From the Departments of Surgery and Pathology of Harvard Medical School at Peter Bent Brigham Hospital, Boston, Massachusetts *Current Address: Department of Surgery, University of Chicago, Chicago, Illinois. (Previously, Post Doctoral Fellow, National Institutes of Health.) **Current Address: Department of Surgery, Universidad del Valle. Cali, Colombia. (Previously, Post Doctoral Fellow, National Institutes of Health.) ***Medical Corps, U. S. Army. †Assistant Professor of Pathology, Harvard Medical School and Associate Pathologist, Peter Bent Brigham Hospital. ††Moseley Professor of Surgery, Harvard Medical School and Surgeon-in-Chief, Peter Bent Brigham Hospital.