LESSON XXVI 



THE PIGMENTS OF THE URINE 



The urinary pigments are numerous, and have from time to time been 

 described under different names by various observers. 



1. Urochrome. This is the essential yellow pigment of the urine. The 

 word was originally introduced by Thudichum, and the substance he obtained 

 is now recognised to have been a mixture of several pigments, of which, 

 however, the essential yellow pigment formed a large proportion. Garrod's 

 method of separating it from the urine is as follows : 



The urine is saturated with ammonium sulphate and filtered. The 

 filtrate contains the pigment ; this is shaken with alcohol. The alcohol 

 separates readily from the saline mixture, and as it does so dissolves out 

 much of the urochrome. By repeated extraction all the pigment passes into 

 solution in the alcohol. The alcoholic solution is diluted with water, and 

 the mixture again saturated with ammonium sulphate. The alcohol con- 

 taining the pigment in solution again separates out. The second alcoholic 

 solution is made faintly alkaline with ammonia and evaporated to dryness. 

 The residue is extracted once or twice with acetic ether, and then again 

 dissolved in strong alcohol. Finally the alcohol is concentrated till it is 

 deep orange in tint, and poured into an equal volume of ether. The pure 

 pigment is by this means precipitated as an amorphous brown powder. 



Urochrome shows no absorption bands. As already stated (p. 143), it is 

 probably an oxidation product of urobilin. 



2. Urobilin. Urobilin is a derivative of the blood-pigment, and is identical 

 with stercobiliii (see pp. 92, 143). Probably both reduction aud hydration 

 occur in its formation. It is very like the substance named hydrobilirubin 

 by Maly, which he obtained by the action of sodium amalgam on bilirubin. 

 The following formulae show the relationship between these allied pig- 

 ments : 



Haematin. . . .... C 32 H 32 N 4 4 Fe 



Hydrobilirubin . . C. i2 H 40 N t O 7 



Urobilin is probably a further stage in reduction. 



Normal urine contains but little urobilin ; what is present is chiefly in 

 the form of a colourless chromogen, which by oxidation is converted into 

 urobilin. In numerous pathological conditions urobilin is abundant. 



The following are the two methods introduced by Garrod and Hopkins 

 for its separation from the urine : 



(a) The urine is first saturated with ammonium chloride, and the urate 



