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Direct cell to cell transfer of Bittner virus.

Bittner virus consists of an internal component which arises in the cytoplasm and becomes enveloped by budding through a cell membrane (Moore, 1962). During a study of this process we obtained evidence that the virus could be transmitted directly from cell to cell and that in some instances an unusual form of particle was involved. In this communication we describe this unusual form and the engulfment of virus particles. Pieces of spontaneous mammary tumours from C3H mice, originally obtained from the Christie Institute, Manchester, were fixed in 3% glutaraldehyde in Sorensen's phosphate buffer of pH 7.2 for 2 hr at 4°, post-fixed in 1% osmium tetroxide for 2 hr at 4° and embedded in Maraglas by standard techniques. Sections were stained by alcoholic uranyl acetate followed by lead citrate. Budding particles were found at cytoplasmic vacuoles and at the plasma membrane. Particles which budded at the plasma membrane were not randomly distributed at the periphery but tended to concentrate at free cell surfaces (Fig. 1).