60 HANDBOOK OF PHYSIOLOGY. 



to the clot is squeezed out. When the whole of the serum has trans- 

 uded, 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-cor- 

 puscles, and clotted blood of serum and clot. 



Liquid Blood. 



Plasma. Corpuscles. 



Serum. Fibrin. 



Clot. 



Clotted Blood. 



Under ordinary circumstances coagulation occurs, as we have men- 

 tioned above, before the red corpuscles have had time to subside; 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." 



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. 



Formation of Fibrin. That the clotting of blood is due to the 

 gradual appearance in it of fibrin is universally acknowledged. It may 

 l>e easily demonstrated. For example, if recently drawn blood be 



