A CRITIQUE OF THE BODY-SURFACE LAW. 195 



12. RECAPITULATION AND DISCUSSION. 



According to Rubner's "law" or the body-surface "law" the heat- 

 production of an organism is proportional to its superficial area. 

 Otherwise stated, heat-production measured in calories per square 

 meter of body-surface is a constant. 



In this chapter we have outlined the historical development of the 

 physiologist's belief in the validity of this "law," have discussed 

 certain experimental evidences for its inapplicability to man, and have 

 tested its validity by the application of statistical criteria to the largest 

 available series of data on human basal metabolism. 



Historically, the idea of proportionality between body-surface and 

 heat-production was originally based upon the assumed physical law, 

 confused by many physiologists with Newton's law of cooling, that 

 heat-loss is proportional to the surface-areas of similar solids, and upon 

 the further assumption that heat is produced to maintain the body- 

 temperature constant. The idea of a causal relationship between 

 body-surface and heat-production has frequently been strongly empha- 

 sized in foreign writings and is distinctly to be inferred from those of 

 a number of American writers. 



The validity of the body-surface law has long been held in question 

 by the workers at the Nutrition Laboratory. In a series of papers 84 

 its universal applicability was challenged and it was stated that the 

 loss of heat from the body-surface could not be considered as the deter- 

 mining factor of metabolism. Certain factors, such as sex, age, and 

 athletic training, were shown to affect the basal metabolism, even when 

 measured on the basis of calories per square meter of body-surface, 

 thus affording illustrations of exceptions to the so-called law. 



In dealing with the problem of the constancy of heat-production 

 per square meter of body-surface in the human species two phases 

 must be recognized. The first is that of the constancy of heat-produc- 

 tion within the same individual at different times. The second is that 

 of the constancy of heat-production per square meter of body-surface 

 from individual to individual. 



From the side of controlled individual experimentation it has been 

 shown that animals at different nutritional levels, or under varying 

 external conditions, differ in their heat loss to a degree which can not 

 be explained by differences in body-surface. 



A man who fasted 31 days showed a decrease of 28 per cent in heat- 

 production per square meter of body-surface. Squads of college men 

 recently investigated on prolonged reduced diet at the International 

 Y. M. C. A. College at Springfield gave ample corroborative evidence. 

 Such experiments can be interpreted only as proof of the inapplicability 



84 Benedict, Emmes, Roth, and Smith, Journ. Biol. Chem., 1914, 18, p. 139; Benedict and 

 Roth, ibid, 1915, 20, p. 231; Benedict and Smith, ibid., 1915, 20, p. 243; Benedict and 

 Emmes, ibid., 1915, 20, p. 253; Benedict, ibid., 1915, 20, p. 263. 



