A substance allied to mucoitisulphuric acid and a physiological anticoagulant found in most tissues of a body, especially the liver and lung. It inhibits the clotting of blood in vivo and in vitro by preventing the conversion of prothrombin to thrombin and by antagonizing the action of thrombokinase. It requires to be injected, being inactive by mouth, and is used to prevent or limit thrombosis and to stop the clotting of shed blood (BP 1973).