Production of Virus by Embryonic Cultures co-cultivated with Breast Tumour Cells or infected with Milk from Breast Cancer Patients

VIRIONS morphologically similar to mouse mammary tumour virus (MMTV) have been found by electron microscopy of human milk samples1–4 and in thin sections of breast tumour tissue and of pleural effusion cells from breast cancer patients5. Viruses isolated from human milk have similarities to those of the oncornavirus group a, a buoyant density in a sucrose: gradient (1.16–1.19 g ml.−)1; b, the presence of the RNA-dependent DNA polymerase or “reverse transcriptase”6–9; c, the existence of 60S-70S RNA template in the virions10,11.