Significance of Thromboplastic Activity of Antigens Used in Complement-Fixation Tests

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Abstract
Thromboplastic substances such as cephalin or extracts of fresh tissues not only accelerate markedly the coagulation of recalcified oxa-lated plasma but inhibit the hemolytic activity of complement. When saline extracts of fresh mammalian tissue were tested as antigens with normal rabbit sera inactivated 1/2 hr. at 56[degree]C, both activities were enhanced in similar degree. When sera were inactivated at 60[degree] and 65[degree]C, respectively, the diminution in complement fixation was closely paralleled by the decrease in clotting activity. Thus it appears that the fixation of complement obtained is not due to the presence of normal antibodies in the rabbit sera, but to an enhancement of the thromboplastic activity of the tissue extracts.