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, re-dissolved, 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 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 

 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, 1 

 fibrinogen, 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 composition, fibrin containing a trifle more 



