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cavity in the left side； with which correspond in the same manner two
canals in size equal to or larger than the preceding； viz。； the venous artery
（arteria venosa）； likewise inappropriately thus designated； because it is
simply a vein which es from the lungs； where it is divided into many
branches； interlaced with those of the arterial vein； and those of the tube
called the windpipe； through which the air we breathe enters； and the great
artery which； issuing from the heart； sends its branches all over the body。
I should wish also that such persons were carefully shown the eleven
pellicles which； like so many small valves； open and shut the four orifices
that are in these two cavities； viz。； three at the entrance of the hollow veins
where they are disposed in such a manner as by no means to prevent the
blood which it contains from flowing into the right ventricle of the heart；
and yet exactly to prevent its flowing out； three at the entrance to the
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DISCOURSE ON THE METHOD OF RIGHTLY CONDUCTING THE REASON； AND
SEEKING TRUTH IN THE SCIENCES
arterial vein； which； arranged in a manner exactly the opposite of the
former； readily permit the blood contained in this cavity to pass into the
lungs； but hinder that contained in the lungs from returning to this cavity；
and； in like manner； two others at the mouth of the venous artery； which
allow the blood from the lungs to flow into the left cavity of the heart； but
preclude its return； and three at the mouth of the great artery； which suffer
the blood to flow from the heart； but prevent its reflux。 Nor do we need
to seek any other reason for the number of these pellicles beyond this that
the orifice of the venous artery being of an oval shape from the nature of
its situation； can be adequately closed with two； whereas the others being
round are more conveniently closed with three。 Besides； I wish such
persons to observe that the grand artery and the arterial vein are of much
harder and firmer texture than the venous artery and the hollow vein； and
that the two last expand before entering the heart； and there form； as it
were； two pouches denominated the auricles of the heart； which are
posed of a substance similar to that of the heart itself； and that there is
always more warmth in the heart than in any other part of the body… and
finally； that this heat is capable of causing any drop of blood that passes
into the cavities rapidly to expand and dilate； just as all liquors do when
allowed to fall drop by drop into a highly heated vessel。
For； after these things； it is not necessary for me to say anything more
with a view to explain the motion of the heart； except that when its
cavities are not full of blood； into these the blood of necessity flows； … …
from the hollow vein into the right； and from the venous artery into the left；
because these two vessels are always full of blood； and their orifices；
which are turned towards the heart； cannot then be closed。 But as soon as
two drops of blood have thus passed； one into each of the cavities； these
drops which cannot but be very large； because the orifices through which
they pass are wide； and the vessels from which they e full of blood；
are immediately rarefied； and dilated by the heat they meet with。 In this
way they cause the whole heart to expand； and at the same time press
home and shut the five small valves that are at the entrances of the two
vessels from which they flow； and thus prevent any more blood from
ing down into the heart； and being more and more rarefied； they
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DISCOURSE ON THE METHOD OF RIGHTLY CONDUCTING THE REASON； AND
SEEKING TRUTH IN THE SCIENCES
push open the six small valves that are in the orifices of the other two
vessels； through which they pass out； causing in this way all the branches
of the arterial vein and of the grand artery to expand almost
simultaneously with the heart which immediately thereafter begins to
contract； as do also the arteries； because the blood that has entered them
has cooled； and the six small valves close； and the five of the hollow vein
and of the venous artery open anew and allow a passage to other two drops
of blood； which cause the heart and the arteries again to expand as before。
And； because the blood which thus enters into the heart passes through
these two pouches called auricles； it thence happens that their motion is
the contrary of that of the heart； and that when it expands they contract。
But lest those who are ignorant of the force of mathematical
demonstrations and who are not accustomed to distinguish true reasons
from mere verisimilitudes； should venture。 without examination； to deny
what has been said； I wish it to be considered that the motion which I have
now explained follows as necessarily from the very arrangement of the
parts； which may be observed in the heart by the eye alone； and from the
heat which may be felt with the fingers； and from the nature of the blood
as learned from experience； as does the motion of a clock from the power；
the situation； and shape of its counterweights and wheels。
But if it be asked how it happens that the blood in the veins； flowing in
this way continually into the heart； is not ex