Virus-Like Particles in Established Murine Cell Lines: Electron-Microscopic Observations

Abstract
Virus-like particles identical in morphology to the RNA tumor vi ruses have been observed by electron microscopy in six lines of murine L cells and one line of murine liver cells. Control cultures of embryonic mouse cells and 3T3 cells do not contain the particles, and no biologic activity has as yet been associated with them.