200 D. RiTTENBERG 



ammonia is known to arise from deamination of the free 

 amino-acids of the blood. Further, it is known from experi- 

 ments in which rats are kept on a diet deficient in an essential 

 amino-acid that to produce growth the essential amino-acid 

 must be fed at the same time as the deficient protein. If any 

 considerable time elapses between the feeding of the amino- 

 acid and the deficient protein, the supplement will all be 

 destroyed before the incomplete protein enters the system. 

 Protein can only be formed when all the required amino-acids 

 are present. 



The values we obtain for S have been corrected for the feed- 

 back of isotope from the protein pool to the metabolic pool. 

 The values for S are approximately 0-4 g. nitrogen per day 

 per kilo weight. This does not differ greatly from the values 

 calculated by Sprinson and Rittenberg. Indeed, it is possible 

 to show that the value of S does not depend on the system 

 assumed. 



The value of P calculated here is much lower than pre- 

 viously. It is about 2 grams nitrogen rather than 35 

 previously found. The reason for this large discrepancy is 

 quite obvious, and in defence I would like to point out that 

 Sprinson and Rittenberg stated that their metabolic pool 

 was a mathematical construct. I believe that the present 

 pool is a reality. 



The conclusions which we previously drew concerning the 

 metabolic heterogeneity of human muscle are still valid. 



The further analysis of this question may clarify many 

 obscure corners of nutrition. 



REFERENCES 



Bertalanffy, L. von (1950). Science, 111, 23. 



Burton, A. C. (1939). J. cell. comp. Physiol., 14, 327. 



Denbigh, K. G., Hicks, M., and Page, F. M. (1948). Trans. Faraday 



Soc, 44, 479. 

 Eddington, a. (1949). Philosophy of Physical Science. Cambridge 



University Press. 

 Rittenberg, D. (1948-49). Harvey Leet., Series XLIV. Springfield^ 



111.: Charles C. Thomas. 

 Shemin, D., and Rittenberg, D. (1944). J. biol. Chem., 153, 401. 



