Wherefore, in order to form a just notion of the body of man, it ought to be considered as a hydraulic machine contrived with the most exquisite art, in which there are numberless tubes properly adjusted and disposed for the conveyance of fluids of different kinds. Of these the principal is the blood, from which are derived the several humors subservient to the various uses and purposes of life; and in particular that subtile and remarkably elastic fluid, generated in the brain, and known by the name of animal spirits, the instrument of sense and motion; which functions it never could be capable of executing, were it not contained in proper organs. For this purpose the Almighty Creator has formed two sorts of fibres, the fleshy and the nervous, as receptacles for this active principle; and each sort of these is partly interwoven in the membranes of the body, and