between the age groups were less apparent if the platelet counts were expressed as per cent of the control group. 4.6 : . wee ee Tenoweregrmiep were ste cee 4 of the total white blood count (coetticient of Correlation of 0.9). Thus (he, duetiuations ur total count were due Co changes in (he neulrophile coun( This was true of both the older and younger age groups. Tt can be seen from Table 4.2 that the neulrophile count’ was cousistently greater than the lymphocyte count in the older age group. En the younger groups, differences tn the neatrophile and lymphocyte count were less marked and on six occasions the lymphocyte count was greater than the neutrophile count. Platelets were first counted_10 days after exposure, at which time platelet values of the older age groups were approximately 70 per cent of the control group (Fig. 4.4). Following this, the platelet count fell reaching a low of approximately 35 per cent of control value during the fourth week, The platelet count rose during the 5th week and reached the value noted for the initial counts on the 10th day. A second decrease in the platelet count (P « 0.01) developed during the 7th and 8th weeks, and values remained at approximately 70 per cent of the control group during the remainder of the observation period. The pattern of platelet counts in the below 15-year troup was remarkably similar to that noted in the older age groups. Differences AILINGINAE GROUP In this group there were only three individuals below age 5, For this reason, remarks will be confined essentiafly to the older age group. The absolute neutrophile count fluctuated around the control value for the first six weeks . of observation (Table 4.3). At this time the counts began to fall, and a value approximately 75 i per cent of the control count was reached and maintained throughout the duration of the obser- vation period. The lymphocyles in this group fell to a value of 55 per cent of normal during the first week. The counts then fluctuated around this value throughout the period of observatic a, and no definite upward trend of the lymphocyte count was noted during the period of observa- _ tion. As was noted in the Rongelap group the lymphocyte counts remained at an essentially con- stant low level throughout the period of observation. The total leukocyte eount inthis grour also reflected changes in the neutrophile count. ” The platelet counts in the Ailinginae group were low, approximately 75 per cent of normal, when first enumerated on pust-exposure day 10. The counts remained at this level during the second and third week; however, a definite fall in count was noted during the fourth week when a low value 45 per cent of control was attained. The counts returned during the fifth week toa value approximately 70 per cent of the control level, where they remained for the duration of t : : the observation period. A secondary fall, as observed in the Rongelap group was not detected. 4.7 UTIRIK GROUP In the greater than 5 age groupthe total white blood cell and neutrophile counts were depressed slightly below control values during the first and second weeks (Table 4.4). The lymphocyte counts were below control levels consistently, and the total white count equal to the control value obtained on day 29 was due to a neutrophilic leukocytosis. Platelet counts on the 29th day were significantly lower than on the 19th day and were lower than control values. The 29th day coincides with the time of maximum depression for the more heavily exposed groups. 4.8 RONGERIK GROUP (AMERICANS) The neutrophile count in general reflected the time course of the total leukocyte count (Fig. 4.5). Neutrophiles accounted almost entirely for the marked rise in total count on postexposure day one, and the values for absolute neutrophile count fluctuated near the control ‘ « . » ’ . ee vere . nner ae | oe 80