718. The color of the hair varies in different individuals, and is generally supposed to depend on the fluids contained in the pith. There are two causes which act in changing the hair gray. The first is, defective secretion of the coloring fluid. The second is, the canals, which convey the fluid into the hair, become obliterated. In the first instance, the hair will remain; in the second, it dies, and drops out; the cuticle of the scalp grows over the canal, which is soon obliterated, and the head becomes bald.
Observation. It is related that the hair of Marie Antoinette, Queen of France, and others, from excessive mental agitation, changed from black to gray in a single night. This is not strictly true; the secretion may be arrested, but that already deposited in the pith will require days or weeks to be removed.
719. Upon the upper part of the head, the oil-tubes open into the hair-sacs; consequently, the secretion of the oil-glands is spread over the surface of the hair, and not upon the cuticle. This is the cause of the dry, white, branny scales, called “scurf,” or “dandruff,” upon the head. This is natural, and cannot be prevented. When scurf exists, the only necessary application to remove it, is the frequent use of the hair-brush, and washing with pure water.
Observation. The secretion of the oil-glands may become impacted around the hairs as they issue from the skin, and thus prevent their outward movement in growing. The pressure of the matter deposited at their bulbs will then cause itching. The comb and the brush may be used to remove the impacted matter, and relieve the disagreeable sensation.
720. The oil is most abundant near the roots of the hair 324 A free use of the brush spreads it along the hairs, and gives them a smooth, glossy appearance. Soap should rarely be used in washing the head, as it will remove the oil which is essential to the health and appearance of the hair.
718. Upon what does the color of the hair depend? What are the causes of the hair becoming gray? What is the cause of the hair dropping out? What is related of Marie Antoinette? 719. How is “dandruff” on the scalp produced? What is the only necessary application to remove it? Give observation. 720. Where is the oil of the hair most abundant?
721. The uses of the hair vary in different regions of the body. Upon the head, it aids in shielding the brain from injury by blows, and it likewise serves to protect this part of the system from heat and cold, thus maintaining equal temperature of the cerebral organ. About the flections of the joints, as in the axilla, (armpit,) they prevent irritation of the skin from friction; in the passages to the ears and nostrils, they present an obstacle to the ingress of insects and foreign bodies; while in the eyebrows and eyelids, they serve to protect the organ of vision.
Fig. 119.