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



the eflfect of radiation on motivation rather than on capacity. This distinc- 

 tion is particularly obvious when food is the motivation. 



Many military and civil problems relating to performance under stress 

 depend upon wrhat men do vs^hen subjected to long-continued low level stress 

 while engaged in critical, but relatively undemanding, tasks. In both war and 

 peace, man performs for brief periods of excitement and intense demand 

 interspersed with long stretches of monotony and low level demand. We 

 believe that there is a wide gap between what men can do and what men 

 will do; the latter may be more sensitive to stress and may be as important 

 to study as what man can do. 



In choosing low levels of radiation and lightly motivated behavior, we 

 expected to encounter and did encounter difficulty from individual variation. 

 A weak effect is obviously harder to establish than a strong effect. In the 

 first series, the radiation levels were even lower than we had intended. This 

 occurred because the available studies designed to determine the lethality 

 curve for the macaque monkey included tubercular monkeys and gave an 

 LD/50/30, which was too low. Our monkeys, free of tuberculosis and well 

 nourished, were considerably more resistant than the normative data led us 

 to predict. 



Method 



Tests used in the first series of experiments were described previously 

 (Leary, 1955; Leary and Ruch, 1955). The psychologic and physiologic 

 functions studied were: (1) lightly motivated performance tests, such as the 

 puzzle manipulation of Harlow et al. (1950) and the plastic pedometer 

 sandwich devised by Leary and Ruch (1955); (2) routine cage activity, 

 spontaneous activity, and food and water intake; and (3) hematologic 

 values. 



Sixteen immature male Macaca mulatta were divided into 4 groups of 

 4 each. In each group, 3 monkeys received radiation doses of 300, 400, and 

 500 r, respectively; a control monkey was not irradiated but was subjected to 

 all other experimental procedures, including rotation before x-ray machine. 

 The monkeys were tuberculin tested before and after a 30 day isolation 

 period, and, by these tests and by general observation, they appeared to be 

 in good health when the experiment began. No illness attributable to inter- 

 current infection occurred during the experimental period, and, excepting 

 one monkey which died of generalized septicemia during the 11th postir- 

 radiation week, the animals remained in good health for months after the 

 close of the experiment. 



The monkeys lived and were tested in expanded metal cages, 18 X 24 X 

 22 in., with double screen bottoms. A false floor of large mesh was inserted 



