The infectivity of fluid from regressing Rous sarcomas.

Fluid was withdrawn from the site of regressing Rous sarcomas in chickens and inoculated into the wing-webs of untreated chickens from three strains of chickens with divergent degrees of resistance to Rous sarcomas. The transfer of fluid initiated progressive tumors in all three strains of chickens. The infectivity of the fluid was apparently due to tumor cells and not to virus.