Viewing page 285 of 504

This transcription has been completed. Contact us with corrections.

[[in right hand corner]](94
besides the particular structure, there is required an absolute freedom of the blood-vessels, and the nerves.
[margin -  Two sorts of muscular motion, [[underlined]] [[viz.?]] [[underlined]] voluntary, & involuntary.]
   Muscular motion is observed to be voluntary, and involuntary. Of the first kind are almost all the muscles of an animal body; of the latter, the only complete instance is the heart. The first seems more complex than the latter, since, besides the motion, it implies an additional act of the will. Effects, that are less compounded, ought naturally to precede effects, that are more; these receiving light from the former, where both are homogeneous. For this reason, I have placed here two lemma's relating to automatic, or involuntary motion.
                                Lemma I.
[Margin - Motion of the heart, how caused, [[underline]] [[viz?]] [[underline]] by warm-blood. Experiment.]
   The heart, in its natural state, in a living animal body, being given, its contraction proceeds solely from, or is mechanically caused by, the warm blood, flowing into and filling its fleshy substance in every part.
   If this be denied, let the body of an animal be taken quickly after death, and let a warm mild fluid of any kind be injected gently into the heart, so as to fill it.  When this is done, we shall see the heart quicken and contract, as in the life of the animal.  This experiment was first distinctly mentioned by Teyer a Switzer (see a small treatise of his, printed [[underline]] anno [[/underline]] 1682, at Amsterdam, and entitled [[underline]] Miraculum anatomicum in cordibus suscitatis [[/underline]]) and is now known to every anatomist. But if this effect is thus constantly produced soon after death, how much more, when the animal is alive? And if, by the induction of any common fluid, with the bare addition of a warmth cognizable by our senses, how much more by the introduction of the living blood, an inimitable and wonderful fluid, and the immediate subject of the vital warmth?
   If therefore it is granted, that we ought not to admit more causes of natural things than are real (and present for the occasion)and sufficient for explaining the appearances ([[underline]] a [[/underline]]), and we must grant a rule, whose use is so obvious in the Newtonian, which is the philosophy of nature; we shall, I say, also grant, that the contraction of the heart, in its natural state, in a living animal body proceeds solely from, or is mechanically caused by, the warm blood, flowing into, and filling, its fleshy substance in every part. Which was to be proved.
                  [[underline]] Corollary. [[/underline]]
[Margin - Relaxations of the heart. caused, by the abscence of the warm-blood.
Contractions & relaxations of the muscles.
Experiment.]
  The subsequent relaxation admits no difficulty: for if the blood is the immediate mechanical cause of the contraction, when the blood is removed, the effect ceases.
                                Lemma II
   A muscle of voluntary motion, in its natural state, in a living animal body, being given, it will contract by the introduction of a warm mild fluid, into its fleshy substance in every part.
If this be denied, let the body of an animal be taken quickly after death, and the crural artery be pierced, and a warm mild fluid be injected into it: we shall then see the muscles, to which the artery belongs, quicken and contract, as if the living animal moved them.  This experiment was known to Mr. Cowper, and is confirmed by Albinus (see [[underline]] Hist. Musc. [[/underline]] p. 21.)
[line across page]
                                  (a) Newton, R.I.