230 



TIIE BLOOD. 



Fig. 65. 



Vertical section of a RE- 

 CENT CoAauLUM, showing 

 the greater accumulation of 

 blood-globules at the bottom. 



If the blood be allowed to coagulate in a bowl, and the clot be 

 then divided by a vertical section, it will be seen that its lower 

 portion is softer and of a deeper red than the upper. (Fig. 65.) 

 This is because the globules, which are of 

 greater specific gravity than the plasma, sink 

 toward the bottom of the vessel before coagu- 

 lation takes place, and accumulate in the 

 lower portion of the blood. This deposit of 

 the globules, however, is only partial; be- 

 cause they are soon fixed and entangled by 

 the solid mass of the coagulum, and are thus 

 retained in the position in which they hap- 

 pen to be at the moment that coagulation 

 takes place. 



If the coagulation, however, be delayed 

 longer than usual, or if the globules sink more rapidly than is cus- 

 tomary, they will have time to subside entirely from the upper por- 

 tion of the blood, leaving a layer at the surface which is composed 

 of plasma alone. When coagulation then takes place, this upper 

 portion solidifies at the same time with the rest, and the clot then 

 presents two different portions, viz., a lower portion of a dark red 

 color, in which the globules are accumulated, and an upper portion 

 from which the globules have subsided, and which is of a grayish 

 white color and partially transparent. This whitish layer on the 

 surface of the clot is termed the " buffy coat ;" and the blood pre- 

 senting it is said to be " buffed." It is an appearance which often 

 presents itself in cases of acute inflammatory disease, in which the 

 coagulation of the blood is unusually retarded. 



When a clot with a buffy coat begins to contract, the contrac- 

 tion takes place perfectly well in its upper 

 portion, but in the lower part it is impeded 

 by the presence of the globules which have 

 accumulated in large quantity at the bottom 

 of the clot. While the lower part of the 

 coagulum, therefore, remains voluminous, 

 and hardly separates from the sides of the 

 vessel, its upper colorless portion diminishes 

 very much in size ; and as its edges separate 



Bowl of COAGULATED J 



BLOOD, showing the clot from the sides of the vessel, they curl over 

 buffed and cupped. toward each other, so that the upper surface 



of the clot becomes more or less excavated or cup-shaped. (Fig. 66.) 



Fig. 66. 



