 
         
         Summary
         
         Commercial thrombin was shown to contain appreciable amounts of thrombokinase. Passage
            through a DEAE-cellulose column substantially reduced the thrombokinase titer, although
            significant contamination could still be detected. Similarly, repeated barium sulfate
            adsorptions failed to remove the thrombokinase completely.
         
         However, barium sulfate adsorptions followed by passage through a column of DEAE-cellulose
            resulted in an essentially complete removal of the contaminant. Thrombin, so obtained,
            did not accelerate activation of prothrombin in the presence of calcium, phosphatide
            and barium carbonate adsorbed serum.
         
         Thrombokinase, separated by chromatography, was able to activate prothrombin very
            slowly in the presence of oxalate. Comparably dilute thrombin fractions and the unfractionated
            commercial preparation either did not possess this capability, or else this capability
            was obscured by a concomitant loss of thrombin.