148 PHYSIOLOGY OF MUSCLES AND NERVES. 



able when some of its neiglibours liave been removed. 

 AVitbout, therefore, assuming other resemblances be- 

 tween the forces w^hich act on the magnetic needles 

 and those present in the nerve, we may accept the 

 comparison so far that we may imagine the nerve to 

 consist of separate minute particles, arranged one behind 

 the other in the longitudinal direction of the nerve, 

 and mutually retaining each other in their position. 

 Now, if there are forces which retain the particles in 

 this relative position yet more firmly, it is evident that 

 they must lessen the excitability ; while, on the other 

 hand, such forces as tend to move the nerve-j^articles 

 from their relative positions must at the same time 

 decrease the strength of their connection, and must 

 therefore render the nerve more excitable. As regards 

 the electric current, we have seen that the two poles 

 act on the nerve in opposite w^ays. We may, therefore, 

 assume that by one pole, the positive, the nerve par- 

 ticles are retained in their quiescent position, wliile by 

 the negative pole, on the other hand, they are disturbed 

 from this position. If this is the case, it explains the 

 fact that excitement occurs only at the negative pole 

 w^hen the current is closed. The excitability is in- 

 creased at the positive pole on the opening of the cur- 

 rent; here, therefore, there occurs a movement of the 

 particles such as follows the closing in the negative 

 pole, so that in this case the excitement can occur on 

 the opening of the current. 



The fact that the nerve remains luiexcited by 

 changes in its condition, although these same changes 

 if they occur suddenly do induce excitements, bears so 

 significantly on the explanation of the nervous processes, 

 that we must study it in yet greater detail. The fact 



