90 METABOLISM AND GROWTH FROM BIRTH TO PUBERTY. 



A careful control of the muscular activity was secured through 

 graphic records. With the youngest children, and especially the 

 infants, however, it was not possible to obtain the required degree of 

 muscular repose when there was no food in the stomach, because the 

 want of food caused restlessness and frequently crying. In recognition 

 of this difficulty, it was necessary to compromise by supplying as 

 small an amount of food as would produce comfort and consequent 

 muscular repose. This amount of food, even though small, inevitably 

 influenced the metabolism. When older children were studied, it 

 was possible to postpone the observations after a meal for a longer 

 period of time, even for 4 or 5 hours. Accordingly, in the subsequent 

 analysis of the metabolism data for the children of various ages, it 

 must be remembered that as the age of the children increases the 

 influence of the ingestion of food decreases correspondingly. The 

 basal metabolism of children under 2 years of age can thus be com- 

 pared with that of older children only on the distinct understanding 

 that the values for the basal metabolism for the younger children are 

 higher than they normally would be, owing to the influence of food. 



The quantitative measurement of the influence of the ingestion of 

 food upon the metabolism of infants should be given special study, 

 such as has been done for adults in a previous publication from this 

 laboratory. 1 Certain more or less fragmentary evidence has, however, 

 been accumulated in the present research with children, in part by 

 design and in part by accident. With several of the children, a pro- 

 longed series of observations was made after food had been taken, 

 some of these continuing 9 or 10 hours without interruption. The 

 results of these observations give some information as to the possible 

 influence of food. Here again we find a difficulty in interpretation in 

 that the somewhat subtle influence of food is profoundly affected by a 

 change in the activity; hence only periods of comparable muscular 

 activity, or preferably muscular repose, can legitimately be used to 

 determine the influence of food upon the metabolism. That is, it must 

 be assured that the increase in the metabolism after food is not due 

 to muscular activity before assuming it is due to the stimulus of food. 



The data contributing to a study of this problem are brought to- 

 gether in table 23, in the order of increasing age. Unfortunately, 

 long observations during which the minimum metabolism after feeding 

 has been measured were made only with relatively young children, 

 the oldest being but 13^ months old. This table gives not only the 

 age and weight of the individual children, but also the energy content 

 of the food, the tune of feeding, the interval between the food and the 

 end of the period of observation, the heat produced on the basis of 

 24 hours, the pulse-rate, and the relative activity. The time when 

 presumably basal metabolism was reached is indicated by an italiciza- 

 tion of the lowest value for heat. 



1 Benedict and Carpenter, Carnegie Inst. Wash. Pub. No. 261, 1918. 



