Any discussion of pulmonary embolism must concern itself primarily with a consideration of the fundamental problem of venous thrombosis. Many years ago Virchow,1 Aschoff2 and Welch3 set forth the fundamentals of the mechanics of red and white thrombus formation, which can still be found in any modern textbook. Innumerable publications on pulmonary embolism and thrombophlebitis have since confirmed the findings of the original investigators.
The word thrombophlebitis poorly describes the spontaneous venous thrombosis which occurs postoperatively and in medical patients at rest in bed, because the ending of the word suggests that inflammation is present. Any inflammation in the wall of the vein or in the thrombus is a secondary manifestation and not a primary cause. The type of thrombophlebitis caused by local trauma or infection does not pertain to this discussion. Our concern is with spontaneous intravenous clotting, and this will be referred to in the