318 THE BLOOD. 



appreciable amounts of prothrombin. This body, according to him, 

 passes before coagulation from the form-elements into the plasma, and 

 is there converted into thrombin by the calcium salts. The observa- 

 tion that uncoagulated leech-plasma does not coagulate on the addition 

 of calcium salts, while it does coagulate on the addition of prothrombin 

 solutions, seems to support this view; still it is not quite conclusive. 

 Leech-extract contains a body, hirudin, which, seems to be an anti- 

 body toward thrombin and quantitatively neutralizes it. On the addi- 

 tion of prothrombin, new thrombin may be formed, which may act 

 if the hirudin is not present in too great an excess. 



Other observations which dispute the occurrence of prothrombin in 

 the circulating plasma can be explained in various ways and it is the 

 general view at present that the prothrombin is a preformed constituent 

 of the plasma. l 



Although the opinions are rather united as to the occurrence of at 

 least three bodies, fibrinogen, prothrombin (thrombogen) and lime salts 

 in the plasma, still the question arises how the thrombin is formed from 

 the thrombogen. The zymoplastic substances must be here considered, 

 and the starting-point in these new investigations is the accelerat- 

 ing action upon coagulation, of different tissue extracts, an action which 

 has been known for a long time and was especially studied by DELE- 

 ZENNE on the plasma from bird's blood. Unfortunately we are not in 

 accord as to the nature and manner of action of the active constituents 

 of these extracts. According to MORAWITZ the active body is not 

 thrombin, but another substance called thrombokinase, besides lime- 

 salts, which are necessary for the transformation of prothrombin (throm- 

 bogen according to MORAWITZ). The production of thrombokinase is, 

 according to MORAWITZ, a general property of the protoplasm, and also 

 occurs in the leucocytes (and blood-plates). Three substances are nec- 

 essary, according to his view, for the formation of thrombin, namely: 

 thrombogen, thrombokinase and lime salts. Thrombogen is, he claims, 

 not quite identical with the prothrombin (other investigators), which 

 he calls a-prothrombin, but is a mother-substance of it. The process 

 of thrombin formation can be given as follows: The kinase first trans- 

 forms the thrombogen into a-prothrombin, which latter then is converted 

 into thrombin (a) by the lime salts. 



1 Arthus, Journ. de Physiol. et Pathol., 3 and 4, and Compt. rend. soc. biol., 56. 

 The works of Morawitz may be found in Hofmeister's Beitrage, 4 and 5, Deutsch. 

 Arch. f. klin. Med., 79 and 80, and in Oppenheimer's Handb. der Bioch., 2; Fuld, 

 Centralbl. f. Physiol., 17, p. 529; with Spiro, Hofmeister's Beitrage, 5; Schittenhelm 

 and Bodong, Arch. f. exp. Path. u. Pharm., 54; Bordet and Gengou, Annak Institut 

 Pasteur, 18. For more recent literature see Loeb, Biochem. Centralbl., 6, p. 907. 

 P. Nolf, Arch, internat. de Physiol., 6, 1908. 



