<SPAN name="part5"></SPAN>
<h3> PART V </h3>
<p>I would here willingly have proceeded to exhibit the whole chain of
truths which I deduced from these primary but as with a view to this it
would have been necessary now to treat of many questions in dispute
among the earned, with whom I do not wish to be embroiled, I believe
that it will be better for me to refrain from this exposition, and only
mention in general what these truths are, that the more judicious may
be able to determine whether a more special account of them would
conduce to the public advantage. I have ever remained firm in my
original resolution to suppose no other principle than that of which I
have recently availed myself in demonstrating the existence of God and
of the soul, and to accept as true nothing that did not appear to me
more clear and certain than the demonstrations of the geometers had
formerly appeared; and yet I venture to state that not only have I
found means to satisfy myself in a short time on all the principal
difficulties which are usually treated of in philosophy, but I have
also observed certain laws established in nature by God in such a
manner, and of which he has impressed on our minds such notions, that
after we have reflected sufficiently upon these, we cannot doubt that
they are accurately observed in all that exists or takes place in the
world and farther, by considering the concatenation of these laws, it
appears to me that I have discovered many truths more useful and more
important than all I had before learned, or even had expected to learn.</p>
<p>But because I have essayed to expound the chief of these discoveries in
a treatise which certain considerations prevent me from publishing, I
cannot make the results known more conveniently than by here giving a
summary of the contents of this treatise. It was my design to comprise
in it all that, before I set myself to write it, I thought I knew of
the nature of material objects. But like the painters who, finding
themselves unable to represent equally well on a plain surface all the
different faces of a solid body, select one of the chief, on which
alone they make the light fall, and throwing the rest into the shade,
allow them to appear only in so far as they can be seen while looking
at the principal one; so, fearing lest I should not be able to compense
in my discourse all that was in my mind, I resolved to expound singly,
though at considerable length, my opinions regarding light; then to
take the opportunity of adding something on the sun and the fixed
stars, since light almost wholly proceeds from them; on the heavens
since they transmit it; on the planets, comets, and earth, since they
reflect it; and particularly on all the bodies that are upon the earth,
since they are either colored, or transparent, or luminous; and finally
on man, since he is the spectator of these objects. Further, to enable
me to cast this variety of subjects somewhat into the shade, and to
express my judgment regarding them with greater freedom, without being
necessitated to adopt or refute the opinions of the learned, I resolved
to leave all the people here to their disputes, and to speak only of
what would happen in a new world, if God were now to create somewhere
in the imaginary spaces matter sufficient to compose one, and were to
agitate variously and confusedly the different parts of this matter, so
that there resulted a chaos as disordered as the poets ever feigned,
and after that did nothing more than lend his ordinary concurrence to
nature, and allow her to act in accordance with the laws which he had
established. On this supposition, I, in the first place, described
this matter, and essayed to represent it in such a manner that to my
mind there can be nothing clearer and more intelligible, except what
has been recently said regarding God and the soul; for I even expressly
supposed that it possessed none of those forms or qualities which are
so debated in the schools, nor in general anything the knowledge of
which is not so natural to our minds that no one can so much as imagine
himself ignorant of it. Besides, I have pointed out what are the laws
of nature; and, with no other principle upon which to found my
reasonings except the infinite perfection of God, I endeavored to
demonstrate all those about which there could be any room for doubt,
and to prove that they are such, that even if God had created more
worlds, there could have been none in which these laws were not
observed. Thereafter, I showed how the greatest part of the matter of
this chaos must, in accordance with these laws, dispose and arrange
itself in such a way as to present the appearance of heavens; how in
the meantime some of its parts must compose an earth and some planets
and comets, and others a sun and fixed stars. And, making a digression
at this stage on the subject of light, I expounded at considerable
length what the nature of that light must be which is found in the sun
and the stars, and how thence in an instant of time it traverses the
immense spaces of the heavens, and how from the planets and comets it
is reflected towards the earth. To this I likewise added much
respecting the substance, the situation, the motions, and all the
different qualities of these heavens and stars; so that I thought I had
said enough respecting them to show that there is nothing observable in
the heavens or stars of our system that must not, or at least may not
appear precisely alike in those of the system which I described. I
came next to speak of the earth in particular, and to show how, even
though I had expressly supposed that God had given no weight to the
matter of which it is composed, this should not prevent all its parts
from tending exactly to its center; how with water and air on its
surface, the disposition of the heavens and heavenly bodies, more
especially of the moon, must cause a flow and ebb, like in all its
circumstances to that observed in our seas, as also a certain current
both of water and air from east to west, such as is likewise observed
between the tropics; how the mountains, seas, fountains, and rivers
might naturally be formed in it, and the metals produced in the mines,
and the plants grow in the fields and in general, how all the bodies
which are commonly denominated mixed or composite might be generated
and, among other things in the discoveries alluded to inasmuch as
besides the stars, I knew nothing except fire which produces light, I
spared no pains to set forth all that pertains to its nature,--the
manner of its production and support, and to explain how heat is
sometimes found without light, and light without heat; to show how it
can induce various colors upon different bodies and other diverse
qualities; how it reduces some to a liquid state and hardens others;
how it can consume almost all bodies, or convert them into ashes and
smoke; and finally, how from these ashes, by the mere intensity of its
action, it forms glass: for as this transmutation of ashes into glass
appeared to me as wonderful as any other in nature, I took a special
pleasure in describing it. I was not, however, disposed, from these
circumstances, to conclude that this world had been created in the
manner I described; for it is much more likely that God made it at the
first such as it was to be. But this is certain, and an opinion
commonly received among theologians, that the action by which he now
sustains it is the same with that by which he originally created it; so
that even although he had from the beginning given it no other form
than that of chaos, provided only he had established certain laws of
nature, and had lent it his concurrence to enable it to act as it is
wont to do, it may be believed, without discredit to the miracle of
creation, that, in this way alone, things purely material might, in
course of time, have become such as we observe 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.</p>
<p>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.</p>
<p>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.</p>
<p>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 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.</p>
<p>But if it be asked how it happens that the blood in the veins, flowing
in this way continually into the heart, is not exhausted, and why the
arteries do not become too full, since all the blood which passes
through the heart flows into them, I need only mention in reply what
has been written by a physician of England, who has the honor of having
broken the ice on this subject, and of having been the first to teach
that there are many small passages at the extremities of the arteries,
through which the blood received by them from the heart passes into the
small branches of the veins, whence it again returns to the heart; so
that its course amounts precisely to a perpetual circulation. Of this
we have abundant proof in the ordinary experience of surgeons, who, by
binding the arm with a tie of moderate straitness above the part where
they open the vein, cause the blood to flow more copiously than it
would have done without any ligature; whereas quite the contrary would
happen were they to bind it below; that is, between the hand and the
opening, or were to make the ligature above the opening very tight.
For it is manifest that the tie, moderately straightened, while
adequate to hinder the blood already in the arm from returning towards
the heart by the veins, cannot on that account prevent new blood from
coming forward through the arteries, because these are situated below
the veins, and their coverings, from their greater consistency, are
more difficult to compress; and also that the blood which comes from
the heart tends to pass through them to the hand with greater force
than it does to return from the hand to the heart through the veins.
And since the latter current escapes from the arm by the opening made
in one of the veins, there must of necessity be certain passages below
the ligature, that is, towards the extremities of the arm through which
it can come thither from the arteries. This physician likewise
abundantly establishes what he has advanced respecting the motion of
the blood, from the existence of certain pellicles, so disposed in
various places along the course of the veins, in the manner of small
valves, as not to permit the blood to pass from the middle of the body
towards the extremities, but only to return from the extremities to the
heart; and farther, from experience which shows that all the blood
which is in the body may flow out of it in a very short time through a
single artery that has been cut, even although this had been closely
tied in the immediate neighborhood of the heart and cut between the
heart and the ligature, so as to prevent the supposition that the blood
flowing out of it could come from any other quarter than the heart.</p>
<p>But there are many other circumstances which evince that what I have
alleged is the true cause of the motion of the blood: thus, in the
first place, the difference that is observed between the blood which
flows from the veins, and that from the arteries, can only arise from
this, that being rarefied, and, as it were, distilled by passing
through the heart, it is thinner, and more vivid, and warmer
immediately after leaving the heart, in other words, when in the
arteries, than it was a short time before passing into either, in other
words, when it was in the veins; and if attention be given, it will be
found that this difference is very marked only in the neighborhood of
the heart; and is not so evident in parts more remote from it. In the
next place, the consistency of the coats of which the arterial vein and
the great artery are composed, sufficiently shows that the blood is
impelled against them with more force than against the veins. And why
should the left cavity of the heart and the great artery be wider and
larger than the right cavity and the arterial vein, were it not that
the blood of the venous artery, having only been in the lungs after it
has passed through the heart, is thinner, and rarefies more readily,
and in a higher degree, than the blood which proceeds immediately from
the hollow vein? And what can physicians conjecture from feeling the
pulse unless they know that according as the blood changes its nature
it can be rarefied by the warmth of the heart, in a higher or lower
degree, and more or less quickly than before? And if it be inquired
how this heat is communicated to the other members, must it not be
admitted that this is effected by means of the blood, which, passing
through the heart, is there heated anew, and thence diffused over all
the body? Whence it happens, that if the blood be withdrawn from any
part, the heat is likewise withdrawn by the same means; and although
the heart were as-hot as glowing iron, it would not be capable of
warming the feet and hands as at present, unless it continually sent
thither new blood. We likewise perceive from this, that the true use
of respiration is to bring sufficient fresh air into the lungs, to
cause the blood which flows into them from the right ventricle of the
heart, where it has been rarefied and, as it were, changed into vapors,
to become thick, and to convert it anew into blood, before it flows
into the left cavity, without which process it would be unfit for the
nourishment of the fire that is there. This receives confirmation from
the circumstance, that it is observed of animals destitute of lungs
that they have also but one cavity in the heart, and that in children
who cannot use them while in the womb, there is a hole through which
the blood flows from the hollow vein into the left cavity of the heart,
and a tube through which it passes from the arterial vein into the
grand artery without passing through the lung. In the next place, how
could digestion be carried on in the stomach unless the heart
communicated heat to it through the arteries, and along with this
certain of the more fluid parts of the blood, which assist in the
dissolution of the food that has been taken in? Is not also the
operation which converts the juice of food into blood easily
comprehended, when it is considered that it is distilled by passing and
repassing through the heart perhaps more than one or two hundred times
in a day? And what more need be adduced to explain nutrition, and the
production of the different humors of the body, beyond saying, that the
force with which the blood, in being rarefied, passes from the heart
towards the extremities of the arteries, causes certain of its parts to
remain in the members at which they arrive, and there occupy the place
of some others expelled by them; and that according to the situation,
shape, or smallness of the pores with which they meet, some rather
than others flow into certain parts, in the same way that some sieves
are observed to act, which, by being variously perforated, serve to
separate different species of grain? And, in the last place, what
above all is here worthy of observation, is the generation of the
animal spirits, which are like a very subtle wind, or rather a very
pure and vivid flame which, continually ascending in great abundance
from the heart to the brain, thence penetrates through the nerves into
the muscles, and gives motion to all the members; so that to account
for other parts of the blood which, as most agitated and penetrating,
are the fittest to compose these spirits, proceeding towards the brain,
it is not necessary to suppose any other cause, than simply, that the
arteries which carry them thither proceed from the heart in the most
direct lines, and that, according to the rules of mechanics which are
the same with those of nature, when many objects tend at once to the
same point where there is not sufficient room for all (as is the case
with the parts of the blood which flow forth from the left cavity of
the heart and tend towards the brain), the weaker and less agitated
parts must necessarily be driven aside from that point by the stronger
which alone in this way reach it I had expounded all these matters with
sufficient minuteness in the treatise which I formerly thought of
publishing. And after these, I had shown what must be the fabric of
the nerves and muscles of the human body to give the animal spirits
contained in it the power to move the members, as when we see heads
shortly after they have been struck off still move and bite the earth,
although no longer animated; what changes must take place in the brain
to produce waking, sleep, and dreams; how light, sounds, odors, tastes,
heat, and all the other qualities of external objects impress it with
different ideas by means of the senses; how hunger, thirst, and the
other internal affections can likewise impress upon it divers ideas;
what must be understood by the common sense (sensus communis) in which
these ideas are received, by the memory which retains them, by the
fantasy which can change them in various ways, and out of them compose
new ideas, and which, by the same means, distributing the animal
spirits through the muscles, can cause the members of such a body to
move in as many different ways, and in a manner as suited, whether to
the objects that are presented to its senses or to its internal
affections, as can take place in our own case apart from the guidance
of the will. Nor will this appear at all strange to those who are
acquainted with the variety of movements performed by the different
automata, or moving machines fabricated by human industry, and that
with help of but few pieces compared with the great multitude of bones,
muscles, nerves, arteries, veins, and other parts that are found in the
body of each animal. Such persons will look upon this body as a
machine made by the hands of God, which is incomparably better
arranged, and adequate to movements more admirable than is any machine
of human invention. And here I specially stayed to show that, were
there such machines exactly resembling organs and outward form an ape
or any other irrational animal, we could have no means of knowing that
they were in any respect of a different nature from these animals; but
if there were machines bearing the image of our bodies, and capable of
imitating our actions as far as it is morally possible, there would
still remain two most certain tests whereby to know that they were not
therefore really men. Of these the first is that they could never use
words or other signs arranged in such a manner as is competent to us in
order to declare our thoughts to others: for we may easily conceive a
machine to be so constructed that it emits vocables, and even that it
emits some correspondent to the action upon it of external objects
which cause a change in its organs; for example, if touched in a
particular place it may demand what we wish to say to it; if in another
it may cry out that it is hurt, and such like; but not that it should
arrange them variously so as appositely to reply to what is said in its
presence, as men of the lowest grade of intellect can do. The second
test is, that although such machines might execute many things with
equal or perhaps greater perfection than any of us, they would, without
doubt, fail in certain others from which it could be discovered that
they did not act from knowledge, but solely from the disposition of
their organs: for while reason is an universal instrument that is
alike available on every occasion, these organs, on the contrary, need
a particular arrangement for each particular action; whence it must be
morally impossible that there should exist in any machine a diversity
of organs sufficient to enable it to act in all the occurrences of
life, in the way in which our reason enables us to act. Again, by
means of these two tests we may likewise know the difference between
men and brutes. For it is highly deserving of remark, that there are
no men so dull and stupid, not even idiots, as to be incapable of
joining together different words, and thereby constructing a
declaration by which to make their thoughts understood; and that on the
other hand, there is no other animal, however perfect or happily
circumstanced, which can do the like. Nor does this inability arise
from want of organs: for we observe that magpies and parrots can utter
words like ourselves, and are yet unable to speak as we do, that is, so
as to show that they understand what they say; in place of which men
born deaf and dumb, and thus not less, but rather more than the brutes,
destitute of the organs which others use in speaking, are in the habit
of spontaneously inventing certain signs by which they discover their
thoughts to those who, being usually in their company, have leisure to
learn their language. And this proves not only that the brutes have
less reason than man, but that they have none at all: for we see that
very little is required to enable a person to speak; and since a
certain inequality of capacity is observable among animals of the same
species, as well as among men, and since some are more capable of being
instructed than others, it is incredible that the most perfect ape or
parrot of its species, should not in this be equal to the most stupid
infant of its kind or at least to one that was crack-brained, unless
the soul of brutes were of a nature wholly different from ours. And we
ought not to confound speech with the natural movements which indicate
the passions, and can be imitated by machines as well as manifested by
animals; nor must it be thought with certain of the ancients, that the
brutes speak, although we do not understand their language. For if
such were the case, since they are endowed with many organs analogous
to ours, they could as easily communicate their thoughts to us as to
their fellows. It is also very worthy of remark, that, though there
are many animals which manifest more industry than we in certain of
their actions, the same animals are yet observed to show none at all in
many others: so that the circumstance that they do better than we does
not prove that they are endowed with mind, for it would thence follow
that they possessed greater reason than any of us, and could surpass us
in all things; on the contrary, it rather proves that they are
destitute of reason, and that it is nature which acts in them according
to the disposition of their organs: thus it is seen, that a clock
composed only of wheels and weights can number the hours and measure
time more exactly than we with all our skin.</p>
<p>I had after this described the reasonable soul, and shown that it could
by no means be educed from the power of matter, as the other things of
which I had spoken, but that it must be expressly created; and that it
is not sufficient that it be lodged in the human body exactly like a
pilot in a ship, unless perhaps to move its members, but that it is
necessary for it to be joined and united more closely to the body, in
order to have sensations and appetites similar to ours, and thus
constitute a real man. I here entered, in conclusion, upon the subject
of the soul at considerable length, because it is of the greatest
moment: for after the error of those who deny the existence of God, an
error which I think I have already sufficiently refuted, there is none
that is more powerful in leading feeble minds astray from the straight
path of virtue than the supposition that the soul of the brutes is of
the same nature with our own; and consequently that after this life we
have nothing to hope for or fear, more than flies and ants; in place of
which, when we know how far they differ we much better comprehend the
reasons which establish that the soul is of a nature wholly independent
of the body, and that consequently it is not liable to die with the
latter and, finally, because no other causes are observed capable of
destroying it, we are naturally led thence to judge that it is immortal.</p>
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