Despite their reported stability, the platelets of hemophilic blood function normally. The prothrombin content of such plasma is also normal. Confirming the findings of Addis, the delayed coagulation observed in hemophilic blood is due to an unexplained retarded activation of prothrombin to thrombin. The addition of an excess of platelets, whether normal, hemophilic, or animal in origin, accelerates thrombin production and makes hemophilic blood clot normally; but cephalin, despite the fact that it accelerates thrombin production in normal plasma, is unexplainedly ineffective when added to hemophilic plasma.

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