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 solution, 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), CgHgCU = 

 This acid, which was discovered by MARSHALL 1 



. 

 \CH 2 COOH(5) 



and calle:l 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 c cid, 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, 

 BLOCK 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. Che:::., 52. 



