AFTER ELECTRICAL STIMULATION. 261 



stimulation. This is the third and by far the best method of in- 

 vestigating the positive after- variation. In this case an aperiodic 

 magnet is unnecessary. 



With investigations carried out in this manner, the correctness of 

 the above supposition was shown, in so far that I got appreciably 

 stronger positive deflections than when the galvanometer-circuit 

 was closed during stimulation. In this investigation I used the 

 same double switch which I used for the researches on polarisation 

 described in my twelfth contribution. 



In one position of the switch the stimulating circuit (in this case 

 generally the circuit of the secondary coil) is broken in two places, 

 while the galvanometer-circuit is closed ; in the other position the 

 galvanometer-circuit is broken in two places, while the stimulat- 

 ing circuit is closed. From this last position the switch is re- 

 versed in such a way that the time of its passage, i. e. the interval 

 between the opening of the stimulating circuit (end of stimulation) 

 and the closing of the galvanometer-circuit was always the same. 

 In our experiments it amounted to between 0-026 and 0-034 of a 

 second l . 



With this method of investigation a determination of the amount 

 of negative variation is not obtained. For this purpose two ob- 

 servers and two galvanometers, each with a special compensator, 

 would be necessary. The electrodes conducting the nerve current 

 would have to be arranged by means of a switch so as to permit of 

 their being connected now with the one, now with the other galvano- 

 meter. In both galvanometers the nerve current would have to be 

 compensated. On one the negative variation would have to be ob- 

 served, and at the end of stimulation the electrodes would have to be 

 quickly connected with the other galvanometer, on which the positive 

 variation would have to be read. At the same time the above- 

 mentioned drawback is to some extent remedied, if observations are 

 made with the same nerve and with equal strength and duration 

 of stimulation alternately according to the third and second methods. 

 If it is desired to make an observation according to the second method 

 after one has been made according to the third, it is only necessary, 



1 It is not to be understood that the transmission time varied between these 

 limits ; I can even venture to say that it was always tolerably nearly the same. 

 The method which I adopted to determine the time in question does not permit of 

 direct measurement of that time, but gives on the one hand a duration which the 

 transmission time cannot possibly exceed, on the other hand a duration of which it 

 cannot possibly fall short. Whether the true transmission time approaches more 

 nearly to the one or the other cannot be decided by this method. 



