THE CLOT. 199 



ferent conditions of the blood, we are alike incapable of explaining 

 why the blood of persons killed by lightning, of those who have 

 died from the effects of narcotic poisons or asphyxia, or from 

 hanging, should not coagulate, whilst it coagulates very rapidly 

 after the infliction of venomous bites, &c., and in the plague. 



The consistence of the clot is also liable to very great variations. 

 As the fibrin actually constitutes the main consolidating substance 

 of the clot, the opinion long prevailed, and has only recently been 

 relinquished, that the cause of this difference was to be sought in 

 a difference in the chemical constitution of this substance ; but 

 here we have, in the first place, to take into account both the 

 external and the internal mechanical influences, which make the 

 clot appear at one time more dense and compact, and at another 

 softer and more gelatinous. The vessel in which the blood coagu- 

 lates, is not without its influence, for in a shallow vessel, a softer 

 coagulum will be formed than in a high and narrow one. 



We reckon, among internal mechanical causes, the relations in 

 which the blood-corpuscles and the water stand to the quantity of 

 the fibrin. When the number of blood-corpuscles is small in rela- 

 tion to the quantity of fibrin, its molecules approximate more 

 closely to one another, and the coagulum is more densely com- 

 pressed. But when an excess of blood-corpuscles is imbedded in 

 fibrin which separates gelatinously, the latter may remain imper- 

 fectly contracted during its further consolidation, and thus give 

 rise to a highly friable clot. As the lower part of the clot, more- 

 over, contains the greater number of blood-corpuscles, it is evident 

 that this portion will continue to be softer and looser in texture, 

 whilst the upper part becomes more dense and connected. On 

 this account, we find that the clot in the blood of plethoric persons 

 is large and soft, whilst in that of chlorotic patients it is small and 

 firm. 



The fact that too large a quantity of water diminishes the con- 

 sistence of the clot, has chiefly been proved by Nasse, both by direct 

 experiments and by observations on morbid watery blood. It 

 would appear as if the molecules, which are separated in a gelati- 

 nous form at the commencement of coagulation, could not be 

 brought into sufficiently close contact with one another to admit 

 of their firm contraction ; and hence, the clot may in such cases 

 retain too much serum, which will render it soft and friable. This 

 excess of water may also contribute to produce that greater soft- 

 ness which we observe in the clot of young animals, and may be 

 the cause of the softness noticed in the clot after frequent blood- 



