( '. / A7/( >// ) DR. 1 TES AND RELATED SUBSTANCES. 607 
ilch'cR'il, .-Mill l-jiniin iiic acid, a related substance, is an importanl consti- 
tuent of dog's urine. 1 
Pathologically, the substances just described may become of considerable 
importance. In carbolic acid poisoning many of them are excreted in greatly 
increased amount; pyrocatechin and hydrochinon may be present in large 
quantity, and then give rise, by their oxidation, to the peculiar coloration seen 
in carboluria. In certain diseases other members of the group are increased, 
and give rise to the phenomena of alcaptonuria. In this state the urine 
develops, on standing, a dark colour, like that seen in carboluria : and 
Boedecker in 1861 isolated a substance which he termed alkapton, to the 
oxidation of which he held the colour due. Alkapton was shown by Marshall 
and Kirk to be impure uroleucic acid (vide supra). This latter substance, 
however, is not wholly responsible for the coloration phenomenon. "Wolkow 
and Baumann - have recently shown that in a case investigated by them the 
" alkaptonuria " was almost wholly due to the presence of homogentisic acid 
(supra). Pyrocatechin is doubtless sometimes the cause. 3 Most hydroxy- 
derivatives of benzene in alkaline solution develop a dark coloration on 
exposure to the air 4 (cf. p. 630). 
The quantity of phenol and kresol in the urine is increased in extreme 
constipation, in obstruction of the lower bowel, in peritonitis, and in pyaemia 
(cf. indoxyl, infra, and p. 631). 
Indoxyl and skatoxyl. — These, although nitrogenous compounds, 
are closely related to the substances just treated, and may fitly be 
considered here. 
Indoxyl (C 6 H 4 .NH.CH.C.OH). — The so-called urinary indican is 
indoxylsulphuric acid. In normal urine on a mixed diet, the quantity 
present is only from 5 to 20 mgrms. In herbivora the quantity 
is much larger. It is absent from the urine of new-born children 
(Senator). Indoxyl is derived from oxidation in the body of the indol 
absorbed from the bowel, and its amount is increased, like that of the 
urinary phenols, by all causes which lead to increased bacterial decom- 
position of proteids, in the intestine or elsewhere ; and by circumstances 
which favour the absorption of the indol when formed (intestinal 
obstruction, etc.). Skatoxyl (C 9 H 8 NOH) is derived from skatol (methyl- 
indol), and accompanies indoxyl into the urine by parallel paths and 
froin kindred causes. Like indoxyl, it is present as a conjugated 
sulphate. 
By oxidation indoxyl forms indigo-blue and indigo-red, while skatoxyl 
similarly yields red pigments. The consequent colour phenomena 
which arise in the urine are discussed under the bead of the pigments. 
Carbohydrates and Eelated Substances. 
Normal urine contains small quantities of 'certain carbohydrates. 
Under ordinary circumstances the physiological limit extends only to 
a minute quantity of any one of these substances : but, in the urine of 
women during lactation, milk-sugar may occur in very considerable 
aim Hint, without departure from what must be considered physiological 
conditions. 
1 For phenaceturic acid, see under hippuric acid. 2 Loc. cit. 
3 Cf. v. Jakseh, " Klinische Diagnostik," 4th edition, 1896, p. 415. 
4 The behaviour of the alkaline solution of pyrogallic acid used in photography will 
be an example familiar to many. 
