THE BLOOD. 137 



in that fibrin is formed by a reaction between fibrinogen and thrombin. 

 Beyond this, however, there is some difference of opinion. The chief 

 points at issue are: (1) the origin of fibriuogen; (2) the nature of 

 thrombiu; (3) the nature of the reaction between fibrinogen and 

 thrombin. 



1. Hammarsten has shown that the presence of paraglobulin is not 

 necessary for coagulation. Schmidt believes, however, that fibrinogen 

 is derived from paraglobulin after the blood is shed from the body. 



2. The nature of thrombin is not as yet satisfactorily determined. 

 Pekelhariug has concluded from experiment that thrombin is a com- 

 pound of a nucleo-albumin with the calcium salts of the blood. He has 

 succeeded in separating from blood-plasma a nucleo-albumin, which 

 when brought into solution with fibrinogen and calcium salts will form 

 fibrin. If, however, this nucleo-albumin be brought into contact with 

 either fibrinogen alone or calcium salts alone, no clotting will occur. 



Pekeiharing further supposes that thrombin is not present in blood 

 circulating in the body at any rate in greater than minimal quantities; 

 but that when blood is f drawn or for other reasons coagulates in the 

 body, the white blood-cells break down, nucleo-albumin is liberated, and 

 then unites with the calcium salts to form thrombin. 



3. The nature of the reaction between fibrinogen and thrombin has 

 not been definitely determined. Hammarsteu has proved, however, that 

 the entire fibrinogen molecule does not enter into the reaction to become 

 fibrin. A part of it splits off and passes into solution as fibrin-globulin. 



SCHEMA OP COAGULATION. 



Blood 



I 



Plasma Corpuscles 



White 



I 



Nucleo-albuonin 



Fibrin 



There is strong evidence that fibrin is a compound of calcium with a 

 portion of the fibrinogen molecule. There are three factors, then, in 

 the reaction fibrinogen, nucleo-albumin, calcium salts. According to 

 Pekeiharing, the nucleo-albumin first combines with the calcium salts, 



