700 



T. C. RUCH, WALTER ISAAC, AND ROBERT W. LEARY 



MEAN LYMPHOCYTE 



»300r 



T V 



1 



14 



21 



28 



35 



42 



49 



56 



63 DAYS 



Fig 

 were : 



7. Lymphocyte counts before and after irradiation. The preirradiation values 

 control group, 8,370; 300 r, 9,266; 400 r, 7,328; and 500 r, 6,380. 



the mean of the 500 r group did not differ significantly from that of the 

 control group. At 28 days after irradiation, the variance among the group 

 means was not significant, but the combined experimental group mean dif- 

 fered significantly from the mean of the control group. Thereafter, the 

 experimental groups were in the normal range. 



The response of the red blood cells (Fig. 8) was prompt, their number 

 decreasing significantly in 24 hours, and some decrease was sustained 

 throughout most of the study. Even at 28 days, the mean for the 300 r 

 group was significantly different from the control means. After 5 weeks, the 

 400 and 500 r groups still differed significantly from the control group, and 

 in the 500 r group a significant difference persisted after 6 weeks. The 

 decrease in hemoglobin content was somewhat more gradual than the de- 

 crease in the red blood cells but followed a similar course (Fig. 9), reaching 

 a nadir at 21 days. The mean of the combined group differed significantly 

 from the mean of the control group 2, 3, and 4 weeks after radiation. 



Discussion 



Whereas in our first series, the radiation levels (50, 100, 200, and 300 r) 

 were too low, the 300, 400, 500 r series seem to bracket the threshold for 

 changes in activity and food and water intake. However, although 16 



