Platelets were identified in 1865, and their function was elucidated by Giulio Bizzozero in 1882. The theory that thrombin is generated by the presence of tissue factor was consolidated by Paul Morawitz in 1905. At this stage, it was known that "thrombokinase/thromboplastin" (factor III) is released by damaged tissues, reacting with "prothrombin" (II), which, together with calcium (IV), forms "thrombin", which converts fibrinogen into "fibrin" (I). The remainder of the biochemical factors in the process of coagulation were largely discovered in the 20th century. A first clue as to the actual complexity of the system of coagulation was the discovery of "proaccelerin" (initially and later called Factor V) by Paul Owren (1905–1990) in 1947. He also postulated its function to be the generation of accelerin (Factor VI), which later turned out to be the activated form of V (or Va); hence, VI is not now in active use. Factor VII (also known as "serum prothrombin conversion accelerator" or "proconvertin", precipitated by barium sulfate) was discovered in a young female patient in 1949 and 1951 by different groups. Factor VIII turned out to be deficient in the clinically recognised but etiologically elusive hemophilia A; it was identified in the 1950s and is alternatively called "antihemophilic globulin" due to its capability to correct hemophilia A.  Factor IX was discovered in 1952 in a young patient with hemophilia B named Stephen Christmas (1947–1993). His deficiency was described by Dr. Rosemary Biggs and Professor R.G. MacFarlane in Oxford, UK. The factor is, hence, called Christmas Factor. Christmas lived in Canada, and campaigned for blood transfusion safety until succumbing to transfusion-related AIDS at age 46. An alternative name for the factor is "plasma thromboplastin component", given by an independent group in California. Hageman factor, now known as factor XII, was identified in 1955 in an asymptomatic patient with a prolonged bleeding time named of John Hageman. Factor X, or Stuart-Prower factor, followed, in 1956. This protein was identified in a Ms. Audrey Prower of London, who had a lifelong bleeding tendency. In 1957, an American group identified the same factor in a Mr. Rufus Stuart.