The main living rooms should be so arranged as to admit the direct rays of the sun some time during the day. This can best be accomplished when these rooms are on the southeast. Each room should be so arranged with respect to window space that there will be ample lighting and proper ventilation of the whole house. Care must be exercised, however, that there is not too much window space which will give excessive heat in summer or too much cold in winter. In large dwellings there is a tendency for the halls and stairways to be poorly lighted and poorly ventilated. This should not be. Ample provision supplying light through windows, and ventilation from the outside should be made to insure plenty of light and air. Bedrooms should be well lighted and if possible direct sunshine should be admitted some time during the day, preferably in the morning. Soil The soil bears a close relation to health. The porous soils such as sand and gravel are considered the most healthful because they are driest. But there are objections to these, since they are easily polluted by leaky drains and cesspools, and are capable of holding a notable volume of ground water and ground air. Such air is almost invariably impure. The rain percolates through the soil until it reaches an impervious stratum which prevents it from penetrating any further, and it is held in the interstices or interspaces of the soil and forms the ground water. Ground Water and Ground Air There is a certain fluctuation of ground water and ground air. As the water rises the air is forced out of the ground, and as it recedes air is drawn in to occupy its place. There are other factors which influence the ground air, such as the perflating action of the wind and certain climatic changes. Thus the ground may be spoken of as breathing. If the ground water is near the surface the ground air will be noticeably moist and will produce a dampness of the atmosphere which will result in a decided cooling of the air by evaporation. If the ground water is deep the ground air will be comparatively dry, although the ground near the surface is generally moist owing to the capillary attraction and evaporation from the surface of the ground water. For this reason it is important that damp soils be properly drained to permanently lower the level of the ground water. This may be accomplished by properly laid tile. This will reduce the fluctuation of the ground water since it will be carried off when it rises to the level of the drains. In this way the ground air will not be forced out into the breathing zone to pollute the atmosphere.