Having acquired information regarding the principles of metabolism and the general laws governing the nutrition of the body, we may next consider briefly the dietetic habits of mankind, with a view to learning how far such habits coincide with actual nutritive requirements. Eventually, we shall need to ask the questions: What are the _true_ nutritive requirements of the body? How much food and what kinds of food does the ordinary individual doing an average amount of work need each day in order to preserve body equilibrium, and to maintain health, strength, and vigor under the varying conditions of life? What amount of nitrogen or proteid, and what the total calorific value required to supply the physiological needs of the body? How closely do the so-called “normal diets” and “standard diets,” which have met with such general acceptance, conform to a rational conception of true physiological needs? These are vital questions of great physiological and economic importance, and they are not easily answered; but theoretical considerations based on scientific data, and experimental evidence combined with practical experience, should point the way to some very definite conclusions. Observations made in many countries regarding the dietetic customs and habits of the people have resulted in the establishment of certain dietary standards, which have been more or less generally adopted as representing the requirements of the body. As a prelude to the discussion of this question, let us consider briefly some of the results of these dietary studies. In Sweden, laborers doing hard work were found by Hultgren and Landergren to consume daily, on an average, 189 grams of proteid, 714 grams of carbohydrate, and 110 grams of fat, with a total fuel value for the day’s ration of 4726 large calories. In Russia, workmen at moderately hard labor, having perfect freedom of choice in their food, were found by Erisman to take daily 132 grams of proteid, 584 grams of carbohydrate, and 79 grams of fat, this ration having a fuel value of 3675 calories. In Germany, soldiers in active service consumed daily, according to Voit, 145 grams of proteid, 500 grams of carbohydrate, and 100 grams of fat, with a fuel value of 3574 calories. In Italy, laborers doing a moderate amount of work were found by Lichtenfelt to consume daily 115 grams of proteid, 696 grams of carbohydrate, and 26 grams of fat, with a fuel value of 3655 calories. In France, Gautier states that the ordinary laborer working eight hours a day must have 135 grams of proteid, 700 grams of carbohydrate, and 90 grams of fat daily, with a fuel value of 4260 calories. In England, weavers were found to take daily 151 grams of proteid, with carbohydrates and fats sufficient to make the total fuel value of the day’s ration equal to 3475 calories. In Austria, farm laborers consumed daily 159 grams of proteid, with carbohydrates and fats sufficient to raise the fuel value of the food to 5096 calories.