We should, therefore, always keep a window open and never close the ventilator. Fresh air is the thing we are most in need of to carry on the oxidizing processes in our body. Exclude this and you exclude health. We must also remove from the rooms all those things which can absorb the air or hinder its entrance. There should never be flowers, and particularly no potted plants, in a living room, as they require air like ourselves; while to sleep in a room with plants is very deleterious (see chapter on sleep). Curtains should all be removed, especially those of a heavy nature and dark color, which would prevent the entrance of the beneficial sunshine. Every room should be provided with openings for ventilation, and the transoms used in America are especially useful when they are open, and not used only to let the electric light into the sleeping room during the night, thus disturbing sleep. As a close room tends to shorten life it should be the policy of the government authorities never to allow the use of any newly built house, especially of public buildings, unless it contains openings for ventilation, the closing of which should be very severely punished by law. If, during the day, it is necessary to have fresh air in every room, there is still greater necessity for this during the night, as we require more air during sleep than while awake; and, therefore, we should never sleep in a room that is entirely closed, but always leave the window (the upper part by preference) or the ventilator open. We can easily convince ourselves how injurious it is to sleep in a close room by leaving our room in the morning, taking a walk in the fresh air, and then re-entering our sleeping chambers that have remained closed as we left them, and we shall at once realize the unhealthy condition of the air in such a room, filled as it is with carbonic acid that has been exhaled during the night, and also loaded with the other deleterious toxic substances cast off by our lungs and skin. We shall then certainly make up our minds not to inhale during the next night the same air again, but to allow it to escape by the open window and thus permit the entrance of fresh air into our lungs, whose need for air is much increased during sleep in order to replace the large volume of carbonic acid exhaled. As a consequence of passing the night in such a close room, we feel, on the following morning, very heavy, and often have a headache; we also often have no appetite for breakfast after such a night, unless we first take a walk in the fresh morning air.