30 GASEOUS METABOLISM OF INFANTS. 



with men by Atwater and his associates at Wesleyan University, 

 Middletown, Connecticut, where it was shown in experiments of long 

 duration that the heat output as measured directly by the respiration 

 calorimeter and the heat output as computed from the respiratory 

 exchange agreed remarkably well. It should be pointed out, however, 

 that these computations were based upon 24-hour periods. In certain 

 experiments the computation has likewise been successful for periods as 

 short as 6 hours, but it remained for Howland 1 to demonstrate with 

 Lusk's calorimeter the complete agreement of the direct calorimetric 

 measurements and of the computation from the gaseous exchange for 

 short periods and particularly with an infant as subject. 



Howland has, temporarily at least, forsaken direct calorimetric 

 research, as he is not now supplied with a respiration calorimeter, but it 

 is much to be hoped that these few observations, which imply such a 

 remarkable agreement between the direct and indirect calorimetry, 

 may be extended in the near future to cover other cases. Until later 

 evidence disproves this assumption, workers in this field are perfectly 

 justified in assuming that the comparison between direct and indirect 

 calorimetry has been made with infants with more than ordinary scien- 

 tific accuracy. This being the case, the field is open for making a large 

 number of metabolism experiments with the respiration apparatus in 

 laboratories and institutions where a respiration calorimeter for direct 

 calorimetry is not available. 



BASAL METABOLISM. 



While the normal life of the infant is a relatively simple and constant 

 one, yet it does include periods of muscular activity which vary greatly, 

 the extremes ranging from perfect muscular repose during deep sleep to 

 the violent exercise incidental to vigorous crying. As a result of these 

 changes in muscular activity, the output of heat would likewise vary 

 largely, with a minimum output during sleep and quiet and a maximum 

 during the period of crying. An attempt has been made to find the 

 average value for the heat output of an infant by experiments with 

 24-hour periods, thus securing an average for the life of the day; but 

 when one considers that the difference between the heat output in 

 complete muscular repose during sleep and the heat given off when the 

 infant is crying vigorously may be as great as 60 or more per cent, it 

 will be seen that this method of averaging does not furnish information 

 with regard to the minimum metabolism. 



With adults, the best condition which has been found for a basis of 

 comparison has been when the subject was in complete muscular repose 

 and in the so-called " post-absorptive" state, %. e., when absorption of 

 material from the alimentary tract had ceased, this being with adults 

 generally 12 hours after the last meal. With an adult who is capable 

 of a certain degree of muscula r relaxation and repose, suitable experi- 



^owland, Trans. 15th Int. Congress on Hygiene and Demography, Washington, 1913, 2, p. 451. 



