“…The plasminogen activator has not been adequately identified biochemically but a crude form is certainly extractable from the lining of blood vessels especially venous endothelium (Astrup, 1966). It is rather odd that the endothelium of large arteries has little fibrinolytic activity (Astrup 1966) but the endothelium of large veins and most small vessels are rich sources of plasminogen activator (Pandolfi, 1970;Astedt, Pandolfi & Nilsson, 1971). In the skin, the deep dermal veins and capillaries are more active than the subpapillary vessels (Haustein, 1966;Turner & Ryan, 1969).…”