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ABSORPTION OF PROTEINS. 529
of the leucocytes taking up the proteoses and fixing them, it seems, in
the cell substance.
It is for the present impossible to say with certainty whether or
not and to what extent the proteoses, as such, are absorbed and to give
their further fate thereafter in the intestine. The present view is prob-
ably as follows: That they do not pass as such into the blood, and
that they are transformed into amino-acids in part in the intestinal
-contents and in part in the intestinal mucosa, and then from these amino-
acids the coagulable proteins are constructed by synthesis. In sup-
port of the theory of a protein synthesis from amino-acids we have a
series of experiments where deeply split or completely split proteins
were fed. In these experiments by Loewi, Henderson and Dean,
Henriques and Hansen, and especially by Abderhalden and his
co-workers l
on dogs, mice and rats, it was possible to keep the animals
in nitrogenous equilibrium or indeed nitrogen retention for a long time
with the cleavage products of proteins besides non-nitrogenous food-
stuffs and salts. According to the recent experiments of Abderhalden
the organism can build up proteins from amino-acids when the indi-
vidual amino-acids are supplied in proportions as they exist in the cell
proteins. Certain, sometimes absent amino-acids seem to be capable
of being produced within the organism (for example, glycocoll, proline)
while other (tryptophane) cannot be produced. This explains why
gelatine which does not contain any tryptophane cannot replace protein
in the food.
The results of the experiments are generally considered as proof of
the ability of the animal body to construct proteins from amino-acids
by synthesis, and in the present state of our knowledge we can hardly
draw other conclusions from them or advance any simpler theory.
Where does the protein synthesis take place? If it were positively
sure that the amino-acids did not pass into the blood then we would
have transferred this synthesis to the intestinal walls. Otherwise we
must think in the first place of the liver; but this organ does not seem
to play an important role in this synthesis. Abderhalden and London 2
made an experiment on a dog with an Eck fistula (see page 397), feeding
the dog with decomposed protein, and they found that this animal
behaved exactly like a normal animal, as it was kept for eight days not
only in nitrogenous equilibrium but also in nitrogen retention. On
1
Loewi, Arch. f. exp. Path. u. Pharm., 48. See also Henderson and Dean, Amer.
Journ. of Physiol., 9; Abderhalden and Rona, Zeitschr. f. physiol. Chem., 42, 44, 47, and
52; Henriques and Hansen, ibid., 43, 49; Henriques, ibid., 54; Abderhalden with
Olinger, ibid., 57, with Messner and Windrath, ibid., 59; Abderhalden, ibid., 77, 22,
78, 1 (1912).
* Zeitschr. f. physiol. Chem., 54.
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