which seems to me to be the main and most difficult Phænomenon , relating to the Heart and the Circulation of the Blood. But in Mr. Cowper 's ingenious Introduction to his Anatomy of Humane Bodies , I find the Share which Dr. Lower hints the Blood to have in that Action, further prosecuted, and improved into the main Instrument of the Dilatation of the Heart, wherein I agree intirely with him. But as to the manner, and reasons of its being so very instrumental, I can't be so perfectly of his mind.
The Heart (says this accurate Anatomist) of an Animal bears a great Analogy to the Pendulums of those Artificial Automata, Clocks and Watches, whilst its motion is performed like that of other Muscles, the Blood doing the Office of a Pondus.
This Explication, being but a Simile without a distinct application to Particulars, is beside so very short, that I can at best but give a conjecture at the meaning; which if I mistake, I shall deserve to be excused, and expect to be better inform'd.
By the Bloods doing the Office of a Pondus, I suppose he means, that the Blood contributes in the same manner to the motion of the Heart, as the Weights do to that of the Pendulum of a Clock. If so, the Blood, according to him, must be the Instrument of Constriction; and Dilatation must be the Natural State, or Spontaneous Motion, to which it wou'd, when under no violence, return; the contrary of which, I presume, will appear e're I have done.
But if he means, that the Blood in its reflux, by gravitating on the Auricles and Ventricles, dilates and expands 'em, acting therein as a Counterpoise to its contractions as a Muscle, I cou'd wish his Design had not bound him up to so narrow a compass, and that he had given us an explication at large of so abstruse and so important a Phænomenon: Because the Specifick Gravity of the Blood seems