After Medical School, Harrington interned at Howard Hospital in
Philadelphia. In November 1914 he became a fellow in surgery at the
Mayo Clinic. He earned a Master of Science degree in surgery from the
University of Minnesota. In 1920, Harrington became head of a section of surgery at the Mayo Clinic, eventually becoming a full professor. On the advice of
William James Mayo, Harrington changed his subspeciality from gastrointestinal and urologic surgery to thoracic and breast surgery. Eventually Harrington developed an international reputation in the diagnosis and treatment of diaphragmatic hernias and mediastinal tumors. He was honored several times by the
American Medical Association for work on chronic postpneumonic empyema, and pericardiectomy for chronic constrictive pericarditis. In 1937, Harrington was elected the 20th president of The
American Association for Thoracic Surgery and in 1948 he helped found the
American Board of Surgery. Harrington came on the staff at Mayo's in 1917 and retired in 1954. He started the department of Thoracic Surgery after a trip to Germany to study thoracotomy methods. He worked with anesthesiologist John Lundy to develop early methods of intubation and anesthesia for open chest cases. Harrington originated the trans-abdominal approach for the repair of hiatal and diaphragmatic hernias. He performed more than 25,000 mastectomies for breast cancer in his long career. Harrington wrote 38 peer-reviewed articles in professional journals and lectured extensively. ==Football coach==