24 FIBRIN FERMENT. [BOOK i. 



all events, these fluids, when a little blood, or a piece of blood clot, 

 or a little serum is added to them, will clot rapidly and firmly, 1 

 giving rise to an unmistakeable clot of normal fibrin, differing only 

 from the clot of blood in that, when serum is used, it is colourless, 

 being free from red corpuscles. 



Now, blood (or blood clot, or serum) contains many things, to 

 any one of which the clotting power thus seen might be attributed. 

 But it is found that in many cases clotting may be induced in the 

 fluids of which we are speaking by the mere addition and that 

 even in exceedingly small quantity, of a substance which can be 

 extracted from blood, or from serum, or from blood clot, or even 

 from washed fibrin, or indeed from other sources, a substance 

 whose exact nature is uncertain, it being doubtful whether it is a 

 proteid at all, and whose action is peculiar. 



If serum, or whipped blood, or a broken-up clot be mixed with 

 a large quantity of alcohol and allowed to stand some days, the 

 proteids present are in time so changed by the alcohol as to 

 become insoluble in water. Hence if the copious precipitate 

 caused by the alcohol, after long standing, be separated by filtration 

 from the alcohol, dried at a low temperature, not exceeding 40 C., 

 and extracted with distilled water, the aqueous extract contains 

 very little proteid matter, indeed very little organic matter at all. 

 Nevertheless even a small quantity of this aqueous extract added 

 alone to certain specimens of hydrocele fluid or other of the fluids 

 spoken of above, will bring about a speedy clotting. The same 

 aqueous extract has also a remarkable effect in hastening the 

 clotting of fluids which, though they will eventually clot, do so 

 very slowly. Thus, plasma may, by the careful addition of a 

 certain quantity of neutral salt and water, be reduced to such a 

 condition that it clots very slowly indeed, taking perhaps days to 

 complete the process. The addition of a small quantity of the 

 aqueous extract we are describing will, however, bring about a 

 clotting which is at once rapid and complete. 



The active substance, whatever it be, in this aqueous extract 

 exists in small quantity only, and its clotting virtues are at once 

 and for ever lost when the solution is boiled. Further, there is no 

 reason to think that the active substance actually enters into the 

 formation of the fibrin to which it gives rise. It appears to belong 

 to a class of bodies playing an important part in physiological 

 processes and called ferments, of which we shall have more to say 

 hereafter. We may therefore speak of it as the fibrin ferment, the 

 name given to it by its discoverer Alexander Schmidt. 



This fibrin ferment is present in and may be extracted from 

 clotted or whipped blood, and from both the clot 2 and the serurn 

 of clotted blood ; and since in most if not all cases where blood or 



1 In a few cases no coagulation can thus be induced. 



2 A powerful solution of fibrin ferment may be readily prepared by simply 

 extracting a washed blood clot with a 10 p.c. solution of sodium chloride. 



