38 NEUTRON EFFECTS ON ANIMALS 



degenerative changes in the testes were the only significant gross findings 

 observed at autopsy. None of these rats showed any gross indications of 

 tumors during the period of observation. 



Microscopic Pathology 



Females — 251 doses of 1.8 n: The spleen showed varying degrees of 

 atrophy with inactivity of the germinal centers. Numerous neutrophils 

 and foci of hematopoiesis were also present. The thymus showed atrophy 

 with occasional edematous areas. 



Females — 172 doses of 1.8 n: The spleen and thymus showed various 

 degrees of atrophy while the ovaries were frequently congested, although 

 germinal follicles were present and oogenesis was going on. 



Males — 172 doses of 1.8 n: The spleen showed numerous foci of hemato- 

 poiesis and a few neutrophils and the germinal follicles were somewhat 

 smaller than normal. The thymus in one rat showed slight atrophy of the 

 germinal centers. All testes were markedly atrophied with little or no 

 indications of spermatogenesis. 



Under these conditions of irradiation, only moderate changes were pro- 

 duced outside of the action responsible for the initiation of malignant 

 growths. 



DISCUSSION 



Before considering the detailed discussion and interpretation of the 

 experimental data reported, the purposes and limitations of these data 

 must be realized. The data, though incomplete, are presented at this time 

 to serve as a guide to other workers in this field and as a basis for future 

 detailed studies concerning the mechanism of action of neutron rays on 

 organisms and biological systems. The scope of the data is definitely 

 limited for the following reasons: 



1. The data are based on a relatively small number of rats of a single 

 strain. Whether or not comparable information would be obtained for 

 other strains of rats as well as for other mammalian species remains to be 

 investigated. 



2. Only a small number of neutron doses has been studied, but, never- 

 theless, these cover what may be considered as heavy, "acute", lethal doses 

 (120 to 240 n) and light, "chronic'", doses (1.8 n daily) as well as some 

 intermediate values (17 to (iO n in a single day). Therefore, the data give 

 an over-all picture of the results that may be expected from whole-body 

 irradiation of white rats. 



3. Animal studies were limited in this preliminar}- survey to general 

 hematology, body weight and gross pathology. 



In the subsequent discussion, the above limitations must be kept in mind 

 together with the fact that final interpretation or explanation of many 



