ORGANS OF PERCEPTION. 171 



motions, the pliability and strength of the fingers, and the 

 softness of the surface, is the most extensive and perfect 

 organ of touch possessed by any animal. 



II. SENSE OF HEAT. 



The sense of touch is exclusively occupied with the ex- 

 amination of the conditions of resistance. Contact, there- 

 fore, is indispensably requisite for enabling the organ to act 

 upon the object, and muscular exertion, to examine its con- 

 dition. Neither of these are necessary to enable the sense 

 of heat to act. Calorific rays emanate from a heated body, 

 though at a distance, and, in order to ascertain their direc- 

 tion and intensity, no muscular effort is required. When 

 the heated body happens to be in contact with us, we in 

 like manner examine its conditions, in reference to tem- 

 perature, without any muscular exertions, or rather, we 

 try to avoid them. Thus, when I lay my hand upon the 

 table, to examine its hardness or smoothness, I make an 

 obvious muscular effort with my fingers ; but when I lay 

 my hand on the table to examine its temperature, I endea- 

 vour to check all motion, so as to keep my hand in the 

 same position. 



These qualities of the sense of heat, sufficiently distin- 

 guish it from that of touch, with which it has been con- 

 founded, and justify its establishment as a distinct power 

 of perception. 



The organ of heat, like that of touch, is seated in the 

 skin, and appears to be co-extensive with those portions of 

 it where the cuticle is thin and destitute of appendices. 



By means of the sense of heat, we are enabled to judge 

 of the relative quantity of caloric in our own bodies and in 

 surrounding objects. When no sensation is produced, we 

 conclude, that our body, and the object with which it is 



