on Aging and Life Shortening in Human Populations 495 GAMMA GLOBULIN 2.25 1— 14 PE 2.00 + GRAMS/100 mi 1.75 -—- we 1.25 1.00 -—- (b) AGE Fig. 4. Age related change in y-globulins showing the mean level for each decade with standard deviation, O—-OUnexposed, y = 1.69 + 0,006 x. O——©O Exposed, y = 1.60 + 0.001 x. those of unexposed levels) with reduced immunoglobulin levels particularly IgG and IgA [11,12] (see fig.4). The response of cultured lymphocytes from peripheral blood to phytohemagglutinin stimulation, however, was about the same in the exposed as compared with the unexposed population. Though these findings may indicate impairment of immunological capacity in exposed people, such impairment has not been evident based on incidence and severity of diseases compared with the unexposed groups overthe 16 years of examinations [9]. Growth and development. Thoughlarge dosesof irradiation to the bones are knownto retard growth in children, it is questionable if such bone ex- posures in the sublethal dose range can bring about retardation of growth. Some degree of retardation in growth and development in the Japanese children, particularly in males, has been reported by RENOLDs [26], NEHEMIAS [24] and GREULICHet al. [16]. The latter authors emphasize the importance ' i ae 7 iad We 1 trek ee Re pee oy