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REESE LIBRARY



UNIVERSITY OF CALIFORNIA.
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-li'(\'SS!<)HS .V(). 7/ 6 // . CA/SN M).



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The Contemporary Science Series.

Edited by Havelock Ellis.

I. THE EVOLUTION OF SEX. By Prof. PATRICK GEDDES

and J. A. THOMSON. With oo Illustrations. Second Edition.
" The authors have brought to the task as indeed their names guarantee
a wealth of knowledge, a lucid and attractive method of treatment, and a
rich vein of picturesque language." Nature.

II. ELECTRICITY IN MODERN LIFE. By G. W. DE

TUNZELMANN. With 88 Illustrations.

" A clearly-written and connected sketch of what is known about elec-
tricity and magnetism, the more prominent modern applications, and the
principles on which they are based." Saturday Review.

III. THE ORIGIN OF THE ARYANS. By Dr. ISAAC

TAYLOR. Illustrated Second Edition.

" Canon Taylor is probably the most encyclopaedic all-round scholar now
living. His new volume on the Origin of the Aryans is a first-rate example
of the excellent account to which he can turn his exceptionally wide and
varied information. . . . Masterly and exhaustive." fall Mall Gazette.

IV. PHYSIOGNOMY AND EXPRESSION. By P. MANTE-

GAZZA. Illustrated.

"Brings this highly interesting subject even with the latest researches.
. . . Professor Mantegazza is a writer full of life and spirit, and the natural
attractiveness of his subject is not destroyed by his scientific handling of it."
Literary World (Boston).

V. EVOLUTION AND DISEASE. By J. B. SUTTON, F.R.C.S.

With 135 Illustrations.

"The book is as interesting as a novel, without sacrifice of accuracy or
system, and is calculated to give an appreciation of the fundamentals of
pathology to the lay reader, while forming a useful collection of illustrations
of disease for medical reference." -Journal of Mental Science.

VI. THE VILLAGE COMMUNITY. By G. L. GOMME.

Illustrated.

"His book will probably remain for some time the best work of reference
for facts bearing on those traces of the village community which have not
been effaced by conquest, encroachment, and the heavy hand of Roman
law." Scottish Leader.

VII. THE CRIMINAL. By HAVELOCK ELLIS. Illustrated.

Second Edition.

"The sociologist, the philosopher, the philanthropist, the novelist
all, indeed, for whom the study of human nature has any attraction will
find Mr. Ellis full of interest and suggestiveness." Academy.

VIII. SANITY AND INSANITY. Dy Dr. CHARLES MERCIER.
Illustrated.

"Taken as a whole, it is the brightest book on the physical side of
mental science published in our time." Pall Mall Gaze'te.



IX. HYPNOTISM. By Dr. ALBERT MOLL. Fourth Edition.

" Marks a step of some importance in the study of some difficult physio-
logical and psychological problems which have not yet received much
altention in the scientific world of England." Nature,

X. MANUAL TRAINING. By Dr C. M. WOODWARD, Director

of the Manual Training School, St. Louis. Illustrated.
" There is no greater authority on the subject than Professor Woodward."

Manchester Guardian.

XL THE SCIENCE OF FAIRY TALES. By E. SIDNEY

HARTLAND.

" Mr. Hartland's book will win the sympathy of all earnest students,
both by the knowledge it displays, and by a thorough love and appreciation
of his subject, which is evident throughout." Spectator.

XII. PRIMITIVE FOLK. By ELIE RECLUS.

"An attractive and useful introduction to the study of some aspects of
ethnograpy. " Nature.

XIII. THE EVOLUTION OF MARRIAGE. By Professor

LETOURNEAU.

"Among the distinguished French students of sociology, Professor Letour-
neau has long stood in the first rank. He approaches the great study of
man free from bias and shy of generalisations. To collect, scrutinise, and
appraise facts is his chief business. In the volume before us he shows these
qualities in an admirable degree." Science.

XIV. BACTERIA AND THEIR PRODUCTS. By Dr. G.

SIMS WOODHEAD. Illustrated. Second Edition.
"An excellent summary of the present state of knowledge of the subject."
Lancet.

XV. EDUCATION AND HEREDITY. By J. M. GUYAU.

"It is at once a treatise on sociology, ethics, and pcedagogics. It is
doubtful whether among all the ardent evolutionists who have had their say
on the moral and the educational question any one has carried forward the
new doctrine so boldly to its extreme logical consequence." Professor
SULLY in Mind.

XVI. THE MAN OF GENIUS. By Prof. LOMBROSO. Illus-
trated.

" By far the most comprehensive and fascinating collection of facts and
generalizations concerning genius which has yet been brought together."
Journal o) Menial Science.

XVII. THE GRAMMAR OF SCIENCE. By Prof. KARL

PEARSON. Illustrated.

" The problems discussed with great ability and lucidity, and often in a
most suggestive manner, by Prof. Pearson, are such as' should interest all
students of natural science." Natural Science.

XVIII. PROPERTY: ITS ORIGIN AND DEVELOPMENT.

By CH. LETOURNEAU, General Secretary to the Anthropo-
logical Society, Paris, and Professor in the School of Anthropo-
logy, Paris.
"M. Letourneau has read a great deal, and he seems to us to have

selected and interpreted his facts with considerable judgment and learning."

Westminster Review.



XIX. VOLCANOES, PAST AND PRESENT. By Prof.

EDWARD HULL, LL.D., F.R.S.

" A very readable account of the phenomena of volcanoes and earth-
quakes. " Nature.

XX. PUBLIC HEALTH. By Dr. J. F. J. SYKES. With

numerous Illustrations.

"Not by any means a mere compilation or a dry record of details and
statistics, but it takes up essential points in evolution, environment, prophy-
laxis, and sanitation bearing upon the preservation of public health."
Lancet.

XXL MODERN METEOROLOGY. AN ACCOUNT OF THE
GROWTH AND PRESENT CONDITION OF SOME BRANCHES
OF METEOROLOGICAL SCIENCE. By FRANK WALDO, PH.D.,
Member of the German and Austrian Meteorological Societies,
etc.; late Junior Professor, Signal Service, U.S.A. With 112
Illustrations.

"The present volume is the best on the subject for general use that we
have seen." Daily Telegraph (London).

XXII. THE GERM-PLASM : A THEORY OF HEREDITY.
By AUGUST WEISMANN, Professor in the University of
Freiburg-in-Breisgau. With 24 Illustrations.

"There has been no work published since Darwin's own books which
has so thoroughly handled the matter treated by him, or has done so much to
place in order and clearness the immense complexity of the factors of heredity,
or, lastly, has brought to light so many new facts and considerations bearing
on the subject." British Medical Journal,

XXIII. INDUSTRIES OF ANIMALS. By F. HOUSSAY.

With numerous Illustrations..

" His accuracy is undoubted, yet his facts out-marvel all romance. These
facts are here made use of as materials wherewith to form the mighty fabric of
evolution. " Manchester Guardian.

XXIV. MAN AND WOMAN. By HAVELOCK ELLIS. Illus-
trated. Second Edition.

" Mr. Havelock Ellis belongs, in some measure, to the continental school of
anthropologists; but while equally methodical in the collection of facts, he is
far more cautious in the invention of theories, and he has the further distinction
of being not only able to think, but able to write. His book is a sane and
impartial consideration, from a psychological and anthropological point of
view, of a subject which is certainly of primary interest." Athenaum.

XXV. THE EVOLUTION OF MODERN CAPITALISM.

By JOHN A. HOBSON, M.A.

" Every page affords evidence of wide and minute study, a weighing of
facts as conscientious as it is acute, a keen sense of the importance of certain
points as to which economists of all schools have hitherto been confused and
careless, and an impartiality generally so great as to give no indication of his
[Mr, Hobson's] personal sympathies." Pall Mall Gazette.



XXVI. APPARITIONS AND THOUGHT-TRANSFER-
ENCE. By FRANK PODMORE, M.A.

" A very sober and interesting little book. . . . That thought-transference
is a real thing, though not perhaps a very common thing, he certainly
shows. " Spectator.

XXVII. AN INTRODUCTION TO COMPARATIVE
PSYCHOLOGY. By Professor C. LLOYD MORGAN. With
Diagrams.

" A strong and complete exposition of Psychology, as it takes shape in a
mind previously informed with biological science. , . . Well written, ex-
tremely entertaining, and intrinsically valuable." Saturday Review.

XXVIII. THE ORIGINS OF INVENTION : A STUDY OF
INDUSTRY AMONG PRIMITIVE PEOPLES. By OTIS T. MASON,
Curator of the Department of Ethnology in the United States
National Museum.

"A valuable history of the development of the inventive faculty."
Nature.

XXIX. THE GROWTH OF THE BRAIN: A STUDY OF
THE NERVOUS SYSTEM IN RELATION TO EDUCATION. By
HENRY HERBERT DONALDSON, Professor of Neurology in
the University of Chicago.

"We can say with confidence that Professor Donaldson has executed his
work with much care, judgment, and discrimination." 7^he Lancet.

XXX. EVOLUTION IN ART: As ILLUSTRATED BY THE
LIFE-HISTORIES OF DESIGNS. By Professor ALFRED C.
H ADDON. With 130 Illustrations.

*' It is impossible to speak too highly of this most unassuming and
invaluable book. " Journal Anthropological Institute.

XXXI. THE PSYCHOLOGY OF THE EMOTIONS. By

TH. RIBOT, Professor at the College of France, Editor of the

Revue Philosophique.

XXXII. HALLUCINATIONS AND ILLUSIONS: A STUDY
OF THE FALLACIES OF PERCEPTION. By EDMUND
PARISH.

XXXIII. THE NEW PSYCHOLOGY. By E. W. SCRIP-
TURE, Ph.D. (Leipzig). With 124 Illustrations. Shortly.

XXXIV. SLEEP : ITS PHYSIOLOGY, PATHOLOGY, HYGIENE, AND
PSYCHOLOGY. By MARIE DE MANACEINE (St. Petersburg).
Illustrated. Shortly ,



THE CONTEMPORARY SCIENCE SERIES.



EDITED BY HAVELOCK ELLIS.



EVOLUTION AND DISEASE



XXVI. APPARITIONS AND THOUGHT-TRANSFER-
ENCE. By FRANK PODMORE, M.A.

" A very sober and interesting little book. . . . That thought-transference
is a real thing, though not perhaps a very common thing, he certainly
shows. " Spectator.

XXVII. AN INTRODUCTION TO COMPARATIVE
PSYCHOLOGY. By Professor C. LLOYD MORGAN. With
Diagrams.

" A strong and complete exposition of Psychology, as it takes shape in a
mind previously informed with biological science. , . . Well written, ex-
tremely entertaining, and intrinsically valuable." Saturday Review.

XXVIII. THE ORIGINS OF INVENTION : A STUDY OF
INDUSTRY AMONG PRIMITIVE PEOPLES. By OTIS T. MASON,
Curator of the Department of Ethnology in the United States
National Museum.

"A valuable history of the development of the inventive faculty."
Nature.

XXIX. THE GROWTH OF THE BRAIN: A STUDY OF
THE NERVOUS SYSTEM IN RELATION TO EDUCATION. By
HENRY HERBERT DONALDSON, Professor of Neurology in
the University of Chicago.

"We can say with confidence that Professor Donaldson has executed his
work with much care, judgment, and discrimination." The Lancet.

XXX. EVOLUTION IN ART: As ILLUSTRATED BY THE
LIFE-HISTORIES OF DESIGNS. By Professor ALFRED C.
HADDON. With 130 Illustrations.

" It is impossible to speak too highly of this most unassuming and
invaluable \>QQ\H." Journal Anthropological Institute.

XXXI. THE PSYCHOLOGY OF THE EMOTIONS. By
TH. RIBOT, Professor at the College of France, Editor of the

Revue Philosophique.

XXXII. HALLUCINATIONS AND ILLUSIONS: A STUDY
OF THE FALLACIES OF PERCEPTION. By EDMUND
PARISH.

XXXIII. THE NEW PSYCHOLOGY. By E. W. SCRIP-
TURE, Ph.D. (Leipzig). With 124 Illustrations. Shortly.

XXXIV. SLEEP : ITS PHYSIOLOGY, PATHOLOGY, HYGIENE, AND
PSYCHOLOGY. By MARIE DE MANACEINE (St. Petersburg).
Illustrated. Shortly.



THE CONTEMPORARY SCIENCE SERIES.



EDITED BY HAVELOCK ELLIS.



EVOLUTION AND DISEASE



EVOLUTION
AND DISEASE



J. BLAND-SUTTON




With 136 Illustrations



LONDON :

WALTER SCOTT,
24, WARWICK LANE, PATERNOSTER ROW.

1890.



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UNIVERSITY




CONTENTS.



PAGE

INTRODUCTION ... i



CHAPTER I.

THE ENLARGEMENT OF PARTS FROM INCREASED USE,

OVERGROWTH AND IRRITATION ... ... ... 14

CHAPTER II.
DISUSE AND ITS EFFECTS... ... ... ... 35

CHAPTER III.
VESTIGIAL PARTS ... ... ... ... ... 60

CHAPTER IV.
VESTIGIAL PARTS (continued] ... ... ... 79

CHAPTER V.
DICHOTOMY 102

CHAPTER VI.
ATAVISM OR REVERSION ... ... ... , M 134



viii CONTENTS.

CHAPTER VII.

ATAVISM (continued) SUPERNUMERARY DIGITS, LIMBS,

MAMMARY GLANDS ... ... ... ... 158

CHAPTER VIII.

PAGE

THE TRANSMISSION OF MALFORMATIONS AND ACQUIRED

DEFECTS ... ... ... ... 176



CHAPTER IX.

ANATOMICAL PECULIARITIES OF THE TEETH IN RELATION

TO INJURY AND DISEASE ... ... ... ... 199

CHAPTER X.
CAUSES OF DISEASE INFLAMMATION AND FEVER ... 213

CHAPTER XI.
TUMOURS AND CANCERS ... ... ... ... 228

CHAPTER XII.
THE ZOOLOGICAL DISTRIBUTION OF 'DISEASE ... 250

INDICES 279




LIST OF ILLUSTRATIONS.



GOLDEN HEN-PHEASANT IN COCK'S PLUMAGE ... Frontispiece

FIG. PAGE

1. A DACE WITH SPOTS OF BLACK PIGMENT DUE TO

THE IRRITATION OF A PARASITE ... ... 4

2. HEAD OF FEMALE MOOSE WITH ANTLERS ... 5

3. ANTLERS OF ROE-DEER WITH NODE ... ... 7

4. HEAD OF COW WITH AN ABNORMAL HORN .,. 8

5. HEAD OF RHINOCEROS... ... ... ... 9

6. THE LEG OF AN OYSTER-CATCHER WITH HORN IO

7. HEAD OF THE HORNED PUFFIN... ... ... II

8. SECOND TOE ENLARGED FROM EXCESSIVE USE... 1$

9. FINGER OF HORSE AND MAN ... ... ^ ... l8

10. OVERGROWN HOOF OF GOAT ... ... 2O

11. HEAD OF COCK WITH SPUR ... ... ... 22

12. SPINA BIFIDA OCCULTA ... ... ... 23

13. HEAD OF POLISH FOWL ... ... ... 24

14. HEAD OF DUCKLING WITH FOOT ... ... 25

15. STOMACH OF DARTER ... ... ... ... 27

1 6. A FISH EMBEDDED IN PEARL ... ... 30

17. THE OWL-PARROT ... ... ... .-.36

1 8. HEAD AND SUCKING DISC OF LEPIDOSTEUS ... 37

19. ASCIDIAN AND ASCIDIAN TADPOLES ... ... 39

20. THE HEAD OF VARANUS ... ... ... 42



x LIST OF ILL USTRA TIONS.

FIG. PAGE

21. BRAIN OF HATTERIA ... ... ... ...43

22. A SECTION OF THE PINEAL EYE OF HATTERIA... 44

23. OVIDUCT IN A MALE SKATE ... ... .-47

24. THE EMBRYONIC ALIMENTARY CANAL ... 49

25. DIAGRAM OF THE ALIMENTARY CANAL AND NERVOUS

SYSTEM ... ... ... ... ... 50

26. AN AFRICAN CHILD WITH A TUMOUR ... 53

27. A FAUN ... ... ... ... ... 54

28. AN jEGIPAN AND FAUN ... ... ... 55

29. OVERGROWN NAIL IN A SLOTH ... ... ... 57

30. HEAD OF A PARROT WITH OVERGROWN BEAK... 58

31. A HORNED SHEEP WITH CERVICAL AURICLES ... 63

32. THE CLOACA OF A HEN ... ... ... 64

33. VERMIFORM APPENDIX OF A GIBBON ... ... 66

34. FOLLICULAR CYST IN A PORCUPINE ... ... 72

35- AN ODONTOME IN A HORSE ... ... ... 73

36. AN ELASMOBRANCH FISH WITH ITS YOLK-SAC ... 76

37. DIAGRAM OF THE ALIMENTARY CANAL AND YOLK-SAC 77

38. AN EARLY HUMAN EMBRYO ... ... 8 1

39. DIAGRAM INDICATING SITUATIONS OF BRANCHIAL

SLITS... ... ... ... ... 82

40. GIRL WITH CERVICAL AURICLES... ... ... 83

41. A CHILD WITH CERVICAL AURICLES ... ... 83

42. A COMMON GOAT WITH CERVICAL AURICLES ... 84

43. AN EGYPTIAN GOAT WITH CERVICAL AURICLES... 85

44. MICROSCOPIC STRUCTURE OF A CERVICAL AURICLE 86

45. SECTION OF CERVICAL AURICLE FROM A GOAT... 87

46. HEAD OF A SEAL ... ... ... ... 89

47. HEAD OF AN .EGIPAN WITH CERVICAL AURICLE 90

48. FAUN AND GOAT FROM THE CAPITOL ... ... 9!

49. CONCRETION FROM THE GUTTURAL POUCHES OF A

HORSE ... ... ... ... ... 95



LIST OF ILL USTRA TIONS. xi

FIG. PAGE

50. MALLEOLI OF MAN AND CHIMPANZEE ... 99

51. SUPERNUMERARY RAYS IN STAR-FISH ... ... 103

52. FEATHERS AND AFTERSHAFTS ... ... 105

53. GEMINATED TEETH ... ... ... ... 106

54. REDUPLICATED ANTLER OF MOOSE ... ... 107

55. SUPERNUMERARY DIGITS IN A CHILD ... ... Io8

56. SUPERNUMERARY DIGITS IN A GIBBON ... 109

57. A DOUBLE HAND ... ... ... ... IIO

58. MUD-FISH WITH DICHOTOMIZED LIMB ... Ill

59. SUPERNUMERARY HIND-LEG IN A TOAD ... ... Ill

60. SUPERNUMERARY FORE-LEG IN A FROG ... 112

6 1. SUPERNUMERARY LEG IN A CHICK ... ... 113

62. SUPERNUMERARY WING IN A DOVE ... ... 114

63. SUPERNUMERARY FORE-LEG IN A SHEEP ... ... 115

64. SECTIONS OF EMBRYO WORMS ... ... 117

65. A TWO-HEADED COLT ... ... ... ...119

66. A DOUBLE SHARK... ... ... ... 121

67. A DOUBLE-HEADED SNAKE ... ... ... 122

68. A MONSTROUS CALF ... ... ... 123

69. A TWO-TAILEDED LIZARD ... ... ... 124

70. A SIX-LEGGED FROG ... ... ... 126

71. A SIX-LEGGED LAMB ... ... ... ... 127

72. A FOUR-LEGGED CHICK ... .., ... 128
73- A FIVE-LEGGED FROG ... ... ... ... 129

74. A FOUR-LEGGED DRAKE ... ... ... 130

75. A MITRAL VALVE CONTAINING MUSCLE ... ... 136

76. A HAIRY MAN ... ... ... ... 138

77. A ROCK LOBSTER (CEPHALON) ... ... ... 140

78. PILIFEROUS CORNEA OF OX ... ... 142

79. PATAGIUM IN THE LEG OF A GIRL ... ... 143

80. WEBBED FINGERS IN A MONKEY ... ... 145

Si. HOUR-GLASS CONTRACTION OF THE STOMACH ... 147



xii LIST OF ILL USTRA TIONS.

FIG. PAGE

82. FEMALE ROE-DEER WITH ANTLERS ... ... 155

83. HEAD OF A FEMALE MOOSE WITH ANTLERS ... 156

84. MANUS OF HIPPARION ... ... ... l6o

85. DICHOTOMY OF A HORSE'S DIGIT ... ... l6l

86. DWARF LEMUR ... ... ... ... 164

87. BRACHIAL MAMMA OF HAPALEMUR ... ... 165

88. LEMUR MACACO AND YOUNG ... ... l66

89. SUPERNUMERARY NIPPLES IN MAN ... ... l68

90. SUPERNUMERARY NIPPLES IN A MONKEY ... 169

91. INGUINAL RECESSES IN A LAMB ... -..173

92. MARSUPIUM AND NIPPLES OF A PHALANGER ... 174
93- THE HUMAN PINNA ... ... ... ... 177

94. A MALFORMED AURICLE ... ... ... I7&

95. SO-CALLED SUPERNUMERARY AURICLES ... ... l8(>

96. DEVELOPMENT OF THE AURICLE ... ... l8l

97. DEFECTIVE PINN^ ... .... ... ... 183

98. SO-CALLED TAILLESS TROUT OF ISLAY ... 1 86

99. TAIL OF A NORMAL TROUT FOR COMPARISON ... 1 86

100. THE NOSE OF A HARE ... ... ... 189

101. THE NOSE OF A DOG... ..= ... ... 189

102. CLEFT LIP AND NOSE OF A DOG ... ... iga

103. PART OF THE SKULL OF A DOG WITH A CLEFT

PALATE... ... ... ... ... 191

104. HEAD OF A HUMAN EMBRYO OF THE FIFTH WEEK 192

105. AN EXOSTOSED RAY FROM CH^TODON ... ... 195

1 06. HORNED MAN (SO-CALLED) ... ... 197

107. INCISORS OF THE KANGAROO ... ... ... 2OO

1 08. INCISORS OF KANGAROO SHOWING EFFECTS OF

INJURY ... ... ... ... 200

109. OVERGROWN TUSKS OF BOAR ... ... ... 203

1 10. ERRATIC INCISORS OF BABIRUSSA ... ... 204

111. BULLET IN AN ELEPHANT'S TUSK ... ... 207



LIST OF ILL USTRA TIONS. xiii

FIG. PAGE

112. THE ROSTRUM OF MESOPLODON ... ... 2IO

113. SECTION OF A PYTHON'S TOOTH .. ... 211

114. LEUCOCYTES ATTACKING BACILLI ... ... 2l8

115. LEUCOCYTES INGESTING BACILLI ... ... 219

1 1 6. CYSTIC KIDNEY OF A TERRIER ... ... 229

Iiy. THE CLOACA OF A HEN WITH CYST ... .-.231

1 1 8. TRACHEAL POUCH OF THE EMU ... ... 232

119. AN ACTINOMYCES TUFT ... ... ... 235

120. SARCOMA IN THE NECK OF A FOWL ... 237

121. MICROSCOPICAL CHARACTERS OF A SARCOMA ... 239

122. MICROSCOPICAL CHARACTERS OF AN EPITHELIAL

TUMOUR ... ... ... ... 243

123. CANCER IN A PHALANGER ... ... ... 247

124. ARTICULAR CARTILAGE OF A PIG WITH GUANIN

GOUT ... ... ... ... 257

125. GOUTY FOOT OF A PARROT ... ... ... 258

126. AN ENDEMIC CRETIN ... ... ... 260

127. A SPORADIC CRETIN ... ... ... ... 261

128. A CALF-CRETIN ... ... ... ... 262

129. PTAH ... ... ... ... ... 264

130. MOUSE WITH CUTANEOUS HORN ... ... 267

131. SECTION OF HORN ... ... ... ... 267

132. HEAD OF A MOUSE WITH WART HORN ... 268

133. HEAD OF A SHEEP WITH WART HORN ... ... 269

134. HEAD AND LEG OF A THRUSH WITH WART HORN 270

135. HEAD OF A LEPER ... ... ... ... 272




PREFACE.



MY object in writing this book is simply to indicate
that there is a natural history of disease, as well as of
plants and animals. I have not attempted to deal with
the subject at great length, far less exhaustively, but
merely to illustrate general principles by a few carefully
selected examples.

The subject is a novel one, and doubtless a more
extended study will serve to show that many of my
conclusions are fallacious. I trust that such errors may
be speedily rectified by any person who has opportu-
nities of testing my opinions practically. It must be
borne in mind that it is a much easier task to write
concerning the habits of animals than to describe their
diseases ; nevertheless, the facts at our disposal clearly
indicate that disease is controlled by the same laws
which regulate biological processes in general.

J. B. S.




EVOLUTION AND DISEASE.



INTRODUCTION.

MOST persons believe Pathology, as the Science of
Disease is called, to be so outside the comprehension
of ordinary individuals, and even in its general bearings
so utterly devoid of interest to all but medical men, that
much misconception prevails in the minds of even
educated persons in regard to its fundamental principles.
As a matter of fact Pathology is only a department of
Biology, and it is very important to bear this in mind if
we wish to study successfully the origin, cause, and
spread of disease. Yet paradoxical as it seems, whilst so
many regard Pathology as occupying an isolated position
among sciences, medical writers always point out the
difficulty they find in framing a definition of disease, and
indeed the impossibility of stating where health ends and
disease begins.

It is not my object in the present work to attempt the
framing of a definition of disease, or even to offer a
suggestion as to the borderland between it and health,
This difficulty is frequently illustrated in a striking
manner in a law court ; it is not uncommon for a judge

2



2 E VOL UTION AND DISEASE.

in the course of a criminal trial to ask a medical witness,
when the plea of insanity is urged on a prisoner's behalf,
either to define insanity, or to state his opinion where
sanity ends and insanity begins. The judge knows full
well the difficulty, indeed the impossibility of even a
skilled witness making a satisfactory reply to such a
question.

As with mental so with bodily conditions, it is im-
possible to state definitely the borderland between health
and disease, either in relation with functional aberration
or textural alteration. And in many instances we shall
find conditions which we regard as abnormal in man,
presenting themselves as normal states in other animals.

If it be difficult to define disease when our remarks
are restricted to the human family, it becomes obviously
more difficult when we attempt to investigate disease on
a broad zoological basis. As the great barrier which
exists between man and those members of his class most
closely allied to him consists, not in structural characters,
but in mental power, it necessarily follows that there
should be a similarity in the structural alterations in-
duced by diseased conditions in all kinds of animals,
allowing, of course, for the differences in environment.
This we now know to be the case, and it is clear that as
there has been a gradual evolution of complex from
simple organisms, it necessarily follows that the principles
of evolution ought to apply to diseased conditions if
they hold good for the normal, or healthy, states of
organisms : in plain words there has been an evolution
of disease pari passu with evolution of animal forms.
For a long time it has been customary to talk of physio-



INTRO D UCTION. 3

logical types of diseased tissues, and my earlier efforts
were directed in searching among animals for the
purpose of detecting in them the occurrence of tissues,
which in man are only found under abnormal conditions.
The sdarch was of great value to me, for the statement
proved to be true in only a limited sense ; at the same
time the truth of an opinion held by nearly all thoughtful
physicians, that disease may in many instances be re-
garded as exaggerated function, was forcibly illustrated,
and I quickly saw that the manifestations of disease
were regulated by the same laws which govern physio-
logical processes in general, and that many conditions
regarded as pathological in one animal are natural in
another. It will be useful to illustrate this by some
concrete examples. To take a simple case. The inside
of our cheeks has a soft lining known as mucous mem-
brane. In very rare instances children have been born
with tufts of hair growing in this situation. Such a
condition is truly abnormal. A physiological type for
such a phenomenon is found in the mouths of rodent
mammals ; the inside of the cheeks of rabbits, hares,
porcupines, and the like, present naturally patches of
hairy skin. Pigment is widely diffused in animal bodies,
both under natural and unnatural conditions, using the
term unnatural as equivalent to disease ; this explana-
tion is necessary, for disease being controlled by
natural conditions cannot logically be regarded as un-
natural.

In the dace (fig. i) we notice sundry collections of
black pigment dotted among the scales. When ex-


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