HAMSTER CELLS, UNTREATED AND TREATED WITH CHEMICAL CARCINOGENS, MAINTAINED IN VITRO FOR 22 YEARS

Summary.-We have maintained in culture, for a prolonged period, untreated hamster cells from whole embryo, foetal brain and lung from newborn animals. Among the 7 lines studied we observed only one spontaneous transformation during the first year of culture. The cells of the 6 other control lines remained normal and diploid, and were not transplantable during the first 9 to 12 months of culture. After the 12th month, changes appeared in their in vitro behaviour and their transplant-ability: grafts of 0*5-2 x 106 cells induced tumours in the hamster; fewer cells did not. In vitro chemically transformed hamster cells were fundamentally different from untreated cells of the same origin, not only in morphological and growth character-istics but also in transplantability: of the 9 lines obtained, 7 induced tumours after injection of 101-104 cells, and 2 after injection of 105 cells per animal. ACCORDING to several authors, normal diploid hamster cells survive only 2 to 3 months in culture (Berwald and Sachs, 1965; Borek, 1976). After this time th