THE SKIN AND THE APPENDAGES 



199 



Embedded in the dermis, or true skin, are several distinct kinds 

 of structures having distinct functions. 



1. Sweat glands. A sweat gland consists of a delicate tubule 

 opening upon the surface of the skin at one end, the pore, and 

 twisted or coiled into a clump at the other. Surrounding the 

 coiled end is a network of very fine capillaries, from which the 

 water and dissolved wastes diffuse into the tube (see Fig. loi). 



2 . Oil glands. Groups of cells in the 

 deeper layers of the dermis convert 

 some of their food (obtained from the 

 capillaries) into an oily substance. 



Cortcx-r,.^}''f^ 



Medulla 



Hair- 

 muscle 



Horny 



laijcr 

 yDermis 

 ,Sebaceou$ 



gland 



''I- 



Fig. 99. Touch organs of the skin 



We perceive touch or heat or cold according to the 

 end organ which is stimulated. These end organs, 

 d, lie beneath the epidermis, a, and contain the end- 

 ings of the nerve fibers, e; b, the dermis, or true skin; 

 c, blood vessels 



Papilla with 

 blood vessels 



Fig. 100. Hair of 

 mammals 



Human hair follicle, show- 

 ing mode of growth. The 

 dead shaft is pushed for- 

 ward by the new growth 

 about the papilla 



This oil the glands secrete on the surface of the skin all over 

 the body, but especially at the roots of the hairs (see Fig. 100). 



3. Nerve endings. The sense organs in the skin consist of 

 delicate clumps of nerve tissues connected with nerve fibers. 

 Some are sensitive to touch only, others to cold, and still others 

 to warmth. It is probable that the amount of perspiration is 

 controlled at least in part by the response of these nerve organs 

 to changing temperature in the surroundings (see Fig. 99). 



4. Hairs. Like the external portion of the skin, the part of 

 the hair which we see consists of dead matter. The root of the 



