THE SKIN 



10. Hair is very durable ; that found on Egyptian 

 mummies has remained unchanged through several thou- 

 sand years. It is elastic and is said to stretch one third 

 of its length without breaking. Find out whether this 

 is true by attaching weights to a hair. Hair absorbs 

 moisture readily, and for a time its length is considerably in- 

 creased thereby. Each hair follicle has fine muscles con- 

 nected with it. Cold or fear may cause the muscles to 

 contract and the hairs, which are usually in a slanting posi- 

 tion, to stand erect. This causes the 



hair to afford a better protection to the 

 animal from cold or blows. " Goose 

 skin," which occurs if a cold bath is 

 unduly prolonged, is caused in the 

 same way ; but the hair on the human 

 skin is so fine that the goose skin 

 avails little against cold. 



11. The Oil Glands, or sebaceous 

 glands, are small, irregularly shaped 



FIG. 8. Piece of Human 

 Hair, magnified. 



Cavities Which Open intO the little A, seen from the surface. B, in 



section, c, cuticle; m, pith, 

 the air having been expelled by 

 Canada balsam. 



pits from which the hairs grow (Fig. 

 i). A few oil glands open directly 

 upon the surface. They are lined with epithelial cells. 

 The cells deposit a kind of oil, which flows out of the 

 mouth of the glands, renders the epidermis flexible and 

 less penetrable by water, and prevents it from drying out 

 by evaporation and cracking open. It is also the natural 

 " hair oil," for softening the hair and keeping it from 

 becoming brittle. The oil glands of the center of the face 

 are especially large and numerous. When their mouths 

 are stopped by dirt, they become distended with oily mate- 

 rial and are called blackheads. Oil glands are absent from 

 the soles and palms. 



12. The Nails, as well as the hair, are a growth of the 

 epidermis ; and like the epidermis, only the lowest cells, 



