CHAPTER XVIII. 



ELIMINATION CONCLUDED: THE SKIN. NAILS AND HAIR. 

 BODILY HEAT: PRODUCTION OF HEAT; LOSS OF HEAT. 

 DISTRIBUTION OF HEAT; REGULATION OF HEAT. 



Having described the mechanism by means of which the lungs 

 rid the body of carbon dioxide and water, and of how the kid- 

 neys relieve it of urea, salts, and water, it now remains for us to 

 explain how the skin plays its part in elimination by yielding 

 up water, and a certain amount of carbon dioxide and salts. 



The skin. — The skin is not, like the kidneys, set apart to per- 



"^■^;^?w.3;::ffip 





Fig. 127. — Section of Epidermis. (Ranvier.) H, horny layer, consisting of 

 s, superficial horny scales; sw, swollen-out horny cells; s.l. clear layer; M, Malpig- 

 hian layer, consisting of s.fir. granular layer; p, many-sided or prickle cells: c, 

 columnar cells. Nerve fibrils may be traced passing up between the epithelium cells 

 of the Malpighian layer. 



212 



