Certain Theoretical and Practical Tuberculosis Problems *

Prior to discovery of the tubercle bacillus interest in the nature of tuberculosis was focused largely on the types of human constitution most susceptible or resistant to the disease. For a generation after discovery of the bacillus, infection was considered so nearly universal that it was thought to be a minor factor in the pathogenesis of tuberculosis, the resistance of the host being the major consideration in determining whether or not a person succumbed to the disease in the course of his life. Within the course of the generation, however, distinction was drawn dearly between native resistance and acquired. Immunity, or increased resistance, of the host due to mild infection became a concept of great significance in the understanding of tuberculosis. Among those who developed our understanding in this field was Willard Soper, to whom this volume is dedicated. When the researches of Roemer, Krause, Soper, and others were at their height, the current view was that most tuberculosis of adult life, i.e., the majority of all tuberculosis, was endogenous. Such immunity as developed from a mild self-terminated infection in childhood was exercised not only against fresh invasion of tuberde bacilli from without, but also, and in a more important role, against renewed invasion from within. In the succeeding years the emphasis shifted from endogenous to exogenous infection as the precursor of progressive disease of adult life, but a universally satisfactory agreement on the question of the relative frequency of endogenous and exogenous infections has never been reached. Evidence of the failure of acceptable solution of the question is the growing tendency toward diagnosis of "hematogenous tuberculosis" in a time when a huge and successful antituberculosis campaign is based on the recognition of adult tuberculosis as an exogenous infection. Exogenous and endogenous infection. Behring described tuberculosis as a story that began in the cradle and ended in the grave. He believed in alimentary infection as the original source, and sub-