HEMATOLOGIC EFFECTS OF RADIATION 1049 



10 r of X ray per day the erythrocyte values of the dog and rabbit were 

 reduced by sixteen weeks, whereas it required thirty-two weeks for 

 erythrocyte values to decrease in the rat. The same number of roentgens 

 per day was also required to bring about a depression of the leukocyte, 

 absolute heterophil, and platelet values in the rabbit by four, five, and 

 twelve weeks, respectively, whereas a daily dose of only 6 r/day produced 

 depressions of these elements in the dog by sixteen and eight weeks. 

 The leukocyte and absolute lymphocyte values of the rat decreased in 

 four weeks with 10 r/day, but the same elements were decreased in 

 monkeys by one to two weeks by the same dose. 



Suter (1947) also studied the effects of chronic exposure to 10.2 n/week 

 on the peripheral blood of the dog, rabbit, and rat. A decrease in the 

 erythrocyte values was produced by thirty-eight, thirty-two, and six 

 weeks, respectively. The leukocytes and absolute neutrophils were 

 reduced in the dog by 2%, weeks and the absolute lymphocytes by 4>^ 

 weeks. These same elements were decreased in the rabbit by 5, 73^, and 

 2}4 weeks, respectively, whereas in the rat only l}4, %, and 1% weeks, 

 respectively, were required to bring about a reduction with 10.2 n/week. 



CHRONIC EXPOSURE TO SMALL DAILY DOSES OF FAST NEUTRONS 



Fast-neutron doses of 4.3 n/day, 6 days per week, produced a dramatic 

 and uniform decrease in leukocyte levels in CFi female mice, involving 

 both the lymphocytes and the heterophils (Henshaw, Riley, and Staple- 

 ton, 1947). Death occurred at eight to twelve weeks. In another group, 

 daily exposures of 1.15 n were compared with 8.6 r of pile-produced y rays 

 (Henshaw, Riley, and Stapleton, 1947). The roentgen-to-neutron ratio 

 of 1:7.5 for the acute killing of mice was the criterion used for selecting 

 these dosages. Only slight hematologic changes, if any, were produced 

 with these doses after forty to sixty weeks of exposure. Henshaw 

 reported, however, that a daily exposure to 0.25 n of fast neutrons or to 

 8.6 r of pile 7 rays had the same effect on survival of mice, and thus an 

 r:n ratio of 1:35 for daily doses was calculated for these radiations. 

 This investigator is of the opinion that threshold responses of the periph- 

 eral blood are at least ten times less sensitive than survival. Mice (C-58) 

 treated with single weekly doses of 51.6 r (X rays) showed slightly lower 

 leukocyte values, with a terminal drop at thirty weeks, than those 

 exposed to the equivalent of 8.6 r of 7 rays per day, 6 days per week. A 

 significant, gradual, and progressive decline in erythrocyte values was 

 apparent with 51.6 r/week (X rays), whereas 8.6 r/day (7 rays) produced 

 only a slight and minimal reduction of the erythrocyte values. 



CHRONIC EXPOSURE TO GAMMA RAYS (RADIUM) 



The general plan of exposure employed by Lorenz, Heston, et al. (1946) 

 and Lorenz, Heston, and Eschenbrenner (1947) is referred to here only to 



