Abstract
A review of recent investigations on the fibrinolytic process in blood is presented. Using the simple and sensitive fibrin plate method for the estimation of fibrinolytic activity it was possible to follow the activation of plasminogen to plasmin produced by the tissue activator: fibrinokinase. This reaction was of a stoichiometrical and not of a catalytic nature. Ox lung contains a fibrinolytic inhibitor, which could be purified. The term "pulmin" is suggested for this inhibitor, which differs from heparin. A general principle for the formation of biologically active substances in the blood is suggested.