312 URINE. [CH. XII. 



7. Fructose (laevulose). 



Fructose occasionally occurs in the urine, sometimes 

 being accompanied by glucose. The significance of fructo- 

 suria is not yet clear. 



385. Seliwanoff's test (Borchardt's modification). To a few 

 cc. of urine in a test-tube add an equal volume of 25 per cent, 

 hydrochloric acid and a speck or two of resorcin. Heat to boiling, 

 cool under the tap, and transfer to an evaporating dish. Make the 

 reaction alkaline by means of solid sodium hydroxide and return it 

 to a test-tube. Add 3 cc. of acetic ether (ethyl acetate) and shake. 

 A yellow colouration in the acetic ether indicates the presence of 

 fructose. 



8. Pentoses. 



Pentoses, that is carbohydrates with 5 carbon atoms, 

 appear in the urine in three conditions, alimentary, 

 persistent or true pentosuria, and admixed with glucose in 

 cases of glycuresis. 



Alimentary pentosuria is sometimes seen after the 

 mgestion of considerable quantities of certain fruits, as 

 prunes, cherries, grapes and plums. The sugar found 

 varies, but is usually d-arabinose. In true pentosuria it 

 is ^/-arabinose. Its origin and significance have not yet 

 been clearly established. 



Pentoses are indicated when the urine gives a positive 

 Benedict's or Cole's test, but a negative fermentation test. 

 The results of the phenyl-hydrazine test are variable, the 

 osazones being somewhat soluble. The two colour re- 

 actions described are also given by glycuronic acid, which 

 can, however, be demonstrated by Ex. 392. 



386. Tollen's test. To 5 cc. of urine add an equal volume 

 of strong hydrochloric acid and a little phloroglucin (a piece about 

 the size of a pea) and heat the mixture on a boiling water bath. 

 A cherry-red colour develops and the solution shows an absorption 

 band between D and E. On cooling a dark precipitate separates 



