Lymphatics in many places are distended and plugged by fibrinous thrombi, whereas elsewhere softening of the thrombus has been brought about by suppuration. Suppuration, both within the lymphatic and in adjacent alveoli, appears to be secondary to lymphatic obstruction. In some instances the lymphatic appears to have undergone distention after the thrombus has formed, for between the thrombus and the wall of the lymphatic a channel is occasionally found containing uncoagulated lymph. [Illustration: Fig. 14.—Endophlebitis occurring in association with suppurative pneumonia; the intima contains lymphoid cells in great number; at one spot there is a small thrombus adherent to the intima. Autopsy 325. ] Acute endophlebitis has been repeatedly observed in association with interstitial suppurative pneumonia (Fig. 14). The lesion usually occurs in veins situated within the septa which are the site of intensely acute inflammation associated with necrosis. The wall of the vein appears to be so injured by the surrounding changes that polynuclear leucocytes and small mononuclear cells accumulate below the endothelium. Throughout the circumference of the veins, often 0.5 to 1 mm. in diameter, the endothelium is separated from the underlying media by polynuclear leucocytes which form a conspicuous zone encircling the lumen. Some cells of lymphoid type are usually present among the polynuclear leucocytes. Polynuclear leucocytes are often adherent to the endothelial lining of the vessel and are not infrequently fixed in the process of passing through the endothelium. The lesion may be more severe (Autopsy 325), so that the endothelium has disappeared, and upon the exposed surface fibrin is deposited; within this fibrin polynuclear leucocytes are numerous and nuclear fragmentation has occurred. The middle coat of the vessel usually contains few cells; some polynuclear leucocytes within it may be stretched out as if in process of wandering through the wall. In other instances the accumulation of cells below the endothelium is almost wholly mononuclear. Cells of the type of lymphocytes occur, but more abundant are slightly larger cells with more abundant cytoplasm. These cells may form a thick zone below the intima throughout the entire circumference of the lesion. It seems probable that these cells, like the polynuclear leucocytes, are derived from circulating blood within the lumen of the vessel, for small cells of the type of lymphocytes are not infrequently found adherent to the lumen and occasionally one is fixed in process of passing through the endothelium.