PLASMA IN VITRO 1 2

Previous studies from this laboratory have dem-onstrated that, at least, 2 protein fractions can be prepared from cell and calcium-free human plasma-which have a definite effect of lowering the coagulation time of hemophilic blood (1 to 4). One of these protein fractions requires the pres-ence of both calcium ion and prothrombin in or-der to exhibit its activity. The other acts as a true thrombin since it can convert fibrinogen to fibrin in the absence of calcium and prothrombin. It has been further demonstrated that the for-mer protein preparation, presumably associated with the euglobulin fraction, can by treatment with chloroform be converted into a protein preparation having proteolytic activity (5, 6). The physiologic role of this enzyme has not been determined. However, it is known that it can convert prothrombin to thrombin and hence in appropriate amounts induce blood coagulation (7). In larger amounts it can digest fibrinogen before fibrin formation can take place. Various preparations of globulin fractions from pooled normal human plasma were placed at our disposal for study of their coagulation properties.3 A summary of our results has been presented by other workers (8). The present communication concerns the ac-tivity of these globulin fractions in vitro. In th