Deviation of the nasal septum means displacement of the partition dividing the two nostrils, so that more or less obstruction exists. This condition may be occasioned by blows on the nose received in the accidents common to childhood. The deformity which results leads in time to further obstruction in the nose, because when air is drawn in through the narrowed passages a certain degree of vacuum is produced and suction on the walls of the nose, as would occur if we drew in air from a large pair of bellows through a small thin rubber tube. This induces an overfilling of the blood vessels in the walls of the passages of the nose, and the continued congestion is followed by increased thickness of the lining mucous membrane, thus still further obstructing the entrance of air. A one-sided nasal obstruction in a child with discharge from that side leads one to suspect that a foreign body, as a shoe button, has been put in by the child. Polypi are small pear-shaped growths which form on the membrane lining the nasal passages and sometimes completely block them. They resemble small grapes without skins. These, then, are the usual causes of mouth-breathing, but of most importance, on account of their frequency and bearing on the health and development, are adenoids and enlarged throat tonsils in children. Adenoids and enlarged tonsils are often due to inflammation of these glands during the course of the contagious eruptive disorders, as scarlet fever, measles, or diphtheria; probably, also, to constant exposure to a germ-laden atmosphere, as in the case of children herded together in tenements. =Symptoms.=--The mouth-breathing is more noticeable during sleep; snoring is common, and the breathing is of a snorting character with prolonged pauses. Children suffering from enlarged tonsils and adenoids are often backward in their studies, look dull, stupid, and even idiotic, and are often cross and sullen; the mouth remains open, and the lower lip is rolled down and prominent; the nose has a pinched aspect, and the roof of the mouth is high. Air drawn into the lungs should be first warmed and moistened by passing through the nose, but when inspired through the mouth, produces so much irritation of the throat and air passages that constant "colds," chronic catarrh of the throat, laryngitis, and bronchitis ensue.