Constriction only. 'Tis true, he immediately after joins the Influx of the Blood as a concurrent Cause; but from the slight notice that he takes of it, 'tis plain, that he did not so much as dream of any great share it had in that Action. His Words are these:
Quin & (ut obiter hoc moneam) omnis motus contractione perficiatur, & Cordis Fibræ ad constrictionem solum factæ sint, apparet quoque Cordis motum totum in Systole positum esse; cumque Fibræ ultra tonum suum in omni constrictione eius tendantur, idcirco ubi nixus iste absolvitur, motu quasi restitutionis* Cor iterum relaxatur, & sanguine
à Venis influente rursus distenditur; à nullo enim cordis motu, nisi tensionem suam remittente, & ab irruente sanguine Diastole ejus libratis adeo viribus succedit.*
I have transcrib'd the intire Paragraph, because it contains his whole Hypothesis of the Diastole, and all the notice that he takes of it through his whole Work. But how slender soever this may prove, it is the most substantial that I have any where met with, except a late one of Mr. Cowper, which is properly an Improvement of this, and shall be consider'd in the Sequel.
But if Contraction be the sole Action of these Fibres (as this Great Man confesses it to be) and as indeed it is of all Muscular Fibres, I wonder how so judicious a Writer came to slip into such an Absurdity, as to call their Distention (vulgarly but improperly call'd Relaxation) a Motion of Restitution. For from the Nature of those Fibres, and their disposition in the Structure of the Heart, the natural State of the Heart appears manifestly to be Tonical, and its Dilatation a State of Violence; and consequently, the Constriction is the true motion of Restitution, and the State to which it will spontaneously return, when the Force is taken off, which is the work of the Intercostal Muscles and Diaphragm.
Thus we are left still to seek for the true Cause of the Diastole ,