This chapter discusses the causation of phthisis, and the factors which have produced the decline already secured in the death-rate from tuberculosis. To remove infection most completely people must have the earliest diagnosis of disease. The early recognition of an infectious disease is therefore the first step in preventive measures against it. The chapter outlines the indirect measures against phthisis, which in the aggregate are very important in its prevention. It considers the relation of poverty to phthisis. The chapter focusses on the teaching of hygiene, the removal of over-fatigue and mal-nutrition, the encouragement of alcoholic temperance, and of cleanliness, represents the practical issue of this investigation. It also considers the influence of housing. Alcoholism, like excessive fatigue, loads the circulation with toxic matter, diminishes the normal phagocytic action of the body cells, and makes the individual more prone to every form of infection, and especially to tuberculosis.