COAGULATION OF BLOOD. 297 



followed by an alarming loss of blood. This condition is spoken 

 of as hemophilia or hemorrhagic diathesis. It is probable that in 

 such cases the fibrinogen is very deficient. 



Theories of Blood-coagulation. From the many theories which 

 have from time to time been advanced to explain this process, we 

 shall select a few, each of which, although perhaps not now held 

 in its entirety, still has elements in it which, combined with those 

 of other theories, enter into the opinions held by the best authorities 

 in regard to this as yet unsolved problem. 



All explanations have as their basis the production of insoluble 

 fibrin from soluble fibrinogen, but as to how this change comes 

 about, or the agencies which cause it, there is great disagreement. 



Theory of Schmidt. The proteid now known as paraglobulin 

 Schmidt termed fibrinoplastin, and in his theory this substance, 

 under the influence of fibrin-ferment, which he later called 

 thrombin, enters into combination with fibrinogen, the result 

 being fibrin. This ferment was obtained by adding alcohol to 

 blood-serum, and extracting it from the precipitate by water; it 

 was destroyed by a temperature of 65 C., and had the power of 

 coagulating a considerable amount of fibrinogen ; it resembled, 

 therefore, the ferments or enzymes, and was considered by Schmidt 

 to belong to that class. He later considered that fibrinogen was 

 derived from paraglobulin. 



Theory of Hammarsten. This experimenter demonstrated that 

 paraglobulin takes no part in the process of coagulation, so that 

 at the present time it does not enter as a factor into any of the 

 theories of blood-coagulation. In Hammarsten's theory there are 

 but two factors : fibrinogen and fibrin-ferment. The action of 

 the ferment splits the fibrinogen into fibrin, which is insoluble, 

 and fibrin-globulin, which remains in solution. 



Schmidt, Hammarsten, Freund, Page's, and others have shown 

 that salts of calcium play a very important part in the coagulation 

 process. 



Theory of Pekelharing. This theory supposes that the fibrin- 

 ferment of Schmidt is composed of nucleo-albumin and calcium, 

 and that the calcium leaves the nucleoproteid and unites with 

 fibrinogen, the compound of the two being fibrin. The nucleo- 

 albumin comes from the leukocytes and plaques, but does not 

 exist in normal blood. As soon, however, as blood is shed, these 

 cells disintegrate, with the result of setting free the nucleoproteid. 

 As has already been stated, analyses show the same amount 

 of lime in fibrinogen as in fibrin, so that this theory cannot be 

 sustained. 



Theory of Lilienfeld. The originator of this theory attributes 

 to the nucleoproteid the power of splitting the fibrinogen into a 

 globulin and thrombosin, which latter unites with lime to form 

 fibrin. He regards this power as due to the nucleic acid, and 



