Of much importance is the selection of a locality where good and pure water can be easily procured, as otherwise disastrous consequences are sure to follow. The soil should be of a light and porous character, easily permeable by water, and free from the decomposing remains of excretions of man or animals. There is much reason for the belief also that the level of the ground-water plays a somewhat important part in the salubrity of any given locality, and it is generally considered that this should be at least ten feet below the surface. It is generally thought, and probably with truth, that those sites are most healthful which have their location on a basis of granite, or other rock-foundation; in such localities there is usually a considerable slope of the general surface of the ground, with the result that water rapidly runs off after rains, and consequently stagnant pools, which might serve as a breeding place for mosquitoes and bacteria, do not form. Soils through which water easily permeates are likewise, as a rule, healthy, though this depends in a measure upon whether or not they contain a very considerable proportion of vegetable matter. Clay foundations are healthful where there is a considerable slope to the surface of the ground, but where this does not exist the soil is damp, owing to its impermeability, and often has stagnant pools upon its surface. Marls and alluvial soils are not regarded as being wholesome, but it is not unlikely that their bad reputation is largely due to the fact that they generally exist in the neighborhood of rivers and other considerable bodies of water where mosquitoes are numerous. There are no reasons going to show that cultivated lands are unhealthy--even where they receive yearly abundant additions of manure. Where it is necessary to build in damp localities the site should be thoroughly drained, and the space upon which the house is constructed should be carefully covered with some impermeable cement. _Building Materials._--Of all building materials, the one most commonly employed in America is wood. This arises from the fact that in the past we have had unlimited quantities of timber from which lumber could be procured at a price so reasonable that no other material could ordinarily be considered. That the wooden house has some advantages cannot be denied; its walls rapidly cool following the torrid days that so commonly occur during the summer in almost all portions of the United States, and it is usually well ventilated as a result of the numerous fissures naturally existing in its structure.