EFFECTS OX BIOELECTRIC ACTIVITY OF NERVES 577 



stimulus utilized. Studies on refractory period were not conducted for 

 compound nerve trunks. 



Results 



X-irradiation of rat caudal nerves in vitro. Irradiation was begun after a 

 period of stabilization during which the output of the nerve was shown to 

 be constant for a period of time exceeding that of the period of irradiation. 

 Most of this period of stabilization is not shown in the accompanying figures, 

 since the nerves were sufficiently stable after the initial adjustment on the 

 platinum electrodes to make the curves appear as straight lines at the 

 value of 1.0, with little deviation for well over an hour. The values on the 

 ordinates, designated A/Aq, represent the ratio of the activity, A, at a given 

 time, to the activity, Aq, at zero time. The activity at zero time, which con- 

 stituted the point of reference in all figures, unless otherwise noted, was the 

 activity at the beginning of irradiation. The abscissas are given in minutes, 

 from which the dose can be calculated from the dose rate. The plotted 

 values were calculated by determining the average time at which the re- 

 sponses reached their maximum value as well as various fractions of the 

 maximum value. The abscissas, therefore, represent mean time values for 

 various definite relative activities, which are plotted on the ordinate. 



An immediate eflfect of x-irradiation on electrophysiologic responses is evi- 

 dent in Fig. 2. An enhancement of activity, attributable to x-irradiation, 

 precedes the suppression of activity. The curves show three degrees of en- 

 hancement of activity, spike amplitude showing the greatest, and conduction 

 velocity the least. Not only were there different degrees of enhancement for 

 the \arious factors considered, but the peak of enhancement manifested itself 

 at different times for the various factors. During most of the period of 

 increasing spike amplitude, conduction velocity decreased, while sensitivity 

 occupied a mid-position. The values shown in Fig. 2 are based on nerves 

 which were essentially unstimulated, since they were stimulated only once 

 each time a recording was made. Figures 3 and 4 show the effect of stim- 

 ulation at 50 per sec and 100 per sec on the response to x-rays. Square- 

 wave pulses of 10"'^ sec duration and of amplitude just sufficient to elicit a 

 maximal response were administered to the nerve after the usual initial 

 period of stabilization. The activity of the nerves dropped under such 

 repeated stimuli. The nerves were therefore stimulated for 20 minutes before 

 irradiation in order to move into a period of relatively stable activity. The 

 initial drop in activity shown in Figs. 3 and 4 represents the fall in acti\ity 

 due to stimulation. After 20 minutes of stimulation, the nerve was irradiated, 

 with stimulation and irradiation continuing until the nerves failed to re- 

 spond. A comparison of the effects of x-irradiation on nerves without stimu- 



