Virus Particles in Hamster Tumors as Revealed by Electron Microscopy.∗

Summary Examination of 11 transplan-table hamster tumors by electron microscopy revealed virus particles in 9. Seven of the tumors contained particles morphologically identical with murine leukemia viruses. Five of these tumors also contained another type of particle which appears to be identical with one reported by other Workers. Two of the tumors contained only the murine leukemia-like agent, and two contained only the second agent.