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On Increasing the Yield and Potency of Typhus Vaccine Prepared from Infected Yolk Sacs^*

From the Biological Laboratories, E. R. Squibb & Sons, New Brunswick, New Jersey

Abstract

Increased yields of typhus vaccine per inoculated egg may be obtained by:

(a) Reducing the number of early non-specific embryo deaths through incubation of the inoculated eggs in the vertical position with the air-sac up.

(b) Utilizing the daily increment in weight of the yolk-sac in the course of embryonic development by inoculating eggs on the 7th instead of the 6th day of development and by delaying the peak of deaths through appropriate dilution of the inoculum.

(c) Harvesting the membranes from living embryos on the day when the peak of deaths occurs.

Increased potency, as indicated by complement-fixing activity of the vaccine, can be achieved by harvesting yolk-sacs only from embryos dead 1 day before and at the peak of deaths and from embryos still living when the peak of embryo deaths occurs.

The authors wish to acknowledge the technical assistance of Mr. Jack O. Davis throughout the course of these studies.

Footnotes

^* Withheld from publication for reasons of National Security.