216 THE BLOOD 



5 drops of thrombin yield 0.2046 gm. of fibrin. 

 10 drops of thrombin yield 0.3575 gm. of fibrin. 

 20 drops of thrombin yield 0.6089 gm. of fibrin. 

 40 drops of thrombin yield 1.5872 gm. of fibrin. 



Besides, it has been noted that thrombin actually becomes a part of the final 

 product, and that this reaction does not vary with the temperature, i.e., it takes 

 place at 17 C. as well as at 40 C. Rettger, therefore, draws the conclusion that 

 fibrin is not derived exclusively by a progressive conversion of the fibrinogen, 

 but may also be produced by a direct combination of these bodies. The product, 

 however, is unstable, because the thrombin may be separated from it with relative 

 ease. Thrombin may also be prepared in accordance with the directions given by 

 Schmidt. 1 A certain quantity of blood having been permitted to clot, the serum 

 is precipitated by the addition of 15 to 20 volumes of alcohol, in excess. The pre- 

 cipitate is removed after several days or months and is dried, pulverized and ex- 

 tracted with water. While this solution contains different protein bodies and salts, 

 it may be concluded that the coagulation which it induces when added to solutions 

 of pure fibrinogen, is caused by its thrombin constituent. Buchanan and Gamgee 

 advise to extract the ordinary washed fibrin for several days with an 8 per cent, 

 solution of sodium chlorid. The filtrate is not pure, but contains dissolved 

 proteins in addition to much thrombin. Howell 2 purifies this extract by shaking 

 it repeatedly with chloroform. In this way, the coagulable proteins are removed, 

 while the thrombin is left behind in a pure state, although somewhat diminished 

 in quantity. This author states that it is easily soluble in water and is not coagu- 

 lated by boiling. Moreover, while it is difficult to precipitate it with alcohol in 

 excess, it may be precipitated with ammonium sulphate in half saturation. As 

 it gives positive results with several of the ordinary protein reagents, it must be 

 regarded as a protein substance. 



Fibrinogen exists as an independent body in the plasma of the circulating 

 blood. It is also present in lymph, chyle, and certain transudates and exudates, 

 but not in the blood serum, inasmuch as it is used up in the process of clotting. 

 While its place of origin is not definitely known, it is certain that it is not derived 

 from the corpuscular elements of the blood. It should be mentioned, however, 

 that some evidence is at hand to show that it may be formed in the liver and in the 

 myeloid tissue of the bone-marrow. Thus, Nolf has found that the quantity of 

 fibrinogen in the blood may be greatly diminished by extirpating the former organ 

 or by the administration of poisonous amounts of phosphorus or chloroform. Men- 

 tion should also be made of the observation of Dastre that the blood of the mesen- 

 teric vein is richer in fibrinogen than that of the corresponding artery. This fact 

 has been interpreted as showing that the intestinal wall is one of the sources of 

 this substance. 



Fibrinogen may be obtained in solution and free from other proteins in the 

 following manner: A quantity of fresh blood is mixed with a solution of sodium 

 oxalate in amounts sufficient to give a 0.1 per cent, oxalate mixture. The latter 

 is then centrifugalized and its plasma portion precipitated by the addition of an 

 equal amount of a saturated solution of sodium chlorid. The resulting precipitate 

 of fibrinogen is pressed out or centrifugalized, redissolved in an 8 per cent, salt 

 solution, and the filtrate precipitated by a saturated salt solution. Having been 

 subjected to this process three times, the final precipitate is pressed between filter 

 paper and is then finely divided in water. The precipitate may be dissolved 

 in a 1 per cent, solution of sodium chlorid. If it does not dissolve readily, a few 

 drops of a 0.5 per cent, solution of sodium bicarbonate should be added. The 

 traces of sodium oxalate may be removed by dialysis in a colloidin sac, against a 

 1 per cent, solution of sodium chlorid. 



1 Pfluger's Archiv, xi, 1887, 515. 



2 Am. Jour, of Physiol., xxvi, 1910, 26. 



