456 PRACTICAL PHYSIOLOGY 



The method is as follows : 



Some ox bile is placed in a stoppered cylindrical vessel, and mixed 

 with ether and hydrochloric acid in the proportion of ten parts of the 

 former and four parts of the latter, for every hundred parts of bile. A 

 few crystals of glycocholic acid are added to the mixture so as to start 

 the crystallisation, the vessel is stoppered, vigorously shaken, and then 

 allowed to stand in a cool place. After some time the mass will be 

 found to be ' solid ' with crystals. These are collected in a filter paper, 

 and washed with cold distilled water till no more pigment can be 

 removed. They are then removed to a flask and dissolved in boiling 

 water ; the solution is filtered hot, and the filtrate, on cooling, deposits 

 numerous acicular crystals of the acid. These may now be collected, 

 washed with distilled water, and dried (for Chemistry and Reactions see 

 p. 233). 



The other amido acid is Taurin, and is peculiar in that it contains 

 sulphur. 



Preparation of Taurin. Bile from a carnivorous animal cat or 

 dog is heated on a sand bath with one-third its bulk of concentrated 

 hydrochloric acid until a resinous-like mass of the anhydride of 

 cholalic acid (called Dyslysiri) has formed. This can be drawn out 

 into brittle threads by means of a glass rod. The dyslysin is filtered 

 off and the filtrate is evaporated to small bulk, the sodium chloride, 

 which crystallises out during the evaporation, being removed by 

 filtration. The thin syrup is then poured into fifteen times its bulk 

 of alcohol, and left standing twenty-four hours, when the taurin will 

 have crystallised out. It can be purified by collecting the crystals 

 on a filter paper, washing with cold water, redissolving in boiling 

 water, and allowing the solution to cool. 



Properties of Taurin. It crystallises in long glancing needles. 

 It is insoluble in alcohol, but soluble in boiling water. If heated on 

 a piece of platinum foil it turns black, and gives off fumes of sulphur 

 dioxide. If fused with solid sodium carbonate on a piece of platinum 

 foil, and the melt dissolved in water, a solution is obtained which 

 evolves sulphuretted hydrogen on the addition of a mineral acid. 

 The sulphuretted hydrogen can be detected by means of a piece 

 of filter paper soaked in lead acetate solution. Its chemical con- 

 stitution is demonstrated by the following reactions : 



If ethylic alcohol be treated with concentrated sulphuric acid, one of the hydro- 

 gen atoms is replaced by the radicle S0 3 H, and isethionic acid is formed. 



C 2 H 4 < H + OH - S0 3 - H = C 2 H 4 <^ H + H 2 0. 

 Ethylic alcohol. Sulphuric acid. Isethionic acid. 



