THE CIRCULATING LIQUIDS OF THE BODY 39 



obtained by precipitating blood-serum, or defibrinated blood, 

 with fifteen to twenty times its bulk of alcohol, letting the 

 whole stand for a month or more, and then extracting the 

 precipitate with water (Schmidt). All the ordinary proteids 

 of the blood having been rendered insoluble by the alcohol, 

 the fibrin-ferment passes into solution in the water, and the 

 addition of a trace of the extract to a solution of fibrinogen 

 causes coagulation. The active substance itself does not 

 seem to be used up in the process, nor to enter bodily into 

 the fibrin formed ; a small quantity of it can cause an 

 indefinitely large amount of fibrinogen to clot ; its power is 

 abolished by boiling. For these reasons it is considered to 

 be a ferment. 



This action of the fibrin-ferment on fibrinogen helps to 



FIG. 5. DIAGRAM OF CLOT WITH BUFFY COAT. 



v, Lower portion of clot with red corpuscles ; w, white corpuscles in upper layer 

 of clot ; c, cupped upper surface of clot ; s, serum. 



explain many experiments in coagulation. Thus, transuda- 

 tions like hydrocele fluid do not clot spontaneously, although 

 they contain fibrinogen, which can be precipitated from 

 them by a stream of carbon dioxide or by sodium chloride. 

 But the addition of a little fibrin-ferment causes hydrocele 

 fluid to coagulate. So does the addition of serum, not 

 because of the serum-globulin which it contains, as was 

 once believed, but because of the fibrin-ferment in it. The 

 addition of blood-clot, either before or after the corpuscles 

 have been washed away, or of serum -globulin obtained 

 from serum, also causes coagulation of hydrocele fluid, and 

 for a similar reason, the fibrin-ferment having a tendency to 

 cling to everything derived from a liquid containing it. On 

 the other hand, serum, which does not of itself clot, although 



