those of a real man:[73] I desire, I say, that you
should consider that these functions in the machine naturally
proceed from the mere arrangement of its organs, neither more nor
less than do the movements of a clock, or other automaton, from
that of its weights and its wheels; so that, so far as these are
concerned, it is not necessary to conceive any other vegetative or
sensitive soul, nor any other principle of motion, or of life, than
the blood and the spirits agitated by the fire which burns
continually in the heart, and which is no wise essentially
different from all the fires which exist in inanimate bodies."[74]

The spirit of these passages is exactly that of the most advanced
physiology of the present day; all that is necessary to make them
coincide with our present physiology in form, is to represent the
details of the working of the animal machinery in modern language, and
by the aid of modern conceptions.

Most undoubtedly, the digestion of food in the human body is a purely
chemical process; and the passage of the nutritive parts of that food
into the blood, a physical operation. Beyond all question, the
circulation of the blood is simply a matter of mechanism, and results
from the structure and arrangement of the parts of the heart and
vessels, from the contractility of those organs, and from the
regulation of that contractility by an automatically acting nervous
apparatus. The progress of physiology has further shown, that the
contractility of the muscles and the irritability of the nerves are
purely the results of the molecular mechanism of those organs; and that
the regular movements of the respiratory, alimentary, and other internal
organs are governed and guided, as mechanically, by their appropriate
nervous centres. The even rhythm of the breathing of every one of us
depends upon the structural integrity of a particular region of the
medulla oblongata, as much as the ticking of a clock depends upon the
integrity of the escapement. You may take away the hands of a clock and
break up its striking machinery, but it will still tick; and a man may
be unable to feel, speak, or move, and yet he will breathe.

Again, in entire accordance with Descartes' affirmation, it is certain
that the modes of motion which constitute the physical basis of light,
sound, and heat, are transmuted into affections of nervous matter by the
sensory organs. These affections are, s