Disease and Its Causes

by W. T. Councilman

No age is immune to tumors. They may be present at birth or develop shortly afterwards. The age from five to twenty years is the most free from them, that from forty-five to sixty-five the most susceptible, particularly to the more malignant forms.

A tumor is a local disease. The growing tissue of the tumor is the disease, and it is evident that if the entire tumor were removed the disease would be cured. This is the end sought by surgical interference, but notwithstanding seemingly thorough removal, the tumor often reappears after an interval of months or years. There are many conditions which may render the complete removal of a tumor difficult or impossible. It is often impossible to ascertain just how far the tumor cells have invaded the neighboring structures; the situation of the tumor may be such that an extended removal would injure organs which are essential for life, or at the time of removal the tumor cells may have been conveyed elsewhere by the blood or lymphatic vessels.

Successful removal depends mainly upon the length of time the tumor has been growing. At an early stage even the most malignant tumor may be successfully removed. It is evident from this how disastrous may be the neglect of proper surgical treatment of a tumor. The time may be very short between the first evidence of the presence of a tumor and the development of a condition which would render complete removal impossible.

The effect of a tumor upon its bearer depends upon its character and situation. Pain is very commonly present, and is due to the pressure which the growing tumor exerts upon the sensory nerves. Pain may, however, not be present or appear only at the last. A condition of malnutrition and emaciation often results due to the passage into the blood of injurious substances formed in the tumor, or to the destruction of important organs by the growing tumor. The growth of a tumor in the intestine may obstruct or close the canal and thus interfere with nutrition.

The cause or causes of tumors are unknown. We know that the tumor represents essentially an abnormal growth, and that this growth is due to new formation of cells. In certain cases the tumor repeats the structure of the organ or tissue in which it originates, in others it departs widely from this; always, however, its structure resembles structures found in the body at some period of life. The tumor cells, like all other cells of the body, grow by means of the nutriment which the body supplies; they have no intrinsic sources of energy. The great problem is what starts the cells to grow and why the growth differs from that of normal tissue, why it is not regulated and coördinated as are other forms of growth. When a small piece of the skin, for instance, is cut out growth as rapid as that in tumors takes place in the adjoining cells, but it ceases when the loss is restored. The same is true when a piece of the liver is removed.

Various hypotheses have been formed to explain the tumor, all of them of interest, and they have had great importance in that the attempt to prove or disprove the hypothesis by continued observation and experiment along definite lines has produced new knowledge. The various theories as to cause may be divided into three heads.

The parasitic theory. This supposes that a living parasite invades the body, and by its presence excites the cells of certain tissues to grow in tumor form. It is known that active growth of the cells of the body can be excited in a number of ways, by chemical substances such as certain of the coal tar products, and that it often takes place under the influence of bacteria. It is further known that parasites can produce tumor-like growths in plants. The large, rough excrescences on the oaks are produced by a fly which lays its eggs in or beneath the bark, and the larva which develops from the egg secretes a substance which causes the cells about it to multiply, and a huge mass is formed which serves the developing insect for both food and protection. Large tumor-like masses are formed on the roots and stalk of cabbages as the result of the invasion of the cells by a minute organism: the tumors of olive trees are due to a bacterium; the peculiar growths on cedar trees, the so-called "witches' brooms," are produced by a fungus, and there are many other such examples. These have many analogies with tumors in animals. Under the stimulus of the parasite the cells seem to have unlimited growth capacity and a greater nutritive avidity than have the normal plant cells; the character of the mass produced differs as does the tumor, to a greater or less extent, from the normal growth; on the cedar, for instance, the "witches' broom" consists of a thick mass of foliage with small stems less green than the usual foliage, the leaves wider and not so closely applied to the stems. The entire plant suffers in its nutrition and a condition resembling tumor cachexia[3] is produced, and there are no fundamental differences between the plant and animal tumors. Support has also been given to the parasitic theory by the discovery within tumor cells of bodies which were supposed to be a peculiar sort of parasite. If the truth of the parasitic theory could be proved, there would be justifiable expectation that the tumor disease might be controlled as are many of the parasitic diseases, but the hypothesis awaits the demonstration of its correctness. Despite the study of tumors which is being actively pursued in many places and by the most skilled investigators, no parasites have been found in animal tumors; the objects previously described as parasites have been found not to be such. It is difficult to bring in accord with the parasitic theory the great variation in tumor structure, the relation of certain tumors, as the malignant tumors of the breast and uterus, with the age of the bearer, the congenital tumors which develop in intra-uterine life, and there are many other conditions which oppose the theory.

The traumatic[4] theory. There is much in favor of this. In a certain number of cases tumors do develop at the site of injuries. The coincidence of injury and tumor is apt to be overestimated because of the strong tendency to connect succeeding events. Tumors are not most common on those parts of the body which are most exposed to injury. They are rare, for instance, on the hands and feet, and very rarely do they appear at the site of wounds caused by surgical operations. For those tumors which develop in intra-uterine life it is difficult to assign injury as a cause. There does, however, seem to be a relation between tumors and injuries of a certain character. The natives of Cashmere use in winter for purposes of heat a small charcoal stove which they bind on the front of the body; burns often result and tumors not infrequently develop at the site of such burns. Injuries of tissue which are produced by the X-ray not infrequently result in tumor formation and years may elapse between the receipt of the injury and the development of the tumor. These X-ray injuries are of a peculiar character, their nature but imperfectly understood, and the injured tissues seem to have lost the capacity for perfect repair.

In regard to the possible action of both injuries and parasites in causing tumors, the possibility that their effects on different individuals may not be the same must be considered. In addition to the trauma or the parasite which may be considered as extrinsic factors, there may be conditions of the body, intrinsic factors, which favor their action in tumor development. The peculiar tissue growth within the uterus called decidua, which occurs normally in pregnancy and serves to fasten the developing ovum to the inner lining of the uterus, may be produced experimentally. This growth depends upon two factors, an internal secretion derived from the ovary and the introduction into the uterus of a foreign body of some sort; in the case of pregnancy the developing embryo acts as the foreign body. It is not impossible that some variation in the complex relations which determine normal growth may be one factor, possibly the most important, in tumor formation.

Another theory is that the tumor is the result of imperfect embryonic development. The development of the child from the ovum is the result of a continued formation and differentiation of cells. A cell mass is first produced, and the cells in this differentiate into three layers called ectoderm, entoderm and mesoderm, from which the external and internal surfaces and the enclosed tissues respectively develop, and the different organs are produced by growth of the cells of certain areas of these layers. The embryonic theory assumes that in the course of embryonic development not all the cell material destined for the formation of individual organs is used up for this purpose, that certain of the embryonic cells become enclosed in the developing organs, they retain the embryonic capacity for growth and tumors arise from them. There is no doubt that something like this does take place. There is a relation between malformations due to imperfect development of the embryo and tumors, the two conditions occurring together too frequently to be regarded as mere coincidence. Also tumors may occur in parts of the body in which there is no tissue capable of forming structures which may be present in the tumors. The theory, however, is not adequate, but it may be among the factors.