CHAP, i.] BLOOD. 25 



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 concluding 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 approximately 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 de- 

 scribed above, or serous fluids which contain fibrinogen, can be made, 

 by means of fibrin ferment, to yield quite normal fibrin in the com- 

 plete absence of paraglobulin. A solution 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 

 favourable 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 para- 

 globulin, 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 fibrinogen 

 is isolated from plasma by repeated precipitation and solution, the 

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

 ogen, ultimately obtained, does not clot spontaneously. 



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

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

 the intervention of other proteids, converted into the less soluble 

 fibrin. Our knowledge of the constitution of proteid bodies is too 

 imperfect to enable us to make any very definite statement as to 

 the exact nature of the change thus effected ; but we may say this 

 much. Fibrinogen and fibrin have about the same elementary com- 

 position, fibrin containing a trifle more nitrogen. When fibrinogen 

 is converted into fibrin by means of fibrin ferment, the weight of 



