THE PIGMENTS OF THE URINE. 309 



urates or uric acid. Of its chemical nature, however, nothing defi- 

 nite is known, but there is evidence to show that it also is a deriva- 

 tive of the normal coloring-matter of the blood. It contains 

 62.51 per cent, of carbon and 5.79 per cent, of hydrogen. Its 

 amount is noticeably increased in extensive disease of the liver, as 

 also in conditions associated with an increased destruction of red 

 corpuscles. 



Isolation of Uroerythrin. As has been stated, the salmon color of 

 sediments of urates and uric acid is due to this pigment. In their 

 absence the urine is precipitated with neutral acetate of lead or 

 barium chloride. If uroerythrin is present beyond traces, it is thrown 

 down, and colors the resulting precipitate a more or less intense 

 salmon red. The pigment is soluble in boiling alcohol, and may 

 thus be extracted. Its solutions are said to give rise to two bands 

 of absorption to the left of F. 



Urobilin. Urines which contain much urobilin, viz., the patho- 

 logical urobilin of Jaife, present a dark-yellow color, which may be 

 imparted to the foam on shaking. They are thus quite similar to 

 icteric urines. 



Tests. To identify the substance, the urine is precipitated with a 

 mixture of barium hydrate and barium chloride. If notable quanti- 

 ties of urobilin are present, the precipitate is thus colored a more or 

 less intense brownish-red. On boiling with acidulated alcohol the 

 pigment is then extracted, and imparts a brownish or pomegranate- 

 red color to the alcoholic solution (v. Jaksch). 



Gerhardt's test also is very serviceable. To this end, 10-20 c.c. 

 of urine are extracted with chloroform by shaking. A few drops 

 of a dilute solution of iodopotassic iodide are added to the extract, 

 when, upon the further addition of a dilute solution of sodium 

 hydrate, the solution is colored yellow or yellowish brown and ex- 

 hibits a beautiful greenish fluorescence. 



If the substance cannot be demonstrated with these tests, the 

 urine is acidulated with hydrochloric acid and allowed to stand 

 exposed to the air, so that any urobilinogen that may be present 

 is transformed into the free pigment. The fluid is then examined 

 with the spectroscope, when in the presence of urobilin a distinct 

 band of absorption is obtained between b and F, extending beyond 

 F to the right. A similar band is also obtained in alkaline solu- 

 tion, but is not so intense and does not extend beyond F. 



Isolation. To isolate the pigment, if present in large amounts, 

 the urine is directly precipitated with ammonia and chloride of 

 zinc. The precipitate is thoroughly washed with water, extracted 

 with alcohol by boiling, dried, and then dissolved in ammonia. The 

 resulting solution is precipitated with subacetate of lead, the precipi- 

 tate washed with water, and extracted with boiling alcohol as before, 

 and decomposed with acid alcohol. The filtered alcoholic solution is 

 treated with one-half its volume of chloroform and diluted with 

 water; the urobilin passes into the chloroform on moderate agita- 



