It is remarkable how long this picture in the trachea and bronchi may persist without showing any marked variation. It is encountered, not only in the most acute and fulminating types of the disease (that have been examined), but a similar picture may be present in cases which end fatally only after a period of weeks of severe illness. In the latter cases, however, the exudate, particularly in the bronchioles, assumes a more purulent character and after this accumulation is wiped away from the surface of the tube, the intensity of the dark red color of its lining membrane presents an even more striking contrast on account of the opaque, yellowish-green exudate in the lumen. At this stage, too, the bronchioles are more distended with pus, which oozes from each one when the lung is sectioned (1, 108, 110). In the cases still more chronic, the terminal bronchioles may be sharply outlined with a thick grey wall which surrounds the dilated opening from which the accumulated yellowish exudate oozes as soon as the pressure is relieved (Figs. XXXIX and XL). _Histological Picture._ The changes are less marked, perhaps, in the trachea than in its finer ramifications. The mucosa is constantly more or less destroyed and large areas, usually focal, are entirely devoid of their epithelial covering. This is replaced by a sparse exudate, composed largely of red blood cells, mucus, a small amount of fibrin, and nuclear fragments (Fig. II). It may dip into the submucosa for a short distance, but usually these indentures are associated with the ducts of the mucous glands into which the inflammatory reaction extends. A more striking feature than the exudate, however, is the edema and the congestion of the submucosa. The loose areolar tissue of the submucosa is spread widely apart, and throughout it distended blood vessels are very conspicuous. Occasionally such a vessel is broken and actual hemorrhage appears in the submucosa. Occasionally, too, the inflammation extends down the duct to the mucous gland itself, and here, also, aplastic inflammatory reaction is evident, inasmuch as the acini now stain intensely red with the cells undifferentiated from each other and specked here and there by broken remains of the dead nuclei (Fig. III). After the disease has continued for a short period, even at the end of five or six days, some regeneration of the epithelial lining may be seen (3) (Fig. IV). But despite this, the acute picture persists, and there goes on, side by side, an attempted repair characterized by epithelial regeneration and the same evidence of acute change. Since the lesion is essentially a superficial one, scars or contractures of any extent are not encountered in the trachea, even in examples of the disease that have ended fatally only after many weeks.[4] [Illustration: