For many reasons it is impossible for a housewife to make an _exact_ calculation of the amount of nourishment which she gives her family. The figures in even the most carefully made tables are, of necessity, averages or approximates, for food varies in quality in different localities and at different seasons. Moreover, the figures in the various government reports upon food values and in books giving such statistics differ somewhat, nevertheless, there is sufficient general agreement upon which to base an intelligent effort to make wise as well as agreeable menus.
On this account, a housewife who is neither very learned nor very experienced can yet wisely regulate her menus by keeping in mind the general character of a day's nourishment and helping out her lack of chemical knowledge with a table of food values such as the one below. The general aim in providing food, as has already been said, is to furnish all the varieties of nourishment which the body requires and the chief ones in about the proportion of a fifth protein to a fifth fat to three-fifths carbohydrates. That is, either the per cent. of protein or the per cent. of fat multiplied by three should about equal the carbohydrates. This is, of course, a very rough and general way of estimating, but I believe it to be a practical way to begin the study and application of a branch of difficult and as yet slightly established knowledge.