“…Biggs, Douglas and Macfarlane (1953), in a study ofthe initial stages of blood coagulation, thought that at least five separate factors (antihaemophilic globuh (AHG), Christmas factor, Factors V and VII, and platelets), in the presence of calcium, were necessary for the generation of normal intrinsic thromboplastin. It is now considered that Factor VII does not take part in this reaction, but that it is only required for the action of tissue thromboplastin (Ackroyd, 1956). It was thought unlikely that all these factors reacted at once, and Bergsagel (195s) in an attempt to define the stages of throniboplastin generation considered that the initial stage of thromboplastin formation involved the interaction of AHG and Christmas factor in the presence of calcium.…”