A thousand feet of air space where the air is constantly renewed, is necessary for a healthy adult; a sick person should have two or three times as much, because with them there is increased susceptibility to draughts. Be very careful that the sick are not placed so that a direct current of air can blow on any part of the body, but either by the use of fans or in some other way the air must be renewed around their bed. VENTILATION. The problem to be solved is, how can fresh, pure air be best supplied? The inequalities of temperature within and without the room produces some natural ventilation, as this sets the air in motion and effects an exchange of air, if there are some apertures around the doors and windows. This, however, is seldom sufficient, and artificial ventilation is often necessary. An open fire is a good apparatus for this purpose. The draught which it creates carries the air from the room up the chimney, while a fresh supply is drawn in to take its place. This supply should be from the outward air, or from an adjoining room in which the air is not contaminated. The inlets and outlets for air should be of equal capacity, on opposite sides of the room, and of different heights to secure thorough ventilation. They should be as far as possible from the patient and from each other. In cold and damp weather great care is necessary to keep the air fresh and wholesome and at the same time to avoid chilling the patient. But even in cold weather the doors and windows may be thrown open for a minute at a time, if the patient is at the time protected by additional clothing. However, during the night and in cold and wet weather, the principal supply of air will be from an adjoining room, air that is warmed, but it should be as pure as possible. When the weather is cold, and especially the latter part of the night, have more heat in the room and not less fresh air; if needed give your patient additional clothing and foot warmers. The windows may be thrown open once or twice a day in cold weather, if the patient is protected by putting additional clothing on the bed, and using some sort of a screen, (an umbrella may be used for a screen), as a protection from the cold and direct draughts. But as the contamination of the air continues, the purification of it should be equally so, and some fresh air must constantly be admitted—some device used for the purpose. The window may be raised two or three inches and the aperture closed with a board, then the air will find admittance through the opening between the two sash; or when the window is raised three inches, a board six inches wide may be placed on the window sill a little inside of it; thus there will be an aperture both at the top and bottom of the lower sash. Or the upper sash may be lowered a little. The current of air which comes in (this is usually the lower one) should be directed upwards.