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CHAPTER VII. 



PERCEPTION. 



THE object of nature in establishing the organizations we 

 have been reviewing is to produce certain modified impres- 

 sions on the extremities of particular nervous filaments pro- 

 vided to receive them; but these impressions constitute only 

 the commencement of the series of corporeal changes which 

 terminate in sensation; for they have to be conveyed along 

 the course of the nerves to the brain, or central organ of the 

 nervous system,* where, again, some physical change must 

 take place, before the resulting affection of the mind can be 

 produced. The particular part of the brain, where this last 

 physical change, immediately preceding the mental change, 

 takes place, is termed the Sensorium. Abundant proofs 

 exist that all the physical changes here referred to really oc- 

 cur, and, also, that they occur in this order of succession: 

 for they are invariably found to be dependent on the healthy 

 state, not only of the nerve, but, also, of the brain; thus, the 

 destruction, or even compression of the nerve, in any part 

 of its course between the external organ and the sensorium, 

 totally prevents sensation; and the like result ensues from 

 even the slightest pressure made on the sensorium itself. 



Although the corporeal or physical change taking place in 

 the sensorium, and the mental affection we term sensation, 

 are linked together by some inscrutable bond of connexion, 



* It is usual to designate the end of the nerve which is next to the jenso- 

 rium, as the origin of that nerve; whereas, it should more properly be re- 

 garded as its termination; for the series of changes which end in sensation 

 commence at the organ of sense, and are thence propagated along the nerve 

 to the sensorium. 



