This clears the ground at once of a considerable amount of useless lumber in the shape of advice to train the child to keep his mouth shut. I have even known mothers who were in the habit of going around after their helpless offspring were asleep and gently but firmly pushing up the little jaw and pressing the lips together until some sort of an attempt at respiration was made through the nostrils. Advertisements still appear of sling-like apparatuses for holding the jaws closed during sleep. To attempt to stop mouth-breathing before providing abundant air-space through the nostrils is not only irrational, but cruel. Of course, after the child has once become a mouth-breather, even after the nostrils have been made perfectly free, it will not at once abandon its habit of months or years, and disciplinary measures of some sort may then be needed for a time. But the hundred-times-repeated admonition, "For heaven's sake, child, shut your mouth! Don't go around with it hanging open like that!" unless preceded by proper treatment of the nostrils, will have just about as much effect upon the habit as the proverbial water on a duck's back. No use trying to close his mouth by any amount of opening of your own. Fortunately, as does not always happen, with our discovery of the cause has come the knowledge of the cure; and we are able to say with confidence that, widespread and serious as are disturbances of health and growth associated with mouth-breathing, they can be absolutely prevented and abolished. What, then, is the cause of this nasal obstruction, and when does it begin to operate? The primary cause is catarrhal inflammation, with swelling and thickening of the secretions, and it may begin to operate anywhere from the seventh month to the seventh year. A neglected attack, or series of attacks, of "snuffles," colds in the head, catarrhs, in infants and young children, will set up a slow inflammation of this glandular mass at the back of the nostrils--a tonsil, by the way--and start its enlargement.