Disease and Its Causes by William Thomas Councilman

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DISEASE AND ITS CAUSES

by

W. T. COUNCILMAN, A.M., M.D., LL.D.
Professor of Pathology, Harvard University

New York
Henry Holt and Company
London
Williams and Norgate
The University Press, Cambridge, U.S.A.

1913

PREFACE

In this little volume the author has endeavored to portray disease as
life under conditions which differ from the usual. Life embraces much
that is unknown and in so far as disease is a condition of living
things it too presents many problems which are insoluble with our
present knowledge. Fifty years ago the extent of the unknown, and at
that time insoluble questions of disease, was much greater than at
present, and the problems now are in many ways different from those in
the past. No attempt has been made to simplify the subject by the
presentation of theories as facts.

The limitation as to space has prevented as full a consideration of
the subject as would be desirable for clearness, but a fair division
into the general and concrete phases of disease has been attempted.
Necessarily most attention has been given to the infectious diseases
and their causes. This not only because these diseases are the most
important but they are also the best known and give the simplest
illustrations. The space given to the infectious diseases has allowed
a merely cursory description of the organic diseases and such subjects
as insanity and heredity. Of the organic diseases most space has been
devoted to disease of the heart. There is slight consideration of the
environment and social conditions as causes of disease.

Very few authors are mentioned in the text and no bibliography is
given. There is lack of literature dealing with the general aspects of
disease; the book moreover is not written for physicians, and the list
of investigators from whose work the knowledge of disease has been
derived would be too long to cite.

It has been assumed that the reader has some familiarity with
elementary anatomy and physiology, and these subjects have been
considered only as much as is necessary to set the scene for the
drama. I am indebted to my friend, Mr. W. R. Thayer, for patiently
enduring the reading of the manuscript and for many suggestions as to
phrasing.

CONTENTS

CHAPTER PAGE

CHAPTER I

DEFINITION OF DISEASE.--CHARACTERISTICS OF LIVING MATTER.--CELLS AS
THE LIVING UNITS.--AMOEBA AS TYPE OF A UNICELLULAR ANIMAL.--THE
RELATION OF LIVING MATTER TO ENVIRONMENT.--CAPACITY OF ADAPTATION TO
ENVIRONMENT SHOWN BY LIVING MATTER.--INDIVIDUALITY OF LIVING
MATTER.--THE CAUSES OF DISEASE EXTRINSIC.--THE RELATION OF THE HUMAN
BODY TO THE ENVIRONMENT.--THE SURFACES OF THE BODY.--THE INCREASE OF
SURFACE BY GLAND FORMATION.--THE REAL INTERIOR OF THE BODY REPRESENTED
BY THE VARIOUS STRUCTURES PLACED BETWEEN THE SURFACES.--THE FLUIDS OF
THE BODY.--THE NERVOUS SYSTEM.--THE HEART AND BLOOD-VESSELS.--THE
CELLS OF THE BLOOD.--THE DUCTLESS GLANDS 9

CHAPTER II

NO SHARP LINE OF DEMARCATION BETWEEN HEALTH AND DISEASE.--THE
FUNCTIONAL NUTRITIVE AND FORMATIVE ACTIVITIES OF CELLS.--DESTRUCTION
AND REPAIR CONSTANT PROCESSES IN LIVING MATTER.--INJURIES TO THE
BODY.--THE EFFECT OF HEAT.--THE ACTION OF POISONS.--THE LESIONS OF
DISEASE.--REPAIR.--THE LAWS GOVERNING REPAIR.--RELATION OF REPAIR TO
COMPLEXITY OF STRUCTURE AND AGE.--THE RESERVE FORCE OF THE
BODY.--COMPENSATORY PROCESSES IN THE BODY.--OLD AGE.--THE DIMINUTION
OF RESISTANCE TO THE EFFECTS OF THE ENVIRONMENT A PROMINENT FACTOR IN
OLD AGE.--DEATH.--HOW BROUGHT ABOUT.--CHANGES IN THE BODY AFTER
DEATH.--THE RECOGNITION OF DEATH 40

CHAPTER III

THE GROWTH OF THE BODY.--GROWTH MORE RAPID IN EMBRYONIC PERIOD.--THE
COOeRDINATION AND REGULATION OF GROWTH.--TUMORS.--THE GROWTH OF TUMORS
COMPARED WITH NORMAL GROWTH.--SIZE. SHAPE AND STRUCTURE OF
TUMORS.--THE GROWTH CAPACITY OF TUMORS AS SHOWN BY THE INOCULATION OF
TUMORS OF MICE.--BENIGN AND MALIGNANT TUMORS.--EFFECT OF
INHERITANCE.--ARE TUMORS BECOMING MORE FREQUENT?--THE EFFECT PRODUCED
BY A TUMOR ON THE INDIVIDUAL WHO BEARS IT.--RELATION OF TUMORS TO AGE
AND SEX.--THEORIES AS TO THE CAUSE OF TUMORS.--THE PARASITIC
THEORY.--THE TRAUMATIC THEORY.--THE EMBRYONIC THEORY.--THE IMPORTANCE OF
THE EARLY RECOGNITION AND REMOVAL OF TUMORS 62

CHAPTER IV

THE REACTIONS OF THE TISSUES OF THE BODY TO INJURIES.--INFLAMMATION.--
THE CHANGES IN THE BLOOD IN THIS.--THE LMIGRATION OF THE CORPUSCLES OF
THE BLOOD.--THE EVIDENT CHANGES IN THE INJURED PART AND THE MANNER IN
WHICH THESE ARE PRODUCED.--HEAT REDNESS SWELLING AND PAIN.--THE
PRODUCTION OF BLISTERS BY SUNBURN.--THE CHANGES IN THE CELLS OF AN
INJURED PART.--THE CELLS WHICH MIGRATE FROM THE BLOOD VESSELS ACT AS
PHAGOCYTES.--THE MACROPHAGES.--THE MICROPHAGES.--CHEMOTROPISM.--THE
HEALING OF INFLAMMATION.--THE REMOVAL OF THE CAUSE.--CELL REPAIR AND NEW
FORMATION.--NEW FORMATION OF BLOOD VESSELS.--ACUTE AND CHRONIC
INFLAMMATION.--THE APPARENTLY PURPOSEFUL CHARACTER OF THE CHANGES IN
INFLAMMATION 79

CHAPTER V

INFECTIOUS DISEASES.--THE HISTORICAL IMPORTANCE OF EPIDEMICS OF
DISEASE.--THE LOSSES IN BATTLE CONTRASTED WITH THE LOSSES IN ARMIES
PRODUCED BY INFECTIOUS DISEASES.--THE DEVELOPMENT OF KNOWLEDGE OF
EPIDEMICS.--THE VIEWS OF HIPPOCRATES AND ARISTOTLE.--SPORADIC AND
EPIDEMIC DISEASES.--THE THEORY OF THE EPIDEMIC CONSTITUTION.--THEORY
THAT THE CONTAGIOUS MATERIAL IS LIVING.--THE DISCOVERY OF BACTERIA BY
LOEWENHOECK IN 1675.--THE RELATION OF CONTAGION TO THE THEORY OF
SPONTANEOUS GENERATION.--NEEDHAM AND SPALLANZANI.--THE DISCOVERY OF THE
COMPOUND MICROSCOPE IN 1605.--THE PROOF THAT A LIVING ORGANISM IS THE
CAUSE OF A DISEASE.--ANTHRAX.--THE DISCOVERY OF THE ANTHRAX BACILLUS IN
1851.--THE CULTIVATION OF THE BACILLUS BY KOCH.--THE MODE OF
INFECTION.--THE WORK OF PASTEUR ON ANTHRAX.--THE IMPORTANCE OF THE
DISEASE 97

CHAPTER VI

CLASSIFICATION OF THE ORGANISMS WHICH CAUSE DISEASE.--BACTERIA SIZE
SHAPE STRUCTURE CAPACITY FOR GROWTH MULTIPLICATION AND SPORE
INFORMATION.--THE ARTIFICIAL CULTIVATION OF BACTERIA.--THE IMPORTANCE
OF BACTERIA IN NATURE.--VARIATIONS IN BACTERIA.--SAPROPHYTIC AND
PARASITIC FORMS.--PROTOZOA.--STRUCTURE MORE COMPLICATED THAN THAT OF
BACTERIA.--DISTRIBUTION IN NATURE.--GROWTH AND
MULTIPLICATION.--CONJUGATION AND SEXUAL REPRODUCTION.--SPORE
FORMATION.--THE NECESSITY FOR A FLUID ENVIRONMENT.--THE FOOD OF
PROTOZOA.--PARASITISM.--THE ULTRA MICROSCOPIC OR FILTERABLE
ORGANISMS.--THE LIMITATION OF THE MICROSCOPIC.--PORCELAIN FILTERS TO
SEPARATE ORGANISMS FROM A FLUID.--FOOT AND MOUTH DISEASE PRODUCED BY AN
ULTRA MICROSCOPIC ORGANISM.--OTHER DISEASES SO PRODUCED.--DO NEW
DISEASES APPEAR? 116

CHAPTER VII

THE NATURE OF INFECTION.--THE INVASION OF THE BODY FROM ITS
SURFACES.--THE PROTECTION OF THESE SURFACES.--CAN BACTERIA PASS THROUGH
AN UNINJURED SURFACE?.--INFECTION FROM WOUNDS.--THE WOUNDS IN MODERN
WARFARE LESS PRONE TO INFECTION.--THE RELATION OF TETANUS TO WOUNDS
CAUSED BY THE TOY PISTOL.--THE PRIMARY FOCUS OR ATRIUM OF
INFECTION.--THE DISSEMINATION OF BACTERIA IN THE BODY.--THE DIFFERENT
DEGREES OF RESISTANCE TO BACTERIA SHOWN BY THE VARIOUS ORGANS.--MODE OF
ACTION OF BACTERIA.--TOXIN PRODUCTION.--THE RESISTANCE OF THE BODY TO
BACTERIA.--CONFLICT BETWEEN PARASITE AND HOST.--ON BOTH SIDES MEANS OF
OFFENSE AND DEFENSE.--PHAGOCYTOSIS.--THE DESTRUCTION OF BACTERIA BY THE
BLOOD.--THE TOXIC BACTERIAL DISEASES.--TOXIN AND ANTITOXIN.--IMMUNITY.--
THE THEORY OF EHRLICH 135

CHAPTER VIII

SECONDARY TERMINAL AND MIXED INFECTIONS.--THE EXTENSION OF INFECTION IN
THE INDIVIDUAL.--TUBERCULOSIS.--THE TUBERCLE BACILLUS.--FREQUENCY OF THE
DISEASE.--THE PRIMARY FOCI.--THE EXTENSION OF BACILLI.--THE DISCHARGE OF
BACILLI FROM THE BODY.--INFLUENCE OF THE SEAT OF DISEASE ON THE
DISCHARGE OF BACILLI.--THE INTESTINAL DISEASES.--MODES OF
INFECTION.--INFECTION BY SPUTUM SPRAY.--INFECTION OF WATER
SUPPLIES.--EXTENSION OF INFECTION BY INSECTS.--TRYPANASOME
DISEASES.--SLEEPING SICKNESS.--MALARIA.--THE PART PLAYED BY
MOSQUITOES.--PARASITISM IN THE MOSQUITO.--INFECTION AS INFLUENCED BY
HABITS AND CUSTOMS.--HOOKWORM DISEASE.--INTERRELATION BETWEEN HUMAN AND
ANIMAL DISEASES.--PLAGUE.--PART PLAYED RATS IN TRANSMISSION.--THE PRESENT
EPIDEMIC OF PLAGUE 159

CHAPTER IX

DISEASE CARRIERS.--THE RELATION BETWEEN SPORADIC CASES OF INFECTIOUS
DISEASE AND EPIDEMICS.--SMALLPOX.--CEREBROSPINAL
MENINGITIS.--POLYOMYELITIS.--VARIATION IN THE SUSCEPTIBILITY OF
INDIVIDUALS.--CONDITIONS WHICH MAY INFLUENCE SUSCEPTIBILITY.--RACIAL
SUSCEPTIBILITY.--INFLUENCE OF AGE AND SEX.--OCCUPATION AND
ENVIRONMENT.--THE AGE PERIOD OF INFECTIOUS DISEASES 185

CHAPTER X

INHERITANCE AS A FACTOR IN DISEASE.--THE PROCESS OF CELL
MULTIPLICATION.--THE SEXUAL CELLS DIFFER FROM THE OTHER CELLS OF THE
BODY.--INFECTION OF THE OVUM.--INTRAUTERINE INFECTION.--THE PLACENTA AS A
BARRIER TO INFECTION.--VARIATIONS AND MUTATIONS.--THE INHERITANCE OF
SUSCEPTIBILITY TO DISEASE.--THE INFLUENCE OF ALCOHOLISM IN THE PARENTS
ON THE DESCENDANTS.--THE HEREDITY OF NERVOUS DISEASES.--TRANSMISSION OF
DISEASE BY THE FEMALE ONLY.--HEMOPHILIA.--THE INHERITANCE OF
MALFORMATIONS.--THE CAUSES OF MALFORMATIONS.--MATERNAL IMPRESSIONS HAVE
NO INFLUENCE.--EUGENICS 197

CHAPTER XI

CHRONIC DISEASES.--DISEASE OF THE HEART AS AN EXAMPLE.--THE STRUCTURE
AND FUNCTION OF THE HEART.--THE ACTION OF THE VALVES.--THE PRODUCTION
OF HEART DISEASE BY INFECTION.--THE CONDITIONS PRODUCED IN THE
VALVES.--THE MANNER IN WHICH DISEASE OF THE VALVES INTERFERES WITH
THEIR FUNCTION,--THE COMPENSATION OF INJURY BY INCREASED ACTION OF
HEART.--THE ENLARGEMENT OF THE HEART.--THE RESULT OF IMPERFECT WORK OF
THE HEART.--VENOUS CONGESTION.--DROPSY.--CHRONIC DISEASE OF THE
NERVOUS SYSTEM.--INSANITY.--RELATION BETWEEN INSANITY AND
CRIMINALITY.--ALCOHOLISM AND SYPHILIS FREQUENT CAUSES OF
INSANITY.--THE DIRECT AND INDIRECT CAUSES OF NERVOUS DISEASES.--THE
RELATION BETWEEN SOCIAL LIFE AND NERVOUS DISEASES.--FUNCTIONAL AND
ORGANIC DISEASE.--NEURASTHENIA 219

CHAPTER XII

THE RAPID DEVELOPMENT OF MEDICINE IN THE LAST FIFTY YEARS.--THE
INFLUENCE OF DARWIN.--PREVENTIVE MEDICINE.--THE DISSEMINATION OF
MEDICAL KNOWLEDGE.--THE DEVELOPMENT OF CONDITIONS IN RECENT YEARS
WHICH ACT AS FACTORS OF DISEASE.--FACTORY LIFE.--URBAN LIFE.--THE
INCREASE OF COMMUNICATION BETWEEN PEOPLES.--THE INTRODUCTION OF PLANT
PARASITES.--THE INCREASE IN ASYLUM LIFE.--INFANT MORTALITY.--WEALTH
AND POVERTY AS FACTORS IN DISEASE 241

GLOSSARY 250

INDEX 252

DISEASE AND ITS CAUSES

CHAPTER I

DEFINITION OF DISEASE.--CHARACTERISTICS OF LIVING MATTER.--CELLS AS
THE LIVING UNITS.--AMOEBA AS TYPE OF A UNICELLULAR ANIMAL.--THE
RELATION OF LIVING MATTER TO THE ENVIRONMENT.--CAPACITY OF ADAPTATION
TO THE ENVIRONMENT SHOWN BY LIVING MATTER--INDIVIDUALITY OF LIVING
MATTER.--THE CAUSES OF DISEASE.--EXTRINSIC.--THE RELATION OF THE HUMAN
BODY TO THE ENVIRONMENT.--THE SURFACES OF THE BODY.--THE INCREASE OF
SURFACE BY GLAND FORMATION.--THE REAL INTERIOR OF THE BODY REPRESENTED
BY THE VARIOUS STRUCTURES PLACED BETWEEN THE SURFACES.--THE FLUIDS OF
THE BODY.--THE NERVOUS SYSTEM.--THE HEART AND BLOOD-VESSELS.--THE
CELLS OF THE BLOOD.--THE DUCTLESS GLANDS.

There is great difficulty, in the case of a subject so large and
complex as is disease, in giving a definition which will be accurate
and comprehensive. Disease may be defined as "A change produced in
living things in consequence of which they are no longer in harmony
with their environment." It is evident that this conception of disease
is inseparable from the idea of life, since only a living thing can
become diseased. In any dead body there has been a preexisting disease
or injury, and, in consequence of the change produced, that particular
form of activity which constitutes life has ceased. Changes such as
putrefaction take place in the dead body, but they are changes which
would take place in any mass similarly constituted, and are not
influenced by the fact that the mass was once living. Disease may also
be thought of as the negation of the normal. There is, however, in
living things no definite type for the normal. An ideal normal type
may be constructed by taking the average of a large number of
individuals; but any single individual of the group will, to a greater
or less extent, depart from it. No two individuals have been found in
whom all the Bertillon measurements agree. Disease has reference to
the individual; conditions which in one individual would be regarded
as disease need not be so regarded in another. Comparisons between
health and disease, the normal and the abnormal, must be made not
between the ideal normal and abnormal, but between what constitutes
the normal or usual and the abnormal in a particular individual.

The conception of disease is so inseparably associated with that of
life that a brief review of the structure and properties of living
things is necessary for the comprehension of the definition which has
been given. Living matter is subject to the laws which govern matter,
and like matter of any other sort it is composed of atoms and
molecules. There is no force inherent in living matter, no vital force
independent of and differing from the cosmic forces; the energy which
living matter gives off is counterbalanced by the energy which it
receives. It undergoes constant change, and there is constant
interchange with the environment. The molecules which compose it are
constantly undergoing change in their number, kind and arrangement.
Atom groups as decomposition products are constantly given off from
it, and in return it receives from without other atom groups with
which it regenerates its substance or increases in amount. All
definitions of life convey this idea of activity. Herbert Spencer
says, "Life is the continuous adjustment of internal relations to
external conditions." The molecules of the substances forming the
living material are large, complex and unstable, and as such they
constantly tend to pass from the complex to the simple, from unstable
to stable equilibrium. The elementary substances which form living
material are known, but it has hitherto not been found possible
artificially so to combine these substances that the resulting mass
will exhibit those activities which we call the phenomena of life. The
distinction between living and nonliving matter is manifest only when
the sum of the activities of the living matter is considered; any
single phenomenon of the living may appear also in the non-living
material. Probably the most distinguishing criterion of living matter
is found in its individuality, which undoubtedly depends upon
differences in structure, whether physical or chemical, between the
different units.

Certain conditions are essential for the continued existence of living
matter. It must be surrounded by a fluid or semi-fluid medium in order
that there may be easy interchange with the environment. It must
constantly receive from the outside a supply of energy in the form of
food, and substances formed as the result of the intracellular
chemical activity must be removed. In the case of many animals it
seems as though the necessity of a fluid environment for living matter
did not apply, for the superficial cells of the skin have no fluid
around them; these cells, however, are dead, and serve merely a
mechanical or protective purpose. All the living cells of the skin and
all the cells beneath this have fluid around them.

Living matter occurs always in the form of small masses called
"cells," which are the living units. The cells vary in form, structure
and size, some being so large that they can be seen with the naked
eye, while others are so small that they cannot be distinctly seen
with the highest power of the microscope. The living thing or organism
may be composed of a single cell or, in the case of the higher animals
and plants, may be formed of great numbers of cells, those of a
similar character being combined in masses to form organs such as the
liver and brain.

In each cell there is a differentiated area constituting a special
structure, the nucleus, which contains a peculiar material called
"chromatin." The nucleus has chiefly to do with the multiplication of
the cell and contains the factors which determine heredity. The mass
outside of the nucleus is termed "cytoplasm," and this may be
homogeneous in appearance or may contain granules. On the outside
there is a more or less definite cell membrane. It is generally
believed that the cell material has a semi-fluid or gelatinous
consistency and is contained within an intracellular meshwork. It is
an extraordinarily complex mass, whether regarded from a chemical or
physical point of view. (Fig. 1.)

[Illustration: FIG. 1.--DIAGRAM OF CELL. 1. Cell membrane. 2. Cell
substance or cytoplasm. 3. Nucleus. 4. Nuclear membrane.
5. Nucleolus.]

A simple conception of health and disease can be arrived at by the
study of these conditions in a unicellular animal directly under a
microscope, the animal being placed on a glass slide. For this purpose
a small organism called "Amoeba" (Fig. 2), which is commonly present
in freshwater ponds, may be used. This appears as a small mass,
seemingly of gelatinous consistency with a clear outline, the exterior
part homogeneous, the interior granular. The nucleus, which is seen
with difficulty, appears as a small vesicle in the interior. Many
amoebae show also in the interior a small clear space, the contractile
vesicle which alternately contracts and expands, through which action
the movement of the intracellular fluid is facilitated and waste
products removed. The interior granules often change their position,
showing that there is motion within the mass. The amoeba slowly moves
along the surface of the glass by the extension of blunt processes
formed from the clear outer portion which adhere to the surface and
into which the interior granular mass flows. This movement does not
take place by chance, but in definite directions, and may be
influenced. The amoeba will move towards certain substances which may
be placed in the fluid around it and away from others. In the water in
which the amoebae live there are usually other organisms, particularly
bacteria, on which they feed. When such a bacterium comes in contact
with an amoeba, it is taken into its body by becoming enclosed in
processes which the amoeba sends out. The enclosed organism then lies
in a small clear space in the amoeba, surrounded by fluid which has
been shown to differ in its chemical reaction from the general fluid
of the interior. This clear space, which may form at any point in the
body, corresponds to a stomach in a higher animal and the fluid within
it to the digestive fluid or gastric juice. After a time the enclosed
organism disappears, it has undergone solution and is assimilated;
that is, the substances of which its body was composed have been
broken up, the molecules rearranged, and a part has been converted
into the substance of the amoeba. If minute insoluble substances, such
as particles of carmine, are placed in the water, these may also be
taken up by the amoeba; but they undergo no change, and after a time
they are cast out. Under the microscope only the gross vital
phenomena, motion of the mass, motion within the mass, the reception
and disintegration of food particles, and the discharge of inert
substances can be observed. The varied and active chemical changes
which are taking place cannot be observed.

[Illustration: FIG. 2.--AMOEBA. 1. Nucleus. 2. Contractile vesicle.
3. Nutritive vacuole containing a bacillus.]

Up to the present it has been assumed that the environment of the
amoeba is that to which it has become adapted and which is favorable
to its existence. Under these conditions its structure conforms to the
type of the species, as do also the phenomena which it exhibits, and
it can assimilate food, grow and multiply. If, during the observation,
a small crystal of salt be placed in the fluid, changes almost
instantly take place. Motion ceases, the amoebae appear to shrink into
smaller compass, and they become more granular and opaque. If they
remain a sufficiently long time in this fluid, they do not regain
their usual condition when placed again in fresh water. None of the
phenomena which characterized the living amoebae appear: we say they
are dead. After a time they begin to disintegrate, and the bacteria
contained in the water and on which the amoebae fed now invade their
tissue and assist in the disintegration. By varying the duration of
the exposure to the salt water or the amount of salt added, a point
can be reached where some, but not all, of the amoebae are destroyed.
Whether few or many survive depends upon the degree of injury
produced. Much the same phenomena can be produced by gradually heating
the water in which the amoebae are contained. It is even possible
gradually to accustom such small organisms to an environment which
would destroy them if suddenly subjected to it, but in the process of
adaptation many individuals will have perished.

It is evident from such an experiment that when a living organism is
subject to an environment to which it has not become adapted and which
is unfavorable, such alterations in its structure may be produced that
it is incapable of living even when it is again returned to the
conditions natural to it. Such alterations of structure or injuries
are called the _lesions_ of disease. We have seen that in certain
individuals the injury was sufficient to inhibit for a time only the
usual manifestations of life; these returned when the organism was
removed from the unfavorable conditions, and with this or preceding it
the organisms, if visibly altered, regained the usual form and
structure. We may regard this as disease and recovery. In the disease
there is both the injury or lesion and the derangement of vital
activity dependent upon this. The cause of the disease acted on the
organism from without, it was external to it. Whether the injurious
external conditions act as in this case by a change in the surrounding
osmotic pressure, or by the destruction of ferments within the cell,
or by the introduction into the cell of substances which form stable
chemical union with certain of its constituents, and thus prevent
chemical processes taking place which are necessary for life, the
result is the same.

The experiments with the amoebae show also two of the most striking
characteristics of living matter. 1. It is _adaptable_. Under the
influence of unusual conditions, alterations in structure and possibly
in substance, may take place, in consequence of which the organisms
under such external conditions may still exhibit the usual phenomena.
The organism cannot adapt itself to such changes without undergoing
change in structure, although there may be no evidence of such changes
visible. This alteration of structure does not constitute a disease,
provided the harmonious relation of the organism with the environment
be not impaired. An individual without a liver should not be regarded
as diseased, provided there can be such an internal adjustment that
all of the vital phenomena could go on in the usual manner without the
aid of this useful and frequently maligned organ. 2. It is
_individual_. In the varying degrees of exposure to unfavorable
conditions of a more serious nature some, but not all, of the
organisms are destroyed; in the slight exposure, few; in the longer,
many. Unfavorable conditions which will destroy all individuals of a
species exposed to them must be extremely rare.[1] There is no such
individuality in non-living things. In a mass of sugar grains each
grain shows just the same characteristics and reacts in exactly the
same way as all the other grains of the mass. Individuality, however
expressed, is due to structural variation. It is almost impossible to
conceive in the enormous complexity of living things that any two
individuals, whether they be single cells or whether they be formed of
cell masses, can be exactly the same. It is not necessary to assume in
such individual differences that there be any variation in the amount
and character of the component elements, but the individuality may be
due to differences in the atomic or molecular arrangements. There are
two forms of tartaric-acid crystals of precisely the same chemical
formula, one of which reflects polarized light to the left, and the
other to the right. All the left-sided crystals and all the
right-sided are, however, precisely the same. The number of possible
variations in the chemical structure of a substance so complex as is
protoplasm is inconceivable.

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