of food. But, in making changes, great care is requisite in order to
supply the needful amount of nourishment, or the cow will fall off in
flesh, and eventually in milk. It should, therefore, be remembered that
the food consumed goes not alone to the secretion of milk, but also to
the growth and maintenance of the bony structure, the flesh, the blood,
the fat, the skin, and the hair, and in exhalations from the body. These
parts of the body consist of different organic constituents. Some are
rich in nitrogen, as the fibrin of the blood and albumen; others
destitute of it, as fat; some abound in inorganic salts, phosphate of
lime, and salts of potash. To explain how the constant waste of these
substances may be supplied, a celebrated chemist observes that the
albumen, gluten, caseine, and other nitrogenized principles of food,
supply the animal with the materials requisite for the formation of
muscle and cartilage; they are, therefore, called flesh-forming
principles.

Fats, or oily matters of the food, are used to lay on fat, or for the
purpose of sustaining respiration.

Starch, sugar, gum, and a few other non-nitrogenized substances,
consisting of carbon, oxygen, and hydrogen, supply the carbon given off
in respiration, or they are used for the production of fat.

Phosphate of lime and magnesia in food principally furnish the animal
with the materials of which the bony skeleton of its body consists.

Saline substances--chlorides of sodium and potassium, sulphate and
phosphate of potash and soda, and some other mineral matters occurring
in food--supply the blood, juice of flesh, and various animal juices,
with the necessary mineral constituents.

The healthy state of an animal can thus only be preserved by a mixed
food; that is, food which contains all the proximate principles just
noticed. Starch or sugar alone cannot sustain the animal body, since
neither of them furnishes the materials to build up the fleshy parts of
the animal. When fed on substances in which an insufficient quantity of
phosphates occurs, the animal will become weak, because it does not find
any bone-producing principle in its food. Due attention should,
therefore, be paid by the feeder to the selection of food which contains
all the kinds of matter required, nitrogenized as well as
non-nitrogenized, and mineral substances; and these should be mixed
together in the proportion which experience points out as best for the
different kinds of anim