32 the mortality data suggest that exposure of the population to this factor has decreased recently. Schwartz and Upton" have considered the role of ionizing radiation in the general incidence of leukemia and lymphomas. Amongotherfactors considered are age, race, sex, geographical location, climate, genetic factors, constitutional factors, and other extrinsic agents such as chemicals and infectious agents. These authors considerthe increase in radiation background from all causes (medical, dental. fallout, etc.) to be “clearly not sufficient to account for the tremendousrise in the recorded incidence of leukemia. . .”” Burnet’! points out that the present peak of incidence of leukemia at age 3 to 4is a relatively recent development and suggests the possibility that exposure to some new mutagenic agent at the timeof birth is the cause. He cites data which indicate that at most 5 to 10% of leukemia incidence in the United States can be ascribed to radiation from all sources, and points out that the etiology of the other 90% is unknown. Otherconstituents of fallout have not received as much publicity as Sr®*°, but their study has not been neglected.**-** Anderson‘? reports an extensive series correlating Cs'*” and K’°levels in people and in milk supplies. He states that the importanceof Cs’** relative to Sris increasing. The levels in both people and milk representing various locales in the United States ranged upto 60 uC Cs'*"*/g K, with fairly good correlation between the twolevels. These results are consistent with those reported by Miller and Marinelli," who have further data suggesting a rather uniform distribution of fallout in the Northern Hemisphere. The significance of low doses of radiation has not been evaluated fully, the chief reason being the absenceof positive data on low-dose effects, particularly in humans. Perhaps more subtle methods will be found by means of which low-dose effects can be documented, but it is to be hoped that the radiation dose can be maintained below the level at which effects appear with any method. In the meantime, the Rongelap people provide an interesting group of subjects exposed to a level of radiation appreciably above the world average. Present indications are that the body burdensof radionuclides will not reach levels which, from known data, will result in morbid processes. As pointed out before, the developmentof leukemia associated with their exposure to a sublethal dose of gammaradiation in March 1954, based on ex- 20067250 periences with the exposed Japanese,*”~** is held to be improbable,particularly in view of the small numberof people involved. The superimposition of the low level body burdens from environmental! contamination would not seem likely to be sufficient to increase this possibility substantially. The habitation of these people on Rongelap Island affords the opportunity for a most valuable ecological radiation study on humanbeings. Since only small amounts of radioisotopes are necessary for tracer studies, the various radionuclides present on the island can be traced from thesoil through the food and into the humanbeing, where the tissue and organdistributions, biological halftimes, and excretion rates can be studied. Summary The medical survey of the Rongelap people in March 1958, 4 years after exposure to accidental fallout radiation, was carried out at Rongelap Island, to which these people had been returned in July 1957 after the radiation level ofthe island wasdeclared safe for habitation. They were adjusting satisfactorily to life in their newly reconstructed village. No apparent acute or subacute effects were foundat this time related to the gamma dose of 175 r received, with the possible exception of hemopoietic findings indicating a persisting lag in complete recovery of platelet levels of the peripheral blood. In the males these meanlevels were 11 to 16% andin the females 9% below thecorresponding meanlevels of the comparison population. The lymphocytes had recoveredto a level about the sameas in the comparison population, although many of these counts were lower than in the latter group. The stress of childbearing and menstruation did not appearto be reflected in any lowered hemopoietic reserve in the exposed women, based on comparative studies of the levels of peripheral blood elements. The suggestive incidence, previously reported, of slight lag in growth and developmentofthe irradiated children at 2 and 3 years after exposure, based on height, weight, and bone age studies, needs re-evaluation in thelight of the finding that the ages of some of the children werenot as firmly established as previously thought. History and physical examinations revealed no clinical evidence of any illnesses or findings during the past year or at the time of the present survey which could berelated to whole-body exposure.