eir 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