CHAKACTERS OF THE COLOR. 721 



within a quarter of an hour. Experience shows that blood may be re- 

 tained in occluded vessels, and yet continue fluid for a considerable 

 time, or that blood may be extravasated in the midst of the living tis- 

 sues, and yet preserve its fluidity for many days, though it will soon 

 coagulate when afterwards withdrawn from the body. From these and 

 other facts, it has been inferred that the living tissues possess some 

 special property, by which they maintain, or preserve, the fluidity of 

 the blood ; according to one view they actively prevent its coagulation ; 

 according to another, they operate negatively, by not determining that 

 process, as dead matter would, whether it were an inorganic solid, or 

 a dead animal substance, such as brain-substance, dead muscle, or pus. 

 The poisons and the modes of death, which influence the coagulation of 

 the blood, for the most part retard or prevent it. Sudden destruction 

 of the substance of the brain or spinal cord in an animal, causes coagu- 

 lation of the blood even in the living vessels, in which clots are found 

 after a few minutes. The poison of venomous serpents appears al- 

 together to destroy the coagulating property of the blood ; narcotic 

 poisons, and prussic acid have the same effect ; asphyxia or suffocation, 

 whether from hanging, drowning, or the action of gases unfit to sup- 

 port respiration, also cause the blood to remain fluid after death. In 

 cases of death by lightning, by electric shocks, by blows on the epi- 

 gastrium, or after a severe chase, the blood has been said not to un- 

 dergo coagulation ; but this seems to be untrue, the blood being often, 

 though not always, found fluid, but after a time undergoing, coagulation. 

 In cholera, the coagulation is also postponed. 



The/or/^, consistence, and color of the clot, exhibit many varieties. 

 From healthy blood, the clot is flat or slightly concave on the upper 

 surface, especially if the blood has been received in a shallow basin, 

 when the clot is soft, and very little serum exudes from it. When an 

 upright vessel is used, the surface of the clot is a little more concave. 

 The consistence of a healthy clot is firm and uniform ; its color is 

 bright red on the top, from exposure to the air, but dark in its lower 

 portions. In inflammatory diseases, especially in pneumonia or in- 

 flammation of the lungs, the blood is very rich in fibrin, containing, 

 instead of 3, above 5, often 7, and even as many as 13 parts- in 1000 ; 

 nevertheless it coagulates slowly, and the coagulurn presents a remark- 

 able peculiarity known as the huffy coat. Such a coagulum shrinks 

 more than usual, is exceedingly firm, and very concave on its upper 

 surface, forming what is called the u cwp," which presents a thick 

 layer of a nearly coloress, yellowish, or greenish-yellow hue, the so- 

 called buff or buffy coat. This coat, and the cupped form are more 

 marked when the blood is received into a narrow and deep basin, than 

 into a shallow one ; in the former case, the coagulation is slower, and 

 in the latter quicker, as with healthy blood. The buffy coat is very 

 firm and tough, and, when examined under the microscope, is found to 

 consist of fibrillated fibrin, intermixed with many white corpuscles ; 

 from some cause, the red corpuscles partly subside before the com- 

 mencement of coagulation, and so escape being entangled in the upper 

 portion of the clot. It was formerly supposed that the slower rate of 

 coagulation of inflammatory blood, accounted for this subsidence of 



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