ELEMENTARY PHYSIOLOGICAL CHEMISTRY 233 



EXPERIMENT III. Test another portion of the bile for bile salts by 

 Pettenkofer's reaction. To do this place a drop of bile in a capsule 

 and move this about so that a thin film is produced. Now add to the 

 film a drop of a concentrated watery solution of cane sugar, and then a 

 drop of concentrated sulphuric acid. A purple colour is produced. 

 This pigment shows absorption bands in the spectrum. The 

 chemistry of this reaction is that the sulphuric acid acts on the 

 cane sugar to produce a body called furfuraldehyde, which then 

 reacts with the cholalic acid of the bile salts to produce the 

 pigment. Where only traces of bile salts are present, the test may be 

 made more delicate by using a solution of furfuraldehyde (1 in 1000) 

 instead of cane sugar. 



EXPERIMENT IV. Matthew Hay's Sulphur Test. If some flour of 

 sulphur be sprinkled on the surface of bile, or of a solution containing 

 bile salts, it will sink to the bottom of the vessel, whereas with most 

 other fluids it remains floating on the surface. This reaction depends 

 on the fact that bile salts lower the surface tension of fluids in which 

 they are dissolved. 



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 amido 

 acid. The amido acid, which is obtained from glycoholic acid, is 

 glycin. The other amido acid is taurin, and is peculiar in that it 

 contains sulphur (for Chemical Constitution, see Advanced Course). 

 Scarcely anything is known of the chemical constitution of cholalic acid 

 with which these two bodies are combined. Its empirical formula is 

 C 24 H 40 5 . 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 carnivora the only acid is taurocholic. In 

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

 These 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. 



It is evident, therefore, that most of the bile salts are reabsorbed 

 from the intestine into the portal blood, and perhaps into the thoracic 

 duct, to be ultimately re-excreted in the bile. This explains why 

 fistula bile should contain so very much lower a percentage of these 

 salts than does gall bladder bile. It also shows that these salts must 

 subserve some very important function, and that they are too valuable 



