(5) In =rheumatic fever= I have similarly shown that the supposed connection between damp soil and this disease is erroneous, the disease being most prevalent, both in this and other countries, in years of exceptional drought. (6) =Epidemic or Summer Diarrhœa= has been supposed to have a special relationship with soil-temperature, Ballard having found that the summer rise in the mortality from this disease does not commence until the mean temperature recorded by the four-foot earth thermometer has attained somewhere about 56°F. The soil-temperature may be accepted as a convenient index of the conditions causing this disease. The disease I have elsewhere shown occurs most severely with a high temperature of the air and a deficient rainfall, and its fundamental cause is an unclean soil, the particulate poison from which infects the air, and is swallowed most commonly with food, especially milk. (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.