374 CHEMISTR Y OF THE DIGESTIVE PROCESSES. 



The alkaline salts of the bile acids are soluble in water and alcohol, 

 but insoluble in ether, and these solubilities form the basis of Plattner's 

 method of separating them from the other biliary constituents. This 

 is best done by mixing the bile with freshly-heated animal charcoal, 

 evaporating to complete dryness, and then extracting with absolute 

 alcohol, which takes up the bile salts along with cholesterin and traces 

 of lecithin, fats, and soaps ; but, on addition of excess of ether, only the 

 bile salts are thrown out of solution. 



The relative amount of each of the bile acids present in bile varies 

 within wide limits. In the bile of carnivora, glycocholate of sodium is 

 present in very small quantity ; for example, the bile salts of dog's bile 

 consist exclusively of taurocholate of sodium, 1 while in most herbivora 

 the glycocholate is usually present in^greater quantity than the tauro- 

 cholate ; to this rule the goat and sheep are said to be exceptions. 



In human bile most of the cholalic acid is combined with glycocoll, 

 occasionally the whole of it. 2 Hammarsten's 3 analysis of the mixed bile 

 salts of healthy human bile gave 13*1 per cent, taurocholic acid, 86'9 

 per cent, glycocholic acid. Since glycocholic acid is sulphur-free, and 

 the percentage in taurocholic acid is known, the relative amount of the 

 two acids may be determined from the percentage of sulphur in a 

 preparation of Plattners crystallised Hie, obtained from any given sample 

 of bile. 



The isolation of each of the bile acids from a mixture of their 

 salts is usually a lengthy and difficult process, especially in the case of 

 taurocholic acid, which can only with great difficulty be freed from 

 glycocholic acid, so that taurocholic acid is usually prepared from dog's 

 bile, while glycocholic acid is prepared from ox bile. 



Both free acids behave like their sodium salts in being soluble in 

 alcohol and insoluble in ether, but differ in that taurocholic acid is easily 

 soluble in water, while glycocholic acid is soluble with great difficulty. 

 On this property is based the simplest method of obtaining pure 

 glycocholic acid, that of Hiifner; 4 unfortunately, the presence of 

 taurocholic acid confers solubility on the glycocholic acid, so that the 

 method often fails when too much taurocholate is present in the sample 

 of bile experimented upon. 



The method consists in adding to fresh ox bile a few drops of hydrochloric 

 acid, and filtering from the precipitated pseudo-mucin. To 100 c.c. of this 

 filtrate 5 c.c. of concentrated hydrochloric acid and 30 c.c. of ether are added. 

 The hydrochloric acid sets free both bile acids, and the glycocholic acid is 

 precipitated in crystalline form (unless too much taurocholic acid be present), 

 either immediately, or on standing some hours in the cold. The ether added 

 aids in the production of this crystalline precipitate, which is next washed 

 with acidulated water saturated with ether, and finally recrystallised from 

 boiling water. 



Marshall 5 tested Hiifner's method with 543 samples of ox bile, and 

 obtained a precipitation in 121 cases. A similar method was employed by 

 Strecker, 6 using a watery solution of crystallised bile instead of fresh bile. 



1 Strecker, Ann. d. Chem., Leipzig, 1849, Bd. Ixx. S. 178; Hoppe-Seyler, Journ. f. 

 praU. Chem., Leipzig, 1863, Bd. Ixxxix. S. 283. 



2 Jacobson, Ber. d. deutsch. chem. Gesdlsch., Berlin, 1873, Bd. vi. S. 1028. 



3 Schmidt's Jahrb. , Leipzig, 1879, Bd. clxxxi. S. 5. 



4 Jahresb. ii. d. Fortschr. d. Thier-Chem., Wiesbaden, 1874, Bd. iv. S. 301. 



5 Ztschr. f. physiol. Chem., Strassburg, 1887, Bd. xi. S. 233. 



6 Ann. d. Chem., Leipzig, 1848, Bd. Ixv. S. 1. 



