THEORIES OF COAGULATION 123 



of sodium chloride, and portions of this macerated tissue were put into fi- 

 brinogen solutions. Of another part of the irrigated tissue filtered saline 

 extracts were made, and these were tested from time to time on fibrinogen 

 solutions. In not a single case in the repeated series of experiments was 

 there found any evidence of coagulation." "Terrapin's blood taken 

 carefully through an oiled cannula and put into a perfectly clean beaker will 

 remain fluid for days. The blood may be centrifuged, and the clear super- 

 natant plasma is then equally or more resistant to spontaneous clotting. If, 

 however, tissue extracts or pieces of tissue be added, the coagulation is pro- 

 nounced and immediate. The most apparent explanation is that of a 

 thrombin or coagulin or kinase present in the extract. But this blood or 

 plasma can be made to clot equally well and equally rapidly in ways which 

 preclude the presence of such a definite agent. If, for instance, dust par- 

 ticles, loose sweepings, or linty shreds be added, the coagulation is equally 

 prompt and in a number of experiments was more rapid than with tissue 

 extract." "The bird's blood or plasma clots with practically the same 

 rapidity and firmness if dust particles are generously added. Bits of down 

 or feathers introduced bring about a speedy clotting. Surely there can be 

 no question of a 'kinase' in these instances." "The existence of 'kinase' 

 or 'coagulins' in the various tissues is improbable. Using carefully pre- 

 pared fibrinogen solutions, extracts of tissues, irrigated to remove every 

 trace of thrombin-containing blood, cause no clotting. When the addition 

 of such extracts produces coagulation in bloods of bird or reptile, similar 

 results can be secured by the addition of substances, such as dust, lint, 

 shreds, etc., which preclude the presence of definite coagulating agents. 

 These results render very probable the assumption that in such plasmas all 

 the factors of coagulation are in reality present, and the addition of tissue 

 extract or other foreign substance brings into the mixture nothing that can 

 be regarded as a coagulin or as a kinase." 



One may restate Morawitz' view in a word as follows: The coagulation 

 of the blood takes place because of the formation of fibrin from fibrinogen 

 by the action of thrombin. The fibrinogen is constantly present in the plasma. 

 The thrombin is formed by the interaction of three substances, prothrombin, 

 calcium, and thrombokinase. The prothrombin arises chiefly from the 

 disintegration of the blood platelets and leucocytes when the blood leaves the 

 blood vessels. The calcium is present in the blood plasma at all times. 

 The thrombokinase originates in tissue cells of the blood and of the organs of 

 the body in general. 



Rettger's view is best given in his own words: 



"On the basis of the work here presented it is not necessary to assume 

 the existence of a kinase in explaining the clotting of shed blood. The pro- 

 thrombin formed from the platelets and leucocytes by secretion or by proc- 

 esses of disintegration is activated to thrombin by the calcium salts present, 



