Of the various processes classified by Professor Armsby1 as prior to actual digestion, the work of prehension is hardly suitable for experimental study, since it would vary greatly with different individuals and with the different kinds of food consumed. On the other hand, mastication is a physiological function accompanying all ingestion of food. Indeed, a cult with many adherents has been established to advocate prolonged mastication. Hence information regarding the probable energy transformations as a result of mastication has unusual interest. To study this question, a series of experiments was made in which the subject chewed gum for a considerable length of time. This study was supplemented by a second series of experiments in which a rubber stopper was substituted for the chewing gum.

Statistics Of Experiments

The calorimeter experiments included 3 experiments with the respiration calorimeter at Middletown, Connecticut (tables 52 to 54), 4 with the chair calorimeter (tables 55 and 57 to 59) and 1 with the bed calorimeter in Boston, Massachusetts (table 56). In all of these the subject chewed gum. In addition, 5 respiration experiments were made with the subject chewing gum (tables 60 to 64) and two respiration experiments in which a rubber stopper was chewed vigorously (tables 65 and 66). A summary of the values obtained for the heat production in these experiments is included in tables 67 and 68.

1Armsby, The principles of animal nutrition, 2d ed., 1906, p. 374.

For the respiration experiments the output of heat was computed by the indirect method. These experiments consisted of two series of periods, in the first of which the subject was without food and did no chewing. As the measurements of the metabolism were not continuous, it was necessary to compute the values given in tables 67 and 68 for the total increment due to chewing by the best method obtainable and to make certain assumptions.

Tables 60 to 66 show both the average heat production for the periods without food or chewing, i. e., the basal value for the day, and the heat output for each of the periods with chewing. The increase in the metabolism in the periods with chewing has been obtained by comparing the basal value for the day with the heat computed for each period. These increments of heat represent the results of two to four periods in which the metabolism was measured. The total time of chewing in the several respiration experiments varied from 53 minutes to 2 hours 19 minutes; the total duration of the measurement of the metabolism (not continuous) was from 30 to 60 minutes. In computing the total increment in the metabolism due to chewing (see table 68), it was assumed that the increase was coincident with the beginning of chewing. It was furthermore assumed that the rate of increase in the periods between the beginning of chewing and the beginning of the measurements (6 to 14 minutes), also in the intervals between the periods of measurement (6 to 40 minutes), was the same as that in the measured periods and that the average increment obtained for these periods represents the rate of increase in the metabolism for the total time of observation - i. e., from the beginning of chewing to the end of the last period. The total increment in the metabolism for this time was therefore computed by direct proportion.

For example, in the experiment with V. G., January 5, 1911 (see table 62, page 133), the average basal value for the heat output per minute obtained in periods without food and without the work of chewing, was 1.13 calories. The subject began chewing 10 minutes before the measurements of the metabolism commenced. The values obtained for the respective chewing periods were 1.46, 1.52, 1.43, and 1.32 calories for a total period of measurement of 53 minutes. The average increment in the metabolism during the measured periods of chewing was therefore 0.30 calorie per minute. Using this value and the total time of chewing, that is, the period from llhllm a. m. to lh30m p. m., or 2 hours 19 minutes, the total increase in the metabolism (139 X 0.30) was computed to be 42 calories. The basal value corresponding to this period (139 by 1.13) was 157 calories. The percentage increase in the metabolism (42%157) was therefore 27 per cent.

Statistical data not included in the tables or in the discussion are given for all of the experiments in the following paragraphs. The data for pulse rate and respiration rate represent averages of the individual records for the basal and chewing periods. Records of the body-temperature, when available, were made with the rectal thermometer at the beginning of the periods and at the end of the experiment. Analyses of chewing gum give 62 to 69 per cent of soluble carbohydrates. When the basal values were determined immediately before the chewing periods, the times given include both basal and chewing periods.