No single nutrient, when ingested, produces so great an effect upon the metabolism as protein does. In fact, the earlier observations, particularly those made by Rubner and Magnus-Levy with dogs and man, appeared to show that protein was the only nutrient which measurably increased the metabolism. At the time of beginning our study on the effect of food upon the metabolism, the varieties of pure protein available were relatively limited. Accordingly the largest number of experiments were made with beefsteak, for though this food material was not a pure protein, it was palatable and easily obtained. Furthermore, as the beefsteak given the subject was freed from all visible fat, it was assumed that the amount of fat ingested would play but a small part in the metabolism. In a number of the beefsteak experiments small amounts of bread or potato chips were also taken. In some of the observations approximately pure protein materials were used, these being gluten, plasmon, and in the later experiments in Boston, glidine. The gluten and plasmon were both taken with skim milk.

In the experiments with relatively pure protein and in a large proportion of the beefsteak experiments the observations were made with the calorimeter. While these experiments do not by any means fulfill the demands of the technique at the present time, they do represent the first attempt with man to determine by direct calorimetry the influence upon the metabolism of the ingestion of protein; consequently they are discussed in some detail. One defect in the plan of experimenting for all of the Middletown calorimeter experiments and for the majority of the Boston calorimeter experiments is the fact that the basal values and the values after the ingestion of protein were not determined on the same day.

Although the experiments with gluten and skim milk and plasmon and skim milk were made in 1906, while those with beefsteak were not begun until 1907, it seems desirable to consider first the data with the single food materials, especially as so large a number of observations were made with beefsteak.