The growth of Rickettsia mooseri was accelerated and quantitatively increased in embryonate eggs containing tritium oxide at levels of 180, 90, and 45 mc./egg during the growth period. The eggs of a group containing 22.5 mc./egg showed only a slight increase in the rate of growth of organisms; the infections in the eggs of a group given 11.2 mc./egg did not differ significantly from those of the control group. On the other hand, growth of R. akari was inhibited in embryonate eggs containing tritium oxide at levels of 180, 90, and 45 mc./egg, and partially inhibited in groups containing 22.5 and 11.2 mc./egg. The patterns of growth of R. mooseri and of R. akari exposed to tritium oxide for 6 hours prior to inoculation into embryonate eggs did not differ significantly from that of the control group.
Single and divided doses of x-rays to the host resulted in partial inhibition of the growth of R. akari.