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 coming down into the heart, and becoming more and more rarefied, they
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.
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