1. Received from the Anaesthesia Laboratory of the Harvard Medical School at the Massachusetts General Hospital, Boston, Massachusetts; accepted for publication May 10, 1965. *Instructor in Anaesthesia, Harvard Medical School.‡ Visiting Lecturer in Anaesthesia, Harvard Medical School. Present Address: University of Lund, Lund, Sweden.‡ Research Fellow in Oral Medicine, Harvard Medical School.§ Assis