v THE BLOOD: PLASMA 139 



According to Schmidt, we have a zyinogen, pro-thrombin, 

 which in splitting gives rise to the ferment and to a substance, 

 the nature of which he does not define, which arrests the splitting 

 of the pro-thrombin : according to Lilienfeld, we have nucleo- 

 histone, which divides into leuconuclein with a coagulating action, 

 and histone with an anti-coagulating action. It seems probable 

 enough, one may almost say certain, from the researches of 

 Pekelharing, that the ferment and the zymogen are nucleo- 

 proteins. Finally, according to Schmidt, the pro-thrombin is 

 transformed into thrombin (ferment) solely by the action of 

 unknown substances which he terms zymoplastic ; according to 

 Pekelharing zymogen is transformed into ferment solely by the 

 action of lime salts, and Lilienfeld's leuconuclein becomes active 

 as a ferment only in the presence of calcium. 



To sum up, it is admitted that the exciting agent of coagulation 

 (fibrin -ferment, thrombin) is a derivative of nucleohistone, a 

 derivative of acid character, which becomes active solely in the 

 presence of calcium-ions ; we may therefore represent the formation 

 of the ferment by the following scheme : 



Nucleohistone 

 (paralyses the coagulating action of leuconuclein) 



Leucon uclein. Hist on r. 



(In presence of Ca-ions becomes (Arrests splitting of nucleohistone 



a coagulating ferment.) and paralyses action of leuco- 



nuclein.) 



The predominance of one or other of these three substances gives 

 rise to various normal or abnormal states of the blood, which can 

 be tested after the injection of albumose, or substances with 

 similar action. 



The latest researches of Morawitz and others have led to a 

 more exact acquaintance with the so-called zymoplastic substances, 

 i.e. substances capable of accelerating the process of coagulation. 

 Delezenne had already observed with birds' plasma that various 

 extracts of organs or tissues have a similar action. Morawitz 

 has indicated the active principle of these extracts by the 

 name of thrombo-kinase, which he considers indispensable, in 

 addition to the calcium salts, for the transformation of pro- 

 thrornbin into thrombin. The production of thrombokinase is 

 thus a general property of protoplasm, while more particularly 

 characterising the leucocytes of birds and the blood-platelets of 

 mammals. 



(g) Lastly, one further question has to be explained. As 

 under normal conditions the old blood-corpuscles are continually 

 breaking up, and young, new cells substituted for those which 



