The home constitutes the important part of environment for most persons, and for children in particular, since they spend the greater part of their time in or about it, and get there the foundation on which their health in later years depends. For persons employed away from home, industrial and occupational hygiene is hardly less important; but those subjects are too extensive to be considered here. Most people live where they must, and few have any part in planning the construction of their own houses. In choosing a house, however, one should remember that rooms where sunshine never enters are unfit for continued occupation. For children in particular fresh air and sunshine are essential, and it may be economy in the end to pay a comparatively high rent for an apartment having sunshine during at least a part of the day. Ignorance and carelessness, unfortunately, can spoil the best living conditions, and sometimes even in the country fresh air and sunshine are excluded from sleeping and living rooms. VENTILATION.--Ventilation has a direct bearing on health, although, contrary to former belief, the actual amount of oxygen in the air is not ordinarily the most important factor; even badly ventilated rooms contain more than enough oxygen to support life. The factors of prime importance in ventilation are temperature, humidity, air movement, and the number of persons in a given space since the greater the distance from one another the less is the probability that diseases will be spread. Room temperature should not be above 70° F. and, except for the aged or sick, it is better to be between 60° and 65°. Some moisture in the air is desirable; the amount needed is from 50% to 55% of the total moisture that the air can hold at a given temperature. We have no apparatus to decrease humidity in the air of houses, and in summer we are obliged to endure humidity, if excessive, no matter how uncomfortable we may be. But in winter the air in most houses is too dry, so that the mucous membranes of the nose and throat often become irritated and susceptible to infection. Most heating systems, particularly in small buildings, make no provision for supplying moisture. Keeping water in open dishes on or near radiators is often recommended, and would greatly improve the condition of the air, if people remembered to keep the dishes filled. The following is a simple but effective device to increase humidity: Roll an ordinary desk blotter into a cone about 8 inches in diameter at the base, and keep it constantly submerged for about one inch in a dish of water. The water rises to the top of the blotter and a large surface for evaporation is thus afforded. [Illustration: FIG. 7.] Stagnant air is harmful. Air should be in constant though not necessarily perceptible motion. Air about the body, if motionless, acts like a warm moist blanket, preventing the passage of heat from the body.