THE CIRCULATING LIQUIDS OF THE BODY 37 



which exhibit amoeboid movements. They become entangled 

 by the interlacing of the pseudopodia which they protrude 

 (L'. Loeb). In the blood of some mammals (rabbit) many leuco- 

 cytes, especially the polymorphonuclear leucocytes, disappear, 

 but in man, the pig, and the ox this is not the case. It must be 

 remembered, however, that the leucocytes in shed blood, with- 

 out actually being destroyed, may, under the influence of what 

 is for them a foreign environment, undergo changes which permit 

 the escape of thrombokinase and other substances. Further, 

 the white layer or ' buffy coat ' which tops the tardily-formed 

 clot of horse's blood, and consists of the lighter, and 

 therefore more slowly sinking, platelets and white corpuscles, 

 causes clotting in otherwise incoagulable liquids like hydrocele 

 fluid much more readily than the red portion of the clot, and 

 yields far more of Schmidt's fibrin-ferment on treatment with 

 alcohol. 



In blood collected in paraffined vessels, so as to delay clotting, 

 and immediately centrifugalized, coagulation is seen to begin in 

 and around the layer of white elements, and then to spread 

 upwards in the stratum of plasma and downwards in the stratum 

 of erythrocytes. 



Thrombokinase has not only been shown to exist in the 

 leucocytes, the platelets, and the stromata of the coloured 

 corpuscles, but, as already stated, in all tissues hitherto examined. 

 Under ordinary circumstances it appears that a larger amount 

 of thrombogen is liberated or is already present in shed blood 

 than can be changed into thrombin by the thrombokinase set 

 free, since serum contains a surplus of thrombogen in addition 

 to the fully-formed ferment. This is shown by the fact that the 

 activity of a given quantity of serum in causing the coagulation 

 of a plasma not spontaneously coagulable or of a fibrinogen 

 solution is increased by the addition of tissue extract (containing 

 thrombokinase) . 



The thrombin of any particular kind of vertebrate blood has 

 no marked specific action that is, will cause coagulation in 

 solutions of fibrinogen or plasma of very different origin. For 

 example, the sera of all vertebrates hitherto investigated induce 

 clotting in goose's plasma. On the other hand, it appears that 

 a greater degree of specificity exists in the case of the thrombo- 

 kinase and thrombogen, the specificity being absolute in some 

 cases, relative in others. That is to say, the thrombokinase of 

 one animal may activate the thrombogen of an animal of another 

 group, while it may fail to activate the thrombogen of an animal 

 belonging to a third group. But it will always activate the 

 thrombogen of an animal of the same kind. 



To sum up, we may say that when blood is shed fibrin-ferment 



