266 



ON POSITIVE VARIATION OF THE NERVE CURRENT 



IV. Duration of stimulation 30 sec. + 4 



V. 20 +3 



VI. 10 +2-5 



VII. 5 + 2 



VIII. 30 +3-5 



IX. 30 +3 



The circumstance that it is sufficient to tetanise the nerve for 

 a fraction of a second in order to obtain positive after-variation, 

 suggested that even a single momentary excitation might be suffi- 

 cient to produce this result to a slight extent. My attempts to 

 demonstrate this by means of the repeating method failed from 

 causes which we shall have to discuss in a further communication 

 on the negative variation. 



As negative variation increases with the strength of the stimu- 

 lating current, so likewise does positive variation, but only up to a 

 certain limit. In this case again more accurate data can only be 

 arrived at from a very large number of researches. Naturally the 

 decrease in consequence of repeated stimulation is very evident 

 in this case, where we are dealing with increasingly stronger 

 stimulations. 



In the following series of experiments the lapse of time between 

 two successive stimulations was about 3 minutes. 



Cold frog. Du Bois induction coil. Galvanometer tract 9 mm. Intermediate 

 tract 34 mm. With switch. Duration of stimulation 10 sees, in each case. 

 Current of electrodes +30. Nerve current + 133. 



II. 



III. 



IV. 



V. 



VI. 



VII. 



VIII. 



IX. 



X. 



XI. 

 XII. 



without switch 



20 



+ 5 



Cold frog. Stimulation as in foregoing. Galvanometer tract 9 mm. Inter- 

 mediate tract 27 mm. Duration of stimulation 10 sees. With switch. 

 Current of electrodes + 30. Nerve current +151. 



I. Distance apart of coils 50 cm. +o 

 II. 40 +3.5 



III. 30 +5-5 



IV. ao + 7 



V, 20 1 . without switch 



