110 Alison on the Theory ascrihitig Secretion 



suppose it subject to change, from changes in the condition of 

 the spinal marrow. In that case, an experimentum crucis in fa- 

 vour of the latter supposition was afforded, by the observation 

 of Dr. Wilson Philip, that the gradual destruction of the spinal 

 marrow, or its removal from the body, is not attended with 

 any such change on the action of the heart. 



The principal stated above has been fully recognised by Dr. 

 Wilson Philip, in reference to involuntary muscular action, but 

 he seems to me to have overlooked it in his speculations on se- 

 cretion and animal heat. 



After having seen reason to think, that muscular irritability, 

 although often influenced through the medium of nerves, is in 

 no case dependant upon any influence derived from the nervous 

 system, I think we may go a step farther in laying down the fun- 

 damental principles of this kind of inquiry. 



Wliatever other purposes the nervous system may be destined 

 to serve in the animal economy, it seems obvious, that it is in- 

 tended to serve as a medium of communication between mind 

 and body, and that all the changes in the bodily functions 

 which are observed to follow mental acts, are produced through 

 its intervention. 



It is generally agreed among physiologists, and I think it 

 cannot be doubted, that some physical change is produced in 

 the nervous system by every mental act which, through its in- 

 tervention, influences any bodily function. If this be so, it 

 may naturally be expected, that these changes in the nervous 

 system may be readily imitated by the application of physical 

 agents, which furnishes a ready explanation of the effect of 

 such agents, applied to the nervous system, on the various 

 functions. And, therefore, when any effect is observed in any 

 function from the application of physical agents to the nervous 

 system, analogous to the changes produced in the same func- 

 tion by mental acts or aft'ections, instead of arguing from that 

 fact, the necessary dependance of the function in question, on 

 any influence derived from the nervous system, it seems more 

 reasonable merely to suspect that those physical agents must 

 have wrought a change on the nervous system, somewhat ana- 



