GENERAL METABOLISM AND DIETETICS 



331 



approximately the same, it is fair to assume that any change in the 

 oxygen intake, and also in the CO 2 output, are due to the conditions 

 of experiment, such as exposure to cold, warmth, wind, etc. The 

 respiratory exchange is therefore often used to estimate the amount 

 of energy liberated in the tissues. 



It is necessary for very accurate work to remember that different 

 foodstuffs liberate different amounts of energy for the same amount 

 of oxygen absorbed. Thus, 100 grammes of oxygen will burn 



35 grammes of fat, giving energy equal to 325 calories. 



84-4 grammes of carbohydrate, giving energy equal to 



346 calories. 

 74.4 grammes of protein, giving energy equal to 362 calories. 



Given the respiratory quotient and total energy output of the body, 

 calculations can be made of the relative use of glycogen and fat for 

 each litre of oxygen consumed (see Respiratory Quotient, p. 319). 



FIG. 187. FIGURE OF RESPIRATION CHAMBER FOR MAX. 



The rir is drawn from the chamber by the rotary blower and pii.s.-sed over vessels 

 A E back to the chamber. Oxygen may be added as required from F. 



The Direct Method. This is done by placing the man or animal 

 in a respiration calorimeter. In the case of an animal it is difficult to 

 estimate the exact amount of energy lost as muscular work; the 

 animal is therefore in these direct observations kept as quiet as possible. 

 The forms of water calorimeter which were first used have been given 

 up, on account of large experimental error, and replaced by some 



