66 SCIENCE PROGRESS 



From the thymus, lymphatic glands, or the stromata of red 

 corpuscles, a thermolabile substance can be extracted with a 

 weak saline solution. This substance is, for the most part, 

 thrombo-kinase, which soon becomes unstable in solution, 

 though the extract, dried in a vacuum, yields a powder which 

 only slowly changes. On fibrinogen solutions, even in the 

 presence of lime, this extract produces no change; it is 

 therefore not a thrombin such as occurs in serum. Exactly 

 the same negative result follows when extracts from mammalian 

 tissues are added either to solutions of fibrinogen or to oxalate- 

 or fluoride-plasma, and it is immaterial whether the extracts 

 are previously treated with calcium chloride or not. 



On the other hand, the clotting of blood is accelerated, and 

 the coagulation process in the plasma of birds, in peptone 

 plasma, and sometimes in hirudin-plasma, forthwith commences 

 on the addition of thrombo-kinase, provided calcium salts are 

 present. The ferment-power of serum is also exalted by 

 thrombo-kinase. From these facts Morawitz concludes that the 

 development of thrombin results from the interaction of kinase 

 with a body in coagulable liquids or in serum in the presence 

 of calcium salts. This body is the substance recognised by 

 Fuld as plasmozym, and may be termed thrombogen. This 

 corresponds to a-prothrombin. Since a-prothrombin exists 

 in fluoride-plasma as well as in all the non-coagulated but co- 

 agulable plasmata hitherto examined, the following conception 

 of the coagulation process may be suggested. In the plasma of 

 circulating blood a certain amount of fibrinogen, calcium, and 

 thrombogen will be found. It does not coagulate, since thrombo- 

 kinase is entirely absent, or if present in small amount is 

 neutralised by anti-bodies in the blood. Solutions of thrombo- 

 kinase or of substances capable of setting this free in the blood 

 will forthwith give rise to thrombin, and be followed by intra- 



