PEODUCED BY A CONSTANT CURRENT. 43 



length of the polarising current and that quite independently of the 

 ttion in which the current flows along the nerve. 



N.B. An exception to the above occurs in the case of the diminution 

 and final cessation of the muscular contractions when with an ascend- 

 ing current the nerve is stimulated in the region of the negative pole. 

 For the explanation of this phenomenon see further on. 



How the change of excitability is developed during the first 

 moments after contact is made, and in what manner it declines after 

 interruption of the current, is more difficult to demonstrate than 

 are the persistent changes of excitability of the nerve. The former 

 changes are of a more fugitive nature than the latter, and for 

 their demonstration special experimental arrangements are requisite. 

 The proper aim of my investigation was not to enquire into this, 

 bat its chief object was to examine the persistent changes of 

 excitability which establish themselves while the current is closed. 



My investigations have, however, yielded results relating to the 

 duration of the change which confirm those previously arrived at on 

 this subject. Thus in general the following statements hold good 

 as well for mechanical as for other kinds of stimulation processes, 

 when the nerve is traversed by a constant current. 



At the negative pole the change of excitability on closure appears 

 immediately in its full strength. 



At the positive pole the change of excitability on closure attains 

 its maximum only by degrees. ' 



At the negative pole, after interruption of the current, supposing the 

 current not too weak, there is exhibited at first a diminution of excit- 

 ability, which is afterwards followed by an increase. 



At the positive pole, on opening, a rise of excitability occurs 

 directly. 



Here it should be observed that both the increase of excitability 

 occurring at the negative pole after the current is opened, and the 

 diminution of excitability perceptible there at the very first, are 

 not nearly so sharply marked with mechanical stimulation as with 

 electrical, and often cannot be made out at all. 



The following statements hold good for the changes of excitability 

 when the current is in action for several seconds. 



At the negative pole in many cases the muscular contractions decline 

 after having first reached a maximum. This decrease is for the 

 part exceedingly slight, and proceeds very slowly. 



