No reason can be assigned, based on our present knowledge of bacteriology, why upturned earth or manured fields should be unhealthy except as the breeding of insects may be encouraged thereby. The two essentials, however, which should be considered are: first, the topography or the formation of the soil in order that the surface water may run off freely, and second, the character of the soil so that ground water may not remain too near the surface. Whether the soil is rock or gravel makes very little difference. _Made ground._ One kind of soil, however, is distinctly objectionable, although, fortunately, in the country such a soil is unusual: That is, a soil made up of refuse, whether it be garbage, street sweepings from a near-by city, or factory refuse. The writer has in mind one enterprising landowner and farmer who offered a near-by city the free privilege of dumping the city garbage on his land. This was done for several years, and the low-lying districts of his farm were all filled to a more advantageous level. This garbage was then covered with about a foot of dirt and the land sold in building lots to enterprising laborers determined to own their own homes. According to the old theories of hygiene, the occupants of such houses should have died like rats, but no particular excess of sickness in the one hundred houses so located could be observed. One must, however, believe, as we shall see later, that the repeated breathing of air drawn from such polluted soil must be unhealthy, even though the mortality records fail to show it. It is interesting in this connection to note that the organic matter in soil gradually disappears, just as a body buried in a grave will finally decompose. Experiments show that such organic matter as wheat straw or cloth in small pieces rots and decays in about three years. But this depends very largely on an excess of air. If the soil is open and the organic matter loose, oxidation takes place rapidly; but if a large pile of organic matter is buried in clay soil, it will take decades for it to disappear. The vegetable matter in soil is usually produced by the decay of plants which have either grown on the soil or have been washed down into its voids. A great deal was formerly written on the relation between this organic matter and the prevalence of malaria, and some earlier writers believed that the amount of malaria in a district was dependent upon the amount of vegetable debris in the soil. Since we have learned that malaria is carried by mosquitoes, we are less interested in the amount of organic matter in the soil. Its mere presence is not likely to be injurious. _Water in the soil._