sé A large population of genetically uniform mice, 6-12 weeks of age, was exposed to atomic detonation, and after recording the zortality rates during the first few weeks after exposure, the animals were transported to Oak Ridge for study of the delayed effects of irradiation, Radiations from atomic detonation were composed predoninantly of high energy gama rays, with a wall component of fast and a still malle fiux of slow neutrons, the gamma to neutron ratio inereasing with the distance from ground sero. Small susbers of mice were irradiated beneath lead shields, so as to receive predominantly neutron radiation. Survival patterns, shom in Table 1, indicate that the 1Dgy/30 days was approximately 755 r, with little difference between males and famales. At one year postirradiation the LDgp had dropped to 733 r for miles and 7L6 vr for femmles. Significant shortening of the life span resulted fran doses well beneath the threshold for acute lethality. This reduction of longevity, appreciably gretter in fenales, resulted from degenerative and neoplastic diseases induced or exaggerated by irradiation, as will be disclosed. The first of the delayed effects noted was cataract, which appesred furing the third month postirradiation, Within 90 days after exposure virtually all so yo4e "| DORARCHIVES-