THE COAGULATION OF THE BLOOD. 367 



change in the proteid called caseinogen ; die second stage is 

 due to calcium salts, which precipitate the changed casein- 

 ogen, as the curd of casein. Fibrin is similarly believed to 

 be a calcium compound of fibrinogen. On the other hand, 

 Pekelharing showed that calcium salts have the additional 

 action of assisting the formation of fibrin-ferment from its 

 precursor or zymogen. The main outcome of Hammar- 

 sten's work is to show that this is the only part that the soluble 

 calcium salts of the plasma play. They are undoubtedly 

 essential for coagulation, but after fibrin-ferment has once 

 been formed their presence is no longer necessary. Or to 

 put it another way, and adopt a new nomenclature : in the 

 living blood no thrombin or fibrin-ferment is present ; that 

 substance exists in the form of a zymogen, which may be 

 l^xiVi^di p7'0-thrombin ; calcium salts act by converting pro- 

 thrombin into thrombin. 



Any one who has ever tried to prevent coagulation in 

 blood by adding a soluble oxalate to it immediately it is 

 shed will know that they will often fail. This is because 

 they are not quick enough. If the oxalate is mixed with 

 the blood sufficiently rapidly, it will prevent the formation 

 of thrombin ; but if there is the least delay, prothrombin 

 will pass into the condition of thrombin, and no amount of 

 oxalate subsequently added will prevent the thrombin or 

 fibrin-ferment from converting fibrinoo-en into fibrin. 



In the present research, Hammarsten prepared speci- 

 mens of oxalated plasma, specimens of oxalated solution of 

 fibrinogen, specimens of oxalated solution of fibrin-ferment, 

 and specimens of oxalated serum, which is practically a 

 solution of fibrin-ferment with numerous other things as w^ell. 

 On mixinor tosj'ether such solutions of fibrinogen with such 

 solutions of fibrin-ferment he always obtained, and frequently 

 rapidly obtained, a typical and abundant formation of fibrin. 



In this connection it is important to notice that oxalated 

 preparations of this kind are not in the strictest sense of 

 the word, decalcified. They are only decalcified in what 

 Hammarsten calls Arthus' sense of the word. That is, 

 the oxalate added is unable to combine with and displace 

 the calcium which is directly in union with proteid matter. 



