THROMBIN, FIBRIN FORMATION. 249 



less 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 r 1 

 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 and by PEKELHARiNG. 2 



The preparation of a thrombin solution as free as possible from lime 

 may be accomplished by removing the lime salts from the serum by means 

 of an oxalate and precipitating the serum with alcohol and allowing it to 

 stand under alcohol for several months. The dried powder is rubbed with 

 water, and freed from soluble salts by repeated lixiviation with water and 

 by the use of centrifugal force. Then each gram of powder is allowed to 

 stand some time with 100150 cc. water, is filtered, and in this way a 

 solution is obtained which contains only about 0.3-0.4 p. m. solids and 

 about 0.0007 p. m. CaO (HAMMARSTEN). 



If a fibrin ogen 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, as shown by ALEX. SCHMIDT, 

 PEKELHARING, and HAMMARSTEN, S thrombin can transform fibrinogen 

 into typical fibrin in the absence of lime salts precipitable by oxalate. 

 The fibrin is not richer in lime than the fibrinogen used in its prepar- 

 ation 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 the amount 

 of fibrinogen from which the fibrin is derived, and we always find a small 

 amount of protein substance in the solution. It is therefore not improbable 

 that the fibrin coagulation, in accordance with the views first proposed 

 by DENIS, is a cleavage process in which the soluble fibrinogen is split 

 into an insoluble protein, the fibrin, which forms the chief mass, and a 

 soluble protein substance which is produced only in small amounts. 

 We find a globulin -like substance which coagulates at about 64 C. in 

 blood-serum as well as in the serum from coagulated fibrinogen solutions. 



1 Pfliiger's Arch., 0. 



2 Hammarsten, ibid., 18; Pekelharing, 1. c. 



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

 Schmidt and Pekelharing, and ibid., 28. 



