NEUTRON EFFECTS ON ANIMALS 27 



Lawrence and Tennant (5), using Swiss mice, G to 8 weeks old, found the 

 following relationship between neutron dose and mortality: 



They conclude on the basis of gross pathology that the mucosa of the small 

 intesfne and the lymphoid and hematopoietic systems were the most 

 sensitive to irradiation and that the mechanism of death for both X-rays 

 and neutrons is a combination of tissue destruction and enterogenous in- 

 fection. The former effect predominated in acute deaths following large 

 doses. 



Yamashita (0) studied the effects of neutrons on young rats weighing 

 from 14 to 30 grams. Afte* 30.8 r, the body weight decreased continu- 

 ously until death on the 11th to 17th day. Following 26 r, the body 

 weight remained stationary for two weeks while after 12 r there was an 

 increase after one week, but the growth rate was still very poor after four 

 weeks. The leukocytes decreased as also did the proportion of lympho- 

 cytes even at 12 r and remained low for 17 days. Yamashita also reports 

 that the red blood cells and blood hemoglobin gradually decreased and that 

 in some eases nucleated red blood cells appeared in the peripheral blood. 



Since only a small amount of data is available in the literature on whole- 

 body irradiation with neutrons involving a wide variety of conditions, 

 no definite conclusions may, at present, be made concerning the relation- 

 ship between dose and effect. In general, however, decreased body weight, 

 leukopenia, and possibly erythropenia are associated with irradiation with 

 relatively heavy doses of neutrons. In the work of Lawrence and Law- 

 rence (4) and Lawrence and Tennant (5), the neutron beam contained 

 some gamma rays, the effects of which were considered by these authors 

 as insignificant in comparison with those of neutrons. Only in the results 

 of Yamashita (6) can the effects be attributed to neutrons alone since he 

 used a deuteron-deuteron reaction for the production of the neutrons in 

 which no gamma radiation is formed. 



In the expei'iments to be reported, proper shielding eliminated gamma 

 rays (Enns ci al, 7) so that the radiation affecting the rats was composed 



