THE BLOOD. 6} 



whipped with a bundle of twigs which presents numerous points of con- 

 tact and so, as we shall presently see, facilitates coagulation, the fibrin 

 may be withdrawn .from the blood before it can entangle the blood- 

 corpuscles within its meshes, as it adheres to the twigs in stringy threads 

 almost free from corpuscles; whereas the blood from which the fibrin 

 has been withdrawn no longer exhibits the power of spontaneous coagu- 

 lability. Although these facts have long been known, the closely asso- 

 ciated problem as to the exact manner in which fibrin is formed is still 

 only partially solved. It will be most convenient to treat of the question 

 step by step. 



In the first place it appears that under the ordinary conditions of 

 experiment, fibrin is chiefly, if not entirely to be obtained from plasma ; 

 for although the colorless corpuscles may be intimately connected with 

 the process, as will be shown later on, yet the colored corpuscles do not 

 appear to take an active part in it. 



This statement does not exclude the possibility that fibrin may be 

 derived from the colored corpuscles under certain conditions. Indeed, 

 this is more than probable, as experiments have shown that if a little 

 defibrinated blood be added to serum, the haemoglobin leaves the stroma 

 of the colored corpuscles of the blood, and a substance arises from it 

 called stroma-fibrin, indistinguishable from ordinary fibrin, which pro- 

 duces clotting of the serum. 



This may be shown by experimenting with plasma free from colored 

 corpuscles. 



Plasma maybe procured by delaying coagulation in blood by keeping 

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

 which are of a higher specific gravity than the other constituents of 

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

 to leave an upper stratum of colorless plasma, in the lower layers of 

 which, however, are many colorless corpuscles. The blood of the horse 

 is specially suited for the purposes of this experiment, as might have 

 been expected from what has been stated as to its naturally slow coagu- 

 lating power. A portion of the colorless plasma, if decanted into 

 another vessel and exposed to the ordinary temperature of the air, will 

 be seen to coagulate just as though it were the entire blood, producing 

 a clot similar in all respects to blood clot, except that it is almost color- 

 less from the absence of red corpuscles. But if some of the plasma be 

 diluted with * neutral saline solution, coagulation is delayed, and the 

 stages of the gradual formation of fibrin may be more conveniently 

 watched. The viscidity which precedes the complete coagulation may 

 be actually seen to *be due to fibrin fibrils developing in the fluid first 



1 Neutral saline solution commonly consists of a .6 to .75 solution of common salt 

 (sodium chloride) in water. 



