PHENOMENA OF MUSCLE AND NERVE. 283 



of physical discussion. The original molecular theory of du Bois is 

 quite an allowable assumption in so far as it explains the phe- 

 nomena of the current of rest, (whether it is necessary is another 

 question). The second assumption of du Bois-Reymond's, that the 

 force of the molecules decreases during- the condition of activity, 

 is also a permissible one, for as physiological conditions produce 

 the force of these molecules, other physiological conditions may be 

 able to diminish it. But with his theory of electrotonus du Bois- 

 Reymond entered another field ; here, from the existence of the 

 molecules, he drew conclusions as to the influence exercised upon 

 them by physical processes which admit of strict definition. Im- 

 mediately the question arises as to the special physical charac- 

 teristics of these molecules, and it is not possible to agree with 

 Bernstein in characterising as ridiculous either the experiments in 

 which such physical characteristics are assumed or the objections 

 founded upon them. If a molecule is in truth such an unapproach- 

 able thing that it is not possible to think about it in a definite 

 physical way, then no assertion is permissible as to the effect of 

 electrical currents upon it V 



The simple theory of electrotonus I have advanced, a theory 

 founded upon proved facts, du Bois-Reymond is naturally unwilling 

 to admit, at all events for the present, for in ten years he has not 

 found time to make any investigations with regard to it (du Bois- 

 Reyrnond, p. 301). His own position has changed in a most 

 notable fashion. Formerly he assumed as a pure hypothesis the 

 intrapolar rotation of molecules in the direction of the current, in 

 order to be able to deduce from it the extrapolar effects. Now he 

 believes that he has directly proved the intrapolar rotation (with 

 what amount of truth has been already discussed and will be, clearly 

 explained in what follows), that he may be able to give up extrapolar 

 electrotonus. Thus he says (p. 201), ' It is certain that even if the 

 extrapolar electrotonic currents depend merely on diffusion of current, 

 the nature of electrotonus as consisting in positive polarisation is 

 not thereby affected. We should only be rid of the doubtful neces- 

 sity of explaining its spread beyond the electrodes.' The bank- 

 ruptcy of the molecular hypothesis could not be more distinctly 

 declared. The intrapolar molecular change was originally invented 

 merely to explain the extrapolar effects, and on its proving inade- 



1 Further remarks upon the value of the molecular hypothesis may be found in 

 Pfluger'a ' Archiv,' vol. xxvi. p. 485 ; to this passage I refer as being more accessible 

 to most readers. 



