To repeat, hygienic perfumery has to deal with such substances as have really a favorable effect on health. No one will deny that soap takes the first place among them. Soap promotes cleanliness, and cleanliness in itself is essential to health. But it would exceed the scope of this work were we to treat in detail of the manufacture of soap and its employment in the toilet; we must confine ourselves to some specialties exclusively made by perfumers and into the composition of which soap enters. We do so the more readily since perfumers are but rarely in a position to make soap, and in most cases find it more advantageous to buy the raw material, that is, ordinary good soap, from the manufacturer and to perfume it. Next to soap in hygienic perfumery stand the so-called emulsions and creams (crêmes) which are excellent preparations for the skin and pertain to the domain of the perfumer. The human skin consists of three distinct parts: the deepest layer, the subcutaneous cellular tissue which gradually changes into true skin; the corium or true skin (the thickest layer); and the superficial scarf skin or epidermis which is very thin and consists largely of dead and dying cells; these are continually shed and steadily reproduced from the corium. The skin contains various depressions, namely, the sudoriparous glands which excrete sweat; the sebaceous glands which serve the purpose of covering the skin with fat and thereby keep it soft, glossy, and supple; and lastly the hair follicles which contain the hairs, an appendage to the skin. The main object of hygienic perfumery with reference to the skin is to keep these glandular organs in health and activity; it effects this by various remedies which, besides promoting the general health, improve the appearance of the skin. As a special group of preparations is intended exclusively for the care of the skin, so another class is devoted to the preservation of the hair, and still another to the care of the mouth and its greatest ornament, the teeth. Accordingly the preparations belonging under this head will be divided into three groups—those for the skin, the hair, and the mouth. CHAPTER XX. PREPARATIONS FOR THE CARE OF THE SKIN. GLYCERIN. Pure glycerin is a substance that has a powerful beautifying effect on the skin, by rendering it white, supple, soft, and glossy; no other remedy will clear a sun-burnt skin in so short a time as glycerin. An excellent wash may be made by the perfumer by mixing equal parts of thick, colorless glycerin and orange-flower water (or some other aromatic water with fine odor), possibly giving it a rose color by the addition of a very small amount of fuchsine. Concentrated glycerin must not be used as a wash, because it abstracts water from the skin and thereby produces a sensation of heat or burning.