314 THE BLOOD. 



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. Of the 

 nature of these two substances, however, we know but little ; it is 

 possible that one is the so-called fibrinoglobulin, which, as we shall 

 see later, is formed during coagulation of the blood. Fibrinogen 

 turns the plane of polarized light to the left ; its rotation for the 

 yellow D line corresponds 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 tendency to the formation of fibrin, and upon this its 

 specific test and quantitative estimation are based. This transforma- 

 tion will be considered in detail later (see Coagulation). 



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

 chyle, the lymph, and various exudates and transudates. 



Serum -globulin. This substance has also been termed para- 

 globulin, Alexander Schmidt's fibrinoplastic substance, and serum- 

 casein. Like fibrinogen, it is found in the plasma of the blood, in 

 the lymph, in various exudates and transudates; but it likewise 

 occurs in the serum, in the white and red corpuscles of the blood, 

 and in traces at least in all cellular elements of the animal body. 

 In the urine it has been encountered in association with serum- 

 albumin under various pathological conditions. 



Isolation. Serum-globulin is most conveniently obtained from 

 blood-serum by half-saturation with ammonium sulphate /. e., by 

 treating a given volume of the serum with the same amount of a 

 saturated solution of the salt. Saturation with magnesium sulphate 

 in substance may also be employed. In either case the precipitated 

 serum-globulin is filtered off, washed with the corresponding salt 

 solution, dried at 115 C., then washed with boiling water to remove 

 the remaining salts, extracted with alcohol, then with ether, and 

 finally dried and weighed. In any case the original solution should 

 be nearly neutral in reaction. 



