Ian C. Roddie CBE, DSc, MD, FRCPI Emeritus Professor of Physiology, The Queen's University of Belfast; former Head of Medical Education, National Guard King Khalid Hospital, Jeddah, Saudi Arabia William F.M. Wallace BSc, MD, FRCP, FRCA, FCARCSI, FRCSEd Emeritus Professor of Applied Physiology, The Queen's University of Belfast;former Consultant in Physiology, Belfast City Hospital, Belfast, N. Ireland