86 THE BLOOD 



would bo the case if, in accordance with van't HofFs law, the 

 reaction were a chemical one. 



A conservative statement of the process of coagulation 

 would be as follows: The blood plates and the leukocytes 

 in their disintegration in shed blood yield prothrombin. Pro- 

 thrombin with calcium salts and possibly zymoplastic substances 

 gives rise to thrombin. Thrombin plus fibrinogen gives fibrin. 



That thrombogen has its origin in the leukocytes is shown 

 by the following facts : 



1. In microscopic preparations of coagulating blood the 

 fibrin fibrils radiate from broken-down leukocytes and from 

 blood plates. 



2. Whatever prevents the disintegration of the white blood 

 cells retards the coagulation of the blood. 



Clotting within the bloodvessels may be brought about by 

 the presence of foreign bodies or by injury to the epithelial 

 lining of the vessels. When the clot is confined to the injured 

 area it is called a thrombus. General intra vascular clotting 

 is brought about by the injection of fibrin ferment, nucleo- 

 albumins, etc.; but this is not accomplished easily, owing to 

 a defensive function for the body exerted by the cells of the 

 liver. Sometimes the blood is rendered less coagulable by the 

 injection of the above substances, constituting the negative 

 phase of the injection. This is explained by the assumption 

 of the predominance of histon over leukonuclein, both of which 

 are formed by the breaking down of leukocytes. Histon retards 

 the coagulation, while leukonuclein favors it. Normally the 

 blood of the body^is prevented from clotting by the integrity 

 of the lining epithelium of the vessels. In the living test-tube 

 experiment, for example, the jugular vein with its contained 

 blood are removed from the neck of the horse, and it is found 

 that the blood under these conditions remains fluid until the 

 epithelial. cells of the bloodvessels undergo degenerative changes. 



It is not known ichat percentage of blood may be lost by man 

 through hemorrhage without fatal results, but judging from experi- 

 ments upon the lower animals, it may be put at about 3 per cent, 

 of the body weight, or one-fourth of the total blood. 



Regeneration of the blood takes place rapidly and is com- 

 pleted in from twenty-four to forty-eight hours. After severe 

 hemorrhage recovery is more certain if a solution of sodium 



