The Measurement of the Efficiency of Diets. New Apparatus and Procedures

New equipment and two experimental procedures were demonstrated, with growing albino rats as subjects, for the comparison and the measurement of the nutritive values of human diets. The equipment was a series of water-sealed respiration chambers, for the determination of the quantitative and the qualitative character of metabolism, by means of the carbon and nitrogen balance method, under normal conditions of physical activity of the subjects. One of the procedures consisted of growth experiments, in the course of which were determined series of carbon and nitrogen balances, at intervals, with the same food intake throughout, for the purpose of observing the character of the metabolism as affected by the progressively increasing severity of the nutritive conditions imposed by the gain in weight of the subjects. This procedure yielded results in terms of gross efficiency, covering requirements for maintenance and production together. The second procedure consisted of nutritive measurements, also by means of carbon and nitrogen balances, representing the net energy point of view. Balances were determined during 1) fast, 2) feeding at the maintenance level, and 3) feeding at a higher plane; and upon these balances were based values for heat increment and net energy, separately for maintenance and for growth. The two distinctly different methods of experimental management afforded equally distinct means of comparison and measurement of the values of diets as sources of nutritive energy and protein. The respective advantages and limitations of the two procedures are pointed out. In the comparison of the nutritive values of diets the results obtained by the two procedures were in harmony, insofar as they were comparable.