In conclusion, the facts here presented bearing on food requirements, especially those that relate to the need for proteid food, are seemingly harmonious in indicating that the physiological necessities of the body are fully met by a much more temperate use of food than is commonly practised. Dietary standards based on the habits and usages of prosperous communities are not in accord with the data furnished by exact physiological experimentation. Nitrogen equilibrium can be maintained on quantities of proteid food fully fifty per cent less than the every-day habits of mankind imply to be necessary, and this without increasing unduly the consumption of non-nitrogenous food. A daily metabolism of proteid matter equal to an exchange of 0.10–0.12 gram of nitrogen per kilogram of body-weight is quite adequate for physiological needs, provided a sufficient amount of non-nitrogenous foods--fats and carbohydrates--is taken to meet the energy requirements of the body. The long-continued experiments on many individuals, representing different types and degrees of activity, all agree in indicating that equilibrium can be maintained indefinitely on these smaller quantities of food, and that health and strength can be equally well preserved, to say nothing of possible improvement. The lifelong experience of individuals and of communities affords sufficient corroborative evidence that there is perfect safety in a closer adherence to physiological needs in the nutrition of the body, and that these needs, so far as proteid food is concerned, are in harmony with the theory of an endogenous metabolism, or true tissue metabolism, in which the necessary proteid exchange is exceedingly limited in quantity. There are many suggestions of improvement in bodily health, of greater efficiency in working power, and of greater freedom from disease, in a system of dietetics which aims to meet the physiological needs of the body without undue waste of energy and unnecessary drain upon the functions of digestion, absorption, excretion, and metabolism in general; a system which recognizes that the smooth running of man’s bodily machinery calls for the exercise of reason and intelligence, and is not to be intrusted solely to the dictates of blind instinct or to the leadings of a capricious appetite. CHAPTER VII THE EFFECT OF LOW PROTEID DIET ON HIGH PROTEID ANIMALS