3 o THE POPULAR SCIENCE MONTHLY 



of the epithelium is at first slow, but later metastases form in the lymph 

 glands and a typical malignant carcinoma is now present (E. T. Nere). 



Eelated processes — namely the gradual transformation of epithelium 

 into cancerous growth — have been observed in cases of chronic ulceration 

 of various kinds with incomplete healing of the epithelial surface as for 

 instance in the case of the chronic ulcer of the leg, in the case of lupus, 

 a tuberculous skin affection and in other similar conditions. Another 

 class of cancers is produced directly or indirectly through the action of 

 certain parasites, especially of certain worms (nematodes and trema- 

 todes). Thus in Egypt infection with bilharzia (Distoma haemato- 

 bium) is relatively common. This trematod lives in the veins of the 

 abdomen and lays its eggs in the mucosa of the bladder; they cause 

 inflammation in the bladder, mostly in older persons, and later cancer 

 develops in about 3^—5 per cent, of patients infected with bilharzia. 

 In Bosnia, after bites of sandvipers, chronic ulcers without a tendency 

 to heal may develop, and they may become carcinomatous. Also in 

 other cancers a causal connection between a metazoan parasite and the 

 tumor has been suggested in man, but this connection can not yet be 

 considered as proven. Thus Askanazy found in a case of primary car- 

 cinoma of the liver Opistorchis felineus, while in Japan in similar cases 

 a Distoma has been observed. In cases of chronic trichinosis carcinoma 

 was found in organs which were situated in the neighborhood of the 

 infected muscles. The presence of certain mites were noticed by Borrel 

 in the case of mammary cancers and considered as its cause. It ap- 

 pears however that these latter parasites are just as frequently found in 

 the non-cancerous breast as in cases of mammary cancer. The importance 

 of nematodes as the cause of certain cancers in animals has been recently 

 demonstrated, as we shall later explain more in detail. Of especial 

 interest is the fact that while in the large majority of cancers caused 

 by external irritation carcinoma developed, a few sarcomata have been 

 observed in the skin under the influence of Rontgen rays, in the bladder 

 in aniline dye workers and in persons infected with hilharzia. 



We see then that under the influence of a considerable variety of 

 agencies, cancer can develop in the human body and that in many cases 

 cancer is preceded by the formation of warty or papillomatous excres- 

 cences and in other cases by long-continued ulceration, which in itself 

 seems to be able to lead to the formation of cancer. At present we 

 leave out of consideration the mechanism through which these agencies 

 produce cancer, especially the question whether their action consists in 

 a direct specific stimulation of the epithelial cells by the light and Ront- 

 gen rays, chemical substances and parasites or whether all these agencies 

 act indirectly causing primarily ulceration, which later is followed by 

 the development of cancer. We know indeed that chronic ulceration 

 due to various causes may in itself lead to the development of cancer. 

 Later we shall have occasion to return to this question. 



