On the Inactivation of Thrombin by Plasma Protein.

It has been known for many years that an excess of thrombin is formed during the clotting of blood or plasma, that the excess is rapidly inactivated, and that such inactivation is important in maintaining normal fluidity of the blood (1). Considerable attention has been given to the question of what happens to the excess of thrombin, but little conclusive information has been obtained concerning the phenomenon. Quick, in a study of the mode of action of heparin in preventing coagulation, obtained evidence supporting the opinion of early workers that the property of inactivating thrombin resides in the plasma protein,