Study of toxic factors associated with mouse mammary carcinomas in egg cultures.

An electron microscope study has shown virus-like particles to be associated with mouse mammary carcinomas grown in the yolk sacs of chicken eggs. Large numbers of such particles were discovered in these tumors after they had been in egg culture for several generations. Similar particles were found in egg fluids exhibiting chick embryo toxicity, which was apparently initiated by the tumors. It has been concluded that these particles are the embryo toxic factors or that they are closely related mani fegtations. The morphological similarity of these particles to those associated by other workers with various mouse mammary carcinomas and with the Bittner milk factors suggests that they actually may be related to the milk factor.