306 THE BLOOD. 



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 (thrombogen 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 necessary, accord- 

 ing 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 transforms the 

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

 thrombin (a) by the lime-salts. 



The thrombokinase also does not occur to any appreciable extent in the 

 circulating blood, but is supplied by the form-elements. The accelerating 

 action upon coagulation of tissues or parts of tissues depends, as above 

 stated, upon their content of kinase; but it also in part depends upon the 

 fact that the tissue fluids excite the secretory activity of the form-elements. 



FULD l has arrived at about the same results independently of MORA- 

 WITZ, but he has selected other names. The three substances throm- 

 bogen, kinase, and thrombin are called by him plasmozym, cytozym-, 

 and holozym. The chief reason why circulating blood remains fluid is, 

 according to FULD, because the cytozym is only slowly formed therein 

 and the ferment (holozym) produced thereby is quickly changed into an 

 inactive form. Another reason is that the blood contains an antibody 

 for the fibrin ferment. The assumption of ALEXANDER SCHMIDT that 

 the blood contains substances retarding coagulation (anti-thrombins) 

 has recently also received support by the observations of FULD and 

 SPIRO, MORAWITZ, LOEB, NOLF, PiiGLiESE 2 and others. 



According to the theory of MORAWITZ, FULD and SPIRO, of those substances 

 necessary for coagulation, only the thrombokinase (the cytozym) is absent in the 

 circulating blood, and this is the reason why the circulating blood remains fluid. 

 The reason why the plasma does not contain any thrombokinase lies in the fact 

 that the healthy endothelium of the vessels does not have any irritating action upon 

 the form-elements, and therefore no mentionable quantity of kinase is given off 

 under these circumstances. Su^h an elimination occurs first outside of the blood 

 vessels, and indeed very quickly in contact with foreign bodies. The formation 

 of thrombin from the thrombogen takes place in an unknown manner by the 

 action of the -kinase only in the presence of lime salts (in the plasma), and this 

 thrombin then transforms the fibrinogen into fibrin. 



1 Centralbl. f. Physiol., 17. See also Fuld and Spiro, Hofmeister's Beitrage, 5. 

 *Fuld and Spiro, 1. c.; Morawitz, 1. c.; Loeb, Hofmeister's Beitrage, 5; Nolf, Arch, 

 internat. de Physiol., 6; Pugliese, Biochem. Centralbl., 5, p. 930. 



