This chapter considers the experiences of large communities over long periods of time, and compares the variations in the figures measuring the incidence of tuberculosis and those, where they can be obtained, which measure the variations in the element of experience under consideration. Communities may be grouped most broadly according as they are urban or rural, and the experience now to be examined shows the remarkable result that urban conditions have promoted the prevalence of tuberculosis. In Birmingham and Sheffield the female death-rate from phthisis is actually lower at most ages than that in England and Wales as a whole. The chapter shows that enormous changes have occurred both in the extent of urbanisation and in the prevalence of phthisis in each of the countries examined, and that in every country town life has been associated with a greater prevalence of tuberculosis than has country life.