306 THE SENSORIAL FUNCTIONS. 



sh^ll postpone their consideration ; and, proceed- 

 ing upon the assumption that this connexion 

 exists, shall next inquire into the nature of the 

 intervening steps in the process, of which sen- 

 sation and perception are the results. 



Designating, then, by the name of brai7i this 

 primary and essential organ of sensation, or the 

 organ of which the physical affections are imme- 

 diately 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 is intended that this sentient being 

 shall 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 communication should be provided between 

 the external organ and the brain. Such a me- 

 dium is found in the nerves, which are white 

 cords, consisting of bundles of threads or fila- 

 ments of medullary matter, enveloped in sheaths 

 of membrane, and extending continuously from 

 the external organ to the brain, where they all 

 terminate. It is also indispensably requisite 

 that these notices of the presence of objects 

 should be transmitted instantly to the brain ; for 

 the slightest delay would be attended with se- 

 rious evil, and might even lead to fatal conse- 

 quences. The nervous power, of which, in our 



