BRINK AND OTHERS: CHEMICAL EXCITATION OF NERVE 479 



as a function of the number of the impulse in the sequence. Obviously, 

 the intervals are grouped about certain values, which are 6, 12, and 18 

 milliseconds. These same data are presented in the form of a dis- 

 tribution plot in FIGURE 20, where the number of intervals in a certain 

 range is plotted against the length of the interval. Since the ordinate 

 is a measure of the probability of occurrence of the interval indicated 



52- 



"I- 

 30 

 29 

 ;6 

 27 

 26 

 29 

 24 

 23 

 22 

 21 

 n 20 



a 



- 19 



S '■' 



f 12 



• • ••• •. 



• • • • 



■■■■''■''■' ■ ' ' ' ■ 



30 40 50 



NUMBER OF IMPULSE IN TRAIN 



I I I I I I I 1 I I I I I I I 



Figure 19. The intPirals bptv.een impulses ipiorded from a chemirallv exritp<I .=infr'e filipr 

 (fiog) .Tre aplHoxiiiKitelv intpfrial in I't.p'ps <if ;i !r;ist intni\nl. In lliis filipr, the least interval 

 was about 6 milliseconds. Stimulation by localized rcmoxal of calcium fiom the axon. 



on the axis of abscissae, it is obvious that all intervals are not equally 

 probable. The most probable values are 6, 12, and 18 milliseconds. 

 In all the frog fibers thus far examined, the most probable values of 

 the least interval are in the range of 3-6 milliseconds. 



The aliquot relations between these most probable values for Ihc 

 fiber just cited suggest, again, that the longer intervals are due to the 

 omission of one or more impulses from an otherwise continuous series. 

 Such omissions could be due to failure of the impulses to be initiated in 

 the chemically excited region, or to blocked conduction between that 

 region and the recording electrodes. If the nerve is stimulated at 

 high frequency by repeated electric shocks, the impulses travel over 

 the nerve fiber and through the treated region. Consequently, there 

 is no reason why each impulse initiated by chemical excitation should 

 not, likewise, be conducted to the recording electrodes. We conclude, 



