n is the surest index of the amount of injury
which the sample of flour has sustained. Whether, therefore, the
sample contains a certain proportion of nitrogen, or whether it
contains albumen, fibrine, and caseine in sufficient quantity, it
may still want the very condition which is essential to the
manufacture of good bread. My objection, therefore, to the mere
determination, however accurate, of the proportion of nitrogen
contained in wheat flour, or of the various principles which form
the gluten, is, that it does not represent the value of the various
samples for the only use to which they are applied, viz., the making
of bread. The remarks of Mulder, the celebrated Dutch chemist, upon
the subject of manures, are so applicable to this point that I
cannot refrain from quoting them. "It has," he says, "become almost
a regular custom to determine the value of manures by the quantity
of nitrogen they yield by ultimate analysis. This method is entirely
erroneous; for it is based upon the false principle, that by
putrefaction all nitrogeneous substances are immediately converted
into ammonia, carbonic acid, and water! But these changes sometimes
require a number of years. Morphine, for example, is prepared by
allowing opium to putrefy; and the process for preparing leucin, a
substance which contains 10.72 of nitrogen, is to bring cheese into
putrefaction. Cheese, therefore, does not perhaps in a number of
years resolve itself into carbonic acid, ammonia, and water, but
produces a crystalline substance, which contains no ammonia. Hence
the proportion of nitrogen yielded by manures is not a proper
measure of their value, and therefore this mode of estimating that
value ought to be discontinued."[38] We infer, therefore, that the
proportion of nitrogen furnished by food of various kinds is not the
true measure of their nutritious value, and cannot for practical
purposes take the place of that process by which the amount of rough
gluten is determined.

No better illustration can be given of the uncertainty which attends
the inferences drawn from the ultimate composition, than the fact
heretofore stated in regard to hay, the nutritive value of which is
placed in the tables containing the results of these analyses, at a
figure nearly the same as that of ordinary wheat flour.[39] In the