- 358 - does not necessarily mean that they are related to mortality which is a more pertinent correlation. Such criteria as hair greying, arcus senilis, neuromuscular function, etc., would not seem to have any obvious relation to mortality, On the other hand, loss of vigor and organ disfunction could well predispose to the development of old age diseases which would enhance mortality. Increase in mortality and life-shortening in the exposed Marshallese is difficult to assay in view of the small numbers of people involved and the slightly greater number of older people in the exposed group compared with the unexposed group, One radiation effect which might be classified as ageing is the induction of malignant disease at an earlier time than it would ordinarily be manifest. One aspect of this phenomenon may be related to rapidity of cell proliferation (generation cycle) in a particular tissue, i.e. with more rapidly proliferating cells of the bone marrow, leukaemia occurs relatively soon after irradiation, while malignant lesions of the skin would not become manifest until later in this more slowly proliferating tissue. In the Marshallese, the high incidence of adenomatoid goitre in the more rapidly proliferating thyroid glands of the children may possibly represent premature appearance of lesions which are known to occur later in life and thus in a sense represent an ageing process, On the other hand, the fact that no tumours (except benign nevi) have been noted in the heavily irradiated skin of these people might indicate a longer induction period was necessary due to slower cell turnover of the skin. In considering future ageing studies in the Marshallese it is hoped that more sensitive tests of vigour and organ function suitable to the conditions of study may be used, However, it must be borne in mind that such subtle ageing effects may not become detectable’ by ordinarydinical means until the organ or tissue shows advanced morbidity. It is hoped that longitudinal studies of ageing criteria in Rongelap individuals and groups may be more rewarding as time goes by. Acknowledgments The work reported here is supported by the United States Atomic Energy Commission. Tmtdere ae The authors are grateful to the Armed Service Medical Procurement Agency, Fort Totten, New York for loan of the audiometer. te 00 | i.Sb2 e *