260 ON POSITIVE VARIATION OF THE NERVE CURRENT 



The Roman numerals in this and in the following table refer to 

 the order of the individual stimulations. The number with a minus 

 sign gives the diminution of the nerve current during stimulation, 

 that with a plus sign gives the amount of transitory increase of the 

 nerve current at the close of stimulation. The duration of stimula- 

 tion is given in seconds in each case. 



Current of electrodes +40. Nerve current +154. 

 I. 5 sees. ; 1 !; III. 10 sees. ; l 



II. 5 secs.{~ T 4 IV. 20 sees. | ~ l6 



V 20 sees |~ l6 

 -I- 6-5 



8-5 



Cold frog. Stimulation with rotation apparatus. Galvanometer tract 8 mm. 

 Intermediate tract 38 mm. 



Current of electrodes + 7. Nerve current -f- 195. 

 I. Duration of stimulus 15 sees. J ~~ 41 



II. -sec,{;38. 6 



The increase of nerve current after close of stimulation is a transi- 

 tory one. I often noticed that the magnet, when negatively de- 

 flected during the stimulation of the nerve, suddenly moved in an 

 opposite direction at the moment the stimulation ceased, this 

 movement being out of relation with the final amount of the 

 deflection : thus it seemed probable that the positive increase of the 

 nerve current is greater immediately after stimulation than it ap- 

 pears to be from the weak positive deflection which the magnet 

 eventually shows, that is, that before the dilatory magnet as it 

 slowly returns to zero has reached that point, an appreciable amount 

 of the positive increase of nerve current may already have been 

 spent, so that only the remainder conducts the magnet through its 

 position of equilibrium to a position of positive deflection. From 

 this may be explained the fact that occasionally, and especially with 

 feebly excitable or fatigued nerves, the positive deflection is quite 

 lost when this method of observation is adopted. 



3. Hence it is desirable, after accurate compensation of the nerve 

 current, to open the galvanometer-circuit 'during stimulation and 

 only to close it again immediately after ceasing to stimulate. This 

 plan has another advantage, viz. that a portion of the compensation 

 current corresponding in amount to the negative variation is pre- 

 vented from passing through the nerve during the period of 



