82 PHYSIOLOGICAL CHEMISTRY. 



5. Fibrinogen. 



This substance exists in a fluid form in the biood of the living body, 

 and at the time of its coagulation is converted into fibrine. It is pres- 

 ent in the blood in much smaller quantity than its other albuminous 

 ingredients, amounting to not more than 3 parts per thousand. Like 

 paraglobuline, it is insoluble in water, but soluble in neutral saline 

 solutions, and in this condition is coagulable by heat. It is also 

 thrown down from fluids which contain it by a stream of carbonic acid, 

 or by dilute acetic acid. Its most striking character is its liability to 

 coagulate by contact with a special ferment, the so-called " fibrine- 

 ferment," which is considered as the natural exciting cause of its coag- 

 ulation. This process is analogous to the coagulation of caseine by 

 rennet ; the fibrin e-ferment acting only by contact, while the fibrinogen 

 supplies the material of the solidified fibrine. If pure fibrinogen, in a 

 dilute saline solution, be coagulated by heat, the quantity of coagulum 

 so obtained is as great as that produced from coagulation by action of 

 the ferment (Fredericq). This shows that the spontaneous coagulation 

 of fibrinogen in the blood does not depend upon its union with another 

 substance, but that it is simply a change of molecular condition, like that 

 which occurs in other coagulable substances. 



Fibrinogen is best obtained from horse's blood, according to the 

 method of Hammarsten.* The blood, as it escapes from the vessels, is 

 received into ^ of its volume of a saturated solution of magnesium 

 sulphate, with which it is thoroughly mingled. This arrests its coag- 

 ulation. The mixture is then slowly filtered, to separate the blood- 

 globules, and the clear filtered fluid is treated with its own volume of 

 a saturated sodium chloride solution. This throws down the fibrinogen 

 with some other albuminous matters. To effect its purification, the 

 precipitate is cleansed from the adherent liquid by pressure with bibu- 

 lous paper, finely divided, dissolved in a sodium chloride solution of the 

 strength of 8 per cent., and again precipitated by the same salt in 

 saturated solution. This operation is once more repeated ; and after 

 the third precipitation with saturated sodium chloride solution, the 

 fibrinogen is redissolved in pure water. It is then in a state of purity. 



Fibrine, produced by the coagulation of fibrinogen, is a tenacious 

 whitish substance, of firmer consistency than coagulated albumen. It 

 has a considerable degree of extensibility and elasticity, and will 

 retract with sufficient force to gradually expel any surplus liquid 

 entangled in it. It is insoluble in water and in neutral saline solu- 

 tions. It is swollen and softened, but not liquefied, at ordinary temper- 

 atures, by dilute acids, and is slowly dissolved by dilute alkalies. If 

 heated in contact with moisture, or treated with alcohol, it is rendered 

 opaque, loses its extensibility and elasticity, and becomes in appearance 

 more like coagulated albumen. It forms the solidified portion of inflam- 

 matory exudations on serous surfaces or in the tissue of diseased organs. 



Archiv fur die gesaramte Physiologie. Bonn, 1879, Band XIX., p. 563. 



