Abstract
Summary
Both mouse-avirulent LH-a and mouse-virulent LH-v variants of Leon (Type III) poliovirus represented mixed populations, but LH-a yielded more avirulent plaques while LH-v yielded more virulent plaques. On replating, virulent and avirulent plaques usually yielded corresponding virulent and avirulent progeny, although intermediate forms sometimes appeared. After purification, virus from 3 avirulent plaques derived from LH-v was serially passed in Eagle's medium and in 2 of them reversion to virulence occurred; however, in another set of experiments, virus from 2 avirulent plaques derived from LH-a was passed in the same way and reversion did not occur. Titration in TC of suspension of the spinal cords of some inoculated mice indicated that LH-v multiplied more readily in the host than LH-a.
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