to nitrogenous matters is
still higher.

In considering the composition of the food of animals, it will be
readily admitted that the milk, the nutriment supplied by nature for the
maintenance of the young animal, must afford special instruction as to
its requirements during the early stages of existence, and indicate, at
least, some of the points to be attended to under the altered conditions
of mature life. The following table gives the average composition of the
milk of the most important farm animals:--

Cow. Ewe. Goat.
Caseine 3.4 4.50 4.02
Butter 3.6 4.20 3.32
Sugar of milk 6.0 5.00 5.28
Ash 0.2 0.68 0.58
Water 86.8 85.62 86.80
------ ------ ------
100.00 100.00 100.00

In examining these, and all other analyses of food, it is necessary to
draw a distinction between the flesh-forming and the respiratory
elements; the former including the nitrogenous compounds which are used
in the production of flesh, the latter, the non-nitrogenous substances
which produce fat and support the process of respiration. The former,
however much they may differ in name, are nearly or altogether identical
in chemical composition, the latter embracing two great classes--the
fats which exist in the body and the saccharine compounds, including the
different kinds of sugar and starch which are not found in the animal
tissues. It was at one time supposed that these substances were entirely
consumed in the respiratory process, and eliminated by the lungs in the
form of carbonic acid and water, but it has been clearly shewn that they
may be and often are converted into fat, and accumulated in the system.
Careful experiments on bees have demonstrated that when fed on sugar
they continue to produce wax, which is a species of fat, and animals
retain their health and become fat, even when their food contains
scarcely any oil. There is, however, an important difference between
these two classes of substances as regards their fat-producing effect. A
pound of fat contained in the food is capable of producing the same
quantity within the animal; but the case is different with starch and
sugar, the most trustworthy experiments shewing that two and a half
pounds of these substances are necessary for that purpose. Hence we talk
of the fat equivalent of sugar, by which is