THE SKIN AND ITS FUNCTIONS. 343 



like the rest of the surface of the skin, are covered by one or more layers 

 of epithelium, forming the cuticle or epidermis. The papilla? adhere 

 very intimately to the cuticle, which is thickest in the spaces between 

 them, but tolerably level on its outer surface: hence, when stripped off 

 from the cutis, as after maceration, its internal surface presents a series 

 of pits and elevations corresponding to the papillae and their interspaces, 

 of which it thus forms a kind of mould. Besides affording by its imper- 

 meability a check to undue evaporation from the skin, and providing the 

 sensitive cutis with a protecting investment, the cuticle is of service in 

 relation to the sense of touch. For by being thickest in the spaces, be- 

 tween the papillae, and only thinly spread over the summits of these pro- 

 cesses, it may serve to subdivide the sentient surface of the skin into a 

 number of isolated points, each of which is capable of receiving a distinct 

 impression from an external body. By covering the papillae it renders 

 the sensation produced by external bodies more obtuse, and in this manner 

 also is subservient to touch : for unless the very sensitive papillae were 

 thus defended, the contact of substances would give rise to pain, instead 

 of the ordinary impressions of touch. This is shown in the extreme sensi- 

 tiveness and loss of tactile power in a part of the skin when deprived of 

 its epidermis. If the cuticle is very thick, however, as on the heel, touch 

 becomes imperfect, or is lost. 



(3.) The Secretion of Sebaceous Glands, and Hair-follicles. 

 The secretion of the sebaceous glands and hair-follicles (for their products 

 cannot be separated) consists of cast-off epithelium-cells, with nuclei and 

 granules, together with an oily matter, extractive matter, and stearin; 

 in certain parts, also, it is mixed with a peculiar odorous principle, which 

 contains caproic, butyric, and rutic acids. It is, perhaps, nearly similar 

 in composition to the unctuous coating, orvernix caseosa, which is formed 

 on the body of the foetus while in the uterus, and which contains large 

 quantities of ordinary fat. Its purpose seems to be that of keeping the skin 

 moist and supple, and, by its oily nature, of both hindering the evapora- 

 tion from the surface, and guarding the skin from the effects of the long- 

 continued action of moisture. But while it thus serves local purposes, its 

 removal from the body entitles it to be reckoned among the excretions of 

 the skin; though the share it has in the purifying of the blood cannot be 

 discerned. 



(4.) The Excretion of the Skin: the Sweat The fluid secreted 

 by the sudoriferous glands is usually formed s% gradually, that the watery 

 portion of it escapes by evaporation as fast as it reaches the surface. But, 

 during strong exercise, exposure to great external warmth, in some dis- 

 eases, and when evaporation is prevented, the secretion becomes more 

 sensible, and collects on the skin in the form of drops of fluid. 



The perspimfion of the skin, as the term is sometimes employed in 

 physiology, includes all that portion of the secretions and exudations from 



