280 C. T. GAFFEY 



ity after exposure to some specified dose of irradiation. For this purpose the 

 following method was adopted. After obtaining oscillograms of the preirradi- 

 ated neural activity of both isolated sciatic nerves of a frog, one nerve of the 

 pair was bombarded in the cyclotron's beam while contained in a plastic 

 vial filled with Ringer's solution. Following irradiation, the neural activities 

 of the exposed and control nerve were again monitored after transferral to 

 a moist chamber (Fig. 1). This routine was repeated at 2 hour intervals for 

 a minimum of 24 hours. Control nerves maintained in Ringer-filled vials 

 were treated in an identical manner. 



In Fig. 2 are shown three rows of oscillograms of the action potentials of 

 the right (upper photographs) and left (lower photographs) sciatic nerves 

 of a frog. Preirradiation action potentials were recorded, and the right sciatic 

 nerve was subjected to 72 krad of 910 Mev alpha particles. The left sciatic 

 nerve functioned as a control. Immediately after alpha particle irradiation 

 (oscillograms above "0 hr" in Fig 2), a transformation in the action poten- 

 tial complex of the exposed nerve was apparent. Oscillograms recorded at 2, 

 4, 6, 8, 10, and 12 hours after irradiation trace the deleterious effects caused 

 by alpha particles. At 14 hours postirradiation, there was complete cessation 

 of the bioelectric activity of the alpha-bombarded nerve, while the action 

 potential of the control nerve was still present. 



The spike potential changes for the irradiated and control nerve illustrated 

 in Fig. 2 are summarized in Fig. 3. On the ordinate of Fig. 3 (and also on 

 the ordinates of Figs. 4, 5, and 6) is plotted the percentage of the initial spike 

 potential, i.e., the ratio of the amplitude of the spike potential at some t-hours 

 after irradiation over the preirradiated spike potential amplitude multiplied 

 by 100. 



In Fig. 4 is presented a sample of the data obtained for alterations in the 

 neural activity resulting from alpha particle irradiation. It is clear that larger 

 doses of alpha particles (greater than 300 krad) eliminate neural excitability 

 rapidly. With lower doses of 910 Mev alpha particle irradiation, the survival 

 of neural activity is progressively extended. It would appear from Fig. 4 that 

 at 6 hours postirradiation there is considerable enhancement of the neural 

 output. That all this enhancement is a direct consequence of irradiation 

 seems doubtful, because when the irradiated nerve of a pair demonstrated 

 an enhanced neural output, so did its nonirradiated control (Fig. 5). How- 

 ever, bombarded nerves with enhanced activity were usually 5 to 10% higher 

 in their neural output than their controls. The nonirradiated nerves mani- 

 fested the enhancement phenomena most strongly during the winter season. 



The time course for the abolition of neural activity was also studied as a 

 function of deuteron dose. A sample of the findings for the degeneration of 

 the spike potential due to different doses of deuterons is presented in Fig. 6. 

 Deuteron experiments, which were carried out in the spring and summer 

 seasons, showed only a small enhancement of neural output. 



