134 PRACTICAL PHYSIOLOGY. [XX. 



bile-pigment absorbed from the intestinal canal and excreted by 

 the urine, 



(2.) [Febrile Urobilin. —This gives the dark colour to urines in fever. It 

 seems to be a less oxidised form of urobilin, is isolated in the same way, its 

 spectrum shows the band near F, and two additional bands, one near D and 

 one between D and E.] 



(3.) Indigo-forming Substance (Indican). — This is derived from indol, 

 C8H7N, which is developed in the intestinal canal from the pancreatic diges- 

 tion of proteids, and also from the ])utrefaction of albuminous bodies. It may 

 also be formed from bilirubin. In urine it is a yellow pigment, and is more 

 plentiful in the urine of the dog and horse. It exists in the urine as a 

 conjugated sulpho-acid salt of potassium, viz., as indoxyl-sulphate of potas- 

 sium (CBHeNSO.K). 



13. General Reactions for Urine Pigments. 



(a.) Add to normal urine a quarter of its volume of HCl, and 

 boil = a fine pink or yellow colour. 



(h.) Add nitric acid = a yellowish- red colour, usually deeper than 

 the original colour. 



(c.) To two volumes of sulphuric acid in a test-tube add one of 

 urine, but drop the latter from a height. The mixtu^ becomes 

 more or less garnet-red if indican be present. 



(d.) Add acetate of lead = a precipitate of chloride, sulphate, and 

 phosphate of lead. Filter ; the filtrate is an almost colourless 

 solution. This substance is used to decolorise urine for the sac- 

 charimeter. 



(e.) Filter urine through animal charcoal; the urine will be 

 decolorised. 



(/.) If possible, obtain a dark-yellow coloured urine, and perform the 

 following test : — Take 40 drops of urine + 3 to 4 cc. of strong HCl and 2 to 3 

 drops of HNO3 ; on heating, a violet red colour with the formation of true 

 rhombic crystals of indigo-blue indicates the presence of indican. 



(f/.) Test for Indican. — Mix equal volumes of urine and HCl, add, drop by 

 drop, a saturated solution of chloride of lime {i.e., bleaching powder, which 

 also contains hypochlorite of calcium) = a blue colour. Shake up with chloro- 

 form and the blue colour is absorbed by the latter. 



14. Phenol (carbolic acid), CeH,;0, occurs in the urine as phenol-sulphate of 

 potassium, CuHjO - SO3 — OK. There is a corresponding salt of Cresol, most 

 abundant in the urine of herbivora. Add sulphuric acid to urine until the 

 latter contains 5 per cent, of the acid. Distil as long as the distillate becomes 

 cloudy with bromine water. Test the distillate as follows : — 



(a.) Bromine water = precipitate of tri-bromo-phenol (CgH-^BrgOH). 



{b.) Neutralise and add neutral ferric chloride = violet colour. 



(c. ) Heated with Millon's reagent it gives a red colour. (See also p. 82.) 



The pathological pigments — bile, blood, &c. — occurring in urine 

 will be referred to later. 



