108 Metabolism of Healthy Max. 



stant, not only from day to day, but also in experiments with an interval of 

 several months. 



In the results for heat production there is the concordance that one would 

 expect after having observed the constancy of carbon-dioxide excretion and 

 oxygen consumption. Differences of 10 calories are relatively uncommon; 

 usually the agreement between duplicate experiments is 3 or 1 calories. These 

 experiments show conclusively, therefore, that in conditions of rest, either with 

 or without food, and likewise during sleep, the metabolism of the same indi- 

 vidual is surprisingly constant from day to day. 



With such constancy in metabolism under conditions of rest, it is to be re- 

 gretted that special experiments have not been made to study the constancy 

 during muscular work. No experiments on work or when the subject is exer- 

 cising are here included, for it is verv difficult to insure the exact amount of 

 muscular activity in an experiment of this character unless a special form of 

 ergometer is employed, such as was used in the previously published experi- 

 ments on muscular work. 



DUPLICATION IN EXPERIMENTS DURING MUSCULAR WORK. 



A striking instance of constancy during work with a bicycle-ergometer has 

 appeared in a previously published report on muscular work, 1 and although 

 none of the new experiments presented in this publication deal with the ques- 

 tion of muscular work, it is possible to refer briefly to the results there ob- 

 tained. From those results it is seen that with the same individual, exercising 

 the same amount, the metabolism is likewise remarkably constant. This is 

 particularly well shown in the table on page 31 of that report, where the results 

 of the experiments with the professional athlete are calculated to the per hour 

 basis. It is there seen that experiments on the bicycle-ergometer, with the 

 same amount of work per hour, were made on October 22, 1904, and January 

 23, 1905, two experiments being made on the latter date. In these three ex- 

 periments, the heat equivalent of muscular work performed varied from 114 

 to 116 calories per hour. The total heat production varied from 608 to 626 

 calories, and the carbon-dioxide production from 208 to 231 grams. The 

 oxygen consumption was determined in only two of the experiments, the amount 

 in one being 183 grams and in the other 175 grams per hour. Considering the 

 large amount of mechanical work performed, with the enormous heat production 

 of over 600 calories per hour, the agreement between these duplicate experi- 

 ments is certainly striking. All the evidence furnished by the experiments 

 with the respiration calorimeter therefore substantiates fully the hypothesis that 

 with the same individual under similar conditions of bodily activity and diet 

 the metabolism is relatively constant. 



In the following discussion of the results of the experiments in this report, 

 special emphasis is laid upon the experimental period from 1 a. m. to 7 a. m., 



1 Benedict and Carpenter, U. S. Dept. Agr., Office Expt. Stas. Bui. 208, 1909. 



