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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
COÖRDINATION 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 preëxisting 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
amoebæ 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 amoebæ 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 amoebæ 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 amoebæ appear: we say they
are dead. After a time they begin to disintegrate, and the bacteria
contained in the water and on which the amoebæ 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 amoebæ 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 amoebæ 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 amoebæ 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.
In no way is the individuality of living matter more strongly
expressed than in the resistance to disease. The variation in the
degree of resistance to an unfavorable environment is seen in every
tale of shipwreck and exposure. In the most extensive epidemics
certain individuals are spared; but here care must be exercised in
interpreting the immunity, for there must be differences in the degree
of exposure to the cause of the epidemic. It would not do to interpret
the immunity to bullets in battle as due to any individual
peculiarity, save possibly a tendency in certain individuals to remove
the body from the vicinity of the bullets; in battle and in epidemics
the factors of chance and of prudence enter. No other living organism
is so resistant to changes in environment as is man, and to this
resistance he owes his supremacy. By means of his intelligence he can
change the environment. He is able to resist the action of cold by
means of houses, fire and clothing; without such power of intelligent
creation of the immediate environment the climatic area in which man
could live would be very narrow. Just as disease can be acquired by an
unfavorable environment, man can so adjust his environment to an
injury that harmony will result in spite of the injury. The
environment which is necessary to compensate for an injury may become
very narrow. For an individual with a badly working heart more and
more restriction of the free life is necessary, until finally the only
environment in which life is even tolerably harmonious is between
blankets and within the walls of a room.
The various conditions which may act on an organism producing the
changes which are necessary for disease are manifold. Lack of
resistance to injury, incapacity for adaptation, whether it be due to
a congenital defect or to an acquired condition, is not in itself a
disease, but the disease is produced by the action on such an
individual of external conditions which may be nothing more than those
to which the individuals of the species are constantly subject and
which produce no harm.
[Illustration: FIG. 3.--A SECTION OF THE SKIN. 1. A hair. Notice there
is a deep depression of the surface to form a small bulb from which
the hair grows. 2. The superficial or horny layer of the skin; the
cells here are joined to form a dense, smooth, compact layer
impervious to moisture. 3. The lower layer of cells. In this layer new
cells are continually being formed to supply those which as thin
scales are cast off from the surface. 4. Section of a small vein. 9.
Section of an artery. 8. Section of a lymphatic. The magnification is
too low to show the smaller blood vessels. 5. One of the glands
alongside of the hair which furnishes an oily secretion. 6. A sweat
gland. 7. The fat of the skin. Notice that hair, hair glands and sweat
glands are continuous with the surface and represent a downward
extension of this. All the tissue below 2 and 3 is the corium from
which leather is made.]
[Illustration: FIG. 4.--DIAGRAMMATIC SECTION OF A SURFACE SHOWING THE
RELATION OF GLANDS TO THE SURFACE. (_a_) Simple or tubular gland,
(_b_) compound or racemose gland.]
All of the causes of disease act on the body from without, and it is
important to understand the relations which the body of a highly
developed organism such as man has with the world external to him.
This relation is effected by means of the various surfaces of the
body. On the outside is the skin [Fig. 3], which surface is many times
increased by the existence of glands and such appendages to the skin
as the hair and nails. A gland, however complicated its structure, is
nothing more than an extension of the surface into the tissue beneath
[Fig. 4]. In the course of embryonic development all glands are formed
by an ingrowth of the surface. The cells which line the gland surface
undergo a differentiation in structure which enables them to perform
certain definite functions, to take up substances from the same source
of supply and transform them. The largest gland on the external
surface of the body is the mammary gland [Fig. 5] in which milk is
produced; there are two million small, tubular glands, the sweat
glands, which produce a watery fluid which serves the purpose of
cooling the body by evaporation; there are glands at the openings of
the hairs which produce a fatty secretion which lubricates the hair
and prevents drying, and many others.
[Illustration: FIG. 5.--A SECTION OF THE MAMMARY GLAND. (_a_) The
ducts of the gland, by which the milk secreted by the cells which line
all the small openings, is conveyed to the nipple. All these openings
are continuous with the surface of the skin. On each side of the large
ducts is a vein filled with blood corpuscles.]
[Illustration: FIG. 6.--PHOTOGRAPH OF A SECTION OF THE LUNG OF A MOUSE.
_x x_ are the air tubes or bronchi which communicate with all of
the small spaces. On the walls of the partitions there is a close
network of blood vessels which are separated from the air in the
spaces by a thin membrane.]
The external surface passes into the interior of the body forming two
surfaces, one of which, the intestinal canal, communicates in two
places, at the mouth and anus, with the external surface; and the
other, the genito-urinary surface, which communicates with the
external surface at one place only. The surface of the intestinal
canal is much greater in extent than the surface on the exterior, and
finds enormous extensions in the lungs and in the great glands such as
the liver and pancreas, which communicate with it by means of their
ducts. The extent of surface within the lungs is estimated at
ninety-eight square yards, which is due to the extensive infoldings of
the surface [Fig 6], just as a large surface of thin cloth can, by
folding, be compressed into a small space. The intestinal canal from
the mouth to the anus is thirty feet long, the circumference varies
greatly, but an average circumference of three inches may safely be
assumed, which would give between seven and eight square feet of
surface, this being many times multiplied by adding the surfaces of
the glands which are connected with it. A diagram of the microscopic
structure of the intestinal wall shows how little appreciation of the
extent of surface the examination with the naked eye gives [Fig. 7].
By means of the intestinal canal food or substances necessary to
provide the energy which the living tissue transforms are introduced.
This food is liquefied and so altered by the action of the various
fluids formed in the glands of the intestine and poured out on the
surface, that it can pass into the interior of the body and become
available for the living cells. Various food residues representing
either excess of material or material incapable of digestion remain in
the intestine, and after undergoing various changes, putrefactive in
character, pass from the anus as feces.
[Illustration: FIG. 7.--A SECTION OF THE SMALL INTESTINE TO SHOW THE
LARGE EXTENT OF SURFACE. (_a_) Internal surface. The small finger-like
projections are the villi, and between these are small depressions
forming tubular glands.]
By means of the lungs, which represent a part of the surface, the
oxygen of the air, which is indispensable for the life of the cells,
is taken into the body and carbonic acid removed. The interchange of
gases is effected by the blood, which, enclosed in innumerable, small,
thin-walled tubes, almost covers the surface, and comes in contact
with the air within the lungs, taking from it oxygen and giving to it
carbonic acid.
The genito-urinary surface is the smallest of the surfaces. In the
male (Fig. 8,--27, 28, 30) this communicates with the general external
surface by the small opening at the extremity of the penis, and in the
female by the opening into the vagina. In its entirety it consists in
a surface of wide extent, comprising in the male the urethra, a long
canal which opens into the bladder, and is continuous with ducts that
lead into the genital glands or testicles. The internal surface of the
bladder is extended by means of two long tubes, the ureters, into the
kidneys, and receives the fluid formed in these organs. In the female
(Fig 9) there is a shallow external orifice which is continued into
the bladder by a short canal, the urethra, the remaining urinary
surface being the same as in the male; the external opening also is
extended into the short, wide tube of the vagina, which is continuous
with the canal of the uterus. This canal is continued on both sides
into the Fallopian tubes or oviducts. There is thus in the female a
more complete separation of the urinary and the genital surfaces than
in the male. Practically all of the waste material of the body which
results from cell activity and is passed from the cells into the fluid
about them is brought by the blood to the kidneys, and removed by
these from the blood, leaving the body as urine.
[Illustration: FIG. 8.--A LONGITUDINAL SECTION THROUGH THE MIDDLE OF
THE BODY SHOWING THE EXTERNAL AND INTERNAL SURFACES AND THE ORGANS.
1. The skull.
2. The brain, showing the convolutions of the gray exterior in which
the nerve cells are most numerous.
3. The white matter in the interior of the brain formed of nerve
fibres which connect the various parts of this.
4. The small brain or cerebellum.
5. The interior of the nose. Notice the nearness of the upper part of
this cavity to the brain.
6. The hard or bony palate forming the roof of the mouth.
7. The soft palate which hangs as a curtain between the mouth and the
pharynx.
8. The mouth cavity.
9. The tongue.
10. The beginning of the gullet or oesophagus.
11. The larynx.
12. The windpipe or trachea.
13. The oesophagus.
14. The thyroid gland.
15. The thymus gland or sweetbread.
16. The large vein, vena cava, which conveys the blood from the brain
and upper body into the heart.
17-25. Lymph nodes; 17, of the neck; 25, of the abdomen.
18. Cross section of the arch of the aorta or main artery of the body
after it leaves the heart.
19. The sternum or breast bone.
20. The cavity of the heart.
21. The liver.
22. The descending aorta at the back of the abdominal cavity.
23. The pancreas.
24. The stomach.
26. Cross section of the intestines.
27. The urinary bladder.
28. The entrance into this of the ureter or canal from the kidney.
29. Cross sections of the pubic bone.
30. The canal of the urethra leading into the bladder.
31. The penis.
32. The spinal cord.
33. The bones composing the spinal column.
34. The sacrum. The space between this and No. 29 is the pelvis.
35. The coccyx or extremity of the back bone.
36. The rectum.
37. The testicles.]
Between these various surfaces is the real interior of the body, in
which there are many sorts of living tissues,[2] each, of which, in
addition to maintaining itself, has some function necessary for the
maintenance of the body as a whole. Many of these tissues have for
their main purpose the adjustment and coördination of the activities
of the different organs to the needs of the organism as a whole. The
activity of certain of the organs is essential for the maintenance of
life; without others life can exist for a time only; and others, such
as the genital glands, while essential for the preservation of the
life of the species, are not essential for the individual. There is a
large amount of reciprocity among the tissues; in the case of paired
organs the loss of one can be made good by increased activity of the
remaining, and certain of the organs are so nearly alike in function
that a loss can be compensated for by an increase or modification of
the function of a nearly related organ. The various internal parts are
connected by means of a close meshwork of interlacing fibrils, the
connective tissue, support and strength being given by the various
bones. Everywhere enclosing all living cells and penetrating into the
densest of the tissues there is fluid. We may even consider the body
between the surfaces as a bag filled with fluid into which the various
cells and structures are packed.
[Illustration: FIG. 9.--A LONGITUDINAL SECTION THROUGH THE FEMALE
PELVIS.
1. The Fallopian tube which forms the connection between
the ovary and the uterus.
2. The ovary.
3. The body of the uterus.
4. The uterine canal.
5. The urinary bladder represented as empty.
6. The entrance of the ureter.
7. The pubic bone.
8. The urethra.
9. The vagina.
10. The common external opening or vulva.
11. The rectum and anus.]
[Illustration: FIG. 10.--THE LUNGS AND WINDPIPE. Parts of the lungs
have been removed to show the branching of the air tubes or bronchi
which pass into them. All the tubes and the surfaces of the lungs
communicate with the inner surface of the body through the larynx.]
The nervous system (Fig. 8) represents one of the most important of
the enclosed organs. It serves an important function, not only in
regulating and coördinating all functions, but by means of the special
senses which are a part of it, the relations of the organism as a
whole with the environment are adjusted. It consists of a large
central mass, the brain and spinal cord, which is formed in the embryo
by an infolding of the external surface, much in the same way that a
gland is formed; but the connection with the surface is lost in
further development and it becomes completely enclosed. Connected with
the central nervous mass, forming really a part of it and developing
from it, are the nerves, which appear as white fibrous cords and after
dividing and subdividing, are as extremely fine microscopic filaments
distributed to all parts of the body. By means of the nerves all
impressions are conveyed to the brain and spinal cord; all impulses
from this, whether conscious or unconscious, are conveyed to the
muscles and other parts. The brain is the sole organ of psychical
life; by means of its activity the impressions of the external world
conveyed to it through the sense organs are converted into
consciousness. Whatever consciousness is, and on this much has been
written, it proceeds from or is associated with the activity of the
brain cells just as truly as the secretion of gastric juice is due to
the activity of the cells of the stomach. The activity of the nervous
system is essential for extra-uterine life; life ceases by the
cessation of circulation and respiration when either the whole or
certain small areas of its tissue are destroyed. In intra-uterine
life, with the narrow and unchanging environment of the fluid within
the uterine cavity which encloses the foetus, life is compatible with
the absence or rudimentary development of the nervous system. The
foetus in this condition may be otherwise well developed, and it would
be not a misuse of words to say that it was healthy, since it is
adjusted to and in harmony with its narrow environment, but it would
not be normal. The intra-uterine life of the unborn child, it must be
remembered, is carried out by the transmission of energy from the
mother to the foetus by means of the close relation between the
maternal and foetal circulation. It is only when the free existence
demands activities not necessary in intra-uterine life that existence
without a central nervous system becomes impossible.
It is essential in so complicated a structure as the body that some
apparatus should exist to provide for the interchange of material. The
innumerable cell units of the body must have material to provide
energy, and useless material which results from their activity must be
removed. A household might be almost as much embarrassed by the
accumulation of garbage and ashes as by the absence of food and coal.
The food, which is taken into the alimentary canal and converted by
the digestive fluids into material more directly adapted to the uses
of cells, must be conveyed to them. A supply of oxygen is essential
for the life of the cells, and the supply which is given by
respiration must be carried from the lungs to every cell of the body.
All this is effected by the circulation of the blood, which takes
place in the system of branching closed tubes in which the blood
remains (Fig. 11). Certain of these tubes, the arteries, have strong
and elastic walls and serve to convey and distribute the blood to the
different organs and tissues. From the ultimate branches of the
arteries the blood passes into a close network of tubes, the
capillaries, which in enormous numbers are distributed in the tissues
and have walls so thin that they allow fluid and gaseous interchange
between their contents and the fluid around them to take place. The
blood from the capillaries is then collected into a series of tubes,
the veins, by which it is returned to the heart. This circulation is
maintained by means of a pumping organ or heart, which receives the
blood from the veins and by the contraction of its powerful walls
forces this into the arteries, the direction of flow being determined
as in a pump, by a system of valves. The waste products of cell life
pass from the cells into the fluid about them, and are in part
directly returned into the blood, but for the greater part pass into
it indirectly through another set of vessels, the lymphatics. These
are thin-walled tubes which originate in the tissues, and in which
there is a constant flow towards the heart, maintained by the constant
but varying pressure of the tissue around them, the direction of flow
being maintained by numerous valves. The colorless fluid within these
vessels is termed "lymph." At intervals along these tubes are small
structures termed the lymph nodes, which essentially are filters, and
strain out from the fluid substances which might work great injury if
they passed into the blood. Between the capillary vessels and the
lymphatics is the tissue fluid, in which all the exchange takes place.
It is constantly added to by the blood, and returns fluid to the blood
and lymph; it gives material to the cells and receives material from
them.
[Illustration: FIG. 11.--A DIAGRAMMATIC VIEW OF THE BLOOD VESSELS. An
artery (_a_) opens into a system of capillaries, (_c_) and
after passing through these collects into a vein (_b_). Notice
that the capillaries connect with other vascular territories at
numerous points (_d_). If the artery (_a_) became closed the
capillaries which it supplies could be filled by blood coming from
other sources.]
In addition to the strength and elasticity of the wall of the
arteries, which enables them to resist the pressure of the blood, they
have the power of varying their calibre by the contraction or
expansion of their muscular walls. Many of the organs of the body
function discontinuously, periods of activity alternating with
comparative repose; during the period of activity a greater blood
supply is demanded, and is furnished by relaxation of the muscle
fibres which allows the calibre to increase, and with this the blood
flow becomes greater in amount. Each part of the body regulates its
supply of blood, the regulation being effected by means of nerves
which control the tension of the muscle fibres. The circulation may be
compared with an irrigation system in which the water supply of each
particular field is regulated not by the engineer, but by an automatic
device connected with the growing crop and responding to its demands.
[Illustration: FIG. 12.--THE VARIOUS CELLS IN THE BLOOD. (_a_) The red
blood cells, single and forming a roll by adhering to one another;
(_b_) different forms of the white blood cells; those marked "1" are
the most numerous and are phagocytic for bacteria.]
The blood consists of a fluid, the blood plasma, in which numerous
cells are contained. The most numerous of these are small cup-shaped
cells which contain a substance called _hæmoglobin_, to which the
red color of the blood is due. There are five million of these cells
in a cubic millimeter (a millimeter is .03937 of an inch), giving a
total number for the average adult of twenty-five trillion. The
surface area of all these, each being one thirty-three hundredth of an
inch in diameter, is about thirty-three hundred square yards. The
hæmoglobin which they contain combines in the lungs with the oxygen in
the inspired air, and they give up this indispensable substance to the
cells everywhere in the body. There are also eight thousand leucocytes
or colorless cells in a cubic millimeter of blood, this giving a total
number of four billion in the average adult, and these vary in
character and in relative numbers (Fig. 12). The most numerous of
these are round and slightly larger than the red cells; they have a
nucleus of peculiar shape and contain granules of a definite
character. These cells serve an important part in infectious diseases
in devouring and destroying parasites. They have power of active
independent motion and somewhat resemble certain of the free living
unicellular organisms. The blood plasma, when taken from the vessels,
clots or passes from a fluid into a gelatinous or semi-solid
condition, which is due to the formation within it of a network of
fine threads termed fibrin. It is by means of the clotting of the
blood that the escape of blood from ruptured vessels is arrested.
Several of the organs of the body, in addition to the formation of
secretions which are discharged on the surfaces by means of their
ducts, produce also substances which pass directly into the blood or
lymph, and have an influence in stimulating or otherwise regulating
the activity of other organs. There are also certain organs of
glandular structure which are called the _ductless glands_; these
are not connected with the surface and all their secretion passes into
the blood. It is a part of recent knowledge that the substances
produced in these glands are of great importance for the body, some of
them even essential for the maintenance of life. In front of the neck
is such an organ, the thyroid gland (Fig. 8, 14). Imperfect
development or absence of this organ, or an inactive condition of it,
produces in the child arrested growth and deficient mental development
known as cretinism, and in the adult the same condition gives rise to
mental deterioration, swelling of the skin, due to a greater content
of water, and loss of hair. This deficiency in the production of
thyroid secretion can be made good and the symptoms removed by feeding
the patient with similar glands removed from animals. The very complex
disease known as exophthalmic goitre, and shown by irregular and rapid
action of the heart, protruding eyeballs and a variety of mental
symptoms, is also associated with this gland, and occasioned not by a
deficiency but by an excess or perversion of its secretion.
Adjoining the thyroid there are four small glands, the parathyroids,
each about the size of a split pea. The removal of these glands in
animals produces a condition resembling acute poisoning accompanied by
spasmodic contraction of the muscles. A small glandular organ at the
base of the brain, the pituitary body, produces a secretion, one of
the most marked properties of which is a control of growth,
particularly that of the bones. Most cases of giantism, combined as
they are with imperfect mentality, are due to disease of this gland.
There are glands near the kidney which regulate the pressure of the
blood in the arteries by causing contraction of their muscular walls.
The sexual characteristics in the male and female are due to an
internal secretion produced by the respective sexual glands which
affects growth, body development and mentality.
So is the body constituted. A series of surfaces, all connected, of
enormous size, which enclose a large number of organs and tissues, the
activities of which differ, but all are coördinated to serve the
purposes of the organism as a whole. We should think of the body not
as an assemblage of more or less independent entities, but as a single
organism in which all parts are firmly knit together both in structure
and in function, as are the components of a single cell.
FOOTNOTES:
[1] They do, however, take place, since within comparatively
few years whole species have completely disappeared; for example, the
great auk and the passenger pigeon. In these cases it is not known
what part disease played in the destruction.
[2] A tissue represents an aggregate of similar cells with
the intercellular substances in relation with these as connective
tissue, muscular tissue, etc. Where such cell aggregates are localized
and where the cells are arranged in structures having definite form
and size and performing a definite function, it is customary to
designate such structures as organs, as the brain, liver, etc.