330 THE BLOOD. 



Of these albumins, fibrinogen is of especial interest, as it represents 

 the mother-substance of fibrin, and is thus intimately connected with 

 the process of coagulation. 



Fibrinogen. Isolation. Fibrinogen is most conveniently ob- 

 tained from the plasma by half-saturation with sodium chloride 

 i. e., by treating one volume of the plasma with an equal volume of 

 a saturated solution of common salt. The resulting precipitate of 

 fibrinogen is filtered off, washed with a half-saturated solution of 

 sodium chloride, and dissolved in an 8 per cent, solution of the salt. 

 To further purify the substance, this solution is reprecipitated, redis- 

 solved, and the process repeated twice. The final precipitate is 

 pressed between filter-paper and suspended in water, in which it 

 readily dissolves owing to the small amount of salt that still remains. 

 This may be removed by dialysis. The purified substance, in a moist 

 state, appears in the form of white flocculi, which readily coalesce to 

 form a tough elastic mass. 



The isolation of the fibrinogen must be performed rapidly, as pro- 

 longed exposure to the half-saturated salt solution tends to render 

 the substance insoluble. 



Properties. Fibrinogen belongs to the class of globulins. It is 

 insoluble in distilled water, but soluble in dilute solutions of the 

 neutral salts. From these solutions it may be precipitated by dial- 

 ysis, by increasing the amount of the salt, and by passing a stream of 

 carbon dioxide through the solution. When kept under water for a 

 comparatively short time it is rendered insoluble. When heated to 

 56 C. coagulation occurs, but it appears that the fibrinogen is at 

 the same time decomposed into two other globulins, one of which 

 coagulates at .the temperature just mentioned, while the other 

 remains in solution until the temperature reaches 65 C. The 

 latter has been termed fibrinoglobulin and, according to Hammarsten, 

 is also formed during ferment coagulation. This, however, is 

 apparently not necessarily the case. Fibrinogen turns the plane of 

 polarized light to the left ; its rotation for the yellow I) line corre- 

 sponds to 52.5 degrees. It consists of carbon, hydrogen, nitrogen, 

 sulphur, and oxygen, in the proportion of 52.93, 6.9, 16.6, 1.25, 

 and 22.26 respectively. Its most characteristic property is its ten- 

 dency to undergo coagulation under the action of a specific ferment, 

 and upon this its specific test and quantitative estimation are based. 

 This transformation will be considered in detail later (see Coagula- 

 tion). 



In addition to the blood-plasma, fibrinogen has been found in the 

 chyle, the lymph, and various exudates and transudates. 



Through the researches of Doyon, Morel, Kareff, and Nolf it has 

 been rendered probable that fibrinogen is formed in the liver, as its 

 quantity in the blood rapidly diminishes after extirpation of the 

 organ, or when fatty degeneration has been caused by the adminis- 

 tration of phosphorus. 



Serum-globulin. On half-saturation of the blood-plasma with 



