1. Assistant Professors, Department of Anesthesia, University of Pennsylvania
2. Postdoctoral trainees in the Department of Anesthesia, University ot Pennsylvania, supported by U.S.P.H.S. Research Training Grant 2-T1-GM-215–06.
3. Presently at the National Institutes of Health, Bethesda, Maryland.
4. Resident in Anesthesia at the University of Pennsylvania. Dr. Cohen's present address is Walter Reed Army Institute of Research, Washington, D. C. From the Departments of Anesthesia and Neurology, Schools of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania; accepted for publication February 25, 1965. This work was supported (in part) by grants GM-09070–02, 2-T1-GM-215–06, HE-07857