3.38 THE SENSORIAL FUNCTIONS. 



of some medium, exterior to our bodies, through 

 which their influence extends; thus, the air is the 

 usual medium through which both light and sound 

 are conveyed to our organs. Hence, in order to 

 understand the whole series of phenomena be- 

 longing to sensation, regard must be had to the 

 physical laws which regulate the transmission 

 of these agents. We are now to consider these 

 intermediate processes in the case of each of the 

 senses. 



Chapter II. 



TOUCH. 



I HAVE already had occasion to point out the struc- 

 ture of the integuments, considered in their mecha- 

 nical office of protecting the general frame of the 

 body ; but we are now to view them in their rela- 

 tion to the sense of touch, of which they are the 

 immediate organ. It will be recollected that the 

 corium forms the principal portion of the skin ; 

 that the cuticle composes the outermost layer ; and 

 that between these there occurs a thin layer of a 

 substance, termed the corpus mucosum. The co- 

 rium is constructed of an intertexture of dense and 

 tough fibres, through which a multitude of blood 

 vessels and nerves are interspersed ; but its ex- 

 ternal surface is more vascular than any other 

 part, exhibiting a fine and delicate network of 

 vessels, which is termed by anatomists the vas- 

 cular plexus. This portion of the skin is most 



