348 ANATOMY FOR NURSES [Chap. XVIII 



of elongated cells. These cells and the intercellular spaces contain 

 a varying amount of pigment, and the color of the hair depends 

 upon the quantity. The gray hair of old age is produced by loss 

 of pigment. 



(3) Medulla — a central pith formed of round cells. Minute air 

 bubbles may be present in both the medulla and fibrous layer, 

 and cause the hair to look white by reflected light. 



The root of the hair is enlarged at the bottom of the follicle 

 into a bulb or knob. This bulb is composed of soft-growing 

 cells, and fits over a vascular papilla which projects into the 

 bottom of the follicle. Hair has no blood-vessels but receives 

 nourishment from the blood vessels of the papilla. 



Growth of hair. — Hair grows from the bottom of the follicle 

 by multiplication of the soft cells which cover the papilla. These 

 cells become elongated to form the fibres of the fibrous portion, 

 and as they are pushed to the surface, they become flattened and 

 form the cuticle. If the scalp is thick, pliable, and moves freely 

 over the skull it is favorable to the growth of hair. A thin scalp 

 that is drawn tightly over the skull tends to constrict the blood- 

 vessels, lessen the supply of blood, and cause atrophy of the roots 

 of the hair by pressure. In such cases massage of the head loosens 

 the scalp, improves the circulation of the blood, and usually stimu- 

 lates the growth of hair. 



With the exceptions of the palms of the hands, the soles of the 

 feet, and the last phalanges of the fingers and toes, the whole 

 skin is studded with hair. The hair of the scalp is long and coarse, 

 but most of the hair is very fine and extends only a little beyond the 

 hair follicle. 



Arrector muscles. — The follicles containing the hairs are narrow 

 pits which slant obliquely upward, so that the hairs they contain 

 lie down on the surface of the body. Connected with each follicle 

 is a small muscle called the arrector muscle. It is composed of 

 bundles of plain muscular tissue which pass from the surface 

 of the true skin, on the side to which the hair slopes, obliquely 

 downward, to be attached to the bottom of the follicle. When 

 these muscles contract, as they will under the influence of cold or 

 terror, the little hairs are pulled up straight, and stand " on end " ; 

 the follicle also is dragged upward, and in this way the roughened 

 condition of the skin known as " gooseflesh," is produced. 



