354 AN AMERICAN TEXT-BOOK OF PHYSIOLOGY. 



which a theory of coagulation has to explain is the formation of fibrin ; second, 

 that all theories unite in the common belief that the fibrin is derived, in part at 

 least, from the fibrinogen of the plasma. 



Schmidt's Older Theory of Coagulation. The first theory which gained 

 general acceptance in recent times was that of Alexander Schmidt. It was 

 proposed in 1861, and it has served as the basis for all subsequent theories. 

 Schmidt held that the fibrin of the clot is formed by a reaction between para- 

 globulin (he called it " fibrinoplastin ") and fibrinogen, and that this reaction is 

 brought about by a third body, to which he gave the name of fibrin ferment. 

 Fibrin ferment was believed to be absent from normal blood, but to be formed 

 after the blood was shed. Further reference will presently be made to the 

 nature of this substance. Schmidt was not able to determine its nature 

 whether it was a proteid or not but he discovered a method of preparing it 

 from blood-serum, and demonstrated that it cannot be obtained from blood 

 immediately after it leaves the blood-vessels, and that consequently it does not 

 exist in circulating blood, in any appreciable quantity at least. Finally, 

 Schmidt believed that a certain quantity of soluble salts is necessary as a 

 fourth "fibrin factor." 



Hammarsten'' 's Theory of Coagulation. Hammarsten, who repeated 

 Schmidt's experiments, demonstrated that paraglobulin is unnecessary for 

 the formation of fibrin. He showed that if a solution of pure fibrinogen is 

 prepared, and if there is added to it a solution of fibrin ferment entirely free 

 from paraglobulin, a typical clot is formed. This experiment has since been 

 confirmed by others, so that at present it is generally accepted that paraglob- 

 ulin takes no direct part in the formation of fibrin. Hammarsten's theory 

 is that there are two fibrin factors, fibrin ferment and fibrinogen, and that 

 fibrin results from a reaction between these two bodies. The nature of this 

 reaction could not be determined, but Hammarsten showed that the entire 

 fibrinogen molecule is not changed to fibrin. A dissociation or splitting 

 occurs, so that in place of the fibrinogen there is present after clotting, on the 

 one hand, fibrin representing most of the weight of fibrinogen, and, on the 

 other hand, a newly-formed globulin-like proteid retained in solution in the 

 serum, to which proteid the name fibrin-globulin has been given. Ham- 

 marsten supposed that although paraglobulin took no direct part in the process, 

 it acted as a favoring condition, a greater quantity of fibrin being formed 

 when it was present. Some recent experiments x show that this supposition 

 is incorrect, and that paraglobulin may be eliminated entirely from the theory. 

 The theory of Hammarsten, which is perhaps generally accepted at the present 

 time, is incomplete, however, in that it leaves undetermined the nature of the 

 ferment and of the reaction between it and the fibrinogen. The aim of the 

 newer theories has been to supply this deficiency. 



Schmidt's Recent Theory of Coagulation. In a recent book 2 containing 

 the results of a lifetime of work devoted to the study of blood-coagulation, 



1 Frederikse : Zeitschri/t fur physiologische Chemie, vol. 19, 1894, p. 143. 



2 Zur Blulkhre, Leipzig, 1893. 



