The biological assay of myxoma virus.

lesion and the remaining rather variable inflamed area disregarded. In the preliminary experiment the animals were observed at 6-hr. intervals for the occurrence of death. Mice. Eighteen randomly bred new-born mice of Agouti parents were employed. Mice were inoculated intracerebrally with 0-02 ml. of 100 Glenfield strain virus by means of an Agla micrometer syringe and 27-gauge hypodermic needle. At the appropriate time three mice were killed by decapitation and the heads, together with 6 ml. penicillin solution (50,000 u./ml.), were ground in a mortar with carborundum grit. Periodically during grinding the mortar and contents were placed in the deep freeze (- 20') to provide alternate freezing and thawing and thus break down cells. The resultant suspensions were centrifuged at 2500 r.p.m. for 15 min. and the supernatant stored in glass ampoules on dry ice prior to testing.