Towns often present one specially dangerous, and therefore specially objectionable soil--that where hollows have been filled up with refuse of all kinds. This refuse is made up of all kinds of vegetable, and, more or less, animal matter, often of the most noxious character, together with cinders, old mortar, and no one knows what besides. This becomes a foul fermenting mass, which is often built upon and the houses inhabited before the process of decomposition is completed, and the noxious gases cease to be given off. Many outbreaks of disease have been traced most unmistakably to this criminal act of putting up jerry buildings on pestilential sites. It is easy for any one to understand how this may be when he thinks of the way the house acts on the soil it is built upon, or rather on the moisture and gases contained in the soil. The house is warmed by the fires and by the people living in it, and the heated air has a tendency to rise. The pressure on the gases in the soil is lessened, and they are drawn up into the house, which acts as a suction pump. This could not happen if the foundation were air-tight; but this is rarely the case, and too often indeed “cottage property” is built without any foundation at all. Drs. Parkes and Sanderson recommended that such soil should not be built upon “for at least two years,” but it would be well to give it another year. Attention must also be paid to the “ground water”--the great underground sea of which we find evidences almost anywhere that we seek for them. Sometimes it is found even a foot or two only from the surface, in other places at 15, 20, or 40 ft. This water rises and falls in some places rapidly, rising after heavy rains, and falling in dry weather. If it is always near the surface, the place must be damp and unhealthy; and we should try to find out something about the ground water before fixing on the site of our house. If possible, do not live where it is less than 5 or 6 ft. from the surface. _Trees._--Vegetation assists in rendering the soil healthy. Trees absorb large quantities of moisture from the soil, and sometimes, as in the case of the blue gum-tree of Australia, they seem even to do something more than this. It is said that the common sunflower of our gardens has a considerable influence in this way. Trees should not be crowded close to a house, as they keep off much sun, and so neutralise some of their good effects, but at a reasonable distance they are beneficial.