Abstract
Summary
A method is described for quantitative counting of polyoma virus particles with a precision of about 16%. The method involves sedimentation of virus upon agar in the swinging-bucket ultracentrifuge rotor, pseudoreplication, and electron microscopy of the particles. The particle counts were correlated quantitatively with biological activity. Aggregation is an outstanding feature of this strain of polyoma virus. When this was minimized, a particle count to infectivity ratio of 38:1 was obtained. Approximately 5 × 106 particles were equivalent to 1 hemagglutinating unit.
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