. A healthy body. A textbook on anatomy, physiology, hygiene, alcohol, and narcotics. For use in intermediate grades in public and private schools . perspire freelyafter exercise is good; but suddenly to check the perspi-ration, or to allow the body to cool rapidly, is positivelyinjurious, and may prove fatal. The Oil-Glands. The oil-glands do not come to thesurface, as do the sweat-glands, but each empties into asac in which a hair rests ; so a hair has an oily substancepoured around it continually. This is Natures hair-oil. It makes the hair smooth and glossy, and, if thescalp be in a health
. A healthy body. A textbook on anatomy, physiology, hygiene, alcohol, and narcotics. For use in intermediate grades in public and private schools . perspire freelyafter exercise is good; but suddenly to check the perspi-ration, or to allow the body to cool rapidly, is positivelyinjurious, and may prove fatal. The Oil-Glands. The oil-glands do not come to thesurface, as do the sweat-glands, but each empties into asac in which a hair rests ; so a hair has an oily substancepoured around it continually. This is Natures hair-oil. It makes the hair smooth and glossy, and, if thescalp be in a healthy condition, it will furnish oil enoughto keep the hair soft and smooth. The Hair. The hairs are placed obliquely in the skin,as shown in Fig. 48. Hair is not hollow, as many peoplesuppose, although in its centre there is a substance moreporous than the outside. Hair grows from the bottom, from the bulb. When onehair is removed, another will grow in its place, provided THE SKIN. 149 the deeper parts of the skin be in a healthy are many diseases of the hair, of which somecause it to fall out, others to shorten, and still others. Fig. 50. A human hair in its sheath, or follicle, magnified : H, the hair; M, themuscle; G, the oil-gland. 150 A HEALTHY BODY, cause the hairs to split. When we grow old. Naturefurnishes us with a crown of beauty/ not by givingus a dye to color the hair with, but by taking out the color of the hair and leav-ing it a beautiful gray or apure white. In the major-ity of cases, though notall, it is possible to tell towhat animal a hair belongsby its appearance underthe microscope. The Use of the Skin. The skin is of great service tothe body in many ways. Itprotects the delicate partsbeneath it; it throws offwaste products of the body ;it regulates the tempera-ture of the body ; it con-tains the hair and theorgans of touch.
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