CHAP. XVIII.] ELIMINATION CONCLUDED. 



217 



keeps it soft and flexible. An accumulation of this sebaceous 

 matter upon the skin of the foetus furnishes the thick, cheesy, 

 oily substance, called the vernix caseosa. 



The sudoriferous or sweat-glands, All over the surface of the 

 skin are minute openings or pores. These pores are the open- 

 ings through which the sweat-glands pour their secretions upon 

 the surface of the body. The sweat-glands are tubular glands 

 with their blind ends coiled into little balls which are lodged 

 in the true skin or subcutaneous tissue ; from the ball the tube 

 is continued as the excretory duct of the gland up through 

 the true skin and epidermis, and finally opens on the surface 

 by a slightly widened orifice. Each tube is lined by a secreting 



epithelium continuous 

 with the epidermis. The 

 coiled end is closely in- 

 vested by a meshwork of 

 capillaries, and the blood 

 in the capillaries is only 

 separated from the cav- 

 ity of the glandular tube 

 by the thin membranes 

 which form their respec- 

 tive walls. The secre- 

 tory apparatus in the 

 skin is somewhat simi- 

 that which obtains 



FIG. 131. COILED END OF A SWEAT-GLAND, 

 a, the coiled end ; b, the duct ; c, network of capil- in the kidney ; in the 

 laries, inside which the sweat-gland lies. ,, 



one case the blood- 



vessels are coiled up within the tube, while in the other the 

 tube is coiled up within the meshwork of blood-vessels. 



The sweat-glands are abundant over the whole skin, but 

 they are most numerous on the palm of the hand and on the sole 

 of the foot; in the groin, and especially in the axilla, they are 

 larger than in other parts of the body. At a rough estimate, 

 the whole skin probably possesses from two to two and a half 

 millions of these glands, and their combined secreting power is 

 therefore very great. 



Perspiration or sweat. The sweat is a transparent colourless 

 fluid, of a distinctly salt taste and with a strong, distinctive odour. 

 When the secretion is scanty it has an acid reaction, but when 



