EXPERIMENT WITH MAN. 

 TABLE 15. Intake and Output of Energy, Metabolism Experiment No. jo. 



In this discussion the intake of energy is the energy from the mate- 

 rial actually katabolized, i. e., broken down and oxidized in the body, 

 including, therefore, not only the energy of katabolized food but also 

 that of the body material lost. The output of energy is that given 

 off by the body as heat, measured either as sensible heat by the respi- 

 ration calorimeter or as heat of vaporization of water. The intake of 

 energy may be measured in a number of ways. First, we may con- 

 sider the intake as the potential energy of the food ingested and consider 

 the potential energy of the unoxidized material in the urine and feces 

 as a part of the output. Second, we may correct the potential energy 

 of the food for that of the feces and urine by deducting the amount of 

 energy in these latter, thus obtaining the so-called ' ' available ' ' energy. 

 Without entering into any discussion here as regards the merits of 

 the two methods of computation, we may proceed to the discussion of 

 Table 15. The available energy of the food is calculated from the heat 

 of combustion of the food, column (a), the heats of combustion of the 

 unoxidized material in the feces, column (), and urine, column (c}. 

 These quantities are taken from Tables 6 and 7, respectively. As 

 previously explained, they are the results of actual determinations. 



When the available energy of the food is more than sufficient for the 

 needs of the body, more or less of the surplus food may be stored as 

 body material, and the quantity of energy in the material so stored 

 must be subtracted from the available energy of the food to obtain the 

 energy of the material actually metabolized, which is the energy of 

 intake here considered. On the other hand, if the available energy of 

 the food is not sufficient, the body will draw upon its own previously 

 stored material, and the amount of energy thus derived must be added 

 to that available from the food to give the total energy of material 

 oxidized in the body. 



