cell units which carry hereditary mtericl}) or perm cells suitable doses of radiation, usually Xerays. Increases of sevxenl thousand per cent are usual Spsculating on a rough aporoximation of effects on tae genetic structure of a humun popel-tion exposed to gamma radiation (high energy, he .vily penetrating rays) such as wold accompany the detonation of an atouic bomb at a height comparable with those used in Japan, Dr. Bellemy emphasized that the approximation would be "very rough indeed, since no available information permits anything like an accurate estimate." Mutation ratss are not kcnown for men, he said, and are not likelg to be known for some tine to come. Haldane, a British scientist, hag however, estimated the mutation frenvency of human genes as one in 100,000, Continuing his imarinary set of circumstances, Ur. Bellamy assumed a typieclL American city 2s heving a popul:tion dencity of 10,000 per square mild, and thet it was exposed to radiaticn from a source some distance in the aire Ve essumee further thet 40 per cent, or 4,000 persons per siuerc mile were betuecn th: ages of 15 ond 39; anc thet the propertien of mles end females was 50-50. He negiceted nen-prucuctive matings anc assumed ansveorare of three effspring er peir, or 6,000 offspfing per stware adlee Dre Beilamy based one estimate cn the knorn mutation rates for Droepenile, the hanens fly, whose totel yield of lethal changes is iocut three perccat per LOO Reentpen unite of total body radiation. He corrected this dosage for man--humana cannot take 1000 Roentgen units of radiaiten and live--and correlatedqythe result with caiculationg based on Haldane's estimate for one in 100,000 for the natural mutation rate in mane The 2000 mothers (half of the 4,000 persons per square mile) would have among them 12 mole-determining chromosomes carryihg a sex linked lethal, seid Dr. Bellamy. Half of the sons from these 12 mothers would receive this mutated chromosome and wuld die. There would be sbout five males less per thousand populations Increases in visible recessives, based on Haldane's estimate of one in 100,000 would be increased about 30 times after radiation. of about three in 10,000 after radiation, Dr. Bellamy éaid. This gives a mutation rate