The atmospheric air contains about four parts of carbonic acid gas to 10,000 parts of air. The exhaled air becomes quite heavily charged with this gas, about 400 to 500 parts in 10,000. It does not take long before the air in a closed, occupied room is so heavily charged with this gas and so poor in oxygen that its constant rebreathing is detrimental. The blood stream becomes poisoned, which immediately depresses the physical and mental powers. Warning is often given by a feeling of languor and perhaps a slight headache. People accustom themselves to impure air so that they apparently feel no bad effects, but this is always at the expense of health. The senses may be blunted, but the evil results always follow. To keep a house sealed up as tightly as possible in order to keep it warm saves fuel bills, but the resultant bodily deterioration and disease cause enough discomfort and result in doctor bills which more than offset this saving. It is poor economy. A constant supply of the purest air obtainable must be furnished to the lungs; otherwise the blood becomes so laden with poison that health, in its best and truest sense, is impossible. The air should be inhaled through the nose. It does not matter much how it is exhaled. The nose is so constructed that it fits the air for the lungs. The inspired air is often too dry, dusty and cold. The normal nose remedies all these defects. The mucous membrane in the nasal passages contains cilia, which catch the dust. The nasal passages are very tortuous so that during its journey through them the air is warmed and takes up moisture. Habitual mouth breathing is one of the causes of the hardening and toughening of the mucous membrane of the respiratory passages, for the mouth does not arrest the irritating substances floating in the air, nor does it sufficiently warm and moisten the inspired air. Irritation produces inflammation and this in turn causes thickening of the membranes. Then it is very easy to acquire some troublesome affliction such as asthma. Very cold air is irritating, but the passage through the nose warms it sufficiently. The evil results of mouth breathing are well seen in children, in whom it raises the roof of the mouth and brings the lateral teeth too close together. Then the dentists have to correct the deformity and the children are forced to suffer protracted inconvenience. This mouth breathing is mostly due to wrong feeding, especially overfeeding, which causes swelling of the mucous membrane, thus impeding the intake of the air through the nose and forcing it through the mouth. The chief curative measure is obvious. Cut down the child's food supply and give food of better quality. Remember that children should not be fat.