SKIN, CARE OF.—From the detailed description given in the INTRO DUCTORY CHAPTERS (pp. 110-115), it will be seen that the human skin is an extremely complicated organ. It regulates the temperature of the body and the circulation of the blood, and serves as an avenue for the excretion of consumed or harmful products. It probably plays a part also in the respi ratory functions. Disturbances of the activity of the skin will bring about the most important consequences for the entire body ; and what is usually designated as " general good health " depends, to a great extent, upon the condition of the skin.
The healthy skin has a certain uniform colour, which is composed of a blending of the red colour of the blood, the yellowish blonde of the line wool hairs, and the alabaster-\ hite tinge of the numerous microscopic scales which are constantly cast off from the horny layer. The colour of the skin of different parts of the body may vary between all shades from white to dark brown. This depends upon the amount of blood contained in the different parts, and also upon the presence of certain pigments (originating in the blood) in the deep layers of the skin. According to the character of these pigments, certain radical differences are recognised. The peculiar gloss of the skin, which is different in the different parts of the body, is brought about by fatty substances secreted by millions of minute cutaneous glands, and is modified by innumerable, very fine wool-hairs. These wool-hair. grow very close together on the so-called " hairless " parts of the body ; and by their refraction of the light, they produce a soft, shining, velvety lustre.
The surface of the skin, being very large, it is not surprising that certain diseases (particularly those of the blood or of the kidneys) may often be recognised by reason of alterations in the appearance of the skin (see Plate XIV.). The peculiar lustre of the skin in chlorosis is absolutely distinctive. It is indicative of the blood's poverty in red colouring-matter, as well as of changes in metabolism. A bluish skin, recognisable especially by blue lips and cheeks and by the bluish appearance of the otherwise white crescents of the nails, points to the presence of an excessive amount of carbon dioxide in the blood. This condition may occur as a result of deficient or
impaired respiratory functions, and in sluggishness of the circulation of the blood (cyanosis). Bronzed skin occurs in affections of the suprarenal bodies ; while a greyish colour is clue to excessive use of silver for internal medication, or to silver-poisoning in workmen who handle the metal. A yellowish colour is produced by diseases which interfere with the discharge of bile. Malignant tumours also impart to the skin a peculiar and characteristic pallor. A peculiar, sallow paleness, combined with dryness, which gives the skin a withered appearance, and in which dark wrinkles become noticeable (par ticularly around the eyes), is sometimes characteristic of more or less severe nervous disturbances. The bluish colour sometimes noticed on the lower eyelids is due to the fact that these parts are not provided with cushions of fat, wherefore any reduction of blood-pressure readily becomes noticeable. Such reduction of blood-pressure may be due to hunger, mental or psychic emotions, dissipation, etc. These rings under the eyes are, therefore, usually indicative of mental or bodily exhaustion. Simple fatigue may call them forth.
When the necessary fatty substances of the skin are secreted in insufficient quantities, the skin may become chapped, and peel off. In very cold weather the skin is likewise apt to become brittle and fissured, either because the watery excretions are prevented from evaporating, or because the fatty substances. instead of liquefying, become hard and render the skin dry.
Frequent irritation as by chemicals, soap, lye, warm and moist air, etc.—renders the skin red. This is particularly noticeable in the hands, where the blood supply is very abundant. In persons who have very sensitive skin, redness of the hands may be due merely to a special irritability of the readily dilatable vessels of the skin. In such cases the difference between the temperatures of the covered and the uncovered parts of the skin suffices to cause a noticeable redness of face and hands. Distinct lines of demarcation between the white skin of the covered and the darker skin of the uncovered parts are noticed on the neck and arms of most persons.