One prime object which the dairyman should keep constantly in view is, to maintain the animal in a sound and healthy condition. Without this, no profit can be expected from a milch cow for any considerable length of time; and, with a view to this, there should be an occasional change of food. But, in making changes, great care is required to supply an equal amount of nourishment, or the cow falls off in flesh, and eventually in milk. We should therefore bear in mind 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, albumen, &c.; others destitute of it, as fat; some abound in inorganic salts, phosphate of lime, salts of potash, &c. To explain how the constant waste of these substances may be supplied, Dr. Voelcker observes that the albumen, gluten, caseine, and other nitrogenized principles of food, supply the animal with materials required for the formation of muscle and cartilage; they are, therefore, called flesh-forming principles. “Fats, or oily matters of the food,” says he, “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. “Phosphates 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, because 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 principles in its food. Due attention, therefore, ought to 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 animals, or the particular purpose for which they are kept.”