THE CLOTTING OF BLOOD 103 



a clean cut, and why, when calcium ions arc withdrawn from the 

 blood by the addition of a soluble oxalate or citrate, the blood will 

 not clot. The enzyme thrombin thus formed then acts upon the 

 librinogen of the plasma and transforms it into so.id fibrin, which 

 entangles the red corpuscles and forms the blood-c'ot. 

 The process may be represented as follows : 



Thrombokinase (from Free Ca ion Prothrombin or thrombogen 



tissue fluid, possibly (,'ix.m plasma) (from white corpuscles, blood-platelets) 

 also white corpuscles) 



FIBRINOGEN 



(soluble protein of plasma) 



4< 



FIBRIN 



(insoluble protein or clot 

 entangling red corpuscles) 



In accordance with the above view of enzymic action it is supposed 

 that oxalate, fluoride, and citrate, prevent the formation of the enzyme 

 by withdrawing calcium ions, and that fluoride also destroys throm- 

 bokinase. Hirudin is believed to be an antithrombin. Cobra poison 

 is held somehow to interfere with the action of thrombokinase. 

 Roughened surfaces, etc., break down white corpuscles and provide 

 points d'appui from which the enzyme can act. Cold inhibits enzymic 

 activity; on the other hand body temperature hastens it. Oil and 

 smooth surfaces deprive the enzyme of points for action. 



COAGULATION TIME, TESTED IN A GLASS VESSEL AT ROOM TEMPERATURE. 



Man . . . . . . 2 to 6 minutes Ox . . . . . . 8 to 10 minutes 



Dog 4 to 8 Pig 10 to 15 



Sheep . . . . 4 to 8 Horse . . . . 15 to 30 



According to the above view the tissue extract has only an indirect 

 action on clotting; other authorities believe that the tissue juices 

 have a direct clotting action. Recently it has been suggested that 

 thrombin results from the interaction of two substances, cytozyme 

 and serozyme. The former is said to be present in tissue cells and 

 blood-platelets, and is not destroyed by heating to 100 C., while the 

 latter is present in serum and is destroyed by heat at 56 C. . Very 

 little serozyme is said to be in plasma, and its origin is unknown. 



According to another view of clotting, thrombin and its antibody, 

 antithrombin, are present in the blood. When blood is shed the 

 tissue fluid combines with the anti-thrombin, leaving the thrombin 

 free to convert fibrinogen into fibrin. 



According to still another view, thrombin does not bring about 

 clotting, but is a body produced as the result of clotting. Upon this 

 view the bodies which take part in the clotting are fibrinogen, 

 thrombogen, thrombokinase (sometimes called thrombozyme), and 

 calcium salts. When blood is shed the three colloids fibrinogen, 



