910 METABOLISM. 



Recent investigations, especially those of FoLiN, 1 which show that the 

 amount of certain nitrogenous urinary constituents, such as creatinine, 

 uric acid and the combinations containing neutral sulphur, are almost 

 independent of the quantity of protein taken as food, while the quantity 

 of urea is determined by the protein partaken of, tend to substantiate 

 VOIT'S view that we must differentiate between the real cell protein 

 and the food protein. This has also led FOLIN to differentiate between 

 endogenous and exogenous protein metabolism. The chief point in 

 VOIT'S theory that all the proteins in the body do not behave alike 

 and that the organized proteins which have been fixed in the cells and 

 have been introduced into the cell structure are less readily catabolized 

 than the proteins occurring in the nutritive fluids or temporarily taken 

 up from these, must also be considered as not disputed. RuBNER 2 

 differentiates also between the deposited protein (growth protein, and 

 deposited by the activity of the cells melioration protein) in the body on 

 the one hand and the protein temporarily incorporated with the body 

 (supply protein and catabolized in passing to a protein-poor diet, transitory 

 protein) on the other hand. 



This question is intimately connected with another, namely, whether the 

 food proteins taken up by the cells are metabolized as such or whether they are 

 first organized, i.e., are converted into specific cell protein. The observations 

 of PANUM, FALCK, ASHER and HAAS and others 3 on dogs have shown that the 

 nitrogen elimination increases almost immediately after a meal and in the fifth or 

 sixth hour according to these experimenters, when according to SCHMIDT-MULHEIM 4 

 about 59 per cent of the eaten protein is absorbed, do not indicate that a trans- 

 formation of the food protein into organized protein occurs before it is catab- 

 olized. The recent investigations upon the deep cleavage of proteins in digestion 

 and the generally accepted protein syntheses from amino-acids have made this 

 question lose its special interest. 



On account of the above-stated action of the concentration of the 

 catabolizable nitrogenous material upon the protein decomposition or 

 nitrogen elimination, it is not possible to replace the quantity of protein 

 catabolized in starvation by the exclusive feeding of protein administered 

 at one time and in quantities corresponding to the food proteins. This 

 always requires large amounts of protein. Even on the fractional intro- 

 duction of natural protein v. HOESSLIN and LESSER were unable to pro- 

 duce a nitrogen equilibrium with quantities of protein equal to the starva- 



1 Amer. Journ. of Physiol., 13. 



2 Arch. f. (Anat. u.) Physiol., 1911. 



3 Panum, Nord. Med. Arkiv., 6; Falck, see Hermann's Handbuch, 6, Part I, 107; 

 Asher and Haas, Bioch. Zeitschr., 12. For further information in regard to the curve 

 of nitrogen elimination in man, see Tschenloff, Korrespond. Blatt Schweiz. Aerzte, 

 1896; Rosemann, Pfluger's Arch., 65, and Veraguth, Journ. of Physiol., 21; Schlosse, 

 Maly's Jahresber., 31. 



4 Arch. f. (Anat, u.) Physiol., 1879. 



