WHEN PROTEIDS ARE FED 



289 



the proteid food rapidly undergoes cleavage into nitrogenous and 

 non-nitrogenous moieties, and is not used as a tissue-builder. 

 E. Voit reckons the amount of proteid required for nitrogenous 

 equilibrium to be no less than 2-J- to 3 times more than that 

 metabolised in the starving animal. Thus if 25-42 per cent, of 

 the total energy expended by the fasting animal be given as 

 proteid food, nitrogenous equilibrium results, and the remaining 

 58-72 per cent, of the energy is derived from the body fat. 

 Examples : 



These and many similar experiments of Rubner show how 

 material a loss of fat occurs on a proteid ration which is sufficient 

 to prevent any loss of N 2 from the body. 



An animal puts itself promptly into equilibrium with its supply 

 of nitrogen, and only a slight and evanescent gain of body proteid 

 can be produced in the adult by the most liberal supply of proteid 

 food. Muscular work plus a sufficient diet of proteid increases the 

 flesh of the body. 



The food proteids are cleaved into a nitrogenous and a non- 

 nitrogenous moiety. The nitrogenous moiety is rapidly excreted 

 as urea, while the fate of the non-nitrogenous residue cannot 

 as yet be traced. It may become glycogen or fat. That it is 

 not oxidised simultaneously with the excretion of the nitro- 

 genous moiety is shown by the fact that the heat production 

 of the body does not rise after a meal. Much of the proteid 

 we eat is used wastefully for the energy of the non-nitrogenous 

 moiety. That it is oxidised in due course is shown by the fact 

 that any excess of proteid extra to that required for N equili- 

 brium is substituted for more or less body fat as a source of 

 energy. 



