in reality, be very much inferior. If the phosphate of lime
in the manure, containing 40 per cent. of that body, were derived from
coprolites or apatite, and its ammonia from horns, the former would be
worth little or nothing, and the latter, by reason of its exceedingly
slow evolution from the horns, would possess a very low value. If, on
the contrary, the phosphate of lime, in the manure comparatively poor
in phosphate, were a constituent of bones, and its ammonia ready formed
(say as sulphate of ammonia), then, its value, both commercial and
manurial, would be far greater than the other.

In estimating the money value of an article of food, we should omit
such considerations as the relative adjustment of its flesh-formers and
fat-formers, and its suitability to particular kinds of animals, as well
as to animals in a certain stage of development. The manure supplied to
plants contains several elements indispensable to vegetable nutrition;
and, although the agriculturist most commonly purchases all these
elements combined in the one article, still he frequently buys each
ingredient separately. Ammonia is one of these principles, and, whether
it be bought _per se_, or as a constituent of a compound manure, the
price it commands is invariable. This principle should prevail in the
purchase of food: each constituent of which should have a certain value
placed upon it; and the sums of all the values of the constituents would
then be the value of the article of food taken as a whole. There are, no
doubt, practical difficulties in the way which prevent this method of
valuation from giving more than approximatively correct results; but
are there not precisely similar difficulties in the way of the correct
estimation of the value of a manure according to its analysis? There
are several constituents of food, the money value of which is easily
determinable: these are sugar, starch, and fat. No matter what substance
they are found in, the nutritive value of each varies only within very
narrow limits. The value of cellulose and woody fibre is not so easily
ascertained, as it varies with the age and nature of the vegetable
structure in which these principles occur. There is little doubt but
that the cellulose and fibre of young grass, clover, and other succulent
plants, are, for the most part, digestible; and we should not be far
astray if we were to assume that four pounds weight of soft fibre and
cellulose are equivalent to three p