The Reaction of Haemophilic Plasma to Thromboplastin

Two well-known observations on the clotting defect of haemophilic blood would seem to be of basic importance. The first is that haemophilic blood responds quite normally to a strong suspension of tissue thromboplastin; the second, that it will clot in practically the normal time on the addition of a small proportion of normal plasma. The normal response to thromboplastin naturally suggests that the part of the clotting mechanism which is set in motion by thromboplastin is in normal working order. Certainly no defect has been demonstrated in haemophilic prothrombin, fibrinogen, or calcium, and the various factors recently described as being concerned in prothrombin conversion, such as Factor V (Owren, 1947) and " serum prothrombin conversion accelerator " (Alexander and de Vries, 1949), are stated by these respective authors to be normal in haemophilia.