7*> OF STIMULUS AND EXERTION. SECT. XII I. 



is performed with greater velocity as well as with 

 greater force by vigorous confutations, as in throw- 

 ing a javelin. 



There is however another circumftance, which 

 may often contribute to caufe the quicknefs of the 

 puiie in nervous fevers, as in animals bleeding to 

 death in the Daughter- houie ; which is the deficient 

 quantity of blood ; whence the heart is but half 

 diftended, and in confequence fooner contracts. See 

 Seel. XXXIL 2- i. 



For we muft not confound frequency of repeti- 

 tion with quicknefs of motion, or the number of 

 pulfations with the velocity, with which the fibres, 

 which conftitute the coats of the arteries, contract 

 themfelves. For where the frequency of the pul- 

 fations is but feventy-five in a minute, as in health ; 

 the contracting fibres, which conftitute the fides of 

 the arteries, may move through a greater fpace in a 

 given time, than where the frequency of pulfation 

 is one hundred and fifty in a minute, as in fome 

 fevers with great debility. For if in thofe fevers 

 the arteries do not expand themfelves in their 

 diaftole to more than half the ufual diameter of 

 their diaflole in health, the fibres whkh conftitute 

 their coats, will move through a lefs fpace in a mi- 

 nute than in health, though they make two pulfa- 

 tions for one. 



Suppofe the diameter of the artery during its 

 fyftole to be one line, and that the diameter of the 

 fame artery during its diaftole is in health is four 

 lines, and in a fever with great debility only two 

 lines. It follows, that the arterial fibres contract in 

 health from a circle of twelve lines in circumfe- 

 rence to a circle of three lines in c'^u inference, 

 that is they move through a fpace of nine lines in 

 length. While the arterial fibres in the fever with 

 debility would twice contract from a circle of fix 

 lines to a circle of three lines j that is while they 



move 



