Induction of neoplasms in planarians with carcinogens.

Carcinogens were used to produce nodular growths in the planarian, Dugesia dorotocephala . The growths increased in size, became necrotic, and eventually caused the death of the animals. When whole animals were treated with 1,2-benzanthracene, 3′-methyl-4-dimethylaminoazobenzene, and 3,4-benzpyrene, nodules developed in 9, 6, and 5 per cent of the animals, respectively. When benzanthracene treatment was followed by sectioning, 21 per cent of the regenerating sections were affected. The stress of regeneration appeared to promote the action of the carcinogen. Although the histological changes in these neoplasms were difficult to assess, several features were similar to those of neoplasias of higher forms. In some animals, highly basophilic nests of cells with increased nucleocytoplasmic ratio had invaded the intestinal tract. Excessive pigmentation, giant cells, and cells containing pigment globules occurred in the sub-epidermal layer underlying areas of epidermal hyperplasia. Numerous mitotic figures and pyknotic nuclei were seen in the hyperplastic intestinal tract. The normal tissue separating the channels of the intestinal tract was invaded and obliterated by hyperplastic intestinal tissue. On the basis of the histological and gross morphological changes observed, it is suggested that these nodular, progressive growths should be considered neoplastic.