With this peribronchial pneumonia the smallest bronchi are distended with pus and their walls are infiltrated with polynuclear leucocytes, lymphoid and plasma cells. In a broad zone encircling the bronchus the alveoli are filled with plugs of fibrin. Bronchioles are similarly distended with polynuclear leucocytes; the alveoli which occur upon the wall of the bronchiole are often limited to one side of the wall and are filled with fibrin. This fibrin occasionally projects into the lumen of the bronchiole and forms a continuous layer in contact with the wall on the same side. The alveolar duct and infundibulum are distended with polynuclear leucocytes. The alveoli upon the wall of the alveolar duct and upon the proximal part of the infundibulum are filled with fibrin. The bronchus, bronchiole, alveolar duct and part of the infundibulum are thus surrounded by a continuous zone of alveoli containing fibrin. The alveoli about the distal part of the infundibulum may be filled with polynuclear leucocytes. Lung tissue between adjacent zones of fibrinous pneumonia may contain serum and desquamated epithelial cells. Organization of peribronchial fibrin was found in 10 of the 22 autopsies in which peribronchial fibrinous pneumonia had been found. Fibroblasts have invaded the fibrin and newly formed capillaries have penetrated into it. In some instances the interalveolar septa are thickened and infiltrated with lymphoid and plasma cells, and in 7 instances there was chronic pneumonia with thickening and mononuclear infiltration of the interstitial tissue about the bronchi and blood vessels, and elsewhere. The duration of the fatal illness in 12 instances with no organization was usually from ten days to two weeks, though in 3 instances there was no organization although the respiratory disease had lasted from seventeen to nineteen days (average duration with no organization, 13.5 days). The duration of illness in 10 instances with organization of fibrin was slightly less than three weeks (average 18.9 days). These figures do not accurately represent the duration of pneumonia which usually develops after a period of several days following onset of influenza. This group of instances of peribronchial fibrinous pneumonia has offered an opportunity to study the bacteriology of pneumonia with organization and to determine if it presents any unusual characters. The bacteriology of autopsies with peribronchial fibrinous pneumonia with no organization is shown in Table XLIII: TABLE XLIII