LIFE AND ORGANISATION. 97 



attested by the beautiful experiments of M. Helmholz on 

 the crural nerves of the frog, which show that a space of 

 somewhat more than eighty feet is passed through in a second 

 of time. To subsequent observations of M. Helmholz we 

 owe the further remarkable facts that the rate of motion 

 of the nervous power in Man is more than double that 

 observed in the frog ; and that it sensibly augments with any 

 augmentation of animal temperature. These experiments 

 are so delicate in apparatus and manipulation, that few can 

 undertake them ; but their principle is one which in skillful 

 hands may hereafter illustrate some of those variations and 

 anomalies of nervous power, which at present perplex all 

 our reasoning. Meanwhile the fact ascertained of the propa- 

 gation of power in definite time, brings us to the conception 

 of a physical force, like to those which act on matter through 

 its molecular structure elsewhere in the natural world. And 

 this presumption is strengthened when we consider the actual 

 relation of these forces, and of electricity especially, to the 

 functions and phenomena of the nervous system. 



At this point, however, a serious doubt suggests itself. 

 Can these functions, so diverse in nature and quality as well 

 as degree, be due to any single agent of motion and power ? 

 Can we possibly predicate unity of any proximate cause, in 

 actions which combine the functions of the several senses ; 

 voluntary and involuntary muscular contractions ; the ner- 

 vous influence directed to the various secreting organs ; 

 and the sympathies between different organs, which John 

 Hunter well describes as the ' internuncial office ' of the 

 nervous system ? This question will be directly seen as one 

 of great, perhaps insuperable difficulty* As we cannot multi- 

 ply agents to meet the many conditions just stated, or find 

 adequate explanation of them in any structural differences 

 of the conducting nerves, we can only approach a solution 

 by looking to the diversities of organisation upon which the 



