Influence of Serum Factors on the Species-specificity of Tissue Thrombo-plastin

Abstract

It is well recognized that a difference in species may influence the time of clotting of recalcified plasma in the presence of tissue extract. Using Quick's one-stage procedure, tissue extract will give a shorter clotting-time with homologous plasma than with plasma from a different vertebrate. Mann and Hurn¹ demonstrated that the specificity of a tissue extract could be eliminated by incubating it with a small amount of homologous serum in the presence of calcium ions before adding the heterologous test plasma. At this time, factor VII (cothrom-boplastin, S.P.C.A., proconvertin) and factor IX (Christmas factor, P.T.C.) were the only clotting factors known to be present in serum, and as factor IX plays no part in the conversion of prothrombin to thrombin by tissue thromboplastin, Mann and Hurn concluded that the species-specificity was eliminated by the presence of homologous factor VII.