IMPROVED. <J3 



of which, when prafticable, may be feen under 

 the Chapter of an Aneurifm. 



The Pulfe is thus accounted for: When theThePulfe 

 Left Ventricle of the Heart contrails or draws toge- in the Ar- 

 ther, and throws its Blood into the Aorta or great '^^^'^^ ^*-: 

 Artery, the Blood in the Artery is not only thrult " * 

 forward towards the Extremities, but the Channel 

 of the Artery is likewife dilated; becaufe Fluids, 

 when they are prefs'd, prefs again to all Sides, and 

 their Preifure is always perpendicular to the Sides of 

 the containing VeiTels : But the Coats of the Arte- 

 ry, by any fmall Impetus or Force, ( as one Bowl 

 ftriking againll another) may be diftended. There- 

 fore, upon the Contraftion of the Heart, the Blood 

 from the Left Ventricle will not only prefs the 

 Blood in the Artery forwards, but both together 

 will diftend the Sides of the Artery. When the 

 Impetus of the Blood againft the Sides of the Arte- 

 ry ceafes, that is, when the Left Ventricle ceafes 

 to contrail, then the Spiral Fibres of the Artery, 

 by their natural Elafticity or Springinefs, return 

 again to their former State, and contraft the Chan- ' 



nel of the Artery, till it is again dilated by the 

 Syftole of the Heart. This Diaftole of the Artery 

 is called its Pulfe ; and the Time the Spiral Fibres 

 are returning to their natural State, is the Diftance 

 between two Pulfes, This Pulfe is in all the Arte- 

 ries of the Body at one and the fame Time ; for 

 while the Blood is thruft out of the Heart into the 

 Artery,' the Artery being fiill, the Blood mufl move 

 in all the Arteries at the fame Time. And becaufe 

 the Arteries are Conical, and the Blood moves from 

 the Eajis or larger End of the Cone, to the Jpex or 

 Point ; therefore the Blood mull llrike againft the 

 Sides of the Vefiel, and ccnfequently every Point 

 of the Artery muil be dilated at the fame Time that 

 the Blood is thrown out of the Left Ventricle of the- 

 Heart : And as foon as the Elafticity of the fpiral 

 Fibres can overcome the Impetus of the Blood, the 

 Arteries are again contracted. Thus, two Caufes 



operating. 



