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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-
ncient 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 1
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 lcxes 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, Pfiuger’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 peptones
see Maly, Pfliiger’s Arch., 9; P16sz and Gyergyay, ibid., 10; Adamkiewicz, ’Die Natur
und der Niihrwerth des Peptones" (Berlin, 1877); Pollitzer, Pfiuger’s Arch., 37, 301;
Zuntz, ilrid., 37, 313; Munk, Centralbl. f. d. med. Wissensch., 1889, 20, and Deutsch.
med. Wochenschr., 1889; Ellinger, Zeitschr. f. Biologie, 33 (literature). Blum, Zeitschr.
f. physiol. Chem., 30; Henriques and Hansen, Zeitschr. f. physiol. Chem., 48.
4
Weiske, Zeitschr. f. Biologie, 15 and 17, and Centralbl. f. d. med. Wissensch., 1890,
945; Munk, Virchow’s Arch., 94 and 98; Politis, Zeitschr. f. Biologie, 28. See also
Mauthner, ibid., 28; Gabriel, ibid., 29; and Voit, ibid., 29, 125; Kellner, Maly’s Jahres-
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