Abstract
A method for measuring the inhibitory activity of heparin on the clotting of blood has been worked out by Fischer and Schmitz. 1 Instead of using as Howell 2 does an arbitrary effect as a unit for the inhibitory activity, this method gives a curve of the action of varying concentrations of the anticoagulant, and from the equation for this curve the activity of the substance is denned. From the activity (k) obtained in this way a unit for inhibitory substance has been defined by Astrup and Behrnts Jensen 3 as the quantity of active substance contained in one gram of a material which gives the value 1 for k under the given experimental conditions.
This method has been modified by Chargaff, Bancroft and Stanley-Brown 4 and used in their recent work on blood coagulation. By this modification, curves for the inhibitory action of various concentrations cannot be determined as by the original method of Fischer and Schmitz (l.c.) and the necessity of determining such curves is here pointed out.
As the measurement of the clotting time of a blood plasma is far from being an ideal method, it is obvious that the accuracy is greatly increased with the estimation of an inhibition curve. For 5 different concentrations of an inhibitory dye, Chlorazol fast pink (Boot's Pure Drug), the activity was determined only from the differences between the clotting time of these solutions and the solutions containing one-half the original concentrations (Fischer and Schmitz 1 ). The following values for k were obtained: 0.184, 0.247, 0.232, 0.140, 0.304. The average value was 0.221 in good agreement with the value 0.215 obtained from the slope of the straight line established when the logarithm of the clotting time was plotted against the concentration of the inhibitory substance.
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