56 PHYSIOLOGICAL CHEMISTRY. 



I. Blood-plasma and Blood-serum. 

 The Blood-plasma. 



In the coagulation of the blood a chemical transformation takes 

 place in the plasma. A part of the albumins separates as insoluble 

 fibrin. The albuminous bodies of the plasma must therefore be 

 first described. They are fibrinogen, serum globulin, and serum 

 albumin. 



Fibrinogen occurs in blood-plasma, chyle, lymph, and in certain 

 transudations and exudations. 1 



It has the general properties of the globulins, but differs from 

 other globulins as follows: In a moist condition it forms white 

 flakes which are soluble in dilute common salt solutions, and 

 which easily conglomerate into tough, elastic masses or lumps. 

 The solution in NaCl of 5-10$ coagulates on heating to -j- 52 

 to 55 C., and the faintly alkaline or nearly neutral weak salt 

 solution coagulates at -f- 56 C., or at exactly the same tem- 

 perature at which the blood-plasma coagulates. Fibrinogen solu- 

 tions are precipitated by an equal volume of a saturated common 

 salt solution, and are completely precipitated by adding an excess 

 of NaCl in substance (thus differing from serum globulin). It 

 differs from myosin of the muscles, which coagulates at about the 

 same temperature, and from other albuminous bodies, in the prop- 

 erty of being converted into fibrin under certain conditions. Fi- 

 brinogen has a strong decomposing action on hydrogen peroxide. 



The fibrinogen may be easily separated from the salt-plasma by 

 precipitation with an equal volume of a saturated NaCl solution. 

 For further purification the precipitate is pressed, redissolved in 

 an 8$ salt solution, the filtrate precipitated by a saturated salt 

 solution as above, and after precipitating in this way three times, 

 the precipitate at last obtained is pressed between filter-paper and 

 finely divided in water. The fibrinogen dissolves with the aid of 

 the small amount of NaCl contained in itself, and the solution may 

 be made salt-free by dialysis with very faintly alkaline water. From 

 transudations we ordinarily obtain a fibrinogen which is strongly 



1 The question as to the occurrence of other fibrinogens (WOOLDRIDGE) 

 will be spoken of in connection with the complete discussion of the coagula- 

 tion of the blood. (See further on.) 



