56 AN AMERICAN TENT-BOOK OF PHYSIOLOGY. 



of clotting waits upon a better knowledge of the nature of these proteids. It 

 is possible that at any moment new facts may be discovered that will alter 

 present ideas of the nature of the process. In considering the different 

 theories that have been proposed there are two general facts that should 

 always be kept in mind : first, that the main phenomenon that 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 < 'oagulation. — The first theory that 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." 



Uammarsten'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 

 was 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. In place of the fibrinogen 

 there is present after clotting, on the one hand, fibrin representing most of 

 the weight of fibrinogen (60-90 per cent.), and, on the other hand, a newly- 

 formed globulin-like proteid retained in solution in the serum, to which pro- 

 teid the name fibrin-globulin has been given. Hammarsten supposed that 

 although paraglobulin took no direct part in the process, it acted as a favor- 

 ing condition, a greater quantity of fibrin being formed when it was present. 

 Later experiments 1 indicated that this supposition was incorrect, and that 

 paraglobulin may be eliminated entirely trom the theory. The theory of 

 Hammarsten, which is perhaps generally accepted at the present time, is 

 incomplete, however, in that it have.- undetermined the nature of the ferment 

 1 Frederikse: Zeitschrift fur physioloyische Chemie, lid. 19, 1814, S. 143. 



