148 METABOLISM AND GROWTH FROM BIRTH TO PUBERTY. 



in the heat production per kilogram of body-weight, the chart certainly 

 shows with children a great diversity with age changes. The figures 

 indicate a somewhat lower general metabolism per kilogram of body- 

 weight during the first 6 months, with the highest metabolism per 

 kilogram throughout the age-range of this study to be at 1 or 2 years 

 of age. While the values for the period from 3 to 5 years are but few 

 in number, they indicate a rather rapid fall; after the age of 5 years 

 the decline is definite, though not so marked. The small number of 

 individuals studied over 13 years of age hardly justifies a continuation 

 of this curve beyond that period. 



The heat production per kilogram of body-weight has frequently 

 been considered as somewhat of a physiological constant, but we find 

 on this chart a range in values extending from 29 to 64 calories per 

 kilogram, in other words, a variation of over 100 per cent. Even 

 during the first year of life there is a range of from 41 to 64 calories. 

 After the fifth year the range is from 29 to 48 calories. While the 

 smoothed curve laid on this chart does imply a slight general trend, 

 there is nothing here approximating mathematical constancy, and 

 certainly nothing that can be considered as a physiological law estab- 

 lishing a relationship between the heat production per kilogram of 

 body-weight and the age. 



The charts comparing total calories do not permit a comparison of 

 individuals at different weights or different ages; hence this method 

 is of value, since it supplies some suggestion as to the relative intensity 

 of metabolism at different ages. On the assumption, erroneous though 

 it is, that each kilogram of body-substance has the same heat-producing 

 capacity, one can conclude that at the age of 1 to 2 years there is a 

 greater relative intensity of metabolism than at any other period of 

 life up to 13 years, and that the young organism per unit of mass 

 produces a larger amount of heat than does the older. 



It would appear from this chart that with children we are dealing 

 with physiological entities and not with crystalline structures, each 

 having its mathematically established planes. Although the method 

 of expressing the metabolism on the basis of per kilogram of body- 

 weight permits a very gross comparison of different individuals, the 

 entire absence of uniformity and the wide scatter of the points about 

 the central tendency show that such comparison can have but very 

 slight individual mathematical significance. Between the ages of 5 

 and 13 years, although the points are widely scattered, it would appear 

 as if a straight line represented the trend as well as any other form of 

 curve. This is of significance as being preliminary to the straight-line 

 tendency exhibited with male adults, and this curve therefore brings 

 out primarily the high metabolism per unit of mass noted with boys 

 at about the age of 1 to 2 years. 



