Abstract
Summary Comparative studies were carried out using 5 strains of virus known by the designations EMC, COL SK and Mengo. Hemagglutination-inhibition tests showed that the strains were antigenically similar although not necessarily identical. Each was highly neurotropic and produced myocardial damage in mice. Plaques produced by the 5 virus strains in L cell monolayers differed morphologically. The size of the plaques formed by 3 mouse-adapted strains was roughly correlated with sensitivity to an inhibitor in extracts of agar and increased when DEAE-dextran was incorporated in the overlay. However, evidence is presented which indicates that factors other than inhibitor sensitivity also contribute to differences in plaque size. Each of the strains hemagglutinated erythrocytes of 4 mammalian species. Hemagglutination by some strains was temperature dependent, whereas with others it was not.

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