GENERAL AND SPECIAL SENSATIONS. 529 



929. It is difficult to speak with any precision, as to the functions 

 of the Sympathetic system. There is much reason to believe, how- 

 ever, that it constitutes the channel through which the passions and 

 emotions of the mind affect the Organic functions ; and this especially 

 through its power of regulating the calibre of the arteries. We ha~ve 

 examples of the influence of these states upon the Circulation, in the 

 palpitation of the heart which is produced by an agitated state of feel- 

 ing ; in the Syncope, or suspension of the heart's action, which some- 

 times comes on from a sudden shock ; in the acts of blushing ' and 

 turning pale, which consist in the dilatation or contraction of the small 

 arteries ; in the sudden increase of the salivary, lachrymal, and mam- 

 mary secretions, under the influence of particular states of mind,' which 

 increase is probably due to the temporary dilatation of the arteries that 

 supply the glands, as in the act of blushing ; and in many other phe- 

 nomena. It is probable that the Sympathetic system not only thus 

 brings the Organic functions into relation with the Animal, but that it 

 also tends to harmonize the former with each other, so as to bring the 

 various acts of secretion, nutrition, &c., into mutual conformity. For 

 whilst the quantity of a secreted product, or the amount of tissue gene- 

 rated in a part, may be affected by an increase or diminution in the 

 calibre of the vessels supplying it, the quality of the secretion, or the 

 character of the tissue, may be likewise affected (there seems valid 

 reason to believe) by that Nervous force, whose relations to the Physical 

 and Chemical, as well as to all other Vital forces, are so intimate 

 ( 396). 



CHAPTER XIII. 



1". Of Sensation in general. 



930. ALL beings of a truly Animal Nature possess (there is good 

 reason to believe), a consciousness of their own existence, first derived 

 from a feeling of some of the corporeal changes taking place within 

 themselves ; and also a greater or less amount of sensibility to the con- 

 dition of external things. This -consciousness of what is taking place 

 within and around the individual, is all derived from impressions made 

 upon its Afferent nervous fibres ; which, being conveyed by them to the 

 central sensorium, are there felt ( 390). Of the mode in which the 

 impression, hitherto a change of a physical character, is there made to 

 act upon the mind, we are absolutely ignorant; we only know the 

 fact. Although we commonly refer our various sensations to the parts 

 at which the impressions are made, as, for instance, when we say 

 that we have a pain in the hand, or an ache in the leg, we really use 

 incorrect language ; for, though we may refer our sensations to the 



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