CHABACTEBS OF THE CLOT. 145 



ence in color at its superior portion. The blood having re- 

 mained fluid for some time, the red corpuscles settle, by virtue 

 of their greater weight, leaving a colorless layer on the top. 

 This is the bufiy coat so frequently spoken of by authors. 

 The buffed and cupped appearance of the clot has been sup- 

 posed to indicate an inflammatory condition of the circulating 

 fluid; inasmuch as the quantity of fibrin is generally in- 

 creased in inflammation, and the greater the quantity of 

 fibrin the more rapid is the gravitation of the red corpuscles. 

 Though this frequently presents itself in the blood drawn in 

 inflammations, it is by no means pathognomonic of this con- 

 dition, and is liable to occur whenever coagulation is slow, or 

 retarded by artificial means. It is always present in the 

 blood of the horse. Examined microscopically, the bufty 

 coat presents fibrils of coagulated fibrin with some of the 

 white corpuscles of the blood. On removing a clot of ve- 

 nous blood from the serum, the upper surface is florid from 

 contact with the air, while the rest of it is dark ; and on 

 making a section, if the coagulation has not been too rapid, 

 the gravitation of the red corpuscles is apparent. The sec- 

 tion, which is at first almost black, soon becomes red from 

 contact with the atmosphere. The clot from arterial blood 

 has a dark-red color. If the clot be cut into small pieces, it 

 will undergo further contraction, and express a part of the 

 contained serum. If the clot be washed under a stream of 

 water, at the same time kneading it with the fingers, we may 

 remove almost all the red corpuscles, leaving the meshes of 

 fibrin, which, on microscopic examination, will present the 

 fibrillated appearance to which we have already referred. 

 This is a method sometimes employed for the extraction of 

 the fibrin. It was in this way that fibrin was isolated by 

 Malpighi ; who made the first experiments which rendered 

 it probable that coagulation of the blood depended upon this 

 principle. In a few days, as the result of putrefaction, the 

 clot softens, mixes with the serum, and the blood regains its 

 fluidity. 



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