INTRODUCTION. O 



stimulating the cells to greater activity. This stimulus is greatest 

 with protein foods and least with fats. To secure comparable results, 

 therefore, the ideal condition would be to study all subjects in the 

 post-absorptive state, i. e., about 12 hours after the last meal, when the 

 influence of the preceding diet had disappeared. With such differ- 

 ences in dietetic habits, times of eating, and stomach capacity as 

 exist between infants a year old and children 12 years old, the obtaining 

 of ideally comparable conditions in this respect is likewise difficult. 



The third factor to be considered in determining the basal meta- 

 bolism is that of sleep. While certain observations made in a number 

 of laboratories imply that sleep, per se, is without profound effect 

 upon the metabolism, yet in the light of our experience in this labor- 

 atory during the past decade we are strongly inclined to think that 

 this is an erroneous conception. Furthermore, the opportunities for 

 error in the usual methods of determination of the metabolism during 

 deep sleep are great. When breathing appliances, such as mouth- 

 piece, nosepieces, or mask, are used in our experiments, the subjects 

 have been for the most part required to keep awake on the general 

 ground that with sleep the facial muscles relax, especially those about 

 the mouth, and there is danger of leakage of air under these conditions. 

 Practically the only method of experimenting which gives dependable 

 results with a sleeping subject is the chamber method, i. e., with the 

 subject asleep inside one of the several forms of respiration chamber. 

 That sleep is a factor of great significance was clearly demonstrated 

 in this laboratory with the subject of a fasting experiment. 1 Recent 

 experiments, as yet unpublished, show that the metabolism of a 

 sleeping subject differs appreciably from that of a subject awake, 

 even though in both periods there is the greatest degree of muscular 

 repose. 



A cursory examination of the data presented in the literature on 

 the metabolism of children shows a wide diversity of results. The 

 literature on the metabolism of infants, especially of the new-born, 

 has already been reviewed briefly in the two publications giving the 

 results of our earlier studies. 2 While it is unnecessary to refer here 

 in detail to the work already cited, it seems desirable, before giving 

 the results of our own observations, to supplement the previous review 

 of the literature by a citation of the observations made by other 

 workers with older children. 



1 Benedict, Carnegie Inst. Wash. Pub. No. 203, 1915, pp. 343 ct seq. 



2 Benedict and Talbot, Carnegie Inst. Wash. Pub. No. 201, 1914, pp. 11 to 22, and Carnegie 



Inst. Wash. Pub. No. 233, 1915, pp. 12 to 38. 



