Differences in the Resistance of Human Plasmas to Staphylocoagulase *

Several observers have reported that plasmas differ in their susceptibility to staphylocoagulase. Chapman' tested 81 fresh human blood samples with a ten-hour staphylococcus culture, and noted that at two hours firm clots had formed with 35, partial clots with 25, while 21 bloods remained unclotted. The suggestion that such variation in human plasmas may be due to the activity of "inhibitors" has received support from the observation that slightly diluted plasmas may be clotted more rapidly than are the undiluted samples. Fisher' and Cruikshank4 therefore advocated the use of plasma diluted 1:10 for routine coagulase testing. Chapman2 and his associates, working with rabbit plasma, recommend a dilution of 1:4, but found higher dilutions unsatisfactory. However, no attempt was made to restore fibrinogen to the diluted plasma. Lominski and Roberts' approached the problem by titrating serum for the limiting dilution which would inhibit the clotting of plasma by coagulase. Of 348 sera, 212 contained inhibitory substances. On the other hand, 104 plasmas subjected to the same test only rarely inhibited coagulation, and then only in the undiluted state. The authors explain this difference in the behavior of serum and plasma on a greater affinity of coagulase for fibrinogen than for the inhibitory substance. Smith and Hale,8 in a test of 40 human plasmas noted one which failed to clot with viable staphylococci, and gave a low titer with a cell-free filtrate. They suggest' that this is due not so much to inhibitory substances, as to a lack of the "activator" in the plasma. Recent studies have reopened the controversial problem of the antigenicity of coagulase. It has been shown that following hyperimmunization with concentrated purified coagulase, rabbit plasmas become more resistant to the action of coagulase, that an enhanced serum neutralization develops, and that complement-fixing and collodion particle agglutinating bodies appear.3 The specificity of the inhibition