CHAPTER IX. 

 THE COAGULATION OF BLOOD. 



In spite of the immense amount of work that has been 

 done on the subject, it is impossible to explain fully the 

 fact that when blood is shed it rapidly sets to a jelly, which 

 subsequently contracts. The clot consists of the corpuscles 

 entangled in a contracting meshwork of fibrin : the yellowish 

 fluid that exudes is the serum. 



The following account of some of the factors concerned 

 and the appended scheme of their interaction does not 

 allow for a great deal of important work that has been done 

 in recent years. It is almost certain that the phenomenon 

 is considerably more complicated than that indicated 

 below. 



Factors concerned. 



1. Fibrinogen, a globulin, present in blood-plasma. 

 It is soluble in dilute salt solutions, acids and alkalies, 

 insoluble in distilled water. It coagulates at 57 C. It is 

 precipitated by half-saturation with sodium chloride. 



2. Pro-thrombin, a substance of unknown composi- 

 tion, found in plasma, attached to the fibrinogen. It is 

 destroyed by boiling. 



3. Thrombokinase, a substance found in all tissues 

 and also liberated in the blood by the disintegration of 

 leucocytes and blood-platelets. It converts pro-thrombi n 

 into thrombin, under certain conditions. 



4. Calcium salts, found in plasma, and necessary for 

 the action of thrombokinase. The calcium salts must be 

 of such a nature that they are ionised in solution. 



