BENJAMIN ALEXANDER AND ANDRE DE VRIES TABLE II Restorative

In 1943 Quick (1) reported on the multiple nature of plasma prothrombin. On the basis of his data, which have been repeatedly confirmed (24), he concluded that prothrombin consists of two essential factors combined with calcium. The two components, "prothrombin A" and "prothrombin B," had different properties. The former was labile in oxalated or citrated plasma stored at refrigerator temperatures, not adsorbable by aluminum hydroxide, fairly heat stable, and not reduced in dicumarolized blood. Its deterioration was said to account for the high prothrombin time of stored plasma. "Prothrombin B," on the other hand, remained intact in refrigerated plasma, was removed by aluminum hydroxide, was labile at 600 C. for 15 minutes, and was decreased by the administration of dicumarol. More recently other entities were described which affect the conversion of prothrombin to thrombin by thromboplastin plus calcium (5-7). These are apparently distinct from both "prothrombin B" and the factor which deteriorates in stored plasma. The term "prothrombin A" is now reserved by Quick (5) for one of these substances, and the term "labile factor" for the moiety which is found wanting in stored plasma. Normal prothrombin activity, as determined by the one-stage method, requires the presence of adequate amounts of all these substances. Loomis and Seegers (4) found that the prothrombin activity of aged plasma could be restored remarkably by the addition of purified fibrinogen. Accordingly, they concluded that deterioration of fibrinogen accounts for lengthening of the prothrombin time in stored plasma and that "reactive