In spite of the amount of literature devoted to sanitary matters, it is astonishing how little is understood of the principles of ventilation, and its supreme importance to the general welfare. We do not, of course, refer to ventilation in its broadest scientific sense, such as the securing of an adequate air supply in large auditoriums, for it is a melancholy fact that even our prominent architects not only display a pitiably deficient grasp of that phase of the subject, but of the simple, yet fundamental principles of the science, which every intelligent adult should be familiar with. How many heads of families, for instance, can intelligently ventilate a sleeping room? They will open a window for a few minutes in the morning, without opening the door also, to create a current, and think that is amply sufficient to displace the accumulated carbon dioxide and other substances inimical to health. No wonder so many people are tormented by bad dreams! In sleeping apartments the bed should be in the center of the room--never near a wall. A current of air should be maintained, but without a draught upon the bed. It is better to open the window two inches at the bottom, and the same distance at the top, than to have it open for a foot either at the top or bottom only. If, through inclemency of the weather, or other causes, the window can only be opened for a few minutes, then by waving the door back and forth rapidly ten or a dozen times, the displacement of the vitiated air will be infinitely more rapid and thorough. Considering the length of time that is spent in the sleeping apartment, the paramount importance of a constant supply of fresh air is readily perceived. No matter how perfect digestion and assimilation may be, if the blood is not thoroughly oxygenated, the best of foods fail of their intended effect. Even the least fastidious would object to drinking water that had been used for washing purposes by others; yet it is quite as objectionable to breathe air that is charged with the waste products of bodies that may even be diseased. It is impossible to overestimate the importance of ventilation. Better let in cold air and put on more bedclothes, as long as you do not sleep in a draught. Oxygen keeps up the animal heat of the body, and you can really keep warmer in a room with plenty of fresh air than in a close room where the air is vitiated. But in the sick room fresh air is of paramount importance, not only for the patient, but for the attendants, who are otherwise compelled to inhale the poisonous exhalations from the diseased body. Let no consideration blind you, either in sickness or in health, to the imperative necessity of plenty of fresh air. The next great natural agency, and one to which scant attention is paid, compared with its hygienic importance, is Light, but more especially Sunlight.