DIGESTION. 



275 



F. The bile of the sheep and ox give three bands in a thick layer, and 

 four or five bands with a thinner layer, one on each side of D, one near 

 E, and a faint line at F. (McMunn.) . 



There seems to be a close relationship between the color-matter of the 

 "blood and of the bile, and it may be added, between these and that of the 

 urine (urobilin), and of the fa?ces (stercobilin) also; -it is probable they 

 are, all of them, varieties of the same pigment, or derived from the same 

 source. Indeed it is maintained that Urobilin is identical with Hydro- 

 bilirubin, a substance which is obtained from bilirubin by the action of 

 sodium amalgam, or by the action of sodium amalgam on alkaline haema- 

 tin; both urobilin and hydrobilirubin giving a characteristic absorption 

 band between b and F. They are also identical with stercobilin, which 

 is formed in the alimentary canal from bile pigments. 



A common test (Gmelin's) for the presence of bile-pigment consists of 

 the addition of a small quantity of nitric acid, yellow with nitrous acid; 

 if bile be present, a play of colors is produced, beginning with green and 

 passing through blue and violet to red, and lastly to yellow. The spec- 

 trum of Gmelin's test gives a black band 

 extending from near b to beyond F. 



Fatty substances are found in variable 

 proportions in the bile. Besides the ordinary 

 saponifiable fats, there is a small quantity 

 of ChoUsforin, a so-called non-saponifiable 

 fat, which, with the other free fats, is prob- 

 ably held in solution by the bile salts. It 

 is a body belonging to the class of mon- 

 atomic alcohols (c 26 H 44 o), and crystallizes in 

 rhombic plates (Fig. 205). It is insoluble in 

 water and cold alcohol, but dissolves easily 

 in boiling alcohol or ether. It gives a red 

 color with strong sulphuric acid, and with nitric acid and ammonia; also 

 a play of colors beginning with blood red and ending with green on 

 the addition of sulphuric acid and chloroform. Lecithin (c 44 H 90 ^P0 9 ), 

 a phosphorus-containing body and Neurin (c 6 H 1B NO a ), are also found in 

 bile, the latter probably as a decomposition product of the former. 



The Mucus in bile is derived from the mucous membrane and glands 

 of the gall-bladder, and of the hepatic ducts. It constitutes the residue 

 after bile is treated with alcohol. The epithelium with which it is mixed 

 may be detected in the bile with the microscope in the form of cylindrical 

 cells, either scattered or still held together in layers. To the presence of 

 the mucus is probably to be ascribed the rapid decomposition undergone 

 by the bilin; for, according to Berzelius, if the mucus be separated, bile 

 will remain unchanged for many days. 



The Saline or inorganic constituents of the bile are similar to those 



FIG. 205. Crystalline scales of 

 cholestefin. 



