164 PHILOSOPHY OF ZOOr.OcY. 
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 1s 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 mforma- 
tion which they convey to the mind, with regard to the 
properties of external objects. 
CHAP. X. 
ORGANS OF PERCEPTION. 
Ly 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- 
