A general examination of the details of the experiments discussed in the preceding part of this section shows conclusively that following the ingestion of protein there is a distinct increase in the metabolism which may persist for a considerable period of time. In an attempt to establish a quantitative relationship between the amounts of protein ingested and the subsequent increments in the metabolism, and likewise to study the time relations, we have summarized in table 230 the results of the calorimeter experiments. The data for heat production in the respiration experiments have already been presented in table 215. (See page 284).

Most of the experiments were made with animal protein, these including the large number in which beefsteak was ingested. Even the beefsteak experiments in which small amounts of bread and potato chips were taken may, for reasons previously discussed, be considered as primarily animal-protein experiments. The experiments with plasmon and skim milk likewise showed the influence of animal protein upon the metabolism. In the experiments with gluten bread and skim milk the effect of a combination of vegetable and animal proteins was studied, but the greater part of the nitrogen was supplied by the gluten. The only experiments with pure vegetable protein were those with glidine, but with two exceptions the amounts of nitrogen in the glidine ingested were relatively small.

It is somewhat difficult to present in tabular form the results of experiments extending over a period of many years, which were made with different apparatus, very considerably different amounts of food, and varying experimental periods. The table is, however, reasonably self-explanatory. Special attention should be called to the considerable variations in the length of the individual periods in the experiments, these being shown in the first column with the initials of the subject. In all cases they were 2 hours, 1 hour, or 45 minutes in length. The total increments in carbon-dioxide production, oxygen consumption, and heat production during the entire period of observation are given in the next to the last column; in the last column may be found the percentages of increment above the basal values for the same peri.

A positive increment was obtained in all of the experiments except in that with F. M. M., January 20, 1910. Even in this experiment there was an increment of 10 calories in the heat production, but the values for the carbon-dioxide production and the oxygen consumption both present slight negative values. An examination of the details of the experiment shows that positive increments occur in the first two periods, these amounts being counterbalanced by negative values in subsequent periods. In the first two experiments given in table 230 the food taken had practically the same nitrogen content and the experiments may therefore be considered as duplicates, although with different subjects; both indicate a considerable increase in all of the three factors. In the next two experiments, which were made with the same subjects, the food taken was approximately one-half that ingested in the preceding experiments; the increments found were proportionally smaller than those in the first two experiments. In both pairs of experiments, the values for A. W. W. are lower than those for A. H. M., especially for carbon-dioxide production and heat production. From these four experiments, therefore, one may infer that the influence of the ingestion of beefsteak is by no means the same with different individuals. The values for oxygen consumption for the two subjects are considerably at variance, as in the high-nitrogen experiments the increments are alike, while with the low-nitrogen intake the increment for A. H. M. was but half that with A. W. W., thus showing the difficulties in comparing results by direct and indirect calorimetry for experimental periods less than 24 hours.

Table 230. - Summary Of Results Of Protein Experiments With The Respiration Calorimeter

1Total increase and total basal value are for actual duration of the experiment, i. e., 5 hours 40 minutes. 2Total increase and total basal value for oxygen are for 3 hours; the oxygen was lost in second period.

1Individual measurements of the oxygen consumption were not obtained in periods 2 and 3, but the total increment for the two periods (4 hours) was 11 grams. See table 224, p. 294. 2This includes 100 grams plasmon, 70 grams plasmon milk biscuit, and 206 grams skim milk. 3Total increase and total basal value for oxygen are for 6 hours; the oxygen was lost in first period. 4This includes 100 grams plasmon meal, 47 grama plasmon graham biscuit, and 439 grams skim milk.

In comparing the data for experiments such as these, we should expect to find that each gram of ncrement in carbon dioxide produced would correspond to an increment in heat production of 2\ to 3 calories. An examination of the results in table 230 shows that this ratio holds true in but few instances. Thus, in the first four experiments the amount is more nearly 2 calories per gram of carbon dioxide than 3 calories; this is true, also, for many other experiments. In the experiment with V. G., January 21, 1911, we find that the ratio is 7 calories per gram of carbon dioxide, while in the following experiment it is only 1.2 calories, and in the two succeeding experiments the ratios are less than 1 calorie. Such irregularities as these discredit the use of direct calorimetry in short experiments. On the other hand, when the computations of indirect calorimetry are based upon carbon dioxide alone, they are open to the serious objection that the increase found may be due to change in the character of the katabolism or to a formation of fat from carbohydrate, but when the measurements are made by direct calorimetry it provides positive evidence that the increment in heat production is due to the food alone. The data for heat production in table 230 show that such an increment was found in every experiment in which protein food was ingested, although in some cases the increment was very small.