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absorptive power of soils for the gases. It keeps the soil
warm and at a constant degree of temperature, and, like
clay, aids materially in retaining its moisture. But instead
of increasing the stiffness of soils as clay does, it renders
them, on the contrary, porous and friable, so that the more
a soil contains of humus, the more of clay can it contain
without becoming close and difficult to be plowed. Its prin-
cipal feature, however, is its intimate connection with nitro-
genous compounds, the transformation of which into ammo-
niacal products advances statedly with the decomposition of
the humus. In this way, humus furnishes to the plants,
besides water and carbonic acid, (the product of its own
decay,) a constant and appropriate supply of ammonia to the
very last of its existence.

As to the latter, (the directly nourishing substances,) it is
evident that stable manure contains all the nutriments that
were once extracted from the soil by plants, and subsequent-
ly removed from it with the crop, and that its application
to the soil is therefore simply an act of restitution, at least
so far as it concerns these particular matters. The experi-
ments made by Boussingault with grown animals, by a feed-
ing not more than necessary for their sustenance, have in fact,
directly proven the identity of the ultimate composition of
the food consumed, and of those matters which in the mean-
time, were ejected from the animal body, as also their equal
absolute quantity, if calculated for a certain period of time,
at the beginning and end of which, the weight of the animal
remained stationery. The totality, however, of the matters
ejected from the animal body is in no way fully represented
by the solid and liquid excrements alone; we know that a
considerable part of these matters (amounting to about 2-5
of the whole) are evolved in the form of water, carbonic acid
and ammonia, from the lungs and through the skin of the
animal, by the process of breathing and perspiration. These
substances being volatile, are diffused in the atmosphere, and
consequently waste a large portion of the food, by the trans-
formation of which, under the process of life, they were pro-
duced; and it is only the remaining portion of the food which
reappears in the form of solid and liquid excrements, and
such other substances as milk, &c, as may be collected by the
farmer, and thus be of direct benefit to him.

From these facts, relative to the connection between excre-
ments and food, we may judge, a priori, of the most probable
Composition of the former. We have seen that carbon, hy-
drogen, nitrogen and oxygen, the constituents of the organic
portion of food, become partly separated from it in the animal
4