Knowledge of the pathogenesis of primary tuberculous infection in childhood has been increasing by leaps and bounds in the last fifteen years. And with this has come a revolution in the conception of the part that the blood stream plays in the postprimary development of tuberculosis.
Originally dissemination by the blood stream was conceived of as an occasional, much dreaded, invariably fatal accident, the main pathologic feature of which consisted of tubercles of miliary size scattered throughout the body or rarely localized to the meninges or lungs.
With the newer knowledge that in probably all cases of primary tuberculosis a few bacilli at least find their way into the blood, there is introduced a different conception of the part that the blood stream plays, and on the basis of clinical and pathologic observations many facts can be interpreted which heretofore have seemed obscure.
The conception of tuberculosis as a systemic