only in degree. Machines fashioned by
the hand of man perform their functions by means of visible and tangible
instruments, while natural bodies employ organs which, for the most part,
are too minute to be perceived. As the clock-maker constructs a clock from
wheels and weights so that it is able to go of itself, so God has made
man's body out of dust, only, being a far superior artist, he produces a
work of art which is better constructed and capable of far more wonderful
movements. The cause of death is the destruction of some important part of
the machine, which prevents it from running longer; a corpse is a broken
clock, and the departure of the soul comes only as a result of death. The
common opinion that the soul generates life in the body is erroneous. It
is rather true that life must be present before the soul enters into union
with the body, as it is also true that life must have ended before it
dissolves the bond.

The sole principles of physiology are motion and heat. The heat (vital
warmth, a fire without light), which God has put in the heart as the
central organ of life, has for its function the promotion of the
circulation of the blood, in the description of which Descartes mentions
with praise the discoveries of Harvey _(De Motu Cordis et Sanguinis in
Animalibus_, 1628). From the blood are separated its finest, most fiery,
and most mobile parts, called by Descartes "animal spirits" _(spiritus
animales sive corporales_), and described as a "very subtle wind" or "pure
and vivid flame," which ascend into the cavities of the brain, reach
the pineal gland suspended in its center _(conarion, glans pinealis,
glandula_), pass into the nerves, and, by their action on the muscles
connected with the nerves, effect the motions of the limbs. These views
refer to the body alone, and so are as true of animals as of men. If
automata existed similar to animals in all respects, both external and
internal, it would be absolutely impossible to distinguish them from real
animals. If, however, they were made to resemble human bodies, two signs
would indicate their unreality--we would find no communication of ideas by
means of language, and also an absence of those bodily movements which
take their origin in the reason (and not merely in the constitution of the
body). The only thing which raises man above the brute is his rational
soul, which we are on no account to consider a product of matter, but which
is an express creatio