METABOLISM DURING CHEWING. 139 



namely, 18 and 14 per cent, respectively, or 16 per cent on the average, 

 thus verifying completely the more carefully planned experiments on 

 chewing gum. It would appear from the data obtained in this study 

 that the work of mastication, such as would be involved in chewing 

 gum or a rubber stopper continuously, may temporarily require an 

 increment in the metabolism of approximately 17 per cent. 



In general agreement with the rise in metabolism due to chewing 

 gum and a rubber stopper, the pulse rate is found to have increased 

 in nearly all of the experiments. In the calorimeter experiments in 

 Boston the pulse rate increased 9 to 10 beats per minute in all except 

 those with J. J. C., March 25, 1910, and V. G., January 2, 1911. In 

 the experiments with the respiration apparatus an increase was found 

 in practically all of the experiments, the increase in the averages rang- 

 ing from 3 beats per minute with F. G. B. on May 5, 1911, to 25 beats 

 with V. G. on January 5, 1911. 



At this point we are certainly justified in calling attention to the 

 relation of the measured increase in the metabolism to the question of 

 prolonged mastication. One of the arguments which has been advanced 

 is that such mastication insures the absorption of a larger proportion 

 of material from the ingested food. The fallacy of this reasoning is 

 clearly shown when it is seen that digestion experiments have estab- 

 lished the fact that with ordinary mastication from 90 to 95 per cent 

 of the total energy of foodstuffs is completely absorbed. 



The common method of making digestion experiments is to deter- 

 mine the protein, fat, and carbohydrates in the food eaten, and to calcu- 

 late or determine its heat of combustion. The quantities of the same 

 factors are determined in the feces and the ratios of the differences 

 between these two series of values to those of the food itself are reported 

 as the coefficients of digestibility. This method of determining the 

 digestibility is based upon the archaic conception that feces consist 

 primarily of the undigested residue of food. As is now known, undi- 

 gested food forms but a small part of the feces and the ratio is in fact 

 much higher than the commonly stated proportion of 90 to 95 per cent. 

 Even on the basis of the older interpretation, however, the possibility 

 of increasing the digestibility or availability of foodstuffs by extreme 

 mastication seems very small. Furthermore, when we find that this 

 prolonged mastication demands an excess heat production of approxi- 

 mately 17 per cent above the basal value it is easily seen that any 

 advantage gained from a possible increase in the digestibility of the 

 food is more than compensated by the increase in the heat production. 

 The conception of an increase in the digestibility and in the utilization 

 of the energy of foodstuffs as a result of prolonged mastication thus 

 finds no support in fact. 



