1. Department of Physics in Relation to Surgery, Surgical Sciences, Royal College of Surgeons, 35–43 Lincoln's Fields, London WC2A 3PN, U.K.
2. Academic Department of Surgery, Royal Free Hospital Medical School, London NW3 2QG, U.K.
3. Department of Applied Physiology and Surgical Sciences, Royal College of Surgeons, 35–43 Lincoln's Fields, London WC2A 3PN, U.K.