This section is from the book "The Principles And Practice Of Modern House-Construction", by G. Lister Sutcliffe. Also available from Amazon: How Your House Works: A Visual Guide to Understanding & Maintaining Your Home.
The nature of building-sites from a medical point of view will be considered in a subsequent section. The architect's point of view may now be taken, and the first observation which the architect makes is that he is, unfortunately, very seldom consulted as to the site of a building; usually his employer comes to him and says: "Build me a house on this ground I have bought", and the architect must do what he can to make a habitable home, though the site be a bed of stiff clay or a swamp.
The mould or "humus" which usually forms the superficial layer of the soil warms with living organisms. Many of these are quite harmless to man, - indeed are Nature's scavengers, beneficial to man by reducing noxious organic matters to innocent inorganic pabulum for plants. Others, however, are pathogenic, and may cause disease in man, some when inhaled, some when received into the alimentary canal, and others only by actual inoculation. Miers and Crosskey enumerate four conditions as necessary for their life and growth - food (organic carbon and nitrogen), moisture, favourable temperature, and absence of inimical compounds. The architect can only concern himself with the first two conditions, food and moisture. These he may remove from a building-site, the former by excavation and the latter by subsoil-drainage; he must also, by means of impervious ground-layers and perfect walls and drains, prevent their subsequent access.