Induction of malignant and benign tumors with embryonic tissues

The inoculation of viruses into the placenta of fetectomized rats induces the development of malignant tumors from extraembryonic fetal membranes. The same membrane--visceral yolk sac--gives rise to benign teratomas if displaced outside the uterus after fetectomy. Moreover, the transplantation of 3 to 7 day old embroys under the kidney capsule of adult mice gives rise of malignant teratocarcinoma. The methods to induction of these tumors are described.