Evidence is presented which suggests that urethan (ethyl carbamate) increases the expected incidence of lymphosarcoma in Xenopus laevis laevis when this animal is repeatedly immersed in or given injections of a urethan solution. Similar results were observed when urethan was used as an anaesthetic in experiments involving forelimb autografts or homografts to the dorsal lymph sac. The implantation of hind-leg muscle without lymphosarcoma condensations led to the development of tumors in immature Xenopus as quickly as did the implantation of liver from the same animal bearing advanced tumors. Lymphosarcoma implants to adult Xenopus eyes did not grow well, but visceral lymphosarcomas resulted in four of five hosts. Eight young Xenopus, developed from tadpoles given lymphoid tumor grafts, all had lymphosarcomas when killed after metamorphosis. This indicates that metamorphosis does not prevent the growth and spread of the tumor.

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Supported by the Fonds national suisse pour la recherche acientifique (No. 2551).

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