68 SCIENCE PROGRESS 



even more doubt. This body is not precipitated by cooling a 

 liquid which contains it to o° C, nor is it of a nucleo-protein 

 nature. Suspensions of blood-platelets, obtained by centri- 

 fugalisation, have been regarded as yielding a supply of 

 thrombogen. The prothrombin claimed by Schmidt to be 

 present in circulating blood is apparently identical with throm- 

 bogen, and though this body is absent from plasma in cases of 

 experimental phosphorus poisoning, the blood-platelets are 

 present in large, if not excessive amount, and appear quite 

 normal under the microscope. The repetition of old observa- 

 tions of Freund and Haycraft shows, moreover, that blood 

 received in parafined or oiled tubes can be centrifugalised with- 

 out clotting, and a perfectly cell-free plasma obtained, which 

 clots on transference to a glass vessel. 1 But such a plasma 

 contains no thrombin while in contact with paraffin, since the 

 plasma can be decalcified. The contact-action of a foreign body 

 therefore appears to be a deciding factor for the actual co- 

 operation of those bodies which the researches of Morawitz 

 have indicated as the probable factors in the formation of 

 thrombin. 



A large number of substances which possess toxic and ferment 

 properties have been described as constituents of various snake- 

 venoms. It is known that exceedingly minute amounts of the 

 venoms of certain Australian and Indian snakes 2 — 'oooi gramme 

 per kilogramme body-weight — will cause intravascular clotting 

 in dogs, cats, rabbits, and other animals. Such venoms contain 

 veritable thrombins or fibrin ferments, which can clot blood 

 in vitro (Lamb). They are destroyed in fifteen minutes by a 

 temperature of 75 C. and impaired in power by filtration through 

 a gelatine filter. Further, the ferment does not appear to be 

 used up in the process of coagulation (C. J. Martin). That the 

 clotting properties of venoms is dependent upon a formed 

 thrombin appears certain. Their clotting power " is not due 

 to their action upon prothrombins or thrombogens contained 

 in plasma, as the presence of calcium ions is unnecessar}^." 

 The venoms clot 10 per cent, oxalate plasma in vitro as rapidly 

 as '2 per cent, and their action is the same upon the following : 

 citrate, fluoride and magnesium sulphate plasma, hydrocele fluid 



1 Bordet and Gengou, Annul, de Plnst. Pusteur, 1903 and 1904. 

 ' Pseudechis porphyriacus, Notechis scututas (Australia) ; Echis carinatus, 

 Viperu Russellii (India). 



