18 beings with a remarkable reserve margin of safety in protecting against infection. Even at the lowest ebb of hematopoietic depression, when the leukocytes and platelets in the Marshallese were about half their normal values, there was no detectable evidenceof increased susceptibility to infection or increased tendency to bleeding. Indeed, at no time during the past three years has there been any increased incidenceofdiseases, infectious or noninfectious, in the exposed population compared with the unexposed groups. These people have sustained epidemics of measles, chicken pox, upperrespiratory infections, and gastroenteritis, apparently without any greater incidence or severity of these diseases compared with unexposed groups. A limited study ofimmuneresponses at three years post-exposure showed that the antibody response to tetanus toxoid antigenic stimulus wasnotsignificantly different in the exposed and unexposed people. However, had this type of study been carried out soon after irradiation,it is possible that some degree of impairmentofantibody production might have been demonstrated. Metabolic effects: Weight changes. A possibleeffect of penetrating radiation noted duringthefirst few monthsafter exposure wasa fairly constant weight loss of several pounds in manyofthe people, both adults and children. This occurred despite the fact that their appetites were good andtheir food consumption was greater than had beentheir custom. It is not known whetherthis weight loss represented an effect of radiation on metabolism or whetherit was related to the change in environment. Growth and development. It is difficult to evaluate the effects of the radiation exposure on growth and developmentbecause of the small numbers of children involved. The lag in growth and development as evidenced by differences in weight and height of the 4 to 10-year age group of exposed children wasslight, and definite statements cannot be madeat this time aboutthe significance of these differences. However, the bone development studies seem to indicate a slight degree of retardation in the exposed group. Lag in growth and development was observed in the Japanese children exposed to the atomic bombs at Hiroshima and Nagasaki.'? It was uncertain whether psychic and physical trauma or economic conditions might be responsible in the Japanese children. Theslight effect on growth and developmentin the Mar- shallese was most probably dueto the penetrating dose of gamma irradiation. Certainly external beta radiation would not contribute to the dose to the bones, and the internal adsorption of boneseeking isotopes is not believed to have been large enough to have contributed significantly. The Marshallese children probably received a slightly higher dose than did the adults because of their shorter stature and thinner bodies in a field of radiation producedby the fallout. Even so, the dose of penetrating radiation received was probably too small to have produced a directeffect on the epiphyses. It would seem morelikely that arrest of bone maturation might be from some non- specific or indirect metabolic effect or possibly hormonaleffect resulting from the radiation. Irradiation of the thyroid gland may have depressed thyroid hormonesecretion and thus delayed bone growth. Further studies of thyroid activity are planned. In utero effects and effects on pregnancy. Four women were pregnantat the time of exposure, two in the first, one in the second, and onein thethirdtri- mester. These pregnancies progressed uneventfully to normal-term deliveries. The babies all appeared normal in every way, and no micro- encephaly waspresentas has been reported in some babies irradiated im utero in Japan.'*:'* Since the event, nine other normal births have taken place. One miscarriage and two infant deaths have occurred, but this incidence does not seem greater than that in unexposed Marshallese people based on limited numbersof observations. Fertility. It is entirely possible that a temporary loss of fertility may have occurred shortly after exposure in someof the people. However,careful investigation of the possible effects of the radiation exposure onfertility has not been possible. Comparison of the frequency of pregnanciesin the exposed and unexposed groups does notindicate any detectable effect of radiation exposure onfertility. As pointed out, however,satisfactory vital statistics are lacking, and the numbersofindividuals are too small to reach any definite conclusions. In a limited medical survey of the Central Pacific Islands carried out by the U.S. Navy in 1949 and 1950,'° limited statistics on pregnancies in the Marshallese were reported. Pregnancies among the exposed Rongelap women during the past three years are within the range 18 to 32 per 1000 population reported in the above survey.