The problem of practical nutrition is really much broader than this, for protein constitutes but a single factor of importance in nutrition. The content of the essential mineral elements in the diet, and of the several unidentified factors, the absence of which leads promptly in each case to the development of specific pathological conditions, are of equal importance from the standpoint of the well-being of the body. The discovery of the means of making the nice adjustments in a quantitative way among all the factors best adapted to promote optimum development and of the means of preserving the harmonious rhythm of the metabolic processes in the best possible manner, is the end sought by students of nutrition. The various factors mentioned will receive attention in later chapters.