The series of respiration experiments with beefsteak included 14 experiments with 10 subjects made between November 3, 1910, and December 12, 1914. The routine in these experiments was not unlike that followed in similar experiments in this laboratory, the basal value being determined on the same day prior to the ingestion of food. After the food was eaten, measurements of the metabolism were usually begun immediately and continued at intervals in periods of approximately 15 minutes for a varying length of time. In one instance, the experiment with H. L. H., on July 1, 1911, the observations continued for 12 hours after the food was given, but in the majority of cases they ended inside of 3 to 6 hours. Throughout the whole experiment the subject lay quietly upon a couch and every effort was made to maintain constant muscular repose. The urine was usually obtained for both the basal and food periods. All available data regarding nitrogen excretion in these experiments are given in table 216. In most of the experiments the diet consisted of beefsteak alone, but in two instances small amounts of other food materials were added. It was assumed that these small amounts had practically no influence upon the metabolism.

The pronounced effect upon metabolism occasioned by the ingestion of even moderate amounts of a protein food material has been so clearly shown, not only in all of the experiments cited in the literature but likewise in our calorimeter experiments with beefsteak, that the results of these respiration experiments may be treated differently from those of the carbohydrate respiration experiments. The average respiratory quotient of normal man in the post-absorptive condition is not far from 0.83. Since this is approximately the respiratory quotient of protein katabolism, the respiratory quotients in our experiments with a protein diet do not have the special interest that they have in the carbohydrate experiments. Consequently it seems unnecessary to publish the details of these experiments, as our main interest lies in the influence of the ingestion of protein upon the heat production as computed from the values for oxygen consumption and carbon-dioxide production. We shall therefore confine our discussion chiefly to the changes in the energy output as the observations continued. The results of the respiration experiments with beefsteak have been summarized on this basis in table 215, which gives the amount of steak eaten, the basal heat production expressed in calories per minute, and the heat production in calories per minute for successive periods. The data are arranged according to the amount of beefsteak eaten, the largest amount being 362 grams and the smallest 150 grams. The data for the nitrogen excreted, so far as available, are given in table 216.

Table 215. - Heat Produced (Computed) In Respiration Experiments With Beefsteak. (Values Per Minute)

1Time from the moment subject finished eating to the end of the last experimental period; see pp. 151 and 152 for method of obtaining total increase.

2Also 15 grams potato chips. Nitrogen in food includes the nitrogen in both beefsteak and potato chips.

3Additional values were obtained for 7 to 8, 8 to 9, 9 to 10, 10 to 11, 11 to 12 hours as follows: 1.39, 1.32, 1.29, 1.21, and 1.31 cals.

4Also 15 grams butter and 200 grams beef tea. Nitrogen in food includes nitrogen for all of the food eaten.

In computing the calories per minute the respiratory quotients as determined were used and not the non-protein respiratory quotients. A calculation of a few of these experiments showed practically no important changes due to a use of the non-protein quotient;1 accordingly we may disregard the calculation and employment of the nonprotein respiratory quotient and consider that the calorie output recorded in table 215 represents the heat production.

1See p. 203 for comparison made in typical experiments with levulose; similar comparisons made in experiments with beefsteak showed like small differences in the heat production.

Table 216. - Nitrogen Excreted In Urine In Respiration Experiments With Beefsteak

The pronounced increase over the basal metabolism is instantly noted in practically all experiments. As might be expected, the higher values are usually obtained with the larger amounts of steak. For instance, in the experiment with J. J. C. on April 25, 1911, when 362 grams of beefsteak were eaten, the basal value of 1.11 calories was increased to 1.49 calories between 3 and 4 hours after the food. As a matter of fact, the highest absolute increment was noted with only 182 grams of beefsteak, this being in the experiment with D. M. on October 28, 1911, when the basal value of 1.09 calories was increased in 3 hours to 1.58 calories, or approximately 45 per cent. Of special significance is the fact that the basal value was not reached in any of these experiments, even when the observations were continued for 12 hours.

It should again be pointed out that these results are open to the objection that, unlike Gigon's admirably planned experiments, the food material used was not a pure protein, but that there was a certain admixture of fat, even though all visible fat was removed. The data obtained in these respiration experiments show clearly, however, that the ingestion of beefsteak in amounts varying from 150 to 362 grams results in a sustained increase in metabolism which is for the most part greater than that noted either with carbohydrate food materials or with fats. This effect in practically all instances continues over a much longer time than with either of the other nutrients, thus putting this protein food material in a distinctly special class so far as the influence upon the metabolism is concerned.