4 8 OF STIMULUS SECT. XII. i. 4. 



received at each interval of the aftivity of the fibres. Hence in 

 repeated motions, as of the fingers in performing on the harpfi- 

 chord, it would -at firft fight appear, that fwiftnefsand ftrength 

 were incompatible : nevertheless the (ingle contraction of a muf- 

 cle is performed with greater velocity, as well as with greater 

 force by vigorous confHtutions, as in throwing a javelin. 



There is however another circumftance, which may often 

 contribute to caufe the quicknefs of the pulfe in nervous fevers, 

 as in animals bleeding to death in the flaughter-houfe ; which is 

 the deficient quantity of blood, whence the heart is but half 

 diftended, and in confequence fooner contracts. See Set 

 XXXII. 2. i. 



For we mud not confound frequency of repetition with 

 quicknefs of motion, or the number of puifations with the ve- 

 locity, with which the fibres, which conftitute the coats of the 

 arteries, contract themfelves. For where the frequency of the 

 puifations is but feventy-five in a minute, as in health ; the con- 

 tracting 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 diaflole to more than 

 half the ufual diameter of their diaftole in health, the fibres 

 which conftitute their coats, will move through a lefs fpace in 

 a minute than in health, though they make two puifations 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 di- 

 aftole is in health 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 circumference to a circle 

 of three lines in circumference, 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 ; that is, while they move through a fpace 

 equal to fix lines. Hence though the frequency of pulfation 

 in fever be greater as two to one,, yet the velocity of contrac- 

 tion in health is greater as nine to fix, or as three to two. 



On the contrary, in inflammatory difeafes with ftrength, as in 

 the pleurify, the velocity of the contracting fides of the arteries 

 5s much greater than in health : for if we fuppofe the number of 

 puifations in a pleurify to be half as much more than in health, 

 that is, as one hundred and twenty to eighty, (which is about 

 what generally happens in inflammatory difeafes) and if the di- 

 ameter of the artery in diaftole be one third greater than in 



health, 



