No disease is so serious as tuberculosis, whether with respect to morbidity or mortality. Consequently, it has been studied more intensely anatomically, clinically and experimentally than any other disease. Physicians have advanced some distance in the investigation of the disease; they know its cause, its most important anatomic forms and its manifold clinical appearances. They are aware of its curability—in all stages, all ages and all localizations; they know that even a tuberculous meningitis now can be cured. They also have had their eyes opened to the chronicity of the tuberculous infection and of the tuberculous diseases. A pulmonary tuberculosis can last not only through years but also through decades and indeed through the whole of a long life.
Many questions concerning tuberculosis still remain obscure; for example, the importance of a slight infection that has been overcome. Does it leave behind it immunity or an increased power of resistance