Ox. Sheep. Horse. Average

Organic matter 4.0 4.4 2.0 3.3 3.4
Nitrogen 31.0 54.8 42.3 60.7 47.2
Mineral substances 43.1 34.3 41.0 37.5 39.0[137]

We have now considered briefly the composition of the solid excrements
and urine of the common farm animals, and have also enumerated some of
the principal causes of the variation in their composition.

The solid excreta consist, as we have seen, of _undigested_ food, while
the urine contains the manurial ingredients of the food which have been
_digested_ by the animal system.[138] The latter is, weight for weight,
as a rule, very much more valuable as a manure than the former. From
the table given in the Appendix[139] it will be seen that the
proportions of the nitrogen and ash-constituents originally present in
the food consumed, which are voided in the excrements, vary with
different circumstances. Wolff, in summarising his results, points out
that, as a rule, the solid and liquid excrements will contain about 46
per cent of the organic matter, 87.3 of the nitrogen, and 98.7 of
mineral matter; while the experiments of Lawes and Gilbert at Rothamsted
show that, with fattening oxen and sheep and with horses, more than 95
per cent of the nitrogen and 96 per cent or more of the ash-constituents
are voided in the manure. The pig retains a larger proportion of the
nitrogen--about 85 per cent appearing in the manure--while in the
milking-cow only about 75 per cent is returned in the excrements.
Generally speaking, we may say that the nitrogen originally present in
the food suffers very little loss in passing through the animal system,
and that, practically speaking, the ash-constituents suffer no loss
whatever.

As to the distribution of the manurial ingredients, much will depend on
the nature of the food. Almost invariably more than a _half_ of the
total nitrogen excreted will be found in the urine, in many cases very
much more.[140] Of the mineral constituents, about a third on the
average may be said to be excreted in the urine. Of this mineral matter
it may be noted that nearly all the alkalies (potash and soda), or about
98 per cent, are found in the urine. Of phosphoric acid and lime, on the
other hand, there are the merest traces in the urine. Horse-urine,
however, is an exception with regard to lime, as it contains about 60
per cent of the lime consumed in the food. For information on the
subject of