PHILOSOPHY OF ZOOLOGY. 



Of the elementary nature of this exciting power, we indeed 

 know nothing. Physiologists have termed it a secretion of 

 the nervous system, without perceiving that, in the manner 

 of its operations, it is essentially different from any other 

 secretion in the system. That it results from organization, 

 is disproved by the phenomena of death ; that it is of an 

 electrical or magnetical nature, is contradicted by the totali- 

 ty of its phenomena. 



Having thus examined the structure of the nervous sys- 

 tem, and attended to its functions of sensation and voli- 

 tion, -let us now take a view of the mind. The intimate 

 connection which subsists between this mysterious part of 

 the animal frame and the nervous system, points out this 

 place as the most suitable for the investigation of the pheno- 

 mena which it exhibits. But, in order to give to this subject 

 the requisite illustration, it is necessary to examine more 

 particularly, the nature of our different sensations, the or- 

 gans employed in their production, and the kind of informa- 

 tion which they convey to the mind, with regard to the 

 properties of external objects. 



CHAP. X. 



ORGANS OF PERCEPTION. 



IN the numerous references which we have hitherto made 

 to the faculty of Sensation, as a display of the operation of 

 the nervous system, we have considered it as indicating 

 merely the presence of bodies, and as giving no information 

 respecting their character. If we attend more minutely to 

 this faculty, we shall find, that all the sensitive parts of the 

 body, are not equally capable of warning us of the presence 

 of the same kind of objects. The rays of light make no im- 



