From the data presented in Table XIII it is evident that a mixed infection existed in all cases. The results obtained by stained sputum films and by direct culture on blood agar plates are of special significance. B. influenzæ was present in all cases, being the predominant organism in 6 cases, abundantly present in others, and few in number in 2. Of other organisms the pneumococcus was most frequently found, occurring in 11 of the 13 cases, in all but 2 instances being present in considerable numbers. S. viridans was encountered twice, once in association with a Gram-negative micrococcus resembling M. catarrhalis culturally. S. hemolyticus was found once, together with M. catarrhalis and a few pneumococci, Type IV, coming through in the mouse only and of doubtful significance. The stained sputum films and direct cultures always showed these organisms present in sufficient abundance to indicate that they were present in the bronchial sputum and were not merely contaminants from the buccal mucosa. It seems quite probable from these results that purulent bronchitis following influenza is, in most cases at least, due to mixed infection of the bronchi and should be looked upon as a complication of influenza. Whether the condition may be caused by infection with B. influenzæ alone is difficult to say. No evidence that it may be caused by B. influenzæ alone was obtained in the cases studied. It is not intended to enter here into a discussion as to whether B. influenzæ should be regarded as a secondary invader or not; the other organisms encountered certainly are. It would seem most probable that purulent bronchitis is caused by the mixed infection of B. influenzæ and various other organisms, commonly the pneumococcus, but that the condition is initiated by the invasion of the bronchi by these other organisms in the presence of a preceding infection with B. influenzæ.