Summary
The prothrombin concentration of dog plasma was lowered by giving large doses of Dicumarol. The dog blood was then mixed with progressive increments of purified bovine prothrombin. When the concentration of prothrombin was equivalent to normal the whole blood clotting time and the prothrombin time were normal. The purified prothrombin supplied all that was essential and did not add detectable amounts of extraneous pro coagulant power. The residual prothrombin in the serum was generally higher when clotting occurred in silicone lined test tubes than in glass. In silicone tubes very little hemophilia B (factor IX, autoprothrombin II) activity developed. This activity was found in the glass tubes in a concentration proportional to the original prothrombin added. The transformation of prothrombin to autoprothrombin II occurred in plasma when there was a glass surface.
