Newborn hamsters were injected subcutaneously with a suspension of finely minced Rous chicken sarcoma (Schmidt-Ruppin strain). After an interval of about 2 weeks, progressively growing sarcomas developed at the site of injection in almost all animals. Also in adult hamsters inoculated intramuscularly with the same material sarcomas developed at the site of injection within 2 to 4 months. Secondary growths appeared on the peritoneal surface, in the retroperitoneal and mediastinal lymph nodes and in the lungs. The sarcomas usually had a pleomorphic appearance and showed a certain resemblance to rhabdomyosarcoma, but sometimes they had the character of spindle cell sarcomas of varying degree of maturity. Sarcomas were not only obtained in hamsters injected with cellular material from the Rous chicken sarcoma but were also seen in hamsters which were injected at birth or when 2 months' old with supernatant fluid obtained by repeated centrifugation of suspensions of homogenized chicken sarcoma, and presumed to be cell-free.

The hamster sarcoma was transplanted to a newborn hamster and could then without difficulties be passed in series in hamsters. All attempts to transfer the sarcoma from hamster to hamster by means of cell-free material from the hamster sarcoma failed. On the other hand, material from the hamster sarcomas inoculated into chickens induced rapidly growing Rous sarcomas at the site of inoculation. This proved possible not only with material from the first but also from later passages of the tumor in hamsters.

It is concluded that the strain of Rous virus used has the capacity to induce sarcomas not only in chickens but also in hamsters.

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