A CRITIQUE OF THE BODY-SURFACE LAW. 153 



weight and in calories per square meter of body-surface, or even 

 simpler tests of the relative variability of the two sets of measures, are 

 quite inadequate as criteria for selecting the best method of correcting 

 for the size of the individual, a detailed treatment of this question is 

 in order. 



In the past the physiologist has been seeking to determine whether 

 metabolism is proportional to body-weight or to surface-area. The 

 difficulty has lain in the fact that body-weight and body-surface area 

 are correlated characters. If individuals varied in weight only, and not 

 in physical configuration, body-surface would be given at once by 

 kX^w 2 . This is, indeed, the basis of the Lissauer and the Meeh 

 formulas. Thus if heat-production be in any degree correlated with 

 one of these physical measurements, it must be in some degree corre- 

 lated with the other. The degree of correlation between metabolism 

 and either of the physical measurements due to its correlation with the 

 other will depend upon the intensity of the correlation between the 

 two physical measurements. 



Thus the problem of the physiologist is not so simple as has been 

 suggested when it is said that he must determine " whether metabolism 

 is proportional to body-weight or to surface-area." What he has to 

 do is to determine whether it is more nearly proportional to body-surface 

 or to body- weight. 



The difficulty in doing this has not been due solely to the fact that 

 large series of actual measurements of body-surface and metabolism 

 have not been available, but also to the fact that the physiologist has 

 had no means of comparing directly the degree of interdependence of 

 body-weight measures and metabolism and body-surface measures and 

 metabolism. Results expressed in calories per kilogram of body-weight 

 are unquestionably better than those expressed in calories per indi- 

 vidual irrespective of size for standard periods of time. Results 

 expressed in calories per square meter of body-surface are also more 

 nearly comparable from individual to individual than those expressed 

 merely in number of calories per individual for the same standard 

 periods of time. The fundamental question is: Are results expressed 

 in calories per square meter of body-surface so constant from individual 

 to individual as to justify the statement that heat-production per 

 square meter of body-surface is a constant? Or, in other words, to 

 justify the statement that it is a physiological law that organisms have 

 a heat-production proportional to their body-surface? 



Now the closeness of agreement of a series of figures which shall 

 be demanded to justify their designation as representing a constant 

 must depend, in the last analysis, upon the judgment of the workers in 

 a particular field. Specifically, in the case of metabolism investigations, 

 physiologists, not physical chemists or astronomers, must decide how 

 great a variation in the number of calories per square meter of surface 



