THE LIBRARY

OF

THE UNIVERSITY

OF CALIFORNIA

PRESENTED BY

PROF. CHARLES A. KOFOID AND

MRS. PRUDENCE W. KOFOID

THE

CAUSATION OF DISEASE

BALLANTYNE, HANSON AND CO.
EDINBURGH AND LONDON

THE

CAUSATION OF DISEASE

AN EXPOSITION OF THE ULTIMATE
FACTORS WHICH INDUCE IT.

BY

HARRY \CAMPBELL

M.D., B.S. (LOND.)

MEMBER OF THE ROYAL COLLEGE OF PHYSICIANS ; ASSISTANT-PHYSICIAN AND
PATHOLOGIST TO THE NORTH-WEST LONDON HOSPITAL

LONDON
H. K. LEWIS, 136 GOWER STREET

1889

, *■

K) 11 / .A^

KB 1 57
C3

PUBLIC
HEALTH
LIBRARY

PREFACE.

The object of this work is to trace out the ultimate causes
of disease — not of particular diseases — but of disease in
general.

In writing a work of this kind two courses are open to the
author. One is to saturate himself with all the available litera-
ture on the subject, and, having done so, to connect into an
intelligible whole the facts and opinions thus gleaned, adding,
amending, and omitting as may seem fit. The other is for
him to think the subject out independently from beginning to
end, and to draw upon the resources of literature only just so
far as apposite matter may chance to present itself in the
ordinary course of his reading, or as his line of thought may
from time to time suggest some special reference.

I have adopted the latter course, not, indeed, from any
preconceived plan, but rather from the force of circumstances,
which led me in the first instance to think out the subjects
here treated of for my own personal benefit.

And, on the whole, I am inclined to think that the second
of these two methods is the better ; for, although the author is
put to the pains of thinking out for himself questions which
have already been decided, and, moreover, runs the risk of
being charged with plagiarism, his work is far more likely to

M375SS0

VI PREFACE.

bear the stamp of originality, and lie escapes the very con-
siderable danger of being a mere compiler.

While correcting the proof-sheets, I had the advantage or
reading Mr. Mitchell's work on "Evolution and Dissolution,"
and this suggested some of the remarks on this subject
contained in Chap. XII. , Part I. My indebtedness to this
author was, through oversight, not acknowledged in the text ;
but with this exception I have, I believe, in all cases acknow-
ledged the authorities I have made use of.

H. C.

CONTENTS.

PART I.

CHAP. PAGE

I. General Eemarks on Causation i

II. The Causation of Gross Material Effects — The Causation of Atomic

and Molecular Effects 6

III. The Causation of the Vital Changes of Protoplasm— Definition of

Structure as applied to Living Matter — Proper Method of
Studying the Causation of Disease 1 1

IV. The Environment — The Environment of Unicellular Organisms —

The Internal-Cell-Environment of Multicellular Organisms —
The Primary Mai-Environment — The Secondary Mai-Environ-
ment— Remarks on the Nomenclature of Disease . . .17

V. The External-Body-Environment — An Analysis of it — Its Divisions
into Organic, Inorganic, Mental, and Physical — The Distinc-
tion between a Diverse and Complex External-Environment —
Summary of this and the preceding Chapters .... 29

VI. The Causation of Structure — The Two Great Causes of Structure :

Heredity and Environment 36

VII. The Causation of Structure {continued) — Heredity — Sexual and
Asexual Reproduction — Reproduction by Simple Division —
Parthenogenesis — Graft Hybridism — Partial Reproduction —
General Principles .40

VIII. The Causation of Structure {continued) — Heredity — The Grand

Rhythm of Life — Minor Vital Rhythms 49

IX. Causation of Structure (continued) — Heredity at Corresponding
Ages — Heredity at Corresponding Seasons — Sexual Heredity
— Some Comparisons between Man and Woman 57

viii CONTENTS.

CHAP

PAGE

X. Heredity (continued)— The Principle of Structural Mean— Pre-
potency— Physiological and Pathological Blendings . . 74

XI. Heredity (continued) — The Fixity of Structural Characters in
Inverse Proportion to their Age, Ancestral or Individual —
All Diseases' of Recent Ancestral Date — The Vis Medicatrix
Naturce — The Tendency of Recently Acquired Characters to
Disappear under Ancestral Forms of Environment ... 84

XII. Heredity (continued) — Reversion—Its Two Chief Causes — Pecu-
liarity in the Evolutionary Process and Partial Dissolution of
a Mature Tissue . . . 104

XIII. Heredity (continued)— A Consideration of the Different Modes by
which Organic Potentialities may become Actualities — Some
further Bearings of the Principle of Reversion upon Pathology
— Summary 115

XIV. Heredity (continued) — Influence of the Male Element upon the
Female Organism — Inheritance of Acquired Structural Cha-
racters 123

XV. The Causation of Structure {continued) — The Influence of Ante-

partem Environment upon Structure 127

XVI. The Influence of Environment upon Structure — The Influence of •

the Ante-partem Environment (continued) — Differences in E
the Prime Cause of Natural Variations 138

XVII. The Influence of Environment upon Structure (continued) —
The Influence of the Post-partem Environment, considered
from the Pathological Point of View 147

XVIII. The Morbid Inter-action of Structure and Environment— All
Disease Processes probably attended by Structural Change,
and therefore Natural Variations — Structural Deficiency . 156

XIX. The Symbolical Method of Expressing the Relative Share taken

by Structure and Environment in Causation .... 163

XX. Some Further Applications of the Symbolical Method . . .168

XXI. Recapitulation j^.

CONTENTS. IX

PAET II.

CHAP. PAGE

I. The Evolution of Species — Natural Selection — Sexual Selection

— The Action of the Environment independently of Selection 185

II. Natural Selection — " Instinct and Eeason '" — Instinct a Perfect

— Reason an Imperfect Guide 191

III. Natural Selection (continued)— The Influence of " Reason" upon

Natural Selection 201

IV. Natural Selection (continued) — The Purely Accidental Causes of

Death — Mai-Environments — The Necessarily-Fatal Environ-
ment— The Not-Necessarily-Fatal Environment — The Neces-
sary Mai-Environment 205

V. Natural Selection (continued) — Deficiency of Food only an In-
direct Cause of Death in Civilized Communities . . . 210

VI. Natural Selection (continued) — The Frequency of Natural Varia-
tions in Man — The Influence of Natural Selection on the
Mental Side of Man 214

VII. Natural Selection (continued) — Its Influence on the Corporeal Side
of Man — Disease, a Necessary Evil — Active Operation of
Natural Selection in consequence of Instability of the Envi-
ronment—Perfect Adaptation Impossible — Illustrations . . 222

VIII. Natural Selection (continued) — Adaptation to Micro-organisms —
The Instability of these latter interferes with the Process
of Adaptation 232

IX. Natural Selection (continued) — The Necessarily-Fatal Environ-
ment 240

X. Natural Selection (continued) — The Environment afforded by the

Country 249*

XI. Natural Selection (continued)— The Comparative Activity of the

Process in Civilized and Primitive Man and in the Lower
Animals — The Relation between the Activity of the Process
and the Health of the Community 253

XII. Natural Selection (continued) — Curtailment of the Number of

Births in a Community hinders Evolution and favours Dis-
solution 261

c CONTENTS.

CHAP. PAGE

XIII. Activity of Natural Selection at the Different Periods of Life
Compared— Its Influence on the Hereditary Transmission of
Disease at these Periods — Natural Selection Inoperative after
the Procreative Period— Non-Transmission of Evolutionary
Gains after this Period— Average Limit of the Procreative
Period of Life in the Two Sexes 264

XIV. Sexual Selection 273

XV. Action of E upon Structure independently of Selection . -277

XVI. Criticism of Dr. Mott's Views — Concluding Eemarks on Evolution 280

PART III.

I. The Distinction between a " Natural " and an " Artificial En-
vironment" 284

II. What constitutes Normality in Structure and Environment —
Definition of Health— Test of Healthy Inter-action — The
Actually and Potentially Normal — The Inevitably Abnormal
— Justification of the Term Kesistance as Applied to Disease . 290

III. To what extent Structural Abnormality occurs during the Actual

Time of Disease 303

IV. The Advantage of Changed Conditions of Life upon the Vital

Organism 3x5

V. Heredity 3^

VI. Disease not an Entity — All Disease comes through E — The

Variability of Disease— A Perfect Classification Impossible . 331

VII. The Parasitic Origin of Malignant Growths 342

THE

CAUSATION OF DISEASE,

P A E T I.

CHAPTER I.

GENERAL REMARKS ON CAUSATION.

Since the chief object of this essay is to inquire into the
ultimate causes of disease, it is necessary at the outset to
attach a definite meaning to the word Cause.

There is ,no subject in the whole range of philosophy which
has excited greater interest than that of Causation ; but this
is not the place to enter fully into it. I propose, therefore, to
say only just so much upon it as is needful for a philosophic
treatment of the subject in hand, and my remarks on this head
will furnish the keynote to the method adopted throughout this
work.

Suppose the question were asked : What is the cause of
gravitation ? The reply would be : Gravitation is an ulti-
mate and undecomposable property of matter — that is to say,
one which cannot be simplified or referred to any wider
principle behind or beyond it. It has, therefore, no cause,
for cause implies an antecedent, and gravitation has, as far
as we know, no antecedent.

Again, let the questions be asked : What is the cause of 0
uniting, or, in simpler language, why does 0 unite, with H
in the proportion to form water ? Why does H unite with
CI to form hydrochloric acid? Why, in short, does each

2 THE CAUSATION OF DISEASE.

element behave in a way peculiar to itself in respect of its
power to combine with other elements ? The answer again
is : These properties of elements are ultimate and unanalysable
properties, just as gravitation is ultimate and unanalysable.
Such ultimate properties — or, as we may term them, primitive
causes — have, as far as we know, no beginning, and therefore
we cannot say that they themselves are caused, for cause
implies an antecedent, and therefore a beginning, and that
which has no beginning can have no cause.

Starting, however, with these ultimate or primitive causes,
we observe that an infinite variety of effects may be produced
by a modification of the material conditions; indeed, every
effect with which we are acquainted may be thus produced,'
whether mental or physical. What do I mean by material
conditions ? Under this term I include : kind of matter
(0, CI, H), quantity of matter, motion of matter (atomic,
molecular, or massive) ; finally, disposition of matter, or, as
I should be inclined to denominate it, " structure"

Now, given certain material conditions, the same result
will always follow. This is the Law of Causation. Man has
discovered — that is to say — from long observation of Nature,
that her operations are fixed and unchangeable. We do not
find a certain effect follow upon certain material conditions
to-day, and another effect follow upon the same conditions
to-morrow. We observe, on the contrary, certain regular
sequences, and these, when put into words, are called laws.
Thus, none of Nature's laws are fickle and irregular, but fixed
and unchangeable.

I shall then define the cause of any particular effect as the
sum of those material conditions from which that effect has
necessarily followed*

How far it is psychologically permissible to refer all
phenomena to "material conditions," as above defined, matters

* I desire to make two remarks on this definition. First, I do not mean
by li any particular result" any like result, but one particular result which
has happened. The same result may follow from different causes— e.g., heat
—therefore in the definition I prefer to speak of one special instance.
Secondly, I wish it to be understood that I use the term nun in the strict
algebraical sense, it includes certain conditions and excludes all conditions
which do not take part in, or would interfere with, the result.

THE CAUSATION OF DISEASE. 3

little to us, so long- as the conclusions deducible from this
assumption shall aid us in the practical concerns of life. The
physician can have nothing to say to any portion of philosophy
which cannot be reconciled with utilitarianism ; but, although
I would gladly escape the psychological aspect of the question,
it is advisable to state — very briefly — wherein the a,bove defini-
tion of cause is psychologically deficient.

First, the definition assumes a material world, but it is
utterly impossible to prove the existence of such material
world, since we have no knowledge of anything but our own
mental states. Of anything outside of or apart from mind, we
can know nothing. Inasmuch, however, as the assumption of
a material world and of material conditions, as above defined,
by no means interferes with the conclusions based thereon, so
far as they affect the practical conduct of daily life, we are at
perfect liberty to assume the existence of a material world. I,
therefore, unhesitatingly speak of material conditions, although
it would be psychologically more correct to speak of phenomena
— of that which seems to be (= the phenomenal) as dis-
tinguished from that which is (= the noumenal).

A second point which, from the psychological point of view,
deserves notice, is that no mention is made of " Force " among
the material conditions. Our conception of force is the mental
ingredient out of which our conceptions of matter, space,
time, and motion are built.* It will only be necessary to refer
to the first two of these. Matter is ultimately known to us
through its manifestations of force, through the resistance,
namely, which it opposes to our muscular energies. This
resistance is twofold ; for, first, matter resists our efforts to
push it out of position, and is capable of pushing us out of
position — whence arises the idea of repulsion ; and, secondly,
it resists our efforts to rend its several parts asunder
(= cohesion), and hence arises the idea of attractive force.
We conceive of force, therefore, as something which attracts
and repels. A little thought will show that matter can only
be known to us through its manifestation of force (= resist-
ance), for '-abstract this, and nothing but empty extension
remains." But, on the other hand, we cannot think of force

* Vide Herbert Spencer's " First Principles," § 50.

B 2

4 THE CAUSATION OF DISEASE.

(= resistance) apart from matter ; and, being thus unable to
mentally separate the two, we are justified in including, under
kind of matter and quantity of matter (= mass), both the
matter and the force which is inseparable from it. As regards
the different " kinds " of matter, this force is peculiar for each
kind, since each separate kind has specific powers of attraction
and repulsion.

It follows that there is no need to make specific allusion
to " Force " among the material conditions above defined. It
will further be observed that no mention is made of " Space,"
but this idea is embodied under "Disposition of Matter,"
which signifies the relative positions which the particles of
matter occupy in space.

Out of the material conditions above enumerated all the
effects within our experience can be obtained, be they physical
or mental. I mean by this, that all phenomena (the word is
convenient) could be referred to these material conditions, did
we possess the power of analysing the conditions out of which
they arise ; that, in investigating the origin of any phenomenon,
our search should be directed towards this end ; and that,
when we have discovered the material conditions out of which
that phenomenon has arisen, we possess the most perfect
knowledge of its causation which it is possible for us to obtain.

I say the causation of mental phenomena, alike with that
of physical phenomena, can be expressed in terms of " material
conditions." Whatever psychological incongruity there may
appear in this, we shall find nevertheless — once more to
appeal to utilitarianism — that the conclusions obtainable from
this assumption are such as help us practically. What is
the connection between mind and matter matters little to us,
for it is now generally recognized that in every mental
sequence there is a corresponding physical sequence, and that
there is a close correlation between mental capacities and
tendencies on the one hand, and cerebral structure on the
other ; so that, in dealing with causes of mental phenomena
we shall still have to do with material conditions.

According to the Law of Causation the same conditions
are always followed by the same result, and, while speaking
of the causation of mental phenomena, it is well to remark

THE CAUSATION OF DISEASE. 5

that there is only one exception to this law which has
been advanced with any cogency — viz., the Power of the
Will. It is argued by the supporters of the Freedom of the
WW, that this faculty may act differently under exactly the
same circumstances — that is to say, the motives to action
remaining the same (both in respect of quality and quantity),
the Will, unfettered by any rigid principle of cause and
effect, is free, by a power peculiarly its own, to determine
action in any given direction. It is probable, however, that the
will forms no exception to the Law of Causation.

Since, then, every effect can be referred to material con-
ditions, it follows that in studying the causes of disease our
search must be directed into the material conditions out of
which disease arises.

CHAPTER II.

The Causation of Gross Material Effects— The Causation of Atomic and
Molecular Effects.

Let ns now briefly apply the conclusions arrived at in the last
chapter — first, to gross material effects; and secondly, to the
more minute atomic and molecular effects. Under this latter
head are included the chemical changes of protoplasm, the
sum of which constitutes life. Having thus acquired a scientific
insight into the causation of atomic and molecular pheno-
mena, and consequently of the vital changes of protoplasm,
we shall (I believe) be in a position to define the cause of
disease in intelligible terms, disease being an abnormal mode
of life.

First, as regards gross material effects : let us, in theory,
construct a planetary system containing a given number of
worlds, each having a definite mass and velocity, and all bear-
ing definite relations to one another. In such a case, we are
ourselves the choosers of the material conditions, and we can,
from two well-known laws, calculate the resulting complex
series of movements with the utmost accuracy, the two being :
the law of universal gravitation and the first law of motion.
These laws are simply verbal expressions of sequences which
are the outcome of the ultimate properties of matter already
spoken of. What then is the cause, in this hypothetical case,
of the complex series of movements ? It is the sum of the
material conditions. Let any one of them be altered — e.g.,
the mass of any one world— and the entire series of move-
ments will be changed. It is very important to note that
all the material conditions which take part in the produc-
tion of a given effect constitute the cause, and not any one
of them.

To make this point clear, let us conceive a nicely constructed

THE CAUSATION OF DISEASE. 7

balance placed in vacuo ; let all friction be removed, and then
let us suspend from each arm a ton weight. There will be
perfect equilibrium. If now, a grain weight be added to one
of these ton weights, the latter, we can assert positively, will
descend with a certain degree of momentum. Now, it would
be vulgarly said that the particular grain is the cause of the
descent, for, the two ton weights exactly balancing one another,
the grain will fall to the earth as it would do if left unsup-
ported in vacuo ; but, as a matter of fact, every other grain in
the descending ton weight takes an equal share in pulling it to
the earth j and, if the slightest particle be removed from the
other ton, the result, as expressed in terms of momentum, will
be modified, and the same will happen if the slightest friction
be added. We cannot, therefore, refer the cause of descent
to any one particular grain of matter ; the sum of the material
conditions of our conception constitutes the cause.

Secondly, as regards atomic and molecular effects. In the
above examples we are dealing with gross material conditions,
with obvious and palpable matter — matter, that is, which is
capable of being recognized as such by the senses. But beneath
the world of our every-day life there is a world of the infinitesi-
mal. Our senses take cognizance of quantities ranging within
very narrow limits, and although the intellect can reason with
vast and infinitesimal quantities, our knowledge of quantity above
and below a certain narrow range is merely symbolical — that
is to say, we can only represent it by symbols — it is beyond our
realization. Let us remember that this difficulty of conception
in respect of quantity is not confined to the immense. We
are apt to forget this, unmindful of the fact that a second is
split up into billions of parts by a vibration of the violet
ray of the spectrum, and that the atomic particles of a proto-
plasmic cell may be as small in comparison with the cell as is
this latter in comparison with our earth. Knowledge (I use the
term advisedly, assuming that we can measure such quantities
accurately) of this kind is only symbolical; but because our
senses are thus limited in range, we must not turn in disdain
from the subject, but rather try diligently — let the success be
never so slight — to form some faint conception of these infi-
nitesimal quantities.

8 THE CAUSATION OF DISEASE.

Now, according to the theory of Dalton, matter is not
continuous, but consists of particles called atoms. This theory
has been steadily gaining in .strength since Dalton's time,
and is now placed upon a firm basis. There are about seventy
different kiuds of atoms. These are united, by what is called
chemical force, into molecules, and these latter are, in the case
of solids and liquids, held together by the physical force of
cohesion. I mentioned kind of matter as one of the material
conditions which are at the root of all phenomena. The term
refers to the different varieties of atoms. Each kind of atom,
we must suppose, possesses certain fundamental, undecompos-
able properties, and these properties relate to the power which
each atom possesses of attracting to itself other atoms, so as to
form different kinds of molecules. It may be that all these
atoms are decomposable,* all possibly consisting of different
groupings of still smaller particles of only one kind of matter ;
and it may also be that the chemical and cohesive forces are
but varieties of one force — the universal force of gravitation.
Such possibilities must have occurred, I imagine, to most men
who have thought carefully over this subject, but whether it
be so or not — whether the atoms and these two forces be analys-
able or not — none of them have yet been analysed, none
therefore have, logically, any cause. We must accept each as
a fundamental, undecomposable fact. This remark also applies,
of course, to gravity, which itself may possibly not be an
ultimate property ; but the possibility of any presumed ulti-
mate property being decomposable does not prohibit the
assumption of its undecomposability until the reverse is proved.
It does not, that is, negative on the ground of illogical treat-
ment, the general results arrived at.

We are now in a position to apply the definition of cause to

* Loekyer has put forward the hypothesis that all the elements are really
compound— i.e., different kinds of aggregation of one kind of matter. Accord-
ing to this hypothesis, the matter of which the universe is composed, was at
one time equally distributed through space, and uniform in kind, although
made up of atoms. These then aggregated into two's, three's, or more, and
then again into " elements." This hypothesis rests upon evidence gained by
observing different elements under excessively high temperatures (as of the
sun) by means of the spectroscope ; the spectroscopic characters suggesting
decomposition of the elements into simpler bodies. — Phil. Trans., 1874, V- 49
ct eeq.

THE CAUSATION OF DISEASE. 9

chemical action. All chemical action is governed by " material
conditions/' and the material conditions of which chemical
action is the outcome are — (i) The presence of certain kinds
of atoms. (2) The arrangements of these atoms — i.e., their
relation one to another. (3) The kind of motion by which
these atoms, and -the molecules formed of them, are agitated —
namely, heat, light, electricity and such like modes of .motion.
In seeking for the " cause " of any particular chemical change,
we can do no more than discover the material conditions as just
set forth. These, as Bain would say, " are the final terms of
the explanation." Viewing the matter thus, we see how little
is the difference between astronomy and chemistry. We must
not, in our blindness, despise the tiny atom, for, in the eye of the
natural philosopher, it is as important as any great world rolling
through space, and, indeed, the analogies between the two are
very great : both world and atom are indestructible and eternal ;
each is governed by fixed and unchangeable law ; and, if an
atom is small by the side of the world, so is a world small
by the side of the universe. A group of worlds, arranged
in a planetary system, is akin to a group of atoms forming a
molecular system ; the atom, like the world, is the seat of
movements both about its own axis and about a point outside
itself; finally, both the planetary and the molecular systems
have a definite structure, which may be defined as the mutual
positions which the constituent parts, whether worlds or atoms,
bear to one another.

That the structure, or mutual position of the several atoms
in the molecule determines very largely the nature of that
molecule, is well shown in the case of the so-called isomeric
bodies — that is to say, unlike bodies whose molecules contain
the same number of the same kind of atoms. The primary,
secondary, and tertiary alcohols afford a familiar example.
These are isomeric, but each differs from the other in its
chemical properties, and chemists have actually attempted to
determine the molecular structure in each case. Thus :

10 THE CAUSATION OF DISEASE.

H
H-C-H

I I

H — C-H H — C — H

H — C — H H — C — OH ** V

H-C-H H-C-H H-C-C-C-H

H-C-H H-C-H H C H

I I

H H

OH

Primary Secondary Tertiary alcohol,

alcohol. alcohol.

Not only have the constituent elements of a planetary and of a
molecular system a definite relation to one another, but each of
these smaller systems forms part of a larger system, for each
planetary system stands in definite relations to other celestial
groups, and each molecular system is definitely related to the
surrounding molecules.

CHAPTER III.

The Causation of the Vital Changes of Protoplasm — Definition of Structure
as applied to Living Matter — Proper Method of Studying the Causation
of Disease.

In the latter portion of the last chapter we dealt with the
causation of atomic and molecular phenomena in general. Let
us now treat of the causation of those atomic and molecular
changes occurring within living protoplasm.

A protoplasmic cell consists of myriads of molecules, and in
contemplating the structure of such a cell we must include
both the mutual relations of the atomic constituents of the
molecules, and the relations which these latter bear amoug them-
selves. Protoplasm is often spoken of as homogeneous. If
the molecules were regularly arranged throughout the entire
cell protoplasm, the latter would be in a sense homogeneous,
though still possessing a structure, but we have no right to
assume auy such regular arrangement of molecules in proto-
plasm; indeed, we are a priori compelled to conclude otherwise.
The fact that the cells of different tissues have different func-
tions proves that their structure is different. This follows from
the law of causation, but it is not possible for the most
accomplished histologist to refer to its proper order every
individual cell that is at haphazard given him for examination,
though he may recognize them when grouped together into
tissues.

When it is said that protoplasm is homogeneous, it is
meant that it is a homogeneous jelly-like matter, which,
however, may be moulded into various forms — that is to say,
though the general configuration of the cell may differ, it is
assumed that the substance of which it is built up is homo-
geneous. For instance, nerve ganglion cells, blood corpuscles,
and kidney epithelial cells — notably some of them — -are quite

12

THE CAUSATION OF DISEASE.

unlike in gross configuration, though they are made up, it is
supposed, of a homogeneous substance. This is a false suppo-
sition, and is disproved by three facts: — (i) Dr. Klein has

Fie. i.

Ganglion Cell from anterior Horn or Cornu of Grey Matter in the Spinal
Cord of a Calf, b, Processes abruptly broken off. a, The axis cylinder pro-
cess. Magnified about 800 diameters. (Max Schultze.)

long proved that protoplasm contains a complex network.
(2) Many cells, especially nerve-cells, show a very distinct

THE CAUSATION OF DISEASE. I 3

structure {see fig. 1). (3) Finally, as I have already said,
differences in function are a distinct proof of differences in
structure. Think, for an instant, of an impregnated ovum
and of the vast potentialities locked up within it. There is
little difference between the apparent structure of a human
ovum and that of many belonging to the lower animals ; but
the fact that each develops into an entirely different being,
shows what a vast difference there must be in the minute
structure of each. One might be pardoned for lingering long
on a subject like this. Who, possessed of any imagination, can
think of the microscopic ovum-cell without feeling wonder?
It appears to consist of nothing but a very slightly differen-
tiated protoplasm ; but this is simply because our senses are
limited in scope, and are unable to take account of what we
may, somewhat paradoxically, term the vast world of the in-
finitesimal. The potentialities of the ovum are the outcome of
certain material conditions. In this tiny cell are aggregated
billions of atoms and molecules. These are arranged in
peculiar ways, and it is upon the nature of the atoms, the
arrangement of the atoms into molecules, and of these latter
among themselves, that the subsequent developmental changes
depend — just as the complex movements of the heavenly bodies
depend upon the nature (mass, &c.) of the individual heavenly
bodies, the arrangement of these into planetary systems, and
the relations of the planetary systems one to another. Thus
we may speak of the heavens as possessing an infinitely
complex structure, and thus also all analogy leads us to
assume that an ovum-cell, or indeed any other mass of
living protoplasm, is endowed with a structure so subtle and
intricate as to be out of the reach of man's limited faculties.

I have thus far only spoken of the " structure "' of individual
cells ; but in considering this term as applied to living matter,
we must, in the case of multicellular organisms, include the
relations of cell to cell— that is to say, the grouping of cells
into tissues. It is in this latter sense that the term is more
ordinarily employed, but it appears to me to have a wider
scientific meaning : thus, I include under the word " Struc-
ture," as applied to living matter — (a) the mutual relations of
the constituent atoms in the molecules ; (b) the relative positions

14 THE CAUSATION OF DISEASE.

of the molecules in the cell ; (c) finally, the relations of the cells
among themselves.

It may be thought that nothing in this or the preceding-
chapters has any connection with the causation of disease ;
but I hope that the foregoing remarks have helped us in this
wise — that they have placed us in a position to define the
cause of life ; and it is very important that we should have
clear ideas as to the causation of life, because if we cannot
give an intelligible definition of life, we certainly cannot of
disease, for disease is a peculiar mode of life.

How, then, shall we define life, and what shall we say is
the cause of it ? In order to answer this, let us take the
simplest form of life — a unicellular organism, or simple pro-
toplasmic cell. Such a simple cell consists of a peculiar
grouping of certain kinds of atoms into molecules, and a
peculiar grouping of the molecules among themselves, each
grouping — the atomic and molecular — being such that, when
the protoplasmic cell is placed within a certain environment
— when there is, that is to say, a certain material arrange-
ment round and about the cell, a certain interaction takes
place between the cell and the cell-environment. This inter-
action we term life;* it constitutes the life of the cell, and the
cause of life, according to our definition of cause, is the sum of
the material conditions of the cell and those material conditions
of cell-environment which share in the mutual interaction^

* By saying that life is a certain interaction of cell and cell-environment, I
am, of course, not attempting a logical definition of it. After life is over a
" certain interaction " occurs between the two. The above statement, although
a very inadequate definition of life, is correct so far as it goes, and is sufficient
for our purpose.

f I have here assumed that the phenomena of life may be expressed in
terms of natural laws, for the peculiar interaction of cell and cell-environ-
ment, is in the last resort a chemical action, and chemistry, as we have seen, is
nothing else than molecular physics. In the language of Huxley, " Life is a
form or mode of ordinary force." This is now the prevailing view. A few
writers, however, still cling to the old notion that life is sustained by a force
which U <juitc unique, which cannot, namely, be correlated with ordinary
chemical and physical forces. Thus Beale says: "Life is a power, force, or
property of a special and peculiar kind, temporarily influencing matter and its
ordinary forces, but entirely different from, and in no way correlated with, anv

THE CAUSATION OF DISEASE. I 5

We must very carefully observe that the external material
conditions can in no way be excluded from the field of causation.
They are as necessary as the internal material conditions. In
other words, the environment takes as large a share in the
vital processes as the cell itself.

Life, then, being an interaction of cell and cell-environment,
disease, which is a peculiar mode of life, must have a similar
causation. Assuming an ideal standard of healthful life —
which is easy enough to conceive but most difficult to define *
— we may speak of disease as an abnormal mode of life. We
arrive, therefore, at this important principle : all disease depends
upon either (i) peculiarity of cell- or tissue-structure; (2) pecu-
liarity of cell-environment ; or, finally, (3) peculiarity of both.
If a cell be perfectly fashioned as regards the kind of its
component atoms, the arrangement of these into molecules,
and the disposition of the latter among themselves ; and, if,
moreover, the environment be a fit one, the vital processes
must of necessity proceed healthily. The cell is endowed
with certain powers, the outcome of structure, and, like a wound-
up clock, must run through its course of action. This follows
from the law of causation : given the same conditions, the same
results must always follow. But if, on the other hand, the
cell-structure be abnormal, or if its environment be unfitted to
its proper working, the vital processes will no longer go on
normally : there will be, not health, but disease.

Disease, then, having two sides — (1) cell-structure, (2) cell-
other." Further, the Duke of Argyll remarks: "Let us never forget that
life, as we know it here below, is the antecedent or the cause of organization,
and not its product ; that the peculiar combinations of matter, which are the
homes and the abodes of life, are prepared and shaped under the control and
guidance of that mysterious power which we know as vitality ; and that no
discovery of science has ever been able to reduce it to a lower level, or to
identify it with any purely material force." Quatrefages speaks in a like
strain : " Living beings are heavy, and therefore subject to gravitation ; they

are the seat of numerous and various physico-chemical phenomena But

these phenomena are under the influence of a notlier force ( = Life)." It is
worthy of note that both of these latter authors are anti-Darwinists. This
question has, I hold, been permanently set at rest by the lucid writings of
Huxley.

* The question of ideal normality of structure and environment will be
considered in a future chapter (Part II.).

1 6 THE CAUSATION OF DISEASE.

environment — we must study its causation under two aspects.
We must discover, as far as is possible to us, what are the
determining factors of

(i) cell- or tissue-structure,
(2) cell-environment ;

and it will be convenient to symbolize these two factors by
the letters S and E respectively.

CHAPTER IV.

The Environment — The Environment of Unicellular Organisms — The Internal-
- Cell-Environment of Multicellular Organisms — The Primary Mai-Environ-
ment—The Secondary Mai-Environment— Remarks on the Nomenclature
of Disease.

This and the following chapter will be devoted to the con-
sideration of that great factor in the vital process which we
may denominate " The Environment." The Environment,
or to use a convenient symbol, the " E " of multicellular
organisms, falls under a twofold division : into («), internal-
cell-E, and (b) external-body-E. The latter has to be divided
into organic and inorganic E, and further into mental and
physical E.

A fit E, be it carefully noted, implies certain positive con-
ditions, and also certain negative ones. It requires, to wit, as
positive conditions, particular kinds of food, water, salts, oxygen,
and a particular temperature ; negatively, it requires the
absence of certain nocuous substances, notably, many products
of cell-action. Here let me remark that the term " material
conditions " embraces this absence of certain conditions as well
as the presence of others ; for if, to these positive conditions
Nvhich are necessary to life, others be added, the material con-
ditions will obviously not be the same. When, therefore, I
speak of " certain material conditions of E necessary to
healthful life," I obviously exclude such as are injurious or
fatal to it, and I take no account whatever of that large range
of indifferent conditions which do not affect it one way or the
other — for better or for worse.

The influence of E upon cell-action is best studied in
unicellular organisms. We may instance the yeast plant
among numberless possible examples. This organism mul-
tiplies far more rapidly in some fluids than in others, but its

c

1 8 THE CAUSATION OF DISEASE.

activity is checked by the products of its own cell-action —
by alcohol for instance. Thus we see that the E controls cell
activity, a rich food-supply hurrying on the vital process, while
the presence of certain poisonous substances has the opposite
effect. So much for unicellular organisms.

The Internal- Cell-Environment. — I have hitherto, for the
sake of simplicity, spoken chiefly of single unit cells — for I
wish to proceed from the simple to the more complex — but
it is now necessary to remember that the tissues of a complex

Fig. 2.

Cell

Lymphatic.

Fluid Plasma in which
the cells lie bathed.

organism consist of many such cells. Each cell is fixed in
its proper place by a connecting tissue substance, and each
(excepting those lying upon the surfaces) dwells in a tiny
chamber, where it lies bathed in a nutrient fluid, which
percolates the wall of the capillary blood-vessel, and after
passing into the cell-chambers, escapes by the lymphatic
vessels leading out of them. Every cell is thus, like the
amceba, bathed in a nutrient fluid, from which it derives its
food, and to which it returns its refuse. (See Fig. 2.)

The life of a complex organism may be defined as the sum
of all those interactions luhich take place between the various
cells constituting the organism and their several environments.

Much that is highly interesting and instructive might be
written on the part played by individual cell-E in the processes
of hypertrophy, degeneration, and development, but my re-
marks on this head can only be few. In treating of the
factors which determine structure, I shall attempt to show how
important is the role played by E. For the present I will only

THE CAUSATIOX OF DISEASE. 1 9

briefly allude to the processes of hypertrophy and degeneration.
The former is due to a modification of cell-E. Consider the case
of muscle. Increased exercise leads to a larger supply of blood,
the E of individual muscle-cells is thus richer in food-stuffs
and Oxygen, and the cells therefore grow to their fullest limit,
or may even be excited into multiplication. But what will
happen if, on the contrary, their blood-supply be cut off wholly,
or in part, while at the same time all agents of putrefaction
be excluded ? Degeneration occurs, fat taking the place of
protoplasm. Again, the influence of E upon cell-action is
well shown in . the case of those cells which congregate in
an inflamed area. If the blood-supply to them be deficient, as
it often is, they degenerate into fat, and perish, and may thus
(if circumstances do not permit of their removal) form cheesy
masses ; if, however, the E be compatible with life, they
continue to live and grow. There is every possible grade —
according to the nature of the E — between the extremes of
rapid and complete degeneration, on the one hand, and of
advanced and permanent development, on the other.

Many unicellular organisms float freely in a fluid medium
from which they derive their food, and to which they return
their refuse. But the component cells of complex tissues are
fixed ; it becomes therefore necessary to provide for them a
fitting cell-environment, and to this end organs are required
for the manufacture of nutrient blood-plasma for securing
the proper supply of 0, for conveying the fluid food and 0 to
the tissues, and lastly, for removing the refuse matters. If
any one of these systems is thrown out of gear, it is obvious
that the cell-environment will be interfered with. There will
cease to be that proper interaction of cell and cell-envi-
ronment which constitutes health. The interaction will be
abnormal. There will, in other words, be disease.

All disease is ultimately such an improper interaction of
cells and their environment. We have therefore now to
inquire into the several ways and means by which this cell-
environment may be influenced j for disease — it is , obvious
from our definition of it — may come through any of them.
The following list exhibits some of the ways in which cell-
environments may be morbidly modified : —

C 2

20 THE CAUSATION OF DISEASE.

1. By insufficient, excessive, or improper ingesta. The
latter, of course, includes poisons, germinal or otherwise.

2. By disease of the blood-plasma-forming tissues — i.e.,
those organs which convert the ingesta into suitable food for
the cells.

3. By inhalation of insufficient 0 or of nocuous matters,
mechanical, germinal, or gaseous ; also imperfect exhalation of
lung excreta. The temperature and dampness of the atmo-
sphere may also exert an ill effect upon the body.

4. By disease of the blood-cell-forming organs.

5. By disease of the respiratory organs.

6. By disease of the vascular system : Heart, blood-vessels,,
and their nervous regulating systems.

7. By disease of the excretory organs : the cell sewage not
being properly drained off, the cell-E contains matters injurious-
to life.

8. By direct nervous influence upon cells. The striking of
a nervous impulse upon a cell constitutes a modification of
E, since the influence comes from without. In this way the
muscle dynamite is exploded, and the zymogen of the gland
converted into zyme, wThile the direct influence of the nervous
system upon cellular elements is abundantly shown in the
field of pathology.

Since every tissue and system is dominated by the nervous
system, we see howT potently it may control the individual
cell-E's. Thus the vascular, the excretory, the respiratory
system, &c, are under its direct control.

These considerations should prepare us for the fact that the
nervous system plays an enormous role in the 'phenomena of
disease.

9. By injurious influence upon the exterior of the body —
e.g., violence, extremes of temperature, filth, parasites.

Now, if one tissue is capable of modifying the environment
of another, it is obvious that disease in one tissue may set up
disease in another, and this again in a third, and so on.
Disease in a complex organism, such as man, is thus often
a very complicated process.

All the tissues of the body are in fact knit together into one
physiological whole, so that if a disease originates in any tissue;

THE CAUSATION OF DISEASE. 2 1

in any one of the ways just enumerated, it is apt to rapidly
implicate the other tissues. Thus, a slight defect in one of
the heart-valves may ultimately lead to an altered E of every
cell in the body. A leakage in the mitral valves may entail
a terrible series of troubles, beginning with an excessive accu-
mulation of fluid in the cell-chambers, and leading on to a
universal growth of fibrous tissue. Aortic regurgitation, too,
may profoundly modify the bodily nutrition by causing the
blood to flow in jerks through the capillaries, and thus inter-
fering with the proper interchange between the intra- capillary
blood and tissues. How soon does kidney disease, again, make
its influence felt throughout the body ! The circulatiou of
nitrogenous sewage renders the tissues more apt to inflame ;
hence the tendency to bronchitis and inflammation of the
serous textures. It may be that the circulation of these
poisonous matters through the tissues is alone sufficient to
excite inflammation, or perhaps the inflammatory process is
due to their presence, plti$ something else which could not by
itself provoke inflammation. J3e this as it may, inflammation
always occurs sooner or later. All the other complications of
granular kidney are due to the retention in the blood of these
same nitrogenous products. I imagine few will dispute this.
The universal mal-nutrition, the disordered digestion, the en-
larged left heart, the thickened, contracted and atheromatous
arteries, the breaking of blood-vessels whether in the brain or
elsewhere, and the paralytic stroke : these are, each and all,
links in the same vicious chain. It is interesting to specu-
late upon the proper position of these several links, more
especially so far as concerns the vascular changes, but
whatever their proper place, none can doubt that they all
actually are links in the same chain. None can doubt, I
say, that a defect in the sewage system may so implicate the
vascular system as to lead slowly but surely to a riddling
of one of the cerebral vessels, to the flooding of the brain-
substance with blood, and to the paralysis of one-half of the
body.

In like manner a defect in the secretory system may
work evil by producing a universal modification of cell-E.
Suppose, for instance, a digestive juice to be faulty : blood-

2 2 THE CAUSATION OF DISEASE.

plasma will be imperfectly formed, and thus every cell
in the body will suffer for the error in one — it may be
very limited — patch of tissue, for the fluid medium
which surrounds each individual cell — at all events, all those
which are engaged in active vital processes — will be defective
in composition.

We thus see how potent is one tissue to modify the cell-E
of others. In respect of this power, there is, however, none
so far-reaching in its influence as that constituting the nervous
system. Every individual system of the body is controlled by
the nervous system : by it the most subtle changes in capillary
blood-pressure may be brought about, and the amount of
capillary blood-pressure doubtless influences the circulation of
the plasma environing the cells ; the nervous system again
exerts a most potent control over secretion, excretion, the pro-
duction of heat, and many other processes which it is needless
here to enumerate. When we reflect, indeed, that every active
cell in the body, such, for instance, as the gland and muscle cell,
is directly supplied with a nerve filament, it becomes at once
obvious what a dominant influence the nervous system wields
over the rest of the body. The nerve twigs are, as it were,
the reins with which the nervous system governs the body, now
curbing the cell activities, now allowing them full play — nay, it
may even be urging them on to some specific effort, as when
the muscle inogen is exploded, the invisible muscle motion
being converted into sensible motion ; or when in a gland-cell
the zymogen is converted into the zyme.

There is, however, one method by which the nervous system
influences the cell-E of the tissues which needs a special men-
tion. I allude to the influence of the mind. The operations of
the mind, or, as some would prefer to say, " mind," may influ-
ence cell-E in two ways : (i) directly, (2) indirectly. (1) That
mental states are capable of directly influencing bodily states
there can be no doubt. This subject has been fully dealt with
by Dr. Tuke in his classical work, and consequently needs no
elucidation here. Although the direct influence of mind over
body deserves to be considered under a separate head, yet,
physiologically speaking, the process is in no way peculiar ; it
acts in the same manner as the non-mental nervous influences

THE CAUSATION OF DISEASE. 23

— i.e., through the vasomotor system, trophic nerves, and so
forth. (2) The mind indirectly affects the individual cell-E
of the body through its power of regulating the external-
body-E. A very large number of diseases are caused by an
improper mental regulation of this external -body-E. (For
the present, however, I wish to confine myself to the internal
cell E ; the external bodily E will require separate considera-
tion.)

Owing to the dominant influence which the nervous system
wields over the other tissues, it often happens that a disease
originates in it, although this connection entirely escapes our
observation. Of late years, several disorders, which the older
writers would never for one moment have thought of associ-
ating with the nervous system, have been traced primarily to
it, such as gout, rheumatism (?), and diabetes, not to mention
Charcot's disease, perforating ulcer, rheumatoid arthritis, and
such like disorders.

I do not propose to exhibit, in any further detail, the in-
fluence of the various tissues upon one another, an influence
which, as we have seen, is due to the power which one tissue
possesses of modifying the cell-E of another. My object has
simply been to emphasize the fact.

Now, the various parts of the bodily machinery being thus
closely connected, it becomes almost impossible to get one
portion unhinged without throwing the entire machine out of
gear, and here we may fairly ask, How far is it possible to get
a strictly local disease ? A disease may remain strictly local.
This happens in many surgical disorders, such as a slight
wound or dislocation, or a benign tumour situated in some
part of the body, such as the buttock, where its influence is
incapable of being reflected far and wide. It is possible, too,
to get a small patch of atheroma which shall exert no remote
effects. Most local diseases of this kind are, however, capable
of causing more or less general trouble : an atheromatous patch
may develop into an aneurism, a slight scratch may lead to
tetanus or pyaemia, and a dislocation to much general discom-
fort. It is well to remember, moreover, that many disorders
which are apparently strictly local, are not really so ; thus
cataract, by damaging eyesight, may lead to considerable

24 THE CAUSATION OF DISEASE.

alteration of the external-body-E. A decayed tooth may
cause neuralgia or dyspepsia, and thus, in an indirect way,
bring about a universal modification of cell-E.*

Diseases, then, may be roughly classified into the general
and the local, but it is difficult to draw the dividing line sharply
between them, few diseases being local in the strict sense of
the word. We meet, in fact, with every possible grade
between a strictly local and a thoroughly general disease.
Scarlatina is a typical general disease : in it rapid and pro-
found changes are wrought throughout the body. Organic
heart disease might be accounted local, at all events in its
early stages, although it eventually becomes general, and,
indeed, the most strictly general diseases usually begin locally
— that is, in one particular tissue. Some few, however, have
a more general origin, such as the specific fevers, for although
the poison is commonly introduced through one particular
tissue, it is rapidly disseminated throughout the body. Scurvy,
too, cannot be said to originate in any particular tissue : it is
really due to a universal mal-E, some essential element in the
blood being absent. f

Disease, it has just been said, usually begins locally. When
this is the case it is of the first importance to specify, if we
can, the tissue first affected, and the nature of the E acting
upon it.J

* Supposing a condition such as atheroma or fatty tumour to be strictly
local, and supposing, moreover, that it cause no trouble or inconvenience what-
ever to the individual, the question arises : are we justified in regarding it as
disease ? I have no hesitation in saying that we are not justified in regarding
it as actual disease. If it contain within it the germ of some future mischief :
if a fatty tumour be destined one day to press upon some nerve and cause
pain, or if an atheromatous patch be but the germ of a future aneurism, then
we have in these two diseases examples of potential but not actual diseases.
We have no more right to speak of them as actual diseases than we have to
assert that an individual is afflicted, in the embryo, with all those diseases
which he is destined to suffer. The mere possession of obvious structural
abnormality does net, in my mind, constitute actual disease.

f. The use of the term " blood disease " in medical literature is very mis-
leading, for, owing to the mutual dependence of tissue upon tissue, there are
few, if any, general diseases in which the blood is not sooner or later involved.

X In order to complete our knowledge of causation, it would be further
necessary to discover the part played by structural weakness of the affected
tissue. If we can assign to E and S respectively their proper share in causation

THE CAUSATION OF DISEASE. 25

If we are satisfied that the S of the tissue in which the
morbid process starts is normal, we may for all practical purposes
speak of its mal-E as the sole agent in causation. (I say for
all practical purposes, for disease being an abnormal interaction
of S and E, we can never logically exclude the S from causa-
tion.) This E may be spoken of as the primary mal-environment.
As the result of this primary morbid action the E of tissues
other than that primarily affected is modified, and there occurs
in them also a morbid interaction of cell and cell-environment.
This may be spoken of as the secondary mal-environment. In
this way one morbid action is set up after another in tissue
after tissue, and there is established a complex chaiu of morbid
actions, which it should be our business to trace back, link by
link, to its origin. We have seen that disease is a morbid in-
teraction of cell and cell-environment, and we had then in
mind a simple unicellular organism, but in a complex organism
built up of many cells, disease consists of many such morbid
interactions, and any given disease may be defined as the
morbid interaction of the primary mal-environment and the
tissue primarily affected plus all those morbid interactions of
the secondary mal-environments and the tissues secondarily
affected ; the name of the disease connoting the sum of these
morbid interactions.

As regards the primary mal-environment, it may be defined
as that mal-environment of a tissue which is not due to disease
of another tissue. It may consist of an external agent acting
upon a tissue and either (1) producing disease in it, or (2) in
some other tissue through it, the tissue first acted upon escaping
disease. External agents setting up disease in the surface-
tissues (skin and mucous membranes) afford examples of the first
order. Thus are produced wounds, typhlitis, scabies, silicosis : dis-
eases in which the action of the external agent is disseminated
throughout the tissues also come more or less under this head
■ — e.g., trichinosis, tuberculosis, specific fevers — but not entirely.
Pneumonia affords an example of the second kind of primary
mal-environment, this disorder being sometimes brought about

we should then have the fullest explanation of causation which the case
admits of. We are for the present, however, only concerned with the influ-
ence of E. The influence of S will be considered hereafter.

26 THE CAUSATION OF DISEASE.

through the agency of a tissue (viz., the nervous) not sharing
in actual diseased action. Although it is now the fashion
to narrow the sphere of cold as a cause of disease, none, I
imagine, deny that it is adequate to cause ordinary croupous
pneumonia. This it probably does through the agency ot the
nervous system ; the external-mal-E acting upon the nervous
system of the lungs leads in them to a mal-environment, and
it is a -primary mal-environment, for we may presume that
no actual disease is set up in the nervous system, though
through it another tissue is morbidly affected. Some may think
I have not chosen a happy example in pneumonia, and they
may say the lung-trouble is a local expression of a general dis-
order. Be this as it may, the case, as I have put it, illustrates
my meaning.

I have said that when a disease has a local beginning, it
should be our business to fix upon the tissue first affected, and
to trace all the resulting ill- consequences link by link. This
we do by a careful study of the morbid symptoms — past and
present — and of the external-body-environment. What are
the symptoms of disease ? They are the morbid changes which
show themselves during life either subjectively to the patient,
or objectively to him or to the examiner.* Yellow skin, itching,
&c. &c, are symptoms of obstructive jaundice ; uraemia, bron-
chitis, and hemiplegia, of granular kidney. All these symptoms,
be it noted, are due to secondary mal-environment, and, indeed,
most symptoms have a like origin. A feeling of weight
and pain in the chest from the ingestion of indigestible
food is apparently a symptom due to a primary mal-environ-
ment of the stomach's interior, but it is really due to a
secondary mal-E in the sensorium : impulses starting in the
gastric mucous membrane travel up to the sensorium, and set
up in it those mysterious changes which, in psycho-physiological
language, we are pleased to term the physical side of con-
sciousness. Almost all pains — the most terrible symptoms of
disease — are due to mischief outside the sensorium, for it is a
curious fact that disease of the cerebral grey matter generally

* It is wise to make no distinction between signs and symptoms, for such a
distinction is both useless and confusing.

THE CAUSATION OF DISEASE. 2 J

causes no pain. The pain in cortical disease is probably due to
involvement of the meninges — at all events, experimental
injury to the cortex causes no pain. Among symptoms due
to primary mal-E, the swelling of typhlitis, the eruption of
scabies, and traumatic haemorrhage may be instanced.

When in any given case of disease we have observed all the
symptoms, they are to us so many marks of morbid action ; and
it is then our duty to put each in its proper place in the chain
of morbid action. In most diseases this chain is so complex
that it is often very difficult, and sometimes quite impossible, to
work out the puzzle. But this should always be our aim, and
we should above all endeavour, by the aid of the symptoms, to
determine the primary link. When we cannot do this, we must
seek for the nearest attainable. For example, a patient suffers
from cerebral tumour, but presents no other symptom than
hemiplegia, we cannot in such a case refer the hemiplegia to
anything behind it — this is the most remote link discoverable
— and, though really a symptom of something else, it is raised
to the full dignity of the substantive disease. If, how-
ever, the tumour be afterwards diagnosed, the disease is
no longer styled hemiplegia, but cerebral tumour ; and thus,
when we travel backwards, link by link, to the primordial
one, the disease of to-day may become the symptom of the
morrow.

This seems a fit place to say a few words on the subject of
nosology. The nomenclature of disease is not based on one,
but on several methods, (i) The most obtrusive symptom
may be signalled out, as in scarlatina, small-pox, con-
sumption ; (2) the mal-E, if very obvious, may serve to
designate the malady, as in tapeworm, sun-stroke; or (3) the
disease may be named after its discoverer. This last method
is probably the most objectionable of all. It would be difficult to
find a common basis of nomenclature ; in regard to diseases
beginning locally, we should, I think, where possible, choose a
term which shall not only specify the tissue primarily affected,
but shall also indicate, as far as possible, the nature of the
morbid process — e.g., rheumatic mitral endocarditis, mammary
carcinoma, puerperal peritonitis. It matters little, however,

2 8 THE CAUSATION OF DISEASE.

by what word, or combination of words, we choose to designate
any particular disease so long as we have a clear idea of the
morbid interactions (or what is known of them) which the
name chosen is intended to connote ; and inasmuch as the
morbid interactions are in no two cases, even of the so-called
" same " disease, exactly alike, we must allow a considerable
latitude to the meaning of the same term, modifying it in
different cases according to our exact knowledge of the morbid
process.

CHAPTER V.

The External-Body-Environment — An Analysis of it — Its Divisions into
Organic, Inorganic, Mental, and Physical — The Distinction between a
Diverse and Complex External-Environment — Summary of this and the
preceding Chapters.

The External-Body-Environment. — The distinction which I have
drawn between the internal-cell-E and the external-body-E is
obvious : the one refers to the ex-corporeal material conditions
which operate upon the body ; the other signifies the imme-
diate E of each individual cell.

It may be thought that the external-body-E is very
simple, but this is not so, and it is highly important to
understand how very varied and complex it is. The ex-
ternal-body-E is divided by Darwin into the inorganic and
the organic. The former includes, among other things, the
state of the atmosphere as to purity, temperature, dampness,
and a host of telluric conditions whereof we have little or no
knowledge ; also the amount of sunlight and the nature and
degree of muscular exercise (for when we exercise we are
working against the force of gravity).

But over and above these various inorganic environments we
have to take into account a highly complex organic E. Every
organism is one of a community, and is brought into intimate
relation with several other organisms, which therefore stand to
it in the relation of external-body-E.

Thus we may divide the external E into the organic and the
inorganic ; but it is necessary to make still another division
of this external E — viz., into the physical and the mental. This
division is convenient and indeed necessary, yet each in reality
falls under the same head, for the mental E operates through
the physical world. All those agencies which act upon the
brain and go to build up the mental world of an individual are-

30 THE CAUSATION OF DISEASE.

included under this mental E. These agencies are not im-
material : they are essentially physical. For mind can only
be affected from without by impressions made upon the senses,
and our sense organs are stimulated by physical forces, in a
manner more or less perfectly understood — the retina by ether-
waves, the ear by waves of air, the skin by a material contact
more or less massive. Thus the active physical world operates
upon the material brain, giving rise to a series of changes,
which are the physical accompaniments of mental states. Con-
cerning the nature of the connection between the physical and
the accompanying mental chain, I say nothing. All we know,
but that we know most certainly, is that while we inhabit
u this muddy vesture," there is such a connection, and that for
practical purposes it is both useless and unscientific to treat
of mind as a separate entity ; we had best regard it, with
Bain, as a double-faced unity.

It is thus through a physical medium that the animate and in-
animate worlds (in their purely physical aspect) affect our mental
being, as when we observe the forms, colour and movements of
objects, animate and inanimate, about us. Thus also are we
affected by the mental world outside us — namely, are brought
into communion with the minds of others, living and dead.
Our mental education consists in a series of physical influences
coming from without. When a boy is sent to school it is with
the object of bringing such influences to bear upon his brain.
His education consists in the skilful regulation of the exter-
nal-mental-E. In this way his nerve centres are moulded
in divers subtle ways, and thus is built up a character good
or bad, and an intellectual being great or small, according to
the nature of the influences brought to bear upon the indi-
vidual, and the peculiar plasticity, as determined by the laws of
heredity, of the nervous matter operated upon.

These observations on external-body-E render it evident
that the environing influences of living organisms are not
simple, but complex in the extreme. The infinite variety and
complexity of the conditions which go to make up the external-
body-E, can be best appreciated by bearing in mind that every
separate species of plant and animal has a distinct and specific
extern al-E ; nay, more than this, it is utterly impossible, as we

THE CAUSATION OF DISEASE. 3 I

shall presently see, for any tivo individuals to be surrounded by
exactly the same external-E. That every species — and let us
now speak of the animal kingdom only — has a specific external-
E is sufficiently obvious. Each species has its own particular
haunt, food, and mode of life ; each stands in peculiar rela-
tions to numberless other forms of animal life. When, for
instance, many animals compete for the same food, each one
must include within its E all the others. This struggle is not
only between species and species, but between the various
members of the same species ; indeed, as Darwin observes, the
struggle is always greatest between members of the same
species. Many animals, again, prey upon others, and thus
both the preying animal and the animals preyed upon are
brought into relation with one another, each therefore falling
within the E of the other — and among the preying animals we
must of course include the parasites. Further, the relation of
animal to animal in social communities, as of the ant and bee,
is very definite, and the whole remaining colony falls within
the organic E of any one ant or bee. Wherefore it is very
evident that every animal has a complex living E to
which it must adapt itself, or it must die. The wild rabbit,
for instance, has to compete against other rabbits, and
many other animals in the neighbourhood living upon the
same food, and has further to contend against many actual
foes, such as man. foxes, stoats, and its own particular body
parasites.

A consideration of the above facts renders it sufficiently
obvious that the E of each species must differ considerably ;
and, further, that it differs for each individual of the same
species, though not to the same extent. No two beings ever
have been, nor can they ever be, exactly similarly circumstanced,
from the beginning to the end of life.

In the case of man, the E is still more diverse and complex.
By " diverse," I mean that it differs for different individuals ;
by " complex," that the forces operating upon the individual
are not few and simple, but many and complicated. The im-
portance of making this distinction will be evident in another
part of this work. In savage communities the E of each
individual is comparatively simple, and is very much the

32 THE CAUSATION OF DISEASE.

same for all ; but as we advance from barbaric to civilized
peoples, the E grows more and more complex and diverse;
not only, that is to say, is it more elaborate and comprehen-
sive for each individual, but, owing to the division cf
labour, the E of different individuals gets very different ; for
just as each species of the animal kingdom has its own specific
E, so likewise has each occupation. Contrast the E of the
sedentary brain-toiler and of the unskilled muscular worker.
The marked difference in the E of each is sufficiently attested
by the different ways in which the S has become moulded in
each case, for I may anticipate a part of the next chapter by
observing that E is capable of working a marked effect upon S,
and what a difference there will be in the S of these two indi-
viduals ! In the one the muscles will be flabby, the skeleton
light, the heart small, the blood-vessels thin ; in the other
the muscles will be firm, hard, and hypertrophied, the bones
thick, the surfaces for muscular attachment rough and promi-
nent, the heart hard, and the valves and blood-vessels thickened;
in the one the higher nervous centres will be developed to
the furthermost limits, while in the other they will remain very
largely in statu quo. These are but a few of the structural differ-
ences in each case, and these differences are wrought through E.
The influence of education must be said to belong to E, for, as
we have seen, it essentially comes through E, and the same
may be said of muscular exercise. Muscular exercise is a
working against gravity, and this is essentially an external
force. When the weight lifted is not part of the body itself,
this is quite evident ; when it consists of the body, or part of
it, some of the force to be overcome lies within the body, since
the latter and the earth mutually act upon one another, but
the share taken by the body in producing the weight is of
course infinitesimal. Indeed, the effect of use and disuse on
body structure is in the last resort always an effect wrought
through the external E ; and I desire to lay particular stress
on this fact, for I shall utilize it in support of a hypothesis
to be subsequently advanced regarding the cause of natural
variations. The structural difference between the sedentary
scholar and the active labourer is the test and criterion of the
different E in each case ; and thus we have palpable evidence

THE CAUSATION OF DISEASE. 33

of the great difference of the E of different occupations. For
every occupation moulds the individual in a special and peculiar
manner, so that in many instances we can say at once what is
his particular calling, whether he be soldier, sailor, navvy,
groom, policeman, or what not. The E of every trade or pro-
fession or calling is, in fact, different. It would he tedious to
mention a tithe of them. Among manual workers there is a
great difference in respect of the muscles acted upon. Thus the
muscular action is different in the farm-labourer, mason, smith,
miner, and the workers in the finer kinds of handicrafts; it differs
both in respect of the particular muscles acted upon and as to
the kind of muscular action. With some the work is long
continued, with others it consists of gigantic spasmodic efforts ;
sometimes the individual remains stationary — standing, sitting,
or even lying; sometimes he moves about, and the effect is
very different in the different cases.

Again, the nature of the atmosphere differs enormously :
bakers, miners, masons, and hundreds of other kinds of workers
are compelled by the very nature of their calling to breathe an
atmosphere laden with, solid particles. Some, such as stokers,
are confined in heated atmospheres, others are exposed to
repeated draughts, while others, again, are much in the open
air, whether on land or sea. And apart from this diversity in
the physical E, there is a similar wide difference in the mental E.
Each profession or calling impresses and moulds the mind in a
particular way, and did we possess the proper analytic power,
we should be struck with the different mental states of the
members of different professions.

It is not possible to analyse the external E, mental and phy-
sical, of each of the many callings which go to build up our
complex social organism ; nor is it necessary, my sole wish
being to bring home to the readers mind the comprehensive
nature of that which we have termed the external-body-E, and
to show how infinitely complex and diverse it is. It is neces-
sary to take a careful note of this diversity, for, as we shall
see, it tends to render perfect adaptation impossible. In
order to attain perfect adaptation, several generations must be
exposed to an E more or less similar; but if one genera-
tion follows one occupation, and the succeeding generation

P

34 THE CAUSATION OF DISEASE.

another, the adaptive process will be constantly interfered
with.

We have seen that the E differs not only for different
species of animals and for the different occupations of men,
but that it differs also for all individuals. This is evident on
the face of it, but it becomes doubly obvious when it is
remembered that the E even of no two unicellular organisms is
the same. Among a colony of such organisms inhabiting the
same medium, it might perhaps be thought that the E would
be the same for each. Nevertheless, as Herbert Spencer tells
us, it is utterly impossible for any two particles of matter, no
matter how microscopic, "to be similarly circumstanced in
respect of the incidence of external forces." And if this be
true of a unicellular organism, how much more must it be true
of a being whose constituent cells are to be counted by the
million ?

Summary. — Here let us stop for a moment and survey our
present position.

The various phenomena of Nature depend upon material
conditions, as defined. The same material conditions always
tend to the same results.

The material conditions of a living protoplasmic cell —
which conditions are more or less perfectly embraced under the
term Structure — are such, that when it is placed amid certain
other material conditions, conveniently summed up under the
term Environment, an inter action takes place between cell and
environment. This inter-action is what we call Life, and the
sum of the inter-actions between any given cell and its en-
vironment constitutes the entire life of the cell. When these
inter-actions depart from a certain standard termed Health
' — which no man has yet been able to define, but of which
our notion is sufficiently clear — we have Disease. Life, how-
ever, is still going on ; disease is, then, an altered mode of life,
an abnormal inter-action of S and E, depending on peculiarities
in either or both. It is, as Huxley says, a branch of biology.
In the complex organism, man, we depart from the simple
unit-cell, and we have, instead, to deal with millions of cells,
grouped into organs, and all knit into a physiological whole in
such a way that any one tissue is able to modify the E of

THE CAUSATION OF DISEASE. 35

•some other, or even all tlie other, tissues. Disease, in such a
multicellular organism, consists not of one, but of many,
morbid inter-actions, both such as occur in the tissue or
tissues primarily affected, and such as occur in those secondarily
affected by the secondary mal-E's.

We have hitherto said nothing as to the causation of S, but
have engaged ourselves with the E. We have seen that in
multicellular organisms this falls under two heads : the
internal and the external E, and that the latter is far
more complex than appears at first sight. Space did not
permit a minute analysis of the external-body-E, but enough
was said to show its complexity, both in its mental and its
physical side. It is with the physical E that the physician
has more particularly to do. It is his business to dis-
cuss what forms of E are good for the physical well-being
of man and what are hurtful, just as it is the business of
those responsible for his mental welfare to seek out the good
and bad forms of mental E ; and it is a very happy fact
that our external-body-E, both mental and physical, is very
largely under our control.

If an individual have no tendency to disease — if, that is
to say, his S is perfect, and if he pass from infancy to man-
hood under a perfect external-E — the vital processes will
go forward in orderly fashion: there will be health. Given
a healthy body, evil can only come through E; and indeed,
as we shall see, all disease originates, on final analysis,
through E, and through E alone. And just as evil can only
come through E, so it is through E alone that we can exert
a beneficial influence on cell-action. In practical medicine
this is done by enforcing the principles of hygiene and by
administering drags. The wise physician well knows upon
which he places most faith.

D 2

CHAPTER VI,

The Causation of Structure — The Two Great Causes of Structure :
Heredity and Environment.

The second aspect under which we must study the Causation,
of Disease is that of structure ; and this word, be it remem-
bered, refers not only to the grouping of individual cells,
into tissues, but also to the individual structure of the cells,
themselves.

Upon what does structure depend ? What, in other words,,
are the factors which determine the particular structure of any
individual ? This is the problem which now confronts us —
this the question we must now answer, would we gain a philo-
sophical insight into the Causation of Disease ; for disease
being a two-sided process, of which the one side is structure
and the other environment, it follows that whatever affects
structure may play a part in its production.

If we fix the mind on any one individual, disregarding for
the time those subtle agencies which, during the long past,
have moulded man into his present shape, we shall find the
great determining factor to be " Heredity " — this word con-
veniently summing up an inconceivably complex assemblage of
forces. The structure of any given individual depends chiefly,
in fact, upon the structure of his more immediate progenitors.
Compared with this great controlling influence, any other is
small and insignificant. If an elephant could give birth to a
cow, a bird to a fish, or a human being to a cat — if, in fact,
the principle of Heredity were fickle and irregular — we should
assign to it a minor part in shaping structure ; but inasmuch
as each of the many species of plant and animal gives origin
to an offspring like to itself, it is evident that heredity is
the great power which determines the particular structure of

"THE CAUSATIOX OF DISEASE. 37

tin individual. It behoves us, then, to examine into the
principle of heredity.

Let us first take a general glance at the process. Man
multiplies by gamogenesis — that is to say, two separate elements,
.germ and sperm, enter into union, and there is gradually built
np man. The whole series of changes depends', of course,
upon the structure of the two elements and the nature of
the E.* The case may be briefly put thus : By virtue of
<: heredity," the offspring tends towards a structural standard,
which is a certain mean between the parental structures.
Owing to the sexes, this mean is different for each — the male
•offspring tending towards one structural type, and the female
■offspring towards another structural type.

But although there is such a tendency towards a given type,
peculiar to each sex, this type is, as a matter of fact, departed
from, otherwise children of the same parents would be exactly
alike — the male progeny on the one hand, and the female on
the other. There must, then, be at work agencies interfering
with " Heredity." These agencies are nothing more nor less than
peculiarities of environment. If the E were in all cases identical
— aud such an identity is totally impossible — there would be a
perfect likeness between the sons and between the daughters,
tind the likeness would be exact in every particular, even to
the subtlest evolution of thought. (It is necessary to observe,
however, that, inasmuch as the parents may acquire several
structural peculiarities between the births of their first and last
children, the parental structures are not fixed quantities, and
this would tend to prevent identity among the offspring even
though the E were identical. We may conveniently neglect
this fact for the present.) But the E is not the same in any
two cases, hence there are deviations from the standard. These
deviations are called natural variations. The term is generally
applied to such of the offspring as differ markedly from the
immediate ancestors, but it is clear that the narrowest varia-
tion is quite as much a variation as the widest, and, inasmuch
tis all the children of the same parents differ, they are all
natural variations from this fixed theoretical mean. It is

* See the remarks on cause. Chairs I., II., and III., Part I.

38 THE CAUSATION OF DISEASE.

necessary to observe, however, that, even though they all
exactly corresponded to the structural mean,' they would still
be natural variations ; for, being a mean of the two parental
structures, they would differ from each. But, upon ultimate
analysis, it becomes evident that variations in E are the prime
.cause of natural variations, for, if the world were peopled
afresh from two individuals, identical in all respects save in
such structural peculiarities as depend upon sex, and if the E
of all their descendants were identical, all men on the one
hand, and all women on the other, would be exactly the same.

Now, the E may give rise to variations both compatible and
incompatible with health. The former alone are usually
spoken of as natural variations, but let us bear the fact care-
fully in mind that a disease attended by structural change (and
most diseases are*) is quite as much a natural variation as an
ordinary physiological variation. Shakespeare was a physio-
logical variation. Pope was both a physiological and a patho-
logical variation : he was a genius, but he had a crooked back.

Here let me remark that it is necessary to distinguish two
classes of pathological variations. We may speak of these as
the sub-pathological and the true-pathological.

Sub-pathological variations are such as render the individual
prone to respond pathologically to specific forms of E, and it is
very necessary to bear in mind that an otherwise perfectly
healthy individual may vary in this way. This fact will be
insisted upon elsewhere. Meanwhile it is sufficient to point
out that an individual who responds pathologically to an E,
which to the community at large is healthy, is, in a manner of
speaking, a pathological variation, even although he be healthy
in all other respects ; and the same is true of an otherwise
healthy individual who succumbs to an ordinary zymotic virus ;
for any individual who is incapable of doing successful battle
against an average quantity of mal-environment, succumbs to
the law of natural selection — is, in fact, an unfit, and, therefore,
so to speak, a pathological, variation.

An individual may be said to be a true-path ological variation
when his tissues are altered by actual disease.

* The part which structural change plays in disease will be considered in
Part III.

THE CAUSATION OF DISEASE. 39

What I particularly want to emphasize is the fact that all
variations, be they pathological or physiological, fall under the
one great class ot" natural variations, and it is by no means easy
to sharply separate the two. In the true-pathological varia-
tions, however^ the structural change is probably always one of
dissolution.

It is clear, then, that the two great powers which deter-
mine structure are Heredity and Environment. We may thus
frame two important propositions, and these together will serve
as a text for this portion of our subject.

1 . If " heredity " were unhampered, there would be com-
plete identity among the male offspring born of the same
parents on the one hand, and among the female on the other,
each structural type being a certain mean between the
parental structures.

2. This identity is destroyed by a diversity of E.

Each of these two factors, Heredity and Environment, must
now be considered in greater detail. The latter thus comes in.
for a second consideration — this time as a power capable of
influencing structure. I shall treat of them separately, so far
as possible, but it will bo quite impossible to keep them
rigidly apart.

CHAPTER VII.

The Causation of Structure (continued) — Heredity — Sexual and Asexual Ke-
production — Keproduction by Simple Division — Parthenogenesis — Graft
Hybridism— Partial Keproduction — General Principles.

Heredity. — This term signifies a highly compounded process.
Heredity is not a simple undecomposable force like gravity :
a vast assemblage of forces are conveniently grouped together
under the word. One day they will, doubtless, be analysed,
and referred to ultimate laws, just as Newton analysed the
complex movements of the heavenly bodies, showing how they
were all the outcome of two simple laws — the law of gravita-
tion and the first law of motion. Meanwhile, until this second
Newton comes, we shall find it somewhat convenient to regard
heredity in the vulgar way — namely, as a separate entity — as
a mysterious something which moulds the offspring into the
likeness of the parents. Thus I shall, to a large extent, here
regard it, setting forth some of the more important facts of
the process, without attempting anything further than a super-
ficial analysis of them.

Man multiplies sexually, but there are other methods of
reproduction, and it would be impossible to obtain any philo-
sophical insight into the principle of heredity without duly con-
sidering them. All the various methods fall under two main
heads — asexual and sexual.

Asexual. — The most simple variety of asexual reproduction
is by simple division, such as so commonly occurs among
unicellular organisms, animal and vegetable. Complex organ-
isms, however, may be thus reproduced, as, for instance, the
fresh-water worm (nais) ; for, if it be cut into many pieces,
each will grow into the likeness of the mature organism.
This method by division, and that by " budding," are essen-
tially the same. The bud of a plant can, as we know, repro-

THE CAUSATION OF DISEASE. 4 1

duce the entire organism, but other parts of the plant possess
the same power ; thus the smallest part of a Begonian leaf
will grow into the entire plant, and, indeed, in some of the
lower plants, any single cell is alone capable of reproducing the
entire organism.

Reproduction by Parthenogenesis is really asexual, although
in one sense it comes under the head of sexual reproduction.
In this method the organism is reproduced by the development
of an unimpregnated ovum. A partial development of the
ovum takes place, independently of impregnation, even in the
highest animals, in man for instance ; but complete develop-
ment of the ovum, independently of impregnation, has been
shown to occur sometimes in certain organisms.

Reproduction by " Graft Hybridism." — This method consists
in grafting one variety into the stock of another. The blending
of the two tissues does not always occur, but in some rare
cases it does happen. This method is, strictly speaking,
asexual, but it approaches in character to sexual reproduction,
since it results from the blending of the tissues of two distinct
organisms — a hybrid mongrel resulting. It differs from sexual
reproduction in that the blending is not of two specific portions
of tissue thrown off by the reproductive organs, but of piece?
of tissue chosen more or less indefinitely.

Partial Reproduction is always asexual. Broadly speaking,
this power varies inversely, as the complexity of the organism.
Nevertheless, some vertebrates possess it in a high degree ; for
instance, the tail and limbs of the same salamander have been
cut off, and have regrown, eight successive times. The healing
of wounds belongs, of course, to this method of partial asexual
reproduction.

Sexual Reproduction is clearly allied to the above asexual
method. In parthenogenesis, for instance, we have a differen-
tiated portion of tissue, which is strictly speaking an egg, largely
dependent upon impregnation for development, but capable
sometimes of developing independently of such impregnation.
The process is in this case analogous to reproduction by budding.
Moreover, as just now observed, the hybrid in graft hybridization
results from the union of the tissues of two distinct plants.
Finally, in proof that sexual and asexual reproduction are*

42 THE CAUSATION OF DISEASE.

closely related, we may cite the fact that many alga? are repro-
duced by a process termed conjugation, in which a cell of one
alga unites with that of another, the united mass growing into
a separate organism.

All the highest forms of life are reproduced by the sexuaL
method. Every naturalist must have asked himself why such
union of two distinct elements is necessary for the reproduction
of the higher forms of life. Now, respecting sexual reproduc-
tion, there are two conclusions to which we are easily led. First.
that the whole object of sexual reproduction is to secure the
union of two pieces of protoplasm derived from separate organ-
isms ; for it has been beautifully shown by Darwin, especially
in the case of plants, that organisms containing in themselves
both sexes are most cunningly supplied with appliances whereby
an occasional fertilization by another organism is ensured.

Sexual reproduction, then, having for its object the union
of protoplasmic masses belonging to distinct individuals,
the question arises, why is this ? Can we make any further
generalization? Certainly we can. And this leads to the
second conclusion to which I referred — namely, that the
object of sexual reproduction is to secure the union of masses
of protoplasm belonging to separate unlike organisms of
the same species : if, that is to say, the separate organisms
were exactly alike, reproduction would not occur. This im-
portant generalization rests upon observation. In proportion
as the organisms coming into sexual union are like ono
another, in that same proportion is the propagation of the
species rendered difficult. Perpetual breeding in and in
leads to deterioration and eventual extinction of the species.
But in proportion as judicious crossing between different
varieties takes place, in that proportion is the stock im-
proved. " It is," says Darwin, " a great law of Nature that
all organic beings profit by an occasional cross with indi-
viduals not close!)/ related to them in blood, and that, on the
other hand, long-continued close inter-breeding is injurious.'"*
Darwin adduces irrefutable evidence in proof of this. He
reminds us that in this controversy the good resulting from
inter-crossing has not been so frequently discussed as the
* "Variation under Domestication," vol. ii. p. 94 (2nd edit, revised).

THE CAUSATION OF DISEASE. 43

evil effects of inter-breeding, which may not become manifest
for a long period of time. The good effects are shown in
increased constitutional vigour, while the evil results consist
in diminished size and vigour, and sometimes in actual malfor-
mation. Part of the evil effect, no doubt, must be attributed (in
the case of animal-organisms) to the fact that the same morbid
tendencies are apt to exist in parents of near blood, which
morbid tendencies thus have no chance of diminution in the
offspring'. But this will not account for the diminished size he
speaks of, far less for the tendency to malformation.

It is very interesting to observe that much of the evil of
inter-breeding may be mitigated if some of the stock be kept
in different localities. The explanation is obvious. Differences
of E work differences in the S, and thus the inter-breeding-
animals are rendered more unlike. We may therefore lay it
down as proven that one great purpose which Nature has in
view in resorting to sexual reproduction is to secure the union of
protoplasmic masses derived from unlike organisms.* Inasmuch,
therefore, as distinct advantages accrue from sexual reproduction,
we can easily see how this method has become fixed by natural
selection.

Can we push our reasoning farther, and answer the question :
How is it that close resemblance of the organisms brought
into sexual contact is inimical to proper reproduction ?
Darwin points out that changed conditions of life act bene-
ficially upon ?oii organism — we shall have occasion to allude to
this interesting fact again | — and he considers that the good
resulting from a cross may be due to the fact that each parent
has been subjected to different conditions. He seems to think
that in this way the more or less stable equilibrium of the-
germ and sperm is broken, and the formative forces thus
initiated. Herbert Spencer's hypothesis is more elaborate than
Darwin's, though in complete harmony with it. He asks the

* Intercrossing not only benefits by sustaining the vigour of a race. It
further helps in this wise: "When species are rendered highly varied by
changed conditions of life, the free intercrossing of the varying individuals-
tends to keep each form fitted for its proper place in Nature, and crossing can>
be effected only by sexual generation." — Variation under Domestication^
p. 355. See also Spencer's " Principle of Biology," vol. i. § 95.

f See Part III.

44 *THE CAUSATION OF DISEASE.

question, " Why does gamogenesis occur?" and to this he
replies, that "The approach towards general equilibrium in
organisms is accompanied by an approach towards molecular
equilibrium in them ; and that the need for this union of
sperm-cell and germ-cell is the need for overthrowing this
equilibrium, and re-establishing active molecular change in the
detached germ — a result which is probably effected by mixing
the slightly different ' physiological units ' of slightly different
individuals."* It would be quite beside our purpose to discuss
the question here ; but I imagine that both these great philoso-
phers are hovering near the mark, and that, although the
phraseology may eventually be altered, the whole question will
eventually be found to turn on '; equilibrium."

We have already seen that there is no sharp dividing line
between asexual and sexual reproduction. Each method is in
the last resort very similar. The question now occurs, Can we
make any generalization embracing the several methods of re-
production ? All the facts seem to point to the conclusion that
each part of an orgauism possesses a tendency to reproduce the
whole. The twig of a plant placed in the ground will grow into
the likeness of the mature organism. A siugle cell taken from
the leaf of the Begonian plant will reproduce the plant ; where-
fore in this plant the power of reproduction belongs impartially
to every part of the organism, and the same is true of very many
of the lower forms of plant life. The like tendency is observed
in the animal world, for if the hydra be divided into several
pieces, each will grow up into a separate and entire organism.
As the scale of structural complexity in the animal world is
ascended, however — that is to say, as the process of division
of labour proceeds, and groups of cells become " specialized "
for some one particular function, this power wanes — individual
•cells gradually losing the power of producing the entire organ-
ism, and the power of reproduction is confined to cells which
have not undergone this specialization — viz., to those formed
by the ovary and testicle. This is the view taken by Herbert
Spencer. Here are his exact words : —

" The marvellous phenomena initiated by the meeting of sperm-
oall and germ-cell, naturally suggest the conception of some quite

§ 92, vol. i. •

THE CAUSATION OF DISEASE. 45

special and peculiar properties possessed by these cells. It seems
obvious that this mysterious power which they display, of originating
a new and complex organism, distinguishes them in the broadest way
from portions of organic substance in general. Nevertheless, the
more we study the evidence, the more is the assumption shaken — the
more are we led towards the conclusion, that these cells have not been
made by some unusual elaboration, fundamentally different from all
other cells. The iirst fact which points to this conclusion, is the fact
recently dwelt upon, that in many plants and inferior animals, a small
fragment of tissue that is but little differentiated, is capable of deve-
loping into the form of the organism from which it was taken. Con-
clusive proof obliged us to admit, that the component units of
organisms, have inherent powers of arranging themselves into the
forms of the organism to which they belong. And if to these com-
ponent units, .... such powers must be conceded — if, under fit
conditions, and when not much specialized, they manifest such powers
in a way as marked as that in which the contents of sperm-cells and
germ-cells manifest them ; then, it becomes clear that the properties
of sperm-cells are not so peculiar as we are apt to assume. Againr
the organs for preparing sperm-cells and germ-cells, have none of the
speciality of structure which might be looked for, did sperm-cells and
germ-cells need endowing with properties essentially unlike those of
other organic agents. On the contrary, these reproductive centres
proceed from tissues that are characterized by their low organization. 'r

He then proceeds to exemplify this statement in the case of
plants and animals : —

" The embryo cells are formed in the undifferentiated part of the
cambium-layer; the pollen grains are formed at the little-differen-
tiated extremities of the stamens ; and both are homologous with
simple epithelial-cells. Among many inferior animals devoid of special
reproductive organs, such as the Hydra, the ova and spermatozoa
originate in the layer of indifferent tissue that lies between the
endoderm and ectoderm ; that is, they consist of portions of the least
specialized substance. And in the higher animals these same
generative agents appear to be merely modified epithelial cells — cells
not remarkable for their complexity of structure, but rather for their
simplicity."

He next remarks that undifferentiated epithelial cells are often
observed to exhibit the like property. Thus, referring to a cer-
tain plant, he learns from Dr. Hooker that " many young plants

46 THE CAUSATION OF DISEASE.

are developed by a single scale " of the leaf or stem ; and
finally lie observes that sperm- and germ-cells " differ from the
rest mainly in not having undergone modifications such as
those by which the rest are adapted to particular functions."*

Finally, the question occurs : How conies it that a single cell,
-or the union of two cells, is able to reproduce the entire
organism ? Darwin and Spencer have started hypotheses of a
kindred character. The hypothesis of the former goes by the
name of Pangenesis. It is now universally admitted that all
organisms consists of cells, and that the latter are themselves
separate, and more or less independent organisms. Each cell
Darwin supposes to throw off tiny particles, or gemmules, which
are capable of reproducing the particular cells from which* they
are derived, and he accounts for the various methods of asexual
reproduction by supposing these gemmules to be scattered
throughout the body. Thus, when the entire tree grows from a
small twig, it is because that twig contains gemmules derived
from each separate cell in the entire plant ; and in a similar way
he would explain the development into entire animals of each
of the many fragments into which a Hydra may be divided.
The re-growth of an amputated limb he considers to be " the
same process partially carried out." In organisms which are
reproduced sexually, these gemmules are supposed to aggregate
themselves into the sexual elements — in the case of man,
namely, into the ovum and spermatozoon. Suppose, for
instance, an organism to cousist of homogenous, gelatinous
matter, then a small part separated from the rest would be able
io reproduce the whole. But if the upper, central, and lower
portions of the organism be of different textures, each would
have to throw off a different kind of gemmule, and these,
" when aggregated by mutual affinity, would form either buds
or sexual elements." There is no difficulty in allowing this
origin of gemmules from all the many cells of an organism, but
it is more difficult to understand why the gemmules should
aggregate themselves in proper order, why, for example, in the
case of germ and sperm, the countless gemmules for brain, liver,
lung, and other tissues, should be arranged according to a
definite plan. Darwin assumes a certain " elective affinity," in

* "Principles of Biology," vol. i. § 77.

THE CAUSATION OF DISEASE. 47

virtue of which the developing cells attract to themselves the
proper gemmules, and in regard to this he says : " There are no
doubt ten thousand of Compositee, and if the pollen of all of
them were placed on the stigma of a particular species this
would elect ' with unerring certainty ' its proper pollen "
It is this second half of Darwin's hypothesis wherein the
great difficulty lies. Whether his way of putting the matter
is really an explanation is doubtful ; but there is no doubt
that from the beginning to the end of development the proper
aggregation of molecules is the result of affinities, and that
these are the outcome of material conditions.

Herbert Spencer's doctrine is somewhat similar to Darwin's.
He, however, substitutes his " physiological units " for the
gemmules of Darwin.*

Wherefore we may sum up the main facts of reproduction in
the four following propositions : —

1 . Every cell of an organism has a tendency to reproduce
the whole organism.

2. This power diminishes as specialization proceeds, becom-
ing more and more confined to special cells.

3 . The cells capable of reproducing the entire organism may
consist of aggregated "gemmules," or "physiological units"
(using these terms in the sense their respective authors attach,
to them).

4. The object of sexual reproduction is to secure the union
of reproductive cells from unlike organisms, so as to disturb the
equilibrium into which such reproductive cells tend to fall.

Now, without further indulging in speculation, it is evident,
whether this, that, or the other hypothesis be correct, that the
whole mystery of reproduction or heredity hinges upon the
structure of the reproductive cell or cells. The difficulty lies
in the question — What determines the structure of the repro-
ductive element ? For, given a definite structure of germ and
sperm, there is no difficulty — I, at all events, see none — in
explaining, on the principle of causation already enunciated,
the development of the mature organism from them. When the

* For a complete exposition of Darwin's doctrine of Pangenesis, see
" Variation under Domestication,'' vol. ii. chap, xxviii. See also Herbert
Spencer's " Principles of Biology," vol. i. chap. iv. a id viii.

48 THE CAUSATION OF DISEASE.

two come into contact, a series of associated changes ensue?
which are the outcome of the " material conditions " as repre-
sented by the structure of germ and sperm, and the nature of
their environment. Each successive change in the material
conditions occurring during the development of the embryo
is the cause of those changes immediately succeeding — just
as the material conditions of a planetary system at any one
moment are the cause of the changes immediately following,
this new material state being again the cause of the succeeding-
changes, and so on to the end of time. Life, like the move-
ments of the planetary systems, is a simple rhythm — a per-
petually recurring cycle — the last changes in the cycle provoking
the first. This, I take it, is the explanation of all rhythms.

The analogy I have drawn between the cycles of the
heavenly bodies and of living beings seems to me a just one,
although there is one great difference. In the case of growing*
organic beings matter is being continually added to the living-
systems, but this does not happen in the case of the planetary
systems. I cannot, however, afford the space to discuss this
matter here, and must content myself with stating my belief
that the two processes are, upon ultimate analysis, of a similar
nature, and that, given a definite structure of reproductive cells,
of germ and sperm, for instance, there is no difficulty in
accounting for the embryonic changes resulting from their union.
The whole difficulty, as I have said, hinges upon the cause of the
structure of the reproductive cells. How do these elements come
by their structure? Therein lies the difficulty. That germ
and sperm do possess a structure, and that an exceedingly
complex one, there can be no doubt. But here we are brought
face to face with the world of the infinitesimal, where our
senses fail us. Belying only upon these, we pronounce proto-
plasm to be homogeneous and structureless ; whereas reason
urges to a different conclusion, and in its light the tiny homo-
geneous flecks of protoplasm, with their infinite potentialities,
become two vast and complex worlds — two microcosms, in fact.
It were as possible for man to develop out of glass as out of
homogeneous jelly !

CHAPTER VIII.

The Causation of Structure (continued) — Heredity — The Grand Rhythm
of Life— Minor Vital Rhythms.

Rhythms. — The subject of cycles, or rhythms, is a very
important one, and it is necessary to take here some account
of it, for not only is life itself a rhythm, but the animal
organism is the seat of very many and diverse rhythmical
processes — minor rhythms within the great vital rhythm — and
it is because we are now treating of the great vital rhythm
as determined by heredity that it is proper to allude to the
subject of rhythm here. To treat of it in full detail would be
beyond the scope of this work ; for a short but comprehensive
article upon it the reader is referred to Herbert Spencer's " First
Principles," chap. x.

All motion is characterized by rhythm. " This is an
inevitable corollary of the persistence of Force ; " more than
this it is unnecessary to say as to the causation of rhythm.
No matter what motion we examine we shall find it rhyth-
mical, be it the movement of an atom or of a world ; and
there is every degree of rapidity. The rhythm of the violet
ray of the spectrum occupies less than the 700 billionth part
of a second, while some of the rhythms of the heavenly bodies
extend over thousands, nay, even millions, of years. Turn
where we may, we find all movements rhythmical, — heat, light,
sound, electricity, vital phenomena, even social changes.

As regards the minor rhythms occurring within the
great vital rhythm, some of these occur in response to
rhythms in the external-body-E, others independently of
such external rhythm. The body rhythms due to the
rhythmical changes of our planetary system afford the best
examples of the former. Thus day and night impress im-
portant rhythms upon plants and animals. The rhythmically

50 THE CAUSATION OF DISEASE.

altering E causes rhythmical alterations of functions. This is
what determines the rhythm of sleep and the peculiar rhythm
of temperature, noticeable in man, at all events. In those
parts of the world where the rhythm of day and night is
absent altogether, the inhabitants are wont to take their sleep
in snatches, and we may be quite sure that there is considerable
difference between them and ourselves in respect of many of
the bodily rhythms. It would be very interesting to make
physiological observations as regards temperature, &c, among
the inhabitants of such countries, for the rhythm of day and
night also determines many others in our bodies — e.g., the hours
of our meals, and therefore of the important processes of diges-
tion and absorption — processes whose influences are felt through
the entire body ; it also determines, or should do, a rhythmical
emptying of the rectum, and perhaps even of the bladder.

Now, it is interesting to note that the subjection of our body
to this rhythmically altering E leads to rhythmically recur-
ring changes, even after we cease to continue the rhythmical
practices. In other words, we can educate the body to go
through rhythmical changes. These we may term rhythmical
habits. Thus man can educate himself to feel sleepy at a
definite hour at night ; to wake at a particular time in the
morning, and that too — note well — no matter what hour he
goes to bed, thus showing that the awakening is not necessarily
due to mere satiation in the matter of sleep. He can further
educate himself to wake at a certain hour in the night, in
order to pass water or what not, and, in this regard, it is
worthy of note — I have observed this many times — that if
an individual perchance wake up one night to pass water,
there is a great likelihood that he will do so two or three nights
in succession. A man can further educate himself (and for
the matter of that, many of the lower animals can also be
taught) to defecate at a certain hour, always after breakfast,
for instance, and so exacting is this rhythm, that very often
if the individual do not go to stool at the proper time, if
he delay an hour, or perhaps even half-hour, he will fail to
have a motion. We can further educate ourselves to feel
hungry at particular hours. " Yes," it may be retorted,
" because the last meal is digested, and the tissues are

THE CAUSATION OF DISEASE. 5 I

crying out for more." This, no doubt, is one' element in
the causation of the recurring hunger, but the sensation
tends to return at the wonted hour altogether indepen-
dently of the time of the previous meal, nay, even though
the customary previous meal has been omitted ; moreover, the
sensation of hunger will often disappear if the meal be not
taken at the proper hour, just as the sleepiness at the wonted
bedtime may pass off if the individual, through force of will or
through necessity, keep himself awake beyond this time. A girl
of fifteen, for instance, sits up for several nights in succession with
her mother ; at the usual bedtime the heaviness of sleep comes
over her, but it quite passes off after she has struggled against
it' for half an hour or so. The same principle applies to
the practice of smoking. A man, accustomed to smoke at a
particular hour, will experience the desire to indulge his habit
at that particular hour, and generally at that hour only. Now
all the above phenomena are due to rhythmical changes im-
pressed upon the system by subjecting the body to certain other
rhythmical changes. Each and all are distinct rhythms, the
interval being, for the most part, twenty-four hours. Thus,
in the case of the ordinary sleep rhythm, at the end of each
twenty-four hours the body passes through a particular change.
The molecules of the brain, namely, fall into a material state
which expresses itself psychically as a desire for sleep. In like
manner the digestive organs and that part of the sensorium
which has to do with appetite are thrown into rhythmical
change, and hence the rhythmical desire for food.

So much for the bodily rhythms connected with the daily
rotation of the earth on its axis. The yearly movement of the
earth round the sun leads in like manner to rhythmical organic
changes. These are especially noticeable in the plant world,
but they are likewise very marked among animals. Thus, many
animals change their abode at stated seasons. A large number,
again, hybernate. In others, marked dermal changes take place
at particular seasons, such as the casting of the shell in certain
Crustacea, the shedding of the horns and of the coat in many
quadrupeds, and the moulting of birds — not to mention the
extraordinary tegumental changes which take place in a large
number of animals during the season of sexual activity.

E 2

5 2 THE CAUSATION OF DISEASE.

Is there any evidence that a rhythm depending npon the
seasons takes place in man? It is, a priori, highly improbable
that man should be exempt from a principle which operated so
palpably in his not very remote ancestors. I believe Dr. Lay-
cock was the first to teach that the skin exhibits distinct
peculiarities at the different seasons. It seems to be generally
acknowledged that the sexual instinct is most active during the
spring time, and owing to the close connection between the
sexual and cutaneous systems, one would expect to find a
peculiar condition of the skin in the spring, and such undoubt-
ably is the case.

Dr.Creighton Brown* says " it is certain that the seasons have
still a powerful hold upon the human organism. There is a
gain of body weight in winter and a loss in summer, and vital
statistics show that each season has diseases which may be
called peculiarly its own," and he alludes to the excitement of
the nervous system which occurs at the time of spring, quoting
the lines of Tennyson —

" In the Spring a livelier iris brightens on the wing of dove ;
In the Spring a young man's fancy lightly turns to thoughts of love."

At this time of the year nervous diseases abound — crime and
insanity increase ; " crimes against the person are most
numerous in spring and early summer, when the stags' horns
are budding and his aggressive instincts are most pronounced ;
while crime against property are most numerous in autumn
and summer, when squirrels lay by their stores." And in this
connection it would be interesting to discover at what period
of the year rape is most frequent. Creighton Brown further
observes that many children in springtime exhibit " a restless-
ness and excitability, a perversity and irascibility of temper, or a
listlessness and indisposition to exertion that are not displayed
at other times."

Now, it may be thought that these organic rhythms are
entirely due to the yearly rhythm in the external -body-E ; it is,
however, very probable that they tend to occur independently of
this external rhythm, seeing that a structure may be educated

* Article, Education and the Nervous System : " The Book of Health,"
London, p. 315.

THE CAUSATION OF DISEASE. 5 3

to pass spontaneously through rhythmical changes, by being
repeatedly subjected to a rhythmically recurring E.

Are there any rhythmical changes in man answering to the
rhythmical movements of the moon round the earth ? It is
difficult to say. I have heard people wonder at the curious
fact that the ordinary menstrual rhythm coincides,- as regards
the length of the rhythm, with the monthly lunar cycle. If,
however, the two were in any way causally related, one would
expect menstruation to recur at the same time in every woman,
but it does not. In one passage, Darwin vaguely alludes to
the influence of the lunar rhythm on man. He points out that
it distinctly influences many aquatic animals through its in-
fluences upon the tides, and he obscurely hints that man may
have faintly inherited the rhythmical impress from some far off
aquatic ancestor.

When a rhythm is once established it tends to go on inde-
finitely ; one would therefore marvel that the menstrual rhythm
should cease, as it is supposed to do, during pregnancy and at
the menopause. Probably, however, this does not occur.
Throughout the whole of pregnancy the monthly rhythm goes
on. I have satisfied myself that this is so from observation,*
though there is probably no ripening of an ovum, nor is there
loss of blood, unless it be exceptionally. It is recognized that
the uterus undergoes muscular contraction throughout the whole
term of gestation (indeed, such rhythmic contractions have
been regarded as an absolute sign of pregnancy), but they
are palpably increased at the time when the period would
have occurred, were the woman not pregnant. These monthly
contractions are related to the ordinary menstrual contractions,
for at the menstrual epochs the uterus undergoes considerable
muscular contraction ; and it is to the latter, I take it, that the
pain of menstruation is chiefly due. At all events, Dr. J. Mat-
thews Duncan, probably the greatest authority on the subject,
teaches that the chief form of dysmenorrhea is spasmodic ; the

* Laycock maintained that the menstrual change took place during preg-
nancy. He observes, "it is singular that this doctrine maintained by the
ancients should have fallen into neglect. Aetius expressly states, • circa con-
sueta purgationis menstruae tempora aggravantur prsegnantes et mamma intu-
mescunt lumbi difficulter moventur, vesica rubens et ignitum lotium excernit.' "
— Laycock, Nervous Diseases of Women, p. 46.

54 THE CAUSATION OF DISEASE.

woman, in fact, suffering from uterine colic. This rhythmical
contraction is beautifully displayed at the time of labour, which
occurs at the tenth month (lunar) of gestation. Labour is, there-
fore, the ordinary monthly rhythmical contraction, exaggerated
by the presence of the foetus, which, about this time, owing to a
combination of circumstances needless to discuss, begins to act
as a foreign body. In like manner the suppressed monthly
rhythm occurs during the months of lactation, though it is for the
most part entirely overlooked by the woman. In regard to the
post-menstrual period of life : for the first few years perhaps all
women experience some monthly symptoms, and a large number
will acknowledge this, if asked ; but the rhythm, in all pro-
bability, continues for many years to come. I am, indeed, not
at all sure that it ceases before death. Upon very careful
inquiry, evidence of post-climacteric menstrual rhythm can be
obtained, in a fair sprinkling of cases, up to sixty, but I have
distinctly traced the rhythm past seventy. The woman will
complain of backache, or flushes, or a curious headache, or she
will grow dark under the eyes ; and sometimes the symptoms are
highly interesting, and not infrequently different to those she
was wont to experience when the periods were actually upon her.
Although by far the larger proportion of women — at all events,
among hospital and infirmary patients — will deny any monthly
indication after sixty, yet I imagine that this is due to the fact
that they do not themselves recognize the rhythm, although
they actually experience it.

Does the male sex undergo any monthly rhythm, akin to
menstruation ? This question cannot at present be scientifically
answered, but it is worthy of investigation, although, perhaps,
to many, such a supposition may appear fanciful. I have known
several cases of disease, which have exhibited a monthly rhythm.
They have mostly been nervous cases. One medical man, who
suffered from monthly migraine, was in the habit of speaking
of them as his " monthlies;" and I have met with a case of
monthly-bleeding piles in an elderly gentleman ; and it is a
very interesting fact that, when, at the age of sixty-six, the
hasmorrhagic flux became irregular, this gentleman experienced
many of the symptoms which women complain of at the
climacteric — he became emotional, and, among other things,

THE CAUSATION OF DISEASE. 55

suffered from very marked flashings, headache, and backache,
and a symptom which I have never yet found absent among those
menopausic patients who seek medical relief — soreness of the scalp.

These remarks on rhythm would be out of place here, did
they not bear upon disease and its causation. Diseases them-
selves are very frequently rhythmical, such as asthma, migraine,
angina, ague, remittent fevers, and a host of minor nervous
disorders, which have no name, but which are numerous enough
to the careful observer. For it requires the greatest care,
patience, and tact, to get the proper history from a patient ; and
I have not the slightest doubt there are hundreds of important,
though simple, diagnostic signs, which have hitherto escaped
our notice.

I have already pointed out the analogy between the rhythms
of the heavenly bodies, the grand rhythm of life, and the
minor rhythms displayed by living beings. Many other forms
of minor rhythm might be cited, such as the rhythm of the
heart and respiration, and other physiological rhythms, but I
must content myself with merely stating the fact ; for the
rhythms of the body are, in fact, innumerable. Muscle and
nerve action, for instance, are distinctly rhythmical ; what is
apparently a continuous muscle-contraction is made up, as we
know, of a series of individual contractions (= tetanus) ; and
even the most seemingly continuous sensation is really rhyth-
mical. " An apparently unbroken mental state is in truth
traversed by a number of minor states, in which various other
sensations and perceptions are rapidly presented and disappear."

I wish now briefly to point out a further analogy between these
several rhythms. Every planetary system, like every organism,
has an environment, which consists in the universe outside ; and
this E reacts upon the planetary system (just as the E of a living
organism acts upon it), and may cause modifications of planetary
structure, as we may term it, which may be transmitted to suc-
ceeding cycles, or, as we may call them, planetary offspring.
I have already said that E is the great cause of natural varia-
tions ; indeed, as we have already seen, it is in the last resort
the only cause. We may therefore speak of the changes in
planetary structure thus effected from without as examples of
' ' natural variation " in an astronomical organism.

56 THE CAUSATIOx\ OF DISEASE.

Examples might be multiplied ad lib. to show that all the
vital rhythms exhibit a similar tendency to natural variation.
In order to make this clear, we must separate in imagination
— and this is quite admissible — the tissue, or tissues, especially
engaged in the rhythm. Let S stand for such tissue or tissues ;
then be it observed that under a given environment, which
must include both the external and internal environment, the
rhythm will steadily continue to recur, and, if only the material
conditions represented by S and E remain the same, the rhythm
will recur with undeviating regularity until the end of time. But
these material conditions will not remain the same. In the
first place, the S is continually altering as life advances —
through infancy, childhood, youth, maturity, and old age.
In the second place — and it is on this that I wish especially
to lay stress — the external-body-environment is no constant
factor, and this irregular external-E, reacting upon the S, will
tend to modify it, and with it the rhythmical phenomena,
which will thus vary; and this alteration, or natural varia-
tion, will tend to be inherited by the next rhythm. Thus, to
speak only of pathological processes, we know that rhythmical
neuralgias and asthmas are apt to vary from one attack to
another ; any peculiarity which has been impressed upon the
asthmatic paroxysm, by peculiarity of climate or otherwise, will
tend to reappear in the next attack. Who that has read
Darwin can fail to be struck by the following passages :
" If asthma is relegated to unchanging external influences, its
cycle of phenomena will go on repeatedly, with a marvellous
exactness, but the maintenance of this unvarying repetition is
strictly dependent on the maintenance of identical external
conditions, and any change, however trifling, is capable of
breaking the existing habit, and of introducing fresh pheno-
mena."* Again: "Any peculiarity that has once been
acquired, (although, perhaps, from some transient accidental
circumstance), will, as the time comes round, recur, and thus be
formally adopted among the symptoms, and become a constituent
part of the clinical phenomena. There are hardly any circum-
stances of the disease, that may not thus be lost and acquired. "f
* "On Asthma" (Salter), chap. iv. f Ibid.

CHAPTER IX.

Causation of Structure (continued) — Heredity at Corresponding Ages — Heredity
at Corresponding Seasons — Sexual Heredity — Some Comparisons between
Man and Woman.

Having thus briefly touched upon the important subject
of vital rhythms, we must now pass in review some of the
special facts of heredity. I shall first consider the principle of
heredity at corresponding ages ; next, sexual heredity. I shall
then allude to the principle of, what I shall term, " structural
mean." Whether or not I am right in saying that the off-
spring tend towards a certain structural mean between the
two parents, which mean would never be departed from, were
they all exposed to exactly the same E, we shall, I think, find
this to be a very good working hypothesis. While dealing
with this blending of the two parental tendencies into a certain
mean, I shall naturally be led to speak of pathological and
physiological blendings — that is to say, of the blending in
the offspring of certain tendencies derived from the parents : of
disease tendencies with other disease tendencies, or with physio-
logical peculiarities ; and under this head it will be convenient
to touch briefly upon the subject of crossing. I shall next
consider the " fixity of structural characters " — namely, the
degree of tenacity with which they cling to a race from
generation to generation, or, when acquired by an individual,
the fixity of the acquisition in the individual himself. The
principle of reversion will next come in for consideration.
This subject will suggest a few remarks on potentiality. I
shall then notice the influence of the male element upon the
female, and finally, the inheritance of acquired characters.

I. Heredity at Corresponding Ages. — The fact that the
developmental and other changes occur at the same rate in the
offspring as in the parents, leads to the reproduction of similar

58 THE CAUSATION OF DISEASE.

tissue-structure, and therefore similar disease tendencies, or
actual disease, at corresponding ages. The S varying with the
age, the effect of E upon it will likewise vary at different
periods of life, and hence the tendency to disease will vary too.
In some cases there seems to be a tendency towards inheritance,
not at the corresponding age, but at an earlier age, in the off-
spring than in the parent. This often happens, for instance, in
gout ; and Darwin points out that, when the rule is departed
from, the inherited peculiarity appears earlier rather than
later, for he says, "the exceptions in the other direction are
very rare." The facts of embryology certainly bear out this
observation.*

We may also speak of an heredity at corresponding seasons ;
for, as we have seen, there is an annual organic cycle
corresponding to the annual cycle in the E. We may in-
stance the horns of the stag, which appear at certain seasons,
or indeed, the skin appendages of most animals, such as the
feathers of birds, the fur or hair of animals, the scales of fish,
which undergo periodic changes at different seasons. These
changes are, as we have seen, ultimately dependent upon the
seasons ; but they come to be very largely inherited, so that,
although the alteration of the seasons is necessary to show them
in their most typical form, they would tend to appear independ-
ently of the seasons, through the force of inheritance pure and
simple. It is probable that the same kind of skin changes occur
in man. This would account, in some measure, for the espeeial
prevalence of certain skin diseases at particular periods of the

* When an inherited character appears earlier in the offspring than in the
parents, we have an example of "precocity." One of the most interesting
instances of precocity is the occurrence of puberty before the wonted time.
There is a fair number of such cases on record. I have now under observa-
tion a boy, who, at the age of two years, attained full sexual maturity. His
testicles and penis are fully developed ; there is abundance of hair on the
pubes, his voice is gruff, and his muscles stand out boldly like those of a well-
grown man. The sexual instinct is strong and troublesome. All will agree
that this case is abnormal and unfortunate ; but when a similar precocity is
exhibited in other directions, the parents are often apt to regard the individual
as a prodigy, as a wonder of whom great things must be expected. I refer
especially to cases of premature cerebral development. No doubt, in certain
cases, this promise of youth is an earnest of a great future, but, as a general
rule, precocity is abnormal— a thing altogether to be regretted, whether of the
brain or of the reproductive system.

THE CAUSATION OF DISEASE. 59

year. And what is true of the skin is true also of other
organs — notably, of the sexual. These, it is well known,
undergo marked changes at certain seasons in many of the
lower animals, and, as we have already seen, there is a faint
tendency to such a periodicity in man. How far the other
organs in man partake of this periodic change, itr is impos-
sible to tell ; yet who can say that such hidden rhythmical
changes may not j largely help to determine the prevalence of
certain disorders at particular seasons of the year, even though
it be readily acknowledged that alteration of E at the different
seasons plays the largest share in determining such preva-
lence ?

II. Sexual Heredity. — When only one individual is
concerned in procreation, as in the case of all asexual
organisms, the principle of heredity may be put thus : The
offspring tends to pass through the same series of changes,
and at the same rate as the parents, the rhythms being
in fact like all others. Inasmuch, however, as in the case
of man, two individuals take part in the process, the off-
spring tends to be neither exactly like the one nor the other,
but a certain mean of the two. This mean is interfered with
by the structural peculiarities of each sex, for each has pecu-
liarities connected with the difference of sexual function. But
although these peculiarities chiefly relate to the sexual func-
tion, they are not confined to it, as we shall presently see.

The various sexual differences have been undoubtedly acquired
during the course of ages, under the different conditions (E) to
which each sex has been exposed. This subject has been care-
fully worked out by Darwin, who has shown that a character
acquired by one sex at one particular period of life tends, in
the offspring, to appear in the same sex and at the same
period of life. Illustrations of this fact abound in the animal
world. Thus, the antlers of the stag attain their full strength
when sexual maturity is reached. At this time many males
compete for the female, and success depends upon the strength
and prowess of the competitors. The horns are powerful
weapons, and thus a stag with strong antlers would have an
advantage over another having weaker ones, and would be more
likely to succeed in the struggle for the female, and to leave

60 THE CAUSATION OF DISEASE.

offspring which would tend to inherit his peculiarities. In
this way, by accumulation from generation to generation, the
antlers of the stag have attained their present dimensions.
And the same is true of countless other sexual peculiarities,
which enable the male to secure the female.

Darwin has further shown that characters acquired by one sex
at an early period of life — before the time of sexual activity —
tend to be transmitted to either sex alike ; but that characters
appearing in one sex during the period of sexual activity tend to
be inherited by that sex alone. He further points out that new
characters tend to attach themselves by preference to the male
sex.* These facts have an undoubted application to pathology,
for we find that diseases attack the two sexes with much greater
impartiality during childhood than in the period of sexual life ;
and perhaps the same is true, though in a far less degree, of the
period of post-sexual life. This tendency of special structural
characteristics to be transmitted along either sex, may be
termed the principle of " sexual heredity." But such sexual
heredity is not confined to sexual differences. It holds good
universally — that is to say, any character whatever, when
acquired by one sex, be it physiological or pathological, tends
in the offspring to appear in the same sex. Many diseases
illustrate this truth. Thus, gout is acquired by the male at a
particular period of life, and tends to appear in the male
descendants at the same age.

Mr. Sedgewick has published some interesting papers on
" The Influence of Sex in Limiting Hereditary Transmission," t
and amongst other cases he records several of congenital
abnormities — such as an abnormal number of fingers or
phalanges — descending along the one sexual line.

Concerning this tendency for structural peculiarities to
appear in one sex only, of successive generations, be it care-
fully noted that the peculiarity may pass potentially throvgh the
opposite sex. Thus A suffers from gout : his sons will be apt
to inherit the complaint, and his sons' sons ; the daughters, on
the other hand, will tend to escape, but their sons will be liable

* " Descent of Man," second edition, p. 32.

f Medico- Chirurgical Review, April and July 1863.

THE CAUSATION OF DISEASE. 6 1

to contract the disorder. (It is, of course, understood that in all
such cases of inherited disease it is a peculiarity of structure
which is inherited.)

I say the peculiarity passes potentially through the opposite sex.
This means that the possibility of it exists in this sex, but that
it is, in some way or other, kept under and prevented from
showing itself. This subject of potentiality is highly interest-
ing. Man is a compound of many potentialities, and we can
never know what strange property he may show, if only the
fitting conditions for its development occur. A large number
of such potentialities are inherited from remote ancestors,
but this subject will be best considered under the head of
reversion. At present we are occupied with sexual heredity,
and the tendency of structural potentialities to pass through
one particular sex. The special sexual characters of each
sex lie dormant in the opposite sex, for if the ovaries or
testicles be atrophied, diseased, or removed, the characters
of the opposite sex develop. Thus, an old duck has been
known to acquire the plumage of the drake ; and " a hen,
which had ceased laying .... assumed the plumage, voice,
spurs, and warlike disposition of the cock ; when opposed
to the enemy she would erect her hackles and show fight.
Thus every character, even to the instinct and manner of fight-
ing, must have lain dormant in the hen as long as her ovaria
continued to act."* Again, the influence of the menopause on
woman is very striking : the body is then apt to undergo
marked change, and the mental alteration is one affording the
psychologist an interesting study. The opposite condition — viz.,
disease, atrophy, or removal of the testicles — has a like effect,
that is to say, the male tends to approach in character to the
female. .Now these facts show most strikingly how characters
can pass latently through one sex, and manifest themselves in
the opposite sex in the offspring — how, for instance, it is
possible for a good milking cow to transmit her good qualities
through her male offspring to future generations."! But they
further explain those cases of non-sexual characters which are

* "Animals and Plants under Domestication," vol. ii. p. 36.

\ Ibid., p. 27. Darwin's remarks on this head deserve careful study.

62 THE CAUSATION OF DISEASE.

transmitted along one sex only.* The potentialities are evi-
dently kept in abeyance by some restraining influence, upon
the removal of which they are ever ready to spring into exist-
ence.

If we are not careful to bear in mind that a character may
pass potentially through one sex, we shall have some difficulty
in comprehending aright the doctrine of sexual heredity, and
apparent exceptions will frequently meet us. It is often said,
for instance, that certain peculiarities pass — not from father to
son, or from mother to daughter — but from father to daughter,
and from mother to son. Take the case of intellectual capacity :
it is vulgarly thought that this passes from the mother to the
son rather than from the father. Doubtless, mental ability
often comes through the mother, just as gout may, and sundry
other characters ; but it may also come from the father's
side.

Indeed, this very instance of hereditary ability illustrates
and strengthens the doctrine of sexual heredity. Through
untold ages the mental E of the two sexes has differed. The"
man has had to use his brain the most, and it has been the
fashion to stifle the intellectuality of the woman ; there are,
indeed, many men now-a-days who regard an intellectual
woman with aversion. Hence, the smaller head of the woman
— I speak of averages — and correspondingly smaller mental
capacity. The old-fashioned plan of dwarfing the woman's

* In the " Proceedings of the Zoological Society," December 1886, Mr. Bland
Sutton advances an hypothesis to account for this latency of male sexual
characters in the female. He alludes to the fact that the secondary sexual
characters are chiefly in connection with the skin, and this, no doubt, in the
case of many lower animals, is in a large measure correct. Now, the skin is
developed from the epiblast, and in Mr, Sutton's opinion, founded on observa-
tion, the epiblast is chiefly derived from the male element, the hypoblast and
greater part of the mesoblast from the female. The non-development of those
male (epiblastic) sexual characters in the female is due, according to Mr.
Sutton, to the large demands made upon the rest of the economy, by the female
generative system. This hypothesis affords no explanation of the larger and
more comprehensive problem, " What determines the sexes ? " nor does it
explain how non-sexual characters— altogether independent of the epiblast —
such, for instance, as the deformities I have alluded to, may pass along one
sex only. This latter fact alone is strong evidence against the tenability of
his hypothesis. It, moreover, takes no account of the fact, that the male
contains the potentialities of the female.

THE CAUSATION OF DISEASE. 63

mental and bodily activities, by not allowing her — on the ground
that it is un womanish — to give mind and muscle the full play
they crave, is as foolish as it is cruel. It lays the foundation
of miserable hysterias and dyspepsias, and tends to produce
a narrowness and bigotry of mind which, to a thinking being,
is intolerable. To suppose that a high degree 'of mental
education would injuriously affect the generative system is
fallacious. "Why should it in woman any more than in
man ? It may happen if a delicate girl be subjected to high
mental pressure ; the capacity for nursing children, namely,
or even fertility, may possibly be diminished. But no educa-
tion should be under high mental pressure. All proper mental
education is under no pressure at all. One single important
fact, learnt easily, gains a hold on the mind, and does more
good than 10,000 facts forcibly crammed into the brain. If
the special interest of the pupil be awakened, he or she will
remember the facts taught, even though dull to the very brink
of idiocy ; and if a child cannot understand a thing, how foolish
to attempt to make it ! What terrible piece of blindness, ay,
and oi: cruelty, to teach Euclid and intricate grammar at
so young an age as is the custom. The child is mentally
akin to the savage, in whom the power of abstract thought is
scarcely developed at all, and before this power is evolved
we are attempting to draw upon it — forcing the young mind
as we would a hothouse plant. But the human mind is some-
thing subtler than a vegetable, and will have none of it. No
doubt mental evolution is far more rapid in some than in others,
and the most precocious have all the advantage at school. They
are called sharp and clever, and are made much of, whilst a more
backward playfellow is accounted dull, even perhaps obstinate ;
and in consequence receives sundry cuffs from his master ; and
yet when the angry pedagogue sleeps — forgotten — this dull and
stupid boy is, perhaps, adding a chapter to the history of his
country.

In touching upon the subject of education, I ought, per-
haps, to speak nearer home. What about medical educa-
tion ? I hold it to be equally defective. I do not mean as
regards quantity, but method. Think of the atrocious non-
sense the poor medical student has to get up for physiology —

64 THE CAUSATION OF DISEASE.

the ridiculous theories, which, starting, as he does, in utter
ignorance of the subject, the poor lad is unable "to see in all
their naked absurdity. But what happens ? He acquires a
morbid thirst for them, and while cramming himself with this
trash, he is apt to make one slight error — to entirely lose sight
of the fact that he is supposed to be studying Physiology.
Every principle of physiology, as known and proven, could be
put down within a very narrow compass : I am not talking of
isolated and disconnected facts which, as such, are not embodied
in the science of physiology, but of facts which have been in-
telligibly connected into principles. These main principles
should be taught thoroughly, and nothing else. The student
should know something about blood-pressure, which he does
not, and something about the nervous paths in brain and
cord, of which he is equally ignorant. 'But it may be argued,
and I have no doubt will be, that- this worrying out of
complex theories is good intellectual exercise. Yes, but so is
studying a disease at the bedside ! It is surely more important
to know the treatment of iritis, than the size and weight of a
red corpuscle. Yet the one is as easy to learn as the other. It is
surely more important to know how to treat the alimentary canal
in the child, than to be acquainted with the complex chemistry
of digestion. Yet brand-new practitioners are yearly turned
out by the hundred who know nothing at all about these
subjects. It may be said, " These things can be learned in
practice." But are they always so learned ? Certainly by
some, but not by all ; and, even when thus learned, at
what expense to the patients! Think what great good can
be done by the knowledge of a few simple facts which could
be, but often enough are not, taught at hospitals ; and let us
remember that, as the vessel is launched so will it sail. An
important fact, properly taught, clings to the memory with
wonderful tenacity, and it is surprising what good fruit it will
yield through the course of a long life. Without the know-
ledge of such a fact, a man may go on blundering in ignorance,
for many years, allowing much abateable suffering to go on
unrelieved, or, perhaps, even adding to his patient's misery.
This may very easily be done in some diseases, as, for
example, those of the eye — and behold the strange incon-

THE CAUSATION OF DISEASE. 65

gruity-7-one man inflicting an injury upon another, and demand-
ing a reward in return ! But is the blame of this iniquity to
be laid solely at the door of the practitioner, and are those
who regulate our system of medical education wholly to escape
censure ?

Before I wind up this digression, I cannot resist briefly
alluding to an opinion occasionally expressed — probably by
men chiefly — that woman is a vastly inferior animal to man. I
have heard this conviction stated by a number of men, and
these by no means woman-haters. The whole question turns upon
the meaning of superior and inferior. Inferior as regards what ?
There can be no doubt that man for man, and woman for
woman, men are stronger in muscle and intellect. But muscle
and intellect do not exhaust the capacities of mankind, and it
is incorrect to suppose -that the inferiority of the woman is a
necessary outcome of a uterus, as some seem to think, many hold-
ing that this organ necessarily implies inferiority. No doubt
the uterus indirectly leads to the inferiorities of woman, both
in muscular and intellectual strength, but such differences as
obtain between the two sexes in these respects can veiy largely
be accounted for on the principles of (a) use and disuse, (b) sexual
heredity. Women are intellectually and muscularly weaker
because they use mind and muscles less. So far as the muscular
system is concerned, it is well known that in those countries
where women do manual labour, they can equal or even surpass
the men in strength of muscle. Quite lately a medical journal
recorded the case of a pitbrow woman who wagered that she
would lift as heavy a shovelful of coals as any man in the mine ;
and among many animals the female is the muscular equal of
the male. Indeed, in some cases, the female is infinitely the
stronger, as in a certain kind of spider, which is so much
more powerful than the male, that it is common for many
males to perish in the attempt to effect sexual connection ;
the successful animal owing his success rather to his wariness
in taking the female off her guard than to greater strength of
body. The like is true of intellectual capacity. So far as I
know, there is no proof that this is greater in the male sex
among the lower animals, and there appears to be no reason
why the generative organs in the woman should make a

F

66 THE CAUSATION OF DISEASE.

greater demand upon the rest of the body than an excessive
muscular system in the man.

Woman will always be more emotional than man. The
emotions are grounded on the feelings, or, to speak more pre-
cisely, on the sensations,* and these latter originate in impres-
sions made upon peripheral nerve- terminations. Let c (Fig. 3)

Fig. 3.

filtl ^"'~ Sensory centre.

O Sensory nerve.

— O. Sensory nerve-ending.

be a cortical sensory centre ; 5, its sensory nerve ; a, the peri-
pheral nerve-termination. An impression upon a causes a nerve
impulse to pass up &, and this striking upon c brings about a
series of molecular changes. The " material conditions " of c
represent the physical side of a sensation, and, so far as it is
possible to define the cause of a sensation, they are the cause
of such sensation. What may be the exact connection between
the material conditions, as represented by c, and the resulting
mental state, it is not for us here to inquire. It is enough to
state the simple fact that the peculiar material state of c is
accompanied by the mental state. This is the " explanation "
of all sensations : a is, as it were, the keyboard, c the pipe
(or series of pipes) of an organ. An impression upon the key-
note calls forth sound from the pipe, just as an impression upon
a sensory nerve-termination calls forth sensation from its sensory
centre. The animal body contains myriads of such sensory
peripheral nerve-endings, and corresponding cortical centres.
Impulses are continually streaming up these sensory nerves

* The feelings include the simple sensations, and the emotions. These latter
are founded upon the sensations, more especially the organic sensations.

THE CAUSATION' OF DISEASE.

67

to the cortical centres, and thus striking, as it were, a volu-
minous chord of feeling (see Fig. 4). It is this which gives

Fig. 4.

V Cortical sensory
\^ centres, ana-
logous to the
organ pipes.

- Peripheral expansions of the
sensory nerves, analogous
to the keyboard of the
organ.

Diagram showing the different sensory system. To the right are
the intellectual senses in the order of their intellectual value.
These all give information of the outer world. The muscular
sense occupies a peculiar and independent position. To the left
are the organic sense-systems.

rise to the sense of existence — to the feeling " I am" The
sensations of sight and hearing, and, in a lesser degree, of
taste, are essentially the intellectual sensations, those, namely,
which give us accurate information of the world without, which
we can remember best, and between minute differences in which
we can discriminate most accurately. The organic sensations of
the muscles,* viscera, and, to a large degree, of touch, are more
voluminous ; our memory of them is also less ; we have, further,
only a small power of discriminating between minute shades of
difference in these sensations, and (excepting touch sensations)
they give us no information concerning the outer world. It is
on these voluminous and n on- intellectual sensations that the
emotions are grounded. The accompanying diagrams are in-
tended to show the mode in which sensations are produced.

* These must be carefully distinguished from the " muscular sense " or power
of estimating the degree of muscular contraction. This plays a very important
part in intellectual processes.

F 2

68 THE CAUSATION OF DISEASE.

Among the different sensory systems (of stomach, lungs, heart,
reproductive organs, &c, see Fig. 4) which take part in the

Fig. 5.

^yf\^^xJl'\ """"x. \, Posterior part of the corona

A '/T\ >^V \"\ ^\\ radiata containing sen-

rx. \ \ I \ \ sory fi^res-

'? XSy-~*^ y^\ /_/ Posterior third of posterior

limb of the internal cap-
sule.
— - Crus.

-- Pons.

Medulla,
nerve.

-Spinal cord.

Diagram showing the sensory system of nerves passing up towards
and terminating in the cortex.

production of the non-intellectual sensations, the reproductory
is certainly second to none. Indeed, it very probably stands

Sight sensory ganglion.

Fig. 6.

Ether waves passing on to pupil.

Luminous object
whence ether

Eiagram showing how the sight sensory system is thrown into
activity by ether waves.

first during the period of reproductive life. It is well known
that at the time of puberty a marked change comes over the

THE CAUSATION OF DISEASE.

69

Fig. 7.

Diagram similar to the last.

JO THE CAUSATION OF DISEASE.

feelings. This is especially marked in the girl. With the
development of ovaries, uterus, and mammas, an extensive and
highly irritable sensory surface is added to the nervous system,
and a corresponding development occurs in the sensory cortex.
A new keyboard and a fresh series of pipes have been added to the
instrument ; consequently additional chords can now be struck,
and effects produced which were before impossible.

The reproductive system is far more extensive in the female
than in the male, for not only has the woman to prepare the
ovum — an effort which in itself involves far more sensory dis-
turbance than the manufacture and discharge of semen (which
practically sums up man's share in the reproductive process),
as is evidenced by the wide and varied sensations which are
apt to accompany menstruation — but she has also to support- the
child nine months within her body ; and for the same, or even
longer, period of extra-uterine life. The effect of pregnancy and
parturition on the feelings is even observed in many of the
lower animals.

Wherefore it is obvious that woman must have more feeling
than man, and must needs be more emotional. It is also mani-
fest that the sexual calls upon the woman must necessarily
handicap her in the intellectual race. If a woman does not
marry she will be capable of greater intellectual exertion than
if she does, and the brain will grow accordingly ; but this will
not affect future generations. We must, therefore, conclude
that mental differences will ever exist between the sexes.

The intellectual difference is, I repeat, solely due to disuse. I
cannot believe, as some do, that high intellectual development in
woman is incompatible with proper child-bearing. If we can
adduce one single example of a highly intellectual woman who
has healthily reared children, such a case once and for all puts
this question at rest. I doubt not many such could be given.
That of Mary Somerville at once occurs to me. If there is one
department of mental activity which, above all others, requires
sheer intellect, it is surely mathematics. Now, Mary Somer-
ville was one of the greatest mathematicians our country has
produced ; but she was also a woman of essentially feminine
parts, and the devoted mother of several healthy children.

One proof of the necessary and a priori inferiority of the

THE CAUSATION OF DISEASE. 7 1

woman's mind lies, it has been argued, in the fact that few
women excel in the arts : music, poetry, painting. Surely,
it is said, woman ought to excel in these, since they rest so
largely on the feelings, and the fact that she does not shows
conclusively that she is necessarily inferior in mind. It is
perfectly true that we have no woman Shakspeare, "Mozart, or
Raphael ; but to suppose that such men succeed without in-
tellect is to show a complete ignorance of the meaning of the
word. No man can be great as these men were without
colossal intellect. Hear what Carlyle says on this head : —

" Hero, Prophet, Poet, — many different names in different times
and places do we give to Great Men ; according to the varieties we
note in them, according to the sphere in which they have displayed
themselves ! . . . . The Hero can be Poet, Prophet, King, Priest, or
what you will, according to the kind of world he find himself born
into. I confess I have no notion of a truly great man that could not
be all sorts of men. The Poet who could merely sit on a chair and
compose stanzas, would never make a stanza worth much. He could
not sing the heroic warrior unless he himself were at least a Heroic
warrior too. I fancy there is in him the Politician, the Thinker,
Legislator, Philosopher ; — in one or the other degree he could have
been all these, he is all, all ... . Napoleon has words within
him that are like Austerlitz Battles. Louis Fourteenth's Marshals
are a kind of poetical men withal ; the things Turenne says are full
of sagacity and geniality; like sayings of Samuel Johnson. The
great heart, the clear deep-seeing eye : there it lies ; no man what-
ever, in what province soever, can prosper at all without these.
Petrarch and Boccaccio did diplomatic messages, it seems, quite well :
one can easily believe it ; they had done things a little harder than
these ! Burns, a gifted song-writer, might have made a still better
Mirabeau. Shakespeare, — one knows not what he could not have
made, in the supreme degree.

" True, there are aptitudes of Nature too. Nature does not make
all great men, more than all other men in the self-same mould.
Varieties of aptitude doubtless ; but infinitely more of circumstance

( = E) Given your Hero, is he to become Conqueror, King,

Poet?" &c. &c.

In considering the differences, mental and physical, between
the two sexes — and a knowledge of such difference is very

72 THE CAUSATION OF DISEASE.

necessary to the medical man — we must ever keep clearly in
mind this doctrine of sexual heredity. This principle shows us
that many of the differences between the sexes depend upon
use and disuse, and are not necessary differences. Hence it
would be possible to cancel, to a greater or less extent, many
of the sexual differences ; the exceedingly irritable nervous
system of woman, for instance, might be rendered more stable
by judicious bringing-up during many successive generations.

George Eliot recognized the principle of sexual heredity, —
the fact that a peculiarity passes potentially through the sex in
which it does not appear ; for in " Middlemarch" she makes
Mr. Brooke say : " I had it myself — that love of knowledge ....
though that sort of thing does not often run in the female line ;
or it runs underground, like the rivers in Greece — it comes out
in the sons."

Although the characters acquired by one sex tend in the
offspring to appear more especially in the same sex, we should
err in concluding that the other sex is wholly unaffected.
Were such the case, the daughters of a man who had per-
sistently, from youth upward, abused his health, would in no
wise suffer from the father's transgressions. Whether, how-
ever, in such cases of parental transgression the male offspring
necessarily suffer most, I cannot say, but the question is cer-
tainly worthy of investigation.

Are there any special conditions favourable to the strict
limitation to one sex of an inherited structural peculiarity ?
We have already seen that one necessary condition is the
acquisition of the peculiarity during the period of sexual life.
A further favourable circumstance is the operation during many
generations upon one sex only of the E tending to produce the
peculiarity. Finally, I think it probable that when the tissue
specifically acted upon is more or less limited, the resulting
change is more apt to be confined to the sex in which it is
acquired — one would expect, namely, that a strictly local modi-
fication of tissue (although this must to some extent modify
other tissues by altering the E) would be more apt to be
sexually limited than one more general.

This view may be rendered clearer by stating the converse case.
When the entire organism is affected for good or evil, one would
expect the good or evil effect to be more impartially inherited

THE CAUSATION OF DISEASE J I

by the two sexes than when the acquired structural change is
strictly local. In such a disease as chronic gout, one would
therefore expect the female progeny to be more or less affected,
because, although two of the above conditions are fulfilled —
namely, (i) the operation of the specific E upon one sex for
many generations, (2) its operation during the sexual period of
life — nevertheless the third condition is absent — to wit, strict
localization of the acquired structural change ; for in chronic
gout, although the primarily erring tissue may be strictly local,
the tissues are more or less universally depraved. But if we
suppose a gout-producing E to affect a limited set of tissues in
the male throughout countless generations without causing any
general depravity of health — which, however, is impossible —
we might predict, with a fair measure of certainty, that the
affection would appear chiefly, if not solely, in the males — the
female line escaping. In a similar way the antlers of the stag
have been acquired ; but it is worthy of note that rudimentary
antlers also appear in the female, showing that the hereditary
transmission is not entirely confined to the one sexual line.

Wherefore the doctrine of sexual heredity may be thus
enunciated : the more exclusively a specific E acts upon one sex,
the greater the number of generations acted upon, and the more
limited the affected tissue, the more apt is the resulting variation
to pick out that one sex in the offspring. Moreover, a character
is more apt to be transmitted along one sex when it is acquired
during the period of sexual activity, and it is probably more apt
to attach itself to the male than to the female sex. Nevertheless,
in all cases there is a tendency for the opposite sex to be affected.

From the above observations on sexual heredity, it is mani-
fest that sex influences structure. It may thus be a predis-
posing cause of disease. Sex may further predispose to disease
in so far as it determines occupation, and therefore the ex-
ternal-body-E, mental and physical.

The influence of sex in determining the heredity of par-
ticular diseases is a subject still requiring careful investigation.
Patient and laborious statistical work is needed to clear up
many points on which we are still ignorant. Meanwhile, how-
ever, much error may be averted by keeping this principle of
sexual heredity clearly before us. Ignorance of it is continually
leading to wrong conclusions.

CHAPTER X.

Heredity (continued') — The Principle of Structural Mean — Pre-potency —
Physiological and Pathological Blendings.

The Principle of Structural Mean. — This has already
been denned. Inasmuch as two individuals are engaged in
the reproductive process, the offspring cannot be exactly like
either of them, but must, on the contrary, be some sort of
mean between the two. There is probably an ideal or standard
mean which they all tend to approach, but this is subject of
course to such differences as depend upon the principle of
sexual heredity, so that the case will be more accurately put
thus: The male offspring all tend toward a certain fixed standard,
the female offspring to a certain other fixed standard.

Whatever differences occur between brothers on the one hand,
and sisters on the other, are due to differences of the E, which, as
we shall see, has a considerable power in altering S. This will be
more particularly shown in treating of E as a power capable of
modifying structure, and wre shall then be the better able to
understand how utterly impossible it is for the E to be anything
like the same in any two cases. Such differences in E must
inevitably cause corresponding differences among the brothers
on the one hand, and among the sisters on the other. The
only point about which there can be any doubt is whether this
is the sole cause of the difference. I contend that it is.

It will be observed that the above hypothesis assumes an
ideal, standard E. It is- obviously impossible to scientifically
define such an ideal ; but in reality all that is necessary is to
assume one. The hypothesis is rendered sufficiently clear by
the statement that all the male progeny on the one hand, and all
the female on the other, would be exactly alike under the same E.

It must not be thought that the structural mean of which I
am speaking is an exact mean of the two parental structures.

THE CAUSATION OF DISEASE. 75

It often happens that there is a " pre-potency " of some charac-
teristic or characteristics of one of the parents in the offspring,

"When individuals belonging to the same family, but distinct
enough to be recognized, or when two well-marked races, or two
species are crossed,, the usual result .... is, that the offspring in the
first generation are intermediate between the two parents, or resemble
one parent in one part and the other parent in another part. But
this is by no means the invariable rule; for in many cases it is
found that certain individuals, races, and species, are preponent in

transmitting their likeness It would appear that in certain

families some one ancestor, and after him others of the same family,
have had great power in transmitting their likeness through the
male line; for we cannot otherwise understand how the same features
should so often be transmitted after marriages with many females, as
in the case of the Austrian emperors ; and so it was, according to
Niebuhr, with the mental qualities of certain Roman families. The
famous bull, Favourite, is believed to have had a preponent influence
on the short-horned race. It has also been observed with English
race-horses, that certain mares have generally transmitted their own
character, whilst other mares of equally pure blood have allowed
the character of the sire to prevail. A famous black greyhound,
Bedlamite, as I hear from Mr. C. M. Brown, ' invariably got all his
puppies black, no matter what was the cr.1 our of the bitch ; ' but then
Bedlamite has a preponderance of black in his blood, both on the
sire and dam's side." — Variation under Domestication, vol. ii. p. 40.

Again, Quatrefages writes : —

"After having attributed a prepondering action to the
mother, Nott declares with surprise that in point of intelligence
the mulatto (negro and white) approaches in character to his
white father." * He goes on to observe that Lislet Geoffrey,
though entirely a negro physically, was in character and in-
telligence entirely a white.

The above quotations on pre-potency seem to invalidate my
remarks on the structural mean. Be it noted, however, I am
careful to say a certain mean, and not the exact mean. From
the time the ovum and spermatozoon meet, until development is
complete, or perhaps even later than this, there is a struggle
between two tendencies : the tendencies of the ovum will gain

* International Science Series, Quatrefages, p. 268.

7 6 THE CAUSATION OF DISEASE.

the upper hand in some respects ; those of the male element in
others : the final result being a structural product which is a cer-
tain mean between the two. I am contending that this particu-
lar mean, whether it takes chiefly after the male or the female
parent, would not be departed from if the E were in each case
the same. What it is that specially determines this u pre-
potency " is a difficult matter to decide, but I shall return to
this question presently.*

The principle of structural mean applies equally, of course,
to normal and abnormal structures, and has therefore an im-
portant bearing upon disease, for it opens up the question :
what will be the effect upon the offspring of the union of a
healthy with an unhealthy individual, or the union of two un-
healthy individuals, having either the same or different diseases
or disease tendencies ? And this leads us to the interesting
subject of hybridization or mongrelization of disease.

Viewed from the pathological standpoint, these blendings fall
under three heads : —

1. Physiological blendings.

2. The blending of normal with abnormal.

3. The blending of abnormal with abnormal.

1 and 3 admit of subdivision into three classes. I should
observe, however, that such division, though logical, is perhaps
too mechanical to serve a practical purpose. We may, neverthe-
less, I think, adopt it provisionally. These subdivisions are —

a. Blendings of the same peculiarities of the same tissue.

b. Blending of different peculiarities of the same tissue.

c. Blending of different peculiarities of different tissues.
Thus—

la. Here the blending characters are normal, of the same
kind, and affect the same tissue. Thus, father and
mother may have great strength of limb, strong diges-
tion, genius for music or art.

lb. The blending characters are normal, affect the same
tissues, but are of unlike kind. Father has taste for
poetry, mother for mathematics. Father large hands,
mother small hands.

ic. The blending characters are normal, but unlike, and
* Vide Chapters XI. and XII.

THE CAUSATION OF DISEASE. 7 7

affect different tissues. Father remarkable for mus-
cular strength, mother for intellect. In one sense
this comes under the last head (lb), for there is a
blending of remarkable with ordinary muscular
strength, and a blending of remarkable with ordinary
intellectual powers.
2b. One of the blending characters is -normal, the other
abnormal, and they affect the same tissue. The
mother is emmetropic, the father hypermetropic. All
abnormal blendings resulting from the union of a
healthy with an unhealthy parent are of this kind.
yi. The blending characters are abnormal, of the same kind,
and involve the same tissues. The father and mother
are gouty, rheumatic, neurotic, or what not.
3&. The blendings are abnormal, affect the same tissue, but
are of unlike kind. Thus the father is myopic, the
mother hypermetropic. The father suffers from a ten-
dency to eczema, the mother to psoriasis. In such a
case one would theoretically expect a hybrid or mongrel
disease to result.
3c. The blending characters are abnormal, but unlike, and
affect different tissues. Thus the father is gouty, the
mother epileptic — the father rheumatic, the mother
phthisical. Here, again, the possibility of hybridiza-
tion arises.
It will be necessary now to consider these classes more in
detail.

1 a. Like physiological blending of the same tissue. — Here, of
course, the offspring will tend to inherit the peculiarity in
undiminished vigour — as when, for instance, both sides of the
house are remarkable for strength of muscle. In such a case
there is no reason why the offspring should be muscularly
weaker than the parents ; nor is there any reason why they
should be stronger — why, namely, there should be any intensi-
fication of the peculiarity, although one is rather apt to assume
such an intensification.

lb. The blending of unlike normal characters affecting the
same tissue. — If each parent present a different physiological
peculiarity of the same tissue, one would expect the blending

7§ THE CAUSATION OF DISEASE.

of them to give a more or less exact mean ; but here the com-
plicated question of pre-potency comes in. If the father's
nose be aquiline, that of the mother being retroussee, one
would rather expect the nose in the offspring to be some
sort of mongrelized product of the two. But this is not neces-
sarily the case : either kind of nose may be inherited un-
changed. It is well known, as already mentioned, how tena-
ciously an aquiline nose will cling to a family. Why such' a
character should be pre-potent it is difficult to say. Possibly
one element in causation may be the ancestral age of the pre-
potent character. One would expect a character which had
constantly belonged to a race for many generations to have a
greater propagating power than one recently acquired. I

"imagine, for instance, that in the mulatto (half white and
half negro) the flattened nose of the negro, which has belonged
to the race for thousands of generations, would gain the
ascendency. I only mention this influence of ancestral age as
one possible element in the causation of pre-potency.

It sometimes happens, however, that unlike Mendings of
the same tissue give a compound quite unlike the two elements,
just as the compound of two chemical elements may be quite
unlike either of them. "Who can say, for instance, what will be
the exact result of two peculiar mental blendings ; the diversity
among mental characters is so enormous, and the nature of the
acting forces so subtle, that we can well understand how their
several blendings may yield mental traits whose parentage we

.are quite unable to trace. The like is true of other proper-
ties. Now, in such cases it may be said that the product
is not inherited ; nor is it in the sense that the same peculiarity
is inherited, bat strictly speaking it is inherited, inasmuch as
each element is derived from the parents.

The coming together of unlike physiological characters of the
same tissue may give a curious result — one which is in no sense

.a blending — and may similarly lead us to suppose that the char-
acter resulting from their union is not inherited, though such is
actually the case. If, namely, the two characters be of recent
ancestral acquisition, it may happen that they are dropped in the
offspring, which lapses to a status quo ante the acquisition of

. these characters. This reversion, for such it is, does not occur

THE CAUSATION OF DISEASE. ?g

if the characters are in the same direction, but only when
they are unlike. These unlike characters refuse to combine,
and the offspring inherits a structural condition belonging to
an ancestral period antecedent to the acquisition of such char-
acter. This subject will be considered again hereafter.

These considerations show how difficult it is to foretell what
will be the result of the union of unlike physiological characters.
For, first, one of the combining elements may be pre-potent ;
or the two may fuse into a more or less exact mechanical mean
(as in the case of features, size, &c.) ; or again, the resulting
compound may be unlike either component element; finally,
the two characters may refuse to blend altogether, both dis-
appearing, and revealing a character of earlier ancestral date.

It will be long before we can lay down precise rules
which shall enable us to predict the effect upon the offspring of
different parental unions. This could only be done by observ-
ing the actual results of different unions. We should
probably, however, be for the most part correct in predicting
pre-potency of a character in those cases where its ancestral
age is much greater than that of the other blending element ;
and, on the other hand, a total disappearance of each character,
with reversion, where both are of recent ancestral origin and
divergent nature. Little more can be said in the shape of
general statements.

ic. The blending characters are normal, and belong to
different tissues. This, strictly speaking, falls under the last
head, and therefore needs no further consideration.

In regard to the blending of unlike physiological characters,
an interesting question arises — viz., Is it possible for two
physiological bl endings to lead to a pathological result?
Suppose A. and B. to be healthy men, and C. a healthy
woman. Is it possible that while the children of A. and C.
are healthy, those born of C. by B. shall (cwleribus paribus)
be unhealthy ? This may seem an astounding question, but
it is one deserving our serious thought. In a healthy
organism there is, in the language of Spencer, equilibrium
between the inner and outer relations. The living organism
is what he would call a moving equilibrium — that is to say,
it consists of an inconceivably complex array of forces, which

So THE CAUSATION OF DISEASE.

are able to keep in equilibrium with the forces of the outer
world as represented by E. When such perfect equilibrium
obtains, the organism is said to be perfectly adapted to its E.
And if any marked alteration in the E occurs, this has to be
met by a modification in the distribution of the bodily forces,
by a process of adaptation, as it is called. Now, although
each individual parent may be in perfect equilibrium with his
or her respective E, it is quite possible that the mean struc-
tural product of the two shall be in no such perfect equili-
brium with its E. Herbert Spencer, so far as I know, does not
consider the possibility of disease thus resulting, being content
to deal with generalities. Nevertheless, there is no doubt
that some forms of disease may thus result. Let us see how.

It is a well-known fact that crossing is a cause of varia-
bility.* And, as might be expected, the variations thus
resulting may be ill adapted to the E, and in this way pre-
dispose to disease ; in some cases they may appear as actual
disease, for, as we shall presently see, these new characters
may be simple reversions, and such reversions, though nor-
mal in the remote ancestors from whom they are derived,
may be entirely abnormal in their remote progeny. A
branchial cleft, for example, though normal in a fish, would
be totally abnormal during the post-partem life of a mammal.
The crossing referred to is one between distinct varieties ; but
inasmuch as all human beings differ from one another, and
some far more than others, it may occasionally happen that
father and mother exhibit, in some particular, a great differ-
ence, so that their union may be, in respect to the particulars
wherein they differ, more or less a cross, leading to a reversion,
perhaps not to a very remote ancestral state, but to a condition
of body entirely out of harmony with the existing civilized E.

But setting aside the question of reversion, it is quite possible
that a considerable variation may arise from such a union, for it
appears certain that " quite new characters" may result from
crossing. " The common opinion of floriculturists proves that the
crossing and recrossing of distinct but allied plants .... induces
excessive variability, having the appearance of quite new charac-
ters " (that is, not mere reversions). Now, are we justified in
* Vide Darwin, " Variation under Domestication," pp. 252-255.

THE CAUSATION OF DISEASE. 8 1

assuming that the variations resulting from such crossings
shall be always physiological ? It may be thought that it
is incorrect to speak of "crossings" between the members of
the human race, seeing that the term "crossing" refers to
the union of separate varieties; but, be it noted, there is no
strict difference between varieties of the same ..species and
between individuals of the same variety, seeing that no two
beings are exact alike, and that beings apparently very much
alike may in some one particular be very much unlike, so
that the union of two such individuals may be regarded as a
cross in respect of that particular. In this sense, crosses are
continually occurring among us. I do not assume that the
hypothetical variations thus resulting will consist in such
typical pathological states as gout or rheumatism, which have,
for the most part, a known etiology, but I venture to suggest
that certain anomalous states of the body may thus occa-
sionally arise, and perhaps a condition of body rendering it
especially prone to disease — rendering it, namely, very apt to
respond pathologically to certain Environments.

2 . The Mending of normal with abnormal, — In this case the
result is, as we should expect, a considerable diminution of
the abnormality. If the normal parent be especially sound and
strong in that point wherein the other fails, we might expect
a good result, as when a man of strong and vigorous nervous
system, digestion, or what not, marries a woman possessing the
reverse. But the result may depend upon subtler conditions
than we can always analyse. Sometimes the union of normal
with abnormal may result in the complete annihilation of the
abnormality, on the principle of reversion by crossing already
alluded to.

We now have to consider the blending of abnormal with
abnormal.

3«. The abnormalities are of the same kind and affect the
same tissue. — Thus, the father and mother are, let us say, both
neurotic, rheumatic, or phthisical. In such cases there will
be a very strong tendency in the offspring to inherit the dis-
order. We have no right to assume that there will be an exag-
geration of the pathological state, but we should scarcely
expect a diminution of it. Nevertheless, if both parents

G

$2 THE CAUSATION OF DISEASE.

be strongly saturated with the same disease-tendency, it is
rare to find all the children inheriting it. There seems,
indeed, to be a great tendency in Nature to right herself in
the offspring, if she be allowed a fair chance — if the offspring,
namely, follow a hygienic mode of life.- We shall presently
see that this is due to the fact that diseases having for the
most part a recent ancestral origin tend, like all recently
acquired characters, to disappear in the offspring, not yet
having attained a sufficiently strong hold upon the race to
ensure their continued inheritance. But this tendency to
revert to a pre-pathologic state will of course be far greater
when only one parent is diseased (as in 2). Indeed, in such
cases it will often be very strong ; for, as already observed,
if one parent be especially vigorous in that particular wherein
the other fails, the two may be regarded as a cross in respect
of that particular, and hence there may be. a reversion to the
pre-pathologic state — namely, health.

Some of the evil resulting from consanguineous marriages is
due to the blendings now under consideration — namely, of like
abnormalities of lika tissues, for the same morbid tendencies
are apt to exist in parents of near blood, as rheumatism, gout,
phthisis. In regard to consanguineous marriages Darwin
says :* " Whether consanguineous marriages, such as are
permitted in civilized nations, and which would not be con-
sidered as close inter-breeding in the case of our domesticated
animals, cause any injury, will never be known with certainty
until a census be taken with this object in view. My son,
George Darwin, has done what is possible at present by a
statistical investigation, and he has come to the conclusion,
from his own researches and those of Dr. Mitchell, that the
evidence as to any evil thus caused is conflicting, but, on
the whole, points to the evil being very small." But of
course the result will differ vastly according to the health -value
of the intermarrying family. If both parents, no matter how
closely related, be perfectly healthy, so also will be their
offspring. History tells us that consanguineous marriages
were once the custom among certain peoples, and that such
unions were attended with the happiest results as regards

* " Variation under Domestication," vol. ii. p. 104.

THE CAUSATION OF DISEASE. 83

the offspring. We have distinct evidence that marriage of
brother and sister, uncle and niece, nephew and aunt — nay,
even of father and daughter, mother and son — has been
countenanced by law.# Nevertheless, although no ill effect
may be noticed during- the first few generations, long- continued
intermarriage has, there can be no doubt, an injurious effect
upon a race, and it may be positively asserted that it is a
" great law of Nature " that individuals- of distant relationship
should occasionally come into union.

3 b and c. Abnormal blending of unlike hinds. — The two
abnormal characters may remain distinct, as when a man in-
herits gout from his father's side and phthisis from the maternal
line ; or possibly, in some rare cases, the two may blend into a
hybrid, when we should have a true " intermarriage of disease. "•
Rheumatoid arthritis, or " rheumatic gout,*' has been thought
to be a hybrid of gout and rheumatism, though, as Garrod has
shown, these two diseases are perfectly distinct. I can think of
no examples of such mongrel diseases worth mentioning, but
it seems to me quite certain that many disorders must be of
mongrel origin; for disease-tendencies are nothing else than
peculiar structural states, and if normal structural states are
capable of blending, the like must surely be true of abnormal
ones. When we reflect upon the mongrelization of dis-
eases which must be thus perpetually going on, we can under-
stand how intricately compounded many diseases must be.
This consideration alone should warn us against regarding all
diseases as specific and unchangeable. We shall, however, in
due course, meet with other evidence which will show the
absurdity of such a supposition.

In treating of this subject of Mendings, I have somewhat
mechanically dissected the body into different elements or
systems, and have considered the bl endings of such individual
systems as though they were so many independent units ; but
we know, as a matter of fact, that each part of the body
works in harmony with all the others, and that the several parts
are capable of influencing one another in many mentally dis-
entangleable ways. Wherefore the blendings can only in rare
instances be localized in their effects.

* Vide Huth on " Intermarriage of Near Kin."

G 2

CHAPTER XL

Heredity (continued*)— The Fixity of Structural Characters in Inverse Propor-
tion to their Age, Ancestral or Individual — All Diseases of Recent Ancestral
Date — The Vis Medicatrix Naturae — The Tendency of Recently Acquired
Characters to Disappear under Ancestral Forms of Environment.

The Fixity or Stability of Structural Peculiarities. —

All living organisms tend to vary — that is to say, to take
on new characters from generation to generation. In this
way, structural peculiarities are continually being acquired and
thrown off again. This is true whether we regard many
generations of a successive species or a single individual. As.
regards the former, we find structural characters which have
belonged to a species during thousands of generations gradually
disappearing as the environment of the organism alters ; and,,
as regards the individual, we shall find that structural pecu-
liarities acquired by the individual himself may similarly be-
dropped, — such, for instance, as habits (which are nothing else
than the functional manifestations of structural acquisitions)
and pathological states of the tissues — namely, disease ; and
further, that under disease racial characters are apt to dis-
appear.

Now, the fixity of such structural peculiarities, be they racial
or individual, depends in large measure upon their age, ances-
tral and individual. Those structural peculiarities which are of
greatest age are generally the most fixed and stable ; on the other
hand, those last acquired are usually the most unstable — most apt
to disappear. Speaking of the race as a whole, the age of a
structural peculiarity is measured by the number of successive
generations in which it has occurred : the greater this number^
the more tenacious is the structural character in question ;.
while as regards characters acquired by the individual himself,
those are the most fixed which he acquired earliest. Concerning;

THE CAUSATION OF DISEASE. 85

the fixity of what we may term racial, as distinguished from
individual, peculiarities, this does not, perhaps, altogether result
from the mere fact that a peculiarity has been repeated during
many generations. This repetition may not be the cause, but
the result, of a fixedness which is independent of repetition ;
for many species have, on domestication, more or less readily
lost characters which they retained during countless ages in the
wild state; and, in many cases, at all events, there "does not
appear to be any relation between the force with which a char-
acter has been transmitted and the length of time during which
it has been transmitted." * Nevertheless, although certain
characters of great ancestral age readily disappear under an
altered environment, we shall find the principle above enunciated
to be on the whole a safe one. Darwin thus expresses his
conclusion upon this head : " Notwithstanding these considera-
tions, it would perhaps be rash to deny that characters become
more strongly fixed the longer they are transmitted ; but I believe
that the proposition resolves itself into this, — that characters of
all kinds, whether new or old, tend to be inherited, and that
those which have already withstood all counteracting influences
and been truly transmitted, will, as a general rule, continue to
withstand them, and consequently be faithfully transmitted." f

A consideration of the embryonic changes would appear
to afford a proof that repetition does actually fix a character.
The early developmental changes of the embryo date back
through millions of generations, and by incessant repetition
have become rigidly fixed. In this way many remote ances-
tral characters, such as the branchial clefts, appear. It is true
they soon vanish, but they are nevertheless fixed in the race,
for they have in this way appeared during untold generations,
and probably will continue to do so as long as man exists. But
although many remote ancestral characters are thus retained,
how great is the number that have been dropped ! Charac-
ters which have been present during hundreds and thousands,
nay, perhaps, even millions of generations, alike with such as
have lasted for a few generations only, have thus been gra-
dually lost, as the organism has become moulded to an ever-

* "Variation under Domestication," vol. ii. p. 38.
•f Ibid., vol. ii. p. 39.

$6

THE CAUSATION OF DISEASE.

changing environment, while other characters, which have
remained structurally active during yet longer periods, have,
by their tremendous repetition, become so fixedly organized in
the great vital rhythm that they even now have a transient
existence in the embryo. The accompanying diagram is in-
tended to represent the mode in which characters are acquired
and dropped again in the progress of organic evolution, also
the ancestral age of different characters : —

Fig. 8.

Characters acquired during the
post -anthropoidal stage.

Characters acquired during the

anthropoidal stage.
Do. during primitive mammalian

stage.
Do. during amphibian stage.
Do. during pre-vertebral and

piscian stage.

Amphibian.

Primitive mammal.

Anthropoid.

Diagram representing the Evolution of Man.

Evolution starts at x. The vertical lines, A, B, c, D, repre-
sent the developmental processes of man's ancestry at the
following stages : — A, the primitive fish stage ; B, the amphi-
bian stage ; c, the stage of the primitive mammal ; D, the
anthropoidal stage. The vertical line, E, represents the develop-
mental processes of man himself. In all these cases the embryo-
logical processes are supposed to start from the centre of the
vertical lines and to spread outwards. The horizontal shaded
portions indicate the ancestral age of man's several structural
characteristics. Thus, fixing the mind upon the vertical line,
E, and remembering that development is supposed to start from
the centre, we find the most early structural manifestations
of the embryo to be of oldest date. These characters were
acquired during the invertebrate and piscian stage of man's

THE CAUSATION OF DISEASF. 87

ancestry.* They are represented by the central darkly shaded
portion, d. The human embryo then takes on structural cha-
racters which were acquired during the amphibian stage. These
are represented by the shaded portion, c. It then assumes
characters acquired during the primitive mammalian stage, as
represented by b, and so on. The unshaded parts of the
diagram represent characters which belonged to the different
ancestors of man, but which no longer appear in the human
cycle, f

It will be convenient, while treating of this subject of
structural stability or fixity, to consider, first, the tendency
of structural characters, actually possessed by the individual,
to disappear in the inverse order of their age — a, ancestral,
or &, individual ; and, secondly, the tendency of structural
characters, of recent ancestral date, and possessed by either or
both parents, not to appear in the offspring — this tendency
being in proportion to the ancestral youth of the structural
character.

We may accordingly frame the following propositions : —
la. Characters which the individual possesses by virtue of
heredity, tend, under disturbing influences, to disappear in the

* The line from X to A should be very much longer than here represented ;
for the distance in point of time between X and A is infinitely greater than
that between A and E.

f It must be borne in mind that the various changes which take place in
development (ontogeny), are not an exact epitome of the several ancestral
forms of life, for not only have numberless ancestral characters been dropped
as indicated in the above diagram, but there is an actual vitiation in the pro-
cess of development, so that it no longer gives us a perfect ancestral history
of the organism. So far as the process of embryological development is an
exact reproduction of ancestral life, it is termed by Haeckel, Palingenesis, or
inherited history (7raXt^= reproduced). So far as it is not such an exact re-
production, he terms it Kenogenesis = vitiated history, (icevos = strange,
meaningless). This aberration of development, as we may in a manner term
it, has reference («) to the period at which the different organs appear, some
developing sooner, and others later, than in the ancestral forms of life ; thus, in
man there is an acceleration in the appearance of the gill openings, of the
brain and eyes ; and it has reference (b) to position — i.e. , an organ may develop
from a different tissue from that in which it originally developed. Thus, the
sexual organs — both male and female— in man originate from the mesoblast,
while in the lower animals the male sexual organs originate from the epiblast ;
the female from the hypoblast. It would appear that in such cases certain
embryo cells have migrated from one germ-layer to another. (See, on this sub-
ject, " The Evolution of Man," by Ernest Haeckel, vol. i. p. 10, London, 1879.)

8-8 THE CAUSATION OF DISEASE.

inverse order of their ancestral age — that is to say, of their
evolution.

This truth is particularly well shown under the disturbing
influences of disease. It is further exemplified in the gradual
dissolution of old age.

lb. Characters acquired by the individual himself tend, under
disturbing influences, to disappear in the inverse order of their
acquisition.

This truth also is well exemplified in disease and old age.

II. The tendency of parental characters not to appear in the
offspring is in inverse proportion to their ancestral age.

Let us now consider each of these propositions separately.

la. The instability of characters which are of recent ancestral
date is well known to all biologists, and examples of it abound
in the animal and vegetable kingdoms. The tendency of the
moral nature to disappear before the other parts of the mind,
under the disturbing influence of disease, or even of excite-
ment, affords a familiar example of its truth. The advent
of insanity, for instance, is generally heralded by an upset of
the moral faculty ; in other words, that mental ingredient
which was last acquired is the first to go, the other parts of the
mental organism being successively disorganized as the morbid
process deepens. We have only to look around to have most
painfully impressed upon us how slack is the hold of morality
upon the multitude under certain disturbing influences. Let
us take, for instance, the recent execution of the criminal,
Pranzini, in Paris. The following I give from memory, but it
fairly tallies with the description I read of it : —

"For several nights before the execution a huge multitude col-
lected about the prison in the greedy expectation of seeing him
guillotined. All classes of society were there, from the wealthy
in their chariots to the most degraded portion of the populace.
On these nights the crowd amused itself by singing filthy
songs, having for their theme the poor wretch who was about
to be hurried into eternity. At last the fatal night arrived, and
in the first hours of the morning the victim was aroused from
a deep sleep, and led pinioned through the gloating and
screaming throng to his place of execution. When the knife
had severed the head, the blood gushed out, staining the

THE CAUSATION OF DISEASE. 89

ground about the place. The multitude then wildly pressed
in upon the fatal spot, and the foremost among them dipped
their hands or handkerchiefs in the- blood. One of these
rushed with bloody fingers after a group of gay women, striving
to add to the rouge on their faces, and the women ran shriek-
ing away."

Here we see the humanity of man for the time completely
stifled, and the dormant instincts of his savage ancestors
awakened. The history of the civilized world shows how ever
ready these savage instincts are to crop up on the removal of
the inhibitory influence of a loosely-attached humanity. The
events of Pranzini's execution call to mind many very similar
instances furnished by the history of the persecutions of the
Christian Church.

Again, in the gradual dissolution of old age, how often do
we observe the mental faculties falling away in the inverse
order of their ancestral evolution ; * and it not unfrequently
happens that the moral faculty dwindles, while the intellectual
powers remain in full vigour.

That structural characters of latest ancestral origin are most
apt to disappear under disturbing influences is nowhere better
shown than in the processes of disease. This conclusion might,
I think, be arrived at a priori.

Whether or not all diseases are accompanied by structural
alteration is a question that will be discussed in another part ;
but this much is at once certain, that where distinct structural
change does occur, the process is one of dissolution. In a few
instances, such as the more highly organized tumours, this
may not seem to be the case ; but it is at once evident that, in
the vast majority of diseases accompanied by structural change,
there is distinct tissue dissolution. There is no advance, no
improvement, in the affected tissue ; on the contrary, there is
retrogression, deterioration — and this is dissolution.

Evolution and dissolution are opposite processes : the one
may be roughly defined as a building-up, the other as a pulling-
to-pieces. Now, the fact that disease is a vital process suggests

* I use the term " ancestral evolution " in contradistinction to those evolu-
tionary processes which take place in the individual, not as the direct result
of heredity, but of personal acquisition.

90 THE CAUSATION OF DISEASE.

at once that this pulling-to-pieces will take place in the inverse
order of the putting-together — that the dissolution will be a
more or less exactly inverted evolution. Often enough dissolu-
tion is by no means an exact inversion of evolution. At death,
for instance, rapid dissolution occurs ; but when, let us say, a
full-grown man dies, we do not find him passing through the
several phases of youth, childhood, and foetal life, finally becom-
ing an ovum again. There is, however, a great difference
between the dissolution which occurs after death and that which
attends disease : while in the one case evolution is completely
undone, in the other it is only partially undone, for disease
being, as just now observed, a vital process — i.e., the tissue
undergoing dissolution being still alive — it must have, if we
may so put it, a certain amount of evolution still left in it —
the structure has not been pulled to pieces to its very founda-
tions. Now, as dissolution proceeds from stage to stage, one
would naturally expect the tissues to be unbuilt in an inverse
order to that in which they were put together — from roof to
foundation, so to say ; for if the process commenced at the
foundation, all analogy leads us to assume that complete disso-
lution would at once occur. These are the grounds on which
I have concluded that the principle for which we are now con-
tending follows from a priori reasoning.

I am not for one moment contending that the dissolution
in disease is always an exact inversion of evolution, but merely
that there is a tendency to such inversion. No one, for instance,
would assert that in pneumonia or nephritis the lungs and
kidney pass inversely through the various phases of embryonic
development. Although the principle applies more or less to
the organ as a whole, it is in the study of the individual
elements of the tissues that we have the best proof of its truth.
When the morbid process leads to rapid dissolution, it is im-
possible to trace carefully the various phases of the backward
process, but when it takes place by slow and steady steps this
may be sometimes done.

No disorder presents a more favourable opportunity for this
study than progressive muscular atrophy. In the first place,
the disease is a slow and, for the most part, steady one ; then,
again, the process limits itself to a specialized tract of cells ;

THE CAUSATION OF DISEASE. 9 1

and, finally, these cells possess a well-marked structure, by
which I mean one that we can detect by examination, for we
have seen all cells possess a highly complex structure.

The degeneration of the anterior ganglionic cells in progres-
sive muscular atrophy is undoubtedly, to a large extent, an
inverted evolution. In order to be sure of this, it is necessary
to study the evolution of these cells. This has been done by
observing their appearance at different stages of development.
If we examine the cervical region of the cord during early
infancy, the anterior ganglionic cells will be found to be not
only simple in structure, but also comparatively few in number,
this immaturity corresponding with the volitional incapacity of
the young infant, who is, as yet, utterly helpless. Gradually,
however, they increase in number and complexity : at first
round and small, they enlarge, and, at the same time, push out
a number of branching processes. Thus are formed complex
motor centres, and it is upon the grouping of these cells into
centres that the proper grouping of muscles in ordinary
voluntary acts, in very large measure, depends ; for, be it
remembered, what is apparently a very simple muscular act,
is found, when dissected into its component parts, to be a
very complex process. It may be remarked, by the way, that
the growth of voluntary power is not a mere matter of educa-
tion, as taught by Bain, for, as just observed, the structural
basis whereby voluntary action becomes possible, is, at birth, not
yet developed in the nerve ganglia. Moreover, the voluntary
cortical centres are at this time equally backward in develop-
ment; so that, even if the new-born infant possessed fully
developed mental powers, voluntary action would be quite
impossible.*

In considering the structure of the anterior ganglionic cell,
we have to remember that one of its processes is prolonged
into the axis cylinder process of a motor nerve fibre, this
axis cylinder process, as it has been termed, becoming, in
due course, coated with medullary sheath and neurilemma ;
and the entire nerve fibre thus constituted terminates in the

* Bastian. I do not intend to imply by the above that voluntary power is not
gained by education, but rather that the immaturity of the motor mechanism
at birth must be taken into account when studying the growth of the will.

9 2 THE CAUSATION OF DISEASE.

motor-end- pi ate of the striped muscle fibre, so that the motor-
nerve-ganglion-cell,* the nerve fibre, and motor-end-plate form
one continuous strand of protoplasm — a more or less inde-
pendent tissue unit — whereof the ganglion-cell forms the head
and governing portion ; for anything which cuts off its influ-
ence, whether it be destruction of the cell itself or a severance
of the nerve fibre, causes degeneration of the fibre thus de-
tached from the governing influence of the cell.

If we study the development of the nerve fibre, we shall find
the axis cylinder first appearing ; next, the medullary sheath ;
and, finally, the neurilemma.

Now, in progressive muscular atrophy, it is found that, so
far as we are able to observe, the process of dissolution of
motor- nerve-ganglion- cell and nerve fibre is an inversion of
the evolutionary process as above sketched. First, as regards
the cell : degeneration affects first the finer ramifications of the
branching processes ; these become less complex, and gradually
disappear ; soon the main stalks begin to fade away, leaving the
cell a mere round mass, which in course of time becomes
angular, and finally, it may be, disappears. As regards the
nerve fibre : the neurilemma is the first to disintegrate ; next the
medullary sheath breaks up ; and, finally, the primitive axis
cylinder degenerates.

The above remarks upon the evolution and pathological dis-
solution of the motor- nerve- ganglion- cell and fibre apply with
equal force to the striped muscular fibre, which receives its
nerve supply therefrom ; but there is no need to give a detailed
account of the evolution and pathological dissolution of the
muscle-cell. It is sufficient to state that the one is, in large
measure, an exact inversion of the other.

With the exception of these two examples of complex
ganglion-cell and complex muscle-cell, we are unable to trace
with any accuracy the evolution and pathological dissolution of
individual cells, and this for manifest reasons. Few, if any,

* This term is, I think, preferable to "anterior ganglion cell," because it
can be applied to the similar ganglion cells (forming the so-called " nerve
nuclei ' of the brain) whence the motor cranial nerves take their origin. By
using the same term to denote all these fundamentally similar structures,
we at once mentally group them under the same head, and it is right that they
should be so grouped both for physiological and pathological purposes.

THE CAUSATION OF DISEASE. 93

other cells possess an obvious, discoverable structure, and such
being the case, it is impossible to trace the steps of their
evolution in any detail, and equally impossible to study the
reverse process with any minuteness. But what little we know
of the evolution and dissolution of such cells fully accords with
the conclusion we have reached ; and could we trace accurately
the several phases in the evolution of, say, a liver-cell — (and
the process is infinitely more complex than at first sight appears,
for, as I have already insisted, every active cell in the body has
a highly complex structure, and therefore a highly complex
evolution) — all analogy leads us to conclude that we should find
the pathological dissolution in very large measure an inverted
evolution.

Hitherto I have spoken only of structural dissolution ; func-
tional dissolution has not been mentioned. It should, however,
be remembered that function is dependent upon structure : the
two, therefore, must stand or fall together. A careful study of
the perverted functions of disease and the order of their appear-
ance fully bears out the conclusion we have already reached.
Indeed, we have in such a study a far more accurate test of its
truth, for not only are we able to study the functional changes
from day to day, and even from moment to moment — a thing
manifestly impossible in the case of internal structural changes
— but we have in functional change a far more delicate test of
dissolution, seeing that a structural change which is quite
outside the reach of microscopic observation is capable of pro-
ducing very obvious functional alteration. A large chapter
might be written on Dissolution in Disease as manifested by
altered function, but there is no need to pursue this subject
further.

lb. We have now to consider the influence of age upon char-
acters acquired by the individual himself. The second of the
above propositions affirms that ' ' characters acquired by the
individual himself tend to disappear in the inverse order of their
acquisition." The truth of this proposition is forcibly shown by a
study of human nature ; the longer a habit is indulged in, the
more difficult it is to shake it off. The latest acquisitions are
certainly the most fleeting, and this fleeting tendency of recent
acquisitions becomes more and more pronounced as life advances,

94 THE CAUSATION OF DISEASE.

when the habits and thoughts of early years are apt to re-assert
themselves in full sway. Since all habits are acquired struc-
tural peculiarities, it follows that the shaking off of a habit is
•the disappearance of such a structural peculiarity.

Now these considerations have practical application for the
physician, because many habits are capable of affecting the
health for good or evil. It is needless to speak of the countless
healthy and unhealthy ones, such as the habit of regularly
going to stool, or the baneful habit of " drinking."

Our proposition again holds true in respect of actual disease.
The longer a disease lasts, the less is the chance of recovery.
Hence the necessity, where possible, of nipping it in the bud. For
instance, an acute disease like pneumonia or acute nephritis has a
much better prognosis than one that is chronic — to wit, granular
kidney — from the very fact that the one is of recent origin
while the other has lasted some time. It might be argued, " Of
course, because the very fact of its chronicity suggests that it
was from the beginning destined to become chronic." This
is quite true, but, altogether apart from such a consideration,
a chronic disorder is less likely to get cured, for the longer
it lasts the faster does it cling, by making a deep impress upon
the body fabric; and even if we were able to check the progress
of a chronic disease — that is to say, remove those causes which
may have destined it to be chronic from the beginning — this
deep impress would still remain. Take as an example granular
kidney. The precious protoplasm, so cunningly adapted to the
removal of the nitrogenous sewage, is crushed and destroyed by
the growth of a dense fibrous tissue, which it were folly for us
to attempt to remove ; moreover, the heart, arteries, and many
other tissues are markedly affected, so that the disease can no
longer be flung off, leaving the body as it was before. But
"this may happen in acute pneumonia or nephritis, because the
structural changes of a few weeks' duration are, so to speak, of
a more superficial nature.

II. What is true of the individual is true of the race.
" Those characters which are of most recent ancestral date show
the greatest tendency to disappear, or, more accurately, not to
appear, in the offspring." Natural variations of great ancestral
age — characters, that is to say, which have passed down many

THE CAUSATION OF DISEASE. 95

generations, become so structurally welded with other parts that
they are with as great difficulty dropped from the race as is
"granular kidney" from the individual; for. all parts of the
body being more or less interdependent, a variation in one
part necessarily leads to alterations in other parts, these again
to others, and so on ; and thus, in the course, of ages, the
initial variations may become so ingrained as to be incapable
of suddenly vanishing; and this seems to afford a strong
argument in favour of the proposition that mere repetition must
render a character more permanent. I suspect that whenever
traits of great ancestral age are rapidly dropped under
changed conditions of life, they are of a so-to-speak superficial
character, not largely influencing or being influenced by other
tissues ; and thus, not being intricately interwoven with the
rest of the body-fabric, they are detached with comparative
ease.

It is very important to note that the ancestral age of any
particular pathological variation — that is to say, the number of
afflicted generations — is usually not great. In thus speaking
of the ancestral age of any particular disease, it will be observed
that I refer, not to the date of its first appearance in the human
race, but, as I say, to the number of successive generations
■of the same family labouring, actually or potentially, under
that disease.

What are the grounds for thus asserting that the ancestral
age of disease is short ? This conclusion follows from the
doctrine of natural selection. Through untold ages there has
been a survival of the fittest, such survival leading to the
evolution of organisms structurally adapted to their respective
environments. Now, an individual afflicted with disease — that
is, a pathological variation — is not thus adapted, and tends, in
consequence, to be weeded out. Thus it happens that a serious
disease would have little chance of being handed down through
many successive generations of one family, for ultimately extinc-
tion must ensue. These remarks do not so forcibly apply to the
lesser ailments which seem to be a necessary accompaniment
of animal life, nor do they apply in any way to diseases which
only appear after the procreative period of life, since these can
in no way affect the offspring : but such diseases are very rare.

96 THE CAUSATION OF DISEASE.

Wherefore we may say that, in proportion as any particular
disease is dangerous to life, and in proportion as it occurs early
in life, its chance of passing along several generations becomes
less.

As regards those lesser ills to which flesh is heir, natural
selection will play some part. Such of them as depend upon
a general weakness of body will tend to be weeded out, through
the weeding out due to such general weakness. But there are
many local morbid actions quite consistent with thorough vigour
of health, and having no power to shorten life. Thus, a family
of remarkable bodily vigour is very liable to nasal catarrh.
The father and several of the children suffer therefrom, and
the tendency can be traced back through several generations.
Let me instance more particularly one member of the family —
a son, approaching the prime of life. In mind and body he
far surpasses the average man, his sole apparent weak-
ness, excepting perhaps a slight dash of the nervous tempera-
ment, being this tendency to nasal catarrh. Let him expose
himself as he will, there is not the slightest inflammation of the
throat, bronchi, or lungs, not the faintest rheumatic twinge ;
but he is rarely free from some degree of nasal catarrh, and
this under exposure becomes acute. The tendency runs back,
along the father's side, so long as there is any family record ;
but, inasmuch as the ailment is no part of a constitutional state
tending to premature death, and is, moreover, strictly local and
devoid of danger, it might as such be transmitted ad infinitum,,
were it not that the proclivity tends to be diluted at each
successive marriage. Let us, however, suppose the catarrh in
question to be part of a strumous diathesis, it would then
have less chance of transmission, seeing that this diathesis
tends to family extinction ; or, let a similar catarrhal tendency
affect the larynx in place of the nose, there would, under such
circumstances, be no possibility of a long-continued transmis-
sion, for it would inevitably kill by occluding the larynx.
Thus, natural selection explains the interesting fact that
hosts of persons now living have suffered from absolute
occlusion of both nares, while there are none, excepting
such as have been saved by tracheotomy — and their number
is very few — who have suffered from a similar complete occlu-

THE CAUSATION OF DISEASE. 97

sion of the larynx. Natural selection, alike merciful and
merciless, prevents the inheritance of such a fatal tendency,
by yearly sacrificing thousands. From these examples we see
how fatal disorders, occurring before the period of procreative
life, cannot well pass through many generations, while such as
are not fatal may attain considerable ancestral age.

We, may, therefore, conclude that any given instance of
serious pathological variation is of comparatively recent ancestral
date : whence it follows, from the principle just now enunciated
(namely, that the fixity of a variation depends in large
measure upon its age), that pathological variations are for the
most part unstable. In other words, a diseased state shows a
great teudency to revert to the status quo ante — viz., health.
This tendency shows itself in a twofold way : first, in the
tendency of a permanently diseased state in the parent
not to appear in the offspring ; for, although disease is un-
doubtedly hereditaiy, yet we see " Nature " ever making a strong
effort to throw it off. (This is best shown where man and wife
have very many children : speaking generally, we shall find
that only a small minority will inherit the disease. It is in
such large families, indeed, that heredity in disease can best be
studied.) Secondly, the tendency to fling off a disease is shown
in an individual who has himself acquired it. Instance the
several acute disorders, such as pneumonia and nephritis. It
is, of course, not to be supposed that the pathological acquisi-
tion can be thrown of — that there can be reversion to the status
quo ante — where there is a gross organic lesion, such as a
mutilated heart valve or a fibrotic kidney ; but the truth of the
principle is shown in the tendency of these parts to be healthy
in the offspring.

Disease must, then, be regarded as a more or less temporary
acquisition, tending under a proper E to disappear. This
tendency shown by diseased tissues to revert to their ante-
morbid state is learnedly called the vis medicatrix natural*
I find that Paget, if I understand him rightly, explained this
vis medicatrix in a somewhat similar way.f

* H. Spencer biings the etf medicatrix naturce under his principle of equili-
bration. See his " First Principles," chapter xxii.

f " It seems probable that in embryo life there is, generally, a tendency to

H

98 THE CAUSATION OF DISEASE.

It is impossible for the physician to exaggerate the import-
ance of the vis medicatrix naturce. It shows him how much
he has to hope from a careful regulation of the E, not only
in acquired disease, but in inherited tendencies ; it makes him
feel, under a crushing sense of the terrible power of heredity,
that he has yet within his hands the means by which he can
do successful battle with it. His problem, in any case of
hereditary tendency, becomes how to produce a reversion by
placing the individual, as far as possible, in an E as like that
of his primitive ancestors as the altered conditions of life
will allow, and to supplement or correct this E by care-
fully applying the medical knowledge he has so laboriously
acquired.

We may here fittingly turn aside for a moment to inquire
into the nature of such an E. From the habits of the primi-
tive savage we learn that man was intended to live in the open ;
— or, to speak more scientifically, he has evolved from a lowly
being under an exposed E ; to go no further back than his simian
ancestors, we find them living in the open, under no other shelter
than that afforded by the branches of trees. Man having then
evolved under exposure — beneath the free canopy of heaven,
it follows that he must be, in the main, adapted to a life of
exposure, — not, like the mole, to a subterranean existence,
nor, like the whale, to an aquatic life. Now, both of these
last-named animals have evolved from ancestors living upon
the dry land, by gradual adaptation to a changing E. In like
manner and through unnumbered generations the human body
has been changing in response to a changing E ; and it might
be argued that, just as the mole has become modified for
a life underground, and the whale for an aquatic life, so has
primitive man become structurally adapted to a life spent
under a roof. But he has not. As we shall see later on,

recovery from the morbid conditions transmitted from parents: a tendency
to revert to the true healthy type of structure and composition. Such a
tendency would be in accordance with the general rule of tendency to rever-
sion from all variations of specific characters, and would be a part of that
tendency to recovery of health which suggested a vis medicatrix naturce, and
which we may observe through life, diminishing as age increases, but never
quite lost." — Clinical Lectures, by Sir J. Paget, p. 408.

TLIE CAUSATION OF DISEASE. 99

such a sheltered E is necessarily fatal to man : one or
two generations may linger on under it, but soon extinc-
tion occurs. It is, I say, " a necessarily fatal E," an E
to which the human organism cannot adapt itself. Other
organisms can — beetles, rats, mice ; but the monarch of the
earth sickens and dies under it. Wherefore, casting our eyes
back through the long past, we learn a lesson from our
far-off ancestors. We find that man was " intended " to live
in the open.

The same conclusion is forced upon us if we seek informa-
tion in another direction. Let us watch a healthy child ; study
his instincts. They are worthy of study, for, as we shall see
in another part,* instinct is, in the strictest sense, the voice of
" Nature." The child is living, let us suppose, in the country.
So soon as he can toddle, what does he do ? Stay in doors ?
No. He is soon roving about the country, for no healthy child
will keep in doors unless compelled. Wind and storm have
little fear for him — off he will go. What country-bred child
does not remember the agony of being kept in during a rainy
morning ! Soon, as he grows older, he begins to climb the trees,
like his simian ancestors. What healthy boy — nay, may I not
even say, girl? — living in the country, has not climbed every
available tree in the neighbourhood ? Dickens somewhere
speaks of the little sparrows in some old London "inn," flying
about from tree to tree, and " playing at being in the country."
How many of the London children make a more ghastly
imitation of Nature !

In the suburbs, however, the attempt may be more successful.
For example, a gentleman, living in the suburbs of London,
has a few well-grown trees at the end of his tiny garden. When
his eldest girl was five or six, she took to climbing these trees.
No one had shown her how, for, being the eldest of the family,
her brothers were too young. A short time ago I visited this
gentleman on a summer's afternoon, and, looking out of the
window, beheld the same maiden (now fourteen) sporting among
the branches of the trees. This habit of the girl has given
great trouble to a kindly old lady next door. She has

* Vide Part II.

IOO THE CAUSATION OF DISEASE.

been living in fear that the child would kill herself (how
many children, I would like to know, have thus killed
themselves?), and now, perhaps, she thinks it very "im-
proper." Happily, the parents of this young lady have
brains, and so they leave her alone. Unfettered by the con-
ventionalities of Society, they have allowed her to follow the
ways of Nature, and her limbs have grown in Nature's own
way.

Wherefore let all children be brought up in the country r
let them be out of doors while it is light, and let them climb
trees, and indulge in all such pranks (except the mere
savage ones) as Nature dictates. Those instinctive habits of
which they will require to be cured are not the hygienicallyy
but the morally bad, for the morality of the young child is
very largely that of his savage ancestors, and ill-adapted to
the requirements of a civilized community, which demands a
morality of great complexity and refinement. Thus, the innate
tendency to cruelty should be stamped out, the habit of throw-
ing stones, of making grimaces, and so forth. Some of these-
habits are most interesting. To wit, the tendency of boys
(not girls !) to go about in tribes armed with sticks and stones
— Nature's own weapons — and to engage similar tribes of
other boys in battle. I quite recently saw this in a London
suburb. A tribe of small boys thus armed was at cne end
of a short street, engaged in animated talk about the enemy.
Presently, at the other end of the street, the latter appeared.
Then, with a distinct icar whoop, the battle commenced by a
throwing of stcnes. The enemy proved to be the weaker, for,
upon their antagonists attempting to engage them at close-
quarters, they rapidly fled ! I say, I do not counsel th&
education and development of the savage qualities here exem-
plified. We must civilize the young, and bring them up in a
beautiful morality, but let us beware lest at the same time we
annihilate all those instincts which show so distinctly what are-
the proper ways of youth.

So much for fresh air and exercise. What about food ?
Nature has provided a food for the first year : therefore, let
the child have it, and nothing else. But when Nature's fount
begins to run dry, what then ? Again watch the ways of

THE CAUSATION OF DISEASE. IOI

children. All children in the country help themselves largely
to the vegetable diet provided by Nature. They eat herbs and
berries, roots and nuts, like their savage and simian ancestors.
Sometimes they even rob orchards ! I think it may safely be
said that children, as a body, prefer a vegetable to a meat diet.
Almost every child prefers fruit to meat. No- doubt allow-
ance must be made for vitiation of instinct, and some children
may manifest a great liking for meat ; they may be taught to
like it, just as pigeons and other vegetable feeders may, or as
they might be taught to like many other things — gin, for
instance. Here, again, we are aided by the study of man's remote
ancestors. His simian progenitors were entirely vegetable
feeders, and, although cannibalism is indulged in by certain
savage tribes, yet their staple diet is undoubtedly a vegetable
one. Apart, however, from these considerations, we have the
evidence of experience, which shows that an excess of meat
diet is injurious. (Butchers are short-lived.) Therefore, man's
diet should be mainly vegetable ; that of children almost
entirely so. Our medical experience teaches us, moreover, that
the supply should be abundant. All doctors now agree that,
till the period of development has ceased, the individual should
have as much food as he can eat — provided, of course, that it
be suitable.

Nor should the mind of youth be unduly stimulated,
Here, again the natural instincts of the child help us. Every
healthy child revolts against the enforced incarceration of
school hours, and against the effort of fixing the mind long on
the same subject. Indeed, the early education of the young,
more especially of such as come of a nervous stock, requires
the greatest skill.

I say it is well to study the E of our remote ancestors, and,
making due allowance for subsequent evolution, to erect a
system of bringing-up for our children. And let us be careful
that all children coming of an unhealthy stock be placed, as
far as possible, under this E, for we have seen that the age of
any particular disease is not great, and that its tendency to
disappear increases in proportion as the E approaches that of
our remote ancestors. One is, I think, justified in assuming that
a reversion to an ancestral state would be more likely to occur

102 THE CAUSATION OF DISEASE.

under the E which obtained during the exhibition of that
particular state than under any other. It does not, of course,
necessarily follow that reversion to an ancestral state will in all
cases follow on a return to such E — that all domesticated
plants and animals, for instance, will necessarily revert to their
wild state if exposed to their original E. All I maintain
is, that such reversion is far more apt to occur under that
form of E than under any other. Darwin was careful to point
out that the evidence in favour of the common statement, that
reversion to the wild state always takes place under the pre-
domestic E, is difficult to obtain. He, nevertheless, writes as
follows : "As our varieties certainly do occasionally revert, in
some of their characters, to ancestral forms, it seems to me not
improbable that, if we could succeed in naturalizing, or were
to cultivate, during many generations, the several races, for
instance, of the cabbage, in very poor soil (exposing them, that
is to say, to an E very like the original ancestral one), they
would, to a very large extent, or even wholly, revert to the
wild aboriginal stock."*

I make no doubt that, under the kind of E 1 have denoted,
many hereditary weaknesses might be obliterated — nay, even
more than this, that a most deteriorated race could again
recover its original perfection. Let us take a typical cockney,
stunted in body and mind — 5ft. 2in. in height, with his
other measurements proportionally dwindled — I make no
doubt that if this man, with his cockney wife, were placed
under such an E as I have sketched, and their children
and grandchildren after them, the physique would rapidly
assume its pristine mould. Such thoughts should give us
hope. Are there not many particulars wherein we are
inferior to our ancestors? Take the single instance of the
teeth. It is known that the teeth of civilized peoples are
getting worse and worse. What others think of this I know
not, but to my mind it is a very serious matter. I suppose
primitive man practically never suffered from toothache. How
different with us ! If we could reckon up the agony suffered
by those now living from toothache, what a terrible total we

* " Origin of Species," sixth edition, p. II.

THE CAUSATION OF DISEASE. 103

should get, leaving out of account the secondary but even
greater evils of digestive and reflex troubles, to say nothing
of the unsightliness. Now, may we not believe that, under a
proper E, a race most degenerate as to its teeth might in
course of time become completely regenerated in this respect,
recovering to the full the strong and beautiful teeth of their
ancestors ?

CHAPTER XII.

Heredity {continued)— Reversion— Its Two Chief Causes — Peculiarity in the
Evolutionary Process and Partial Dissolution of a Mature Tissue.

Beversion. — In the disappearance of a recently acquired
character, whether physiological or pathological, we have an
example of what is technically termed reversion. This prin-
ciple must now be considered somewhat in detail.

The following I hold to be the three great causes of rever-
sions : —

1. Peculiarities of ante-partem E, causing arrest or per-
version of development.

2. The union of parents having uncombinable tendencies
— such uncombinable tendencies being for the most part of
recent origin, and of divergent character.

3. Peculiarities of E, ante or j^ost partem, whereby a mature
tissue is compelled to revert to one of inferior order.

In the first two varieties the reversion is due to a peculiarity
in the process of development — to a peculiarity, namely, in
the grand evolutionary process ; in the last, it is due to an
undoing of evolution, or, to speak more accurately, to the
partial undoing of a more or less completely evolved tissue.

Peculiarities of ante-partem E may lead to reversion in a
twofold way — (a) by interference with the due sequence of
embryonic events : in this way the development of certain
organs and tissues may be arrested, the individual being born
with characters belonging to remote ancestors ; (b) the peculiar
E may lead to such perversion of embryonic processes that
development proceeds more or less on remotely ancestral lines.

As an example of arrest, we may instance the occasional
persistence of a branchial cleft, and many forms of idiocy in
which far-off ancestral mental traits may appear. Thus
Maudesley has recorded several cases of idiocy where the indi-

THE CAUSATION OF DISEASE. 105

vidual has shown marked likeness in his ways and instincts
to certain of the lower animals. There can be little doubt, I
imagine, that the arrest in such cases is due to peculiarity of
ante-partem E. As an example of reversion, due to peculiar
ante-partem E, causing not a simple arrest merely, but such a per-
version of embryonic processes, that development proceeds on
old lines, we may instance the stripes which sometimes occur
on the young foal. These are evidently derived from the
zebra — a far-off progenitor of the horse. The fact that they
are observed every now and again in the foal shows that they
must always potentially exist in the embryo. What is it
that causes this potentiality every now and again to become
an actuality ? The union of parents having unconibinable
tendencies may afford the true explanation of the reversion
— of which more presently. Another possible cause of
the reversion in question is the one under consideration,
namely, a peculiarity in antc-parlcm E, which prevents the
development of the skin from proceeding on the lines peculiar
to the horse, causing it, on the other hand, to progress on more
ancient lines. Thus, at the time of foetal life, when the
embryo is most like the zebra as to its integuments and such
tissues as influence their development, one may suppose some
such accidental dislocation of the molecular processes of the
one or the other to take place, that the further development
of the integuments proceeds on the old lines peculiar to the
zebra.

This mode of viewing the matter may be rendered clearer
by a diagram. In Fig. 9, ab represents the fully developed
zebra skin ; CD, the fully developed horse skin ; o being the
starting point of development. Up to the point x we may
suppose the development the same for each. But hencefor-
ward there is a divergence, — in the case of the zebra develop-
ment proceeding in the direction of A and B ; in the case of the
horse, of C and D. So far as the latter is concerned, the un-
shaded part represents a dropped character (this being dia-
grammatically indicated as in Fig. 8).

Now, if we suppose that the integuments of the foal have
arrived in their development at the point x, we can imagine
that a peculiarity of E might lead to such molecular dislocation

106 THE CAUSATION OF DISEASE.

of the developmental processes that further development shall
proceed on the old lines xa, xb.

It may be that stripes like those met with in the zebra are

Fig. 9.

B

D
Diagram showing how a character existing potentially in the embryo
may be converted into an actuality.

always normally present in the embryo foal at some period of
its development, and, if such is the case, one may account for
their presence in the young foal by supposing a simple arrest
in development, be the cause what it may, peculiar E or not.
But let it be well noted that many reverted characters are
never actually present in the embryo — only latently present ;
and whether the zebra stripes are always present in the embryo
foal, or whether their occurrence in the young foal is merely
the conversion into an actuality of a power latent in the embryo,
matters not much. The diagram assumes the undoubted fact
that the embryo has latent powers which may or may not
develop into actualities, and we shall not err greatly if we
assume the pronounced stripes of the zebra to be only latently
present in the embryo foal.

Whether this method of viewing the conversion of a latency
into an actuality be correct, I know not. It will be observed
that in this attempted explanation I am regarding the life of an
organism as a cycle — a complex rhythm, and the development
of a latency as the substitution of a previous rhythm for a present
one, owing to peculiarity of E. But, be the explanation what
it may, let us ever bear in mind that an organism is the seat
of many thousand such latencies.

2. We now come to the second cause of reversion, namely,

THE CAUSATION OF DISEASE. 107

the union of parents showing structural characters of diver-
gent character; in consequence of this divergence they refuse
to blend, and thus display a status quo ante. Such characters
are of more or less recent acquisition.

It is a well-established biological fact that reversions most
frequently occur when distinct species, or pronounced varieties
of the same species, are crossed. Whatever the explanation,
the fact remains, and, as wre shall see, it has a most important
application in medicine. In the fifth chapter of his " Origin of
Species," Darwin illustrates this result of crossing. He tells us
that zebra-like stripes frequently result from the crossing of
the several species of the horse genus : the ass, horse, quagga,
hemionus — all of which are descended from the zebra. Another
striking illustration of the same principle is afforded by the
pigeon. There are over three hundred varieties of this bird, all
of which are undoubtedly descended from the Blue Rock pigeon,
a bird very like our Wood-pigeon. Now, wThen distinct breeds of
various colour are crossed, there is " a strong tendency for the
blue tail and bars and marks to reappear in the mongrels."
The author goes on to say that there is evidently c; a tendency
in the young of each successive generation to produce the long-
lost characters " (note this in reference to my remarks on
potentiality), c: and this tendency from unknown causes pre-
vails " in such crosses. The above hypothesis affords, I imagine,
some explanation. We may suppose, namely, that the recently
acquired characters refuse to blend ; that the parents are, in
fact, barren in respect of them, so that there is a reversion to
a status quo ante — to the condition of things which obtained
before the acquisition of the non-blending characters.

Up to the point of ancestral divergence, any two different
species of the same genus may, in fact, be regarded as of the same
species, and therefore, as we should expect, the development of
the mongrel offspring thus far proceeds harmoniously ; for are
not these the lines on which it has proceeded for many genera-
tions— thousands, it may even be tens of thousands ? The germ
and sperm, thus far, are, so to speak, perfectly adapted to
each other; but beyond this point each element has dif-
ferent tendencies : from the one parent comes a tendency
to reproduce one set of peculiarities, and from the other

108 THE CAUSATION OF DISEASE.

a tendency to produce another set — perhaps of a totally
opposite order. Therefore, henceforward the process of de-
velopment tends to be somewhat chaotic. The two tendencies,
coming into union for the first time, show a disinclination to
blend, and in this chaotic state, pre-potency no doubt plays an
important part, certain recently acquired characters occasionally
showing great proneness to appear in the offspring ; but the
general rule is that such recently acquired characters tend to be
dropped, the offspring revealing characters peculiar to a remote
ancestor — that is to say, the status quo ante the divergence.
Or, putting the matter in another way, we may say that the
two sets of characters acquired after the point of divergence
are barren, one with another. Viewed from the embryological
standpoint, each organism is, as far as this point, practically of
the same species, and therefore capable of perfect sexual repro-
duction one with the other, but after it the two are of different
species, and more or less barren.

The above explanation may be rendered clearer by the
accompanying diagram. The line axb represents the develop-

Fig. IO.

B
/

X

ment of the integuments of the ass, axd that of the horse,
AC, AC = development of zebra. X in each line marks the
point of divergence. From A to x the lines are parallel. This
signifies that the developmental processes are thus far parallel
and in harmony. But beyond this point the diverging lines,
xb, xd, signify diverging tendencies. So that if axb represents
the germinal tendencies of the ass, and axd those of the horse,
there will be perfect union up to x ; beyond this xb, xc will
more or less refuse to blend, and development will tend to pro-
ceed on the old lines to C

THE CAUSATION OF DISEASE. 109

3. In the different kinds of reversion hitherto considered,
the cause is an error or peculiarity in the process of develop-
ment ; but there is another kind of reversion, which is apt to
be left out of account — namely, the reversion of a mature
and properly developed tissue to a remotely ancestral state. I
Jhave already instanced the loss of the moral nature in the
commencement of an attack of insanity. In such a case,
the cortical tissue reverts to a state belonging to pre-moral
times. Now, all the tissues of the body exhibit a like ten-
dency to reversion. If the cell-E necessary to the maintenance
of a high state of evolution, be vitiated, we find the tissue
reverting to a more elementary form — to one belonging to a
remote ancestor. What, for instance, is the effect of an irri-
tant when applied to living tissues ? That curious process which
still continues to bother the pathologist occurs — inflammation.
Now, if an inflammation is not so slight as to end in resolu-
tion, nor sufficiently violent to destroy the tissue, the mature
tissue is replaced — as Cornil and Ranvier put it — by an
embryonic tissue ; in other words, there is reversion of the part
to a remotely ancestral state. Take, for instance, inflammation
of muscle-tissue : the mature muscle fibres disappear, and their
place is occupied by small round cells, amongst which small
capillaries presently develop, forming the so-called granula-
tion-tissue. If the irritant be removed, this tissue will attain
higher development : there will be an abortive attempt at the
production of muscle-tissue, although little more than fibrous
tissue will be formed. In round-cell sarcoma, the process
is similar. Sarcomatous and granulation-tissue are, I sup-
pose, fundamentally the same. In sarcoma, as I shall argue
in another part, the irritant, or as I should prefer to put it,
the mal-cell-E, consists of a specific bacillus. This consti-
tutes an abiding mal-E. Hence the morbid process is con-
tinuous, and the cells, being continually irritated, are prevented
from developing into a mature tissue. In the round-celled
sarcomata no higher development whatever is permitted, but
in the other varieties a faint effort is made in that direction.
In the epitheliomata, we probably have a similar reversion to
an elementary form of gland-tissue, and it may be that the
same is true of the acinous carcinomata. In the myxomata,

I I O THE CAUSATION OF DISEASE.

again, under a cell-E- concerning the nature of which
I do not profess to know anything, a mature tissue takes
on a remotely ancestral form — a form, namely, that is met
with in the most lowly organisms, as, for example, the jelly-
fish ; and in this connection it is interesting to note the ten-
dency which the sarcomata show to undergo mucous degeneration.
In old age, again, the higher epithelial tissues perish at the
expense of those which are merely connecting : under the failing
supply of healthy blood, there is a reversion to a simpler tissue.
Let it ever be remembered that the human organism contains
the potentialities of countless ancestors, and that these poten-
tialities may, under fitting conditions of E, be converted into
actualities.

In the Lancet, £so. XXII. vol. i. 1887, will be found an
interesting communication by Dr. Gresswell, on the " Origin
of Tumours by Reversion." This communication suggested the
following remarks from me, which I venture to quote here,
since they bear upon the present subject : —

" I have been inclined, for some little time past, to regard certain
new formations as reversions, of limited patches of tissue, to an
ancestral type — notably, the enchondromata, myxomata, sarcomata,
and the new formation occurring in consequence of inflammation —
namely, granulation-tissue, including, of course, the granulomata.
It must not be forgotten that the reversion of which Dr. Gresswell
speaks is not the ordinary reversion which occurs during the embryo-
logical development of an organism, but the reversion of a fully
■evolved and specialized tissue to one of remotely ancestral type. That
such a fully developed tissue may thus revert is a well-recognized fact.
Dr. Maudesley points out that during the cerebral disturbance which
heralds an attack of insanity, the moral faculty — viz., that mental
element which has been last acquired — is generally the first to go.
This shows a reversion of cerebral tissue to an ancestral type. It is
well to bear in mind that the tissues of a fully developed organism
have many potentialities which only need fitting opportunities to
display themselves. These consist in modifications of cell environ-
ment. A good example of such latent capacities is afforded by
disease, atrophy, or removal of the ovaries or testicles, when the
organism tends to take on certain character of the opposite sex. This
shows that each sex contains potentially certain actualities of the
,other, and similarly the most highly specialized organism contains

THE CAUSATION OF DISEASE. I I I

the potentialities of remote ancestral actualities, which display them-
selves under modifications of cell environment.

& As regards tumours, the nature of this environment is known in
certain instances, as in the granulomata : parasites enter the tissue,
and so disturb the cell environment that they can no longer maintain
their high grade of specialization, and revert in consequence to an
ancestral type. The malignant tumours have, I believe, a like para-
sitic origin : but there is no need here to adduce arguments in favour
of this view. Now, sarcomatous tissue is distinctly of an ancestral
type : one cannot, however, speak so positively of the carcinomatous.
In epithelioma, however, we see changes allied to embryological
ones. The squamous epitheliomata originate by an involution of the
epithelium, such as occurs in the development of all open glands
(even the liver is thus developed) ; but in this instance the invested
cylinders have no lumen ; nevertheless, the manner of development
is that of a crude form of gland. In the cylindrical variety we have
a higher effort, for a distinct lumen is developed. I cannot compare
the carcinomata with any embryological or ancestral tissue, through
dearth of knowledge ; but let us bear in mind that the affected tissues
must possess the potentiality of this mode of growth ; and whence, it
may be asked, have they this power 1 I should not be surprised if
one of wide histological knowledge could throw light upon the
subject by studying it on the lines laid down by Dr. Gresswell."

It is certain that such reversions of a mature tissue to an
ancestral state play a very important part in pathology ; but
the subject stands in need of careful investigation. In this
connection gout at once occurs to mind. Abnormal quantities of
uric acid are produced in this disorder. Now, in certain classes
of animals the nitrogen is eliminated chiefly in the form of
uric acid, and the question arises whether gout be not such
a reversion. It is impossible to say, because we know practi-
cally nothing concerning the mode of production of uric acid,
and it may turn out that the physiology of uric acid in
mammals is fundamentally distinct from that in birds and
reptiles. However, this case of gout suggests to us that in
many diseases the process of reversion plays an important part.
If we bear in mind the countless potentialities of every
complex organism — potentialities derived from an untold
number of ancestors — we shall be the less inclined to think
the suggestion fanciful and unworthy of further investigation.

I I 2 THE CAUSATION OF DISEASE.

What can be more interesting than the mode of growth of
squamous epithelioma ? The process is strictly analogous to
the development of tubular glands, but I can have no doubt
that the affected tissues in this disease, be the exact nature
of the process what it may, display potentialities which in far-
off ancestors had, in very large measure, an actual existence.
Indeed, it may be said that most, if not all, diseases are tinged
witli an element of reversion. By this I do not mean that the
body in disease reverts, as a whole — that each and all of the
tissues take on the exact characters of some particular ancestor
— but rather that certain local reversions of the tissues take
place. It was just now said that all diseases accompanied by
distinct structural change are, without doubt, examples of dis-
solution. This dissolution being incomplete (for when complete
dissolution takes place we are dealing, not with disease, but
with death of the part), it necessarily follows that the tissue or
tissues which have thus undergone partial dissolution must
possess characters which belonged to a past era of evolution.
Such local reversion need not be a perfect reversion, as we
shall presently see ; but that the change must, in some degree,
be a reversion, appears to me an a priori conclusion.

We must not, however, leave out of account the part played
by evolution in the process of disease. Evolution is not un-
frequently observed to follow on the structural dissolution, or
even to accompany it. Indeed, it is often by no means easy
to separate the two processes. Let us instance the process
of inflammation, which affords a very good example of local
reversion.

It very frequently happens that, as a result of inflammation,
the affected tissue is converted into granulation or embryonic
tissue. This, in fact, always happens when the process is
neither so severe as to completely destroy the tissue, nor so
slight as to permit of complete absorption of inflammatory
products. Now, granulation- tissue belongs to an order common
in lowly and remote forms of ancestral life. It, therefore,
follows that, when a mature tissue is replaced by granulation-
tissue, it reverts, in the truest sense of the word. The
question we have to decide is, bow far the process whereby the
mature and perfectly evolved tissue has been changed into this

THE CAUSATION OF DISEASE. I I 3

granulation-tissue, is one of dissolution, and how far it is
one of evolution. The exact origin of the cells composing
granulation-tissue is still a subject of dispute ; for, while all
pathologists agree that the majority of them are derived from
the blood, there is not yet complete agreement as to whether the
fixed cells of the affected part help in their formation. Now, if
allthe cells are derived from the blood, we must look upon the
process whereby a mature tissue is converted into granulation-
tissue as a complete dissolution, followed by a separate and
independent evolution ; but, if some of the cells, as is probably .
the case, are derived from the fixed cells of the part under-
going dissolution, it follows that the cells of the affected part
are, at one and the same time, undergoing dissolution and
evolution ; for, while the mature cells are breaking up and thus
descending from their high state of evolution, they are, at the
same time, giving birth to offspring, and this must be consi-
dered as a step in the direction of evolution.

In such a disease as epithelioma, again, it is very difficult to
separate the two processes — dissolution and evolution. Let us
take the squamous variety. There is a great multiplication of
epithelial cells, and, in so far as this multiplication is at the
expense of mature cells, there is dissolution. The young
progeny, however, grow, or seem to grow, into mature cells.
There is, therefore, a more or less complicated evolution. But
the evolution is not complete ; we have seen that the word
11 structure " does not apply merely to the conformation of
individual cells, but also to the arrangement of them into
tissues, and in squamous epithelioma the arrangement of the
cells is imperfect ; wherefore, taking the tissue as a whole, it
is obvious that evolution is partial.

But it matters little whether we can or cannot, in any given
instance of disease, mentally separate the two processes of
dissolution and evolution. The important fact for us, at this
place, is — that the local evolution in disease, alike with the
local dissolution, leads to reversion, or, more accurately, to a
series of reversions ; for while a cell or tissue is evolving, it
must, unless it evolve on lines entirely different from those on
which the species itself evolved — a thing obviously impossible
— pass through various phases cf past ancestral life.

1

114 THE CAUSATION OF DISEASE.

The evolutions of which we are speaking are, for the most
part, partial ; but a partial evolution is, in some sense, the
equivalent of incomplete dissolution, and, in either case, a
tissue state is produced which is tinged, more or less, with
ancestral characters. In so far, then, as all diseases accom-
panied by distinct structural change are undoubtedly examples
of either partial dissolution or of partial evolution, they may be
regarded as local reversions.

Here, however, we have to ask the important question — Are
these reversions true ? Does the affected tissue take on exactly
all the characters of some remotely ancestral tissue ? It may, I
think, be asserted a priori that this cannot happen in all cases.
In healthy granulation-tissue, we have an example of more or
less perfect reversion; but here, be it noted, the cell E is
healthy. In all cases of partial dissolution and evolution the
cell E is unhealthy. The elements of the tissues are subjected
to a species of mal-E unlike any which they have experienced
during the long course of their ancestral life. Now, we have
seen that E is capable of modifying S, and from this it is
obvious that a perfect reversion is quite impossible under a
mal-E ; for, even supposing, for the sake of argument, such
perfect reversion to occur, the altered E would necessarily
cause some modification in the truly reverted character. It
therefore happens that, in almost all cases of local reversion
occurring in disease, the evolutionary or dissolutionary process
is not only incomplete, but erratic. Wherefore it is more
accurate to style these reversions " local vitiated reversions."

CHAPTER XIII.

Heredity (continued)— A Consideration of the Different Modes by which
Organic Potentialities may become Actualities — Some further Bearings
of the Principle of Reversion upon. Pathology — Summary.

Potentiality. — Allusion has been made more than once to
that curious property termed potentiality. This property is
possessed by living aggregates in common with other aggrega-
tions of matter; here, it is only necessary for us to speak of the
potentialities of living organisms. A property is said to exist
potentially when it is not actually present, but is capable, under
certain circumstances, of being called into actual being.

I am led to consider this subject here, because the partial
dissolutions and evolutions of which we have just spoken
afford very good examples of the way in which potentialities
may become actualities. There are, however, other ways in
which this may take place.

In treating of the causes of potential manifestations, I shall
consider the individual and not the race : the reappearance of
a long-lost ancestral character in the offspring of crossed
parents may be said to pertain rather to the race than the in-
dividual, seeing that it is not so much the manifestation of a
potentiality by an individual, as of parental potentialities.

Confining our attention, then, to the individual, we shall
find that there are at least four causes of potential manifesta-
tions : —

1 . Partial dissolutions of disease.

2 . Partial evolutions of disease.

3. Normal organic evolutions.

4. Interference with the proper action of ovaries or

testicles.
I. The partial dissolutions of disease affords a particularly
good example of the manner in which a potentiality may become

1 2

Il6 THE CAUSATION OF DISEASE.

an actuality; for it is, as we have seen, in large measure, an
inverted evolution, and when a structure is taken to pieces in
the inverse order to that in which it was put together, there
are necessarily revealed characters which belonged to the indi-
vidual at successive periods of his evolution. Characters
which were before potential now become actual. This method
of potential manifestation may be illustrated very simply.
At a certain stage in the building, or evolution, of a house,
before the roof has been put on or the windows fixed, it will
be both draughty and, in rainy weather, wet ; but when the
house is finished — when its evolution is complete — it will,,
if properly constructed, become perfectly dry and free from
draughts. If, now, we invert the evolution, and cause a partial
dissolution by removing the roof and taking out the windows,,
the house will again display characters which belonged to it
at a certain stage of its evolutionary career: it will become
once more damp and draughty. Characters, before potential
only, now become actual.

Yet another example may be given. The process of evolu-
tion may be observed in the invention and gradual improvement,,
during the long course of years, of a machine, until, finally,
perfection is reached — that is to say, the highest possible pitch
of adequacy. Owing to the enormous competition between
different machines, belonging, as we may say, to the same
species, there is a struggle among them for existence, and this,
struggle will eventuate in the survival of the fittest. Every
new improvement is, as it were, a happy variation, which will
be seized upon by the market, which constitutes, so to speak,,
the environment ; and thus, by an accumulation of improve-
ments (natural variations), perfection is at length attained. It
is true that, as the evolution proceeds, there is not necessarily
an increased aggregation of matter, nor a greater complexity of
structure, for sometimes a great improvement may be made
by simplifying the structure and diminishing the bulk, and in
such cases the various phases in evolution would not fulfil the
terms of Spencer's formula. But this is simply because that
artificial evolution which is the product of man's mind, is less
orderly and perfect in its progress than the unconscious evolu-
tion which isever at work throughout Nature. It not unfrequently:

THE CAUSATION OF DISEASE. I I J .

happens, however, that the evolution displayed in the history of
a machine fulfils the terms of Spencers formula, many machines
being improved by successive additions, whereby the structure
becomes more " integrated '"' and more complex (heterogeneous).

Let us now suppose that some particular machine has been
thus very much improved by some slight addition to its struc-
ture. It will contain potentially the ability to work in the
old-fashioned manner ; for, if the recent addition be removed,
a partial dissolution being thus effected, this potentiality will
be manifested.

2. The incomplete local evolutions which take place in
disease afford another example of the conversion oi potentialities
into actualities, for it is obvious that, in this process, the
affected tissues take on characters which they did not possess
before.

Both in partial evolution and partial dissolution the pro-
cess, as we have seen, is often, indeed generally, vitiated ;
and it therefore by no means follows that when the poten-
tiality becomes manifested by either of these methods, such
potentiality has ever existed as a normal actuality in the
ancestral history of the individual ; for, owing to the action of
E upon S, the S will cause, so to speak, natural variations in
the partially evolved or dissolved tissue. Nevertheless, such
structural characters must have existed potentially in the
tissues. Thus, the tissues contain myriads of potentialities,
many of which never have been nor ever will be manifested, for,
to suppose that every potentiality has been manifested, is to
suppose that the tissues have been subjected to every con-
ceivable form of E, seeing that every different form of E is
capable of affecting the tissues in a different way.

3. In both the methods already given, the potentiality
becomes an actuality by the local falling away in the evo-
lutionary value of a mature tissue. An actuality, before
only latent, may, however, also be developed by an advance in
evolution. Thus, an embryo contains all the potentialities of
the future individual. Of this method little need be said.
Many such potentialities are displayed in the natural and, so
to speak, unaided process of evolution, and many may be
developed by a special education ; indeed, it often happens that

I I 8 THE CAUSATION OF DISEASE.

an individual is potentially endowed with qualities whereof he
and his friends are wholly ignorant. Undeveloped heroes —
" village Hampdens" — are, perhaps, more common than most
people imagine ; certain it is that great crises call into pro-
minence men who would otherwise have passed their lives
in obscurity, and some historians would perhaps class Cromwell
among their number. It often falls to the duty of the physi-
cian to develop potentialities by this process of evolution ; for
he is not infrequently able to render an individual proof
against some particular disorder by favouring the evolution of
certain tissue or tissues — such as the tissues whereof the ner-
vous system is built.

4. Finally, a potentiality may be converted into an actuality
by disease, atrophy, or removal of the ovaries or testicles, for,
under these circumstances, each sex tends to take on certain of
the proper sexual characters of the opposite sex. Patholo-
gically this fact has its importance, for, when the ovaries
remain long inactive, the woman tends to become masculine —
probably owing to an atrophy of these organs from disuse,
and this more notably occurs after the menopause. In so far
as sex is capable of colouring disease, we shall accordingly find
these modifications in the sexual characteristics giving a corre-
sponding colour to the diseases from which the individual thus
sexually altered suffers.

Let us now consider what further bearing the principle of
reversion has upon pathology. In treating of the fixity of
structural characters, we saw that the vis medicatrix rested
upon the principle of reversion. But this principle has further
application in pathology. In the first place, it is manifest
that a reversion may be both pathological and physiological.
The latter variety is the most common. As an example of such
physiological variation we may again instance the reversion in a
fancy pigeon to the blue plumage of its far-off ancestor, the
Rock pigeon. We have seen, however, that reversion may
occur to a condition which, though normal to the ancestor
from whom it is derived, is abnormal to the individual in whom
it reverts, as when a branchial cleft persists in a mammal.
The latter then is, in one sense, a pathological reversion.

THE CAUSATION OF DISEASE. I 1 9

The question now arises, may reversion occur to a condition
which from the beginning has been pathological ? — may, in other
words, an individual inherit a disease from a remote ancestor —
e.g., gout, rheumatism, or insanity ? Diseases are, as we have
seen, pathological variations ; and why, it may be asked, should
not an individual tend to revert to a pathological t quite as much
as to a physiological, state ? A little consideration will show that
the tendency to revert to the diseased state of a remote ancestor
is infinitely less than to revert towards a physiological state.
We saw that a pathological variation must necessarily have a
much looser hold upon a race than one that is physiological, for
such variations are, owing to a survival of the fittest, being
continually weeded out. Total extinction inevitably prevents
them from being handed along many generations of a particular
family line ; therefore they never leave a deep impress upon
the organism, and, after they have been dropped for a few gene-
rations, we may expect this impress to have completely faded
away. "We saw that certain minor ills that do not endanger
life may obtain a firmer hold, and therefore we should expect a
greater tendency towards a reversion to such. Eeversions to
pathological states belonging to a few generations back may, of
course, occur; but it is highly improbable — indeed I should
say absolutely impossible — for them to occur to a patho-
logical state of such far-off ancestral date as may happen in
the case of reversions to physiological states. The stripes of
the mule are derived from a very remote ancestor, but then
they were a constant ancestral character during many thousands
of generations, and made a correspondingly deep impress upon
the organism and its embryological processes. No pathological
character could acquire such a hold. These considerations
should tend to dispose of the theory that many sporadic diseases
are reversions to such remote pathological states. (It has been
suggested, for instance, that leprosy sporadically occurring in
non-leprous countries has such an origin.)

Nevertheless, I see theoretical grounds for assuming that
disease may result from reversion to a remote ancestral state.
Thus, the tissues may revert to remote ancestral states, which,
though perfectly physiological in themselves, may be injuriously
susceptible to influences which are incapable of hurting the

120 THE CAUSATION OF DISEASE.

normally evolved tissues — that is to say, although reversions
to remotely ancestral pathological states are improbable, yet
reversions to physiological states of a bygone era may lead
to pathological states under our present E. We must, how-
ever, allow that reversions to true-pathological states of a few
generations back are quite possible ; and this fact alone should
guard us against asserting that a disease has no element of
heredity in it when we can get no history of its heredity, for, as
Sir James Paget observes, it is impossible, in the most fortu-
nate cases, to trace the family history beyond five generations.

The tendency to reversion when two animals are crossed has,
I believe, an interesting application in pathology. We may, I
think, safely infer from this principle that the more unlike any
two individuals are, the greater will be the tendency towards a
reversion in the offspring of their union ; nay, I believe we may
go further than this, and expect that, if the parents show a
great unlikeness in any one particular, there will be a special
tendency to a reversion as regards that particular.

Now, if by thus uniting individuals showing great unlike-
ness in one particular we can effect a reversion to a status quo
ante, might we not hope, by judiciously mating an individual
showing a strong tendency to a particular disease, to cause
by reversion a complete disappearance of this in the offspring ?
Not that I am sanguine enough to suppose that men and women
will ever trouble themselves very much about such very un-
romantic considerations, but it occasionally falls to the lot of
the physician to advise as to the desirability of a particular
marriage, and it behoves him, therefore, to consider all the aspects
of the case. All will admit that nothing could justify assent
to marriage between individuals showing a tendency to a
serious disease, say insanity; but should we be altogether
justified in withholding our sanction if one of the two showed
a clean ancestral chart as regards that disease ? I know many
physicians regard the probability of the disorder appearing
in some of the offspring of such a couple as very strong, and
they are ready to cite several cases in which insanity was
inherited from one side only. But, it may be retorted : What
proof is there that the other ancestral line is perfectly free from
insanity, or some allied neurosis ? Of how few families could this

THE CAUSATION OF DISEASE. 121

be truthfully said ? Modern civilization has wrought the nervous
system into a high state of instability. Hence, in the union of
an individual having a tendency to insanity with an average
individual, the combining tendencies would be more or less in
the same direction. Evolution in the case of each having pro-
ceeded quite recently upon lines more or less identical, there will
be no sharp divergence as regards the nervous system. I hold,
nevertheless, that the offspring would show a strong tendency
to reversion if the non-affected parent presented a perfectly
vigorous and stable nervous system ; and I should not consider
this position false, without the strongest evidence, in any sup-
posed instance of the contrary, of this parental perfection. The
sole crucial test would be the union of a highly neurotic individual
with a healthy savage. Let it be noted, however, I do not for
one moment assert that there would be no tendency in such a
case to the inheritance of the weakness. Brown- Sequard's
experiments on guinea pigs would at once disprove any such
assertion.

I imagine that this tendency of ' ' crossing " to produce a
status quo ante plays an important part in the inheritance of
disease, and may help to explain how the same intensity of the
same disease in the one parent is in a certain number of cases
strongly inherited, but in others absolutely uninherited. For this
frequently occurs, and leads one to think that the principle of
heredity is very fickle.

The following case illustrates this point : A. suffered from
ichthyosis inherited through his father's side. He married
twice. The children by his first wife were quite free from the
complaint. Those by his second wife — three in number —
were all afflicted with it. It is manifest that the integu-
mental system in the first wife, or some tissue or tissues govern-
ing it, prevented the inheritance of the defect. Therefore,
putting aside all theory, we have distinct evidence that certain
crossings are capable of diminishing the inheritance of a
particular disease; and it would, indeed, be a great triumph
if we could discover what particular order of constitution is
capable of weakening or obliterating, on this principle of cross-
ing, the inheritableness of different diseases — if we knew, for
instance, what body-habit would prevent rheumatism in the

122 THE CAUSATION OF DISEASE.

mother from being inherited. That there are hidden principles
capable of such practical application, I doubt not ; but it would
need one endowed with the genius and thoroughness of a
Darwin to discover them, and, even if we could discover them,
they would be of little practical use, for how many young
marriageable folk would listen to our words of wisdom ?

To sum up the chief points regarding reversion, so far as
they bear upon practical medicine : —

1. Reversions to serious pathological states rarely occur,
because the graver forms of disease have no great ancestral age.

2. Reversions to physiological states may occur under
certain conditions of E and as a result of particular crossings.
These may be physiological in the reverting individual, as in
the ancestor from whom they are derived ; or it may happen
that the physiological characters show a tendency to become
pathological in the reverting individual, through their imperfect
adaptation to modern environments ( = sub-pathological varia-
tions) ; or, finally, these originally physiological characters may
be distinctly pathological in the reverting individual, as in
persistent branchial clefts.

3. The principle of reversion explains the vis medicatrix
natures. This is favoured by subjecting the individual to an
environment as like as possible to that of primitive man ;
or, by crossing an individual showing a disease-tendency
with one showing a character very unlike the pathological
one, on the principle that crossing of unlike individuals tends
to a reversion to the status quo ante the development of the
unlike points, namely, health.

4. Most, if not all, diseases are attended by or rather, consist
in, a multitude of reversions, for, in so far as the structural
alterations of disease are partial dissolutions, they must in
some degree be reversions ; for a partial dissolution must
necessarily tend to disclose a tissue state belonging to a past
evolutionary era.

CHAPTER XIV.

Heredity (continued) — Influence of the Male Element upon the Female
Organism — Inheritance of Acquired Structural Characters.

Influence of the Male Element upon the Female
Organism. — It is well known that the sperm not only affects
the germ or the female element, impressing upon it the power
of growing up into a more or less mean parental likeness, but
that it likewise influences the mother organism. This holds
good both of plants and animals. Thus, in plants, the ovarium
and the contents of the ovule, which " are obviously parts of
the female organism,"* and quite distinct from the embryo,
are frequently affected by the male element — the most common
alteration being one of colour. This is best shown by fer-
tilizing the flowers of one species with the pollen of a different
species or variety, when it is found that " sometimes the whole
ovarium, or all the seeds, are thus affected, sometimes only a cer-
tain number of the seeds If we could imagine the same

flower to yield seeds during successive years, then it would not
be very surprising that the flower of which the ovarium had
been modified by foreign pollen, should next year produce,
when self-fertilized, offspring modified by the previous male
influence." Similarly in the case of animals. The mother is
in some way influenced by the male element, so that future
progeny by another father tend to partake of the characters of
the former sire. Thus, a thoroughbred mare was crossed with
a quagga, and bore to it a hybrid animal ; this same mare was
afterwards crossed with a black Arabian horse, and produced
two colts, which were more plainly striped than the quagga ;
" but what makes the case still more striking is the fact that in
these two colts the hair of the mane resembled that of the

* See ''Animals and Plants under Domestication," vol. i. p. 428, second edit.

124 THE CAUSATION OF DISEASE.

quagga, being short, stiff, and upright." * Many such cases
might be cited, but there is no need, for the principle in
question is so well recognized that no breeder would allow a
good animal to be crossed by one of inferior breed, for fear of
damaging the future progeny.

Now, these considerations raise a question of some interest to
the physician. If the male, by impregnating the female, tends
to make all the future progeny like himself, one would expect
the second child of the same parents to be more like the father
than the first, for it would inherit the ordinary mean likeness
plus, an additional degree of likeness derived from the previous
impregnation, and this latter we may suppose to increase with
each successive impregnation by the same male ; so that, if such
is the case, each successive child should be more like the father,
and in consequence show a greater tendency to inherit disease
from him. Whether this inference is true or not, I cannot
say, but the subject is one deserving of investigation, and ]
should be somewhat surprised were it not found that the first
child is, on the whole, least like the father ; but I should not
be surprised if it were discovered that, after the second, each
successive child was not more like the father, because we can
well imagine that the sire, having once, by an impregnation,
influenced the mother in a particular way, may be incapable of
adding to this influence by subsequent impregnations. There
is no reason why the question should not be settled by a series
of experiments on animals and plants.

Inheritance of Acquired Structural Characters. — Of
course characters once acquired tend to be inherited. Some
authors — even great ones — have been at much trouble to prove
that acquired characters, as well as inherited ones, may be
handed down by parents to their offspring. To me the fact
seems self-evident ; it matters little how a parent has come by
a character, for, according to the great doctrine of heredity, the
offspring tend to reproduce more or less exactly the likeness of
the parents. What we have seen is, that acquired characters
are less likely to be inherited than others, for they are not so
deeply impressed upon the organism.

* " Animals and Plants under Domestication," vol. i. p. 436.

THE CAUSATION OF DISEASE. 12$

Some very interesting instances of the inheritance of ac-
quired characters are on record. Quite recently the Lancet
recorded the case of a bitch transmitting to one of its pups a
peculiar trick which it had learnt. The pup was removed from
its mother while very young, so that the case cannot be ex-
plained on the theory of imitation. Similar instances might be
recorded by the score.

There are also on record many cases of the inheritance of
obvious tissue-alterations wrought by violent means. Thus,
a cow, which had lost a horn from u accident and consequent
suppuration," produced three calves which were hornless on
the corresponding side, and it is well known that mutilations
in man are apt to be inherited, as has happened with injury
of the eyes, face, hand, fingers, and other organs. Again, the
effects of operations are sometimes inherited : thus, the epilepsy
which Brown-Sequard produced artificially in some guinea-pigs
by section of the sciatic nerve and injury of the cord, was
transmitted to their offspring. The following conditions, arti-
ficially induced in the parents, were also transmitted : absence
of two or three toes in the hind leg, exophthalmia, haematuria,
and dry gangrene of the ears. It is noteworthy that in all
these operations the nervous system was markedly involved in
the injury ; wherefore, this system has been assumed to play
an important part in such inheritances.

On the other hand, mutilations may be inflicted upon
several successive generations without showing the slightest
tendency to inheritance. Many savage tribes mutilate their
bodies in sundry ways, but, so far as we know, such mutila-
tions are never inherited. Moreover, the practice of circum-
cision, which has been followed for many generations by the
Jews, seems to have left no permanent effect upon the race.

All this shows us that we have yet much to learn concerning
heredity. Yet there can be no doubt that the subtlest changes
wrought upon an organism by peculiarities of E tend to be
inherited. There is not an act or thought of a parent but
may have its effect upon the offspring. What tremendous
responsibilities, therefore, rest upon fathers and mothers ! The
individual is an embodiment of the hereditary principle.
What he is, such future generations springing from him will

126 THE CAUSATION OF DISEASE.

tend to be, for none of us can escape the inexorable law of
heredity. Though the influence of the Environment is great,
it may truly be said that we are what we are — great or small,
strong or weak — by virtue of heredity. But we have the
power to make ourselves better or worse. Wherefore, let
every potential parent remember that the strengthening or
weakening of his structure not only concerns himself, but
those who come after him — that his conduct of life may, in
other ways than by example and intellectual legacy, echo
through posterity.

Seeing that disease is an abnormal inter-action of S and E,
and that S is almost entirely determined by heredity, it is
manifest that heredity must take an overwhelming share in
the causation of disease. But we shall the better be able to
appreciate this fact after certain other topics have been con-
sidered, and, therefore, the part played by heredity in disease
will be considered separately (see Part III).

CHAPTER XV.

The Causation of Structure — The Influence of Ante-partem Environment
upon Structure.

Having now firmly grasped the fact that the structure of an
organism chiefly depends upon heredity, and that, compared
with it, any other moulding power is altogether insignificant,
we have now to study more particularly the part which E plays
in moulding the organism.

Although its influence is infinitely less than that of
heredity, it is nevertheless capable of profoundly modifying
structure, and its effects are deserving of most careful study.

I have endeavoured hitherto to keep the treatment of these
two great plastic powers as far as possible apart, for the sake
of clearness, but it has not been possible to succeed in this
entirely.

The influence of E disturbs heredity. Were the E exactly
alike for every child born to the same parents, all the children
would be exactly alike, save, of course, for such differences as
depend upon sex : that is to say, the sons would exactly re-
semble each other, and the daughters likewise. And if the
world were peopled afresh from another Adam and Eve under
an identical E for all, all men on the one hand and all women
on the other, would be exactly alike at corresponding ages.

This proposition may seem a bold one, but I shall bring forward
strong evidence in support of it. Should, however, the reader
deem this evidence inconclusive, the hypothesis will, neverthe-
less, be found to be a good working one. To me the conclu-
sion seems so tempting, that I am surprised biologists have not
embraced it eagerly. Perhaps some have actually done so,
but certainly neither Darwin nor Spencer have committed
themselves to it, although the latter philosopher, by implication
at least, would almost seem to hold the view.

128 THE CAUSATION OF DISEASE.

It is obvious that such a proposition can admit of no experi-
mental proof. How is it possible to subject any two brothers
or sisters to exactly the same E from the earliest period
of their existence, the E, it must be remembered extending back
beyond the period of embryonic life to the actual coming into
being of germ and sperm? But, although our proposition admits
of no absolute experimental proof, neither does the first law of.
motion. The two, indeed, allow of the same kind of proof —
namely, that termed by logicians the " method of residues."
The first law of motion runs thus : "A body in motion will con-
tinue to move with the same velocity in a straight line for ever,
if no other force than that by which it is impelled act upon it."
But the conditions of the "if" obtain nowhere. Nowhere
is it possible to isolate a body from the action of other forces ;
the tiniest fleck acts upon, and is acted upon by, every other
particle of matter in the universe, however remote it be. He
who denies this must be prepared to confute the law of universal
gravitation. It is found, however, that the nearer the conditions
of the " if " are approached, the closer does the result accord
with the terms of the proposition. In our own world, friction
and atmospheric resistance are ever present to counteract the
tendency of the first law of motion, but such outside resisting
forces are reduced to a minimum in the case of the heavenly
bodies, which, suffering practically no resistance, maintain a
more or less uniform rate of movement ; nevertheless, the
motion is not in a uniform straight line, for gravity still acts,
causing the movements in curves, and maintaining eacli system
in "moving equilibrium."*

The same line of argument applies to heredity : the nearer
the requirements of the case are complied with, the closer do
we find the result according with the assertion. In both cases
we have to deal with an E which represents the conditions of
the " if ; " in the one, we require a completely negative E, and
in the other an E which shall be alike for all the children born
of the same parents, and it is, as I have said, manifestly im-
possible to obtain either of these requisites.

* The truth of the principle, however, is placed beyond the possibility of
confutation by the fact that it forms a correct basis for astronomical calcu-
lation.

THE CAUSATION OF DISEASE. I 29

The impossibility of any two organisms being subjected to
exactly the same E is evident from Herbert Spencer's dictum,
that "no two parts of any aggregate can be similarly con-
ditioned in respect of incident forces." * So that even uni-
cellular organisms inhabiting the same fluid medium cannot be
subjected to exactly the same E ; and not only this, but no two
parts of any one organism " are similarly circumstanced in
respect of incident forces."

Hence different organisms, being subjected to forces which
are more or less unlike, tend themselves to become more or less
unlike — that is to say, they form natural variations, and not only
does the organism as a whole alter, but owing to different parts
of the same organism being subjected to different forces, the
structure of these different parts becomes differently modified :
the homogeneous passes into the heterogeneous. Now if the
E can never be the same even for simple organisms, we see
how utterly impossible it is that it should be the same for such
a complex organism as man.

The Influence of the Ante-partem E upon S. — Let us,
for instance, consider briefly man's ante-partem E. In so
doing, it will be necessary, of course, to start at a period ante-
cedent to the birth of germ and sperm, and to inquire into the
conditions under which they come into being ; and it will be
further necessary to take account of the agencies environing the
embryo to which they give origin. Concerning the former, it
is manifest that the circumstances under which germ and
sperm spring into being, and the subsequent E of each, must
differ from time to time with the general bodily health of the
father and mother, with the kind of food taken, the amount of
physical exercise, and so forth. We can well understand how
these and other conditions, many quite outside our knowledge,
may so modify the cell-E of the tissues, including those of
ovary and testicle, as to lead to differences in their cell struc-
ture— to deviations, that is, from the ideal form — and, conse-
quently, to differences in the reproductive elements to which
these latter structures give origin. Even supposing, however,
the bodily state of the parents to be exactly the same from day

* See Spencer's " First Principles," § 109. Also Spencer's " Biology,"
vol. i. § 88.

130 THE CAUSATION OF DISEASE.

to day and year to year, it would follow, from the Spencerian
dictum above quoted, that no two germs or sperms could be
exactly alike, for it is utterly impossible for the conditions
of birth to be exactly alike in any two cases ; but, inasmuch
as the bodily state does vary from day to day and from year
to year, we should expect those germs and sperms to be most
alike which are produced at or about the same time, for in
such cases the conditions of germ and sperm birth are most
alike ; and this, as we shall see, is the case.*

We have next to take into account the influence of the E
upon the embryo during the months of gestation. This,
though very important, is far less so than the earlier influence
just spoken of. It is wrought in a twofold way, and in a two-
fold way only — (i) Through the mother's blood ; (2) Through
modifications of external pressure. Such being the case, one
is induced a priori to doubt the popular notions concerning
maternal impressions.! Dr. R. Lee believes that many cases
of idiocy are caused by mental distress in the mother whilst
with child, and it is noteworthy that from time immemorial
men have attributed great influence to the woman's surround-
ings while pregnant. Thus, in some countries, curious objects
are placed about the chamber, and are supposed, by working
on the mother's mind, to influence her offspring. All will
certainly agree that the mind of the pregnant woman should
be kept in a quiet and composed state, but this is chiefly for
her own sake, for the emotional being of the pregnant woman

* In connection with this subject the reader may recall the opening words of
" Tristram Shandy" : — "I wish either my father, or my mother, or, indeed, both
of them, as they were in duty both equally bound to it, had minded what they
were about when they begot me ; had they duly considered how much depended
upon what they were then doing ; that not only the production of a rational being
was concerned in it, but that possibly the happy formation and temperament
of his body, perhaps his genius and the very cast of his mind ; and, for aught
they knew to the contrary, even the fortunes of his whole house might take
their turn from the humours and dispositions that were then uppermost. Had
they duly weighed and considered all this and proceeded accordingly, I am
verily persuaded I should have made quite a different figure on the whole from
that in which the reader is likely to see me. Believe me, good folk, this
not so inconsiderable a tiling as many of you may think it." — La URENCE
Sterne.

f Tot & resume" of the main facts connected with this subject see Dr.
Fordyce Barker, "American Gynaecological Trans.," 1887.

THE CAUSATION OF DISEASE. I 3 I

is wrought into a high pitch of irritability. Every tissue in
her body is, in fact, at this time, modified, and the nervous
system forms no exception. Wherefore it happens that de-
pressing mental shocks are doubly apt to depress the pregnant
woman, and thus the mother's health suffers, and through it
that of the child. The effect on the latter is probably wrought
through the mother's blood, which must necessarily suffer from
any great disturbance in nervous action. Owing to this
irritable state of the nervous system in the pregnant woman,
it rarely happens that she passes through the period of child-
carrying without some fright or trouble, so that little difficulty
is found by believers in maternal impressions in accounting for
any peculiarity in the child that may happen to be present.

Although it is not easy to conceive of any other ways by
which the mother can impress her child, it is, of course, open
for any one to assert that there are unknown agencies — powers
quite beyond the reach of discovery — capable of bringing about
this result ; and, however improbable such a view may seem
to us, we are not justified in rejecting it unless we can prove
that certain results can be explained on either of the methods
mentioned.

Let us first inquire how the child may be influenced through
the mother's blood. A rich and abundant supply of blood —
and the quantity will chiefly depend upon the size of the
placenta — will necessarily lead to a larger and better nourished
foetus than one that is poor and scanty. We may be quite
sure that this early difference in blood-supply will leave an
impress upon the embryo which will be felt throughout
the whole ensuing life. No matter how perfect the post-
partum environment, it cannot compensate for such an imper-
fect blood-supply. If the foundation of the young human
being be not properly laid, it is impossible to erect thereon a
solid, well-built structure ; patch it up as we may, the funda-
mental weakness will be for ever showing itself. In regard to
the nature of the mother's blood we must remember, how-
ever, that the foetus is, in some respects, a parasite upon the
mother, and will appropriate the nutritive elements of the
maternal blood far more vigorously and abundantly, relatively
to its size, than the mother ; so that an intensely emaciated

132 THE CAUSATION OF DISEASE.

mother may bring forth a stout child ; but mere bulk is not a
sign of excellence, and we must not too hastily assume from
such a case that the state of the maternal nutrition can have
little influence on the child. There cannot be the slightest
doubt that the general state of the mother's health, by deter-
mining the quality of her blood, works a marked effect upon
the destiny of the child.

The mother's blood may likewise affect the foetus by contain-
ing some poison, such as the virus of syphilis or scarlatina.

It is difficult to see how the maternal blood can influence the
foetus, except in one of the three ways just mentioned —
namely, by being abundant or scanty ; rich or . poor in its
proper constituents; or, finally, by containing some noxa. It
is not easy to understand how it can convey an impression
from a particular tissue in the mother to a corresponding one
in the foetus, as must occur (if there be any truth in such
cases) when the mother having, let us say, been struck during
pregnancy across the face with a rat, the child is horn with
a mark corresponding exactly in position. I repeat, one
cannot well see how the mother's blood can influence the child
so as to bring about such a result. If the maternal im-
pression occur before the complete development of the Ovum,
the explanation is easy : the tendency. of the ovum is to repro-
duce the structure of the mother. Such is the law of heredity.
Therefore, if the mother's body undergoes some change in
structure before the ovum has ripened (and this takes place
just before conception), the child would tend to inherit it; and
that mental shocks may work a specific effect upon particular
tissues, there can be no doubt. For instance, a woman sees
the foot of a child crushed under a gate, and she is forthwith*
seized with great pain in her own foot, and • th-is afterwards
becomes actually diseased.* Such a local change might so
impress the ovum as to lead to a peculiarity in the correspond-
ing foot of the foetus developing therefrom. Indeed; this
might well occur, even though the mother's foot were ' not
obviously affected; for, supposing the doctrine of Pangenesis
to be correct, one can understand how the maternal blood

* See on this subject Tuke's interesting ivork on the influence of the mind
on the body.

THE CAUSATION OF DISEASE. I 33

might convey specific influences from certain maternal tissues
to corresponding parts in the child, the " gemmules " thrown
off from such maternal tissues would, according to this doctrine,
show a. tendency, by their inherent attractive power, to attach
themselves to corresponding parts in the child, and so influence
the development of these parts. But this is obviously sheer
speculation.

The second and sole remaining method by which the foetus
may be affected is by pressure. It is well known that all
sorts of mutilations may result in this way, and it is needless
to enumerate them. Possibly the shape of the child's head
may in some degree depend upon the shape of the mother's
pelvis,, for the moulding of the head at birth is probably never
entirely recovered from; and thus it may happen that the
different kinds of presentation permanently influence the shape
of the head by moulding it in different ways, so that a head, born
for instance by breech, may be permanently different in shape
from what it would have been had it been born by vertex. As
showing the influence of pressure upon the shape of the head,
it may be remembered that some savage tribes alter the shape
thereof by pressure between boards ; nevertheless, the compres-
sion which they employ extends over a prolonged period, differing
very markedly in this respect from the merely temporary pres-
sure of birth.* • •

* It may be remarked here that the shape of the child's head bears a
definite relation to that of the female pelvis. This may be seen by examining
the pelves and crania of the different races of man. The two have become
mutually adapted to one another, and the adaptation has doubtless been
largely wrought by natural selection. On the one hand, any variation in the
shape of the head which hindered its birth would tend to the destruction of
the child. Hence the shape of the pelvis doubtless largely determines that of
the child's head", because in a state of nature, at all events, only those heads
are born which are properly adapted to the pelvis. On the other hand, if the
pelvis does not properly admit of the passage of the child's head, the mother
would be more apt' to die, so. that natural selection maintains the proper
adaptation of the pelvis to the shape of the head ; wherefore the shape of
the foetal head likewise determines that of the maternal pelvis. Now, the
main distinction between the male and female pelvis is undoubtedly the
width of the pubic arch. Almost all the other differences follow from it,
as . I have proved to myself on a soft artificial pelvis ; for if the tuber ischii
be pulled outwards, the arch widens, the symphysis and the pelvic cavity
become shallower, the thyroid foramina triangular, and the transverse

L

134 THE CAUSATION OF DISEASE.

I. Geoffroy St. Hilaire has made several important experi-
ments upon the lower animals, with a view to study the effect
of ante-partem E upon the offspring. His writings should be
carefully studied by those wishing to work in this direction.*

It is proper here to allude to the effect of premature birth
upon the child's future. When the foetus is born before its
time, the E undergoes a sudden and .premature alteration. In
place of the uniformly warm medium afforded by the amniotic
fluid, it is prematurely subjected to the vicissitudes of tem-
perature. This may be more or less successfully guarded
against ; more important is the premature substitution of
feeding by mouth, for nourishment drawn directly from the
mother's blood. The child has now to elaborate for itself the
blood which hitherto has been conveyed to it through the
placenta, and, its digestive system not yet being prepared to
properly digest the mother's milk, it cannot possibly be so well
nourished as by the placental blood. Hence, every prematurely
born individual is less vigorous than he would have been if born
at the full time.

From what I have said it is manifest that the ante-partem E
is no* such simple thing as some might think. There is, indeed,

diameters increase. The only other important distinction between the male
and female pelvis, which cannot thus be accounted for, is the greater
conjugate in the female. Now the advantage to woman of this widening
of the pubic arch is obvious. In all vertex or face presentations, the part
to be born first, namely, the occiput or chin, rotates, or should rotate, under
the symphysis. If either of these parts are from the first anterior (as is the
rule), the depth of the bony pelvis through which they have to pass is very-
small, to wit : the depth of the symphysis pubis. Thus they are readily-
pushed out under the arch, one end of the long pole being thereby released,.
and, if the arch be wide, birth of the remaining part of the head readily
occurs. In rarer cases backward rotation takes place ; but mark the difference
— the part to be born first has to travel through three times the distance of
bony pelvis, and, further, it does not pass under an arch, but over a sharp
point. The width of the arch, therefore, stands in a most important relation
to the child's head. The larger the latter the greater is the necessary pubic
span, so that we should expect the female pubic span to be largest in those-
races which are the most intellectual. Now the width of the pubic arch
determines the width of the hips, for, as the arch increases, the acetabula,
and with them the femora, are thrust outwards. Wherefore we may con-
clude that the women of intellectual races are large-hipped, and that, as
evolution proceeds, they will become more so. These theoretic considerations
are, I believe, substantiated by fact.

* Vide " Me*moire sur la Production Artificielle des Monstruosites, 1862,"
pp. 8-12 ; "Recherches sur les Conditions, &c, chez les Monstres," 1863.

THE CAUSATION OF DISEASE. 1 35

a wide field of study here. We have seen that the spermatic
and germatic E cannot possibly be the same for any two germs
or sperms, and we have farther seen that the embryonic E is
capable of much diversity, and that the nature of this E exer-
cises an important influence on the destinies of the individual,
though one far less than that of the earlier germatic and
spermatic E. And here we may enunciate an important prin-
ciple, namely : the influence of E is great in proportion as it
acts early in the life-history of the individual. It is most
potent during the evolution of germ and sperm : it is more
potent during the earlier than during the later periods of em-
bryonic life : and after birth its influence grows less and less,
as time wears on, the diminution being most marked after
maturity has been reached ; for the E is then incapable of
interfering with development.

The above principle follows from the fact that a small
initial difference will, in the course of time, lead to a very
wide deviation. In the germ and sperm, how inconceivably
complex must be the arrangement of the ultimate particles,
and how important, at this early date, the influence of the E
upon their delicate fabric ! We can well see how the slightest
dislocation of the ultimate germ and sperm particles will
modify the entii'e future development of the embryo to which
these two elements give origin ; and when we further reflect
upon the rapid and important changes occurring during the
earlier period of embryonic life, it is not difficult to understand
how influential the E is at this time iu directing the processes
of development in this or that direction.

Inasmuch, then, as the ante-partem E differs for different in-
dividuals, it follows that all children born to the same parents
must differ, for a difference of E necessitates a difference
of structure. According to our principle of structural mean, all
children born to the same parents would be the same under
exactly the same E, save, of course, for such differences as
depend upon sex. But variations become an a priori necessity
from the diversities of E. The only point about which doubt
can exist is whether this diversity of E is competent to account
for all the differences.

L 2

136 THE CAUSATION OF DISEASE.

Now it is a very suggestive fact that the more nearly
identical the ante-partem E, the more alike are the children.
The nearest approach to identity occurs in the case of twins,
and these, as every one knows, are more like one another than
brothers and sisters not of twin birth; The germs, and -sperms
from which twins are evolved have sprung into being under
very similar conditions, and the E, moreover, of the embryos, as
determined by blood, is very similar. As regards quality
of blood, ' it is practically the same, but the quantity may,
of course, differ, as when the placentae are not of the same size ;
and as regards pressure, the effect upon the two children may
be very different. Thus, even in the case of twins, some
structural differences may be a priori postulated ; sometimes
the difference is considerable. Professor Lucas, whose work
on. Heredity, so far as it is a record of facts, is the most
important one yet published, quotes from Pierre Beielly : *
" Twins differ in expression, voice, writing, gesture, carriage,
and in many other respects. . . . The Siamese brothers
themselves — these more-than-twin beings — were not of the
same height, and the truly striking likeness of countenance
showed a marked difference on close study." ..." A similar
diversity is met with among the young of animals," continues
Dr. Lucas ; " the difference among the pups of the same litter,
even when one has taken care to cross the bitch with the
one dog is often prodigious." Herbert Spencer speaks in a
like strain : " Plants grown from seeds out of one pod, and
animals produced at one birth are not alike, and sometimes
differ considerably. In a litter of pigs or of kittens, we rarely
see uniformity of markings, and occasionally there are im-
portant structural contrasts. I have, myself, recently been
shown a litter of Newfoundland puppies, some of which had
four digits to their feet, while in others there was present
on each hind foot what is called the ' Dew claw,' a rudimentary
fifth digit."!

Some diversity among offspring born at the same time is an
a priori necessity, as I have again and again insisted. No two
peas from the same pod, nor any two members of the same litter

* " Traite de L'Heredite Naturelle." Par le Dr. Prosper Lucas, vol. i. p. 105.
f Herbert Spencer, " Principles of Biology," vol. i.. § 86.

THE CAUSATION OF DISEASE. 1 37

or brood, are " similarly circumstanced in respect of incident
forces/' and therefore they must differ. Nevertheless, plants
grown from the seeds out of one pod, and animals produced at
one birth, are more like one another than plants grown
from the seeds of pods produced at different times, and anim,als
produced at different litters. The only remaining question is,
whether the differences in E are adequate to account for
the differences of the individuals? The fact that among
animals born at one birth, some may take after the father and
others after the mother, is an apparent argument against
the principle for which I am contending, but. one can well
understand how the nature of the E under which germ and
sperm spring into existence may so affect their delicate
structure as to strengthen or weaken, as the case may be,
the capacity of the one or the other to cause the offspring to
grow like the being from which it is derived.

The remarkable likeness between human twins is nowhere
better shown than in the tendency which they display towards
the same diseases ; it proves that they are like one another,
not only in gross configuration, but also in the more delicate
structure of the tissues. I shall have occasion in another part
to speak of the pathological likeness of twins. Here I will
briefly mention two cases. A mother brought her twin babies
to me. Each of them was suffering from a syphilitic rash of
like character and distribution ; considering how varied are
the rashes met with in congenital syphilis, this likeness was
remarkable. The eruption appeared when the children were
three weeks old, in the one a few hours before the other.
Each child having developed under an almost identical E, not
only in respect of physiological conditions, but in respect also
of the specific mal-environment, what wonder that they should
exhibit this marvellous pathological likeness ! Again, I have,
the very day I write this, seen twin girls, of whom the mother
says : " They are always ill together ; the one never suffers
without the other."

CHAPTER XVI.

The Influence of Environment upon Structure — The Influence of the Ante-
partem Environment (continued) — Differences in E the Prime Cause of
Natural Variations.

We have already seen that the E is not so effective after birth
as before it. Nevertheless, from a health point of view, it is
of far greater importance, because there is greater room for
morbid influences after birth, when the E abounds in evils.
Moreover, before birth the organism is, in a sense, parasitic,
but after birth it becomes independent and capable of regu-
lating its own E.

Indeed, although the post -partem E is less able to influence
S than the ante-partem E, owing to the great plasticity of the
embryo, it is nevertheless a fact that the post-partein E is
capable of inducing very considerable structural change, the
growing complexity of the E as the individual waxes older
being to some extent a set-off against the lessening plasticity
of his tissues. If the E of different individuals must be
unlike before birth, how much more unlike must it be after
birth ! The complexity and necessary diversity of the post-
partem E was insisted on in a former chapter. We there saw
how, in a complex society, the number of different E's in-
creases as the division of labour proceeds, for the E differs
in every occupation. And thus it happens that, if all people
came from their mother's womb exactly alike, they would
soon begin to differ in a recognizable way. Let one of
twins become a soldier, the other a shoemaker, and we shall
have no difficulty in telling the one from the other, no matter
how great their original likeness. And not only will they
be altered in obvious bodily structure, but a careful look
into the mental world of each will disclose a marked
difference there alsOv Thus do our surroundings mould

THE CAUSATION OF DISEASE. 1 39

us. The plastic being is shaped by the E in all sorts of
different ways, both as regards mind and body. We do
not always take this sufficiently into account ; certainly not
as regards mind. In our commerce with the world we forget
how vast is the difference between the mental worlds of different
individuals, so apt are we to judge others by ourselves. The
natural mental diversity accounts, of course, for much of the
difference, but over and above this, there can be no doubt that
the general cast of the mind is enormously influenced by the
surroundings. How different, for instance, are the mental
worlds of the artisan, doctor, lawyer, divine ! The fact is no
doubt readily allowed in theory, but it is not practically acted
up to. And thus when an argument is started, each looks at
the matter from his own particular standpoint, and views it in
a different light. If we could only rightly estimate the in-
fluence of E upon mind, there would be less of that terrible
bigotry which so often warps the judgment, and makes an
otherwise powerful intellect as ineffectual as a child's.

The animal organism is very pliant, very plastic. The
process of moulding is termed education, and this is both con-
scious and unconscious, although the term is more commonly
applied to the voluntary, conscious process. AVe may define
the latter, or the " art of education,"' as the voluntary
application of a specific E to plastic organic matter, with
intent to improve its structure.* Plasticity is greatest in
early life, and education is then most effectual. This pro-
cess, be it remembered, includes not only mental moulding,
but physical moulding likewise. Indeed, the two fall, in
the long run, under the same head, for all mental training
has a physical basis ; wherefore mental training is physical
training.

Now every structural change impressed upon an organism
by its E, and other than that which is the distinct outcome of

* The structural change -wrought by education is, of course, an evolutionary
process. When a specific E, voluntarily applied, causes dissolution, as in
a voluntary maiming of the body, the process would obviously not be one
of education. Nor could surgical operations be classed under the head of
" education." Nevertheless, they appear to me to be, in a, sense, educatory,
since the body is thereby altered for the better by the application of a specific
environment in the shape of surgical skill.

140 THE CAUSATION OF DISEASE.

heredity, is a natural variation — a natural variation from the
structural mean. In other words, every acquisition is a natural
variation. The difficulty here is to distinguish, in scientific
language, between what is hereditary and what is acquired,
for it is by no means easy to say whether a structural
peculiarity is the distinct outcome of heredity, or whether
it is not rather due to the application of some specific E ;
but even in the latter case heredity plays a most im-
portant part, since it is this, as will be more particularly
shown later on, which determines the capacity of varying in a
particular way.

Scientifically, it is perfectly justifiable to distinguish sharply
between the hereditary and the acquired ; practically, how-
ever, it is quite impossible. Scientifically, we may dis-
tinguish as follows : — If an individual is exposed to as
negative an E as is compatible with life, it is evident that
there will be little or no acquisition. We may, for
purposes of argument, assume such a negative E — an E,
namely, under which an individual will pass through a series
of developmental changes, which are the outcome of the force
of heredity, pure and simple — i.e., altogether independent of
external influences. It is, of course, impossible really to
exclude altogether the influence of E, since life is due to
the interaction of S and E. Assuming, however, such a
theoretic standard negative E, both ante and post partem, we
should then discover the individual to be that mean structural
product whereof we have spoken. As a matter of fact, it
would be utterly impossible to prevent acquisitions, for the
organic textures are so plastic, so impressionable, that they
are ever ready to be moulded by a multiplicity of diverse
external agencies.

It is absolutely necessary to assume the theoretical existence
of a hereditary product, pure and simple, in order to dis-
tinguish between that which is acquired and that which is
inherited. Of course, we inherit the power of acquiring, but
we do not entirely inherit the acquisition, for if we did not
place ourselves under an E capable of effecting this structural
change or acquisition, it would never appear, and such an E may
in no way be necessary to life. Wherefore we are justified in

THE CAUSATION OF DISEASE. 1 4 1

theoretically supposing an individual to pass through life with-
out being exposed to such E, and we may speak of the indi-
vidual such as he would then be, as the strict and sole product
of heredity. What he is capable of becoming under particular
environments belongs to the region of acquisition, and every
such acquisition is a natural variation. There is no real differ-
ence between conscious education (or the conscious application
of a specific E to plastic organic matter, in order to induce a
specific variation or acquisition), and the more or less uncon-
scious moulding of our bodies by the agencies around us
— the semblance of difference lying in this : that the one
is done consciously and for a purpose, while the other is
not. And, again, between this latter kind of moulding and
that moulding in nature whereby distinct and well-recognized
variations arise, there is no distinction whatever. Both are
due to E. In brief, the structural states which are not
strictly inherited — i.e., which would not appear under our
theoretic negative E — are acquisitions, and all acquisitions are
natural variations.*

It is therefore evident that the subtlest habit (supposing this
to be strictly an acquired habit) is a natural variation, since
fundamentally it is a structural variation wrought through
a peculiarity of E. Indeed, pushing the matter yet further,
we shall be compelled to admit that that part of our mental
world, which is not strictly inherent, but acquired, falls
under this same head of natural variation. We inherit in
their fulness all the so-called instincts — our simple sensations
and emotions — these would manifest themselves under the

* While it is correct to say that all acquisitions are natural variations, it is
hardly true that all natural variations are acquisitions, or, in other words, that
the latter are the sole cause of variations, and this for two reasons — (i) Because
the union of unlike parents leads to a mean, unlike either, and this is a well-
recognized cause of natural variations ; nevertheless, it is only a secondary and
minor cause, since it would be inoperative without the other. Acquisition is
undoubtedly the primary cause, for if the world were peopled afresh from two
individuals perfectly alike in all respects, save such as depend upon sex, the
primary variation would be acquired. Unlikeness would thus appear, and this,
in course of time, would tend to marked variations. Marriage of unlike indi-
viduals would still further increase the variation. (2) Eeversions are natural
variations. These, we have seen, are very largely due to E, but they are also
due to the sexual union of unlike individuals.

142 THE CAUSATION OF DISEASE.

most negative E compatible with existence ; but all that part
of the mental world which results from conscious education
certainly belongs to the region of natural variation ; for it has
a structural equivalent which has been acquired, and an acquired
structural peculiarity is a natural variation. We inherit, be it
remembered, no knowledge, only the power of acquiring it. We
inherit, in fact, an inconceivably plastic cortex, one ever ready,
under specific forms of E, to take on natural variations. It is true
that a considerable amount of knowledge could originate under
the most negative E consistent with life ; and this shows how
largely the distinction between hereditary and acquired charac-
ters rests upon theory. Indeed, it is probable that many of
our mental powers that are apparently acquired are in reality
strictly inherent — the sheer outcome of heredity. For much of
what is apparently acquired may be due, as Bastian observes,*
to a post-partem evolution of the nervous system which is
strictly developmental. The ganglia in the cervical region of
the spinal cord are, as we had already occasion to observe, very
imperfectly developed, and much of the subsequent development
of them, whereby the individual becomes capable of executing
complex movements, may be in a large measure purely develop-
mental.

I have already said enough, I think, to make clear what I
mean by the statement that the offspring of the same parents
tend towards a certain mean, and that the deviations from this
mean are due to differences of E. Such deviations, we have
seen, are natural variations. Now, the theoretical mean is
itself a natural variation, seeing that it differs from each
parent, so that the nnlikeness of the parents may be looked
upon as one cause of natural variations. But if all individuals
were to come into the world exactly alike, differences would
be rapidly impressed upon them by the varying E, and it is
this varying E which must be regarded as the primary cause
of the variations. Having once got these differences, the
marriage of unlike individuals must lead to still further
variations, owing to the tendency towards the mean structural
product of the two. Hence we may regard differences in E

* " Brain as an Organ of Mind " : International Science Series.

THE CAUSATION OF DISEASE. 1 43

as the 'primary cause of natural variations. Although I can see
no escape from this conclusion, yet it is as well to note the fact
that Darwin always wrote most guardedly concerning the causes
of variability ; and he evidently regarded it as quite impossible
to explain variation on any general principle. The causes of
variability are grouped by him under the following heads : * —

(a) Conditions of life.

(b) Habit.

(c) The use and disuse of parts.
(W) Correlation.

(e) Inheritance.

Now it seems to me that the causes of variations, as above
grouped, all operate through peculiarity of E, and this is a
convenient place to make good that assumption. Let us,
therefore, consider briefly these several causes seriatim.

(a) Conditions of Life. — By this Darwin means the ex-
ternal forces to which the organism is exposed, such as food
(this when taken into the body is a force derived from without),
climate, &c. The nature of the food, both as regards quality and
quantity, undoubtedly influences structure, and, inasmuch as
different animals of the same species differ in regard to their
food supply, they tend to vary. In such a case, of course,
the external E — " food " — makes itself felt by modifying the
internal E. Numerous examples of the influence of food and
climate might be given. f

(b) Habit. — " Change of habits," says Darwin, " produces
an inherited effect," as in the period of the flowering of
plants when transported from one climate to another. This
effect is obviously due to the altered E. The rhythm of the S
is altered in response to an alteration in the rhythm of the E.
The human organism may in similar fashion be educated to a
different rhythm. A man may be taught to sleep by night or day,
or at intervals of a few hours, and the organism may be so
educated that defecation shall take place at equal intervals of
time. There are many such rhythms, and they are of the utmost

* Crossing is an important cause of variations, but this is included under
(e) Inheritance.

f " Animals and Plants under Domestication," vol. ii. p. 243 (second edit,
revised).

144 THE CAUSATION OF DISEASE.

interest. Now, in all cases in which the organism is educated to
a rhythm, the effect is produced by a rhythm in the external E
impressing a corresponding rhythm upon certain tissues.

(c) Use and Disuse of Parts. — The former, we know, causes
hypertrophy of a part, the latter atrophy or dwindling of
it. The result is due in both cases to an alteration of E.
Let us instance the case of muscle. The E of each individual
muscle-fibre is widely different when a muscle is constantly
used to what it is when kept in constant disuse. This fact
is so obvious to the physiologist that it is unnecessary to
specify the difference in the two cases. Now, this modification
in muscle-cell-E is in response to a modification in the ex-cor-
poreal-E, and therefore the effect upon the muscle is indirectly
brought about by the external-E of the individual. If an
animal ceases to have need of a part, it is because the external
conditions have altered.

The drooping of the ears in domesticated animals, for in-
stance, is manifestly due to an alteration in their external condi-
tions, and this latter is also the cause of the structural alterations
in such cases as the following : — " In the domesticated duck,*
the bones of the wing weigh less, and the bones of the leg more,
in proportion to the whole skeleton, than do the same bones in
the wild duck ; and this change may be safely attributed to the
domestic duck flying much less, and walking more, than its wild
parents. The great and inherited development of the udders
in cows and goats in countries where they are habitually
milked, in comparison with the state of these organs in other
countries, is probably another instance of the effect of use.
Not one of our domestic animals can be named which has not
in some countries drooping ears ; and the view which has been
suggested that the drooping is due to the disuse of the muscles
of the ears from the animals being seldom much alarmed seems
probable."

(d) Correlation. — According to this principle, alteration in one
part is apt to go hand in hand with alteration in some other part
or parts. Thus, white torn cats have blue eyes ; hairless dogs,
imperfect teeth ; pigeons with short beaks have small feet, and

* " Origin of Species," p. 8, sixth edition.

THE CAUSATION OF DISEASE. 1 45

those with long beaks, large feet. In all these cases, the parts
sympathetically affected must, in some way, be anatomically and
physiologically united, so that an E affecting one of them must
necessarily affect the other, or others, at the same time. It may
not be easy to trace this connection in all cases, but in some it is
possible. The teeth, for instance, are dermal appendages, and
anything interfering with the development of the skin will tend
to affect the formation of the teeth. Wherefore the effects of
'■'correlation" are wrought through modifications of internal
cell-E, and the latter is ultimately dependent upon the ex-
ternal-E.

(e) Inheritance. — We have seen that the offspring cannot be
like either parent, and hence one cause of variation. We also
saw, however, good reasons for assuming that upon an ultimate
analysis the variation is primarily due to E. " But," it is argued,
"the principle of heredity is fickle." "No one can say . . . why
the child often reverts in certain characters to its grandfather,
or grandmother, or more remote ancestors ; why a peculiarity is
often transmitted from one sex to both sexes, or one sex alone."
Now, reasons have already been given which favour the view
that reversions are often brought about by peculiarities of E.
Thus, a peculiarity of E may hinder development at a cer-
tain stage, and the individual may be born with some remote
ancestral characteristics ; and it is probable also that special
likeness to one or other parent is chiefly connected with the E
of germ and sperm during their birth and development. We saw
that, if the parents are of unlike species, there is a tendency to
reversion. But this is no real exception to the law of heredity,
for the offspring is a mean structural product of the parents,
leaving out of account all those characters which have been
acquired since the period of ancestral divergence, and which
refuse to blend in the offspring.

It is necessary now to observe that individuals differ vastly in
the readiness with which they respond to different kinds of E.
In other words, one organism will more readily take on
new characters than another, or, in the usual language of the
biologist, one organism will more readily "vary" in a particular
•direction than another. This diversity in respect of the

146 THE CAUSATION OF DISEASE.

impressionability of an organism to a specific E manifestly
depends upon inborn structure, and inborn structure depends
upon heredity. Wherefore, the readiness with which an organism
responds to a specific E depends upon heredity. In other
words, we inherit the fower of acquiring.

So vast is the part played by Structure in determining
whether it shall vary or not, that Darwin maintained that
peculiarity in variation depends more upon the Structure of
an organism than upon the nature of its Environment.

CHAPTER XVII.

The Influence of Environment upon Structure (continued) — The Influence of
the Post-partem Environment, considered from the Pathological Point of
View.

I have" been at pains to consider somewhat in detail the in-
fluence of the post-partem E upon S. Though its influence
over structure is insignificant as compared with that of heredity,
which is the great determining power, it is nevertheless one
which must be seriously taken into account, and it is utterly
impossible to take a wide and philosophical view of the
causation of disease unless we make a careful study of all
those influences which are capable of affecting the body-
structure. Pathology is a branch of biology, and must be
studied on the lines of general biology. We have seen that
disease is nothing more nor less than an improper inter-action
of S and E, and our task has hitherto been confined to the
elucidation of the question, " What are the causes of S ? " for, in
order to state in the most comprehensive terms the causation of
disease, we could not be content with specifying the E which
takes share in the morbid inter-action — we had also to state
all we know as to the causation of the morbidly inter-acting S.
I have already observed that, from the pathological point
of view, the post-partem E is the most important. Not
that the ante-partem E is by any means powerless for evil.
The nature of the mother's blood is capable of exerting an
enormous effect for good or evil ; and it is highly neces-
sary to preserve the mother's nutrition during the months of
gestation. Amongst the poorer classes, especially in large
towns, the evils of bad E commence before birth ; for the
blood of most of their women is both impoverished and im-
pure. Wherefore, if we wish to place an individual under a
proper E from the earliest period of his existence, we must

148 THE CAUSATION OF DISEASE.

not neglect the period of his uterine life, and . we shall best
secure the advantage of the child by placing the mother under
a perfect E. To take a single instance, the development of the
permanent teeth commences in the first months of embryonic
life. If the mother's blood be deficient in certain elements, we
can well understand how the germ of the future tooth will be
improperly formed, and thus a tendency to early decay result.
Unfortunately, the effect of bad teeth is not local : many
secondary evil results may follow — neuralgia, indigestion, and
consequent mal-nutrition — indeed, the effects may make them-
selves felt through the whole body.

In regard to our regulation of the post-partem E, let us ever
bear in mind that it is potent in proportion as it acts early.
I have more than once said that a small initial change may
eventually lead to a very vast difference. Hear what Herbert
Spencer says on this head : —

" In any series of dependent changes a small initial difference
often works a marked difference in the results. The mode in which
a particular breaker bursts upon the beach, may determine whether
the seed of some foreign plant which it bears, is or is not, stranded,
may cause the presence or absence of this plant from the flora of the
land, and may so affect for millions of years, in countless ways, the

living creatures throughout the land The whole tenor of a

life maybe changed by a word of advice ; or a glance may determine
an action which alters thoughts, feelings, and deeds throughout a
long series of years A hair's-breadth difference in the direc-
tion of some soldier's musket at the battle of Areola, by killing
Napoleon, might have changed events throughout Europe."

Now, such being the case, we must, if we wish an individual

to grow up healthily, most carefully regulate the E of his early

extra-uterine life, for a slight neglect here may leave an effect

which the greatest after-care cannot amend. But, unhappily,

the young infant is but too often exposed to an injurious E.

r< The child cries, when it is born, because it feels, as

Shakespeare says, ' that it has come on to the stage of fools.'

It has its mouth stuffed with butter and sugar, its belly cramped,

and its legs not allowed to kick. l It has come on to the stage

of fools.' " *

* H. G. Sutton.

THE CAUSATION OF DISEASE. 1 49

It is probable that the entire future health of the individual
differs according as he has been naturally or artificially fed.
Some children, no .doubt, do fairly well on the artificial
method, but it is highly doubtful whether they would not
do better still on the natural food. The following case is
interesting in showing the different effects of the artificial
and natural system of feeding. A woman brought to the
hospital twin infants who were afflicted with congenital
syphilis.* The ante-partem E of these twins was very
similar, both in respect of the Normal and the Abnormal
(namely, the syphilitic virus) ; one would therefore expect the
two infants to be very similar in structure. And such is the
case ; they bear the usual resemblance of twins, and are both
afflicted with the same disease. Nevertheless, they show a
considerable difference, and herein lies the great interest of the
case. The great similarity of E for each twin ended at birth :
the mother having only milk enough for one babe, the girl —
for they were of different sex — was suckled, the boy being
brought up b}r hand. The following note was copied from Dr.
xlbercrombie's note-book, whose patients the children were.
" Both thrush badly for six weeks, with much rash about but-
tocks " — this from the mother. The note continues : " The
boy has great bosses, most marked and characteristic cachexia,
depressed nose, and a palpable spleen — rachitic. The girl has
no bosses, nor spleen, nose depressed. Is healthier than the boy,
and can stand, whereas he cannot." This case shows most
strikingly the influence of the early post-partem E upon the
child.

We cannot, indeed, exaggerate this influence — it demands
our closest attention. It is not too much to say that in civilized
countries the vast bulk of the young of man are subject to an
improper E. This is the case among the poor especially, and
notably among the poor of large towns. The cruelty practised
on infants year after year is a blot on our civilization — nay, it is

* It may be noted in passing that the so-called congenital syphilis is an
acquired disease of ante-partem date — the foetus having been exposed to a
syphilogenic E. The so-called hereditary syphilis is probably no more here-
ditary than opium poisoning would be in an infant born of a woman under the
influence of this drug. How it is that the mother so largely escapes in the
ordinary cases of congenital syphilis I am at a loss to explain.

M

150 THE CAUSATION OF DISEASE.

so serious that it almost tempts one to ask : Has such civiliza-
tion any justification ? The destruction of life among savages
is, no doubt, greater than among civilized peoples, but death
is at least prompt : whereas in civilized countries, tens
of thousands of children are yearly tortured slowly to
death, while as many grow up crippled for life. A number
of children doubtless die of scarlatina, diphtheria, and so
forth, through no fault of the parents — and here again death
is more or less prompt ; but the chief number die of impro-
per feeding — of a disease popularly known as " consumption
of the bowels." This is a sort of dysenteric diarrhoea, the
main features of which are — large belly, slimy, bad- coloured,
foul-smelling, and, sometimes, bloody motions. It is ob-
viously an enteritis due to improper feeding. The unhealthy
bowel is no longer able to properly act upon the food, which,
therefore, decomposes, causing flatulent distension of the belly
and foul-smelling motions. Such being the case, no wonder,
then, that the child should get thin and die, or that, if it
survive, it should grow up puny and delicate. At a time of
life when every cell in the body is craving for food, the
tissues are being both starved and poisoned : starved by the
non- conversion of food into blood, poisoned by the absorption
of abnormal intestinal products. I am inclined to think that
this disease takes some share in the causation of both rickets
and scrofula ; but let this pass. Certain it is that it is a
very common complaint ; among the poor of London, in a
greater or less degree, it is universal. I have scarcely ever failed
to get a history of slime and foul-smelling motions in those
children whose history I have thoroughly investigated; and that,
not only in the case of children artificially fed, but in those
brought up at the breast also, though to a much less extent.
A history of slime and foul- smelling motions is a perfect test of
the disorder. The mother should always be questioned concern-
ing this latter symptom. Healthy motions have an unpleasant
smell, but there is a wide gap between this unpleasantness
and that due to the disease whereof I speak. If we have a
history of foul-smelling motions extending over long periods
of time, we have a distinct evidence of chronic intestinal disease ;
and chronic disease of this mucous tract, whose business it is

THE CAUSATION OF DISEASE. I 5 I

to change the food into the unformed part of the blood, neces-
sarily leads to a universal modification of cell-E, which
occurring at a period of active body- growth, produces an evil
effect which no amount of subsequent care can entirely obli-
terate. How far this disorder is prevalent among the upper
classes I cannot say, but I do know that it is fairly common
among them. Wherefore, owing to this tendency to in-
testinal disease in children, the first question in almost
every disease in children, should be, a What are the motions
like?"

If we could keep the motions always normal, we should have
few or no delicate children.

Now I have instanced this disorder, because it plays a fearful
part in the destiny of man ; exaggerated though this statement
may appear, it is sober truth. Let it not be thought that
those who survive its ravages are only temporarily affected.
Their whole future is influenced thereby. If among a large
family the majority are strong and vigorous, while two or
three have been delicate from infancy, the chances are a
hundred to one that a history of chronic intestinal trouble can
be elicited as the cause of the delicacy.

And thus also it is with many other diseases ; owing to the
mutual dependence of the different tissues, it is impossible
to localize a trouble : the effects ramify throughout the entire
body. A neglected whooping-cough, a chronic tonsillitis, or
what not, may stamp a life-long impress upon the body. How
marked and extensive, for instance, are the secondary effects of
prolonged tonsillar enlargement ! The proper growth of the
nostrils is interfered with, the mouth is kept continually
open, indeed, the whole physiognomy is altered. Moreover,
air is prevented from properly entering the lungs, and collapse
is apt to take place ; at all events, the lungs are imperfectly
filled, and thus the normal development of the chest wall is
interfered with. Now this interference with the proper growth
of lung and thoracic wall will rapidly make itself felt throughout
the entire organism. In the first place, the respiratory capa-
city being diminished, the entire bodily processes will sink, as it
were^ to a lower level, and the development and growth of the
body will no longer proceed at their wonted rate ; in the second

M 2

152 THE CAUSATION OF DISEASE.

place, the altered shape of the bony framework of the chest will
cause secondary modifications in other parts of the skeleton —
in the curves of the spine, the inclination of the clavicles,
the peculiar hanging of the scapula?, and so forth. These are
some of the results that may follow chronic enlargement of the
tonsils in children ; and such enlargement is itself the mere
expression of a more general morbid condition.

This case is a good example of correlation, i.e., of one or
more parts specifically varying in correspondence with another
part ; and I have already said that the true explanation of
correlation is to be sought in the influence of one tissue upon
another, through a modification of internal cell-E. The so-
called strumous condition, of which the enlarged tonsils are an
outcome, results from imperfection of external-E. The child!
has been subjected to improper influences, and no doubt, in.
many cases, there is a hereditary cc strumous " tendenc}r
through imperfection of ancestral E. Thus, we see that u cor-
relation " ultimately depends upon' modification of external
E. But this by the way. My object in citing this case of
enlarged tonsils is to show how a small local change is capable
of causing a serious upset in the developmental processes of
the body.

Similarly, how far-reaching may be the effects of a chronic
constipation during the period of development, say, in
a boy of six to ten years. In consequence of, it may be, a
slight error in diet, he suffers from constipation. The mucous-
membrane of the rectum takes on catarrhal inflammation ;.
threadworms soon infect the lower bowel, and cause an
intolerable itching. The sexual system is sympathetically
excited ; there is priapism and a kindling of sexual desire ;
or the evil may result solely from a too long prepuce and
the consequent accumulation of irritating smegma. Now the
feelings control the thoughts. Unhealthy sexual thoughts
will rage in the brain of this young child ; soon the vice of
masturbation is contracted, and practised, it may be, for
years. Talk as we may, this must interfere with proper-
development. I am convinced it interferes with proper cere-
bral evolution, and that indirectly the entire individual is»
thereby altered.

THE CAUSATION OF DISEASE. I 53

See, then, what a simple constipation may bring about : it
may produce effects which shall be felt throughout the body
even to the end of life. And this constipation and unhealthy
state of mucous membrane may result from an error in diet,
in other words, from an imperfection in external-E ; and
thus an apparently slight imperfection in E is capable of
moulding the S into a distinctive shape, and no power of
ours can subsequently put it right — cast it into its true
natural mould.

It is an interesting task to endeavour to trace the influ-
ence of the external E upon the post-partem developmental
processes in some particular case. Biographers have analysed
in the most painstaking way the influence of mental surround-
ings upon the minds of many great men, but very little
has been written as to the influence of the physical E upon
the physical man. The best minds, like the best bodies,
have undoubtedly grown up under a favourable physical
environment. Occasionally we see a strong brain in a weak
body, but in such cases the cerebral result would, I think, cer-
tainly have been better if circumstances had permitted the free
growth of the body. Pope would have been a greater man
if his body had grown to greater perfection. It is sometimes
argued that, because a particular man drinks inordinately for
many years, and nevertheless lives to a good old age, there-
fore alcohol does no harm ; the real fact being, however, that
he lives on in spite of the alcohol, and that without it he would
have lived yet longer. And so it is with the strong brain and
the weak body ; the mind is great in spite of the deteriorating
influences of unhealthy surroundings, which must necessarily
tell injuriously upon the entire body structure, whether of the
brain or any other tissue. The mental capacity would have
been greater under more favourable external surroundings.
Mark, I say, the capacity — that is, the potential power. Often
the weakness of body develops a reflective turn of mind, by
rendering an individual dead to many alluring distractions
which draw the minds of others outwards. The sickly indi-
vidual thus mentally thrust in upon himself, will develop
to the full faculties which would otherwise have remained
latent.

154 THE CAUSATION OF DISEASE.

Be tliis as it may, there can be no doubt that many physical
peculiarities of individuals may be accounted for by a careful
study of the physical E of their youth. See what a hard life
Dickens had ! The greater part of his early years was spent in
the impure air of central London. London air is bad enough
under the most favourable circumstances, and it was probably
very bad in the rooms where much of Dickens's youth was
spent. Then there can be little doubt that he was starved
as a boy for many years. Subsequently to this unhealthy
bringing up, he led a life of altogether excessive mental toil
and excitement, and the end was just what we might have
expected. "But," it will be argued, "his mental success was
great." It was indeed. Yet there have been greater men than
Dickens, and Dickens had probably been a greater man under
more favourable physical circumstances. He had, of course,
the advantage of mental surroundings favourable to the de-
velopment of his capacity, such as it was ; but I contend that,
under more favourable physical surroundings, and with equally
favourable mental surroundings, that capacity would have been
greater.

Such being the potency for evil of an early mal-E, we
must, I repeat, most religiously see to it that our children are
placed under a proper E, and our care should be great in pro-
portion to the youth of the child. A serious affection in a child
must influence all the developmental processes occurring after it. A
similar disease in a full-grown man is infinitely less damaging,
for in him development has come to a standstill.*

For this reason, too, we should be prompt in our efforts to
cut short every malady, no matter how slight, occurring before
the period of complete maturity ; for, while the malady is
present, there must be an interference with proper develop-
ment, and, if that interference lasts long, the individual will
lose ground which he cannot afterwards recover. Take a case
of chlorosis. One might be inclined to argue : so long as we
ultimately cure the complaint, it does not matter whether we

* Minor processes of evolution may continue till a very late period in life,
and this is more particularly true as regards the nervous sj-stem ; nevertheless,
the statement that development has come to a standstill in a full-grown man is
to all intents and purposes accurate.

THE CAUSATION OF DISEASE. I 5 5

do so now or a few months' hence, except for the temporary
inconvenience of the patient. Never was error more fatal, for,
apart altogether from the fact that chlorosis may immediately
predispose to other ills, such as gastric ulcer, and possibly
phthisis and heart disease, it stands to reason that rapidly
developing tissues must suffer considerably if they are bathed
for months together in thin watery blood. On no tissue will
this evil effect be greater than the nervous. I have seen cases
of chlorosis in quite young girls lasting over a year. Surely this
must lead to a permanent crippling of the young and rapidly
growing ganglion-cells!

CHAPTER XVIII.

The Morbid Inter-action of Structure and Environment — All Disease Processes
probably attended by Structural Change, and therefore Natural Varia-
tions— Structural Deficiency.

Having inquired into the causation of S and E separately, it
now becomes necessary to consider these tw6 vital factors in
the mutual inter- action of disease, for we have seen that disease
is an abnormal inter- action of S and E. It will be remembered
that we first inquired into the nature of E, and that the
last chapters were devoted to the consideration of the causa-
tion of S. We found that S was mainly the outcome of
heredity, but that it was also influenced, though in a lesser
degree, by E. Accordingly we treated of the causation of S
under two heads : Under the one we considered the general
principle of heredity ; and under the other the influence of E
upon S. So that E has had to be treated of in a twofold
manner — ( I ) As one of the two great vital factors ; (2) As
a plastic agent.

We now cease to study the two great factors of disease
apart, and proceed to consider their morbid inter-action —
namely, disease.

One of the first things that strikes us regarding the power
of E to set up disease is, that it varies widely with the
nature of S. This is, of course, as we should expect; for,
while speaking of the simple cell, we saw how S + E repre-
sents certain material conditions, and how, as a result of such
conditions, a definite inter-action takes place. Now, differences
of S signify differences of these material conditions, and, in
consequence, differences in the result. S may be such that
S + a particular E shall call forth healthful inter-action, or
such that S + this same E shall issue in morbid inter-action.
This truth is abundantly exemplified in the diseases of man.

THE CAUSATION OF DISEASE. I 57

One often sees, e.g., two individuals — we will call them A. and
B. — exposed to an exactly similar E. A. contracts disease,
while B. escapes unhurt. In such a case, we say A. has a
greater proclivity or predisposition to the disease. The two
cases stand thus —

(A.) S + E = Disease. (B.) S + E = Health.

Since the result differs, it follows from the law of causation
that the material conditions must be different, and, the E being
the same in both cases, the S of A. must differ from that of B.
Hence the power of the same E to call forth a given result
differs in the two cases. This E is, perhaps, as powerless to
produce disease in the case of B. as is a spark to explode damp
gunpowder. In short, the nature of S determines whether it
shall or shall not take a morbid action.

There is no more conclusive way of proving how differently
different individuals respond to the same E, than by studying
the actions of drugs upon different individuals, since, in this
case, we can regulate the specific E most accurately, and be
quite certain, moreover, that we are exposing different indi-
viduals to exactly the same.

So differently, indeed, do different individuals respond to the
same dose of the same drug, that we have thus a ready means
of testing and proving individual differences of structure,
which are quite undiscoverable by microscopic or other modes
of examination; just as, in fact (I am using Darwin's simile),
we can discover chemical differences in different fluids by the
different ways in which they respond to different re-agents.*

The nature of the S determines, therefore, whether a particular

E shall or shall not throw it into morbid action.

* By means of drugs we are able to subject a number of different individuals
to exactly the same specific E, and with what diversity of results everybody
knows. These differences in S are termed idiosyncrasies. In this connection,
Darwin makes the following remarks : " There appears to me a strong analogy
between the same infection or contagion producing the same result, or one
closely similar in two distinct animals, and the testing of two distinct fluids
by the same chemical re-agent "(" Descent of Man," p. 7). And, just as we
infer similarity or difference between two fluids by the similarity or difference
in their behaviour towards certain re-agents, so likewise can we infer similarity
or difference among different living organisms, for it is, as above remarked, the
nature of S which determines whether it shall or shall not take on a particular
action, when exposed to a particular E.

153 THE CAUSATION OF DISEASE.

That the manner in which S responds to E depends in large
measure upon the nature of the S is a fact familiar to the
biologist. Darwin is very careful to insist upon the important
part played by S in determining whether an animal or plant
shall vary under a particular E.# He maintains, indeed, that
the occurrence of the variation depends more upon the organism
(=S) than upon the E.

It is easy to show that the " nature of the organism" (= S) has
much to do with its tendency to variability, for of many organ-
isms subjected to practically the same conditions, some will vary,
and others will not, and this difference in response to E must
depend upon differences in S. Gardeners have often great
difficulty in getting plants to vary in a particular direction,
and much care is directed towards this end.

The term ''variation" is generally applied solely to such
structural changes as are obvious to the senses, but it
should be remembered that the physiological response to a
specific E need not display itself in a discoverable structural
change. This is sufficiently proved by the fact that many
plants do not obviously vary until after they have been
exposed to a specific E for several successive generations.
There can, however, be no doubt that all this time a steady
structural change has been taking place. Indeed, the subtlest
and most infinitesimal force falling upon a living organism
causes a modification of its structure. Hence, when the E
appears to cause a simple functional change only, without any
corresponding structural alteration, we may, nevertheless,
regard the organism (for the time being, at least) as a natural
variation, for there can be little doubt that it does undergo a
temporary structural change. I say, a temporary structural
change, for, unless the specific E be persistent, the structural
change may only be temporary. It need hardly be said that
organisms differ quite as much in respect of this "functional
reaction," as we may conveniently term it, as they do in
regard to the more obvious structural response. Indeed, the
latter is but the prolonged result of the former.

The same remarks apply to pathological variations. In a

* " Animals and Plants under Domestication," vol. ii. pp. 275-282 (second
edit, revised).

THE CAUSATION OF DISEASE. I 59

later chapter we shall discuss the question whether structural
alteration is a necessary concomitant of disease. The above
observations prepare us for the conclusion that some structural
change is a constant accompaniment of morbid processes. It
is quite obvious that a very large number of disorders are
attended by distinct structural changes — e.g., pneumonia, and
cirrhosis of the liver. All such diseases constitute distinct
natural variations. But even when the E causing the disease
produces what seems to be only functional change, there must,
according to the arguments just used when speaking of phy-
siological functions, be some structural alteration.

All natural variations, whether physiological or pathological,
are, therefore, in the last resort, the same — viz., alterations
in structure, wrought by the peculiar action of E. If the
action of the E does not tend to break the harmony between
the S and the external-E, the variation may be spoken of
as physiological ; if, however, it tends to upset, in a very
marked degree, what Spencer would term " the equilibrium
between the inner and outer forces," it may be spoken of as
pathological. The two classes, in fact, pathological and physio-
logical, run into one another, and it is by no means an easy
matter — as we shall see in another place — to define an ideally
normal S.

Some, however, will be inclined to say that the distinc-
tion between pathological and physiological variations is very
great, their criterion being this : that all pathological varia-
tions are dissolutionary.* There are objections to this view ;
but even supposing that physiological and pathological varia-
tions are thus sharply separated from one another, the two
none the less fall under the great class of natural variations.
And my object in the foregoing remarks has been to empha-
size this fact — namely, that pathology, being a branch of
biology, has to be studied on the same general lines. It is,
at all events, convenient to regard all morbid processes as
natural variations (temporary or permanent) ; but if some
contend that diseased processes need not be accompanied by

* I am here speaking of actual pathological variations — i.e., of actual dis-
ease. For the distinction between actual and sub-pathological variations,
vide p. 38.

l6o THE CAUSATION OF DISEASE.

structural alteration, and are not, therefore, natural variations,
it matters not ; both pathological and physiological changes
can yet be brought under the same general principles. I
shall, therefore, in this chapter, regard all cases of disease as
pathological variations. I do not think I shall greatly err in
so doing.

Diseases, then, belonging, as they do, to the great class of
natural variations, will obviously be governed by the same laws
as to causation. Just as, in response to specific E's, some
organisms will readily take on certain physiological variations,
so some organisms will readily take on certain pathological
variations. And just as, on the other haud, some organisms
refuse to take on certain physiological cbaracters, so some
equally refuse to take on certain pathological characters.

We can no more compel an animal or a plant to vary in
any given pathological direction, by subjecting it to different
forms of pathogenic E, than we can force on animal or plant
any particular physiological variation by exposing it to specific
modifications of E. And we shall have no difficulty in believing
this, if we keep ever before us the kinship between pathological
and physiological variations.

No doubt we can fracture a skull or inoculate a poison, but
who will engage to produce general paralysis of the insane in
any given individual (to make no mention of other more subtle
forms of mental disease) by applying to him a specific patho-
genic E ? Where, again, is the experimentalist that can
produce at will such diseases as bulbar paralysis, ophthalmo-
plegia interna, primary lateral sclerosis, goitre, haemorrhage into
the internal capsule, mediastinal tumour ? Even disorders whose
causation is more or less perfectly understood, such as drunkard's
liver and granular kidney, do not always occur under the E
which is wont to produce them.

"I do not believe," says Sir J. Paget,* "that through any
external conditions whatever, and independent of inheritance,
any one can become the subject of cancer, gout, tuberculosis, or
any disease allied to them. External conditions may hasten
the appearance of such diseases, determine their seat, and

* " Clinical Lectures/' p. 414.

THE CAUSATION OF DISEASE. l6l

variously modify them in the person affected, but seem to me
utterly inadequate to originate them."

Although more recent evidence tends to negative this con-
clusion (for gout may perhaps be induced independently of
heredity — more especially if the individual come under the
influence of lead in addition to other gout-producing agents —
and tuberculosis has been inoculated in a large number
of animals), nevertheless, this conclusion emphasizes Paget's
belief, which is surely correct, that the special tendency to the
disorders in question is gradually evolved, and that without
such tendency, such peculiarity of S, they are never met with
under any ordinary circumstances.

The same line of argument might be pursued in respect, of
all sorts of disease. Can we even guarantee to infect every child
with a given specific fever ? Are there not some children, who,
although they continually consort with others suffering from a
specific febrile disorder — nay, who, although they be even
inoculated with the virus thereof, will yet remain untouched by
the disease ? This inability of the S to be morbidly affected by
a specific virus is well shown in the case of individuals who
have already been thus morbidly affected. Such, we know, are
generally protected against future attacks of the disease, but
some are from the beginning proof against the poison ; and
in this connection it is interesting to remember that some
races are proof against specific E's, which to others are highly
injurious.

Instance the ague poison. And this disparity of different
individuals in the matter of responding morbidly or other-
wise to parasitic organisms, does not apply to the micro-
scopic parasites only ; it is a curious fact that different
races of men differ in their liability to be attacked by the
several macroscopic parasites. tt The surgeon of a whaling
ship in the Pacific assured me that when the pediculi, with
which some Sandwich Islanders on board swarmed, strayed on
to the bodies of some English sailors, they died in the course of
three to four days."* Humboldt remarks : " White men, born
in the torrid zone, walk barefoot with impunity in the same

* " Variation under Domestication," vol. ii. p. 265.

162 THE CAUSATION OF DISEASE.

apartment where a European, recently landed, is exposed to the
attacks of pulex penetrans."* There is no occasion to pursue
this subject further, for it is known to all that certain indi-
viduals refuse to respond morbidly to E's which are capable of
setting up distinct morbid action in others.

But among such as do respond there is vast difference in
respect of the readiness of response to any particular pathogenic
E. This " readiness of response " signifies the inherent tendency
to particular diseases, and may be spoken of as structural
deficiency. Many persons would quarrel with this term, since of
two individuals, one of whom, we will suppose, is proof against
the attack of the common flea, while the other is exceedingly
liable to be bitten by it, they would be unwilling to attribute to
the latter a structural deficiency, although, no doubt, they would
allow the term in the case of an individual who responded
readily to a gouty or tubercular E ; but we shall see, in another
place, that normality and abnormality of structure are relative
terms, and can only be considered in relation to E. If S-f E
be such that healthful inter-action results, then both may be
regarded as normal, but if S+this same E = disease, then S is
abnormal in regard to that E, and, therefore, the term structural
deficiency, used in this relative sense, is justifiable.

We may have any degree of structural deficiency, or ten-
dency to particular disease. In the case of such diseases as gout,
tubercle, or cancer, we may, perhaps, speak of this deficiency
as an actual " disease taint" but in many cases of structural
deficiency there is obviously no condition of tissue meriting
this designation, as when an individual is structurally deficient
as regards certain skin parasites. In thus speaking of the
intensity of disease proclivity, I wish to denote the quantity
of pathogenic E necessary to call forth the actual disease —
the less the structural deficiency, the larger the quantity of
pathogenesis needful to call forth the actual disease, and vice
versa. Wherefore we arrive at this principle : the c^iiantity of
mal-E needful to call forth disease is in inverse ratio to the
structural deficiency.

* Quoted by Darwin, " Variation under Domestication," vol. ii. p. 265.

CHAPTER XIX.

The Symbolical Method of Expressing the Kelative Share taken by-
Structure and Environment in Causation.

We shall do well, if we can, to assign to S and E respectively
their relative share in the production of any given case of
disease — to say what is the extent of the structural deficiency,
and what the intensity of the mal-E.

Since disease depends upon an inter-action of S and E,
it is obviously impossible to eliminate E from causation, even
though the disease burst out spontaneously under the most
favourable E. But if the inherent tendency to disease in any
individual be so strong that the disease must needs break out,
no matter how favourable the E, we may, for all practical
purposes, eliminate the share of E in its causation. In such a
case the individual may be said to contain within himself the
full potentiality of the disorder.

In considering the degree of structural deficiency, or pro-
clivity to some particular disease, we shall discover two
extremes. At one extreme end we have the class of cases
whereof mention was just now made — namely, in which the
proclivity to a particular disease is so great that it must needs
break forth under the most favourable Environment ; and at
the other extreme, a condition of S which refuses altogether
to be thrown into morbid action under the most intense
pathogenic E possible. These remarks do not, of course,
apply to all pathogenic E's, for there are many mal-E's which
excite disease in all alike — e.g., prussic acid, or the continued
breathing of foul air. Be it noted, moreover, that, by struc-
tural deficiency, or proclivity to disease, I wish to denote
proclivity towards some special disease. While a vast number
of specific E's will produce disease in all mankind, each one
-does not always produce the same disease. Prussic acid, e.g.,

1 64 THE CAITSATIOX OF DISEASE.

will produce practically the same morbid action in all, but this
is not true of a foul atmosphere, which will tend to induce
several distinct disorders, according to several distinct struc-
tural proclivities, or, as I have called them, deficiencies.

Between the above two extremes of absolute impunity
from a particular disease, and absolute inability to escape
therefrom, there is a long series of fine gradations. An
individual may, in fact, have any shade of structural
deficiency, or tendency towards a particular disease, from
absolute security to impossible escape. This fact may be
well illustrated in the case of insanity. Some there are who
will not lose the even balance of the mind under the most
dire provocation. Let them be subjected to the rudest mental
shocks, the sharpest pangs of grief, the insidious torment of
worry, the wear and tear of excessive intellectual toil, or any
mental agitation whatsoever — the mind still pursues the even
tenor of its way. But there are others in whom the slightest
disturbance is sufficient to upset the mental balance, who will
become insane even though every possible care be taken to
guard them from exciting influences ; and between these ex-
tremes we can fill up a long series of fine gradations needing
an ever-increasing quantity of specific pathogenesis to call
forth the disorder. By a specific pathogenesis I mean such
E as tends to call forth a particular disorder, and it is impos-
sible to enumerate all the various forms of E which would
tend to excite into actual being an insane proclivity.

Now, cau we in any way symbolize the relative share
taken by S and E in the causation of disease ? Let us
suppose a given disease to be made up of eleven units, and
let the share in causation taken by S and E respectively be
represented by any number from one to ten : it would be
manifestly incorrect to assign the full number (eleven) to
either, seeing that neither S nor E alone can constitute dis-
ease. Then, inasmuch as S-f E = the disease, we may arrange
the following table : —

(An individual in whom the disease bursts a
out spontaneously).

a

^10

+ E,

= ii

h

S9

+ E2

= ii

c

s8

+ Es

= ii

d

s7

+ E4

= n

e

s6

+ E5

- ii

THE CAUSATION OF DISEASE. 1 6$

f S5 + Ed =

9 S4 + E7 =

h S3 + E8 =

i S2 + E9 =

3 8, + E1§ =

(An individual in whom the largest k S0 + E,0 =

quantity of specific pathogenesis is

unable to induce the disease.)

In the first case (a), the inherent tendency is represented by
ten and the E by one. In such a case the disease breaks
out spontaneously, i.e., is fully inherent, for it occurs under the
most favourable E possible. It is necessary to represent this by
the number one, because we can never entirely eliminate the E,
seeing that disease is an inter-action of S and E. In the last
case (k), the largest quantity (ten) of specific pathogenesis, that
is, the most intense disease-producing E, is unable to excite
the disease ; the S totally refuses to respond morbidly in the
specific way, and the inherent tendency may therefore be
represented by o.

Let us apply this numerical method to illustrate the share
in causation taken by S and E respectively in a particular
disease — e.g., insanity. " It must be borne in mind,'' says
Maudsley, speaking of the causation of insanity,* " that
hereditary predisposition may be of every degree of in-
tensity, so as, on the one hand, to conspire with certain more
or less powerful exciting causes, or, on the other hand, to
suffice of itself to give rise to insanity, even amidst the most
favourable external circumstances." Let us endeavour to give
numerical expression to these words of Maudsley. The formula
S,0 + E1 signifies that, under the most favourable E, the indi-
vidual will become insane; S9 + El5 that, with the greatest con-
ceivable care, the disorder may be averted. In the latter case
it would be necessary to protect the individual from a long
array of influences; for there are many diverse circumstances
included under the specific pathogenesis of insanity, such as
mental excitement or shocks, child-bearing, fevers, and indeed
anything and everything which tends to reduce the bodily
nutrition, be it bad air, improper or deficient food, lack of
exercise, or what not. It would, indeed, be impossible to

* "A System of Medicine," edited by J. Russell Reynolds, M.D., &c, p. 13.

N

1 66 THE CAUSATION OF DISEASE.

enumerate all the causes which would directly or indirectly tend
to ignite the very ample supply of neurotic dynamite, and
which would, therefore, have to be included under the specific
pathogenesis.

It would, of course, be possible for the disease to be called
forth by a more powerful exciting cause — e.g., E5 ; but in such
a case the excess of E (three) is in a manner inoperative.
For, speaking, as we are, of the pathogenesis of insanity
without any regard to the intensity of the morbid action, we
cannot get more than I r, since this number represents the
full disease. No doubt a greater quantity of specific mal-E —
e.g., prolonged mal-hygiene — might induce a more intense at-
tack of the disease, and we might represent this by S9 + E10 =
ig, but I am not attempting to represent numerically the
intensity of the disease ; I am dealing only with the actual
presence or absence thereof, the number 1 1 , or any higher
number, denoting the presence of insanity, the numbers below
this its absence. It would, perhaps, be possible, however, to
somewhat roughly denote in this numerical way the intensity —
the dose, if we may so put it — of the malady. Thus the most
hopeless case of insanity might be represented thus : S10 + E10.
Here we have nine units in excess of the minimum quantity
of genesis, and this formula would signify that an individual
in whom the tendency to insanity was very rife had been sub-
jected to the largest possible quantity of insanity-producing E.
Let it be noted that a specific pathogenesis dates from the
earliest period of life. It is well known, e.g., that many neuroses
attend rickets, and this may be the starting-point of very
serious nervous disorders in after-life.

To return to the symbols: Ss.5-fE..5 would indicate that
each vital factor takes an equal share in causation ; Sx + E10,
that an exposure to the largest possible quantity of specific
mal-E is needed to call out the disease ; while S0 + E10 implies
that the individual refuses to become insane, even though he be
rigorously subjected to every possible insanity-producing cause.
Some may think no such individual exists. It might be
argued, for instance, that insanity can always be induced by
traumatic causes. It is, however, only exceptionally that such
a result follows upon a head injury. By voluntarily disor-

THE CAUSATION OF DISEASE. 1 67

ganizing the brain (and this is out of the sphere of practical
causation) we might, no doubt, render any given individual
insane ; but who would engage to induce in this or any other
way the many different kinds of insanity from which man
suffers ? For the diseases of mind are" many and subtle, and
we may lay it down as a fact that individuals exist in whom
it would be impossible to induce any given variety of insanity.
The following instance of the same disease affecting twins
is interesting, inasmuch as the relative shares taken by 8 and
E in causation were probably exactly the same for each indi-
vidual. " Dr. Gregory's twin children .... were both seized
with croup on the same night, having been walking together in
the sunshine during the evening in a cold wind."* There was
doubtless some structural peculiarity in these children, which
rendered them particularly prone to croup, for it is probable
that few others would have contracted the complaint under
like external circumstances. A similar instance is the fol-
lowing : " I once saw .... twin boys, eight months
old, in each of whom a small abrasion formed in the raphe
of the perineum, and became covered with membrane. This
membrane extended, though unaccompanied by any other local
symptoms of diphtheria, to the margin of the anus, and to just
within the internal sphincter. Both children died within a
week from the commencement of the illness, sickening, as
under some grave constitutional disease, with troublesome
diarrhoea and exhaustion, which stimulants failed to remove.
The identity of this disease with ordinary diphtheria is
established beyond doubt."

• Hilton Fagge, "Practice of Medicine," vol. i. p. 79, quoting Sir T. Watson.

X 2

CHAPTER XX.

Some Further Applications of the Symbolical Method.

It has been observed that a particular mal-euvironment may
extend over many years : it may, in fact, date from the very
first moments of life. Now it is obvious that, if the E has been
in operation during a long time, rendering the individual from
day to day more and more prone to the disease, a gradual
change in S must have been taking place all this time ; a specific
u deficiency " may thus go on increasing, until finally the disease
is capable of being set up by a numerically small E, and thus, at
the time of the actual occurrence, the causation might be repre-
sented by such a formula as the following : S9-r-E2= 1 1.

In the foregoing table, however, the S is supposed to represent
that part of the individual which is the pure and simple outcome
of heredity as distinguished from those structural peculiarities
which have been wrought through E, while E symbolizes the
entire specific mal-environment from the period of birth. It
would be more accurate to start from the earliest period of
uterine life, for we have seen that the intra-uterine E plays a
very important part in shaping the destiny of the individual,,
but it is sufficient for our purpose to take the period of birth as
our starting-point. At this time the tendency to a particular
disease might be S, ; during a number of years' exposure to<
a specific mal-E this might change to S]0. In such a case the
causation would be best symbolized : S1+9 + Ej= 1 1.

If we wish to ascertain the entire share which E has taken
in causation, it is in fact necessary, in the case of very many
diseases, to extend our survey over the whole previous life.
Thus, in discussing the causation of insanity, Maudsley says :
u What should ever be borne in mind is, that all the conditions'''
(italics are mine: by "all the conditions" the author is here
referring to conditions of structure as well as of E) " which

THE CAUSATION OF DISEASE. 1 69

conspire to the production of an effect are alike causes, alike
agents, and that there is, in most cases of insanity " (I should
have preferred to say " all cases"), c:a concurrence of con-
ditions, not one single effective cause. Mental alienation often
appears as the natural issue of all precedent conditions of life,
mental and bodily, the outcome of the individual character as
affected by circumstances ; in such case, the germs of the
disease may have been latent in the foundation of the character,
and the final outbreak is but the explosion of a long train of
antecedent preparation. In vain, then, is it to try to fix
accurately upon a single cause, moral or physical/'

In the above symbolical formulae, E has always referred to
the external environment ; but in certain cases of disease this
letter may conveniently symbolize the share taken by local
bodily change in provoking disordered action in another part
of the body. We have seen that diseases rarely remain strictly
localized ; that, owing to the mutual dependence of tissue upon
tissue, disease in one part is very apt to set up morbid action in
others. Now, it often happens that the most obtrusive, and, in-
deed, the most important, morbid action is not the primary oue,
but some morbid action secondary to it. Thus, the local
trouble of indigestion, or the irritation of a worm in the bowel,
may excite an epileptic fit ; thus also, gastric disturbance or
bronchitis may bring on an asthmatic paroxysm ; and, in like
manner, a decayed tooth may cause neuralgia.

In considering the causation of disorders thus arising, we may,
then, conveniently regard the central erring tissue as an indepen-
dent S, and the peripheral irritation as an E acting thereon, and
in all such cases we may lay down the general principle that the
amount of peripheral irritation needful to call forth the abnormal
central state is in inverse proportion to the abnormal tendency
of the centre. The latter may, as it were, be so fully charged
with dynamite, that it will explode spontaneously : as when
an asthmatic or epileptic fit occurs though every care be taken
to prevent any peripheral irritation. On the other hand, the
morbid tendency may be so slight that a very intense peripheral
irritation is requisite to bring out the morbid action. In such
a case the causation may be numerically expressed thus :

I70 THE CAUSATION OF DISEASE.

Sj -f E10 = 1 1 ; and when the fit is excited by the barest peri-
pheral irritation, we may symbolically express the fact thus :
S9 + E2= ii.

And it is worthy of note that in such cases as the above we
may cure the disease by reducing the number of units whether
of S or of E. An individual is suffering, let us say, from
neuralgia of the fifth nerve. He is anasmic and haggard-looking,
and on inquiry we find that he has been over- worked and worried.
Examination of the teeth discloses on the side of the pain a de-
cayed molar, which is tender to the touch. Now, it may happen
that the neuralgia disappears after withdrawal of the offending
tooth, in which case the causation may have been somewhat as
follows : S6 + E5= 1 1 . By removing the five units of causation,
we cure the disease. On the other hand, the neuralgia may
continue unabated after the tooth has been drawn, when the
causation would be thus represented: Sn-fE0= II. Such a
case, however, may not infrequently be cured by diminishing the
pathogenic value of S. Supposing, for instance, the causation
to be more or less accurately represented by the formula
S6 + E., it will follow that, if by tonics and rest we can reduce
the S6 to S„ the patient will be cured.

We are, indeed, often called upon to fix the pathogenic value
of E and S respectively in cases like the above, for our treatment
may depend upon the conclusion we arrive at. Some physicians,
for instance, value E (note, that I am not now talking of the
external E) at a very low figure in such disorders as epilepsy and
neuralgia — practically ignoring it, in fact ; while others assume
the chief or a large share of causation to reside within it.*

I have given these few instances, and might add many more,
with a view to show how much the numerical expression of
our thoughts would tend to give them a precision which they
otherwise lack.

A structural deficiency, or disease proclivity, may be tem-

* It is evident, from a perusal of Dr. Gowers' work upon Epilepsy, that he
does not attach much importance to the part played by "peripheral irritation"
in the causation of this disorder ; and it may be said that the great purpose of
Dr. Anstie's treatise on Neuralgia was to show that the essential cause of this
complaint lay in the sensory centres.

THE CAUSATION OF DISEASE. 171

porary or permanent. It is well known that an individual will
sometimes escape unhurt when exposed to a given mal-E, while
on other occasions this same E will cause disease. These differ-
ences are due to temporary modifications of S. At one time an in-
dividual may be S, as regards a given mab-E, at another S1+3, so
thatE. , which, in the one instance, is powerless to harm him, will,
in the other, cause disease, owing to temporary structural altera-
tion. But, in such cases as these, the effective mal-E, although
apparently the same, is not actually so ; for the temporary altera-
tion in S must itself be due to temporary peculiarity of E, and
this latter may be unwittingly excluded from the sphere of causa-
tion ; yet, if it predisposes to the disease, it ought obviously to be
included under the specific pathogenic E. A child, for instance, is
on two separate occasions equally exposed to the scarlatina E.
The first time it escapes unhurt, but on the second occasion con-
tracts the disorder. There must, therefore, be some difference
in S on the two occasions. On examination it is perhaps dis-
covered that in the one instance the child was exposed to the
influence of the poison on a full stomach, but that on the second
occasion it had been without food for some time. Now it is ob-
vious that this want of food ought to be included with the specific
virus as part of the pathogenic E, since in this case the two
together were necessary to produce the disease. To give a
further illustration of this point. Troops under privation and
exhaustion are more liable to suffer from dysentery than others,
and, therefore, the privation and exhausting influences, as well as
the virus, must be included under the effective mal-E. Neverthe-
less in such cases we probably have actually to do with temporary
structural alterations induced by E.

It may be asked what place in the above list external vio-
lence ought to occupy as a mal-environment ? Traumatism
is so potent to produce disease that we shall perhaps be inclined
to give it a high numerical value. The fact is, however, that
the numerical value of S is equally high, for the S is very
susceptible to external violence, and this susceptibility varies
with the individual. A twist that would snap the limb of an
infant would have no effect upon that of an adult ; a bullet that
would flatten impotently against the side of a hippopotamus would
destroy most other animals. But there is no occasion whatever

172 THE CAUSATION OF DISEASE.

to use this symbolical method in the case of injuries, and, there-
fore, I will not attempt to show how it could be rendered
accurate. I am, indeed, not ambitious enough to hope to reduce
to scientific precision this method of valuing the relative shares
taken by S and E in the causation of particular diseases. It is
obviously impossible to do so. I have used it simply as an in-
strument of thought, and it may perhaps be occasionally useful
in studying the causation of a particular disease, by presenting
the actual state of things to the mind in a more or less tangible
form.

In the light of our present position, let us examine the
following statement made by Dr. Kussell Reynolds in the intro-
duction to his " System of Medicine."

In speaking of " predisposing causes " of disease, he reminds
us that heredity, sex, age, constitutional peculiarity, congenital or
acquired, are generally included among them. We have seen
what a potent part heredity takes in determining S, and that
age and sex necessarily fall under the same principle. More-
over, it is obvious, from former remarks, that " constitutional
peculiarity/' which is nothing else than structural peculiarity, is
either hereditary or acquired ( = due to E). According to our
manner of viewing it, it must be one or the other, for we have
seen that no peculiarity can arise spontaneously ; if not due to
heredity, it must be due to E, a congenital peculiarity being
either hereditary or the result of peculiar ante-partem E.

Now to proceed to Dr. Reynolds' statement : "In regard
to heredity-taint and constitutional peculiarity, we must admit
that they are in reality diseases " (my own italics). Later
on he affirms them to be part of the disease itself. Thus, a
" man of tuberculous family, and with latent tubercle, was
yesterday apparently well, but he was exposed to cold, and to-
day he has tubercular pneumonia. This constitutional state
predisposed him to the evil which the exposure excited into
activity. It was not a cause of the disease that uxcs there, hut
an integral part of the affection''

We have already seen that we cannot separate S from
causation, seeing that disease is a peculiar inter-action of S
and E. But, whether we are justified in calling any pecu-

THE CAUSATION OF DISEASE. 1 73

liarity of S which renders it apt to be thrown into morbid
action by a specific E, an integral part of the affection, is
an open question, for such a proceeding rather suggests that
disease is a one-sided process, in which S alone takes part
— that the individual actually contains , within himself the
slumbering entity. There is no objection whatever to our thus
regarding disease, provided we bear the fact clearly in mind
that disease is a two-sided process, but we must then be
prepared to admit that every man contains within himself an
integral part of every disease to which his flesh is heir, be it
tubercle, measles, fractured skull, flea-bite, or what notj that
is to say, each of us contains an integral part of fractured skull,
for instance, seeing that we alike suffer therefrom if we do but
expose ourselves to the necessary E. Most of us, too, contain
an integral part of the specific fevers, for do we not respond to
the noxious action of the several parasites which cause these
diseases ? and there are few who do not contain an integral
part of " flea-bite.'' Indeed, it is not necessary to individualize
the diseases which on this view slumber potentially before we
actually suffer from them, seeing that they comprise, as just now
stated, every disease which it is possible for man to contract.

When the tendency to a particular disease is very strong — Ss
for example, or S10 (in which case it bursts out spontaneously) —
there is certainly a great inclination to regard the individual as
containing within himself a part of the disease before he actually
suffers from it, but we cannot sharply divide individuals into the
predisposed and the non-predisposed — into the tubercular and
the non-tubercular, for example — for we meet with every shade of
predisposition, from complete immunity, in some diseases at all
events ( = S0) to impossible escape (S10). Probably, no individual
is absolutely impregnable to tubercle. Hilton Fagge is very
explicit on this point. "Probably," he says, "there is no
family in which the consumptive tendency is so strong that it
could not be kept in abeyance by hygienic precautions if they
were thoroughly and vigorously carried out ; and, on the other
hand, there are very few families (if any) in which the disease
may not show itself in such members of it as systematically
neglect their health, or are exposed year after year to un-
favourable circumstances."

CHAPTER XXI.

Kecapitulation.

I now propose to summarize some of the more important con-
clusions arrived at in the preceding chapters.

The various phenomena of nature are found to be definite
and regular in their sequences, the same results always follow-
ing upon the same conditions. Such being the case, we
speak of the conditions upon which a particular event always
follows as the cause of that event.

There is a natural tendency for the mind to personify
" Cause," and to raise it to the dignity of a separate entity.
This probably results from the fact that we. finding ourselves
capable of voluntarily bringing about definite results, assume
that there must be in every event a somewhat similar causing
agency. Hence it was that primitive man referred the causa-
tion of the various natural phenomena to special Deities.

When, however, we come to examine into the matter, we
find that causation is, in the last resort, a complete mystery
to us — belongs to the infinite region of nescience. By care-
fully observing the various sequences in nature, we are able to
formulate a number of laws concerning them — propositions,
namely, by which we can foretell the results of certain
conditions ; and, as we proceed in this inquiry, these laws
become more and more general — include in their sweep a wider
and wider range of phenomena. By thus grouping the various
sequences in Nature, our knowledge of them becomes more
and more profound, and we are said to ' ' explain " these
sequences — to clear up the mystery of causation. But as a
matter of fact the simplest sequence is a complete mystery to
us. Why one event follows upon another none can say. We
must rest content with the simple assertion of the fact. '

Happily, however, the psychological mystery attaching to

THE CAUSATION OF DISEASE. 1 75

cause has no corresponding practical disadvantage. It is suffi-
cient for us to know that the same results always follow from
the same conditions, and it becomes the business of the
scientist to investigate the order of phenomena, to discover as
many laws as possible, so that he may know what will be the
result of any given conditions.

And this is the task which the pathologist has before him.
He inquires into the laws which govern disease, but, be it
remembered that, in stating the cause of disease, he, in the
last resort, can do no more than enumerate those conditions
out of which it has arisen.

The conditions from which different results follow may be
spoken of as material conditions — conditions of matter. For,
although we have no absolute knowledge of the existence of a
material world (since we can know of nothing apart from our
own mental states), such an assumption is, to say the least,
convenient, and aids us in the practical concerns of life.

The material conditions embrace : kind of matter, quantity
of matter, disposition of matter, motion of matter. Every
result of which we have any knowledge may be brought about
by a modification of these material conditions. Even mental
phenomena may, for all practical purposes, be said to follow
from them, for, although the exact relation between mind and
matter surpasses all understanding, of a relation between the
two there can be no doubt, inasmuch as every mental sequence
is accompanied by a physical sequence, and any disturbance in
the latter causes a corresponding disturbance in the former.

In seeking, therefore, the cause of disease, our object must
be to discover the material conditions out of which it has
arisen ; and, further, to formulate as many laws relating to
disease as possible.

Disease is a vital process. It may be defined as an " ab-
normal mode of life.'*' This definition assumes a perfect
knowledge of what constitutes normal life, but it is no easy
matter, as we shall see in a future chapter, to say what is
normal life. We are, nevertheless, justified in assuming an
ideal or normal life. Disease may then be very readily
defined as an abnormal mode of life.

176 THE CAUSATION OF DISEASE.

And being thus an aberrant or abnormal mode of life, it is
advisable, in seeking the material conditions out of which dis-
ease arises, to first ask the question, What are the material
conditions out of which life arises ?

To speak first of unicellular organisms. We may say that
the immediate causation of life in such = ' ' the material con-
ditions as constituted by the cell plus all those material con-
ditions of the cell-environment which take part in the vital
inter-action." The causation of life in such an organism may
be therefore represented by the formula, S -f E.

If S be properly constructed, and if the E be fit, the vital
processes go on in orderly fashion ; but if either the one or
the other be unfit, an abnormal inter-action occurs, and this is
disease. Disease, being thus an abnormal inter-action of S and
E, must be caused by some fault in S, in E, or in both.

We have, therefore, in investigating the causes of disease, to
inquire most carefully into the material conditions of S and E.
We cannot state these exactly, even in the case of unicellular
organisms ; for who will engage to define accurately the mate-
rial conditions of a unicellular organism — to specify the exact
relations of atom to atom in the molecule, of the molecules
among themselves, or the precise movements whereby either is
agitated ? Our knowledge of the material conditions of the
cell is, in fact, limited to its microscopic characters and
chemical composition, and even in these respects it is very
inadequate. The same is true of the cell-E, the exact material
conditions of which we can by no means state accurately.

But although it is impossible, even in the case of unicellular
organisms, to specify in minute detail the material conditions
out of which the vital processes arise, this should, nevertheless,
be our aim, if we wish to discover the cause of life, and the
more accurately we can define these material conditions, the
more complete will be our knowledge of vital causation, be
it physiological or pathological.

The Environment. — The internal-cell-E. — In multicellular
organs, the E falls into a twofold division, into (a) the internal-
cell-E and (b) the external-body-E. The life of such an
organism may be defined as the " sum of the inter-actions of

THE CAUSATION OF DISEASE. 1 77

the various cells of the body and their respective environments,"
and disease in such an organism consists of the sum of the
abnormal inter-actions.

Owing to the mutual inter-action of tissue upon tissue in a
multicellular organism it very rarely happens that disease in
such an organism remains strictly localized to one tissue.
When disease of one tissue leads to morbid action in another,
it is by modifying its cell-E. Such an abnormal cell-E
may be spoken of as a secondary mal-E, while one which
occurs independently of any previous morbid action may be
said to constitute a primary mal-E. External violence and
indigestible food constitute forms of primary mal-E ; the pre-
sence of nitrogenous sewage in the cell-spaces in renal disease,
and the diminution of oxygen in phthisis, are examples of
secondary mal-E.

When the vital processes of a multicellular organism are more
or less universally thrown out of gear by disease in some one
part, we may define the disease as " the morbid inter-action of
the primary mal-E and the tissue primarily affected, plus all
those morbid inter-actions of the secondary mal-E's and the
tissues secondarily affected." The name of the disease connotes
the sum of these morbid inter-actions.

In studying a disease in a multicellular organism, our object
should be to discover the tissue primarily affected and the
exact nature of the morbid E, and to assign to each, as far as
possible, its exact share in causation. We can never entirely
exclude 8 from causation, but when we are able to satisfy
ourselves that the E is distinctly abnormal, and that the S
is perfectly normal (a very difficult task in many cases, owing
to the difficulty of defining a normal S or E), we may, for
all practical purposes, attribute the entire causation to E.
But when the morbid process is facilitated by some peculiar
structural weakness, practical account must be taken of this
latter, and, according to our ability to gauge accurately the
degree of structural weakness and the intensity of environmental
abnormality, in that same proportion is our knowledge of the
causation perfect.

Having fixed upon the primarily erring tissue, and
assigned to S and E their relative share in causation, it is

178 THE CAUSATION OF DISEASE.

next our business to trace out the several secondary morbid
inter-actions — those, namely, due to secondary mal-E's — and to
place in its proper order each of the many links of the morbid
chain.

It is very seldom that the method, as above set forth, can
be followed with any minuteness, for the- difficulties are many
and great ; these are, nevertheless, the lines on which our search
should be carried out.

As regards the cjctcrncd-body-E, this is far more compli-
cated than at first sight appears. It may be classified as
follows : —

T ~ . (a. Mental.

[b. Physical.
II. Inorganic.

The inorganic E refers to temperature, atmospheric conditions,
and so forth. The organic E embraces the relations of the
individual to the organic world, animal and vegetable. The
relations of man to the animal world are many and complex.
Those of man to man are very largely considered under
the science of Sociology and Ethics, but they also fall within
the province of the pathologist, for disease may be the out-
come of these relations. As regard the relations existing
between man and other animals, this is twofold — for first, our
food supply is largely derived from the animal kingdom ; and
secondly, we are brought into contact, offensive and defensive,
with many of the members of the animal kingdom, though in
civilized countries this only happens to a slight extent.

Concerning our relation to the vegetable world, this like-
wise is twofold. (1) We are absolutely dependent upon it
for our existence, for not only is our food supply chiefly drawn
from the vegetable kingdom, but plants break up the C02
excreted by the animal world, and thus render animal life
possible. (2) We are brought into defensive contact with
myriads of unicellular organisms belonging, for the most part,
to the vegetable kingdom. Indeed, our struggle against these
is infinitely greater than that against the members of the
animal kingdom.

THE CAUSATION OF DISEASE. 1 79

The external-body-E is not only complex ; it is also un-
stable. By a complex E is meant one that embraces many
different conditions ; by an unstable E, one that is not con-
stant from day to day, or even from moment to moment.

The complexity of the external-body-E " in a civilized com-
munity is shown by the fact that every separate calling has
its own peculiar E ; while its instability can be readily realized
by remembering that, even in the case of unicellular organ-
isms, it is impossible for any two individuals to be " similarly
circumstanced in respect to incident forces."

Structure. — In considering the part played by S in disease,
it is necessary to bear carefully in mind the fact that we can
never exclude it from the sphere of causation, seeing that
the causation of any particular disease is represented by the
formula S + E.

When the S is normal (we may, for convenience, assume
an ideal normality) we are justified, from a practical point
of view, in excluding it from causation in certain cases, as
when an individual contracts scurvy through insufficiency of
vegetable diet. But, even viewing the matter from a strictly
practical standpoint, it is by no means easy to do this in all
cases where the S would certainly be accounted normal. If,
for instance, two individuals, enjoying perfect health, be
exposed for the first time to the scarlatina virus, and the one
contracts the disorder while the other escapes, it is obvious
that the S must be taken into practical account in stating
the cause of the disease. This one case, indeed, shows us that
the inclusion of S in the causation of all diseases is not a mere
logical quibble.

Seeing, then, that the S takes a share in the causation of
all disease-processes, it behoves us to inquire most carefully
into its causation.

The nature of S depends upon two great factors — (i)
Heredity ; (2) Environment.

As regards the influence of E upon S, this is well shown
by the different ways in which different occupations mould
the individual. In estimating this influence, we must, be it
remembered, start at a period antecedent to the birth of

l8o THE CAUSATION OF DISEASE.

germ and sperm. This influence is more potent the earlier
it acts. The smallest alteration in germ- or sperm-struc-
ture, wrought by the subtlest force, will be sufficient to cause
an alteration in the development of the embryo, this altera-
tion increasing with every stage of development. Hence the
strictest care should be taken to place the mother, prior to
and during gestation, under the most perfect E, and we
should moreover be particularly careful to regulate the E
during the whole period of post-partem development. When
maturity is reached, the E is less capable of influencing S.

Although the E possesses a considerable power in moulding
S, it occupies a position far below heredity in this respect.
This term embraces an infinite complexity of forces which tend
to mould the individual into the likeness of the parent or
parents.

Without going any further into the question, it is sufficient to
say that, in the case of gamogenetic organisms, the immediate
cause of heredity consists in the material conditions as con-
stituted by the impregnated ovum and its environment.
Given these material conditions, the offspring will develop
into a more or less mean likeness of the parents. How germ
and sperm come by their structure is another question ; but,
given the proper material conditions, there is no difficulty in
explaining, on the principle of causation already set forth, the
subsequent developmental changes.

Be it noted, that the material conditions, as constituted by
the impregnated ovum and its E, represent the immediate
cause of the hereditary process ; but in every instance of
causation we can increase our knowledge of the causative
process by tracing out the remoter links in the chain of
causation. Thus, if we can trace the causation of germ and
sperm structure — i.e., specify the material conditions out of
which they themselves have risen into being— we shall
possess a fuller knowledge of the causation of heredity. But
indeed, in order to get a complete and philosophical insight
into this marvellous moulding agency, it is necessary to cast
the eye into the long past, and follow, one by one, the
various steps of organic evolution. In this way we extend and

THE CAUSATION OF DISEASE. l8l

amplify the history of the causation of hereditary structure.
Such a proceeding, however, would have interfered with the
proper sequence of our argument ; and hence this subject will
be treated of in the second part of this work, for much that is
pathologically important is brought to light by examining
into the evolutionary history of man.

The Principle, of Structural Mean. — Inasmuch as, in the
case of man, two individuals are engaged in the reproductive
process, the offspring tend towards a certain mean of the two
parental structures. A certain mean, be it noted, but not an
exact mean, for some one or other paternal or maternal charac-
ter may be prepotent.

If the E were exactly the same for each and every child
born to the same parents, all the offspring would be exactly
alike, save only such differences as depend upon sex — the
male offspring on the one hand, the female on the other.
But, owing to the instability of the E, no two children
can be exactly the same. Under the principle of structural
mean, the blending in the offspring of tendencies derived from
the two parents has to be considered — notably, the blending of
physiological with pathological tendencies, and of pathological
with pathological, the latter constituting the so-called inter-
marriage of disease.

When the pathological tendencies are alike in both
parents, the chances of the offspring inheriting the disease are
very strong. Nevertheless, even in this case, there is a
tendency to revert to the normal state, owing to the vis
medicatrix naturce. But when the morbid tendency comes
from the one parent only, there is less tendency to inherit-
ance. This may be partly explained by regarding the parents
as a cross in respect of this pathological particular, for, when
parents are very unlike in some one particular they may be
regarded as a cross in respect to it ; and when two individuals
are crossed, there is a tendency to reversion to the status quo
ante the development of that particular or those particulars
in virtue of which they become a cross. If one parent, for
instance, is highly neurotic, while the other possesses a strong

0

1 82 THE CAUSATION OF DISEASE.

and stable nervous system, the two may be regarded as a cross
in respect of the nervous system, and we should expect the
offspring to show a strong tendency to revert to the status quo
ante the acquisition of the neurotic state — i.e., to a normal
condition of nervous system.

The Fixity of Structural Characters depends, in large mea-
sure, upon their age, ancestral or individual. The ancestral
age of serious pathological characters is never great — that is to
say, the number of successive generations of the same family
afflicted, actually or potentially, with the same serious disease
is never great. And such being the case, it follows that there
is a strong tendency for the offspring of parents afflicted with
serious disease to revert to the normal. In like manner, in
regard to characters acquired by the individual himself, the
more recent the acquisition the greater is the facility with
which it is cast off.

This principle of " Structural Fixity," taken in conjunction
with what we know of the effects of crossing, explains, in large
measure, the vis medicatrix natural.

That the fixity of a structural character largely depends
upon its age, ancestral or individual, is well shown under the
disturbing influence of disease, in which structural characters
tend to disappear in the inverse order of their age ; for almost
all disease is a process of dissolution, and, be it noted, so long
as the actual process of disease is going on, the dissolution
is partial, for, if it be complete, there is death of the part
affected, and this is not disease. Since, then, disease is
a process of partial dissolution — i.e., an incomplete undoing
of evolution — it follows that a number of ancestral characters
will tend to display themselves during disease, which must,
therefore, be largely tinged with an element of reversion. The
reversions, however, which take place during actual disease
are very rarely exact reproductions of ancestral states, because
the E causing the dissolution is probably always unlike that
which was normal to the evolutionary epoch to which the
reversion belongs ; and, inasmuch as E is capable of modifying
S, the reversion cannot be true : it will be, so to speak, a
natural variation of the true reversion. We may, therefore,
speak of a disease which is accompanied by distinct dissolution

THE CAUSATION OF DISEASE. I 83

as a vitiated reversion, and every complicated disease is a
bundle of vitiated reversions.

The 'principle of Sexual Heredity is an important one. Ac-
cording to it, characters acquired by one sex at a particular
period of life tend, in the offspring, to appear in the same sex
and at the same period of life. This principle is not only true
as regards sexual characters, but applies in some degree to
each and every acquisition, whether sexual or not. Characters
acquired before the period of sexual life show a tendency to be
inherited by either sex indifferently, though at corresponding
ages ; hence, the diseases in children are in only a small degree
influenced by sex. Characters acquired during the post-sexual
period of life can obviously have no effect upon the offspring.

It is to be noted that the male sex takes on structural
characters more readily than the female. This should prepare
us for a greater variety of disease in the male.

Characters can pass potentially through one sex to the
opposite sex in the offspring. In all such cases it is certain that
the potentialities are kept under by a restraining influence, on
the removal of which they are ever ready to become actualities.

The principle of heredity at corresponding ages asserts that
characters acquired by one parent at a particular period of life
tend to develop themselves in the offspring at the same period.
The truth of this principle is amply illustrated by disease.

Such is a brief consideration of the principle of heredity.
It has prepared us for the fact that heredity plays an extensive
role in disease. In a later portion of this work we shall be in
a better position to establish this statement.

Having considered the two factors of disease, S and E,
separately, we must next study them together, disease being a
mutual inter-action of the two ; and, although this subject has
been already trenched upon in this chapter, it is advisable to
make some further allusion to it.

The S differs considerably in its manner of responding to
the E. An E which will have no evil effect upon one indi-
vidual, will in another produce the most dire results.

o 2

1 84 THE CAUSATION OF DISEASE.

The tendency which a particular S has to respond abnormally
to a particular E may be spoken of as "a specific structural
deficiency." The less this structural deficiency, the greater is
the quantity of specific mal-E requisite to call forth the dis-
order. In other words, the quantity of mal-E requisite to call
forth a particular disorder is in inverse proportion to the
degree of structural deficiency. Suppose a disease, such as
insanity, be represented by eleven units, then the formula
Sx + E]0 indicates that the structural deficiency as regards
insanity-producing causes — i.e., the tendency of the mind-
centres to take on pathological action in response to specific
insanity-producing causes — is very slight ; while S10 + Ex
indicates a very intense structural deficiency — one, in fact,
which will spontaneously blossom into the full disease.

All of us, even the most typically healthy, respond patho-
logically to some forms of E, and it may therefore be thought
that the term structural deficiency is inaccurate. The objec-
tion would have force, if there were one unchangeable standard
or normal S, but such is not the case. If an individual, who
would otherwise be accounted healthy, falls a very ready
victim to a certain skin parasite, he may be said to have a
structural deficiency as regards that parasite, just as an indivi-
dual who is incapable of resisting the attack of the tubercular
bacillus, or ague poison, may be said to be structurally defi-
cient in respect to these agents ; and it by no means follows
that the proclivity to disease depends on a weakened and
unhealthy bodily state. An individual having a structural
deficiency as regards a particular E is, in fact, one who is very
ill-adapted to that U, or who, as Spencer might say, is altogether
out of equilibrium with it.

It does not, of course, follow that, because an organism is
ill-adapted to its E, disease must ensue. All the weeding-out
effected by natural selection is due to ill-adaptation ; but this
weeding-out is, except in the case of civilized man, in only a
small degree due to disease, which is the result of very signal
mal-adaptation of S to E.

PART II.

CHAPTER I.

The Evolution of Species— Natural Selection — Sexual Selection — The Action
of the Environment independently of Selection.

Species are evolved in a threefold manner — (i) By natural
selection ; (2) by sexual selection ; (3) by the action of the
environment, independently of either natural or sexual selec-
tion.

It is necessary to inquire how far man comes under the
influence of these three methods, for a knowledge of the laws
by which the human organism is built up must be of use to
us in our search after the causation of disease, seeing that S
plays such an important part in it. In our study of this sub-
ject, moreover, many important side issues will be raised, which
might otherwise be passed over unnoticed.

The first requisite is a clear understanding of the methods
in question.

Natural Selection is, so to speak, the selection by " nature"
of those organisms most fit to live — that is, best adapted to
their own particular environments. This is the term by which
Darwin himself denoted the great law he discovered. Herbert
Spencer's Survival of the Fittest expresses the same idea,
and it has found greater favour among biologists, because the
term M natural selection " seems to imply (what Darwin cer-
tainly did not mean it to do) a voluntary choice on the part
of a personified nature.

There are two main factors underlying natural selection —
(1) The existence of natural variations; (2) a struggle for
existence. Were there no natural variations, it is obvious

1 86 THE CAUSATION OF DISEASE.

that that there could be no survival of the fittest, since all
members of the same species would be the same ; and if
there were no struggle for existence, there would be no need
of such survival, since all organisms would be adequately
provided for.

Natural variations are, as we have seen, an a priori neces-
sity : the E cannot be the same for any two individuals, and,
inasmuch as the latter is capable of influencing S, differences
of E signify differences of S. Hence there must be a differ-
ence even among the individuals reproduced asexually from
a single parent. Such differences in E are undoubtedly
the primary cause of natural variations j but, once started
in this way, they are still further increased by the method of
reproduction from two parents, for, in this case, the offspring
cannot be exactly like either the one or the other, and,
differing from either, will form a natural variation.

Let us now inquire into the cause of the struggle for exist-
ence, and we may limit our observations to the animal
kingdom. One great cause is the dearth of food ; for, since
organisms tend to increase in geometrical ratio, while the
supply of food is limited, a certain number only can secure
the proper quantity. There is, consequently, a survival of
those best able to do so — of those, namely, which vary in a
direction enabling them to compete successfully with their
fellows. This struggle is fiercest between individuals of the
same species, all of which will be struggling for the same kind
of food.

But there is another element in the struggle; there is a
struggle against unfavourable conditions both of the inanimate
world, in the shape of excessive heat and cold and so forth,
and of the animal world, in the shape of attacks of other
animals, parasitic or otherwise. If an individual cannot pro-
tect himself against climatic extremes, or the attacks of other
animals, he is not properly adapted to his E and succumbs,
while such of his fellows as are so happily constructed as to
meet the exigencies of their individual E's survive — being
fitter or more in harmony therewith.

It follows that there is a perpetual weeding out of

THE CAUSATION OF DISEASE. 1 87

the unfit and a survival of the fit, and thus by a gradual
accumulation, during long periods of time, of favourable
variations, species are in large measure evolved, the ultimate
result being that each creature tends to become more and
more improved in relation to its external conditions, and
" this improvement eventually leads to the gradual advance-
ment of the organization of the greater number of living
beings throughout the world, the degree of advance being
measured by the completeness of the division of physiological
labour."

The law of " Natural Selection," or " Survival of the
Fittest," is one of the greatest natural laws yet discovered, and
although its exposition originally met with some opposition, it
is now accepted as an uncontrovertible fact. Herbert Spencer
says of it : " When once enunciated the truth of the hypothesis
is so obvious as scarcely to need proof." It has passed from
the realm of hypothesis into that of law.

I would particularly emphasize the distinction between the
struggle for food, or, what is the same thing, the struggle
against starvation, and the struggle against the remaining
adverse conditions. When we come to speak of man, we shall
see what a host of diverse conditions are included under the
latter, and that with him — at all events with civilized man —
it is as regards these latter that natural selection plays its
chief part.

Sexual Selection consists in the struggle between the mem-
bers of one sex for possession of individuals of the other;
and it is generally between the males for the female. Success
may depend upon general strength and vigour, in which case
the strongest and most vigorous males will tend to have the
most offspring (we may even assume that such a struggle
takes place between myriads of spermatozoa for the possession
of the ovum, the hardiest and lustiest proving successful) ; or it
may depend upon the possession of special weapons, such as
the horns of the stag, or the spurs of the cock, which, there-
fore, tend to increase from generation to generation; or, finally,
success may depend upon freedom of choice. The beautiful
plumage of cock birds is due to a selection by the hens of

I 88 THE CAUSATION OF DISEASE.

the most beautiful males during many generations. Speaking
of the method by battle, Darwin says : —

" How low in the scale of Nature the law of battle descends I
know not : male alligators have been described as fighting, bellow-
ing, and whirling round, like Indians in a war-dance, for the
possession of the females ; male salmons have been seen fighting all
day long ; male stag-beetles sometimes bear wounds from the huge
mandibles of other males ; the males of certain hymenopterous in-
sects have been frequently seen by that inimitable observer,
M. Fabre, fighting for a particular female, who sits by, an appa-
rently unconcerned beholder of the struggle, and then retires with
the conqueror."*

The Action of E independently of Selection. — We have seen
that the E is capable of modifying structure in a marked
degree, and that any of the variations thus induced may be
accumulated and intensified by selection, the organism thus
becoming, by indirect means, adapted to its E. Wherefore
Herbert Spencer speaks of this process as indirect equilibration.

The E may, however, work marked and definite changes upon
a race, in the course of a few generations, altogether independently
of selection. This process the same writer terms direct equili-
bration; while Darwin speaks of it as the direct and definite
action of the conditions of life. Thus, the woolly hair of the
negro is not the product of selection, but results from the
direct action of certain atmospheric conditions, and the
characteristic conformation of the true Yankee — his spare
form, high shoulders, pigmented skin, and more or less
hairless face, are evidently due to the action of his E,
independently of selection, natural or sexual. It is indeed
quite astonishing how rapidly the E may thus modify a
race ; any one practising among the poor of London may
very soon prove this for himself. It is very easy, for in-
stance, to distinguish between the crania of London and
country-born individuals, for the bones undergo considerable
change, even in the space of one generation.

In considering this action of E independently of selection,
we must be careful to remember the very wide significance of

* "Origin of Species," p. 101.

THE CAUSATION OF DISEASE. 1 89

the word i: environment;' and what a vast assemblage of
diverse conditions it embraces (vide Part I.). Thus, as I have
said, the effects of use and disuse are embraced under " the
environment" of the individual, and there can be no doubt
that species are in this way moulded in a very marked degree.
To take a single example from Spencer : the aesthetic sense
cannot have attained its present high development through the
process of natural selection, since it is one that can only help
in a very minor degree in the struggle for existence. It has
grown through long cultivation or exercise, from generation to
generation — that is to say, through use. Chiefly in this way,
too, the moral sense has been evolved. The average civilized
child is taught morality from its earliest age ; it finds itself
in a society whose very existence depends upon the observance
of social law, and such cultivation, assiduously carried on
through many generations, has led to the development of an
innate moral sense. Thus, the aesthetic and the moral faculty
have both been evolved by the continuous operation of an
aesthetic and moral E on the human organism, independently
of selection, at all events in large measure.

Herbert Spencer, as I have said, designates this process
direct equilibration. It consists, in his language, " of changes
of function and structure that are directly consequent on
changes in the incident forces — inner changes, by which the
outer changes are balanced and equilibrium restored." Even
in the lifetime of an individual this process plays an im-
portant part, for in this way he tends to become more
and more adapted to his E. Let us suppose twin brothers to
be as like one another as it is possible for them to be :
then, if one be brought up as a peasant and the other as a
clerk, a steady divergence in structure will gradually ensue,
each individual becoming adapted to his own particular
E. We may speak of this individual tissue-alteration as
personal to distinguish it from racial adaptation ; and we can
see how, by a summation of such personal adaptations
through many generations, a race may be very considerably
modified.

A study of this threefold method whereby animal organisms
are evolved shows us, therefore, that evolution depends upon

190 THE CAUSATION OF DISEASE.

simple mechanical causes {causes efficicntes). Such a mechani-
cal explanation is, in the language of Haeckel, " one entirely
based on natural science." We are thus able to dispense
with designing or teleological causes {finales vausce) .

We have now to inquire how far the methods by which
organic evolution proceeds are severally applicable to man,
for whatever pertains to organic evolution may fall within
the province of the pathologist, pathology being a branch of
biology.

CHAPTER II. ■

Natural Selection — "Instinct and Reason" — Instinct a Perfect — Reason an
Imperfect Guide.

I PROFOSE, then, to consider separately and in relation to man
eacli of the methods by which organic evolution proceeds.

Natural Selection. — Herbert Spencer believes that evolution
by a survival of the fittest — i.e., indirect equilibrium — plays
a progressively smaller and smaller part as the animal scale
is mounted, until, in the case of civilized man, the process
is mainly by direct equilibration. " While yet," says he,
" organisms had comparatively feeble powers of co-ordinat-
ing their actions and adjusting them to the environment,
natural selection acted almost alone in moulding organisms,
and it has remained almost the sole agency by which
plants and inferior orders of animals have been modified
and developed." He believes that as fast as the " essential
faculties multiply, and as fast as the number of organs that
co-operate in any given function increase, indirect equilibration
through natural selection becomes less and less capable of
producing specific adaptations ; and remains fully capable only
of maintaining the general fitness of constitution to conditions,
direct equilibration taking place, until at length among civilized
races the equilibrium becomes mainly direct, the action of
natural selection being restricted to the destruction of those
who are constitutionally too feeble to live even with external
aid. As the preservation of incapables is habitually secured
by our social arrangements, and as very few except criminals
are prevented by their inferiorities from leaving the average
number of offspring (indeed, the balance of fertility is probably
in favour of the inferior), it results that survival of the
fittest can scarcely at all act in such a way as to produce
specialities of nature either bodily or mental."

192 THE CAUSATION OF DISEASE.

There can be no doubt that the above propositions of Spencer
are in the main correct. Man will advance in the future
chiefly by a process of direct equilibration. Nevertheless,
natural selection plays a very important part, even in the case
of civilized man — a part, too, which, viewed from a pathological
standpoint, is of the utmost iiuportance. It demands, there-
fore, our serious study.

In 1 8 8 1 I read a paper at the Abernethian Society * on
"Instinct and Reason," wherein I had occasion to draw
certain contrasts between man and the dumb animals, and one
of these was founded on the very small part played by natural
selection among men as compared with the brutes. On re-
considering the subject, after fuller investigation, I have found
that my conclusion was immature, but I propose here to give
certain extracts from the paper, because, in the first place, I
shall thereby avoid having to deal separately with " Instinct
and Reason," a subject closely connected with the causation of
disease ; and, in the next place, because this proceeding will
serve to emphasize certain important facts.

The grand purpose of instinct and reason is to place the
individual in proper connection with the outer world. They
are both the outcome of nervous action, and it is interesting
to note that the nervous system develops from the epiblast or
outer part of the ovum, thus clearly showing that its first and
primordial function was to regulate the relations of the indivi-
dual with the outer world.

Put scientifically, we may say that the essential purpose of
instinct and reason is to regulate the E of the individual, to
surround him by such conditions as are best suited to his
existence. No doubt reason — I use the term in its widest
sense, to include all the higher faculties of the mind — has
advanced to a stage altogether beyond this ; but its essential
function is, and ever will be, to regulate the environment of
the individual, whether he be a Shakespeare or only "common
clay."

Every animal, indeed, every organism, has its particular E.
* St. Bartholomew's Hospital.

THE CAUSATION OF DISEASE. 1 93

Thus, the E of the fish differs from that of the mammal,
which again is different from that of the bird. Nor is this
all. The E of each species of fish, bird, and mammal — .
indeed, of every species of animal — is different from that of
any other ; and it is the special purpose of instinct and
reason to secure the proper E for each. If the ant had the
instinct of the worm, or the latter that of the lizard, neither
could provide itself with the proper E, and both would
inevitably perish. But matters are so happily arranged that
each animal has the inborn power of regulating its E more or
less correctly.

The E of man is infinitely complex. As the division
of labour proceeds in the social organism, the number of
different kinds of E increases, and thus every man following a
different calling is surrounded by a different E. There is not,
therefore, one limited and more or less stereotyped E for each
and every member of the human species, such as obtains in
the case of any one species of the dumb animals.

Now, so far as the en viro- regulating apparatus is concerned,
man and the brutes stand out in bold contrast, in that reason
is the chief means of the one, instinct of the other. I will not
here set forth in critical detail the distinctions between instinct
and reason. It is sufficient to observe, that the one impels by an
inborn power, which ties down the individual to act mechani-
cally, so to speak, on a narrow and stereotyped plan ; while
the other is a more or less complex mental process, in which
the inborn guiding voice finds but little place. The subtle
psychological distinctions between instinct and reason need
not, however, detain us. That there is a distinction is clear,
and for pathological purposes, if for no other, it is very
necessary to recognize it. And why ? Because the one regu-
lates the E perfectly, while the other is a defective regulator ;
the one places the individual amid the E to which he is
best adapted, while the other frequently fails to do so. And
inasmuch as disease essentially originates in improper E, this
deficiency in the enviro -regulating system becomes a fertile
source of disease.

Instinct is the most perfect possible guide. Few, I imagine,
will deny this proposition ; but lest any should, we have

194 THE CAUSATION OF DISEASE.

an a priori proof of its truth in the fact that instinct has
been built up very largely by natural selection ; it must, there-
fore, as a guide, be as near perfection as possible. One is apt
to think that natural selection acts solely upon the corporeal
side of an individual ; whereas, the function of instinct
comes equally under its influence, for in the battle of life
correct instinct is quite as requisite as correct bodily struc-
ture. In order that natural selection shall operate on the
instinctive side of the organic being, it is necessary for the
instincts to vary, and there is no reason why they should
not vary quite as freely as the bodily structure ; indeed, this
is obviously an a priori deduction, since instinct is the
functional expression of a certain part of the bodily structure
— namely, the nervous system.

Darwin gives several examples of such variations in
instincts. Thus, birds vary in their choice of nests ; the
magpie is tame in Norway, the crow in Egypt ; and natural
selection would not be slow to seize upon any variation
favourable to the animal in its struggle for existence.
Indeed, man himself has not failed to turn such varia-
tions in instinct to his own good account ; for, as Darwin
observes, he has actually built up instincts artificially, by
artificially selecting such variations as are of service to him.
A well-bred pointer will point the first day he is taken out ;
and the shepherd's dog, while quite a puppy, shows a tendency
to run round, not at, a flock of sheep. If, then, man can,
in the course of a few generations, build up an instinct wholly
useless to the animal, and solely for his own pleasure, by arti-
ficial selection, one can well see how natural selection must tend
to preserve any slight variation in instinct which is helpful
to the animal in its struggle for existence ; and further, how it
has come about that instinct is an accurate guide, regulating
the environment of the animal, indeed, with a wisdom that is
well-nigh unerring.

Now, the guiding voice of reason is not, like the voice of
instinct, the outcome of natural selection. The evolution of
reason itself has doubtless been largely governed by natural
selection ; but there is a great distinction between reason as
such and the guiding voice of reason — that part of reason,

THE CAUSATION OF DISEASE. 1 95

namely, which impels to action; just as there is a great
distinction between, a government and the laws which it
enacts. The actions dictated by reason have not the fixed
and stereotyped character belonging to instinctive acts ; for a
reasoned act is not, like an instinctive one, the result of the
impulsive prompting of an inborn voice ; it is, on the contrary,
the result of a complex mental process, and this mental result
cannot possibly have come under the influence of natural
selection; wherefore we are at once led to expect reason to
be a less perfect guide than instinct.

With the many imperfections of reason I shall presently deal,
but before doing so let me remark how important is that stage
in evolution when reason first appears in full force. Although
many of the brutes are endowed with reason, they are all tied
down by instinct to act more or less mechanically on a narrow
stereotyped plan. Man, on the other hand, is essentially a
reasoning being, guided only in a small degree by instinct ; so
that, as I have already said, we may more or less sharply
separate him from the brutes, in that he is governed by reason,
they by instinct. Now, prior to the evolution of reason, such
as we find it in man, we observe Nature at work in her more
simple physical aspect, life being a mere complex play of
chemico-physical force, and instinct (although in its higher
developments largely tinged with a mental element) essen-
tially a nervo-automatic process, the product, in a large
degree, like the body itself, of natural selection. But with the
evolution of reason, such as we find it in man, an entirely
different order of things obtains; for whether we regard
mind as necessarily linked with matter, or as something
quite distinct and separate from it, the fact remains that we
have in its higher creations something very different from
anything which has hitherto taken part in the operations of
nature* — a power, namely, which diverts the course of mere

* There can be no doubt that the evolution of mind as it appears in man,
more especially in civilized man, marks an important epoch in the history of
evolution, for the reasons I have given in the above text, and in order to em-
phasize this fact — the fact, namely, that mind henceforth exercises an im-
portant influence over natural processes hitherto more or less independent of
it, and, secondly, that the process of natural selection in man is interfered
with — I have kept my text unaltered, but I can now see that neither of these

I96 THE CAUSATION OF DISEASE.

chemico-physical nature. Now for the first time there occurs
the clashing of two great systems — chemico-physical nature
on the one hand, mind on the other. The former is no longer
able to pursue her unchecked course, for man is capable
of modifying the processes of physical nature at will. He
cannot, indeed, suspend them — he must, as Bacon observes,
rule by obeying, but in this way he can compel natural
laws to work together towards a definite end, and thus not
only the inanimate but the animate world is largely under
his control. Man's influence over the brutes is not, be it noted,
one of mere personal mastery : he can mould both plant and
animal forms at will, namely, by modifying their environ-
ment and by artificial selection. For these reasons, if for no
other, the appearance of mature reason, such as we find it in
man, marks an important epoch in the history of evolution.
But two other noteworthy effects must be mentioned, and they
relate to man alone. (1) Reason being a far less perfect
guide than instinct, man, forsaken by the all-wise guide, but
too often finds himself plunging in the dark, and unwittingly
rushing into destruction. (2) Owing to the evolution of reason
in man, he is to a very large extent exempt from the opera-
tion of natural selection, and, inasmuch as this process is
continually weeding out the inferiors and securing the survival
of the fittest alone, the effect on the human race must be
injurious. I will consider the latter propositions presently.
Meanwhile, let us examine the former, namely — Reason is a
less perfect guide than instinct.

conclusions is altogether correct. In the first place, the distinction above drawn,
between "chemico-physical nature" and the voluntary operations of the mind,
though useful, is arbitrary. Now that I have become better acquainted with
psychology, I cannot do otherwise than accept the doctrine of necessity, and
hence the sharp distinction I have drawn between a voluntary mental impulse
and a chemico-physical process does not exist. The apparently voluntary
efforts of the mind are nothing else than the expression of chemico-physical
nerve change, the "voluntariness" being a delusive creation of the mind.
It is quite obvious, in fact, that the doctrine of necessity is inconsistent
with my assertion that " with the evolution of reason we have a something
quite distinct from chemico-physical nature." Secondly, although doubt-
less there is some interference with the operation of natural selection among
men, I cannot doubt, on maturer thought, that natural selection here still
operates very potently, as I shall show hereafter.

THE CAUSATION OF DISEASE. 1 97

It is necessary to remember that reason has a far more
difficult task before it than instinct, for, along with the deve-
lopment of the higher mental faculties, society has become
more and more complex, and thus civilized man finds himself
in the midst of a highly complex E. Moreover, this E is
not fixed and stereotyped like that of the brutes, but ever
variable, and man is continually encountering combinations
of circumstances which have never occurred to him before.
Reason has, therefore, to serve as guide through an E which
is both complex and variable. Furthermore, the E of
man comprises an abundance of luxuries, many of which are
tempting and fascinating sources of evil, and lure to destruc-
tion, just as a flame entices the moth, or as the false beacon of
old lured the passing vessel to its doom. To safely guide an
individual through all the intricacies, temptations, and dangers
of a civilized E, is indeed a difficult task for reason. On
the other hand, the E of the instinct-led brute is far simpler
and more stable, for instinct compels the animal to remain in
certain fixed and well-trodden grooves ; wherefore, its task is
comparatively easy. But altogether apart from the question
of difficulty, instinct is as a guide much surer and safer than
reason. We have seen why instinct is a sure and perfect
guide ; let us now inquire why, in this respect, reason is so
far inferior to it.

The knowledge of how to act upon any given occasion is
largely based upon man's experience, both individual and
ancestral — i.e., he learns personally what is good and bad for
him, and this experience is often dearly bought ; and he further
profits by the accumulated experience of those who have gone
before him. This experience is transmitted from generation to
generation by word of mouth and written record — not, in
the way of instinct, by direct heredity. Now, when a man finds
himself in an altogether new position, a position which he has
not experienced before, he must, unless the experience of
others be available, fall back upon the guidance of reason,
pure and simple — that is to say, intellect. But this often
fails him. To set forth in critical detail the imperfections of
reason would be to write a large volume. Certain it is that
every one does not know how to reason correctly on even the

p

19^ THE CAUSATION OF DISEASE.

most simple questions. A perfect reasoner, indeed, is very
rarely met with. Our own medical literature affords abundant
proof of this, and this work is doubtless no exception. But,
apart from the fact that reason may fail to work properly,
there is the additional fact that the material for reason may
not be to hand — we may be ignorant of the data from which
to derive the proper conclusion. Wherefore, in order that reason
shall on all occasions give a correct result, two things are re-
quisite— man must be acquainted with every natural law, and
he must be gifted with perfect reasoning power.

By the aid of experience and reason, however, he can fre-
quently learn what is the proper course to take. But here
another imperfection arises : he may know, but he may not
choose to be guided by his knowledge. Perfect knowledge of
right and wrong does not imply virtue. Socrates held know-
ledge to be virtue, but we may, with more correctness, say
virtue is the correct application of, or the proper acting up to,
knowledge.

When an individual fails to act up to his knowledge in a
matter relating to his personal well-being, he is said to be im~
'prudent (Bain). An imprudent man is one who is unable to
see that the evil ultimately resulting from a present pleasure
quite outweighs it, and that the algebraical sum gives a minus
quantity — he cannot correctly weigh between a present pleasure
— e.g., unwise eating — and future misery — dyspepsia. Impru-
dence is therefore a mental defect, or a defect of reason,
employing this word as an antithesis to instinct, and as signi-
fying all those mental forces, other than the instinctive, which
impel to action (not as signifying intellect, which is perhaps
its proper signification).

"No one who pays any attention to this subject .... can fail
to see that the vast difference which exists between what actually is
and what might be depends, not so much upon wrant of knowledge,
as on want of action. Ignorance, no doubt, has much to do with
sickly lives and early deaths, but surely the indisposition and want of
will to act on what is clearly understood has much more to do with
the presence of disease and premature decay. As an instance of this,
let us refer for a moment to the influence of intoxicating liquors on
the population. Is the absence of any effort to control or mitigate

THE CAUSATION OF DISEASE. 1 99

the evil due to any doubt of its effects on life and health ? Has not
the potency of alcohol as an active agent of various diseases, as the
chief cause of that condition of body and mind in which both will
easily succumb to trivial forms of mischief, been established beyond
all question 1 And then is it exaggeration to say that, if the abuse
of alcohol were unknown, half the sin and three-fourths of the
poverty and misery of the world would disappear from it 1 Or, for
another illustration, let us recur to the subject of infection. Do we
avail ourselves of what is clearly known, and even generally recog-
nized, of the laws which regulate the propagation of infectious
diseases 1 Are we still waiting for the necessary knowledge ? When
will the time for action come 1 " *

Wherefore we must conclude that man's guide is imperfect :
first, through his deficiency of knowledge, whether gained
through experience (personal or otherwise) or by an intellectual
process; and, secondly, through his inability! to act up to
what knowledge he has.

Now, inasmuch as instinct secures to the dumb animal a
more perfect E than that with which reason provides man, it
follows that the brute creation is less afflicted by disease than
man, for an improper E is the great cause of disease. Disease,
no doubt, does exist among the brutes, as it does even in the
vegetable world ; it is, indeed, as I have already pointed out,
an a priori necessity. Nevertheless, there is a wide difference
between the standard of health in man, more especially civilized
man, and in the brutes.

It is not fair to select the domesticated animals as standards
of comparison, because they have, in many cases, been largely
moulded by artificial selection. Not only have their instincts
become vitiated in this way, but they have further suffered
from prolonged domestication. The common domestic cow,
for instance, is a very different being from its wild progenitor,

* W. S. Savory, " The Book of Health," pp. 96, 97.

f A believer in the " Freedom of the Will " would preEer the word failure
here, and this word would better harmonize with the statement made on
p. 198, that a man " may know, but he may not choose to be guided by his
knowledge," since this statement implies a freedom of choice ; but whether
we have or have not such freedom of choice, the fact that we do not act up
to our knowledge must be accounted a mental defect — " a defect of reason "
us distinguished from instinct.

r 2

200 THE CAUSATION OF DISEASE.

alike in its instincts and bodily conformation. The product
of artificial selection, confined for long periods, and fed
upon artificial food, what wonder that this pampered creature
should suffer from acute flatulent distension if let loose upon a
field of fresh clover ! Yet I imagine that such an accident rarely,
if ever, occurs in the wild state. The instincts of animals
may, however, be rapidly corrupted by domestication. Jumbo,
the great elephant, was said to be very fond of alcohol, and
almost all our domesticated animals may be educated into liking
articles of diet quite unlike those they feed upon in the natural
state; thus, most of the vegetable feeders, e.g., horses and
pigeons, can be taught to eat meat, and I frequently see a pet
lamb which eats fat, tea-leaves, and many other strange things
with great eagerness.

CHAPTER III.

Natural Selection (continued) — The Influence of u Reason" upon Natural

Selection.

The most serious accusation to be laid at the door of ". reason"
is that it has rendered the law of natural selection more or less
inoperative among men. If this be true, it is a very serious
indictment, since by natural selection there is a continual
weeding out of the evil from the good, and surely the cessation
of this beneficial process must work very great harm upon the
race.

In the following observations let me remind the reader that
I am repeating arguments used in the paper already alluded
to — arguments which certainly must often have been used
before, since they would occur to any one who would take the
trouble to think the subject out for himself ; indeed, I have
often heard similar arguments used in ordinary conversation.
I shall presently show, however, that they do not represent
the complete truth.

In studying the effects of natural selection upon the animal
organism, it is advisable to regard the latter in a twofold aspect
« — (i) from the corporeal, (2) from the instinctive or mental
point of view, and the one is as important as the other.

First, as to the corporeal side. Does natural selection, in
the case of man, secure the survival of those corporeally the
most fit ? Assuredly not. Do the strongest and healthiest
always survive their inferiors, and hand down their superiorities
to posterity ? Alas, no ! for it is a matter of common notice
that the fine young fellow " goes to the dogs/' He poisons
his blood with drink, or with a yet viler thing, thus wrecking
in a single generation a beautiful organisation which has
slowly and laboriously evolved through myriads of genera-
tions, each one of which, be it remembered, has had the good

202 THE CAUSATION OF DISEASE.

fortune to vary in the right direction and to secure the
proper E.

Every man will do well to cast his mind into the past, and
essay to picture to himself the fierce conflict which has raged
from the beginning to the end of his evolutionary career. Let
him travel back through the long ancestral line until he arrives
at his unicellular ancestors. How countless the generations !
and yet each individual member in the long line has been
subject to enormous competition, has had to struggle with
countless adverse conditions, and has emerged successfully
from the conflict. Out of such a conflict have we risen.
Each one in our long line of ancestors has been chosen from
very many other individuals ; so that in every successive
generation the birth of every animal into the world becomes
more and more a matter of "chance'** — results more and
more from an inconceivably complex assemblage of pre-exist-
ing combinations.

Surely, therefore, some dignity is attached to the existence
of every animal, and to man above all others. The thought
may well kindle a feeling of pride in every healthy man,
for is he not the expression and the result of a series of
successful conflicts extending back into the dim past — to the
period, in fact, of life's first evolution ? Thus does the biologist
soliloquize when he contemplates a beautiful animal. How
painful a thing is it to him to see a healthy man, the chosen
of the chosen, damning and wrecking his beautiful organiza-
tion, and leaving no likeness of himself to future generations,
or, if a likeness, one that bears upon it the curse of his mis-
deeds !

Nor is it only by the indiscretions and misconduct of the
individual that the long slow work of ages is wasted. War,
too, interferes with the process of natural selection, reversing
it, in fact, and weeding out the healthy and vigorous, while the
halt and maimed are left at home to perpetuate the race.
Already this weeding out of the "fittest" has worked with terrible
effect on the physique of the French nation . Where, now, are
the stalwart warriors who formed the body-guard of the first
Napoleon ? And it is not merely on his physical side that man
* I use the word " chance n here in the popular sense.

THE CAUSATION OF DISEASE. 203

has suffered since natural selection has been interfered with by
the course of European history. His mental side has suffered
too. As Mr. Galton remarks, u all the finest intellects, and
the most modest and gentle natures, fled to the convent from
the disturbed and terrible world," which thus underwent double
loss, its best and noblest withdrawn from it, its basest and
most ignoble left to raise up the future generations.

It is clear that in modern civilized life the elimination of the
healthy from the diseased is not of the rigorous primordial
kind. Very many sickly and diseased people, who in a wild
state of nature would be rapidly weeded out, survive the pro-
creative period, and leave offspring, who tend to inherit the
same diseases. This new order of things is the outcome of
morality, which has evolved pari passu with the development
of society ; for morality is a necessary concomitant of social
development. Civilized man, as at present constituted, would
never suffer natural selection to run its merciless course wholly
unchecked. In a litter of pigs, the weakest is destroyed, but
in the young human family does not the sickly, crippled child
absorb an extra share of the mothers love ?

" His mother, too, no doubt above
Her other children him did love ;
For, was she here, or was she there,
She thought of him with constant care,
And more than mother's love." — Woedswoktii.

Morality cries out against oppression of the weaker; far from
crushing them under foot, it bids us help them, it kindles our
sympathy for them, and thus asylums are founded where many
live on, who, otherwise, must needs die. The well-ordered
mind shrinks from the thought of taking human life, or of
suffering a fellow-creature to die without help ; such store,
indeed, do we set on life, that we exhaust every effort to pro-
long it, even though it be but one long agony. Nay, when
certain death is near at hand, we still strive to delay the fatal
moment, if only for a few seconds.

Let us now consider the effect of natural selection on the
mental side of man. We may broadly say that in his case
natural selection operates chiefly on this side. We must
remember that in man the strength of intellect far transcends

204 THE CAUSATION OF DISEASE.

that of the body : which man do we account the stronger,
the muscular or the intellectual — which in the battle of life
comes to the fore ? Among savage communities bodily and
mental superiority take about equal shares in giving one man
an advantage over his fellows, but among civilized peoples, a
man who is, so to speak, a mere walking brain, can command
the destinies of nations. Thus, among the latter, natural selec-
tion is not so much a matter of life or death as of personal and
social well-being. If, however, man had no morality prompt-
ing him to help the weaker, we may be pretty sure that the
fool would go to the wall, not only in the sense of sinking in
the social scale, but in the matter of life or death. Intellectual
superiority would be the great criterion of fitness if — as it
probably would — the absence of morality did not prevent this,
and thus, in the course of time, there would be an accumulation
of mental superiority by natural selection, and consequent
rapid mental evolution. As it is, there is a tendency to remain
at a certain fixed mean, intellectual and physical, for the clever
man marries a stupid wife and the clever woman a stupid
husband, and, in like manner, physical strength unites itself
with physical weakness.

CHAPTER IV.

Natural Selection {continued)— The purely Accidental Causes of Death — Mai-
Environments — The Necessarily-Fatal Environment — The Not-Neces-
sarily-Fatal Environment — The Necessary Mai-Environment.

The distinction I have drawn in the last two chapters between
instinct and reason is a very necessary one. There is no man-
ner of donbt that the one is a safer guide than the other, and it
is equally true that the moral nature in man offers a severe check
to the operation of natural selection. My object has been to
throw these two facts into bold relief. Having done so, it
is now necessary to study in greater detail the operation of
natural selection in man, and in this inquiry we must have an
eye chiefly to its pathological side.

The fact that man has been many thousands of years upon the
earth, while the entire population thereof is only a little more
than 14,000 millions, shows us that the checks to increase must
have been enormous. If the world were peopled afresh from
two individuals, all checks to increase being removed, the present
population might be reached in a comparatively short period of
time. Now, it is at once manifest that in this vast destruction
of life in the past there must have been a survival of the fittest.
Wherefore, it is ci priori evident that the principle of natural
selection has played some considerable part in the evolution of
the human race — the evolution of man from the ape-like man.

No doubt, in many cases, the survival has not been of the
fittest — to wit, when death has been due to sheer accident ; but
we may be quite sure that, on the whole, it has been the fittest
which have survived and given to posterity the largest number
of offspring. The checks to increase are, of course, far the
greatest among savage communities, whose population may not
increase during many centuries. In many civilized communi-
ties, on the other hand, the population is steadily increasing,

206 THE CAUSATION OF DISEASE.

the checks to increase being more or less inoperative among
them ; indeed, since the advance of sanitary science, the popula-
tion in some cases has been increasing by leaps and bounds,
and in such countries natural selection cannot be so rigorous
as among those savage communities where the population is
stationary.

The checks to increase consist of such violent agencies as
famine, warfare, accident, and infanticide, or of the more in-
sidious operations of bad hygienic surroundings, and the many
different forms of disease which result therefrom.

Among savage tribes the larger proportion of deaths is
probably due to violent causes rather than to disease, but the
latter is certainly the chief cause of death among civilized
peoples, although warfare still plays a sadly prominent part.

Let us now see how far these checks to increase result in the
survival of the fittest.

All deaths occurring before or during the procreative period
of life, save such as are due to purely accidental causes, fall under
the law of natural selection, for they are deaths of the unfit.
Unfit individuals are thus weeded out and prevented entirely
or in part from transmitting their unfitness to posterity, while
the fitter survive and propagate the species.

By u purely accidental causes," I mean such as would in-
evitably lead to the death of anybody exposed to them, and
which are, moreover, in no way due to personal carelessness.
For, if the mental self be responsible for the death, the individual
may be regarded as mentally unfit, the fault residing largely
in himself ; and if the E be one which would not cause death
in every one, death cannot in that case be said to be strictly
accidental, since it is due to an individual weakness as regards
a special E,* a weakness which is not shared by all others.
If, therefore, personal weakness, mental or physical, plays a
part in causing death, we cannot say that the death is due to
accident, and in all such cases adaptation is possible by a sur-
vival of the fittest.

The causes which inevitably lead to the death of each and
every individual coming under their influence are violent and
non-violent : the former include, among others, traumatism,
* See chapter on " Normality of S and E," Part III.

THE CAUSATION OF DISEASE. 207;

poisoning, heat, starvation, suffocation, and drowning. If a
person be killed in a railway accident, deliberately poisoned,
burnt to death, starved, drowned, or suffocated by another, he
may be said to have met with a purely accidental death ; but if,
on the other hand, through a careless neglect of proper pre-
caution, through deliberate purpose or uncontrollable impulse,
he break his neck, poison, burn, starve, drown, or suffocate him-
self, the cause of death resides in large measure within himself;
it is due to an imperfection in his mental self,- rather than to
the E — others mentally fitter being naturally selected.

The non-violent agencies include, among others, all such
as are comprised under the term insanitation. Vast numbers
of people yearly succumb to these, and in at all events a
large number of cases the fault is not their own — is not
due to personal carelessness. Thus, many occupations are
necessarily fatal, if not to the first, at all events to the second
or third generation following them. Deaths thus caused are
purely accidental, since the individual is in no way personally
responsible for them, and since, moreover, the E is necessarily
fatal to all. But it is far otherwise with those — and their
number is large — who willingly transgress the laws of health.
Here, again, we are dealing with the mentally unfit, who are
thus weeded out from the mentally fitter.

In order to properly understand the influence of natural
selection it is necessary to classify E's. As will be pointed out
in a future chapter, there is no such thing as a fixed and unalter-
able normal E for all. The E can only be considered in relation
to the individual. It must be regarded as normal if the indivi-
dual is capable of enjoying perfect health within it, but only
so far as that individual is concerned ; and it may be regarded
as a maUE if the individual cannot live healthily in it. Roughly
speaking, we may regard an E as a mal-E when it works an
ill effect upon all men, or upon a limited number of men who
under a different E can live healthily.

Now these mal-E's fall into two important classes — (i)
The necessarily-fatal -E ; (2) The not-necessarily-fat al-E. By
the former I mean an E which is necessarily fatal to each and
every member of the human race; by the latter, a mal-E,
which produces ill effects in some, but not in all, or, at all

208 THE CAUSATION OF DISEASE.

events which does not cause death in all. The one is incom-
patible, the other compatible, with human existence.

Now, it is obvious that natural selection only operates as
regards the not-necessarily-fatal-E, for if the E be inconsistent
with the permanent continuance of the race, there is no
natural selection in the proper sense of the term, natural selec-
tion implying adaptation ; but by natural selection a race may
become adapted to the not-necessarily-fatal mal-E's. I was
careful to point out that a strictly accidental death has two
characteristics — first, that it is independent of carelessness or
other mental deficiency on the part of the individual ; secondly,
that it is due to an E which must necessarily lead to the death
of any one exposed to it. Such an E corresponds to what we
have called the necessarily-fatal-E, with this difference that it
signifies an E which necessarily causes death in the first
generation, while the necessarily-fatal-E of which I am now
speaking is one which need not cause death in the first genera-
tion, but which sooner or later leads to extinction.

While speaking of mal-E's it is necessary to observe that no
one can pass through life without meeting with a certain quan-
tity of mal-E, such as sudden changes in the weather — damp, fog,
and so on. We may speak of this as the necessary-mcd-E. The
quantity of this varies, of course, for all, but there is a certain
mean or average quantity from which none can escape. It is
true that it can be reduced to a minimum, but it can never be
quite obliterated, and it is only a certain number who success-
fully run the gauntlet of this necessary -mal-E ; a large number
succumb, whether it be from a cold or a bacillus : and these
individuals are weeded out, being imperfectly adapted to an
average E. Take the case of children, for instance. Athough,
doubtless, their survival or non-survival depends rather upon
differences of E than of S,* yet it may, and often does,
depend upon differences in the capacity to resist certain
noxious agents. Thus, one child may succumb to diphtheria,
a second to tubercle, while two others, to all appearances
equally exposed to the poisons of these disorders, survive.
We may suppose that the two former children have been

* The large mortality of children among the poorer classes of large cities is
dne, not to differences in the children, but to differences in the E.

THE CAUSATION OF DISEASE. 209

weeded out, by reason of their having less capacity than the
others to resist the average or necessary-mal-E. On the
other hand, such premature deaths may be due not so much to
specific inborn " tissue deficiencies," as to excessive quantities
of mal-E, and, in considering this E, we must not merely
include the specific E which caused the disease, but one ex-
tending, it may be, over a long period.

CHAPTER V.

Natural Selection (continued)— Deficiency of Food only an Indirect Cause
of Death in Civilized Communities.

When considering the struggle for existence among the
lower animals, we saw that it was of two kinds — (a) a
struggle for food ; (b) a struggle against adverse conditions
having no connection with the procuring of food. The chief
cause of weeding-out among the lower animals is probably the
inability to secure sufficient food, and the same is true of
savage communities. Unable to develop the natural resources
of the country (the most degraded tribes being even incapable
of tilling the soil), these find their supply of food a fixed
limited quantity ; some check to the tendency to increase in
geometric ratio is therefore absolutely necessary, and the two
most potent checks are probably war and infanticide ; occa-
sionally, also, famine, floods, and "cold cause great destruction
of life.

In civilized communities, however, the deficiency of food
is no such dominant factor, the chief cause of death lying in
conditions having little or no immediate connection with the
procuring of food, conditions which we shall have occasion
presently to consider more particularly. No doubt the struggle
for food is an important factor even among civilized peoples,
but we might, in this case, more correctly say that the struggle
is for wealth rather than for food alone. There is, indeed, a
perpetual struggle for wealth and the benefits which it brings,
and no doubt in this struggle many are actually destroyed,
body and mind breaking down under the effort, and death
being thus caused indirectly by it ; but in the vast bulk of
cases it is not a matter of immediate life or death, and the
principle of survival chiefly applies in the sense that, in the
struggle, some succeed, while others fail, in securing wealth and

THE CAUSATION OF DISEASE. 211

position. Comparatively few in civilized communities die from
sheer want of food, the necessities of life being placed prac-
tically within the reach of all. Famine does unfortunately
occur from time to time among such,, and when this happens
there is probably in some degree a survival of the fittest ; for
though the provident, as well as the improvident, are apt to
be swept away by a widespread famine, the former would on
the whole stand a better chance of surviving.

Thus, owing to the keen competition for the necessities of
life among the lower animals, and among savages, many must
die, but in civilized communities few need die from this cause
directly.

I say that among the civilized the actual struggle is rather for
wealth than for the actual necessities of life, since food is, to all
intents and purposes, placed within the reach of all ; but indi-
rectly wealth — and I do not necessarily mean immense wealth
— tends to increase the chance of survival. In the country
many of the poor live to extreme old age, yet I doubt not that,
even here, the moderately wealthy rear a larger number of
offspring than the extremely poor, who are unable to bestow that
care upon their children which is absolutely necessary to suc-
cessful rearing. In towns, however, the difference in mortality
between rich and poor children must be very large. This fact
is, I believe, well known to insurance companies. It is possible,
indeed, that the lower classes are more prolific, be the causes
what they may; but, as we shall presently see, the poorer parts
of large towns necessarily lead to extinction, if not in the first,
at all events in the second or third generation, so that the
excessive fruitfulness of the poorer classes doss not lead to a cor-
respondingly larger survival. The wealthy congregate around the
large squares, or fly to the suburbs, where the conditions of life
are more favourable. There can be no doubt whatever that in
large towns these latter stand an infinitely better chance of
survival than the poor, not only because they are less apt to be
carried off by starvation, but because they can command more
favourable health-conditions. Now wealth for the most part
signifies ability. When the individual has acquired wealth for
himself, such acquisition obviously signifies some special apti-
tude on his part, and when wealth is inherited the inheritor

2 12 THE CAUSATION OF DISEASE.

is apt to inherit also the mental aptitude of the ancestor who
actually acquired it.*

Seeing that scarcity of food is very rarely a direct cause of
premature death among civilized communities, let us now
inquire into those other conditions with which animal
organisms have to cope ? They are countless. Foremost
among them must be reckoned that long array of evils due to
insanitary conditions. We have also to take into account
peculiar atmospheric conditions, extremes of heat and cold, and
innumerable other injurious conditions.

Such injurious external E's obtain frequently enough among
the lower animals, and are a fruitful source of disease in them,
wherefore it may be said that there is a perpetual struggle
against these conditions, those animals which are least capable
of withstanding their evil effects being weeded out, the " fitter "
surviving ; but injurious external E's are far less numerous
for the lower animals than for man, and, notably, civilized
man. The brutes are tied down to a comparatively limited
plan of action by a simple instinct. They are, in short, sur-
rounded by a comparatively simple environment, but as instinct
is replaced by the higher developments of mind the environ-
ment is rendered more and more complex, and disease-causing
agencies are multiplied a thousandfold. For, as mind evolves, the
social division of labour proceeds : we have this man following
one calling, that man another, till in a complex social com-
munity such occupations are to be reckoned by the thousand.
The environment of each of these, be it remembered, is dis.
tinct : it is distinct for the sweep, navvy, knife-grinder, butcher,
publican, acrobat, sempstress, actor, painter, lawyer, doctor, and
the countless other callings which help to build up the highly
complex fabric of civilization. Some of these occupations
are perfectly consistent with health, but many tend directly or
indirectly to excite disease, and a large volume might be written
on diseases peculiar to special callings.

Again, there are many forms of mal-E in a civilized society
to which large numbers are exposed, independently of calling,
such as drink, sexual excess, damp dwellings, draughts, absence

* These remarks do not apply so forcibly to individuals who inherit their
wealth by entail from a far-off ancestor.

THE CAUSATION OF DISEASE. 213

of sunlight ; pestilences, moreover, are apt to arise where many
human beings congregate, unless special precautions be taken.
Now, primitive tribes are less exposed to these several forms
of mal-E on account of their wandering habits, but they and
even the lower animals may be carried off by epidemics when
their number gets too abundant. This, for instance, not un-
frequently occurs in the case of grouse and salmon. Where-
fore it is obvious that man has to struggle against many
unfavourable circumstances besides the mere absence of food,
and it is these which cause the active weeding-out of civilized
man, not the scarcity of food. Although poverty does not
often entail death from sheer starvation, it may lead to ex-
posure to a variety of mal-conditions, and so a very active
elimination occurs among the poorer classes, especially in large
cities.

CHAPTER VI.

Natural Selection (continued) — The Frequency of Natural Variations in Man —
The Influence of Natural Selection on the Mental Side of Man.

Since natural selection deals with natural variations (for in
this process unfavourable variations are weeded out, while
favourable variations stand the best chance of survival), it is
worth while inquiring how far these occur in the human
race.

It is well known that variations are far more common
among domestic animals than their wild congeners. Animals
in the wild state become by degrees adapted to their E, which,
be it noted, varies but little from generation to generation ;
it possesses, namely, the important element of stability, and
more or less perfect adaptation to a stable form of E is only
a matter of time. When, however, a wild animal is domes-
ticated, the E is suddenly altered, and variations appear in
abundance. The E now differs in two respects : in the first
place it is far more complicated, in the second it is more
unstable from generation to generation. In spite of the
greater complexity, however, we may safely assert that more
or less perfect adaptation would sooner or later occur — the
variations becoming less in number and degree — if only the E
remained exactly the same during several successive genera-
tions.

We may be sure that variations are not so abundant among
savage races as among civilized peoples, because the E is both
more simple and more stable, being, in fact, more or less
identical during successive generations. How different is the
case of civilized peoples ! Not only is their E infinitely more
complex, it is also immeasurably more unstable. The com-
plexity of the social fabric increases pari passio with the
division of labour, each special calling having its own par-

THE CAUSATION OF DISEASE. 21 5

ticular E, and the instability of the E is sufficiently evidenced
by the fact that successive generations of individual families
follow in a large degree different callings. Wherefore we can,
11 priori, conclude that civilized people exhibit variations greatly
in excess of primitive tribes, and the greater the number of
natural variations the greater the room for unfavourable varia-
tions, and therefore for disease. The converse is also true : the
greater the number of natural variations, the greater is the
room for favourable variations. Hence it is that prodigies —
i.e., individuals, who in some respect, or respects, stand head
and shoulders above their fellows — are probably more common
in civilized communities.

Similarly, we may be equally sure that owing to the com-
parative simplicity and stability of the E, variations are less
numerous among simple agricultural communities than among
the inhabitants of towns.

A further cause of increase in the number of variations
occurring in civilized communities is the commingling and
intermarriage of different races ; for crossing is a recognized
cause of variations.

Variations, then, being so abundant among civilized peoples,
we may be sure that natural selection will be active.

In our study of this subject from the pathological point of
view, it will be convenient to arrange the variations under four
heads. Man maybe regarded as a two-sided organism — (1) as
a thinking being, (2) as merely corporeal — and he may vary
in one or other of these respects. Thus we have two great
classes of variations — (1) mental variations and (2) bodily
variations. Although it is convenient thus to make a distinc-
tion between the mental and physical sides of man, the dis-
tinction is more or less artificial, owing to the close inter-
dependence of the two. Mind is in some way connected with
matter, more particularly with nervous matter : it is depen-
dent upon the nervous organization of the cortex, and all
mental variations are in reality structural variations of a certain
portion of the nervous system.

Setting aside this objection, however, the division into
mental and bodily variations admits of a further subdivision,
and one especially important from the medical point of view —

Q 2

2l6 THE CAUSATION OF DISEASE.

namely, into physiological and pathological variations. Thus,
we have four kinds of variations in all — physiological and
pathological mental variations, physiological and pathological
bodily variations — and these four may be typified by the
following examples — geniuses, idiots, giants, cripples.

I shall first speak of mental variations, and shall endeavour
to discover how far natural selection operates upon them. In
my essay on " Instinct and Reason," already quoted, I came to
the conclusion that natural selection operated solely on the
mental side, and that the selection was not so much a matter
of life or death, as the sorting of society into various classes.
Both of these conclusions were wrong, for natural selection is
not only busily at work on the moral fabric of man — it operates
very actively on the physical side also. Moreover, its effect
upon the mental side is not only to cause an unequal distribu-
tion of wealth, but to lead to an active weeding-out of certain
mental types.

What are these types ? In the first place individuals of
distinctly unsound mind have far less chance of leaving off-
spring than the sane. They are less likely to be married, and
this for many reasons. During the latent stage of insanity,
no doubt, some get married, but when once the individual has
been actually insane the chances of matrimony are very small.
Few, indeed, would marry such an individual. Perhaps there
would be less objection among some of the lower classes than
among those higher in the social scale, yet, even where the objec-
tion may be less strong, there are many checks to such unions.
For a large number of the insane are under restraint, and, even
if not actually under restraint, they are, for the most part,,
placed outside the pale of society. Again, it is a well-known
fact that the criminal class is very largely constituted of
individuals showing distinct mental deficiency. They come
of neurotic families, and are, in fact, pathological variations.
Now the checks to the increase of this class are very great,
for much of the criminal's life is spent in prison, and a
number of the most depraved kind are executed ; indeed, the
destruction of these poor wretches in the past has been
terrible.

Further, among the sane, mental aptitude plays a distinct

THE CAUSATION OF DISEASE. 2\J

part in determining whether or not an individual shall leave
offspring. Some are so mentally constituted as to prefer single
life, be it from constitutional coldness, the lack of domestic
instinct, the love of a restless and roving life (which is a relic
of the past), or what not. This class tends to be weeded out,
members of it leaving few or no offspring. Again, the sober,
steady, persevering man is better able to support a wife, and
is, therefore, more likely to marry, and to transmit these
qualities to posterity, than an individual possessing the oppo-
site characteristics. Unfortunately, this rule does not apply
with any great force to the lower classes, whose fruitfulness
seems to be in direct ratio to their extravagance and impru-
dence. Nevertheless, as I have already pointed out, although
the poor are very prolific, this class stands on the whole less
chance of handing down offspring to remote posterity, for in
larg9 towns the E of the poor is the " necessarily fatal," and
even in the country the comparatively wealthy stand a better
chance of rearing a numerous progeny than the very poor.

But over and above this weeding- out of criminals, of those
who, from other mental causes, do not marry, and, finally, of
those who, although married, stand, on account of poverty,
less chance of rearing a healthy offspring which shall con-
tinue fruitful in a remote futurity, there is a terrific weeding-
out of those mentally tin fit to cope with their environment ; not
only of these who break the laws of the land, but of such as
voluntarily transgress the simple canons of health. Man, as
we have seen, differs very largely from the brutes in that he
possesses greater controlling power over his E. Now, if he
voluntarily places himself amid a disease-causing E, he may
be said to be incapable of coping with his E : it is not the
E that is so much at fault as himself. All individuals are
surrounded more or less by such pathogenic E's. Some avoid
them (for I am only speaking of such as are avoidable), others
plunge voluntarily into their midst. To recount, one by one,
the many ways in which individuals can thus damage their
health, were an endless task. They consist, for the most part,
of excesses, whether of eating, drinking, or sexuality — de-
bauchery, in fact. Individuals leading such debauched lives
tend to be weeded out, it may not, indeed, be in the first

21 8 THE CAUSATION OF DISEASE.

generation, but, if successive generations of the same family
thus inordinately indulge themselves, complete family extinc-
tion must sooner or later result. Let any one glance around
and he will see the truth of this : not only will he find isolated
individuals, young and old, thus destroying themselves, but he
will discover whole families on the rapid road to extinction.

In this way there is a perpetual weeding- out of those
mentally incapable of resisting certain pathogenic E's, and be
it remembered that this result lies chiefly with the individual ;
its cause is structural, and due to some deficiency in the brain
cortex. I say the result lies " chiefly " with the individual,
because we must take into account the amount of pathogenic
E to which he is exposed. Some are carefully sheltered from
injurious moral influences ; others are brought up in a very
hot-bed of immorality; and if the one escapes unhurt, while
the other falls, it is not necessarily because the former pos-
sesses greater resisting power. Nevertheless, the element of
individual resistance must be taken into account. A member of
a civilized community has to contend against certain mal-E's,
and, if he cannot resist their evil influences, he is weeded
out, being, in fact, structurally unfit to cope with his E. Drink
is a more terrible poison than any zymotic virus — a more
deadly enemy than the most powerful armies, and he who
cannot withstand its alluring influence — he who cannot with-
stand the mal-E, " Drink" — alike with him who is incapable
of resisting the evil effects of the ague or typhoid poisons,
succumbs to the inexorable law of natural selection, and in
this way adaptation to the complex E of a civilized community
is perpetually going on.

I do not for one moment wish to suggest that this weeding-
out process should be allowed to run its course unchecked. It
is the duty of those in authority to render the E as harmless
and innocent as may be, to bring up children in a beautiful
morality, and to so strengthen the mental self, that the indi-
vidual may escape unhurt from the many moral evils which in
spite of care must always surround him.

So much for the actual weeding-out process, but, as already
observed, natural selection also operates upon the mental side of
man without directly leading to actual destruction of life —

THE CAUSATION OF DISEASE. 219

namely, in causing some to rise and others to sink in the social
scale. In all the ordinary affairs of life, we find the principle
of a the survival of the fittest "' in full play, and I cannot here
refrain from extending my observations on this head, although,
by so doing, I shall be travelling somewhat beyond the scope of
this work.

Just as the physical self and the physical E coming into
contact, act and react upon one another, so also do the
mental self and the mental E. The latter pair work of
course in a physical medium, for mind is inseverably con-
nected with matter, and the mental E operates by impres-
sing the organs of sense through a physical medium. Now
the mental success — that is to say, the intellectual or moral
success — of any individual is the outcome of the mutual inter-
action of the mental self and the mental E, just as the success
of an individual, from a physical point of view, is the out-
come of the inter-action of the physical self and the physical
E. A man's success or failure in life is not a matter of
chance, but the outcome of fixed and immutable law. The
more we study the career of any individual the more we shall
be struck with this fact. If we observe a rival outstripping
us in the race of life, we are sometimes apt to attribute his
greater success to greater luck, or, in more scientific terms, to
a more favourable mental E ; and we are the more disposed to
do so, if We have ourselves achieved but a small measure
of success. But if we closely scrutinize the character of
our rival, we shall find in him all the elements of success,
intellectual and moral qualities which we ourselves do not
possess. These qualities, individually, may appear insignificant,
but collectively, they make up a force which surely, steadily,
irresistibly, wins the goal. Whether a man achieve a proud
position in life, or whether he prove an abject failure, we may
safely assert that his success or failure is the logical and
inevitable result of the mutual inter-action of his mental self
and mental E, and that that result might be calculated with
as much mathematical exactness as any purely mechanical
problem in physics, did we possess the necessary insight.

The part played by the E in the result is no doubt im-
portant, but we must not overrate it. " Some men," says

220 THE CAUSATION OF DISEASE.

Shakespeare, " are born great." We may interpret this in
two ways. An individual of exalted position, such as a here-
ditary king, may be said to be born great — but his greatness
is only external, nominal ; or we may suppose the phrase to
mean that the individual is born great in the sense of having
a great intellect, which is bound to do great things. Of this
intrinsic greatness, no better example can be given than that
of Shakespeare himself.

Then " some achieve greatness." These are they who, start-
ing in a mediocre position, lift themselves into a high one.
In such cases the mental self is strong, and the mental-E more
or less favourable. We may liken one of this class to a tree
which has grown to lofty and beautiful proportions in a natural
soil ; while those who have had " greatness thrust upon them,"
are, I take it, such as have been surrounded by a very favour-
able E, and we may compare them with the plant which has
been carefully and artificially nurtured — which has been sur-
rounded by the most favourable E.

I have said that the success of an individual in life depends
upon the nature of the mental self, and of the mental-E. Eor
the sake of clearness, I have made no mention of the physical self.
Physical strength, however, is absolutely necessary to success
in certain walks in life, as, for instance, in politics and the pro-
fession of arms. Many an individual has had within him the
germ of a great politician, bat has not possessed the physical
strength to give proper effect to his genius. The same is also
true of the warrior ; one recalls at once the kindly Wolfe.*
Physical weakness, and, indeed, continued ill-health, are con-
sistent with fame in certain departments of activity, as in
philosophy and the fine arts, for bodily weakness favours
a contemplative turn of mind. Many men are shallow-minded
in consequence of excessive muscular strength. Their strong
animal spirits allow them little time to brood over the problems
of life; the mind goes out to the objects round and about

* Some may not think this a happy example. Speaking of Wolfe, Ban-
croft says : " He crowded into a few hours actions that would have given
lustre to length of life ; and, rilling his day with greatness, completed it
before its noon." They cannot, I think, take exception to Arthur Henry
Hallam as an instance in point. Of him it has been said that he "had always
more intellect than he had the physical strength to use."

THE CAUSATION OF DISEASE. 22 1

them, and the reflective faculties remain in abeyance. But if
an individual is weak and sickly, the mind is bent in upon
itself, and acquires a reflective turn. We often find such
individuals doing very well in examinations. They surpass
their more vigorous brothers, because mental labour is less
effort to them ; complete health and strength are apt to revolt
against the long hours of physical quiet necessary to laborious
mental work, the muscles cry out for exercise, and a strong
effort of will — not always forthcoming — is needed to bring
the restless mind to a task in which those physically less
favoured find actual delight.

CHAPTER VII.

Natural Selection (continued) — Its Influence on the Corporeal Side of Man —
Disease, a Necessary Evil — Active Operation of Natural Selection in con-
sequence of Instability of the Environment — Perfect Adaptation impos-
sible— Illustrations.

We have now to consider how far natural selection operates
on the corporeal side of man, and this question is, from the
medical point of view, of even greater importance than how far
it influences the mental side, since the great majority of the
diseases with which we have to do are diseases of the body.

That natural selection has always been actively at work on
primitive man is evidenced by the stationary state of the
population. For, since the human race tends to increase in
geometric ratio, the population can only be kept at a fixed
level by a terrific destruction of life, and such destruction must
necessarily, on the whole, be a destruction of the least fit.
Warfare has doubtless been the chief check to increase. If we
look into the past history of man we see one continued conquest
of the weaker. Tribe has conquered tribe, nation, nation ; and
often enough such conquest has led to the actual extermina-
tion of the conquered. This may arise in a threefold
way — (i) by actual violent destruction, (2) through long-
continued subsequent oppression, or (3) through the inability
of the conquered to adapt themselves to the mode of life of
the conquerors ; thus, the coloured races often die out in con-
tact with the white man, not so much from destruction in
actual warfare as from an inability to adapt themselves to his
ways.

Among savage races the continued warfare has doubtless, on
the whole, led to a survival of the corporeally fittest, although
sagacity has certainly played a not inconsiderable part in the
result. Among the civilized, however, victory rather belongs to

THE CAUSATION OF DISEASE. 223

the best disciplined, the best equipped, the most skilfully
commanded troops. Since the introduction of firearms, bodily
strength and activity play far less part in the result than
formerly. Modern warfare, moreover, does not lead to the sur-
vival of the fittest, but rather to a destruction of them, since
the best physical types are chosen for soldiers, bodily weakness
exempting from service.

Infanticide is also largely practised by primitive man. This
and warfare have doubtless been the chief checks to his increase.
But no doubt disease plays some part also.

And here let it be observed that disease is a necessary evil.
Let no man lay to himself the flattering unction that any por-
tion of the animal kingdom can ever be wholly free from disease.
This would be impossible under any theoretical system of living
which he might devise. We have good reason to believe that
pathological variations must ever and anon occur under the most
favourable conditions which can be commanded — i.e., an indi-
vidual may vary in an unfortunate direction, independently of
any distinctly pathogenic E on the part of his parents. He
may, for instance, vary in such wise that under an averagely
hygienic E he will develop tubercle, rheumatism, or other
disease ; and such unhappy variation, does not, as I have already
insisted, necessarily imply a lack of bodily vigour, since, in the
case of many of the tt germ " diseases, an individual may in
all respects be healthy save in his ability to resist the attack
of some specific germ.

But apart from such subtle tissue-variations, which render
the organism apt to take on pathological change under E's
which, to the community at large, are normal, patho-
logical variations which are quite obvious and palpable not
infrequently occur. I allude to such cases as hydroce-
phalus, idiocy, and monstrosity. Children thus afflicted may
be born to perfectly healthy parents. No doubt, in some
at least of these cases, there is a bad family history ; and
in others the mother may have been exposed, during gesta-
tion, to some form of mal-E, which, with due care, might
have been avoided. Nevertheless, it may with certainty be
asserted that such abnormal beings must inevitably occur
from time to time, even although the parents be selected after

2 24 THE CAUSATION OF DISEASE.

the most approved fashion, and the mother be most care-
fully sheltered, during the period of gestation, from every
possible form of improper influence. "Wherefore, I am com-
pelled to confute the assertion of Mr. Lawson Tait — namely,
that disease did not exist in wild ancestral man, but first crept
in upon him with the advent of civilization.

The belief that disease results solely from the abuse of
natural laws has been held by many. John Hunter, amongst
others, taught this view. C. B. Sutton, after speaking about
the "easy" working of the body, observes : " But we, in our
ignorance, hinder the working, and bring about uneasiness,
disease, incapacity — and that is the origin of pain." If the
writer here means that ignorance is the sole and essential
origin of pain, his statement can only be deemed correct
in a limited sense. Pain, undoubtedly, often results from
ignorance — in a sense, indeed, it always does — since we
might, with supreme knowledge, prevent it. But in this
sense an earthquake is equally the result of " ignorance."
Also, the pain suffered by the lower animals. But using
the term in the limited sense which the author is evidently
attaching to it, ignorance cannot be said to be the origin of
pain.

It is necessary to bear in mind that the capacity for
pain is a physiological attribute : without it no sentient being
— at all events, no such sentient being as a vertebrate
animal — could exist. I speak not of the invertebrata,
since of their capacities for sensation we know little or
nothing. I say the capacity for pain is physiological ; for if
an individual were not apprised of an injurious agent by the
pain which it causes, he would suffer something more serious
than pain — total destruction. Although pain in certain in-
stances serves no beneficial purpose, as in cancer, I cannot,
therefore, doubt that it is in the main a physiological capacity ;
and I protest against our speaking of it as a very unpleasant
and disagreeable result of ignorance, when it is a highly
beneficial and essentially physiological capacity, which affords
us very real and effective knowledge ; for without it we
should not in many instances knoio of the evil residing in
the pain-producing object. There can be no doubt that the

THE CAUSATION OF DISEASE. 225

capacity for pain, like every other useful attribute, lias slowly
and laboriously evolved by natural selection.

The notion that disease is solely due to ignorance or wilful
misconduct is, therefore, erroneous. No doubt, civilization has
multiplied the forms of disease, and vastly increased its pro-
portion, but a proper application of biological laws enables us
to assert, a priori, that disease must always have existed, apart
from the actual observation of facts pointing in the same
direction. #

From the above observations, it follows that, even supposing
the E to be the most stable possible, varying but little (I say
"but little,'"' for we have seen that actual equality of E is not
possible for any two individuals) from generation to genera-
tion, the principle of natural variation must be ever at 'work,
weeding out a number of unlucky variations, and thus main-
taining the proper level of adaptation.

It is quite impossible, even in savage communities, for the
E to be perfectly stable from generation to generation. It
could not be from the geological fact, if from no other cause,
that a ceaseless change is going on in the outer world. Not
only is it the detail of the E that is different for individuals
born at the same epoch ; but far greater and grander differ-
ences are caused by the long lapse of time. Thus, in addition
to marked astronomical differences, the geological state of the
earth is undergoing steady change, and these geological
changes entail meteorological changes also. Wherefore, as
Herbert Spencer observes, "throughout all time there has
been an exposure of organisms to endless successions of
modifying causes."' f

As an example of changes in the E dependent upon the
natural physical processes taking place upon the earth, let us
suppose a savage tribe to inhabit a tract of country where
subsidence is going on — in the neighbourhood of a large lake or
a river-bed, it may be. A portion of the dry land thus becomes
gradually converted into a miasmatic swamp. A marked
change will thus have been gradually taking place in the E of
this savage tribe, and, pari passu, the process of adaptation to

* See Lawson Tait, Dublin Quarterly Journal of Med. Science, Feb. 1874.
f Spencer's "Biology," ch. ix.

226 THE CAUSATION OF DISEASE.

this altering E will proceed. The ultimate result will depend
upon whether or not the E is a necessarily fatal one — i.e., alto-
gether incompatible with human life ; for if so, the process of
natural selection cannot be said to take place, the E leading
to the gradual extinction of the race. If,* however, the chang-
ing E be not necessarily fatal, the process of adaptation will
be set on foot. Some members of the community will probably
be very susceptible to the miasmatic fever, others less so,
while others again may be entirely proof '.against its evil in-
fluence. Such a community would afford an example of a
number of individuals varying in their power of withstanding
the evil effects of a particular E, independently of a previous
mal-E, and independently of general physical weakness, for, as
already observed, we have no right to suppose that the capa-
city to resist the evil effects of a miasmatic poison is in
direct proportion to the general bodily vigour of the indi-
vidual.

Now, what will be the inevitable result of this process ? There
will be a weeding-out of those least capable of withstanding the
noxious E, and thus in course of time a race may evolve per-
fectly adapted to this particular E. It is, indeed, well known
that certain tribes thrive in ague-stricken districts which to
surrounding tribes are most deadly ; and this immunity has
•doubtless been acquired by a survival, during long ages past, of
such as, quite independently, it may be, of any extraordinary
physical vigour, happen to vary in the right direction.

There are, however, other causes of unstable E than those
due to geographical change. As man has struggled from a
barbaric to a civilized state, there has been an alteration in
his E. But the chief cause of the instability of the E among
civilized peoples arises from the division of labour ; for, inas-
much as each calling has its special E,* it follows that,
unless generation after generation of the same family pursue
the same occupation, the E of successive generations will be
different. Hence the process of adaptation to these different
E's, by a survival of the fittest and by ' ' direct equilibration "
during successive generations, will be interfered with, adapta-
tion being for the most part personal and nothing more — that
* Vide Chapter V. Part I.

THE CAUSATION OF DISEASE. 227

is to say, the individual will tend by a direct action of the E
upon him to become adapted to it, but seeing that, in many
instances, several generations of the same family do not follow
the same occupation, there can be no racial adaptation.

Now many of the -occupations which the social division of
labour has called into existence are necessarily harmful, and can-
not be rendered harmless by the most careful State control. So
potent for evil, indeed, are certain occupations, and so diverse
the forms of pathogenesis belonging to them (for each par-
ticular occupation has its own particular set of evils attach-
ing to it), that it would require several large volumes to
adequately describe what might be well termed '; the occupa-
tion diseases."

Nevertheless, in spite of the injurious effects of many
occupations, adaptation to some of them is at least theoreti-
cally possible. Unfortunately, the E is but too often
" necessarily fatal," if not to the first, at all events to the
second or third generation living under it. Knife-grinding
affords a familiar instance. In others, more or less per-
fect adaptation by natural selection and direct equilibration
may be said to occur ; but in order that this may take place,
it is necessary for several generations of the same family to
follow the same occupation. We do not, however, find this
occurring on any large scale. How, then, is it possible that
a perfect adaptation to these manifold E's should take place ?
It is, nevertheless, probable that the community at large
becomes, by natural selection, better adapted to the average
artificial E ; or, if not much better adapted, we must at all
events acknowledge that the standard of adaptation is thus
maintained at a certain mean ( = racial) level.

These observations have a very wide application ; but it will
be sufficient for our purpose to take a few simple illustrations.

First, let us take the case of a publican. Now, his E is
probably of the necessarily fatal order ; for if he does not him-
self succumb to it, the second, third, or fourth generation from
him living under it almost certainly will. Nevertheless, a per-
fect "class" adaptation (meaning, in this case, the "class of
publicans") to such an E is theoretically possible by a survival
of the fittest. Direct equilibration here would play no part,

228 THE CAUSATION OF DISEASE.

for the continued soaking of the tissues with alcohol does not
the better enable them to withstand its evil effects. In such
a case, therefore, the adaptation would be by indirect equili-
bration, and it would further be a mental adaptation : there
would be a survival, namely, of those capable of resisting the
temptation. It is impossible for any class to become corpo-
really adapted to an unlimited indulgence in alcohol.

Again, let us take the case of the brain worker, leading
a life of muscular inactivity.

Out of many individuals devoting their lives to mental
work, several will undoubtedly succumb to the E which it
entails. If an individual, for instance, have a strong muscular
development, and if, as not unfrequently happens, his brain
work entails a life of muscular inactivity, such inactivity
may lead to serious health disturbance — it may, indeed,
indirectly cause death. Such a person should on no account
be suffered to remain inactive, for his muscular development
is a clear indication that he comes of a stock which for
numerous generations has been accustomed to a vast amount
of bodily activity, and his entire corporeal and mental being
has become organized with a view to such activity. An
active E is normal to such an individual, an inactive one,
abnormal. Doubtless, a considerable degree of personal adap-
tation may occur, but it can never take place to the fullest
extent in the case of a very actively constituted individual.
People thus circumstanced will tell us how strongly their
instincts urge them to exercise, and that they never feel well
when they are unable to indulge in it daily.

Many individuals, however, and such may be quite healthy,
are of more slender muscular build. These probably come of
a stock unaccustomed for many generations to great muscular
activity. I do not, of course, allude to such as are muscularly
weak through a general depravity of health and physique. A
typical "cockney," for instance, may be descended from very
muscular, country-born grandparents, and yet possess a very
feeble muscular system, but this muscular inadequacy will be
due to a universal physical depravity, consequent upon the un-
favourable conditions under which he has grown up. Of such
I am not now speaking, but rather of those who, while they

THE CAUSATION OF DISEASE. 229

are healthy in all respects, are of delicate muscular build.
Individuals thus constituted may enjoy good health though
they lead a life of comparative muscular inactivity, and this
often happens in the case of active brain workers.

It is possible that perfect adaptation to a muscularly inac-
tive mode of life might in the course of time take place —
always supposing the individual to lead in every other respect
a perfectly healthy life, the change being wrought by a sum-
mation of personal adaptations and a survival of the fittest, that
is, by both direct and indirect equilibration. An excess of
motor activity is not an inevitable concomitant of life, for some
animal organisms are actually stationary. It is true that great
muscular activity characterizes the vast majority of animals,
since in the struggle for food the muscular system is kept in
constant use, and, indeed, its very evolution arises out of this
struggle ; but there is no reason why, if no longer needed for
active work, it should not dwindle to very scanty propor-
tions without injury to health, mental vigour, and longevity,
the whole organism gradually adapting itself to the new mode
of life. Thus there might evolve a mere " walking brain,"
so to speak. The physiologist may cry out against this argu-
ment, urging that a certain measure of muscular activity is a
physiological necessity, that without it the various glandular
organs — as, for instance, the skin and liver — would fail in
their duty, and that such an inactive mode of life must
inevitably lead to degeneration and extinction,* I see, how-
ever, no reason why the whole of the body should not become
adapted to the new order of things, provided the E remained
stable from generation to generation.

But the E not being thus stable from generation to genera-
tion, such an adaptation will probably never take place, and
it is very unlikely that many successive generations will ever
lead a highly inactive mode of life ; moreover, the pro-
creative power of man would appear, according to Herbert
Spencer, to diminish with the advance of mental evolution.
These considerations, however, do not negative the fact that

* Kingsley, in his " Water Babies," makes the over-developed heads collapse
like " watery turnips ! "

R

230 THE CAUSATION OF DISEASE.

individuals differ markedly as to the degree of muscular
exercise requisite to maintain them in health.

Let it not be supposed from these remarks that I would for
one moment counsel a life of muscular inactivity. Man in his
present state of evolution cannot expect to be a walking
brain. I have merely wished to point out that a considerable
degree of adaptation to a life of comparative muscular inac-
tivity might occur. Such adaptation can, however, only take
place in rare instances. It therefore follows that a fair amount
of muscular exercise is absolutely necessary to health and to
the full enjoyment of life. An enormous amount of suffering
might be averted by due indulgence in it.

In regard to the quantity of muscular exercise needful to
health, each indivividual, as my remarks have already implied,
is a law in himself : some can lead more or less inactive lives
with impunity, nay, even with distinct advantage, while
others suffer much ill-health if circumstances do not permit
a large amount of bodily exercise. Over and over again I
have observed this among young men, chiefly of the muscular
kind, while working up for examination. The higher nerve
centres are then being spurred on to a great effort, while
the muscular system is kept in a state of almost complete
rest. Under these circumstances it not unfrequently hap-
pens that a mental gloom, among other evil effects, comes
over the individual ; but this, and, indeed, all the bad symp-
toms, are speedily removed by a brisk walk across country.
I have also frequently heard young men with a tendency to
uratic deposits observe that a good walk would clear the urine
and remove many unpleasant symptoms.

It must not be supposed, on the other hand, that excess
of muscular exercise, even under the most favourable condi-
tions, as those of the agriculturalist, is an unmixed blessing.
Man was never intended to work like a horse ; his frame is
not constructed with a view to strength primarily. He has
evolved under conditions of moderate muscular exercise, and
such may be said to be the normal condition for the healthy
man. Other things being equal — constitution, food, hygienic
conditions — the hard-working farm labourer does not live
longer than the leisurely- working country squire. Doubtless,

THE CAUSATION OF DISEASE. 23 I

the average life of the labourer is longer than that of his more
fortunate (?) brother, but there are other influences at work to
explain this.

That laborious muscular exercise is not essential to the health
of man is proved by studying the families of our aristocracy.
There is no proof that lack of laborious exercise has reduced
their standard of health. The deterioration in type which
often occurs among such families can be explained in other
ways. Be it remembered that it is only during a compara-
tively recent period in man's history that the muscular system
has been subjected to continued, laborious work. Many primi-
tive tribes, it is true, are accustomed to long- sustained mus-
cular exercise, as in hunting and fighting, but this is very
different to continuous heavy labour, which has only fallen
to the lot of man within comparatively recent times. Hard
work not being the original lot of man, few men take to
it naturally, easily, and willingly. Men work through neces-
sity, and only by practice does what was once difficult become
easy. But in civilized communities there is always a large
number of idle vagrants who will not work. Such are rever-
sions, for they exhibit that disinclination to muscular work
which belonged to their primitive ancestors. What is true
of muscular, is also true of intellectual, work. Although many
children take naturally to their books, the majority do not :
they exhibit the mental tendencies of their remote ancestors,
their chief mental delight being derived from a direct contact
w^ith nature, such as is obtained by roving about the fields
and woods.

I have taken two instances — viz., that of the publican, and that
of the brain-worker leading an inactive mode of life — in order
to illustrate my statement that more or less perfect adaptation
to many of the pathogenic E's which obtain in a civilized com-
munity would take place, if several successive generations were
placed under the same E. Many other examples might be
given, and the reader has ample opportunity of applying this
principle for himself, and of testing its applicability.

R 2

CHAPTER VIII.

Natural Selection (continued) — Adaptation to Micro-organisms — The Insta-
bility of these latter interferes with the Process of Adaptation.

Instability of E has been a great check to perfect adaptation.
Granting stability of E, adaptation to it must sooner or later
occur, provided only that it be not necessarily fatal.

Such being the case, the question may be asked, How is it
that mankind has not become perfectly adapted to the poisons
of scarlatina, measles, typhoid, and so forth ? To this it might
be replied that these are ' ; necessarily fatal " forms of E,
and that man has only survived them because, fortunately,
they are limited in quantity ; but this is not the correct
explanation. The failure of adaptation to these poisons lies in
their instability. We have seen that adaptation to the specific
mal-E constituted by the ague poison is possible. In this
case the poison is probably fairly constant from one generation
of man to another. In the case of the specific fevers the poisons
are essentially fickle, as is very simply proved by the fact that
each epidemic has its own special characters. Nor should this
fickleness, or " variability," surprise us, seeing that the disease-
causing agent consists of a living organism, and remembering
that all organisms must necessarily vary from generation to
generation. We cannot exempt the countless varieties of
unicellular organisms from this universal biological law. In
a very short space of time they pass through many thousands
of generations ; hence, during each successive generation of
man, they have ample opportunity of becoming modified.

But despite their instability, a very active adaptation to
these specific E's does take place among men. This adaptation
is in no way personal, but results from the survival of the
fittest, .viz., the survival of those best able to resist their
harmful effects. It is well known that the introduction of

THE CAUSATION OF DISEASE. 233

a fresh, contagious disease into a country is wont to play great
havoc. This has been amply proved in the case of scarlatina,
small-pox, and measles. It must be fresh in the memory of
many how the North Canadian voyageurs were destroyed almost
to a man by small-pox soon after their landing at Gravesend,
on their return from the Nile expedition. Some of them, it is
true, had been vaccinated, but their susceptibility was probably
far greater than that of the average Englishman. Darwin
observes that on the island of St. Helena scarlatina is dreaded
as a plague.* Now it is possible that communities may from
the first differ from one another in their susceptibility to
various contagia, irrespective of any process of adaptation —
before, namely, any adaptation by a survival of the fittest
could have occurred ; but it is none the less certain that the
difference in respect of resisting power to a particular virus
between communities which have for a long time been exposed
to its influence, and such as never have been exposed to it
at all, is chiefly, if not entirely, due to such process.

It may be thought that I am exaggerating the part
played by natural selection in respect of specific contagia.
A little thought will, I think, show that this is not the
case. Individuals differ prodigiously in the resisting power
which they offer to the various contagia, wherefore natural
selection — the survival of those best able to resist these
poisons — must inevitably occur. Some families there are who
show a great susceptibility to measles ; others are, in like
manner, particularly susceptible to scarlatina; others, again,
to typhoid, contracting the disorder readily and in the most
virulent form. Our present Royal family, for instance,
displays a peculiar susceptibility to the typhoidal and allied
poisons. The individuals thus unfortunately varying are being
continually weeded out with an unsparing hand, albeit they
may, in all other regards, be perfectly healthy ; and when it
is remembered that, of the many who are exposed to these
several poisons before the procreative period, such only are
suffered to leave offspring as can successfully battle against
them, it is clear that the incapacity to withstand the poison is
not, in such cases, transmitted. Surely this active elimination
* " Voyage of Beagle" p. 434.

234 THE CAUSATION OF DISEASE.

must be tending towards a complete adaptation, for how count-
less is the number which are yearly thus destroyed ! And that
such a complete adaptation would actually occur, I doubt not,
were the virus constant in its properties during several genera-
tions of men. Since it is not, perfect adaptation is impossible ;
but there is a continual struggle towards it, and in this way a
certain level of adaptation is maintained.

Next to instability of E, the growth of hygienic science is the
most important check to the process. Take the case of typhoid
fever : a number of individuals congregate, the typhoid germ
comes into being, and disease results.* Forthwith the process
of adaptation is set on foot, but the reasoning power of man at
once steps in to check its progress. He searches out the cause
of typhoid, and directs his efforts to its destruction. A perfect
adaptation to a typhoidal E, even were it possible, would
involve a terrible sacrifice of life, so that man wisely deter-
mines to control the E ; that is to say, he adapts the E to
himself, instead of allowing himself, or rather his race, to be
adapted to the E during the long course of ages.

There is nothing absurd in the supposition that man could
ultimately become adapted to a typhoidal E, provided only its
fixity could be guaranteed. The yellow fever, so fatal to the white
man, rarely or never attacks coloured races. This poison, there-
fore, does not constitute a necessarily fatal form of E. Now I
do not contend that the coloured races have adapted themselves
to the yellow fever virus by a process of natural selection.
Whether or not this is so, I do not pretend to say : so far as
I know, there is no evidence in favour of it. I merely wish to
emphasize the fact that a poison, probably generated by the

* I confess I am one of those who believe in the de novo origin of specific
fevers. It may be regarded as proved that these fevers are due to " germs,"
but many hold the theory of spontaneous generation to be untenable. Sup-
posing, then, spontaneous generation never to occur, and the specific fevers
to be due to germs, how can we account for their de novo origin ? In a very
simple way. We have only to suppose the de novo assumption by non-patho-
genic germs of pathogenic properties, such assumption resulting from
peculiarities of germ E ; in which case, looking on spontaneous generation as
an impossibility (which I for one am far from doing, for at the most we can
but prove that this never occurs in a test tube), and on the specific fevers as
due to specific germs, we can yet readily account for their de novo origin.
Vide " The Evolution of Morbid Germs : " K. W. Millican.

THE CAUSATION OF DISEASE. 235

crowding of coloured men, has no effect upon them, while to the
white man it is terribly fatal. Did we not know the black to
be proof against yellow fever, we should doubtless assert with
confidence that the poison of this fever was one which must
inevitably provoke disease in all, but since such is the case, what
justification have we for asserting off-haud that the typhoidal
poison constitutes a necessarily fatal form of E, and that adapta-
tion to it is impossible, provided its stability were guaranteed ?
The aim of hygiene being to destroy, as far as may be, these
specific zymotic E's in the interests of humanity, we may
ask — Does it not, by checking adaptation, in some measure
defeat its own ends? The answer is decidedly — Yes. But
the good effects far outweigh the evil. Instance the case
of scarlatina. The poison is, as it were, hunted down by a
system of isolation and disinfection. If this system be carried
out with great care from year to year, the number of cases of
scarlatina will tend to diminish ; for, if fewer be exposed to
the poison, fewer can contract the fever, and in this way it
might be possible to exterminate the parasite altogether. The
effect of this would be meanwhile to increase the severity of the
cases which do occur — always supposing the virus to remain
the same — for the process of elimination will be interfered with,
and the standard of adaptation consequently lowered. Where-
fore the hygienist has two powerful arguments to justify his
course. First, there is the possibility of completely hunting
down the poison (and there is no doubt that with great care
this could be done) ; secondly, the poison being the product of
living organisms, and therefore essentially variable in cha-
racter, it necessarily constitutes a great check to adaptation by
natural variation.*

* Mr. Parker {British Medical Journal, Nov. 5, 1878, Jan. 7, 1887) does not
regard the system of isolating cases of scarlatina as an unmixed blessing, for he
contends that the adult is quite as liable to contract the disease as the child,
and that the disease is more serious in adult life than in early youth. Facts,
however, speak strongly against both these views. Murchinson long ago asserted
that the adult is both less liable to contract the disease, and more likely to have
it in a mild degree, and the Registrar-General's report for the past year bears
out these statements. Mr. Parker further contends that " strict isolation will
gradually increase the number of persons unprotected by a previous attack,
and, therefore, the number of persons liable to be attacked during any given
epidemic." This, he tells us, is " his main contention." No one would con-

236 THE CAUSATION OF DISEASE.

Enough has now been said to show that a continual adapta-
tion to those morbific agencies which are not necessarily
fatal is taking place, and that as regards contagia, the success
varies in different instances. Perfect success has apparently
been achieved in the case of the ague poison (or, perhaps, it
would be more correct to say, certain varieties of the ague
poison, for there are many different kinds), but only very
imperfect adaptation to the ordinary zymotic poisons has been
effected. Yet I doubt not that man has by natural selection
become adapted to many microbes which in the past were
fraught with the greatest evil for him.

Many zymotic diseases which, as we know from history, once
wrought great havoc, have completely vanished, but how many
more must have existed of which history is silent ? We may
be sure that man suffered from zymotic disease long before he
took on his present shape, far down in the genealogical tree.

How, then, are we to explain the disappearance of these
diseases ? Many of them have doubtless vanished with the E
which brought them into being. The great epidemics of the
Middle Ages arose out of grossly impure hygienic conditions,
and the pathogenic germs causing them disappeared with the
hygienic improvement. It may be that the germs died
right out ; or we may suppose them to have lost their patho-
genecy through natural variation, for it is well known that
unicellular organisms, in common with the more complex forms
of life, are capable of being modified by a modification of
their E. It is highly probable, however, that perfect adapta-
tion to them has taken place in the past by natural selec-
tion. Let it ever be borne in mind that man, like all other
living things, has gradually evolved by a continued adaptation
to his E. He has been gradually moulded so as to fit more or

fute it, but this is no argument against isolation ; the number of individuals
attacked " during any given epidemic " might be greater, but the proportion
of individuals attacked during a given long period of time, would not be nearly
so great, although the process of natural selection would be interfered with, and
the number of the susceptible thus increased, but no mention was made of the
influence of natural selection during the discussion of this subject in theBritish
Medical Journal. A further point was left out of consideration in the discus-
sion. If the disease is to kill or cripple its victim, is it not better that it should
do so as late in life as possible ? If a man dies of scarlatina at forty instead of
at three, he has gained thirty-seven years of a possibly healthy life.

THE CAUSATION OF DISEASE. 237

less accurately, if one may so put it, into his E ; and at what
prodigious sacrifice of life only those can realize who have
examined thoroughly the doctrine of evolution in its many
ramifications. And I doubt not but that one of man's most
malignant foes has been the one-celled organism, and that his
struggle against it has been severe in the extreme. One
would not, a priori, suppose that any unicellular organ-
ism was necessarily fatal to a multicellular being, for is not
the basis of life one and the same for all — viz., protoplasm ?
No fact of biology is more remarkable than that one form of
protoplasm should be capable of exerting a poisonous effect on
another. This effect is brought about by the emission of
certain poisonous matters. In pysemia, for instance, the evil
results from chemical matter given out by certain micro-
organisms. These chemical products are powerless to harm the
micro-organisms emitting them, but are, nevertheless, capable
of destroying many multicellular organisms — man among others.
Now, the fact that a certain chemical substance is harmless to
one form of protoplasm, but capable of producing disease in
another, is suggestive, at least, that this latter form might also
become capable, by adaptation, of withstanding its evil effect ;
and this suggestion is rendered all the more probable by the
fact that different species of animals differ most extraordinarily
in their manner of responding to different micro-organisms, for
what will produce rapid death in one will be quite harmless as
regards another : nay, more than this, a like difference may, as
we have already seen, be observed among the various members
of the same species.

Now, all these facts tend to show that adaptation to almost
every variety of pathogenic micro-organism would be possible,
provided the latter were fixed in properly. The variability
in unicellular organisms has tended to prevent this, and, but
for this variability, it seems to me highly probable that
perfect adaptation to all forms of pathogenic micro-organisms
would long ago have occurred. Even as it is, this adapta-
tion has probably taken place to a large extent, and who
knows but that we may be living in the midst of an infinite
variety of micro-organisms which at one time were capable of
striking our ancestors (near or remote) with the most fearful

238 THE CAUSATION OF DISEASE.

diseases, but which now, by a gradual process of adaptation on
the part of our forefathers, have become powerless to do harm ?

A curious fact which I have recently learned tends in some
measure to confirm these views. According to the Rev. J.
Williams, the first intercourse between natives and Europeans "is
universally attended with the introduction of fever, dysentery,
or some other disease, which carries off numbers of the people.
. . . Most of the diseases," he continues, " which have raged

in ■ ■ during my residence there have been introduced by

ships, and what renders this fact remarkable is that there
might be no appearance of disease among the crew of the ship
which conveyed this destructive importation."* Darwin also
observes that " the first meeting of distinct and separate
peoples generates disease." Now these facts show that each
separate community is exposed to some specific form, or forms,
of E, which, although perfectly innocuous to itself, may be
distinctly pathogenic to others. What is the exact nature of
the pathogenic E or E's in each case it is impossible to say,
but it is probable that the virus is not that of any well-known
" specific " fever. The important fact to remember is that
each community is perfectly adapted to its particular virus, or
varieties of virus. This adaptation may be the result of natural
selection continued through long ages. Nevertheless there is
evidence that the mere congregation of individuals may beget
a poison to which gradual personal adaptation may occur.

In the Black Assizes, for instance, the prisoners brought to
trial from the putrid gaols communicated a fatal form of fever
to the judges sitting in court, the prisoners themselves heing quite
free from any trace of fever. Now, seeing that the latter must
have swarmed with the morbid germs, it seems probable that
they had gradually become adapted to the mal-E of the prisons,
just as a mouse can in some measure adapt itself to an atmo-
sphere exhausted by respiration ; for if one of these animals be
placed in a vessel till the air has been in this way greatly
exhausted, and a second one be then introduced, the latter will
be the first to succumb, showing that a certain amount of
adaptation has occurred in the survivor. The same line of
argument might be applied to the prisoners of the Black Assizes.
* Quoted by Sir William Aitkin : "Evolution in Pathology."

THE CAUSATION OF DISEASE. 239

Another construction, however, may be put upon the case ; it
is possible that the unfortunate wretches who were brought up
for trial were but a surviving few, the greater number of the
prisoners having succumbed to the fever, and, supposing this
to be the correct interpretation, we have in it a good example
of natural selection — the survival of those who were fittest as
regards a specific mal-E.

The following is a very similar instance : " In the early part
of the reign of George III., a prisoner who had been confined
in a dungeon was taken in a coach with four constables before
a magistrate, and, although the man himself was not ill, the
four constables died from a short putrid fever ; but the con-
tagion extended to no others." From these facts " it would
appear as if the effluvium of one set of men, shut up for some
time together, were poisonous when inhaled by others ; and
possibly more so, if the men be of different race."* In this
case also two explanations may be offered. We may suppose
the prisoner to have gradually adapted himself to the dungeon
atmosphere, or, again, that he was one of a very few who from
the first were proof against it.

A consideration of the different effects of the same contagion
on the human organism brings one important fact into promi-
nence— namely, that normality both as regards S and E is only
a relative expression. If an individual can live healthily in
any particular E, he may be regarded as normal to it, and it
to him When, in short, there is perfect adaptation between S
and E, each is normal as regards the other. A tribe of savages
living healthily in an ague-haunted district might, with some
show of truth, exclaim: " You white men are abnormal, for
you sicken and die in an E which is perfectly normal." With
equal justice the white man might retort, u No ; your E is
abnormal, and therefore I, who am perfectly normal, sicken
when exposed to it." Each statement would be correct. To
the savage tribe the ague-stricken E is perfectly normal, but
to the white man intensely abnormal.!

* Darwin, quoted by Sir William Aitkin : "Evolution in Pathology."
f This question of Abnormality will be considered in Part III.

CHAPTER IX.

Natural Selection {continued) — The Necessarily -fatal Environment.

When treating of natural selection it was found advisable to
divide the different varieties of E into two classes — namely,
those to which the human organism is adaptable, and those
to which it is not. The latter class was spoken of as the
class of " necessarily fatal " E's, inasmuch as such E's necessarily
lead to destruction, and it is this class that we may now with
advantage consider at greater length. As regards many forms
of E, such as poisons and violence, their necessary fatality is
at once obvious; but besides these there are others, which,
although not necessarily fatal to the individual in the sense of
causing more or less immediate death, are yet necessarily in-
jurious to him, and " necessarily fatal " to racial life, or,
perhaps I ought to say, family life. By this I mean that, if
successive generations of the same family be reared amid
such E's, a total extinction of the family will sooner or later
follow.

Now the number of these forms of necessarily fatal E is
exceedingly great in a civilized community, far greater indeed
than mere casual observation would lead us to think. We may
lay down the broad rule that (other things being equal) the
E of any given individual is healthy in proportion as he lives in
the open air, and exercises therein ; and contrariwise, the E is
unhealthy in proportion as his life is spent in confinement and
muscular inactivity. Civilization entails much indoor confine-
ment, and herein lies, I believe, its chief evil. It is probable
that all occupations which necessitate prolonged confinement
from a tender age upwards, whether in town or country, are
necessarily fatal, and certainly all those are which prevent
the enjoyment of fresh air and proper bodily exercise from
time to time. But, apart from the injurious effects directly

THE CAUSATION OF DISEASE. 2 4 1

traceable to confinement, pure and simple, and which are
experienced, even though every hygienic precaution be taken
to render the air breathed pure and healthy, there are many
occupations, both indoor and out, which necessitate the breath-
ing-in of irritating particles, and there are a host of others
which injure in ways innumerable. Such E's are probably
all necessarily fatal.

This may at first sight appear to be a gross exaggeration ;
we must, however, bear in mind that there are several circum-
stances tending to mitigate and to obscure the fatal results.
In the first place the injurious occupation is in many instances
not followed until the individual has nearly arrived at, or has
actually reached, maturity ; and, some little time being re-
quired for the E to work its injurious effect, he may mean-
while rear healthy offspring, more especially if he live in the
country, where the children can have abundant outdoor exer-
cise. Seeing that legislation cannot render all occupations
strictly healthy, we ought at least to see to it that as far as
possible boys and girls be not allowed to follow injurious
occupations. It is during the growing period of life that
a mal-E works its greatest evil, for it then interferes with
proper body-growth, and leads to rapid physical deterioration.
If possible, then, we should prevent a young growing indivi-
dual from following an injurious calling. Such a prohibition
is, however, often impracticable, for most of these very occu-
pations require early apprenticeship, sometimes, indeed, com-
mencing in extreme youth.

A second circumstance tending to prevent this family extinc-
tion is the very obvious one that all the members of the same
family rarely follow the same injurious occupation for several
successive generations, and if only a few of the children engage
in healthy outdoor pursuits, the family may thus continue its
existence.

In large towns, however, most of the children, although
not often all following the same occupation, nevertheless
very generally follow some other injurious calling, or are from
the beginning of life brought up under unfavourable condi-
tions ; wmerefore, as we shall presently see, a large town con-
stitutes in itself a necessarily fatal form of E. But, leaving

242 THE CAUSATION OF DISEASE.

for the moment out of account the injurious effects of large
towns, we may affirm, with perfect assurance, that if two or
three generations engage in indoor occupations from a tender
age upwards, or follow such an occupation as stone-grinding,
which necessitates the breathing of an irritating atmosphere,
or, indeed, any occupation which exerts a markedly injurious
effect upon the body, family extinction will inevitably occur.
The gaps thus created are, however, eagerly filled up in the
fierce struggle for existence, and thus it is that, while extinc-
tion of individual families is ever and again occurring, each
class maintains its integrity, just as does a living organism :
fresh material is ever at hand to take the place of the cast-
off, worn-out products ; and it matters not to the social
organism whence it shall be recruited — whether it shall be
from persons whose parents formed part of it or not.

I have not attempted to enumerate the many different kinds
of occupation which entail upon the luckless individuals fol-
lowing them a necessarily fatal E, for this would occupy too
much space ; but it is well that we should be alive to their
great number, and I therefore venture to recommend a serious
study of this question to such of my readers as have not gone
into it thoroughly.

The mal-E's of which I have hitherto spoken, are such as
are entailed by bread-winning occupations ; but over and above
these there are many to which the individual voluntarily
exposes himself for the sake of pleasure, such as intemperance
in eating and drinking. These belong to the necessarily fatal
class of E?s, for they must lead to family extinction if several
generations of the same family indulge in them from youth
upwards.

Let us now briefly turn our attention to the E obtaining
in large cities as distinguished from that belonging to the
country. There is no doubt that the E obtaining in the
central parts of all large towns is necessarily fatal, owing to
the lack of sunlight and fresh air. As Mr. Oantlie observes,
fresh country air has not blown over the central parts of
London for fifty, or it may be even a hundred, years. He
attributes the evil results to the lack of ozone, which is entirely
absent from London air ; and he adds that sun-burning never

THE CAUSATION OF DISEASE. 243

occurs in London, remarking that an omnibus driver never
gets brown; " he gets red, and you can see the cause of the
redness to be dilated vessels in the skin of his face." But,
although bronzing does not probably take place so readily in
London as in the country, even though the exposure to the
sun be the same in each case, I am nevertheless convinced
that it does actually occur. However, setting aside this
question as to the special effect of the absence of ozone, the
fact remains that residence in central London rapidly tends
to deterioration, and finally to family extinction. Mr. Cantlie
has been unable to find an individual whose ancestors
from the grandparents downwards were born and bred in
London. The following two cases are the nearest approach
to such an ancestry : " The first is that of a 'man with a
Somersetshire grandfather,' whose folks had lived in London,
commencing from the grandparents. Height, 5 ft. 1 in. ; age, 2 I ;
chest measurement, 28m. His head measured around above
the eyebrows is 1 9m. (nearly three inches below the average) ;
measured across from tip of ear to tip of ear, 1 1 in. ( 1 ^in.
below the average). His aspect is pale, waxy ; he is very
narrow between the eyes, and with a decided squint ; solemnity
intense." The second case is that of a Ut man with an Irish
grandmother,' but the others of whose predecessors have lived
rigidly in London from the grandparents downwards. Height,
5 ft. 3m.; age, 19; chest measurement, 29m. His head
measures 20m. round (2 in. below the average). His face is
mottled, pale, and pimpled. He squints rather badly. His
jaws are misshapen ; he cannot bring his front teeth within
half an inch of each other ; his upper jaw is pointed, and falls
within the arch of the lower ; his teeth spiculated, and must

be well-nigh useless to him. Solemnity great These

specimens I have come across, as I say, after much inquiry. I
have never come across the children of any such, and I believe
it is not likely I ever shall. Nature steps in and denies the
continuance of such, and weakness of brain power gives such a
being but little chance in this struggling world." *

I do not altogether agree with this author in regarding defi-
ciency of ozone as a potent cause of degeneration. The Jewish race
* " Degeneration amongst Londoners," by James Cantlie.

244 THE CAUSATION OF DISEASE.

lias for thousands of years lived in towns, large and small, and
there must be many Jews who can trace their London ancestry
through several generations, but these are of the comparatively
wealthy class. The chief cause of degeneration I believe to be
close confinement in rooms. Children of the well-to-do, living
as they do about the large squares and parks, may grow up
well and strong (although it is doubtful whether even they
attain the same vigour which a country bringing-up would
have secured) ; and, moreover, we must remember that many
such children are educated in the country, and spend several
weeks every year at the seaside. But the children of the
poorer classes in London are brought up under conditions
which inevitably lead to marked and rapid degeneration.
Probably all of them have rickets. None of them can get the
pure air which the laws of health demand, for they are confined
during almost the entire period of their babyhood in dark and
ill -ventilated rooms. When, however, a Londoner leads an out-
door life, considerable physical strength may be attained. Many
instances might be cited in proof of this : Jem Smith, the
champion English prizefighter, was born and brought up in
the East End of London (a considerable period of his youth
was spent in an open timber-yard, where he had the
advantages of open air and muscular exercise), and one may
observe in London-born navvies, too, very good development
of body. Wherefore I attribute the physical degeneracy of
Londoners to the bringing-up of the children in close, ill-
lighted rooms, and to their subsequently following employments
which entail prolonged confinement indoors. During the
whole period of his life, indeed, the true cockney — namely, the
individual who is London-born and strictly London-bred, gets
neither that amount of exercise nor that purity of atmosphere
which the laws of health demand. He is placed under an
environment totally different from that in which the human
race has evolved ; and it therefore follows that the vast
majority of the true Londoners — I allude not to the inhabi-
tants of the suburban districts nor to the well-to-do, who can
battle more or less successfully against the unfavourable con-
ditions— have the seal of fate stamped upon them : they can
never leave a remote posterity.

THE CAUSATION OF DISEASE. 245

I have little doubt, however, that, even among the well-to-
do, continuous and uninterrupted residence in London would
sooner or later lead to family extiuction. Probably such ex-
tinction would not occur until several successive generations
had been so brought up — a thing that never happens with
these classes. In the case of the lower classes, however, there
can be no doubt that the family line practically never passes
beyond the third generation of the London-born and -bred.

There can be no better place to observe the degenerating
effect of London life than a London Children's Hospital.
Here one has the opportunity of watching the mother
and her children till the latter reach the age of twelve or
thirteen. A very large number of the mothers, though living in
London, are country-born, and in such cases we can compare
the country-born mother with her London-born children, and
can thus discover how much deterioration may be wrought in
a single generation. The contrast is, in many instances, posi-
tively startling, and it is best observed in the bony conforma-
tion of the head ; but it is unnecessary to particularize the
points of change.

I may here remark that a London out-patient room affords
an interesting place of study for the anthropologist, for he
can there observe people who have come from all parts of the
country. It has surprised me to find how distinctive is the
cranial conformation in various districts ; for instance, the head
of the Essexer is very different from that of the Devonshire
or Oxfordshire man or woman. I believe a careful study
would enable one to form a very shrewd opinion as to the
birth-place of different individuals. I was led to notice this
when inquiring into the ancestry of London-born children. I
ascertained the ancestry, as far as the grandparents, of over
two hundred London-born children while helping Dr. Aber-
crombie at the Great Ormond Street Hospital ; in only two
or three instances were the parents and grandparents born and
bred in London, and in each of these cases the children were
particularly delicate.

In a London Children's Hospital, then, we read the naked
truth about degeneration, for we see the process going on
from week to week under our very eyes, and this leads one to

s

246 THE CAUSATION OF DISEASE.

ask, What can the London hospitals do for the sickly children
brought to them ? If they are ill of acute disease, their lives
may indeed often be saved, and when suffering from other
affections they may be patched up ; but at best it is a mere
"patch-up." Only a few cases can be taken into hospital ; the
great majority have to be treated as out-patients. Children
are brought dying for want of proper air and food, and the
physician is often sick at heart as he feels the futility of
for ever prescribing cod-liver oil and iron while the struggle
is one against the very conditions of existence, when what is
wanted is not physic, but good wholesome food, and sunshine,
and the sweet breath of heaven — the eternal requirements of
Nature — to substitute drugs for which is a wretched mockery.
These can but patch up the ailing little bodies — a poor
triumph for a noble art, and yet all that the inevitable
deterioration consequent on the conditions under which they
grow up leaves possible.

The typical full-grown cockney is in truth a painfully dete-
riorated type of humanity. Who that has observed a London
mob can have failed to be struck by this ? I once saw such a
mob, some four or five hundred strong, marching, with banner
and trumpet, to a " demonstration." They were indeed a
blighted band — pale, wizen, stunted ; and as they marched
along, thinking no doubt that their many troubles arose from
unfair legislation, and vaguely dreaming, it may be, that a
happier lot would fall to their descendants, I could not but be
struck with the irony of Fate, for it was painfully evident that
not one of the sad faced crowd would live in a remote posterity.
The seal of doom was plainly marked upon them all : a few
sickly children perhaps they might rear, but it was clear that
sooner or later each family line must ingloriously end.

Healthy, honest country folk come up to the great city to seek
their fortune, little knowing how they will be swallowed up by
the devouring monster, that their children will not be like
them or their fathers before them, but will help to fill the
ranks of a diminutive and degenerate race — of a race which is
perpetually rushing towards extinction. And yet, if you ask
these people whether they like London or the country best, the
answer is almost always in favour of the former.

THE CAUSATION OF DISEASE. 247

Our giant city affords an example of Social Evolution
pushed to the farthest limit yet attained, but at what a cost to
individual health ! Government is careful to educate the
rising generations of Londoners, oblivious of the fact that it
is educating a race which is continually travelling towards
extinction. Herbert Spencer, with his marvellous power of
detecting similarities, has likened a society to an animal or-
ganism. London is such an organism : as this process of ex-
tinction proceeds among its various family units, a fresh
stream of healthy country blood continually pours in to replace
them, and thus the great monster is kept alive.

We have seen that the central parts of large towns neces-
sitate an E which is incompatible with the survival of more
than two or three generations of the same family, and that
the population of such towns is kept up by the continued influx
of healthy country-bred people. Some maintain that the
same argument applies with equal force to the modern American
race — that it, too, is only prevented from extinction by the
continued inpouring of fresh European blood. According to
this view, the E, as determined by the conditions of American
climate and society, is necessarily fatal to Europeans. Be
this as it may, there can be no doubt that the American, in
certain of the States, is undergoing a profound change, and it
is quite clear that this modification is not due to natural
selection, but to the action of E upon S, irrespective of any
selective process — i.e., by direct equilibrium. It must be remem-
bered the United States are of large extent, and that the E
•differs very much in different parts. In certain States the
immigrated European is undergoing marked deterioration, and
in these, I take it, the E is necessarily fatal, so far as the
'European is concerned ; but this is by no means true of all
parts of the country ; and it would be easy to find many where
the inhabitants are strong and vigorous.

I may refer to one other example of necessarily fatal E. It is
well known that when the white man takes up his abode in an
uncivilized country the aborigines generally become extinct. In
certain cases, doubtless, they are actually destroyed by violence
or oppression, but it also very often happens that extinction
results from the inability of the aborigines to adapt themselves

s 2

248 THE CAUSATION OF DISEASE.

to a civilized E. This E is, in such instances, by no means
one that is hygienically fit in every respect ; nevertheless,
taking the good with the bad, the white race is capable of
thriving in it. Many instances of extermination from this
cause might be cited, but it is enough to remind the reader
of the rapid extermination of the natives of New Zealand and
Australia. Seeing that all men are descendants of one com-
mon ancestor, it is a remarkable fact that these people should
be incapable of living in an E which is perfectly favourable
to the white race. The explanation must be sought for in
the fact that the growth of civilization has been gradual, and
man has meanwhile been adapting himself to a civilized E.

Dr. Knox has written an interesting and elaborate work*
with the object of proving that each race of man is capable
of thriving in that particular part of the world alone in which
it is found, and, among many instances, he cites the case just
alluded to of the modern American people, who, he asserts,
would rapidly die out were it not for the abundant influx of
fresh European blood. Although I believe this position to be
untenable, Dr. Knox's assumption contains, nevertheless, some
germ of truth : it emphasizes the facts that every race has
become more or less perfectly adapted to its own particular-
region, and that, when migration to a totally different climate
occurs, some time is needed for re-adaptation, and it further
prepares us for finding that in certain cases adaptation cannot
occur at all. It is probable, for example, that the English
people could never become adapted to the Indian climate, for,
unless brought up among the " Hills," English children seem
quite incapable of growing up healthy in India. Suppose,
however, a colony of English people were to gradually migrate,
generation after generation, eastward towards the Asiatic
continent, and ultimately to arrive in India — then, doubtless,
by a gradual process, they would become more or less perfectly
adapted to the Indian climate. The process of adaptation,
would, in fact, be spread over many generations.

* "On the Eaces of Man."

CHAPTER X.

Natural Selection (continued) — The Environment afforded by the Country.

Having considered the injurious effects of town life, we may
now briefly turn our attention to the E as it obtains in the
country.

Here, with the pure air and the open spaces, E stands
in very striking contrast to that of the central parts of large
towns. So favourable indeed is country life to health that
one wrould scarcely expect to find there any deteriorated types.
Nevertheless, we do find such side by side with the best samples
of the race. The noblest specimens of men, taking them from
the physical point of view, are the outcome of long ancestral
country life. The country is, in fact, the great breeding
ground for man, as for so many other animals : it is the men
born and bred in the country who will be the forefathers of
future generations.

How, then, are we to account for the inferior types of
physique and for the sickliness which are found often enough
in the country ?

The good effects of country life are due to the purity of the
atmosphere and the abundant opportunity afforded for out-
door exercise, for in genuine country life the greater portion of
each day is spent out of doors, and not in confinement. Pure
air and proper exercise are the most important elements of a
healthy E. If to these we add proper food and clothing, we
have all that is wanted to make it physically complete and
perfect, and, given such an E, a healthy race must needs grow
up. No doubt, even under a perfect E many individuals
would be destroyed by accident, fever, and so forth, but death
due to such causes leaves no evil effect upon the race ; it, on
the contrary, rather tends to its improvement.

2 SO THE CAUSATION OF DISEASE.

The inferior physical types found in the country are due
to the fact that all who are born and bred there do not enjoy
in perfection the several hygienic requisites just enumerated.
In the first place, a large number of country folk are under-
fed, and this undoubtedly leads to decrease in stature and
general physical deterioration, just as an abundant food
supply has the opposite effect, as our domesticated animals so
well show. Many country folk get little meat, and have to
subsist chiefly on vegetable diet. It is doubtful, however,
whether an ample vegetable diet is injurious, for our remote
ape-like ancestors were entirely vegetable feeders. Be this as
it may, no one can doubt that the country folk suffer much
from lack of sufficient food.

In the second place, although living in the heart of the
country, many of the poorer folk enjoy the fresh air in only a
very small degree. The men, it is true, spend the greater part
of the twenty-four hours in the open, but the women live almost
entirely indoors, seldom going farther than a few steps from
the house, domestic duties practically compelling them to stay at
home during the greater part of their married life. And ' ' home *
— sadly misleading word — is often only another name for a
badly built, ill- ventilated, overcrowded hovel, where the win-
dows will not open and the doors will not shut, where the
sunlight cannot get in and the damp cannot be kept out. I
would not for a moment overlook the much that has been done
in late years by landlords and others — all honour to them — to
bring about improvement in these matters, but there can be
no doubt that the wretched insanitary condition of the cottages
of the peasantry in the past has largely to answer for the pre-
sent deterioration of many from among our country popula-
tion. And these unhealthy conditions are by no means
altogether things of the past even yet ; there are still many
" dark places of the earth " to be found on open hill-side,
breezy moorland, sea-washed coast. One particular coast
village that I have now in mind bears out this remark pain-
fully. It is not more than a year or two since I noted it.
Here was a community living upon the very edge of the
Atlantic, and if there was one spot on eartli where the air
might be expected to be pure and healthy, this was it. Yet I

. THE CAUSATION OF DISEASE. 25 1

found the people huddled together in a very nest of abomina-
tion, doing, it would seem, their utmost to shut out the fresh
sweet breezes.

Nor was it only in the village — and there were only too
many like it in the neighbourhood — that there was such a
contrast between natural features and the habitations man had
made for himself: it was the same in the scattered, outlying
cottages with which that part of the country abounds. I went
one day to visit a patient who dwelt high up on the slope of
a hill a few miles distant from the village. It was late
summer, and gorze and heather were in their full glory of gold
and purple. Below was the clear, blue water, breaking in white
foam upon the rocks, a crisp, invigorating breeze swept up
from the sea, the sun was warm and bright — everything sug-
gested life, purity, health. Surely here disease could find no
lurking-place ? Yet the little rustic cottage whither I was
bound, for all its picturesqueness, was a very hot-bed of
disease-engendering organisms. In the small dark attic lay a
young girl sinking fast under consumption : she was, in fact,
already in a typhoid state, and she soon after died. The
odour of this little room was overpowering, and no wonder —
for a whole family of eight slept in it, and the tiny casement
was seldom opened !

The great contrast, so often noticed, between the physique
of the two sexes is explained when we remember how much
of the women's lives is spent in houses such as these. This
contrast is very striking in the particular village in question.
The women grow rapidly old and wizen after marriage, and
this, doubtless, because they are cooped up all day in dark and
foul- smelling rooms, while the men — sturdy, handsome fellows
— are busied either upon the sea or by the shore.

Indoor life is, to a very large extent, a necessity with the
women, but habit so affects them that in course of time they
grow quite indifferent to the confinement, and care no more for
fresh air than for the beauties of the surrounding scenery ;
indeed, in some cases there is an actual aversion to going out.
One woman in this village had not stirred from her house for
fourteen years, and a few steps would have brought her to the
brink of the Atlantic ! I may add that, after persistent per-

252 THE CAUSATION OF DISEASE.

suasion, I managed to entice this curious soul out of her hole,
and had the satisfaction of seeing her brought face to face with
the healthy natural surroundings.

These considerations render it very evident that one may
live in the country and yet be deprived of that very particular
which constitutes the essence of its healthiness — namely, pure
air.

CHAPTER XL

Natural Selection (continued) — The Comparative Activity of the Process in
Civilized and Primitive Man and in the Lower Animals — The Relation
between the Activity of the Process and the Health of the Community.

We have seen that natural selection is still rigorously at work
among men. Let us now inquire whether it is as rigorous in
their case as among the lower animals.

This question is one of great moment to the pathologist,
for, if the process of natural elimination be checked, the health
standard will tend to be lowered ; I had almost written,
" whatsoever tends to check the process of natural elimination
will tend at the same time to lower the health standard," but
such a statement would not be altogether correct, for, by-
checking the spread of epidemics, for instance, we do not
necessarily lower the health standard, because, as we have seen,
the capacity of withstanding the deadly influence of a particular
contagion is no true measure of health or bodily vigour. A
sickly individual might fare better in this respect than a strong
and lusty one. It is, nevertheless, possibly true that, by con-
trolling the spread of epidemics, we have lowered the standard
of health, though this is by no means necessarily the case.
Such is the conclusion to which Orichton Browne arrives.*
He thinks, for instance, that nervous diseases have, in this
way, become more common. I am inclined, however, to receive
this statement with some reservation, for I can see no connec-
tion between the nervous diathesis and susceptibility to the
various contagia.

But whatever be the truth regarding the influence of dimin-
ished zymotic disease on the health of the community, there can
be no doubt that the general diminution in mortality which

* Vide British Medical Journal, Feb. n, 1888 : Address to the Neurological
Society of London.

254 THE CAUSATION OF DISEASE.

has resulted from interference with natural selection must
tend to lower the health standard. It therefore behoves us
to compare the process as at work in man at present and in
the lower animals.

The weeding-out process is quite as rigorous among savages
as among many, at least, of the lower animals. This is at
once obvious, for savage races do not increase in number, and,
inasmuch as they are highly prolific, a very active weediug-out
must occur. No doubt the population is largely kept down by
infanticide, but we may be quite sure that there is in the main
a " survival of the fittest." The process, I say, is as rigorous
among savages as among many of the lower animals ; but, since
man does not tend to multiply at the same rate as most of
these, fewer human beings need die prematurely than is the
case with the animals that very rapidly multiply.

In those communities whose population is increasing, the
process of elimination must necessarily be least rigorous ; and
this is the case with most civilized peoples.

In some few civilized countries, and notably in France, the
population is kept at a standstill by a careful regulation of the
births on the part of the parents. The tendency of this, as
we shall see in the next chapter, is probably to lower the
standard of health and to hinder the evolutionary process.

There is no analogy between a stationary population such as
that of France and the population of a savage community,
because, in spite of infanticide frequently checking the operation
of natural selection in the latter, a larger number of children,
in proportion to the population, are permitted to grow up than
in a country like France, and an active elimination occurring
among the adults by warfare and so forth, natural selection is
permitted to operate there. Moreover, among many savages
the practice of infanticide is unknown ; in which case the
population is kept down by continual warfare, and it is chiefly
the inferior who are destroyed.

The cause of the increase in the population of civilized com-
munities lies in the altered E. Whereas savages do little or
nothing to increase the natural food supply, civilized peoples
exert themselves to the utmost to make the yield as large as
possible by tilling the soil, rearing live stock, &c. ; and, taking

THE CAUSATION OF DISEASE. 255

the various civilized communities one with another, the food
supply has by this process hitherto been made sufficient for the
most rapidly growing populations ; for, if the total food supply
of a country be insufficient at any time, one of two things
happens : either there is an importation of the necessary food
to it — this, of course, only occurring when the country contains
an equivalent amount of wealth in some other shape, which it
can offer in exchange — or there is a migration of the surplus
population to some other part of the world where the adequate
supply can be obtained. Hence, among the civilized, that
great natural check to increase of population, the limitation of
the food supply, has been removed.

We have further to observe that, by the mutual consent of
the better-off, a sufficiency of food is placed at the disposal of
the needy, so that, excepting those rare and isolated cases of
starvation, and the now still rarer cases of widespread famine,
there is no weeding-out among the civilized through lack of
food, and hence the survival of many who, except for such
intervention, would be destroyed.

Among this number we must distinguish two classes. There
are, first, those who cannot obtain food through lack of the
necessary mental qualifications — the lazy, the dissolute, or the
actually incapable, it may be. Such are more interesting to
the political economist than to the pathologist. Secondly,
there is the class of the physically unfit. Very many indi-
viduals, simply because physically incapable of providing for
themselves, would, in the ordinary course of nature, assuredly
succumb. Such are either helped by their friends or provided
for by the community at large, and it may be said of them
that, in order to secure their survival, their E is rendered less
rigorous.

Let me define this term. By it I intend to signify the
amount of struggle which the E entails, or, what comes to the
same thing, the difficulty of adaptation. I do not include
under the rigorous E's those which are necessarily fatal : the
term only applies to those to which the community is capable
of becoming adapted. In contradistinction to a rigorous E
we may speak of an " easy " one.

Now we shall find that the efficiency of S is in direct pro-

256 THE CAUSATION OF DISEASE.

portion to the rigour of the E ; or, to put it in another way,
the greater the struggle against the E the higher the efficiency
of S. This truth is well exemplified in the common affairs of
life. Every one is aware that the efficiency of a railway
service, for instance, is heightened by opposition. Organic
evolution is indeed entirely due to rigour of E, and, so soon as
that rigour is diminished, evolution ceases and dissolution begins.
Examples illustrating this truth are so numerous and obvious
that there is no occasion to mention any.

An adequate supply of food, then, being within the reach
of every member of a civilized community, the E is thus far
rendered more easy, and this will tend to check the progress
of evolution, inasmuch as a number will continue to live who
would otherwise die.

It must not be supposed, however, because the population
of civilized communities is increasing and the food supply
adequate for all, that therefore the struggle for existence —
using this term in the most literal sense — is less among civilized
than among primitive communities. The very fact that civilized
communities are possessed of such enormous wealth and such
abundant food supplies, as compared with primitive commu-
nities, shows that, taking one individual with another, the
actual struggle must be far greater in the former, for the
increased wealth is the outcome of increased labour. Most
civilized men, having the capacity and the need for work, do
it voluntarily, and play an active part in the great social
machinery, so that, as a matter of fact, they struggle hard for
existence, and, as a result of this struggle, man is still evolv-
ing to something higher than a mere bread-winner. But,
although in this sense the struggle for existence is greater in
civilized than among primitive communities, yet in another
sense it is less severe, seeing that in all civilized communities
there is a large number of individuals physically and morally
incapable of providing for themselves, and such being, by the
forbearance of their brethren, permitted to live, evolution to
that extent suffers.

The E of civilized man is rendered less rigorous in other
ways. The individual may be surrounded by the most " easy "
E which it is within the power of man to create. In the first

THE CAUSATION OF DISEASE. 2$7

place, lie may possess hereditary wealth. In this case he does
not require to struggle for food, and, like the parasite, is apt
to retrograde, but such deterioration is rather a moral than a
physical one, and does not immediately concern the pathologist.
In the second place, the E of a sickly individual may be made
easy by scrupulous and unremitting care. Have we to deal
with a weak and sickly child, we may, by great care, and, it
may be, skill, rescue it from a death which was otherwise
certain, and the like is true of those suffering from many
diseases, such as pneumonia, stone, strangulated hernia. Now,
whenever life is thus artificially preserved, the operation of
natural selection is interfered with. The physician is, in fact,
part and parcel of the E of sick people, and whenever he
rescues an individual not past the procreative period from
a disease due to other causes than accident, he interferes with
the operation of natural selection, and so far, by rendering
the E less rigorous, tends to lower the health standard of the
race. I advisedly say tends, for, as we shall see in a future
chapter, the health standard is not in all cases thus necessarily
lowered. If a number of sickly, delicate children are by skilful
treatment successfully reared, the general health standard is
necessarily lowered, no doubt, but the like cannot be said when
life is saved by operating on a strangulated hernia.

Nevertheless, for the reasons just mentioned — i.e., because
sufficient food is placed within the reach of the weak as well
as the strong ; and, secondly, by reason of a wise and careful
manipulation of the E — we may safely conclude that in civilized
communities the physical health tends to deteriorate. The
individual tends to become levelled down to a less rigorous E.

And what is true of the physical man is true also of the moral.
A perusal of Spencer's " Sociology " will make this manifest.
Therein he deals with the moral man. He points out the
harmful influence on the poor of excessive State aid ; for, in
proportion as they are helped — that is to say, as the E is made-
easy for them — in that same proportion will there occur a
degeneration of the moral self, so far, at least, as the capacity
of self-help is concerned. Not only does no moral improve-
ment result from excessive State intervention, but there is an
actual levelling down of the individual to his more easy E.

258 THE CAUSATION OF DISEASE.

Mr. Spencer does not, of course, contend that the E should not
be as morally healthy as possible, but rather that it should not
be rendered easy beyond certain limits which it should be
the business of political economists to define, and, having sur-
rounded the poor with a scientifically rigorous E, he would con-
fidently look forward to a levelling up of the moral self.

In short, if an individual is helped too much, he generally
exerts himself less to help himself. This is true of all organisms,
whether plant or animal. I heard a good illustration of this
quite recently, for on asking a gardener whether it would be
advisable to water a particular kind of bean which had just
been set, he said: "No; if you look after them too much,
they won't look after themselves — they'll get the water right
enough if left alone, but if you once begin to water them they'll
always want to be watered." Thus, in his simple, practical
language, he enunciated a most important and far-reaching law.

The physician is continually applying this principle. He
knows well that, by physically pampering a child, he favours
physical degeneration, just as moral pampering favours moral
degeneration. And many of the particulars wherein the female
sex is inferior to the male are, I believe, due to the difference
in their bringing up — to the fact that the one has been sub-
jected to a less rigorous E than the other.

It is clear, however, that we cannot regulate the physical
E of the community at large with the precision of the political
economist, saying, " To this extent shall your E be made easy,
and no further." The reason is obvious : in the one case failure
is a mere social one ; in the other case it is a matter of life
or death.

The above observations render it obvious that the weeding-
out process is less severe among civilized communities than
among the more primitive, and the causes of disease being
greater in the former, we have a further reason why the standard
of health should in them be lower.

And here let me allude to a common fallacy. Many point
triumphantly to the fact that our own race is markedly increas-
ing in size — that the average man of to-day is too big for the
armour worn in bygone centuries, and so forth; and the evidence

THE CAUSATION OF DISEASE. 259

in favour of this conclusion is very strong. It is true that the
chest measurement of the recruit has been declining of recent
years, but this is probably owing to the fact that more recruits
are now drawn from the large towns than formerly. Granting,
however, that the stature of the ordinarily healthy man is
greater now than two or three centuries ago, it by no means
follows that health has improved pari passu with this increase.
Most domesticated animals are considerably bigger than their
wild congeners, but they are, if anything, inferior in health
and vigour. Their increase in size is certainly due to better
diet, and good food undoubtedly tends to physical improve-
ment. If all our agricultural population were perfectly fed, I
have no doubt that, with their healthy* surroundings, a marked
physical improvement would take place in the course of a few
generations, and that health would improve in the same ratio.
But against the increased stature and strength resulting from
better food we have to set the thousand evils which accompany
civilization, and which tend to mitigate the advantages arising
from improved diet, and therefore it is that I say we must be
careful not to point to mere increase in stature as evidence of
an improved standard of health.

How far can this levelling down process go on ? It is
obvious that, taking the community at large into account, it
cannot pass below a certain average level, and this by no means
a low one. We have seen that, despite the more easy E which
many members of civilized communities enjoy, natural selection
is busily at work among them. This does not permit the
physique and health standard to sink below a certain fairly
high level ; for although in a number of isolated instances
sickly individuals are enabled to survive, yet this, be it noted,
is true of isolated cases only. The community at large is
exposed to a decidedly rigorous E 5 nevertheless, the population
goes on increasing ; and we may, I think, lay down the
principle that a community rapidly increasing under a rigorous
E must have a fairly high standard of physique and health.
There must be a strong backbone to that community.

* I use the wor 1 healthy here, with the qualifications contained in the last
chapter.

260 THE CAUSATION OF DISEASE.

Under such a rigorous E, the searching process of natural
selection is ever at work. The sickly ones who reach maturity
in virtue of an artificially easy E do not live on through
many generations. Though they survive, and though many
of them rear children, Nature has, so to speak, her eye upon
them, and sooner or later the unhealthy line is exterminated.
The sickly and feeble will not, in fact, be represented in remote
posterity ; genealogically speaking, they are on the road to
extinction. It is only the best physical specimens among us
who can enjoy the prospective honour of living through their
descendants in a remote posterity. These constitute the main
stem of the genealogical tree : from it weak and slender
offshoots are perpetually branching : for a few generations
they live on, but sooner or later they break off and decay.

Wherefore, viewing the subject from a far-off standpoint, we
see that a very high physical level of health must be main-
tained in the case of a fortunate few ; and that the effect
of rendering the E less rigorous is, on the whole, rather to
delay the hand of Nature than to stop it. In estimating the
average health standard of the community, however, we must
include every member of it in our reckoning ; and, such being
the case, it is obvious that the health of the community at
large is lowered by rendering the E less rigorous.

CHAPTER XII.

Natural Selection (continued) — Curtailment of the Number of Births in a
Community hinders Evolution and favours Dissolution.

In the last chapter, while considering communities whose
population does not increase, we had occasion to notice that
this stationary condition of the population might be due to two
causes : either to active weeding out, as in savage communities,
or to limitation in the number of births, as in France, for
instance, and I said that, whenever the number of births is
thus curtailed, the health of the community must suffer, evolu-
tion being hindered. We will now briefly inquire into this
statement.

In a large family, inasmuch as it is impossible to get
equality, some of the children will certainly be more vigorous
than others; and some one must be the strongest and most
vigorous. Now, if the number of children which any one
couple is capable of rearing be curtailed, and especially if it
be limited to so small a number as three or four, the chances
are against the potentially strongest individual being born,
and so the nation is deprived of those who might have been
its best children. Other things being equal, the most prolific
nation has the best chance of physical improvement and the
least chance of degeneration.

In reference to this tendency of any artificial check to
population, it would be interesting to inquire at what particular
period in the lives of the two parents the reproductive power
is at its prime — i.e., at what age the capacity of producing the
best offspring exists ? In France the father is often past
middle life ; and although this has its advantages, yet there
can be little doubt that in the male the procreative power is
at its prime before middle life. Late marriages on the part
of the. man are certainly not altogether favourable to racial

T

262 THE CAUSATION OF DISEASE.

improvement; but there is another unfavourable circumstance

attending artificial checks to increase — i.e., that the children

of women adopting this practice are generally born during the

early period of their procreative life, and, in those cases where

the father and mother are about the same age, when the father

is young also. For, as a rule, the check is applied after the

first two or three children are born at natural intervals ; it is

not, that is to say, applied so as to allow an interval of several

years between the two or three children who are permitted to

be born, in which case some of them might be born at the

prime of sexual life. We must also take account of the fact

that the first child is generally inferior to those immediately

following ; this is, at all events, the popular belief. From these

several facts, it is obvious that a limitation in the number of

births must tend to prevent the best children from being born.

So far as the intellectual side of man is concerned, there

ought to be little difficulty in testing the truth of the above

conclusion, since it is an easy enough matter to obtain a list

of intellectual prodigies. I have taken twenty-two celebrated

men at haphazard, with the object of discovering what position

they occupy, in order of birth, among their brothers and sisters.

The following is the result of my investigation : —

Poets : Poet-philosopher :

Shakespeare, eldest son. Two Goethe, only son, eldest child,

daughters born before him. Warriors :

Both died young. Wellington, third son.

Tennyson, third son. Robert Blake, eldest of 13

Painter: sons and 2 daughters.

Michael Angelo, second son. Statesmen-orators :

Musician : Chatham, second son.

Beethoven, second child, and Burke, second son.

son, of 5 sons and 2 daughters. Gladstone, youngest son.

Ruler: Warrior -statesmen:

Cromwell, second son. Clive, eldest son.

Philosophers : Warren HASTINGS, only child.

Bacon, youngest son. Man of letters :

Kant, second of 9 children. Swift, second child.

Carlyle, eldest of 9 children. Historian :

Scientists : Gibbon, eldest of 5 brothers and

Newton, only child. 1 sister, all of whom died in

Darwin, youngest but one of 6 their infancy.

children. Novelist :

Lyell, eldest son. Dickens, eldest son ; second

child of family of 8.

THE CAUSATION OF DISEASE. 263

In almost all the above cases it was impossible to discover
in what exact order in the family the illustrious individual
came. In the dictionaries and encyclopaedias consulted, the
sisters were left out of consideration.

It is remarkable how frequently in this list the intellectual
prodigy has been the eldest son. This happened in the case
of Shakespeare, Carlyle, Newton, Goethe, Kobert Blake, Clive,
Warren Hastings, Gibbon, Dickens — in nine out of twenty-
two ! Moreover, seven others were second children. Whether
this proportion would be maintained in a larger list, I know
not : I cannot but doubt it. Among the nine eldest sons,
Shakespeare and Newton are certainly two of the greatest men
who have ever lived — perhaps, intellectually, the greatest of
whom we have proper record. Shakespeare, however, was the
third child. So that, if only two children had been permitted
to be born to his parents, Shakespeare would not have come
into being. Nor would Darwin, Wellington, Gladstone — three
of the most remarkable Englishmen of the present century.
(Think how these three men have impressed European
history and thought !) The same is true of the great Bacon,
who was the youngest, and of Tennyson, who was the
third son. From such a small number of cases it would be
impossible to draw any general principles — moreover, no
account is taken of the physical side of man ; but even these
few cases — taken, as I say, entirely haphazard — show most
emphatically how much mankind would have lost by inter-
ference with biological laws.

T 2

CHAPTER XIII.

Activity of Natural Selection at the Different Periods of Life Compared — Its
Influence on the Hereditary Transmission of Disease at these Periods —
Natural Selection Inoperative after the Procreative Period — Non-Trans-
mission of Evolutionary Gains after this Period — Average Limit of the
Procreative Period of Life in the Two Sexes.

We have seen how natural selection tends, by an active
weeding-out process, , to prevent the hereditary transmission
of disease. It is evident that this process is inoperative after
the procreative period of life, for, if a disease then kills, the
race is in no way affected, the individual having already had
abundant opportunity to leave offspring, who will, if the disease
be due chiefly to peculiarity in S, tend to inherit it at the
same period of life as that at which the afflicted parent suffered
from it.

Natural selection operates most actively before the procrea-
tive period, for, if during this period an individual be destroyed
by a disease due to faulty S, there is no possibility of his
leaving offspring to inherit the disease-tendency. Similarly,
it operates more rigorously during the early than in the later
part of this period, because, when the individual is cut off
in early procreative life, the possible progeny is less. In short,
natural selection is most vigorous before the procreative period,
inoperative after, and, during the period, severe in inverse pro-
portion to the number of possible children.

We may, I think, safely conclude from the above that cases
of fatal disease due to inherited structural peculiarity are least
common before procreative life, that they gradually increase as
it advances, and suddenly increase after its limit has been
reached, not necessarily, however, becoming augmented year by
year, for the process of racial elimination is as inoperative
during the first as during the last year of post-procreative life.

THE CAUSATION OF DISEASE. 265

Note that I say fated diseases, for it is manifest that the
minor inheritable diseases, which do not cause death, cannot
fall under the influence of natural selection ; and that I make
the further qualification, elite to inherited structured peculiarity —
that is to say, not to peculiarities of E.

Now, there are several circumstances which render it difficult
to test the truth of the above statement. In the first place, it
is necessary to remember that many diseases begin early in
life, yet do not kill till the individual is far advanced in pro-
creative life or has actually passed it. A good example is
afforded by rheumatic diathesis. I suppose the majority of
people who suffer from rheumatism outlive procreative life ;
certainly many live on far into it. It is true that this disorder
must diminish the chances of matrimony, but it is questionable
whether it does so in a marked degree. It therefore follows
that many rheumatically-disposed individuals may rear children,
even though they have suffered from the disease in early life.

Then, again, it might be thought that the rate of the mor-
tality at different periods of life would give us the proportion
of inherited structural peculiarities at these several periods, but
this is by no means the case, and for these reasons : First,
the "disease-tendency at the several periods of life is not the
same thing as the amount of disease, because much depends
upon the nature of the E, and this is more pathogenic during
certain periods than others. Every one knows, for instance,
that in men the mortality is largely increased by the nature of
their occupation, by overwork, worry, accident, and so forth ;
that in women there are many disorders connected with their
peculiar mental and physical surroundings ; and that infants
and young children, notably those of the lower classes, are
(owing to defect in "reason" on the part of the parents)
subjected to peculiar unhealthy conditions, such as improper
feeding and clothing. Secondly, the disease-tendency ' at
any particular period of life may not be due to any
special inherited weakness, but to a condition of body more
or less common to all members of one or both sexes at that
period. Thus during the procreative period all women are
subject to dangers from which they are free before and after
this period. Children, too, are especially prone to respond

266 THE CAUSATION OF DISEASE.

morbidly to certain mal-E's, such, for instance, as those just
mentioned, not by virtue of any specific state of the tissue
peculiar to this child or that, but in consequence of a condition
of body belonging to the whole race at that time of life. If,
therefore, we were to take the mortality of children as a measure
of the extent to which special morbid tendencies are inherited,
we should be erring, owing to the fact that children, as a class,
are peculiarly susceptible to certain morbid influences, and to
the further fact that they are freely exposed to these influences.
I have purposely made no mention, hitherto, of the zymotic
fevers. Is the excessive frequency with which children suffer
from these zymotic fevers due to a peculiar susceptibility on
their part, or to the fact that they are more exposed to a first
attack of the poison than adults ? It is probable that children
are, on the whole, more prone to be affected by them than
adults ; but the chief reason of the greater frequency of the
specific fevers during childhood is undoubtedly that one attack
confers immunity from another, and that the great majority
of adults have already been exposed to the poisons.

A further source of error is the fact that the longer an indi-
vidual lives, the greater is the quantity of mal-E to which he
is exposed. So that, other things being equal, the mortality
would increase with each successive year.

In order to estimate properly the mortality at the several
periods of life from disease due to inherited specific structural
weakness, it would be necessary to expose an entire community
to an average healthy E, and then, making due allowance for
the above and all other possible sources of error, we should
doubtless discover our inference to be correct.

We usually find very little disease before the procreative
period which is not due to mal-E. For instance, the mortality
in a properly regulated boys' school is very small, and this in
spite of the fact that many of the boys have had their health
injured by an improper bringing-up in the nursery.

It is very seldom, in fact, that we find children carried off
by disease due to an inherited morbid taint. Indeed, if we
eliminate the deaths due to the specific contagia, and to the
neglect of the simplest sanitary laws, such as those pertaining
to food, exercise, air, and clothing, we shall find that children

THE CAUSATION OF DISEASE. 26 J

are rarely destroyed by disease. I have no hesitation in saying
that, practically, all cases of bronchitis, "consumption of the
bowels," and so-called "struma" (all of which cause an enor-
mous number of deaths) are due to neglect — neglect as to
feeding, ventilation, the simplest common-sense precautions.
I say this deliberately. Can any one point to a single case of
"struma" — say, hip-joint disease — in which the motions have
not been for a long time unhealthy, in which that vast mucous
tract whose business it is to convert the crude food-stuffs into
suitable, soluble nutriment for the whole body, is not diseased?
And what is the cause of this unhealthy state of the ali-
mentary mucous tract, which of necessity leads to miserable
and puny growth ? It is due to errors in diet alone, or to
this in conjunction with other forms of mal-E. In such a case
the mother will probably tell us that the child has always been
delicate, that for a long time, perhaps from earliest infancy,
the motions have been unhealthy, and she will attribute all the
trouble to an inborn weakness in the child; but on close inquiry
we shall find in the majority of such cases that the initial fault
is with the feeding, or other external conditions, and not with
the child, or, even if with the child, that it was a mere tempo-
rary fault, one which, with judicious management, might have
been easily overcome. And day by day the disease becomes
more fixed, more difficult of cure ; day by day the child grows
more delicate, and the parents are more and more convinced
that all the evil is due to an inborn weakness. When we re-
member that a mal-E acts perniciously in proportion as it acts
early in life, we shall have no difficulty in seeing how a child's
whole constitution may be modified for ill by a small initial
neglect — that a long train of troubles may result from a simple
malady which might very easily have been nipped in the bud.
It has been to me, for several years, a very interesting task
to compare the health of brothers and sisters, and I have come
to the conclusion that when one or two of a family are delicate
while the others are healthy _, the delicacy has always had such
an accidental beginning, as we may call it ; and, further, that
in most cases where the majority, or all, the children are sickly,
the cause is not an inherited weakness, but the faulty system
of bringing-up to which all the children have been subjected.

268 THE CAUSATION OF DISEASE.

It would, of course, be absurd to disregard altogether the influ-
ence of hereditary weakness, but I am convinced that, so far as
diseases of children are concerned, this plays a very subordinate
part, and that whatever weakness belongs to the new-born
infant is rather the result of ante-partem conditions of E (of
germ, sperm, and embryo).

I have tested the truth of the above statements by a large
number of observations, and I could cite numerous cases where
weakly infants have, with judicious management, grown up
strong and vigorous, just as, on the other hand, I could give
a dismal list (as who indeed could not ?) of strong and
vigorous infants who, through faulty management, have grown
up into sickly, miserable specimens of humanity, if, indeed,
they have not been actually destroyed in their infancy or
childhood.

Inasmuch as natural selection does not operate after pro-
creative life, it is important for us to answer the question :
When does the procreative period terminate ? Few women
bear children after two or three and forty ; in men, however,
the reproductive power may extend into extreme old age.
Nevertheless, the average age at which men cease to beget is
much less than that at which the power leaves them, seeing
that the wife becomes sterile a long time before the average
husband is physiologically impotent. If we place the average
age at which women cease to bear children at forty, and assume
the husband to be on an average three years older than his
wife, it will follow that the average age at which men cease to
procreate is forty-three.

We may fittingly ask the question here, Is this limitation
to the natural procreative period of the man advantageous or
otherwise to the race ? I cannot but see in it one serious dis-
advantage, namely, that racial evolution is prevented from
taking place beyond this age. Whatever may be said of the
physical side of our being, it must be acknowledged that the
human mind is capable of much culture and improvement
after forty or thereabouts, but, as things are, gains in this
direction are lost to the race. It is, however, possible that
the same applies to the physical side also. Suppose, for

THE CAUSATION OF DISEASE. 269

instance, the men of twenty successive generations lead
physically healthy lives till fifty-three years of age, then any
individuals whom they beget at this period will reap the full
advantage of ten years spent by the father in healthful physical
life. Under existing circumstances, however, the race is largely
deprived of this advantage, and it is needless to say that, as
far as the hereditary principle is concerned, old age can have
no influence on it, physically.

In short, the limit of procreative life, so far as I can see,
practically determines the limit of evolution as regards age.
Unless the procreative period be extended in women, we can
never expect evolution in her to proceed beyond the present
average climacteric period, but it might be pushed on to a much
further limit in man. This conclusion follows from (1) the
principle of heredity as limited by sex ; (2) the principle of
heredity at corresponding ages.

It is much easier to study the mental evolution of the
human race than its physical evolution, for mental evolution
leaves monuments as lasting as they are various. That the
rate of evolution is different for the two sexes there can be
no doubt, the female sex evolving more rapidly, both in mind
and body, than the male.*

But whether the evolution goes on much longer in the life
of the man than of the woman, I have not been able to satisfy
myself. I have before me a series of notes which were taken
with a view to estimate the rate and limit of mental evolution
in the woman, and most of them tend to show the period

* The earlier occurrence of puberty in the female results, I suggest, from
the fact that the sexual struggle has chiefly been among the males for the
females. For the sake of argument, let us suppose that puberty occurred
originally at the same age in both sexes. Directly the female attained sexual
life she would be eagerly sought after ; the younger males would, however,
have very little chance in the struggle against older and more vigorous males,
so that the tendency would be for the male sexual system to remain idle
until some time after puberty ; and, supposing this to occur for thousands of
generations, it would follow from the principle of heredity at corresponding
ages, and from what we know of the effects of use and disuse, that the onset
of puberty would tend to be postponed in the male. If this explanation be
correct, we may expect the period of puberty to gradually recede in the
female, owing to the fact that the woman— at all events, in civilized countries
— seldom marries until some years after puberty.

270 THE CAUSATION OF DISEASE.

may extend far on into life. Of these notes I append the
following : —

Madame de Stael, b. 1766; cl. 181 7. — Intellect very early devel-
oped, and remained unimpaired up to the last moment : great con-
versational powers, delighting intellectual men as early as 11 or 12.
Wrote nothing, however, of any importance till of middle age — partly
because of her father's objection, partly because her ideas found vent
in her brilliant conversations. Her chief works were :

"Corinne" aged 39-40

" L'Allemagne " aged 42-44

" Dix Annees d'Exil " aged 46-47 (about)

Eminent Women Series.

Madame de Sevigne, b. 1626 ; d. 1696. — Bright and spirituelle
from a very early age. Left no works from which to judge of the
development of her intellect ; but from her letters, which have been
preserved, it is evident that her mind retained its vividness and
brilliancy till the end. Some of her most striking and original
passages are to be found in her later letters. She enjoyed excellent
health all her life, having had only one illness (rheumatic fever, at
the age of 50), besides small-pox, which killed her at the age of 70.

Miss Thackeray, Foreign Classics.

Maria Edgeworth, b. 1767 ; d. 1849. — Showed cleverness at an
early age, and retained a remarkable degree of mental activity up to
her death, at the age of 82. Wrote chiefly at her father's instiga-
tion (first attempt, " Letters to Literary Ladies," when 27), and at
his death gave it up almost entirely, but continued to live an active
busy life to the last. At the age of 70 set herself to learn a new
language. Her best efforts are, perhaps :

" Castle Eackrent " aged 33

"Ormond" aged 50

Helen Zimmern, Eminent Women Series.

Harriet Martineau, b. 1802 ; d. 1876. — Began to write at the age
of 20 (1822, chiefly essays), and continued to write voluminously
(articles, political, philosophic, &c, and stories for reviews and
magazines) till 64 years of age, when the pressure of ill-health closed
her literary life. Her first success was not attained till the age of
29 ("Illustrations of Political Economy," 1831-2). She may be
said to have reached the maturity of her powers about the age of 46.

THE CAUSATION OF DISEASE. 27 1

" Eastern Life, Past and Present " aged 46

"The Thirty Years' Peace" aged 46-48

Though she stopped writing in 1866, her intellectual powers con-
tinued all but unabated till her death, at the age of 74. She had
very bad health all her life, and for the last twenty-one years
suffered intensely from the disease which ultimately killed her.

Mes. Fenwick Miller, Eminent Women Series.

Charlotte Bronte, b. 1816; d. 1855. — Wrote tales, poems, &c,
of considerable merit from the early age of 13. Her first novel,
however, did not appear till she was 30 ; in the same year she
wrote what is generally accepted as her masterpiece (" Jane Eyre,"
1846). Her other two novels (" Shirley," 1849 ; " Villette," 1882—
the latter by some people accounted her best) appeared at intervals
of three years, her work being interrupted by very bad health, from
which she suffered all her life. She was only 39 when she died,
and would in all probability have done much more good work if she
had lived longer. She belonged to a clever, precocious, unhealthy
family.

Mrs. Gaskell.

George Eliot, b. 181 9; d. 1880. — Her literary career extends
over a period of thirty-six years. She began with translations at the
age of 24, and wrote her last work (" Theophrastus Such ") the year
before her death, which took place at the age of 61. The following
is a list of her works, with dates :

1848. "Translations" .... begun at the age of 24

1852-8. Contributions to Westminster Review begun at age of 33

1856-7. " Scenes of Clerical Life " aged 37-38

1859. "AdamBecle" aged 40

i860. " Mill on the Floss " and " Lifted Veil" . . aged 41

1861. " Silas Marner " aged 42

1862-3. "Komola" aged 43-44

1864-8. " Spanish Gipsy " aged 45-49

1866. "Felix Holt" aged 47

1 87 1. " Middlemarch " aged 52

1876. " Daniel Deronda " aged 57

1879. "Impressions of Theophrastus Such". . . aged 60

Mathilde Blind, Eminent Women Series.

George Sand, b. 1804; d. 1876. — Began to write at the age of 27,
and continued to do so with unabated vigour till ivithin a few days
of her death, at the age 0/72. She cannot be said, for any length

272 THE CAUSATION OF DISEASE.

of time, to Lave risen above or sunk below a certain level of ex-
cellence. From the time of her first novel (*' Indiana," 1832), written
at the age of 28, she continued to produce at the rate of two novels
a year, and at rare intervals was the product a failure. The power
shown in her earliest works is to be seen in an equal degree in those
of 40 years later date :

" La Marquise " . . . aged 28 *

" Francia " aged 68

Bertha Thomas, Eminent Women Series.

Mary Wollstonecraft Godwin, b. 1759; & I797- — Ifc mav De
said that her intellect did not awake till she was 16, when she first
began to study, and that it went on developing till her death. The
work on which her fame as an author rests (" Vindication of the
Rights of "Women," 1791) was written at the age of 32. Her next
work (on the " French Revolution," written two or three years later,
1793-4) marks an enormous advance in her mental development.
She died at the age of 38, in the full prime of her powers. Her best
work probably remained to be done. The increased merit of her
later work somewhat confirms Southey's declaration that " M. "W.
Godwin was but beginning to reason when she died."

Elizabeth Robins Pennell, Eminent Women Series.

It would appear from these few cases, chosen at random,
that mental evolution goes on as long in the life of the female
as the male, and this accords with the conclusion arrived
at a priori- — namely, that the limit to evolution would be about
the same in the two sexes, seeing that the actual procreative
limit is about the same. Judging from these examples, it
would seem that the climacteric exercises no injurious influence
upon the intellectual faculties; indeed, some of the most
brilliant work appears to have been accomplished at this
period. That the wave of emotional excitement which comes
over the woman at the climacteric tends to give a distinct
colouring to the work then produced, I can have little doubt,
but it has surprised me somewhat that there is no evidence
of even a temporary intellectual falling off among celebrated
women at this time ; this, however, is not the place to discuss
the subject further.

CHAPTER XIV.

Sexual Selection.

I have considered the part played among civilized peoples by
natural selection. There are two remaining factors which help
to mould the animal organism — namely, sexual selection ; and
the direct action of the E, independently of natural or sexual
selection. It will be unnecessary to speak of these at great
length.

Sexual selection plays, comparatively speaking, a very inferior
part in moulding civilized man. It will be advisable to treat
of it, first, from the point of view of the man ; and, secondly,
from that of the woman.

I. As regards the man. — Among savage peoples the strongest
and most vigorous men, doubtless, secure the largest number of
wives, and leave behind them the most numerous progeny, but
in civilized communities monogamy for the most part prevails ;
wherefore, one male cannot well leave behind him more than a
limited progeny; for, although promiscuous intercourse fre-
quently occurs among civilized communities, and illegiti-
mate births are frequent, yet the children born to any one
man in this way cannot be very numerous. Even supposing,
however, one man to leave a large number of illegitimate chil-
dren, it by no means follows that such a one enjoys excep-
tionally good health and strength, or a total freedom from
disease taint, seeing that the tendency to beget illegitimate
children depends upon a moral, not upon a physical depravity
on the part of the parents. Indeed, the procreative power
bears little or no relation to physical fitness ; for it is well
known that feeble and unhealthy parents are frequently capable
of rearing large families, while, on the other hand, strong and
healthy parents have, often enough, very few children.

274 THE CAUSATION OF DISEASE.

Thus, whereas in a savage community the inferior physical
types stand little chance of rearing offspring, in civilized
countries the sickly individual, possessing, as he unfortunately
does, the power of procreation, can, practically, always gratify
his desire for offspring, for there is little difficulty in securing
a wife. Many women have assuredly highly crude notions
concerning physical fitness, so much so that a sickly man is
often voted ' ' interesting ; " and although one can scarcely go
so far as Thackeray, who tells us any man can marry any
woman, yet I think it will be generally allowed that there are
few men desiring matrimony who cannot gratify their wish.
All may not succeed in the first instance, but he must indeed
be a very bad specimen of humanity who meets with universal
failure.

Men are, moreover, actuated by other considerations than
those of physical fitness. There is a beauty of mind as well as
of body. A noble mind is an irresistible force, and it is well
that it is, for so the superior mental type tends to be propa-
gated. Hence we may fittingly speak of a" mental fitness ; "
and are not many mentally unfit to marry, some because inca-
pable of acting up to the full morality of married life, others
because possessing minds too degraded to be transmitted to
posterity ?

And here I would ask — Does the thought often occur to
those who desire to marry and to have children, " Am I worthy
to be represented in posterity ? Have I myself been such a
success that I should wish to leave another like me ? " I doubt
not that, as regards physical ineptitude, the question does very
frequently arise, and that the answer is usually — "Aro/;' But
what of mental ineptitude ? Life has pain and troubles for all.
Some are so constructed, are so buoyed up with animal spirits —
and a precious heritage they are — that they ride safely through
the storm and tempest of life — the pains and sorrows of to-day
melting into the ocean of the past to-morrow, and forgotten.
This is physiological. But there are others — and they are
many — who are keenly alive to the pains and trials which all
must suffer, who are apt to brood unduly over the mysteries
of life, for ever seeking to gaze into ,the unfathomable. Ought
such to marry ? I think not. The hypochondriac is often

THE CAUSATION OF DISEASE. 275

advised to do so. It is argued that, with the affection of a
good woman, and with the diverting interests which children
bring with them, he will be gradually drawn out of himself,
and will forget his imaginary ailments. Be it so. But is not
such a course a highly selfish one? The true hypochondriac
is a pathological variation, and should think twice before he
determines to multiply the number.

Wealth constitutes a further attraction for men, and this is
a possession that by no means goes hand in hand with either
mental or bodily fitness. Young men are perpetually counselled
by their elders to "look out for money." The advice of the
" Northern Farmer " is, perhaps, less objectionable: "Doant
thou marry for munny, but goii wheer munny is." Among
the lower orders wealth is assuredly a greater attraction for
the men than physical fitness : a deformed cook, with small
savings, would, in many cases, be deemed a greater prize than
a penniless beauty, and it is truly astounding how large a
number of crippled women get married. No doubt, in marry-
ing women with money, a particular type of mind is uncon-
sciously selected. A saving cook is a prudent woman, and an
heiress comes of a stock in whom the faculty of acquiring
wealth is prominent. Galton has remarked of heiresses that
they tend to have few children : this is what we should expect ;
for the fact of their being heiresses often depends upon small
procreative power on the part of one or other of their parents,
and this writer very ingeniously accounts for the rapid extinc-
tion of many newly created peerages by the frequency with
which the eldest son marries an heiress — marries into an un-
productive family.

In spite of the above facts, it must be allowed that sexual
selection, considered from the point of view of the man, does
play some part in moulding the race. In the first place, there
are some men who are actually incapable of procreation, either
through a general feebleness of constitution or local sexual
defect. In the next place, it must be granted that there are
also some rare individuals whom nobody would have at any
price. Finally, there are men who either do not care to marry,
or who, while washing to do so, have not the means. Unfortu-
nately, this latter is no great obstacle among the poorer classes.

276 THE CAUSATION OF DISEASE.

It is obvious, from these considerations, that particular
bodily and mental types tend to be eliminated.

2. From the woman* 8 point of view. Since there are more
marriageable women than marrying men, a large number of
women remain unmarried. No doubt, the most beautiful speci-
mens get married ; but if we except what may be termed the
exceptionally beautiful, whether in body or mind, who are
eagerly sought after, the chances which the remaining number
have of being married are about equal, always eliminating the
element of wealth. A certain number of women prefer spins-
terhood, and their number is probably larger than is generally
known, for so great is the tendency to believe otherwise that
few elderly spinsters are accredited with having remained in
spinsterhood for its own sake. In the case of women, choice
is frequently influenced by considerations of social position.
How often do we see women of surpassing physical beauty
wedding the most miserable male specimens for the sake of
rank ? Such unions must surely grate upon the feelings of
the physiologist and anatomist — ay, and of the moralist, too.
On the other hand, the instincts of a lovely woman — using the
word lovely in its widest sense — are averse to such a union,
and she happily often mates herself with her equal. It is from
these unions that the ancestors of remote posterity spring.
They should in every way be encouraged ; and I hold that
every parent who can rear a family of children healthy in
mind and body, may justly, like the Vicar of Wakefield, con-
sider his country his debtor.

CHAPTER XV.

Action of E upon Structure independently of Selection.

A particular E acting during several successive generations is
able to modify the structure of the organism in a particular
way independently of selection, natural or sexual. This factor,
however, has played a very subordinate part in evolution. It
is chiefly natural selection, and in a lesser degree sexual selec-
tion, which have brought about the complex specializations of
organisms.

Now, selection can have played no part in the evolution of
disease, since all pathological variations, far from being selected,
tend to be vjeedcd out. " Natural selection acts exclusively by
the preservation and accumulation of variations which are
beneficial under the organic and inorganic conditions to which
each creature is exposed at all periods of life. The ultimate
result is that each creature tends to become more and more
improved in relation to its conditions/'* Thus selection is ever
busy tending to prevent disease, and I wish to draw particular
attention to this fact because we hear a great deal about the
" evolution of disease." But it is obvious that if a disease
evolve during several successive generations, it must essentially
be by this third method — viz, by the action of E upon
structure, independently of selection.

I use the term " evolution of disease," but it must be
confessed that it is somewhat paradoxical, for disease is
essentially a dissolutionary process, and it would, therefore,
be more accurate to speak of the dissolution of disease. Indeed,
if we hold by the meaning attached to the word by Herbert
Spencer, the illustrious propounder of the doctrine of evolution,
we cannot, without contradiction, speak of the evolution of

* " Origin of Species," p. 97.

U

278 THE CAUSATION OF DISEASE.

disease. When due to pathogenic germs, a disease may, it is
true, evolve by natural selection or otherwise, since here the
specific mal-E is a living organism, which in mode of evolu-
tion differs in no wise from other organisms, but in such cases
the evolution belongs to the E and not to the S. When,
however, we speak of the evolution of disease, we are not
referring to the evolution of a pathogenic organic E, but of a
structural state on the part of the suffering organism — a
change wrought in the S, it may be during several successsive
generations.

Repeated allusion has been made to the influence of a
mal-E operating during several successive generations. All the
necessarily-fatal-E's which do not kill in the first generation
operate in this way. There is a gradual deterioration in struc-
ture which eventually leads to family extinction, and in such
cases there may perhaps be said to be an evolution of disease.
The S during successive generations is gradually modified in
such a way that presently S + a particular E, which perhaps
would have no ill-effect upon a healthy individual, induces a
fatal disease.

In this way many disease-tendencies — e.g., to insanity and
gout — are slowly evolved.

Intemperance is so well known to be a fruitful cause of
insanity that we might, in certain cases of this disease at all
events, have little difficulty in tracing its evolution during
successive generations and in determining its proper cause,
and the same is true of gout and other disorders. But how
many are the subtle causes of disease which quite elude our
observation ! Generation after generation of men exposed to an
ever-operating but unknown E may in this way be gradually
and imperceptibly changed in the direction of disease. Such
changes are of course structural, and constitute natural varia-
tions ; they are wrought in the finer textures of the individual,
and for long may lead to no obvious change, but finally, after
several generations, the specific E calls out the actual disease,
which is then recognizable as a true pathological variation.

Now it is interesting to note that this is exactly what
happens in the case of ordinary physiological variations. A
gardener has often to alter the E of a plant for many

THE CAUSATION OF DISEASE. 2/9

generations before lie can get it to vary at all. A hidden
silent change meanwhile goes on, the tendency to obviously
vary increasing : the numerical value of S rises from I to I o.
■' We have good grounds," says Darwin,* " for believing that
the influence of changed conditions accumulates, so that no
effect" (he evidently means here obvious effect) "is produced
on a species until it has been exposed during several genera-
tions to continued cultivation and domestication."

Our case of insanity is therefore parallel with the variations
of wild plants under domestication. In both a peculiar E
operates during many generations, leading to a hidden specific
change, which finally breaks out into an obvious variation — •
physiological in the one case, pathological in the other.

* Vol. II. "Animals under Domestication," p. 249.

V 2

CHAPTER XVI.

Criticism of Dr. Mott's Views — Concluding Remarks on Evolution.

In concluding my remarks on evolution, I should like to allude
to an interesting and suggestive paper,* which I read after
the foregoing chapters were written. The object of the author
is to show that " the outcome of modern intellectual develop-
ment in the production of great social changes is to produce a
widespread physiological dissolution — namely, a lowering of the
vitality of the individual."

As the result of civilization, the rich, he tells us, get too
much, the poor too little ; people, moreover, tend to accumulate
in unhealthy towns, to suffer from alcoholism, syphilis, over-
pressure of business, &c. A further evil, he believes, results
from the fact that artificial selection is " replacing natural selec-
tion," and that medical science preserves degenerate types.
So far (as my remarks have, I hope, made clear), I entirely
concur with this author, but I think he under-estimates the
influence of natural selection among civilized peoples. Imper-
fect and inferior types are, as I have shown, being perpetually
weeded out. Moreover, we may, I believe, conclude that so
long as the population of a country (like our own, for instance)
goes on increasing, the physical standard of the nation, as a,
ivhole, must keep at a high level, for, owing to the rigour
of the E — which is in direct proportion to the severity of the
struggle for existence — a high average strength is required.

I further take exception to another opinion which Dr. Mott
arrives at. In a huge, social organism like London, where
waste and repair are ceaselessly going on, fresh material for
assimilation is provided in the shape of a continually in-pouring
populace, notably from the country. But Dr. Mott believes
* Dr. Mott, Edinhurgh Medical Journal, April 1887.

THE CAUSATION OF DISEASE. 28 1

that the agricultural population itself is dying out. He
adds : ' ' This refreshing influence on town population has
almost reached its limit, and it seems to me that nothing
but a grand scheme of State-aided emigration will serve to
relieve the plethora of our overgrown cities." Now, if the
immigration of country folk has reached its limit, there is no
need of thus relieving our congested towns. As we have
already seen, family extinction proceeds rapidly in large towns ;
and if country and other immigration should cease, the town
population would probably sooner or later begin to diminish.
A fair standard of health is kept up in the suburbs, and it is
from these that the resident population in the more central
parts would, in such a case, have to be replenished. That the
waste would be repaired with marvellous accuracy and celerity
from some source or other there can be no doubt, for fresh
openings would be perpetually recurring, and we know how
wonderfully the balance between supply and demand is kept
up. For my part, I see no reason for believing that the
supply from the agricultural population will fail, for we must
remember that human beings tend to increase in geometric
proportion. But even supposing that it should fail us, are we
to believe that there is no other pabulum to feed the organism ?
There are countless people scattered over the globe who would
soon find themselves in our own great city, for instance, if the
necessary openings presented themselves, and a " grand scheme
of State-aided emigration"' would merely result in a grand
counter-scheme of immigration which would require but little
State-aid.

I cannot, therefore, agree with Dr. Mott when he concludes
that the physiological dissolution which inevitably attends
civilization must necessarily tend to the decay of nations.
Dr. Mott attempts to fortify himself in his conclusion by citing
the well-known fact that every civilization has had its growth,
arrest, and decay ; but has this decay always, or even ever,
gone on, pari passu, or with the growth, arrest, and decay
of the physiological unit, viewed in its physical aspect ?
Can we trace the decadence of past civilizations to such
physiological dissolution? Kather shall we find its origin
in an intricate web of causes — political, social, economic,

2 82 THE CAUSATION OF DISEASE.

religious — an origin clue in large measure to the subtle play
of the human mind — and what will determine the decay of our
English nation — if decay there must be — will assuredly not
be any change which the physiologist can point to, but one
belonging to the region of social and political economics.

To sum up : — We have seen in the last chapters that direct
equilibration (the operation of E upon S independently of
selection), indirect equilibration (natural selection or survival
of the fittest), and sexual selection are all operative among
civilized men, though in varying degree.

No doubt Herbert Spencer is correct when he tells us that
natural selection does not play such a potent part in modifying
structure among the higher orders of animals as among the
lower. We must, nevertheless, not neglect the part played by
it, and from the pathological point of view I venture to think
that its operation is still of the utmost importance. In order
to realize adequately how important a part natural selection
has taken in the evolution of our race, we must bear in mind
that each one of us has an ancestiy stretching far back into
the dim past, through countless generations of life growing
ever simpler till the unicellular protoplasmic unit is reached,
and that each individual in this long chain has successfully
contended against many competitors — has varied in the right
direction. The mind fails to grasp the number that have
been unable to struggle against the conditions of their E, and
the enormous destruction of life the operation of natural selec-
tion has entailed. The present population of the world is as
nothing compared with what it would have been had no pro-
cess of elimination taken place, always supposing (what is, in
fact, impossible) that evolution could have taken place at all
without such elimination.

And as it has been in the past, so it is now. Natural
selection is not so active among civilized, as among primitive,
communities, a fact which the rapid increase in the population
of many civilized countries at once attests. Nevertheless, now
as always, individuals are born who are incapable of coping
with their E. Often enough — indeed, only too often — the E is
a necessarily fatal one — destroying ruthlessly, no matter how

THE CAUSATION OF DISEASE. 283

strong and vigorous the body : but over and above such neces-
sarily-fatal-E's, there are numerous forms of E which, while
they induce disease in many, have not power to hurt all, or, if
capable of hurting, are incapable of destroying all. To such
E's adaptation is obviously possible by a process of natural
selection, and in this way numbers are carried off by rheu-
matism, heart disease, tubercle, and similar disorders, induced
by conditions which have no power to harm their more for-
tunate brethren. Such unlucky variations are, no doubt, often
enough the result of ancestral mal-E, but not necessarily, for
an individual may so vary as to become unduly susceptible to
some contagia — for instance, the tubercle bacillus, or other
similar agents incapable of working harm on the average
healthy individual — even though he and his more immediate
ancestors have been sound in body and healthy in mode of life.
The like is true of many diseases. Wherefore unfit variations
must necessarily occur from time to time under the most
perfect hygienic system, and a fortiori, under that quantity of
mal-E which is the common lot of all — the necessarily-mal-E.
Whatever, therefore, the far-off future may bring with it in
the way of hygienic advance, disease must ever remain a neces-
sary evil ; and, although much improvement will unquestion-
ably take place, let us bear in mind that the instability of E
will certainly tend to increase with the steady progress of
evolution, and that this instability is a great check to perfect
adaptation, whether affected through natural selection or
otherwise.

PART III.

CHAPTER I.*

The Distinction between a "Natural " and an " Artificial Environment."

We have seen that an adaptation, both personal and racial, is
continually taking place to the E obtaining in civilized com-
munities, and that this adaptation consists in a structural
change. We have further seen that man obtains an ever
stronger and more complete control over his E as evolution
advances, for it becomes more and more the result of complex
mental operations. Already this control has reached a high
pitch, and civilized man has surrounded himself by an E which
differs widely from the comparatively simple E of a primitive
community. The former is usually spoken of as an " arti-
ficial " E, the latter as a " natural " one ; and it is necessary
for us to ask ourselves if there is any fundamental difference
between the two, for it is very certain that, as time advances,
the E will tend to become more and more artificial, and the
question arises : What effect will this have upon the health
of the race ?

In our study of this point we had best direct our atten-
tion to one or two very highly artificial forms of E, and the
conclusions which we shall arrive at concerning them will be,
a fortiori, applicable to less artificial E's.

Practical surgery constitutes a highly artificial order of E.
A patient suffers, let us say, from ovarian cyst, strangulated
hernia, or stone, from any one of which diseases he must

* In some of the following chapters the reader will find here and there a
repetition of what has gone before. This is notably the case with the chapters
on " Normality of S and E," and on the " Origin of Cancer." I shall be par-
doned, I trust, for these repetitions, since they tend to emphasize points which
seem to me important.

THE CAUSATION OF DISEASE. 285

needs die unless placed under proper surgical treatment. The
surgeon stands in the relation of a specific form of E to such
a sufferer, who, if he be placed amid the artificial E created
by surgical skill, may be, practically, always rescued from
otherwise certain death. Delivery by forceps and the arti-
ficial rearing of iufants are other modes of artificial E : upon
them, indeed, the lives of many children depend.

The physician occupies a similar position to the surgeon,
and, although he cannot claim such rapid and startling results,
there can be no doubt that numbers come safely out of
illnesses, which, but for his skill, would necessarily destroy
them ; delicate children also are frequently, by a careful regu-
lation of the E, enabled to survive.

In like manner, many domesticated animals are wholly
dependent upon the artificial E supplied to them by man ; for
instance, some kinds of camel cannot be brought into proper
sexual connection without man's aid, and bees may become so
vitiated in instinct by artificial treatment as to be absolutely
dependent upon the help of man.

Now, what effect upon the race has the interference of the
doctor ? It is manifest that the process of elimination is
checked, and the amount of disease thereby increased ; for not
only are diseased individuals kept alive, but they are enabled
to rear offspring to inherit the like diseases. Thus, while
benefiting the individual, we help, as we have already seen, to
cause racial deterioration.

I am careful to say, " help to cause racial deterioration," for
it will be presently manifest that these artificial checks to
natural elimination need not in all cases have such a result.
We must first, however, answer the question : Is there any
intrinsic difference between a highly artificial form of E and
so-called " Nature " ? We will take as an instance that most
highly artificial E — surgical skill. Given this E, then ovarian
cysts, vesical calculus, and strangulated hernia are compatible
with life ; wherefore it follows that the human race might
persist, even though these diseases became universal, provided
the necessary surgical skill were at hand. Hence whereas
S -I- natural E = death in some cases, S + artificial E would be
consistent with continued healthful life. If, then, all indi-

2 86 THE CAUSATION OF DISEASE.

vichials were afflicted with one or other of these diseases, the
surgeon would become as necessary a part of man's E as oxygen,
and, under the artificial E supplied by him, the human race
might continue to flourish in undiminished vigour. Perhaps I
ought not to include stone under these remarks, since this
disease is not a local one ; but the other two, strangulated
hernia and ovarian cysts, are strictly localized, and from
either of these an individual may suffer, and yet be in all
other respects perfectly healthy. Indeed, the race is already
being modified by the artificial E of surgery in the manner
indicated, and not necessarily for the worse. Through untold
ages there has been a destruction of individuals suffering from
ovarian cysts and strangulated hernia, and a survival of those
only who are not afflicted with these diseases ; but the process
of elimination being now checked, the number of afflicted
individuals is necessarily increasing, and yet, since the neces-
sary artificial E in the shape of surgical skill is at hand, with
no necessarily deteriorating effects on the race.

In like manner, it is theoretically possible for the mother
and infant to become permanently modified by the continued
use of the forceps. Such an artificial mode of delivery, carried
on through many generations, would necessarily lead, through
disuse, to diminished expulsive power of the womb, so that, in
course of time, delivery would become impossible without arti-
ficial help. The number of cases of post-partem haemorrhage
would probably be increased for a time, but a proper adapta-
tion to the new order of things would assuredly occur through
natural selection, and that, too, very possibly, without any
racial disadvantage, for the children, in their turn, would
become permanently adapted by a survival of those best able
to withstand the evil pressure-effects of the forceps. I am
not, of course, contending for an indiscriminate use of this
instrument ; any such adaptation as I hint at could only be
effected after a terrible sacrifice of women and children. I
merely wish to show that a perfect adjustment between the
S and such a highly artificial E might, in the end, result.

The same line of argument applies to the artificial rearing
of children. The time may come — nay, I almost believe it will
come — when the mammas of woman shall have disappeared, and

THE CAUSATION OF DISEASE. 287

when all infants will be reared by hand. Mammary atrophy
is, I believe, already taking place among the npper classes.*
There is nothing to make it impossible that infants should,
by a terrific weeding-ont process, become thoroughly adapted
to artificial feeding, those only surviving whose digestive
organs varied in the direction of being able to digest arti-
ficial food.

Yet another instance may be given. The teeth of many
nations appear to be undergoing rapid degeneration, so much
so, indeed, that some have supposed that man will eventually
be a toothless animal, requiring, as a matter of course, artificial
teeth for mastication. Now, although I have my doubts as to
whether this will ever happen, I do not for a moment doubt
that it could happen, and, under these circumstances, it would
appear as natural to wear artificial teeth as to wear boots, or to
eat with a knife and fork.

From the above instances, it is obvious that a race may
adapt itself to certain most highly artificial forms of E. I say,
certain of them, not all ; for many forms of artificial E are, as
we have seen, necessarily fatal — that is, quite incompatible
with racial existence.

Now, the fact that perfect adaptation to artificial forms of E
is possible, raises the question, Is there any fundamental dis-
tinction between a so-called " natural " E and an M artificial " E
to which adaptation has already occurred ? There is a strong
tendency to the belief (such is my experience) that as civi-
lization advances, and men live more and more artificially, they
must necessarily degenerate, and the ground for the belief is
that they do not lead "natural lives." But when we reflect
that natural selection is playing a conspicuous part among
civilized men, a doubt at once occurs as to the truth of this
assumption. For, viewed in the light of evolution, it is
obvious that the ' ' artificial " E does not stand in any broad
antithesis to the " natural " E (say that of the savage), or what
would be vulgarly called Nature. There is nothing intrinsically
peculiar in the natural E, since it differs for the different orders
of brutes, each species of which inhabits its own particular E,

* It is quite possible, though not probable, that the mamma; will be retained
through sexual selection, even though their secretive function be lost.

2 88 THE CAUSATION OF DISEASE.

an E to which, in the course of ages, it has become adapted.
This harmonious working between each individual and its
specific E is the outcome of personal adaptation and natural
selection — of direct and indirect equilibration. What may,
therefore, be termed the natural E of an animal is that E to
which, in the course of ages, it has become adapted. Now the
human race is adaptable to certain forms of artificial E, and
wThen, by natural selection or otherwise, perfect adaptation to
any artificial E is effected, that E becomes in its turn quite as
" natural " as the E of the savage. A savage, if he understood
his relation to his comparatively near relatives, the apes, would
no doubt think his E very artificial as compared with theirs.

To sum up. the only criterion of " naturalness " is the degree
of adaptation ; perfect naturalness means perfect adaptation,
and thus it may well be that an E wThich we regard to-day as
highly artificial — such, for instance, as the artificial feeding of
children — will in the future come to be looked upon as quite
natural.

Although I have frequently used the term " artificial " E, I
have not yet attempted a definition of it. The best definition
I can give is : u An E determined by an elaborate reason." If
we did not qualify the word " reason " in some way, it would
follow from the definition as it would then stand that the E
of the most primitive savage, and of many of the higher
animals (I exclude the domesticated animals) wTould come
under the head of artificial E's. The definition is, however,
very imperfect, from the fact that " elaborate " is, in common
with most epithets, a comparative term, but, in truth the case
admits of no better, inasmuch as " artificial " is also compara-
tive, and the thing to which it is attached, therefore, does not
admit of an absolute definition.

As wTe ascend the scale of life, we find the enviro-regulating
apparatus becoming more and more complex. Starting as a
simple, undifferentiated nervous system, it passes through the
successive phases of reflex mechanism, conscious reflex
mechanism (or simple instinct), and finally, reasoning reflex
mechanism, the latter obtaining only in man and the higher
brutes. And, side by side wTith this growing complexity of
the E -regulating system, there is a corresponding increase in

THE CAUSATION OF DISEASE. 289

the complexity of the E. Now, remembering our criterion of
naturalness, when are we to say that the artificial E begins
and the natural E ends ? The E of the ape-like man, as we
look back and try to realize it, appears very artificial as com-
pared with that of his more primitive ancestors ; that of the
savage, again, highly artificial as compared with the E
of the ape-like man, and our own stands out as yet more
highly artificial compared with that of the savage. Yet to all
there is, or has been, adaptation ; and since the extent of the
adaptation determines the degree of the " naturalness," the
limits of what can be termed artificial E become more and
more restricted. The same line of argument might be pursued
in respect of any member Or section of a civilized community
having increasingly complex E's ; and, viewing the matter
thus, it becomes yet more evident that there is no sharp dis-
tinction between a natural and an artificial E.

CHAPTER II.

What constitutes Normality in Structure and Environment — Definition of
Health— Test of Healthy Interaction — The Actually and Potentially
Normal — The Inevitably Abnormal — Justification of the Term Resistance
as Applied to Disease.

In treating of life we have to make a distinction between
(a) the organism, and (b) its environment. If each of these be
properly constituted an inter-action takes place, and there is
healthy life. If S be normal and E be normal, S 4- E will
represent a set of material conditions which will inevitably
issue in healthful vital action.

I say, if S and E be normal ; but is it possible to define a
normal S and a normal E ? Is there a criterion of normality
of S and E — a fixed standard capable of rigid definition ? The
answer is certainly iVb, although we are somewhat apt to
assume one.

What, then, is to be understood by a normal S or a
normal E ? In answering this question the great fact to be
borne in mind is that it is quite impossible to define either
without reference to the other. Life being a two-sided pro-
cess, of which the one side is represented by S and the other
by E, we may say that when S + E results in healthy inter-
action, both are normal ; each is normal as regards the other.
But if S + E results in morbid action, both are abnormal ;
each is abnormal as regards the other.

This position will, I believe, shortly be rendered evident,
and meanwhile we must ask what constitutes healthful inter-
action of S and E. The reply is that a condition of S and E
which will permit life to go on without the slightest pain,
and with the fullest possible enjoyment of it, until death
occurs through sheer wear-out, represents the ideal of health.
In such a case both S and E are perfectly normal. On the

THE CAUSATION OF DISEASE. 29 1

other hand, if there is any peculiarity of the one or of the other
which shall lead to pain, or shall cut short by a fraction of
time the full term of life, the inter-action is morbid, and S
and E are abnormal.

But another question arises — Can we always be certain that
the inter-action is healthful ? Can we always assert con-
fidently that a particular E is not working an injurious influ-
ence upon the body ? I think not, for a long time may be
required to render the evil obvious. An individual, for instance,
indulges for many years in alcohol, not, apparently, to an
injurious extent, for he seems to enjoy good health. Suppose,
however, that, as a result of such indulgence, his life is
shortened by never so short a time, it is obvious that, though
no evil effect has manifested itself concomitantly with the
indulgence, the alcohol has nevertheless all along been operat-
ing injuriously. Perhaps in such a case we should be able,
on close scrutiny, to detect distinct evil results, such as
morning headache, occasional indigestion, or what not ; but on
the whole it is doubtful whether the insidious effects would
indicate themselves at all at the time. Few, I think, will deny
that an injurious E may work altogether silently and unper-
ceived. We may take as another instance the case of a man
living in London under the most healthy conditions which he
can command, and enjoying in his own belief, and, indeed, to
■all appearances, perfect health ; he dies, let us suppose, from
causes more or less natural, at the age of seventy. Now, it
may well be that, had this man spent the latter years of his
life in the country, he would have lived five years longer than
he did in London, in which case there could not have been
perfectly healthy inter-action, as we have defined it, in London,
in spite of no indication to the contrary.

But although it may not always be easy to say whether
healthy inter-action between S and E is taking place, such
inter-action, however imperfect our estimation of it, is the only
criterion of normality of S and E.

It must not, however, be supposed from the above remarks
that there is no such thing as an absolute and inevitable
abnormality of S and E. The following statement sums up
the whole truth respecting normality of S and E.

292 THE CAUSATION OF DISEASE.

If the S is so constituted that healthy vital inter-action is im-
possible under any conditions of E, that S is absolutely and
inevitably abnormal ; and conversely ', if an E is such that no S
can respond healthily to it, that E is absolutely and inevitably
abnormal. But if a set of conditions exists in which the S can
act healthily, that S must be regarded, as possessing, at all events,
a potential normality ; and conversely, if there is a set of condi-
tions to which some individuals are capable of responding healthily,
that E is normal to them.

In order to show how normality of S and E can only be
considered in relation to one another, let us take, again, the
instance of a coloured tribe living healthily in an ague-
stricken district. Here S + E results in perfect health, and,
therefore, both are normal — the S on the one hand, and the E
(including the ague poison) on the other ; for this being in-
capable of striking disease into these black people, it is not
abnormal to them, and therefore must be normal. Let us
further take the case of a .number of white men living healthily
amid an ordinary civilized E — say, in England. Here again
both the S and the E are normal — health being the criterion
of normality for each. But now let the white and the black
change places : the former would quickly sicken in the ague-
stricken district, and the like would in a large degree be the
fate of the black suddenly transplanted to a civilized E. The
black might, with some show of justice, exclaim : " These
white men are unhealthy creatures, for they sicken and die in
this district where we thrive so well ; " while the white, with
equal justice, might retort : "You blacks are poor, sickly,
unhealthy creatures, for you rapidly sicken under this healthy
E of ours." Hence this paradox — the structure of each is
both normal and abnormal ; each is normal to its own par-
ticular E, but abnormal to the other. The clue, as I say, to
the situation is this : normality of S has no meaning by itself,
and can only be considered in relation to E. Every individual
who can live healthily in a particular E is structurally normal
as regards that E, and there is no fixed normality for all. The
same is true of the several forms of E. E must always be
considered in relation to S, and any E is normal to a par-
ticular S if it permits that S to live healthily amid it. Thus
an ague-engendering E may be normal to some, but virulently

THE CAUSATION OF DISEASE. 293

abnormal to others, and this is true of many other similar E's.
Many individuals, for instance, are incapable of being in-
juriously affected by the poisons of the specific fevers, and, so
far as such individuals are concerned, the presence of these
around and about them does not constitute abnormality of E.
Who knows, indeed, how many unseen agencies there may not
be about us, which, in days gone by, were capable of working
great ill upon our race, but which, by adaptation through the
course of long ages, have come to be quite innocent — agencies
which once constituted an abnormal E, but which are now
quite normal. And what is true of the poisonous products of
micro-organisms is doubtless true of innumerable simple forms
of E. The homely saying, ,: What is one man's meat is another
man's poison," bears witness to the truth of this. To some,
for instance, ordinary quantities of alcohol are quite harmless
— nay, they may even be beneficial ; to others — e.g., the rheu-
matic and gouty — they are actually poisonous. In the first
case, S and E permit the vital processes to proceed healthily :
each is normal as regards the other. In the second case,
unhealthy action results : each is abnormal as regards the
other.

Let us now turn to some of the more complex forms of E.
Those of which we more particularly spoke just now are of
the simplest kind, consisting, in fact, of a simple agent —
namely, some animal or vegetable substance. The E of an
individual, however, consists of the sum total of influences
(mental and physical) operating upon him, and hence it follows
that E is infinitely complex and diverse. A long chapter
would be needed to illustrate the complexity and diversity of
man's E. My purpose, for the moment, is to call attention
once again to the diversity of E in a civilized community more
especially. In a primitive community the E is very much
alike for all, but as the division of labour proceeds in the
social organism, we have in the same community a multiplicity
of environments, for each separate occupation has an E peculiar
to it. It were a long task to tell in detail how the E's of
particular occupations differ, but it will be readily granted that
they do differ. Compare the surroundings of the soldier,
sailor, scholar, peasant, miner, butcher. The great difference

x

294 THE CAUSATION OF DISEASE.

of E in each of these cases is manifested by the special and
peculiar way in which these several occupations mould the
individual. Who cannot discriminate between a soldier, a
sailor, or a butcher, and that not only by the outward mould-
ing of the body, but, if opportunity for observation offers, by
the inward and more subtle moulding of the mind ? Now if
we take E to represent the entire environment of any one of
these occupations, and if the inter-action of S and this E result
in health, the E of this occupation may be regarded as normal.
A large number of occupations in civilized societies are neces-
sarily injurious, and nothing could make them otherwise ;
indeed, it maybe said of very many (I believe, of the majority),
that they are necessarily fatal, if not always to the first gene-
ration, yet certainly to the second or third ; and it would be
well for us boldly to acknowledge the grim fact. Neglect-
ing, however, those occupations in which S and E cannot, by
any possibility, work healthily, and considering only such as are
compatible with perfect health, we shall still find among indi-
viduals, who yet would be accounted healthy, a considerable
difference as regards their normality to their respective E's. This
occupation might especially suit one individual ; that, another.
An individual leading, as a brain worker, a comparatively
sedentary life, attains, let us suppose, a ripe old age ; but it
is very possible that early death might have resulted if he had
followed the laborious occupation of a navvy ; and on the
other hand, there may be many an old and healthy workman
who would have died early had a sedentary, scholastic career
fallen to his lot. The workman who attains a ripe old age
might, for instance, under an inactive mode of life, develop
kidney disease, while the brain-worker might suffer from
aneurism or hernia had his life been one of muscular labour.
Of course, there are many who, provided they observe the
ordinary laws of hygiene, would reach old age in any occupa-
tion, but it is none the less true that individuals differ greatly
in their power of living healthily in different employments,
even though they studiously regulate their lives according to
those laws.

What is true of the physical side is true also of the mental
side of man. Many miss their vocation in life, and un-

THE CAUSATION OF DISEASE. 295

happiness and failure result, while success and happiness
might have been theirs had they chosen the right calling.
In the former instance we may justly say that the mental S
and the mental E are abnormal to one another ; in the latter,
normal.

The following passage from the pen of one who had a deep
knowledge of human nature and its workings, so thoroughly
embodies this idea that I venture to give it in cxtenso : —

" Some of my amiable readers, no doubt, are in the habit of visiting
that famous garden in the Regent's Park, in which so many of our
finned, feathered, and four-footed fellow-creatures are accommodated
wTith board and lodging, in return for which they exhibit themselves
for our instruction and amusement : and there, as a man's business
and private thoughts follow him everywhere and mix themselves
with all life and nature round about him, I found myself, whilst
looking at some fish in the aquarium, still actually thinking of our
friends the Virginians. One of the most beautiful motion-masters I
ever beheld, sweeping through his green bath in harmonious curves,
now turning his black glistening back to me, now exhibiting his fair
white chest, in every movement active and graceful, turned out to
be our old homely friend the flounder, whom we have all gobbled up
out of his bath of water souchy at Greenwich, without having the
slightest idea that he was a beauty.

"As is the race of man, so is the race of flounders. If you can
but see the latter in his right element, you may view him agile,
healthy and comely : put him out of his place, and behold his beauty
is gone, his motions are disgraceful ; he flaps the unfeeling ground
ridiculously with his tail, and will presently gasp his feeble life out.
'Take him up tenderly, ere too late, and cast him into his native

Thames again But stop : I believe there is a certain proverb

about fish out of water, and that other profound naturalists have
remarked on them before me. Now Harry Warrington had been
floundering for ever so long a time past out of his proper element.
As soon as he found it, health, strength, spirits, energy, returned to
him, and with the tap of the epaulet on his shoulder he sprang up
an altered being. He delighted in his new profession ; he engaged
in all its details, and mastered them with eagerness," &c. — The
Virginians, Vol. II. chapter xviii.

This is one of many similar passages which might be taken
from works of fiction, to show what the discernment of the

x 2

296 THE CAUSATION OF DISEASE.

moralist sees to be the evil effects of incongruous, and the
good effects of harmonious, surroundings.

It is not always easy to find out what walk in life will best
accord with the mental proclivities. Some there are who will
adapt themselves to any surroundings, and, like Mark Tapley,
be happy anywhere and under any circumstances ; others,
again, will be always grumbling and unhappy, and these latter
are abnormal, for no mental E admits of harmonious inter-
action with their mental S.

It happens occasionally that an individual will, from an early
age, show a liking — nay, it may even be a passion — for a par-
ticular calling ; such as the profession of engineering, arms, or
music. In some of these cases the voice of inclination speaks
with the loudness and wisdom of an instinct, and its prompt-
ings may safely be obeyed. More frequently, however, these
early promptings are fallacious. How many children have
expressed their determination to be engine-drivers or police-
men ! I remember one boy at school, who, when asked what
he was going to be, always replied, " a philosopher ; " and I
may remark of him that he certainly gave promise of being no
ordinary man, for in him was combined with very extraordi-
nary mental powers, an innocence which was almost infantine.

Many young men are indifferent as to what profession or
calling they follow, and leave others to choose for them ; but
when any special proclivity is displayed, it is not only unwise,
but morally wrong, to thwart it ; for by so doing we are
shutting out the individual from that E to which he is by
nature adapted, which is, in fact, normal to him. Let us not
try to make a round peg fit a square hole.

That normality of S and E can only be considered in the
relation of the one to the other is well shown by allowing indi-
viduals following very opposite kinds of employment to suddenly
exchange places. Let, for instance, two healthy individuals, one
a brain-worker, the other a muscle-worker, change places — a
learned professor, let us say, with a navvy, — and it is quite
needless to recount in detail the ill effect on each. We can
imagine the evils which would result from the sudden strain
on the heart and vascular apparatus of the one, and the multi-

THE CAUSATION OF DISEASE. 297

tude of functional troubles which would be entailed upon the
other, compelled, as he would be, to sit for hours together
over a book ! If he were a man of nervous temperament,
he would probably go mad. Yet had these two individuals
from the first followed each the other's occupation, it is
very possible that each would have become adapted to it ;
and this leads to the distinction between actual and potential
normality of S in relation to a particular E. By an " actual
normality " of S, I mean existing normality of S, to a particu-
lar E — admitting, that is, of harmonious inter-action with it ;
by a "potential normality," a capacity to become normal to it.
The process by which such normality is attained is none other
than personal adaptation (= direct equilibration), so that, from
the medical point of view, we may define personal adapta-
tion or direct equilibration as that process of structural alteration
by ivhich an organism becomes capable of living healthily in a
particular E. Perfect adaptation of S to E constitutes normality
for both, and there is not normality of either until this occurs.
During life there is a continual struggle towards a perfect
adaptation of the S to the E by which it is surrounded, that
is, the S is continually striving to become normal as regards
its E, and this adaptation occurring during the brief span of
human life is but a part of that grand scheme of adaptation
which underlies the whole process of organic evolution.

Thus it is that a man who works chiefly with his brain,
who uses his muscles but little, becomes gradually adapted
to his mode of life — the muscular system, including the heart,
sinks to the level of his inactive life, and the nutritive,
nervous, and muscular systems all act in harmony. The
change is a work of time. Few individuals take naturally to
long hours of reading and muscular inactivity, and, indeed, all
school work is for the most part forced ; but by degrees the
power of attention is acquired, till what was once effort
becomes ease — nay, till what was at first, perhaps, actually
injurious, becomes beneficial — till books and thoughts are as
so much food for which the mind craves, and without which
life were a misery. The individual, in short, grows into
harmony with his surroundings : the S and E, at first abnormal,
become normal. So again with the muscle-worker : his tissues,

298 THE CAUSATION OF DISEASE.

by long exercise, are hardened and strengthened to work
against gravity ; the mind, never awakened into full activity,
soon becomes adapted to the narrow world in which it lives,
and is happy therein. What wonder, then, that if two such
individuals could exchange places, there should be terrible
commotion, and, it may be, actual disease !

In order to test the potential normality or adaptability of
a particular S to a particular E, the exposure to that E should
be as gradual as possible, to allow time for a gradual altera-
tion to the structural state normal to it. By suddenly altering
the E we do not test the potential normality, but the actual
normality to it at the time of change. The truth of this is
manifested in training for athletic feats. If a man who for
many months has been sitting at a desk, suddenly attempts to
climb a mountain 10,000 feet high, or to run 100 yards at full
speed, nothing but disaster can result. Think of the sudden
strain put upon the attenuated heart-walls and delicate valves !
Put scientifically, the essence of training is the compelling
the heart, valves, arteries, and muscular system to gradually
undergo their maximum physiological hypertrophy.

And, indeed, to bring out the total potentiality of adapta-
bility, much skill is required, and the physician is often called
upon to exercise it. He, too, has to train the body ; he has
to modify the delicate S, to convert potential normality into
actual, and thus, by a very careful process of education, to
adapt a weak tissue to its E. Thus, a nervous system here-
ditarily weak may, by skilful treatment, be so strengthened
during the period of development as to be rendered practically
normal as regards an average external-body -E. Such training,
however, requires the greatest skill, and we have probably not
yet acquired a tithe of what we may one day hope to possess.

From the above considerations, it is clear that the whole
question of normality turns upon the healthy inter-working
of S and E — that health is the only real criterion of normality.
Is an individual healthy ? Then are his S and E both normal.
But there is no fixed, unalterable standard of normality for
either. Each can only be considered in relation to the other.
Is there, then, no proximate standard ? We may, in truth,

THE CAUSATION OF DISEASE. 299

construct such a proximate standard, and it is more or less
necessary to do so, but let it be borne in mind that it can be
no more than a ''proximate'*' standard. The simplest way to
erect one will be by constructing a theoretical standard E ;
having done this, our task is completed, for a normal S may
then be defined as one which interacts healthily with such a
standard E. We might, indeed, attempt the definition of a
normal S first ; the standard E would then be one which would
allow such a normal S to live healthily in it. But it is far
easier to begin with the E, for, complex though it is, it is
infinitely simpler than 8.

We have seen that individuals differ enormously in their
response to different modes of E. Now we can, in theory, so
narrow the E as to exclude all that which is capable of
working ill on any individuals, and to include only that
which shall have a beneficial action on all. In order to do
this we must contract it to the narrowest limits, including
in it, indeed, only the positive essentials to life, such as food,
warmth, air, and so forth, and excluding every non-essential.
But, even with such restrictions, how are we to fix upon the
standard diet, temperature, and atmospheric conditions ?
Different races, and, moreover, different individuals, differ
much in respect of the kind of food best suited to them, and
a like difference obtains in regard to climate. Wherefore
this, our standard E, can be proximate only, and further, it
is theoretic only : it would be quite impossible to obtain such
an E.

Then as to S : as I have said, we may regard it as at least
potentially normal if there exists anywhere an E in which
healthful inter-action with it can take place. Thus, according
to Salter, there is probably no case of true asthma but might
be cured by residence in some particular part of the earth ;
hence, such a place must be regarded as normal to the asth-
matically-inclined S, and the latter normal as regards it. It
may be thought that it is absurd to regard an individual
prone to asthma as structurally normal ; but, if we push the
matter to its logical conclusion, there is no escaping this
result.

Nevertheless, for ordinary purposes, the be&t test of nor-

300 THE CAUSATION OF DISEASE.

mality of S is the capacity of the S for living with a fair
measure of health in an average E. It is, as a matter of fact,
impossible to pass through life without being exposed over and
over again to an E which is abnormal to the vast bulk of the
community; every individual must be exposed to a certain
quantity of "necessary mal-E," and in our conception of
normality we must take into consideration the power of suc-
cessfully battling against this — the quality (if I may so put
it) , of being affected in a small degree by it, or of readily
recovering from the diseases which it causes. And here the
element of constitutional vigour comes into consideration. If
a weakly individual could live under a carefully regulated E
to extreme old age, he would not, in the ordinary sense of
the word, though yet he would in one sense, be regarded as a
normal man, for he would be incapable of successfully battling
against the " necessary mal-E " — against, namely, the average
quantity of mal-E.

This leads us to consider an expression which is often used
— "resistance to disease." During life the body possesses a
power of resistance, " so that exposure to noxious agents of
various kinds does not always, or usually, result in the mani-
festations of disease. In this way must be explained the
escape of many from what must be regarded as very serious
risks." In a limited sense, we are justified in speaking of
" resistance " to disease ; but if an individual continually escape
unhurt by a so-called noxious agent, it is, perhaps, more
correct to say that such an E is not abnormal to that indi-
vidual. We should be no more justified in speaking of
" resistance " in such a case than of endowing an ordinary
individual with a resisting power to the asthma-exciting influ-
ence of ipecacuanha. When, however, a person in full bodily
vigour is proof against the evil influence of a particular germ,
but falls a ready prey thereto when exhausted from any cause,
then we may conveniently speak of the natural vigour of the
body affording resistance to the evil effects of the specific
poison. Unless we are careful, however, this word "resist-
ance " may lead us into error. Let us, for instance, consider
the following remarks : —

" We are all of us habitually doing many things, living under

THE CAUSATION OF DISEASE. 301

various conditions, not altogether good for us ; yet, at least through
a long series of years, if we do not trespass beyond certain limits,
no apparent harm comes of it. And this should form part of the
answer to be given to the very frequent inquiry whether this or
that thing is wholesome or injurious. Many of these things are not
strictly beneficial, but the contrary; and yet, in moderation, they
may be indulged in, because, during life, there is a power in reserve
which enables us to cope with these comparatively insignificant
effects, and to overcome them again and again, without, for the most
part, any permanent injury. Take the case of alcohol. It is diffi-
cult to show that there is any advantage whatever in its habitual use
by a healthy man ; and yet it is equally difficult, in most instances,
to demonstrate any evil effect from moderate indulgence in it

through lifetime. Or, take the instance of tobacco That the

influence of these habits is rather injurious than otherwise to most
men, is suggested by the fact that when an effect appears at all it is
usually on the side of evil. But the explanation of the impunity
with which these and other practices are indulged in is probably to
be found in the fact that, in most of us, there is a power in reserve
— analogous, perhaps, to that of repair in the case of wound or
injury — by which mischief is, in great degree, resisted or overcome.
Yet, withal, it must be borne in mind that various habits may work
much evil in the long run, without the relation of cause to effect
becoming at any time apparent" — Introduction to " The Book of
Health," by W. S. Savory.

Here Mr. Savory assumes a power of reserve by virtue of
which the body is capable of resisting more or less effectually
certain nocuous influences. I am more inclined, however, to
regard a particular agent as nocuous or innocuous in respect of a
particular individual only. Mr. Savory assumes that alcohol
and tobacco, even in small quantities, are injurious to every
one, but that the body possesses a "reserve power"' capable of
fighting against their ill effects. According to my view, each
man is a law in himself as regards the influence of any specific
E — e.g., alcohol and tobacco — upon him : a quantity of such E
that to one might be injurious, might to another be quite
harmless — nay, even beneficial. I say, the thing is either
doing him injury, or it is not ; and if it is not doing him
injury, I see no occasion to call upon any reserve power. In
those cases where alcohol and tobacco — notably the former —

302 THE CAUSATION OF DISEASE.

are taken inordinately, it often happens that no ill effects are
experienced at first ; but this must not lead ns to suppose that
no harm is being done, and that a resisting power is all the
time effectually combating the injurious influence. Suppose a
healthy countryman comes up to London and works on the
Underground Kailway, it may be many years before any evil
effect becomes manifest ; the evil is, however, all along at
work, silently and unperceived. The resistance is only
apparent.

Hence, I maintain that if an individual has the power of
resisting an agent which is universally regarded as nocuous,
we are not justified in assuming a reserve power ; it is better
in such a case to look upon the individual as normal in regard
to that particular agent. Were the capacity of being un-
harmed by such nocuous agents in all cases in direct propor-
tion to bodily vigour, then, perhaps, it would be convenient to
speak of a reserve power, but this is not the case, for a sickly
individual may be less susceptible to a particular nocuous
agent than one of extraordinary vigour, and one cannot sup-
pose such a person to possess a resisting power in the shape
of excess of health, as Mr. Savory apparently assumes. The
explanation is rather this : what is normal to the one is ab-
normal to the other.

CHAPTER III.

To what extent Structural Abnormality occurs during the Actual
Time of Disease.

We have seen that it is by no means easy to say offhand what
constitutes normality of structure. Although it is impossible
to fix any criterion of abnormality available for all, it is
nevertheless convenient to have some sort of criterion, other-
wise it would often be impossible to say of any given structure
that it was abnormal, for we could never be certain that there
might not be an E somewhere in which that S could carry
on its functions normally.

There are two tests whereby to judge of the abnormality.
The first is examination of the structure either with the naked
eye or by the aid of the microscope. We are in this way able
to discover certain structural states which our knowledge of
normal anatomy, macroscopic and microscopic, tells us are
abnormal beyond any doubt. The criterion here is experience.
We should not be justified in regarding any structural appear-
ance as abnormal unless it differed beyond all manner of doubt
from the condition obtaining in the vast majority of ordinary
healthy human beings.

But although by the examination of a tissue we can, in many
instances, pronounce it to be abnormal beyond all question, we
cannot, conversely, be certain that it is normal if we fail to
detect structural alterations, for the tissue may be the seat of
some subtle structural change altogether beyond the reach of
discovery. These remarks apply more particularly to nerve
centres, in which the finest shades of structural change may
mean all the difference between perfect health and serious
disease. They do not apply with equal force to the cruder
tissues — such, for instance, as the connective tissues. If a
practised observer fails to detect altered structure in these, we

304 THE CAUSATION OF DISEASE.

may almost certainly conclude that there is no abnormality ;
and the same may, perhaps, be said of most of the glands. I
suppose, for instance, that, given a perfectly healthy liver, a
skilled observer could with certainty pronounce it to be such.

A second test remains to us — viz., functional efficiency. This,
as we saw in the last chapter, is the great criterion of
normality. We ask ourselves : Do the tissues carry on their
functions properly ? But if we wish to obtain a criterion of
normality for S it is obvious that we must qualify the question,
seeing that individuals differ in respect to different E's. We
must ask : Do the tissues carry on their functions properly
when the body is subjected to a standard normal E ? We
saw, however, that it is no easy matter to determine such a
standard ; that in endeavouring to erect a standard E, the only
plan open to us is to exclude all those forms of E to which
different individuals respond very differently, such as the
ague poison and extremes of temperature, and to include the
bare essentials to life, such as food, air, certain temperature,
and exercise. Given such a standard environment, the
functional test may be expressed as follows : — If the tissues of
the body do not carry on their functions properly under this
standard E, there must be distinct abnormcdity of structure.*

These two methods — i.e., the method of direct examination
of the tissues, and that founded on the observation of functional
efficiency — together afford the most perfect test of structural
abnormality at our disposal.

But although this double method is the most perfect of
which the circumstances of the case allow, it has its imperfec-
tions. As regards the method by examination, it is for the
most part available only after death, and even then an ab-
normality of tissue may escape our most diligent search. And
as regards the observation of functional efficiency, it, on the
other hand, is obviously one that can only be applied during life,
when it is no easy matter, as we saw in the last chapter, to be
absolutely certain that the functions of an organ are going on
perfectly; as a matter of fact, the most serious structural
disease may, quite unknown to us, lurk in an individual, for

* These remarks are subject to the qualifications contained in the last
chapter.

THE CAUSATION OF DISEASE. 305

we often discover in the cadaver marked structural abnormality,
to say nothing of minor structural abnormalities, such as small
atheromatous patches, which may give no evidence of their
existence during life by altered function. I shall presently
discuss the question whether we are justified in regarding all
such minor structural changes as distinct abnormalities.

Having, then, in the above tests, a means whereby an ap-
proximate criterion of abnormality may be obtained, let us now
inquire how far structural abnormality occurs during actual
disease.

It has been over and over again remarked that disease may
result from abnormality of S, abnormality of E, or abnormality
of both. Given any of these, an abnormal inter-action must
ensue. When the E alone is abnormal, we theoretically
assume the S to be normal — that is, normal when the abnormal
E first acts upon it ; the propositions take no account of the
condition of the S during the abnormal inter-action — whether
or not, namely, it retains its normal structure.

In respect of this question, we may divide diseases into two
classes : —

1. Diseases accompanied by obvious structural abnormality
of tissue, as determined by macro- or microscopic exami-
nation.

2. Diseases in which there is no discoverable abnormality
of tissue.

This latter class falls into two subdivisions : —

a. Diseases in which the S acted upon is normal at the time

the nocuous E acts upon it, as may happen, for instance,
in poisoning by opium and in indigestion from a gross
error in diet. The E in such cases is for the most
part a necessarily mal-E — that is, one which would
produce an injurious effect upon all. (I say, for the
most part, because individuals differ in their response
to poisons and indigestible articles of food.)

b. Diseases in which the S is abnormal at the time the

nocuous E acts upon it, as epilepsy, insanity. In these
cases the E calling out the disease need not be a
necessarily mal-E.

306 THE CAUSATION OF DISEASE.

Let us now consider each of these three classes separately.

I . Diseases in which there is obvious Structural Abnormality.
— As an example of these we may instance the inflammations
which play such a large part in disease. In these cases the E
acting upon the S produces obvious abnormality in structure.
Such a pronounced structural change implies disease, but it
must be carefully borne in mind that a distinct and marked
structural abnormality may exist without giving rise to any
symptoms — to wit, patches of atheroma, miliary aneurisms,
deep-seated tumours, and many other gross structural changes.
It would be a great mistake to suppose that disease necessarily
exhibits symptoms, or that the presence of these is the test and
criterion of disease. The symptoms of disease are only the
evidence of it to be got during life, whether by altered function
or otherwise, and that evidence may not be forthcoming ; and
this for two reasons — first, because it is sometimes from its very
nature undiscoverable (as may happen in atheroma) ; and
secondly, because of failure on our part to detect the discover-
able—i.e., that which by a fuller development of human
resource might be discovered.

Be it noted, in respect of such non-symptomatic disorders,
that the potential germ of symptomatic disturbance resides
within them, and further that all such cases are covered by the
definition of disease already given — viz., that it is abnormal
inter- action between S and E. These non-symptomatic
disorders are in a large measure localized — that is, they lead
to a very slight secondary mal-E. In the site of an athero-
matous patch an abnormal inter-action between S and E has
been going on from the earliest date of the disease. It might
be urged that an atheromatous patch, when it arrives at its
final stage of calcification, would not, according to this defini-
tion, constitute disease, seeing that little or no inter-action of S
and E would then be taking place. This is, however, no
cogent objection, for it is evident that there is not taking place
in the particular part of the body where the patch is located
that inter-action of cell and cell-E which constitutes health.
It is quite obvious that, if there is no inter-action at all, there
is interference with proper inter-action.

If, however, exception be taken to this mode of argument,

THE CAUSATION OF DISEASE. 307

then it may be pointed out that, even supposing no abnormal
inter-action is taking place in the atheromatous patch, this
latter may lead to abnormal inter-action elsewhere, by inter-
fering, for instance, with proper vasomotor action, and thus it
still will constitute disease as above defined ; but if it be further
urged that not only need there be no abnormal inter-action
between cell and cell-E in the atheromatous patch, but that no
secondary trouble need follow in other parts, then I reply that
such an atheromatous patch cannot constitute actual disease ;
and, if this be true, it follows that there may he distinct ah-
normality of structure without actual disease. All will acknow-
ledge that this is true of mere anatomical curiosities, such as
horse- shoe kidneys and supernumerary digits ; but if our defini-
tion of disease is accepted it is also true of other structural
abnormalities which do not fall under the category of mere
curiosities, such, for instance, as cases of dried-up abscesses
and fatty tumours, which interfere in no way with the func-
tional efficiency of the tissues. There is ample scope here for
scholastic discussion, but there is no occasion to pursue the
subject further.

2. Diseases in which there is no Discoverable Abnormality of
Structure. — Such diseases are frequently styled u functional "
diseases. A functional disease may therefore be defined as
one in which no lesion is discoverable as a cause.

We shall have presently to inquire whether, in such func-
tional disorders, there is necessarily structural change ; mean-
while, there is something to be said about this term functioned
as applied to disease. It is clearly a bad term, since altera-
tion in function is not peculiar to disease unaccompanied
by obvious structural change ; it very rarely happens that any
gross structural change is unattended by disordered function.
In some few cases, such as those cited above, of dried-up abscess,
fatty tumour, and such like, there may be no functional abnor-
mality, but this is very exceptional, for even if no symptoms
are forthcoming — no evidence of the disorder during life,
whether in the shape of altered function or otherwise — this
does not show that there is actually no alteration of function.
I hold that in almost all cases of gross structural change
there actually is a modification of function ; but whether this

308 THE CAUSATION OF DISEASE.

is so or not clearly depends upon the meaning we set upon the
word function.

The term Function is familiarly used to designate some
obvious purpose which a structure fulfils. Thus, we say the
function of a muscle is to contract ; of a gland, to secrete ; of a
nerve-centre, to start or modify nervous impulses ; of connective-
tissue, to bind together the elements of the tissues ; of a blood-
vessel, to conduct blood. Now, using the term in this sense,
it is obvious that we must make a distinction between the
active functional state of which the first three instances afford
examples, and the mere passivity of which the last two are
examples. It will be quite unnecessary to say anything further
of this latter kind of function ; but it is necessary to say some-
thing of the former kind. Still using the word function in
the sense indicated — i.e., to designate some obvious purpose
which a tissue fulfils — we may define the active function of a
tissue as that part of its activity which is not necessary to its
own vitality, but is displayed for the benefit of the organism
at large. Thus we may regard the secretion of bile by the
liver- cells as apart from and independent of the nutrition or
vital process of the liver-cell : according to this view, the
liver-cell is a machine for the elaboration of bile out of certain
crude materials brought to it, and the process of bile manu-
facture is something quite distinct from the vital process of
the machine or cell itself. In a similar way we may regard
a muscle-cell as a machine for getting force out of the food
materials supplied to it, the process by which the machine is
kept alive constituting its nutrition, that by which it converts
insensible into sensible motion constituting its function.

How far we are justified in thus sharply separating nutri-
tion and function it is difficult to decide. According to the
older views, such functional exercise was the outcome of actual
protoplasmic break-down — e.g., the force spent in muscular
contraction was, it was thought, the result of an equivalent
break-down or destruction of muscle-tissue, and the secretion
of a gland-cell was supposed to take place at the expeuse of
actual protoplasmic destruction. Now, if this view be correct,
it follows that "function" in the sense here used is part and
parcel of the nutrition of the cell, or, at all events, it cannot

THE CAUSATION OF DISEASE. 309

be separated from it. The term nutrition would more particu-
larly refer to the building-up, as distinguished from the
breaking-down, of the cell, to construction as against destruc-
tion (the latter constituting ' function '), but each process
would be essentially bound up with the vitality of the cells.
According to the later view, the muscle- cell elaborates muscle-
dynamite or inogen, the gland-cells elaborate zymogens, and
both are independent of and distinct from the actual fabric of
muscle or gland-cells.

Which of these views is correct, or if either, I cannot tell ;
but this much may be said, that it is certainly convenient to
separate the nutrition or vital process of the cell from its
function, using the latter term as indicated. We can then
explain functional errors by imperfect nutrition of cells, without
presupposing any actual structural change, for, if the nutritive
processes of the cell fabric do not go on properly, the latter
will not be able to perforin its functions properly. I confess,
however, that I am not at all certain that we are justified in
making this distinction between nutrition and function, except
for purposes of convenience. And I have somewhat enlarged
upon the subject in order that the reader may henceforth
attach some definite meaning to the word function, as used in
the physiological sense, for I have nowhere been able to find
any intelligible definition of it.

It may be asked: What is the meaning of "function" as
applied to a unicellular organism ? It seems to me that it here
simply refers to the vital processes of the organism. But in
a multicellular organism some one cell-capacity is exceedingly
developed, or there is an evolution of some new property which
is not actually necessary to the life of the cell, but serves some
purpose in the general economy of the organism, and it is
convenient to speak of this as the function of the cell.

Viewed thus from the point of view of evolution, it is,
in a manner of speaking, impossible to separate such special
property from the vital process of the cell, for it has become
through long practice part and parcel of cell vitality — so much
so that if the cell were not to exercise its "function," atrophy
or degeneration would ensue. It is very probable, for instance,
that if the liver- cells ceased to secrete bile, they would

Y

310 THE CAUSATION OF DISEASE.

degenerate; if they did not, we should, indeed, have the
strongest possible justification for making the distinction
between function and nutrition. It is certain that if a
muscle remains inactive for some time degeneration ensues,
but this may be due to the mechanical effect of muscular
contraction on the circulation in the blood-vessels and lym-
phatics through the substance of the muscle.

With these remarks on function, let us proceed to consider
the part which abnormality of structure plays in the so-called
functional disorders.

a. Functioned disorders, in which the S remains normal when
the nocuous E operates upon it. — I will give two instances of this
kind of disorder. A healthy person takes an indigestible meal
and suffers from dyspepsia ; or, again, he is poisoned by opium,
and in both cases perfect recovery ensues upon removal of
the nocuous E. The fact that rapid recovery occurs
when the hurtful E is removed — that is to say, after
the poison has been eliminated from the body and the indi-
gestible matter disposed of — is sufficient proof that these
disorders are functional. No one would for a moment contend
that there is any gross structural change in either of them.
But the question we have now to ask is, does any undiscover-
able structural alteration attend these disorders ? An ab-
normal E necessarily leads to disordered inter-action of S and
E, but does it necessarily lead to an abnormal disposition of
the cell particles, or of the cells among themselves ? If it
does, this much at least is certain : the change must be a
temporary one, for there is rapid return to health after the
removal of the nocuous agent.

If the disorder continues for some time after the complete
removal of the nocuous E, we are justified in assuming ab-
normality of structure, as I shall presently show ; but in the
cases mentioned there is no such continuance of disease-action.
And here we are met with the old difficulty — what constitutes
normality of cell-structure ? If the structural state of the
cerebral cortex which accompanies pain be considered ab-
normal, we must obviously predicate a lesion for painful
dyspepsia ; and in opium poisoning we are compelled, I think,
to conclude that there is an actual deviation from normality

THE CAUSATION OF DISEASE. 3 I I

in certain cell-structures. In this case, all the positive con-
ditions of healthful cell action (I allude to the tissues primarily
and chiefly affected by the drug) such as the presence of
oxygen, food-stuffs, &c, obtain ; therefore, the opium must
render the S abnormal, otherwise the proper inter-action would
occur. The only alternative supposition is that the drug so
acts upon the cell-E as to render the positive conditions im-
perfect. This, indeed, occurs in some poisons — e.g., CO, which
seizes upon the O needful for the tissues. All those poisons
which do not modify the E so as to render the positive conditions
imperfect, must react upon the cell and modify its molecular
structure, in such a way as to prevent the proper inter-action
of S and E. It is obvious, however, that when rapid recovery
occurs, this molecular dislocation cannot be very serious, and
hence we may practically disregard the existence of structural
change in this class of malady. But if, on the other hand,
the administration of a poison be persisted in for a long time,
or any habit capable of producing functional disorder be
systematically indulged, it is well known that permanent
structural alteration may ensue ; and this fact suggests that
some structural alteration must attend even a temporary
functional disorder.

A large number of the functional disturbances which occur
in what may be called the genuinely structural diseases would,
considered by themselves, come under the class of disorders we
are now considering, such functional disturbances being caused
by secondary mal-E. The faintnessin aortic regurgitation from
the irregular supply of blood to the brain affords an example.
Often the secondary mal-E consists of a poison, as in Bright's
disease, and I have already had occasion to allude to the profound
structural changes and fatal consequences directly traceable in
this disorder to the retention of nitrogenous excreta in the
blood.

h. Diseases in which the S is abnormal when the E operates
upon it. — It is these disorders to which the term u Functional
Disease " is more commonly applied. The so-called " neuroses n
afford the best example of this class. If an individual is exposed
to an averagely healthy E and develops one of the neuroses,
there must be a structural deficiency in some part of the

Y 2

312 THE CAUSATION OF DISEASE.

nervous system, for E being normal, and disease depending
npon an inter-action of S and E, S must be abnormal.

In such cases the structurally deficient tissue may be
limited, and the abnormality may possibly be so subtle as to
be absolutely undiscoverable, but structural abnormality there
certainly is. This, it is obvious, from the definition of struc-
ture already given, may consist in peculiarity in respect of —
a, the arrangement of the atoms into molecules ; Z>, the dis-
position of these latter among themselves; c, the mutual
arrangement of the individual cells into tissues ; and, finally,
d, the mutual connection of physiologically distinct tissues.
Thus, in normal nerve centres there must not only be a proper
structure of individual cells, but also a. proper connection of
these by processes, or what not, into individual centres, and,
further, a proper connection between the individual centres
themselves. We can well understand how a nervous system
might be deficient in one of these particulars without our
being able to detect the deficiency by the most elaborate
search.

A deficiency in any one or other of them constitutes
the lesion in this class of functional diseases, and it exists
before the actual disease is present. The exciting cause
of these pure neuroses leads to an exaggeration of the
abnormality, and the weakness is then suddenly revealed.
This sudden increase of abnormality is certainly of the nature
of molecular change ; its very suddenness, as well as the char-
acter of the exciting cause — e.g., strong emotion (which may
set up epilepsy, hysteria, neuralgia, or chorea), proves this.
A sudden emotion cannot induce alteration in the connections.
of cell with cell, or centre with centre ; it can only lead to an
atomic or molecular commotion. In these cases the centres
immediately affected may be very limited, but eventually,
owing to the mutual connection of tissue with tissue, a large
portion of the nervous system may become involved.

It is worthy of note that the neurosis thus suddenly induced
may last a long time ; indeed, its effects may not wear off
for months. Seeing that disease = an abnormal inter-action
between S and E, it is conceivable that its continuance might be
due to a continuously-operating mal-E, the abnormality of S-

THE CAUSATION OF DISEASE. 313

being in 110 way heightened ; but when the exciting cause
is some shock, sudden, or even, it may be, instantaneous, it
cannot be the mal-E which sustains it. It must, therefore, be
kept up by some permanent alteration of S, and we have
thus actual proof of the important part which mere atomic or
molecular alterations play in disease.

The fact that disease is self-sustaining — that it continues
after removal of the exciting cause — is conclusive proof that
there is a more or less permanent alteration in some tissue or
tissues. Hence, the great test of the existence of a purely
functional lesion is to ascertain whether or not the disease
continues after the removal of the exciting cause and under
a perfect system of hygiene. If it does continue, there must
be some more or less permanent abnormality of S, and the
disease is not purely functional ; but if it does not, it does not
follow that there is no structural alteration whatever, for there
may be a temporary imperfection in cell structure, as in opium
poisoning or in profound exhaustion. When, however, the
functional disturbance is only temporary, we may, as already
observed, disregard the change in S.

Let us take an example. A man is so over-worked and
jaded that he can do nothing for himself. He is suffering
from functional disease, and few would doubt that in such a
case there is serious molecular alteration in some of the nervous
tissues ; but after a few hours' rest and proper food complete
recovery occurs. In such a case the alteration has been very
temporary, and one cannot designate it a lesion, seeing that
the centres have the power of reverting almost at once to
their proper state if they be allowed a fair chance. But if
this over- work be continued for a long period, the centres
may get into a condition which is not curable by a few hours'
rest and proper food ; months of most careful treatment, entire
cessation of work, change of scene, and so forth, may be needful
to effect recovery ; nay, so serious may the disturbance be, that
complete recovery will not occur under the most favourable
conditions. Here, then, we have to deal with a distinct lesion,
undiscoverable indeed, but nevertheless there.

I have spoken much of nerve centres, as though they consti-
tute the tissues chiefly affected in functional disorders, and this

314 THE CAUSATION OF DISEASE.

is indeed the truth. So far as I know, all the purely functional
diseases included in Class b originate in such a lesion of the
nerve centres, for these structures have under their immediate
control the entire working of the body. If an organ presents
no obvious lesion, we may safely reckon upon its healthy
action, provided its nervous apparatus be efficient. On the
other hand, an undiscoverable lesion of this or that nerve-
centre may profoundly modify the E of any cell in the body,
and may give rise to symptoms referable to any organ which it
governs, be it heart, lungs, stomach, muscle, or any other.

CHAPTER IV.

The Advantage of Changed Conditions of Life upon the Vital Organism.

It is a well-established fact that, within certain limits, changed
conditions of life are beneficial to both the plant and animal
organism. This fact has long been known to horticulturists
and breeders of animals. In order to obtain the best results,
the horticulturist takes care to vary continually the soil of
the successive generations of a plant, and breeders of animals
are equally careful not to confine several successive generations
of the same breed to a narrow and fixed locality.*

How are we to explain the beneficial effects thus obtained ?

According to Herbert Spencer, the forces of Nature are
ever working towards an equilibrium. Thus, when a fire
burns, the tendency is towards the arrangement of atoms in
their most stable form. In like manner the aggregated forces
constituting a living organism tend to fall into a state of stable
equilibrium. Such a condition is, however, inconsistent with
vital activity, in which the acting forces, far from being stable,
are undergoing incessant change. By change of E, a new
series of force is introduced, so that the approach towards
equilibrium is for the time checked, and this has a beneficial
effect upon the body processes.

Darwin explains the beneficial effects of changed conditions
of life in a very similar way, and he believes that the neces-
sity for sexual reproduction admits of a like inteq^retation.
We have seen that the whole purpose of sexual reproduction
is to secure the union of two unlike individuals. Such a
union, according to Darwin, tends, by a disturbance of forces,
to check the progress towards equilibrium, in the same manner
as changed conditions of life ; for when the germ and sperm

* See on this subject Darwin, "Variation under Domestication," Vol. II.
Chap, xviii.

3 l6 THE CAUSATION OF DISEASE.

come from unlike individuals, there is a struggle of opposing
tendencies.

Wherefore two important facts regarding man stand out
prominently, viz. : —

1. That advantage accrues from change of E from time to
time.

2. That advantage accrues from the marriage of unlike
individuals.

The above considerations explain the good effects of " send-
ing a patient away." I have been accustomed to associate the
benefit derived from this course with the habit of primeval
man to wander about from place to place. Our ancestors
were nomadic probably for many thousands of generations,
and the wandering instinct is even now strong among us, so
that the human organism is still more or less adapted to a
continual change of locality, and at times actually craves it.
But this explanation, though probably correct so far as it goes,
is only partial. That offered by Spencer and Darwin goes far
beyond it, for it approximates to an ultimate explanation — to an
explanation, i.e., which does not leave anything further to be
explained, cannot be rendered plainer, cannot be referred to
any more general principle.

It is not only in respect of climate that " change " is
beneficial to man. Within proper limits it does good in many
ways. See what a potent influence it has upon the mind !
Most people sooner or later find out for themselves that the
great secret of enjoyment lies in continual mental change — not
necessarily in change between very many things, but in, at all
events, change from one thing to something else.* Indeed,
the mind even more perhaps than the body craves for variety.
This is, at any rate, true of the cultured mind, though the
desired change is not necessarily change of scene. The man of
culture does not need to change his locality in order to get
mental variety : he has never-failing sources of mental diver-
sion in his library, in his acquaintances, in the world arouud
him. But although the mind can thus, as it were, create its

* In reference to the subject of change as a necessary factor in mental pro-
cesses, see Bain's " Law of Kelativity :" Mental and Moral Science. Alexander
Bain, p. 83.

THE CAUSATION OF DISEASE. 317

own diversion, such change does not work the same exhilarating
effect upon it as diversity of external surroundings. It is better
that the change should strike through the senses ; and there
can be no doubt that the good effect of travel upon health
is in very large measure due to change of scene, social sur-
roundings, and general mode of life. Reading, to take the
commonest form of mental diversion, is essentially a subjective
process ; when occupied with it, the mind is largely bent in
upon itself ; the thoughts do not actively go out to surrounding
objects. It is true that by many kinds of reading the indi-
vidual is to a large extent drawn out of himself, but by no
means to the same extent as by actual observation of the outer
world. But if his surroundings are quite new, and at the
same time capable of commanding his rapt attention, then
indeed he becomes self-forgetful, and has little opportunity to
harbour gloomy thoughts, which depress the vital processes
and retard recovery. It is very remarkable what a potent
influence the mind has upon the body. A careful study
of Dr. Tuke's book on this subject will bring this truth
forcibly home to the reader. There are many ways of in-
fluencing mind ; but when our object is to draw the individual
out of himself, there is no method so effectual as that of sending
him away from home, and, by so doing, diverting the current
of his thoughts out of the channel in which they have too long
stagnated. The altered mental state that rapidly ensues reacts
upon the body ; there is increase of appetite, a quickening of
the circulation, better sleep, a rapid improvement in general
bodily health. No doubt such improvement is due in large
measure to the direct effect of changed locality upon the body ;
nevertheless, all will allow that the mental effect of the
altered surroundings often plays a very considerable — in some
cases the chief — share in the process, and it is indeed very
remarkable that those subtle cortical changes which are the
concomitants of thought should be capable of working such
marked effect upon the body — turning the balance, it may be,
in favour of Life or Death !

CHAPTER Y.

Heredity.

I NOW propose to make some further remarks on the subject of
heredity, as we are in a position to form a just estimate of the
extent of its influence in the causation of disease.

There can be no doubt — and I say this emphatically — that
pathologists do not sufficiently recognize the important part
played by heredity in disease. Yet mankind in general, without
seeking for the why or the wherefore, tacitly acknowledges its
potent influence in determining the conformation of mind and
body. In respect of the latter, it has been recognized by
breeders of animals, as Darwin is so careful to insist, since
time immemorial ; and as regards its influence on the mental
portion of our being, we have only to study biographies and
works of fiction to see how well the writers have understood
its significance.

In nothing, perhaps, is the influence of heredity more
manifest than in the evolution of the moral faculty, and
this branch of the subject has been thoroughly discussed
by Herbert Spencer, who demonstrates how the finer shades
of moral faculty have been, and are now being, evolved.
Man being a social animal, it is necessary for him to observe
certain rules of conduct towards his fellows. If lying, and
theft are accepted practices, no social community can exist,
except in an inchoate condition ; therefore, the social community
of which man forms part must be bound together by certain
ties of mutual conduct, such ties constituting "a code of
morality." Generation after generation of men being thus
compelled to observe certain rules of conduct towards one
another, the moral faculty gradually rises into being : it
begins to exist, that is to say, independently of inculcation,
although, of course, capable of being strengthened and

THE CAUSATION OF DISEASE. 319

developed thereby. We first find it existing among the dif-
ferent members of a family — notably, between mother and
child, in the form of instinctive affection ; then among the
different members of a tribe, taking the form of crude laws ;
and, finally, among the different members of a nation. But what
is noticeable is that, at first, there is no sense of any obliga-
tion extending beyond these comparatively narrow limits ; there
is no recognition of the moral tie between family and family,
tribe and tribe, nation and nation. A certain code of morality
among the individuals of each of these aggregations is abso-
lutely necessary to its separate existence, but it is not
equally necessary that any morality should exist between
the separate aggregations themselves. Hence we often find
it altogether absent, and perpetual warfare going on between
them. But just as families have united to form tribes,
and tribes to form nations, and these again to form larger
nations, so, in course of time, we may look for the latter
uniting to form one vast federation ; and then, but not
till then, the obligations always existing between the com-
munities into which mankind naturally falls, will be recog-
nized, and warfare cease. Thus, the conduct of individuals
towards one another must become more and more exact as
civilization advances, and since the moral principles thus in-
culcated from generation to generation leave upon the mental
organization an actual impress which tends to be inherited,
it follows that with progressive civilization the moral faculty
grows stronger and stronger.

Such an evolution of morality rests upon the principle
of heredity. It assumes the capacity of heredity to trans-
mit fine shades of mental alteration, and this capacity has
been, as I observed just now, long recognized by biographers
and writers of fiction. Mr. Henry Drummond points out
how careful the former are to study in detail the working
of hereditary influence. " Students of biography," says he,
'4 will observe that in all well-written lives attention is concen-
trated for the first few chapters upon two points. We are first
introduced to the family to which the subject of the memoir
belonged. The grand-parents, or even the most remote ances-
tors, are briefly sketched, and their chief characteristics brought

320 THE CAUSATION OF DISEASE.

prominently into view. Then the parents themselves are pho-
tographed in detail : their appearance and physique, their
character, their disposition, their mental qualities, are set before
us in critical analysis ; and, finally, we are asked to observe how
much the father and mother respectively have transmitted of
their peculiar nature to their offspring — how faithfully the
ancestral lines have met in the latest product ; how myste-
riously the joint characteristics of the body and mind have
blended, and how unexpected, yet how entirely natural, a
combination is the result. These points are elaborated with
cumulative effect until we realize at last how little we are deal-
ing with an independent unit, and how much with a survival and
reorganization of what seemed buried in the grave." Here the
influence of heredity upon the conformation of both mind and
body is recognized. Mr. Drummond then continues : "In the
second place, we are invited to consider mere external in-
fluences ( = E) — schools and schoolmasters, neighbours, home,
pecuniary circumstances, scenery, and, by and by, the religious
and political atmosphere of the time. These, also, we are assured,
have played their part in making the individual what he is; we
can estimate these early influences in any particular case with
but small imagination if we fail to see how powerfully they
have moulded mind and character, and in what subtle manner
they have determined the character of the future life." Mr.
Drummond, be it noted, speaks only of the mental E, for a
biographer treats essentially of the mental, and only by the
way, as it were, of the physical, man. Innumerable illustrations
of this method might be given. The following will suffice.
The subject is Abraham Lincoln : — " He seldom spoke of his
early life, or of his parents ; but the researches of some of his
biographers have indicated the hereditary sources of his chief
characteristics* We know that the grandfather was a vigorous
backwoodsman, who died a violent death ; that his uncle was a
grim and determined man- slayer, carrying out for years the
blood feud provoked by the murder of his parent ; that his
mother was habitually depressed ; and that his father was a
favourite of both men and women, though a mere savage
when irritated, fond of fun, an endless story-teller, physically
* The italics are mine.

THE CAUSATION OF DISEASE. 32 I

powerful, and hating hard work. Out of these preceding traits
it is not difficult to imagine how the great Abraham came
to be inflexible of purpose and strong of will, though indolent
— why he was good-natured to excess in his excess of strength
— and why he was a great humourist, and, at the same time,
a melancholy man." Having thus traced the hereditary influence,
the writer proceeds to consider the influence of the E. How
often, I would ask, does the pathologist, when investigating
the influence of heredity in disease, in the same way try to
analyse minutely the several ancestral traits ? It must be
acknowledged that it is very seldom. His task, I admit, is
much more difficult, for while the mental traits of an indi-
vidual are obvious, being, so to speak, on the surface, the
same cannot be said of the minute structural characteristics
of his several tissues ; but difficulties should not deter from a
task when great issues are at stake.

Writers of fiction are equally ready to recognize the influence
of heredity. George Eliot, describing Adam Bede, writes :
" He was not an average man; yet such men as he are reared,
here and there, in every generation of our peasant artisans,
with an inheritance of affections nurtured by a simple family
life of common need and common industry, and an inheritance
of faculties trained in skilful, courageous labour."

Seeing, therefore, how thoroughly the influence of heredity
upon the mental organization has been recognized by those
whose close study of human nature entitles them to speak
with authority, it scarcely needed the work of Galton to prove
the inheritability of genius. (I say this with no want of
appreciation of his most interesting book.)

To turn now to the physical side, the prominent part
played by heredity in the causation of disease will be at once
evident if we bear in mind that disease is a morbid inter-action
of S and U, and that S is determined almost entirely by here-
dity. Strictly speaking, every disease from which an individual
suffers is hereditary. Although this may seem to be an
exaggeration, the truth of it will presently be apparent.

We have seen that the offspring is in a large degree the
resultant of many ancestral tendencies, and that, could we only

322 THE CAUSATION OF DISEASE.

guarantee an equality of E, all brothers and sisters would, save
for sexual differences, be exactly alike. All other differences
are, as we have seen, due to differences of E, for E is capable
of modifying S. Let the letter S stand for the structural mean
to which the sons or the daughters of any given couple tend,
and let s1? s^,, and s3 represent the alterations which the
different E's work upon this S ; then Ssp Ss2, Ss3 will represent
the structure of the several children.

Although it is convenient to speak of an inherited structural
mean, such a mean is, be it remembered, entirely ideal,
since it assumes an ideal E, and one which it would be impos-
sible to define scientifically. In attempting the definition of
such an ideal E, all one can say is that it should be as negative
as possible — one, namely, tending to alter the S in as slight a
degree as possible.

The formulae Ss,, Ss„, &c, represent the actual structure of
any individual at any particular period of life — S representing
that part of an individual which is the direct outcome of here-
dity, and s, such modification in it as has been brought about
by E. Now it is important to observe that the nature of s is
very largely dependent upon the nature of S ; I have already
remarked how particular Darwin was to emphasise the fact
that a variation depends more upon S than upon E ; and inas-
much as S, or the structural mean, is strictly the outcome of
heredity, we see what an enormous part heredity plays in
determining Ss, or the actual structure at any given time.

Disease being the abnormal inter-action of the individual
and his E, it follows that Ss + E will express the causation
of any particular disease. Now the nature of Ss determines
whether or not it shall respond pathologically to a particular E,
and therefore heredity must play a large part in the causation of
every disease. Let me illustrate this by a very simple example.
The diversity of diseases among different species of animals
depends of course very largely upon differences of E — for, as
we have seen, every species has its own specific form of E ;
but the chief cause of the diversity is certainly difference of
structure. Thus, a child and a dog are exposed to a distemper-
giving E : the one contracts the malady, the other escapes.
This difference of response is obviously due to differences in

THE CAUSATION OF DISEASE. 323

the Ss ; and since, as we have seen, the Ss is almost entirely
the outcome of heredity, it follows that heredity determines
the disease in the dog. Again, let each be exposed to the
virus of measles : the child will this time contract the disease,
while the dog will escape ; and here again the character of the
response is determined by heredity.

Some may doubt the legitimacy of the above implication,
namely, that measles is hereditary. It is, however, allowed on
all hands that a special tendency to contract the different
specific fevers displays itself in particular families, and does
anyone doubt that this excessive proclivity is inherited ? The
above argument, I think, renders it clear that all cases of
specific fever are hereditary in the strictest sense of the word ;
and if it be thought that this view requires further justification,
let the reader compare any specific fever, say measles, with
tubercle. None will deny that tubercle is hereditary, but
how ? The answer is, by an inheritance of a peculiar
structure (or soil) favourable to the development of the tuber-
cular bacillus ; but let the specific pathogenic E be what it
may, there can be no doubt that a peculiar S is necessary,
and that this peculiarity is inherited. Exactly the same line
of argument applies, of course, to measles.

So much for the influence of heredity in the production of
the specific fevers. There are probably few who will not
acknowledge this influence ; but will they so readily allow that
such a disorder as flea-bite has quite as much of the hereditary
element in it as phthisis ? There is, however, no escape
from this conclusion. Some persons, if exposed to the attack
of fleas, are furiously bitten, and suffer the direst incon-
venience, while others wholly escape, or, if bitten, suifer
little or no discomfort. There is, in fact, a very great
difference between different races and different individuals in
respect of the tendency to be attacked by the different
parasites,' microscopic or macroscopic ; and these differences are
due to Ss, which, as we have seen, is almost entirely the
work of heredity. But if the element of heredity in such
disorders is apt to be lost sight of, how much more likely is it
to be overlooked in traumatic injuries ? In such injuries the
cause resides chiefly in the E, of which the chief element in

324 THE CAUSATION OF DISEASE.

this case is violence. How, then, it is asked, can heredity
play a part in the production of injuries ? I reply, through
the power of S to modify E by means of mind. If an indi-
vidual places himself in the way of receiving injury, then S
must have much to do with the causation, since it is the
S that in this case determines the E. If the injury be such
as it would have been impossible for the individual to avert,
it may be regarded as purely accidental ; but if it be due to
carelessness or recklessness, or love of adventure, the S must
be held largely responsible for the injury ; and all the various
mental characteristics are inherited.* Suppose, therefore, an
individual, through utter carelessness on his part, sustains a
fractured skull — say, from a falling brick-bat — such injury
must, if the carelessness be inherited, which it often is, be
allowed to be an inherited disease. Similarly, an individual
may be seriously injured in the hunting field, and if this be
due to an inherited recklessness, such injury will be clearly
inherited also. The remark applies equally to such a case
as that of that brilliant soldier, Colonel Burnaby, who, impelled
by a love of danger and a dauntless courage, courted death
upon the battle-field ; indeed, the very virtue of a man may
tend to his death, as it did with the martyrs of old and with
the hero Gordon. But do love of danger, courage, or other
virtue arise spontaneously, and independently of heredity ?

Whenever, therefore, an individual suffers disease through
imperfect regulation of his E, and this imperfect regulation is
the result of some peculiar inherited mental organization, that
disease is emphatically inherited. We have already seen that
man is to a large extent the controller of his destiny. His
power of control lies, of course, in his S, and if the control be
defective, the defect is in the S. Such defective control may
lead to multitudinous disasters, for a man can wreck his con-
stitution in a thousand and one ways. As civilization advances
the E of man becomes more and more complex, and greater
skill is needed in order to regulate it properly. Causes of
disease are multiplied. Unfortunately, over a large number
of these the individual has no control, as, for instance, over

* Herbert Spencer remarks, " Awkwardness is continually entailing injuries
and death " (" Principles of Biology," Vol. II. p. 496).

THE CAUSATION OF DISEASE. 325

the rnal-E attaching to many occupations, and in such cases S
is in no way responsible for the mal-E ; nevertheless, there
are manifold mal-E's at hand, which the individual may court
or shun at his pleasure, such as drink and other excesses ;
and the tendency to indulge in these is inherited. It is
generally acknowledged, for instance, that such is the case with
intemperance ; and thus a man may inherit cirrhosis of the liver,
not through any very special tendency of that organ to
undergo morbid change, but through an inherited tendency on
his part to expose himself to an E which has the power of
calling forth this particular disease.

Let us now inquire into some of the reasons which have led
medical men to under-estimate the share taken by heredity in
the causation of disease.

1. It is quite obvious from the above remarks that an in-
dividual may suffer from a hereditary disease, even though none
of his progenitors have ever contracted it. We have seen that
measles is quite as hereditary as phthisis ; but there are, I
take it, isolated tribes of men existing in remote corners of the
earth where the measles bacillus has never spread, who yet
would be highly susceptible to the poison if exposed to it.* Such
would, if attacked, inherit the disease in the strictest sense,
notwithstanding the immunity of their ancestors. From this
conclusion there is no escape if we grant that the inheritance in
measles, as in tubercle, is an inheritance of soil, for exactly the
same argument applies to tubercle. There are, I presume,
some parts of the world where " consumption " has never yet
ravaged, but where the inhabitants, even though free from
a " tubercular history," are susceptible enough to the dis-
order— quite as susceptible, perhaps, as what would be termed
a phthisical family. It is well known that negroes are pecu-
liarly apt to suffer from phthisis when they come to this country,
and we should probably not be beside the mark if we said of
some of them, at all events, that none of their ancestors had
suffered from phthisis, and the same remarks apply to monkeys.

How comes it that the hereditary element is in such cases

* Before the Fiji Islands were placed under English protection, measles teas
unknown there, but shortly after intercourse with the English the disease
broke out in a malignant form.

Z

326 THE CAUSATION OF DISEASE.

overlooked ? It is because when we speak of a disease being
hereditary, we have in mind the inheritance of something
peculiar to a few individuals. We do not concern ourselves
about the inheritance of measles, for since practically all are
susceptible (though in different degrees) to the poison, we
look upon this as quite a natural thing. But the inheritance
of the typical tubercular diathesis belongs to a few only ; it is
regarded as abnormal, and therefore much attention is paid to
it. And yet in a theoretical sense we are perhaps not alto-
gether justified in regarding the diathesis as abnormal, for the
negro in whom the tubercular diathesis is pronounced, might
live quite healthily in his native negro E. Nor is it necessary
to assume that the peculiar condition of tissue favourable to
the production of tubarcle must be the same in each case, for
it is conceivable that the bacillus might thrive in two or more
different kinds of soil.

Although, as we have seen, all diseases are, strictly speaking,
hereditary, we shall find that even in regard to those diseases
which are universally acknowledged to be so, such as
insanity and rheumatism, many important considerations are
overlooked. One point entirely lost sight of by pathologists
when inquiring into hereditary history is that a disease may
gradually evolve, the predisposition to it increasing from
generation to generation ; the S may, for instance, gradually
change from S, to Ss, when the disease will break out under
a specific E3 ; that is, S8 + E3=n. There is no doubt that
such a disease-tendency may evolve in the course of successive
generations by the continual operation on these several genera-
tions of an E capable of generating such a predisposition. Now
in such a case we might be inclined to regard the disease
tendency as quite outside the sphere of hereditary influence,
and, as far as I am aware, this point is always overlooked by
statisticians. That they err in so doing let me demonstrate
by the numerical method. Alcohol, it is well known, is a
constant cause of insanity, and this peculiar effect of it is
probably due to the fact that it has a special action upon nerve
centres, notably the higher nerve centres of the cortex. Now
let us suppose five generations to have led intemperate lives,
and in each generation the predisposition to have increased by

THE CAUSATION OF DISEASE. 327

two ; then in the fifth generation the predisposition of an
individual at birth will be represented by Ss. Later on in
life this will increase to S10, when, on a slight exciting
cause ( = Ej), he will develop the disease and the formula will
stand thus: S10 + Et = 1 1. Many may object that we have
no right, in such a case, to term the disease inherited, seeing
that it has not actually occurred in the ancestors of the sufferer.
Yet if we suppose an individual inherits S2 from an ancestor
who has actually suffered from insanity, and that he develops the
disease from an exposure to Ey, the case would universally be
acknowledged to be hereditary ; but surely the former case,
with an inherited tendency of S8, has a greater heritage of
disease.

The subject of the gradual evolution of disease through many
generations has already been treated of, and let it be remem-
bered that in all diseases thus arising the tendency is to over-
look the influence of heredity.

2. In searching into the influence of heredity in the
causation of any particular disease, the fact is neglected that
a separate disease-tendency in each of the parents may give
rise to a third and different tendency in the offspring. This
hybrid result would not by many be regarded as hereditary,
seeing that in such a case the parents do not suffer from
exactly the same conditions, but inasmuch as each element
in the resulting disease is inherited, so in a sense is the entire
•disease ; and the same holds true of the combination in the
■offspring of two healthy tendencies in the parents, whereby an
abnormality results (supposing such a thing to be possible,
■vide p. 79).

3. Another very common source of error is the difficulty
of obtaining a proper family history. Some important incident
in this history may be purposely concealed, or, what is much
more likely, overlooked. In order to discover the full weight
of hereditary influence in the causation of any particular dis-
ease, it is necessary to go into the family history of many
■generations, a course quite impossible. When we reflect that
the zebra-like stripes of the horse are descended from ancestors
belonging to many thousands of generations back, it is obvious
that the hereditary character of these stripes could not be

z 2

328 THE CAUSATION OF DISEASE.

ascertained if we possessed a family history dating back
a few generations only, and the same remark applies here.
Nevertheless, when inquiring into the hereditary history in
cases of disease in man, we are only able to go back through
the most recent generations ; indeed, Sir James Paget, with
his large experience, tells us that he has never been able to
trace the family history beyond five, and that very rarely.

And here let me briefly indicate some of the apparent ex-
ceptions to the principle of heredity. According to our
principle, differences other than the sexual between brothers
and sisters are due to differences in the E, this E dating
back to the earliest period of germ and sperm life. A very
small initial difference in the E may ultimately lead to a very
wide divergence. The differences of ante-partem E account
for the differences among brothers and sisters at birth, but
in the present state of our knowledge it would be useless for
us to attempt to explain minutely the influence of ante-partem
E on the child. We can, however, trace the influence of post-
partem E more exactly, and I propose to touch briefly upon
this influence, in order to show how it tends to obscure the
hereditary principle.

Occasionally we see among children of the same parents
great differences as regards mental faculty. One may grow
into a remarkably clever man or woman, while another may
exhibit very ordinary ability. Now, differences in mental
power depend upon differences in brain organization ; and
inasmuch as this is inexpressibly subtle and complex, we can
understand how a very slight influence may interfere with
cerebral development, and thus alter, in a very marked degree,
for good or for evil, the mental characteristics of the indi-
vidual. And the change wrought need not be visible to the-
naked eye, or even with the aid of the microscope. The subtle-
ties of thought are represented by subtleties of organization
quite out of the reach of observation ; so that, setting aside
the ante-partem E — which, however, I doubt not, plays the
more effective part — we can understand how, during the post-
partem life of a child, many influences, silent and unobserved,
may be modifying cerebral organization. But some of these-

THE CAUSATION OF DISEASE. 329

may be of a very palpable nature, and effect gross and
obvious alteration upon the nervous system. See what a
profound change rickets works upon the body : not a single
part escapes, and many of the tissues are quite as seriously
affected as the bones. That the nervous S}Tstem is very
profoundly modified is clearly shown by the great tendency
to convulsions (which, as Dr. Gowers tells us, often lead to
epilepsy later in life), and also to laryngismus stridulus.
Dr. Barlow has never met with this disorder in a child that
was not rickety.

There is no doubt that infantile convulsions and epilepsy
are due to cortical change. Indeed, it has often struck
me with wonder that pathologists, in seeking for the
primary seat of these diseases, have so persistently ignored the
large mass of cortical grey matter. Herein are situated the
highest and most elaborately constructed nerve-centres ; we
should therefore expect them to be the most unstable in
the body, the most easily unhinged and thrown out of gear.
Why, therefore, seek for the primary cause of such diseases
as epilepsy, hysteria, and chorea in the lower inferior reflex
centres, which common sense should tell us must be more stable
than the more highly evolved and supreme cortical centres, and
which collectively form in weight but a small fraction of the
cortical grey matter ? But this by the way. Now, seeing that
rickets works a profound change upon the cortical grey matter,
it is obvious that the mental powers of a rickety individual
must suffer from this disorder. Would Shakespeare have been the
man he was if the first few years of his life had been spent
in a dark and narrow London alley, even though his subse-
quent E had been that which he actually experienced ? I have
no hesitation in answering this question in the negative.
Rickets must necessarily have resulted from the early E, and
this disorder would have wrought a profound change in the
cortical grey matter of that remarkable brain ; there would
have been serious disturbance with the finer developmental
changes, and thus the proper progress of mind-evolution
would have been interfered with. In estimating the differences
in the intellectual traits of brothers and sisters, we must there-
fore be careful to take into account external influences. Many

3 30 THE CAUSATION OF DISEASE.

are, doubtless, so subtle as to escape observation, but I doubt
not that often enough the difference could be easily accounted
for by observable differences in the E.

And in a similar manner we can account for marked
differences between parents and offspring. Let us suppose a
healthy couple, of exceptionally good physique, to come up from
the country to live in the centre of London. We may safely
say of their children that all of them born and reared in
the lanes and alleys of the great city, will be very inferior,
physically, to their parents ; and we should, when comparing
the parents with the children, observe an apparent contradiction
to the law of heredity, for, according to it, a well-grown man
and woman should have well-grown sons and daughters. Cases
of this description are very common. I know of several myself,
and I have heard great surprise expressed that fine, strong
parents should have such puny and miserable -looking offspring.
Now, let the degenerate progeny of such healthy, well-grown
parents remove to healthy hygienic surroundings — such, e.g.,
as obtain in the country — and the offspring of these will, if
reared in this healthy breeding ground, tend to grow up into
the physical likeness of their grand-parents — will revert, in fact.
Here we have the reverse picture of puny and ill-developed
parents rearing a well-grown and vigorous progeny, and again
it is argued that the principle of heredity is fickle and myste-
rious. Yet I maintain that it is nothing of the kind, and that
it only appears so because we fail to take into account the
many influences that may disguise it. I have purposely taken
extreme cases, where the difference in the E of parents and
offspring has been abrupt and marked, and in which, conse-
quently, the apparent contradiction to the law of heredity
can be easily explained, if we take care to compare the E
of parents and offspring ; but how many are the subtler
alterations of E which entirely escape our notice, and which
are, nevertheless, capable of profoundly affecting mental and
physical organization ?

CHAPTER VI.

Disease not an Entity — All Disease comes through E — The Variability of
Disease — A Perfect Classification Impossible.

There is a tendency to regard diseases as fixed and unchange-
able types, or, if varying, as varying within narrow limits only.
This belief still clings to us as a relic of the past, for it pro-
bably arose out of the old notion that diseases were separate
and independent entities.

At that period of his evolution when man was first able to
reason on the subject of disease, he attributed it, as he did all
the various phenomena of nature, to some spiritual agency. To
him a disease was an evil spirit which had taken up its abode
in his body, and all his attempts at cure had for their object
the driving out of the unclean thing — the exorcism of the
spirit. Later on, the belief in spiritual agencies gave way to
the theory of humours, which, resting though it did but very
slenderly on fact, was yet more in accord with his wider
knowledge of natural processes.

We shall presently see that both these views, crude and
fanciful though they are, had more of truth in them than a
hasty consideration would lead us to believe. One thing, how-
ever, is quite certain — viz., that it is impossible to regard disease
as a separate entity, as something capable of mechanical sepa-
ration from the body, of being corked up, as it were, in a bottle.
One might, perhaps, be inclined so to regard it in such a case
as "tapeworm," for here the mal-E consists of a worm, which,
taking up its abode within the body, produces a series of
symptoms, all of which disappear with the disappearance of
the nocuous agent. In this case, however, the disorder con-
sists, not of the tapeworm, but of the abnormal inter- actions
which are set up by it — of improper inter-action, be it noted, of
S and E. The tapeworm no more constitutes the disorder

332 THE CAUSATION OF DISEASE.

than does prussic acid in prussic acid poisoning. It is utterly
unallowable to regard the disease-producing agent as the disease
itself ; not only is it incorrect in point of fact, but it cannot
even be permitted for practical purposes, and this for two
reasons — first, because we cannot, in all diseases, accurately
define the mal-E ; and, secondly, because the same mal-E will
sometimes induce totally different disorders in two separate
individuals. Similarly, when the disease consists of a tumour,
some might be inclined to regard it as a separate entity, more
especially if the removal of the tumour should lead to a per-
manent removal of a series of symptoms caused by it ; but the
same objections apply here as in the previous case.

What is the fundamental truth underlying the old spiritual,
(as we may conveniently term it) and the humoural pathology,
and after which they were dim gropings ? I take it to be
this — that they tacitly assume — and in this they agree —
that the essential cause of disease lies in the environment.
The "unclean spirit," or "devil," and the corrupt humour,
correspond to what I have termed the mal-E, or, more accu-
rately, the abnormal internal-cell-E. In both cases the evil is
supposed to be, not of the body — not part and parcel of the
body fabric — but something independent of it — an independent
agency, yet capable of causing disordered action in it ; for
although the corrupt humour was probably in all cases regarded
as a product of the body itself, it was evidently thought to be
independent of it (as, of course, was also the evil spirit, or de-
moniacal possession), and all efforts were, in either case, directed
to its removal. These primitive pathologies erred in that they
concentrated the attention entirely upon the E, the part
played by S being largely, if not altogether, left out of
account ; nor would there be much need to take account of
the S if every individual responded in exactly the same way
to the same mal-E ; but, inasmuch as different S's respond
differently to the same E, we cannot possibly neglect the part
played by S in causation.

Nevertheless, the E is, in the last resort, the sole cause of
disease. This will be clear if we keep before us the formula
" S + E = disease."* If it can be shown that S is the out-

* This formula signifies vital inter-action, whether of health or disease.

THE CAUSATION OF DISEASE. 333

come of structural modifications wrought through E, then it
becomes obvious that S + E, or disease, is produced by E,
and by E alone. And that such is the origin of S, there can,
I think, be little doubt. Organic evolution results from the
summation during countless generations of individual niodifica-
tions of structure. But whence these modifications ? I have
again and again insisted that all are ultimately traceable to E.
To assume the existence of " spontaneous " variations is to
fling aside the law of causation, which tells us that nothing can
happen without a cause ; and what, besides E, is there that can
cause a modification of S ? One other cause, and one other
only, can be named — viz., sexual reproduction, for this leads
to the production of an organism which is exactly like neither
parent, but some sort of a mean of the two. Yet I think
that, even here, it may truly be said that E is the cause of the
structural modification.

In order to render this evident, let us suppose that all
human beings were born exactly alike, save for sexual differ-
ences, and that the E were exactly the same for all ; it would
logically follow that all individuals would — except for these dif-
ferences— be exactly alike at corresponding ages. And if the E
continued the same for each individual during successive genera-
tions, this likeness would remain permanent in the race ; for the
material conditions attending the coming-into-being, and the
evolution of every individual of the same sex being exactly the
same, each successive generation of individuals of the same sex
would necessarily be exactly the same also. To deny this is to
deny the law of causation. But, given modifications of E,
modifications of S necessarily ensue, and it will then be impos-
sible to get any two individuals exactly alike. It follows from
this that the E is the primary cause of natural variations ;
once given such natural variations, however, the union of unlike
individuals will still further increase the tendency to vary.

Now, the question we have to ask ourselves is this : Are we
to consider the sexual union of unlike individuals as a separate
and entirely independent cause of the variations thus resulting,
or are we to conclude that E is here also the real cause of
the variations ? I contend that the latter is the correct view.
To make this clear, we will suppose two individuals — male

334 THE CAUSATION OF DISEASE.

and female — to be born into the world exactly alike, save for
sexual differences. We know that in course of time each will
diverge in structure, owing to the necessary differences in the
E. Let us represent these structural differences, or acquired
characters — say, at the age of twenty-five — by the symbols s,,
s., respectively. Then, if S represent those structural characters
of each individual which are the pure outcome of heredity, Ssx
and Ss., will represent the structure of each at the above age,
when differences of E have had time to affect it. If the two
individuals now come into sexual union, they will be a cross in
respect of Sj and s.„ and the coming together in the offspring
of these two different tendencies will lead to a condition which
may be represented by Ss? — the offspring differing from the
parents in respect of s?. Now, seeing that the structural
differences represented by Bj, s., have been wrought through
the E, may we not justly conclude that s?, which is a product
of the two, has a similar origin ? Each ingredient in a com-
pound being the result of E, is it not true that the compound
itself has a similar origin, even though it be quite unlike
any of its ingredients ? Let us suppose that in a world where
0 and H do not exist, each is called into being by a particular
agency, at such a temperature that the two fly together to form
water ; should we not attribute to this agency a preponderating
share in the causation of water ? and similarly, if we grant that
the S of two individuals coming into sexual union is ultimately
due to E, we must grant that the S of their offspring is
due to E, even though the offspring may manifest structural
characters not present in either parent.

It is therefore, I think, clear that, directly or indirectly, all
modifications of S come through E, and since organic evolution
results from the accumulation during countless generations of
individual modifications, we see that the causation of S in its
entirety is ultimately traceable to E. Wherefore the material
conditions represented by S and E are solely due to E, and as
this formula represents not only healthy vital inter- action, but
also unhealthy inter-action — i.e., disease — it follows that all
disease ultimately comes through E.

But lest any one should still maintain that such structural
states as depend upon the coming together of unlike parental ten-

THE CAUSATION OF DISEASE. 335

clencies are not wrought through E, then let me point out that the
above proposition is yet to a large extent true. Although the
forms of disease may undoubtedly be modified by the blending in
the offspring of disease-tendencies derived from the parents,* yet
it can very rarely happen that disease originates in this way. I
have suggested f that it may occasionally happen that a con-
dition of body rendering it liable to respond pathologically to
an average healthy E, or even leading to pathological states
directly, as in certain reversions — e.g., persistent branchial clefts
— may result from the crossing of two unlike individuals. In
the former instance, however, disease is set up by the E, which
must therefore be looked upon as the active cause, whether it
be markedly pathogenic to the community at large or not ;
and as regards the second class of disorders, they are very
rare, and even they, in almost all instances, result from pecu-
liarity in the ante-partem E.

Seeing that the old notions concerning the nature of disease
cannot be entertained, but that it must be regarded as an
abnormal inter-action of S and E, we are prepared for the fact
that diseases do not adhere rigidly to definite types, but are,
on the contrary, ever variable. If no two S's and no two E's
are the same, how is it possible to get any two cases where
S + E = the same ? To assume that every disease is fixed
and unalterable is to assume not only that S never varies,
but that each form of specific mal-E is fixed and unalterable
also, both in respect of nature and of quantity — an assump-
tion which is obviously absurd.

Our next point is how far it is possible to classify dis-
eases. Diseases, as we have seen, are natural variations, and,
consequently, the subject must be considered from the broad
point of view of biology. Let us ask how the biologist pro-
ceeds to classify ? A number of living organisms, agreeing in
certain fundamental particulars, by virtue of which they con-
stitute a particular class, % are taken. Certain differences are
observed among the various members, and by means of these
the class is split up into subdivisions. Now, we may, for

* Vide Chapter X. Part I. f Pp. 78, 79.

% I use this word in its simple logical sense.

336 THE CAUSATION OF DISEASE.

convenience, leave out of consideration those fundamental
particulars by which the different members are bonnd together
into a common class, and concentrate our attention on those
points only which are the criteria of the subdivisions, and it
is allowable to regard these differences as separate and inde-
pendent entities — call them species, varieties, or what we
choose. In like manner the pathologist takes a class of indi-
viduals— let us say, man — suffering from various diseases, and,
as every disease is probably characterized by certain structural
changes, these are natural variations. Here, also, we may
consider the structural peculiarities apart from those structural
characters which bind men together into one common class, and
thus we may speak of the different species of disease.

My object is to draw an analogy, as far as possible, between
physiological variations and pathological variations, and to
show that, just as physiological peculiarities of structure are to
the biologist the criteria of his classification into species,
varieties, and so forth, so pathological peculiarities of structure
will be found to be the only rational basis for pathological
classification.

How far it is possible to subdivide the several classes of
disease I will not attempt to decide. I do not wish to
push the analogy too far. All I want to emphasize is the fact
that when we use the term species in reference to disease,
we are simply referring to that structural state which constitutes
the disease, abstracted, as it were, from the rest of the body,
and in this sense, but in this sense only, it is allowable to
regard the disease as a separate entity, just as different classes
of animals or plants are separate entities.

But if we now further compare the divisions of the biologist
with those of the pathologist, we shall be struck with a very
marked difference between them, one so great, indeed, as
to make us wonder how disease can be classified at all.
Let us instance the so-called species, the lowest accurate
subdivision of the biologist. In ordinary organic evolution
there are constant factors at work tending to fix the species.
Each is more or less perfectly adapted to its E, and if the E
remained exactly the same, would undergo no alteration, seeing
that perfect equilibrium (adaptation) between -S and E must

THE CAUSATION OF DISEASE. 337

sooner or later occur. Inasmuch, however, as the most stable E
does change from generation to generation, the species also
must of necessity undergo modifications in course of time, in
order to maintain the standard of adaptation ; yet, since changes
in E are for the most part slow and steady, they are compelled
to maintain a certain degree of fixity. They are, in fact, kept
within certain limits in accordance with the great biological
principle that equilibrium between S and E must be maintained.
But when we turn to pathological classes, do we find that
there is any principle at work tending in like manner to
keep them fixed ? On the contrary, pathological variations
place the individual out of harmony with his surroundings,
and, far from there being any factors at work tending to fix
and preserve such variations, there are strong forces for ever
crushing them out of existence — above all, that most potent
agency, Natural Selection. Hence the wonder is that diseases
admit of any classification except of a very crude order, and
that any tendency whatever to definite types is manifested ; for
it must be allowed that there is such a tendency, although we
should be greatly erring in regarding the types as fixed and un-
alterable. The explanation is to be sought for in the fact that phy-
siological species are necessarily kept within certain limits, and
consequently all individuals in a species are more or less alike.
The S's, then, being more or less alike, and the various mal-E's
having a certain degree of stability in them, it follows that
diseases tend towards similarity — i.e., towards definite types.
It is, however, only permissible to assume fixed types for pur-
poses of classification, and with the limitation that we allow for
wide deviations from such types. Unless we are thoroughly
alive to the extent of the possible deviations, and are, more-
over, willing to acknowlege that in many cases they render
classification utterly impossible, we shall be constantly falling
into error.

The following two hypothetical cases will illustrate this
statement. We will first suppose the S to be constant, the E
varying ; and, secondly, the specific mal-E to be constant,
the S varying.

I . Where the S is constant, the JE varying. — Even suppos-
ing all individuals to be exactly alike, it would still be

338 THE CAUSATION OF DISEASE.

impossible to arrange diseases as fixed and unalterable types,
owing to the fact that the several specific mal-E's are not fixed
and unalterable. In some few cases it would be possible to get
exactly the same mal-E, as in the case of the ordinary chemical
poisons ; for instance, if we suppose two individuals exactly
alike structurally to take exactly the same dose of the same
poison, the resulting disorder will in each case be exactly the
same. But, as a matter of fact, such coincidences as regards E very
rarely occur, and if in so simple a case the mal-E is not stable,
how much more unstable shall we find it in other cases ? Take,
for example,- the gout-producing E. In. this case the E extends
over a long period of years, and, in consequence, it is utterly
impossible for it to be exactly alike for any two individuals.
This will be readily granted when the highly complicated
nature of the external-E is borne in mind. As another
instance, we may cite a specific -fever-engendering E. Inas-
much as the mal-E is in this case a poison, it might be
thought that therefore its inter-action with S would be identi-
cal in all individuals coming under its influence ; but such is
not the case, for the poison being the product of living-
organisms, and these being liable to vary, the poison is liable
to vary also. Hence it is that no two epidemics are exactly
the same, and that they are apt to die out, disappearing from
the face of the earth, while new ones come continually into
being. So wide, indeed, are the deviations from the classical
types of the so-called " specific fevers," and so numerous the
unnamed and unrecognized forms of allied disorders, that it
becomes at once evident how very imperfect their classification
must be, and that a very elastic meaning to any terms, we
employ to denote these types must be allowed. This subject
has been so ably discussed by Dr. W. J. Collins * and Mr.
Millican,f that it is unnecessary to pursue it further.

The same line of argument applies to all forms of mal-E.
They are essentially variable, and such being the case, the
diseases which they cause must be variable also, even though
the S be the same ; and inasmuch as the S of all individuals

* " Specificity in Evolution," by W. J. Collins, M.D., &c. This is a valuable
paper, and deserves careful study.

(• "The Evolution of Morbid Germs," by Kenneth W. Millican, M.B.

THE CAUSATION OF DISEASE. 339

differs considerably, how much greater reason is there that
diseases should be variable ?

2. Where each specific form of mal-E is constant, the S varying.
— As an example of a theoretically fixed mal-E, let us take a
chemical poison — say, prussic acid. Now, since the S is in no two
cases the same, it follows that the resulting disorder — prussic
acid poisoning — can never be exactly the same either. It may be
thought that this is mere hair-splitting ; but I maintain that
it is simply logical, and consistent with the admissions we have
been compelled to make. Suppose that the resulting disturb-
ance were entirely different in the two cases, should we still be
justified in regarding the disease as at all the same, even though
due to the same amount of the same poison ? In prussic acid
poisoning the effects would, I admit, probably be very much the
same in all cases ; but we know that different individuals differ
very considerably in their mode of response to different kinds
of poisons — and this shows us that the nature of the E is not an
absolute criterion of the nature of the disorder, and hence, as
we have seen, one reason why we cannot classify diseases
according to their external causes. In the case of chemical
poisons, the specific mal-E no doubt forms a valuable means of
classification — for practical purposes at all events — and when
called to a patient suffering from prussic acid poisoning we
should not enter into a disquisition on the nature of the morbid
changes, bat, knowing prussic acid to be the disturbing agent,
should proceed with all promptitude to take such steps as are
known to be useful in counteracting its effects.

Seeing, then, that even if, on the one hand, the S were
.always constant, or if, on the other, E were always constant,
diseases would still vary very considerably in type, and seeing,
moreover, that, as a matter of fact, both S and mal-E are
variable, the truth that disease types are variable becomes at
once obvious.

Variability in S, perhaps even more than variability in E, is
a cause of variability in disease. No doubt there is a certain
likeness in all individuals of the same species in respect of
their response to specific mal-E's, and since these latter also

340 THE CAUSATION OF DISEASE.

maintain a certain degree of constancy, it is possible to recog-
nize diseases as belonging to a particular species, and to apply-
to them the term " specificity," with certain qualifications. No
one will doubt that rheumatism, tubercle, diphtheria, carcinoma,
and typhoid fever are distinct and definite diseases ; but even
these well-defined diseases deviate very widely from their classical
types, so much so, indeed, that they may be utterly unrecogniz-
able, in the truest sense of the term. But if this is true of such
well-recognized disorders, how much more is it true of others ?
Instance cutaneous and nervous diseases. Diseases of the skin are
so variable that they have completely baffled the most diligent
attempts at classification. Yet if a rare case come before the
specialist, he is not content unless he can refer it to one class in
his long category ; he is unwilling to regard it as a unique
disorder, as one the like of which has, perhaps, never occurred
before, and may never occur again. He might, I will venture
to say, learn a lesson from the horticulturist. Diseases are,
as we have seen, natural variations. Now, when a gardener
meets with a natural variation in one of his plants, he knows
very well that such variation may never have occurred before,
and may not be repeated, and in consequence, if the variation
be one favourable for his purposes, he is most careful to " fix" it,
as it were, to preserve the seeds, and to exert all his efforts to
accumulate and intensify the peculiarity during successive
generations of the plant. In like manner unique pathological
variations of the skin may occur. We have seen that variations
are more abundant among domesticated animals and plants, and
among civilized peoples than among organisms in their wild
u natural " state, and that this is largely due to instability of E.
Just as plants vary abundantly in an unstable E, and from the
crossing and recrossing of varieties, so may the human skin vary
abundantly in the unstable civilized E, and from the crossing
and recrossing of unlike individuals ; and, inasmuch as mal-E's
are numerous in civilized communities, there is no wonder that
pathological variations should be numerous, that they should
baffle the most careful attempts at classification, and that fresh
ones, quite unlike any which have before occurred, or which
may ever occur again, should from time to time appear.

Then, as regards nervous diseases. Let us first instance the

THE CAUSATION OF DISEASE. 34 1

affections of the spinal cord. In most text-books these are
classified with great care and precision, and the student sets
himself to learn them diligently. But what does he find when
he comes to observe for himself? That he very rarely meets
with the disease exactly as described in the book. He soon learns
that, with few exceptions, he must consider each case on its
own merits, and that that physician makes the best diagnosis
who can specify the particular parts of the cord that are diseased
and the nature of the pathological process, and who is content
to rest there, without necessarily pigeon-holing the disease into
any special department, and racking his brain to make the case
accord with some particular classical type.

These remarks apply with double force to mental disorders.
It is truly pitiable to examine into the ponderous literature of
those most wonderful of all diseases — diseases of the mind — and
to contemplate this craving for classification. Of all diseases,
mental diseases are the most subtle, and of all, perhaps, the most
variable ; but the author, in his desire to classify, is painfully
anxious to set rigid limits even to them ; and so it is with all.
Every man, when he leaves hospital, and has to deal with
diseases on his own responsibility, must be struck with the
vast difference between disease as he has learnt it from the
books and as he actually finds it. For some time he endeavours
to name every case, but, if he is a thoughtful man, he soon
discovers the futility of this ; he learns to consider every disease
on its own merits, and thus, while he makes full use of classi-
fications and types, he is ever prepared to meet with cases which
stand alone, which never have " been"' before, and perhaps never
will "be" again.

These considerations it was that led me, when speaking of
terminology, to say that " it matters little by what word, or com-
bination of words, we choose to designate any particular disorder,
so long as we have a clear idea of the morbid inter-actions (or
what is known of them) which the name chosen is intended to
connote ; and inasmuch as the morbid inter-actions are in no
two cases even of the so-called ' same ' disease, exactly alike,
we must allow a considerable latitude to the meaning of any
term, modifying it in different cases according to our exact
knowledge of the morbid process."

A A

CHAPTER VII.

The Parasitic Origin of Malignant Growths.*

Some little time ago I came to the conclusion, on a priori
grounds, that malignant growths must be caused by para-
sites, and I wrote down my arguments with the intention
of publishing them on a suitable occasion, not knowing that
the theory had already been advanced. Having read the inter-
esting experiments of Mr. Ballance and Mr. Shattock, I am
led to publish my views.

The phenomena of life fall under two main heads, the first
relating to the organism, the second to its environment. Let
us symbolize the former by the letter S, the latter by E. Now,
confining for the moment our attention to a unicellular or-
ganism, we know that if the cell and its environment be
properly constituted, a certain interaction takes place, and this
is healthy life. S + E represents a set of material conditions
which inevitably issue in healthy inter-action, and these
material conditions are the cause of life. But if either S or
E be improperly constituted, either no vital inter-action takes
place at all, which is death, or an improper vital inter-action
occurs, and this is disease. Wherefore disease may be defined
as an abnormal mode of life. These remarks apply likewise
to multi-cellular organisms. Every cell in such organisms is
surrounded by a space which constitutes its E, and the life
of a multicellular organism at any one moment consists-

* This chapter is inserted here to show the principles set forth in this work
in actual application. It was originally intended for publication in one of the
medical journals, but as it only appeared there in abstract, I deem it advisable
to insert it here in full, and at the risk of some repetition, as the method of
argument followed is based upon the principles I have been endeavouring to
enunciate. I should add that when it was first written the parasitic theory
was unknown to me.

THE CAUSATION OF DISEASE. 343

of the sum of the inter- act ions of the several cells composing
the organism and their individual environments. Where-
fore, in speaking of E, we must remember that we have
to deal, not only with an external-body-E, in the shape of
food, air, and so forth, but with an internal-cell-E also. This
latter is, in great measure, dependent upon the external-
body-E, but it is also very largely under the control of the body
itself ; so closely, indeed, are the several tissues of the body
bound up into one physiological whole that it is quite im-
possible to get a serious change in one part which shall not
lead to a more or less universal modification of cell environment.
And here let me remind the reader that a properly constituted
E not only includes certain positive conditions, such as the
presence of oxygen and proper food, but also certain negative
conditions, such as the absence of waste products.

Now, disease being an improper inter-action of S and E,
it follows that the cause of disease must depend upon — (1)
peculiarity of S ; (2) peculiarity of E ; or (3) peculiarity
of both. Wherefore, in seeking for the causation of dis-
ease we must first inquire into the causation of S and E.
As regards S, at least -^ of its causation must be referred
to heredity, and there remains but one other factor capable of
affecting it — viz., the environment. The influence of E may be
summed up in the following proposition : whatever structural
peculiarity an individual exhibits which is not the pure out-
come of heredity is wrought through E. I have elsewhere shown
my reasons for what may seem a somewhat dogmatic asser-
tion, and we need not therefore discuss the matter again here.
Heredity and E are, then, the two great moulding powers. Let
S represent such of the structure of an individual as is the pure
outcome of heredity, and s that part of him which has been
shaped by E, then Ss expresses the causation of structure at
any particular time. If, now, the individual come into con-
tact with an agent producing disease in him, the formula
Ss -f E represents the causation of that disease. It represents,
in fact, a set of material conditions which necessarily issue in
unhealthy inter-action. Let us, for instance, suppose it proven
that cancer is due to parasitic action, then, if E stand for
the environment of the individual (including the parasite),

A A 2

344 THE CAUSATION" OF DISEASE.

Ss + E will represent the causation of cancer in any given
case. Observe the importance of s. It might so happen in a
particular case that Ss 4- this same E would not cause the dis-
ease, even though the S were the same as in the first case.
The s, which represents the moulding of the body through
a series of years, might have been a totally different quantity
from that in the first case, and one preventing the specific E
from working its dire effect upon the body.

Let it ever be borne in mind that we can never exclude S
from the causation of disease. How is it possible to do so,
seeing that disease is an abnormal inter-action of S and E ?
Occasionally, for practical purposes, we may. When a man
breaks his leg from a fall, we do not say it is his leg that
is the cause ; but if two healthy individuals be equally exposed
to the scarlatina poison, and only one contracts the disease, it
is evident that it is impracticable to exclude the S from a share
in causation.

One word on what may be termed the potentiality of S. The
tissues are endowed with a vast number of potentialities — that
is, slumbering possibilities — dormant states needing but a
fitting E to awaken them into actual being. This subject
has not, in my belief, received its proper attention from
pathologists. Whatever be the evil factor in the causation of
malignant growths, it is to be noted that the affected tis-
sues must possess the potential power of taking on the par-
ticular morbid action, and in the cancers the structure of the
growth is by no means simple. The power of thus growing
must have been previously locked up in the affected tissue, so
that even if we find a parasite to be the exciting cause of
cancer, we must remember that the power of growing in this
peculiar way belongs to the body.

With these remarks on the Causation of Disease in general,
let us now proceed to discuss the causation of cancer in par-
ticular.

The question — Does the tumour originate in a multiplication
of the few cells initially constituting it, or in a transformation
of the affected tissues ? — must first engage our attention. It
may obviously originate in either, or in both, of these ways. All

THE CAUSATION OF DISEASE. 345

are agreed that the primary carcinomata increase, for the most
part, by an actual transformation into malignant tissue of the
tissue primarily affected, and in no case is this more beautifully
shown than in carcinoma of the kidney. But some patholo-
gists doubt whether the sarcomata ever originate in this way,
the tumour growing, in their view, simply and solely by a
multiplication of the few cells initially constituting it.

It is, with our present knowledge, almost impossible to decide
this question. Inasmuch, however, as all are agreed that primary
carcinoma is a transformation — at all events, in part — there is
no need to assume in carcinoma a group of previously existing
embryonic cells, as some have done, because we have very distinct
proof that the tumour is, to a large extent, developed from
mature tissue. Although many of the cells constituting a
primary carcinoma are derived from the normal cells of the
parts, yet there is not the slightest doubt that very many of
them arise from a multiplication of the cells already con-
stituting the tumour. Indeed, this seems to me to be more
certain of the carcinomata than of the sarcomata, for connec-
tive-tissue elements are everywhere present ; therefore, in no
matter what direction sarcoma spreads, or in what parts it is
secondarily produced, the proper elements are always at hand
to share in the formation of the growth ; but it often happens
that carcinoma spreads to tissues, either directly or by secondary
reproduction, in which there are no epithelia — the growth in such
cases evidently occurring by a multiplication of cells already
belonging to the tumour. Squamous epithelioma, to wit, may
directly extend to bone, or it may be secondarily reproduced
in a tissue containing no squamous epithelia. The reason
why the primary tumour contains squamous epithelial cells is
certainly because the tissue in which the growth started is
largely made up of such cells. The tissues secondarily affected
contain none such. Now, if the cancer had first attacked the
tissues thus secondarily affected, the tumour would certainly
not have contained squamous cells, for a primary squamous
epithelioma never starts in tissues devoid of these cells. From
this, two conclusions seem to follow — (1) The primary tumour
derives its squamous epithelial cells from previously existing
similar cells ; (2) the squamous epithelium of the secondary

346 THE CAUSATION OF DISEASE.

growth is derived from a multiplication of cells transported
from the primary tumour. Now, if this is true of one form
of carcinoma, why may it not also be true of the others, and,
indeed, of the secondary sarcomata likewise ? When the carci-
noma is reproduced in a tissue containing no epithelia, these
cells are probably derived solely from the multiplication of trans-
ported cells; but when the secondary carcinoma occurs in a
suitable epithelial tissue, the growth may be both by a multi-
plication of transported cells and of the normal epithelia of the
part. Such a twofold cell-origin is possible with all the sarco-
mata, for connective-tissue elements everywhere abound.

How comes it that a tissue, hitherto normal, suddenly takes
on malignant growth ? * The cause must, as we have seen,
depend either upon — (i) an innate tendency of the tissue
primarily affected to undergo the malignant change inde-
pendently of a peculiar E ; (2) upon a distinctly peculiar E ;
or (3, and finally), upon abnormal tissue tendency combined
with peculiar cell-E.

Is malignant disease due to an innate tendency on the part
of the tissue primarily affected to become malignant, in-
dependently of a peculiar cell-E ? Is the process analogous,
in fact, to the differentiation of tissue which occurs in the pro-
cess of development, a differentiation which certainly takes place
independently of distinctly peculiar E ? I say " distinctly
peculiar E," for doubtless the nature of individual cell-E plays
an important part in development. This fact is sufficiently
attested by a study of the laws of correlation, for if one particular
part be peculiarly affected in development, others are sym-
pathetically influenced, doubtless through the influence of one
tissue on the cell environment of others. Sir James Paget, in
his clinical lectures, evidently assumes such an innate origin, an
origin essentially through S and not through E. For he
argues thus : — Some individuals exhibit a tendency to super-

* I say suddenly, for although Hutchinson has spoken of a pre-cancerous
stage — an inflammatory state preceding the actual cancerous change — it must
be conceded that there is by no means proof that this always occurs ; malig-
nant change may, beyond all doubt, be suddenly set up in a healthy tissue,
and this practically always happens in the case of the secondary growths.

THE CAUSATION OF DISEASE. 347

numerary fingers ; there is no hard distinction between these
and hereditary fatty, glandular, cartilaginous, or osseous growths ;
these again cannot be separated from definite tumours of
similar structure ; finally, there is no abrupt step from
innocent tumours to recurrent fibroids from which true cancer
may be evolved. Now, I do not allude to this particular view
in order to subvert it ; for Paget is most careful to impress
upon his readers that the above may not be the exact mode of
evolution, and that he merely ' ' hazards a guess " ; I men-
tion it only because it shows that when he wrote the lecture
his mind was dwelling upon the S — that he was thinking of
cancer as evolving through S, and this indeed is one possible
origin of malignant disease.

The growth of a malignant tumour is most remarkable.
A tissue which, it may be, for many years has been living
healthily, suddenly and sharply diverges from its wonted mode
of growth. The change is not a mere hypertrophy or atrophy,
nor is it simple degeneration, any one of which may be brought
about by the body through its own power of modifying cell-E
— of increasing or decreasing blood-supply or of modifying
nerve influence. The process is quite peculiar, for, while
the nutritive activity of the part is actually increased, and
sometimes enormously so, the change is a retrogressive one,
the tumour-tissue, taken as a whole, being not only quite
different from that of the surrounding parts, but also of inferior
value from an evolutionary point of view. Now, bearing in mind
that every cell in the body is a separate organism, surrounded
by its own special E, this peculiar behaviour on the part of a
tissue which for years has been calmly and peacefully carrying
on its proper functions, is strongly suggestive of a sudden and
peculiar modification of its cell-E. In a meadow we sometimes
observe dark patches of grass growing more luxuriantly than
the rest, and, on seeking for the cause, we find that it is due
to altered E, in the shape of a different soil ; similarly, if in
the body we observe one patch of tissue taking on luxuriant and
abnormal growth, a modification of E is strongly suggested.

But, even though the abnormal growth be due to a peculiar
cell-E, this might conceivably be independent of any peculiar
external E ; it might, namely, be wrought by the body itself

348 THE CAUSATION OF DISEASE.

through the power of one tissue to alter the cell-E of another,
in which case the chief share of causation would belong to S —
that is, to the body, and not to any agent independently of the
body : the growth would, in short, be due to an innate tendency
of the body to undergo the change independently of external
nocuous agent. But is the body capable of affording the
necessary E ? By modifications of blood-supply and nerve
influence, the nutrition of a part may be influenced, and thus
we may get hypertrophy, atrophy, or degenerative changes,
but I know of no nutritive change thus wrought which is at
all akin to the malignant change. In derangement of the
nervous system, for instance, rashes, sloughings, and many
other changes may occur through modification of cell-E ; but
these differ from the malignant changes in several important
particulars. In the first place, a malignant tumour starts
from a microscopic centre, and spreads thence, while . or-
dinary "trophic" and degenerative changes start more or less
evenly throughout the whole of the affected area ; then again,
in trophic changes, there is, for the most part, diminution in
the bulk of the affected part ; further, in the case of secondary
growths we can eliminate any such trophic influence.

A study of the mode of growth of the malignant tumours
is, I say, strongly suggestive of a sudden change in the cell-E
of the affected parts. There is nothing to be said in favour of
the growths being due to an innate structural tendency,
independently of a localized specific mal-environment, and there
are several arguments against this view. If we assume the
chief element of causation to reside in S, we must narrow
down the primarily faulty S to a very minute area — to an
area, indeed, of microscopic proportions. Then, again, all
acknowledge a sudden .change of E in the case of the
secondary tumours : these never occur from an innate ten-
dency of the affected tissue to undergo the malignant change,
independently of altered E. Finally, the change is retrogres-
sive ; there is not evolution, but dissolution, and one patch of
tissue never takes on a dissolutionary change independently of
altered cell-E. I shall have shortly to revert to this subject
of retrogression.

The theory that malignant growths are developed from

THE CAUSATION OF DISEASE. 349

unused embryonic tissue, although it does not entirely
exclude a specific E from, a share in causation, obviously
refers a large part of causation to peculiarity of S in the
shape of unused embryonic tissue. This theory is at once
improbable and useless. We do not find, except perhaps in
a few cases of sarcomata, that malignant growths have a
predilection for parts where we should expect such embryonic
remains to abound. There is no part of the body which
may not be affected with some one or other form of malig-
nant disease. Local irritation, rather than embryonic remains,
determines the exact site. This is very noticeable in epithe-
lioma. Why should embryonic remains be more particularly
present in such part of the tongue as lies under a sharp
tooth, or in those parts of the alimentary canal most subject
to irritation ? Indeed, if the embryonic view be correct,
embryonic remains must be scattered throughout the whole
body, and this surely robs the theory of all its force. And
it is not only an improbable, it is a useless, theory — it explains
nothing. If there were distinct evidence that the entire
tumour in all cases originated from the first few cells consti-
tuting it, the fact would be in favour of the embryonic theory ;
but. inasmuch as it can be proved that in many cases of
malignant change the tumour is formed by a transformation of
previously existing mature tissue, the theory is useless, for we
can do without it. It may perhaps help us to explain inno-
cent growths, but it in no way helps us to explain the leading
characteristic of malignant growths, viz., their infectiousness.

I said that malignant change was a retrogressive one. In
all cases of new formation occurring as the pure outcome of
heredity, the change is evolutionary, from the homogeneous to
the heterogeneous, from the less complex to the more complex.
Malignant change, on the other hand, is essentially dis-
solutionary. We are thus led to discuss the nature of
sarcomatous and carcinomatous tissue. All agree that the
tissue of sarcoma is of a very elementary kind. The same
kind of tissue is abundantly met with in the embryo and in
the simpler forms of life. The sarcomatous change is, there-
fore, a reversion ; it is the manifestation of one of the many

350 THE CAUSATION OF DISEASE.

tissue-potentialities. The carcinomata, however, have no such
simple structure ; but I have no hesitation in affirming that in
their case also the change is a backward one. Some patho-
logists have spoken of endothiomata and other hypothetical
kinds of malignant growth, and I doubt not that eventually
our classification of the malignant tumours will be less simple
than it is now. For the present I wish to leave all such
doubtful forms out of account, and to speak only of the well-
recognized and typical forms of cancer. There can, I think,
be little question that such forms belong to the glandular type.
This is very plainly shown in the case of the epitheliomata. In
the squamous variety the epithelial cells dip down just as in
the development of all open glands. All the intestinal open
glands are thus developed, not even excepting the liver ; but,
observe, the down-growing cylinders never become hollowed
out. ' The glandular tissue is, therefore, of a very crude, imma-
ture form — of a form like that which probably obtained in some
very remote form of ancestral life, for, at its first evolution, the
in-growing gland was almost certainly solid. In the cylin-
drical-celled variety a more perfect type of tissue is approached,
for the cylinders contain a distinct lumen; nevertheless, the
process is disorderly, and the gland-tissue, taken as a whole,
is decidedly imperfect. In the acinous forms of cancer the
glandular type is maintained, but it is distinctly of an erratic
kind, and the fact that the acini are generally crammed with
epithelial cells is probably due to the rapid multiplication of
these latter. But it is a noteworthy fact that in many instances
there is a distinct tendency to a regular arrangement of the
cells as a single layer on the walls of the acini, when the
true glandular nature of the tissue becomes manifest ; where-
fore we may say that the carcinomata consist of an immature
and disorderly form of gland-tissue. The change is, conse-
quently, a backward one ; it is not an evolution, but a disso-
lution, the affected tissues manifesting some one or other of
the countless potentialities locked up within them.

I mentioned the dissolutionary nature of the malignant
change as an argument in favour of its being due to some
modification in E, for, so far as I know, rapid dissolution
cannot take place except by alteration of cell-E. Many pages

THE CAUSATIOX OF DISEASE. 35 I

would be required to make good this assertion. I must
content myself with asking the reader to believe that I do
not make it without sufficient reason. Even the slow retro-
gressive changes of old age can in most cases be traced to
imperfections in the cell-E, from failure in the organs which
make and conduct the blood. It is at this time that fatty
changes abound, and that fibrous tissue begins to replace the
epithelial. The cell-E is no longer capable of enabling the
tissues to maintain their high structural standard, wherefore
reversion to a lower order of tissue occurs ; under the im-
perfect cell-E a struggle for existence ensues, and it is no
wonder that the hardy connective tissues increase at the expense
of the delicate epithelia.

Here let me point out an important distinction between such
degenerations as the above, and the malignant degeneration.
In all cases of senile degeneration the imperfection of cell-E
lies in the absence of some positive essential to life, but in
the carcinomata there is no such absence, since growth is
excessive ; therefore, although the malignant growths are
degenerative in the strictest sense of the word, and must in con-
sequence be due to some modification of E, this modification is
quite different from that which causes the degenerations whereof
I. have just spoken. In malignant degeneration the abnormal
E must be a plus quantity ; it must contain some irritant. The
essentials of organic life, such as food, oxygen, and so forth,
must be at hand in abundance, and over and above these essen-
tials there must be a something which disturbs the growth of
the tissue as a whole (not necessarily of individual cells, for in
carcinoma the epithelia may grow most luxuriantly). We saw
that a perfect E requires not only the presence of the essential,
but the absence of the hurtful ; wherefore the abnormality of
the E of malignant tumours lies in this second particular.
Our present position may be thus summed up :
(i) Malignant disease is due to an abnormal cell-E of the
affected tissue.

(2) The abnormality consists, not in the absence of the
essentials to life, but in the presence of some noxious agent.

(3) The mal-environment is not wrought through the body,
but consists of something not of the body.

352 THE CAUSATION OF DISEASE.

We have now to inquire into the nature of this mal-E.
Malignant disease is often precipitated by mere mechanical
irritation, such as that caused by a blow, soot, a sharp tooth,
and the like. The effect of mechanical irritation in causing
malignant disease, notably cancer, is well known. Thus we
explain the great frequency of this disease in the mamma?,
the cervix uteri, the lips and tongue, and such other parts
of the alimentary canal as are most exposed to injury. But
is this irritation alone sufficient to account for the abnormal
growth ? It seems on the face of it very improbable that
it should lead to the production of a tissue totally unlike that
produced by mechanical irritation in general. It is, of course,
open to us to suppose that the tissues have an innate tendency
towards malignant change, and that a mechanical irritation is
capable of starting it. Of starting it, I say, but not of con-
tinuing it. We have already seen that a specific mal-E must
play a large share in the causation, but mere mechanical irrita-
tion does not fulfil the necessary conditions. In the first
place, malignant tumours occur over and over again indepen-
dently of such irritation ; indeed, this is always the case with
the secondary malignant tumours, when, therefore, some other
mal-E must be at work. In the second place, the malignant
degeneration is continuous ; once started it goes on with awful
determination, and a continuous effect implies a continuous
cause. And since a peculiar cell-E plays an essential part in
the causation, we require a mal-E which abides during the whole
period of growth. Consider, for instance, the primary carcinoma,
which grows chiefly from the mature cells of the tissue affected ;
every newly affected cell requires the specific mal-E. Now,
inasmuch as the tumour continues growing after the removal
of the mechanical irritation, it is obvious that this latter
cannot constitute the specific mal-E.

The form of mal-E which meets all the peculiarities of the
case is one consisting of a living organism, for it is an abiding
mal-E ; and if satisfactory proof has been given that the
essential portion of malignant pathogenesis belongs to some
continuous mal-E, then, I think, we may take it as all but
experimentally proved that this mal-E consists in some specific
bacterium, which thus comes to be a necessary element in

THE CAUSATION OF DISEASE. 353

causation. Such an organism accounts for the characteristic
feature of the malignant growths — viz., their infectiousness.

My view is this : Under the bacterial irritation, the tissues
are unable to keep at their normal level, and revert to a lower
order of tissue, thus exhibiting some one of their many potenti-
alities. The type of morbid tissue thus produced depends ( 1 )
upon the nature of the tissue primarily affected and (2) upon
the nature of the parasite.

We have seen that the secondary growths are not always due
to the transformation of the affected tissues, and in such cases
we cannot say that the affected tissues revert. The secondary
tumour in these cases results, I believe, from the transference
vf tissue-cells + the bacteria from tlie seat of the primary affec-
tion. Under the stimulus of the parasite, these transported
cells take on, by virtue of their potentialities, the same
morbid action as at the primary seat of infection. It is im-
possible, however, to deny the cells of the tissue secondarily
affected some share in the process.

Here, however, a difficulty presents itself. The question
may be pertinently asked : Why should the transported cell
show such a tendency to grow in the new site ? One can
understand, it might be argued, how a specific parasite may
cause a reversion in the primary site, but it is not so easy to
understand how it can cause the transplanted cell to grow
in the secondary site, since this does not occur in the case of
innocent tumours. As a matter of fact, however, it has been
known to happen. Simple adenoma of the liver has been
known to give rise to secondary adenoma of the kidney. This
is a very important fact, for it relieves the parasitic theory of
what might otherwise be a great difficulty. The greater
frequency of secondary growths may, I believe, be explained
as follows : — ( 1 ) Certain anatomical peculiarities of the primary
tumour permit the transference of the tumour cells. In the
innocent tumours the cells are far more fixed than in the
malignant, and in reference to this question of fixity it is
important to note that the rate of secondary reproduction is
generally in direct ratio to the rate at which the primary
growth develops ; that is to say, to the looseness of the cells.
A further anatomical peculiarity favouring the transference of

354 THE CAUSATION OF DISEASE.

cells from a malignant growth, is the peculiar arrangement of
the lymphatics in the carcinomata, and the peculiar embryonic
condition of the capillaries in the sarcomata. (2) Not only
are the tumour cells more frequently carried away from the
malignant growths, but the conditions obtaining in the tissues
in which they lodge are more favourable for their development
than for the development of cells carried away from innocent
tumours, because in the former case the transported parasites
probably set up an inflammatory hyperemia in the area of
secondary infection, and thus the transported tumour cells have
a better chance of survival.

Although, therefore, the presence of the parasite in the site
of the secondary tumour probably does actually increase the
chance of survival of the transported cell, the parasitic theory is
not essential to an explanation of this survival ; but it is needed
to explain the fact that the cells thus surviving in the abnormal
site take on the same form of retrogressive change as in the
primary site. The material conditions being the same in each
case, viz. : (1) certain tissue cells ; (2) specific mal-E, the result
is in each case the same.

It would, however, need far more space than I can here give
to develop this bacterial theory in all its details, and I must
confine myself to its more leading features. There are
probably several varieties of " malignant " bacteria. In the
first place, the carcinoma parasite must be different from that
causing sarcoma ; it differs both as regards its habitat and
its virulency. As regards the former, it is apparently in the
epithelia alone that it can thrive, but it further differs from
the sarcoma parasite in that it is much less virulent. Car-
cinomatous tissue is infinitely more complex than sarcomatous,
for not only does it contain mature connective-tissue and
epithelial cells, but the tissue elements are arranged in a
very definite way. Sarcomatous tissue, on the other hand,
contains, besides the embryonic blood-vessels, connective-tissue
elements only, and these, moreover, in a very immature form,
and with little, if any, tendency to definite arrangement.
In short, the dissolution is far more complete in sarcoma
than in carcinoma, and consequently the irritation must be
greater — the parasite must be more virulent. Connective tissue

THE CAUSATION OF DISEASE. 355

is capable of surviving under conditions in which the epithelial
cannot. How well this is shown in the example already
quoted, of the fibrous degeneration of old age, when, owing to
the imperfect cell-E consequent upon failing blood-making and
blood-carrying organs, the fibrous tissue develops at the ex-
pense of the epithelial.

The presence of the carcinoma parasite is not incompatible
with the growth and multiplication of epithelial cells ; on the
contrary, under the general disturbance of bacterial irritation,
their activities are actually hurried on, and a more or less
crude form of gland is produced, and the dissolutionary nature
of the process shows itself chiefly in the imperfect arrangement of
the cells. Whether the epitheliomata are caused by a different
parasite from the acinous varieties I will not venture to say, but
all the latter are probably produced by the same organism.

In the sarcomata, on the other hand, the bacterial irritation
is so virulent that under it only the most elementary forms of
connective tissue can survive. Inasmuch as this latter order of
tissue is everywhere present, there is no very pressing reason
to suppose a special tissue habitat for this organism. How far
the varieties of sarcomata are due to differences in the organ-
isms causing them it would be difficult to decide, for who can
say how far the type of malignant tissue is determined by the
structural proclivities of the tissues affected, and how "far by
specific parasitic action ? Certain it is, however, that the structural
differences of the sarcomata are very largely due to corresponding
differences in the bacteria causing them ; thus the small, round-
celled variety is probably due to an excessively virulent parasite —
one so virulent, indeed, that it permits the survival of the most
rudimentary order of tissue only. That, on the other hand, the
nature of the tissue affected plays a part in determining the
type of morbid tissue, is shown by the fact that myeloid sarcoma
most frequently originates from the medulla of bone where
giant cells abound, and the melanotic variety solely from the
pigmented tissues. This fact is equally well shown in the case
of the carcinomata : the primary cylindrical-celled epitheliomata
originate in tissues containing cylindrical epithelial cells ar-
ranged in tubular glands, and the primary squamous variety
solely from tissues containing squamous epithelia.

356 THE CAUSATION OF DISEASE.

The above remarks are borne out by what we know of
nutgalls, the structure of which depends, as is well known,
upon the structure of the plant-tissue affected, and upon the
nature of the parasite. Darwin speaks of the important share
taken by the latter in determining the structure of the gall.
Many species, he observes, may grow on the same tree, and
their difference is due to the subtle differences in the chemical
composition of the poison emitted by the several species of
gnats. A subtle shade of difference in chemical poison is,
then, capable of producing a palpable difference of structure.
Surely, a most noteworthy fact.

I have said that the transported malignant cells share in the
production of secondary growths. Consider the carcinomata ;
their complex structure is faithfully reproduced in the secondary
growths, even though the tissue secondarily affected contains
no epithelia. Assuming that the transported cells do not
multiply, the secondary growths may be accounted for in two
ways, (i) We may suppose that the specific bacterium is
capable of producing the same tissue-transformation in what-
soever tissue it may happen to lodge, for, be it observed, the
essential part of my hypothesis consists in this : that under
the bacterial irritation the tissues primarily affected undergo
dissolution, manifesting some or other of their many poten-
tialities— undergoing, in fact, what may be called vitiated
reversion. But it would be ridiculous to assume such an origin
for all cases of secondary growths — to suppose for instance, that
a secondary epithelioma, whether squamous or cylindrical, of —
let us say — a lymphatic gland, could originate by reversion ;
there is no ground whatever for supposing that adenoid tissue,
belonging as it does to the connective group, contains within
itself the potentiality of such a complex gland-like structure.
(2) The other hypothesis is sufficiently designated by the word
" spermatic," and, judging from the attention it has received
in works on pathology, it has been widely accepted. Yet it is
utterly unscientific. It assumes that the cells of one tissue
can, by mere contact with the cells of another tissue, compel
the latter to grow like themselves. What warrant have we for
such an assumption ? Certainly not one biological fact ; in-

THE CAUSATION OF DISEASE. 3 57

deed, the theory involves an entire misconception of true
spermatic influence. The sperm does not, by mere contact,
compel the germ to grow like itself, or like the being from
which it is derived. What happens is this : The two unite,
and the blended mass grows into a being which is a mean of
the two from which each sprang. If, therefore, the spermatic
theory were correct, the secondary growth should be a structural
mean between the tissue of the primary growth, and the tissue
in which the secondary growth occurs, which it is not. We
are driven, therefore, to the conclusion that the transported
cells take an active share in the production of those secondary
carcinomatous growths which occur in tissues unlike that
primarily attacked. The tissue-cells are carried away from
the primary growth, together with the specific bacterium, and
under the irritation of the parasite they continue in their
new site to behave exactly as before ; for they will of course
go on living if they find a suitable E, — if proper food and
oxygen be brought them, and if the cell-excreta be removed.
And this suitable E is provided by new blood-vessels and
lymphatics, which are developed under the bacterial stimulus.
The conditions of epithelial life thus obtaining, there is active
epithelial growth, and, given such growth, what wonder that
the epithelial cells should exhibit the same arrangement and
general tendencies as in their native site ? Let us reflect that a
single cell taken indifferently from an organism — from a be-
gonium leaf, for instance — is often capable of reproducing the
entire organism ; and that, as Herbert Spencer has argued, this
power is probably possessed in greater or less degree by every
cell of every organism, be it ever so complex. Shall we then
grant such tremendous potentialities to a single cell, and deny
to our transported epithelial cells the narrow powers of growing
and arranging themselves in a manner like that obtaining in
their native tissues ?

I have said that the carcinoma parasite is favourable to cell
life : the subsequent degenerative changes are in large part
accidental, so to speak, for the most serious result either from
a contraction of fibrous tissue or from the breaking down of too
rapidly forming blood-vessels.

What has been said concerning the part played by trans-

B B

358 THE CAUSATION OF DISEASE.

ported cells in the production of the secondary carcinomata
applies also to the secondary sarcomata, but with less force,
seeing that connective-tissue elements abound everywhere, and
that sarcomatous tissue has no very definite arrangement.
We might, with some show of probability, suppose the same
sarcoma parasite to bring about the same kind of dissolution,
no matter in what tissue it lodged, one kind of bacterium
producing round-celled sarcoma, another the giant-celled variety,
and so on, in whatever tissue it happened to strand. There
is, nevertheless, strong evidence that even in the sarcomata
the transported cells share in the production of the secondary
growths. I was careful to point out that the giant-celled
structure of central bone sarcoma depended rather upon the
nature of the tissue primarily affected than upon any special
power of the bacterium to cause this particular mode of growth,
that in another part this same bacterium would have produced
a different kind of sarcoma. Now, inasmuch as secondary
myeloid sarcoma of bone exactly resembles the primary growth
in structure, the probabilities are very strongly in favour of the
former having arisen in large part, not from a transformation
of the tissues secondarily affected, but from a multiplication of
the transported medullary cells, these behaving under the bac-
terial irritation just as in the primary growth. The same line of
argument applies to the secondary osteoid sarcomata ; it is
not likely that the bony tissue in these growths is due to trans-
formation. I have little doubt, however, that this latter pro-
cess does take an active share in the secondary sarcomata, more
especially as regards round and spindle cells.

The fact that malignant growths occur by preference in
tissues whose vitality is lowered from any cause is strongly
in favour of the parasitic theory. There can be little doubt
that a continual struggle for existence takes place between the
tissue-cells of a multicellular organism on the one hand, and
independent unicellular organisms on the other. Under ordinary
conditions of health the former obtain the mastery, but what-
ever lessens tissue vitality places the tissue-cells at a disad-
vantage in the struggle, and hence it is that their diminished
vitality favours parasitic development.

THE CAUSATION OF DISEASE. 3 59

It may be asked how the " malignant " bacteria irritate
the tissues. I can conceive of only two ways — (i) by mere
mechanical irritation ; (2) through some poison which they
emit. The latter is, doubtless, the source of all the trouble,
just as it is in the case of the gall-gnat. In the latter case,
however, the growth never exceeds certain well-defined limits,
because, of course, the supply of poison is limited.

The granulomata are admitted to be caused by parasites,
and why not the malignant growths also ? All these forma-
tions are bound together by the common bond of infectiousness,
and this suggests, nay, almost demands, some common cause.
Further, there is a marked similarity in the structure of
granulomata and sarcomata. The simplest way of explain-
ing infectiousness is to assume the existence of a parasite, for
this gives us an abiding mal-E, and hence a continuance of the
morbid process. The bacteria causing the several varieties of
granuloma and those causing the sarcomatous growths, are
equal in virulence, as is proved by the extent of dissolution
being equal in both. It is important to distinguish between
virulency and capacity to live on in the tissues. This latter
power is possessed in a far greater degree by the " malignant "
than by the granuloma parasites, for, in the first place, the
granulomata have far less tendency to spread at the periphery,
and, secondly, they are more apt to abort, as not unfrequently
happens with tubercle, for instance. The granulomata are
generally thought to be inflammatory, and some have even
maintained that all inflammations are due to bacteria. This
view is probably erroneous ; but, be that as it may, it is quite
certain that in those cases where inflammation is permanently
arrested the mal-E must cease with the cessation of the in-
flammation ; wherefore, if this mal-E consists of a bacterium,
this must lose its activity, as not unfrequently happens with
the granulomata. The malignant growths, on the other hand,
very seldom abort.

How are we to account for the fact, for fact it unquestionably
is, that malignant disease so often runs in families ? Doubtless,

B B 2

360 THE CAUSATION OF DISEASE.

because such families afford the fitting soil. Let him who is
inclined to scoff at the " soil " theory explain the preferences of
other parasites for particular individuals and for particular bodily
states. Let him tell us how it is that ordinary skin parasites
show undoubted partialities — that, of two individuals equally
exposed to the same bacterial influence, one is stricken with
fever while the other escapes unhurt; that the heads of
patients who have been tended with the utmost care will
sometimes of a sudden swarm with vermin ; and that, as death
creeps upon an individual, myriads of bacteria, hitherto quite
powerless to hurt him, swarm the tissues, beginning their work
of destruction ere life is yet extinct. These and kindred facts
can only be explained by supposing that certain states of the
body are particularly favourable to parasitic growth. Thus,
also, we can explain the tendency of cancer to run in families,
and to occur after middle life.

The comparative infrequency of the malignant growths is
not, in my belief, due to the rarity of the parasites causing
them, but to the happy infrequency of soil favourable to the
growth of the parasite ; and this fact must be borne in mind
in attempts at inoculation, and although all such attempts have
failed, let it be remembered (a fact which is apt to be for-
gotten) that this failure is equally difficult of explanation,
whether the parasitic theory stand or fall, for certain it is that
the body inoculates itself. I say the tendency to malignant
disease is due to the power of growing the parasite, and not to
the affected tissues having any particular and special tendency
to undergo the malignant change, for I hold that the tissues of
all alike possess these potentialities. Exemption from malignant
disease depends, in fact, upon exemption from the evil cell-E,
and this, again, upon some peculiar body state unfavourable
to the bacterial cultivation, and not upon any inability of the
tissues to take on malignant change should they be subjected
to the necessary mal-E. The capacity to undergo malignant
dissolution belongs to all vertebrates : all possess the same
potentialities, and what wonder? All the members of this
vast kingdom are knit together under the one grand scheme
of evolution. At every onward step there is divergence — a

THE CAUSATION OF DISEASE. 36 1

change from the homogeneous to the heterogeneous, and the
several members become more and more unlike one another ;
but, under the stimulus of bacterial irritation, there is disso-
lution, and the affected tissues revert to ground common to
the whole class.

Wherefore I am led, on a priori grounds, to conclude that
malignant disease is due to peculiarity of both S and E — pecu-
liarity of S, as already set forth, and peculiarity of E in the
shape of a specific parasite.

INDEX.

Acquired structural characters, inheri-
tance of, 124
influence of age upon, 93
Acquisition, every, is a natural varia-
tion, 140
"Actual" normality, meaning of, 297
Adaptation a work of time, 297

personal and racial, 189
Age, ancestral and individual, influence

of, on structural fixity, 84
Ague poison, 161
Ague-stricken district, a, and white

and coloured men, 292
Air, importance of fresh, 100
Alcohol, indulgence in, 291

and tobacco, Mr. Savory on, 301
Alcoholism a cause of insanity, 326

in the fifth generation, 327
American race, the modern, 247
Ancestral age of disease is short, 95

state, reversion to, 101
Animal organism, very plastic, 139
viewed from the corporeal side, 201
from the mental standpoint,
203
Anstie, Dr., on causes of neuralgia, 170
Ante -partem E, influence of the, upon
S, 129
more nearly identical the more

alike are the children, 136
peculiarities of, 104
Anthropologist, a place of study for the,

245
Argyll, Duke of, on "life," 15
"Artificial" and "natural" E, dis-
tinction between, 284
Asexual reproduction, 40

Bacteria, malignant, how they irritate

the tissues, 359
Bacterial irritation, effect of, 353
Bain's "Law of Relativity," 316
Barker, Dr. Fordyce, on maternal im-
pressions, 131
Barlow, Dr., on convulsions, 329
Bastian, many supposed acquired cha-
racters are inborn, 91, 142
Beale on "life," 14
Births, curtailment of, 261
Black Assizes, the, 238
Blendings, normal with normal, ab-
normal, of same kind, 83
characters normal, and belong to

different tissues, 79
of normal with abnormal, 81
of unlike normal characters affect-
ing the same tissue, 77
physiological, of the same tissue,

77
Brown, Creighton, 52, 253
Brown-Sequard's experiments^ on

guinea-pigs, 121
Brain, strong, and a weak body, 153
Brain-worker, the E of a, 228

0

Cancer, causation of, 344

well-recognized forms of, 350

Carcinoma, 345, 356

Carlyle on intellect, 71

Causation, law of, 2

Cause, definition of, 1, 9

Cell E, influence of the mind on, 22
one tissue modifies, of others, 2

INDEX.

363

Cell-environments may be morbidly

modified, 20
Changed conditions of life, advantages
of, on the vital organism, 315
Darwin on, 315
Spencer on, 315
Chemical force, 8
Chemico-physical nature and mind,

clashing of, 196
Child, importance of cutting short a

malady in a, 154
Child's head bears definitive relation

to shape of female pelvis, 133 n
Children, artificial rearing of, 286
instinctive habits of, 100
rarely die from disease due to
inherited morbid taint, 266
Civilization, and the degeneration of
man, 287
its effects on the rich and poor, 280
Climacteric, post-, rhythm, 54

influence of, on intellect, 270
" Cockney," a typical, 102, 228, 246
Collins, Dr. W. J., 338
Complex organism, definition of the

life of a, 18
Confinement, indoor, 240
Constipation, chronic, effects on de-
velopment, 152
Consumption of the bowels universal
among the London poor, 150
plays a large part in the destiny
of man, 151, 267
"Correlation," 144, 152
Cortical grey matter, 329
Country, causes of disease in, 250
overcrowded hovels in, 250
the great breeding-ground for

man, 249
contrast between the lives of men
and women in, 251
Criterion of mortality of S and E, 298
"Crossing" a cause of reversion, 120
influence of, in causing reversion,
107

D

Dalton, theory of, 8

Darwin, 29, 31, 42, 43, 46,47, 53, 59,
60, 61, 75, 80, 82, 85, 102, 143, 144,
157, 158, 161, 162, 188, 277, 279,
315, 3i8
Death, deficiency of 'food an indirect
cause of, in civilized commu-
nities, 210
inevitable causes of, 206
purely accidental causes of, 206,
207
Deficiency, structural, 162
Delivery, artificial mode of, 286
Dickens, and London air, 154
Direct equilibration, 188
Disease, a more or less temporary ac-
quisition, 97
an abnormal mode of life, 15, 34
ancestral age of, is short, 95
an essentially disillusionary pro-
cess, 277
attributed to spiritual agency, 331
a two-sided process, 173
definition of, 175

hip-joint, due to errors in diet, 267
may remain strictly local, 23
must have always existed, 225
not an entity, 331
partial dissolution in, 115
resistance to, 300
sole cause of, 332
selection played no part in the

evolution of, 277
symptoms of, 26
taint, 162
tendency, 265

ultimately comes through E, 334
Diseases, division into two classes, 305
example of potential, 24 n
how far it is possible to classify,

335 t

in which S is abnormal, E
nocuous, 311

in which there is no discoverable
abnormality of structure, 307

in which there is obvious struc-
tural abnormality, 306

of the mind, 341

zymotic, disappearance of many,
236
Dissolution, 89

3^4

INDEX.

"Diverse" and "complex" environ-
ments, definition of, 31

Drink, a more terrible poison than any
zymotic virus, 218

Drug?, action of, on different indi-
viduals, 157

Duncan, J. Matthews, on dysmenor-
rhea, 53

E

E, action of, independently of selec-
tion, 185
importance of studying the, of

our ancestors, 85
is the primary cause of natural
variation, 333
Education, 30, 63
Eliot, George, on sexual heredity, 72,

321
Embryo during gestation, influence of

the E upon, 130
Emotions, physiology of, 66
Environment, definition of easy and
rigorous, 255
distinction between natural and

artificial, 284
influence of, upon cell action, 17,

19

is the primary cause of natural

variations, 333
varies widely with the nature of
structure, 156
Epithelioma, squamous, 113, 345
Equilibration, direct and indirect, 188
Europeans and savages, first meeting

of, and disease, 238
Evolution, and dissolution opposite pro-

in the two sexes, 269

of species, 185

of man, diagram representing, 86

of disease, a paradoxical term,
277
Exercise, importance of, 100
Existence, cause of struggle for, 186

struggle for, far greater amongst
civilized than amongst primi-
tive peoples, 256

External-body-E, 178

its influence on the structure of

the individual, 147
analysis of, 29
Darwin's division of, 29
diversity of, 33

Fagge, Hilton, on the causation of

tubercle, 173
Fallacy, a common, 258
Family history, difficulty in obtaining,

327

Fatty changes abound in old age, 351
Fevers, specific, de novo origin of,

234 n
Fiji Islands, and measles, 325
Fixity of structural peculiarities, 84
Flea-bite hereditary, 173
Foetus, affected by mother's blood, 131

by pressure, 133
Food, the proper, for man, 100

natural and artificial, 149
Forms of E, complex, 293
Function, 308

meaning of, as applied to a multi-
cellular organism, 309
Functional disorders in which S is
normal, E nocuous, 310

dissolution, 93

efficiency, 304

G

Galton, on hereditary genius, 321

Gamogenesis, 37, 44

Garrod on gout and rheumatoid

arthritis, 83
Gout-producing E, the, 338
Gowers, Dr., on the causes of epilepsy,

170 n, 329
" Graft hybridism," 41
Granulation tissue, cells composing,

"3

Granulomata and sarcomata, 359
Gravitation, meaning of, I
Greswell, Dr., on the origin of tumours
by reversion, no

INDEX.

365

II

Habits, changes of, 143
Haeckel, Ernest, on evolution, 87, 190
Health, definition of, 291
Healthy- and disease-tendency in pa-
rents, 327
Heiresses tend to have few children,

275
Hereditary product, absolutely neces-
sary assumption of the theoretical
existence of a, 140
Heredity and the causation of disease,
321
apparent exceptions to principle

of, 328
at corresponding ages, 57, 183
at corresponding seasons, 58
immediate cause of, 1 80
influence of, on morals, 318
Mr. Drummond on, 319
influence of E disturbs, 127
reversion, 104
sexual, 59, 73
what it is, 40
Hereditary taint, Dr. Eeynolds on, 172
Hip-joint disease due to errors in diet,

267
Hooker, Dr., 345

Humoural and spiritual pathology, 332
Huth, on intermarriage of near kin, 83
Hutchinson, on the pre-cancerous stage,

346 n
Huxley on " life," 14

pathology, a branch of biology, 343
Hygiene, aim of, 235
Hypertrophy and degeneration, pro-
cesses of, 19

Impossibility of localizing a trouble,

Imprudence a mental defect, 198
Indirect equilibration, 188
Infanticide and savage races, 254
Infants, "civilized," cruelty practised

on, 149
Inheritance, 145
Insanitation and death, 207, 212, 240

Insanity, 165

and marriage, 120, 216
Instinct, and reason, 192

a safer guide than reason, 197
Instincts, importance of observing a
child's, 99

variations in, 194
Intemperance a fruitful cause of in-
sanity, 278
Interaction, morbid, of structure and

environment, 156, 157
Inter-crossing and inter-breeding, 42

Darwin on, 42, 43

Spencer on, 43
Intermarriage, 83

of disease, 83
Internal-cell-E, 18, 176

Jews and large towns, 244

Knox, Dr., and'the races of man, 248

Latent male sexual characters in -the

female, 61
Law of battle, Darwin on, 188
Laycock on the menstrual change,

Lee, Dr. E., on maternal impressions

131

Levelling-down process, a, 259
Life, a simple rhythm, 48

Beale on, 14 n

conditions of, 143

definition of, 14

Duke of Argyll on, 15 n

Huxley on, 14 n

Quatrefages on, 15 n
Lincoln, Abraham, 320
Lockyer, hypothesis of, 8 n.
London, absence of ozone in, 242
Londoners, degeneration amongst, 243

and outdoor life, 244
Lucas, Dr. Prosper, on heredity, 136

366

INDEX.

M

Mal-E, in civilized society, forms of,

212

in primitive tribes, 213
primary, 25
secondary, 25
Male and female, muscularity of, 65

intellectual capacity of, 65
Male element, influence of, on the

female organism, 123
Malignant bacteria, several varieties
of, 345
change a retrogressive one, 349
growths, parasitic origin of, 342
Man, Spencer on the moral, 257
Marriages, late, 261
Marrying for money, 275
Masturbation, 152
Material conditions, 4, 175, 176
effects, 6

a theoretical planetary sys-
tem, 5
Maternal impressions, 131
Maudsley on insanity, 165, 168
Menopause, its influence on women,

61
Menstrual rhythm, in woman, 53

in man, 54
Mental E of the two sexes different, 62
evolution in women, notes on,
270
Micro-organisms, adaptation to, 232
hygienic science and, 234
individuals differ in their resisting
power to, 233
Millican, K. W., 338
Mind, influence of the, upon the body,

317
Modifications of S come through E,

334
Molecule, arrangement of the atoms in,

9, 10
Monsters may be children of healthy

parents, 223
Motions, foul-smelling, of children,

150
Mott, Dr., a paper by, 280
Muscular exercise, quantity of, needful
to health, 230

N

" Naturalness," degree of adaptation,

the only criterion of, 288
Natural selection, 185, 191

and the procreative period, 264
comparative activity of, in man

and the lower animals, 253
influence of reason on, 201
Spencer on, 191
war and, 203, 222
Natural variations, are always altera-
tions wrought by E, 142, 159
causes of, 143

differences in E the primary
cause of, 142
Nature's laws fixed and unchangeable,2
Necessarily-fatal-E, 207, 208, 240
Nervous diseases, 340

system and disease, 20
New Zealand and Australia, extinction

of aborigines in, 248
Non-infectability of some children with

certain febrile disorders, 161
Non-symptomatic disorders, 306
Normality of S and E, 290, 292
of S, best test of, 299
potential, 298
Nosology, 27
Not-necessarily-fatal- E, 207

0

" Occupation diseases," 227

Outdoor life contrasted with indoor
life, 99

Ovaries, their influence on the indivi-
dual, 61

Ovum, the, 13

Ozone, absence of, in London, 242

Paget, on the vis medicatrix naturce,
97

on the difficulty of obtaining a
hereditary history, 120

on the dependence of the tuber-
cular diathesis upon external
conditions, 160

on cancer, 346

INDEX.

367

Pain, 224

Pangenesis, 46

Parents and offspring, 181, 330

Parents showing structural characters

of divergent character, 107
Parker, Mr., and scarlatina, 235 n
Parthogenesis, 41
Parts, use and disuse of, 144
Pathology a branch of biology, 147
Physical E the physician's province,

35

Physique of the two sexes, contrast

between, 251
Plants and the specific E, 158
Populations, stationary and increasing,

254
Post-partem E, capable of producing
structural change, 138
potent as it acts early, 148
" Potential " normality, meaning of,

297
Potentialities of disease, conversion of,

into actualities, 117
Potentiality of S, 1 15, 344
Pranzini, execution of, 80
Precocity, 58 n
Premature birth, effect of, on child's

future, 135
Prepotency, 75

Procreative period, natural selection
and the, 264
termination of the, 268
Prodigies, intellectual, a list of, 262
Protoplasm, causation of the vital

changes of, 11
Protoplasmic cell, 14

of what it consists, 1 1
Prussic acid, 339
Puberty, causation of early, in woman,

26971
Publican, the E of a, 227

Q

QUATREFAGES, 75

R

Race, the, modified by surgery, 286
Reason, defects of, as a guide, 195
first in full force, 195

Reason, guiding voice of, 194

has a far more difficult task than

instinct, 197
influence of, on natural selection,
201
Recapitulation of Part I., 174
Relations of one animal to another, 31
Relative share of S aud E in causation

of disease, table of, 164
Reproduction of species, methods of —
asexual, 40
by parthogenesis, 41
by "graft hybridism," 41
partial, 41
sexual, 41

object of, 42
Reproductive power at its prime, 261
Reproductive organs, their influence

on the emotions, 68
Resistance to disease, 300
Reversion, tendency of disease towards,

97

the two chief causes of, 104
bearing of, upon pathology, 118
to a remotely ancestral state,
109

Reynolds, Dr. Russell, on causation of
disease, 172

Rheumatic diathesis, 265

Rhythmical habits, 50
organic changes, 51

Rhythms, 49

Rigorous E, definition of, 255

S

Sarcoma parasite, the, 358
Sarcomata, secondary, 346
Sarcomatous and carcinomatous tissue,

nature of, 349
Salter, H., on the rhythm of asthma,

56
Savory, Mr., on alcohol and tobacco,

301
Sedentary scholar and active labourer,

difference in E and S in, 32
Sedgewick, Mr., on " The Influence of

Sex in limiting Hereditary Trans-
mission," 60
Selection, action of E independently

of, 188

3^8

INDEX.

Sexes, the mental differences between,

7i

Sexual heredity, 59, 63
doctrine of, 73
principle of, 183
reproduction, 41
selection, 187, 273

as regards the man, 273
as regards the woman, 276
Size, increase in, does not neces-
sarily indicate improved health,

259
11 Soil " theory, the, 359
Somerville, Mary, 70
Species, evolution of, 185
Spencer, Herbert, 43, 44, 45, 46, 47,
49, 97, 129, 136, 148, 188, 247,
257, 277, 282, 315, 319, 324
Spermatic theory, 357
Spiritual and bumoural pathology, 332
St. Hilaire, Geoffroy, on ante-partem

influences, 134
State-aided emigration, 281
Sterne, Lawrence, on ante-partem in-
fluences, 131
Structural abnormality, the extent to
which it occurs during the
actual time of disease, 303
characters, fixity of, 182
deficiency, 162

mean, principle of the, 74, 181
peculiarities, fixity of, 84
disappearance of, 87
Structure, examination of, 303

on what it depends, 36
Structures, parental, 37

sub-pathological variations, 38
true pathological variations, 38
Struggle for existence, cause of, 186
Sub-pathological variations, 38
Success or failure in life, 219
Surgery, practical, a highly artificial

order of E, 284
Sutton, Dr. H. G., 148
Sutton, Mr. Bland, 62 n
Survival of the fittest, 185

Symbolical method of expressing the
relative share taken by struc-
ture and environment in the
causation of disease, 163
further application of, 168

Teeth, influence of reversion on
artificial, 287

Testicles, their influence on the indi-
vidual, 52

Thackeray, 295

Tissue-alteration, 189

Training, the essence of, 298

True-pathological variations, 38

Tumour, growth of a malignant, 347

Tumours, Dr. Greswell on origin of, by
reversion, remarks thereon, no

Tuke, on the influence of the mind
on the body, 132

Twins, human, likeness between, 137
unlikeness of, due to differences in

ante-partem E, 149
same disease affecting, 167

" Variation under Domestication,"

quotation from, 75
Variations, mental and bodily, 215

natural, in the human race, 214
Vegetable diet, 250
Vis medicatrix naturce, 97

importance of the, 98

w

Watson, Sir Thomas, 167
Wealthy, the, a better chance of sur-
vival than the poor, 211, 217
Woman, the smaller headfyf, 62

more emotional than man, 66
Women and indoor life, 25 1

celebrated, 270

Yeast plant, the, 17

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Catalogue of Works Published by H. E. Lewis.

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CONTRIBUTIONS TO REPARATIVE SURGERY:

Showing its Application to the Treatment of Deformities, produced by
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Administrator of Anesthetics at University College Hospital and the Hospital for Women,

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ANESTHETICS THEIR USES AND ADMINISTRA-
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[Lewis's Practical Series.]

ALFRED H. CARTER, m.d. lond.

Member of the Royal College of Physicians ; Physician to the Queen's Hospital, Birmingham ;
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ELEMENTS OF PRACTICAL MEDICINE. Fifth Edition,
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P. CAZEAUX.

Adjunct Professor in the Faculty of Medicine of Paris, &c.

AND

S. TARNIER.

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Paris.

OBSTETRICS: THE THEORY AND PRACTICE; in-
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EXPERIMENTAL RESEARCHES IN ARTIFICIAL

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Assistant Surgeon to, and Senior Demonstrator of Anatomy and Operative Surgery at,

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in Surgery to the University of Oxford.

THE DIAGNOSIS AND TREATMENT OF DISEASES

OF THE KIDNEY AMENABLE TO DIRECT SURGICAL IN-
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Catalogue of Works Published by H. K. Lewis.

JOHN COCKLE, m.a., m.d.

Physician to the Royal Free Hospital.

ON INTRA-THORACIC CANCER. 8vo, 4s. 6d.

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Medical Superintendent of the Eastern Hospitals.

ON FEVERS: THEIR HISTORY, ETIOLOGY, DIAG-
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WALTER S. COLMAN, m.b. lond.
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SECTION CUTTING AND STAINING: A Practical

Guide to the Preparation of Normal and Morbid Histological Specimens.

[In the press.

ALFRED COOPER, f.r.c.s.

Surgeon to the St. Mark's Hospital for Fistula and other Diseases of the Rectum.

A PRACTICAL TREATISE ON THE DISEASES OP

THE RECTUM. Crown 8vo, 4s. [Just published.

W. H. CORFIELD, m.a., m.d. oxon.

Professor of Hygiene and Public Health in University College, London.

DWELLING HOUSES : their Sanitary Construction and

Arrangements. Second Edit., with Illustrations. Cr. 8vo, 3s. 6d.

EDWARD COTTERELL, m.r.cs. eng., l.r.c.p. lond.

Late House Surgeon, University College Hospital.

ON SOME COMMON INJURIES TO LIMBS; their

Treatment and After-treatment, including Bone-setting (so-called).
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1.
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11.
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in.
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Catalogue of Works Published by H. E. Lewis.

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A TREATISE ON DISEASES OF THE SKIN" AND

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EDGAR M. CROOKSHANK, m.b. lond., f.r.m.s.

Professor of Bacteriology, King's College, London.
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MANUAL OP BACTERIOLOGY: being an Introduction

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11.
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RIDLEY DALE, m.d., l.r.c.p. edin., m.r.c.s. eng.
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HENRY DAVIS, m.r.c.s. eng.
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GUIDE TO THE ADMINISTRATION OP ANESTHE-
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Physician in Charge of the Electro-therapeutical Department at St. Mary's Hospital.

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J. THOMPSON DICKSON, m.a., m.b. cantab.

Late Lecturer on Mental Diseases at Guy's Hospital.

THE SCIENCE AND PRACTICE OF MEDICINE IN

RELATION TO MIND, the Pathology of the Nerve Centres, and the
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Catalogue of Works Published by H. K. Lewis.

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II.
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JOHN EAGLE.

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A NOTE-BOOK OF SOLUBILITIES. Arranged chiefly

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JOHN ERIC ERICHSEN.

Ex-President of the Royal College of Surgeons ; Surgeon Extraordinary to
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MODERN SURGERY ; its Progress and Tendencies. Be-
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DR. FERBER.

MODEL DIAGRAM OF THE ORGANS IN THE

THORAX AND UPPER PART OF THE ABDOMEN. With
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King's Professor of Practice of Medicine in School of Physic, Ireland; Clinical Physician

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NOTES ON THE PHYSICAL DIAGNOSIS OF LUNG

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AUSTIN FLINT, jr., m.d.

Professor of Physiology and Physiological Anatomy in the Bellevue Medical College, New
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I.

A TEXT-BOOK OF HUMAN PHYSIOLOGY; De-
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II.
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Catalogue of Works Published by H. K. Lewis,

J. MILNER FOTHERGILL, m.d.

Member of the Royal College of Physicians of London; Physician to the City of London
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I.

A MANUAL OP DIETETICS : Large 8vo, ios. 6d.

ii.

THE HEART AND ITS DISEASES, WITH THEIR

TREATMENT; INCLUDING THE GOUTY HEART. Second
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in.
INDIGESTION AND BILIOUSNESS. Second Edition, post
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IV.

GOUT IN ITS PROTEAN ASPECTS. Post 8vo, 7s. 6d.

v.

HEART STARVATION. (Reprinted from the Edinburgh

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ERNEST FRANCIS, f.c.s.

Demonstrator of Practical Chemistry, Charing Cross Hospital.

PRACTICAL EXAMPLES IN QUANTITATIVE ANA-
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Examiner to the Pharmaceutical Society * Teacher of Pharmacy and Demonstrator of

Materia Medica at University College Hospital.

ELEMENTS OP MATERIA MEDICA AND PHAR-
MACY. Crown 8vo, 8s. 6d. [Just published:

HENEAGE GIBBES, m.d.

Lecturer on Physiology and on Normal and Morbid Histology in the Medical School of
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PRACTICAL HISTOLOGY AND PATHOLOGY. Third
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Catalogue of Works Published by H. K. Lewis. 9

C. A. GORDON, m.d., c.b.

Deputy Inspector General of Hospitals, Army Medical Department.

REMARKS ON ARMY SURGEONS AND THEIR

WORKS. Demy 8vo, 5s.

JOHN GORHAM, m.r.c.s.

TOOTH EXTRACTION : a Manual on the proper mode

of extracting Teeth. Second Edition, fcap. 8vo, is.

JOHN W. S. GOULEY, M.D.

Surgeon to Bellevue Hospital.

DISEASES OF MAN : Data of their Nomenclature, Clas-
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W. R. GOWERS, M.D., F.R.C.P., M.R.C.S.

Physician to University College Hospital, &c.

DIAGRAMS FOR THE RECORD OF PHYSICAL SIGNS.

In books of 12 sets of figures, is. Ditto, unbound, is.

J. B. GRESSWELL, m.r.c.v.s.
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VETERINARY PHARMACOLOGY AND THERAPEU-

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SAMUEL D. GROSS, m.d., ll.d., d.c.l. oxon.

Professor of Surgery in the Jefferson Medical College of Philadelphia.

A PRACTICAL TREATISE ON THE DISEASES, IN-
JURIES, AND MALFORMATIONS OF THE URINARY
BLADDER, .THE PROSTATE GLAND, AND THE URETHRA.
Third Edition, revised and edited by S. W. GROSS, A.M., M.D.,
Surgeon to the Philadelphia Hospital. Illustrated by 170 engravings,
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SAMUEL W. GROSS, a.m., m.d.

Surgeon to, and Lecturer on Clinical Surgery in, the Jefferson Medical College Hospital,
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A PRACTICAL TREATISE ON TUMOURS OF TH&

MAMMARY GLAND : embracing their Histology, Pathology, Dia-
gnosis, and Treatment. With Illustrations, 8vo, 10s. 6d.

10 Catalogue of Works Published by H. K. Lewis.

THE MODERN TREATMENT OP HEADACHES.

Square i6mo, 2s. 6d. [Just published.

WILLIAM A. HAMMOND, m.d.

Professor of Mental and Nervous Diseases in the Medical Department of the University of
the City of New York, &c.

I.

A TREATISE ON THE DISEASES OP THE NERVOUS

SYSTEM. Seventh edition, with 112 Illustrations, large 8vo, 25s.

II.
A TREATISE ON INSANITY. Large 8vo, 25s.

in.

SPIRITUALISM AND ALLIED CAUSES AND CON-
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post 8vo. 8s. 6d.

ALEXANDER HARVEY, m.a., m.d.

Emeritus Professor of Materia Medica in the University of Aberdeen; Consulting Physician
to the A berdeen Royal Infirmary, &c.

FIRST LINES OP THERAPEUTICS ; as based on the

Modes and the Processes of Healing, as occurring Spontaneously in Dis-
ease ; and on the Modes and the Processes of Dying, as resulting
Naturally from Disease. In a series of Lectures. Post 8vo, 5s.

ON THE FCETUS IN UTERO AS INOCULATING THE

MATERNAL WITH THE PECULIARITIES OF THE PATER-
NAL ORGANISM. In a series of Essays now first collected. Fcap.
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ALEXANDER HARVEY, m.d.

Emeritus Professor of Materia Medica in the University of A berdeen, &c.
AND

ALEXANDER DYCE DAVIDSON, m.d., f.r.s. edin.
Late Regius Professor of Materia Medica in the University of Aberdeen.

SYLLABUS OP MATERIA MEDICA FOR THE USE

OF STUDENTS, TEACHERS AND PRACTITIONERS Based
on the relative values of articles and preparations in the British
Pharmacopoeia. Eighth Edition, 32mo, is. 6d.

Catalogue of Works Published by H. K. Lewis. 11

K. M. HEANLEY.

Matron of Boston Cottage Hospital.

A MANUAL OP URINE TESTING. Compiled for the

use of Matrons, Nurses, and Probationers. Post 8vo, is. 6d.

GRAILY HEWITT, m.d.

Professor of Midwifery and Diseases of Women in University College, Obstetrical Physician
to University College Hospital, &c.

OUTLINES OP PICTORIAL DIAGNOSIS OP DIS-
EASES OF WOMEN. Folio, 6s.

C. HIGGENS, F.R.c.s.

Ophthalmic Surgeon to Guy's Hospital; Leeturer on Ophthalmology at Guy's Hospital

Medical School.

MANUAL OP OPHTHALMIC PRACTICE.

Crown 8vo. [Just ready.

[Lewis's Practical Series.]

BERKELEY HILL, m.b. lond., f.r.c.s.

Professor of Clinical Surgery in University College ; Surgeon to University College
Hospital and to the Lock Hospital.

THE ESSENTIALS OP BANDAGING. With directions

for Managing Fractures and Dislocations ; for administering Ether and
Chloroform ; and for using other Surgical Apparatus ; with a Chapter
on Surgical Landmarks. Sixth Edition, revised and enlarged, Illustrated
by 144 Wood Engravings, crown 8vo, 5s.

BERKELEY HILL, m.b. lond., f.r.c.s.

Professor of Clinical Surgery in University College ; Surgeon to University College
Hospital and to the Lock Hospital.

AND

ARTHUR COOPER, l.r.c.p., m.r.c.s.

Surgeon to the Westminster General Dispensary.
I.

SYPHILIS AND LOCAL CONTAGIOUS DISORDERS.

Second Edition, entirely re-written, royal 8vo, 18s.

THE STUDENT'S MANUAL OP VENEREAL DIS-
EASES. Being a Concise Description of those Affections and of their
Treatment. Fourth Edition, post 8vo, 2s. 6d.

12 Catalogue of Works Published by H, K. Lewis.

C. R. ILLINGWORTH, m.d. ed., m.r.c.s.

THE ABORTIVE TREATMENT OP SPECIFIC FE-
BRILE DISORDERS BY THE BINIODIDE OF MERCURY.
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SIR W. JENNER, Bart., m.d.

Physician in Ordinary to H.M. the Queen, and to H.R.H. the Prince oj Wales.

THE PRACTICAL MEDICINE OF TO-DAY: Two

Addresses delivered before the British Medical Association, ami the
Epidemiological Society, (1869). Small 8vo, is. 6d.

C. M. JESSOP, m.r.c.p.

Associate of King's College, London ; Brigade Surgeon H.M. British Forces.

ASIATIC CHOLERA, being a Report on an Outbreak

of Epidemic Cholera in 1876 at a Camp near Murree in India. With
map, demy 8vo, 2s. 6d.

GEORGE LINDSAY JOHNSON, m.a., m.b., b.c. cantab.

Clinical Assistant, late House Stir geon and Chlor of ormist, Royal Westminster Ophthalmic

Hospital, &c.

A NEW METHOD OF TREATING CHRONIC GLAU-
COMA, based on Recent Researches into its Pathology. With Illus-
trations and coloured frontispiece, demy 8vo, 3s. 6d.

NORMAN KERR, m.d., f.l.s.

President of the Society for the Study of Inebriety ; Consulting Physician, Dalrymple Home
for Inebriates, etc.

INEBRIETY: its Etiology, Pathology, Treatment, and

Jurisprudence. Crown 8vo, 12s. 6d. [Just published-

RUSTOMJEE NASERWANJEE KHORY, m.d. brux.

Member of the Royal College of Physicians.

THE PRINCIPLES AND PRACTICE OF MEDICINE.

Second Edition, revised and much enlarged, 2 vols., large 8vo, 28s.

NORMAN W. KINGSLEY, m.d.s., d.d.s.

President of the Board of Censors of the State of New York; Member of the American
Academy of Dental Science, &c.

A TREATISE ON ORAL DEFORMITIES AS A

BRANCH OF MECHANICAL SURGERY. With over 350 Illustra-
tions, 8vo, 16s.

Catalogue of Works Published by H. K. Lewis. 13

E. A. KIRBY, M.D., M.R.C.S. ENG.
Late Physician to the City Dispensary.

I.

A PHARMACOPOEIA OF SELECTED REMEDIES,

WITH THERAPEUTIC ANNOTATIONS, Notes on Alimentation
in Disease, Air, Massage, Electricity and other Supplementary Remedial
Agents, and a Clinical Index ; arranged as a Handbook for Prescribers.
Sixth Edition, enlarged and revised, demy 4to, 7s.

II.
ON THE VALUE OF PHOSPHORUS AS A

REMEDY FOR LOSS OF NERVE POWER. Sixth Edition, 8vo,
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J. WICKHAM LEGG, f.r.c.p.

Assistant Physician to Saint Bartholomew's Hospital, and Lecturer on Pathological
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I.

ON THE BILE, JAUNDICE, AND BILIOUS DISEASES.

With Illustrations in chromo-lithography, 719 pages, roy. 8vo, 25s.

11.
A GUIDE TO THE EXAMINATION OF THE URINE ;

intended chiefly for Clinical Clerks and Students. Sixth Edition, revised
and enlarged, with Illustrations, fcap. 8vo, 2s. 6d.

III.
A TREATISE ON HEMOPHILIA, SOMETIMES

CALLED THE HEREDITARY HEMORRHAGIC DIATHESIS.
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ARTHUR H. N. LEWERS, m.d, lond., m.r.c.p. lond.

Assistant Obstetric Physician to the London Hospital; Examiner in Midwifery and

Diseases of Women to the Society of Apothecaries of London ; Physician

to Out-patients at the Queen Charlotte's Lying-in Hospital, etc,

A PRACTICAL TEXTBOOK OF THE DISEASES OF

WOMEN. With Illustrations, crown 8vo, 8s. 6d. [Now ready.

[Lewis's Practical Series.]

DR. GEORGE LEWIN.

Professor at the Fr. Wilh. University, and Surgeon-in-Chief of the Syphilitic Wards and
Skin Disease Wards of the Charite Hospital, Berlin.

THE TREATMENT OF SYPHILIS WITH SUBCUTA-
NEOUS SUBLIMATE INJECTIONS. Translated by Dr. Carl
Prcegle, and Dr. E. H. Gale, late Surgeon United States Army.
Small 8vo, 7s.

14 Catalogue of Works Published by U.K. Lewis.

LEWIS'S PRACTICAL SERIES.

Under this title Mr. Lewis is publishing a Series of Monographs, em-
bracing the various branches of Medicine and Surgery.

The volumes are written by well-known Hospital Physicians and Sur-
geons, recognized as authorities in the subjects of which they treat. The
works are intended to be of a thoroughly practical nature, calculated
to meet the requirements of the practitioner and student, and to present the
most recent information in a compact and readable form.

MANUAL OF OPHTHALMIC PRACTICE.

By C. HIGGENS, F.R.C.S., Ophthalmic Surgeon to Guy's Hospital; Lecturer
on Ophthalmology at Guy's Hospital Medical School. With Illustrations, crown
8vo. [_N early ready.

A PRACTICAL TEXTBOOK OF THE DISEASES OF WOMEN.

By ARTHUR H. N. LEWERS, M.D. Lond., M.R.C.P. Lond., Assistant Ob-
stetric Physician to the London Hospital ; Examiner in Midwifery and Diseases
of Women to the Society of Apothecaries of London ; Physician to Out-patients
at the Queen Charlotte's Lying-in Hospital, etc. With Illustrations, crown 8vo,
8s. 6d. [Ready.

AN/ESTHETICS THEIR USES AND ADMINISTRATION.

By DUDLEY W. BUXTON, M.D., B S., M.R.C.P., Administrator of
Anaesthetics in University College Hospital and the Hospital for Women, Soho
Square. Crown 8vo, 4s. [Ready.

TREATMENT OF DISEASE IN CHILDREN: INCLUDING THE OUT-
LINES OF DIAGNOSIS AND THE CHIEF PATHOLOGICAL DIFFER-
ENCES BETWEEN CHILDREN AND ADULTS. By ANGEL MONEY,
M.D., M.R.C.P., Assistant Physician to the Hospital for Children, Great Ormond
Street, and to University College Hospital. Crown 8vo, 10s. 6d.

ON FEVERS: THEIR HISTORY, ETIOLOGY, DIAGNOSIS, PROGNOSIS,

AND TREATMENT. By ALEXANDER COLLIE, M.D. Aberd., Member
of the Royal College of Physicians of London ; Medical Superintendent of the
Eastern Hospitals ; Secretary of the Epidemiological Society for Germany and
Russia. Illustrated with Coloured Plates, crown 8vo, 8s. 6d.

HANDBOOK OF DISEASES OF THE EAR FOR THE USE OF STUDENTS

AND PRACTITIONERS. By URBAN PRITCHARD, M.D. Edin., F.R.C.S.
Eng., Professor of Aural Surgery at King's College, London ; Aural Surgeon to
King's College Hospital ; Senior Surgeon to the Royal Ear Hospital. With
Illustrations, crown 8vo, 4s. 6d.

A PRACTICAL TREATISE ON DISEASES OF THE KIDNEYS AND

URINARY DERANGEMENTS. By CHARLES HENRY RALFE, M.A.,
M.D. Cantab., Fellow of the Royal College of Physicians, London ; Assistant
Physician to the London Hospital ; Examiner in Medicine to the University of
Durham, etc., etc. With Illustrations, crown 8vo,ios. 6d.

DENTAL SURGERY FOR GENERAL PRACTITIONERS AND STUDENTS

OF MEDICINE. By ASHLEY W. BARRETT, M.B. Lond., M.R.C.S., L.D.S.,
Dental Surgeon to, and Lecturer on Dental Surgery and Pathology in the Medical
School of, the London Hospital. With Illustrations, cr. 8vo, 3s.

BODILY DEFORMITIES AND THEIR TREATMENT: A HANDBOOK OF

PRACTICAL ORTHOPAEDICS. By H. A. REEVES, F.R.C.S. Edin., Senior
Assistant Surgeon and Teacher of Practical Surgery at the London Hospital;
Surgeon to the Royal Orthopaedic Hospital, &c. With numerous Illustrations',
cr. 8vo, 8s. 6d.

Further volumes will be announced in due course.

Catalogue of Works Published by H. K. Lewis. 15

LEWIS'S POCKET CASE BOOK FOE. PRACTITIONERS

AND STUDENTS. Designed by A. T. BRAND, M.D. Roan, with
pencil, 3s. 6d. nett.

LEWIS'S POCKET MEDICAL VOCABULARY.

Over 200 pp., 32mo, roan, 3s. 6d.

T. R. LEWIS, M.B., F.R.S. ELECT, ETC.
Late Fellow of the Calcutta University, Surgeon-Major Army Medical Staff, etc.

PHYSIOLOGICAL AND PATHOLOGICAL RESEAR-
CHES. Arranged and edited by Sir Wm. Aitken, M.D., F.R.S. ,
G. E. Dobson, M.B., F.R.S., and A. E. Brown, B.Sc. Crown 410,
portrait, 5 maps, 43 plates including 15 chromo-lithographs, and 67
wood engravings, 30s. nett. [Just published.

J. S. LOMBARD, m.d.

Formerly Assistant Professor of Physiology in Harvard College.
I.

EXPERIMENTAL RESEARCHES ON THE REGIONAL

TEMPERATURE OF THE HEAD, under Conditions of Rest, In-
tellectual Activity and Emotion. With Illustrations, 8vo, 8s.

II.
ON THE NORMAL TEMPERATURE OF THE HEAD.
8vo, 5s.

WILLIAM THOMPSON LUSK, a.m., m.d.

Professor of Obstetrics and Diseases of Women in the Bellevue Hospital Medical College, &c.

THE SCIENCE AND ART OP MIDWIFERY.

Third Edition, with numerous Illustrations, 8vot 18s.

RAWDON MACNAMARA.

Professor of Materia Meiica Royal College of Surgeons, Ireland; Senior

Surgeon to the Westmoreland (Lock) Government Hospital;

Surgeon to the Meath Hospital, etc.

AN INTRODUCTION TO THE STUDY OF THE

BRITISH PHARMACOPCEIA. Demy 32mo, is. 6d. [Just published

JOHN MACPHERSON, m.d.

Inspector-General of Hospitals H.M. Bengal Army {Retired).
Author of" Cholera in its Home," &c.

I.

ANNALS OF CHOLERA FROM THE EARLIEST

PERIODS TO THE YEAR 1817. With a map. Demy 8vo, 7s. 6d.

11.
BATH, CONTREXEVILLE, AND THE LIME SUL-

PHATED WATERS. Crown 8vo, 2s. 6d.

16 Catalogue of Works Published by H. K. Lewis.

DR. V. MAGNAN.

Physician to St. Ann Asylum, Paris; Laureate of the Institute.

ON ALCOHOLISM, the Various Forms of Alcoholic

Delirium and their Treatment. Translated by W. S. Greenfield,
M.D., M.R.C.P. 8vo, 7s. 6d.

A. COWLEY MALLEY, b.a., m.b., b.ch. t.c.d.

PHOTO-MICROGRAPHY; including a description of

the Wet Collodion and Gelatino-Bromide Processes, together with the
best methods of Mounting and Preparing Microscopic Objects for Photo-
Micrography. Second Edition, with Photographs and Illustrations,
crown 8vo, 7s. 6d.

PATRICK MANSON, m.d., cm.
A tnoy, China.

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PROFESSOR MARTIN.

MARTIN'S ATLAS OF OBSTETRICS AND GYNECO-
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Catalogue of Works Published by H. K. Lewis. 17

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18 Catalogue of Works Published by H. K. Lewis.

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Medical Superintendent, Grove Hall Asylum, London, &c.
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Catalogue of Works Published by H. K. Lewis. 19

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PAUL F. MUNDE, m.d.

Professor of Gynecology at the New York Polyclinic; President of the New York Obstetrical
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11.
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in.

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20 Catalogue of Works Published by H. K. Lewis.

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Catalogue of Works Published by H. K. Lewis. 21

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isprudence, University College; Assistant!
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BRIGHT'S DISEASE AND THE ALLIED AFFECTIONS

OF THE KIDNEYS. With Illustrations, large 8vo, 8s. 6d.

22 Catalogue of Works Published by H. K. Lewis.

CHARLES HENRY RALFE, m.a., m.d. cantab., f.r.c.p. lond.

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A PRACTICAL TREATISE ON DISEASES OF THE

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[Lewis's Practical Series.]

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Professor of the Anatomy and Physiology of the Nervous System in the New

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THE APPLIED ANATOMY OF THE NERVOUS SYS-
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H. A. REEVES, f.r.cs. edin.

Senior Assistant Surgeon and Teacher of Practical Surgery at the London Hospital;
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BODILY DEFORMITIES AND THEIR TREATMENT :

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RALPH RICHARDSON, m.a., m.d.

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ON THE NATURE OF LIFE : An Introductory Chap-
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Catalogue of Works Published by H. K. Lewis. 23

FREDERICK T. ROBERTS, m.d., b.sc, f.r.c.p.

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*** Copies may also be had bound in two volumes cloth for is. 6d. extra.
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THE OFFICINAL MATERIA MEDICA.

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R. LAWTON ROBERTS, m.d., m.r.c.s.

ILLUSTRATED LECTURES ON AMBULANCE WORK.

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A. R. ROBINSON, m.b., l.r.c.p., and l.r.c.s. edin.

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Professor of Diseases of the Eye and Ear in the University of the City of New York ; Surgeon

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24 Catalogue of Works Published by H. K. Lewis,

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GOUT, AND ITS RELATIONS TO DISEASES OP

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UNIVERSITY COLLEGE COURSE OP PRACTICAL

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LECTURES ON MENTAL DISEASE. Second Edition, with
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DR. B. S. SCHULTZE.

Professor of Gyncecology ; Director of the Lying-in Hospital and of the

Gyno3cologibal Clinic at Jena.

THE PATHOLOGY AND TREATMENT OP DIS-
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J. J. Macan, M.A., M.R.C.S. With Illustrations, medium 8vo.

[In the press.

Catologne of Works Published by H. K. Lewis. 25

JOHN V. SHOEMAKER, a.m., m.d.

Professor of Skin Diseases in the Medico-Chirurgical College and Hospital of Philadelphia ;
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ALDER SMITH, m.b. lond., f.r.c.s.

Resident Medical Officer, Christ's Hospital, London.

RINGWORM : Its Diagnosis and Treatment.

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Physician to the New York Infants' Hospital; Clinical Lecturer on Diseases of Children
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26 Catalogue of Works Published by H. K. Lewis.

ADOLF STRUMPELL.
Director of the Medical Clinic in the University of Erlangen.

TEXT-BOOK OP MEDICINE FOR STUDENTS

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A HANDBOOK OF THE DISEASES OF THE EYE AND

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Catalogue of Works Published by H. K, Lewis. 27

EUGENE S. TALBOT, m.d., d.d.s.

Professor of Dental Surgery in the Woman's Medical College ; Lecturer on Dental
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IRREGULARITIES OP THE TEETH AND THEIR

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1.
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28 Catalogue of Works 'Published by H. if. Lewis.

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FREE PHOSPHORUS IN MEDICINE WITH SPE-
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EDWARD T. TIBBITS, m.d. lond.

Physician to the Bradford Infirmary ; and to the Bradford Fever Hospital.

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H. H. TOOTH, M.A., M.D., M.R.C.P.
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Hunterian Professor at the Royal College of Surgeons of England ; Surgeon to and Lecturer

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THE INSANE IN THE UNITED STATES AND

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Catalogue of Works Published by H. K. Lewis. 29

LAURENCE TURNBULL, m.d., ph.g.

Aural Surgeon to Jefferson Medical College Hospital, &c, &c.

ARTIFICIAL ANAESTHESIA : A Manual of Anaesthetic

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DR. R. ULTZMANN.

ON STERILITY AND IMPOTENCE IN MAN. Translated
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Professor in the University, and Member of the Academy of Sciences of Berlin, &c, &c.

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30 Catalogue of Works Published by H. K. Lewis.

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CONTRIBUTIONS TO PATHOLOGY AND THE PRAC-
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DISEASES OP THE NOSE AND ITS ACCESSORY

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FRANCIS H. WELCH, f.r.c.s.

Surgeon Major, AM.D.

ENTERIC PEVER : as Illustrated by Army Data at Home

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Deputy Coroner for Central Middlesex.

SUICIDE ; its History, Literature, Jurisprudence, and

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JOHN WILLIAMS, m.d., f.r.c.p.

Professor of Midwifery in University College, London ; Obstetric Physician to University
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CANCER OP THE UTERUS : Being the Harveian Lec-
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[Just published.

Physician to the Cheltenham General Hospital and Dispensary.

DISINFECTANTS AND HOW TO USE THEM. In

Packets of one doz. price is.

Catalogue of Works Published by H. K. Lewis. 31

DR. F. WINCKEL.
Formerly Professor and Director of the Gynecological Clinic at the University of Rostock.

THE PATHOLOGY AND TREATMENT OF CHILD-
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EDWARD WOAKES, m.d. lond.

Senior Aural Surgeon and Lecturer on Aural Surgery at the London Hospital ; Surgeon

to the London Throat Hospital.

I.

ON DEAFNESS, GIDDINESS AND NOISES IN THE

HEAD.

Vol. L— POST-NASAL CATARRH, AND DISEASES OF THE NOSE
CAUSING DEAFNESS. With Illustrations, cr. 8vo, 6s. 6d.

Vol. II.— ON DEAFNESS, GIDDINESS AND NOISES IN THE
HEAD. Third Edition, with Illustrations, cr. 8vo. [In preparation.

11.

NASAL POLYPUS: WITH NEURALGIA, HAY-FEVER,

AND ASTHMA, IN RELATION TO ETHMOIDITIS. With
Illustrations, cr. 8vo, 4s. 6d. [Now ready.

DAVID YOUNG, m.c, m.b., m.d.

Licentiate of the Royal College of Physicians, Edinburgh ; Licentiate of the Royal College

of Surgeons, Edinburgh ; Fellow of, and late Examiner in Midwifery to

the University of Bombay ; etc.

ROME IN WINTER AND THE TUSCAN HILLS IN

SUMMER. A Contribution to the Climate of Italy. Small
8vo, 6s.

HERMANN VON ZEISSL, m.d.
Late Professor at the Imperial Royal University of Viennat

OUTLINES OF THE PATHOLOGY AND TREAT-
MENT OF SYPHILIS AND ALLIED VENEREAL DISEASES.
Second Edition, revised by M. von Zeissl, M.D., Privat-Docent for
Diseases of the Skin and Syphilis at the Imperial Royal University of
Vienna. Translated, with Notes, by H. Raphael, M.D., Attending
Physician for Diseases of Genito-Urinary Organs and Syphilis, Bellevue
Hospital, Out-Patient Department. Large 8vo, 18s. [Just published.

Clinical Charts For Temperature Observations, etc.

Arranged by W. Rigden, M.R.C.S. 50s. per 1000, 28s. per 500,
15s. per 250, 7s. per 100, or is. per dozen.

Each Chart is arranged for four weeks, and is ruled at the back for making notes of
cases ; they are convenient in size, and are suitable both for hospital and private practice.

Catalogue of Works Published by H. K. Lewis.

THE NEW SYDENHAM SOCIETY'S PUBLICATIONS.

President : — Sir Spencer Wells, Bart., F.R.C.S.

Honorary Secretary : — Jonathan Hutchinson, Esq., F.R.S.

Treasurer: — W. Sedgwick Saunders, M.D., F.S.A.

Annual Subscription, One Guinea.

The Society issues translations of recent standard works by continental authors on sub-
jects of general interest to the profession, and an Atlas of Pathology with Coloured Plates.
The Society also has in hand a valuable and exhaustive " Lexicon of Medicine and the
Allied Sciences."

Amongst works recently issued are " Spiegelberg's Midwifery," " Hirsch's Historical and
Geographical Pathology," "Essays on Micro-Parasites," works by Charcot, Duchenne,
Begbie, Billroth, Graves, Koch, Hebra, Guttmann, etc.

The Annual Report, with full list of works published, and all further information will be
sent on application.

PERIODICAL WORKS PUBLISHED BY H. K. LEWIS.

THE NEW YORK MEDICAL JOURNAL. A Weekly Review of Medicine. Annual
Subscription, One Guinea, post free.

THE THERAPEUTIC GAZETTE. A Monthly Journal, devoted to the Science of
Pharmacology, and to the introduction of New Therapeutic Agents. Edited by Drs. H.
C. Wood and R. M. Smith. Annual Subscription, ios., post free.

THE GLASGOW MEDICAL JOURNAL. Published Monthly. Annual Subscription,
20s., post free. Single numbers, 2s. each.

LIVERPOOL MEDICO-CHIRURGICAL JOURNAL, including the Proceedings of
the Liverpool Medical Institution. Published twice yearly, 3s. 6d. each number.

THE INDIAN MEDICAL JOURNAL. A Journal of Medical and Sanitary Science
specially devoted to the Interests of the Medical Services. Annual Subscription, 24s.,
post free.

TRANSACTIONS OF THE COLLEGE OF PHYSICIANS OF PHILADELPHIA.
Volumes I. to VI., 8vo, ios. 6d. each.

MIDDLESEX HOSPITAL, REPORTS OF THE MEDICAL, SURGICAL, AND
Pathological Registrars for 1883 to 1886. Demy 8vo, 2s. 6d, nett each volume.

%* Mr. Lewis is in constant communication with the leading publishing
firms in America, and has transactions with them for the sale of his pub-
lications in that country. Advantageous arrangements are made in the
interests of Authors for the publishing of their works in the United States.

Mr. Lewis's publications can be procured of all Booksellers in any part of
the world.

London: Printed by H. K Lewis, 136 Gower Street, W.C.

/

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Renewed books are subject to immediate recall.

WAR 2 4 1977

JAN 5 — «&e-

DCC 3 2 1959

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