Abstract
In attempting to use serum rather than tissue extract for the coagulant in clotting heparin-plasma it was found that frequently a plasma rendered incoagulable with heparin could not be clotted with serum but could be clotted with tissue extract. This observation suggested that the coagulant in serum (thrombin) might be more sensitive to heparin than the coagulant in tissue extract (tissue fibrinogen).
One must consider the possibility of the concentration of coagulant in the tissue extract being greater than in the serum. This factor was controlled by rendering the 2 coagulants isocoagulant by dilution of the stronger of the 2 with physiological saline. They were regarded as isocoagulant when similar amounts of either shortened the coagulation time of a recalcified citrate plasma to the same extent.
The citrate plasma is from adult rabbits, titrated to 0.5%; serum is obtained from the clotted recalcified citrate plasma.
The tissue fibrinogen was kindly furnished by the Wm. S. Merrell Co. (“Fibrogen” for subcutaneous use).
In Experiment A. Table I, the plasma has a fairly long recalcification time of 13 1/2 minutes; this is reduced to 3 minutes by 4 drops of either coagulant. The heparin concentrations are high at the start being reduced by dilution, the clotting time becoming consistently shorter for both coagulants. In each set the serum is more inhibited than the tissue fibrinogen. Control at the end shows the coagulants to be isocoagulant and within 15 seconds of the original value.
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