x ELECTROMOTIVE ACTION IN NERVE 319 



intimately related, if they are not identical; i.e. the transmitted 

 state of excitation is constituted by the transmitted movement of the 

 electromotive molecules" 



The difficulties in the way of such a schematic and one-sided 

 point of view, under even the most favourable instances of excita- 

 tion by the electrical current (e.g. the fact of the rapid diminution 

 of intensity of electrotonic action with distance from the point of 

 excitation), have not prevented attempts to explain the mode of 

 action of other stimuli on the same principle. Eckhardt, for 

 instance, thought it possible to refer the effect of chemical excita- 

 tion of the nerve to a transmitted change of position of the 

 supposed molecules, starting from the erroneous presumption that 

 the necessary condition of every non-electrical excitation is the 

 momentary death of the excited part of the nerve. The 

 destruction of the electromotive molecules in the part that has 

 been killed, and consequent loss of their directive influence on 

 their uninjured neighbours, causes these to take up new positions, 

 and thus progressively alters the position of all the following 

 molecules. 



But even the simple molecular theory of electrical excitation, 

 as set forth above, is shown to be wholly untenable, so soon as the 

 law of the exclusively polar excitation of " excitable " substances 

 is recognised as universally valid. In particular, the evidence 

 brought forward by Pfliiger to show that there are antagonistic 

 changes of state, expressed in opposite alterations of excitabilty 

 in the vicinity of the two poles of a constant current led through 

 the nerve, as well as the further proof that excitation starts at 

 closure from one electrode only (the kathode), at opening from 

 the other (the anode), cannot, as is evident even from the 

 standpoint of the molecular theory, be reconciled with the 

 idea of complete identity between the progressive " pile-like " 

 polarisation and excitation. For it is not conceivable that 

 the molecule should change its position at closure at the kathode 

 only, on opening, on the contrary, at the anode ; much rather 

 would every point of the whole tract traversed participate equally 

 in the discharge of the excitatory process, since the primary 

 changes of position of the molecules, according to du Bois' theory 

 of electrotonus, occur equally between the two poles throughout 

 the intrapolar area. 



Without directly subscribing to du Bois-Reymond's molecular 



