Abstract
The chick embryo fibroblast infected by Rous sarcoma virus in vitro acquires the capacity to produce the acid mucopolysaccharides which are found in the tumors caused by this virus and which are also produced by tumor cells in vitro. The transformed cell acquires synthetic as well as morphologic, metabolic, and proliferative properties characteristic of Rous sarcoma tumor cells in vivo and in vitro and the transformed cell may be analogous to the tumor cell produced by virus infection in vivo.