The essential processes and stages in the evolution of pulmonary tuberculosis include the primary tuberculosis forming the uncomplicated primary complex, and the progressive primary complex resulting in a bronchogenic or - more frequently - in a haematogenic dissemination. The postprimary (secondary) tuberculosis of the adult develops from haematogenic apical lesions either immediately or after a prolonged interval. Generally, the postprimary tuberculosis is caused by reactivation, spreads bronchogenically in apicocaudal direction, thus leading to an isolated phthisis of the lung.