CHEMICAL EXAMINATION OF THE BLOOD. 319 



which is considered at this place, as it is usually regarded as an 

 albuminous substance. 



The Fibrin Ferment. The fibrin ferment, or thrombin of Alex- 

 ander Schmidt, is thought to result from decomposition of the cellu- 

 lar elements of the blood, and notably the leucocytes and blood- 

 plates, in which it is supposedly present in the form of a pro- 

 enzyme, the so-called prothrombin of Alexander Schmidt. As a 

 matter of fact, it is possible to prevent the formation of the ferment 

 by allowing blood to flow directly from the vessel into a solution of 

 one of the neutral salts. In the circulating blood the ferment is 

 manifestly not present, as its solution when injected into the blood- 

 vessels of a living animal will cause almost instantaneous death 

 from thrombosis. 



Isolation. The isolation of the fibrin ferment is most conveni- 

 ently accomplished in the following manner : taking the serum of the 

 ox, the globulins are first precipitated by saturation with magnesium 

 sulphate. The filtrate is then diluted with water, and treated while 

 stirring with a very dilute solution of sodium hydrate until an 

 abundant and flocculent precipitation of magnesium hydroxide has 

 been brought about. This precipitate, which contains a large pro- 

 portion of the ferment, is washed with water, pressed between filter- 

 paper, and dissolved in water by neutralizing the solution with 

 diluted acetic acid. The salts are then removed by dialysis, when 

 the ferment can be precipitated by a suitable addition of acetic acid. 



Properties. Of the nature of the product which can thus be ob- 

 tained little is known. By some observers it is regarded as a globu- 

 lin, while others class it as a nucleo-albumin. On digestion with 

 pepsin it is said to yield a nuclein or a pseudonuclein. As is the 

 -case with all ferments, its solutions are rendered inactive by exposure 

 to a moderately high temperature (70-75 C.), while the various 

 .antiseptic substances which do not interfere with the activity of 

 other ferments are likewise without effect upon the fibrin ferment. 

 Its specific activity is manifested when brought into contact with 

 fibrinogen, which is apparently decomposed by hydrolysis into fibrin 

 and fibrinoglobulin. To effect this change, however, the presence 

 of a neutral salt and of a soluble calcium salt is essential. In their 

 absence coagulation does not take place. According to Pekelharing, 

 the fibrin ferment is a calcium compound of the pro-enzyme, and it 

 is supposed that during the process of coagulation the calcium is 

 transferred to the fibrinogen, whereby this is transformed in part 

 into the insoluble calcium-containing fibrin. At the same time the 

 ferment is retransformed into its pro-enzyme, which again combines 

 with calcium to form the ferment ; this, in turn, deposits its calcium 

 on the fibrinogen, and is thus changed back into the pro-enzyme, and 

 so on. 



Fibrin. Fibrin is formed during the spontaneous coagulation of 

 all albuminous solutions which contain fibrinogen and cellular ele- 

 ments that can give rise to the fibrin ferment. It is most conveni- 



