912 METABOLISM. 



value, and when two-thirds of the total calories partaken of were sup- 

 plied by carbohydrates, 63 per cent of the total nitrogen could be replaced 

 by gelatin nitrogen. 



The reason why gelatin cannot entirely replace protein has been sought 

 for in the fact that gelatin does not contain all the amino-acids of the 

 proteins (such as tyrosine and tryptophane), or does not contain a suf- 

 ficient amount of the various amino-acids. The correctness of this 

 explanation was first shown by KAUFMANN by an experiment on himself, 

 where he showed that gelatin after addition of tyrosine, tryptophane 

 and cystine could be made equivalent to protein. The conclusive proof 

 was given later by ABDERHALDEN l when he showed that completely 

 decomposed gelatin on the addition of a mixture of amino-acids, among 

 them also tyrosine and tryptophane, could be made equivalent to proteins. 



As it has been possible to replace the proteins in the food by their 

 cleavage products or mixtures of amino-acids, 2 it is easily understandable 

 that also proteoses or peptones can completely or partly replace the 

 protein. Their ability in this regard is essentially dependent upon their 

 constitution, i.e., their content of the different amino-acids. As the 

 proteoses and peptones are produced by cleavage and as therefore in 

 one proteose we hae certain atomic comp loies and in others again 

 these may be absent or only exist to a slight extent, it is conceivable that 

 different investigators 3 have obtained contradictory results because of 

 the use of different proteoses and peptones. 



We have a number of investigations on the action of amides upon 

 metabolism, which are mostly connected by the use of asparagin. These 

 investigations have in part led to conflicting results; but they indicate 

 that carnivora 'and herbivora act differently, that the results are depen- 

 dent upon the rapidity with which the asparagin is absorbed and also 

 upon the bacterial action in the intestine, and that in herbivora a protein- 

 sparing action can be brought about by asparagin. 4 If, as is generally 



1 Martin Kaufmann, Pfliiger's Arch., 109; Abderhalden, Zeitschr. f. physiol. Chem., 

 77. 



2 See Abderhalden and collaborators, Chapter VIII; also Abderhalden, Zeitschr. 

 f. physiol. Chem., 77, and especially 83. 



3 In regard to the literature on the nutritive value of the proteoses and peptonea 

 see Maly, Pfltiger's Arch., 9; P16sz and Gyergyay, ibid., 10; Adamkiewicz, 'Die Natur 

 und der Nahrwerth des Peptones" (Berlin, 1877); Pollitzer, Pfliiger's Arch., 37, 301; 

 Zuntz, ibid., 37, 313; Munk, Centralbl. f. d. med. Wissensch., 1889, 20, and Deutsch. 

 med. Wochenschr., 1889; Ellinger, Zeitschr. f. Biologic, 33 (literature). Blum, Zeitschr. 

 f. physiol. Chem., 30; Henriques and Hansen, Zeitschr. f. physiol. Chem., 48. 



4 Weiske, Zeitschr. f. Biologic, 15 and 17, and Centralbl. f. d. med. Wissensch., 1890, 

 945; Munk, Virchow's Arch., 94 and 98; Politis, Zeitschr. f. Biologic, 28. See also 

 Mauthner, ibid., 28; Gabriel, ibid., 29; and Voit, ibid., 29, 125; Kellner, Maly's Jahres- 



