A preliminary reaction of coagulation factors found in plasma and serum.

THERE are so many factors concerned in the coagulation of blood that intermediate reactions between them are inevitable. According to the classic theory, thromboplastin, a lipoprotein or lipid released by injury to cells or platelets, initiates the coagulation of blood. There is evidence (Flynn and Coon, Mann and Hum) that before it reacts with prothrombin, thromboplastin reacts with at least two different substances. These will be referred to as the stable factor and the labile factor. I t is recognized that each may be several substances. For the numerous divergent views as to the substances concerned in coagulation, reference is made to several extensive reviews (Alexander, Deutsch, Seegers, Mann). Evidence has been presented that separate reactions between thromboplastin and the stable and labile factors result in the formation of complexes between thromboplastin and each individual factor.' 6 Each of these incomplete complexes containing only one factor is inactive alone but will add the missing factor to form a product which, isolated by high speed centrifugation, is capable of rapid conversion of prothrombin to thrombin. However, mixtures of the incomplete complexes are inactive, although such mixtures contain all the needed factors. It appears to be necessary for both of the conversion factors to be combined on the same particle of thromboplastin. This paper is concerned with the question of whether the two conversion factors may be associated when not combined with thromboplastin.