 Two years later Dr. Wittmann defended a Ph.D. thesis in Neurophysiology/Toxicology at University of Düsseldorf on the affinity of carbon monoxide to hemoglobin of various laboratory animals and men.Following medical school he continued his surgical training in Hamburg, Philadelphia, Annaba, Algeria, () to become Board certified General Surgeon and after an additional two years a Board certified (surgeon for soft tissue, visceral and orthopedic trauma).In 1988, after organizing an International Congress in Hamburg, Germany, with the sole topic of intra-abdominal infection and founding the Surgical Infection Society - Europe, he accepted a position as Professor of Surgery at the Medical College of Wisconsin.He worked first at the of University of Hamburg Medical School.