Fig. 18.—Acute bronchiectasis showing fissures in the bronchial wall extending into neighboring alveoli which in zone about are filled with fibrin; one fissure has separated widely; peribronchial fibrinous pneumonia (fibrin is black). Autopsy 425. ] Recently dilated bronchi have an irregularly stellate lumen as the result of clefts penetrating at intervals into or through the bronchial wall (Fig. 26). Longitudinal fissures mark the lining of these dilated bronchial tubes. When the fatal illness has lasted more than two weeks, abundant new formation of fibrous tissue occurs in a zone surrounding the dilated bronchus. Adjacent alveolar walls are thickened by young fibrous tissue. Alveoli, much diminished in size, are filled by hyaline fibrin into which fibroblasts and newly formed blood vessels have penetrated. These changes are limited to a wide zone in immediate contact with the dilated bronchus, whereas at a greater distance alveolar walls have undergone no thickening and alveoli contain no fibrin. [Illustration: Fig. 19.—Acute bronchiectasis; the bronchial wall indicated by engorged mucosa shows a varying degree of destruction, fissures extending into and through the bronchial wall. Autopsy 352. ] [Illustration: Fig. 20.—Acute bronchiectasis; with destruction of bronchial wall exposing alveoli filled with fibrin; peribronchial fibrinous pneumonia is seen about several bronchi present in the section; Gram Weigert fibrin stain. Autopsy 425. ] This stage is well represented by Autopsy 421 after an illness of nineteen days. Bronchiectatic cavities, from 3 to 6 mm. in diameter, are numerous in sections of the lung; their lumina are irregular in outline and often irregularly stellate. Microscopic examination shows the presence of clefts which interrupt the bronchial wall at intervals throughout its entire circumference. The original wall is well indicated by the very richly vascularized connective tissue containing scattered muscle bundles and is infiltrated with lymphoid and plasma cells in great number. Where fissures have occurred the adjacent edges of the interrupted wall have separated from one another, leaving a wide interval where underlying alveolar tissue is exposed. Two changes tend eventually to render the fissures inconspicuous, namely, regeneration of epithelium and new formation of fibrous tissue. Exposed alveoli filled with fibrin are in process of organization and epithelium which has assumed a squamous type has grown down over the exposed surfaces of the interrupted bronchial wall. It has begun to cover or in some instances has completely covered the surface of rents entering alveoli plugged with fibrin (Fig. 21). In the periphery of the bronchus alveolar walls are thickened and infiltrated with lymphoid and plasma cells. The same changes affect bronchi containing cartilage which is undergoing atrophy.