Overcrowding must l>e regarded from two points of view. The individual requires a certain amount of airspace for the due preservation of his health. Therefore, too many people must not be crowded into a single room. The population of a town district requires a sufficient amount of fresh air and sunlight. Therefore, too many rooms must not be crowded into a limited area by increasing the height of the buildings, even though each room contain only its due number of inhabitants. The violation of these rules leads respectively to what are known as lateral and vertical overcrowding. As regards the former, the Model By-law suggest 300 cubic feet per head as the minimum air-space for dwelling-rooms. Various building acts and by-laws regulate the height of buildings in relation to width of streets, and also the amount of air-space to be left at the backs of houses. The evils of overcrowding are mainly those of deficient ventilation already alluded to. Statistics show very clearly the relation between a high death-rate and density of population. But it must be borne in mind that in these eases it is not merely overcrowding which is to blame: other insanitary evils are commonly also present, and it is the poorest class, badly-clad and ill-fed, which commonly inhabits an overcrowded area.

Dirt has a good deal to do with the production of disease, and this in several ways. Uncleanliness of person prejudices the health of the individual by impeding the free action of the skin, and not only his own health but that of those around him, by increasing the amount of organic effluvium in the air. A dirty person is more likely than a cleanly one to carry about with him the germs of infectious disease. The value which is attached nowadays to personal cleanliness is shown by the increased demand for bathrooms in house's, and there can be no doubt that a daily bath largely increases the robustness of the individual and his capacity for resisting disease. Un-cleanliiKas <>f the dwelling produces much the same effects as personal unclean-ness, and is usually associated with it. Dust and dirt are media which harbour the germs of disease: soap and water, fresh air and sunlight, are the cheapest and most effective disinfecting agents. In the construction of hospitals it is now common to round off all angles at the junction of wall and floor, and to lay down parquet floorings which leave no wide cracks in which dirt can accumulate. In this way a serious source of danger is avoided. Dirt in houses consists largely of organic matter, some of which is liable to decomposition, whereby the impurity of the air is increased. The condition of an ash-pit which has remained long unemptied may be repeated in miniature in the unswept corner of a room. Of the grosser forms of uncleanliness in dwelling-houses there is scarcely need to speak here; the points upon which stress should be laid are the removal of all dust and dirt, and the avoidance of everything which can harbour them.