PREPARATION AND PROPERTIES OF FIBRIN. 225 



that a third agent which acted as a ferment was necessary to put 

 into operation the fibrin-producing properties of the other two 

 factors. He moreover succeeded in separating the third agent, 

 to which he gave the name of fibrin ferment. By treating blood 

 serum with twenty times its volume of strong alcohol and allow- 

 ing it to stand a month or two, the proteids are precipitated and 

 rendered quite insoluble in water, and with them the ferment is 

 carried down. From the dried and powdered precipitate the fer- 

 ment is extracted with water. This solution when added to the 

 mixture of the pure fibrin factors, which by themselves did not 

 coagulate, caused rapid coagulation, but not when added to either 

 one or the other of them singly (Schmidt). 



This material seems to have been influenced by those circum- 

 stances which affect the activity of ferments in general : it has a 

 minimum, C., maximum, 80 C., and optimum, 38 C., temper- 

 ature of activity, with various gradations of rapidity of action 

 between each, and it is destroyed by a temperature above 80 C. 

 The amount of fibrin ferment only seems to influence the rapidity 

 with which the fibrin is formed, not the amount, which rather 

 depends on the quantity of serum globulin (paraglobulin). 



The source of the three fibrin generators is a question of much 

 difficulty, and may be discussed with more profit, together with 

 the question of blood coagulation, within and without the vessels, 

 after the morphological elements have been described. 



PREPARATION AND PROPERTIES OF FIBRIN. 



Fibrin may be procured either from plasma or blood by whip- 

 ping and then washing the insoluble fibrin with water. When 

 fresh it has a pale yellow or whitish color, a filamentous structure, 

 and is singularly elastic. It is not soluble in water, weak saline 

 solution, or ether. Alcohol makes it shrink by removing its 

 water. When quite dry it is brittle and hard, and can be reduced 

 to a powder. It swells in 1 per cent, hydrochloric acid, and if 

 then warmed is soon converted into acid albumin. 



The amount formed varies very much even in the blood drawn 

 from the same animal at the same time, but is always very small 

 compared with the size of the blood clot. It never reaches as 



