NEUTRON EFFECTS ON ANIMALS 43 



a long period of time. If such a similarity in action could be demonstrated, 

 it would make available another method for the induction and study of 

 such tumors in experimental animals. 



SUMMARY 



1. Neutron doses of 180 n and above caused death in from 6 to 8 days 

 accompanied by extreme loss in weight indicative of tissue destruction 

 and also a maximum leukopenia. 



2. The median lethal dose for deaths occurring within two weeks lies 

 between the 60-n and 120-n levels. In this range, death was associated 

 with a severe weight loss but with recovery from the extreme leukopenia 

 as indicated by increasing leukocyte counts prior to death. In addition, 

 erythropenia was present for the week prior to death. 



3. Neutron doses from 17.5 n to -17.5 n caused some leukopenia and 

 weight loss followed by complete recovery. At this level of irradiation, 

 the rats did not appear to be seriously ill at any time during the month's 

 period of observation. 



4. A reduced rate of growth and the formation of tumors but without 

 changes in the hematological picture of the peripheral blood was found 

 following neutron doses of 1.8 n given six days a week for seven and nine 

 months, respectively. 



5. Of 28 rats surviving for more than 150 days after repeated doses of 

 neutrons, 11 showed malignant tumors, which were classified as follows: 

 mammary adenocarcinoma 6, mammary carcino-sarcoma 1, nephroma 1, 

 reticulum cell sarcoma 1, unidentified 2. 



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