Variations in the prothrombin complex of different species

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Abstract
The prothrombin concentration of man, dog, rabbit, cat and cow as determined by the two-stage method is about the same but in sheep is only half as great. The one-stage prothrombin time of the plasma of these species varies greatly and is dependent upon the type of thromboplastin employed, the exposure to foreign surface and various serum factors as well as the concentration of prothrombin. Factor V (labile factor) is present in excess in all so that it is not a determinant. Acetone-dehydrated brain tissue is a satisfactory source of the thromboplastin factor since it can be prepared fairly free of contamination with serum. Variation of activity on various brain preparations cannot be explained satisfactorily on species or group specificity but can in part be accounted for by the synergistic action of an agent in brain tissue with a serum factor or factors which appear to be related to both factor VII (stable factor) and factor IX (PTC). A high yield of thrombin is obtained from human plasma by the thrombin production test but a strikingly low amount from the plasmas of the five other species.