48 THE ACTIVE FORCES OF LIVING ORGANISMS 



ligature, it may be argued that the difference in 

 electrical potential between one part of the body and 

 another being always very slight — much less indeed 

 than that which exists between the two plates of a 

 battery — the interruption of the nerve current might 

 be more easily effected than that of the electrical 

 current. The former is also very much the weaker of 

 the two, and the rate at which it travels suggests 

 either that it has to overcome a certain degree of 

 resistance, due possibly to the slight difference of 

 electrical potential already mentioned, or that it is 

 generated anew all along the fibre. When a nerve 

 impulse takes place, it is accompanied by an electrical 

 change passing along the nerve-fibre. This change, 

 the negative variation or current of action, as it is 

 called, is evidently bound up with certain changes in 

 the nerve-cell, the nerve-fibre, and its peripheral 

 ending. Yet no development of heat nor signs of 

 chemical action have hitherto been detected in a 

 nerve-fibre after action, so that either they are so 

 minute as to escape detection, or the only change is a 

 molecular one, accompanied by an electrical move- 

 ment or variation. What, then, is the nature of 

 the nervous impulse ? 

 Electrical To meet all the necessities of the case, it seems as 



■vibration , . , . , 



is always though we must look on it as a compound m which 

 with the elements are chemical, molecular, and electrical. 



or^tV Eeally, if we reflect, we shall probably find it im- 

 vibiStion^ possible to exclude any one of the three. Prom the 

 electrical variation, or current of action, of which 



