The condition of plants in the house is a good test of home sanitation. If the leaves drop off, probably the rooms are overheated and the air too dry. There is some truth in the saying, “Where plants will not grow, people ought not to live.” The breathing of impure air causes a feeling of discomfort; the habitual breathing of bad air causes headache and lessens the resistance of the body to disease. =Impurities of air in homes.= Many conditions may help cause bad air in our homes; among these are mentioned overcrowding, oil stoves, gas stoves, and the kind of housekeeping which permits the accumulation of dust and waste. =Good ventilation.= By good ventilation we mean a sufficient supply of fresh air of suitable temperature and moisture, kept systematically in motion. Moving air serves a double purpose—that of bringing to us a fresh supply and of taking away the warm, moist, impure air by which we are surrounded. The best and simplest way to ventilate a room is to have one or two windows open at both the top and the bottom. During storms or in the winter time, ventilation may be secured by covering a wire screen with thin outing flannel. This allows the entrance of fresh air without drafts. [Illustration: IDEAL VENTILATION] =Drafts.= There is a superstition that colds are caused by drafts. As a matter of fact, moving air is a necessity, and drafts do not cause colds. Drafts, sudden chilling of the body, and dampness may be predisposing causes, but in themselves they will not produce a cold. Such conditions lower the general vitality of the body and favor the development of infection when the specific cause is introduced. =Temperature of air.= The temperature of the air has a very important bearing on health. The harmful effect of extremes of temperature has caused the death of many babies. The temperature of heated rooms, during the day, should be between 68° and 70°F. =Humidity.= By humidity we mean the moisture in the air. Many of the colds which occur in the winter are due to the dry air in homes and places of work. Extreme dryness irritates the mucous membranes of the nose and throat, and this irritation is favorable to the development of infection. Moisture may be added to the air in two simple ways: by keeping a dish of water on the radiator and by keeping plants in the rooms, for plants constantly throw off moisture. =Water.= The purity of the water that is used in the household, whether it comes from a public water supply or from a well in the country, is a question of great importance. Every housewife should know the source from which the water used in her household comes. Water is considered pure from the standpoint of health when it is free from pollution, color, odor, poisonous salts, and turbidity. Clear, sparkling water is not necessarily pure however. The purity of water can be determined only by analysis.