BILE. 247 



zone next to the acid will be the most oxidized, and will be of a 

 yellow-red color : the product is choletelin, C 16 H 18 N 2 O 6 . Above 

 this will be a zone of red or purple, becoming blue : this product 

 is called bilicyanm ; above all will be a green zone, biliverdin, 

 which being farthest from the acid has undergone the least oxi- 

 dation. This constitutes Gmelin's reaction, arid is employed to 

 detect the presence of bile-pigments, as in the urine. A modified 

 form of applying this test consists in wetting a piece of filter-paper 

 with bile, or the solution which is suspected to contain bile, 

 and dropping the fuming nitric acid upon it, when the character- 

 istic colors will appear. 



Biliary urine gives an absorption spectrum showing a wide 

 band beginning at the red side of D and ending between D and 

 E. Choletelin gives a band between C and F. 



Hydrobilirubin. This substance has the formula C 32 H 40 N 4 O 7 . 

 It is a reduction-product of bilirubin, and is obtained by the 

 action of nascent hydrogen, from sodium amalgam, in an alkaline 

 solution of bilirubin. It gives an absorption spectrum, a dark 

 band between C and F. It is with difficulty oxidized to bilirubin 

 or biliverdin. Although bilirubin and biliverdin as constituents 

 of the bile enter the intestine, still neither is found in the feces, 

 but hydrobilirubin is there found, which is undoubtedly derived 

 from the bile-pigments. This pigment of the feces has been 

 described as stercobilin. A similar pigment in the urine is uro- 

 bilin, and it is now claimed that hydrobilirubin, stercobilin, and 

 urobilin are one and the same substance. 



As already stated, it is believed that bilirubin comes from 

 hemoglobin, the coloring-matter of the blood. In the liver this 

 is decomposed into a proteid and hematin, the latter containing 

 iron. The hematin takes up water, the liver-cells remove the 

 iron, and bilirubin is formed. This may be expressed by the fol- 

 lowing equation : 



+ 2H 2 - Fe = C 32 H 36 N 4 O 6 or 2(C 16 H 18 N 2 O 3 ). 



Hematin. Water. Iron. Bilirubin. 



Bile-salts. These are sodium glycocholate and sodium tauro- 

 cholate i. e., sodium united with glycocholic acid, C^H^NOg, and 

 taurocholic acid, C 26 H 45 NSO 7 . These acids are known as bile-acids. 

 Both occur in human bile, as a rule, though taurocholic acid may 

 be absent. When glycocholic or taurocholic acid is boiled with 

 an acid or an alkali, it takes up water and then splits up, or, as it 

 is expressed, " undergoes hydrolytic cleavage/' into cholic or chola- 

 lic acid, and an amido-acid i. e., an organic acid, one or more of 

 whose hydrogen atoms is replaced by amidogen (NH 2 ). Glyco- 

 cholic acid produces glycocoll or amido-acetic acid, and cholic acid ; 

 while taurocholic acid yields taurin or amido-ethylsulphonic acid. 

 This is represented by the following equations : 



