SECRETION. 



85 



is poured out upon the skin destined to protect it from the action oi 

 the sun and air. They are sometimes the seat of a minute parasite 

 called the demodex folliculorum. 



Fig. 18. 



Fig. 19.t 



The perspiration is formed by small 

 tubes of peculiar conformation, very 

 much convoluted, and seated just be- 

 neath the cutis vera, and pouring out 

 their secretion by minute pores upon the 

 epidermis. The ducts pass through the 

 epidermis and cutis vera in a spiral di- 

 rection, and their openings upon the 

 epidermis, which are seen along the ele- 

 vated lines of the skin of the palm and 

 sole, are called jpores. (Fig. 19.) Ac- 

 cording to Mr. E. Wilson, the number 

 of these sweat glands in the whole sur- 

 face of the body is about seven inillions^ 

 and the conjoined length of the perspi- 

 ratory tube 28 miles. 



The secretion from these glands is continually taking place, but 

 as it is usually evaporated as fast as it is formed it does not become 

 sensible. If, however, from excessive secretion, or a moist condi- 



* Fig. 18. a a. Sebaceous follicles, b. A hair with its follicle c, surrounded by fat cells, 

 t Fig. 19. a. Epidermis, b. Upper layer of cutis vera. c. Cutis vera, d Sweat gland 

 surrounded by fat cells, with its duct running spirally through the layers of the skin. 



8 



