Having thus, in this sort of general way, sketched to you what I may
call, perhaps, the architecture of the body of the Horse (what we term
technically its Morphology), I must now turn to another aspect. A horse
is not a mere dead structure: it is an active, living, working machine.
Hitherto we have, as it were, been looking at a steam-engine with the
fires out, and nothing in the boiler; but the body of the living animal
is a beautifully-formed active machine, and every part has its different
work to do in the working of that machine, which is what we call its
life. The Horse, if you see him after his day's work is done, is
cropping the grass in the fields, as it may be, or munching the oats in
his stable. What is he doing? His jaws are working as a mill--and a very
complex mill too--grinding the corn, or crushing the grass to a pulp. As
soon as that operation has taken place, the food is passed down to the
stomach, and there it is mixed with the chemical fluid called the
gastric juice, a substance which has the peculiar property of making
soluble and dissolving out the nutritious matter in the grass, and
leaving behind 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.