“In order to have good ventilation, provision should always be made for a _circulation of air_. It is not sufficient to provide an entrance for outside air; exit through an opposite door or window or flue should also be secured. A good way to do this is to let down a window two or three inches at the top, and the air thus let in becomes somewhat warmed by the heat which rises. Here then you have warm fresh air. Now bad air, being loaded with carbonic acid gas, sinks to the bottom of the room. Some way must therefore be provided for its escape. A transom near the bottom of the door would answer the purpose; an open fireplace furnishes an outlet for impure air, or if both these are wanting, the door may be left slightly ajar, or a simple or inexpensive ventilator may be made by fitting into the stove-pipe, above its damper, another piece of pipe that shall be cut off within two inches of the floor; this pipe also to be provided with a damper which can be opened at will. A very effective draft is thus created near the floor, which takes all foul air up into the chimney. “I do not approve, on the contrary I condemn the habit of sleeping, even in the coldest weather, in a small room, windows closed, weather strips on the doors and sashes, and every possible device used to keep out the outside air. In such a room one must necessarily respire the same air many times, and the fact that it is cold does not make it the less injurious. Nature throws off by the breathing process certain poisonous elements which to re-breathe and re-absorb is most pernicious. No one who is not robust should sleep in a room so cold that the windows and doors must all be closed to keep warm. A much more healthful way is to have the temperature of the sleeping room the same as that of the living room; under no circumstances do I deem it advisable for an invalid to sleep in a room that can not have pure, warm air. “Remember that the important point is _circulation_, and that this may be had without letting in a great volume of cold air.” A small amount of outside air can be let into a room by raising the window four or five inches and fitting a board at the bottom. There is a space left between the sashes that allows some air to enter. This, however, is not sufficient in a small bedroom, unless for the coldest weather. “The only objection to a draft is, that the draft is generally not strong enough. An influx of fresh air into a room is a ray of light into darkness, a messenger of Vishnu visiting an abode of the lost.” Even the weak and enfeebled can accustom themselves to plenty of pure air, and also to drafts.