them at present; and their nature is much more easily conceived when they
are beheld coming in this manner gradually into existence, than when they
are only considered as produced at once in a finished and perfect state.

From the description of inanimate bodies and plants, I passed to animals,
and particularly to man.  But since I had not as yet sufficient knowledge
to enable me to treat of these in the same manner as of the rest, that is
to say, by deducing effects from their causes, and by showing from what
elements and in what manner nature must produce them, I remained satisfied
with the supposition that God formed the body of man wholly like to one of
ours, as well in the external shape of the members as in the internal
conformation of the organs, of the same matter with that I had described,
and at first placed in it no rational soul, nor any other principle, in
room of the vegetative or sensitive soul, beyond kindling in the heart one
of those fires without light, such as I had already described, and which I
thought was not different from the heat in hay that has been heaped
together before it is dry, or that which causes fermentation in new wines
before they are run clear of the fruit.  For, when I examined the kind of
functions which might, as consequences of this supposition, exist in this
body, I found precisely all those which may exist in us independently of
all power of thinking, and consequently without being in any measure owing
to the soul; in other words, to that part of us which is distinct from the
body, and of which it has been said above that the nature distinctively
consists in thinking, functions in which the animals void of reason may be
said wholly to resemble us; but among which I could not discover any of
those that, as dependent on thought alone, belong to us as men, while, on
the other hand, I did afterwards discover these as soon as I supposed God
to have created a rational soul, and to have annexed it to this body in a
particular manner which I described.

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
shown 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
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 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.

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 come
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 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