Koch teaches on a priori grounds that direct infection has a preponderating influence on the prevalence of phthisis. Prior to 1884 when Koch's discovery of the tubercle bacillus was first fully set out, suspicion of infectivity had no notable influence on medical or public action. This chapter provides tabulation for giving the quinquennial percentage decline of the phthisis rate before and since 1885 in England and Wales and in Scotland. As the matter stands, there is no evidence of a causal connection sufficiently large to be traceable between the decline of the phthisis death-rates and the progress of education in hygienic matters. The action taken in consequence of knowledge of the infectiousness of phthisis has doubtless varied greatly in different countries and in different parts of the same country. Sanatorium treatment, furthermore, has, with the exception, been employed chiefly for well-to-do patients who from the public health standpoint need it least.