1. Departments of Biomedical Engineering, Chemical Engineering, Applied Physics, Mechanical Engineering, and Electrical Engineering, Yale University, P.O. Box 208248, New Haven, Connecticut 06520, Department of Chemical Engineering, The City College of New York, 138th Street at Convent Avenue, New York, New York 10031, and Department of Biochemistry, Ohio University, 350 West State Street, Athens, Ohio 45701