■ Groups identified with capital letters are 400-day-old rats; groups identified with lower case letters; 

 90-day-old rats. 



Radiation and Breeding Procedures 



The x-ray facilities consisted of a standard x-ray with parallel tubes run 

 at 180 kvp, 30 ma; filtration was 0.28 mm Cu and 0.50 mm Al. Both 

 upper and lower tubes were used with a half value layer of 0.6 Cu, 67 cm 

 target distance at 50 r per min for 200 r, 150 r, 100 r, and 50 r. For rats 

 receiving 25 r, only the upper tube was used with 69 cm target distance at 

 25 r per min. For subjects exposed to 10 r, only the upper tube was used, 

 with filtration of 0.5 mm Cu, 0.5 mm Al, half value layer of 0.8 mm Cu, 

 91 cm target distance at 10 r per min. 



To determine the gestation period, females were placed with males at 

 5 PM and examined the next morning at 9 am for presence of vaginal plugs. 

 Those found with such signs of successful copulation were recorded as 

 pregnant and in the 0.5 day of gestation. All irradiation for successive days 

 based day of exposure in utero on this method of calculation. 



Experiment One 



Because cortical ablation studies have shown the Lashley III maze 

 (Lashley, 1929) to differentiate between learning ability of animals with cor- 



