356 THE VITAL FUNCTIONS. 



At other times, the chemical quality of their 

 contents appears to be the immediate stimulus 

 inciting them to contraction. But numerous in- 

 stances occur, in the higher orders of animals, 

 in which these causes alone are inadequate to 

 explain the phenomena of the vital functions. 

 No mechanical hypothesis will suffice to account 

 for the infinite diversity in the modes of action 

 of the organs which perform these functions, or 

 afford any clue to the means by which they are 

 made to co-operate, with such nicety of adj iist- 

 ment, in the production of the ultimate effect. 

 Still less will any theory, comprising only the 

 agency of the muscular power, and the ordinary 

 chemical affinities, enable us to explain how an 

 irritating cause, applied at one part, shall pro- 

 duce its visible effects on a distant organ ; or in 

 what way remote and apparently unconnected 

 parts shall, as if by an invisible sympathy, be 

 brought at the same moment to act in concert, 

 in the production of a common effect. Yet such 

 co-operation must, in innumerable cases, be 

 absolutely indispensable to the perfect accom- 

 plishment of the vital functions of animals. 



Nature has not neglected objects so important 

 to the success of her measures ; but has pro- 

 vided, for the accomplishment of these purposes, 

 a controlling faculty, residing in the nervous 

 system, and denominated the nervous power. 



