132 THE HEMORRHAGIC DIATHESIS 



incision or laceration which excites the haemorrhage 

 provides also the wherewithal to stop it. The 

 nucleoprotein furnished in this way by the tissues is 

 called thrombokinase. 



Next, we know that calcium salts are needful for 

 clotting, and if they are withdrawn by oxalates or 

 citrates, no fibrin will be formed. An excess of 

 calcium salts, however, delays clotting. 



Concerning thrombogen or prothrombin we cannot 

 speak so confidently. It is intimately associated 

 with, and hard to separate from, fibrinogen, but is 

 probably derived eventually from the leucocytes 

 and platelets. Hydrocele fluid, which does not 

 contain any corpuscles, will not clot until blood or 

 fibrin is added. 



The actual mother substance of the fibrin is of 

 course the fibrinogen, a protein in the plasma. There 

 is really a double reaction, thus : — 



(i) Prothrombin + Thrombokinase + Calcium salts 

 (= thrombogen) (from damaged (in plasma) 



(? from leucocytes) leucocytes or 



tissue-cells) 



I I i 



t 

 Thrombin ( = fibrin ferment) 



(ii) Thrombin + Fibrinogen (in plasma) 



Fibrin 



According to Mellanby, the name fibrin ferment 

 is a misnomer, as a particular weight of thrombin 

 will liberate only a certain definite quantity of fibrin 

 from fibrinogen, whereas a ferment knows no limits 

 to its activities. 



