THE COAGULATION OF THE BLOOD 61 



Into fibrin, and the latter body is certainly not a calcium 

 compound of the former. A series of analyses confirmed this, 

 since it was shown that the calcium content of fibrin is not 

 higher than the fibrinogen which yielded it, and fibrin can be 

 produced which contains only a trace of lime — 0*007 to 0*0095 

 per cent. However, the absolute proof that calcium does take 

 a specific part in the formation of fibrin-ferment, as Pekelharing 

 believed, was confirmed by Hammarsten, since the material 

 separated from cooled oxalated plasma contained a zymogen 

 which could be directly and specifically activated by calcium 

 salts, and induce coagulation of fibrinogen solutions, a property 

 it did not possess unless these salts were added. Calcium salts 

 or calcium ions, therefore, play an essential role in the first 

 phase of the coagulation process by activating a zymogen. In 

 this way thrombin, non-existent in living blood, originates in 

 blood after it is shed. The absolute amount of calcium present 

 is stated by Sabbatani 1 to be a negligible factor for the formation 

 of thrombin. Only that portion which is in the ionic state is 

 concerned in the process. The arguments for this view are 

 that all physical methods which, like heat and cold, exalt or 

 depress the amount of ionisation or affect the velocity of the 

 ions, equally affect, accelerate, or retard the onset of coagulation. 

 In the case of fluoride-plasma, which clots simply on the 

 addition of water, the dilution' may promote a sufficient degree 

 of ionisation of the suspended lime salts. 



6. Thrombin or Fibrin-Ferment 



The interest attaching to this part of the question may be 

 grouped around the three following facts : 



1. The production of intra-vascular clotting by the injection 

 of various tissue-extracts, and the development of a clot in 

 vitro from non-coagulable or feebly coagulable liquids by the 

 addition of tissue-extracts. 



2. The discovery of Delezenne that the blood of those 

 vertebrates which possess nucleated red corpuscles often does 

 not spontaneously clot. Blood removed from birds such as the 

 goose or pigeon with every aseptic precaution will yield a 

 clear plasma which may actually commence to putrefy before 

 it coagulates. 



1 Arch. ital. de Biologie, xxxix. 1, p. 333. 



