COAGULATION OF THE BLOOD. 39 



(B.) With Admixture. Blood flowing from an artery is caught in a 

 tall graduated measure containing |th of its volume of a concentrated 

 solution of sodic sulphate (Hewson) or in a 25 per cent, solution of 

 magnesic sulphate (1 vol. to 4 vols. blood : Semmer) or 1 vol. blood 

 with 2 vols. of a 4 per cent, solution of monophosphate of potash 

 (Masia). When the blood is mixed with these fluids and put in a 

 cool place, the corpuscles subside, and the clear stratum of plasma 

 mixed with the salts may be removed with a pipette. If the salts be 

 removed by dialysis, coagulation occurs; or it may be caused by the 

 addition of water (Joh. Miiller). Blood which is mixed with a 4 per 

 cent, solution of common salt does not coagulate, so that it also may 

 be used for the preparation of plasma. [For frog's blood Johannes 

 Miiller used a J per cent, solution of cane sugar, which permits the 

 corpuscles to be separated from the plasma by filtration. The plasma 

 mixed with the sugar coagulates in a short time.] 



27. Fibrin Coagulation of the Blood. 



General Characters. Fibrin is that substance which, becoming 

 solid in shed blood, in plasma and in lymph causes coagulation. In 

 these fluids, when left to themselves, fibrin is formed, consisting of 

 innumerable, excessively delicate, closely-packed, microscopic, doubly 

 refractive (Hermann) fibrils (Fig. 6, E). These fibrils entangle the 

 blood-corpuscles as in a spider's web, and form with them a jelly-like, 

 solid mass called the BLOOD-CLOT (placenta sanguinis). At first the 

 clot is very soft, and after the first 2 to 1 5 minutes a few fibres may be 

 found on its surface; these may be removed with a needle, while the 

 interior of the clot is still fluid. The fibres ultimately extend throughout 

 the entire mass, which, in this stage, has been called cruor. After 

 from 12 to 15 hours the fibrin contracts, or, at least, shrinks more 

 and more closely around the corpuscles, and a fairly solid, trembling, 

 jelly-like clot, which can be cut with a knife, is formed. During this 

 time the clot has expressed from its substance a fluid the BLOOD-SERUM. 

 The clot takes the shape of the vessel in which the blood coagulates. 

 Fibrin may be obtained by washing away the corpuscles from the 

 clot with a stream of water. 



Crusta Phlogistica. If the corpuscles subside very rapidly, and if 

 the blood coagulates slowly, the upper stratum of the clot is not red, 

 but only yellowish, on account of the absence of coloured corpuscles. 

 This is regularly the case in horse's blood, and in human blood it is 

 observed especially in inflammations ; hence this layer has been called 

 crusta phlogistica. Such blood contains more fibrin, and so coagulates 

 more slowly. 



