494 THE SOLIDS. 



where this sense exists only as common sensation, the 

 epidermis is very thin, while over the palmar surface of the 

 hands it is very thick ; the epidermis must not be too thick, 

 however, even in this situation, as is shown by the fact, that 

 where it has been greatly thickened by manual labour, 

 touch is totally obscured. 



The density of the epidermis in certain situations is 

 evidently due to pressure, and may be explained by the fact 

 that such pressure induces an increased determination of 

 blood to the part, which is followed by increased nutrition 

 and development. Between the sense of touch and the 

 number of sudoriferous glands, there would appear to be a 

 certain relation : thus on the palmar aspect of the hands, 

 where this sense exists in its highest perfection, the number 

 of sweat glands is very great. 



The use of these glands in this situation in such increased 

 numbers, may readily be conceived to be to keep the epidermis 

 in a moist and flexible condition, whereby impressions would 

 be more readily conveyed to the papillae and more distinctly 

 felt, the acuteness of the entire sense being thus greatly aug- 

 mented. 



The epidermis is very accurately adapted to the papillae, 

 so that when detached and viewed upon its under surface, 

 it is seen to contain exact impressions of each and all of 

 them ; it is in this manner that their form, size, number, 

 and arrangement are best studied, and it will then be noticed 

 that, in all these particulars, considerable variations exist. 



(See Plate LXIII. figs. 5, 6.) 







TASTE. 

 Papillary Structure of the Mucous Membrane of the Tongue. 



The mucous membrane of the tongue, the principal if not 

 the sole seat of the sense of taste, is divisible, like the skin, 

 into a chorion, a papillary structure, and an epidermis or epi- 

 thelium. 



The chorion is a firm and tough membrane, formed of 

 mixed fibrous tissue, and containing in its substance the 



