FIG. VIII. AUTOPSY NO. 97. ALTHOUGH THE EPITHELIUM IS STILL VISIBLE AS A HYALINE BAND LIFTED FROM THE UNDERLYING MUCOSA, BOTH MUCOSA AND SUBMUCOSA ARE INVOLVED IN A NECROTIZING PROCESS. BACTERIA ARE ABUNDANT IN THE DEAD TISSUE. ] [Illustration: FIG. IX. AUTOPSY NO. 105. THE NECROTIC EPITHELIUM IS INVADED BY POLYMORPHONUCLEAR LEUCOCYTES AND THESE, AS WELL AS ROUND CELLS, CAUSE A THICKENING OF THE BRONCHIOLAR WALL. ] [Illustration: FIG. X. AUTOPSY NO. 106. THE SMALL BRONCHIOLE IS FILLED WITH PUS CELLS, WHICH, IN SOME PLACES, EXTEND THROUGH ITS WALL. ] There is considerable evidence to support the view that the disease spreads from bronchus to bronchus, and in keeping with this view, various stages in the inflammatory processes are more readily determined in these smaller structures than in the trachea. Furthermore, it must be emphasized that even the mildest and the most extreme of these stages are not infrequently encountered in the same lung. The earliest lesion is manifested by an increased homogeneity of the protoplasm of the epithelial lining of the bronchus. The cell protoplasm loses its normal granulation and the nucleus, somewhat darker than usual, becomes conspicuous on a red base (Fig. V). In the lumen of such a tube a serous exudate, perhaps mixed with mucus, is encountered, and there is some spreading apart of the surrounding muscular tissue with engorgement of the vessels. This picture merges gradually into one where the epithelium appears as a homogeneous, red-staining ribbon, devoid of nuclei, often exfoliated, in part at least, from the underlying submucosa (92). The change is traceable through the larger bronchi, even to the ducti alveolares, and not infrequently, bacteria, either as a diffuse, minute dotting or in the form of circumscribed, colony-like formations, are spread through the red, ribbon-like strand (Fig. XVI). With the exfoliation of the epithelial lining, the submucous vessels become more and more conspicuous and may bulge into the lumen of the tube (Fig. VI). That they actually weep into the lumen is proved by the presence of red blood cells in the exudate, now rich in mucus, broken-down nuclei, and desquamated cells. The necrotizing process may not extend deeper than the epithelial lining as is the status described above (140, 162), but it also frequently involves the underlying submucous and muscular layers, so that these lose their identity and stand out as homogeneous masses, in which fragmented nuclei and bacterial accumulations are prominent. Such deeper necrotizing areas may be focal (Fig. VII), or may involve the entire circumference of the tube (Fig. VIII). Occasionally, the epithelium, now dead and staining homogeneously, is lifted from the underlying submucosa in the form of a blister (66), and has very much the same appearance as the well known, early reaction which follows the application of croton oil to the rabbit’s ear. Where this occurs, the