METABOLISM DURING CHEWING. 137 



DISCUSSION OF RESULTS OF CHEWING EXPERIMENTS. 



In two of the Middletown calorimeter experiments, slight incre- 

 ments in the heat output were observed; the third showed a slight 

 decrease. The data in tables 52 to 54 also show that the increments 

 in the values for the gaseous metabolism approximated those found 

 for the heat production. Thus the work of chewing gum performed 

 by these subjects during a period of approximately 4 hours usually 

 produced on the average a slight increase over the basal metabolism. 



In the five experiments made with the chair and bed calorimeters 

 in Boston, the time of actual chewing was considerably shorter than in 

 the Middletown experiments, being approximately If to 2f hours in 

 duration. In two of the experiments there was practically no varia- 

 tion in the metabolism; the other three experiments showed an incre- 

 ment of 5, 9, and 16 per cent, respectively. In one of these experi- 

 ments, that with T. M. C. on January 7, 1911, the increment in the 

 heat production was actually somewhat less than the increment noted 

 in the gaseous metabolism, yet it points towards a true increase in the 

 metabolism. In the bed-calorimeter experiment with V. G. on Decem- 

 ber 19, 1910, in which the high increment of 16 per cent was obtained, 

 the increase in the heat output was somewhat higher than that shown 

 for the carbon-dioxide production, which was but 8 per cent, and for 

 the oxygen consumption, which was but 7 per cent. It is thus not 

 impossible that errors in the measurement of the heat production may 

 account for the abnormally high percentage increase in this factor. 

 Disregarding the heat value obtained in this experiment with V. G. 

 and substituting that obtained for the gaseous metabolism of about 

 8 per cent, the increment in the calorimeter experiments due to chewing 

 gum will average approximately 3 per cent, with wide variations which 

 include three negative values. 



Measuring the metabolism with a respiration apparatus during the 

 chewing of gum has certain technical difficulties which at first were 

 thought to be insurmountable. By using nosepieces instead of a 

 mouthpiece and giving careful instructions to the subjects, it was pos- 

 sible to make five experiments with four subjects. In all of the respira- 

 tion experiments it was necessary to obtain the heat output by the 

 indirect method of computing it from the gaseous metabolism. In 

 considering the results of the chewing experiments, therefore, it is 

 especially important to note any possibility of loss of carbon dioxide 

 or intake of oxygen through the mouth during chewing, for naturally 

 any leakage of air into or out of the mouth during the periods of obser- 

 vation would cause a disturbance in the measurements of the metab- 

 olism. If the results recorded show similar changes in the values for 

 the carbon-dioxide production and oxygen consumption, it may be 

 taken as an indication that there was little, if any, leakage of air 



