1044 RADIATION BIOLOGY 



fourth and tenth day) after fast-neutron exposure and is comparable to 

 that observed following the exposure of rabbits to X rays. 



The morphologic changes in the cellular constituents of the peripheral 

 blood after fast-neutron exposure are identical with those occurring in 

 the peripheral blood of rabbits after "comparable" doses of X rays. 

 These observations in rabbits are comparable with those after single 

 exposure to X rays (Figs. 16-1, 16-3). Henshaw's observations (1946) of 

 mice likewise are qualitatively similar to X-ray studies of these species 

 when the differential factor of effectiveness between X rays and fast 

 neutrons is considered. 



COMPARISON OF EFFECTS PRODUCED 

 BY CYCLOTRON FAST NEUTRONS AND X RAYS 



Sacher and Pearlman (1947) have made a statistical analysis of exten- 

 sive hematologic data obtained by Jacobson and Marks (1947) and by 

 Jacobson et al. (1947) from rabbits exposed to X rays and fast neutrons 

 and have derived a ratio of the relative effectiveness of these two radia- 

 tions. Using the data on the effect of fast-neutron and X-ray exposure on 

 the number of circulating heterophils and lymphocytes, they estimated 

 the X:n ratio to be of the order of 6.3. These estimates are in essential 

 agreement with the X:n ratio derived from survival data on rabbits 

 (using the same type of instruments) by Hagen and Zirkle (1950). 

 Evans (1948) derived a ratio of 8.1 in Swiss mice. It should be pointed 

 out again that the n unit is arbitrary and that the X : n ratio given does 

 not mean that neutrons are 6.3 times more effective than X rays in pro- 

 ducing the same biological effect. 



FACTORS CONCERNING COAGULATION 

 FOLLOWING SINGLE EXPOSURES 



A prolonged bleeding time, impaired clot retraction, fragility, thrombo- 

 cytopenia, and a prolonged whole-blood clotting time were observed in 

 laboratory animals following single exposures to dosages of penetrating 

 radiation in the LD 60 range and above by Shouse, Warren, and Whipple 

 (1931), Allen and Jacobson (1947a), Allen et al. (1948), Cronkite (1950), 

 Cronkite et al. (1949, 1950), Prosser et al. (1947), and others. The only 

 cellular element in the circulating peripheral blood known to be concerned 

 with this problem is the platelet. 



Platelets are, in general, found to be reduced in the peripheral blood of 

 all the various species of laboratory animals after exposure to dosages in 

 the range that reduces the polymorphonuclear cells. Qualitatively, the 

 megakaryocytes and granulocyte precursors are of approximately equal 

 sensitivity to irradiation injury. According to Lawrence, Dowdy, and 

 Valentine (1948) and Cohn (1952) the platelet values of the peripheral 

 blood of the rat are significantly reduced after whole-body exposure to 



