FIBRIN FORMATION. 257 



SCHUTZ'S law while on increasing dilution deviates more and more 

 and finally shows a proportionally slow, and more irregular procedure. 

 MARTIN 1 has found another law from experiments with plasma and snake- 

 poisons containing thrombin. According to him the behavior is as 

 follows : As in the casein coagulation with rennin, the celerity of coagula- 

 tion is inversely proportional to the quantity of ferment; and LOEB 

 has observed a similar conduct with invertebrates. The optimum of the 

 thrombin action lies at about 40 C.; at 70-75 C., in neutral solution, 

 the enzyme is destroyed. According to HOWELL and RETTGEE 2 throm- 

 bin, under proper conditions, can withstand boiling for a short time. The 

 question as to whether the thrombin found in different animals is the 

 same substance or whether we have several thrombins, has not been 

 decided. The latter is not improbable; nevertheless a definite specificity 

 of different thrombins has not been observed with certainty. 



The isolation of thrombin has been tried in several ways. Ordinarily, 

 it may be prepared by the following method, proposed by ALEX. SCHMIDT: 

 Precipitate the serum or defibrinated blood with 15-20 vols. of alcohol 

 and allow it to stand a few months. The precipitate is then filtered 

 off and dried over sulphuric acid. The ferment may be extracted from 

 the dried powder by means of water. Other methods have been suggested 

 by HAMMARSTEN, PEKELHARING, and HOWELL. S According to a method 

 suggested by HAMMARSTEN a solution of thrombin so poor in lime salts 

 that it contains only 0.3-0.4 p. m. solids and about 0.0007 p. m. CaO 

 can be prepared. 



If a fibrinogen solution containing salt, as above prepared, is treated 

 with a solution of thrombin, it coagulates at the ordinary temperature 

 more or less quickly and yields a typical fibrin. Besides the thrombin, 

 the' presence of neutral salts is necessary, for ALEX. SCHMIDT has shown 

 that fibrin coagulation does not take place without them. The presence 

 of soluble calcium salts is not, as is generally assumed, a positive con- 

 dition for the formation of fibrin, because, thrombin can transform 

 fibrinogen into typical fibrin in the absence of lime salts precipitable by 

 oxalate. 4 The fibrin is not richer in lime than the fibrinogen used in its 

 preparation if the fibrinogen and thrombin solutions are employed as lime- 

 free as possible, and the view that the fibrin formation is connected with 

 a taking up of lime has been shown to be untenable (HAMMARSTEN). 

 The quantity of fibrin obtained on coagulation is always smaller than 



1 Martin, Journ. of PhysioL, 32; Fuld, Hofmeister's Beitrage, 2; Loeb, ibid., 9; 

 Stromberg, Biochem. Zeitschr., 37. 



2 Howell, Amer. Journ. of Physiol., 26; Rettger, iUd., 24. 



3 Hammarsten, ibid., 18; Pekelharing, 1. c.; Howell, 1. c. 



4 See Hammarsten, Zeitschr. f . physiol. Chem., 22, which also cites the works of 

 Schmidt and Pekelharing, and ibid., 28. 



