3. %Man.%

The human body, like all organic bodies, is a machine.  Artificial automata and natural bodies are distinguished 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 creation of God, superadded.  The union of the soul or the mind (anima sive mens) with the body is, it is true, not so loose that the mind merely dwells in the body, like a pilot in a ship, nor, on the other hand, in view of the essential contrariety of the two substances, is it so intimate as to be more than a unio compositionis.  Although the soul is united to the whole body, an especially