EFFECTS ON BIOELECTRIC ACTIVITY OF NERVES 595 



increase in activity initially, a period of enhanced activity, a fall in activity, 

 and, ultimately, cessation of activity. The degree of enhancement observed 

 was not the same for all activities, nor did the time of maximum enhance- 

 ment coincide for all activities. Spike amplitude, for example, consistently 

 showed great enhancement, whereas conduction \elocity inconsistently 

 showed slight enhancement. 



Enhancement of activity, attributable to bombardment with x-rays or with 

 UV, rarely observed in biologic investigations of this sort, was followed by 

 deterioration of activity and eventual blocking of activity, representative 

 of the lethal action of irradiation commonly observed. The time at which 

 maximum activity of one factor occurred did not coincide with the time 

 at which the maxima of other activities occurred ; spike amplitude, for exam- 

 ple, was observed to increase, while conduction velocity had already reached 

 its maximum and was rapidly declining. 



The energy supplied by bombardment with x-rays or with UV did not 

 act synergistically during the enhanced response; that is, concomitant irradi- 

 ation was not necessary to produce the enhanced response, once the nerve 

 had been altered by irradiation. Once the nerve was responding in an en- 

 hanced manner, cessation of irradiation for short periods had no effect on 

 the response. In certain types of experiments, the response would continue 

 to rise if it was in the rising phase when irradiation was stopped, and con- 

 tinue to fall if it was in the falling phase. The rise or fall proceeded at 

 slower rates when irradiation was stopped. 



Stimulation at higher frecjuencies considerably reduced the enhancement 

 of spike amplitude attributable to x-rays, showed a somewhat lesser effect 

 on enhancement of sensitivity, and showed no effect on enhancement of 

 conduction velocity. Nerves under both stimulation and irradiation failed 

 to respond as long as nei'ves under irradiation alone. Stimulation apparently 

 imposed an additional stress on the nerves. 



The magnitude of enhancement of activity was dependent on dose rate. 

 At low dose rates the enhancement was greater than at high dose rates. It 

 was possible to increase the dose rate to the point that no enhancement was 

 observed. 



Acknowledgments 



With the collaboration of Sister Miriam Eugene Gautereaux of Holy 

 Names College, Spokane, Washington. These investigations were supported 

 by a research grant between the U. S. Atomic Energy Commission and the 

 University of Notre Dame. 



