le for absorbing this quantity of excrementitious matter at
from 4 to 8 lb., then we shall find that the manure produced by a pig
will contain from .06 to .074 lb. nitrogen and .545 to .772 lb. mineral
matter. These quantities, calculated for a year, give from 22 to 27 lb.
of nitrogen, and from 1 cwt. 87 lb. to 2 cwt. 57 lb. of mineral matter.
That is about as much nitrogen as would be contained in 1-1/4 to 1-1/2
cwt. of nitrate of soda (95 per cent purity); or from slightly less than
1 cwt. to slightly over 1 cwt. of sulphate of ammonia (97 per cent
purity).

As has already been pointed out, the excrements of the pig are, as a
rule, very poor in nitrogen. This accounts for the fact that pig-manure
is a "cold" manure, slow in fermenting.[160]

4. _Sheep-manure._

The dung and the urine of the sheep, as we have already seen, are,
weight for weight, the most valuable of any of the common farm animals.
The total weight of the excrements voided by a sheep in a day may be
taken, on an average,[161] at 3.78 lb., of which .97 lb. is dry matter.
These excrements contain .038 lb. of nitrogen and .223 lb. mineral
matter. Taking the amount of straw most suitable for absorbing this
quantity of excrementitious matter at three-fifths of a pound, then the
manure produced by a sheep in a day will contain .0429 lb. nitrogen and
.264 lb. mineral matter. That is, in a year the quantities of nitrogen
and mineral matter in the manure produced by a sheep would be 15.66 lb.
of nitrogen and 96.36 lb. of mineral matter.

From its richness in nitrogen, and from its dry condition, sheep-dung is
peculiarly liable to ferment. While richer in fertilising substances
than horse-manure, it is not so rapid in its fermentation. This is due
to the harder and more compact physical character of the solid excreta.
The risks of loss of volatile ammonia are, in its case, exceptionally
great. The use of artificial "fixers" is therefore to be strongly
recommended.[162]

_Fermentation of Farmyard Manure._

Having now considered the nature of the different manures produced by
the four common farm animals separately, it is of importance to consider
the exact nature of the fermentation, decomposition, or putrefaction
which takes place in the manure-heap.

It is now more than thirty years since Pasteur showed that the
fermentation which ensued on keeping a sample of urine was due to the
action of a minute organism, for the propagation of which a certain