METABOLISM AS AFFECTED BY GROWTH. 131 



When children are considered as a class, the gross differences in age, 

 weight, and stature make it extremely difficult to find two children of 

 exactly the same age, weight, and height. Certainly any series of 

 metabolism measurements would have to be greatly extended and 

 include a large number of subjects to secure two individuals who were 

 strictly comparable in these respects. The time and expense required 

 for such measurements would prohibit any attempt to make sufficient 

 studies with a large number of individuals for the establishment of 

 probable standards for the many combinations of the four variables- 

 sex, age, weight, and height. This likewise holds true for adults; 

 and yet it is very important, physiologically at least, to have some 

 conception of differences in metabolism with different individuals. 



METHOD OF GROUPING DATA. 



Any plan for the comparative study of the metabolism of children 

 involves one or more forms of classification. Following the custom of 

 physiologists, we have charted the values first on the basis of age, then 

 of body-weight, and finally of body-surface. Since with adults it has 

 been clearly shown that there is a sexual differentiation, it seems desir- 

 able to consider the boys and girls separately, even though a critical 

 analysis of the data for new-born babies 1 showed no sexual differen- 

 tiation during the first week of life. A comparison of the various 

 individual charts (figs. 15 to 21), in which the sex was indicated, or 

 even a superficial inspection of these general charts (figs. 22 to 47) 

 for boys and girls, gives but little, if any, suggestion of a sexual differ- 

 entiation. Such grouping is of value, however, for use in a more 

 thorough comparison of all the data in several large plots (see figs. 

 48 to 51, pages 179 to 181), by which the differences in the results due 

 to sex may be discerned. 



As previously stated on page 101, during the period of growth 

 represented by the observations in this study there are such rapid 

 changes in weight and age that it has been considered perfectly legiti- 

 mate, when appreciable variations in these two factors occur, to regard 

 the child as a different individual and to plot the values accordingly 

 in these group charts. In determining the points on the charts in 

 figures 22 to 47, each child was considered a new individual after 

 (1) an increase in weight of 1 kg. for children weighing less than 10 

 kg.; (2) an increase in weight of 10 per cent for children over 10 kg.; 

 (3) an increase in age of 6 months. Change in height per se was not 

 considered. While the classification for weight and age was not 

 strictly adhered to, there was but little deviation from the rule. So 

 far as possible, breaks in the continuity of evidence were avoided, and 

 if an observation was made at the end of a series, it was not necessarily 



1 Benedict and Talbot, Carnegie Inst. Wash. Pub. No. 233, 1915; Harris and Benedict, Carnegie 

 Inst. Wash. Pub. No. 279, 1919. 



