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In recent tradescantia inflorescences experiments the chromosome aberration yield was enhanced if the centrifuge was started immediately after irradiation. It was also noticed that centrjfuging for long periods of time, either previous t o or during irradiation, decreased the aberration yield, apparently because the temperature rise due to friction of the centrifuge is enough t o hasten the rejoiding of broken chromosome ends. Tfie fact that post-irradiation centrifugation can increase the chromosome aberration yield indicates t h a t radiation-induced breaks are not latent. a new tool for determining whether o r not the same number of breaks are induced by irradiation in air as i n nitrogen. It was demonstrated t h a t treatment of Paramecium aurelia with latK concentrations of H202 either before or after irradjation decreases the mount of detectable mutation. findings which had indicated t h a t the.peroxide can act as a mutagen. It 0 0 shows that peroxide, acting after irradiation, does not enhance the effect of the radiation, as had been reported i n England f o r bacteriophage. The effect decreased with time after irradiation but was still detectable a day later, following four cell divisions. paramecia were killed and there was only as light prolonging of the interdivision interval by the radiation. selection of non-mutant animals i s involved. yet be offered. This finding i s contrary toall previous A large effect was found even when none of the Thus it seems unlikely thata simple No satisfactory hypothesis can It was found that in the human the bacterial recovery factor previously reported is present in t h e urine of both males and the females, including pregnant females. yields a product purified approximately 10-fold. graphy is being used in attempts t o purify this product. io duplicate the recovery effect on a complex synthetic medium, are i n progress. A 9s percent ethanol extraction of fresh urine Pathology and Physiology Adult mice and rats surviving a nearly lethal dose of fast neutrons, produced i n t h e 86-inch cyclotron, developed complete cataracts within 6 and ,O nonths, respectively; however, guinea pigs given the same dose developed only relatively mild opacities of the lens within the first year. tions indicate the relatively high radio sensitivity of the lens of the mouse and the rat and suggest that severe cataract i n the guinea pig results only from a dose of neutrons which exceeds the lethal dose for whole-body radiation.
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