ANIMAL GUMGL YCURONIC ACID. 613 



quantities of a sugar, which, though not fermentable, gives a well- 

 crystallised osazone, and reduces Fehling's solution. According to the 

 researches of Baisch, 1 the properties of this substance agree with those 

 of " isomaltose." 



(f) Animal gum. The third and remaining carbohydrate which 

 separates from normal urine when this is treated with benzoylchloride, 

 is a dextrin-like substance, in all probability identical with "animal 

 gum." This was first isolated from urine by Landwehr, 2 who took 

 advantage for this purpose of the insolubility of its copper compound. 

 Its presence has been confirmed both by Wedenski and Baisch, who 

 employed the benzoylchloride method. 



The substance does not reduce metallic salts, but, on the other hand, 

 on boiling with mineral acids, it yields a derivative which will reduce 

 Fehling's and Nylander's reagents freely. Simultaneously it yields 

 (like many other carbohydrates and certain of the aromatic constituents 

 of the urine) with acids a brown flocculent precipitate of the " humous 

 substances " of v. Udransky. 3 It is due to the presence of this substance 

 that the reducing power of most urines is increased after boiling with 

 mineral acids. 



(g) G-lycuronic acid. The chemical relationship of this acid to the 

 glucoses is seen by a comparison of their respective formulas : 



CH 2 HO(CH.OH) 4 CHO COOH.(CH.OH) 4 CHO 



(glucose) (glycuronic acid) 



It is derived from these sugars by oxidation of the primary alcohol 

 group, CH 2 .OH, to the carboxyl group, COOH. It is at once, therefore, 

 an aldehyde and an acid. As an aldehyde, it reduces copper solutions. 



It should be understood that glycuronic acid is never a constituent 

 of normal urine in appreciable amount, nor does it appear as the result 

 of pathological processes in the ordinary sense. Its presence almost 

 always depends upon the ingestion of special substances, which are for 

 the most part foreign to ordinary foodstuffs ; and, when excreted, it is 

 " conjugated " with these, or with derivatives of these. 



It is apparently an intermediate product in the metabolism of 

 carbohydrates, which, normally, becomes fully oxidised in the body ; 

 but which, when conjugated with the exceptional substances referred to, 

 escapes oxidation, and appears in the urine, just as the easily oxidisable 

 glycin is protected by conjugation with benzoic acid and appears as 

 hippuric acid. 



Some of the substances which form these conjugated compounds 

 with glycuronic acid, are those which ordinarily form conjugated or 

 ethereal sulphates (cf. pp. 606 and 631), especially the aromatic hydroxy- 

 compounds. Phenol- indoxyl- and skatoxyl-glycuronic acids and many 

 analogues have been described in the urine. But apparently the sulphate 

 conjugation is the more constant process, and it is only when the above 

 substances are present in very large amount that their glycuronic con- 

 jugates appear in addition to their sulphuric acid compounds, in 

 general, only when they, or their precursors, are given abundantly by 

 the mouth for the purposes of experiment. 



Of more practical importance are those conjugated compounds of 



1 Baisch, Ztschr. f, physioL OJiem., Strassburg, Bd. xx. S. 249. 



2 Centralbl.f. d. med. Wissensch., Berlin, 1885, S. 369. 



3 Ztschr. f. physioL Chem., Strassburg, 1888, Bd. xii. S. 33. 



