356 BILE-SALTS. [Book ii. 



though soluble in hot alcohol and readily soluble in ether, chloro- 

 form &c, it is dissolved by the bile-salts in aqueous solution and 

 hence is present in solution in bile Its physiological functions 

 are obscure. 



The ash of bile consists laryelv of soda, derived partly from the 



O v ? It/ 



sodium chloride and partly from the bile-salts, of sulphates derived 

 chieHy if not wholly from the latter, and of phosphates partly 

 ready formed, and in part derived from the lecithin. 



§ 206. Pigments of Bile. The natural golden red colour of 

 normal human or carnivorous bile, is due to the presence of Bili- 

 rubin. 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 amorphous pow- 

 der, 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 bili- 

 rubin is the basis of the so-called Gmelin's test for bile-pigments. 

 Each of these stages represents a distinct pigmentary substance. 

 As alkaline solution of bilirubin, exposed in a shallow vessel to 

 the action of the air, turns green, becoming converted into Bdi- 

 verdin (C 1(! H 18 N 4 ), the green pigment of herbivorous bile. Bili- 

 verdin 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. 



§ 207. The Bile-salts. These consist, in man and many ani- 

 mals, 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 



