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FORMATION OF UREA. 683
urea in the animal body, as shown by the investigations of Abderhalden
and his collaborators. 1
There is no doubt that the ammonia formation is of great importance
in the production of urea in the animal body.
A great number of older investigations 2
on the behavior of ammo-
nium salts in the animal body have shown that not only ammonium car-
bonate, but also those ammonium salts which are burned into carbonate
in the organism, are transformed into urea by carnivora as well as her-
bivora. v. Schroeder,3
by irrigating the surviving dog’s liver with
blood treated with ammonium carbonate or ammonium formate, has
shown that the formation of urea takes place, at least in part, in this organ.
Nencki, Pawlow, Zaleski and Salaskin 4
have also found that, in dogs,
the quantity of ammonia in the blood from the portal vein is considerably
greater than that from the hepatic vein, and they claim that the liver
retains in great part the ammonia thus supplied. The formation of urea
from ammonia in the liver is a positively proved fact.
The assumption of a splitting off of ammonia from amino-acids
stands in agreement with the experience that a deamidation of the amino-
acids takes place in the animal body. The ammonia split off finds, in
the blood and tissues, the carbon dioxide necessary for the formation
of carbonate, and the investigations of Nolf, as well as those of Macleod
and Haskins,5
on the equilibrium of carbonate and carbamate solutions
and the conditions for the formation of both salts, must also be abundant
evidence of a carbamate formation.
Important observations have been made which give support to the
views of Schultzen and Nencki,6
namely, that the amino-acids are
transformed into urea with ammonium carbamate, H4N.O.CO.NH2,
as an intermediate step. Drechsel has shown that the amino-acids
yield carbamic acid by oxidation in alkaline fluid outside of the organism,
and he obtained urea from ammonium carbamate by alternate oxidation
and reduction. Carbamate has also been found in the blood (Drechsel)
as well as in the urine (Drechsel, Abel and Muirhead) 7
and Nexckt
1
Abderhalden with Teruuchi and with Babkin, Zeitschr. f. physiol. Chem., 47,
with Schittenhelm, ibid., 51.
2
v. Knieriem, Zeitschr. f. Biologie, 10; Feder, ibid., 13; Salkowski, Zeitschr. f.
Biologie, 1; Munk, ibid., 2; Coranda, Arch. f. exp. Path. u. Pharm., 12; Schmiede-
berg and Walter, ibid., 7; Hallervorden, ibid., 10; Pohl and Miinzer, Arch., f. exp.
Path. u. Pharm., 43.
3
Arch. f. exp. Path. u. Pharm., 15. See also Salomon, Virchow’s Arch., 97.
4
Arch, des sciences biol. de St. Petersbourg, 4; see also Chapter V, p. 336.
6
Nolf, Zeitschr. f . physiol. Chem., 23; Macleod and Haskins, Journ. of biol. Chem., 1.
6
Zeitschr. f. Biologie, 8.
7
Drechsel, Ber. d. sachs. Gesellsch. d. Wissensch., 1875. See also Journ. f. prakt.
Chem. (N. F.), 12, 16, and 22; Abel, Arch. f. (Anat. u.) Physiol., 1891; Abel and
Muirhead, Arch. f. exp. Path. u. Pharm., 31.
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