ON THE FUNCTIONS OF THE HBART AND ARTERIES. | jQ 



more probable, that a debility of the heart is the primary 

 cause of this affection. 



Beside these general causes of derangement, which ap- Local infiam- 

 pear to be more or less concerned in different kinds of fever, "^^'i®^- 

 there are other more partial ones, which seem to have a si- 

 milar relation to local inflammations. The most obvious of 

 these changes are such as must be produced by partial dila- PartJal affec- 

 tations or contractions of the capillary vessels: since, as I ^'onsofthecm- 

 , , ■> , piUary veiiels, 



have endeavoured to demonstrate, any supposed derange- 

 ment in the actions of the larger vessels must be excluded 

 from the number of causes which can materially affect the 

 circulation. It cannot be denied, that a diminution of the 

 elastic, or even of the muscular force of the small arteries, 

 must be immediately followed by such a distension, as will 

 produce a resistance equal to the pressure : the distension 

 will occasion an increase of redness, and in most cases pain: InflamroatioE. 

 the heat will also generally be increased, on account of the 

 increased quantity of blood, which will be allowed to pass 

 through the part ; and since the hydrostatic pressure of the 

 blood acquires greater force, as the artery becomes more 

 distended, it may be so wedk as to continue to give way, 

 like a ligament which has been strained, until supported by 

 the surrounding parts. In this state a larger supply of blood 

 will be ready for any purposes which require it, whether an 

 injury is to be repaired, or a new substance formed; and it Perhaps the 

 is not impossible, that this change in the state of the minute properties of _ 

 vessels may ultimately produce some change in the proper- niatdy alteied. 

 ties of the blood itself. 



The more the capillary arteries are debilitated and dis- 

 tended, the greater will be the mean velocity of the circu- 

 lation ; but whether or no the velocity will be increased an 

 the vessels which are thus distended, must depend on the 

 extent of the affected part ; and it may frequently happen, 

 that the velocity may be much more diminished on account 

 of the dilatation of the space which the blood is to occupy, 

 than increased by the diminution of the resistance. And 

 on the other hand, the velocity may be often increased, for 

 a similar reason, at the place of a partial contraction. Hence Experiments 

 we may easily understand some of the experiments, which i" Wilson on 

 Dr. Wilson has related in his valuable treatise on fevers : ^^^'^** 



the 



