

THE ENERGY BALANCE. 87 



mal ; thus, a man doing work on a bicycle ergometer in the Bene- 

 dict calorimeter gave out as actual heat, 4,833 C., and did work 

 equalling 602 C., giving a total of 5,435 C. By drawing up 

 a balance sheet of his intake and output of food material during 

 this period, it was found that the man had consumed an amount 

 capable of yielding 5,459 C., which may be considered as ex- 

 actly balancing the actual output. 



Having thus satisfied ourselves as to the extreme accuracy of 

 the method for measuring energy output, we shall now consider 

 some of the conditions which control it. To study these we must 

 first of all determine the basal heat production, that is, the small- 

 est energy output which is compatible with health. This is as- 

 certained by allowing the man to sleep in the calorimeter and 

 then measuring his calorie output while he is still resting in bed 

 in the morning, and fifteen hours after the last meal. When 

 the results thus obtained on a number of individuals are calcu- 

 lated so as to represent the calorie output per kilogramme of 

 body weight in each case, it will be found that 1 C. per kilo per 

 hour is discharged. That is to say, the total energy expenditure 

 in 24 hours in a man of 70 kilos, which is a good average weight, 

 will be 70 X 24 = 1,680 C. 



When food is taken the heat production rises, the increase over 

 the basal heat production amounting for an ordinary diet to 

 about ten per cent. Besides being the ultimate source of all the 

 body heat, food is therefore a direct stimulant of heat production. 

 This specific dynamic action, as it is called, is not, however, the 

 same for all groups of foodstuffs, being greatest for proteins and 

 least for carbohydrates. Thus, if a starving animal is given an 

 amount of protein which is equal in calorie value to the calorie 

 output during starvation, the caloric output will increase by 30 

 per cent, whereas with carbohydrates it will increase only by 

 6 per cent. Evidently, then, protein liberates much free heat 

 during its assimilation in the animal body ; it burns with a hot- 

 ter flame than fats or carbohydrates, although as in the case 

 of fats, at least, before it is completely burnt, it may not yield so 

 much energy. This peculiar property of proteins accounts for 

 their well-known heating qualities. It explains why protein com- 



