COAGULATION OF THE BI^rOD. 317 



According to PEKELHARING l thrombin is the lime compound of 

 prothrombin, and the process of coagulation consists, according to him, 

 in the thrombin transferring the lime to the fibrinogen, which is thereby 

 converted into an insoluble lime compound, fibrin. Among the objec- 

 tions to this theory can be mentioned, the fact that fibrin has not 

 been obtained absolutely free from lime, but still so poor in lime 

 (HAMMARSTEN 2 ) that if the lime belongs to the fibrin, its molecule 

 must be more than ten times greater than the haemoglobin molecule, 

 which is not probable. These as well as many other observations 

 indicate that the lime is carried down by the fibrinogen only as a 

 contamination. 



If, as it seems, the lime is not of importance in the transformation 

 of fibrinogen into fibrin in the presence of thrombin, still this does not 

 contradict the above-mentioned observations of ARTHUS and PAGES that 

 the lime salts are necessary for coagulation of blood and plasma. It 

 is very probable that the lime salts, as admitted by PEKELHARING, are 

 a requisite for the transformation of prothrombin into thrombin. 



If we attempt to summarize the more or less contradictory investi- 

 gations and views as given in the preceding pages, we can consider the 

 following facts as conclusive: In the first place, two bodies, the fibrin- 

 ogen and the thrombin, are necessary for the coagulation. The fibrinogen 

 exists preformed in the plasma. The thrombin, on the contrary, does 

 not occur in living blood, at least not in appreciable amounts as such, 

 but is formed from another substance, the prothrombin. The presence 

 of calcium salts is necessary for the formation of this thrombin, while 

 the calcium salts are not necessary for the enzymotic transformation 

 of fibrinogen into fibrin. Besides the calcium salts also other substances, 

 the zymoplastic active substances, are active in the formation of thrombin 

 from its mother-substance, and these zymoplastic substances stand in 

 some relation to the form-elements of the blood. 



The formation of thrombin and the relation of the form-elements 

 therewith are still unexplained and disputed questions. 



It is a question whether the mother-substance of thrombin exists in 

 the plasma of the circulating blood or whether it is a body eliminated 

 from the form-elements before coagulation. We have two opposing 

 views on this question, namely, those of ALEX. SCHMIDT and of PEKEL- 

 HARING. According to SCHMIDT prothrombin occurs preformed in the 

 circulating plasma, and it is transformed into thrombin by the zymo- 

 plastic substances which pass out from the form-elements. PEKEL- 

 HARING, on the contrary, holds the view that the plasma does not contain 



1 See footnote 4, p. 256, and especially Virchow's Festschrift, 1, 1891. 

 2 Zeitschr. f. physiol Chem., 28. 



