abbit takes
into its body complex and unstable organic compounds containing
nitrogen, carbon, hydrogen, a certain amount of oxygen, a small
quantity of sulphur, and still smaller amounts of other elements. It
also breathes in oxygen.

Section 11. It returns a certain rejected part of its food comparatively
unchanged. Besides this, it returns carbon dioxide and water, which
are completely oxydised, and very simple and stable bodies, and
urea-- a less completely oxydised compound, but a very simple one
compared with the food constituents.

Section 12. Now the chemist tells us that when a stable body is
formed, or when an unstable compound decomposes into simpler
stable ones, force is evolved. The oxydation of carbon, for instance,
in the fireplace, is the formation of the stable compound called
carbon dioxide, and light and heat are evolved. The explosion of
dynamite, again is the decomposition of an unstable compound.
Hence, we begin to perceive that force-- the vital force-- which keeps
the rabbit moving, is supplied by the decomposition and partial
oxydation of compounds continued in its food, to carbon dioxide,
water, urea, and smaller quantities of other substances.

Section 13. This is the roughest statement of the case possible, but it
will give the general idea underlying our next chapters. We shall
consider how the food enters the body and is taken up into the
system, how it is conveyed to the muscles in the limbs, to the nerve
centres, and to wherever work is done, to be there decomposed and
partially oxydised, and finally how the products of its activity-- the
katastases, of which the three principal are carbon dioxide, water,
and urea-- are removed from the body.

Section 14. There are one or two comparatively modern terms that
we may note here. This decomposition of unstable chemical
compounds, releasing energy, is called kataboly. A reverse process,
which has a less conspicuous part in our first view of the animal's life
action, by which unstable compounds are built up and energy
stored, is called anaboly. The katastases are the products of
kataboly.

Section 15. In an ordinary animal, locomotion and other activity
predominate over nutritive processes, which fact we may express, in
the terms just given, by saying that kataboly prevails over anaboly.
An animal, as we have just explained, is an apparatus for the
decomposition and partial oxydation of certain compounds, and
these are obtained