Abstract
Summary
1) A glycerinated control smallpox vaccine of calf lymph origin was titrated for a total of 28 times, over a period of 2 years, by the chick embryo LD50 method. Calculations of LD50 titers were made at the end of 5, 6, 7, and 8 days incubation, and those of the 7th day were found to be optimal. Individual titers on the 7th day ranged from 10-6.7 to 108.4 giving a geometric average titer of 10-7.5 for the control vaccine with a standard deviation of 0.33 log unit. No significant seasonal variations of the average LD50 titers were noted. 2) The precision of the method and its applicability to the potency testing of smallpox vaccine have been discussed.
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