478 HANDBOOK OF PHYSIOLOGY. 



seen in acid solutions; and by giving u green fluorescence when excess 

 of ammonia with a little chloride of zinc is added to it. The very 

 vexed question of the relation of the pigments of urine to bile pigments 

 turns largely upon the spectroscopic appearances of urobilin ; for orange- 

 colored solutions having the same absorption band as urobilin may be 

 prepared from bile pigments in two different ways i, by reduction with 

 sodium amalgam HydroUliruUn (Maly) ; ii, by oxidation with nitric 

 acid Choletelin (Jaffe), and both these bile derivatives give a fluores- 

 cence with ammonia and a drop of chloride of zinc. It is not satisfac- 

 torily settled which of these, if either, is the same as urobilin of urine. 

 It is worth noting that choletelin may be oxidized a stage further; it 

 then loses its absorption band, remaining however of a yellow color. It 

 is very possible that the urochrome of normal urine may be this oxi- 

 dized choletelin, and that the presence of the absorption band of urobilin 

 in urines may mean that some of the pigment is in the stage of cholete- 

 lin; i.e., that its oxidation is not quite completed. 



Those who believe urobilin to be identical with hydrobilirubm sup- 

 pose that the bilirubin is reduced by the putrefactive processes in the 

 intestines, and is conveyed in its reduced form by the blood stream to 

 the kidneys. 



3. Uro-erytlirin is the pigment which is found in the pink deposits 

 of urates which are sometimes seen in urines; it communicates a rich 

 red-orange color to urine when in solution, and its solutions have two 

 broad faint absorption bands in the green. 



4. Uromelanin. When urine is boiled with strong acids it darkens 

 to a reddish- brown color. This change, once ascribed to the forma- 

 tion of a new pigment uromelanin, is now believed to be due to the 

 presence in urine of pyrocatechin and allied bodies which are capable 

 of taking up oxygen when boiled with acids, yielding C0 2 and brown 

 or black residual products. 



5. Indigo is rarely found in urines, to which it may communicate a 

 blue or green color. Urine frequently contains a compound which is 

 either a glucoside, Indican; or more probably a salt of indoxyl-sulphuric 

 acid. It yields indigo blue when treated with strong hydrochloric acid 

 and left to stand for some hours exposed to the air; the indigo may be 

 separated by treatment with boiling chloroform, which takes it up, 

 forming a blue solution. 



There is a similar compound of skatol and sulphuric acid which is 

 sometimes recognized in the urine, by the production of a red color 

 when nitric acid is added to it. 



Many medicinal substances color the urine, for instance Ehubarb, 

 Santonin, Senna, Fuchsine, Carbolic Acid. 



Bromides and Iodides yield Bromine or Iodine, when nitric acid is 

 added to the urine of patients taking these drugs. In the case of iodides 



