This change may occur within six days after onset of influenza, though in most instances the duration of illness has been two weeks or more. It may affect either large or small bronchi, but it is more frequently found in the latter. Whenever ciliated columnar cells are lost, superficial cells tend to become flat. Epithelium on one side of a bronchus may have a squamous character, whereas that elsewhere is columnar and ciliated. The flat epithelium may undergo thickening so that it is 0.1 mm. or more in thickness. It is noteworthy that regenerating epithelium growing over a denuded surface has the squamous character which has been described (Plate XIV, Fig. 22). =Bacteriology of the Bronchitis of Influenza.=—With the pneumonia of influenza, bronchitis is invariably present. Cultures have been made from the right or left main bronchus or from the very small bronchi which contained purulent exudate. A routine method of making the culture has been adopted. The right main bronchus, exposed by drawing the right lung out of the chest and toward the midline, was widely seared with a hot knife; the bronchus was partially cut across through the seared surface with a heated knife and a platinum needle inserted into the lumen. The bacteria obtained named in the approximate order of their relative frequency have been: B. influenzæ, pneumococci, hemolytic streptococci, staphylococci (aureus and albus), B. coli, S. viridans, M. catarrhalis, and diphthoid bacilli which have not been identified. Mixed infections occurred in most instances. The following list arranged by grouping bacteria in the order cited above, shows how varied have been the combinations which occur: