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ANIMAL BIOLOGY 



over most of the body except the palms of the hands and 

 the soles of the feet. Over most of the surface of the body 

 these hairs are inconspicuous; they represent the mere 

 remnant of the coat that once covered our hairy ancestors. 

 There are usually two oil glands to each hair follicle and 

 their secretion serves to keep the hair oily. The hair 

 of the head may be supplied with more oil if the glands are 

 stimulated by massaging the scalp or vigorously brushing 

 the hair. 



FIG. 206. Section of skin of man. (From Wiedersheim.) Co, 

 derma (corium) ; D, oil gland; F, fat; G, blood-vessels; GP, vascular papilla; 

 H, hair; N, nerves; NP, nerve papilla; Sc, stratum corneum; SD, SD 1 , 

 sweat gland and duct; SM, stratum Malpighii. 



Each hair grows from a little papilla at the bottom of 

 the hair follicle, where there are many small blood vessels 

 and nerves. Sometimes hairs fall out, but if the papilla 

 is uninjured they may be grown again. Hairs contain 

 pigment which gives them different colors in different 

 individuals, but all kinds of hairs tend to become gray 

 with old age owing to the central part of the hairs being 

 filled with air. When the scalp is ill nourished the hairs 



