the third to the eleventh dorsal nerves, and
for the hind-limb in the anterior roots of the eleventh dorsal to the
third lumbar. Stimulation of most of these roots causes constriction
of the vessels, but stimulation of the eleventh dorsal may cause
dilatation (Bayliss and Bradford).
The Vaso-motor Nerves of Muscle. — When the motor nerve
of the thin mylo-hyoid muscle of the frog, which can be
observed under the microscope, is cut, the vessels are seen
to dilate. On stimulation of the peripheral end of the cut
nerve they dilate still more, and this effect is not abolished
when contraction of the muscle is prevented by a dose of
curara insufficient to paralyze the vaso-motor nerves
(Gaskell). The dilatation on section of the nerve has been
held to indicate the existence in it of vaso-constrictor fibres,
and the dilatation on stimulation of the nerve, the existence
of a larger number of vaso-dilators, which overcome the
constrictors when both are excited. And it has been argued
that this is of use to the contracting muscle, which requires
a free flow of blood to supply it with food materials and to
carry off its waste products. The average flow of blood
through a mammalian muscle is also increased during con-
traction, apart from the initial increase due to the com-
pression of the muscular veins. The outflow of blood from
the main vein of one of the muscles used in mastication in
the horse was found to be three times as great during
voluntary work with it (in chewing) as in rest. And although
no increase in the blood-flow through the skeletal muscles of
a completely curarized mammal has ever been satisfactorily
demonstrated, we can hardly doubt that they are provided
with vaso-dilator fibres, and more scantily with vaso-con-
strictors. The existence in the vagus of vaso-constrictor
fibres for the coronarv arteries of the heart has also been
154 A MAXUAL OF PHYSIOLOGY
asserted (Porter). It has been suggested that the muscular
vessels are widened in contraction, not through vaso-motor
nerves, but by the direct action of the acid products of the
active muscle itself, since it has been found that very dilute
acids (lactic acid, t'.^^) cause general dilatation of the small
vessels. A similar explanation has been extended to the
dilatation of the vessels of the brain during cerebral activity
by some of those who deny the existence of vaso-motor
nerves for that organ. But this ingenious speculation rests
upon a very narrow basis of fact.
Vaso-Diotor Nerves of the Lungs. — There has been much
discussion as to the course, and even as to the existence, of
vaso-motor fibres for the lungs. The problem is perhaps the
most difficult in the whole range of vaso-motor topography,
for the pulmonary circulation is so related to other vascular
tracts, that changes produced in the vessels of distant
organs by the stimulation or section of nerves may affect
the quantity of blood received by the right side of the heart,
and therefore the quantity propelled through the lungs and
the pressure in the pulmonary artery. All that we really
know is that the lungs are supplied with vaso-constrictor
fibres, although in all probability less richly than most other
organs. Some of these fibres appear to pass out from the
upper half of the dorsal spinal cord (Bradford and Dean),
but perhaps others reach their destination by the vagus.
In most of the peripheral nerves vaso-dilator fibres are
mingled with vaso-constrictors ; but in certain situations,
for an anatomical reason that will be mentioned presently,
nerves exist in which the only vaso-motor fibres are of the
dilator type. Of these, the most conspicuous examples are
the chorda tympani and the ncrvi erigcntcs ; and, indeed, it
was in the chorda that vaso-dilators were first discovered by
Bernard. The chorda tympani contains vaso-dilator and
secretory fibres for the submaxillary and sublingual salivary
glands. With the secretory fibres we have at present
nothing to do ; and the whole subject will have to be
returned to, and more fully discussed in Chapter IV. But
a most marked vascular change is produced by stimulation
of the peripheral end of the divided chorda tympani nerve.
THE CIRCULATION OF THE BLOOD AND LYMPH 155
The glands flush red ; more blood is evidently passing
through their vessels. Allowed to escape from a divided
vein, the blood is seen to be of bright arterial colour and
shows a distinct pulse. The small arteries have been dilated
by the action of the vaso-motor fibres in the nerve. The
resistance being thus reduced, the blood passes in a fuller
and more rapid stream through the capillaries into the
veins, and on the way there is not time for it to become
completely venous. These vaso-dilator fibres are apparently
not in constant action, for section of the nerve, as a rule,
produces little or no change. Vaso-constrictor fibres pass
to the salivary glands from the cervical sympathetic, along
the arteries, and stimulation of that nerve causes narrowing
of the vessels and diminution of the blood-flow, sometimes
almost to complete stoppage.
The ncrvi crigentcs are the nerves through which erection
of the penis is caused. When they are divided there is no
effect, but stimulation of the peripheral end causes dilatation
of the vessels of the erectile tissue of the organ, which
becomes overfilled with blood. During stimulation of these
nerves, the quantity of blood flowing from the cut dorsal
vein of the penis may be fifteen times greater than in the
absence of stimulation. It spurts out in a strong stream,
and is brighter than ordinary venous blood (Eckhard).
Stimulation of the peripheral end of the nerviis pudendus
causes constriction of the vessels of the penis, so that it
contains vaso-constrictor fibres which are the antagonists of
the nervi erigentes.
Vaso-motor Nerves of Veins. — Like arteries, veins have
plexuses of nerve -fibres in their walls, and contract in
response to various stimuH. In some cases, e.g., in the wing
of the bat, rhythmical contractions of the veins are strikingly
displayed, but they do not seem to depend on the nervous
system, as they persist after section of the brachial nerves.
But up to a very recent date there was no clear proof of
the existence of vaso-motor nerves for veins. In 1892,
however. Mall showed that vaso-constrictor fibres for the
portal vein exist in the splanchnic nerves. When these were
stimulated, after the disturbing effect of changes in the
1 56 A A/A NUA L OF I'll } 'SIOL OGY
circulation through the intestines had been eliminated by
compression of the aorta in the thorax, an actual shrinking
of the vein could be observed. The fibres appear to issue
from the spinal cord by the anterior roots of the third to
the eleventh dorsal nerves, but chiefly in the fifth to the
ninth dorsal (Bayliss and Starling;, When the liver is
enclosed in a plethysmograph of special construction, and
the central end of an ordinary sensory nerve, like the sciatic,
excited, reflex vaso-constriction takes place in the portal
area, the volume of the organ diminishes, and the blood-
pressure rises in the portal vein (Franvois-F"ranck and
Hallion).
The vena portae and its branches are in the physiological
sense arteries rather than veins, since they break up into
capillaries, and it was to be expected that the regulation of
the blood-flow in them would be carried out in the same
way as in ordinary arteries, namely, by means of vaso-motor
nerves. But we must not, without special proof, extend the
results obtained in the portal system to ordinary veins. A
certain amount of evidence, however, exists that even such
veins as those of the extremities are supplied with vaso-
constrictor ^fibres. After ligation of the crural artery,
stimulation of the peripheral end of the sciatic has been
seen to cause contraction of the crural vein (Thompson).
Course of the Vaso-motor Nerves. — In the dog the vaso-ccn-
strictors pass out as fine meduUated fibres (i'Sto3"6/t in
diameter) in the anterior roots of the second dorsal to about
the second lumbar nerves (Gaskell). They proceed by the
white rami communicantes to the lateral sympathetic
ganglia, where, or in more distal ganglia such as the inferior
mesenteric, they lose their medulla, and their axis-cylinder
processes (Chap. XII.) break up into fibrils that come into
close relation with the nerve-cells of the ganglia. These
ganglion cells in their turn send off axis-cylinder processes,
which, acquiring a neurilemma, become non-medullated nerve
fibres, and now pass by various routes to their final destina-
tion, the unstriped muscular fibres of the bloodvessels.
Their course to the head has been already described. To
the limbs they are distributed in the great nerves (brachial
THE CIRCULATION OF THE BLOOD AND LYMPH 157
plexus, sciatic, etc.), which they reach from the sympathetic
ganglia by the grey rami communicantes.
The outHow of vaso-dilator fibres, which also takes place
through the anterior roots, does not seem to be restricted to
any particular part of the cord, although their existence has
been most clearly demonstrated in nerves springing from those
regions of the cerebro-spinal axis from which vaso-constrictor
fibres do not arise, and where, therefore, we have not to
contend with the difficulty and doubt of mixed effects.
Some even emerge in the roots of origin of certain of the
cranial nerves, as the trigeminus, although many of the
vaso-dilator fibres contained in the trunk of this nerve
distal to the Gasserian ganglion are derived from the cervical
sympathetic, and originally come off from the upper dorsal
portion of the spinal cord. The vaso-dilators appear upon
the whole to, pursue much the same course towards the
periphery as the vaso-constrictors, although they often run
for a greater distance after leaving the cord without
losing their medulla. But eventually they too come into
relation with ganglion cells, sometimes scattered along their
course, or lying near or in the organs to which they are
distributed ; and as in the case of the vaso-constrictors,
these ganglion cells with their axis-cylinder processes con-
tinue the nervous path to the periphery. It is believed that
every vaso-motor fibre is interrupted by one, and only by
one, ganglion cell between the cord and the bloodvessels.
Eflfect of Nicotine on Nerve-cells. — A method which has been
found most fruitful in studying the relations of sympathetic ganglion
cells to the vaso-motor fibres, as well as to the pilo-motor* and
secretory fibres which in certain situations are so intricately mingled
with them, must here be mentioned. It depends upon the fact that
when a suitable dose of nicotine (10 milligrammes in a cat) is in-
jected into a vein, or a solution is painted on a ganglion with a
brush, the passage of nerve-impulses through the ganglion is blocked
for a time (Langley). The seat of the 'block' is probably the felt-
work of fibrils in which the central nerve-fibres terminate around the
ganglion cells (Cushny and Huber). The nerve-fibres peripheral to
the ganglion are not affected. The question whether efferent fibres
are connected .with nerve-cclls between a given point and their
* Pilo-motor nerves supply the smooth arrecior pili muscles, whose
contraction causes the hair to ' stand on end.'
I5« A MAXl'AL OF P/fys/OL()(;y
peripheral distribution can, therefore, be answered by observing
whether any efltct of stimulation is abolished by nicotine. If, for
instance, the excitation of a nerve caused constriction of certain
bloodvessels before, and has no effect after, the application of
nicotine to a ganglion, its vaso-constrictor fibres, or some of them,
must be connected with nerve-cells in that ganglion.
We have thus traced the vaso-motor nerves from the
cerebro-spinal axis to the bloodvessels which they control ;
it still remains to define the portion of the central nervous
system to which these scattered threads are related, which
holds them in its hand and acts upon them as the needs of
the organism may require.
Vaso-motor Centres. — Now, experiment has shown that there
is one very definite region of the spinal bulb which has a most
intimate relation to the vaso-motor nerves. If while the blood-
pressure in the carotid is being registered, say, in a curarized
rabbit, the central end of a peripheral nerve like the sciatic
is stimulated, the pressure rises so long as the bulb is intact,
this rise being largel}- due to the reflex constriction of
the vessels in the splanchnic area. If a series of trans-
verse sections be made through the brain, the rise of
pressure caused by stimulation of the sciatic is not affected
till the upper limit of the bulb is almost reached. If the
slicing is still carried downwards, the blood-pressure sinks,
and the rise following stimulation of the sciatic becomes less
and less. W'hen the medulla has been cut awa\- to a certain
level, only an insignificant rise or none at all can be obtained.
The portion of the medulla the removal of which exerts an
influence on the blood-pressure, and its increase by reflex
stimulation, extends from a point 4 to 3 mm. above the
point of the calamus scriptorius to within i to 2 mm. of the
corpora quadrigemina (Owsjannikow). Other observers give
narrower limits. Stimulation of the medulla causes a rise,
destruction of this portion of it a fall, of general blood-
pressure. There is evidently in this region a nervous
'centre' so intimately related, if not to all the vaso-motor
nerves, at least to such very important tracts as to deserve
the name of a vaso-motor centre. Experiment has shown
that this is much the most influential centre, and it is
usually called the chief or general vaso-motor centre. But
THE CIRCULATIOX OF Till: BLOOD AXD / }'.!/'/'// 159
there arc subsidiary centres all along the cord, and while a
very large number of the constrictor fibres are related to the
chief centre in the medulla, some are either normally under
the control of subordinate centres, or may in special circum-
stances come to be dominated by them.
Thus, in the frog it is possible to go on destroying more
and more of the cord from above downwards, and still to
obtain reflex vaso-motor effects, as seen in the vessels of
the web, b}' stimulating the central end of the sciatic nerve.
Although these effects indeed diminish in amount as the
destruction of the cord proceeds, yet a distinct change can
be caused when onl)- a small portion of the cord remains
intact.
Similarly, in the mammal evidence has been obtained of
the existence of ' centres ' at various levels of the cord,
capable of acting as vaso-motor centres after the chief
centre in the bulb has been cut off. For example, after
section of the cord at the upper limit of the lumbar region,
erection of the penis, which is known to be due to a reflex
dilatation of its arteries through the nervi erigentes, can still
be caused by mechanical stimulation of the glans penis, so
long as the afferent fibres of the reflex arc contained in the
nervus pudendus are intact. Destruction of the lumbar
cord abolishes the effect. It is impossible to avoid the con-
clusion that a vaso-dilator or erection centre, which is in
relation on the one hand with the nervi erigentes, and on
the other with the nervus pudendus, exists in the lower
portion of the spinal cord. Vaso-motor centres for the
hind-limbs have also been located in the same region. And
such centres appear to exist even beyond the limits of the
central nervous system. For when the lower portion of
the cord is completely destroyed, the dilatation of the
vessels of the hind-limbs, which is at first so conspicuous,
passes away after a time ; and the only plausible explanation
seems to be that the functions of vaso-motor centres have
been assumed by some of the peripheral (sympathetic)
ganglia (Goltz and Ewald).
Of the anatomical relations of the nerve-cclls that make up the
bulbar and spinal vaso-motor centres, little more is known than may
i6o A MANUAL OF PHYSIOLOGY
be deduced from the physiological facts we have been reciting. It
has been surmised that certain cells of small si/c scattered up and
down the cord in the anterior horn and intermedio-lateral tract, and
cropping out also in the bulb, are vaso-motor cells. It must be
assumed that their axis-cylitider processes are connected with the
vaso-motor fibres which we have already discovered emerging from
the brain in certain cranial nerves and from the cord in the anterior
spinal roots. And, indeed, there is reason to believe that, in the case
of the spinal vaso-motor cells at any rate, the connection is made
without the intervention of any other nerve-cells, and that the axis-
cylinders of these vaso-motor fibres are the axis-cylinder processes of
the vasomotor cells. So that the simplest efferent p'ath along which
vasomotor impulses can pass may be considered as built up of two
neurons, one with its cell-body in the central nervous system, and the
other in a sympathetic ganglion. But since it would af)i)ear that the
spinal vasomotor centres are under the control of the chief centre
in the bulb, it is necessary to suppose that the axis-cylinder processes
of some of the cells of the bulbar centre come into relation with the
spinal vasomotor cells, and that impulses passing, let us say, from
the bulb to the vessels of the leg, would have to traverse three
neurons (see Chap. XII.).
Vaso-motor Reflexes. — We have already seen that the
cardiac centres are constantly influenced by afferent im-
pulses, and that in the direction either of augmentation or
inhibition. The vaso-motor centre in the bulb is equally
sensitive to such impulses. They reach it for the most part
along the same nerves, and by increasing or diminishing its
tone cause sometimes constriction and sometimes dilatation
of the vessels, the result depending partly upon the anato-
mical connection of the afferent fibres, but apparently in
part also upon the state of the centre.
Of the afferent nerves that cause vaso-dilatation, the most
important is the depressor, whose refle.x inhibitory action on
the heart has been already described. The fall in the
arterial pressure is due chiefly, not to the inhibition of the
heart, but to the inhibition of the portion of the vaso-motor
centre that presides over the great area ruled by the
splanchnic nerves, and the consequent dilatation of the
vessels of the abdominal viscera. For if these nerves have
been previously cut, stimulation of the depressor is ineffective,
while it produces its usual result after section of the vagi.
It has been suggested that the function of the depressor is
to act as an automatic check upon the blood-pressure in the
THE CIRCULATION OF HIE BLOOD AND LYMI'll i6i
interest of the heart, its terminations in the ventricular wall
being mechanicall)' stin)ulated when the pressure tends to
rise towards the danger limit. In rare cases, efferent inhi-
bitory fibres for the heart have been found in the depressor
of the rabbit.
Many of the peripheral nerves contain fibres whose
stimulation is followed by dilatation of the bloodvessels in
special regions, usually the areas to which they are them-
selves distributed, accompanied by constriction of distant
and, it may be, more extensive vascular tracts. Thus, the
usual local effect of Ptimulatintr the afferent fibres of the
Fig. 54. —Diagram oi- Dk
PREssoR Nerve in Rakbi 1.
X, vagus iSL.superiorlaryn- ,,,^, -- _Blood-i-ressure Tracing (Rahbit;
geal branch of vagus ; D de- (MERCURY MANOMETER.)
pressor fibres. The arrows show ^
the course of the impulses that ("entral end of depressor stimulated at i ; stimula-
affect the blood-pressure. tion stopped at 2. Time trace seconds.
lowest three thoracic nerves, in whose anterior roots run the
vaso-motor fibres for the kidney, is a dilatation of the renal
vessels (Bradford), and the usual local effect of stimulating
the infra-orbital or supra-orbital nerve a dilatation of the
external maxillary artery. But the general effect in both
cases is vaso-constriction in other regions of the body,
v^hich more than compensates the local dilatation, so that
the arterial blood-pressure rises. It is not difficult to see
that both of these changes render it easier for the part to
obtain an increased supply of blood.
II
i62 A MAXUAL OF PHYSIOLOGY
The kind of stimulus seems to have something to do with
the direction of the reflex vaso-motor change, for while
electrical stimulation of every muscular nerve, even of the
very finest twigs that can be isolated and laid on electrodes,
provokes always, whether the shocks follow each other
rapidly or slowly, a rise of general blood-pressure, mechanical
stimulation of a muscle, as by kneading or massage, causes
a fall. The condition of the afferent fibres also exerts an
influence. For example, excitation of the central end of a
sciatic nerve that has been cooled is followed by vaso-
dilatation and fall of pressure, the opposite of the ordinary
result. These and similar facts have led to the idea that
most aflerent nerves contain two kinds of fibres, whose
stimulation can affect the activity of the vaso-motor centres,
'reflex vaso-constrictor," or 'pressor' fibres, and 'reflex
vaso-dilator,' or 'depressor' fibres. The branch of the
vagus, however, to which the name ' depressor ' has been
specially given, is the only peripheral nerve the excitation of
which is in all circumstances followed by a general diminu-
tion of arterial pressure. If specific ' depressor ' fibres exist
elsewhere, they are so mingled with ' pressor ' fibres that
their action is masked when both are stimulated together.
The state of the vaso-motor centre is a third factor, which
has some importance in determining the result of reflex
vaso-motor stimulation. For instance, in an animal deeply
anaesthetized with chloroform or chloral, excitation of an
ordinary sensory nerve may cause, not a rise, but a fall of
blood-pressure.
An interesting illustration of the reciprocal relation
between difterent parts is found in the opposite behaviour of
the vessels of the skin and those of the internal organs,
which is often observed during reflex stimulation of the
vaso-motor centres. For example, stimulation of the cut end
of the sciatic causes, as we have already seen, a notable rise
in the blood-pressure and extensive vaso-constriction. This
certainly involves the splanchnic area ; but superficial parts,
as the lips, may be seen to be flushed with blood. In
asphyxia, when the vaso-motor centres are directly stimu-
lated by the venous blood, this antagonism is still better
THE ClRCl'LATIOX OF Till. liLOOD AM) f.YMl'll 163
marked : the cutaneous vessels are widely dilated and
engorged, the face is livid, but the abdominal organs are
pale and bloodless (Heidenhain). The blood-pressure rises
rapidly, reaches a maximum, and then gradually falls as the
vaso-motor centre becomes paralyzed (Figs. 56 and 57).
These facts enable us to some extent to understand the
manner in which the distribution of the blood is adjusted to
the requirements of the different parts of the body, so that
to a certain degree of approximation no organ has too much,
and none too little. The blood-supply of the organs is
always shifting wdth the calls upon them. Now, it is the
actively-digesting stomach and the actively-secreting glands
of the alimentary tract which must be fed with a full stream
KiG. 56. — Rise of Blood-pressure in Asphyxia (in Rabbit).
Respiration stopped at i. Interval between 2 and 3 (not reproduced) 44 seconds,
during which the blood-pressure steadily rose. At 4, respiration resumed. Time
tracing marks seconds.
of blood, to supply waste and to carry away absorbed nutri-
ment. Again, it is the working muscles of the legs or of the
arms that need the chief blood-suppl}'. But wherever the
call may be, the vaso-motor mechanism is able, in health,
to answer it by bringing about a widening of the small
arteries of the part which needs more blood, and a compen-
satory narrowing of the vessels of other parts whose needs
are not so great.
It is also through the vaso-motor system, and especially
by the action of that portion of it which governs the
abdominal vessels, and of the nerves that regulate the work
of the heart, that in animals to which the upright position
II — 2
1 64 A M.Wr.lL or PHYSIOLOGY
is normal (monkey) and in man the influence of changes of
posture on the circulation is almost completely compensated.*
The pressure in the upper part of the human brachial artery
has been measured by a special form of sphygmo-manometer,
first in the horizontal and then immediately afterward in
the standing posture, and in health it has been found to
remain practically unchanged. But if the person was
over-worked or out of sorts, the compensation was less
complete. In such animals as the rabbit this compen-
sation is totally inefficient. When a domesticated rabbit,
which has been kept in a hutch, is suspended vertically
with the feet down, the blood drains into the abdominal
vessels, syncope speedily ensues, and in a period that
ranges from less than a quarter to three-quarters of an
hour the animal dies in the convulsions of acute cerebral
anaemia (Salathc, Hill). The head-down position has no
ill effects. In wild rabbits, whose abdominal wall is more
tense and elastic, these fatal symptoms are not easily
produced, and the same is true of cats and dogs. But in
all animals, when the compensation is destroyed, as in
paralysis of the vaso-motor centre by chloroform, the cir-
culation may be profoundly influenced by the position of the
body : elevation of the head may lead to cerebral anaemia,
syncope, and even death ; elevation of the legs, and par-
ticularly the abdomen, may restore the sinking pulse by
filling the heart and the vessels of the brain. If a chloralized
dog be fastened on a board which can be rotated about a
* Two factors may be distinguished in the blood-pressure, the hydro-
static and the hydrodynamic elements. The hydrostatic portion of the
pressure is due to the weight of the column of blood acting on the vessel ;
the hydrodynamic portion of the pressure is due to the work of the heart.
If a dog be securely fastened to a holder arranged in such a way that the
animal can be placed vertically, with the head up or down, and the mean
blood-pres-ure in the crural artery be measured in the two positions, there
will be a considerable difference. For when the legs are uppermost the
heart has to overcome the weight of the column of blood rising above it
to the crural artery ; when the head is uppermost the action of the heait
is reinforced by the weight of the blood. And if no change were produced
in the action of the heart, or in the general resistance of the vascular path,
by the change of position, this difference would be equal to the pressure
of a column of blood twice as high as the straight-line distance between
the cannula and the point of the arterial system at which the pressure is
the same with head up as with head down i' indifferent point).
THE CIRCULATIOX Of THE nLOOl) A.\7J lA'Mril 165
horizontal axis passing; under the neck, the blood-pressure
in the carotid artery falls greatly when the animal is made
to assume the vertical position with the head up, and either
rises a little or remains relatively unchanged when the head
is made to hang down. So great may the fall of pressure be
in the former position that death may occur if it be long
maintained (Practical Exercises, p. 187).
Finally, it is in virtue of the amazing power of accommoda-
tion possessed by the vascular system, as controlled by the
vaso-motor and cardiac nerves, that so long as these are
m-^
"'*'^
t t ! ' ' ' 1 ' 1 ' 1 1 ' I 1 i ■ ' i f 1 I t I I I ! I I t 1 I I 1 M 1 It 1 1 i . i 1^ j i I 1 H
P'tG. 57.— Bi.ooD-PRESsuRK Tka<;ing rKcni a Dog poison eo with Aia ohou
The respiratory centre being paralyzed, respiration stopped, and the typical rise of
blood-pressure in asphyxia took place. The pressure had again fallen, and total
paralysis of the vaso-motor centre was near at hand, wlien at A the animal made a
single respiratory movement. The quantity of oxygen thus taken in was enough
to restore the vaso-motor centre, and the blood-pressure again rose. This was re-
peated five or six times.
not disabled the total quantity of blood ma}- be greatly
diminished or greatly increased, without endangering life,
or even causing more than a transient alteration in the
arterial pressure. It is not until at least a quarter of the
blood has been withdrawn that there is any notable effect
on the pressure, for the loss is quickly compensated by an
increase in the activity of the heart and a constriction of
the small arteries. An animal may recover after losing con-
siderably more than half its blood.* Conversely, the volume
* It is not usually possible to obtain quite two-thirds of the total blood
by bleeding a dog from an artery like the carotid.
i66 J MAMW/. OF I'llYSIOLOCY
of the ciicuUitinf,' liquid may be almost doubled by the in-
jection of blf)od or normal saline solution without causinp^
death, and increased by 50 per cent, without any marked
increase in the pressure. The excess is promptly stowed
away in the dilated vessels, especially those of the splanchnic
area; the water passes rapidly into the lymph, and is then
more gradually eliminated by the kidneys.
From these facts we can deduce the practical lesson,
that blood-letting, unless copious, is useless as a means of
lowering the general arterial pressure, while it need not be
feared that transfusion of a considerable quantity of blood,
or of salt solution, in cases of severe ha:;morrhage will
dangerously increase the pressure. And from the physio-
logical point of view the term 'haemorrhage ' includes more
than it does in its ordinary sense. For as dirt to the
sanitarian is ' matter in the wrong place,' haemorrhage to
the physiologist is blood in the wrong place. Not a drop of
blood may be lost from the body, and yet death may occur
from haemorrhage into the pleural or the abdominal cavity,
into the stomach or intestines. Not only so, but a man
may bleed to death into his own bloodvessels ; in shock, as
well as in ordinary fainting or syncope, the blood which
ought to be circulating through the brain, heart and lungs
may stagnate in the dilated vessels of the splanchnic area.
The Lymphatic Circulation. — As has already been mentioned,
some of the constitiunts of the blood, instead of passing back to
the heart from the capillaries along the veins, find their way by
a much moru tedious route along the lymphatics. The blood-
capillaries are everywhere in very intimate relation with lymph-
capillaries, which are simply irregular spaces, more or less completely
lined with epithelioid cells, in the connective-tissue that everywhere
accompanies and supports the bloodvessels. The constituents of the
blood-plasma are filtered through, or, as some say, secreted by the
capillary walls into the lymph spaces, and there form the clear liquid
known as lymph, from which the cells of the tissues take up food,
and into which they discharge waste products. The lymph spaces
are connected with more regular lymphatic vessels, with lymphatic
glands at intervals on their course. These fall into larger trunks,
and finally the greater part of the lymph reaches the blood again by
the thoracic duct, which f)pens into the venous system at the junction
of the left subclavian and internal jugular veins. The lymph from
the right side of the head and neck, the right extremity, and the
right side of the thorax with its viscera, is collected by the right
THE CIRCULATION OF THE BLOOD AND LVMl'// \(q
lymphatic duri, which opLiis at ihc junction of the right subclavian
and internal jugular veins. The openings of both ducts are guarded
by semilunar valves, which prevent the reflux of blood from the
veins. Serous cavities like the pleural sacs are really large lymph
spaces, and they are connected through small ojK-nings, called
stomata, with lymphatic vessels.
The raie of flow of the lymph in the thoracic duct is very small
compared with that of the blood in the arteries — only about 4 mm.
per second, according to one observer. Nevertheless, a substance
injected into the blood can be detected in the lymph of the duct in
four to seven minutes (Tschirwinsky). The factors which contribute
to the maintenance of the lymph flow are :
(i) The pressure under which it passes from the capillaries into
the lymph spaces. The pressure in the thoracic duci of a horse may
be as high as 1 1 mm. of mercury ; in the dog it may be less than
I ram. The difference is probably due, in part at least, to a differ-
ence in the experimental conditions, dogs being usually anassthetized
for such measurements, horses not. The pressure in the lymph
spaces must, of course, be higher than in the thoracic duct, how
much higher we do not know.
(2) The contraction of muscles increases the pressure of the
lymph by compressing the channels in which it is contained, and
the valves, with which the lymphatics are even more richly provided
than the veins, hinder a backward and favour an onward flow. The
contractions of the intestines, and especially of the villi, are an im-
portant aid to the movement of the chyle. By the contraction of
the diaphragm, substances may be sucked from the peritoneal cavity
into the lymphatics of its central tendon, through the stomata in the
Serous layer with which its lower surface is clad. It is even possible
by passive movements of the diaphragm in a dead rabbit to inject
its lymphatics with a coloured liquid placed on its peritoneal surface.
Passive movements of the limbs and massage of the muscles are also
known to hasten the sluggish current of the lymph, and are some-
times employed with this object in the treatment of disease.
(3) The movements of respiration aid the flow. At every inspira-
tion the pressure in the great veins near the heart becomes negative,
and lymph is sucked into them.
(4) In some animals rhythmically-contracting muscular sacs or
hearts exist on the course of the lymphatic circulation. The frog
has two pairs, an anterior and a posterior, of these lymph hearts, which
pulsate, although not with any great regularity, at an average rate of
sixty to seventy beats a minute, and appear to be governed by motor
and inhibitory centres situated in the spinal cord. Such hearts are
also found in reptiles. It is possible that in animals without localized
lymph hearts the smooth muscle, which is so conspicuous an element
in the walls of the lymphatic vessels, may aid the flow by rhythmical
contractions.
J6i .1 M.WUM. OI- Pny<i/OLOGV
PRACTICAL KXKRCISKS ON CHAPTKR II.
1. Microscopic Examination of the Circulating Blood. — (i) Take
a tadpole and lay it on a glass slide. Cover the tail with a large
cover-slip, and examine it with the low power (Lcitz, oc. III., obj. 3).
Generally the tail will stick so closely to the slide, and the animal will
move so little, that a sufficiently good view of the circulation can he
obtained. If there is any trouble, destroy the brain with a needle.
Observe the current of the blood in arteries, capillaries and veins.
An artery may be easily distinguished from a vein by looking for a
place a*^ which the vessel bifurcates. In veins the blood flows in the
two branches of the fork knvards the point of bifurcation, in arteries
mvay from it.
vSketch a part of a tield.
To Pitli a Frog. — Wrap the animal in a towel, bend the head
forwards with the index-finger of one hand, feel with the other for the
depression at the junction of the head and backbone, and push a
narrow-bladed knife right down in the middle line. The spinal cord
will thus be divided with little bleeding. Now push into the cavity
of the skull a piece of pointed lucifer match. The brain will thus
be destroyed. The s[)inal cord can be destroyed by passing a blunt
needle down inside the vertebral eanal.
(2) Take a frog and pith its brain only, inserting a match to prevent
bleeding. Pin the frog on a plate of cork into one end of which a
glass slide has been fastened with sealing-wa.x. Lay the web of one
of the hind-legs on the glass and gently separate two of the toes, if
necessary by threads attached to them and secured to the cork plate.
Put the plate on the microscope-stage and fasten by the clips (see
pp. 26, 107).
2. Anatomy of the Frog's Heart. — Expose the heart of a pithed
frog by pinching up the skin over the abdomen in the middle line,
dividing it with scissors up to the lower jaw, and then cutting through
the abdominal muscles and the bony pectoral girdle, 'i'he external
abdominal vein, which will be observed on reflecting the skin, can
be easily avoided. The heart will now be seen enclosed in a thin
membrane, the pericardium, which should be grasi)ed with fine-
pointed forceps and freely divided. Connecting the posterior surface
of the heart and the pericardium is a slender band of connective
tissue, the fra;num. A silk ligature may be passed around this with
a threaded curved needle and tied, and then the fra;num may be
divided posterior to the ligature. The anatomical arrangement of the
various parts of the heart should now be studied. Note the single
ventricle with the bulbus arteriosus, the two auricles, and the sinus
venosus, turning the heart over to see the latter by means of the
ligature. Observe the whitish crescent at the junction of the sinus
venosus and the right auricle (Fig. 58).
3. The Beat of the Heart. — Note that the auricles beat fust, and
then the ventricle. The ventricle becomes smaller and paler during its
systole, and blushes red during diastole. Count the number of beats
of the heart in a minute. Now excise the heart, lifting it by means
I'KA Lin : I /. / .\7:A'C7S/iS
169
of the ligature, and taking care to cut wide of the sinus venosus,
I'iace the heart in a small i)orcelain capsule on a little blotting [)ai)er
moistened with normal saline. Observe that it goes on beating.
Put a little ice or snow in contact with the heart, and count the
number of beats in a minute. The rate is greatly diminished. Now
remove the ice and blotting-paper, cover the heart with normal
saline, and heat, noting the temperature with a thermometer. Observe
that the heart beats faster and faster as the temperature rises. At
40° C. to 43" C. it stops beating in diastole (heat standstill). Now
at once pour off the heated liquid, and run in some cold normal
saline. I'he heart will begin to beat again.
4. Cut off the apex of the ventricle a little below the auriculo-
ventricular groove. The auricles, with the attached portions of the
ventricle, goon beating. The apex does not contract spontaneously,
but can be made to
beat by stimulating
it mechanically (by
pricking it with a
needle) orelectrically.
Divide the still con-
tracting portion of
the heart by a longi-
tudinal incision. The
two halves go on
beating.
5. Heart -tracings.
— (1) Fasten a myo-
graph-plate (Fig. 59)
on a stand. Take a
long light lever con-
sisting of a straw or
a piece of thin chip,
armed at one end
with a writing-point of parchment-paper, supported near the other
end by a horizontal axis, and pierced not far from the axis by
a needle carrying on its point a small piece of cork or a ball of
seaiing-wax. A counterpoise is adjusted on the short arm of the
lever in the form of a small leaden weight. Cover a drum with
glazed paper and smoke it. The paper must be put on so tightly
that it will not slip. To smoke the drum, hold it by the spindle
in both hands over a fish-tail burner, depress the drum in the
flame, and rotate rapidly. Avoid putting on a heavy coating of
smoke, as a more delicate tracing is obtained when the paper is
lightly smoked. The speed of the drum can be varied by putting
in or taking out a small vane. Arrange an electro-magnetic time-
marker for writing seconds (Fig. 60). Pith a frog (brain only),
expose the heart, and put under it a cover-slip to give it support. Pin
the frog on the myograph-plate, and adjust the foot of the lever so that
it rests on the ventricle or the auriculo-ventricular junction. Bring
the writing-point of the lever and that of the time-marker vertically
I'lc. 58. — Frog's Hkakt with Stannin's Liga-
T'jREs IN Position (Cyon).
Anterior surface of heart shown on the left, posterior
surface on the right, a, right auricle ; 6, left auricle ; c,
ventricle ; d, bulbus arteriosus ; e, /, aortoe ; g, sinus
venosus.
170
A M.WUAL OF PIIYSIOLOGY
under each other on the surface of the drum. Set off the drum at
the slow speed (say, a centimetre a second). When the lever rests
on the auriculo-ventricular junction, the part of the tracing corre-
sponding to the contraction of the heart will be broken into two
Ccu\i,ttyf>o\iL
Fin. 59. — Arranckmknt for OKi.\iM.N<; a Heart Tka< ing irom a Fiuh;.
portions, representing the systole of the auricles and ventricle re-
spectively. C'ut the paper off the drum with a knife and carry it
to the varnishing-trough, holding the tracing by the ends with both
Fic. 60. — Ei.kijiko-.ma(;nkti(: 'I'imk-makkkk < d.nnki i ij> with Mkironomk.
]'he pendulum of the metronome carries a wire which closes the circuit when it dips
into either of the mercury cups, Hg.
hands, smoked side up. Immerse the middle of it in the varnish,
draw first one end and then the other through the varnish, let it
drip for a minute into the trough, and fasten it up with a pin to
dry.
(2) Heart Tracings ivitli Simiiltojicoui Record of Auricular and
/'A'. I c TIC. [ I. /:.\/:rcisI':s
171
Ventricular Contrattions. — {a) Yox this purpose iwo levers may We
arranged, one resting on the auriele, the other on the ventricle, ilie
writing points being placed in the same vertical straight line on the
drum. A convenient form of apparatus is shown in Fig. 61.
{b) GaskeU's Afet/iod {<i inodificatioii of). — -Attach a silk ligature to
the very apex of the ventricle. Divide the frxMium, cut the aorta
across close to the l)ulbus, pinch up a tiny portion of the auri( le and
ligature ii. Remove the intestines, liver, lungs, etc., care ijcing taken
in cutting away thr liver not to injure the sinus. Then remove the
lower jaw, and cut away the whole of the body except the head, part
of the (.esophagus, and the tissue connecting it with the heart. l"ix
the head in a clamp sliding on an ordinary stand. The heart is held
at the auriculo ventricular junction in a CJaskell's clamp supjinrtvd on
__nnhuutv^ 'Mn/f
Fi.
61. — Apparatus kor obtaining a Simultaneous Tracing ok
Auricular and Ventricular Contractions.
a separate stand. The thread connected with the ventricle is brought
round a pulley and attached to a lever above the heart. The
auricle is connected with another lever. The writing points of
the two levers are arranged in a vertical line on the drum. The
small pulley must be oiled from time to time to lessen the friction
(Fig. 63).
6. Dissection of the Vagus and Cardiac Sympathetic Nerves in
the Frog. — (i) Put the tissues in the region of the neck on the
stretch by passing into the gullet a narrow test-tube or a thick glass
rod moistened with water, and by pinning apart the anterior limbs.
Expose the heart by cutting through the pectoral girdle in the way
described in 2 (p. 168). On clearing away a little connective tissue
and muscle with a seeker, three large nerves will come into view.
The upper is the glosso-pharyngeal, the lower the hypoglossal ; the
172
A MAMAL Ul- I'UYSIOLOt.Y
vagus crosses diagonally between them (Fig. 63). Above the vagus
trunk, running parallel to it, and separated from it by a thin muscle
and a blood-vessel (the carotid artery), lies its laryngeal branch. The
vagus should he traced up to the ganglion situated on it near its exit
from the skull.
(2) Then cut away the lower jaw, dividing and reflecting the
membrane covering the roof of the mouth. At the junction of the
CtKI
Flu. 62. — ARRANGBMfcNT FOR KECORDING AURICULAR A.ND \ ENTRICULAR
CCNTRACIIOXS (AND .STUDVIN'^ THE InFI lENCE OF TEMPERATURE ON
THE Heart).
C, clamp holdini^ the heart at the aiiriculo-ventincular groove. F, pulley round
which a thread attached to the ape.x of the ventricle passes to the lever L'; L. lever
connected with auricle. (The rest of the arrangement i~ for studying the influence of
temperature on the heart and its nerves, (i being a vessel filled with normal saline
solution in which the heart is immersed ; R. an inflow tube from a reservoir containing
salt solution at the temperature required ; O", an outflow tube by which G may be
emptied into the beaker B' ; O, a tul>e passing to the beaker B to prevent overflow from
G ; T. a thermometer. )
skull and the backbone will be seen on each side the levator anguli
scapulae muscle (F'ig. 64). Remove this muscle carefully with fine
forceps. Clear away a little connective tissue lying just over the upper
cervical vertebrae, and the sympathetic chain, with its ganglia, will
be seen. Pass a fine silk thread beneath the sympathetic about the
level of the large brachial nerve, by means of a sewing-needle which
has been slightly bent in a flame and fastened in a handle. Tie the
/'AM ( //< AL EXEKCIsr.S
Glass rod
Glo ssofiharyn ^e a I
Hyppcflossi
branch of
-1^ Vayus
ligature, divide the sympatlietic below it, and isolate it carefully with
fine scissors up to its junction with the vagus ganghon.
Batteries. — To set up a Danull Cell. - - I'^ill th(; porous pot ( I'ig. 1 43,
p. 51 7)previously well soaked in water, with dilute sulphuric acid( 1 part
of commercial acid to 10 or 15 parts of water) to within i .', inches of
the brim, and place i n
it the piece of amalga
mattd zinc. If the
zinc is not properly
amalgamated, leave
it in the pot for a
minute or two to
clean its surface.
Then lift it out, pour
over it a little mer-
cury, and rub the
mercury thoroughly
over it with a cloth.
Put the pot into the
outer vessel, which
contains the copper
plate, and is filled
with a saturated solu-
tion of sulphate of
copper, with some
undissolved crystals
to keep it saturated.
After using the
Daniell, it must
alwaysbe taken down.
The outer pot is left
with the copper plate 1
and the sulphate solu-
tion in it. The zinc is
washed and brushed bright. The sulphuric acid is poured into the
stock bottle, and the porous pot put into a large jar of water to soak.
27ie BicJironiate Cell contains only one liquid — a mixture of i part
of sulphuric acid with 4 parts of a 10 per cent, solution of potassium
bichromate. In this is placed one, or in some forms two, carbon
plates and a plate of amalgamated zinc. After using the battery,
take the zinc out of the liquid.
The Leclanche battery consists of a porous pot filled with a
mixture of manganese dioxide and carbon packed around a carbon
plate, which forms the positive pole. The pot stands in an outer
jar of glass filled with a saturated solution of ammonium chloride,
into which dips an amalgamated zinc rod, which constitutes the
negative pole.
7. Stimulation of the Vagus in the Frog. — Make the same
arrangements as in 5 (i) (p. 169), but, in addition, set up an induction
machine arranged for an interrupted current (Fig. 65), with a Daniell,
Zuncf
63-
Thk Relations ok ihe V.agus i.\ thk
Froc.
174
A MAACAL Ol l'liySlOLO(,Y
a bichromate, or a Leclanche cell in the primary circuit, which
should also include a simple key. Insert a short-circuiting key
in the secondary circuit. Attach the electrodes to the short-cir-
cuiting key, push the secondary coil up towards the primary until the
shocks arc distinctly felt on the tongue when the N'eef's hammer is
set going and the short-circuiting key opened. I'ith the brain of a
frog, expose the heart, dissect out the vagus on one side, ligature it
as high up as possible, and divide above the ligature. I'asten the
electrodes on the cork plate by means of an indiarubber band, and
lay the vagus on them.
Set the drum off (at slow
speed). After a dozen
heart-beats have been re-
corded, stimulate the vagus
for two or three seconds by
opening the short-circuiting
key. If the nerve is active,
the heart will be slowed,
weakened, or stopped. In
the la>t case the lever will
trace an unbroken straight
line : but even if the stimu-
lation is continued the
i)eats will again begin.
S. Stimulation of the
Junction of the Sinus and
Auricles. — After a suf-
ficient number of the obser-
\ ations described in 7 have
been taken with varying
time and strength of stimu-
lation, take the writing-
points off the drum, apply
the electrodes directly to
the crescent at the junction
of the sinus venosus with
the right auricle, and
stimulate. The heart will
be affected very much in
the same way as by stimula-
tion of the vagus, except that during the actual stimulation its beats
may be quickened and the inhibition may only begin after the
electrodes have been removed (Fig. 46, j). 135).
9. EflFect of Muscarine and Atropia. — Paint on the sinus venosus
with a small caniel's-hair brush a very dilute solution of muscarine,
'i'he heart will soon be seen to beat more slowly, and will ultimately
stop in diastole. Now apply a dilute solution of sulphate of atropia
to the sinus. The heart will again begin to beat. Stimulation of
the vagus will now cause no inhibition of the heart, because its
endings have been paralyzed by atropia. (Muscarine has also been
ii
64. — RELAriON OK THE SVMPATHElIt
TO THE Vagus in the Frog.
I, 2, 3, 4 are spinal nerves.
/'AM cm : I r. exercises
'75
applied to the lieart, but it could he shown by a separate experiment
that atropia by itself has the same effect on the vagus endings.)
(1>. 141.)
10. Stannius' Experiment. — Pith a frog. I'lxpose the lieart in the
way described under 2 (p. 168). Ligature the fra,'num with a fine silk
thread, and use the thread to manipulate the heart. With a curved
needle pass a moistened silk thread between the aorta and the
superior vena cava, and tie it round the junction of the sinus and
right auricle (I'ig. 58). The auricles and ventriclestop beating as soon
as the ligature is tightened. The sinus venosus goes on beating. Now
separate the ventricle from the rest of the heart by an incision through
the auriculo-ventricular groove, or tie a second ligature in the groove.
The ventricle begins to beat again, the auricle remaining quiescent
in diastole (p. 142). Occasionally both auricle and ventricle, or only
the auricle, may begin to beat.
11. Stimulation of Cardiac Sympathetic Fibres in the Frog.-
( 1 ) In the vago-sytnpathetic ajter the inhibitory fibres have been cut out />\'
atropia. — Arrange everything as in 7 (p. 173). Assure yourself, by
1-10.65. — Arrangemem 01' Induction Machine for Teianls.
B, battery ; K, simple key ; P. primary coil ; S, secondary coil.
stimulating the vagus, that it inhibits the heart, and take a tracing
during stimulation. Then paint a dilute solution of atropia on the
sinus. Stimulation of the vagus, which is really the vago-sympathetic
(see Fig. 64), will now cause, not inhibition, but augmentation (increase
in rate or force, or both), since the endings of the inhibitory fibres
have been paralyzed by atropia. The strength of the stimulating
current required to bring out a typical augmentor effect is greater than
that needed to stimulate the inhibitory fibres. Take a tracing to show
augmentation produced by stimulating the nerve.
(2) By direct stimulation of the cervical sympathetic. — Make the
same arrangements as in 11 (i), but, instead of isolating the vagus,
dissect out the sympathetic on one side in the manner described in
6 (2) (p. 172), and do not apply atropia to the heart. Lay the upper
(cephalic) end of the sympathetic on very fine and well-insulated
electrodes, and stimulate. (To insulate electrodes the points may
be covered with melted paraffin. When the paraffin has cooled, a
narrow groove, just sufficient to lay bare the wires on the upper side,
is made in it, and the nerve is laid in this groove.) (Fig. 52, p. 143.)
176
A MAM'AI. or rilYSIOI.OGY
Exptrimentb 7, 11 (i) and 11 (2) will be rendered more exact
by connecting a second electro magnetic signal with a Pohl's com-
mutator without cross-wires (I'ig. 66), in such a way that the circuit
is interrupted at the instant when stimulation begins.
12. The Action of the Mammalian Heart. — Inject under the
skin of a dog (preferably a small one) i cc. of a 2 per cent, solution
of morphia hydrochlorate for every kilogramme of body-weight. As
soon as the morphia has taken effect (in 15-30 minutes), fasten the
animal back down on a holder (as in l"ig. 100), pushing the mouth-
FiG. 66.
-ARRANGE.MKNT I'OR KECORDINC. THE BEGINNING AND EnU OK
Stimulation.
C. Pohl's commutator without cross-wires ; B, battery in circnit of primary coil P ;
B', battery in circuit of electro-magnetic signal T ; K, simple key in primary circuit ;
S, secondary coil. When the bridge of the commutator is tilted into the position
shown in the figure, the primary circuit is closed and the circuit of the signal broken.
pin behind the canine teeth and screwing the nut home.* In the
meantime select a tracheal cannula"!" of suitable size, and get ready
"*" A siinple but efficient and convenient holder for a dog may be
easily constructed as follows. Take a board of the length required (2^ to
6 feet, accoiding to the size of the dog). At one end fasten two short
upright wooden pins, 4 to 6 inches apart. These are pierced from side to
side with four or five holes at different heights. .An iron pin passing
behind the canine teeth of the animal through tw(j corresponding holes
in the uprights, and tied over the muzzle by a cord arranged in a figure
of eight, secures the head. For a large dog an upper pair of holes is
used, for a small dog a lower pair. 'Jhe feet are fastened by cords to
staples inserted into the sides of the board, the fore-legs being drawn tail-
wards for all operations on the nei k or head, headwards for operations on
the thorax. A rabbit-holder can be made in exactly the saine way.
f A tracheal cannula is easily made by heating a piece of glass tubing,
about 6 inches long, a short distance from one enil, and drawing it out
slightly so as to form a * neck.' 'i"he tubing is then bent about its middle
to an obtuse angle, and the end next the neck is ground obliquely on a
stone. The diameter of the cannula should be about the same as that of
the trachea, into which it is to be inserted by its oblique end.
PRACTICAL EXERCISES 177
instruments for dissection — one or two pairs of artery-forceps, a pair
of artery-clamps (bulldog pattern), two or three glass cannulx- of
various sizes for bloodvessels, ten strong waxed ligatures, sponges,
hot water, a towel or two, and a pair of bellows to be connected with
the tracheal cannula when the chest is opened. Arrange an in-
duction-coil and electrodes for a tetanizing current (I'ig. 65, p. 175).
With scissors curved on the flat clip away the hair from the front of
the neck and the anterior surface of one thigh below Poupart's
ligament. Put the hair carefully away, and remove all the loose
hairs with a wet sponge so that they may not get into the wounds.
If the animal is not fully anaesthetized, give ether. Insert a glass
cannula, which should have a piece of indiarubber-tubing 2 to 3
inches in length on its wide end, into the central end of the femoral
vein. Feel for the femoral artery, cut down over it, and with forceps
or a blunt needle separate the femoral vein from it for about an inch.
Pass two unwaxed ligatures under the vein, and tie a loose loop on
each. Put a pair of bulldog forceps on the vein between the liga-
tures and the heart. Now tie the lower (distal) ligature, and cut one
end short. The piece of vein between it and the bulldog forceps is
thus distended with blood, and this facilitates the next step. With
fine-pointed scissors make a snip in the wall of the vein. The
cannula is now pushed through the slit in the vein, and the upper
ligature tied firmly round its neck. By the aid of a pipette, made by
drawing a piece of glass tubing out to a long point, the cannula and
rubber tube are then completely filled with normal saline solution.
Be sure to pass the point of the pipette right down to the point of
the cannula, so as to dislodge any bubble of air that may tend to
cling there. Then, holding up the open end of the rubber tube,
close it, without allowing any air to enter, by means of a screw clamp
or bulldog forceps, or a small piece of glass rod. i or 2 cc. of
the 2 per cent, solution of morphia may be injected from time to
time, when necessary, by pushing the needle of the hypodermic
syringe through the rubber tube. When the needle is withdrawn the
little hole closes completely, and nothing escapes from the cannula.
To put a Cannula in the Trachea. — The hair having been clipped
in the middle line of the neck and the skin shaved, a mesial incision
is to be made, beginning a little below the cricoid cartilage, which
can be felt with the finger. The trachea is then cleared from its
attachments by forceps or a blunt needle, and two strong ligatures
are passed beneath it. A single loop is placed on each of those,
but is not drawn tight. Raising the trachea by means of the upper
ligature, the student makes a longitudinal incision through two or
three of the cartilaginous rings, inserts the cannula, and ties the
lower ligature firmly around its neck. It is well also, though not
necessary, to now tie the upper ligature, and additional security may
be obtained by tying together the ends of the two ligatures around
the cannula.
Clip off the hair on each side of the sternum. Make an incision
on each side through the skin and down to the costal cartilages about
2 inches from the edge of the breast-bone, and long enough to
12
178 A MANUAL OF PHYSIOLOGY
exjwse about four costal cartilages (say, 3rd to 6th). With a curved
needle pass waxed ligatures round the cartilages, and tie firmly to
compress the intercostal vessels. Then pass a waxed ligature under
the upper portion of the sternum, and tie it very tightly round that
bone so as to occlude the internal mammary arteries. The bellows
should now, or earlier if any symptoms of impeded respiration have
appeared, be connected with one end of the horizontal limb of a
glass T-piece, the other end of which is similarly connected with the
tracheal cannula. The stem of the T-piece is provided with a short
piece of rubber tubing, which, when artificial respiration is being
carried on, is to be alternately closed and opened — closed during
inflation of the lungs, and opened when the air is to be allowed to
escape from them. Ether may, if necessary, be administered by
passing this short tube through one neck of a Woulffs bottle con-
taining the anesthetic, and alternately comi)ressing and opening it as
described. If the cannula has a side-opening, as is usually the case
with metal cannulce, the T-piece may be dispensed with. One
student should take sole charge of the artificial respiration, which
ought to be begun as soon as the chest has been opened, and con-
tinued at the rate of about twenty inflations per minute. The costal
cartilages and sternum are rapidly cut through with strong scissors
just on the sternal side of the ligatures, and the sternum is divided
below its ligature, the artificial respiration being sus])ended for an
instant, as each cut is made, to avoid wounding the lungs. The
lower part of the sternum is turned down like the lid of a box, tied
out of the way or cut off altogether, and the heart, enclosed in the
pericardium, comes into view. If the ligature round the sternum has
not properly compressed the internal mammary arteries, hc'emorrhage
from the central ends may now occur. In this case they must be
seized with artery-forceps and ligatured. .A. cotton thread is now
passed with a suture-needle through each side of the pericardium,
which is then stitched to the chest wall and opened. The following
observations and experiments should now be made :
{a) Note the various portions of the heart, right and left ventricles,
right and left auricles, with the auricular appendices. Feel the heart
with the hand, and observe that the right ventricle is softer and has
thinner walls than the left, and that the auricles are softer than the
ventricles. Note how all the parts of the heart harden in the hand
during systole and soften during diastole (pp. 74-76).
{b) Dissect out the vago-sympathetic on one side in the neck of
the dog. The guide to the nerve is the carotid artery. These two
structures and the internal jugular vein lie side by side in a common
sheath. Feel for the artery a little external to the trachea, cut down
on it, open the sheath, isolate the vago-sympathetic for about an
inch, pass two ligatures under it, tie them, and divide between the
ligatures. The peripheral and central end of the nerve may now be
successively stimulated. Stimulation of the peripheral end causes
slowing of the heart or stoppage in diastole. I'eel that it softens
when it stops. It soon begins to beat again. Stimulation of the
central end of the vagosympathetic may or may not cause inhibition.
PRACTICAL KXERCISES 179
If it does, expose the other vagosympathetic, di\idc it, and repeat
the stimulation of the central end. There will now be no inhibition
of the heart. Incidentally it may be seen that stimulation of the
central end of the vagosympathetic causes strong, though, of course,
with opened chest, abortive, respiratory movements.
{c) Pith a frog (brain and cord), dissect out the sciatic nerve on
one side up to the sacral plexus. Cut off the whole leg. 1 )rop the
cut end of the nerve on the heart, and hold the preparation so that
the nerve touches the heart also by its longitudinal surface. At
each cardiac beat the nerve is stimulated by the action current
(Chap. XL), and the muscles of the leg contract.
{(i) Raise the board so that the head of the animal is down and
the hind-feet up, and note whether there is any effect on the action
and filling of the heart. Repeat the observation with head up and
feet down.
{e) Compress the aorta with the fingers, and observe the effect on
the degree of dilatation of the various cavities of the heart. Repeat
the experiment with the inferior vena cava, and compare the
results.
(/) Stop the artificial respiration, and observe the changes which
take place in the auricles and ventricles, comparing particularly the
right side of the heart with the left. Before the heart has stopped
beating, recommence the artificial respiration.
{g) When the heart is again beating with a fair degree of regularity
and strength, make a small penetrating wound with a scalpel in the
left ventricle. Observe the course of the haemorrhage, and note
especially the difference in systole and diastole.
{h) Lay the electrodes on the heart, and stimulate it with a strong
interrupted current. The character of the contraction soon becomes
profoundly altered. Shallow irregular contractions flicker over the
surface, with a kind of simmering movement suggestive of a boiling
pot (delirium cordis, fibrillar contraction). Now kill the animal by
stopping the artificial respiration. Observe how long the heart
continues to beat, and which of its divisions stops last.
(/) Make a dissection of the cervical sympathetic up to the superior
cervical ganglion, and down through the inferior cervical ganglion to
the stellate or first thoracic ganglion. Make out the annulus of
Vieussens and the cardiac sympathetic (accelerator) branches going
•off from the annulus or the inferior cervical ganglion to the cardiac
plexus (Fig. 50, p. 139).
13. Action of the Valves of the Heart.— (i) Study the action of
the valves of the ox-heart in the artificial scheme. Connect the ox-
heart provided with the pump P and bottle B, as shown in Fig. 67.
The cavity of the heart is illuminated by means of a small electric
lamp, the wires of which pass in at A. When the piston of the pump
is pushed down, water is forced through the aorta D along the tube
T into the bottle, and flows back again into the left auricle by the
tube T'. During each stroke of the pump the auricub-ventricular
valve is seen through the glass disc inserted into C to close, and the
semilunar valve is seen through the glass in D to open. When
12 — 2
i8o
A MANUAL OF PJIYSIOLOUy
tlie piston is raised, the semilunar valve is seen to be closed and the
auriculo-ventricular valve to be opened. For comparison a human
heart with a valvular lesion might be used.
KiG. 67.
-Arrangement to illustrate Action of Cardiac Valves in
THE Heart ok an Ox (Gad).
C. glass window in left auricle ; D, window in aorta ; E, tube inserted through apex
of heart info left ventricle and connected with pump P ; A, side tube on E, through
which wires are connected with a tiny incandescent lamp in the ventricle ; W, water
in bottle B ; T. T' tubes.
(2) With the sheep's or dog's heart provided, perform the following
experiments :
PR A CTICA I. r.XllRClSES
l8(
((7) Open the pericardium and notice how it is rcllectcd around
the great vessels at the base of the heart. Distinguish tlie pulmonary
artery, the aorta, the superior and inferior vence caviv;, and the |)ul-
monary veins. The trachea and portions of the lungs may also be
attached. If so, remove them carefully without injuring the heart.
(/') Take two wide glass tubes, drawn slightly into a neck at one
end. One of the tubes should be about lo cm. long, and the other
about 50 cm. Tie the short tube A firmly by its neck into the
superior vena cava, the long tube B into the pulmonary artery.
Ligature the inferior vena cava. Connect A by a small piece of rubber
tubing with a funnel supported in a ring on a stand. Pour water into
the funnel till the right side of the heart is full. It will escape from
the left azygos vein, which must be tied. Put on any additional
ligatures that may be needed to render the heart water-tight. Support
B in the vertical position by a clamp. Fill the funnel with water,
and it will rise in B to the same level as in the funnel. Now com-
press the right ventricle with the hand, and the water will rise higher
in B. Relax the pressure, and notice that the water remains at the
higher level in B, being prevented by the semilunar valves from
The valves are supposed to
be viewed from above, the
auricles having been partially
removed. ^, aorta with semi-
lunar valve ; D, position of
corpora Arantii ; P, pulmonary
artery ; B, wall of left auricle ;
M, mitral valve, with i and 2,
its posterior and anterior seg-
ments; C, wall of right auricle;
T, tricuspid valve, with i, its
posterior, 2, its anterior, and
3, its external segment.
Fig. 68.— Diagram ok Valves of Heart.
flowing back into the ventricle. By alternately compressing the
ventricle and allowing it to relax, water can be pumped into B till it
escapes from its upper end, and if this is so curved that the water
falls into the funnel, a ' circulation ' which imitates that of the blood
can be established. Note that during the pumping the sinuses of
Valsalva, behind the semilunar valves at the origin of the pulmonary
artery, become prominent.
{c) Take out B and tear out one of the segments of the semilunar
valve. Replace B, and notice that while compression of the ventricle
has the same effect as before, the water no longer keeps its level on
relaxation, but regurgitates into the ventricle. This illustrates the
condition known as insufficie?icy or iticompetence of the valves. But
if the injury is not too extensive, it is still possible, by more
vigorously and more rapidly compressing the heart, to pump water
into the funnel. This illustrates the establishment of compensation
in cases of valvular lesion.
1 82 A MAX UAL OF PHYSIOLOGY
{d) Now remove both tubes. Tie the pulmonary artery. Cut
away the greater part of tlie right auricle. Pour water into the
anriculo ventricular orifice, and notice that the segments of the
tricuspid valve are floated up so as to close the orifice. Invert the
heart, and the ventricle will remain full of water. Open the right
ventricle carefully, and study the papillary muscles, and the chordre
tendineiK, noting that the latter are inserted into the lower surface of
the segments of the tricuspid valve, as well as into their free edges.
{e) Repeat [l>), {c), and [d) on the left side of the heart, tying tube
B into the aorta as far from the heart as possible, and A into the left
auricle.
(/) Separate the aorta from the left ventricle, cuttuig wide of its
origin so as not to injure the semilunar valves, and tie a short wide
tube into its distal end. Fill the tube with water, and notice that
the valves support it. Cut open the aorta just between two adjacent
segments of the valve, and notice the pockets behind the segments,
and how they are related to each other, and connected to the wall of
the vessel.
14. Sounds of the Heart. — {a) In a fellow-student notice the
position of the cardiac impulse, the chest being well exposed. Use
both a binaural and a single-tube stethoscope. Place the chest-piece
of the stethoscope over the impulse, and make out the two sounds
and the pause, {b) W'wh the hand over the radial or brachial artery,
try to determine whether the beat of the pulse is felt in the period
of the sounds or of the pause, {c) Listen with the stethoscope over
the junction of the second right costal cartilage with the sternum,
and compare the relative intensity of the two sounds as heard here
with their relative intensity as heard over the cardiac impulse.
15. Cardiogram. — Smoke a drum, and arrange a recording tambour
and a time-marker beating half or quarter seconds to write on it
(Fig. 60, p. 170). Apply the button of a cardiograph (Fig. 18, p. 79) over
your own cardiac impulse, and fasten it round the body by the bands
attached to the instrument. Connect the cardiograph by an india-
rubber tube with a recording tambour. Set the drum off at a fast speed,
take a tracing, and varnish it. Compare with Fig. 19 (p. So), and
measure out the time-value of the various events in the cardiac
revolution as indicated on the cardiogram.
For the cardiograph, a small glass' funnel, the stem of which is
coi nected with the recording tambour, may be substituted, the broad
end of the funnel being pressed over the apex-beat.
16. Sphygmographic Tracings. — Attach a Marey's sphygmograph
(Fig. 26, p. 90) to the arm. Fasten a smoked paper on the plate D.
Apply the pad C of the sphygmograph to the wrist over the point
where the pulse of the radial artery can be most distinctly felt. Adjust
the pressure by moving the screw G. The writing-point of the lever
E will rise and fall with every pulse-beat. When everything is satis-
factorily arranged, set off the clockwork which moves the plate I\
and a pulse-tracing will be obtained. Study the changes which can
be produced in the pulse curve — {a) by altering the position of the
body (sitting, standing, and lying down) ; (/') by exercise ; (c) by in-
PRACTICAL EXERCISES
'83
iV,M^-J^
halation of 2 drops of amyl nitrite poured on a handkerchief; {J) by
raising the arm above the head and letting it hang at the side ; (<■) by
compression of the brachial artery at the bend of the elbow; (/) by
altering the pressure of the pad. Varnish the tracings after marking
on them the conditions underwhich
they were obtained.
A Dudgeon'ssphygmograph may
also be employed. Or a small glass
funnel connected with a recording
tambour may be pressed over the
carotid artery. The lever of the
tambour writes on a drum, on which
at the same time half or quarter
seconds are marked by an electro-
magnetic signal.
17. PlethysmograpMc Tracings.
— Connect the vessel C (Fig. 39,
p. 116) with B, place the arm in it,
and adjust the indiarubber band
to make a watertight connection.
Support C so that the arm rests easily within it, and fill it with water
at body temperature. Adjust a writing-point, carried by the float A,
U\jU-.^JUWUUviv
Fic;. 69. — Ekkect of E.XKKCisii on
THK Pulse (Marey).
Upper tracing, normal ; lower tracing,
after running.
Fig. 70. — Eei-ect ok Amyl Is'itrite on the
Pulse (Marev).
Upper tracing, normal ; lower, after inhalation
of amyl nitrite.
Fig. 71.— Pulse -tracings
erom difeerent arteries.
T, temporal ; R, radial ; F,
artery of foot. (v. Frey.)
to write on a drum, and close the upper tubulure of C with a cork.
The quantity of blood in the arm is increased with every systole of
the left ventricle, diminished in diastole. The float will therefore rise
when the ventricle contracts, and sink when it relaxes. Or C may be
i84
A MANUAL OF PHYSIOLOGY
connected by a rubber tube with a recording tambour writing on the
drum. No water must get into the tambour, and it is well to insert
a piece of glass tubing in the connection between it and the plethysmo-
graph, so that it may be seen when the water is rising too high. Adjust
a time-marker to write half or quarter seconds (Fig. 60, p. 170),
(i) Take tracings with arm {a) horizontal, {l>) hanging down.
(2) With the arm horizontal, take tracings to show the effect
(a) of closing and opening the fist inside the plethysmograph ; {b) of
applying a tight bandage round the arm a little way above the india-
rubber band ; {c) of inhaling 2 drops of amyl nitrite.
1 ! ,. 72. — rLKTUYSMOilRAlll (CYON).
AI, balanced test-tube, in communication with D. Wiien water passes from vessel
D to M, or from M to D, M moves down or up, and its niovemenis are recorded by
the writing-point A'. M is steadied by the liquid in P, into which it dips.
18. Pulse-rate. — (i) Count the radial pulse for a minute in the
sitting, supine, and standing positions. Use a stop-watch, setting it
off on a pulse-beat and counting the next beat as one. Make three
observations in each position.
(2) Count the pulse in a person sitting at rest, and then again in
the sitting position immediately after active muscular exertion. Note
how long it takes before the pulse-rate comes back to normal.
(3) Count the pulse in a person sitting at rest. Repeat the obser-
vation while water is being slowly sipped, and note any change.
PRACTICAL EXERCISES \t^
(4) With one hand over the thorax of a rabbit, count its pulse.
Then notice the eflect {a) of suddenly closing its nostrils, \l)) of
bringing a small piece of cotton-wool sprinkled with ammonia or
ihloroforni in front of the nose {rcjhx inhibition of the heart).
19. Blood pressure Tracing. — {a) Put a dog under morphia (p. 58).
Set up an induction-machine arranged for an interrupted current
(Fig. 65, p. 175). Fill the U-shaped manometer-tube (if this has not
already been done) with clean mercury to the height of 10 to 12 cm.
in each limb. .Then, tilting the tube carefully, fill the proximal limb
(/>., the limb which is to be connected with the bloodvessel) with a
saturated solution of sodium carbonate or a 25 per cent, solution of
magnesium sulphate. This is easily done by means of a pipette
furnished with a long point. Now attach a strong rubber tube to
the proximal end of the manometer, and fill it also with the solution.
All air must be got out of the manometer and its connecting-tube.
Blow into the rubber tube so as to cause a difference of about
10 cm. in the height of the mercury in the two limbs of the mano-
ineter, and, without releasing the pressure, clamp the tube with a
pinchcock or screw clamp (Fig. 28, p. 99).
Now smoke a drum, and arrange the writing-point of the mano-
meter-float so that it will write on it. Suspend a small weight by a
piece of silk thread from a support attached to the stand of the
drum so that it hangs down outside of the writing-point of the
manometer-float and always keeps it in contact with the smoked
surface without undue friction. A piece of glass rod drawn out to a
fine thread in the blowpipe flame answers very well. In the same
vertical line below the writing-point of the float, adjust the writing-
point of a time-marker beating seconds (F^ig. 60, p. 170).
Next, fasten the animal on a holder, back down. Give ether and
insert a tracheal cannula (p. 177). (The tracheal cannula is not
absolutely required for the experiment, but it is convenient, as the
animal is more under control, and artificial respiration can be begun
at any moment, should this be necessary.) Insert a glass cannula,
armed with a short piece of rubber tubing, into the central (cardiac)
end of the carotid artery (p. 58). Leaving the bulldog forceps on
the artery, fill the cannula and tube with the magnesium sulphate or
sodium carbonate solution. Slip the rubber tube over a short glass
connecting-tube. Fill this also with the solution, and connect it
with the manometer-tube, seeing that both are quite full of liquid,
so that no air may be enclosed. Now take off the bulldog forceps,
and allow the drum to revolve at slow speed. The writing-point of
the manometer float will trace a curve showing an elevation for each
heart-beat, and longer waves due to the movements of respiration.
{b) Now isolate the vagosympathetic nerve in the neck. Ligature
doubly, and cut between the ligatures. Stimulate first the peripheral
(lower) and then the central (upper) end, and note the effect on the
blood-pressure curve.
{c) Expose and divide the other vago-sympathetic while a tracing
is being taken. Again stimulate the central end of the nerve, and
observe whether there is any effect.
1 86
A MANUAL OF PHYSIOLOGY
{d) Expose the sciatic nerve in one leg. This is very easily done
as follows. The leg having been loosened from the holder, the foot
is seized by one hand and lifted straight up, so as to put the skin
of the ihigh on the stretch. An incision is now made in the
middle hne on the posterior aspect of the thigh, the skin and sub-
cutaneous tissue being divided at one sweep. 'l"he muscles are
separated in the line of the incision with the fingers, and the sciatic
nerve comes into view lying deeply between them. Place a double
ligature on it, and divide between the ligatures. Stimulate the upper
(central end) ; the blood-pressure probably rises, and the heart may
Fig. 73. — Bi.ooD-i'KiissuKK Tracinc kkom a Doc;, cumulation oi-
Central and rFRiPHEKAi. Ends oi- Vaci's.
The other vagus was intact. Siinuilation of the peripheral end caused stoppage of
the heart and a marked fall of pressure. Stimulation of the central end produced a
great rise of pressure, witli, perhaps, a slight acceleration of the heait.
be accelerated. Stimulate the peripheral end of the nerve ; there is
little change in the blood-pressure and none in the rate of the heart.
{e) Note, incidentally, that stimulation of the central end of the
sciatic or the upper (cephalic) end of the vagosympathetic may
cause increase in the rate and depth of the respiratory movements.
Dilatation of the pupil may also be caused by stimulation of the
upper end of the vago-sympathetic through the sympathetic fibres-
that supply the iris.
(/) Again, stimulate the peripheral end of one vagus, or of both
at the same time, while a tracing is being taken, and see how long it
PRACTICAL EXERCISER 187
is possible to keep the heart from heating. Sometimes in the dog
inhibition can be kept up so long that the animal dies.
(j,-) Close the tracheal cannula so tliat air can no longer entc-r the
lungs. In a very short time the blood-pressure curve begins to rise
(rise of asphyxia). After some minutes the pressure falls, and finally
becomes zero ; i.e., the level of the mercury is the same in the two
limbs of the manometer (or, rather, the mercury in the distal limb is
higher than that in the proximal limb by the amount needed to
exactly balance the pressure of the column of sodium carbonate in
the latter). Disconnect the arterial cannula from the manometer,
and allow the writing-point to trace a horizontal straight line (line of
zero pressure) on the drum (l''igs. 56 and 57).
20. The Influence of the Position of the Body on the Blood-
pressure. — Inject into the rectum of a dog 3 to 4 grammes of
chloral hydrate dissolved in a little water. See that it does not run
out again immediately after injection. In ten minutes ancesthetize the
animal fully with the mixture of equal parts of alcohol, chloroform and
ether, known as the ACE mixture, or with chloroform, and tie it very
securely, back downward, on a board which can be rotated around a
horizontal axis, corresponding in position to the point at which the
cannula is to be inserted.* Set up a drum and manometer as in 19
(p. 185), but with a rubber connecting-tube of such length as will
allow free rotation of the board. Insert a cannula into the central
end of the carotid artery at a point immediately above the axis of
rotation of the board, and connect it with the manometer, {a) Take
a blood-pressure tracing with the board horizontal. (J)) Whilst the
tracing is being taken, rotate the board so that the position of the
animal becomes vertical, with the feet down. Mark on the tracing
the moment when the change of position takes place. The pressure
falls. Replace the dog in the horizontal position. The manometer
regains its former level. Now rotate the board, till the animal is again
vertical, but with feet up and head down, and observe the effect on
the blood-pressure. The respiratory variations are greater with feet
down than with head down. Notice in both cases whether there is
any change in the rate of the heart, {c) Take the board off the
stands, lay it on a table, expose the femoral artery, and insert a
cannula into it. Shift the axis so that it now lies below this cannula.
Replace the board on the stands, and repeat ia) and ifi). The fall
of pressure will now take place in the head-down position.!
* A simple arrangement for this purpose is a board with a number of
staples fastened in pairs into its lower surface, so that an iron rod can be
pushed through any pair, and form a horizontal axis at right angles to
the length of the board. The dog having been tied down, the rod is
pushed through the pair of staples corresponding to the position of the
cannula in the artery that is to be connected with the manometer. The
projecting ends of the rod rest in two ordinary clamp-holders, fastened at
a convenient height on two strong stands, whose bases are clamped to the
end of a table. The other end of the board is supported by a piece of
wood that rests on the floor, and can be removed when the board is to be
rotated.
t In 16 dogs the fall of pressure in the carotid in the feet-down
t88 A MANUAL OF PHYSIOLOGY
1 1 . EflFects of Haemorrhage and Transfusion on the Blood-
pressure. — Ancesthcti/.(j a doy with iiiorpliia and ether, and insert a
cannula into the carotid artery, another into one femoral vein
(p. 177), and a third into the femoral artery on the opposite side.
Connect the first cannula with a manometer, arranged to write on
a drum as in experiment 19 (j). 185). Take the bulldog off the
carotid, and measure the difference in the level of the mercury in the
two limbs of the manometer with a millimetre scale.
(i) {a) While a tracing is being taken, draw off about 10 c.c. of
blood from the femoral artery, and observe whether there is any
effect on the tracing. Mark on the tracing the moment when the
removal of the blood begins and ends.
{b) Repeat ia), but run off about 100 c.c. of blood, and let this be
immediately defibrinated. Then draw off portions of 100 c.c. at
short intervals until a distinct fall of blood-pressure has been pro-
duced. All the samples of blood should be defibrinated.
(2) (a) Now, while a tracing is being taken, inject the whole of
the defibrinated blood slowly through the cannula in the femoral
vein by means of a funnel supported by a stand at such a height that
the blood runs in easily. A stopcock should be introduced in the
connection between the funnel and the cannula, and this should be
closed before the funnel is quite empty, so as to obviate any risk of
air getting into the vein. Of course, the cannula and connecting-
tubes must all be freed from air before injection is begun. Again,
measure the difference in the level of the mercury in the manometer
and compare the pressure with that observed before the first
hnemorrhage.
{I)) Inject into the vein, while a tracing is being obtained, about
100 c.c. of normal saline solution heated to 40^ C, and go on
injecting portions of 100 c.c. until a distinct rise of pressure has taken
place, keeping a record of the total amount injected, and marking the
time of each injection on the curve.
{c) After an interval of thirty minutes, again measure the height of
the mercury in the manometer. Then bleed the dog to death while
a tracing is being recorded.
22. The Influence of Albumoses on the Blood-pressure — Albu-
mose (' Peptone ') Plasma. — Set up the apparatus for taking a blood-
pressure tracing as in experiment 19, but omit the induction coil.
Weigh a dog. Dissolve 0*5 gramme Witte's 'peptone' for every
kilo of body-weight in ten times its weight of normal saline solution.
Anaesthetize the dog with morphia and ether or ACE mixture. Put
cannulce into the central end of one carotid, of one crural artery, and
of the crural vein on the opposite side. Connect the carotid with
the manometer, and the femoral vein with a burette or large syringe
containing all the peptone solution except 15 drops, which are put
position varied from 12 to 100 mm. of mercury ; average fall, 44.4 mm.
In 12 out of the 16 animals the rise of pressure in the head-down position
varied from 2 to 36 mm. ; in i there was no change ; in 3 there was a fall
of 5 to 24 mm.
PRACTICAl EXERCISES
189
into a test tube labelled A. Take care thai tiie connecting-tube and
cannula are free from air. Label another test-tube H. Run into
both test-tubes about 5 c.c. of blood from the femoral artery, and set
them aside. Now commence to take a blood-pressure tracing, and
while it is going on quickly inject the peptone solution. Notice the
eftect on the tracing. The pressure falls owing largely to a dilatation
of the small arteries through the direct action of the peptone on their
muscular tissue or on the endings of the vaso-motor nerves. As
soon as the injection is finished, draw off a sample of 5 c.c. of blood
into a test-tube labelled C, and let it stand. In ten minutes collect
three further samples of 5 c.c, I), E, and F, and a large one, G ; in
half an hour another set of three small samples, and at as long an
interval as possible thereafter three more. Add to E 15 drops of a
2 per cent, solution of calcium chloride, to F 5 c.c. of a solution of
fibrin ferment containing some calcium chloride, and put D, E, and
F into a water-bath at 40°. Treat the other sets of small samples in
the same way, and also the plasma obtained by centrifugalising G.
Note how long each specimen takes to clot, and report your results.*
rptora irtject'.-d.
,r,.„f«'v,v,'^'^^'^'^\^-\^^
.^^m^'^'^
Fig. 74.
-Effect of Injection of Tei'tone on the Blood-pressure
IN A Dog. (To be read from right to lekt. )
23. Effect of Suprarenal Extract on the Blood-pressure. — See
p. 604.
24. Section and Stimulation of the Cervical Sympathetic in the
Rabbit. — Weigh out f gramme chloral hydrate. Dissolve in as small
a quantity of water as possible, and inject into the rectum of a rabbit»
preferably an albino. Half a gramme is sufficient for a small rabbit.
Put a pair of bulldog forceps on the anus to prevent escape of the
solution. Set up an induction coil arranged for an interrupted
current (Fig. 65, p. 175), and connect it through a short-circuiting
* Sometimes the injection of peptone hastens coagulation instead of
hindering it. It has been asserted that this is only the case when small
doses are used less than o'02 gramme per kilo of body-weight). But in 2
dogs out of 1 1 a dose of o'5 gramme per kilo has been seen to hasten coagu-
lation, and in i out of 1 2 to leave it unaffected ; in the other 9 coagulation
was markedly retarded. The blood-pressure always fell, the amount of
the fall varying from 81 to 21 mm. of mercury (average, 60 mm.). It
sometimes returned to normal in twenty to thirty minutes, but usually
required a longer time.
I90 A MANUAL OF PIIYS/OLOGY
key with electrodes. The preparations necessary for an operation
with antiseptic precautions are supposed to have been previously
made — the instruments, sponges, and ligatures Itoiled in water; the
instruments then immersed in a 5 per cent, solution of carbolic acid,
the sponges and ligatures in corrosive sublimate solution (o*i per
cent.). The hands are to be thoroughly washed, with diligent use of
the nailbrush, in soap and water before the cutting operation begins,
and then soaked in the corrosive sublimate solution.
Fasten the rabbit on a holder, back downwards, as in Fig. 43. Clip
off the hair on the anterior surface of the neck. Remove loose hairs
with a wet sponge, shave the neck, and wash it thoroughly, first with
soap and water, and then with corrosive sublimate. Give ether if
necessary. Make a longitudinal incision in the middle line over the
trachea, beginning a little below the thyroid cartilage and e.xtending
downwards for an inch and a half. Feel for the carotid artery,
expose, and raise it up. Two nerves will now be seen coursing beside
the artery. The larger is the vagus, the smaller the sympathetic.
A third and much finer nerve (the depressor, or superior cardiac
branch of the vagus) may also be seen in the same position, but the
student should neglect this for the present. Get as little as possible
of the antiseptic solutions in the wound till your observations have
been completed, as the nerves may be injured by them. Also keep
the animal warm by covering it with a cloth, and do not handle or
wet its ears. Pass a ligature under the sympathetic, and tie it, the
ear being held up to the light while this is being done, so that its
vessels may be clearly seen. A transient constriction of the arteries
may be seen at the moment when the nerve is ligatured. This is
due to stimulation of the vaso-constrictor fibres. Then follows a
marked dilatation of the bloodvessels, due to paralysis of these fibres.
_ The ear is flushed and hot. Note also that the pupil is probably
narrower on the side on which the nerve has been tied. On stimula-
tion of the upper (cephalic) end of the sympathetic with the electrodes,
the vessels are markedly constricted, the ear becomes pale and
cold, and the pupil dilates. Cut out the ligature, wash the wound
thoroughly with corrosive sublimate, and close it, the muscles being
first brought together by a row of interrupted sutures, and then the
skin by another row. Since it is difficult, if not impossible, to
thoroughly disinfect the hair-follicles, and a suture passed through
a septic follicle 's apt to give rise to suppuration, subcutaneous
stitches — i.e., stitches passed by a curved needle through the deep
layer of the skin without coming through to the surface — may be
employed. The wound is to be protected by a coating of collodion.
No other dre.ssing is required. The animal is now removed from the
holder and put back to its hutch. The student must examine it at
least once a day for the next week, and study the differences between
the two ears (p. 151) and the two pupils.
25.* Stimulation of the Depressor Nerve in the Rabbit. — Set up
the apparatus for a blood-pressure tracing as described in 19 (p. '85).
Arrange an induction coil and electrodes for an interrupted current.
♦ This experiment is only suitable for advanced students.
/ Vv'/l CTWA L i:\EKCISES
191
Anresthetizc a rabbit with i gramme chloral hydrate, and if neces-
sary with ether. For l)lood-prcssurc experiments only small doses of
chloral hydrate or chloroform can be given, as they affect the vaso-
motor centre. Put the animal on the holder. Insert a cannula in
the trachea and another cannula in the central end of the carotid
artery. Isolate the depressor nerve. Put double silk ligatures on it,
and divide between them. Connect the cannula in the carotid with
Fig. 75.— Artificial Scheme to illustrate a Mlthou of measuring
THE Circulation-time.
B, bottle containing water, the rate of outflow of which is regulated by screw clanip
a ■ s' syringe filled with methylene-blue solution, connected with T-piece A ; M, beaker
containing methylene-blue solution ; b, c, screw-clamps ; C, T-piece inserted in the
course of the flexible tube E, and connected with the glass tube T, which is hlled with
beads • F, outflow tube. The clamp c having been closed and b opened, the syringe is
filled with the methylene-blue solution, b is then closed, c opened, and a definite
quantity of the solution injected into the system. The tune from the beginning ot
injection till the appearance of the blue at G is measured with the stopwatch.
the manometer and take a blood-pressure tracing. Stimulate the
central (upper) end of the depressor. A marked fall of blood-
pressure, accompanied with a slowing of the heart, will be obtained
(Fig. 55). Stimulate the peripheral (lower) end ; no effect. Divide
both vagi, and again stimulate the central end of the nerve. The
blood-pressure again falls, but there is no alteration in the rate of the
192 A MANUAL OF PlfYSIOLOC.Y
heart (i). i6o). Close the tracheal cannula, and obtain another
tracing, showing the effect of asphyxia (Fig. 56, p. 163).
Auh>/>sy. — Dissect the nerve that has been stimulated, up to the
origin of the superior laryngeal branch of the vagus, to make sure
that it is the depressor (l"'ig. 54, p. 161).
26. Determination of the Circulation-time. -(r?) Begin with an
artificial sclicnie (l"'ig. 75). I'lll the syringe with a 0*2 per cent,
solution of methylene blue. Allow the water to flow from the bottle
by loosening the clamp. Inject a definite (quantity of the methylene-
blue solution, and with a stop-watch observe how long it takes to
pass from the point of injection to the end of the glass tube filled
with beads. Make ten readings of this kind and take the mean.
Then raise the bottle so as to increase the rate of flow of the water,
and repeat the observations. The 'circulation-time' will be found
to be diminished. This corresponds to an increase of blood-pressure
due to increased activity of the heart without change in the calibre
of the bloodvessels. Next, leaving the bottle in its present position,
diminish the outflow by tightening the clamp ; the circulation-time
will be increased. This corresponds to an increase of blood-pressure
due to diminution in the calibre of the small arteries.
(b) Fill the syringe* with methylene-blue solution (0*2 per cent, in
normal saline), as in {a). Keep the solution warmed to 40" C. by
immersing the small beaker containing it in a water-bath, or heating
over a bunsen with a small flame. Weigh a rabbit, and inject
-^ gramme chloral into the rectum. Fasten it on a holder, back
downwards (Fig. 43, p. 125). Clip off the hair on the front of the
neck, and after giving ether if the animal shows the least sign of
pain, make an incision \h inches long in the middle line, beginning
a little way below the cricoid cartilage. Reflect the skin and isolate
the external jugular vein, which is quite superficial. Carefully
separate about 'l inch of the vein from the surrounding tissue, and
pass two ligatures under it, but do not tie them. Compress the
vein with a pair of bulldog forceps between the heart and the
ligatures. Now tie the uppermost of the two ligatures (that next the
head), but only put a single loose loop on the other. The piece
of vein between the upper ligature and the bulldog is now dis-
tended with blood. With fine-pointed scissors make a small slit in
the vein, taking great care not to divide it completely, insert the
cannula, and tie the loose ligature firmly over its neck. Fill the
cannula and the small piece of rubber tubing attached to it with
normal saline by means of a pipette with a long point. Expose the
carotid on the other side, isolate it for ^ inch, clear it carefully from
its sheath, slip under it a strip of thin sheet indiarubber, and between
this and the artery a little piece of white glazed paper. Connect
* A burette, sloped so as to make a small angle with the horizontal,
may be substituted for the syringe. The burette is su|)ported on a stand
at such a height that the methyiene-blue solution runs without great force
into the jugular (say 10-15 cm. above the level of tiie cannula). The
danger of producing an abnormal result by suddenly raising the pressure
in the right side of the heart is thus avoided.
PRACTICAL /■:xi:rlis/:s 193
the cannula in the jugular with the T-piece attached to the syringe,
("are must be taken that no air remains in the cannula or its con-
necting tube, as an animal not unfreiiuently dies instantaneously when
a bubble of air is injected into the right heart.
Now take off the bulldog from the vein, and make a series of
observations on the pulmonary circulation-time. The animal must
be so placed that a good light falls on the carotid. If necessary, the
light of a gas-flame may be concentrated on it by a lens. The
student holds the stop-watch in one hand, and injects a measured
quantity of the methylene-blue solution with the other. Uniformity
in the quantity injected is secured by fastening on the piston of the
syringe a screw-clamp, which stops the piston at the desired point.
The observation consists in setting off the watch at the moment when
injection begins and stopping it when the blue appears in the carotid.
After each injection the screw-clamp or pinchcock on the tube con-
nected with the cannula must be tightened, the other opened, and
the syringe refilled. Great care must be taken never to open the two
clamps at the same time, as in that case blood may regurgitate through
the jugular and fill the syringe, or methylene blue may be sucked
into the circulation. As many observations as possible should be
taken, and the mean determined. The circulation-time observed is
approximately that of the lesser circulation, the time taken by the
blood to pass from the left ventricle to the carotid being negligible.
The specific gravity of the blood may also be tested at the beginning
and end of the experiment by Hammerschlag's method (p. 57).
Autopsy. — Observe particularly the state of the lungs, whether the
bladder is distended or not, and whether any of the serous cavities
or the intestines contain much liquid : so as to determine, if possible,
by what channel the water injected into the blood may have been
eliminated. Notice the distribution of the methylene blue in such
organs as the kidneys and the muscles immediately after death, and
notice that the blue colour becomes more pronounced after exposure
for a time to the air. Make a longitudinal section through a kidney,
and observe that the pigment is found especially in the cortex and
around the pelvis at the apices of the pyramids, or it may be only in the
cortex. The urine is greenish. If some methylene blue has been
injected after the heart ceased to beat, the bloodvessels, particularly
in the mesentery, may be beautifully mapped out by the pigment.
This is not the case if the last injection took place before death,
since the blue is rapidly reduced by living tissues.
13
CHAPTER III.
RESPIRATION.
Respiration in its widest sense is the sum total of the
processes by which the ultimate elements of the body gain
the oxygen they require, and get rid of the carbon dioxide
they produce.
Comparative. — In a unicellular organism no special mechanism of
respiration is needed ; the oxygen diftuses in, and the carbon dioxide
diffuses out, through the general surface. The simple wants of such
multicellular animals as the ccelenterates, the group to which the sea-
anemone belongs, are also supplied by diffusion through the ectoderm
from and into the surrounding water, and through the endoderm from
and into the contents of the body-cavity and its ramifications.
But in animals of more complex structure special arrangements
become necessary, and respiration is divided into two stages :
( I ) External respiration, an interchange between the air or water
and a circulating medium or blood as it passes through richly
vascular skin, gills, trachea?, or lungs ; and (2) internal respiration,
an interchange between the blood, or lymph, and the cells.
In the lower kinds of worms respiration goes on solely through the
skin, under which plexuses of bloodvessels often exist, but in some
higher worms there are special vascular appendages that play the part
of gills. The Crustacea also possess gills, while in the other arthro-
poda respiration is carried on either by the general surface of the
body (in some low forms), or more commonly by means of tracheae,
or branched tubes surroundea by blood spaces and communicating
externally with the air and internally by their finest twigs with the
individual cells. Most of the mollusca breathe by gills, but a few
only by the skin.
Among vertebrates the fishes and larval amphibians breathe by
gills, but most adult amphibians have lungs. The skin, too, in such
animals as the frog has a very important respiratory function, more
of the gaseous exchange taking place through it than through the lungs.
One small group of fishes, the dipnoi, has the peculiarity of
A'/l'S/'/A'A/VO.V I(;3
possessing both gills and a kinil of lungs, the swinvhlacklur hcing
surroundctl with a [)1l'\iis of bloodvessels and taking on a respiratory
function.
In all the higher vertebrates the respiration is carried on by lungs ;
the trifling amount of gaseous interchange which can possibly take
place through the skin is not worth taking into account. The lungs
are to be regarded as developed from outgrowths of the alimentary
canal, beginning near the mouth.
The object of all special respiratory arrangements being, in the
first instance, to facilitate the gaseous exchange between the sur-
rounding medium (air or water) and the blood, a prime necessity of
a respiratory organ, be it skin, gill, trachea, or lung, is a free supply
of blood, in vessels so C\ne and thin that diffusion readily takes place
into them and out of them. But a free supply of blood would be of
no avail if the medium to which the blood gave up its carbon dio.\ide
and from which it drew its oxygen was not being constantly and
sufficiently renewed.
Sometimes the natural currents of the water or the air are of
themselves sufficient to secure this renewal ; in other cases, artificial
currents are set up by cilia, or special bailing organs, like the scapho-
gnathites of the lobster. In all the higher animals active move-
ments, by which air or water is brought into contact with the respira-
tory surfaces, are necessary; and it is possible that such movements
take place even in the trachec^ of insects and other air-breathing
arthropoda. Fishes, by rhythmical swallowing movements, take in
water through the mouth and pass it over the gills and out by the
gill-slits, while the frog distends its lungs by swallowing air.
Physiological Anatomy of the Respiratory Apparatus. — In man
the respiratory apparatus consists of a tube (the trachea) widened at
its upper part into the larynx, which contains the special mechanism
of voice, and communicates through the nose or mouth with the
external air. Below, the trachea divides dendritically into innumer-
able branches, the ultimate divisions of which are called bronchioles.
Each bronchiole breaks up into several wider passages, or infundibula,
the walls of which are everywhere pitted with recesses or alcoves,
called alveoli. The trachea and larger bronchi are strengthened by
hyaline cartilage in the form of incomplete rings, connected behind
by non-striped muscular fibres, which also exist in the intervals
between the rings. The middle-sized bronchi within the lungs have
the cartilage in the form of detached pieces in the outer portion of
the wall, while nearer the lumen lies a complete ring of non-striped
muscle.
In the bronchioles, no cartilage is present, but the circularly-
arranged muscular fibres still persist, and also form a thin layer in
the infundibula. In the air-cells, or alveoli, however, there are no
muscular fibres. Their walls consist essentially of a network of
elastic fibres, continuous with a similar layer in the intundibula and
bronchioles, and covered on the side next the lumen by a single
layer of large, clear epithelial scales, with here and there a few
smaller and more granular polyhedral cells.
13—2
196 .1 MANUAL or PI {YSIOLOCY
From the larynx to the l)ronchioles the iinicous membrane is
ciHated on its free surface, the cilia lashing upwards so as to move
the secretion towards the larynx and mouth. In tiie infundibula the
ciliated epithelium begins to disappear, and isal)scnt from the alveoli.
Part of the nasal cavity and the upper [)art of the pharynx are also
lined with ciliated epithelium. Mucous glands are present in
abundance in the upper portions of the respiratory passages, but
disappear in the smaller bronchi.
Blood supply of the Lungs. — The quantity of blood traversing the
lungs bears no proportion to the amount required for their actual
nourishment. Small, however, as this latter ([uantity is. it cannot
apparently be derived from the vitiated blood of the right ventricle,
but is obtained directly from the aortic system by the bronchial
arteries. These are distributed with the bronchi, which they supply
as well as the connective-tissue of the interlobular septa running
through the substance of the lung, the pleura lining it and the walls
of the large bloodvessels. Most of the blood from the bronchial
arteries is returned by the bronchial veins into the systemic venous
system, but some of it finds its way by anastomoses into the pul-
monary veins.
The branches of the pulmonary artery are also distributed with
the bronchi, and break up into a dense capillary network around the
alveoli. From the capillaries veins arise which, gradually uniting,
form the large pulmonary veins that pour their blood into the left
auricle.
The same (quantity of blood must, on the whole, pass per unit of
time through the lesser as through th(i greater circulation, otherwise
etjuilibrium could not exist, and blood would accumulate either in
the lungs or in the systemic vessels. But it does not follow that at
each heart-beat the output of the two ventricles is e.xactly equal. If,
indeed, the capacity of the lesser circulation were constant, the
quantity driven out at one systole by the right ventricle would be
the same as that ejected at the next by the left ventricle. But it is
known that the capacity of the pulmonary vessels is altered by the
movements of respiration and probably in other ways, so that it is
only on the average of a number of beats that the output of the two
ventricles can be supposed equal.
The time required by a given small portion of blood, (■.,i,^, by a
single corpuscle, to complete the round of the lesser circulation, is,
as we have seen (p. 124), much less than tlie average time needed to
complete the systemic circulation. In the rabbit the ratio is probably
about 1:5 Since all the blood in avascular tract must pass out of it
in a period equal to the circulation time, the average quantity of
blood in the lungs and right heart of a rabbit must be about one-
fifth of that in the systemic vessels. On the assumption that the
same proportion holds for a man, not less than 900 grm. out of the
5^ kilos of blood in a seventy kilo man must be contained in the lesser
circulation, and rather more than ^,\ kilos in the greater. This
corresponds sufficiently well with calculations from other data.
For example, the average weight of the lungs in three persons,
RESPIRATION igy
executed by beheading, was 457 grm. ((Huge). The average weight of
the kings in a great number of persons who had died a natural death
was 1024 grm. (Juncker). The weight of the jjuhnonary tissue alone
in the first set of cases must be less than 457 grm., for the lungs of
a person who has bled to death are never bloodless. In a dog killed
by bleeding from the carotid, one-(iuarter of the weight of the lungs
consisted of blood. Assuming the same proportion for the de-
capitated individuals, we get 343 grm. as the net weight of the blood-
free lungs. Deducting this from 1024 grm., we arrive at 681 grm.
as the average quantity of blood in the lungs. Adding to this the
(juantity in the right side of the heart (p. 127), we get, in round
numbers, 750 grm. as the amount in the lesser circulation. It is
true that in the living body the conditions are not the same as after
death ; but it is j)robable that in a large number of cases taken at
random the differences would be approximately equahzed.
It has been further calculated — but here the data are less certain —
that the total area of the alveolar surface of the lungs of a man is
about 100 square metres (sixty times greater than the area of skin),
of which, perhaps, 75 square metres are occupied by capillaries.
The average thickness of this immense sheet of blood has been
reckoned to be equal to the diameter of a red blood-corpuscle, or,
say, 8/x. This would give 600 c.c. (630 grm.) as the quantity of
blood in the lungs, which is probably somewhat too low an estimate.
If we take the pulmonary circulation-time as 13 seconds (p. 124),
1 , • r 1 1 1 ■ 1 1 r, .L o"8 X 60 X 60
and the quantity of blood in the lungs as 800 grm,, then
= 221 kilos of blood will ])ass through the lungs in an hour, or
5,304 kilos (say, 5,000 litres) in twenty-four hours. This would fill
a cubical tank in which the man could just stand upright with the
lid closed.
Mechanical Phenomena of Respiration.
The lungs are enclosed in an air-tight bo.\, the thorax ;
or it may be said with equal truth that they form part of
the wall of the thoracic cavity, and the part which has
by far the greatest capacity of adjustment. The alveolar
surface of the lungs is in contact with the air. The pleura,
which covers their internal surface, is reflected over the
chest-walls and diaphragm, so as to form two lateral sacs,
the pleural cavities. In health these are almost obliterated,
and the visceral and parietal pleurae, separated and
lubricated by a few drops of lymph, glide on each other
with every movement of respiration. I3ut in disease the
pleural cavities may be fllled and their walls widely separated
by e.xudation as in pleurisy, or by blood as in rupture of an
198
A MANUAL OF PI/YS/OLOUY
aneurism, or by air in the condition known as pneumo-
thorax. Between the two pleural sacs lies a mesial space,
the mediastinum, commonly divided into an anterior medias-
tinum in front of the heart, and a posterior mediastinum
behind it. The pleural and pericardial sacs and the medias-
tinum constitute together the thoracic cavity. The external
surface of the chest-wall and the alveolar surface of the lungs
are subjected to the pressure of the atmosphere, to which
the pressure in the thoracic
cavity (intra - thoracic pres-
sure) would be exactly equal if
its boundaries were perfectly
yielding. But in reality the
intra - thoracic pressure is
alwa}'s normally something
less than this. For even the
lungs, the least rigid part of the
boundary, oppose a certain
resistance to distension, and
so hold off, as it were, from
the thoracic cavity a portion
of the alveolar pressure ; and
T is a bottle from which the bottom in any given position of the
has been removed ; I) a flexible and r i ■
elastic iniiiibiane tied on ilif bottle, and ChCSt the mtra-thoraClC prCS-
capable of beins? pulled out by the string • i ^ .u otmn
S so as to increase the capacity of the ^Ure IS equai TO ine aimo-
bottle L is a thin elastic bag represent- gphcric preSSUre miuUS this
ing the lungs. It communicates with the -^ *
external air" by a glass tube fitted airtight elastic tension of the lungS.
through a cork in the neck of the bottle. _,, , . r i
When I) is dmwn down, the pressure of 1 lie ODject Ot trie respu-a-
the external air causes L to expand. j.^„.. .^,„,. .^,^.,4.^ ;^ tU^ ^^^..,>.,^1
When the string is let go. L contracts tor}" mo\cments IS the renewal
again, in virtue of its elasticity. of x_he air in coutact with the
alveolar membrane — in other
words, the ventilation of the lungs. Two main methods are
followed by sanitary engineers in the ventilation of buildings:
they force air in, or they draw it in. In both cases the
movement of the air depends on the establishment of a
slope of pressure from the inlet to the interior. In the first
method, this is done by increasing the pressure at the inlet ;
in the second, by diminishing the pressure at the outlet. In
certain animals Nature, in solving its problem of ventilation,
FlC. 76. — SrilKMK TO ll.LUSTR.ATE
THE Movements ok ihe Lt'Nc.s
IN THE Chest.
A'/:S/>/A'.l //ON
199
has made use of the rtrst principle. Thus, tlie frog forces
air into its lungs by a swallowing movement. In artificial
respiration, as practised in physiological e.xperiments, the
same method is usually employed : air is driven into the
lungs under pressure. But in the vast majority of animals,
including man, the opposite principle has been adopted ;
and the ' indraught ' of air from nose and pharynx to alveoli
is not set up by increasing the pressure in the former, but b}'
diminishing it in the latter. This ' indraught,' or inspiration,
is brought about by certain movements of the chest-wall,
which increase the capacity of the thoracic cage and lower
the pressure in the thoracic cavity. The expansion of the
highl}'-distensible lungs keeps pace with the diminution of
pressure in the pleural sacs, and they follow at every point
the retreating chest-w-all and diaphragm. The pressure of
the air in the alveoli during the rapid expansion of the
lungs necessarily sinks below that of the atmosphere, and
air rushes in through the trachea and bronchi till the
difterence is equalized. Then commences the movement of
expiration. The expanded chest falls back to its original
limits ; the pressure in the thoracic cavity increases ; the
distended lungs, in virtue of their elasticity, shrink to their
former volume ; the pressure of the air in the alveoli rises
above that of the atmosphere, and with this reversal of
the slope of pressure air streams out of the bronchi and
trachea.
In inspiration the chest dilates in all its diameters. Its
vertical diameter is increased by the contraction of the
diaphragjii, which, composed of a central tendon and a
peripheral ring of muscular tissue, bulges up into the thorax
in the form of a flattened dome, and closes its lower
aperture. When the diaphragm contracts, the central
tendon descends ; the acute angle which the muscular ring
makes during relaxation with the thoracic wall opens out
around its whole circumference, so as to form a deep groove
of triangular section. The lungs follow the descending
diaphragm, their lower borders keeping accurately in contact
with it, while their apices move ver}^ slightly or not at all.
Since the diaphragm is attached to the lower ribs, there is a
200 A MAXL'AL OF PIIYSIOLUC.Y
tendency durinj^ its contraction for these to be drawn in-
wards and upwards ; but this is opposed by the pressure of
the abdominal viscera, and b\ the action of the (juadratus
Innibonun, which fixes the twelfth rib, and of the serraius
posticus inferior, which draws the lower four ribs backward.
When these and the other inspiratory muscles that act
especially upon the ribs are paraly;^ed by injur3'to the spinal
cord, and respiration is carried on by the diaphragm alone,
the line of its attachment to the ribs is distinctly marked
during inspiration by a shallow circular groove.
The antero-posterior and transverse diameters of the
thorax are enlarged by the action of certain muscles that
elevate the ribs. Of these, the most important are the
levatorcs costaruin — twelve in number on each side. They
arise from the transverse processes of the last cervical and
first eleven dorsal vertebrae, and, passing obliquely down-
wards and outwards, are inserted between the tubercle and
the angle into the first or second rib below their origin.
The scalene muscles, which may in a lean person be felt to be
tense during inspiration, fix the first and second ribs (scalenus
anticus and medius, the first ; scalenus posticus, the second
rib), and so afford a fixed line for the intercostal muscles to
work from on the lower ribs.
The action of the iiiiercostals has been much debated ; but it
seems to be certain that the external intercostals do aid to a
slight extent in raising the ribs when the upper two have
been fixed by the contraction of the scaleni. The inter-
cartilaginous portion of the internal intercostals also con-
tracts simultaneously with the diaphragm, and may there-
fore be reckoned in the list of inspiratory muscles ; but the
function of the interosseous portion is still in doubt. It is
probable that the chief importance of the intercostal muscles
(both external and internal) is not so much to act upon the
ribs, as to increase by their contraction the rigidity of the
intercostal spaces, and so prevent them from being drawn in
when the chest is expanded by the action of the diaphragm,
the levatores, and the scaleni. Since the ribs slant down-
wards and forwards to their sternal attachments, the sternum
is raised when they are elevated ; or, rather, since the upper
NJ'Sr/A'A 770N 20I
eiul of that bone is practically immovable in ordinary breath-
ing, its lower extremity is tilted forwards. This causes an
increase in the antero-posterior diameter of the thorax.
Further, since the arches formed by the ribs widen in regular
progression from above downwards, at least in the upper
portion of the thoracic cage, so that the second rib is a
segment of a larger circle than the first, and the third than
the second, it is clear that a general elevation of the chest
will tend also to increase the transverse diameter at any
given level. Such an increase is also favoured by the open-
ing out of the angles between the bony ribs and the costal
cartilages under the influence of the couple (or pair of
oppositely directed forces) that acts on them — viz., the
upward pull of the levatores costarum and the other elevators
exerted on the ribs, and the resistance of the sternum to
further displacement exerted on the cartilages. The widening
of the thorax from side to side may also be in a slight degree
ascribed to a twisting movement of the ribs, which tends to
evert their lower borders.
Expiration in perfectly tranquil breathing is brought about
with very little aid from active muscular contraction. The
sense of effort disappears as soon as the chest ceases to
expand. The diaphragm and the elevators of the ribs relax.
The structures ihat have been stretched or twisted recoil
into their original positions ; the structures that have been
raised against the force of gravity fall back by their weight,
and in the measure in which the pressure increases in the
thoracic cavity the elasticity of the lungs causes them to
shrink. The pressure in the alveoli, w'hich at the end of
inspiration was just equal to that of the atmosphere, is thus
increased, and the air expelled. It is possible that, even
in man and in quiet respiration, a slight contraction of the
abdominal muscles hastens the return of the diaphragm to its
position of rest, and that the triangularis stcrni helps in
depressing the costal cartilages. In reptiles and birds,
expiration is normally effected by an active muscular con-
traction. This is also true in some mammals — the rabbit,
for instance, in which the external oblique muscle of the
abdominal wall takes an important share in the expiratory act.
202 A MANUAL OF PHYSIOLOGY
Types of Respiration. — Differences exist also, not only
between (liftcrent ^Moups of animals, but even between
women and men, in the relative importance in inspiration
of the diaphragm on the one hand, and the muscles that
elevate the ribs on the other. When the movements of the
diaphragm predominate, the respiration is said to be of the
ahdomxnal or diaphragmatic type; when the movements of
the ribs and sternum are most conspicuous, of the costal or
thoracic type. In abdominal respiration, the inspiratory
movement commences at the diaphragm, and then involves
the lower ribs and the tip of the sternum. In costal
respiration, the upper ribs initiate the movement, and are
followed by the abdomen. In the rabbit, during quiet
breathing, the respiration is purely diaphragmatic, the ribs
remain motionless ; and herbivorous animals in general
conform more or less closely to this type. In the carnivora,
on the contrar}', the costal type prevails. Man allies him-
self as regards his respiration with the rabbit and the sheep ;
he uses his diaphragm more than his ribs. Civilized woman
falls into the class of the wolf and the tiger ; she uses her
ribs more than her diaphragm. The cause of the difference
between men and women has been much discussed. It is
not a primitive sexual difference, for it is far from being
universal ; in the uncivilized and semi-civilized races that
have been investigated, the women breathe like the men.
It is therefore probable that the predominance of the costal
type among women of European race is a peculiarity
developed by a mode of dressing which hampers the move-
ments of the diaphragm while permitting the elevation of
the ribs. This conclusion is strengthened by the fact that
in children no difference exists ; both bo\s and girls show
the abdominal type of respiration.
All this refers to ordinary breathing. In forced respira-
tion, when the need for air becomes urgent, costal breathing
always becomes prominent alike in men, in women, and in
animals, for by elevation of the ribs the capacity of the
chest can be increased to a greater degree than by any
contraction of the diaphragm.
In forced inspiration, indeed, all the muscles that can
A'/:S/VA'.l 7/i)\ 203
elo\ate the ribs may be thrown into contraction, as well as
other muscles which ^ive these fixed points to act from.
During a paroxysm of asthma, for example, the patient may
grasp the back of a chair with his hands, so as to fix the
arms and shoulders and allow the pectoral and serratus
magnus to raise the ribs. Similarly in forced expiration
all the muscles are used which can depress the ribs, or
increase the intra-abdominal pressure and push up the
diaphragm.
Certain accessory phenomena (movements and sounds) are
associated with the proper movements of respiration. The
larynx rises in expiration, and sinks in inspiration. The
glottis (and particularly its posterior portion, the glottis
respiratoria) is widened during deep inspiration and
narrowed during deep expiration. The same is the case
with the nostrils, and, indeed, in some persons the ake nasi
move even in ordinary breathing.
As regards the respiratory sounds, all that is necessary to
be said here is that when we listen over the greater portion
of the lungs with the ear, or, much better, with a stetho-
scope, a soft breezy murmur, that has been compared to the
rustling of the wind through distant trees, is heard. This
has been called the vesicular ninruiuv. It is only heard in
health during inspiration and the very beginning of expira-
tion, and is louder in children than in adults. It is not
definitely settled whether this sound arises at the glottis
and is modified by transmission through the pulmonary
tissue, or whether it arises somewhere in the terminal
bronchi, the infundibula or the alveoli. Both views may be
supported by certain arguments, and to both some objec-
tions may be raised. But it is generally admitted, and this
is of great importance in practical medicine, that when
the normal sound is heard over any portion of the lung
tissue, it may be inferred that this portion is being properly
distended, and that air is freely entering its alveoli. Around
the larger bronchi and the trachea a blowing sound is heard.
In health this is not recognised over the greater portion of
the lung, but in certain diseases in which the alveoli are
filled up with exudation, this bronchial or tubular breathing
:o4
.1 MAXCAL 01' rilYSIOLOGY
may be heard over a large area, the vesicular sound being
now suppressed, and the bronchial sound being better con-
ducted by the consolidated tissue than by the portions of
the lung that still contain air.
Up to this point we have contented ourselves with a
purely qualitative description of the mechanical pheno-
mena of respiration. We have now to consider their
quantitative relations, and the methods by which these
have been studied.
The expansion of the lungs in inspiration may be easily demon-
strated in man, and even a rough estimate of its amount obtained,
by the clinical method of percus-
sion. For example, the resonant
note that is elicited when a finger
laid on the chest at a part where
it overlies the right lung is smartly
struck can be followed down until
it is lost in the 'liver dulness. '
If the lower limit of the resonant
area be marked on the chest-wall
first in full inspiration and then
in full expiration, the mark will
be lower in the former than in
the latter, and the difference will
represent the difference in the
vertical length of the shrunken
and distended lung. A similar
enlargement in the transverse
direction may be demonstrated
in the same way, the inner
borders of the lungs coming
nearer to the middle line in in-
spiration, and receding from it in
expiration.
For most physiological pur-
poses, however, we require
methods more delicate and more exact, and in many investigations a
faithful graphic record of the respiratory movements is indispensable.
This may be obtained :
(i) By registering the movements of a single point, or the varia-
tions in a single circumference, of the boundary of the thoracic
cavity. In animals the end of a lever, or a small compressible bag
containing air and connected with a recording tambour, may be
placed between the lower surface of the diaphragm and the liver,
through an incision in the abdominal wall. In man changes in the
circumference of the chest at any level can be recorded by means of
a tambour so adjusted that in inspiration the pressure of the air in
Fk;. 77. — .SriiKME t)!- Tami-.ouk
(Bro.ndokest's) for kecokdinc
Resi'ikatory Movements.
C, a metal capsule connected airtight
with B, A, two caoutchouc membranes, the
chamber formed by which can be inll.ited
bv means of the tube and stopcock K.
The tube D connects the space H with a
registering tambour provided with a lever.
The membrane A is applied to the chest,
round which the inextensible strings F are
tied. .At every expansion of the chest the
pressure in H is increased, and the increase
of pressure is transmitted to the registering
tambour.
RESr/A'A TION 205
it is increased and in expiratiun diminished. This tambour is in
communication with another, which is i)rovided with a writing lever
(Marey's pneumograph, Sanderson's stelliometer, Brondgeest's pan
sphygmograph). (Fig. 77.) Or an elastic tube, with a spiral spring
in its lumen, may be fastened around the thorax or abdomen and
connected with a piston-recorder (a small cylinder in which works a
piston carrying a writing-point) (l''it/).
(2) By recording the changes of pressure produced in the air-
passages by the res[)iratory movements. This can be done by con-
necting a cannula in the trachea of an animal with a recording
tambour in the manner described in the Practical Hxercises, p. 272.
The changes of pressure may be measured by connecting a mano-
meter with the trachea, or in man with the nostril.
(3) By writing off the changes of pressure which occur in the
thoracic cavity during respiration. For this purpose a trocar is
Fk;. 78.
The upper tracing is .1 record of the respiratory movements in a rabbit, taken with
Kronecker's kver between the diaphragm and liver. The lower curve is a blood-
pressure tracing showing large oscillations (like Traube-Hering waves). E, expiration ;
I, inspiration. Time trace, seconds. The animal was under the influence of gelsemin.
introduced through an intercostal space into one of the pleural sacs,
without the admission of air, or into the pericardium, and then con-
nected with a manometer or other recording apparatus. Or a tube,
similar in construction to a cardiac sound (p. 86), and, like it,
terminating in an elastic bag, may be pushed down the oesophagus.
The variations in the intra-thoracic pressure are transmitted to the
air in the bag, and thence to a tambour connected with the sound.
When the respiratory movements are studied in any of
these ways, it is found that there is practically no pause
between the end of inspiration and the beginning of expira-
tion. Nor, although the chest collapses more gradually
than it expands, is there any distinct interval in ordinary
2o6 A MANUAL Of I'// YS/O/ax;)'
breathinfj between the end of expiration and the beginning
of the succeeding inspiration. When, however, the respira-
tion is unusually slow, an actual pause (expiratory pause) may
occur at this point. Expiration takes somewhat longer
time than inspiration, the ratio varying from 7:6 to \ : 2,
according to age, sex, and other circumstances.
The frequency of respiration is by no means constant even
in health. All kinds of influences affect it. It is difficult
even to direct the attention to the respiratory act without
bringing about a modification in its rhythm. In the adult
15 to 20 respirations per minute may be taken as about the
normal. In young children the frequency may be twice as
great (new-born child, 50 to 70 ; child from i to 5 years old,
20 to 30 per minute). It is greater in a female than in a
male of the same age. A rise of temperature increases it,
and this is probably one of the causes of the increased rate
of respiration in fever; 150 respirations per minute have
been seen in a dog with a high temperature. Sudden
cooling of the skin, exercise, and various emotional states,
increase the rate, and sleep diminishes it. The will can
alter the frequency and depth of respiration for a time, and
even stop it altogether, but in about a minute, in ordinary
individuals, the desire to breathe becomes imperative, nor
can any training extend this interval of voluntary inhibition
beyond three minutes. Cato's assertion that he could kill
himself at any time ' merely by holding his breath ' is only
a proof that he was a better philosopher than physiologist.
In animals the rate can be greatly affected by drugs and by
the section and stimulation of certain nerves ; but to this
we shall return when we come to consider the nervous
mechanism of respiration.
It cannot fail to be observed that to a great extent the
rate of respiration is affected by the same circumstances as
the frequency of the heart (p. 95), and in the same direc-
tion. And, indeed, in health, these two physiological
quantities, amid all their absolute variations, maintain to
each other a fairly constant ratio ( i to 4 or i to 5 in man).
Even in many diseases this proportion remains tolerably
stable, although in others it is disturbed.
RESPIKA TION
207
The total quantity of air expired, or, what conies to the
same thing, the alteration in the capacity of the chest during
expiration, can be measured by means of a spirometer, which
consists of an in\erted graduated glass bell dipping by its
open mouth into water and balanced by weights. The
vessel is sunk till it is full of water, the air being allowed
to escape by a cock. The expired air is now permitted to
enter it through a tube, and displaces some of the water.
The spirometer is adjusted so that the level of the water
inside and outside is the
same, and then the volume
of air contained in it is read
off. This gives the volume
of the expired air at atmo-
spheric pressure. Similarly,
by breathing air from the
spirometer the amount in-
spired can be measured.
From 400 to 500 c.c. of
air* are taken in and given
out at each respiration in
quiet breathing. This is
called tidal air. It amounts
to 35 pounds by weight in
c -i I l""i<;- 79.— Diagram of Spirometer.
twenty-four hours, or enough , , c„ ^ • u . d 1
■^ . ° A, vessel filled with water, B, glass
to fill, at atmospheric pres- cylinder with scale C, swung on pulleys
, . , . . , . , and counterpoised by weights W. D, tube
sure, a cubical box with a side for breathing through.
of 8 feet. With the deepest
possible inspiration room can be made for 2,000 c.c. more ;
this is called complemental air. By a forced expiration
1,500 c.c. can be expelled besides the tidal air ; and to this
quantity the name of supplemental or reserve air has been
given. After the deepest expiration there always remain
about 700 or 800 c.c. of air in the lungs, and this is called
* The average for 56 healthy students, with an average body-weight of
66 kilos, was 457 c.c, or 6"9 c.c. per kilo. In 4 newborn children the tidal
air varied from 20 to 30 c.c, and from 7'6 to 7"3 c c per kilo, which is not
very different froin the amount in the adult. The pulmonary ventilation
must therefore be far more rapid in the child, since its respiratory
frequency is so inuch greater.
2o8
.1 M.LVf.lL OF niYSIULOGY
the residual air. After a normal expiration following a
normal inspiration the lungs still contain stationary air to
the amount of about 2,500 c.c.
The residual air may be measured by causing a person, starting
immediately after the deepest possible expiration, to breathe out and
in several times into a vessel (a spirometer) filled with hydrogen, till
it can be assumed that the hydrogen and the residue of air in the
lungs have been completely mixed. Knowing the quantity of
hydrogen originally contained in the vessel, we can calculate from
the percentage at the end of the experiment the quantity of air with
which it has been mixed — that is, the residual air (Davy).
Let V be the quantity of hydrogen in the spirometer at first, and
/ the percentage amount in it at the end of the experiment. Let x
be the volume of residual air in the lungs at the beginning.
Then, since the quantity of hydrogen remains unchanged after the
mixture,
Suppose V
and p-
we get .r^
100
V ( 1 00 - />)
/
4,000 c.c,
85 per cent.,
12,000 ,
= al:oi.t 70-
Caftactty
lWl!il!lllill|lii!l!l!ll
Comjile mental air
Tidal air
Sufiplcniental air
Residual air
Yic. 80.
-Diagram to ii.lusiraik the Kelaiixe Amoim ok Compi.e-
MENiAL, TiUAi., Supplemental, and Residual Air.
But some carbon dioxide would be given off by the lungs, and some
oxygen, and perhaps hydrogen, absorbed, during the experiment, and
therefore slight corrections might have to be made. Sir Humphry
Davy actually calculated the residual air in his own lungs, as deter-
mined by this method, at 672 c.c.
The coefficient of ventilation, that is, the ratio of the quantity of air
taken in at each inspiration to the quantity already in the lungs, has
been estimated at about ' or ^.
The term vital or respiratory capacity is applied to the
quantity of air which can be expelled b}- the deepest expira-
tion following the deepest inspiration, and amounts in an
adult of average height to 3,500 or 4,000 c.c. The maximum
k'/:SP/A'A HON 209
cjiiantity of air which the hin;::[s can contain is cvidcntl}'
equal to vital capacity plus residual air. At one time the
vital capacity was thought to be capable of affording valuable
information in the diagnosis of chest diseases; but little
stress is now laid upon it, as it varies from so many causes.
It is greater in mountaineers than in the inhabitants of
lowland plains.
It is clear from the figures we have given that in ordinary
breathing only a small proportion of the air in the lunj:^s
comes in direct at each inspiration from the atmosphere,
and only a small proportion escapes into the atmosphere
at each expiration. The greater part of the air in the
lungs is simply moved a little farther from the upper
respiratory passages, or a little nearer them ; and fresh
oxygen reaches the alveoli, as carbon dioxide leaves them,
mainly by diffusion, aided by convection currents due to
inequalities of temperature, and to the churning which the
alternate expansion and shrinking of the lungs, and the
pulsations of their arteries, must produce. But that some
of the tidal air strikes right down to the alveoli is evident
enough. For the respiratory ' dead space ' — that is, the
capacity of the upper air passages and the bronchial tree
down to the infundibula — is only 140 c.c, or one-third of the
amount of the tidal air [Zuntz, Loewy). The immense
extent of the pulmonary surface, and the extreme thinness
of the layer of blood in the capillaries of the lungs, facilitate
the interchange between the gases of the blood and the gases
of the alveoli.
The Amount and Variations of the Intra-thoracic Pressure. — In
the deepest expiration the lungs are never completely
collapsed ; their elastic fibres are still stretched ; and the
tension of these acts in the opposite direction to the external
atmospheric pressure, and diminishes by its amount the
pressure inside the thoracic cavity. In the dead body
Bonders measured the value of this tension, and therefore
of the negative pressure of the thorax, by tying a mano-
meter into the trachea, and then causing the lungs to
collapse by opening the chest. It varied from 7*5 mm. of
14
2IO A MANUAL Of P/IYSIOLOCY
mercury in the expiratory position to 9 mm. in the in-
spiratory. So far as can be judpjed from observations made
on persons suffering from various diseases of the respiratory
organs, the alterations during ordinary breathing do not
amount to more than 3 or 4 mm. of mercury. But when an
attempt is made in the dead body to imitate a deep in-
spiration by making traction on the chest-walls so as to
expand the lungs, the intra-thoracic pressure may fall to
— 30 mm. of mercury; and in a living rabbit during a
deep natural inspiration, a pressure of —20 mm. has been
seen.
The reason why the lungs collapse when the chest is
opened is that the pressure is now equal on the pleural and
alveolar surfaces, being in both cases that of the atmosphere.
There is therefore nothing to oppose the elasticity of the
lungs, which tends to contract them. So long as the chest
is unopened, the pressure on the pleural surface of the lungs
is less than that on the alveolar surface, and the elastic
tension can only cause them to shrink until it just balances
this difference.
In intra-uterine life, and in stillborn children who have
never breathed, the lungs are completely collapsed (atelec-
tatic), and there is no negative intra-thoracic pressure.
They are kept in this condition by adhesion of the walls of
the bronchioles and alveoli. If the lungs have been once
inflated, this adhesion ceases to act, and they never com-
pletely collapse again.
Amount and Variations of the Respiratory Pressure. — As we
have already remarked, the pressure in the alveoli and air-
passages is less than that of the atmosphere while the
inspiratory movement is going on, greater than that of the
atmosphere during the expiratory movement, and equal to
that of the atmosphere when the chest-walls are at rest.
When the external air-passages are closed, e.g. ,hy connecting
a manomejter with the mouth and pinching the nostrils, the
greatest possible variations of pressure are produced. In
the deepest inspiration under these conditions a negative
pressure of about 75 mm. of mercury {i.e., a pressure less
than that of the atmosphere by this amount) has been found,
RESPIRATION 21 1
and in deep expiration a somewhat greater positive pressure*
(Practical Exercises, p. 274).
But with ordinary breathing, the variations of pressure as
measured by this method do not exceed 5 to 10 mm. of
mercury above or below the pressure of the atmosphere.
When the external openings are not obstructed, as, for
example, when the lateral pressure is taken in the trachea
of an animal by means of a cannula with a side-tube con-
nected with a manometer, still smaller, and doubtless truer,
values have been found (2-3 mm. of mercury as the positive
expiratory pressure, and i mm. as the negative inspiratory
pressure in dogs). But since the respiratory passages are
abruptly narrowed at the glottis, the variations of pressure
must be greater below than above it, and in general they
must increase with the distance from that orifice, being
greater, for instance, in the alveoli than in the bronchi.
Relation of Respiration to the Nervous System. — Unlike the
beat of the heart, the respiratory movements are entirely
dependent on the nervous system ; and the ' centre ' which
presides over them is situated in the spinal bulb. It is a
bilateral centre — that is, it has two functionally symmetrical
halves, one on each side of the middle line ; and each of
these halves seems to have to do more particularly with the
respiratory muscles of its own side, for destruction of one-
half of the spinal bulb causes paralysis of respiration only
on that side. Anatomically the respiratory centre has not
been sharply localized ; but it lies higher than the vaso-
motor centre. It is brought into relation with the muscles
of respiration by efferent nerves. The phrenic nerves to
the diaphragm, and the intercostal nerves to the muscles
which elevate the ribs, are the most important of those
concerned in ordinary breathing. The circular muscles of
the bronchi are also supplied with motor fibres that run in
the pneumogastric. The bronchial tubes are narrowed by
their artificial excitation, but their function in respiration
is unknown. The respiratory centre is further related to
* The maximum negative pressure in deepest inspiration averaged for
41; students, -y^ mm. (highest observation - 137 mm.) of mercury ; the
maximum positive pressure in deepest expiration, -I- 80 mm. (highest
observation + 140 mm.).
14—2
212 A MANUAL OF PIIYSIOLOdY
afferent nerves, of which the most influential is the vagus,
particularly its pulmonary fibres, and its superior laryngeal
branch. But almost any afferent nerve may powerfully
affect the centre ; and it is also influenced by fibres
passing to it from the higher parts of the central nervous
system.
Section of the spinal cord in animals above the origin of
the phrenic nerves causes complete paralysis of respiration,
and consequent death. The phrenics arise from the third
and fourth cervical nerves, and are joined by a branch from
the fifth ; and in man fracture of any of the four upper
cervical vertebrae is, as a rule, instantly fatal. But in one
case respiration was carried on, and life maintained for
thirty minutes, merely by the contraction of the muscles of
the neck and shoulders in a man entirely paralyzed below
this level (Bell). Section of the cord just below the origin
of the phrenics leaves the diaphragm working, although the
other respirator}- muscles are paralyzed. A case has been
recorded of a man in whom, from disease of the spine in
the lower cervical region, all the ribs became completely
immovable. He was able to lead an active life, and to
carry on his business, although he breathed entirely by his
diaphragm and abdominal muscles (Hilton).
Section of one phrenic is followed by paralysis of the
corresponding half of the diaphragm, section of both
phrenics by complete paralysis of that muscle, and although
respiration still goes on by means of the muscles which act
upon the ribs, it is usually inadequate to the prolonged
maintenance of life. In the horse, however, not only has
survival been seen after this severe operation, but the
animal, after the first temporary increase in the frequency
of the breathing had disappeared, could be driven in a light
vehicle without any marked dyspnoea. The phrenic nuclei
in the two halves of the cord are connected across the
middle line. For when a hemisection of the cord is made
between this level and the respiratory centre in the medulla,
respiratory impulses are still able to reach both phrenic
nerves. In some animals both halves of the diaphragm go
on contracting. But when, as usually happens, this is not
K/:SPIRA TION 2 1 3
the case, and the diaphragm vtw the side of the hemisection
has ceased to act, it at once begins to contract again when
the opposite phrenic nerve is cut, and the respiratory
impulse, descending from the bulb, is blocked out from the
direct, and forced to follow the crossed path. It has been
shown that the crossing takes place at the level of the
phrenic nuclei, and nowhere else (Porter).
When one vagus is divided, there is little or no change
in the respiratory movements. Half an inch of one vagus
nerve has been excised in removing a tumour, and the
patient showed no symptoms whatever (Billroth). But
section of both vagi generally (though not always) causes re-
spiration to become for a time much deeper and slower, the
one change just compensating the other, so that the total
amount of air taken in and given out, and the amount of
carbon dioxide eliminated, are not altered. Gad has shown
that the effect is really due to the loss of impulses that
normally ascend the vagi, not to any irritation of the cut
ends. For a nerve can be frozen without exciting it ; and
when a portion of each vagus is frozen, the respiration is
affected in precisely the same way as when the nerves are
divided.
A similar change follows the blocking of the paths connect-
ing the respiratory centre with the brain above, by injection
of paraffin wax into the common or internal carotid. The
bloodvessels supplying the nerve-iibres which connect the
respiratory centre with the brain may in this way be closed
by artilicial emboli. The nerves lose their function, as if
they had been cut ; no impulses now reach the respiratory
centre from above ; and the respiration becomes markedly
slowed and deepened, just as happens when the vagi are
divided. Where only the vagus or these ' higher paths,'
but not both, are cut off, the respiration remains regular,
although deep, and perhaps in course of time tends to
resume its original type. But when both paths are cut, the
character of the respiration is entirely changed ; periods of
rapid and spasmodic breathing alternate with periods of
complete cessation, till the animal dies (Marckwald).
From these facts it appears that the periodic automatic
214 A MANUAL OF I'lIYSIOLOUY
discharges of the respiratory centre arc bein;:^ continually
controlled and modified by impulses passing up the vagus or
down from the brain, but especially up the \agus. When
the vagus is severed, the control of the higher paths becomes
more complete, and is sufficient still to keep the breathing
regular. When the higher paths are cut off, the vagus of
itself is able to regulate the discharge. But when both are
gone, the respiratory centre, freed from control, passes into
a condition of alternate spasm and exhaustion.
The continuous excitation of the regulating vagus fibres
must be brought about either by mechanical stimulation of
the nerve-endings in the lungs, due to the alternate stretching
Fig. 8i. — Resi'IRAtokv Tracings (Dot;)-
A, normal ; B, effect of stimulation of the central end of the vagus ; C, effect of
section of both vagi. (Tracing taken with arrangement shown in Fig. loo, p. 273).
Time-tracing marks seconds.
and shrinking, or by chemical stimulation depending on the
state of the blood. Both views have found advocates, but
neither has been definitely proved. Nor are the results of
experimental stimulation of the nerve-trunk so clear or so
constant that we can confidently appeal to them in making
a decision. Excitation, with induction shocks, of the central
end of the cut vagus below the origin of its superior laryn-
geal branch certainly causes quickening of respiration, or,
if the excitation be strong, arrest in the inspiratory phase.
A brief mechanical stimulus, or a series of such, has a
similar effect. But chemical stimulation ^c.g., with a strong
R/:SPIA\ I TlOX
215
solution of potassium chloride) or lon^'-continued mechanical
excitation like that produced by stretching or compression
of the nerve, or certain kinds of electrical stimulation — for
instance, the closure of an ascendinj:;; voltaic current* —
cause slowing of the respiratory movements or expiratory
standstill. This is also the usual, though not the invariable,
result of stimulating the superior laryngeal, even when in-
duction shocks are employed. These facts undoubtedly
suggest the existence in the vagus of two kinds of afferent
nerve-fibres that affect the respiratory centre in opposite
ways — inspiratory fibres, which stimulate it to greater
activity of discharge, and expiratory fibres, which inhibit
its action. The latter variety we may suppose to be more
numerous in the superior laryngeal, the former in the pul-
monary branches of the vagus. And there is nothing forced
in the hypothesis that certain kinds of stimuli act par-
ticularly on the one set of fibres, and certain kinds on the
other, for we have already seen an instance of this in
studying the differences between the vaso-constrictor and
the vaso-dilator nerves (p. 150). It is possible, however
(although this view has less inherent probability, in spite
of the fact that it has been maintained by some of the most
recent writers on the subject), that, at any rate in the vagus
trunk, only one set of fibres exists, and that these are
affected differently by different kinds of stimulation —
momentary stimuli, for example, setting up in them im-
pulses which we may call inspiratory, and long-lasting
stimuli impulses which we may call expiratory (Boruttau,
Lewandowsky).
However this may be, the facts we have been discussing
have an importance of their own, apart from any hypo-
thetical explanations of them ; and they may be readily
demonstrated by means of such a graphic method as is
described in the Practical Exercises (p. 273), or by merely
opening the abdomen in a rabbit, and observing the lungs
through the thin diaphragm (Gad). Some of them have
been more than once unintentionally illustrated on man. In
one case the left vagus trunk was included in a ligature
* I.e., a current passing towards the head in the nerve.
2l6 A MANUAL OF I'J/YSIOLOGY
with the common carotid. The respiratory movements imme-
diately stopped, the pulse was slowed, and death occurred
in thirty minutes (Rouse). The superior laryngeal fibres,
unlike those of the vagus proper, do not appear to be con-
stantly in action, as section of both nerves has no effect on
respiration. Any source of irritation in the larynx may
stimulate these fibres and produce a cough, which may
also be caused by irritation of the pulmonary fibres of the
vagus.
The cutaneous nerves, and especially those of the face
(fifth nerve), abdomen and chest, have a marked influence
on respiration. They can be easily excited in the intact
body by thermal and mechanical stimulation. A cold
bath, for instance, usually causes acceleration and deepen-
ing of the respiratory movements ; and the efficacy of
mechanical stimulation of sensory nerves in stirring up
a sluggish respiratory centre is well known to midwives,
who sometimes slap the buttocks of a newborn child to
start its breathing.
Another set of afferent nerves that seem to have an
important relation to the respiratory centre are those which
supply the muscles. We have already noticed that the
frequency of respiration is greatly augmented by muscular
exercise. This seems to be brought about in part through
the stimulation of those afferent muscular nerves either by
mechanical compression of their terminal ' spindles," or by
the chemical action on them of certain waste products
produced in contraction. But this cannot be the only way
in which the respiratory centre is affected by muscular
activity. For everybody is agreed that an increase in the
respiratory movements is caused by tetanizing the muscles
of a limb whose nerves have been completely severed, and
which is indeed connected with the rest of the body by no
other structures than its bloodvessels. This can only be
due to two things : a direct action on the respiratory centre
by the blood that has passed through, and been altered
in, the contracting muscles, or an action exerted by the blood
indirectly on the centre through the excitation of afferent
respiratory nerves whose connection with it is still intact —
J^ESriRATION 317
for example, the other muscular nerves or the pulmonary
branches of the vagus.
That the respiratory centre is greatly affected by the
quality of the blood which circulates through it is well
known. And it is generally acknowledged that it may be
excited both by blood that is rich in carbon dioxide and by
blood that is poor in oxygen, the actual stimulating sub-
stance in the latter case being, perhaps, an easily oxidizable
body which rapidly disappears from properly oxygenated
blood (Pfluger).
But it has been the subject of long-continued discussion
whether excess of carbon dioxide or deficiency of oxygen is
the more potent stimulus. The truth appears to be that
much depends upon the conditions of the experiment, upon
the size of the chamber, for instance, in which an animal
or a man is made to breathe. The best evidence points
to the conclusion that comparatively small alterations in
the amount of carbon dioxide in the inspired air cause a
relatively great increase in the respiration, while in the case
of the oxygen the departure from the normal proportion
must be much more decided to bring about any notable
effect (Zuntz and Loewy). Nor is it at all out of harmony
with this that, when very large quantities of carbon dioxide
(30 per cent, and upwards in rabbits) are inhaled, a condi-
tion of narcosis comes on without any previous respiratory
distress (Benedicenti). For many substances act differently
in large and in small doses.
Be this as it may, when the gaseous interchange from any
cause becomes insufficient, the respiratory movements are
exaggerated, and ultimately every muscle which can directly
or indirectly act upon the chest-walls is called into play in
the struggle to pass more air into and out of the lungs. To
a lesser and greater degree of this exaggeration of breathing
the terms Hypcrpncea and Dyspmca have been respectively
applied. If the gaseous interchange remains insufficient,
or is altogether prevented, asphyxia or suffocation sets in.
Sometimes in man impending asphyxia from loss of function
by a part of the lungs, as in pneumonia, may be warded off
by inhalations of oxygen. Increase in the temperature of
21 8 A MAXUAL OF PHYSIOLOGY
the blood circulating through the spinal bulb, as when the
carotid arteries of a dog are laid on metal boxes through
which hot water is kept flowing, also causes dyspnoea (licat-
dyspnaa), (p. 272). But if the temperature be too high, the
respiratory movements may be slowed, perhaps by a partial
paralysis or inhibition of the respiratory centre. When the
blood is cooled the respiration becomes deeper and slower,
but if the temperature is greatly and suddenly lowered, the
centre may be stimulated and the breathing quickened. In
man the increased temperature of the blood in fever is prob-
ably connected with the increase in the rate of respiration.
The physiological opposite of dyspncea is apncca. This
condition may be produced in an animal by rapid artificial
respiration. For some seconds, in a successful experiment,
after the artificial respiration is stopped, the animal remains
without breathing. The apnoeic state seems to be due
partly to an excess of oxygen in the arterial blood or in the
lungs, partly to some nervous effect produced through the
vagi on the respiratory centre. Possibly the pulmonary
nerve-endings of the vagi are affected mechanicall}- by the
inflation ; for rapid and repeated inflation of the lungs with
hydrogen may cause apnoea (Traube). The venous blood in
apncea is, if anything, poorer in oxygen than normal venous
blood.
That poorly oxygenated blood produces dyspncea by acting
on some portion of the brain may be shown in an interesting
manner by establishing what is called a cross-circulation in
two rabbits or dogs. The vertebral arteries and one carotid
are tied in both animals ; the remaining carotids are divided
and connected crosswise by glass tubes, so that the brain of
each is supplied by blood from the other (Bienfait and
Hogge). When the respiration is artificially hindered or
stopped in one of the animals, it shows no dyspncea ; it
is in the other, whose brain is being fed with improperly
oxygenated blood, that the respirator}' movements become
exaggerated. The point of attack of the * venous ' blood
has been further localized in the spinal bulb by the observa-
tion that when the brain has been cut away above it, the
cord severed below the origin of the phrenics, and all other
RESI'IRATfON 219
nerves connected with the region between the two planes of
section divided, any interference with the gaseous exchange
in the lungs is at once followed by dyspnoea.*
The question has been raised whether, in the absence of
this ' natural ' stimulation by the blood, and of the impulses
that constantl}' reach the centre along its afferent nerves, it
would continue to discharge itself, or whether it would sink
into inaction. We have already discussed a similar question
in regard to the cardiac and vaso-motor centres, and the
subject must again present itself when we come to examine
the functions of the central nervous system. In the mean-
time it is only necessary to say that the apparent auto-
matism of the respiratory centre, although modified by
the quality of the blood which circulates in it, is not essen-
tially dependent on it ; for in animals whose blood has been
replaced by normal saline solution or serum, and in frogs
after excision of the heart, quiet, regular breathing has been
seen to go on.
Action of Drugs on the Respiratory Centre. — The respiratory
centre is directly affected by numerous drugs. Pituri and nicotin,
for instance, cause in various animals a quickening and deepening
of the respiration, followed, if the dose has been large, by slowing
and ultimate cessation. The action of the great majority of such
substances, however, possesses only a pharmacological interest, and
it would be out of place even to enumerate them in a text-book of
physiology. But there are one or two points in the action on the
respiratory centre of chloroform and alcohol— substances so greatly
employed in practical medicine and in physiological research — which
may properly be touched on here :
Chloroform. — The cause of the deaths from chloroform which, at
rare intervals, startle the operating theatre of every great hospital
where this anaesthetic is used, has been, on account of its extreme
practical interest, the subject of prolonged discussion and experiment.
Is it the heart that fails ? Or is it the respiration ? The answer of
what is known as the ' Edinburgh School ' is that the respiration (in
physiological terms, the respiratory centre) is always first paralyzed.
Their golden rule of doctrine in chloroform administration is,
'Watch the respiration ; the heart will take care of itself — a rule
which, however, in ' Edinburgh ' practice does not exclude careful
observation of the pulse. This view, having the merit of simplicity,
has been widely adopted. It has been lately upheld by a scientific
* The conclusion is doubtless correct, but this experiment is not
decisi\ e. For the phrenic nerves themselves contain atteient fibres,
through which the respiratory centre tnig/tt have been aftected.
220 A MANUAL OF /'/lYSIOLOGY
( ommission appointed by the Nizam of Hyderabad for the special
purpose of investigating the question with the aid of modern
physiological methods. But the conclusions of the Hydera1)ad
Commission, valuable as they are, seem to have been too abso-
lutely drawn. For it has been shown by a number of observers
(MacWilliam, Gaskcll and Shore, etc.) that chloroform undoubtedly
may paralyze the heart without affecting the respiration ; and, further,
that the paralysis of the vaso-motor centre, and the consequent
withdrawal of blood from the heart and brain to the dilated
si)lanchnic area, may be an important factor in bringing about a
fatal result (p. 164). A second table might therefore be added to the
' Edinburgh law': ' Watch the breathing ; watch the pulse. If the
heart threatens to fail for want of blood, fill it by raising the legs and
compressing the abdomen.'
Alcohol in small doses, when given by the stomach or (in animals)
injected into the blood, causes stimulation of the respiratory centre
and increase in the pulmonary ventilation. In man, this increase
usually amounts to S-15 per cent., but is occasionally much greater.
But the limit which separates the favourable action of the small dose
from the hurtful action of the large, is easily overstepped. When
this is done, and the dose is continually increased, the activity of the
respiratory centre is first diminished and finally abolished. In dogs,
for instance, after the injection of considerable (juantities of alcohol
into the stomach, death takes place from respiratory failure, and the
breathing stops while the heart is still unweakened (Fig. 57, p. 165).
This is the final outcome of a ])rogressive impairment in the activity
of the centre, of which the slow and heavy breathing of the drunken
man represents an earlier stage.
Although the chief respiratory centre undoubtedly lies in
the medulla oblongata, it appears that under certain condi-
tions impulses to the respiratory muscles may originate in
the spinal cord. Thus, in young mammals (kittens, puppies),
especially when the excitability of the cord has been in-
creased by strychnia, in birds and in alligators, movements,
apparently respiratory, have been seen after destruction of
the brain and spinal bulb. But no proof has ever been
given that in the intact organism the spinal cord below
the level of the bulb takes any other part in respiration than
that of a mere conductor of nerve impulses ; and it is not
justifiable to assume the existence of spinal respiratory
centres on the strength of such experiments as these.
Death after Double Vagotomy. — Alterations in the rhythm
of respiration are not the only effects that follow division of
both vagi. In certain animals, at least, this operation is
RESPII^ATION 221
incompatible with life. In the rabbit, as a rule, death takes
place in twenty-four hours. A sheep may live three days,
and a horse five or six. Dogs often live a week, occasionally
a month or even two, and in rare instances they ma}- survive
indefinitely. The most prominent symptoms (in the dog),
in addition to the marked and permanent slowing of
respiration, quickening of the pulse and contraction of the
pupils, are the frequent vomiting and progressive emacia-
tion. The appetite is sometimes ravenous, but no sooner is
the food swallowed than it is rejected ; and this is par-
ticularly true of water or liquid food. The fatal result is
usually caused, or at least preceded, by changes of a
pneumonic nature in the lungs. The precise significance of
the pulmonary lesion is obscure. But it would seem that
paralysis of the laryngeal and oesophageal muscles, with the
consequent entrance of food, foreign bodies, and perhaps
bacteria, into the lungs, is responsible to a great extent.
And when only a partial palsy of the glottis is produced, b}-
dividing the right vagus below the origin of the recurrent
laryngeal, and the left, as usual in the neck, pneumonia either
does not occur or is long delayed. It may be that the
tissue of the lungs is rendered particularly susceptible to
such insults in consequence of a hypera;mic condition in-
duced by the section of pulmonary vaso-motor fibres in the
vagi. The vomiting is certainly connected with the paralysis
and consequent dilatation of the cesophagus ; and b}- pre-
viously making an artificial opening into the stomach, or by
a surgical prophylaxis still more heroic, the establishment
of a double gastric and cesophageal fistula, certain observers
have been able to prevent death for man}- months.
Special Modifications of the Respiratory Movements. — Chcync-
Stokcs Respiration is the name given to a peculiar type of
breathing, marked by pauses of many seconds alternating
with groups of respirations. In each group the movements
gradually increase to a maximum amplitude, and then
become gradually shallower again, till they cease for the
next pause. The cause is unknown. The phenomenon is
not peculiar to pathological conditions, although it often
occurs in certain diseases of the brain, and although pressure
223 A MANUAL OF PHYSIOLOGY
on the spinal bulb may produce it. lUit it is also seen, more
or less perfectly, in normal sleep, especially in children, and
in morphia and chloral poisoning. A periodic change in the
activity of the respiratory centre, corresponding to the
change in the vaso-motor centre which is credited with the
production of Traube-Hering oscillations in the blood-
pressure (p. 250), has been suggested as the cause, but there
is no certainty as to this.
In frogs, Cheyne-Stokes' breathing has been observed as
the result of interference with the circulation in the spinal
bulb, ' drowning,' or ligature of the aorta, and also as a con-
sequence of removal of the brain, or parts of it (hemispheres
and optic thalami) (Langendorff, Sherrington, etc.).
Peculiarly modified, but more or less normal respiratory
acts are coughing, sneezing, yawning, sighing and hiccup.
A cou'^h is an abrupt expiration with open mouth, which
forces open the previously closed glottis. It may be excited
reflexly from the mucous membrane of the respiratory tract
or stomach through the afferent fibres of the vagus, from the
back of the tongue or mouth, and (by cold) from the skin.
Sneezing is a violent expiration in which the air is chiefly
expelled through the nose. It is usually excited reflexly
from the nasal mucous membrane through the branch of
the fifth nerve which supplies it. Pressure on the course of
the nasal nerve will often stop a sneeze. A bright light
sometimes causes a sneeze, and so in some individuals does
pressure on the supra-orbital nerve, when the skin over it is
slightly inflamed.
Yaivning is a prolonged and very deep inspiration, some-
times accompanied with stretching of the arms and the
whole body. It is a sign of mental or physical weariness.
A si'^Jt is a long-drawn inspiration, followed by a deep
expiration.
Hiccup is due to a spasmodic contraction of the diaphragm,
which causes a sudden inspiration. The abrupt closure of
the glottis cuts this short and gives rise to the characteristic
sound. The following readings of the intervals between
successive spasms were obtained in one attack : 13 sees.,
12 sees., 15 sees., 9 sees., 14 sees., etc. — i.e., one-fourth or
RESPIRATION 2 33
one-fifth of the frequency of the ordinary respiratory move-
ments. The mere fixing of the attention on the observations
soon stopped the hiccup.
Chemistry of Respiration.
Our knowledge of this subject has been entirely acquired
in the last 200 years, and chieily in the last century.
Boyle showed by means of the air-pump that animals die
in a vacuum, and Bernouilli that fish cannot live in water
from which the air has been driven out by boiling.
Mayow, of Oxford, seems to a considerable extent to have
anticipated Black, who in 1757 demonstrated the presence
of carbonic acid (carbon dioxide) in expired air by the
turbidity which it causes in lime-water.
A most fundamental step was the discovery of oxygen by
Priestley in 1771, and his proof that the venous blood could
be made crimson, like arterial, by being shaken up with
o.xygen.
Lavoisier discovered the composition of carbonic acid,
and applied his discovery to the explanation of the respira-
tory processes in animals, the heat of which he showed to be
generated like that of a candle by the union of carbon and
oxygen. He made many further important experiments on
respiration, publishing some of his results in 1789, when the
French Revolution, in which he was to be one of the most
distinguished victims, was breaking out. He made the
mistake, however, of supposing that the oxidation of the
carbon takes place in the blood as it passes through the
lesser circulation.
That some carbon dioxide is formed in the lungs there is
no reason to doubt, and the quantity may even be consider-
able (Bohr and Henriques). But that they are not the chief
seat of oxidation was sufficiently proved as soon as it was
known that the blood which comes to them from the right
heart is rich in carbon dioxide, while the blood which leaves
them through the pulmonary artery is comparatively poor.
There are two main lines on which research has gone in
trying to solve the chemical problems of respiration : (i)
The analysis and comparison of the inspired and expired
224 ^1 MAXrAL OF PIIYSIOLOC.Y
air, or, in f;^eneral, the investigation of the gaseous inter-
change between the hlc^od and the air in the lungs. (2) The
anal3sis and coinpririson of the gases of arterial and venous
blood, of the other liquids, and of the solid tissues of the
body, with a view to the determination of the gaseous inter-
change between the tissues and the blood. We shall take
these up as far as possible in their order.
The methods which have been used for comparing the
composition of inspired and expired air are very various.
(i) Breathing into one spirometer and out of another, the inspired
and ex])ired air being directed by valves. The contents of the spiro-
meters are analyzed at the end of the experiment (Speck).
(2) A small apparatus, much on the same principle, was used for
rabbits by i^fliiger and his pupils. A cannula in the trachea was
connected with a balanced and self-adjusting spirometer containing
oxygen, and the inspired and expired air separated by caustic potash
valves, which absorbed the carbon dioxide. The amount of oxygen
used could be read off on the spirometer, and the amount of carbon
dioxide produced estimated in the lifjuid of the valves.
(3) Larger and more elaborate arrangements, such as Pettenkofer's
great respiration apparatus, in which a man can remain for an in-
definite period, working, resting, or sleeping. Smaller chambers of
the same kind have also been used for animals. In Pettenkofer's
apparatus air is drawn through by an engine, its volume being
measured by a gasometer. But as it would be far too troublesome
to analyze the whole of the air coming from the chamber, a sample
stream of it is constantly drawn off, which also passes through a
gasometer, through drying tubes containing sulphuric acid, and
through tubes filled with baryta- water. The baryta solution is
titrated to determine the (quantity of carbon dioxide ; the increase in
weight of the drying tubes gives the quantity of aqueous vapour. A
similar sample stream of the air before it passes into the chamber is
treated exactly in the same way, and from the data thus got the
quantity of carbon dioxide and aqueous vapour given off can readily
be ascertained. But the oxygen has to be calculated by difference,
and all the errors fall upon it.
(4) Haldane and Pembrey have elaborated a gravimetric method,
which is the most suitable of any — at least, for small animals. It
depends upon the absorption of carbon dioxide by soda lime. See
Practical Exercises, p. 276.
The expired air is at or near the body temperature, is
saturated with watery vapour, and contains about 4 per cent,
more carbon dioxide and 4 to 5 per cent, less o.xygen than
the inspired. There may be in addition in expired air small
quantities of hydrogen or ammonia, but these are probably
RESPfA'A TION 225
derived from the alimentary canal, either directly or after
absorption into the blood. It is entirely free from floating
matter (dust), which is always present in the inspired air.
The volume of the expired air, owing to its higher tempera-
ture and excess of watery vapour, is somewhat greater than
that of the inspired air, but if it be measured at the tem-
perature and degree of saturation of the latter, the volume
is somewhat less. Since the oxygen of a given quantity of
carbon dioxide would have exactly the same volume as the
carbon dioxide itself at a given temperature and pressure, it
is clear that the deficiency is due to the fact that all the
oxygen which is taken up in the lungs is not given off as
carbon dioxide ; some of it, going to oxidize hydrogen,
reappears as water — a small amount of it unites with the
sulphur of the proteids (p. 390). The quotient of the volume
of oxygen given out as carbon dioxide by the volume of
oxygen taken in is the respiratory quotient. It shows what
proportion of the oxygen is used to oxidize carbon. It may
approach unity on a carbo-hydrate diet, which contains
enough oxygen to oxidize all its own hydrogen to water.
With a diet rich in fat it is least of all ; with a diet of lean
meat it is intermediate in amount. For ordinary fat con-
tains no more than one-sixth, and proteids not one-half,
of the oxygen needed to oxidize their hydrogen. In man
on a mixed diet the respiratory quotient may be taken
as "8 or "9. So long as the type of respiration is not
changed, the respiratory quotient may remain constant for
a wide range of metabolism. In hibernating animals, how-
ever, the respiratory quotient becomes very small during
winter sleep (as low as '4), the output of carbon dioxide falling
far more than the consumption of oxygen. On the other
hand, in excised mammalian muscles at a low temperature
the consumption of oxygen is lessened to a greater extent
than the production of carbon dioxide, and the respiratory
quotient may be as high as 3*2 (Rubner). Muscular work
increases the respiratory quotient, because carbo-hydrates
are chiefly used up. In starvation the respiratory quotient
diminishes, the production of carbon dioxide falling off at
a greater rate than the consumption of oxygen, for the
15
226 A MANUAL OF PHYSIOLOGY
starving organism lives on its own fat and protcids, and
has onl}' a trifling carbo-hydrate stock to draw upon. In a
diabetic patient, fed on a diet of fat and proteid alone, the
respiratory quotient was only "6 to '7, just as in a starving
man.
In an average man weighing 70 kilos the mean produc-
tion of carl)(:)n dioxide is about *Soo grammes (400 litres) in
twenty-four hours, and the mean consumption of oxygen about
700 grammes (490 litres) (Pettenkofer and \'oit). But there
are very great variations depending upon the state of the
body as regards rest or muscular activit}', and on other
circumstances. In hard work the production of carbon
dioxide was found to rise to nearly 1,300 grammes, and in rest
to sink to less than 700 grammes, the consumption of
oxygen in the same circumstances increasing to nearly 1,100
grammes and diminishing to 600 grammes. In rest, in
moderate exertion, and in hard work, the production of
carbon dioxide was found to be nearly proportionate to the
numbers 2, 3 and 6, respectively. In a case of diabetes the
consumption of oxygen was 50 per cent, greater than in a
healthy man, corresponding to the higher heat-equivalent
of the food of the diabetic patient (Weintraud and Laves).
Taking 400 litres per twenty-four hours, or 1 7 litres per hour, as
the mean production of carbon dioxide by an average male adult at
rest or doing only light work, we can calculate the quantity of fresh
air which must be supplied to a room in order to keep it properly
ventilated.
It has been found that when the carbon dio.xide given off in
respiration amounts to no more than 2 parts in 10,000 in the air of
an ordinary room, the air remains sweet. When the carbon dioxide
given off reaches 4 parts in 10,000, the room feels distinctly, and at
6 in 10,000 disagreeably, close, while at 9 parts in 10,000 it is
oppressive and almost intolerable. This has been supposed by some
to be due to a volatile poison exhaled from the lungs, for pure carbon
dioxide added alone in similar proportions to the air of a room has
not the same bad effect. Certain observers, indeed, alleged that the
condensed vapour of the breath, when injected into rabbits, produced
fatal symptoms. But this has been shown to be erroneous ; and the
most careful experiments have failed to detect in the air expired by
healthy persons any trace of such a poison. It has therefore been
suggested that the odour and other ill effects of a close room are due
to substances given off in the sweat and the sebum, and allowed by
persons of uncleanly habits to accumulate on the skin, and also to
A'L^/'/A'.inux 227
the products of slow putrefactive processes constantly going on, under
favourable conditions, on the walls, floors or furniture, but only
becoming perceptible to the sense of smell when ventilation is in-
sufficient. In a small, newly-painted chamber, presumably free
from such impurities, it was not until the carbon dioxide reached
3 to 4 per cent, that discomfort began to be felt and the respiration
to be quickened.* No close odour could be detected (Haldane and
Lorrain Smith).
Xeveriheless, e.xperience has shown that it is a good working rule
for ventilation to take the limit of permissible respiratory impurity
at 2 parts of carbon dioxide per 10,000; and the 17 litres of carbon
dioxide given off in the hour will require 85,000 litres (or 3,000 cubic
feet) of air to dilute it to this extent. This is the average quantity
required for the male adult per hour. For men engaged in active
labour, as in factories or mines, twice this amount may not be too
much. For women and children less is required than for men. If a
room smells close, it needs ventilation, whatever be the proportion of
carbon dioxide in the air.
It must be remembered that in permanently-occupied rooms mere
increase in the size will not compensate for incomplete renewal of the
air, although it may be easier to ventilate a large room than a small
one without causing draughts and other inconveniences. But as few
apartments are occupied during the whole twenty-four hours, a large
room which can be thoroughly ventilated in the absence of its
inmates has a distinct advantage over a small one in its great initial
stock of fresh air.
The cubic space per head in an ordinary dwelling-house should be
not less than 28 cubic metres or 1,000 cubic feet.
The quantity of carbon dioxide given off (and of oxygen
consumed) is not only affected by muscular work, but also by
everything which influences the general metabolism. In
males it is greater than in females (in the latter there is a
temporary increase during pregnancy), and greater in pro-
portion to the body-weight in the young than the old. This
depends, partly at least, on the fact that the metabolism is
relatively more active in a small than in a large organism.
The taking of food increases it, chiefly in consequence
of the increased mechanical and chemical work per-
formed by the alimentary canal and the digestive glands.
Sleep diminishes the production of carbon dio.xide partly
♦ Hyperpnoea from defect of oxygen also appears when the amount of
it in the air has fallen to a point which varies in dilferent individuals (m
one case 12 per cent.). Warm-blooded animals confined in a small air-
space die from want of oxygen, and not from the accumulation of carbon
dioxide ; but the opposite appears to be the case with cold-blooded
animals.
15-2
228
A MANUAL or rilYSIOLOGY
because the muscles are at rest, but also to some extent
because the external stimuli that in waking life excite the
nerves of special sense are absent or ineffective. Even a
bright light is said to cause an increase in the amount of
carbon dioxide produced and of oxygen consumed ; but
recent experiments have cast doubt on the statement
(C. Evvald). The external temperature also has an influence.
In poikilothennal animals (such as the frog), the temperature
of which varies with that of the surrounding medium, the
production of carbon dioxide, on the whole, diminishes as
the external temperature falls, and increases as it rises. In
homoiothcrmal animals, that is, animals with constant blood
temperature, external cold increases the production of
carbon dioxide and the consumption of oxygen. But if the
connection of the nervous system with the striated muscles
has been cut out by curara, the warm-blooded animal behaves
like the cold-blooded (Pfluger and his pupils in guinea-pig
and rabbit). These interesting facts will be returned to
under Animal Heat.
Cold-blooded animals produce far less carbon dioxide,
and consume far less oxygen, per kilo of body-weight than
warm-blooded.
The following table shows the relation between the body-
weisrht and the excretion of carbon dioxide in man :
Age.
Weight in kilos.
COl- excreted per
kilo per hour.
[35
Male- -\
ID
I 9-6
65
82
577
22
■51 gramme
■49
•59
■92
■45
•83 „
Female/ ;9
557
23
The next table illustrates the difference in the intensity of
metabolism in different kinds of animals, a difference, how-
ever, largely dependent upon relative size :
RESr/K'.\7I().\ 22')
. . , Oxygen absorbed per Carbon dioxide given Respiratory .juoueni
Animal. ^^j,^ ^^^^ ^f^ ^,,^ f,^^^ CO, ^^ (>., (m CO,).
. , O, O,
1
1
in grms.
in c.c.
in grms.
in c.c.
Cireenfinch
i3'ooo
9091
13-590
6909
•76
Hen - -
roc8
740
1-327
675
•91
Dog - -
'•303
911
'•325
674
■74
Rabbit- -
0-987
690
1-244
632
•91
Sheep - -
0490
343
0-671
341
•99
Hoar - -
0391
273
0-443
225
-82
Frog - -
0T05
73"4
o"i 13
57-7
•78
Crayfish -
0054
38
0-064
327
•86
Forced respiration, although it will temporarily increase
the quantity of carbon dioxide given off by the lungs, does
not sensibly affect the production ; it is only the store of
already formed carbon dioxide in the body which is drawn
upon. The amount of oxygen taken up is little altered by
changes in the movements of respiration except for a very
short time.
How it is that the depth of the respiration may affect the
rate at which carbon dioxide is eliminated, we can only
understand when we have examined the process by which
the gaseous interchange between the blood and the air of
the alveoli is accomplished; and before doing this it is
necessary to consider the condition of the oxygen and carbon
dioxide in the blood.
The Gases of the Blood.
Physical Introduction.— Matter may be assumed to be made up
of molecules beyond which it cannot be divided without altering its
essential character. A molecule may consist of two or more particles
of matter (atoms) bound to each other by chemical links. The kinetic
theory of matter supposes the molecules of a substance to be in
constant motion, frequently colliding with each other, and thus having
the direction of their motion changed.
In a gas the mean free path, that is, the average distance which a
molecule travels without striking another, is comparatively long, and
far more time is passed by any molecule without an encounter than
is taken up with collisions. Although the average velocity of the
molecules is very great, these collisions will produce all sorts of
differences in the actual velocity of different molecules at any given
time. Some will be moving at a greater, some at a slower rate,
than the average ; while some may be for a moment at rest. If the
230 A MAX UAL OF PHYSIOLOGY
gas is in a closed vessel, the molecules will be constantly striking its
sides and rebounding from them. If a very small opening is made
in the vessel, some molecules will occasionally hit on the opening
and escape altogether. If the opening is made larger, or the e.xperi-
ment continued for a longer time with the small opening, all the
molecules will in course of time have passed out of the vessel into
the air, while molecules of the oxygen, nitrogen, and argon of the air
will have passed in. In a gas, then, not enclosed by impenetrable
boundaries, there is no restriction on the path which a molecule may
take, no tendency for it to keep within any limits.
When two chemically indifferent gases are placed in contact with
each other, diffusion will go on till they are uniformly mixed. The
ditiusion of gases may be illustrated thus : Suppose we have a
perfectly level and in every way uniform field divided into two
equal parts by a visible but intangible line, the well-known whitewash
line, for instance. On one side of the line place 500 blind men in
green, and on the other 500 blind men in red. At a given signal let
them begin to move about in the field. Some of the men in green
will pass over the line to the ' red ' side ; some of the men in red
will wander to the ' green ' side. Some of the men may pass over
the line and again come back to the side they started from. But,
upon the whole, after a given interval has elapsed, as many green
coats will be seen on the red side as red coats on the green. And if
the interval is long enough there will be at length about 250 men in
red and 250 in green on each side of the boundary-line. When this
state of equilibrium has once been reached, it will henceforth be
maintained, for, upon the whole, as many red uniforms will pass
across the line in one direction, as will recross it in the other.
In a liquid it is very different ; the molecule has no free path. In
the depth of the liquid no molecule ever gets out of the reach of
other molecules, although after an encounter there is no tendency to
return on the old path rather than to choose any other ; so that any
molecule may wander through the whole liquid. Although the
average velocity of the molecules is much less in the liquid state
than it would be for the same substance in the state of gas or vapour
(gas in presence of its liquid), some of them may have velocities
much above the average. If any of these happen to be moving near
the surface and towards it, they may overcome the attraction of the
neighbouring molecules and escape as vapour. But if in their
further wanderings they strike the liquid again, they may again
become bound down as liquid molecules. And so a constant inter-
change may take place between a liquid and its vapour, or between
a liquid and any other gas, until the state of e<iuilibrium is reached,
in which on the average as many molecules leave the liquid to
become vapour as are restored by the vapour to the liquid, or as
many molecules of the dissolved gas escape from solution as enter
into it.
For the sake of a simple illustration, let us take the case of a
shallow vessel of water originally gas-free, standing exposed to the
air. It will be found after a time that the water contains the atmo-
HESriKATION 231
spheric gases in certain i)ro])ortions — in round numbers, aljout ,,',,, of
its volume of oxygen and .'(5 of its volume of nitrogen (measured at
760 mm. mercury and 0° C.).
Now, let a similar vessel of gas-free water he i)laced in a large air-
tight box filled with air at atmos|iheric pressure, and let the oxygen
be all absorbed before the water is exposed to the atmosi)here of the
box. The latter now consists practically only of the nitrogen of the
air, and its pressure will be only about four-fifths that of the external
atmosphere. Nevertheless, the quantity of nitrogen absorbed by the
water will be exactly the same as was absorbed from the air. If
the box was completely exhausted, and then a quantity of oxygen,
equal to that in it at first, introduced before the water was exposed
to it, the pressure would be found to be only about one-fifth that of
the external atmosphere ; but the quantity of oxygen taken \i\) by
the water would be exactly equal to that taken up in the first
experiment.
Two well-known physical laws are illustrated by our supposed
experiments: (i) In a mixture of gases ivJiich do not act chemically
on each other the pressure exerted by each gas (called the partial pres-
sure of the gas) is the same as it would exert if the others were absent.
(2) The quantity {mass) of a gas absorbed by a liquid which does not
act chemically upon it is proportional to the partial pressure of the gas.
It also depends upon the nature of the gas and of the liquid, and on
the temperature, increase of temperature in general diminishing the
quantity of gas absorbed. It is to be noted that when the volume
of the absorbed gas is measured at a pressure equal to the partial
pressure under which it was absorbed, the same volume of gas is
taken up at every pressure.
Suppose, now, that a vessel of water, saturated with oxygen and
nitrogen for the partial pressures under which these gases exist in the
air, is placed in a box filled with pure nitrogen at full atmospheric
pressure. As we have seen, there is a constant interchange going on
between a liquid which contains gas in solution and the atmosphere
to which it is exposed. Oxygen and nitrogen molecules will there-
fore continue to leave the water ; but if the box is large, few oxygen
molecules will find their way back to the water, and ultimately little
oxygen will remain in it. In other words, the quantity of oxygen
absorbed by the water will become again proportional to the partial
pressure of oxygen, which is now not much above zero. On the
other hand, molecules of nitrogen will at first enter the water in
larger number than they escape from it, for the pressure of the
nitrogen is now that of the external atmosphere, of which its partial
pressure was formerly only four-fifths. In unit volume of the gas
above the water there will be 5 molecules of nitrogen for every 4
molecules in the same volume of atmospheric air. Therefore, on the
average 5 nitrogen molecules will in a given time get entangled by
liquid molecules for every 4 which came within their sphere of attrac-
tion before. On the whole, then, the water will lose oxygen and gain
nitrogen, while the atmosphere of the air-tight box will gain oxygen
and lose nitrogen.
A MANUAL OF PHYSIOLOGY
If, now, the partial pressures of oxygen and nitrogen under which
the water had been originally saturated were unknown, it is evident
that by exposing it to an atmosphere of known composition, and
afterwards determining the changes produced in the composition of
that atmosphere by loss to, or gain from, the gases of the water, we
could find out something about the original partial pressures. If,
for example, the quantity of oxygen in the atmosphere of the chamber
was increased, we could conclude that the partial pressure of oxygen
under which the water had been saturated was greater than that in
the chamber at the beginning of the experiment. And if we found
that with a certain partial pressure of oxygen in the atmosphere of
the chamber there was neither gain nor loss of this gas, we might be
sure that the partial pressure (the temperature being supposed not
to vary) was the same when the water was saturated. We shall see
P, frictionless piston ; L, liquid ia
cylinder ; G. gas beginning to es-
cape from liquid. P is exactly
counterpoised. In addition to the
manner described in the text, the ex-
periment niity be supposed to be per-
formed thus. Let tiieweisjht, W, be
determined which, when the receiver
is complettly exhausted, suffices just
to keep the piston in contact with the
liquid. The pressure of the gas is
then just counterbalanced by W ;
and if S is the are.i of the cross-
section of the piston the pressure of
W
the gas i^er unit of area is .. Or if
the piston is hollow , and mercury is
poured into it so as just to keep it in
contact with the liquid, the height of
the column of mercury required is
also equal to the pressure or tension
of the gas.
FlC. 82. — I.MAcaNAkV EXIF.RIMKNT TO ILLUSTRATE 'TkN.3ION' OK A GAS IN
A Liquid.
later on how this principle has been applied to determine the partial
pressure of oxygen or carbon dioxide which just suffices to prevent
blood, or any other of the liquids of the body, from losing or gaining
these gases. This pressure is evidently equal to that exerted by the
gases of the liquid at its surface, which is sometimes called their
' tension ' ; for if it were greater, gas would, upon the whole, pass
into the blood ; and if it were less, gas would escape from the blood.
Thus, the tension of a gas in solution in a li(]uid is equal to the partial
pressure of that gas in an atmosphere to 7i>hieh the liquid is exposed,
7vhich is just sufficient to prevent g^in or loss of the gas by the liquid
(p. 240).
The following imaginary experiment may further illustrate the
meaning of the "term 'tension' of a gas in a liquid in this connection:
Suppose a cylinder filled with a liquid containing a gas in solution,
and closed above by a piston moving air-tight and without friction,
in contact with the surface of the licfuid (Fig. 82). Let the weight
RESPIRA TION
233
of the piston be balanced l)y a counterpoise. The pressure at the
surface of the hquid is evidently that of the atmosphere. Now let
the whole be i)ut into the receiver of an air pump, and the air gradu-
ally exhausted Let exhaustion proceed until gas begms to escape
from the liciuid and lies in a thin layer between its surface and the
piston the (luantity of gas whicii has become free bemg very small
in proportion to that still in solution. At this pomt the piston is
A, the blood bulb ; B, th<- froth
chamber ; C, the drying tube ; U, fixed
mercury tube ; I',, movable mercurv bulb
connected by a flexible tube with D ; F.
eudiometer ; G, a narrow delivery lube ;
I, 2, 3, 4, taps, 4 being a three-way tap.
A is filled with blood by connecting the
tap I by means of a tube with a blood-
vessel. Taps I and 2 are then closed.
The rest of the apparatus from B to D
is now exhausted by raising E. with tap
4 turned so as to place E only in com-
munication with G, till the mercury fills
D. Tap 4 is now turned so as to con-
nect C with D, and cut off G from D,
and E is lowered. The mercury passes
out of D, and air passes into it from B
and C. Tap 4 is again turned so as to
cut off C from D and connect G and D.
E is raised, and the mercury passes into
D and forces the air out through G, the
end of which has not hitherto been
placed under F. This alternate raismg
and lowering of E is continued till a
manometer connected between C and 4
indicates that the pressure has been
sufficiently reduced. The tap 2 is now
opened : the gases of the blood bubble
up into the froth chamber, pass through
the drving-tube C, which is filled with
pumice-stone and sulphuric acid, and
enter D. The end of G is placed uiider
the eudiometer F, and by raising E,
with tap 4 turned so as to cut off C,
the gases are forced out through G and
collected in F. The movements re-
quired for exhaustion can be repeated
several times till no more gas comes oft.
The escape of gas from the blood is
facilitated by immersing the bulb A in
water at 4o'-50^ C.
Fic. S3. — Scheme of Gas-pump. .
acted upon by two forces which balance each other, the pressure of the
air in the receiver acting downwards, and the pressure of the gas escap-
ing from the liquid acting upwards. If the pressure in the receiver
is now slightly increased, the gas is again absorbed. The pressure at
which this just happens, and against which the piston is sti 1 sup-
ported by the impacts of gaseous molecules flying out of the liquid
while no pressure is as yet exerted directly between the liquid and
the piston, is obviously eciual to the pressure or tension of the gas in
the liquid. , , , • 1 .•
From the above principles it follows that a gas held in solution
234 -1 MA.M'AL OF J>//)S/()LO(:y
may be extracted by exposure to an atmosphere in which the partial
pressure of the gas is made as small as possible. Thus, oxygen can
be obtained from liijuids in which it is simply dissolved by putting
them in an atmosphere of hydrogen or nitrogen, in which the partial
pressure of oxygen is zero, or in the vacuum of an air-jjunjp, in
which it is extremely small. Heat also aids the expulsion of dis-
solved gases. Some gases held in weak chemical union, like the
loosely-combined oxygen of oxyha.'mogloi)in, can be obtained by dis-
sociation of their compounds when the partial pressure is reduced.
More stable combinations may reijuirc to be broken up by chemical
agents — carbonates, for instance, by acids.
Extraction of the Blood-gases. — This is best accomplished by
exposing blood to a nearly perfect vacuum. The gas-pumps which
have been most largely used in blood analysis are constructed on the
principle of the Torricellian vacuum. A diagram of a simple form of
Pfliiger's gas-pump is given in F'ig. 83. The gases obtained are
ultimately dried and collected in a eudiometer, which is a graduated
glass tube with its mouth dipping into mercury. The carbon dioxide
is estimated by introducing a little caustic potash to absorb it. The
diminution in the volume of the gas contained in the eudiometer
gives the volume of the carbon dioxide. The oxygen may be
estimated by putting into the eudiometer more than enough hydrogen
to unite with all the oxygen so as to form water, and then, after
reading off the volume, exploding the mixture by means of an
electric spark passed through two platinum wires fused into the glass.
One-third of the diminution of volume represents the quantity of
oxygen present. It can also be estimated by absorption with a
solution of pyrogallic acid and potassium hydrate. The remainder
of the original mixture of blood-gases, after deduction of the carbon
dioxide and oxygen, is put down as nitrogen (with, no doubt, a small
proportion of argon). For the sake of easy comparison, the observed
volume of gas is always stated in terms of its ecjuivalent at a standard
pressure and temperature (760 mm., or sometimes on the Continent
I metre of mercury, and o" C).
It is also possible in various ways to estimate the amount of
oxygen in blood without the use of the pump. Thus, since a definite
volume of oxygen (i'338 c.c. at 0° C and 760 mm. pressure)
combines with a gramme of haemoglobin, we can calculate the total
volume of oxygen present if we know how much of the blood-pigment
is in the form of oxyha^moglobin ; and this can be determined by
means of the spectrophotometer (Hiifner). Or the blood may be
shaken with carbon monoxide (carbonic oxide), which expels the
oxygen from its combination with the haemoglobin. The oxygen can
then be estimated in the gas collected (IJernard).
In dog's blood, which has been up t(j this time chiefly in-
vestigated, there are considerable variations in the quantity
of oxygen and carbon dioxide which can be extracted ; and
this is particularly true of the venous blood, as might
HESriA'ATION 235
naturally be expected, since even to the eye it varies greatly
according to the vein it is obtained from, the rapidity of the
circulation, and the activity of the tissues which it has just
left. On the average,
Volumes of
O... CO^. N...
100 volumes of aiterial blood yield - - - 20 40 1-2
„ mixed venous blood (from riyht
heart) yield 10 12 45-50 '-2
(reduced to o' C. and 760 mm. of mercury^.
Average venous blood contains 7 or 8 per cent, by volume
less oxygen, and 7 or 8 per cent, more carbon dioxide, than
arterial blood. Thus, in the lungs the blood gains about
twice as many volumes of oxygen per cent, as the air loses,
and the air gains about half as many volumes of carbon
dioxide per cent, as the blood loses. And it is easy to see
that this must be so, for the volume of the air inspired in a
given time is about twice as great as that of the blood which
passes through the pulmonary circulation (pp. 197, 207, 224).
Even arterial blood is not quite saturated with oxygen ; it
can generally still take up one-tenth to one-fifteenth of the
quantity contained in it. Nor is venous blood nearly
saturated with carbon dioxide ; when shaken with the gas it
can take up about 150 volumes per cent.
When the gases are not removed from blood immediately
after it is drawn, its colour becomes darker, and it yields
more carbon dioxide and less oxygen than if it is evacuated
at once (Pfluger). From this it is concluded that oxidation
goes on in the blood for some time after it is shed. The
oxidizable substances appear, however, to be confined to the
corpuscles, which suggests that ordinary metabolism simply
continues for some time in the formed elements of the shed
blood, and that the disappearance of oxygen is not due to
the oxidation of substances which have reached the blood
from the tissues.
The Distribution of the Gases in the Blood. — The oxygen is
nearly all contained in the corpuscles. A little oxygen can
be pumped out of serum ("i to '2 per cent, by volume), but
this follows the Henry-Dalton law of pressures : that is, it
236
A MANUAL OF PHYSIOLOGY
comes oft' in proportion to the reduction of the partial
pressure of the oxygen in the pump, and is simply in solution.
When blood is being pumped out. very little oxygen
comes off till the pressure has been reduced to about half an
atmosphere. At about a third of an atmosphere, if the
blood is nearly at body temperature, the oxygen begms to
escape a little more freely ; and when the pressure has fallen
i^e/'oendoye of 0-x.y^e-n
10 U II J3 /V IS It n IS 19 so 2'
WSS
III
Pill
lUHlBI
■■■■
■■■■■■I
■■■■■■'
■■■■■■
!■■■■■ !■!
■■■■■■■■I
■■■■■■■I
0 7A Z5-2 Sl« 30.» 35 H5b SSi 603 68.1 16 836 9/a 9St lOb* in I2H ?ss 2 uss '«» /« /5-X|
PcLrttol T>re5su.re of Oxyyen in wiUfmetres of mercury
Fi(
84.— CuKVK OF Dissociation of OxYH.tMOGi.OBiN at 35° C.
HCfner's results.)
(AKrER
Along the horizontal axis are plotted the partial pressures (numbers below the
curve) of oxygen in air, to which a solution of hrvmoglobin was exjjosed. The corre-
sponding percentages of oxygen are given above the curve. Along the vertical axis is
plotted the percentage saturation of the haemoglobin with oxygen. Thus, on exposure
to an atmosphere in which oxvgen existed to the extent of i per cent., correspondmg
to a partial pressure of 7-6 millimetres of mercury, tiie ha-moglobin took up about
75 per cent, of the amount of oxvgen required to saturate it. When the oxygen was
present in the atmosphere to the amount of about 10 per cent., corresponding to a
partial pressure of 76 millimetres of mercury, the quantity taken up by the haemo-
globin was about 96 per cent, of that required for saturation.
to about one-sixth of an atmosphere (corresponding to a
partial pressure of oxygefi of 25-30 mm. of mercury), it is
disengaged with a burst. This shows that it is not simply
absorbed, but is united by chemical bonds to some con-
stituent of the blood. The same thing is seen when de-
fibrinated blood is saturated at body temperature with
oxygen at different pressures. The quantity taken up
RESPIKA 7/O.V 237
lessens but slowly as the pressure is reduced, till at about
-5 to 30 mm. of mercury an abrupt diminution takes place.
It is found that a solution of pure haemoglobin crystals
behaves towards oxygen just like blood; and there is no
doubt that the body in blood with which the oxygen is
loosely united is haemoglobin.
We may suppose that at the ordinary temperature and pressure*
some oxygen is continually escaping from the bonds by which it is
tied to the hcemoglobin : but, on the whole, an equal number of
free molecules of oxygen, coming within the range of the haemoglobin
molecules, are entangled by them, and thus eciuilibrium is kept up.
If now the atmospheric pressure, and therefore the partial pressure of
oxygen, is reduced, the tendency of the oxygen molecules to break off
from the haemoglobin will be unchanged, and as many molecules on
the whole will escape as before ; but even after a considerable
reduction of pressure the haemoglobin, such is its avidity for oxygen,
will still be able to seize as many atoms as it loses. The more, how-
ever, the partial pressure of the oxygen is diminished — that is to say,
the fewer oxygen molecules there are in a given space above the
haemoglobin — the smaller will be the chance of the loss being made
up by accidental captures. At a certain pressure the escapes will
become conspicuously more numerous than the captures ; and the
gas-pump will give evidence of this, although it could give us no
information as to mere molecular interchange, so long as equilibrium
was maintained.
The higher the temperature of the haemoglobin is, the greater will
be the average velocity of the molecules, and the greater the chance
of escape of molecules of oxygen. The ' dissociation tension ' of oxy-
haemoglobin, or the partial pressure of oxygen at which the oxyhemo-
globin begins to lose more oxygen than it gains, is increased by raising
the temperature. The curve of dissociation of oxyhcemoglobin at a
temperature of 35° C. is shown in Fig. 84.
The Carbon Dioxide of the Blood. — Blood freed from gas
absorbs carbon dioxide partly in proportion to the pressure,
and in part independently of it. Some of the carbon dioxide
must therefore be simply dissolved ; some, and this the
greater portion, is chemically combined. The serum con-
tains a larger percentage of carbon dioxide than the clot, but
this percentage is not great enough to allow us to assume
that the whole of the carbon dioxide is confined to the
serum. Some of it must belong to the corpuscles.
* The partial pressure of oxygen in airatj6omm. atmospheric pressure
21
IS X 760, or I5Q'6 mm.
100 ' ^
238 .1 MAXL'AL Of P/IYSIOLOOY
Since the serum contains alkalies (especially soda), it is
natural to suppose that the combined carbon dioxide must
exist chiefly as carbonate or bicarbonate of sodium. That
there is something more, however, is shown by the fact that
from defibrinated blood the whole of the carbon dioxide can
in time be pumped out without the addition of an acid to
displace it from the bases with which it is combined. It is
hardly necessary to say that this could not be done with a
solution of sodium carbonate. Yet when sodium carbonate
is added to blood, even in considerable amount, all the
carbon dioxide in it can be obtained by the pump. From
serum a great deal, but not the whole, of the carbon
dioxide can be likewise pumped out. The residue is set
free on the addition of an acid, phosphoric acid, for
example.
The most satisfactory explanation seems to be that in the
serum there exist substances which can act as weak acids
in gradually driving out the carbon dioxide, when its escape
is rendered easier by the vacuum, but which, nevertheless,
do not affect litmus paper (since the reaction of serum is
alkaline). The quantity of these, however, is so small that
a portion of the carbon dioxide remains in the serum. The
proteids of the serum, such as serum-globulin, behave in
certain respects like weak acids, and may contribute to the
driving out of the carbon dioxide.
When defibrinated blood is pumped out, the whole of the
carbon dioxide can be removed, apparently because sub-
stances of an acid nature pass from the corpuscles into
the liquid part of the blood and help to break up the
carbonates.
In the red corpuscles a portion of the carbon dioxide may
be in combination with alkalies. We know that the cor-
puscles contain alkalies, for the alkalinity of ' laked ' blood
(pp. 34, 35), in which the red corpuscles have been broken
up, is found to be greater than that of unlaked blood, unless
a long time is allowed in the case of the latter for the
alkalies of the corpuscles to reach the acid used in titration
(Loewy). Some observers believe that a weak compound
of carbon dioxide can be formed with hccmoglobin ; for
Ni:Sl'/h'A 770X 239
a solution of h?emoglobin absorbs more of this gas than
water, and the quantity absorbed is not proportional to the
pressure. The hccmoglobin of the corpuscles may therefore
hold a portion of the carbon dioxide in combination (Bohr).
This cannot, however, be considered as settled.
When blood is saturated with carbon dioxide and then
separated into serum and clot, the serum is found to yield
more gas than the clot ; but if the serum and clot are
separately saturated, the latter takes up more carbon dioxide
than the former. From this it is argued that a substance
combined with carbon dioxide must in blood saturated with
the gas pass out of the corpuscles into the serum. This
cannot be haemoglobin, for it remains in the corpuscles, but
it may very well be an alkali, combined with the carbon
dioxide, and thus set free from its connection with the
haemoglobin. And, as a matter of fact, under the circum-
stances described, it has been found that alkalies, and,
perhaps, certain food-substances (proteid, fat, and sugar)
do pass from the clot into the serum (Zuntz, Hamburger),
and chlorine from the serum into the corpuscles (Lehmann),
which at the same time gain water and become larger. On
the other hand, when blood is saturated with oxygen,
alkalies and possibly the food-substances mentioned pass
out of the serum into the corpuscles, which at the same
time lose water and shrink in volume. Hamburger has
extended these observations to living blood, and has shown
that the plasma of venous blood has more alkali, proteid,
sugar and fat than the plasma of arterial blood, and that
the corpuscles have a greater volume, though not a greater
diameter. In the pulmonary capillaries, according to him,
food-substances go over, under the influence of oxygen,
from the plasma to the corpuscles. In the systemic
capillaries the blood becomes loaded with carbon dioxide,
and therefore the corpuscles give up proteids, etc., to the
plasma, which accordingly has a greater supply of food-
substances to offer to the tissues than the plasma of arterial
blood itself. In both cases he sees in this interchange an
arrangement by which oxidation is favoured. Whatever
may be thought of this view— and it is a serious objection
240 A MA.M'AL OF PHYSIOLOGY
to it that the amount of oxidation which can be supposed to
take place in the red corpuscles is small — the current theory,
that the corpuscles are simply passive carriers of oxygen,
and exercise no further influence on the plasma, breaks
down in face of the facts. We must admit that an active
and many-sided commerce exists between them and the
liquid in which they float.
The nitrogen of the blood is simply absorbed.
The Tension of the Blood gases. — If the gases of the blood existed
in simple solution, their tension or partial pressure could be deduced
from the amount dissolved and the co-efficient of absorption. Since
they are chemically combined, it is necessary to determine it directly.
This has been done by means of an apparatus called the aerotono-
meter (Pfliiger, Strassburg). The blood is made to pass directly from
the vessel to two tubes, which it traverses at the same time, the
stream being divided between them ; it then passes out again. The
tubes are warmed by means of a water-jacket to the body-temperature.
One of them is filled with a gaseous mixture having a greater, and
the other with a mixture having a smaller, j^artial pressure, say of
carbon dioxide, than is expected to be found in the blood. As the
latter runs in a thin sheet over the walls of the tubes, it loses carbon
dioxide to the one and takes up carbon dioxide from the other.
From the alteration in the proportion of the carbon dioxide in the
two tubes, it is easy to calculate the partial pressure of that gas in
the blood ; that is, the partial pressure which it would be necessary
to have in the tubes in order that the blood might pass through them
without losing or gaining carbon dioxide (p. 232).
The pressure of oxygen in arterial blood was given by
Strassburg as about 30 mm. of mercury in the dog, and in
venous blood as something like 20 mm. If we were to
accept the recent experiments of Bohr, made by means of a
special form of aerotonometer constructed and worked much
in the same way as Ludwig's stromuhr (p. no), and inserted
into the course of a bloodvessel, it would be necessary to
treble or quadruple these numbers.
The pressure of carbon dioxide in arterial blood we may
take at 10 to 40 mm., in venous blood at 30 to 50 mm.,
according to the results of different observers.
Whenever the venous blood has to pass through a region
in which the pressure of carbon dioxide is kept lower than
in itself, it will begin to lose carbon dioxide by diffusion.
If the pressure of oxygen in this region is at the same time
RI^SP/K.\7/l)N 241
higher than in the venous blood, some of it will be taken up.
And to bring about these results no peculiar ' vital ' force
need be invoked ; ordinary physical processes will, under the
assumed conditions, be alone required.
Now, we know that in the lungs carbon dioxide is given
off from the blood, and oxygen taken up by it. We have,
therefore, to inquire what the partial pressures of these
gases are in the alveoli, and whether they are so related to
the corresponding partial pressures in the blood that a
simple process of dissociation and diffusion will be sufficient
to explain pulmonary respiration.
The percentage of carbon dioxide in expired air cannot
tell us the pressure of that gas in the alveoli, for the air in
the upper part of the respiratory tract is necessarily expelled
along with the alveolar air. But it gives us a minimum value,
below which it is not conceivable that the alveolar partial
pressure can lie, for we cannot imagine that any air in the
respiratory tract can be richer in carbon dioxide than that of
the alveoli. Now, Vierordt found with the deepest possible
expiration a little over 5 per cent, of carbon dioxide in the
expired air. From this it seems justifiable to conclude that
in man the partial pressure of carbon dioxide in the alveoli
may be at least one-twentieth of an atmosphere, or 38 mm.
of mercury.
In animals, samples of the alveolar air have been drawn
off directly (Wolff berg) by means of Piiiiger's pulmonary
catheter. This consists of two tubes, one within the other.
The inner tube, which is a fine elastic catheter, projects
free from the other for a little distance at its lower end.
The outer tube terminates in an indiarubber ball, which can
be inflated so as to block the bronchus into which it is
passed, and cut off the corresponding portion of the lung
from communication with the outer air. A sample of the
air below the block can be drawn off through the inner tube.
In this way the proportion of carbon dioxide in the alveoli of
the dog was found to be only about 3-8 per cent., corre-
sponding to a partial pressure of about 29 m.m. of mercury.
But this would be undoubtedly too high, owing to the im-
possibility of interchange with the external atmosphere, and
16
242 A MANUAL OF PHYSIOLOGY
would represent the partial pressure of the carbon dioxide
in the blood rather than in the alveolar air under normal
conditions. For gaseous equilibrium is soon established
between blood and air separated only by a thin membrane
like the alveolar wall.
In Bohr's experiments, in some of which the animals
were made to breathe air containing carbon dioxide in
various proportions, the tension of that gas in the air of
the lungs varied from 5'8 to 34*6 mm. of mercury, while in
arterial blood, taken at the same time, it usually ranged
from 10 to 38 mm., and was often less than in the alveolar air.
If we accept these results, we seem shut up to the con-
clusion that carbon dioxide does not pass through the walls
of the alveoli solely by diffusion. And although Bohr's
experiments have been severely criticised, it does not seem
improbable in itself that the physical process of diffusion is
aided by some other process, which may provisionally be
termed secretion. It is possible, too, that when the con-
ditions are especially unfavourable to diffusion — when, for
instance, the partial pressure of carbon dioxide is artificially
increased in the alveoli — the cells which line them are
stimulated to increased activity.
As to the oxygen, we are in the same position. Its partial
pressure does not appear to be always higher, even under
normal conditions, in the alveoli than in the arterial blood
as it leaves the lungs. Indeed, Bohr found that, in the
majorit}' of his observations on dogs, the oxygen tension
was distinctly greater in the blood than in the pulmonary
air. And Haldane and Smith, using a new method, have
obtained a value for the oxygen tension in human blood
(26*2 per cent., equal to 200 mm. of mercury) that even
exceeds the partial pressure of oxygen in the external air,
and is about twice as great as that of the air of the alveoli.
This extraordinary result cannot be reconciled with any
purely physical explanation of the absorption of oxygen, and
would settle the question, if the accuracy of the method
could be relied on.
Additional evidence in favour of the view that there is,
besides diffusion, an element of selective secretion in the
A'L'S/'/A'A riON 243
interchanj^c of j^^ases through the puhnonary membrane is
afforded by a study of the gases of the swim-bladder in
fishes. These consist of oxygen, nitrogen, and usually a
small quantity of carbon dioxide, but in very different pro-
portions from those in which they exist in the air or the
water. Thus, Biot found as much as 87 per cent, of oxygen
in the bladder of fishes taken at a considerable depth, but a
smaller amount in those captured near the surface. Moreau
observed that when the gas is withdrawn by puncturing
the bladder with a trocar, the organ rapidly refills, and the
percentage of oxygen increases. Further, this process of
gaseous secretion is under the influence of nerves, for gas
ceases to accumulate in the organ when the branches of the
vagi that supply it are cut (Bohr).
We have now completed the description of the pheno-
mena of external respiration, with the discussion of its
central fact, the exchange of gases between the blood and
the air at the surface of the lungs. It remains to trace the
fate of the absorbed oxygen, and to determine how and
where the carbon dioxide arises.
Internal Respiration — Seats of Oxidation. — The suggestion
which lies nearest at hand, and which, as a matter of fact,
was first put forward, is that the oxygen does not leave the
blood at all, but that it meets with oxidizable substances in
it, and unites with their carbon to form carbon dioxide.
While there is a certain amount of truth in this view,
oxygen, as already mentioned, being to some extent taken
up by freshly-shed blood, and also by blood under other
conditions, to oxidize bodies, other than haemoglobin, either
naturally contained in it or artificially added, there is no
doubt that the cells of the body are the busiest seats of
oxidation. This is shown by the presence of carbon dioxide
in large amount in lymph and other liquids which are, or
have been, in intimate relation with tissue elements ; by its
presence, also in considerable amount, in the tissues them-
selves— in muscle, for instance ; by its continued and
scarcely lessened production not only in a frog whose blood
has been replaced by normal saline solution, and which
continues to live in an atmosphere of pure oxygen, but in
16 — 2
244 ^'1 MANUAL OF J'/IYSIOLOGY
excised muscles; and by the remarkable connection between
the amount of this production and the functional state of
those tissues. In insects the finest twigs of the tracheae,
through which oxygen passes to the tissues, actually end in
the cells ; and in luminous insects, like the glowworm, it has
been noticed that the phosphorescence, which is certainly
dependent on oxidation, begins and is most brilliant in those
parts of the cells of the light-producing organ that surround
the ends of the tracheae.
Lymph, bile, urine, and the serous fluids contain very
little oxygen, but so much carbon dioxide that the pressure
of that gas in all of them is greater than in arterial blood,
while in lymph alone (taken from the large thoracic duct)
has it been found less than that of venous blood. And it is
extremely probable that lymph gathered nearer the primary
seats of its production (the spaces of areolar tissue) would
show a higher proportion of carbon dioxide.
Strassburg found that with a pressure of carbon dioxide in
the arterial blood of 21 mm. of mercury, the pressure in bile
was 50 mm., in peritoneal fluid 58 mm., in urine 68 mm., in
the surface of the empty intestine 58 mm. Saliva, pan-
creatic juice, and milk, also contain much carbon dioxide,
and only a little, if any, oxygen.
From muscle (to facilitate pumping, the muscle is minced,
and often warmed) no free oxygen at all can be pumped out,
but as much as 15 volumes per 100 of carbon dioxide, some
of which is free, that is, is given up to the vacuum alone,
while some of it is fixed, and only comes off after the addi-
tion of an acid, such as phosphoric acid. If the muscle be
left long in the pump, putrefaction begins to appear, and
this causes a discharge of carbon dioxide, which may last
indefinitely.
Muscle may be safely taken as a type of the other tissues
in regard to the problems of internal respiration. It is
instructive, therefore, to observe that the great scarcity of
oxygen in the parenchymatous liquids which bathe the tissues,
here in the tissues themselves deepens into actual famine.
The inference is plain. The active tissues are greedy of
oxygen ; as soon as it enters the muscle it is seized and
A'ESPIRATION 24;
' fixed ' in some way or other. The traces of oxygen in the
lymph cannot therefore be journeying away from the tissue
elements ; they must have come from another source, and
this can only be the blood. Could we gather lymph for
analysis directly from the thin sheets that lie between the
blood capillaries and the tissues, we might find more oxygen
present as well as more carbon dioxide. But if we did find
more oxygen, it would still be oxygen in transit from the
capillaries towards places where the partial pressure of
oxygen is less. In the lymph, the pressure is kept low by
the avidity of the tissues with which it is in contact, and
possibly by the existence in it of oxidizable substances which
have come from the tissues. In the tissues there is no
partial pressure at all, because the oxygen that reaches
them is at once stowed away in some compound, in which
it has lost the properties of free oxygen.
Assuming, then, that at least a great part of the oxidation
and consequent production of carbon dioxide goes on in the
tissues, we have yet to follow the steps of the process, as far
as we can, in the light of our knowledge of the respiration of
muscle.
Respiration of Muscle. — Three methods have been used to
determine the respiratory changes going on in resting muscle,
or to compare them with those in the excited state :
(i) The excised muscles of cold-blooded animals are exposed for
a considerable time to an atmosphere of known composition in a
small chamber ; and the changes in this atmosphere are then deter-
mined (G. Liebig, Matteucci, Hermann).
(2) Samples of the blood coming to and leaving a muscle of a
warm blooded animal may be taken in its natural position, and the
gases analyzed and compared (Ludwig, Chauveau and Kaufmann).
(3) Artificial circulation may be kept up through a muscle or
group of muscles ; for example, through one or both hind-limbs of a
dog. In the newest forms of apparatus for artificial circulation the
blood is oxygenated in a special chamber from a graduated cylinder
containing oxygen, and the carbon dioxide collected in baryta or
caustic potash valves. The oxygen consumption can be read off
from the cylinder, and the production of carbon dioxide estimated
by titrating from time to time samples of the baryta water or potash
(v. Frey and Gruber, and Jacobi). (Fig. 85.)
By the first of these methods a very remarkable fact,
among others, has been brought to light. It has been
246
A MANUAL OF PHYSIOLOGY
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RESPIRA TION 247
found that a frog's muscle is capable of going on producing
carbon dioxide, and that at an undiminished rate, in the
entire absence of oxygen, when the chamber, for instance,
is filled with nitrogen or other indifferent gas. Not only so,
but it can be made to contract many times and to perform
a comparatively large amount of work in this oxygen-free
atmosphere, and to produce a correspondingly large quantity
of carbon dioxide. In mammals the muscles can also be
made to contract repeatedly when the dissociable oxygen
has, as far as possible, been got rid of from the blood by
asphyxiating the animal, although they lose their con-
tractility much more rapidly than the muscles of the frog.
This leads us to the very important conclusion that the
carbon dioxide does not arise, so to speak, on the spot, from
the immediate union of carbon and oxygen. Oxygen is
essential to muscular life and action. But a stock of it is
apparently taken up by the muscle, and stored in some
compound or compounds which are broken down during
muscular contraction, and more slowly during rest, carbon
dioxide in both cases being one of the end products. It is
very possible that there may be an ascending series of
bodies through which oxygen passes up, and a descending
series through which it passes down, before the final stage is
reached.
When muscle goes into rigor (p. 565) — and this is most
strikingly seen when the rigor is caused by raising the
temperature of frog's muscle to about 40° or 41° C. — there
is a sudden increase in the quantity of carbon dioxide given
off. Moreover, in an isolated muscle the total quantity of
carbon dioxide obtainable during rigor is less if the muscle
has been previously tetanized, and less, it is said, by just
the amount given out during the contractions (Hermann).
From this it has been argued that the hypothetical substance
(inogen), the decomposition of which yields carbon dioxide
in contraction, is also the substance which decomposes so
rapidly in rigor ; that a given amount of it exists in the
muscle at the time it is removed from the influence of the
blood ; and that this can all explode either in contraction
or in rigor, or partly in the one and partly in the other.
248 A MA. y UAL OF PHYSIOLOGY
Many of the older experiments made by method (2) are
too inexact to yield more than qualitative results, and the
same is true of some of the researches with the more primi-
tive and imperfect methods of artificial circulation. The
mere difference of colour between the venous and arterial
blood of a muscle, or other active organ, is sufficient to
show that oxygen is taken up and carbon dioxide given out
by it to the blood. This is the case in muscles at rest,
and even in muscles with artificial circulation after they have
become inexcitable.
In active muscles more oxygen is used up and more
carbon dioxide produced than in the resting state. Chauveau
and Kaufmann, in their experiments on one of the muscles
used by the horse in feeding, found that the consumption of
oxygen and the production of carbon dioxide might be three
times as great in activity as in rest.
In the submaxillary salivary gland there was also an
increase of carbon dioxide during activit}', but not propor-
tionally so great as in muscle. In the active brain it is not
easy to demonstrate any increase at all (Hill).
For excised mammalian muscles (hind-limbs of dog), as
has been said, the respiratory quotient increases when the
temperature is reduced. As the temperature is raised, the
opposite effect is observed. Stimulation of the muscle causes
a rise in both ox3gen consumption and carbon dioxide pro-
duction, but proportionally more in the former, and the
respiratory quotient diminishes. When the excised muscle
begins to deteriorate in the course of some hours, the con-
sumption of oxygen falls off more quickly than the produc-
tion of carbon dioxide.
All this goes to show that the two processes are to a great
extent independent of each other. At the higher tempera-
tures, during muscular contraction, and when the vitality of
the muscle is still but little injpaired, the conditions are
relatively favourable to the chemical changes in which
oxygen is combined. Low temperature, rest, and diminished
vitality, are relatively favourable to the splitting up of sub-
stances that yield carbon dioxide. But it must be remem-
RESPIRA T/O.y
249
bered that in the intact organism the conditions are different
(p. 225).
The Influence of Respiration on the Blood-pressure. — We have
already stated, in treating of arterial blood-pressure (p. 103),
that a normal tracing shows a series of waves corresponding
with the respiratory movements.
When the respiratory movements are recorded simul-
taneously with, and immediately below the pressure curve, it
is seen that although the mean blood-pressure is falling for a
short time at the beginning of inspiration, it soon reaches
its minimum, then begins to rise, and continues rising during
the rest of this period. At the commencement of expiration
it is still mounting, but soon reaches its maximum, begins
to fall, and continues falling
through the remainder of
the expiratory phase.
The explanations given
of this phenomenon are
many, but they may all
be grouped into two divi-
sions, in which nervous and i'"- ^^•
mechanical influences are '^'"^^ "PP^"^ tracing shows the respiratory
mecnanicai mnuenceb are n,ovements in a rabbit ; the lower tracing is
respectively invoked as the the blood-pressure curve; I, inspiration; E,
. expiration, including the pause.
chief cause.
Theory of Nervous Influences. — Everybody admits that in
certain animals (the dog, for instance), and very often, if not
constantly, in man, the rate of the heart is greater during
inspiration, especially towards its end, than in expiration.
This is due to nervous influence, to a rhythmical rise and
fall in the activity of the cardio-inhibitory centre, synchronous
with the respiratory movements, for the difference disappears
after division of both vagi. Now, it might be said that the
rise of blood-pressure during the latter part of inspiration is
simply caused by the increased rate of the heart, which, as
we know, can raise the blood-pressure. Nevertheless, this is
not the explanation, for the respiratory oscillations persist
after section of the vagi, and they are seen in animals like
the rabbit, in which little or no variation in the rate of the
heart is connected with the phases of respiration.
/ i
/ 1
1
ztV
yi
250 A A/A A UAL OF VlIYSrOLOGY
(Juite a number of observers have supposed that rhyth-
mical discharges from the vaso - motor centre, either
automatic or due to stimulation of the centre by the venous
blood, and causing a periodic increase and diminution in the
peripheral resistance, are responsible for the respiratory
oscillations. Such rhythmical variations in the blood-
pressure (Traube-Hering curves) may, under certain condi-
tions, appear in the absence of respiratory movements, e.g.,
when in a curarized animal the artificial respiration is
stopped. But this is hardly an argument in favour of the
central origin of the normal respiratory waves, since the
Traube-Hering curves have a much longer period. This is
well seen when, as sometimes happens, Traube-Hering
oscillations appear while respiration is still going on. Their
long sweeping curves then show the ordinary respiratory
waves superposed on them.
Mechanical Theory. — A more satisfactory explanation is
afforded by a consideration of the mechanical changes pro-
duced in the thorax by the respiratory movements. Of
these two are of special importance: (i) the changes of
intra-thoracic pressure, (2) the changes of vascular resist-
ance in the lungs.
The intra-thoracic pressure, which, as we have seen, is
always less than that of the atmosphere, unless during a
forced expiration when the free escape of air from the lungs
is obstructed, diminishes in inspiration and increases in
expiration. The great veins outside the chest, the jugular
veins in the neck, for example, are under the atmospheric
pressure, which is readily transmitted through their thin
walls, while the heart and thoracic veins are under a smaller
pressure. The venous blood both in inspiration and ex-
piration will, therefore, tend to be drawn into the right
auricle. In inspiration the venous flow will be increased,
since the pressure in the thorax is diminished ; and upon
the whole more venous blood will pass into the right heart
during inspiration than during expiration. But all the blood
which reaches the right heart during an inspiration is at
once sent into the lungs, although not even the first of it
can have passed through to the left side of the heart at the
A'/:S/'/A'.l770N
!5'
end of the inspiration, since the pulmonary circulation-time
(four to five seconds in a small dog, two to three seconds
in a rabbit) is lon^i^er than the time of a complete inspira-
tion at any ordinary rate. The increase in the quantity of
blood pumped into the pulmonary artery will, if not counter-
acted by other circumstances, tend to raise the blood-
pressure in the artery and its branches, and therefore at
once to accelerate the outflow through the pulmonary vein.
This will be greatly aided if at the same time the vascular
resistance in the lungs is reduced, as there seems good reason
for believing is the case.
The increased blood-flow into the left ventricle will of
■course correspond to better filling of the systemic arteries ;
that is, to a rise of arterial blood-pressure.
In expiration the contrary will happen. The return of
blood to the thorax will be checked. This is well shown by
the swelling of the veins at the root of the neck in expiration,
their shrinking in inspiration, the so-called pulsus venosus.
Less blood being drawn into the right heart, less will be
pumped into the pulmonary artery, in which the pressure
will, of course, fall. The outflow into the left auricle will
thus be diminished — all the more as in the expiratory phase
the vascular resistance in the lungs is increased — and the
systemic arterial pressure will be lowered. Now, this is
just what is seen on the blood-pressure curve, except that
in both cases the change is somewhat belated, and does not
coincide exactly with the commencement of the inspiration
or the expiration. But this delay may be explained on
several grounds. First, we cannot expect the curve of
pressure to alter its course quite suddenly, at the very
moment when the respiration changes its phase ; for the
•change in the blood-flow through the lungs must require
time to establish itself, in the face of the opposite tendency
to which it succeeds. The same is true of the systemic
arteries, in which at the end of expiration the movements of
the blood associated with the falling pressure are going on.
It is impossible that these movements can be checked at
once ; inertia must carry them on into inspiration.
The negative pressure of the thorax acts also on the
252 A MANUAL or rilYSIOLOGY
aorta, although, on account of the greater thickness of its
walls, to a much smaller extent than on the thoracic veins.
The diminution of pressure in inspiration tends to expand
the thoracic aorta, and to draw blood back out of the
systemic arteries, while expiration has the opposite effect.
And although the hindrance caused in this way to the
flow of blood into the arteries during inspiration, and the
acceleration of the flow during expiration, cannot be great,
the tendency will be to diminish the pressure in the one
phase and increase it in the other. As soon as the changes
of pressure produced by alterations in the flow of venous
blood into the chest and through the lungs are thoroughly
established, the slight arterial effect will be overborne ; but
before this happens, that is, at the beginning of inspiration
and expiration, it will be in evidence, and will help to delay
the main change.
Another factor in this delay may be found in the changes
of vascular resistance and capacity which take place in the
lungs when they pass from the expanded to the collapsed
condition.
According to the most careful of recent observations, the
expansion of the lungs in natural respiration causes a
widening of the pulmonary capillaries, with a consequent
increase of their capacity and diminution of their resistance
(De Jager). This is supported by experiments on the
rabbit, in which the vessels at the base of the heart were
ligatured either at the height of inspiration or the end of
expiration, so as to obtain the whole of the blood in the
lungs. It was found that the lungs invariably contained
more blood in inspiration than in expiration (Heger and
Spehl).
During inspiration, as we have seen, the right ventricle
is sending an increased supply of blood into the pulmonary
artery ; bat before any increase in the outflow through the
pulmonar}- veins can take place, the vessels of the lung must
be filled to their new capacity. The first effect, then, of the
lessened vascular resistance of the lungs in inspiration is a
temporary falling off in the outflow through the aorta, and
therefore a temporary fall of arterial pressure. As soon as
A'ESI'IA\lT/0\
253
a more copious stream begins to tlow through the lungs,
this is succeeded by a rise.
In Hke manner the first effect of expiration, which
increases the resistance and diminishes the capacity of the
pulmonary vessels, is to force out of the lungs into the left
auricle the blood for which there is no room. This causes
a temporary rise of arterial blood-pressure, succeeded by a
fall as soon as the lessened blood-flow through the lungs is
established.
In artificial respiration oscillations of blood -pressure,
synchronous with the movements of the lungs, are also
seen, even when the thorax is opened. In the latter case
Fig. 87. — EiM-.L 1 on Blood-pressure ok Inklahon of iiie Lungs
(Rabbit).
Artificial respiration stopped in inflation at i. Interval between 2 and 3 (not repro-
duced) 51 seconds, during which the curve was alnaost a straight line. Time-tracing
shows seconds.
there are, of course, no variations of intra-thoracic pressure,
and the oscillations must be connected with the changes in
the pulmonary circulation. The respiratory waves differ in
certain respects from those in natural breathing, as might
be expected from the very different mechanical conditions.
During inspiration (inflation) there is first a small rise and
then a large fall of pressure. In expiration (collapse) there
is first a slight fall and then a great rise.
The meaning of this is clearly seen when artificial respira-
tion is stopped at the height of inflation (Fig. 87). The
arterial blood-pressure then falls rapidly, and continues low
until the stock of oxygen is exhausted and the rise of
254
A MANUAL OF I'lIYSIOLOGY
asphyxia begins. When the respiration is stopped in
collapse, instead of a fall a steady rise of pressure occurs
(as in Fig. 56, p. 163). This ultimately merges in the
elevation due to asphyxia, which shows itself sooner than
in inflation, since the lungs contain less air. The difference
in the course of the blood -pressure curve in the two cases
immediately after stoppage of respiration cannot, however,
depend on this latter circumstance. It is undoubtedly due
to the fact that in artificial inflation the vascular capacity
of the lungs is less and the resistance greater than in
collapse. When the tracheal cannula is closed in natural
respiration, no initial fall of pressure takes place (Fig. 88).
To sum up the causes of the respiratory oscillations in the
Fir.. 88. — lil.OOD-I'RKSSUKE TkACINC (KAliltIT, UM>ER ClII.ORAL).
Natural respiration stopped at I in inspiration, at E in expiration. Tlie mean blood-
pressure is scarcely altered ; but the respiratory waves become much larger owing to
the abortive efforts at breathing. Time-tracing shows seconds.
arterial blood-pressure : The changes of intra-thoracic pressure
and of the vascular resistance in the lungs seem the most important
factors, but nervous influences may also play a subordinate part.
The respiratory oscillations in the veins, as might be
expected, run precisely in the opposite direction to those in
the arteries, and so do the Traube-Hering curves. The
increased flow from the veins to the thorax during inspira-
tion lowers the pressure in the jugular vein, while it
increases the pressure in the carotid. The constriction of
the small bloodvessels to which the Traube-Hering curves
are due increases the blood-pressure in the arteries, because
it increases the peripheral resistance to the blood-flow ; in
the veins it lowers the pressure, because less blood gets
through to them. Accordingly, when the Traube-Hering
AVf.SV'/AM TION
255
curve is ascenclinjj^ in the carotid, it is descending in the
jugular.
The respiratory variations in the volume of the brain,
which are so striking a phenomenon when a trephine hole is
made in the skull, have by some been attributed to inter-
ference with the venous outflow from the cranial cavity
during expiration, and by others to those changes in the
arterial pressure whose causes we have just been discussing.
The question turns largely upon the time-relations of the
movements. The swelling of the brain is usually syn-
chronous with expiration, and the shrinking with inspiration ;
and this is in favour of the first view. But sometimes the
dura mater bulges into the trephine hole in inspiration and
sinks down in expiration. This is in favour of the second.
The truth appears to be that both factors may be involved.
The effects of breathing condensed and rarefied air are — (i)
mechanical, shown chiefly by changes in the circulation, in
the blood-pressure, for instance ; (2) chemical.
The mechanical effects differ according to whether the
whole body, or only the respiratory tract, is exposed to the
altered pressure. When the trachea of an animal is con-
nected with a chamber in which the pressure can be raised
or lowered, it is found that at first the arterial blood-pressure
rises as the pressure of the air of respiration is increased
above that of the atmosphere. But a maximum is soon
reached ; and when respiration begins to be impeded, the
pressure falls in the arteries and increases in the veins.
When the pressure of the air in the chamber is diminished
a little below that of the atmosphere, there is a slight sinking
of the arterial blood-pressure, which rises if the air-pressure
is further diminished (Einbrodt).
It is clear that any change of the air-pressure which tends
to diminish the intra-thoracic pressure will favour the
venous return to the heart, and therefore, if the exit of
blood from the thorax is not proportionally impeded, the
filling of the arteries. An increase in the intra-alveolar
pressure must tend on the whole to increase, and a diminu-
tion in it to lessen, the pressure inside the thorax, which
always remains equal to the intra-alveolar pressure, minus
256
A MANUAL OF PHYSIOLOGY
xJ^-JUUU-
the elastic tension of the lun;,'s. Breathing compressed air
should, therefore, under the conditions described, be upon
the whole unfavourable to the venous return to the heart
and to the fillin/^ of the arteries, and the arterial pressure
should fall ; while breathing rarefied air should have the
opposite effect. But a very great diminution of the intra-
thoracic pressure is not necessarily favourable to the cir-
culation.
Certain chest diseases have been treated by the use of apparatus
by which the patient is made to breathe either conii)ressed or rarefied
air ; or to insi)ire air at one pressure and to expire into air at another
pressure. And it has, upon the whole, been found, in agreement
with theory, that condensed air cannot help the circulation however
it is applied, but always hinders it ; while rarefied air aids the cir-
culation both in inspiration and in expiration. But the increased
work of the inspiratory
muscles may counter-
balance the advantage.
Valsalva's experiment,
which is performed by
closing the mouth and
nostrils after a previous in-
spiration, and then forcibly
trying to expire, is an imi-
tation of breathing into
compressed air. The intrathoracic pressure is raised, it may be, to
considerably more than that of the atmosphere ; the venous return
to the heart is impeded, and may be stopped ; and the pulse curve
is altered in such a way as to indicate first an increase and then a
decrease of the arterial blood pressure (Fig. 89).
Midler s experiment, which
should be bracketed with Val-
salva's, consists in making, after a
previous expiration, a strong in-
s[)iratory effort with mouth and
nostrils closed. Here the intra-
thoracic pressure is greatly dimin-
ished, more blood is drawn into
the chest, and upon the whole
effects opposite to those of Valsalva's ex|>eriment are produced
(Fig. 90). Neither experiment is fjuite free from danger. In both
the dicrotism of the pulse becomes more marked.
When the whole body is subjected to the changed
pressure, as in a balloon or on a mountain, in a diving-bell
or a caisson used in building the piers of a bridge, the
Fit;
89. — I'UI.Sli-TRAONd IN VaI.SAIAA's
EXPKRIMENT (ROI.I.KT)).
Fk;. 90. — Pui.sE-TKAciNc; in Ml I i.i-.k's
EXI-KRIMKNT (RoI.I.ETT).
KESl'/RA T/O.y 257
conditions are very different. For the blood-pressure, the
intra-thoracic pressure, and the intra-alveolar pressure, all
fall tofjether when the pressure of the atmosphere is
diminished, and all rise together when it is increased. It is
possible not only to live, but to do hard manual labour, at
very different atmospheric pressures. Loewy found that
the quantity of oxygen absorbed by a man breathing air in
the pneumatic cabinet remained constant at all pressures
between about two atmospheres and half an atmosphere.
At 440 mm. of mercury dyspnoea became evident ; but if
the person was now made to work, the dyspnoea passed
away, and did not again manifest itself till the pressure was
reduced to 410 mm. There are towns on the high table-
lands of the Andes, and in the Himalayas, where the
barometric pressure is not more than 16 to 20 inches, yet
the inhabitants feel no ill effects. And in the caissons of
the Forth Bridge the workmen were engaged in severe toil
under a maximum pressure of over three atmospheres, while
in the caissons of the St. Louis Bridge in America a maximum
pressure of more than four atmospheres was reached.
Inside the caissons the men sometimes suffer from pain and noise
in the ears, due to excessive pressure on the external surface of the
tympanic membrane. If the pressure in the tympanum is raised
by a swallowing movement, which opens the Eustachian tube and
permits air to enter it, the symptoms generally disappear. The
suddenness of the change of pressure has a great deal to do with its
effects, and it is found that the men are most liable to dangerous
symptoms while passing through the air-lock from the caissons to
the external air. It is probable, from experiments on animals, that
the most serious and permanent of these — for instance, the localized
paralysis and the circulatory disturbances — are due to the formation
of gaseous emboli, by the liberation of nitrogen in the blood when
the pressure is abruptly reduced. And, indeed, it is found that the
symptoms can often be caused to disappear, both in animals and
men, by again subjecting them to compressed air.
But that the action of oxygen under a high pressure is not merely
mechanical seems to follow from the experiments of Bert. He
discovered the singular fact that in pure oxygen at a pressure of three
atmospheres, which corresponds to air at fifteen atmospheres, animals
die in convulsions. The consumption of oxygen and elimination of
carbon dioxide are both much diminished. Even seeds and vegetable
organisms in general are killed in a short time ; and an atmosphere
of pure oxygen, equal to five atmospheres of air, hinders the develop-
ment of eggs.
17
258 A MA NUA L OF I 'II YSIOLOGY
When the air-pressure is diminished below a certain
limit, death takes place from asphyxia, more or less gradual
according to the rate at which the pressure is reduced. The
haemoglobin cannot get or retain enough oxygen to enable
it to perform its respiratory function; its dissociation tension
is no longer balanced by an equal or greater partial pressure
of oxygen in the air. The quantity of carbon dioxide in the
blood is also lessened. These belong to the chemical effects
of changes of pressure in the air of respiration.
To such changes, as well as to the cold, some of the
deaths in high balloon ascents must be attributed. Messrs.
Glaisher and Coxwell reached the height of 36,000 feet ; the
former became unconscious at 29,000 feet (8,800 metres),
at which height the amount of oxygen in the arterial blood
would probably not exceed 10 volumes per cent., but
recovered during the descent. The symptoms of the
' mountain sickness,' so familiar to Alpine climbers, are also
undoubtedly due in part to deficiency of oxygen in the blood.
But evidence has been brought forward that changes in the
mechanics as well as in the chemistry of respiration are
concerned, and that there is something not connected with
the want of oxygen which diminishes the capacity for
muscular work. This ' something ' is perhaps a peculiar
excitation of the nervous system in the fierce light of those
high levels, which acts not only on the retina, but on the
skin, and may even affect the distribution of the blood
(Zuntz and Schumburg).
Cutaneous Respiration. — It has already been remarked that a frog
survives the loss of its lungs for some time, respiration going on
through the skm. Indeed, it has been calculated that in the intact
frog as much as three-quarters of the total gaseous interchange is
cutaneous. In mammals the structure of the skin is different, and
respiration can only go on through it to a very slight extent. The
amount of carbon dioxide excreted in man, although only about
4 grm. or 2 litres in twenty-four hours, is much greater than cor-
responds to the quantity of oxygen absorbed through the skin. It
has been asserted, and no doubt with justice, that some at least of
the carbon dioxide given off is due to putrefactive processes taking
place on the surface of the body. Such processes, as has already
been pointed out, seem also responsible in part for the heavy odour
of a ' close ' room. For no harmful products appear to be exhaled
from the skin when it is properly cleansed. In spite of the romantic
A'ES/'/A\lT/()X
= 59
statements to the contrary in ancient and modern books (for instance,
the story of the child that was gilded to play the part of an angel at
the coronation of a niediivval pope, but died before the ceremony
began), the whole of the human skin may be coated with an im-
])ermeable varnish without any ill effects. The entire surface of the
body of a patient with cutaneous disease was covered with tar, and
kept covered for ten days. There was not the least disturbance of
any normal function (Senator). The serious effects of varnishing
the skin in animals are due, not to retention of poisonous sub-
stances, but to increased heat loss. \'arnishing is not so rapidly
harmful in large animals like dogs, as in rabbits, which have a
relatively great surface and a delicate skin. The danger of wide-
spread superficial burns is well known. But it is not due to
diminished excretion by the skin, for death occurs when large
cutaneous areas remain uninjured. The patient nearly always dies
when a quarter of the whole skin is burnt ; yet the remaining three-
quarters may surely be considered capable, from all analogy, of
making up the loss by increased activity. One kidney is enough to
eliminate the products of the nitrogenous metabolism of the whole
body. It is difficult to see why the excretion of the trifling amount
of solid matter in the perspiration should be interfered with by the
loss of 25 per cent, of the sweat-glands. The real explanation of
the serious effects of extensive superficial burns is perhaps the ex-
cessive irritation of the sensory nerves, which may lead to changes
in the nervous centres, or reflexly in other organs. Some observers
have supposed that the chemical changes in the damaged tissue,
for example, in the blood-corpuscles, may be the cause of death
(Hunter), and others that it may be due to the transudation of lymph
at the injured part, and the consequent increase in the concentration
of the blood.
Voice and Speech.
Voice. — Sounds of various kinds are frequently produced
by the movements of animals as a whole, or of individual
organs. The muscular sound, the sounds of the heart and
of respiration, we have already had to speak of. Such
sounds may be considered as purely accidental as the foot-
fall of a man or the buzzing of a fly. The wings of an insect
beat the air, not to cause sound, but to produce motion ;
the respiratory murmur is a mere indication that air is
finding its way into the lungs, it is in no way related to the
oxidation of the blood in the pulmonary capillaries. But in
many of the higher animals mechanisms exist which are
specially devoted to the utterance of sounds as their prime
and proper end. In man the voice-producing mechanism
consists of a triple series of tubes and chambers: (i) The
J J — 2
26o A MANUAL OF PHYSIOLOGY
trachea, through which a blast of air is blown ; (2) the
larynx, with the vocal cords, by the vibrations of which
sound waves are set up ; and ( ;) the upper resonance
chambers, the pharynx, mouth, and nasal cavities, in which
the sounds produced in the lar}nx are modified and intensi-
fied, and in which independent notes and noises arise.
The larynx is a cartilaginous box, across which are
stretched, from front to back, two thin and sharp-edged
membranes, the (true) vocal cords. In front the cords are
attached to the th}Toid cartilage, one a little to each side of
the middle line ; behind they are connected to the vocal or
anterior processes of the pyramidal arytenoid cartilages.
The thyroid and the two arytenoids are mounted upon a
cartilaginous ring, the cricoid, on which the former can
rotate about a transverse horizontal axis, the latter around
a vertical axis. The thyroid can thus be depressed by the
contraction of the crico-thyroid muscle, and the vocal cords
stretched. By the pull of the posterior crico-arytenoid
muscles, attached to the external or muscular processes of
the arytenoid cartilages, the vocal processes are rotated out-
wards, the cords separated from each other or ahdnctcd, and
the chink between them, the rima glottidis, widened. When
the vocal processes are approximated by contraction of the
lateral crico-arytenoid muscles and the consequent forward
movement of the muscular processes, the vocal cords are
brought closer together, or adductcd, and the rima is narrowed.
The transverse or posterior arytenoid muscle, which con-
nects the two arytenoid cartilages behind, also helps by its
contraction to narrow the glottis by shifting the cartilages
on their articular surfaces somewhat nearer the middle line.
Running in each vocal cord, and, in fact, incorporated with
its elastic tissue, is a muscle, the thyro-arytenoid, the ex-
ternal portion of which may to some extent cause inward
rotation of the vocal processes and adduction of the cords;
but the main function, at least of its inner part, is to alter
the tension of the cords. The diagrams in Figs. 91 and 92
illustrate the action of the abductors and adductors of the
vocal cords.
The crico-thyroid muscle and the deilectors of the epi-
.. 'ti
AWiS/'/A'A T/ON
:6i
glottis are supplied by the superior laryngeal branch of the
vagus, which also contains the sensory hbres for the mucous
membrane of the larynx above the \ocal cords. All the other
intrinsic muscles are supplied by the recurrent larynj;eal
branch of the vagus. It receives these motor fibres from
the spinal accessory, and supplies sensory fibres to the
mucous membrane of the larynx below the vocal cords and
to the trachea.
The voice is produced, like the sounds of a reed instru-
ment, by the rhythmical interruption of an expiratory blast
of air by the vibrating vocal cords. When a bell is struck,
Fic. 91.— Diagrammatic f"'*^"- 92-— Direction .if
HORIZONTAL SfXTION OF I'U^L OF THE LATERAL
Larynx to show the Crico- Arytenoids,
DIRECTION OF PULL OF WHICH ADDUCT THE
THE Posterior Crico- Vocal Cords.
Arytenoid Muscles, Dotted lines show position in
WHICH ABDUCT THE adduction.
Vocal Cords.
Dotted lines show position in
abduction.
vibrations are set up in the metal, which are communicated
to the air. It is not the same with the vibrations of the
vocal cords ; if they were plucked or struck, they would only
produce a feeble note. The air in the mouth, pharynx,
larynx, trachea, and lungs is the real sounding body; a pulse
of alternate rarefaction and condensation is set up in it by
the interference, at regular intervals, of the vocal cords with
the expiratory blast. Forced abruptly from their position
of equilibrium as the blast begins, they almost immediately
regain and pass below it, in virtue of their elasticity, and
continue to vibrate as long as the stream of air continues to
issue in sufficient strength. The sound-waves thus set up
262 A MAX (I A I. OF I'llYSIOLOGY
spread out on every side, impinge on the tympanic mem-
brane, set it quivering in response, and give rise to the
sensation of sound.
We may sa}-, in a word, that the whole exquisite
mechanism of cartilages, ligaments, and muscles, has for its
object the production of a sufficient pressure in the blast of
air driven through the windpipe by an expiratory act, and
of a suitable tension in the vibrating cords. An approxima-
tion of the cords, a narrowing of the glottis, is essential to
the production of voice ; with a widely-opened glottis the
air escapes too easily, and the necessary pressure cannot be
attained. The pressure in the windpipe was found in a
woman with a tracheal fistula to be about 12 mm. of mer-
cury for a note of medium height, about 15 mm. for a high
note, and about 72 mm. for the highest possible note. The
period of vibration of structures like the vocal cords depends
on their length, thickness, and tension ; the shorter, thinner,
more tense and less dense a stretched string is, the greater
is the vibration frequency, the higher the note. In the child
the cords are short (6 to 8 mm.), in woman longer (10 to
15 mm. when slack, 15 to 20 mm. when stretched), in man
longest of all (15 to 20 mm. in the relaxed, and 20 to
25 mm. in the stretched position); and the lower limit of
the voice is fixed by the maximum length of the relaxed
cords. A boy or a woman cannot utter a deep bass note,
because their vocal cords are relatively short, and do not
vibrate with sufficient slowness. It is true that by the action
of the crico-thyroid muscle the cords can be lengthened,
and that the maximum length in a woman approaches or
exceeds the minimum length in a man. But the lengthening
of the vocal cords in one and the same individual is always
accompanied by other changes — increase of tension, decrease
of breadth and thickness — which tell upon the vibration
frequency in the opposite way, and more than compensate
the effect of the increase of length. It is probable that when
the highest notes are uttered, only the anterior portions of
the cords are free to vibrate, their posterior portions being
damped by the approximation of the vocal processes of the
arytenoid cartilages by the contraction of the lateral crico-
Ki: SI 'I A' A HON 263
arytenoid and trans\erse arytenoid muscles. The range of
an ordinary voice is 2 octaves; b)- training 2\ octaves can
be reached ; but in exceptional cases a range of 3, and even
3i, octaves has been known.
The development of the voice in children is of great interest. At
the age of six years the boy's voice has a rather narrower range than
the girl's in both directions. The boy's voice reaches its full height
in the twelfth and its full depth in the thirteenth year, when the
range is almost 3 octaves, its upper limit being a semitone higher
than the girl's, but its lower limit a whole tone deeper. When the
voice. ' breaks ' in boys at the age of puberty, the control of the vocal
organs becomes so incomplete that only in one-fourth of the cases
can notes of sufficient steadiness to be used in music be produced.
The vocal cords, as may be seen with the laryngoscope, are
frequently, though not always, congested (Paulsen).
The pitch of a note, while it depends chiefly, as has been
said, on the tension of the vocal cords, rises and falls some-
what with the strength of the expiratory blast ; the highest
notes are only reached with a strong expiratory effort. The
intensity of all sounds is determined by the strength of the
blast, for the amplitude of vibration of the vocal cords is
proportional to this. Besides pitch and intensity, the ear
can still distinguish the quality or timbre of sounds; and the
explanation is as follows : Two simple tones of the same
pitch and intensity, that is, the sounds caused by two series
of air-waves of the same period and amplitude — of the same
frequency and height, if these terms seem simpler — would
appear absolutely identical to the sense of hearing; just as
the aerial disturbances on which they depend would be
absolutely alike to any physical test that could be applied.
But no musical instrument ever produces sound-waves of
one definite period, and one only ; and the same is true of
the voice. When a stretched string is displaced in any
way from its position of rest, it is set into vibration ; and
not onl}' does the string vibrate as a whole, but portions of
it vibrate independently and give out separate tones. The
tone corresponding to the vibration period of the whole
string is the lowest of all. It is also the loudest, for it is
more difficult to set up quick than slow vibrations. The ear
therefore picks it out from all the rest ; and the pitch of the
compound note is taken to be the pitch of this, its funda-
264
A MANUAL OF PHYSIOLOGY
mental tone. The others are called partial or over-tones,
or harmonics of the fundamental tone, their vibration
frequency being twice, three times, four times, etc., that of
the latter. Now, the fundamental tone of a compound note
or clani^ produced by two musical instruments may be the
same, while the number, period, and intensity of the har-
monics are different ; and this difference the ear recognises
as a difference of timbre or quality. The timbre of the voice
depends for the most part on partial tones produced or in-
tensified in the upper resonance chambers.
Kit;. 93. — Dia(;kam 01 Laryncosioi-e.
A great deal of our knowledge as to the mode and
mechanism of the production of voice has been acquired by
means of the laiyngoscopc (Fig. 93). This consists of a small
plane mirror mounted on a handle, which is held at the
back of the mouth in such a position that a beam of light,
reflected from a larger concave mirror fastened on the
forehead of the observer, is thrown into the larynx of the
patient. The observer looks through a hole in the centre
of the large mirror ; and a reversed image of the interior of
the larynx is thus seen in the small mirror, the arytenoid
cartilages appearing in front, the thyroid behind, and the
vocal cords stretching between. The small mirror is
A'ES/'/A'A TION
265
^\•annccl to body temperature before beinj^' introduced, so
as to prevent the condensation of moisture on it. And the
tendency to retch which is caused by contact of the instru-
ment with the soft palate may be removed or lessened by
the application of a solution of cocaine.
Examined with the laryngoscope during quiet respiration,
the glottis is seen to be moderately, though not widely,
open, and the vocal cords almost motionless. Although the
portion between the arytenoid cartilages has received the
name of glottis respiratoria, in contradistinction to the
glottis vocalis between the vocal cords, the rima in its whole
Fuj. 94. — Position ov the
Glottis vkeliminaky 10
the utterance ok sounl).
IS, false vocal cord ; ri, true
vocal cord ; iir, arytenoid carti-
lage ; b, pad of the epiglottis.
Fig. 95. — Position ok open
Glottis.
/, tongue ; e, epiglottis ; ae, ary-
epiglottidean fold ; c, cartilage of
Wrisberg ; ar. arytenoid cartilage ; c,
glottis ; V, ventricle of Morgagni ; //,
true vocal cord ; (s, false vocal cord.
extent from front to back is really concerned in the re-
spiratory act. In deep expiration the vocal cords come
nearer to the middle line, and the glottis is narrowed ; in
deep inspiration they are widely separated, and the rings of
the trachea, and even its bifurcation, may be disclosed to
view. When a sound is produced, a note sung, for example,
the cords are approximated (Figs, 94 and 95) ; and with a
high note more than with a low.
The essential difference between the production of notes in the
lower register, or chest voice, and in the higher register, or falsetto,
has been much debated. The lowest notes which can be uttered by
any given voice are chest notes, the highest are falsetto notes ; but
there is a debatable land common to both registers, and medium
notes can be sung either from the chest or from the head. Chest
notes impart a vibration or Jymitus to the thoracic walls, from the
resonance of the lower air-chambers, the trachea and bronchi ; and
266 A MANUAL OF Pin'SIOLOCY
this can be distinctly felt by the hand. In head notes or falsetto
the resonance is chiefly in the upper cavities, the pharynx, mouth,
and nose. As to the mechanical conditions in the larynx, there is a
pretty general agreement that during the production of falsetto notes
the vocal cords are less closely approximated than in the sounding of
chest notes. The escape of air is consequently more rapid in the
head voice, and a falsetto note cannot be maintained so long as a
note sung from the chest. But it is only the anterior part of the
rinia glottidis that is wider in the falsetto voice ; the whole of the
glottis respiratoria, and even the jiosterior portion of the glottis
vocalis, are closed during the emission of falsetto notes.
Oertel has stated, and the statement has been confirmed by others,
that the free edge of the vocal cord alone vibrates in the falsetto
voice, one or more nodes or motionless lines parallel to the edge
being formed by the contraction of the internal part of the thyro-
arytenoid muscle, which thus acts like a stop upon the cord.
Approximation of the vocal cords may take place in
certain acts imconnected with the production of voice.
Thus, a cough, as has already been mentioned, is initiated
by closure of the glottis. During a strong muscular effort,
too, the chink of the glottis is obliterated, and respiration
and phonation both arrested. The object of this is to fix
the thorax, and so afford points of support for the action
of the muscles of the limbs and abdomen. But consider-
able efforts can be made even by persons with a tracheal
fistula.
Speech. — Ordinary speech is articulated voice — voice
shaped and fashioned by the resonance of the upper air
cavities, and jointed together by the sounds or noises to
which the varying form of these cavities gives rise. Here
we come upon the fundamental distinction between vowels
and consonants. Vowels are musical sounds ; consonants
are not musical sounds, but noises — that is to say, the\- are
due to irregular vibrations, not to regularly recurring waves,
the frequency of which the ear can appreciate as a definite
pitch. This difference of character corresponds to a differ-
ence of origin : the vowels are produced by the vibrations of
the vocal cords; the consonants are due to the rushing of the
expiratory blast through certain constricted portions of the
buccal chamber, where a kind of temporar}- glottis is estab-
lished by the approximation of its walls. One of these
' positions of articulation ' is the orifice of the lips ; the
RESriNA 17 ON 267
consonants formed there, such as/) and h, are called labials.
A second articulation position is between the anterior part
of the tongue and the teeth and hard palate. Here are
formed the dentals, /, d, etc. The ordinary English r, and
the y of the Berwickshire and East Prussian 'burr,' also arise
in this position through a vibratory motion of the point of
the tongue. The third position of articulation is the narrow
strait formed between the posterior portion of the arched
tongue and the soft palate. To the consonants arising here
the name of gutturals has been given. They include k, g,
the Scottish cli, and the uvular German r. The latter is
produced by a vibration of the uvula. The aspirated li is a
noise set up by the air rushing through a moderately wide
glottis, and some have therefore included the glottis as a
fourth articulation position for consonants. Certain sounds
like n, in, and ng, when final (as in pen, dam, ring), although
produced at the glottis, are intensified by the resonance of
the air in the nose and pharynx, and are sometimes spoken
of as nasal consonants.
As we have said, the vowels are produced by vibrations of
the vocal cords, but thej'^ owe their special timbre to the
reinforcement of certain overtones by the resonating cavities,
the shape and fundamental tone of which are different for
each vowel. When a vowel is whispered, the mouth assumes
a characteristic shape, and emits the fundamental tone proper
to the form and size of the particular * vowel-cavit>',' not as
a reinforcement of a tone set up by the vibrations of the
vocal cords, but in response to the rush of air through the
cavity; just as a bottle of given shape and size gives out a
definite note when the air which it contains is set in vibra-
tion, by blowing across its mouth. A whisper, in fact, is
speech without voice ; the larynx takes scarcely any part in
the production of the sounds ; the vocal cords remain apart
and comparatively slack ; and the expiratory blast rushes
through without setting them in vibration.
The fundamental tone of the 'vowel-cavity' may be found
for each vowel by placing the mouth in the position necessary
for uttering it, then bringing tuning-forks of different period
in front of it, and noting which of them sets up sympathetic
268 .1 M.Wr.iL OF I'UYSIOIaX.Y
resonance in the air of the mouth, and so causes its sound
to be intensified. The fundamental tone is lowest for n (as
in hitc). Next comes o; then a (as in path): then c ; while
i is highest of all. A simple illustration of this may be
found in the fact that when the vowels are whispered in the
order given, the pitch rises.
Such is the explanation of the difference of the vowels in quality
which was first given by Helniholt/. Universally accepted for a time,
it has been in recent years assailed by Hermann, who bases his
criticisms (i) on microscopic examination of curves obtained by the
Edison [)honograph, and (2) on the results of his phono-photographic
method. (The record of an Edison phonograph is magnified by a
system of levers, the last of which carries a small mirror, on which
a beam of light is allowed to strike. The reflected beam falls on a
moving drum covered with sensitive paper. Thus the movements of
the mirror are greatly exaggerated and photographed.) Hermann
has come to the conclusion that the mouth does not act as a mere
resonator, but that for each vowel, in addition to the fundamental
note due to the vibration of the vocal cords, the pitch of which is,
of course, variable, one or, it may be, two other notes, not necessarily
harmonics of the laryngeal note, but separated from it by a constant
or nearly constant musical interval, are directly produced by the
passage of the expiratory blast through the mouth. For example,
the buccal note for a is in the middle of the second octave of the
laryngeal note, the buccal notes for t' in the beginning of the second
and the end of the third octave. The fact that it is by no means
difficult to sing and whistle at the same time shows the possibility of
Hermanns view, that a fixed tone can be generated in the mouth
by the intermittent stream of air issuing from between the vibrating
vocal cords, just as a tone is generated in a pipe by blowing into or
over it (Onitzner). McKendrick has also made important investiga-
tions on this subject, and has obtained curves by enlarging the
phonographic records by mechanical means.
When // or o is sounded, the buccal cavity has the form of a wide-
bellied flask, with a short and narrow neck for //, a still shorter but
wider neck for o. For / the tongue is raised and almost in contact
with the palate, and the cavity of the mouth is shaped like a flask
with a long narrow neck and a very short belly. For c the shape is
similar, but the neck is not so narrow. For a the vowel-cavity is
intermediate in form between that of u and /, being roughly funnel-
shaped, and the mouth is rather widely opened (Figs. 96 to 98).
When the vowels are being uttered, the soft palate closes
the entrance to the nasal chambers completely, as may be
shown by holding a candle in front of the nose, or trying to
inject water through the narcs. If the cavities of the nose
Rr.SPlRA TION
l(iC)
are not completel}- blocked oft", the voice assumes a nmal
character in pronouncing^ certain of the vowels ; and in some
langjuages this is the ordinary and correct pronunciation.
Many animals have the power of emittinfj articulated
sounds ; a few have risen, like man, to the digjnity of
sentences, but these only by imitation of the human voice.
Both vowels and consonants can be distinguished in the
notes of birds, the vocal powers of which are in general
higher than those of mammalian animals. The latter, as a
rule, produce only vowels, though some are able to form
consonants too.
The nervous mechanism of voice and speech will ha\e to be
Fig. 96.
Fir.. 97.
Fic;. 98.
again considered when we come to study the physiology of
the brain and spinal cord. But the curious physiological
antithesis between the functions of abduction and of adduc-
tion of the vocal cords may be mentioned here. The abductor
muscles are not employed in the production of voice ; the}- are
associated with the less specialized, the less skilled and pur-
posive function of respiration. The adductor muscles are not
brought into action in respiration ; they are associated with
the highly-specialized function of speech. Corresponding to
this difference of function, we find that the adductors only
are represented in the cortex of the brain, the abductors in
the medulla oblongata. Stimulation of an area in the lower
part of the ascending frontal convolution, near the fissure of
270 A MAXUAL OF PHYSIOLOGY
Rolando, in the macaque monkey, causes adduction of the
vocal cords, never abduction. Stimulation of the medulla
oblongata (accessory nucleus) causes abduction, never adduc-
tion (Horsley and Semon). The skilled adductor function
is, therefore, placed under control of the cortex. The vitally
important, but more mechanical, abductor function is
governed by the medulla. The abductor movements are
more likely to be affected by organic disease, the adductor
movements by functional changes. But the distinction
between the two groups of muscles is not entirely due to a
difference of central connections : for Hooper has found that
in an animal deeply narcotized with ether, stimulation of
the recurrent laryngeal nerve causes invariably abduction of
the vocal cords ; in an animal slightly narcotized, adduction.
On the other hand, when the nerve is cooled the abductors
give way before the adductors. The same is true when it
is allowed to become dry. And after death in a cholera
patient it was observed that the posterior crico-ar3tenoid,
an abductor muscle, was the first of the intrinsic laryngeal
muscles to lose its excitability. Lesions of the medulla
oblongata are often accompanied by marked changes in the
character of the voice and the power of articulation.
Section or paralysis of the superior laryngeal nerve causes
the voice to become hoarse, and renders the sounding of
high notes an impossibility, owing to the want of power to
make the vocal cords tense. Stimulation of the vagus within
the skull causes contraction of the crico-thyroid muscle and
increased tension of the cords. Section or paralysis of the
inferior laryngeal nerves leads to loss of voice or aphonia,
and dyspncea (Fig. 99). Both adductor and abductor
muscles are paralyzed ; the vocal cords assume their mean
position — the position they have in the dead body — and the
glottis can neither be narrowed to allow of the production
of a note, nor widened during inspiration. It is said, how-
ever, that young animals, in which the structures around the
glottis are more yielding than in adults, can still utter shrill
cries after section of the inferior laryngeals, the contraction
of the crico-thyroid muscle alone being able, while increasing
the tension of the cords, to draw them together. Strong
RESPIRA TION
271
Stimulation of the inferior laryngeal causes closure of the
glottis, for although it supplies both abductors and adductors,
the latter prevail. With weak stimulation, and in young
animals, the abductors carry off the victory, and the glottis
is opened (Risien Russell).
Interference with the connections on one side, between
the higher cerebral centres and the medulla oblongata, as by
rupture of an artery and effusion of blood into the posterior
portion of the internal capsule (giving rise to hemiplegia,
or paralysis of the opposite side of the body), is not followed
Fig. 99. — Diagram ok Vocal Cords in Paralyses of the Larynx.
a, Paralysis of both inferior laryngeal nerves. The vocal cords have taken up the
' mean ' position, b, Paralysis of right inferior laryngeal nerve. .An attempt is being
made to narrow the glottis for the utterance of sound. The right cord remains in its
' mean ' position. <■, Paralysis of the abductor muscles only, on both sides. The
cords are approximated beyond the ' mean ' position by the action of the adductors.
by loss of voice ; the laryngeal muscles on both sides are
still able to act.
In stainiucriiig, spasmodic contraction of the diaphragm
interrupts the effort of expiration. The stammerer has full
control of the mechanism of articulation, but not of the
expiratory blast. His larynx and lips are at his command,
but not his diaphragm. To conquer this defect he must
school his respiratory muscles to calm and steady action
during speech. The stutterer, on the other hand, has full
control of the expiratory muscles. His diaphragm is well
drilled, but his lips and tongue are insubordinate.
A MAM'AL OF l'I/ySIOL<)(;y
PRACTICAL EXERCISES OX CHAPTER III.
I. Tracing of the Respiratory Movements. — (a) Set up the
arrangement shown in lig. loo, and test whether it is air-tight. Have
also in readiness an induction machine and electrodes arranged for
an interrupted current. Anaesthetize a dog with morphia and ether
or ACE mixture. Insert a cannula into the trachea (p. 177), and
connect it with the large bottle by a tube. Connect the bottle with
a recording tambour adjusted to write on a drum, and regulate the
amount of the excursion of the lever by slackenmg or tightening the
screw-clamp. Set the drum off at slow speed, and take a tracing.
{/>) Then disconnect the cannula from its tube. Dissect out the
vagus in the lower part of the neck, pass a ligature under it, but do
not tie it. Connect the cannula again with the bottle, and while a
tracing is being taken ligature the vagus. Then stimulate its central
end with weak shocks, marking the time of stimulation on the drum.
Repeat the stimulation with strong shocks, and observe the results.
{c) Apply a strong solution of potassium chloride with a camel's-
hair brush to the central end of the vagus while a tracing is being
taken, and observe the effect.
id) Isolate the sciatic nerve (p. 185), ligature it, and cut below the
ligature. Stimulate its central end while a tracing is being taken.
The respiratory movements will be increased.
{e) Disconnect the cannula, and isolate the vagus on the other
side. While a tracing is being taken, divide it. The respiratory
movements will probably at once become deeper and less frequent.
(/) Again disconnect the cannula. Isolate the superior laryngeal
branch of the vagus, which will be found coursing inwards to the
larynx at the level of the thyroid cartilage. Ligature the nerve, and
divide it between the larynx and the ligature. Reconnect the
cannula. Take a tracing first with weak and then with strong
stimulation of the central end of the superior laryngeal.
(^) Insert a cannula into the carotid artery. A\'hile a tracing is
being taken, allow the blood to flow. Dyspncea and exaggeration of
the respiratory movements will be seen when a considerable quantity
of blood has been lost. Mark and varnish the tracings. In the
whole of this experiment the cannula is to be disconnected, except
when the lever is actually writing on the drum, in order that the
period during which the animal must breathe into the confined space
of the boltle may be diminished as much as po-sihle.
2. The Effect of Temperature on the Respiratory Centre— Heat
Dyspnoea. — Set up an arrangement for taking a respiratory tracing as
in 1. .Anajsthetize a dog, and fasten it, back downward, on a holder.
Make an incision in the middle line of the neck, commencing a
little below the cricoid cartilage, and extending down for 4 or 5
inches. Insert a cannula into the trachea. Isolate both carotid
arteries for as great a distance as possible. Take two pieces of lead
tube' about 9 inches long, and bend up about 2 inches at each end
nearly to a right angle. Place one of the tubes in contact length-
PKA CTICA L EXERCISES
!73
wise with each carotid, securing contact by loose Ugatures. Support
the tubes in clamps, so that the arteries are not pressed on. Connect
two adjacent ends of the tul)es by a short rubber tube. Connect
one of the remaining ends to a funnel, supported on a stand, and the
other to a rubber tube hanging over the table above a large jar.
Slip two or three folds of paper between the tubes and the vagus
nerves. Heat two or three litres of water to 55° or 60' C Now
connect the tracheal cannula with the bottle. As soon as the tracing
is under way, let the hot water run through the funnel and lead tubes
18
274 A MAXUAL OF PHYSIOLOGY
into the jar. Mark on the tracing the point at which the circulation
of the hot water was begun, and go on jjassing it until it has
produced an effect. Then stop the drum, and circulate water at the
ordinary temperature till the breathing is again normal. Then, while
a tracing is being taken, pass ice-cold \s-ater through the tubes, and
again notice the effect.
3. Measurement of Volume of Air inspired or expired — Vital
Capacity. — A spirometer of sufficient accuracy for this experiment
can be made by removing the bottom of a large bottle with a
capacity of not less than 4 litres. A good cork, through which
passes a glass tube connected with a rubber tube, is fitted into the
neck. The bottle is then fixed vertically, mouth downwards, the glass
tube being blocked for the time, and graduated by pouring in
measured quantities of water, say 100 c.c. at a time, and marking the
level. The divisions are then etched in. If the cork does not fit air-
tight, it is covered with wax. The bottle is swung on two pulleys and
immersed, bottom down, in a large glass jar or a small cask nearly full
of water. A smaller bottle may be used for the determination of the
tidal air, so as to reduce the error of reading.
(i) Submerge the bottle to the stopper, after opening the pinch-
cock on the rubber tube. Breathe into the bottle, close the cock,
adjust the bottle so that the level of the water is the same inside and
outside, and then read off the level. Determine the volume of air
expired in :
{a) A normal expiration after a normal inspiration (tidal air) :
{b) The greatest possible expiration after a normal inspiration
(supplemental air) ;
{i) The greatest possible expiration after the greatest possible
inspiration (vital capacity).
[2) Open the cock, and raise the bottle till it is nearly full of air.
Determine the volume of air inspired in :
{a) A normal inspiration after a normal expiration (tidal air) ;
(b) The greatest possible inspiration after a normal e.xpiration
(complemental air) ;
{c) The greatest possible inspiration after the greatest possible
expiration (vital capacity).
Make several observations of each quantity, and take the mean.
(3) Count the rate of respiration for three minutes, keeping the
breathing as nearly normal as possible ; repeat the observation ; and
from the mean result and the amount of the tidal air calculate the
quantity of air taken into the lungs in twenty-four hours (pulmonary
ventilation).
4. Respiratory Pressure. — Connect a strong rubber tube to one
limb of a mercurial manometer provided with a scale, (i) Fasten
the tube with a little cotton-wool in one nostril, breathe through the
other with closed mouth, and observe the amount by which the level
of the mercury is altered in ordinary inspiration and expiration.
(2) Repeat the observation with forced breathing, pinching the
tube at the height of inspiration and expiration, and reading off the
maximum inspiratory and expiratory pressure.
PRALTICAL EXERCISES 275
(3) Repeat ( i) with the tube connected to the mouth by a glass
tube held between the hps, and tlie nostrils open.
(4) Repeat [2) with the tube in the mouth and nostrils closed.
5. Determination of Carbon Dioxide and Oxygen in Inspired and
Expired Air - ( 1 ) Estimation of Carbon Dioxide. — Fill a burette
Willi water, and close the pinchcock on the rubber tube. Immerse
the wide end of the burette in a large vessel of water, and fill it with
carbon dioxide by putting into it below the water a tube connected
with a bottle in which carbon dioxide is being evolved by the action
of hydrochloric acid on marble chips. See that gas has been coming
off freely from the bottle for a little time before the tube is put under
the burette. Do not fill the burette with gas beyond the graduated
part. Hold the burette in the vertical position, its mouth being still
immersed, make the level of the water the same inside and outside,
and read off the meniscus. Then introduce a piece of stick sodium
hydrate, close the burette with a finger or the palm of the hand, lift
it out of the water, and by a sort of sce-saw movement shake the
sodium hydrate repeatedly from end to end of it. Again immerse
the burette, and read the level of the meniscus. Most of the gas
will be absorbed. Repeat the shaking. If the reading is still the
same, absorption is now complete
(2) Estimation of Oxygen (Analysis of Inspired Air). — Fill the
burette with the air of the laboratory. Open the pinchcock, and
immerse the wide end of the burette till the water reaches the gradua-
tion. Then close the cock, and read off the meniscus. Introduce a
piece of sodium hydrate, and proceed as in (i). Notice that there
is no appreciable absorption (This method is not suitable for the
measurement of the small quantity of carbon dioxide in ordinary
air.) Now introduce, under water, some pyrogallic acid. This can
be done conveniently by wrapping up some of the crystals in thin
paper so as to form a kind of small cigarette, which is pushed up into
the burette. A little more sodium hydrate may also be added, if the
piece first introduced is entirely dissolved. Shake as described in
(i), till no more absorption takes place. Then read off the meniscus
again (always making the level the same inside and outside the burette).
The difference in the two readings gives the amount of oxygen present.
What remains in the burette is nitrogen (and a little argon). Its
amount is, of course, equal to the reading of the burette, plus the
capacity of the ungraduated part at the narrow end of the burette,
which must be determined once for all by a separate measurement.
(3) Analysis of Expired Air. — {a) Fill the spirometer with water,
breathe into it several times in your ordinary way, but be careful not
to inspire any air from the spirometer : then fill the burette with the
expired air from it. Or simply expire several times through the
burette, seeing that none of the inspired air comes through it.
Determine, as in (i) and (2), the percentage amount of carbon
dioxide, oxygen and nitrogen. (/') Repeat {a) with air expired
after the lungs have been thoroughly ventilated by taking a number
of deep breaths in succession, and determine whether there is any
difference in the percentage amounts.
276
A MAXi'AL OF I'l[YSIOLO(,y
(k Estimation of the Quantity of Water and of Carbon Dioxide
given off by an Animal (//ci/(/ir//c's Method). {\) Connt'ct the
apparatus shown in Fig. 101 with the water-pump. Allow a negative
pressure of 5 or 6 inches of water to he established in it, as shown
Fit;. loi. — Haldane's Api-ARArt's kor measuring the (Quantity of CO.,
AND AfJlEorS VAI'OLK i;iVEN OFF BY AN ANIMAL.
A, chamber into which the animal is put ; i and 4, Woulff s bottles filled with
soda-lime to absorb carbon dioxide ; 2, 3, and 5. Woulff's bottles filled with pumice-
stone soaked in sulphuric acid to absorb watery vapour ; B. glass bell-jar suspended in
water, by means of which the negative pressure is known ; 1', waier-pump which sucks
air through the apparatus ; i and a are simply for absorbing the carbon dio.xide and
water of the ingoing air.
by the rise of water in the Ijell-jar, B. Then close the open tube of
carbon dioxide bottle i, and clamp the tube between the water-pump
and the bell-jar. If the negative pressure is maintained, the arrange-
ment is air-tight. Now weigh bottle 3 and bottles 4 and 5, the last
two together. Place a cat in the respiratory chamber A, connect the
.■\, soda-lime tube ; B, sulphuric
acid tube ; C, wooden frame, in
which .\ and B are supported by
wires </,- b, wire hook, which grips
the glass tube firmly, and by
means of which the tubes are lifted
out of the frame in order to be
weighed ; a, short piece of glass
tubing, by taking out which the
absorption tubes are disconnected
from the rest of the apparatus ; <;.
glass tube going off to animal
chamber. The right-hand glass
tube of B should not touch the
sulphuric acid as depicted.
N Ti i;i> lok CO.. AM) Moisri'RE.
chamber directly with the water-pump, and test whether it is tight.
Then take the stopper out of bottle i, and adjust the rate at which
air is drawn through the apparatus. Let the ventilation go on for a
few minutes, then^insert bottles 3, 4, and 5 again. Note the time
exactly at this point, and after an hour disconnect 3, 4, and 5, and
again weigh. The difference of the two weighings of 3 shows the
rRACTlCAL EXERCISES 277
quantity of water Ljivcn off by the animal in an liour : the difference
in the combined weight of 4 and 5, the ([uantity of carbon dioxide.
Weigh the cat, and calculate the amount of water and of carbf^n
dioxide given off per kilo per hour.
(2) For the student it is more convenient to use smaller animals.
The mouse may be taken as an example of a warm-blooded animal,
and the frog of a cold-blooded. Instead of the Woulff's bottles use
wide test-tubes connected as in Fig. 102, and for the animal chamber
a small beaker, closed with a very carefully-fitted cork which has
been boiled in paraffin. The inlet and outlet tubes of the chamber
are to be introduced through this cork. The holes for these are to
be bored with the greatest care, and the tubes to be put in while the
cork is still hot from boiling in paraffin. Also insert a thermometer
about 6 inches long registering from o' C. to 45° C Modeller's wax
is to be used finally to render all the junctions air-tight.
Add to the series of tubes described in the apparatus a single
tube containing baryta-water. This is placed after the tube 5, and
so arranged that the air-current bubbles through the water. As long
as the absorption of carbon dioxide is complete, the baryta-water
remains clear. Beyond this a water-bottle should be placed to act
as a valve and to indicate the negative pressure in the apparatus.
It can be most simply constructed by using a cylinder of stout glass
tubing in a wide-mouthed bottle containing some water, the inlet and
outlet tubes passing through a parai^ned cork which seals the u{)per
end of the cylinder.
Before making an observation, test whether the apparatus is air-
tight, as explained above, after introducing the animal into the
chamber, sealing the latter with wax, and connecting it with the
absorption tubes. But a negative pressure of 2 or 3 inches of water
is a sufficient test for the small apparatus.
To make an observation, set the air-current going at the desired
rate. Allow it to run for a few minutes till the carbon dioxide, which
has accumulated during the testing, has been swept out. At a time
which has been decided on and noted, stop the current by discon-
necting the water-pump. Disconnect and stopper up the animal
chamber, and weigh it as quickly as possible. Connect up again,
using only recently-weighed absorption-tubes, and finally connect
with the water-pump and allow the current to pass for a definite
period, say an hour. If a consecutive series of observations is to be
made, two sets of tubes should be prepared for use during alternate
periods. Use in each case two soda-lime tubes, the most recently
filled one being placed second of the two.
The soda-lime should not be too dry, or absorption is not
sufficiently rapid. The following facts are made out in the observation :
{a) The loss of weight by the animal chamber (chiefly loss by the
animal). (/') The gain of the sulphuric acid tube in water, {c) The
gain of the soda-lime tubes in carbon dioxide.
If we compare total loss and total gain, we find they do not corre-
spond, the gain being always greater than the loss. 'J"he surplus can
only be oxygen which has been absorbed by the animal and added to
278 A MA.XUAL ()/ I'lIYSIOLOGY
the hydrogen and carbon of its substance to form water and carbon
dioxide. Calculate the resjjiratory quotient (p. 225).
The following series of experiments may be done with this
apparatus by advanced students : ( i ) Observe the amount of gaseous
exchange per kilo and hour at room temperature in : {a) A cold-
blooded animal (frog), {b) a warm-blooded animal (mouse), {c) Cal-
culate the respiratory quotient in each case. (2) Observe: {a) The
effect of exercise in increasing, and of rest in diminishing, the
total gaseous exchange ; (/') the effect of food in increasing the
total gaseous exchange ; (c) the effect of different kinds of food
(carbo-hydrates, proteids, etc.) on the respiratory quotient (p. 225).
(3) Observe the reaction of: {a) A cold-ljlooded animal, (b) a warm-
blooded animal, to changes in tem[)erature of the surrounding air, as
shown in the rise and fall of the gaseous exchange. For this, arrange
round the beaker a water-jacket through which a current of water
flows. Allow cold water to flow through the jacket for half an hour,
and read off the temperature of the chamber (say 10° C.). For the
next half-hour heat the water in the jacket till the air of the chamber
is at 30° C. Lastly, take another observation of a cold period.
Compare the exchange for the three periods (p. 228).
7. Section of both Vagi. — Proceed as in experiment 24, p. 189,
but use an ordinary rabbit : and instead of cutting the symjiathetic,
])ass threads under both vagi, divide them, and sew up the wound.
An induction coil is not required, unless the student has any diffi-
culty in deciding which nerve is the vagus. The point may be at
once settled by stimulating the nerves before division. Stimulation
of the vagus will cause slowing or stoppage of the heart, and there-
fore of the pulse in the carotid, and quickening of respiration.
Stimulation of the sympathetic will have neither of these effects.
A dog may also be used, and the vago-sympathetics divided. Count
the pulse and the rate of respiration before and after the section of
each nerve, and observe carefully any change that may occur. Also
note whether the depth of the breathing is affected. The animal
must be looked at once at least on the day of the operation, and its
behaviour carefully observed. It should be seen daily thereafter so
long as it survives. A rabbit does not usually live much more than
twenty-four hours.
As soon after death as possible, make an autopsy, observing
especially the state of the lungs. Harden portions of the lungs that
appear to contain the most exudation in MuUer's fluid (ten times as
much fluid as tissue). Change the fluid next day, and again at the
end of a week. In three or four weeks wash out the Miiller's fluid
under the tap, and transfer the tissue to 90 per cent, alcohol. After
a few days it is to be prepared for cutting by being passed succes-
sively through absolute alcohol (two days), absolute alcohol and
ether mixture (two days), thin celloidin (two or three days), thick
celloidin (one day). Fasten on vulcanized wood-fibre and cut
sections with a sliding microtome, moistening the knife with 80 per
cent, alcohol. Stain, mount, and examine under the microscope.
Note the exudation in the alveoli, and make drawings. Write a
report of your complete experiment.
Plate T I
Herou* alveolui
m
Uueoui alveolu$
Creicentt of Oianuzzi
J^'
Supporting eonneetive tUiue
1. Section of submaxillary gland showing both mucona and aeroas alveoli, x 250.
(Stained with hsBm&toj^y .i.^
Bfjore teeretion {retting)
•♦•
• •
♦ ■•'
• •
2. Section of seroas gland, x 800. (Stained with borax carmine.)
Ifveou* eelU
Creteenti of
Siantutei
'■very large)
Cotmeetire tUtue
An ocinu*
Btoodrveual
Duet (intralobular)
InteriH'
leading from aeini of gland
to intralobular duct
3. Section af mucous gkad (after secretion), x 300. (Stained with picrooarmioe.)
Vfrtt Newiuaji ohr hth
CHAPTER IV.
DIGESTION.
In the last chapter we have described the manner in which
the interchange of gases between the tissues and the air is
carried out. We have now to consider the digestion and
absorption of the sohd and hquid food, its further fate in
relation to the chemical changes or metabolism of the
tissues, and finally the excretion of the waste products by
other channels than the lungs.
Logically, we ought to take metabolism after absorption
and before excretion, tracing the food through all its vicissi-
tudes from the moment when it enters the blood or lymph
till it is cast out as useless matter by the various excretory
organs. Unfortunately, however, the steps of the process
are as yet almost entirely hidden from us ; we know only
the beginning and the end. We can follow the food from
the time it enters the alimentary canal till it is taken up by
the tissues of absorption ; and we have really a fair know-
ledge of this part of its course. We can collect the end
products as they escape in the urine, or in the breath, or in
the sweat ; and our knowledge of them and of the manner
in which they are excreted is considerable. But of the
wonderful pathway by which the dead molecules of the food
mount up into life, and then descend again into death, we
catch only a glimpse here and there. Only the introduction
and the conclusion of the story of metabolism are at present
in our possession in fairly continuous and legible form. We
will read these before we try to decipher the handful of torn
leaves which represents the rest.
28o A MAXrAI. OF lUIYSIOI.OGY
Comparative. — In the lowest kinds of animals, such as the
Aniteba, there is neither mouth, nor alimentary canal, nor anus : the
food, wrapped round by pscudopodia, is taken in at any part of the
animal with which it happens to come in contact. A vacuole is
formed around it. .\cid is secreted into the vacuole, the food is
digested within the cell-substance, and the part of it which is useless
for nutrition is cast out again at any part of the surface.
Coming a little higher, we find in the Ccelenterates a mouth and
alimentary tube, which opens into the body-cavity, where a certain
amount of digestion seems to take place, and from which the food is
absorbed either through the cells of the endoderm, or, as in Medusa,
by means of fine canals, which radiate from the body-cavity into its
walls, and form part of the so-called gastro-vascular system. In the
Echinoderniata we have a further development, a complete alimentary
canal with mouth and anus, and entirely shut off from the body-
cavity. In many Arthropods it is possible already to distinguish
parts corresponding to the stomach, and the small and large intes-
tines of higher forms, the digestive glands being re])resented by
organs which in some groups seem to be homologous with the liver,
and in others with the salivary glands of the higher vertebrates. A
few Molluscs seem in addition to possess a pancreas.
Among Vertebrates fishes have the simplest, and birds and mam-
mals the most complicated, alimentary system. In the lowest fishes
the stomach is only indicated by a slight widening of the anterior
part of the digestive tube. In water-living \'ertebrates there are no
salivary glands. In Birds the oesophagus is generally dilated to form
a crop, from which the food passes into a stomach consisting of two
parts, one pre-eminently glandular (proventriculus), the other pre-
eminently muscular (ventriculus). Among Mammals a twofold
division of the stomach is distinctly indicated in rodents and cetacere,
but this organ reaches its greatest complexity in ruminants, which
possess no fewer than four gastric pouches- The differentiation of
the intestine into small and large intestine and rectum is more
distinct, both anatomically and functionally, in Mammals than in
lower forms ; but there are marked differences between the various
mammalian groups both in the relative size of the several parts of
the digestive tube, and in the proportion between the total length of
the alimentary canal and the length of the body. In general, the
canal is longest in herbivora, shortest in carnivora. Thus, the ratio
between length of body and length of intestine is in the cat i : 4,
dog I : 6, man i : 5 or 6, horse 1:12, cow 1 : 20, sheep 1:27. The
relative capacity of the stomach, small intestine, and large intestine,
is in the dog 6:2:1-5, in the horse i : 35 : 7, in the cow 7:2:1.
The area of the mucous surface of the alimentary canal is very con-
siderable, in the dog more than half that of the skin, the surface of
the small intestine being three times that of the stomach and four
times that of the large intestine. In the horse the mucous surface
has twice the area of the skin.
Anatomy of the Alimentary Canal in Man. — The alimentary canal
is a muscular tube, which, beginning at the mouth, runs under the
DIGESTION 281
various names of pharynx, (esophagus, stomach, small intestine, large
intestine, and rectum, till it ends at the anus. Its wails are largely
comjioscd of muscular fibres ; its lumen is clad with epithelium, and
into it open the ducts of glands, which, morphologically s|)eaking,
arc involutions or diverticula formed in its course. In virtue of its
muscular fibres it is a contractile tube : in virtue of its epithelial
lining and its special glands it is a secreting tube; in virtue of both
it is fitted to perform those mechanical and chemical actions upon
the food which are necessary for di!:^estion. Its inner surface is in
most [)arts richly supplied with bloodvessels, and in special regions
beset with peculiarly-arranged lymphatics : by both of these channels
the alimentary tube performs its function of absorption. From the
beginning of the tesophagus to the end of the rectum the muscular
7i'all consists, broadly speaking, of an outer coat of longitudinally-
arranged fibres, and a thicker inner coat of fibres running circularly
or transversely around the tube. Between the layers lies a plexus of
non-medullated nerves and nerve-cells (Auerbach's plexus). In the
stomach the longitudinal fibres are found only on the two curvatures,
and a third incomplete coat of oblique fibres makes its appearance
internal to the circular layer. In the large intestine, again, the
longitudinal fibres are chiefly collected into three isolated strands.
In the pharynx the typical arrangement is departed I'rom, inasmuch
as there is no regular longitudinal layer ; but the three constrictor
muscles represent to a certain extent the great circular coat. The
muscles of the mouth and of the pharynx are of the striped variety.
So is the muscle of the upper half of the tesophagus in man and the
cat, and of the whole cesophagus in the dog and the rabbit. In the
rest of the alimentary canal the muscle is smooth, except at the very
end, where the external sphincter of the anus is striped. In certain
situations the circular coat is developed into a regular anatomical
sphincter, a definite muscular ring, whose function it is to shut one
part of the tube off from another (sphincter pylori), or to help to
close the external opening of the tube (internal sphincter of anus).
Elsewhere a tonic contraction of a portion of the circular coat,
not anatomically developed beyond the rest, creates a functional
sphincter (cardiac sphincter of stomach).
Throughout the greater part of the digestive tract the peritoneum
forms a thin serous layer, external to the muscular coat. Internally
the muscular coat is separated from the mucous nwmbraue, the lining
of the canal, by some loose areolar tissue containing bloodvessels,
lymphatics and nerves (Meissner's plexus), and called the submticous
coat. Between the mucous and submucous layers, but belonging to
the former, in the whole canal below the beginning of the cesophagus,
is a thin coat of smooth muscular fibre, the muscularis mucosae, con-
sisting in some parts, e.g., in the stomach, of two, or even three,
layers. Between this and the lumen of the canal lie the ducts and
alveoli of glands, surrounded by bloodvessels and embedded in
adenoid or lymphoid tissue, which in particular regions is collected
into well-defined masses (solitary follicles, Beyer's patches, tonsils),
extending, it may be, into the submucous tissue. In the mouth,
282 A MANUAL OF PHYSIOLOGY
pharynx and cesophagus, the glands lie in the submucosa, as do the
glands of Brunner in the duodenum ; everywhere else they are con-
fined to the mucous membrane proper. Between the openings of the
glands the mucous membrane is lined with a single layer of columnar
epithelial cells, sometimes (in the small intestine) arranged along the
sides of tiny [)rojections or villi. At the ends of the alimentary canal,
viz., in the mouth, pharyn.x and cesophagus, and at the anus, the
epithelium is stratified squamous, and not columnar.
The purpose of food is to supply the waste of the tissues
and to maintain the normal composition of the body. In
the body we find a multitude of substances marked off from
each other, some by the sharpest chemical differences, others
by characters much less distinct, but falling upon the whole
into a few fairly definite groups. Thus, there are bodies like
serum-albumin, serum-globulin, myosin, and so on, which
are so much alike that they can all be placed in one great
class, as proteids. Then we have substances like glycogen
and dextrose, vastly simpler in their composition, and
belonging to the group of carbo-hydrates. Then, again, fats
of various kinds are widely distributed in normal animal
bodies; and iiiori^'anic materials, such as water and salts, are
never absent.
Now, although it is by no means necessar}- that a sub-
stance in the body belonging to one of these great groups
should be derived from a substance of the same group in the
food, it has been found that no diet is sufficient for man
unless it contains representatives of all ; a proper diet must
include proteids, carbo-hydrates, fats, inorganic salts and
water. These proximate principles have to be obtained
from the raw material of the food-stuffs ; it is the business
of digestion to sift them out and to prepare them for
absorption. This preparation is partly mechanical, partly
chemical.
The water and salts and some carbo-hydrates, such as
dextrose, are ready for absorption without change. Fats are,
probably, for the most part, only mechanically altered. In-
diffusible carbo-hydrates, like starch and dextrin, are changed
into diffusible sugar, and the natural proteids into diffusible
peptones. Mechanical division of the food is an important
aid to the chemical action of the digestive juices. We shall
see that this mechanical division forms a great part of the
DIG/: ST/ON 283
work of the stomacli, but it is normally l)ej,'iin in the rnouth,
and it is of consec|uence that this preliminary staple should
be properly performed.
I. The Mechanical Phenomena of Digestion.
Mastication. — It is among the manimaha that regular
mastication of the food first makes its appearance as an
important aid to digestion. The amphibian bolts its fly, the
bird its grain, and the fish its brother, without the ceremony
of chewing. In ruminating mammals we see mastication
carried to its highest point ; the teeth work all day long,
and most of them are specially adapted for grinding the
food. The carnivora spend but a short time in mastication ;
their teeth arc in general adapted rather for tearing and
cutting than for grinding. Where the diet is partly animal
and partly vegetable, as in man, the teeth are fitted for all
kinds of work ; and the process of mastication is in general
neither so long as in the purely vegetable feeders, nor so
short as in the carnivora.
In man there are two sets of teeth : the temporary or milk
teeth, and the permanent teeth. The milk-teeth are twenty
in number, and consist on each side of four incisors or
cutting-teeth, two canines or tearing-teeth, and four molars
or grinding-teeth. The central incisors emerge at the
seventh month from birth, the other incisors at the ninth
month, the canines at the eighteenth, and the molars at the
twelfth and twenty-fourth month respectively. Each tooth
in the lower jaw appears a little before the corresponding
one in the upper jaw. Each of the milk-teeth is in course
of time replaced by a permanent tooth, and in addition the
vacant portion of the gums behind the milk set is now filled
up by twelve teeth, six on each side, three above and three
below. These twelve are the permanent molars ; they raise
the number of the permanent teeth to thirty-two. The
permanent teeth which occupy the position of the milk
molars now receive the name of premolars. The first tooth
of the permanent set (the first true molar) appears at the
age of 6^ years; the last molar, or wisdom tooth, does not
emerge till the seventeenth to the twenty-fifth year.
284 A MANUAL OF PHYSIOLOGY
In mastication the lower jaw is moved up and down, so
as to alternately separate and approximate the two rows of
teeth. It has also a certain amount of movement from side
to side, and from front to back. The masseter, temporal
and internal pteryj^'oid muscles raise, and the digastric, with
the assistance of the mylo- and genio-hyoid, depresses, the
lower jaw. The external pterygoids pull it forward when
both contract, forward and to one side when only one-
contracts. The lower fibres of the temporal muscle retract
the jaw. The buccinator and orbicularis oris muscles
prevent the food from passing between the teeth and the
cheeks and lips. The tongue keeps the food in motion,
works it up with the saliva, and finally gathers it into a
bolus ready for deglutition.
' That mastication may be properly performed, the teeth must be
sound : and that they may remain sound, they should be kept clean.
For the particles of food that adhere to the teeth after a meal become
the feeding-ground of bacteria, whose acid products injuriously affect
the enamel, and often by corroding it expose the dentine. Entrance
is thus afforded to the micro-organisms of caries, which, although
they cannot live on enamel, with its small proportion of organic
matter, flourish upon dentine, and especially upon the contents of
the pulp cavity when this is at length opened. In addition to the
deformity and the loss of distinctness in speech which extensive
destruction of the teeth entails, a vast number of cases of foul
breath are entirely due to filthy and carious teeth. And since in
most countries bad breath subtracts more from the sum of human
happiness than bad laws, there is perhaps, even in this relation alone,
no single hygienic measure that costs so little and yields so much
as the thorough and systematic cleansing of the mouth. But the
proper care of the teeth is by no means of merely a.'sthetic interest ;
it is of great importance for the maintenance of health. In certain
cases of severe and even serious dyspepsia, the cause of the mischief
lies no deeper than the mouth, and the patient needs, not physic for
his stomach, but filling for his carious teeth. And although no
l)hysician at the present day can take all medicine for his province
as Bacon took all knowledge, every man who busies himself with the
treatment of alimentary diseases (and how {qw diseases are not in
some degree alimentary !) should know enough about the teeth to be
able to tell when a patient has mistaken the doctors door for the
dentist's.'
Deglutition. — This act consists of a voluntary and an in-
voluntary stage. During the former the anterior part of
the tongue is pressed against the hard palate so as to thrust
DIGESTION 285
the bolus throuf;h the isthmus of the fauces. As soon as
this has happened and the food has reached the posterior
portion of the tongue, it has passed beyond the control of the
will, and the second or involuntary sta^^e of the process begins.
This stage may be divided into two parts: (i) pharyngeal,
(2) oesophageal — both being reflex acts. During the tirst
the food has to pass through the pharynx, the upper portion
of which forms a part of the respiratory tract, and is in free
communication with the larynx during ordinary breathing.
It is therefore necessar}- that respiration should be inter-
rupted and the larynx closed while the food is being moved
through the pharynx. But that the interruption may be
short, the food must be rapidly passed over this perilous
portion of its descent. The pharynx is accordingly provided
with rapidly-contracting striped muscle ; and that none of
its purchase may be lost, the pharyngeal cavity is cut off
from the nose and mouth as soon as the bolus has entered
it. The soft palate is raised by the levator palati ; at the
same time the upper part of the pharynx, narrowed by the
contraction of the superior constrictor, comes forward to
meet the soft palate, closes in upon it, and so prevents the
food from passing into the nasal cavities. The pharynx is
cut off from the mouth by the closure of the fauces through
the contraction of the palato-pharyngeal muscles which lie
in their posterior pillars. The larynx is pulled upwards
and forwards by the contraction of the thyro-hyoid muscle,
and the elevation of the hyoid bone by the muscles which
connect it to the lower jaw. The glottis is closed by the
approximation of the vocal cords and the arytenoid car-
tilages, assisted it ma}' be by the folding down of the
epiglottis like a lid. But this organ can hardly play the great
part which has been assigned to it in closing the larynx, since
swallowing proceeds in the ordinary way when it is absent.
The morsel of food, grasped by the middle and lower con-
strictors as it leaves the back of the tongue, passes rapidly
and safely over the closed larynx, the process being accele-
rated by the pulling up of the lower portion of the pharynx
over the bolus by the action of the palato- and stylo-pharyngei.
The second or oesophageal portion of the involuntary
286 A MA.\l\\L OF PHYSIOLOCY
Stage is a more leisurely performance. The bolus is carried
along by a peculiar contraction of the muscular wall of the
cesophagus, which travels down as a wave, pushing the food
before it. When the food reaches the lower end of the
gullet the tonic contraction of that part of the tube is for
a moment relaxed, apparently by reflex inhibition, and the
morsel passes into the stomach.
Such is the view of ihe mechanism of deglutition that has hitherto
commanded the largest amount of support ; and when the food is
of such consistence and is swallowed in morsels of such size that it
actually distends the oesophagus, there is little doubt that this view
is substantially correct. On the other hand, there are reasons for
supposing that liquid or semi-solid food is shot down to the bottom
of the lax (esophagus mainly by the contraction of the mylo-hyoid
muscles, and that it is only after lying there for about six seconds
that it is forced through tiie cardiac sphincter into the stomach by
the arrival of the tardy peristaltic contraction of the fjesophageal wall
(Kronecker and Meltzer).
There are certain remarkable peculiarities which dis-
tinguish this peristaltic movement of the cesophagus from
that of other parts of the alimentary canal. It is far more
closely related to the nervous system, and, unlike the
peristaltic contraction of the intestine, can pass over any
muscular block caused by ligature, section, or crushing, so
long as the nervous connections are intact. But division
of the oesophageal nerves causes, as a rule, stoppage of
(esophageal movements ; although under certain circum-
stances an excised portion of the tube may go on contract-
ing in the characteristic way after removal from the body.
Again, the peristaltic wave when artihcially excited seems
always under normal conditions to travel do'vjn the (jesophagus,
never to spread upwards or in both directions, as may
happen in the intestine. Stimulation of the mucous mem-
brane of the pharynx will cause reflex movements of the
(esophagus, while stimulation of its own mucous membrane
is ineffective. From these facts we learn that although the
muscle of the oesophagus mav possess a feeble power of
spontaneous peristaltic contraction, yet this is usually in
abeyance, or at least overmastered b\- nervous control : so
that impulses, passing from a nerve centre and travelling
DIGESTION 287
down in regular progression along the cesophageal nerves,
excite the muscular fibres in succession from the upper to
the lower end of the tube.
The centre for the whole involuntary stage (both
pharyngeal and cesophageal) of deglutition lies in the upper
part of the medulla oblongata, a little above the respiratory
centre. When the brain is sliced away above the medulla
deglutition is not affected, but if the upper part of the
medulla is removed, the power of swallowing is abolished.
In man disease of the spinal bulb interferes far more with
deglutition than disease of the brain proper.
Normally the afferent impulses to the centre are set up by
the contact of food or saliva with the mucous membrane of
the posterior part of the tongue, the soft palate and the
fauces, the nerve-channels being the superior laryngeal, the
phar3-ngeal branches of the vagus, and the palatal branches
of the fifth nerve. A feather has sometimes been swallowed
involuntarily by a reflex movement of deglutition set up
while the soft palate or pharynx were being tickled to
produce vomiting. Artificial stimulation of the central end
of the superior laryngeal will cause the movements of degluti-
tion independently of the presence of food or liquid ; but if
the central end of the glosso-pharyngeal nerve be stimulated
at the same time, the movements do not occur. The glosso-
pharyngeal is therefore able to inhibit the deglutition centre,
and it is probably owing to the action of this nerve that in a
series of efforts at swallowing, repeated within less than a
certain short interval (about a second), only the last is
successful.
The efferent nerves of the reflex act of deglutition are the
hypoglossal to the tongue and the thyro-hyoid and other
muscles concerned in raising the larynx ; the glosso-pharyn-
geal, vagus, facial and fifth to the muscles of the palate,
fauces, and pharynx ; and the vagus to the larynx and
oesophagus. Section of the vagus interferes with the passage
of food along the oesophagus ; stimulation of its peripheral
end causes (esophageal movements.
Movements of the Stomach and Intestines. — Here the peri-
staltic movements become much more independent of the
288 A M. 1 XL -A L OF PI/ YSIOL OG } '
nervous system, and much more dependent upon the con-
tinuity of the muscular tissue than in the oesophagus. The
whole of the stomach does not take part equally in these
movements. We may divide the organ, both anatomically
and functionally, into two portions — a pyloric portion, or
antrum pylori, and a larger cardiac portion, or fundus. At
the junction of the antrum and the fundus the circular
muscular coat is thickened into a ring called the ' transverse
band,' or ' sphincter of the antrum." When the stomach is
empty it is contracted and at rest. A few minutes after
food is taken contractions begin in the antrum, and run on
in constricting undulations (in the cat at the rate of six in
the minute) towards the pyloric sphincter. Feeble at first,
they become stronger and stronger as digestion proceeds,
and gradually come to involve the portion of the fundus
next the sphincter of the antrum, but apparently their
direction is always towards the pylorus, never, in normal
digestion, away from it. The food is thus subjected to
energetic churning movements in the pyloric end of the
stomach, and worked up thoroughly with the gastric juice.
Kept in constant circulation, it gradually becomes reduced
to a semi-liquid mass, the chyme, which is at intervals driven
against the pylorus by strong and regular peristaltic con-
tractions of the lower end of the stomach, the sphincter
relaxing from time to time by a sort of reflex inhibition to
admit the better-digested portions into the duodenum, but
tightening more stubbornly at the impact of a hard and
undigested morsel. The cardiac end, with the exception of
the portion that borders the transverse band, appears to
take no share in these peristaltic movements. And, indeed,
it is far more difticult to cause such contractions by artificial
stimulation in the fundus than in the pylorus. The two
portions of the stomach seem to be partiall}-, or in certain
animals from time to time completely, cut off from each
other by the contraction of the sphincter of the antrum.
The fundus, so far as its mechanical functions are con-
cerned, appears to act chiefly as a reservoir for the food,
which it gradually passes into the antrum as digestion goes
on, by a tonic contraction of its walls. These facts have
DIGESTION 289
been mainly ascertained by observations on animals, such as
the dog and the cat, either by direct inspection after opening
the abdomen (Rossbach), or in the intact body by means of
the Rcintgen rays (Cannon), In the latter method the food
is mixed with subnitrate of bismuth, which is opaque to
these rays, so that when the animal is looked at through a
fluorescent screen the stomach appears as a dark shadow in
the field.
The peristaltic movements of the small intestine are the
most typical of their kind. Normally, the constriction
travels slowly down the tube, squeezing the contents before
it, and the wave ends at the ileo-caecal valve, which separates
the small intestine from the large. The cause of this
definite direction of the peristaltic wave is not understood,
but it is grounded in the anatomical relations of the intes-
tinal wall. For when a portion of the intestine is resected,
turned round in its place and sutured, so that what was
before its upper is now its lower end, the contraction wave
appears to be unable to pass, and the obstruction to the
onward flow of the intestinal contents causes marked dila-
tation of the gut, and sometimes serious disturbance of
nutrition. But under certain conditions a reverse or anti-
peristalsis is set up even in the intact body, and by artificial
stimulation it is easy to excite peristaltic waves which travel
in both directions. The movements of the large intestines
do not differ essentially from those of the small. They start
at the ileo-caecal valve and travel downwards, but do not
normally reach the rectum, which, except during defaecation,
remains at rest.
Influence of Nerves on the Gastro-intestinal Movements. — As
we have said, these movements are much less closely
dependent on the nervous system than are those of the
oesophagus ; they can go on when the nervous connections
are cut ; they cannot spread when the continuity of the
muscle is destroyed, and the mere presence of food will
excite them when reflex action has been excluded by section
of the nerves. Nevertheless, the nervous system does
exercise some influence in the way of regulation and control,
if not in the way of direct initiation of the movements, and
19
290 A MANUAL OF PHYSIOLOGY
the swallowing or even the smell of food has been observed
to strengthen the contractions of a loop of intestine severed
from the rest, but with its nerves still intact. The vagus is
the efferent channel of this retiex action : stimulation of its
peripheral end may cause movements of all parts of the
alimentary canal from ctsophagus to large intestine, except
apparently the cardiac end of the stomach (Meltzer), and
may strengthen movements already going on ; but section
of it does not stop them, nor hinder the food from causing
peristalsis wherever it comes. It is only the distant and
reflex action of food which division of the vagi can abolish ;
and we do not know to what extent the movements of
normal digestion are directly excited, and to what extent
they are reflex. The splanchnic nerves contain fibres by
which the intestinal movements can be inhibited, but they
are certainly not always in action, for section of these nerves
has no distinct effect upon the movements, in spite of the
vascular dilatation which it causes. On the other hand,
stimulation of the peripheral end of the cut splanchnic
usually, but by no means invariably, causes arrest of the
peristalsis. Occasionally, however, it has the opposite
effect. We have no evidence that the ganglion-cells in the
walls of the alimentary canal are either automatic or reflex
centres for its movements.
The lower part of the large intestine is influenced by the
sacral nerves (second, third and fourth sacral in the rabbit),
and by certain lumbar nerves, in the same way as the higher
parts of the alimentary canal, and particularly the small
intestine, are influenced by the vagus and the splanchnics.
Stimulation of these sacral nerves within the spinal canal
causes contraction, tonic or peristaltic, of the descending
colon and rectum; stimulation of the lumbar nerves or of
the portions of the sympathetic into which their visceral
fibres pass (lumbar sympathetic chain from second to sixth
ganglia, or the rami from it to the inferior mesenteric
ganglia) causes inhibition of the movements, preceded, it
may be, by a transient increase.
Stimulation of the sacral nerves causes or increases the
contraction of both coats of the descending colon and
DIGESTION 291
rectum ; stimulation of the lumbar nerves inhibits both.
And in the small intestine the same law holds good ; the
two coats are contracted together by the action of the
vagus, or inhibited together by that of the splanchnics
(Langley). With the establishment of these facts an in-
genious theory, originated by v. Basch and adopted by
Gaskell, falls to the ground. They supposed that the same
nerve which causes contraction of the circular coat in all
tubes whose walls are made up of two layers of muscle,
also contains fibres that bring about inhibition of the
longitudinal coat, and vice versa. It was suggested that
in this way antagonism between the two coats was pre-
vented.
Some drugs, such as strychnia, stimulate peristaltic move-
ments by acting through the central nervous system ; others,
like nicotine and muscarine, by acting directly on the intes-
tine. Atropia antagonizes the action of muscarine, and
morphia that of nicotine, in both cases by local influence ;
but after morphia the intestinal walls are steadily contracted,
not relaxed. An isolated loop of intestine, fed with properly
oxygenated blood, remains altogether, or nearly, at rest ; if
the blood is allowed to become venous, movements are set
up which much surpass the normal movements, both in their
vigour and in the speed with which they travel. For this
reason the peristaltic contractions seen on opening the
abdomen in a recently killed animal give an exaggerated
picture of what actually occurs in the intact body.
Defaecation is partly a voluntary and partly a reflex act.
But in the infant the voluntary control has not yet been
developed ; in the adult it may be lost by disease ; in an
animal it may be abolished by operation, and in each case
the action becomes wholly reflex. In the normal course of
events, the rectum, which is empty and quiescent in the
intervals of defaecation, is excited to contraction as soon as
faeces begin to enter it through the sigmoid flexure, and the
sensations caused by their presence give rise to the desire to
empty the bowels. This desire may for a time be resisted
by the will, or it may be yielded to. In the latter case the
abdominal muscles are forcibly contracted, and the glottis
19 — 2
292 A MANUAL OF PHYSIOLOGY
being closed, the whole effect of their contraction is ex-
pended in raising the pressure within the abdomen and pelvis,
and so driving the f?eces from the colon to the rectum. The
sphincter ani is now relaxed by the inhibition of a centre in
the lumbar portion of the spinal cord, through the activity
of which the tonic contraction of the sphincter is normally
maintained. This relaxation is partly voluntary, the im-
pulses that come from the brain acting probably through the
medium of the lumbar centre ; but in the dog, after section
of the cord in the dorsal region, the whole act of defaeca-
tion, including contraction of the abdominal muscles and
relaxation of the sphincter, still takes place, and here the
process must be purely reflex. The contraction of the
levatores ani helps to resist over-distension of the pelvic
floor and to pull the anus up over the faeces as they escape.
Vomiting. — We have seen that under normal conditions
the movements of the alimentary canal always tend to carry
the food in one definite direction, along the tube from the
mouth to the rectum. The peristaltic waves generally run
only in this direction, and, further, regurgitation is prevented
at three points by the cardiac and pyloric sphincters of the
stomach and the ileo-csecal valve. But in certain circum-
stances the peristalsis may be reversed, one or more of the
guarded orifices forced, and the onward stream of the
intestinal contents turned back. In obstruction of the bowel,
the facal contents of the large intestine may pass up beyond
the ileo-caical valve, and, reaching the stomach, be driven
by an act of vomiting through the cardiac orifice ; in what is
called ' a bilious attack,' the contents of the duodenum may
pass back through the pylorus and be ejected in a similar
way ; or, what is by far the most common case, the contents
of the stomach alone may be expelled.
Vomiting is usually preceded by a feeling of nausea and a
rapid secretion of saliva, which perhaps serves, by means of
the air carried down with it when swallowed, to dilate the
cardiac orifice of the stomach, but may be a mere by-play
of the reflex stimulation bringing about the act. The
diaphragm is now forced down upon the abdominal
contents, the glottis closed, and the abdominal muscles
DIGESTION 293
Strongly contracted. At the s;une time the stomach itself,
and particularly the antrum pylori, contracts, the cardiac
orifice relaxes, and the gastric contents are shot up into
the pharynx, and issue by the mouth or nose. Either
the diaphragm and abdominal muscles alone, wirHout the
stomach, or the diaphragm and stomach together, without
the abdominal muscles, can carry out the act of vomiting.
For an animal whose stomach has been replaced by a bladder
filled with water can be made to vomit by the administra-
tion of an emetic (Magcndie) ; and Hilton saw that a man
who lived fourteen years after an injury to the spinal cord
at the height of the sixth cervical nerve, which caused
complete paralysis below that level, could vomit, though
with great difficulty. In a young child, in which very slight
causes will induce vomiting, the stomach alone contracts
during the act. But in the adult such a contraction is
ineffectual, and the same appears to be the case in animals,
for a dog under the influence of a moderate dose of curara,
which paralyzes the voluntary muscles but not the stomach,
cannot vomit.
The nerve centre is in the medulla oblongata. It may be
excited by many afferent channels : irritation of the fauces
or pharynx, of the stomach or intestines (as in strangulated
hernia), of the liver or kidney (as in cases of gallstone or
renal calculi), of the uterus or ovary, and of the brain (as
in cerebral tumour), are all capable of causing vomiting by
impulses passing from them to the vomiting centre.
The vagus nerve in man certainly contains afferent fibres
by the stimulation of which this centre can be excited,
for it has been noticed that when the vagus was exposed
in the neck in the course of an operation, the patient
vomited whenever the nerve was touched (Boinet, quoted
by Gowers). In meningitis, vomiting is often a prominent
symptom, and is sometimes due to irritation of the vagus
nerve by the inflammatory process.
Some drugs act as emetics by irritating surfaces in which
efficient afferent impulses may be set up, the gastric mucous
membrane, for example ; sulphate of zinc and sulphate of
copper act mainly in this way. Apomorphia, on the other
294 A MANUAL OF PHYSIOLOGY
hand, stimulates the centre directly, and this is also the
mode in which vomiting is produced in certain diseases
of the medulla oblongata. The efferent nerves for the
diaphragm are the phrenics, for the abdominal muscles the
intercos'tals. The impulses which cause contraction of the
stomach pass along the vagi. Dilatation of the cardiac
orifice is brought about partly by the shortening of muscular
fibres, which spread out upon the stomach from the lower
end of the oesophagus, perhaps partly by nervous inhibition.
11. The Chemical Phenomena of Digestion.
The chemical changes wrought in the food as it passes
along the alimentary canal are due to the secretions of
various glands, which line its cavities, or pour their juices
into it through special ducts. These secretions owe their
power for the most part to substances present in them
in very small amount, but which, nevertheless, act with
extraordinary energy upon the various constituents of the
food, causing profound changes without being themselves
used up, or their digestive power affected. These marvellous
and as yet mysterious agents are the unformed or un-
organized ferments — unorganized because, unlike some other
ferments, such as yeast, their action does not depend upon
the growth of living cells. Their chemical nature has not
been exactly made out ; some of them at least do not appear
to be proteids. But it is doubtful whether even one of the
ferments of the digestive juices has as yet been satisfactorily
isolated, and at present it is only by their effects that we
recognise them. Some of them act best in an alkaline, some
in an acid medium; they all agree in having an 'optimum'
temperature, which is more favourable to their action than
any other ; a low temperature suspends their activity, and
boiling abolishes it for ever. The action of all of them seems
to be hydrolytic ; i.e., it is accompanied with the taking up
of the elements of water by the substance acted upon. The
accumulation of the products of the action first checks and
then arrests it.
Beside these unformed ferments, certain formed ferments,
or micro-organisms, are present in parts of the alimentary
DIGESTION 295
canal, and even in normal digestion contribute to the
changes brought about in the food ; while under abnormal
conditions they may awaken into troublesome, and even
dangerous, activity. It is possible that many of these act
by producing unorganized ferments, and that the distinction
between the two kinds of ferments is rather superficial.
It is now necessary to consider in detail the nature of
the various juices yielded by the digestive glands, and the
mechanism of their secretion, so far as it is known to us.
Since it is along the digestive tract that glandular action
is seen on the greatest scale, this discussion will practically
embrace the nature of secretion in general. And here it
may be well to say that, although in describing digestion it
is necessary to break it up into sections, a true view is only
got when we look upon it as a single, though complex,
process, one part of which fits into the other from beginning
to end. It is, indeed, the duty of the physiologist, wherever
it is possible to insert a cannula into a duct and to drain off
an unmixed secretion, to investigate the properties of each
juice upon its own basis; but it must not be forgotten that
in the body digestion is the joint result of the chemical
work of five or six secretions, the greater number of which
are actually mixed together in the alimentary canal, and of
the mechanical work of the gastro-intestinal walls.
The Chemistry of the Digestive Juices.
(i) Saliva. — The saliva of the mouth is a mixture of the
secretions of three large glands on each side, and of many
small ones. The large glands are the parotid, which opens
by Stenson's duct opposite the second upper molar tooth ;
the submaxillary, which opens by Wharton's duct under the
tongue ; and the sublingual, opening by a number of ducts
near and into Wharton's. The small glands are scattered
over the sides, fioor, and roof of the mouth, and over the
tongue.
Two types of salivary glands, the serous or alhnimnoiis and
the mucous, are distinguished by structural characters and
by the nature of their secretion ; and the distinction has
been extended to other glands. The parotid of many, if not
296 A MA NUA L OF PI I YSIOL OGY
all, mammals is a purely serous gland; it secretes a watery
juice with a general resemblance in composition to dilute
blood-serum. The submaxillary of the dog and cat is a
typical mucous gland ; its secretion is viscid, and contains
mucin. The submaxillary gland of man is a mixed gland ;
mucous and serous alveoli, and even mucous and serous cells,
are intermingled in it (Plate II., Fig. i). The submaxillary
of the rabbit is purely serous. The sublingual is in general a
mixed gland, but with far more mucous than serous alveoli.
The mixed saliva is a somewhat viscous, colourless liquid
of alkaline reaction and low specific gravity (average about
1005). Besides water and salts, it contains mucin (entirely
from the submaxillary, the sublingual and the small mucous
glands of the mouth), to which its viscidity is due, traces of
serum-albumin and serum-globulin (chiefly from the parotid),
and a ferment — ptyalin. The salts are calcium carbonate
and phosphate (often deposited as 'tartar' around the teeth,
occasionally as salivary calculi in the glands and ducts),
sodium and potassium chloride, and usually, but not always,
a trace of sulphocyanide of potassium, detected by the red
colour which it strikes with ferric chloride.* The total
solids amount only to five or six parts in the thousand. A
great deal of carbon dioxide can be pumped out from saliva,
as much as 60 to 70 c.c. from 100 c.c. of the secretion, i.e.,
more than can be obtained from venous blood. Only a
small proportion of this is in solution, the rest existing as
carbonates. A very small quantity of oxygen (about
0*5 volume per cent.) appears also to be present even in
saliva which has not come into contact with the air
(Pfluger). Under the microscope epithelial scales, leucocytes
(the so-called salivary corpuscles), bacteria, and portions of
food, may be found. All these things are as accidental as
the last — they are mere flotsam and jetsam, washed by the
saliva from the inside of the mouth. But greater significance
attaches to certain peculiar bodies, either spherical or of
irregular shape, that are seen in the viscid submaxillary
* The sulphocyanide is absent from the sahva of many animals. In
12 dogs the saliva obtained from the submaxillary gland by stimulation
of the chorda tympani only once contained a trace of it.
DIGES'IIUX 297
saliva of the dog or cat. They appear t(^ be masses of
secreted material. The quantity of saliva secreted in the
twenty-four hours varies a good deal. On an average it is
from I to 2 litres. (Practical Exercises, p. 374.)
Besides its functions of dissolving sapid substances, and
so allowing them to excite sensations of taste, of moistening
the food for deglutition and the mouth for speech, and of
cleansing the teeth after a meal, saliva, in virtue of its
ferment, ptyalin, is amylolytic ; that is, it has the power of
digesting starch and converting it into maltose, a reducing
sugar. In man the secretion of any of the three great
salivary glands has this power, although that of the parotid
is most active. In the dog, on the other hand, parotid
saliva has little action on starch, and submaxillary none at
all; while in animals like the rat and the rabbit the parotid
secretion is highly active. In the horse, sheep, and ox, the
saliva secreted by all the glands seems equally inert. A
watery or glycerine extract of a gland whose natural secre-
tion is active also possesses amylol}tic power.
Starch-grains consist of granulose enclosed in envelopes
of cellulose. Only the granulose is acted upon by ptyalin,
and hence unboiled starch, in which the cellulose envelopes
are intact, is but slowly affected by saliva. When starch is
boiled, the envelopes are ruptured, and the granulose passes
into imperfect solution, yielding an opalescent liquid. If a
little saliva be added to some boiled starch solution which
is free from sugar, and the mixture be set to digest at a
suitable temperature (say 40° C), the solution in a very short
time loses its opalescence and becomes clear. It still,
however, gives the blue reaction with iodine; and Trommer's
test (p. 23) shows that no sugar has as yet been formed.
The change is so far purely a physical one ; the substance in
solution is soluble starch. Later on the iodine reaction
passes gradually through violet into red ; and finally iodine
causes no colour change at all, while maltose is found in
large amount, along with isomaltose, a sugar having the
same formula as maltose, but differing from it in the melting
point of the crystalline compound formed by it with phenyl
hydrazine (p. 426). Traces of dextrose, a sugar which rotates
298 A MANUAL OF PHYSIOLOGY
the plane of polarization less than maltose, but has j2^reater
reducing power, are produced by the further action of the
saliva on maltose itself. When a small quantity of ferment
acts for a short time, the production of isomaltose is
favoured. The production of maltose and dextrose is
favoured by the action of a large quantity of ferment for a
long time (Kiilz and Vogel).
The red colour indicates the presence of a kind of dextrin
called erythrodextrin ; the violet colour shows that at first
this is still mixed with some unchanged starch. Soon the
erythrodextrin disappears, and is succeeded by another
dextrin, which gives no colour with iodine, and is therefore
called achroodextrin. This is partly, but in artificial
digestion never completely, converted into maltose, and can
always at the end be precipitated in greater or less amount
by the addition of alcohol to the liquid. It is probable that
a whole series of dextrins is formed during the digestion of
starch. Some of these may appear as forerunners of the
sugar, others merely as concomitants of its production. The
latter may never pass into sugar; and it is certain that sugar
may appear before all the starch has been converted into
achroodextrin. When the sugar is removed as it is formed,
as is approximately the case when the digestion is performed
in a dialyser, the residue of unchanged dextrin is less than
when the sugar is allowed to accumulate (Lea). In ordinary
artificial digestion, for instance, under the most favourable
circumstances at least 12 to 15 per cent, of the starch is left
as dextrin ; in dialyser digestions the residue of dextrin may
be little more than 4 per cent. This goes far to explain the
complete digestion of starch which apparently takes place in
the alimentary canal, a digestion so complete that, although
soluble starch and dextrin may be found in the stomach
after a starchy meal, they do not occur in the intestine, or
only in minute traces. Here the amylolytic ferment of the
pancreatic juice, which, as we shall see, is essentially the
same in its action as ptyalin, only more powerful, must be
able to effect a very complete conversion.
DIGESTION 299
It is impossible with our present knowledge to represent the entire
process by a chemical ecjuation. If we look only to the final product,
the equation
{c,n,,o.x + - H,o = 'i(c,,H,,o„)
2 2
Starch. Water. Maltose.
or
2(QHioO,)„ + «H,0 = fl!Ci.,Ho.,Oi,
will represent the change in natural and complete digestion. The
molecule of starch being taken as some unknown multiple, a, of the
group C^HjyO-,, the first equation suits the case of a being an even
number, and the second that of a being an odd number.
If we accept 4 per cent, as the minimum residue of unchanged
dextrin in the best artificial digestion, or, in other words, if we suppose
that of 25 parts of starch 24 are changed into maltose, and i remains
as dextrin, our equation, taking the dextrin molecule as a multiple l>
of C,,Hi,0„ will be :
Starch. Water. Maltose. Dextrin.
for the case where 7- is a whole number. If - is not a whole
0 b
number, we should have to clear of fractions by multiplying both
sides by — , where m is the greatest common measure of a and b.
m
We should thus get :
Starch. Water. Maltose. Dextrin.
It is a notable fact that amylolytic ferments are not
confined to the animal body. Diastase, which is present in
all sprouting seeds, and may be readily extracted by water
from malt, forms maltose and dextrin from starch. Its
optimum temperature, however, is about 65° C, while that
of ptyalin is about 40° C.
Salivary digestion goes on best in a neutral or slightly
alkaline medium. It can, however, still proceed when the
medium is made faintly acid ; but an acidity equal to that
of a 'I per cent, solution of hydrochloric acid stops it
completely, although the ferment is still for a time able to
act when the acidity is sufficiently reduced. Strong acids
or alkalies permanently destroy it. These facts are of con-
sequence, for they show that in the mouth, where the
reaction is alkaline, the conditions are favourable to salivary
joo A MANUAL OF PHYSIOLOGY
digestion ; while in the stomach, where, as we shall see, it
is acid durinj^ the greater part of digestion, the conditions
are not so favourable, but may be, on the contrary, inimical.
Although the food stays but a short time in the mouth,
there is no doubt that, in man at least, some of the starch
is there changed into sugar (p. 375). But this does not seem
to be the case in all animals. Something depends on the
amylolytic activity of the saliva, and something upon the
form in which the starchy food is taken, whether it is cooked
or raw, enclosed in vegetable fibres or exposed to free
admixture with the secretions of the mouth.
It is important to note here that hydrolytic changes of
very much the same nature as those produced by ptyalin
can be brought about in other ways. If starch is heated for
a time with dilute hydrochloric or sulphuric acid, it is
changed first into dextrin, and then into a form of reducing
sugar, which, however, is not maltose, but dextrose. If
maltose is treated with acid in the same way, it is also
changed into dextrose. When glycogen (p. 439) is boiled
with dilute oxalic acid at a pressure of three atmospheres,
isomaltose and dextrose are formed (Cremer). We shall see
later on that the action of other ferments can also be to a
certain extent imitated by purely artificial means. In fact,
some of the ferments accomplish at a comparatively low
temperature what can be done in the laboratory at a higher
temperature, and by the aid of what we may call more
violent methods.
(2) Gastric Juice.— The Abbe Spallanzani, although not,
perhaps, the first to recognise, was the first to study system-
atically, the chemical powers of the gastric juice, but it was
by the careful and convincing experiments of Beaumont
that the foundation of our exact knowledge of its composi-
tion and action was laid.
It is difficult to speak without enthusiasm of the work of Beaumont,
if we consider the difficulties under which it was carried on. hx\
army surgeon stationed in a lonely post in the wilderness that was
then called the territory of Michigan, a thousand miles from a
University, and four thousand from anything like a physiological
laboratory, he was accidentally called upon to treat a gun-shot
wound of the stomach in a Canadian voyageur, Alexis St. Martin.
DIGESTION 301
When the wound healed a permanent fistulous opening was left, by
means of which food could be introduced into the stomach and
gastric juice obtained from it. Beaumont at once perceived the
possibilities of such a case for physiological research, and began a
series of exi)eriments on digestion. .After a while, St. Martin, with
the wandering spirit of the voyageur, returned to Canada without
Dr. Beaumont's consent and in his absence. l>eaumont traced him,
with great difficulty, by the help of the agents of a fur-trading
company, induced him to come back, provided for his family as well
as for himself, and proceeded with his investigations. A second
time St. Martin went back to his native country, and a second
time the zealous investigator of the gastric juice, at heavy expense,
secured his return. And although his experiments were necessarily
less exact than would be permissible in a modern research, the
modest book in which he published his results is still counted
among the classics of physiology. The production of artificial
fistulie in animals, a method that has since proved so fruitful, was first
suggested by his work.
Gastric juice when obtained pure, as it can be from an
accidental fistula in man, or by mechanically stimulating the
mucous membrane of the stomach of a fasting dog through
an artificial gastric fistula, is a thin, colourless liquid of low
specific gravity (1002 to 1005) and distinctly acid reaction.
The total solids average about 5 parts per thousand, about
one half being inorganic salts, chiefly sodium and potassium
chloride. Two ferments are present : pepsin, which changes
proteids into peptones ; and rennin, which curdles milk.
The acidity is due to free hydrochloric acid, the proportion
of which in man is usually something like '2 per cent., but
more in the dog ('3 to "5 per cent.). It is said that in
cancer of the stomach the free hydrochloric acid is replaced
by lactic acid, and it is known that in health some lactic
acid is often present when the stomach contains food, being
produced from the carbo-hydrates by the action of a ferment
or ferments, not specific to gastric juice, but found every-
where in the alimentary canal. That in normal gastric
juice the acidity is not due to lactic acid can be shown by
Uffelmann's test (Practical Exercises, p. 378).
More than this, it is not due to an organic, but to an
inorganic acid, for healthy gastric juice causes such an
alteration in the colour of aniline dyes like congo-red and
methyl violet, as would be produced by dilute mineral acids,
and not by organic acids, even when present in much greater
.1 MANUAL OF PHYSIOLOGY
Strength. lMnall\-, when the bases and acid radicals of the
juice are quantitatively compared, it is found that there
is more chlorine than is required to combine with the
bases ; the excess must be present as free hydrochloric acid.
The quantity of gastric juice secreted is very great ; it has
been estimated at as much as 5 to 10 litres in twenty-four
hours, or five times as much as the quantity of saliva
secreted in the same time. But such estimates are loose
and uncertain.
The great action of gastric juice is upon proteids. In this
two of its constituents have a share, the pepsin and the free
acid. One member of this chemical copartnery cannot act
without the other; peptic digestion requires the presence
both of pepsin and of acid ; and, indeed, an active artificial
juice can be obtained by digesting the gastric mucous
membrane with -2 per cent, hydrochloric acid. A glycerine
extract of a stomach which is not too fresh also possesses
peptic powers ; but it requires the addition of a sufficient
quantity of acid to render them available.
Well-washed fibrin obtained from blood is a convenient
proteid for use in experiments on digestion. Since the
blood contains traces of pepsin, the fibrin should be boiled
to destroy any which may be present.
If we place a little fibrin in a beaker, cover it with '2 per
cent, hydrochloric acid, add a small quantity of pepsin or
of a gastric extract, and put the beaker in a water-bath
at 40° C, the fibrin soon swells up and becomes translucent,
then begins to be dissolved, and in a short time has dis-
appeared (see Practical Exercises, p. J77).
If we examine the liquid before digestion has proceeded
very far, we shall find chiefly acid-albumin in solution ;
later on, chiefly albumoses ; and still later, chiefly peptones.
From this we conclude that acid-albumin is a stage in the
conversion of fibrin into albumose, and albumose a half-way
house between acid-albumin and peptone.
Similar, but not identical, intermediate substances occur in the
digestion of the other proteids, as well as in that of bodies like
gelatin, which are not true proteids, but which pepsin can digest.
The generic name of proteose properly includes all bodies of the
albumose type, the term ' albumose ' itself being sometimes reserved
DIGESTION 303
for such intermediate products of the digestion of albumin ; while
those of fibrin are called fibrinoses ; of globulin, globuloses ; of
casein, caseoses ; and so on. Probably the peptones produced from
different proteids are also not absolutely identical.
Beyond peptone gastric dijE^estion does not go. Indeed,
in no case does the whole of the original proteid, in an
artificial digestion, ever reach the stage of peptone ; although
the pancreatic juice, as we shall see later on, can split up
peptone itself into substances which are no longer proteid.
Since the subject of proteid digestion must come up again,
it will be well to postpone any closer discussion of the
process till we can view it as a whole. In the meantime it
is only necessary to repeat that pepsin alone cannot digest
proteids at all. Its action requires the presence of an acid ;
in a neutral or alkaline medium peptic digestion stops. As
in the case of other ferments, there is a certain temperature
at which pepsin acts best, an 'optimum' temperature
(35° to 40^ C, or about that of the body). At 0° C. it is
inactive, except in cold-blooded animals (frog). Boiling
destroys it.
Dilute acid alone does not dissolve coagulated proteids
like boiled fibrin, or does so only with extreme slowness.
Uncoagulated proteids, however, are readily changed by it
into acid-albumin ; and by the prolonged action of acids,
especially at a high temperature, further changes may be
caused in all proteids, apparently of much the same nature
as those produced in peptic digestion. But under the
ordinary conditions of natural or artificial gastric digestion,
it may be said that the acid alone does little until it is aided
by the ferment, just as the ferment alone does nothing
without the aid of the acid. One striking difference, how-
ever, there is : the acid is used up during the process ; the
ferment is little, if at all, affected. Although hydrochloric
acid acts most powerfully, other acids, such as lactic, phos-
phoric, or sulphuric, can replace it.
The milk-curdling ferment, rennin, is contained in large
amount in an extract of the fourth stomach of the calf,
which has long been used in the manufacture of cheese.
It exists in the healthy gastric juice of man, but disappears
in cancer of the stomach and in chronic gastric catarrh.
304 ./ MAXCAL OF PIIYSrOLOCY
It can be separated from pepsin by precipitating an acid
extract of calf's stomach with magnesium carbonate in
powder, and some neutral acetate of lead. The pepsin is
mechanically carried down with the precipitate, but most of
the rennin remains in solution. The curdling of milk by
rennin is essentially a coagulation of casein. It seems to
be produced by the splitting up of a more complex body,
cascinogen, into two substances, one of which, casein, is
insoluble (in the presence of calcium phosphate, but not
otherwise), and forms the curd ; while the other, ivhcy-
proteid, is soluble, and passes into the whey. Dilute acid
will of itself precipitate casein, and the presence of acid,
and particularly hydrochloric acid, in the gastric juice helps
the action of the milk-curdling ferment. That a ferment is
really concerned in the process is, however, shown by the
fact that the juice, after being made neutral or alkaline, still
curdles milk, and that this power is destroyed by boiling.
The optimum temperature is the same as that of the other
ferments of the digestive tract, about 40° C. (p. 377).
As to the exact function which the milk-curdling ferment
of the gastric juice performs in digestion, we have no precise
knowledge. It seems superfluous if we suppose that the
free acid is able of itself to do all that the ferment does
along with it. But there is evidence that the curd pro-
duced by the ferment is more profoundly changed than the
precipitate caused by dilute acids ; for the latter may be
redissolved, and then again curdled by rennin, while this
cannot be done with the former. We may suppose, then,
that the ferment is capable of effecting changes more
favourable to the subsequent action of the pepsin upon the
casein than those which the acid alone would effect. Or it
may be that the ferment acts in the early stages of digestion
before much acid has been secreted. We do not know
whether the curdling of milk renders it easier for the
watery portion to be absorbed by the walls of the stomach.
If this were the case, it would be a raison d'etre for early
curdling, since milk is a very dilute food, and the immense
proportion of water in it might weaken the gastric juice too
much for rapid digestion of the proteids.
DIGESTION 305
On fats and carbo-hydrates gastric juice has no action,
although it will dissolve the proteid constituents of fat-cells,
and the proteid substances which keep the fat-globules of
milk apart from each other ; while swallowed saliva will
continue to act on starch in the stomach, so long as the
acidity is not too great. Healthy gastric juice has no
action on cane-sugar, but when there is much mucus
present, it seems to contain a ferment which changes this
sugar into dextrose, or into a mixture of dextrose and
levulose (' invert ' sugar).
(3) Pancreatic Juice. — Pancreatic juice, bile, and intestinal
juice, of which the first two only are important, are all
mingled together in the small intestine, and act upon the
food, not in succession, but simultaneously. But by artificial
fistulae in animals they can all be obtained separately ; and
occasionally some of them can be procured through accidental
fistula:; in the human subject.
Pancreatic juice, as obtained from a dog, by means of a
cannula tied in the duct of Wirsung through an opening in
the linea alba, is a clear, viscid liquid of distinctly alkaline
reaction. It differs notably from saliva and gastric juice in
its high specific gravity (about 1030), and the large pro-
portion of solids in it, which may be as much as 10 per
cent., or, roughly speaking, about the same as in blood-
plasma. About nine-tenths of the solids consist of proteids,
and rather less than one-tenth of inorganic material (chiefly
sodium carbonate, to which the alkaline reaction is due, and
sodium chloride). Traces of fats, soaps and leucin may
also be present. When the juice is heated to near the
boiling-point, a copious precipitate of coagulated albumin is
formed. The fresh juice coagulates spontaneously, especially
at a low temperature ; but the coagulum is soon digested.
Possibh' cold hinders the destructive power of the juice on
the factors necessary for coagulation more than it restrains
the process of clotting. The quantity of pancreatic juice
secreted during the twenty-four hours in an average man
has been estimated at 200 to 300 c.c. An artificial pan-
creatic juice can be made by extracting the pancreas, which
must not be too fresh (p. 378), with water or glycerine.
20
3o6 A MANUAL O/P/IYSIOLOlSY
Pancreatic juice contains four ferments : (i) A proteolytic
or proteid-digesting ferment, trypsin ; (2) an amylolytic fer-
ment, amylopsin ; (3) a fat-splitting or lipolytic ferment,
stcapsi)!, also called pialyn ; (4) a milk-curdling ferment.
The last cannot be considered as taking any practical
share in digestion, since it can hardly ever happen that
milk passes through the stomach without being curdled.
Trypsin, to a certain extent, corresponds with pepsin in its
action on proteids. But it has two remarkable peculiarities:
it acts energetically in an alkaline as well as in a not too
acid medium (a very slight amount of digestion may go on
in distilled water) ; and its action does not stop at the
peptone stage — it can split up peptones into leucin, tyrosin
and aspartic acid, crystalline nitrogenous substances very
different from proteids.
If hbrin is digested at a temperature of 40 C. with a i per
cent, solution of sodium carbonate, to which a little
pancreatic extract or juice has been added, along with a
trace of thymol to prevent putrefaction, it is gradually eaten
away without swelling up and becoming transparent as it
does in peptic digestion ; but some granular debris is always
left (p. 379). This undigested residue is soluble in i per
cent, sodium hydrate, but it is never entirely dissolved in
any artificial digestion. In natural digestion, on the
contrary, it is never found ; just as some dextrin always
remains when ptyalin has done its utmost upon starch
outside the body, while in the intestine little or no dextrin
can be detected. When the undigested residue is filtered
off, the solution may still contain : (i) a substance or
substances having resemblances both to alkali-albumin and
to globulin, (2) albumoses, (3) peptone, (4) leucin and
tyrosin. It will depend on how far the digestion has been
carried whether, and in what quantity, any one of these
bodies is present.
The order in which they appear and their relative amount
at different stages of the digestion show that the alkali-
albumin and albumoses are, like the acid-albumin and
albumoses of peptic digestion, mainly, at any rate, inter-
mediate substances through which proteid passes on its
DIGEST/ Oi\ 307
way to peptone; and there is no reason to believe that up to
this point there are any essential differences between the
action of trypsin and pepsin. In both cases the action
seems to consist in a splitting up of the complex protcid
with assumption of water, so that each successive product
is further hydrated than the last ; nor is it, as yet at least,
possible to point out any radical distinction between
the peptone of gastric and the peptone of pancreatic
digestion. It is not necessary to suppose that the further
splitting up of some of the peptone by trypsin into leucin
and tyrosin is an action differing in kind so much as in
degree from that which leads to the formation of peptone
both in tryptic and in gastric digestion. Trypsin is in
almost all respects a more powerful ferment than pepsin ;
it can do most things which pepsin can do, and a few
things which pepsin cannot do ; but it can do nothing
which is not right in the line of peptic digestion. Thus, a
pancreatic digest almost always contains less albumose than
a peptic digest ; more of the albumose is carried on to the
further stage of peptone by the more powerful ferment ; but
we ascribe this not to a peculiar property, but to a more
energetic action on the common lines. And when this
action suffices to push the peptone still farther along the
downward path, it is not necessary to assume that an
influence radically different from that of pepsin is at work.
This argument is strengthened when we find that without a
ferment at all, by the prolonged action of various agents
which cause hydration, such as dilute acids or alkalies, or
superheated steam, or oxidizing substances like ozone, albu-
moses and peptones first, and ultimately leucin and tyrosin,
may be formed from ordinary proteids. In fact, it would
seem that when the complex proteid molecule is split up by
proteolytic ferments, or by other and not too violent agents,
there are certain favourite ' sets ' or combinations into which
its constituents are apt to fall, no matter how the decom-
position may be brought about, bodies of the fatty and of
the aromatic series being especially constant and con-
spicuous among the products. Leucin, for instance, is
amido-caproic acid, in which amidogen (NH^) has replaced
20 — 2
3o8 A MANUAL OF PHYSIOLOGY
one atom of hydrogen in the fatty acid, and tyrosin is an
amidated aromatic acid (p. 379)- So we may perhaps con-
sider the proteid molecule as partly built up out of fatty
acid and aromatic groups united with amidogen.
As much as 8 to 10 per cent, of leucin, and 2 to 4 i)er cent, of
tyrosin, may be produced in artificial tryptic digestion of fibrin (Lea,
Kiihne), but only a portion (about the half) of the peptones formed
ever undergoes this change, no matter how long the digestion may be
continued.
This and other facts have led to the theory that every natural
proteid consists of two elements as regards the products into which
it may be split by digestion — a hemi element and an cviti element.
Thus, albumin is supposed to consist of hemi-albumin and anti-
albumin. When digested by trypsin, the hemi-albumin gives rise
eventually to hemi-peptone, and the anti-albumin to anti-pei)tone.
The hemi-peptone is comparatively unstable, and is further split up
into leucin and tyrosin ; the anti-peptone is comparatively stable,
and resists further change.
As to the method in which the ferments bring about these pro-
found changes, and the role played by the auxiliary acid or alkali,
we are almost completely in the dark. ^Vurtz has supposed that
papain, a ferment obtained from the juice of the fruit of the Carica
papaya, which acts powerfully on proteids in much the same way as
trypsin, unites temporarily with the proteid — with fibrin, for instance
— and after the hydration of the latter is comjilete, is again set at
liberty, and free to act on some more of the unchanged fibrin. He
compares its action with that of some inorganic bodies, such as
sulphuric acid, a small quantity of whicli may cause the hydration of
a large amount of certain substances by forming temporary com-
pounds with them, and being then set free to act again. In peptic
digestion, however, the hydrochloric acid seems certainly to be used
up. In the gastric juice it is perhaps united to the pepsin ; and it is
capable of forming combinations with all proteids, the lower proteids,
such as peptone, combining with a greater proi^ortion of the acid
than the higher, such as fibrin or albumin.
In all that we have hitherto said regarding tryptic diges-
tion we have supposed that putrefaction has been entirely
prevented. If no antiseptic is added to a tryptic digest, it
rapidly becomes filled with micro-organisms, and emits a
very disagreeable fa-cal odour ; and now various bodies
which are not found in the absence of putrefaction make
their appearance, such as indol, skatol, and other sub-
stances to which the fa;cal odour is due. They are not true
products of tryptic digestion, but are formed by the putre-
factive micro-organisms, which can themselves break up
/)/<;/■: ST/OX
309
proteids into Icucin and tyrosin, ;ind readily change tyrosin
into indol.
Ainylopsiii, the sugar-forming ferment of pancreatic juice,
changes starch into dextrin and maltose, just as ptyalin
does; but it is more powerful, and readily acts on raw
starch as well as boiled.
Sicapsiji splits up neutral fats into glycerine and the
corresponding fatty acids. The latter unite with the alkalies
of the pancreatic juice and the bile to form soaps, which
aid in the emulsification of fats. In this important process,
so essential to digestion, bile acts as the helpmate of pan-
creatic juice ; together they effect much more than either or
both can accomplish by separate action.
(4) Bile. — Bile is a liquid the colour of which varies greatly
in different groups of animals, and even in the same species
is not constant, depending on the length of time the bile
has remained in the gall-bladder and other circuTistances.
When it is recognised that the colour depends on a series of
pigments, which are by no means stable, and of which one
can be caused to pass into another by oxidation or reduction,
this want of uniformity will be easily intelligible. The fresh
bile of carnivora is golden red ; the bile of herbivorous
animals is in general of a green tint, but, when it has been
retained long in the gall-bladder, may incline to reddish-
brown. Human bile is generally described as being of a
reddish or golden-yellow colour, but it is doubtful whether
this is true of the perfectly fresh secretion, for bile flowing
from a fistula has been observed to be green (Robson,
Copeman and Winston). That of a monkey taken from the
gall-bladder immediately after death is dark green, but if
left a few hours in the gall-bladder it is brown, the green
pigment having been reduced. This would seem to indicate
that human bile, originally green, may alter its colour in the
interval which must elapse before it can usually be obtained
after death. Bile, as obtained from accidental fistuke in
otherwise healthy persons, has a much lower specific gravity
than pancreatic juice (1008 to loog). The composition of
human bile is approximately as follows :
3IO A MANUAL OF PHYSIOLOGY
Water
Solids :
982 parts in 1,000
Mucin and pij^ments
Bile-salts
Lecithin and soaps
Cholesterin
Inorganic salts -
- r5\
- 7-5
- I r>8
It will be observed that no proteids are enumerated in
this table ; bile contains none, and it is unlike all the other
digestive juices in this respect.
Mucin is scarcely to be looked upon as an essential constituent of
bile ; it is not formed by the actual bile-secreting cells, but by
mucous glands in the walls and goblet-cells in the epithelial lining
of the larger bile-ducts, and especially of the gall-bladder. The
mucin of human bile is a true mucin, but that of ox-bile is a nucleo-
albumin (p. 17). Although bile (or at least free bile-acids) has in
itself considerable antiseptic power, the mucin causes it rapidly to
putrefy. It may be removed by preci])itation with alcohol or dilute
acetic acid.
Bile-pigments. — It has been said that these form a series, but
only two of the pigments of that series appear to be present in
normal bile, bilirubin and biliverdin. In human bile as usually
obtained, the former, in herbivorous bile and that of some cold-
blooded animals, such as the frog, the latter, is the chief pigment.
But in fresh human bile biliverdin may be chiefly present, and
bilirubin can be extracted in large amount from the gallstones of
cattle ; while in the placenta of the bitch biliverdin is present in
quantity, although, as in all carnivora, it is either absent from the
bile or exists in it in comparatively small amount. All these facts
show that the two pigments are readily interchangeable.
Bilmibin is best obtained from powdered red gallstones by dis-
solving the chalk with hydrochloric acid, and extracting the residue
with chloroform, which takes up the pigment. From this solution,
on evaporation, beautiful rhombic tables or prisms of bilirubin
separate out ; and the crystals are finer when the solution also con-
tains cholesterin than when it is pure.
Biliverdi7i can be obtained from the placenta of the bitch by
extraction with alcohol. It is insoluble in chloroform, and by means
of this i)ro[)erty it may be separated from bilirubin when the two
hapiten to be present together in bile. Biliverdin can also be formed
from bilirubin by oxidation. By the aid of active oxidizing agents,
such as yellow nitric acid (which contains some nitrous acid), a
whole series of oxidation products of bilirubin is obtained, beginning
with biliverdin, and passing through bilicyanin, a blue pigment, to
choletelin, a yellow substance. It is ])ossible that there are other
intermediate bodies. This is the foundation of Gmelin's test for biU-
pigiiients (see Practical Exercises, j). 380).
The positive pole of a galvanic current causes the same oxidative
changes, the same play of colours, while the reducing action of the
DIGESTION 311
negative pole reverses the effect, if the action of the positive electrode
has not gone too far. Starting from biliverdin, the negative pole
causes the green to pass through yellowish-green into golden-yellow,
and ultimately into jjale yellow, indicating a series of bodies formed
by reduction of the biliverdin. i'hese reactions can also be used for
the detection of bile-pigments.
By the reducing action of sodium amalgam, or of tin and hydro-
chloric acid, on bilirubin, but not apparently by electrolysis, hydro-
bilirubin is obtained. This is identical with the ' febrile ' urobilin
of some pathological urines, and with stercobilin, a pigment found
in the fi\;ces from birth onwards, although not in the meconium
(pp. 358, 389), and therefore probably derived from the normal bile-
pigment by reduction in the intestine itself, where reducing sub-
stances due to the action of micro-organisms are never absent in
extra-uterine life. The changes occurring in oxidation and reduction
of the bile-pigment may be partially represented as follows :
(C32H36N4O0) + O., = (C3.,H3,N A)> + 2O., = (C,,H3,N,0,.,) ;
Bilirubin. I'lliverdin. Choletelin.
2(C.,3H3,N,0,,) - 0.3 + 4H0O = 2(C32H3,3N A-.2HoO).
Biliiuliin. Hydrobilirubin.
Judging from the analogy of the blood-pigment — from which, as
we shall see, the bile-pigment is derived, and the changes in which,
through oxidation and reduction, have a certain superficial resem-
blance to those which bilirubin undergoes when it- is converted into
biliverdin, and which biliverdin undergoes when it passes back again
to bilirubin — we might have expected bile to possess a characteristic
spectrum.
This, however, is not the case. The bile of most animals shows no
bands at all. The fresh bile of certain animals, the ox, for instance,
does show bands — a strong one over C, and two weaker bands, one
of which is just to the left of D, and the other to the right of it, but
nearer D than E. The two last bands grow stronger when the bile
is allowed to stand for twenty-four hours, and in about three days,
in warm weather, a fourth sharp band may appear between C and B.
But none of these bands are due to the normal bile-pigment, and
they are not essentially changed when this is oxidized or reduced by
electrolysis. MacMunn attributes the spectrum of the bile of the ox
and sheep to a body which he calls choloha^matin, and which does
not belong to the bile-pigments proper. Of the derivatives of the
bilirubin set, only the lowest and the highest members, hydro-
bilirubin and choletelin, are described as giving absorption spectra.
The Bile-salts. — These are the sodium salts of two acids, glyco-
cholic and taurocholic. In human bile both are present, but the
former in greater quantity than the latter. In the bile of the dog
and cat only taurocholic acid is found ; in that of the carnivora
generally it is by far the more important of the two acids ; in the
bile of herbivora there is much more glycocholic than taurocholic
acid.
Both acids are made up of a non-nitrogenous body, cholic or
312 A MANUAL OF PHYSIOLOGY
cholalic acid, and a nitrogenous body, glycin in glycocholic, and
taurin in taurocholic acid.
The decomposition of the bile-acids into these substances is
effected by boiling them with dilute acid or alkali, a molecule of
water being taken up ; thus —
Co«H,3NO, + H,0 = CoH.NO, + C,,H,oO, ;
Glycocholic acid. Glyciii. Cholic acid.
C.fiH,,NSO; + H,,0 = C.H-NSOs + Co.H^oO,.
Taurocholic acid. Taurin. Cholic acid.
Taurocholic acid is much more easily broken up than glycocholic ;
even boiling with water is sufficient.
Glycin is amido-acetic acid, taurin is amido-isethionic acid, an
atom of the hydrogen of the acid being in each case replaced by
NHo. A notable difference between glycocholic and taurocholic
acid is that the latter contains sulphur. The whole of this belongs
to the taurin.
Traces of cholic acid, probably formed by the action of putre-
factive products on the bile-salts, are found in the intestines,
especially in the lower portion.
Pettefiko/er' s test /or bile-acids (Practical Exercises, p. 380), acci-
tjentally discovered in examining the action of bile upon sugar,
depends upon three facts: (1) That cholic acid and furfurol give a
purple colour when brought together ; (2) that the bile-salts yield
cholic acid when acted upon by sulphuric acid ; (3) that when cane-
sugar is decomposed by strong sulphuric acid, furfurol is formed.
Since a similar colour is given when the same reagents are added
to a solution containing albumin, it is necessary to remove this, if
present, from any liquid which is to be tested for bile-acids.
Lecithifi and cholcsteriii are by no means peculiar to bile. They
are found in almost all the liquids of the body, and are especially
important constituents of the nervous substance. The former is a
crystallizable fat of a peculiar nature, containing nitrogen and
phosphorus. It is unstable, and when heated with baryta-water it
yields a soap, barium stearate, which is i)recipitated, and two other
substances, choline and glycero-phosphoric acid, which remain in
solution.
Cholesterin is a triatomic alcohol. It is best obtained from white
gallstones, of which it is the chief, and sometimes almost the sole,
constituent (see Practical Exercises, p. 380).
The chief inorganic salt of bile is sodium chloride. The phos-
phoric acid of the ash comes partly from the phosphorus of organic
compounds (lecithin and bile-mucin), the sulphuric acid from the
sulphur of taurocholic acid, the sodium largely from the bile-salts.
Iron is a notable inorganic constituent of bile, although it exists only
in traces, in the form of phosphate of iron. Manganese is also
present. 100 c.c. of fresh bile yields 50 to 100 c.c. of carbon dioxide,
part of which is in solution and part combined with alkalies.
DIGESTION 313
The quantity of bile secreted in twenty-four hours in an
average man is probably from 750 c.c. to a litre.
The great action of the bile in digestion is undoubtedly
the preparation of the fats for absorption, either in the form
of a mechanical suspension or emulsion, or in solution as
soaps ; and this it accomplishes, not by itself, but in conjunc-
tion with the pancreatic juice.
No completely satisfactory explanation has been given of
the precise nature of this partnership, but it is certain that
the fat-splitting ferment of the pancreatic juice, on the one
hand, and the bile-salts on the other, contribute largely to
the total action. An alkaline solution, a solution of sodium
carbonate, e.g., is unable of itself to emulsify a perfectly
neutral oil ; but if some free fatty acid be added, emulsifica-
tion is rapid and complete. Now, there is no doubt that
here a soap is formed by the action of the alkali on the fatty
acid, and there is equally little doubt that the formation of
the soap is an essential part of the emulsification. But it is
not clear in what manner the soap acts, whether by form-
ing a coating round the oil-globules, or by so altering the
surface tension, or other properties of the solution in which
it is dissolved, that they no longer tend to run together.
However this may be, in pancreatic juice we have the two
factors present which this simple experiment shows to be
necessary and sufficient for emulsification ; we have a
ferment which can split up neutral fats and set free fatty
acids, and an alkali which can combine with those acids to
form soaps. Accordingly, pancreatic juice is able of itselr
to form emulsions with perfectly neutral oils. It is possible
that the proteid constituents of pancreatic juice, and par-
ticularly a substance resembling alkali-albumin, may have a
share in emulsification. In bile, on the contrary, although
the alkali is present, there is no fat-splitting ferment, and
according to the best experiments, bile alone has no emulsi-
fying power. But we now come to a remarkable fact : this
inert bile when added to pancreatic juice greatly intensifies
its emulsifying action, and a solution of bile-salts has much
the same effect as bile itself. The fact is undoubted, but
the explanation is obscure. What it is that bile or bile-salts
314 A MANUAL OF PHYSIOLOGY
can add to the pancreatic juice which so increases its power
of emulsification, we do not know. It is indeed true that
the bile, in virtue of its alkahne salts, can, in presence of a
free fatty acid, rapidly form an emulsion. But the pan-
creatic juice itself contains a considerable quantity of sodium
carbonate.
A part of the effect of the bile seems to be due to its
favouring in some way the fat-splitting action of the pan-
creatic juice. The capacity of dissolving soaps, which is a
property of the bile-salts, would undoubtedly be important
if it were definitely proved that this is the form in which
the chief part of the fat is absorbed, as some have held.
It would also be important on the emulsion theory of fat
absorption if it could be shown that the comparatively small
emulsifying power of pancreatic juice by itself is due to its
want of solvent power for the soaps which it forms, and espe-
cially if it were shown that soaps such as the alkaline stear-
ates produced in the digestion of ordinar}- fatty food, which
are soluble in water, were much less soluble in the pancreatic
secretion. However the mutual action of the two juices on
the digestion of fats may be explained, there is no doubt
that they are equally necessary. For in some diseases of
the pancreas fat often appears in the stools, and this token
of imperfect digestion of the fatt}' food may be confirmed by
the wasting of the patient ; and the same occurs when the
bile is prevented by obstruction of the duct or by a biliary
fistula from entering the intestine. The white stools of
jaundice owe their colour, not merely to the absence of
bile-pigment, but also to the presence of fat. In suckling
children it is not uncommon to see the faeces white with
fat. This is a less serious symptom than in adults, and
perhaps betokens merely that the milk in the feeding-bottle
is undiluted cow's milk, which is richer in fat than human
milk, and ought to be mixed with an equal quantity of water.
Bidder and Schmidt found that the chyle in the thoracic
duct of a normal dog contained y i per cent, of fat. In a
dog with the bile-duct ligatured the proportion fell to o"2
per cent.
Bile has been credited with a physical power of aiding the
DIGESTION 315
passage of fat through membranes, and it has been inferred
that this has an important bearing on the absorption of fat
from the intestine. But the inference does not follow from
the statement, and the statement has been itself denied.
On proteids bile has no digestive action. The addition
of it to a gastric digest causes a precipitate of acid-albumin
(parapeptone), albumose, and pepsin. The precipitate is
soluble in excess of bile, or of a solution of bile-salts, but the
pepsin has no longer any power of digesting proteids. Part
of the bile-acids is also thrown down by the acid of the
digest.
It has been vaguely, and almost helplessly suggested, in the
laudable endeavour to find functions for the bile, that by neutralizing
the chyme bile prepares it for the action of the pancreatic juice.
But since the contents of the small intestine are acid throughout the
whole of digestion, it is evident that the excess of bile required to
neutralize the chyme and redissolve the precipitated proteids does
not actually exist. And it is difficult to see in what way the preci-
pitation of a substance can prepare the way for its digestion. The
whole discussion is, indeed, an illustration of the hazard that is run
in transferring without great care the results of digestion in vitro to
the normal and natural processes in the alimentary canal.
Although bile has sometimes a feebly amylolytic action, this is
not to be included among its specific powers, for a diastatic ferment
in small quantities is widely diffused in the body.
Succus Entericus. — This is the name given to the special
secretion of the small intestine, which is supposed to be a
product of the Lieberkiihn's crypts and of Brunner's glands.
In order to obtain it pure, it is of course necessary to prevent
admixture with the bile, the pancreatic juice, and the food.
This is done by dividing a loop of intestine from the rest by
two transverse cuts, the abdomen having been opened in the
linea alba. The continuity of the digestive tube is restored
by stitching the portion below the isolated loop to the part
above it ; one end of the loop is sutured to the lips of the
wound in the linea alba, and the other being ligatured, the
whole forms a sort of test-tube opening externally (Thiry's
fistula). Or both ends are made to open through the
abdominal wound (Vella's fistula). Another method is to
make a single opening in the intestine, and by means of two
indiarubber balls, one of which is pushed down, and the
3i6 A MANUAL OF PHYSIOLOGY
other up through the opening, and which are afterwards
inflated, to block off a piece of the gut from communication
with the rest. The intestinal juice so obtained is a thin
yellowish liquid of alkaline reaction. Its specific gravity is
about loio. It contains a small amount of proteids, and
about the same proportion of inorganic salts as most of the
liquids and solids of the body, namely, 7 or "8 per cent.;
but its composition seems to be far from constant. It has
been credited with various digestive powers ; in fact, accord-
ing to one or two enthusiastic observers, it would almost
seem to sum up in itself the actions of all the other diges-
tive juices, and to possess besides a peculiar activity of its
own. But we need not hesitate to say that in the work of
digestion it plays at most a very subordinate part. The
sodium carbonate, in which it is exceedingly rich, may
form soaps with fatty acids produced by the action of the
pancreatic juice or of the fat-splitting bacteria in which the
intestine abounds, and may thus aid in the emulsification
of fats. That a great deal of fat may be split up in the
alimentary canal in the absence both of bile and pancreatic
juice is well ascertained. The alkali of the succus entericus
will at the same time check the growing acidity of the in-
testinal contents. A ferment called invertin — which is not
introduced with the food or formed by bacterial action as
has been suggested, since it occurs in the aseptic intestine
of the new-born child — changes cane-sugar into a mixture
of dextrose and levulose, both reducing sugars, but rotating
the plane of polarization in opposite directions, as indicated
by their names ; some maltose may be changed into dex-
trose. But here the catalogue of the powers of the succus
entericus ceases ; on proteids and starch it has little or no
action.
Having now finished our review of the chemistry of the
digestive juices, our next task is to describe what is known
as to their secretion — the nature of the cells by which it is
effected and their histological appearance in activity and
repose, and the manner in which it is called forth and
controlled.
DIGESTION 7,\7
III. The Secretion of the Digestive Juices.
The dij:,'estive glands are formed originally from involu-
tions of the mucous membrane of the alimentary canal, the
salivary glands from the epiblast, the others from the hypo-
blast (Chap. XIV.). Some are simple unbranched tubes, in
which there is either no distinction into body and duct, as
in Lieberkiihn's crypts in the intestines, or in which one or
more of the tubes open into a duct, as in the glands of the
cardiac end of the stomach. Some are branched tubes,
several of which may end in a common duct ; such are the
glands of the pyloric end of the stomach, and the Brunner's
glands in the duodenum. In others the main duct ramifies
into a more or less complex system of small channels, into
each of the ultimate branches of which one or more (usually
several) of the secreting tubules or alveoli open. The
salivary glands and the pancreas belong to this class of
compound tubular or racemose glands, and so does the liver
of such animals as the frog. But in the latter organ the
typical arrangement is obscured in the higher vertebrates by
the predominance of the portal bloodvessels over the system
of bile-channels as a groundwork for the grouping of the cells.
In every secreting gland there is a vascular plexus outside
the cells of the gland -tubes, and a system of collecting
channels on their inner surface ; and in a certain sense the
cells of every gland are arranged wdth reference to the blood-
vessels on the one hand, and the ducts on the other. But
in the ordinary racemose glands the blood-supply is mainly
required to feed the secretion ; the cells of the alveoli have
either no other function than to secrete, or if they have other
functions, they are not such as to entail a great disproportion
between the size of the cells and the lumen of the channels
into which they pour their products. For both reasons the
relation of the grouping of the cells to the duct-system is
very obvious, to the blood-system very obscure. In the liver
the conditions are precisely reversed. We cannot suppose
that the manufacture of a quantity of bile less in volume
than the secretion of the salivary glands, though doubtless
containing far more solids, requires an immense organ like
3l8 A MAXTAL OF I'l/YSIOLOUY
the liver, and a tide of blood like that which passes through
the portal vein. And, as we shall see, the liver has other
functions, some of them certainly of at least equal im-
portance with the secretion of bile, and one of them
evidently requiring from its very nature a bulky organ.
Accordingly, both the richness of the blood-supply and the
size of the secreting cells are out of proportion to the calibre
of the ultimate channels that carry the secretion away.
The so-called bile-capillaries, which represent the lumen of
the secreting tubules, are mere grooves in the surface of
adjoining cells ; and the architectural lines on which the
liver lobule is built are : (i) the interlobular veins which carry
blood to it ; (2) the rich capillary network which separates
its cells and feeds them ; (3) the central intra-lobular vein
which drains it. Thus a network of cells lying in the meshes
of a network of blood-capillaries takes the place of a regular
dendritic arrangement of ducts and tubules ; and in accord-
ance with this the bile - capillaries, instead of opening
separately into the ducts, form a plexus with each other
within the hepatic lobule.
The ducts and secreting tubules of all glands are lined by
cells of columnar epithelial type, but the type is most closely
preserved in the ducts. In none of the digestive glands is
there more than a single complete layer of secreting cells.
But the alveoli of the mucous salivary glands show here and
there a crescent-shaped group of small deeply-staining cells
(crescents of Gianuzzi) outside the columnar layer (Plate II.,
I, 3), and between it and the basement membrane, while
the gland-tubes of the cardiac end of the stomach have in
the same situation a discontinuous layer of large ovoid cells,
termed parietal from their position, oxyntic (or acid-secreting)
from their supposed function (Fig. 104). The serous salivary
glands, the pancreas, the pyloric glands of the stomach, the
Lieberkiihn's crypts, have but a single layer of epithelium ;
and since there is no hepatic cell which is not in contact
with at least one bile-capillary, the liver may be regarded as
having no more. Remarkable histological changes, evidently
connected with changes in functional activity, have been
noticed in most of the digestive glands. In discussing these,
DIGESTION
319
it will be best to omit for the present any detailed reference
to the liver, since, althou^^^h there arc histological marks of
secretive activit\- in this gland as well as in others, and of
the same general character, they are accompanied, and to
some extent overlaid, by the microscopic evidences of other
functions (p. 440). The serous salivary glands and the
pancreas can be taken together ; so can the cardiac and
pyloric glands of the stomach ; the mucous salivary glands
must be considered separately.
Changes in the Pancreas and Parotid during Secretion. — The
cells of the alveoli of the pancreas or parotid during rest, as
can be seen by examining thin lobules of the former between
Fig. 103. — Serous Glands in 'Loaded' and 'Discharged' State.
A, rabbit's pancreas, ' loaded' (resting) ; A', ' discharged' (active), observed in the
living animal (Kiihne and Lea). B, loaded, B', discharged, alveolus of parotid (fresh
preparations), (Langley).
the folds of the mesentery in the living rabbit, or fresh
teased preparations of the latter, are filled with fine granules
to such an extent as to obscure the nucleus. In the parotid
the whole cell is granular, in the pancreas there is still a
narrow clear zone at the outer edge of the cell which
contains few granules or none ; in both, the divisions
between the cells are very indistinct, and the lumen of the
alveolus cannot be made out. During activity the granules
seem to be carried from the outer portion of the cell towards
the lumen, and there discharged ; the clear outer zone of
the pancreatic cell grows broader and broader at the
expense of the inner granular zone, until at last the latter
may in its turn be reduced to a narrow contour line around
320 A MANUAL OF PHYSIOLOGY
the lumen. In the uniformly clouded parotid cell a similar
change takes place; a transparent outer zone arises ; and,
after prolonged secretion, only a thin edging of granules
may remain at the inner portion of the cell. In both glands
the outlines of the cells become more clearly indicated, and
a distinct lumen can be now recognised. The cells are
smaller than they are during rest, and in the pancreas they
stain more readily with carmine and other protoplasmic
dyes, the outer zone always staining more deeply than the
inner, as is the case with the same zone even in the resting
pancreatic cell (Plate II., 2).
When the glands are hardened with alcohol, or most of the
ordinary hardening reagents, the appearances in the serous salivary
cells differ from those described, for the granules, unlike those ot
the pancreatic cells, are altered by the treatment, and the two zones
in the discharged gland are not distinguishable by any difference in
the depth of the carmine stain. But in the rabbit's parotid after the
scanty secretion caused by prolonged stimulation of the sympathetic
the whole cell stains more deeply than the loaded cell. Its protoplasm
is turbid with fine and uniformly diffused granules ; its nucleus is
large and spherical, and contains well-marked nucleoli, in contrast
to the pale and transparent protoplasm and the small shrivelled
nucleus of the resting cell, in which nucleoli are indistinct or invisible.
Now, carmine being a protoplasmic dye, it is fair to conclude that
depth of stain is proportional to amount of protoplasm [^resent. The
deeper stain of the outer rim of the pancreatic cell during rest indicates
that here the protoplasm predominates over the dead and unstained
products of its activity, which are accumulated in the remainder
of the cell. The increase of the deeply-staining zone during secretion
shows that these products are being moved towards the lumen of the
alveolus, and that the relative amount of protoplasm in the outer
zone is being increased, although the absolute size of the cell may be
diminished. The deejjer stain of the parotid cell after sympathetic
stimulation, as well as the changes in the nucleus, indicate regenera-
tion of protoplasm as much as elimination of non-protoplasmic
elements. For in the dog changes similar to those in the rabbit are
caused, although the amount of secretion on stimulation of the
sympathetic is very small, and generally only sufficient to block the
ducts without appearing externally. The disappearance of granules
from without inwards during activity suggests that these are manu-
factured products eliminated in the secretion.
Changes in the Glands of the Stomach during Secretion. — The
mucous membrane of the stomach is covered with a single layer of
columnar efjithelium, largely consisting of mucigenous goblet-cells.
It is studded with minute pits, into which open the ducts of the
peptic and pyloric glands, the ducts being lined with cells just like
DIGESTION
321
those of the general gastric surface. The peptic or cardiac glands
have short ducts, into each of which open one to three gland-tubes
seldom branched. The ducts of the pyloric glands are longer, and
the secreting tubules, which also open by twos or threes into the
ducts, are branched. The secreting parts of both kinds of glands are
lined by short columnar, finely granular cells ; and in the pyloric
tubules no others are present. But, as we have said, in the peptic
Fig. 104.— The Gastric Glands.— On the left cardiac, right pyloric (Ebstein).
glands there are besides large ovoid cells scattered at intervals like
beads between the basement membrane and the lining or chief cells.
The histological changes connected with secretion do not
differ essentially from those described in the pancreas and
the parotid, but there is much greater difficulty in making
observations on the living, or at least but slightly altered,
cells. During digestion the granules seem to disappear from
21
322 A MA NUA L OF PI I } 'SIOL OGY
the outer part of the chief cells of the peptic glands,
leaving a clear zone, the lumen being bordered by a granular
layer. Or, more rarely, there may be a uniform decrease in
the number of granules throughout the cell. The ovoid
cells swell up, so as to bulge out the membrana propria, but
no definite changes in their contents, such as those observed
in the other cells, have been made out.
Changes in Mucous Glands during Secretion. — In the mucous
salivarj' and other mucous glands similar, but apparently
more complex, changes occur. During rest the cells which
line the lumen may be seen in fresh, teased preparations to
be filled with granules or * spherules.' After active secretion
there is a great diminution in the number of the granules.
Those that remain are chiefly collected around the lumen,
although some may also be seen in the peripheral portion of
the cell ; and there is no very distinct differentiation into
two zones. That a discharge of material takes place from
these cells is shown by their smaller size in the active gland.
That the material thus discharged is not protoplasmic is
indicated by the behaviour of the cells to protoplasmic stains
such as carmine. The resting cells around the lumen stain
but feebly, in contrast to the deep stain of the demilunes,
while the discharged cells take on the carmine stain much
more readily. Further, when a resting gland is treated
with various reagents (water, dilute acids, or alkalies), the
granules swell up into a transparent substance apparently
identical with mucin, which appears to fill the meshes of a
fine protoplasmic network (Fig. 105).
In ordinary alcohol-carmine preparations only the network and
nucleus are stained ; the nucleus, small and shrivelled, is situated close
to the outer border of the cell. When a discharged gland is treated
in the same way there is proportionally more ' protoplasm ' and less
of the clear material, what remains of the latter being chiefly in the
inner portion of the cell, while the nucleus is now large and spherical,
and not so near the basement membrane (Plate II., i and 3).
Everything, therefore, points to the granules in what we
may now call the mucin-forming cells as being in some way
or other precursors of the fully-formed mucin; manufactured
during ' rest ' by the protoplasm and partly at its expense^
D/GCSTION
323
moved towards the lumen in activity, discharged as mucin
in the secretion. It has been asserted that not only is the
protoplasm lessened in the loaded cell and renewed after
activity, but that many of the mucigenous cells may be
altogether broken down and discharged, their place being
supplied by proliferation of the small cells of the demilunes.
This conclusion, however, is not supported by sufficient
evidence. But the fact on which we would specially insist
is that the granules of the resting mucigenous cell may be
looked upon as a mother-substance from which the mucin
of the secretion is derived ; they are not actual, but potential,
mucin.
So in the pancreas, the serous or albuminous salivar}'
Fig. 105.— Mucous Cells (from Submaxillary of Dog) in Rest
AND Activity (Langley).
A, B, fresh ; A', B', after treatment with dilute acetic acid ; A", B", alveoli
hardened in alcohol and stained with carmine. A, A' and A" represent the loaded ;
B, B' and B", the discharged condition.
glands, and the glands of the stomach, there is every reason
to believe that the granules which appear in the intervals of
rest, and are moved towards the lumen and discharged
during activity, are the precursors, the mother-substances, of
important constituents of the secretion. These granules are
sharply marked off from the protoplasm in which they lie
and by which they are built up. By every mark, by their
reaction to stains, for instance, they are non-living sub-
stance, formed in the bosom of the living cell from the raw
material which it culls from the blood, or, what is more
likely, formed from its own protoplasm, then shed out in
granular form and secluded from further change. The
21 — 2
324 A .VAX UAL OF PHYSIOLOGY
proteolytic power of an extract of the pancreas, or the
gastric mucous membrane, seems to be, roughly speaking,
in proportion to the quantity of granules present in the cells.
Therefore it is concluded that the granules are related in
some way to trypsin and pepsin.
But we should greatly deceive ourselves if we supposed
that granules of this nature in gland-cells are necessarily
related to the production of ferments. The mucigenous
granules have no such significance. Most digestive secre-
tions contain proteid constituents, with which the granules
may have to do, as well as with ferments. And bile, a
secretion which contains no mucin, no proteids, and no
ferments, as essential constituents, is formed in cells with
granules so disposed and so affected by the activity of the
gland as to suggest some relation between them and the
process of secretion. In the liver -cells of the frog, in
addition to glycogen and oil-globules, small granules may
be seen, especially near the lumen of the gland tubules ;
they diminish in number during digestion, when the secre-
tion of bile is active, and increase when food is withheld
and secretion slow. And in Brunner's glands, as well as in
the pyloric glands, many of the granules, as seen in fasting
dogs (Savas), appear to be of fatty nature. It is possible
that these represent the fat which is known to be excreted
into the alimentary canal (pp. 371, 374, 447).
The granules in the ferment - forming glands are not
composed of the actual ferments, and, indeed, the actual
ferments are present in the secreting cells only in small
amount, if at all, as is shown by the following facts :
A glycerine extract of a fresh pancreas has hardly any
effect on proteids ; a similar extract of a stale pancreas is
very active. Therefore the fresh pancreas is devoid of
trypsin. But it contains a substance which can readily
be changed into tripsin ; and this substance is soluble in
glycerine, for the inert extract becomes active when it is
treated with dilute acetic acid, or even when it is diluted
with water and kept at the body-temperature. If the fresh
pancreas be first treated with dilute acetic acid, and then
with glycerine, the extract is at once active. All this goes
DIGESTION 325
to show that in the fresh pancreas not trypsin, but a mother-
substance, which has been named trypsinopfen, is present,
and that the latter yields trypsin, gradually when the pan-
creas is simply allowed to stand, more rapidly when the
dilute acid is used. The natural secretion of the gland is
active when the gland-cells contain no ferment, therefore
during secretion the trypsinogen must be changed into
trypsin.
Similarly, a glycerine extract of a fresh gastric mucous
membrane is inert as regards proteids, or nearly so. But
if the mucous membrane has been previously treated with
dilute hydrochloric acid, the glycerine extract is active, as is
an extract made with acidulated glycerine. Here we must
assume the existence in the gastric glands of a mother-
substance, pepsinogen, from which pepsin is formed. Only
the chief cells of the cardiac, and the similar if not identical
cells of the pyloric glands, are believed to manufacture the
pepsin-forming substance. The ovoid cells of the former
are supposed to secrete the hydrochloric acid. The evidence
on which this belief is based is as follows :
The pyloric glands, in which in most situations no ovoid
cells are to be seen, secrete pepsin, but no acid. The
pyloric portion of the stomach has been isolated, the con-
tinuity of the alimentary canal restored by sutures, and the
secretion of the pyloric pocket collected. It was found to
be alkaline, and contained pepsin. The glands of the frog's
cesophagus, which contain only chief cells, secrete pepsin,
but no acid. It seems fair to conclude that the chief cells
of the cardiac glands in the mammal secrete none of the
free hydrochloric acid, but certainly some of pepsin. But it
does not follow that all the pepsin is formed by these cells,
although it would seem that all the hydrochloric acid must
be secreted by the only other glandular elements present,
the ovoid or ' border ' cells. And, indeed, the glands in
the fundus of the frog's stomach, which are composed only
of ovoid cells, while secreting much acid, also form some
pepsin, although far less than the oesophageal glands.
Attempts made to demonstrate an acid reaction in the border cells
have hitherto failed, perhaps because the acid is poured into the
326 A MANUAL OF PHYSIOLOGY
ducts as fast as it is formed. But it should be mentioned that some
observers deny that the acid is secreted in the depths of any cell
from the chlorides of the blood, and believe that it is formed at the
surface of contact of the stomach-wall with the gastric contents from
the sodium chloride of the food by an exchange of sodium ions (p. 362)
for hydrogen ions from the blood or lymph. It is in favour of this
view that when, instead of sodium chloride, sodium bromide is given
in the food, the hydrochloric acid in the stomach is to a large extent
replaced by hydrobromic acid. This is not due to the decomposi-
tion of the bromide by hydrochloric acid, for it occurs in animals
deprived for a considerable time of salts, and in ' salt-hunger ' the
stomach contains no acid (Koeppe). There are, however, certain
weighty theoretical objections to this hypothesis.
The rennet ferment, according to Langley, is formed in
the chief cells, and has a precursor or zymogen Hke the
others.
A glycerine or watery extract of the salivary glands always
contains active amylolytic ferment, if the natural secretion
is active. So that if ptyalin is preceded by a zymogen
in the cells, it must be very easily changed into the actual
ferment.
The Quantitative Estimation of Ferment Action. — Since we have
as yet no certain method of freeing ferments from imjiurities, our only
quantitative test is their digestive activity. And since a very small
quantity of ferment can act upon an indefinite amount of material
if allowed sufficient time, we can only make comparisons when the
time of digestion and all other conditions are the same. If we find
that a given quantity of one gastric extract, acting on a given weight
of fibrin, dissolves it in half the time required by an equal amount
o( another gastric extract, or dissolves twice as much of it in a given
time, we conclude that the digestive activity of the pepsin is twice
as great in the first extract as in the second, or, as it is sometimes
more loosely put, that the one contains twice as much pepsin as the
other. A convenient method of estimating the rate at which the
fibrin disappears is to use tibrin stained with carmine. As solution
goes on, the dye colours the liciuid more and more deeply, and by
comparing the depth of colour at any time with standard solutions
of carmine, the quantity of the dye set free, and therefore of the fibrin
digested, can be approximately arrived at. This method cannot be
used for trypsin. As a test of the activity of a diastatic ferment, we
take the amount of sugar formed in a given time in a given quantity
of a standard starch solution.
We have spoken more than once of the gland-cells as
wanufacturing their secretions. It is an idea that rises
DIGESTION 327
naturally in the mind as we follow with the microscope the
traces of their functional activity. And when we compare
the composition of the digestive juices with that of the
blood-plasma and lymph, the suggestion that the glands
which produce them are not merely passive filters, but
living laboratories, acquires additional strength. It is
evident that everything in the secretion must, in some form
or other, exist in the blood which comes to the gland, and
in the lymph which bathes its cells. No glandular cell, if
we except the leucocytes, which in some respects are to be
considered as unicellular glands, dips directly into the blood ;
everything a gland-cell receives must pass through the walls
of the bloodvessels into the lymph. And since lymph is
practically diluted blood-plasma, anything which we find in
the secretion and do not find in the blood must have been
elaborated by the gland from raw material brought to it by
the latter.
Take, for example, the saliva or gastric juice. These liquids both
coutain certain things that also exist in the blood, but in addition
they contain certain things specific to themselves : mucin in saliva,
hydrochloric acid in gastric juice, ferments in both. It is. true that a
trace of pepsin and trace of a diastatic ferment may be discovered
in blood ; but there is no reason whatever to believe that this is the
source of the pepsin, of the gastric juice,
or the ptyalin of the salivary glands. On
the contrary, it is possible that the fer-
ments of the blood may be in part
absorbed from the digestive glands, the
rest being formed by the leucocytes and
liberated when they break down. The
liver affords an even better example of
this ' manufacturing ' activity of gland-
cells, and many facts may be brought
forward to prove that the characteristic Fig. 106.— H.^matoidin.
constituents of the bile, the bile-pigments
and bile-acids, are formed in the liver, and not merely separated
from the blood. Bile-pigment has indeed been recognised in the
normal serum of the horse, and bile-acids in the chyle of the dog,
but only in such minute traces as are easily accounted for by absorp-
tion from the intestine. Frogs live for some time after excision of
the liver, but no bile-acids are found in the blood or tissues. But if
the bile-duct be ligatured, bile-acids and pigments accumulate in the
body, being absorbed by the lymphatics of the liver, as was shown
by Ludwig and Fleischl in the dog. If the thoracic duct and the
bile-duct are both ligatured, no bile-acids or pigments appear in the
32« A MANUAL OF PHYSIOLOGY
blood or tissues. In mammals life cannot be maintained for any
length of time after ligature of the portal vein, since this throws
the whole intestinal tract out of gear. But after an artificial
communication has been made between the portal and the left
renal vein or the inferior cava, the portal may be tied and the
animal live for months (Eck). The liver can now be completely
removed, but death follows in a few hours. In birds there exists
a communicating branch between the portal vein and a vein (the
renal-portal) which passes from the posterior portion of the body
to the kidney, and there breaks up into capillaries ; and not only
may the portal be tied, but the liver may be completely destroyed
without immediately killing the animal. In the hours of life that
still remain to it no accumulation of biliary substances takes place
in the blood or tissues. A further indication that bile-pigment is
produced in the liver is the fact that the liver contains iron in relative
abundance in its cells (p. 381), and eliminates small (juantities of iron
in its secretion. Now bile-pigment, which contains no iron, is
certainly formed from blood-pigment, which is rich in iron, for
hsematoidin (Fig. 106), a crystalline derivative of haemoglobin found
in old extravasations of blood, especially in the brain, is identical with
bilirubin. The seat of formation of bile-pigment must therefore be
an organ peculiarly rich in iron. The existence of haematoidin,
however, shows that bile-pigment may, under certain conditions, be
formed outside of the hepatic cells. The occurrence of biliverdin
in the placenta of the bitch points in the same direction. But the
pathological evidence in favour of the pre-formation of the biliary
constituents tends rather to shrink than to increase. For many cases
of what used to be considered ' idiopathic ' or ' haematogenic '
jaundice, i.e., an accumulation of bile-pigments and bile-acids in the
tissues, due to defective elimination by the liver, are now known to
be caused by obstruction of the bile-ducts and consecjuent re-absorp-
tion of bile (' obstructive ' or ' hepatogenic ' jaundice).
But if substances such as the ferments, mucin, hydrochloric
acid, the bile-salts and bile-pigments, are undoubtedly manu-
factured in the gland-cells, it is different with the water and
inorganic salts which form so large a part of every secre-
tion. No tissue lacks them ; no physiological process goes
on without them ; they are not high and special products.
As we breathe nitrogen which we do not need because it is
mixed with the oxygen we require, the secreting cell passes
through its substance water and salts as a sort of by-play or
adjunct to its specific work. But this is not the whole truth.
The gland-cell is not a mere filter through which water and
salts pass in the same proportions as they exist in the liquids
from which the cell draws them. The secretions of different
DIGESTION 329
glands differ in the nature, and especially in the relative
proportions, of their inorj:,'anic constituents ; and the secre-
tion of one and the same gland is by no means constant in
this respect, as we shall have to note more especially when
we come to deal with the influence of the nervous system on
secretion (p. 338).
The proteid substances, such as serum-albumin and
globulin, common to blood and to some of the digestive
secretions, take a middle place between the constituents
that are undoubtedly manufactured in the cell and those
which seem by a less special and laborious, though a
selective, process to be passed through it from the blood.
Their absence from bile, and, as we shall see, from urine,
their abundance in pancreatic and scantiness in gastric
juice, point to a closer dependence upon the special activity
of the gland-cell than we can suppose necessary in the case
of the salts.
x\lthough it is in the cells of the digestive glands that the
power of forming ferments is most conspicuous, it is by no
means confined to them. It seems to be a primitive, a
native power of protoplasm. Lowly animals, like the
amoeba, lowly plants, like bacteria, form ferments within the
single cell which serves for all the purposes of their life.
The ferment - secreting gland-cells of higher forms are
perhaps only lop-sided amoebae, not so much endowed with
new properties as disproportionately developed in one
direction. The contractility has been lost or lessened, the
digestive power has been retained or increased ; just as in
muscle the power of contraction has been developed, and
that of digestion has fallen behind. The muscle-cell and the
cartilage-cell are parasites, if we look to the function of
digestion alone. They live on food already more or less
prepared by the labours of other cells ; and it is a universal
law that in the measure in which a power becomes useless it
disappears. But the presence of pepsin in the white blood-
corpuscles, the parasites as well as the scavengers of the
blood, and of amylolytic ferments in many tissues, should
warn us not to conclude that the power of forming ferments
belongs exclusively to any class of cells. And it is possible
330 A MANUAL OF PHYSIOLOGY
that food-substances absorbed from the blood are further
elaborated by ferment action within the tissues themselves ;
while many facts show that the power of contraction is
widely diffused among structures whose special function is
very different, and a few point to its possession in some
degree even by glandular epithelium. On the other hand,
it must be remembered that none of the digestive glands
absorb food directly from the alimentary canal to be then
digested within their own cell-substance ; the ferments
which they form do their work outside of them ; their cells
feed also upon the blood.
Why are the Tissues of Digestion not affected by the Digestive
Ferments? — This is the place to mention a point which has
been very much debated, though never satisfactorily ex-
plained : Why is it that the stomach or the small intestine
does not digest itself? This is really a part of a wider
question : Why is it that living tissues resist all kinds of
influences, which attack dead tissues with success ? The
living leucocyte destroys bacteria by which the dead
leucocyte is broken up ; it kills and digests them by sub-
stances formed within itself, but its own living protoplasm
is not digested. Or if the battle goes the other way, the
bacteria kill the leucocyte, and break it up, perhaps, by the
aid of ferments of their own manufacture which affect it but
not them. The amoeba digests food in its cell-substance,
but does not digest itself. The pancreatic cell produces
ferments which ruin it soon after death, but are perfectly
harmless during life. The pancreatic juice acts with great
intensity upon proteids, but the living pancreas and the
living intestinal wall are immune to it. When we ascribe
these things to the resistance of living tissues, we play with
words. And we have to inquire whether this is a general
resistance of all living tissues, or a specific resistance of
certain tissues to certain influences; whether all living
tissues, or only the gastric and intestinal walls, are shielded
from the attack of the digestive ferments; and if all living
tissues are protected, whether they are protected against all
ferments, or only against those produced by themselves or
by the organism of which they form a part, against com-
DIGESTION
331
paratively inactive ferments, or equally against the most
powerful.
That all living tissues cannot withstand the action of the
gastric juice has been shown by putting the leg of a living
frog inside the stomach of a dog ; the leg is gradually eaten
away (Bernard). It is scarcely to the point to say that it
has first been killed and then digested, for the question is,
why the stomach-wall is not first killed and then digested ?
When the wall has been injured by caustics or by an em-
bolus, the gastric juice acts on it. But the living epithelium
that covers it is able to resist the action of the acid and
pepsin, which destroy the tissues of the frog's leg. The
alkalinity of the blood has nothing to do with the explana-
tion, for the frog's blood is also alkaline, and the cells that
line the pancreatic ducts are preserved from the pancreatic
juice, which is intensely active in an alkaline medium. In
the gland-cells of the pancreas the protoplasm is, no doubt,
shielded from digestion by the existence of the ferment in
an inert form as zymogen ; and it is possible that this is the
reason, or at least one of the reasons, for the existence of
the mother-substance. But this is not the whole explana-
tion, for the living frog's leg is not harmed by a weakly
alkaline pancreatic extract, which does not digest the epi-
thelium, because it cannot kill it. A certain amount of
protection may be afforded to the walls of the stomach by
the thin layer of mucus which covers the whole cavity, for
mucin is not affected by peptic digestion. And a mucous
secretion seems in some other cases to act as a protective
■covering to the walls of hollow viscera, whose contents are
such as w^ould certainly be harmful to more delicate mem-
branes, e.g., in the urinary bladder, large intestine, and gall-
bladder. Still, however important such a mechanical pro-
tection may be, it does not explain the whole matter, and it
is necessary to suppose that the gastric epithelium has
some special power of resisting the gastric juice, possibly by
turning any of the ferment which may invade it into an
inert substance like the zymogen, or by opposing its entrance
as the epithelium of the bladder opposes the absorption of
«rea. That each membrane becomes accustomed, and, so
332 A MANUAL OF PHYSIOLOGY
to speak, * immune,' to the secretion normally in contact
with it is certain ; but this is not a general, but a special,
vital action.
What living tissues but the lining of the urinary tract or
of the large intestine could bear the constant contact of
urine or faeces ? When urine is extravasated under the skin
or the contents of the alimentary canal burst into the peri-
toneal cavity, they are still in contact with a living surface,
but with a surface much less fitted to resist them than that
by which they are normally enclosed ; and the consequences
are often disastrous. Leucocytes thrive in the blood, but
perish in urine ; blood does not harm the living cells of the
vessels, but kills a muscle whose cross-section is dipped into
it. The defensive, or rather in some cases offensive, liquids
secreted by many animals are harmless to the tissues which
produce and enclose them : a caterpillar investigated by
Poulton secretes a liquid so rich in formic acid, that the
mere contact of it would kill most cells. The so-called
saliva of Octopus macropiis contains a substance fatal to the
crabs and other animals on which it preys. The blood of
the viper contains an active principle similar to that secreted
by its poison-glands, but its tissues are not affected by this
substance, so deadly to other animals.
The Influence of the Nervous System on the Digestive Glands.
The greater part of our knowledge of this subject has been
gained by the study of the salivary glands, and especially
the submaxillary and sublingual, which lie superficially and
are easily exposed.
(i) The Influence of Nerves on the Salivary Glands. — All the
salivary glands have a double nerve - supply, from the
medulla oblongata through some of the cranial nerves, and
from the spinal cord through the cervical sympathetic
(Fig. 107).
In the dog the chorda tympani branch of the facial nerve carries
the cranial supply of the sublingual and submaxillary glands. It
joins the lingual branch of the fifth nerve, runs in company with it
for a little way, and then, breaking off, after giving some fibres to the
lingual, passes, as the chorda tympani proper, along Wharton's duct
to the submaxillary gland. In the hilus of this gland most of its-
DIGESTION
333
fibres become connected with nerve-cells and lose their medulla in
them, a few having lost it before entering the hiliis, and a few doing
so deeper in the gland. The lingual, the chorda tympani proper,
and Wharton's duct form the sides of what is called the chordo-
lingual triangle. Within this triangle are situated many ganglion
cells, a special accumulation of which has received the name of the
submaxillary ganglion. This, however, should rather be called the
sublingual ganglion, since its cells, as well as the others in the
chordo-lingual triangle, are the cells of origin of neurons (p. 639),
which proceed as non-medullated fibres to the sublingual gland.
The sublingual gland receives its cerebral fibres partly from
branches given off from the lingual in the chordo-lingual triangle
after the chorda tympani proper has separated from it, and joining
the nerve-cells within that triangle, partly from the chorda itself in
the terminal portion of its course. These statements rest on
SM and SL, submaxillary
and sublingual glands ; P,
parotid; V, fifch nerve ; VII,
facial ; GP, glosso-pharyn-
geal ; L, lingual; CT,
chorda tympani ; CL,
chordo-lingual ; D, submax-
illary (Wharton's) duct ; C,
ganglion cell of so-called
submaxillary ganglion in
the chordo-lingual triangle,
connected with a nerve fibre
going to sublingual gland ;
C", ganglion cell in hilus of
submaxillary gland ; SSP,
small superficial petrosal
branch of the facial ; OG,otic
ganglion; JN, Jacobson's
nerve ; C, ganglion cells in
superior cervical ganglion
(SO) connected with sym-
pathetic fibres going to
parotid, submaxillary and
sublingual glands.
Fig. 107.-
-SCHEME OK THE NeRVES OK THE
Salivary Glands.
anatomical and physiological evidence. The latter we shall
return to.
The cerebral fibres for the parotid (in the dog) pass from the
tympanic branch of the glosso-pharyngeal (Jacobson's nerve) through
connecting filaments to the small superficial petrosal branch of the
facial, with this nerve to the otic ganglion, and thence by the
auriculo-temporal branch of the fifth to the gland.
The sympathetic fibres for all the salivary glands appear to arise
from nerve-cells in the upper dorsal portion of the spinal cord.
Issuing from the cord in the anterior roots of the upper thoracic
nerves (first to fifth, but mainly second thoracic for the submaxillary),
they enter the sympathetic chain, in which they run up to the
superior cervical ganglion. Here they break up into terminal twigs,
and thus come into relation with ganglion cells, whose axis-cylinder
processes pass out as non-medullated fibres, and, surrounding the
334 A MANUAL OF PIIYSIOLOCY
external carotid, reach the salivary glands along its branches.
Langley has shown, by means of nicotine (p. 157), that the sym-
pathetic fibres for the submaxillary and sublingual, and, indeed, for
the head in general in the dog and cat, are connected with nerve-
cells in this ganglion, but not between it and their termination, or
between it and their origin from the spinal cord.
Stimulation of the Cranial Fibres, — When in the dof( a
cannula is placed in Wharton's duct, and the saliva collected
(p. 375), it is found that stimulation of the peripheral end of
the divided chorda causes a brisk flow of watery saliva, and
at the same time a dilatation of the vessels of the gland,
which we have already described in dealing with vaso-motor
nerves (p. 155). That the increased secretion is not due
merely to the greater blood-supply, and the consequent
increase of capillary pressure, is shown by the injection of
atropia, after which stimulation of the nerve, although it
still causes dilatation of the vessels, is not followed by a flow
of saliva. Further, mere increase of pressure could not in
any case of itself account for the secretion, since it has been
found that the maximum pressure in the salivary duct may,,
during stimulation of the chorda, much exceed the arterial
blood-pressure (Ludwig). In one experiment, for example,,
the pressure in the carotid of a dog was 125 mm., in
Wharton's duct 195 mm. of mercury.
Even in the head of a decapitated animal a certain
amount of saliva may be caused to flow by stimulation of
the chorda, but too much may easily be made of this.
And since the blood is the ultimate source of the secretion,
we could not expect a permanent or copious flow in the
absence of the circulation, even if the gland-cells could
continue to live. In fact, when the circulation is almost
stopped by strong stimulation of the sympathetic, the flow of
saliva caused by excitation of the chorda is at the same time
greatly lessened or arrested, even though the sympathetic
itself possesses secretory fibres. So that, while there is no
doubt that the chorda tympani contains fibres whose function
is to increase the activity of the gland-cells, its vaso-dilator
action is, under normal conditions, closely connected with,
and, indeed, auxiliary to, its secretory action, although the
former does not directly produce the latter. This is only a
DIGESTfOxY 335
particular case of a physiological law of wide application,
that an organ in action in general receives more blood than the
same organ in repose, or, in other words, that the tissues are fed
according to tJieir needs. The contracting muscle, the secreting
gland, is flushed with blood, not because an increased blood-
flow can of itself cause contraction or secretion, but because
these high efforts require for their continuance a rich supply
of what blood brings to an organ, and a ready removal of
what it takes away.
The quantity of blood passing through the parotid of a
horse when it is actively secreting during mastication may
be quadrupled (Chauveau). The parallel between the
muscle and the gland is drawn closer when it is stated that
electrical changes accompany secretion (p. 623), and that
the rate of production of carbon dioxide and consumption of
oxygen rises during activity. The temperature of the saliva
flowing from the dog's submaxillary during stimulation of
the chorda has been found to be as much as i"5° C. above
that of the blood of the carotid, although with the gland at
rest no constant difference could be found (Ludwig). But
such measurements are open to many fallacies ; and while
there is no doubt that more heat is produced in the active
than in the passive gland, it will not be surprising, when the
vastly increased blood-flow is remembered, that no difference
of temperature between the incoming and outgoing blood has
been satisfactorily demonstrated, although we must assume
that such a difference exists.
How the secretory fibres of the chorda end in the gland
we do not know. We can hardly doubt that they must be
connected with the secreting cells, although Pfliiger's obser-
vations, which seemed to establish this connection, have not
been confirmed. In the * salivary glands ' of the cockroach,
however, ner\e-fibres have been shown to end in the cells.
It has already been mentioned that most of the fibres of the chorda
tympani proper become connected with ganglion-cells, and lose their
medulla inside the submaxillary gland, only a few having already lost
it by a similar connection with ganglion-cells in the chordo-lingual
triangle. These facts have been made out by means of the nicotine
method already described (p, 157). Thus, it is found that, after the
injection of nicotine (5 to 10 mg. in a rabbit or cat, 40 or 50 mg. in a
336 A MANUAL OF PHYSIOLOGY
dog), stimulation of the chorda tympani proper or of the chordo-lingual
nerve causes no secretion from the submaxillary gland ; but stimula-
tion of the hilus of the gland is followed by a copious secretion — as
much, if the stimulation is fairly strong, as was caused by excitation
of the nerve before injection of nicotine. That this is due neither to
any direct action on the gland-cells, nor to stimulation of the sym-
pathetic plexus on the submaxillary arter)-, but to stimulation of
chorda fibres beyond the hilus, is shown by the fact that after atropia
has been injected in sufiicient amount to paralyze the nerve endings
of the chorda, but not of the sympathetic, stimulation of the hilus
causes little or no flow of saliva. The application of nicotine solution
to the chordo-lingual triangle does not affect the submaxillary secre-
tion caused by stimulation of the chordo-lingual nerve, even in cases
where a few secretory fibres for the submaxillary do not leave the
chordo-lingual nerve in the chorda tympani proper, but are given off
to the chordo-lingual triangle. This shows that none of the ganglion-
cells in the triangle are connected with the cerebral secretory fibres
of the submaxillary gland. By observations of the same kind they
are known to be connected with fibres going to the sublingual. In
a similar way, by observing the eftects of stimulation of the chorda
on the bloodvessels before and after the application of nicotine, it
has been found that the vaso-dilator fibres are connected with
ganglion-cells in the same positions as the secretory fibres (Langley).
Stimulation of the Sympathetic Fibres. — The sympathetic, as
has been already indicated, contains both vaso-constrictor
and secretor}- fibres for the salivary glands. If the cervical
sympathetic in the dog is divided, and the cephalic end
moderately stimulated, a few drops of a thick viscid and
scanty saliva flow from the submaxillary and sublingual
ducts, while the current of blood through the glands is
diminished. As a rule, no visible secretion escapes from the
parotid, but microscopic examination shows that many of
the ductules are filled with fluid, which is apparently so
thick as to plug them up (Langley); while the cells show
signs of ' activity.'
Simultaneous Stimulation of Cranial and Sympathetic Fibres. —
When the chorda and sympathetic are stimulated together,
the former prevails so far, with moderate stimulation of the
latter, that the submaxillary saliva is secreted in considerable
quantity, and is not particularly viscid ; it is, however, richer
in organic matter than is the chorda saliva itself. When
the chorda is weakly, and the sympathetic strongly excited,
the scanty secretion (if there is any) is of sympathetic type.
DIGESTION 337
thick and rich in organic matter. With strong stimulation
of both nerves, the secretion, at first plentiful and watery,
soon diminishes, even below the amount obtained by
stimulation of the chorda alone, perhaps because of the
diminution in the blood-flow produced by the vaso-con-
strictors of the sympathetic. With stimulation just strong
enough to cause secretion when applied separately to either
nerve, there is no secretion when it is applied simultaneously
to both.
All this refers to the dog. In this animal, then, there
seems to be a certain amount of physiological antagonism
between the secretory action of the two nerves. l^ut it
differs in one respect from the antagonism between their
vaso-motor fibres ; for with strong stimulation the con-
strictors of the sympathetic always swamp the dilators of
the chorda, while the secretory fibres of the chorda appear
upon the whole to prevail over those of the sympathetic.
And in all probability this apparent secretory antagonism is
very superficial ; and whatever interference there may be
between the two nerves, apart from any possible effect of
their vaso-motor interference, is not due to the one annulling
the influence of the other on the gland-cells, but to the cells
being called by them to different labours, in general com-
plementary to each other, and only incompatible in so far as
the working power of the cells may not be able to respond
at the same time to large demands from both sides. For
the sympathetic always adds something to the common
secretion when there is a secretion at all, this something
being represented by an increase in the percentage of
organic matter. Not only so, but the sympathetic effect
persists after stimulation has been stopped ; and excitation
of the chorda after previous stimulation of the sympathetic
causes a flow of saliva richer in organic matter than would
have been the case if the sympathetic had not been
stimulated.
Indeed, the distinction between chorda and sympathetic
saliva, which, by taking account of the parotid as well as the
submaxillary and sublingual glands, has been generalized
into a distinction between cerebral and sympathetic saliva,
338 A M Ay UAL OF I'lIYSIOLOGY
and which holds j^ood in the dog and the rabbit, breaks down
before a wider induction. For in the cat the sympathetic
sahva of the submaxillary gland, although much more
scanty, is more watery than the chorda saliva (Langley),
which, however, is by no means viscid ; and the two secre-
tions differ far less than in the dog. In accordance with
this functional similarity, there is a much smaller difference
in the action of atropia on the two sets of fibres in the cat
than in the dog, although even in the cat the sympathetic is
less readily paralyzed than the chorda.
In their secretory action there is not even an apparent
antagonism in the cat, with minimal stimulation of both
nerves, which causes as much secretion as would be pro-
duced if both were separatel}' excited. Further, even in the
dog, after prolonged stimulation of the sympathetic, the
-submaxillary saliva is no longer viscid, but watery, the pro-
portion of solids, and especially of organic solids, being
-much lessened, as it also is in chorda saliva after long
excitation. When the cerebral nerve of the resting gland
is strongly excited, it is found that up to a certain limit the
percentage of organic matter in a small sample of saliva
subsequently collected during a brief weak excitation
increases with the strength of the previous stimulation ;
this is also true of the inorganic solids. But there is a
striking difference when the experiment is made on a gland
after a long period of activity ; here increase of stimulation
causes no increase in the percentage of organic material,
while the inorganic solids are still increased. In both cases
the absolute quantity of water, and therefore the rate of flow
of the secretion, is augmented.
All this points to the same conclusion as the microscopic
appearances in the gland-cells, that the cells during rest
manufacture the organic constituents of the secretion, or
some of them, and store them up, to be discharged during
activity. The water and the inorganic salts, on the other
hand, seem rather to be secreted on the spur of the moment,
so to speak, and not to require such elaborate preparation.
And it has been stated that when the chorda tympani is
stimulated with currents of varying strength, the quantity of
DIGESTION 339
organic substances in small samples of saliva collected from
a fresh gland is more nearly proportional to the rate of
secretion than is the quantity of water and salts, which
varies also with the blood-suppl\-.
In order to explain the difference between the cerebral and
sympathetic secretion, Heidenhain has supposed the existence of
two kinds of secretory fibres : (i) secretory fibres proper, the excita-
tion of which causes an actual outpouring of liquid from the gland-
cells into the ducts; (2) 'trophic' fibres, which not only promote
the changes by which already formed organic constituents of the
secretion pass into solution, but also stimulate the growth of the
glandular protoplasm. In such animals as the dog the cranial nerve
(the chorda in the case of the submaxillary and sublingual glands)
was supposed to contain many fibres of group (i), comparatively few
of group (2): and the sympathetic few of (i) and more of (2). Since
these trophic fibres, according to Heidenhain's original statement of
his hypothesis, possess two distinct functions, his second group is
sometimes subdivided into a set of kataboHc fibres which favour the
breaking down of material in the cell as a preliminary to its removal
in the secretion, and a set of anabolic fibres which have to do with
the building up of fresh substance. But it must be remembered that,
although it may be convenient for certain purposes to make such a
physiological 'classification, there is no proof of the existence of any
corresponding anatomical distinction ; and Langley has shown that
in the cat's chorda atropia acts simultaneously on all the secretory
fibres; the moment it paralyzes one group all are paralyzed. If they
were anatomically distinct, it might have been supposed that atropia
in a certain dose would pick out one or other group, and leave the
rest still active.
It is conceivable that the differences between chorda and
sympathetic saliva are due, not to the nerve-fibres, but to
the end organs with which they are connected ; that is, the
two nerves may supply, not the same, but different gland-
cells. And it is well known that even after prolonged
stimulation of the chorda or chordo-lingual alone, some
alveoli of the dog's submaxillary gland remain in the
' resting ' state ; after stimulation of the sympathetic alone,
the number of unaffected alveoli is much greater ; while after
stimulation of both nerves, few alveoli seem to have escaped
change. However suggestive these facts may be, they will
not as yet bear the weight even of a hypothesis of salivary
secretion. There must in any case be some overlapping in
the nerve-supply ; that is, some cells must be supplied by
22 — 2
340 A MANUAL OF PIIYSIOLOGV
both nerves, since excitation of the sympathetic influences
the amount of organic material in the sahva obtained by
subsequent stimulation of the chorda, and this organic
matter certainly comes, for the most part at least, from
substances stored up in the cells. And, indeed, we know
nothing of a division of labour between the cells of a gland,
except when there are obvious anatomical distinctions.
Thus, the submaxillary gland in man contains both serous
and mucous acini, and mucin-making cells are scattered
over the ducts of most glands, and, indeed, on nearly every
surface which is clad with columnar epithelium. In these
cases we cannot doubt that one constituent — mucin — of the
entire secretion is manufactured by a portion only of the
cells. In the cardiac glands of the stomach, too, the ovoid
cells, in all probability, yield the whole of the acid of the
gastric juice. But, so far as we know, every hepatic cell is
a liver in little. Every cell secretes fully-formed bile ; every
cell stores up, or may store up, glycogen. So it is with
the secretory alveoli of the pancreas; one cell is just like
another ; all apparently perform the same work ; each is a
unicellular pancreas. (But see p. 473.)
Paralytic Secretion. — When the chorda tympani is divided, a
slow ' paralytic ' secretion from the submaxillary gland begins in a
few hours, and continues for a long time accompanied by atrophy of
the gland. There is also a secretion of the same kind from the
submaxillary on the opposite side, but it is less copious. This is
called the ' antilytic ' secretion, which is most pronounced in the
first few days after the operation, and seems to be a transient
phenomenon. It can be at once abolished by section both of the
chorda and the sympathetic on the corresponding side, and is there-
fore due to impulses arising in the central nervous system. The
cause of the paralytic secretion has not been fully made out. If
■within two or three days of division of the chorda the sympathetic
on the same side is cut, the secretion is greatly diminished or stops
altogether ; and it is concluded that up to this time it is maintained
by impulses passing along the sympathetic to the gland from the
salivary centre, the excitability of which has been in some way in-
creased by division of the chorda. But if section of the sympathetic
is not performed for several days, it has no effect on the paralytir
secretion, which at this stage seems to depend on local changes in
or near the gland itself, leading to a mild continuous excitation
of those nerve-cells on the course of the fibres of the chorda to
which reference has already been made. Section of the sympathetic
DIGESTION 341
alone causes neither secretion nor atrophy, nor docs removal of the
superior cervical ganglion. The histological characters of the gland-
cells during paralytic secretion are those of ' rest.'
Reflex Secretion of Saliva. — The refle.\ mechanism of
salivary secretion is very mobile, and easily set in action by
physical and mental influences. It is excited normally by
impulses which arise in the mouth, especially b}- the contact
of food with the buccal mucous membrane and the gustatory
nerve-endings. The mere mechanical movement of the
jaws, even when there is nothing between the teeth, or only
a bit of a non-sapid substance like indiarubber, causes
secretion. The vapour of glacial acetic acid or ether gives
rise to a rush of saliva, as does gargling the mouth with
distilled water. The smell, sight, or thought of food, and
even the thought of saliva itself, may act on the salivary
centre through its connections with the cerebrum, and make
* the teeth water.' A copious flow of saliva, reflexly excited
through the gastric branches of the vagus, is a common
precursor of vomiting ; the introduction of food into the
stomach also excites salivary secretion.
In most animals and in man the activity of the large
salivary glands is strictly intermittent. But the smaller glands
that stud the mucous membrane of the mouth never entirely
cease to secrete, and the same is the case with the parotid
in ruminant animals.
The centre is situated in the medulla oblongata, stimula-
tion of which causes a flow of saliva. The chief afferent
paths to the salivary centre are the lingual branch of the
fifth and the glosso-pharyngeal ; but stimulation of many
other nerves may cause reflex secretion of saliva. In ex-
perimental stimulation, the sole efferent channel seems to
be the cerebral nerve-supply of the glands. After section
of the chorda, no reflex secretion by the submaxillary gland
can be caused, although the sympathetic remains intact.
It was alleged by Bernard that, after division of the
chordo-lingual, a reflex secretion could be obtained from the
submaxillary gland by stimulating the central end of the
cut lingual nerve between the so-called submaxillary ganglion
and the tongue, the ganglion being supposed to act as
342 A MA yUA L OF PI J > -S/OLOG } '
' centre.' It has been shown, however, that this is not a
true reflex effect, but is due, mainly at least, to the excitation
of certain secretory fibres of the chorda that run for some
distance in the lingual, then bend back on their course and
pass to the gland.
The salivary centre can also be inhibited, especially by
emotions of a painful kind — for instance, the nervousness
which often dries up the saliva, as well as the eloquence, of
a beginner in public speaking, and the fear which sometimes
made the medieval ordeal of the consecrated bread pick out
the guilty.
In rare cases the reflex nervous mechanism that governs
the salivary glands appears to completely break down ; and
then two opposite conditions may be seen — xerostomia, or
' dry mouth,' in which no saliva at all is secreted, and
chronic ptyalism, or hydrostomia, where, in the absence of
any discoverable cause, the amount of secretion is per-
manently increased. Both conditions are more common in
women than in men.
(2) The Influence of Nerves on the Gastric Glands. — Like saliva,
gastric juice is not secreted continuously, except in animals,
such as the rabbit, whose stomachs are never empty. The
normal and most efficient stimulus is the presence of food
in the stomach. Faintly alkaline liquids, such as saliva,
excite an active secretion, but it is only early in digestion,
before the reaction of the gastric contents has become
distinctly acid, that swallowed saliva can have any effect.
Mechanical stimulation of the gastric mucous membrane
causes a certain amount of secretion, but not a great deal.
No nerve has been shown with certainty to have any
influence over the gastric glands. So that at first thought
there is nmch to suggest that these are normally stimulated
in a more direct manner than the salivar}- glands, perhaps
by the local action of food substances reaching the cells by
a short-cut from the cavity of the stomach, or in a more
roundabout way by the blood. And it might be very
plausibly argued that the gastric glands are favourably
situated for direct stimulation, while the salivary glands are
not ; and that the great function of saliva being to aid
DIGESTION 343
deglutition, an almost momentary, and at the same time a
perilous act, it is necessary to provide by nervous mechanism
for an immediate rush of secretion at any instant, while it is
not important whether the gastric juice is poured out a little
sooner or a little later, and therefore it is left to be called
forth by the more tardy and haphazard method of local
action. Nevertheless, on looking a little closer, we hnd that
this does not exhaust the subject, and that the gastric secre-
tion can be influenced by events taking place in distant parts
of the bod\-, just as the salivary secretion can. In a boy
whose oesophagus was completely closed by a cicatrix, the
result of swallowing a strong alkali, and who had to be fed
by a gastric hstula, it was found that the presence of food
in the mouth, and even the sight or smell of food, caused
secretion of gastric juice (Richet); and in dogs with the
cesophagus divided so that nothing could pass through it to
the stomach, a similar result was obtained (Pawlow).
Here there must have been some nervous mechanism at
work. The secretion can hardly have been excited by the
direct action of food products absorbed from the mouth and
circulating in the blood — an explanation which has been
given of the secretion seen in an isolated portion of the
cardiac end of the stomach during the digestion of food in the
rest. What the nervous channels are through which these
effects are produced has not been clearly made out. After
division of the sympathetic hbres going to the stomach, and
also the vagi, gastric secretion is still caused by the intro-
duction of food into the stomach, so long as the latter nerves
are cut below the origin of their cardiac and pulmonary
branches, and disturbance of the heart and respiration thus
avoided (Heidenhain). Not only so, but the vascular
dilatation, which accompanies the activity of the gastric as
well as the salivary glands, and is shown by flushing of the
mucous membrane of the stomach, is not interfered with
by section of the vagi in the position mentioned.
The most probable conclusion would seem to be that, while
a great part must be assigned to the local effects of the
food, and the action of the products of digestion absorbed
into the blood on the gland-cells or on nervous centres,
344 A M.lXf'AL OF PHYSIOLOGY
these ma}- be supplemented and controlled by a truly reflex
mechanism.
(3) The Influence of Nerves on the Pancreas. — Our know-
ledpje of the inHuence of nerves on the pancreas is a little
more definite, but not much. Stimulation of the medulla
oblongata causes or increases secretion even after section of
the vagi. Stimulation of the central end of the vagus and
of other nerves inhibits the secretion ; the inhibition caused
by vomiting is probably due to impulses ascending the
vagus. These facts point to the existence of a reflex
mechanism, but neither has the centre been located nor
the afferent and efferent
paths definitely ascer-
tained. The natural secre-
tion of pancreatic juice is
b}' no means so intermit-
tent as that of saliva. In
the rabbit the pancreatic,
like the gastric, juice flows
continuously. In a well-
,. ., „ , , fed dog it is probable that
ri(.. loS. — KATE (>!■ .secretki.n nr- Fan- ° ^
cREATic Jlice. it seMom stops altogether,
S shows the variation in the rate of secretion for it waS fouud that after
of the pancreatic juice in a dog ; P, the varia-
tion in the percentage of solids in the juice, a meal it tOOk frOm twenty
It will be seen that the maxima of .S fall at the . . .^k,*-,- fVM,t- V.,-.i,t-c? f/^t-
sanie time as the minima of P. The numbers '■O IW eni} -lOUr nours lOr
along the horizontal axis are hours since the ^^e floW tO CCaSe entirelv-
last meal. •'
It begins abruptly as soon
as the food enters the stomach, probably through reflex
impulses originating in the gastric mucous membrane, rises
in two or three hours to a maximum, then falls till the
fifth or sixth hour, after which it mounts again about the
ninth or tenth hour to a second lower maximum, and then,
gradually diminishing, ultimately stops. During activity the
bloodvessels of the gland are dilated ; but we have as yet no
precise information as to the vaso-motor nerves which govern
them. When the nerves of the pancreas, which pass to it
from the solar plexus along the vessels, are divided, 'paralytic '
secretion of thin watery juice takes place. There is one
very remarkable difference between the normal secretion of
DIGESTION
345
pancreatic juice and of saliva : the pressure of the latter
in tht^ submaxillary duct may, as we have seen, greatly
exceed the arterial blood-pressure, without reabsorption and
conseiiuent ccdcma of the ;:,fland occurring' ; but the secn-tory
pressure of the pancreatic cells is very low, not more than a
tenth of that of the salivary glands, (I'2dema begins before a
manometer in the duct shows a pressure of 20 mm. of mercury.
(4) The Influence of Nerves on the Secretion of Bile. —
Although bile is secreted constantly, it only passes at
intervals into the intestine. For the liver in many animals,
unlike every other gland except the kidney, has in connection
with it a reservoir, the gall-bladder, in which its secretion
accumulates, and from which it is only expelled occasionally.
\\'e have therefore to distinguish the bile-secreting from the
bile-expelling mechanism. Of the direct influence of nerves
on either we have scarcely any knowledge, scarcely even
any guess which is worth mentioning here. It is true the
secretion of bile may be distinctly affected by the section
and stimulation of nerves which control the blood-supply of
the stomach, intestines, and spleen, for the quantity of blood
ptissing by the portal vein through the liver depends upon
the quantity passing through these organs, and the rate of
secretion is closely related to the blood-supply. In this way
stimulation of the medulla oblongata, the spinal cord, and
the splanchnic nerves stops or slows the secretion of bile by
constricting the abdominal vessels ; and the same effect can
be reflexly produced by the excitation of afferent nerves.
The muscular fibres of the gall-bladder and the larger
bile-ducts are thrown into contraction by stimulation of the
spinal cord. It is possible that this takes place naturally in
response to reflex impulses from the mucous membrane of
the duodenum, for the application of dilute acid to the
mouth of the bile-duct causes a sudden flow of bile, and the
acid contents of the stomach, when projected through the
pylorus into the intestine, have a similar effect.
The pressure under which the bile is secreted is remarkably
small, the maximum being no more than 15 mm. of mercury.
But small as this is, it is higher than the pressure of the
portal blood, and therefore the liver ranges itself with the
346
A MANUAL OF PHYSIOLOGY
high-pressure salivary glands rather than with the low-
pressure pancreas. But although the biliary pressure is high
relatively to that of the blood with which the secreting cells
are supplied, it is absolutely very low ; and this is a point of
practical importance, for a comparatively slight obstruction
to the outflow, even such as is offered by a congested or
inflamed condition of the duodenal wall about the mouth
of the duct, may be sufficient to cause reabsorption of the
bile through the lymphatics, and consequent jaundice. Of
course, complete plugging of the
duct by a biliary calculus is a
much more formidable barrier,
and inevitably leads to jaundice,
just as ligature of a salivary duct,
in spite of the great secretory
pressure, inevitably causes oedema
of the gland.
When food passes into the
stomach, there is at once a sharp
rise in the rate of secretion of
Fio. loq. — Rate oi' Secretion , ., . • • u j r
OK BiiE. '^ile. A maxmium IS reached from
S shows how the rate of secretion the fourth tO the eighth hour —
of bile falls in a dog when a biliary , . • l-i ^l r j • • ^l
fistula is first made, and the bile tnat IS, WDUe tnc lOOQ IS m me
thus prevented from entering the intestine; there is then a fall, SUC-
mtestme ; V shows the fall m the '
percentage of solids. The numbers cecded by a sccond Smaller risc
along the horizontal axis are ^ ,i nc^ ^i • ^ ^i
quarters of an hour smce bile began abOUt the htteenth or Sixteenth
to escape through the fistula. The i frnm wVii'rh fhp Qf^rrption
numbers along the vertical axis refer nOUr, irom WHlcn tnc SecretlOn
only to curve s. and represent the grfadually declines to its minimum.
rate of secretion in arbitrary units. <=> ■'
Upon the whole, the curves of
secretion of pancreatic juice and bile show a fairly close
correspondence, which lends additional support to the view
derived from their chemical and physical properties, that in
digestion they are partners in a common work.
We do not know in what way the rate of secretion of bile
is influenced by digestion, although it has been conjectured
that the first abrupt rise may be started by reflex nervous
action, and that later on absorbed food products may directly
excite the hepatic cells. Rutherford found that when the
mucous membrane of the stomach and duodenum is irritated
DIGESTION 347
by a substance like gamboge, there is no increase in the
rate of secretion of the bile, notwithstanding jthe greatly
increased How of blood through the intestinal vessels which
the irritation causes. This tells in favour of the direct
influence of substances derived from the food rather than
of any important reflex action.
(5) The Influence of Nerves on the Secretion of Intestinal
Juice. — As to the influence of nerves on the secretion of the
succus entericus, our knowledge is almost limited to a single
experiment, and that an inconclusive one. Moreau placed
four ligatures on a portion of the small intestine, so as to
form three compartments separated from each other and
from the rest of the gut. The mesenteric nerves going
to the middle loop were divided, and the intestine returned
to the abdomen. After some time a watery secretion was
found in the middle compartment, little or none in the
others. This is a true * paralytic "" secretion, and not a
mere transudation depending simply on the vascular dilata-
tion caused by section of the vaso-constrictor nerves, for it
has the same composition and digestive action as normal
succus entericus obtained from a fistula.
Effect of Drugs on the Digestive Secretions. — A small dose of
atropia, as has been said, abolishes the secretory action of the chorda
tympani. This it does by paralyzing the nerve-endings. The gland-
cells are not paralyzed, for the sympathetic can still cause secretion.
The nerve-fibres are not paralyzed, because the direct application of
atropia does not affect them ; nor is the seat of the paralysis the
ganglion-cells on the course of the fibres, for stimulation between
those cells and the gland-cells is ineffective. Pilocarpine is the
physiological antagonist of atropia, and restores the secretion which
atropia has abolished. In small doses it causes a rapid flow of
saliva, its action being certainly a peripheral action, and probably an
action on the nerve-endings, for it persists after all the nerves going
to the salivary glands have been divided, and after the ganglion-cells
have been paralyzed by nicotine. Atropia and pilocarpine act
similarly on some of the other digestive glands, the former paralyzing
the pancreatic secretion, the latter increasing the secretion of gastric,
and probably of intestinal, juice ; but atropia does not stop the
secretion caused by division of the intestinal nerves. Physostigmine
and muscarine act on the whole like pilocarpine.
The action of a host of drugs on the secretion of bile has been
investigated by various observers, but till something like unanimity
has been reached, it would not be profitable to go into details here.
348 A MANUA L OF I'll ) 'SIOL OGV
'I'he only real cholagogues at present positively known appear to be
the salts of the bile acids, and the less effective salol and salicylate of
sodium. The former when given by themselves or in the bile cause
not only an increase in the volume of the biliary secretion, but also an
increase in its solids. The latter, while increasing the flow, seem to
diminish the concentration of the bile. The injection of haemoglobin
into the blood-stream, or its liberation there by substances, such as
toluylene-diamin and arseniuretted hydrogen, which cause solution
of the cori)uscles, leads to an increased secretion of bile-pigment as
well as a more rapid flow of bile.
Summary. — Here let us sum up the most important points
relating to the secretion of the digestixe juices. They arc
all formed by the activity of ^land-cells oriij^iiially derived from the
epithelial lining of the alimentary canal. The organic constituents
(>r their precursors {including the mother-substances of the ferments)
are prepared in the intervals of rest — absolute in some glands,
relative in others — and stored up in the form of granules, which
during activity are moved toicards the lumen of the gland tubules,
and there discharged.
The nerves of the salivary glands arc, as regards their origin,
(a) cerebral, (b) sympathetic ; the former group is vaso-dilator,
the latter vaso-constrictor — both are secretory. Secretion of saliva
depends strictly on the nervous system. That nerves influence the
gastric and pancreatic secretions is made out, but nothing definite
IS known as to the nervous paths. As regards the intestinal
glands and the liver, it has not been proved that their secretive
activity is at all under the control of the nervous system, except
tn so far as the latter may indirectly govern it through the blood-
supply, although various circumstances suggest the probability of a
more direct action. In all the glands the blood-fiow is increased
during activity — in some {salivary glands) this is known to be
caused through nerves. In the salivary glands electromotive
changes accompany the active state, while more heat is produced,
more carbon dioxide given off, and more oxygen used up, during
secretion than during rest, hi the other glands we may assume
that the same occurs.
IV. Digestion as a Whole.
Having discussed in detail the separate action of the
digestive secretions, it is now time to consider the act
of digestion as a whole, the various stages in which are
DlC.ESriON 349
co-ordinated for a common end. The solid food is more or
less broken up in the mouth and mixed with the saliva,
which its presence causes to be secreted in considerable
quantity. Liquids and small solid morsels are shot down
the open gullet without contraction of the constrictors of
the pharynx, and reach the bottom of the cesophagus in a
comparatively short time (,V second) ; while a good-si^ed
bolus is grasped by the constrictors, then by the cesophageal
walls, and passed along by a more deliberate peristaltic con-
traction. Beaumont saw, in the case of St. Martin, that
the cesophageal orifice of the stomach contracted firmly
Fic, no. — Secketidn of Pkisin.
C shows the quantity of pepsin in the mucous membrane of the cardiac end of the
stomach at different times during digestion ; P, the quantity of pepsin in the mucous
membrane of the pyloric end ; S, the c|uantity of pepsin in the secretion of the cardiac
glands. The numbers marked alons; the horizontal axis are hours since the last meal.
-About live iiours after the meal S reaches its maximum. From the very beginning of
the meal C falls steadily down to the tenth hour, and then begins to rise, i.e., the gland-
cells of the cardiac end of the stomach become poorer in pepsin as secretion proceeds.
after each morsel was swallowed, and so did the gastric
walls in the neighbourhood of the fistula when food was
introduced by this opening. Two sounds may be heard in
man on listening in the region of the stomach or cesophagus
during deglutition of liquids, especially when, as generally
happens, they are mixed with air. The first sound occurs
at once, and is supposed to be due to the sudden squirt of
the liquid along the gullet ; the second, which is heard after
a distinct interval (six seconds), seems to be caused by the
350 A MANUAL OF rilYSIOLOGY
forcing of the fluid through the cardiac orifice of the stomach
by the contraction of the oesophagus.
Chemical digestion in man begins already in the mouth, a
part of the starch being there converted into dextrins and
sugar (maltose), as has been shown by examining a mass of
food containing starch just as it is ready for swallowing
(P- 375)- This process is no doubt continued during the
passage of the food along the oesophagus.
The first morsels of a meal which reach the stomach find
it free from gastric juice, or nearly so. They are alkaline
from the admixture of saliva ; and the juice which is now
beginning to be secreted, in response to the presence of the
food, and to reflex excitement starting in the mouth, is for
a time neutralized, and amylolytic digestion still permitted
to go on. For about fifteen minutes after digestion has
begun there is no free hydrochloric acid in the stomach,
although some is combined with proteids, and at least
during this period the ptyalin of the swallowed saliva will be
able to act, in spite of the lactic acid produced during the first
part of the digestive period by the action of the Bacillus acidi
lactici on the carbo-hydrates of the food. But as the meal
goes on, the successive portions of food which arrive in the
stomach will find the conditions less and less favourable for
amylolytic digestion ; and, upon the whole, a considerable
proportion of the starches must escape complete conversion
into sugar until they are acted upon by the pancreatic juice.
This is particularly the case with unboiled starch, as con-
tained in vegetables which are eaten raw; and, indeed, we
know that sometimes a certain amount of starch may escape
even pancreatic digestion, and appear in the fa;ces. Mean-
while, even during the short amylolytic stage of gastric
digestion, pepsin and hydrochloric acid are already being
poured forth ; the latter is entering into a peculiar combina-
tion with the proteids of the food ; and before the end of an
ordinary meal peptic digestion is in full swing. The move-
ments of the pyloric end of the stomach increase, and eddies
are set up in its contents, which carry the morsels of food
with them, and throw them against its walls. In this way
not only are the contents thoroughly mixed, and fresh
DIGESTION 351
portions of food constantly biouf^ht into contact with the
gastric juice secreted mainly in the more passive cardiac
end, but a certain amount of mechanical disintegration is
brought about ; and this is aided by the digestion of the
gelatin-yielding connective tissue which holds together the
fibres of muscle and the cells of fat, and the digestible
structures in vegetable tissue which enclose starch granules.
If milk has formed a portion of the meal, the casein will
have been curdled soon after its entrance into the stomach,
by the action of the rennet ferment alone when the milk
has been taken at the beginning of digestion before the
gastric contents have become distinctly acid, by the acid and
rennin together when it has been taken later. The casein
and other proteids of milk, like the myosin and other
proteids of meat, and the globulins, phytovitellins, and
other proteids of bread and of vegetable food in general, are
all acted upon by the pepsin and hydrochloric acid, yield-
ing ultimately peptones ; while variable quantities of acid-
albumin and proteoses may escape this final change, and
pass on as such into the duodenum. In the dog, indeed, a
meal of flesh has been found to be almost entirely digested
to the peptone stage while still in the stomach, leaving little
for the pancreatic juice to do. But we may safely assume
that, in the case of a man living on an ordinary mixed diet,
much of the food proteids passes through the pylorus
chemically unchanged, or having undergone only the first
steps of hydration. For, even a few minutes after food has
been swallowed, the pyloric sphincter may relax and allow
the stomach to propel a portion of its contents into the in-
testine ; and such relaxations occur at intervals as digestion
goes on, although it is not for several hours (three to five)
that the greater portion of the food reaches the duodenum.
During this period the acidity has at first been constantly
increasing, although for about half an hour after the short
amylolytic stage the hydrochloric acid has combined, as it is
formed, with the proteids of the food. The combination,
however, does not prevent it from causing an acid reaction,
although up to this time no free acid is present. Then comes
a stage where the hydrochloric acid has so much increased
352 A MAXUAL OF PHYSIOLOGY
that, after combining with all the proteids, some of it
remains over as free acid. The lactic acid now rapidly
disappears from the stomach ; and after a time the total
acidity begins to fall, the fully-digested proteids being con-
tinually absorbed in the form of peptones, which are only
found in traces, if at all, in the chyme. This fall continues
till the third or fourth hour, the proportion of free to com-
bined acid continuing, nevertheless, to rise, since nearly all
that is now secreted remains free. Easily-diffusible bodies,
such as sugars and some of the organic crystalline con-
stituents of meat, c.if., kreatin, w^ill also pass through the
gastric mucous membrane into the blood.*
* Seventeen dogs, after twenty-four hours' fast, were fed with a meal
of raw mai/.e-starch, minced meat, and milk. They were caused to
vomit, after an interval varying from fifteen minutes to five and three-
(|uarter hours, by the subcutaneous injection of 2 milligrammes of
apomorphine. The results of an examination of the vomit are embodied
in the following table :
Starch granules and fat globules were found in every case. The reac-
tion was always acid, as is generally the case in the dog" even twenty-four
hours after a meal.
Six other dogs, after a twenty-four hours' fast, were fed with raw starch
and lard. In twenty minutes apomorphine was injected. It acted in
from three to five minutes. In no case was any sugar found in the vomit.
DIGESTION 353
The substances whjch reach the duodenum are : (i) the
whole of the fats, with no chemical and Httle physical change.
Hut the partial digestion in the stomach of the envelopes
and protoplasm of the cells of adipose tissue, and of the
proteid which keeps the fat of milk in emulsion, prepares
the fats for what is to follow in the intestine. (2) All
the proteids which have not been carried to the stage of
peptone, and perhaps some peptone. (3) All the starch
and dextrins — and glycogen, if any be present — which have
not been converted into maltose, and possibly a little
maltose. (4) Elastin, nuclein, cellulose, and other sub-
stances not digestible or digestible only with difficulty in
gastric juice. (5) The constituents of the gastric juice
itself, including pepsin. The ptyalin of the saliva has been
already digested and destroyed.
It must be remembered that all this time, even from the
beginning of digestion, a certain amount of pancreatic juice
has been finding its way into the duodenum in response to
that distant action of the food which we have discussed,
and the reflex nature of which we have not been able either
definitely to admit or altogether to reject. The secretion of
bile, too, always going on, has quickened its pace, and the
gall-bladder is getting more and more full as the meal
proceeds and gastric digestion begins. When the acid
chyme, a grayish liquid, turbid with the debris of animal
and vegetable tissues — with muscular fibres, fat globules,
starch granules, and dotted ducts — gushes through the
pylorus and strikes the duodenal wall, a rush of bile takes
place, which perhaps precipitates some of the soluble consti-
tuents— parapeptones, proteoses (albumoses), and pepsin — as
a granular coating on the surface of the mucous membrane.
The pepsin, although afterwards redissolved along with the
rest of the precipitate, is thus rendered inert, and prevented
from destroying the trypsin already present in the duodenum,
as it would otherwise do, since the reaction of the chyme
This is interesting in connection with the well-known fact that dog's
saliva usually contains no ptyalin. In saliva obtained from twelve dogs
by stimulation of the chorda tympani, the presence of a diastatic
ferment was only once made out.
23
354 A MAXrAL OI- PHYSIOLOGY
still remains acid. ]>y-and-by, as bile and pancreatic juice
continue to be poured out, the reaction becomes less acid
though never alkaline unless for a short time in the duo-
denum, and the trypsin begins its work upon the proteids.
The undigested proteids are all carried on to the stage of
peptone, much of this being absorbed as it is formed, some
even in perfectly normal digestion, in the dog at least, being
further split up into leucin and tyrosin.
The common statement that the contents of the intestine are
alkaline requires to be qualified by reference to the indicator used.
The reaction in the duodenum, as tested by litmus, may possibly
become alkaline for a time, when the inflow of bile and pancreatic
juice is at its height ; but the chyme soon becomes acid again, and
its acidity continually increases as it passes down the gut. In the
lower end of the small intestine the reaction may again become
alkaline. To phenolphthalein, which is very sensitive to weak organic
acids, the reaction is acid throughout the whole intestine. But methyl
orange, which readily reacts to inorganic acids, gives no indication
of their presence, but shows, on the contrary, an alkaline reaction
from duodenum to caecum, caused probably by the alkaline salts of
organic acids (Moore and Rockwood). The acidity of the intestinal
contents appears to be largely due to the lactic acid produced by the
action of micro-organisms on the carbo-hydrates, and the fatty acids
set free from the fats by the action of the steapsin of the pancreatic
juice and the fat-splitting bacteria. .So that although trypsin, like
pepsin, performs its work, for the most part, at any rate, in an acid
medium, the cause of the acidity and the character of the medium
are by no means alike. We are not, however, without other examples
of digestive juices destined to act in a medium with an opposite
reaction to their own. The ' saliva ' of Octopus macropus, strongly
acid though it is, contains a proteolytic ferment which in vitro acts,
like trypsin, better in a neutral or alkaline than in an acid solution.
The pepsin of the (in itself) alkaline secretion of the pyloric end of
the stomach becomes a constituent of the acid gastric juice ; and it
may, perhaps, be considered a morphological accident, so to speak,
that the oxyntic cells of the cardiac end should mingle their acid
products with the (presumedly) alkaline secretion of the chief cells
in the lumen of each gland-tube, instead of being massed as a
separate organ with a special duct.
In the lower portions of the small intestine bacteria of
various kinds are present and active ; and it is not unlikel}'
that even throughout its whole length a certain range of
action is permitted to them, checked by the acidity of the
chyme, and perhaps by the antiseptic properties of the bile.
DIGESTION 355
The stomach, with its acid contents, forms (iiirinj^ the
greater part of j^astric digestion a valve or trap to cut off
the upper end of the intestine from the bacteria-infested
regions of the mouth and pharynx, and to destroy the
micro-organisms swallowed with the food and saliva. The
occasional presence in vomited matter of sarcina; or
regularly arranged groups of micrococci, generally four to a
group, shows that under abnormal conditions the gastric
contents are not perfectly aseptic ; and even from a normal
stomach active micro-organisms of various kinds can be
obtained. But upon the whole there is no doubt that the
acidity of the gastric juice is an important check on bacterial
activity during the first part of digestion, and in the upper
portion of the alimentary canal.
And, indeed, Koch has shown that the acidity of the gastric
juice of a guinea-pig is sufficient to kill the comma bacillus
of cholera. Normal guinea-pigs fed with cholera bacilli
were unaffected. But if the gastric juice was neutralized
by an alkali before the administration of the bacilli the
guinea-pigs died.
It has been supposed by some that this bactericidal action
is the chief function of the stomach, and the question has
been asked, why we should attribute any digestive im-
portance to the secretion of that viscus, since the pancreatic
juice can do all that the gastric juice does, and some things
which it cannot do. Further, it has been shown that a dog
may live five years after complete excision of the stomach,
comport himself in all respect like a normal dog, and
when killed for autopsy show every organ in perfect health
(Czerny). Recently, too, the stomach has been excised in
man with a successful result. But if this is to be admitted
as evidence against the digestive function of the stomach, it
is just as good evidence against the bactericidal function,
particularly as it has in addition been shown that even
putrid flesh has no harmful effect on a dog after excision of
the stomach, any more than on a normal dog. And, indeed,
the reasoning is fallacious which assumes that what may
happen under abnormal conditions must happen when the
conditions are normal. For nothing is impressed more often
23—2
356 .1 J/.IATJZ or PHYSIOLOGY
on the physiological observer than the extraordinary power of
adaptation, of making the best of everything, which the
animal organism possesses. Doubtless, a dog without a
stomach will use to the best advantage the digestive fluids
that remain to him ; and the pancreatic juice may be
adequate to the task of complete digestion. So, too, a man
from whom the surgeon has removed a kidney, or a testicle,
or a lobe of the thyroid gland, ma}- be in no respect worse
off than the man who possesses a pair of these organs.
But what do we deduce from this? Not, surely, that the
excised thyroid, or testicle, or kidney was useless, or the
gastric juice inactive, but that the organism has been able to
compensate itself for their loss.
The lower end of the small intestine is not cut oft" by any
bacteria-proof barrier from the large intestine, in which
putrefaction is constantly going on. So that micro-organisms
may be able to work their way above the ileo-cacal valve,
even against the downward peristaltic movement. But even
if this were not the case, a few bacteria or their spores,
passing through the stomach with the food, would be enough
to set up extensive changes as soon as they reached a part
of the alimentary canal where the conditions were favourable
to their development. Indeed, from the time when the first
micro-organism enters the digestive tube soon after birth, it
is never free from bacteria ; and their multiplication in one
part of it rather than another depends not so much on the
number originally present to start the process, as on the
conditions which encourage or restrain their increase.
The fats are in part broken up into their fatty acids and
glycerine by the fat-splitting ferment of the pancreatic juice.
The acids will form soaps with alkalies wherever they meet
them in the intestinal contents, or even in the mucous
membrane. A portion of those soluble soaps may be imme-
diately absorbed ; the rest may aid in the emulsification of
that unknown but probabl} large balance of the fats which
is not chemically decomposed. The starch and dextrine
which have escaped the action of the saliva are changed into
maltose by the pancreatic juice. A little dextrine may be
absorbed as such (Bleile).
DIGESTIOX
357
The succus entericus plays no very important part,
although, as an alkaline liquid, it doubtless aids in lessening
the acidity of the chyme and establishing the reaction
favourable to intestinal digestion. It will invert any cane-
sugar which may reach the intestine ; but it cannot be
doubted that cane-sugar may be absorbed by the stomach,
being inverted either by a ferment in the mucus lining that
viscus, or on its way through the gastric walls.
Upon the whole no great amount of water is absorbed in
the small intestine, or at least the loss is balanced by the
gain, for the intestinal contents are as concentrated in the
duodenum as in the ileum. But as soon as they pass beyond
the ileo-caecal valve, water is rapidly absorbed, and the
contents thicken into normal f*ces, to which the chief con-
tribution of the large intestine is mucin, secreted by the vast
number of goblet-cells in its Lieberkiihn's crypts.
Bacterial Digestion. — So far we have paid no attention to
other than the soluble ferments of the digestive tract. It
is now necessary to recognise that the presence of bacteria
is an absolutely constant feature of digestion ; and although
their action must in part be looked upon as a necessary evil
which the organism has to endure, and against the conse-
quences of which it has to struggle, it is not unlikely that in
part it may be ancillary to the processes of aseptic digestion.
But bacteria are not essential, as some have supposed. For
it has been shown that a young guinea-pig, taken by
Cesarean section from its mother's uterus with elaborate
antiseptic precautions, and fed in an aseptic space on sterile
milk, grew apparently as fast as one of its sisters brought
up in the orthodox microbic way. The alimentary canal
remained free from bacteria (Xuttall and Thierfelder).
Among the more important actions of bacteria on the
proteid food-products in the intestines may be mentioned
the formation of indol, phenol, and skatol, the first having
tyrosin for its precursor, and being itself after absorption
the precursor of the indican in the urine ; the second being
to a small extent thrown out with the faeces, but chiefly
absorbed and eliminated by the kidneys as an aromatic com-
pound of sulphuric acid ; the third passing out mainly in
358 A MANUAL OF I'lIYSlOLOijY
the faeces. From carbo-hydrates lactic acid is formed in
increasing amount as the lower portion of the intestine is
reached, so that the reaction, which is acid in the upper part
of the tube, owing to the acidit\' of the chyme, in spite of
the outflow of bile and pancreatic juice remains acid in the
ileum. In the dog, indeed, on a flesh diet, and therefore
under conditions which leave little scope for lactic acid
fermentation, the reaction of the whole of the small intestine
has been found acid. But this is perhaps not constantly the
case ; and when it does occur, it may be connected with the
very thorough and almost exhaustive digestion of proteids,
which, as we have already mentioned, the stomach of the
dog is of itself able to accomplish, so that little being left
for the intestine to do, little of the alkaline digestive juices
is poured into it, and this little is swamped by the acid
gastric contents.
The large intestine is the chosen haunt of the bacteria of
the alimentary canal ; they swarm in the fa;ces, and by their
influence, especially in the caecum of herbivora, but also to
a small extent in man, even cellulose is broken up, the
final products being carbon dioxide and marsh gas. The
contents of the large bowel are generally acid from the
products of putrefaction, although the wall itself is
alkaline.
Faeces. — In addition to mucin, secreted mainly by the large
intestine, the fatces consist of indigestible remnants of the
food, such as elastic fibres, spiral vessels of plants, and in
general all vegetable structures chiefly composed of cellulose.
They are coloured with a pigment, stercobilin, derived from
the bile pigments. Stercobilin is identical with ' febrile *
urobilin, with the urobilin which forms a common, though not
an invariable, constituent of bile itself, and probably with the
urobilin of normal urine. No bilirubin or biliverdin occurs
in normal faces, although pathologically the\- may be present.
The dark colour of the faces with a meat diet is due to
hsematin and sulphide of iron, the latter being formed by
the action of the sulphuretted hydrogen which is constantly
present in the large intestine on the organic compounds
of iron contained in the food or in the secretions of the
DIGESTION
359
alimentary canal.* A small amount of altered bile acids and
their products is also found : and in respect to these, and to
the altered pigments, bile is an excretion. And although its
important function in digestion, and the fact that the greater
part of the bile salts is reabsorbed, show that in the adult
it is ver\- far from being solel}' a waste product, the equally
cogent fact, that the intestine of the new-born child is filled
with what is practically concentrated bile (mac;znn«), proves
that it is just as far from being purely a digestive juice.
Skatol and other bodies, formed by putrefactive changes in
the proteids of the food, are also present in the fatces, and
are responsible for the f&cal odour. Masses of bacteria are
invariably present. Of the inorganic substances in faces
the numerous crystals of triple phosphate are the most
characteristic. When the diet is too large, or contains too
much of a particular kind of food, a considerable quantity
of digestible material may be found in the faeces, e.g.,
muscular fibres and fat. But it should be remembered that
under all circumstances the composition of the faeces differs
from that of the food. The intestinal contribution is always
an important one, although relatively more important with
a flesh than with a vegetable diet.
* It was supposed by Bunge that only such organic compounds of iron
could be absorbed, and that the undoubted benefit derived from the
administration of inorganic in^n compounds, such as ferric chloride, in
amemia, was due not to their direct absorption, but to their shielding the
organic compounds from the attack of the sulphuretted hydrogen. But
this theory has been shown to be inconsistent with the facts. For
instance, while iron accumulates in the liver of an animal to which
inorganic salts of iron are given, it does not accumulate when salts of
manganese are substituted, although these are equally decomposed by
sulphuretted hydrogen. Stockman, from careful estimations of the
quantity of iron in a number of actual dietaries, concludes that the
greater part of it must be retained in the body and used over and over
again.
CHAPTER V.
ABSORPTION.
Physical Introduction — Diffusion. - When a solution of a substance
is placed in a vessel, and a layer of water carefully run in on the top
of it, it is found after a time that the dissolved substance has spread
itself through the water, and that the composition of the mixture is
uniform throughout. The result is the same when two solutions
containing different proportions of the same substance, or containing
different substances, are placed in contact. The phenomenon is
called difusiou. The time required for complete diffusion is com-
paratively short in the case of a substance like hydrochloric acid or
sodium chloride, exceedingly long in the case of albumin or gum.
In both it is more rapid at a high temperature than at a low.
Osmosis. — If the solution be separated from water by a membrane
absolutely or relatively impermeable to the dissolved substance, but
permeable to water, water passes through the membrane into the
solution. This phenomenon is called osmosis. E.g.^ a membrane of
ferrocyanide of copper, nearly impermeable to cane-sugar, can be
formed in the pores of an unglazed porcelain pot by allowing potas-
sium ferrocyanide and cupric sulphate to come in contact there. If
the pot is filled with, say. a i per cent, solution of cane-sugar, closed
by a suitable stopper, connected to a manometer, and then placed
in a vessel of water, water passes into it till the pressure indicated
by the manometer rises to a certain height. With a 2 per cent,
solution it reaches twice this height, and in general the osmotic
pressure, as it is called, is in any solution proportional to the
molecular concentration* of the solution, or, in other words, to the
number of molecules of the dissolved substance in a given volume
of the solution. If in this sentence we substitute ' gaseous
pressure' for 'osmotic pressure,' and 'gas' for ' solution,' we have
a statement of Boyle's law, which asserts that the pressure of a
gas is proportional to its density. And, indeed, it has been
shown that the osmotic pressure of the dissolved substance is the
* The molecular concentration is strictly defined as the number of
grammes of the dissolved substance in a litre of the solution divided by the
gramme-molecular weight. The gramme-molecular weight, or gramme-
molecule, is the number of grammes corresponding to the molecular
weight. Thus, the gramme-molecular weight of sodium chloride (NaClj is
58*36 grammes, and of cane-sugar (CioH-i-On), 342 grammes.
Plate III
vaiuM
Pat globule in central lacteal _ .
'* , JMt glohuUs pasting through
mnar epithelium
Oireular mxitcular
coat
1. Section of frog's intestine to show absorption of fat, x 300.
(Stained with picrocarmiTi? and osniin aeid.\
ViUi
Store Highly magnified
portion of Tfillvs
Ooblcl cell with plug of mucin - -^ ,
Capillary pUxu*
- A Lieberkului'f erypt
Circular mtMCitlar eoat
Longifudinal tntueu1ar eoat
2. Section of small intestine. Blood-vessels injected.
(Stained with hsamatozylin and eoain.)
West Newman ciir iith.
ABSORPTION 361
same as the pressure that would be exerted by a gas, say hydrogen,
if all the water were removed, and a molecule of hydrogen substituted
for each molet ule of the substance, or as would be exerted by the
substance itself if, after removal of the solvent, it could be left as a
gas filling the same volume. And the osmotic pressure of a solution
of one substance is the same as that of a solution of any other
substance which contains in a given volume the same number of
molecules of the dissolved substance. In other words, the osmotic
pressure is not dependent on the nature, but on the molecular con-
centration, of the substance. The analogy of the laws of osmotic to
those of gaseous pressure becomes still more obvious when it is
added that the osmotic pressure of a substance with any given
molecular concentration is proportional to the absolute temperature ;
and that when a solution contains more than one dissolved substance,
the total osmotic pressure is the sum of the partial osmotic pressures
which each substance would exert if it were present alone in the
same volume of the solution.
The osmotic pressure of a solution may reach an enormous amount.
Thus, a I per cent, solution of cane-sugar has a pressure at 0° C. of
493 mm. of mercury. A 10 per cent, solution of cane-sugar would have
an osmotic pressure of more than six atmospheres, and a 17 per cent,
solution of ammonia a pressure of no less than 224 atmospheres.
The osmotic pressure must be due to the kinetic energy of the
moving molecules. Where the molecules are hindered from passing
a bounding membrane, the pressure exerted by their impacts on the
boundary is greater than where the membrane is easily permeable,
because in the latter case many of the molecules pass through,
carrying with them their kinetic energy. The pressure must be still
less when a dissolved substance diffuses freely into water ; but how-
ever small it may become, it is in the osmotic pressure of the
molecules of the dissolved substance that the force which causes
diffusion must be sought.
In practice it is inconvenient, and in many cases impossible, to
directly measure the osmotic pressure by means of a non-permeable
or semi-permeable membrane like ferrocyanide of copper. Recourse
is therefore had to indirect methods. Of these, one of the most
generally used depends on the fact that the freezing point of a
solution is lower than that of the solvent ; for example, salt water
freezes at a lower temperature than fresh water. The amount by
which the freezing-point is lowered depends on the molecular con-
centration of the dissolved substance, to which, as we have seen, the
osmotic pressure is also proportional. When a gramme-molecule of
a substance is dissolved in a litre of water, the freezing-point is
lowered by I'S"^ C. ; the osmotic pressure is 22*35 atmospheres
(16,986 mm. of mercury). It is therefore easy to calculate the
osmotic pressure of any solution if we know the amount by which its
freezing-point is lowered. A i per cent, solution of cane-sugar, for
example, would freeze at about -o'o52' C. Its osmotic pressure
= - """ X 16,986 = 490 mm. of mercury.
362 A MANUAL OF PHYSIOLOGY
The osmotic pressure of different solutions may also be compared
by observing the effect produced on certain vegetable and animal
cells. When a solution with a greater osmotic pressure than the
cell-sap (a JiyperisoUmic solution) is left for a time in contact with
certain cells in the leaf of Tradescantia discolor, plasnwlysis occurs —
that is, the |)rotoplasm loses water and shrinks away from the cell-
wall. If the osmotic pressure of the solution is lower than that of
the coloured cell-sap {hypoisotonic solution), no shrinking of the
protoplasm takes place. By using a number of solutions of the same
substance but of different strength, two can be found, the stronger of
which causes plasmolysis, and the weaker not. Between these lies
the solution which is isotonic with the cell-sap — that is, has the same
molecular concentration and osmotic pressure. I'he strength of an
isotonic solution of some other substance can then be determined in
the same way with sections from the same leaf.
Animal cells (red blood-corpuscles) may also be employed, the
liberation of haemoglobin or the swelling of the corpuscles, as
measured by the ha.miatocrite (p. 35), being taken as evidence that
the solution in contact with them is hypoisotonic to the contents of
the corpuscles. If the corpuscles shrink, the solution is hypcrisotonic
to their contents. But since the cells are much more permeable to
certain substances than to others, this method does not always yield
trustworthy results.
Electrolytes. — We have said that the osmotic pressure is propor-
tional to the concentration of the solution, but this statement must now
be qualified. For certain compounds, including all inorganic salts and
many organic substances, the osmotic pressure decreases less rapidly
than the theoretical molecular concentration as the solution is diluted.
The explanation appears to be that in solution some of the molecules
of these bodies are broken up into simpler groups or single atoms,
called ions. Each ion exerts the same osmotic pressure as the
molecule did before. The proportion between the average number
of these dissociated molecules and of ordinary molecules is constant
for a given concentration of the solution and a given temperature.
But as the solution is diluted, the proi)orlion of dissociated mole-
cules becomes greater. The bodies which behave in this way are
electrolytes — that is, their solutions conduct a current of electricity ;
bodies which do not exhibit this behaviour do not conduct in
solution. And there are many reasons for believing that the dis-
sociation of the electrolytes is the essential thing in electrolytic
conduction. We may suppose that in a solution of an electrolyte —
sodium chloride, for instance — a certain number of the molecules
fall asunder into a kation (Na), carrying a charge of positive
electricity, and an anion (CI), carrying an equal negative charge.
These electrical charges, it must be remembered, are not created by
the passage of a current through the solution. We do not know how
they arise, but the ions must be supposed to be electrically charged
at the moment when the molecule is broken up. And the ions of
different substances must each be supposed to carry the same
quantity of electricity. But since they are all wandering freely in
ABSOR/'TfON 363
the solution, 110 excess of negative or of positive electricity can
accumulate at any part of it — in other words, no difference of potential
can exist. When electrodes connected with a voltaic battery are
dipped into a solution of an electrolyte, a difference of potential
(p. 518), an electrical slope, is established in the li(|uid, and the
positively charged kations are compelled to wander towards the
negative pole, the negatively charged anions towards the positive
pole. In this way that movement of electricity which is called
a current is maintained in the solution. It is clear that the greater
the number of ions, and the faster they move in the solution, the
greater will be the cjuantity of electricity carried to the electrodes
in a given time, when the difiference of potential between the
electrodes, or the steepness of the electric slope, remains constant.
In other words, the specific conductivity of a solution of an electrolyte
varies as the number of dissociated molecules in a given volume and
the speed of the ions. It increases up to a certain point with the
concentration, because the absolute number of dissociated molecules
in a given volume increases. '\:\\t molecular condiictivity — that is, the
conductivity per molecule, or, strictly, the ratio of the specific con-
ductivity to the molecular concentration, increases with the dilution,
because the relative number of dissociated molecules, as compared
with undissociated, increases. At a certain degree of dilution the
molecular conductivity reaches its maximum, for all the molecules
are dissociated. The ratio of the molecular conductivity of any given
solution to this maximum or limiting value is therefore a measure of
the proportion between the number of dissociated and the total number
of molecules. The molecular conductivity of the salts dissolved in
the liquids of the animal body, for the degree of dilution in which
they exist there, is such that we must assume them to be for the most
part dissociated.
Absorption of the Food. — In the preceding chapter we
have traced the food in its progress along the alimentary
canal, and sketched the changes wrought in it by diges-
tion. We have next to consider the manner in which it is
absorbed. Then, for a reason which has already been
explained, instead of following its fate within the tissues,
until it is once more cast out of the body in the form of
waste products, it will be best to drop the logical order and
pick up the other end of the clue — in other words, to
pass from absorption to excretion, from the first step in
metabolism to the closing act, and afterwards to return and
fill in the interval as best we can.
And here, first of all, it should be remembered that the epithelial
surfaces, through which the substances needed by the organism
enter it, and waste products leave it, are, physiologically considered,
outside the body. The mucous membranes of the alimentary.
364
J MAXCAL or I'lIYSIOLOCY
respiratory and urinary tracts are in a sense as much external as the
fourth great division of the physiological surface, the skin. The two
latter surfaces are in the mammal purely excretory. Absorption is
the dominant function of the alimentary mucous membrane, but a
certain amount of excretion also goes on through it. The pulmonary
surface both excretes and absorbs, and that in an equal measure.
But It is by no means necessary that the surface through which
oxygen is taken in and gaseous waste products given off should be
buried deep in the body, and communicate only by a narrow channel
with the exterior. In the frog the skin is largely an absorbing as
well as an excreting surface : oxygen passes freely in through it, just
as carbon dioxide passes freely out. In most fishes, and many other
gill-bearing animals, the whole
gaseous interchange takes place
through surfaces immersed in the
surrounding water, and therefore
distinctly external. In certain forms
it has even been shown that the
alimentary canal may serve con-
spicuously for absorption and ex-
cretion of gaseous, as well as lic}uid
and solid substances. Still lower
down in the animal scale, the sur-
face of a single tube may perform
all the functions of digestion, ab-
sorption and excretion. Lower still,
and even this tube is wanting, and
everything passes in and out through
an external surface pierced by no
permanent openings.
Indeed, even in man the func-
tions of the various anatomical
rnaT/slTfa'ce: KXTrfLfof^'; divisions of the physiolog.cal sur-
renal epithelium ; .'\, the alimentary face are not (juite sharply marked
canal ; .s, the skin. off from each Other. Though
gaseous interchange goes on far
more readily through the pulmonary membrane than anywhere else,
swallowed oxygen is easily enough absorbed from the alimentary
canal and carbon dioxide given off into it ; and to a small extent
these gases can also pass through the skin. Though water is ex-
creted chiefly by the skin, the pulmonary and the urinary surfaces,
and on the whole absorbed chiefly from the digestive tract, there is
no surface which in the twenty-four hours pours out so much water
as the mucous membrane of the stomach. Under normal condi-
tions, it is true, by far the greater i)art of this is reabsorbed in the
intestine, yet in diarrhoea, whether natural or caused by purgatives,
the intestines themselves may, instead of absorbing, contribute
largely to the excretion of water. -Again, although the solids of the
excreta are normally given ofl" in far the greatest quantity in the
urine and faeces (only part of the latter is truly an excretion, since
Fli;. III. DiAl.KAM OK Absoki-
rioN AM) Excretion.
Carbon <■, nitrogen n, hydrogen //,
AliSOk'l'T/OX 365
much of the f;vces of a mixed diet has never been physiologically
inside the body at all), yet salts are constantly, and urea occasionally,
found in the excretions of the skm, and of the respiratory tract.
I'urther, althouj;h the solids and li(|uids of the food are usually taken
in by the alimentary mucous surface, it is possible to cause sul)-
stances of both kinds to pass in through the skin ; and a certain
amount of absorption may also take place through the urinary
bladder. So that really it may be considered, from a physiological
point of view, as more or less an accident that a man should absorb
his food by dipping the villi of his intestine into a digested mass,
rather than by dipping his fingers into properly prepared solutions,
as a plant dips its roots among the litiuids and solids of the soil ; or
that he should draw air into organs lying well in the interior of his
thorax, instead of letting it play over special thin and highly vascular
portions of his skin ; or that the surface by which he excretes urea
should be buried in his loins, instead of lying free upon his back.
It has been already explained that, although digestion is
a necessary preliminary to the absorption of most of the
solids of the food, we are not to suppose that all the food
must be digested before an}- of it begins to be absorbed. On
the contrary, the two processes go on together. As soon as
any peptone has been formed from the proteids, or sugar
from the starch, they begin to pass out of the alimentary
canal ; and by the time digestion is over, absorption is well
advanced.
Even in the mouth it has already begun, and it is con-
tinued with far greater rapidity in the stomach. Here
peptones, sugar, and diffusible substances like alcohol, and
the extractives of meat, which form an important part of
most thin soups and of beef-tea, are undoubtedly absorbed.*
But it is in the small intestine that absorption reaches its
height. The mucous -membrane of this tube offers an
immense surface, multiplied as it is by innumerable villi,
and by the valvula; conniventes. Here the whole of the fat,
much sugar and peptone, certain products of the further
action of the unformed and formed ferments of the intestine
on the food, and certain constituents of the bile are taken in.
* The following table illustrates the rapidity of absorption of cane-
sugar. After a twenty-four hours" fast, nineteen dogs were fed with
known amounts of cane-sugar, and killed after an interval varying from
thirty minutes to four hours. The contents of the stomacli and intestines
were separately collected, and the amount of sugar (estimated as glucose)
determined before and after boiling with hydrochloric acid. In the first
sixteen experiments the sugar was given in the form of a 10 per cent.
366
A MANUAL OF PHYSIOLOGY
In the large intestine, as has been already said, water and
soluble salts are chiefly absorbed.
What now is the mechanism by which these various
products are taken up from the digestive tube, and what
paths do they follow on their way to the tissues ?
Theories of Absorption. — Not so very long ago it was supposed by
many that the processes of diffusion, osmosis and filtration offered a
tolerably complete explanation of physiological absorption. At that
time the dominant note of physiology was an eager appeal to
chemistry and physics to ' come over and help it '; and as new facts
were discovered in these sciences they were applied, with a confidence
that was almost naive, to the problems of the animal organism. The
phenomena of the passage of liquids and dissolved solids through
animal membranes, upon which the work of Graham had cast so
much light, seemed to find their parallel in the absorptive processes
of the alimentary canal. And when digestion was more deeply
studied, facts appeared which seemed to show that its whole drift
was to increase the solubility and diffusibility of the constituents of
the food. But as time went on, and more was learnt of the phenomena
of absorption and the powers of cells, these crude physical theories
broke down, and discarded ' vitalistic ' hypotheses began once more
to arouse attention. Then came the recent investigations of De
Vries, Van't Hoff, and others in the domain of molecular physics,
which gave to our notions of osmosis the precision that was wanted
before its relation to many physiological processes could be profitably
discussed. At the present time it must be admitted that we possess
no explanation of absorption which is more than a confession of
ignorance, and does not itself need to be explained. Some physiolo-
gists, impressed with the vast progress of physics and chemistry, and
especially with the strides that have recently been made in the study
solution, in the last three in the solid state, a little lard being always
mixed with it to render it more palatable.
^
Found in
> c
Stomach,
in grm.
Glu-
cose.
Cane-
sugar.
5
30
0
1-66 1
.■;
.30
0
0 '
lO
30
0
Trace ]
5
90
0
>• 1
5
90
0
0 1
ID
90
0
° i
II
go
0
° 1
7-5
105
0
0
133
105
•58
0
25
120
0
0
Found in
Intestine,
in grm.
Glu- I Cane-
cose. I sugar.
-<
0
8
0
75
0
7-5
0
7 5
0
7-5
0
75
0
20
0
20
0
50
•83
180
240
240
240
240
240
60
120
120
Found in
.Stomach
in grm.
Glu-
cose.
•277
O
O
o
o
o
3-6i
1-2
I^
Cane-
sugar.
O
o
o
o
o
o
1 2 89
13-3
i8-2
Glu-
cose.
Found in
Intestine,
in grm.
Cane-
sugar.
O
o
«5
o
o
o
•25
4-5
f-o.i
ABSORPTION 367
of osmosis, believe that as our knov/ledge of these sciences increases,
it will become possible to explain on physical i>rinci[jles all the
peculiar phenomena which we observe in the passage of substances
through the walls of the alimentary canal. Others, taking account of
the number and nature of these peculiarities, oppressed with the
perennial paradox of vital action, incline to the less sanguine view,
that after all physical explanations have been exhausted, the real
secret of the cell will still lurk m some ultimate ' vital ' property of
structure or of function, and still elude our search. lloth the
optimist and the pessimist, the adherent of the physical and the
adherent of the vitalistic hypothesis, admit that the phenomena of
absorption are essentially connected with the cells that line the
alimentary canal. And the one must confess what the other pro-
claims, that while the processes carried on in these cells are definite,
well ordered, and evidently guided by laws, these laws have as yet
denied themselves to the modern physiologist, with chemistry in one
hand and physics in the other, as they denied themselves to his pre-
decessor, equipped only with his scalpel, his sharp eyes, and his
mother-wit. So that in the present state of our knowledge all we
can really say is that, while absorption is certainly aided by physical
processes like osmosis, it is at bottom the work of cells with a
selective power which we do not understand, and which is probably
peculiar to living structures. Thus, when the cells that line the intes-
tine are injured or destroyed, absorption from it is diminished or
abolished. And in their normal state they do not take up indis-
criminately all kinds of diffusible substances, nor absorb those which
they do take up in the direct ratio of their diffusibility, nor do they
reject everything which does not diffuse. Albumin, for example,
which does not pass through dead animal membranes, is to a certain
extent taken up from a loop of intestine without change. And it has
been shown that the water, organic and inorganic solids of the serum
of an animal are absorbed from a loop of its intestine when the
pressure in the capillaries of the intestinal wall is considerably greater
than in the cavity of the gut. Since the serum in the intestine is
isotonic with the plasma in the capillaries, the absorption cannot be
due to osmosis or diffusion. Nor can it be due to filtration, since
the slope of pressure is from the capillaries to the lumen of the gut
(Waymouth Reid). It is therefore extremely difficult to reconcile
this experiment with any physical theory of absorption.
But if it be true that the action of the columnar epithelium of the
intestinal mucous membrane is governed by a secretive and selective
power,' that makes use of purely physical processes, but is not
mastered by them, the possibility must be admitted that in the cells
of endothelial type which line the serous cavities, the lymphatics, the
bloodvessels, the alveoli of the lungs, and the Bowman's capsules
of the kidney (p. 395), the element of secretion is less marked, and
more overshadowed by the physical factors. And it may very plausibly
be urged that changes of considerable physiological complexity can
only be wrought on substances that have to pass through a cell of
considerable depth, while a mere film of protoplasm suffices for, and
368
A .11. 1 A UAL or rUYSlOLOCY
indeed favours, mechanical filtration and diffusion. \Ve have already
seen (p. 242), in the case of the lungs, that whatever the complete
explanation may be of the gaseous exchange which takes i)lace
through the alveolar membrane, physical diffusion undcjubtedly j)lays
a certain part. We shall see, too (p. 403), that in the case of the
kidney the endothelium of the Bowmans capsule, although by no
means devoid of selective power, does seem to have allotted to it a
simpler task than falls to the share of the ' rodded ' epithelium.
Further, it has been stated that interchange between blood-serum,
circulated artificially in the vessels of dogs and rabbits which have
been dead for hours, and liquids introduced into the peritoneal
cavity, is essentially the same as
in the living animal, and can be
explained on purely physical
[principles (Hamburger). Ligation
of the thoracic duct has little
effect on the fate of liquids injected
into serous cavities, since the
bloodvessels play the chief part in
their absorption, just as strychnia,
when injected under the skin — />.,
into the lymph-spaces of areolar
tissue — is taken up by the blood
and does not appear in the lymph.
xVnd if substances can pass, by
physical processes alone, from the
serous cavities, which are really
expanded lymph-spaces, into the
blood, and from the blood into
serous cavities, it is natural to in-
jng the villus— the outer edge of the quire whether anything else is con-
cells is striated ; b. central lacteal of -^rr.*./1 Jr. tV.f» mccnap c\^ \\\(^ rr>n
villus ; c. unstriped muscular fibres ; d, cemed in the passage ot the con-
niucin-forming goblet-cell. stituents of the lymph through the
capillary walls.
Formation of Lymph. — The teaching of Ludwig, that filtration is
the great factor in the formation of lymph, was called in question by
Heidenhain, whose theory of secretion at first bade fair to totally
supplant the older view. But a reaction has set in. A zealous band
of investigators has revived the old doctrine of filtration, and a con-
troversy has sprung up which has yielded a rich harvest of new facts
and new ideas, but as yet shows no sign of coming to an end. One of
the strongest arguments in favour of the secretion theory has been
the existence of substances which, when injected into the blood,
increase the flow of lymph, without affecting appreciably the arterial
pressure. Heidenhain divides these so-called lymphago^^ues into two
classes : ( i ) substances like peptone, leech-extract, extract of crayfish,
egg-albumin, etc., which cause not only an increase in the rate of
flow, but an increase in the specific gravity and total solids of the
lymph ; (2) crystalloid substances, like sugar, salt, etc., which cause
an increased flow of lymph more watery than normal. Starling has
n^"~rl,
P"io. 112. — Vkriicai. Section- ok a
Villus (Cat) x 300.
layer of columnar epithelium cover-
ABSORPTION 369
shown that although the lymphagogues of the second class do not
raise the arterial pressure, they do, by attracting water from the
tissues and thus causing hydremic plethora (an excess of blood of
low specific gravity), bring about a marked rise of venous, and there-
fore, what is the important thing for lymph filtration, of capillary
pressure. The action of the first class of lymphagogues, which
cannot be explained in this way because the pressure in the capillaries
is not increased, he attributes to an injurious effect on the capillary
endothelium (and especially on the endothelium of the capillaries of
the liver, since nearly the whole of the increased lymph-flow comes
from that organ), which increases its permeability. Starling's expla-
nation is supported by various facts, but it is not easy to distinguish
an increase of permeability produced by lymphagogues from an
increase of secretive activity of the endothelial cells. Hamburger,
too, has brought forward results which it is difficult to reconcile with
a theory of filtratfon even for the second class of lymphagogues.
Further, Heidenhain has shown that some time after injection of a
crystalloid substance, like sugar, into the blood, a greater percentage
of the substance may be found in the lymph than in the blood.
Now, when a mixture of crystalloids and colloids is filtered through
a thin membrane, the percentage of crystalloids in the filtrate is
never, at most, greater than in the original liquid (Cohnstein). And
although Cohnstein states that if time enough be allowed, the
maximum concentration of sodium chloride in the lymph, after intra-
venous injection, becomes approximately the same as the maximum
in the blood, this fact does not enable us to decide against the
secretion and in favour of the filtration hypothesis. Lazarus-Barlow
argues strongly against the physical view, and points out, among
other interesting conclusions, that the maximum outflow of lymph
from the thoracic duct does not occur at the time of maximum intra-
venous pressure, and that in the great majority of his experiments
the injection of a concentrated solution of sodium chloride, glucose
or urea into a vein was followed, not by an initial diminution in the
outflow of lymph (as might have been expected if the exchange of
water between the blood and the tissue spaces was regulated solely
by differences in osmotic pressure), but by an immediate increase.
To sum up, we may say that the general trend of research is at
present in the direction of abridging to a certain extent the field of
specific vital action so far as the capillary endothelium is concerned, and
of enlarging the ' sphere of influence ' of the more purely physical pro-
cesses of filtration a?id osmosis.
It ought to be remembered in this whole discussion that the
epithelium of ordinary glands derives its supplies of material from
the lymph. The vicissitudes of blood-pressure affect it only in a
secondary and indirect manner. On the other hand, the endothelial
cells which have to do with the formation of lymph are in direct
contact with the blood. And it is interesting to observe that in this
respect the glomeruli of the kidney and the alveoli of the lungs (if the
endothelial lining of Bowman's capsule and the alveolar membrane
24
370 A MANUAL OF PHYSIOLOGY
are assumed to be complete) take a middle place between the glands
proper and the quasi-glandular capillaries.
The increase in the quantity of chyle flowing from the thoracic
duct during digestion may be, on the mechanical theory, associated
with the dilatation of the intestinal arterioles and the consequent
increase of blood-pressure in the capillaries of the splanchnic area in
general, and of the liver in particular. But it may be equally well
harmonized with the doctrine of secretion. In consequence of the
quickened flow of lymph the number of lymphocytes in the blood is
increased during digestion, a fact which ought to be remembered in
enumerating the corpuscles for clinical purposes.
Absorption of Fat. — It has been already mentioned that
some of the fat is spHt up in the intestine into glycerine
and fatty acids, but how much undergoes this change is
unknown. It is believed by some that the whole of the fat
is so split up, to be absorbed in the form of soaps, or of free
fatty acids, or of both. If this be the case, neutral fat must
again be built up in the epithelial cells, covering the villi
from the absorbed fatty acids or soaps. For if an animal is
killed during digestion of a fatty meal, these cells are found
to contain globules of different sizes, which stain black with
osmic acid, are dissolved out by ether, leaving vacuoles in
the cell substance, and are therefore fat (Plate III., i). But
the usual view is that the greater portion of the fat escapes
decomposition, and is absorbed in a state of fine division by
the epithelial cells. It is not known in what manner the
cells take up the emulsified fat from the intestine, but it
certainly passes into them, and not between them. When
fat is found in the cement substance between the cells, it has
been mechanically squeezed out of them by the shrinking of
the villi in preparation. Leucocytes have been asserted to
be the active agents in the absorption of fat. They have
been described as pushing their way between the epithelial
cells, fishing, as it were, for fatty particles in the juices of
the intestine, and then travelling back to discharge their
cargo into the lymph. This view, however, is erroneous.
But although the leucocytes do not aid in the absorption
of fat from the intestine, they appear to take it up from
the epithelial cells, conveying it through the spaces of
the network of adenoid tissue that occupies the interior of
the villus, to discharge it into the central lacteal, where it
ABSORPTION 371
mingles with the lymph and forms the so-called molecular
basis of the chyle. A part of the fat reaches the lacteal in
some other way, without being carried by the leucocytes.
The contraction of the smooth muscular fibres of the villus
and the peristaltic movements of the intestinal walls alter
the capacity of the lacteal chamber, and so alternately fill it
from the lymph of the adenoid reticulum, and empty it into
the lymphatic vessel with which it is connected. By this
kind of pumping action the passage of fat and other sub-
stances into the lymphatics is aided. In the dog no fat
is absorbed by the bloodvessels, except perhaps a small
quantity in the form of soaps ; it nearly all goes into the
lacteals, and thence by the general lymph stream through
the thoracic duct into the blood. And in man the chyle
collected from a lymphatic fistula contained a large propor-
tion of the fat given in the food (Munk). But this bare
statement would be misleading if we did not add that the fat
taken in can never be entirely recovered in the chyle collected
from the thoracic duct. A portion of it disappears, and its
fate is unknown. And even after ligature of the thoracic duct
a large proportion of a meal of fatty acids is absorbed from
the intestine, by what channel is uncertain (Frank).
A dog normally absorbs 9 — 21 per cent.' of the fat in a
meal in three to four hours; 21 — 46 per cent, in seven
hours; and 86 per cent, in eighteen hours (Harley). After
excision of the pancreas not only is the absorption of fat
abolished, but more fat can be recovered from the intestine
than is given in the food. This at first sight paradoxical
result is explained by the well-established fact that a certain
amount of fat is normally excreted into the intestine.
Absorption of "Water, Salts, and Sugar. — The water, salts,
and sugar pass normally into the rootlets of the portal vein,
not into the chyle, for no increase in the quantity of these
substances flowing through the thoracic duct takes place
during digestion, while the sugar in the portal blood is
increased after a starchy meal. In man not i per cent, of
the sugar corresponding to the carbo-hydrates of the food
could be recovered in the chyle escaping from a lymphatic
fistula. But when a large amount of a dilute solution of
24 — 2
372 A MA A UAL OF PHYSIOLOGY
sugar is introduced into the intestine some of it is taken
up by the lacteals.
Absorption of Proteids. — The proteids of the food and
their digested products also pass directly into the blood-
capillaries which feed the portal system. For it has been
shown that after ligature of the thoracic duct proteid sub-
stances are still absorbed from the intestine, and the urea
corresponding to their nitrogen appears in the urine. And
the proteids in the lymph flowing from a lymphatic fistula
in man were not found to be sensibly increased during the
digestion of proteid food (Munk).
Although a certain amount of egg-albumin, myosin, alkali-
albumin, and other proteid substances can be absorbed as
such by the small, and even by the large intestine, there can
be no doubt that the greater part of the proteids of the
food is first changed into peptones. But peptones are either
not found at all in the blood or only in small amount, and,
indeed, when injected into the blood they are excreted in
the urine. When injected in larger amount they pass also
into the lymph, from which they gradually reach the blood
again, and are eventually, as before, eliminated by the
kidneys. The clear inference is that when absorbed from
the alimentary canal they must be changed into one or both
of the chief proteids of blood and chyle (serum-albumin and
serum-globulin) in their passage through its w^alls. And
it has actually been shown that during the digestion of a
proteid meal the mucosa of the stomach and intestine
contains peptone, while none is present in the muscular
coat or in any other organ. The peptone rapidly disappears
from a portion of the mucous membrane kept at a tempera-
ture of about 40° C. outside of the body; but not if it has
been thrown into boiling water immediately after excision,
nor even if it has been heated to 60° C. for a few minutes.
Now, a temperature of 60' C. does not destroy an un-
organized ferment, but kills a living cell. The regenera-
tion of peptone must therefore presumably take place in
cells, and the only available cells in this locality are those
which line the intestine, or the leucocytes which wander
between them. Accordingly, both have been credited with
ABSORPTION 373
the power of absorbing and transforming peptone, but the
balance of evidence is in favour of the epithelial cells. We
cannot, however, as in the case of the fat, single out any
particular tract of these cells as alone engaged in the
absorption of peptone, or, indeed, of the diffusible sub-
stances in general. In all likelihood the cells covering the
villi are actively concerned, but there is no valid reason for
denying a share to the general lining of the stomach and
small intestine, even including the Lieberkiihn's crypts,
which morphologically form a kind of inverted villi. It is,
indeed, true that the crypts do not take part in the absorp-
tion of fat, for no granules blackened by osmic acid occur in
them during digestion of a fatty meal. But this is a ground
for attributing to them other absorptive functions rather
than for altogether denying to them a share in absorption,
especially as it seems unlikely that the secretion of the
comparatively scanty and relatively unimportant succus
entericus should engross the whole activity of such an
extensive sheet of cells. Even the large intestine, which
possesses Lieberkiihn's crypts but no villi, is able to absorb
not only peptones and sugar, but also undigested proteids ;
and although these are powers which can be rarely exercised
in normal digestion, they form the physiological basis of the
important method of treatment by nutrient enemata.
We may add to the proof of the varied powers of the cells
of the intestinal wall given by the change which peptones
undergo in their passage through them, the fact, already
mentioned, that cane-sugar does not pass into the blood as
such unless large quantities are given, but is first converted
into dextrose, even in the absence of an inverting ferment,
and the remarkable discovery of Munk, that fatty acids given
by the mouth appear in the lymph of the thoracic duct as
neutral fats, having somewhere or other, in all probability
on their way through the epithelium of the gut, been com-
bined with glycerine, although no free glycerine is known to
occur in the body.
Since, however, the amount of neutral fat recovered from
the thoracic duct is not equivalent to more than one-third
of the fatty acids given, it has been suggested that this
374 A MAiYCAL OF PHYSIOLOGY
synthesis of fat is only apparent, and that the whole of the
fat which appears in the chyle after a meal of fatty acids
comes from the fat excreted into the intestine (Frank),
which is increased when fatty acids are given by the mouth.
But the suggestion is more ingenious than the evidence
advanced in its support is convincing.
PRACTICAL EXERCISES ON CHAPTERS IV. AND V.
I. Saliva. — Collection and Microscopic Examination of Saliva. —
Chew a piece of paraffin-wax, or inhale ether or the vapour of strong
acetic acid. The flow of saliva is increased. Collect it in a porcelain
capsule. Examine a drop under the microscope. It may contain a
few flat epithelial scales from the mouth and a few round granular
bodies, the salivary corpuscles, the granules in which often show a
lively, dancing movement (Brownian motion). Filter the saliva to
free it from air-bubbles, and perform the following experiments :
{a) Test the reaction with litmus paper. It is usually alkaline.
An acid reaction may indicate that bacterial processes are abnormally
active in the mouth.
{b) Add dilute acetic acid. A precipitate indicates the presence
of mucin (p. 296). Filter.
{c) Add a drop or two of silver nitrate solution. A precipitate
soluble in ammonia, insoluble in nitric acid, proves that chlorides
are present.
{d) Add to another portion a few drops of dilute ferric chloride,
and the same quantity to as much distilled water in a control test-
tube. A red coloration is obtained, due to the presence of potassium
sulphocyanide (KCNS). The colour is discharged by mercuric
chloride. This reaction is not given by the saliva of most animals,
nor by that of some men.
(f) To the filtrate from (/') add Millon's reagent. A red coloration
or precipitate shows that proteid is present.
(/) Take some boiled starch mucilage, and test it for reducing
sugar by Trommer's test (p. 23). If no sugar is found, take three
test-tubes, label them A, B, and C, and nearly half fill each with the
boiled starch. To A add a little saliva, to B some saliva which has
been boiled, to C an equal volume of 04 per cent, hydrochloric acid
and a little saliva which has been neutralized, so as to make the
strength of the acid in the mixture 0*2 per cent., or the same as that
of the gastric juice. I'ut the test-tubes into a water-bath at about
40° C. In a few minutes test the contents for reducing sugar.
Abundance will be found in A, none in B nor in C. In B the
ferment ptyalin has been destroyed by boiling ; in C its action has
been inhibited by the acid. If the test-tubes have been left long
enough in the bath, no blue colour will be given by A on the
PRACTICAL EXERCISES 375
addition of iodine, but a strong blue colour by H and C ; i.e., the
starch will have completely disappeared from A.
{g) Put some starch in a test-tube, add a little saliva, and hold in
the hand or place in a bath at 40° C. On a porcelain slab place
several separate drops of dilute iodine solution. With a glass rod
add a drop of the mixture in the test-tube to one of the drops of
iodine at intervals as digestion goes on. At first only the blue colour
given by starch will be seen ; a little later a violet colour, due to the
presence of erythrodextrin in addition to some unaltered starch. A
little later the colour will be reddish, the starch having disappeared,
and the erythrodextrin reaction being no longer obscured. Later still
no colour reaction will be obtained, the erythrodextrin having under-
gone farther changes, and only sugar (maltose, isomaltose, and
perhaps a trace of dextrose) and achroodextrin — a kind of dextrin
which gives no colour with iodine — being present.
{h) Put a little distilled water in a porcelain capsule, and bring the
water to the boil. Nov put into the mouth some boiled starch
paste, and move it about as in mastication. After half a minute spit
the starch out into the boiling water. Divide the water into two
portions. Test one for sugar, and the otlier for starch. Repeat the
experiment, but keep the starch two minutes in the mouth. Report
the result.
(/) Starch solution to which saliva has been added is placed in a
dialyser tube of parchment paper for twenty-four hours. At the end
of that time the dialysate (the surrounding water) should be tested
for sugar and for starch. Sugar will probably be found, but no
starch. If no reaction for sugar is obtained, the dialysate should be
concentrated on the water-bath, and again tested.
2. Stimulation of tlie Chorda Tympani. — (i) Having previously
studied the anatomy of the mouth and submaxillary region in the dog
by dissecting a dead animal (Fig. 115, p. 383), put a good-sized dog
under morphia. Set up an induction-machine for a tetanizing current
(p. 175), and connect it with fine electrodes. Fasten the dog on the
holder, give ether if necessary, and insert a cannula in the trachea
(p. 177). Then make an incision 3 or 4 inches long, through
skin and platysma muscle, along the inner border of the lower jaw
beginning about the angle of the mouth, and continuing backwards
towards the angle of the jaw. Ligature doubly, and divide such
branches of the jugular vein as come in the way, except those
belonging to the submaxillary gland. Feel for the facial artery, so
as to be able to avoid it. Divide the digastric muscle about its
anterior third, and clear it carefully from its attachments. The
broad, thin mylo-hyoid muscle will now be seen with its motor nerve
lying on it. Divide the muscle about its middle at right angles to
its fibres, and raise it carefully. The lingual nerve will be seen
emerging from under the ramus of the jaw. It runs transversely
towards the middle line, and then, bending on itself, passes forwards
parallel to the larger hypoglossal nerve. In its transverse course the
linguil will be seen to cross the ducts of the submaxillary and sub-
lingual glands. These structures having been identified, the lingual
376 A MANUAL OF PHYSIOLOGY
nerve is to be ligatured before it enters the tongue and cut peri-
pherally to the ligature. Then a suitable glass cannula with a
rectangular elbow is to be inserted into the submaxillary duct (the
larger of the two), just as if it were a bloodvessel (p. 58). The
lingual is now to be lifted by means of the ligature, and traced back
towards the jaw till its chorda tympani branch is seen coming off and
running backwards along the duct. The chordo-lingual nerve
(Fig. 107, p. 333) is then to be cut centrally to the origin of the
chorda tympani, which can now be easily laid on electrodes by
means of the ligature on the lingual. On stimulating the chorda,
the flow of saliva through the cannula will be increased. The
current need not be very strong. If the flow stops after a short time,
it can be again caused by renewed stimulation after a brief rest. A
quantity of saliva may thus be collected, and the experiments already
made with human saliva repeated.
(2) Expose the vago-sympathetic nerve in the neck on the same
side ; ligature it ; divide below the ligature, and note the effect
produced by stimulation of the upper end on the flow of saliva.
(3) Set up another induction-machine, and connect it with
electrodes. Stimulate the chorda, and note the rate of flow of the
saliva. Then, while the chorda is still being excited, stimulate the
vago-sympathetic and observe the effect. If the experiment is suc-
cessful, finish by stimulating the chorda lor a long time. Then
harden both submaxillary glands in absolute alcohol, make sections,
stain with carmine and compare them.
3. Effect of Drugs on the Secretion of Saliva. — (i) Proceed as
in 2 (i), but, in addition, insert a cannula into the femoral vein, and
while the chorda is being stimulated inject into the vein, in the
manner described on p. 177, 10 to 15 milligrammes of sulphate of
atropia. This will stop the flow of saliva, and abolish the effect of
stimulation of the chorda.
(2) Now empty the cannula in the submaxillary duct by means of
a feather, and fill it with a 2 per cent, solution of pilocarpine nitrate
by means of a fine pipette. Then, attaching a small syringe to the
cannula, force into the duct about \ c.c. of the solution. Dis-
connect the syringe. Secretion of saliva will again begin, and
stimulation of the chorda will again cause an increase in the flow.
But after a few minutes the action of the atropia will reassert itself
and the flow will stop. Renewed secretion may be caused by a fresh
injection of pilocarpine.
4. Gastric Juice — {a) Preparation of Artificial Gastric Juice. —
Take a portion of the pig's stomach provided, strip off the mucous
membrane (except that of the pyloric end), cut it into small pieces
with scissors, and put it in a bottle with fifty times its weight of
o"4 per cent, hydrochloric acid. Label and put in a bath at 40° C.
for twelve hours. Then filter.
{b) Take another portion of the mucous membrane, cut it into
pieces, and rub up with clean sand in a mortar. Then put it in a
small bottle, cover it with glycerine, label, and set aside for two or
three days. The glycerine extracts the pepsin.
PRACTICAL EXERCISES 377
{c) Take five test-tubes, A, B, C, D, E, and in each put a little
washed and boiled fibrin. To A add a few drops of glycerine
extract of pig's stomach, and fill up the test-tube with 0*2 per cent,
hydrochloric acid. To B add glycerine extract and distilled water ;
to C glycerine extract and i per cent, sodium carbonate ; to D
o"2 per cent, hydrochloric acid alone ; to E glycerine extract which
has been boiled, and o'2 per cent, hydrochloric acid.
Put up another set of five test-tubes in the same way, except that a
few drops of a watery solution of a commercial pepsin are substituted
for the glycerine extract. Label the test-tube A', B', C, D', E'.
Into another test-tube put a little fibrin, and fill up with the
filtered acid extract from {a). Label it F. Place all the test-tubes
in a tumbler, and set them in a water-bath at 40' C
After a time the fibrin will have almost completely disappeared in
A, A', and F, but not in the other test-tubes. Filter the contents of
A, A', and F.
{d) Test the filtrate for the products of gastric digestion :
(a) Neutralize a portion carefully with dilute sodium
hydrate. A precipitate of acid-albumin may be
thrown down. Filter.
{(i) To a portion of the filtrate from (a) add excess of
sodium hydrate and a drop or two of very dilute
copper sulphate. A rose colour indicates the
presence of proteoses or peptones. The cupric
sulphate must be very cautiously added, because an
excess gives a violet colour, and thus obscures the
rose reaction. If still more cupric sulphate be
added, blue cupric hydrate is thrown down, and
nothing can be inferred as to the presence or the
nature of proteids in the liquid.
(7) Heat another portion of the filtrate from (a) to 30° C,
and add crystals of ammonium sulphate to satura-
tion. A precipitate of proteoses (albumoses) may
be obtained. Filter off.
(S) Add to the filtrate from (7) a trace of cupric sulphate
and excess of sodium hydrate. A rose colour in-
dicates that peptones are present. More sodium
hydrate must be added than is sufficient to break
up all the ammonium sulphate, for the biuret
reaction requires the presence of free fixed alkali.
A strong solution of the sodium hydrate should
therefore be used, or the stick caustic soda. The
addition of ammonium sulphate will cause the red
colour to disappear ; so will the addition of an
acid. Sodium hydrate will bring it back. Ammonia
does not affect the colour.
{e) To some milk in a test-tube add a drop or two of rennet
extract, and place in a bath at 40" C. In a short time the milk is
curdled by the rennin.
5. (i) To obtain Normal Chyme. — Inject subcutaneously into a
378 A MAXUAL OF PHYSIOLOGY
dog, one and a half hours after a meal of meat, 2 mg. of
apomorphine. One-half of one of the ordinary tabloids is enough.
Collect the vomit.
(2) To obtain Pure Gastric Juice. — Put a fasting dog under ether,
and fasten on the holder. Clip the hair and shave the skin in the
middle line below the sternum. Make a longitudinal incision
through the skin and subcutaneous tissue
from the xiphoid cartilage downwards for
3 or 4 inches. The linea alba will now
be seen as a white mesial streak. Open
the abdomen by an incision through it.
Pull over the stomach towards the right,
stitch it to the abdominal wall, open it, and
J 1 -.—Stomach- insert a stomach-cannula (Fig. 113). By
Cannula. mechanically stimulating the mucous
membrane of the stomach with a feather,
or by the introduction of pieces of indiarubber, a flow of gastric
juice can be caused.
(3) (^) Test the proteolytic and milk-curdling powers of the filtrate
from the chyme obtained in (i), and of the pure juice obtained
in (2). Both will dissolve fibrin, but probably neither will curdle
milk when neutralized. For the gastric juice of many animals
contains no rennin, although the fully-formed ferment or its zymogen
may be present in the gastric mucous membrane. The rennet
ferment is active in an acid or neutral, but inactive in an alkaline
medium. Examine a drop of the unfiltered chyme under the
microscope. Partially digested fragments of the food will be seen —
muscular fibres, or fat cells. Filter, and proceed as in 4 (d).
(4) Test the filtrate from the chyme and the gastric juice for
lactic acid by Ueffelmann's test, and for hydrochloric acid by Giins-
burg's reagent.
Ueffelmann's Test for Lactic Acid. — The reagent is a dilute solu-
tion of carbolic acid to which a trace of ferric chloride has been
added (say a drop of a i per cent, ferric chloride solution to 5 c.c.
of a I per cent, carbolic acid solution). The blue colour of the
mixture is turned yellow by lactic acid, but not by dilute hydro-
chloric acid ; normal healthy gastric juice does not affect it, there-
fore its acidity is not caused by free lactic acid.
GUnsburg's Reagent for Frea Hydrochloric Acid in Gastric Juice
is made by dissolving 2 parts of phloroglucinol and i part of vanillin
in 30 parts by weight of absolute alcohol. A few drops of the reagent
are added to a few drops of the filtered gastric juice in a small
porcelain capsule, and the whole evaporated to dryness over a small
bunsen flame. If free hydrochloric acid is present, a carmine-red
residue is left. If all the hydrochloric acid is united to proteids in
the stomach contents, the reaction does not succeed. It is also
hindered by the presence of leucin.
6. Pancreatic Juice. — {a) Take a piece of the pancreas of an ox
or dog which has been kept twenty-four hours at the temperature of
the laboratory, and make a glycerine extract in the same way as in
PRACTICAL EXERCISES 379
the case of the pig's stomach 4, (</). Put in a small bottle, and set
■aside for a day or two.
{/') Put a little fibrin into each of six test-tubes, A, B, C, D, K, F.
To A add a few drops of glycerine extract of pancreas, and fill up
with I per cent, sodium carbonate solution ; to B add glycerine
■extract and distilled water ; to C glycerine extract and excess of
•o"i per cent, hydrochloric acid; to I) i per cent, sodium carbonate
alone ; to E i per cent, sodium carbonate in which a few drops
of glycerine extract of pancreas has been previously boiled ;
to F glycerine extract and excess of 0*4 per cent, hydrochloric
•acid.
Set up six test-tubes, A', B', C, D', E', F', in the same way, but
■substitute a few drops of a solution of commercial pancreatin for the
glycerine extract. Put all the test-tubes in a tumbler, and place in
a bath at 40° C The fibrin will be gradually eaten away in A and A'
by the action of the trypsin, but will not swell up or become clear
before disappearing, as it does in dilute hydrochloric acid with
glycerine extract of stomach. Filter the contents of these test-tubes.
Neutralize the filtrate with dilute acid ; a precipitate will consist of
alkali-albumin. If such a precipitate is obtained, filler it off and test
the filtrate for proteoses and peptones as in 4 [d), p. 377. Digestion
will also have taken place in C and C, but not in the other test-
tubes (pp. 306, 354).
{c) Leucin and Tyrosin. — If pancreatic digestion be allowed to go
on for some time, part of the peptone first formed may be broken up
into leucin and tyrosin. If the ' digest ' be neutralized to separate
alkali-albumin, then filtered, and the filtrate concentrated and allowed
to stand, a crop of tyrosin crystals will separate out, since tyrosin
is only slightly soluble in watery solutions of neutral salts. These
crystals having been filtered off, the proteoses (albumoses) and
peptones can be precipitated together by alcohol, and afterwards
separated, if that is desired, by redissolving the precipitate in water
and throwing down the proteoses by saturation with ammonium
sulphate. The alcoholic filtrate will contain any leucin that may be
present, since that body is moderately soluble iti alcohol, as well as
traces of tyrosin, which, however, is much less soluble in this medium.
On concentration, crystals of both substances will be obtained.
Tyrosin crystallizes characteristically from animal liquids in beautiful
silky needles united into sheaves, leucin in the form of indistinct
fatty-looking balls, often marked with radial stride and coloured with
pigment (Figs. 122 and 123, p. 394).
{d) Add a few drops of the glycerine extract to a test-tube con-
taining starch mucilage, which has been previously found free from
reducing sugar. Put in a bath at 40" C. After a short time abund-
ance of reducing sugar will be found, owing to the action of the
ferment, amylopsin.
7.* To obtain Normal Pancreatic Juice. — {a) Give a rabbit \ grm.
chloral hydrate per rectum. Put on a holder. Open the abdominal
cavity by an incision in the linea alba 2\ inches long. Pull the
* This experiment is only suitable for advanced students.
38o A MANUAL OF PHYSIOLOGY
duodenum, which will be found in the right hypochondrium, through
the wound, and follow it down till its mesentery prevents it from
coming out any farther. Here the pancreatic duct will be found.
' Resect 2 inches of the intestine at this point, leaving the
mesenteric attachment, tie the cut ends of the intestine above and
below, and drop them in the cavity, bringing the resected portion
through the wound.' Open the resected piece of intestine opposite
the mesenteric attachment, and spread it out on the abdominal wall.
Clamp the ends to stop hemorrhage. Push into the pancreatic duct
a small glass cannula through the papilla on which the duct opens.
The juice begins to flow immediately, and the flow lasts four to si.x
hours, although it is slow, and only a comparatively small quantity
can be collected. The exposed intestine must be kept moist by
pads of cotton-wool soaked in normal saline (Rachford). The
animal must be killed as soon as the flow has ceased. The juice "
has an alkaline reaction.
{b) With the juice so obtained perform the following experiments
to demonstrate its fat-splitting action : Shake a little of it with neutral
olive-oil ; the oil becomes acid owing to the formation of fatty acid.
Take with a pipette a drop of the oil from the surface of the mixture
of oil and pancreatic juice, and put it on a ^ per cent, solution
of sodium carbonate in a watch-glass. An emulsion is formed.
Sodium carbonate and neutral olive-oil do not form an emulsion;
some fatty acid must be present.
8. Bile. — (a) Test the reaction of ox bile. It is alkaline.
(/') Add dilute acetic acid. A precipitate of bile-mucin (really
nucleo-albumin) falls down. Some of the bile-pigment is also pre-
cipitated. Filter.
{c) Dilute the filtrate from {b). Put a little of it into a porcelain
capsule, add a few drops of strong sulphuric acid, and a drop or
two of a dilute solution of cane-sugar. A purple colour appearing
at once, or after gentle heating, shows the presence of bile-acids
(Pettenkofer's reaction). Examine the purple liquid in a test-tube
with a spectroscope (p. 62). Two absorption bands are seen, one
between 1) and E, the other between E and F.
{d) Add yellow nitric acid (containing nitrous
acid) to a little bile on a white porcelain-slab.
A play of colours, beginning with green and
lunning through blue to yellow and yellowish-
brown, indicates the presence of bile-pigment
(Gmelin's reaction).
(f) CIiol ester in (Fig. 114). — Preparation. —
Extract a powdered gallstone (preferably a
white one) with hot alcohol and ether in a test-
tube. Heat the test-tube in warm water. Put
^terin"*cTystai's^'^ ^ ^""^P °^ ^^^ extract on a slide. Flat crystals
of cholesterin, often chipped at the corners,
separate out. Carefully allow a drop of strong sulphuric acid and a
drop of dilute iodine to run under the cover-glass. A play of colours
— violet, blue, green, red — is seen.
PRACTICAL EXERCISES 381
Evaporate a drop of the solution of cholestcrin in a small porcelain
capsule, add a drop of strong nitric acid, and heat gently over a
flame. A yellow stain is left, which becomes red when a drop of
ammonia is poured on it while it is still warm.
(/) Preparation of Bile Salts from Bile. — Evaporate bile to a
small bulk, mix the residue with animal charcoal, dry to a paste at
100° C, extract with absolute alcohol, and precipitate the solution
with ether. The bile-salts separate as a mass of needle-shaped
crystals, often in sheaf-like bundles. On dissolving the crystals in
water, and adding dilute sulphuric acid to displace the bile-acids, the
latter are precipitated as crystalline needles.
i^g) To demonstrate the Presence of Iron in the Liver Cells. — Steep
sections of liver in a solution of potassium ferrocyanide, and then in
dilute hydrochloric acid. They become bluish from the formation
of Prussian blue. A fine-pointed glass rod or a platinum lifter should
be used in manipulating the sections. A steel needle cannot be
employed. Mount in glycerine or Farrant's solution. Blue granules
may be seen under the microscope in some of the hepatic cells.
(//) To some starch, shown to be free from sugar, add a little bile,
and place in a bath at 40°. After a time test for reducing sugar.
Report the result.
9. Microscopical Examination of Fseces. — Examine under the
microscope the slides provided. Draw, and as far as possible deter-
mine the nature of, the objects seen (p 358).
10. Absorption of Fat. — Feed a rat or frog with fatty food; kill
the rat in three or four hours, the frog in two or three days. Strip
off tiny pieces of the mucous membrane of the small intestine, and
steep them in \ per cent, solution of osmic acid for forty-eight hours.
Then tease fragments of the mucous membrane in glycerine, take off
the glycerine with blotting-paper, mount in Farrant, and examine
under the microscope. Other portions of the mucous membrane
may be hardened for a fortnight in a mixture of 2 parts of jMiiller's
fluid and i part of a i per cent, solution of osmic acid. Sections
are then made with a freezing microtome after embedding in gum.
No process must be used by which the fat would be dissolved out
(Schafer).
II.' Time required for Digestion and Absorption of various Food
Substances. — Feed three dogs, A, B and C, which have previously
fasted for twenty-four hours, with a meal containing starch (proved
to be free from sugar), lard and meat.
(i) After fifteen minutes inject subcutaneously into A 2 c.c. of a
o"i per cent, solution of apomorphine. Note the time which elapses
before the animal vomits. Collect the vomit.
(a) Examine a little of it under the microscope, and make out fat
globules, muscular fibres and starch granules. The latter can be
* Experiments 11 and 12 are conveniently done in a class by assigning
each of the three animals to a separate set of students. The contents of
the stomach and intestine are divided into three portions, so that each
set has a sample from each dog.
382 A MANUAL OF PHYSIOLOGY
recognised by their being coloured blue by a drop or two of iodine
solution.
(/') Filter the chyme, mixing it, if necessary, with a little water^
and test it as in 4 {d) for the products of digestion. In addition, test
for starch, dextrin and reducing sugar.
(2) One and a quarter hours after the meal 'inject apomorphine
into dog B, and proceed as in (i).
(3) Two and a half hours after the meal inject apomorphine into
dog C, and proceed as in (i). Compare the results from the three
specimens of chyme.
12.* Quantity of Cane-sugar inverted and absorbed in a Given
Time. — Take three dogs, A, B and C, which have fasted for twenty-
four hours. Feed A and B with 50 c.c. of a standard solution of cane-
sugar (about a 10 per cent, solution), and some lard to render the
sugar more ))alatable. If the dogs have been kept without water for
a day they will more readily take the sugar solution. Feed C with
10 grammes of i)Owdered cane-sugar mixed with lard, the mixture
being rolled into little balls.
(i) After half an hour put A under chloroform or the ACE mixture ;
fasten it on a holder, open the abdomen in the linea alba, lift a loop
of the small intestine gently up and observe the lacteals in the
mesentery. Now kill the animal, tie the oesophagus, place double
ligatures on the pyloric end of the stomach and the lower end of the
small intestine, and divide between them. Cut out the stomach and
intestine ; wash their contents into separate vessels, and test the re-
action with litmus-paper. Add water and rub up thoroughly. Filter.
Wash the residue repeatedly with small quantities of water, and pass
all the washings through the filter. Make up each of the two filtrates
to 200 c.c.
{a) Examine the residue microscopically for fat.
{b) Test the filtrates from the contents of the stomach and intes-
tines qualitatively for glucose by Trommer's (p. 23) and the phenyl-
hydrazine test (p. 426).
{c) If no reducing sugar is present, add to 20 c.c. of each filtrate
I c.c. of liydrochloric acid, boil for half an hour, and again test for
reducing sugar. If it is now found, some cane-sugar is present.
(^) If reducing sugar is found, estimate its amount as glucose by
Fehling's solution (p. 427) in a measured quantity of the filtrate
before and after boiling with one-twentieth of its volume of hydro-
chloric acid.
(e) Estimate in the same way the amount of the glucose in the
standard solution of cane sugar after inversion, and before inversion
if it gives the qualitative test for reducing sugar before it has been
boiled with acid.
From the data obtained (and taking 95 parts of cane-sugar as
equal to 100 parts of glucose) calculate the amount of cane-sugar
absorbed, left unchanged, and inverted, though not absorbed.
(2) One and a half hours after the meal anaesthetize B, and
proceed as in (i).
* See note, p. 381.
PRACTICAL EXERCISES
383
(3) Two hours after the meal proceed in the same way with C.
Compare your results.
13. Auto-digestion of the Stomach. — In some of the previous
experiments the stomach of an animal killed during digestion should
be removed from the body after double ligation of uusophagus and
duodenum, and placed in a water-bath at 40' C. After several
hours tlie contents should be washed out, and the mucous membrane
examined. It may be entirely eaten away in parts.
14. Time required for Food to pass through the Alimentary
Canal. — Feed a dog with bones. Keep in a special cage, and
observe how long it takes before the easily-recognised white bone-
faeces appear.
Submaxillary Carotid
Gland. .Arterv.
Digastric
Muscle (cut).
H>-poglossal Mylo-hyotid
Ner\e. Muscle (cut).
Lingual Wharton's
Nerve. Duct.
Fig. 115.— Dissection for Stimulation of Chorda Tvmpani
(after Bernard).
CHAPTER \' I .
EXCRETION.
We have now followed the ingoing tide of gaseous, liquid
and solid substances within the physiological surface of the
bod3\ There we leave them for the present, and turn to the
consideration of the channels of outflow, and the waste
products which pass along them. In a body which is
neither increasing nor diminishing in mass the outflow must
exactly balance the inflow ; all that enters the body must
sooner or later, in however changed a form, escape from it
again. In the expired air, the urine, the secretions of the
skin, and the faeces, by far the greater part of the waste pro-
ducts is eliminated. Thus the carbon of the absorbed solids
of the food is chiefly given off as carbon dioxide by the lungs ;
the hydrogen, as water by the kidneys, lungs and skin, along
with the unchanged water of the food ; the nitrogen, as urea
by the kidneys. The faeces in part represent unabsorbed
portions of the food. A small and variable contribution to
the total excretion is the expectorated matter, and the secre-
tions of the nasal mucous membrane and lachrj-mal glands.
Still smaller and still more variable is the loss in the form of
dead epidermic scales, hairs and nails. The discharges from
the generative organs are to be considered as excretions
with reference to the parent organism, and so is the milk,
and even the foetus itself, with respect to the mother.
Excretion by the lungs and in the faces has been already
dealt with. All that is necessary to be said of the expectora-
tion and the nasal and lachrymal discharges is that the
first two generally contain a good deal of mucin, and are
produced in small mucous and serous glands, the cells of
»
Plate IV.
3. Crystals of phenyl glucosazone from oriDa,
^:
^*
-;%■■
m'm
Malpighian tnfl
^^^^i^^'..
Botcri \j
^
^-1.^::^
V^/
..^-
Jiewd iMhvXc
4. Section of cortex oi injected kidney.
1. Crystals of uric acid
from urine.
2. Crystals of ammonium urate
from urine.
5. Section of medulla of injected kidney
showing rasa recta and collecting tubalea>
West Nemnan chrhth
EXCRETION 385
which are of the same general type as those of the imicous
and serous sahvary glands. The lachrymal glands are
serous like the parotid ; and the tears secreted by them
contain some albumin and salts, but little or no mucin. The
sexual secretions and milk will be best considered under
reproduction (Chap. XIV.), so that there remain only the
urine and the secretions of the skin to be treated here.
I. Excretion by the Kidneys,
The Chemistry of the Urine. — Normal urine is a clear
yellow liquid of acid reaction, and with an average specific
gravity of about 1020, the usual limits being 1015 and 1025,
although when water is taken in large quantities, or long
withheld, the specific gravity may fall to 1005, or even less,
or rise to 1035, or even more. The quantity passed in
twenty-four hours is very variable, and is especially
dependent on the activity of the sweat-glands, being, as a
rule, smaller in summer when the skin sweats much, than
in winter when it sweats little. The average quantity for
an adult male is 1200 to 1500 c.c. (say, 40 to 50 oz,).*
Composition of Urine. — It is essentially a solution of urea
and inorganic salts, the proportion of the latter being about
I "5 per cent., or double the usual amount in physiological
solids and liquids. Besides urea, there are other nitrogenous
bodies in much smaller quantity, such as uric acid and the
allied xanthin bases, hippuric acid, and kreatinin. Some of
these at least are products of the metabolism of proteids
within the tissues ; and besides the inorganic salts there are
certain organic bodies — indol, phenol, pyrokatechin, skatol
— united with sulphuric acid, which are primarily derived
from the products of the putrefaction of proteids within the
digestive tube. In tabular form the composition of urine,
* The average quantity of urine varies not only with the season, but
also with the habits of the person, especially as regards the amount of
liquid taken. The average for seventeen healthy (American) students,
whose urine was collected for six to eight successive days in winter, was
1 166 c.c. The highest average in any one individual for the observation
period was 1487 c.c. (for seven days), and the lowest 743 c.c. (for eight
days). The greatest quantity passed in any one period of twenty-four
hours was 2286 c.c. (by the individual whose average was the highest).
The smallest quantity passed in twenty-four hours was 650 c.c. (by the
individual whose average was the lowest).
25
r looo.
In 24 hours.
960
1440 )>ramnies.
40
60
20
30
r8
075
0-5
-'1
3275 grammes
9
2-5
075
075
-26*5 grammes.
7
8
35
386 A MA.XUAL 01- rilYSIOLOay
and the total excretion by an average man of 70 kilos, may
be given thus :
P(
Water . . . .
Solids . . - -
Urea - . -
Uric arid and \antliin basest
Hippuric acid - -
Kreatinin - J
Sodium - - -"j
Potassium - - - 1
Ammonia - - - j
Calcium and magnesium - '
Chlorine - - - \
Phosphoric acid - - 1
Sulphuric acid - -J
Mucus, pigment, etc.
The acidity of urine is not due to free acid, for the tests which
reveal the presence of free acid in a mixture, such as the {)recipitation
of sulphur on the addition of sodium hyposulphite, and the change
of colour of many organic substances, give a negative result when
applied to urine. The acidity is chiefly due to the acid phosphates
of sodium and potassium ; in a less degree to dissolved carbon
dioxide. That a considerable proportion of the phosphoric acid is
normally present in the form of acid sodium phosphate (NaH^PO^)
is shown by the fact that barium chloride usually precipitates only
about 40 per cent, of the phosphoric acid, leaving the rest in solution.
Now, barium chloride does not cause a precipitate in a dilute solution
of acid sodium phosphate, but does precipitate the disodium-hydrogen
phosphate (Na^HPO^). The acidity is estimated by running into a
given quantity of urine a dilute solution of sodium hydrate, which has
been previously titrated with a pure acid solution (say, oxalic acid)
of known strength, until a neutral reaction is just obtained. From
the amount of sodium hydrate required the acidity can be calculated
in terms of the standard acid. Normally the acidity of urine is about
equal to that of a ci per cent, solution of sulphuric acid. It diminishes
distinctly, or even gives place to alkalinity, during digestion when
the acid of the gastric juice is being secreted, and varies with the
quantity of vegetable food in the diet. The urine of herbivora is
alkaline, and turbid from precipitated carbonates and phosphates of
earthy bases, while that of carnivora and of fasting herbivora, which
are living on their own tissues, is strongly acid and clear. Normal
human urine may deposit urates soon after discharge, as they are
more soluble in warm than in cold water. They carry down some
of the pigment, and therefore usually appear as a pink or brick-red
sediment. When urine is allowed to stand after being voided, what
is generally described as ' acid fermentation ' occurs. The acidity
gradually increases, owing apparently to the formation of lactic acid;
acid sodium urate is produced from the neutral urate, and comes down
in the form of amorphous granules, while the liberated uric acid is
deposited often in 'whetstone ' crystals, coloured yellow by the pigment
EXCRETION
387
(Fig. 116 ; Plate IV'., i). Calcium oxalate may also be thrown down
as ' envelope,' a, l\ or, less frec}uently, ' sand-glass ' crystals, c ( Fig. 117).
If the urine is allowed to stand for a few days, especially in a warm
place, or in a place where urine is decomposing, the reaction becomes
ultimately strongly alkaline, owing to the formation of ammonium
carbonate from urea by the action of micro-organisms {Micrococcus
ureic. Bacterium urae, and others) which reach it from the air, and
Fio. 116.— Uric Aim.
Calcium Oxalate.
produce a soluble ferment, in whose presence the urea is split up
under absorption of water. Thus :
CON.H,
UreR.
2H.,0 =
(NH,).,C03.
Ammonium carbonate.
Fig. iiS.— Triple Phosphate.
The substances insoluble in alkaline urine are thrown down, the
deposit containing ammonio-magiiesic or triple phosphate^ formed
by the union of ammonia with the magnesium phosphate present in
fresh urine, and precipitated as clear crystals of ' knife-rest ' or ' coffin-
lid ' shape (Fig. 118), along with amorphous earthy phosphates, and
often acid ammonium urate in
the form of dark balls occa-
sionally covered with spines
(Plate IV., 2).
It is only in pathological con-
ditions that this alkaline fermen-
tation takes place within the
bladder. The reaction of the
urine can readily be made alka-
line by the administration of alkalies, alkaline carbonates, or the
salts of vegetable acids like malic, citric, and tartaric acid, which
are broken up in the body and form alkaline carbonates with the
alkalies of the blood and lymph. It is not so easy to increase the
acidity of the urine, although mineral acids do so up to a certain
limit. If the administration of acid be pushed farther, ammonia is
split off from the proteids, and is e.xcreted in the urine as the
ammonium salt of the acid.
Urea, CO(NHo)o, is the form in which by far the greater part of
the nitrogen is discharged from the body. Its amount is as im-
portant a measure of proteid metabolism as the quantity of carbon
dioxide given out by the lungs is of the oxidation of carbonaceous
material. It is soluble in water and in alcohol, and crystallizes from
25—2
3«8
A MANUAL OF PHYSIOLOGY
its solutions in the form of long colourless needles, or four-sided
prisms with pyramidal ends (p. 41 9^
Uric acid (C-H^N^OJ exists in large amount in the urine of birds.
The excrement of serpents consists almost entirely of uric acid. In
man and mammals the quantity is comparatively small in health, but
is increased after a meal, particularly one containing substances rich
in nucleo-proteids, e.g.^ the thymus of the calf.
The xanthin bases are a group of substances allied to uric acid,
and including, besides xanthin itself (Cr,H^N^O.,), hypoxanthin
(Cr,H^NjO), guanin and other bodies. They exist in very small
amount in urine, but, like uric acid, are increased in amount by the
ingestion of nucleo-proteids.
■_;^Hippuric acid (C,|H,,NO..) occurs in considerable (juantity in the
urine of herbivora ; in the urine of carnivora and of man only in
traces; in that of birds not at all. It is much more dependent on
the presence of particular substances in the food than the other
organic constituents of urine. Anything which contains benzoic
Ku;. 119. — Kreatin.
Fic. 120.— Kkkatimn-zinc-chi.okidk.
acid, or substances which can be readily changed into it (such as
cinnamic and quinic acids), causes an increase of the hippuric acid in
urine. In fact, one of the best ways of obtaining the latter is from
the urine of a person to whom benzoic acid is given by the mouth ;
the sweat may also in this case contain a trace of hippuric acid.
Chemically it is a conjugated acid formed by the union of benzoic
acid and glycin. Thus :
QH,,0,, + C.^Hj,NO., = C.,H,,N03 + H.p.
Benzoic acid. Glycin. Hippuric acid. Water.
Benzoic acid, therefore, meets glycin in the body, and combines with
it, as fatty acids meet glycerine and combine with it. But neither
free glycin nor free glycerine have been detected in the blood or
tissues (p. 424).
Kreatinin (C4H-N3O) has only been found as a constant con-
stituent in the urine of man and a few other mammals. It is possibly
EXCRETION 38.;
the form in which the kreatin of muscle leaves the body. Its formula
differs from that of kreatin only in i)ossessing the elements of one
molecule of water less ; and kreatinin can be obtained by boiling
kreatin with dilute sulphuric acid, tiien neutralizing with barium
carbonate, filtering, evaporating the filtrate to dryness on the water-
bath, and extracting the residue with alcohol. From its alcoholic
solution it crystallizes in colourless prisms. It forms crystalline
compounds with zinc chloride and other salts (p. 424).
Pigments of Urine. — The pigments of urine have not hitherto
been exhaustively studied ; but we already know that normal urine
contains several, and pathological urines probably additional, pig-
mentary substances. The best-known pigments in normal urine are
urochrflmt\ the yellow substance which gives the liquid its ordinary
colour ; iiroerythrin, the pink pigment which often colours the
deposits of urates that separate even from healthy urine ; and
urolu7iii, sometimes termed normal la-olnlifi, to distinguish it from
the so-called febrile urobilin, which, as has been already mentioned.
Fic. 121. — Pepsin in Urine. Diastatic Ferment in Urine.
At Different Times ok the Day (Hoffmann).
is identical with the faecal pigment stercobilin, and occurs not only
in many febrile conditions, but also in cases with no fever, such as
functional derangements of the liver, dyspepsia, chronic bronchitis,
and valvular diseases of the heart. Normal and febrile urobilin are
said to present certain spectroscopic differences, but are probably
one and the same substance.
The pigments of the blood and bile and some of their derivatives
are of common occurrence in the urine in disease. Hcematopor-
phyrin has not only been found in some pathological conditions, but
appears to be constantly present in minute traces in normal urine.
In paroxysmal hsemoglobinuria, met/iff/iioglobin is found in the urine
in large amount ; and it is worthy of note that it is not formed in the
urine after secretion, but is already present as such when it reaches
the bladder.
Ferments. — The urine contains traces of proteolytic and amylolytic
ferments (Fig. 121).
Of the inorganic constituents of urine the most important
390 ^'l MANUAL OF /'// YS/OLOGV
and most easily estimated arc the chlorine, phosphoric acid,
and sulphuric acid.
Chlorine. — Much the greater part of the chlorine is united with
sodium, a smaller amount with potassium. The chlorides of the
urine are undoubtedly to a great extent derived directly from the
chlorides of the food, and have not the same metabolic significance
as the organic, and even as some of the other inorganic consti-
tuents. But it is noteworthy that in certain diseased conditions the
chlorine may disappear entirely from the urine, or be greatly
diminished, e.g., in pneumonia, and in general in cases in which
nuich material tends to pass out from the blood in the form of
effusions (p. 416).
Phosphoric Acid. — The phosphoric acid of the urine is chiefly
derived from the phosphates of the food, but must partly come from
the waste products of tissues rich in phosphorus-containing sub-
stances, such as lecithin and nuclein. The phosphoric acid iu united
l)artly with alkalies, especially as acid sodium phosphate, and partly
with earthy bases, as phosphates of calcium and magnesium. The
eartliy phosphates are precipitated by the addition of an alkali to
urine, or in the alkaline fermentation. In some pathological urines
they come down when the carbon dioxide is driven off by heating ; a
precipitate of this sort differs from heat-coagulated albumin in being
readily soluble in acids (p. 417).
Sulphuric Acid. — This is only to a slight extent derived from
ready-formed sulphates in the food. The greater part of it is formed
by oxidation of the sulphur of proteids. About nine-tenths of the
sulphuric acid of normal urine are united to alkalies ; the other tenth
is combined, m the form of ethereal sulphates, with aromatic bodies
derived from the putrefaction of proteids in the intestine. Such are
potassium -phenyl-sulphate (C,.H:^KS04), potassium -kresyl- sulphate
(C7H-KSO4), potassium-indoxyl-sulphate (C>,H,.NKSOJ, potassium-
skatoxyl-sulphate (C,,Hj^NKSO^), and two double sulphates of potas-
sium and pyrocatechin. Most of those aromatic compounds are
present in greater amount in the urine of the horse than in the normal
urine of man ; but in disease the quantity in the latter may be much
increased ; and to a certain extent it must be looked upon as an
index of the intensity of putrefactive processes in the intestine and of
absorption from it. Munk made the curious observation that in the
urine of a starving dog the phenol-forming substances are absent,
while in the urine of a starving man they are present in abnormally
large amount. The indigo-forming substances ('indican'), on the
other hand, are in hunger excreted in considerable (juantity by the
dog, and not at all by man (p. 418).
Phenol and kresol can easily be obtained from horse's urine by
mixing it with strong hydrochloric acid, and distilling. These aromatic
bodies pass over in the distillate. Pyrocatechin remains behind,
and can be extracted by ether ; it gives a green colour with ferric
chloride, which becomes violet on the addition of sodium carbonate.
A small amount ol phosphorus and of sulphur may appear in the
EXCRETION
39 •
urine in less oxidized forms than phosphoric and sulphuric acids.
Such sulphur compounds are potassium sulphocyanide, which is
l)robably, in part at least, derived from that of the saliva ; and ethyl
sulphide, a substance with a penetrating odour, which appears to be
a constant constituent of dogs' urine (Abel).
Thiosulphuric acid (HoS.O..) occurs almost constantly in cat's
urine, often in dog's. It is not free, but combined with bases.
The Urine in Disease. — Although, strictly speaking, a truly
pathological urine has no place in physiology, the line which
separates the urine of health from that of disease is often
narrow, sometimes invisible ; while the study of abnormal
constituents is not only of great importance in practical
medicine, but throws hght upon the physiological processes
taking place in the kidney, and upon the general problems of
metabolism. Even in health the quantity of the urine, its
specific gravity, its acidity, may vary within wide limits. A
hot day may increase the secretion of sweat, and correspond-
ingly diminish the secretion of urine, and the deficiency of
water may lead to a deposit of brick-red urates. A meal
rich in fruit or vegetables may render the urine alkaline, and
its alkalinity may determine a precipitate of earthy phos-
phates. But neither the scanty acid urine, with its sediment
of urates, nor the alkaline urine with its sediment of phos-
phates, comes under the heading of pathological urines ;
the deviation from the normal does not amount to disease.
The maximum deviation from the line of health is the total
suppression of the urine. If this lasts long, a train of
symptoms, of which convulsions may be one of the most
prominent, and which are grouped under the name of
uraemia, appears. At length the patient becomes comatose,
and death closes the scene. Suppression of urine may be
the consequence of many pathological conditions, but there
is one case on record which, in the human subject, in effect,
though not in intention, belongs to experimental physiology.
A surgeon diagnosed a floating kidney in a woman. With
a natural impatience of loose odds and ends of this sort, he
offered to remove it, and in an evil hour the patient con-
sented. The surgeon, a perfectly skilful man, who acted for
the best, and to whom no blame whatever attached, carried
the kidney to a well-known pathologist for examination.
39:? A MANl'AL OF PHYSIOLOGY
The latter, to the horror of the operator, sugp^ested, from
the appearance of the organ, that it was the only kidney
the woman possessed. This turned out to be the fact.
Not a drop of urine was passed. Apart from this ominous
symptom, all went well for seven or eight days ; but then
ura^mic troubles came on, and the patient died on the
eleventh or thirteenth day after the operation. The autopsy
showed that her onl\ kidne}- had been taken away.
In disease the urine may contain abnormal constituents,
or ordinary constituents in abnormal amounts. Of the
normal constituents which ma} be altered in quantity, the
most important are the water, the inorganic salts, the urea,
the uric acid, and the aromatic substances.
"Water. — A marked and persistent diminution in the
quantity of urine, that is to say, practically in the water, with
or without an increase in the specific gravity, is suggestive
of disorganization of the renal epithelium. In some infective
diseases the kidney is liable to be secondarily involved, its
secreting cells being perhaps crippled in the attempt to
eliminate the bacterial poisons. In the form of parenchy-
matous or tubal nephritis which so frequently complicates
scarlet fever, the quantity of urine has in some cases fallen
to 50 or 60 c.c. in the twenty-four hours.
In interstitial nephritis, on the other hand, where the
structural changes in the tubules are for a long time at least
comparatively circumscribed, the quantity of urine is often
increased, seldom diminished. In these cases the increase
in the blood-pressure, associated with hypertrophy of the
heart, may be considered responsible for the exaggerated
renal secretion. In diabetes mellitus the (juantity of urine
is greatly increased, perhaps in some cases because more
urea is excreted than normal and urea acts as a diuretic,
perhaps also because the elimination of sugar draws with it
an increased excretion of water to hold it in solution.
inorganic Salts. — The changes in the quantity of the in-
organic constituents of the urine in disease are not, in the
present state of our knowledge, of as much importance as
the changes in the organic constituents. The chlorides may
totall}' disappear from the urine in pneumonia, and their
EXCRETIOS 393
reappearance after the crisis is, so far as it goes, a favour-
able symptom. In most cases in which the quantity of the
urine is markedly lessened, all the inorganic substances are
diminished in amount.
Urea. — The quantity of urea is, as a rule, increased in
fever, either absolutely or in proportion to the amount of
nitrogen in the food. In the interstitial varieties of kidney
disease the urea is usually not dmiinished, but when the
stress of the change falls on the tubules (parenchymatous
nephritis), it is distinctly decreased — it may be even to one-
twentieth of the normal.
Uric acid is diminished in the urine in gout (perhaps to
one-ninth of the normal), not only during the paroxysms,
but in the intervals. It accumulates in the blood and tissues,
and, as sodium urate, may form concretions in the joints,
the cartilage of the ear, and other situations. Watson
relates the case of a gentleman who used to avail himself of
his resources in this respect by scoring the points at cards
on the table with his chalky knuckles. In leukaemia the
quantity of uric acid and xanthin bases in the urine is
greatly increased.
The aromatic bodies, of which indoxyl may be taken as the
type, are increased when the conditions of disease favour
the growth of bacteria in the intestine, e.g., in cholera, acute
peritonitis, carcinoma of the stomach. A marked increase
in the amount of the ' paired " sulphuric acid in the urine is
to be taken as an indication that the bacteria are gaining
the upper hand in the intestinal tract ; a marked diminution
is usually a sign that the battle has begun to turn in favour
of the organism (Practical Exercises, p. 418J.
Sugar, proteids, the pigments of bile and blood, or their derivatives,
are the most important abnormal substances found in solution in the
urine. Toxalbumins produced by bacterial action have also been
demonstrated in the urme in certain diseases, as in erysipelas (Brieger
and Wassermannj. Red blood - corpuscles and leucocytes (pus
corpuscles, white blood-corpuscles, mucus corpuscles) are the chief
organized deposits ; but spermatozoa may occasionally be found, as
well as pathogenic bacteria, e.g., the typhoid bacillus ; and in disease
of the kidney casts of the renal tubules are not uncommon. These
tube-casts may be composed chiefly of red blood-corpuscles, or of
leucocytes, or of the epithelium of the tubules, sometimes fattily
394
A MANUAL OF PHYSIOLOGY
degenerated, or of structureless proteid, or of amyloid substance.
Abnormal crystalline substances, such as leucin, tyrosin, and cystin,
may be on rare occasions found in urinary sediments : but generally
the unorganized deposits of pathological urine consist of bodies
actually present in, or obtainable from, the normal secretion, but
present in excess, either absolutely, or relatively to the solvent power
of the urine.
Sugar. — In diabetes mellitus, although the ijuantity of urine is
usually much increased, its specific gravity is above the normal ; and
this IS due chiefly to the presence of sugar (glucose), which generally
amounts to i to 5 per cent., but may in extreme cases reach 10 or
even 15 per cent., more than half a kilogramme being sometimes
given off in twenty-four hours.
The name of the tests for glucose is legion. They are mostly
Fir,. 122.— I.EuciN Crystals.
Fk;, 123.— Tvkosin Cryst.als.
founded on its reducing action in alkaline solution. Hydrated oxide
of bismuth (Boettcher), salts of gold, platinum and silver, indigo
(Mulder), and a host of other substances, are reduced by glucose,
and may be used to show its presence. The reduction of cupric
salts (Trommer) and the formation of crystals of phenyl-glucosazone
(Plate IV., 3) are perhaps the best established tests. (See Practical
Exercises, p. 426).
Proteids. — Serum-albumin and serum-globulin are the proteids
most commonly found in pathological urine. Both are coagulated
by heating the urine, slightly acidulated, if it is not already acid, or
by the addition of strong nitric acid in the cold. Proteoses (albu-
moses) and peptones are also occasionally present, and may be
recognised by the tests given in the Practical Exercises (p. 424).
The pigments of blond and bile may be detected by the char-
acters described in treating of these substances ; the spectrum of
oxyhremoglobin, or meth;emoglobin, or any of the other derivatives
of haimoglobin, with the formation of haemin crystals, would afford
proof of the presence of the former, and Gmelin's test of the latter.
The red blood-corpuscles, seen with the microscope, are the most
decisive evidence of the presence of blood, as leucocytes in abundance
are of the presence of pus. It should be remembered that pus in
the urine of women has sometimes no significance except as showing
that there has been an admixture of leucorrheal discharge from the
vagina. (See Practical Exercises, pp. 62, 66, 3.S0).
EXCRKTJON
395
The Secretion of the Urine, — We have now to consider the
mechanism by which the urine is formed in the kidney
from the materials brought to it by the blood. And here the
same questions arise as have already been discussed in the
case of the salivary and other digestive glands: (i) Are the
urinary constituents, or any of them, present as such in the
blood ? (2) If they do exist in the blood, are they separated
from it by processes mainly physical or mainly vital — in
other words, by filtration and diffusion, or by the selective
action of living cells ? In the case of the digestive juices
it has been seen that some constituents are already present
in the blood, but that physical laws alone cannot explain the
proportions in which they occur in the secretions, nor the
conditions under which they are separated ; while other
constituents — and these the more specific and important —
are manufactured in the gland-cells.
In the kidneys the conditions seem at first sight favourable
to physical filtration, as opposed to physiological secretion.
Urine has been described as essentially a solution of urea
and salts, and both are ready formed in the blood. The
arrangement of the bloodvessels, too, suggests an apparatus
for filtering under pressure.
Bloodvessels and Secreting Tubules of Kidney. — The renal artery
splits up at the hilus into several branches, which pass in between
the Malpighian {pyramids, and form at the boundary of the cortex
and medulla vascular arches, from which spring, on the one side, inter-
lobular arteries running up into the cortex between the pyramids of
Ferrein, and, on the other, vasa recta running down into the boundary
layer of the medulla. The interlobular arteries give off at intervals
afferent vessels \ each of these soon breaks up into a glomerulus or
tuft of vascular loops, which gather themselves up again into a single
efferent vessel of somewhat smaller calibre than the afferent. The
glomerulus is fitted into a cup or capsule (of Bowman), which is
closely reflected over it, except where the afferent and efferent vessels
pass through, and forms the beginning of a urinary tubule. If ive
suppose the tuft pushed into the blind end of the tubule so as to
indent it, it will be easily understood that the single layer of flattened
epithelium reflected on the glomerulus is continuous with that lining
the capsule, which in its turn is continuous with the epithelial layer
of the rest of the urinary tubule. This has been divided by histo-
logists into a number of parts which it is unnecessary to enumerate
here, further than to say that the urinary tubule proper begins in the
cortex in Bowman's capsule and the proximal convoluted tubule
396
A MAMfAL OF rUYSIOLOGY
(with its continuation, the spiral tubule), and ends in the cortex with
the distal convoluted tubule, the connection between the two being
made by a long loop (Henle's) with a descending and an ascending
limb (Fig. 124).
The distal convoluted tube joins by means of the short connecting
tubule one of the straight tubules which form the pyramids of
Ferrein in the cortex, and which run down into the medulla, always
Ejjereni- A/fe
Cortex
DBDlmKKBft
Boundary
Zone of
Medulla
Pofiillaru
Zone.
nil
Yasa "
Recta
s^ ,Ca/iil/ary plexus fnrmec/
NX^ i/u efferent vessels
^^Distal \convcluleci
IJlLProxtmal J ^"^^
t/' 'Glo merulus with
I Bowman's cansu^le ,
^^^-Renal arch
Y 'Collecting /"uiule
I \ running into cortex as
part of a /lyramid of Ferret ft
--Descending limb \ofNenh's
\- Ascending Hml \ ^""H'^^"
Collecting tuhuJe
FlU. 124.— DiAf.KAM OK BLtH.DVRSSKl.S ANM) TUKUI.ES IN TUt KiDNliV.
Tlie arrows show the direction in which the urine flows,
uniting into larger and larger tubes as they go, until at length they
open as ducts of Bellini on the apex of a papilla. The two con-
voluted tubules and the ascending limb of Henle's loop are lined by
similar epithelial cells with granular contents and a striated or
' rodded ' appearance. We shall see directly that this morphological
agreement is the index of a functional likeness. The blood-supply
of the tubules, especially of the convoluted portions, is exceedingly
rich, the efferent vessels of the glomeruli breaking up around them
into a close-meshed network of capillaries, from which the blood is
collected into interlobular veins running parallel to the interlobular
arteries between the ]:)yramids of Ferrein. The straight tubules of
the medulla are also surrounded by capillaries given off from straight
arteries (arterire rectre) running down into it partly from the arterial
arches and partly from efferent vessels of the glomeruli nearest the
boundary layer, the blood passing away by straight veins (vena;
rectas), which join the veins accompanying the arterial arches. The
greater part of the blood going through the kidney has to pass
through two sets of capillaries, one in the glomeruli, the other around
the tubules. Even the portion of it which does not go through the
glomeruli has for the most part a long route to traverse in narrow
arterioles and venules to and from its capillary distribution. And
the mean circulation-time through the kidney has been found to be
longer than that through most other organs.
Theories of Renal Secretion. — To come back to our problem
of the nature of renal secretion, the anatomical structure
of the kidney might be expected to throw light upon the
question. And, indeed, it was on a purely histological foun-
dation that Bowman established his famous ' vital ' theory of
renal secretion. Impressed with the resemblance between the
renal epithelium and the epithelial cells of other glands, and
with the distribution of the bloodvessels in the kidney, he
came to the conclusion that the characteristic constituents
of urine, including urea, were secreted from the blood by
the tubules. To the Malpighian bodies he assigned what
he doubtless considered the humbler office of separating
water from the blood for the solution of the all-important
solids. To Ludwig, on the other hand, with his whole
attention fastened on the mechanical factors by which the
flow of urine could be influenced, the tubules seemed of
secondary importance, while the glomeruli appeared a com-
plete apparatus for filtering urine from the blood into Bow-
man's capsule. He saw that the efferent vessel was smaller
than the afferent ; that it was therefore easier for blood to
come to the glomerulus than to get away from it, and that
the pressure in the capillaries of the tuft must be higher
than in ordinary capillaries, because the resistance beyond
them in the comparatively narrow efferent vessel, and
especially in the second plexus, is greater than the resist-
ance beyond a single capillary network. And experimental
398 A MAXUAL OF /'//YS/OLOGY
investigation soon showed him that the rate at which urine
was formed could be greatly influenced by changes in the
blood-pressure.
On such considerations, Ludwig founded the 'mechanical'
theory of urinary excretion, which, although in a much
modified form, still divides with the vital theory the
allegiance of physiologists. It is impossible here to enter
in detail into a controversy that has extended over half a
century and produced an extensive literature. The result
of the discussion has been, in our opinion, to establish in
its essential principles the ' vital * theory of Bowman, or at
least to show that no purely mechanical theory as yet con-
structed will account for all the facts.
Ludwig supposed that the urine, qualitatively complete
in all its constituents, was simply tillered through the
glomeruli ; but as the proportion of salts, and especially of
urea, is very far from being the same in urine as in blood,
he further assumed that the liquid which passes into Bow-
man's capsule is exceeding dilute, and that absorption of
water, and perhaps of other constituents, takes place in its
passage along the renal tubules. The great length of these
tubules, as compared with those of most other glands,
might seem to indicate a long sojourn of the urine in them,
and the probability of important changes being caused in
its passage along them. But if we consider the immense
length (60 to 70 cm.) of the seminal tubules and of their
gigantic ducts (epididymis 6 metres), where, of course,
absorption of water on a large scale is out of the question.
It will be granted that little can be built upon the mere
length of the renal tubules. On the other hand, the salivary
glands, where there are no glomeruli, secrete as much water
as the kidneys are supposed to filter ; and the pancreas,
whose capillaries form the first of a double set, and there-
fore in this respect correspond to the renal glomeruli,
secretes less water than the liver, whose capillaries corre-
spond to the low-pressure plexus around the convoluted
tubules of the kidney. So that deductions drawn from the
anatomical relations of the bloodvessels are not in this case
of much value, unless supported by physiological results.
EXCRETION 399
Tried by the latter test, the mechanical theory breaks down
for the kidney, as it does for other glands.
In the first place, the absence from urine of the proteids
and sugar of the blood under normal circumstances — if
infinitesimal quantities of these substances, as some have
asserted, are really to be found in healthy urine, it makes
no difference to the argument — and the elimination by the
kidney of egg-albumin, peptone, and other bodies when
injected into the veins, show a selective power inexplicable
except by reference to the vital activit}' of cells. Urea and
sugar, both highly diffusible substances, circulate side by
side in the bloodvessels of the kidney. The one is taken
and the other left. The urea is a waste-product of no
further use in the economy. The sugar is a valuable food-
substance. The kidney selects with unerring certainty the
urea, of which only 4 parts in 10,000 are present in the
blood, but rejects the sugar, of which there is five times
as much.
Egg-albumin injected into the blood passes through the
renal circulation side by side wath the serum-albumin of
the plasma. Both are indiffusible through membranes, and
to the chemist the differences between them may appear
superficial and minute. But the kidney does not hesitate
for an instant. The egg-albumin is promptly excreted
as a foreign substance ; the serum - albumin passes on
untouched.
Not only does the kidney exercise a power of qualitative
selection : it also takes cognizance of the quantitative com-
position of the blood. So long as there is less sugar in the
plasma than about 3 parts in 1,000, it is refused passage
into the renal tubules. But when this limit is passed, and
the proportion of sugar in the blood becomes excessive, the
kidney begins to excrete sugar, and continues to do so till
the balance is redressed.
The advocates of the theory of filtration, driven from one
position to another, have made their firmest stand on the
excretion of the inorganic constituents of the urine. But
even here the theory has at length become untenable ; and
there is little more reason to believe that the copious flow of
400 A MANUAL OF PIIYSIOLOCY
urine which follows the absorption of a large quantity of
water is due to a mere process of filtration than there is to
believe that filtration, and not selective secretion, is the
cause of the gush of saliva which precedes vomiting, or the
sudden outburst of sweat on sudden and severe exertion.
It is true that the direct introduction of water into the
blood, or its attraction from the lymph spaces when the
osmotic pressure of the blood is increased by the injection
of substances like urea, sugar and sodium chloride, may
cause a condition oihydramic plcihoyci, and that this plethora
may sometimes be associated with an increase of pressure in
the capillaries in general, and therefore in the vessels of the
Malpighian tuft. It may also be admitted that such an
increase of pressure might be accompanied by an increased
filtration of water and salts into the Bowman's capsule.
But who will believe that the addition of a tumbler of water,
absorbed from the alimentary canal, to 5^ litres of blood
circulating in a system of vessels whose capacity can and
does vary within wide limits, should cause in the capillaries
of the kidney an increase of pressure exactly proportional to
the increase in the elimination of water in the urine, lasting
for the same time and disappearing at the moment when
the normal composition of the blood is restored ? Nor is
it easier to explain on any filtration hypothesis how it is
that in a starving animal, the quantity of inorganic sub-
stances eliminated in the urine drops almost to zero, while
the proportional amount in the blood and tissues is little,
if at all, affected. Such facts suggest that the secreting
cells of the kidney are stimulated by the contact of blood
or lymph in which the normal constituents are present in
too small or in too great amount, and that the strength
of the stimulus is proportional to the degree of deficiency
or excess.
But, secondly, there is positive proof that the ' rodded '
epithelium of the tubules, which no one supposes to be
abandoned more to mere physical influences than the
epithelium of the salivary glands, plays a part in the
secretion of some of the urinary constituents. For Bowman
saw crystals of uric acid in the epithelium of the convoluted
EXCRETION 401
tubules of birds. Heidcnhain found that urate of soda and
indigo-carmine injected into the blood of a rabbit are
excreted by the epithelium of the convoluted tubules and
the ascending part of Henle's loop. And Nussbaum's experi-
ments, although not perhaps quite conclusive, have made it
probable that in the frog urea is actuall}- separated by the
epithelium of the tubules.
The experiments of Heidenhain and Nussbaum deserve more
detailed description. The former injected indigo-carmine
into the blood of rabbits and after a variable time killed
them, cut out the kidneys,
and flushed them with alcohol.
His results were as follows :
(i) When the spinal cord was
cut before the injection in order
to reduce the blood-pressure,
the blue granules were found in
the 'rodded' epithelium of the
convoluted tubules and the
ascending limb of Henle's loop, ^lo. i25.-Dia.;ram ok Distribu-
° ^ TiON OF Pigment in Kidney
and m the lumen of the tubules, after injection into Blood.
but nowhere else. The renal The cortex between a and b and
between c and d was cauterized before
cortex was coloured blue, the injection. In tiie black wedge-
/\-.Tri >i • 1 J shaped portions i there was no pig-
(2) When the spinal cord was ^en,. in the zones shaded like 2
not cut, the pigment was found ^^"l '"^^ '°'"^ P'^T"i'^^,^' "°' '°
' ^ ° much as in the areas shaded like 3.
in the medulla and pelvis of the
kidney, as well as in the cortex, but always in the lumen
of the tubules, and not in the epithelium, except in the
situations mentioned. (3) If a portion of the cortex of the
kidney had been cauterized with nitrate of silver before
injection of the pigment, the spinal cord being left intact,
a wedge of the renal substance, corresponding to this area,
remained coloured only in the cortex, although the rest
was blue in the medulla also. The rodded epithelium was
filled with blue granules as before (Fig. 125).
(i) shows that the epithelium is capable of excreting
some substances at least. (2) appears to show that when
the blood-pressure is normal water is poured out from some
part of the tubule, and washes the pigment separated by the
26
402 A MAX UAL OF rilYSIOLOGY
' rodded ' epithelium down towards the papillne. (]) suggests
that it is through the glomeruh that most of the water
passes. For cauterization has not destroyed the power of
the epithehum to excrete pigment, and therefore, presumably,
would not have destroyed its power to excrete w^ater if it
possessed this power in any great degree ; and the glomeruli
and their capsules are the only other part of the renal
mechanism which can have been affected. The fact that
in birds and serpents, whose urine is solid or semi-solid, the
glomeruli are smaller than in mammals is corroborative
evidence that the glomeruli have to do with the excretion of
water.
An attempt has recently been made by Sobieranski, on the strength
of a reinvestigation of the microscopical appearances presented by
the kidney after injection of pigments into the blood, to revive
Ludwig's theory that absorption takes place from the tubules. He
asserts that, although pigment granules are found in the rodded
epithelium, they are always near the lumen of the tubule, never near
the basement membrane. From this he concludes that the pigment
is not passed through the cells from the blood, but absorbed by them
from the tubules after excretion by the glomeruli. It cannot, how-
ever, be admitted that his observations are decisive.
Nussbaum's experiments were founded on the anatomical
fact that the kidney of batrachians, and, indeed, that of fishes
and ophidia as well, has a double blood-supply. The renal
artery gives off afferent vessels to the glomeruli, and the
ve>ia advchens or renal portal vein breaks up, like the
portal vein in the liver, into a plexus of capillaries sur-
rounding the tubules, with which plexus the efferent arterioles
of the glomeruli communicate. By tying the renal arteries
in the frog, Xussbaum thought he could at will stop the
circulation in the glomeruli, and he found that after this was
done, sugar, peptones and egg-albumin, injected into the
blood, no longer passed into the urine, although they readily
did so when the arteries were not tied. Urea, however, was
still eliminated by the kidneys after ligature of the renal
arteries, and water along with it. He concluded that the
Malpighian corpuscles have the power of excreting water,
sugar, peptone, and albumin, while the epithelium of the
tubules excretes urea as well as water.
EXCRETION 403
Adami has since shown that the circulation in the glomeruli
is not wholly stopped by Xussbaum's operation, for there is
a certain amount of anastomosis between the arteries of the
generative organs and the renal arteries. He therefore
suggests that the water secreted during the elimination of
urea after ligature of the renal arteries may really come
through the Malpighian tufts. At the same time, this
objection does not touch the conclusion of Nussbaum, that
the glomeruli are alone concerned in the separation of the
other bodies mentioned. For his operation, whether it com-
pletely cut off the circulation in the tufts or not, interfered
with it so much as to stop the excretion of these substances,
while leaving the epithelium of the tubules as able to con-
tinue that function, if it possessed it, as it was before.
Adami himself has shown that hamoglobin when free in the
blood-plasma is excreted by the glomeruli, even when the
renal artery has been ligatured, and that menisci of this sub-
stance may be coagulated within the lumen of the Bowman's
capsules by plunging the kidney into boiling water. In the
dog, too, haemoglobin is excreted by the glomeruli, and may
be washed out of the capsule by the increased quantity of
water secreted when sodium nitrate is administered. This
shows that a diuretic may act upon the glomerular epithelium,
which is thus brought into line with the ' rodded ' epithelium
of the tubules.
What, then, is the significance of the peculiar arrangement of the
glomerular bloodvessels, if the epithelium of the capsules has secretive
powers like that of ordinary glands ? It is difficult to believe that
these unique vascular tufts have not a near and important relation to
the renal function ; but it is by no means clear what that relation is.
The secretion of water, and even its rapid secretion, is not at all
bound up with any set arrangement of bloodvessels. Gland-cells all
over the body secrete water under the most varied conditions of
blood-pressure, although a comparatively high pressure is upon the
whole favourable to a copious outflow.
But the kidney has, as we now know, other functions than mere
excretion (p. 472). And it maybe that the simplest part of the latter
process, the elimination of water and salts, is largely thrown upon
the Malpighian corpuscles, as a physiologically cheaper machine
than the epithelium of the tubules, which is left free for more complex
labours. These may include not only the separation of nitrogenous
metabolites, but perhaps the building up of urea, or of less completely
26 — 2
404 A MANUAL OF I'HYSIDLOCY
metabolized substances which precede it, into higher combinations,
and llie consequent regulation of thetiuantity of urta finall) excreted,
and the ultimate proteid waste which this expresses. The epithelium
of the glomerulus, being a less highly organized and less delicately
selective mechanism than that of the convoluted tubules, may more
easily respond to increase of blood-pressure by increased secretion.
At the same time, placed as it is at the last flood-gate of the circula-
tion, where the escape of anything valuable means probably its total
loss, the glomerular epithelium may be endowed with a general power
of resistance to transudation, which renders a comparatively high
blood-pressure a necessary condition of its acting at all. And as a
matter of fact, water ceases to be secreted by the kidney long before
the blood-pressure in the glomeruli can have fallen below that which
suffices for the highest activity of the liver. Perhaps, however, the
high minimum pressure required (30 to 40 mm. of mercury in the
dog) is merely the necessary consequence of the long and difficult
path which most of the blood going through the kidney has to take,
and that a sufficient blood-flow cannot be kept up with less. It may
be, too, that the comparatively small surface of the glomeruli,
restricted in order to leave room for the more highly organized parts
of the renal mechanism, entails the more intense and concentrated
activity, which the high blood-pressure renders possible, and the
simplicity of work and organization renders harmless.
This brings us to a second suggestion as to the meaning of the
double capillary supply of the kidney, namely, that the more highly
organized parts of the renal tubules are shielded from an excessive
blood-pressure by the interposition of the glomeruli as a block. This
may be either because the epithelium of the tubules would not perform
its i)roper work so well under a high blood-i)ressure, or because there
would be a danger of substances which ought to be retained being
cast out into the urine. In this connection it is interesting to note
that the specific constituents of urine are separated by epithelium
surrounded by capillaries of the second order, and therefore with a
smaller blood-pressure than exists in the capillaries of most glands,
while the same is true of bile, another proteid-free secretion. The
sweat-glands, too, the second great outgate of licjuid excretion, are
surrounded by capillaries separated from the main arterial branch by
a rete mirabile corresponding to a glomerulus.
The maximum secretory pressure in the kidney, as shown
by a manometer tied into the divided ureter, is about
60 mm. of mercury in the dog, or less than half that of
saliva. If the escape of the urine is opposed by a greater
pressure than this, or if the ureter is tied, the kidney
becomes oedematous. Whether the cjedema is due to re-
absorption of urine or to the pouring out of lymph owing to
the pressure of the dilated tubules on the veins has not been
definitely settled. It has been already pointed out that
ExiK/rnoN
405
there is no necessary relation between the blood-pressure in
the capillaries of a gland and its secretory pressure; and, so
far as this goes, water might just as well be secreted at a
pressure of 60 mm. of mercury from the low-pressure blood
of the second set of renal capillaries as from the high-
pressure blood of the glomeruli.
The Influence of the Circulation on the Secretion of Urine. —
Although the activity of no organ in the body is governed
more by the indirect effects of nervous action than that of
the kidney, no proof has yet been given of the existence of
secretory fibres for it comparable to those of the salivary
glands. All the changes in the rate of renal secretion which
R, metal box in
two halves opening
on the hinge H :
M, thin membrane ;
A, space filled with
oil ; O, organ en-
closed in onco-
meter ; V, vessels of
organ ; /, tube for
filling instrument
with oil ; T, tube
connected with D,
which opens into
cylinder C ; C is
also filled with oil ;
P, piston attached
by E to a writing
lever.
Fk;. 126. — DlAC,KA.\[ UF ORC, \N-Pl.ETHYSMO(iRAPH OK ONCOMETER.
follow the section or stimulation of nerves can be explained
as the consequences of the rise or fall of local or general
blood-pressure, and of the corresponding variations in the
velocity of the blood in the renal vessels.
The best way to study variations in the calibre of the renal vessels
is the plethysmographic method, and the oncometer of Roy is a
plethysmograph adapted to the kidney. It consists of a metal
capsule lined with a loose membrane, between which and the metal
there is a space filled with oil. The two halves of the capsule open
and shut on a hinge ; and the kidney, when introduced into it, is
surrounded on all sides by the membrane, the vessels and ureter
passing out through an opening. The oil-space is connected with a
cylinder also filled with oil, above which a piston, connected with a
lever, moves. The lever registers on a drum the changes in the
volume of the kidney, i.e., practically the changes in the quantity of
blood in it, and therefore in the calibre of its vessels.
Nerves of the Kidney. — Both vaso-constrictor and vaso-dilator
4o6 A MANUAL OF PHYSIOLOGY
fibres for the renal vessels, but most clearly the former, have been
shown to leave the cord (in the dog) by the anterior roots of the sixth
thoracic to second lumbar nerves, and especially of the last three
thoracic. They run in the splanchnics, and then through the renal
l)lexus — around the renal artery— into the kidney. The vaso-
constrictors predominate, so that the general effect of stimulation of
the nerve-roots, the splanchnics, or the renal nerves is shrinking of
the kidney, with diminution or cessation of the secretion of urine.
But slow rhythmical stimulation of the roots causes increase of
volume, the dilators being by this method excited in preference to
the constrictors.
Section of the renal nerves is followed by relaxation of the
small arteries in the kidnc)-, and consequent swelling of the
organ. The flow of urine is greatly increased, and some-
times albumin appears in it, the excessive pressure in the
capillaries (particularly in those of the glomeruli) being
supposed to favour the escape of substances to which the
renal epithelium refuses a passage under normal conditions.
The recent investigations of Berkel}- have shown that the
renal nerves, entering at the hilum, branch repeatedly, so
as to form a wide-meshed plexus around the arteries, and
accompany them even to their finest ramifications in the
cortex. No nerve-fibres have as yet been seen on the veins
in the kidney-substance or on the straight arteries. Coming
off from the nerves surrounding the arteries are fine fibres
which are distributed to the convoluted tubules, and are
perhaps secretory nerves. Some of them terminate in
globular ends, others in fine threads that pass through the
membrana propria.
It is often assumed that the renal nerves affect chiefly
the afterent arterioles of the glomeruli ; but there seems to
be no experimental ground for this view, which is merely a
doctrinaire deduction from Ludwig's filtration theory. For
if that theory, or any modification of it which postulates a
close connection between the blood-pressure in the glome-
rular capillaries and the rate of secretion of urine, be accepted,
it is evidently an advantage that there should be no similar
influence on the efferent arterioles, since constriction of
both would not necessarily cause any fall, nor dilatation of
both any rise, of intra-glomerular pressure. Heidcnhain's
suggestion, that the velocity of the blood-flow, and not the
EXCRETION
407
pressure in the glomeruli, is the determining factor in
urinary secretion, does not require any arbitrary restriction
of the tract influenced by the renal vaso-motor nerves. If
both afferent and efferent vessels were constricted, the blood-
flow would be diminished; if both were relaxed, it would be
increased ; if only the vas afferens were affected, the changes
would be in the same sense, although less marked, since the
total alteration of resistance would be less.
An experiment which is sometimes quoted as a decisive
test of the relative importance of changes in the rate of flow,
Fig. 127. — Nerves of Kidney (Berkelv).
(16) medium-sized artery with its nerve-plexus ; A, terminal knobs ; R, aberrant
branch ending in terminal knob E; the dotted lines outline the artery. (17) Nerve-
fibres surrounding a Bowman's capsule, which is indicated by a dotted hne ; some of
the endings are close to the membrane ; (18) convoluted tubule shown in outline with
fine nerve-fibres on it, which seem to enter the basement membrane.
and in the pressure of the blood within the glomeruli, is that
of tying the renal vein. This undoubtedly does not lower the
intra-glomerular pressure — on the contrary, it must increase
it — but the secretion of urine stops. If the venous outflow
from the kidney is only partially interfered with, the flow of
urine is immediately diminished, but the administration of
a diuretic like potassium nitrate causes an increase. It is
suggested that in these experiments the secretion stops or
slackens because an active circulation, and not a high
4o8 A MAXr.lL OF PHYSIOLOijY
blood-pressure, is its necessary condition. The conclusion
is probably correct, but the experiment does not prove it.
For few f^lands can go on performing their function after the
circulation has ceased. The kidney must be able to feed
itself in order to continue its work ; and it might be urged
that if the blood in the glomeruli could be kept at the normal
standard of arterial blood, secretion might still go on after
ligature of the renal vein.
According to Ludwig, indeed, the experiment really teaches
that the liquid part of the urine is, at any rate, not separated
by the epithelium of the tubules, since the blood-pressure
in the capillaries around the tubules must rise very greatly
after ligature of the vein, and yet secretion is stopped. It
might equally well be argued, however, that the renal epi-
thelium normally secretes water under a loic blood-pressure,
but is disorganized under the excessive and entirely un-
accustomed pressure which follows the closure of the vein.
But the whole discussion is an illustration — and this is the
reason we have gone into it so fully — of the complexity, the
many-sidedness of physiological phenomena, even when
reduced by well-planned experiments to their simplest terms,
and the unconscious bias which theory sometimes gives to
even the most acute and original minds in interpreting the
results of observation.
It is not only through nerves directly governing the calibre
of the vessels of the kidney that the rate of urinar\- secretion
can be affected. Any change in the general blood-pressure,
if not counteracted by, still more if conspiring with, simul-
taneous local changes in the renal vessels, may be followed
by an increased or diminished flow of urine ; and the law
which explains all such variations, or at least serves to sum
them up, is that in general an increase in the rate of the blood-
fiow thron^^h the kidney is folloived by an increase in the rate of
secretion. It will be remarked that this is the converse of
the great law, of which we have already seen so many illus-
trations, that functional activity increases blood-flow. It is
probable that this law holds for the kidney as well as for
other organs, but that the influence of activity on blood-
supply is subordinated to that of blood-supply on activity,
EXCRETION AO)
while in most tissues, as in the muscles, the opposite is the
case. It is evident that an increase in the blood-flow would
favour the secretory activity of the renal cells, since the
average concentration of the blood presented to them as
regards those constituents which they select would remain
relatively high in its circuit through the kidney. The
* stimulus ' to secretion would, therefore, be relatively
intense.
Destruction of the medulla oblongata {i.e., of the vaso-
motor centre), or section of the cord below it, diminishes
the secretion of urine, because the arterial pressure is
lowered so much as to over-compensate the dilatation of the
renal vessels, which the operation also brings about. If the
blood-pressure falls below 40 mm. of mercury, the secretion
is abolished. Stimulation of the medulla or cord also
lessens the flow of urine by constricting the arterioles of the
kidney so much as to over-compensate the rise of general
blood-pressure, caused by the constriction of small vessels
throughout the body.
If the renal nerves have been cut, stimulation of the
medulla oblongata increases the urinary secretion, because
now the rise of general blood-pressure is no longer counter-
balanced by constriction of the renal vessels. Puncture of a
certain part of the floor of the fourth ventricle may produce
a copious flow of urine, perhaps by destroying the portion
of the vaso-motor centre governing the renal nerves, while
the rest remains uninjured and keeps up the general blood-
pressure, but possibly by stimulating a secretory ' centre.'
Section of the splanchnic nerves causes a fall of arterial
pressure, which is, however (in animals like the dog, in
which compensation soon takes place), more than balanced
by the simultaneous dilatation of the renal vessels, and
therefore for some time the flow of urine is increased, but
not so much as when the renal nerves alone are cut. In the
rabbit there is no increase. On the other hand, stimulation
of the splanchnics stops the urinary secretion, because the
general rise of pressure is not enough to make up for the
constriction of the renal vessels.
4IO A MANUAL OF PHYSIOLOGY
Diuretics are substances that increase the flow of urine. Some of
them appear to act mainly by increasing the general blood-pressure,
others mainly by a direct influence on the secreting mechanism.
Digitalis is a representative of the first class ; urea and caffein belong
to the second. The action of digitalis is to strengthen the beat of
the heart, which is at the same time somewhat slowed, and to con-
strict the arterioles. Both eff"ects contribute to the increase of
pressure. It is possible that in addition this drug directly stimulates
the renal epithelium. Cafi"ein, when injected into the blood, affects
the pressure but little. It causes dilatation of the renal vessels after
a passing constriction, and an increase in the flow of urine after a
temporary diminution. The vascular dilatation is not the chief
reason for the diuretic effect, for the latter is still obtained when the
vaso-motor mechanism has been paralyzed by chloral hydrate, and
even after the secretion of urine has been stopped by the fall of
pressure consequent on section of the .spinal cord. Caffein, there-
fore, acts directly on the renal epithelium. The action of urea,
potassium nitrate, and the saline diuretics is probably also a direct
action on the secreting structures, although some have supposed that
their primary effect is to cause vaso-dilatation in the kidney, and a
consequent local increase in the capillary pressure.
Summary.— Our knowledge of renal secretion may be thus
summed up : The water and salts of the urine are partly, and
perhaps chiefly, separated by the glomeruli : the process is not a
physical filtration, but a true secretion. Substances like sugar,
peptone, egg-albumin, and hcemoglobin when injected into the blood
are excreted by the glomeruli : so probably is the sugar of diabetes.
Urea, uric acid, and presumably the other organic constituents of
normal urine, with a portion of the water and salts, are excreted
by the physiological activity of the ' rodded ' epithelium of the
renal tubules. The rate of secretion of urine rises and falls with
the pressure, and probably still more with the velocity, of the
blood in the renal vessels. No secretory nerves for the kidney
have been definitely found ; the effects of section or stimulation of
nerves on the secretion can all be explained by the changes pro-
duced in the renal blood-flew. Some diuretics act by increasing
the blood-flo'a\ others directly on the epithelium of the tubules.
Micturition. — The urine, like the bile, is being constantly
formed ; although secretion varies in its rate from time to
time, it never ceases. Trickling along the collecting tubules,
the urine reaches the pelvis of the kidney, from which it is
propelled along the ureters by peristaltic contractions of
their walls, and drops from their valve-like orifices into the
EXCKET/ON 411
bladder. W^hen this becomes distended, rhythmical peri-
staltic contractions are set up in it, and notice is jjjiven of its
condition by a characteristic sensation, which is perhaps
aided by the squeezing of a few drops of urine past the
tonically contracted circular fibres that form a sphincter
round the neck of the bladder, and into the first part of the
urethra. The desire to empty the bladder can be resisted
for a time, as can the desire to empty the bowel. If it is
yielded to, the smooth muscular fibres in the wall of the
viscus are thrown into contraction. This is aided by an
expulsive effort of the abdominal muscles. The sphincter
vesicae is relaxed ; and the urine is forced along the urethra,
its passage being facilitated b)' discontinuous contractions
of the ejaculator urinae muscle, which also serve to squeeze
the last drops of urine from the urethral canal at the com-
pletion of the act.
The pressure in the bladder of a man may be made as high
as 10 cm. of mercury during the act of micturition ; about
half this amount is due to the contraction of the vesical walls
alone, the rest to the contraction of the abdominal muscles.
Although the whole performance seems to us to be com-
pletely voluntary, there are facts which show that it is at
bottom a reflex series of co-ordinated movements, that can
be started by impulses passing to a centre in the spinal
cord from above or from below — from the brain or from the
bladder. In dogs, with the spinal cord divided at the upper
level of the lumbar region, micturition takes place regularly
when the bladder is full, and can be excited by such slight
stimuli as sponging of the skin round the anus (Goltz).
Here, of course, the act is entirely reflex ; and the centre
is situated at the level of the fifth lumbar nerves. The
efferent nerves of the bladder, like those of the rectum,
come partly from the cord directly through the sacral nerves,
and partly through the lumbar sympathetic chain (second to
sixth ganglia). The sacral fibres are connected with nerve
cells in the hypogastric plexus, and the sympathetic, partly
at least, in the inferior mesenteric ganglia. This anatomi-
cal coincidence acquires interest in view of the striking
physiological similarity between the processes of micturition
412 A MANUAL OF PHYSIOLOGY
and defaecation, a similarity which is emphasized by the fact
that the latter is almost invariably accompanied by the
former. An important difference, however, is that the will
can far more readily set in motion the machinery of micturi-
tion than that of defaecation : a man can generally empty
his bladder when he likes, but he cannot empty his bowels
when he likes.
Sometimes in disease, and especially in disease of the
spinal cord, the mechanism of micturition breaks down ;
the bladder is no longer emptied ; it remains distended with
urine, which dribbles away through the urethra as fast as
it escapes from the ureters. To this condition the term
incontinence of urine is properly applied.
Reflex emptying of the bladder, without an act of will or
during unconsciousness, is not true incontinence. The in-
voluntary micturition of children during sleep, for example,
is a perfectly normal reflex act, although more easily excited
and less easily controlled than in adults.
II. Excretion by the Skin.
Besides permitting of the trifling gaseous interchange
already referred to (p. 25S), the skin plays an important part
in the elimination of water by the sweat-glands.
Sweat is a clear colourless liquid, alkaline when pure, and
consisting chiefly of water with small quantities of salts,
neutral fats, and volatile fatty acids, and. under certain con-
ditions at least, the merest traces of proteids and urea. It
is secreted by simple gland-tubes, which form coils lined
with a single layer of colunmar epithelium, in the sub-
cutaneous tissue, with long ducts running up to the surface
through the true skin and epidermis. Unless collected from
the parts of the skin on which there are no hairs, such as
the palm, it is apt to be mixed with sdmm, a secretion
formed by the breaking down of the cells of the sebaceous
glands, which open into the hair follicles, and consisting
chiefly of fats, soaps, and salts.
Although it is only occasionally that sweat collects in
visible amount on the skin, water is always being given off
EXCRETION 4,3
in the form of vapour. This invisible perspiration leaves
behind it on the skin, or in the glands, the whole of the
non-volatile constituents, which may be to some extent
reabsorbed ; and since even the visible perspiration is in
large part evaporated from the very mouths of the glands in
which it is formed, the sweat can hardly be considered a
vehicle of solid excretion, even to the small extent indicated
by its chemical composition.
The total quantity of water excreted by the skin, and the
relative proportions of visible and invisible perspiration, vary
greatly. A dry and warm atmosphere increases, and a
moist and cold atmosphere diminishes the total, and, within
limits, the invisible perspiration. Visible sweat — given the
condition of rapid heat-production in the body as in mus-
cular labour — is more readily deposited on freely exposed
surfaces when the air is moist than when it is dry. The air
in contact with surfaces covered by clothing is never far
from being saturated with watery vapour. Here, accordingly,
a comparatively slight increase in the activity of the sweat-
glands suffices to produce more water than can be at once
evaporated ; and the excess appears as sweat on the skin,
to be absorbed by the clothing without evaporation, or to be
evaporated slowly, as the pressure of the aqueous vapour
gradually diminishes in consequence of diffusion.
The quantity of sweat given off by a man in twenty-four
hours varies so much that it would not be profitable to quote
here the numerical results obtained under different conditions
of temperature and humidity of the air. It is enough to say
that the excretion of water from the skin is of the same
order of magnitude as that from the kidneys : a man loses
upon the whole as much water in sweat as in urine. But it
is to be carefully noted that these two channels of outiiow
are complementary to each other; when the loss of water by
the skin is increased, the loss by the kidneys is diminished,
and vice versa.
Tlie Influence of Nerves on the Secretion of Sweat. — The
sweat-glands are governed directly by the nervous system ;
and though an actively perspiring skin is, in health, a
flushed skin, the vascular dilatation is a condition, and not
414 A MANUAL OF PirVSIOLOCY
the chief cause of the secretion. Stimulation of the peri-
pheral end of the sciatic nerve causes a copious secretion of
sweat on the pad and toes of the corresponding leg of a
young cat, and this although the vessels are generally con-
stricted by excitation of the vaso-motor nerves. Not only
so, but when the circulation in the foot is entirely cut off by
compression of the crural artery or by amputation of the
limb, stimulation of the sciatic still calls forth some secretion.
As in the case of the salivary glands, injection of atropia
abolishes the secretory power of the sciatic, while leaving
its vaso-motor influence untouched ; and pilocarpin stimu-
lates secretion chiefly by direct action on the cells of the
sweat-glands, or nerve fibres within them.
That the sweating caused by a high external temperature
is normally brought about by nervous influence, and not by
direct action on the secreting cells, is shown by the following
experiments. One sciatic nerve is divided in a cat, and the
animal is put into a hot-air chamber. No sweat appears
on the foot whose nerve has been cut, but the other feet are
bathed in perspiration. Similarly, a venous condition of
the blood (in dyspnoea) causes sweating in the feet whose
nerves have not been divided, but none in the other foot ;
and stimulation of the central end of the cut sciatic has
the same effect. All this points to the existence of a reflex
mechanism ; and it is certain that dyspnoea acts by direct
stimulation of the centre or centres. The vaso-motor
centre is at the same time stimulated, and the bloodvessels
constricted, as in the cold sweat of the death agony. Fear
may also cause a cold sweat, impulses passing from the
cerebral cortex to the vaso-motor and sweat centres.
The exact position and number of the sweat centres have not been
settled. It is possible that a general sweat-centre exists in the
medulla oblongata, but its existence has never been definitely proved.
On the other hand, it is known that in the cat there are at least two
spinal centres, one for the fore-limbs in the lower part of the cervical
cord, and another for the hind-limbs where the dorsal portion of the
cord passes into the lumbar. That this latter centre does not exist or is
comparatively inactive in man, is indicated by the following case. A
man fell from a window and fractured his backbone at the fifth dorsal
vertebra. The lower half of the body was paralyzed for a time, but
EXCRETION ' 415
recovered. Ultimately, however, the paralysis returned ; and shortly
before his death (twenty one years after the accident) it was noticed
that a copious perspiration broke out several times on the upper part
of the body, while the lower portion remained perfectly dry. If there
is any spinal centre in man, it appears to lie above the fifth spinal
segment. For it was seen in a professional diver who fractured his
neck at that level, and lived three months after the accident, that
sweat frequently appeared on the parts of the body above the lesion,
but never below. At the autopsy the whole thickness of the cord,
except perhaps a small portion of the anterior columns, was found
destroyed.
The secretory fibres for the fore-limbs (in the cat) leave the cord
in the anterior roots of the fourth to ninth thoracic nerves. They
pass by white rami communicantes to the sympathetic chain, in which
they reach the ganglion stellatum, where they are all connected with
nerve-cells. Then, as non-medullated fibres, they gain the brachial
nerves by the grey rami, and run in the radial and ulnar to the pads
of the feet. The fibres for the hind-limbs leave the cord in the
anterior roots of the twelfth thoracic to the third lumbar nerves, pass
by the white rami to the sympathetic ganglia, in which they form
connections with ganglion cells, then, as non-medullated fibres, run
along the grey rami, and are distributed to the foot in the sciatic.
The evidence of the direct secretory action of nerves on
the sweat glands is singularly striking and complete, in con-
trast to what we know of the kidney. In the latter, blood-
flow is the important factor ; increased blood-flow entails
increased secretion. In the former, the nervous impulse to
secretion is the spring which sets the machinery in motion ;
vascular dilatation aids secretion, but does not generally cause
it. It would, however, be easy to lay too much stress on this
distinction, for in the horse the mere dilatation of the blood-
vessels of the head after section of the cervical sympathetic
has been found to be accompanied by increased secretion of
sweat, and urinary secretion can certainly be affected by
the direct action of various substances on the secretory
mechanism, independently of vascular changes. But the
broad difference stands out clearly enough, and the reason
of it lies, perhaps, in the essentially different purpose of the
two secretions. The water of the urine is in the main a
vehicle for the removal of its solids ; the solids of the sweat
are accidental impurities, so to speak, in the water. The
kidney eliminates substances which it is vital to the organism
to get rid of; the sweat-glands pour out water, not because it
4i6 A MANUAL OF PHYSIOLOGY
is in itself hurtful, not because it cannot pass out by other
channels, but because the evaporation of water is one of the
most important means by which the temperature of the
body is controlled. In short, urine is a true excretion,
sweat a heat-regulating secretion. No hurtful effects are
produced when elimination by the skin is entirely prevented
by varnishing it, provided that the increased loss of heat is
compensated. A rabbit with a varnished skin dies of cold,
as a rabbit with a closely-clipped or shaven skin does ; sup-
pression of the secretive function of the skin has nothing to
do with death in the first case any more than in the second.
PRACTICAL EXERCISES ON CHAPTER VI.
Urine.
For most of the experiments human urine is employed — in the
quantitative work the mixed urine of the twenty-four hours. Urine
may also be obtained from animals. In rabbits pressure on the
abdomen will empty the bladder. Dogs may be taught to micturate
at a set time or j^lace, or kept in a cage arranged for the collection of
urine. Or a catheter may be used (p. 429).
1. Specific Gravity. — Pour the urine into a glass cylinder, and
remove froth, if necessary, with filter-paper. Place a urinometer
(Fig. 128) in the urine, and see that it does not come in contact
with the side of the vessel. Read off on the graduated stem the
division which corresponds with the bottom of the meniscus. This
gives the specific gravity.
2. Reaction. — Test with litmus-paper. Generally the litmus is
reddened, but occasionally in health the urine first passed in the
morning is alkaline. Sometimes urine has an amphicroic reaction,
i.e., aftects both red and blue litmus paper. This is the case when
there is such a relation between the bases and acids that both acid
and ' neutral ' (dibasic) phosphates are present in certain proportions.
The acid phosphate reddens blue litmus, and the ' neutral ' phosphate
turns red litmus blue.
3. CMorides — {a) Qualitative Test. — Add a drop of nitric acid
and a drop or two of silver nitrate solution. A white precipitate
soluble in ammonia shows the presence of chlorides. The nitric
acid is added to prevent precipitation of silver phosphate.
[0) Quantitative Estimation. — The quantitative estimation of the
chlorine in urine without previous evaporation and incineration is
best made by one of the modifications of VolhanVs method. It
depends ui)on the comi)lete precipitation of the chlorine combined
with the alkaline metals, and also of sulphocyanic acid, by silver
PKA CT/( A I. EXERCISES
4«7
' -ICCIO
— J 010
— 1020
— 1030
— lOiO
Fk;. 128. — Ukino-
MF.TER.
from a solution containing nitric acid in excess ; and avoids the
error introduced into simpler methods, Hke Mohr's, by the union of
some of the silver with other substances than chlorine. A i^iven
quantity of a standard solution of silver nitrate (more than sufficient
to combine with all the chlorine) is added to
a given volume of urine. The excess of silver
is now estimated by means of a standard solution
of ammonium sulphocyanide. A solution of the
double sulphate of iron and ammonium (known
as iron-ammonia-alum) is taken as the indicator,
since a ferric salt does not give the usual red colour
with a sulphocyanide so long as any silver in the
solution is uncombined with sulphocyanic acid.
To carry out the method, put 10 c.c. of urine,
which must be free from albumin, in a stoppered
flask, with a mark corresponding to 100 c.c.
Add 50 c.c. of water, 4 c.c. of pure nitric acid
(specific gravity 1 •2), and 15 c.c. of the standard
silver solution (of which x c.c. corresponds to
•01 gramme NaCl, or -00607 gramme CI);
shake well, fill with water to the mark, and
again shake. After the precipitate has settled,
filter it off. Take 50 c.c. of the filtrate, add
5 c.c. of a concentrated solution of iron-am-
monia-alum, and run in from a burette the standard solution of
ammonium sulphocyanide until a weak but permanent red coloration
appears. 2 c.c. of the sulphocyanide solution correspond exactly
to I c.c. of the silver solution, so as just to allow of the end reaction
with the iron solution being seen, and no more.
Suppose -V c.c. of the sulphocyanide solution are required, then
the chlorine in 10 c.c. of urine evidently corresponds to (15 -v)
CGI gramme NaCl.
4. Phosphates — (i) Qualitative Tests. — [a) Render the urine alka-
line with ammonia. A precipitate of earthy phosphates (calcium
and magnesium phosphates) falls down. Filter. To the filtrate add
magnesia mixture (a mixture of sulphate or chloride of magnesium,
ammonium chloride and ammonia) ; a precipitate shows the presence
of alkaline phosphates (sodium, potassium, or ammonium phos-
phates). The precipitate is ammonio-magnesic or triple phosphate.
{li) Add to urine half its volume of nitric acid and a little molybdate
of ammonium, and heat. A yellow precipitate of ammonium phospho-
molybdate shows that phosphates are present.
(2) Quantitative Estimation. — The quantitative estimation of phos-
phoric acid in urine is best done volumetrically, by titration with a
standard solution of uranium nitrate, using ferrocyanide of potassium
as the indicator. Uranium nitrate gives with phosphates, in a solu-
tion containing free acetic acid, a precipitate with a constant pro-
portion of phosphoric acid. As soon as there is more uranium in
the solution than is required to combine with all the phosphoric acid,
a brown colour is given with potassium ferrocyanide, due to the
27
4 1 8 A MA .\U. 1 L OF I'll ) -SIOLOC, \ '
formation of uranium ferrocyanide. In carrying out the method,
5 c.c. of a mixture of acetic acid and sodium acetate (there are
lo grammes of sodium acetate and lo grammes of glacial acetic acid
in loo c.c. of the mixture) are added to 50 c.c. of urine, which is
then heated in a beaker on the water-bath to about 80" C. The
standard uranium solution (which contains 35"5 grammes of uranium
nitrate in the litre, and i c.c. of which corresponds to 0005 gramme
P0O5) is now run in from a burette, until a drop of the urine gives,
with a drop of potassium ferrocyanide solution, on a porcelain slab,
a brown colour. Uranium acetate may be used instead of uranium
nitrate, but the latter keeps best.
5. Sulphates — (1) Qualitative 7\st. — Add to urine a drop of
hydrochloric acid and then a few drops of barium chloride. A
white precipitate comes down, showing that inorganic sulphates
are present. The hydrochloric acid prevents precipitation of the
phosphates.
(2) Qtiantitative Estimation of the Sulphuric Acid united with
Inor^^anic Bases. — Acidulate 100 c.c. of albumin-free urine with acetic
acid, add excess of barium chloride, and heat on the water-bath till
the precipitate has settled ; filter through an ash-free filter, wash the
precipitate with water, with dilute hydrochloric acid, then again with
water. Dry, incinerate in a platinum dish, and weigh. From the
weight of barium sulphate the inorganic sulphuric acid is easily cal-
culated (SO4 in I gramme of barium sulphate = 0*41 187 gramme).
(3) Quantitative Estimation of the Sulphuric Acid utiited 7vith
Aromatic Bodies (aromatic or organic sulphuric acid). — Add to the
filtrate and the washings from (2) a little hydrochloric acid, and heat
in order to break up the aromatic sulphates. The elements of water
are thus taken up by these salts ; and the sulphuric acid is able to
unite with the barium. Add more barium chloride if necessary, and
treat the precipitate as before. Its weight after incineration gives the
quantity of barium sulphate corresponding to the sulphuric acid of the
aromatic compounds.
6. Indoxyl can be oxidized into indigo, and so estimated.
A qualitative test is the following : Ten c.c. of horse's urine is
mixed with 10 c.c. of strong hydrochloric acid, and a dilute solution
of sodium hypochlorite added dro]) by drop ; a bluish colour appears
it", as is generally the case, indoxyl is present, indigo (Cj,,Hj,^N.,0.,^
being formed by the oxidizing action of the hyi)ochlorite on the
indoxyl, the compound of which with sulphuric acid has been broken
up by the hydrochloric acid. The number of drops of the hypo-
chlorite required to give the maximum change of colour is deter-
mined. Then the experiment may be repeated by dropping this
quantity of hypochlorite into 10 c.c. of the hydrochloric acid, and
adding 10 c.c. of the urine. The urine must be free from albumin.
If too much hypochlorite be added, the indigo is itself oxidized.
In performing the test in human urine, which contains a smaller
quantity of the indigo- forming substance, the urine should first
be concentrated. If the faint blue liijuid be shaken up with a
few drops of chloroform, the latter takes up the colour, which
rRACTlCAL EXERCfS/iS 419
is thus rendered more evident. The skatoxyl of urine can also be
oxidized to indigo, but it is present in far smaller amount. The
average quantity of indigo obtained from a litre of horse's urine is
about 150 milligrammes ; from a litre of human urine, not a twentieth
of that cjuantity.
7. Urea (i) Preparation. — Urea can be obtained from dog's
urine by evaporating it to a syrup, extracting with absolute alcohol,
evaporating most of the alcohol, and allowing the mass to crystallize.
Or human urine may be concentrated to a small bulk, cooled to o\
and mixed with excess of strong pure nitric acid. A mass of rhombic
or six-sided tabular crystals of nitrate of urea separates. From the
nitrate, after purification, urea itself is obtained by addition of barium
carbonate till carbon dioxide ceases to be given off. What remains
is a mixture of urea and barium nitrate, from the dry residue of which
urea can be dissolved out by alcohol (Hoppe-Seyler).
Urea can also be obtained artificially by heating its isomer, ammo-
nium cyanate (NH^ - O - CN), to 100' C. This reaction is of great
historical interest, as it forms the final step in Wohler's famous
synthesis of urea, the first example of a complex product of the
activity of living matter being formed from the ordinary materials of
the laboratory.
Urea is also formed when ammonia is allowed to act on carbonyl
chloride. Thus : C0Cl., + 4NHo = C0.2(NH,) + 2NH^C1.
(2) Deavnposition of Urea. — Heated dry in a test-tube, it gives off
ammonia. The residue contains biuret, which, when dissolved in
water, gives a rose colour, with a trace of cupric sulphate and excess
of sodium hydrate (or of the hydrates of certain other metals of the
alkalies and alkaline earths, p. 20). Some proteids — peptones and
albumoses — in the presence of the same reagents, give a similar
colour, the so-called biuret reaction.
Heated in watery solution in a sealed tube to iSo' C, urea is
entirely split up into carbon dioxide and ammonia, a change which
can also be brought about, as already mentioned, by the action of
micro-organisms. Nitrous acid, hypochlorous acid, and salts of hypo-
bromous acid carry the decomposition still further, carbon dioxide,
nitrogen, and water being the products of their oxidizing action on
urea. Thus: C0.2(NH,) 4- 3NaBrO = sNaBr + 2H,0 + C0., + N.3.
(3) Qinvititatire Estimaiioti — The Hypobromite Method. — This
reaction is the basis of a method for the quantitative estimation of
urea in urine. The urea is split up by sodium hypobromite, and
the carbon dioxide being absorbed by the excess of sodium hydrate
used in preparing the hypobromite, the nitrogen is collected over
water in an inverted burette. It is easy to calculate the weight of
urea corresponding to a given volume of nitrogen measured at a
given temperature and pressure. The nitrogen of urea is f§, or y^^
of the whole molecular weight. Now, i c.c. of N weighs, at 760
millimetres of mercury and o' C, "00125 gramme. Therefore, i c.c.
of N corresponds to -00125 x -y'= -00268 gramme urea. Suppose,
now, that i c.c. of urine was found to yield 10 c.c. of N measured at
17° C. and 750 millimetres barometric pressure. Since a gas expands
420
A MA XUA I. or PI I YSI OL OC ) '
„l.j part of its volume at o'' for every degree above o", we must
correct the apparent volume of the nitrogen by multiplying by n-;,j}.
Since the volume of a gas is inversely proportional to the pressure,
we must further multiply by I;";y. Thus we get iox^io^?«S =
-Ay/' = 9*29 c.c. as the volume of
the nitrogen reduced to 0° C. and
760 millimetres of mercury. Multi-
plying this by "00268, we get "0249
gramme urea for i c.c. urine, which
for the daily yield of 1,200 c.c.
would correspond to 29 '88 grammes
urea.
As a matter of fact, however, it
has been found that there is always
a deficiency of nitrogen, that is, a
given quantity of urea yields less
than the estimated amount of gas.
A gramme of urea in urine, instead
of giving olf 373 c.c. of nitrogen,
gives only 354 c.c. at 0° C. and
760 millimetres pressure. We must
therefore take 1 c.c. of N as corre-
sponding to '00282 gramme, instead
of '00268 gramme urea. But it is
aftectation to make this correction
if, as is constantly done in hospitals,
the temperature is not taken into
account.
A convenient apparatus for clini-
cal use is shown in Fig. 129.
Five c.c. of urine is put into the
thimble A, which is then set in the
small bottle B. In B, 15 c.c. of a
solution made by adding bromine
to ten times its volume of 40 per cent, sodium hydrate solution has
already been placed. The cork through which the connecting tube
C passes is now carefully fixed in B, the graduated tube D is im-
mersed in the water contained in the cylinder E, and the stopcock
F being open to the air, the level of the water in it is read off. The
stopcock having been closed to the air and opened to tube C, the
bottle B is tilted so that the urine in the thimble is gradually mixed
with the hypobromite solution, and the nitrogen given off is added
to the air in the graduated tube and its connections. The level of
the water in the tube is therefore depressed, ^^'hen gas ceases to be
given off, and a short time has been allowed for the whole to cool,
the tube is raised till the level of the water is once more the same
inside and out. The level is again read off; the difference of the
two readings gives the volume of nitrogen at the temperature of the
air and the barometric pressure. An ordinary burette may also be
used, the tube C being closed by a pinchcock. A second short tube
Fui. 129. — IIyi'obkomh K Meth(ii)
OF ESTIMATING UkEA.
F is a stopcock which may be turned
so as to place the interior of the cylinder
D either in communication with the
external air. or with the bottle B,
through the tube C.
PRACTICAL J-XEKCISES 421
passing tluoiigh the cork of H is left open till the cork, has been
adjusted, and then closed.
8. Estimation of the Total Nitrogen. — It is often more important
to determine the total nitrogen of the urine than the urea alone ;
and this is conveniently done by Kjeldahl's method (or some modifi-
cation of it), which can also be applied to the estimation of the
nitrogen in the fa;?ces, or in any of the solids or li([uids of the body.
It depends on the oxidation of the nitrogenous matter in such a
way that the nitrogen is all represented as ammonia. The ammonia
is then distilled over, collected and estimated, and from its amount
the nitrogen is easily calculated. In urine the method can be carried
out by adding to a measured quantity of it (say 5 c.c. ) four times
its volume of strong sulphuric acid, and boiling in a long-necked
flask (capacity 200 c.c), after the addition of a globule of mercury
(about oT c.c), which hastens oxidation and obviates bumping. A
part of the mercuric sulphate formed remains in solution ; the rest
forms a crystalline deposit. The heating should continue for half an
hour, or until the liquid is decolourized. This completes the process
of oxidation : and the next step is to liberate the ammonia from the
substances with which it is united m the solution, and to distil it
over. Dilute the liquid with water, after cooling, up to about 150 c.c,
and pour into a larger long-necked flask. Add enough of a solution
of sodium hydrate (specific gravity about i'2 5) to render the liquid
alkaline, avoidmg excess, as this favours bumping. The proper
quantity can be found by determining beforehand how much of the
alkali is needed to neutralize the acid used for oxidation, and this
amount should be added. Bumping may further be prevented by
the addition of a little granulated zinc. Shake the flask two or three
times. Add also about 1 2 c.c of a concentrated solution of potassium
sulphide (i part to i.', parts water), which favours the setting free of
the ammonia from the amido-compounds of mercury that have been
formed during oxidation. Commercial ' liver of sulphur ' will do
quite well. Immediately connect the distilling-flask with the worm,
as shown in Fig. 130, and distil the ammonia over into 50 c.c. of
standard (decinormal) sulphuric acid contained in a flask into vvhich
a glass tube connected with the lower end of the worm dips. Heat
the distilling flask at first gently, then strongly, and boil for three-
quarters of an hour, or until about two-thirds of the liquid has passed
over. Then lift the tube out of the standard acid, and continue the
distillation for two or three minutes longer. The ammonia is now all
united with the sulphuric acid. The quantity of potassium or sodium
hydrate required to neutralize a given volume of this solution, before
and after the ammonia has been passed into it, is estimated by
titration ; from the difference the amount of ammonia is calculated.
In titrating, a decinormal solution of potassium hydrate may be
used (i.e., a solution containing 5'6 grammes in 1,000 c.c), and the
strength of this solution, as well as of the decinormal sulphuric acid
solution, may be controlled by titration with a decinormal solution of
sodium carbonate (Na.iCO..) (5*3 grammes in 1,000 c.c.) or of oxalic
acid (6-3 grammes in 1,000 c.c). One c.c. of any one of these solutions
422
A j/ANrAL o/' /7/ys/0L()<;y
is equivalent to i c.c. of any other. A little methyl orange solution
is added to the standard sulphuric acid before titration, to serve as
indicator. The potassium hydrate is added till the pink tinge gives
jMace to a jjermanent but just recognisable yellow. One c.c. of deci-
normal sodium or ])otassiuni hydrate = '0014 gramme nitrogen.
9. Uric Acid — (i) Prcparatiotj. — Uric acid can be prepared in a
pure form from serpents' excrement, by dissolving it in dilute sodium
hydrate, and filtering. The filtrate contains sodium urate, which is
precipitated by a current of carbon dioxide. The uric acid is set
free by boiling the precipitate with dilute hydrochloric acid, and is
deposited as a colourless crystalline powder on cooling.
Fig. 130.
.\kkan(;emf.m for Di.stii.latm.n in Estimation ok Total
NiTROC.EN.
(2) Qualitative Test for Uric Acid — Mure.xide Test. — A small
(]uantity of uric acid or one of its salts is heated with a little dilute
nitric acid. The colour of the residue left by evaporation becomes
yellow, and then red, and on the addition of ammonia changes to
deep purple-red. Potassium or sodium hydrate changes the yellow to
violet. The purple-red substance is murexide or ammonium furfurate,
which is also formed by the action of nitric acid and ammonia on
theobromine (dimethylxanthin), the alkaloid of cocoa, and theine or
caffeine (trimethylxanthin), the alkaloid of tea and coffee.
(3) Quantitative Estimation — {a) by J^recipitation and Weighing. —
Uric acid is precipitated like grains of cayenne pepjjer on the sides
and bottom of the vessel in which urine, strongly acidulated with
pure hydrochloric acid, is allowed to stand for forty-eight hours.
By collecting the crystals from a measured quantity of urine (say
PRACTICAL /:xj:rcises .423
200 c.c. with 10 c.c. hydrochloric acid added) on a small weighed
filter, washing the preciiMtate on the filter with as small a cjuantity of
water as possible (not more than 30 c.c), drying at no" C, and
weighing, an estimate may be made of the amount of uric acid present
(Heintz). Notwithstanding that the pigment carried down with the
uric acid is added to the weight of the latter, this method gives
results somewhat too small, as a portion of the uric acid is left in
solution.
(/>) T/ic Silver Metliod of estimating Uric .J^/^.— Salkowski has
therefore devised a method founded on the precipitation of the uric
acid with an ammoniacal silver solution. This, in one or other of
the modified forms which have been introduced by E. l.udwig and
Haycraft respectively, is probably the most accurate method at
present at our disposal ; and of the two modifications we may say
that Ludwig's is the more exact, but Haycraft's the less tedious.
Haycraft's method (with certain alterations by Herrmann) is as
follows : 50 c.c. of urine are mixed with 5 c.c. of a magnesia mixture*
and 5 c.c. of an ammoniacal silver solution.! The mixed precipitate
of urate of silver and aminonio-magnesium i)hosphate is allowed to
settle. The clear liquid is filtered by means of a suction-pump
through an asbestos or glass-wool filter. About 4 grammes sodium
bicarbonate in substance are sprinkled on the filter, and the filtration
of the precipitate and the rest of the liquid proceeded with. The pre-
cipitate is washed on the filter with water containing ammonia, until
the filtrate gives no precipitate either on the addition of hydrochloric
acid or of silver nitrate and nitric acid. The precipitate is then dis-
solved in pure nitric acid, and the silver in it estimated by titration
with ammonium sulphocyanide (Volhard's method, p. 417). On the
assumptions (which, however, are by no means granted by all chemists
who have studied the question) that the uric acid combines only with
the silver, and the silver only with the uric acid, and that the com-
pound formed has a constant composition, the amount of silver enables
us to calculate the quantity of uric acid present. If the ammonium
sulphocyanide solutionis made of centinormal strength (so that i c.c.
of it corresponds to 1 c.c. of a silver solution containing 17 grammes
AgNO.; in the litre), i c.c. of it will correspond to •00168 gramme
uric acid. The method is not suitable for urine containing a great
deal of uric acid.
(c) Estimation of Uric Acid by Precipitation as Ammonium Urate
— Whitney's Modification of Hopkin's Method. — Thirty grammes of
ammonium chloride are added to 100 c.c. of urine. After two hours
the precipitate is filtered off and washed on the filter with a saturated
solution of ammonium chloride. Filter and precipitate are placed in
* The magnesia mixture is made by dissolving 100 grammes crystal-
lized magnesium chloride in water, then adding excess of ammonium
chloride and as much ammonia as is necessary to impart a distinct odour
to the liquid. The solution is then made up to i litre.
f The ammoniacal silver solution is made by dissolving 26 grammes
silver nitrate in excess of ammonia, and making up with distilled water
to I litre.
424 A MANUAL OF rinSlULOijY
an Erlcnmeycr llask, and treated with lo c.c. of a decinormal solution
of hydrochloric acid. The volume is made up to about 30 c.c. with
distilled water. The liquid is then heated to boiling to decompose
the ammonium urate, and the excess of hydrochloric acid is estimated
by titration with a decinormal solution of sodium hydrate, methyl
orange being used as indicator. If x is the number of c.c. of the
sodium hydrate solution used, then (10 -.v) x -0168 is the amount in
grammes of the uric acid in 100 c.c. of urine.
10. Kreatinin. — Qualitatively, kreatinin may be recognised in veiy
small amounts by WeyPs test. A few drops of a dilute solution of
sodium mtro-prusside are added to urine, and then dilute sodium
hydrate. A ruby-red colour appears, which soon turns yellow. If
the urine is now acidified with acetic acid and heated, it becomes
first greenish and then blue.
Kreatinin forms crystalline compounds with various acids and
salts, of which the most important is kreatinin-zinc-chloride, formed
on the addition of zinc chloride to an alcoholic or watery .solution of
kreatinin, often in the shape of beautiful thick-set rosettes of needles.
Neubauer has made this reaction the basis of a method for the
quantitative estimation of kreatinin (Fig. 120, p. 388).
11. Hippuric Acid. — From horse's or cow's urine hippuric acid is
prepared by evaporating to a small bulk, and adding strong hydro-
chloric acid. The crystalline precipitate is washed with cold water,
then dissolved in hot water, and filtered hot. Hippuric acid separates
out from the filtrate in the cold in the form of long four-sided prisms
with pyramidal ends. Heated dry in a test-tube, the crystals melt,
and benzoic acid and oily drops of benzonitrile, a substance with a
smell like that of oil of bitter almonds, are formed.
ABNORMAL SUHSTANCES IN UKINF:.
12. Proteids— ( I ) Qualitative Tests. — (a) Boil and add a few
drops of nitric acid. A precipitate on boiling, increased or not
affected by the acid, shows the presence of coagulable proteids
(serum-albumin or globulin). A precipitate of earthy phosphates
sometimes forms on boiling. It can be distinguished from a pre-
cipitate of proteids by dissolving on the addition of acid.
(/') Heller s Test. — Put some nitric acid in a test-tube. Pour
carefully on to the surface of the acid a little urine. A white ring at
the junction of the liquids indicates the presence of albumin, globulin
(or albumose?). When this test is performed with undiluted urine,
uric acid may be precipitated and cause a brown colour at the junc-
tion. A similar ring may be found in the absence of proteids when
the test is made on the urine of a patient who has been taking
copaiba.
{c) Filter some urine, and add to the filtrate excess of acetic acid
and a few drops of potassium ferrocyanide. If proteids are present
a precipitate forms.
(<y) Test for Globulin in Urine. — Serum-globulin probably never
occurs in urine apart from serum-albumin. It may be detected by
PRACTICAL EXERCISES 425
Kauder's test. Make the urine alkaline with ammonia, let it stand
for an hour and filter. Half saturate the filtrate with ammonium
sulphate, i.e., add to it an eijual volume of a saturated solution of
ammonium sulphate. Serum-globulin is preci[Mtated, serum-albumin
is not.
{e) Test for Albuinose in Urine {All'ianosuria). — Coagulable proteids
are removed by boiling the urine (acidulated if necessary), and filtering
off the precipitate if any. The filtrate is neutralized. If a further
precipitate falls down it is filtered off, the clear filtrate is heated in a
beaker placed in a boiling water-bath, and saturated with crystals of
ammonium sulphate. A ])recipitate indicates that albumoses (pro-
teoses) are present. A slight precipitate might possibly be due to the
formation of ammonium urate. A further test may be performed on
the original urine if it is free from coagulable proteids, or on the
filtrate after their removal. Add a few drops of pure nitric acid. If
albumoses are present, a precipitate is thrown down which disappears on
heating, and reappears on cooling the test-tube at the cold-water tap.
{/) Test for Fcptotie iu Urine {Peptonuria). — Place some of the
urine in a beaker on a boiling water-bath for thirty minutes, and
saturate with ammonium sulphate crystals. Then boil over a small
flame or in an air-bath for half an hour. All the proteids, including
peptones, are precipitated. But the peptones can still be redissolved
by water, the others not. Filter hot. Wash the precipitate on the
filter with a boiling saturated solution of ammonium sulphate. Then
extract the residue with cold water, filter, and test the filtrate by the
biuret test (addition of very dilute cupric sulphate and excess of
sodium hydrate). A rose colour indicates the presence of peptone
(P- 377' (^))) but if the reaction is only a faint one, it may be due to
urobilin (Stokvisj.
(2) Quantitative Estimation of Coagulable Proteids {Serum-
A/l'umi7i and Globulin) — {a) Gravimetric Method.— W&Sii 50 to 100
c.c. of the urine to boiling, adding a dilute solution (2 per cent.) of
acetic acid by drops as long as the precipitate seems to be increased.
Filter through a weighed filter, ^^'ash the precipitate on the filter
with hot water, then with hot alcohol, and finally with ether. Dry
in an air-bath at no C., and weigh between watch-glasses of known
weight.
{b) Method of Roberts and Stolnikow {modified by Brandberg). —
This method is founded on the fact that the time taken for the white
ring to appear in Heller's test depends on the proportion of coagulable
proteid present. It has been found that when i part of albumin is
contained in 30,000 parts of an albuminous solution (o"oo33 per cent.),
the ring appears in two and a half to three minutes. The amount of
dilution of the urine which is necessary to delay the formation of the
ring for this length of time is what has to be determined. To do
this, proceed as follows : Dilute a portion of the urine (say 5 c.c.) ten
times : that is, add to it nine times its volume of distilled water (45 c.c.)
from a burette. Place some pure nitric acid in a test-tube with a
pipette, taking care not to wet the sides of the test-tube with the
acid. Now run on to the surface of the nitric acid some of the
426 A MANUAL OF I'lIYSIOLOGY
diluted urine, and note the interval that elapses before formation
of the white ring. If it is more than three minutes, the diluted urine
contains less than i part in 30,000, and the untiiluted urine less
than I part in 3,000 {i.e., less than "033 per cent.) of coagulable
proteid, and the experiment must be repeated with urine diluted
to a smaller extent. If the ring appears after a shorter interval
than three minutes, the diluted urine contains more than i part in
30,000 (the original urine more than "033 per cent.), and must be
further diluted. Fill a burette with the diluted urine. Run i c.c. of
it into a test-tube and add 9 c.c. of distilled water. Repeat the
test with this second dilution. If the ring appears at a longer
interval than three minutes, the twice-diluted urine contains less than
I part of albumin in 30,000, and the original undiluted urine less
than I part in 300, i.e.., less than 0-33 \^^x cent. So far, then,
we have found, let us suppose, that the proportion of albumin in the
original urine lies between 0*033 and 033 per cent. Now run i c.c.
of the urine of the first dilution (the urine diluted ten times) into
a test-tube, and add 4 c.c. of distilled water, i.e., dilute again five
times. If this gives the white ring in Heller's test in three minutes,
...... 30,000 -
the origmal urme will contam i part of albumin m > ^-'-j i"
10x5
600 parts, or ot6 per cent. If the interval is longer or shorter than
three minutes, the urine of the first dilution (i to 10) must be diluted
less or more than five times until the interval amounts to about
three minutes. I'he total dilution corresponding to a percentage of
©•0033 of albumin is thus known, and the percentage in the undiluted
urine can be easily calculated.
13. Sugar — (i) Qualitative Tests — (a) Troinmer's Test. — See p. 23.
It is to be remarked that some substances present in small amount
in normal urine reduce cupric sulphate, e.g., uric acid and kreatinin,
but this action is so slight that it can cause no error in the test, as
usually performed. Glycuronic acid, which is said to occur even in
normal urine in very slight traces, and which also reduces cupric
salts, appears in considerable amount after the administration of
chloroform, chloral, nitro-toluol and other substances. If less than
o"5 per cent, of sugar is present in the urine, no precipitate of cuprous
oxide will be formed till the urine is cooled. The test may also be
performed with Fehlings solution.
{h) Phenyl-hydrazine Test. — This test depends upon the fact that
phenyl-hydrazine forms with sugars such as glucose, maltose, isomal-
tose, etc., but not with cane-sugar, characteristic crystalline substances
(phenyl-glucosazone, phenyl-maltosazone, etc.) which can be recog-
nised under the microscope, and are distinguished from each
other by melting at different temperatures. Phenyl-glucosazone
(Cjt;Ho.^N40j melts at 205° C. To perform the test for glucose in
the urine, proceed thus : Put 5 c.c. of urine in a test-tube, add
I decigramme of hydrochlorate of phenyl-hydrazine (' twice as much
as will lie on the point of a knife-blade ' — v. Jaksch), and one and a
half times as much sodium acetate as is taken of the phenyl-hydrazine
salt. Heat the test-tube in a boiling water-bath for half an hour.
/'A' A i T/c ■. 1 /. j:x/:a'i 7s/-:s 427
Then cool at the tap and examine the yellow crystalline deposit
under the microscope (Plate IV., 3). Very minute traces of sugar
can be detected in this way (as little as o'l j)er cent, in urine).
Often in normal urine yellow crystals are deposited during the first
fifteen minutes' lieating. They must not be mistaken for glucosazone.
They probably consist of a compound of glycuronic acid and jihenyl-
hydrazine. They are changed as the heating goes on into an
amorphous brownish-yellow precipitate (Abel).
(c) The Yeast Test is an important confirmatory test for distin-
guishing the fermentable sugars from other reducing substances, but it
is not very delicate, and will with difficulty detect sugar when less than
0-5 per cent, is present. It can be performed thus : A little yeast
(the tablets of compressed yeast do very well) is added to a test-tube
half filled with urine. The test-tube is then filled up with mercury,
closed with the thumb, and inverted over a dish containing mercury.
The dish may be placed on the top of a water-bath whose temperature
is about 40° C. After twenty-four hours the sugar will have been
broken up into alcohol and carbon dioxide. The latter will have
collected above the mercury in the test-tube, and the former will be
present in the urine. The tests for sugar will either be negative or
will be less distinct than before.
(2) Quantitative Estimatioji 0/ Sugar in Urine.— {a) Vobonetrically^
the sugar can be estimated by titration with Fehling's solution. As
this does not keep well, two solutions containing its ingredients
should be kept separately and mixed when required. Solution I. :
Dissolve 34 '64 grammes pure cupric sulphate in distilled water, and
make up the volume to 500 c.c. Solution II. : Dissolve 173 grammes
Rochelle .salt in 400 c.c. of water, add to this 51-6 grammes
sodium hydrate, and make up the volume with water to 500 c.c.
Keep in well-stoppered bottles in the dark. For use, mix together
equal volumes of the two solutions. Ten c.c. of this mixture is
reduced by 0-05 gramme dextrose. To estimate the sugar in urine,
put 10 c.c. of the mixture into a porcelain capsule or glass flask, and
dilute it four or five times with distilled water. Dilute some of the
urine, say ten or twenty times, according to the quantity of sugar
indicated by a rough determination. Run the diluted urine from
a burette into the Fehling's solution, bringing it to the boil each
time urine is added, until, on allowing the precipitate to settle, the
blue colour is seen to have entirely disappeared from the supernatant
liquid.
Suppose that 10 c.c. of Fehling's solution is decolourized by 20 c.c.
of the ten-times diluted urine. Then 2 c.c. of the original urine
contains 0-05 gramme dextrose. If the urine of the twenty-four
hours (from which this sample is assumed to have been taken)
amounts to 4,000 c.c, the patient will have passed 0-05 x 2,000= 100
grammes sugar, in twenty-four hours.
(d) The polarimeter affords a rapid and, with practice, a delicate
means of estimating the (juantity of sugar in pure and colourless
solutions, but diabetic urine must in general be first decolourized by
adding lead acetate and filtering off the precipitate. What is
428 A .V.LXUAL OF I'lIYSlOLOCA'
measured is the amount by which the plane of polarization of a ray
of polarized light of given wave-length (say sodium light) is rotated
when it passes through a layer of the urine or other optically active
solution of known thickness. Let a be the observed angle of rota-
tion, / the length in decimetres of the tube containing the solution,
IV the number of grammes of the optically active substance per c.c. of
solution, and {a)^ the specific rotation of the substance for light of
the wave-length of the part of the spectrum corresponding to the
D line {i.e., the amount of rotation expressed in degrees which is
produced by a layer of the substance i decimetre thick, when the
solution contains i gramme of it j^er c.c). Then (^),,= ± *
In this equation a and / are known from direct measurement ;
(«')„ has been determined once for all for most of the important active
substances, and therefore 7c' is easily calculated. For de.xtrose (<7),, may
be taken as 52•6^ It varies somewhat with the concentration, but
for most investigations on the urine these variations may be neglected.
It is not possible to describe here the numerous forms of
polarimeter that are in use. Among the best are those constructed
on what is called the ' half-shadow ' system. A half-shadow polari-
meter consists, like other polarimeters, of a fixed Nicol's prism (the
polarizer), and a nicol capable of rotation (the analyzer). In addition,
there is an arrangement which rotates by a definite angle the plane
of polarization in one half of the field, but not in the other, e.g., a
small nicol occujjying only half of the field. In the zero position of
the analyzer, both halves of the field are equally dark. The solution
to be investigated is placed in a tube of known length, the ends of
which are closed by glass discs secured by brass screw caps. The
glass discs must be slid on, so as to exclude all air. The tube
having been introduced between the polarizer and analyzer, the sharp
vertical line which indicates the division between the two half-fields
is focussed with the eye-piece, and then ihe analyzer is rotated till
the two halves are again equally shadowed. The angle of rotation,
a, is read oft' on the graduated arc, which is provided with a
vernier.
Systematic Examination of Urine. — In examining urine, it is con-
venient to adopt a regular plan, so as to avoid the risk of overlooking
anything of importance. The following simple scheme may serve as
an example ; but no routine should be slavishly followed, the object
being to get at the important facts with the minimum of labour :
T. Anything peculiar in colour or smell ? If colour suggests blood,
examine with spectroscope ; if it suggests bile, test for bile-pigments.
(See pp. 62, 64, 380.)
2. Reaction.
3. Sediment or not ? If the appearance of the sediment suggests
anything more than a little mucus, examine with microscope.
4. Specific gravity.
5. Quantity of urine in twenty-four hours. If quantity abnormally
large and specific gravity high, test for sugar.
6. Inorganic constituents not generally of clinical importance, but
PRACTICAL EXERCISES 429
in special diseases they should be examined— <?.^^^, chlorides in
])neumonia.
7. Normal organic constituents. Quantitative estimation of urea
in fever, and often in diabetes and Bright's disease.
,.„,., , , , ( Albumin,
8. Chemical exammation for abnormal ^,
- buear,
organic constituents. y Bile-salts and pigments.
14. Catheterism. — In many physiological experiments it is
necessary to obtain urine from the bladder by means of a catheter.
The most suitable form for animals is the flexible vulcanized rubber
tubes, which are also often employed in man. It is possible to pass
a fine catheter into the bladder of a male dog, but it is easier to
cathetenze a bitch, which is generally used for such experiments.
Even in the bitch the opening of the urethra lies entirely concealed
within the vagina, much deeper than the cul-de-sac in the mucous
membrane, into which the beginner usually tries to force the catheter.
For a first attempt the animal should be etherized and fastened on a
holder. The little or index finger of the left hand is passed into the
vagina till the symphysis pubis can be felt. A little below this is the
opening of the urethra. With the right hand the point of a flexible
catheter of suitable calibre is directed along the finger, and after a
little ' guess and trial ' it slips into the bladder, its entrance being
announced by the escape of urine.
When the animal is to be used in a long series of experiments an
operation is sometimes performed first of all to render the urethral
orifice more accessible.
CHAPTER \II.
METABOLISM, NUTRITION AND DIETETICS.
Wk return now to the products of digestion as they are
absorbed from the ahmentary canal, and, still assuming a
typical diet containing proteids, carbo-hydrates and fats, we
have to ask. What is the fate of each of these classes of
proximate principles in the body ? what does each contribute
to the ensemble of vital activity ? It will be best, first of
all, to give to these questions what roughly qualitative
answer is possible, then to look at metabolism in its quanti-
tative relations, and lastly to focus our information upon
some of the practical problems of dietetics.
I. Metabolism of Proteids. — The two chief proteids of the
blood-plasma, serum-globulin and serum-albumin, must, as
has been already pointed out, be recruited from proteids
absorbed from the intestine and for the most part altered in
their passage through the epithelium which lines it. ^^'hat
at bottom the reason and the mechanism of this alteration
are, we do not know ; but we do know that it is imperative
that peptone (or at least albumose) should not appear in
quantity in the blood, for when injected it causes profound
changes in that liquid, one expression of which is the loss
of its power of coagulation, and is rapidly excreted by
the kidneys, or separated out into the lymph. It is not
definitely known whether the peptones formed in digestion
yield, under the influence of the epithelial cells, both the
chief proteids of the blood in the proportions in which the}-
exist in the plasma, or only one of them, which is afterwards
META HOLISM, XTTK/T/OX AN/) DIETETICS 431
and elsewhere partially changed into the other. P>ut there
is some evidence that serum-albumin is more directly related
to the proteids of the food than serum-globulin. And it
is said that during starvation the albumin is relatively
diminished, and the globulin relatively increased. However
this may be, it cannot be doubted that the conversion of
peptones, directly or indirectly, into the proteids of the
blood-plasma forms the hrst recognisable step in the trans-
formation of the greater part of the digested proteids.
Living and Dead Proteids. — Now and again a living proteid
molecule in the whirl of flying atoms which we call a muscle-fibre,
or a gland-cell, or a nerve-cell, falls to pieces. Now and again a
molecule of proteid, hitherto dead, coming within the grasp of the
molecular forces of the living substance, is caught up by it, takes on
its peculiar motions, acquires its special powers, and is, as we phrase
it, made alive. But it is not any difference in the kind of proteid
which determines whether a given molecule shall become a part of
one tissue rather than of another. For it is from the serum-albumin
and serum-globulin of the blood that all the proteid material required
to repair the waste of the body must ultimately be derived ; and a
particle of serum-albumin may chance to take its place in a liver-cell
and help to form bile, while an exactly similar particle may become
a constituent of an endothelial scale of a capillary and assist in
forming lymph, or of a muscular fibre of the heart and help to drive
on the blood, or of a spermatozoon and aid in transferring the
peculiarides of the father to the offspring. Indeed, although there
are differences of detail, the broad lines of nutrition are the same for
all tissues ; and just as a tomb or a lighthouse, a palace or a church,
may be, and has been built with the same kind of material, or even
in succession with the very same stones, so every organ builds up its
own characteristic structure from the common quarry of the blood.
In the case of the more highly developed tissues at least, no mere
change of food will radically alter structure. A cell may be fed with
different kinds of food, it may be over-fed, it may be ill-fed, it may
be starved ; but its essential peculiarities remain as long as it con-
tinues to live. But in proportion as the advance of physiology has
emphasized the dominant position of organization, it has taken away
the hope of our ever being able to understand in what it is that the
difference between the living and the dead cell, between living and
dead proteid, or protoplasm, really consists.
The speculation of Pfliiger, that the nitrogen of living proteid
exists in the form of cyanogen radicals, whilst in dead proteid it
is in the form of amides, and that the cause of the characteristic
instability of the living substance — its prodigious power of dissocia-
tion and reconstruction — is the great intramolecular movement of
the atoms of the cyanogen radicals, is very interesting and ingenious,
but it remains, and is likely to remain, a speculation. And the same
432 A AfA.Xl'AL OF PlIYSlOLOiA'
is true of the suggestion of Loew and I>okorny, that the endowments
of living protoplasm depend on the presence of the unstable aldehyde
group H - C = O. Nor do the known differences of chemical com-
position in dead organs give any insight into the peculiarities of
organization and function which mark off one living tissue from
another. For so far as they do not depend upon differences in the
dead plasma which interpenetrates the living substance, they only
show that the latter does not split up quite in the same way at death
in all the tissues, while the general similarity in the elementary
composition of excitable structures leaves us free to imagine as great
or as small a similarity as we ]ilease in the grouping of the atoms
in the living combinations. Be this as it may, the living proteid
molecule, whatever function it may have been fulfilling in the
organized elements of the body, has certainly a much greater
tendency to fall to pieces than the dead proteid molecule. And
it falls to pieces in a fairly definite way, the ultimate products, under
the influence of oxygen, being carbon dioxide, water, and compara-
tively simple nitrogen- containing substances, which after further
changes appear in the urine as urea, uric acid, kreatinin, and
ammonia. We have no definite information as to the production
of water from the hydrogen of the tissues, except what can be
theoretically deduced from the statistics of nutrition (p. 463). A
few words will be said a little farther on about the production of
carbon dioxide from proteids ; we have now to consider the seat and
manner of formation of the nitrogenous metabolites. And since in
man and the other mammals urea contains by far the greater part of
the excreted nitrogen, it will be well to take it first.
Formation of Urea. — The starting-point of all inquiries into
the formation of urea is the fact that it occurs in the blood,
although in very small quantities (2 to 4 parts per 10,000).
Evidently, then, some, at least, of the urea excreted in the
urine may be simply separated by the kidney from the
blood ; and analysis shows that this is actually the case, for
the blood of the renal vein is poorer in urea than that of
the renal artery. If we knew the exact quantity of blood
passing through the kidneys of an animal in twenty-four
hours, and the average difference in the percentage of urea
in the blood coming to and leaving them, we should at once
be able to decide whether the whole of the urea in the urine
reaches the kidneys ready made, or whether a portion of it
is formed by the renal tissue. Although data of this kind
are as yet too inexact and too incomplete to enable us,
without other evidence, absolutely to say that all the urea
is simply separated by the kidney, it is not difficult to see,
META/:OlJSM, M'TR/TION AXf) DIETETICS 433
from such rouf;h measurements as have been made, that
this is at least possible, if not probable.
If we take the weight of the kidneys of a dog of 35 kilos at
160 grammes (.^Joth of the body-weight is the mean result of a great
number of observations in man), and the average quantity of blood
in them at rather less than one-fourth of their weight, or 35 grammes,
and consider that this quantity of blood passes through them in the
average time required to complete the circulation from renal artery
to renal vein, or, say, ten seconds, we get about 300 kilos of blood as
the flow through the kidneys in twenty-four hours. At "3 per 1,000,
the urea in 300 kilos of blood would amount to 90 grammes. Now,
Voit found that a dog of 35 kilos body-weight, on the minimum proteid
diet (450 to 500 grammes lean meat per day) which sufficed to main-
tain its weight, excreted 35 to 40 grammes urea in the twenty-four
hours. If, then, the renal epithelium separated somewhat less than
half of the 90 grammes urea offered to it in the circulating blood, the
whole excretion in the urine could be accounted for, and the blood
of the renal vein would still contain more than half as much urea
as that of the renal artery. So that the whole of the urea in the urine
may be simply separated by the kidney from the ready-made urea of
the blood.
But it is necessary to add that urea may be formed to a
small extent in the kidney itself; for when blood is caused
to circulate through an excised ' surviving ' kidney, urea
accumulates in it to a certain extent, and apparently in
greater amount than can be accounted for on the supposi-
tion that it is merely washed out of the secreting cells.
Another line of evidence leads us to the same conclusion :
that the kidnev is, at all events, not an important seat of
urea-formation. When both renal arteries are tied, or both
kidneys extirpated, in a dog, urea accumulates in the blood
and tissues ; and, upon the whole, as much urea seems to
be formed during the first twenty-four hours of the short
period of life which remains to the animal as would under
normal circumstances have been excreted in the urine.
Where, then, is urea chiefly formed? We should naturally
look first to the muscles, which contain three-fourths of the
proteids of the body ; but we should look there in vain for
any great store of urea — none, or only a trace, is normally
present. The liver contains a relatively large amount, and
there is very strong evidence that it is the manufactory in
which the greater part of the nitrogenous relics of broken-
28
434 -i MAIVLJAL OF PI/YSIOLOCY
down protcids reach the Hnal stage of urea. This evidence
may be summed up as follows :
(i) An excised 'surviving' liver forms urea from ammonium
carbonate mixed with the blood passed through its vessels,
while no urea is formed when blood containing ammonium
carbonate is sent through the kidney or through muscles.
Other salts of ammonium, such as the lactate and the car-
bamate, undergo a like transformation in the liver. It is
difficult, in the light of this experiment, to resist the con-
clusion that the increase in the excretion of urea in man,
when salts of ammonia are taken by the mouth, is due to a
similar action of the hepatic cells.
(2) If blood from a dog killed during digestion is perfused
through an excised liver, some urea is formed, which cannot
be simply washed out of the liver-cells, because when the
blood of a fasting animal is treated in the same way there is
no apparent formation of urea (v. Schroeder). This suggests
that during digestion certain substances which the liver is
capable of changing into urea enter the blood in such
amount that a surplus remains for a time unaltered. These
substances may come directly from the intestine ; or they
may be products of general metabolism, which is increased
while digestion is going on ; or they may arise both in the
intestine and in the tissues. Leucin — which, as we have
seen, is constantly, or, at least, very frequently, present in
the intestine during digestion — can certainl}- be changed
into urea in the body, and there is every reason to believe
that the change takes place in the liver.
(3) Uric acid — which in birds is the chief end-product of
proteid metabolism, as urea is in mammals — is formed in
the goose largely, and almost exclusively, in the liver. This
has been most clearly shown by the experiments of Min-
kowski, who took advantage of the communication between
the portal and renal-portal veins (p. 328) to extirpate the
liver in geese. When the portal is ligatured the blood from
the alimentary canal can still pass by the roundabout road
of the kidney to the inferior cava, and the animals survive
for six to twenty hours. \\'hile in the normal goose 50
to 60 per cent, of the total nitrogen is eliminated as uric
METABOLISM, NUTRITION AXI) DIETETfCS 435
acid in the urine, nnd only 9 to 18 per cent, as ammonia,
in the operated ^oose uric acid represents only 3 to 6 per
cent, of the total nitrogen, and ammonia 50 to 60 per cent.
A quantity of lactic acid equivalent to the ammonia appears
in the urine of the operated animal, none at all in the urine
of the normal bird. The small amount of urea in the
normal urine of the goose is not affected by extirpation of
the liver. And while urea, when injected into the blood, is
in the normal goose excreted as uric acid, it is in the animal
that has lost its liver eliminated in the urine unchanged.
(4) After removal of the liver in dogs whose portal vein
has been previously connected with the inferior vena cava
by an Eck's fistula (p. 328), the quantity of urea excreted is
markedly diminished, and the ammonium salts in the urine
are increased.
(5) In acute yellow atrophy, and in extensive fatty de-
generation of the liver, urea may almost disappear from
the urine, and be replaced by leucin and tyrosin.
If it be granted, as in the face of the evidence it must,
that the liver plays an important part in the formation of
urea, we have still to ask what the materials are upon which
it works, and in what organs they are formed before being
brought to the liver. To the latter question it may be at
once replied that proteid metabolism, although its final
stages may be worked out in the hepatic cells, must go on
in all the organized elements of every tissue. The living
substance everywhere contains proteid ; proteid is every-
where and at all times breaking down. In the muscles
especially nitrogenous substances on the road to urea must
be constantly produced. Can we lay our finger on any
such intermediate substances ? Can we with certainty state
that any of the separate links of the chain of proteid
metabolism, except the first and the last, have actually
been discovered, identified, and labelled ? The answer is
that a whole series of bodies containing nitrogen, simpler
than proteids and with a greater proportion of oxygen, more
complex and less oxidized than urea, has been found in
muscle and other tissues; but we cannot say definitely that
any or all of them, although they are undoubtedly stages
28—2
436 A MANUAL OF rilYSIOLOGY
in the downward course of worn-out proteids, have arisen
the one from the other, or must necessarily pass into the
form of urea before being finally excreted.
Such substances are :
("luanin, C-H.,N O In the pancreas, liver, and
muscles
Sarkin, or hypoxanthin, C-,H,NjO
Xanthin, C,H,N^O,
Uric acid, C^H-N^Og
'In spleen, liver, muscles, and
bone-marrow.
In spleen, liver, muscles,
brain, pancreas, and in the
urine.
In liver, spleen, lungs, pan-
creas, brain, and in urine.
Kreatin, C4H.,N..0.j ... ... In muscles, blood, brain.
The increase in the proportion of o.xygen from guanin to
uric acid is ver\- striking, and particularly the regular series
formed by hypoxanthin, xanthin and uric acid ; and Bunge
has suggested that the first three may be stages on the way
to uric acid or urea. But kreatin is the substance of this
class which exists in greatest amount in the body, muscle
containing from 0*2 to 0*4 per cent, of it; and the total
quantity of nitrogen present at any given time as kreatin
is not only greater than that of the nitrogen present in urea,
but greater than the whole excretion of nitrogen in twenty-
four hours. To kreatin, then, we should naturally look first,
among all these nitrogenous metabolites, in our search for
a forerunner of urea. But there is a difficulty in accepting
it as such, for although in the laboratory kreatin can be
changed into kreatinin, and kreatinin into urea, there is no
proof that in the body anything more than the first step in
this process is accomplished. W^hen kreatin is introduced
into the intestine, it appears in the urine, not as urea, but
as kreatinin ; injected into the blood, it is excreted without
change by the kidneys. Uric acid is, indeed, very closely
related to urea, and can be made to yield it by oxidation
outside the body. Not only so, but it is e.xcreted as urea
when given to a mammal by the mouth, and it replaces
urea as the great end-product of nitrogenous metabolism
almost wholly in the urine of birds and reptiles, partially
in the human subject in leukaemia, and possibly to some
METABOLISM, NUTRITION AND DIETETICS 437
extent in gout. lUit none of these things can be admitted
as evidence that in the normal metaboHsm of mammals
uric acid lies on the direct line from proteid to urea.
Then, again, the amido-acids, Icucin, glycin and aspara-
ginic acid, when given by the mouth, increase the output
of urea, so that the Icucin formed in the intestine during
digestion is probably, in part at least, a precursor of urea.
And since leucin and tyrosin are very widely spread in the
solids and liquids of the body, it has been asserted that the
amido-acids are the form in which nitrogen leaves the tissues
to be converted into urea in the liver. But it is against this
view that there is not enough carbon in proteids to convert
their nitrogen into amido-acids (Bunge). Lea has suggested
that the amido-acids and the amidated aromatic acid, tyrosin,
have quite another significance than that of intermediate
steps in the downward metabolism of proteids — that they
are destined, in fact, to take part in synthetic processes
within the liver — that they are on the up, and not on the
down, grade. And he points out, in support of this view,
that even when the urea in the urine is increased by the
administration of these substances, the increase does not
correspond to the whole of their nitrogen : a part of it is
therefore devoted to other purposes in the body.
The conclusion of the whole matter is that, if anyone
chooses to assert that the proteids of the tissues fall by a
single descent nearly to the stage of urea, there is as yet little
real evidence to contradict him. What is certain is that
from most tissues the nitrogen does not pass out chiefly in the form
of urea, that it appears in the urine mainly as urea, and that the
change is effected to a large extent, but not exclusively, in the
liver.
Uric acid, like urea, is separated from the blood by the
kidneys, not to any appreciable extent formed in them. In
birds it can be detected in normal blood ; in man in the
blood and transudations of gouty patients, in whose joints
and ear- cartilages it often forms concretions. 'Chalk-
stones ' may contain more than half their weight of sodium
urate. The spleen yields a small quantity of uric acid,
which may be increased by blowing air through a mixture
438 A MAXCAL OF I'lIYSIOLOGY
of splenic pulp and calf's blood. The fantastic theory that
the presence of uric acid in large amount in the urine of
birds was due to deficiency of oxidation is happily now
defunct, and need mA detain us here.
Hippuric acid can undoubtedly be produced in the kidney.
If an excised kidney is perfused with blood containing
benzoic acid, or, better, benzoic acid and glycin, hippuric
acid is formed. In herbivora hippuric acid cannot normally
be detected in the blood ; it is present in large quantities in
the urine; it must therefore be manufactured in the kidney,
not merely separated by it. In certain animals, as the dog,
the kidney is the sole seat of the production of hippuric
acid. But in the rabbit and the frog some of it may also
be formed in other tissues, for after extirpation of the
kidneys the administration of benzoic acid causes hippuric
acid to appear in the blood. It is not known how the
nitrogenous glycin, which combines with the benzoic acid
derived from vegetable food, appears on the spot where it
is wanted to form hippuric acid, since glycin has not been
found anywhere in the tissues. It is, however, a constituent
of glycocholic acid, and may be derived from that part of
the bile which is reabsorbed.
Kreatinin can be so readily obtained from kreatin outside
the body, that it is very tempting to suppose that the
kreatinin of the urine is manufactured by the kidney from
the kreatin of muscle carried to it by the blood. It seems,
however, more likely that some, at any rate, of the kreatinin
of the urine is derived from ready-formed kreatin in the food.
But we have little definite knowledge on the subject.
Formation of Carbon Dioxide from Proteids. — We cannot say
whether carbon dioxide is normally produced at the moment
when the nitrogenous portion of the proteid molecule splits
off, or whether a carbonaceous residue may not still hang
together and pass through further stages before the carbon
is fully oxidized. We shall see that under certain condi-
tions some of the carbon of proteids may be retained in
the body as glycogen or fat ; and this suggests that in all
cases it may run through intermediate products as yet
unknown, before being finally excreted as carbon dioxide.
METABOLISM, M'TRITIOX AM) D/I-TF/f/CS 439
2. Metabolism of Carbo-hydrates — Glycogen. — The carbo-
hydrates of the food, passin<j^ into the blood of the portal vein
in the form of dextrose, are in part arrested in the liver, and
stored up as glycogen in the hepatic cells, to be gradually given
out again as sugar in the intervals of digestion. The proof of
this statement is as follows :
Sugar is arrested in the liver, for during digestion, espe-
cially of a meal rich in carbo-hydrates, the blood of the
portal contains more sugar than that of the hepatic vein.
In the liver there exists a store of sugar-producing material
from which sugar is gradually given off to the blood, for
in the intervals of digestion the blood of the hepatic vein
contains more sugar (2 parts per 1,000) than the mixed
blood of the body or than that of the portal vein (i to i"5
part per 1,000). When the circulation through the liver is
cut off in the goose, the blood rapidly becomes free, or
nearly free, from sugar (Minkowski). And a similar result
follows such interference with the hepatic circulation as is
caused by the ligation of the three chief arteries of the
intestine in the dog, even when the animal has been pre-
viously made diabetic by excision of the pancreas (p. 472).
The nature of the sugar-forming substance is made clear by
the following experiments : (i) A rabbit after a large carbo-
hydrate meal, of carrots for instance, is killed, and its liver
rapidly excised, cut into small pieces, and thrown into acidu-
lated boiling water. After being boiled for a few minutes,
the pieces of liver are rubbed up in a mortar and again
boiled in the same water. The opalescent aqueous extract is
filtered off from the coagulated proteids. No sugar, or only
traces of it, are found in this extract ; but another carbo-
hydrate, glycogen, an isomer of starch giving a port-wine
colour with iodine and capable of ready conversion into
sugar by amylolytic ferments, is present in large amount.
(2) The liver after the death of the animal is left for a time
in situ, or, if excised, is kept at a temperature of 30° to 40"^ C,
or for a longer period at a lower temperature ; it is then
treated exactly as before, but no glycogen, or comparatively
little, can now be obtained from it, although sugar (dextrose)
is abundant. The inference plainly is that after death the
440 A MANUAL OF PHYSIOLOGY
hepatic glycogen is converted into dextrose by some influence
which is restrained or destroyed by boiling. This influence
may be due to an unformed ferment or to the direct action of
the liver-cells, for both unformed ferments and living tissue
elements are destroyed at the temperature of boiling water.
And the post-mortem change is to be regarded as an index
of a similar action which goes on during life : sugar in the
intact body is changed into glycogen ; glycogen is constantly
being changed into sugar. (See Practical Exercises, p. 511.)
(3) With the microscope, glycogen, or at least a substance
which is very nearly akin to it, which very readily yields it,
and which gives the characteristic port-wine colour with
iodine, can be actually seen in the liver-cells. The liver
of a rabbit or dog which has been fed on a diet containing
much carbo-hydrate is large, soft, and very easily torn. Its
large size is due to the loading of the cells with a hyaline
material, which gives the iodine reaction of glycogen, and is
dissolved out by water, leaving empty spaces in a network
of cell-substance. If the animal, after a period of starvation,
has been fed on proteid alone, only a little glycogen is found
in the shrunken liver-cells ; if the diet has been wholly fatty,
no glycogen at all may be found.
In the liver-cells of the frog in winter-time, a great deal
of this hyaline material — this glycogen, or perhaps loose
glycogen compound — is present ; in summer, little or none.
The difference is very remarkable if we consider that in
winter frogs have no food for months, while summer is
their feeding-time ; and at first seems inconsistent with
the doctrine that the hepatic glycogen is a store laid up
from surplus sugar, which might otherwise be swept into
the general circulation and excreted by the kidneys. But it
has been found that the 'summer' condition of the hepatic
cells can be produced merely by raising the temperature
of the air in which a winter frog lives : at 20' or 25° C.
glycogen disappears from its liver. Conversely, if a summer
frog is artificially cooled, a certain amount of glycogen
accumulates in the liver. The meaning of this seems to
be that at a low temperature, when the wheels of life are
clogged and metabolism is slow, some substance, possibly
METABOLISM, NUTRITION AND DIETETICS 441
dextrose, is produced in the body in greater amount than
can be used up, and that the surplus is stored as glycogen ;
just as in plants starch is put by as a reserve which can be
drawn upon — which can be converted into sugar — when the
need arises.
When a fasting dog is made to do severe muscular work
glycogen soon disappears from its liver. When a dog is
starved, but allowed to remain at rest, the glycogen still
vanishes, although it takes a longer time ; and at a period
when there is still plenty of fat in the body, there may not
be a trace of hepatic glycogen left. The glycogen which is
usually contained in the muscles also disappears early during
hunger. These facts have been taken to indicate that
glycogen and the sugar formed from it are the readiest
resources of the starving and working organism. The fat
of the body is a good security, which, however, can only
be gradually realized ; its organ-proteids are long-date bills,
which will be discounted sparingly and almost with a
grudge ; its glycogen, its carbo-hydrate reserves, are consols,
which can be turned into money at an hour's warning.
Glycogen is drawn upon for a sudden demand, fat for a
steady drain, proteid for a life-and-death struggle.
While the liver in the adult may thus be looked upon
as the main storehouse of surplus carbo-hydrate, depots of
glycogen seem to be formed, both in
adult and fatal life, in other situations
where the strain of function or of growth
is exceptionally heavy — in the muscles
of the adult (0*3 to 0*5 per cent, of the
moist muscle), in the placenta, in the
developing muscles of the embryo (as
much as 40 per cent, of the soHds). j..j^. ^^^ _ ^^^^^ ^^
Although it cannot be doubted that Placenta contain-
, r ^1 1 ^-1 1 iNG Glycogen.
much 01 the hepatic glycogen leaves
the liver as sugar, there is no proof that it all does
so. It is known that fat may be formed from carbo-
h}drates (p. 449) : and globules of oil are often conspicuous
among the contents of liver-cells, side by side with glycogen.
It is possible, therefore, that some of the glycogen may
44:: A MAXUAL OF I'l/YS/OLOdY
represent a half-way house between su^'ar and fat, or, since
fat can also be formed from proteid, and a purely proteid
diet produces some glycogen, a half-way house between
proteid and fat. That glycogen may be produced from
proteids even during starvation is shown by the following
experiment : A fasting animal was put under the influence
of strychnia to remove all glycogen from the liver. Then
the strychnia spasms were cut short by chloral, and the
animal allowed to sleep for eighteen hours. At the end of
that time a considerable amount of glycogen was found in
the liver and muscles, and this must have come from the
proteids of the body.
Pavy has put forward the heterodox view that the glycogen formed
in the liver from the sugar of the portal blood is never reconverted
into sugar under normal conditions, but is changed into some other
substance or substances, and he denies that the post-mortem forma-
tion of sugar in the hepatic tissue is a true picture of what takes
place during life. But in spite of the brilliant manner in which he
has defended this thesis both by argument and by experiment, it
must be said that the older doctrine of Bernard, which in the main
we have followed above, is attested by such a cloud of modern
witnesses that it seems to be firmly and finally established.
Fate of the Sugar. — What, now, is the fate of the sugar
which either passes right through the portal circulation
from the intestine without undergoing any change in the
liver, or is gradually produced from the hepatic glycogen?
When the proportion of sugar in the blood rises above a
certain low limit (about 3 parts per 1,000), some of it is
excreted by the kidneys (Practical Exercises, p. 512).
A large meal of carbo-hydrates is frequently followed by a
temporary glycosuria, but something seems to depend ui)on the form
in which the sugar- forming material is taken. Miiira, for example,
after an enormous meal of rice (etjuivalent to 6'4 grammes ash- and
water-free starch per kilo of body-weight), which, as he mentions,
tasked even his Jaj^anese powers of digestion to dispose of, found not
a trace of sugar in the urine. Glucose, cane-sugar and lactose, on
the other hand, when taken in large amount, were in part excreted
by the kidneys, as was also the case with levulose and maltose in a
dog (Practical Exercises, p. 513).''
* Twenty-four healthy students, wliose urine had previously been
shown to be free from sugar, ate quantities of cane-sugar varying from
250 grammes to 750 grammes. The urine was collected in separate
portions for twelve to twenty-four hours after the meal. In only three
METABOLISM, NCITRrTION AND DIETETICS 443
But, except as an occasional phenomenon, such an ex-
cretion is inconsistent with health ; and therefore in the
normal body the sugar of the blood must be either destroyed
or transformed into some more or less permanent con-
stituent of the tissues. The transformation of sugar into fat
we have already mentioned, and shall have again to discuss;
it only takes place under certain conditions of diet, and no
more than a small proportion of the sugar which disappears
from the body in twenty-four hours can ever, in the most
favourable circumstances, be converted into fat. Accordingly,
it is the dcstrndion of sugar which concerns us here, and
there is every reason to believe that this takes place, not in
any particular organ, but in all active tissues, especially in
the muscles, and to a less extent in glands.
It has been asserted that the blood which leaves even
a resting muscle, or an inactive salivary gland, is poorer in
sugar than that coming to it ; and the conclusion has been
drawn that in the metabolism of resting muscle and gland
sugar is oxidized, the carbon passing off as carbon dioxide
in the venous blood. This is indeed extremely likely, for
we know that when the skeletal muscles of a rabbit or
guinea-pig are cut off from the central nervous system by
curara, the production of carbon dioxide falls much below
that of an intact animal at rest ; and the carbon given off
by such animal on its ordinary vegetable diet can be shown,
by a comparison of the chemical composition of the food
and the excreta, to come largely from carbo-hydrates.
But, considering the relativel}' feeble metabolism of muscles
and glands when not functionally excited, the large volume
of blood which passes through them, the difticulty of deter-
mining small differences in the proportion of sugar in such
a liquid, the possibility that even in the blood itself sugar
may be destroyed, or that it may pass from the blood, with-
cases was reducing sugar found in the urine (by Fehling's and the
phenylhydrazine test), and then merely in traces. In eight cases cane-
sugar was found, and estimated by the polarimeter, and, after boihng
with hydrochloric acid, by FehHng's sokition. The greatest quantity of
cane-sugar recovered from the urine was 8 grammes (7"9i8 grammes by
FehHng's method and 8'288 grammes by the polarimeter) ; the highest
proportion of the quantity taken which appeared in the urine was 2*5 per
cent. When glucose was found, cane-sugar was always present as well
444 ^1 MANUAL OF PHYSIOLOGY
out being oxidized, into the lymph, too much weight may
easily be given to the results of direct analysis of the
in-coming and out-going blood. And although the recent
results of Chauveau and Kaufmann, obtained in this way, fit
in fairly well with what we have already learnt b\' less
direct, but more trustworthy, methods, they cannot be
accepted as yielding exact quantitative information. They
found that in one of the muscles of the upper jaw of the
horse the quantity of grape-sugar used up during activity
(chewing movements) was 3*5 times as much as in the same
muscle at rest, and this corresponded with the deficit of
oxygen in the blood entering the muscle, and with the excess
of carbon dioxide in the blood leaving it. More dextrose
was also destroyed in the active than in the passive parotid
gland of the horse, but the excess per unit of weight of the
organ was far less than in muscle.
Diabetes. — In the disease known as diabdcs mdlitns, sugar
accumulates in the blood, and is discharged by the kidneys,
and it has been supposed that a derangement in the gly-
cogenic function of the liver is the cause of this accumula-
tion and of this discharge. An artificial and temporary
diabetes, in which the sugar in the urine undoubtedly arises
from the hepatic glycogen, can, indeed, be caused by punc-
turing the medulla oblongata in a rabbit at or near the
region of the vaso-motor centre (p. 513). If the animal has
been previously fed with a diet rich in carbo-hydrates — that
is, if it has been put under conditions in Nvhich the li\er con-
tains much glycogen — the quantity of sugar excreted by the
kidneys will be large. If, on the other hand, the animal has
been starved before the operation, so that the liver is free
or almost free from glycogen, the puncture will cause little
or no sugar to appear in the urine. That nervous influences
are in some way involved is shown by the absence of
diabetes if the splanchnic nerves, or the spinal cord above
the third or fourth dorsal vertebra, be cut before the
puncture is made. But sometimes these operations are
themselves followed by temporary diabetes. Section of the
vagi has no effect either in causing glycosuria of itself or in
preventing the 'puncture' diabetes, although stimulation of
M/rfAIWLrSM, NUTRITION AND DITTET/CS 445
the central ends of these and of other afferent nerves ma}'
cause sugar to appear in the urine. Curara, morphia,
phlorid/in (p. 51 j), and other substances, also cause diabetes.
But phloridzin diabetes differs from 'puncture' diabetes in
this, that it can be produced in an animal free from glycogen,
and is accompanied by extensive destruction of proteids.
Although several of the operations which lead to this
temporary glycosuria undoubtedly bring about changes in
the hepatic circulation, it is as yet impossible to say whether
the whole phenomenon is at bottom a vaso-motor effect, or
is due to direct nervous stimulation of the liver-cells, or to
withdrawal of such stimulation or control.
Recent experiments point to the pancreas as intimately
concerned in the metabolism of sugar. Excision of this
organ in dogs causes permanent diabetes (v. Mering and
Minkowski), which is prevented if a portion of the pancreas
be left, or if it be transplanted under the skin of the
abdomen (p. 472).
In the natural diabetes of man it is possible that in some cases
the sugar coming from the alimentary canal passes entirely or in too
large amount through the liver, owing to a deficiency in its power of
forming glycogen. J5ut although in certain cases of diabetes speci-
mens of the hepatic cells, obtained by plunging a trocar into the
liver, have been found free from glycogen, in others glycogen has
been present. And it is remarkable that levulose may be entirely
used up in the tissues of a diabetic patient, or of a dog rendered
diabetic by extirpation of the pancreas, while dextrose, which is so
closely alHed to it, and from which an identical form of glycogen is
produced, is promi)tly cast out by the kidneys. In many cases even
when carbo-hydrates are completely, or almost completely, omitted
from the food, sugar, probably derived from the breaking-down of
proteids, still continues to be excreted, although in smaller quantity.
Other products of the incomplete combustion of proteids, such as
acetone, aceto-acetic acid, and oxybutyric acid, may also appear in
the urine, or, accumulating in the blood, may, by uniting with its
alkalies, seriously diminish the quantity of carbon dioxide which that
liquid is capable of carrying, and thus lead to the condition known
as diabetic coma. The most rational way of explaining many of the
facts of diabetes is to suppose that, from some change in the tissue
elements, sugar has ceased to be a food for them, or is used up in
smaller amount than in the healthy body, while the actual production
of sugar is no greater than in a normal person with the same diet
and the same intensity of metabolism of substances other than carbo-
hydrates.
Normal blood seems to contain a ferment which has the power of
446 A MANUAL OF PHYSIOLOGY ,
destroying sugar and forming lactic acid ; and the statement of
Lcpine and Barral that extirpation of the pancreas, which is followed
by diabetes, causes a diminution in the activity or in the amount of
this ferment, appeared to afiford the basis for a theory of diabetes.
But Spitzer has asserted that the sugar-destroying power of blood
taken from diabetic patients, or from animals in which glycosuria
had been caused by phloridzin, is not at all inferior to that of healthy
blood. And, indeed, results that depend upon the determination of
minute difterences in the quantity of sugar must be accejjted with
reserve.
3. Metabolism of Fat. — The fat, passing along the thoracic
duct into the blood stream, is very soon removed from the
circulation, for normal blood contains only traces, except
during digestion. Where does it go ? What is its fate ?
The presence of adipose tissue in the body might suggest
a ready answer to these questions. The fat cells of adipose
tissue are apparently ordinary fixed connective-tissue cells
which have become filled with fat, the protoplasm being
reduced to a narrow ring, in which the nucleus is set like a
stone. It would, at first thought, seem natural to suppose
that the fat of the food is rapidly separated by these cells
from the blood, and slowly given up again as the needs of
the organism require, just as carbo- hydrate is stored in the
liver for gradual use. And it has been found that a lean
dog, fed with a diet containing much fat and little proteid,
puts on more fat, as estimated by direct analysis, or keeps
back more carbon, as estimated by measurements of the
respiratory interchange, than can be accounted for on the
supposition that even the whole of the carbon of the broken-
down proteid corresponding to the excreted nitrogen has
been laid up in the form of fat. Even with a diet of pure
fat — and with such a diet digestion and absorption are
carried on under unfavourable conditions — more carbon is
retained than can have come from the metabolism of the
proteids of the body, as measured by the nitrogen given off
in the urine and faeces : the fat passes rapidly from the
blood into the organs, and especially into the liver (Hofmann,
Pettenkofer and Voit). It is thus certain that some of the
absorbed fat may be stored up as fat in the body. The
observation of Radziejewski, that a starved dog fed with
lean meat and rape-oil — which contains erucic acid, a fatty
MjyjAnOUSM, NUTA'/770X A.M) DIl'.TETICS 447
acid not found in animal fat — put on fat of normal com-
position without a trace of erucic acid, is not borne out by
the careful experiments of Munk, who finds that when do;:^s
are fed with excess of foreign fat (linseed-oil, rape-oil, mutton-
fat), a fat is laid down which is quite different from dofij's
fat, and has the greatest resemblance to the fat of the food.
But it does not follow that the cells of adipose tissue in
normal nutrition simply separate the fats of the food from
the blood ; while there are facts which show that the fat of
the body has other sources, and that some of it at all events
is produced by more complex processes.
The fat of a dog consists of a mixture of palmitin, olein,
and stearin. When a starved dog was fed on lean meat and
a fat containing palmitin and olein, but no stearin, the fat
put on contained all three, and did not sensibly differ in its
composition from the normal fat of the dog (Subbotin).
Stearin must, therefore, have been formed in some way or
other in the body. If it was formed from the olein and
palmitin of the food, the portion of these deposited in
the cells of the adipose tissue must have undergone changes
before reaching this comparatively fixed and final position.
But there is conclusive evidence that fat may be derived
from proteids ; and it is more likely that the stearin was
formed from the proteids of the food or tissues than directly
from fat. And if the stearin was produced from proteids,
it is evident that the olein and palmitin might have been
formed from proteids too, the portion of the latter devoted
to this purpose being sheltered from oxidation by the
combustion of the fats of the food. It might further be
asked whether the fat which is normally excreted into the
intestine (p. 371), and which is perhaps derived from broken-
down proteids, might not be reabsorbed, and take its place
among the fat ' put on.' But as yet there are few ascertained
facts to guide us in such speculations.
As to the ultimate fate of the absorbed fat, from what-
ever source it may be derived, our knowledge may be
compressed into a single sentence : Some of the fat may
be stored up as fat ; the greater part, often the whole, is oxidized
forthwith to carbon dioxide and water, its energy being converted
448 A MA NUA L OF /'/I YSIOL Ol.Y
into licat or, directly or indirectly, into mechanical or chemical
work.
Formation of Fat from other Sources than the Fat of the
Food. — (i) From Proteids. — Dry protcid contains on the
average 15 per cent, of nitrogen and 50 per cent, of carbon ;
and urea contains 46 per cent, of nitrogen and 20 per cent,
of carbon. Urea is therefore rather more than three times
as rich in nitrogen as the proteid from which it is derived,
but two and a half times poorer in carbon ; and less than
one-seventh of the carbon of proteid will be eliminated in
the urea, which carries off all the nitrogen. A carbonaceous
residue is left, which under certain circumstances may be
converted into fat. The proof of this statement is very
complete, but only an outline of it can be given here.
A dog fed for a time on a liberal diet of lean meat may go
on excreting a quantity of nitrogen equal to that in the
food, while there is a deficiency in the carbon given off Or
if the dog is not in nitrogenous equilibrium (p. 452), but
putting on nitrogen in the form of ' flesh,' the deficienc}- in
the carbon given off may be too great in proportion to the
nitrogen deficit to warrant the assumption that all the
retained carbon has been put on in the form of proteid. In
either case, carbon in large amount can only come from the
proteids of the food, and can only be stored up in the body
in the form of fat ; for lean meat contains but a trifling
quantity of carbon in any other proximate principle than
proteid, and the non-proteid carbon of the animal body is
only to a very small extent contained in carbo-hydrates or
other substances than fat.
For example, in an experiment of Pettenkofer and Voit on a dog
in nitrogenous equilibrium, with a diet of 2,000 grammes of lean
meat, the animal on the first day
Grammes. Grammes.
Took in in the food - - 68"o N 250*4 C
( urine - - 66'5 N 39'9 C
Gave out in < ficces - - r4 9'2
( respiration - o 1 58*3
67-9 207-4
Difference - +o'i N +43'o C
Here the nitrogen of the body remained unaltered, but carbon
METABOLISM, XUTA'/r/O.V AND DIETETICS 449
was put on to the extent of 43 grammes, or 17 per cent, of the
amount in the food, representing about 58 grammes of fat.
This is an e.xact quantitative proof of the conversion of
proteids into fat. Qualitative indications of its possibility
and of its actual occurrence are numerous. Such are the
readiness with which fatty degeneration occurs in the tissues
in pathological states — for example, after phosphorus poison-
ing ; the accumulation of fat between the hepatic cells caused
by phloridzin, which, as we know, hastens the disintegration
of proteids ; the formation of adipocere sometimes seen in
dead bodies which have remained a long time under water
or in moist graveyards ; the formation of fat in the cells of
the sebaceous glands ; and the transformation of the cell-
substance of the mammary glands into the fat of milk.
This last case is of great practical importance, for it
explains the rule which experience has taught, that a
woman during lactation requires an excess of proteids in
her food corresponding not only to the proteids, but also
to the fat given off in the milk.
(2) From Carbo-hydrates. — It has been found that the
addition of proteid to a diet of fat, and especially to a diet
of carbo-hydrate, in larger amount than is just necessary
for nitrogenous equilibrium, leads to a more rapid increase
in the carbon deficit — that is, in the fat put on — than if the
minimum quantity of proteid required for nitrogenous equi-
librium had been given. From this it is inferred that the
carbonaceous residue of the broken-down proteid is shielded
from oxidation by the fat, and to a still greater extent by
the carbo-hydrates, and so retained in the body as fat.
And it is certain that the high repute of carbo-hydrates
as fattening agents is in part due to their taking the place
of proteids and fats in ordinary ' current ' metabolism, and
so allowing body-fat to be laid down from these. Voit,
indeed, has gone so far as to assert that this is the only
sense in which carbo-hydrates can be said to form fat, and
that, in carnivorous animals at least, a direct conversion never
occurs. But the experiments of Rubner have shown that in
a dog fed with a diet rich in carbo-hydrates, and containing
but little fat and no proteids at all, the carbon deficit was
29
.|5o A MANUAL OF /'//VS/OLOGV
greater than could be accounted for by the proteids broken
down in the body and the fat of the food. In the pig and
goose, too, the direct formation of fat from carbo-hydrates
has been demonstrated. It is probable that the carbo-
hydrates are first split up to some extent, and that the fats
are then constructed from their decomposition products,
oxygen being lost in the process, since fat is poorer in
oxygen than carbo-hydrate. The production of wax by
bees, which used to be given as a proof of the formation
of fat from sugar, is not decisive, for in raw honey proteids
are present ; and even when bees fed on pure hone\' or sugar
manufacture wax, it may be derived from the broken-down
proteids of their own bodies.
Suniinary. — At this point let us sum up what we have
learnt as to the relation between the proximate principles
of the tissues and the proximate principles of the food.
Inside the body we recognise representatives of the three groups
of organic food -substances in a typical diet — proteids, carbo-
hydrates, and fats. But we should greatly err if we were to
imagine that the three streams of food-materials have flowed
from the intestines into the tissues each in its separate
channel, neither giving to nor taking from the others. The
fats of the body may, indeed, in part be composed of molecules
which were present as fat in the food ; but they may also be formed
from proteids — they may also be formed from carbo-hydrates. The
carbo-hydrates of the body — the glycogen of the liver and muscles,
the sugar of the blood — may undoubtedly be derived from carbo-
hydrates in the food, but they may also be derived from proteids ;
from fats they probably cannot come. The proteids of the body
arise solely from the proteids of the food ; neither fats nor carbo-
hydrates can form proteids, although both can econoinize them and
shield them from an over-hasty metabolism.
4. The Income and Expenditure of the Body. — (i) Income and
Expenditure of Nitrogen. —
Freliminafy Data. — The purpose of food is to maintain the con-
stituents of the body upon the whole in their normal proportions.
A knowledge of the chemical composition of the body is, therelore,
an important datum in the consideration of the statistics of its
metabolism. The body of a man analyzed by Volkmann had the
following composition :
METAIiOHSM, NUTRITION AND DIETETICS
45'
Inorganic substances
Organic substances
Water
Mineral matter -
Carbon 184 per cent.
Hydrogen 27 „
Nitrogen Tb „
Oxygen 6*o „
65 "9 per cent.
4'4
297
The muscles, the adipose tissue, and the skeleton form nearly
four-fifths of the total body-weight in the adult. The following table
shows the percentage amount of each of these tissues in a man, a
woman, and a child (Bischoff) :
Voluntary muscles
Adipose tissue -
Skeleton
Rest of body
Man.
Woman.
41-8
i8-2
15-9
24*1
35-8
28'2
151
209
New-born
Child.
23'5
13-5
157
47"3
The nitrogen is contained chiefly in the muscles, glands, and
nervous system, and in the constituents of the connective tissues,
which yield gelatin, chondrin, and elastin. The proteids make up
about 9 per cent, of the weight of the body, or 22 per cent, of its
solids; the albuminoids (gelatin-yielding material, etc.) about 6 per
cent, of the body-weight. Nitrogen exists in proteids to the extent
of 15 per cent., so that the 6'5 kilos of proteid of a 70-kilo body
contain nearly i kilo of nitrogen.
The carbon is contained chiefly in the fat, which forms a very
large proportion of the water-free substance of the body, and in the
bones. In the body of a strong young man weighing 68'6 kilos,
Voit found the following quantities of dry fat in the various tissues :
Adipose tissue ....
Skeleton .....
Muscles .-.---
Brain and spinal cord
Other organs
Total - - . - 12363-5 „
equivalent to 18 per cent, of the whole body-weight, or 44 per cent.
of the solids. In dry fat rather more than 75 per cent, of carbon
is present, and in proteid about 50 to 55 per cent. ; so that while the
fat of the body analyzed by Voit contained more than 9 kilos of
carbon, only about a third of this amount would be found in the
proteids.
In the fat there is, roughly speaking, 12 per cent, of hydrogen,
in proteids only 7 per cent. ; so that from three to four times as much
hydrogen is contained in the fat of the body as in its proteids.
Oxygen forms about 12 per cent, of fat, and 20 to 24 per cent,
of proteids ; the proteid constituents of the body, therefore, contain
about as much of iis oxygen as the fat.
29 — 2
)"4 grammes.
2617-2
636-8
226-9 )»
73*2
452
A MANUAL OF PHYSIOLOGY
Nitrogenous Equilibrium. — It is a matter of common ex-
perience that the weight of the body of an adult may remain
approximately constant for many months or years, even
when the diet varies greatly in nature and amount. And
not only may the weight remain constant, but the relative
proportions of the various tissues of the body, so far as
can be judged, may remain constant too. Here it is evident
that the expenditure of the body must precisely balance
its income : it must lose as much nitrogen as it takes
in, otherwise it would put on flesh ; it must lose as much
I
42/ Muscle
26-2 Fal
S7 Skin
S-5 Bone s
4S Liirer
Zd Blood
0-6 Kidneys
05 Sjtleen
O'J Lunt/s
Ol Teitfs
\0-LBrainUord
\OlHcmt
Heart
3
Bones
i4
Pancreas 1 7
/nhsHiui
IB
Lun^s
JS
Skin
ZJ
Ktdneffi
26
Blood
27
Muscles
31
Testes
UO
Litter
5U
Sftleen
61
Fal
91
Fig. 132. — Diagram showing Loss of Weight ok the Organs in
Starvation.
The numbers under I. are the percentages of the total loss of body-weight borne by
the various organs and tissues. The numbers under II. give the percentage loss of
weight of each organ calculated on its original weight as indicated by comparison with
the organs of a similar animal killed in good condition.
carbon as it takes in, otherwise it would put on fat. Or,
again, the body may be losing or gaining fat, giving off
more or less carbon than it receives, while its * flesh ' (its
proteid constituents) remains constant in amount, the ex-
penditure of nitrogen being e.xactly equal to the income.
In both cases we say that the body is in nitrogenous equi-
librium.
A starving animal or a fever patient, on the other hand, is
living upon capital, the former entirely, the latter in part ;
the expenditure of nitrogen is greater than the income. A
growing child is living below its income, is increasing its
METABOLISM, NUTRITIOX AXD DIETETICS
453
capital of flesh. In neither case is nitrogenous equiUbrium
present.
The starving animal, as long as life lasts, excretes urea and
gives off carbon dioxide ; but its expenditure, and especially
its expenditure of nitrogen, is pitched upon the lowest scale.
It lives penuriously, it spins out its resources ; its glycogen
goes, its fat goes, a certain part of its proteid goes, and
when its weight has fallen from 25 to 50 per cent., it dies.
At death the heart and central nervous system are found to
have scarcely lost in weight ; the other organs have been
sacrificed to feed them. Fig. 132 shows the percentage loss
ISqrains
I0gram%
ograms
1 A15 A30 MS AGO R?/
B6' Bii BIG Q21 °~^
A is a curve representing
the quantity of urea excreted
daily by a fat dog in a star-
vation period of sixty days.
B is the curve of urea ex-
cretion in a lean young dog
in a starvation period of
twenty-four days. Both are
constructed from Falck's
numbers, but in A only
every third day is put in, in
order to save space. The
numbers along the vertical
axis represent grammes of
urea ; those along the hori-
zontal axis days from the
beginning of starvation.
Fig. i;;.— E.\cretio.\ of Urea in Starvation.
of weight and the proportion of the total loss which falls
upon each of the organs of a cat in starvation (Voit).
For the first day of starvation the excretion of urea in a dog
or cat is not diminished ; it takes about twenty-four hours
for all the nitrogen corresponding to the proteids of the last
meal to be eliminated. On the second day the quantity of
urea sinks abruptly ; then begins the true starvation period,
during which the daily output of urea diminishes very slowly
until a short time before death, when it rapidly falls and
soon ceases altogether. If the animal has little fat in its
body to begin with, the urea excretion rises somewhat
after the first few days, because as soon as the fat is all
consumed more proteid is used up. So long as the fat
lasts, the rate at which it is destroyed — as estimated from
the amount of carbon given off minus the carbon corre-
454 -1 MANUAL OF PHYSIOLOGY
spending to the broken-down proteids — remains very nearly
constant after the first day. The fat to a certain extent
economizes the proteids of the starving body, but however
much fat may be present, a steady waste of the tissue-
proteids goes on.
The results obtained on * fasting men ' differ in some
respects from those obtained on starving animals. The
excretion of nitrogen has been found to diminish con-
tinuously during a fast extending over several days. The
quantity of chlorine and alkalies in the urine was also
diminished, while the phenol was increased. The respi-
ratory quotient sank to o'66 to o'Gg — even less than the
quotient corresponding to oxidation of fats alone. The
meaning of this, in all probability, is that some of the
carbon of the broken-down proteids was laid up in the
body as glycogen (Zuntz). The nitrogenous metabolism has
also been investigated during long-continued hypnotic sleep
(Hoover and Sollmann). The results were very much the
same as in an ordinary starvation experiment.
It might be supposed that if an animal was given as much
nitrogen in the food in the form of proteids as corresponded
to its daily loss of nitrogen during starvation, this loss would
be entirely prevented and nitrogenous equilibrium restored.
The supposition would be very far from the reality. If a
dog of 30 kilos weight, which on the tenth day of starva-
tion excreted 11*4 grammes urea, had then received a daily
quantity of proteid equivalent to this amount — that is to
say, about 34 grammes of dry proteid, or 175 grammes of
lean meat — the excretion of nitrogen would at once have
leaped up to nearly double its starvation value. If the
quantity of proteid in the diet w'as progressively increased,
the output of urea would increase along with it, but at an
ever-slackening rate ; and at length a condition would be
reached in which the income of nitrogen exactly balanced the
expenditure, and the animal neither lost nor gained flesh.
In an experiment of Voit's, for instance, the calculated loss
of flesh in a dog with no food at all was 190 grammes a day.
The animal was now fed on a gradually increasing diet of
lean meat with the following result :
METABOLISM, NUTRITION AND DIETETICS
455
Flesh in the
Flesh used up in
Net Loss of
Food.
the Body.
Body-flesh.
o
190
190
250
341
91
350
411
61
400
454
54
450
471
21
480
492
12 1
The loss of nitrogen in the urine and fteces is what was measured.
Knowing the average composition of 'body-flesh' (muscles, glands,
etc.), it is easy to translate results stated in terms of nitrogen into
results stated in terras of 'flesh.' Muscle contains approximately
34 per cent, nitrogen. Here, with a diet of 480 grammes meat, the
dog was still losing a little flesh ; it would probably have required
from 500 to 600 grammes for equilibrium. The results are graphi-
cally represented m Fig. 134.
The quantity of proteid food necessary for nitrogenous
equilibrium varies with the condition of the organism : an
emaciated body requires less than a muscular and well-
nourished body. The least quantity which would suffice
to maintain in nitrogenous equilibrium the famous 35 kilo
dog of Voit, even in very meagre condition, was 480 grammes
of lean meat, corresponding to 16 grammes of nitrogen,
or 35 grammes of urea ; that is, about three times the
daily loss during starvation. From this lower limit up to
2,500 grammes of meat a day nitrogenous equilibrium
could always be attained, the animal putting on some flesh
at each increase of diet, until at length the whole 2,500
grammes were regularly used up in the twenty-four hours.
A further increase was only checked by digestive troubles.
A man, or at least a civilized man, can consume a much
smaller amount both absolutely and in proportion to the
body-weight. Rubner, with a body-w-eight of 'ji kilos, was
able to digest and absorb over 1,400 grammes of lean meat:
Ranke, with about the same body-weight, could only use up
1,300 grammes on the hrst day of his experiment, and less
than 1,000 grammes on the third.
So much for a purely proteid diet. When fat is given in
addition to proteid, nitrogenous equilibrium is attained with
a smaller quantity of the latter (7 to 15 per cent. less). A
456
A MANUAL OF PHYSIOLOay
dog which, with proteid food alone, is putting on flesh,
will put on more of it before nitrogenous equilibrium is
reached if a considerable quantity of fat be added to its
diet. Fat, therefore, economizes
proteid to a certain extent, as we
have already recognised in the case
of the starving animal. On the
other hand, when proteid is given
in large quantities to a fat animal,
the consumption of fat is increased ;
and if the food contains little or
none, the body-fat will diminish,
while at the same time ' flesh ' may
be put on. The Banting cure for
corpulence consists in putting the
patient upon a diet containing much
proteid, but little fat or carbo-
hydrate ; and the fact just men-
tioned throws light upon its action.
All that we have here said of fat
is true of carbo-hydrates. To a great
extent these two kinds of food sub-
stances are complementary. Carbo-
hydrates economize proteids as fat
does, but to a greater extent, and
they also economize fat, so that when
a sufficient quantity of starch or
sugar is given to an otherwise starv-
ing animal, all loss of carbon from
the body, except that which goes off
of 480 grammes the expenditure in the urca Still excreted, can be pre-
is 492 and the loss 12 grammes. . , , •
vented. Of course the anmial ulti-
mately dies, because the continuous,
though diminished, loss of proteid
cannot be made good.
It is only necessary to add that peptone can, while
gelatin cannot, completely replace the natural proteids in
the food. Fully five -sixths, however, of the necessary
nitrogen may be obtained from gelatin, at least for a few
Fig. 134. — Curves con-
structed TO ILLUSTRATE
Nitrogenous Equilib-
KiUM (trom an Experi-
ment OF Voit's).
The loss of flesh in grammes
is laid off along the horizontal
axis. The income and expen-
diture corresponding to a given
loss are laid off (in grammes of
'flesh') along the vertical axis.
The continuous curve is the
curve of income ; the dotted
curve, of expenditure. With no
income at all the expenditure is
190 grammes ; with an income
Nitrogenous equilibrium is re-
presented as being reached with
an income of about 530grammes ;
here the two curves cut one
another.
META HOLISM, NUTRITION A ND DIE IE 71 C S 457
days (Munk); so that gelatin economizes proteid in a much
greater degree than fat and carbo-hydrates do.
The Laws of Nitrogenous Metabolism. — Within the hmits of
nitrogenous equilibrium, which is the normal state of the
healthy adult, the body lives up to its income of nitrogen ;
it lays by nothing for the future. In the actual pinch of
starvation the organism becomes suddenly economical.
When a plentiful supply of proteid is presented to the
starving tissues, they pass at once from extreme frugality to
luxury ; some ilesh may be put on for a short time, some
nitrogen may be stored up; but the tissues soon pitch
their wants to the new scale of supply, and spend their
proteid income as freely as they receive it. This is the first
great law of nitrogenous metabolism, and we ma}- formu-
late it thus : Consumption of proteid is largely determined by
supply (p. 515).
Various hypotheses have been offered to explain this remarkable
fact. It has been suggested that a large proportion of a heavy
proteid meal may be broken up into leucin and tyrosin in the
alimentary canal, and may pass by this short cut to the stage of urea
without ever joining the proteid of the blood, much less that of the
organs. This would be a form of true hixus-consumption, of really,
and not apparently, wasteful expenditure. The surplus proteids
would be shunted out of the main metabolic current at its very
source \ and it is conceivable that in this short-cut from proteid to
urea we have a kind of physiological safety-valve to protect the
tissues from the burden of an excessive metabolism. But it is
doubtful whether such a process occurs to any great extent in normal
digestion. If it does occur, it may bear a different interpretation,
and in any case it probably plays only a subordinate part, and cannot
of itself explain all the facts of nitrogenous equilibrium.
Then, again, it has been said that the luxus-consumption takes the
form of oxidation of the surplus proteids in the blood and lymph.
Here the shunting would take place farther down the stream, but
still high enough up to shield the tissue elements from excessive
metabolic work. This theory of luxus-consumption breaks down,
however, under the accumulating evidence that the oxidative changes
go on chiefly in the living cells and not in the extra-cellular fluids.
We seem driven to locate the metabolism of actually absorbed
proteids, as well as of other food substances, within the cells of the
body ; and there are three chief views as to the manner of this
metabolism :
{a) That the actual protoplasmic substance, the living framework
of the cell, is comparatively stable ; that it does not break down
4S8 A MANUAL OF PHYSIOLOGY
rapidly ; and that only a relatively small and fairly constant amount
of food- or circulating-proteid is required to supply the waste of the
organ-proteid. It is assumed that the greater part of the former,
without being incorporated with the protoplasm, is nevertheless acted
upon, rendered unstable, shaken to pieces, as it were, by the whirl
of life in the organized framework, the interstices of which it fills.
{b) That we have no right to draw a distinction between the
consumption of organ- and circulating-proteid ; that the whole of the
latter ultimately rises to the height of organ-proteid, and passes on
to the downward stage of metabolism only through the topmost step
of organization. An increase in the supply of nitrogenous material
in the blood must, on this view, be accompanied with an increased
tendency to the break-up, the dissociation, as Pfluger puts it, of the
living substance. The actual organised elements, however, the
existing cells, are not supposed to be destroyed ; the building
remains, for although stones are constantly crumbling in its walls,
others are being constantly built in.
(^) That the tissue elements themselves are short-lived ; that the
old cells disappear bodily and are replaced by new cells ; and that
the whole of the proteids of the food take part in this process of
total ruin and reconstruction.
Histological evidence is on the whole strongly against (r).
Although the cells of certain glands, such as the mammary
sebaceous, and perhaps the mucous glands, are known to break
down bodily as an incident of functional activity, in most organs
there is no proof of the production of new cells on the immense
scale which this theory would require. There is but little evidence
which would enable us to decide with confidence between {a) and
ib)^ although the observation of Munk, that a dog fed with proteids
and carbo-hydrates after a thirty days' fast used up less proteid than
the minimum in starvation, certainly suggests that, under those
conditions at least, the proteids of the food were all built up into
the protoplasm of the tissues.
A second law of nitrogenous metabolism is that within
normal limits it is nearly independent of muscidar work, that
is to say, the quantity of nitrogen excreted by a man on a
given diet is practically the same whether he rests or works.
Before this was known it was maintained by Liebig that
proteids alone could supply the energy of muscular contrac-
tion— that, in fact, proteids were solely used up in the
nutrition and functional activity of the nitrogenous tissues,
while the non-proteid food yielded heat by its o.xidation.
As exact experiments multiplied, it was found that muscular
work, the production of which is the function of by far the
greatest mass of proteid-containing tissue, had little or no
effect upon the excretion of urea in the urine. More than
METABOLISM, NUTRITION AND DIETETICS 4S';
this, it was shown that a certain amount of work acconi-
phshed (by Fick and Wislicenus in cHmbing a mountain) on
a non-nitrogenous diet had double the heat equivalent of the
whole of the proteid consumed in the body, as estimated by
the urea excreted during, and for a given time after, the work.
On the assumption that all the urea corresponding to the
proteid broken down was eliminated during the time of this
experiment, a part at least of the work must have been
derived from the energy of non-nitrogenous material. And
the increase in the carbon dioxide given off, which is as con-
spicuous an accompaniment of muscular work as the con-
stancy of the urea excretion, showed that during muscular
exertion carbonaceous substances other than proteids — that
is to say, fats and carbo-hydrates — are oxidized in greater
amount than during rest.
So the pendulum of physiological orthodoxy came full-
swing to the other side. Liebig and his school had taught
that proteids alone were consumed in functional activity ;
the majority of later physiologists have denied to the proteids
any share whatever in the energy which appears as muscular
contraction. The proteids, they say, * repair the slow waste
of the framework of the muscular machine, replace a loose
rivet, a worn-out belt, as occasion may require ; the carbo-
hydrates and fats are the fuel which feeds the furnaces of
Hfe, the material which, dead itself, is oxidized in the inter-
stices of the living substance, and yields the energy for its
work.'
Now, it is a singular circumstance, and full of instruction
for the ingenuous student of science, that the facts which
have been supposed absolutely to disprove the older theory,
and absolutely to establish its modern rival, do neither the
one thing nor the other. The fact — and it is a fact — that
the excretion of nitrogen is but little affected by muscular
contraction, does not prove that none of the energy of
muscular work comes from proteids ; the fact that, under
certain conditions, some of the muscular energy must
apparently come from non-nitrogenous materials, does not
prove 'that these are the normal source of it all. The dis-
tinction has again been made too absolute. The pendulum
46o A MANUAL OF PHYSIOLOGY
must again swing back a little ; and the recent experiments
of Pfliiger and others have actually set it moving.
In the first place, it is not perfectly correct to say that
work causes no increase in the excretion of nitrogen ; exces-
sive work in man, and work, severe but not excessive, in a
flesh-fed dog (Pfliiger), do cause somewhat more nitrogen to
be given off. The increase affects not only the urea but also
the ammonia, kreatinin, and if the subject is in poor training,
the uric acid and xanthin bases. (Paton, Stockman, etc.)
In the second place, even if the excretion of nitrogen were
entirely unaffected by work, this would not prove that none
of the energy of the work comes from proteids. For the
animal body is a beautifully-balanced mechanism which
constantly adapts itself to its conditions. If it saves
proteids by the use of fat and carbo-hydrates when its
nitrogenous food is restricted or its organ-proteid runs low,
it may also, when called upon to labour, save proteids from
lower uses to devote them to muscular contraction. In this
case the excretion of nitrogen would not necessarily be
altered ; the proteids which, in the absence of work, would
have been oxidized within the muscular substance or else-
where, their energy appearing entirely as heat, may, when
the call for proteid to take the place of that broken down
in muscular contraction arises, be diverted to this purpose.
Thirdly, there is no doubt that a dog fed on lean meat
may go on for a long time performing far more work than
can be yielded by the energy of fat and carbo-hydrates
occurring in traces in the food, or taken from the stock in
the animal's body at the beginning of the period of work.
A large portion, and perhaps the whole, of the work, must
in this case be derived from the energy of the proteids
(Pfluger).
Experience has shown that the minimum quantity of
nitrogen required in the food of a man whose daily work
involves hard physical toil is higher than the minimum
required by a person leading an easy sedentary life. This is
evidently in accordance with the view that proteid is actually
used up in muscular contraction ; but it is not inconsistent
with the opposite view. For the body of a man fit for con-
METABOLISM, NUTRITION AND DIETETICS 461
tinuoiis hard labour has a greater mass of muscle to feed
than the body of a man who is only fit to handle a com-
posing-stick, or drive a quill, or ply a needle ; and the
greater the muscular mass, the greater the muscular waste.
But if an animal just in nitrogenous equilibrium on a diet
of lean meat when doing no work, is made to labour day
after day, it will lose flesh unless the diet be increased.
This must mean that some of the proteid is being diverted
to muscular work, and that the balance is not sufficient to
keep up the original mass of ' tiesh ' (see p. 468).
(2) Income and Expenditure of Carbon. — This division of the
subject has been necessarily referred to in treating of the
nitrogen balance-sheet, and may now be formally completed.
Carbon Equilibrium. — A body in nitrogenous equilibrium
may or may not be in carbon equilibrium. It has been
repeatedly pointed out that the continued loss or gain of
carbon by an organism in nitrogenous equilibrium means
the loss or gain of fat ; and, since the quantity of fat in
the body may vary within wide limits without harm, carbon
equilibrium is less important than nitrogen equilibrium. It
is also less easily attained when the carbon of the food is
increased, for, although the consumption of fat is to a certain
extent increased with the supply of fat or fat-producing food,
there is by no means the same prompt adjustment of ex-
penditure to income in the case of carbon as in the case of
nitrogen.
Carbon equihbrium can be obtained in a flesh-eating
animal, like a dog, with an exclusively proteid diet ; but
a far higher minimum is required than for nitrogenous
equilibrium alone. Voit's dog required at least 1,500
grammes of meat in the twenty-four hours to prevent his
body from losing carbon. For a man weighing 70 kilos,
the daily excretion of carbon on an ordinary diet is about
300 grammes. More than 2,000 grammes of lean meat
would be required to yield this quantity of carbon ; and,
even if such a mass could be digested and absorbed, more
than three times the necessary nitrogen would be thrown
upon the tissues.
Not only may carbon equilibrium be maintained for a
462 A MANUAL OF PIIYSIOLOGY
short time in a dog on a diet containing fat only, or fat and
carbo-hydrates, but the expenditure of carbon may be less
than the income, and fat may be stored up. But, of
course, if this diet is continued, the animal ultimately dies
of nitrogen starvation.
So far we have spoken only of the income and expenditure
of carbon and nitrogen ; and from these data alone it is
possible to deduce many important facts in metabolism,
since, knowing the elementary composition of proteids, fats
and carbo-hydrates, we can, on certain assumptions, translate
into terms of proteids or fat the gain or loss of an organism
in nitrogen and carbon, or in carbon alone. But the
hydrogen and oxygen contained in the solids and water of
the food, and the oxygen taken in by the lungs, are just as
important as the carbon and nitrogen; it is just as neces-
sary to take account of them in drawing up a complete and
accurate balance-sheet of nutrition. Fortunately, however,
it is permissible to devote much less time to them here, for
when we have determined the quantitative relations of the
absorption and excretion of the carbon and nitrogen, we
have also to a large extent determined those of the oxygen
and hydrogen.
(3) Income and Expenditure of Oxygen and Hydrogen. — The
oxygen absorbed as gas and in the solids of the food is
given off chiefly as carbon dioxide by the lungs ; to a small
extent as water by the lungs, kidneys, and skin ; and as
urea and other substances in the urine and faeces. The
hydrogen of the solids of the food is excreted in part as
urea, but in far larger amount as water. The hydrogen and
oxygen of the ingested water pass off as water, without, so
far as we know, undergoing any chemical change, or existing
in any other form within the body. But it is important to
recognise that although none of the water taken in as such is
broken up, some water is manufactured in the tissues by the
oxidation of hydrogen. We have already considered (p. 225)
the gaseous interchange in the lungs, and we have seen that
all the oxygen taken in does not reappear as carbon dioxide.
It was stated there that the missing oxygen goes to oxidize
other elements than carbon, and especiall}- to oxidi;ce
MF.TA HOLISM, NUTRITION AND DIETETICS 463
hydrogen. We have now to explain more fully the cause
of this oxygen deficit.
The Oxygen Deficit. — The carbo-hydrates contain in themselves
enough u\yL;cn to torm water with all their hydrogen ; they account
for a part of the water-formation in the body, but for none of the
oxygen deficit.
The fats are very different ; their hydrogen can be nothing like
completely oxidized by their oxygen. A gramme of hydrogen is
contained in 8"5 grammes of dry fat, and needs 8 grammes of oxygen
for its complete combustion. Only i gramme of oxygen is yielded
by the fat itself; so that if a man uses 100 grammes of fat in twenty-
four hours, rather more than 80 grammes of the oxygen taken in must
go to oxidize the hydrogen of the fat.
The proteids also contribute to the deficit. In 100 grammes of
dry proteids there are 15 grammes of nitrogen, 7 grammes of
hydrogen, and 21 grammes of oxygen. The carbon does not concern
us at present. The 33 grammes of urea, corresponding to 100
grammes of proteid, contain 15 grammes of nitrogen, a little more
than 2 grammes of hydrogen, and a little less than 9 grammes of
oxygen. There remain 5 grammes of hydrogen and 12 grammes of
o.xygen. But 5 grammes of hydrogen need for complete combustion
40 grammes of oxygen ; therefore 28 grammes of the oxygen taken
in must go to oxidize the hydrogen of 100 grammes of proteid.
Taking 140 grammes of proteid as the amount in the diet of a man,
we get 39 grammes as the required quantity of oxygen. This, added
to the 80 grammes needed for the hydrogen of the fat, makes a total
of, say, 120 grammes, equivalent to about 85 litres of oxygen. A
small amount of oxygen also goes to oxidize the sulphur of proteids.
With a diet containing less fat and proteid and more carbo-hydrate,
the oxygen deficit would of course be less.
The Production of Water in the Body. — One gramme of hydrogen
corresponds to 9 grammes of water. In 140 grammes of proteids
and 100 grammes of fat there are, in round numbers, 22 grammes
of hydrogen; in 350 grammes of starch, 21 "5 grammes. With this
diet, 43 "5 grammes of hydrogen are oxidized to water within the body
in twenty-four hours, corresponding to a water-production of 391
grammes, or 15 to 20 per cent, of the whole excretion of water. It
has been observed that during starvation the tissues sometimes
become richer in water, even when none is drunk. The only
explanation is, that the elimination of water does not keep pace with
the rate at which it is produced from the hydrogen of the broken-
down tissue-substances, or set free from the solids with which it is
(physically ?) united.
Inorganic Salts. — The inorganic salts of the excreta, like
the water, are for the most part derived from the salts of
the food, which do not in general undergo decomposition
in the body. A portion of the chlorides, however, is broken
464 A MANUAL OF PHYSIOLOGY
up to yield the hydrochloric acid of the gastric juice.
Within the body some of the salts are intimately united to
the proteids of the tissues and juices, some simply dissolved
in the latter. The chlorides, phosphates and carbonates are
the most important ; the potassium salts belong especially to
the organized tissue elements, the sodium salts to the liquids
of the body ; calcium phosphate and carbonate predomi-
nate in the bones. The amount and composition of the
ash of each organ only changes within narrow limits. In
hunger the organism clings to its inorganic materials, as
it clings to its proteids; the former are just as essential
to life as the latter. In a starving animal chlorine almost
disappears from the urine at a time when there is still much
chlorine in the body ; only the inorganic salts which have
been united to the used-up proteids are excreted, so that a
starving animal never dies for want of salts.
On the other hand, when an animal is fed with a diet as
far as possible free from salts, but otherwise sufficient, it
dies of sali-hungcr. The blood first loses inorganic material,
then the organs. The total loss is very small in proportion
to the quantity still retained in the body ; but it is sufficient
to cause the death of a pigeon in three weeks, and of a dog
in six, with marked symptoms of muscular and nervous
weakness. In pigeons on a diet containing very little
calcium the bones of the skull and the sternum become
extremely thin and riddled with holes, while the bones
concerned in movement scarcely suffer at all (E. Voit).
(4) Dietetics. — There are two ways in which we can
arrive at a knowledge of the amount of the various food
substances necessary for an average man : (a) By consider-
ing the diet of large numbers of people doing fairly definite
work, and sufficiently, but not extravagantly, fed — e.i^.,
soldiers, gangs of navvies, or plantation labourers ; (b) by
making special experiments on one or more individuals.
Voit concluded that an ' average workman,' weighing 70
to 75 kilos, and working ten hours a day, required in the
twenty-four hours iiS grammes proteid, 56 grammes fat,
and 500 grammes carbo-hydrate, corresponding to about
i8"3 grammes nitrogen and at least 328 grammes carbon.
METABOLISM, NUTRITION AND DIETETICS 465
Ranke found the following a sufficient diet for himself,
with a body-weight of 74 kilos :
Proteids -
- 100 grammes,
Fat ...
- loo
Carbo-hydrates
- 240
This corresponds to only 14 grammes nitrogen and, say,
230 grammes carbon.
A German soldier in the field receives on the average
Proteids -
- 151 grammes.
Fat - - -
- 46
Carbo-hydrates
- 522
representing about 21 grammes nitrogen and 340 grammes
carbon. But the diet of certain miners (Steinheil) and
lumberers (Liebig) contained respectively 133 and 112
grammes proteid, 113 and 309 (!) grammes fat, and 634
and 691 grammes carbo-hydrates. The diet of athletes in
training is richer in proteid than any of these. So that a
definite and typical diet for severe labour does not exist.
And although perhaps the hardest work ever done in the
world is to break records, to cut and handle timber, to mine
coal and to make war, the diet on which these things are
accomplished is very variable.
Nevertheless, we may conclude that, for a man of 70 kilos,
doing fairly hard, but not excessive, work, 20 grammes
nitrogen and 300 grammes carbon are a sufficient, and
indeed a liberal, allowance, while many men are well fed
with 15 grammes of nitrogen. The 20 grammes nitrogen
will be contained in 140 grammes dry proteid, which will
also yield 70 grammes of the required carbon. The balance
of 230 grammes carbon could theoretically be supplied chhcr
in 517 grammes starch or in 300 grammes fat. But it has
been found by experiment and by experience (which is
indeed a very complex and proverbially expensive form of
experiment) that for civilized man a mixture of these is
necessary for health, although the nomads of the Asian
steppes, and the herdsmen of the Pampas, are said to
subsist for long periods on flesh alone, and a dog can live
very well on proteids and fat. The proportion of fat and
carbo-hydrates in a diet may, however, be varied within
30
466
A MAXi'AL OF PIIYSIOLOGY
wide limits. Probably no ' work ' diet should contain much
less than 50 j^rammes of fat, but twice this amount would
be better ; 100 grammes fat give about 75 grammes carbon,
so that from proteids and fat we have now got 145 grammes
of the necessary 300, leaving 155 grammes carbon to be
taken in 350 grammes starch, or an equivalent amount of
cane-sugar or glucose. Adding 30 grammes inorganic salts,
we can put down as the solid portion of a good normal diet
for a man of 70 kilos :
140 grammes proteids
100 „ fat
350 „ carbo-hydrates
30 „ salts.
620
= -^j„ of body-weight.
— ' 1
Now, knowing the composition of the various food stuffs,
we can easily construct a diet containing the proper quan-
tities of nitrogen and carbon, by using a table such as the
following :
Quantity
(juantity
Carbo-
required
required
X. in
C. in
Proteid
Fat in
hydrate
in 100
Water
to yield
to yield
100
TOO
in 100
100
in 100
20 grms.
N.
300 grms.
C.
grms.
grms.
grms.
grms.
grms.
grms.
Cheese
(Ciruycre)
400
770
5
39
31
31
—
34
Peas (dried)
570
840
3-5
357
22
2
55
15
Lean meat -
590
2230
3-4
13-5
21
35
—
74
Wheat-flour
870
750
2-3
39-8
12
2
70
^5
Oatmeal
7fco
740
2-6
40-3
13
5'5
65
15
Eggs -
1040
2040
1-9
147
II-5
12
—
75
Maize
1080
7?>o
1-85
40-9
10-5
7
65
15
Wheat
bread
1590
1340
1-25
22-4
8
'■5
49
40
Rice -
2040
820
09
36-6
5
I
«3
10
Milk -
3>7o
4250
0-6
7
4
4
5
85
Potatoes
5000
2860
0-4
10-5
2
015
21
75
Good butter
13000
430
015
69
»
90
—
8
Economic and social influences — prices and habits — and not purely
physiological rules, fi.\ the diet of populations. The Chinese labourer,
for example, lives on a diet which no physiologist would commend.
In order to obtain 20 grammes nitrogen or 140 grammes proteid,
he must consume nearly 2,000 grammes rice, which will yield 700
grammes carbon, or twice as much as is required ; but if the Chinese
labourer could not live on rice, he could not live at all. The Irish
peasant is even in worse case ; he must consume 5 kilos of potatoes
m/:ta!!o/./sm, xutri riox and dieii-.tics 467
to obtain his 20 ji:raniines nitrogen, while little more than half this
amount would furnish the necessary 300 grammes carbon.* A man
attempting to live on flesh alone would be well fed as regards
nitrogen with 600 grammes of meat, but nearly four times as much
would be required to yield 300 grammes carbon. Oatmeal and
wheat-flour contain nitrogen and carbon in nearly the right propor-
tions (i N : 15 C), oatmeal being rather the better of the two in this
respect; and the best-fed labouring populations of Europe still live
largely on wheaten bread, while, one hundred years ago, the Scotch
peasant still cultivated the soil, as the Scotch Reviewer the Muses,
'on a little oatmeal.' But although bread may, and does, as a rule,
form the great staple of diet, it is not of itself sufficient.
Wq may take 500 grammes of bread and 250 grammes of lean
meat as a fair quantity for a man fit for hard work. Adding 500
grammes milk, 75 grammes oatmeal (as porridge), 30 grammes butter,
30 grammes fat (with the meat, or in other ways), and 450 grammes
potatoes, we get approximately 20 grammes nitrogen and 300 grammes
carbon contained in 135 grammes proteid, rather less than 100
grammes fat, and somewhat over 400 grammes carbo-hydrates.
Thus :
N. C. Proteids. ! Fat. ' y^^^^^_ Salts. ]
(9 oz.) 250 grms. lean meat
(18 02.) 500 grms. bread
{\ pint) 500 grms. milk
(I oz.) 30 grms. butter
(i oz.) 30 grms. fat
(16 oz.) 450 grms. potatoes
(3 OZ-) 75 grms. oatmeal
8
6
3
1-5
17
33 55
112 40
35 20
20 —
22 1 —
47 1 10
30 10
8-5
7-5
20
27
30
4
245
25
95
48
4 '
6-5 1
3-5
0-5
4-5
2
20'2 299I 135 97 1 413 \ 21
This would be a fair ' hard work ' diet for a well-nourished labourer.
But the great elasticity of dietetic formulae is shown by comparing
the ration of the English and German soldier as given in the follow-
ing tables :
Ration oj the English Soldier.
Bread . - . . 680 grammes.
Meat .... 240 ,,
Vegetables - - - 226 ,,
Potatoes - - - . 453 ,,
Milk - - - - 92 ,,
Sugar . - - . 377 „
Coffee ... - g-4 ,,
Tea ... - 4-5 ,,
Salt - - - - 7 »
* Of course a diet consisting, week in week out, entirely of potatoes or
rice, would represent an extreme case. A certain amount of the necessary
nitrogen is often obtained even by the poorest populations, in the form of
fish, milk, eggs or bacon.
30—2
468
A
MAXUAL
OF
PHYSIO LOG
}•
Radon of the C
rt-rinan So/dier.
Peace.
War.
Bread -
750 grammes.
I i read -
750 K
rammes
Meat -
•5°
Biscuit -
-
500
Rice -
-
50
Meat -
375
or barley
groats -
120 „
Smoked meat
250
Legumes
-
230
or fat -
170
Potatoes
-
1500
Rice -
-
125
or barley groats -
125
Legumes
-
250
In prisons the object is to give the minimum amount of the
plainest food which will suffice to maintain the prisoners in health.
A 'hard work' prison diet in Munich was found to contain 104
grammes proteids, 38 grammes fat, and 521 grammes carbo-hydrates;
a 'no work' diet, only 87 grammes proteids, 22 grammes fat, and
305 grammes carbo-hydrates. Here we recognise the influence of
price ; carbon can be much more cheaply obtained in vegetable
carbo-hydrates than in animal fats ; the cheapest possible diet contains
a minimum of fat and proteids.
Many poor persons live on a diet which would not maintain a
strong man, for an emaciated body has a smaller mass of flesh to
keep up, and therefore needs less proteid ; it can do little work, and
therefore needs less food of all kinds. A London needlewoman,
according to Playfair, subsists, or did subsist, thirty years ago, on
54 grammes proteid, 29 grammes fat, and 292 grammes carbo-
hydrates. But this is the irreducible minimum of the deepest
poverty ; and a woman, with a smaller mass of flesh and leading
a less active life than a man, requires less food of all sorts. Even
the Trappist monk, who has reduced asceticism to a science, and,
instead of eating in order to live, lives in order not to eat, consumes,
according to Voit, 68 grammes proteid, 1 1 grammes fat, and 469
grammes carbo-hydrates ; but manual labour is a part of the dis-
cipline of the brotherhood, and this must be still above the lowest
subsistence diet.
A growing child needs far more food than its weight alone would
indicate ; for, in the first place, its income must exceed its expendi-
ture so that it may grow ; and, in the second place, the expenditure
of an organism is pretty nearly proportional, not to its mass, but to
its surface. Now, speaking rou<;hly, the cube of the surface of an
animal varies as the square of the mass ; when the weight is doubled,
the surface only becomes ^yT, or one and a half times as great.
The surface of a boy of six to nine years, with a body-weight of
18 to 24 kilos, is two-fifths to one-half that of a man of 70 kilos;
and he should have about half as much food as the man — say, 70
grammes proteids, 40 grammes fat, and 200 grammes carbo-hydrates.
A child of four months, weighing 5 '3 kilos, consumed per diem food
containing '6 gramme nitrogen per kilo of body-weight, or 3 '18
grammes nitrogen altogether, as against a daily consumption of only
•275 gramme nitrogen per kilo in a man of 71 kilos (Voit) (p. 497).
An infant for the first seven months should have nothing except
METABOLISM, NUTRITION AND DIETETICS 469
milk. Up to this age vegetable food is unsuited to it ; it is a purely
carnivorous animal. Human milk contains about 4 per cent, of
proteids (casein), 26 per cent, of fat, 4-3 per cent, of carbo-hydrates
(milk-sugar). Of the solids the proteids make up 36 per cent., the
fats 24 per cent., the carbo-hydrates 39 per cent. In the typical diet
for an adult, which we have given above, the proteids amount to
20 per cent, of the solids, the fats to 15 per cent., the carbo-hydrates
to more than 60 per cent. The diet of the infant is therefore nearly
twice as rich in proteids, half as rich again in fats, and little more
than half as rich in carbo-hydrates, as that of the adult. It is m
a physiological sense a generous and even a luxurious diet. ' The
poorest mother in London or New York feeds her child as if he were
a prince. Perhaps not once in a hundred times is the man as richly
fed as the young child, unless accident has made him a Gaucho or
study and reflection a gourmand.' And the reason is that the strain
of growth falls heavier upon the more precious proteids than upon
the more cheap and common carbo-hydrates.
As to the place of water and inorganic salts in diet, it is
neither necessary nor practicable to lay down precise rules.
In most well-settled countries they cost little or nothing;
very different quantities can be taken and excreted without
harm ; and both economics and physiology may well leave
every man to his taste in the matter. Salt is indeed for
the most part used, not as a special article of diet, but as a
condiment to give a relish to the food, just as a great deal
more water than is actually needed is often drunk in the
form of beverages. It is certain that the quantity of salt
required, in addition to the salts of the food, to keep the
inorganic constituents of the body at their normal amount,
is very small. A 30-kilo dog obtains in his diet of 500
grammes of lean meat only 0"6 gramme sodium chloride,
and needs no more. An infant in a litre of its mother's
milk, which is a sufficient diet for it, gets only 0"8 gramme
sodium chloride. Bunge, however, has shown that the pro-
portion of potassium and sodium salts in the food is a factor
in determining the quantity of sodium chloride required.
A double decomposition takes place in the body between
potassium phosphate and sodium chloride, potassium chloride
and sodium phosphate being formed and excreted ; and the
loss of sodium and chlorine in this way depends on the
relative proportions of potassium and sodium in the food.
In most vegetables the proportion of potassium to sodium
470 A MANUAL OF PHYSIOLOGY
is much greater than in animal food, so that vegetable-
feeding animals and men as a rule desire and need relatively
great quantities of sodium chloride. But it is stated that
the inhabitants of a portion of the Soudan use potassium
chloride instead of sodium chloride, obtaining the potassium
salt by burning certain plants which leave an ash poor in
carbonates, and then extracting the residue with water and
evaporating (Dybowski). A beef-eating English soldier
consumes about 7 grammes {\ oz.), a rice-eating Sepoy
about 18 grammes (f oz.), of common salt per day.
Wine, beer, tea, coffee, cocoa, etc., belong to the im-
portant class of stimulants. Some of them contain small
quantities of food substances, but these are of secondary
interest. In beer, for example, there are traces of proteids,
dextrin, and sugar. But 18 litres of beer would be required
to yield 20 grammes nitrogen, and 12 litres to give 300
grammes carbon ; and nobody, except a German corps
student, could consume such quantities.
In some cocoas there is as much as 50 per cent, of fat,
4 per cent, of starch, and 13 per cent, of proteids ; and in
the cheaper cocoas much starch is added. Still, a large
quantity of the ordinary infusion would be needed for a
satisfying meal. Frederick the Great, indeed, in some of
his famous marches dined off a cup of chocolate, and beat
combined Europe on it ; but his ordinary' menu was much
more varied and substantial.
The great social and hygienic evils connected with the abuse of
alcohol, as well as its applications in therapeutics, render it necessary,
or at least permissible, to state a little more fully, though only in the
form of summary, some of the chief conclusions that may be drawn
as to its action and uses.
(i) In small quantities alcohol is oxidized in the body, a little of
it, however, being excreted unchanged in the breath and urine. It
is therefore to some extent a food substance, although it is never
taken for the sake of the energy its oxidation can supply, but always
as a stimulant.
(2) There is no reason to suppose that this energy cannot be
utilized as a source of work in the body. Heat can certainly be
produced from it, but this is far more than counterbalanced by the
increase in the heat loss which the dilatation of the cutaneous vessels
caused by alcohol brings about.
(3) It is a very valuable drug, when judiciously employed, as a
cardiac and general stimulant in certain diseases, e.g., pneumonia.
METABOLISM, NUTRITION AND DIETETICS 471
(4) Alcohol is occasionally of use in disorders not amounting to
serious disease, ('..if., in some cases of slow and difficult digestion..
(5) Alcohol is of no use for healthy men.
(6) Alcohol in strictly moderate doses is not harmful to healthy
men, living and working under ordinary conditions.
(7) Recent experience goes to show that in severe and continuous
e.\ertion, coupled with exposure to all weathers, as in war and in
exploring expeditions, alcohol is injurious, and it is well known that
it must be avoided in mountain climbing.
Tea, coffee, and cocoa are more suitable stimulants for healthy
persons, because they are less dangerous than alcohol, and they leave
no unpleasant effects behind them. But it should be remembered
that there is no stimulant which is not liable to be abused.
Certain organic acids contained in fresh vegetables, although
neither in the ordinary sense foods nor condiments, seem to be
necessary for the maintenance of health, for in circumstances in
which these cannot be obtained for long periods, scurvy is liable to
break out. It is prevented by the use of lime or lemon-juice, in
which citric, and a trace of malic acid are contained.
INTERNAL SECRETION.
It is long since Caspar Friedrich Wolff expressed the idea
that 'each single part of the body, in respect of its
nutrition, stands to the whole body in the relation of an
excreting organ,' and thus emphasized the importance
of substances produced by the activity of one kind of
cell for the normal metabolism of another. But it is only in
recent years that it has become possible to illustrate this
mutual relation by any large number of experimental facts.
Certain of the substances taken in from the blood by the
liver find their way, after undergoing various changes, into
the biliary capillaries, and are excreted as bile ; certain other
substances, such as sugar and the precursors of urea, are
taken up by the hepatic cells, transformed and sometimes
stored for a time within them, and then given out again to
the blood. Bile we may call the external accretion of the liver,
glycogen and urea constituents of its internal secretion. In
one sense it is evident that all tissues, whether glands in the
morphological sense or not, may be considered as manu-
facturing an internal secretion. For everything that an
organ absorbs from the blood and lymph it gives out to
them again in some form or other except in so far as it
472 A MANUAL OF PHYSIOLOGY
forms or separates a secretion that passes away by special
ducts. But it is usual to emplo}' the term only in relation to
organs of glandular build, whether provided with ducts
or not.
It is known that in the case of the liver the internal
secretion is more important than the external, for an animal
cannot live without its liver, while it is but little affected by
the continuous escape of the bile through a fistulous open-
ing. The internal secretions of the pancreas and the kidney
are also indispensable. For when the pancreas is excised
death follows in many species of animals ; and in man severe
and ultimately fatal diabetes is often associated with pan-
creatic disease, while the mere loss of the pancreatic juice
through a fistula does not necessarily shorten life, although
the absorption of fat is seriously interfered with. And when
the half or two-thirds of one kidney and the whole of the other
have been removed from a dog by successive operations,
death also ensues, although the quantity both of water and
urea excreted b}^ the fragment of renal substance that remains
is far above the normal (polyuria). The cause of death in
both these cases seems to be a profound disturbance of
metabolism, of which the most significant token after
extirpation of the pancreas is the increased production of
sugar and its appearance in the urine, and after interference
with the kidneys the increased production of urea. Both
in pancreatic diabetes and in experimental polyuria the
destruction of proteids is increased. When only one kidney
is excised the other hypertrophies and no ill effects ensue ;
nor does diabetes appear after partial removal of the
pancreas, so long as a comparatively small fraction (one
quarter or one-fifth) of it is left, even when this remnant is
transplanted from its original position and grafted in the
peritoneal cavity or indeed under the skin. Although as yet
we are entirely ignorant of the manner in which the kidney
and the pancreas influence the metabolism of the body, it
is impossible to doubt, in view of the facts we have men-
tioned, that both of these organs, like the liver, are, in
addition to the preparation of their ordinary or external
secretions, engaged in an active and all-important commerce
METABOLISM, NUTRITION AND DIETETICS 473
with the circulating fluids, giving to them or taking from
them substances on the manufacture or destruction of which
the normal metabolic processes depend. Schafer has sug-
gested that the seat of the internal secretion of the pancreas
is the ver}- vascular epithelioid tissue which is peculiar to
this gland, and occurs in islands between the alveoli. For
animals survive the complete atrophy of the ordinary secret-
ing epithelium caused by the injection of paraffin into the
ducts ; no sugar appears in the urine, and the grafting of
such an atrophied organ prevents pancreatic diabetes.
The influence of castration in preventing the physical
and psychical changes that normally occur at puberty, is no
doubt also, in part at least, due to the loss of the internal
secretion of the testes. And the efficacy of orchitic extract
in increasing the capacity for muscular work, as tested by
the ergograph (p. 597), is sufficient to encourage the hope
that it may possess a certain therapeutic value.
But the capacity of manufacturing internal secretions of
high importance can neither be attributed to all glands with
ducts nor denied to all other organs. For the salivary,
mammary and gastric glands may be completely removed
without causing any serious effects, while death follows
excision of the, so far as mere bulk is concerned, apparently
insignificant masses of tissue in the ductless thyroid,
suprarenal and pituitary bodies.
When the thyroid is completely removed, symptoms and
pathological changes ensue which differ in different species
of animals, but in monkeys (and in man when the thyroid
has been excised for goitre) resemble those of the disease
known as myxoedema, in which the characteristic change is
an increase (a hyperplasia) of the connective tissue in and
under the true skin. The newly-formed connective tissue is
of embryonic type, and for this reason contains more than
the usual amount of mucin. Carnivorous animals do not,
as a rule, survive the operation long enough for these
changes to be developed (p. 515). Muscular weakness soon
becomes marked ; tremors of central origin appear, and
increase in severity until at length they culminate in general
spasmodic attacks. The tissues waste, the temperature
474 A MANUAL OF PHYSIOLOGY
becomes subnormal, and this is associated with changes in
the heat regulation (p. 498). Dogs and cats often die in a
few days after the operation ; occasionally thev survive some
months, and in rare cases a year. If a portion of the
thyroid be left, or a graft be made, these effects are entirely
obviated. Not only so, but the administration of extracts
of the th3Toid glands by subcutaneous injection, or the
glands themselves by the mouth, brings about a cure in
cases of myxoedema in man, and sometimes, but with far
less certainty, prevents the development of the symptoms in
animals or removes them when they have appeared. The
same is true, although in a minor degree, of certain com-
pounds rich in iodine, for instance the so-called thyro-iodine,
which have been extracted from the organ. While the
precise role played by the thyroid in the economy remains
obscure, it is very evident that its secretion is of the utmost
importance, whether it be solely the quasi-external secretion
of ' colloid ' that collects in its alveoli and slowly passes out
of them by the lymphatics, or some other substance, which,
like the glycogen of the liver, never finds its way into the
lumen of the gland tubes at all. And it seems certain that
the main function of the organ is not to destroy toxic bodies
produced elsewhere, but to form substances indispensable to
the organism. It is a remarkable, and as yet inexplicable,
fact that in birds thyroidectomy appears to be harmless.
The apparent immunity of rodents to this operation is due,
it has been suggested, to the presence of sporadic masses of
thyroid tissue (accessory thyroid glands), or to the presence
of small bodies in the neighbourhood of the thyroid but of
a different structure (parathyroids). Some have even gone
so far as to assert that, in animals which possess them, it is
the parathyroids and not the thyroids which are important,
and that the extirpation of the latter is harmless unless the
former be also removed. But the matter is not yet beyond
the pale of controversy.
Suprarenal Capsules. — It had been observed by Addison that
the malady which now bears his name, and in which certain
vascular changes, with muscular weakness and pigmentation
or ' bronzing ' of the skin, are prominent symptoms, was
META HOLISM^ NUTRITION AND DII'/TF/nCS 475
associated with disease of the siiprarenals. This chnical
result was soon supplemented by the discovery that extirpa-
tion of the capsules in animals is incompatible with life
(Hrown - Scquard). Our knowledge of the functions of
these hitherto enigmatic organs has been greatly extended
by the experiments of Oliver and Schiifer, who have in-
vestigated the action of extracts of the suprarenals (of calf,
sheep, dog, guinea-pig and man) when injected into the
veins of animals. The arteries are greatly contracted, and
this independently of the vaso-motor centre. The blood-
pressure rises rapidly, although the heart is strongly
inhibited through the vagus centre. When the vagi are cut
the action of the heart is markedly augmented, and the
arterial pressure rises enormously (to four or five times its
original amount). Stimulation of the depressor is of no
avail in combating this increase of blood-pressure. The
curve of contraction of the skeletal muscles is lengthened
as in veratria poisoning (p. 551), though to a less extent.
The active principle that produces these effects is solely
■contained in the medulla of the gland, and such is its
extraordinary power that a dose of one-millionth of a gramme
per kilo of body-weight is sufficient to cause a distinct
effect upon the heart and bloodvessels. It was entirely
absent from the suprarenals of a person who had died of
Addison's disease. Oliver and Schafer conclude that the
function of the capsules is to secrete a substance, probably
of great physiological importance for maintaining the
tonicity of the muscular tissues in general, and especially of
the heart and arteries.
When the pituitary body is removed (in cats), death
generally occurs within a fortnight, with symptoms not
unlike those that follow excision of the thyroid. It has been
stated, too, that the pituitary undergoes (compensatory ?)
hypertrophy after thyroidectomy, and many observers have
accordingly assumed a similarity of function for these
organs. But, according to Schafer, there is no basis for
this assumption. For in man pathological changes in the
pituitary body are associated, not with myxcedema, as
disease of the thyroid is, but with another condition, called
476 A MANUAL OF PHYSIOLOGY
acromegaly, in which the bones of the limbs and face
become hypertrophied. And the effects on the vascular
system of intravenous injection of extracts of the gland are
just the reverse of those caused by thyroid extract ; while
thyroid extract brings about a fall of blood-pressure without
affecting the heart-beat, pituitary extract causes a rise of
pressure, due partly to increase in the force of the heart
(without any change in rate) and partly to constriction of
the arterioles (Oliver and Schafer).
The removal of the thymus in the frog, in which animal the organ
persists throughout life, is said to cause death. The chief symptoms
are muscular weakness going on to paralysis, trophic disturbances,
including discolouration of the skin and certain alterations in the
blood.
The spleen does not appear to produce an internal secretion, or at
least an internal secretion of any great importance, for it can be
removed both in animals and in man, not only without endangering
life, but often without the development of any symptoms. It is
possible that its blood-forming and blood-destroying functions
(p. 32) are taken on by other structures (the red bone-marrow and
the lymphatic glands).
The salivary glands may also be extirpated without the slightest
change being produced in the normal metabolism.
CHAPTER VIII.
ANIMAL HEAT.
From the earliest ages it must have been noticed that the
bodies of many animals, and particularly of men, are warmer
than the air and than most objects around them. The
'vulgar opinion ' of Bacon's time, 'that fishes are the least
warm internally, and birds the most,' if it does not imply
a very extensive knowledge of animal temperature, at least
shows that the fundamental distinction of warm and cold-
blooded animals, which is to-day more accurately expressed
as the distinction between animals of constant temperature
(homoiothermal) and animals of variable temperature
(poikilothermal), had been grasped, and was even popularly
known. Since that time the accumulation of accurate
numerical results, and the advance of ph}sical and physio-
logical doctrine, have given us definite ideas as to the rela-
tion of animal heat to the metabolic processes of the body.
It is impossible to understand the present position of the
subject without an elementary knowledge of the science of
heat. For this the student is referred to a text-book of
physics. All that can be done here is to preface the physio-
logical portion of the subject by a few remarks on the
physical methods and instruments employed :
Temperatiire. — Two bodies are at the same temperature if, when
placed in contact, no exchange of heat takes place between them.
They are at different temperatures if, on the whole, heat passes from
one to the other, and that body from which the heat passes is at the
higher temperature. It is known by experiment that if two bodies of
different temperature are placed in contact, heat will pass from one
to the other till they come to have the same temperature. If, then,
478 A MANUAL OF PIIYSIOLOCY
we have the means of finding out the temperature of any one body,
we can arrive at the temperature of any other by placing the two
in contact for a sufificiently long time, under the proviso that the
quantity of heat necessary to bring the temperature of the first body,
which may be called the * measuring ' body, to ec^uality with that of
the second, is so small as not to make a sensible difference in the
latter. This is the principle on which thermometric measurements
depend. A mercurial thermometer consists of a (juantity of mercury
ordinarily contained in a thin glass bulb, the cavity of which is con-
tinued into a tube of very fine bore in the stem. Like most other
substances, mercury expands when the temperature rises, and con-
tracts when it sinks, and the amount of expansion or contraction is
shown by the rise or fall of the mercurial column in the stem of the
thermometer. I'he point at which the meniscus stands when the
bulb is immersed in melting ice or ice-cold water is, on the centi-
grade scale, taken as zero ; the point at which it stands when the
thermometer is surrounded by the steam rising from a vessel of
boiling water is taken as loo degrees. The intermediate portion of
the stem is divided into degrees and fractions of degrees. When,
now, we measure the temperature of any part of an animal with such
a thermometer, we place the bulb in contact with the part until the
mercury has ceased to rise or fall. We know then that the mercury
has ceased to expand or contract, and therefore that its temperature
is stationary, and presumably the same as that of the part. It is to be
noted that we have gained no information whatever as to the amount
of heat in the body of the animal. We have only observed that the
mercury of the thermometer when its temperature is the same as that
of the given part expands to an extent marked by the division of the
scale at which the column is stationary. And we know that if the
mercury rises to the same point when the thermometer is applied to
another part, the temperature of the latter is the same as that of the
first part ; if the mercury rises higher, the temperature is greater ;
if not so high, it is less. The thermometer, then, only informs us
whether heat would flow from or into the part with which it is in
contact if the part were placed in thermal connection with any other
body of which the temperature is known. In other words, the
temperature is a measure of the heat 'tension,' so to speak; and
difference of temperature between two bodies is analogous to differ-
ence of potential between the poles of a voltaic cell (p. 518), or to
difference of level between the surface of a mill-pond and the race
below the wheel.
The temperature of an animal is measured in one of the natural
cavities, as the rectum, vagina, mouth, or external ear, or in the axilla,
or at any part of the skin. For the cavities a mercury thermometer
is nearly always used ; the ordinary little maximutn thermometer is
most convenient for clinical i)uri)oses. The temperature of the skin
may be measured by an ordinary mercury thermometer, the outer
portion of the bulb of which is covered by some badly conducting
material. An uncovered thermometer, heated nearly to the tem-
perature expected, will also give approximate results, especially if the
ANIMAL III: A I
479
bulb is in the form of a flat spiral, which can be easily applied to the
surface. Hut a certain error is always introduced by the interference
with the normal heat loss from the portion cjf skin covered by the
thermometer. A better method is the use of a thermo electric
junction, or a resistance thermometer formed of a grating cut out
of thin lead-paper or tinfoil (Fig. 135). This is especially useful for
comparing the temperature of two portions of skin. The tempera-
ture of the solid tissues and liquids of the body may also be measured
or compared by the insertion of mercurial or resistance thermometers
or thermo-electric junctions (p. 560).
Galorimetry. — The quantity of heat given off by an animal is
generally measured by the rise of tem-
perature which it produces in a known
mass of some standard substance.
Sometimes, however, as in the ice-
calorimeter of Lavoisier and Laplace
and the ether calorimeter of Rosenthal,
a physical change of state — -in the one
case liquefaction of ice, in the other
evaporation of ether — is taken as token
and measure of heat received by the
measuring substance, the number of
units of heat corresponding to liquefac-
tion of unit mass of ice or evaporation
of unit mass of ether being known.
The unit generally adopted in the
measurement of heat is the quantity
required to raise the temperature of a
kilogramme of water 1° C., which is
called a calorie, or kilocalorie, or large
Fig. 135.— Resistance Ther-
mometer FOR Measuring
Temperature of Skin.'
G, grating of lead-paper, attached
to a cover-slip, and mounted on a
holder ; W , W, wires to tlie
Wheatstone's bridge. An increase
in the resistance of the lead. The
balance of the bridge is thus dis-
turbed. By experimental gradua-
tion the temperature value of the
deflection, or of the change of
resistance that balances it, is known
(P- 519)-
calorie. The thousandth part of this, of temperature causes an increase
the quantity needed to raise the tem-
perature of a gramme of water by 1°,
is termed a small calorie or millicalorie.
In the calorimeters which have been
chiefly used in physiology either water
or air has been taken as the measuring
substance. The most convenient form of w^ater calorimeter is a box with
double walls, the space between which is filled with a weighed quantity
of water. The animal is placed inside the vessel, and the temperature
of the water noted at the beginning and end of the experiment.
Suppose that the quantity of water is ro kilos, and that the temperature
rises one degree in thirty minutes, then the amount of heat lost by
the animal is 10,000 small calories in the half-hour, or 480,000 in
the twenty-four hours ; and if the rectal temperature is unchanged,
this will also be the amount of heat produced. Here we assume
(1) that all the heat lost by the animal has gone to heat the water,
and none to heat the metal of the calorimeter ; (2) that none has been
radiated away from the outer surface of the latter. The first assump-
tion will seldom introduce any sensible error in a prolonged physio-
48o A MAXi'AL OF PHYSIOLOGY
logical experiment ; but it is very easy to determine by a separate
observation the water- equivalent of the calorimeter — that is, the
quantity of water whose temperature will be raised i ' by a quantity
of heat which just suffices to raise the temperature of the metal by
1° (p. 514). Then the water-equivalent is added to the quantity of
water actually present, and the sum is multiplied by the rise of
temperature. If the temperature of the room is constant, as will be
a])proximately the case in a cellar, any error due to interchange of
heat between the calorimeter and its surroundings may be eliminated
by making the initial temperature of the water as much less than that
of the air as the final temperature exceeds it. Then if the loss of
heat by the animal is uniform, as much heat is gained during the first
half of the experiment by the calorimeter from the air as is lost by it
to the air during the last half. Or, without lowering the temperature
of the water, the amount of heat lost by the calorimeter during an ex-
periment may be previously determined by a special observation,
and added to the (juantity calculated from the observed rise of
temperature. Or, finally, two similar calorimeters may be used, one
containing the animal and the other a hydrogen flame, or a coil of
wire traversed by a voltaic current, which is regulated so as to keep
the temperature the same in the two calorimeters. From the quantity
of hydrogen burnt, or electricity passed, the heat-production of the
animal can be calculated.
Of late years air calorimeters have come into vogue ipx physio-
logical purposes. A diagram of one is shown in Fig. 136. Such
calorimeters are really thermometers with an immense radiating
surface, for only a small proportion of the heat given off by the
animal goes to heat the measuring substance. The specific heat of
air, or the (juantity of heat required to raise the temperature of unit
mass of air by one degree, is very small in comparison with that of
water. A given quantity of heat raises the temperature of an air
calorimeter much more than that of a water calorimeter of the same
dimensions ; and the loss of heat to the surroundings being propor-
tional to the elevation of temperature, in the water calorimeter the
chief part of the heat is actually retained in the water, while in an air
calorimeter the greater portion passes through the air space, and is
radiated away. When the amount of heat lost by the calorimeter
becomes equal to that gained from the animal, the 'steady' reading
Ui liic insiiumeni is taken, and lioni ihis the hL-.n [>;oduciiun can be
deduced by an experimental graduation of the apparatus. One advan-
tage of an air calorimeter is that it follows more closely rapid variations
in the heat jjroduction of the animal, or, to speak more correctly, in
the heat loss. It should be carefully noted that in calorimetry what
is directly measured is the quantity of heat given out by the animal,
not the quantity produced. The two quantities are identical only
when the temperature of the animal has remained unchanged through
out the experiment. If the temperature has fallen, the quantity of
heat produced is equal to the quantity measured by the calorimeter
minus the difference between the quantity in the animal at the begin-
ning and at the end of the observation. This difference is equal to
AM A/ A/. 11 EAT
481
the average specific heat of the animal inultiplied by its weight and
by the fall of temperature. It can be approximately f(;und by
multiplying the weight (in kilogrammes or granmies) by the fall of
rectal temperature (in degrees), since the average specific heat of the
body of a mammal at least is not very different from that of water,
and the specific heat of water is taken as unity.
All the higher animals (mammals and birds) have a prac-
tically constant internal temperature (swallow 44°, mouse 41°,
^og 39°> man 38^ in the rectum), but a few hibernating
mammals, such as the marmot, are homoiothermal in summer,
Fiu. 136. — Air Calorimeter.
(A), cross-section ; (//.), longitudinal section ; A, cavity of calori-
meter for animal ; B, copper cylinder corrugated so as to increase
the radiating surface ; C, air space enclosed between B and a con-
centric copper cylinder F ; C is air-tight, and is connected by the tube 2 with the mano-
meter M. The other end of the manometer is connected with an exactly similar
calorimeter, in which a hydrogen flame is burnt in the space corresponding to A, or in
which the air in A is heaied by a coil of wire traversed by an electrical current. The
flame or current is regulated so as to keep the coloured petroleum or mercury in the
manometer M at the «ame level in both limbs ; the amount of heat given off to the one
calorimeter by the flame or current is then equal to that given off by the animal to the
other. D is an external cylinder of copper or tin perforated by holes (6, 7) at intervals.
The purpose of it is to prevent draughts from affecting the loss of heat from F ; 4,5,
are tubes through which thermometers can be introduced into C ; i is the terminal of a
spiral tube, which is coiled in the end portion of the air space C. The sections of the
coils are indicated by small circles. The other end of the spiral tube is 3; through
this tube air is sucked out. and so the proper ventilation of the animal is kept up. The
object of the spiral arrant:ement is that the air aspirated out of A may give up its heat
to the air in C before passing out. E is a door with double glass walls.
poikilothermal during their winter sleep. In the lower forms
the body temperature follows closely the temperature of the
environment, and is never ver}- much above it (frog o'5° to
3' above external temperature). Both in a frog and in a
pigeon heat is evolved as long as life lasts ; but per unit of
weight the amphibian produces far less than the bird, and
loses far more readily what it does produce. The tempera-
ture of the frog may be 30° in June and 5° in January. The
structure of its tissues is unaltered and their vitality un-
31
48- .1 MAXUAL OF PJ/YS/OLOi^Y
impaired by such violent fluctuations, l^ut it is necessary,
not only for health, but even for life, that the internal
temperature (the temperature of the blood) of a man should
vary only within relatively narrow limits around the mean
o^^7'' to 38' C.
Why it is that a comparatively high temperature should
be needed ftjr the full physiological activity of the tissues
of a mammal, while the in many respects similar tissues
of a hsh work perfectly, although perhaps more sluggishly,
at a much lower temperature, is not quite clear ; nor do
we know the precise significance of that constancy of
temperature in the warm-blooded animal, which is as im-
portant and peculiar as its absolute height. The higher
animals must possess a superior delicacy of organisation,
hardly revealed by structure, which makes it necessary that
they should be shielded from the shocks and jars of varying
temperature that less highly-endowed organisms endure with
impunity. Leaving the discussion of the local differences
and periodic variations of the temperature of warm-blooded
animals to a future page, let us consider now the mechanism
by which the loss of heat is adjusted to its production, so
that upon the whole the one balances the other.
Heat Loss. — Heat is lost (i) from the surfaces of the body
by radiation, conduction, and convection ; (2) as latent heat
in the watery vapour given off by the skin and lungs ; and
(3) in the excreta. Even in the bulky excrement of herbivora
a comparatively trifling part of the total heat is lost. The
second channel of elimination is much more important ; the
first is in general the most important of all.
The loss of heat by direct radiation from a ])ortion of the skin
or clothes, or from hair, fur, or feathers covering the skin, may
be measured by means of a thermopile or a resistance radiometer
(bolometer). The latter instrument is similar in principle and allied
in construction to the resistance thermometer used in measuring
superficial temperatures, and already described (Fig. 135, p. 479).
It may consist of a grating of lead-paper or tinfoil fixed vertically
in a small box which protects it from draughts. The box has a
sliding lid, which is kept closed till the moment of the observation,
when it is withdrawn and the portion of skin ajiplied to the opening
at a fixed distance (5 to 10 cm.) from the grating. The intensity
of radiation depends on the excess of temperature of the radiating
surface over that of the surroundings, as well as on the nature of the
, < ANIMAL 1 1 HAT 483
surface. 'I'lie uncovered pans of the skin (face and hands in man)
radiate more per unit of area than the clothes or hair ; and the warm
forehead more than the comparatively cool lobe of the ear or tip of
the nose. When a man is sitting at rest in a still atmosphere, pure
radiation plays a greater, and conduction and convection play a
smaller, part in the total loss of heat from the skin than when he is
walking about or silting in a draught. The more rapidly the air in
contact with the skin and clothes is renewed, the lower, other things
being equal, is the temperature of the radiating surfaces kept, the
greater is the loss of heat by conduction to the adjacent portions of
air, and the smaller the loss by radiation to the walls of the room,
the furniture, and other surrounding objects. It is probable that,
under the most favourable conditions, the amount of heat lost from
the surface by true radiation does not exceed the amount lost by
conduction and convection.
The loss of heat by evaporation of water from the skin can be
calculated if we know the quantity of water so given off. For a
gramme of water at the ordinary temperature (say, 15° C.) needs
555 millicalories to convert it into aqueous vapour at the average
temperature of the skin. If we take the average quantity of water
excreted as sweat in twenty-four hours as 750 c.c, this will be
equivalent to a heat loss of 416,250 — say, in round numbers, 400,000
millicalories.
The quantity of heat given off by the lungs may be also deduced
from calculation, the data being (1) the weight, temperature, and
specific heat of the expired air, and (2) the excess of water it contains
in the form of aqueous vapour over that contained in the inspired
air. Helmholtz calculated the quantity of heat needed to warm the
air expired by a man in twenty-four hours from an initial temperature
of 20° to body temperature, at 70,000 small calories, and that required
to evaporate the water given off by the lungs at 397,000, making the
total heat-loss by the lungs from 400.000 to 500,000 small calories.
By direct calorimetric observations it was found that a man of 70
kilos weight gave off in normal breathing, with an air temperature
of 12° to 15° C, from 350,000 to 450,000 small calories. Forced
respiration, as might be expected, increased the amount often to
double or even treble. A diagram of a respiration calorimeter is
shown in Fig. 137. (See Practical Exercises, p. 515.)
The following table gives an analysis of the heat-loss of
an average man. It must be understood that the figures are
only approximate.
Per cent. Millicalories.
[Evaporation of water - - 15 ] 400,000
Skin J Radiation - - - - 30 - 80 750,000
(^Conduction (and convection) - 35 j 900,000
-J I Evaporation of water - - 15 ) ... 1400,000
° \ Heating the expired air- - 2-5) ' -^ I 70,000
Heating the excreta - - 2-5 70,000
100 2,590,000
31—2
4S4
A MANUAL or I'IIYSlOLOL,Y
In the rabbit, according to Nebclthau, the heat lost by evaporation
of water is about 16 per cent, of the whole, or about half the pro-
portion in man, according to the above calculation. This is not
surprising when we reflect that the rabbit does not sweat, and drinks
comparatively little water.
Sources of the Heat of the Body. — Heat-production. — Some
heat enters the body as such from without — in the food,
and by radiation from the sun and from fires. The ultimate
source of all the heat produced in the body is the chemical
enerj^^y of the food substances. Whatever intermediate
forms this energy may assume — whether the mechanical
energy of muscular contraction ; the energy of electrical
separation b}- which the currents of the tissues are pro-
duced ; the energ}- of the nerve impulse ; or the energy, be
it what it may, which enables
the living cells to perform their
chemical labours- — it all ultimately,
except so far as external mechani-
cal work may be done, appears in
the form of heat. We do not
know at what precise stage of
metabolism the chief outburst of
heat takes place, but we may be
sure that the food, whether it is
burned in a calorimeter to simple
end-products like carbon dioxide
and water, or more slowly oxidized
in the body, yields the same
V\v.
137. — ResI'IKATION
Cai.orimetkr.
B, copper tube with mouthpiece,
connected with the thin brass cap-
sule 4 ; 4 is connected with a similar , r i ^ • j j i
capsule 3 by a short tube, which amount of heat, provided always
passes out from it at the side ^^ ■ ^^y^ j^^ j entirely
opposite to that at which B enters ; ^
2 and I are similar capsules. From conSUmed, and that no VVOrk Is
I an outlet tube C passes off. The . ,
whole is set in a copper cylinder .\ transferred to the outside. In the
filled with water. A piece is sup- i j .1 1 .• r 1
posed to be cut out of A in order to t>ody the couibustion of carbo-
show the capsules. A is placed in hydrates and fats is complete ; but
another wider copper cylinder. ■/ * '
the nitrogenous residues of the
proteids — urea, uric acid, etc. — can be further oxidized, and
the remnant of energy which they yield must be taken into
account in any calculation of the total heat -production
founded on the heat of combustion of the food substances.
AM MA I. HEAT 485
From careful experiments, it has been foiuid that a f^'ranmie of
clryproteid(ef?{;-albumin), when burned in a calorimeter, yields
5,735 millicalories of heat, a gramme of grape-sugar 3,742,
and a gramme of animal fat 9,500 millicalories (Stohmann).
Calories.
Heat cciuivalent of i gramme of albumin - - 5,735
Albumin (minus urea produced from it) - 4,949
Cane-sugar ------- 3.955
Kreatin (water-free) - - - - - 4,275
Starch - - - - - - -4,182
In applying such results to the calculation of the heat-production
of the body, it is not sufficient to deduct from the heat of combustion
of the proteids the heat which the residual urea would yield if fully
oxidized. For other incompletely oxidized products arise from
proteids when consumed in the body, and Rubner has shown, by
actually determining the heat of combustion of the urine and fseces,
that the real equivalent of a gramme of albumin is at most only
4,420 millicalories. The heat-equivalent of our specimen diet (p. 467)
will be approximately :
I'roteid, say, 130 grammes
Fat, 100 grammes
Carbo-hydrate (reckoned
glucose), 400 grammes
But this is the diet of a man doing a fair day's work ; and to
get the quantity of energy which actually appears as heat, the heat-
equivalent of the mechanical work performed must be deducted.
A fair day's work is about 150,000 kilogramme-metres^ — that is, an
amount equal to the raising of 150,000 kilogrammes to the height
of a metre. Now, a kilogramme-degree or calorie of heat is equiva-
lent to (say) 427 kilogramme-metres of work, and a kilogramme-
metre to - millicalories. The heat-equivalent of the day's work
427
1000
IS, therefore, 150,000 x = 351,000 millicalories. Deducting this
from the heat-equivalent of the food, we get in round numbers
2,670,000 millicalories as the quantity of heat given off. This cor-
responds fairly well with the calculated heat-loss (p. 483). Calori-
metric observations have given results in some cases not widely
different, in others considerably higher. Thus, Him found that a
man of 73 kilos weight produced 140,000 millicalories per hour
during rest, and 229,000 during an hour's work of 32,550 kilogramme-
metres. At the same rate for the twenty-four hours these numbers
would correspond respectively to 3,360,000 and 5,496,000 small
calories. But it is not legitimate to apply the results of compara-
tively short observations in this way ; for, on the one hand, the heat-
Millicalories.
X
4,420
574,6co
X
9,500
= 950,000
as
X
3,742
= 1,496,800
3,021,400
486 A xMANL'AL OF PHYSIOLOGY
production during sleep is much less than in the ' rest ' of ordinary
waking life ; and, on the other, continuous labour for twenty-four
hours at the rate of more than 30,000 kilogramme-metres per hour
would either be impossible, or would be associated with a greater
consumption of food or of tissue than corresponds to the diet on
which our calculation was based. During the normal eight hours
of sleep the heat-production of a 73 kilo man is only about 45,000
millicalories per hour (Helmholtz), or 360,000. Adding to this
2,240,000 (16 X 140,000), for the sixteen resting but waking hours,
we get 2,600,000 as the total heat-production of the 'resting' man.
Dividing the day into eight hours of work at the rate of 32,550
kilogramme-metres per hour (a hard day's labour), eight hours'
waking rest, and eight hours' sleep, we get a heat-production of
3,312,000 small calories in twenty-four hours, made up thus:
Eight hours' work x 229,000 = (,832,000
Eight hours' ' rest ' x 140,000 = 1,120,000
Eight hours' sleep x 45,ooo = 360,000
Observations have also been made on man by Ott with
a water, and b}- D'Arsonval with an air, calorimeter. Such
experiments are still open to considerable errors, and the
heat-production necessarily varies widely with the diet. But
from the general agreement of calculated results with actual
measurements we can safely conclude that mo%t healthy adults
produce between 2,000,000 and 3,000,000 small calories on a
' rest ' day, or a day of light labour, and between 3,000,000 and
4,000,000 on a day of hard manual work.
Rubner has calculated from the diet the heat-production
of various classes of men, reducing everything to the standard
of a body-weight of 67 kilos. The fasting man, of 67 kilos
body-weight, produces 2,303,000 calories in the twenty-four
hours. The class of brain-workers, represented b\- physicians
and officials, produce only a little more heat than the fasting
man, viz., 2,445,000 calories. The second class, represented
by soldiers (presumably in time of peace) and day-labourers
(probably of a cautious and conservative type), work up to
2,868,000 calories. The third class, composed of men who
work with machines and other skilled labourers, attain a
heat-production of 3,362,000 calories. The fourth class,
tj'pified by miners (who are engaged, usually by the piece
and not by the day, in severe and exhausting toil), produce
as much as 4,790,000 calories. In the fifth and last class.
AM MM. lll.AI
487
represented by lumberers and other out-of-door labourers
(who, in addition to excessive exertion, have often to face
intense cold), the heat-production rises to 5,^60,000 calories.
The Seats of Heat-production. — We have already recognised
the skeletal muscles as important seats of heat-production.
A frog's muscle, contracting under the most favourable con-
NUTRIENTS, CRAHS
POTENTIAL ENERGY. CALORIES
DIETARY STANDARDS.
SUBSISTENCE DIET (PLAYFAIr)
MAN AT MODERATE WORK (J/OIt)
MAN AT HARD W0RK<'ATWATER)
MAN WITH MODERATE EXERCISE (PLAYFAIRl
ACTUAL DIETARIES.
10 00 adoo MOO <4obo soeo eouo
liiilll
j^^«a
w^imx
illillil
^^^^^$
mM
LAWYER, MUNICH, GERMAN v.
PHYSICIAN, MUNICH, GERMANY,
WELL-FED BLACKSMITH, ENGLAND.
GERMAN SOLDIERS, PEACE FOOTING
GERMAN SOLDIERS, WAR FOOTING.
lllll*>f*k^«^M
■■■il
"^^^1
r.
AMD.
iiiiiiiiyiiiyjt#^^^^^^x^m^ ■■!
Fic;. 138. — Diagram showing the Heat Equivalent ok various
Dietarip:s.
A, proleids ; 15, fats ; C, carbo-hydrates ; D, heat equivalent.
ditions, docs not convert at most more than one-fourth or
one-fifth of the energy it expends into mechanical work ; at
least three-fourths or four-fifths of the energy appears as
beat. If we assume that the muscles of the human body
do not, upon the whole, work more economically than
the frog's muscles at their maximum efficiency^ — ^ an
assumption in favour of which a good deal of evidence can
be brought forward, and which, at any rate, does not seem
to be very wide of the truth — then it is easy to show that
488 A MANCAL OF PI/YSlOLOi.)'
the ^'reater part of the heat-production of the body of a
man doing ordinary \vori< is accounted for l)y the contraction
of involuntary and voluntary muscles.
If the work of the heart is taken as 27,000 kilogramme-metres in
twenty-four hours (p. 126), the total heat produced by this organ
will be equivalent (on the above assumption) at least to 108,000
kilogramme-metres, or 252,000 small calories, since, practically, the
whole work is expended in overcoming the friction of the vessels,
and finally appears as heat. Elnough energy is transformed in
twenty-four hours in the heart of the colonel of a regiment of 1,000
men to lift the whole regiment to a heiglu of nearly 2 metres, if it
could be all changed into mechanical work. The work of the
inspiratory muscles may be reckoned at 13,000 kilogramme-metres,
equal to 30,500 small calories, and the heat produced by thetn at,
say, four times the equivalent of this, or 122,000 small calories. In
sum, the muscular work of the circulation and respiration is
responsible for the production of at least 374,000 small calories
(without including the heat produced by the smooth muscle of the
bronchi and bloodvessels), or nearly one-sixth of the total pro-
duction of a man doing ordinary labour. During eight hours of
sleep a man produces altogether about 320,000 small calories. Of
this the share due to the heart and respiratory muscles may be taken
374,000
as • = 124,000: or, since the work of the circulation and
3
respiratory system is less during sleep, say, 120,000 small calories.
Taking into account the production of heat in the smooth muscle of
the alimentary canal, etc., we see that muscular contraction may be
the source of the greater part of the heat formed during sleep.
Again, it follows from Hirn's mean results that a 70 kilo man
doing 27,700 kilogramme-metres of work in an hour gives off
283.000 small calories of heat. Now, 27,700 kilogramme-metres =
say, 65,000 small calories ; and on the assumption that the skeletal
muscles produce four or even three times as much heat as work, the
contraction of these alone, without reckoning the heat produced by
the heart, would account for by far the greatest part of the total heat-
production. But even in muscles completely at rest a certain
amount of metabolism goes on, a certain amount of heat is pro-
duced. The muscles of a dog's legs, through which an artificial
circulation of defibrinated blood is kept up, consume at body
temperature on the average about 150 c.c. of oxygen per kilo per
hour. This is about one-fifth the rate of" consumption per kilo of a
normal rabbit in a bath at 39 C., reckoned on the net weight of the
animal after deduction of the contents of the alimentary canal
(770 c.c. per kilo per hour). Taking the muscles as 45 per cent, of
the body-weight, and assuming (i) that oxygen consumption and
heat-production are under the given conditions approximately pro-
portional, and (2) that the oxygen consumption of isolated muscles
150 45 3
of dog and rabbit is not very different, we get -^^ x = - or,
770 100 32
ANIMAL HEAT 4^9
say, 1 : lo, as the ratio of the heat-production of muscles absolutely
at rest, and removed from the influence of the nervous system, to
the total heat-production. And in man the gaseous metabolism
easily rises to five times, in severe work to nine times, its resting
value ; although persons inured to labour work more economically
than amateurs.
It is probable that in the skeletal muscles of curarized animals
the heat-production is not far different from that in isolated muscles
at body ten-perature, and subjected to a good artificial circulation.
Now, curara reduces the oxygen consumption of a rabbit from
770 c.c. to 500 c.c. per kilo per hour; 270 c.c. per kilo of body-
weight, or 600 c.c. per kilo of muscle, may therefore be taken as the
portion of the oxygen consumption of skeletal muscle which is
under the control of the nervous system. Adding 150 c.c, the
hourly oxygen consumption of a kilo of isolated muscles, we get
750 c.c. per kilo per hour as the total consumption of skeletal
muscles connected with the nervous system, though not in active
contraction. Separation from the nervous system therefore cuts away
four-fifths of ihe muscular metabolism, and leaves one-fifth intact.
In a curarized dog or rabbit the heat-production or respiratory
e.xchange are diminished by about 35 per cent. The remaining
^5 per cent, may perhaps be apportioned as follows: heart 15,
skeletal muscles 10, smooth muscle, glands and other tissues 40. So
that the heat-production of the heart may be nearly one-fourth of
the total production in a curarized animal, that of the skeletal muscles
one-sixth.
The glands, and then the central nervous system, rank
after the muscles, though at a great distance, as seats of heat-
production. The liver and brain (?) are the hottest organs
in the body ; and that this is not altogether due to their
being well protected against loss of heat is shown, in the
■case of the liver, by the excess of temperature of the blood
of the hepatic over that of the portal vein. In view,
however, of the exaggerated importance which some have
given to these organs, as foci of heat-production, it may
be well to point out that although many of the chemical
changes in the animal body are undoubtedly associated with
the setting free of heat, other, and not less weighty and
characteristic, reactions may cause the absorption of heat ;
and it is possible that some of the syntheses which the
hepatic and other glandular tissues seem to be capable of
performing may be included in this latter category. For
example, when urea is decomposed so as to yield ammonium
carbonate (p. 387), heat is set free. We must assume,
490 A MAXUAL OF rilYSIOLOi.Y
therefore, that if ammonium carbonate were transformed into
urea in the Hver, an equal amount of heat would be, on the
whole, absorbed. So that the heat-production of an organ
may depend, not only on the quantity, but also on the
quality, of its chemical activity. When we consider the
enormous tide of blood which during digestion sets through
the portal system, we shall look with suspicion upon results
that announce a difference of more than a small fraction of
a degree in the temperature of the incoming and outgoing
blood of the liver. Probabl}- not less than 200 litres of
blood pass in twenty-four hours through the liver of a 2 kilo
rabbit. If the temperature of this blood is raised even
one-tenth of a degree in its passage through the hepatic
capillaries, this would correspond to a heat-production of
20,000 small calories, or one-tenth of the whole heat pro-
duced in the animal.
In the case of the brain it has been shown by comparison of the
gases of blood taken from the carotid and from the venous sinuses
(torcula Herophili) that the metabolism is feeble as compared even
with that of resting muscles (Hill). Nor is it possible to demon-
strate any marked or constant increase when the cerebral cortex is
roused to such an active discharge of impulses as leads to general
epileptiform convulsions. The rise of temperature of certain regions
of the scalp observed by Lombard during mental activity cannot,
therefore, be supposed due to conduction of heat from the brain
through the skull. It is perhaps caused by vasomotor changes in
the scalp, associated, it may be, with corresponding changes in related
areas of the cortex. And, indeed, if we remember how large a pro-
portion of the central nervous system is made up of nerve-fibres, in
which, or at any rate in the fibres of peripheral nerves, no sensible
production of heat has ever been demonstrated, it will not appear
surprising if even a considerable increase in the metabolism of the
really active elements should fail to make itself felt.
With regard to the muscles, we are as yet in the dark as
to the precise relation of the energy which appears as heat
and of that which is converted into work. The original
source of both is, of course, the oxidation of the food sub-
stances ; but we do not know whether in a muscle, as in a
heat-engine, the chemical energy is first converted into heat,
and part of the heat then transformed into work, or whether
the chemical energy is immediately changed into work, or
whether there is an intermediate form of energy other than
ANIMAL HEAT 491
heat. Some have supposed that the chemical energy is first
converted into electrical energy, and that the latter in giving
rise to the work of the contracting muscle is partly wasted
as heat. It has been stated that under certain conditions
a muscle, instead of becoming warmer, may become colder
during contraction. If this were established, it would be
in favour of the view that heat is directly transformed into
muscular work. But it would not be an unequivocal proof;
for the cooling might be due merely to chemical or physical
reactions between the products formed in the active muscle
and other muscular constituents.
It has been very generally admitted that the chief seat of
excessive metabolism in fever is the muscles ; but U. Mosso
has stated that cocaine fever — the marked rise of tempera-
ture produced by injection of cocaine — can be obtained in
animals paralyzed by curara. This, even if true, would not
support the conclusion that a ' nervous fever ' — that is to
sa)-, a fever due solely to increased metabolism in the nervous
system — exists ; for in a curarized animal a large amount of
' active ' tissue (glands, heart, smooth muscle) still remains
in physiological connection with the brain and cord. But,
as a matter of fact, in an animal under a dose of curara
sufficient to completely paralyze the skeletal muscles cocaine
causes no rise of rectal temperature ; and this is strongly
in favour of the view that the fever produced in the non-
curarized animal is connected with excessive muscular
metabolism.
Thermotaxis. — What, now, is the mechanism by which the
balance is maintained in the homoiothermal animal between
heat-production and heat-loss? In answering this question
we have to recognise that both of these quantities are
variable, that a fall in the production of heat may be com-
pensated by a diminution of heat-loss, and an increase in
the loss of heat balanced by a greater heat-production.
The loss of heat from the surfaces of the body may be
regulated both by involuntary and by voluntary means. It
is greatly affected by the state of the cutaneous vessels, and
these vessels are under the influence of nerves. A cold skin
is pale, and its vessels are contracted. In a warm atmo-
49:: A MANUAL OF PHYSIOLOGY
sphere the skin is flushed with blood, its vessels are dilated,
its temperature is increased ; an effort, so to speak, is being
made by the organism to maintain the difference of tempera-
ture between its surface and its surroundings on which the
rate of heat-loss by radiation and conduction depends. A
still more important factor in man, and in animals like the
horse, which sweat over their whole surface, is the increase
and decrease in the quantity of water evaporated and of
heat rendered latent. It is owing to the wonderful elasticity
of the sweat-secreting mechanism, and to the increase of
respiratory activity, and the consecjuent increase in the
amount of watery vapour given off by the lungs, that men
are able to endure for days an atmosphere hotter than the
blood, and even for a short time a temperature above that
of boiling water. The temperature of a Turkish bath may
be as high as 65'' to 80" C. Blagden and Fordyce exposed
themselves for a few minutes to a temperature of nearly
127 C. Although meat was being cooked in the same
chamber by the heat of the air, they experienced no ill
effects, nor was their body temperature even increased.
But a far lower temperature than this, if long continued,
is dangerous to life. In the summers of 1892 and 1896
hundreds. of persons died in the United States within a few
days from the excessive heat. During the unusually hot
summer of 1819 the temperature at Bagdad ranged for a
considerable time between 108^ and 120° F. (42" to 49° C),
and there was great mortality. A much higher temperature
may be borne in dry air than in air saturated with watery
vapour. A shade temperature of 100^ F. (37'7° C.) in the
dry air of the South African plateaux is quite tolerable,
while a temperature of 85 F. (2g'4° C.) in the moisture-
laden atmosphere of Bombay may be oppressive. The
reason is that in dry air the sweat evaporates freely and
cools the skin. In saturated air at the body temperature
no loss of heat by perspiration or by evaporation from the
pulmonary surface is possible ; the temperature of an animal
in a saturated atmosphere at 35" to 40 C. soon rises, and
the animal dies. In animals like the dog, which sweat little
or not at all on the general surface, the regulation of the
AN J MA/. Ill: A r 493
heat-loss by respiration is relatively more important than in
man.
The winter fur of Arctic animals is a special device of
Nature to meet the demands of a rigorous climate, and
combat a tendency to excessive loss of heat. The experi-
ments of Hcisslin and the experience of squatters in Australia
go to show that even domesticated animals have a certain
power of responding to long-continued changes in external
temperature by changes in the radiating surfaces which
affect the loss of heat. It is said that in the hot plains of
Oueensland and New South Wales the fleeces of the sheep
show a tendency to a progressive decrease in weight. And
Hosslin found that a young dog exposed for eighty-eight days
to a temperature of 5° C, developed a thick coat of fine woolly
hairs. Another dog of the same litter, exposed for the same
length of time to a temperature of 3i'5° to 32° C, had a
much scantier covering. The increased protection against
heat-loss in the case of the ' cooled ' dog was not sufficient
fully to compensate for the lowered external temperature.
The metabolism — that is to say, the heat-production — was
also increased. And although the food was exactly the same
for both animals in quantity and quality, the dog at 5° C.
put on less than half as much fat in the period of the
experiment as the ' heated ' dog, but the same amount of
' flesh.'
The voluntary factor in the regulation of the heat-loss is of
great importance in man. Clothes, like hair and other
natural coverings, retard the loss of heat from the skin
chiefly by maintaining a zone of still air in contact with it^
for air at rest is an exceedingly bad conductor of heat. A
man clothed in the ordinary way has two or three concentric
air-jackets around him. The air in the intervals between
the inner and outer garments is of importance as well as
that in the pores of the clothes themselves ; and it is for
this reason that two thin shirts put on one above the other
are warmer than the same amount of material in the form
of a single shirt of double thickness. When a man feels
himself too hot, and throws off his coat, he really removes
one of the badly conducting layers of air, and increases
494 -' MAXCAL OF PIIYSIOLOCY
the rate of heat -loss by radiation and conduction. At
the same time the water-vapour, which practically saturates
the layer of air next the skin, is allowed a freer access to
the surface, and the loss of heat by the evaporation of the
sweat becomes greater. The power of voluntaril}- influencing
the heat-loss must be looked upon in man as one of the most
important means by which the equilibrium of temperature
is maintained. In the lower animals this power also exists,
but to a much smaller extent. A dog on a hot day puts out
its tongue and stretches its limbs so as to increase the
surface from which heat is radiated and conducted. The
mere placing of a rabbit on its back, with its legs apart,
may cause in an hour or two a fall of i° to 2" C. in the rectal
temperature. The power of covering themselves with straw
or leaves, of burrowing and of forming nests, may be in-
cluded among the voluntary means of regulation of the heat-
loss possessed by animals. A man opens the window when
he is too hot, and pokes the fire when he feels cold. Both
actions are a tribute to his status as a homoiothermal animal,
and illustrate the importance of the voluntar}' element in the
mechanism by which his temperature is controlled.
The production of heat, like the loss, is to a certain
extent under voluntary control. Rest, and especially sleep,
lessen the production ; work increases it. The inhabitants
of the tropics, human and brute, often tide over the hottest
part of the day by a siesta ; and it is as natural, and as
much in accordance with physiological laws, that a man
overpowered by the heat should lie down, as it is that he
should walk about and stamp his feet or clap his hands on
a cold winter morning. In the one case a diminution, in the
other an increase, in the heat-production is aimed at by a
corresponding change in the amount of muscular contrac-
tion. The quantity and quality of the food also influence
the production of heat. The Eskimo, who revels in train-oil
and tallow-candles, unconsciously illustrates the experimental
fact that the heat of combustion of fat is high ; the rice
diet of the ryot of the Carnatic, with its low heat equivalent,
seems peculiarly adapted to the dweller in tropical lands.
But it would be easy to attach too much weight to con-
ANIMAL HEAT
495
siderations such as these. The Arctic hunter eats animal
fat, and the Indian peasant vegetable carbo-hydrate, not
only because fat has a high and carbo-hydrate a low heat-
equivalent, but because in the climate of the far North
animals with a thick coating of badly-conducting fat are
plentiful, and vegetable food scarce ; whereas in the river-
valleys of India nature favours the growth of rice, and
religion forbids the killing of the sacred cow.
The production of heat is also controlled by an involuntary
nervous mechanism, upon which much light has been thrown
by the researches of the last twenty years, and especially
by those of Pfliiger and his school (p. 228). It is a matter
of everyday experience that cold causes involuntary shiver-
ing— involuntary muscular contractions — the object of which
seems a direct increase in the heat-production. But besides
this visible mechanical effect, the application of cold to a
warm-blooded animal, when not carried so far as to greatly
reduce the rectal temperature, is accompanied by a marked
increase in the metabolism, as shown by an increased pro-
duction of carbon dioxide and consumption of oxygen. In
cold-blooded animals like the frog the metabolism, on the
other hand, rises and falls with the external temperature ;
there is no automatic mechanism which answers an in-
creased drain upon the stock of heat in the body by an
increased supply. Or, perhaps, in the light of recent experi-
ments, we ought rather to say that, although the rudiments
of a heat-regulating mechanism may exist in such animals
as the frog, the newt, and even the earthworm (Vernon), it is
only able to modify to a certain extent the effects of changes
of external temperature, not to balance or even override
them, as in the homoiothermal animal. The warm-blooded
animal loses its heat-regulating power when a dose of curara
sufficient to paralyze the voluntary muscles is given. A
curarized rabbit, kept alive by artificial respiration, reacts
to changes of external temperature like the cold-blooded
frog. Now, the only action of curara adequate to account
for this effect is its power of paralyzing the motor nerve-
endings, and so cutting off from the skeletal muscles impulses
which in the intact animal would have reached them. The
496 .1 .VA.YUAL 01' PIIYSIOLOCY
excitation by cold of the cutaneous nerves, or some of them,
which in the unpoisoned animal is reflected alonp; the motor
nerves to the muscles, and causes the increase of meta-
bolism, is now blocked at the end of the motor path ; and
the muscles, the great heat-producing tissues, are abandoned
to the direct influence of the external temperature.
How is it, then, that nervous impulses from the skin
produce in the intact animal their effect upon the chemical
processes in the muscles ? We know that the heat-produc-
tion of a muscle is greatly increased when it is caused to
contract ; but it has not hitherto been possible by artificial
stimulation to demonstrate that any chemical or physical
effect is produced in a muscle by excitation of its motor
nerve unless as the accompaniment of a mechanical change.
When the gastrocnemius of a frog poisoned with not too
large a dose of curara is laid on a resistance thermometer
(p. 479), and its nerve stimulated from time to time as the
curara paralysis deepens, heating of the muscle is observed as
long as, and only as long as, there is any visible contraction.
The gaseous metabolism of a rabbit immersed in a bath of
constant temperature may sink by as much as 30 to 40 per
cent, when curara is given. One obvious cause of this is the
complete muscular relaxation. And the whole secret of the
regulation of the heat-production might be plausibly sup-
posed to lie in the bracing effect of cold upon the skeletal
muscles and the relaxing effect of heat. And, indeed, in
man it has been observed that cold causes no metabolic
increase when shivering is prevented by a strong effort of the
will (Loewy). Nevertheless, the explanation is inadequate
in the case of small animals, such as guinea-pigs, rabbits,
and cats ; for very great changes in the metabolism may be
brought about by external cold without any outward token
of increased muscular activity.
It must be admitted, then, that — at least in the smaller
homoiothermal animals — the metabolic changes normally
going on in the resting muscles may be reflexly increased
without the usual accompaniment of mechanical contrac-
tion, and that such an increase of ' chemical tone ' may be
an important means by which the temperature is regulated.
ANIMAL 111: AT
497
It is possible that other organs besides the muscles may be
concerned, though not to a sufficient extent to secure the
due regulation of temperature during curara paralysis. It is
obvious that in man, whose environment is so much under
his own control, a mere automatic regulation is less required
than in the inferior animals, and that a regulative power, if
present in rudiment, would tend to ' atrophy ' by disuse. In
the larger animals, again, mere bulk is an important safe-,
guard against any sudden change of internal temperature.
To reduce the temperature of a horse or an elephant by
I , a considerable quantity of heat must be lost, while a very
slight loss would suffice to cool a mouse by that amount.
Not only so, but the surface by which heat is lost is greater
in proportion to the mass of the body in small than in
large animals. The power of rapidly increasing the heat-
production to meet a sudden demand is, therefore, far more
important to the mouse than to the horse ; and the fact
(p. 468) that the metabolism of an animal varies approxi-
mately as its surface, and not as its mass,* is an illustration
of the nice adjustment by which heat-equilibrium is main-
tained.
The following table, calculated by Rubner from the
quantity of tissue-proteid and fat consumed, shows the rela-
tive intensity of heat-production in fasting dogs of different
sizes :
Body- weight.
Small calories per
kilo per hour.
31 K
24
20
18
10
6
3
1,580
1,700
1,870
1,920
2,550
2,840
3,780
* The relation between mass and surface in man is approximately
expressed by the equation ,,— = K, where S is the surface expressed in
square centimetres, M the mass expressed in grammes, and K a constant
whose mean value is 12-3 (Meeh). The equation — ^ ' ' =K''
32
498 A MANUAL OF PHYSIOLOGY
Rubner has found that animals abundantly fed do not
show so much change in the production of heat when the
external temperature is varied as starving animals, perhaps
because the thicker coat of subcutaneous fat so steadies the
rate at which heat is lost that it becomes easy for the
vaso-motor mechanism alone to hold the balance between
loss and production. In well-fed animals it is the heat-loss
which is chiefly affected, and it may be that this has some-
thing to do with the explanation of Loewy's results on man.
Lorrain Smith has discovered the curious and interesting
fact that after removal of the thyroid glands (in cats), the
heat-production, as measured by the amount of carbon
dioxide given off, is more sensitive to changes of external
temperature than in the normal animal.
But it must not be imagined that the production of heat
can be increased indefinitely to meet an increased heat-loss.
The organism can make considerable efforts to protect itself,
but fhe loss of heat may easily become so great that the
increase of metabolism fails to keep pace with it. The
internal temperature then falls, and if the fall be not
checked, the animal dies. A mammal, when cooled arti-
ficially to the temperature of an ordinar}- room (15" to
20° C), does not recover of itself, but may be revived by the
employment of artificial respiration and hot baths, even when
the rectal temperature has sunk to 5" to 10' C. If the skin
of a rabbit be varnished, and the air which it is the function
of the fur to maintain at rest around it be thus expelled, the
animal dies of cold, unless the loss of heat is artificially
prevented. If, without varnishing at all, the greater portion
of the skin of a rabbit or guinea-pig be closely clipped or
shaved, similar phenomena are observed. Prevented from
covering itself with straw, the animal dies, sometimes in
twenty -four hours. The radiation from the skin, as
measured by the resistance-radiometer ^p. 482), is greatly
increased ; the animal shivers constantly, and the rectal
expresses the relation between surface (S), mass (Ml, length of body (L),
and circumference of chest (C) just above the nipples in ihe 'mean"
position of respiration. K' is a C()nstant whose mean \alue is 4*5. .S is
expressed in square centimetres, M in grammes, L and \' in centimetres.
.l.V/.l/.l/. m.AT
499
temperature falls. Placed in a warm chamber before the
temperature in the rectum has fallen below 25', the animal
recovers perfectly. If the fall is allowed to go on, it dies.
If it is kept from the hrst in the warm chamber, no fall of
temperature occurs. When the increased loss of heat is less
perfectly compensated — when, for example, the animal is left
at the ordinary temperature, but supplied with sufficient
straw to cover itself, or allowed to crouch among other
animals — a curious phenomenon ma\' sometimes be seen.
The rectal temperature, which has fallen sharply during the
operation, remains subnormal (as much as 2° to 3' below the
ordinary temperature) for a time (a week or more), and
then gradually rises as the coat again begins to grow. The
meaning of this seems to be that the power of regulating
the temperature by increasing the metabolism is overtasked
by the removal of the natural protective covering, unless
the escape of heat is artificially diminished. When the loss
of the fur is entirely compensated, no fall of temperature
occurs ; when it is not compensated at all, the animal cools
till it dies ; when it is partially compensated, the increased
metabolism may onl}- suffice to maintain a temperature
lower than the normal, although constant muscular con-
tractions (shivering) are brought in to supplement the efforts
of the regulative chemical processes.
Hitherto we have only spoken of a reflex regulation of
the heat-production called into play by external cold. It
might be supposed — and, indeed, has often been assumed —
that heat would lessen the metabolism, as cold increases it ;
and there are indications that in the smaller animals this is
the case, although the influence of heat seems to be much
smaller than the influence of cold. But neither experi-
mental results nor general reasoning have as yet shown
that in man, either in the tropics (Eykman) or in the north
temperate zone (Loewy), the chemical tone is diminished
by a rise of external temperature much above the mean of
an ordinary English summer, apart from the effect of the
muscular relaxation which heat induces. In a man, indeed,
at rest in a hot atmosphere, the production of carbon dioxide
and consumption of o.xygen are, if anything, greater than
32-2
500 A MANUAL OF PHYSIOLOGY
at the ordinary temperature. The rej^Milation of tempera-
ture in an environment warmer than the normal seems, in
fact, to be brought about more by an increase in the loss
than a decrease in the production of heat. Evaporation
from the skin and lungs is an automatic check upon over-
heating as important as the involuntary increase of meta-
bolism upon excessive cooling.
While it is known that the skeletal muscles, and perhaps
the glands and other tissues, are at one end of the reflex arc
by which the impulses pass that regulate the temperature
through the metabolism, we are as yet ignorant of the
precise paths by which the afferent impulses travel, of the
nerve-centres to which they go, and even of the end-organs
in which they arise. There are nerves in the skin which
minister to the sensation of temperature (Chap. XIII.). A
change of temperature is their ' adequate ' and sufficient
stimulus ; and it is a tempting hypothesis, though nothing
more, that these are the afferent nerves concerned in the
reflex regulation of temperature — that impulses carried up
by them to some centre or centres in the brain or cord are
reflected down the motor nerves to control the metabolism
of the skeletal muscles, and down the vaso-motor nerves to
control the loss of heat from the skin.
Heat Centres. — It is known that certain injuries of the
central nervous system are related to disturbance of the
heat-regulating mechanism. Puncture of the median portion
of the corpus striatum in the rabbit by a needle thrust
through a trephine hole in the skull is followed by a rise of
rectal temperature (i° to 2°), heat-production and respira-
tory exchange, which may last for several days (Ott, Richet,
Aronsohn and Sachs). This is due to stimulation of the
portions of the brain in the immediate neighbourhood of
the injury, and electrical stimulation of this region has a
similar effect. When the temperature has returned to
normal, a fresh puncture may again cause a rise. Injury
to various portions of the cortex cerebri in the dog and
other animals, and lesions of the pons, medulla oblongata
and cord in man may also be followed by increase of
temperature. When the spinal cord is cut below the level
ANIMAL HEAT 501
of the vaso-motor centre the increased loss of heat from the
skin due to dilatation of the cutaneous vessels masks any
increase of the heat-production which may possibly have
taken place, and the internal temperature falls ; but if the
loss of heat is diminished by wrapping the animal in cotton-
wool the temperature may rise. From such phenomena it
has been surmised that certain ' centres ' in the brain have
to do with the regulation of temperature by controlling the
metabolism of the tissues ; that they cause increased meta-
bolism when the internal temperature threatens to sink,
diminished metabolism when it tends to rise. The cutting
off, it is said, of the influence of the 'heat centres' by
section of the paths leading from them allows the meta-
bolism of the tissues to run riot, and the temperature to
increase.
Fever is a pathological process generally caused by the
poisonous products of bacteria, and characterized by a rise
of temperature above the limit of the daily variation (p. 509).
It is further associated with an increase in the rate of the
heart and the respiratory movements, often with an increase
in the excretion of urea and ammonia in the urine, and a
diminution in the alkalies and carbon dioxide of the blood.
It has been suggested that the proximate cause of fever is
the action of bacterial poisons or of other substances on the
* heat centres,' and that antipyretics, or drugs which reduce
the temperature in fever, do so by restoring the centres to
their normal state, by preventing the development of the
poisons, aiding their elimination, or antagonizing their action.
In favour of this view, it has been stated that when the
basal ganglia are cut off, by section of the pons, from their
lower nervous connections, fever is no longer produced by
injection of cultures of bacteria which readily cause it in
an intact animal, while antipyrin has no influence upon the
temperature (Sawadowski). But some observers have been
unable to find any clear evidence of the existence of ' heat
centres ' — that is, of localized portions of the central nervous
system specially concerned in the regulation of the body
temperature. And while it is almost certain that some
pyrogenic or fever-producing agents — cocaine, t^i,^ — act in-
502
A MAXIMAL OF ri/YSIOLOGY
directly, throuj^h the brain or cord, it is quite possible that
others affect directly the activity of the tissues in general,
just as some antipyretics or fever-reducing agents, such as
quinine, seem to act immediately upon the heat-forming
tissues, while others, like antipyrin, affect them through the
nervous system.
Fever is a condition so interesting from a physiological
point of view, and of
such importance in
practical medicine, that
it will be well to con-
sider a little more
closely the possibleways
in which a rise of tem-
perature may occur. It
must not be forgotten
that the febrile increase
of temperature is always
accompanied by other
departures from the
normal, and that all
the fundamental febrile
changes may even, in
certain cases, be present
without elevation, and
even with diminution of
,, T, ^ temperature. But here
Pig. 139. — Diagram to show the i'Ossibli. ^
Relations between HEAT-rRonucTiON we have only to do with
AND HEAT-LOSS IN Fkvek. ^^^ disturbance of the
normal equilibrium between the loss and the production
of heat ; and it is evident that any of the five conditions
illustrated in the diagram may give rise to an increase
of temperature. It is not necessary to discuss whether
cases of fever can actually be found to illustrate every
one of these possibilities. It is probable that not infre-
quently diminished loss and increased production may
be both involved ; and it ought to be remembered that
the healthy standard with which the heat-production of a
fever patient should be compared is not that of a man
ANIMAL HEAT 503
doin^ hard work on a full diet, but that of a healthy person
in bed, and on the meagre fare of the sick-room. When
this is kept in view, the comparatively low heat-production
and respiratory exchange which have sometimes been found
in fever cease to excite surprise. But, in any case, no mere
change in the relative proportions of heat formed and lost
is sufficient to explain the febrile rise of temperature.
That an increase in heat-production is not of itself enough
to produce fever is proved by the fact that severe muscular
work, which increases the metabolism more than high fever,
only causes a slight and transient rise of temperature in a
healthy man. The essence of the change is a derangement
of the mechanism by which in the healthy body excess or
defect of average metabolism, or of average heat-loss, is at
once compensated and the equilibrium of temperature main-
tained.
This derangement only lasts as long as the temperature is
rising. When it becomes stationary at its maximum we
have again adjustment, again equality of production and
escape of heat ; but the adjustment is now pitched for a
higher scale of temperature. A rough analogy, so far as
one part of the process is concerned, may be found in the
behaviour of the ordinary gas-regulator of a water-bath. It
can be ' set ' for any temperature. That temperature, once
reached, remains constant within narrow limits of oscilla-
tion ; but the regulator can be equally well adjusted for a
higher or a lower temperature.
Rosenthal has concluded from calorimetric observations
that, in the first stage of fever, while the temperature is
rising, there is always increased retention of heat. Marag-
liano actually found evidence, by means of the plethysmo-
graph, that the cutaneous vessels are at this stage con-
stricted, and that the constriction may even precede the
rise of temperature. Both observations lend support to the
famous ' retention ' theory of Traube. At the height of
the fever there is often, though apparently not always, an
increase in the heat-production. After the crisis, while the
fever is subsiding, the rate at which heat is being lost rises
sharply. As to the explanation of the increase of metabolism
504 A MANUAL OF PHYSIOLOGY
in fever, various views have been held. Some have gone so
far as to say that the increase is merely the consequence,
not the cause, of the rise of temperature, liut the rebutting
evidence which has been brought against this view is strong
and, indeed, overwhelming. The increase of urea, for
example, is often much greater in fever than any increase
which can be brought about by artificially raising the tem-
perature of a healthy individual by means of hot baths.
Further, this excessive excretion of urea does not run parallel
with the rise of temperature in fever, but is generally most
marked after the crisis. During the stage of defervescence an
enormous amount of urea is sometimes given off. In a case
of typhus, in the mixed urine of the third and fourth days
after the crisis, no less than i6o grammes urea was found
(Naunyn), or nearly three times the normal amount for a
man on full diet. Again, when fever is caused by the in-
jection of bacteria or their products, the increase in the
carbon dioxide eliminated and oxygen consumed occurs even
when the temperature is prevented from rising by cold baths.
It seems perfectly clear, then, that the increase of metabolism
is, in many cases at least, a primary phenomenon of fever,
and it remains to ask whether the rise of temperature is
anything more than a superficial, and, so to speak, an
accidental, circumstance. The orthodox view for many
ages has undoubtedly been that the increase of temperature
is in itself a serious part of the pathological process, a
symptom to be fought with, and, if possible, removed. And,
indeed, it is not denied by anyone that the excessive rise of
temperature seen in some cases of febrile disease (to 43 C,
and, it is said, even to 44' in influenza, e.g.), is, apart from
all other changes, a most imminent danger to life. But
some evidence has of late been brought forward, mostly
from the field of bacteriology, to support the idea that
the rise of temperature is of the nature of a protective
mechanism, that fever is, indeed, a consuming fire, but a
fire that wastes the body, to destroy the bacteria. The
streptococcus of erysipelas, for example, does not develop
at 39° to 40° C, and is killed at 39*5° to 41" C. Anthrax
bacilli, kept at 42° to 43° C. for some time, are ' attenu-
ANIMAL HEAT 505
ated,' and when injected into animals confer immunity to
the disease. Heated for several days to 41' to 42° C,
pneumococci render rabbits immune to pneumonia. These
bacteriological results are supported to a certain extent by
clinical experience. For it has been observed that a cholera
patient with distinct fever has a better chance of recovery
than a case which shows no fever. But too much weight
ought not to be given to isolated facts of this sort, and
adverse evidence can be produced both from the laboratory
and the hospital. For although hens are immune to anthrax
under ordinary conditions, but can be infected by inocula-
tion when artificially cooled, frogs, equally immune at the
temperature of the air, become susceptible when artificially
heated. And it is impossible to deny that the use of
cold baths in typhoid fever is sometimes of remarkable
benefit.
Distribution of Heat. — The great foci of heat-formation — the
muscles and glands — would, if heat were not constantly leaving
them, in a short time become much warmer than the rest of the
body ; while structures like the bones, skin, and adipose tissue, in
which chemical change and heat-production are slow, would soon
cool down to a temperature not much exceeding that of the air.
The circulation of the blood ensures that heat produced in any
organ shall be carried away and speedily distributed over the whole
body ; while direct conduction also plays a considerable part in
maintaining an approximately uniform temperature. The uniformity,
however, is only approximate. The temperature of the liver is
several degrees higher than that of the skin, and the temperature of
the brain several degrees higher than that of the cornea. The blood
of the superficial veins is colder than that of the corresponding
arteries. The crural vein, for example, carries colder blood than the
crural artery, and the external jugular than the carotid. The heat
produced in the deeper parts of the regions which they drain is
more than counterbalanced by the heat lost in the more superficial
parts. When loss of heat from the surface is sufficiently diminished
by an artificial covering, or prevented by the protected situation of
any organ with an active metabolism, the venous blood leaving it is
warmer than the arterial blood coming to it. The temperature of
the blood passing from the levator labii superioris muscle of the
horse during mastication may be sensibly higher than that of the
blood which feeds it ; the blood in the vena profunda femoris, and
in the crural vein of a dog with the leg wrapped in cotton-wool, is
warmer by '1° to -3° than the blood of the crural artery. This
difference of temperature is due to the heat produced in the muscles,
5o6 A MANUAL OF I'llYSIOLOGY
and it is not difficult to show that the difference ought to be of this
order of magnitude. The quantity of blood in a 7 kilo dog is about
I kilo ; j of this, or J, kilo, is in the skeletal muscles, and the
average circulation-time through them may be taken as ten seconds.
Six times in the minute, or 360 times in the hour, \ kilo of blood
passes through the muscles, and is heated on the average by "a". If
we take the specific heat of blood as about equal to that of water,
360 2
this represents a heat-production of "^ x — x 1,000, or 9,000 small
8 10
calories per hour. Now, the total heat-production of a 7 kilo dog
is about 19,000 small calories per hour, of which somewhat less than
one-half is probably formed in the skeletal muscles.
The blood of the inferior vena cava at the level of the kidneys
may be 'i" colder than that of the abdominal aorta, but is
warmer than the blood of the superior cava. The right heart,
therefore, receives two streams of blood at different temperatures,
which mingle in its cavities. A controversy was long carried on as
to the relative temperature of the blood of the two sides of the
heart ; but the researches of Heidenhain and Korner have shown
that a thermometer passed into the right ventricle through the jugular
vein stands, as a rule, slightly higher than a thermometer introduced
through the carotid into the left ventricle. They consider that the
method gives not so much the temperature of the blood in the two
cavities as that of their walls. The thin-walled right ventricle,
according to them, is heated by conduction from the warm liver,
from which it is only separated by the diaphragm, while the left
ventricle loses heat to the cooler lungs. They deny that the
difference of temperature is caused by cooling of the blood in its
passage through the pulmonary capillaries. Under ordinary circum-
stances, they say, the inspired air is already heated almost to body
temperature before it reaches the alveoli ; but, while this is the case,
it is jjossible that much of the water-vapour required to saturate it is
evaporated from the alveolar walls. Even when respiration is
suspended, they find a difference of temperature between the two
sides of the heart. A slight difference, however, might be caused in
the blood of the two ventricles, even in the absence of respiration,
by the heat developed in the cardiac muscle itself during con-
traction. A large proportion of this heat must be conveyed by the
blood of the coronary veins into the right side of the heart. But
the whole of it would only suffice to raise the temperature of the
blood in the right ventricle by .ja° to i'o° ; while a fall of i\,° in the
temperature of the blood passing through the lungs would account for
all the heat lost by the expired air, and if half of the loss took place
in the upper air-passages, ;J,-,° would be sufficient.
The surface temperature varies between rather wide limits with
the temperature of the environment. The temperature of cavities
like the rectum, vagina, and mouth approximates to that of the
blood in the great vessels or the heart, and undergoes only slight
changes. An increase in the velocity of the blood causes the
/L\7.1/.J/, HEAT 507
internal and surface temperatures to come nearer to each other, the
former falling and the latter rising, ^\'hen the loss of heat from a
portion of the surface is prevented, the temijcrature of this portion
approaches the internal temperature. For this reason a thermometer
placed in the axilla approximately measures the internal temperature,
and not that of the skin ; and a thermometer in the groin of a rabbit,
and completely covered by the flexed thigh, may stand as high as,
or, it is said, even higher than, a thermometer in the rectum (Hale
White).
The surface temperature is a rough index of the rate of heat-loss ;
the internal temperature, of the rate of heat-production. A normal
skin temperature and a rising rectal temperature would probably indi-
cate increased production of heat ; an increased rectal temperature, in
conjunction with a diminished surface temperature, as in the cold
stage of ague, might be due either to diminished heat-loss while the
heat-production remained normal, or to diminished heat-loss plus
increased heat-production.
The following tables illustrate the differences of tempera-
ture found in the body. It should be remembered that the
numbers are not strictly comparable with each other ; there
is no constant ratio between the temperature of the blood
in two vessels or of the skin at two points. Even in the
same vessel the temperature may vary with many circum-
stances, such as the velocity of the stream, and the state
of activity of the organ from which it comes. Apart from
physiological variations, experimental fallacies sometimes
cause a want of constancy, especially in measurements of
blood temperature. The insertion of a mercurial ther-
mometer into a vessel is ver}- likely to obstruct the passage
of the blood ; and if the blood lingers in a warm organ, it
will be heated beyond the normal.
Blood. {Doc:.)
Right heart . . . - 38-8° C.
Left „ .... 38-6
Aorta ... - - 387
Superior vena cava - - - 36-8
Inferior „ ... 38-1
Crural vein .... 37-2
Crural artery - - - - 3^'
Profunda femoris vein - - 38'2
Portal vein - - 38-39 I ^'aries with activity
Hepatic vein - - - 38'4-397 1 of digestive organs.
;oS
A MANUAL or PHYSIOLOGY
Leg of dog lightly ivrappcd in wool.
Crural artery - . . . 34'95
,, vein - - . . 34-76 ^ Rectum, 362.
Leg more carefully ivrapped up. [Air, i^>'3-
Crural artery - - . . 3470
„ vein - - . . 34"i52/
Tissues.
Brain
Liver . . - . .
Subcutaneous tissue 21 lower
than that of subjacent muscles
(man).
Anterior chamber of eye
Vitreous humour
40
40"6-40"9
3i"9l
36-:/
(rabbit).
Cavities. {Man.)
Axilla
Rectum
Mouth
Vagina
Uterus
External auditory meatus
(Bladder, urine) -
36-3-37"5° C.(97-3-99-5' F-)
37"5-38
37-25
37 '5-38
37 ■7-38-3
37-3-37-8
37-03
Natural Surfaces.
Cheek (boy, immediately after running) -
, Anterior surface of forearm -
(Man) Posterior ,, ,, - - -
Room Skin over biceps -----
temperature," „ ,, head of tibia - - - -
1 7 "5° j „ immediately below xiphoid cartilage
' „ over sternum
On hair (boy)
Under hair over sagittal suture (boy)
Shaved skin of neck (rabbit) -
On hair „ ,, ,, - - ■
,, between eyes „ - ■ ■
Artificial Surfaces.
(Man) fe r f u- u
Room Surface of trousers over thigh
temperature, j "
17-5° I
Normal Variations in the Temperature. — The internal tem-
perature, as has been already said, is not strictly constant.
coat over arm
waistcoat
36-25
33-5-34-4
34-
35-
31-9
34-7
33-2
30-
33-7-34*
36-5
31-5
30-7
237-28-7
26-8
26-
ANIMAL hi: AT
509
It varies with the time of day; with the taking of food;
with age ; to a shght extent with violent changes in the
external temperature, such as those produced by hot or cold
baths ; and possibly with sex.
The daily curve of temperature shows a minimum in the
early morning (two to six o'clock), and a maximum in the
evening (five to eight o'clock) (Fig. 140). The extreme daily
range in health may be taken as a little over i" C. In fever
it is generally greater, but the maximum and minimum fall
at the same periods; and it is of scientific, and perhaps of
practical, interest that
the early morning, when
the temperature and
pulse-rate are at their
minimum, is often the
time at which the
flagging powers of the
sick give way. From
two to six o'clock in the
morning the daily tide
of life may be said to
reach low-water mark.
Even in a fasting man ^'^^''- 140. —Curve sho\vin(, ihe Daily
, ,. , \ ARIATION OK BODY TEMrERATURE.
the diurnal tempera-
ture curve runs its course, but the variations are not so
great. The taking of food of itself causes an increase of
temperature, although in a healthy man this rarely amounts
to more than half a degree. The rise of temperature is
certainly due in part to the increased work of the alimentary
canal, but may also be connected with the increase of
metabolic activity which the entrance of the products of
digestion into the blood brings about. The solution of the
solids of the food by the digestive juices is associated
with absorption of heat, as has been observed in artificial
digestion, and even in a case of gastric fistula. The
increased heat-production, however, is more than suffi-
cient to prevent any fall of body temperature from this
cause.
As to the relation of age and sex to temperature, it is
.1 MANUAL or PIIYSIOLO(;y
only necessary to remark that the mean temperature of the
younpf child is somewhat hi^'her, and that of the old man
somewhat lower, than that of the vigorous adult ; but a
])oint of more importance is the relative imperfection of the
heat-regulation in infancy and age, and the greater effect of
accidental circumstances on the mean temperature. Thus, old
people and young children are specially liable to chills, and
a fit of crying may be sufficient to send up the temperature
of a baby. The tem-
perature of women is
^^enerally a little higher
than that of men, and
is also, perhaps, some-
what more variable.
After death the body
cools at first rapidly,
then more slowly (Fig.
141). Hut occasionally
a post-mortem rise of
temperature may take
place. In certain acute
iliseases (like tetanus)
associated with exces-
sive muscular contrac-
iii.. 141.-
Al 1 EK DkATH
-Ci;K\ E OF L'OOLIN
(Guinea-pig).
lime marked along horizontal, and temperature tion this haS been CSpC-
along vertical axis. .\t a ether and chloroform ... .
given to kill animal; death, as indicated by stoppage Cially noticed ; m bodies
of the heart, took place at />. The dotted line *■ A \ . 1 A
shows the course the curve would have taken if WaStea Dy prolonged
death had occurred at the moment the anaesthetics iHnesS it doeS not OCCUr.
were given. Air of room 17-6 . >. ^v./ o y^^ ^^k,,..
Nearly an hour after
death, in a case of tetanus, the temperature was found to be
45'3 (Wunderlich). In dogs a slight post-mortem rise may
be demonstrated, especially when the body is wrapped up ;
but when an animal has been long under the influence of
anaesthetics, no indication whatever of the phenomenon
may be obtained. The explanation of post-mortem rise of
temperature is to be found: (i) In the continued meta-
bolism of the tissues for some time after the heart has
ceased to beat, for the cell dies harder than the body.
(2) In the diminished loss of heat, due to the stoppage of
/'AM CTICAL r.XERCI^ES
the circulation, fj) Possibly to a small extent in physical
changes (rigor mortis, coagulation of blood) in which heat
is set free.
PRACTICAL EXERCISES ON CHAPTERS VII. AND VIII.
I. Glycogen — (i) Preparation. — {a) Place in a mortar some fine
sand and a mixture of equal volumes of saturated solution of
mercuric cliloride and Esbach's reagent.* Put one or two oysters
in the mortar, rub up thoroughly, and let the mass stand till {b) and
(^) have been done, stirring it occasionally. Then filter and pre-
cipitate the glycogen from the filtrate with alcohol. Eilter again,
wash the precipitate on the filter with a little alcohol, dissolve it in
I or 2 c.c. of water, and test for glycogen as in [h). The mercuric
chloride and Esbach's reagent are added to precipitate the proteids,
which are more completely thrown down in this way than by the
methods used in (/') and (t) (Huizinga).
{b) Cut an oyster into two or three pieces, throw it into boiling
water, and boil for a minute or two. Rub up in a mortar with clean
sand, and again boil. Filter. Precipitate any proteids which have
not been coagulated, by adding alternately a drop or two of hydro-
chloric acid and a few drops of potassio-mercuric iodide so long as
a precipitate is produced. Only a small quantity of these reagents
will be required, as the greater part of the proteids has been already
coagulated by boiling. Filter if any precipitate has formed. The
filtrate is opalescent. Precipitate the glycogen from the filtrate (after
concentration on the water-bath if it exceeds a few c.c. in bulk) by
the addition of four or five times its volume of alcohol. Filter off
the precipitate, wash it on the filter with alcohol, and dissolve it in a
little water. To some of the solution add a drop or two of iodine ;
a reddish-brown (port v;ine) colour is produced, which disappears on
heating, returns on cooling, is removed by an alkali, restored by an
acid. Add saliva to some of the glycogen solution, and put in a
bath at 40° C. In a few minutes reducing sugar (maltose) will be
found in it by Trommer's test (p. 23).
Note that dextrin (erythrodextrin) gives the same colour with
iodine as glycogen does. Dextrin is also precipitated by alcohol,
but a greater proportion must be added to' cause complete precipita-
tion. Glycogen is completely precipitated by saturation with mag-
nesium sulphate or ammonium sulphate, while a pure solution of
erythrodextrin is not precipitated. Digest a solution of sugar- free
dextrin with saliva at 40' C. Reducing sugar is formed, but the
digestion is neither so rapid nor so complete as in the case of
glycogen.
{c) Cut another oyster into pieces, throw it into boiling water
acidulated with dilute acetic acid, and boil for a few minutes. Rub
up in a mortar with sand, boil again, and filter. Test a portion of
* Esbach's reagent is a solution of 10 grm. picric acid and 20 grni.
citric acid in a litre of water.
512 A MA NUA L OF I'll YSIOL OG Y
the filtrate with iodine for glycogen. Precipitate the rest with alcohol,
filter, dissolve the precipitate in water, and test again for glycogen.
(2) Deeply etherize a dog or rabbit five hours after a meal rich in
carbo-hydrates {e.g., rice and potatoes). Fasten it on a holder. Clip
off the hair over the abdomen in the middle line. Make a mesial
incision through the skin and abdominal wall from the ensiform car-
tilage to the pubis. The liver will now be rapidly cut out [by the
demonstrator] and divided into two portions, one of which will be
[distributed among the class and] treated as in {a) or {/>) ; the other
will be kept for an hour at a temperature of 40 C., and then sub-
jected to processes (a) or (/-'). Little, if any, sugar and much
glycogen will be found in the portion which was boiled imme-
diately after excision. Abundance of sugar will be found in the
portion ke[)t at 40' C ; it may or may not contain glycogen.
2. Glycosuria. — (i) Weigh a dog (female by preference) or rabbit.
Ciive morphia to the dog or chloral to the rabbit, as described on
pp. 176, 189. Fasten on a holder, and etherize. Insert a glass cannula
into the femoral or saphena vein of the dog, or into the jugular of
the rabbit (p. 177). Fill a large syringe with a 2 per cent, solution
of dextrose (glucose) in normal saline, connect it with the cannula
by means of an indiarubber tube, taking care that there are no air-
bubbles in the tube, and slowly inject as much of the solution as
xrill amount to ^ to 'I grm. sugar per kilo of body-weight. Tie the
vein, remove the cannula, and in half an hour evacuate the bladder
by passing a catheter (p. 429), by pressure on the abdomen, or, if
both of these methods fail, by tapping the bladder with a trocar
pushed through the linea alba (supra-pubic puncture). In an hour
again draw off the urine. Test both specimens for sugar.
In this experiment, the opportunity may also be taken to demon-
strate that egg-albumin, when injected into the blood, is excreted by
the kidneys, a filtered solution containing the albumin of one egg and
sugar in the quantity mentioned being injected.
The catheter may be inserted before the injection is begun, and
the bladder evacuated. After the injection the urine that drops
from the catheter may be collected in test-tubes, first every minute,
and then, as soon as sugar is found, every ten minutes. Determine
the interval between injection and the appearance of the first trace
of sugar and albumin. If a sufficient amount of urine is obtained,
the quantity of sugar in successive specimens may be estimated and
compared. The rate of flow of the urine as measured by the number
of drops falling from the catheter may also be estimated from time to
time, in order to determine whether diuresis is taking place.
(2) Phloridzin Diabetes. — Dissolve \ grm. of phloridzin in warm
water, and inject it subcutaneously into a rabbit. Obtain a sample
of the urine at the end of two hours, by pressure on the abdomen,
and test for sugar. If none is present, wait for another interval, and
again test the urine.
This experiment can also be performed without risk on man.
One grm. of phloridzin has been injected twice a day without dis-
turbing the individual. Much sugar is found in the urine, but it
I'RACTICM. EXERCISES 513
disappears the day after the administration of phloridzin is stopped.
The phloridzin may also be given by the mouth, but more is required,
and it is not very easily absorbed, and often causes diarrh<i,a
(v. Mcring).
(3) J'uniture Diabetes.'*' — Ani\;stheti/e a rabbit with ether, and
fasten it (belly down) on a holder. Put a pad or a rolled-up towel
under the neck so as to raise the back of the head Divide the skin
over the occipital protuberance down to the bone. Make a small
trephine hole just behind the protuberance. I'ush in through the
cerebellum a thin glass rod drawn out to not too sharp a point in the
blowpipe flame. Hold the rod so that it will bisect the line joining
the external openings of the two ears, and send it in till it is felt to
have met the basilar bone. Empty the bladder in an hour, and test for
sugar by Trommer's (p. 23) and the phenyl hydrazine test (p. 426).
(4) Aliiitentary Glycosuria. — The urine having been tested for
sugar for two successive days, and none being found, {a) a large
quantity of cane-sugar is to be taken in the form which is most
agreeable to the student. The urine of the ne.xt twenty-four hours
is to be collected and measured. A sample of it is then to be tested
for reducing sugar by Trommer'> and the phenyl hydrazine test. If
any sugar is found, the reducing power of a definite quantity of the
urine is to be determined by titration with Fehling's solution (p. 427)
(a) before and (/i) after boiling with hydrochloric acid (p. 382).
Or {b) a large meal of rice or arrowroot, sweetened with as much
dextrose as the observer can induce himself to swallow, is to be
taken, and the urine treated as in {a).
Or (r) a large number of sweet oranges may be eaten.
If experiments {a), {l>) and (c) are all unsuccessful, (a) and (b) may
be repeated on a dog.
3. Measurement of the Quantity of Heat given off in Respiration.
— This may be done approximately as follows : I'ut in the inner copper
vessel, A, of the respiration calorimeter (Fig. 137, p. 484) a measured
quantity of water sufficient to completely cover the series of brass
discs. Place A in the wider outer cylinder, the bottom of which it
is prevented from touching by pieces of cork. The outer cylinder
hinders loss of heat to the air. Suspend a thermometer in the water
through one of the holes in the lid. In the other hole place a glass
rod to serve as a stirrer. Read off the temperature of the water. Put
the glass tube connected with the apparatus in the mouth, and breathe
out through it as regularly and normally as possible, closing the
opening of the tube with the tongue after each expiration and
breathing in through the nose. Continue this for five to ten minutes,
taking care to stir the water frequently. Then read off the tem-
perature again. If W be the quantity of water in c.c, and / the
observed rise of temperature in degrees Centigrade, W/ equals the
quantity of heat, expressed in small calories (p. 479), given off by the
respiratory tract in the time of the experiment, on the assumptions
(i) that all the heat has been absorbed by the water. (2) that none
of it has been lost by radiation and conduction from the calorimeter
* This experiment is only suitable for advanced students.
33
5U
A MANTAL OF PHYSIOLOCY
to the surrounding air. Calculate the loss in twenty-four hours on
this basis ; then repeat the experiment, breathing us rapidly and
deeply as possible, so as to increase the amount of ventilation. The
quantity of heat given off will be found to be increased.*
In an experiment of short duration (2) is approximately fulfilled.
As to (1), it must be noted that in the first place the metal of the
calorimeter is heated as wl-11 as the water, and the water-equivalent of
the apparatus must be added to the weight of the water (p. 480). The
water (.-(juivalent is determined by puttinga definite weight of water at
air temperature T into the calorimeter, and then allowing a quantity
of hot water at known temperature T'to run into it, stirring well, and
noting the temperature of the water when it has ceased to rise. Call
this temperature T". Enough hot water should be added to raise
the temperature of the calorimeter about 2" C. The quantity run
in is obtained by weighing the calorimeter before and after the hot
water has been added. Suppose it is »i. Let the mass of the cold
water in the calorimeter at first be M, and let M' = the mass of water
which would be raised C C. in temperature by a quantity of heat
sufficient to increase the temperature of all the metal, etc., of the calori-
meter by 1° — in other words, the water-ecjuivalcnt of the calorimeter.
The mass >/i of hot water has lost heat to the amount of ///
(T' - T "), and this has gone to raise the
temperature of a mass of water M and metal
equivalent to a mass of water M' by (T" - T) de-
grees. . -. m (T' - T") = M(T" - T) + M'(T" - T).
Everything in this equation except M' is known,
and .'. M', the water-equivalent of the calori-
meter, can be deduced, and must be added
in all exact experiments to the mass of water
contained in it.
Secondly, all the excess of heat in the ex-
pired over that in the inspired air is not given
off to the calorimeter, for the air passes out
of it at a slightly higher temperature than that
of the atmosphere. At the beginning of the
experiment this excess of temperature is zero.
If at the end it is 1° C, the mean excess is
o"5° C. Now, when respiration is carried on
in a room at a temperature of 10° C, the expired air has its
temperature increased by nearly 30° C. About ,.\y of the heat given
off by the respiratory tract in raising the temperature of the air of
respiration would accordingly be lost in such an experiment. But
since the portion of the heat lost by the lungs which goes to heat the
expired air is only 1 of the whole heat lost in respiration (p. 483), the
error would only amount to ,.!g^of the whole, and this is negligible.
Thirdly, the air leaves the calorimeter saturated with watery vapour
at, say, io'5°, while the inspired air is not saturated for 10° C.
* The average heat-loss by the lunys for 5ijmen (calculated for the 24
hours) was 312,000 small calories for normal, 919,000 for the fastest, and
195,000 for the slowest breathing.
Fk;. 142. Hoi 11. K
ARKAiNGElJ KOK
Water-vai.ve.
PRACTICAL EXERCISES 515
Now, the cjuantity of heat rendered latent in the evaporation of water
sufficient to saturate a given cjuantiiy of air at 40^ C. (the expired air
is saturated for body temperature) is six times that required to saturate
the same quantity of air at 10°. If, then, the inspired air is half
saturated, the error under this head is ,'.. , or 8^ per cent. If the
inspired air is three-quarters saturated, the error is }^, or about
4 per cent. If the air is fully saturated before inspiration, as is the
case when it is drawn in through a water- valve (Fig. 142) by a tube
fixed in one nostril^ the only error is that due to the slight excess of
temperature of the air leaving the calorimeter over that of the inspired
air. The latent heat of the aqueous vapour in saturated air at lo's'' C.
is about .}j^ more than the latent heat of the aqueous vapour in
the same mass of saturated air at 10' C, or about ^\j^ of the latent
heat in saturated air at 40'. The error in this case would therefore
be under i per cent. The tubes must be wide and the bottle large.
4. Variations in the Quantity of Urea excreted, with Variations
in the Amount of Proteids in the Food. — The student should put
himself, or somebody else if he can, for two days on a diet poor in
pijoteids, then (after an interval of forty-eight hours on his ordinary
food) for two days on a diet rich in proteids. A suitable table of diets
will be supplied. The urine should be collected on the six days of the
period of experiment, on the day before it begins, and on the day after
it ends. Small samples of the mixed urine of the twenty-four hours
for each of these eight days should be brought to the laboratory, and
the quantity of urea determined by the hypobromite method. The
volume of the urine passed in each interval of twenty-four hours
being known, the total excretion of urea for the twenty-four hours
can be calculated, and a curve plotted to show how it varies during
the period of experiment.*
5. Thyroidectomy. — Study the anatomy of the neck and the rela-
tions and blood-supply of the thyroid glands in a dog used for some
previous experiment.
(i) Then select a half-grown dog, weigh it, inject morphia subcu-
taneously (p. 176), and fasten on the holder back down. Clip the hair
from the neck, and shave a wide space on each side of the middle
line. Scrub with soap and water, then with corrosive sublimate solu-
tion (o'l per cent). Sponges, instruments, ligatures, etc., must have
been boiled in water; the instruments are immersed in 5 per cent,
carbolic acid solution, everything else in the corrosive solution. The
hands and nails must be carefully cleansed and washed with the cor-
rosive sublimate. A longitudinal incision is made through the skin and
subcutaneous tissue in the middle line of the neck, beginning a little
below the projecting thyroid cartilage. By separating the longitudinal
muscles just external to the trachea on one side, the corresponding
thyroid lobe will be seen as an oval red body. It is now to be care-
* In 17 healthy students the average amount of urea excreted in twenty-
four hours on the ordinary diet was 29"5i grm. (minimum I9"35 grm.,
maximum 46-007 grm.) ; on a diet poor in proteid, average 2075 grm.
(minimum 95 17 grm., maximum 32857 grm.) ; on a diet rich in proteid,
average 38"83 grm. (minimum 23'265 grm., maximum 67'82 grm.).
33—2
5i6 .1 MAXi'AL OF P/IYS/OLOGY
fully freed from its attachments ; all vessels connected with it are to
be tied with double ligatures, and divided between the ligatures. In
tying the superior thyroid artery (a short large vessel coming off from
the carotid), care must be taken not to ])ut the ligatures too near its
origin, as the rapid current in the carotid may prevent closure of the
vessel by clot, and secondary ha.'morrhage may occur some days after
the operation. The thyroid lobe is thus shelled out of the tissues in
which it lies. If, as rarely happens, an isthmus is present (connecting
the two lobes across the front of the trachea), it must also be removed.
All bleeding having been stopped, the wound is washed out with
corrosive solution, and the muscles brought together over the trachea
by a row of interrupted sutures, which should not be drawn too
tight. The wound in the skin is then closed by a similar row,
preferably of subcutaneous sutures (see p. 190). Collodion is
painted over the wound, and the animal is returned to its cage. It
should be kept for a week, or, better, a fortnight, and examined care-
fully during that time. Probably, unless the wound has become
infected, its behaviour will be perfectly normal.
(2) The second part of the experiment, which consists in removing
the remaining thyroid lobe, is now to be performed just as in ( i ). The
animal must be examined next morning, and then twice a day for the
following week, as the symptoms of cachexia strumipriva generally
come on very rapidly in young dogs, and death may even ensue
within two days. Trembling of the limbs, associated with instability
of movement, spasms resembling those of tetany, sometimes passing
into general epileptiform convulsions, and progressive emaciation,
are the most marked symptoms. The animal nmst be weighed daily,
the temperature taken in the rectum, the thermometer being always
pushed in to the same distance ; and it will also be well to determine
the number of the red corpuscles in samples of the blood. To
obtain the samples punctures may be made in the gluteal region with
the point of a narrow-bladed knife or lancet, the skin having been
first shaved and thoroughly dried. The blood should flow freely
without pressure (p. 61). A record of the experiment from the
operation to the autopsy must be kept. At the autopsy search must
be made to see whether the thyroid was completely removed, and
whether any accessory thyroids exist. Such are occasionally found
in the form of small reddish masses, either in the neck or within the
chest in the neighbourhood of the aorta. If any are found, they
must be hardened in alcohol and sections made. Portions of the
muscles, spleen, and central nervous system are also to be preserved ;
and it is to be observed whether the pituitary body has undergone
any increase in size or other change (pp. 474, 475).
(k Thyroidectomy with Thyroid Feeding. — Some of the members
of the class should modify experiment 5 by feeding the animal, as
soon as symptoms have appeared, with fresh sheep's thyroid glands
or commercial thyroid extracts, and noting any alleviation of the
symptoms. If, as only rarely hajiiKns, they disappear, the animal is
to be allowed to live for a considerable time, then killed by chloro-
form, an autopsy made, and portions of the tissues hardened and
compared with those from experiments done as in 5.
CHAPTER IX.
MUSCLE.
It is impossible to understand the general physiology of muscle and
nerve without some acquaintance with electricity. It would be out
of place to give even a complete sketch of this preliminary but
essential knowledge here ; and the student is expressly warned that in
this book the elementary facts and principles of physics are assumed
to be part of his mental outfit. But in describing some of the
electrical apparatus most commonly used in the study of this portion
of our subject, it may be useful to recall the physical facts involved.
Batteries. — The Daniell cell is perhaps better suited for physio-
logical work than any other
voltaic element, although for
special purposes fjunsen, Grove,
Leclanche, and bichromate of
potassium batteries may be em-
ployed.
The Daniell is a two-fluid
cell. Saturated solution of sul-
phate of copper is contained in
an outer vessel, and a dilute
solution of sulphuric acid in a
porous pot standing in the
copper sulphate solution. The
latter is kept saturated by a few
crystals of copper sulphate. A
piece of sheet-copper, generally
bent so as to form a hollow
cylinder, dips into the sulphate of copper, and a piece of amalga-
mated zinc into the contents of the porous pot. Inside the cell the
current (the positive electricity) passes from zinc to copper ; outside,
from copper to zinc. The copper is called the positive, the zinc the
negative, pole. When the current is passed through a tissue, the
electrode by which it enters is termed the anode, and that by which
it leaves the tissue the kathode. The anode is, therefore, the elec-
trode connected with the copper of the Daniell's cell ; the kathode
is connected with the zinc.
Fir,. 143. — Daniell Cell.
A, outer vessel ; B, copper ; C, porous
pot ; D, zinc rod ; D is supposed to be
raised a little so as to be seen.
5i8 A MANUAL OF PlIYSfOLOGY
Potential— Current Strength— Resistance.— We do not know
what in reality electricity is, but we do know that when a current
flows along a wire energy is expended, just as energy is expended
when water Hows from a higher to a lower level. Many of the
phenomena of current electricity can, in fact, be illustrated by the laws
of How of an incompressible liquid. The difference of level, in virtue
of which the flow of liquid is maintained, corresjionds to the difference
of electrical level, ox potential, in virtue of which an electrical current
is kept up. The positive pole of a voltaic cell is at a higher potential
than the negative. When they are connected by a conductor, a flow
of electricity takes place, which, if the difference of level or potential
were not constantly restored, would soon e(]ualize it, and the current
would cease ; just as the flow of water from a reservoir would ulti-
mately stop if it was not replenished. If the reservoir was small, and
the discharging-pipe large, the flow would only last a short time ; but
if water was constantly being pumped up into it, the flow would go on
indefinitely. This is practically the case in the Daniell cell. Zinc is
constantly being dissolved, and the chemical energy which thus dis-
appears goes to maintain a constant difference of potential between
the poles. Electricity, so to speak, is continually running down from
the place of higher to the place of lower potential, but the cistern is
always kept full.
The difference of electrical [potential between two points is called
the electromotive force ; and from its analogy with difference of pressure
in a liquid, it is easy to understand that the intensity or strength of the
current^ that is, the rate of flow of the electricity lietwecn two points
of a conductor, does not depend upon the electromotive force alone,
any more than the rate of discharge of water from the end of a long
pipe depends alone on the diflerence of level between it and the
reservoir. In both cases the resistance to the flow must also be
taken account of With a given difference of level, more water will
pass per second through a wide than through a narrow pipe, for the
resistance due to friction is greater in the latter. In the case of
an electrical current, a wire connecting the two poles of a Daniell's
cell will rejjresent the pipe. A thick short wire has less resistance
than a thin long wire ; and for a given difference of potential, of
electric level, a stronger current will flow along the former. But for
a wire of given dimensions, the intensity of the current will vary with
the electromotive force. The relation between electromotive force,
strength of current, and resistance w-ere experimentally determined by
E
Ohm, and the formula C = , which expresses it, is called Ohm's Law.
It states that the current varies directly as the electromotive force,
and inversely as the resistance.
Although we do not know in what electrical resistance consists, it
may be defined as that property of a conductor in virtue of which a
flow of electricity cannot be kept up through it without the expendi-
ture of energy. In treating of the circulation of the blood, we have
already seen that the flow of a liquid along a tube involves the
expenditure of energy to overcome the friction of the liquid molecules
MUSCLE
5'9
on each other, and tliat this energy is transformed into heat (p. 72).
In Hke manner electrical energy is transformed into heat whenever a
current fiows along a wire. The heat [)roduced in a circuit in which
no external work is done is exactly eciual to the energy which has dis-
appeared in the transference of the electricity from the place of higher
to the place of lower potential ; just as the heat produced in the flow
of a liquid is equal to the difference in its total energy at the
beginning and end of the path. If C is the current strength, and E
the electromotive force, the energy represented by the transference of
electricity in time / is ECV, or (since E = CR by Ohm's Law), C'-R/";
and this represents the heat produced in the circuit when no work
is done.
For the measurement of electrical quantities a system of units is
necessary. The common unit of resistance is the oJuii, of current the
ampere, of electromotive force the volt. The electromotive force of a
Daniell's cell is about a \olt. An electromotive force of a volt,
acting through a resistance of an ohm, yields a current of one
ampere ; but the current produced by a Daniell's cell, with its poles
connected by a wire of r ohm resistance, would be less than an
ampere, because the internal resistance of the cell itself, that is, the
resistance of the liquids between the zinc and the copper, must be
added to the external resistance in order to get the total resistance,
which is the quantity represented by R in Ohm's Law.
Measurement of Resistance. — To find the resistance of a con-
ductor, we compare it with known resistances, as a grocer finds the
Fig. 144. — VVheatstone's
Bridge.
Fig. 145. — Diagram ui- Resistanci.
Box.
weight of a packet of tea by comparing it with known weights. The
Wheatstone's bridge method of measuring resistance depends on the
fact that if four resistances, AB, A I), BC, CD, are connected, as in
Fig. 143, with each other, and with a galvanometer G and a battery F,
AP RO
no current will flow through the galvanometer when -— = ^^.
For when no current passes through the galvanometer, B and D
are at the same potential. Let the fall of potential from C to B or
from C to I) be a ; then, since the total fall of potential from C to A
must be the same along either of the paths CBA or CDA, the fall from
B to A must be equal to that from D to A. Call this ft. Now, the
520
A MAXCAL or PHYSIOLOGY
fall of potential which takes place in any given portion of a circuit is
to the whole fall of potential in the circuit as the resistance of the
given portion is to the whole resistance. That is,
Similarly :
a _ BC
u + /i " BC + AB '
y8 ^ AB
a+^~BC+AB'
CD BC
CD
BC
AB'
AB
/i AD'
AB
Af)'°^\D
BC
CD'
In making the measurement, a resistance-box, containing a large
number of coils of wire of different resistances, is used (Fig. 145).
The resistances corresponding to AB and AD, called the arms of the
bridge, may be made equal, or may stand to each other in a ratio
i
Fig. 146. — Scheme ok Wiedemann's Galv.anometek (with telescope
KEADINr,).
T, telescope; S, scale; M, mirror; w, ring magnet suspended between the two
galvanometer coils G, the distance of which from m can be varied ; F, fibre suspending
mirror and magnet.
of I : 10, 1 : 100, etc. Then, the unknown resistance being CD,
BC is adjusted by taking plugs out of the bo.x till, on closing the
current, there is either no deflection, or the deflection is as small as
it is possible to make it with the given arrangement.
Galvanometer. — A galvanometer is an instrument us6d to detect a
current, to determine its direction, and to measure its intensity.
•Since, by Ohm's law, electromotive force, resistance, and current
strength are connected together, any one of them may be measured
by the galvanometer. A galvanometer of the kind ordinarily used in
physiology consists essentially of a small magnet suspended in the
axis of a coil of wire, and free 10 rotate under the influence of a
current passing through the coil. The most sensitive instruments
possess a small mirror, to which the magnet is rigidly attached. A
ray of light is allowed to fall on the mirror, from which it is reflected
on to a scale ; and the rotation of the mirror is magnified and
measured by the excursion of the spot of light on the scale. In
MUSCLE 521
the Thomson galvanometers the magnet is very light. A strip or
two of magnetized watch-spring does very well. The magnet is
' damped,' that is, its tendency, when once displaced, to go on
oscillating about its new position of equilibrium is overcome by
enclosing it in a narrow air space. In the Wiedemann instrument the
magnet is heavier (I'ig. 146). It swings in a chamber with copper
walls. Every movement of the magnet ' induces ' currents in the
copper ; these tend to oppose the movement, and so ' damping ' is
obtained. It is usual to read the deflections of the Wiedemann
galvanometer by means of a telescope. An inverted scale is placed
over the telescope at a distance of, say, a metre from the mirror ; an
upright image of the scale is formed in the telescope after reflection
from the mirror, and with every movement of the latter the scale
divisions appear to move correspondingly. The method of reading
by a telescope can be applied to any mirror galvanometer, and is
often extremely convenient in physiological work. Sometimes a
small scale is fastened on the mirror itself, and observed directly
through a low-power microscope.
A suspended magnet, if no other magnets are near, takes up a
definite position under the influence of the earth's magnetism ; its
long axis, in the position of rest, lies in a vertical plane, called the
plane of the magnetic meridian at the given place. The ' marked ' or
north pole points north, the south pole south. If the magnet is dis-
turbed from this position, it tends to return to it as soon as the dis-
turbing force ceases to act. If, for instance, the north pole is displaced
in an eastward direction, the earth's magnetism will produce a couple
(a pair of parallel forces acting in opposite directions), one member
of which may be considered to pull the north pole towards the west,
and the other to pull the south pole towards the east. Displacement
of the magnet, then, is opposed by this couple ; and where the dis-
placing force is small, that is, the current passing through the galva-
nometer weak, as is usually the case in physiological observations, it
becomes important to reduce the effect of the magnetism of the
earth, in other words, the strength of the magnetic field, as much as
possible. This can be done by bringing a magnet into the neigh-
bourhood of the galvanometer with its north pole pointing north.
This pole, which is the one attracted by the earth's north pole, is
magnetized in the opposite sense ; and by properly adjusting its
distance from the galvanometer magnet, the influence of the earth
on the latter can be almost neutralized, and the system made nearly
'astatic' In many galvanometers the magnets attached to the mirror
form an ' astatic ' pair (Fig. 147). Two small magnets of nearly equal
strength are connected to a light slip of horn or an aluminium wire,
with their poles in opposite directions. The earth's magnetism affects
them oppositely, so that the resultant action is nearly zero. It is not
possible to make the magnets exactly equal in strength, nor is it
desirable, for then the system would not tend to come to rest in
any definite position, and the zero point would be constantly shifting.
Either one or both magnets may be surrounded by the galvanometer
coils. If both are so surrounded, each must be within a separate
522
A .VANUAL OF PHYSIOLOGY
I47-— Astatic Pair
<ii-" Magneis.
Fig. 149.— Compensator.
Fig. 148. — DiAi.kAM ok Rhekccru
(aktek Di; Bois - Reymonu's
Model).
Description of Fig. 147. — SX and NS are the magnets, fixed to the vertical piece F.
M is a mirror. The arrow-heads show the direction of a current which deflects both
magnets in the same direction.
Description of Fig. 148. — I. to VII. are pieces of brass connected with the wires
a to/ in such a way that by taking out any of the brass plugs i to 5. a greater or less
resistance may be interposed l>etween the binding screws A and B.' The two wires a
are connected by a slider ., filled with mercury or otherwise making contact between
the wires. The current from the battery B' divides at A and B, part of it passing
through the rheocord, part through N, the nerve, muscle, or other conductor which
forms the alternative circuit. When a sufficient resistance R is interposed in the chief
circuit to make the total strength of the current independent of changes in the
resistance of the rheocord, the strength of the current passing through N will vary
inversely as the resistance of the rheocord. When all the plugs are in. and the slider
close up to A, there is practically no resistance in the rheocord, and all the current
passes across the brass pieces and plugs to B, and thence back to the battery. As j is
moved further away from A, the resistance of the rheocord is increased more and
more, and tlje intensity of the current passing through N becomes greater and greater.
The scale S shows the length of wire interposed for any position of j, and this gives a
rough measure of the fraction of the current passing through N. When plug i or 2 is
taken out. a resistance equal to that of the two wires c is interposed ; plug 3, twice thai
of a ; plug 4, five times ; plug 5, ten times.
Description of Fig. 149.— W is a wire stretched alongside a scale .S. A battery B is
connected to the binding screws at the ends of the wire. A pair of unpolarizable electrodes
are connected, one with a slider moving on a wire, the other through a galvanometer
with one of the terminal binding screws. In the figure a nerve is shown on the elec-
trodes, one of which is in contact with an uninjured portion, the other with an injured
part. The slider is moved until the twig of the compensating current just balances the
demarcation current of the nerve and the galvanometer shows no deflection.
MUSCLE
523
coil, and the current must pass in opposite directions in the two coils,
otherwise they would neutralize each other.
The deflection of a magnet by a current of given strength is pro-
portional to the number of turns of wire around it. Where an
increase in the number of turns does not sensibly cut down the
current, as in experiments on tissues like nerves, whose resistance is
large in comparison with that of the galvanometer, an instrument
with a great number of turns of wire, that is, a high-resistance
galvanometer, is suitable. The resistance of the galvanometers
generally used in electro-physiology varies from 3,000 or 4,000 ohms
up to five times as much.
A rheocord is an instrument by means of which a current may be
divided, and a definite portion of
sent through a tissue (Fig. 14S). ^^|^^|||^^^Hi^^^^HH
A compensator a ^^^^H^^^^^^^^^^H
rheocord from which a branch of ^^^^^n^^l^^^^^^^^l
led off, to balance ^^^^^K^^^P^^^^^^^I
compensate electrical dif- ^^^^^VRHB^^^^^^^I
ference in a tissue, like that which ^l^^^f^^^S^^B^^^I
gives rise to the current of rest of ll^fllyi^^VH^^^^^^H
a muscle, for example (Fig. 149). B^^^wj^^K^H^^^^^H
An electrometer is an instru- H^^^^^P^B^^H^^^B
ment for measuring electromotive ^^H^^^S^^^^^^^^BI
force, that is, differences of electric ^^^^^^^^H^^^^^^^H
potential. Lippmann's capillary
electrometer is being more and I""- 150.— Diagram ok a simple
more employed in physiology. A ^i;;';.'^^/'' Capillary Electro-
simple form can be conveniently „ ' ,, , „ ^ , ^ ,
J c -w » 1 L ■ B, parallel-Sided glass bottle containing
made as follows. A glass tube is sulphuric acid, S ; Hg, mercury in glass
drawn out to a Capillar\" at one tube, the capillary end of which projects
end and filled with mercury. The '"f° ^ ■ ^ ^- P'^tinum wires ; T. tube
... , . -' ,, hlled with mercury, and connecting the
tube IS mserted mtO a small capillary with a pressure bottle ; C, capil-
parallel- sided glass bottle, and lary magnified,
fastened in its neck with a plug
of sealing-wax. The bottle is partially filled with 10 to 20 per
cent, sulphuric acid, under which the capillary dips. By means of
a small pressure-bottle filled with mercury, and connected with the
glass tube, a little mercury is forced through the capillary so as to
expel the air in it. When the pressure is lowered again, sulphuric
acid is drawn up, and now lies in the capillary in contact with the
meniscus of the mercury. A platinum wire fused through the tube
dips into the mercury. Another, passing through the sealing-wax,
makes contact with the sulphuric acid through some mercury at the
bottom of the bottle. The bottle is fastened on the stage of a micro-
scope, the capillary brought into focus, and the meniscus adjusted
by raising or lowering the pressure-bottle. \N'hen the platinum wires
are connected with points at different potential, the mercury and
sulphuric acid receive charges at their surfaces of contact in the
capillary tube, by which the equilibrium previously existing between
the three surface-tensions (between mercury and glass, between
5=4
A MANUAL OF P/IVS/OLOGV
sulphuric acid and glass, between sulphuric acid and mercury) and
the hydrostatic pressure of the mercury is disturbed, and the
mercurial meniscus moves along the capillary. If the mercury is
connected with a surface at a higher potential than that in con-
nection with the sulphuric acid, the meniscus moves towards the
point of the capillary, and 7u'ce versd.
Induced Currents. — When a coil of wire in which a current is
flowing is i)r()ught up suddenly to another coil, a momentary current
is developed in the stationary coil in the opposite direction to that
in the moving coil. Similarly, if instead of one of the coils being
moved a current is sent through it, while the other coil remains at
rest in its neighbourhood, a transient oppositely-directed current is
It consists (i)of a small
table carrying a parallel-
sided glass vessel con-
taining mercury and sul-
phuric acid. (2) The
capillary tube, which can
be moved in two direc-
tions at right angles to
each other, and so ad-
justed in the field of the
microscope. (3) A pres-
sure-vessel, and a mano-
meter connected with it
for measuring the pres-
sure. (4) Two binding-
screws connected by wires
to the mercury in the
capillary tube and in the
parallel-sided vessel. The
iiinding-screws can be
short-circuited by closing
the friction-key shown at
the right side of the figure,
thus preventing any dif-
ference of electromotive
force between two points
connected with the screws
. ir y from affecting the electro-
ll [I ^' meter.
Fic. i5i.--C.\i'ii.i.ARY Elkctrometer (after Frev), as arranged for
.MOUNTING ON IHE MICROSCOPE SlAC.E.
/
set \i\) in the latter. When the current in the first coil is broken, a
current in the same direction is induced in the other coil.
Du Bois Raymond's Sledge Inductorium (I'ig. 152). — This consists
of two coils, the jjrimary and the secondary, the former having a
comparatively small number of turns of fairly thick copper wire, the
latter a large number of turns of thin wire. The object of this is
that the resistance of the j)rimary, which is connected with one or
more voltaic cells, may not cut down the current too much ; while
the currents induced in the secondary, having a high electromotive
force, can readily [lass through a high resistance, and are directly
proportional in intensity to the number of turns of the wire.
By means of various binding-screws and the electro-magnetic
interrupter, or Neef's hammer, shown in the figure and e.xplained
MUSCLE
525
below it, the current can be made once in the i)rimary or broken
once, or a constant alternation of make and break can be kept up.
We can thus get a single make or break shock in the secondary, or a
series of shocks, sometimes called an interrupted current. Such a
series of stimuli can also be got by making and breaking a voltaic
current at any given rate.
A ' self-induced ' current can also be obtained from a single coil ;
for instance, from the primary coil alone of the induction ai)paratus.
The reason of this is, that when a current begins to flow through any
turn of a coil of wire, it induces in all the other turns a current in the
opposite direction, and, when it ceases to flow, a current in the same
direction as itself. The former current, ' the make extra shock,'
being in the opposite direction to the inducing current, is retarded in
its development, and reaches its maximum more slowly than the break
extra shock. But, as we shall see, the suddenness with which an
Fig. 152.— Dr Bois-Revmond's Indlctorum.
B, primary, B', secondary, coil ; H, guides in which B' slides, with scale ; D, electro-
magnet ; E, vibrating spring ; /, wire connecting wire of D to end of primary ; v, screw
with platinum point, connected with other end of primary ; A, A', binding screws to
which are attaclied the wires from battery. A' is connected with the wire of the electro-
magnet D, and through it and / with the primary.
electrical change is brought about is one of the most important factors
in electrical stimulation, and therefore the break extra shock is a
much more powerful stimulus than the make. Owing to these self-
induced currents, the stimulating power of a voltaic stream may be
much increased by putting into the circuit a coil of wire of not too
great resistance.
The self-induction of the primary also aftects the stimulating power
of the currents induced in the secondary ; the shock induced in the
secondary by break of the primary current is a stronger stimulus
than that caused at make of the primary. The reason is, that with a
given distance of primary and secondary, and a given intensity of the
voltaic current in the primary, the abruptness with which the induced
current in the secondary is developed depends upon the rapidity
526 A MAXIAL OF I'lIYSIOLOGY
with which the primary current reaches its maximum at closing, or
its minimum (zero) at opening. Now, the make extra current retards
the development of the primary current, while in the opened circuit
of the primary coil the current intensity falls at once to zero.
The inequality between the make and break shocks of the
secondary coil can be greatly reduced by means of Helmholtz's wire.
Connect one pole of the battery with ?■ (Fig. 152), and the other
with A'. Join A and A' by a short, thick wire. With this arrange-
ment the primary icircuit is never opened, but the current is alter-
nately allowed to flow through the primary, and short-circuited
when the spring touches v. The ' make ' now corresponds to the
sudden increase of intensity of the current in the primary when the
short-circuit is removed, and the ' break ' to its sudden decrease
when the short-circuit is established. In both cases self-induced
currents are developed, and therefore both shocks are weakened.
But the opening stimulus is now slightly the weaker of the two,
Fig. 153.— Unpolarizabi.e Electrijdes.
A, hook-shaped; B, U -tubes ; C, straight. D, clay in contact with tissue; S,
saturated zinc sulphate solution ; Z, amalgamated zinc wire.
because the opening extra shock has to pass through a smaller
resistance (the short-circuit) than the closing extra shock (which
passes by the battery), and therefore opposes the decline of current
intensity on short-circuiting, more than the closing shock opposes
the increase of current intensity on long circuiting through the
primary.
By means of wires connected with the terminals of the secondary
coil, and leading to electrodes, a nerve or muscle may be stimulated ;
and it is usual to connect the wires to a short-circuiting key (Fig.
155), by opening which the induced current is thrown into the tissue
to be stimulated. For some purposes the electrodes may be of
platinum ; but all metals in contact with moist tissues become
polarized when currents pass through them, that is, have decom-
position products of the electrolysis of the tissues deposited on them.
And as any slight chemical difference, or even perhaps a difference
of physical state, between the two electrodes will cause them and the
tissues to form a battery evolving a continuous current, it is often
desirable to use uv.polarizable electrodes.
Unpolarizable Electrodes. — Some convenient forms of these are
represented in Fig. 153. A piece of amalgamated zinc wire dips into
MUSCLE 527
saturated zinc sulphate solution contained in the upper i)art of a glass
tube. The lower end of the tube may be straight, but drawn out so
as to terminate in a not very large opening, or it may be bent into a
hook, in the bend of which a hole is made. Hefore the tube is
filled with the zinc sul[)hate solution, the lower part of it is plugged
with china clay made up with normal saline. The clay just projects
through the opening, and thus comes in contact with the tissue.
When these electrodes are properly set up, there is very little polariza-
tion for several hours, but for long experiments, U-shaped tubes, filled
with saturated zinc sulphate solution, are better. The amalgamated
zinc dips into one limb, and a small glass tube filled with clay, on
which the tissue is laid, into the other.
Pohl's Commutator (Fig. 154) consists of a block of paraffin or
wood with six mercury cups, each in connection with a binding-screw
(not shown in the figure). Cups i and
6 and 2 and 5 are connected by copper
wires, which cross each other without
touching. The bridge consists of a
glass or vulcanite cross-piece «?, to
which are attached two wires bent into
semicircles, each connected with a
straight wire dipping into the cups 3
and 4 respectively. With the bridge
in the position shown in the figure, a
current coming in at 4 would pass out Kh;. 154.— Pohi/s Com-
by the wire connected with i, and back mltator.
again by that connected with 2, in the
direction shown by the arrows. When the bridge is rocked to the
other side so that the bent wires dip into 5 and 6, the direction of
the current is reversed. The cross-wires may be taken out altogether,
and the commutator used to send a current at will through either of
two circuits, one connected with i and 2, and the other with 5
and 6.
Du Bois-Reymond's Short-circuiting Key. — Acheao and convenient
form is shown in Fig. 155.
Time-Markers — iJlectric Signal. — It is of importance to know the
time relations of many physiological phenomena which are graphically
recorded ; for example, the contraction of a skeletal muscle or the
beat of a heart. For this purpose a tracing showing the speed of
the travelling-surface in a given time is often taken simultaneously
with the record of the movement under investigation. For a slowly-
moving surface it is sufficient to mark intervals of one or two seconds,
and this is very readily done by connecting an electro-magnetic
marker (such as the electric signal of Deprez) with a circuit which is
closed and broken by the seconds pendulum of an ordinary clock
(Fig. 156) or a metronome (Fig. 60, p. 170). For shorter intervals
a tuning-fork is used, which makes and breaks a circuit including an
electro-magnetic marker, or writes on the drum directly by means of
a writing-point attached to one of the prongs.
528
A MANUAL or I'llYSlOLOGY
In all the great functions of the body we find that muscular
movements play an essential part. The circulation and the
respiration, the two functions most immediately essential to
life, are kept up by the contraction and relaxation of muscles.
The movements of the digestive canal, the regulation of the
blood-supply to its glands and to all parts of the body, and
that immense class of movements which we call voluntary,
are all dependent upon muscular action, which, again, is
indebted for its initiation, continuance, or control, to
impulses passing along the nerves from the nerve-centres.
Fig. 155. — Du Bois-Reymond's Key.
150. — TlME-MAKKER.
Arrangement for marking 2 intervals.
D, seconds pendulum, with platinum
point E soldered on ; A, mercury trough,
into which K dips at end of its swing ;
B, Daniell cell ; C. electro-magnets,
which draw down writing-lever F when
the current is closed by E dipping into
A ; G, spring (or piece of indiarubber),
which raises 1-' as soon as current is
broken.
Hitherto we have not gone below the surface fact, that
muscular fibres have the power of contracting, either auto-
matically, or in response to suitable stimuli. In this chapter
and the two ne.xt we shall consider in detail the general
properties of muscle, nerve, and the other excitable tissues.
Lying deeper than the peculiarities of individual muscles,
muscular tissue has certain common properties, physical,
chemical, and physiological. The biceps muscle flexes the
arm upon the elbow, and the triceps extends it. The
external rectus rotates the eyeball outwards. The inter-
costal muscles elevate the ribs. The sphincter ani seals up
by a ring-like contraction the lower end of the alimentary
MUSCLE 529
canal. These actions are very different, but the muscles
that carry them out are at bottom very similar. And it
cannot be doubted that the functional differences are due
entirely, or almost entirely, to differences of anatomical
connection, on the one hand with bones and tendons, on
the other with the nerve-cells of the spinal cord and brain.
The common properties in which all the skeletal muscles
agree are the subject-matter of the general physiology of
striated muscle.
The cardiac muscle differs more, both in structure and in
function, from the skeletal muscles than these do among
themselves; the smooth muscle of the intestines and blood-
vessels still more. But every muscular fibre, striped or
unstriped, resembles every other muscular fibre more than
it does a nerve-fibre or a gland-cell or an epithelial scale.
The properties common to all muscle make up the general
physiology of muscular tissue.
A nerve-fibre is at first sight very different from a muscular
fibre. It has diverged more widely from the primitive type
of undifferentiated protoplasm. It has lost the power of
contraction, or contractility, but it retains, in common with
the muscle-fibre, susceptibility to stimulation, or excitability,
the capacity for growth, and to a limited extent the capacity
for reproduction. This inheritance of primitive properties,
retained alike by both tissues, is the basis of the general
physiology of muscle and nerve.
The electrical organ of the Torpedo or the Malapterurus
is intermediate in some respects between muscle and nerve,
and has properties common to both.
In the gland-cell the chemical powers of native proto-
plasm have been specialized and developed. Contractility
has been, in general, entirely lost ; but excitability remains.
The properties shared in common by muscle, nerve, electrical
organ, gland, and certain other structures, make up the
general physiology of the excitable tissues.
Amoeboid movement is the most primitive, the least elabo-
rated form of contraction.
An amoeba may be seen under the microscope to send out
pseudopodia, or processes, of its substance, and to retract
34
530 A MANUAL OF PHYSIOLOGY
them, and it is even able by such movements to chanj^e its
place. Stimulation with induction shocks causes the whole
of the processes to be drawn in. and the amceba to gather
itself into a ball. This illustrates a uni\ersal property of
protoplasm, excitability, or the power of responding to certain
external influences, or stimuli, by manifestations of the
peculiar kind which we distinguish as vital or physiological.
Certain of the white blood-corpuscles behave like the amoeba;
and we have already dwelt upon some of the important
functions fulfilled by such amoeboid movement in the higher
animals and in man. But a great distinction between this
kind of contraction and that of a muscular fibre is that it
takes place in any direction.
Cilia. — Cilia possess a higher and more specialized grade
of contractility. They are very widely distributed in the
animal kingdom ; and analogous structures are also found
in many low plants, such as the motile bacteria.
In the human subject ciliated epithelium usually consists
of several layers of cells, the most superficial of which are
pear-shaped, the broad end being next the surface and
covered with extremely fine processes, or cilia, about 8 /z in
length, which are planted on a clear band. It lines the
respiratory passages, the middle ear and Eustachian tube,
the Fallopian tubes, the uterus above the middle of the
cervix, the epididymis, where the cilia are extremely long,
and the central cavity of the brain and spinal cord.
Ciliary motion can be very readily studied by placing a
scraping from the palate of a frog, or a small portion of the
gill of a fresh-water mussel under the microscope in a drop
of normal saline solution. The motion of the cilia is at
first so rapid that it is impossible to make out much, except
that a stream of liquid, recognised by the solid particles
in it, is seen to be driven by them in a constant direction
along the ciliated edge, \\hen the motion has become
less quick, which it soon does if the tissue is deprived of
oxygen, it is seen to consist in a swift bending of the cilia
in the direction of the stream, followed by a slower recoil
to the original position, which is not at right angles to the
surface, but sloping streamwards. All the cilia on a tract
MUSCLE 531
of cells do not move at the same time ; the motion spreads
from cell to cell in a regular wave. The energy of ciliary
motion may be considerable, although far inferior to that
of muscular contraction. The work which cilia are capable
of performing can be calculated by removing the membrane,
fixing it on a plate of glass, cilia outwards, putting weights
on the glass plate, and allowing the cilia, like an immense
number of feet, to carry it up an inclined plane. Bowditch
found in this way that the cilia on a square centimetre of
mucous membrane did nearly 7 gramme-millimetres of work
per minute (equal to the raising of 7 grammes to a height of
a millimetre).
Since the cilia in the respiratory tract all lash upwards,
they must play an important part in carrying up foreign
particles taken in with the air, and the mucus in which they
are entangled, as well as pathological products. Engelmann
found that the energ}- of ciliary motion increases as the
temperature is raised up to about 40 C, after which it
diminishes quickly. Overheating causes cilia to come to
rest, but if the temperature has not been too high, and has
not acted too long, they recover on cooling.
Muscle. — Nearly all our knowledge of the physiology of
muscle has been gained either from striped skeletal muscle
or from the muscle of the heart, and chiefly from the former.
Of non-striped muscle we know comparatively little except
by inference, owing to the difficulty of obtaining it in suffi-
cient quantity and in suitable preparations for experiments.
In what follows we always refer to ordinar}^ skeletal muscle,
unless it is otherwise stated.
Physical Properties of Muscle— Elasticity. — All bodies may have
their shape or volume altered by the application of force. Some
require a large force, others a small force, to produce a sensible
amount of distortion. The elasticity of a body is the property in
virtue of which it tends to recover its original form or bulk when
these have been altered. Liquids and gases have only elasticity of
volume; solids have also elasticity of form. Most solids recover
perfectly, or almost perfectly, from a slight deformation. The limits
of distortion within which this occurs are called the limits of elasticity,
and they vary greatly for different substances. Living muscle has
very wide limits of elasticity ; it may be deformed — stretched, for
34—2
532 A MANUAL OF PIIYSIOLOCY
example — to a very considerable extent, and yet recover its original
length when the stretching force ceases to act.
The extensibility of a body is measured by the ratio of the increase
of length, {troduced by unit stretching force per unit of area of the
cross-section, to the original length of a uniform rod of the substance.
If e is the extensibility, «?= . .,, where / is the increase of length,
L the original length, s the cross-section, and K the stretching force.
The reciprocal of this, . , is called Young's modulus of elasticity,
or the co-efificient of elasticity. Suppose we wish to compare the ex-
tensibility of two substances. Let A and B be strips or rods of the
substances, the length of A being 500 mm., that of P. 1,000 mm. ;
the cross-section of A, 100 sq. mm., of }5, 200 sq. mm. Let the elon-
gation produced by a weight of i kilo be 10 mm. in each. Then the
extensibility of A is - — 2 : and that of B is = 2 ;
^ 500 X I ' 1,000 X I
that is, the substances are equally extensible.
Living muscle is very extensible ; a small force per unit area of
cross-section of a prism of it will produce a comparatively great
elongation. The extensibility, how-
ever, diminishes continually with the
elongation, so that equal increments
of stretching force produce always less
and less extension. If, for instance,
the sartorius or semi-membranosus of a
frog be connected with a lever writing
on a blackened surface, and weights
increasing by equal amounts be suc-
cessively attached to it, the recording
surface being allowed to move the same
FiG. i57.-CuKVi.:s of Exten- distance after the addition of each
siBiLiTv. weight, a series of vertical lines, re-
M, of muscle; .s, of an ordinary presenting the amount of each elonga-
inorganic solid. tion, will be traced. When the lower
ends of all the vertical lines are joined
by a smooth curve, it is found to be a hyperbola with the concavity
upwards (Fig. 157). This is a property common to living and dead
muscle and to other animal structures, such as arteries. Marey's
method, in which the weight is continuously increased from zero
and then continuously decreased to zero again by the flow of mercury
into and out of a vessel attached to the muscle, gives directly the
hyperbolic curve of extensibility.
The elongation of a steel rod or other inorganic solid is propor-
tional within limits to the extending force per unit of cross-section ;
and a curve plotted with the weights for abscissit; and the amounts
of elongation for ordinates would be a straight line. But this is not
a fundamental distinction between animal tissues, and the materials
of unorganized nature, as some writers seem to suppose. For when
the slow after-elongation which follows the first rapid increase in
MUSCLE 533
length in tlic loaded, excised muscle is waited for, the curve of
extensibility comes out a straight line (W'undt), and within limits
this is also the case for human muscles in the intact body. And
although a steel rod much more quickly reaches its maximum elon-
gation for a given weight when loaded, and its original length when
the weight is removed, than does a muscle, time is required in both
cases, and the difference is one of degree rather than of kind.
Dead muscle is less extensible and much less elastic than living.
In the state of contraction the extensibility is increased in frog's
muscle ; but Donders and Van Mansveldt have found that contrac-
tion causes little difference in the muscles of a living man, although
fatigue increases the extensibility. The great extensibility and
elasticity of muscle must play a considerable part in determining the
calibre of the vessels, and in lessening the shocks and strains which
the heart and the vascular system in general are called upon to bear,
and must contribute much to the smoothness with which the move-
ments of the skeleton are carried out, and immensely reduce the
risk of injury to the bones as well as to the muscles themselves, the
tendons and the other soft tissues. And not only is smoothness
gained, but economy also ; for a portion of the energy of a sudden
contraction, which, if the muscles were less extensible and elastic,
might be wasted as heat in the jarring of bone against bone at the
joints, is stored up in the stretched muscle and again given out in its
elastic recoil. The skeletal muscles, too, are even at rest kept
slightly on the stretch, braced up, as it were, and ready to act at a
moment's notice without taking in slack. This is shown by the fact
that a transverse wound in a muscle ' gapes,' the fibres being retracted,
in virtue of their elasticity, towards the fixed points of origin and
insertion.
If a muscle is so overweighted that it cannot contract, it elongates
slightly on stimulation (VVundt). This has by some been held to
indicate that the increase of extensibility associated with contraction
still occurs in the excited state when actual contraction is mechanically
prevented.
In the further study of muscle it is necessary first of all to consider
the means we have of calling forth a contraction — in other words, the
various kinds of stimuli.
Stimulation of Muscle. — A muscle may be excited or
stimulated either directly or through its motor nerve ; and
the stimulus may be electrical, mechanical, chemical, or
thermal. Electrical stimuli are by far the most commonly
used, and will be discussed in detail. A prick, a cut, or a
blow are examples of mechanical stimuli. A fairly strong
solution of common salt or a dilute solution of a mineral
acid will act as a chemical stimulus, which always tends to
cause, not a single contraction, but a tetanus. Sudden
cooling or heating acts as a stimulus for muscle, but thermal
534 ^ MANUAL OF PHYSIOLOGY
stimulation is somewhat uncertain. In all artificial stimula-
tion there is an element of sudden or abrupt change, of shock,
in other words ; but we cannot tell in what the * natural '
or ' physiological ' stimulus to muscular contraction in the
intact body really consists, nor how it differs from artificial
stimuli. All we know is that there must be a wide difference,
and that our methods of excitation must be very crude and
inexact imitations of the natural process.
Direct Excitability of Muscle. — The famous controversy on
the existence of ' independent muscular irritability' has long
been forgotten, and has no further interest except for the
antiquaries of science, if such exist. The direct excitability
of muscle in the modern sense is very different from the
question which occupied Haller and his contemporaries.
What the modern physiologists have been called upon to
decide is whether muscular fibres can be caused to contract
except by an excitation that reaches them through their
nerves. In this sense there can exist no doubt that muscle
is directly excitable, and the proofs are as follows :
(i) The ends of the frog's sartorius contain no nerves, the
apex of the frog's heart contains neither nerves nor nerve-
cells, yet both respond to direct stimulation. (2) Certain
chemical stimuli — ammonia, for instance — do not act on
nerve, but excite muscle. (3) When the motor nerves of
a limb are cut they degenerate, and after a certain time
stimulation of the nerve-trunk causes no muscular contrac-
tion, while the muscles, although atrophied, can be made
to contract by direct stimulation. (4) Finally, there is the
celebrated curara experiment of Claude Bernard, which is
described in a somewhat modified form in the Practical
Exercises, p. 593. A ligature is tied firmly round one thigh
of a frog, omitting the sciatic nerve; then curara is injected,
and in a short time the skeletal muscles are paralyzed.
That the seat of the paralysis is not the muscles themselves
is shown by their vigorous response to direct stimulation.
The ' block ' is not in the nerve-trunk, nor above it in
the central nervous system, for the ligatured leg is often
drawn up — that is, its muscles are contracted, although the
poison has circulated freely in the sacral plexus and the
MUSCLE 535
spinal cord, l-urther, if the nerve of the ligatured leg be
prepared as high up above the ligature as possible, where
the curara must undoubtedly have reached it (just above the
ligature the nerve has been isolated and the circulation in it
more or less interrupted), stimulation of it will cause con-
traction of the muscles of the limb ; while excitation of the
other sciatic is ineffective.
It can be also shown, by means of the negative variation
or current of action (p. 607), that a nerve-trunk on which
curara has acted remains excitable, and capable of conduct-
ing the nerve-impulse. The conclusion, therefore, is that
the curara paralyzes neither nerve-fibre nor muscular fibre,
Fic. 158.— Tonk: CoNTRAciioN OF Muscle during Passage of Constant
Current.
Two sartonus muscles of frog connected by pelvic attachments Current from 12
small Daniell cells in series passed through their whole length. Current closed at /«.
opened at b. Time trace, two-second mtervals.
but the link between the two which we call the nerve-
ending. In coming to this conclusion, the assumption is
made that the nerve-fibres within the muscle, since they are
anatomically similar to those in the nerve-trunk till near
their terminations, are similarly affected by curara. We
must carefully remember that the 'nerve-endings' which
are paralyzed by curara do not necessarily, nor even pro-
bably, coincide exactly with the ' nerve-endings ' of histology.
Still, it is significant that the histological differences between
the nerve-terminations in striped and smooth muscle should
correspond to a physiological difference in the action of
536
A MANUAL or PHYSIOLOGY
curara on them. This druj,' paralyzes the nerve-endings
in smooth muscle — the muscles of the bronchi, for instance
— with much j^^reater difficulty than those in ordinary skeletal
muscle, and the same is true of the vagus-endings in the
heart.
The action of curara gives us the means of stimulating
muscle directly : when electrical currents are sent through
a non-curarized muscle, there is in general a mixture of
direct and indirect stimulation, for the nerve-fibres within
the niuscle are also excited. Induced currents stimulate
nerve more readily
than muscle. Vol-
taic currents may
excite a muscle
whose nerves ha\'e
degenerated, while
induced currents
are entirely with-
out effect.
For direct
stimulation, a
curarized frog's
sartorius or semi-
,59. -ToNMc CoNTKAcnoN n-KiNG AND mcmbranosus is
Al' I ER r \x^\\ .
Curve from frog's gastrocnemius. At M constant generally USeu On
current closed, at R broken. Contracture continues after oppoiint nf thpir
opening of current. Time trace, two-second intervals. L Ul L
long parallel
fibres ; for indirect excitation, a muscle-nerve preparation,
composed of a frog's gastrocnemius with the sciatic nerve
attached to it, is commonl)- employed, as it is easy to isolate
the muscle without hurting its nerve.
Stimulation by the Voltaic Current. — While the current con-
tinues to pass through a nerve without any sudden or great
change in its intensity, there is no stimulation, and the
muscle connected with the nerve remains at rest. The
same is generally true of muscle when the current is passed
directly through it. But here the constancy of the rule is
far more frequently broken b\- exceptional results than in
nerve, especiall}- if the current is at all strong, when a state
MUSCLE 537
of fibres in which the ' fixinj^ ' reagent has caught a wave
of tetanus is very apt to show itself during the whole time
of flow (Wundt) (Fig. 158) ; and a similar condition, the
so-called '^alvanotonm, is normally seen in human muscles
when traversed by a stream of considerable intensity.
For nerve, and with these qualifications for muscle, too,
we may lay down the law that the voltaic current stiimilates
at make and at break, but not during its passage. Or, general-
izing this a little, since it has been shown that a sudden
increase or decrease in the strength of a current already
flowing also acts as a stimulus, we may say that the voltaic
current stimulates only ichen its intensity is suddenly and suffi-
ciently increased or diminished, but not while it remains constant.
A second law of great theoretical importance is that at
make the stimulation occurs only at the cathode; at break only
at the anode : and that the make is stronger than the break
contraction. This is true both for muscle and nerve, but it
is most directly and simply demonstrated on muscle. A
long parallel-fibred curarized muscle is supported about its
middle ; the two ends, which hang down, are connected
with levers writing on a revolving drum, and a current is
sent longitudinally through the muscle. It is not difficult
to see from the tracings that at make the lever attached to
the cathodic end moves first, and that the other lever only
moves when the contraction started at the cathode has
had time to reach it in its progress along the muscle.
Similarly^ at break the lever connected with the anodic end
moves first.
The Muscular Contraction. — When a muscle contracts, its
two points of attachment, or, if it be isolated, its two ends,
come nearer to each other ; and in exact proportion to this
shortening is the increase in the average cross-section. The
contraction is essentially a change of form, not a change of
volume. The most delicate observations fail to detect the
smallest alteration in bulk (Ewald). Living fibres kept
contracted by successive stimuli can be examined under the
microscope ; or fibres may be ' fixed ' by reagents like osmic
acid, and sometimes a very good opportunity of studying
the microscopic changes in contraction is given by a group
53« A MANUAL OF P//VS/OLOGV
of contraction, and, so to speak, pinned it down. It is
then seen that the process of contraction in the fibre is
a miniature of that in the anatomical muscle. The indi-
vidual fibres shorten and thicken, and the sum-total of this
shortening and thickening is the muscular contraction
which we see with the naked eye. The phenomena of the
muscular contraction may be classified thus: (i) Optical,
(2) Mechanical, (3) Thermal, (4) Chemical, (5) Sonorous,
(6) Electrical. (5) will be treated under 'Voluntary Con-
traction' ; (6) in Chapter XI.
(i) Optical Phenomena — Microscopic Structure of Striped
Muscle. — The structure of striped muscle has long Ijeen the enigma
of histology : and the labours of many distinguished men have not
sufficed to make it clear. On the contrary, as investigations have
multiplied, new theories, new interpretations of what is to be seen,
have multiplied in proportion, and a resolute brevity has become the
chief duty of a writer on elementary physiology in regard to the
whole question.
The muscle-fibre, the unit out of which the anatomical muscle is
built up, is surrounded by a structureless membrane, the sarcolemma.
The length and breadth of a fibre vary greatly in different situations.
The maximum length is about 4 cm. ; the breadth may be as much
as 70 ^ and as little as 10 /x. When we come to analyze the muscle-
fibre and to determine out of what units it is built up, the difficulty
begins. The fibre shows alternate dim and clear transverse stripes,
and can actually be split up into discs by certain reagents. It also
shows a longitudinal striation, and can be separated into fibrils.
Some have supposed that the discs are the real structural units
which, piled end to end, make up the fibre. The fibrils they con-
sider artificial. Others have held that the fibres are built up from
fibrils ranged side by side, and that the discs are artificial. The
most probable view is that the contents of the muscle-fibre consist
of two functionally different substances, a contractile substance, and
an interstitial, perhaps nutritive, non-contractile material of more
fluid nature. The contractile substance is arranged as longitudinal
fibrils embedded in interfibrillar matter (sarcoplasm).
According to Rutherford, each fibril is made up of a longitudinal
row of segments of two kinds alternating with each other : (i) ' Bow-
man's element,' shaped like an elongated hour-glass, and containing
a substance readily stained by various dyes; (2) an 'intermediate
segment ' of cylindrical shape, the general substance of which does
not readily stain. The intermediate segment contains in its centre a
globule (Dobie's globule), which is easily stained.* The fibrils are
* In the muscles of certain invertebrate animals, though not in those
of vertebrates, the intermediate segment contains, in addition to Uobie's
globule, two pear-shaped bodies (Flogel's elements), each of which
MUSCLE 539
regularly arranged in bundles within the fibre. The apposition of
Bowman's elements gives rise to the dim stripe ; the apposition of
the intermediate segments to the clear stripe ; the a[)position of the
Dobie's globules to a line in the middle of the clear
stripe (Dobie's line). Some have supposed that this line
is due to a membrane (Krause's membrane) stretching
across the fibre in the middle of each light disc, dividing
it into a number of compartments. Kiihne, however, was
fortunate enough to find one day a nematode worm in the
interior of a fibre. He followed its movements, and saw
it pass along the fibre with perfect freedom, ignoring
Krause's membrane ; so that if such a partition exists, it
must either be incomplete, or much more easily ruptured ^ic, i6o. —
than the sarcolemma. H u n d i, e
When a muscle contracts, the' intermediate segment <>!• Fibrils
first shortens, so that the ends of Bowman's elements come ^^ Newt s
close up to Dobie's globules. There is, apparently, no (Ruther-
lateral bulging of the intermediate segments while this kokd).
shortening is going on, so that the fluid in them must uncontracted
enter Bowman's elements. The Bowman's elements condition ; b,
begin to shorten a little later than the intermediate seg- ^g°,en"s?^ "/
ment. The easily-stainable substance in them passes to Dobie's line.
their ends, which swell and become dimmer, while their
shafts become clear. The result of these changes is that in the fully
contracted fibril the clear stripe occupies the middle of what was the
dim stripe in the uncontracted fibril, and the dim stripe of the con-
tracted fibril is made up of ' the swollen ends of Bowman's elements
with the Dobie's globules and other tissue elements of the inter-
mediate segments ' (Rutherford). This curious phenomenon is
known as the reversal of the stripes. Schiifer has described the
contractile elements of the muscle-fibre as fine columns (sarcostyles)
divided by septa, in the position of Krause's membrane, into segments
(sarcomeres). Each sarcomere contains a sarcous element with a
clear fluid at its ends, which produces the appearance of the light
tripes. During contraction, according to him, this fluid is squeezed
into fine longitudinal canals, which pierce the sarcous elements.
Schafer's muscle columns are units of greater transverse diameter
than the fibrils of Kolliker, Rutherford, etc. ; and Schafer considers
that the appearance of longitudinal fibrillation in his sarcous ele-
ments is due to the presence of these canals, and does not indicate
a truly fibrillar structure.
Some observers, using chloride of gold as a stain, have asserted
that an apparent network, brought out by that reagent, and which is
stated to be connected with the nuclei or muscle-corpuscles, is the
contractile part of the fibre. But this view has met with great
opposition ; and the substance stained by the gold appears to be only
interstitial material.
occupies an intermediate position between Dobies globule and the end
of the adjoining Bowman's element. Flogel's elements also stain well,
and are doubly refracting.
540
A MANUAL Of I'lIYSIOLOGY
Appearance of the Fibres in Polarized Light.— A ray of ordinary
light consists of vibrations of the ether in all planes at right angles
to the direction of the ray. In a ray of plane polari/ed light all the
particles vibrate in one plane. A ray of light which has been polarized
by a Nicol's prism cannot pass through another Nicol's prism with
its principal plane at right angles to that of the first. If the second
or analyzing prism be rotated so that the principal planes are no
longer at right angles, some of the light will pass through. The
same effect is produced if, without altering the original 'crossed'
position of the nicols, a substance capable of rotating the polarized
ray is introduced between the prisms. A rough illustration will
perhaps tend to make this point clearer. Suppose that a string fixed
at one end is set vibrating in various directions by a twisting move-
ment. If the string has to pass through a narrow vertical slit, e.g.,
between two fingers held vertically, all vibrations except those in the
vertical plane will be extinguished ; but vertical vibrations will be
able to i)ass beyond the slit. The movement may be said to be
plane polarized, and the effect of the slit corresponds to that of the
first nicol. Now make the string pass also through a horizontal slit ;
the vertical vibrations will then be extinguished too ; in other words,
none of the movements will pass beyond the 'crossed' slits. This
corresponds to the dark field of the crossed nicols. But if the vertical
vibrations which have passed the first slit could be in any way
changed into horizontal vibrations, they would no longer be extin-
guished by the second. This would correspond to rotation of the
plane of polarization through 90'. A ray of light polarized by the
first nicol will, if its plane of
polarization be rotated through
90°, pass entirely (except for
loss by ordinary reflection and
absorption) through the
second. If the angle of rota-
tion is less than 90 , a portion
, ^m ,«,:„,,, .«i.,!||i— ^^^^^^^^^^ ^'"'^^ P^^^ through.
''I'lilUWi The substance of the Bow-
Fig. 161. — LiviN 1.1 iiHKF. mans element, and particu-
(from Geotrupes stkrcorarius). larly the easily-stained material
I, in ordinary; 2, in polarized light. (Van i» 't, is doubly refracting, and
Gehuchten.) In living muscle (at least in therefore rotates the plane of
fibres ^vhich are not extended) in contrast to polarization. The same is true
dead muscle after treatment with reagents, ^^^ , ,-. t • • 111 u
the doubly refracting or anisotropous sub- O' the Dobie S globule, but
stance is present m the greater part of the the rest of the intermediate
fibre ; and with crossed nicols the position of eppmpnt ic ^infrlv rpfnrtine
the singly refracting or isotropous material is segment IS suigl) leiracting.
indicated only by narrow transverse black " hen an uncontracted fibre
lines or rows of dark dots. is viewed with crossed nicols,
the dim stripe accordingly ap-
pears bright in the otherwise dark field. In the contracted fibre
the stripe that is dim in ordinary light is bright when looked at with
crossed nicols, since the ends of the Bowman's elements, filled
with the doubly refractive stainable material, and the doubly re-
MUSCLE 541
fractive Dobie's globule are there approximated. The strijjc which
in the contracted fibre is the brighter of the two in ordinary
light is the dimmer of the two in the field of the crossed nicols,
although it is not absolutely dark, since the shafts of the Bowman's
elements cause some rotation of the plane of polarization even in the
absence of the stainable material (Rutherford).
Diffraction Spectrum of Muscle. — When a beam of white light
passes through a striped muscle, it is broken up into its constituent
colours, and a series of diffraction spectra are produced, just as
happens when the light passes through a diffraction grating (a piece
of glass on which are ruled a number of fine parallel equidistant
lines). The nearer the lines are to each other, the greater is the dis-
placement of a ray of light of any given wave-length. It has accord-
ingly been found that when a muscular fibre contracts, the amount
of displacement of the dift'raction spectra increases. At the same
time the whole fibre becomes more transparent.
(2) Mechanical Phenomena, — The muscular contraction may
be graphically recorded by connecting a muscle with a lever
which is moved either by its shortening or by its thickening.
The lever writes on a blackened surface, which must travel
at a uniform rate if the form and time-relations of the
muscle-curve are to be studied, but may be at rest if only
the height of the contraction is to be recorded. The whole
arrangement for taking a muscle- tracing is called a myograph
(Fig. 184). The duration of a ' twitch ' or single contraction
(including the relaxation) of a frog's muscle is usually given
as about one-tenth of a second, but it may vary considerably
with temperature, fatigue, and other circumstances. It is
measured by the vibrations of a tuning-fork written imme-
diately below or above the muscle curve. When the muscle
is only slightly weighted, it but very gradually reaches its
original length after contraction, a period of rapid relaxation
being followed by a period of ' residual contraction,' during
which the descent of the lever towards the base line becomes
slower and slower, or stops altogether some distance
above it.
Latent Period. — If the time of stimulation is marked on
the tracing, it is found that the contraction does not begin
simultaneously with it, but only after a certain interval,
which is called the latent period.
This can be measured by means of the pendulum myo-
graph or the spring myograph, in both of which the carrier
542
I .UA.YL'A/. OFI'I I Y BIOLOGY
of the recording plate opens, at a dehnite point in its
passage, a key in the primary coil of an induction machine,
and so causes a shock to be sent through the muscle or
nerve, which is connected with the secondary. The precise
point at which the stimulus is thrown in can be marked
on the tracing by carefully bringing the plate to the position
m which the key is just opened, and allowing the lever to
trace here a vertical line (or, rather, an arc of a circle). The
portion of the time-tracing between this line and^a parallel
P'k;. 162.— Spring MvoGKArn.
A, B, iron uprights, between which are stretched the guide-wires on which the
travelhng plate a runs ; k, pieces of cork on the guides to gradually check the plate at
the end of its excursion, and prevent jarring ; b, spring, the rele;ise of which shoots the
plate along ; //, trigger key, which is opened by the pin d on the frame of the plate.
line drawn through the point at which the contraction
begins gives the latent period.
Helmholtz measured the length of the latent period by
means of the principle of Pouillet, that the deflection of a
magnet by a current of given strength and of very short
duration is proportional to the time during which the current
acts on the magnet. He arranged that at the moment of
stimulation of the muscle a current should be sent through
a galvanometer, and should be broken by the contraction of
the muscle the moment it began. In this wa)- he obtained
MUSCLE
543
the value of ^\^ second for the latent period of frog's
muscle. The tendency of later observations has been to
make the latent period shorter. Burdon Sanderson finds
TG
Fig. 163. — Pendulum Mvograi'H.
At the left as seen from the side, at the right as seen from the front. A, bearings
on which the pendulum swings ; P, pendulum ; G, G', glass plates carried in the
frames T, T , ; a, pin which opens the trigger-key. The key, when closed, is in
contact with c, and so completes the circuit of the primary coil.
that the change of form probably begins in muscle with
direct stimulation in tthto second after, and the electrical
change (p. 607) simultaneously with, the excitation. It is
5-14
A MA NUA L OF 1 '// YS/OLOG Y
known that the apparent latent period depends upon the re-
sistance which the muscle has to overcome in beginning its
contraction. A heavily-weighted muscle, for instance, can-
not begin to shorten until as much energy has been developed
as is necessary to raise the weight ; and its latent period
will be distinctly longer than that of unweighted or very
slightly weighted muscles, such as those with which Sander-
son worked.
The maximum shortening, or ' height of the lift,' depends
upon the length of the muscle, the direction of the fibres,
the strength of the stimulus, the excitability of the tissue,
and the load it has to raise.
In a long muscle, other things being equal, the absolute
shortening, and therefore the maximum height of the curve,
will be greater than in a short muscle ; in a muscle with
Fig. 164. — CuKVF. of a Single Muscular Con ikac iion or Twrrcii taken
ON Smoked Glass with Spring Myograi'h and photographed.
Vertical line A marks the point at which the muscle was stimulated ; time-traciny;
shows 1,75 of a section (reduced).
fibres parallel to its length — the sartorius, for instance —
it will be greater than in a muscle like the gastrocnemius,
with the fibres directed at various angles to the long axis.
For stimuli less than maximal, the absolute contraction
increases with the strength of stimulation, and a given
stimulus will cause a greater contraction in a muscle with
a given excitability than in a muscle which is less excitable.
Finally, increase of the load per unit of cross-section of the
muscle diminishes above a certain limit the 'height of the
lift,' although below that limit it may increase it.
Influences which aflfect the Time-relations of the Muscular
Contraction. — Many circumstances afl'ect the form of the
muscle-curve and its time-relations.
{a) Influence of the Load. — The first effect of contraction
is to suddenly stretch the muscle, and the more the muscle
MUSCLE
545
is loaded the greater will this elongation be. So that at the
beginning of the actual shortening part of the energy of
contraction is already expended without visible effect, and
has to be recovered from the elastic reaction during the
ascent of the lever.
Then the inertia of the lever itself and of its load comes
into play, and may carry the curve too high during the
up-stroke and too low during the down-stroke. This can
be minimized by making the lever very light, and attaching
the weight close to the fulcrum, so that it has only a small
range of movement, and never acquires more than a small
velocity. The contraction of a muscle loaded by a weight
which is not increased or diminished during the contraction
is said to be iso-tonic, for here the tension of the muscle
Fig. 165. — Influence of Load on the Form of the Muscle Curve.
I, curve taken with unloaded lever ; 2, 3, 4, weight successively increased ;
5, abscissa line ; time-trace yS^ sec. (reduced).
is the same throughout, and its length alters. When the
muscle is attached very near the fulcrum of the lever, so
that it acts upon a short arm, while the long arm carrying
the writing-point is prevented from moving much by a
spring, the muscle can only shorten itself very slightly ; but
the changes of tension in it will be related to those in the
spring, and therefore to the curve traced by the writing-
point. Such a curve is called iso-metric, since the length of
the muscle remains almost unaltered.
The maximum of the iso-metric curve (the maximum tension with
practically constant length) is sooner reached than that of the iso-
tonic (the maximum contraction with constant tension). From this
it has been concluded that during contraction the co efficient of
elasticity of the muscle continuously diminishes (Fick), or, what
comes to the same thing, its extensibility continuously increases.
35
546
A MANUAL OF PHYSIOLOGY
The work done by a muscle in raising a weight is equal to the
product of the weight l)y the height to which it is raised. Beginning
with no load at all, it is found that the weight can be increased up to
a certain limit without diminishing the height of the contraction ;
perhaps the height may even increase. Up to this limit, then, the
work evidently increases with the load. If the weight is made still
greater, the contraction becomes less and less, but up to another
limit the increase of weight more than compensates for the diminu-
tion of ' lift,' and the work still increases. Beyond this, further
increase of weight can no longer make up for the lessening of the
lift, and the work tails off till ultimately the muscle is unable to raise
the weight at all.
j\/\,\W\A/\AMAfW\AA/\/\AW\MW\/\/\/^^
Fig. i66. — Influence of Temperature on the Muscle Curve.
2, air temperature ; i, 25" — 30° C. ; 3, 7° — 10'^ C ; 4, ice in contact with muscle.
The 5th curve was taken at a little above air temperature.
The manner of application of the weight has an influence on the
work done by the muscle. If it is applied before the contraction
begins, so that the muscle is already stretched at the moment of
stimulation, a cause of error and uncertainty is introduced ; for it is
known that mere stretching of muscle affects its metabolism, and
therefore its functional power. So that it is usual in experiments of
this kind to after-load the muscle — that is, to support the lever and
its load in such a way that the weight does not come upon the
muscle till contraction has just begun. The ' absolute contractile
force ' of an active muscle may be measured on this principle by
determining the weight which, brought to bear upon the muscle at
the instant of contraction, is just able to prevent shortening without
MUSCLE
547
stretching the muscle. It, of course,
depends, among other things, on the
cross-section of the muscle. During
the contraction the absolute force di-
minishes continually, so that a smaller
and smaller weight is sufficient to stop
any further contraction, the more the
muscle has already shortened before it
is applied. At the maximum of the
contraction the absolute force is zero.
Hence a muscle works under the most
favourable conditions when the weight
decreases as it is raised, and this is the
case with many of the muscles of the
body. During flexure of the forearm
on the elbow, with the upper arm
horizontal, a weight in the hand is felt
less and less as it is raised, since its
moment, which is proportional to its dis-
tance from a vertical line drawn through
the lower end of the humerus, continu-
ally diminishes.
(b) Influence of Temperature on
the Muscular Contraction. — Increase
of temperature of the muscle up
to a certain limit diminishes the
latent period and the length of the
curve, and increases the height of
the contraction, but beyond this
limit the contractions are lessened
in height. Marked diminution of
temperature causes, in general, an
increase in the latent period and
length, and a decrease in the
height of the contraction. It is
evident that much depends upon
the normal temperature which we
start from, and moderate cooling
may increase the height of the
curve. In the heart the effect of
cold in strengthening the beat is
often very marked.
(c) Influence of Previous Stimulati
Fig. 167. — FAiKiUE Curve of
Muscle (Frog's Gastro-
cnemius).
Below is Ghown the armngement
with which the curve figured was
obtained. A, femur with gastro-
cnemius atiacheH, supported in
clamp ; C, metal hook with fine
wire attached to lever F. The wire
is continued along the lever and
connected with a sewing-needle,
the point of which just dips into
the mercury cup D. .A w ire from
one pole of the Daniell cell E dips
permanently into the mercury ; the
wire B from the other pole is
attached to the upper end of the
muscle or the clamp. Or a wire
on the lever may be made to close
and open the primary circuit of an
inductorium, the muscle or nerve
being connected with the secon-
dary. Every time the needle
touches the mercury the muscle is
stimulated automatically.
on. — If a muscle is stimu-
35—2
548
A MANUAL OF PHYSIOLOGY
lated by a series of equal shocks thrown in at regular
intervals, and the contractions recorded, it is seen that
at first each curve overtops its
predecessor by a small amount.
This phenomenon, which is
regularly seen in fresh skeletal
muscle, although it was at one
time supposed to be peculiarly
a property of the muscle of the
heart, is called the ' staircase,*
and seems to indicate that
within limits the muscle is
benefited by contraction and
its excitability increased for a
Fig. i68.-'Staik. a.i.:' in Skki.e- "^w stimulus. Soon, however,
TAL Muscle (Frog). in an isolated preparation, the
^Stimulation by arrangement shown in contractions begin tO decline
in height, till the muscle is at
length utterly exhausted, and reacts no longer to even the
strongest stimulation.
A conspicuous feature of the contraction-curves of fatigued
muscle is the progressive lengthening, which is much more
Fig. 169. — 'Staircase' in Cardiac Muscle.
Contractions recorded on a much more quickly moving drum than in V\g. 168. The
contractions were caused by stimulating a heart reduced to standstill by the first
Stannius' ligature (p. 175). The contractions gradually increase in height.
marked in the descending than in the ascending period ;
in other words, relaxation becomes more and more
difficult and imperfect. It is by no means so easy to fatigue
a muscle still in connection with the circulation as an
isolated muscle. But even the latter, if left to itself, will to
MUSCLE
549
some extent recover, and be again able to contract, although
exhaustion is now more readily induced than at first.
What is the cause of muscular fatigue ? An exact answer
is not possible in the present state of our knowledge, but
we may fairly conclude that in an isolated preparation it is
twofold : (i) The material necessary for contraction breaks
down more quickly than it can be reproduced or brought
to the place where it is required ; (2) waste products are
Fig. 170. —Fatigue Curve of Skeletal Muscle
(Gastrocnemius of frog, indirect stimulation), taken with arrangement shown in
Fig. 184. Time-tracing, xJa of a second.
formed by the active muscle faster than they can be removed.
That even an isolated muscle has a certain store of the
material needed for contraction which cannot be all exhausted
at once, or which can to a certain extent be replenished by
processes going on in the muscle, is shown by the beneficial
effect of mere rest. That the accumulation of fatigue
products has something to do with the exhaustion is shown
by the fact that the muscles of a frog, exhausted in spite of
the continuance of the circulation, can be restored by bleed-
550 A MANUAL OF PIIYSIOLOHY
ing the animal, or washing out the vessels with normal saline
solution, while injection of a watery extract of exhausted
muscle into the bloodvessels of a curarized muscle renders it
less excitable (Ranke). This observer supposed that it was
specially the removal of the acid products of contraction
(sarcolactic acid and acid potassium phosphate) which
restored the muscle. Injection of arterial blood, or even
of an oxidizing agent like potassium permanganate, into
the vessels of an exhausted muscle also causes restoration
(Kronecker).
When a fatigued muscle responds no longer to indirect
stimulation, it can still be directly excited. The seat of
exhaustion must therefore be either the nerve-trunk or the
nerve-endings. It is not the nerve-trunk which is first
fatigued, for this still shows the negative variation on being
excited. And if the two sciatic nerves of a frog or rabbit
be stimulated continuously with interrupted currents of
equal strength, while the excitation is prevented from reach-
ing the muscles of one limb till those of the other cease to
contract, it will be found that when the 'block' is removed
the corresponding muscles contract vigorously on stimulation
of their nerve. The passage of a constant current through
a portion of the nerve or the application of ether between
I he point of stimulation and the muscles may be used to
]irevent the excitation from passing down (p. 596).
The possible seats of fatigue caused by voluntary muscular
contraction are (i) the muscle, (2) the nerve-endings, (3) the
nerve-trunk, and (4) the central nervous system. Actual
experiments (Mosso and Alaggiora, Lombard — p. 597) have
shown that fatigue after voluntary effort is chiefly central,
and not in the muscles and nerves themselves. Electrical
stimulation, either of a 'tired' muscle or of its nerve, is
readily responded to at a time when voluntary contraction
is impossible,
{d) The Influence of Dnii^^s on the Contraction of Muscle. —
The total work which a muscle can perform, its excitability
and the absolute force of the contraction, may all be altered
either in the plus or the minus sense by drugs. But in
connection with our present subject those drugs which con-
MUSCLE 551
spicuousl}' alter the form and time-relations of the muscle-
curve have most interest. Of these vcratria is especially
important. When a small quantity of this substance is
injected below the skin of a frog, spasms of the voluntary
muscles, well marked in the limbs, come on in a few minutes.
These are attended with great stiffness of movement, for
while the animal can contract the extensor muscles of its
legs so as to make a spring, they relax very slowly, and
some time elapses before it can spring again. If it be killed
before the reflexes are completely gone, the peculiar altera-
tions in the form of the muscle-curve caused by veratria
will be most marked. The poisoned muscle, stimulated
directly or through
its nerve, con-
tracts as rapidly as
a normal muscle,
while the height
of the curve is as
great, or even yw,. izi.-ViiRAiRiA Curve.
greater, but the Frog's gastrocnemius.
relaxation is enor-
mously prolonged (Fig. 171). This effect seems to be to a
considerable degree dependent on temperature, and it ma)^
temporarily disappear when the muscle is made to contract
several times without pause. Barium salts, and in a less
degree those of strontium and calcium, have an action on
muscle similar to that of veratria (p. 598).
ie) The individuality of the muscle itself has an influence
on the muscle-curve. Not only do the muscles of different
animals vary in the rapidity of contraction, but there are
also differences in the skeletal muscles of the same animal.
In the rabbit there are two kinds of striped muscle, the red
and the pale (the semitendinosus is a red, and the adductor
magnus a pale muscle), and the contraction of the former
is markedly slower than that of the latter.
In many fishes and birds, and in some insects, a similar
difference of colour and structure is present, although a
physiological distinction has not here been worked out.
Even where there is no distinct histological difference,
552 A MA XL' A L OF PH YSIOL OGY
there may be great variations in the len^'th of contraction.
In the frog, for instance, the hyoglossus muscle contracts
much more slowly than the gastrocnemius. The wave of
contraction, which in frogs' striped muscle lasts only about
■07 second at any point, may last a second in the forceps
muscle of the crayfish, though only half as long in the
muscles of the tail. In the muscles of the tortoise the con-
traction is also very slow. The muscles of the arm of man
contract more quickly than those of the leg.
Summation of Stimuli and Superposition of Contractions. —
Hitherto we have considered a single muscular contraction
as arising from a single
stimulus, and we have
assumed that the muscle
has completed its curve
and come back to its
original length before the
next stimulus was thrown
in. We have now to in-
FiG. 172.— .Superposition ok Contrac- quire what happens when
^^°^^" a second stimulus acts
I is the curve when only one stimulus is , 1 j •
thrown in ; 2, when a second stimulus acts Upon the muSCle durmg
hsm.Vi'rlllfm'teTght"'''" ' ^^^ °'^"^ "^^""^^^ the Contraction caused by
a first stimulus, or during
the latent period before the contraction has actually begun ;
and what happens when a whole series of rapidly-succeeding
stimuli are thrown into the muscle.
First let us take two stimuli separated by a smaller
interval than the latent period (p. 541). If they are both
maximal {i.e., if each by itself would produce the greatest
amount of contraction of which the muscle is capable when
e.xcited by a single stimulus), the second has no effect what-
ever, the contraction is precisely the same as if it had never
acted. But if they are less than maximal, the contraction,
although it is a single contraction, is greater than would
have been due to the first stimulus alone ; in other words,
the stimuli have been summed or added to each other during
the latent period so as to produce a single result.
Next let us consider the case of two stimuli separated by
MUSCLE 553
a greater interval than the latent period, so that the second
falls into the muscle during the contraction produced by the
first. The result here is very different : traces of two con-
tractions appear upon the muscle-curve, the second curve
being that which the second stimulus would have caused
alone, but rising from the point which the first had reached
at the moment of the second shock (I'^ig. 172). Although
the first curve is cut short in this manner, the total height
of the contraction is greater than it would have been had
only the first stimulus acted ; and this is true even when
both stimuli are maximal. Under favourable circumstances,
when the second curve rises from the apex of the first, the
l-'n;. 173. — Tetanl's.
I, 5 stimuli per second ; 2, ijpersecond ; 3, 15 per second, when muscle was more
exhausted than in 2.
total height may be twice as great as that of the contraction
which one stimulus would have caused (p. 599).
Not only may we have superposition or fusion of two
contractions, but of an indefinite number ; and a series
of rapidly following stimuli causes complete tetanus of the
muscle, which remains contracted during the stimulation, or
till it is exhausted (Fig. 173).
The meaning of a complete tetanus is readily grasped if,
beginning with a series of shocks of such rapidity that the
muscle can just completely relax in the intervals between
successive stimuli, we gradually increase the frequency
(p. 600). As this is done, the ripples on the curve become
smaller and smaller, and at last fade out altogether. The
554 A MANUAL OF PHYSIOLOGY
maximum height of the contraction is greater than that pro-
duced by the strongest single stimulus ; and even after com-
plete fusion has been attained, a further increase of the
frequency of stimulation may cause the curve still to rise.
It is evident from what has been said that the frequency
of stimulation necessary for complete tetanus will depend
upon the rapidity with which the muscle relaxes ; and
everything which diminishes this rapidity will lessen the
necessary frequency of stimulation. A fatigued muscle may
be tetanized by a smaller number of stimuli per second
than a fresh muscle, and a cooled by a smaller number than
a heated muscle. The striped muscles of insects, which
can contract a million times in an hour, require 300 stimuli
per second for complete tetanus, those of birds 100, of man
40, the torpid muscles of the tortoise only 3. The pale
muscles of the rabbit need 20 to 40 excitations a second, the
red muscles only 10 to 20 ; the tail muscles of the crayfish
40, but the muscles of the claw only 6 in winter and 20 in
summer. The gastrocnemius of the frog requires 30 stimuli a
second, the h30glossus muscle only half that number (Richet).
We see, then, that there is a lower limit of frequency of stimula-
tion below which a given muscle cannot be completely tetanized, and
the question arises whether there is also an upper limit beyond which
a series of stimuli becomes too rapid to produce complete tetanus,
or, indeed, to cause contraction at all. We may be certain that every
stimulus requires a finite time to produce an effect, and it is possible
that if the duration of each shock were reduced below a certain
minimum, without lessening at the same time the interval between
successive excitations, no contraction would be caused by any or all
of the stimuli in the series. But above this minimum there appar-
ently lies a frequency of stimulation — at least, when the interval
between the stimuli is reduced exactly in the same proportion as the
duration — at which an interrupted current comes to act like a constant
current, causing a single twitch at its commencement or at its end,
but no contraction during its passage.
As to this last limit, on the fixing of which much labour has been
expended without any harmony of result, it undoubtedly does not
depend upon the frequency of stimulation alone ; the intensity of the
individual excitations, the temperature of the muscle, and probably
other factors, affect it. For Bernstein found that with moderate
strength of stimulus tetanus failed at about 250 per second, and was
replaced by an initial contraction ; with strong stimuli at more than
1,700 per second, tetanus could still be obtained. Kronecker and
Stirling, stimulating the muscle by a novel and ingenious method
MUSCLE 555
(by induced currents set uj) in a coil by the longitudinal vibrations of
a magnetized bar of iron), saw complete tetanus even at 24,000
stimuli a second ; while v. Kries in a cooled muscle found tetanus
replaced by the simple initial twitch at 100 stimuli per second,
although in a muscle at 38° C. stimulation of ten times this frequency
still caused tetanus. But it is doubtful whether the electrical method
of stimulation is capable of solving the problem, because of the
difficulty of being sure that the number of excitations is the same as
the nominal number of shocks, all the more that even very short
currents leave alterations of conductivity and excitability behind
them (Sewall), which we shall have to discuss in another chapter
<P- 574).
It is only while the actual shortening is taking place that
a tetanized muscle can do external work. But although
during the maintenance of the contraction no work is done,
energy is nevertheless being expended, for the metabolism of
a muscle during tetanus is greater than during rest. Among
other changes, the carbon dioxide given off is increased, and
lactic acid produced. And upon the whole a muscle is
more quickly exhausted by tetanus than by successive single
contractions, although there are great differences between
different muscles. For example, the muscles which close the
forceps of the crayfish or lobster have, as everyone knows,
the power of most obstinate contraction. Richet tetanized
one for over seventy minutes, and another for an hour and
a half, before exhaustion came on, while a tetanus of a
single minute exhausted the muscles of the crayfish's tail.
The gastrocnemius of a summer frog kept up for twelve
minutes, and a tortoise muscle for forty minutes.
Continuous stimulation is not always necessary for the
production of continuous contraction ; in some conditions
a single stimulus is sufficient. A blow with a hard instru-
ment may cause a dying or exhausted, and in thin persons
even a fairly normal, muscle to pass into long-continued
contraction. This so-called * idio-muscular ' contraction
seems to depend, in part at least, on the great intensity of
the stimulus.
The rate at which the wave of muscular contraction travels
ma}' be measured by stimulating the muscle at one end, and
recording, by means of levers, the movements of two points
of its surface as far apart from each other as possible.
556 .1 .U.LYUAL OF PIIYSIOLOGY
Time is marked on the tracing by means of a tuning-fork,
and the distance between the points at which the two
curves begin to rise from the base-Hne divided by the
time gives the velocity of the wave. Another method is
founded upon the measurement of the rate at which the
negative variation (p. 607) passes over the muscle, this being
the same as the velocity of the contraction-wave. In frog's
muscle it is about three metres a second, or six miles an hour.
Rise of temperature increases, fall of temperature lessens it.
When a muscle is excited through its nerve, the contrac-
tion springs up first of all about the middle of each mus-
cular fibre where the nerve-fibre enters it, and then sweeps
out in both directions towards the ends. But so long is the
wave, that all parts of the fibre are at the same time in-
volved in some phase or other of the contraction. And this
is the case even when the end of a long muscle like the
sartorius is artificially stimulated.
The wave of contraction in unstriped muscle lasts a
relatively long time at any given point, and in tubes like the
intestines and ureters, the walls of which are largely com-
posed of smooth muscle arranged in rings, the wave shows
itself as a gradually-advancing constriction travelling from
end to end of the organ. There is no evidence that the con-
traction of smooth muscular fibres is discontinuous — that is,
composed of summated contractions like a tetanus; it appears
to be a greatly-prolonged simple contraction of the kind
called 'tonic' An artificial stimulus, mechanical or elec-
trical, causes, after a long latent period, a very definitely-
localized contraction in a rabbit's ureter, which slowly
spreads in a peristaltic wave in one or both directions along
the muscular tube. Here, as in the cardiac muscle, the
excitation passes from fibre to fibre, while in striped skeletal
muscle only the fibres excited directly or through their
nerves seem to contract. That the rhythmical contraction
of the heart is not a tetanus has already been seen. It is
a simple contraction, intermediate in its duration and other
characters between the twitch of voluntary muscle and the
tonic contraction of smooth muscle. The contraction both
of unstriped and of cardiac muscle is lengthened and made
MUSCLE 557
stronger by distension of the viscera in whose walls they
occur, just as a skeletal muscle contracts more powerfully
against resistance.
Voluntary Contraction. — It is often stated that the volun-
tary contraction is a tetanus, but in favour of this belief
there is very little direct evidence. One of the strongest
buttresses of the theory of natural tetanus has been the
muscle-sound. Discovered about eighty years ago, first by
Wollaston and then by Erman, half a century passed away
before it was investigated more fully by Helmholtz. The
latter observer, confirming the results of his predecessors,
put down the pitch of the low rumbling sound heard when
the masseter contracts in closing the jaws at 36 to 40 vibra-
tions per second. He found, however, that little vibrating
reeds with a rate of oscillation of about ig"5 per second,
were more affected, when attached to muscle thrown into
voluntary contraction, than those that vibrated at a smaller
or a greater rate. He therefore concluded that the funda-
mental tone of the muscle corresponded to this frequency,
although, since such a low note is not easily appreciated, the
sound actually heard was really its octave or first harmonic
(p. 263). The objection has been brought forward that the
resonance tone of the ear also corresponds to a vibration
frequency of 36 to 40 a second. Now, if this resonance
tone were elicited by the muscular vibrations in sufficient
strength to overpower the proper note of the muscle, then,
whatever the rate of these vibrations might be, the resonance
tone would appear to be the sound produced by the muscle.
But while this renders it highly probable that the resonance
of the ear contributes to the production of the muscle-sound,
and shows that we cannot from the pitch of the muscle-
sound alone deduce the rate at which the muscle-sub-
stance is vibrating, it does not invalidate Helmholtz's objec-
tive observations with the oscillating reeds. And several
observers (Schafer, Horsley, v. Kries) have noticed periodic
oscillations, at the rate of 8 to 10 per second, in the curves
taken from voluntarily contracted muscles, and from muscles
excited through stimulation of the motor areas of the surface
of the brain. Since this rate remains the same whether
558 A .VAX UAL OF PHYSIOLOGY
the motor cortex, the corona radiata, or the spinal cord is
excited, and, unHke the rate of response to excitation of
peripheral nerves, is independent of the frecjuency of stimu-
lation, it has been supposed to represent the rhythm with
which impulses are discharged from the motor cells of the
cord (Fig. 174). Other observers have seen a rhythm of 20
per second ; while Haycraft denies that regular oscillations
occur at all, and thinks that irregularities in the contraction,
connected with a want of co-ordination of all the fibres, cause
the muscle-sound by drawing forth the resonance tone of the
ear itself. Loven, however, found the rhythm of strychnia
tetanus in the frog about S to 10 per second, and asserted
that by means of the capillary electrometer '^p. 524) an
Fig. 174. — Contractions caused by Sti.mulation ok thk Spinal Cord.
electrical oscillation of 8 per second could be demonstrated
in voluntarily contracted muscle. This last statement, if
confirmed, would be strong evidence for the discontinuity of
at least some voluntary contractions. But against it we
must put the fact that secondary tetanus (p. 621) is not
caused by muscle in voluntary contraction, except (and even
this is doubtful) just at the beginning. This, indeed, is not
incompatible with the existence of natural tetanus, since
chemical stimulation, which certainly sets up a state of con-
traction analogous to experimental tetanus, does not cause
secondary tetanus ; but we still lack a decisive proof that
voluntary contraction is maintained by a strictly intermittent
outflow of nervous energy, and not by a continuous outflow,
MUSCLE 559
which, it may be, remits and is reinforced at intervals. In
any case, some voluntary contractions, namely, the shortest
possible, do not seem to be tetanic. For a voluntary move-
ment can be executed in iV to ^V of 3- second, which, if we
take the greatest frequency of discharge in natural tetanus
that has been suggested, would allow time only for a single
oscillation, caused by a single impulse.
(3) Thermal Phenomena of the Muscular Contraction. — When
a muscle contracts its temperature rises ; the production of
heat in it is increased. This is most distinct when the
muscle is tetanized, but has also been proved for single con-
tractions. The change of temperature can be detected by
a delicate mercury or air thermometer ; and, indeed, a
thermometer thrust among the thigh-muscles of a dog may
rise as much as i' to 2" C. when the muscles are thrown
into tetanus. In the isolated muscles of cold-blooded animals
the increase of temperature is much less ; and electrical
methods, which are the most delicate at present known,
have generally been used for its detection and measurement.
They depend either upon the fundamental fact of thermo-elec-
tricity, that in a circuit composed of two metals a current is set up if
the junctions of the metals are at different temperatures ; or upon
the fact that the electrical resistance of a metallic conductor varies
with its temperature.
On the former principle the thermopile has been constructed
(Fig. 175), on the latter the bolometer, or '■electrical-resistance tlier-
moi7ieter. '
Where no very fine differences of temperature are to be measured,
a single thermo-junction of German silver and iron, or copper and iron,
is inserted into a muscle or between two muscles. But the electro-
motive force, and therefore the strength of the thermo-electric
current, is proportional for any given pair of metals to the number of
junctions, and for delicate measurements it may be necessary to use
several connected together in series. A thermopile of antimony-
bismuth junctions gives a stronger current for a given difference of
temperature than the same number of German silver-iron couples,
but from its brittle nature is otherwise less convenient.
The direction of the current in the circuit is such that it passes
through the heated junction from bismuth to antimony, and from
copper or German silver to iron. Knowing this direction, we are
aware of the changes of temperature which take place from the move-
ments of the mirror of the galvanometer with which the pile is con-
nected. The galvanometer must be of low resistance, since the
electromotive force of the thermo-electric currents is small, and a
high resistance would cut down their intensity too much.
560
A MANUAL OF PHYSIOLOGY
The muscle which is to be excited is brouji^ht into close
contact with one junction or set of junctions, the other set
being kept at constant temperature by immersing them in
water, or covering them with muscle that is not to be
stimulated. The image will now come to rest on the scale ;
and excitation of the muscle will cause a movement indicat-
ing an increase of temperature in it, the amount of which
can be calculated from the deflection.
In this way Helmholt/ observed a rise of temperature of
•14° to '18° C. in ex-
cised frogs' muscles
when tetanized for a
couple of minutes.
Heidenhain, with a
very delicate pile,
found a rise of 'ooi"
to '005° C. for a single
contraction of a frog's
muscle. On the as-
sumption that the pile
had time to take on
the temperature of the
muscle before there
was any appreciable
loss of heat, this would
be equal to the pro-
duction by every gramme of muscle of a thousandth to tive-
thousandths of a small calorie (p. 479) of heat. From Pick's
observations we may take about three-thousandths of a
small calorie as the maximum production of a gramme of
frog's muscle in a single contraction.
It is certain that when work is done by a muscle an equi-
valent amount is subtracted from its sum-total of energy,
and we might therefore expect that the heat produced in
contraction should diminish as the work increases. But
experiment does not fulfil this expectation. The manner
and the rate of its expenditure of energy depend upon the
conditions under which the muscle is placed. The mere
stretching of a muscle increases its metabolism, and there-
FiG. 175.
A, a single copper-iron thermo-electric couple ;
B, two pairs, one inserted into the tissue b, the
other dipping into water in a beaker a. The tem-
perature of the water may be adjusted so that the
galvanometer shows no deflection. The temperature
of the tissue is then the same as that of the water.
MUSCLE 561
fore its heat-production ; and a stretched muscle, when
caused to contract, produces more heat than if it had started
without tension, and still more heat when it is fixed so that
it cannot shorten during stimulation. This last fact does
not, however, prove that the heat-production is greater
when no work is done, because the tension increases during
excitation when contraction is prevented, and we know that
increase of tension alone causes more heat to be given out.
For example, more heat is produced by a muscle when it
contracts isometrically than when it contracts isotonically.
When a muscle, excited by maximal stimuli, is made to
lift continuously increasing weights, both the work done and
the heat given out increase up to a certain limit. The
muscle, as it were, burns the candle at both ends. This
would be of itself enough to show that there is no fixed
relation between the work and the heat-production; although
the latter reaches its maximum somewhat sooner than the
former.
We have already seen that when a muscle is cooled, or
fatigued, or poisoned with veratria or with suprarenal extract,
the stress of the change falls chiefly upon the relaxation.
This indicates that the relaxation is by no means a mere
elastic recoil, but a physiological process as important as
the contraction itself; and this conclusion is strengthened
by the fact we have now to mention, that not only is heat
produced during the actual shortening, but also during the
relaxation. If a muscle is allowed to contract without
raising any weight, and is loaded just at the top of its lift,
so that the load acts only during relaxation, more heat is
produced than when no weight is applied ; and the heavier
the weight, the greater is the heat-production.
The fraction of the total energy transformed which
appears as muscular work, varies with the conditions of the
contraction. The greater the resistance, the larger is the
proportion of the energy which appears as work, the smaller
the proportion which appears as heat ; but even in the most
favourable case, an excised frog's muscle never does work
equal to more than \ of the heat given off. Generally the
ratio is much less, and may sink as low as .}-,. In the intact
36
562 .1 MA.XL'AL OF PHYSIOLOGY
mammalian body it is probable that the muscles work at
least as economically as the excised frog's muscle under
the most favourable conditions ; for both experiment and
calculation show (p. 488) that in a normal man not less
than \, nor more than \, of the whole energy transformed
in the body is converted into work. But in any case
the heat -producing mechanism and the work -producing
mechanism of muscle are certainly in some respects distinct,
and a variation in the activity of the one is not necessarily
associated with a corresponding variation in the activity' of
the other.
(4) Chemical Phenomena of the Muscular Contraction. We as
yet know but little regarding the chemical composition of living
muscle, and are unlikely ever to know much, since most chemical
operations cause the immediate death of the tissue. 1 he composition
of dead tnammalian muscle may be stated, in round numbers, as
follows, but there are considerable variations, even within the same
species.
Water
Proteids
Fats
>,., ( Kreatin
, ,f ,• Xanthin
metabolites. , Hypoxanthin
Carbohydrates. {saSc" c acid |
Inosit J
Salts, chiefly carbonate and phosphate of potassium, less than
I per cent.
There is more water in the muscles of young than of old animals
(v. Bibraj, and more in tetanized than in rested muscle (Ranke).
The fats probably belong to a small extent to the actual muscle-
fibres. Yox even when the visible fat is separated with the utmost
care, nearly i per cent, of fat still remains (Steil). In lean horse-
flesh Pfliiger found 0-35 per cent, of glycogen, but no sugar. The
total nitrogen was 321 per cent, of the moist tissue.
It would be natural to expect that the proteids, which
bulk so largely among the solids of the dead muscle, and
which are so obviously important in the living muscle,
should be affected by contraction. But up to the present
time no quantitative difference in the proteids of resting and
exhausted muscle has ever been made out. The following
chemical changes, however, have been definitely established.
In an active muscle —
... 75
per
cen
20
11
'>
5>
MUSCLE 563
(a) More carbon dioxide is produced.
(/^) More oxygen is ronsumed.
{c) Sarcolactic acid is formed.
(</) (Ilycogen is used up.
{e) The substances soluble in water diminish in amount ; those
soluble in alcohol increase.
That the carbon dioxide is not formed by direct oxida-
tion, but by the spHtting up of a substance or substances
with which the oxygen has previously combined, is, as has
already been shown (pp. 247, 248), highly probable. For (to
recapitulate) (a) no free oxygen exists in muscle. None can
be pumped out. (6) A frog's muscle isolated from the body
will go on contracting for a long time in an atmosphere
devoid of oxygen, c.<^., in an atmosphere of hydrogen,
(t) When artificial circulation is maintained through isolated
muscles, the amount of carbon dioxide produced does not
run parallel with the quantity of oxygen consumed. The
latter is dependent on the temperature of the muscle,
being increased when the muscle is heated, diminished
when it is cooled. The production of carbon dioxide, on
the contrary, is, within a wide range, independent of the
temperature.
Formation of Sarcolactic Acid — Reaction of Muscle. — To
litmus paper fresh muscle is amphicroic ; that is, it turns
red litmus blue and blue litmus red. This is due, partly
at least, to the phosphates. Monophosphate (tribasic phos-
phoric acid in which one hydrogen atom is replaced, say
by sodium or potassium) reddens blue litmus, while diphos-
phate (where two hydrogen atoms are replaced) turns red
litmus blue. Litmoid (lacmoid) differs from litmus in not
being affected by monophosphates. Diphosphates turn red
litmoid blue. A cross -section of fresh muscle is about
neutral to turmeric paper (sometimes faintly acid), while
that of a rigid or tetanized muscle is distinctly acid, brown
turmeric being turned strongly yellow. The sarcolactic acid
produced in rigor and activity is at once neutralized, as is
shown by the fact that blue litmoid paper is not reddened,
as it would be by free sarcolactic acid. The neutralization
takes place at the expense of the sodium carbonate and
disodium phosphate, the latter being changed into mono-
36—2
564 A MAX UAL or PHYSIOLOGY
phosphate, which, in part at least, causes the acid reaction
to turmeric (Rohmann).
Glycogen is the one solid substance which has been
definitely proved to diminish in muscle durmg activity. It
accumulates in a resting muscle, especially in a muscle
whose motor nerve has been cut ; rapidly disappears from
the muscles of an animal made to do work while food is
V. ithheld ; or from the muscles of an animal poisoned by
strychnia, which causes violent muscular contractions.
What substance is the sarcolactic acid formed from ?
From what we know of the production of lactic acid both
outside the body and in the intestine from carbo-hydrates,
it might seem a most plausible suggestion that in the active
muscle it comes from gljcogen. But all the evidence points
the other way ; e.g., in rigor mortis sarcolactic acid is pro-
duced just as in muscular contraction. Not only so, but
according to Ranke every isolated muscle has a certain
maximum of acidity, which it reaches either through con-
traction, or through rigor, or through contraction followed
by rigor. Yet in rigor mortis the quantity of glycogen is
unaltered (Boehm). The probability is that the sarcolactic
acid is formed from proteid, perhaps by the action of a
ferment.
Source of the Energy of Muscular Contraction. — The facts
just mentioned show that glycogen may be one of the
sources of muscular energy, but it cannot be the only
source, for its amount is too small.
For example, the heart of an average man, which weighs 280
grammes, contains about 60 grammes solids, and among these not
more than i 5 grammes glycogen. In twenty-four hours it produces,
even on a low estimate, at least 250,000 calories of heat, equivalent
to the complete combustion of about 60 grammes of glycogen. To
supply this amount, the whole store of glycogen in the heart would
have to be used and replaced every half-hour. But the accumulation
of glycogen is immensely slower in the muscles of a rabbit made
glycogen-free by strychnia, and therefore we have to look around for
some other source of energy to supplement the glycogen. We have
already brought forward evidence (p. 459) that, under ordinary cir-
cumstances, not a great deal, at any rate, of the energy of muscular
contraction comes from the proteids. Of carbohydrates, the only
one except glycogen which is at all adequate to the task of supplying
so much energy is the glucose of the blood. The quantity of blood
MUSCLE 565
passing through the coronary circulation has been estimated at 30 c.c.
per 100 grammes of cardiac muscle per minute (IJohr and I Icnriques),
which would be equivalent for an average man to about 120 litres
in twenty-four hours. This quantity of blood will contain at least
150 grammes of glucose, and 70 grammes will suffice to supply all
the heat produced by the heart. Of i)roteids a little less than
60 grammes would be needed, of fat more than 25 grammes. We
see, therefore, how intense must be the metabolism that goes on in
an actively contracting muscle. On any probable assumption as to
the source of muscular energy a quantity of material equal to the
whole of its solids must l)e used up by the heart in twenty-four hours.
Or, to put it in another way, the heart requires not less than Iialf its
7veight, possibly its 'weight, of ordinary solid food in a day. The body
as a whole requires /^ to ^\ of its weight.
To sum up : It is universally admitted that carbohydrates
can yield energy for muscular work. It has been demon-
strated by Zuntz and his pupils and by others that fat can
do so. The experiments of Pfluger, to which we have
already alluded (p. 460), have shown than when an animal
is fed on lean meat, the muscular work done is far too great
to have come from non-proteid substances. We must
conclude, therefore, that when carbohydrates and fats are
plentiful in the food, the greater part of the energy of
muscular contraction comes from them ; it comes on the
other hand from proteids, when the carbohydrates and the
fats are restricted, and the proteids plentifully suppHed.
Not only so, but these three groups of food substances yield
muscular energy in isodyiiamic relation. In other words, a
given amount of muscular work requires the expenditure
of approximately the same quantity of chemical energy,
whether it comes almost entirely from proteid, or chiefly
from carbohydrates, or chiefly from fat. Some observers have
stated that the taking of even a comparatively small quantity
of sugar vastly increases the capacity for muscular work as
measured by the ergograph (p. 597). But although it is not
to be doubted that sugar is under normal circumstances one
of the most important substances used up in muscular con-
traction, the claim that sugar is, par excellence, the food for
muscular exertion has not yet been made out.
Rigor Mortis. — When a muscle is dying its excitability,
after perhaps a temporary rise at the beginning, diminishes
566 A MAA'l/AL OF I'UYSIOLOGY
more and more until it ultimately responds to no stimulus,
however stronj^. The loss of excitability is not in itself a
sure mark of death, for, as we have seen, an inexcitable
muscle may bo partially or completely restored : but it is
followed, or, where the death of the muscle takes place
very rapidly, perhaps accompanied, by a more decisive
event, the appearance of rigor. The muscle, which was
before soft and at the same time elastic to the touch,
becomes firm : but its elasticity is gone. The Hbres are no
longer translucent, but opaque and turbid. If shortening
of the muscle has not been opposed, it will be somewhat
contracted, although the absolute force of this contraction
is small compared with that of a living muscle, and a slight
resistance is enough to prevent it. The reaction is now
distinctly acid. This is rigor mortis, the death-stiffening of
muscle.
An insight into the real meaning of this singular and
sometimes sudden change was first given b\- the experiments
of Kiihne, He took living frog's muscle, freed from blood,
froze it, and minced it in the frozen state. The pieces were
then rubbed up in a mortar with snow containing i per cent,
of common salt, and a thick neutral or alkaline liquid, the
muscle-plasma, was obtained by filtration. This clotted
into a jelly when the temperature was allowed to rise, but
at o'' C. remained fluid. The clotting was accompanied by
a change of reaction, the liquid becoming acid. An equally
good, or better, method is to use pressure for the extraction
of the plasma from the frozen fragments of muscle. A low
temperature is essential, otherwise the plasma will coagulate
rapidly within the injured muscle.
A similar plasma can be expressed from the skeletal
muscles of warm-blooded animals (Halliburton), and with
greater difficulty from the heart. Attempts to obtain it
from smooth muscle have hitherto failed, possibh" because
of the unfavourable anatomical conditions.
When the muscle, after exhaustion with water, is covered
with a solution of a neutral salt, a 5 per cent, solution of
magnesium sulphate or 10 per cent, solution of ammonium
chloride being probably the best, a proteid passes into
MUSCLE 567
solution, which is identical with the myosin of the clotted
plasma. If the solution is diluted, it clots just as the muscle-
plasma clots, and the clot or precipitate can be dissolved
and reproduced at will (Practical Exercises, p. 602). The
addition of potassium oxalate does not prevent coagulation
of muscle-extracts, as it does of blood and blood-plasma.
I'^rom all this we gather that rigor mortis is essentially a
clotting or coagulation of a substance which yields myosin.
What this substance is we cannot tell. Some have sup-
posed that in the living muscle there exists a body, myo-
sinogen, which is the direct precursor of the myosin in the
muscle-clot or within the fibres in rigor mortis, and which is
related to it as fibrinogen is related to fibrin in the clotting
of blood. It has even been assumed that this very myosin-
ogen is formed when myosin is dissolved in a salt solution ;
but this hypothesis is not backed by sufficient evidence.
Why does coagulation of myosin occur at the death of
the muscle ? To this question no clearer answer can be
given than to the question why blood clots when it is shed.
Just as a fibrin ferment is developed when blood begins to
die, a myosin ferment, which aids coagulation, is perhaps
developed in dead or dying muscle.
It has been suggested that myosin, sarcolactic acid, and
carbon dioxide are all products of some complex body
which breaks up both at the death of the muscle, and
during contraction, and that, indeed, contraction is only a
transient and removable rigor (Hermann). But it cannot
be admitted that there is any fundamental connection
between rigor and contraction, although there are some
superficial resemblances. In both there is (i) shorten-
ing ; (2) heat-production : (3) formation of fixed acid and
carbon dioxide; (4) an electrical change (p. 607). Another
analogy might be forced into the list by anyone who
was determined to see only rigor in contraction : the rigor
passes off as the contraction passes off, although the ' resolu-
tion ' of a rigid muscle takes days, the relaxation of an
active muscle a fraction of a second. The disappearance of
rigor is not dependent on putrefaction ; it takes place when
growth of bacteria is prevented (Hermann).
5f'.S A MAATAL OF I'lIYSIOLOCY
Various influences affect the onset of rigor. Fatigue
hastens it ; heat has a similar effect ; the contact of caffeine,
chloroform and other drugs causes most pronounced and
immediate rigor. Blood applied to the cross-section of a
muscle first stimulates the fibres with which it is in contact,
and then renders them rigid. But it is to be remembered
that normally the blood does not come into direct contact
even with the sarcolemma, much less with its contents.
The effect of heat is of special interest. A skeletal muscle of a
frog, like the gastrocnemius, if dipped into normal saline solution at
40° or 41" C. goes into rigor at once ; the frog's heart requires a
temperature 3^^ or 4° higher ; the distended bulbus aortas can with-
stand even a temperature of 48° for a short time. An excised
mammalian muscle passes into immediate rigor at 45' to 50^ In
heat rigor the reaction of the muscle becomes strongly acid, and the
acidity is due to a fixed acid (sarcolactic), not to carbon dioxide,
although the production of the latter is greatly increased. A small
quantity of heat is produced, and the temperature of the muscle may
be raised as much as }^f C. This is probably due chiefly to the
increased chemical change, and only to a slight extent to the physical
alteration in the myosin. Heat rigor is, in fact, a greatly accelerated
rigor mortis, and the myosin, although clotted, is not rendered
insoluble like a heat-coagulated proteid (p. 603).
When muscle is suddenly raised to a temperature of 75" to 100" C.,
we have quite a different series of events. There is no acid reaction,
no evolution of carbon dioxide ; the muscle is indeed rigid, but true
rigor has not taken place, and the rigidity is due to coagulation of
the proteids by heat. Rigor is a change which cannot go on when
once the comparatively mobile substance of the living muscle, or of
the muscle in the act of dying, has been converted into the stable
form of coagulated proteid. No sarcolactic acid is produced in
scalded muscle, perhaps because the acid-forming ferment (p. 567)
is killed by the high temperature. The so-called rigor caused by
alcohol and by acids is a coagulation of the proteids, and not true
rigor. No heat is produced, and no carbon dioxide given off.
In a human body rigor generally appears not earlier than
an hour, and not later than four or five hours, after death.
In exceptional cases, however, it may come on at once, and
the annals of war and crime contain instances where a man
has been found after death still holding with a firm grip the
weapon with which he had fought, or which had been thrust
into his hand by his murderer. It is related that after one
of the battles of the American Ke\olutionary War some of
the dead were found with one eye open and the other closed
MUSCLE 569
:is in the act of taking aim. A high temperature favours
a rapid onset ; a body wrapped up in bed will, other things
being equal, become rigid sooner than a bod\' lying stripped
in a field. Muscular exhaustion, as we have said, is another
favouring condition : hunted animals and the victims of
wasting diseases go quickly into rigor. It is a rule, but not
an invariable one, that rigor, when it comes on quickly, is
short, and lasts longer when it comes on late. All the
muscles of the body do not stiffen at the same time ; the
order is usually from above downwards, beginning at the
jaws and neck, then reaching the arms, and finally the legs.
After two or three days the rigor disappears in the same
order. The position of the limbs in rigor is the same as
at death ; the muscles stiffen without contracting. This can
be strikingly shown on a newly-killed animal by cutting the
tendons of the extensors of one leg and the flexors of the
other; when natural rigor comes on the legs remain just as
they were. If heat rigor, however, is caused, the one leg
becomes rigid in flexion and the other in extension.
The Removability of Rigor. — It has been asserted that rigor
can be removed and excitability restored. After interrupt-
ing the circulation in the hind-legs of rabbits by compres-
sion or ligation of the abdominal aorta, and so causing the
muscles to become rigid, Brown-Sequard saw them recover
their irritability when the blood was again allowed to reach
them. He performed a similar experiment with artificial
circulation through the hand of an executed criminal, with
a like result. But grave doubt has been cast upon these
experiments by later observations, and it is now almost
universally believed that no really rigid muscle has ever
been restored, and that the apparent recovery which Brown-
Sequard saw was due to the muscles not having been
completely rigid. Heubel has, however, stated that the
rhythmical contractions of the frog's heart can be restored
by filling its cavity with blood, after rigor has been caused
by heat and in other ways ; and although we cannot transfer
these results directly to skeletal muscle, they would show, if
confirmed, that the question is not yet closed.
CHAPTER X.
NERVE.
The voluntary movements are originated by impulses from
the brain, which reach the muscles along their motor nerves.
The involuntary movements are in many cases able to go
on in the absence of central connections, but are normally
under central control. Everywhere the connection between
the brain and cord and the peripheral organs, be they
muscles, glands, or sensory mechanisms, is made by nerve-
fibres ; and these are called peripheral nerve-fibres to dis-
tinguish them from the fibres of the central nervous system
itself.
An ordinary periplieral nerve like the sciatic is made up of a
number of bundles of nerve-fibres. Connective tissue surrounds
and separates the bundles, and also penetrates in fine septa within
them and between the individual fibres, forming a framework for
their support, and carrying the bloodvessels and lymphatics.
Each medullated nerve-fibre (Plate V. i) consists of two sheaths
enclosing an axis-cylinder, which runs from end to end of it without
break, and is connected centrally, either directly or indirectly, with
a nerve-cell. The axis-cylinder is the essential conducting part of
the fibre, for it is present in every nerve-fibre, and towards the
periphery it is alone present. The innermost, and by far the thickest,
of the sheaths is the medullary sheath, or white substance of
Schwann, which is of fatty nature, and is blackened by osmic acid.
It undergoes a kind of coagulation at death, loses its homogeneity,
and shows a double contour. This sheath is not continuous, but is
liroken by constrictions of the outer sheath, called nodes of Ranvier,
into numerous segments. The outer sheath, or neurilemma, is a
thin, structureless envelope immediately external to the medulla. It
invests the nerve-fibre, as the sarcolemma does the muscle fibre. In
each internodal segment immediately under the neurilemma lies a
nucleus surrounded by a little protoplasm. Medullated fibres such
as those described are by far the most numerous in the cerebro-
NERVI- 571
spinal nerves ; but they are mixed with a few fibres which contain
no white substance of Schwann, and are, therefore, called non-
medullated (Plate V. i). In these the axis-cylinder is covered only
by ti«e neurilemma. In the sympathetic system the non-medullated
variety is present in greater al)undance than the medullated. In
the central nervous system the medullated fibres possess no neuri-
lemma.
So far as we know, the only function of nerve-fibres is to
conduct impulses from nerve-centres to peripheral organs,
or from peripheral organs to nerve-centres, or from one
nerve-centre to another. And in the normal body these
impulses never, or only very rarely, originate in the course
of the nerve-fibres : they are set up either at their peripheral
or at their central endings. By artificial stimulation, how-
ever, a nerve-impulse may be started at any part of a fibre,
just as a telegram may be despatched by tapping any part of
a telegraph wire, although it is usually sent from one fixed
station to another.
The Nerve-impulse : its Initiation and Conduction.
What the ner\e-impulse actually consists in we do not
know. All we know is that a change of some kind, of which
the only external token is an electrical change, passes over
the nerve with a measurable velocity, and gives tidings of
itself, if it is travelling along efferent fibres (that is, out from
the central nervous system), by the contraction or inhibition
of muscle or by secretion ; if it is travelling along afferent
fibres (that is, up to the central nervous system), by sensa-
tion, or by reflex muscular or glandular effects.
Whether the wave which passes along the nerve is a wave
of chemical change, or a w-ave of mechanical (molecular)
change, there is no definite experimental evidence to decide.
That chemical changes go on in living nerve, we need not
hesitate to assume ; and, indeed, if the circulation through
a limb of a warm-blooded animal be stopped for a short
time, the nerves lose their excitability. But the metabolism
appears to be ver}- slight compared with that in muscle or
gland. Even in active nerve no measurable production of
carbon dioxide has ever been observed, nor, in fact, has any
chemical or physical difference between the excited and the
572 J MA.YUAL OF PHYSIOLOGY
resting state ever been unequivocally made out. Neither in
cold-blooded nor in mammalian nerves does there seem to
be any sensible rise of temperature durinj^' stimulation.
Stimulation of Nerve. — With some differences, the same
stimuli are effective for nerve as for muscle (p. 533) ; but
chemical stimulation is not in general so easily obtained.
In fact, it is doubtful whether any great reliance should be placed
on many of the observations hitherto made with this mode of excita-
tion. For it has been shown that the current of rest of the nerve
(p. 606), when a short-circuit is formed for it by a drop of any con-
ducting liquid applied to a fresh cross-section (the usual method of
experimenting on chemical stimulation), may of itself cause excitation
(Hering).
Grutzner uses equimolecular solutions for experiments on chemical
stimulation — i.e., solutions which contain an equal number of
molecules of the substances to be tested in a given volume of water.
He has found that for motor nerves the halogen salts have a stimu-
lating power in the order of their molecular weights ; e.g., sodium
iodide (Nal) is stronger than sodium bromide (NaBr), and sodium
bromide than sodium chloride (NaCl). Sensory nerves are much
less susceptible to chemical stimulation. Bile or bile salts, for
example, which stimulate motor nerves, have no effect on sensory.
A sugar solution, which excites motor nerves, does not alter the rate
of respiration when applied to the central end of the vagus, which,
however, is excited by potassium chloride (p. 214). In non-narcotized
animals reflex secretion of saliva is caused by stimulation of the
central end of the lingual with sodium chloride (Wertheimer).
Mechanical stiviulatioi has been carried to great perfection by
Heidenhain, and esi)ecially by Tigerstedt. By means of an instru-
ment invented by the latter, not only may a regular tetanus be
obtained, but the strength of the stimulus (fall of a weight) can be
graduated with fair accuracy within a considerable range. He found
that the smallest amount of work spent on a frog's nerve which would
suffice to excite it was a little less than a gramme-millimetre — ^that is,
the work done by a gramme falling through a distance of a miUi-
metre. No doubt a great part of this is wasted, as a much smaller
quantity of work done by an electrical current, whicii may be
supposed to act more directly on the excitable constituents, suffices
to stimulate a nerve. Thus, while the minimal mechanical stimulus
may have a heat-equivalent of about x ^ gramme-degree, the
4-2 10'
heat-equivalent of the minimal electrical stimulus may easily be less
than X yj gramme-degree, or one-millionth part of the former.
A kilogramme-degree is equivalent to 427 kilogramme-metres of
work; therefore, a gramme -millimetre of work is ecjuivalent to
NERVE 573
- Kramme-degree, or, say, x Lrramnic-decree. This
427,000 ^ ^ ' ■" 4-2 10 ^ ^
corresponds to Tigerstedt's minimum mechanical stimulus.
A piece of nerve of 100,000 ohms resistance may be excited by
a current passed for ,',^ second when the difference of potential
between its ends is only j,'y,y of a volt. Taking the work done in
this case as measured by the heat produced, we get work (\V) = H
E t
= :.^ , where E is the electromotive force, t the time of flow of the
current, J Joule's equivalent, and R the resistance. Expressing
these in C.G.S. (centimetre — gramme — second) units, we have
\ 100 / lOi
, .^-, iOO I I
W= T. = X — ,, gramme-degree
42 X TO*' X I o-' X 100,000 4*2 10^^
as the work done by an electrical stimulus sufficient to excite a nerve.
S. P. Langley has shown that the work done by the minimal, natural
or specific, stimulus for the retina (green light) may be as little as
erg*: i.e., — x - gramme-degree, or 10,000 times less than
10'' 4-2 10^^'
the minimal electrical stimulus, on our assumptions, for the naked
nerve-trunk of a frog. But these assumptions are quite rough, and
it is possible that the energy of the minimum artificial stimulus is
no greater than that of the minimum natural stimulus of the retina.
The laws of electrical stimnlatio7i for nerve are essentially the same
as those we have already discussed for muscle (p. 537). The voltaic
current stimulates a nerve, as it does a muscle, at closure and
opening, and not in general during the flow, but the exceptions to
this rule are less frequent in nerve than in muscle. Induction
shocks are relatively more powerful stimuli for nerve than the make
or break of a voltaic current. The opposite, as we have seen, is true
of muscle ; and, upon the whole, we may say that muscle is more
sluggish in its response to stimuli, and is excited less easily by very
brief currents, than nerve is. An apparent illustration of this differ-
ence is the fact that the nervous excitation has no measurable latent
period, while muscular excitation has. But it is quite possible that,
if the conditions of experiment were as favourable in nerve as in
muscle, a sensible latent period might be found here too.
In nerve as in muscle, strength of stimulus and intensity of
response correspond within a fairly wide range, when we take the
height of the muscular contraction or the amount of the negative
variation (p. 607) as the measure of the nervous excitation. Super-
position of stimuli, superposition of contractions, and complete
tetanus, are caused by stimulating a muscle through its nerve, just
as by stimulating the muscle itself (p. 552).
The excitability of nerve, as measured by the muscular
response to stimulation, is increased, for induction shocks
* Here we take an erg as equivalent to loVo gramme-centimetre.
574 A MANUAL OF PHYS/OLOGY
or voltaic currents of short duration, by rise of temperature
up to about 30" C, and diminished by fall of temperature.
It has been supjgested that this increase of excitability is
only apparent, and due to the strengthening of the current
by diminution of the resistance, since the resistance of all
animal tissues, like that of electrolytic conductors in general,
diminishes as the temperature rises (Gotch). Cooling of the
nerve, even to 5*^ C, increases the excitability for currents
of long duration (several hundredths of a second). The con-
ductivity for the nervous impulse — that is, the power of a
portion of the nerve to conduct an impulse set up elsewhere
— is undoubtedly increased by heat and diminished by cold.
Drying of a nerve at first increases its excitability ; and
the same is true of separation of a nerve from its centre.
In the latter case the increase of irritability begins at the
proximal end of the nerve, and travels towards the peri-
phery. As time goes on, the excitability diminishes, and
ultimately disappears in the same order (^Ritter-Valli Law).
At a certain stage it may be found that a given stimulus
causes a smaller and smaller contraction the farther down
the nerve — that is, the nearer to the muscle — it is applied.
On this was based the now abandoned ' a\ alanche theory,"
according to which the impulse continually unlocked new
energy as it passed along the nerve, and so gathered strength
in it? course like an avalanche.
Electrotonus. — Although the constant current does not,
unless it is very strong or the nerve very irritable, cause
stimulation during its passage, it modifies profoundly the
excitability and conductivity of the nerve. (In man a
certain amount of tonic contraction — galvanotoniis — is
normally seen during the passage of a strong current
through a nerve). In the neighbourhood of the kathode
the excitability is increased (condition of katelectrotonus),
while around the anode it is diminished (anelectrotonus).
Immediately after the opening of the current these relations
are for a brief time reversed, the excitability of the post-
kathodic area (area which was at the kathode during the
flow) being diminished, and that of the post-anodic in-
creased. In the intrapolar area there is one point the
NER VE
575
excitability of which is not altered. This indifferent point, as
it is called, shifts its position when the intensity of the
current is varied.
These statements have been made on the strength of
experiments in which
the height of the mus-
cular contraction was
taken as the index
solely of the excita-
bility of the nerve at
any given point. But
it is now known, partly
from observations on
muscular contraction
in which changes of
excitability of the
nerve were eliminated
by proper choice of the
point of stimulation,
and partly from obser-
vations on the action
stream (p. 620), that
very striking altera-
tions of conducti v i ty
are also produced by
the constant current,
which even outlast its
flow. For all currents
except the weakest the
conductivity at the
kathode and in its im-
mediate neighbour-
hood is diminished,
and with currents still only moderately strong dowrro
ampere, e.^^.) the block deepens into utter impassability.
The conductivity at the anode is, during all this stage, but
little affected, and is at any rate much higher than at the
kathode, so that at the time of full kathodic block the nerve-
impulse still freely passes through the region around the
positive pole. With still stronger currents the conduc-
FiG. 176.— Diagram of Changes of Ex-
citability AND Conductivity produced
IN A Nerve by a Voltaic Currlnt.
E, changes of excitability during the flow of the
current, according to Pfltiger. The ordinates drawn
from the abscissa axis to cut the curve represent the
amount of the change. C(i), changes of conduc-
tivity during the flow of a moderately strong current.
Conductivity greatly reduced around kathode ; little
affected at anode. C(2i. changes of conductivity
during flow of a very strong current. Conductivity
reduced both in anodic and kathodic regions, but
less in the former. C , changes of conductivity just
after opening a moderately strong current. Con-
ductivity greatly reduced in region which was
formerly anodic ; little affected in region formerly
kathodic.
576
A MANUAL OI-l'liySIOLO(,Y
ti\ ity here, too, begins to diminish, until at last the anode is
also blocked : but this is to be looked upcjn as merely an
extension of the defect of conductivity which has been creep-
ing along the intrapolar area from the kathode. After
the opening of the current, the relation between kathodic
and anodic conductivity is reversed, for now the post-
kathodic region conducts the nerve-impulse relatively better
than the post-anodic.
Fic;. 177. — Ka'ielfctrotonus.
Weak tetanus of muscle (the right-hand
elevation), greatly intensified in katelec-
trotonus of the motor nerve (the left-hand
elevation).
Fig. 178. — Anelkctrotonu.s.
Strong tetanus of muscle (left-hand
elevation), lessened in strength by an-
electrotonic condition of the motor nerve
(right-hand elevation).
The above facts serve to explain the manner in which
the effects of stimulation of a nerve with the constant
current vary with the strength and direction of the stream.
These effects, so far as the contraction of the muscles
supplied b} the nerve is concerned, have been formulated
in what has been somewhat loosely termed the law of con-
traction. In this formula the direction of the current in the
nerve is commonly distinguished by a thoroughly bad but
now ingrained phraseology, as asccndiui^ when the anode is
next the muscle, and descending when the kathode is next
the muscle.
Ltiw of Cpniraction.
\ Ascending.
Current.
M. j B.
Descending.
M. B.
Weak - - C
Medium - C
Strong - - —
C
C
C —
c c
C 1 —
Here M means ' make," B, ' break,' of the current ; C means ' contraction follows.'
NERVE 577
The explanation generally given of the facts summed up
in the ' law of contraction ' is as follows : Wherever there
is an increase of excitability sufficiently rapid and sufficiently
large, stimulation is supposed to take place ; where there is
a fall of excitability, stimulation does not occur. Accord-
ingly, at closure the kathode stimulates— the anode does
not ; while at opening, the anode, at which the depressed
excitability jumps up to normal or more, is the stimulating
pole : the kathode, at which it declines to normal or under
it, is inactive.
With a 7i'eak current, (i) contraction only occurs ai make, and
(2) the direction of the current is indifferent. The explanation of
the first fact is that the make is a stronger stimulus than the break,
and when the current is weak enough the break is less than a mini-
mal stimulus. No sensible change of conductivity is caused by
weak currents, which suffices to explain (2).
With a ' medium ' current, contraction occurs at make and break
with both directions. Here the break excitation is effective as well
as the make. With anode next the muscle (ascending current), there
is of course nothing to prevent the opening excitation, which starts
at the anode, from passing down the nerve and causing contraction ;
and since there is no block around the anode or in the intrapolar
region with ' medium ' currents, there is nothing to keep the closing
(kathodic) excitation from reaching the muscle too. With the
kathode next the muscle (descending current), the closing excita-
tion, which starts from the kathode, has no region of diminished
conductivity to pass through, nor has the opening (anodic) excitation,
for the kathodic block, caused by moderately strong currents, is
removed as soon as the current is broken.
With ' strong ' currents there are only two cases of contraction
out of the four, just as with ' weak,' but for very different reasons.
There is a break-contraction with ascending, and a make-contraction
with descending current. With ascending current the anode is next
the muscle, and the break-excitation starting there has nothing to
hinder its course. The make-excitation, although as strong or
stronger, has to pass through the whole intrapolar region and over
the anode, and here the conductivity is depressed and the nerve-
impulse blocked. With descending current the kathode is next the
muscle, and there is no hindrance to the passage of the make excita-
tion. The break-excitation, however, has to traverse the intrapolar
region, and the anodic end of this area has a smaller conductivity
immediately after opening than during the flow, while the kathodic
end does not at once, after a strong current, become passable. The
break-excitation, accordingly, cannot get through to the muscle.
In all these cases of complete or partial block, during or after the
flow of a constant current, the progress of the nerve-impulse, its
Z7
578
.1 MANUAL OF PHYSIOLOGY
gradual weakening, and final extinction can be very well shown by
means of the action stream (p, 619).
The above formula can on!}- be verified upon isolated
nerves, and. even for these, exceptional results are apt to be
obtained as soon as the nerves begin to die.
A formula similar to the law of contraction has been
shown to hold for the inhibitory fibres of the vagus (Donders),
'inhibition' being substituted for 'contraction.' There is
also some evidence that a similar law obtains for sensory
nerves.
The Law of Contraction for Nerves ' in Situ.' — When a nerve
is stimulated without previous isolation — in the human body,
for instance, through elec-
trodes laid on the skin — the
current will not enter and
leave it through definite
small portions of its sheath,
nor will it be possible to
make the lines of flow nearly
parallel to each other and to
the long axis of the nerve,
as is the case in a slender
strip of tissue when there is
a considerable distance be-
tween the electrodes.
Fig. 179. — Diagram ok Lines oi-
Flow of a Current passing
THROUGH A NeRVE.
A, an isolated nerve ; B, a nerve in
situ. Secondary anodes ( + ) are formed
where the current re-enters the nerve
below the negative electrode after passing^
througli the tissues in which it is em-
bedded, and secondary kathodes ( — )
where the current passes out of the nerve
into the surrounding tissues below the
positive electrode.
On the contrary, even when a
single electrode — say, the positive
— is placed over the position of
the nerve, and the other at a
distance on some convenient part
of the body, the current will enter the nerve by a broad fan of
stream-lines cutting it more or less obliquely, and pass out again
into the surrounding tissues ; so that both an anode (surface of
entrance) and a kathode (still larger surface of e.xit) will correspond
to the single positive pole. Similarly, the single negative electrode
will correspond to an anodic surface where the now narrowing sheaf
of lines of flow enters the nerve, and a smaller kathodic surface,
where they emerge.
If the two electrodes were on the course of the nerve, the stream-
lines would still cut it in such a way that each electrode would corre-
spond both to anode and kathode (Fig. 179).
NERVE
579
It is impossible under these circumstances to define the
direction of a current in a nerve, or to connect direction with
any specific effect. The terms * ascending ' and ' descending '
current are, therefore, meaningless. When we place one of
the electrodes over the nerve and the other at a distance,
the law of contraction only appears in a disguised form ;
for since a kathode and an anode exist at each pole, there
is, with a current of sufficient strength, excitation at each
both at make and break. The negative make-contraction
is, however, stronger than the positive, for the excitation
corresponding to the latter arises at the secondary kathodic
surface, where the sheaf of current-lines spreading from the
positive electrode passes out of the nerve. Now, this is
much larger than the primary kathodic surface, through
which the narrow wedge of stream-lines passes to reach the
negative electrode, and the current density at the latter is
accordingly much greater. The positive break-contraction
is, for a similar reason, stronger than the negative.
With a ' weak ' current, the only contraction is a closing
one at the kathode ; with a ' medium ' current there are
both opening and closing contractions at the positive pole,
and a closing but no opening contraction at the negative.
The conductivity of the nerve, as we have seen in various
examples, is not necessarily altered in the same sense as
the excitability. In the neighbourhood of the kathode it
is easier to cause excitation than in the normal nerve (in-
creased excitability), but it is less easy for an excitation set
up elsewhere to pass through (diminished conductivity).
Change of temperature seems also, for stimuli of not very
short duration, to act in the opposite way on these two
properties of nerve. Carbon dioxide appears to depress
the excitability without affecting the conductivity, and
alcohol to have the contrary effect (Gad and Sawyer).
Munk found that in a dying sciatic nerve certain points may
be quite inexcitable to the strongest stimuli, while weak
stimulation of points lying nearer the central end may cause
muscular contraction. These facts seem to show that the
process by which the nerve-impulse is propagated (an exci-
tation of each nerve-element by the one next it, as some
37—2
58o A MANUAL OF IW/YSIOLOGY
have supposed) is not the same as that by which it is
orifijinated.
Double Conduction. — When a nerve is stimulated artificially,
the excitation runs along it in both directions from the
point of stimulation ; so that fibres which in the intact body
are afferent can conduct impulses towards the periphery,
and efferent fibres can conduct impulses away from the
periphery. In the normal state, however, double conduc-
tion must seldom occur, for efferent fibres are connected
centrally, and afferent fibres peripherally, with the structures
in which their natural stimuli arise. In general, too, an
impulse, if it did pass centrifugally along an afferent fibre,
would not give any token of its existence, for the peripheral
organ would not be able to respond to it ; and we have no
reason to believe that the central mechanisms connected
with efferent fibres are better fitted to answer such foreign
and unaccustomed calls as impulses reaching them along
normally efferent nerves. There is some evidence that
muscular excitation is not carried over to the motor nerve-
fibres ; in other words, the wave of action flows from the
nerve to the muscle, but cannot be got to flow backwards.
Whether such an organ as the retina can be excited by
impulses reaching it ' the wrong way ' along the optic nerve
we do not know, although the point might possibly be
decided by means of the retinal currents to be mentioned
later on (p. 624), We shall see that a nutritive influence is
exerted over afferent fibres by the spinal ganglia (p. 585),
an influence which must spread along these fibres in the
opposite direction to that of the normal excitation ; but
from this we cannot deduce anything as to the behaviour
of ordinary nerve-impulses.
The best proofs of double conduction in nerves, with
artificial stimulation, are: (i) The propagation of the nega-
tive variation or action current in both directions. This
holds for sensory as well as for motor fibres, as du Bois-
Reymond showed on the posterior roots of the spinal nerves
of the frog and the optic nerves of fishes. (2) Stimulation
of the posterior free end of the electrical nerve of Malap-
terurus (p. 625) causes discharge of the electric organ.
NERII-: 581
although the nerve-impulse travels normally in the opposite
direction. (3) If the lower end of the frof:^'s sartorius is split
into two, gentle stimulation of one of the tongues causes
contraction of individual fibres in the other. This is supposed
to he due to conduction of the nerve-impulse up a twig f)f
a nerve -fibre distributed to the one tongue, and down
another twig of the same fibre going to the other tongue.
A similar experiment can be done on the gracilis of the
frog. This muscle is divided by a tendinous inscription into
two parts, each supplied by a branch of a nerve which divides
after entering the muscle. Stimulation of either twig is
followed by contraction of both parts of the muscle (Kuhne).
Bert's much-quoted experiment on the rat is valueless as a proof
of double conduction. He caused union of the point of the tail
with the tissues of the back, then divided the tail at the root, and
found that stimulation of what was now the distal end caused pain.
From this he concluded that the sensory fibres of the ' transposed '
tail conducted in the direction from root to tip. But the conclusion
is not warranted, for sensation disappeared in the tail after the
section, and did not return till some months later, when the nerve-
fibres, after degenerating, would have been replaced by new sensory
fibres growing down from the dorsal nerves (Ranvier). For a similar
reason the so-called union of the peripheral end of the cut hypoglossal
nerve (motor) with the central end of the cut lingual (sensory) proves
nothing as to double conduction, nor as to the possibility of motor
nerves taking on a sensory function.
Every fibre of a nerve is physiologically isolated from
the rest, so that an impulse set up in a fibre runs its
course within it, and does not pass laterally into others
(law of isolated conduction). In connection with this physio-
logical fact there is the anatomical fact that nerve-fibres
do not branch in the trunk of a peripheral nerve. It
has, however, been shown recently that bifurcation of
nerve - fibres may occur in the spinal cord (Sherrington).
The axis-cylinder of a peripheral nerve-fibre onl)^ begins to
branch where isolation of function is no longer required, as
within a muscle. The experiment of Kiihne on double con-
duction, mentioned above, seems to show that an excitation
set up in one fibril of an axis cylinder can spread to the
rest.
Velocity of the Nerve-impulse. — We have said that the nerve-
582 A MANUAL OF PHYSIOLOGY
impulse travels with a measurable velocity. It is now time
to describe how this has been ascertained (p. 600). For
moioY fibres the simplest method is to stimulate a nerve suc-
cessively at two points, one near its muscle, the other as far
away from it as possible, and to record the contractions on
a rapidly-moving surface (pendulum or spring myograph)
(p. 542). The apparent latent period of the curve corre-
sponding to the nearer point will be less than that of the
curve corresponding to the point which is more remote, by
the time which the impulse takes to pass between the two
points. The distance between these points being measured,
the velocity is known. Helmholtz found the velocity for
frog's nerves at the ordinary temperature of the air to be
a little under, and for human nerves, cooled so as to ap-
proximate to the ordinary temperature, a little over 30
metres per second. For observations on man the contrac-
tion curves of the flexors of one of the fingers or of the
thumb may be recorded, first with stimulation of the
brachial plexus at the axilla, and then with stimulation of
the median or ulnar nerve at the elbow. Probably at the
same temperature there is little difl'erence in the rate of
transmission in the nerves of warm-blooded and cold-blooded
animals, but temperature has an enormous influence.
By cooling a frog's nerve Helmhokz reduced the rate to ~j^ of its
value at the ordinary temperature, and in the human arm it may
vary from 30 to 90 metres per second, according to the temperature,
50 metres being about the normal rate. This is greater than the
speed of the fastest train in the world.
The passage of a voltaic current through an isolated nerve also
affects the velocity of the nerve-impulse. When the current is weak,
the velocity is increased in the neighbourhood of the kathode, but
diminished near the anode : when it is stronger, the velocity is
diminished, not only around both poles, but in the whole intrapolar
area. This agrees with what we have already seen as to the effect of
the constant current on the conductivity of nerve.
The velocity with which the negative variation is propa-
gated (p. 610) is the same as that of the nerve-impulse.
In sensory nerves there is no reason to believe that the
velocity of the nerve-impulse differs from that in motor
nerves, but experiments really free from objection are as yet
wantinsf.
NERVE 583
The usual method is to stimulate the skin first at a point distant
from the brain, and then at a much nearer point. The person
experimented on, as soon as he feels the stimulation, makes a signal,
say, by closing or opening with the hand a current connected with
an electric time-marker, writing on a moving surface. There is, of
course, a measurable interval between the excitation and the signal,
and this being in general longer the more remote the point of stimu-
lation is from the brain, it is assumed that the excess represents the
time taken by the nerve-impulse to pass over a length of sensory
nerve equal to the difference in the length of the path. But there is
this difficulty, that the propagation of the impulse from the point of
stimulation to the brain is only one link in the chain of events of
which the signal marks the end. The impulse has first to be trans-
formed into a sensation, and then the will has to be called into action,
and an impulse sent down the motor nerves to the hand. And while
the time taken by the excitation in travelling up and down the
peripheral nerve-fibres is, perhaps, fairly constant, the time spent in
the intermediate psychical processes is very variable.
Chemistry of Nerve. — Our knowledge of this subject is
scanty in the extreme ; and most of what we do know has
been obtained from analyses, not of the peripheral nerves,
but of the white matter of the central nervous system.
Proteids are present, especially in the axis cylinder. They include
a globulin and a nucleo-proteid.
Substances soluble in ether include c/io/esterin, lecithin^ cerebrin,
and protagon, which, according to some, is a mixture — to others, a
compound of lecithin and cerebrin. The cholesterin and lecithin,
at least, belong chiefly to the medullary sheath, which further con-
tains a kind of network of a peculiar resistant substance called
neurokeratin (Kiihne).
The tieiirilemma consists of substances insoluble in dilute sodium
hydrate.
Gelatin is obtained from the connective tissue which binds the
nerve-fibres together. There may also be ordinary fat in the meshes
of the epineurium connecting the bundles. Small quantities of
xanthin, hypoxanthin, and other extractives, can also be obtained
from nerve.
The composition of the white matter of the brain is as follows :
Solids
Water -
-
68 per cent.
Proteids-
S~
Cholesterin -
- 16
Lecithin
x
Cerebrin
0
3
-32 per cent.
Salts
- °'5
Other substances -
- i-sJ
Solids-
584 A MANUAL OF PIlYSIOUMrY
An analysis of the sciatic nerve of man gave in round numbers :
Water - . . . r,6 per cent.
[Cercbrin, lecithin, choles- "i
terin, and fatty acids 17 |
I Proteids and glutin - 16 ^-^ P"-' *'''''^^-
lOther substances - - i /
The only difference between living and dead nerve whicli has been
made out with any degree of certainty is that the former is neutral or
faintly alkaline, and the latter acid, in reaction.
Nutrition of Nerve. — Nerve-fibres are ' bound in the bundle
of life ' with certain nerve-cells on their course ; the con-
nection once severed, the nerve-fibre dies inevitably. In
other words, fibre and cell have a ' nutritive unity ' : and
this is what we should expect, for they also have a mor-
phological unity ; the fibre is a process of the cell. When
a spinal nerve is cut below the junction of its roots,
muscular paralysis and impairment of sensation at once
follow in the region supplied b}' the nerve ; but for a time
the nerve remains excitable to direct stimulation. The
excitability gradually diminishes, and in a few days is com-
pletely gone.
If portions of a nerve are examined at different periods
after section, a remarkable process of degeneration is seen
to be going on. The nuclei of the sheath of Schwann pro-
liferate, and insinuate themselves into the medullary sheath
and axis cylinder, which break up into detached pieces, and
ultimatel}' disappear, leaving the nerve-fibre represented
only by a kind of mummy of connective tissue. This process
goes on simultaneously along the whole nerve, from the cut
end to the periphery. In a mammal it is complete in about
a fortnight, but takes longer in cold-blooded animals.
Degeneration of the nerve is followed, if its divided ends
are not kept artificially apart, by a process of regenera-
tion, already distinct in from three to four weeks after the
section, but in some cases commencing as early as the
second week. This consists in the outgrowth of new axis
cylinders, in the form of fine fibres, from the ends of the
divided axis cylinders of the central stump of the nerve.
These push their wa\' into and along the degenerated fibres,
ultimately acquire a medullar} sheath, and develop into
NERVE 585
complete nerve-fibres, restorinj^ first sensation, and later on
voluntary motion, to the paralyzed part. The process needs
several months for its completion, even in warm-blooded
animals. It takes place under the influence of the nutritive
centre, and never occurs if the nerve is permanently sepiii -
ated from its cell. It is a remarkable and as yet unex-
plained fact that regeneration of the fibres of the central
nervous system, at least in the higher animals, either does
not occur at all or is exceedingly uncommon.
The nutritive centre for the fibres of the posterior root of
a spinal nerve — i.e., for the afferent fibres — is the ganglion on
that root ; the centres for nearly the whole of the fibres of
the anterior root lie in the spinal cord itself fp. 657).
Fig. 180. — Degeneraiion oi- Siinai, Nerves and their Roots amer
Section. — The shading shows the degenerated portions.
The proof of these statements is contained in Waller's
e.xperiments, which may be summarized as follows :
(i) Section of the anterior root causes degeneration on
the peripheral, but not on the central side of the lesion.
Only the anterior root fibres in the mixed nerve degenerate.
(2) Section of the posterior root above the ganglion causes
degeneration of the central stump, but not of the portion
still connected with the ganglion, nor of the posterior root
fibres below the ganglion or in the mixed nerve.
(3) Section of the posterior root below the ganglion causes
degeneration of the fibres of the root below the section and
in the mixed nerve, but not above it.
586 A MANUAL OF P/IYS/O/.OGV
(4) As has already been mentioned, section of the mixed
nerve causes degeneration on the peripheral, but not on the
central side of the lesion.
A few fibres in the peripheral stump of the anterior root
do not degenerate after its division, and a few fibres in the
central stump do. These are 'recurrent tibres' (p. 669),
which, leaving the spinal cord by the posterior root, run down
the nerve for a short distance, and then pass upwards in the
anterior root, probably to the pia mater and the connective
tissue of the root. The nutritive, or trophic, centre of these
fibres being the spinal ganglion, they do not degenerate so
long as the connection with it is intact.
Experimental section or, in man, traumatic division or
compression of a nerve leads not only to its degeneration,
but ultimately, if regeneration of the nerve does not take
place, to degeneration of the muscles supplied by it as well.
The muscle-fibres dwindle to a quarter of their normal
diameter; the stripes disappear; the longitudinal fibrilla-
tion fades out ; and at length only hyaline moulds of the
fibres are left, filled and separated by fatty granules and
globules, and surrounded by engorged capillaries. Amidst
the general decay, the muscular fibres of the terminal
' spindles,' with which the afferent nerves of muscles are
connected, alone remain unchanged (Sherrington). Certain
diseases of the cord which interfere with the cells of the
anterior horn cause degeneration of motor nerves, and
ultimately of muscles.
Muscles whose motor nerves have been separated from their
trophic centres show, when a certain stage in degeneration
has been reached, a peculiar behaviour to electrical stimu-
lation, called the 'reaction of degeneration.' To the constant
current the muscles are more excitable, and the contraction
slower and more prolonged than normal ; to the induced
current they are less excitable than normal, or not excitable
at all. The closing anodic contraction is stronger than the
closing kathodic — the opposite of the ordinary law. The
nerves are inexcitable either to constant or induced currents.
The reaction of degeneration is only obtained from paralyzed
muscles when the paralyzing lesion is situated below the
m-k\-j: 587
level of the cells of the anterior horn from which the motor
nerves take origin. Accordingly, it is sometimes of use in
localizing the position of a lesion.
Trophic Nerves. — The fact that the proper nutrition of
nerve-tibres is dependent on their connection with nerve-
cells has been by some writers generalized into the doctrine
that all tissues are provided with ' trophic ' nerves, which,
apart from any influence on functional activity, regulate
the nutrition of the organs they supply. But the evidence
for this view, when weighed in the balance, is found want-
ing; and it may be said that up to the present no unequivocal
proof, experimental or clinical, has ever been given of the existence
of specific trophic nerves.
It is true that division of the trigeminus nerve within the
skull is sometimes followed by cloudiness of the cornea,
going on to ulceration, and ultimately inflammation and
destruction of the eyeball. Ulcers also form on the lips and
on the mucous membrane of the mouth and gums; and the
nasal mucous membrane on the side corresponding to the
divided nerve becomes inflamed. But in this case the sen-
sibility of the eye is lost, and reflex closure of the eyelids
ceases to prevent the entrance of foreign bodies. The
animal is no longer aware of the contact of particles of dust
or bits of straw or accumulated secretion with the conjunc-
tiva, and makes no effort to remove them. The lips, being
also without sensation, are hurt by the teeth, particularly as
the muscles of mastication on the side of the divided nerve
are paralyzed, and decomposed food, collecting in the
mouth, and inhaled dust in the nose, will tend still further
to irritate the mucous membranes. There is thus no more
need to assume the loss of unknown trophic influences in
order to explain the occurrence of the ulcerative changes
than there is to explain the production of ordinary bed-
sores, bunions or corns on parts peculiarly liable to pressure.
And, as a matter of fact, if the eye be artificially protected,
after section of the trigeminal nerve, the ophthalmia either
does not occur or is much delayed.
In man, too, a case has been recorded in which both the
fifth and the third nerves were paralyzed. The eye was still
58S .1 MANUAL OF PHYSIOLOGY
shielded by the contraction of the orbicularis oculi supplied
by the seventh nerve, as well as In- the drooping of the
upper eyelid that accompanies paralysis of the third. It
remained perfectl}- sound for many months, till at length
the tumour at the base of the brain which had affected the
other nerves in\'olved the seventh too. The eye was now
no longer completely closed ; inflammation came on, and
vision was soon permanently lost (Shaw). In another case
a patient lived for seven years with complete paralysis of
the fifth nerve, yet the eye remained free from disease and
sight was unimpaired (Gowers).
The so-called ' trophic ' effects following division of both
vagi we have already discussed (p. 221) so far as the}- are
concerned with the respiratory system. The degenerative
changes sometimes seen in the heart are perhaps due to its
being overworked in the absence of nervous restraint on its
functional activity. The nutritive alterations in muscles and
salivary glands after section of motor and secretory nerves
seem to depend largely on functional and vaso-motor changes.
In muscles they may be in part due to the loss of a tonic
influence exerted on them by the motor cells of the spinal
cord, through the ordinary motor nerves (p. 683).
Section of the cervical sympathetic in young rabbits and
dogs is said to increase the growth of the ear and of the
hair on the same side ; but it is impossible to separate these
consequences from the vaso-motor paralysis ; and the same
is true of the hypertrophy following section of the vaso-
motor nerves of the cock's comb and of the nerves of bones.
The statement has been made that on section of the superior
laryngeal nerve in the horse the laryngeal muscles on the
corresponding side undergo rapid atrophy. Since the nerve
in this animal is destitute of motor fibres this seemed to
indicate either that the nerve contains efferent ' trophic '
fibres for the muscles, or that the activity of its afferent
fibres has a profound influence on their nutrition. But by
means of the larjngoscope it has been shown that after
section of the superior laryngeal the \ocal cord on the side
of the section is at once rendered motionless, and remains
so. The atrophy of the muscles is therefore due to their
NEKVE
5S9
inaction in the absence of the sensory impulses by which
the centre controhinj; them is noruially roused to activity.
And Mott and Sherrington have found that, ahhough section
of the posterior roots in monkeys is followed after a time
(three weeks to three months) by ulceration over certain
portions of the foot, no corresponding lesions occur in the
hand. They believe, therefore, that the lesions are not due
to the withdrawal of a reflex trophic tone, but are accidental
injuries in positions specially exposed to mechanical or
microbic insults.
Omitting the group of ' trophic ' nerves, and the even more pro-
blematical 'thermogenic' fibres, peripheral nerves may be classified
as follows
rSmell.
Taste.
I Hearing.
Isi
Centripetal
or afferent
fibres
2. Nerves of general sensation
PossiV)ly nerves other than
those included under i
and 2, concerned in reflex
chanties in
I. Nerves of special sensation
Vsight.
Tactile sensation (per-
haps including the
nerves of muscular
sense).
Temperature.
Pain.
Calibre of small arteries
(pressor, depressor).
Action of heart.
Visceral movements.
Respiratory move-
ments.
Glandular secretion.
Ordinary skeletal
muscles.
('Skeletal muscles.
Visceral ,,
j Vasoconstrictor.
Vascular „ - Cardio - augmen-
\ tor.
Erector muscles of hairs
motor fibres),
f Visceral muscles.
I r Vasodilator.
[Vascular ,, - Cardio -inhi-
^3. Secretory nerves. [ bitory.
* It is not known whether the aft'erent portion of a reflex arc is alioays
composed of fibres included in the first two categories, although
undoubtedly in some cases it is.
Centrifugal
or efferent
fibres
I. Motor nerves for
2. Inhibitory nerves for-
(pilo-
590 A MAXCAL OF PHYSIOLOGY
PRACTICAL EXERCISES ON CHAPTERS IX. AND X.
I. Difference of Make and Break Shocks from an Induction
Machine. -Connect a Daiiiell cx-U 15 (i). 173) with the two upper
binding-screws of the primary coil P, and interpose a spring key K
in the circuit. Connect a pair of electrodes with the binding-screws
of the secondary coil (Fig. 181).
Electrodes can be very simply made by pushing copper wires
through two glass tubes, filling the ends of the tubes with sealing-
wax, and binding them together with waxed thread, 'i'he projecting
points may be filed, and the nerve laid directly on them, or they
may be tipped with small pieces of platinum wire soldered on.
{a) Push the secondary away from the primary, until no shock can
be felt on the tongue when the current from the battery is made or
broken with the key. Then bring the secondary gradually up towards
Fk;. 181. — Akkangkmkn r ok Con. i-oR Si.n>.li-; SiiocKi).
the primary, testing at every new position whether the shock is per-
ceptible. It will be felt first at break. If the secondary is pushed
still further up, a shock will be felt both at make and at break.
From this we learn that for sensory nerves the break shock is
stronger than the make. The same can easily be demonstrated for
motor nerves and for muscle.
(b) Smoke a drum and arrange a myograph, as shown in l'"ig. 184.
But omit the brass piece F, and do not connect the primary through
the drum, as there shown, but connect it as in Fig. 181. Pith a frog
(brain and cord), and make a muscle-nerve preparation.
To make a A[usclc-Nen>e Preparation. — Hold the frog by' the
hind-legs ; the front part of the body will hang down, making an
angle with the posterior portion. With strong scissors divide the
backbone anterior to this angle, and cut away all the front portion of
the body, which will fall down of its own weight. Make a circular in-
cision at the level of the tendo Achillis, and another at the lower end
of the femur, through the skin. The sciatic nerve must now be dis-
/'A'. I cm \ I L l-XERi ISES 59 1
sected out, as follows : Remove the skin from the thigh, and, holding
the leg in the left hand, slit up the fascia which connects the external
and internal groups of muscles on the back of the thrgh. Complete
the separation with the two thumbs. Cut through the iliac bone,
taking care that the blade of the scissors is well pressed against the
bone, otherwise there is danger of severing the sciatic plexus. Now
divide in the middle line the part of the spinal column which remains
above the urostyle. A piece of bone is thus obtained by means of
which the nerve can be manipulated without injury. Seize this piece
of bone with the forceps, and carefully free the sciatic ple.xus and
nerve from their attachments right down to the gastrocnemius muscle,
taking care not to drag upon the nerve. The muscles of the thigh
will contract, as the branches going to them are cut. This is an
instance of mechanical stimulation. Now pass a thread under the
tendo Achillis, tie it, and divide the tendon below it. Strip up the
tube of skin that covers the gastrocnemius, as if the finger of a glove
were being taken off. Tear through the loose connective tissue
between the muscle and the bones of the leg, and divide the latter
with scissors just below the knee. Cut across the thigh at its middle.
Fix the preparation on the cork plate of the myograph by a pin
passed through the cartilaginous lower end of the femur, and attach
the thread to the upright arm of the lever by one of the holes in it.
Hang not far from the axis by means of a hook a small leaden weight
(5 to 10 grammes) on the arm of the lever which carries the writing-
point, and move the myograph plate or the muscle-nerve preparation
until this arm is just horizontal, hasten the electrodes from the
secondary coil on the cork plate with an indiarubber band ; lay the
nerve on them ; and cover both muscle and nerve with an arch of
blotting-paper moistened with normal saline, taking care that the
blotting-paper does not touch the thread. Adjust the writing-point
to the drum. Begin with such a distance between the coils that a
break contraction is just obtained on opening the key in the primary
circuit, but no make contraction. The lever will trace a vertical line
on the stationary drum. Read off on the scale of the induction
machine the distance between the coils, and mark this on the drum.
Now allow the drum to move a little, still keeping the writing-point
in contact with it ; then push up the secondary coil i centimetre
nearer the primary, and close the key. If there is a contraction, let
the drum move a little before opening the key again, so that the lines
corresponding to make and break may be separated from each other.
If there is still no contraction at make, go on moving the secondary
up, a centimetre (or less) at a time, till a make contraction appears.
When the coils are still further approximated, the make may become
equal in height to the break contraction, both being maximal, i.e., as
great as the muscle can give with any single shock (Fig. 182).
{c) Attach a thin insulated copper wire to each terminal of the
secondary. Loop the bared end of one of the wires through the
tendo Achillis, and coil the other round the pin in the femur, so
that the shocks will pass through the whole length of the muscle.
Repeat the experiment of (/^), with direct stimulation of the muscle.
592
A MANUAL OF PHYSIOLOGY
2. Stimulation of Nerve and Muscle by the Voltaic Current. — {a)
Connect a Daniell cell through a key with a pair of electrodes on
which the nerve of a muscle-nerve preparation lies. Observe that
the muscle contracts when the current is closed or broken, but not
during its passage.
Connect the cell with a simple rheocord, as shown in Fig. 183, so
MB MB MB
22 20 IB
M 8 MB
10
Y\-,. 182. — Contractions caused kv Make anu Break Shocks from an
Induction Machine.
M, make, H, break, contractions. The numbers give the distance between the
primary and secondary coils in centimetres.
that a twig of the current of any desired strength may be sent through
the nerve. As the strength of the current is decreased by moving
the slider S, it will be found that it first becomes impossible to obtain
a contraction at break. The current must be still further reduced
before the make contraction disappears, for the closing of a galvanic
stream is a stronger stimulus than the breaking of it. The break
or make contraction obtained by stimulating a nerve with an in-
Fk.. 183. — bl.MI'l.K RHEixOKI) AkKAN(;EI) lO SENl' A Tw If. OK A CCKKENT
IHROLOH A MlSCl.E OR NERVE.
B, battery. R, rheocord wire (German silver) ; S, slider formed of a short piece of
thick indiarubber tubing filled with mercury ; K, spring key ; W, W, wires connected
with electrodes.
duction-machine must not be confused with the break or make
contractions caused by the voltaic current. In the case of the
induction-machine, the break or make applies merely to what is done
in the primary circuit, not to what happens to the current actually
passing through the nerve. The current induced in the secondary at
make of the primary circuit is, of course, both made and broken in
PRACTICAL EXERCISES 593
the nerve — made when it begins to flow, broken when the flow is
over ; the shock induced at break of the primary is also made and
broken in the nerve. And although make and break of the actual
stimulating current come very close together, the real make, hure, too,
is a stronger stimulus than the real break.
{d) Repeat (a) with the muscle directly connected by thin copper
wires, or, better, unpolari/able electrodes (p. 526), to the cell.
3. Mechanical Stimulation. — Pith a frog. Cut away the anterior
portion of the body, dissect out one sciatic nerve, and separate the
leg to which it belongs from the other. Pinch the end of the nerve
or prick the muscles, and they contract.
4. Thermal Stimulation. — Touch the nerve of the same prepara-
tion with a hot wire ; the muscle contracts. The nerve is killed at the
point of contact, but can be again stimulated by touching it with the
wire lower down.
5. Chemical Stimulation.— (a) Cut off the injured portion of the
nerve used in 3 and 4. Apply to the cut end a crystal of common
salt, or let the nerve dip into a watch-glass containing a saturated
solution of salt. In a short time the muscles supplied by the nerve
begin to twitch, and soon enter into irregular tetanus. Take a
tracing of the contractions. Cut off the piece of nerve in contact
with the salt, and the tetanus stops. This shows that the seat of
irritation is the portion of the nerve into which the salt has pene-
trated, and from which water has been withdrawn by osmosis. Con-
traction can also be caused by applying the salt directly to the
muscles.
{b) Wrap the leg in blotting-paper moistened with normal saline,
and expose the nerve to the vapour of strong ammonia ; it will be
killed, but not stimulated, for the muscles will not contract. Expose
the muscles themselves to the ammonia, and contraction will occur.
Accordingly muscle is stimulated by ammonia, while nerve is not.
6. Ciliary Motion. — Cut away the lower jaw of the same frog, and
place a small piece of cork moistened with normal saline on the
ciliated surface of the mucous membrane covering the roof of the
mouth. It will be moved by the cilia down towards the gullet. Lay
a small rule, divided into millimetres, over the mucous membrane,
and measure with the stop-watch the time the piece of cork takes to
travel over 10 millimetres. Then pour normal saline heated to
30° C. on the ciliary surface, rapidly swab with blotting-paper, and
repeat the observation. The piece of cork will now be moved more
quickly than before, unless the normal saline has been so hot as to
injure the cilia.
7. Direct Excitability of Muscle — Acliojt of Ciirara. — Pith the
brain of a frog, and prevent bleeding by inserting a piece of match.
Expose the sciatic nerve in the thigh on one side. Carefully separate
it, for a length of half an inch, from the tissues in which it lies. Pass
a strong thread under the nerve, and tie it tightly round the limb,
excluding the nerve. Now inject into the dorsal or ventral lymph-
sac a few drops of a i per cent, curara solution. As soon as paralysis
is complete, make two muscle-nerve preparations, isolating the sciatic
38
594 A MANUAL 01' PHYSIOLOGY
nerves right up to the vertebral column. Lay their upper ends on
electrodes and stimulate; the muscle of the ligatured limb will
contract. This proves that the nerve-trunks are not paralyzed by
curara, since the poison has been circulating in them above the
ligature. The muscle of the leg which was not ligatured will
contract if it be stimulated directly, although stimulation of its nerve
has no effect. The muscular fibres, accordingly, arc- not paralyzed.
The seat of paralysis must therefore be some structures physio-
logically intermediate between the nerve-trunk and the muscular
fibres (p. 534).
8. Graphic Record of a Single Muscular Contraction or Twitch.
■ — Pith a frog (brain and cord), make a muscle-nerve preparation,
and arrange it on the myograph plate, as in i (/-). Lay the nerve on
electrodes connected with the secondary coil of an induction machine
arranged for single shocks. Introduce a short-circuiting key (Fig. 155)
between the electrodes and the secondary coil, and a spring key in
the primary circuit. Close the short-circuiting key, and then press
down the spring key with the finger. Let the drum off (fast speed) ;
the writing-point will trace a horizontal abscissa line. Open the
short-circuiting key, and then remove the finger from the spring-key.
The nerve receives an opening shock, and the muscle traces a curve.
Now adjust the writing-point of an electrical tuning-fork (Fig. 184),
vibrating, say, 100 times a second, to the drum, and take a time-
tracing below the muscle-curve. Stop the drum, or take off the
writing-point, the moment the time-tracing has completed one cir-
cumference of the drum, so that the trace may not run over on itself.
Cut off the drum-paper, write on it a brief description of the experi-
ment, with the time-value of each vibration of the fork, the date,
and the name of the maker of the tracing, and then varnish it. An
exactly similar tracing can be obtained by directly stimulating the
muscle (curarized or not).
9. Influence of Temperature on the Muscle-curve. — Pith a frog
(brain and cord), make a muscle-nerve preparation, and arrange it
on a myograph. Lay the nerve on electrodes connected through a
short-circuiting key with the secondary coil of an induction-machine,
or connect the muscle directly with the key by thin copper wires.
Take a Daniell cell, connect one pole through a simple key with
one of the upper binding-screws of the primary coil, and the other
pole with the metal of the drum. A wire, insulated from the
drum, but clamped on the vertical part of its support, and with its
bare end projecting so as to make contact with a strip of brass
fastened on the spindle, is connected with the other upper terminal
of the primary (Fig. 184). At each revolution of the drum the
primary circuit is made and broken once as the strip of brass brushes
the projecting end of the wire. The object of this arrangement is to
ensure that when the writing-point of the myograph lever has been
once adjusted to the drum, successive stimuli will cause contractions,
the curves of which all rise from the same point. Close the key in
the primary, set the drum off (fast speed), open the short-circuiting
key, and as soon as the muscle has contracted once, close it again.
PRACTICAL EXERCISES
595
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Now stop the drum, mark with a pencil the position of the feet of the
stand carrying the myograph plate, take the writing-point off the drum,
and surround the muscle with pounded ice or snow. After a couple
of minutes brush away any ice which would hinder the movement of
the muscle, rapidly replace the stand in exactly its original position,
with the writing-point on the drum, and take another tracing. Again
38-2
596 A MANUAL OF PHYSIOLOGY
take off the writing-point, and remove all unmelted ice or snow. With
a fine-pointed pipette irrigate the muscle with normal saline at 30° C,
and quickly take another tracing. Then put on a time-tracing with
the electrical tuning-fork. Fig. 166, p. 546, shows a series of curves
obtained in this way.
10. Influence of Load on the Muscle curve. — Arrange everything
as in 9. Take a tracing first with the lever alone, then with a weight
of 5 grammes, then with 10, 20, 50, and 100 grammes (Fig. 165,
P- 545)-
11. Influence of Fatigue on the Muscle-curve. — Arrange as in 10,
but leave on the same weight (say, 10 grammes) all the time. Place
the nerve on the electrodes. Leave the short-circuiting key open.
The nerve will be stimulated at each revolution of the drum, and the
writing-point will trace a series of curves, which become lower, and
especially longer, as the preparation is fatigued. Two or four curves
can be taken at the same time, if both ends of one or of two brass
slips be arranged so as to make contact with the projecting wire at
an interval of a semicircumference or quadrant of the drum (Fig. 184).
(For specimen curve, see Fig. 170, p. 549.)
12. Seat of Exhaustion in Fatigue of the Muscle-nerve Prepara-
tion for Indirect Stimulation. — \\'hen the nerve of a muscle-nerve
preparation has been stimulated until contraction no longer occurs,
the muscle can be made to contract by direct stimulation. The seat
of exhaustion is, therefore, not the muscular fibres themselves. To
determine whether it is the nerve-fibres or the nerve-endings, perform
the following experiments :
{a) Pith a frog ; make two muscle-nerve preparations ; arrange
them both on a myograph plate, which has two levers connected
with it. Attach each of the muscles to a lever in the usual way, and
lay both nerves side by side on the same pair of electrodes. Cover
■with moist blotting-paper. The electrodes are connected with the
secondary of an induction-machine arranged for tetanus. With a
camel's-hair brush moisten one of the nerves between the electrodes
and the muscle with a mixture of equal parts of ether and alcohol,
diluted with twice its volume of water, to abolish the conductivity.
Or put the mixture in a small bottle, in which dips a piece of filter-
paper. The projecting end of the filter-paper is pointed, and the
nerve is laid on the point. As soon as it is possible to stimulate
the nerves without obtaining contraction in this muscle, proceed to
tetanize both nerves till the contracting muscle is exhausted. If the
other muscle begins to twitch during the stimulation, more of the
ether mixture must be painted on the nerve. As soon as the stimula-
tion ceases to cause contraction in the non-etherized preparation,
wash off the mixture from the other nerve with normal saline, and
soon contraction may be seen to take place in the muscle of this
preparation. This shows that the nerve-trunk is still excitable.
Now, both nerves have been equally stimulated, and therefore the
exhaustion in the non-etherized preparation was not due to fatigue
of the nerve-fibres, but of the nerve-endings.
{h) Inject \ gramme chloral hydrate into the rectum of a rabbit,
PRACTICAL EXERCISES 597
and put a pair of bulldog forceps on the anus. Fix the animal on a
holder as soon as the chloral has taken effect. Clip the hair from
the front of the neck and insert a tracheal cannula (p. 177)- Now
inject subcutaneously enough of a i per cent, solution of curara to just
paralyze the skeletal muscles. As soon as symptoms of paralysis of
the muscles of respiration have appeared, connect the tracheal cannula
with the artificial respiration apparatus. Now expose the sciatic nerve
(p. 186) on one side, put on a ligature, and divide it above the ligature.
Lay the nerve on electrodes connected with the secondary coil of
an induction machine arranged for tetanus, and stimulate it. If the
muscles supplied by the nerve contract, curara must be injected till
contraction is no longer obtained. Then the nerve is continuously
stimulated for a long time. After some hours the curara action will
begin to wear off, and it may be seen that the muscles of the leg
again contract. This shows that even a very prolonged stimulation
is not sufficient to exhaust the extra-muscular nerve-fibres (Bowditch).
Fig. 185. — Arrangement for studying Voluntary Muscular Fatigue.
13. Seat of Exhaustion in Fatigue for Voluntary Muscular Con-
traction.— Support the arm, extensor surface downwards, on a rest
such as that shown in Fig. 184, and connect the middle finger of
one hand, by means of a string passing over a pulley on the edge
of a table, with a weight of 3 or 4 kilos. The string is attached to
the finger by a leather collar surrounding the second phalanx of the
finger, but allowing free movements of the joints. The extent of the
vertical movements of the string (and therefore the work done) may
be registered on a drum by a writing-point connected with it, the
whole arrangement forming what is called an crgograph. Two collar
electrodes (strips of copper covered with cotton-wool soaked in salt
solution, and bent to a circular form) are placed on the forearm, and
connected through a short-circuiting key with the secondary coil of an
induction machine arranged for tetanus (p. 175), and having a battery
of four or five Daniell cells, coupled in series,* in its primary circuit.
The middle finger is now made to raise the weight repeatedly by
vigorous contractions of the flexor muscles until at length a failure
* I.e., the copper of one cell connected with the zinc of the next.
59^ A MANUAL OF PHYSIOLOGY
occurs. At this moment the short-circuiting key is ojiened, and the
flexor muscles stimulated electrically. They again contract and raise
the weight, therefore the seat of exhaustion in voluntary muscular
effort is not in the muscles. That it is not usually in the nerve-
endings nor in the nerves may be shown by inducing fatigue of the
finger for voluntary contraction in the same way, and then stimu-
lating the median nerve at the bend of the elbow by sponge elec-
trodes. The usual seat of fatigue for voluntary muscular contraction
must therefore be in the spinal cord or brain, and as we have no
reason to believe that the nerve-fibres of the central nervous system
are essentially different from peripheral nerve-fibres, we conclude that
the fatigue is in the nerve-cells or the network of fibrils around them
(p. 640).
14. Influence of Veratria on Muscular Contraction.- — Arrange a
drum as in Fig. 184. Pith a frog (brain only), expose the sciatic
nerve in one thigh, and isolate it for \ inch from the surrounding
tissues. Pass under it a strong thread, and ligature everything except
the nerve. Now inject into the dorsal or ventral lymph-sac a few
drops of o"i per cent, solution of sulphate of veratria. In a few
minutes make two muscle-nerve preparations from the posterior limbs.
First put the preparation from the unligatured limb on the myograph
plate. Lay the nerve on electrodes connected through a short-circuit-
ing key with the secondary of an induction machine arranged as in
Fig. 184. Put the writing-point on the drum and set it off (fast
speed). Open the short-circuiting key till the nerve has been once
stimulated, then close it again. The curve obtained differs from a
normal curve, in that the period of descent (relaxation) is exceedingly
prolonged. Now connect the preparation from the ligatured limb
with the lever, and take a tracing of a single contraction. Put on a
time-tracing with the electrical tuning-fork (see Fig. 171, p. 551).
15. Measurement of the Latent Period of Muscular Contraction.
— Use the spring myograph (Fig. 162, p. 542), raising it on blocks of
wood. Smoke the glass plate over a paraffin flame, or cover it with
paper, and smoke the paper. Connect the knock-over key of the
myograph with the primary circuit of an induction coil. Pith a frog,
and make a muscle-nerve preparation. Arrange it on the myograph
plate. Place electrodes below the nerve as near the muscle as
possible, and connect by a short-circuiting key with the secondary.
Bring the writing-point in contact with the smoked surface of the
spring myograph, so as to get the proper pressure. See that the
writing-point of the tuning-fork is in the right position for tracing
time. Then push up the plate so as to compress the spring, till the rod
connected with the frame which carries the plate is held by the catch.
With the short-circuiting key closed, press the release and allow
an abscissa line to be traced. Again shove back the frame till it is
caught. Push home the rod by means of which the prongs of the
tuning-fork are separated, and rotate it through 90°. Close the
knock-over key, open the short-circuiting key, shoot the plate again,
and a muscle-curve and time-tracing will be recorded. Again close
the short-circuiting key, withdraw the writing-point of the tuning-
PRACTICAL EXERCISES 599
fork, push back the plate, close the trigger-key, then open the short-
circuiting key, and holding the travelling frame with the hand, allow
it just to open the knock-over and stimulate the nerve. The writing-
point now records a vertical line (or, rather, an arc of a circle), which
marks on the tracing the moment of stimulation. The latent period
is obtained by drawing a parallel line (or arc) through the point of
the muscle-curve where it just begins to diverge from the abscissa
line. The value of the portion of the time-tracing between these two
lines can be readily determined, and is the latent period.
1 6. Summation of Stimuli. — Arrange two knock-over keys on the
spring myograph at such a distance from each other that the plate
travels from one to the other in a time less than the latent period.
Connect each key with the primary circuit of a separate induction
coil having a couple of Daniells in it. Join two of the binding-screws
of the secondaries together : connect the other two through a short-
circuiting key with electrodes, on which the nerve of a muscle-nerve
preparation is arranged. Push up the secondaries till the break
shocks obtained on opening the two knock-over keys are maximal.
Then shoot the plate as described in 15, first with one trigger key
closed, and then with both. The curves obtained should be of the
same height in the two cases, as a second maximal stimulus falling
within the latent period is ignored by the nerve or muscle. Repeat
the experiment with submaximal stimuli, i.e., with such a distance of
the coils that opening of either trigger key does not cause as strong
a contraction as is caused when the coils are closer. The curve will
now be higher when the two shocks are thrown in successively than
when the nerve is only once stimulated. This shows that (sub-
maximal) stimuli can be summed in the nerve. The same could be
demonstrated for muscle (p. 552).
17. Superposition of Contractions. — Smoke a drum arranged for
automatic stimulation as in Fig. 1S4. Adjust the brass points with
a distance of, say, one centimetre between them, so that a second
stimulus may be thrown into the nerve at an interval greater than the
latent period of muscle. Put two Daniells in the primary circuit.
Lay the nerve of a muscle-nerve preparation on electrodes connected
through a short-circuiting key with the secondary. Allow the drum
to revolve (fast speed); open the short-circuiting key till both brass
points have passed the projecting wire, then close it. Now bend
back the second brass point, and take a tracing in which the first
curve is allowed to complete itself. This will not rise as high as the
second curve obtained when the two stimuli were thrown in. Repeat
the experiment with varying intervals between the brass points —
that is, between the two successive stimuli. Put on a time-tracing
with the electrical tuning-fork. (For specimen curve see Fig. 172,
P- 552).
18. Composition of Tetanus. — {a) Adjust a muscle-nerve prepara-
tion on a myograph plate, the nerve being laid on electrodes con-
nected through a short-circuiting key with the secondary of an induc-
tion machine, the primary circuit of which contains a Daniell cell
and is arranged for an interrupted current (Fig. 65, p. 175). The
6oo
A MA Nl 'A L or PIf YSIOLOGY
lever should be shorter than that used for the previous experiments,
or the thread should be tied in a hole farther from the axis of rota-
tion, so as to give less magnification of the contraction. Set the
Neefs hammer going, let the drum revolve (slow speed), and open
the key in the secondary. The writing-point at once rises, and traces
a hori;^ontal or perhaps slightly-ascending Hne. Close the short-
circuiting key, and the lever sinks down again to the abscissa line.
If it does not quite return, it should be loaded with a small weight.
This is an example of complete tetanus.
{l>) Connect the spring shown in Fig. i86 with one of the upper
terminals of the primary coil, and the mercury cup with the other.
Fasten the end
of the spring in
one of the
notches in the
upright piece of
wood by means
of a wedge, so
that its whole
length can be
made to vibrate.
Let the drum off,
set the spring
vibrating by de-
pressing it with
the finger, then
open the key in
the secondary.
The muscle is
thrown into in-
complete tetanus,
and the writing-
point traces a wavy curve at a higher level than the abscissa line. Close
the short-circuiting key, and the lever falls to the horizontal. Repeat
the experiment with the spring fastened, so that only 'l, ^, \, ^ of its
length is free to vibrate. The rate of interruption of the primary
circuit increases in proportion to the shortening of the spring, and
the tetanus becomes more and more complete till ultimately the
writing-point marks an unbroken straight line. Put on a time-tracing
by means of an electro-magnetic marker connected with a metronome
beating seconds or half-seconds (Fig. 60, p. 170). (For specimen
curves see Fig. 173. P- 553-)
19. Velocity of the Nerve-impulse. — Use the spring myograph
(Fig. 162, p. 542). Make a muscle-nerve preparation from a large
frog (preferably a bull-frog), so that the sciatic nerve may be as long
as possible. Connect the knock-over key with the primary circuit of
an induction machine, which should contain a single Daniell cell.
Arrange two pairs of fine electrodes under the nerve on the myograph
plate, one near the muscle, the other at the central end. Connect
the electrodes with a Pohl's commutator (without cross-wires), the
Fig. 186. — Arrangement for Tetanus.
A, upright with notches, in which the spring S is fastened
(sho\vn in section) ; C, horizontal board to which .A isattached,
and in a groove in which the mercury-cup E slides. The primary
coil V is connected with E, and through a simple key, K, with
the battery B, the other pole of which is connected with the end
of the spring. The wires from the secondary coil, P'. go to a
short-circuiting key, K', from which the wires F go off to the
electrodes.
PRACTICAL l.XKRCISES 601
side-cups of which are joined to the terminals of the secondary coil,
as shown in Fig. 187. By tilting the bridge of the commutator the
nerve may be stimulated at either point. (Ireat care must be taken
to keep the nerve in a moist atmosphere by means of wet blotting-
paper ; but at the same time it must not lie in a pool of normal
saline, as twigs of the stimulating current would in this case spread
down the nerve, and we could never be sure that the apparent was
always the real point of stimulation. The writing-points of the lever
and tuning-fork having been adjusted to the smoked plate, as in 15,
the bridge of the Pohl's commutator is arranged for stimulation of
the distal point of the nerve, the plate is shot with the short-circuit-
ing key in the secondary closed, and an abscissa line and time-curve
traced. Then the writing-point of the fork is removed and the plate
again shot with the key in the secondary open, and a muscle-curve
Fig. 187. — Akran(;eme.nt for measuring the Velocity of the Nerve-
impulse.
A, travelling plate of spring myograph; M, muscle lying on a myograph plate;
N, nerve, lying on two pairs of electrodes, E and E' ; C, Pohl's commutator without
cross wires ; K, knock-over key of spring myograph (only the binding-screws shown) ;
K', simple key in primary circuit ; B, battery ; P, primary coil ; .S, secondary coil.
is obtained. The commutator is now arranged for stimulation of
the central end of the nerve, and another muscle-curve taken.
Vertical lines are drawn through the points where the two curves
just begin to separate out from the abscissa line. The interval
between these lines corresponds to the time taken by the nerve-
impulse to travel along the nerve from the central to the distal pair
of electrodes. Its value in time is given by the tracing of the
tuning-fork. The length of the nerve between the two pairs 'of
electrodes is now carefully measured with a scale divided in milli-
metres, and the velocity calculated (p. 582).
20. Chemistry of Muscle. — Mince up some muscle from the hind-
legs of a dog or rabljit (used in some of the other experiments), of
which the bloodvessels have been washed out by injecting normal
6o2 A MANUAL OF VIIYSIOLOGY
saline solution through a cannula lied into the abdominal aorta until
the washings are no longer tinged with blood. To some of the
minced muscle add twenty times its bulk of distilled water, to another
portion ten times its bulk of a 5 per cent, solution of magnesium
sulphate. Let stand, with frequent stirring, for twenty-four hours.
Then strain through several folds of linen, press out the residue, and
filter through paper, (i) With the filtrate of the watery extract make
the following observations :
{a) Reaction.— -'Yo litmus pa[)er acid.
{/') Determine the temperatures, at which coagulation of the various
proteids in the extract takes place, according to the method described
on p. 21. Put some of the watery extract in the test-tube, and
heat the bath, stirring the water in the beakers occasionally with a
feather. Note at what temperature a coagulum first forms. It will
be about 47° C. Filter this off, and again heat ; another coagulum
will form at 56° to 58'. Filter, and heat the filtrate ; a third slight
coagulum may be formed at 60'' to 65"^ C. A fourth precipitate
(of serum-albumin) will come down at 70" to 73°. Saturate some
of the watery extract with magnesium sulphate ; a large pre-
cipitate will be formed, showing the presence of a considerable
amount of globulin. Filter off the precipitate and heat the filtrate ;
coagulation will again occur at very much the same temperatures as
before. The substance coagulating at 47 ' to 48' has been described
by Halliburton as a globulin, by Demant as an albumin. If it is a
single substance, it possesses some of the characters of both globulins
and albumins, for it is partially but not entirely precipitated by
saturation with magnesium sulphate, and is not precipitated by
sodium chloride.
(2) {a) Test the reaction of the magnesium sulphate extract. It
will usually be faintly acid.
(/>) Heat some of it. Precipitates will be obtained at the same
temperatures as in (i) {b), but those at 47° to 48" and 56" to 58° will
be more abundant. Of the two, that at 47^ to 48" will be the larger
when time is given for it to come down and the heating is gradual.
{c) Dilute some of the magnesium sulphate extract with three times,
another portion with four times, and another with five times, its volume
of water in a test-tube, and put in a bath at 40 C. Coagulation will
occur in one or all of these test-tubes. To another test-tube of the
extract diluted in the proportion which has given the best ' muscle-
clot ' add a few drops of a dilute solution of potassium oxalate, and
place in the bath at 40". Coagulation occurs as before. Filter off
the clot from all the test-tubes. The filtrate is the ' muscle-serum,'
and yields a precipitate of serum-albumin at 70° to 73° C. Dissolve
the muscle-clot in 5 per cent, magnesium sulphate. It consists of
the substances which coagulate at 47' to 48° and 56° to 58°. These
are supposed by Halliburton to be two distinct bodies — paramyosin
and myosin. Kut it should be remembered that the temperature of
heat-coagulation of any substance is by no means an absolute con-
stant. It depends on the reaction, the profwrtion and kind of neutral
salts present, perhaps on the strength of the proteid solution and the
PRACTICAL EXERCISES (rOT,
manner of heating. A solution of egg-albumin, e.g., can be coagulated
at a temperature much below 70^ when it is heated for a week. Small
differences in the temperature of heat-coagulation, unless supported
by well-marked chemical reactions, arc not enough to characterize
proteid substances as chemical individuals.
(3) Myosin, like other globulins, is insoluble in distilled water, but
soluble in weak saline solutions. Saturation with neutral salts like
sodium chloride and magnesium sulphate precipitates myosin, but
not albumin, from its solutions ; saturation with ammonium sulphate
precipitates both. Myosin is said to be dissolved without change in
very weak acids. Stronger acids precipitate it. Verify the following
reactions of myosin, using either a solution of the muscle-clot, or the
original magnesium sulphate extract of the muscle.
{a) Dropped into water, it is precipitated in flakes, which can be
redissolved by a weak solution of a neutral salt (say 5 per cent, mag-
nesium sulphate).
{b) When a solution of myosin is dialysed, it is precipitated on
the inside of the dialyser as the salts pass out.
{/) If a piece of rock-salt is suspended in a solution, the myosin
gradually gathers upon it, diffusion of the salt out through the precipi-
tated myosin always keeping a saturated layer around it.
{d) Saturate a solution containing myosin with crystals of mag-
nesium sulphate, stirring or shaking at frequent intervals. The
myosin is precipitated.
{e) Without adding any salt, simply shake a myosin solution
vigorously ; a certain amount of the myosin will be precipitated, and
the solution will become turbid. This reaction can also be obtained
with solutions of other proteids, such as albumin (Ramsden).
E.xtracts in all essentials similar to those obtained from the muscles
of a freshly-killed animal can be got from muscles that have entered
into rigor.
21. Reaction of Muscle in Rest, Activity, and Rigor Mortis. —
{a) Take a frog's muscle, cut it across, and press a piece of red litmus
paper on the cut end ; it is turned blue. Yellow turmeric paper is
not affected.
{b) Immerse another muscle in normal saline solution at 40' to
42° C. It becomes rigid. The reaction becomes acid to litmus
paper, and also turns brown turmeric paper yellow.
(f) Plunge another muscle into boiling normal saline solution. It
becomes even harder than in {l)\ but its reaction remains alkaline to
litmus paper.
((/) Stimulate another muscle with an interrupted current from
an induction machine (Fig. 65, p. 175), till it no longer contracts.
The reaction is now acid to litmus paper. Brown turmeric paper
may also be turned yellow.
22. Effect of Suprarenal Extract on Muscular Contraction — (i)
On Skeletal Ahiscle. — Proceed as in 14, but instead of veratria inject
a watery solution of the suprarenal capsules (calf, sheep, dog, etc.).
The curve of the gastrocnemius acted upon by the extract is pro-
longed as in veratria poisoning, although not to such a great extent.
6o4 A MANUAL OF PHYSIOLOGY
(2) On the Smooth Muscle of the Bloodvessels. — Make the arrange-
ments for a blood-pressure tracing from a dog as in ig, p. 185. Put
a cannula in the carotid and another in the femoral vein or one of
its branches (p. 177). Expose both vagi in the neck, and pass
threads loosely under them. Connect the carotid with the mano-
meter and take a tracing. Then, while the tracing is continued,
inject slowly into the femoral vein an amount of watery extract
corresponding to about -J-th gramme of suprarenal. The blood-
pressure rises* owing to constriction of the arterioles by direct
action of the extract on their muscular tissue. The heart is greatly
slowed owing to stimulation of the cardio-inhibitory centre. At
once cut both vagi while a tracing is being taken ; the blood-pressure
rises still more (p. 475). The rise is not long maintained, but a
second injection causes a renewed increase of pressure.
* The amount of the initial rise of pressure is ver)' variable, since the
slowing of the heart tends to diminish the pressure, while the constriction
of the arterioles tends to increase it. Thus, in one experiment the increase
of pressure on injection of the extract was only 6 mm. of mercur)-, while
in another it was 56 mm. On section of the vagi in this second experi-
ment, there was an additional rise of 64 mm., and after a second injection
a further rise of 70 mm., making an increase of 190 mm. in all above the
original pressure.
CHAPTER XI.
ELECTRO-PHYSIOLOGY.
A LITTLE more than a hundred years ago the foundation both of
electro-physiology and of the vast science of voltaic electricity was
laid by a chance observation of a professor of anatomy in an Italian
garden. It is indeed true that long before this electrical fishes were
not only popularly known, but the shock of the torpedo had been to
a certain extent scientifically studied. But it was with the discovery
of Galvani of Bologna that the epoch of fruitful work in electro-
physiology began. Engaged in experiments on the effect of static
electricity in stimulating animal tissues, he happened one day to
notice that some frogs' legs, suspended by copper hooks on an iron
railing, twitched whenever the wind brought them into contact with
one of the bars (p. 627). He concluded that electrical charges were
developed in the animal tissues themselves, and discharged when the
circuit was completed. Volta, professor of physics at Padua, fixing his
attention on the fact that in Galvani's experiment the metallic part of
the circuit was composed of two metals, maintained that the contact
of these was the real origin of the current, and that the tissues served
merely as moist conductors to complete the circuit ; and he clinched
his argument by constructing the voltaic pile, a series of copper and
zinc discs, every two pairs of which were separated by a disc of
wet cloth. The pile yielded a continuous current of electricity.
' So,' said Volta, ' it is clear that the tissue in Galvani's experiment
only acts the part of the cloth.' Galvani, however, showed that con-
traction without metals could be obtained by dropping the nerve of a
preparation on to the muscle (p. 627); and it soon began to be recog-
nised that both Cialvani and Volta were in part right, that two brilliant
discoveries had been made instead of one ; in short, that the tissues
produce electricity, and that the contact of different metals does so
too. Although it is curious to note how completely the growth of
that science of which Volta's discovery was the germ has over-
shadowed the parent tree planted by the hand of Galvani, yet
animal electricity has been deeply studied by a large number of
observers, and many interesting and important facts have been
brought to light.
6o6
A MA NUA L or PI I J 'SIOL OGY
Since it is in muscle and nerve that the phenomena of
electro-physiology are seen in their simplest expression, and
have been chiefly studied, we shall develop the fundamental
laws with reference to muscle and nerve alone, and after-
wards apply them to other excitable tissues.
I. All points on the surface of an uninjured reding:; muscle are
approximately at the same potential. In other words, if any
two points are connected with a galvanometer by means of
unpolarizable electrodes, little or no current is indicated.
(Although it is scarcely possible to isolate a muscle without
its showing some current, the more carefully the isolation
is performed the feebler is the current ; and between two
points of the inactive, uninjured ventricle of the frog no
electrical difference has been found.)
Fig. i88. — A, uninjured, B, injured,
portion of nerve ; G, galvanometer.
The large arrows show direction of
demarcation current or current of rest,
the small arrows direction of negative
variation or action current.
1' JG. 189.— Diagram ok Currents
OF Rest in a Regular Milscle,
OR Musci.E Cylinder,
E, equator. The dotted lines join
points at the same potential, between
which there is no current.
2. Any uniiijured point on the surface of a restinf( muscle or
nerve is at a higher potential than any injured point ; so that a
current will pass through the galvanometer from uninjured
to injured point, and in the tissue from the latter to the
former (current of rest or demarcation current — Fig. 188).
3. Any uncxcitcd point on the surface of a muscle or nerve is
at a higher potential than any excited point, and any less excited
point is at a higher potential than any more excited point.
The best object for experiments on the demarcation
current is a straight-fibred muscle like the frog's sartorius.
If this muscle be taken, and the ends cut off perpendicularly
to the surface, a muscle-prism is obtained (Fig. 189). The
strongest current is got when one electrode is placed on
the middle of either cross-section and the other on the
* equator ' — that is, on a line passing round the longitudinal
ELECTRO-PI I ) 'SIOL OGY 607
surface midway between the ends. The direction of this
current is from the cross-section towards the equator in the
muscle. If the electrodes are placed on symmetrical points
on each side of the e(iuator, there is no current.
A particular case of this symmetrical or ' streamless ' arrangement
is where the middle i)oints of the two cross-sections are led off to
the galvanometer ; here, if the sections are similar, their potential
is the same, and the needle remains at zero. Between two points
of the longitudinal surface at unequal distances from the equator
there is a current in the galvanometer from the nearer to the more
distant point, the potential of a longitudinal point nearer a cross-section
being lower than that of one more remote. Between two points on
the same cross-section there is a current if they are not symmetrically
placed with reference to its centre, the direction in the muscle being
from more central to more peripheral point.
The above may be taken as applying to nerve also, with
the proviso that less is known as to electrical differences
between points on the same cross-section, since ordinary
cold-blooded nerves are too small for such experiments.
Current of Action, or Negative Variation. — When a muscle
or nerve is excited, a wave of diminished potential (nega-
tivity) sweeps over it. Suppose two points, A and B
(Fig. 190), on the longitudinal surface of a muscle to be con-
nected with a capillary electrometer (p. 524), the movements
of the mercury being photographed on a travelling sensitive
surface. Let the muscle be excited at the end, so that the
wave of excitation will be propagated in the direction of
the arrow. The wave will reach A first, and while it has not
yet reached B, A will become negative to B. If there is a
resting difference of potential between A and B, this will
be altered, the new and transitory difference adding itself
algebraically to the old. When the wave reaches B, it may
already have passed over A altogether, and B now becoming
negative to A, there will be a movement of the meniscus of
the electrometer in the opposite direction. This is called
the diphasic current of action. If the wave has not passed
over A before it reaches B, as would in general be the case
in an actual experiment, there will be first a period during
which A is more negative than B (first phase) ; this will end
as soon as B has become equally negative with A, and will
be succeeded by a period during which B is more negative
6o8
A MANUAL OF PHYSIOLOGY
than A (second phase). Since the wave takes time to reach
its maximum, it is evident that a well-marked first phase
will be favoured when the interval between its arrival at
A and B is long, for in this case A will have a chance of
becoming strongl}- negative while B is still normal. Simi-
larly, if A has again become normal, or nearly normal,
before the maximum negativity has passed over B, a strong
second phase will be favoured. The heart-muscle, accord-
ingly, where the wave of contraction, and its accompanying
electrical change, move with comparative slowness, is better
Fk;
190. — DiACRAM VO II.l.UsrKAlK PkOI'AIIATION OK IIIK NEGATIVE
Change along an Active Muscle or Nerve.
Suppose A B to be a horizontal bar representing the muscle or nerve. Let C be a
curved piece of wood representing the curve of the electrical change at any point.
Let W W be two glass cylinders connected by a flexible tube, the whole being
filled with water. Suppose the rims of the cylinders originally to touch .A B at the
points A and B, and let them be movable only in the vertical direction. Tiie level of
the water being the same in botli, there is no tendency for it to flow from one to the
other. This represents the resting state of the tissue when A and B are symmetrical
points. Now let C be moved along the bar at a uniform rate. The cylinder W, being
free to move down, but not horizontally, will be displaced by C, and, if it is kept
always in contact with its curved margin, will, after describing the curve of the
electrical variation, come again to rest in its old position at A. B will do the same
when C reaches it. But since C reaches .\ before B, the level of the water in B will
at first be higher than that in A, and water will flow from B to .\. This will corre-
spond to the time during which the point of the tissue represented by .A. would be
negative to a pomt represented by B. Later on, when C has reached the position
shown by the dotted lines, the level of the water in A will be higher than that in B,
and a flow will taUe place in the opposite direction to the first flow. This corresponds
to a second phase of the negative variation.
suited for showing a well-marked diphasic variation than
skeletal muscle, and still better suited than nerve. In the
gastrocnemius muscle of the frog, when excited through its
EL ECTR 0- 1 'II ) SIOL OGV O09
nerve, the electrical response begins about ,tjVF second, and
the change of form of the muscle about 1^5^ second after
the stimulation. The apex of the curve, or change of sign,
corresponds to 1^5 second after excitation. It is believed
that in a muscle directly excited the electrical change begins
in less than j^Vo second, and the mechanical change in
i^Vo second (Burdon Sanderson). (Figs. 192-194.)
When one electrode is placed on an injured part, the
wave of action and of electrical change diminishes as it
reaches the injured tissue ; and if the tissue is killed at this
part, it diminishes to zero ; so that here the second phase
may be greatly weakened or may disappear altogether.
In this case the current of action can be demonstrated,
even for a single excitation, but still better for a tetanus,
with the galvanometer, which in general is not quick enough
to analyze a diphasic variation with equal phases, and gives,
therefore, only their algebraic sum — that is, zero. When
the muscle or nerve is tetanized, the negative variation
appears, while stimulation is kept up, as a permanent
deflection representing the ' sum ' of the separate effects.
The action current of .the phrenic nerve which accompanies
the natural respiratory discharge has been recently demon-
strated (Reid and Macdonald).
When the current of rest is compensated by a branch of an
external current just sufficient to balance it and bring the galva-
nometer image back to zero, the action current appears alone in
undiminished strength. This shows that the latter is not due to a
change of electrical resistance during excitation, since such a change
would equally affect current of rest and compensating current, and
they would still balance each other. The action current is really due
to a change of potential, which can be measured by determining
what electromotive force is just required to balance it, and which
may actually exceed that of the current of rest. Thus, Sanderson and
Gotch found an average of o'oS of a Daniell cell (the electromotive
force of the Daniell would be about a volt) as the electromotive force
of the action current due to a single indirect excitation of a vigorous
frog's gastrocnemius, and about 0-04 Daniell as that of the current of
rest. The electromotive force of the current of rest in rabbit's nerve
was found by du Bois-Reymond to be o"o26 ; Gotch and Horsley
found the average for the cat 001, and for the monkey only o'oo5.
Before Burdon Sanderson introduced the capillary electro-
meter for the study of the electrical phenomena of living
39
6io
A MANUAL OF PHYSIOLOGY
tissues, and Burch perfected a method for the measurement
of the curves, the differential rheotomc, originally constructed
by Bernstein, was the most valuable instrument we pos-
sessed for experiments on the time -relations of these
phenomena. By its aid, for instance, it was shown that
the rate of propagation of the electrical change in muscle is
the same as that of the mechanical change, and in nerve the
same as that of the nervous impulse.
The differential rheotome consists essentially of a stationary metal
ring, the whole or part of which is graduated, and of a portion which
can be made to revolve at a known rate. The latter carries two
contacts : a, an obliquely-placed platinum wire which touches at
every revolution a horizontal
wire b on the fixed ring, thus
making and breaking the pri-
mary circuit P of an induc-
tion machine, and so causing
stimulation of a muscle or
nerve M connected with the
secondary S ; and, c, a double
contact, either in the form of
two platinum wires, which dip
into two mercury troughs, or
of two wire brushes rubbing
on copper blocks d, at a
certain part of the revolution.
The troughs or blocks are con-
nected with a circuit contain-
ing a galvanometer G, and a
portion of the muscle or nerve
arranged so as to give a strong
action current. This circuit
is completed by the wires or
brushes, which are in metallic
contact with each other ; and the relative position of the fixed con-
tact in the primary circuit and of the troughs or copper blocks can
be altered so as to alter at will the interval between stimulation and
closure of the galvanometer circuit. The proportion of the whole
revolution during which this circuit is closed can be varied by
changing the relative position of the two copper blocks. Suppo.se
the tissue is stimulated at one end while the leading-off electrodes
are at the other. When the contact a, l>, is made at the same time
as c, d, no deflection will be shown by the galvanometer if the
rheotome is revolving ra[)idly (the demarcation current being
accurately compensated), because the circuit will be opened before
the negative change has time to travel to the leading-off electrodes.
But as the distance between b and d is increased, a small deflection
Fk
191.— Diagram ok Difierential
Rheotome.
ELECTROPHYSIOL OGY 611
will appear, which, with further increase of the distance, will become
larger, reach a maximum, and then begin to fall off again. The
first small deflection corresponds to the position in which the negative
change has just had time to reach the leading-off electrodes before
the galvanometer circuit is opened. The maximum deflection cor
responds to a period a little later than this, because the electrical
variation does not at once reach its maximum at any point.
In human muscles the current of action has been demonstrated by
connecting a galvanometer with ring electrodes passing round the
forearm, and throwing the muscles into contraction. A diphasic
variation is thus obtained ; and the electrical change travels with a
velocity of as much as 1 2 metres per second, which is greater than
the velocity in frogs' muscles.
As to the interpretation of the facts we have been de-
scribing, and which are summed up in the three propositions
on p. 606, two chief doctrines have divided the physiological
world : (i) the theory of du Bois-Reymond, the pioneer of
electro-physiology, and (2) the theory of Hermann. It was
believed by du Bois-Reymond that the current of rest seen
in injured tissues is of deep physiological import, and that
the electrical difference which gives rise to it is not de-
veloped by the lesion as such, but only unmasked when the
electrical balance is upset by injury. He looked upon the
muscle or nerve as built up of electromotive particles, with
definite positive and negative surfaces arranged in a regular
manner in a sort of ground-substance which is electrically
indifferent. The ' negative variation ' he supposed to depend
on an actual diminution of previously-existing electromotive
forces ; and from this conception arose its historic name.
This theory has been highly elaborated and extended to
include new facts as they have arisen, and it explains certain
phenomena, such as the currents of a prism of muscle,
better than the simpler theory associated with the name
of Hermann. The latter observer and his school assume
that the uninjured muscle or nerve is ' streamless,' not
because equal and opposite electromotive forces exactly
balance each other in the substance of the tissue, but
because electromotive forces are absent until they are called
into existence at the boundary, or plane of demarcation,
between sound and injured tissue. For this reason in the
terminology of Hermann du Bois-Reymond's current of rest
is called the ' demarcation ' current.
39—2
6 1-2
A MANUAL OF PHYSIOLOGY
i\j\r\j\r\
••- The experiments of Burdon Sanderson, who photoj^raphed
the excursions of the capillary electrometer on a sensitive
plate carried by a rapidly-
moving pendulum, have tended
to revive under new and striking
aspects the old ' pre-existence '
theory of du Bois-Reymond,
which some physiologists seem
to have regarded as moribund,
f-j^. if not actually defunct. For
Electrical response to single mo- Sanderson has shown that in
mentary excitations of an injured ^(]A\f\(^r. f^ *Up npo-ativp wavp
gastrocnemius by its nerve, as projected '^aai'-ion lO ine negative wave
on a plate moving at a comparatively (excitation wave of Bemstein)
plow rate, showing a contour like that
of a spike in optical section. The which is Set Up by a momen-
' spike' is followed by a 'hump,' 'and , ,• i j • ji
if the former be taken to mean a sudden tary StimuluS, and runS rapidly
electrical swing of such a character as ol^no- fUp mncrl*:^ in hr\th Hirpr-
to indicate that the proximal electrode ^^^ng the muSCle lU DOtH airec-
becomes first negative, then positive, tions, there OCCUrS in iniured
the latter must indicate that it is ■'
followed by a change in the same direc- mUScle a morC slowly-developed
tion, but of slower progress. . • . j • . . i. r
This slower change not only cui- and more persistcnt Change Ot
minates, but begins later, and is there- r>nfpnf\^] in the t;amp dirprtinn
fore called the "after-effect."' The poteniiai in me Same Qireciion
upper curves show the excursion of the aS the first phase of the ex-
meniscus of the electrometer, the lower . . '^
the vibrations of a tuning-fork (Burdon Citation wave, when the mUSCle
Sanderson). • -j. j i.u u "a
' IS excited through its nerve
either continuously or by recurring stimuli, or even, in a
less degree, by a single momentary stimulus. The amount
F\c,. 193.
The ' spike ' and ' hump ' of a gastrocnemius muscle, whose lower end had been
injured bv dipping it into water just sufficiently warmed to produce rigor. The record
was taken on a plate moving ten times faster than that with which Fig. 192 was obtained.
The lowest curve shows the movements of the meniscus, the one above, the vibrations
of the tuning-fork marking time (Burdon Sanderson).
of this more permanent difference of potential is roughly
proportional to the intensity of the injury as measured
ELECTRO-PHYSIOLOGY
6>3
by the previously-existing difference of potential between
the two electrodes, and, according to Sanderson, it repre-
sents a true negative variation in du Bois-Keymond's
sense — that is, a diminution of the electrical difference to
A. B.
Fig. 194.— 'Si'ike' ok Umn.R'RED Gastrocnemius (Burdon Sanderson).
A photographed on slow, B on fast-moving plate.
which the current of rest is due. In an uninjured muscle
only the passage of the transient excitation wave is indi-
cated by the electrometer. But there is reason to believe
that even in intact muscles excitation, both momentary and
Fig. 195.— Curve ok an Injured Muscle excited Sixty Times a Second.
' Shows the characteristic curve of the negative variation of du Bois-Reymond. The
previous difference of potential exceeded 0-03 volt. At the end of the period of excita^
tion the diminution amounted to 0-054 volt. Each excitation was followed by an after-
effect in the same direction, the character of which is best seen after the tenth excita-
tion'(Burdon Sanderson).
recurrent, as in experimental tetanus, causes electromotive
effects that outlast the excitation wave, although, since the
muscle is everywhere equally affected, these do not influence
the electrometer. Injured parts of a muscle, on the other
hand, are less capable of responding to these changes thaii
6i4 A MANUAL OF PHYSIOLOGY
the intact tissue, so that they become less nep^ative towards
the uninjured tissue than they were before excitation, and
the demarcation current is thus diminished.
Although the electromotive changes caused by excitation
are much more transient than those caused by injury,
everything suggests that there must be some deep analogy
between the two conditions. But we cannot say definitely
how far whatever
^^^Mmiffjg/ggttKt^^KKt^^^KK^ chemical or physical
changes underlie the
electrical phenomena
are alike in injured or
dying, and in active
muscle or nerve.
Some writers seem to
Fig. 196. suppose that an increase
• The normal response to a series of excitations of chemiCal activity
recurring with a frequency of 84 per second in a "I i, 4.
wholly uninjured muscle, in which there was no mUSt nCCeSSarily be at
previous difference of potential between the middle xl l-»nt+r>m r\f V-»ntVi
and terminal contacts. Each excitation produces a "-"^ uuiiuiii ui uuiii
spike which is the expression of the passage of a chan°^es ' in the dyin?
wave of excitation of which the direction is atter- *? '. . .
minal [i.e., towards the ends]. The first phase muscle, it is Said, the
expresses a change in the direction of propagation, u ' 1 l-i
the second opposed to it. But after the wave has CliemiCal CnangCS mUSt
E:fort-'(BLSS;:so^^^^^^^^ increased, and we
know that they are in-
creased in the living active muscle. This may be so, but
the electrical changes are very marked in injured and in
active nerve, and here we know nothing of measurable
chemical changes. And warmed living muscle is positive to
muscle less warm, although the metabolism must in general
be more active in the former. It is, of course, quite clear
that energy must be running down, for electrical currents
capable of doing work are being produced ; but whether
this energy comes from chemical changes or from physical
changes, or from both, or how much of it comes from either,
we cannot tell.
Others have said that there is really a subdued kind of
more or less permanent excitation in the neighbourhood of
the injured tissue, and that this explains the similarity of
electrical condition in activity and injury. This pushes the
ELECTRO- PI I } 'SIOL OGY 615
inquiry a step further back, but does not touch the question
of the nature of the changes underlying both action and
injury. Physical explanations of the action current of muscle
have been based on the hypothesis that in contraction
variations in surface-tension, with accompanying electrical
changes, occur at certain surfaces (surface of separation
between light and dim discs, or between fluid contents
and wall of sarcous capillary tubes). A great objection to
these theories is that in nerve, so far as we know, no
sensible mechanical change whatever takes place during
excitation, and that differences of potential exist or may be
developed in tissues of the most diverse structure.
Polarization of Muscle and Nerve.* — We have already spoken
of electrical excitation and of the changes of excitability
caused by the passage of a constant current (p. 574). We
are now to see that these physiological effects are accom-
panied by, and indeed very closely related to, more physical
changes which the galvanometer or electrometer reveals to
us. When a current is passed by means of unpolarizable
electrodes (Fig. 153, p. 526) through a muscle or nerve for
several seconds, and the tissue thrown on to the galvano-
meter immediately after this polarizing current is opened, a
deflection is seen indicating a current (negative polarization
current) in the opposite direction.
This negative polarization differs from the polarization of the
electrodes seen after passage of a current through any ordinary elec-
trolytic conductor, like dilute sulphuric acid. The latter is due to the
deposition of hydrogen on the Icathode and oxygen on the anode,
the electrodes being converted for the time into the plates of a
secondary battery. But in muscle, nerve, and other animal tissues,
as well as in vegetable structures, and indeed, to a certain extent, in
unorganized porous bodies soaked with electrolytes, the polarization
is not confined to the neighbourhood of the electrodes, but distributed
all the way between them ; in other words, it is an internal polariza-
tion depending on the separation of ions in the mass of the tissue. In
muscle and nerve this internal negative polarization is very strongly
marked ; and although it is not bound up with the life of the tissue,
and may be obtained when this has become quite inexcitable, it is
nevertheless dependent on the preservation of the normal structure,
for a boiled muscle shows but little negative polarization.
* The portions in small type on pp. 615-620 may be omitted except by
students interested in the subject or reading for a special purpose.
6i6
A MANUAL OF PHYSIOLOGY
When the polarizing current is strong, and its time of closure
short, we obtain, on connecting the tissue with the galvanometer
after opening the current, not a negative, but a positive deflection,
indicating a so-called positive polarization current in the same direc-
tion as that of the polarizing stream. The ' positive polarization ' is
only obtained when the tissue is living ; and it is far more strongly
marked in the anodic than in the kathodic region. There is, in fact,
a great weight of evidence that the ' positive polarization ' current is
really an action stream, due to the opening excitation set up at the
anode (p. 537).
Suppose that the nerve in Fig. 197 is stimulated by the opening
of the Ijattery B, and that, immediately
after, the nerve is connected with the
galvanometer G by the electrodes E, Ej.
Suppose, further, that the shaded region
near the anode remains more excited
for a short time than the re.st of the
nerve, and we have seen (p. 577) that
after the opening of a strong current
there is a defect of conductivity, espe-
cially in the neighbourhood of the
anode, which would tend to localize
excitation. The portion of nerve at
E being negative relatively to that at
Ep an action current will pass through
the galvanometer from E^ to E, and
through the nerve in the same direc-
tion as the original stimulating stream ;
that is, it will have the direction of the
positive polarization current.
Under certain conditions a state of
continuous excitation in the anodic
region of a nerve is shown by a tetanus of its muscle {fitter s tetanus^
p. 633, and Fig. 198).
Griitzner and Tigerstedt have put forward a different theory of the
break contraction. They say it is really a closing contraction due to
the closure of the negative polarization current through the tissue
itself, as soon as the polarizing current is opened. In fact, they
admit only one kind of electrical stimulus, the kathodic, or make.
But this theory does not adequately take account of positive polari-
zation, and there are also other objections to it.
Electrotonic Currents. — During the flow of the polarizing
current, there are very remarkable galvanoscopic evidences
of the changes produced by it. And although it is not
possible directly to demonstrate polarization in the region
between the electrodes while the current continues to pass,
this is easily done in the extrapolar regions, although much
more readily on nerve than on muscle.
] ji;. 197. — Diagram jo show
Distribution ok ' Positive
Polarization ' after open-
ing Polarizing Current.
B, battery ; G, galvanometer.
The dark shading signifies that the
excitation to which the positive
polarization current is due is
greatest in the immediate neigh-
bourhood of the anode, and fades
away in the intrapolar region.
ELECTRO-PHYSIOLOGY
617
If a current be passed from the battery (Fig. 199) in the
direction indicated by the arrows, while a galvanometer is
connected with
either of the extra-
polar areas, as
shown in the figure,
a current will pass
through the galva-
nometer, in the
same direction in
the nerve as the
polarizing current.
so long as the latter
continues to flow.
These currents arc
called elecirotonii, and
seem to depend on
the spread of the polar-
izing stream along the
nerve outside the elec-
trodes, owing to a
polarization taking
place at the boundar\
between some part of
the nerve-fibre which
may be called a core.
and another part which
may be called a sheath. The exact seat of this polarization is
unknown ; it may be between axis-cylinder and medullary sheath, or
between the latter and the neurilemma. In any case, such a polari-
zation would practically act as a resistance to the direct passage of
A strong voltaic current was
passed for some time through the
nerve of a muscle-nerve prepara-
tion. On opening the circuit,
the muscle gave one strong con-
traction, and then entered into
irregular tetanus, which con-
tinued for four minutes. (Only
the first part of the tracing is
renrodiiced. )
Fk;
199. — Diagram showing Direciio.n oi' the Exikaiolar Ei.ec-
TROTOxic Currents.
the current from the anode down into the ' core,' or from the core
out to the kathode, and would cause it to spread longitudinally along
the sheath in the extrapolar regions. On this view the electrotonic
currents are really twigs of the polarizing stream. And. as a matter
of fact, such currents can be produced on a model in which a platinum
wire is surrounded with a sheath of saturated zinc sulphate solution.
6i8 A MANUAL OF PI/YS/OLOGY
A current led into the latter tries, so to speak, to pass mostly by the
good conducting wire. If this is not polari/.able — if it is, e.g., a zinc
wire — there is little or no spreading of the current outside the elec-
trodes ; it passes at once into the core, and so on to the other
electrode. If, however, there is polarization when the current passes
from the liquid into the wire, as is the case when the latter is
platinum, the stream spreads longitudinally. Indeed, we know
that both nerve and muscle, and especially the former, are far
more polarizable in the transverse than in the longitudinal direc-
tion ; the apparent transverse resistance* of nerve may be seven
times the longitudinal resistance, and this is a condition which favours
electrotonus.
This physical electrotonus must be distinguished from the
changes of excitability produced by the constant current, to
which the name of electrotonus is also sometimes given.
For although the decline in the intensity of the electrotonic
currents as we pass away from the electrodes, has its
analogue in the distribution of the electrotonic changes of
excitability, and there are other facts which suggest a rela-
tion between the two, we are ignorant of the real nature of
this relation.
The electrotonic currents cannot spread beyond a ligature;
they are stopped by anything which destroys the structure
of the tissue ; they are affected by reagents such as carbon
dioxide and ether. But this does not show that they are
other than physical in origin, for what destroys the structure
of the tissue or modifies its molecular condition may destroy
or diminish its capacity for polarization.
Stimulation of the nerve while the polarizing current is flowing
causes in general in the extrapolar regions a negative variation of the
electrotonic current, but in the intrapolar region a positive variation.
The latter is undoubtedly an action stream. Hermann has explained
its direction on the assumption that the excitation diminishes in
intensity as it approaches the kathode or recedes from the anode,
and increases in intensity as it passes towards the anode or away
from the kathode (law of polarization increment). But the fact that
* The great apparent transverse resistance of nerve may be due, in
part if not wholly, to the resistance of the neurilemma, if that membrane,
like the boundary of a red blood corpuscle, has a much higher resistance
than the contents of the fibre or the lymph between the fibres. Or it
may be that the resistance of the medullary sheath is greater than that
of the axis cylinder. Examples of such differences of resistance even
in the fluid constituents of one and the same animal structure are not
wanting. For instance, the resistance of the yolk of a hen's egg may
be three times greater than that of the white.
ELECTRO-J'J/YSJOL OG Y
619
Fig. 200. — Diagram showing Direction
OF THE Stimulation Effect in the
Intrapoi.ar Region during the Flow
OF the Polarizing Current.
during the flow of a current the conductivity of the nerve is far
more depressed around the kathode than near the anode affords a
sufficient explanation.
The nerve-impulse, starting from the stimulating electrodes S
(Fig. 200), will pass over 1'], the anode, in greater intensity than over
Ej, the kathode ; and therefore, upon the whole, during tetanus E
will be negative to Ej, and
a current of action will be
developed in the same
direction as the polarizing
current, and reinforcing it.
When the kathodic block
is complete, and the excita-
tion has to pass over the
kathode before reaching
the intrapolar region, no
effect is produced by stimu-
lation.
The stimulation effects
in the extrapolar regions are probably due partly to action currents,
as is shown by the fact that when the polarizing current is strong
enough to markedly depress the conductivity in the neighbourhood
of the anode, the variation becomes positive instead of negative
when one of the galvanometer electrodes lies near the anode. For
here the excitation coming from S passes Eo in far less intensity than E3
(Fig. 201). E.j is therefore, on the whole, during tetanus negative to E.,,
and the direction of the action current in the nerve is from Eo to E.^.
The negative variation in the extrapolar kathodic region could
also be explained as an action current due to diminished conduc-
tivity in the neighbourhood of the kathode. But the negative anodic
variation cannot be an
action current, unless we
suppose that with the
weaker polarizing currents
the conductivity is in-
creased around the anode ;
and for this there is not
sufficient proof. It is pro-
bable, therefore, that there
is another factor mixed up
with the currents of action,
and in part opposing them.
Some have supposed that
the capacity for polariza-
tion between core and sheath is diminished during excitation, and
that, accordingly, less of the current spreads beyond the electrodes,
and an apparent negative variation is caused in the extrapolar regions
by stimulation ; but there is no direct evidence for this.
After the opening of the polarizing current, electromotive changes
can, as we have seen, be recognised for a short time in the intrapolar
Fig. 201. — Diagram to show Direction
OF THE Positive Stimulation Effect
in the Anodic Extrapolar Region
during the Flow of a Strong Polari-
zing Current.
6:o
.1 MANUAL OF PIIYSIOLUUY
area. This is also true of both extrapolar regions. The main after
current in the anodic region is in the opposite direction to the
polarizing stream ; but this is, under certain circumstances, preceded
by a very short kick of the galvanometer magnet in the same direc-
tion. The kathodic after-current is in the same direction as the
polarizing stream, and is, except with strong currents and a compara-
tively long time of closure, much weaker than the main anodic.
The latter is to be looked upon as having the same origin as the
positive polarization current of the intrapolar region, a state of open-
ing excitation around the anode ; in other words, it is an action
current. The kathodic and the preliminary anodic after-currents are
probably due to negative polarization.
Stimulation of the nerve after opening the polarizing current causes
well-marked effects ;
in the intrapolar
region the stimula-
tion effect is in the
opposite direction
to the polarizing
current : in the ex-
trapolar anodic
area, in the same
direction as the
polarizing stream.
In the extrapolar
kathodic region, it
is in the opposite
direction, and, ex-
cept with strong
polarizing currents, and a more than momentary time of closure, less
in amount than the stimulation effect in the anodic region.
All these cases are readily explained by the fact that immediately
after opening the polarizing current the conductivity of the nerve is
more depressed in the anodic than in the kathodic region, although
with strong currents it is depressed in both. An excitation reaching
the extrapolar anodic area from S will pass over E., in greater intensity
than over E^ (Fig. 202). E^ will therefore be positive to E.5, and the
action current will go through the nerve in the direction of the arrow.
An excitation reaching the kathodic extrapolar area from S' will
arrive at H,., in greater intensity then at Er,. The resultant action
stream will therefore have the direction in the nerve from E,. to Ey
And the effects in the intrapolar region can be similarly explained.
A nerve may be stimulated by an electrotonic current
produced in nerve-fibres lying in contact with it. A well-
known illustration of this is the experiment known as the
paradoxical contraction (Practical Exercises, p. 630).
The current of action of a nerve can also, under certain
conditions, stimulate another nerve, as Hering has shown.
Fu;. 202.— DiAt;k.\M .showi.ng the Directio.n ok
THE STI.MULATIOX EFFECTS AFTER OI'E.MNG THE
Poi.AKiziNG Currents in the Anodic and
Kathodic Extrapolar Regions (A and K), and
in the Intrapolar Region Ej, E.^.
ELECTRO-PHYSIOLOG Y
621
This comes under the head of secondary contraction. But
the best-known form of secondary contraction is where a
nerve, placed on a muscle so as to touch it in two points
(Fi^. 203), is stimulated by the action-current of the muscle.
and causes its own muscle to
contract. A secondary tetanus
can be obtained in this way by
dropping a nerve on an arti-
ficially tetanized muscle. The
beat of the heart causes usuall}-
only a single secondary con-
traction when the sciatic nerve
of a frog is allowed to fall on it
(p. 179). But when the diphasic
variation is well marked, as it is
in an uninjured heart, there may
be a secondary contraction for
each phase, i.e., two for each
heart-beat. Excitation of one
muscle may in the same way
cause secondary contraction of
another with which it is in close contact.
The electromotive phenomena of the heart and of the
central nervous system are naturally included under those
of muscle and nerve.
Fig, 203. — .Secondary Ci'N-
traction.
The nerve of muscle M touches
muscle M' at ./ and b. Stimulation
of the nerve of M' at S causes con-
traction of M.
Heart. — The current of action has been chiefly studied. In the
frog's heart the variation shown by the capillary electrometer is
diphasic. During the first phase the base is negative to the apex ;
during the second phase the apex is negative to the base. The
meaning of this is that the negative electrical change, like the con-
traction, starts at the base, and passes on to the apex. Sometimes a
third phase is seen (triphasic variation), in which the base again
becomes negative to the apex. It has been supposed that this is due
to the contraction of the arterial bulb, which follows that of the rest
of the heart. If the tissue is injured at either leading-off electrode,
the corresponding phase disappears.
In the uninjured mammalian heart, beating as far as possible
under normal conditions, the sequence is the same, the diphasic
variation showing first base negative to apex, then apex negative to
base. Statements to the contrary seem to have been founded on
observation of injured hearts, or hearts placed under abnormal
conditions. For example, when the base of the heart is cooled, the
622
A MANUAL OF PHYSIOLOGY
variation first becomes triphasic, the sequence of the relative nega-
tivity being base — apex — base ; and finally diphasic with a sequence
the reverse of the normal, the apex being first negative, then the base.
An electrical change accompanies every beat of the human heart.
Waller has shown how this may be demonstrated by means of the
capillary electrometer. His experiments seemed to indicate a
diphasic variation in which
the apex first became nega-
tive to the base and the base
then negative to the apex.
From later work by Bayliss
and Starling, however, it
would seem that this is incor-
rect, the variation being really
triphasic, first base negative
to apex, then apex negative to
base, and then again base
negative to apex.
When the heart is directly
stimulated by induction shocks
at the rate of about three per
second, an artificial rhythm
is set up. The interval which
elapses between stimulation
either of auricle or ventricle
and the beginning of the elec-
trical change is about ^\j^ of
a second.
Central Nervous System. — It was discovered by du Bois-Rey-
mond that the spinal cord, like a nerve, shows a current of rest
between longitudinal surface and cross-section, and that a current of
action is caused by excitation. Setschenow stated that when the
medulla oblongata of the frog was connected with a galvanometer,
spontaneous variations occurred which he supposed due to periodic
functional changes in its grey matter. Gotch and Horsley have
made elaborate experiments on the spinal cord of cats and monkeys.
Leading off from an isolated portion of the dorsal cord to the capil-
lary electrometer, and stimulating the motor part of the cortex cerebri,
they obtained a persistent negative variation followed by a series of
intermittent variations. This agrees remarkably with the muscular
contractions in an epileptiform convulsion started by a similar excita-
tion of the cortex, which consist of a tonic spasm followed by clonic
(interrupted) contractions, and suggests that it is the nature of the
cortical discharge which determines the character of the convulsion.
By means of the galvanometer the same observers have made
investigations on the paths by which impulses set up at different
points travel along the cord. To these we shall have to refer again
(p. 671).
On the currents of the cerebral cortex only a few experiments have
hitherto been made by Caton, Beck, and Fleischl. But if well-
FiG. 204. — Electro - cardiograms
FROM MAN (EiNTHOVEN). — Lower
led off in oi)posite way from upper.
ELECTRO-PHYSIOLOGY 623
marked changes of potential could be localized on the cortex as a
result of stimulation of sensory fibres, the method would probably be
of great value for tracing these to their central connections.
Glandular Currents. — These have been studied with any care only
in the submaxillary gland and in the skin, although the liver, kidney,
spleen, and other organs, also show currents when injured. In the sub-
maxillary gland the hilus is positive to
any point on the external surface of the
gland ; a current passes from hilus to
surface through the galvanometer, and
from surface to hilus through the gland
(Fig. 205). AVhen the chorda tympani
is stimulated with rapidly - succeeding
shocks of moderate strength, there is a
positive variation ; />., the surface be-
comes still more negative to the hilus y\g. ao!;.— Current ok Sub-
This variation can be abolished by a maxillary Gland.
small dose of atropia, and then stimula-
tion causes a slight negative variation. A further dose of atropia
abolishes this, too. With slowly-interrupted shocks (not more than
five per second) a large negative variation is caused, and no positive
variation, and the same is true of rapid stimuli too weak to excite
secretion.
Single induction shocks cause a diphasic variation, the surface of
the gland becoming first more negative and then more positive to the
hilus, so that a positive deflection of the galvanometer is followed by
a negative.
In nearly all circumstances stimulation of the sympathetic causes
a negative variation. Bradford, to whom, and to Bayliss, we are
indebted for our knowledge of this subject, explains the different
behaviour of the chorda tympani to different kinds of stimulation as
due to the existence in it of anabolic fibres, which increase the build-
ing up of the proper substance of the gland, in addition to the
katabolic fibres, which increase destructive metabolism and cause
secretion (p. 339).
Skin Currents, — So far as has been investigated, the integument
of all animals shows a permanent current passing in the skin from the
external surface inwards. This is feebler in skin which possesses no
glands. In skin containing glands the current is chiefly, but not
altogether, secretory. As such, it is affected by influences which
affect secretion, a positive variation being caused by excitation of
secretory nerves, e.g., in the pad of the cat's foot by stimulation of
the sciatic. The deflection obtained when a finger of each hand is
led off" to the galvanometer, which was at one time looked upon as
a proof of the existence of currents of rest in intact muscles, is due
to a secretion current, and the variation seen during voluntary con-
traction of the muscles of one arm is certainly in part, and probably
altogether, a secretion stream.
Of more doubtful origin is the current of ciliated mucous mem-
brane, which has the same direction as that of the skin of the frog
624 -1 M.iXL'AL OF PHYSIOLOGY
and the mucous membrane of the stomach of the frog and rabbit —
viz., from ciliated to under surface through the tissue, or from ciUated
surface to cross-section, if that is the way in which it is led off. The
current is strengthened by induction shocks, by heating, and in
general by influences which increase the activity of the cilia. Some
circumstances point to the goblet-cells in the membrane as the source
of the current ; but, on the whole, the balance of evidence is in
favour of the cilia being the chief factor (Engelmann), although the
mucin-secreting cells may be concerned, too.
Eye-currents. — If two electrodes connected with a galvanometer
are placed on the excised eye of a frog or rabbit, one on the cornea
and the other on the cut optic nerve, it is found that a current of
rest due to the injury passes in the eye from optic nerve to cornea.
The same is true if the anterior electrode is placed on the retina
itself, the front of the eyeball being cut away. There is nothing of
interest in this : but the important point is that if light be now
allowed to fall upon the eye, an elec-
trical change is caused (Holmgren,
Dewarand McKendrick), generally first
a positive and then a negative varia-
tion, succeeded by another positive
movement when the light is cut off.
The variation depends upon the
retina alone, and does not occur when it
is removed. Bleaching of the visual
purple does not much affect the varia-
tion, so that it is not connected with
chemical changes in this substance.
Flo. 2o6.-EvK-cLRK£NT. And of the spectral colours, yellow
light, which affects the visual purple
comparatively little, causes the largest variation ; blue, the least ;
but white light is more powerful than either. (For ' visual purple '
see Chapter XIII.)
Electric Fishes. — Except lightning, the shocks of these fishes were
probably the first manifestations of electricity observed by man.
The Torpedo, or electrical ray, of the coasts of Europe was known to
the (ireeks and Romans. It is mentioned in the writings of Aris-
tode and Pliny, and had the honour of being described in verse 1,500
years before Faraday made the first really exact investigation of the
shock of the Gymnotus, or electric eel, of South America. The
third of the electric fishes, Malapterurus ekctricus, although found
in many of the African rivers, the Nile in particular, and known for
ages, was scarcely investigated till forty years a^io.
In all these fishes there is a special bilateral organ immediately
under the skin, called the electrical organ. It is in this that the
shock is developed. It consists of a series of plates arranged parallel
to each other. To one side of each plate a branch of the electrical
nerve supplying each lateral half of the organ is distributed. This
side of the plate during the shock becomes negative to the other
(Pacini's rule), so that each half of the organ represents a battery of
ELECTRO rilYSIOLOGY.
62$
many cells arranged in series. The direction of the shock through
the organ depends on the side of the plate to which the nerve-supply
goes, and the arrangement of the plates with reference to the natural
position of the animal.
Thus, in Gymnotus the plates are vertical, and at right angles to
the long axis of the fish, and the nerves are distributed to their pos-
terior surface ; the shock accordingly passes in the animal from tail
to head. In Malapterurus, although the arrangement of the plates is
the same, the nerve-supply is to the anterior surface ; for Max
Schultze has shown that although the nerve appears to sink into the
posterior surface, it really passes through a hole in the plate, and
spreads out on its anterior face. The shock passes from head to tail.
In Torpedo, the plates or septa dividing the vertical hexagonal
prisms of which each lateral half of the organ consists are horizontal;
the nerve-supply is to the lower or ventral surface ; and the shock
Fig. 207.— Diagram showing Direction of Shock in Gymnotus.
passes from belly to back through the organ. In all electric fishes
the discharge is interrupted : an active fish may give as many as
200 shocks per second.
The electrical nerve of Malapterurus is very peculiar. It consists
of a single gigantic nerve-fibre on each side, arising from a giant
nerve - cell. The fibre has
an enormously thick sheath,
the axis cylinder forming a
relatively small part of the
whole ; and the branches
which supply the plates of
the organ are divisions of
this single axis cylinder.
The electromotive force
of the shock of the (iym-
notus may be very consider-
able ; and even Torpedo and
Malapterurus are quite able
to kill other fish, their enemies or their prey. Indeed, Gotch has
estimated the electromotive force of i cm. of the organ of Torpedo
at 5 volts, and Schonlein finds that the electromotive force of the
40
208.— Diagram showing Direction
OF Shock in >rAi.APTERURUS.
626 A MANUAL OF PHYSIOLOGY
whole organ may be equal to that of 31 Daniell cells, or o'o8 volt for
each plate, and it is one of the most interesting questions in the
whole of electro-physiology, how they are protected from their own
currents. There is no doubt that the current density inside the fish
must be at least as great as in any part of the water surrounding it,
and probably much greater. The central nervous system and the
great nerves must be struck by strong shocks, yet the fish itself is not
injured ; nay more, the young in the uterus of the viviparous Torpedo
are unharmed. The only explanation seems to be that the tissues of
electric fishes are far less excitable to electrical stimuli than the tissues
of other animals ; and this is found to be the case when their muscles
or nerves are tested with galvanic or induction currents. It requires
extremely strong currents to
stimulate them : and the elec-
trical nerves are more easily
excited mechanically, a.> by liga-
turing or pinching, than elec-
trically. In general, too, the
shock is more readily called
^ ^ ^ forth by reflex mechanical
Fig. 209. — Diagram showing Direc- ■ , -^ ^ ^, 1 ..u \
TioN OF Shock in Torpedo. stimulation of the skin than by
electrical stimulation. But that
the organ itself is excitable by electricity, has been shown by Gotch.
He proved that in Torpedo a current passed in the normal direction
of the shock is strengthened, and a current passed in the opposite
direction weakened, by an action current in the direction of the
shock. And indeed a single excitation of the electrical nerve is
followed by a series of electrical oscillations in the organ which
gradually die away.
Whether the electrical organ is the homologue of muscle or of
nerve-ending, or whether it is related to either, has not been
definitely settled. That curara does not aftect the electrical organ in
Torpedo, although it paralyzes the motor nerve-endings, is, as far as
it goes, against the nerve-ending theory. That there is a measurable
latent period (about .,-i^ second) cannot be considered as in favour
of the muscle theory, for the latent period is probably determined
more by functional than by morphological considerations.
The skate must now be added to the list of electric fishes.
Although its organ is relatively small, and its electromotive force
relatively feeble, yet it is in all respects a complete electrical organ.
It is situated on either side of the vertebral column in the tail. The
plates or discs are placed transversely and in vertical planes. The
nerves enter their anterior surfaces ; the shock passes in the organ
from anterior to posterior end. Gotch and Sanderson have estimated
the maximum electromotive force of a length of i cm. of the
electrical organ of the skate at about half a volt.
PRACTICAL EXERCISES
627
PRACTICAL EXERCISES ON CHAPTER XI.
1. Galvani's Experiment. — Pith a frog (brain and cord). Cut
through the backbone above the urostyle, and clear away the anterior
portion of the body and the viscera. Pass a copper hook beneath
the two sciatic plexuses, and hang the legs by the hook on an iron
tripod. If the tripod has been painted, the paint must be scraped
away where the hook is in contact with it. Now tilt the tripod so
that the legs come in contact with one of the iron feet. Whenever
this happens, the current set up by the contact of the copper and
iron is completed, the nerves are stimulated, and the muscles
contract (p. 605).
2. Make a muscle-nerve preparation from the same frog. Crush
the muscle near the tendo Achillis, so as to cause a strong demarcation
current. Cut off the end of the sciatic nerve. Then lift the nerve
with a small brush or thin glass rod, and let its cross-section fall on
the injured part of the muscle. Every time the nerve touches the
muscle a part of the demarcation current passes through it, stimulates
the nerve, and causes contraction of the muscle (p. 605).
3. Make a muscle-nerve preparation. Lay it on a glass plate A,
supported on a block of wood.
Snip off the end of the nerve N,and
arrange the cut surface on a pad of
kaolin B, moistened with normal
saline. Another pad B' is placed
under the nerve a little way from
its cut end. Both pads project
down over the edge of the glass
plate. A watch-glass C filled with
normal saline solution is lifted up
below the projecting ends till they
are immersed. Whenever this
happens, a circuit is completed for
the demarcation current of the
nerve itself, by which it is stimu-
lated, and the muscle M contracts
(Fig. 209).
4. Secondary Contraction. — Make two muscle-nerve preparations.
Lay the cross-section of one of the sciatic nerves on the muscle of
the other preparation (Fig. 203, p. 621). Place under the nerve near
its cut end a small piece of glazed paper or of glass rod, and let the
longitudinal surface of the nerve come in contact with the muscle
beyond this. Lay the nerve of the other preparation on electrodes
connected with an induction machine arranged for single shocks, with
a Daniell cell and a spring key in the primary circuit (Fig. 181).
On closing or opening the key both muscles contract. Arrange the
induction machine for an interrupted current. When it is thrown
into one nerve, both muscles are tetanized ; the nerve lying on the
muscle whose nerve is directly stimulated is excited by the action
current of the muscle.
40 — 2
Fig. 210. — Stimulation of a Nerve
BY ITS OWN' Demarcation Cur-
rent.
6-8
A MANUAL OF PHYSIOLOGY
5. Demarcation Current and Current of Action with Capillary
Electrometer. — {a) Study the construction of the capillary electro-
meter (Fig. 151, p. 524). Raise the glass reservoir by the rack and
pinion screw, so as to bring the meniscus of the mercury into the field.
Place two moistened fingers on the binding-screws of the electrometer,
open the small key connecting them, and notice that the mercury
moves, a difference of potential between the two binding-screws
being caused by the moistened fingers.
(/') Demarcation Current. — Set up a pair of unpolarizable elec-
trodes (Fig. 153, p. 526). Fill the glass tubes about one-third full of
kaolin mixed with normal saline solution till it can be easily moulded.
To do this, make a piece of the clay into a little roll, which will slip
down the tube. Then with a match push it down until it forms a
Fig. 211.— Moist Chamber.
E, unpolarizable electrodes supported in the cork C ; M, muscle stretched over the
electrodes and kept in position by the pins A B stuck in the cork plate P ; B, binding-
screws connected with galvanometer or capillary electrometer. The other pair of
binding-screws serves to connect a pair of stimulating electrodes inside the chamber
with the secondary coil of an induction machine.
firm plug. Next put some saturated zinc sulphate solution in the
tubes, above the clay, with a fine-pointed pipette. Fasten the tubes
in the holder fixed in the moist chamber (Fig. 211). Now amal-
gamate the small pieces of zinc wire (p. 173), which are to be con-
nected with the binding-screws of the chamber.
The zincs are now placed in the tubes, dipping into the ziiK
sulphate. A piece of clay or blotting paper moistened with normal
saline is laid across the electrodes to complete the circuit between their
points, and they are connected with the electrometer to test whether
they have been properly set up. There ought to be little, if any,
movement of the mercury on opening the side-key of the electro-
meter. If the movement is large, the electrodes are ' polarized,* and
must be set up again. The second pair of binding-screws in the
chamber are connected with a pair of platinum-pointed electrodes on
PRACTICAL EXERCISES 629
the one side, and on the other, through a short-circuiting key, with
the secondary coil of an induction machine arranged for tetanus.
Next pith a frog (cord and brain), and make a muscle-nerve pre-
paration. Injure the muscle near the tendo Achillis. Lay the
injured part over one unpolarizablc electrode, and an uninjured part
over the other. Put a wet sponge in the chamber to keep the air
moist, and place the glass lid on it. Focus the meniscus of the
mercury, and open the key of the electrometer ; the mercury will
move, perhaps right out of the field. Note the direction of move-
ment, and remembering that the real direction is the opposite of the
apparent direction, and that when the mercury in the capillary tube
is positive to the sulphuric acid, the movement is from capillary to
acid, determine which is the positive and which the negative portion
of the muscle (p. 606).
{c) Action Cu7-renf. — Now fasten the muscle to the cork or parafifin
plate in the moist chamber, without disturbing its position on the
electrodes, by pins thrust through the lower end of the femur and
the tendo Achillis. Lay the nerve on the platinum electrodes.
Open the key of the electrometer, and let the meniscus come to rest.
This happens very quickly, as the capillary electrometer has but little
inertia. If the meniscus has shot out of the field, it must be brought
back by raising or lowering the reservoir. Stimulate the nerve by
opening the key in the secondary circuit ; the meniscus moves in the
direction opposite to its former movement.
{d) Repeat (/') and {c) with the nerve alone, laying an injured part
(crushed, cut, or over-heated) on one electrode, and an uninjured
part on the other. Of course the nerve does not need to be pinned.
Clean the unpolarizable electrodes, and be sure to lower the reser-
voir of the electrometer ; otherwise the mercury may reach the point
of the capillary tube and run out.
In 5 a galvanometer may be used instead of the electrometer, the
unpolarizable electrodes being connected to it through a short-
cicuiting key. The spot of light is brought to the middle of the
scale by moving the control-magnet ; or if a telescope-reading
(Fig. 146, p. 520) is being used, the zero of the scale is brought by
the same means to coincide with the vertical hair-line of the tele-
scope. The short-circuiting key is then opened.
6. Action-current of Heart. — ^Pith a frog (brain and cord). Excise
the heart, and lay the base on one unpolarizable electrode, and the
apex on the other, having a sufficiently large pad of clay on the tips
of the electrodes to ensure contact during the movements of the
heart, or having little cups hollowed in the clay and filled with normal
saline, into which the organ dips. Connect the electrodes with the
capillary electrometer and o])en its key. At each beat of the heart
the mercury will move (p. 622).
7. Electrotonus. — Set up two pairs of unpolarizable electrodes in
the moist chamber. Connect two of them with a capillary electro-
meter (or galvanometer), and two with a battery of three or four small
Daniell cells, as in Fig. 199. Lay a frog's nerve on the electrodes.
When the key in the battery circuit is closed, the mercury (or the
630
A MANUAL OF PHYSIOLOGY
needle of the galvanometer) moves in such a direction as to indicate
that in the extrapolar regions parts of the nerve nearer to the anode
are positive to parts more remote, and parts nearer to the kathode are
negative to parts more remote. The direction of movement of the
mercury (or galvanometer needle) must be made out first for one
direction of the polarizing current. Then the latter must be reversed,
and the movement of the mercury (or needle) on closing it again
noted (p. 617).
8. Paradoxical Contraction. — Pith a frog (brain and cord). Dis-
sect out the sciatic nerve down to the point where it splits into two
divisions, one for the gastrocnemius b, and the
other for the peroneal muscles a. Divide the
peroneal branch as low down as possible, and
make a muscle-nerve preparation in the usual
way. Lay the central end of the peroneal
nerve on electrodes connected through a
simple key with a battery of two Daniell cells.
When the peroneal nerve is stimulated the
gastrocnemius muscle contracts. This result
is not due to the current of action, for it is
not obtained with mechanical stimulation of
the nerve ; but it is not the result of an
escape of current, for if the peroneal nerve
be ligatured between the point of stimulation
and the bifurcation, no contraction is obtained.
Ihe contraction is really due to a part of the
electrotonic current set up in the peroneal
nerve passing through the fibres for the
gastrocnemius, where they lie side by side in the trunk of the sciatic.
9. Alterations in Excitability and Conductivity produced in
Nerve by the Passage of a Voltaic Current through it.— (<?) Set
up two pairs of nnpolarizable electrodes in the moist chamber.
Fig. 212. — I^\rai)0
cal contractio.n
Fig. 213.— Arrangement ior showinc; Changes ok Excitahilitv
rRODUCED BY THE Voi.TAlC CURRENT.
M, muscle ; N, nerve ; Ei, E2, electrodes connected with secondary coil S ; Ej. E4,
unpolarizable electrodes connected with Pohls commutator (with cross-wires) C ;
B', • polarizing ' battery ; B, ' stimulating " battery in primary circuit I' ; K, K", simple
keys ; K', short-circuiting key.
Connect a battery of two or three Daniell cells, arranged in series
through a simple key with the side-cups of a Pohl's commutator with
PRACTICAL EXERCISES 631
cross-wires in. Connect the commutator to one pair of the unpolar-
izable electrodes (' the polarizing electrodes'), as in Fig. 213. The
other pair of unpolarizable electrodes ('the stimulating electrodes')
are to be connected through a short-circuiting key with the secondary
of an induction machine arranged for tetanus. A single Daniell is
put in the primary coil. Pith a frog (brain and cord), make a muscle-
nerve preparation, pin the lower end of the femur to the cork jjlate
in the moist chamber, attach the thread on the tendo Achillis to the
lever connected with the chamber through the hole in the glass pro-
vided for this purpose, and arrange the nerve on the electrodes so
that the stimulating pair is between the muscle and the polarizing
pair. By moving the secondary, seek out such a strength of stimulus
as just suffices to cause a weak tetanus when the polarizing current
is not closed. Set the drum off (slow speed), and take a tracing of
the contraction. Then close the polarizing current with the Pohl's
commutator so arranged that the anode is next the stimulating
electrodes, i.e., the current ascending in the nerve. Again open the
short-circuiting key in the secondary; the contraction will now be
weaker than before, or no contraction at all maybe obtained. Allow
the preparation two minutes to recover, then stimulate again, as a
control, without closing the polarizing current. If the contraction is
of the same height as at first, close the polarizing current with the
bridge of the commutator reversed, so that the kathode is now next
the stimulating electrodes. On stimulating, the contraction will now
be increased in height. (See Figs. 177, 178, p. 576.)
{p) Arrange everything as in (a), except that one of the polarizing
electrodes is placed at each end, and the two stimulating elec-
trodes close together in the middle of the nerve. A large carbon
resistance (say 500,000 ohms) is introduced into the circuit of the
secondary coil, to prevent more than a very small fraction of the
polarizing current from passing through the coil. Seek out the
strength of stimulation which just causes contraction when the
polarizing current is not closed. Xow close the polarizing current in
such a direction that the anode is between the stimulating electrodes
and the muscle. If no contraction occurs on stimulation, push up
the secondary towards the primary till the muscle contracts. Then
stop stimulation, open the polarizing current, and allow an interval
of two minutes. Now pass the polarizing current through the nerve
in the opposite direction, so that the kathode is between the stimu-
lating electrodes and the muscle. No contraction will be obtained
on exciting with the same strength of stimulus as caused contraction
when the anode was next the muscle. The kathode has diminished
the conductivity of the nerve : and if four or five small Daniell cells
are put on in the polarizing circuit, no contraction may be obtained,
even with the coils close together, while the excitation will still pass
the anode and cause contraction.
if) Connect a galvanometer or capillary electrometer by unpolar-
izable electrodes with a frog's sciatic nerve, as shown in Fig. 214, the
cut end being on one electrode, the longitudinal surface on the other.
Arrange two polarizing electrodes (unpolarizable) one at each end of
632
A MANUAL OF PHYSIOLOCY
the remaining portion of the nerve, and connected through a simple
key and a commutator with cross-wires with a battery of two or three
small Daniells. A pair of fine platinum, or a third pair of very fine-
pointed unpolari/able electrodes is placed under the nerve midway
between the two polarizing electrodes, and connected, through a
large carbon resistance, with the secondary of an induction-machine
arranged for tetanus. Let the mercury of the electrometer or the
spot of light on the scale of the galvanometer (or the telescope image
of the scale) come to rest when the demarcation current of the nerve
is thrown in. On stimulating the nerve when the polarizing circuit
is open, a movement of the mercury in the capillary electrometer or
of the spot of light (or telescope image, as the case may be) in the
galvanometer takes place (current of action). Now close the polariz-
ing current in such a direction that the anode is next the leading-off
electrodes. An action current is still indicated on stimulation.
Reverse the polarizing current so as to bring the kathode next the
B, battery ; C, Pohl's
commutator with cross-
wires ; E,, E.,, unpolar-
izable electrodes con-
nected with C ; D,
platinum electrodes
connected with S, the
secondary coil, through
the large carbon resist-
ance R : E;^ E4, unpo-
l.uizable electrodes con-
nected with Hg and
H..SO4. the mercury and
sulphuric acid of the
capillary electrometer j
K', simple key ; K", a
short-circuiting key ; N,
nerve.
Fig. 214. — ARRANtiEMENT KOR SHOWINO, BY MEANS
OF THK Capillary Electrometer, tkai thi.
Kathode blocks the Nerve-imi'Clse.
leading-off electrodes. The excitation is now blocked by the kathode,
and no movement of the mercury or of the spot of light takes place.
10. Pfltiger's Formula of Contraction (p. 576). — To demonstrate
this, connect two uni)olarizable electrodes, through a spring key and
a commutator, with a simple rheocord (Fig. 183), so as to lead off
a twig of a current from a Daniell cell. The unpolarizable elec-
trodes are placed in a moist chamber. A muscle-nerve preparation
is arranged with the nerve on the electrodes and the muscle attached
to a lever. The effects of make and break of a weak current, ascend-
ing and descending, can be worked out with the simple rheocord.
The effects of a medium current will probably be obtained with
a single Daniell connected directly with the electrodes through a
key. The effects of a strong current will be got when three or four
Daniells are connected with the electrodes. Care must be taken to
keep the preparation in a moist atmosphere, and more than one
preparation may be needed to verify the whole formula.
PRACTICAL EXERCISES
633
11. Ritters Tetanus. — Lay the nerve of a muscle-nerve prepara-
tion on a pair of unpolarizable electrodes connected through a sinii)le
key with a battery of three or four small Daniells. Connect the
muscle with a lever. Pass an ascending current (anode next the
muscle) for a i^w minutes through the nerve, and let the writing-point
trace on a slowly moving drum. When the current is closed there
may be a single momentary twitch, or the muscle may remain same-
what contracted (galvanotonus) as long as the current is allowed to
pass, or it may continue to contract spasmodically (' closing tetanus ').
When the current is opened the muscle will contract once, and then
immediately relax, or there may be a more or less continued tetanus
(Ritter's or 'opening tetanus'). If opening tetanus is obtained,
divide the nerve between the electrodes : the tetanus continues.
Divide it between the anode and the muscle : the tetanus at once
disappears. This shows that the seat of the excitation which causes
the tetanus is in the neighbourhood of the anode (p. 617). That there
is a state of excitation in this region after a voltaic current is opened
may be shown electrically thus :
12. Positive Polarization. — Connect a pair of unpolarizable elec-
trodes by double leads with a battery of twelve or fifteen small Daniells
and a galvanometer or
capillary electrometer, as
in Fig. 215. A Pohl's
commutator without
cross-wires is introduced
in such a way that when
the bridge is in one direc-
tion the battery circuit is
made and the galvano-
meter or electrometer
circuit broken, and vice
versa when the bridge is
tilted in the other direc-
tion. A frog's nerve is
laid on the electrodes in
the moist chamber, with
its cut ends at the same
distance from the elec-
trodes (streamless arrange-
ment), to eliminate as far
as possible the demarcation current. The battery current is now
passed for an instant through the nerve ; the commutator is at once
reversed, and the electrometer or galvanometer shows a movement
indicating that the anodic area is negative to the kathodic ('positive
polarization '). The positive polarization current is in the same
direction as the polarizing current. The positive polarization effect
may be preceded by a ' kick ' in the opposite direction (' negative
polarization '). The negative polarization effect is much increased if
the polarizing current be allowed to flow for some time. For accu-
rate experiments it is better to employ two pairs of unpolarizable
DEMONSTRATING
BY THE CaPIL-
Fu;. 215. — Scheme i-or
' Positive Polarization
LARv Electrometer.
El, Ej, unpolarizable electrodes connected with
the 'polarizing' battery B through a Pohl's com-
mutator (without cross-wires) C ; K, simple key ;
Hg and H-..S04, the mercury and sulphuric acid of
the capillary electrometer ; N, nerve ; K', key in
electrometer circuit.
634 A MANUAL OF J'lIYSlOLOGY
electrodes, one for leading in the polarizing current to the tissue, and
the other for leading off the polarization current to the galvanometer
or electrometer.
13. Galvanotropism. — Place at each end of a rectangular trough
filled with tap-water a metallic plate, or a plate of carbon, connected
through a commutator and key with the poles of a (irove or bichro-
mate battery of several cells, or, if the laboratory is provided with a
current from the street, with the switch through one or more incan-
descent lamps. Put into the water a number of tadpoles, which
should not be too young. When the current is closed, the tadpoles
will arrange themselves in a definite way with their long axes in the
direction of the lines of flow, the head being turned towards the
anode. Reverse the current, and they turn their heads in the
opposite direction. If the current is taken from the laboratory
supply, the anode may be known as the electrode at which least
gas conies off, or at which a mixture of potassium iodide and starch
becomes blue.
Plate V
2. Cover-glasa preparation of spinal oord of ox, x 250. (Stained with methyl blue.)
AxU-rylinder
Dcndritie proccstc»
• \>i
Dttaehfd
CLcit-eylinder
proecia
Larfif
multipolar
neroe-eeU
A*U-ejiU%der proct**
Bipolar nerve-etU
Anterior column
Anteriur nerre-root
Kerve-eelU of
anterior eomu.
CapiUarif
Ant. median Jltture
w
Inei'!un
; i.n-medullatt
ncrve-fih:ei
Hucleut
f '• MedulUaed
nerve-flhra
- SeuriUmvui
•Icdullatu thtulli
Nerve-fibrei of
vhite 'natttr
Potterwr nerve-root
I. Nei^e-tiores of frog, teased in
osmic acid, x 300.
{Stained with hasmatoxylin,)
--* PoBUrior eoiumn
3. Transverse section of spinal cord. (Stained with aniline blue-black.)
Sylrinnjioure
Internal car^tUl.
Ratilar artery
IteduUtt oblongata
Anterior cerebral
C^ , . Mid<Ui cerebral
Cvrjtora mamillori'i
Pont
Vertebi al artern
Cerebellim
4. Batie of brain, with arteries injected.
West i'«: win an chr.i^iii
CHAPTER XII.
THE CENTRAL NERVOUS SYSTEM.
In other divisions of our subject, we have been able to
follow to a greater or less extent the processes which take
place in the organs described. The chemistry and the
physics of these processes have bulked more largely in our
pages than the anatomy and histology of the tissues them-
selves. In dealing with the central nervous system we must
adopt a method the very reverse of this. Its anatomical
arrangement is excessively intricate. The events which
take place in that tangle of fibre, cell, and fibril are, on the
other hand, almost unknown. So that in the description of
the physiolog}^ of the central nervous system we can as yet
do little more than trace the paths by which impulses may
pass between one portion of the system and another, and from
the anatomical connections deduce, with more or less pro-
bability, the nature of the physiological nexus which its
parts form with each other and the rest of the body. And
here it may be well to remark that, although for convenience
of treatment we have considered the general properties of
nerves in a separate chapter, there is not only no funda-
mental distinction between the central nervous system and
the outrunners which connect it with the periphery, but
obviously a central nervous system would be meaningless
and useless without afferent nerves to carry information to
it from the outside, and efferent nerves along which its
commands may be conducted to the peripheral organs.
636 A MANUAL Of PIIYSIOLOCY
I. Structure of the Central Nervous System.*
In unravelling the complex structure of the central nervous
system, we avail ourselves of information derived (i) from
its gross anatomy ; (2) from its microscopical anatomy ;
(3) from its development ; (4) from what we may call,
although the term is open to the criticism of cross-division,
its physiological and pathological anatomy.
The study of development enables us not only to determine the
homology, the morphological rank, of the various parts of the brain
and cord, but also, by comparison of animals of different grades of
organization, sometimes to decide the probable function and physio-
logical importance of a strand of nerve-fibres or a column of nerve-
cells. It is of special value in helping us to differentiate and to
trace the various tracts or paths into which the white matter of the
central nervous system may be divided. For the medullary sheath
is not developed at the same time in all the tracts, and a strand of
nerve-fibres without a medulla — e.g., the pyramidal tract (p. 650) at
birth — is readily distinguished under tht microscope.
Then, again — and this is what we propose to include under the
fourth head — experimental physiology and clinical and pathological
observation throw light not only on the functions, but also on the
structure, of the central nervous system. For instance, complete or
partial section, or destruction by disease, of the white fibres of the
cord or brain, or of the nerve roots, or removal of portions of the
grey matter, is followed by degeneration in definite tracts. And
since, as we have already seen, degeneration of a nerve-fibre is caused
when it is cut off from the cell of which it is a process, the amount
and distribution of such degeneration teaches us the extent and
position of the central connections of the given tract. And, particu-
larly in young animals, removal of a peripheral organ — an eye or a
liml) — may be followed by atrophy of portions of the central nervous
system immediately related to it. Certain tracts of white or grey
matter are also differentiated from each other by the size of their
fibres or cells. For example, the postero-median column of the
spinal cord has small fibres, the direct cerebellar tract large fibres ;
the pyramidal cells in what we shall afterwards have to distinguish as
the 'leg area' (p. 707) of the cerebral cortex are large ; those of the
'face area ' are comparatively small.
Certain tracts may also be marked out by means of the electrical
variation, which gives token of the passage of nervous impulses along
them when portions of the central nervous system or peripheral
nerves are stimulated (Horsley and Gotch).
* It is unnecessary to say that a complete description of the structure
of the brain and cord from the anatomical standpoint would be out of place
in a book like this. As in the other divisions of our subject, a knowledge
of anatomy is assumed on tlie pait of the reader.
THE CENTRAL NERVOUS SYSTEM
637
Development of the Central Nervous System. — Very early in
development (Fig. 216) the keel of the verteljrate embryo is laid
down as a groove or gutter in the epiblast of the blastodermic area
(Chap. XIV.). The walls of this 'medullary groove' grow inwards,
and at length there is formed, by their coalescence, the 'neural canal '
(Fig. 217), which expands at its anterior end to form four cerebral
Fig. 216.— Formation of the Neural Canal at an Early Stage.
vesicles (Fig. 218). Thus there is a continuous tunnel from end to
end of the primary cerebro- spinal axis ; and this persists in the adult
as the central canal of the spinal cord and the ventricles of the brain,
whose ciliated epithelium represents the epiblastic lining of the primi-
tive neural canal.* From the wall of this canal is developed the
cerebro-spinal axis, with the motor roots of the spinal nerves. The
■'<^'^' '
^"«^
^^■flEP/'
\-
Fig. 217.— Neural Canai. at a Later Stage.
ganglia on the posterior roots arise from a series of epiblastic thicken-
ings arranged along the neural canal, but outside its wall. From both
poles of each ganglion cell a process grows out, one towards the
periphery, which forms a peripheral nerve-fibre, the other centrally
* Gaskell and Bland Sutton regard the central canal as the representa-
tive of the alimentary canal of the (crustacean) ancestor of the verte-
brates.
63S
A MANUAL Of PHYSIOLOGY
to connect the cell witl/the cord. From the after-brain is developed
the medulla oblongata, from the hind-brain the cerebellum and pons,,
from the mid-brain the corpora quadrigemina and crura cerebri.
The fore-brain, or primary fore-
"/
TO II.LUSTRATK
THE Cerebral
brain, gives rise of itself only
to the third ventricle and optic
thalamus, but a secondary fore-
brain buds off from it and soon
divides into two chambers,
from the roof of which the
cerebral hemispheres, and from
the floor the corpora striata,
are derived. Their cavities
persist as the lateral ventricles,
which communicate with the
third ventricle by the foramen
of Monro. The olfactory tracts
are formed as buds from the
secondary fore-brain.
To complete the story of
the development of the brain,
it may be added that the retina
is really an expansion of its
nervous substance. A hollow
process, the optic vesicle, buds
out on each side from the
primary fore- brain. A button
of epiblast, which afterwards
becomes the lens, grows against
the vesicle and indents it, so
that it becomes cup-shaped, the inner concave surface of the cup
representing the retina proper, the outer convex surface the choroidal
epithelium. The stalk becomes the optic nerve.
Histological Elements of the Central Nervous System. — The
central nervous system is built up (i) of true nervous elements, (2) of
supporting tissue. The nervous elements have usually been described
as consisting of nerve-fibres and nerve-cells, but the antithesis of a
time-honoured distinction must not lead us to forget that the essential
part of a nerve-fibre, the axis-cylinder, is a process of a nerve cell,
and the medullary sheath perhaps a product of the axis-cylinder.*
In strictness, the term ' nerve-cell ' ought to include not only the cell-
body, but all its processes, out to their last ramifications. But the
habit of speaking of the position of the cell-body as that of the nerve-
* Although each internode of the medullary sheath of a peripheral
nerve-fibre has been supposed to be formed from a cell that, in the course
of development, comes in contact with the axis-cylinder and ultimately
encircles it, a similar origin can hardly be admitted for the medulla of the
fibres of the spinal cord and brain, where, indeed, a segmental genesi.s
seems e.vcluded by the absence of regularly placed internodal nuclei and
nodes of Ranvier.
- Diagram
thk fokmaiion of
Vesicles.
\. I indicates the cavity of the secondary
fore-brain, which eventually becomes the
lateral ventricles. In B the secondary fore-
brain has grown backwards so as to overlap
the otlier vesicles. I, first cerebral vesicle
(primary fore-brain or 'tween brain) ; II,
second cerebral vesicle (mid-brain) ; III,
third cerebral vesicle (hind-brain) ; IV, fourth
cerebral vesicle (after-brain).
THE CENTRAL NERVOUS SYSTEM
639
cell is so ingrained that it seems better to continue the use of the
latter term in its old signification, and to speak of the cell and
branches together as a nervous element. A nerve-cell from the
anterior horn of the spinal cord (Plate V., 2), which may be taken as
a typical nerve-cell, is a knot of granular protoplasm, apparently
destitute of a cell-wall, but containing a large nucleus inside of which
lies a highly refractive nucleolus. Pigment may also be present,
especially in old age. By certain methods of staining it may be
shown that fibrils run through the cell-substance, while between the
fibrils lie round or spindle-shaped bodies (Nissl's bodies) which stain
Fig. 219.
a—e shows the development of the pyramidal nerve-cells of the cerebral cortex in a
typical mammal ; a, neuroblast with commencing neuron ; b, dendrons appearing ;
d, commencing collaterals. A— D shows the different degree of comple.xity in the fully-
developed pyramidal cells in different vertebrates : A, frog ; B, lizard ; C, rat ; D, man.
(Donaldson, after Ram6n y Cajal. )
with basic dyes. These bodies vary in appearance in different kinds
of nerve-cells, and in the same nerve-cell under different conditions.
Several processes — it may be five or si.x — pass off from the cell-body,
one of which is distinguished from the rest by the fact that it main-
tains its original diameter for a comparatively great distance from the
cell, and gives off comparatively few branches. This process, which
in favourable preparations can be traced on till it becomes the axis-
cylinder of a nerve-fibre, is called the axis-cylinder process, or more
shortly the neuron. The few slender branches that come off from it,
usually at right angles, are called collaterals. Both the main thread
of the neuron and the collaterals end by breaking up into brushes of
fibrils. The rest of the processes of the cell, which are termed
640
A MANUAL OF PHYSIOLOGY
tIenJrons, or protoplasmic processes, very rapidly diminish in diameter,
as they pass away from the cell, by breaking up into fibrils like the
branches of a tree. They lose themselves at a little distance from
the cell in the surrounding network, which forms the greater portion
of the ground material of the grey substance, and in which the
dendritic systems of neighbouring cells come into relation with each
other, and with the terminal brushes of the neurons. Probably the
relation is not one of actual anatomical continuity, but the processes
come so close together that nerve impulses are able to pass across
from the terminal brush of the neuron of one nervous element to the
dendrons of another. All the nerve-cells of the cerebrospinal axis
are believed to agree with the cells of the anterior horn in the pos-
session of a neuron and one or more dendrons. In the cerebral
cortex the typical cells are of pyramidal shape. From the base
comes off the neuron, and from the angles the dendritic processes.
Fig. 220.
Cells from the Gasserian ganglion of a developing guinea-pig. The originally bipolar
cells are seen changing into cells apparently unipolar. The same process occurs in the
cells of the spinal ganglia. (Van Gehuchten. )
Sometimes a nreuon, instead of ending in a brush of fibrils which
come into relation with the dendrons of another nervous element,
breaks up into a sort of basket-work of fibrils surrounding the cell-
body. The cells of Purkinje, for instance, in the cerebellum, are
surrounded by such pericellular baskets. The cells of the spinal
ganglia have two neurons, which in the embryo arise one from each
end of the bipolar cell, but in the adult are connected to the cell
by a single process (Fig. 220). They have no dendrons. The
sympathetic ganglion cells seem also to be often devoid of true den-
dritic processes, although it is not certain that this is always the case.
Another kind of cell which seems undoul)tedly to be of nervous
nature is the ' granule-cell.' Graniile-celis are much smaller than
the nerve-cells we have been describing. Their processes are much
less easily followed, but all appear to give off a neuron and one or
more dendrons. They contain a relatively large nucleus (5 to 8 /x in
diameter), with only a mere fringe of cell-substance. The nucleus,
unlike that of a large nerve-cell, stains deeply with hrematoxylin.
Some parts of the grey matter are crowded with these granule-
cells, e.g., the nuclear layer of the cerebellum and the substantia
THE CENTRAL NERVOUS SYSTEM 641
gelatinosa, or substance of Rolando, which caps the posterior horn
in the cord. In other parts they arc more thinly scattered, but pro-
bably they are as widely diffused as the large nerve-cells proi)er, and
no extensive area of the grey matter is wholly without them.
The layer of ciliated epithelium lining the central canal of the
spinal cord and the ventricles of the brain in the lower animals and
in early life in man, has also been considered by some as of nervous
nature ; and the fact that the deep ends of the cells are continued
into processes which pierce far into the grey substance lends weight
to this opinion.
Growth of Nerve-cells. ^The growth of a nervous element is
a comparatively slow i)rocess. Early in foetal life (about the third
or fourth week, in man) certain round germinal cells make their
appearance amid the columnar epiblastic cells surrounding the
neural canal. From their division are formed, in the first months of
embryonic life, the primitive nerve-cells or neuroblasts. These soon
elongate and push out processes, first the neuron or neurons, and
then the dendrons (Fig. 219). As development goes on the cell-
body grows larger, and the processes longer and more richly
branched. The neuron, in the case of the great majority of the
nervous elements of the brain and cord, ultimately acquires a medul-
lary sheath, although, as we have said, the time at which meduUation
is completed varies in different groups of elements, and in some
nervous tracts it is even wanting at birth. At birth, too, the
branches of many of the cells are less numerous, and the connections
between different nervous elements therefore less intimate than they
will afterwards become. For many years the processes, and par-
ticularly the neurons, continue not only to grow longer, but also to
grow thicker. The cell-body also enlarges, and the quantity of
material in it that stains with basic dyes increases. Even after
puberty is reached the anatomical organization of the nervous system
may still continue to advance, although at an ever-slackening rate,
and the finishing touches may only be given to its architecture in
adult life. In old age the nervous elements decay as the body does.
The cell-body diminishes in size ; the stainable material lessens in
amount ; vacuoles form in the protoplasm and pigment accumulates ;
the nucleus shrinks ; the nucleolus is obscured or may disappear
altogether. At the same time the processes of the cell, and espe-
cially the dendrons, tend to atrophy (Fig. 221).
Nerve-cells are the most distinctive histological feature of the grey
nervous substance. Sown thickly in the cerebral cortex, the basal
ganglia, the floor of the fourth ventricle, and the cervical and lumbar
enlargements of the cord, they are scattered more sparingly wherever
the grey matter extends. They also occur in the spinal ganglia and
their cerebral homologues, in the ganglia of the sympathetic system
and the sporadic ganglia in general. But wide as is their distribution
and great as is the size of the individual cells, they yet make up but
a small portion of the whole of the central nervous substance. And
although it is not to be wondered at that objects so notable when
viewed under the microscope should have struck the imagination of
41
642
A MANUAL OF PHYSIOLOGY
physiologists, it is probable that the very high powers which it is so
common to attribute exclusively to them ought to be, in part at least,
shared with the nervous plexus woven from their processes and of
which they form the nodes.
In addition to non-medullated fibres and filaments arising from the
nerve-cells, the grey matter contains also, as may be seen in prepara-
tions stained by Weigert's method,* great numbers of exceedingly
fine medullated fibres.
Only medullated nerve-fibres are met with in the white matter of
the cerebro-spinal axis. They are devoid of a neurilemma. In
Fig. 221.
I, spinal ganglion cells of a still-born male child; 2, of a man ninety-two years
old (X 250)— N, nuclei ; 3, nerve-cells from the antennary ganglion of a honey-bee
just emerged in the perfect form ; 4. of an old honey-bee. The nucleus is black in
the figure. In 3 it is very large, in 4 it is shrunken, and the cell-substance contains
vacuoles. ( Hodge. )
diameter they vary from 2 /x to 20 /a. In Malapterunis eledricus the
fibre in the cord which supplies the electrical organ is of immense
size ; and in the anterior column of many fishes may also be seen a
single gigantic fibre on each side with a diameter of nearly 100 /m.
It cannot be said that any relation between the functions of nerve
fibres and their size has been definitely established. Many afferent
fibres, it is true, are small— this is notably the case with the fibres of
the posterior column and posterior root — and many motor fibres are
large. But the distinction can by no means be generalized, for the
* Weigert's is a special method of staining the medullaiy sheath with
haematoxylin.
THE CENTRAL NERVOUS SYSTEM 643
fibres of the cerebellar tract, which certainly are afferent, are among
the largest in the spinal cord ; and the vaso-motor fibres, which pass
from the cord into the sympathetic, are smaller than the fibres of the
posterior column. Even the motor nerve-fibres of striated muscles
vary considerably in diameter, those of the tongue, e.g., being smaller
than those of the muscles of the limbs. Further, the medullated
fibres of the brain are, without reference to function, in general finer
than the fibres of the cord. The cause of these differences in the
size of nerve-fibres is quite unknown. It is more likely to be morpho-
logical than physiological.
The supporting tissue of the central nervous system consists
partly of ordinary connective tissue derived from the mesoblast, and
partly of a peculiar form of tissue derived from the epiblast, and
called neuroglia. The whole cerebro-spinal axis is wrapped in four
concentric sheaths. Next the walls of the bony hollow in which it
lies is the dura mater. Next the nervous substance itself, following
the convolutions of the brain and the fissures of the cord, and giving
off bloodvessels supported in connective-tissue septa to both, is the
pia mater. Between the dura and the pia, separated from the latter
by a jacket of cerebro-spinal fluid, is the double layer of the arachnoid.
The comparatively coarse processes that run into the nervous sub-
stance from the pia mater are the main beams in the scaffolding of
non-nervous material with which that substance is interwoven, and
by which it is supported. The interstices are filled in by a thick-set
feltworkof interlacing but unbranched neuroglia fibres, which lie close
against the small glia cells, but in the adult at least are perfectly
distinct from them. In preparations impregnated by the Golgi
method* the fibres appear to be processes running out from the
attenuated cell-body like the arms of a microscopic crab or spider.
But this is a deceptive appearance, as Weigert has shown by means
of a special method in which the neuroglia fibres are alone stained.
It is possible, however, that in the embryo the fibres are formed by
the cells, and afterwards become detached from them. The glia
fibres are perfectly distinct from the nervous substance proper, but
they are not ordinary connective tissue. In the white matter nearly
every medullated nerve-fibre is divided from its neighbours by glia
fibres, which form a wide-meshed network. The network is denser
in most parts of the grey substance, though not in all. The
neuroglia is present in greatest abundance in the grey matter imme-
diately surrounding the central canal of the cord and the ventricles
of the brain (the ependyma, as it is called). Contrary to the common
opinion, the substance of Rolando is poor in neuroglia (Weigert).
Another kind of tissue, consisting only of a granular mass, entirely
* The method depends upon the deposition of mercury, or silver, in or
around the cell-bodies and their processes in tissues which have been
hardened in bichromate of potassium and then soaked in a solution of
mercuric chloride or silver nitrate. In Pal's improvement of Golgi's
method a solution of sodic sulphide follows the mercuric chloride.
41 — 2
644 ^ MANUAL OF PHYSIOLOGY
devoid of cells, has been described as filling in the spaces of the
grey matter not occupied by the other elements. It is for this
substance that some authors reserve the name of neuroglia. But
it is probable that the granular appearance seen in microscopic
preparations is due to nothing else than the cross-sections of the
fine neuroglia fibrils or of the nervous plexus.
General Arrangement of the White and Grey Matter in the
Central Nervous System. — (i) Around the central canal, as we
have seen, a tube of grey matter sheathed with white fibres
is developed. This tube, from optic thalamus to conus
Fig. 222. — Nkukoclia Fibrks and Cells (from a human embryo 30 cm. in
length). The small cell on the right is from the grey, the other two from the
white substance ; Golgi's method (Kolliker).
medullaris, may be conveniently referred to as the central
grey axis or stem, which, in the lowest vertebrates, e.g., fishes,
is much the most important part of the central nervous
system.
(2) On the outer surface of the anterior portion of the
neural axis, but not in the part corresponding to the spinal
cord, is laid down a second sheet of cortical grey matter.
Between this and the primitive grey stem are interposed
(a) the sheath of white fibres that clothes the latter, and
connects its various parts, and (h) a new development of
white matter (corona radiata, cerebellar peduncles), which
THE CENTRAL NERVOUS SYSTEM 645
serves to bring the cortex into relation with the primitive
axis, and through it with the rest of the body.
Although there are histological and developmental differ-
ences between the cerebral and the cerebellar cortex, we
may, for some purposes, classify them together as cortical
formations. And we may also include under this head the
corpora striata, which, although generally grouped with the
optic thalami and the other clumps of grey matter at the
base of the brain, as the basal ganglia, are to be regarded as
cortical in character. As we mount in the vertebrate scale,
the cortex formation of the secondary fore-brain and hind-
brain acquires prominence.
In other words, the grey matter developed in the roof of the
cerebral vesicles i and III. (Fig. 218) (the grey matter of the cere-
bral and cerebellar cortex) comes to overshadow the superficial grey
matter hitherto present only in the roof of vesicle II. (in the corpora
bigemina). And this cortex formation becomes larger in amount,
and, in the case of the cerebral grey matter, more richly convoluted,
the higher we ascend, until it reaches its culmination in man. As
the anterior cerebral vesicles develop, they spread continually back-
ward until at length the cerebral hemispheres cover over, and almost
completely surround, the primary fore-brain, and the mid- and hind-
brains, so that the anterior portion of the primitive stem comes,
as it were, to be invaginated into the second wider tube of cortical
grey matter. This development of the cortical grey substance is
accompanied with a corresponding development of white fibres, for
an isolated nerve-cell is no more conceivable than a railway-station
the track from which leads nowhere in particular, or a harbour on
the top of a hill.
But it is to be particularly observed that the new forma-
tion does not supplant the old, but works through and
directs it. The nerve-cells of the cortex do not throw out
their neurons to make direct junction with muscles and
sensory surfaces. Such junction the cortex finds already
established between the primitive cerebro-spinal axis and the
periphery. It joins itself on by new white substance to the
cells of the central stem ; and we have reason to believe
that no fibres pass either from the periphery to the cortex,
or from the cortex to the periphery, without being broken in
the cells of this primitive grey tube.
The fibres from the cortex of each cerebral hemisphere (corona
radiata), radiating out like a fan below the grey matter, are gathered
646 A MANUAL OF PHYSIOLOGY
together into a compact leash as they sweep down through the
isthmus of the brain in the internal capsule, to join the crura
cerebri. The cortex of each cerebellar hemisphere, and the ribbed
pouch of grey matter, known as the corpus dentatum, which is buried
in its white core, are also connected by strands of fibres with the
central stem and the cerebral mantle. The rcstiform body or inferior
peduncle brings the cerebellum into communication with the spinal
cord. The superior peduncle by one path, and the middle peduncle
by another, connect it with the cerebral cortex. A great transverse
commissure, the corpus callosum, unites the cerebral hemispheres
across the middle line, while transverse fibres that pass into the pons,
as well as other fibres that break through the middle lobe or worm,
form a similar junction between the two hemispheres of the cere-
bellum.
The fibres of the nervous system may be divided into
(i) fibres connecting the peripheral organs with nerve-cells
in the central grey axis ; (2) fibres connecting nerve-cells in
this central axis with cells in the external or cortical grey
tube ; and (3) fibres linking cortex with cortex, or central
ganglia with each other. Our first task is, therefore, to trace
the peripheral nerves to their cells or centres in the nervous
stem. And although there is reason to believe that the
whole of the peripheral nerves, cerebral and spinal (with
the exception of the olfactory and optic, which are rather
portions of the brain than true peripheral nerves), form an
unbroken morphological series, it will be well to begin with
the spinal nerves, since their motor and sensory fibres are
gathered into different and definite roots, whose course
within the cord is, in general, more easily traced than the
course of the cerebral root-bundles within the brain.
Arrangement of the Grey and White Matter in the Spinal
Cord. — The grey matter of the spinal cord is arranged on
each side in a great unbroken column of roughly crescentic
section (Plate V., 3), joined with its fellow across the middle
line by a grey bar or bridge, which springs from the con-
vexity of the crescent, and is pierced from end to end by
the central canal. The anterior horn of the crescent,
although it varies in shape at different levels of the cord, is,
in general, broad and massive in comparison with the
slender and tapering posterior horn. In the lower cervical
and upper dorsal region a moulding or projection, forming
THE CENTRAL NERVOUS SYSTEM
647
a lateral horn, springs from the Huted outer side of the grey
substance. Within the grey matter nerve-cells are found,
sometimes so regularly arranged that they form veritable
cellular or vesicular strands. Of these the best marked are:
(i) The tract or tracts made up by the cdh of the anterior
horn (Fig. 223), which practically run from end to end of the
Enlaraernenl-
Cells ofihe — — -
anterior Cornu
Lumbar -|:
Enlargement n -
Si i Hint's Cervical
mtcleus:
^Late ral ce^U-column
(cvlurnn cf the tnter-
. medtc-laieral trad)
-Sttif line's clcrsal
nucleus or Clarke's
Column
Scattered ceJli, of
inte rmecJic -lalaral
trad.
-Stilling's '.<Sacral
nucleus
FiG. 223.— Diagram of Grey Tracts of Cord,
cord, swell out in the cervical and lumbar enlargements,
where the cells are very numerous and of great size (70 /x. to
140 /Lt in diameter), and contract to a thin thread in the
thoracic region, where they are relatively few, scattered, and
small. (2) Clarke's column, whose cells are situated at the
inner side of the root of the posterior horn just where it
648 A MANUAL OFl'IIYSIOLOGY
joins on to the grey cross-bar. It gradually increases in
si^e from above downwards, usually appearing first at the
level of the seventh or eighth cervical nerve, attaining its
maximum development at the eleventh or twelfth dorsal and
disappearing altogether, as a continuous strand, at the level
of the second or third lumbar nerves. The so-called
cervical and sacral nuclei of Stilling, however, occupy the
same position towards the upper and lower ends of the
cord, and may be looked upon as isolated portions of
Clarke's column. (3) A tract called the intermcdio-lateral
tract, which is best marked in the thoracic region, but
extends also down into the lumbar swelling and up until it
blends with certain cells of the anterior horn of the cervical
cord. (4) The cells of the posterior horn are less numerous
and smaller than those of the anterior horn. Throughout
the whole cord, however, two small groups of cells may be
distinguished, one on the lateral and the other on the mesial
side of the isthmus or neck of the horn a little in front of
(i.e., ventral to) the edges of the substance of Rolando.
The white matter of the cord is anatomically divided by
the position of the nerve-roots and the anterior and posterior
fissures into three columns on each side : the anterior, lateral,
and posterior columns (Plate V., 3). The first two are often
grouped together as the antero-lateral column. In the
cervical region it may be seen with the microscope that
the posterior white column is almost bisected by a septum
running in from the pia mater towards the grey commissure.
The inner half is called the postero-median column, or
column of GoU ; the outer half the postero-external column,
or column of Burdach (Fig. 224). No localization of any
of the other conducting paths in the cord is possible by
anatomical examination ; but by means of the develop-
mental method and the method of degeneration the columns
of Goll and Burdach can be followed throughout the cord,
and several similar areas can be mapped out. We shall
only mention those that are physiologically the most im-
portant.
When the spinal cord is divided, and the animal allowed
to survive for a time, certain tracts are picked out b}- the
THE CENTRAL M'.RVOrs SYS'/ EM
649
degeneration of their fibres, althoiijj^h in every degenerated
tract some fibres remain unaffected. We may distinguish
the tracts that degenerate above the lesion (ascending de-
generation) from those that degenerate below the lesion
(descending degeneration).
Ascending Tracts. — Above the lesion degeneration is found
both in the posterior and the antero-lateral columns.
Immediately above the section nearly the whole of the
KiKsr Ckkvicai.
Antero-lateral
ground-bundle
Direct pyramidal
.Antero-lateral, ascend-
ing and descending
Crossed pyramidal
Direct cerebellar
Postero-external (Burdach's)
I'osiero-medinn (GoU's)
Six M! < 'l' I' \ I' \1 .
Sixth Dorsal.
.A
Fourth Lumbar.
\ It:''
vr
/^-^^AJV
Fig. 224. — Diagrammatic Secjtons of the Spinal Cord to show the
Tracts ok White Matter at Different 1 evels.
posterior column is involved. Higher up the degeneration
clears away from Burdach's tract, and, shifting inwards,
comes to occupy a position in the column of Goll. In the
antero-lateral column two degenerated regions are seen, both
at the surface of the cord, one a compact, sickle-shaped area
extending forwards from the neighbourhood of the line of
entrance of the posterior roots, and the other an area of
scattered degeneration, embracing many intact fibres, and
completing the outer boundary of the column almost to the
650 .1 MANUAL OF PHYSIOLOGY
anterior median fissure. The compact area is called the
direct ccYchcllar tract, the diffuse area the antcro-latcral ascend-
ing tract, or tract of Gowers.
Descending Tracts. — When the cord is divided, say in the
upper dorsal or cervical region, the following tracts de-
generate below the lesion :
(i) A small group of fibres close to the antero-median
fissure, which has received the name of the direct pyramidal
tract — pyramidal, because higher up in the medulla oblongata
it forms part of the pyramid ; direct, because it does not
cross over at the decussation of the pyramids, but continues
down on the same side.
(2) A tract of degenerated fibres in the posterior part of
the lateral column. This is the lateral or crossed pyramidal
tract, and is much larger than the direct. In the medulla it
also lies within the pyramid, but, unlike the direct pyramidal
tract, it crosses to the opposite side of the cord at the
decussation.
(3) A tract of scattered degeneration overlapping the
tract of Gowers, and called the antero-latcral descending tract.
(4) A small comma-shaped island of degeneration (comma
tract) can be followed downwards for a short distance in the
posterior column.
When we have deducted the long ascending and descend-
ing tracts which have been described, there still remains,
both in the anterior and in the lateral column, a balance of
white matter unaccounted for. This white substance, which
does not degenerate for any great distance either above or
below a lesion, is called the antero-lateral ground-bundle, and
lies chiefly in the form of an incomplete ring around the
anterior cornu. It is believed to consist of fibres which run
only a comparatively short course in the cord, and serve to
connect nerve-cells at different levels.
The next question which arises is : How are the long
tracts connected below, i.e., with the periphery, and above,
i.e., with the higher parts of the central nervous system ?
The answer to this question, partly derived from clinical
records and partly from experimental results, is in the case
of some of the tracts unexpectedly full and minute, though
THE CENTRAL NERVOUS SYSTEM
651
meagre in regard to others. But to render it intelligible it
is necessary, first of all, to describe bncHy—
The Arrangement of the Grey and White Matter in the Upper
Portion of the Cerebro-spinal Axis. — In the medulla oblongata
the grey and white matter of the spinal cord is rearranged,
and, in addition, new strands of fibres and new nuclei of
grey substance make their appearance. Of these nuclei the
most conspicuous is the dentate nucleus of the inferior olive,
which, covered by a crust of white fibres, appears as a pro-
jection on the antero-
lateral surface of the me-
dulla. In front of the
olive, between it and the
continuation of the an-
terior median fissure, is
another projection, the
pyramid, which looks like
a prolongation of the an-
terior column of the cord,
but is made up of very
different constituents.
Dorsal to the olive is the
restiform body or inferior
peduncle of the cere-
bellum, and behind the
restiform body lie two thin columns, the funiculus cuneatus,
which continues the postero-external column of the cord,
and the funiculus gracilis, which continues the postero-
internal column. In these funiculi are contained respec-
tively the nucleus cuneatus and the nucleus gracilis. The
rearrangement of the constituents of the cord is due mainly
to two causes : (i) The opening up of the central canal to
form the fourth ventricle, and the folding out, on either side,
of the grey matter which lies posterior to it in the cord
(2) the breaking up of the grey matter of the anterior horn
by strands of fibres as they sweep through it from the lateral
pyramidal tract to take up a position in the pyramid of the
opposite side (decussation of the pyramids).
The cerebro-spinal axis passes up from the medulla
Fk;. 225. — Diagrammatic Transverse
Section of Medulla Oblongata.
a, nucleus gracilis ; b, nucleus cuneatus ;
c, internal arcuate fibres crossing the middle
line from a and b to the fillet, d ; t', anterior
median fissure.
652 A MANUAL OF PHYSIOLOGY
through the pons, encircled and traversed by the transverse
pontine fibres derived from the middle cerebellar peduncle
or commissure, which enclose everywhere between them
numerous collections of nerve-cells (nuclei pontis). En-
larged by the accession of many of these fibres which come
from the cortex of the cerebellum on the opposite side, as
well as of fibres from the nuclei of the cranial nerves that
take origin in this neighbourhood (fifth and eighth), the
central nervous stem bifurcates above the pons into the two
diverging crura cerebri. From each crus a great sheet of
fibres passes up between the optic thalamus and the caudate
nucleus of the corpus striatum on the one hand, and the
globus pallidus of the lenticular nucleus on the other, as
the internal capsule, from which they are dispersed, in the
corona radiata, to the cerebral cortex. Both in the upper
part of the pons and in the crus a ventral portion, or crusta,
containing the fibres of the pyramidal tract, and a dorsal
portion, or tegmentum, can be distinguished, the line of
separation being marked in the crus by a collection of grey
matter, called from its usual, though not invariable, colour
the substantia nigra (Fig. 225). A portion of the tegmentum
is continued below the optic thalamus.
Coming back now to our question as to the connec-
tions of the long tracts of the cord, let us consider, first
of all.
The Connections of the Postero-median and Postero-external
Columns. — When a single posterior root is divided, say in the
dorsal region, between the cord and the ganglion, its fibres,
as we have already seen (p. 585), degenerate above the
section. If a series of microscopic sections of the spinal
cord be made, well-marked degeneration will be found at
the level of entrance of the root on the same side of the
cord, while below that level there will be only a few
degenerated fibres in the comma tract. Immediately above
the plane of the divided root the degeneration will be
confined to Burdach's column and to its external border.
Higher up it will be found in the internal portion of
Burdach's and the external rim of Goll's column. Still
higher up the degenerated fibres will be confined to the
THE CENTRAL jWERVOUS SYSTEM
653
postero-median column ; the postero-external will be entirely
free from degeneration.
'Mm..
When a number of consecutive posterior roots are cut, the whole
of the postero-external column in the sections immediately above the
highest of the divided roots will be found occupied by degenerated
fibres, while GoU's column may be free from degeneration, or de-
generated only at its outer border. Higher up degeneration will be
found to have involved the whole of
the postero-median column, and to
have cleared away altogether from
the postero-external. The degene-
ration in the column of Goll may
be traced along the whole length of
the cord to the medulla, although
the number of degenerated fibres
diminishes as we pass upward. The
explanation of these appearances
seems to be as follows. It may be
seen in preparations of the cord
impregnated by Golgi's method
that the fibres of the posterior roots
soon after their entrance into the
cord divide into two processes, one
of which runs up and the other
down in the posterior column, or in
the adjoining portion of the pos-
terior horn. From both of these
collaterals are given off at intervals.
The descending branches probably
run downwards only for a short dis-
tance, and the degeneration in the comma tract seen after section of
the cord may be due to the division of these branches. Many of the
ascending branches pass up for a short distance in the postero-external
column, sweeping obliquely through it to gain the tract of Goll. In
this tract some of them run right on to the medulla oblongata, to end
in a collection of grey matter, the nucleus gracilis. Others must end
at various levels in the cord, their collaterals, and ultimately the main
branches themselves, coming into relation with nerve-cells in the
grey matter. When the cervical posterior roots are cut, many of the
degenerated fibres remain in Burdach's column up to the medulla,
where they make junction with the nucleus cuneatus. In the pos-
terior column, then, the fibres of the posterior roots which do not
suffer interruption in nerve-cells in the spinal cord are arranged in
layers, the fibres from the lower roots being nearest the median
fissure, and those from the higher roots farthest away from it. Other
collaterals from the posterior root-fibres, and many of the root-fibres
themselves, run into the anterior horn ; some pass into the posterior
horn, and doubtless come into relation with its scattered cells.
Fir.. 226. — Posterior Roots
ENTERING Spinal Cord (at the
left of the figure). (From a prepara-
tion stained with aniline blue-
black.)
654 '1 M.iyUAL OF P/IYSIOLOGY
Other collaterals cross the middle line in the posterior commissure
and end in the grey matter of the opposite side.
We may, therefore, conclude without hesitation that some
of the fibres of the posterior roots ascend to the medulla in
the posterior column of the cord without making junction
with any cells until they reach the gracile and cuneate
nuclei, where they end by breaking up into terminal brushes
of fibrils. The cell -bodies of these neurons lie in the
posterior root-ganglia.
Connections of the Direct Cerebellar Tract. — Since the direct
cerebellar tract does not degenerate after section of the
posterior nerve-roots, but does degenerate above the level
of the lesion after section of the spinal cord, the nerve-cells
of which its fibres are the neurons must be situated some-
where or other in the cord. The cells of the anterior horn
are known, in great part at any rate, to be connected with
other tracts, so that there are left over, to all intents and
purposes, only the scattered cells of the posterior horn and
the vesicular column of Clarke. Now, it has been observed
that the column of Clarke first becomes prominent in the
lower dorsal region, and that in this same region the direct
cerebellar tract begins. Atrophy of the cells of Clarke's
column has sometimes been shown to accompany de-
generation of the direct cerebellar fibres. Further, axis-
cylinder processes may be seen sweeping out from Clarke's
column in the direction of the direct cerebellar tract, and
although, in all probability, nobody has as yet been able
definitely to follow any of those axis-cylinder processes into
fibres of the tract, the evidence when put together is pretty
strong that the cells of Clarke's column, or some of them
at least, are their cells of origin. Clarke's cells are sur-
rounded by a fibrillar network which seems to represent the
terminations of some of the posterior root-fibres and of their
collaterals. The direct cerebellar tract runs right up to the
cerebellum through the restiform body, without crossing and
without being further interrupted by nerve-cells. The fibres
of the restiform body end partly in the dentate nucleus of
the cerebellum, partly in the vermis.
Connections of the Antero-lateral Ascending Tract. — It is not
THE CENTRAL NERVOUS SYSTEM 655
known with any certainty with what cells in the spinal cord
this tract is connected. All we can say is that none of its
fibres can come directly from the posterior nerve-roots, since
no degeneration is seen in the tract on section of the roots
alone.
It passes up through the medulla, where it perhaps makes junction
with the cells of the lateral nucleus, a collection of grey matter in
the lateral portion of the spinal bulb. Thence through the formalio
reticularis it is supposed to reach the pons, and, turning back through
the superior peduncle, ends in the cerebellum.
The formatio reticularis is the mosaic of grey and white matter
formed in the medulla by the interlacing of longitudinal and trans-
verse fibres with each other and with the relics of the grey matter of
the anterior horn. Its longitudinal fibres are derived from the fillet
and from the remains of the anterior and lateral columns after the
direct and crossed pyramidal tracts have taken up their position
in the pyramid and the direct cerebellar tract has passed into the
restiform body. The anterolateral ascending tract seems to pass
bodily into the formatio reticularis and to form part of its longitudinal
fibres. The transverse fibres sweep in bold curves towards the raphe
from the gracile and cuneate nuclei and the dentate nucleus of the
olive. The reticular formation occupies the whole of the anterior
and lateral portions of the medulla behind the pyramids and olivary
bodies, and is continued upwards in the dorsal portion of the pons
and crura.
Through the gracile and cuneate nuclei, but particularly
the latter, the postero- internal and postero external columns
of the cord are further connected on the one hand with the
cerebellar hemisphere by fibres passing up in the restiform
body of the same, and to a smaller extent of the opposite side,
and on the other hand with the fillet by fibres which sweep
in wide arches (internal arcuate fibres) across the mesial
raphe to the opposite side. The fillet is a well-marked
bundle which is formed from those fibres and lies imme-
diately behind the pyramid. Receiving fibres from other
sources on its way, and also giving off fibres, it runs upwards
in the dorsal or tegmental portion of the pons and crura
cerebri, posterior to the formatio reticularis, with the longi-
tudinal fibres of which it blends in the region below the
optic thalamus. One well-marked strand of these longi-
tudinal fibres receives the name of the posterior longitudinal
bundle (Fig. 227). In the subthalamic region and in the
656
A MANUAL or PJ/YSIOLOGY
optic thalamus itself the neurons of the fillet, whose cells
of origin lie in the gracile and cuneate nuclei, end for the
most part. Their terminal brushes come into relation with
nerve-cells whose neurons, entering into the corona radiata,
continue the path to the cerebral cortex. A few of the fibres
of the fillet may, however, pass straight on to the cortex
without being interrupted in nerve-cells (Monakow).
Connections of the Pyramidal Tracts. — When the cortex
around the fissure of Rolando is destroyed by disease in
man, or removed by operation in animals, it is found that in
Fig. 227.— Diagkammatic TRANsvEKsii Sixtion or Crura Cekehri anu
Aqueduct ok Sylvius.
a, anterior corpora quadrigemina ; /', aqueduct ; c, red nucleus ; d, fillet ; e, sub-
stantia nigra ; /, pyramidal tract in the crusta of the crura cerebri ; g, fibres from
frontal lobe of cerebrum ; //, fibres from temporo-occipiial lobe ; /', posterior longi-
tudinal bundle.
a short time degeneration has taken place in the fibres of the
corona radiata which pass off from this area. The degenera-
tion can be followed down through the genu and the anterior
two-thirds of the posterior limb of the internal capsule
(Fig. 227), and the crusta of the cerebral peduncle of the
corresponding side into the medulla oblongata. Below the
decussation of the pyramids it is found that the degenera-
tion has involved the two pyramidal tracts, and only these —
the crossed pyramidal tract on the side opposite the cortical
lesion, the direct pyramidal tract on the same side — and
THE CENTRAL NERVOUS SYSTEM 657
that the cross-section of the two degenerated tracts goes
on continually diminishing as we pass down the cord. (We
overlook, for the moment, in the interest of simplicity of
statement, the fact that in the monkey and in man, at any
rate, some degenerated fibres may be found in the crossed
pyramidal tract on the same side as the lesion.) This is
proof positive that the trophic cells of these tracts are
situated in the cerebral cortex. The fact that the degenera-
tion does not spread to the anterior roots is proof probable
that nerve-cells intervene between the pyramidal iibres and
the root-fibres. The results both of normal and morbid
histology complete the proof, and enable us to identify the
cells of the anterior horn as the cells in question. For
(i) Axis-cylinder processes have been actually observed
passing out from certain of the so-called motor cells of the
anterior horn to become the axis-cylinders of fibres of the
anterior root.
(2) In the pathological condition known as anterior
poliomyelitis, the cells of the anterior horn degenerate, and
so do the anterior roots of the affected region, the motor
fibres of the spinal nerves, and the muscles supplied by them.
(3) An enumeration has been made in a small animal
(frog) of the cells of the anterior horn and of the anterior
root-fibres, and it has been found that the numbers agree in
a remarkable manner. From all this it cannot be doubted
that most, at any rate, of the cells of the anterior horn are
connected with fibres of the anterior root. But since the
number of fibres in the pyramidal tracts falls far short of
the number of cells in the anterior horn, and of the number
of fibres in the anterior roots, it is necessary to assume that
one pyramidal fibre may be connected with several cells.
Connections of the Antero-lateral Descending Tract. — Degenera-
tion is caused in this tract by a lesion in the cerebellum on the same
side. The degeneration lessens as we pass down the cord. From
this we conclude that the trophic cells of the antero-lateral descending
tract lie in the cerebellum. It is said that some degenerated fibres
are found in the anterior roots. This would point to a direct con-
nection between the cortex of the cerebellum and the motor nerves,
but recent observations, on the whole, cast doubt upon the state-
ment. The descending antero-lateral tract passes down from the
cerebellum in the restiform body.
42
658 A MAA'UAL 01' PHYSIOLOGY
Thus far, then, we have been able to map out two great
paths from the cerebral cortex to the periphery, one efferent,
the other afferent.
(i) The great efferent or motor path, which, starting in the
cortex around the Hssure of Rolando, and sweeping down
the broad fan of the corona radiata, passes through the
narrow isthmus of the posterior limb of the internal capsule
into the crusta of the crus cerebri, and thence into the
pyramid of the bulb. Here the greater part (usually about
90 per cent.) of the fibres decussate, appearing in the
cervical cord as the massive crossed pyramidal tract of the
opposite side. A few (usually about 10 per cent.) remain
on the same side, as the slender direct pyramidal tract ; but
the breadth of this tract constantly diminishes as its fibres
continue to decussate across the anterior white commissure,
and to reinforce the crossed tract of the opposite side. The
fibres of this crossed tract are, in their turn, continually
passing off into the grey matter of the anterior horn, where
they break up into fibrils, and thus make connection (physio-
logical if not anatomical) with the fine nerve-plexus in the
vicinity of the cells, whose axis-cylinder processes enter the
anterior roots of the spinal nerves. The losses which it
suffers as it passes along the cord may be partly compen-
sated by the bifurcation of some of its fibres (geminal fibres),
but ultimately the whole tract makes junction with the grey
matter, and dwindles away as the lumbar region is reached
(Fig. 224). It has been asserted that on their way down
the cord the two crossed pyramidal tracts exchange some
fibres with each other (recrossed fibres) ; and it was sup-
posed that this would explain the escape in hemiplegia
(paralysis of one side of the body) of those muscles which
are accustomed to work with the corresponding muscles on
the opposite side. But although there is no doubt that
such muscles are innervated to some extent from both
cerebral hemispheres, it is more probable that this is due to
u}icrosscd {homolateral) than to recrossed fibres.
(2) A great afferent or sensory path by which some, at least,
of the impulses carried up through the posterior roots of the
spinal nerves, after passing through various relays of nerve-
THE CENTRAL NERVOUS SYSTEM 659
cells, reach the cortex of the cerebellum ; or the upper
portions of the central grey tube, the corpora quadrigemina
and optic thalamus; or, hnally (both indirectly and by a
more direct route which certain ftbres of the hllet and the
formatio reticularis follow through the tegmentum and the
posterior limb of the internal capsule behind the motor
tibres), the cerebral cortex itself.
The efferent path from the cortex of the brain is broken
by but one relay of nerve-cells, the motor cells of the anterior
horn. The afferent path is interrupted by at least two
relays, one in the ganglion on the posterior root, another in
the medulla ; and on some of the routes another, or even
more than one, between the medulla and the cortex.
Connections of the Grey Matter of the Cerebellum with the
Periphery and other Parts of the Central Nervous System. —
Numerous as are the nervous ties of the cerebral cortex, those of the
grey matter of the cerebellum are, in proportion to its mass, still
more extensive, and perhaps not less important. Speaking broadly,
we may say that the restiform body connects chiefly the dentate
nucleus and the grey matter of the worm with both sides of the
spinal cord, and through it with the periphery. The middle
peduncle is in the main a link between the cerebellar cortex and the
cerebral cortex of the opposite side, through the relay of the pontine
grey matter, and, to a smaller extent, a link between the cortical
matter of the two cerebellar hemispheres. The superior peduncle
connects mainly the dentate nucleus of one side with the cortex of
the opposite cerebral hemisphere through the red nucleus of the
tegmentum of the crus cerebri on the opposite side. Through the
restiform body afferent impulses pass up to the cerebellum. From
the cerebellum they may proceed to the cerebrum. So that the
path by the restiform body, dentate nucleus, and superior peduncle
may form an alternative route for afferent impressions passing from
the periphery to the great brain — a path broken by at least four
relays of nerve-cells. The cerebellar cortex /nay be connected by an
efferent path through the restiform body and the descending antero-
lateral tract with the motor roots of the same side. An uncrossed
connection also exists between the cerebellum and the vestibular
branch of the auditory nerve, through one of its nuclei of origin, and
possibly between it and other cranial nerves, such as the optic and
trigeminal.
The Internal Capsule. — We must now learn that the internal
capsule embraces other fibres than those which pass down
into the spinal cord as the pyramidal tracts, and up from it
as the afferent tegmental path. In the first place, it contains
42—2:
66o
A MANUAL OI'l'llYSIOLOGY
numerous fibres running from the Rolandic area, and
destined to make connection with the motor nuclei of the
cranial nerves in the grey matter underlying the aqueduct
of Sylvius and the fourth ventricle.
The cranial and spinal fibres, indeed, form but one com-
pact bundle (pyramidal tract) in their passage through the
corona radiata and internal capsule, the knee of which is
occupied by the former, the posterior limb by the latter, and
may be followed as a distinct strand through the middle of
Anterior
Clatjstrum
J-. Harh'aticn
rosttricr
Fio. 228. — Diai;rammatic Horizontal Skction ok Leki Half oi' Bkain
TO SHOW Internal Capsule.
the crusta into the pons. Here the fibres for the nuclei of
the cranial nerves decussate.
But we have not yet exhausted the constituents of the
internal capsule. Two great cones of fibres sweep down
into ic, one from the frontal, the other from the occipital
and temporal portions of the cerebral cortex. The first
passes through its anterior limb, the second behind the
sensory path in its posterior limb. Running on through the
crusta of the cerebral peduncle (Fig. 227), the frontal tract
THE CENTRAL NERVOUS SYSTEM
66i
internal, the occipito-temporal external, they end in the grey
matter of the pons, and probably serve as one segment of an
extensive commissural connection between the cerebral and
the cerebellar cortex of the opposite side, the other segment
being formed by fibres which reach the pons through the
middle cerebellar peduncle. Although their further con-
nections are unknown, it is evident that the junction of the
cerebral cortex with this pontine grey matter, through and
into which so many nerve-tracts pass, multiplies the number
Fig. 229. — Association Fibres (after Siarr).
Cerebral hemisphere seen from the side. A, A, association fibres between adjacent
convolutions ; B, between frontal and occipital lobes ; C, cingulum, connecting frontal
and temporo-sphenoidal lobes ; D, uncinate fasciculus ; E, inferior longitudinal bundle ;
O.T. , optic thalamus ; C.N., caudate nucleus.
of possible routes by which impulses may travel between one
part of the brain and another. The pons itself is in part a
transverse commissure between the two halves of the cere-
bellum, as the corpus callosum is between the two cerebral
hemispheres. And intertwined in the corona radiata with
the callosal fibres are other systems, of which it is especially
necessary to mention the fibres that link nearly every part of
the cerebral cortex with the optic thalamus. These fibres
pass from the frontal and parietal regions through the
anterior, and from the occipital region through the posterior
border of the internal capsule, those from the occipital
cortex forming what is called the optic radiation. The
thalamus is also connected with the cortex of the temporal
662 A MANUAL OF I'flYSlOLOGV
lobe, with the cerebellum, and through the fillet with the
posterior part of the tegmental system, the medulla oblon-
gata and the spinal cord (p. 656).
We have purposely omitted to enumerate many other
paths by which the various tracts of grey matter in the brain
are brought into communication with each other, and our
knowledge of such connections is constantly augmenting.
When we add that not only arc the cerebral hemispheres
united by many ties to the subordinate portions of the
cerebro-spinal axis and to each other, but that cortical areas
of one and the same hemisphere are in communication by
short connecting loops of 'association' fibres(Fig. 229), it will
be seen that the linkage of the various parts of the central
nervous system is extremely complex; that an excitation,
blocked out from one path, may have the choice of many
alternative routes ; and that the apparent simplicity and
isolation of the pyramidal tracts must not be allowed too far
to govern our views of the possibilities open to a nervous
impulse once it has been set going in the labyrinth of the
nervous network. Nor is it onl}- by the white fibres that
nervous impulses can be conducted. There is the clearest
evidence that they can also spread along continuous sheets
of grey matter. And the actual route taken by a given
impulse is, in all probability, determined as much by mole-
cular conditions, particularly in the terminal fibrils of the
neurons and dendrons and in the substance, whatever it
may be, which intervenes between them, as by anatomical
relations ; so that a road open at one moment may be closed
at another. We may suppose that the greater the number
of connections between the cells of the central nervous
system, the greater is the complexity of the processes which
may be carried on within it. And, indeed, comparison of
the brains of different animals shows us that it is not so
much by excess in the quantity of grey matter as by the
increased complexity of linkage, that a highly developed
brain differs from a brain of lower type ; the higher the
brain, the smaller is the proportion of grey to white sub-
stance, but the greater is the number of possible paths
between one nerve-cell and another.
THE CENTRAL NERVOUS SYSTEM 665
II. Functions of the Central Nervous System.
Much of our knowledge of the functions of the central
nervous system and of its divisions has been gained by the
removal or destruction of more or less extensive tracts of
nervous substance, or the cutting off of connection between
one part and another. But it is well to warn the reader at
the very outset that in no other part of physiology is such
caution required in making deductions as to the working
of the intact mechanism from the phenomena which mani-
fest themselves after such lesions.
In the first place, every operation of any magnitude on the brain
or cord is immediately followed by a depression of the functional
power of the nervous tissue, a depression which may extend far from
the actual seat of injury and manifest itself by various phenomena,
which are grouped together under the name of ' shock.' Thus, when
the spinal cord of a dog is divided, e.g.^ in the dorsal region, all power,
all vitality, one might almost say, seems to be for ever gone from the
portion of the body below the level of the section. The legs hang
limp and useless. Pinching or tickling them calls forth no reflex
movements. The vasomotor tone is destroyed, and the vessels
gorged with blood. The urine accumulates, overfills the paralyzed
bladder, and continually dribbles away from it. The sphincter of
the anus has lost its tone, and the faeces escape involuntarily. And
if we were to continue our observations only for a short time, a few
hours or days, we should be apt to appraise at a very low value the
functions of that part of the cord which still remains in connection
with the paralyzed extremities. But these symptoms are essentially
temporary. They are the results of shock ; they are not true ' defi-
ciency ' phenomena. And if we wait for a time, we shall find that
this torpor of the lower dorsal and lumbar cord is far from giving a
true picture of its normal state ; that, cut off as it is from the in-
fluence of the brain, it is still endowed with marvellous powers. If
we wait long enough, we shall see that, although voluntary motion
never returns, reflex movements of the hind-limbs, complex and
co-ordinated to a high degree, are readily induced. Vaso-motor
tone comes back. The functions of deftecation and micturition are
normally performed. Erection of the penis and ejaculation of the
semen take place in a dog. A man with comj)lete paralysis below
the loins and destitute of all sensation in the paralyzed region has
been known to become a father (Brachet). Pregnancy carried on to
labour at full term has been observed in a bitch whose cord was
completely divided above the lumbar enlargement.
We cannot doubt that the spinal cord takes an important share in
this recovery of function. But here again it would be erroneous to
conclude that everything is due to the cord. For Goltz and Ewald
664 A MANUAL OF PHYSIOLOGY
have been able to keep dogs alive for long i)eriods after preliminary
section of the cord in the cervical region and subsequent removal of
large portions of it. They find that even after destruction of the
lumbar and sacral regions of the cord the external sphincter of the
anus, striped and even voluntary muscle though it be, regains its
tone, although it is temporarily lost after the first cervical section.
The bladder ultimately recovers the power of emptying itself spon-
taneously and at regular intervals. A pregnant bitch in which the
lumbar enlargement and the whole cord befow it to the cauda equina
had been removed, and tlierefore all the nerve-roots supplying
fibres to the uterus cut, whelped in a normal manner, and -the
corresponding mammary glands behaved exactly as the rest. Diges-
tion went on as usual when practically nothing of the cord except
its cervical portion was left. Certain vaso-motor phenomena were
also observed which suggest that the sympathetic system, inde-
pendently of the cerebro-spinal system, is itself possessed of regula-
tive powers.
Secondly, we must not run into the opposite error, and assume,
without proof, that all the functions which the brain or cord is capable
of manifesting under abnormal circumstances are actually exercised
by either when, under ordinary conditions, it is working along with
and guiding, or being guided by, the other. For example, in many
animals the reflex powers of the cord are, if not increased, at all
events more freely exercised when the controlling influence of the
higher centres has been cut off" than when the central nervous system
is intact.
Thirdly, there is another class of phenomena which we must make
allowance for, and perhaps more frequently in the case of patho-
logical lesions in man than in experimental lesions in the lower
animals. This is the class of 'irritative' phenomena. The irritation
set up by a blood clot or a collection of pus, or in any other way, in
a wound of the grey or white matter, may cause a stimulation of
nervous tracts by which, for a time, the ' deficiency ' effects of the
lesion may be masked.
In the fourth place, we must not hastily conclude that when no
obvious deficiency seems to follow the removal of a portion of the
central nervous system, the function of that portion must necessarily
be of such a nature as to give rise to no objective signs. For we
have reason to believe that, to a certain extent, the function of one
part may, in its absence, be vicariously performed by another.
Bearing in mind the cautions we have just been empha-
sising, we may broadly distinguish between the functions of
the cord (including the bulb) and those of the brain proper
by saying that the cord is essentially the seat of reflex
actions, the brain the seat of automatic actions and con-
scious processes. But neither of these conceptions is
THE CENTRAL NERVOUS SYSTEM 665
entirely correct. Both err by defect and by excess. The
brain, it is true, is pre-eminently automatic. The move-
ments which are started in the grey matter of the cerebral
cortex are pre-eminently voluntary (p. 704), but we cannot
deny to the brain the possession of reflex powers as well.
The movements in which the only nerve centres concerned
are those of the spinal cord are above all reflex (p. 674).
But some of its centres, and especially those lying in the
medulla — for example, the respiratory centre — are perhaps,
much as they are influenced by afferent impulses, capable of
discharging automatic impulses too. And while conscious-
ness is certainly bound up with the integrity of the brain,
and in all the higher mammals is probably associated with
cerebral activity alone, it has been plausibly maintained
that the spinal cord, even of such an animal as the frog, is
also endowed with something which might be called a kind
of hushed consciousness. If this is so for the frog, with its
distinct though relativel)^ ill-developed cerebral hemispheres,
it must be still more likely in the case of fishes and animals
below them, which are practically devoid of a cerebral cortex
altogether.
Functions of Spinal Cord (including Medulla Oblongata).
The functions of the spinal cord may be classified thus :
1. The conduction of impulses set up elsewhere — either
in the brain or at the periphery.
2. The modification of impulses set up elsewhere (reflex
action).
3. The origination of impulses (?).
T. Conduction of Nervous Impulses by the Cord. — The old
controversy as to whether the white fibres of the spinal
cord are directly excitable may be considered as definitely
settled in the affirmative. Long strands of white matter
have been isolated, and laid on electrodes, and contractions
of distant muscles have been seen to follow stimulation,
even when every precaution has been taken to avoid escape
of current on to the anterior roots. And indeed, apart from
direct experimental evidence, the fact that the white fibres
666 A MANUAL OF PHYSIOLOGY
of the brain are universally admitted to be excitable by
artificial means would be of itself almost sufficient to decide
the question, for we know of no essential difference between
the cerebral and the spinal fibres. But the conditions must
rarely occur under which direct stimulation of white fibres
in their course is possible in the intact body ; and the only
impulses with which we need concern ourselves here are
those that reach the conducting paths from grey matter
in the cord itself or in the brain, or from the peripheral
organs.
What sort of impulses, then, do the various tracts of the
spinal cord conduct ? For the posterior roots this question
was first fully answered by Magendie ; for the anterior roots
by Sir Charles Bell. Bell observed that, when he cut the
motor roots in an animal just killed, and stimulated the
peripheral ends, muscular contractions were obtained. He
concluded from this that the anterior roots are motor ; but
although he is often credited with the discovery of the
functions of the posterior roots as well, he was not the first
to make the decisive experiment necessary to show that
they are the conductors of sensory impulses.
When the posterior roots are divided, loss of sensation
occurs in the region to which they are distributed. If only
one root is cut, the loss of sensation is never complete in
any part of the skin ; and Sherrington has found that the
areas of distribution of consecutive nerve roots are not
sharply marked off from each other, but to some extent
overlap. Stimulation of the peripheral end of the divided
posterior root has no effect. Stimulation of the central end
gives rise, if the animal be conscious, to evidences of pain,
and other signs of the passage of afferent impulses, e.g.,
a rise in blood-pressure. The latter may also be observed
when the animal is anaesthetized.
Head's clinical observations have thrown light on the distribution
of the sensory nerves of the viscera and their relation to the sensory
nerves of the skin. It has long been known that in disease of an
internal organ the pain is often referred to some superficial part at
a distance from the actual seat of the lesion. Head finds that the
pain is referred to definite regions of the skin for each organ. In
THE CESTRAL NERVOUS SYSTEM
&,7
hese regions the excitalnlity for impressions of touch or temperature
s increased, and the reflexes eHcited l)y stimulation are exaggerated.
For example, in diseases of the larynx, hyperalgesia (increased sensi-
Fibre connectinc^
C^rebei w:Me d nu cle u s
i^thus w. cerebral cortex
Ctrebellu rr^\
Fibres connect in tj \J^
^racile S(; cuneate Vs^
nuclei, tir. Cerebellum \\
th ro uqh re sti-
form body i
.Py ram idal Cell
\ A -xis-cylin de r "1
\.nrocess of ,, I
:'\'SmaUNerve-ceU \
\/Cerebral\
I \^
..-}^- Fibre ofPyramJracl
(cutshorr)
IsFerve Cells--'""
cf (^racile ^
cuneate nuclei.
Fibre of Direct
Cerebellar Tract.
Fibre of QoU's Cot-— -
^ i XFillet
^Medulla^
ObloT^ata
-Fihre. of QoMrersFracl
Nerv£-cell ofFost.Hom (?)
t
Po st Foot of Can gllon Cell
Nert^e-Cellof—hf
Ant.Norti^^^^
Ganglion-Cell /^
FostFoot
Fibres
^^^fj^Nerve-CellofAnt. Horn
-"Nerve- Cell of Clarke's Coh
\Middle line.
Possible Afferent Paths.
Fic, 230.— Po^siuLF. Paths of Afferent Impulses in the Central
Nervous System (Schematic).
bility to pain) is present in a region extending from the middle Ime
of the throat to the median border of the sterno-cleido-mastoid
muscle, and downwards to the sterno-clavicular articulation ; and
stimulation of the skin in this area often causes reflex coughing.
668
A MANUAL OF PIIYS/OLOGY
Head suggests that the bond of connection is a common anatomical
origin or a physiological correlation, somewhere or other in the
central nervous system, between the sympathetic sensory fibres of
any viscus and the sensory sup])ly of the corresponding cutaneous
Ce-r e bral
Cortex
J^ilre for-
Head
Po\ns
Decussation
of Pyramids.
Filr£ of Direct, .
Py rami da I /rod.
Nerire-Cells^
of Ant. Horn ._J^>—
Term inaJ Arborisation T
ofaPyramidal Fibre J
around Cell of — *^
Anl. Horn
I Medulla
I Oblongata
yRccrcssedFilrt ?\
....... '.''. . Uncrossed Fib re. J
Spinal
{ ^ Cord
Anterior
Root-
Fibres
Eff^ren/- Pa //is
Fig. 231.— Possible Paths of Eiferent Impulses in tme Central
nekvdps svsikm (schematic).
area. According to him, when there is a close central connection
between the sensory nervous mechanism of a part of low sensibility
and that of a part of high sensibility, a painful stimulus applied to
the former is felt in the latter.
Tin: CEM'RAL XERVOUS SYSTEM 66(>
In the case of some of the viscera the sensory fibres seem to arise
from the same sensory root or roots as the sensory fibres of tlie
related cutaneous areas, but in others this docs not hold.
Eecurrent Sensibility. — Although muscular contraction is
the most conspicuous event that follows stimulation of the
peripheral end of an anterior nerve-root, it is by no means
the only one. It is frequently observed, though not in all
kinds of animals, that here, too, pain is caused. That this
pain is not due to the muscular contraction is proved by
the fact that it can still be elicited when the nerve-trunk is
divided between the junction of the roots and the periphery.
The real explanation of the phenomenon seems to be that
certain fibres from the posterior roots bend up for some
distance into the anterior roots, and then turn around again
and pursue their course to their peripheral distribution in
the mixed nerve, or run on in the motor roots to supply the
sheath surrounding them (nervi nervorum), and even the
membranes of the spinal cord.
The afferent impulses that enter the cord along the pos-
terior roots have the choice of many paths by which they
may reach the brain (Fig. 230).
(1) They may pass directly up through the postero-mediau
column. If they take this route, their course will be first interrupted
by nerve-cells in the gracile or cuneate nuclei in the medulla
oblongata. Thence they may find their way across the middle line
by the arcuate fibres of the upper or sensory decussation, and
sweeping along the fillet and the longitudinal fibres of the reticular
formation of medulla, pons and crus, and the sensory path in the
hinder third of the posterior limb of the internal capsule, finally
arrive at the cerebral cortex. Between the gracile and cuneate
nuclei and the cortex they may pass through nerve-cells in the optic
thalamus and the neighbouring region.
(2) They may pass up by the direct cerebellar tract and restiform
body. If they take this route, their course will be interrupted by
nerve-cells very soon after their entrance into the cord, presumably
in Clarke's column, and again in the dentate nucleus of the cere-
bellum. The impulses may then cross the middle line by the
superior peduncle to the tegmental region of the crus cerebri, where
they may again pass through cells in the red nucleus. From the
red nucleus they may find their way by the tegmental sensory path
to the cerebral cortex.
(3) They may reach the cerebellum by the antero-lateral ascend-
ing tract, passing through nerve-cells in the lateral nucleus of the
670 A MA.XUAL OF PHYSIOLOCY
medulla (?), then by the formatio reticularis of the medulla and
pons to the superior peduncle of the cerebellum, and thence to the
grey matter of the worm on the same side.
(4) They may cross the middle line through collaterals (p. 654)
which run in the posterior grey commissure, enter one of the ascend-
ing tracts on the other side, and continue without further decussation
up to their central destination.
(5) They may spread in the tangle of the grey matter itself and
pass out again at a different level into one of the white tracts on ihe
same or on the opposite side of the cord.
Efferent impulses, originating in the brain, may travel :
(i) Through the direct or crossed pyramidal tract. If they do
so their course will not be interrupted by nerve cells anywhere
between the cerebral cortex and the motor cells of the anterior horn.
(2) From one side of the cerebral cortex to the other, and then
down the pyramidal tracts corresponding to that side (?).
(3) From the pre-frontal part of the cerebral cortex, through the
anterior limb of the internal capsule to the grey matter in the pons,
and thence to the cerebellum by its middle peduncle.
(4) From the occipital or temporal cortex in the hinder rim of the
internal capsule to the pontine grey matter and through the middle
peduncle to the cerebellum. From the cerebellum they may possibly
be reflected down the antero-lateral descending tract to the cord, and
indirectly, if not directly, to the periphery.
All the paths enumerated, as well as others to which it
would be tedious to formally refer, and which the ingenuity
of the reader may be profitably employed in constructing
for himself, from the data already given, are to be looked
upon as possible channels for the passage of impulses between
the brain and the periphery. But what is certain is in
this case much more limited than what is possible. It
is certain that the pyramidal tracts are the conductors of
voluntary motor impulses, and that in most individuals the
great majority of such impulses decussate in the medulla
oblongata, only a small minority in the cord. For a lesion
involving the pyramidal tract above the decussation of the
pyramids causes paralysis of the opposite side of the body,
a lesion below the decussation paralysis of the same side.
But it is possible that when one pyramidal tract has been
destroyed, in some animals at least, the motor cortex from
which it leads may to a certain extent place itself again in
communication with the paralyzed muscles through its com-
missural connections with the opposite hemisphere.
THE CENTRAL NERVOUS SYSTEM 671
On the other hand, it is certain that pathological or
traumatic lesions, involving the destruction of one lateral
half of the cord in man and experimental hemisections in
animals, are usually followed by symptoms which suggest
that the sensory impulses decussate chiefly in the spinal
cord — viz., increase of sensibility (hyperaesthesia) below and
on the same side as the injury, and diminution of sensibility
on the opposite side. This was first pointed out by Brown-
Sequard, although long after he saw cause to retract this
interpretation of his experiments. It seems, however, that
no ascending degeneration is to be found on the opposite
side of the cord either after hemisection or after division of
posterior roots (Mott). But while this latter fact shows
that none of the afferent fibres cross the middle line before
being interrupted by nerve-cells, it by no means proves that
afferent impulses do not decussate in the cord. And, indeed,
we know that some afferent impulses do decussate far below
the level of the medulla. For, (i) A part of the negative
variation (p. 622) crosses the middle line and ascends in the
opposite half of the cord when the central end of one sciatic
is stimulated (Gotch and Horsley). (2) Crossed reflex
movements are possible ; and when excitation of the central
end of the sciatic is followed by contraction of the muscles
of the opposite fore-limb, the afferent impulses must either
decussate in the lumbar cord, and then run up on the
opposite side to the level of the brachial plexus, or must
ascend on the same side and cross over somewhere between
the plane of the sciatic and the brachial nerve-roots. The
only other hypothesis on which crossed reflex action can be
explained — but a hypothesis for which there is not a tittle of
evidence — is that the afferent impulse always acts on motor
cells whose axis-cylinder processes pass over to the opposite
side, and there enter anterior nerve-roots. But while, for
these reasons, it cannot be denied that some afferent im-
pulses decussate in the cord, it would be an error to argue
from this that all, or even the majority, do so. And, indeed,
there is evidence that many of the impulses concerned in
sensation do in reality remain on the side of the cord which
they first enter, right up to the medulla oblongata.
6-2 A MANUAL OF PHYSIOLOGY
To sum up, we may say that iJi'hile it is certain that most of
the motor, and many of the sensory, impulses decussate in the
medulla, unanimity has not as yet been reached with reference to
the place of decussation of the whole of the sensory impressions, and
it is possible that some of them decussate in the cord, others in the
bulb. And when it is remembered how difficult it sometimes
is to interpret the account which a man gives of his sensa-
tions and to recognise precisely the degree and nature of
sensory defects produced by disease in the human subject, it
will not be thought surprising that experiments on animals,
from the time of Galen onwards, should have yielded evidence
which, although perhaps now at length tending to a definite
result, is still unfinished and in part conflicting. If this is
true where the problem is merely to determine the crossing-
place of afferent impulses which are certainly known to
cross, it is only to be expected that we should be still more
in the dark as regards the routes by which different kinds
of afferent impulses thread their way through the maze of
conducting paths in the neural axis to reach their planes of
decussation and gain the ' sensory crossway ' in the internal
capsule. Some authors have indeed cut the Gordian knot
by assuming that any kind of sensory impression may travel
up any afferent path. Direct stimulation of a naked nerve-
trunk, it has been argued in favour of this view, gives rise
to a sensation of pain ; stimulation of the skin in which the
end-organs of the nerve lie gives rise to a sensation of touch
or a sensation of temperature, according as the stimulus is
a mild mechanical or a thermal one, the contact of a feather
or of a hot test-tube. Why, it has been asked, should we
imagine that the difference in the result of stimulation
depends on a difference in the nerve-fibres excited, and not
on a difference in the kind of impulses set up in the same
nerve-fibres ? This is a question which we shall have again
to discuss (p. 721). But apropos of our present problem,
we may say that there is very clear proof from the patho-
logical side that a limited lesion in the conducting paths of
the central nervous system may be associated with defect or
total loss of one kind of sensation, while all the other kinds
remain intact. And there seems no other tenable hypo-
THE CENTRAL XERVOUS SYSTEM 673
thesis than that in such cases the pathological change has
picked out a particular group of fibres, either collected into
a single strand or scattered among unaltered fibres of
different function. For example, in locomotor ataxia, a
disease in which inco-ordination of movement and derange-
ment of the mechanism of equilibration are prominent
symptoms, degeneration in the posterior column of the cord
is a most constant lesion. And there is strong evidence that
afferent impulses from muscles and tendons, which give rise
to impressions belonging to the group of tactile sensations,
and which, according to the most widely accepted doctrine,
serve as the basis of the muscular sense, and play an im-
portant part in the maintenance of equilibrium (p. 6g6),
pass up in the posterior column. A case has been
observed where a man received a stab which divided the
whole of one side of the cord and the posterior column of
the other side. Sensibility to touch was lost on both sides
of the body below the level of the injury, sensibilit}' to pain
only on the side opposite to the main lesion. This tactile
path in the posterior column, however, is the only tract
which has been associated, on evidence at all sufficient, with
the passage of sensory impressions of a particular kind.
Definite paths for temperature sensations have, indeed,
been described in the lateral column. And Schiff has
credited the grey matter of the cord with the power of
conducting the impulses that give rise to pain, and has
asserted that such impulses can be propagated along a cord
in which hardly a vestige of white substance remains uncut.
But these statements cannot be considered as resting on
adequate proof, although it is certain that impressions of
pain and of temperature do pass up somewhere or other in
the antero-lateral column, and Gowers has brought forward
some facts which he interprets as indicating that the
antero-lateral ascending tract is the path for sensibility to
pain.
The impulses which descend the cord give token of their
arrival at the periphery by causing either contraction of
voluntary muscles, or contraction of the smooth muscles of
arteries, or secretion in glands. They all pass down in the
43
674 '-1 ^^ANUAL OF PHYSIOLOGY
antero-lateral column, but the path of the voluntary impulses
in the pyramidal tracts is the best known and most sharply
defined.
2. Modification of Impulses set up elsewhere (Reflex Action).
— The spinal cord, although it is a conductor of nervous
impulses originating elsewhere, is by no means a mere con-
ductor. Many of the impulses which fall into the cord are
interrupted in its grey matter. Some of the efferent impulses
proceeding from the brain are perhaps modified in the cord,
and then transmitted to the muscles. Some of the afferent
impulses are modified, and then transmitted to the brain ;
some are modified, and deflected altogether into an efferent
path. These last are the impulses which give rise to reflex
effects. Strictly speaking, a reflex action is an action carried
out in the absence of consciousness ; not necessarily, how-
ever, in the absence of general consciousness, but in the
absence of consciousness of the particular act itself. But
the term is often used so as to embrace all kinds of actions
which are not directly voluntary, whether the individual is
conscious of them or not. For example, when the sole of
the foot is tickled, the leg is irresistibly and involuntarily
drawn up by reflex contraction of its muscles ; yet the
person is perfectly cognisant both of the movement and of
the sensation which accompanies the afferent impulse. Then
there is a class of reflex actions in which consciousness is
entirely in abeyance ; during sleep most of the ordinary
reflexes can be elicited.
Normally, it is believed that reflex niovements are governed
by impulses descending from the higher centres, for {a) it is a
matter of common experience that a reflex movement may be to a
certain extent controlled, or prevented altogether by an eflbrt of the
will, and it is worthy of remark that only movements which can
be voluntarily produced can be voluntarily inhibited ; (/>) an animal
like a frog responds to stimuli by reflex movements more readily
after the medulla oblongata has been divided from the spinal cord ;
{c) long-continued muscular contractions may be caused in animals
after removal of the cerebral hemispheres by stimulation of sensory
nerves, for example by scratching the mucous membrane of the
mouth in a 'brainless' frog or Menobranchus ; {d) by stimulation
of certain of the higher centres reflex movements which would other-
wise be elicited may be suppressed or greatly delayed. If the
THE CENTRAL XERVOUS SYSTEM 675
cerebral hemispheres are removed from a frog, and one leg of ihe
animal dipped into dilute acetic acid, a certain interval, the (un-
corrected) reflex time, will elapse before the foot is drawn u[) (Tiirck's
method, p. 729). If now a crystal of common salt be applied to
the optic lobes or the u[)per part of the s[)inal cord, and the experi-
ment repeated, it will be found that either the interval is much
lengthened, or that the rellex disappears altou;ether. Strong stimula-
tion of any afferent nerve will also abolish or delay a rellex movement.
That the brain, in man and the higher animals at least, exerts
more than a merely inhibitory influence on the production of reflex
movements is suggested by many facts. The knee-jerk, for example,
often disappears in pathological lesions, situated high up in the cord
in man, and is markedly impaired after high section of the cord in
dogs. In hemiplegia (paralysis of one side of the body, caused by
disease in the brain) the cutaneous reflexes on the paralyzed side
may sometimes be absent for years. Some observers have even
gone so far as to say that, under normal conditions, the so-called
spinal reflexes are really cerebral, in other words, that the afferent
impulses run up to the cortex of the brain and there discharge
efferent impulses, which pass down to the motor cells of the anterior
horn and cause their discharge. It may be admitted that there is no
physiological ground for supposing that the afferent impulses which
have to do with the reflex contraction of the muscles of the leg when
the sole is tickled, stop short at the motor cells of those spinal
segments from which the efferent nerves coine off, while the afferent
impulses which have to do with the sensation of tickling pass up to
the bram. The probability is that under ordinary circumstances
such afferent impulses pass up the cord in long afferent paths, as well
as directly towards the motor cells, along those fibres of the posterior
roots and their collaterals which bend forward into the anterior horn
at the level of their entrance into the cord. And the only question
is whether, as a matter of fact, the spinal motor cells are most easily
discharged by the impulses that reach them directly, or by the
impulses that come down to them by the roundabout way of the
cortex and the efferent fibres that connect it with the motor ceils.
It is evident that the answer to this question need not be the same
for all kinds of animals. It may well be that in the higher animals,
in which the cortex has undergone a relatively great development,
the spinal motor mechanisms are more easily discharged from above
than from below, while in lower animals the opposite may be the
case. When the cord is cut off from the brain, the afferent impulses
may overflow more easily into the spinal motor cells since their
alternative path is blocked. In the frog, where there is already a
beaten track between the posterior root-fibres and the cells of the
anterior horn, this overflow may be established immediately after
section of the cord, and may of itself lead to an exaggeration of the
reflexes. In animals like the dog, a longer time may be necessary
before the unaccustomed route from the afferent neurons and their
collaterals to the dendrons of the motor cells becomes natural and
easy ; in man a still longer interval may be required.
43—^
7 6 A MANUAL OF PHYSIOLOGY
In order that a reflex action may take place, the reflex
arc — afferent nerve, central mechanism, and efferent nerve —
must be complete; and in fact a whole series of simple reflex
movements exists, the suppression, diminution, or exaggera-
tion of which can be used in diagnosis as tests of the con-
dition of the reflex arc. Such are the plantar reflex (the
drawing-up of the foot when the sole is tickled), the cremasteric
reflex (retraction of the testicle when the skin on the inside
of the thigh just below Poupart's ligament is stroked, espe-
cially in boys), the knee-jerk (a sudden extension of the leg
by the rectus femoris muscle when the ligamentum patellae
is sharply struck), the <:;litteal, abdominal, epigastric, and inter-
scapular reflexes (contraction of the muscles in those regions
when the skin covering them is tickled). The jaw-jerk (a
movement of the lower jaw when, with the mouth open, the
chin is smartly tapped) and ankle-clonus (a series of spasmodic
movements of the foot, brought about b}' flexing it sharply
on the leg) are phenomena of the same class, which can
be elicited only in disease. Any condition which impairs
the conducting power of the afferent or efferent fibres of
the reflex arc necessarily diminishes or abolishes the reflex
movement, even if the centre is intact. E.g., in locomotor
ataxia the disappearance of the knee-jerk is one of the
most important diagnostic signs. This disease involves
the posterior roots and the fibres that continue them in the
posterior column. The anterior nerve-roots are perfectly
healthy. The grey matter of the cord — at least, in the earlier
stages of the disease — is unaffected. The weak link in the
chain is the afferent path. In anterior poliomyelitis (p. 657)
the afferent link is intact, but the other two are broken, and
the reflexes also disappear. Certain lesions which cut off
the spinal cord from the higher centres without affecting the
integrity of the reflex arcs increase the strength of reflex
movements and the facility with which they are called forth.
In paraplegia, e.g. (paralysis of the legs and the lower portion
of the body), caused suddenly by accident to the cord, or
more slowly by acute or chronic trajisverse myelitis, or in
hemiplegia, the knee-jerk can usually be elicited with start-
ling promptitude and exaggeration, and ankle-clonus may
THE CENTRAL NERVOVS SYSTEM
677
also be obtained. In pYimary spastic paraplegia, which is
associated with degenerative changes in the lateral columns,
a similar increase in the true and pseudo-rellexes may be
seen, due either to the cutting off of inhibitory impulses or
to an actual increase of excitability in the grey matter of
the cord. The position of the
centres in the cord for the
various simple reflex move-
ments is shown in Fig. 232.
Myotatic Irritability (Muscle
Reflex). — Although for con-
venience of treatment we have
included the knee-jerk (with
the jaw-jerk and ankle-clonus)
among reflex movements, it
might more properly be termed
a pseudo-reflex, for there is
evidence that the mechanism
by which it is produced is
different from that concerned
in the reflex blinking of the
eyelid, or the reflex retraction
of the testicle, or the drawing-
up of the foot when the sole is
tickled. The strongest part
of this evidence is the fact
that the interval which elapses
between the tap and the jerk
(xto to y^ second) is distinctly
shorter than the reflex time of
the extremely rapid lid-reflex,
and is not much greater than
the latent period of the quadri-
ceps muscle for direct electrical stimulation, as measured
under the ordinary conditions of its contraction. The knee-
jerk is obtained in undiminished strength when the nerves
of the ligamentum patellae have been divided. It is therefore
not a reflex movement caused by stimulation of afferent
nerves coming from the tendon, and the name ' tendon-
V V
C
, Y...
2 ^
i
3 \
^- .: ■
S....-: ..
(;....*:
I
7...
8
Jtiterscapuht r
D
/:.::::::-.:-: it i
.2
A
5...... •_...
.6..
'Epiqa^tric
.7-
[S.
.9.
^
IC.
\ '^. ^P^f/*tf.nri /
IJ
L
<*. -
./. ,
2 C/yw«i;/?r<
3 ■-
Knee-Jerh
-4. ..-
s:...
5
/ l/tsical \
2"R,'ctat'_ \
3 Genii r/l \
.It.:::::..:::...
]Aniie-Cl(/itm
\Plantar-
Fig. 232. — Diagram of Rkki.ex
Centrks in Cord (after Hill).
67S A MAXUAL OF rilYSIOLOGY
reflex ' is clearly a misnomer. But that it is related in some
way or other to afferent impulses is certain, for division of
the posterior roots that enter into the anterior crural nerve
abolishes the knee-jerk. The phenomenon probably comes
under the head of what by some authors is called myotatic
irritability — that is, it depends on mechanical stimulation of
the slightly-stretched muscle by the pull of the tendon when
it is struck. It seems to be necessary for this stimulation
that the muscle should be to a certain extent tonically con-
tracted. So that when the afferent fibres are interrupted,
or the grey matter of the cord disorganized, and the reflex
tone abolished, the knee-jerk disappears. In addition to
the direct stimulation of the muscle on the same side, the
tendon-tap may cause also a true reflex knee-jerk on the
opposite side, the interval between tap and contraction
being about 1, second.
Anatomical Basis of Reflex Action. — Since the essence of reflex
action i^ that the arrival of afferent impulses in the spinal cord causes
the discharge of efferent impulses, there must be some connection
between the incoming and the outgoing nerve-fibres. Moderate
stimulation of an afferent nerve causes contraction of muscles con-
nected with the same segment of the cord on its own side, and it has
been shown that the sensory nerves of a skeletal muscle are derived
from the spinal ganglion corresponding to the segment of the cord
containing its motor-cells. Stronger excitation, particularly of the
end-organs of a nerve, as in stimulation of the skin, will be followed
by more extensive movements involving higher or lower segments
of the cord, or crossing over to the opposite side. Sometimes the
reflex movements are coordinated to a high degree, and even
'puqjosive' in their action. This also is less true of movements
caused by stimulation of naked nerve-trunks than of movements
caused by stimulation of sensory surfaces. Let a piece of skin in a
brainless frog be severed from the rest, but left in connection with
its nerves. Excitation of the latter will produce simple and com-
paratively aimless contractions, while pinching of the skin or painting
it with dilute acid may cause extensive movements evidently aimed
at the removal of the irritation. If a drop of dilute acid be applied
to the flank of a 'reflex' frog, it will attempt to wipe it off" with the
foot which is situated most conveniently for the purpose. If this
foot be held, it will use the other.
It is evident that the connections between the fibres of the posterior
and anterior roots must be very extensive. Indeed, the phenomena
of str)'chnia-poisoning seem to show that every afferent fibre is
potentially connected with the motor mechanisms of the whole cord.
For in a frog under the influence of this drug, "stimulation of the
THE CENTRAL NERVOUS SYSTE.U 679
smallest portion of the skin will cause violent and general convulsions,
which are unaffected by destruction of the brain, but cease at once
on destruction of the cord (p. 729). Our problem, then, is to find
connections — first, between the afferent fibres of each spinal segment
and its efferent fibres, and, secondly, between the central mechanisms
of all the segments of the cord. When the nervous system is still
only a process of an epi-
thelial (sensory) cell joining
hands with a muscular cell,
the distinction between affer-
ent and efferent fibre does not
exist. When development has
gone a step further, and the
neuro-muscular process is in-
terrupted by a second epi-
thelial cell transformed into
a nerve-cell, the afferent fibre pj,,_ 233._diagram of a Simple
enters one pole and the effer- Reflex Arc.
ent fibre leaves the other pole .,., • j- . .u a- .■ r .u
^ . I he arrows indicate the direction of the
of the same cell. With in- afferent and efferent impulses,
creasing complexity of organ-
ization the nervous impulse passing up the afferent fibre is offered a
choice of many routes when it reaches the nerve cell. This is
effected by means of the feltwork formed by its branching processes
with the processes of other cells.
We have already described (p. 653) the course taken by the fibres
of the posterior roots on entering the spinal cord, and have seen that
the fibres or their collaterals are distributed to the grey matter of the
anterior horn, of the posterior horn, and of Clarke's column on the
same side, while collaterals cross the middle line in the posterior
commissure and run into the grey matter of the opposite side.
Many of the fibres, too, which ascend in the columns of Burdach
and Goll ultimately make junction with nerve-cells higher up in the
cord. There is thus formed an ample connection between the
posterior roots and the efferent nerves of the same segment on both
sides of the cord, and also between any one posterior root and the
spinal grey matter at different levels. The grey matter of adjoining
segments is further united by the commissural fibres of the antero-
lateral ground bundle already spoken of (p. 650), and doubtless also
by the numerous fibres and fibrils that interlace in its own substance.
Under ordinary conditions we must suppose that the resistance to
the passage of impulses is greater for certain paths than for others,
that it is easier, e.g., in a brainless frog for an impulse travelling up
a posterior root to reach the anterior root-fibres of the same segment
on the same side than to cross the middle line and tap the opposite
efferent tract, or to extend longitudinally along the cord and flow over
into efferent tracts coming off at a higher or lower level. The action
of strychnia must be to diminish the resistance in the whole of the
spinal cord, so that an impulse, instead of being confined to a fairly
definite path, spreads indiscriminately over the grey matter.
68o A MANUAL OF PHYSIOLOGY
The transition from the afferent to the efferent fibres of a refiex
arc, so far as we know, never takes place in highly organized animals
except through a nervous plexus. In the peripheral ganglia the
nerve-cells do not appear to he junctions through which impulses
may be shunted from one kind of fibre to another. Thus, the cells
of a spinal ganglion represent the original neuroblasts from which
the posterior root-libres grew out as processes towards the cord on
the one side and the periphery on the other. A sensory fibre
passing into the ganglion makes connection with a cell by a T-shaped
junction (which may be considered as a stalk formed by the coales-
cence of a portion of the entering and outgoing fibres), and passes
on its course again. Here it is evident that there is no possibility of
a complete reflex arc, and accordingly no reflex function has ever
been associated with the spinal ganglia. In the sympathetic ganglion-
cells, also, it is doubtful whether the anatomical foundation for a
reflex arc exists, and the most careful physiological experiments have
failed to demonstrate any reflex function in the sympathetic ganglia.
Sokownin, indeed, observed that stimulation of the central end of
the hypogastric nerve caused contractions of the bladder, and he
considered these movements to be reflex, the centre being the in-
ferior mesenteric ganglion. Langley and Anderson have also
found that when all the nervous connections of the inferior mesen-
teric ganglion, except the hypogastric nerves, are cut, stimulation
of the central end of one hypogastric causes contraction of the
bladder, the efferent path being the other hypogastric. In addition,
they have observed an apparent reflex excitation of the nerves which
supply the erector muscles of the hairs (pilo-motor nerves) through
other sympathetic ganglia. But they believe it likely that in neither
case is the action truly reflex, but that it is caused by stimulation of
the central ends of spinal motor fibres, which break up into fibrils
around the ganglion cells. These motor fibres, in the case of the
inferior mesenteric ganglion, send a branch to the sympathetic nerve-
cells which give origin to the fibres of the opposite hypogastric.
Reflex Time. — When a reflex movement is called forth, a
measurable period elapses between the application of the
stimulus and the commencement of the movement. This
interval may be called the uncorrected refiex time. A part
of the interval is taken up in the transmission of the afferent
impulse to the reflex centre, a part in the transmission of
the efferent impulse to the muscles, a part represents the
latent period of muscular contraction, and the remainder is
the time spent in the centre, or the true reflex time. When
the conjunctiva or eyelid is stimulated on one side both
eyelids blink. This is a typical reflex action reduced to its
simplest expression, and the true reflex time is correspond-
ingly short — only about ^rV second. An additional y^ second
THE CENTRAL NERVOUS SYSTEM 68l
is consumed in the passage of the afferent impulse along the
fifth nerve to the medulla oblongata, of the efferent impulse
from the medulla to the orbicularis palpebrarum along the
seventh nerve, and in the latent period of the muscle. When
a naked nerve, like the sciatic, is stimulated, the true reflex
time is reduced to y^^ to -V second. As estimated by
Tiirck's method (p. 729), the uncorrected reflex time is
greatly lengthened, it may be to several, or even many,
seconds. For here it is evident that the time taken by the
acid to soak through the skin and reach the nerve-endings
in strength sufficient to stimulate them is included. But
even when the peripheral factors remain constant, the
central factor may vary. With strong stimulation, e.g., the
reflex time is shorter than with weak stimulation. Fatigue
of the nerve centres delays the passage of impulses through
them ; and strychnia, while it increases the excitability of
the cord, also lengthens the reflex time.
3. The Origination of Impulses in the Spinal Cord.
Automatism. — A physiological action is termed automatic
when it depends upon a nervous outburst which seems to
be spontaneous, in the sense that it is not brought about by
any evident reflex mechanism, or, in other words, is not
discharged by afferent impulses falling into the centre where
it arises. An action known to be caused or conditioned by
such afferent impulses is called a reflex action. Automatic
actions being thus defined in a negative manner by the
defect of a quality, there is always a possibility that some
day or other it may be demonstrated that any given action
which at present seems automatic in its origin depends on
afferent impulses hitherto unnoticed. As a matter of fact,
the supposed proofs of spinal automatism have in more than
one case vanished with the advance of knowledge, and as
the domain of purely automatic action has been narrowed,
that of reflex action has extended, until the controversy as
to the boundaries between the two seems not unlikely to be
ended by the absorption of the automatic in the reflex.
And as we seem almost driven to conclude that from the
anatomical standpoint the nervous system is essentially a
682 A MAXL'AL OF I'UYSIOLOGY
vast collection of looped conducting paths, each with an
afferent portion, an efferent portion, and connections
between them formed by cells and cell networks, so it may
be that no true physiological automatism really exists either
in cord or brain, that every form of physiological activity —
muscular movement, secretion, intellectual labour, conscious-
ness itself — would cease if all afferent impulses were cut off
from the nervous centres. But there are certain groups of
actions so widely separated from the most typical reflex
actions that, provisionally at least, they may be distin-
guished as automatic. Such are the voluntary movements^
and certain involuntary movements, like the beat of the
heart. And we may proceed to inquire whether the spinal
cord has any power of originating movements or other
actions of this high degree of automatism.
Muscular Tone. — So long as a muscle is connected with
the spinal segment from which its nerves arise, it is never
completely relaxed ; its fibres are in a condition of slight
tonic contraction, and retract when cut. If a frog whose
brain has been destroyed is suspended so that the legs hang
down, and one sciatic nerve is cut, the corresponding limb
may be observed to elongate a little as compared with the
other. At one time this tone of the muscles was supposed
to be due to the continual automatic discharge of feeble
impulses from the grey matter of the cord along the motor
nerves. But it has been proved that if the posterior roots
be cut, or the skin removed from the leg, its tone is com-
pletely lost although the anterior roots are intact. So that
the tone of the skeletal muscles depends on the passage of
afferent impulses to the cord, and must be removed from
the group of automatic actions and included in the reflexes.
The ' rigidity ' of the muscles, often observed in paralysis
from lesions of the central nervous system, and denominated
' early' or ' late ' according as it comes on within a few "days
or a few weeks after the occurrence of the lesion, is also
probably in part a reflex phenomenon, although possessing
some of the characters of a tonic contraction due to auto-
matic discharge from the spinal centres. For in such cases
myotatic irritability is increased ; the knee-jerk is exag-
THE CENTRAL NERVOUS SVSTEJ/ 683
gerated ; a finger-jerk may be elicited by tapping the wrist,
an arm-jerk by striking the skin over the insertion of the
biceps or triceps, ankle-clonus by flexing the foot (Gowers).
Now, myotatic irritability depends on reflex muscular tone
(p. 677).
It is probable that the tone of such visceral muscles as
the sphincters of the anus and bladder has also a reflex
element, and possible that the same is true of the tone of
the smooth muscular fibres of the bloodvessels on which
the maintenance of the mean blood -pressure so largely
depends. And it may be that if all afferent impulses could
be cut off from the vaso-motor centre, as by section of the
whole of the posterior spinal roots and other centripetal
paths to the medulla, general dilatation of the arterioles
would take place, and the blood - pressure be greatly
diminished. But, as has been already more than once
pointed out, there exist peripheral mechanisms which, after
a time, make good to some extent the loss of tone caused
by destruction of the spinal centres (p. 664).
Trophic Tone. — The degenerative changes that oc3 ir in
muscles, nerves, and other tissues when their connection with
the central nervous system is interrupted have been already
referred to (p. 584). It is possible to explain these changes
in some cases without the assumption that tonic impulses
are constantly passing out from the brain and cord to
control the riutrition of the peripheral organs ; and we have
seen that there is no real evidence of the existence of
specific trophic fibres. But the degeneration of muscles
after section of their motor nerves is difficult to understand
except on the hypothesis that impulses from the cells of
the anterior horn influence their nutrition. The only ques-
tion is whether these are the impulses to which muscular
tone is due, and therefore reflex, or different in nature and
automatically discharged. Now, degeneration of a muscle is
not usually caused, or at least not for a long time, by interrup-
tion of its afferent nerve-fibres, as in locomotor ataxia, or
after section of the posterior nerve-roots (Mott and Sherring-
ton). We can hardly suppose that in any case the trophic
influence of the cells of the spinal or sympathetic ganglia
684 -1 MANUAL OF J'lIYSIOLOGY
to which all other reflex powers have been denied, is of
reflex nature. And there is, indeed, more evidence in favour
of trophic tone being an automatic action of the cord than
for any of the other tonic functions hitherto considered.
Respiratory Automatism. — But the evidence upon which the
spinal cord has been credited with true automatic action is
chiefly connected with the central respiratory mechanism.
It is known (p. 211) that a section above a certain level
in the medulla oblongata does not abolish the respiratory
movements. The respiratory centre, then, must be con-
tinually sending out impulses which are not originated by
impulses reaching it from the brain. But this is far from
being a proof of definite automatic action by the spinal
cord, for although afferent impulses do not, under the con-
ditions of that experiment, reach the respiratory centre from
the brain, they may and do reach it from the periphery ;
and the only true test of automatic activity would be to
sever the whole of the afferent paths leading to the centre,
and then to observe whether or no the respiratory move-
ments continued. This is an experiment which it is difficult,
if not almost impossible, to carry out. But to say this is
merely to confess that, in the present state of experimental
physiology, it is difficult or impossible to apply a crucial
test to the doctrine of respiratory automatism.
The ' Centres ' of the Cord and Bulb. — We have frequently used
the word 'centre' in describing the functions of the spinal cord, but
the term, although a convenient one, is apt to convey the idea that
our knowledge is far more minute and precise than it really is. When
we say that a centre for a given physiological action exists in a definite
portion of the spinal cord, all that is meant is that the action can be
called out experimentally, or can normally go on, so long as this
portion of the cord and the nerves coming to it and leaving it are
intact, and that destruction of the 'centre' abolishes the action.
For example, a part of the medulla oblongata on each side of the
middle line in the floor of the fourth ventricle above the calamus
scriptorius is so related to the function of respiration that when
it is destroyed the animal ceases to breathe. But this respiratory
centre, the ' nceud vital ' of Flourens, does not correspond in position
with any definite collection of grey matter, although it includes the
nuclei of origin of several cranial nerves, and forms an important
point of departure for efferent, and of arrival for afferent, fibres con-
nected with the respiratory act. Its destruction involves the cutting
off of the impulses constantly travelling up the vagus to modify the
THE CENTRAL NERVOUS SVSTE.U 685
respiratory rhythm, and of the impulses constantly passing down the
cord to the phrenics and the intercostal nerves. And just as the
traffic of a witle region can be paralyzed at a single blow by severing
the lines in the neighl)ourhood of a great railway junction, or more
laboriously, though not less effectually, by separate section of the
same tracks at a radius of a hundred miles, so destruction of the
respiratory centre accomplishes by a single puncture what can be
also performed by section of all the respiratory nerves at a distance
from the medulla oblongata. But while nobody speaks of the
destruction of a 'centre' when a reflex action is abolished by
division of the peripheral nerves concerned in it, there is a tendency,
when the same effect is brought about by a lesion in the brain or
cord, to invoke that mysterious name, and to forget that the cerebro-
spinal axis is at least as much a stretch of conducting paths as a
collection of discharging nervous mechanisms.
It is, perhaps, a profitless task to enumerate all the so-called
centres in the bulb and cord with which the perverse ingenuity of
investigators and systematic writers has encumbered the archives
and text-books of physiology. In addition to the great vaso-motor,
respiratory, cardio-inhibitory and cardio-augmentor centres in the
bulb, which, perhaps, have more right than the rest to be regarded
as distinct physiological mechanisms, if not as definitely bounded
anatomical areas, there have been distinguished ano-spinal, vesico-
spinal, and genito-spinal centres in the lumbar cord, a cilio-spinal
centre for dilatation of the pupil in the cervical cord, and in the
medulla centres for sneezing, for coughing, for sweating, for sucking,
for masticating, for swallowing, for salivating, for vomiting, for the
production of general convulsions, for closure of the eyes. It would
be just as correct, and more practically useful (for it would perhaps
encourage the student who has lost his way amidst these intermin-
able distinctions), to say that the cerebral cortex contains a centre
for learning sense, and another for forgetting nonsense, and that in
a healthy brain it is the latter which is generally thrown into activity
in the study of this portion of modern physiology.
The Cranial Nerves.
Unlike the spinal nerves, which arise at not very unequal intervals
from the cord, the nuclei of origin of the cranial nerves, with the
exception of the olfactory and optic, are crowded together in the
inch or two of grey matter of the primitive neural axis in the
immediate neighbourhood of the fourth ventricle and the Sylvian
aqueduct. Of these nuclei some are sensory — sensory nucleus of
fifth, both nuclei of eighth, and probably the common nucleus of
ninth, tenth, and eleventh. The motor nuclei lie, upon the whole, in
two longitudinal rows — a median row, which consists of the nuclei
of the third and fourth nerves in the floor of the aqueduct, and those
of the sixth and twelfth nerves in the floor of the fourth ventricle ;
and a lateral row comprising the motor nuclei of the fifth, tenth, and
eleventh nerves, and the nucleus of the seventh. The clumps of
686
A MANUAL OF PHYSIOLOGY
grey matter which make up these nuclei may be considered as homo-
logous with the grey matter of the anterior (including the lateral)
horn of the spinal cord ; and the motor fibres of the nerves them-
selves as homologous with the anterior spinal roots, although it does
not follow that each cranial motor nerve represents one anterior root
and one only.
The first or olfactory nerve of anatomists is really a lobe of the
Fig. 234. — .SciiKMATic Tkansi-akent Seciion lH' Meuui.la Ohloncata.
The numerals V to XII refer to the nuclei of origin of the respective cranial nerves.
V is the motor nucleus ; RV, the roots of the fifth nerve ; V, sensory nucleus ;
V", sensory nucleus and ascending or spinal root. R\'I, root of si.xth nerve ; RVII,
root of seventh nerve; Py. pyramid; Py. kr. , decussation of the pyramids; O.s. ,
superior olive ; O, olive ; G. genu of the facial.
brain, and is better termed the olfactory tract or bulb, the real
olfactory nerves being the short terminal twigs that pierce the cribri-
form plate of the ethmoid bone to reach the upper part of the nasal
mucous membrane. The olfactory tract can be traced to the
uncinate gyrus of the same side. It seems, however, to be also
related in some indirect way to the opposite side of the brain, for an
injury to the posterior part of the internal capsule has been found
associated with impairment of smell in the opposite nostril. Exces-
THE CENTRAL NERVOUS SYSTEM 687
sive stimulation of the olfactory nerve by exposure to a strong odour
has been known to cause complete and permanent loss of smell.
The second or optic nerve is connected centrally with the lateral
geniculate body and pulvinar (or posterior portion) of the optic
thalamus, the anterior corpus ciuadrigeminum, and both directly and
indirectly with the occipital cortex (Fig. 244). Peripherally it expands
into its end-organ, the retina. At the chiasma the fibres of the optic
nerve decussate partially in man and some mammals, as the dog,
cat, and monkey, completely in animals whose visual field is
entirely independent for the two eyes, as in fishes and in many
mammals (horse, sheep, deer). In man the fibres for the nasal
halves of both retinae cross the middle line at the chiasma, those
for the temporal halves do not. Since the field of vision of the
nasal side of the retina is more extensive than that of the temporal
side, more than half of the fibres decussate. A lesion involving
the whole of the upper part of the occipital cortex, or the posterior
portion of the optic thalamus, or the optic tract, causes hemi-
anopia* (blindness of the corresponding halves of the two retinae)
on the side of the lesion. Thus, a lesion equivalent to complete
section of the right optic tract would cause blindness of the nasal
half of the left, and of the temporal half of the right eye, and the
left half of the field of vision would be blotted out — the patient would
be unable, with his eyes directed forwards, to see an object at his
left. A lesion, e.g., a tumour of the pituitary body, involving the
whole of the optic nerve in front of the chiasma, would cause
complete blindness of the corresponding eye. Sometimes in disease
of the optic nerve vision is not totally destroyed in the eye to which
it belongs, but the field is narrowed by a circumference of blindness.
In this case the pathological change involves the circumferential
fibres of the nerve. When the chiasma is affected by disease, a very
frequent symptom is nasal hemianopia, blindness of the nasal halves
of the retiutC, with loss of the outer or temporal half of each field of
vision.
It may be added that not only does a central lesion lead to
peripheral atrophy, but a peripheral lesion may cause central atrophy.
Extirpation of the eyeball in young animals is followed by atrophy
of the anterior corpus quadrigeminum, lateral geniculate body,
pulvinar, and occipital cortex.
The third nerve, or oculomotor, arises from a series of nuclei in
the floor of the Sylvian aqueduct below the anterior corpora quadri-
gemina. The root-bundles coming off from the most anterior of
the nuclei carry fibres that have to do with the mechanism of
accommodation. The nuclei behind these are connected with fibres
that cause contraction of the pupil when light falls on the retina ;
while, in dogs at least, the posterior portion of the series gives off
fibres for the muscles of the eye in the following order from before
* The terms 'hemiopia,' 'hemianopia,' 'hemianopsia,' are sometimes
used with reference to the blind side of the retin;i?, sometimes to the dark
half of the visual field. We shall always use the word 'hemianopia'
with reference to the retina.
688 A MANUAL OF PHYSIOLOGY
backwards : internal rectus, superior rectus, levator palpebrae
superioris, inferior rectus, inferior oblique. Complete paralysis of
the third nerve causes loss of the power of accommodation of the
corresponding eye, dilatation of the pupil by the unopposed action
of the sympathetic fibres, diminution of the power of moving the
eyeball, ptosis, or drooping of the upper lid, external squint, and
consequent diplopia, or double vision.
The fourth or trochlear nerve arises from the posterior part of
the same tract of grey matter which gives origin to the third nerve.
It supplies the superior oblique muscle. Paralysis of the nerve
causes internal squint when an object below the horizontal plane is
looked at, owing to the unopposed action of the inferior rectus.
There is also diplopia on looking down. Unlike the other cranial
nerves, the two trochlear nerves decussate completely after they
emerge from tiieir nuclei of origin.
The fifth or trigeminus nerve appears on the surface of the pons
as a large sensory root and a smaller motor root. Its deep origin is
more extensive than that of any of the other cerebral nerves, stretch-
ing as it does from the level of the anterior corpus quadrigeminum
above to the up])er part of the spinal cord below. Its sensory root,
in fact, seems to include the sensory divisions of all the motor cranial
nerves.
The motor root arises partly from a nucleus in the floor of the
fourth ventricle below the pons, partly as the so-called descending
root from large nerve-cells scattered in the grey matter around the
aqueduct of Sylvius all the way from the anterior quadrigeminate
body to the point at which the motor root is given off
The sefisory root has likewise two deep origins : a nucleus in the
neighbourhood of the motor nucleus in the floor of the fourth
ventricle, and a long spinal root running up from the level of the
second cervical nerve through the medulla oblongata and the
tegmentum of the pons, where it lies external to the descending
root.
The motor fibres of the fifth nerve supply the muscles of mastica-
tion and the tensor tympani. The sensory fibres confer common
sensation on the face, conjunctiva, the mucous membranes of the
mouth and nose, and the Structures contained in them, and special
sensation, through branches given off to the facial and glosso-
pharyngeal nerves, on the organs of taste. Complete paralysis of the
nerve causes loss of movement in the muscles of mastication, some-
times impaired hearing, and loss of common sensation in the area
supplied by it. Loss or impairment of taste in the corresponding
half of the tongue is also often seen in disease involving the sensory
root, although not in affections of the trunk of the nerve, since the
taste-fibres leave it near its origin. Both taste and touch are lost in
the monkey in the anterior two-thirds of the tongue after intracranial
section of the trigeminus.
^'aso-motor changes are occasionally, and 'trophic' changes
frequently, observed in disease of the fifth nerve. The trophic
disturbance is most conspicuous in the eyeball (ulceration of the
THE CENTRAL NERVOUS SYSTEM 6S9
cornea, going on, it may be, to complete disorganization of the eye).
These effects seem to be partly due to the loss of sensation in the
eye, and the consequent risk of damage from without, and the un-
regarded presence of foreign bodies and accumulation of secretion
within the lids.
The sixth or abducens nerve takes origin from a nucleus in the
floor of the fourth ventricle at the level of the posterior portion of the
pons. It supplies the external rectus muscle of the eyeball. Paralysis
of it causes internal squint.
The seventh or facial nerve arises from a nucleus in the reticular
formation of the medulla oblongata, and running up some distance
into the pons. It supplies the muscles of the face ; and when these
are greatly developed, as in the trunk of the elephant, the nerve
reaches very large proportions. Since the fibres which connect the
nucleus with the cerebral cortex decussate about the middle of the
pons, a lesion above this level which causes hemiplegia paralyzes
the face on the same side as the rest of the body, i.e., on the side
opposite the lesion. But the paralysis is confined to the muscles of
the lower portion of the face, and affects especially the muscles about
the mouth. Sometimes the pyramidal tract and the facial nerve, or
nucleus, are involved in a common lesion. In this case paralysis of
the face is on the side of the lesion, and is total, while the rest
of the body is paralyzed on the opposite side. Complete facial
paralysis is often caused by an inflammatory process in the nerve
itself (neuritis). The symptoms of complete facial paralysis are very
characteristic. The face and forehead on the paralyzed side are
smooth, motionless, and devoid of expression. The eye remains
open even in sleep, owing to paralysis of the orbicularis ]jalpebrarum.
A smile becomes a grimace. An attempt to wink with both eyes
results in a grotesque contortion. The mouth appears like a diagonal
slit in the face, its angle being drawn up on the sound side, and the
patient cannot bring the lips sufficiently close together to be able to
blow out a candle or to whistle. Liquids escape from the mouth,
and food collects between the paralyzed buccinator and the teeth.
The labial consonants are not properly pronounced. Taste is lost in
the anterior two-thirds of the tongue when the nerve is injured
between the entrance of the gustatory fibres from the trigeminus
and their exit by the chorda tympani, but not when the lesion is in
the nucleus of origin, or anywhere above it. Hearing is sometimes
impaired because the auditory and facial nerves, lying close together
for part of their course, are apt to suffer together, but perhaps also
because the stapedius muscle is supplied by the seventh nerve.
The eighth or auditory nerve arises from the medulla oblongata
by two roots, one of which passes in on each side of the restiform
body. The auditory nucleus in the floor of the fourth ventricle con-
sists of two parts, a lateral and a mesial nucleus, the first of which is
connected with the fibres of the ventral, and the second with those
of the dorsal root. The accessory nucleus on the ventral surface of
the restiform body forms an additional nucleus for the dorsal root.
It is believed that the two roots of the auditory nerve are physiologi-
44
690 A MANUAL OF PHYSIOLOGY
cally as well as anatomically distinct, for the dorsal root seems to
carry the fibres which are distributed in the cochlear division of the
auditory nerve to the cochlea, the ventral root those which pass to
the semicircular canals and the vestibule of the internal ear. And,
as we shall see (p. 698), it is extremely probable that the cochlea
subserves the function of hearing, the semicircular canals and vesti-
bule the function of equilibration. We must assume, from clinical
and experimental data, that the dorsal root is connected through its
nuclei with the first or first and second temporo-sphenoidal convolu-
tions on the opposite side. Two prominent symptoms may be
associated with disease of the auditory nerve — {a) disturbance or
loss of hearing ; (/') loss or impairment of equilibration.
The ninth or glossopharyngeal nerve arises from the upper portion
of an elongated nucleus in the medulla oblongata, the lower portion
of which gives origin to the accessory division of the spinal accessory,
and the middle to the vagus. An additional origin is formed by a
bundle of fibres, the ascending root of the glosso-pharyngeal, which
arises from the grey matter of the lateral horn of the cord and the
formatio reticularis of the medulla, and commences as far down as
the fourth cervical nerve. The glosso-pharyngeal has both sensory
and motor fibres — sensory for the posterior third of the tongue and
the mucous membrane of the back of the mouth, motor for the
middle constrictor of the pharynx and the siylo-pharyngeus. It also
contains the nerves of taste for the posterior third of the tongue, but
these reach it from the fifth nerve.
The tenth or vagus or pneumogastric nerve is joined near its
origin by the accessory portion of the spinal accessory, that is, the
portion which arises from the medulla oblongata, and we shall
describe them together. The mixed nerve contains both sensory and
motor fibres, the latter chiefly derived from the accessory, the former
entirely from the vagus. The distribution of the nerve is more
extensive than that of any other in the body. The oesophagus
receives both motor and sensory branches from the oesophageal
plexus. The pharyngeal branch of the vagus is the chief motor
nerve of the pharynx and soft palate (including the tensor palati).
The superior laryngeal branch is the nerve of common sensation for
the larynx above the vocal cords, and the motor nerve of the crico-
thyroid muscle. The inferior or recurrent laryngeal supplies the rest
of the laryngeal muscles, and the sensory fibres for the mucous
membrane of the trachea and the larynx below the glottis. The
superior laryngeal contains afferent fibres, stimulation of which
gives rise to coughing, slows respiration, or stops it in expiration.
Reflex movements of deglutition are also caused. The vagus
supplies the lung both with motor and sensory filaments through the
pulmonary plexus. The motor fibres when stimulated cause con-
striction of the bronchi ; excitation of the afferent fibres causes reflex
changes in the rate or depth of respiration. The cardiac branches
contain inhibitory fibres probably derived from the spinal-accessory,
and depressor fibres which pass up in the vagus trunk (dog), or as a
separate nerve to join the vagus or its superior laryngeal branch or
Tin: CENTRAL XERVOUS SYSTEM 691
both (rabbit). The gastric and intestinal branches contain both
motor and sensory nerves for the stomach and intestines. The sensory
are probably large medullated fibres (7 /i to 9 //.). The afferent vagus
fibres from the stomach carry up impulses which excite the action of
vomiting. Lesions of the vagus, its nuclei of origin, or its branches,
are associated with many interesting forms of paralysis and other
symptoms. Paralysis of the pharynx is generally caused by disease
of the nucleus in the medulla. From its anatomical relation to
the nuclei of the glosso pharyngeal and hypoglossal, it will be easily
understood that these nerves are often involved in localized central
lesions along with the vagus. But the fact that in glosso labio-
laryngeal palsy — a condition characterized by progressive p?ralysis
and atrophy of the muscles of the tongue, lips, larynx, and pharynx
— the orbicularis oris is paralyzed, while the other muscles supplied
by the facial remain intact, would seem to show that in system
diseases it is not so much anatomical groups of nerve-cells which are
liable to simultaneous degeneration and failure, as physiological
groups normally associated in particular functions. Such functional
groups of cells, occupied with the same kinds of labour at the same
times and under the same conditions, may be supposed to take on a
similar bias or tendency to degeneration, a tendency not indicated, it
may be, by any structural peculiarity, but traced deep in the molecular
activity of the cells. Difficulty in swallowing is the chief symptom
of pharyngeal paralysis. The symptoms of laryngeal paralysis have
been already described under 'Voice' (p. 270). Tachycardia, or a
permanent increase in the rate of the heart, has been stated to
occur in certain cases of paralysis of the vagus, caused by disease or
accidental interference ; and a persistent slowing of the respiration
has been occasionally attributed to the same cause. But it is difficult
to reconcile many of these cases with experimental results, for in
most of them the lesion only involved one vagus : and in animals
section of one vagus has no permanent effect on the rate of the heart
or of the respiratory movements.
Destruction of the nerve near its origin has been sometimes found
associated with disappearance of the food-appetites, hunger and
thirst, and it has been assumed that this was due to loss of afferent
impulses from the stomach. But clinical testimony is by no means
unanimous on this point, and experiments on animals show that other
factors are involved in these sensations.
The eleventh or spinal-accessory nerve consists of two parts : the
accessory or internal branch, which arises from the medulla oblongata,
and which we have just considered in conjunction with the vagus ;
and the external or spinal branch, which, arising from the lateral rim
of the anterior horn of the cord from the sixth or seventh cervical
nerve upwards, passes out to supply the trapezius and sterno-mastoid
muscles with motor fibres.
The twelfth or hypoglossal nerve contains the motor supply of the
intrinsic and extrinsic muscles of the tongue and of the thyro- and
genio-hyoid. Paralysis of it causes deficient movement of the corre-
sponding half of the tongue. When the tongue is put out, it deviates
44—2
692 A MA NUA L OF PI I \ 'SIOL OG Y
towards the paralyzed side, being pushed over by the unparalyzed
genio-hyoglossus of the opposite side, which is thrown into action in
protruding ihc tongue.
The Functions of the Brain.
The paths by which the various parts of the central nervous
system are connected with each other and with the periphery
have been already described, and we have completed the
examination of the functions of the spinal cord and medulla
oblongata. The events that take place in the upper part of
the central nervous stem and in the cortex of the cerebellum
and cerebrum now claim our attention.
From very early times the brain has been popularly believed to be
the seat of all that we mean by consciousness — sensation, ideation,
emotion, volition. And he who loves to trace the roots of things
back, into the past may see, if he choose, running through the whole
texture of the older speculations a belief that the brain does not act
as a whole, but is divided into mechanisms, each with its special
work — a foreshadowing, often in grotesque outlines, of the doctrine
of localization so widely held to-day. But until comparatively recent
times, cerebral physiology remained a kind of scientific terra incog-
nita ; and no notable additions were made for a thousand years to
the doctrines of Galen. Even to day the utmost limit of our know-
ledge is reached when in certain cases we have connected a particular
movement or sensation with a more or less sharply defined anatomical
area. How the cerebral processes that lead to sensations and
movements, to emotions and intellectual acts, arise and die out ;
what molecular changes are associated with them : above all, how
the molecular changes are translated into consciousness — how, for
example, it is that a series of nerve-impulses flickering across the
labyrinth of the occipital cortex should light up there a visual
sensation— these are questions to which we can as yet give no
answer, and the answers to some of which must for ever remain
hidden from us.
Functions of the Upper Part of the Central Stem and Basal
Ganglia. — Some of the transverse fibres of the pons form a com-
missure between the hemispheres of the cerebellum, but many of
them are the cerebellar portions of commissural arcs mterrupted by
pontine grey matter, and continued by fibres of the corona radiata to
the pre-frontal, temporal and occipital portions of the cerebral cortex
(P- 659).
The posterior corpora quadrigemina (testes) and internal geniculate
bodies are connected with the cochlear division of the auditory
nerves, and therefore have some relation to the sense of hearing.
Stimulation of the testes causes a peculiar cry, and the pupils dilate.
The anterior corpora ijuadrigemitia (nates) and the lateral corpora
geniculata are connected with the optic tracts. Their development
THE CEXTRM. NERVOUS SYSTEM
693
is arrested after extirpation of the eyeball in young animals, and
they may therefore be assumed to be concerned in vision, although
the size of their homologues, the optic lobes or corpora bigemina, in
animals below the rank of mammals (birds, reptiles, amphibians),
does not seem to be related to the development of the organs of
sight. The Proteus and the Hag-fish, c.:^'., have large optic lobes,
rudimentary eyes and optic tracts. The optic nerve, the nuclei of
the oculo-motor nerve in the wall of the Sylvian aqueduct, and the
fibres which it carries to the iris, form reflex arcs for the contraction
of the pupil to light and during accommodation.
The functions of the optic thalanti have not been satisfactorily
defined either by e.vperiment or pathological observation. Lying as
they do in the isthmus of the brain, begirt by the great motor and
Corpus striaiuni
^Blllll'""''
^,...^ \\ .Anterior pillar of ine
^^VT 1 fornix
-Optic thalamus
.Third ventricle
Fig. 235,
-Horizontal Section through Brain to show the Basal
Ganglia and Third Ventricle (Human).
sensory paths, it is to be expected that lesions of the thalami should
affect also the internal capsule, and give rise to the symptoms of
motor and sensory paralysis. But no definite defect of motor power
or common sensation has ever been unequivocally connected with a
lesion restricted to the thalami. They have, however, extensive
connections with the cerebral cortex, each of the thalamic nuclei
being connected with a definite cortical region in such a way that
destruction of the cortical area in young animals or human beings
leads to degeneration of the corresponding nucleus. The posterior
portion of the thalamus, or pulvinar, forms part of the central
visual apparatus ; for (a) it is found to be undeveloped in animals
from which the eyeballs have been removed soon after birth ; {b) a
portion of the optic tract is certainly connected with it ; {c) in some
cases of atrophy of the occipital cortex, which, as we shall see, is
094
.1 MAXUAL OF PHYSIOLOGY
undoubtedly a central area for visual sensations, atrophy of the
pulvinar has also been noticed ; {d) a lesion of the pulvinar may
apparently give rise to hemianopia (p. 687).
Haemorrhage into the caudate or lenticular nucleus of the corpus
striatum often causes hemiplegia, but this is always due to implica-
tion of the internal capsule. Experimental lesions in dogs and
rabbits are followed by disturl^ances of the heat-regulating mechanism
and rise of temperature.
Certain structures, belonging to the primary fore-brain, which have
now no functional importance, may nevertheless be mentioned as
milestones in the
march of develop-
ment. The pineal
body is made up of
the vestiges of the
single mesial eye of
the ancient amphi-
bians, which r e-
sembled the eye of
i n ve rtebrates i n
having the retinal
rods directed towards
the cavity instead of
towards the circum-
ference of the eye-
ball. The ganglia
habetiuhe seem to
represent the optic
ganglia of this Cyclo-
pean eye. The in-
fundibulu7n is pro-
bably what remains
of the gullet of the
ancestors of the ver-
tebrates. The pitui-
tary body consists of
two portions, the an-
terior being derived
from the buccal cavity, the posterior from the primary fore-brain.
It has been stated that after excision of the thyroid glands, the anterior
division, the tissue of which has a resemblance to thyroid tissue, has
sometimes been found hypertrophied (but see p. 475).
Functions of the Cerebellum. — The elaborate pattern of the
arbor vit^e, the appearance given by the branched laminae in
a section of the cerebellum, e.xcited the speculation of the
old anatomists. A structure so marvellous must be matched,
they thought, with functions as unique. At a time when
the discoveries of Galvani and \'olta were fresh, and the
Fig. 236. — LoNGiTUDiNAi, Section of tmk Grkv
Matter of a Lamella of the Cerebellum
(Diagrammatic, after Kolliker).
gr, a ' granule ' cell with its neuron, n ; ;/', bifurcation
of fi, in the molecular layer, into two fine longitudinnl
branches ; ;//, a I'urkinjc's cell ; jn', antler process (Golgi's
method).
THE CENTRAL NERVOUS SYSTEM 693
world ran mad on electricity, the hypothesis of Rolando,
that ' nerve-force ' was generated by the lamella; of the
cerebellum as electrical energy is generated by the plates
of the voltaic pile, ridiculous as it now appears, was not
unnatural. The speculation of Gall, who connected the
cerebellum with the development of sexual emotions and
the action of the generative mechanisms, was based on no
fact. It has been definitely disproved by the observations
of Luciani, who found that a bitch deprived of its cerebellum
showed all the phenomena of heat or * rut,' was impregnated,
whelped at full term in an en-
tirely normal manner, and mani-
fested the maternal instincts in
their full intensity. Flourens
put forward the doctrine that
the cerebellum is an organ
especially concerned in the co-
ordination of movements and
the maintenance of equilibrium,
supporting his conclusions by
an elaborate series of experi-
ments. Notwithstanding the
very large amount of experi-
mental and clinical study which
has been devoted to the cere-
bellum since the time of
Flourens, our knowledge of its F1G.237.— apurkinje'sCell from
fnnrh'nn:; bp=; hnrrllv advanrpH THE Cerebellum OF A Cat (AFTER
lunctions nas narai} amancea c^j^l ; Golgi's Method).
beyond the point then reached.
Indeed, it may be said that the tendency has been rather to
abridge than to extend the field of current physiological
doctrine on this subject. For while it has been shown that
the integrity of the cerebellum is essential to equilibration, it
is by no means certain that it is essential for the co-ordination
of movements other than those concerned in the maintenance
of equilibrium and in locomotion. Animals entirely deprived
of the cerebellum have shown, after the primary effects of
the operation have passed away, no impairment in general
co-ordinative power ; and cases are on record in which the
696 J MAXCAL OF PHYSIOLOGY
human cerebellum has been found at death to be utterly
disorganized, and yet in which many classes of movements
have been well co-ordinated during life. But what has been
noticed in such cases is a marked inability to maintain the
upright posture, a staggering gait, twitching movements of
the eyes (nystagmus) — in a word, a general disorder of the
mechanism of equilibration. In cases of congenital defect
of the cerebellum, the power of walking, and even of
standing, is late in being acquired, and usually imperfect.
The connections of the cerebellum with other parts of the
central nervous system and with the periphery corroborate
the direct results of experiment. For the most important
afferent impulses concerned in equilibration are those from
the muscles, the skin, the semicircular canals and vestibule
of the internal ear, and the eyes. And the cerebellum, as
we have seen (p. 655J, is linked with all of these, and has
besides an extensive crossed connection through the middle
and superior peduncles with the opposite cerebral hemi-
sphere.
We do not as yet know the full significance of this extra-
ordinarily free communication of the grey matter of the
cerebellum with every part of the central nervous system.
But it is evident that by the broad highway of the restiform
body, or the cross-country routes from cerebral cortex to
cerebellum, impulses may pass into it from every quarter ;
and it is an organ so connected that is suited to take
cognizance of the multitudes of impressions concerned in
the maintenance of equilibrium. This is a convenient place
to consider a little more in detail the nature and peripheral
sources of the most important of these impressions.
(i) AflFerent Impressions from the Muscles. — Muscles are richly
supplied with afferent fibres, for about half of the fibres in the nerves
of skeletal muscles degenerate after section of the posterior roots
beyond the ganglia (Sherrington). Various kinds of impressions
may pass up these muscular nerves : {a) Impressions giving rise to
pain, as in muscular cramp and in experimental excitation of even
the finest muscular nerve-filament ; (?') impulses causing a rise of
blood-pressure ; {c) impulses which are not associated with a distinct
impression in consciousness, but enable us to localize the position
of the limbs, head, eyes, and other parts of the body ; {d) impulses
which inform us as to the extent and force of muscular contraction,
THE CENTRAL NERVOUS SYSTEM
697
.and seem to underlie the so-called muscular sense. It is the last
two kinds — if, indeed, they are distinct — which must be concerned
■in equilibration. In locomotor ataxia such impressions are blocked
by degeneration in a part of the afferent path (p. 673), and disorders
of equilibrium are the result.
(;:) Afferent Impressions from the Skin. — Of the various kinds of
nerve-impulses that arise in the nerve-endings of the skin, only those
of touch and pressure seem to be concerned in the maintenance of
■equilibrium. When the soles of the feet are anaesthetized by chloro-
form or by cold, and the person is directed to close his eyes, he
staggers and sways from side to side.
The disturbance of equilibrium in
locomotor ataxia must be partly attri-
buted to the loss of these tactile
sensations, for numbness of the feet
is a frequent symptom, and the patient
asserts that he does not feel the
ground. An interesting illustration of
the importance of afferent impulses
from the skin in the maintenance of
■equilibrium is afforded by the behaviour
of a frog deprived of its cerebral hemi-
spheres. Such a frog will balance itself
on the edge of a board like a normal
animal, but if the skin be removed
from the hind-legs, it will fall like a log
(3) Afferent Impulses from the
Semicircular Canals. — The semicir-
cular canals are three in number, and
lie nearly in three mutually rectangular
planes : the external canal in the horizontal plane, the superior
■canal in a vertical longitudinal plane, and the posterior canal
in a vertical transverse plane. Each canal bulges out at one
■end into a swelling, or ampulla, which opens into the utricular
• division of the vestibule (Fig. 292) The other extremities of the
superior and posterior canals join together, and have a common
aperture into the utricle, but the undilated end of the external or
horizontal canal opens separately. The utricle and the semicircular
■canals are thus connected by five distinct orifices. The greater part
•of the internal surface of the membranous canals, utricle and saccule,
is lined by a single layer of flattened epithelium. But at one part of
• each ampulla projects a transverse ridge, the crista acustica, covered
not with squamous, but with long columnar epithelium. Hair-like
processes (auditory hairs), borne either by the columnar cells or by
spindle-shaped cells scattered among them, project into the endo-
lymph, which fills all the membranous labyrinth, and are covered by
■a thin membrana tectoria. The utricle and saccule have each a
somewhat similar but broader elevation, the macula acustica, covered
with epithelium and hair-cells of the same character, and the hairs
project into an otolith, or small mass of carbonate of lime. The
Fig. 238. — The Semicircular
Canals (Diagrammatic).
H, horizontal or external ; S,
superior ; P, posterior.
698 A MANUAL OF PHYSIOLOGY
vestibular branch of the auditory nerve breaks up into five twigs :
one for each ampulla, one for the utricle, and one for the saccule.
The nerve-fibres, on which lie ganglion-cells, lose their medulla as
they approach the layer of hair cells in which they terminate. There
is very strong evidence that the semicircular canals are concerned,
not in hearing, but in equilibration. A pigeon from which the
membranous canals have been removed still hears perfectly well
so long as the cochlea is intact, but exhibits the most profound
disturbance of equilibrium. If the horizontal canal is destroyed
or divided, the pigeon moves its head continually from side to
side around a vertical axis ; if the superior canal is divided, the
head moves up and down around a horizontal axis. The power
of co-ordination of movements is diminished, but not to the same
extent in all kinds of animals. Thrown into the air, the pigeon is
helpless ; it cannot fly ; but a goose with divided semicircular canals
can still swim. The condition is only temporary, even when the
injury involves the three canals on one side ; but if the canals on
both sides are destroyed, recovery is tardy, and often incomplete.
In mammals the loss of co-ordination is much less than in birds ;
and movements of the eyes, the direction of which depends on the
canal destroyed, take to a large extent the place of movements of
the head. The effects of destructive lesions have their counterpart
in the phenomena caused by stimulation ; excitation of a posterior
canal, for example, in the pigeon causes movements of the head from
side to side.
Lee"s results in fishes are, on the whole, of similar tenor. Mechanical
stimulation of the ampullae in the dogfish, by pressing on them with
a blunt needle, calls forth characteristic movements of the eyes and
fins, and electrical stimulation of the auditory nerve causes move-
ments compounded of the separate movements obtained by stimula-
tion of the ampullae one by one. Lee concludes that the semicircular
canals are the sense-organs for dynamical equilibrium (/.f., equilibrium
of an animal in motion), and the utricle and saccule for statical
equilibrium {i.e., equilibrium of an animal at rest).
The evidence from all sources points strongly to the conclusion
that afferent impulses are actually set up in the fibres of the auditory
nerve, through the hair-cells, by alterations of pressure or by stream-
ing movements of the endolymph when the position of the head is
changed. Rotation of the head to the right may be supposed to
cause the endolymph in the right external canal, in virtue of its
inertia, to lag behind the movement, and to press upon the anterior
surface of the ampulla. The disorders of movement after lesions of
the canals may be explained as the result of the withdrawal of certain
of these afferent impulses, and the consequent overthrow of that
equipoise of excitation necessary for the maintenance of equilibrium.
Even in man there is evidence of the existence of some mechanism
not depending on the muscular sense or on impressions passing up
the channels of ordinary or special sensation, by which orientation
(the determination of the position of the body in space) is rendered
possible. For a man lying perfectly still, with eyes shut, on a hori-
THE CENTRAL NERVOUS SYSTEM Gg^.}
zontal table which is made to rotate uniformly, can not only judge
whether, but also in what direction, and approximately through what
angle, he is moved (Crum Brown). The phenomena of pathology
afford weighty additional testimony in favour of the equilibratory
function of the semicircular canals. For many cases of vertigo are
associated with changes in the internal ear (Meniere's disease). And
while nearly every normal individual becomes dizzy when rapidly
rotated, 35 per cent, of deaf-mutes are entirely unaffected (James),
and the proportion seems to be much higher among congenital deaf-
mutes. Kreidl and Bruck, too, have found that abnormalities of loco-
motion and equilibration are much more common in deaf and dumb
children than in others. Now, in these cases the defect is usually
in the internal ear. We must conclude, then, that the coordination
of muscular movements necessary for equilibrium is achieved in
some centre, to which afferent impulses pass from the internal ear
by the vestibular branch of the auditory nerve, and from which
efferent impulses pass out to the muscles. If, as there is strong
reason to believe, this centre is situated in the cerebellum, the
efferent path is in all probability an indirect one (perhaps by com-
missural fibres to the Rolandic area, and then out along the pyramidal
tract) ; for, as we have seen, the cerebellum is either not connected
directly with the anterior roots at all, or only by a few fibres. Ewald
has made a curious observation which illustrates the peculiar relation
of the semicircular canals to the muscular system, namely, that the
labyrinth (in rabbits) influences the course of rigor mortis in the
striped muscles. Rigor does not come on so soon on the side from
which the labyrinth has been removed.
It is the middle lobe of the cerebellum which seems to be concerned
in the co-ordination of movements and maintenance of equilibrium.
In birds and lower vertebrates the worm is alone present. The
cerebellar hemispheres become more prominent the higher we
ascend, and it cannot be doubted that they have important functions,
but what these are is entirely unknown. The fact that they are con-
nected chiefly with those parts of the cerebral cortex which are sup-
posed to be concerned in psychical and sensory processes suggests
that, at any rate, the superficial grey matter of the cerebellum is not
motor, and no movements can be obtained on stimulating it ; while
stimulation of the worm may cause movements of the eye. Excita-
tion of the line of junction of the superior worm with the lateral lobe
in animals which exhibit tonic contraction of extensor muscles after
excision of the cerebral hemispheres (acerebral tonus, as it is called)
causes relaxation of the extensors accompanied by contraction of the
antagonistic flexors— for example, relaxation of the triceps and con-
traction of the biceps (Horsley and Lowenthal).
Forced Movements. — We have incidentally mentioned that in fishes
injuries to the semicircular canals may give rise to movements which
seem to be beyond the control of the animal, and which have
consequently received the name of * forced movements.' It may be
added that when the internal ear of a Menobranchus (one of the
tailed amphibia) is destroyed on one side, rapid movements of rota-
700 A MANUAL OF PHYSIOLOGY
tion around a longitudinal axis are observed. The animal spins
round and round apparently without voluntary control, purpose, or
fatigue. The direction of rotation is towards the side of the lesion,
the observer being supposed to look down upon the animal as it lies
in its normal position. After a time it becomes quiescent ; but the
forced movements can be again produced by pinching or exciting it
in other ways. In man, too, during the passage of a galvanic current
between the two mastoid processes, a tendency to move the head
towards the anode is experienced. The person may resist the
tendency, but if the current be strong enough his resistance will be
overcome ; he will execute a forced movement. Complex as such
an experiment is, involving as it does stimulation of so many struc-
tures within the cranium, there is reason to believe that it is the
excitation of the semicircular canals that is responsible for this forced
movement. For when the experiment is performed on a pigeon,
forced movements are caused so long as the membranous canals are
intact, but not after they have been destroyed (Ewald).
But forced movements may also follow injuries (especially uni-
lateral) to many portions of the brain — e.g., the pons, crus cerebri,
posterior corpora quadrigemina, corpus striatum, cerebellum, and
even the cerebral cortex. The movements are of the most various
kinds. The animal may run roimd and round in a circle (circus
movements) ; or, with the tip of its tail as centre and the length of
its body as radius, it may describe a circle with its head, as the hand
of a clock does (clock-hand movement) ; or it may rush forward,
turning endless somersaults as it goes. Intervals of rest alternate
with paroxysms of excitement, and the latter may be brought on by
stimulation. In man forced movements associated with vertigo have
been sometimes seen in cases of tumour of the cerebellum— ^.^.,
involuntary rotation of the body in tumour of the middle peduncle.
No entirely satisfactory explanation of these forced movements has
been given. They are evidently connected with disturbance of the
mechanism of co-ordination, leading to a loss of proportion in the
amount of the motor discharge to muscles or groups of muscles
accustomed to act together in executing definite movements. For
instance, in circus movements the muscles of the outer side of the
body contract more powerfully than those of the inner side, and the
animal is therefore constrained to trace a circle instead of a straight
line, the excess of contraction on the outer side being analogous to
the acceleration along the radius in the case of a point moving in a
circle.
Co-ordination of Movements. — The capacity of executing some
co-ordinated movements, occasionally of considerable complexity,
seems to be inborn in man, and to a still greater extent in many of
the lower animals. The new-born child brings with it into the world
a certain endowment of co-ordinative powers ; it has inherited, for
example, from a long line of mammalian ancestors the power of
performing those movements of the cheeks, lips, and tongue, on
■which sucking depends ; perhaps from a long, though somewhat
shadowy, race of arboreal ancestors the power of clinging with hands
THE CEXTRAL NERVOUS SYSTEM 701-
and feet, and thus suspending itself in the air. Many movements,
such as walking and the co ordinated muscular contractions involved'
in standing, and even in sitting, which, once acciuired, appear so
natural and spontaneous, have to be learnt by painful effort in the
hard school of (infantile) experience. Most people learn, and are
willing to confess that they have learnt, to execute a considerable
number of co-ordinated movements with the arms, and especially
with the fingers ; but few have considered that the extreme dexterity
of jaws, tongue, and teeth displayed by a hungry mouse or school-
boy is the result of the much practice which maketh {)erfect. The
exquisite co-ordination of the muscles of the eyeball, which we
shall afterwards have to speak of, and the no less wonderful balance
of effort and resistance, of power put forth and work to be done, of
which we have already had glimpses in studying the mechanism
of voice and speech, become to a great extent the common property
of all fully-developed persons. But the technique of the finished
singer or musician, of the swordsman or acrobat, and even the
operative skill of the surgeon, are in large part the outcome of a
special and acquired agility of mind or body, in virtue of which,
highly-complicated co-ordinated movements are promptly deternu'ned
on and immediately executed.
With such special and elaborate movements it is impossible to
occupy ourselves in a book like this. Their number may be almost
indefinitely extended, and their nature almost infinitely varied, by
the needs and training of special trades and professions. It will
be sufficient for our purpose to sketch in a few words the mechanism
of one or two of the most common and fundamental co-ordinations
of muscular effort, passing over the rest with the general statement
that the more refined and complex movements are in general brought
about not by the abrupt contraction of crude anatomical groups of
muscles, but by the contraction of portions of muscles, perhaps even-
single fibres or small bundles of fibres, while the rest remain relaxed.
The excitation may gradually wax and wane as the different stages
of the movement require. Antagonistic muscles may be called into
play to balance and tone down a contraction which might otherwise
be too abrupt.
A most interesting illustration of this process of ' give and take '
between opposing muscles has been reported by Sherrington. In
the cortex cerebri, as we shall see (pp. 708, 712), there is an area
in the frontal region, and another in the occipital region, stimulation
of which gives rise to conjugate deviation of the eyes — that is, rotation
of both eyes — to the opposite side. Sherrington divided the third
and fourth cranial nerves in monkeys — say on the left side. The
external rectus, which is supplied by the si.xth nerve, caused now by
its unopposed contraction external squint of the left eye. When
either of the cortical areas referred to, or even the subjacent portion
of the corona radiata, was stimulated on the left side, both eyes
moved towards the right, the left eye, however, only reaching the
middle line— that is, the position in which it looked straight forward.
The same thing was observed when the animal, after complete re-
702 A MAXUAL OF PHYSIOLOGY
covery from the operation, was caused to voluntarily turn its eyes to
the right by the sight of food. Here an inhibitory influence must
have descended the fibres of the abducens, the only nervous path
connected with the extrinsic muscles of the left eye, and the relaxa-
tion of the left external rectus must have kept accurate step with the
contraction of the right internal rectus. (See also p. 699).
Standing. — In the upright posture the body is supported chiefly
by non-muscular structures, the bones and ligaments. But muscles
also play an essential part, for it is only peculiarly-gifted individuals
like some of the fishermen of the North Sea who can go to sleep on
their feet, and a dead body cannot be made to stand erect. The
condition of equilibrium is that the perpendicular dropped from the
centre of gravity to the ground should fall within the base of support
— that is, within the area enclosed by the outer borders of the feet
and lines joining the toes and heels respectively. The centre of
gravity alters its position with the position of the body, which tends
to fall whenever the perpendicular cuts the ground beyond the base
of support.
The centre of gravity of the head is a little in front of the vertical
plane passing through the occipital condyles. A slight degree of
contraction of the muscles of the nape of the neck is required to
balance it. When these muscles are relaxed, as in sleep, the head
must fall forward, and this is the reason why Homer or any lesser
individual nods. In animals which go upon all fours, none of the
weight of the head bears directly upon the occipito-atloid articula-
tion ; its support by muscular action alone would be an intolerable
fatigue, and the ligamentum nuchas is specially strengthened to hold
it up
The %ertebral column is kept erect by the ligaments and muscles
of the back. The centre of gravity of the trunk lies between the
ensiform cartilage and the eighth or tenth dorsal vertebra. The
perpendicular dropped from it passes a little behind the horizontal
line joining the two acetabula ; but the body is prevented from falling
backward by the tension of the ileo-femoral ligament and the fascia
lata, and perhaps by slight contraction of some of the muscles on the
front of the thigh. The perpendicular let fall from the centre of
gravity of the whole of the body above the knee passes very slightly
behind the axis of rotation of that joint, so that but little muscular
action is required to keep the knee joints rigid. The whole weight
of the body is finally transferred to the astragalus on each side, the
perpendicular from the centre of gravity of the whole, which is
situated near the sacral promontory, falling a little in front of these
bones. By means of the muscular senee, and the tactile sensations
set i>p by the pressure of the soles on the ground, alterations in the
position of the centre of gravity, and consequent deviations of the
perpendicular passing through it, are detected, and equilibrium is
maintained by adjustment of the amount of contraction of this or the
other muscular group.
In standing at 'attention,' the heels are close together, the legs
and back straightened to the utmost, and the head erect : the weight
THE CENTRAL NERVOUS SYSTEM 703
falls equally upon both legs, but the advantage is much more than
counterbalanced by the considerable muscular exertion required to
maintain this more ornamental than useful position. In 'standing
at ease,' practically the whole weight is supported by one leg, the
perpendicular from the centre of gravity passing through the knee
and ankle-joints. The centre of gravity is brought over the support-
ing leg by flexure of the body to the corresponding side, and com-
paratively little muscular effort is required. The other foot rests
lightly on the ground, the weight of the leg itself being almost
balanced by the atmospheric pressure acting upon the air-tight and
air-free cavity of the hip-joint. The light touch of this foot varies
slightly from time to time, so as to maintain equilibrium.
When the arms or head are moved, or the body swayed, the
centre of gravity is correspondingly displaced, and it is by such
movements that tight-rope dancers continue to keep the perpen-
dicular passing through it always within the narrow base of support.
In sitting, the base of support is larger than in standing, and the
equilibrium therefore more stable. The easiest posture in sitting
without support to the back or feet is that in which the perpendicular
from the centre of gravity passes through the horizontal line joining
the two tubera ischii.
Locomotion. — In walking, the legs are alternately swung forward
and rested on the ground. In military marching, it is directed that
toe and heel be simultaneously set down. But with most persons
the swinging foot first strikes the ground by the heel ; then the sole
comes down, the heel rises, the leg is extended, and, with a parting
push from the toe, the leg again swings free. By this manoeuvre the
body is raised vertically, tilted to the opposite side, and also pushed
in advance.
The forward swing of the leg is only slightly, if at all, due to
muscular action ; it is more like the oscillation of a pendulum dis-
placed behind its position of equilibrium, and swinging through that
position, and in front of it, under the influence of gravity. For this
reason the natural pace of a tall man is longer and slower than that
of a short man ; but it may be modified by voluntary effort, as when
a rank of soldiers of different height keeps step.
The lateral swing of the body is illustrated by the everyday
experience that two persons knock against each other when they
try to walk close together without keeping step. In step, both swing
their bodies to the same side at the same moment, and there is no
jarring.
Even in the fastest walking there is a short time during which
both feet are on the ground together, the one leg not beginning its
swing until the other foot has been set down. In running, on the
other hand, there is an interval during which the body is completely
in the air.
Functions of the Cerebral Cortex. — When an animal, like a
frog, is deprived of its cerebral hemispheres, the power of
704 A MA XL' A L OF PHYSIOLOGY
automatic voluntary movement appears to be definitively
and entirely lost. The animal, as soon as the effects of the
anaesthetic and the shock of the operation have passed away^
draws up its legs, erects its head, and assumes the charac-
teristic position of a normal frog at rest. So close may be
the resemblance, that if all external signs of the operation
have been concealed, it may not be possible to tell merely
by inspection which is the intact and which the ' brainless '
frog. The latter will jump if it be touched or otherwise
stimulated. It will croak if its flanks be stroked or gently
squeezed together. It will swim if thrown into water. If
placed on its back, it will promptly recover its normal
position. But it will do all these things as a machine would
do them, without purpose, without regard to its environ-
ment, with a kind of ' fatal ' regularity. Every time it is
stimulated it will jump, every time its flanks are squeezed
it will croak, and, in the absence of all stimulation, it will
sit still till it withers to a mummy, even by the side of the
water that might for a while preserve it.
A Menobranchus, without its cerebral hemispheres, will,
like the frog, refuse to lie on its back. On stimulation it
moves its feet or tail, or its whole body ; but if not interfered
with, it lies for an indefinite time in the same position. Its
gills are seen to execute rhythmic movements, which never
stop, and rarely slacken, except for an instant, when some
part of the skin, particularly in the region of the head, is
mechanically or electrically stimulated. The normal Meno-
branchus, on the other hand, lies for long periods with its
gills at perfect rest, and when stimulated moves for a con-
siderable distance. After a time, two months or more, it is
true the ' brainless frog,' if it be kept alive, as may be done
by careful attention, will recover a certain portion of the
powers which it has lost by removal of the cerebral hemi-
spheres; and, indeed, the longer it lives, the nearer it
approximates to the condition of a normal frog. A brain-
less frog has been seen to catch flies and to bury itself as
winter drew on. A fish even three days after the destruction
of its cerebrum has been seen to dart upon a worm, seize
it before it had time to sink to the bottom of the aquarium.
THE CENTRAL XERVOUS SYSTEM 705
and swallow it. Even in the pigeon the loss of the hemi-
spheres, which at first induces a state of profound and
seemingly permanent lethargy, is to a great extent com-
pensated for, as time passes on, by the unfolding in the
lower centres of capabilities previously dormant or sup-
pressed. A brainless pigeon has been known to come at
the whistle of the attendant and follow him through the
whole house. In the dog, as might be expected from its
greater intellectual development, recovery is more imperfect
than in the bird, much more imperfect than in the frog.
But even in the dog wonderful resources lie hidden in the
grey matter of the central neural axis, and are called forth
by degrees to replace the lost powers of the cerebral cortex.
It is true that a brainless dog is a less efficient animal than
a brainless fish, or even than a brainless frog ; but in favour-
able cases even in the dog, the movements of walking may
still be carried out with tolerable precision in the absence
of the cerebral hemispheres. The animal can swallow food
pushed well back into the mouth, although it cannot feed
itself. Stupid and listless as it is compared with the normal
dog, it seems to be by no means devoid of the power of
experiencing sensations as the result of impressions from
without, nor of carrying on many mental operations of a
low intellectual grade.
Goltz had a dog which lived more than a year and a half without
its cerebral hemispheres, and another which lived thirteen weeks.
He believes that they had lost understanding, reflection, and memory,
but not sensation, special or general, nor emotions and voluntary
power. Their condition may be best described as one of general
imbecility. Hunger and thirst are present. They experience satis-
faction when fed, become angry when attacked, see a very bright
light, avoid obstacles, hear loud sounds, such as those produced by a
fog-horn, and can be awakened by them. They are not completely
deprived of sensations of taste and touch. But it ought to be re-
membered that the interpretation of the objective signs of sensation
in animals is beset with difficulties ; and although everybody admits
the accuracy of Goltz's description of what is to be seen, his inter-
pretation of the facts has been severely criticised, particularly by
H. Munk.
To the monkey it is probable that the loss of the cerebral
hemispheres is a heavier and more irremediable blow than
to the dog.
45
7o6
A MANUAL OF PHYSIOLOGY
We see, then, that homologous organs are not necessarily,
nor indeed usually, of the same physiological value in different
kinds of animals. A loss which perhaps hardly narrows the
range of the psychical, and certainl}' restricts only to a slight
extent the physical powers of a fish, cuts off from the dog
a great part, from the monkey almost all, of its intellectual
life, and is in man incompatible with life altogether.
The results of the removal of the entire cerebral hemi-
spheres help us to fix their position as a whole in the
physiological hierarchy. A more minute analysis shows us
that the cerebral cortex itself is not homogeneous in function,
that certain regions of it have been set aside for special
labours. Our knowledge of this localization of function in
the cerebral cortex has been deri\ed partly from clinical,
coupled with pathological observations on man, and partly
from the results of the
/2
e:m
removal or stimulation
of definite areas in
animals. And so varied
and extensive have been
the contributions from
both of these sources,
that it is difficult to
decide to which we owe
most.
It is a fact which might
appear strange and almost
inexplicable did the history
of science not constantly
present us with the like,
that thirty years ago the
universal opinion among
Fic;. 239.— MoroR Arkas ok Dog's Brain, physiologists, pathologists,
n, neck ;//., fore-limb ; h.L, hind-limb ; /, tail ; and physicians was that the
/, face; r.i.. crucial sulcus ;e;«.. eye movements; cerebral COrtex is inexcit-
*, dilatation of the pupil m both eyes, but especially , c • , • i-
in the opposite eye. All the areas are marked in able tO artlhcial Stimuli,
the figure only on the left side except the eye that no visible response
areas, whose position, to avoid confusion, is in- , ^Uf„:„„j f,^,-,, it
dicated on the right hemisphere. ^^n be obtauied from It
The great names of
Flourens and Magendie stood sponsors for this error, and re-
pressed research. In 1870, however, Hitzig had occasion to pass
a voltaic current through the brain of a soldier wounded in
the Franco-German war, and observed that movements of the eyes
THE CENTRAL XERVOUS SYSTEM
707
were produced, and, along with Fritsch, he entered on a series of
experiments. These observers were rewarded by finding that not
only was it possible to elicit muscular contractions by stimulation of
the cortex of the brain in the dog with voltaic currents, but that the
excitable area occupied a definite region in the neighbourhood of
the crucial sulcus, which
lies over the convexity
of the hemispheres
nearly at right angles to
the longitudinal fissure.
In this region they were
further able to isolate
several distinct areas,
stimulation of which was
followed by movements
respectively of the head,
face, neck, hind-leg, and
fore-leg. This was the
starting-point of a long
series of researches by
Ferrier, Munk, Horsley,
Schafer, Heidenhain,
and many others, on the
brains of monkeys as
well as dogs — researches
which have formed the
basis of an exact cortical
localization in the brain
of man, and have en-
riched surgery with a
new province. In these
later experiments the
interrupted current from
an induction machine
has been found the most
suitable form of stimulus (see Practical Exercises, p. 730).
Fig. 240. —Dog's Brain with Lesion.
A portion of the cortex indicated by the shaded area
was destroyed by cauteriaition. The symptoms were
complete blindness of the opposite eye (in this case the
right) ; weakness of the muscles of the limbs and of the
neck on the right side ; slight weakness of the limbs on
the left side. When the animal walked there was a
tendency to turn to the left in a circle. In eating or
drinking the head was turned to the left, so that the
mouth was oblique, and the right angle of the mouth
was lower than the left. The tail movements were
normal, and there was no deviation of the tail to one
side.
Motor Areas. — Lying around the fissure of Rolando, and
lapping over on the mesial surface of the hemisphere in this
region, are the so-called motor areas (Figs. 241, 242, 243).
They occupy the whole of the ascending frontal and parietal
convolutions, running forward a little into the horizontal
frontal convolutions, backward a little into the superior
parietal convolution, and turning over on the mesial surface
into the marginal convolution. Highest of all on the con-
vexity of the hemisphere lies the area of the leg ; below this,
in order, the areas for the arm, face, mouth, pharynx, and
45—2
7o8
A MANUAL OF PHYSIOLOGY
larynx. In front of the leg and arm areas lies the area of
the head, neck, and eyes, passing out into the posterior
portions of the first and second frontal convolutions. On
the mesial surface in the marginal convolution lie areas for
Fig. 241. — Lateral View of Left Hemisphere (Max), with Motor and
Sensory Areas.
The front of the brain is towards the left.
the head, arm, trunk, and leg in order from before back-
wards.
It is to be particularly noted (i) that within the larger
areas, such as those of the arm and leg, smaller foci can be
mapped off which are related to movements of the separate
joints — thus, in the leg area, the hip, knee, and ankle joints,
THE CENTRAL NERVOUS SYSTEM 709
and the great toe, are represented by separate and special
centres ; (2) that stimulation of any one of these areas leads,
not to contraction of individual muscles, but to contraction
Fig. 242.— Cerebral Cortex (Man) seen from Above.
The front of the brain is towards the right. The dotted line shows the position of
the fissure of Rolando, as fixed by Thane's rule (p. 711).
of muscular groups which have to do with the execution of
definite movements.
Fig. 243.— Motor and Sensory Areas ov Mesial Surface of Human
Brain.
The front of the brain is towards the right.
Removal of the whole of the motor cortex of one hemi-
sphere causes paralysis of movement on the opposite side
7IO A MANUAL OF PHYSIOLOGY
of the body. The paralysis is less marked in the case of
bilateral muscles that habitually act together than in the
case of those which ordinarily act alone. Thus the muscles
of respiration and the muscles of the trunk in general are,
although perhaps weakened, never completely paralyzed.
This is an indication that each member of such functional
pairs of muscles is innervated from both hemispheres ; and
this physiological deduction is supported by the anatomical
fact already referred to, that after removal of the motor
cortex, or injury to the pyramidal tracts in the internal
capsule or crus, some degeneration is found in the crossed
pyramidal tract on the side of the lesion, as well as in the
anterior pyramidal tract on that side and the opposite
crossed pyramidal tract (p. 658). It was supposed by some
that these fibres are really recrosscd, i.e., have decussated
twice — once, perhaps, in the medulla oblongata, and again
at a lower level in the cord ; but this view has since been
modified.
Removal of a single motor region leads to paralysis only
of the corresponding limb, or part of a limb, on the opposite
side. In the dog after a time the paralysis may more or
less completely disappear, the loss of the cortical centres on
one side being perhaps compensated by increased activity
of those that are left. In the monkey restoration is less
complete ; in man it is more imperfect still.
The movements with which the motor areas are con-
cerned are essentially skilled movements, and we may sup-
pose that it is more difficult for a monkey to educate again
a centre for such complex and elaborate manceuvres as are
performed by its hand than for a dog to regain cortical
control of the comparatively simple movements of its paw.
In man in cases of hemiplegia, when the patient lives for
some time, a certain amount of recovery usually takes place,
especially in young persons, in the paralyzed leg, but much
less in the paralyzed arm.
It is in the light of the results obtained in monkeys, and by the
aid of clinical and pathological observations, that the motor areas in
man have to a great extent been mapped out An extensive
haemorrhage involving the cerebral cortex on both sides of the fissure
of Rolando, or an embolus blocking the middle cerebral artery,
THE CENTRAL NERVOUS SYSTEM 711
causes paralysis of the opposite side of the body. An embolus of
a branch of the middle cerebral artery causes paralysis of the muscles,
or rather movements, represented in the area supplied by it. A
tumour causes symptoms of irritation, motor or sensory — con-
vulsions beginning in, or an aura referred to, the j^arts represented
in the regions on which it presses. In connection with the localiza-
tion of lesions in the motor area of the cortex, and operative inter-
ference for their cure, the exact position of the fissure of Rolando
becomes important ; and Thane has given the following simple
method for fixing it : The point midway between the root of the nose
and the occipital protuberance is fixed by measuring the distance with
a tape. The upper end of the fissure of Rolando lies half an inch
behind this middle point. The fissure makes an angle of 07 ' with the
longitudinal fissure (Fig. 242).
When we have deducted from the cortex of the hemi-
sphere the whole Rolandic area, there still remains a large
portion unaccounted for. The greater part of the frontal
lobe anterior to the ascending frontal convolution responds
to stimulation by neither motor nor sensory sign ; and by a
process of exclusion it has been supposed that it is the seat
of intellectual processes. Extensive destruction and loss of
substance of this pre-frontal region may occur without any
marked symptoms, except some restriction of mental power
or loss of moral restraint. Thus in the famous 'American
crowbar case,' an iron bar completely transfixed the left
frontal lobe of a man engaged in blasting. Although
stunned for the moment, he was able in an hour to climb a
long flight of stairs, and to answer the inquiries of the
surgeon. Finally, he recovered, and lived for nearly thirteen
years without either sensory or motor deficiency, except that
he suffered occasionally from epileptic convulsions. But his
intellect was impaired ; he became fitful and vacillating,
profane in his language and inefficient in his work, although
previously decent in conversation and a diligent and capable
workman.
Sensory Areas — Visual Centres. — In the occipital lobe an
area of considerable extent has been found, destruction of
which causes hemianopia, i.e., loss of vision in the corre-
sponding halves of the retinae. Thus, if the right occipital
cortex is destroyed, the right halves of the two retinae are
paralyzed, and the left half of the field of vision is a blank.
Destruction of this region on both sides causes, according
7i:
A MAM'AL or PHYSIOLOGY
to Munk, complete blindness. Ferrier believes that for this
it is necessary that the angular gyrus should also be de-
stroyed. When the same region is stimulated, the eyes
and head are turned to the left — that is, to the opposite
side. The movements differ from those produced by stimu-
lation of the Ro-
landic area. They
are not so certain,
their latent period is
longer, and they are
considered to be not
direct, but reflex
movements. It can-
not be doubted that
the occipital region
is concerned in
vision, and it is a
very natural sugges-
tion that the move-
ments are the result
of visual sensations
in the excited occi-
pital cortex. The
right occipital lobe is
concerned with vision
in the right halves of
the two retinae. Now,
under normal con-
ditions a visual image
would be cast on the
two right retinal
halves by an object placed towards the left of the field.
The movements of the head and eyes to the left may there-
fore be plausibly explained as an attempt to look at, and a
rotation towards, the supposed object.
The pathological evidence is very clear that disease of the occipital
lobe, especially of the cuneus, causes hemianopia in man. A limited
lesion may even be associated with an incomplete hemianopia, and
cases have been recorded in which colour hemianopia (blindness
of the corresponding halves of the two retince for coloured objects)
Fii;. 244.^Di.\GKAM OF Relations of Occi-
pital Cortex to the Retin.^.
RO, LO, right and left occipital cortex ; RE,
LE, right and left retina ; C, optic chiasma ; RF,
LF, right and left visual fields. The continuous
lines passing back from the retince to the occipital
cortex represent the crossed, the broken lines the
uncrossed, fibres of the optic nerves and tracts.
THE CENTRAL NERVOUS SYSTEM 713
existed with normal vision for white light. Sometimes dimness of
vision in the opposite eye (crossed amblyopia), and not hcmianopia,
is caused by a lesion of the occipital cortex. It seems impossible to
explain this and other facts without postulating the existence of more
than one visual centre in the occipital lobe; and it has been supposed
that in the angular gyrus a higher visual centre exists which is con-
nected with the lower occipital centres for the two halves of the
opposite eye. Thus, the right angular gyrus would be in cormection
with the part of the right occipital cortex which has to do with
vision in the nasal half of the left eye, and with the part of the left
occipital cortex which has to do with vision in the temporal half of
that eye. It has been stated that after complete removal of the
occipital lobes in young monkeys, the power of vision, lost for a
time, is gradually regained, the growth of new nerve-cells and nerve-
fibres having made good the deficiency (Vitzou).
Auditory Centre. — On the outer surface of the temporo-
sphenoidal lobe, in the hinder portion of the first and second
temporal convolutions, lies an area associated with the
sense of hearing. Stimulation in the region of the first
temporal convolution may cause the animal to prick up its
ear on the opposite side. Destruction of this area on both
sides is followed by complete and irremediable loss of hear-
ing. If it is destroyed only on one side there is deafness of
the opposite ear, which, however, is gradually recovered
from. In deaf-mutes the first temporal convolution may be
atrophied. There is evidence that the posterior corpora
quadrigemina and the mesial geniculate body form an
inferior relay on the route between the fibres of the auditory
nerve and the temporal cortex.
Centre for Smell. — As to the position of the centre for
smell, direct experiment on animals cannot teach us much,
for if the outward tokens of visual and auditory sensations
are dubious and fluctuating, still more is this the case with
the signs of sensations of smell. A further source of fallacy
is the fact that other sensations than those of smell are
caused by stimulation of the mucous membrane of the nose.
Substances like ammonia, for example, affect entirely the
endings of the trigeminus, which is the nerve of common
sensation for the nostrils. Pathological and clinical evidence
would be of great value, but it is as yet scanty, and of itself
indecisive. So far as it goes, however, it undoubtedly
supports the view derived from the anatomical connections
714 A MANUAL OF PHYSIOLOGY
of the olfactory tracts, that the centre for smell is situated
in the uncinate gyrus on the mesial aspect of the temporal
lobe, for the olfactory tract may be traced into this region.
In animals with a very acute sense of smell, this gyrus
is magnified into a veritable lobe, called from its shape
the pyriform lobe ; from its supposed function, the rhin-
encephalon.
Ordinary sensation and in part tactile sensation are located
on the mesial surfaces of the hemispheres — by Ferrier in the
hippocampal convolution, by Schafer and Horsley in the
gyrus fornicatus. But whatever may be the truth in this
matter, it would appear that this is not the only region
where ordinary sensation is represented. For example, it
is certain that the Rolandic area has sensory as well as
motor functions.
Pathological evidence in man agrees, upon the whole, with
wonderful precision with the results of experiments on
animals ; and, indeed, before any experimental proof of the
minute and elaborate subdivision of the cortex had been
obtained, Broca had already, from the phenomena of the
sick-bed and the post-mortem room, located a centre for
speech in the left inferior frontal convolution, and Hughlings
Jackson had associated pathological lesions of the Rolandic
area with certain cases of epileptiform convulsions.
Aphasia. — In most persons the inferior frontal convolution
on the left side is concerned in the expression of ideas in
spoken or written language. It is even said that oratorical
powers have been found associated with marked development
of this convolution (as in the case of Gambetta, the French
statesman). Words are, at bottom, arbitrary signs by
which certain ideas are expressed. The power of intelligent
communication by spoken or written language may be lost :
(i) by paralysis of the muscles of articulation or the muscles
which guide the pen ; (2) by inability to hear or see the
spoken or written word, i.e., by deafness or blindness ; (3) by
inability to comprehend the meaning of spoken or written
language, although sensations of hearing and sight may not
be abolished — that is to say, by inability to interpret the
auditory or visual symbols by which ideas are conveyed ;
THE CENTRAL NERVOUS SYSTEM 715
(4) by inability to clothe ideas in words, although the ideas
conveyed by speech or writing may be perfectly compre-
hended. Neither (1) nor (2) is considered to constitute the
condition of aphasia ; (3) represents what is called amnesia,
or sensory aphasia ; (4) is aphasia in the ordinary restricted
sense, or motor aphasia. In motor aphasia the patient
understands quite well what is said to him, and also
knows quite well what to reply, but the words necessary to
express his meaning do not come to him. He makes no
answer whatever, or strings together a series of words each
correctly articulated but having no meaning, or utters a
jargon not composed of known words at all. The failure
does not lie in the articulatory mechanism. The patient
uses the same muscles of articulation, without any sign of
impairment of function, for chewing and swallowing his
food. He may sometimes sing a song without a single slip
in words or measure, and yet be unable to speak or write it.
In certain cases the change is confined to loss of the power
of spontaneous speech, and the patient may be able to read
intelligently. Sometimes he can express his ideas in speech
but not in writing (agraphia). Sometimes the loss is re-
stricted to certain sets of ideas. For example, a boy was
injured by falling on his head. Typical symptoms of motor
aphasia developed, but the power of dealing with ideas of
number was not interfered with, and the boy continued to
learn arithmetic as if nothing had happened. Proper names
and nouns are more easily lost than adjectives and verbs.
Motor aphasia is generally accompanied by paralysis, fre-
quently transient, of voluntary movement on the right side,
sometimes amounting to complete hemiplegia, but more
often involving the arm or the head and face alone. This
association is explained by the proximity of the inferior
frontal convolution to the motor areas of the arm and head,
and their common blood-supply.
Why, now, is it that motor aphasia is commonly due to
a lesion in the left hemisphere alone ? The answer to this
question is partly supplied by the important and curious
observation that in left-handed individuals damage to the
right inferior frontal convolution may cause aphasia. In
7l6 A MANUAL OF PIIYSIOlAX.Y
the rij^ht-handed man the motor areas of the left hemisphere
may be supposed to be more highly educated than those of
the right hemisphere. The movements of the right side
which they initiate or control are stronger and more delicate
and precise than those of the left side. It is only necessary
to assume that this process of specialization, of selective
training, has been carried on to a still greater extent in the
left frontal convolution, that in most men the speech-centre
there has taken upon itself the whole of the labour of
clothing ideas in words, leaving to the right centre only its
primitive but undeveloped powers. In left-handed persons
the speech-centre on the right side may be supposed to
share in the general functional development of the right
hemisphere. That great capabilities are lying dormant
in the right speech-centre of the ordinary right-handed
individual is indicated by the fact that after complete de-
struction of the left inferior frontal convolution the power
of speech may be to a considerable extent, though slowly
and laboriously, regained ; and it is said that this second
accumulation may be swept away, and without remedy, by
a second lesion in the right inferior frontal convolution.
But frail is the tenure of life in a person who has twice
suffered from such a lesion ; and it is possible that recovery
might take place to some extent even after destruction of
both speech centres, if the patient only lived long enough.
Temporary aphasia may occur without any structural
change in the speech-centre — for example, during an attack
of migraine. In children it may even be caused by some
comparatively slight irritation in the digestive tract, such as
that due to the presence of a tape-worm.
Sensory Aphasia. — In typical motor aphasia spoken and
written words convey to the patient their ordinary meaning.
They call up in his mind the usual sequence of ideas, but
the chain is broken at the speech-centre, and the outgoing
ideas cannot be clothed in words. In another class of cases
the patient may be perfectly capable of rational speech ; he
may talk to himself or on a set topic with fluency and sense,
but he may be unable to respond to a question or read a
single line of print. Damage to two regions of the brain
rilE CENTRAL XERVOUS SYSTEM 717
has been found associated with this strange condition, (i)
the occipital, (2) the temporal cortex. When the lesion is
confined to the occipital region, spoken language is perfectly
understood, written language not at all {word -blindness).
When the temporal region is alone affected, it is the spoken
word that is missed, the written that is understood {word-
deafness). Sensory, like motor aphasia may exist in any
degree of completeness, from absolute word-deafness or
word-blindness, in which no spoken or printed word calls
up any mental image, to a condition not amounting to much
more than a marked absence of mind or unusual obtuseness.
Motor and sensory aphasia may be present together. In
well-marked word-deafness speech is always interfered with
to some extent.
Cortical Epilepsy. — While it was still believed that the
cortex w^as inexcitable, epilepsy was supposed to be ex-
clusively due to morbid conditions, structural or functional,
of the medulla oblongata (Kussmaul and Tenner). Some
more recent writers have put forward precisely the opposite
opinion, that the disease is always cortical in origin (Unver-
richt, etc.). What we know for certain is that some cases,
but only a minority, are associated with irritative lesions in
or near the Rolandic area (cortical or Jacksonian epilepsy).
It has even been found possible to localize the position
of the lesion from the part of the body in which the lit, or
the aura (the sensation or group of sensations peculiar to
each case, which precedes and announces it), begins. For
example, if the convulsions commence with a twitching of
the right thumb and extend over the arm, or if the aura
consists of sensations beginning in the thumb, there is a
strong presumption that the seat of the lesion is the part of
the arm-area known as the ' thumb-centre ' in the left
cerebral hemisphere. It is the seat of the convulsion at its
commencement, not the regions to which it may afterwards
spread, that is important in diagnosing the position of the
lesion. For just as strong or long-continued stimulation of
a given ' centre ' of the motor cortex may give rise to con-
tractions of muscles associated with other ' centres,' so the
excitation set up by localized disease may spread far and
7i8 A MANUAL OF PHYSIOLOGY
wide from its original focus, involving area after area of the
Rolandic region first in the one hemisphere and then in the
other. The part of the body to which a sensory aura is
referred is as significant an indication of the seat of the
discharging lesion as is the part of the body which first
begins to twitch.
This is one of the proofs that the Rolandic region is not a purely-
motor, but a sensori-motor area. From the field of experiment
further evidence is forthcoming.
(i) It has been found that if the posterior roots of the nerves
supplying one of the limbs be cut in a monkey, all the most delicate
and skilled movements of the limb are either greatly impaired or
totally abolished (Mott and Sherrington). The limb is not used for
progression or for climbing, but hangs limp, and apparently helpless,
by the side of the animal. That this condition is not due to any
loss of functional power by the peripheral portion of the motor path
may be assumed, since the anterior roots remain intact. That it is
not due to any want of capacity on the part of the motor centres to
discharge impulses when stimulated may be shown by exciting the
cortical area of the limb — either electrically or by inducing epileptic
convulsions by intravenous injection of absinthe — when movements
of the affected limb take place just as readily as movements of the
sound limbs. The cause of the impairment of voluntary motion,
then, can only be the loss of the afferent impulses which normally
pass up to the brain, and presumably to the motor cortex. When
only one sensory nerve-root is cut, no defect of movement can be
seen ; and this is evidently in accordance with the fact already men-
tioned (p. 666), that complete anaesthesia of even the smallest patch
of skin is never caused by section of a single posterior root. And
that it is the loss of impulses from the skin which plays the chief
part is shown by the fact that after division of the posterior roots
supplying the muscles of the hand or foot, which only partially inter-
feres with the sensory supply of the skin, joints, sheaths of tendons,
etc., movement is unimpaired ; while section of the nerve-roots sup-
plying the skin, those of the muscles being left intact, causes extreme
loss of motor power.
(2) If a strength of stimulus be sought which will just fail to cause
contraction of the muscular group related to a given motor area, and
a sensory nerve, or, better, a sensory surface (best of all, the skin
over the corresponding muscles), be now stimulated, contraction will
occur — that is to say, the excitability of the motor centres will be
increased. This shows that the motor region is en rapport not only
with efferent, but also with afferent fibres, that it receives impulses as
well as discharges them.
The same experiment is a proof that the results of excitation of
the motor cortex are due to stimulation of the grey matter, and not,
as has been asserted, of the white fibres of the corona radiala. It is
undoubtedly possible to excite these fibres by electrodes directly
THE CENTRAL NERVOUS SYSTEM 719
applied to the motor cortex, but in the latter case the current has
to be made stronger than is sufficient to excite the grey matter
alone. Further evidence is afforded by the following facts : {a) The
'period of delay,' that is, the period which elapses between stimula-
tion and contraction, is greater by nearly 50 per cent, when the
cortex is stimulated than when the white fibres are directly excited.
(/') Morphia greatly increases the period of delay for stimulation of
the cortex, and at the same time renders the resulting contractions
more prolonged than normal, while the results of direct stimulation
of the white fibres are much less, if at all, affected, {c) Mechanical
stimulation of the motor areas also causes appropriate movements.
id) Stimulation of the grey matter, when separated from tlie sub-
jacent white matter by the knife but left in position, is without
effect unless the strength of stimulus be increased, although twigs of
the current ought, of course, to pass into the corona radiata as easily
as before.
Evidence that the phenomena are not due to accidental excitation
of the corona radiata is a fortiori evidence that they are not caused
by escape of current to the basal ganglia, for the distance of the
basal ganglia from the larger part of the motor cortex is much
greater than the thickness of the grey matter ; and, indeed, that portion
of the grey matter at the bottom of the Sylvian fissure which lies
nearest to the basal ganglia does not respond to stimulation by motor
effects.
Localization of Function in the Central Nervous System. — Let
us now consider a little more closely the real meaning of this
localization of function. Scattered all over the grey matter of the
primitive neural axis, and, as we have seen, over the grey mantle of
the brain as well, are numerous ' centres ' which seem to be related
in a special way to special mechanisms, sensory, secretory or motor.
The question may fitly be asked whether those centres are really dis-
tinct from each other in quality of structure or action, or whether
they owe their peculiar properties solely to differences in situation
and anatomical connection. It is clear at the outset that the nature
of the work in which a centre is engaged must be largely determined
by its connections. The kind of activity which goes on in the vaso-
motor centre in the bulb, for example, may in no essential respect
differ from that which goes on in the respiratory centre. The calibre
of the bloodvessels will alter in response to a change of activity in
the one because it is anatomically connected with the muscular coat
of the bloodvessels. The rate or depth of the respiratory movements
will alter in response to a change of activity in the other because it
is connected with muscles which can act upon the chest-walls.
The localization of function in the cerebral cortex has been likened
to the localization of industries in the multiplex commercial life of
the modern world. The barbarian household in which cloth is
woven and worked into garments, sandals or moccasins cobbled
together, rough pottery baked in the kitchen fire, and all the rude
furniture of the lodge fashioned by the hands which built it, and
which rest beneath its roof at night — this state of things where centrali-
720 A MANUAL OF PHYSIOLOGY
zation has not yet begun, it has been said, is a picture of what goes
on in the undeveloped brains of the frog, the pigeon, and the rabbit.
The ' diffusion ' of industries which is characteristic of a primitive
state has given place among the most highly civilized men to extreme
centralization and concentration. Manchester spins cotton and
Liverpool ships it. Chicago handles wheat and pork that have been
produced on the prairies of Minnesota and Illinois. Amsterdam
cuts diamonds. Munich brews beer. Lyons weaves silk. New
York and London are centres of finance. This, it is said, is the
picture of the highly specialized brain of a monkey or a man. But
ingenious and alluring though such analogies are, they do not rest
upon a sufficient basis of fact.
It has never been shown — nor is it likely that the proof will soon
be forthcoming — that there is any difference whatever in the physical,
chemical or psychical j^rocesses which go on in the various centres
of the Rolandic cortex. It may be supposed, indeed, that the so-
called sensory areas of the cortex differ more widely in their internal
activity from the motor areas than the latter do among themselves,
and that the activity of the anterior portion of the brain, the portion
which has been credited par excellence with psychical functions,
differs in kind, not merely in degree, from that of all the rest. But,
as we have just seen, even the motor areas have sensory functions ;
and although a cast-iron physiology may explain this by the assump-
tion of ' sensory' as well as 'motor' cells in the Rolandic area, there
is absolutely nothing to contradict the supposition that the discharge
of energy from the most circumscribed motor area or element (be it
cell, or nervous network, or both) may be accompanied not only with
consciousness, but with a high degree of psychical activity. And,
indeed, some writers have supposed that such a consciousness of, or
even conscious measurement of, the discharge from the motor areas
is the basis of the muscular sense (Bain, Wundt).
So far, at least, as the Rolandic region and the grey matter imme-
diately around the neural canal is concerned, the analogy of an
electrical switch-board connected with machines of various kinds
might be more correct. Touch one key or another, and an engine
is set in motion to grind corn, or to saw wood, or to light a town.
The difference in result lies not in any difference of material or
workmanship in the switches, but solely in the difference in their
connections.
Grey matter in the upper part of the Rolandic cortex is excited,
and the muscles of the leg contract. Grey matter around the lower
part of the fissure is excited, and there are movements of the face
and mouth. Grey matter in the medulla oblongata is excited,
and the salivary glands pour forth a thin, watery fluid, poor in
proteids, and containing an amylolytic ferment. Another portion of
grey (?) matter in the medulla is thrown into activity, and the pan-
creatic ducts become flushed with a thick secretion, rich in proteids
and in ferments which act on proteids, starch, and fat. Here, too,
there is a variety in result according as one or another nervous
switch is closed ; here, too, the variety is due, not to essential
THE CENTRAL NERVOUS SYSTEM 721
differences in the structure or the activity of the nervous centres, but
to their connection, by nervous paths, with peripheral organs of
different kinds. There is, indeed, a speciaHzation, a locahzation, of
function, but the locaUzation is at the periphery, the speciahzation is
in the peripheral organs.
It may be asked whether, if this is the case for the peripheral
organs of efferent nerves, the converse does not hold true for the
afferent nerves — in other words, whether the localization here is not
at the centre. And that there is in some degree a central localization
of sensation may be considered proved by the well-known clinical
fact, already referred to, that sensations of various kinds may be pro-
duced by pathological changes in the cortex. For example, a tumour
involving the upper part of the temporal lobe may give rise to
epileptiform convulsions preceded by an auditory aura, a sound, it
may be, resembling the ringing of bells ; a tumour involving the
occipital region may cause a visual aura, and so on. Central sensory
localization is, indeed, inevitable if we accept the old doctrine of
'specific energy.' If the impulses set up in the auditory nerve
when sound impinges on the tympanic membrane do not differ
essentially from those set up in the optic nerve when a ray of light
falls upon the retina, or from those set up in the trigeminal nerve by
the irritation of a carious tooth, or from those set up in certain fibres
of all cutaneous nerves when a warm body comes in contact with the
skin ; then, since the results in consciousness are very different, we
must assume that somewhere or other in the central nervous system
there exist organs that are differently affected by the same kinds of
afferent impulses — in other words, that sensory localization is at the
centre. On this view, the visual areas in the cortex respond to all
kinds of stimuli by visual sensations ; the auditory areas by sensations
of sound ; and possibly the whole or part of the limbic lobe (the
convolutions lying around the corpus callosum on the mesial surface
of the hemisphere) by sensations of touch and pain.
But while it cannot be doubted that special sensory regions exist in
the grey matter of the brain, there is no reason to suppose that the
nerve-impulses which travel up the optic and up the auditory nerve
are absolutely similar until they have reached the visual and auditory
centres, and that there they suddenly become, or produce, sensations
absolutely different. And it would seem that the tendency of research
is at present to increase the evidence in favour of a certain amount
of sensory specialization at the periphery, and therefore to diminish
the scope, if not the necessity, of such a specialization in the brain.
For example, when an ordinary nerve-trunk is touched, the resultant
sensation is not one of touch. If there is any sensation at all, it is
one of pain. Heating or cooling a naked nerve-trunk gives rise to
no sensations of temperature. When the ulnar nerve is artificially
cooled at the elbow, the first effect is severe pain in the parts of the
hand supplied by the nerve. The pain disappears somewhat abruptly
as cooling goes on, and is succeeded by gradual loss of all sensation,
the sensations of touch, pain and temperature disappearing in the ulnar
area of the hand in the order named ; but the cooling of the nerve-trunk
46
722 A MAiVUAL OF PHYSIOLOGY
does not give rise to any sensation of cold (Weir Mitchell). Stimu-
lation of the end organs is essential in order that sensations of touch
and temperature should be experienced. The tradition which has
come down from the older surgery before the days of ancesthetics,
that when the optic nerve was cut in removing the eyeball the patient
experienced the sensation of a flash of light, was long looked upon
as the strongest prop of the law of specific energy. But neither the
evidence of the alleged fact nor the consequences deduced from it
have escaped modern criticism. And it is possible that in some
cases, at least, the retina was excited — directly by mechanical stimu-
lation, or by means of fibres carrying impulses peripherally (?) in the
optic nerve — at the moment when the knife entered it, and that
sufificient time elapsed before the section was completed for the ex-
citation to pass up across an isthmus of uncut fibres. Ewald has
indeed stated that even after extirpation of the end organs of the
auditory nerve in the pigeon, sounds too feeble to excite ordinary
tactile nerves are still heard so long as the nerve-trunk is intact.
But the explanation of this might be either that the impulses set up
in this nerve by the mechanical stimulation of aerial waves are of a
special kind, and therefore result in a special sensation, or that, the
impulses being alike in the auditory and other nerves, the former is
peculiarly susceptible to sound-waves. In the first case a certain
amount of specialization in the afferent impulses would be proved to
be accomplished before they reach their centres. One reason, then,
why excitation of the temporal cortex by impulses falling into it along
the auditory nerve-fibres causes a sensation different from that caused
by impulses reaching the occipital cortex through the fibres of the
optic nerve may be a difference in the nature of the impulses. If
this were the only reason, it would follow that were it possible
to physiologically connect the fibres of the optic radiation with the
temporal cortex, and those of the temporal radiation with the
occipital cortex, sights and sounds would still be perceived and dis-
criminated in a normal manner, although now the integrity of the
occipital lobe would be bound up with the perception of sound, the
integrity of the temporal lobe with visual sensation. This state of
affairs would corresi)ond to complete specialization for sensation in
the peripheral organs, complete absence of specialization in the
centres. On the other hand, it is conceivable that, after such an
ideal experiment, sound-waves falling on the auditory apparatus
might cause visual sensations, and luminous impressions falling on
the retina sensations of sound. This would correspond to complete
specialization of sensation in the centres, complete absence of
specialization at the periphery. A third possibility would be that
the ' transposed ' centres, responding at first feebly or not at all to
the new impulses, might, by slow degrees, become more and more
excitable to them. This would correspond to a peripheral specializa-
tion, combined with a tendency to development of central specializa-
tion. And, indeed, it is not easy to conceive in what way, except
as the result of differences in the nature of impulses coming from
THE CENTRAL NERVOUS SYSTEM 723
the periphery, specialization of sensory areas in the central nervous
system could have at first arisen.
Reaction Time. — Just as in a reflex act a certain measure-
able time {reflex time) is taken up by the changes that occur
in the lower nervous centres, so we may assume that in all
psychical processes the element of time is invoh^ed. And,
indeed, when the interval that elapses between the applica-
tion of a stimulus and the signal which announces that it
has been felt (reaction time) is measured, it is found that the
cerebral processes associated with the perception of the
simplest sensation and the production of the simplest
voluntary contraction is longer than the time which
the spinal centres require for the elaboration of even com-
plex and co-ordinated reflex movements. Suppose, e.g.,
that the stimulus is an induction shock applied to a given
point of the skin, and that the signal is the closing of
the circuit of an electro-magnet, then, if both events are
automatically recorded on a revolving drum, the interval
can be readily determined. It is evident that this includes,
not only the time actually consumed in the central pro-
cesses, but also the time required for the afferent impulse
to reach the brain, and the efferent impulse the hand,
along with the latent period of the muscles. The time
taken up in these three events can be approximately cal-
culated, and when it is subtracted, the remainder repre-
sents the reduced or corrected reaction time ; that is, the
interval actually spent in the centres themselves. This is
by no means a constant. It is influenced not only by the
degree of complexity of the psychical acts involved, and the
mental attitude of the person (whether he expects the
stimulus or is taken by surprise, whether he has to choose
between several possible kinds of stimuli and respond to
only one, etc.), but it varies also for different kinds of sensa-
tion, for the same sensation at different times, and as is
recognised in the. personal eqication of astronomers, in different
individuals. For sensations of touch and pain it may be
taken as one-ninth to one-fifth, for hearing one-eighth to
one-sixth, and for sight one-eighth to one-fifth of a second.
So that the proverbial quickness of thought is by no means
46 — 2
724 A MANUAL OF PHYSIOLOGY
great, even in comparison with that of such a gross process
as the contraction of a muscle (one-tenth of a second). Nor
is it the case that the man ' of quick apprehension' has
always a short reaction time, or the dullard always a long
one, although in all kinds of persons practice will reduce it.
Sleep. — Certain gland-cells, certain muscular fibres, and
the epithelial cells of ciliated membranes, never rest, and
perhaps hardly ever even slacken their activity. But in most
organs periods of action alternate at more or less frequent
intervals with periods of relative repose. In all the higher
animals the central nervous system enters once at least in
the twenty-four hours into the condition of rest which we
call sleep. What the cause of this regular periodicity is
we do not know. Some have suggested that sleep is in-
duced bv the action of the waste products of the tissues, and
especially lactic acid, when they accumulate beyond a certain
amount in the blood, or in the nervous elements themselves.
And actual histological changes have been described in
nerve-cells as the result of physiological fatigue or of fatigue
induced by artificial stimulation of nerves (Hodge). Others
have looked for an explanation to vascular changes in the
brain, but so far are the possible causes of such changes
from being understood, that it is even yet a question
whether in sleep the brain is congested or anaemic. In
coma, a pathological condition which in some respects has
analogies to profound and long-continued sleep, the brain is
congested, and the proper elements of the nervous tissue
presumably compressed. And artificial pressure (applied by
means of a distensible bag introduced through a trephine
hole into the cranial cavity) may cause not only unconscious-
ness, but absolute anaesthesia. But it is possible that this
artificial increase of intracranial pressure may produce its
effects bv rendering the brain anaemic, and it has been
actually observed that the retinal vessels, as seen with the
ophthalmoscope and the vessels of the pia mater exposed
to direct observation in man by disease of the bones of the
skull, or in animals by operation, shrink during sleep.
Further, a condition closely resembling, if not identical with,
natural sleep can be induced by tying the cerebral arteries.
THE CENTRAL NERVOUS SYSTEM 725
So that the balance of evidence is decidedly in favour of the
view that sleep is associated with an?emia, although it is not
a good argument to say, as some writers have done, that
when the brain rests the quantity of blood in it uinst be
supposed, as in other resting organs, to be diminished.
For when the whole body rests, as it does in sleep, it has as
much blood in it as when it works ; in sleep, therefore, if
some resting organs have less blood than in waking life,
other resting organs must have more ; and it is the province
of experiment to decide which are congested and which
anaimic.
In general, the depth of sleep, as measured by the intensity of
sound needed to awaken the sleeper, increases rapidly in the first
hour, falls abruptly in the second, and then slowly creeps down to
its minimum, which it reaches just before the person awakens. As
to the amount of sleep required, no precise rules can be laid down.
It varies with age, occupation, and perhaps climate. An infant,
whose main business is to grow, spends, or ought to spend, if mothers
were wise and feeding-bottles clean, the greater part of its time in
sleep. The man, whose main business it is to work with his hands
or brain, requires his full tale of eight hours' sleep, but not usually
more. The dry and exhilarating air of some of the mland portions
of North America, and perhaps the plains of Victoria and New
South Wales, incites, and possibly enables a new-comer to live for a
considerable period with less than his ordinary amount of sleep.
Idiosyncrasy, and perhaps to a still greater extent habit, have also a
marked influence. The great Napoleon, in his heyday, never slept
more than four or five hours in the twenty-four. Five or six hours
or less was the usual allowance of Frederick of Prussia throughout
the greater part of his long and active life.
Hypnosis is a condition in some respects allied to natural slumber ;
but mstead of the activity of the whole brain— or perhaps we should
rather say, the whole activity of the brain — being in abeyance, the
susceptibility to external impressions remains as great as in waking
life, or may be even increased, while the critical faculty, which
normally sits in judgment on them, is lulled to sleep. The condi-
tion can be induced in many ways — by asking the subject to look
fixedly at a bright object, by closing his eyes, by occupying his atten-
tion, by a sudden loud sound or a flash of light, etc. The essential
condition is that the person should have the idea of going to sleep,
and that he should surrender his will to the operator. In the hypnotic
condition the subject is extremely open to suggestions made by the
operator with whom he is efi rapport. He adopts and acts upon
them without criticism. If, for example, the hypnotizer raises the
subject's arm above his head, and suggests that he cannot bring it
down again, it stays fixed in that position for a long time without any
726 A MANUAL OF PHYSIOLOGY
appearance of fatigue ; or the whole body may be thrown, on a mere
hint, into some unnatural pose in which it remains rigid as a statue.
Suggested hemiplegia or hemianaisthesia, or paralysis of motion
and sensation together or a])art in limited areas, can also be realized ;
and surgical operations have been actually performed on hypnotized
persons without any appearance of suffering. If, on the other
hand, the operator suggests that the subject is undergoing intense
pain, he will instantly take his cue, writhing his body, pressing
his hands upon his head or breast, and in all respects behaving
as if the suggestion were in accord with the facts. If he is told that
he is blind or deaf, he will act as if this were the case. If it is sug-
gested that a person actually present is in Timbuctoo, the subject
will entirely ignore him, will leave him out if told to count the
persons in the room, or try to walk through him if asked to move in
that direction. What is even more curious is that the organic
functions of the body are also liable to be influenced by suggestion.
A postage-stamp was placed on the skin of a hypnotized person, and
it was suggested that it would raise a blister. Next day a blister was
actually found beneath it. The letter K, embroidered on a [liece of
cloth, was suggested to be red-hot. The left shoulder was then
' branded ' with it, and on the right shoulder appeared a facsimile of
the K as if burnt with a hot iron. 'i1ie secretions can be increased
or diminished, subcutaneous hemorrhages, veritable stigmata, can be
caused, and many of the ' miracles ' of Lourdes and other shrines,
ancient and modern, repeated or surpassed by the aid of hypnotic
suggestion. Hypnotism has also been practically employed in the
treatment of various diseases, and particularly in functional derange-
ments of the nervous system. But care and judgment are necessary
on the part of the operator, and although as a rule there is no diffi-
culty in putting an end to the condition by a suitable suggestion, it
is said that in rare instances grave mischances have occurred. There
seems to be no ground for the opinion that women are more easily
hypnotized than men. Out of more than a thousand persons, Liebault
found only seventeen absolutely refractory.
Relation of Size of Brain to Intelligence. — While it is the case
that some men of great ability have had remarkably heavy and richly
convoluted brains, it would seem that in general neither great size
nor any other anatomical peculiarity of the cerebrum is constantly
associated with exceptional intellectual power. In the animal
kingdom as a whole, there is undoubtedly some relation between
the status of a group and the average brain development within the
group. But that this is a relation which is complicated by other
circumstances than the mere degree of intelligence is sufficiently
shown by the fact that a mouse has more brain, in j^roporiion
to its size, than a man, and thirteen times more than a horse ; while
both in the rabbit and sheep the ratio of brain-weight to body-
weight is nearly twice as great as in the horse, in the dog only half
as great as in the cat, and not very much more than in the donkey.
The following tables, too, which illustrate the weight of the brain in
man at different ages, show that, although we might give ' the infant
THE CEXTRM. Nl'.RVOUS SYSTEM
phenomenon ' an anatomical basis, we should greatly overrate the
intellectual acuteness of the average baby if we were to measure it
by the ratio of brain to body-weight alone.
Age. Bruin-weight. Age.
I year. 8S5 grm. 8 years,
years. 909 ,, 10
1071
1099
1033
1147
1201
1 1
1 2
13
15
Biain-weight.
1045 grm.
i3'5 >.
1168 „
1286 „
1505 ..
1336 „
1414 „
Age.
10 — ^19
20 — 29
30—39
40—49
Men.
1411 grm .
1419 »
1424 ,-,
1406 „
Women.
1219 grm.
1260 ,,
1272
(Bischoff.)
Age. Men. Women.
50—59 1389 grm- 1239 grm.
60 — 69 1292 ,, 1219 ,,
70—79 1254 „ 1129 ,,
1272 „ 80—90 1303 „ 898 „
(Huschke.)
In some small birds the ratio is as high as i : 12, in large birds as
low as I : 1,200 ; in certain fishes a gramme of brain has to serve for
over 5 kilos of body. As a rule, especially within a given species,
the brain is proportionally of greater size in small than in large
animals.
The Circulation in the Central Nervous System. — The arrange-
ment of che cerebral bloodvessels has certain peculiarities which it is
of great importance to remember in connection with the study of
the diseases of the brain, many of which are caused by lesions in
the vascular system — hgemorrhage or embolism. Four great arterial
trunks carry blood to the brain, two internal carotids and two verte-
brals (Plate V., 4). The vertebrals unite at the base of the skull
to form the single mesial basilar artery, which, running forward in a
groove in the occipital bone, splits into the two posterior cerebral
arteries. Each carotid, passing in through the carotid foramen,
divides into a middle and an anterior cerebral artery ; the latter
runs forward in the great longitudinal fissure, the former lies in
the fissure of Sylvius. A communicating branch joins the middle
and posterior cerebrals on each side, and a short loop connects the
two anterior cerebrals in front. In this way a hexagon is formed at
the base of the brain, the so-called circle of Willis. While the anas-
tomosis between the large arteries is thus very free, the opposite is
true of their branches. All the arteries in the substance of the brain
and cord are ' end-arteries '; that is to say, each terminates within its
area of distribution without sending any communicating branches to
make junction with its neighbours. The consequence of these two
anatomical facts is: (i) that interference with the blood-supply of
the brain between the heart and the circle of Willis does not readily
produce symptoms of cerebral anasmia — e.g., both common carotids
may be tied, in a dog, without any harmful effect ; (2) that the block-
ing of any of the arteries which arise from the circle or any of their
728 A MANUAL OF PHYSIOLOGY
branches leads to destruction of the area supplied by it. The basal
ganglia are fed by twigs from the circle of Willis and the beginning
of the posterior, middle, and anterior cerebral arteries. Of these
the most important are the lenticulo-striate and lenticulo-optic
branches of the middle cerebral, which are given off near its origin,
and run through the lenticular nucleus into the internal capsule, and
thence to the caudate nucleus and optic thalamus respectively. The
chief part of the blood from the circle of Willis is carried by the
three great cerebral arteries over the cortex of the brain. The white
matter, with the exception of that in the immediate neighbourhood
of the basal ganglia, is nourished by straight arteries which penetrate
the cortex. The middle cerebral supplies the whole of the parietal
as well as that portion of the frontal lobe which lies immediately in
front of the fissure of Rolando and the upper part of the temporal
lobe. The rest of the frontal lobe is supplied by the anterior cere-
bral, and the occipital lobe, with the lower part of the temporal lobe,
by the posterior cerebral. The medulla oblongata, cerebellum, and
pons are fed from the vertebrals and the basilar artery before the
circle of ^^'iIlis has been formed.
PRACTICAL EXERCISES ON CHAPTER XII.
I. Hemisection of the Spinal Cord.* — Put a small dog under
morphia (p. 58), and fasten it on a holder in the prone position.
Clip and shave the skin over the three lower dorsal vertebrae. Wash
with soap and water, then with corrosive sublimate solution. Then,
giving ether if necessary, make a longitudinal incision under anti-
septic precautions down to the spines of the vertebic-e. Dissect the
muscles away from the spines and vertebral laminoe ; with bone
forceps or strong scissors cut through the lamina.- on each side of one
of the lower dorsal vertebra?, and remove the posterior portion of the
arch with the sj^inous process. The spinal cord will now come into
view, covered by the dura mater. Seize the dura with fine-pointed
forceps, and divide it freely in the mesial line. Then with a narrow-
bladed, sharp knife (a cataract-knife, e.g.) divide one half of the
cord. If there is not room enough to work satisfactorily in the
spinal canal, remove another vertebral arch. Sponge the wound
with iodoform gauze wrung out of normal saline solution previously
boiled and still as hot as the hand can bear ; then jiut in a row of
deep sutures, bring the skin together by stitches, and paint the surface
with collodion. Place the dog in its cage, and study the loss of
motion and sensation in the two hind-legs during ' the stage of shock '
(first few days), and then later on when a certain degree of recovery
has taken place. Test the sensibility for pain by pinching the legs
or toes ; for temperature by placing them in hot or cold water, and
comparing the promptitude with which they are withdrawn with
* This experiment is difficult, and is only to be attempted by advanced
students selected by the demonstrator.
/VvM CT/LA L EXERCISES 7 ^-')
what happens in the case of the fore-limbs ; for slight tactile sensation
by blowing through a tube on the legs. Note the rectal tempera-
ture from day to day, and observe whether the fieces and urine are
normally under control. After five or six weeks, or a longer or
shorter time according to whether the symptoms are stationary or
not, kill the animal by chloroform. Take put the brain and cord,
noting particularly the state of matters at the site of the hemi-
section. Harden first in Mi.iller's fiuid (essentially potassium bichro-
mate, with a little sodic sulphate) for ten days, then put portions into
Marchi's fluid (a mixture of one part of a i per cent, solution of
osmic acid with two parts of Milller's fluid), cut in celloidin, and
examine the degenerated tracts (p. 649).
2. Section and Stimulation of the Spinal Nerve-roots in the Frog.
—Select a large frog (a bullfrog, if possible). Pith the brain. Fasten
the frog, belly down, on a plate of cork. Make an incision in the
middle line over the spinous processes of the lowest three or four
vertebrit, separate the muscles from the vertebral arches, and with
strong scissors open the spinal canal, taking care not to injure the
cord by passing the blade of the scissors too deeply. Extend the
opening upwards till two or three posterior roots come into view.
Pass fine silk ligatures under two of them, tie, and divide one root
central to the ligature, the other peripheral to it. Stimulate the central
end, and reflex movements will occur. Stimulate the peripheral end :
no effect is produced. Now cut away the exposed posterior roots
and isolate and ligature two of the anterior roots, which are smaller
than the posterior. Stimulate the central end of one : there is no
effect. Stimulation of the peripheral end of the other causes con-
tractions of the corresponding muscles.
3. Reflex Action: Inhibition of the Reflexes.— Pith a frog (brain
only). Pass a hook through the jaws. Holding the frog by the hook,
dip one leg into a dilute solution of sulphuric acid ("2 to -5 per cent.),
and note with the stop-watch the interval which elapses before the
frog draws up its leg (Tiirck's method of determining the reflex time).
Wash the acid off with water. Now touch the skin of one thigh with
blotting-paper soaked in strong acetic acid. The leg is drawn up,
and the foot moved as if to get rid of the irritant. If the leg is held,
the other is brought into action. Immerse the frog in water to wash
away the acid. Again dip one leg into the dilute acetic acid, and
estimate the reflex time. Then apply a crystal of common salt to
the upper part of the spinal cord. If the opening made for pithing
the frog is not large enough to enable the cord to be clearly seen,
enlarge it. Again dip the leg in the dilute acid. It will either not be
drawn up at all, or the interval will be distinctly longer than before.
4. Action of Strychnia. — Pith a frog (brain only). Inject into
one of the lymph-sacs three or four drops of a o'l per cent, solution
of strychnia. In a few minutes general spasms come on, which have
intermissions, but are excited by the slightest stimulus. The extensor
muscles of the trunk and limbs overcome the flexors. Destroy the
spinal cord; the spasms at once cease, and cannot again be excited.
5. Excision of Cerebral Hemispheres in the Frog (Fig. 245). — Put
730 A MANUAL OF rilYSlOLOCY
a frog under a bell-jar with a small piece of cotton-wool soaked in ether.
In a few minutes it will be an;v;slhetized. Then, holding it in a cloth,
make an incision through the skin over the skull in the mesial line.
With scissors open the cranium about the position of a line drawn at
a tangent to the posterior borders of the two tympanic membranes.
Remove the roof of the skull in front of this line with forceps, scoop
out the cerebral hemispheres, and sew up the wound. As soon as
the animal has recovered from the ether, the phenomena described
at p. 704 should be verified. The frog will still swim when thrown into
water, will refuse to lie on its back, and will not fall if the board on
which it lies be gradually slanted. Let the frog live for a day, keeping
it in a moist atmosjhere ; then expose the bram again, determine the
reflex time by Tiirck's method ; apply a crystal of common salt to
the optic lobes, and re])cat the observation. The refle.x movements
will be completely inhibited or delayed. Remove the salt, wash with
normal saline, excise the optic lobes, and see whether the frog will
now swim.
6. Excision of the Cerebral Hemispheres in a Pigeon. — Feed a
pigeon for two or three days on dry food, etherize it by holding a
piece of cotton-wool sprinkled with ether over its beak, or inject into
the rectum \ gramme chloral hydrate. The pigeon being wrapped
up in a cloth, and the head held steady by an assistant, the feathers
are clipped off the head, an excision made in the middle line through
the skin, and the flaps reflected so as to expose the skull. Cut
through the bones with scissors, and make a sufficiently large o|)ening
to bring the cerebral hemispheres into view. They are now rapidly
divided from the corpora bigemina and lifted out with the handle of
a scalpel. The bleeding is very free, but may be partially controlled
by stuffing the cavity with pengawahr yambi, which should be re-
moved in a few minutes, the wound cleansed with iodoform gauze
wrung out of normal salt solution at 50" C, and sewed up. Study
the phenomena described on p. 704.
7. Stimulation of the Motor Areas in the Dog. — (<?) Study a
hardened brain of a dog, noting especially the crucial sulcus (Fig. 239),
the convolutions in relation to it, and the areas majtped out around it
by Hitzig and Fritsch and others, {b) Inject morphia under the skin
of a dog. Set \x\> an induction-coil arranged for tetanus, with a single
Daniell in the ])rimary circuit. Connect a pair of fine but not sharp-
pointed electrodes through a short-circuiting key with the secondary.
Fasten the dog on the holder, belly down, and put a large pad under
the neck to support the head. Clip the hair over the scalj). Feel
for the condyles of the lower jaw, and join them by a string across
the top of the head. Connect the outer canthi of the eyes by
another thread. The crucial sulcus lies a little behind the mid-point
between these two lines. Now give the dog ether if necessary, make
a mesial incision through the skin down to the bone, and reflect the
flaps on either side. Detach as much of the temporal muscle from
the bone as is necessary to get room for two trephine holes, the
internal borders of which must be not less than \ inch from the
middle line, so as to avoid wounding the longitudinal sinus. Care-
PR. 1 LTICA L EXERCISES
11^
fully work the trephine through the skull, taking care not to press
heavily on it at the last. Raise up ihe two pieces of bone with
forceps, connect the holes with bone forceps, and enlarge the opening
as much as may be necessary to reach all the motor areas. At this
stage only enough ether should be given to prevent suffering. Now
unbind the hind and fore limbs on the side opposite to that on which
the brain has been exposed, apply blunt electrodes successively to
the areas for the fore and hind limbs, and stimu-
late.* Contraction of the corresponding groups
of muscles will be seen if the narcosis is not
too deep. Movements of the head, neck, and
eyelids may also be called forth by stimulating
the motor areas for these regions. Stimulation
in front of the crucial sulcus may also cause
great dilatation of the pupil, the iris almost
disappearing. The dilatation takes place most
promptly, and is greatest on the opposite side,
but the pupil on the same side is also widened.
Even after section of both vago-sympathetic
nerves in the neck, a slow and slight dilatation
may be caused by cortical stimulation, greatest
perhaps on the same side. Repeat the whole
experiment on the opposite side of the brain.
In the course of his observations the student
will perhaps have the opportunity of seeing
general epileptiform convulsions set up by a
localized excitation. They begin in the group
of muscles represented in the portion of the
cortex directly stimulated. After the convulsions
have been sufficiently studied, they should be
again induced, and the stimulated motor area
rapidly excised during their course. In some
cases this will be followed by immediate cessa-
tion of the spasms.
8. Kemoval of the Motor Areas on One Side
in the Dog. — Proceed as in 7 , but use antiseptic f' "P^''^ '°^^^,' «'• cerebel-
. ° . . . ' . . . , ' mm ; t', medulld oblongata;
precautions, and mstead ot stmiulatmg, destroy a, upper end of spinal
with the actual cautery or remove with the cord.
knife all the grey matter around the crucial
sulcus on one side. Stop bleeding by iodoform gauze wrung out
of hot normal saline solution. Sew up the muscles by one set of
sutures, the skin by another, and cover the wound with collodion.
When the dog has recovered from the operation, study the deficiency
of motor and sensory power on the opposite side (p. 710). (Fig. 240,.
p. 707.)
* It is not necessary to remove the dura mater.
Fig. 245. — Brain ok
Frog. (Aftk, r
Steiner.)
a, cerebral hemisplieres ;
6. position of opticthalami ;
CHAPTER XIII.
THE SENSES.
Hitherto we have been considering from a purely objective stand-
point the organs that compose the body, and their work. The
student has been assumed to be in the Httle world — ' the microcosm '
— of organization which he has been studying, but not of it. He
has listened to the sounds of the heart, seen its contraction, felt
it hardening under his fingers ; but we have not inquired as to the
meaning or the mechanism of this hearing, seeing, and feeling. We
have now to recognise that all our knowledge of external things
comes to us by the channels of the senses, and, like the light that
falls through coloured windows on the floor of a church, is tinged,
and perhaps distorted, in the act of reaching us.
The Senses in General. — The old and orthodox enumeration
of 'the five senses' of sight, hearing, touch, taste and smell
must be augmented by at least two more, the senses of
pressure and temperature. The power of appreciating the
amount of a muscular effort ; the power of localizing the
various portions of the body in space ; the sensations of
pain, tickling, itching, hunger, and thirst ; the sensations
accompanying the generative act, etc., have also been looked
upon by some as separate senses subserved by special nerves
and connected with definite centres. In the development
of a simple sensation we may distinguish three stages : the
stimulation of a peripheral end-organ, the propagation of
the impulses thus set up along an afferent nerve, and their
reception and elaboration in a central organ.
We do not know in what manner a series of transverse vibrations
in the ether when it falls upon the eye, or a series of longitudinal
vibrations in the air when it strikes the ear, excites a sensation of
light or sound. We can trace the ray of light through the refractive
rilE SENSES
733
media of the eyeball, see it focussed on the retina, lead off the
current of action set up in that membrane, which, doubtless, gives
token of the passage of nervous impulses into and up tlie optic nerve.
We can even follow the nervous impulses to a definite portion of the
cortex of the occipital lobe, and determine that if this is removed
no sensation of sight will result from any excitation of retina or optic
nerve. And it is fair to conclude that in some manner this part of
the cerebral cortex is essential to the production of visual sensations.
But in what way the chemical or physical processes in the axis
cylinders or nerve-cells are related to the psychical change, the inter-
ruption of the smooth and unregarded flow of consciousness which
we call a sensation of light, we do not know. To our reasoning, and
even to our imagination, there is a great gulf fixed between the
physical stimulus and its psychical consequence ; they seem incom-
mensurable (luantities ; the transition from light to sensation of light
is certain, but unthinkable.
Each kind of peripheral end-organ is peculiarly suited to
respond to a certain kind of stimulus. The law of ' adequate '
or ' homologous ' stimuli is an expression of this fact. The
' adequate ' stimuli of the organs of special sense may be
divided into : (i) vibrations set up at a distance without the
actual contact of the object, e.g., light, sound, radiant heat ;
(2) changes produced by the contact of the object, e.g., in
the production of sensations of taste, touch, pressure, altera-
tion of temperature (by conduction). Midway between (i)
and (2) lies the adequate stimulus of the olfactory end-organs^
which are excited by material particles given off from the
odoriferous body and borne by the air into the upper part
of the nostrils.
The end-organs of the special senses all agree in consisting essen-
tially of modified epiblastic cells, but they occupy areas by no means
proportioned to their importance and to the amount of information
we acquire through them. The extent of surface which can be
affected by light in a man is not more than 20 sq. cm. ; the endings
of both nerves of hearing taken together do not at most expand to
more than 5 sq. cm. ; the olfactory portion of the mucous mem-
brane of the nose has an area of not more than 10 sq. cm. ; the
sensations of taste are ministered to by an area of less than
50 sq. cm. ; the end-organs of the senses of pressure, touch, and
temperature are distributed over a surface reckoned by square
metres. As the physiological status of the sensory end-organs
rises, their anatomical distribution tends to shrink. The organs of
comparatively coarse and common sensations are widely spread,
intermingled with each other, and seated in tissues whose primary
function may not be sensory at all. Even the nerve- endings of the
sense of taste are not confined to one definite and circumscribed
734 A MANUAL OF PIIYSIOLOCY
patch, but scatlcrcd over the tongue and palate ; and both tongue
and palate are at least as much concerned in mastication and
deglutition as in taste. The olfactory portion of the nasal mucous
membrane, although a continuous area with fairly distinct boun-
daries, is still a part of the general lining of tlie nostril. The
■epithelial surfaces which minister to the supreme sensations of sight
and hearing — the retina and the sensitive structures of the cochlea —
are the most sequestered of all the sensory areas, as the organs of
which they form a part are, of all the organs of sense, the most highly
specialized in function, and anatomically the most limited. But
although hidden in protected hollows, they are endowed, either in
virtue of their own movements or of those of the head, with the
power of receiving impressions from every side, and their actual size
is thus indefinitely multiplied.
VISION.
Physical Introduction. — Physically a ray of light is a series of
disturbances or vibrations in the luminiferous ether, which radiates
out from a luminous body in what is practically a straight line. The
ether is supposed to fill all space, including the interstices between
the molecules of matter and the atoms of which those molecules are
composed. Suppose a bar of iron to be gradually heated in a dark
room. In the cold iron the molecules are moving on the average
at a relatively slow rate, and the waves set up in the ether by their
vibrations are comparatively long. Now, the long ethereal vibrations
do not excite the retina, because it is only fitted to respond to the
impact of the shorter waves : and, indeed, the long waves are largely
absorbed by the watery media of the eye. As the temjjerature of the
iron bar is increased, the molecules begin to move more quickly, and
waves of smaller and smaller length, of greater and greater frequency,
are set up, until at last some of them are just able to stimulate the
retina, and the iron begins to glow a dull red. As the heating goes
on the molecules move more quickly still, and, in addition to waves
which cause the sensation of red, shorter waves that give the sensa-
tion of yellow appear. Finally, when a high temperature has been
reached, the very shortest vibrations which can affect the eye at all
mingle with the medium and long waves, and the sensation is one
of intense white light.
We have said that a ray of light travels in a straight line, and the
direction of the straight line does not change so long as the medium
is homogeneous. But when a ray reaches the boundary of the
medium through which it is passing, a part of it is in general turned
back or reflected. If the second medium is transparent (water or
glass, f.,i,^), the greater part of the ray passes on through it, a smaller
portion is reflected. If the second medium is opatjue, the ray does
not penetrate it for any great distance ; if it is a piece of polished
metal, e.g.^ nearly the whole of the light is reflected ; if it is a layer of
lampblack, very little of the light is reflected, most of it is absorbed.
Reflection. — The first law of reflection is that the reflected ray, the
THE SENSES
735
ray which falls upon the rejhi/in}:; surface {incident ray), and the
normal to the surface, are in one plane. The second law is that the
reflected ray makes, with the perpendicular {normal) to the reflecting
surface, the same angle as the incident ray. A corollary to this is that
a ray perpendicular to the surface is reflected along its own path.
/Reflection from a Plane Mirror. — Let a ray of light coming from
the point P meet the surface DP^ at B, making an angle PP>A with
the normal to the surface. The re-
flected ray P>C will make an equal
angle ABC with the normal ; and the
eye at C will see the image of P as if
it were placed at P', the point where
the prolongation of BC cuts the
straight line drawn from P perpendicu-
lar to DE. This is the position of an
ordinary looking-glass image.
Reflection from a Concave Spherical
Mirror. — A spherical surface may be
supposed to be made up of an infinite
number of infinitelysmall plane surfaces.
The normal to each of these plane
surfaces is the radius of the sphere, and the reflected ray makes with
the radius at the point of incidence the same angle as the incident
ray. Let D (Fig. 247) be the middle point of the mirror, and C its
centre of curvature, i.e., the centre of the sphere of which it is a
246. — RlKLECTION I'ROM
A Plane Mirror.
Fig.
247. — Reflection ikom a Concave
Spherical Mirror.
Fa;. 24S. — FdKMATiuN
VERTEU I.MACE BY
Spherical Mirror.
OF Real In-
A Concave
segment. Then CD is the principal axis, and any other line through
C which cuts the mirror is a secondary axis. When the mirror is a
small portion of a sphere, rays parallel to the principal axis are
focussed at the principal focus F midway between C and D ; rays
parallel to any secondary axis are focussed in a point lying on that
axis ; and rays diverging from a point on any axis are focussed in a
point on the same axis.
These facts afford a simple construction for finding the position of
the image of an object formed by a concave mir or. Let AB be the
736
A MANi'AL OF PHYSIOLOGY
object (Fig. 248). Then the image of A is the point in which all
rays proceeding from A and falling on the mirror, including rays
l)arallel to the principal axis, are focussed. Ikit the ray Ali), parallel
to the principal axis, passes after reflection through the principal
focus F, therefore the image of A must lie on the straight line EF.
If any secondary axis ACD be drawn, the image of A must lie on
ACl). It must therefore be the point of intersection, a, of EF and
ACD. Similarly, the image of V> must be the point of intersection,
b^ of GF and BCH. The image ah of an object AB farther from
the mirror than the principal focus is real and inverted. 'Jhe
I'urkinje-Sanson image reflected from the concave anterior surface of
the vitreous humour (Fig. 263) is an example.
After refJect ion from a cortvex minor, rays of light always diverge,
and only erect, virtual
1 mages are formed, />.,
images which do not
really exist in space, but
which, from the direc-
tion of the rays of
light, we judge to exist.
'I he position of the
image of an object AB
( Fig. 249) may be
found by a construc-
tion similar to that for
reflection from a con-
cave mirror. The
image of a flame
reflected from the
anterior surface of the cornea or lens is erect and virtual. It
diminishes in size with increase in the curvature or convexity of the
reflecting surface (Fig. 263).
Refraction. — A ray of light passing from one medium into another
has its velocity, and consequently its direction, altered. It is said to
be refracted. The first law of refraction is that the refracted ray is
in the satne phine as the incident ray arid the normal to the surface.
The second law is that the sine 0/ the angle of incidence has a constant
ratio (for any given pair of media) /(? the sine of theani^le of refraction.
The angle of incidence is the angle which the ray makes with the
normal to the surface, separating the two media ; the angle of refrac-
tion is the angle made with the normal in the second medium. This
ratio is called the index of refraction between the two media. For
purposes of comparison, the refractive index of a substance is usually
taken as the ratio of the sine of the angle of incidence to the sine of
the angle of refraction of a ray passing from air into the substance.
When a ray strikes a surface at right angles, it passes through
without suffering refraction. When a ray passes from a less dense
to a denser medium {e.g., from air to water), it is bent towards the
perpendicular. When it passes from a more dense to a less dense
medium (as from water to air), it is bent away from the perpendicular.
Pig. 249. — FuRMAiio.N ok 1.ma(;i-: hy
Mirror.
Convex
THE SENSES
737
When a ray passes across a medium bounded by parallel planes, it
issues parallel to itself; in other words, it undergoes no refraction
(Fig- 251).
Refraction and Dispersion by a Prism. — The beam of light is bent
towards the normal N as it passes across BA and away from the
3
p B y^ •
p'
1/3
yyy-
D
Fig. 250.— Refraction at a Plane Fig, 251. — Refraction by
Surface.
AB is the incident ; BD, the refracted
ray ; CB, the normal to the surface. When
the ray passes from air into another medium,
the refractive index of the latter is the fraction
sin a
sin /3'
Medium bounded by Parallel
Planes, P and P'.
The ray ABDE issues parallel to its
original direction ; CB, FD, normals to
P and P' ; a, angle of incidence ; /3, 7,
angles of refraction.
normal N' as it passes across BC (Fig. 252) ; at both surfaces it is
bent towards the base of the prism AC. At the same time the hght
suffers dispersion ; that is, the rays of shorter wave-length are more
refracted than those of greater wave-length. The deviation of any
Fig. 252. — Refraction and Disi'ersion by a Prism.
given ray is measured by the angle which the refracted ray makes
with its original direction. The amount of dispersion produced by
a prism is measured by the difference in the deviation of the extreme
rays of the spectrum. The dispersion produced by any given sub-
47
738
A MANUAL OF PHYSIOLOGY
stance is proportional to the difference of its refractive index for the
extreme rays.
Refraction by a Biconvex Leas. — A straight line .\CB passing
through the centres of curvature of the two surfaces of the lens is
called the principal axis. A point C lying on the principal axis
between the two centres of curvature, and possessing the property
Fig, 253. — Refraction hy a Biconvex Lkn>.
that rays passing through it do not suffer refraction, is called the
optical centre of the lens. Any straight line, DCE, passing through
the optical centre is a secondary axis. Rays of light proceeding
from a point in the principal axis are focussed in a point on that
axis. When the rays proceed from an infinitely distant point in the
principal^axis, />., when they are parallel to it, they are focussed in F,
Fit;. 254 -FiiRMAiiON OK Imace hv BiC'iNVKX Lens.
the principal focus. Similarly, rays parallel to, or proceeding from, a
point in a secondary axis are focussed in a point on that axis ; but if
the focus is to be sharp, the angle between the secondary and the
principal axis must not be so large as is indicated in Fig. 253.
formation of Image by Biconvex Lens (Fig. 254). — Let AB be the
object; then if AHD be the path of a ray from A parallel to the
THE SENSES
739
Fii
-RErKACTION BY A BICONCAVE LkNS.
principal axis, the image of A will be the intersection of the straight
line DF and the secondary axis passing through A. Similarly, the
image of B will be the intersection of GF and the secondary axis BC.
Where AB is farther from the lens than the principal focus, the image
ab is real and inverted This is the case with the image of an external
object formed on the retina. When the object is nearer than the
principal focus, the image is virtual and erect. The image formed by
the objective of a
microscope when the
object is in focus is
real and inverted; the
ocular forms a virtual
erect image of this
real image.
Refraction by a Bi-
concave Lens { Fig.
255). — Parallel rays
are rendered diver-
gent by the lens ;
there is no real focus ; but if the rays are prolonged backwards they
meet in the virtual focus F, from which they appear to come when
received by the eye through the lens.
Formation of Image by Biconcave Lens (Fig. 256). — Let AB be
the object. Let AHDI be the path of a ray from any point A of
the object parallel to
the principal axis.
Produce DI back-
wards (dotted line) ;
it will pass through
the principal focus F.
Through A draw the
secondary axis AC
The image of A must
lie both on AC and
on IDF ; i.e.^ it must
be the intersection, a, of these straight lines,
of B is b, the intersection of KGF and BC.
and erect
Absorption. — No substance is perfectly transparent ; in addition
to what is reflected, some light is always absorbed. In other words,
in passing through a body some of the light is transformed into heat,
a portion of the energy of the short, luminous waves going to in-
crease the vibrations of the molecules of the medium, just as a wave
passing under a row of barges or fishing-boats sets them swinging
and pitching, and so imparts to them a certain amount of energy,
which is ultimately changed into heat by friction against the water,
and against each other, and by the straining and rubbing of the
chains at their points of attachment. Some bodies absorb all the
rays in the proportion in which they occur in white light ; whether
looked at or looked through, they appear colourless or white. Other
47—2
Fig. 256. — FoK.MATioN of Image by Biconx.we
Lexs.
Similarly, the image
The image is virtual
740
A MANUAL OF I'lIYSIOLOGY
substances absorb certain rays by preference, and the amount of
absorption is proportional to the thickness of the layer. The colours
of most natural bodies are due to this selective absorption. Even
when looked at in reflected light, they are seen by rays that have
penetrated a certain way into the substance and have then been
reflected ; and, of course, a smaller number of the rays which the
body specially absorbs are reflected than of the rays which it readily
transmits, for more of the latter than of the former reach any given
depth. This is called ^ body colour' : and such substances have the
same colour when seen by reflected and by transmitted light. The
colour of haemoglobin is due to the absorption of the violet and many
of the yellow and green rays, as is shown by the position of the
absorption bands in its spectrum (p. 48). In Fig. 257 the violet rays
are represented as being totally absorbed before i)assing through the
substance. Some of
the green rays are re-
flected, some trans-
mitted, some ab-
sorbed. The red rays
are supposed to be
mostly reflected and
transmitted, only to
a slight extent ab-
sorbed. The colour
of such a substance,
iioth when looked at
and when looked
through, would there-
fore be that due to a
mixture of red light
with a smaller
quantity of green.
Then there is another
class of substances
Certain rays only are
Fig. 257. — DiACRAiM to show Connection ok
Body Colour with Selective Absorttion.
which owe their colour to selective reflection
reflected from their surface, and the light transmitted through a thin
layer is complementary to the reflected light ; that is, the reflected
and transmitted rays together would make up white light. These
bodies have what is called '■surface colour^' and include metals, various
aniline dyes, and other substances.
Comparative. — Many invertebrate animals possess rudimentary
sense-organs, by means of which they may receive certain luminous
impressions. It is true that the mere sensation of light is not in
itself suflicient for the exact appreciation of the form and situation of
surrounding oi)jects. But even the closure of the eyelids does not
prevent a person of normal eyesight from distinguishing differences
in the intensity of illumination. And it is possible that many of the
humbler animals may, through the pigment spots which are often
called eyes, or perhaps, as in the earthworm, by means of end-organs
more generally diffused in the skin, attain to some such dim con-
rilE SENSES
741
sciousness of light and shadow as will enable them to avoid an
obstacle or an enemy, to seek the sunny side of a boulder or the
obscurity of an overhanging ledge of rock. But the indispensable
condition of distinct vision is that an image of each part of an object
should be formed upon a separate portion of the receiving or sensitive
surface. This condition is, to a certain extent, fulfilled by the com-
pound eyes of some of the higher invertebrates (insects, e.g.). Here
rays from one point of the object pass through one of the funnel-
shaped elements of the compound eye, and rays from another point
through another. Rays striking obliquely on the facets are stopped
by the opaque partitions between them. In the Cephalopods we
■'C erne a
Vi t r\\e 0 u s
_Ci llcirij Muscle
^3?N^ Sus/ii/f.sny
^ \3 £i ganiini-
^A.. Chnrojri
J^oirea cen/^ya/isW^W
T-Sc/,ro/!cr
Fig. 258. — Diagrammatic Horizontal Section of phe Left Eve.
find that this compound type of eye has already been abandoned ;
the single system of curved refracting surfaces so characteristic of the
vertebrate eye has made its appearance ; and the formation of a
clean-cut image of the object on the retina, with the excitation of a
sharply-bounded area of that membrane., follows as a geometrical
consequence from the theory of lenses.
We have to consider (i) the mechanism by which an
image is formed on the retina, and (2) the events that follow
the formation of such an image and their relations to the
stimulus that calls them forth.
742
A MANUAL OF PHYSIOLOGY
Structure of the Eye.— The eye may be described with sufificient
accuracy as a spherical shell, transparent in front, but opaque over the
posterior five-sixths of its surface, and filled up with a series of trans
parent liquids and solids. The shell consists of three layers concen-
trically arranged, like the coats of an onion : (i) An external tough,
fibrous coat, t/ie sclerotic, the anterior portion of which appears as the
white of the eye. In front this external layer is completed by the
Cones.
l-ii;. 259.
Fn;. 260.
Yu
259-
THK ReI'INA (AKTKk llELM-
IIOLTZ).
lie. 260.— Diagram ok Structurk ok
Retina (Bowditch, aftkr Cajal).
I, internal limiting membrane ; 2, H, layer of
nerve-fibres ; 3, G, layer of ganglion cells ; 4, F,
internal molecular layer; 5, E, internal nuclear
layer ; 6, C, external molecular layer ; 7, B,
cxieriial nuclear layer ; 8, external limiting mem-
brane ; g, A, layer of rods and cones ; 10, pig-
mented epithelium.
transparent cornea. (2) A vascular and pigmented layer, the choroid,
which, in the restricted sense of the term, ends in front in a series of
folds or plaits, the ciliary processes. These abut on the outer
boundary of the iris, which may be looked upon as an anterior con-
tinuation of the choroidal or middle coat of the eyeball. Between
the corneo-sclerotic junction and the anterior portion of the choroid
is interposed a ring of unstriped muscular fibres, the ciliary muscle.
THE SENSES 743
(3) The inner or sensitive coat, termed the retina (Kigs. 259, 260).
This covers the choroid as a dehcate membrane, extending to the
ciHary processes, where it ends in a toothed margin, the ora serrata.
The optic nen'e forms a kind of stalk to which the eyeball is attached.
Its point of entrance at the optic disc is a little nearer the median line
than the antero-posterioraxis, which nearly passes through the centre
of a small depression, the fovea centralis, situated in the middle of
the macula lutca, or yellow spot. From the optic disc (sometimes
called the optic papilla, but ina{)propriately, since it does not project
beyond the general surface), the optic nerve spreads over the retina
as a layer of non-medullated fibres, separated from the mterior of
the eyeball only by the internal limiting membrane. This so-
called membrane is formed by the expanded feet of the fibres of
MiiUer, which run like a scaffolding or framework through nearly the
whole thickness of the retina, terminating at the outer limiting mem-
brane. External to the layer of nerve-fibres is the stratum of large
ganglion cells, whose neurons they are ; next to this the inner
molecular layer, made up largely of the branching dendrons of these
colls. The fifth layer is the inner granular or nuclear layer, containing
many fusiform 'granule ' cells which send out neurons into the fourth,
and dendrons into the sixth, or outer molecular layer, and are thus
connected with the ganglion cells of the third layer on the one hand,
and with the seventh or outer nuclear layer on the other. The seventh
stratum receives its name from the large number of nuclei which it
contains. These are connected with the rods and cones of the ninth
layer, which is divided from the seventh by the external limiting
membrane. At the fovea centralis the rods are entirely absent, and
the other layers of the retina greatly thinned : over the optic disc
neither rods nor cones are present.
External to the rods and cones is a sheet of pigmented epithelial
cells of hexagonal shape, belonging to the choroid, but remaining
attached to the retina when the latter is separated, and therefore often
reckoned as its most external layer.
A little behind the cornea and anterior to the retina is the le7is,
enclosed in a capsule, and attached to the choroid by the suspensory
ligament, or zonule of Zinn. The iris hangs down in front of the lens
like a diaphragm, with a central hole, the pupil. Between the iris
and the posterior surface of the cornea is the anterior chamber of
the eye, filled with the aqueous humour. Between the iris and the
anterior surface of the lens lies the posterior chamber, which is rather
a potential than an actual cavity. The space between the lens and
the retina is accurately occupied by an almost structureless semi-fluid
mass, the vitreous humour, enclosed by the delicate hyaloid membrane,
which in front is reflected over the folds of the ciliary processes, and
blends with the suspensory ligament of the lens.
Refraction in the Eye — Formation of the Retinal Image. — The
amount of refraction which a ray of Hght undergoes at a
curved surface depends upon two factors, the radius of
744 '1 MAXUAL OF PHYSIOLOGY
curvature of the surface, and the difference between the re-
fractive indices of the media from which the ray comes and
into which it passes. The smaller the radius of curvature,
and the greater the difference of refractive index, the more
is the ray bent from its original direction. A ray of light
passing into the eye meets first the approximately spherical
anterior surface of the cornea, covered with a thin layer of
tears. Since the refractive index of the tears and of the
cornea is greater than that of air, refraction must occur
here. At the parallel posterior surface of the cornea, how-
ever, the ray is but slightly bent, for the refractive indices
of aqueous humour and corneal substance are nearly equal.
At the anterior and posterior surface of the lens the ray is
again refracted, since the refractive index of the aqueous and
vitreous humour is less than that of the lens. The following
tables show the radii of curvature of the refracting surfaces
and the refractive indices of the dioptric media, as well as
some other data which are of use in studying the problems
of refraction in the eye :
In accommodation for
Far Vision. Near Vision.
[Cornea - - - 7'8 mm. 7*8 mm.
Radius of curvature of- Anterior surface of lens io"o „ 6"o „
[Posterior surface of lens 6"o „ 5 "5 „
I Anterior surface of cornea and an-
I terior surface of lens - - - yd ., yz „
Distance | Anterior surface of cornea and pos-
between 1 terior surface of lens -
Anterior and posterior surface of lens
I Posterior surface of lens and retina -
Antero-posterior diameter of eye along the axis
Refractive Indices —
Air
Cornea
Aqueous humour - - . .
Vitreous humour - - - .
Lens (mean for all its layers) -
Water
It will be seen that the refractive indices of the cornea and
the aqueous and vitreous humours are all nearly the same as
that of water. That of the lens differs for its various layers,
the central core having a higher refractive index than the
7-2
3-6
14-6
2 1-8
7-2
4-0
„ 146
„ 21-8
.
I 000
-
1-337
1-3365
1-3365
-
1-437
-
I 335
THE SENSES 745
more superficial portions ; but a mean may be struck, and,
although such calculations are open to error, it has been
computed that the lens acts as a homogeneous lens of the
same curvatures, and with a refractive index of i'437,
would do.
The optical problems connected with the formation of the
retinal image are complicated by the existence in the eye of
several media, with different refractive indices, bounded by
surfaces of different and, in certain cases, of variable curva-
ture. For many purposes, however, the matter can be
greatly simplified, and a close enough approximation yet
arrived at, by considering a single homogeneous medium, of
•definite refractive index, and bounded in front by a spherical
surface of definite curvature, to replace the transparent
solids and liquids of the eye. The position of the principal
focus and nodal point {i.e., the point through which rays
pass without refraction) of such a * reduced ' or ' schematic '
eye, and other constants, are shown in the following table :
Reduced Eye —
Radius of curvature of the single refracting surface - 5-1 mm.
Index of refraction of the single refracting medium - i"35''
Antero posterior diameter of reduced eye (distance of
principal focus from the single refracting surface) - 20.0
Distance of the single refracting surface behind the
anterior surface of the cornea - - - i '8
Distance of the nodal point of the reduced eye from
its anterior surface - - - - - 50
Distance of the nodal point from the principal focus
(retina)- - - - - - - - - 15-0
Knowing the position of the centre of curvature of the
single ideal refracting surface, i.e., the nodal point of the
reduced eye, all that is necessary in order to determine the
position of the image of an object on the retina is to draw
straight lines from its circumference through the nodal
point. Each of these lines cuts the refracting surface at
right angles, and therefore passes through without any
deviation. The retinal image is accordingly inverted, and
its size is proportional to the solid angle contained between
the lines drawn from the boundary of the object to the
* Or about the same as that of the aqueous humour.
746
A MANUAL OF PHYSIOLOGY
nodal point, or the equal angle contained by the,''prolonga-
tions of the same lines towards the retina. This angle is
called the visual an^le, and evi-
dently varies directly as the size
of the object, and inversely as its
distance. Thus the visual angle
under which the moon is seen is
much larger than that under which
we view any of the fixed stars,
because the comparative nearness
of the earth's satellite more than
makes up for its relatively small
Fic. 261. TnK Rkduckd Eyk. Size.
S, the single spherical refracting
surface, i 8 mm. behind the an-
terior surface of the cornea ; N,
the nodal point, 5 mm. behind S ;
K, the principal focus (on the
retina), 20 mm. behind S. The
cornea and lens are put in in dotted
lines in the position which they
occupy in the normal eye.
The dimensions of the retinal image
of an object are easily calculated when
the size of the object and its distance
are known. For let AB in Fig. 262
represent one diameter of an object,
A'B' the image of this diameter, and
let AB', BA', be straight lines passing
through the nodal point. Then AB and AT/ may be considered
as parallel lines, and the triangles of which they form the bases,,
and the nodal point the common ape.x, as similar triangles.
I'"i(;. 262. — Fkuirk to show how 1 uk Visu.\l Anci.k and Size ok Retinal.
Image varucs with the Distance of an Object of Given Size.
For the distant position of AB the visual angle is a, for the near position (dotted
lines) fi.
Accordingly, if 1) is the distance of the nodal point from A,.
AB A'B'
and d its distance from B', we have . = , • Now, d may
D d
approximately be taken as 15 mm. Suppose, then, that the size of
the moon's image on the retina is required. Here L) = 238,000 miles,
and AB (the diameter of the moon) = 2, 160 miles. Thus we get
THE SENSES
747
, from which A'H' (the diameter
2,160 AB . V I AH
- ' - = — , or (say) =
238,000 15 no 15
of the retinal image) = — ^ , or about I mm.
no
A ship's mast 120 feet high, seen at a distance of 25 miles, will
throw on the retina an image whose height is x 15 mm.,
25 miles
120 feet I , ^
i-e., — — ^ X 15 mm., or x 15 mm., equal to -oi-? mm.,
5,280 X 25 feet ^ 1,100 ^ ' ^ o '
or 13 /i. in size. This is not much larger than a red blood-corpuscle,
and only four times the diameter of a cone in the fovea centralis,
where the cones are most slender.
Accommodation. — A lens adjusted to focus upon a screen
the rays coming from a luminous point at a given distance
will not be in the proper
position for focussing rays
from a point which is
nearer or more remote.
Now, it is evident that a
normal eye possesses a
great range of vision. The
image of a mountain at a
distance of 30 miles, and
of a printed page at a
distance of 30 cm., can
be focussed with equal
sharpness upon the retina.
In an opera-glass or a
telescope accommodation
is brought about by alter-
ing the relative position of
the lenses ; in a photo-
graphic camera and in the
eyes of fishes and cepha-
lopods (Beer), by altering
the distance between lens and sensitive surface ; in the
eye of man, by altering the curvature, and therefore the
refractive power of the lens. That the cornea is not alone
concerned in accommodation, as was at one time widely
held, is shown by the fact that under water the power of
accommodation is not wholl}' lost. Now, the refractive
Fiu. 263. — Fukkinje-Saxson Imagks.
A, in the absence of accommodation ; B,
during accommodation for a near object.
The upper pair of circles enclose the images
as seen when the light falls on the eye
through a double slit or a pair of prisms ;
the lower pair show the images seen when
the slit is single and triangular in shape.
748 .1 MANUAL OF PHYSIOLOGY
index of the cornea being practically the same as that of
water, no changes of cur\'ature in it could affect refraction
under these circumstances. That the sole effective change
is in the lens can be most easily and decisively shov^'n by
studying the behaviour of the mirror images of a luminous
object reflected from the bounding surfaces of the various
refractive media when the degree of accommodation of the
eye is altered. Three images are clearly recognised : the
brightest, an erect virtual image, from the anterior (convex)
surface of the cornea ; an erect virtual image, larger, but
less bright, from the anterior (convex) surface of the lens ;
and a small inverted real image from the (concave) posterior
boundary of the lens (Purkinje-Sanson images). The second
image is intermediate in position between the other two.
It is possible with special care to make out a fourth image,
and even a fifth ; but since these are reflected from surfaces
(the posterior surface of the cornea, e.g.) at which only a
slight change in the refractive index occurs, they are much
less brilliant than the first three. When the eye is accom-
modated for near vision, as in focussing the ivory point of
the phakoscope (Fig. 294), the corneal image is entirely
unchanged in size, brightness, and position. The middle
image diminishes in size, comes forward, and moves nearer
to the corneal image. This shows that the curvature of the
anterior surface of the lens has been increased — that is to
say, its radius of curvature diminished — for the size of the
image of an object reflected from a convex mirror varies
directly as the radius of curvature. A slight change takes
place in the image from the posterior surface of the lens,
indicating a small increase of its curvature too. By means
of a method founded on the observation of the changes in
these images, and a special instrument called an ophthalmo-
meter which allows of their measurement, Helmholtz has
calculated that, during maximum accommodation, the radius
of curvature of the anterior surface of the lens is only 6 mm.,
as compared with 10 mm. when the eye is directed to a
distant object and there is no accommodation. When the
lens has been removed for cataract, fairly distinct vision may
still be obtained by compensating for its loss by convex
THE SENSES 749
spectacles of suitable refractive power (lo diopters* for
distant vision, and 15 diopters for the distance at which a
book is usually held), but no power of accommodation
remains. The person does indeed contract the pupil in
regarding a near object, just as happens in the intact eye ;
the most divergent rays are thus cut off and the image made
somewhat sharper, and there may appear to be some faculty
of accommodation left. But the loss of the whole iris by
operation does not affect accommodation in the least ; the
iris, therefore, takes no part in it. That no change in the
antero-posterior diameter of the eyeball, caused by its
deformation by the contraction of the extrinsic muscles,
can have any share in accommodation, as has been suggested,
is clearly proved by the fact that atropia, which does not
affect the action of these muscles, paralyzes the mechanism
of accommodation. To the consideration of that mechanism
we now turn.
The Mechanism of Accommodation. — While everybody is
agreed that the main factor in accommodation is the altera-
tion in the curvature of the lens, there is by no means the
same unanimity as to the manner in which this is brought
about. Helmholtz's explanation, which has long been the
most popular, is as follows : In the unaccommodated eye
the suspensory ligament and the capsule of the lens are
tense and taut, the anterior surface of the lens is flattened
by their pressure, and parallel rays (or, what is the same
thing, rays from a distant object) are focussed on the retina
without any sense of effort. In accommodation for a near
object, the meridional or antero-posterior fibres of the
ciliary muscle by their contraction pull forward the choroid
and relax the suspensory ligament. The elasticity of the
lens at once causes it to bulge forwards till it is again
checked by the tension of the capsule.
* A diopter (i D) is the unit of refractive power generally adopted in
measuring the strength of lenses, and corresponds to a lens of i metre
focal length. A lens of 2 diopters (2 D) has a focal length of \ metre,
a lens of 4 diopters (4 D; a focal length of \ metre, and so on. The
diverging power of concave lenses is similarly expressed in diopters, with
the negative sign prefixed. Thus, a concave lens of i metre focal length
has a strength of — i D and will just neutralize a convex lens of i D.
750 A MANUAL OF PHYSIOLOGY
'Ihe explanation of Helmholtz, although widely adopted in the
text-books, is being more and more called in question in the archives.
Tscherning, for example, has put forward the view that when the
ciliary muscle (which consists of a superficial layer of meridional,
and a deep layer of radial, fibres) contracts, the ciliary processes are
drawn back, and pull the zonule of Zinn backwards and outwards.
The tension of the zonule is thus increased, and the curvature of
the lens altered, the region around its anterior pole in particular
becoming more convex. At the same time the contraction of the
posterior portion of both layers of the ciliary muscle pulls the
choroid forward, and so causes the vitreous body to press against the
posterior surface of the lens, and prevent its displacement backwards
by the pull of the anterior portion of the muscle. And Schoen,
reviving a similar theory originated forty years ago by Mannhardt,
believes that the contraction of the ciliary muscle exerts pressure on
the anterior portion of the lens, and so increases its curvature He
likens the increase of curvature to the bulging of an indiarubber
ball when it is held in both hands and compressed by the fingers a
little behind one of the poles. It will be observed that in both of
these theories the suspensory ligament is supposed to be stretched
during acconniiodation, not relaxed as in Helmholtz's theory.
It has been already mentioned that along with the altera-
tion in the curvature of the lens a change in the diameter
of the pupil takes place in accommodation. When a distant
object is looked at, the pupil becomes larger ; when a near
object is looked at, it becomes smaller. Narrowing of the
pupil is thus associated with contraction of the ciliary
muscle, and widening of the pupil with its relaxation.
This physiological correlation has its anatomical counterpart ; for
the third nerve supplies both the iris and the ciliary muscle. Stimu-
lation of the nerve within the cranium causes contraction of the pupil,
while stimulation of certain portions of its nuclei in the floor of the
third ventricle and the Sylvian aqueduct or of the short ciliary nerves
coming off from the ophthalmic ganglion (Fig. 264), which receives
branches from the third nerve, or of the ganglion itself, is followed by
that change in the anterior surface of the lens which constitutes ac-
commodation (Hensen and Voelckers). This can be observed either
through a window in the sclerotic in a dog or by following the move-
ments of a needle thrust into the eyeball. By carefully localized
stimulation near the junction of the aqueduct with the third ventricle,
it is possible to bring about the forward bulging of the lens without
any change in the iris ; but the normal and voluntary act of accom-
modation cannot be disjoined from the corresponding alterations in
the size of the pupil.
It is not only by accommodation that the size of the pupil
may be affected. In the dark it dilates ; when light falls
THE SENSES
75'
upon the retina it contracts, and the amount of contraction
is roughly proportional to the intensity of the light. Con-
traction of the pupil to light is brought about by a reflex
mechanism, of which the optic nerve forms the afferent and
theoculo-motor the efferent path, while the centre is situated
in the floor of the aqueduct of Sylvius. The relation of this
centre to that which controls the changes in the pupil during
accommodation has not as yet been sufficiently elucidated ;
but this we do know, that one of the paths may be inter-
rupted by disease, while the other is intact. For in loco-
Nervks of the Eye.
Ill, third or oculo-motor ner\e ; IV, fourth or trochlear nerve ; V, ophthalmic branch
of fifth nerve ; VI, sixth or abducens ; C, carotid artery with its plexus of sympathetic
fibres ; i, ophthalmic ganglion, with its motor root 2, its sympathetic root 3, and its
sensory root 4 ; 5, direct ciliary filament ; 6, ciliary muscle ; 7, iris ; 8, cornea ; 9, con-
junctiva ; 10, lachrymal gland ; 11, frontal nerve ; 12, nasal nerve ; 13, recurrent branch
of ophthalmic division of fifth. The thick white lines represent the motor nerves ; the
thin continuous lines the synipathetic fibres ; the dotted lines the sensory nerves.
motor ataxia the light-reflex sometimes disappears, while the
constriction of the pupil in accommodation still takes place
(Argyll- Robertson pupil). Artificial stimulation of the optic
nerve has the same effect on the pupil as the ' adequate '
stimulus of light; and in many animals (including man),
though not in those whose optic nerves completely decus-
sate, both pupils contract when one retina or optic
nerve is excited. This should be remembered in using
7S2 A MA.XUA/. OF P/fYSIOLOGY
the pupil-reaction as a test of the condition of the retina.
For although the absence of contraction may show that the
retina of the eye on which the light is allowed to fall is
insensible (unless there is some physical hindrance to its
passage, such as opacity of the lens or cataract), the occur-
rence of contraction does not exclude insensibility of the
retina unless the other eye has been protected from the
light.
But not only is the iris under the control of constrictor
nerve-fibres, it is also governed by dilator nerves ; and the
size of the pupil at any given moment depends on the play
of two nicely-balanced forces.
The dilator fibres pass out by the anterior roots of the first three
thoracic nerves (dog, cat, rabbit), accompanied apparently by vaso-
constrictor fibres for the iris. Reaching the sympathetic chain
through the corresponding rami communicaiites, they traverse the
first thoracic ganglion, the annulus of Vieussens, the inferior cervical
ganglion and the cervical sympathetic. After making junction with
some of the cells of the superior cervical ganglion (Langley), they
eventually arrive at the Gasserian ganglion, and running along the
ophthalmic division of the trigeminal to the eye, reach the iris by its
ciliary branches.
Stimulation of the cervical sympathetic causes marked
dilatation of the pupil (Practical Exercises, p. 820), even
when the third nerve is excited at the same time. All the
evidence at our command goes to show that the pupillo-
dilator fibres do not act by constricting the bloodvessels of
the iris. For dilatation of the pupil can be caused in a
bloodless animal b}- stimulating the sympathetic. And even
when the circulation is going on, a short stimulation of the
sympathetic causes dilatation of the pupil without vaso-con-
striction, while with longer excitation the dilatation of the
pupil begins before the narrowing of the bloodvessels. Nor
does it seem possible to accept the view that the sympa-
thetic fibres arc inhibitory for the sphincter muscle of the
iris. In all probability they act directly upon dilator
muscular fibres. It has, indeed, long been known that in
the iris of the otter and of birds a radial dilator muscle
exists ; and it has been shown by the recent experiments of
Langley and Anderson that in the iris of the rabbit, cat,
TIIH SENSES 753
and do^', the presence of radially arranged contractile sub-
stance, different it may be in some respects from ordinary
smooth muscle, must be assumed. Reflex dilatation of the
pupil through the sympathetic fibres is caused in man by
painful stimulation of the skin, by dyspnoea, by muscular
exertion, and in some individuals even by tickling of the
palms. In animals the stimulation of naked sensory nerves
has the same effect. The ' starting of the eyeballs from
their sockets,' which the records of torture so often note,
is probably due to a similar reflex excitation of the sympa-
thetic fibres supplying the smooth muscle of the orbits and
eyelids.
The statement has been made that in addition to the sympathetic
dilators of the pupil, dilating fibres pass out directly from the brain
along the fifth nerve ; and it has been said that after section of the
cervical sympathetic or excision of the superior cervical ganglion,
reflex dilatation can still be caused. Stimulation of certain cortical
areas causes slight dilatation even after the sympathetic has been
divided. But it is not known whether this is due to inhibition of
the pupillo-constrictor fibres in the third nerve or to excitation of
cerebral pupillo-dilator fibres. The reflex centre for dilatation of the
pupil is in the medulla oblongata. The lower cervical and upper
thoracic portion of the spinal cord has received the name of the
cilio-spinal region from its relation to the pupillo-dilator fibres. It
must not be looked upon as a centre in any proper sense of the
term, but rather as the pathway by which these fibres pass down
from the bulb, and where they may accordingly be tapped by stimu-
lation.
That, in addition to the cerebral centre for the constrictor
and the bulbar centre for the dilator fibres, there exists
within the eye some local mechanism which controls the
muscles of the iris and regulates the size of the pupil is
rendered certain by many facts. The excised eye of a frog
or an eel constricts its pupil on exposure to light, and dilates
it in the dark. It is said that even the isolated iris of the
eel contracts to light ; and it is known, although here the
explanation is less difficult, that the iris both of cold- and
warm-blooded animals contracts in warm, and dilates in
cold normal saline solution. The local application of at/opia
causes temporary paralysis of accommodation and dilatation
of the pupil. When the third nerve is divided, the pupil
dilates ; it dilates still more when atropia is administered
48
754 A MANUAL OF PHYSIOLOGY
after the operation. Dropped into one eye in small
quantity, atropia only produces a local effect ; the pupil
of the other eye remains of normal size, or somewhat con-
stricted on account of the greater reflex stimulation of its
third nerve by the greater quantity of light now entering the
widely-dilated pupil of the atropinized eye. Even in an
excised eye the effect of the drug is the same. Introduced
into the blood, atropia causes both pupils to dilate. Other
mydriatic, or pupil-dilating drugs, are cocaine, daturine, and
hyoscyamine. Escrine, pilocarpine, and morphia are the chief
myotics, or pupil-constricting substances. They also cause
spasm of the cihary muscle, and inability to accommodate
for distant objects. The work of the mydriatics can be
undone by the myotics. Thus the dilatation produced by
atropia is removed by pilocarpine. The most plausible ex-
planation of the action of these drugs is that the mydriatics
paralyze the third nerve, and stimulate the dilator nerve-
fibres of the iris, while the myotics paralyze the dilators and
stimulate the third. Nicotine, which ultimately causes con-
striction of the pupil, does so by paralyzing the cells on
the course of the dilating fibres in the superior cervical
ganglion.
Inward rotation of the eyes is associated with contraction of the
pupil, and the contraction that occurs during sleep is probably to be
thus explained. When the pressure in the anterior chamber of the
eye is diminished, as by tapping the aqueous humour through the
cornea, contraction of the pupil occurs ; and stimulation of the
sympathetic has now a far smaller dilating effect than usual. Re-
moval of the cornea narrows the pui)il, partly by occasioning direct
stimulation of the sphincter pupills, partly by abolishing the pressure
of the aqueous humour. The attached (ciliary) border of the iris
then bulges forward, and the pupil becomes smaller. On the other
hand, an increased pressure in the anterior chamber forces back the
ciliary border of the iris, and causes mechanical dilatation of the
pupil.
Functions of the Iris. — In vision, the iris performs two
chief functions : (i) It regulates the quantity of light allowed
to fall upon the retina. The larger the aperture of a lens,
the greater is its collecting power, the more light does it
gather in its focus. In the eye, the area of the pupil
determines the breadth of the pencil of light that falls upon
THE SENSES
755
the lens. If this area was invariable, the retina would either
be 'dark from excess of light' in bright sunshine, or dark
from defect of light in dull weather or at dusk. In order
that the iris may act as an efficient diaphragm it must be
pigmented, and it is the pigment in it which gives the colour
to the normal eye. The vision of albinos, in whose eyes
this pigment is wanting, is often, though not invariably,
deficient in sharpness. There is always intolerance of bright
light ; and the same is true in the condition known as
irideremia, or congenital absence or defect of the iris,
(2) Another, and perhaps equally important, function of
the iris is to cut off the more divergent rays of a pencil of
light falling upon the eye, and thus to increase the sharpness
of the image. This leads us to the consideration of certain
defects in the dioptric arrangements of the eye.
Defects of the Eye as an Optical Instrument, (i) Spherical
Aberration. — It is a property of a spherical refracting surface that
rays of light passing
through the peri-
pheral portions are
more strongly re-
fracted than rays
passing near the prin-
cipal axis. Hence a
luminous point is not
focussed accurately
in a single point by
a spherical lens ; the
image is surrounded
by circles of diffusion.
In the eye this sphe-
rical aberration is
partly corrected by
the interposition of the iris, which cuts off the more peripheral rays,
especially in accommodation for a near object, when they are most
divergent. In addition, the anterior surfaces of the cornea and lens
are not segments of spheres, but of ellipsoids, so that the curvature
diminishes somewhat with the distance from the optic axis, and,
therefore, the refracting power as we pass away from the axis does not
increase so rapidly as it would do if the surfaces were truly spherical.
Further, the refractive index of the peripheral parts of the lens is
less than that of its central portions.
(2) Chromatic Aberration. — All the rays of the spectrum do not
travel with the same velocity through a lens, and are, therefore,
unequally refracted by it, the short violet rays being focussed nearer
48—2
Fig. 265.— Spherical Aberration.
Rays pasbing through the more peripheral parts of a
biconvex lens L are brought to a focus F nearer the
lens than F', the focus of rays passing through the central
portions of the lens.
756
A MANUAL OF PHYSIOLOGY
the lens than the long red rays. It was al one time supposed that
this chromatic aberration, as it is called, is com[)ensated in the eye ;
and it is said that this mistake gave the first hint that Newton's
dictum as to the proportionality between deviation and dispersion
was erroneous, and led to the discovery of achromatic lenses, liut in
reality the eye is not an achromatic combination ; and the violet rays
are focussed about \ mm. in front of the red. Thus, in Fig. 266
the white light passing through the lens is broken up into its con-
stituents : the violet focus is at V, and the red at R, behind it. A
screen placed at R would show not a jjoint image, but a central
point surrounded by concentric circles of the spectral colours, with
violet outside. If the screen was placed at V, the centre would be
violet and the red would be external. For this reason it is impossible
Chromatic Aukrraik
The violet rays are brought to a focus V nearer
the lens than R, the focus of the red rays.
Fi(;. 267. — To SHOW Disper-
sion IN Eve.
View the figure from a distance
too small for accommodation.
.'\pproach the eye towards it ; the
wliite rings appear bluish owing
10 circles of dispersion falling on
them. A little closer, and the black
rings become white or yellowish-
wlme, being covered by circles of
dispersion and diffusion.
to focus at the same time and with perfect sharpness objects of
different colours : a red light on a railway track appears nearer than a
blue light, partly perhaps for the reason that it is necessary to accom-
modate more strongly for the red than for the blue, and we associate
stronger accommodation with shorter distarK:e of the object, although
other data are also involved in such a visual judgment. When we
look at a white gas flame through a cobalt glass, which allows only
red and violet to pass, we see either a red flame surrounded by a
violet ring, or a violet flame surrounded by a red ring, according as we
focus for the red or for the violet rays. 'J'he dispersive power of the
eye, however, is so small, and the capacity of rapidly altering its
accommodation so great, that no practical inconvenience results from
the lack of achromatism, which, however, may be easily demonstrated
by looking at a pattern such as that in Fig. 267 at a distance too
small for exact accommodation.
It is also reckoned among the optical imperfections of the eye
(3) that the curved surfaces of the cornea and lens do not form a
' centred ' system — that is to say, their apices and their centres of
curvature do not all lie in the same straight line ; (4) that the pupil
is eccentric, being situated not exactly opposite the middle of the
lens and cornea, but nearer the nasal side, and that in consequence
Tin: SENSES 757
ihe optic (ixi'i, or straight line joining the (cntre of curvature of the
lens and cornea, does not coincide with the Ti'sual axis, or straight
line joining the fovea centralis with the centre of the pupil, which is
also the straight line joining the centre of the pupil and any point to
which the eye is directed in vision. The angle between the optic
and visual axis is about 5' (Fig. 258). (5) Muses volitantes, the
curious bead like or fibrillar forms that so often flit in the visual field
when one is looking through a microscope, are the token that the
refractive media of the eye are not perfectly transparent at all parts ;
they seem to be due to floating opacities in the vitreous humour,
probably the remains of the embryonic cells from which the vitreous
body was developed. (6) Lastly, it may be mentioned that slight
irregularities in the curvature of the lens exist in all eyes, so that a
point of light, like a star or a distant street-lamp, is not seen as a
point, but as a point surrounded by rays (irregular astigmatism). In
bringing this review of the imperfections of the dioptric media of the
normal eye to a close, it may be well to explain that what are defects
Fk;. 268. — Rkkkaction in 1111. (Nokmai.j tMMEiKoru Eve.
The image P' of a distant point P falls on the retina when the eye is not accommodated.
from the point of view of the student of pure optics are not
necessarily defects from the freer standpoint of the physiologist, who
surveys the mechanism of vision as a whole, the relations of its
various parts to one another and to the needs of the organism it has
to serve, the long series of developmental changes through which it
has come to be what it is, and the possibilities, so far as we can limit
them, that were open to evolution in the making of an eye. The
optician may perhaps assert, and with justice, that he could easily
have made a better lens than Nature has furnished, but the physio-
logist will not readily admit that he could have made as good an eye.
While the defects hitherto mentioned are shared in
greater or less degree by every normal eye, there are certain
other defects which either occur in such a comparatively
small number of eyes, or lead to such grave disturbances
of vision when they do occur, that they must be reckoned
758
A MANUAL OF PHYSIOLOGY
as abnormal conditions. In the normal or emmetropic eye,
parallel rays — and for this purpose all rays coming from an
object at a distance greater than 65 metres may be con-
sidered parallel — are brought to a focus on the retina
without any effort of accommodation. The distance at
which objects can be distinctly seen is only limited by their
size, the clearness of the atmosphere, and the curvature
of the earth ; in other words, the piinctum remoUim, or far
point of vision, the most distant point at which it is pos-
sible to see with distinctness, is practicall}' at an infinite
distance. When accommodation is paralyzed by atropia,
only remote objects can be clearly seen. On the other hand,
the normal eye, or, to be more precise, the normal eve of
Y\c,. 269. — Myopic Eye.
The image P'of a distant point P falls in front of the retina even without acconinio-
dation. By means of a concave lens L the image may be made to fall on the retina
(dotted lines). To save space, P is placed much too near the eye in Figs. 268-270.
a middle-aged adult, can be adjusted for an object at a dis-
tance of not more than 12 cm. (or 5 inches). Nearer than
this it is not possible to see distinctly; this point is accord-
ingly called the punctnui proximiDn, or near point. The range
of accommodation for distinct vision in the emmetropic eye
is from 12 cm. to infinity.
Myopia, or short-sightedness, is generally due to the
excessive length of the antero-posterior diameter of the eye-
ball in relation to the converging power of the cornea and
the lens. Even in the absence of accommodation, parallel
rays are not focussed on the retina, but in front of it ; and
in order that a sharp image may be formed on the retina
THE SENSES
759
the object must be so near that the rays proceeding from it
to the eye are sensibly divergent — that is to say, it must be
at least nearer than 65 metres ; but as a rule an object at
a distance of more than 2 to 3 metres cannot be distinctly
seen. With the strongest accommodation the near point
may be as little as 5 cm. from the eye. The range of vision
in the myopic eye is therefore very small. The defect may
be corrected by concave glasses, which render the rays more
divergent. It is to be noted that many cases of internal
squint in children are connected with myopia, the eyes
necessarily rotating inwards as they are made to fix an
abnormally near object. The treatment both of the squint
and the myopia in these cases is the use of concave spec-
FiG. 270. — Hypermetropic Eye.
The image P' of a point P falls behind the retina in the unaccommodated eye. By
means of a convex lens it may be focussed on the retina without accommodation (dotted
lines).
tacles (Fig. 269), Myopia, although a condition that shows
a distinct hereditary tendency, is rarely present at birth ;
the elongation of the antero-posterior diameter of the eye-
ball develops gradually as the child grows.
In hypermetropia, or long-sightedness, the eye is, as a rule,
too short in relation to its converging power ; and with the
lens in the position of rest, parallel rays would be focussed
behind the retina. Accordingly the hypermetropic eye must
accommodate even for distant objects, while even with
maximum accommodation an object cannot be distinctly
seen unless it is farther away than the near point of the
emmetropic eye. The far point of distinct vision is at the
same distance as in the emmetropic eye, viz., at infinity ;
7 6o A M. { NUA L OF PHYSIOLOGY
the near point is farther from the eye. The defect is cor-
rected by convex ^dasses (Fig. 270). Hypermetropia, unlike
myopia, is present at birth.
Presbyopia, or the long-sightedness of old age, is not to
be confounded with hypermetropia. It is essentially due
to failure in the power of accommodation, chiefly through
weakness of the ciliary muscle, but partly owing to increased
rigidity and loss of elasticity of the lens. Images of distant
objects are still formed on the retina of the unaccommodated
eye with perfect sharpness ; i.e., the far point of vision is not
affected. But the eye is unable to accommodate sufficiently
for the rays diverging from an object at the ordinary near
point ; in other words, the near point is farther away than
normal. Convex glasses are again the remedy.
The near point of distinct vision can be fixed in various
ways — among others, by means of Scheiner's experiment
(Practical Exercises, p. 816). Two pin-holes are pricked in
a card at a distance less than the diameter of the pupil.
A needle viewed through the holes appears single when it is
accommodated for, double if it is out of focus. The near
point of vision is the nearest point at which the needle
can still, by the strongest effort of accommodation, be seen
single.
Astigmatism. — It has been mentioned that slight differences
of curvature along different meridians of the refracting
surfaces exist in all eyes. But in some cases the difference
in two meridians at right angles to each other is so great as
to amount to a serious defect of vision. To this condition
the name of ' astigmatism ' or ' regular astigmatism ' has
been given. It is usually due to an excess of curvature in
the vertical meridians of the cornea, less frequently in the
horizontal meridians ; occasionally the defect is in the lens.
Rays proceeding from a point are not focussed in a point,
but along two lines, a horizontal and a vertical, the hori-
zontal linear focus being in front of the other when the
vertical curvature is too great, behind it when the horizontal
curvature is excessive. The two limbs of a cross or the two
hands of a clock when they are at right angles to each other
cannot be seen distinctly at the same time, although they
THE SENSES
761
can be successively focussed. The condition ma)' be cor-
rected by glasses which are segments of cylinders cut
parallel to the axis.
The Ophthalmoscope. — The pupil of the normal eye is dark,
and the interior of the eye invisible, without special means
of illuminating it. But this is not because all the light that
falls upon the fundus is absorbed by the pigment of the
choroid, for even the pupil of an albino appears dark when
the eye is covered by a piece of black cloth with a hole in
front of the pupil.
Let the rays from a luminous point P be focussed by the
lens L at P' (l^g. 271 ;. It is plain that rays proceeding from
P' will e.xactly retrace
the path of those from
P and be focussed at P.
Now, the eye receives
rays from all directions,
and, when it is suf-
ficiently well illumi-
nated, sends ra}S out
in all directions. The ^"' -"'
moment, however, that the observing eye is placed in front
of the observed eye, the latter ceases to receive light from
the part of the field occupied by the pupil of the former, and
therefore ceases to reflect light into it.
This difficulty is avoided by the use of an ophthalmo-
scopic mirror. The original and theoretically the most
perfect form of such a mirror is a plate, or several superposed
plates, of glass, from which a beam of light from a laterally
placed candle or lamp is reflected into the observed eye, and
through which the eye of the observer looks (Fig. z^ji). But
the illumination thus obtained is comparatively faint ; and
a concave mirror, with a small hole m the centre for the
pupil of the observer's eye, is now generally used. In the
direct method of examination (Fig. 273), the mirror is held
close to the observed eye. and an erect virtual image of the
fundus is seen. When the eye of the observer and of the
patient are both emmetropic, and both eyes are unaccommo-
dated, the rays of hght proceeding from a point of the retina
762 A MANUAL OF PHYSIOLOGY
of the observed eye are rendered parallel by its dioptric media,
and are again brought to a focus on the observer's retina.
If the observed eye is myopic, the rays of light coming
Fit;. 272. -I-'IGUKE TO ILLUSTRATIi T}1E PrIN'CIPLE OF THE OPHTHALMOSCOPE.
Rays of light from a point P are reflected by a glass plate M (several plates together
in Helmholtz's original form) into the observed eye E'. Their focus would fall, as shown
in the figure, at P', a little behind the retina of E'. The portion of the retina AB is there-
fore illuminated by diffusion circles ; and the rays from a point of it F will, if E' is
emmetropic and unaccommodated, issue parallel from E' and be brought to a focus at
F' on the retina of the (emmetropic and unaccommodated) observing eye E.
Fig. 273.— Direct Method ok using 1 he Ophthalmoscope.
Light falling on the perforated concave mirror M passes into the observed eye E' ;
and, lx)lh E' and the observing eye E being supposed emmetropic and unaccommodated,
an erect virtual image of the illuminated retina of E' is seen by E.
from a point of the retina leave the eye, even when it is
unaccommodated, as a convergent pencil ; and the emme-
THE SENSES 763
tropic non-accommodated eye of the observer must have a
concave lens placed before it in order that the fundus may
be distinctly seen.
Fig. 274.— UbE OF the OPHXHALMOSCorE (Direct Method) iok n-siiNr,
Errors of Refraction in myopic eye.
Rays issuing from a point of the retina of E', the observed (myopic and unaccom-
modated) eye, pass out, not parallel, but convergent. They will therefore be focussed
in front of the retina of the observing (unaccommodated) eye E if the latter is emme-
tropic. By introducing a concave lens L of suitable strength, however, a clear view
of the retina of E' will be obtained, and the strength of this lens is the measure of the
amount of myopia.
Fig. 275.— Testing Errors of Refraction in Hypermetropic Eye.
Rays from a point of the retina of E', the observed eye, issue divergent, and are
focussed behind the retina of the observing (unaccommodated and emmetropic) eye E.
The strength of the convex lens L, which must be introduced in front of E to give clear
vision of the retina of E', measures the degree of hypermetropia.
When the observed e3-e is hypermetropic, the rays emerg-
ing from the unaccommodated eye are divergent, and a
convex lens, the strength of which is proportional to the
r04
A AfA NUA L OF I'll ) 'SIOL OG ) '
amount of hypernietropia, must be placed before the ob-
server's unaccommodated eye if he is to see the fundus
distinctly. By accommodating, the observer can see the
fundus clearl\- without a convex lens.
By this method errors of refraction in the eye may be
detected and measured.* The observer must always keep
his eye unaccommodated, and if it is not emmetropic, he
must know the amount of his short- or long-sightedness,
i.e., the strength and sign of the lens needed to correct his
defect of refraction, and must allow for this in ralcnlatin<::
Fk;. 276. — Indirect Meuiod 01 lsi.ng mik Oi'hi halmoscoi'K.
The rays of light issuing from E', the observed eye, are focussed by the biconvex lens
L. and a real inverted image of a portion of the retina of E , magnified four or five
times, is formed in the air between the lens and the observing eye E. This image is
viewed by E at the ordinary distance of distinct vision { 10 or 12 inches). (The exaggera-
tion of the size of the niirror makes it appear as if some of the rays from the lamp
passed through the lens before being reflected from the mirror. This would not be the
case in an actual observation. )
the defect of his patient. Non-accommodation of the eye
of the latter can always be secured by the use of atropia.
By the direct method of ophthalmoscopic examination,
only a small portion of the retina can be seen at a time, and
this is highly magnified. A larger, though less magnified,
view can be got by the indirect method. The observed eye
is illuminated as before, but the mirror and the observer's
* To a great extent the opthalinoscopic method of measuring errors of
refraction has been replaced by the more modern method of skiascopy
(shadow test;, which, however, it would be out of place to describe here.
Tin: SENSES 765
eye arc at a greater distance (Fig. 276). Here the rays
from a considerable portion of the retina, emerging in
parallel pencils if the observed eye is emmetropic and not
accommodated, are brought to a focus by a convex lens held
near the eye of the patient, so as to form a real and inverted
aerial image of the retina. This image is viewed by the
observer at his ordinary visual distance.
Single Vision with Both Eyes — Diplopia. — Scheiner's experi-
ment shows that it is possible to have double vision, or
diplopia, with a single eye when two separate images of the
same object fall upon different parts of the retina. In vision
with both eyes, or binocular vision, an image of every
object looked at is, of course, formed on each retina, and we
have to inquire how it is that as a rule these images are
blended in consciousness so as to produce the perception of
a single object ; and how it is that under certain conditions
this blending does not take place, and diplopia results. Two
chief theories have been invoked in the attempt to answer
these questions : (i) the theory of identical points, {2) the
theory of projection.
In regard to the second theory, we shall merely say that it
assumes that in some way or other the retina, or, rather, the
retino-cerebral apparatus, has the power of appreciating not
only the shape and size of an image, but also the direction
of the rays of light which form it, and that the position of
the object is arrived at by a process of mental projection of
the image into space along these directive lines. The first
theory we shall examine in some detail.
The Theory of Identical Points. — This theory assumes that
every point of one retina ' corresponds ' to a definite point of
the other retina, and that in virtue of this correspondence,
either by an inborn necessity or from experience, the mind
refers simultaneous impressions upon two corresponding or
identical points to a single point in external space. If we
imagine the two retinae in the position which the eyes
occupy when fixing an infinitely distant object (that is, with
the visual axes parallel) to be superposed, with fovea over
fovea, every point of the one retina will be covered by the
corresponding point of the other retina, so that identical
766 A MANUAL OF PHYSIOLOGY
points could be pricked through with a needle. But since
the actual centre of the retina does not correspond with the
fovea centralis (Fig. 258), but lies nearer the nasal side, the
nasal edge of the left retina will overlap the temporal edge
of the right, and the nasal edge of the right will overlap the
temporal edge of the left ; so that a part of each retina has
no corresponding points in the other.
When the eyes are directed to two distant objects at the same
height as themselves — when, in other words, the visual axes are
parallel and horizontal— neither the middle vertical meridians nor
the middle horizontal meridians of the two retinie, as a rule, exactly
correspond, although the correspondence is much nearer for the
horizontal than for the vertical meridians. A meridian of the left
retina, the upper end of which is slightly inclined towards the left,
contains the points corresponding to a meridian of the right eye
whose upper end is slightly inclined to the right. When \.\\\% physio-
logical inco/ignience of the retina: is taken into account in determining
the points which are to be considered as identical, the adherents of
this theory claim, and with justice, that a small object so situated
that its image must be formed on corresponding points of the two
retins does, as a rule, appear single, and, what is even more striking,
that a phosphene, or luminous circle produced by pressing the blunt
end of a pencil or the finger-nail on a point of the globe of one eye,
is not doubled by pressure over the corresponding point of the other
eye, although two circles are seen when pressure is made upon points
which do not correspond.
But too much weight must not be allowed to such evi-
dence, for it is also a fact that images situated on corre-
sponding points may not, and that images not situated on
corresponding points may, give rise to a single impression.
For example, if one of the closed eyes be held slightly out
of its ordinary position by the finger, pressure on identical
points of the two eyes gives rise to two separate phosphenes.
And some of the phenomena of stereoscopic vision (p. 767)
show clearly that images falling on non-corresponding points
may give a single impression ; while we do not habitually
see double, although it is certain that the images of multi-
tudes of objects are constantly falling on points of the retinae
not anatomically identical.*
* In every fixed position of the eyes, the objects whose images fall on
corresponding points will be arranged on certain definite lines or surfaces,
which vary with the direction of the visual axis, and to which the name
of horopter, or point-horopter, has been given. For most eyes w hen
THE SENSES 767
The question therefore arises, How is it that we do not
see these double images ? This is one of the difticulties of
the theory of identical points. The following is a partial
explanation : (i) The images of objects in the portion of
the field most distinctly seen, that is, the portion in the
immediate neighbourhood of the intersection of the visual
lines, or the part to which the gaze is directed, are formed
on identical points ; and by rapid movements the eyes fix
successively different parts of the field of view. (2) Vision
grows less distinct as we pass out from the centre of the
retina, and we are accustomed to neglect the blurred peri-
pheral images in comparison with those formed on the
fovea. (3) When the images of an object do not fall on
identical points, one of the points on which they do fall may
be occupied with the images of other objects, some of which
may be so boldly marked as to enter into conflict with the
extra image and to suppress it. (4) And lastly, the physio-
logical ' identical point ' is not a geometrical point, but an
area which increases in size in the more peripheral zones of
the retina, so that images which lie wholly or in chief part
within two corresponding areas practically coincide.
Stereoscopic Vision. — Although the retinal image is a projection
of external objects on a surface, we perceive not only the length and
breadth, but also the depth or solidity of the things we look at.
When we look directly at the front of a building, the impression as
to its form is the same whether one or both eyes be used, although
with a single eye its distance cannot be judged so accurately. But
when we view the building from such a position that one of the
corners is visible, we obtain a more correct impression of its depth
with the two eyes. This is partly due to the fact that to fix points at
different distances from the eyes the visual lines must be made to
converge more or less, and of the amount of this convergence we are
conscious through the contraction of the muscles which regulate it.
But there is another element involved. When the two eyes look at
directed to the horizon, that is, with the visual axes parallel, the horopter
is practically the horizontal plane of the ground, so that all objects
within the field of vision, and resting on the ground, fall upon corre-
sponding points, and are seen single. When the eyes are directed to a
point at such a distance that the lines of vision are sensibly convergent,
the horopter consists (i) of a straight line drawn through the fi.xing-point
and at right angles to the plane passing through the fixingpoint and the
two visual lines (visual plane) ; (2) of a circle passing through the fixing-
point and the nodal points of the two eyes (the famous horopteric circle
of MuUer).
768
A MANUAL OF I'/IYS/OLOCY
a uniformly-coloured plane surface, the retinal image is precisely the
same in both. But when the two eyes are directed to a solid object,
say a book lying on a table, the picture formed on the left retina
differs slightly from that formed on the right, for the left eye sees
more of the left side of the book, and the right eye more of the right
side.
'I'hat there is a close connection between uniformity of retinal images
and impression of a plane surface on the one hand, and difference of
retinal images and impression of solidity on the other, is proved by the
facts ol stereoscopy. It is evident that if an exact picture of the
solid object as it is seen by each eye can be thrown on the retina, the
impression produced will be the same, whether these images are really
formed by the object or not. Now, two such pictures can be pro-
duced with a near approach to accuracy by photographing the object
from the point of view of each eye. It only remains to cast the
image of each picture on the cor-
responding retina, while the eyes
are converged to the same extent
as would be the case if they were
viewing the actual object. This is
accomplished by means of a stereo-
scope (Fig. 277).
It is found that the resultant im-
pression is that of the solid object.
It is impossible to reconcile this
with the doctrine of strictly identical
l)oints. A pair of identical pictures
gives with the stereoscope not the
impression of a solid, but of a plane
surface. If the relative position of
any two points differs in the two
pictures, the blended picture has a
corresponding point in high or low
relief. So great is the delicacy of
this test that a good and a bad
banknote will not blend under the
stereoscope to a flat surface, and the
method may be actually used for
the detection of forgery.
\\'hen the pictures are inter-
changed in the stereoscope so that
the image which ought to be formed
on the right retina falls on the left,
and that which is intended for the left eye falls on the right, what
were projections before become hollows, and what were hollows stand
out in relief. The pseudoscope of Wheatstone is an arrangement by
which each eye sees an object by reflection, so that the images which
would be formed on the two retina;, if the object were looked at
directly, are interchanged, with the same reversal of our judgments of
relief.
Fk;. 277. — Bkkwstkk's Sikkko-
SCOFE.
/ and " are prisms, with their re-
fracting angles turned towards eacli
other. The prisms refract the rays
coming from the points c, 7 of the
pictures ab and u/3 so that they
appear to come from a single point ,/.
.Similarly, the points a and u appear
to be situated at /, and the points b
and /9 at ■:.
THE SENSES 769
Visual Judgments. — We %^^ jttdi^ments of relief; for what we call
seeing is essentially an act that involves intellectual processes. As
the retina is anatomically and developnicntally a projection of the
brain pushed out to catch the waves of lii^ht which beat in u[)on the
organism from every side, so physiologically retina, optic nerve and
visual nervous centre are bound together in an indissoluble chain.
We cannot say that the retina sees, we cannot say that the optic
nerve sees — the optic nerve in itself is blind — we cannot say that the
visual centre sees. The ethereal waves falling on the retina set up
impulses in it which ascend the optic nerve ; certain portions of the
brain are stirred to action, and the resulting sensations of light
springing up, we know not where, are elaborated, we know not how
(by processes of which we have not the faintest guess), into the per-
ception of what we call external objects — trees, houses, men, parts of
our own bodies, and into judgments of the relations of these things
among themselves, of their distance and movements.
A child learns to see, as it learns to speak, by a process, often un-
conscious or subconscious, of ' putting two and two together.' The
musical sounds united and terminated by noises which make up the
spoken word ' apple ' are gradually associated in its mind with the
visual sensation of a red or green object, the tactile sensation of a
smooth and round object, and the gustatory and olfactory sensations
which we call the taste or flavour of an apple. And as it is by
experience that the child learns to label this bundle of sensations
with a spoken, and afterwards wiih a written name, so it is by experience
that it learns to group the single sensations together, and to make the
induction that if the hand be stretched out to a certain distance and
in a certain direction {i.e., if various muscular movements, also
associated with sensations, be made), the tactile sensation of grasping
a smooth, round body will be felt, and that if the further muscular
movements involved in conveying it to the mouth be carried out, a
sensation agreeable to the youthful palate will follow. At length the
child comes to believe, and, unless he happens to be specially in-
structed, carries his belief with him to his grave, that when he looks
at an apple he sees a round, smooth, tolerably hard body, of definite
size and colour ; while in reality all that the sense of sight can inform
him of is the difference in the intensity and colour of the light falling
on his retina when he turns his head in a particular direction.
An interesting illustration of the role of experience in shaping our
visual judgments is found in the sensations of persons born blind and
relieved in after-life by operation. A boy between thirteen and four-
teen years of age, operated on by Cheselden, thought all the objects
he looked at touched his eyes. ' He forgot which was the dog and
which the cat, but catching the cat (which he knew by feeling), he
looked at her steadfastly and said, " So, Puss, I shall know you another
time." Pictures seemed to him only parti-coloured planes ; but all
at once, two months after the operation, he discovered they repre-
sented solids.' Nunnely, perhaps remembering the dictum of
Diderot, true as it is in the ma'n, though tinged with the exaggera-
tion of the Encychpedie, that ' to prepare and interrogate a person
49
7/0
A MANUAL OF PHYSIOLOGY
born blind would not have been an occupation unworthy of the
united talents of Newton, Des Cartes, Locke and Leibnitz,' made an
elaborate investigation in the case of a boy nine years old, on whom
he operated for congenital cataract of both eyes, and, what is of
special importance, instituted a set of careful experiments and
interrogations before the operation so as to gain data for comparison.
Objects (cubes and spheres) which before the operation he could
easily recognise by touch were shown him afterwards, but although
' he could at once perceive a difference in their shapes, he could not
In A the opaque body o
is in the plane of the pupil.
The position of the shadow
relatively to the bright field
is not altered when the
illuminating pencil is
focussed at F instead of
V. In H the opaque body
is in front of the plane
of the pupil. When P is
lowered to P'. the shadow
moves towards the upper
edge of the bright field,
and appears to move down-
wards in the visual field.
When P is raised, the
•shadow moves towards the
lower edge of the bright
field, and appears to move
upwards. In C the opaque
body is behind the plane
of the pupil. When P is
moved downwards to P',
the shadow moves towards
the lower edge of the bright
field, and appears to the
person under observation
to move upwards, and vice-
vend when P is moved
upwards. The farther the
opaque body is from the
pupil, the greater is the
apparent movement, or
parallax, of its shadow for
a given movement of the
source of light.
Fii;. 27S.
in the least say which was the cube and which the sphere.' It took
several days, and the objects had to be placed many times in his
hands before he could tell them by the eye. ' He said everything
touched his eyes, and walked most carefully about, with his hands
held out before him to prevent things hurting his eyes by touching
them.'
The apparent size and form of an object is intimately
related to the size, form, and sharpness of its image on the
retina. We are, therefore, able to discriminate with great
precision the unstimulated from the excited portions of that
THE SENSES 771
membrane, especially in the fovea centralis, and also the
decree of excitation of nei^'hbouring excited parts. But
instead of localizing the image on the retina as we localize
on the skin the pressure of an object in contact with it,
we project the retinal image into space, and see everything
outside the eye. In vision, in fact, we have no conception
of the existence of either retina or retinal image; and even
the shadows of objects within the eye are referred to points
outside it. Thus, for instance, an opacity or a foreign body
in any of the refractive media — and no eye is entirely free
from relatively opaque spots — can be detected, and its
position determined by the shadow which it casts on the
retina when the eye is examined by a pencil of light pro-
ceeding from a very small point. Let a diaphragm with a
small hole in it be placed in front of the eye at such a
distance that a pencil diverging from the hole will pass
through the vitreous humour as a parallel beam, equal in
cross-section to the pupil (Fig. 278), and let the aperture
be illuminated by focussing on it the light of a lamp placed
behind a screen. Opaque bodies in the vitreous humour will
cast shadows equal in area to themselves. The shadows of
opacities in the lens and in front of it will be somewhat
larger than the bodies themselves, since the latter intercept
rays which are still diverging ; but since the greater part of
the refraction of the eye occurs at the anterior surface of
the cornea, it is only the shadows of objects on the front of
the cornea, such as drops of mucus, which will be much
magnified. Fig. 278 shows diagrammatically how the shadows
shift their position within the bright field when the direction
of the illuminating beam is altered. Generally opacities in
the vitreous humour are movable, in the lens not.
Purkinje's Figures. — As was first pointed out by Purkinje,
the shadows of the bloodvessels in the retina itself, and even
of the corpuscles circulating in them, although neglected in
ordinary vision, may be recognised under suitable conditions,
a conclusive proof that the sensitive layer must lie behind
the vessels (p. 773).
If a beam of sunlight is concentrated on the sclerotic as far as
possible from the margin of the cornea, and the eye directed to a
49—2
77:
A MANUAL OF PHYSIOLOGY
dark ground, the network of retinal bloodvessels will stand out on it.
Another method is to look at a dark ground while a lighted candle,
held at one side of
the eye at a distance
from the visual line, is
moved slightly to and
fro. In the first
method, a point of the
sclerotic behind the
lens is illuminated,
and rays passing from
it across the interior
of the eyeball in every
direction cast shadows
of the vessels of the
retina on its sensitive
layer. In the second
method, the image of
the flame formed on
retina by rays fall-
obliquely through
pupil becomes in
general darkness
Fig. 279.— Method ok rkndering the Retinal
Bloodves>kls visible by concentrating a
Beam of Light on the Sclerotic.
From the brightly illuminated point of the sclerotic.
<7, rays is?ue, and a shai^ow of a vessel, v, is cast at a'.
It is referred to an fxiernal point a" in the direction of
the straioht line joinini; (7 wih the nodal point. When . ,^ r v u
the light is shifted so as -o be focussed at b, ihe shadow . itselt a SOUrce Ot light,
cast at h' is referred 'o b" , i.e.. it appears to move in the
same direction as the il umirated point of the sc'erot'C.
the
ing
the
the
Fig. 280.— Mli ih>i> oi- klndeking the
Bloodvessels of the Retina visible
BY Or.LiijuE Illlmination throc(;h
the Cornea.
Light from a candle at a illuminates a', and
rays proceeding from a' cast a S'hadow of the
bloodvessel v at a" , which is referred to a'".
When a is moved to b, the shadow on the
retina moves to b'\ and the shadow in the
by interrupting the
rays from which the
retinal vessels form shadows.
The distance of the sensitive
from the vascular layer may
be approximately calculated
by measuring the amount by
which the shadows change
their position, when the posi-
tion of the illuminated point
of the sclerotic is altered.
The nearer a vessel lies to
the sensitive layer, the smaller
must be the angle through
which the apparent position
of its shadow moves for a
given movement of the spot
of light. In this way it has
been calculated that the sensi-
tive layer is about o'2 to
o"3 mm. behind the stratum
which contains the blood-
vessels. This corresponds
sufficiently well with the posi-
visual held of the illuminated eye to /'".
tion of the layer of rods and cones, which all other evidence shows to
be the portion of the retina actually stimulated by light. The shadows
THE SENSES 773
of the blood-corpuscles in the retinal vessels may be rendered visible
by looking at a bright and uniformly illuminated ground, like the milk
glass shade of a lamp or the blue sky, and moving the slightly separated
fingers or a perforated card rapidly before the eye. From the rate
of their apparent movement, Vierordt calculated the velocity of the
blood in the retmal capillaries at 0-5 to 0*9 mm per second. One
reason why the shadows of these intra-retinal structures do not
appear in ordinary vision seems to be their small size. The retinal
vessels are in reality only vascular threads ; the thickest branch of
the central vein is not .r'- mm. in diameter. The apex of the cone
of complete shadow (umbra) cast by a disc of this size, at a distance
of 20 mm. from a pupil 4 mm. wide, would lie only \ mm. behind
the disc — that is to say, the umbra of the retinal vessels would not
reach the layer of the rods and cones at all, and only the penumbra,
or region of relative darkness, would fall upon it
When the eyes, after being closed for some time, are suddenly
opened, the branches of the retinal vessels may be seen for a
moment. This is especially the case after sleep ; and a good view
of the phenomenon may be obtained by looking at a white pillow or
the ceiling immediately on awaking. If the eyes are kept open for
a few seconds, the branching pattern fades away ; if they are only
allowed to remain open for an instant, it may be seen many times in
succession.
Relation of the Rods and Cones to Vision. — We have more
than once referred to the rods and cones as the sensitive
1 lyer of the retina. It is now necessary to develop a little
more the evidence in favour of this statement. And at
the outset, since the sensitive layer has been shown to lie
behind the plane of the retinal bloodvessels, the only com-
petitors of the rods and cones are the external nuclear
layer and the pigmented epithelium. The nuclear layer
may be at once excluded, because in the fovea centralis,
where vision is most distinct, it becomes very thin and
inconspicuous.
The layer of pigmented he.xagonal cells, or at least their
pigment, cannot be essential to vision, for albino rats,
rabbits and men, in whose eyes pigment is absent, can see.
In man and most mammals there are cones, but no rods in
the yellow spot and fovea centralis ; the relative proportion
of rods increases as we pass out from the fovea towards
the ora serrata. But this does not enable us to analyze
the bacillary layer into sensitive cones and non-sensitive
rods, for on the rim of the retina, which is still sensitive to
light, there are only rods ; in the bat and mole there are no
774 A MANUAL OF PHYSIOLOGY
cones in the yellow spot, in the rabbit very few. Reptiles
possess only cones over the whole retinal surface, and birds,
true to their reptilian affinities, have everywhere more cones
than rods, as have also fishes.
One of the most serious difficulties in the way of under-
standing how a ray of light can set up an excitation in a rod
or cone is the transparency of these structures. An absolutely
transparent substance — that is, a substance which would
allow light to traverse it without the least absorption —
would, after the passage of a ray, remain in precisely the
same state as before ; its condition could not be altered by
the passage of the light unless some of the energy of the
ethereal vibrations was transferred to it. But an absolutely
transparent body does not exist in Nature ; and it is not
necessary to suppose that all the energy required to stimulate
the end-organs of the optic nerve comes from the luminous
vibrations. These may, and probably do, act by setting
free energy stored up in the retina, just as the touch of a
child's hand could be made to fire a mine, or launch a ship,
or flood a province. Some have looked upon the transverse
lamellae into which the outer members of the rods and cones
can be made to split as an arrangement for reflecting back
the light to the inner members, and have compared them to
a pile of plates of glass, which, transparent as it is, is a most
efficient reflector. It is even possible, although here we are
already treading the thin air of pure speculation, that the
light may be polarized in the process of reflection, and that
the rods and cones may be less transparent to light polarized
in certain planes than to unpolarized light.
As to the nature of the transformation undergone by the
ethereal vibrations in the rods and cones, various theories
have been formed. Some have supposed that the absorbed
light-waves are transformed into long heat-waves, and that
the endings of the optic nerve are thus excited by thermal
stimuli. This hypothesis has so little evidence in its favour
that it is perhaps an unjustifiable waste of time even to
mention it. It is ruled out of court by the mere fact that
the long radiations of the ultra red, filtered from luminous
rays by being passed through a solution of iodine, and
THE SENSES 77 5
focussed on the eye by a lens of rock-salt, produce not the
slightest sensation of light, although they are by no means
all absorbed in their passage through the dioptric media.
Again, it has been suggested that the energy of the waves of
light is first transformed into electrical energy, and that the
visual stimulus is really electrical. In support of this view it
has been urged that light undoubtedly causes (p. 624) an
electrical change in the retina and optic nerve. But, as has
more than once been pointed out, an electrical change is the
token and accompaniment of the activity of the excitable
tissues in general; and all that the currents of action of the
retina show is that light excites the retina — a proposition
which nobody who can see requires an objective proof of,
and which does not carry us very far towards the solution of
the problem how that excitation is brought about. Lastly,
there is the photo-chemical theory, which owes its origin to
the discovery, or rather re-discovery, of the famous visual
purple or rhodopsin by Boll, and its present form to the
investigations and arguments of Kiihne. Though it has not
fulfilled all the hopes excited in sanguine minds, and has
not explained, or even lessened, the mystery of vision, the
discovery of the visual purple is in itself so interesting and
so suggestive as a basis for future work, that a short account
of the properties of the substance cannot be omitted here.
Visual Purple. — If the eye of a frog or
rabbit, which has been kept in the dark, be
cut out in a dimly-lighted chamber or in a
chamber illuminated only by red light, and
the retina removed, it is seen, when viewed
in ordinary light, to be of a beautiful red or
purple colour. Exposed to bright light, the
colour soon fades, passing through red and
orange to yellow, and then disappearing
altogether. The yellow colour is due to the
formation of another pigment, visual yellow ;
the preceding stages are due to the inter- Fig. 281.— Oi'togram.
mixture of this visual yellow with the un- Part of retina of rabbit,
changed visual purple in different propor- the eye of which had been
tions. With the microscope it may be seen ^j^f '^'l '° ^" illuminated
... . . y ^1 plate of glass covered with
that the pigment is entirely confined to the strips of black paper.
outer segment of the rods, where it exists in
most vertebrate animals. It may be extracted by a watery solution
of bile-salts, and the properties of the pigment in solution are very
n(j A MANUAL OF PHYSIOLOGY
much the same as its properties in situ ; light bleaches the solution
as it docs the retina Examined with the spectroscope, the solution
shows no definite bands, but only a general absorption, which is very
slight in the red, and reaches its maximum in the yellowish-green.
In accordance with this, it is found that of all kinds of monochro-
matic light the yellowish green rays bleach the purple most rapidly,
the red rays most slowly.
If a portion of the retina is kept dark while the rest is exposed to
light, only the latter portion is bleached. And when the image of an
object possessing well-marked contrasts of light and shadow {e.g.^ a
glass plate with strips of black paper pasted on it at intervals, or a
window with dark I)ars) is allowed to fall on an eye otherwise pro-
tected from light, the pattern of the object is picked out on the retina
in purple and white A veritable photograph or ' optogram ' may thus
be formed even on the retina of a living rabbit ; and if the eye be
rapidly excised, the picture may be ' fixed ' by a solution of alum,
and thus rendered permanent.
These facts certainly suggest that light falling on the
retina may cause in some sensitive substance or substances
chemical changes, the products of which stimulate the end-
ings of the optic nerve, and set up the impulses that result
in visual sensations.
The visual purple cannot itself be such a substance, for it is
absent from the cones of all animals and the rods of some.
Frogs and rabbits can undoubtedly see at a time when,
by continued exposure to bright sunlight, the purple must
have been completely bleached. And although the absence
of the pigment in the eye of the bat might seem to afford
a ready explanation of the proverbial * blindness ' of that
animal, such a hasty deduction would be at once corrected
by the fact that birds with as sharp vision as the pigeon are
equally devoid of visual purple. The pigmented retinal
epithelium is undoubtedly sensitive to light, and has im-
portant relations to the formation of the visual purple.
When the eye is exposed to light, the pigmented cells push
down processes between the rods. In the dark they draw
them back again, so that while it is easy to separate the
retina without the pigmented layer from the eye of an
animal kept in the dark, the hexagonal epithelium always
adheres to a retina which has shortly before death been acted
upon by light. The precise meaning of these changes of
form in the pigmented cells is unknown. Some have sup-
TUIi SENSES 777
posed that they alone contain the essential visual substance,
and that, altering their volume under the stimulus of light,
they press upon the cones, and in this way set up impulses
in the optic nerve. By others it has been plausibly urged
that in bright light the processes that stretch in among the
rods serve as insulators to confine the excitation by pre-
venting the lateral passage of scattered light from one
element to another. But it may be that the movements are
related rather to the formation of photo-chemical substances
to act as stimuli to the end-organs of the optic nerve. And
the pigmented epithelium is known to be concerned in the
regeneration of the visual purple. When a frog is curarized,
oedema occurs between the retina and the choroid, so that
the former membrane is separated from the hexagonal
epithelium. If the frog is now exposed to sunlight till the
visual purple is bleached, and the retina then taken out and
placed in the dark, no regeneration of the pigment takes
place. When the same experiment is repeated on a non-
curarized frog, the visual purple is restored in the dark, and
may be seen under the microscope in the rods. The only
difference in the two experiments is that in the latter the
pigmented epithelium adheres to the retina, and it must
therefore have a hand in the regeneration of the pigment.
Even the visual purple of a retina from which the epithelium
has been detached will, after being bleached, be restored if
the retina is simply laid again on the epithelial surface.
And it does not seem to be the black pigment of the hex-
agonal cells which is the agent in this restoration, for it takes
place in the pigment-free retinae of albino rabbits or rats.
Even a retina isolated from the pigmented epithelium, and
then bleached, may, to a certain extent, develop new visual
purple in the dark. This is even true when it has been kept
in the dark in a saturated solution of sodium chloride, and
is then, after washing with normal saline, bleached by light.
Here the regeneration of the pigment cannot be the result
of vital processes, but must be due to chemical changes in
products formed from the original pigment by the action of
light. No such regeneration takes place in a retina which,
after having been bleached in situ, is removed without the
778 A MANUAL OF PHYSIOLOGY
pigmented epithelium and placed in the dark ; and the only
probable explanation of the difference is that in this case
the photo-chemical substances from which visual purple can
be formed have been absorbed into the circulation, and have
so escaped.
The inner segments of the cones of certain animals (birds, reptiles,
and some fishes) contain globules of various colours, ranging over
almost the whole spectrum, and including, besides, the non-spectral
colour, purple. The globules are composed chiefly of fat with the
pigments (chromophanes, as they have been called) dissolved in it.
The function of these globules is unknown. They cannot be con-
cerned in colour vision, or, at least, they cannot be essential to it,
for in the human retina they do not exist.
The yellow pigment of the macula lutea does not belong to the
layer of rods and cones ; it only exists in the external molecular
layer and the layers in front of it ; in the fovea centralis it is absent.
The Blind Spot. — The fibres of the optic nerve are insensible
to light ; light only stimulates them through their end-organs.
This can be proved by directing by means of an ophthalmo-
scope a beam of light upon the optic disc, where the true
retinal layers do not exist. The person experimented on
has no sensation of light when the beam falls entirely upon
the disc ; when its direction is shifted so that it impinges
upon any other portion of the retina, a sensation of light is
at once experienced. The blind spot is not recognised in
ordinary vision, for (i) the two optic discs do not corre-
spond. The left disc has its corresponding points on a
sensitive part of the right retina, and the right disc on a
sensitive part of the left retina ; and the consequence is that
in binocular vision the objects whose images are formed on
the corresponding points fill up the blind spots. (2) The
optic disc does not lie in the line of direct, and therefore
distinct, vision. The eye is constantly moving so as to bring
the surrounding objects successively on the fovea centralis;
and the gap which the blind spot makes in the visual field
of a single eye is thus more easily neglected. In any case
we ought not to see it as a dark spot, for darkness is only
associated with the absence of excitation in parts of the
retina capable of being excited by light. There is no more
reason why the optic discs should appear dark than there is
for our having a sensation of darkness behind us when we
THE SENSES-
779
are lookinf^ straijj^ht in front. And since the experience of
our other senses, the sense of touch, for example, tells us
that the objects we look at do not in general have a gap in
the position corresponding to the part of the image that
falls on the blind spot, we see, so to speak, across the spot.
By Mariotte's experiment, however, the existence of the blind
spot can not only be demonstrated, but its size determined and its
boundaries mapped out. Let the left eye be closed, and fix with the
right the small cross ; then, if the eye be moved towards or away
from the paper, keeping the cross fixed all the time, a position will
Fn;. 282. — Mariotte's Experiment.
be found in which the white disc disappears altogether. In this
position its image falls on the blind spot. (See Practical Exercises,
Figs. 296, 297.)
Time necessary for Excitation of the Retina by Light — Fusion
of Stimuli. — Whatever the exact nature of retinal excitation may be,
it is called forth by exceedingly slight stimuli. A lightning flash,
although it may last only th of a second, lasts long enough
to be seen. A beam of light thrown from a rotating mirror on the
eye stimulates when it only acts for „ th of a second. The
^ ■' 5,000,000
nminimum stimulus in the form of green light corresponds, as we have
already seen (p. 573), to a quantity of work equivalent to no more
II , . I .,,. I
than X — f- gramme-degree, i.e. ,,. gramme-miUmietre, or - ,.
4-2 lo'-" ° '^ ' lO^'^ ° ic'
milligramme millimetre, which is the work done by th
° ■' 10,000,000
of a milligramme in falling through a millimetre ; and it cannot be
doubted that a portion even of this Lilliputian bombardment is
wasted as heat. So quickly, too, is the stimulus followed by the
response that no latent period has as yet ever been measured. It is
certain, however, that there is a latent period, as surely as there is a
latent period in the excitation of a naked nerve-trunk, although this
also has never been experimentally detected. The analogies, in fact,
between a muscular contraction and a retinal excitation are numerous
and close. Like the muscle, the retina seems to possess a store of
explosive material which the stimulus serves only to fire off. The
retina, like the muscle, is exhausted by its activity, and recovers
78o A MANUAL OF PHYSIOLOGY
during rest. Like the muscle curve, the curve of retinal excitation
rises not abruptly, but with a measurable slowness to its height, and
when stimulation is stoi)ped, takes a sensible time to fall again.
With comparatively slow intermittent stimuli the retinal, like the
muscle curve, flickers up and down. When the rate of stimulation
is increased, the steady contraction of the tetanized muscle is
analogous to the fusion of the individual stimuli by the tetanized
retina (or retino cerebral apparatus) into a continuous sensation of
light. But the maximum retinal excitation which a stimulus of given
strength can call forth depends much more closely upon the time
during which the stimulus acts than the maximum contraction does
upon the length of the muscular stimulus.
As the strength of the light increases in geometrical progression,
the time during which it must act in order to jjroduce its maximum
effect decreases approximately in arithmetical progression (Exner).
For light of moderate intensity this time is about \ second. As
soon as the stimulus of light is withdrawn the retinal excitation
begins to sink ; while a stimulated muscle need not even commence
its contraction till the stimulus has ceased to act. The result is, that
while a muscle in complete tetanus reaches a degree of contraction
as great as, or greater than, that produced by any one of a series of
stimuli acting alone, the retinal excitation, as measured by the
resultant sensation, is always less when a succession of similar stimuli
are fused than when any one of the stimuli is allowed to produce its
maximum effect.
If the time of each stimulus is equal to the interval during which
there is no stimulation, the sensation, when complete fusion has been
leached, is the same as would be produced by a constant light of
half the strength employed. And, in general, if /// be the pro-
portion of the time during which the eye is stimulated by a light of
intensity /, and n the proportion of the time during vvhich it is not
stimulated, the resultant impression is the same as that which would
be produced by an uninterrupted light of intensity ( I/. This
is Talbot's law, which may be expressed without the aid of symbols
thus : When a li^:;ht of given intensity is
alloived to act on the eye at intervals so short
that the impressions are completely fused, the
resultant sensation is independent of the abso-
lute h'n}:^th of each flash, and is proportional
only to the fractioti of the whole time which is
occupied by Jlashes and to the intensity of the
light. Talbot's law may be readily demon-
strated by means of a rotating disc with
alternate white and black sectors (Fig. 283),
I.-, - -V-. r>>c,. vr^n ,>l- SO arranged that the same proportion of the
r !(.. 203. — DISC tOK DL- D r 1 /- 1 1
.Mo.NsrKATiNciTAi.Bor's circumfercncc of each of the three concentric
Law. zones is black.
When the rotation is sufficiently rapid to
give complete fusion (say 20 to 30 times a second), the whole disc
THE S EASES 781
ap[)ears equally bright. However much the rate of rotation is now in-
creased, no further change occurs. It has been shown that even for
stimuli as short as the suiT^cTnTTt^' of a second, repeated at intervals
of yliyth second, Talbot's law holds good. So that not only does a
flash so inconceivably brief affect the retina, but it sets up changes
which last for a measurable time.
Colour Vision. — Besides differences in the distance, size,
shape, and brightness of objects, the eye recognises differ-
ences in their colour ; and we have now to consider the
physical and physiological differences on which these depend.
Colours may differ from each other — (i) In /o/ie or hue, e.g., red,
yellow, green. (2) In degree of saturation or fii/fiess or purity, i.e.,
in the degree in which they are free from admixture with white light ;
e.g., a 'pale' or Might' blue is a blue mixed with much white light,
a 'deep' or 'full' blue with little or none. (3) In brightness or in-
tensity, i.e., in the amount of the light coming from unit area of the
coloured object. Thus, a ' dark ' red cloth sends comparatively little
light to the eye, a ' bright ' red cloth sends a great deal.
When a beam of sunlight falls into the eye, a sensation of
' white light ' results. When a prism is placed before the eye,
the sensation is entirely different ; we see a spectrum running
up from red through green to violet, with a multitude of
intermediate shades. What, then, has happened ? Physi-
cally, nothing more has taken place than a rearrangement
of the rays in the beam of white light. A few of them may
have been lost by reflection, but upon the whole the beam
is made up of exactly the same constituents as before ; only
the rays are now arranged in the precise order of their
refrangibility, the more refrangible, which are also those
of shortest wave-length, being displaced more towards the
base of the prism than the longer and less refrangible rays.
Instead of the long and short rays falling together on the
same elements of the retina, as they did in the absence of
the prism, they now fall, if proper precautions have been
taken to secure a pure spectrum, in regular order from
one side to the other of the portion of retina on which
the image is formed. The physical condition, then, of our
sensations of the prismatic colours is, that rays of approxi-
mately the same wave-length should fall unmixed with other
rays upon the retinal elements. Rays of a wave-length of
760yo"oo to 650yii^^ give the sensation of red ; from 650,--^"^^^
782 A MANUAL OF PHYSIOLOGY
to 590tdVo. th^ sensation of orange; from 430,o"uu to 400^^^,
the sensation of violet, and so on. When rays of all these
wave-lengths fall together, in the proportions in which they
are present in sunlight, upon the same part of the retina,
the resultant physiological effect is very different ; we are
no longer able to distinguish red, blue, green, etc. ; we
receive the single sensation of white light. The sensation
is a simple one ; in consciousness we have no hint that it
has a multiple physical cause.
But we find further that it is not necessary for the
sensation of white light that waves of every length present
in the solar spectrum should be mixed. If rays of wave-
length 675y^*^^j (which acting alone produce the sensation
of red) be mixed in certain proportions, i.e., be allowed to
fall on the same part of the retina, with rays of wave-length
4g6y^^ (which give the sensation of bluish-green), the re-
sultant sensation is also that of white light. And an indefi-
nite number of sets can be combined, two and two, so as to
give the same sensation of white. Such colours are called
complementary. The following are pairs of complementary
colours :
Red and bluish-green. Yellow and indigo-blue.
Orange and cyan-blue. Greenish-yellow and violet.
The green of the spectrum has no simple complementary
colour ; purple, a mixture of red and violet, may be considered
complementary to it. Suppose now that one of a pair of
complementary colours is added to the other in greater
intensity than is required to give white, the resultant sensa-
tion is a colour which has a certain amount of resemblance
both to white and to the colour present in excess. Thus, if
the two colours are orange and blue, and the blue is present
in greater intensity than is necessary to give white, the
resultant colour is a whitish or pale blue, or, to use the
technical phrase, an unsaturated blue. The more nearly
the intensity of the blue rays in the mixed light approaches
the proportion necessary to give white, the less saturated is
the resultant colour ; the greater the excess of blue, the more
nearly does the resultant sensation approach that of the
saturated blue of the spectrum. But any non-saturated
THE SENSES
783
spectral colour produced by the mixture of two comple-
mentary colours may be equally well produced by the
mixture of the corresponding spectral colour with a certain
(juantity of ordinary white light. And it is found that when
two spectral colours which are not complementary are mixed
together the resultant is not white, but a colour which may
be matched by some spectral colour lying between the two,
plus a larger or smaller quantity of ordinary white light.
From all this it follows that the retina may be excited by
an infinite number of different physical stimuli, and yet the
resultant sensation may be the same. This leads straight
to the conclusion that somewhere or other in the retino-
Ct^ an Blue
Gj-een
\Y(llcur
In d icfoA-^
Yulet""""
"purple
Fic. 284. — Colour Triangle.
(Ill the description the point marked
referred to as W. )
White '
The ' colour triangle ' is
a graphic method of re-
presenting various facts in
colourniixture : (i) On the
curve the spectra! colours
are arranged at such dis-
tances that the angle con-
tained between straight
lines drawn from the point
W and intersecting the
curve at the positions cor-
responding to any two
colours is proportional to
iheir difference in tone.
(2) The distance of any
point on the curve from
W is proportional to the
stimulation intensity of the
colour corresponding to it. (If the stimulation intensities of all the colours be represented
by proportional weights lying at the corresponding points on the curve, W will be the
centre of gravity of the system.) (3) The position of a colour produced by the mixture
of any pair of spectral colours is found by joining the corresponding points by a
straight line. The mixed colour lies on this line at distances from the two points
inversely proportional to the stimulation intensity of the two colours, i.e., it lies in the
centre of gravity of the weights representing the two colours. (4) It is a particular
case of (3) that the complement4ry colours are situated "at the points where straight
lines drawn through W intersect the curve, since W is the centre of gravity correspond-
ing to a pair of colours only when it lies on the straight line joining them. The non-
spectral purple is represented by a broken line.
cerebral apparatus simphfication, or synthesis, of impressions
must take place ; and we have to inquire what the simplest
assumptions are which will explain all the phenomena.
Now, it is not possible, from two spectral colours alone, to
produce a sensation corresponding to any of the others.
By mixing three standard spectral colours, however, in
various proportions, we can produce not only the sensation
of white light, but that of every colour of the spectrum.
The simplest assumption we can make, then, is that there
784
A MANUAL OI- PIIYSlOLOijy
are three standard sensations, and that either the retina
itself can respond by no more than three distinct modes of
excitation to the muhiplex stimuH of the luminous vibra-
tions, or that complex impulses set up in the retina are
reduced to simplicity because the central apparatus is
capable of responding by only three distinct kinds of sensa-
tion. Which three sensations we select as fundamental or
primary is, to a certain extent, arbitrary. Fick chooses red,
green, and blue ; most commonly red, green, and violet are
accepted as the primary colours. The theory which best
explains the facts, and has been most widely accepted, is
that of Young, generally called, on account of its adoption
and extension by Helmholtz, the Young-Helmholtz theory.
It assumes that in the retina, or in the rctino-cerebral
Fig. 285.— Diagram ok Curves ok ExciTAiuLnv ok the Three Fibre-
groups.
apparatus, there are three kinds of elements — (i) ' red
fibres,' which are chiefly excited by light of comparatively
long wave-length (red), to a less extent by light of medium
wave-length (green), and to a still less extent by the shortest
visible waves (violet); (2) * green fibres,' mainly excited by
medium, but also to a certain extent by long and short
waves; (3) 'violet fibres,' chiefly affected by the short
vibrations, less by the medium, and still less by the long
waves. The curves in Figs. 285 and 286 illustrate these
relations. It must be carefully remembered that here the
word 'fibre' is merely a convenient term to avoid some
such cumbrous phrase as ' physiological unit.' There is no
ground for believing that an anatomical distinction of three
' fibre ' groups can be made in retina, optic nerve, or brain.
This assumption explains the phenomena of colour-
mixture to which we have referred above. When all the
THE SENSES
785
rays of the spectrum act upon the retina together, the three
groups of fibres are about ecjually excited, and this equal
excitation may be supposed to be the condition of the sensa-
tion of white Hght. When the green of the spectrum alone
falls on the retina, the green fibres are strongly excited, the
other two groups only slightly ; this is the relation between
the amount of excitation in the three groups which is
associated with a sensation of spectral green. When two
complementary colours, such as red and bluish-green, fall
together on the same portion of the retina, the three fibre
groups are excited in the relative proportions associated
with the sensation of white lisfht.
Fig. 286. — Curves oi" Excitability of Primary Sensations from
Observations on Colour Mixtures (Konig).
The numbers give wave-lengths of the spectrum in millionths of a mm.
' When the retina is stimulated by a succession of short flashes of
white light, that are not completely fused (as when the image of a
flame is looked at in a small revolving mirror, or the flame directly
viewed through a slit in a revolving disc), the proportion between
the amount of excitation in the three hypothetical groups of fibres is
not constant, and the resultant sensation is not that of white light.
For any given intensity of light, violet preponderates with a certain
duration of each stimulus; with a shorter duration, green; with a still
shorter duration, red.'* These phenomena are especially seen at the
edges of the image, which is surrounded by coloured fringes. The
explanation is that the sensation does not reach its maximum at the
same time for different colours, the excitation in the red fibres in-
creasing at first more rapidly than in the green, and in the green more
rapidly than in the violet. When the flashes are completely fused,
* Stewart, ' Proc. Roy. Soc. Edin.,' 1888, p. 441.
50
786 A MANUAL OF PlIYSIOLOCA'
the colour phenomena disappear, and the resultant impression is
white, because now the maximum excitation for the given intensity
of light and duration of each stimulus is steadily maintained.
It is a point of great theoretical interest that on the Young-Helm-
holtz theory the pure spectral colours, although physically saturated,
ought not to be physiologically saturated, since they all excite the
three fibre groups, although in different degrees. Now, it is found
that this is really the case. If, for example, we look first at the bluish-
green and then at the red of the spectrum, the sensation of red is
fuller or more saturated than if we had looked at the red directly.
Similarly, if we look first at a small bluish-green square on a black
ground, and then at a red ground, we see a more fully saturated
scjuare in the middle of the latter, llie explanation, on the Young-
Helmholtz theory, is that the 'green' fibres being tired before the
eye is turned ui)on the red, the latter colour no longer affects them,
or affects them less than it would otherwise do, and therefore the
excitation is almost entirely confined to the red fibres in the area
fatigued for green. This brings us to the subject of retinal fatigue,
and the related phenomena of after-images and contrast.
After-images. — We have seen that the retinal excitation
always takes time to die away after the stimulus is removed.
If a white object is looked at, especially when the eye is
fresh, for a time not long enough to cause fatigue, and the
eye is then closed, an image of the object remains for a short
time, diminishing in brightness at first rapidly, then more
slowly. This is a positive after-image, and by careful ob-
servation it may, under certain conditions, be seen that the
positive after-image of a white object, of a slit illuminated
by sunlight, for example, undergoes changes of colour as it
fades, passing through greenish-blue, indigo, violet, or rose,
to dirty orange. On the Young- Helmholtz theory this is
explained by the supposition that the excitation does not
decline with the same rapidity in the three hypothetical fibre
groups. If the object is looked at for a longer time, or if
the eye is fatigued, a dark or negative image may be seen
upon the faintly-illuminated ground of the closed eyes ; but
negative after-images may be more easily obtained when the
eye, after being made to fix a small white object on a black
ground, is suddenly turned upon a white or neutral tint
surface.
Here the portion of the retina on which the image of the object
is formed may be assumed to be more or less fatigued. And this
fatigue will extend to all three kinds of fibres ; so that white light of
rilE SENSES 787
a given intensity will now cause less excitation in this part than in
the rest of the retina. It is easy to understand that the negative
after-image of a coloured object will be seen, upon a white ground,
in the complementary colour, for the fibres chiefly excited by the
latter will have been least fatigued. The negative after-images seen
when the eye, after receiving the positive impression, is turned upon
a coloured ground, vary with the colour of the object and ground in
a manner which can be readily explained as due to fatigue of one or
other fibre group.
The phenomena of negative after-images are often included
together as examples of successive contrast, the name implying
mutual influence of the portions of the retina successively stimu-
lated. We have now to consider simultaneous contrast, often spoken
of simply as contrast.
Contrast. — A small white disc in a black field appears whiter,
and a small black disc in a white field darker, than a large surface
of exactly the same objective brightness. A disc with alternate
sectors of white and black, so arranged that the proportion of white
to black increases in each zone from centre to circumference, when
set in rotation, ought, by Talbot's law% to show sharply marked and
uniform rings, of which each is brighter than that internal to it.
But each zone appears brightest at its inner edge, where it borders
on a zone darker than itself, and darkest at its outer edge, where it
borders on a brighter zone. The most natural explanation of this is
that in the neighbourhood of an excited area of the retina, as well as
within the area itself, the excitability is diminished ; and the same
explanation holds for the contrast phenomena of coloured objects.
A small piece of grey paper, e.g.^ is placed on a green sheet, and
the whole covered with translucent tracing-paper. The grey patch
appears in the complementary colour of the ground, viz., rosered
(Meyer). Here we may suppose that the fatigue of the group of
fibres chiefly excited by the ground colour spreads into the portion
of the retina occupied by the image of the grey paper ; the white
light coming from the latter, therefore, excites mainly the fibres which
give the sensation of the complementary colour.
The curious phenomenon of coloured shadows is also an illus-
tration of contrast. They may be produced in various ways. For
example, when a lamp is lit in a room in the twilight, before it has
yet grown too dark, the shadows cast by opaque objects on a white
window-blind are coloured blue. The yellow light of the lamp
overpowers the feeble daylight which passes through the blind, and
the general ground is yellowish : but wherever a shadow is thrown
it appears of a bluish tint in contrast to the yellow ground. Here
the only illumination the eye receives from the region occupied by
the shadow is the feeble daylight. Falling upon an area in which
the fibres chiefly excited by yellow rays are more or less fatigued, it
causes a sensation of the complementary colour. As darkness comes
on, the shadows become black, for now practically no light at all
comes from them.
Helmholtz looked upon simultaneous contrast as a result of false
50—2
788 A MANUAL OF PHYSIOLOGY
judgment, and not a change of excitability in parts of the retina
bordering on the actually excited parts. For the sake of perspective,
it will be worth while to apply this theory by way of illustrating it, to
the explanation of the case of contrast we have just been consider-
ing, from the other point of view in Meyer's experiment. Helm-
holtz's explanation of this experiment is as follows : When a coloured
surface is covered with translucent paper, the latter appears as a
coloured covering spread over the field. The mind does not recog-
nise that at the grey patch there is any breach of continuity in this
covering ; it is therefore assumed that the greenish veil extends over
this spot too. Now, the grey seen through the translucent white
paper is objectively white — i.e., sends to the eye the vibrations
which together would give the sensation of white light. But with a
green veil in front of it, this could only happen if the really grey
patch was of the colour complementary to green — that is, rose-
red. The mind, therefore, judges falsely that the patch is red.
Hering has severely criticised this theory of Helmholtz as to false
judgments ; and the weight of evidence certainly seems to be in
favour of the view that simultaneous, like successive, contrast is due
to the influence of one portion of the retina, or reti no-cerebral
apparatus, on another.
The Young-Helmholtz theory of colour vision has not
met with universal acceptance. The most important rival
theory is that of Hering, who takes his stand upon the fact
that certain sensations of light (red, yellow, green, blue,
white, black) do appear to us to be fundamentally distinct
from each other, while all the rest are obviously mixtures
of these. Accepting these six as primary sensations, he
assumes the existence in the visual nervous apparatus of
substances of three different kinds, which may be called the
black-white, the green-red, and the blue-yellow. Like all
other constituents of the body, these substances are broken
down and built up again — in other words, undergo disassi-
milation and assimilation, destructive and constructive
metabolism. The sensations of black, of green, and of blue
he supposes to be associated with the constructive, and the
sensations of white, of red, and of yellow with the destruc-
tive, processes in the three substances. The black-white
substance is used up under the influence of all the rays of
the spectrum, but in different degrees ; the smaller the
quantity of light falling on the retina, the more rapidly is it
restored, and the more intense is the sensation of black.
The green-red substance is built up by green rays, broken
I HE S£,\'S£S 789
down by red. The blue-yellow substance is destroyed by
yellow rays, restored by blue. When any of the visual
substances are consumed at one part of the retina, they are
supposed to be more rapidly built up in the surrounding
parts, and in this way many of the phenomena of contrast
receive an easy and natural explanation.
Sensibility of Different Parts of the Retina. — The perception of
colours, like the perception of white light, is not equally distinct
over the whole retina. We have repeatedly had occasion to refer to
the fovea centralis as the region of most distinct vision ; but it
would be a mistake to suppose that it is therefore necessarily more
sensitive than the rest of the retina. As a matter of fact, when the
minimum intensity of white light which will cause an impression at all
is determined for each portion of the retina, it is found that the fovea
centralis requires a somewhat stronger stimulus than the zone im-
mediately surrounding it. But, with this exception, the sensibility
of the retina diminishes steadily from centre to periphery, both for
white and for coloured light. Konig has, indeed, upheld the para-
do.xical view that the fovea is absolutely blind for blue rays, support-
ing this assertion by two main experiments : (a) that when a number
of feebly illuminated blue points are looked at, those that fall on the
fovea disappear ; [/?) that when the moon is examined through a
blue glass, her image is blotted out as soon as it falls on the fovea.
But, as Gad has pointed out, the moon's image is of such dimen-
sions that it would lie well within the fovea, and there ought, there-
fore, to be no difficulty in getting it to disappear if Konig's theory
were true. Yet Konig himself admits that his second experiment is
difificult, and succeeds only under special conditions. Hering, too,
seems to have shattered Konig's first argument by showing that the
disappearance of the weakly illuminated blue points is only an illus-
tration of the phenomenon known as Maxwell's spot, a dark-blue or
almost black blot, seen in the visual field when the eye, after being
kept closed for a short time, is directed to a surface illuminated
by a weak blue light. It is due to the absorption of blue light by
the pigment of the yellow spot, and stands out as a rose-coloured
disc when a source of white light is looked at through a solution of
chrome alum, since all the light which the chrome alum permits to
■pass is absorbed by the macula lutea, except the red rays. Hering,
indeed, asserts that the fovea is the most sensitive part of the retina
for colours, in opposition to Charpentier, who finds it slightly
less sensitive for blue than the zone immediately external to it.
When the eye is fixed and the visual field— that is, the whole space
from which light can reach the retina in the given position — or, what
comes to the same thing, the projection of the visual field on the
retina by straight lines passing through the nodal point, explored by
means of a perimeter (Fig. 287), it is found that, under ordinary
conditions, a white object is seen over a wider field than any coloured
object, a blue object over a wider field than a red, and a red over a
790
A MANUAL OF PHYSIOLOGY
wider field than a green object. The exact shape, as well as size, of
the visual field also differs somewhat for different colours. And
although it has been shown by Aubert and others that monochro-
matic light of sufficient
intensity can be per-
ceived over the whole
retina, yet it may be
said that the retinal rim
is even then relatively
and, under ordinary
conditions, absolutely
colour-blind. This and
other facts have given
rise to the theory that
the rods, which are
alone present at the ora
serrata, have for their
function the mere per-
ception of luminous im-
pressions as such, with-
out any distinction of
quality or of colour.
'1 he cones are supposed
on this theory to be
Fig. 287. — Priestley Smith's Perimeter piore highly developed
(Jung, Heidelberg). ^^^^ ^^e rods, their
K. rest for chin ; O, position of eye ; Ob, object, function being COn-
white or coloured, which shdes on the graduated arc '""^i-'"" ". ,'& . !
B ; f, point fixed by the eye. nected especially With
the perception of colour.
And there are, indeed, certain histological facts that favour the view
that the cones are a more highly developed form of the rods.
This brings us to the subject of colour-blindness proper,
a phenomenon of the greatest interest in its theoretical as
well as in its practical bearings.
Colour-blindness. — A considerable number of persons
(about 4 per cent, of all males, but only one-tenth of this
proportion of females) are deficient in the power of distin-
guishing between certain colours. They are said to be
colour-blind ; but the term must not be taken to signify that
they are absolutely devoid of colour-sensations. A very
small minority of the colour-blind appear to have but one
sensation of colour ; a few confuse green with blue ; the
great majority are unable to distinguish between red and
green. The condition will be most easily understood by
considering some of the extraordinary mistakes which may
THE SEA'SES
79 r
be made by the colour-blind without necessarily leadiiif^
them to suspect that there is anything abnormal in their
vision. Thus, to quote the words of a distinguished writer
on this subject, himself a sufferer from the deficiency:
* A naval officer purchases red breeches to match his blue
uniform ; a tailor repairs a black article of dress with
crimson cloth ; a painter colours trees red, the sky pink,
and human cheeks blue.' The shoemaker, Harris, the dis-
FlG. 2i
-Perimetric Chart.
Obtained with the perimeter shown in Fig. 287. The numbers represent degrees
of the visual field measured on the graduated arc of the perin)c!er.
coverer of colour-blindness, picked up a stocking, and was
surprised to hear other people describe it as a red stocking ;
it seemed to him only a stocking. The celebrated Dalton
was twenty-six years of age before he knew that he was
colour-blind. He matched samples of red, pink, orange,
and brown silk with green of different shades ; blue both
with pink and with violet ; lilac with grey.
792 A MANC/AL OF PHYSIOLOGY
When the condition of vision in the great majority of the colour-
hHnd is tested by means of the spectrum, it is found that they fall
into two classes : (i) A class (of green blind) by whom the whole of
the spectrum from red to yellow is described as yellow of different
degrees of brightness (intensity) ; the green appears as a i)ale yellow
with a grey or white band in its midst ; while the violet end is seen
as different shades of blue. (2) A class (of red-blind) whose whole
spectrum, from red to green, is seen as green of different intensities,
the extreme red being entirely invisible. The violet end is blue, as
in (i), and there is a band of white or grey near the blue end of the
green.
The brightest part of the spectrum to a normal eye, and also to a
green blind eye, is the yellow ; to a red-blind person it is the green.
This may perhaps explain the terms which the colour-blind employ
in describing their less refrangible spectral colours. 'To the green-
blind red and yellow are the same colour, but the yellow being the
brighter, he looks on red as degraded or darkened yellow. On the
other hand, to the red-blind green is brighter than yellow or orange,
and these appear as degraded green.'*
Sir John Herschell explained Dalton's peculiarity of vision on the
hypothesis that he only possessed two, instead of three, primary
sensations.
On the Young-Helmholtz theory, the missing sensation is supposed
to be either red or green. At the intersection of the curves that
represent the violet and green sensations (Figs. 285, 286), the red-
blind individual will see what he describes as white — viz., the sensa-
tion produced by the stimulation of the only two fibre-groups he
possesses. Similarly, at the intersection of the red and violet curves,
the green-blind i)erson will see what is white to him.
On Hering's theory the colour blind possess the blue-yellow, but
lack the green-red, visual substance. So that on this theory there
should be no difference between red-blindness and green-blindness.
But v. Kries, in a study of twenty cases of congenital partial colour-
blindness, brings forward strong evidence that the red-green blind
can be divided, as regards the comparison of red (lithium) and
orange (sodium) light, into two sharply-separated groups — a result
which is emphatically in favour of the Young-Helmholtz theory, and
against the theory of Hering. It is, however, equally difficult to
reconcile some of the phenomena of colour-blindness produced by
disease (atrophy of the optic nerve) or by abuse of tobacco with the
Young-Helmholtz theory, for in some of these cases the only colour
seen in the spectrum is blue, the rest is white ; and the theory does
not provide for the production of the sensation of white by excitation
of a single group of fibres with ordinary intensity pf stimulation.
Colour-blindness, in its true sense, is always congenital, often
hereditary ; the colour-blind are ' born, not made.' And although
the condition cannot be cured, it is of great importance that it should
be recognised in the case of persons occupying positions such as
those of engine drivers, railway-guards, and sailors, in which coloured
* Rep. Roy. Soc. Com. on Colour Blindness.
THE S/'J.ys/-S 793
lights liavc to be distinguished, lor, while it is true that the sensa-
tions which red and green lights give the colour-blind are far from
being identical (Pole) under favourable conditions, it is precisely
when the conditions are unfavourable, as in a fog or a snow-storm,
that the capacity of distinguishing them becomes invaluable.
Irradiation was first described by Kei)ler, who gave as an example
the appearance known as the ' new moon in the old moon's arms,*
where the crescent of the new moon seems to overlap and embrace
the unilluminated portion of the lunar disc. A white circle on a
black ground (Fig. 289) api)ears, in a good light, to be larger than
an exactly equal black circle
on a white ground. The ex-
planation seems to be as fol-
lows : Owing to the aberration
of the refractive media of the
eye, all the rays proceeding
from the luminous object are
not brought accurately to a
focus on the retina, and the Fi<:. ^^
image is surrounded by diffu-
sion circles which encroach upon the unilluminated boundary.
Physically these represent a weaker illumination than that of the
image proper, and therefore the latter ought to stand out in its
real size as a brighter area surrounded by weaker haloes. That
this is not the case, and that the image is projected in its full
brightness for a certain distance over its dark boundary, is due to
two things: (1) That the eye does not recognise very small differ-
ences of brightness, and (2) that not only is the neighbourhood of
the directly illuminated field stimulated by the light which falls on
it in diffusion circles, but the excitation set up in a given area of the
retina is propagated for a short distance into the surrounding parts
(Descartes).
When the accommodation is not perfect, the diffusion circles are,
of course, much wider, and irradiation is better marked when the
object is a little out of focus. When it is too much out of focus,
however, the diffusion circles are no longer blended with the rest of
the image ; and since their formation weakens the illumination at
the edge of the true image as much as it strengthens the illumina-
tion beyond the edge, the effect when the light is very weak is a
negative irradiation. Under these conditions, a white disc on a
black ground seems smaller than a black disc on a white ground
(Volkmann).
The Movements of the Eyes. — That the eyes may be efficient
instruments of vision, it is necessary that they should have
the power of moving independently of the head. An eye
which could not move, though certainly better than an eye
which could not see, would yet be as imperfect after its
kind as a ship which could run before the wind, but could
794 A MANUAL OF I'lIYSIOLOdV
not tack. The mere fact that the angle between the visual
axes must be adapted to the distance of the object looked
at renders this obvious ; and the beauty of the intrinsic
mechanism of the eyeball has its fitting complement in the
precision, delicacy, and range of movement conferred upon
it by its extrinsic muscles.
Not only are movements of convergence and divergence
of the eyeballs necessary in accommodating for objects at
different distances, but without compensatory movements
of the eyes it would be impossible to avoid diplopia with
every movement of the head ; for the images of an object
fixed in one position of the head would not continue to fall
on corresponding points of the retinae in another position.
All the complicated movements of the eyeball may be
looked upon as rotations round axes passing through a
single point, which to a near approximation always remains
fixed, and is situated about 177 mm. behind the centre of
the eye.
The position which the eyeballs take up when the gaze is directed
to the horizon, or to any distant point at the level of the eyes, is
called the primary position. Here the visual axes are parallel, and
the plane passing through them horizontal. While the head remains
fixed in this position, the eyeballs can rotate up or down around a
horizontal axis, or from side to side around a vertical axis; or upwards
and inwards, downwards and outwards, downwards and inwards, and
upwards and outwards around oblique axes, which always lie in the
same plane as the vertical and horizontal axes of rotation, i.e., in the
vertical plane passing through the fixed centre of rotation. These
facts, spoken of collectively as Listing's law, and first deduced by
him from theoretical considerations, were afterwards proved experi-
mentally by Helmholtz and Donders. It necessarily follows from
Listing's law (and this is, indeed, another way of stating it) that
in moving from the primary position into any other, there is no
rotation of the eyeball round the visual axis — no wheel-movement,
as it is called.
A true rotation of the eye round the visual axis does, however,
occur when the eyes are converged as in accommodation for a near
object, each eyeball rotating towards the temporal side. This is
especially the case when the eyes are at the same time converged
and directed downwards ; and the rotation may amount to as much
as 5°. When the head is rolled from side to side, while the eyes are
kept fixed on an object, a slight compensatory rotation of the eyeballs
takes place against the direction of rotation of the head. The amount
of rotation of the eyes is relatively greater for small than for large
TlIJi SENSES 795
movements of the head (eye 5 for head 20" ; eye 10° for head 80° —
Kiister).
The Extrinsic Muscles of the Eye. — The eyeball is acted
upon by six muscles arranged in three pairs, which may be
considered, roughly speaking, as antagonistic sets. These
are the internal and external recti, the superior and inferior
recti, and the superior and inferior obliqui.
Although the movements of the eye have been very fully
studied, and are, upon the whole, well understood, our
knowledge of the manner in which any given movement is
brought about, and the exact action of the muscles which
cu
-^ ^
4\
^\ /f Oil. sun
R.SUft.
■ R. inf
Fk;. 290. — Horizontal StciioN ov Left Evt.
Arrows show direction of pull of the muscles. The axis of rotation of the external
and internal recti would pass through the intersection of a and ^ at right angles to the
plane of the paper.
take part in it, is by no means as copious and precise. And
from the nature of the case, the greater part of what we do
know has been inferred from the anatomical relations of the
muscles as revealed by dissection in the dead body rather
than gained from actual observation of the living eye. A
plane, called the plane of traction, is supposed to pass through
the middle points of the origin and insertion of the muscle
whose action is to be investigated, and through the centre
of rotation of the eyeball. A straight line drawn at right
angles to this plane through the centre of rotation is evidently
the axis round which the muscle when it contracts will cause
the eye to rotate, provided that the fibres of the muscle are
796 A MANUAL OF PHYSIOLOGY
symmetrically distributed on each side of the plane of
traction. The axes of rotation of the antagonistic pairs
almost, but not completely, coincide with each other. The
common axis of the external and internal recti practically
coincides with the vertical axis of the eyeball (Fig. 290) in the
primary position. The eye is turned towards the temple
when the external rectus alone contracts, towards the nose
when the internal rectus alone contracts. The common
axis of the superior and inferior recti, /3, lies in the horizontal
visual plane in the primary position, but makes an angle of
about 20° with the transverse axis, its inner end being tilted
forwards. The consequence is that contraction of the
superior rectus turns the eye up, and contraction of the
inferior rectus turns it down, but both movements are also
combined with a slight inward rotation. The common axis
of the oblique muscles, a, makes an angle of 60° with the
transverse axis, the outer end of it being the most anterior.
The direction of traction of the superior oblique is, of course,
given not by the line joining its bony origin and its. insertion,
but by the direction of the portion reflected over the pulley.
When the superior oblique contracts alone, the eyeball is
rotated outwards and downwards; the inferior oblique
causes an outward and upward rotation. None of the
common axes of rotation of the pairs of muscles, except
that of the external and internal recti, lies in Listing's plane.
Now, as we have seen that every movement which the eye,
supposed to be originally in the primary position, can
execute may be considered as a rotation round an axis in
this plane, it is clear that every movement, except truly
transverse rotation, must be brought about by more than
one pair of muscles. For vertical rotation, the inward pull
of the superior rectus is antagonized by a simultaneous out-
ward pull of the inferior oblique; for downward rotation,
the inferior rectus and superior oblique act together. In
oblique movements, a muscle of each of the three pairs is
concerned.
THE S/:A'S£S
797
HEARING.
The transverse vibrations of the ether fall upon all parts of the
surface of the body, but only find nerve-endings capable of giving
the sensation of light in the little discs which we call the retinai. So
the much longer and slower longitudinal waves of condensation and
rarefaction which are being constantly originated in the air or im-
parted to it by solid or licjuid botiics that have been themselves set
vibrating fall upon all [)arts of the surface, but only produce the
sensation of sound when they strike u[)on the tiny mechanism of the
internal ear.
But just as the ethereal vibrations, and especially those of greater
wave-length, are able to excite certain end-organs in the skin which
have to do with the sensation of temperature, so the sound-waves,
tn, external meatus ;
/, head of malleus
o, short process of malleus ;
,0', handle of malleus ;
//, incus ;
/, foot of stapes in oval foramen
r, tympanic membrane.
0 d c I
Fig. 291.— The Ear.
when sufficiently large, are also capable of stimulating certain
cutaneous nerves and of giving rise to a sensation of mtermittent
pressure or thrill. This is readily perceived when the finger is
immersed in a vessel of water into which dips a tube connected
with a source of sound, or when a vibratmg bell or tuning-fork is
touched. So far as we know, what takes place in the ear is essen-
tially similar— that is to say, a mechanical stimulation of the ends ot
the auditory nerve, but a stimulation which acts through, and is
graduated and controlled by, a special intermediate mechanism.
As the visual apparatus consists of a sensitive surface, the
retina, which contains the end-organs of the optic nerve and
of dioptric arrangements which receive and focus the rays of
light, the auditory apparatus consists of the sensitive end-
798 A MANUAL OF I'll Y SI O LOGY
organs of the eighth nerve and of a mechanism which
receives the sound-waves and communicates them to these.
Physiological Anatomy of the Ear. — At the bottom of the external
auditory meatus lies the membrana tyuipani, a nearly circular mem-
brane set like a drum-skin in a ring of bone, and separating the
meatus from the tympanum or middle ear. Its external surface looks
oblitjuely downwards, and at the same time somewhat forwards, so
that if prolonged the membranes of the two ears would cut each
other in front of, and also below, the horizontal line passing through
the centre of each (Figs. 291, 292).
The tympanum contains a chain of little bones stretching right
across it from outer to inner wall. Of these the malleus, or hammer,
is the most external. Its manubrium, or handle, is inserted into
the membrana tympani, which is not stretched taut within its bony
ring, but bulges inwards at the centre, where the handle of the
malleus is attached. The stapes, or stirrup, is the most internal of
the chain of ossicles, and is inserted by its foot-plate into a small
oval opening — the foramen ovale — on the inner wall of the tympanic
cavity. A membranous ring^ — the orbicular membrane — surrounds
the foot of the stapes, helping to fill up the foramen and attaching
the bone to its edges. The incus, or anvil, forms a link between the
malleus and the stapes. The auditory ossicles, as well as the whole
cavity of the tympanum, are covered by pavement epithelium. The
tympanum is not an absolutely closed chamber ; it has one channel
of communication with the external air — the Eustachian tube. By the
action of the cilia which line this tube the scanty secretion of the
middle ear is moved towards its pharyngeal opening. The loosely-
jointed chain of ossicles is steadied and its movements directed by
ligaments and by the tension of its terminal membranes. It forms a
kind of bent lever, by which the oscillations of the membrana
tympani are transferred to the membrane covering the oval foramen,
and at the same time reduced in size. Two slender muscles, the
tensor tympani and stapedius, contained in the tym|)anic cavity, are
also connected with and may act upon the ossicles. The former lies
in a groove above the Eustachian tube, and its tendon, passing round
a kind of osseous pulley (processus cochleariformis), is inserted into
the handle of the malleus ; the stapedius is lodged in a hollow of the
inner bony wall of the tympanum. Its tendon is attached to the neck
of the stapes near its articulation with the incus. This inner wall is
pierced not only by the oval foramen, but also by a routid opening,
the fenestra rotunda, which is closed by a membrane to which the
name of secondary membrana tympani is sometimes given.
The internal ear consists of the bony labyrinth, a series of curiously
excavated and communicating spaces in the substance of the petrous
portion of the temporal bone, filled with a liquid called the peri-
lymph, in which, anchored by strands of connective tissue, floats a
corresponding series of membranous canals (the membranous laby-
rinth), filled with a liquid called endolymph. The labyrinth of the
internal ear is divided into three well-marked parts : the cochlea, the
THE SENSES
79)
vestibule, and the semicircular canals (Fig. 292). The cochlea, the
most anterior of the three, consists of a convoluted tube which coils
round a central pillar or modiolus like a spiral staircase. The
lamina spiralis, which, except that it forms a continuous surface, may
be taken as representing the steps, ])rojects from the modiolus and
,Vcsii ^ule u/^ith
Seal a Vestibuli
Cvchleal
bcala .,
Tymnarii
openings of
Semicircular Canals
/y\^/'^ ■ ■ \Jncu s
j^ \ (( ..\lMalleus
f^ y \\ / JL .Stanes
Ext. A ud.Mealu s
ZMe mhra n a Tymp an t
'^'^ustachian tuh
Fig. 292.— Middle and Internal Ear (Diagrammatic).
divides the tube into an upper compartment, the scala vestibuli, and
a lower, the scala tympani (Fig. 293). The part of the lamina next
the modiolus is of bone, but it is completed at its outer edge by a
membrane, the lamina spiralis membranacea. The scala tympani
abuts on the fenestra rotunda, and its perilymph is only separated
•Reissner's tnemlrane
Nerve. —
Seal a Tymp ant "
^^Xanahs cochleae
^ \^ Tt/T 2 .
1 lectori a
^.Jfair cells
•/m"Meml) r an a
-^ Jj^ baSt/aris
Jm-Ptllars of Corli
Fig. 293.— Transverse Section of a Turn of the Cochlea (Diagram.
MATIC).
from the air of the tympanic cavity by the membrane which closes
that opening. At the apex of the cochlea the lamina spiralis is
incomplete, ending in a crescentic border, so that the scala tympani
and the scala vestibuli here communicate by a small opening, the
helicolrema. The scala vestibuli communicates with the vestibule,
8oo A MANUAL OF PHYSIOLOGY
and the vestibule with the semicircular canals, so that the peri-
lymph of the entire labyrinth forms a coniinuous sheet, separated
from the cavity of the middle ear by the structures that fill uj)
the round and oval foramina. In the membranous labyrinth, and in
it alone, arc contained the end organs of the auditory nerve. The
membranous portion of the cochlea is a small canal of triangular
section, cut off from the scala vestibuli by the membrane of Reissner,
which stretches from near the edge of the bony spiral lamina to the
outer wall (Fig. 293). It has received the name of the scala media,
or canal of the cochlea. Below it ends blindly, but communicates
by a side-channel with the portion of the membranous vestibule called
the saccule, which in its turn communicates with the utricle by a
Y-shaped sac, the saccus endolymphaticus. Into the utricle open
the three semicircular canals, the endolymph of which has, there-
fore, free communication with that of the vestibule and cochlea.
But although the semicircular canals and vestibule belong anatomi-
cally to the internal ear, and are supplied by branches of the auditory
nerve, we have no positive proof that in the higher animals, at least,
they are in any way concerned in hearing ; and since t.xperiment has
assigned them, with a great degree of probability, a definite function
of another kind (p. 698), we shall not consider them further in this
connection. The scala media contains the organ of Corti, which
(Fig. 293) consists of a series of modified epithelial cells planted
upon the membranous spiral lamina or basilar membrane. The
most conspicuous constituent of the latter is a layer of parallel trans-
parent fibrils. The epithelial cells are of two kinds : (i) the pillars
or rods of Corti, sloped against each other like the rafters of a roof,
and covering in a vault or tunnel which r\]ns along the whole of the
scala media from the base to the apex of the cochlea ; (2) the hair-
cells, which are columnar epithelial cells running out below into
processes connected with the terminal fibres of the auditory nerve,
and surmounted by hairs. They are arranged in several rows, one
row lying just internal to the inner line of pillars, and four or five
rows external to the outer line of pillars. A thin membrane, the
membrana reticularis, covers the pillars and hair-cells of Corti, and
is pierced by the hairs ; while a thicker membrane, the membrana
tectoria, springing from the edge of the osseous spiral lamina near
the attachment of Reissner's membrane, forms a kind of canopy over
both pillars and hair-cells. The fact that the hair-cells of Corti's
organ are connected with the fibres of the cochlear division of the
auditory nerve, and its elaborate structure, suggest that it must play
a peculiar part in auditory sensation. Comparative anatomy shows
us that the cochlea is the most highly-developed portion of the
internal ear, the last to appear in its evolution, and the most
specialized. It is absent in fishes, which possess only a vestibule
and one to three semicircular canals. It first acquires importance in
reptiles, but attains its highest development in mammals ; and there
is every reason to believe that it is the terminal apparatus of the
sense of hearing.
THE SENSES 8oi
Function of the Auditory Ossicles. — The anatomical arranj^e-
ments of the middle ear su<,'f^est that the tympanic membrane
and the chain of ossicles have the function of transmitting
the sound-waves to the liquids of the labyrinth ; and obser-
vation and experiment fully confirm this idea. Tracings of
the movements of the ossicles have been obtained by attach-
ing very small levers to them, and their movements have
been directly observed with the microscope. Even in man
it may be shown, by viewing the membrane through a series
of slits in a rapidly-revolving disc (stroboscope), that it
vibrates when sound-waves fall on it.
When the handle of the malleus moves inwards, the joint
between that bone and the incus is locked, on account of
the shape of the articular surfaces, and the stapes is pressed
into the oval foramen. When the tympanic membrane
passes outwards, the handle of the malleus and foot of the
stapes do the same. But the joint now unlocks, and exces-
sive outward movement of the stapes, which might result in
its being torn from its orbicular attachment, is prevented.
The ossicles vibrate en masse. It is only to a trifling
extent that sound can be conducted through them to the
labyrinth as a molecular vibration ; for when they are
anchylosed, and the foot of the stapes fixed immovably in
the foramen ovale, as sometimes occurs in disease, hearing
is greatly impaired.
Of course, every vibration of the tympanic membrane
must cause a corresponding condensation and rarefaction of
the air in the middle ear ; and this may act on the mem-
brane closing the fenestra rotunda, and set up oscillations in
the perilymph of the scala tympani. That this is a possible
method of conduction of sound is shown by the fact that,
even after closure of the oval foramen, a slight power of
hearing may remain. But under ordinary conditions by far
the most important part of the conduction takes place via
the ossicles. And when it is remembered that the tympanic
membrane is about thirty times larger than that which fills
the oval foramen, it will be seen that the force acting on unit
area of the foot of the stapes may be much greater than that
acting on unit area of the membrana tympani, and that the
51
8o2 .1 MAM'A/. Ol' PHYSIOLOGY
mode of transmission by the ossicles is a very advantageous
method of transforming the feeble but comparatively large
excursion of the tympanic membrane into the smaller but
more powerful movements of the stapes. Even the so-called
cranial conduction of sound when a tuning-fork is held between
the teeth or put in contact with the head, which was at one
time supposed to be due solely to direct transmission of the
vibrations through the bones of the skull to the liquids of
the labyrinth or the end-organs of the auditory nerve, has
been shown to take place, in great part, through the mem-
brana tympani and ossicles ; the vibrations travel through
the bones to the tympanic membrane, and set it oscillating.
So that this test, w^hen applied to distinguish deafness caused
by disease of the middle ear from deafness due to disease
of the labyrinth or the central nervous system may easily
mislead, although it enables us to say whether the auditory
meatus is blocked (by wax, ^.o'.) beyond the tympanic
membrane.
AVhen a tuning-fork is held between the teeth, a part of the sound
passes out of the ear from the vibrating membrana tympani ; if one
ear is closed, the sound is heard better in this than in the open ear.
If the tuning-fork is held before the ear till it just ceases to be heard,
it will still be heard on placing it between the teeth ; if it be kept
there till it again becomes inaudible, it will be heard for a short time
if one or both ears be stopped ; and when in this position the sound
again becomes inappreciable, it can still be caught if the handle be
introduced into the auditory meatus.
A membrane like a drum-head has a note of its own, which it
gives out when struck, and it vibrates more readily to this note than
to any other. But the tympanic membrane receives all kinds of
vibrations, and responds to all ; so that if it is in reality attuned to
any particular note, the effect is weakened in some way or other, and
does not obtrude itself. The damping of the movements of the
membrane by the ossicles and the liquids of the labyrinth may partly
account for this ; and it is to be remembered also that it is not
stretched, but lies slackly in its bony frame, so that when the handle
of the malleus is detached from it, it retains its shape and position.
The tensor tympani, when it contracts, pulls inwards the handle
of the malleus, and thus increases the tension of the tympanic mem-
brane. The precise object of this is obscure. It has been suggested
that damping of the movements of the auditory ossicles is thus
secured. Another theory is that the increased tension of the mem-
brane renders it more capable of responding to higher tones, and
that the muscle thus acts as a kind of accommodating mechanism.
rUE SENSES 803:
But Henson has observed that the tensor only contracts at the begin-
ning of a sound, and relaxes again when the sound is continued ;
and this is difficult to reconcile with cither of these hypotheses.
The muscle is normally excited reflexly through the vibrations of the
membrana tympani, but some individuals have the power of throwing
it into voluntary contraction, which is accompanied by a feeling of
pressure in the ear and a harsh sound. The function of the stapedius
is unknown. Its contraction would tend to press the posterior end of
the foot-plate of the stapes deeper into the foramen ovale, and cause
the anterior end to move in the opposite direction ; but it is not easy
to see how this would affect the action of the auditory mechanism.
A desire to explain everything, so far as the fitting of a phrase to
every fact can explain, has led to the suggestion that the role of
the stapedius is to damp the oscillations of the stapes and orbicular
ligament when very loud sounds are listened to, and thus prevent
shocks of too great intensity from being transmitted to the labyrinth.
The tensor tympani is supplied by the fifth nerve through a branch
from the otic ganglion ; the stapedius is supplied by the seventh.
Paralysis of the fifth nerve may be accompanied with difficulty of
hearing, especially for faint sounds. When the seventh nerve is
paralyzed, increased sensitiveness to loud sounds has been observed.
The Perception of Pitch — Analysis of Complex Sounds. —
As the eye, or, rather, the retina /j/ws the brain, can perceive
colour, so the labyrinth plus the brain can perceive pitch.
The colour-sensation produced by ethereal waves of definite
frequency depends on that frequency ; and upon the fre-
quency of the aerial vibrations depends also the pitch of a
musical note. But there is this difference between the eye
and the ear : that while the sensation produced by a mixture
of rays of light of different wave-length is always a simple
sensation — that is, a sensation which we do not perceive to
be built up of a number of sensations, which, in other words,
we do not analyze — the ear can perceive at the same time,
and distinguish from each other, the components of a com-
plex sound. When a number of notes of different pitch are
sounded together at the same distance from the ear, the
disturbance which reaches the membrana tympani is the
physical resultant of all the disturbances produced by the
individual notes, and it strikes upon the membrane as a
single wave. The ear or brain must, therefore, possess the
power of resolving the complex vibrations into their con-
stituents, else we should have a mixed or blended sensation,
and not a sensation in which it is possible to distinguish the
51—2
8o4 A MANUAL OF PHYSIOLOGY
constituents of which it is made up. Two chief hypotheses
have been proposed to explain this physiological analysis of
sound : (i) the theory that the analysis takes place in the
labyrinth ; (2) the theory that it takes place in the brain.
(i) Helmholtz attempted to explain the perception of
pitch on the assumption that in the internal ear there exists
a series of resonators, each of which is fitted to respond by
sympathetic vibration to a particular note, while the others
are unaffected ; just as when a note is sung before an open
piano it is taken up by the string which is attuned to the
same pitch and ignored by the rest. Let us suppose that a
given fibre of the auditory nerve ends in an organ which is
only set vibrating by waves impinging on it at the rate of
100 a second, and that the end-organ of another fibre is
only influenced by waves with a frequency of 200 a second.
Then, on the doctrine of 'specific energy' (according to
which the sensation caused by stimulation of a nerve
depends not on the particular kind of stimulus but on
the anatomical connection of the nerve with certain nerve
centres), in whatever way the first fibre is excited, a sensa-
tion corresponding to a note with a pitch of 100 a second
will be perceived. Whenever the second fibre is excited,
the sensation will be that of a note of 200 a second, or the
octave of the first. If both fibres are excited at the same
time the two notes will be heard together. Now, Hensen
actually observed that in the auditory organs of some
crustaceans the hair-like processes of certain epithelial cells
can be set swinging by waves of sound, and, further, that
they do not all vibrate to the same note unless the sound
is VQvy loud. In the lobster there are between four and
five hundred of these hairs, varying in length from 14 ft to
740 /i; and in some insects, such as the locust, similar
hairs, also graduated in length, exist.
To gain an anatomical basis for his theory, Helmholtz
supposed first of all that the pillars of Corti were the
vibrating structures, and that, directly or through the hair-
cells, their mechanical vibrations were translated into
impulses in the auditory nerve-fibres. But apart from the
fact that their number is too small (about 3,000) to allow
THE SENSES 805
US to assign one rod to each perceptible difference of pitch,
and their dimensions too similar to permit of the requisite
range of vibration frequency, it was pointed out that birds
do not possess pillars of Corti — a fact which was decisive
against the assumption of Helmholtz, since nobody denies
to singing birds the power of appreciating pitch. Helmholtz
accordingly, choosing between the remaining possibilities,
gave up the pillars of Corti, and, adopting a suggestion of
Hensen, substituted the radial fibres of the basilar mem-
brane as his hypothetical resonators. But while it is true
that these are much more adequate to the task imposed on
them, since their range of length is far greater (41 /x at the
base to 495 ix at the apex of the cochlea — Hensen) ; and
while the structure of Corti's organ certainly suggests that
some one or other of its elements may be endowed with
such a function, the theory of peripheral analysis of pitch
tends upon the whole rather to break down than to be
strengthened as evidence gathers.
When two notes of different frequency are sounded together, they
' interfere ' with each other. If two tuning-forks A and B, making
100 and loi vibrations a second respectively, be started together,
at the end of the first vibration of A, B will be x^o^h of a vibration
ahead, at the end of the second yfo^hs of a vibration; at the end of
the fiftieth half a vibration. Here the crest of B's wave will coincide
with the trough of A's, and if the forks are vibrating with the same
amplitude the resultant for this vibration will be zero, the wave will
be blotted out. If the amplitudes are not the same, the wave will
still be weakened. At the end of the hundredth vibration of A, B
will have gained a whole vibration, the tops of the two waves will
coincide, and the sound will be strengthened. We recognise the
alternate changes in the amplitude of the interfering sound-waves by
a change in the auditory sensation, which is called a beat ; and in the
case supposed there will be one beat a second. If the difference in
the frequency of the forks is five there will be five beats a second. If
the difference is twenty there will be twenty beats a second. As the
difference is increased the beats will ultimately follow each other
so rapidly that they will themselves be fused into a note — a beat-tone
as it is called, whose pitch will correspond to the frequency of the
beats. Now, Hermann has found that the ear may perceive a beat-
tone which elicits no response from a resonator attuned to its note and
readily set into vibration by the same note when sounded by a tuning-
fork. This shows that the process by which pitch is appreciated,
whatever it may be, is not entirely explicable on the theory of
resonance.
8o6 A MANUAL OF PHYSIOLOGY
(2) The second theory, in accordance with the simile used
by Rutherford, to whom we owe it in its present form, may
be conveniently labelled the ' telephone theory.' He sup-
poses that the organ of Corti (or, at any rate, the hair-cells)
is set into vibration as a whole by all audible sounds, and
that its vibrations are translated into impulses in the auditory
nerve, which are the physiological counterpart of the aerial
waves and the waves of increased and diminished pressure
in the liquids of the labyrinth to which they give rise.
Thus, a sound of 100 vibrations a second would start 100
impulses a second in the auditory nerve ; a loud sound
would set up impulses more intense than a feeble sound ;
and a complex wave, which is the resultant of several sounds
of different vibration-frequency, would also in some way
or other stamp the impress of its form on the auditory
excitation-wave ; just as in a telephone every wave in the air
causes a swing of the vibrating plate, and thus sets up a
current of corresponding intensity and duration in the wires.
This theory evidently abandons the doctrine of specific energy
for the particular case of the analysis of pitch, for it assumes
that differences of auditory sensation are related to differ-
ences in the nature of the impulses travelling up the auditory
nerve, and not merely to differences in the anatomical connec-
tions (peripheral and central) of the auditory nerve-fibres.
The statement of Ewald, that after extirpation of the membranous
labyrinth on both sides pigeons can still hear, would have an im-
portant bearing on the question of the perception of pitch, if it could
be definitely accepted, and particularly if it were shown that difterences
of pitch could still be appreciated. But it has not been proved
beyond a doubt that the apparent reaction to sound is due to any-
thing else than stimulation of tactile end-organs.
Smell and Taste.
Smell was defined by Kant as 'taste at a distance': and
it is obvious that these two senses not only form a natural
group when the quality of the sensations is considered, but
are closely associated in their physiological action, especi-
ally in connection with the perception of the flavour of the
food. The olfactory end-organs are situated in the mucous
membrane of the upper part of the nostrils, the so-called
THE SENSES 807
regio olfactoria. They are cells prolonged externally into
long narrow rods which terminate at the free surface of the
mucous membrane, and prolonged towards their deep ends
into processes which become continuous with fine branches
of the first nerve. These olfactory cells are scattered among
the ordinary cylindrical cells which line the mucous mem-
brane. In cases of anosmia, in which the olfactory nerve is
absent or paralyzed, smell is abolished; but substances such
as ammonia and acetic acid, which stimulate the ordinary
sensory nerves (nasal branch of fifth) of the olfactory mucous
membrane, are still perceived, though not distinguished from
each other. In fact, the so-called pungent odour of these
substances is no more a true smell than the sense of smarting
they produce when their vapour comes in contact with a
sensory surface like the conjunctiva or a piece of skin devoid
of epidermis.
It was at one time believed that odoriferous particles
could not be appreciated unless they were borne by the air
into the nostrils ; but this appears not to be the case, for
the smell of substances dissolved in normal saline solution is
distinctly perceived when the nostrils are filled with the
liquid; and fish, as every line-fisherman knows, have no
difficulty in finding a bait in the dark.
Beaunis has classified the substances which can affect the olfactory
mucous membrane as follows :
1. Those which act only on the olfactory nerves :
{a) Pure scents or perfumes, without pungency.
ib) Odours with a certain pungency, e.g., menthol.
2. Substances which act at the same time on olfactory nerves
and on nerves of common sensation (tactile nerves),
e.g., acetic acid.
3. Substances which act only on the nerves of common
sensation (tactile nerves), e.g., carbon dio.xide.
Electrical excitation of the olfactory mucous membrane causes a
sensation like the smell of phosphorus. The sensation is experienced
at the kathode on closure and the anode on opening.
Taste. — The sense of taste is not so strictly localized as the
sense of smell. The tip and sides of the tongue, its root,
the neighbouring portions of the soft palate, and a strip in
the centre of the dorsum, are certainly endo^^ed with tha
sense of taste ; but the e.xact limits of the sensitive areas
8o8 A MANUAL OF PHYSIOLOGY
have not been defined, and, indeed, seem to vary in different
individuals.
The nerves of taste are the glosso-pharyngeal, which innervates
the posterior j^art of the tongue; and the lingual, which supplies its
tip. The end-organs of the gustatory nerves are the taste-buds or
taste-bulbs, which stud the fungiform and circumvallate papillae, and
are most characteristically seen in the moats surrounding the latter.
They are barrel-like bodies, the staves of the barrel being repre-
sented by supporting cells ; each bud encloses a number of gustatory
cells with fine processes at their free ends projecting through the
superficial end of the barrel. Their deep ends also terminate in
processes which become continuous with the fibres of the gustatory
nerves.
As to the properties in virtue of which sapid substances
are enabled to stimulate the gustatory nerve endings, we
know that they must be soluble in the liquids of the mouth,
and there our knowledge ends. An attempt has been made
by various authors to connect the taste of such bodies
with their chemical composition, but researches of this kind
have not hitherto yielded much fruit. Sapid substances have
been divided into four classes : i, sweet ; 2, acid ; 3, bitter;
4, saline.
Sweet and acid tastes are best appreciated by the tip, and
bitter tastes by the base, of the tongue.
Normal lymph, which bathes the gustatory end-organs, does not
excite any sensation of taste, but when the composition of the blood
is altered in disease or by the introduction of foreign substances,
tastes of various kinds may be perceived. Sometimes this may be
due to the stimulation of substances excreted in the saliva ; but in
other cases it seems that, without passing beyond the blood and
lymph, foreign substances may excite the gustatory nerves.
When a constant current is passed through the tongue, an acid
taste is experienced at the positive, and an alkaline taste at the nega-
tive, pole ; and it is said that this is the case even when the current
is conducted to and from the tongue by unpolarizable combinations,
which prevent the deposition of electrolytic products on the mucous
membrane (p. 526).
Flavour is a mixed sensation, in which smell and taste arc both
concerned, as is shown by the common observation that a person
suffering from a cold in the head, which blunts his sense of smell,
loses the proper flavour of his food, and that some nauseous medi-
cines do not taste so badly when the nostrils are held.
In common speech, the two sensations are frequently confounded.
Thus the 'bouquet' of wines, which most people imagine to be a
sensation of taste, is in reality a sensation of smell : the astringent
THE SENSES 809
* taste ' of tannic acid is not a taste at all, but a tactile sensation ;
the *hot' taste of mustard is no more a true sensation of taste than
the sensation produced by the same substance when applied in the
form of a mustard poultice to the skin.
Tactile Sensations.
Under the sense of touch it is usual to include a group
of sensations which differ in quality — and that in some
instances to as great an extent as any of the sensations
which are universally considered as separate and distinct —
but agree in this, that the end-organs by which they are
perceived are all situated in the skin, the mucous membrane,
or the subcutaneous tissue. Such are the common tactile
sensations — including pressure — and the sensations of tem-
perature, or, more correctly, of change of temperature. The
sensation of pain cannot be justly grouped along with these.
It is called forth by excessive stimulation of any of the sense-
organs, or by the stimulation of afferent nerve-fibres in their
course ; and it may originate, under certain conditions, in
internal organs which are devoid of tactile sensibility, and
the functional activity of which in their normal state gives
rise to no special sensation at all. The peculiar sensation
associated with voluntary muscular effort, to which the
name of the muscular sense has been given, also deserves
a separate place ; for although it may in part depend on
tactile sensations set up through the medium of end-organs
situated in muscle, tendon, or the structures which enter
into the formation of the joints, other elements are, in all
probability, involved.
The simplest form of tactile sensation is that of mere contact, as
when the skin is lightly touched with the blunt end of a pencil.
This soon deepens into the sensation of pressure if the contact is
made closer ; and eventually the sense of pressure merges into a
feeling of pain. It is not easy to say whether these various sensa-
tions are due to the stimulation of different nervous elements, or to
different grades of stimulation of the same elements. But there is
some pathological evidence in favour of the former view, e.g., it is
said that the sensation of contact is abolished in cicatrices where
the true skin has been destroyed, although sensibility to pressure
persists. The existence of different forms of sensory end-organs in
the skin and other tissues (touch-corpuscles, corpuscles of Pacini,
end-bulbs of Krause, etc.) is also, so far as it goes, in favour of thC:
8io A MANUAL OF PUYSIOLOCY
same view. The minimum pressure necessary to evoke a sensation
of contact is not the same for every portion of the skin. The fore-
head and palm of the hand are most sensitive.
If two points of the skin are touched at the same time there is
a double sensation when the distance between the points exceeds
a certain minim.um, which varies for different parts of the sensitive
surface.
Distance at
can be (list
which two points
inctly felt, in iiini.
Point of tongue
Palmar surface of third
II
phalanx of finger
Dorsal sur.^ace of third
22
phalanx of finger
Tip of nose -
Back - - - -
6-7
67
II -2
Eyelids
I 1'2
Skin over sacrum -
40"5
Upper arm -
67-6
Practice increases the acuity of touch. Even in a few hours it
may be temporarily quadrupled on some parts of the skin. Since
at the same time it is increased in the corresponding part of the
opposite side of the body, it is argued that the modification takes
place in the central nervous system, not in the end-organs them-
selves.
Few of the internal organs seem to be supplied with
tactile nerves. The movements of a tapeworm in the intes-
tines are not recognised as tactile sensations, nor the move-
ments of the alimentary canal during digestion, nor the
rubbing of one muscle on another during its contraction.
It would seem that pressure is only perceived when it affects two
neighbouring areas to a different degree. Thus, the atmospheric
pressure, bearing uniformly on the whole surface of the body, causes
no sensation ; we are so entirely unconscious of it that it needed the
inspiration of genius to discover it, and the patience of genius to
force the discovery on the world. When the finger is dipped in a
trough of mercury at its own temperature, no sensation is perceived
except a feeling of constriction at the surface of the liquid.
Sensations of Temperature. — W^hen a body colder or hotter
than the skin is placed on it, or when heat is in any other
way withdrawn from or imparted to the cutaneous tissues
with sufficient abruptness, a sensation of cold or heat is
experienced. And when two portions of the skin at different
THE SENSES 8ii
temperatures are put in contact, we feel that, relatively to
one another, one is warm and the other cold. But it is
worthy of remark that it is only difference of temperature,
and not absolute height, that we are able to estimate by
our sensations. Thus, a hand which has been working in
ice-cold water will feel water at io° as warm ; whereas it
would appear cold to a warm hand. When the temperature
of the skin is raised above or diminished below a certain
limit, the sensation of change of temperature gives place to
one of pain ; and this may be considered as due either to
excessive stimulation of the end-organs of the temperature
sense, or as due to stimulation of the ordinary sensory
nerves, which are normally insensible to more moderate
variations of temperature.
The recent researches of Blix, Goldscheider, and others
have thrown new light upon the anatomical basis of the
sensations which have their origin in the skin. They have
found that the whole skin is not endowed with the capacity
of distinguishing temperature. The temperature sense is
confined to minute areas scattered over the cutaneous
surface, some of which are 'cold' points, i.e., respond to
variations of temperature only by a sensation of cold, while
others are ' warm ' points and respond only by a sensation
of heat. ' Cold ' points are present in greater number than
* warm.' It has even been stated that electrical or mechani-
cal or thermal stimulation of a nerve-trunk like the radial
in its course, may give rise to sensations of temperature.
But there is strong evidence on the other side, and even if
this were shown to be the case, it might be due merely to
excitation of nerves of the temperature sense supplying the
sheath (nervi nervorum). When a nerve is compressed, the
sensibility of the tract supplied by it disappears for cold
sooner than for heat.
The simplest explanation of these facts seems to be that the skin
is supplied with several kinds of nerve-fibres, anatomically as well as
functionally distinct. Some fibres minister to the sensation of cold,
others to that of heat, others to that of pressure, others, perhaps, to
that of contact, and, possibly, others still to common sensation.
And just as stimulation of the optic nerve gives rise to a sensation of
light, so stimulation of any one of the cutaneous nerves gives rise to
8i3 A MANUAL OF PHYSIOLOGY
the specific sensaiion proper to the group to which it belongs. But
with the eyes closed a thermal may sometimes be mistaken for a
tactile stimulus.
It is not only of physiological interest, but of practical importance,
that most mucous membranes are in comparison with the skin but
slightly sensitive to changes of temperature ; some, as the mucous
membrane of the greater portion of the alimentary canal, seem to be
entirely devoid of nerves of temperature. Only towards its ends in
the mouth, pharynx and rectum, and to some extent in the stomach,
does a blunted sensibility ai)pear. The uterus, too, is quite insensible
to heat; and hot liquids may be injected into its cavity at a temperature
higher than that which can be borne by the hand, without causing
inconvenience — a fact which finds its application in the practice
of gynaecology and obstetrics. It is, indeed, obvious that in the
greater number of the internal organs the conditions necessary for
stimulation of temperature nerves, even if such were present, could
hardly ever exist.
It has already been mentioned that changes of external temperature
exert a remarkable influence on the intensity of metabolism (p. 495),
and it has been supposed that this is brought about by afferent
impulses travelling up the cutaneous nerves. We have also seen
that for certain kinds of stimuli the excitability of nerve-fibres is
increased by cooling (p. 574). It is possible that this is the case for
the fibres in the skin which are concerned in the regulation of the
production of heat, and it has been suggested that this fact may have
a bearing on the reflex regulation of temperature (Lorrain Smith).
The Muscular Sense.
Voluntary muscular movements are accompanied with a
peculiar sensation of effort, graduated according to the
strength of the contraction, and affording data from which
a judgment as to its amount and direction may be formed.
To these sensations the name of the muscular sense has been
given.
Some writers have supposed that the muscular sense
does not depend upon afferent impulses at all, but that
the nervous centres from which the voluntary impulses
depart, take cognizance, retain a record, so to speak, of the
quantity of outgoing nervous force ; that the effort which
we feel in lifting a heavy weight is an effort of the cells of
the motor centres from which the innervation of the groups
of muscles takes origin, and not of the inuscles themselves.
But although this feeling of central effort or outflow (we
can hardl}- say of central fatigue) ma}- play a part in the
THE SENSES 813
muscular sense, it cannot be doubted that the brain is kept
in touch with the contracting muscle by impulses of various
kinds which reach it by different afferent channels.
The corpuscles of Pacini, which exist in considerable numbers in
the neighbourhood of joints and ligaments, and in the periosteum of
bones, would seem well fitted to play the part of end-organs for
the tactile sensations caused by the movements of flexion, extension,
or rotation of one bone on another, which form so large a portion of
all voluntary muscular movements. And it has been stated that
paralysis of these bodies in the limbs of a cat by section of the
nerves going to them causes a characteristic uncertainty of move-
ment which suggests that something necess iry to normal co-ordination
has been taken away. We have already seen that the skeletal muscles
possess numerous afferent fibres (p. 696). Some of these may be
nerves of ordinary sensation. For although, when a muscle is laid
bare in man and stimulated electrically, the sensation does not in
general amount to actual pain, it is capable, under the inlluence of
strong stimuli, of taking on a painful character. And nobody who
has felt the severe and sometimes almost intolerable pain of muscular
cramp would be likely to deny the existence of sensory muscular
nerves. But after deducting these, we must assume that a very large
proportion of the afferent nerves of muscle have other functions, and
among them may be the conveyance of impulses connected with the
muscular sense.
In the spinal cord, these impulses are probably conducted up
through the posterior column ; and, although nothing is known as to
the paths they follow in the higher parts of the central nervous
system, it is certain that there is some afferent bond of connection
between the cortical motor areas and the muscles which they control
(p. 718).
Tactile sensations set up in the skin or mucous membrane lying
over contracting muscles may also help the nervous motor mechanism
in appreciating and regulating the amount of contraction ; but the
fact that, in anaesthesia of the mucous membrane covering the vocal
cords produced by cocaine, the voice is not at all impaired, shows
that muscular contractions of extreme nicety can be carried on without
any such aid.
Pain.
Pain has been defined as ' the prayer of a nerve for pure blood.'
The idea is not only true as poetry, but, with certain deductions and
limitations, true as physiology. That is to say, pain, as a rule, is a
sign that something has gone wrong with the bodily machinery ;
freedom from pain is the normal state of the healthy body. Physio-
logically, pain acts as a danger-signal ; it points out the seat of the
mischief, and even, in certain cases, by compelling rest, favours the
process of repair. Thus, the surgeon has sometimes looked upon
pain as ' Nature's splint.' But as a matter of fact, a certain amount
of pain occurring at intervals is not incompatible with high health ;
8 14 A MANUAL OF PHYSIOLOGY
and probably nobody, even when accidents and indiscretions of all
kinds are avoided, is entirely free from pain for any considerable
time. Sometimes, indeed, the mere fixing of the attention on a
particular part of the body is sufficient to bring out or to detect a
slight sensation of pain in it ; and it is matter of common experience
that a dull continuous pain, like that of some forms of toothache, is
aggravated by thinking of it, and relieved when the attention is
diverted.
In general, the skin is far more sensitive to pain than the deeper
structures. The most painful part of an operation is generally the
stitching of the wound. The cutting of healthy muscle causes no
pain. In an operation in which an artificial connection was estab-
lished between the stomach and the small intestine (gastro-enteros-
tomy), and in which no ancesthetic was administered, the only pain
of which the patient complained was produced by the incision in the
skin (Senn). The spasmodic contraction of the intestines and
stomach causes the intense pain of colic and gastralgia. Labour is
an example of a strictly physiological function which is the occasion
of severe pain. Tissues normally insensible to pain may become
acutely painful when inflamed.
It is not quite settled as yet whether the afferent fibres which
minister to painful sensations are anatomically distinct from the
fibres of tactile sensation, and of the other sensations included under
the sense of touch ; but, upon the whole, the balance of evidence,
physiological and pathological, seems to incline to the view that there
is such a distinction. For the conducting paths in the spinal cord
appear not to be the same for tactile and for painfial impressions.
And in certain cases of disease sensibility to pain may be lost, while
tactile sensations are still perceived ; or, on the other hand, pain may
be felt in cases where tactile sensibility is abolished. Loss of tem-
perature sensation, however, is almost always accompanied by loss of
sensibility to pain.
Relation of Stimulus to Sensation.
It is impossible to measure sensation in terms of stimulus. All
that we can do is to compare differences in the intensity of stimuli
and differences in the resultant sensations, or, in other words, to
compare stimuli together and to compare sensations together. And
when we determine the amount by which a given stimulus must be
increased or diminished in order that there may be a just perceptible
increase or diminution in the sensation, it is found that (with certain
limitations) the two are connected by a simple law : Whatever the
absolute st?-efigth of a . siimtdus of given kind may be, it viiist be
increased by the same fraction of its amount in order that a difference
in the sensation may be perceived (sometimes called Weber's laiv).
Thus, a light of the strength of one standard candle must be increased
by yi^th candle, a light of lo candles by ^oVhs, and a light of loo
candles by a candle, in order that the eye may perceive that an
increase has taken place, just as the weight necessary to turn a
PRACTICAL EXERCISES
815
balance increases with the amount already in the pans. The frac-
tion varies for the different senses. It is about ii,j for light, ?f for
sound. But it would appear that Weber's law does not hold for the
pressure sense, nor for the other senses above and below certain
limits. Fechner, making various assumptions, has thrown Weber's
log X
law into the {oxw\y=k , where y is the intensity of sensation,
X the intensity of stimulation, and x^ the smallest intensity of
stimulus which can be perceived (liminal intensity). This so-called
psycho-physical law of Fechner states that the sensation varies as
the logarithm of the stimulus. But Fechner's law has been subjected
to serious criticism, and the subject cannot be further pursued here.
PRACTICAL EXERCISES ON CHAPTER XIII.
1. Formation of Inverted Image on the Retina. — Fix the eye of
an ox or of a dog or rabbit (preferably an albino), after removal of
part of the posterior surface of the sclerotic, in a hole cut in a
blackened box. Place a candle in front of the eye. Look from
behind, and observe the inverted image of the candle formed on the
retina. Move the candle until the image is as sharp as possible.
Now bring between the candle and the eye a concave lens. The
image becomes blurred, the candle must be put farther away to
render it distinct, and perhaps no position of the candle can be found
which will give a sharp image. If the lens is convex, the candle
must be brought nearer, and a sharp image can always be formed by
bringing it near enough. If both a convex and a concave glass be
placed in front of the eye, they will partially or wholly neutralize
each other.
2. Helmholtz's Phakoscope (Fig. 294). — This instrument is em-
ployed in studyini; the changes that take place in the curvature of
the lens during accommo-
dation. It is to be used
in a dark room. A candle
is placed in front of the
two prisms P, P'. The
observer looks through the
hole B ; the observed eye
is placed opposite the
hole A. The candle or
the observed eye is moved
till the observer sees three
pairs of images, one pair,
the brightest of all, re-
flected from the anterior surface of the cornea ; another, the largest of
the three, but dim, reflected from the anterior surface of the lens ; and
a third pair, the smallest of all, reflected from the posterior surface
Fig. 294. — Phakoscope.
8i6
A MANUAL OF /'//VS/OLOGT^
of the lens (Fig. 263). The last two pairs can, of course, only be
seen within the pupil. The observed eye is now focussed first for a
distant object (it is enough that the person should simply leave
his eye at rest, or imagine he is looking far away), and then for
a near object (an ivory pin at A). During accommodation for a
near object no change takes place in the size, brightness, or position
of the first or third pair of images ; therefore the cornea and the
posterior surface of the lens are not altered. The middle images
become smaller, somewhat brighter, apj^roach each other, and also
come nearer to the corneal images. This proves (a) that the an-
terior surface of the lens undergoes a change ; {/>) that the change is
increase of curvature (diminution of the radius of curvature), for the
virtual image reflected from a convex mirror is smaller the smaller is
its radius of curvature. (The third pair of images really undergo a
I'lG, 295. — SCHEINER'S tXTEKIMEN r.
In the upper figure the eye is focussed for a point farther away than the needle ; in
the lower, for a nearer point. The continuous hues represent rays frotn the needle,
the interrupted lines rays from the point in focus. But the lines inside the eye, whicli
by an error in engraving are drawn as continuous lines, ought to be interrupted, and
vice versd.
slight change, such as would be caused by a small incrcise in the
curvature of the posterior surface of the lens ; but the student need
not attempt to make this out.)
3. Schemer's Experiment. — Two small holes are pricked with a
needle in a card, the distance between them being less than the
diameter of the pupil. The card is nailed on a wooden holder, and
a needle stuck into a piece of wood is looked at with one eye through
the holes. When the eye is accommodated for the needle, it appears
single ; when it is accommodated for a more distant object, or not
accommodated at all, the needle appears double. The two images
approach each other when the needle is moved away from the eye,
and separate out from each other when it is moved towards the eye.
When the eye is accommodated for a point nearer than the needle,
the image is also double ; the images approach each other when the
PRACTICAL EXERCISES 817
needle is brought closer to the eye, and move away from each other
when it is moved away from the eye. If while the needle is in focus
one of the holes be stopped by ihe finger, the image is not affected.
When the eye is focussed for a greater distance than that of the
needle, stopping one of the holes causes the image on the other side
of the field of vision to disappear ; if the eye is focussed for a smaller
distance, the image on the same side as the blocked hole disappears
(Fig- 295)-
4. Kiihne's Artificial Eye. — This is an elongated box provided
with a glass lens to represent the crystalline, and a ground-glass plate
to represent the retina. The box is filled with water to which a little
eosin has been added. The water must be perfectly clear. A' beam
of sunlight or electric light, or, in case these are not available, a
beam from an oil stereopticon, is made to pass through the box.
Many of the facts of vision can be illustrated by means of this piece
of apparatus.
Fu;. 296. — Mai' 01-- Blind Spot (reduced by one-half).
Right eye. Distance of eye from paper, 12 inches.
{a) Let the rays of light pass through an arrow-shaped slit in^a
piece of cardboard. An inverted image of the arrow is formed on
the retina. Move the retina nearer to or farther from the lens to
make the image sharp. In the eye, accommodation is not brought
about by a change in the disiance of retina and lens, but by a change
of curvature in the lens.
{b) Remove the lens. The focus is now far behind the retina.
This illustrates the state of matters after the lens has been removed
for cataract. The arrow can again be sharply focussed on the retina
by putting a convex lens in front of the artificial eye. But this
must be much weaker than the lens which has been removed, for if
the latter be placed in front of the eye, the image is formed a little
behind the cornea.
{c) Replace the lens. Move the retina so far back that the image
is focussed in front of it. This is the condition in the myopic eye.
Put a weak concave lens in front of the eye ; the image now falls
52
8i8 A MANUAL 01- PHYSIOLOGY
more nearly on the retina. Move the retina forward, so that the
focus is behind it. This corresponds to the hypermetropic eye. Put
a weak convex lens in front of the eye to correct the defect.
{d) Observe that a plate with a hole in it, placed in front of the
eye, renders an indistinctly focussed image somewhat sharper by
cutting off the more divergent peripheral rays.
Fig. 297.— Comi'Osite Picture of Blind Spot (not reduced).
The blind spot of the right eye was mapped by 31 men, the eye being always at a
distance of 12 inches from the paper. The maps were then superposed. The amount
of white at any point of the figure is intended to correspond to the number of maps
whicli overlapped at that point. Although the mechanical process of reproduction
gives rather an imperfect view of the composite map, the area in the centre of the figure
where the white is most continuous, and which represents the shape of the majority of
the blind spots, evidently bears a general resemblance to the outline in Fig. 296.
{e) Fill with water the chamber in front of the curved glass that
represents the cornea. The focus is now behind the back of the eye
altogether. Refraction by the cornea is here abolished, as is the
case in vision under water. An additional lens inside the eye, or a
PRACTICAL EXERCISES 819
weaker one in front of it, corrects the defect, lushes have a much
more nearly spherical lens than land animals, and a flat cornea.
(/) Fill the hollow cylindrical lens with water, and place it in
front of the artificial eye. It is now astigmatic. A point of light is
focussed on the retina, not as a point, but as a line. The vertical
and horizontal limbs of a cross cut out of a piece of cardboard and
placed in the path of the beam of light cannot be both focussed at
the same time.
5. Mapping the Blind-spot. — Make a black cross on a piece of
white paper attached to the wall, the centre of the cross being at the
height of the eye in the erect position. Stand about 12 inches from
the wall, the chin supported on a projecting piece of wood. Fix the
centre of the cross with one eye, the other being closed, and move
over the paper a pencil covered, except at the point, with white paper,
until the point just disappears. Make a mark on the paper at this
point, and repeat the observation for all diameters of the field. The
blind-spot is thus marked out (Fig. 296). Its shape is not the same
in all eyes (Fig. 297). Its size and distance from the fovea centralis
can be calculated from the formula on p. 746.
6. Ophtlialmoscope — (i) Human Eye (p. 761). — Let A be the
observer, and B the person whose eye is to be examined. A and B
are seated facing each other. A little behind and to the left of B is
a lamp on a level with his eyes ; the room is otherwise dark. For a
clinical examination, the pupil should be dilated by putting into the
eye a drop of a '5 per cent, solution of atropia sulphate, but this is
not indispensable for the experiment.
{a) Direct Method. — A takes the mirror in his right hand, and,
holding it close to his own eye, looks through the central hole, and
throws a beam of light into B's eye. A red glare, the so-called
' reflex ' from the choroidal vessels, is now seen. A then brings the
mirror to within 2 or 3 inches of B's eye, keeping his own eye
always at the aperture. A and B both relax their accommodation,
as if they were looking away to a distance. If both eyes are emme-
tropic, the retinal vessels will be seen. A should now move the
mirror or B his eye so as to bring into view the white optic disc with
the central artery and vein of the retina crossing it.
{b) Indirect Method. — A takes the mirror in his right hand to
examine B's right eye, places his own eye behind the aperture as
before at a distance of about 18 inches from B, and throws a
beam of light into B's eye. Then A takes a small biconvex lens in
his left hand, and places it 2 or 3 inches in front of B's eye,
keeping it steady by resting his little finger on B's temple. A now
moves the mirror until he sees the optic disc.
(2) Examine a rabbit's eye by the direct and indirect method.
Dilate the pupil by a drop or two of atropia solution.
For practice, before doing (i) and (2) the student should examine
an artificial ' eye ' by both methods, so as to get a clear view of what
represents the retina. A substitute for the artificial eye may be
made by unscrewing the lower lens of the eyepiece of a microscope,
52—2
820
A MANUAL or PHYSIOLOGY
and fastening in its place a piece of paper with some printed matter
on it. The letters must be made out with the ophtiialmoscope.
7. Pupillo- dilator and Constrictor Fibres. — {a) Set up an induc-
tion machine arranj;ed for te'anus, and connect a pair of electrodes
through a short-circuiting key with the secondary. Etherize a
cat by putting it into a large vessel with a lid, slipping into the
vessel a piece of cotton-wool soaked with ether, and waiting till the
movements of the animal inside the vessel have ceased. Then
Fic. 298.— Apparatus for Coi.ouR-MixiNt;.
quickly put the cat on a holder and maintain ana:sthesia with ether.
Expose the sympathetic in the neck ; the carotid is taken as the
guide to it. Ligature the nerve, and cut below the ligature. On
stimulating the upper (cephalic) end, the pupil of the corresponding
eye dilates.
(l>) Observe in the eye of a fellow-student, or, by means of a
looking-glass, in your own eye, that when light falls on one eye both
pupils contract.
(<r) Observe that when the eye is accommodated for a near object
PRACTICAL EXERCISES 821
the pupil contracts, and that it dilates when a distant object is
looked at.
8. Colour-mixing. — {a) Arrange a red and a bluish-green disc on
one of the steel discs of tlie colour-mixing apparatus shown in
Fig. 2y8, so that a part of each is seen. On another arrange a violet
and a yellow disc, and on the third an orange and a blue disc. By
adjustment of the proportions of the two colours a uniform grey can
be obtained from each of these combinations (complementary
colours) when the discs are rapidly rotated.
{b) Mix two colours that are not complementary, c.g.^ blue and
red ; grey or white cannot be obtained by any adjustment of pro-
portions ; the result is always a mixed colour, the precise hue
depending on the amount of each ingredient.
(r) Take papers of any three colours from widely-separated parts of
the spectrum, e.g.^ blue, green, and red, and arrange them on one of
the rotating discs. By varying the proportions white can be produced,
and any other coloured paper fastened on another of the rotating
discs can be matched by adding white to the three colours.
9. Talbot's Law. — Rotate a disc one sector of which is black and
the rest white, or a disc like that in Fig. 283. A uniform shade is
jjroduced as soon as a speed of about 25 revolutions a second has
been attained, and this is not altered by further increase in the
speed.
10. Purkinje's Figures. — {a) Concentrate a beam of sunlight by a
lens on the sclerotic at a point as far as possible from the corneal
margin, i)assing the ray through a parallel-sided glass trough filled
with a solution of alum to sift out the long heat-rays. The eye is
turned towards a dark ground. The field of vision takes on a bronzed
iippearance, and the retinal bloodvessels stand out on it as a dark
network, which appears to move in the same direction as the spot of
light on the sclerotic. A portion of the field corresponding to the
yellow spot is devoid of shadows (p. 771).
{b) Direct the eyes to a dark ground while a flame held at the side
of the eye, and at a distance from the visual line, is moved slightly
to and fro. A picture of branching bloodvessels appears. This
experiment is performed in a dark room (p. 772).
(<f) Immediately on awaking look at a white ceiling for an instant;
a pattern of branched bloodvessels is seen. If the eye be at once
closed, and then opened with a blinking movement, this may be
observed again and again. Ultimately the appearance fades away.
11. Study by means of the monochord, a stretched string with a
movable stop, the relation between the pitch of the note given out
by a vibrating string, and its length and tension.
12. Cause two tuning-forks of nearly equal pitch to vibrate at
the same time. Make out the beats, and count their number per
second.
13. Measure on different parts of the skin and accessible mucous
membranes the distances at which the points of a pair of compasses
must be held apart in order that two distinct sensations may be
experienced (p. 810) {acsthesioincter).
CHAPTER X I \'.
REPRODUCTION.
Regeneration of Tissues. — Since cells are constantly dying within
the body, they must Ije constantly reproduced. In some tissues the
process by which this is accomplished is more evident, and therefore
better known, than in others. The most highly-organized tissues are
with difficulty repaired, or not at all. '1 he epidermis is always
wearing away at its surface, and is being constantly replaced by the
multiplication of the cells of the stratum Malpighii. In the corneous
layer we have only dead cells ; in the Malpighian layer we have every
histological gradation from squames to columns, and every physio-
logical gradation from cells which are about to die to cells that have
just been born. The corpuscles of the blood undoubtedly arise at
first, and are recruited throughout life, by the proliferation of mother-
cells. The gravid uterus grows by the formation of new fibres from
the old, and by the enlargement of both old and new. A severed
muscle is generally united only by connective or scar tissue, but
under favourable conditions a complete muscular 'splice 'may be
formed. A broken bone is regenerated by the proliferation of cells
of the periosteum, which become bone-corpuscles. We do not know
whether there is any new formation of nerve-cells in the adult
organism (but see p. 713), but nerve-fibres which have been destroyed
by accident or operation are readily regenerated by the growth of new
processes from the cells that originally produced them ; and some of
the end-organs of efferent nerves may share in this regeneration.
In lower forms of animals, and in all or most vegetables, the power
of regeneration is much greater than in man. The starfish can not
only repair the loss of an arm, but from a severed arm a complete
animal can be developed. A newt can reproduce an amputated toe,
and every tissue — skin, muscle, nerves, bone — will be in its place.
After extraction of the crystalline lens in triton larva;, a new lens is
formed from the iris ej)ithelium.
Thus, in a sense, reproduction is constantly going on within the
bodies even of the higher animals. But since the whole organism
eventually dies, as well as its constituent cells, a reproduction of the
whole, a regeneration en masse, is required.
A cell of the stratum Malpighii can only, so far as we know,
reproduce a similar cell, and this is characteristic of cells that have
REPRODUCTION 823
undergone a certain amount of differentiation, especially in the
higher animals. The fertilized ovum, on the other hand, has the
power of reproducing not only ova like itself, but the counterparts of
every cell in the body. And this is only the highest development of
a power which is in a smaller degree inherent in other cells in lower
forms. Plants and the lowest animals are far less dependent upon
reproduction by means of special cells. A piece of a Hydra separated
off artificially or by simple fission becomes a complete Hydra, as
was shown by Trembley a century and a half ago. A cutting from a
branch, a root, a tuber, or even a leaf of a plant, may reproduce the
whole plant. It is as if each cell in these lowly forms carried within
it the plan of the complete organism, from which it built up the
perfect plant or animal. But the special bias or trend of growth
characteristic of each form is not a rigid rule. It can be modified ;
it is modified in every garden and pond by influences coming from
without. The inborn rule of life for many plants is to grow straight
up ; but this rule is often traversed by circumstances — by differences
in the amount of sunshine, for example, caught by one side or the
other, or by the position of neighbouring objects which hinder or
help a vertical growth. And in animals Pfliiger has shown that the
direction of the lines of cleavage of the ovum of a frog depends on
the direction in which gravity acts, although Driesch and Hertwig
find that the nucleus can even be made artificially to change its place
with reference to the yolk, without hindering the development of a
normal animal. Artificial mouths, surrounded by tentacles, can be
formed in Cerianthus, an animal belonging to the same group as the
sea-anemones, merely by making a cut in the body-wall and prevent-
ing it from closing. In an Ascidian, too (the Cynone i?itestinaiis),
artificial openings in the branchial sac, surrounded by numerous pig-
mented points similar to the eye-spots around the natural mouth and
anus, have been produced (Loeb). Even in Amphioxus, the lowest
of the vertebrates, the eggs have been broken up by shaking, and a
complete animal evolved from as little as one-eighth of an ovum.
If the separation was incomplete a kind of Siamese twins, or even
triplets, could be obtained (Wilson and Mathews).
Reproduction in the Higher Animals. — In all the higher animals
reproduction is sexual, and the sexes are separate.
In regard to the secretions of the reproductive glands, all that
is necessary to be said here is that, unlike other secretions, their
essential constituents are living cells. The spermatozoa in the
male have, indeed, diverged far from the primitive type. Certain
(spermatogenous) cells in the tubules of the testicle divide so as to
form spermatoblasts. Each spermatoblast becomes a spermatozoon,
the head of the latter representing the nucleus of the former ; and it
is this nucleus which is the essential contribution of the male to the
reproductive process. The tail of the spermatozoon is simply, from
the physiological point of view, a motile arrangement, whose function
it is to carry the nucleus of the spermatoblast, freighted with all that
the father can transmit to the offspring, into the neighbourhood of
the female reproductive element or ovum.
824 A MANUAL OF PHYSIOLOGY
The ovum also begins as a typical cell with nucleus (germinal
vesicle) and nucleolus (germinal spot), and it forms, by its repeated
subdivision, all the cells of the foetal body. But, except in some
{parthenogC7ieiic) forms, it never awakens to this rejiroductive activity
till fecundation has occurred ; and fecundation essentially consists in
the union of the male with the female element, or rather in the union
of the male and female nucleus.
From time to time a Graafian follicle, over-distended by its liquor
folliculi, bursts on the surface of the ovary and discharges an ovum.
The frayed end of the Fallopian tube, rising up finger-like from the
dilatation of its bloodvessels, grasps the ovum, and it is passed
slowly along the tube by the downward-lashing cilia which line it.
If not impregnated, it soon perishes amid the secretions of the
uterus — how soon has been matter of discussion, and can hardly be
considered as settled. If, however, impregnation occurs, the ovum
becomes fixed in one of the crypts or pouches of the uterine mucous
membrane (decidua serotina), which grows round it as the decidua
refiexa.
Menstruation. — In the mature female, from puberty, the age at
which the reproductive power begins (thirteenth to fifteenth year),
on till the time of the menopause (fortieth to fiftieth year), at which it
ceases, an ovum — or it may be in some cases more than one — is dis-
charged at regular intervals of about four weeks. This discharge is
accompanied by certain constitutional symptoms and local signs that
last for a variable number of days. The genital organs are congested,
and a quantity of blood, which varies in different individuals, but is
usually from loo to 200 grammes — that is to say, 4^*'^ to Jjjth of the
whole of the blood in the body — is shed. At the same lime, the
whole or a portion of the mucous membrane of the uterus is cast off.
As to the physiological meaning of this fiiensiruation, as it is
called, opinion is divided. Two chief theories have been proposed to
account for it, both of which agree in considering the phenomenon to
be connected with a preparation of the uterus for the reception of the
ovum. But according to the theory of Pfliiger the mucous membrane
is stripped off (by a process analogous to the 'freshening ' or paring
of the indurated edges of a wound by the surgeon, in order that
union may occur when they are brought together) on iJie chance^ so to
speak, that an impregnated ovum may arrive. On the alternative
theory, this change takes place because the ovum has not been
impregnated, and the bed prepared for it is therefore not required
(Reichert, Williams, etc.).
Development of the Ovum. — Before fecundation, and apparently
as a preparation for it, the ovum is the seat of remarkable changes,
which have been most fully studied in the eggs of certain invertebrate
animals. A spindle-shaped structure appears stretching between the
nucleus and the surface of the ovum ; at its outer end a small round
bodv, the first polar body, rises uj) from the surface of the egg as if it
were being squeezed out of it, and is finally extruded. In most cases
he process is repeated ; a new spindle forms and a second polar
body or directive corpuscle is cast out. As to the significance of
REPRODUCTION 825
these changes there has been much discussion. It seems to be agreed
that the spindle is formed in part, at any rate, from the nucleus or
germinal vesicle, and that the result of the process is the expulsion
of a portion of the chromatin skein (p. 18), which is restored by the
male pronucleus when it arrives and penetrates the ovum.
Not till all these events have taken place — extrusion of the two
polar bodies, or maturalioti, penetration of the spermatozoon and
blending of its head (the male pronucleus) with the remnant of the
nucleus of the ovum (female pronucleus), ox fecundation— x\o\. till then
does the ovum begin to divide. The germinal spot, or nucleus, splits
into two, and the yolk being also cleft by a corresponding furrow,
two complete nucleated cells make their appearance. These divide
in turn, till at length (in the mammal) the embryo is represented by a
hollow sphere or vesicle, with a cellular crust. During division the
upper or outer cells have always been larger than the inner and
lower, and have multiplied more rapidly; and thus it comes about
that the hollow sphere of large cells encloses a mass of smaller cells,
along with remnants of broken-down yolk and of fluid derived by
absorption from the contents of the uterus. The smaller cells con-
tinue to multiply and arrange themselves as a lining to the sphere
already formed, so that in a short time it becomes double, and we
have already difterentiated two of the primary embryonic layers, the
epiblast, or superficial, and the hypoblast, or deep layer. The whole
sphere is called the blastoderm, or the blastodermic vesicle.
While this inner shell of hypoblastic cells is gradually creeping on
to completion, there appears at a part where it is already fully formed
a small opaque whitish disc, the germinal area or embryonal shield.
This represents the stocks on which the framework of the embryo is
to be laid down. The area elongates ; at its posterior end appears a
thickened line, the primitive streak, soon furrowed by a longitudinal
groove, the primitive groove, that marks the direction in which the
long axis of the future embryo will lie, but is not itself a permanent
line in the building, and ultimately vanishes. The appearance of
the primitive streak is the signal that a rapid proliferation of the
cells of the germinal area, and especially of the epiblast, has begun ;
and this goes on until a third layer is formed intermediate in position
to the original two, and therefore named the viesoblast. While this
is pushing its way over the germinal area and into the rest of the
blastodermic vesicle, the epiblast in front of the primitive streak rises
up in two lateral ridges, enclosing between them the medullary
groove. The medullary groove is the beginning of the cerebro-spinal
axis ; its walls first come to overhang the furrow, and then to
coalesce ; and the medullary groove has now become the neural
canal. Immediately under it the mesoblast forms a rod of cells, the
notochord, which is the forerunner of the vertebral column ; around
this the bodies of the vertebrse are afterwards developed from cubical
masses of mesoblastic cells, arranged in pairs along the notochord,
and called the protovertebra;. The rest of the mesoblast, running
out on each side from the protovertebrae, splits into two layers, an
upper or somatic layer, which unites with the epiblast, and a lower or
826 A MAXUAL OF PHYSIOLOGY
splanchnic layet\ which unites with the hypoblast. Between the two
layers is a space called the ccelom, or pleuro-peritoneal cavity
(Fig. 299).
Up to the present, apart from the enclosure of the neural canal,
all this formative activity is buried beneath the surface of the blas-
toderm, and has not showed itself by any e.xternal token ; the
embryo still appears as a portion of the germinal area, and lies in its
plane. But now a pocket, or crease, or moat, beginning at the head
as the head-fold, then pushing under the tail, gradually creeps round
and undermines the whole embryo, which is raised above the general
level, and, as it were, scooped out from the rest of the blastoderm ;
till at length it lies on the latter, something like an uj^turned canoe,
enclosing a tube, complete in front and behind, but still open in the
middle, where it communicates with the interior of the yolk-vesicle.
Since this tube has been formed by the tucking in of the three
ancestral layers of the blastoderm, it follows that it is lined by hypo-
blast, supported externally by the splanchnic sheet of mesoblast.
So that now the body consists of a dorsal tube (the neural canal),
essentially of epiblastic origin, a ventral tube (the alimentary canal),
essentially of hypoblastic origin, and between the two a massive
double layer of mesoblastic tissue, which contributes supporting
elements to both. At this point it may be well to emphasize the
fact that this embryological distinction of the three primitive layers
has a deep and fundamental meaning, and corresponds to a physio-
logical distinction that endures throughout life. The hypoblast, the
lowest layer in position, may also be described as the lowest in the
physiological hierarchy. It furnishes the epithelial lining of the
alimentary canal from the beginning of the oesophagus to near the
end of the rectum, as well as the epithelium of the organs which
arise from diverticula of the primitive intestine, viz., the digestive
glands with the exception of the salivary glands, the lungs, and the
passages leading to them, the thyroid, and the greater part of the
thymus gland in its primitive condition before the lymphoid tissue
derived from the mesoblast has as yet grown into it. According
to some authorities, the notochord is also derived from the
hypoblast.
Upon the whole, it may be said that the tissues of hvpoblastic
origin are essentially concerned in chemical labours, in the absorption
of food material and excretion of waste products. The mesoblastic
tissues are essentially concerned in mechanical labour ; they are the
tissues of movement and of passive support. The epiblastic tissues
are at the top of the pyramid ; they govern the rest.
From the mesoblast arise the muscles, the entire vascular system
with its blood and lymph corpuscles, the bones and connective
tissues ; and the Wolffian body and its appendages, which are the
predecessors of the genital glands and ducts, and of the chief portion
of the renal apparatus.
The epiblast forms the epidermis and its appendages, the epithelial
end-organs of the nerves of special sense, and the nervous system,
cerebro-spinal and sympathetic, although some have asserted that
REPRODUCTION 827
the latter is of mesoblastic origin. The saUvary glands and the
mucous Hning of the mouth and anus are developed from the epi-
blast, which is indented to meet the intestinal canal and give it
access to the exterior at either end.
It is not possible here to trace in detail the development of all the
organs of the embryo. Its nutrition and metabolism not only
distinctly belong to the physiological domain, but, carried on as they
are under conditions that seem so strange, and even so bizarre, to
one acquainted only with adult physiology, are calculated to throw
light on the metabolic processes of the fully developed body. And
they cannot be understood without reference to the peculiarities
of the vascular system in foetal life. These we shall accordingly
describe, but for further details as to the anatomy of the embryo the
student is referred to some standard anatomical text-book, such as
Quain's ' Anatomy.'
Physiology of the Embryo. — In the first period of its develop-
ment the ovum, nestling in the pouch formed by the decidua
serotina and reflexa, is fed simply by imbibition through the hollow
finger-like processes or villi with which its external layer, the zona
pellucida, becomes studded. Soon the heart appears as a tube (at
first double), formed by cells belonging to the splanchnic layer of
the mesoblast. It begins to pulsate in the chick as early as the
middle of the second day, although it as yet contains neither nerve-
cells nor fully-formed muscular fibres. In the mammal pulsation is
late m making its appearance, in man about the beginning of the
third week. A bloodvessel grows out from the anterior end of the
heart and divides into two primitive aortic arches, from each of which
a vessel (omphalo-mesenteric or vitelline artery, runs out in the
mesoblast covering the umbilical vesicle or yolk-sac. The blood is
returned to the heart by the vitelline veins coursing in on the walls of
the vitelline duct. In this way the store of nutriment in the umbilical
vesicle of the chick, which is the only solid or liquid food it receives
or needs during the whole period of development, is tapped, and a
regular channel of supply established. Oxygen is at the same time
absorbed through the porous shell ; but later on this respiratory
function is taken over by the second or allantoic circulation. In the
mammal the circulation on the umbilical vesicle is of much less
consequence, for the quantity of material left over after the formation
of the blastoderm is exceedingly small ; it is only with a few days'
provision in its haversack that the embryo starts out on its develop-
mental march. And the vitelline vessels deriving their further
supply of food and oxygen from the tissues of the mother in contact
with the ovum, cease to be of use as soon as the second and more
perfect placental circulation is established, and soon shrivel up and
disappear, as the umbilical vesicle shrinks.
The second circulation of the embryo is developed in connection
with a remarkable off-shoot from the hind-gut called the allantois,
which, before the fifth day in the chick and during the second week
in man, pushes its way out between the somatic and splanchnic
layers of the mesoblast, i.e., in the pleuro-peritoneal cavity, and
SzS
A MA.XUAL OF I'J/ YSI OLOCJY
grows throu<ili ihc umbilicus, carrying bloodvessels along with it in
its mesoblastic layer. Still earlier, and, indeed, while the embryo is
being separated off from and raised above the level of the rest of the
blastoderm by the deepening of the ditch around it, the further banks
of this furrow, formed of epiblast and somatic mesoblast, have risen
up on every side and, growing over the back of the embryo, have
finally coalesced and enclosed it in a double-walled pouch (Fig. 299).
The superficial layer of the pouch is called ihe false amnion ; it soon
blends with the tufted chorion or common outer envelope of the
ovum. The inner layer persists as the true amnion : a liquid, the
ttinniotic Jluiii, is
secreted in the
cavity which it
encloses; and the
embryo, loosely
anchored for the
rest of its intra-
uierine life by
tlie umbilical
cord alone, floats
freely within it.
The amniotic
fluid acts as a
water jacket or
cushion, to break
the force of the
inevitable shocks
and jars trans-
mitted from the
mother to the
fcetus and from
the fcetus to the
mother.
The allantois,
growing out at
the umbilicus, in
the manner described, insinuates itself between the true and false
amnion and soon blends with the latter. For a time the secretion of
the primitive kidneys continues to be poured into the cavity of the
allantois, so that it serves in part as an excretory organ, while in the
bird it also performs the function of respiration; and in the mammal
both food and oxygen are carried by its vessels to the fcetus during
the greater part of intrauterine life. But later on the outgrowth
atrophies and disappears, all except its origin from the alimentary
canal, which dilates and persists as the urinary bladder, and its
bloodvessels, which grow in the form of tufts or loops into the
chorionic villi. The vessels are fed by two umbilical arteries which
arise from the hypogastric arteries and run out at the umbilicus on the
allantois. The blood is returned by an umbilical vein, whose further
course we shall have soon to trace. The shrivelled stalk of the
Fi<i,
299. — DlAiiKAM TO ILIA'STKATE FORMATION
Amnion.
A, cavity of true amnion ; F, F', folds about to coalesce and
complete the amniotic cavity ; m, mesoblasiic layer of amnion ;
B, allantois; I, iniestinil civity of embryo ; Y, yolk-sac ; h,
hypoblastic layer ; c, epiblastic layer of embryo. The embryo
is the sha-ied portion in the middle of the figure. E is placed
over the head legion. No attempt is made to delineate its actual
form. The mesoblast is represented by the interrupted line.
REPRODUCTION 829
allantois, projecting through the umbih'cus, l)ecoiTics with its blood-
vessels the umbilical cord. The vascular tufts of the chorion, which
at first cover the whole surface of the ovum and suck up food and
oxygen from decidua serotina and reflexa alike, disappear in the
region of the reflexa, hypertrophy all over the serotina — that is,
where the ovum is in actual contact with the uterine wall — and
this part of the chorion is now distinguished as the chorion frondosum.
The giant villi of the chorion frondosum push their way into the
thickened decidua serotina, and ultimately penetrate into the great
capillaries or sinuses of the uterine mucous membrane. At the same
time the tissue of the villi external to the vessels becomes reduced
to a mere film, so that, except for a thin covering of decidual cells,
the foetal vessels are bathed in maternal blood. By this inter-
weaving of decidua and chorion frondosum is formed the placenta,
which for the rest of intra-uterine life acts as the great respiratory,
alimentary and excretory organ of the foetus. 'I'he maternal blood,
as it streams through the colossal capillaries of the decidua, gives up
to the foetal blood oxygen and food substances, and receives from
it carbon dioxide and in all probability urea. It is true that the
blood in the uterine sinuses is not itself fully oxygenated ; it is not
bright red arterial blood. But it yet contains more oxygen than the
jiurest blood of the foetus, and is, therefore, able to part with some of
the surplus to the dark stream of oxygen-impoverished blood brought
by the umbilical arteries to the placenta. Thus, it has been found
that while the blood of the umbilical artery of the foetus of a sheep
had 47 volumes per cent, of carbon dioxide, and only 2-3 of oxygen,
that of the umbilical veins had 6 -3 volumes of oxygen, and only 40*5
of carbon dioxide (Kuntz and Cohnstein). This, although far from
the level of ordinary arterial blood, is yet the best the ffctus ever
gets ; and by a series of contrivances it is assured that this best
should go first to the most important parts, the liver, the heart and
the head, while the legs and most of the abdominal organs have to
put up with an inferior supply. This is brought about mainly by the
existence of three short-cuts for the blood, which disappear in the
adult circulation, the ductus venosus, the ductus arteriosus and the
foramen ovale (Fig. 300).
The blood of the umbilical vein, rich in oxygen for foetal blood,
passes partly through the circulation of the liver, but a part takes the
route of the ductus venosus, and empties itself directly into the inferior
vena cava. The latter gathers up the more or less vitiated blood from
the inferior extremities and the renal and hepatic veins, and pours
its mixed but still fairly oxygenated contents into the right auricle.
By means of the Eustachian valve, the jet coming from the mouth of
the inferior vena cava is directed into the left auricle through the
foramen ovale in the inter-auricular septum. There it is joined
by the trickle of blood which is creeping through the unexpanded
lungs. The left ventricle propels its contents through the aorta,
and thus a large part of this comparatively pure or second-best
blood is sent to the head and upper extremities. It returns in
a vitiated state by the superior vena cava into the right auricle, and
8-,o
A MA NUA L OF PI I ) 'SIOL O G Y
owing to tlie position of tlie Eustachian valve and the direction of
the current, it flows now not through the foramen ovale, but into the
right ventricle. Thence it is driven through the pulmonary artery,
but only a small (juantity of it finds its way through the lungs; the
main stream is short-circuited through the ductus arteriosus, and
mingles with the contents of the thoracic aorta below the origin of
the cephalic and brachial vessels.
We may now give something more of precision to the statements
that different parts of the body receive blood of different quality ;
The arrow is in
the Foramen Ovale
'RiglU Auricle
Right Ventricle
Inf. Vena Cava
Inf. Vena Cava
Ductus Venosus
Livtr
Portal Vein
Intestine
Umbilical Artery
I.ungs
Pulmonary Artery
Aorta
Ductus Arteriosus
Kidney
Umbilical Vein
Fic. 300. — Dia<;ram oi- the Skcond Circulation in the Fcetus.
The arrows show the direction of the blood-flow.
and it is possible roughly to divide the organs in this respect into
four categories : (i) The liver, which partakes both of the best and
the worst, the purified blood of the umbilical veins and the vitiated
blood of the intestines and spleen ; (2) the heart, head, and upper
limbs, which receive the blood from the inferior extremities and
kidneys, mixed with the pure blood of the venous duct ; (3) the legs,
trunk, intestines, and kidneys, which are fed chiefly by the off-
scourings of the cephalic end, mitigated, however, by a proportion
of mixed blood from the inferior cava ; (4) the lungs, which receive
only a feeble stream of unmixed venous blood.
REPKODUCriON 831
These peculiarities of the embryonic circulation are in obvious
correspondence with the physiological events taking place in the
fcctal body. The liver is not only the greatest gland in the embryo,
as it continues to be in the adult, but its activity seems to dwarf that
of all the other glands put together, and is in striking contrast with
the functional torpor of the lungs. From the third month of intra-
uterine life the secretion of bile begins and the intestines gradually fill
with meconium^ of which the principal constituent is bile. Accord-
ingly the liver is most lavishly supplied with blood, while the lungs
are stinted. And since the liver has, as we have already learnt,
other and, in the adult at least, even more important labours than
excretion, a large portion of the blood it receives is of the best
(luality : it enters the gland comparatively rich in oxygen, and passes
out comparatively poor ; while the lungs, which have to be nourished
only for their own sake, and are of no use whatever till the child is
born and respiration has begun, must be content with the poorest
fare — with the crumbs that fall from the table of foetal nutrition. The
full-fed cephalic end of the embryo grows far more rapidly than the
half-starved inferior extremities, and the head of the new-born child is
large in proportion to the rest of the body.
There are some other points in the physiology of intra-uterine life
which call for remark ; and, to sum up in a few words the grand
distinction between fcetal and adult life, we may say that growth is
the keynote of the former, work (functional activity) of the latter.
Thus, the muscles at an early period in their development become
the seat of a great accumulation of glycogen, an accumulation which
would entirely unfit them for the labours of fully-formed muscles,
but which seems to be intimately connected with their own growth,
and perhaps also with the growth of other tissues. Later on, when
the muscles have been formed, their powers still lie dormant, but for
the infrequent and feeble movements, generally regarded as reflex,
but possibly to some extent originated in the cerebral cortex, which
gives the mother the sensation of 'quickening.' But the store of
glycogen now becomes reduced to its permanent amount, and the liver
takes on its glycogenic function. It can hardly be doubted that
the glycogen found in the placenta (bitch) is also deposited there in
the interest of the rapidly growing foetal tissues, as a kind of current
account on which they can operate at any moment of emergency,
when the more distant maternal reserves cannot be drawn upon
in time.
The excretory glands of the embryo, except the liver, scarcely
awaken to activity during fcetal life. Urine may, indeed, be some-
times found in the bladder at birth, but it is often absent ; and
although a portion of the amniotic fluid, which contains traces of
urea and salts, in addition to small quantities of albumin, may be
secreted by the renal tubules, and find its way through the still
open urachus into the amniotic sac, this contribution cannot imply
more than a very slight degree of glandular action. The experi-
ments of Kuntz, indeed, go far to show that this liquid comes
essentially from the mother rather than from the child. He found
832 A MANUAL OF PHYSIOLOGY
that sulphindigotate of sodium injected into the bloodvessels of a
l)regnant animal (sheep) coloured the amniotic fluid and the
placental tissues, but not the foetus ; while after injection into the
latter the fiotal kidneys contained particles of the pigment, while the
amniotic fluid remained uncoloured. The sebaceous glands have
certainly begun their work by the secretion of the vcrnix caseosa, an
oily material which covers the skin and serves to protect it from the
continual irritation of the fluid in which the embryo floats.
The nervous system is even less active than the glandular tissues,
and not more active than the muscles. There is evidently no scope
for the exercise of the special senses. Psychical activity of every
kind must be at the lowest ebb. Consciousness, if it exists at all,
must be dull and muffled. And if motor impulses are discharged
from the cortex, the psychical accompaniments of such discharge are
doubtless widely different from those which we associate with volun-
tary efi'ort.
This functional calm, broken only by the beat of the heart, is
accompanied by a very feeble metabolism. The amount of oxygen
carried to the tissues of an embryo sheep weighing 3 "6 kilos, by the
blood of the umbilical vein, was only i"7 c.c. per minute; 28 c.c. ot
carbon dioxide per minute was given up to the blood of the mother
in the placenta (Kuntz and Cohnstein). The gaseous exchange was,
therefore, not one-tenth as much as in the adult sheep. In fact, the
heat-production of the foetus, sheltered as it is from loss except by
the placental circulation, is only sufficient to raise its temperature by
a small fraction of a degree above that of the mother. And it is not
difficult to see that a large portion of this production must be due to
the action of the heart. This beats at the rate of about 140 times a
minute at full term.* The blood-pressure in the umbilical artery of
the mature embryo (sheep) varies from 60 to 80 mm. of mercury ;
but at the beginning of the aorta it will be more. The pressure in
the pulmonary trunk must be about equal to that in the aorta, since
the comparatively short and easy circuit through the lungs does not
as yet exist ; and in accordance with this equality of pressure (of work
to be done) is the equality of thickness (of working power) in the
walls of the two sides of the heart.
Suppose, now, that the embryo contains 60 grammes of blood for
every kilo of body-weight, and that the whole of the blood passes
through the circulation in twenty seconds. Then in twenty-four
hours 259"2 kilos of blood will be forced through the heart for every
kilo of body-weight against a pressure of, say, 80 mm. of mercury,
* It has not been finally determined whether the rate of the heart
varies with the size, or what probably conies to the same thing, with the
sex of the fcetus. As we have seen, the variation of the rate in the adult
with the size of the body is associated with a corresponding variation in
the metabolism and heat-loss, which are proportionally greater in a small
than in a large animal. If this is a causal connection we should not
expect that in the embryo /// iitcrp, where the conditions as regards heat-
loss are entirely difterent, such a relation should exist, at any rate within
the same species.
REPRODUCTION 833
or I metre of blood. This is equivalent, in round numbers, to 260
kilogramme-metres of work, or 600 small calories. Now, taking the
total heat-production of the heart at four times the equivalent of its
mechanical work, we get 2,400 calories per kilo of body-weight in
twc'ity-four hours (see p. 488), or about -^.^ to j\, of the heat-produc-
tion of a resting adult.
So low is the intensity of metabolism in tlic embryo, so slight the
demand for oxygen, that not only is even the purest blood, as has
already been stated, far from saturated with that gas, but the relative
proportion of h;ximoglobin, the oxygen-carrier, is less than in the
adult ; and although constantly increasing in amount from the moment
of its first appearance, it is still somewhat deficient, even at full term,
but leaps sharply up at birth. At an early period of development
the embryo also contains much more water than the adult; the
specific gravity of its tissues increases as development goes on.
The remarkable vitality of the fcetus, and its resistance to asphyxia,
are related to the feebleness of its metabolism and to the compara-
tively slight excitability of nervous centres like the respiratory, vaso-
motor, and cardio inhibitory. Even when totally deprived of oxygen,
as by pressure on the umbilical cord during delivery, the child does
not perish in the two or three minutes which decide the fate of the
asphyxiated adult ; nor are the convulsions, rise of blood i)ressure,
and slowing of the heart-beat, associated with asphyxia in the latter,
so readily induced, nor premature and fatal efforts at respiration
easily excited in utero. But although in such a case the embryo
behaves as a separate organism, governed by its own laws, there are
circumstances in which it becomes merely a part of the mother and
participates in her fate. Thus, the stream of oxygen which normally
passes from the maternal to the foetal blood is turned back if
asphyxia threatens the mother ; the blood of the umbilical arteries,
instead of being purified in the placenta, loses the little oxygen it
holds to the blood of the uterine sinuses, and the sluggish tissues of
the embryo are impoverished to feed the more active metabolism of
the maternal organs. In the same way, the phenomena of starvation
have taught us that the nutrition of the organism is not subject to
the rules of red tape. In normal circumstances the flow of nutriment
follows definite lines : the blood feeds the tissues through its inter-
mediary, the lymph, and recoups itself from the contents of the
alimentary canal. But when the normal sources of nutrient material
fail, the body falls back upon its stores. The organs immediately
necessary to life are kept, as far as possible, on full diet ; organs of
secondary importance have to be content with half-rations ; organs
less important still are drawn upon for supplies.
At birth, great changes take place in the circulation, and these
are intimately connected with the commencement of the respiratory
activity of the lungs. The causes of the first respiration are : (i) The
increasing venosity of the blood circulating in the bulb, which
stimulates the respiratory centre when the umbilical cord has been
cut or tied and the placental circulation thus interfered with ; (2) the
stimulation of the skin by the air, which, as we have seen, acts
53
834 A MANUAL OF PHYSIOLOGY
reflexly upon the respiratory centre. That both of these factors may
be involved is shown by the fact that either compression of the
umbilical cord alone, or exposure of the foetus by opening the uterus
of an animal without interference with the circulation, has been
observed to be followed by attempts at breathing. Once distended,
the lungs never again completely collapse — not even after death, nor
when the chest is opened. The aspiration caused by the elevation
of the chest-walls in inspiration (for the respiration of the new-born
child is mainly costal) sucks blood into the thorax, and expands the
vessels of the lungs for its reception; and in the measure in which
the blood passing through the pulmonary trunk finds an easy way
through the lungs, the quantity which takes the route of the ductus
arteriosus diminishes. The pulmonary veins, and consequently the
left auricle, are better filled ; and the increasing pressure on this
side of the septum tends to oppose the passage of blood through the
foramen ovale, to approximate its valve, and to close its orifice.
By the second or third day the ductus arteriosus has usually
become obliterated. The umbilical arteries and vein and the ductus
venosus become impervious soon after the interruption of the placental
circulation. The vein and venous duct remain in the adult as the
round ligament of the liver, the arteries as the lateral ligaments of
the bladder.
Although from birth onwards the young mammal obtains its
oxygen and gets rid of its carbon dioxide through its own pulmonary
surface instead of through the placenta, it still lives, as regards its
food proper, on the tissues of the mother, and that in as literal a
sense as when it drew its supplies directly from the maternal blood.
Milk^ indeed, represents in large part the fragments of cells lining
the alveoli of the mammary glands, which have undergone a fatty
change and been bodily broken down. This is particularly the case
with the first milk of each lactation, the colostrum as it is called,
which consists of little else than the debris of fattily degenerated
cells. In addition to the fat, which when milk is allowed to stand
rises to the top as cream, milk contains a considerable quantity of
a nucleo-proteid, casein, to whose coagulation, under the influence of
the lactic acid produced from the lactose, or milk-sugar, by certain
bacteria, spontaneous curdling is due. Another proteid, lact-albumin
(Halliburton), a large amount of water, and some inorganic salts, are
the most important of its remaining constituents.
Pregnancy is accompanied with vascular dilatation and hyper-
trophy of the mammary glands, but the mechanism by which these
changes are produced is unknown. Precisely similar phenomena
are occasionally seen in animals which have not been impregnated
and even in men. Humboldt relates the case of an Indian father,
who so well understood the responsibilities of paternity, and was so
capable of fulfilling them, that he suckled his child for five months
on the death of the mother.
APPENDIX.
COMPARISON OF METRICAL WITH ENGLISH MEASURES.
Measures of Length.
I millimetre =o"03937 inch.
I centimetre = 0-3937 1 „
I decimetre =3"937o8 inches.
I metre =39'37o79 »
I inch =25-3995 millimetres.
Measures of Weight.
I gramme = 15*432349 grains.
I kilogramme = 2 '20462 1 3 pounds.
I ounce ^ 28*3495 grammes.
I pound =453-5926 grammes.
Measures of Volume.
I cubic centimetre = 0-061027 cubic inch.
I litre (1,000 cubic centimetres) = 61-027052 cubic inches.
= 1-760773 pints
= 0-22009668 gallon.
I cubic inch= 16-3861759 cubic centimetres.
I cubic foot =28-3153119 cubic decimetres (or litres).
I pint =0-567932 litres.
I gallon =4'5434579 litres.
Measures of Work.
I kilogrammetre = about 7*24 foot-pounds.
I foot-pound =0-1381 kilogrammetre.
53—2
INDEX.
References to the Practical Exercises are in black figures.
Abdominal breathing, 202
Abducens, or sixth nerve, 689
Aberration, chromatic, 755
spherical. 755
Absorption of hght, 739
of the food, 363
physical introduction to, 360
theories of, 366-368
of cane-sugar, 365, 382
of carbo-hydrates, 371
of fat, 370, 381
of proteids, 372
from the stomach, 352, 365
Accelerator nerves of heart, 139
Accommodation, 747, 815
mechanism of, 749, 750
Acid albumin, 21, 302, 377
Acidity of gastric juice, 301, 351
Action currents, 606, 612-614, 628
diphasic, 607
electromotive force of, 609
of eye, 624
of glands, 623
of heart, 608, 621, 628
of human muscles, 611
of phrenic nerves, 609
in polarized nerves, 620
of spinal cord, 622, 636
theories of, 6n
' Adequate' stimuli, 733
Aerotonometer, 240
Afferent impulses, decussation of, 671
paths of, 669
After-images, 786
Agraphia, 715
Albumin, reactions of, 21
in urine, 392, 402, 424
Albuminates or derived albumins, 21
Albuminous glands, 295
Albumoses, action of, on blood-pressure,
188
on coagulation, 43, 45, 188
tests for, 22, 377
in urine, 425
Alcohol, action of, on respiratory centre,
165, 220
in diet, 470
Alimentary canal, anatomy of, 281
length of, 280
glycosuria, 513
Alkali-albumin, 22, 306, 379
Allantois, formation of, 828
Amnion, 828
Amoeboid movement, 28, 529
Ampere, 519
Amy! nitrite, action on the pulse, 93, 183
Amylolytic stage of gastric digestion, 350
Amylopsin, 306, 379
Anabolic changes in living matter, 19
Anacrotic pulse, 94
Anaesthesia by chloral. 189
by morphia. 58, 176
Anelectrotonus, 574, 576
Animal heat, 477
Anions, 362
Ankle-clonus, 676
Annulus of Vieussens, 139, 179
Anterior horn, cells of, 647
Antero-lateral ascending tract, 649, 654
descending tract, 659
ground bundle, 650
Anti-peptone, 308
Antipyretics, 501
Antiseptics for operations, 190, 515
Antrum pylori, 288
Aorta, effect of compression of, 179
Apex-beat, 79, 182
Aphasia, motor, 714
sensory, 716
temporary, 716
Apncea, 218
Apomorphine as an emetic, 378
Argyll-Robertson pupil, 751
Artery, to insert cannula into, 58
Articulation, positions of, 267
Ascending degeneration, 649
Asphyxia, 217
effect of, on circulation, 162, 179. 187
in the foetus, 833
Association fibres, 662
Astatic system of magnets, 521
Astigmatism, irregular, 759
regular, 760, 819
Atelectasis, 210
Atropia, action of, on heart, 141, 174
on digestive secretions, 347
on pupil, 754
on salivary secretion, 376
Auditory centre, 713
nerve, 689
vestibular branch of, 659
ossicles, 799-801
Auerbach's plexus. 281
Augmentation of heart's beat, 133, 176
primary, 136. 138
secondary, 136
INDEX
837
Auriculo-ventricular junction, stimulation
of, 135, 174
Auto-digfstion of stomach, 330, 383
Automatic actions of spinal cord, 681, 684
Bacteria in intestine, 316, 357
Bactericidal action of gastric juice, 355
Basal ganglia, 692
Batteries, 173, 517
Beat -tones, 805, 821
Beaumont on digestion, 300
Benzoic acid, 388
Bichromate cell, 173, 517
Bidder's ganglia, 129
Bile, 309-315, 380
acids, 311, 312, 380
formation of, 327
composition of, 310
curve of secretion of, 346
in emulsitication offals, 313
influence of nerves on secretion of,
345
mucin, 310, 380
pigments, 310, 327, 380
reactions of, 380
salts, preparation of. 381
secretory pressure of, 345
spectrum of, 311
Biuret reaction, 20, 377
Blastoderm, 825
Blind spot, 778. 817
Blood, coagulation of, 36, 58
composition of, 45
conductivity of, 34
distribution of, 52
functions of, 54
gases of, 235
in embryo, 829
guaiacum test f<jr, 64
laking of, 35, 61
opacity of, 35. 61
quantity of, 51, 52
in lungs, 197
reaction of, 33, 34, 57
sjjecific gravity of, 34, 57
stains, examination of, 66
sugar in, 442
velocity of. 105-115
in arteries, 114
in capillaries, 109, 118
in veins, 109, 122
volume of corpuscles and plasma, 35
why it does not clot in the vessels, 44
Blood-corpuscles, 26
composition of, 46
crenation of, 27
enumeration of, 30, 61
life-history of, 31
Blood-plates, 29
Blood-pressure, mean arterial, 102-105
curves, with elastic manometers, 100
with mercurial manometer, 102,
185
measurement of, 99, 185
effect of haemorrhage on, 165, 188
in capillaries, 119
in right and left ventricles, 82, 105
respiratory variations in, 249-256
Bloodvessels, structure of, 69
Blood-pump. 233
Bones, composition of, 464
Mone-fx'ccs, 383
Hone-marrow and blood-formation, 32
Brain, circulation in, 727
functions of, 692-726
development of, 638
in sleep. 724
respiratory changes m volume ol, 255
size of, and intelligence, 726
Break-contraction, Tigerstedt's theory of,
616
Bronchi, 195
Bronchial breathing, 203
' Buffy ' coat, 41
Brunner's glands, 315, 324
Burdach's column. See Postero-median
column
Burdon-Sanderson on negative variation,
612-614
Calcium, influence of, on coagulation, 42,
59
Caisson disease, 257
Calorie, definition of, 479
Calorimeter, respiration, 484, 513
Calorimetry, 479
Cannula, to put into artery, 58
vein, 177
trachea, 177
gastric, 378
Cane-sugar, absorption of, 365, 382
inversion of, 23, 382
Capillaries, structure of, 70
Capillary electrometer, 523, 524, 628
tubes, flow of liquid through, 73
Carbo-hydrates, composition of, 17
metabolism of. 439-446
reactions of, 23
Carbon dioxide, action of on respiratory
centre, 217
estimation of, 224, 234, 275, 276
formation of, from proteids, 438
production of, in muscular work,
227
in different animals, 229
in blood, 235, 237
in foetal blood, 829
in rigor mortis, 247
in serum, 238
Carbon equilibrium, 461
Carbonic oxide haemoglobin, 49, 63
Cardiac cycle, 75, 76, 87
changes in endo-cardiac pressure
during, 87
impulse, 79, 182
sound (Chauveau and Marey's), 85
Cardiograph, 80, 182
Catheterism, 429
Cells, structure of, 18
Central nervous system, development of,
637
Central nervous system, general arrange-
ment of, 644
functions of, 663
histology of, 638, 639
localization of function in, 719
grey axis, 644
I Centres of cord and bulb, 684
838
INDEX
Centres, cardio-inhibitory and aiigmentor,
144
heat-, 500
motor, of cortex, 707-711
sensory, of cortex, 711-714
vaso-motor, 158, 159
Centre of gravity of body, 702
Centrifuge, 69
Cerebellum, connections of, 659
functions of, 694-699
structure of, 694
Cerebrum, excision of, 703, 729, 730
Chalk-stones, 437
Cheyne-Stokes' respiration, 221
Chiasma, 687
Chloral, anttsthesia by, 189
Chlorides, estimation of, 416
Chloroform, action of, on respiratory
centre, 219
on vaso-motor centre, 162, 164,
187
Cholagogues, 348
Cholesterin, 312, 380
Chorda tympani, 332, 375
hypothetical fibres in, 339
antagonism of sympathetic with,
337. 376
Chordae tenaineae, 75
Choroidal epithelium, 743, 773, 776
Chromatin, 18
Chromatic aberration, 755
Chyle, composition of, 53
Chyme, to obtain, 377
Cilia, 530, 593
Ciliary muscle, 749, 780
nerves, 750, 751
Circulation, artificial, 246
changes in, at birth, 833, 834
comparative, 67
cross, through brain, 218
general view of, 68
in brain, 727
in the capillaries, 117
in the embryo, 827, 830
in the frog's web, 26, 168
in lungs, 196
in the veins, 120
of lymph, 166
time, 122, 192
Clarke's column, 647
Coagulation of blood, 36, 68
prevention of, 37
theories of, 43
temperature, to determine, 21
Coagulated proteids, reactions of, 22
Cocaine fever, 491
Cochlea, 800
Collaterals, 639, 653, 679
Colloids of Grimaux, effect of, on coagu-
lation, 43
Colour, body- and surface-, 740
blindness, 790
mixing, 785, 820
triangle, 783
vision, 781
Hering's theory of, 788
Young-Helmholtz theory of, 784
Colours, complementary, 782, 820
primary, 784
Colostrum, 834
Coloured shadows, 787
Comma tract, 650
Commutator, I'ohl's, 527
Compensator, 523
Compensatory pause of heart, 132
Complemental air, 207, 274
Complementary colours, 782, 820
Condensed air, effects of breathing, 255,
257
Conductivity, molecular, 363
specific, 363
of nerve, effect of temperature on, 574
effect of voltaic current on, 579
Conduction, double, 580
isolated, 581
Consonants, 266, 267
Contraction, law of, 576, 632, 578
without metals, 605, 627
secondary, 621, 627
Contrast, 787
Co-ordination of movements, 700
Cornea, radius of curvature of, 744
Corona radiata, 645, 652
Corpora quadrigemina, 687, 692, 693
striata, 500, 645, 694
Corpus callosum, 646, 661
Cortex of brain, functions of, 704
motor areas of, 707
sensory areas of, 711
Corti's organ, 800
Costal breathing, 202
Coughing, 222
Cranial conduction of sound, 802
nerves, 685-691
Crossed pyramidal tract, 650
Cross-circulation through brain, 218
Crura cerebri, 652
Crusta, 652
Cuneate funiculus, 651
nucleus, 651, 655
Curara, action of, on skeletal muscle, 534,
593
on heart, 141
on heat-production, 495
Curdling of milk by rennin, 304, 377
Currents of action. See Action currents
Cutaneous burns, death from, 259
excretion, 412
respiration, 258
Cybulski's method of measuring velocity
of blood, 113
Daniell cell, 173, 517
' Dead space,' respiratory, 209
Deaf-mutes, ecjuilibration in, 699
Decussation of afferent impulses, 671
of efferent impulses, 670
of optic nerve, 687
of pyramids, 651, 658
DefcEcation, 291
Deficiency phenomena, 664
Degeneration of muscles, 586, 683
of nerves, 584
reaction of, 586
Deglutition, 285
centre, 287
nerves of, 287
sounds, 349
INDEX
839
Demarcation current, 606, 628
tlieories of, 611
Deiidrons, 640
Dentate nucleus of cerebellum, 659
Depressor nerve, 145. 160, 190
Descending degeneration, 650, 656
Development of embryo, 825
Dextrin, tests for, 23
formed in salivary digestion, 298, 376
Dextrose, 'rrommer's test for, 23
estimation of, in urine, 426
Diabetes, 392, 442
levulose used up in, 445
pancreatic, 445, 472
phloridzin, 445. 512
' puncture,' 513
sugar-destroying power of blood in,
446
Diapedesis, 56
Diaphragm in respiration, 199
Diastase, 299
Dicrotic wave, 92
Dietaries, standard, 464-467
Dietetics, 464-471
Differential rheotome, 610
Diffusion, 360
of gases, 230
Digestion, bacteria and, 357
chemical phenomena of, 294-315
of fats, 356
in intestine, 353
in stomach, 350
mechanical phenomena of, 283-289
time required for, 381, 382
Digestive glands, structure of, 318
juices, action of drugs on, 347
secretion of, 317
organs, in different animals, 280
Diopter, 749
Diplopia, 765
Direct cerebellar tract, 650, 654
pvramidal tract, 650
Discharge of ventricle, period of, 87
Dispersion in eye, 756
by a prism, 737
Diuretics, 410
Double conduction in nerve, 580
Double images, neglect of, 767
Dromograph, iii
Ductus arteriosus and ductus venosus,
830
Dyspnoea, 217, 272
heat-. 218, 272
Ear, anatomy of, 798
ossicles of, 798, 801
resonance tone ot, 557
Eck's fistula, 328. 435
Ectoderm, 19 . ^ o <;
Efferent impulses, decussation of, 658, 670
paths of, 670
Egg-albumin, excretion of, 399
reactions of, 21
Elasticity of muscle, 531
Electric fishes, 624
Electrodes, unpolarizable, 526, 628
Electrolytes, 362
Electrometer, capillary, 523, 524, 628
Electromotive force, 518
Electrotonic alterations of excitability and
conductivity, 630
currents, 6i»j, 629
negative variation ot, 010, o^»
Electrotonus, 574
Embryo, asphyxia in, 833
circulation in, 827, 830
development of, 826
gases of blood in, 829
heat-production in, 833
liver in, 831
metatiolism of, 832
physiology of, 827
Emetics, 293, 378
Emmetropic eye, 758
Emulsification of fats, 24, 313
Endocardiac pressure, 8i-88
curves of, 81, 84, 85
amount of, 82
measurement of, 82, 83
Endoderm, 19
Endolymph, 798
Enemata, 373
Epiblast, 825, 826
Epiglottis, 285
Epilepsy, cortical, 717, 731
produced by absinthe, 718
Equilibration, cerebellum and, 695
semicircular canals and, 697
in pigeon, 698
Equimolecular solutions, 572
Ergograph, 597
Erythroblasts, 32
Erythrodextrin, 298, 375
Eserine, action of, on pupil, 754
Eustachian valve, 829
Excitability, direct, of muscle, 534. =>»•»
of nerve, effect of temperature on, 574
effect of voltaic current on, 574.
rA!tn
Expectoration, 384
Expiration, 201
forced, 203
Expired air, composition of.
Extensibility of muscle, 531
Extra contraction of heart, 132
Eye, compound, of insects, 741
currents of, 624
defects of, 755
movements of, 793
muscles of, 795
nerves of, 751
optical constants of, 744
Kiihne's, 817
reduced, 745
structure of, 742
Eyes, primary position of, 794
wheel-movements of, 794
Facial nerve, 689
Faeces, composition of, 358 381
odour of, 359
bone-, 383
Fainting, 166
Falsetto voice, 265
Far point of vision, 758
Fat, absorption of, 370, 381
composition of, 17, 22, 451
digestion of, 313. 35^
emulsification of, 24
[630
275
840
INDEX
Fat, excretion of, into intestine, 324, 374
formation of, from carbo-hydrates,
449
from fatty acids, 373
from proteids, 448
metabolism of, 446-450
proteid-sparing action of, 455
sources of, in body, 446, 447
in fa;ces in jaundice, 314
Fat-splitting action of pancreatic juice,
380
Fatigue, muscular, 549, 596, 597
Fatty acids, absorption of, 373
Fehling's solution, 427
Ferments, 294
mother substances of, 325
quantitative estimation of, 326
Fever, 501-505
produced by cocaine, 491
retention theory of, 503
significance of, 504
Fibrillar contraction of heart, 179
Fibrin-ferment, 39, 60
nature of, 40
source of, 41
Fibrin, formation of, 36
Fibrinogen, 38
Fibrinoglobulin, 38
Fick and VVislicenus' experiment, 459
Fillet, 655
Flavour, 808
Flow of liquids, 71
Focal illumination of eye, 770
Foetus. See Embryo
Food, relation of, to surface, 468
Foods, composition of, 466
isodynamic, 565
Forced movements, 699
Fore-brain, 638
Formatio reticularis, 655
Fourth or trochlear nerve, 688
Funiculis gracilis and cuneatus, 651
Freezing-point and osmotic pressure, 361
Fundus of stomach, in digestion, 288
Gall-bladder, nerves of, 345
Galvani's experiment, 605, 627
Galvanometer, 520, 521
Galvanoionus, 537
Galvanotropism, 634
Ganglion-cells, changes in, with age, 642
Gaseous exchange, 242, 276
Gases, of blood, 235
diffusion of, 230
partial pressure of, 231-233
solution of, 230
Gas-pump, 233
Gasserian ganglion, developing, 640
Gastric digestion, amylolytic stage of, 350
glands, changes in during secretion,
320
influence of nerves on, 342
structure of, 321
juice, 300-305, 376-378
acidity of, 301, 351, 378
artificial, 376
bactericidal action of, 355
Beaumont's researches on, 300
lactic acid in, 350
(iastric juice, to obtain, 378
Gelatin, proteid-sparing action of, 456
Geminal fibres of cord, 658
Geniculate bodies, 687, 692
Gianuzzi, crescents oi, 318
Globulicidal action rtf serum, 62
Globulins, reactions of, 21
in urine, 424
Glomeruli, 395, 403
Glossopharyngeal nerve, 690
Glottis, 265, 266
Glycin, 312, 388
Glycocholic acid, 311
Glycogen, 439, 611
disappearance in fasting, 441
formation of, 442, 450
in embryo, 831
in liver-cells, 440
in muscles, 441
in placenta, 441
preparation of, 611
used up in muscul,ir contraction, 564
in stryclmia-poisoning, 442
Glycosuria, 399
alimentary, 442, 613
in diabetes, 445, 446
after injection of sugar into blood,
512
Gmelin's test for bile-pigments, 380
Golgi's method, 643
GoU's column. See Postcro - median
column
Gower's tract. See Antero-lateral ascend-
ing tract
Graafian follicle, 824
Gracile and cuneate nuclei, 651, 655
Gramme-molecular weight, 360
' Granule-cell,' 640
Gravity, centre ol', in standing, 702
influence of, on circulation, 164, 187
Ground-bundle, antero-lateral, 650
Guaiacum test for blood, 64
Guanin,436
Giinsburg's reagent, 378
Gymnotus, 625
Haematin, 50, 64
Ha.'niatoblasts, 32
Hrt;matocrite, 35, 362
Haematoidin, 328
Hajmatoporphyrin, 50, 64
in urine, 389
Hremautographic tracing, loi
Hsemin, 50
test for blood, 66
Hajmochroniogen, 50, 64
Hremoglobin, composition of, 46
crystals of, 47, 62
derivatives of, 49. 50, 62-64
dissociation of, 236
iron and sulphur in, 47
quantitative estimation of, 65
spectrum of, 49, 62
Hoemometer, Fleischl's, 65
Haemophilia, 42
Haemorrhage, effect of, on blood-pressure,
165, 188
Harmonics, or overtones, 264
Hayem's solution, 29
INDEX
841
Head on referred pain, 666
Hearing, 797
Heart, aciion-current of, 621, 629
action of drugs on, 141, 174
anatomy of frojj's, 168, 169
beat, 74, 168, 176
cause of, 129
voluntary acceleration of, 147
embryonic, 827
fibrillar contraction of, 179
ganglion-cells of, 129
heat produced by, 488
impulse of, 79, 182
mammalian, action of, 176
muscle, 70, 131
nature of contraction of, 132
influence of temperature on, 169,
172
nerves of, augmentor, 136, 140
extrinsic, 133-147
inhibitory, 134, 139
intrinsic, 128
output of, 127
pressure in, 8i-88
refractory period of, 132
sounds of, j-j, 78
tracings, 169, 170, 171
work of, 126
Heat-centres, 500
Heat, distribution of, 505
equivalent of food-substances, 485
of work of heart, 488
given off in respiration, 483, 513
loss from body, 483-486
by evaporation, 483
after varnishing skin, 498
involuntary regulation of, 491
voluntary regulation of, 493
Heat-production, effect of curara on,
489
in brain, 490
in embryo, 833
in fever, 491
in glands, 489
in muscles, 487
in heart, 488
in sleep, 486
and size of body, 497
involuntary regulation of, 495
voluntary regulation of, 494
relation to muscular work, 490, 560
seats of, 487-491
sources of, 484
Heat rigor, 568
units, 479
Heidenhains experiments on renal secre-
tion, 401
Heller's test for albumin, 424
Helmholtz's wire, 526
Hemianopia, 687, 712
Hemisection of cord, 728
Hemi-peptone, 308
Hering's theory of colour vision, 788
Hiccup, 222
Hippuric acid, 388, 438, 424
Holder for animal, 176
Homoiothermal animals, 477
Horopter, 766
Hydrobilirubin, 311
Hydrocele fluid, clotting of, 39
Hydrochloric acid in gastric juice, 301,
378
fornuition of, 326
Hydrolytic action of ferments, 294
Hydrostatic and hydrodynamic elements
in blood-pressure, 164
Hypermelropia, 759
Hyperpnoea, 217
Hypnosis, 725
Hypoblast, 825, 826
Hypobromite method of estimating urea,
419
Hypoglossal nerve, 691
Hypoisotonic solutions, 362
Hypoxanthin, 436
Identical points, theory of, 765
Ueo-crecal valve, 289
Image on retina, size of, 746
Income and expenditure of body, 450
Incongruence of retina-, 766
Incus, 798, 801
Indigo-carmine, excretion of, by kidney,
401
Indol, 308
formation of, in intestine, 357
in urine, 385, 390, 393, 418
Induced currents, 524
Induction machine, 525
arranged for single shocks, 590
tetanus, 175
Inferior peduncle of cerebellum. See
Restiform body
Infundibulum, 694
Inhibition of heart, 133
reflex, 145
by ammonia, 146, 184
nature of, 143
Inspiration, 199
forced, 202
Insufficiency of cardiac valves, 181
Intercostal muscles, 200
Internal capsule, 659-662
Internal secretion. See Secretion
Intestinal juice, 315, 347
Intestines, bacteria in, 354, 357
digestion in, 353
movements of, 289
nerves of, 290
reaction of contents of, 354
Intra-thoracic pressure, 198, 209
in fostus, 210
Intra-vascular clotting, 40
Invertin, 316
Ions, 35, 362
Iris, centre for movements of, 750
functions of, 754
effect of stimulation of sympathetic
on, 752, 820
local mechanism of, 753
nerves of, 751, 752
Iron, absorption of, 359
in bile, 312
in liver, 32, 328, 381
Irradiation, 793
Isodynamic relation of foods, 565
Isotonic solutions, 362
and isometric contraction, 545
842
INDEX
Jaundice, fat in fjeces in, 314
Judgment, false.asexplaining contrast, 788
Karyokinesis, 18
Katabolic changes in living matter, 19
Kations, 362
Key, short-circuiting, 527
Kidney, bloodvessels of, 395
internal secretion of, 472
nerves of, 152, 405, 406
secretory pressure" in, 404
tubules of, 395
Kjeldahl's method for total nitrogen, 421
Knee-jerk, 676, 677
Kreatin, 388, 436
Kreatinin, 388, 424, 438
Kiihne's eye, 817
Kymograph, 99
labyrinth of ear, 798
extirpation of, 722, 806
Lactic acid, action of, on bloodvessels, 154
in gastric juice, 301, 350
in intestine, 358
in muscle, 563. 603
Ueffelniann's test for, 378
' Laky ' blood, 35. 61
Laryngoscope, 264
Larynx, anatomy of, 260
abductors and adductors of, 260, 261,
270
nerves of, 269, 270
paralysis of, 270
Lateral nucleus of bulb, 655
Lavoisier and carbon dioxide, 223
Law of contraction, 576
Lecithin in bile, 312
Leclanche cell, 173, 517
Lens, radii of curvature of, 744
Lenses, refraction by, 738, 739
Leucin and tyrosin, formed in tryptic
digestion, 306, 379
in urinary sediments, 394
Leucocytes, 28
classification of, 29
composition of, 51
formation of, 33
and absorption of fat, 370
of peptone, 372
leukaemia, blood-corpuscles in, 30
uric acid in, 393
Levatores costarum, action of, in respira-
tion, 200
Lieberkiihn's crypts, 315, 317, 373
Liiienfeld's theory of coagulation, 43
Listing's law, 794
Liver, and coagulation of blood, 45
bile-pigments and acids in, 327
formation of sugar in, 439
urea in, 434
glycogen in, 439, 440, 511
internal secretion of, 471
iron in, 32, 328, 381
Minkowski's experiments on, 434 , 435
Living matter, composition, 17
functions, 19
structure, 18
Localization of function in brain, 719
Locomotor ataxia, knee-jerk in, 676
Locomotion, 703
Lungs, influence of, on coagulation, 44
quantity of blood in, 196, 197
secretory action of, 242
vaso-motor nerves of, 154
Luxusconsumption, 457
Lymph, circulation of, 166
composition of, 53
formation of, 368
functions of, 54
hearts, 167
Lymphagogues, 368
Lymphocytes, 29, 370
Malapterurus, 625, 642
Malleus. 798, 8oi
Manometer, P'ick's C-spring, 82
Pick's elastic, 83
Hiirthle's elastic. 83
maximum and minnnuin, 82
Marckwald on respiratory paths, 213
Marioite's experiment, 779
Mastication, 283, 284
Massage of muscle^, effect of, on blood-
pressure, 162
Maturation of ovum, 825
Maxwell's spot, 789
Meconium, 359, 831
Medulla oblongata, anatomy of, 651
centres of, 684
Meissner's plexus, 281
Menstruation, 824
Mesoblast, 825. 826
Metabolism of carbo-hydrates, 439-446
of embryo, 832
of fat, 446-450
of proteids, 430
in fever, 504
in starvation, 453, 454
nitrogenous, laws of, 457-460
in muscular work, 458
Methsemoglobin, 49, 64
in urine, 389
Methylene blue, reduction of, in tissues,
193
Metronome. 170
Micturition, 410 412
centre, 411
Milk. 834
curdling ferment, 303, 306, 377, 378
Millon's reagent, 20
Mirrors, reflection from, 735, 736
Moist chamber, 628
Molecular concentration, 360
Morphia, action of, on motor centres, 719
quantity of, for dog, 68, 176
Mother-substances of ferments, 323, 324
Motor areas, 706-709. 730
removal of, 731
sensory functions of, 718
path, 658
Mountain sickness, 258
Movements, co-ordination of, 700
forced, 699
Mucous glands, changes in activity, 32a,
376
Miiller's ex[>eriment, 256
Murexide test for uric acid, 422
Musc3e volitantes. 757
INDEX
843
Muscarine, action of, on heart. 141. 174
Muscle, afferent impressions from, O96
composition of, 562. 601-603
degeneration of, 683
diflTraclion spectrum of, 541
direct excitability of, 534. °»3
elasticity and extenMbility ot, 531
glycogen in, 441, S'^-t
reaction of, 563, 603
respiration of, 245-248
rigor of, 565, 566
stimulation of, 533
by voltaic current, 530. oSiS
structure of, 538
in polaiized light, 540
sound, 557 , „«
Muscle-nerve preparation, to make oau
Muscular contraction, chemical pheno-
mena of, 562
duration of, 541
formula of, 576, 578, 632
heat produced in, 560
influence of fatigue on, 549, 596
of load on, 544. 596
of suprarenal extract on, 475,
603
of temperature on. 547, 594
of veratria on, 551, 598
isometric and isotonic, 545
lactic acid formed in, 563, 603
latent period of, 542, 598
mechanical phenomena of, 541-
559 , Q
optical phenomena ot, 530
recording of, 594
reversal of stripes in, 539
source of energy of, 564. 5^5
superposition of, 552, 599
velocity of wave ot, 555
voluntary. 557
work done in, 546, 597
Muscular fatigue, 549 . . ... __„
seat of exhaustion in, 596. o»f
exercise, effect on the pulse. 94, 183
sense, 812
tetanus. 553, 599
tone, 682 , ,• • Q
work, nitrogenous metabolism in, 4:,o
relation of. to energy expended.
561
Mydriatics. 754
Myograph, pendulum. 543
spring, 542
simple. 595
Myopia, 758
Myosin, 567, 603
Myotatic irritability, 677
Myotics. 754
Myxoedema and thyroidectomy. 474
Near point of vision. 758
Negative variation. See Action current
Nerve, chemical changes in. 571
composition of. 583
conductivity of._ 579
degeneration of. 584
double conduction in. 580
effect of temperature on excitability
and conductivity of, 573
Nerve, effect of voltaic current on. 574. 630
isolated conduction in. 581
minimum stimulus of. 573
polariKition of, 615, 633
regeneration of. 584
stimulation of, 572
structure of, 570
Nerves, classification of, 589
trophic. 587
Nerve-cells. 639. 641
changes in. with age. 64^:
growth of. 641 , o cAA
Nerve-impulse, velocity of. 582, 600
Nerve-muscle preparation, to make. 590
Neural axis, primitive. 644
canal, development of. 637
Neuroglia. 643
Nfc'llit^ine.^aclion of, on sympathetic cells,
on^ ganglion cells of heart, 141
of salivary glands 335
Nissl's bodies in nerve-cells. 639
Nitrogen of body. 451
in proteids, 45^
estimation of total, 421
Nitrogenous equilibrium, 452-450
metabolism, 430-438. 452-461
influence of latandcarbo-hydrales
on. 456 , Q
of muscular work on, 450
laws of. 457-460
in starvation. 453
Nucleins. 18
Nucleo-proteids, 17. 4°
influence of. on coagulation. 40
Nucleus, structure of, 18
Nussbatlm's experiments on renal excre-
tion. 402
Octopus macropus, saliva of, 332. 354
Oculo-motor. or third nerve. 687
CEsophagus. contraction of, 28b
Ohm, 519
Ohms law, 518
Olfactory nerve, 636
Olive, 651
Oncometer, 405
Opacities in the eye, 77°
Ophthalmoscope, 748 ., „^, „ft, aio
Ophthalmoscope (direct method), ,61, 819
(indirect method), 764, 8l»
testing errors of refraction by. 764
Optical constants of the eye, 744
of reduced eye, 745
Optic axis, 757
disc, 743
nerve, 687
thalami, 661, 693
Optimum temperature, 294
Optogram, 775 , .^
Osmotic pressure, 35. 360. ?P^
Output of heart. 127
Overtones. 264
Ovum, development of. 824
Oxalates and coagulation, 42. &»
in urinary sediments, 387
Oxidation, seats of. 243
Oxygen, amount consumed. 22&
844
INDEX
Oxygen, amount consumed in muscular
work, 227
in blood, 235
deficit, 463
toxic effects of, 257
Oxyntic cells, 325
Pacinian corpuscles, 809, 813
Pain, 815
referred, 666
Painful impressions, paths of, 673
Pancreas, changes in, during secretion,
319
internal secretion of, 472
nerves of, 344
Pancreatic juice, Hrtificial, 378
composition of, 305
ferments of, 306, 378-380
rate of secretion of, 344
secretory pressure ol. 345
to obtain norm.il, 379
Papain, 308
Papillary muscles, 76
Paradoxical contraction, 620, 630
Paralytic secretion, 340, 344, 347
Parotid, changes in, during secretion, 320
Partial pressure, 231
measurement of, 240
of air of alveoli, 241
of blood-gases, 240
Pause of heart, 76
Peduncle, inferior cerebellar. See Resti-
form body
middle cerebellar, 659
sufjerior cerebellar, 655, 659
Pekelliaring's theory of coagulation, 43
Pendulum myograph, 543
Pepsin, 301
rate of secretion of, 349
Peptones, absorption of, 372
reactions of, 22, 377, 425
effect of, on coagulation, 43, 45
Perimeter, 790
Perimetric chart, 791
Peripheral nervous centres, 664
Peristalsis, 289, 291
Personal equation. 723
Pettenkofer's test for bile-acids, 380
Phagocytosis, 54-56
Phakoscope, 748, 815
Phenol, formation of, in intestine, 357
in urine, 385, 390, 393
Phenyl-hydrazine test for sugar, 426
Phloridzin diabetes, 445, 512
Phosphates in urinary sediments. 387
Phosphoric acid, estimation of, 417
Phosphorescence, oxidation in, 244
Phrenic nerves, 212
action current of, 609
nuclei, connections of, 212 [777
Pigmented epithelium of retina, 743, 773,
Pilocarpine, action of, on digestive secre-
tions, 347
on pupil, 754
on salivary secretion, 376
Pilo-motor nerves, 157
Pineal body, 694
Pitch , 263
appreciation of, 804, 806
Pithing a frog, 168
Pitot's tubes, iii
Pituitary body, 694
internal secretion of, 475
Placenta, formation of, 829
glycogen in, 441
Plants and animals compared, 19
Plasma, blood-, 45
Plasmine of Denis, 38
Plethysmograph, ii6, 183
Pneumonia after section of vagi, 220, 278
Poikilothermal animals, 477
Poiseuille's space, 107
Polar bodies, 824
Polarimeter, 427
Polarization of light, 540
of muscle and nerve, 615-620
positive, 616, 633
Poliomyelitis, anterior, degeneration in,
657
knee-jerk in, 676
Pons, 652
Posture, influence of, on blood-pressure,
164. 187
on pulse rate, 147, 184
Posterior horn, cells of, 648
longitudinal bundle, 655
roots, degeneration after section of,
585. 653
loss of movement after section of,
718
Postero - external and postero - median
columns, 649, 652
Potential, 518
Predicrotic wave, 93
Presbyopia, 760
Pressor and depressor nerves, 162
Pressure, arterial, 98-105
endocardiac, 81-88
intra-thoracic, 198, 209
negative, in heart, 82, 88
respiratory, 210
secretory, of saliva, 334
sensations, 809, 810
Primary colours, 784
position of eyes, 794
Projection of image into space, 765
Pronucleus, 825
Proteids, absorption of, 372
composition of, 17, 451
living and dead, 431
reactions of, 20, 22
in urine, 425
Proteid-sparing action of other food sub-
stances, 455, 456
Proteoses, tests for, 377
Protoplasm, 17, 18
Pseudopodia. 29
Pseudo-reflexes, 676, 677
Ptyalin, 297
Pulmonary catheter, 241
Pulse, the, 88-98
anacrotic, 94
characters of, 96
dicrotic wave of, 92
frequency of, 95
influence of posture on, 96, 147
venous, 119
Pulse-tracings, 91, 182
INDEX
845
Pulse-tracings from different arteries, 94,
183
effect of amyl nitrite on, 93, 183
niuscul.ir exercise on, 94, 183
Pulse-wave, velocity of, 97
J^lvinar, 687
PupMl, Argyll-Robertson, 751
changes in, during acconiinodation,
750
constrictor nerves of. 751
dilator nerves of, 752, 753, 820
eccentricity of, 756
influence of drugs 011, 754
light on, 751
Purkinje's cells in cerebellum, 694, 695
figure, 771, 821
Purkinje-Sanson images, 747, 748, 815
Pus cells, origin ot, 57
Pyloric sphincter, 288
Pyramids, 651
decussation of. 651
Pyramidal tracts, 650
connections of, 656
Reaction of degeneration, 586
of intestine, 354
time, 723
Recurrent fibres, 586
sensibility, 669
Red nucleus, 659
Reduced eye, 745
Referred pain. 656
Reflection ot light. 73:5
Reflex action, 674. 729
anatomical basis o'', 678
centres in cord, 677
lime, 680, 729
Reflexes, 676
inhibition of, 674, 730
from sympathetic ganglia, 680
Refraction of light, 736. -]■),•]
in eye, 743
Refractive index, 736
of media of eye. 744
Refractory period of heart, 132
Regeneration of nerve, 584
of nerve-cells. 713
of tissues, 822
Renal secretion, theories of, 397
tubules, 395
Rennin, 303, 377. 378
Reproduction, sexual, 823
Reserve air, 207
Residual air, 208
Resistance, electrical, 518
measurement of, 519
thermometer, 479, 559
Resonance tone of ear, 557
Respiration, accessory phenomena of, 203
afferent nerves of, 214, 272
apparatus, 224
chemistry of, 223-248, 275-278
Cheyne-Stokes', 221
comparative physiology of, 192
cutaneous, 258
efferent nerves of, 211
external and internal, 192
frequency of, 206
heat lost in, 483, 513
Respiration, internal, 243
influence of vagi on, 213, 272, 278
of ' higher [)aths ' on, 213
of muscular exercise on, 216
influence of, on blood-pressure,
249-256
on capacity of pulmonary vessels,
252
in condensed and rarefied air, 255-258
gaseous changes in, 224229
mechanical piienomeiia of, 197
of muscle, 245-248
the first, 833
types of. 202
Respiratory automatism, 684
capacity, 208, 274
centre, 211
action of alcohol on, 165, 220
chloroform on, 219
venous blood on, 217
centres, spinal, 220
'dead space,' 209
impurity, permissible, 227
organs, anatomy of, 193
pressure, 210
quotient, 225, 278
in excised muscles, 248
in muscular work, 227
sounds, 203
tracings, 204, 205, 272
Restiform body, 651, 659
Retina, curves of excitation of, 785
development of, 638
fatigue of, 786
minimal stimulus of, 573, 779
sensibility of, for colours, 789
structure of, 743
Retinal bloodvessels, shadows of, 771, 821
image, formation of, 815
size of, 746
Rheocord, 523
simple, 592
Rigor mortis, 565
analogies to muscular contrac-
tion, 567 [247
production of carbon dioxide in,
removability of, 569
time of onset of, 568
heat-, 603
Ritter's tetanus, 616, 633
Rods and cones in vision, 773
Rolando, fissure of, 711
substance of, 643
Rontgen ravs, for study of gastric move-
ments, 289 [729
Roots of spinal nerves, functions of, 666,
section and stimulation of, 729
Root-fibres, posterior, course of, in cord,
653. 679
Saliva, amylolytic action of, 375
chemistry of, 29-, 374
functions of, 297
paralytic secretion of, 340
reflex secretion of, 340
in vomiting, 292
Salivary centre, 341
corpuscles, 296
glands, 296
846
INDEX
Salivary glands, action-currents of, 623
cranial nerves of, 334
sympathetic nerves of, 336
removal of, 476
SaFts fn diet, .169
in metabolism, 463,464
Salt-hunger, 464
Saponin, action of, on blood-corpuscles,
35.62
Sarcolactic acid in muscle, 563
in riyor mortis, 567, 603
Scalene muscles, in insjjiraiion, 200
Scheiner's experiment, 760, 816
Sciatic nerve, to expose, 186
Secondary contraction, 621. 627
with heart, 621, 179
Secretion, internal, 471-476
of kidney and pancreas, 472
of liver, 471
of pituitary body, 475
of suprarenals, 474, 603
of testes, 473
of thyroid, 473, 515
of thymus, 476
paralytic, 340
Secretory pressure of saliva, 334
Self-digestion of stomach, 383
Semicircular cinals, 697
Sensation, relation of, to stimulus, 814
Senses, the, 732
Sensory areas, 711-714
paths to brain, 658, 659
Sensori-motor functions ol motor cortex,
718
Serous glands, 295
Serum, 36, 45
albumin, 45, 60
globulin, 38, 45, 60
proteids in starvation, 431
source of, 431
Shock, 663
Sighing, 222
Single vision, theories of, 765
Sixth nerve, or abduccns, 689
Skate, electrical organ of, 626
Skatol, 308, 357
Skin currents, 623
impulses from, in equilibration, 697
varnishing of, 259
Sleep, 724
depth of, 725
Smell, 806
centre for, 713
Snake venom, effect of, on coagulation, 43
Sneezing, 222
Soret's hemoglobin band, 49
Sound, cranial conduction of, 802
Specific energy, 721, 804
Spectroscope, 46, 62
Speech, 266
Spermatozoa, development of, 823
Spherical aberration, 755
Sphygmograph, 90, 182
Sphygmomanometer, 104
Spinal accessory nerve, 690, 691
Spinal cord, action currents ot, 622
anatomy of, 646
ascending tracts of, 649
automatic functions of, 681-684
Spinal cord, centres of, 684
conduction of impulses by, 665
descending tracts of, 650
excitability of fibres of, 665
functions of, 665
heniisection of, 671, 728
complete section of, 663
removal of, 664
action of strychnine on, 729
white matter of, 648
Spinal reflexes, 677
Spirometer, 207
Splanchnic nerves, 152
Spleen and blood-formation, 32
and blood-destruction, 33
removal of, 476
Spring myograph, 542
' Staircase' or ' treppe," 133, 548
Stammering, 233
Standing, 702
Stannius' experiment, 142, 176
Stapedius, 803
Stapes, 798, Sot
Starch, action of acids on, 23, 300
digestion by saliva, 297, 374
tests for, 23
Starvation, metabolism in, 453, 454
serum proteidi in, 431
Stasis, 57
Stationary air, 208
Steapsin, 306, 380
Stercobilin, 31 r, 358
Stereoscope, 768
Stereoscopic vision, 767
Stilling's sacral and cervical nuclei, 648
Stimulants, 470
Stimuli, summation of, 552, 699
Stomach, absorption from, 352
auto-digestion of, 383
excision of, 355
movements of, 288
nerves of, 290
Stromuhr, no
Strychnia, action of, on cord, 558, 729
Sublingual ganglion, 333
Succus entericus, 315
action ot, in digestion, 357
influence of nerves on, 347
Sugar, absorption of, 393
destruction of, in blood, 445
estimation of, by Fehling's solution,
427
by polarimeter, 428
in blood, 399, 439
excretion of, by kidneys, 402
fate of, in organism, 442
formation of, in liver, 439
and muscular contraction, 565
in urine, 394
phenyl-hydrazine test for, 426
Trommer's test for, 23
yeast test for, 427
Sulphocyanide in saliva, 296, 374
in urine, 391
Sulphates in urine, estimation of, 418
Summation of stimuli, 552, 699
Superior laryngeal nerve and respiration,
215, 272
Superposition of contractions, 552, 699
IXDEX
847
Supplemental air, 207, 274
Suprarenal capsules, sccrclion of, 474, 603
extract, action of, 147, 475, 604
Surface of body, relation to mass, 468, 497
Susjxrnsorv ligament, 743
Sutures, 190 ^
Swallowing, efloct of, on pulse-rate, 146,
184
Sweat, 412
centres, 414
nerves, 413-415
quantity of, 414
Swim-bladder, gases of, 243
Sympathetic, cardiac fibres of, in frog,
134. 175
in mammals, 139
cervical, vaso-motor fibres in, 150, 189
dissection of, in frog, 172
in dog, 179
fibres for salivary glands, 333, 336
pupiUo-dilator fibres of, 752, 820
ganglia, supposed reflexes from, 680
Syncope, 166
Systole of heart, 75
Tachograph, gas, 112
Tachycardia in disease, 691
Tactile impressions, path of, in cord, 673
sensations, S09
centre for, 714
Talbot's law, 780, 821
Tartar, 296
Taste, 807
nerves of, 808
Taurocholic acid, 311
Tears, 384
Teeth, 283
Tegmentum, 652
Tegmental afferent path, 658
Temperature of blood, 507
of brain, 508
in cavities of the heart, 506
of skin, 508
measurement of, 477, 478
nerves of, 812
paths for impressions of, in cord, 673
post-mortem rise of, 510
regulation of, 491
sensations, 811
' Tendon-reflex,' 676, 677
Tension of blood-gases, 240
of oxygen in human blood, 242
Tensor tympani, 802
Tetanus, 553-555
composition of, 553, 599
frequency of stimulation necessary
for, 554
Ritter s, 616, 633
secondary, 558, 627
Thermo-electric junctions, 479
Thermometers, 478
resistance, 479-559
Thermopile, 559
Thermotaxis, 491-501
Third nerve, 687
Thiry's fistula, 315
Thoracic duct, 166, 370
Thrombosin, 38
Thymus, removal of, 476
Thyroid, effects of excision of, 473
Thyroidectomy, operation of, 616
with thyroid fcedmg, 616
Thyroids, accessory, 616
Thyro-iodine, 474
Tidal air, 207, 274
Timbre, 263
Time markers, 170, 527
Tissue-fibrinogen, 40
Tone, muscular, 682
trophic, 683
Tonus, acerebral, 699
Torpedo, 625
Torricelli's theorem, 71
Touch, acuity of, 810, 821
Trachea, to put a cannula in, 177
Tracts in cord, 649
Transfusion, 166, 188
Traulie-Hering curves, 250, 254
Trigeminus nerve, 688
Triple phosphate, 387
Tristearin, 17
Trochlear, or fourth nerve, 688
Trommer's test for reducing sugar, 23
Trophic nerves, 587
tone, 683
Trypsin, 306
Tryptic digestion, 306-308, 379
Tympanic membrane, 798
Tympanum, 798
Tyrosin, in pancreatic digestion, 307, 379
in urinary sediments, 394
Ueffelmann's test for lactic acid, 378
Unpolarizable electrodes, 526, 628
Urates in urinary sediments, 387
Urea, 387, 393
estimation of, 419, 420
formation of, 432-435
in liver, 434
variation with proteids in food, 457,
515
daily curve of, 509
in fever, 504
Uric acid, 388, 393, 436
estimation of, 422, 423
formation of, in birds, 434
in mammals, 437
from nucleo-proteids, 388
in gout, 393, 437
in leukcemia, 393
Urine, acidity of, 386
acid fermentation of, 386
alkaline fermentation of, 387
aromatic bodies in, 390, 393, 418
blood in, 394
chlorides in, 390, 416
composition of, 385, 386
examination of, 428
ferments in, 389
ha?matoporphyrin in, 389
hippuric acid in, 388
incontinence of, 412
indoxyl in, 390, 393, 418
in disease, 391-394
in starvation, 400
kreatinin in, 388, 424
leucin and tyrosin in, 394, 435
methtemoglobin in, 389
848
INDEX
Urine, phenol in, 390
phosphoric acid in, 390, 417
pigments of, 389
proteids in, 393, 394, 424-426
quantity of, 385, 392
secretory pressure of, 404
sediments of, 387, 393
specific gravity of, 385, 416
sugar in, 393, 426-428
sulpliuric acid in, 390, 418
total nitrogen in, 421
urates in, 387
urea in, 387, 393, 419
xanthin bases in, 388, 393
secretion of, 395
action of glomeruli in, 402
action of ' rodded ' epithelium in,
401
Adami's experiments on, 403
Heidenhain's experiments on, 401
Nussbaum's experiments on, 402
influence of circulation on, 405
of drugs on, 410
of nerves on, 405-409
theories of, 397
Urobilin, 311, 358, 389
Urochrome, 389
Uroerythnn, 389
Vagi, section of both, 220, 278
Vagus nerve, 690
Vagus, cardiac fibres of, in frog, 134, 171,
174
centre, effect of suprarenal extract on,
604
in mammals, 139, 178, 185
tracings, 135, 136, 173
relation of, to respiration, 213, 272
Valsalva's experimeni, 256
Valves of heart, action of, 75, 181
moment of opening and closure
of, 87
of veins, 69
Valvulse conniventes, 365
Varnishing skin, 498
Vaso-constrictors and dilators, differences
between. 150
Vaso-dilator fibres of chorda tympani, 154
nervi erigentes, 155
Vaso-motor centres, 158, 159
peripheral, 159
Vaso-motor nerves, 14S-166
methods of investigating, 148,
149
of brain, 151, 154
cervical sympathetic, 150, 189
course of, 156
of heart, 153
of kidney, 152
of limbs, 152
of lungs, 154
of muscles, 153
of veins, 155
in splanclinics, 152
in trigeminus, 151
Vaso-motor reflexes, 160, 185
Vein, to put a cannula in, 177
Veins, circulation in, 120
Veins, pulse in, 119
vaso-niotor nerves of, 155
velocity of blood in, 122
Vella's fistula, 315
Velocity of blood, 105-115
in arteries, 114, 115
in capillaries, 109, 118
in veins, 109, 122
measurement of, 110-112
Velocity-pulse, curves of, 113, 114
Velocity of the nerve-impulse, 582, 600
Ventilation, 226
Vesicular murmur, 203
Vestibule, 800
Villi, 368
Vision, colour, 781
far point of, 758
near point of, 758
physical introduction to, 734
stereoscopic, 767
Visual angle, 746
axis, 757
centres, 711
judgments, 769
purple, 775
regeneration of, 777
Vital capacity, 208, 274
Vitreous humour, 742
opacities in, 742, 771
Vocal cords, 260, 262
paralysis of, 271
Voice, production of, 259, 261
pressure in trachea in, 262
in children, 263
Volt, 519
Volume of corpuscles and plasnna in
blood, 35
Voluntary contraction, fatigue in, 550,
597
Vomiting, 292
centre, 293
caused by apomorphine, 378
Vowels, Helmholtz's theory of, 267
Hermann's theory of, 268
Vowel cavities, 268
Water, production of, in body, 463
Weber's law, 814
Weyl's test for kreatinin, 424
Wharton's duct, 333
Wheatstone's bridge, 519
Wheel-movements of eyes, 794
Whispering voice, 267
White blood-corpuscles, 28, 51, 54
Work, muscular, 546
of heart, 126
Xanthin, 436
Xanthin-bases in urine, 388, 393
Xanthoproteic reaction, 20
Xerostomia, 342
Yawning, 222
Yellow spot, 743, 789
Yolk-sac, 828
Zonule of Zinn, 743
Zymogens, 323. 324
;K. B. Saunders, 925 Walnut Slreet, Fhiladelphia.
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