The exact measure of institutional segregation of phthisis is the ratio stating how many of the total days of sickness is passed in institutions. In England and Wales, in the period 1866-1903, segregation measured by the fraction of total deaths occurring in institutions has approximately doubled, and the death-rate from phthisis has approximately halved. Workhouse infirmaries have been the most important agency in segregation. In London exactly the same has happened; measured by the fraction of the pauper population treated in institutions, the amount of segregation has more than doubled. There is, however, unanimous and conclusive evidence that the quality of the segregation is notably inferior in Ireland to that given in England or in Scotland. The reduction of phthisis in Copenhagen, therefore, has been associated with a large amount of institutional treatment of the disease in general hospitals. In the cities of the United States a considerable and increasing proportion of cases of phthisis are institutionally treated.