174 FOOD INGBSTION AND ENERGY TRANSFORMATIONS. 



the heat output directly with as high a degree of accuracy as possible. 

 The respiration calorimeter at Middletown was designed primarily 

 for 24-hour periods. On this basis the agreement between direct and 

 indirect calorimetry has almost invariably proved satisfactory, 

 especially after the apparatus was modified to permit the direct 

 measurement of the oxygen consumption. Previous to the beginning 

 of this research on the influence of food upon the metabolism, no 

 attempt was made to compare direct and indirect calorimetry in periods 

 shorter than 24 hours. When such an attempt was made, it was found 

 that at least with the Middletown calorimeter, which had an air con- 

 tent of approximately 5,000 liters, great difficulty was experienced in 

 the measurement of the residual air and particularly of the residual 

 oxygen, and the possibility of experimental error was thus increased 

 as the periods were decreased in length. Direct measurements of the 

 heat production are also complicated by the difficulty in obtaining 

 accurate measurements of the rectal temperature. Furthermore, the 

 ingestion of large masses of food at a temperature above or below that 

 of the body increases the difficulty, as the length of time required to 

 bring the ingested food and the stomach wall to the temperature of the 

 body is a matter of considerable speculation. Still, the general coinci- 

 dence of the results obtained with both direct and indirect calorimetry 

 lends credence to any deduction drawn from either. It should be said, 

 further, that the researches conducted under the skillful guidance of 

 Dr. E. F. Du Bois, at the Russell Sage Institute of Pathology in New 

 York, have definitely demonstrated the fact that accurate comparisons 

 of the direct and indirect calorimetry can be secured, even in periods 

 as short as one hour. 



Such values for the heat production as were obtained in this research 

 by the indirect method were not computed with the idea of establishing 

 a comparison between the direct and indirect heat values, but simply 

 to obtain a general picture of the course of the metabolism after the 

 ingestion of food. If both the direct and the indirect calorimetry show 

 an increment in the metabolism, there is every reason to believe that 

 such an increment actually took place. While the results obtained 

 with the two methods by no means always agree closely, they yet sup- 

 ply a rough confirmation of each other. As a rule, the tabulated 

 values for the heat production in the calorimeter experiments are those 

 obtained by direct measurement. In one case both sets of figures are 

 given for illustration (see table 101, page 179). Unless otherwise stated, 

 the values for the heat measurements are for the heat actually pro- 

 duced that is, the measured heat elimination corrected, in accord- 

 ance with the usage of this laboratory, 1 for changes in body-weight and 

 body-temperature. 



Benedict and Joslin, Carnegie Inst. Wash. Pub. No. 136, 1910, p. 20. 



