ADDENDUM. 543 



in a very recent paper which purports to be a theoretical and 

 experimental criticism of Fleischl's work *. A polarised nerve, 

 he says, is not comparable to a voltameter, because in nerve, 

 the polarised surface is not in the unbranched circuit but in a 

 collateral branch (Zweigkreise), and that consequently the case of 

 the nerve is not strictly represented by substituting- for it the 

 Wollaston's points at w in the diagram, unless at the same time 

 a permanent derivation is introduced as under, in which r 



represents a second bridge which in the experiment remains 

 closed when k k' is opened, and of which the resistance though 

 considerable in itself, is small as compared either with that of 

 w or with that of the unbranched part of the circuit. The reason 

 why a current in passing along a nerve is divided into two 

 channels is to be found, according to Hermann, in the fact that 

 every nerve fibre consists of an axial core and of an envelope of 

 different material, and that, whereas the latter conducts without 

 polarisation, whatever proportion of the current enters the core 

 from the envelope and then leaves the core to reenter the envelope, 

 produces polarisation as it passes from the one to the other and 

 vice versa. The grounds on which Professor Hermann regards a 

 nerve, so long as it is alive, as a conductor of this kind are so well 

 known that it is scarcely needful to refer to them here. It will be 

 sufficient to remind the reader that the electrotonic currents of 

 nerve are reproduced or imitated in a model (Draktmodell or 

 Kernleiter) which, in accordance with the principle above referred 

 to, consists of a core of \vire sheathed in a moist envelope. When 

 in Fleischl's experiment a model of this kind is substituted for 

 the nerve at n (in the first diagram) it is found to behave exactly 

 as a living nerve does. The introduction of the polarised model 

 into the circuit is without influence as regards the reading of the 

 electrometer, i. e. as regards the electromotive force indicated by 

 it. The difference, therefore, between the negative polarisation 

 of a nerve and that of any such polarisable arrangement as a 

 voltameter is that whereas the nerve loses its charge in an open 



1 Hermann, Ueber die Ursache des Electrotonus, Pfluger's ' Archiv,' vol. xxxviii. 

 P- 153. 



