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HOMOGENTISIC ACID. 735
To detect the presence of these oxyacids proceed in the following way (Bau-
mann): Warm the urine for a while on the water-bath with hydrochloric acid
in order to drive off the volatile phenols. After cooling shake three times with
ether, and then shake the ethereal extracts with dilute soda Bollltion, which dis-
solves the oxyacids, while the residue of the phenols which are soluble in ether
remains. The alkaline solution of the oxyacids is now faintly acidified with sul-
phuric acid, shaken again with ether, the ether removed and allowed to evaporate
the residue dissolved in a little water, and the solution tested with Millon’s
reagent. The two oxyacids are best differentiated by their different melting-
points. The reader is referred to other works for the method of isolating and
separating these two oxyacids.
Homogentisic Acid (Dioxyphenylacetic Acid), CsHs’^ =
/OH(l)
CeH3^-OH(4) . This acid, which was discovered by Marshall1
\CH2COOH(5)
and calle 1 by him glycosuric acid, was isolated in larger quantities by
Wolkow and Baumann in a case of alcaptonuria and carefully studied
by them. They called it homogentisic acid because it is a homologue
of gentisic acid, and they showed that the peculiar properties of so-called
alcaptonuric urine in this case were due to this acid. This acid has later
been found in many cases of alcaptonuria. Glycosuric rcid, isolated from
alcaptonuric urine by Geyger,2
seems to be identical with homogentisic
acid.
The quantity of acid eliminated, which varies in most cases between
3 and 7 grams per twenty-four hours, and which is higher—14-16 grams
—
in exceptional cases, is increased by food rich in protein. On the inges-
tion of tyrosine by persons with alcaptonuria, Wolkow and Baumann
and Embden observed a greater quantity of homogentisic acid in the
urine and this has been substantiated by other observers. Since Lang-
stein and E. Meyer showed in a case of alcaptonuria that the quantity
of tyrosine in the protein, even when calculated to a maximum, was
not sufficient to account for the quantity of homogentisic acid, and that
therefore we must admit of another source (the phenylalanine) for the
alcapton, Falta and Langstein 3
have given a direct proof that homo-
gentisic acid can also be formed from phenylalanine. Abderhalden,
Bloch and Rona 4
have shown that in alcaptonurics the excretion of
homogentisic acid is increased by the introduction of tyrosine or phenyl-
1
The Medical News, Philadelphia, January 8, 1887.
2
Wolkow and Baumann, Zeitschr. f. physiol. Chem., 15; Geyger, cited from Emb-
den, 1. c, 18. The literature can be found in Fromherz, Ueber Alkaptonurie, Inaug.-
Dis. Freiburg, 1908.
3
Langstein and Meyer, Deutsch. Arch. f. klin. Med., 78; Falta and Langstein,
Zeitschr. f. physiol. Chem., 37; Falta, Der Eiweiss-Stoffwechsel bei der Alkaptonurie,
Habilitationsschrift, Naumburg, a. S., 1904.
4
Zeitschr. f. physiol. Chem., 52.
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