ments upon the lower animals, to find, if possible, further
proof of this general law. To him the human body was simply a machine, a
complicated mechanism, whose functions were controlled just as any other
piece of machinery. He compared the human body to complicated machinery
run by water-falls and complicated pipes. "The nerves of the machine
which I am describing," he says, "may very well be compared to the pipes
of these waterworks; its muscles and its tendons to the other various
engines and springs which seem to move them; its animal spirits to the
water which impels them, of which the heart is the fountain; while the
cavities of the brain are the central office. Moreover, respiration
and other such actions as are natural and usual in the body, and which
depend on the course of the spirits, are like the movements of a clock,
or a mill, which may be kept up by the ordinary flow of water."(3)

In such passages as these Descartes anticipates the ideas of physiology
of the present time. He believed that the functions are performed by the
various organs of the bodies of animals and men as a mechanism, to which
in man was added the soul. This soul he located in the pineal gland, a
degenerate and presumably functionless little organ in the brain. For
years Descartes's idea of the function of this gland was held by many
physiologists, and it was only the introduction of modern high-power
microscopy that reduced this also to a mere mechanism, and showed that
it is apparently the remains of a Cyclopean eye once common to man's
remote ancestors.

Descartes was the originator of a theory of the movements of
the universe by a mechanical process--the Cartesian theory of
vortices--which for several decades after its promulgation reigned
supreme in science. It is the ingenuity of this theory, not the truth
of its assertions, that still excites admiration, for it has long since
been supplanted. It was certainly the best hitherto advanced--the best
"that the observations of the age admitted," according to D'Alembert.

According to this theory the infinite universe is full of matter, there
being no such thing as a vacuum. Matter, as Descartes believed, is
uniform in character throughout the entire universe, and since motion
cannot take place in any part of a space completely filled, without
simultaneous movement in all other parts, there are constant more or
less circular movements, vortices, or whirlpools of particles, varying,
o