An impregnated porous disc made of an inert material with voids adapted for insertion into a collection tube containing clotted blood which disc upon centrifugation of the tube will allow separation of fibrin and cellular material from the serum by centrifugal force during its controlled descent through...http://www.google.ca/patents/US3972812?utm_source=gb-gplus-sharePatent US3972812 - Blood serum separation filter disc
