own to
possess different properties, as well as to vary in their composition.

What, however, has a still greater influence is the nature of the food.
This is owing to the fact that the solid excreta are made up of
undigested food. We can scarcely expect the same quality of solid
excreta from an animal fed on poor diet as from an animal fed on very
much richer diet. Again, the percentage of the food voided in the solid
excreta varies in the case of different animals.[131]

Another consideration which enters into the question is the age, as well
as the treatment, of the animal. A young animal, during the period of
its growth, absorbs from its food into its system a larger quantity of
the three fertilising substances, nitrogen, phosphoric acid, and potash,
than is the case with an adult animal whose weight is neither increasing
nor diminishing. A working horse, similarly, will return more of the
nitrogen, phosphates, and potash in its dung than one not at work and
which is permitted to gain in weight. The nature of the composition of
the solid excreta, therefore, will depend on the nature of the _food_,
_age_, _breed_, _condition_, and _treatment_ of the animal.

Let us now investigate shortly the influence of the above
considerations. The solid excrements of the common farm animals are
generally distinguished from one another according to the rate at which
they decompose or ferment on keeping. Thus horse-dung is generally known
as a "hot" dung; while cow-dung, on the other hand, is known as "cool."
Why this should be so is not absolutely clear. Probably it is owing to
the fact that the former contains less water, as well as to the fact
(and this probably has more to do with it) that it contains a larger
percentage of fertilising matter, especially nitrogen, thus affording
conditions more favourable for rapid fermentation than in the case of
the more moist and less rich cow-dung.

The composition of the solid excreta of various animals, as we have just
said, varies with the nature of their food; so that it is impossible to
take any analyses as absolutely representing its composition. It may be
interesting, however, to compare the analyses of samples of horse-dung
with those of some other of the commoner farm animals, with a view to
obtaining an _approximate_ idea of this difference.

Stoeckhardt has found that in 1000 lb. of the fresh solid excreta of the
animals below mentioned, there were the following amounts of _n