THE CLOTTING OF BLOOD. 



27 



consist of a feltwork of fine granular fibrils, in the meshes of which are 

 entangled the red and white corpuscles of the blood. In the serum nothing 



[FIG. 2. 



[FIG. 3. 



Bowl of recently coagulated blood, 

 showing the whole mass uniformly 

 solidified. After Daltou.] 



Bowl of coagulated blood, after twelve 

 hours, showing the clot contracted and float- 

 ing in the fluid serum. After Dalton.] 



[FIG. 4. 



can be seen but a few stray corpuscles, chiefly white. The fibrils are com- 

 posed of a substance called fibrin. [Fig. 4.] Hence we may speak of the 

 clot as consisting of fibrin and cor- 

 puscles ; and the act of clotting is 

 obviously a substitution for the 

 plasma of fibrin and serum, fol- 

 lowed by a separation of the fibrin 

 and corpuscles from the serum. 



In man, blood when shed becomes 

 viscid in about two or three minutes, 

 and enters the jelly stage in about 

 five or ten minutes. After the lapse 

 of another few minutes the first 

 drops of serum are seen, and clotting 

 is generally complete in from one to 

 several hours. The time, however, 

 will be found to vary according to 

 circumstances. Among animals the 

 rapidity of clotting varies exceed- 

 ingly in different species. The 

 blood of the horse clots with re- 

 markable slowness ; so slowly, in- 

 deed, that many of the red and also 



some of the white corpuscles (both these being specifically heavier than 

 the plasma) have time to sink before viscidity sets in. In consequence 

 there appears on the surface of the blood an upper layer of colorless plasma 

 containing in its deeper portions many colorless corpuscles (which are lighter 

 than the red). This layer clots like the other parts of the blood, forming 

 the so-called " buffy coat." A similar buffy coat is sometimes seen in the 

 blood of man in certain abnormal conditions of the body. 



If a portion of horse's blood be surrounded by a cooling mixture of ice 

 and salt, and thus kept about C., clotting may be almost indefinitely 

 postponed. Under these circumstances a more complete descent of the cor- 

 puscles takes place, and a considerable quantity of colorless transparent 

 plasma free from blood corpuscles may be obtained. A portion of this 

 plasma removed from the freezing mixture clots in the same manner as does 

 the entire blood. It first becomes vascid and then forms a jelly, which sub- 

 sequently separates into a colorless shrunken clot and serum. This shows 

 that the corpuscles are not an essential part of the clot. 



Coagulated fibrin, showing its fibrillated con- 

 dition. After Dalton.] 



