the Right Ventricle of the Heart to the Left, through the Lungs, to which it could not otherwise pass; and the opposition, which the Blood contain'd in that Ventricle, must otherwise necessarily have made to its Constriction, is taken off, and the Systole thereby facilitated.
Nor is that all. For the Diastole being caus'd (as I shall in the Sequel shew) by the force of the Blood rushing into the Ventricles, this Ampliation and Extension of the Pulmonary Artery is a sort of Check or Counterpoise to it, and prevents an endeavour towards two contrary Actions at once, which must necessarily frustrate both. For the Heart being a Springy, Compressible Body, whose proper Action, which is Contraction, depends on the influx of certain Fluids into its Fibers, or Substance; and containing besides a Fluid in its Ventricles, or great Cavities, in one of which is the Mouth of this Artery, the action of this Vessel must in great measure resemble that of a Syringe, whose extremity is immers'd in Water,
the Enlargement or Expansion of the Chanels of the Artery answering the drawing of the Embolum, as the constrictive motion of the Muscle of the Heart does the pressure of the Atmosphere upon the Surface of the Water, the one making way for the fluid, and the other forcing it to follow, where the resistance is least. In this Sense we may allow a sort of Attraction to the Pulmonary-Artery, depending wholly upon the Action of the Intercostal Muscles and Diaphragm, which we must therefore confess to be very serviceable and instrumental in promoting the Systole of the Heart.
But if the Learned Author be deficient in his Account of the Systole; that is, if he has not observ'd all the Mechanism and Contrivance of Nature for the Contraction of the Heart; much less sufficiently has he accounted for the Diastole, or Dilatation of it, which he ascribes to a motion of Restitution of the over-strain'd Fibres, which yet he confesses are made for