Transcriber’s Notes:
Underscores “_” before and after a word or phrase indicate _italics_
in the original text.
Equal signs “=” before and after a word or phrase indicate =bold=
in the original text.
Small capitals have been converted to SOLID capitals.
Illustrations have been moved so they do not break up paragraphs.
Old or antiquated spellings have been preserved.
Typographical errors have been silently corrected.
THE BODY AT WORK
[Illustration]
[Illustration]
[Illustration]
[Illustration: FIG. 1.—PHOTOMICROGRAPHS OF CELLS OF THE CORTEX OF THE
CEREBELLUM AND CEREBRUM.
_For description see p._ x.
_Frontispiece._]
THE BODY AT WORK
A TREATISE ON THE PRINCIPLES
OF PHYSIOLOGY
BY
ALEX HILL, M.A., M.D., F.R.C.S.
SOMETIME MASTER OF DOWNING COLLEGE, CAMBRIDGE
WITH 46 ILLUSTRATIONS
LONDON
EDWARD ARNOLD
1908
[_All rights reserved_]
PREFACE
Few subjects are as well provided with text-books as physiology; yet
it may be doubted whether the interests of the amateur of science have
been adequately cared for. From his point of view there are certain
obvious drawbacks to even the most admirable of text-books. Writing for
medical students, their authors assume that their readers have passed
through two years of preliminary training in physics, chemistry, and
biology; they take for granted that they will have the privilege of
supplementing their study of the theory of physiology with practical
work in a laboratory; they treat all parts of the subject with equal
thoroughness. In this book I have endeavoured to describe the phenomena
of life, and the principal conclusions which have been drawn as to
their interdependence and as to their causes, in language which will
be understood by persons unacquainted with the sciences upon which
physiology is based. I have omitted all reference to experimental
methods and to the technique of the science, save when a knowledge of
the means by which information has been obtained is essential to a
comprehension of its bearing. I have passed over such sections of the
subject as are generally considered unsuitable for ordinary discussion.
And since this book neither aims at being an introduction to the
systematic study of physiology, nor poses as an aid in the preparation
for professional examinations, I have treated with some thoroughness
the more recondite and the more suggestive results of recent research,
and have tried to indicate the trend of modern thought regarding
problems as yet unsolved. I have endeavoured to reflect the intrinsic
interest of the science apart altogether from its medical applications.
An author who attempts the popular exposition of a science must
stand sufficiently far away from his subject to lose sight of its
details, whilst keeping its outlines clearly in view. The difficulty
of finding such a position is probably greater in the case of
physiology than in that of any other science. Few of its conclusions
are indisputable—even those which seem to be most in accord with
the balance of evidence. If my treatment of any vexed questions is
unjustifiably dogmatic, this will, I trust, be attributed to the
desire to present a definite picture, and not to forgetfulness of
considerations which seem to call for qualified statements. All
physiologists will agree that a book which recorded every piece of
evidence which is difficult to reconcile with the views generally
adopted would not only extend to an inordinate length, but would leave
a very indefinite impression on the mind of the reader.
In many cases the value of a conclusion depends upon the reputation for
insight and accuracy of the physiologist who recorded the observations
upon which it is based. It is no want of appreciation of the genius of
the workers who have contributed most largely to the advance of the
science which has led me to omit, save in a few classical instances,
the names of all authorities. It is solely due to a desire to lighten
this book of all details not essential to the comprehension of the
propositions which it sets forth.
The illustrations are reproductions of blackboard drawings. A few of
them have already appeared in my _Physiologist’s Notebook_ and _Primer
of Physiology_; but the large majority are now printed for the first
time.
ALEX HILL.
_November, 1908._
CONTENTS
CHAPTER PAGE
I. PROLEGOMENA 1
II. THE BASIS OF LIFE 6
III. THE UNIT OF STRUCTURE 26
IV. THE FLUIDS OF THE BODY 37
V. INTERNAL SECRETIONS 84
VI. DIGESTION 96
VII. RESPIRATION 164
VIII. EXCRETION 194
IX. THE CIRCULATION 217
X. MUSCLE 248
XI. THE NERVOUS SYSTEM 293
XII. SMELL AND TASTE 364
XIII. VISION 372
XIV. HEARING 404
XV. SKIN-SENSATIONS 423
XVI. VOICE AND SPEECH 431
INDEX 441
LIST OF ILLUSTRATIONS
FIG. PAGE
1. PHOTOMICROGRAPHS OF BRAIN-TISSUE _Frontispiece_
2. THE ORGANS OF THE CHEST AND ABDOMEN xi
3. MUCOUS GLAND, CAPILLARIES, AND CONNECTIVE-TISSUE SPACES 38
4. BLOOD-CORPUSCLES 60
5. SPLEEN-PULP, WITH PHAGOCYTES 81
6. DUODENUM AND NEIGHBOURING ORGANS 99
7. A LOBULE OF THE LIVER AND LIVER-CELLS 160
8. THE DIAPHRAGM DURING INSPIRATION AND EXPIRATION 172
9. THE KIDNEY 197
10. THE HEART IN LONGITUDINAL SECTION 218
11. HORIZONTAL SECTION OF THE HEART, SHOWING ITS VALVES 225
12. SECTION OF THE WALL OF A SMALL ARTERY 233
13. KYMOGRAPH 238
14. SPHYGMOGRAPH 244
15. BLOOD-PRESSURE TRACINGS 245
16. MINUTE STRUCTURE OF MUSCLE-FIBRES 262
17. THE BICEPS MUSCLE IN ACTION 286
18. ELECTRIC ORGAN OF SKATE 289
19. MINUTE STRUCTURE OF A NERVE-FIBRE 296
20. GANGLION-CELLS WITH NEURO-FIBRILLÆ OF THE LEECH 298
21. THE DEVELOPMENT OF THE GRANULES OF THE CEREBELLUM 304
22. TIGROIDS AND NEURO-FIBRILLÆ 321
23. MINUTE STRUCTURE OF THE CORTEX OF THE CEREBELLUM 339
24. MINUTE STRUCTURE OF THE CORTEX OF THE CEREBRUM 347
25. FUNCTIONAL AREAS OF THE CORTEX OF THE CEREBRUM 352
26. TASTE-BULBS 368
27. HORIZONTAL SECTION OF THE EYE 373
28. DEVELOPMENT OF THE CRYSTALLINE LENS 374
29. PURKINJE’S SHADOWS OF THE VESSELS OF THE RETINA 375
30. RETINA ADAPTED FOR OBSCURITY AND FOR BRIGHT LIGHT 377
31. SIMULTANEOUS CONTRAST 383
32. FORMATION OF AN IMAGE ON THE RETINA 391
33. THE FORM OF THE EYEBALL IN SHORT SIGHT, NORMAL SIGHT,
AND LONG SIGHT 392
34. THE BLIND SPOT 394
35. AN OPTICAL ILLUSION 398
36. AN OPTICAL ILLUSION 401
37. AN OPTICAL ILLUSION 402
38. EXTERNAL, MIDDLE, AND INNER EAR 411
39. THE COCHLEA 414
40. THE ORGAN OF CORTI 415
41. NERVES OF THE CORNEAL EPITHELIUM 424
42. TOUCH-CORPUSCLES 427
43. PACINIAN CORPUSCLE 428
44. THE GLOTTIS 432
45. THE LARYNX IN LONGITUDINAL SECTION 433
46. THE LARYNX FROM THE RIGHT SIDE 435
NOTE ON THE FRONTISPIECE
Four photomicrographs of cells or parts of cells of brain-tissue,
coloured by the chrome-silver method (_cf._ p. 293).
=A.= Cell of Purkinje from the cerebellum of a man aged 45. At the
bottom of the photograph is seen the rounded cell-body, with the
commencement of its axon. The summit of the cell-body bears an
elaborately branched system of dendrites, spread out in the plane of
the section.
=B.= A single basket-cell of the cortex of the cerebellum (very highly
magnified). The oval cell-body gives origin to four dendritic processes
which branch. Thorns are to be seen on the larger process which
ascends on the right. From the same process, near its origin, springs
a delicate axon which thickens as it proceeds to form a basket at the
right hand lower corner of the photograph. Two other branches of the
same axon, which form baskets around other Purkinje-cells, are faintly
visible, although out of focus.
=C.= Seven or eight pyramids from the cortex of the cerebrum of a
hedgehog. A little below the centre of the photograph is seen a large
pyramid with a single thorny apical process which bifurcates, several
basal dendrites and an axon. In the upper part of the photograph are
seen the apical processes of a number of pyramids of which the bodies
were not included in the section.
=D.= The margin of the cortex (subiculum cornu Ammonis) from the same
specimen. A single row of pyramids extends across the photograph. They
are remarkable for the richness of branching of their basal processes,
which has earned for the cells which comprise this sheet the name of
“double pyramids.”
All four sections were cut vertically to the surface.
[Illustration: FIG. 2.—DIAGRAM SHOWING THE RELATIVE POSITIONS OF THE
ORGANS OF THE CHEST AND ABDOMEN.
The ribs from the first to the tenth have been cut
across in the lateral line. The eleventh and
twelfth ribs do not reach sufficiently far forwards
to be cut. With the exception of a short segment
near its junction with the ascending colon, the
small intestine has been removed. The trachea is
seen to divide into bronchi beneath the arch of
the aorta. The right lung has three, the left
two lobes. The kidneys are situate behind all
the other viscera. On their upper ends rest the
two suprarenal capsules. The lower edge of the
right lobe of the liver follows closely the line
of the ribs and costal cartilages. Below the
left lobe of the liver the stomach comes to the
anterior abdominal wall. The transverse colon
(large intestine) comes to the anterior wall below
the stomach. Below the latter the wall is in
contact chiefly with coils of small intestine. The
vermiform appendix rests on the posterior wall.
Spleen and pancreas are not shown in the diagram.]
THE BODY AT WORK
CHAPTER I
PROLEGOMENA
Physiology is the science of the body at work. It is the study of life.
Anatomy records how plants and animals are constructed. It maps and
measures. Physiology ascertains what they do, endeavours to explain how
they do it, and conjectures why.
A knowledge of structure is essential to the right understanding of
function; but the physiologist does not contemplate structure with
a view to divining possibilities of action. He has no interest in
structure as such. To him it is a matter of perfect indifference
whether the tendon of a muscle is at its origin or its insertion. He
would rather not know which end of the muscle terminates in a tendon.
It is waste of his time to notice such a fact, save for the negative,
the protective value of the information. If he did not know how the
muscle and tendon are related, he might possibly imagine the muscle as
doing something of which it is incapable. Observers of living things
are often credited with studying structure with a view to determining
function. The reverse is the true order of thought and observation.
Living things perform certain acts. Having no inherent knowledge of
our own microcosm which enables us to say how it works, we cannot,
by reflecting upon our own internal operations, explain its various
activities. Nor can we make use of the results of introspection when
endeavouring to account for the acts of other beings. Our knowledge
of how things are done is altogether extrapersonal, objective. It is
the result of trial, failure, success in the use of apparatus, our own
essays, or those of others. The body is a combination of organs—a
term used somewhat loosely to designate any piece of the animal
mechanism which has a distinct function to perform. The physiologist
studies the results of the activity of an organ. He watches it in
action, and endeavours to explain the process by which it produces its
effects. Then follows the anatomist, who, taking it to pieces, examines
it with the utmost thoroughness which scalpel and forceps or microscope
allows, with a view to ascertaining whether its structure will support
the physiologist’s hypothesis as to its mode of action. This in the
vast majority of cases has been the history of scientific progress.
The physiologist has preceded the anatomist in drawing inferences as
to the manner in which things are done. The anatomist, after a further
examination of structure, has either admitted the plausibility of
his explanation, or has interposed the objection that the part was
incapable of working in the way supposed.
This comparison of anatomy and physiology must not be pushed too far.
Enough has been said to emphasize the distinction between them. The
one treats of form, the other of function. The one looks at structure,
the other at action. Anatomy in its limited and logical sense has
nothing to do with the uses of a part; its business is to measure it.
Physiology has nothing to do with the measurements of parts; its duty
is to watch for movement. Every living thing may be contemplated either
in its statical or in its dynamical aspect. Physiology looks at it from
the latter point of view.
Surveying his province, the physiologist asks himself: “Who are my
subjects? What am I to find out about them? What methods, in addition
to direct observation, may I use to obtain this information?” His
oversight embraces all living things. It is no longer reasonable to
make a distinction between human and animal physiology, or between
the physiology of animals and the physiology of plants. No human
being can take all science for his field. If he contents himself with
scratching its surface, he will assuredly raise but a meagre crop, and
that mostly weeds. But he is far behind the spirit of his age if he
declines to sow in his own little patch seeds of thought which have
blossomed in other localities, however remote. The man whose purpose
in studying physiology is to obtain a knowledge of the working of
the healthy human body, in order that he may know how to set right
the accidents, perversions, and premature decay to which human flesh
is prone, would remain an empiric of the most rigid type did he not
apply to the elucidation of his problems all conclusions reached from
the study of other organisms which are likely to prove pertinent.
There would be no science of human physiology had observation and
experiment been limited to Man. There would be no science of medicine,
it may be added, had not the mode of working of the human body, and
the influence of drugs upon it, been inferred from the results of
experiments upon animals—experiments which could never have been made
upon men. Blisters, blood-letting, mercury-poisoning, would still be
the physician’s remedies for all human ills. “Give the watch a good
shaking. It sometimes does good. If that fails, I cannot advise you
what to do, as I know nothing about the working of a watch.” Even
though we open the living human body, as must be done for the purpose
of making good such defects as are amenable to surgical treatment,
and for a little while observe its wheels go round, we are unable,
from fear of damaging the wheels, to introduce the mechanical tests
which would tell us how and why they revolve. The man must be allowed
to recover with uninjured organs. But, thanks to anæsthetics, there
is no test which may not be applied to a live animal with as much
propriety as to a dead one. Anæsthetics abolish the distinction, in its
ethical applications, between life and death, because we are under no
obligation, as in the case of the human being, to allow an animal to
recover. Many experiments upon animals will be recorded in this book,
and since the book is intended for the general public, who have been
singularly misled regarding the nature and methods of vivisection, an
opportunity is taken thus early of insisting that anæsthetics have
made all things, not only possible, but legitimate. It is unnecessary
to commence the description of each experiment with the statement that
the animal was first placed in a condition of complete anæsthesia,
or to end it with the statement that it was destroyed before it had
recovered from the effects of the anæsthetic. The reader may take these
facts for granted. In discussing the propriety of operating upon a
living but unconscious animal, we are playing a word game as old as
Plato’s day. What is life? What is the relation of the personality to
the animal machine which it occupies and operates? For a few minutes
a heart removed from the body continues to beat. In a physiological
sense it is alive, although the body from which it was removed is dead.
Yet the personality does not reside in the heart, as many generations
of philosophers believed. It is merely an accident that the body dies
when the co-ordinating mechanism, the heart, ceases to pump blood
through its vessels. Nor is the personality limited to the brain.
Without the sense-organs which place the brain in relation with the
body, and owing to the movements of the body—by which the sources of
sensations of smell, sight, hearing are ascertained—with the world
of which it forms a part, there would be no personality, no Ego. Is
it, then, coextensive with the body which exhibits it? A soldier
returning crippled from the wars does not finish out his days with his
personality curtailed. We are no nearer than was Plato to a definition
of life. Such a discussion soon takes us out of the realm of science.
Science is limited to the sphere in which the whole is greater than the
part. Take away consciousness, and personality ceases. Guarantee that
consciousness shall never return. The animal is dead. When considering
the propriety of vivisection we must regard life and consciousness
as inseparable. There can be no question of right or wrong in regard
to experiments on a dead animal, even though a sensitive mind, from
association, shrinks from contemplating them. A person who dislikes the
idea of dissecting a dead animal is influenced by purely subjective
and personal considerations; nor is he prompted by sympathy with an
unconscious animal when he recoils from the spectacle of its still
moving organs. The term “vivisection” conveys too large a meaning. A
negative term is needed, some word which will hold the emotion of pity
in check. Pity is misplaced when devoted to the unconscious subjects
of physiological experiment; and, happily for animals, as for Man,
anæsthetics suspend conscious life. Only a person who has undergone a
surgical operation can understand how resolutely the intellect declines
to adopt as part of itself things which have not come within its own
experience. The nurse’s testimony, that a long interval separated the
placing of the mask upon the face and the commencement of that dull
half-consciousness which gradually reawakened into interest in one’s
surroundings cannot be set aside. The nurse says that during that
interval knife, saw, and cautery were busy at their work. Her story
is accepted, but it is not believed. All physiological operations are
conducted under anæsthetics. In by far the larger number the experiment
is continued until life terminates, under anæsthetics. The only ground
upon which an objection to vivisection can be based is the ground that
it involves the infliction of pain, and it is with regard to this
that the greatest misapprehension exists in the public mind. Only in
experiments which have for their object the study of the effects of the
removal of a certain part, the diversion of a duct, the elimination
of the control of a particular nerve, is there any possibility, under
existing conditions, that an animal will suffer. In such experiments
as these, observations cannot commence until after the animal has
recovered. The operation is conducted under anæsthetics, and with the
utmost precautions, to prevent any disturbance of the animal’s general
health. The injury is in almost all cases of a comparatively limited
nature, and it is certain that it involves very little pain to the
animal when it has recovered from its anæsthesia, since, thanks this
time to aseptic surgery, there is no inflammation or other secondary
trouble.
The field of physiology embraces the phenomena exhibited by all living
things, whether plants or animals. The vegetable physiologist works
in one part, the comparative physiologist in another. The work of the
human physiologist is more limited in scope. Yet there are few problems
relating to Man’s mechanism concerning which the physiologist can have
direct knowledge. His theories are based upon the results obtained by
experimenting upon animals.