Presence in Murine Sarcoma Virus Stocks of a Third Component which alone initiates Cellular Conversion

STOCKS of mouse sarcoma virus (MSV, Moloney strain)1,2 are known to contain Moloney leukaemia virus (MLV)2,3 as well as MSV, and induce foci of altered cells when inoculated on to monolayers of mouse or rat cells (conversion phenomenon)3–6.