METABOLISM AS AFFECTED BY GROWTH. 145 



METABOLISM PER UNIT OF BODY-WEIGHT REFERRED TO AGE. 



Since it was early recognized that large individuals produce more 

 heat than small ones, the comparison of metabolism values on the 

 basis of mass alone was introduced by some of the first investigators. 

 Thus, we find that Forster 1 in his work with children, expressed the 

 results obtained as metabolism per 10 kg. of weight, attempting thereby 

 a rough grouping of all infants in a 10 kg. class. From this point 

 the step was easy to consider all individuals on the basis of per unit 

 of mass, and physiologists have since that time had a strong tendency 

 to express the values of metabolism for comparative purposes on the 

 basis of the metabolism per kilogram of body-weight. 



A biometric analysis of the metabolism of adults has shown that 

 weight, stature, and age have a specific influence upon metabolism. 

 With adults, the stature of an individual does not appreciably alter. 

 The age influence is small, though definite. The weight changes are 

 considerable, but have rarely been studied with the same individual. 

 On the other hand, with children we have relatively great changes in 

 all three factors, weight, stature, and age, and consequently any com- 

 parative methods used for adults must always be subject to particular 

 criticism when applied to children. It is of course physiologically of 

 much interest to compare the metabolism of a man weighing, say, 

 90 kg. with that of a man weighing 45 kg., if only to find the differ- 

 ence in the absolute metabolism, which would naturally be assumed as 

 greater with the heavier individual. But physiologists have also long 

 sought for some reasonably definite relationship between the physical 

 characteristics of individuals and their metabolism, the simplest of 

 these obviously being body-weight. While the problem is par- 

 ticularly difficult with the age-range in our observations, it is of as 

 great, if not greater, physiological importance to compare the metab- 

 olism of two children varying considerably in age as it is to compare 

 the metabolism for the two men. Thus, the average 5-year-old girl 

 weighs not far from 18 kg., and the average 12-year-old girl weighs 

 approximately twice as much, i. e., 35 kg. So we have here two 

 individuals, one weighing twice as much as the other, as in the case 

 of the two men. 



Two bases for comparison have long been used by physiologists, 

 both of which assume that a definite relationship exists between total 

 metabolism and the physical characteristic of weight and total meta- 

 bolism and the surface area of the body. More recently an entirely 

 different conception has been introduced, in that a biometric analysis 

 of the basal metabolism of a large group of men and women has 

 demonstrated that with each sex there is a distinct correlation between 

 weight and metabolism, between age and metabolism, and between 



'Forster, Amtl. Ber. d. 50 Versamml. deutsch. Naturf. u. Aerzte in Miinchen, 1877, p. 355; 

 also v. Ziemssen's Handbuch der Hygiene, Leipsic, 1882, 1, p. 76. 



