^Ghap. VI. Of Fevers in general. 25 



middle, the Water that runs on each Side will move with 

 greater Rapidity than that which is either before or behind. 

 From all which it is evident, that Obftruclions in the 

 fmall C'apillary Arteries, as they are the Caufe of a greater 

 and more violent Motion of the Blood in thofe that are 

 larger, mull occafion a Fever ; but efpecially as fuch a 

 Motion may bring on a fubfcquent Rarefaction in the 

 Blood ; becaufe whatever agitates the Blood, and puts it 

 in a more than ordinary degree of Motion, muft occa- 

 fion more frequent Conlradtions of the Heart, and alfo 

 of the Arteries, whereby the Blood muft, without doubt, 

 be communicated, and its Parts render'd more fmall. In 

 like manner an over- great Rarefaction maybe the Caufe 

 of a Coagulation of the Blood ; that is, when the Blood 

 liappens to be too much rarefy'd, as in the beginning of 

 a legitimate Fever, the thin Serum being expended in a 

 greater than ordinary Quantity, will leave the remaining 

 Mafs thicker, and more unapt to motion, whereby fe- 

 veral Changes and Alterations may be reaforiably expeCl- 

 ed : And now lince the Extremities of the Veins, which 

 communicate with thofe of the Arteries, are but little dif- 

 ferent from the Arteries themfelves, fave only that they 

 take a contrary Courfe, and that the Blood moves in them 

 backwards towards the Heart ; whereas in the Arteries it 

 moves from the Heart towards the Extremities : And as 

 the Motion of the Blood in thefe fmall communicating 

 Branches of the Veins, is chiefly owing to a continual Suc- 

 ceffion of Blood from the Arteries, when once therefore 

 it gets into them, its Motion cannot be eafily retarded, 

 unlefs in the Extremities of the Limbs, where its afcent 

 upwards muft, no doubt, be a great Hindrance to it. And 

 this is the Reafon why, in feveral Kinds of Fevers, efpeci- 

 ally in thofe where the Blood happens to be of unequal 

 Compolltion, viz. when it is thicker in fome Parts than 

 others, the Pulfation of the Arteries muft alfo be unequal ; 

 becaufe while its groiler Parts are detain'd in the fmalleft 

 Veins and Arteries, the Blood muft move with more Velo- 

 city in fome of the other VefTels, for the Reafons already 

 alledg'd ; but as foon as this Lentor has work'd it felf into 

 the more capacious Veins, which grow wider the nearer 

 they approach the Heart, and that a thinner and more at- 

 tenuated Blood fupplies its Place in thofe fmall Branches, 

 then the Pulfation becomes more moderate and uniform, 

 and the Fever is remov'd, ^t leaft for that Seafon. 



But 



