=Chronic Bronchitis.=—The earliest changes in the bronchial wall with bronchitis of influenza are hyperemia, leucocytic infiltration and hemorrhage, and they may occur even though the lining epithelium remains intact. Epithelium frequently undergoes partial or complete destruction, and with this severe injury the influence of the inflammatory irritant may extend directly through the wall of the bronchus, for in some instances there is hemorrhage into all the alveoli in a zone encircling the bronchus. Since these alveoli have only indirect communication with the affected bronchus through alveolar tissue not involved in the inflammatory process, it is evident that the surrounding hemorrhage is secondary to the lesion of the bronchus. Fibrinous inflammation in other instances, similarly localized in a zone of alveoli encircling a bronchus, is doubtless the result of direct extension of the inflammatory process through the bronchial wall. After the disease has existed during two or three weeks inflammation is still active immediately below the inner surface of the bronchus; here polynuclear leucocytes are numerous whereas in the deeper parts of the mucosa and about the muscularis leucocytes are scant but lymphoid and plasma cells are very numerous. The severity of the inflammatory reaction may be judged by the abundance and extent of this cellular reaction and is in close relation to the intensity of the changes affecting the mucous membrane of the bronchus. Infiltration of the entire bronchial wall with lymphoid and plasma cells is almost invariable when the primary injury to the bronchus has destroyed the epithelial lining, and this infiltration is not limited to the bronchial wall but extends outward into the contiguous alveolar septa which are thickened by it. The sheath of the pulmonary artery which accompanies the bronchus exhibits a similar change, and the alveolar septa, as a fringe about it, are thickened and infiltrated with mononuclear cells. Interlobular septa continuous with the bronchus often show some infiltration.