00 HAND-BOOK OF PHYSIOLOGY. 



stituents of the blood in an apparently solid mass, but soon the fibrinous 

 meshwork begins to contract, and the serum which does not belong to the 

 clot is squeezed out. When the whole of the serum has transuded, the 

 clot is found to be smaller, but firmer and harder, as it is now made up 

 of fibrin and blood corpuscles only. It will be noticed that coagulation 

 rearranges the constituents of the blood according to the following scheme, 

 liquid blood being made up of plasma and blood-corpuscles, and clotted 

 blood of serum and clot. 



Liquid Blood. 



Plasma Corpuscles 



I 



Serum Fibria 



I 

 Clot 



I 



Clotted 



Blood 



Buffy Coat. Under ordinary circumstances coagulation occurs, as 

 we have mentioned above, before the red corpuscles have had time to sub- 

 side; and thus from their being entangled in the meshes of the fibrin, the 

 clot is of a deep red color throughout, somewhat darker, it may be, at the 

 most dependent part, from accumulation of red corpuscles, but not to any 

 very marked degree. When, however, coagulation is delayed from any 

 cause, as when blood is kept at a temperature of 32 F. (0 C.), or when 

 clotting is normally a slow process, as in the case of horse's blood, or, 

 lastly, in certain diseased conditions of the blood in which clotting is 

 naturally delayed, time is allowed for the colored corpuscles to sink to the 

 bottom of the fluid. When clotting does occur, the upper layers of the 

 blood, being free of colored corpuscles and consisting chiefly of fibrin, 

 form a superficial stratum differing in appearance from the rest of the 

 clot, in that it is of a grayish yellow color. This is known as the "buffy 

 coat." 



Cupped appearance of the Clot. When the buffy coat has been 

 produced in the manner just described, it commonly contracts more than 

 the rest of the clot, on account of the absence of colored corpuscles from 

 its meshes, and because contraction is less interfered with by adhesion to 

 the interior of the containing vessel in the vertical than the horizontal 

 direction. This produces a cup-like appearance of the buffy coat, and the 

 clot is not only buffed but cupped on the surface. The buffed and cupped 

 appearance of the clot is well marked in certain states of the system, 

 especially in inflammation, where the fibrin-forming constituents are in 

 excess, and it is also well marked in chlorosis where the corpuscles are 

 deficient in quantity. 



