(7) The close connection of consumption (phthisis) with a damp soil has been independently stated by Drs. Buchanan and Bowditch. Buchanan found that in the districts where improved sanitary arrangements had led to a drying of the soil, the death-rate from phthisis diminished; but where with sanitary improvements the soil was not dried, the death-rate from phthisis remained in one or two instances almost stationary. In Salisbury, Ely, Rugby, and Banbury, the death-rate from phthisis fell from 141 to 49 per cent. The amount of reduction in the death-rate from phthisis did not appear to be consistently proportional to the amount of drying of the subsoil. In a later investigation into the incidence of deaths from phthisis in the south-east of England, Buchanan came to the further conclusions that (a) there was less phthisis among populations living on pervious soils than among populations living in impervious soils; (b) less phthisis among populations living on high-lying pervious soils than among populations living on low-lying pervious soils; and (c) less phthisis among populations living on sloping impervious soils than among populations living on flat impervious soils. He, therefore, concluded that wetness of soil is a cause of phthisis to the population living upon it. (See also page [313]).

Drainage of the Soil.—There are two chief plans for rendering the soil drier—deep drainage and opening the outflow.

Subsoil Drainage should always be carried out by drains, separate from those for sewage. If the sewers are utilised for this purpose, their contents when full contaminate the surrounding soil. The subsoil drains should be composed of agricultural, i.e. unglazed, drain-pipes laid in towns in the same trench, but above the sewers, and they should discharge into the nearest water-course. If it is necessary to join them with a sewer, they should not pass directly into it, but into a disconnecting man-hole.

Opening the Outflow, in order that water may not remain stagnant in the soil, is occasionally required. This may be done by clearing water-courses, removing obstructions, and forming fresh channels.

The provision of sufficient surface-drains to carry off ordinary water and storm-water helps in drying the soil of urban districts.

Vegetation tends to diminish dampness of soil by causing rapid evaporation, and at the same time uses up the organic matter in the soil. Certain plants are more active in producing these effects than others: the Eucalyptus genus, including many species, and represented by the well-known blue-gum tree of Australia, is noted for its power in this respect; and the common sun-flower, which is very easy of cultivation, has a powerful influence in the same direction.

[CHAPTER XXXIV.]
CLIMATE AND WEATHER.

The Climate of a country has an important influence on the health and character of its inhabitants. The character of a climate depends on four main conditions:—