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For after this I need say no more for to unfold the motion of the heart, but that when these concavities are not full of bloud, necessarily there runs some from the vena cava into the right, and from the veinous artery into the left; for that these two vessels are always full of it, and that their openings which are towards the heart cannot then be shut: But that assoon as there is thus but two drops of bloud entred, one in either of these concavities, these drops, which cannot but be very big, by reason that their openings whereby they enter are very large, and the vessels whence they come very full of bloud, are rarified and dilated because of the heat which they find therein. By means whereof, causing all the heart to swel, they drive and shut the five little doors which are at the entry of the two vessels whence they come, hindering thereby any more bloud to fall down into the heart, and continuing more and more to rarifie themselves, they drive and open the six other little doors which are at the entry of the other two vessels whence they issue, causing by that means all the branches of the arterious vein, and of the great artery, to swel (as it were) at the same time with the heart: which presently after fals, as those arteries also do, by reason that the bloud which is entred therein grows colder, and their six little doors shut up again, and those five of the vena cava, and of the veinous artery open again, and give way to two other drops of bloud, which again swell the heart and the arteries in the same manner as the preceding did. And because the bloud which thus enters into the heart, passeth thorow those two purses, which are call’d the ears; thence it comes, that their motion is contrary to the heart’s, and that they fall when that swels.
Lastly, That they who know not the force of Mathematical demonstrations, and are not accustomed to distinguish true reasons from probable ones, may not venture to deny this without examining it, I shall advertise them, that this motion which I have now discovered, as necessarily follows from the onely disposition of the organs (which may plainly be seen in the heart,) and from the heat (which we may feel with our fingers,) and from the nature of the bloud (which we may know by experience,) as the motions of a clock doth by the force, situation and figure of its weight and wheels.
But if it be asked, how it comes that the bloud of the veins is not exhausted, running so continually into the heart; and how that the arteries are not too full, since all that which passeth thorow the heart dischargeth it self into them: I need answer nothing thereto but what hath been already writ by an English Physician, to whom this praise must be given, to have broken the ice in this place, and to be the first who taught us, That there are several little passages in the extremity of the arteries whereby the bloud which they receive from the heart, enters the little branches of the veins; whence again it sends it self back towards the heart: so that its course is no other thing but a perpetuall circulation. Which he very wel proves by the ordinary experience of Chirurgians, who having bound the arm indifferently hard above the the place where they open the vein, which causeth the bloud to issue more abundantly, then if it had not been bound. And the contrary would happen, were it bound underneath, between the hand and the incision, or bound very hard above. For its manifest, that the band indifferently tyed, being able to hinder the bloud which is already in the arm to return towards the heart by the veins; yet it therefore hinders not the new from coming always by the arteries, by reason they are placed under the veins, and that their skin being thicker, are less easie to be press’d, as also that the bloud which comes from the heart, seeks more forcibly to passe by them towards the hand, then it doth to return from thence towards the heart by the veins. And since this bloud which issues from the arm by the incision made in one of the veins, must necessarily have some passage under the bond, to wit, towards the extremities of the arm, whereby it may come thither by the arteries, he also proves very well what he sayes of the course of the bloud through certain little skins, which are so disposed in divers places along the veins, which permit it not to pass from the middle towards the extremities, but onely to return from the extremities towards the heart. And besides this, experience shews, That all the bloud which is in the body may in a very little time run out by one onely artery’s being cut, although it were even bound very neer the heart, and cut betwixt it and the ligature: So that we could have no reason to imagine that the bloud which issued thence could come from any other part.
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