Abstract
The basic reagent used was an eluate obtained from barium sulfate used to adsorb various sera. When this eluate was prepared from normal rabbit serum, it responded to treatment with coagulants from adsorbed plasma, with Stypven, or with 25 per cent sodium citrate to give products with similar if not identical properties. With each preparation a stable complex formed with cephalin which withstood washing, was relatively heat-stable, was inactivated by adsorbed serum, and which required factor V for optimal prothrombin conversion. In eluates prepared from human serum, normal activation occurred in the absence of factor IX, but was defective in the absence of factor X. A preparation of factor X purified by DEAE cellulose chromatography was activated by 25 per cent sodium citrate. It is suggested that product I, the product of Stypven activation, and autoprothrombin C represent similar or identical reagents; it is further suggested that factor X is their common precursor.
