542 LECTURE XXIII. 



regarded as the result of fermentation. The fermentation is brought 

 about by the fibrin-ferment which does not occur as such in the blood but 

 is probably present in the plasma in an inactive condition, the zymogen of 

 the fibrin-ferment. In order for the zymogen to become active, a second 

 substance must act upon it. A true activation must take place. The 

 exact nature of the activator of the zymogen is at present unknown. It 

 is not impossible that calcium salts bring about this effect. Certain 

 observations, however, make it appear improbable that the calcium salts 

 take part directly in the formation of the ferment from its zymogen con- 

 dition. Some facts indicate that a peculiar kinase is active, which is 

 itself set free in some way so that it can act upon the zymogen. Appar- 

 ently it is here that the calcium salts come into play. It may be mentioned, 

 in addition, that two antecedents of the zymogen have been described in 

 the literature. One of these, which has not been mentioned, is said to 

 be activated by acids or alkalies. It has been found, namely, that the 

 serum from clotted blood, which of itself contains but little active ferment, 

 will become very active upon the addition of acid or alkali. There is, 

 nevertheless, no ground for assuming that there are two kinds of zymogen 

 present. We agree with Morawitz that the fibrin-ferment, for some reason 

 or other, becomes inactive after the blood-clot has formed. It is simplest 

 to assume that the fibrin-ferment unites with some other compound, 

 whereby its active group is rendered inactive. It is equally plausible that 

 by means of some intramolecular transformation, perhaps the formation 

 of an anhydride, the inactive condition of the ferment is again obtained. 

 The alkali or acid which is added to the serum would in the first instance 

 set the ferment free, whereas, according to the latter view, the anhydride 

 form would be lost. At all events, it is unnecessary to assume that the 

 fibrin-ferment has two antecedents. It is evident from this attempted 

 explanation, what a complicated process the clotting of blood really is, 

 and how many different minor processes must be cleared up before we shall 

 be able to understand the whole phenomenon of blood-coagulation. 



The point that is of chief interest to us here, is as regards the nature of 

 the fermentation. Does a hydrolysis take place, an oxidation, a reduction, 

 or what? The first assumption only need be discussed. Formerly, it was 

 believed that the fibrinogen took on water and formed fibrin together with 

 a substance soluble in water, which was called fibrin-globulin. Recently 

 every justification for such an assumption has been denied, and mainly 

 because it is possible to prepare solutions of fibrinogen which will not split 

 off fibrin-globulin either by clotting or coagulating by heat. 1 According 

 to the more recent view, the formation of fibrin results from an intra- 

 molecular rearrangement of the atoms. There is at present no prospect of 

 deciding this question definitely. Fibrinogen is an albuminous substance, 



Huiskamp: Z. physiol. Chem. 44, 182 (1905). 



