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HANDBOOK OF PHYSIOLOGY. 



sheep, ox, and crow do so, the most constant of which appears to be a 

 band at F. The bile of the sheep and ox gives 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 coloring matters 

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

 that of the urine (urobilin), and of the fa3ces (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 identi- 

 cal with Hydrobilirubin, a substance which in alkaline solution gives a 

 green fluorescence with zinc chloride, which is obtained from bilirubin 

 by the action of sodium amalgam, or by the action of sodium amalgam 

 on alkaline haamatin; both urobilin and hydrobilirubin giving a charac- 

 teristic absorption band between b and F. They are also identical with 

 stercobilin, which is formed in the alimentary canal from bile pigments. 



Fig. 273. Crystalline scales of cholesterin. 



The Test (Gm elm'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 final 

 yellow substance has been called choletelin. The spectrum of Gmelin's 

 test gives a black band extending from near b to beyond F. 



(c) Fatty substances are found in variable proportions in the bile. 

 Besides these saponifiable fats, there is a small quantity of Cholesterin, 

 which is an alcohol, and, with the free fats, is probably held in solution 

 by the bile salts. It is a body belonging to the class of monatomic alco- 

 hols (C 27 H 45 OH, Obermiiller), and crystallizes in rhombic plates (fig. 

 273). It is insoluble in water and cold alcohol, but dissolves easily in 

 boiling alcohol or in 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 4Q H 84 NP0 9 ) is also found: it is a combina- 

 tion of cholin with glycerophosphoric acid in which two of the hydrogen 



