THE INTEGUMENT, OR SKIN 59 



6. The hairs are produced in a similar manner; the skin 

 forming depressions, or hair-sacs, from the bottom of which 

 they grow and are nourished (Fig. 18). They are found, of 

 greater or less length, on almost all parts of the surface, except 

 the palms of the hands and soles of the feet. On certain parts 

 of the body, they grow to great length ; on other parts they 

 are so short, that they do not rise beyond the hair-sac from 

 which they grow. 



7. The bulb, or root, from which the hair arises, is lodged 

 in a small pouch, or depression of the skin. The shaft is the 

 part which grows out beyond the level of the skin. Its growth 

 is altogether in one direction, in length alone. The outer part 

 of the hair is quite firm, while its interior is softer, and supplies 

 the nutriment by which it grows. The hair is more glossy in 

 health than at other times. 



8. The nail serves as a protection to the end of the finger, 

 and also enables us to grasp more firmly, and to pick up small 

 objects. The hair, too, is a protection to the parts it covers. 

 On the head, it shields the brain from extremes of heat and 

 cold, and moderates the force of blows upon the scalp. On 

 the body, it is useful in affording a more extensive surface for 

 carrying off the perspiration. 



under fortunate circumstances ; that of our cells is short. We all know 

 that the surface of the body is covered by layers of cells. The super- 

 ficial layers are in loose connection ; they are cells hi old age. The fric- 

 tion of our clothing daily removes an immense number of them. A 

 cleanly person who uses sponge and towel energetically every day rubs off 

 a still greater quantity. 



" We swallow ; our tongue acts in speaking ; drink and food pass this 

 way. Now, the mucous membrane of the mouth is covered with layers 

 of cells. Here, also, many thousand senile cells are rubbed off daily. 

 And so on through the entire digestive tract. An immense number of 

 cells these living corner-stones of the body is thus lost daily. 



" To show the duration of life in one kind of cell, let us turn to the 

 human nail. The latter, growing from a furrow of the skin, is made up 

 of skin-cells. In the depth of the furrow, youth prevails ; at the upper 

 margin which we trim old age. Berthold proved that a nail-cell 



6. How are the hairs produced ? Difference in their length ? 



7. Boot of the hair ? Shaft ? Firmness and softness of the hair ? 



8. Office of the nail ? Of the hair ? Give the illustrations. 



