702 T. C. RUCH, WALTER ISAAC, AND ROBERT W. LEARY 



disease-free animals were used in the second series of exp>eriments, this 

 number was not sufficient to establish statistically significant differences in 

 > the weekly means for individual dosage levels for many of the responses 

 tested. Combined data for all groups seems to provide clear evidence for a 

 decrease in food and water intake in the early postirradiation period and a 

 decrease in activity during the 2nd and 3rd weeks. The early decrease in 

 food intake was not expected from the work of other investigators. For 

 example, Eldred and Trowbridge (1954), in referring to dosages in the 

 lethal range, speak of a "symptom-free period following irradiation, in 

 which almost all animals had undiminished appetite." 



These monkeys, unlike several groups which have been used in radiation 

 studies (including that on which the available LD/50 is based), were free of 

 tuberculosis and well nourished. There were no visible signs that would 

 enable an observer to pick out the irradiated animals. In 9 animals at 

 400 r and in all 4 monkeys at 500 r, there were no deaths and no visible 

 pathologic alterations within the experimental period. 



While there is still no published statistically reliable figure for the 

 LD/50/30 for the Macaca mulatta monkey, the early estimate of Eldred 

 and Trowbridge — 600 r — is probably reasonably correct. The 400-500 r 

 level must therefore be considered a just sublethal dosage. 



The observed changes in activity and food and water intake are definite, 

 but are not striking relative to individual variability. The number of red 

 blood cells and the amount of hemoglobin reach their lowest point at about 

 the time that hypoactivity is most pronounced. The reduction in red blood 

 cells by one third is somewhat less than that producing subjective signs in 

 man, but the subjective human and objective simian data do not warrant 

 close comparison, and the rate of onset is a factor. Our data suggest that 

 hematologic changes need to be ruled out as an indirect cause of behavioral 

 alterations before the nervous system is implicated as a primary cause. 

 Whether the blood changes are in the right direction and sufficiently rapid 

 and pronouced to explain the food and water intake data, is doubtful. It is 

 interesting to note that the observed anorexia does not fall in the p>eriod of 

 pronounced gastrointestinal pathologic alteration. This fact suggests that 

 anorexia may result from a primary effect of radiation on the nervous 

 system. 



Summary and Conclusions 



Behavioral and hematologic effects of single dose, whole body irradiation 

 in the sublethal range (300-500 r) were studied. No deaths or visible patho- 

 logic lesions were produced within the experimental period (63 days). 



