256 THE URINE. 



way between gluconic acid and saccharinic acid. These relations 

 are shown by the formulae : 



(11,011 (CH.OH) 4 COH, glucose. 



CH 2 .OH (CH.OH) 4 COOH, gluconic acid. 



COOH - (CH.OH) 4 COH, glucuronic acid. 



COOH - (CH.OH) 4 COOH, saccharinic acid. 



On boiling with water glucuronic acid is, in part at least, trans- 

 formed into its anhydride, glueuron, C 6 H 8 O 6 . 



Aside from its probable origin from glycogen, glucuronic acid may 

 also be derived from c/iondroitin-sulphuric acid, which has also been 

 observed in normal urine. We have seen, as a matter of fact, that 

 this acid occurs in the cartilaginous structures of the higher animals, 

 and that its hyalin component chondroitin first yields chondrosin on 

 hydrolytic decomposition, which is then further decomposed into 

 glucuronic acid and glucosainin, as shown in the equations : 



(1) C 18 H 27 NO U -f 3H 2 = C 12 H 21 NO n + 3CH 3 .COOH 

 Chondroitin. Chondrosin. Acetic acid. 



(2) C, 2 H 2 ,NO n + H 2 O = COOH.(CH.OH) 4 .COH + C 6 H U O 6 .NH 2 

 Chondrosin. Glucuronic acid. Glucosamin. 



Schmiedeberg, indeed, regards the chrondroitin-sulphuric acid as the 

 normal source of the glucuronic acid. 



Glucuronic acid has thus far not been obtained in crystalline 

 form. It is a syrupy substance which is readily soluble in water 

 and alcohol. Its anhydride, however, is a crystalline body, and is 

 likewise soluble in water but insoluble in alcohol. The free acid 

 and its alkaline salts are dextrorotatory, while the conjugate glucuro- 

 nates turn the polarized light to the left. The free acid, moreover, 

 as well as its salts and most of its compound ethers, reduces the 

 oxides of copper, bismuth, and silver in alkaline solution, and it is 

 thus possible to confound them with glucose if reliance is placed upon 

 the corresponding tests alone. With phenyl-hydrazin the free acid 

 is said to form a crystalline compound with a melting-point of 114- 

 115 C. Unlike glucose, it is non-fermentable. It gives the fur- 

 furol reaction and simulates the pentoses in reacting with phloro- 

 glucin hydrochlorate, but not with orcin (see page 284). 



To demonstrate the presence of glucuronic acid in the urine, it 

 is necessary to isolate its compound ethers and to decompose these 

 with superheated steam. Under normal conditions this is practi- 

 cally impossible unless very large quantities of urine are employed. 

 Its presence may, however, be suspected if a urine reduces Fehling's 

 and Nylander's solution, if it is Isevorotatory, and gives the phloro- 

 glucin hydrochlorate reaction, while sugar is absent. 



The Compound Glycocolls. 



As has been pointed out, phenyl-propionic acid and phenyl-acetic 

 acid, which are both formed from albuminous material during the 



