APPARATUS AND METHODS USED IN THIS RESEARCH. 31 



mental conditions can be obtained without great difficulty. With an 

 infant this condition may only be approximated during sleep. It thus 

 becomes necessary to consider seriously a fundamental change in the 

 principle of studying infant metabolism and, instead of attempting to 

 average the life during a 24-hour period, to use only selected periods 

 with complete muscular repose. 



The muscular activity of infants is twofold: (1) internal muscular 

 activity, consisting of muscular tonus, the movements of the organs of 

 circulation and respiration, and possibly the processes of digestion; 

 and (2) external muscular activity such as the movements of the limbs 

 or vigorous body movement incidental to crying. The internal move- 

 ments can be controlled only by minimizing the after-effects of digestion 

 through the absence of food ; the regular involuntary muscular activity 

 of the respiratory and circulatory system and the muscular tonus can 

 not be altered. On the other hand, the external muscular activities are 

 at a minimum only during complete muscular repose, as in deep sleep. 

 It is thus seen that the ideal conditions for studying the basal or 

 minimum metabolism of infants would be the post-absorptive state — 

 that is, sufficiently long after the last meal to insure that there was no 

 longer an absorption of food materials from the alimentary tract, and 

 during deep sleep when there is complete muscular repose. With very 

 young infants, periods of complete muscular repose can not be expected for 

 any great length of time, probably not for more than two successive hours. 



The difficulties incidental to securing these conditions have prevented 

 researches in this line for many months, if not years; the best method 

 for obtaining them is still to be demonstrated. 



We have, then, two factors to deal with, first, the heat elimination 

 incidental to the specific katabolic stimuli of the food materials accom- 

 panying the digestion and absorption of food; and, second, the internal 

 muscular activity of the infant. If the first of these factors can be 

 eliminated, we have what may properly be termed the basal metabolism 

 unaccompanied by extraneous muscular activity of any kind. 



APPARATUS AND METHODS USED IN THIS RESEARCH. 



Certain inherent difficulties in conducting experiments with infants 

 have undoubtedly delayed the accumulation of a large amount of 

 material in regard to infant metabolism. While researches have been 

 actively prosecuted with domestic animals and with men for many 

 years, the technique for the study of the metabolism of infants has been 

 but slowly developed. Nevertheless, the natural difficulties incidental 

 to the separation of the urine and feces of children have been for the 

 most part overcome by careful technique, so that in hospital wards, at 

 least, experiments on the total urine and fecal secretions can now be 

 satisfactorily made. 



But in a more extensive study of infant metabolism certain difficul- 

 ties occur which are not encountered in a study of the metabolism 



