II. The Relation between Clotting Time antl Plasma Concentration in Prothrombin-Time Estimations

As a rule, clotting times obtained in prothrombin-time estimations become longer the more a plasma is filuted. This holds for the original Quick method as well as for any of its modifications. The estimation of the way in which clotting time (t") varies with the concentration (C) of the clotting factors in the plasma being tested, may be of considerable importance. Such estimation is done by analysis of the curve that gives t. as a function of C, which will reveal the nature of the function ts: f(C). It has been claimed (1,2) that, this function is hylerbolic, i. e. that the plot of t against l/C is a straight line. This assumption yields useful results in the study of various kinds of thromboplastins (3, 4). The purpose of this study was to assess the nature of t " : f(C) for the case of dilutions of normal plasma tested with the Thrombotest reagent; to see what influences affect the parameters of this function and to investigate briefly the results with other thromboplastins. Materials and Methoils Normal Plasma (N. Pl.): pooled platelet-free citrated plasma from at least 30 healthy normals (mean age around 30 years), freed of platelets by centri{ugation for 30 ' at l2,5OO g and stored at,-25 " C in 1 mI aliquots. Throe different batches of pooled norrnal plasma were used. Eactor Vll-d,ef,cdent gia,sma: plasma from a patient with congenital factor Vll-deficiency, prepared in the same way as the normal plasma. This plasma contained 80o/o factor X. Iactor X-d,ef,a,ient gtlasma: plasma from a patient suffering fiom amyloidosis with consequen