3 7 4 CHEMISTR Y OF THE DIGESTIVE PR O CESSES. 
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 131 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 Plattncrs crystallised bile, 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 Htifner: 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 Avas employed by 
Strecker, 6 using a watery solution of crystallised bile instead of fresh bile. 
1 Strecker, Ann. d. Chem., Leipzig, 1849, Bd. lxx. S. 178; Hoppe-Seyler, Joum. f. 
prdkt. Chem., Leipzig, 1863, Bd. lxxxix. S. 283. 
2 Jacobson, Ber. d. deutsch. chem. GcscUsch., Berlin, 1873, Bd. vi. S. 1028. 
3 Schmidt's Jahrb., Leipzig, 1879, Bd. clxxxi. S. 5. 
4 Jahresb. ii. d. Fortschr. d. Tlder-Chem., Wiesbaden, 1874, Bd. iv. S. 301. 
6 Ztschr. /. physiol. Chem., Strassburg, 1SS7, Bd. xi. S. 233. 
6 Ann. d. Chem., Leipzig, 1848, Bd. Ixv. S. 1. 
