UNCGLASS) "EDCo — ~— Se BIOLOGY AND MEDICINE to the prevention or reversal of toxic actions on living organisms. Data derived from these Studies are examined to establish maximum permissible levels of exposure for man and laboratory animals and to provide a basis for the prediction of biological damage in cells and tissues after a given exposure. Such studies are important not only for recognition and evaluation of radiation damage but also for the developmentof therapeutic and diagnostic applications in the treatment of diseased cells and tissues. Only a few examples of these investigations can be reported here. Vins SA ae een an Meee 5 Deemer eee NEN + senanles un Effects of X Rays on Frog Retina The University of California Radiation Laboratory, Berkeley, has completed a study of the effect of X rays on animal retina, particularly the retinal response of bull frogs to small doses of X rays to determine adaptation and recovery. It was found that an electrical response could be measured on the retina after an exposure of as little as 0.6 roentgens, that during exposure to X rays the sensitivity to light was reduced, and that the retina recovered Jess rapidly after X ray stimulus than after light stimulus. The recovery of the retina to penetrating radiations indicates that the effect is to a large extent reversible, DOE ARCHIVES Biological Effects of Radiation Los Alamos Scientific Laboratory has been experimenting to determine the biological effects in mice of whole body X radiation. Pretreatment of mice with p-aminopropiophenone (an agent producing a pronounced deficiency in oxygen) or glutathione exerted a marked protective effect against whole body X radiation. But a negligible degree of protection was found when mice so pretreated were exposed to radiation from the thermal column of a reactor (thermal neutrons plus gamma contaminant). Thus, it appears that agents which are protective against one type of ionizing radiation may not be of value against all types. set bee wae he et me oad try OR rt Als onde Radiation Effects on Mortality The effects of whole body irradiation of male rats on mortality among their offspring is being studied by an AEC-University of Tennessee research group. Male rats were exposed to 300 roentgens of gamma rays from a cobalt 60 source, or to K rays froma 250 kilovolt machine. The irradiated maies were mated to virgin females. The pregnant females were sacrificed, and it was found that the fetal death rate showed an increase in comparisor. with nonirradiated control rats. The fetal mortality rate for the various grczps was: control group, 6.46 per cent; gamma-ray exposure, 19.37 per cent; and X rays (250 kv), 19.92 per cent. After 60 days the same male animals were used in repeating the breeding test. The values obtained after sacrifice of the second group of pregnant females were 7.39 per cent for gamme exposure and 8.19 per cent for X rays. The decrease in fetal mortality rate between the first test and the second test of the irradiated males indicates that there is a period of recovery, and that the initial high mortality rate may be due to dominantlethal mutations induced during exposure in the more mature testis cells. hee eee ame Prevention of Tumors Following Irradiation For several years research has been proceeding on the role of the spleen 2s a protective organ in preventing radiation injury. Recent work at Argonne National Laboratory has indicated that a considerable degree of protection is provided ec2zinst subsequent development of lymphoid tumors when the spleens of mice are shielded during irradiation. UN CLASS] FleD