694 



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



Fig. 1. The coeflScients of correlation (N =: 19) on the diagonal measure the 

 reliability (odd versus even minutes). The top row of coefficients can be construed as 

 measures of validity, if the ratings by humans are taken as the validating measure. The 

 electric eye method yields a reliability coefficient of .948 for odd versus even days 

 over a 44 day period. 



index of the monkey's interest in manipulating the objects of his environ- 

 ment. 



Irradiation 



For exposure to radiation, a monkey was placed in a Plexiglas cylinder 

 whose walls were J4 i^- thick and were perforated at about 3 in. intervals 

 by J4 in. ventilation holes. The tube was 16 in. long, and, depending on 

 the size of the animal, was 6 or 8 in. in diameter. The bottom of the cylinder 

 was fixed, but the top could be adjusted to accommodate monkeys of 

 different sizes. The size of the cylinder greatly restricted the monkey's 

 movements, as did the darkening of the room during irradiation. 



The tube was suspended by strings from a metal shaft that was rotated at 

 1 rpm by a synchronous motor. To reduce "back scatter," the metal shaft 

 was made narrow and was never closer than 8 in. to the monkey. Air 

 dosage was calibrated with a Victoreen meter before and at the end of each 

 day's run. The Victoreen meter had been recently calibrated and, on several 

 days, was checked against a second meter. At the point corresponding to the 

 center of the animal's body, the rate of irradiation varied between 8.7 and 

 8.9 r per minute. (For the source distance of 4 ft. used in these experiments, 

 a 5% fall-off at the upper and lower extremes of the body is expected.) 



The x-rays were generated by a Picker pulsating therapy generator using 

 a Machlett FCX tube with a tungsten target. A constant kilovoltage of 200 

 was used at a constant current of 20 ma. The efifective filtration was about 

 0.50 mm Gu and 2.0 mm Al. 



Analysis of the Data 



In an attempt to counter individual variability, the weekly postirradiation 

 scores of each animal were subtracted from its preirradiation score. The 



