18 beings with a remarkable reserve margin ofsafety 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 anyincreased incidence of diseases, infectious or noninfectious, in the exposed population compared with the unexposed groups. These people have sustained epidemics of measles, chicken pox, upperrespiratoryinfections, and gastroenteritis, apparently without any greater incidence or severity of these diseases compared with unexposed groups. A limited study of immuneresponses at three years post-exposure showedthatthe antibodyresponse to tetanus toxoid antigenic stimulus was not significantly 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 impairment ofantibody production might have been demonstrated. Metabolic effects: Weight changes. A possible effect of penetrating radiation noted duringthefirst few monthsafter exposure wasa fairly constant weight loss of several pounds in manyof the people, both adults and children. This occurred despite the fact that their appetites were good and their 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 development because 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 made at this time about the 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 de- P2 Ped er) velopment wasobserved in the Japanese children exposed to the atomic bombs at Hiroshima and Nagasaki.’* It was uncertain whether psychic and phvsical trauma or economic conditions might be responsible in the Japanese children. Theslight effect on growth and developmentin the Mar- shallese was most probably due to 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 isotopesis not believed to have been large enough to have contributed significantly. The Marshallese children probably receiveda slightly higher dose than did the adults because oftheir shorter stature and thinner bodies in a field of radiation produced by thefallout. Even so, the dose of penetrating radiation received was probably too small to have produceda direct effect 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. Ir- radiation 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 the thirdtri- mester. These pregnancies progressed unevent- fully to normal-term deliveries. The babiesall appeared normal in every way, and no micro- encephaly was present as has been reported in some babies irradiated in utero in Japan.'*''* Since the event, nine other normal births have taken place. One miscarriage and twoinfant 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 occurredshortly 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 pregnancies in the exposed and unexposed groupsdoes 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.