THE BLOOD. 07 



Formation of Fibrin. In describing the coagulation of the blood in 

 the preceding paragraphs, it was stated that this phenomenon was due to 

 the development in the clotting blood of a mesh work of fibrin. This may 

 be demonstrated by taking recently-drawn blood, and whipping it with a 

 bundle of twigs; the fibrin is found to adhere to the twigs as a red dish - 

 white, stringy mass, having been thus obtained from the fluid nearly free 

 from colored corpuscles. The defibrinated blood no longer retains the 

 power of spontaneous coagulability. 



The fibrin which makes its appearance in the blood when it is under- 

 going coagulation is derived chiefly, if not entirely, from the plasma or 

 liquor sanguinis; for although the colorless corpuscles are intimately con- 

 nected with the process in a way which will be presently explained, the 

 colored corpuscles appear to take no active part in it whatever. This 

 may be shown by experimenting with plasma free from colored corpuscles. 

 Such plasma may be procured by delaying coagulation in blood, by keep- 

 ing it at a low temperature, 32 ~F. (0 C.), until the colored corpuscles 

 which are of higher specific gravity than the other constituents of blood, 

 have had time to sink to the bottom of the containing vessel, and to leave 

 mi upper stratum of colorless plasma, in the lower layers of which are 

 many colorless corpuscles. The blood of the horse is specially suited for 

 the purposes of this experiment; and the upper stratum of colorless 

 plasma derived from it, if decanted into another vessel and exposed to the 

 ordinary temperature of the air, will coagulate just as though it were the 

 entire blood, producing a clot similar in all respects to blood clot, except 

 that it is almost colorless from the absence of red corpuscles. If some of 

 the plasma be diluted with neutral saline solution, 1 coagulation is de- 

 layed, and the stages of the gradual formation of fibrin may be more con- 

 veniently watched. The viscidity which precedes the complete coagula- 

 tion may be seen to be due to fibrin fibrils developing in the fluid first 

 of all at the circumference of the containing vessel, and gradually extend- 

 ing throughout the mass. Again, if plasma be whipped with a bundle of 

 twigs, the fibrin may be obtained as a solid, stringy mass, just in the 

 same way as from the entire blood, and the resulting fluid no longer 

 retains its power of spontaneous coagulability. Evidently, therefore, 

 fibrin is derived from the plasma and not from the colored corpuscles. 

 In these experiments, it is not necessary that the plasma shall have been ob- 

 tained by the process of cooling above described, as plasma obtained in 

 any other way, e.g., by allowing blood to flow direct from the vessels of 

 an animal into a vessel containing a third or a fourth of the bulk of the 

 blood of a saturated solution of a neutral salt (preferably of magnesium 

 sulphate) and mixing carefully, will answer the purpose, and, just as in 

 the other case, the colored corpuscles will subside, leaving the clear super- 



1 Xcutral saline solution commonly consists of a '75 solution of common salt 

 (sodium chloride) in water. 



