Though pneumonia is commonly believed to be due to exposure to cold or wet, like colds, it has very little to do with these. You will not catch pneumonia after breaking through the ice or getting lost in the snow, unless you already have the germs of the disease in your mouth and throat, and your constitution has already been run down by bad air, under-feeding, overwork, or dissipation. Arctic explorers, for instance, never catch pneumonia in the Frozen North. CHAPTER XV THE SKIN OUR WONDERFUL COAT What the Skin Is. The skin is the most wonderful and one of the most important structures in the body. We are prone to think lightly of it because it lies on the surface, and to speak of it as a mere coating, or covering--a sort of body husk; but it is very much more than this. Not only is it waterproof against wet, a fur overcoat against cold, and a water jacket against heat, all in one, but it is also a very important member of the "look-out department," being the principal organ of one of our senses, that of touch. The eyes in the beginning were simply little colored patches of the skin, sunk into the head for the purpose of specializing on the light-rays. The smelling areas of the nose also were pieces of the skin, as were also the ears. Not only so, but--although it is a little hard for you to understand how this could have happened--the whole brain and nervous system is made up of folds of the skin tucked in from the surface of the back; so that we can say that the skin, with the organs that belong to it and have grown from it--the eyes, nose, ears, brain, and nerves--forms the most wonderful part of the body. Everything that we know of the world outside of us is told us by the skin and the look-out organs that have grown out of it. The skin is not only the surface part and coating of the body, far superior to any six different kinds of clothing which have yet been invented, but it is related to, and assists in, the work of nearly half the organs in the body. Not only all that we learn by touch and pressure, but everything that we know of heat and cold, of moisture and dryness, and most of pain, comes to us through our skin, through the little bulbs on the ends of the nerve twigs in it. It also helps the lungs to breathe, the kidneys to purify the blood, and the heart to control the flow of blood through the body. A healthy skin is of very great importance; and part of this health we can secure directly, by washing and bathing, scrubbing and kneading and rubbing, because the skin lies right on the surface, where we can readily get at it. But, on the other hand, no amount of attention from the outside alone will keep it healthy. All the organs inside the body must be kept healthy if the skin is to be kept in good condition. Although the external washing and cleaning are very important, the greater part of the work of developing a healthy skin and a good complexion must be done from the inside.