vii KATABOLIC CONSTITUENTS OF UKINE 397 



in which absorption of the products of intestinal digestion is 

 defective ; (&) in gastric disease, which causes a block of food in 

 the stomach, and thus obstructs the fermentative processes ; (c) also 

 in diseases localised outside the digestive canal (cystitis, abscesses, 

 suppurative peritonitis), in which putrefactive processes develop. 



It is remarkable that in abdominal typhoid and in cases of 

 simple intestinal constriction, the ethereal sulphates of the urine 

 do not increase to any large extent. 



VI. The urine collected under normal conditions, and still 

 more in different pathological states, is rich in pigments, and sub- 

 stances readily converted into pigments and therefore known as 

 cliromogens. When examined in the spectroscope, however, normal 

 urine exhibits no special absorption bands, but only a simple and 

 partially diffused absorption, which varies in intensity in the 

 different regions of the spectrum. It increases in the direction of 

 red to violet, but in a different degree in different urines (Vierordt), 

 showing that the quantity and number of the urinary pigments 

 may vary, even under physiological conditions. 



Few of the pigments detected by different workers have been 

 obtained in quantities sufficient for chemical analysis : so that the 

 distinct chemical individuality of many of them may be doubted, 

 the more so as they are highly unstable, and readily undergo 

 ' decomposition on treatment with strong reagents. The better- 

 known pigments are urochrome and urobilin, the first being that 

 which 'gives the urine its normal colour, while the second is 

 usually present only in the form of its chromogen in fresh urine, 

 so that it cannot be held (as many claim) to be a primary urinary 

 pigment. 



Urochrome, isolated by Thudichum (1864) in an impure state, 

 mixed with other pigments, was obtained as a distinct chemical 

 substance by Garrod (1894). He showed it to be a nitrogenous 

 but iron-free substance, which gives the xanthoproteic reaction, 

 and must therefore be regarded as an aromatic body. Although 

 in the dry state it is amorphous and brown in colour, its aqueous 

 solutions have, according to their concentration, the normal hue of 

 urine in its various shades of clear yellow to orange and brown. 

 Examined through the spectroscope it shows no special absorption 

 bands, but absorbs the light diffusely, with increasing intensity 

 from red to violet, like normal urine as a whole. It is therefore 

 evident that urochrome is the principal pigment of normal urine. 



The relationship between urochrome and urobilin is shown by 

 their reciprocal conversion, on treating the former with a reducing 

 and the latter with an oxidising agent. Garrod (1897) found in 

 fact that the alcoholic solutions of urochrome treated with pure 

 aldehyde give a pigment that shows all the reactions of urobilin. 

 Riva (1896), on treating the latter with permanganate of potash, 

 obtained a pigment which seems identical with urochrome. 



