Each individual should know, approximately, the chemical constituents and the proportion of these constituents in normal blood, because from the elements in the blood, the tissues are constructed. If certain elements be lacking, the foods containing these elements in largest proportions should be supplied until the blood no longer shows the deficiency. This is Nature’s method of correction. Each meal, or each day’s food, may not contain just the amounts of protein or of fuel ingredients necessary for that day’s work and re-supply, but the body is continually storing material, and this reserve is constantly being drawn upon to provide any element which may be lacking in that day’s supply. Thus, an excess or a deficiency one day may be adjusted the next. Healthful nourishment requires that the balance, as a whole, be kept, and that a deficiency or over-supply be not continued for too long. Many domestic animals take their food elements from air and water, as well as from the compounds which the plants have formed; while others make use of meat, a compound formed by another animal. The digestive forces of the animal has converted these elements into flesh, a compound easily assimilated by another. The greater part of the muscles, nerves, and glands of the animal kingdom is _protein_. The skeleton is composed largely of deposited salts, while the elements which supply heat and keep up muscular activity are _starches, fats, and sugars_. The _proteins_ are appropriated by man from plants, but they are furnished to him in more easily digested form in lean meat and eggs, the lower animals having done much of the work of digestion, converting the proteins from plant life into more condensed form. On the other hand, by access to this concentrated form of easily digested protein, man is in danger of taking in too much of this condensed food, if he eats a large quantity of meat and eggs. It must be apparent to every thoughtful person, since the nerves, muscles, and glands are composed largely of protein and the skeleton largely of salt, that, in order to furnish the body with the elements necessary for growth and repair, these elements must be provided, as also the substances producing the energy for the working body. _Each individual should make a self-study to know how much re-supply is required to renew the daily waste._ About one-third of the food eaten goes to maintain the life of the body in doing its incessant work of repairing and rebuilding, the remaining two-thirds is the reserve for usefulness outside of itself.