Although the health, vigour, and beauty of the hair depend largely upon careful and constant attention to its needs, its physiology has, until recently, been very imperfectly understood."
"The growth and structure of the hair form a most interesting study. Each hair consists of a root and shaft. The former is situated in the skin, the latter projects from it. The hair-sac, or depression in the skin from which the hair grows, consists of two layers, the inner layer being cellular and epidermic, and the outer layer fibrous.
Within this sac the hair takes root, forming at its lower end a bulb. At the bottom of the hair-sac, or follicle, there is a little projection called the papilla, supplied with blood-vessels and nerves, which enters the hair-bulb and forms, really, the germ of the hair.
The hair therefore grows entirely from the root, from this minute papilla. The hair itself is of fibrous substance. Outside it has a thin, scaly surface (termed the hair-cuticle), and in the centre is the core, or medulla. The outside surface consists of minute flat scales, which overlap each other somewhat after the manner of roof-tiles. This explains the well-known phenomenon of the hair feeling rough when drawn between the fingers in one direction, and smooth when drawn in the opposite direction. The medullary substance of the hair is a kind of pith composed of loosely formed cells and air-spaces. These air-spaces, however, though numerous in white hairs, are almost entirely absent in black hairs.
Nutriment, gloss, and pliancy are furnished to each hair by means of sebaceous oil-glands situated on each side of the hair-bulb, which secrete a greasy fluid. The oily matter which is formed in the sebaceous gland is discharged into the hair-follicle, and thus upon the surface of the hair. Some of the secretion extends over the skin, making it soft, and thus preventing it from becoming hard and dry."
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