The basis of all work on tuberculosis is the knowledge of tuberculous infection, and when the question of combating the disease by means of prophylactic vaccination arises the conditions influencing the infection become of vital importance. An account of tuberculous infection will therefore be given, with the observations on which vaccination is based, followed by a description of subcutaneous vaccination with B C G and its results.
The common conception of tuberculous infection is that it generally occurs during the early years of childhood. The many difficulties that continually arise, however, when an attempt is made to bring actual facts concerning tuberculosis into line with this theory, for instance, the morbidity at the ages between 20 and 30 years, make one doubt the truth of the theory. And the facts on which the theory is based do not seem convincing; they are too few and too specialized to justify such