In a study of three subjects with incoagulable blood due to congenital afibrinogenemia, information is presented regarding some basic aspects of coagulation independent, of the fibrinogen-fibrin conversion mechanism. The following facts have been established: (1) Shortly after the blood is exposed to glass, the earliest detectable changes are morphologic alteration in the platelets and their progressive agglutination and lysis. (2) Almost in parallel, plasma antihemophilic activity, originally normal, declines rapidly and practically disappears. (3) Also within minutes, SPCA evolves from its precursor in a normal manner. (4) Acglobulin is rapidly consumed. (5) These changes are well along before detectable amounts of prothrombin have disappeared. (6) Prothrombin consumption proceeds at normal velocity, or slightly faster than normal. (7) Thrombin addition to afibrinogenemic plasma induces platelet agglutination, but this does not occur when thrombin is mixed with platelets alone. (8) The "natural" antithrombic activity of afibrinogenemic plasma is normal. (9) The heparin co-factor of antithrombic activity was demonstrable. (10) Quantitative data were obtained relating the one-stage prothrombin time with the fibrinogen concentration.

The theoretic and practical implications of the observations are discussed.

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