EFFECTS ON BIOELECTRIC ACTIVITY OF NERVES 



587 



•^ 



10 20 30 40 



MINU TES OF X- IRRA D/A TON 



50 



Fig. 11. Relative activity of giant nerve fibers of earthworm, plotted as a function 

 of time of x-irradiation. Mean values of median fibers and of lateral fibers are 

 combined. 



The modification of the basic pattern in Fig. 7 is shown in Figs. 12 to 15. 

 Figure 12 shows the increased sensitivity to external stimulation which pre- 

 ceded the precipitous drop in sensitivity as UV irradiation continued. The 

 average threshold voltage of the stimulus at the beginning of irradiation 

 was 0.24 v for the median fibers and 0.72 v for the lateral fibers. Figure 13 

 shows the relative increase in conduction velocity; the enhancement was 

 slight and was not observed in 26% of the cases. Figure 14 shows the 

 relative increase in spike amplitude; increases were observed in all cases. 

 Absolute values for the amplitude of action potentials at zero time were 

 1.43 mv for the median fibers and 2.29 mv for the lateral fibers. The rela- 



