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A method of obtaining partially purified products of plasmin degradation of fibrinogen (F.D.P.) is described. The F.D.P. passes through dialysing tubes and does not lose its activity during heating for 15 min at a temperature of 56° C. In experiments on isolated organs, F.D.P. in small doses potentiates the contractile action of bradykinin, kallidin, angiotensin, histamine, 5‐hydroxytryptamine, acetylcholine, adrenaline and noradrenaline. In high concentrations, F.D.P. induces an increase in initial tonus of the smooth muscles and simultaneously lowers the sensitivity of the smooth muscles to the action of the pharmacologically active substances mentioned. A similarity in the effect of different concentrations of KC1 and different concentrations of F.D.P. on the contractile reaction of the guinea‐pig intestine to constant doses of histamine and bradykinin and on the initial tonus of the smooth muscles is observed. A hypothesis is presented that F.D.P. in small doses potentiates the contractile action of amines and polypeptides on the smooth muscles and in larger doses increases the initial tonus of these muscles by changing the concentration of the cell electrolytes.

Thromboplastic activity and concentration of plasminogen activator were assayed in the coats of arteries and veins from a number of species. The widely differing patterns found in these species suggest great variation in the tendency to deposit fibrin on the interior surface of the vessels. Several modes of regulating fibrin deposition after intimal injury exist in the animal organism. These observations may assist the evaluation of data obtained in experiments on animals, and they demonstrate certain limitations with respect to conclusions on pathology in man.

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SummaryIn experiments on rabbits it was shown by means of interruption and reestablishment of hepatic and renal circulation that these organs play an essential role in the regulation of the fibrinolytic system of the circulating blood. The kidneys are the source of the plasminogen activator secreted in the blood whereas the liver is responsible for the inactivation of the fibrinolytic system.