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682 URINE.
tion and very great variations seem to occur not only in the healthy
individual, but also and to a greater degree in diseased conditions.1
Formation of Urea in the Organism. The older statements of Bechamp
that urea is directly formed from proteins by oxidation has been denied
by several investigators but according to recent statements of Fosse 2
this is correct. On the hydrolysis of proteins arginine is found among
other products, and as it is also produced in tryptic digestion, it is possible
that a small portion of the urea is produced in this manner, varying
according to the kind of protein. Drechsel claims that about 10 per
cent of the urea can be accounted for in this way.
The possibility of a formation of urea from arginine has gained in
interest since Kossel and Dakin have discovered the presence of an
enzyme, arginase, in the liver and other organs, which has the power
of splitting arginine with the formation of urea. Thompson 3
has given
a direct proof for the formation of urea from arginine. The introduc-
tion of arginine into the body of a dog either per os or subcutaneously
has in his experiments led t© an elimination of urea. While outside of
the body only one-half of the nitrogen of arginine is split off as urea
and the other half as ornithine, in the above experiments the increase
in urea in several instances corresponded to the greater part if not the
whole of the nitrogen of the arginine introduced. This increased forma-
tion of urea makes it probable that also ornithine is deamidized and the
urea is formed from the ammonia split off.
By the action of alkalies, as above mentioned (Chapter X), urea may
be formed from creatinine ; still such an origin of urea in the animal body
has not thus far been proved.
The amino-acids are considered as special mother-substances of urea.
By numerous, generally older experiments with these acids, it has been
proved that the amino-acids of the animal body are transformed in part
into urea. The investigations by Salaskin with the three amino-acids,
glycocoll, leucine, and aspartic acid, have unmistakably shown that the
surviving dog-liver, supplied with arterial blood, has the property of
transforming the above amino-acids into urea or a closely allied sub-
stance.4
Like the amino-acids the polypeptides are also transformed into
1
See Satta, Hofmeister’s Beitrage, 6, which also gives the literature, and Erben,
Zeitschr. f. Heilkunde, 25.
2
Compt. Rend., 154.
3
Kossel and Dakin, Zeitschr. f. physiol. Chem., 41; Thompson, Journ. of Physiol.,
32 and 33.
4
Schultzen and Nencki, Zeitschr. f. Biologie, 8; v. Knieriem, ibid., 10; Salkowski,
Zeitschr. f. physiol. Chem., 4; Salaskin, ibid., 25; Stolte, Hofmeister’s Beitrage, 5;
Levene and Meyer, Arner. Journ. of Physiol., 25; see also Loewi, Zeitschr. f. physiol.
Chem., 25; Richet, Compt. Rend., 118, and Compt. rend. Soc. biol., 49; Ascoli,
Pfliiger’s Arch., 72.
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