METABOLISM 539 



so much energy as is the case, for example, when fats are burned. This 

 peculiar property of proteins accounts for their well-known heating qual- 

 ities. It explains why protein composes so large a proportion of the diet of 

 peoples living in cold regions, and why it is cut down in the diet of those 

 who dwell near the tropics. Individuals maintained on a low protein diet 

 may suffer intensely from cold. 



If we add to the basal heat production of 1,680 C. another 168 C. (or 

 10 per cent) on account of food, the total 1,848 C. nevertheless falls far 

 short of that which we know must be liberated when we calculate the 

 available energy of the diet, which we may take as 2,500 C. What be- 

 comes of the extra fuel? The answer is that it is used for muscular work. 

 Thus it has been found that if the observed person, instead of lying down 

 in the calorimeter, is made to sit in a chair, the heat production is raised 

 by 8 per cent, or if he performs such movements as would be necessary for 

 ordinary work (writing at a desk) it may rise 29 per cent that is to say, 

 to 90 C. per hour. There is, however, practically no difference in the en- 

 ergy output of a person lying flat or lying in a semi-reclining posi- 

 tion, as in a steamer chair. Allowing eight hours for sleep and sixteen 

 hours for work, we can account for about 2,168 C., the remaining 300 odd 

 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 Icilo 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 : 



