PHYSIOLOGICAL CHEMISTRY 399 



The bile salts are two in number, glycocholate and taurocholate of 

 sodium. The two acids (glycocholic C 26 H 43 N0 6 and taurocholic 

 C 26 H 45 NS0 7 ) are very closely related to one another, for they both 

 yield, on boiling with stronger acids, a common non-nitrogenous body 

 called cholalic acid, and a nitrogenous body of the nature of an amino 

 acid. The amino acid, which is obtained from glycocholic acid, is 

 glycin. The amino acid in taurocholic acid is taurin, which is peculiar 

 in that it contains sulphur which can be demonstrated by fusing some 

 taurin (prepared as described below) on a piece of platinum foil with 

 sodium carbonate, dissolving in water, acidifying and heating the 

 resultant solution : sulphuretted hydrogen is given off, which can be 

 detected by holding a piece of filter paper soaked in lead acetate solu- 

 tion over the mouth of the test tube. Taurin is undoubtedly derived 

 from cystin (see p. 393), which when oxidised yields cysteinic acid 

 COOK". CHNH 2 . CH 2 . S0 3 H. By the loss of a molecule of CO^ this 

 becomes taurin : NH 2 . CH 2 . CH 2 . S0 3 H. We see, therefore, that both 

 glycin and taurin are derived from protein disintegration, the latter 

 body being one of the forms in which the sulphur of protein is excreted. 



Cholalic acid is believed to be related to cholesterol. It has recently 

 been shown to contain two primary alcoholic and one secondary 

 alcoholic groups. There are probably several varieties of it. 



The relative amount of these two acids in the bile varies in different 

 animals. In the bile of the herbivora, glycocholic acid is much in 

 excess, whereas in that of many carnivora the only acid is taurocholic. 

 In omnivora (e.g. man, etc.) a variable mixture of the two is present. 

 The bile salts are decomposed into their constituents by the action of 

 the bacteria in the intestine. If we examine the faeces, however, no 

 glycin and only a trace of cholalic acid can be detected. The fate of 

 taurin has not been accurately determined. 



ADVANCED EXPERIMENT. Separation of Bile Salts. To Separate the Bile 

 Salts as a Whole. Thoroughly mix 50 grm. pure animal charcoal with 200 c.c. 

 of ox-bile in an evaporating dish, and evaporate the mixture to dryness on a 

 water bath. During the drying the mixture should be frequently stirred. The 

 black powder thus obtained can be kept a considerable time. To extract the 

 bile salts from it, mix it with absolute alcohol in a flask and place the flask on 

 the boiling water bath for about a quarter of an hour, cool, filter into a dry 

 beaker, and add ether to the filtrate till a permanent haze is produced. Now 

 cover the beaker with a ground glass plate, and allow it to stand in a cool place 

 till next day, when it will be found that a crystalline mass of bile salts has 

 separated out (Plattner's Crystalline Bile). The crystals can now be collected 

 on a filter paper and allowed to dry in the air. 



A 1 % solution of the crystals should now be made, and Pettenkofer's reaction 

 (see p. 398) applied to it by the following method : 



Dissolve a few grains of cane sugar in the solution, and run concentrated 



