482 



WALTER R. STAHL 



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100 r 



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Fig. 2. Effects of 200 r antenatal irradiation (18th day) on the conditional reflex 

 stereotype of white rats. Top series are controls: bottom, irradiated; (1), sound (400 

 cycles per sec) as a strong positive stimulus; (2), light from small bulb as a weak 

 stimulus; (3), sound (800 cycles per sec) as differentiation stimulus. The equalization 

 of reactions to stimuli of various strengths and inhibitory after-effect are noted. Re- 

 drawn from Piontkovsky et al. (1959). 



works referred to by Hicks, Rugh, and others at this symposium. Piontkov- 

 sky and his associates found that CRs in animals antenatally exposed to 

 50-200 r showed certain characteristic forms of injury (Fig. 2). 



Figure 3 provides data on a typical stereotype in control and irradiated 

 rats. The experimental animal had an equalization of reaction to strong 

 and weak stimuli, showed a marked inhibitory after-effect, and displayed 

 considerably greater than normal spontaneous motor activity and erratic 

 CR learning performance. They often gave a correct response sooner than 



