262 AN AMERICAN TEXT-BOOK OF PHYSIOLOGY. 



i. ii. 



Glycocholate ...................... 0.6276 0.761 



Fatty acids from soap .................. 0.1230 0.024 



Cholesterin ...................... 0.0630 0.096 



........... ........... 0.0220 0.1286 



Soluble salts ...... '. .......... ..... 0.8070 0.8051 



Insoluble salts .................... 0.0250 0.0411 



The color of bile varies in different animals according to the preponderance 

 of one or the other of the main bile-pigments, bilirubin and biliverdin. The 

 bile of carnivorous animals has usually a bright golden color, owing to the pres- 

 ence of bilirubin, while that of the herbivora is a bright green from the 

 biliverdin. The color of human bile seems to vary : according to some author- 

 ities, it is yellow or brownish yellow, and this seems especially true of the bile 

 as found in the gall-bladder of the cadaver : according to others, it is of a 

 dark-olive color with the greenish tint predominating. Its reaction is feebly 

 alkaline and its specific gravity varies in human bile from 1050 or 1040 to 

 1010. Human bile does not give an absorption spectrum, but the bile of some 

 herbivora, after exposure to the air at least, gives a characteristic spectrum. 

 The individual constituents of the bile will now be described more in detail, 

 but with reference mainly to their origin, fate, and function in the body. For 

 a description of their strictly chemical properties and reactions reference must 

 be made to the Chemical section. 



Bile-pigments. Bile, according to the animal from which it is obtained, 

 contains one or the other, or a mixture, of the two pigments bilirubin and 

 biliverdin. Biliverdin is supposed to stand to bilirubin in the relation of an 

 oxidation product. Bilirubin is given the formula C 32 H 36 N 4 O 6 , and biliverdin 

 C 32 H 36 N 4 O 8 , the latter being prepared readily from pure specimens of the 

 former by oxidation. These pigments give a characteristic reaction, known 

 as " Gmelin's reaction," with nitric acid containing some nitrous acid (nitric 

 acid with a yellow color). If a drop of bile and a drop of nitric acid are 

 brought into contact, the former undergoes a succession of color changes, the 

 order being green, blue, violet, red, and reddish yellow. The play of colors 

 is due to successive oxidations of the bile-pigments ; starting with bilirubin, 

 the first stage (green) is due to the formation of biliverdin. The pigments 

 formed in some of the other stages have been isolated and named. The 



o 



reaction is very delicate, and it is often used to detect the presence of bile- 

 pigments in other liquids urine, for example. The bile-pigments originate 

 from haemoglobin. This origin was first indicated by the fact that in old 

 blood-clots or in extravasations there was found a crystalline product, the 

 so-called " haematoidin," which was undoubtedly derived from haemoglobin, 

 and which upon more careful examination was proved to be identical with 

 bilirubin. This origin, which has since been made probable by other reac- 

 tions, is now universally accepted. It is supposed that when the blood- 

 corpuscles go to pieces in the circulation (p. 343) the haemoglobin is brought to 

 the liver, and then, under the influence of the liver-cells, is converted to an 



