HIPPURIC ACID. 683 



filtrate evaporated to dryness. The residue is extracted with hot water 

 and then the solution is precipitated with mercuric nitrate. The pre- 

 cipitate is collected and decomposed by H 2 S. From the evaporated 

 filtrate the allantoin crystallizes out. This method, DAKIN claims, is 

 not suited for the quantitative estimation of allantoin. For this pur- 

 pose we make use of the method suggested by WiEcnowsKi, 1 which 

 consists in precipitating the allantoin by a dilute mercuric acetate solu- 

 tion in the presence of concentrated sodium acetate solution. For 

 details we refer to the original publications. 



Glyoxylic Acid, C 2 H 4 4 , 2 , is produced on boiling allantoin as well as 



COOH 



uric acid with alkalies and also on the oxidation of many substances, among 

 which we can mention creatine and creatinine. It is also of interest that allantoin 

 can be prepared synthetically from glyoxylic acid and urea and that glyoxylic 

 acid yields oxalic acid when introduced into the body. The reports in regard 

 to its occurrence in the urine conflict, 2 as it is readily destroyed in the body, and 

 its passage into the urine is very improbable, or at least only occurs seldom. 



Hippuric Acid (BENZO YL-AMINO ACETIC ACID) . , 



HN.CH 2 .COOH. 



This acid decomposes into benzoic acid and glycocoll on boiling with 

 mineral acids or alkalies, and also in the putrefaction of the urine. The 

 reverse of this occurs if these two components are heated in a sealed tube, 

 according to the following equation: C 6 H 5 COOH + NH 2 .CH 2 .COOH = 

 C,H 5 .CO.kH.CH 2 .COOH + H 2 0. This acid may be synthetically pre- 

 pared from benzamide and monochloracetic acid, C 6 H 5 .CO.NH 2 + CH 2 C1. 

 COOH = C 6 H 5 .CO.NH.CH 2 .COOH + HC1, and in various other ways, 

 but most simply from glycocoll and benzoyl chloride in the presence of 

 alkali. 



Hippuric acid occurs in large amounts in the urine of herbivora, but 

 only in small quantities in that of carnivora. The quantity of hippuric 

 acid eliminated in human urine on a mixed diet is usually less than 1 

 gram per day; as an average it is 0.7 gram. After eating freely of vege- 

 tables and fruit, especially such fruit as plums, the quantity may be 

 more than 2 grams. Hippuric acid is also found in the perspiration, the 

 blood, the suprarenal capsule of oxen, and in ichthyosis scales. Noth- 

 ing is positively known in regard to the quantity of hippuric acid in the 

 urine in disease. 



The Formation of Hippuric Acid in the Organism. Benzoic acid and 

 also the substituted benzoic acids are converted into hippuric acid and 

 substituted hippuric acids within the body. Moreover, those bodies 

 .are transformed into hippuric acid which by oxidation (toluene, cinnamic 



1 Loewi, ibid., 44; Wiechowski, Hofmeister's Beitrage, 11, and Arch. f. exp. Path. 

 u. Pharm., 60; Dakin, Journ. of biol. Chem., 3, 73. 



2 The literature on the occurrence and detection of glyoxylic acid in the urine can 

 be found in Granstrom, Hofmeister's Beitrage, 11. 



