METABOLISM 575 



C. that are required to bring the total to that which we know, from statis- 

 tical tables of the diets of such workers, to be the actual daily expenditure, 

 being due to the exercise of walking. If the exercise is more strenuous, 

 still more calories will be expended ; thus, to ascend a hill of 1,650 feet at 

 the rate of 2.7 miles an hour requires 407 extra calories. Field workers 

 may expend, in 24 hours, almost twice as many calories as those engaged 

 in sedentary occupations. 



Standard for Comparison 



"When the energy output per kilo body weight is determined in animals 

 of varying size, the values are greater the lighter the animal. This is 

 evident from the following results obtained on dogs: 



Weight of dog Heat production in calories 



per kilo per day 



(1) 31.2 35.68 



(2) 18.2 46.2 



(3) 9.6 65.16 



(4) 0.5 66.07 



(5) 3.19 88.07 



(Rubner) 



When, on the other hand, instead of body weight, the area of the sur- 

 face of the body is taken as the basis of calculation, results that are almost 

 constant are obtained. Following are the results in the above animals on 

 this basis : 



Heat production in calories 



Surface in square cm. per square meter of sur- 



face per day 



(1) 10,750 1036 



(2) 7,662 1097 



(3) 5,286 1183 



(4) 3,724 1153 



(5) 2,423 1212 



(Rubner) 



Such results have prompted observers to conclude that the determining 

 factor in the calorie output of warm-blooded animals is the relative sur- 

 face of the animal. This is greater the smaller the animal, with the con- 

 sequence that heat is more rapidly lost to the surrounding air from the 

 surface, thus requiring more active combustion. Until quite recently it has 

 been generally believed that such a relationship between body surface and 

 heat production did actually exist, but, thanks to the work of F. G. Bene- 

 dict 7 and E. F. and D. Du Bois 6 , it is now known that the calculations were 

 based upon incorrect computations of the body surface. In the older re- 

 searches the calculation was made by using a formula known as Meeh's, in 

 which weight was multiplied by a certain factor (viz., 12.312 x ^weight). 

 Du Bois, however, has shown that an average error of 16 per cent is in- 

 curred in using this formula. For more accurate measurement of the 



