34 BLOOD. 



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 cer- 

 tain 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 forever 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 1 and the serum of clotted blood ; and 

 since in most, if not all, cases where blood or blood clot or serum produces 

 clotting in hydrocele or pericardial fluid, an exactly similar clotting may be 

 induced by the mere addition of fibrin ferment, we seem justified in con- 

 cluding that the clotting virtues of the former are due to the ferment which 

 they contain. 



Now, when fibrinogen is precipitated from plasma, as above described, by 

 sodium chloride, redissolved, and reprecipitated, more than once, it may be 

 obtained in solution, by help of a dilute neutral saline solution, in an ap- 

 proximately pure condition, at all events free from other proteids. Such a 

 solution will not clot spontaneously ; it may remain fluid indefinitely ; and 

 yet on the addition of a little fibrin ferment it will clot readily and firmly, 

 yielding quite normal fibrin. 



This body fibrinogen is also present and may be separated out from the 

 specimens of hydrocele, pericardial, and other fluids which clot on the 

 addition of fibrin ferment, and when the fibrinogen has been wholly removed 

 from these fluids they refuse to clot on the addition of fibrin ferment. 



Paraglobulin, on the other hand, whether prepared from plasmine by 

 separation of the fibrinogen, or from serum, or from other fluids in which it 

 is found, cannot be converted by fibrin ferment, or indeed by any other 

 means, into fibrin. And fibrinogen isolated, as described above, or serous 

 fluids which contain fibrinogen, can be made, by means of fibrin ferment, to 

 yield quite normal fibrin in the complete absence of paraglobulin. A solu- 

 tion of paraglobulin obtained from serum or blood clot will, it is true, clot 

 pericardial or hydrocele fluids containing fibrinogen, or indeed a solution of 

 fibrinogen, but this is apparently due to the fact that the paraglobulin has 

 in these cases some fibrin ferment mixed with it ; it is also possible that, 

 under certain conditions, the presence of paraglobulin may be favorable to 

 the action of the ferment. 



When the so-called plasmine is precipitated, as directed in 19, fibrin 

 ferment is carried down with the fibrinogen and paraglobulin, and when the 

 plasmine is re-dissolved the ferment is present in the solution and ready to 

 act on the fibrinogen. Hence the re-dissolved plasmine clots spontaneously. 

 When fibrinogeu is isolated from plasma by repeated precipitation and 

 solution, the ferment is washed away from it, and the pure ferment-free 

 fibrinogen, ultimately obtained, does not clot spontaneously. 



So far it seems clear that there does exist a proteid body, fibrinogen, 

 which may by the action of fibrin ferment be directly, without the interven- 



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

 a washed blood clot with a 10 per cent, solution of sodium chloride. 



