ENPages
(seq. 57)
25 Lect. 2
He opened the Carotid Artery of a Mare, & fixed a Glass Tube into it; & after the Blood had rose therein to the Height of some [Feet?], its Weight overcame the Force of the Heart, so that the Animal could not bleed to Death. And the Blood alternately rose & fell again in the Glass Tube, & those two Motions in the Tube represented the two Motions of the Heart & Arteries. When the Heart ontracted & propelled the Blood with a Terk, the Blood rose in the Tube, but on the Intermission thereof, or in the Systole of the Arteries it fell much - The Pulse from the Touch is generally imagined to swell more, than it really does, which is so little, as to be scarce perceptible by the Eye, but the Stroke is larger in Proportion to the size of the Artery, & may be rendred visible by Art vide p 29 [?] This Swell is not in all Parts of the Artery at the same Time; tho' an Explanation of this Proportion is attempted, by supposing, that the Arteries being full of Blood, at each Stroke the Blood is thrust forward thro' the whole Canal, & at both Ends at the same Time by the subsequent Blood, which is thrown out from the Heart, & which at the same Time propells all the Blood, which is before it. If the Arteries were rigid Pipes of Brass or Silver, this might be a proper Method of Reasoning, but as the Coats are elastic, we may judge a priori, that the Motion is successive, which is perceptible indeed by feeling the Carotid Artery, & that in the Inside of the Anele tohether
(seq. 59)
26 Lect. 2
which are not synchronous in their Pulsations, as we have just Time enough to attend to their Difference, so that the Pulse is successive, but very quick. This swell or Pulsation of the Artery will grow less & less perceptibly from the beginning to the End, & the least Arteries will have a lesser Swell in proportion to their Size, because all the Branches together are larger than the Trunk, & hence the Impetus will be taken off - Another Reason is that the Action from the Beginning to the Branch will not be so strong, because the Heart acts by [?] - When the Heart ceases to Act, the nearest Part of the Artery will swell & then contract again, but at a Distance, the Artery will be kept almost always distended, for after the Action of the Heart ceases, the Contraction of the Artery follows successively from it's Trunk to it's Branches; which two Powers acting alternately, & the Power viz the Action of the Heart still growing weaker, the Blood at a Distance from the Heart will not move in Terks, as after the Heart Ceases to act. All the Arteries lying between the Heart, & these distant Vessels contract along in an Undulatory Manner, hence in remote Branches The Blood runs in a more equal Stream for this Reason the pulse diminishes, & in fleshy Parts is not perceptible, because of so many Branches - The Heart originally carries on the Circulation, & the Arteries react in the Blood by contracting. Hence we see the Necessity of their being possessed of muscular or ligamentous Fibres.
