150 THE DIGESTIVE FLUIDS. 



ous animals, hut it also occurs in the bile of man and most herbiv- 

 orous animals. Among these, the sheep and goat are especially 

 noteworthy, as in these, like the pure carnivora, taurocholic acid 

 only is found. It is formed synthetically in the liver from taurin 

 and cholalic acid, and is accordingly resolved into its components 

 by treating with dilute acids or alkalies under the application of 

 heat. The same result indeed is reached by evaporating the bile 

 together with water or allowing it to undergo putrefaction. The 

 chemical change is represented by the equation : 



C 26 H 45 NS0 7 + H 2 = C 2 H 7 NS0 3 + C 24 H 40 O 5 

 Taurocholic Taurin. Cholalic 



5 



c 

 acid. acid. 



In the pure state taurocholic acid occurs in the form of fine deli- 

 quescent needles, which are soluble in water and alcohol, but 

 insoluble in ether. It is capable of maintaining glycocholic acid in 

 solution, and it is for this reason that the latter acid cannot be pre- 

 cipitated from the bile by adding a mineral acid when taurocholic 

 acid is at the same time present in sufficient amount. Like glyco- 

 cholic acid, it is a monobasic acid, and forms salts which for the 

 most part are soluble in water and in alcohol. Its salts with the 

 alkalies are precipitated from their solutions by subacetate of lead 

 and ammoniacal subacetate of lead, but not by the neutral acetate, by 

 copper sulphate, or silver nitrate. Curiously enough, the sodium 

 salt obtained from the bile of the ox is dextrorotatory, while the 

 same salt which is found in that of the dog turns the plane of 

 polarization to the left. An isomerism thus apparently exists which 

 is analogous to that observed in the case of the tartar ic acids. 



Taurocholic acid forms emulsions with the peptones, but does not 

 precipitate them, as is generally stated ; but it does precipitate albu- 

 mins, syntonins, and albumoses. 



Hyotaurocholic acid is the biliary acid which, as a sodium salt, is 

 found in the bile of pigs, and is analogous to the hyoglycocholic acid 

 already described. Its amount, however, is small. On decomposi- 

 tion it yields taurin and hyocholalic acid, as shown in the equation : 



C 26 H 45 NS0 6 + H 2 == CaiHiA + C 2 H 7 NSO 3 

 Hyotaurocholic Hyocholalic Taurin. 



acid. acid. 



Chenotaurocholic acid is the most important biliary acid, which 

 is found in the bile of geese. It is indistinctly crystalline, and is 

 soluble in water and alcohol. Like the acids already described, it 

 gives Pettenkofer's reaction. On prolonged boiling with alkalies 

 it is decomposed into taurin and chenocholalic acid, as shown in the 

 equation : 



C 29 H 49 NS0 6 4- H 2 O == C 27 H 44 4 + C 2 H 7 NSO 3 

 Chenotaurocholic Chenochola- Taurin. 



acid. lie acid. 



Isolation. Taurocholic acid is most conveniently obtained from 

 Platner^s bile of man or the ox, as already described. To isolate 



