and make (as it were) two purses, call'd the ears of the heart, which are composed of a flesh like it; and that there is always more heat in the heart then in any other part of the body. And in fine, that if any drop of bloud enter into these concavities, this heat is able to make it presently swell and dilate it self, as generally all liquors do, when drop by drop we let them fall into a very hot vessel. 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.