276 On the Agency of Nejves. 



the secreting part are cut. It may be, that this is because 

 something continually passing from the brain or spinal marrow 

 to the secreting organ, which is all that I can understand by 

 the term nervous influence, as here used, is intercepted by the 

 division of the nerves ; but I have never seen any proof of this ; 

 — to take it for granted, as Dr. Philip has done in the present 

 argument, is an assumption very little short of a petitio prin- 

 cipii ; — the rule of logic is, qffirmantibus incumbit probatio ; and 

 those who advance any theoretical explanation of a fact are not 

 entitled to shift this onus probandi off themselves, and lay it 

 on their opponents, until they have made it manifest that the 

 fact admits of no other explanation. 



In the mean time, the doctrine of nervous energy, as above 

 explained, being, as far as I know, a mere hypothesis, we are 

 entitled to state on the other side,— Jirst, that there is no lesion 

 whatever of the nervous system, from the effect of which, in 

 stopping any function of the animal body, it necessarily follows, 

 that that function is dependent on nerves, — because there is no 

 lesion, the effect of which may not be equally well explained 

 by supposing it to communicate a noxious influence, as by 

 supposing it to cut off a salutary one*; — and, secondly, that 

 since it has been found, by Dr. Philip himself, that the action 

 of the heart, though very readily influenced by injuries of the 

 nervous system, is truly independent of it, we have the evidence 

 of analogy for thinking, that the action of secretion may be equally 

 independent of the nervous system, notwithstanding the facts which 

 shew, that it may be readily influenced by injuries of nerves. 



But secondly, granting (for the sake of argument only) that 

 there is such an existence in nature as a nervous influence con- 

 tinually passing from the larger masses of the nervous system 

 to the small branches, — it appears to me, that some of the facts 

 which I formerly noticed, exactly answer Dr. Philip's demand ; 



* In using the term noxious influence, I would not be understood to ex- 

 press any opinion as to the mode, in which an injury of the nerves affects 

 secretion ; but merely to indicate, that I conceive the fact demonstrates only 

 the effect of a certain byury of nerves, not the effect of any previously ex- 

 isting influence of nerves. 



