NEUTRON EFFECTS ON ANIMALS 157 



neutrophils occurred on the 7th, 4th and 3rd days respectively. The 

 length of time after irradiation required for the lowest number of leukocytes 

 and neutrophils to be reached was found to be inversely proportional to the 

 size of the dose. 



The lowest white blood cell count for each dose, expressed as percentage 

 of pre-irradiation count, is shown in Fig. 2. The rate of the depression 

 decreased as the dose was increased. 



Inflvence of Neutrons on the Blood Sedimentation Rate. Ten male rats 

 weighing about 300 grams each were divided into two groups of five. 

 Prior to irradiation the blood sedimentation rate of each animal was deter- 

 mined by the Landau-Adams microsedimentation method (15). Blood 

 was obtained from the tail. The rats of one group were given 56.4 n in 

 Box No. 7 and the other group served as a control. The blood sedimen- 

 tation rates of the animals of both groups were determined at five intervals 

 during the succeeding four weeks. 



An increase in the blood sedimentation rate of the irradiated rats was 

 found one day aftei completion of irradiation. Thereafter theie was a 

 gradual increase until the eighth day, when the blood sedimentation rate 

 of the irradiated animals had increased 100 per cent over the pre-irradiation 

 rate and was 29 per cent greater than that of the non-irradiated controls 

 at that time. After the eighth day the rate decreased gradually imtil at 

 the end of four weeks the noimal pre-irradiation ^'alue was reached. The 

 observations weie then discontinued. 



DISCUSSION 



The changes in numbers and kind of white blood cells after neutron 

 irradiation are similar to the reported blood changes after X-radiation. 

 This similarity is particularly emphasized in the sensitivity of the l^mipho- 

 cyte. There is an almost immediate and a profound response: a reduction 

 in numbers of lymphocytes in the peripheral blood stream and an immedi- 

 ate cessation of cellular mitotic activity in lymphoidal organs. The re- 

 versal of the lymphocj^te-neutrophil ratio illustrates the greater radio- 

 sensitivity of lymphocj^tes over that of neutrophils to penetrating radiation. 

 Considering the degree of lymphopenia produced, the recovery of the 

 lymphocyte is extremely rapid. While neutrophils were also affected, 

 the counts never decreased in the same proportion as the lymphocytes. 

 Neutrophils seem to be more resistant to radiation than lymphocytes. 

 This serves to illustrate which cells of the blood aie more responsive to 

 irradiation. In both X-ray and neutron irradiation there were considerable 

 numbei's of degenerated neutrophils. 



It is difficult to interpret the changes in the blood count after irradiation 

 as a direct or an indirect effect. Not all of the changes are necessarily 



