METABOLISM 541 



terns being then cut out, and weighed. From the results it was easy to 

 calculate the actual surface area. 



Where the height and weight are known, a fairly accurate computation 

 of the surface can be secured by using the following formulas : A="W- 425 

 XH- 725 X71.84; A being the surface area in square centimeters; H the 

 height in centimeters; and W, the weight in kilograms. Based on this 

 formula, a chart has been plotted from which the surface area may be de- 

 termined at a glance (Fig. 175). Another method recently employed by 

 Benedict is based on measurements made from photographs of the subject 

 in various poses. 



By the use of these more accurate measurements of body surface, it is 

 now known that, although the surface-area law gives us constant results 

 for the energy output of different individuals of similar build, and offers 

 us a much more accurate basis for comparing those of different laboratory 

 animals, yet it breaks down when applied to men in widely differing states 

 of body nutrition. Thus, in the case of a man who starved for a month, 

 the calorie output per square meter of surface decreased towards the end 

 of the fast by 28 per cent. Obviously, therefore, it would be incorrect to 

 draw conclusions regarding possible changes in energy output of a series of 

 emaciated or corpulent individuals by comparison of their calorie output 

 per square meter of surface with that of normal individuals. 



The determining factor of energy output is undoubtedly the general 

 condition of bodily nutrition the active mass of protoplasm of the body 

 (Benedict). That there is a relationship between the body surface and 

 metabolism is undoubted, but the relationship is not -a causal one. At 

 present, therefore, the only safe method to employ in comparing the 

 metabolism of normal and diseased individuals is that called by Benedict 

 "the group method," in which the metabolism of groups of persons of 

 like height and weight is compared, it being assumed that such individuals 

 have the same general growth relations. For the application of this group 

 method, however, more extensive data will be required than exist at pres- 

 ent, and although some of the conclusions drawn from results computed on 

 the surface-area basis may have to be revised, it is probable that they 

 are in general correct. 



Influence of Age and Sex 



The energy output is low in the newly born ; it increases rapidly during \ 

 the first year, reaching a maximum at about three to six years of age, and 

 then rapidly declining to about twenty, after which' it declines much more 

 slowly. The decline in the earlier years does not proceed steadily, how- 

 ever, for at the period just preceding the onset of puberty a decided in- 

 crease becomes evident, indicating that at this period the metabolism of 



