30 COAGULATION OF THE BLOOD. 



coagulates (owing to the formation of the fibrin), and passes into a trembling jelly. 

 If, however, it be beaten with a glass-rod, the fibrin is obtained as a white stringy 

 mass, adhering to the rod. The quantity of fibrin in a given volume of plasma is 

 very small (p. 31), although it varies much in different cases. 



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

 containing 1th 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 

 Simmer) or 1 vol. blood with 2 vols, of a 4 per cent, solution of monophosphate 

 of potash (Maxia). 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. [The plasma so obtained is called " salted 

 plasma.'] 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 frogs' blood Johannes Miiller used a \ per cent, 

 solution of cane-sugar, which permits the corpuscles to be separated from the 

 plasma by nitration. 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 of these fluids. In these fluids, when left to themselves, 

 fibrin is formed, consisting of innumerable, excessively delicate, closely-packed, 

 microscopic, doubly refractive fibrils (fig. 7, 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 or placenta sanguinis. At first the clot is very soft, and after the 

 first 2 to 15 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 round the corpuscles, and a fairly solid, trembling, jelly-like clot, 

 which can be cut with a knife, is formed. During this time the clot takes the 

 shape of the vessel in which the blood coagulates, and expresses from its substance 

 a fluid the blood-serum. 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. 



The crusta is formed under other circumstances, e.g., with increased sp. gr. of the corpuscles, 

 or diminished sp. gr. of the plasma (as in hydremia and chlorosis), whereby the corpuscles sink 

 more rapidly, aud also during pregnancy. The taller and narrower the glass, the thicker is- 

 the crusta (compare 41). The upper end of the clot, where there are few corpuscles, shrinks 

 more, and is therefore smaller than the rest of the clot. This upper, lighter-coloured layer is 

 called the "buffy coat" ; but it gradually passes both in size and colour into the normal dark- 

 coloured clot. [Sometimes the upper surface of the clot is concave or "cupped." The older 

 physicians attached great importance to this condition, and also to the occurrence of the buffy 

 coat. ] 



Denbrinated Blood. If freshly-shed blood be beaten or whipped with a glass 

 rod, or with a bundle of twigs, fibrin is deposited on the rod or twigs in the form 

 of a solid, fibrous, yellowish-white, elastic mass, and the blood which remains is 

 called " defiljrinated blood" (p. 29). [The twigs and fibrin must be washed in a 

 stream of water to remove adhering corpuscles.] 



