cases one single traumatism may undoubtedly cause the development of cancer. While, however, long-continued irritation usually leads to the formation of carcinoma, one single traumatism causes more frequently the development of sarcoma. Thus cases are known in which two months after a blow on the eye a sarcoma began to grow at the place of injury; in a child sixteen months old a sarcoma of the ciliary body of the eye developed after a blow; a sarcoma of the arm followed a stab wound at the site of injury. There are also cases on record in which a bone sarcoma developed after a fracture of the bone and after an extraction of a tooth the development of a cancer has been observed in the jaw. Also other than connective tissues may assume a rapid cancerous growth after an injury, as for instance the glia cells of the brain which are of the same origin as the nerve cells. Also carcinomata of the jaw originated subsequent to an extraction of a tooth. A carcinoma of the testis followed six weeks after an injury received from a horse.
In all these cases we have to distinguish between two possible results of the traumatism; the latter may either actually cause the new formation of a cancer or it may merely increase the rate of growth of a tumor that existed previous to the injury, which however only became apparent after the injury had increased the rapidity of the tumor growth. The latter condition existed for instance in the case of an embryoma of the testis which assumed a rapid growth after an injury, taking on the characteristic of a malignant tumor with subsequent formation of metastases.
We have now learned to know several sets of conditions which are either alone or in combination with other factors responsible for the occurrence of cancer, namely: (1) Irregularities of embryonic development. (2) Parthenogenetic development of ova. (3) The long-continued action of external stimuli, as for instance Röntgen and light rays, various substances acting chemically, long-continued ulceration and certain parasites. (4) Traumatism.
In certain of these cases we can state definitely that a combination of several factors had to come into play before carcinoma developed, for instance, in those cancers which follow xeroderma pigmentosum. Here a congenital lesion becomes converted under the influence of an external agency—namely, the light rays—into cancer. A pigmented mole is the result of some irregularity of embryonic development; it is present at the time of birth, and therefore a congenital lesion; mechanical stimuli cause its transformation into cancer.
We recognized that the majority of cancers of childhood differ in a definite way from the typical cancers of old age. We found reason to believe that certain embryonic irregularities are in part at least responsible for many cancers of childhood and early adult life. In the light of the data which we gave concerning the significance of external stimuli
