192 



OUR BODIES AND HOW WE LIVE 



hair to stand more 

 up a little. Thus, 



A 



FIG. 119. 



BLACKBOARD SKETCH. 

 Cross-Section of Skin. 

 Magnified 30 diameters. 

 A, outer layer of cuticle; 

 , deeper layer of cuticle ; 

 C, duct of sweat gland; 

 Z>, true skin ; E, sublayer 

 of true skin, with colum- 

 nar cells. The blood ves- 

 sels are injected to show 

 black. 



or less erect, and the skin to bunch 



at the sight of a dog, the hairs on a 



cat's back become erect and bristling. 



Any one who has been frightened 

 suddenly, or has taken a chilly bath, 

 knows what it is to have "goose flesh." 

 These muscles also act to force oil 

 out of the oil glands (Fig. 125). 



The hair serves to protect the parts 

 it covers from heat and cold. On the 

 head, the hair helps to protect the 

 skull from injuries and the brain from 

 extremes of heat and cold. 



260. The Nails. The nails are 

 horny cells^of the epidermis in a hard- 

 ened and thickened form. They grow 

 from roots which are lodged in a 

 groove of the skin, somewhat as a 

 watch crystal is fitted into its case. 

 The part which is beneath the skin 

 is called the root, and the remaining 

 part the body. (Figs. 122-124). 



The nail rests upon a bed, called 

 the nail bed or matrix, to which it is 

 firmly fastened. Nails grow from the 

 root, and as long as this is not injured 

 they are not lost or disfigured by 

 splinters, blows, and bruises. 



Disease or injury of the root gen- 

 erally results in a badly shaped nail. 

 The nails serve by their horny tex- 

 ture to protect the outer portions of 



