With the bronchitis of influenza the small bronchi (with no cartilage or mucous glands) show every stage of transition from early acute inflammation characterized by accumulation of polynuclear leucocytes within the lumen, engorgement of blood vessels, and infiltration of the wall with polynuclear leucocytes, through various stages of destructive changes to complete disappearance of the bronchial wall and formation of an abscess cavity at the site of the bronchus. In the early stages of acute bronchitis, hemorrhage is frequently associated with the lesion. Blood may be abundant within the lumen of the bronchus, and in the mucosa red blood corpuscles often infiltrate the tissue around greatly distended blood vessels, or accumulating below the epithelium, separate it from its basement membrane. Hemorrhage is not limited to the wall of the bronchus, but frequently occurs into the alveoli in a zone encircling the bronchus. With acute bronchitis there may be desquamation of epithelial cells with partial or complete loss of epithelial lining. In the smallest bronchi the single layer of columnar cells may be separated in places from the underlying tissue, so that intact rows of cells are found within the lumen. In somewhat larger bronchi, lined by epithelium in multiple layers, superficial columnar ciliated cells may be lost. In some instances superficial epithelial cells appear to have lost their cohesion and are separated by narrow spaces; in these instances, polynuclear leucocytes are often numerous between epithelial cells. Epithelium is occasionally separated from its basement membrane by small accumulations of serum or blood. Occasionally necrosis of epithelial cells with disappearance of nuclei is seen and is doubtless caused by the action of bacteria; the affected cells may be raised from the underlying tissue by accumulated serum (Autopsy 253). The changes which have been described bring about partial or complete loss of the ciliated lining of the bronchial tube. The severity of changes in the bronchial wall is in direct relation to the extent of destruction of the lining epithelium: when the epithelium remains intact polynuclear leucocytes may be found in considerable number immediately below it, but as the lesion progresses, cells in great part mononuclear, namely, lymphoid and plasma cells, accumulate in large number throughout the wall of the bronchus. There is often abundant cellular infiltration within and about the bundles of the muscular coat. The changes assume the character of chronic inflammation.