A Discourse concerning some Influence of Respiration on the Motion of the Heart, hitherto unobserved. By J. Drake, M. D. F. R. S.
THO' divers accurate Treatises of the Heart, and its Action, have been written by Learned Men of several Nations, especially by two of our own Country; the Great Dr. Harvey, to whose happy Sagacity this Nation owes the Glory of the Invention of the Circulation of the Blood; and the incomparable Dr. Lower, to whom we are beholden for a compleat Display of the Mechanical Structure of the Heart, and a most ingenious Rationale of its Action. Yet there remain several Doubts and Difficulties about it (in my Opinion) not sufficiently accounted for; towards the resolving some of which, I shall offer what my own Thoughts have suggested to me, and leave it to the Consideration of the Reader.
The Learned Dr. Lower (whose accurate Piece on this Argument will insure his Reputation so long as Physical Knowledge shall last in esteem) has so well accounted for the Systole, or Contraction of the Heart, from the Mechanical Structure of it, that he seems almost to have exhausted the Subject; and had he been as happy in discovering the true cause of the Diastole, he had left little room for the Industry and Sagacity of others about this Viscus.
But having judiciously and solidly explain'd the Systole, he contents himself to ascribe the Diastole to a motion of Restitution, which account gives me no Satisfaction: Because the Systole being the proper, and (as himself confesses) the only motion of the Heart, a State of Contraction seems to be the natural State, and consequently without External Violence, it shou'd have no Diastole at all.
This will appear more plain, if we consider the Circumstances of it, and its Motion, as a Muscle, with respect to other Muscles. That Contraction is the proper Action, and State of all Muscles, is evident from Experience of Fact, as well as Reason. For, if any Muscle be freed from the power of its Antagonist, it is immediately contracted, and is not by any Action of the Will, or Spirits, to be reduced to a State of Dilatation. Thus, if the Musculi Flexores of any Joint be divided, the Extensores of that Joint being by that means free'd from the contrary Action of their Antagonists, that Joint is immediately extended without any consent of the Will, and in that State it remains; and so Vice versa, if the Extensores be divided. From whence it is plain, that the Muscles have no restitutive Motion, but what they derive from the Action of their Antagonists, by which they are balanc'd. Thus likewise the Sphincters of the Gula, Anus and Vesica, having no proper Antagonists, are always in a State of Contraction, and suffer nothing to pass them, but what is forced through them by the contrary Action of some stronger Muscles, which, though not properly to be call'd Antagonists, yet on all necessary Occasions perform the Office of such.
That the Heart is a Muscle, furnish'd and instructed for Motion like other Muscles, is (in my Opinion at least) demonstrated beyond Contradiction by Dr. Lower and others. And, as it is a Solitary Muscle without any proper Antagonist, and not directly under the power of the Will, nor exercising Voluntary Motion, it approaches nearest to the Sphincter kind, which only has these Conditions in common with it. But in constant and regular Alternations of Contraction and Dilatation, it differs exceedingly from all the Muscles of the Body.
This reciprocal Æstus of the Heart has given the Learned abundance of trouble; who, finding nothing peculiar in the Structure, which shou'd necessarily occasion it, nor any Antagonist, whose re-action should produce it, have been extreamly perplex'd to find out the cause of it.
But passing over the various Opinions of Authors, to avoid being tedious, I shall take notice here only of the very Learned Dr. Lower's, in whose Account of the Systole, however solid and ingenious, I observe something deficient, and whose Hypothesis of the Diastole I think to be precarious and false.
This Excellent Author, having by sound Arguments drawn from the Structure and Mechanism of the Heart, establish'd the Certainty of its Muscular Motion, rests satisfied, without taking notice of any Assistance, that the Heart receives from any other Part, except from the Brain, by the means of the eight pair of Nerves.
Part 2d.
Prop. 67.
Prop. 73.
Prop. 76.