For the purpose of indicating the protein metabolism of these Boston subjects, we have included in table 35 average values for the nitrogen excretion per hour, not only for the calorimeter experiments, but for other experiments not included in this publication. The values from which these averages are drawn are given in table 36. No marked variation is found with the different individuals, the same subject usually having approximately the same nitrogen excretion per hour under the conditions of measurement employed. It is rarely that such contrasts are noted as that in the results for V. G., with whom a very small excretion of nitrogen occurs on November 21, while 3 days earlier almost the maximum amount is found. That this corresponds to an actual difference in the protein katabolism is by no means definitely assured from these figures, for the difficulty of completely emptying the bladder, especially in the case of young and untrained subjects, is well known to practiced experimenters.

1Emmes and Riche, Am. Journ. Physiol., 1911, 27, p. 406.

Tables 36. - Nitrogen Excreted In Urine During Experiments Without Food

(Amounts per hour).

Subject was without food in first 3 hours of the 5 hours covered by the sample in each case. Sucrose was given at the end of 3 hours.

General Conclusions Regarding 8-Hour Experiments In Boston

With the shortening of the experimental period, the distinction between heat production and heat elimination becomes of considerable consequence. In the 24-hour experiments it was found that the heat production and heat elimination were essentially identical - that is, that the body-temperature as determined by rectal measurements was practically the same each morning at 7 o'clock when the experimental day ended. While the correctness of this assumption as a generalization may fairly be questioned, nevertheless very considerable differences in body-temperature may actually appear and yet not affect the calculation of the total heat production when based on the 24-hour unit. With short periods, on the other hand, temperature fluctuations may normally be expected. It has been demonstrated that there are ordinarily variations of 1° to 2° C. in the normal rectal temperature, the minimum appearing from 3 to 5 a. m., and the maximum in the late afternoon. Even during short periods of rest there may be considerable fluctuation in the body-temperature. Consequently, as the experimental period is shortened, there is an increasing danger of possible error in the measurements of the heat production owing to either a storage of heat in the body, as shown by an increase in the body-temperature, or a loss of heat, as indicated by a fall in the body-temperature. To obtain the true heat production, the values for this storage or loss should be added to or deducted from the values obtained for the heat actually eliminated during the period.

This question is of special significance when the attempt is made to compare the heat production and the gaseous exchange - in other words, to compare the direct and indirect calorimetry - the difficulties lying for the most part in securing a proper measurement of the body temperature. Many inconsistencies that appear at first sight in the results of these experiments, as, for instance, those with L. E. E. (table 32), may properly be ascribed to erroneous measurements of the body-temperature or to the lack of such measurements.

At about the time these experiments were made special attention was devoted to the measurement of heat production and the description of a special apparatus for measuring the body-temperature deep in the rectum was published.1 It has been impracticable in all subsequent researches to take advantage of this method of measurement, and yet experience in this laboratory, as well as elsewhere, has shown that heat elimination as measured by the respiration calorimeter can have but little significance without a definite knowledge of the very considerable change in the body-temperature that may accompany a normal or physiological experiment and is quite likely to accompany observations on pathological cases.

If we make a general study of the metabolism data obtained in these Boston experiments, the results may be summed up as follows: As a rule, the average values for the gaseous metabolism for each subject show uniformity, although at times there is more or less variation in the individual values. Owing, probably, to the fact that the body-temperature measurements were lacking or defective, there is frequently considerable variation in the heat output, although even here the values do not lack uniformity in some cases. With the two subjects who were studied in both the chair calorimeter and the bed calorimeter, lower values were invariably found with the bed calorimeter, this being due to the greater degree of muscular repose.

It should be noted that the criterion for uniformity is a plus or minus variation of 5 per cent - that is, if the values for the carbon dioxide or the oxygen are within 1 gram of each other on the 20 to 25 gram basis, they are considered reasonably uniform. Hence we must admit at the outset the possibility of variations in the individual periods of at least plus or minus 5 per cent. This is important to note in any subsequent use of these values in determining the influence of the ingestion of food, for frequently the effect of the ingestion of food may be not much outside this limit. Accordingly this basis of experimentation for food experiments, while favorable when a large effect of digestion is to be expected, is still of doubtful value when the subtler effects are studied, as they may be entirely lost sight of.

We see no reason, however, why the results of these experiments should not, with intelligent appreciation of their defects, still be used for comparison with the results of experiments made under identically the same experimental conditions after the ingestion of food. One major criticism of so using these values may be made, in that while lBenedict and Slack, Carnegie Inst. Wash. Pub. No. 165, 1911. the temperature curve of the normal body may be reasonably uniform when no food is taken, it is quite likely that the ingestion of food may produce a somewhat rapid rise in temperature which, if not measured accurately, would still further vitiate the calculation of the values for the heat production. It is thus seen that it will be necessary to confine the major discussion of the influence of the ingestion of food upon metabolism to its effect upon the respiratory exchange and the indirect calorimetry computed therefrom, using the grosser heat measurements as subsidiary evidence.