Disease and Its Causes

by W. T. Councilman

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.

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.

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.

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.