166 GASEOUS METABOLISM OF INFANTS. 



INFLUENCE OF VARIATIONS IN THE COMPOSITION OF THE BODY UPON TOTAL 



HEAT-PRODUCTION. 



Since a gross disturbance in the relationship existing between the 

 body-weight and the body-surface as computed from the body-weight is 

 highly improbable, whether the infant is atrophic or well nourished, it 

 is important to find out, if possible, if any relationship exists between 

 the general composition of the body and the total heat-production. Our 

 data are sufficiently extended to permit a somewhat incomplete discussion 

 of this important phase of the comparisons. 



Heretofore, all workers in metabolism have considered only the 

 relationship between body-weight and metabolism, or body-surface 

 and metabolism. Since the body-surface is assumed to have a direct 

 relationship to the body-weight, it can be seen that body-weight is the 

 only fundamental factor which has thus far been seriously considered 

 by investigators in comparing the metabolism of different infants. 



It is obvious that when two infants are of the same weight, the 

 shorter one will have the larger proportion of fat. Furthermore, with 

 two infants of the same length but of different weights, the heavier 

 infant will have the larger proportion of fat. It can be seen, therefore, 

 that an atrophic infant, weighing 4 kilograms and 65 cm. long, when 

 compared to a well-nourished infant of the same weight and length, would 

 have a smaller proportion of fat. Moreover, an atrophic infant, to have 

 the same weight and length as a normal infant, must obviously be older, 

 and we here find a new factor entering into the comparison of infants; 

 as yet the element of age has received scant attention. Table 31 shows 

 that in a number of instances infants with approximately the same 

 body-weight and the same height differ greatly in age. Unfortunately 

 our data are not so extensive as to enable us to compare infants with 

 absolutely the same body-weight and height, but a number of compari- 

 sons are justifiable and these have been included in table 36, which 

 gives eight series of comparisons of the total heat produced, the heat- 

 production per kilogram of body- weight, and the heat-production per 

 square meter of body-surface for infants with the same body-weight and 

 height but of different ages. The difficulties incidental to measuring 

 exactly the length of infants make these measurements slightly proble- 

 matical and there may be a variation of plus or minus 1 cm. We have, 

 therefore, compared infants whose lengths do not vary more than 1 cm. 

 The variations in weight are all within a few tenths of a kilogram. 



We note instantly several striking points in the data as presented. 

 In each comparison the values for the younger infant are given first, 

 and it will be seen that the older infant has invariably the larger total 

 heat-production. The greatest difference is 182 calories in the com- 

 parison of M. M. with J. M., the lowest difference being that of 16 

 calories between E. N. and D. M. Aside from this latter comparison, 

 the increase in the heat-production for the older infants is very con- 

 siderable. The heat-production per kilogram of body-weight and per 



