Prothrombin studies using Russell viper venom

Plasma prothrombin dilution studies, using; a modified Quick's method employing Russell viper venom instead oil brain substance extract, have been carried out on 26 human beings who were found to be normal by clinical tests. In our hands, using normal undiluted (100 per cent) human plasma, this test gave an average prothrombin clotting time of 20.6 seconds. When the normal plasma was diluted with physiologic saline according to the following proportions, the prothrombin clotting time increased as the dilution was increased. OXALATED PLASMA PER CENT MEAN PROTHROMBIN CLOTTING TIME SECONDS 100 20.76 80 22.81 60 26.60 40 33.10 20 51.36 Graphs for computing the plasma prothrombin concentration (in terms of percentage of normal) from a known clotting time were worked out and are presented in Figs. 1 and 2. The probability of an increased prothrombin clotting time being normal was given consideration. If the clotting time increases, the odds that it could still be normal decrease, and a statistical computation of this part of the study has been incorporated into a graph that may be used in connection with any method for determining prothrombin clotting time.