If there is freedom of choice as regards the site of a schoolhouse or similar building, the top of a small elevation is to be selected. Such a position affords the best natural drainage, removes dampness, avoids inundations, gives full sunlight and the purer air. The top of a high hill may be too exposed to the wind. Next to the top of a knoll, the southerly slope of a hill is to be chosen. The building should not be overshadowed by a hill, especially on the western side. Trees are not to be planted close to a building in which children live, and ivy and similar plants should not be permitted to cover the walls. If a building is set in a hollow it will be surrounded with chill air and mists in the cold seasons, even if a costly drainage system keeps the cellar and basement dry. A gravelly or sandy soil beneath a building is the best, provided this soil is not already saturated with organic matter, or is not close above a dense layer of clay or rock. Clay, marl, peat, and made soils should be avoided if possible, because they are full of organic matter; they are cold, and they infect the ground air. Rock does not make a good building site--its seams carry water. {203} The subsoil should be drained four or six feet below the cellar floor, and this floor is to be laid in concrete and cement. At the level of the ground there should be a course of hollow vitrified brick to exclude dampness and to give ventilation. Limestone walls conduct more heat in and out than an equal thickness of glass, bricks, plastering, and wainscoting. The porosity of the building material determines the interchange of the air through the walls, and it affects the temperature of the rooms. If there is water in the pores of the walls heat is conducted rapidly, but air is not permitted to pass. Brick as a building material has many disadvantages, but on the whole it is best for schools, and it resists fire better than most stones. The harder the brick the better it is--vitrified brick is the best. Hard-pressed brick of a light colour makes an excellent outer wall-surface. It is very doubtful that sewer gas escaping into a house will directly carry the micro-organisms of diseases like typhoid and diphtheria, but such gas is poisonous, depressant, and it renders the inmates of a house liable to disease; lessens their power of resistance. The typhoid bacillus and other bacteria can, of course, be carried into a cellar by the seeping in of drainage water. Infants kept in the upper story of a house in hot weather are more liable to intestinal diseases than are those that live on the lower floors, but here the weakening agent is heat. Tuberculosis, scrofula, rheumatism, neuralgias, bronchial, and kidney affections are made worse in damp houses.