CHEMICAL BASIS OF THE ANIMAL BODY. 213 



addition of ammonia and basic lead-acetate. This is next washed, 

 suspended in alcohol and decomposed by sulphuretted hydrogen. After 

 removal of the sulphide of lead by filtration the alcoholic filtrate is 

 concentrated and the taurocholic acid precipitated by an excess of 

 ether. This yields a sirupy mass which may become partly crystalline 

 on standing : the crystals at once deliquesce on exposure to the air 1 . 

 As dog-bile is not readily obtainable in large quantity at any one time 

 it may be desirable sometimes to obtain taurocholic acid from the 

 mother liquor left in the preparation of glycocholic acid. The separa- 

 tion is effected by the addition of a little ammonia and normal lead 

 acetate. This precipitates both glycocholic and cholalic acid but not 

 taurocholic. After the removal of this precipitate the taurocholic acid 

 is prepared as already described by the addition of basic lead acetate 

 to the filtrate. 



This acid as already stated is extremely soluble in water and in 

 alcohol, but not in ether, so also are its salts with the exception of the 

 one formed on the addition of basic lead acetate in presence of 

 ammonia which is insoluble in water and in alcohol. The acid and its 

 salts are dextro-rotatory ; for the sodium salt in alcoholic solution 

 (a) D = +24-5. If dissolved in water the rotatory power is less, and 

 in this respect it resembles glycocholic acid. 



When hydrolysed it readily takes up a molecule of water and is 

 decomposed into taurin and cholalic acid : 



Taurin. Cholalic acid. 



C M H 4B NSO 7 + H 2 O = KE 2 .CH 2 .CH 2 .SO 2 OH + C^H^Og. 



This decomposition may, as in the case of glycocholic acid, be 

 brought about by the action of diluta acids or alkalis, but even mere 

 boiling of an aqueous solution of the acid also suffices, a fact which 

 demonstrates how unstable a substance it is both absolutely and as 

 compared with glycocholic acid. Taurocholic acid has not as yet been 

 observed in the urine in icterus, but since cholalic acid does occur 

 together with glycocholic acid, it is probable that the non-appearance 

 of taurocholic acid is due to its decomposition before excretion as a 

 result of its instability. 



Taurocholic acid possesses a remarkable power of effecting the 

 complete precipitation of ordinary proteids from their solutions, 

 whereas peptones if present at the same time remain unprecipitated. 

 This is possibly of some not inconsiderable importance in connection 

 with the changes which proteids undergo in the small intestine, since 

 it leads to the retention of the peptones in a state of solution and 

 hence facilitates their absorption, while the less completely altered 



1 Parke, Hoppe-Seyler's Med.-chem. Unters. Hft. 1. (1866). S. 160. 



