v.'J THE FOUR AFTER-CURRENTS 91 



indeed did they add to or extend it. Indirectly, however, by 

 the effect produced in the mind of his pupil Biedermann, 

 Hering has " authorised " a very considerable extension of 

 fact and still more of doctrine. Biedermann finds evidence 

 of the existence not only of a positive anodic, but also of a 

 negative kathodic after-current, and further of the counterpart 

 of this first pair, viz., a negative anodic and a positive kathodic. 

 The last pair of currents are, however, asked for by theory 

 rather than offered by simple observation ; Biedermann him- 

 self admits that of his four currents the positive kathodic is 

 very doubtful, and it is clear that the negative anodic, being 

 in the direction of ordinary polarisation, is also on a doubtful 

 footing of fact. Nevertheless he considers theoretically the first 

 pair as being of irritative origin, and the second pair as being 

 of inhibitory origin. His quadrille of after-currents may be 

 put together in the following schema : 



Exciting or primary 

 Anode 4- - Current:. 



> _ 



Irritative or (positive anodic > "the most certain" 



dissimilatory. {negative kathodic < [PpoU3.n3d.Cion] 



Inhibitory or WafrVe anodic < [PpoiarisaCion] 



assimilatory. \oositive kathodic > the most uncertain 



58. A demonstration. I should be sorry to attempt to 

 demonstrate to you the existence of these four currents upon 

 muscle or upon nerve, which are the tissues upon which Bieder- 

 mann claims to have observed them ; you must refer to Bieder- 

 mann's own account for what in his opinion constitutes the 

 evidence of their existence. 



At most, I shall be able to show you the first and " most 

 certain " of them, viz., the positive anodic or post-anodic action- 

 current, and that only in a form that does not exclude a partici- 

 pation in the total effect of a positive kathodic factor. And I 

 will show the experiment in a form intended to associate in 

 your mind this post-anodic action-current with an irritative 

 phenomenon long known to physiologists under the name of 

 Ritter's tetanus. 



