CHAIM.] TISSUES AND MECHANISM* <>l 1>I< ,KS IK >\. 357 



filtrate must be further decolourized with animal charcoal, and th- 

 alcohol distilled off. The dry residue is treated with alu]iit- aic-.h-.], 

 and to the alcoholic filtrate anhydrous ether is add-l a> long as any 

 precipitate is formed. On standing the cloudy precipitate become* 

 transformed into a crystalline mass at the bottom of tin- \. >*!. If tin- 

 alcohol be not absolute, the crystals are very apt to be changed into a 

 thick syrupy fluid. This mass of crystals has been often Hpoken of an 

 bilin. Both salts are thus precipitated, so that in such a bile as that of 

 the ox or man bilin consists both of sodium glycocholate and sodium 

 taurocholate. The two may be separated by precipitation from their 

 aqueous solutions with sugar of lead, which throws down the former 

 much more readily than the latter. The acids may be separated from 

 their respective salts by dilute sulphuric acid, or by the action of lead- 

 acetate and sulphydric acid. 



On boiling with dilute acids (sulphuric, hydrochloric) or caustic 

 potash, or baryta water, glycocholic acid is split up into cholalic 

 (cholic) acid and glycin. Taurocholic acid may similarly be split 

 up into cholalic acid and taurin. Thus 



glycocholic acid cholalic acid glycin 



CseH^NOe + H 2 = C 24 H 40 6 + CH 2 . NH 8 (CO . OH) 



taurocholic acid cholalic acid Launn 



+ H 2 = C 24 H 40 6 + C 8 H 4 . NH 2 . SOJL 



Both acids contain the same non-nitrogenous acid, cholalic 

 acid ; but this acid is in the first case associated or conjugated with 

 the important nitrogenous body glycin, or amido-acetic acid, which 

 is a compound formed from ammonia and one of the " fatty a<-id " 

 series, viz. acetic; and in the second case with taurin, or amido- 

 isethionic acid, that is a compound into which representatives of 

 ammonia, of the ethyl group, and of sulphuric acid enter. The 

 decomposition of the bile acids into cholalic acid and taurin or 

 glycin respectively takes place naturally in the intestine, tin- glyrin 

 and taurin being probably absorbed, so that from the two acids, 

 after they have served their purpose in digestion, the two ammonia 

 compounds are returned into the blood. Each of the two acids, or 

 cholalic acid alone, when treated with sulphuric acid and cane- 

 sugar, gives a magnificent purple colour (Pettenkofer's test with a 

 characteristic spectrum. A similar colour may however often be 

 produced by the action of the same bodies on albumin, aniyl 

 alcohol, and some other organic bodies. 



208. Action of Bile on Food. In some animals at least bile 

 contains a ferment capable of converting starch into sugar ; but its 

 action in this respect is wholly subordinate. 



On proteids bile has no direct digestive action whatever, but 

 being, generally at least, alkaline, and often strongly so, ten 

 neutralise the acid contents of the stomach as they pass into the 

 duodenum air.l as we shall see so prepares th- way for the action 



