The discussion thus far has dealt primarily with the extent to which the basal metabolism may be increased temporarily by the ingestion of varying amounts of carbohydrates and the time relations between the maximum increase and the time of ingestion. As a casual examination of tables 101 to 122 will show, the increase in the heat production after carbohydrate ingestion is, for the most part, only found in the first hour or two. In a number of the experiments the increment continues longer than the first period; it is thus important to note not simply the highest point to which the basal metabolism may be lifted by the ingestion of carbohydrate, but likewise the total effect of the carbohydrate upon the basal metabolism. This can be done only by noting the total increment in the heat production. This increment is secured by measuring the total heat produced during the whole experiment and computing from the basal heat production the increment actually obtained in this period. The values found in the calorimeter experiments for the total increment in heat production after the ingestion of carbohydrate are given in table 124; in the last column of this table are also recorded the percentages of the total increments in terms of the basal value. The values for the basal heat production are included for purposes of comparison.

Table 124. - Total Increment In Heat Production Following Ingestion Of Carbohydrate

(Calorimeter experiments).

1The time given represents the experimental period. The food was usually taken le3s than . half an hour before the beginning of the experiment. See tables 101 to 122 for details. 2Also juice of one lemon.

It is very difficult to obtain a satisfactory method for computing the percentage increment. Obviously the lengthening of the period in which the measurements are made without an increment above the basal metabolism simply increases the denominator of the fraction and thus increases the basal value without affecting the increment. The value of the increment in terms of per cent is thus decreased. In table 123 it will be seen that the percentage for the greatest increment above the basal value is in every instance considerably higher than the percentage for the total increment given in the last column of table 124. This is due in large part to the fact that the total increment in the heat production took place during the first hour or two, while in the subsequent hours the metabolism was essentially the same as the basal value.

When the duration of the experiment is 12 hours instead of 4, 5, or 8 hours, as the case may be, the percentage total increment is naturally greatly decreased. A striking illustration of this is shown by comparing the experiments with A. L. L., on March 30, 1906, and April 19, 1906, in which essentially the same amounts of bananas and sugar were given. The greatest increment was 34 per cent in one case and 31 per cent in the other; in both experiments this increment occurred in some part of the first or second hour. The total increment above the basal value was found to be 88 calories in one case and 72 calories in the other. There was, however, a difference in the basal values of the two experiments of over 300 calories, owing to the fact that in the April experiment the length of the experimental period was 12 hours, while in the March experiment it was only 8 hours. The percentage increment in the March experiment was therefore nearly double that in the April experiment, while in other experiments the values are fairly good duplicates.

The computation of the total increment above the basal value for experiments in which food was ingested is justifiable. The computation of the percentage of the increment is, however, open to serious criticism, and it is difficult to see how such percentages can have real significance. Yet they are frequently computed and reported in experiments of this kind. Perhaps their greatest value for this discussion is the fact that while in these observations the experimental period varied in length only from 3 to 12 hours, and usually from 4 to 8 hours, it can readily be seen that were the remainder of the 24 hours added to the experimental period, the percentage value would be greatly decreased and, in fact, would nearly disappear. It can easily be understood, therefore, why investigators employing the 24-hour period have failed to note a material increase in the metabolism due to the ingestion of carbohydrates, for although there is a distinct temporary increase, which may at times reach 30 per cent or over, this increase, when compared to the total 24-hour basal value, appears almost insignificant. If, on the contrary, we are dealing with a substance which is delayed in effect, even though its intensity may not be so great as that noted in some of our experiments, the use of the base-line for the longer period would be more justifiable and more truly indicative of the actual conditions than a base-line for a short period. Accordingly, while the values given in table 123 for the greatest increment above the basal metabolism may not be taken as indicating a prolonged effect at this level of intensity and should only be interpreted as the possible maximum level to which the basal value may be raised, the percentage values in table 124 must be interpreted by taking into consideration simultaneously not only the total amount of increment measured but the basal value and particularly the length of the experimental period. As uniformity in results may not be expected with experiments of different length, these percentage values can have but little relative mathematical significance other than to explain the low values noted by investigators during 24-hour periods when carbohydrates are given.

Although the experiments with pure carbohydrates are better adapted for comparison purposes than those with mixed carbohydrates, the discussion of the total increments in the metabolism as a result of the ingestion of the former will be deferred until the results of the respiration experiments are considered, as by far the larger number of experiments with the pure carbohydrates were made with the respiration apparatus. Still it is of significance to note from table 124 that with sucrose the total increment above the basal value for the entire period of measurement was 10 per cent in one case, and with the maltose-dextrose mixture it was 14 per cent in two cases.