THE BLOOD. 539 



have been precipitated. According to this, it is easy to assume that the 

 calcium salts effect the activating of the zymogen. The plasma normally 

 contains only the zymogen of the fibrin-ferment and not the ferment itself. 

 In clotting blood, the ferment is made active under the influence of calcium 

 salts, and is now exerting its action upon the fibrinogen. If, on the other 

 hand, the calcium salts are removed by precipitation with oxalic acid 

 before the coagulation has taken place, then the blood does not show the 

 same tendency to form a clot, because the zymogen remains unchanged, 

 and in this condition it is perfectly inactive. Further support for the view 

 that the calcium salts are only active in this phase of the coagulation, and 

 that they do not take part directly in the conversion of fibrinogen into 

 fibrin, is shown by the work of Hammarsten. He pointed out that only 

 those calcium compounds need be considered which are present in such a 

 state that the calcium is precipitable by oxalic acid. The oxalate plasma 

 contains calcium, in addition, which is evidently present in the form of 

 complex organic compounds. It is possible now to convert fibrinogen 

 into fibrin by the action of the fibrin-ferment in the absence, of lime salts 

 that can be thrown down by oxalate. This experiment is perfectly analo- 

 gous to that with the oxalate plasma. Hammarsten was able also to show 

 that the fibrin could not be regarded as a calcium compound. We do not 

 know exactly how the calcium salts cause this conversion of zymogen 

 into ferment. It is possible that it acts directly upon the zymogen, but 

 it is likewise conceivable that the calcium salts have an indirect action in 

 regulating the conditions. For the present, however, we shall consider that 

 they themselves take part directly in the conversion of the zymogen into 

 ferment, and that otherwise they have nothing whatever to do with the 

 formation of the fibrin. 



We shall at this place mention that quite recently it has been noticed 

 that calcium salts exert an activating effect upon trypsinogen. If inactive 

 pancreatic juice be treated with sodium fluoride it will remain in this con- 

 dition, and is only activated by the addition of calcium salts. In such a 

 case as this the calcium salt evidently does not act directly upon the zymo- 

 gen. If the pancreatic juice be filtered through collodion, then it will no 

 longer be activated by the addition of the calcium salt. Delezenne, 1 who 

 performed this last experiment, believes that some substance is held back 

 on filtering the pancreatic juice through collodion, which is capable of 

 activating the trypsinogen. The calcium salts serve in some way to 

 activate the unknown substance just as it is possible that enterokinase 

 may have an antecedent. If we apply this observation, which to be sure 

 has never been explained entirely satisfactorily, to the coagulation of the 

 blood, then we should have to assume that the zymogen of the fibrin-fer- 

 ment is activated by a substance which corresponds to enterokinase, and 



1 Compt. rend. soc. biol. No. 33 (1905). 



