Conarp Effects of Ionizing Radiations 496 of complicating factors such as trauma, nutritional deficiencies, etc. in this population. We have found definite growth retardation in some of the Marshallese children exposed to fallout [30]. As was pointed out earlier, thyroid injury from radiotodine exposure appears to have been responsible for this retarded growth [10]. Nephrosclerotic changes. Such changes have been noted only in patients receiving large doses to the kidney, but have not been reported in personsreceiving sublethal doses of whole bodyirradiation. Summarizing Remarks Malignant transformation is usually viewed as a process of aging since the incidence increases with aging. The development of such malignancies is one of the best correlated late effects of exposure in both animals and human beings andis responsible largely for the life shortening observed. Such malignancies have been noted following whole body, partial body or specific organ exposure due to selective absorption of radioactive isotopes. Following whole body (sublethal) exposures, leukemia is definitely established as a late effect and it appears that thyroid cancer as noted in the exposed Japanese can be added to the list. Since malignancies other than leukemia were increased in radiologists (a study covering a relatively long period of time) other types of radiation-induced malignancies may yet appear in the exposed Japanese and Marshallese populations. Heretofore radioiodines had not been thought to play an importantrole in malignant transformation. However, the recent development of the high incidence of both benign and malignant nodules in the Marshallese described in this paper clearly indicates the importance of radioiodine exposure in this regard. The high incidence of thyroid abnormalities in the Marshallese children along with the related retardation of growth emphasizes the caution that must be observed in the use of radioiodines, Many of the nonspecific effects of irradiation bear similarities to ordinary aging changes. Since the underlying changes of ordinary aging are not clearly defined, it is understandable that such radiation-induced changes are even less understood. There are no pathognomonic radiation changes characterizing late effects. Measurement of the usually-recognized aging changes in the exposed Japanese and Marshallese populations have failed to reveal such effects of irradiation. However, late effects other than neoplasia have been found in irradiated human populations such as life shortening in radiologists, development of lens opacities, persistence of chromosome aberrations and certain immunohematological changes. Most of these effects such as cataracts, skin changes, chromosome aberrations, etc. do not appear to be related to lethality, though collagenous and fibrotic changes in connective tissue and blood vessels may indirectly have a causal relationship to mortality. The individual genetic predisposition to such alterations is an important area about which we know little. Also complicating environmental factors (socio-economic, geographical, stress of trauma, heat, cold, disease epidemics, etc.) no doubt play an important role in the development of late radiation effects. G3 Las53 rd oc ~ SR GTS TR LTE OSS ETE LT . ° a .