590 



C. S. BACHOFER 



1.4 



-i 1.3 



0.9 



0.8 



-o Median Fibers 

 -• Lotero/ Fibers 



Beginning of 

 UV Irradiation 



20 



40 



60 



80 



100 



MINUTES 



Fig. 14. Relative spike amplitude of impulses of giant nerve fibers under UV irradi- 

 ation, plotted as a function of time of irradiation, as in Fig. 12. 



impairment of activity, leading to ultimate block. The lowest curve depicts 

 the effect on refractory period of UV irradiation at a relatively high dose 

 rate and is contrasted with the center curve, which represents a lower dose 

 rate. The enhancement of activity at the lower dose rate was considerably 

 greater than that observed at the higher dose rate. At even higher dose rates, 

 the results of which are not shown, the enhancement was proportionately 

 less. It was possible to increase the dose rate to the point where no enhance- 

 ment of activity was observed, only a decrease in activity. This observation 

 suggested a second type of experiment, the results of which are shown in 



