Microscopic examination shows that the epithelium of dilated bronchi has disappeared and the denuded surface is covered by fibrin and polynuclear leucocytes; fissures extend from the lumen through the bronchial wall into the surrounding alveolar tissue. A zone of fibrinous pneumonia surrounds these bronchi and fissures in the bronchial wall penetrate into this zone. One dilated bronchus 2.4 mm. in diameter with no cartilage in its wall has vascular connective tissue covered by epithelium on one side, whereas the remainder of the circumference is formed by exposed alveoli filled with fibrin, the bronchial wall having disappeared. A section through a part of the abscess which has been mentioned shows a very irregularly formed cavity approximately 1 x 0.7 cm. Remains of bronchial wall, consisting of very vascular tissue covered by flat epithelium in several layers, indicate the origin of the cavity. Between these remnants of bronchi deep pockets extend into the pulmonary tissue which in the margin of the cavity is the site of fibrinous pneumonia. In one place, in contact with the cavity, a wide area of consolidated tissue has undergone necrosis and both alveolar walls and their contents have lost their nuclei. Leucocytes which are accumulating at the margin of the necrotic patch form a line of demarcation between living and dead tissue. Abscess may be the result of the profound changes which occur in the bronchi as the result of influenza. Necrosis caused by bacteria within the bronchi weakens and in places destroys the wall. Bacteria penetrate into the surrounding tissue and hemolytic streptococci (or staphylococci) may produce localized abscesses. These abscesses are usually situated near the pleural surface of the lung, because destructive changes causing rupture of the bronchial wall occur more frequently in the smaller peripheral bronchi than in the larger bronchi containing cartilage. Abscesses occur more frequently at the bases of the lungs, because the most severe changes in the bronchi occur in the dependent part. (See “Bronchiectasis,” p. 240.) =Healing of Abscess.=—The following autopsy is of interest in relation to the treatment of pulmonary abscess and associated empyema.