THE COAGULATION OF THE BLOOD 



213 



into two stages, the first ending with the formation of thrombin and 

 the second with the production of fibrin. Fibrin as such is not present 

 in the circulating blood, but is derived from a precursor through the 

 intervention of thrombin. The substance from which fibrin arises, is 

 known as fibrinogen and is present as such in the plasmatic portion of 

 normal blood. Fibrinogen, however, is an inert body and must first 

 be activated before its conversion into the final product, fibrin, can be 

 achieved. This activation is made possible solely with the help of a 

 fibrin "ferment," commonly designated as thrombin. 



Thrombin as such is not present in normal blood, but is formed from 

 an inactive precursor, called thrombogen or prothrombin. The con- 

 version of the latter into its active form is accomplished by means of 

 an organic thromboplastic agent, called thrombokinase, in the pres- 

 ence of soluble calcium. The kinase is furnished by the cellular 

 elements of the blood, principally the thrombocytes. To recapitu- 

 late, the circulating blood contains fibrinogen, thrombogen and solu- 

 ble calcium salts. If the blood is brought in contact with a foreign 

 body so that a destruction of the thrombocytes results, thrombokinase 

 is liberated which, with the help of ionic calcium, activates the throm- 

 bogen into thrombin. This process constitutes the first phase of 

 coagulation. Its completion in turn insures the second phase which 

 consists in the conversion of fibrinogen into fibrin. 



Blood' 



Plasma 



Fibrinogen Thrombogen Calcium 



Thrombin< 



Solids 

 (Thrombocytes) 



Thrombokinase 



Fibrin 



This explanation of the process of clotting is in accordance with 

 the views expressed by Moravitz, 1 Fuld and Spiro, 2 and is based upon 

 data which have been furnished in large part by Schmidt, Wooldridge, 

 Pekelharing, and Hammarsten. While this view is open to several 

 objections, especially in regard to the action of thrombin, it is the one 

 commonly accepted to-day. A second explanation, which is in part 



1 Hofmeister's Beitrage, iv, 1903, 381; also see: A. Schmidt, Zur Blutlehre, 

 Leipzig, 1892 and Wiesbaden, 1895. 



2 Ibid., v, 19.04, 171. 



