those parts which are not nutritious; so that you have,
first, the mill, then a sort of chemical digester; and then the food,
thus partially dissolved, is carried back by the muscular contractions
of the intestines into the hinder parts of the body, while the soluble
portions are taken up into the blood. The blood is contained in a vast
system of pipes, spreading through the whole body, connected with a
force pump,--the heart,--which, by its position and by the contractions
of its valves, keeps the blood constantly circulating in one direction,
never allowing it to rest; and then, by means of this circulation of
the blood, laden as it is with the products of digestion, the skin, the
flesh, the hair, and every other part of the body, draws from it that
which it wants, and every one of these organs derives those materials
which are necessary to enable it to do its work.

The action of each of these organs, the performance of each of these
various duties, involve in their operation a continual absorption of
the matters necessary for their support, from the blood, and a constant
formation of waste products, which are returned to the blood, and
conveyed by it to the lungs and the kidneys, which are organs that have
allotted to them the office of extracting, separating, and getting rid
of these waste products; and thus the general nourishment, labour, and
repair of the whole machine is kept up with order and regularity. But
not only is it a machine which feeds and appropriates to its own
support the nourishment necessary to its existence--it is an engine for
locomotive purposes. The Horse desires to go from one place to another;
and to enable it to do this, it has those strong contractile bundles of
muscles attached to the bones of its limbs, which are put in motion by
means of a sort of telegraphic apparatus formed by the brain and the
great spinal cord running through the spine or backbone; and to this
spinal cord are attached a number of fibres termed nerves, which proceed
to all parts of the structure. By means of these the eyes, nose,
tongue, and skin--all the organs of perception--transmit impressions
or sensations to the brain, which acts as a sort of great central
telegraph-office, receiving impressions and sending messages to all
parts of the body, and putting in motion the muscles necessary to
accomplish any movement that may be desired. So that you have here an
extremely complex and beautifully-proportioned machine,