Most tissues exhibit fibrinolytic activity because of their content of plasminogen activator (Albrechtsen, 1958; Astrup and Stage, 1952; Pandolfi, Nilsson, Robertson, and Isacson, 1967; Sayers, Tyler, and Lack, 1965). This activity might be demonstrated by applying the tissue itself or a tissue extract on a fibrin plate (Astrup and Permin, 1947; Caughey and Highton, 1967) or by the histiochemic...