PROTEIN REQUIREMENTS 77 



The Rise in the Output of Nitrogen after a Meal. 



It has already been mentioned that there is a rapid rise in the out- 

 put of nitrogen in the urine soon after a protein meal. This rapidity of 

 output naturally leads one to doubt the necessity of a large intake of 

 nitrogen. It has been repeatedly shown that after a protein meal 

 there is an output of about 70 per cent of the ingested protein within 

 eight hours. This output does not occur in a single steady rise follow- 

 ing the protein meal, but in a series of maxima, as a rule, three. 

 Tschlenoff (401), Veraguth (405), and Hass (171) all found that the 

 first rise took place about the second hour, the second between 

 the fifth and sixth hours, and the third, if present, about the seventh 

 hour. In all probability the first rise is due to the increased blood flow 

 causing a washing out from the tissues of accumulations of waste ma- 

 terial ; the second and the third, when present, represent the results of 

 actual protein catabolism. The cause of the fall in output between 

 the first and second rise may be due either to absorption and sub- 

 sequent deaminization proceeding slowly, or it may be that during this 

 period the tissues are taking up the necessary nitrogenous material for 

 purposes of repair, i.e. that a physiological retention occurs, and that 

 the subsequent rise is due simply to the excretion of surplus and effete 

 nitrogen. Graffenberger (158) has shown that the rate of output varies 

 very definitely with the nature of the nitrogenous material which is fed. 

 Curiously enough a partially digested material like peptone does not 

 cause so rapid a rise in the output of nitrogen as proteins like fibrin 

 and gelatin, and although asparagine is a freely soluble substance it 

 is retained for a considerable period in the body. This slow excretion 

 may have been partly due to the fact, although it is extremely im- 

 probable, that part of the asparagine was taken in solid form. Koraen 

 (224) found in his experiments on feeding with protein (8*3 grms. 

 nitrogen) that about 50 per cent, of the ingested nitrogen was excreted 

 in five hours, and that up to 100 per cent, appeared within nine hours. 

 When he lowered the nitrogen intake to 3 '2 grms. all the nitrogen in- 

 gested had not appeared at the end of five hours. It is, however, 

 extremely questionable if these percentage figures of Koraen are right. 

 If, as seems probable from his figures, he has taken the endogenous 

 nitrogen output along with his exogenous, on deducting the endogenous 

 nitrogen figure (the fasting nitrogen output which he gives for the 

 subject used) his nitrogen output during five hours amounts only to 

 about 26 per cent, and for nine hours to a little over 50 per cent. 



