THE NERVES. 237 



deeply into details we should not be able to explain 

 this here. 1 



6. We will now turn our attention to nerves. The 

 resemblance of the phenomena in the case of muscles 

 and of nerves is so great that it is natural at once to 

 transfer the hypotheses assumed for the former to the 

 latter. It is true that in nerves there are not the 

 microscopically visible particles (the so-called muscle- 

 elements) on which we based our theory in the case 

 of muscles, and in which we recognised the presence of 

 electromotive forces. But from what we have already 

 seen of the processes of excitement in the nerve, it is 

 at least evident that in the nerve also separate par- 

 ticles, with independent power of movement and inde- 

 pendent forces, must be arranged in sequence in the 

 longitudinal direction of the nerve. If, without beingf 



O 3 O 



able to say anything further of their nature, but be- 

 cause of the analogy, we call these particles nerve- 

 elements, and if we assume that each of these nerve- 

 elements is the seat of an electromotive force, in 

 consequence of which the longitudinal section exhibits 

 positive tension, the cross-section exhibits negative 

 tension, then the phenomena in the quiescent nerve 

 and the negative variation of the nerve-current during 

 activity are explicable exactly as were the correspond- 

 ing phenomena in muscles. The entirely similar be- 

 haviour of nerves and muscles when irritated is alone 

 sufficient to show satisfactorily that the two must be 

 very much alike in their physical structure ; and the 

 similarity of their behaviour in point of electromotive 

 activit} r is such as to lend weight to our assumption of 



1 See Notes and Additions No. 14. 



