FROM 1915 until 1930, medical literature was filled with discussions concerning the necessity of the treatment of patients whose roentgenograms showed open cavities but who in other respects were relatively asymptomatic. In many instances such patients were offered little or no treatment. From 1925 to 1945 authors questioned the necessity of the treatment of minimal, but otherwise asymptomatic tuberculosis. Now all agree that such cases should be treated. In the early days after the discovery of streptomycin, antimicrobials were reserved for those patients who showed progressive pulmonary tuberculosis while under other forms of treatment. It was common to save chemotherapy until it was needed. Today, in any tuberculosis hospital, approximately 100% of the patients admitted, and proven to have tuberculosis, will be treated with chemotherapy. It is a well-established fact that a primary infection confers a certain degree of resistance to reinfection. The good effects of the primary infection have been so fully studied both in experimental animals and in humans, particularly in regard to the program of vaccination, that the deleterious effects have been frequently overlooked. A person who is a recent tuberculin converter undoubtedly has living tubercle bacilli in his body. No one has yet proven what happens to these bacilli either in the experimental animal or in the human. For years it was assumed, but without positive proof, that they slowly or rapidly died. It is now realized that while they may not multiply, they may remain dormant but living in the lymph node component of the primary complex.