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