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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. Rtjbner 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 *
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 ammo-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.
;
Anh. f. (Ariat. u.) Physiol., 1911.
*Panum, Nord. Med. Arkiv., 6; Falck, see Hermann’s Handbuch, 6, Part I, 107;
Asher and Hums, Bioch. Zeitsr-hr., 12. For further information in regard to the curve
of nitrogen elimination in man, see Tschenloff, Korrespond. Blatt Schweiz. Aerzte,
1896; Rosemann, Pflliger’s Arch., 65, and Veraguth, Journ. of Physiol., 21; Schlosse,
Maly’s Jahresber., 31.
4
Arch. f. (Anat. u.) Physiol., 1879.
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