126 A BIOMETRIC STUDY OF BASAL METABOLISM IN MAN. 



sions by the use of partial correlation formulas. If the partial correla- 

 tion between age and metabolism for constant stature and body-weight 

 be compared with the gross or uncorrected correlations, it will be found 

 that the numerical values of the interdependence of the two variables 

 has been raised from 0.31 to 0.50 for the men and from 0.20 to 

 0.50 for the women. 



These statistical results indicate in the clearest way the existence 

 of fundamental changes in the tissues and their physiological activities 

 with age. This evidence inheres not merely in the fact that the intens- 

 ity of the interrelationship is increased when correction is made for the 

 disturbing influence of body mass in both of the sexes, but that when 

 these corrections are made the results for the two sexes are rendered 

 very nearly identical. 



Expressing the relationships between age and metabolism in terms 

 of the actual decrease in daily heat-production per year, we note that 

 this amounts to about 7.15 calories in men and 2.29 calories in women. 

 Of course men and women differ greatly both in stature and weight 

 and in daily heat-production. The decrease in heat-production per 

 kilogram of body- weight is more nearly identical in the two sexes, i.e., 

 0.112 calorie in men and 0.124 calorie in women. The decrease in 

 calories per square meter of body-surface area, as estimated by the 

 Du Bois height-weight chart, is 3.60 calories per 24 hours per year in 

 men and 2.96 calories per 24 hours per year in women. 



The problem of the regression of heat-production (either gross 

 heat-production or heat per kilogram of body-weight or per square 

 meter of body-surface) on age is one of both great theoretical interest 

 and practical importance. It is of great physiological interest to deter- 

 mine the rate at which metabolism decreases with advancing years, 

 to ascertain whether this changes at some period of life, and (if so) how 

 these rates of change or periods of change correspond with other physio- 

 logical periods. Certainly this phase of the problem of growth, age, 

 and death should take rank with the others which have been investi- 

 gated. The quantitative statement of the laws governing the change 

 in metabolism with age is the first logical step in the analysis of this 

 problem. 



From the practical standpoint, determination of these laws is 

 essential for the calculation of standard control values to be used as a 

 basis of comparison in physiological and pathological research. 



Tests of the rate of change throughout the age-range of adult life 

 indicate that it is essentially uniform, so that, as far as the data at 

 present are adequate to show, it can be expressed as well by the slope 

 of a straight line as by a curve of a higher order. 



The data for the lower and higher age-groups are still inadequate, 

 and the exact limits of applicability of a straight line for the expression 

 of changes in metabolism with age must remain a problem for future 

 consideration. 



