This endophlebitis appears to be the result of changes outside the vessel; there is usually necrosis of the adjacent tissue and the production of the lesion is favored by lymph stasis; as the result of injury to the vessel wall, polynuclear leucocytes in response to chemotaxis, or with milder irritation, mononuclear cells, wander through the endothelium and accumulate below it perhaps on account of the greater impermeability of the middle coat to the passage of cells. The lesion described does not occur exclusively with interstitial suppurative pneumonia caused by hemolytic streptococci, but has been found in association with abscess formation (Autopsies 354 and 383) caused by hemolytic streptococci or (Autopsy 322) caused by staphylococci. In 1 instance it has been found with lobar pneumonia (Autopsy 320) caused by atypical Pneumococcus II and in 2 instances with combined lobar and bronchopneumonia (Autopsy 357 with Pneumococcus IV; Autopsy 392 with Pneumococcus II). In these 3 instances there has been interstitial inflammation, edema and lymphangitis without suppuration. Interstitial suppurative pneumonia of long standing may occasionally be accompanied by chronic changes which bring about thickening of the interlobular tissue. In the following autopsy acute suppurative inflammation in the left lung has been associated with conspicuous thickening of interlobular septa in the right lung. =Autopsy 474.=—I. H., white, aged twenty-one, was a native of Oklahoma and had been in military service one month. His illness began with influenza thirty-six days before death; he was admitted to the base hospital thirty-one days before his death with signs of pneumonic consolidation of the right lower lobe. Evidence of fluid in the right pleural cavity was obtained two weeks before death, and from 100 to 700 c.c. of thick purulent fluid were aspirated on five occasions. Hemolytic streptococci were found in the aspirated fluid. =Anatomic Diagnosis.=—Interstitial suppurative pneumonia in left lung; abscess of right lower lobe with rupture into pleural cavity; thickening of interlobular septa of right lower lobe; double purulent pleurisy with thoracotomy on right side; serofibrinous pericarditis.