With such changes in the dietetic intake as were made in these experiments, changes not only in the total katabolism but likewise in the character of the katabolism would reasonably be expected; hence an analysis of our data for the respiratory exchange should be made with a view to studying the character of the katabolism. The respiratory quotient, that is, the ratio between the carbon dioxide excreted and the oxygen consumed, is the best index we have of the character of the katabolism. A high respiratory quotient indicates that a large proportion of carbohydrate is being burned in the body and a low quotient a large proportion of fat. Since the portable respiration apparatus is designed to give an accurate measure of the oxygen consumption only, our study of the respiratory quotients of these subjects must depend upon the quotients found in the experiments with the respiratory-valve apparatus; these, however, are not numerous. The respiratory quotients obtained are given in the gaseous-metabolism tables for the individual subjects. (See tables 115 to 127).

The respiratory quotient showing the normal basal value prior to the reduction in diet is best obtained from the average respiratory quotients in table 113. This gives an average quotient for the whole squad of 0.80. This normal value is in accord with the value obtained by Benedict, Emmes, Roth, and Smith with the 89 men, and by Carpenter, Emmes, and Hendry with the 17 Harvard Medical School students. An inspection of the respiratory quotients in the several gaseous metabolism tables reveals a tendency for the quotients to be on the whole somewhat lower with the restricted diet, as values below 0.80 appear more frequently than those above. Individual instances of high respiratory quotients are, however, frequently noted in connection with the high metabolism found on the days following the periods of uncontrolled diet on Sundays and during the Thanksgiving and Christmas recesses. Typical illustrations of this are the respiratory quotients for Mon on December 3 and 10, obtained on the Mondays following Sundays with unrestricted diet. The respiratory quotient on December 3 was 0.92 and on December 10 it was 0.89. Likewise on Monday, January 14 (following another unrestricted Sunday diet) the respiratory quotient was 0.88 as compared with 0.75 on January 10 with controlled diet. On the same Monday (January 14) Gul's respiratory quotient was 0.87 as compared with 0.79 on January 9. With Pea on the two Mondays, December 3 and 10, the respiratory quotients were 0.86 and 0.93, respectively. A general inspection of the data shows that these high quotients are characteristic of the Monday mornings following the uncontrolled diets of Sunday or after the holidays. This would imply a storage of carbohydrates as a result of the uncontrolled eating. Aside from these high quotients resulting from the uncontrolled diet, the low-diet quotients show a general uniformity at about 0.79. Certain abnormally low respiratory quotients also appear in our values, but none lower than 0.73 were used in the calculation of the heat production. Those below 0.73 are as follows: Bro, September 29, 0.70; Can, October 10, 0.72; Gul, January 18, 0.72; Mon, November 3, 0.68; Pec, January 7, 0.72; and Vea, October 21, 0.72. No simple explanation for these low values is at hand.

From the foregoing it is seen that the respiratory quotients here given have a general interest in that they show a tendency toward a lowering in the katabolism of carbohydrate and probably of the glycogen storage. After the unrestricted days there was invariably a noticeable tendency for an increase in the respiratory quotient, indicating a higher consumption of carbohydrate on these days. The respiratory quotients in no case approach a level indicating a carbohydrate-free diet or a state of glycogen depletion bordering upon incipient acidosis.

A practical use which was made of the respiratory quotient in this research was to compute from it the calorific value of the carbon-dioxide production in the experiments with the group respiration chamber, for, as is well known, the calorific value of carbon dioxide varies considerably with the respiratory quotient. The quotients obtained on the days nearest to the experiments in the group respiration chamber were used for determining the calorific value of the carbon dioxide produced.