In this preventive work, the nurse will be greatly aided if she knows what agencies she can call upon to reinforce her instruction. She must be familiar with all the forces of social service, and know how to reach them, and how to place her families in touch with them. Just as she must have sufficient knowledge of dietetics to suggest rice as a substitute for cabbage, bread instead of pie; so must she understand the social agencies within call, and know what substitutes they offer for the things that she condemns. A great gain will have been made if instead of the poolroom, the young boy can be given the Settlement club or gymnasium; or instead of the saloon dancehall, the young girl can be offered that of the schoolroom or the church. The aim should not be to deprive, but to substitute. Preventive work consists largely in teaching how to substitute the harmless for the harmful, the healthful for the unhealthful. In some communities, no such agencies exist; in others, they are inadequate to the needs they try to fill. But if they exist, they should be called upon. =Examination of the Family.= Every person constantly exposed to tuberculosis should be examined periodically, whether or not he presents symptoms. The nurse should endeavour to get all members of the patient’s household examined. This is sound in theory, but not always feasible in practice, especially when there are a large number of patients under supervision. When one is working with small numbers, with ten, twenty, or a hundred families, it might be possible to get every member of these households examined, but when one is working with large numbers it becomes proportionately difficult. In Baltimore some 5000 consumptives are annually dealt with by the Tuberculosis Division; if every one of these patients comes in contact with five other persons—a most modest estimate—that would give us a total of 25,000 people to bring forward for physical examination. This task would swamp our dispensaries and leave no time for anything else. After all, it is the positive rather than the potential cases which are a menace to the community. Thus, however much we may advocate the need for general examination of all exposed persons, this course has its drawbacks when it comes to actual practice. The best we can do is to get the suspicious cases examined. The examination of those who have no symptoms would furnish interesting statistics, but they are hardly dangerous enough to the community to warrant the outlay of time and energy.