62 THE BLOOD. 



the coagulating fibrin has entangled the red corpuscles 

 while they were sinking : and, thus placed, it constitutes 

 what has been called a huffy coal. 



When a buffy coat is formed in the manner just de- 

 scribed, it commonly contracts more than the rest of the 

 clot does, and, drawing in at its sides, produces a cupped 

 appearance on the top of the clot. 



In certain conditions of the system, and especially when 

 there exists some local inflammation, this buffed and 

 cupped condition of the clot is well marked, and there has 

 been much discussion concerning its origin under these 

 circumstances. It is now generally agreed that two causes 

 combine to produce it. 



In the first place, the tendency of the red corpuscles to 

 form rouleaux (see p. 73) is much exaggerated in inflam- 

 matory blood ; and as their rate of sinking increases with 

 their aggregation, there is a ready explanation, at least in 

 part, of the colourless condition of the top of the clot. 

 And in the next place, inflammatory blood coagulates less 

 rapidly than usual, and thus there is more time for the 

 already rapidly sinking corpuscles to subside. The colour- 

 less or buffed condition of the upper part of the clot is there- 

 fore, readily accounted far ; while the cupped appearance is 

 easily explained by the greater power of contraction pos- 

 sessed by the fibrin of inflammatory blood, and by its 

 contraction being now not interfered with by the presence 

 of red corpuscles in its meshes. 



Although the appearance just described is commonly 

 the result of a condition of the blood in which there is an 

 increase in the quantity of fibrin, it need not of necessity 

 be so. For a very different state of the blood, such as 

 that which exists in chlorosis, may give rise to the same 

 appearance ; but in this case the pale layer is due to a 

 relatively smaller amount of red corpuscles, not to any 

 increase in the quantity of fibrin. 



It is thus evident that the coagulation of the blood is due 



