Abstract: A method of separating blood plasma from particles including blood cells, in the blood, includes the steps:(a) providing a membrane with holes therethrough of a size to pass the particulate, and supplying blood to one side of the membrane,(b) moving the membrane at sufficiently high velocity that shear conditions created in the blood adjacent the membrane cause particles in the blood to move or remain away from the surface of the membrane and from the holes,(c) creating a pressure differential across the membrane sufficient to cause plasma to pass through the holes from said one side of the membrane to the opposite side thereof,(d) the holes being allowed to reduce in cross-sectional area as by protein collection on the membrane at the holes, or by expansion of the membrane material, and the holes maintained sufficiently open, by virtue of their original size, to continue to pass the plama therethrough.