The disease occurs cesteris paribus in all geographical zones with uniform frequency; equatorial and subtropical regions are visited with consumption not less than countries with a temperate or an arctic climate. A damp subsoil is stated in all text-books of hygiene to be a most important cause of phthisis. The proved infectivity of the disease makes it somewhat difficult to adjudge what importance should still be attached to soil in relation to its causation. It is therefore desirable to summarise the evidence and to discuss it in the light of modern pathology. This chapter also shows the main results of Dr. Buchanan's research, arranging the towns according to the stated influence of sewerage works on the subsoil. Consumption is essentially a disease of crowded populations, of indoor occupations, transmitted by infection, favoured by the rebreathing of respired air, and by organic filth of all kinds.