1. 1. It has been shown that the mosquito Aedes aegypti , in common with other insects, is extremely resistant to high doses of X-irradiation. Thus, the mortality did not reach 100% in the groups exposed to 40,000 r and 30,000 r until the twelfth and twenty-first post-irradiation days respectively, while in the groups exposed to 20,000 r the mortality was 95% on the thirtieth day. In the groups exposed to 10,000 r and 5,000 r the mortality was 28% and 18% respectively at the end of thirty days. It is to be noted that in non-irradiated, control colonies the mortality is 10% at the end of thirty days, and that the average life span of these laboratory mosquitoes is approximately forty-five days.2. 2. It has been demonstrated that X-irradiation in doses ranging from 5,000 r to 30,000 r produces a significant increase in the innate resistance of A. aegypti to infection with the malarial parasite Plasmodium gallinaceum , and that this effect is quantitatively increased with increasing doses of X-irradiation.3. 3. Finally, it has been shown that penicillin, and sulfadiazine, when administered to X-irradiated mosquitoes prior to infection, are capable of reversing the effects on host immunity produced by exposure to X-irradiation and reestablishing what would appear to be a normal host-parasite equilibrium.
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