118 Ali&on 0)1 the Theori/ ascribing Secretion 



that we know of galvanism, there being nothing to make us 

 suppose that the blood can be differently affected by galvanism 

 passing through two different sets of nerves ; and certainly 

 nothing that we know in the structure or composition of the 

 different nerves, induces us to suppose that the nature of 

 the galvanism sent through them can be different. 



In the latter case our explanation only begins where the real 

 difficulty ends. If there be powers in the animal system suffi- 

 cient to prepare the blood so variously, that one chemical agent 

 thereafter operating on it, shall form out of it bone, muscle, 

 tendon, oil, and serum, those powers must surely be adequate 

 to the formation of these different substances without farther 

 help ; or at least it is to those powers, and not to the agent sub- 

 sequently applied, that by much the greater share of the pheno- 

 mena of nutrition and secretion must be ascribed. 



It may be said, that although we have no proof of galvanism 

 being excited in nerves by the application of stimuli, to such a 

 degree as can explain the irritation of muscles through nerves ; 

 and have no proof of galvanism being so different in different 

 situations, as to be capable of producing effects so different 

 from each other as the formation of bone and of serum out of 

 the same blood, — still all this may be true of galvanism ; and 

 we know so little of that power, that we are not entitled to lay 

 down the limits, either of its developement or its action. To 

 this I would answer, that it will be time enough to regard 

 galvanism as identical with nervous actions, when it shall be 

 proved, that it may be excited by as various means, and may 

 produce as various effects. 



To explain a set of phenomena in nature, is to establish 

 their coincidence with another set of phenomena more general 

 and better known. How then can we be said to explain the 

 phenomena of the nervous system by resolving them into the 

 phenomena of galvanism, when it is only by a hypothetical ex- 

 tension of these last phenomena, that they can be made to in- 

 clude the former, and when it is only in consequence of our 

 ignorance of their real nature and limits, that we can venture 

 upon this hypothetical extension ? 



