The most extensive series of experiments was obtained with Mr. H. L. Higgins, who was long connected with the experimental work of the Nutrition Laboratory. The first experiment with this subject was on May 23, 1910, and the last on June 2, 1915; although not made at regular intervals, the observations were reasonably well distributed over this period of about five years. Confining our discussion first to the carbon-dioxide values and considering the influence upon them of the time of day and their variation in the consecutive periods, we find that the carbon-dioxide production per minute shows considerable variation from hour to hour in the individual experiments. (See table 37.) Differences as large as 20 c.c. or more are occasionally noted, this corresponding to an approximate variation of 10 per cent. Thus in the experiment of September 24, 1911, there was a difference between the first and second periods of 26 c.c. and between the first and fourth periods of 31 c.c, or nearly 15 per cent of the average value for the day, while the values for January 13, 1912, show a difference between the second and third periods of 30 c.c, again about 15 per cent of the average for the day. The average values for the consecutive periods are remarkably constant. The highest is that for the first period, 203 c.c, drawn from 10 periods; the lowest is that for the fifth period, 195 c.c, drawn from 21 periods. Although the average value for the fifth period is lower than that for the first, we do not find here, as with some of the experiments made with the 8-hour method, any tendency towards a falling off or material alteration of the values as the day progresses.

The greatest mean variation, 11.3 c.c, occurs in the first period, this being slightly more than 5 per cent of the average value for this period. The mean variation of the averages for all the periods is but 7.8 c.c, an agreement that indicates uniform experimental conditions and accuracy in technique.

From the general picture of the carbon-dioxide production of this subject during the period of five years, which is obtained from the averages in the extreme right-hand column, we find that while there are individual variations there is no general tendency toward a material alteration in the metabolism; this is further confirmed by the small average mean variation. We may therefore infer that the carbon-dioxide production of this subject did not vary to any extent in the course of the five years of experimenting. The average carbon-dioxide production for H. L. H., as shown by the determinations made during this period, may be considered as 198 c.c. per minute.

Table 37. - Carbon-Dioxide Produced At Different Times Of Day In Respiration Experiments; Subject H. L. H., In Post-Absorptive Condition And Lying On Couch

(Values per minute).

Average age, 25 years. Average body-weight (naked), 61.4 kilograms. Height, 172 cm.

The experimental periods were usually 15 minutes in length and there was but one period in each half hour. The total number of periods in which the carbon-dioxide was determined in the 45 experiments was 158.

Table 38. - Oxygen Consumed At Different Times Of Day In Respiration Experiments; Subject, H. L. H., In Post-Absorptive Condition And Lying On Couch

(Values per minute).

Average age, 25 years. Average body-weight (naked), 61.4 kilograms. Height, 172 cm.

1The experimental periods were usually 15 minutes in length and there was but one period in each half hour. 2The total number of periods in which the oxygen was determined in the 46 experiments was 159.

Our study of the results of this series has thus far been based solely upon the data obtained regarding the carbon-dioxide production, but a more logical basis of discussion for changes in metabolism is to be found in the values for the oxygen consumption. These are recorded in table 38. Certain data obtained under special abnormal conditions, as an experimentally induced acidosis, are of course excluded, and so far as we are aware the figures given may properly be used for basal values.

The averages at the bottom of the table show that the oxygen consumption per period as the day advanced remained noticeably constant. The highest average (246 c.c.) is that for the first period; the lowest average (235 c.c.) is found for the sixth period. Inasmuch as the average values for the seventh and eighth periods are materially higher than the average found for the sixth period, it is reasonable to consider that the oxygen consumption of H. L. H. shows no general trend toward a decrease in the metabolism, as the measurements continued from 8 a. m. to midday. This conclusion is further justified by the fact that the mean variation from the general average is only 9 c.c. The mean variations for the individual periods, as shown in the last fine of the table, agree satisfactorily and give evidence of uniformity in the experimental conditions and accuracy of the experimental work.

The average oxygen consumption of this man over a period of five years, as shown by the general average, is 241 c.c. The averages in the extreme right-hand column indicate that the oxygen consumption, like the carbon-dioxide production, had no general tendency to alter in value as time progressed, with the single exception of a group of five experiments from September 20 to 24, 1911, inclusive. On those days the values approached very closely to an average of 270 c.c. During these five days the subject, although in a post-absorptive condition during the observations, was living on a diet containing a liberal amount of protein and fat but only 125 grams of carbohydrate.1 This diet was sufficiently low in carbohydrates to alter the metabolism of the subject materially. We do not feel justified, however, in omitting the results from the table.

It may be stated, therefore, that with the subject H. L. H. the average values for both the carbon-dioxide production and oxygen consumption were notably constant, both from period to period and during a period of five years, but that the individual values varied considerably at times. •