32 THE POPULAR SCIENCE MONTHLY 



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 ex- 

 traction 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 forma- 

 tion 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 develop- 

 ment. (2) Parthenogenetic development of ova. (3) The long-con- 

 tinued action of external stimuli, as for instance Eontgen 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 respon- 

 sible for many cancers of childhood and early adult life. In the light 

 of the data which we gave concerning the significance of external stimuli 



