Chapter I: 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.

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