This report is a summary of work performed by the following investigators of the Mayo Clinic and Mayo Foundation, Rochester, Minn.: Frank H. Krusen, M.D., Section of Physical Medicine and Rehabilitation; J. F. Herrick, Ph.D., Carl F. Schlotthauer, D.V.M., and Khalil G. Wakim, M.D., Ph.D., Division of Experimental Medicine; Warren A. Bennett, M.D., Section of Pathologic Anatomy, Joseph M. Janes, M.D., Section of Orthopedic Surgery; Edward H. Lambert, M.D., Ph.D., Section of Physiology; and Paul A. Nelson, M.D., Thomas P. Anderson, M.D., Ralph E. De Forest, M.D., and Walter J. Treanor, M.B., Fellows in Physical Medicine and Rehabilitation.