554 



WERNER K. NOELL 



effect of this dose was measured by determining the dose of a 2nd irradiation 

 sufficient to produce the sudden ERG decline. This 2nd irradiation was 

 applied continuously and the dose delivered at the time the ERG decline 

 started or reached a certain magnitude was used as a measure of its effec- 

 tiveness. Dose rate was the same for both irradiations. When the 2nd dose 

 followed the first without interruption, 2,150 rads were needed to start the 

 decline. After complete recovery from the latent eflfect of the 1st dose, 

 6,300 rads were required. 



2000 



01/2 2 



control 



HOURS 

 INTERVAL BETWEEN IRRADIATIONS 



Fig. 11. Recovery from the latent effect of irradiation. For explanation see text. 



The results are plotted in Fig. 11, each value representing the average of 

 3-5 animals. Although recovery started immediately and reached a signifi- 

 cant level 30 minutes after irradiation, the effectiveness of the test irradiation 

 was still increased (in a statistically significant manner) after 24 hours, and 

 even after 3 days it differed from that in the control experiment. 



Fractionation of Dose 



Various types of dose fractionation were tested in our studies in order to 

 gain information which might be applicable to problems of clinical radiology. 

 A medium retinal dose of 460 rads of 250 kvp radiation was applied for 

 1 minute 5 times a week. Three animals were carried through 23 exposures. 



After these exposures and a total medium retinal dose of more than 



