Today, tuberculous patients are being treated widely in general hospitals and at home rather than being isolated from society in special sanatoriums. Often, they are discharged from the hospital while tubercle bacilli can still be easily identified in their sputum. This practice has generated considerable concern in some quarters that tuberculosis might thereby be transmitted to unsuspecting persons.An understanding of the transmission of tuberculosis among human beings was slow to evolve, and practices were based largely on fallacious conclusions derived from studies of the problem among nursing and medical students from 1920 to 1940.1 It appeared that tuberculosis must . . .