TISSUE PROTEIN AND CIRCULATING PROTEIN 491 



solved in the milk, to administer to an infant iron, inorganic 

 salts, nucleins and lipoids. Possibly, however, the matter 

 has even a greater significance, as there seems to be here a 

 hint of possibility of utilizing wide stretches of land, hitherto 

 serviceable to man's nutrition only by way of the cattle in- 

 dustry, in a much more direct and rational manner. 21 The 

 proposal to make human beings become grass- and leaf- 

 eaters may, perhaps, at first thought seem very ridiculous. 

 It should not be forgotten, however, that it has not always 

 been the poorest acquisitions of mankind which at the out- 

 start have been recognized by the majority of their con- 

 temporaries in their humorous aspect alone (witness steam 

 machinery, illuminating gas, and electricity). Perhaps here, 

 too, we are confronting one of those possibilities destined to 

 take form more easily for later generations than for the one 

 now in existence. 



Nitrogen Balance. Before we can properly coordinate 

 the phenomena of metabolism in fasting it is necessary that 

 we briefly (for it is impossible in the course of these lectures 

 to deal with detail) take up some of the points in relation to 

 protein metabolism. 



First the matter of nitrogen balance : It is well known 

 to all that a meat eater who has been accustomed to a fixed 

 meat ration, reacts to an increased or a diminished amount 

 of meat ingested by a heightened or lowered nitrogen elimi- 

 nation, and that after a time there gradually comes to be 

 maintained an equilibrium between the total amount of in- 

 taken protein-nitrogen and of the eliminated urinary- 

 nitrogen. 



Tissue Protein and Circulating Protein. This peculi- 

 arity of the animal economy, which is in effect that the 

 amount of protein disintegration is primarily determined by 

 the amount of protein introduced, led Voit to physiologically 

 differentiate between tissue-protein and circulating-protein. 



21 H. Friedenthal (Nikolas Lake in Berlin), Pfliiger's Arch., 1M, 152, 

 1912; Umschau, 1912, 649. 



