THE CIRCULATING LIQUIDS OF THE BODY 33 



a solution which can be obtained by precipitating blood-serum, 

 or defibrinated blood, with fifteen to twenty times its bulk of 

 alcohol, letting the whole stand for a month or more, and then 

 extracting the precipitate with water. All the ordinary proteins 

 of the blood having been rendered insoluble by the alcohol, the 

 fibrin-ferment passes into solution in the water, and the addition of 

 a trace of the extract to a solution of fibrinogen causes coagulation. 

 The supposed distinction between this form of thrombin and the 

 other is not so well established that we need take account of it here. 

 The action of fibrin-ferment on fibrinogen helps to explain 

 many experiments in coagulation. Thus, transudations like 

 hydrocele fluid do not clot spontaneously, although they contain 

 fibrinogen, which can be precipitated from them by a stream of 

 carbon dioxide or by sodium chloride. But the addition of a 

 little fibrin-ferment causes hydrocele fluid to coagulate. So does 

 the addition of serum, not because of the serum-globulin which 

 it contains, as was once believed, but because of the fibrin- 

 ferment in it. The addition of blood-clot, either before or after 

 the corpuscles have been washed away, or of serum-globulin 

 obtained from serum, also causes coagulation of hydrocele fluid, 

 and for a similar reason, the fibrin-ferment having a tendency 

 to cling to everything derived from a liquid containing it. On 

 the other hand, serum, which, although fibrin-ferment is present 

 in it, does not of itself clot, because the fibrinogen has all been 

 changed into fibrin during coagulation of the blood, can be made 

 to coagulate by the addition of hydrocele fluid, which contains 

 fibrinogen. We have thus arrived a step farther in our attempt 

 to explain the coagulation of the blood : it is essentially due to 

 the formation of fibrin from the fibrinogen of the plasma under the 

 influence of fibrin- ferment. 



The Formation of Fibrin- ferment from its Precursors. 

 There is good reason to believe that thrombin is formed by 

 the interaction of three factors : (i) A substance which, since 

 it is a precursor of thrombin, is called thrombogen, or pro- 

 thrombin. It is already present in the circulating plasma. 

 (2) A substance liberated from the formed elements of the shed 

 blood, but which can be obtained also from the cells of all tissues. 

 Since it has been supposed to act upon thrombogen, changing it 

 into fully-formed thrombin, much in the same way as entero- 

 kinase (p. 331) acts upon trypsinogen, changing it into fully- 

 formed trypsin, it is called thrombokinase (Morawitz).* (3) Cal- 



* Others believe, however, that the substances in tissue extracts which 

 favour coagulation do so not by activating prothrombin, but by a direct 

 action upon fibrinogen similar to, but not necessarily identical with, that 

 exerted by thrombin, and speak of them as coagulins (L. Loeb). It is 

 possible that the tissues yield both activating substances (kinases) and 

 coagulins. 



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