Being a physician and by training accustomed to view problems from a medical standpoint, it is natural that I should emphasize the attacks upon the bacillus. As I have said, it seems to me to be firmly established that the most efficient, the most direct, and the cheapest way to enforce isolation and prevent infection is by hospital segregation of cases of advanced pulmonary tuberculosis. While early diagnosis, sanatorium treatment, and education are valuable features of the campaign, their value will be but slight if this one essential feature is neglected. Indeed I am inclined to see the chief value of economic improvement in the indirect influence this improvement exercises upon the facility for infection. With economic advance the æsthetic value of general and personal hygiene grows apace, and the dictates of ordinary cleanliness offer a very strong barrier to infection. Poverty itself does not produce tuberculosis, but the conditions that poverty fosters do, and the advantages of better living reside not so much in an improved personal fitness as in the eradication of the conditions that facilitate infection. This view is in accord with what we have learned of other infections. Plague has been notoriously a scourge to the poor. To improve living conditions lessens plague, and this general fact was known before we learned that cleanliness produced results indirectly by eliminating rats. Malaria has always been particularly prevalent amongst labourers living in unprotected huts. To improve living conditions reduces malaria, but we gain the result more surely and directly by an intelligent campaign against mosquitoes. Unfortunately, we are not sufficiently instructed about tuberculosis to pick out of the whole mass of ills that poverty entails those few essential features that control infection. Perhaps some day we will, and then we shall be able to manage the social campaign more efficiently and economically. For instance, we are quite at sea to know what prophylactic use to make of the firmly grounded fact that tuberculosis infection establishes a strong resistance to reinfection. Upon an analogous principle rests the conquest of smallpox by vaccination. No doubt this immunity reaction has an important influence upon the development of tuberculosis, but as yet we know too little about it to control it and use it to advantage in our fight with the disease.