Disease and Its Causes.
by William Thomas Councilman.
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 s.p.a.ce 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 ill.u.s.trations. The s.p.a.ce 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 s.p.a.ce 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 a.s.sumed 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 ma.n.u.script and for many suggestions as to phrasing.
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 const.i.tutes life has ceased. Changes such as putrefaction take place in the dead body, but they are changes which would take place in any ma.s.s similarly const.i.tuted, and are not influenced by the fact that the ma.s.s 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 const.i.tutes the normal or usual and the abnormal in a particular individual.
The conception of disease is so inseparably a.s.sociated 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 pa.s.s from the complex to the simple, from unstable to stable equilibrium. The elementary substances which form living material are known, but it has. .h.i.therto not been found possible artificially so to combine these substances that the resulting ma.s.s 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 ma.s.ses 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 ma.s.ses to form organs such as the liver and brain.
In each cell there is a differentiated area const.i.tuting 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 ma.s.s outside of the nucleus is termed "cytoplasm," and this may be h.o.m.ogeneous 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 ma.s.s, whether regarded from a chemical or physical point of view. (Fig. 1.)
[Ill.u.s.tration: 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 gla.s.s 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 ma.s.s, seemingly of gelatinous consistency with a clear outline, the exterior part h.o.m.ogeneous, 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 s.p.a.ce, 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 ma.s.s. The amoeba slowly moves along the surface of the gla.s.s by the extension of blunt processes formed from the clear outer portion which adhere to the surface and into which the interior granular ma.s.s 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 s.p.a.ce 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 s.p.a.ce, 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 a.s.similated; 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 ma.s.s, motion within the ma.s.s, 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.
[Ill.u.s.tration: FIG. 2.--AMOEBA. 1. Nucleus. 2. Contractile vesicle.
3. Nutritive vacuole containing a bacillus.]
Up to the present it has been a.s.sumed 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 a.s.similate 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 compa.s.s, 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 a.s.sist 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 const.i.tuents, 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 const.i.tute 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 ma.s.s of sugar grains each grain shows just the same characteristics and reacts in exactly the same way as all the other grains of the ma.s.s. 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 ma.s.ses, can be exactly the same. It is not necessary to a.s.sume 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.
[Ill.u.s.tration: 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 h.o.r.n.y 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.]
[Ill.u.s.tration: 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.
[Ill.u.s.tration: 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.]
[Ill.u.s.tration: 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 s.p.a.ces. On the walls of the part.i.tions there is a close network of blood vessels which are separated from the air in the s.p.a.ces by a thin membrane.]
The external surface pa.s.ses into the interior of the body forming two surfaces, one of which, the intestinal ca.n.a.l, communicates in two places, at the mouth and a.n.u.s, 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 ca.n.a.l 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 s.p.a.ce. The intestinal ca.n.a.l from the mouth to the a.n.u.s is thirty feet long, the circ.u.mference varies greatly, but an average circ.u.mference of three inches may safely be a.s.sumed, 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 ca.n.a.l 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 pa.s.s 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, pa.s.s from the a.n.u.s as feces.
[Ill.u.s.tration: 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 p.e.n.i.s, and in the female by the opening into the v.a.g.i.n.a. In its entirety it consists in a surface of wide extent, comprising in the male the urethra, a long ca.n.a.l which opens into the bladder, and is continuous with ducts that lead into the genital glands or t.e.s.t.i.c.l.es. 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 ca.n.a.l, 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 v.a.g.i.n.a, which is continuous with the ca.n.a.l of the uterus. This ca.n.a.l 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 pa.s.sed 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.
[Ill.u.s.tration: 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.