162 BLOOD AND LYMPH 



may examine the twigs with which we did the beating. 

 These will be covered with a stringy elastic substance 

 which, when washed, is seen to consist of gUstening white 

 strands or fibers. These fibers are composed of a sub- 

 stance called fibrin, and are identical in composition with 

 those which were noted in the clot of human blood. 

 Furthermore, if we test this fibrin with our nutrient tests, 

 we shall find that it responds strongly to one test only, 

 namely, that for proteid. In other words, fibrin is a coag- 

 ulated proteid which was present in the plasma of fresh- 

 drawn blood in a liquid state. If we examine the bottled 

 blood after it has stood for awhile ^ve shall find the con- 

 tents of the bottle fiUed with fresh-drawn blood in a differ- 

 ent condition from the whipped blood. The former will 

 be found to have solidified into a clot of the same shape 

 as the bottle, and to be floating in a small quantitj' of 

 a straw-colored liquid {serian). The whipped blood wiU 

 show no clot, and is in the same condition as when we put 

 it in the bottle. 



If we pour off the serum from the first bottle, and then 

 break the bottle so as to remove the clot entire, we may 

 examine this clot and study its structure. Such examina- 

 tion shows it to be made up of a solid mass of fibrin 

 fibers which inclose masses of corpuscles. The corpuscles 

 give it its color. The whipped blood fails to clot because 

 we have removed its fibrin by whipping. From these 

 observations we must conclude that the seriun is plasma 

 whose fibrin has been removed, and that the presence of 

 this fibrin is necessary to the formation of a clot. 



Our experiments thus far have succeeded in separating 

 only one of the constituents of blood plasma, namely, 

 fibrin. 



