CHANGES IN METABOLISM WITH AGE. 125 



average pulse-rate found by Whiting for these data was 74.22, which 

 is 12.96 beats or 21.2 per cent higher than our average for men. Pos- 

 sibly pulse-rate in older individuals is more susceptible to increase 

 due to physiological or physical activity than it is in younger. If so, 

 this difference in the conditions under which the rates were measured, 

 may be sufficient to account for the differences in the correlations. 



4. RECAPITULATION AND GENERAL CONSIDERATIONS. 



In this chapter we have considered the relationship between age 

 and basal metabolism in adult men and women. The significance of 

 such an investigation is twofold. From the theoretical side the mor- 

 phological and physiological changes which accompany the aging of the 

 individual constitutes one of those groups of fundamental problems 

 which has always attracted the interest of biologists and of the medical 

 profession. Any contribution of actual fact is a valuable addition to 

 the vast literature. From the practical standpoint, a knowledge of 

 the quantitative relations between age and basal metabolism is essen- 

 tial for the establishment of standard controls to be used in applied 

 calorimetry. 



The results of the present study show that throughout the whole 

 range of what we commonly designate as adult life the heat-production 

 of the individual decreases. The correlation between age and heat- 

 production is therefore negative in sign, lower daily heat-production 

 being associated with greater age. The gross correlations are of the 

 order 0.31 for men and 0.20 for women. 



Daily heat-production has been shown in the foregoing chapter to 

 be correlated with both stature and body-weight. Since in adult life 

 these vary for the most part independently of age, it is evident that if 

 the correlation between age and metabolism be due to definite and 

 progressive physiological changes in the tissues of the organism with 

 increasing age, the measure of the correlation between age and metab- 

 olism will be lowered by the disturbing influence of these factors. 



Correcting for the influence of stature makes relatively little differ- 

 ence in the intensity of the correlation between age and metabolism. 

 Correction for the influence of body-size by expressing heat-production 

 in calories per kilogram of body-weight raises the numerical value of 

 the correlation coefficient for age and heat-production from 0.31 to 

 0.41 in the total series of men and from 0.20 to 0.49 in the total 

 series of women. If correction be made for body-size by expressing 

 heat-production in calories per square meter of body-surface as esti- 

 mated by the Du Bois height-weight chart, the correlation is increased 

 (in the negative direction) from 0.31 to 0.47 for the men and from 

 -0.20 to -0.52 for the women. 



Comparable results are obtained by correcting the correlations 

 between age and heat-production for the influence of physical dimen- 



