BILE 63 



cholesterin, lecithin, neutral fats, soaps, traces of urea, and a 

 mucilaginous nucleo-albumin wrongly called mucin. The 

 color of bile in carnivora is a bright golden red, due to the 

 pigment bilirubin, while in herbivora it is green as the result 

 of the pigment biliverdin. The color of the human bile varies 

 from a yellow to a dark olive. It is feebly alkaline, and has 

 a specific gravity of 1010 to 1050. Biliverdin (C 16 H 18 N 2 O 4 ) 

 is an oxidation product of bilirubin (C 16 H 18 N 2 O 3 ). They are 

 detected by Gmelin's reaction, which consists in bringing the 

 solution to be tested in contact with fuming nitric acid, when 

 a series of color changes result. The bile pigments originate 

 in the liver from hemoglobin. They are mixed with the food 

 in its passage along the intestine, and are partly reabsorbed 

 and carried back to the liver in the portal blood. The bile 

 acids are found as the sodium salts of glycocholic and taurocholic 

 acid. Both are present in human bile, and may be detected 

 by Pettenkofer's reaction, which consists in adding to the liquid 

 to be tested a few drops of a 10 per cent, solution of cane sugar, 

 and then, carefully, strong sulphuric acid. The tempera- 

 ture must be kept below 70 F. If bile salts are present a ' 

 violet ring is formed at the junction of the liquids, which is 

 due to the formation of a substance known as furfuroL The 

 latter reacting with the bile salts gives the color. The bile 

 salts are reabsorbed, partially at least, and again given off 

 by the liver. The value of this process is not known unless it 

 is to economize material, since the bile salts serve to hold the 

 excretion cholesterin in solution, which is constantly present 

 in the bile, and serve also to assist in the absorption of fats 

 from the intestine. Cholesterin (C 27 H 46 O) is eliminated by the 

 liver cells and remains unchanged in the feces. It is a crystal- 

 lizable, insoluble substance, found particularly in the medullary 

 substance of nerve fibers. The nucleo-albumin of the bile 

 is formed by the cells of the ducts and gall-bladder, and gives 

 to bile its mucilaginous character. Bile has indirectly feeble 

 antiseptic powers, and to some extent retards putrefactive 

 changes in the intestine, and it also neutralizes the acid chyme 

 from the stomach. The role played by bile in digestion is 

 the preparation of fats for absorption. This it does in con- 

 junction with the pancreatic juice. Neutral fats, after being 

 melted by the heat of the body, are converted partially to 



