40 NEUTRON EFFECTS ON ANIMALS 



Neutron doses between 60 n and 120 n are apparently in the critical range 

 since from the higher dose and upward all rats died, while at the 60 n and 

 62.5 n level only three of twelve died. Deaths at this level of irradiation 

 were comparable to those at the higher level in that there was a continuous 

 weight loss until death. However, at the lower irradiation level the leuko- 

 cyte count was increasing instead of being at a minimum. Furthermore, 

 when the animals survived for more than ten daj's, deaths were always 

 preceded by a gradual decrease in the blood hemoglobin levels. These 

 results suggest that the leukopoietic system is regenerating prior to death 

 and that the erythropoietic system has been damaged. Additional data 

 are reciuired before any definite conclusion can be drawn concerning the 

 relation between the changes in the leukopoietic and erythropoietic systems 

 and death by neutron rays. 



That three of six rats died following a 60-n dose and none following one 

 of 62.5 n can be accounted for on the basis of variation in the initial weight 

 of the rats. Those dying after 60 n had an initial average weight of 19-1 g. 

 while the survivors averaged 221 g. This latter value is practically iden- 

 tical with the average initial weight of 220 g. for those rats receiving 62.5 n 

 and the over-all reactions of these nine animals were the same. These 

 data indicate that the lower the body weight, the more sensitive rats are 

 to neutrons. The one rat at the 120-n level that died in 7 days further 

 supports this relationship since its initial weight was 154 g. as compared to 

 220 g. for the other five animals. This general relationship was expected 

 since it is well known from the fields of radiology and toxicology that the 

 sensitivity to foreign stimuli, whether physical or chemical, increases with 

 decreasing body weight . 



At neutron doses below 60 n, the animals showed a slight decrease in 

 weight and also in the total leukocyte counts, both characteristics decreas- 

 ing to a greater extent the higher the neutron dose. Apparently the leuko- 

 poietic system is specifically, but not irreversibly, injured together with 

 general tissue destruction at low levels of neutron doses. 



Neutron Dose of 10 n Repeated Twelve Tmies. In this group, in which 

 six male and five female rats received twelve 10-n doses of neutrons during 

 the first 14 days of the experiments, initial severe leukopenia followed by 

 erythropenia and decrease in the blood hemoglobin levels were observed 

 for all animals. In addition, the vahies for these three characteristics 

 showed a tendency in all animals to return to normal levels. However, 

 the males showed a continuous loss in weight until all animals had died 

 by the end of 60 days \\hile in the females, after a slight initial loss in 

 weight, a fairly normal growth rate was maintained. Furthermore, only 

 three of the five female rats died during the 244-day observation period. 

 From this experiment it would appear as if the males were much more 



