According to the "old pathological theory" dating back as far as the postmortem findings of Morgagni in the seventeenth century, verified later by Bichat in the clinic and then by Laënnec in the nineteenth century, pulmonary tuberculosis begins in one or both apexes and spreads thence slowly in an apicocaudal direction. In the early part of the twentieth century Ghon introduced the conception of the primary pulmonary infection or complex (called the Ghon tubercle), which might be located anywhere in the lungs. In 1922, however, Assmann1 showed that, in adults exposed to severe tuberculous infection, clinical disease most frequently began from a compact density lying infraclavicularly without a simultaneous lesion in the apex region itself.
At the congress in Wildbad in 1928, the so-called new theory was formulated, championed by Bruening, Redeker and Kayser-Petersen. The new theory maintained that pulmonary tuberculosis usually begins from an "early infiltrate" (Simon), which