248 BILE. [BOOK n. 



a very large amount, and also sulphates, both coming from the 

 bile-salts. The peculiar body cholesterin is conspicuous by its 

 quantity and constancy, but its physiological functions are obscure. 

 The constituents which deserve chief attention are the pigments 

 and the bile-salts. 



Pigments of Bile. The natural golden red colour of normal 

 human or carnivorous bile, is due to the presence of Bilirubin. 

 This, which is also the chief pigmentary constituent of gall-stones, 

 and occurs largely in the urine of jaundice, may be obtained in the 

 form either of an orange-coloured powder, or of well-formed 

 rhombic tablets and prisms. Insoluble in water, and but little 

 soluble in ether and alcohol, it is readily soluble in chloroform, and 

 in alkaline fluids. Its composition is C 16 H 18 N 2 3 . Treated with 

 oxidizing agents, such as nitric acid yellow with nitrous acid, it 

 displays a succession of colours in the order of the spectrum. The 

 yellowish golden red becomes green, this a greenish blue, then 

 blue, next violet, afterwards a dirty red, and finally a pale yellow. 

 This characteristic reaction of bilirubin is the basis of the so-called 

 Gmelin's test for bile-pigments. Each of these stages represents a 

 distinct pigmentary substance. An alkaline solution of bilirubin, 

 exposed in a shallow vessel to the action of the air, turns green, 

 becoming converted into Biliverdin (C 16 H 20 N 2 O 5 or C 16 H ]8 N 2 4 

 Maly), the green pigment of herbivorous bile. Biliverdin is also 

 found at times in the urine of jaundice, and is probably the body 

 which gives to bile which has been exposed to the action of gastric 

 juice, as in biliary vomits, its characteristic green hue. It is the 

 first stage of the oxidation of bilirubin in Gmelin's test. Treated 

 with oxidizing agents biliverdin runs through the same series of 

 colours as bilirubin, with the exception of the initial golden red. 



The bile-salts. These consist, in man and many animals, of 

 sodium glycocholate and taurocholate : the proportion of the two 

 varying in different animals. In man both the total quantity of 

 bile-salts and the proportion of the one bile-salt to the other seem 

 to vary a good deal, but the glycocholate is said to be always the 

 more abundant. In ox-gall, sodium glycocholate is abundant, and 

 taurocholate scanty. The bile-salts of the dog, cat, bear, and other 

 carnivora, consist exclusively of the latter. 



Insoluble in ether but soluble in alcohol and in water, the 

 aqueous solutions having a decided alkaline reaction, both salts 

 may be obtained by crystallisation in fine acicular needles. They 

 are exceedingly deliquescent. The solutions of both acids have a 

 dextro-rotatory action on polarized light. 



Preparation. Bile, mixed with animal charcoal, is evaporated to 

 dryness and extracted with alcohol. If not colourless, the alcoholic 

 filtrate must be further decolorized with animal charcoal, and the 



