PIIYSlnLocJY OF Ml'SCLES AM> .NF.KYI-. 



able when some of its neighbours have been removed. 

 NYithoiit, therefore, a-suming other resemblances be- 

 tween tin: foive.s which act on the magnetic needles 

 and those present ill the nerve, -we may arcept the 

 comparison so far that we may imagine the nerve to 

 consist of -eparate ininiite particles, arranged one behind 

 the other in the longitudinal direct ion 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 

 thev nm-t lesM-u the excitability; while, on the other 

 hand, such forces as tend to move the nerve-part id 

 from their relative positions must at the same time 

 decrease the strength of their connection, and rai^t 

 therefore render the nerve more excitable. As regards 

 the elect rie current, we have seen that the two poles 

 act on the nerve in opposite ways. \Ye may, therefore, 

 as<ume that by one pole, the positive, the nerve pa,-- 

 ti.-K-s are retained in their quiescent position, while by 

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

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

 fact that excitement occurs only at the negative pole 

 when 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 mo\einent of the 

 particles such as follows the closing in the negatise 

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

 the op'-ning of the' current. 



'The fact that the nerve ivnnins niiexcited by 

 change- in Its condition, although these same changes 

 if they occur suddenly do induce excitements, bears so 

 -i^ni Meant! von the explanation of the nervous process* 3, 

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



