The main channel of infection in respiratory diseases, and especially in pulmonary tuberculosis, has confused scientific men for a long time. An effort to avoid infection, especially in the acute diseases, has led to the introduction of many methods of protection, the latest of which is the gauze mask. As complicated as this problem has been in the study of the acute respiratory diseases, it has proved even more baffling and confusing in pulmonary tuberculosis, which disease accounts for at least three fourths of the deaths attributed to the tubercle bacillus. Much of the confusion is of course due to the improper comprehension of the problem at hand and the application of unpractical methods of experimentation and conclusions drawn therefrom. Thus have been overemphasized at intervals prenatal infection, alimentary infection and other phases.
The problem that confronts us in the prophylaxis of pulmonary tuberculosis, though differing slightly, is practically the