ANIMAL FLUIDS AND TISSUES. 441 



The quantity of bile discharged daily by a grown person may be 

 put at forty ounces, but a considerable quantity of this discharged 

 bile is reabsorbed in a changed form by the intestines ; only a small 

 amount of bile matters (in a decomposed state, however) is discharged 

 by the feces. 



The functions of bile have been stated in the previous chapter. 



Biliary pigments. Of these four are known, but it is probable that 

 more exist. Bilirubin, C 16 H 18 N 2 O 3 , is, when amorphous, an orange- 

 yellow powder ; when crystalline, it forms red prisms. It is sparingly 

 soluble in water, alcohol, and ether, readily soluble in hot chloroform 

 and carbon disulphide. When treated with a mixture of concentrated 

 nitric acid and sulphuric acid it turns first green, then blue, violet, red, 

 and finally yellow. This reaction, known as Gmelin's test, is used for 

 the detection of bile-pigments in urine and other fluids. (See Plate 

 VIII., 7.) 



Biliverdin, C 32 H 36 N 4 O 8 , is a green powder existing in green biles; 

 it responds to Gmelin's test. 



Biliary acids. G-lycocholic acid, C 26 H 43 NO 6 , and taurocholic acid, 

 C 26 H 45 NO 7 S, exist as sodium salts in the bile of man and most 

 animals. Both salts may be obtained as colorless crystals, which 

 dissolve in water, forming solutions of an acid reaction and an 

 intensely bitter taste. Both acids are easily decomposed by heating 

 with alkalies or with dilute acids, also by the action of putrefying 

 material or by the chemical changes taking place in the intestines. 

 In all these cases is formed cholic add, C 24 H 40 O 5 , and a second pro- 

 duct, which in the case of glycocholic acid is glycocol, C 2 H 5 NO 2 , and 

 in the case of taurocholic acid taurine, C 2 H 7 NO 3 S. 



Pettenkofer's test. The biliary acids and their salts show a charac- 

 teristic reaction known as Pettenkofer's test. This reaction is shown 

 by adding very little cane-sugar to the liquid substance under exam- 

 ination, and adding concentrated sulphuric acid in such a manner 

 that the temperature does not rise above 70 C. (158 F.). In the 

 presence of biliary acids a beautiful cherry- red color is developed, 

 which gradually changes to dark reddish-purple. (See Plate 



Yin., s.) 



The bile acids are, however, not the only substances which show the above 

 reaction, and, therefore, it becomes in many cases necessary to separate the 

 bile acids from other organic matter. This separation is accomplished by 

 evaporating the substance under examination (urine, for instance), after having 

 been mixed with a small quantity of coarse animal charcoal, to dryness at 



