56 HUMAN PHYSIOLOGY 



prevented and the corpuscles sink and the clear supernatant fluid 

 is the plasma. 



Plasma is a yellowish, alkaline fluid, having a specific 

 gravity of 1.03; it contains 9$ solids which are: 

 I . Proteids (7-8$) : 



(a] Serum albumins (3-5$). 



The albumins differ from each other in their specific rotatory 

 power, their coagulation temperature, and, as far as they are 

 crystallizable (as in serum of horse blood), in the forms of their 

 crystals. 



(b] Serum globulin (3^ 



The quantity of albumin and globulin varies much. In general 

 the albumin predominates in the blood of well-fed animals, while 

 globulin predominates in that of fasting animals. 



(c) Fibrinogen (0.1-0.3$;. 



Fibrinogen is a globulin-like proteid from which fibrin is 

 formed when blood coagulates. The amount of fibrin is but 

 small (0.1-0.3$). Its volume, however, appears large as 

 it is swollen. The fibrin formation is most likely brought 

 about by the splitting of fibrinogen into two parts, one part 

 being the insoluble fibrin, the other a soluble proteid of 

 which little is known. 



The coagulation is brought about by an unformed ferment 

 thrombin. This ferment is not present in blood in healthy 

 blood vessels. It is formed, when blood is shed, by the 

 breaking down of the white blood corpuscles, especially the 

 poly-nuclear. Defibrinated blood is called blood serum. 



As long as blood is inclosed in blood vessels having sound 

 walls, coagulation does not occur. The coagulation of blood is 

 prevented by cooling, by the addition of saturated salt solutions, 

 e.g. magnesium sulphate, and by the addition of salts of oxalic, 

 hydrofluoric, and fatty acids. Soluble calcium salts seem to aid 

 in the formation of the coagulative ferment. The power of 

 coagulation can also be destroyed by the injection of proteoses 

 and of leech extract. 



Coagulation is of importance in that the bleeding from 

 vessels is stopped by the clotting of the shed blood, as the 



