of carbon, hydrogen and oxygen.

What becomes of the nitrogenous parts?

How is the _soluble_ ash of the digested food parted with?

The insoluble?

If any portions of the food are not returned in the dung, how are they
disposed of?]

That portion of the organic part of the hay which has been taken up by
the blood of the ox, and which does not contain nitrogen (corresponding
to the _first_ class of proximates, as described in Sect. I), is emitted
through the lungs. It consists, as will be recollected, of carbon,
hydrogen and oxygen, and these assume, in respiration, the form of
carbonic acid and water.

The organic matter of the digested hay, in the blood, which contains
nitrogen (corresponding to the _second_ class of proximates, described
in Sect. I), goes to the _bladder_, where it assumes the form of urea--a
constituent of urine or liquid manure.

We have now disposed of the imperfectly digested food (dung), and of the
_organic_ matter which was taken up by the blood. All that remains to be
examined is the inorganic or mineral matter in the blood, which would
have become _ashes_, if the hay had been burned. The _soluble_ part of
this inorganic matter passes into the bladder, and forms the _inorganic
part of urine_. The _insoluble_ part passes the bowels, in connection
with the dung.

[How is their place supplied?

Is food put out of existence when it is fed to animals?

What does the solid dung contain? Liquid manure? The breath?]

If any of the food taken up by the blood is not returned as above
stated, it goes to form fat, muscle, hair, bones, or some other part of
the animal, and as he is not growing (not increasing in weight) an
equivalent amount of the body of the animal goes to the manure to take
the place of the part retained.[V]

We now have our subject in a form to be readily understood. We learn
that when food is given to animals it is not _put out of existence_, but
is merely _changed in form_; and that in the impurities of the breath,
we have a large portion of those parts of the food which plants obtain
from air and from water; while the solid and liquid excrements contain
all that was taken by the plants from the soil and manures.

The SOLID DUNG contains the undigested parts of the food, the
_insoluble_ parts of the ash, and the nitrogenous
matters which have _escaped_ from the digestive organs.

"LIQUID MANURE" the nitrogenous or _second class_ of prox