しかし，その論文でわたしがこの問題をどんなぐあいに扱ったかを見ていただけるよう，ここで心臓と動脈の運動を説明しておこう。この運動は，動物において観察される最も重要で，そして最も一般的な運動であるから，ほかのすべての運動をどう考えるべきかは，そこから容易に判断できる。また，これからわたしが述べることを理解しやすくするため，解剖学に通じていない人たちは，これを読む前に，肺を持つ何か大きな動物の心臓を目の前で切り開かせて見ていただきたい。こうした動物の心臓は，あらゆる点で人間の心臓によく似ているからだ。そしてそこにある二つの心室，つまりくぼんだ所を見せてもらうようにしていただきたい。はじめに，心臓の右側の心室，これには二本のひじように太い管が通じている。一つは大静脈で，血液の主要な受容器である。これは木にたとえれば幹で，身体のほかのすべての血管は枝にあたる。もう一つは動脈性静脈で，これは実際には動脈なのだから名前のっけかたが誤っている。心臓に源を発して，心臓を出たあといくつもの枝に分かれ，その枝は肺にくまなく広がっていく。次に，心臓の左側の心室で，これにも同じように二本の管が通じている。前の二本と同じくらいか，あるいはもっと太い。つまりその一は静脈性動脈で，静脈にほかならないから，これもまた誤って名づけられている。肺から来て「肺では多くの枝に分かれていて，動脈性静脈の枝および気管と呼ばれる導管の枝とからみあっており，この導管から呼吸する空気が入ってくる。もう一つは大動脈で，これは心臓から出て，身体全部にその枝を広げている。それからまた，十一の小さな弁を念入りに見せてもらっていただきたい。これは，二つの心室のなかの四つの口を，小さな扉のょうに，開けたり閉めたりする。そのうち三つは大静脈の入り口にあって，この血管のなかにある血液が心臓の右心室に流れ込むのには少しも妨げにならず，そこから血液が出られないようぴったり閉じるような，うまい仕掛けになっている。次の三つは，動脈性静脈の入り口にあり，まったく逆の仕掛けがなされていて，この心室のなかにある血液が肺のなかへ通ることはさせるが，肺のなかの血液がそこに逆戻りすることは許さない。また同じょうに，ほかの二つの弁が静脈性動脈の入り口にあり，肺の血液を左心室へ流れさせるが，その逆流は妨げる。三つは大動脈の入り口にあって，血液が心臓から出ることはできるが，心臓に逆戻りすることは妨げる。そしてこれらの弁の数については，別にその理由を求める必要はない。ただ静脈性動脈の口が，その場所の関係で楕円形になっていて弁二つでうまく閉められるのに，ほかの口は円形で，弁三つのほうがうまく閉められるというだけのことだ。さらに次のこともよく見せてもらっていただきたい。大動脈と動脈性静脈は，静脈性動脈と大静脈よりもずっと硬くしっかりできていること。あとの二つは心臓に入る前に広がって袋のようになり，心耳と名づけられ，心臓と同じ肉でできていること。心臓はつねに身体のどの場所よりも熱があること。最後に，血液が一滴でも心室に入ると，この熱の力によって，一般にどんな液体もひどく熱い器に一滴ずつ垂らされるとそうなるように，急速にふくれあがること。
But, in order to show how I there handled
this matter, I mean here to give the explication
of the motion of the heart and arteries,
which, as the first and most general motion
observed in animals, will afford the means
of readily determining what should be thought
of all the rest. And that there may be less
difficulty in understanding what I am about
to say on this subject, I advise those who
are not versed in Anatomy, before they commence
the perusal of these observations, to take
the trouble of getting dissected in their
presence the heart of some large animal possessed
of lungs, (for this is throughout sufficiently
like the human,) and to have shewn to them
its two ventricles or cavities: in the first
place, that in the right side, with which
correspond two very ample tubes, viz., the
hollow vein, (vena cava,) which is the principal
receptacle of the blood, and the trunk of
the tree, as it were, of which all the other
veins in the body are branches; and the arterial
vein, (vena arteriosa,) inappropriately so
denominated, since it is in truth only an
artery, which, taking its rise in the heart,
is divided, after passing out from it, into
many branches which presently disperse themselves
all over the lungs; in the second place,
the 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 comes 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 it branches all over the
body. I should wish also that such persons
were carefully shewn 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 vein, 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 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 composed 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.