NORMAL PROCESSES OF ENERGY METABOLISM 621 



addition to statistical criteria, physiological norms of growth which will 

 simplify the whole problem of infant feeding. At present it is impossible 

 to formulate even a satisfactory physiological definition of the growth rate. 

 Merely to emphasize the multiplicity of factors contending for energy be- 

 fore growth can be wholly satisfied and to visualize what is known of their 

 quantitative relations, the following tabular arrangement may be presented: 



Basal metabolism 60 Cal. per kgm. 



Activity metabolism (12 to 40% of Basal) 7.2 to 24.0 



'Loss by fcces ( 10 to 15% of Basal ) 6.0 to 9.0 " " 



Dynamic action ( 10 to 20% of Basal) 6.0 to 12.0 " " 



Growth (10 to 20% of Basal) 6.0 to 12.0 



Total 85.0 to 120.0 " " 



This estimate is liberal in all divisions of the caloric needs. Careful 

 reckoning of the fate of the food energy cannot account for more than 

 is here allowed except in such extreme restlessness as would place the case 

 clearly in the pathological field. 



This classification is not to be looked upon as anything fixed. The 

 basal requirement increases steadily up to one year of age or later. The 

 requirement for activity increases steadily in the absolute sense as the 

 child spends more and more time awake, but it is not yet certain whether 

 the increase is also relative to basal needs on the basis of weight or surface. 

 Utilization is not known to change with age, the results with very young 

 infants being often quite as favorable as with older ones. Dynamic action 

 has not been sufficiently studied to say definitely whether it is greater 

 or less as more and more food is ingested at a meal. There are indications 

 that it is greater. Finally, the requirement for growth relative to weight 

 increases certainly for the first three months and possibly up to six months, 

 after which it becomes retarded. We have yet to learn whether the 

 growth increment (in calorics) advances more or less rapidly than the 

 basal requirement. Van Pirquet, who -has recently invented a system of 

 computing food requirements, obviously based iipon energy units (and 

 merely disguised as "nems") estimates the growth quota at one-third the 

 minimal or maintenance requirement. From the observations of Soxhlet 

 on the calf it has been estimated that this animal can utilize over 40 per 

 cent of the food energy for growth but an infant of 7 months was 

 able at best to so dispose of only 13 per cent. Mere fattening should not 

 of course be included in growth. 



E. Energy Metabolism of Pregnancy 



The energy metabolism of the fetus immediately before birth has been 

 determined separately only by noting the difference in respiratory ex- 

 change of the mother produced by clamping off the umbilical cord (see 

 page 619). This method, however, is open to serious objection and has 



