Abstract
Blood was obtained from a dog by the method of Lim,∗ which absolutely excludes admixture of tissue juice. It was kept in contact only with paraffin, was immediately cooled and centrifuged. By differential centrifuging platelets were obtained free of red and white cells. They were washed well in saline and then dissolved in water. This platelet solution was tested for thrombin, prothrombin cephalin and tissue fibrinogen. On treating it with active cephalin and calcium and letting the mixture stand for 15 minutes at room temperature, it was unable to clot a citrated solution of pure blood fibrinogen. A control mixture, using purified prothrombin from fresh blood plasma instead of platelet solution, gave very active thrombin, and clotted fibrinogen in 10 seconds. The platelet solution was capable of replacing cephalin in the activation of the prothrombin solution. This property was unaffected by boiling. It would also directly clot pure blood fibrinogen when free calcium was present, just as well as would an active tissue fibrinogen solution. This action was lost on boiling.
Platelets, therefore, do not contain thrombin or prothrornbin, but do contain free cephalin and tissue fibrinogen, and are thus similar to other body tissues.
This is a preliminary report.
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