Definition of Disease : Part 3

Disease and its Causes
by William Thomas Councilman, M.D.

(Page 3 of 16)

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.

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, 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. 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 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.

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, 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. 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.

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 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 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.

New York, Henry Holt And Company.
London, Williams and Norgate, originally published 1913