formation, the relationship of these morphologic changes to potential leukemogenesis or other abnormalities which might occur later remains highly speculative.*7 “* Other somatic effects. Opacities of the optic lens occur after acute exposure of the lens to doses greater than 200 rads of mixed gamma and neutron radiation,’® 7 although the minimum effective x-ray dose for the production of clinically significant cataract the ABCC investigated 4,781 births to related parents with varying degrees of radiation exposure®! and reported: “No demonstrable, consistent effect of parental exposure on the frequency of malformed infants or perinatal deaths was found.” The massive data from the ABCC survey of pregnancy termination in nonrelated parents®® have been reanalyzed independently, and, on the basis of this separate analysis, a significant total genetic effect has been reinterpretations of the reanalysis have been seriously questioned by Neel and Schull.*’ rays.'® The sensitivity of lenses to radiation than man have shown that the frequency of local gonadal doses of 500 rads or higher."® lowest doses investigated, and that the majority of induced hereditary changes had detrimental consequences.’* Although direct to be more cataractogenic than x- or gamma seems to be greatest in infants under 1 year of age.'* Prolonged temporary or permanent sterility has been reported following single HEREDITARY EFFECTS— HIGH DOSE In the studies of atomic bomb survivors at Hiroshima and Nagasaki by the ABCC, **) ©% 81 it was concluded that the data could demonstrate “no significant and consistent effect of parental radiation exposure on the numberof infants with major defects, among the 76,626 children examined” and failed “to reveal an increase in stillbirths or infant deaths clearly attributable to parental irradiation.” The Japanese study, however, has indicated a change in sex ratio among offspring of irradiated parents. Such a shift would be consistent with the occurrence of sex-linked mutations affecting prenatal survival.** Schull** has examined the genetic interpretation of the data, emphasizing the reality of the effect but indicating that a number of genetic alternatives may account for the change. A slight increase, however, in the number of miscarriages, stillbirths, and neonatal deaths has been reported in the Marshallese women exposed to fallout radia- tion.8* Based on the assumption that children of consanguineous Marriages, owing to their increased homozygosity, are “a more sensitive index of radiation induced genetic damage,” , F ‘ ported.®* 8° However, the methodology and In chronic exposures, neutrons are considered has been estimated to be 600 to 1,000 rads.17 ET Sie a= RTOET these chromosomal aberrations has not been established; in the absence of sufficient in- ra October 1965. Sutow and Conard Experimental studies in organisms other mutations was dose dependent, even at the information is lacking, it appears reasonably certain that similar effects occur in the human being.*® Thus, known exposure to high doses of ionizing radiation requires the disquieting acceptance of genetic hazards, the true magnitude of which may be assessed only with the perspective of time stretching over generations. SOMATIC AND GENETIC EFFECTS OF LOW-LEVEL RADIATION The term “low-level” radiation, regardless of source, requires definition. The United Nations Scientific Committee on the Effects of Atomic Radiation (UNSCEAR) has agreed that doses of less than 50 rad shortterm exposure and 100 to 1,000 mrad cumulative weekly doses should be considered as “low.”*? Two other frames of reference will be useful in this discussion, one being the amount of radiation from natural sources to which man is constantly exposed and the other being the levels accepted by several advisory and regulatory bodies as protection standards for the general population. According to UNSCEAR calculations of dose rates from natural radiation sources,®*°° cosmic rays and terrestrial sources each de- liver about 50 mrem per year to the gonads, bones, and blood-forming cells. The inges- we dere Pee AY G62