It is rare to see such activity on the part of the epithelium as that frequently encountered in influenza. The alveoli may be lined by newly formed cubical cells (Figs. IV, XI, XLVII), and mitotic figures in the injured bronchiolar lining occur in abundance. This might lead to the supposition that, if the epithelium were restricted in its path of development, it would pile up to form a typical nest, just as the epithelium at the edge of a healing chronic ulcer of the skin may pile up and extend fairly deep into the tissue. In a number of cases, epithelial proliferation has been so extensive that it could not be differentiated histologically from an invasive, malignant neoplasm (47) (Figs. XLVIII and XLIX). There is no reason to believe that malignancy might not result from the continuous stimulation of the epithelium to proliferate, in the chronic inflammatory process of the lung in influenza, just as chronic infection in the lung of a mouse results in a much higher percentage of spontaneous neoplasms of the respiratory tract in this species (132) than in those animals where chronic pulmonary inflammatory processes are uncommon. It will be interesting, indeed, to see whether, as a late manifestation, there is an increase in the number of now relatively rare epithelial new growths in the respiratory tract of man. [Illustration: FIG. XLVI. AUTOPSY NO. 128. THE ORGANIZATION IS HERE LARGELY CONFINED TO THE INTERSTITIAL TISSUE. THE ALVEOLI ARE DISTORTED AND COMPRESSED, AND THEIR EPITHELIUM HAS ASSUMED A CUBICAL FORM. ] [Illustration: FIG. XLVIII. AUTOPSY NO. 183. THIS DRAWING SHOWS A DILATED BRONCHUS UNDERGOING OBLITERATIVE BRONCHIOLITIS. THE EXUDATE IN THE SURROUNDING LUNG TISSUE IS BEING ORGANIZED. THE EPITHELIUM OF THE BRONCHUS IS MANY LAYERS THICK AND HAS INVADED THE SURROUNDING LUNG TISSUE. IT HAS THE APPEARANCE OF AN INFILTRATING EPITHELIAL NEOPLASM. COMPARE FIGURES XI AND XLI. ] VII. THE BACTERIOLOGY OF INFLUENZAL PNEUMONIA A. ORGANISMS ASSOCIATED WITH INFLUENZAL PNEUMONIA Certain conclusions may be drawn from the literature on the bacteriology of the respiratory lesions associated with influenza. All reports show that a few organisms have been found more or less constantly in influenza and influenzal pneumonia: the pneumococcus group, the streptococci (hemolytic, non-hemolytic, pandemicus, etc.) and the Pfeiffer bacillus. They may occur alone, together, or with less frequently found organisms. Among the latter, the staphylococcus, the Micrococcus catarrhalis, Bacillus pneumoniæ (Friedlander), diphtheroids, and undetermined organisms, all have been reported (2, 48, 62, 67, 68, 92).