In the study of pulmonary suppuration, intrabronchial drainage1 has not had the attention that it deserves. This drainage is of two types: "external" and "internal." By external drainage I mean the ability of a bronchus to empty itself by cough and expectoration. Internal drainage, on the other hand, is the inability of a bronchus to empty itself adequately, the pus spilling about from place to place within the lung. This spilling, or internal drainage, is a definite entity in pulmonary suppurations, and an understanding of it is important in the diagnosis and treatment of these conditions.
The occurrence of internal drainage has been substantiated by iodized oil studies and bronchoscopic examinations. The injection of oil has permitted a study of the accessibility of either lung to intrabronchial secretions from the opposite side and has shown that internal drainage can occur even in the unanesthetized patient in whom the cough
FAULKNER WB. INTERNAL DRAINAGEITS APPLICATION IN PULMONARY SUPPURATION. JAMA. 1930;95(18):1325–1328. doi:10.1001/jama.1920.02720180019006