THE BILE. 123 



lies, alkaline earths, and iron. The color of the bile is 

 due to the biliary pigments, bilirubin, biliverdin, etc. 



The salts of the biliary acids in the bile of different 

 animals vary in their proportions. In the case of car- 

 nivorous animals only the taurocholic acid is found; in 

 the human bile, as well as that of most cattle, both are 

 present. The biliary acids are both compounds of cholic 

 acid, C 24 H 40 5 . Glycocholic acid, C 26 H 43 N0 6 , is com- 

 posed of cholalic acid united with glycocol, CH 2 ISrH 2 C0 2 H; 

 taurocholic acid, C 26 H 45 ]SrS0 7 , of cholalic acid and taurin, 

 C 2 H 4 NH 2 S0 3 H. They can be decomposed into their con- 

 stituents by the caustic alkalies. With cane-sugar and 

 sulphuric acid the biliary acids give a purple color, and 

 this can be used as a test of their presence. 



This test is an extremely delicate one, and its failure indi- 

 cates that biliary acids are absent. There are, however, other 

 substances like albumin, morphine, and amyl-alcohol which give 

 a similar color. In these cases the spectroscopic test should not be 

 neglected. The biliary acids can be obtained pure by evaporating 

 the solution to dryness, extracting with absolute alcohol, pre- 

 cipitating this solution with ether, and applying the test to the 

 precipitate. The purple solution, when sufficiently diluted with 

 alcohol and examined spectroscopically, gives a dark band between 

 D and E, near to E, and another before F. These are not seen 

 with albumin, etc. 



In concentrated sulphuric acid they give a green color, 

 showing a strong fluorescence. The sodium salts are ob- 

 tainable from the bile by evaporating to dryness and, after 

 dissolving in alcohol, precipitating with ether. 



Cholesterin, C 26 H 43 OH, occurs in most of the fluids 

 of the body, as well as in the bile, and the calculi or 

 concretions of the gall-bladder, of which it forms the 

 principal part. It is not common in the urine, but is a 

 constant ingredient of the faeces. It is insoluble in water, 



