THE CHEMICAL STATE OF THE CALCIUM REACTING IN THE COAGULATION OF BLOOD*

For nearly a half century almost every student of coagulation has accepted the hypothesis that ionized calcium is essential for coagulation. Many in-vestigators, moreover, hold that ionized calcium acts as a catalyst. The origin of these concepts can be traced first to Arthus and Pages (1) who in 1890 showed that blood was made incoagulable by sodium oxalate and that readdition of calcium restored normal coagulation. They justifiably concluded that cal-cium was necessary for the coagulation reaction. Two years later Pekelharing (11) found that sodium citrate was equally effective as an anticoagulant, and, being no doubt influenced by the work of Arthus and Pages, he concluded that the action of sodium citrate was on the calcium. Interestingly, Alexander Schmidt (18) refused to accept he idea that calcium had a specific r61e in coagulationi He attributed the action of both sodium oxalate and sodium citrate to a non-specific salt effect. Considerable uncertainty remained until Sabbatani (17) explained the pe-culiar behavior of sodium citrate by stating that calcium forms a complex wit