202 BLOOD. 



small but very compact clot, which proves that the coagulation of 

 the fibrin acted an important part in this phenomenon. 



We far more frequently observe the converse relations in 

 diseased, and even sometimes in healthy blood that is to say, 

 the corpuscles have a strongly marked sinking capacity, whilst 

 the fibrin coagulates slowly. We must here bear in mind that 

 extreme cases are of the rarest occurrence, and that both pro- 

 perties are wholly relative; for in the one case the fibrin may 

 contract as usual within an average time of coagulation, while the 

 corpuscles sink more rapidly; and in the other case, the corpuscles 

 may sink with their ordinary velocity only, while the fibrin, on the 

 contrary, coagulates very slowly. The result will be much the same 

 in both cases. The influence of these two causes may be perceived 

 even in the normal clot, for here we find that the lower part of 

 the clot is always darker and softer than the upper one; this 

 depends, certainly, only in part upon the circumstance that there 

 are more blood-corpuscles which have already sunk in the lower 

 than in the upper portion, for the light colour of the upper part 

 depends on the one hand upon the access of oxygen, and on the 

 other upon the larger number of colourless blood-corpuscles, 

 which, although they combine in groups, owing to their viscidity, 

 are not so very closely in contact in consequence of their spherical 

 forms, and do not, from their lightness, sink as rapidly as the red 

 corpuscles. When the red corpuscles of fresh blood have sunk in 

 some degree before the fibrin becomes gelatinised, the fibrin 

 coagulating in the uppermost stratum of fluid is unable to 

 enclose any red corpuscles, and consequently forms a colourless 

 crust upon the subsequently deposited clot. As this crust encloses 

 only few foreign elements, the fibrin of which it consists con- 

 tracts more closely than that which is beneath it, and in which the 

 blood-corpuscles are embedded. This crust will therefore not 

 only present a smaller diameter than the red clot, but it must also, 

 from its contiguity, cause an extension of the margins of the latter, 

 while it gives rise to a concavity of the clot. This concave and 

 generally very compact and yellowish white buffy coat is of most 

 common occurrence. It is principally found to occur in the 

 venous blood of horses and in inflamed blood, and sometimes also 

 in human blood, if drawn during the process of digestion. A 

 plane or convex buffy coat is also observed in many morbid con- 

 ditions ; in these cases it is soft, and of a greyish white colour ; 

 and it is not improbable that this character depends no less upon 



