276 R. A. Conard or increased basophil counts indicative of incipient leukaemia was noted. An increased incidence of leukaemia has been reported in radiologists (March 1947, Ulrich 1946, Warren 1956), in children receiving therapeutic radiation in infancy for thymic enlargement (Simpson and Hempelmann 1957), in children exposed in utero from diagnostic x-ray examinations of the mothers (Stewart, Webb, Giles and Hewitt 1956), in patients receiving x-irradiation for treatment of ankylosing spondylitis (Court-Brown and Doll 1957) and in survivors of the atomic bombs in Japan (Maloney and Kastenbaum 1955). Though the incidence of leukaemia in the exposed Japanese was significantly increased, the total incidence was low. Therefore, since the exposed Marshallese population is small, it does not seem likely that leukaemia will be observed as a result of their radiation exposure. 2.2.4. Cataracts During the past five years repeated slit-lamp ophthalmological observations in the Marshallese revealed no opacities typical of the radiation-induced type. The induction of opacities of the lens by radiation is a well-established fact in man. In the Japanese exposed to the atomic bombs, opacities of the lens, including about 10 severe cataracts, have been observed (Cogan, Martin and Kimura 1949, Sinsky 1955). Merriam and Focht (1957) on the basis of clinical cases of radiation-induced opacities calculated that 200 r was the minimum dose of gamma- or x-radiation resulting in lens opacities. Therefore, the dose of radiation received by the Marshallese may be too low to result in such changes. 2.2.5. Reproduction It has long been recognized that reducedfertility may be induced by ionizing radiation in man byrelatively smali doses, possibly even in the dose range that the Marshallese received. Transient effects on fertility may have taken place in this group, but such effects were not observed. Studies such as sperm counts were not feasible. No amenorrhoea was noted in the exposed women. Birth rate during the past five years in the exposed group was not reduced and, if anything, appears to have been higher than in the unexposed comparison population or in the Marshallese people generally. Therefore, the degree of sterility that may have been induced was not detectable based on these findings. A somewhat greater prevalence of miscarriages and still-births has been noted in the exposed women but, due to the paucity of vital statistics in the Marshallese and the small number of people involved, the data are not readily amenable to statistical analyses. 2.2.6. Growth and development Anthropometric measurements on the Marshallese children have revealed findings, previously reported (Conard et al. 1957), which were interpreted as suggestive of a slight lag in growth and developmentin the exposed children during the first few years after exposure. However, certain inconsistencies in the ages of the children were found, and the data are being re-evaluated based on more exact age data obtained during the last survey. The results of this evaluation are not complete enough to make any statements at this time. Such an effect would not be inconsistent with the findings of Greulich et al. (1953)