=Its uses.=--The skin, which seems like a very simple membrane in structure, is, in reality, a very complex and elaborate organ. With its numerous blood-vessels, lymphatic vessels, and nerves; its millions of _papillæ_ and pores and sweat ducts; its innumerable hair-follicles with their sebaceous glands and muscles; its odoriferous glands and special pigment-bearing cells, it is well equipped to perform the various duties assigned it. First, it serves to protect the softer parts of the body which lie underneath it. Secondly, it regulates the temperature of the body by preventing, on the one hand, the too rapid radiation of natural heat, and, on the other hand, by reducing the temperature through the process of perspiration. Thirdly, through its millions of pores, it is constantly throwing off the useless materials found in the excretions of the perspiration and the sebaceous glands. In order that the skin may perform its functions properly, it must be perfectly clean, the pores must be kept open, and the sweat glands free to throw off all the effete matter and prevent its accumulation within the system. While soap and water are necessary and helpful, free perspiration induced by vigorous bodily exercise or artificial heat will also enable the glands to cast off the more solid substances which accumulate at the bottom. An eminent French physician has discovered that the annoying odors from the skin which characterize certain persons have their seat in the bottom of the sweat sack, and can be successfully removed by free perspiration followed by a bath. In addition to the general benefits to the health, of systematic, vigorous exercise and the bath, they will give freshness of color to the skin, prevent the coming of wrinkles, and give to the face a beauty such as no paint or powder can approximate. If ladies with sallow complexions and shrunken countenances would substitute exercise and bathing for facial massage, the benefits of which last only so long as its use is continued, the results would be much more satisfactory. Many of the common diseases of the skin which destroy the beauty of the complexion are believed to be due to certain microbes. If the skin were kept, by exercise and bathing, in a thoroughly healthy condition, these microbes would find no lodgment, or, gaining a temporary foothold, would readily yield to judicious hygienic treatment. =The Hair and Nails.=--These, properly considered, are appendages of the skin. The hair follicles are hollow receptacles, from the bottom of which the hair grows. Alongside each hair follicle are two glands, called the sebaceous glands, which provide the hair with a natural oil or grease, and prevent excessive dryness. This sebaceous matter tends to keep the skin flexible, and serves to protect both skin and hair from the acridity arising from perspiration. The hair serves as a protection, shielding the brain from extremes of heat and cold, and moderating the force of blows upon the head.