OBESITY 31 



excessive eating, or to too little muscular activity, or more usually to a 

 combination of both factors. There is no evidence that mental exertion 

 leads to an increased consumption of energy. There remain a few in- 

 stances, probably only a small fraction of one per cent, in which a lowered 

 basal metabolism is responsible, wholly or in part, for the obesity, though 

 even here it is of course necessary that the calories taken in should be in 

 excess of the consumption. 



The normal person following his natural appetite, takes, according 

 to a universal biological law, just what food he needs, and his weight, 

 with slight variations, remains constant. Under the conditions of modern 

 life, however, it often happens that people overeat, or continue their old 

 habits of eating after changing from an active to a sedentary form of life. 

 The result is obesity. . How small a daily excess in the food will, if long 

 continued, lead to corpulence is shown by a calculation of von Noorden(a), 

 who assumes a daily excess consumption of 200 calories, which is con- 

 tained in 10 ounces of milk, or two large oranges. This would lead in the 

 course of a year to a deposition of 7.8 kg. of fat, or allowing for the water 

 content of fat tissue, an increase in weight of 11 kg. (24 Ibs.). 



The Energy Requirements of the Body 



The Basal Metabolism. By this term is understood the amount of 

 energy consumed by the body when completely at rest and in a fasting 

 condition, at least 14 hours after the last meal. If this is reckoned as 

 calories per square meter of body surface, it is practically constant for 

 healthy men and animals of all sizes, as first shown by Rubner(a). The 

 calory production per unit of weight or height is also fairly constant 

 for persons of average build, but is not a reliable criterion in the case 

 of fat or very thin individuals. 



Until very recently the old Meeh formula has been used to determine 

 the surface area. This is based on the law that the surfaces of similar solids 

 are proportional to the % power of their volumes. Meeh made actual 

 measurements of the surface area of a number of persons, and using the 

 weight in kilograms to represent the volume, found that the % power 

 of the weight, multiplied by a constant (12.312) gave results which 

 agreed within seven per cent with his measurements. Subsequent work 

 has developed the fact that this formula is fairly accurate for individuals of 

 average build, but not for those of unusual shape, giving results which 

 in the case of the obese are much too high (as much as 40 per cent). 



Du Bois and Du Bois have recently developed a formula based 

 on linear measurements of the various parts of the body, which gives 

 a very close approximation of the surface area, as determined by actual 



