Nl.RVOUS SYSTEM. 3*29 



are, in a way that is totally inexplicable, connected 

 with affections of the sentient and intelligent prin- 

 ciple ; a principle which we cannot any otlierwise 

 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 abun- 

 dant proofs ; but as the evidence which establishes 

 them will more conveniently come under our notice 

 at a subsequent period of our inquiry, I shall post- 

 pone their consideration ; and, proceeding upon the 

 assumption that this connexion exists, shall next 

 inquire into the nature of the intervening steps in 

 the process, of which sensation and perception are 

 the results. 



Designating, then, by the name of hrain this 

 primary and essential organ of sensation, or the 

 organ of which the physical affections are immedi- 

 ately attended by that change in the percipient 

 being which we term sensation; let us first inquire 

 what scheme has been devised for enabling the 

 brain to receive impressions from such external 

 objects, as it was intended that this sentient being- 

 should be capable of perceiving. As these objects 

 can, in the first instance, make impressions only 

 on the organs situated at the surface of the body, 

 it is evidently necessary that some medium of com- 

 munication should be provided between the ex- 

 ternal organ and the brain. Such a medimn is 

 found in the nerves, which are white cords, consist- 

 ing of bundles of threads or filaments of medullary 

 matter, enveloped in sheaths of membrane, and 



