THEORIES OF COAGULATION 



105 



blood, and the resulting fluid no longer retains its power of spontaneous 

 coagulability. 



Theories of Coagulation. It is evident that the blood plasma 

 contains some substance or substances which take part in the formation of 

 fibrin. By numerous investigations it has been found that the direct ante- 

 cedent of the fibrin is the proteid substance, fibrinogen. This fibrinogen 

 exists in the blood plasma at all times, but is somewhat increased under 

 certain conditions. The fibrinogen is reacted on by another substance 

 known as thrombin, or by the historical term fibrin ferment. We shall not 

 present the numerous theories which have been held concerning blood coagu- 

 lation, many of which have been more or less disproven, but shall try to present 



Blood 



Tissue Cells 



Plasma 



Blood Plates Corpuscles 



Neutral Salts Fibrinogen Calcium Salts 



(for dissolving 

 fibrinoRen) 



Fibrin-globulin 



Prothrombin 



Thrombokinase 



Thrombin 



Fibrin 

 FIG. 108. Schema of Coagulation. 



the condensed statement of the present explanations of this intricate phenom- 

 enon. One may start from the statement that the fibrinogen of the plasma 

 when acted upon by the thrombin, also of the plasma, produces an insoluble 

 substance, fibrin. The chief interest centers around the origin and char- 

 acter of the fibrinogen, the origin and nature of the thrombin, and the condi- 

 tions which influence its activity. 



The fibrinogen is present in blood plasma of the circulating blood of the 

 body at all times. It can be separated from plasma by various chemical 

 means, and when purified can be made to form fibrin under proper conditions. 

 All observers are agreed that this proteid is the immediate precursor of the 

 insoluble fibrin. Its origin in the blood has been traced with some degree 

 of certainty to the disintegration of the white blood-corpuscles. 



The thrombin is the substance which reacts on the fibrinogen in the proc- 

 esses of fibrin formation. It does not exist in the living blood-vessels, or at 



