NERVOUS SYSTEM. 365 



and no artificial logic or scholastic syllogisms 

 will long prevail over the natural sentiment, 

 which must ever guide our conduct, that animals 

 possess powers of feeling, and of spontaneous 

 action, and faculties appertaining to those of 

 intellect. 



The functions of sensation, perception, and 

 voluntary motion require the presence of an 

 animal substance, which we find to be organized 

 in a peculiar manner, and endowed with very 

 remarkable properties. It is called the medul- 

 lary substance ; and it composes the greater part 

 of the texture of the brain, spinal marrow, and 

 nerves ; organs, of which the assemblage is 

 known by the general name of the nervous system. 

 Certain affections of particular portions of this 

 medullary substance, generally occupying some 

 central situation, are, in a way that is totally 

 inexplicable, connected with affections of the 

 sentient and intelligent principle ; a principle 

 which we cannot any otherwise conceive than as 

 being distinct from matter ; although we know 

 that it is capable of being affected by matter 

 operating through the medium of this nervous 

 substance, and that it is capable of reacting 

 upon matter through the same medium. Of the 

 truth of these propositions there exist abundant 

 proofs; but as the evidence which establishes 

 them will more conveniently come under our 

 notice at a subsequent period of our inquiry, I 



