Abstract
Expts. to increase the strength of the Japanese B encephalitic virus (Nakayama strain) in the hen''s egg indicated that the highest potency would be obtained in chick embryos by using 7- or 8-day-old embryonated eggs inoculated into the yolk with 0.5-ml. amts. of mouse brain virus of a potency of 10-8.5 or better, and incubating 36 hours at 95[degree] to 96[degree]F. Because of the constant lethal effect after 48 hrs., the inoculation of the egg yolk is of value for titrations of this virus and for use in other quantitative expts.

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