X. THE CHANGE OF PROTOPLASM STRUCTURE 311 



denaturation spreads as a chain reaction as above mentioned. 



The denaturated prothrombin is called thrombin, in which active 

 group or groups are being produced as a result of the structural change 

 due to the denaturation. Thrombin, the denaturated prothrombin, can 

 combine with another kind of serum globulin, called fibrinogen, through 

 these active groups to produce the structural disturbance in the latter. 

 The fibrinogen thus denaturated is termed fibrin. During this change 

 polar groups are likewise temporarily liberated, whereby the change 

 is transmitted to other intact fibrinogen molecules. This is the general 

 concept of the writer as regard the mechanism of blood coagulation, 

 by which all the phenomena known concerning blood coagulation may 

 fairly be elucidated. 



Thus it may be clear that the blood coagulation as a whole is a 

 chain reaction given rise to mainly by temporarily liberated polar 

 groups. However, there are ample evidences that active group of 

 thrombin is retained without disappearing long after its formation. 

 Therefore, it must be considered as follows : The active group of 

 thrombin is different from the polar groups which are liberated tem- 

 porarily during the process of the denaturation, but their group may 

 arise as a result of the denaturation and so can remain without dis- 

 appearing. The reason why active group can be produced following 

 denaturation will be discussed in the next Part. 



Further it should be added that thromboplastin may not be present 

 as such in the platelets, but that active groups capable of acting as 

 thromboplastin may be produced upon the disintegration of the cells 

 into elementary bodies just as the active groups of thrombin are raised 

 by the denaturation of prothrombin. In fact, it is said that thrombo- 

 plastin is present in cells as thromboplastinogen or prothromboplastin 

 (154). This latter may be the natural state of elementary bodies 

 present in platelets. During the conversion of prothromboplastinogen 

 into thromboplastin transient liberation of polar groups may take place, 

 leading to the transmission of the denaturation to accelerate the change; 

 thus the phenomenon may appear the more complicated (155). 



Throboplastin seems to be usually produced from platelets, but it 

 can also be isolated from a variety of other materials such as brain, 

 lung, and blood plasm, showing that it is elementary bodies not peculiar 

 to the platelets. Its action is lost by the extraction of lipids ; the 

 lipids may be involved in the combination of the thromboplastin with 

 prothrombin. Thromboplastin fails to act without Ca ion. As was 

 already mentioned, Ca ion is generally necessary for the transmission 

 of structural change of proteins because of its faculty to favour the 

 liberation of polar groups in proteins, and hence the need of Ca ion 

 is never peculiar to blood coagulation. 



