150 A BIOMETRIC STUDY OF BASAL METABOLISM IN MAN. 



group. 68 Suppose, for purposes of argument, that the Nutrition Labora- 

 tory tenet that metabolism is proportional to the active protoplasmic 

 mass, stimulus being considered constant, is valid. Let mi, m 2 , m s 

 .... m n be the active protoplasmic masses of a series of individual 

 animals of weights Wi, w 2 , w 3 , . . . . w n and heat-productions in total 



calories per unit of time hi, h 2 , h 3 , 



hi _h 2 _h 3 

 mi 



h n respectively. Then 



h 



or the ratio of the total heat-production to the active protoplasmic mass 

 (the unknown and undoubtedly highly complex and variable stimuli 

 being taken as the same in all cases) is a constant. 



But practically m is never known, and the ratio which has been 

 used is 



hi h 2 h 3 h n 



> > j .... 



Wi Wz W 3 W n 



The observed fact that this ratio is not a constant has been the ground 

 for the rejection of weight as a basis for expressing heat-production 

 and in part the reason for the adoption of body-surface as a standard 

 for this purpose. 



TABLE 51. Correlation between body-weight and heat-production per kilogram of body-weight. 



Now Wi=mi-{-Xi, w z = m 2 -\-x 2 , . . . . , where x denotes the amount 

 of non-active substances which can not contribute to the total metab- 

 olism. The ratios will be influenced by m and x to an extent pro- 



w 



portional to their respective values. Since in the later stages of growth 

 of the vertebrate organism there is a continuous increase in the amount 



88 In passing, it may be noted that there is another objection to these data. The differences 

 in size are in part due to differences in age. Statements in regard to this factor are not explicit 

 in all cases. The smaller animals were those which produced the most heat, both per unit of weight 

 and per unit of surface. But the smaller animals are probably on the whole younger animals and, 

 as pointed out in the chapter on age, there is (in man at least) a decline in the rate of metabolism 

 during the later periods of growth. 



