THE HAIRS 257 



The hairs also belong to the cuticle. They are distributed 

 over the greater part of the surface of the body, being conspicuous 

 on the scalp by their size and length. 



A hair consists of a root and a shaft. The bulb or (enlargement 

 of the) root rests upon a minute hair papilla in the bottom of a 

 depression called a hair follicle. 1 The nerves and blood-vessels do 

 not run beyond the papilla. 



The shaft extends outward from the root, and contains the 

 pigment which decides the color of the hair. 



The main body of the shaft consists of fibrous or cortical sub- 

 stance. In this is the pigment of dark hairs, but only minute air 

 spaces in white hairs. In all coarse hairs except those of the scalp, 

 and in the roots of most hairs, a central pith or medulla exists 

 within the fibrous substance. The shaft is covered with a cuticle 

 of flat scales which overlap each other. 



The hairs lie obliquely on the skin but may be made to stand 

 erect by the contraction of a tiny muscle bundle placed at the root 

 of each one. These are the erectors of the hairs. It is their action 

 which gives the appearance called "goose-flesh." The softness 

 and the gloss of hair are due to the oil which is poured into the 

 follicles by the oil glands. 



Note. The fine hair on the skin of the new-born child is called lanugo. 

 It begins to grow at about the fifth month of mtra-uterine life, and wears 

 away soon after birth, although some remains permanently. 



The hairs which border the eyelids are called cilia. The hairs 

 of the eyebrows are supercilia. Those of the nostrils are vibrissa; 

 of the head, capili', of the beard, barba. 



PHYSIOLOGY OF THE SKIN 



The skin has a triple function. It is the protective covering of 

 the body; an organ of excretion and an organ of the special sense 

 of touch. Also, it aids in regulating body temperature. 



As a protective it is mechanical only; the insensitive layers 

 receiving first the impressions of external forces heat, cold, blows, 

 etc., diminish their effects on deeper and sensitive ones. 



As an organ of touch it is referred to on page 327. 



1 In the case of curly hair the opening of the follicle leads inward in a curved or 

 spiral direction. 



