Studies of induced Cysticercus sarcoma in rats have demonstrated (1) a direct relationship between the number of parasites in the host's liver and the duration of the latent period. An increase in the number of cysts decreased directly the average time interval before the onset of malignant disease and increased directly the probability of its occurrence, demonstrating that the extent of the surface area of the host's tissue exposed to the incitant is an important factor in the initiation of the malignant process. Previously demonstrated (2) genetic differences in the occurrence of Cysticercus sarcoma were defined (1) as differences in the host's susceptibility to Cysticercus infestation and in longevity or resistance to common laboratory diseases. Families with a low percentage of bearers of Cysticercus sarcoma among the infested rats were relatively short-lived and resistant to Cysticercus disease, while longevity or increased susceptibility to Cysticercus infestation contributed equally to a higher percentage of bearers of induced Cysticercus tumors. The occurrence of neoplastic disease in the walls of Cysticercus cysts was found (3) to be fortuitously distributed among the several lobes of the liver and the several types of cells which composed the cyst wall. Further, malignant disease in Cysticercus cysts was shown to be independent (4) of the age of the rat when infested, and among equally infested rats to be independent of the genetic susceptibility of the host to Cysticercus infestation.

W. F. Dunning

M. R. Curtis

The Carcinogenic Activity of Methylcholanthrene in Rats

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