Studies on Mammary Tumor Inducing Virus in Mice (Bittner Virus).

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Abstract
Bioassays of fractions from virus-containing strain A mouse milk, obtained by defatting, decaseination, high-speed centrifugation, have shown that these pro-cedures do not affect the tumor-inducing activity. Bioassays of high-speed centrifugal pellets of treated milk have consistently demonstrated the pellets to be suitable material for electrophoretic analysis, chemical, treatment, and electron microscope study. Electrophoretic fractions of the high-speed centrifugal pellets has led to localization of the tumor-inducing activity in the electrophoretic pattern. Nucleic acid determinations have shown presence of RNA in the pellets but no detectable DNA. Treatment of the pellets with ribonuclease or cold ethanol retained their tumor-inducing activity. Virus particles of 700 A diameter have been found in the pellets from A, Rlll strain virus-carrying milk, which have high tumor-inducing activity. Treatment of the pellets with fluorocarbon had no effect on the presence of particles or tumor-inducing activity. Similar particles, although in considerably smaller number, have been observed in the pellets from Af strain apparently agent-free milk.