8 52 . METABOLISM. 



tiate bstween endogenous and exogenous protein metabolism. The 

 experience on protein feeding and the endeavor of the body, as observed 

 by ScHREUER, 1 on going to an ordinary diet after abundant protein feed- 

 ing, to remain at the old "state previous to the overfeeding of protein, 

 point to the fact that protein retained by the body is not quite the same 

 as the other body protein. 



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 

 investigations of PANUM, FALCK, ASHER and HAAS and others 2 on the 

 transitory progress of the elimination of nitrogen after a meal rich in 

 proteins throws light on this question. From experiments upon a dog 

 it was found that the elimination of nitrogen increases almost immediately 

 after a meal rich in proteins, and that it reaches its maximum in about 

 ,six hours, when about one-half of the quantity of nitrogen corresponding 

 to the administered proteins is eliminated. If we also recollect that, 

 according to an experiment of SCHMIDT-MULHEIM 3 upon a dog, about 

 37 per cent of the given proteins are absorbed in the first two hours after 

 the meal and about 59 per cent in the course of the first six hours, it may 

 then be inferred that the increased elimination of nitrogen after a meal 

 is due to a catabolization of the digested and assimilated proteins of the 

 food not previously organized. If it is admitted that the catabolized 

 protein paust have been organized, then the greatly increased elimination 

 of nitrogen after a meal rich in proteins supposes a far more rapid and 

 comprehensive destruction and reconstruction of the tissues than has 

 been generally assumed. 



The extensive cleavage of the proteins in digestion and the repeatedly 

 observed deamidation of amino-acids in the animal body make it prob- 

 able that the abundant elimination of nitrogen after a diet rich in pro- 

 teins is in great part due to a progressive demolition of the food protein 

 in digestion, whereby certain atomic complexes are more readily split 

 than others. The abundant elimination of nitrogen by the urine after 

 partaking of considerable protein may also depend in great part upon those 

 nitrogenous atomic complexes which are split off and whose nitrogen is 

 split off as ammonia and therefore cannot be used by the body. The 

 abundant formation of ammonia in the cells of the digestive apparatus 



1 Folin, Amer. Journ. of Physiol., 13; Schreuer, Pfliiger's Arch., 110. 



2 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, Pfliiger's Arch., 65, and Veraguth, Journ. of Physiol., 21; Schlosse, 

 Ma)y's Jahresber., 31. 



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



