106 THE PROTEIN ELEMENT IN NUTRITION 



IY 



' demands of the organism for nitrogen. When the store of fat 

 gives out, there will be an increase in the amount of tissue break- 

 down, since now all forms of energy will come from the kata- 

 bolism of protein, and this will be accompanied by a marked 

 increase in the output of nitrogen " the pre-mortal rise in the 

 nitrogen excretion." 



Accepting the figure 5 grammes as representing the urinary 

 nitrogen, and allowing 0-5 gramme nitrogen for other modes of 

 excretion, the conclusion may be arrived at that the minimum 

 amount of assimilated nitrogen necessary to prevent the dis- 

 integration of tissue proteins is 5-5 grammes. 



If this amount be given to a starving man, it will be found 

 that it is by no means sufficient to establish nitrogenous equili- 

 brium and prevent tissue breakdown. The smallest amount of 

 nitrogen in the food on which it is possible to establish nitrogenous 

 equilibrium is some three to four times the amount excreted 

 during starvation. If the fasting man, however, has a large 

 store of fat, or, if large quantities of fats and carbohydrates are 

 taken as food, the sparing action of these materials may be 

 sufficiently great to allow of nitrogenous metabolism being 

 maintained on quantities as small as 5 or 6 grammes of nitrogen 

 per day i.e., " Man can keep the protein store of his organism 

 unaltered in amount on a supply of protein which lies far below 

 the amount decomposed during starvation." 



This figure may therefore be accepted as representing the 

 lower limits of nitrogenous metabolism, and further decrease of 

 assimilable protein in the food, no matter how abundant the 

 carbonaceous element may be, will entail a falling back of the 

 organism on its own nitrogenous tissues. Numerous observa- 

 tions and experiments by Chittenden, Neumann, Siven, Klem- 

 perer, Peschal, and others, have shown that nitrogenous equili- 

 brium can be maintained with a diet containing about 6 grammes 

 of nitrogen, even when the total energy value was not excessive. 

 In Chittenden's experiments the potential energy was below the 

 ordinary accepted standards. As will be evident, also, the 

 inhabitants of Bengal corroborate this finding on a large scale 

 and over long periods of time. 



For the present we may leave this point, accepting the finding 

 that the metabolism of about 6 grammes of nitrogen is the 

 physiological minimum on which mankind is able to make good 

 the wear and tear of his protoplasmic tissues when the demands 



