1. Laboratory of Hemorheology, College of Physicians and Surgeons, Columbia University, New York, N.Y. 10032, Department of Civil Engineering and Engineering Mechanics, Columbia University, New York, N.Y. 10027; Laboratory of Biorheology, Polytechnic Institute of New York, Brooklyn, N.Y. 11201, and New York Medial College, New York, N.Y, 10029, U.S.A.