164 LOUIS BAUMAN 



Urobilinogen is a colorless compound which forms monoclinic crystals 

 melting at 192 C. Its molecular weight is 600. It is soluble in chloro- 

 form and other organic solvents and is readily oxidized to urobilin by the 

 oxygen of the air and by oxidizing substances. 



II. Fischer synthesized urobilinogen by reducing bilirubin with sodium 

 amalgam ; he also described some of its physical and chemical properties. 

 Ho obtained it to the extent of about 46 per cent of the bilirubin which 

 he employed, and assuming that it was derived from one-half of the 

 bilirubin molecule he named it hemibilirubin. Later Fischer and Meyer- 

 Betz (a) (1911) proved that urobilinogen and hemibilirubin were identi- 

 cal. Fromholdt obtained the same substance by a somewhat similar method. 



When urobilinogen is treated with para-dimethylamino-benzaldehyd, 

 dissolved in hydrochloric acid, the so-called Ehrlich reagent, it forms a 

 red compound which absorbs certain rays in the orange and green regions 

 of the spectrum between the D and E lines. The red compound results 

 from the oxidation of a colorless chromogen. A solution containing one 

 part of urobilinogen in 640,000 parts of water still gives the Ehrlich 

 reaction (Fischer and Meyer-Betz (a), 1911). This reaction is not specific, 

 for it is obtained with any pyrole derivative that contains a free hydrogen 

 atom attached to one of the carbon atoms of the ring. Urine containing 

 indol derivatives also gives the color test but does not exhibit the char- 

 acteristic absorption bands (Fischer). 



Urobilin is easily obtained from urobilinogen by oxidation. It is a 

 reddish yellow or brown substance of uncertain composition, and probably 

 contains a number of urobilinogen molecules that have been oxidized and 

 polymerized. It is soluble in aqueous alkali and in most organic solvents 

 such as alcohol, ether and chloroform. Urobilin absorbs certain rays in the 

 region of the B and F lines of the spectrum. It forms a colored salt with 

 mercuric chlorid, the so-called Schmidt test. When an alkaline solution 

 of urobilin is neutralized with copper sulphate solution a red compound, 

 soluble in chloroform, is formed. This copper compound exhibits the 

 characteristic urobilin absorption bands (Bogomolow). Urobilin is pre- 

 cipitated from watery solution by ammonium sulphate. It can be reduced 

 to urobilinogen by bacteria (Charnas). Fischer isolated 160 grams of 

 urobilin from a large amount of human feces. His analysis, carbon 63.46 

 per cent, hydrogen -7.67 per cent, and nitrogen 4.09 per cent, agreed with 

 that reported by Garrod and Hopkins about 14 years previously. When 

 urobilin was subjected to dry distillation or reduction by glacial acetic 

 acid and zinc dust two substances were obtained. The one contained 

 nitrogen while the other resembled cholesterol or one of the bile acids, 

 and did not contain nitrogen. 



Occurrence. Because urobilin and urobilinogen have the same clinical 

 and physiological significance, and for the sake of brevity, the term uro- 

 bilin will be used to include both substances. 



