40 THE CIRCULATING LIQUIDS OF THE BODY 



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

 immediately centrifugalized, coagulation begins in and around the 

 layer of white elements, and then spreads upwards in the stratum 

 of plasma and downwards in the stratum of erythrocytes. But in 

 this white upper layer platelets are always intermingled with leuco- 

 cytes. It has been shown, however, that the blood of the cray- 

 fish, which coagulates with extreme rapidity, contains certain 

 colourless corpuscles, which immediately it is withdrawn, break 

 up with explosive suddenness, and that substances which hinder 

 the breaking up of these corpuscles restrain coagulation (Hardy). 

 In the blood of another crustacean Limulus, the kingcrab, coagula- 

 tion is preceded by an agglutination of the leucocytes which exhibit 

 amoeboid movements. They become entangled by the interlacing 

 of the pseudopodia which they protrude (L. Loeb). 



The disintegration of the platelets in shed blood has been attributed 

 by Deetjen to an increase in the alkalinity of the blood, by escape 

 of carbon dioxide, it may be. When blood is placed on a quartz 

 slide and covered with a quartz cover-slip, the platelets, according 

 to this observer, do not break up ; but if they are brought into con- 

 tact with a medium whose OH concentration is raised ten times 

 or more above that of freshly drawn blood (still only a weak alka- 

 line reaction), disintegration ensues. He supposes that the contact 

 of glass acts harmfully on account of the alkali in it. It is im- 

 possible to say at present whether this observation has any bearing 

 on normal coagulation. 



Thrombokinase has been shown to exist not only in the leuco- 

 cytes, 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 thrombokinase and throm- 

 bogen, 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. 



