50 SCIENTIFIC FEEDING OF ANIMALS 



must be accurately estimated by direct experiments. 

 When this has been done the energy content of the 

 food and of the excretory products is calculated, 

 and it is found what amount of energy expressed in 

 heat units has been at the disposal of the animal. 

 Further, from the increase in flesh and fat the 

 energy which has remained in the body can be 

 calculated. In this way all the data essential for a 

 clear insight into the metabolism of material and 

 of energy are obtained. The following experiment 

 on a well-fed ox will serve as an example of an 

 energy-metabolism investigation 



Income of energy in food . . . 52929 Cal. 

 Expenditure ,, faeces 15916 Cal. 



urine 1686 



marsh gas 3383 



20985 



Total amount of available energy . 31944 Cal. 



For maintenance of the animal, deter- 

 mined from other experiments . . 17320 



Amount of available energy left for 



production 14624 



Stored in flesh 246 Cal., in fat 8069 Cal. 8315 



Percentage storage of available energy 56-9% 



