From this intermediary stage the picture of actual abscess with mortification of bronchiolar and alveolar tissue, as well as of the exudate itself, is readily approached (25, 48, 110, 140) (Fig. XXXI). In the necrotic mass that forms the center of such a focus, the most prominent feature is the bacteria. With hematoxylin they stain intensely as black, irregular masses, and their prominence is accentuated by the homogeneous staining qualities (with eosin) of the dead tissue, whether lung or exudate (Fig. XXXII). These abscesses may have central cavities which represent a discharge of their contents and may indicate the position of a bronchiole (Fig. XXXI). The necrosis of the alveolar walls, focal in its distribution as previously described, suggests itself as a forerunner of the more extensive necrosis encountered at this stage. The most extreme form of mortification is seen in the wall of a gangrenous cavity, and several layers can be distinguished there. Beginning with that portion of the lung the least involved, the lesion may be limited to congestion of the alveolar wall with a serofibrinous exudate in the lumen, but this stage passes rather rapidly into another where cellular exudate, chiefly of polymorphonuclear leucocytes, predominates. Moreover, the leucocytes form not only the bulk of the alveolar content, but also distend the vessels and accumulate in the interstitial tissue around blood vessels and lymphatics. Passing toward the center of the gangrenous cavity, the lung rapidly changes in appearance. The blue zone of leucocytic infiltration makes more conspicuous the inner area of necrosis—where nuclei no longer stain and the alveolar wall is a homogeneous pink.