BILE-SALTS AND CHOLIC ACID 103 



constituent of the bile-salts in herbivorous animals and in man, but is 

 absent from the bile of carnivorous animals. Sodium taurocholate, 

 on the contrary, only occurs in small amounts in the bile of herbivora 

 and man, while it is abundant in the bile of carnivora. 



The bile-salts are readily soluble in water, yielding solutions which, 

 like solutions of the saponins, have a very low surface-tension, foam 

 readily, and hold otherwise insoluble substances in solution or suspen- 

 sion. This is especially true of the lecithins, which are very readily 

 emulsified by bile-salts. The low surface-tension of these solutions 

 is utilized very frequently in manometers for measuring very minute 

 changes of gas-pressure. The solution of bile-salts does not "stick" 

 or form drops on the sides of the containing tube as water frequently 

 does, and the meniscus or surface of the fluid is flatter than that of 

 water, enabling a reading of the height of a column to be made with 

 greater ease and accuracy. 



The bile-salts and the free acids are further characterized by the 

 peculiar taste of their solutions, at once bitter and sweet. The dry 

 salts form a very fine light powder which is irritating when it comes 

 into contact with the nasal mucous membranes. 



Hydrolysis of glycocholic acid by boiling with barium hydroxide 

 yields Glycocoll and Cholic Acid: 



C23H 39 O 3 .CO.HN.CH 2 .COOH + H 2 O = C^H^Os.COOH + CH 2 NH 2 COOH 

 glycocholic acid + water = cholic acid + ammo-acetic acid. 



while hydrolysis of taurocholic acid yields Cholic Acid and amino-ethyl 

 sulphonic acid (Taurin) : 



C 23 H39O3.CO.HN.CH 2 .CH 2 SO 2 .OH + H 2 O = C 23 H39O3COOH + H 2 N.CH 2 .CH 2 .SO 2 OH 

 taurocholic acid + water = cholic acid + amino-ethyl-sulphonic acid. 



The characteristic peculiarities of the bile-acids are determined 

 by their common radical, the cholic-acid fraction. Free cholic acid, is 

 almost insoluble in water, but its salts readily dissolve, forming bitter- 

 sweet solutions which are dextrorotatory. The alkali salts of cholic 

 acid, on the other hand, are only sparingly soluble in alcohol, while the 

 free acid dissolves readily in this solvent. Cholic acid may also be 

 recognized by the following characteristic reactions: 



Hammarsten's Reaction. If finely powdered cholic acid be added to a 

 twenty-five per cent, solution of hydrochloric acid, a violet-blue colora- 

 tion slowly appears which gradually changes through green to yellow. 



Mylius' Reaction. If an alcoholic (about five per cent.) solution of 

 cholic acid in alcohol be mixed with two volumes of y^ iodine solution 

 in alcohol, and the mixture slowly diluted with water, microscopic 

 needles of an iodine addition-product are formed which are blue by- 

 transmitted light. This reaction is characteristic for cholic acid and is 

 not given by the conjugated bile-acids (glycocholic or taurocholic acids). 



Pettenkofer's Reaction. With a little cane-sugar, on careful addition 

 of strong sulphuric acid, it yields a red coloration. This reaction, 

 which is probably due to furfurol formed from cane-sugar by the action 



