ANIMAL GUM— GLYCURONIC 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 abfmal 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 X\ lander's reagents freely. Simultaneously it yields 
(like many other carbohydrates and certain of the aromatic constituents 
of the urine) with acids a brown tlocculent 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) Glycuronic acid. — The chemical relationship of this acid to the 
glucoses is seen by a comparison of their respective formulae : — 
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 thos. conjugated compounds of 
1 Baisch, Ztschr. f. physiol. Chem., Strassburg, Bd. xx. S. 249. 
2 Centralbl. f. d. mcd. Wissensch., Berlin, 1885, S. 369. 
8 Ztschr. f. physiol. ''hem., Strassburg, 1888, Bd. xii. S. 33. 
