EFFECTS OF IONIZING RADIATION a reached. The count was maintained at approximately 75 percent of control values from the 7th week to the end of the initial study. No further recovery was evident at 6 months. Although both age groups followed the same general time pattern of response, the lower age group was below that of the older throughout most of the observation period. At 12 months the granulocytes had returned to the control range. The absolute lymphocyte count of the older age group (Fig. 4.2) had fallen by the 3d day to a value approximately 55 percent of the control group. This value was maintained throughout the study, and there was no definite evidence of an upward trend during the initial or 6 month studies. At 12 months, complete recovery had not occurred. The values for the younger age group likewise fell before the 3d day to a value approximately 25 percent of the control, following which there was a significant upward trend. With the total lymphocyte count, there is a consistent difference between the two age groups. However, during the first + weeks the difference is accentuated when expressed as percent dlecresse because of the relatively high lymphocyte levels in the lower age control group. After this period the differences expressed as percent are less marked since req T : ors + T Tel | } T LYMPHOCYTES 3103 Tv }_——p—————————conrtmans GROUP A - AGE <3 —4 + POST EXPOSURE Oar FIGURE 4.2.—Seriai changes in lymphocyte count of Group £ (Rongelap) for those leas than 5 years and greater than 3 years of age. LEUKOCYTES, NEUTROPHILES AND LYMPHOCYTES x 10? 48 ' EST aa 6 om s2 40 46 56 POST EXPOSURE DAY 64 AAg 72 @5 Ficure 4.3.—Comparative serial changes in the totat lenkocyte, neutrophile, and lymphocyte counts in thoxe greater than 5 years old, Group I (Rongelap). covery was more rapid in the younger age group. The cellulur elements chiefly responsible for the Huctuations in total white blood cell count cun be determined by comparingthe total white, neutrophile und lymphocyte counts (Fig. 4.3). It is seen that the lymphocyte count remained essentially constant throughout the period of study, while the total neutrophile count fluctuated with a pattern essentially identical to that of the total white blood count (coefficient of correlation of 0.9). Thus the fluctuations in total count were due to changes in the neutrophile count. This was true of both the older and younger age groups. It can be seen from Table 4.2 that the neutrophile count was consistently greater than the lymphocyte count in the older age group. In the younger groups, differences in the neutrophile and lymphocyte count were less marked and frequently the lymphocyte count was greater than the neutrophile count. Platelets were first counted 10 days after exposure, at which time platelet values of the females were approximately 60 percent of the appropriate control group (Fig. 4.4). Follow-