4o:i 



Chapter VII. 



PERCEPTION. 



The object of nature in establishing the organiza- 

 tions we have been reviewing is to produce certain 

 modified impressions on the extremities of parti- 

 cular nervous filaments provided to receive them ; 

 but these impressions constitute only the commence- 

 ment 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 cen- 

 tral 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 occur, and also that they 

 occur in this order of succession ; for they are inva- 

 riably 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 ex- 

 ternal organ and the sensorium, totally prevents 

 sensation ; and the like result ensues from even the 

 slightest pressure made on the sensorium itself. 



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

 the sensorium, as the origin of that nerve; whereas it should more 

 properly be regarded as its termination ; for the series of cliangcs 

 which end in sensation commence at the organ of sense, and are 

 thence propagated along the nerve to the sensorium. 



