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*—‘ooo1 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 unnecessary.” 
The venoms clot Io per cent. oxalate plasma 7 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, Aznal. de Inst. Pasteur, 1903 and 1904. 
2 Pseudechis porphyriacus, Notechis scutatus (Australia); Zchis carinatus, 
Vipera Russellit (India). 
