CHAPTER XX 



THE SKIN AND THE APPENDAGES 



Questions. 1. Why do people sweat ? 2. Why does the skin come to 

 be tougher on some parts of the body than on others ? 3. What causes 

 pimples ? 4. How can the complexion be kept clear ? 5. How often 

 should one bathe ? 



164. The functions of the skin. As a covering of the whole 

 body the skin is a protective organ, shielding the delicate tissues 

 underneath from many possible injuries. As the point of contact 

 between the organism and the outside world it is sensitive to 

 various changes. It is sensitive to touch (which has been called 

 the mother sense), to heat and to cold, and also to light. Con- 

 tact or pressure, heat, and cold affect the nerves of the skin so 

 that we become aware of what is going on. Light, however, 

 does not as a rule arouse consciousness ; yet we see its effect 

 in tan and in the more painful sunburn. The skin maintains 

 the temperature of the body (p. i68) by means of the sweat 

 glands, through which water, salts, urea, and other organic 

 wastes are excreted to the surface. The skin therefore serves 

 four rather distinct functions: it is a protective, a sensory, a 

 heat-regulating, and an excretory organ. 



165. The structure of the skin and its outgrowths. The sur- 

 face layer of the skin consists of dead cells (see Fig. 99 and 

 Fig. 100). These horny cells are constantly rubbing off but are 

 constantly being replaced by new cells from the live layer of 

 dermis beneath. The skin is practically waterproof. Unless 

 the epidermis is broken, it is also proof against the absorption 

 of salts or poisons and against the entry of bacteria. Constant 

 rubbing or pressure will cause the layer of dead cells to increase 



in thickness ; it is thus that we acquire corns and calluses. 



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