Comparison of Table LIV with the analogous figures for acute bronchopneumonia shows little noteworthy difference. Pneumococci are less frequently found in the lung (12.5 per cent) and in the blood (16.6 per cent) with chronic bronchopneumonia than with acute bronchopneumonia (lung 43.9 per cent; blood, 40.3 per cent). Hemolytic streptococci and staphylococci are not more frequently found with unresolved than with acute bronchopneumonia and failure to resolve cannot be referred to either or to both microorganisms, for bronchopneumonia not infrequently remains unresolved in their absence. B. influenzæ is present in the bronchi in at least 80 per cent of instances and perhaps in all; it is usually combined both in the lungs and in the bronchi with one of the pyogenic cocci. The severity of the injury to the walls of bronchi resulting in continued infection with a variety of bacteria, appears to be the factor determining failure of resolution and the persistence of bronchopneumonia. =The Relation of Unresolved Bronchopneumonia to Interstitial Suppurative Pneumonia Caused by Hemolytic Streptococci.=—Hemolytic streptococci have been present in a considerable proportion of those who have had unresolved bronchopneumonia and its occurrence in the bronchi, lung and blood of the heart indicates that it has had an important part in causing death. Unresolved bronchopneumonia, following measles, designated by MacCallum “interstitial bronchopneumonia” in a series of autopsies at Fort Sam Houston in the spring of 1918, was constantly associated with hemolytic streptococci. Among the lesions described as interstitial bronchopneumonia was at least one which was evidently what we have designated interstitial suppurative pneumonia. Lymphangitis was not infrequently found with “interstitial bronchopneumonia” following measles. At Camp Lee and Camp Dix, following the epidemic of influenza, MacCallum found “interstitial bronchopneumonia” with no hemolytic streptococci and noted that lymphatics in the interstitial septa were inconspicuous and that none was found distended with exudate; empyema was not present. We have shown that interstitial suppurative pneumonia is an acute lesion caused by hemolytic streptococci. Unresolved bronchopneumonia is accompanied by chronic pneumonia and has no necessary relation to this microorganism.