TREATMENT OF INFLAMMATION. 193 



vasa vasorum. In either case the changes occurring 

 in the patches of effused fibrine may be productive 

 of the various physical and chemical alterations of 

 structure which precede, and predispose to, the for- 

 mation of an aneurismal pouch. A very slight con- 

 sideration of the constant and reciprocal relation 

 existing between the force and frequency of the 

 ventricular contractions, and the amount of pressure 

 of the aortic blood, will render it. evident that any 

 great increase in the latter force must inevitably 

 produce considerable disorder of the heart's action. 

 For the power exercised by the great instrument of 

 the circulation in propelling the blood, varies with 

 the resistance offered to the entrance of that blood 

 into the aorta ; and this resistance arises from the 

 backward pressure of the fluid previously contained 

 in that vessel. With the diminution of that pressure 

 the contractions of the ventricle, in the absence of 

 unnatural stimuli, become less frequent and less 

 powerful; and the state of the circulation during 

 sleep furnishes an interesting example of the opera- 

 tion of this law. But if, either from inordinate 

 action of the heart itself, or from diminished calibre 

 of the smaller vessels, the general and therefore the 

 backward pressure of the aortic blood be unnaturally 

 increased, the same compensating principle, , con- 

 tinuing in operation, may give rise to very injurious 

 and even fatal consequences. It has long been 

 known that, in certain debilitated states of the 

 system, a very slight exertion may cause momentary 

 exhaustion and syncope ; and where the constitution 

 is very much enfeebled, as in mercurial erythismus, 



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