SIMIAN VIRUS 40: ISOLATION OF TWO PLAQUE TYPES.

Two different morphological plaque types of simian virus 40 were isolated from three of six strains. Increased uptake of neutral red gave one type of plaque a uniform red appearance, whereas the center of the other remained unstained. The viruses showed stability of plaque morphology on passage in tissue culture; cross neutralization studies identified both as simian virus 40.