Heating and Ven'tila'tion. The condition of the atmosphere is houses and public buildings is of such importance to health and vigor of mind, that heating and ventilation are receiving more and more attention as sanitary science is better understood. The lack of proper care has been the cause, and it is still responsible, for an incalculable amount of human disease and suffering. The temperature which is usually considered best in a room whose occupants are not engaged in any exercise varies from 68degree to 70degree Fahrenheit. Individuals may require higher temperature, but overheated rooms are responsible for much sickness in cold weather, because of the inevitable sudden changes experienced in passing in and out of doors. On the other hand, too low a temperature is injurious, especially to those who are sitting quietly. Ventilation is a means of renewing the atmosphere in rooms and of maintaining its purity by driving out foul air and admitting fresh air without drafts. Carbonic acid gas, which is breathed from the lungs of all animals, is destructive of health if breathed again into the lungs. Moreover, the human breath pollutes the air with small quantities of ammonia and with organic matter, especially bacteria, and so tends to make the atmosphere not only unpleasant but dangerous for respiration. Authorities disagree in estimating the amount of pure air necessary for an adult, but it is generally admitted that not less than one thousand cubic feet of fresh air per hour should be allowed for each healthy person. Invalids require from three to four times as much. It is possible, of course, to secure change of air in a room very quickly by throwing open doors and windows, but the sudden change in temperature and the resulting drafts are dangerous to the occupants. Accordingly, in all living rooms some provision must be made for the removal of foul air and the introduction of fresh air. Heating and ventilation are so closely allied that they must be considered together. One of the earliest methods of heating rooms was by the open fireplace, and this still remains an excellent method, though the waste of heat is considerable. It was this waste, in fact, that led to the introduction of closed stoves, first made of earthenware and then of metal. These are now constructed in an infinite number of varieties and are commonly in use throughout America and in Europe. They do save fuel, but in so doing they have prevented the ventilation which fireplaces gave and are liable to overheat the rooms and render the air too dry. Other methods of heating are now generally in use. Air-tight furnaces, surrounded by jackets, connected by pipes with different parts of the building, from which return shafts bring foul air into the furnace proper, are very generally in use. In such cases a conduit from the open air leads a supply of pure air inside the jacket of the furnace. In other systems, steam and hot water are forced through pipes to all parts of buildings by heat, and this forms an effective way of warming the rooms, though a separate system of ventilation must be used to make either steam or hot water satisfactory. From their superior neatness and cleanliness, steam and hot water seem to be gradually displacing the hot air systems. Proper heating and ventilation is one of the most serious problems that confronts the teacher in small schools. Usually large stoves are placed in the room, and these make the temperature too high for the children sitting near them before the air in the remote portions of the room is warm. Such stoves should be surrounded by a jacket of tin or sheet iron, reaching from the floor to a point some distance above the heads of the children. A pipe laid from the outer air, under the floor and through an opening beneath the stove, will give a supply of pure air which, as it is heated by the stove, will be forced up into the room. Provision should be made to carry away the foul air from near the floor in some part of the room distant from the stove. If it is impossible to have the stoves fitted up as described, a screen may be used to protect those sitting near the stove from the heat, and a supply of pure air may be admitted by fastening a board six or eight inches wide at the bottom of the window casing, so that it fits tightly into the space, and then raising the window about four inches. The air is then deflected upward and away from persons sitting in the room.