Organization of fibrin occurs within the smallest bronchi (diameter 0.3 to 0.5 mm.) or within respiratory bronchioles. It has been found in 8 autopsies. In one instance it has been present eleven days after the onset of influenza, but usually it is seen three or four weeks after onset of symptoms of respiratory disease. In the early stages of the lesion a plug of fibrin within the lumen of the bronchus or bronchiole is invaded by fibroblasts, plasma cells and newly formed capillaries. These capillaries have their origin in the wall of the tube and enter the fibrin at points where in consequence of loss of epithelium fibrin is continuous with the connective tissue. When the bronchiole is cut longitudinally, partially or completely organized fibrin may be found adherent at several places with intact epithelium, sometimes beautifully ciliated, between the sites of attachment. The fibrin is finally replaced completely and the lumen of the bronchiole contains a mass of organized fibrous tissue in which young fibroblasts and plasma cells are numerous. The lesion has been associated with chronic bronchopneumonia in 6 of 8 instances. In Autopsy 445, p. 257, organizing bronchitis and bronchiolitis occurred in the right lung unassociated with other chronic lesion, although there was advanced bronchiectasis with fibrous induration in the left lung. In Autopsy 499 (p. 224) organizing bronchiolitis occurred in association with chronic changes which appear to have followed interstitial suppurative pneumonia caused by S. hemolyticus. Other severe lesions of the bronchi have accompanied organizing bronchitis and bronchiolitis. Purulent bronchitis has been present in 7 of 8 instances; bronchiectasis in 5 of 8 instances. The bacteriology of autopsies with organizing bronchitis and bronchiolitis is shown in Table LIII. The bacteriology of these cases presents no constant feature. Invasion of the blood by S. hemolyticus has been present in a large proportion of cultures, namely, in 5 of 7 (71.4 per cent). In one of the 2 instances in which hemolytic streptococci have been found, neither in the blood nor lungs, Pneumococcus III has been found in the blood and S. viridans in the lungs and bronchus; in the other, S. aureus has been found in the lung and bronchus. Staphylococci have been found frequently in the bronchi (60 per cent) and in the lungs (50 per cent). B. influenzæ has been present in the bronchi in the usual proportion of instances (80 per cent). The lesion has occurred in the presence of B. influenzæ combined with streptococci or staphylococci. TABLE LIII