THE CONSTITUENTS OF BILE 431 



(8) Solvent Action of Bile Salts on Fatty Acids containing 

 Oleic Acid. If some fatty acids from mutton or beef fat be stirred with 

 water, they do not dissolve ; on adding a little bile and stirring up again, 

 fatty acids can be detected in the filtrate by evaporating to dryness, heating 

 and noting the characteristic odour. This process no doubt occurs in the 

 digestion and absorption of fats. 



(9) Oliver's Test for Bile Salts. This depends upon the power of 

 the bile acids to precipitate peptone in acid solution and is useful for showing 

 the presence of bile salts in the urine, e.g. 



About 20 c.c. of bile are evaporated to complete dryness on the water- 

 bath. The residue is heated with 20 c.c. of alcohol on the water-bath stirring 

 the mixture thoroughly with a glass rod. A little more alcohol is added and 

 it is filtered. The filtrate is evaporated to dryness on the water-bath and the 

 residue extracted with about 30 c.c. of hot water. A solution of the pigments 

 and the salts of bile, free from proteins, is obtained on filtering. 



If a portion of this solution be acidified with glacial acetic acid, the bile 

 acids are not thrown down, but on adding an equal quantity of i per cent. 

 Witte's peptone solution a turbidity or a precipitate is obtained, insoluble in 

 excess of acid. 



As applied to urine, it is only necessary to acidify with acetic acid, 

 filter till quite clear and treat with an equal volume of i per cent. Witte's 

 peptone solution. 



(10) Cholesterol may be detected as follows (Roaf) : 



10 c.c. of bile are evaporated to dryness on the water-bath. The 

 residue is extracted several times with small quantities of ether, pour- 

 ing each ether extract into another evaporating basin. The ether is 

 allowed to evaporate and the residue is dissolved in about 2 c.c. of 

 chloroform. It gives Salkowski's and Liebermann's reactions. 



III. GALL STONES. 



Calculi of various sizes and shapes and of variable number occur in the 

 gall bladder. Three kinds have been distinguished : 



(1) Pigmented Chalk Stones. 



In man these stones are small ; in the ox and pig stones as large as a 

 walnut have been found. They are heavier than water. They consist almost 

 entirely of the calcium salt of bilirubin and contain very little or no biliverdin. 

 Sometimes black or greenish-black metallic-looking stones, which consist 

 of bilifuscin and biliverdin, occur. Iron and copper are generally present. 



(2) Cholesterol Stones. 



The shape and size of the cholesterol stones are very variable ; they are 

 generally lighter than water and are composed of concentric layers. Their 

 surface if fractured appears crystalline ; if cut, waxy. If the fractured surface be 

 rubbed with the nail it also looks waxy. By rubbing against one another in 

 the gall bladder they are generally faceted. They are almost white and usually 

 show pigmented edges (pigmented chalk). 



(3) Calcium Carbonate and Phosphate. 



These stones are very rare in man. 



