236 PRACTICAL PHYSIOLOGY 



Besides these, bile also contains traces of soaps, fats and urea. 

 Compounds of glycuronic acid have also been found in bile. 



EXPERIMENT I. Examine some ox bile. Note that it has a 

 greenish colour, a peculiar musk-like odour, a bitter-sweet taste, a 

 faint alkaline reaction to litmus paper, and that it is of a slimy 

 consistency. 



EXPERIMENT II. If a few drops of weak acetic acid be added to 

 a few cubic centimetres of bile, a stringy precipitate is produced. 

 This consists in certain animals (ox) of nucleo-protein, in others 

 (man) of mucin. Filter off this precipitate, and note that the filtrate 

 has lost its slimy character. Boil the filtrate ; no coagulum is 

 produced, therefore bile contains no native protein. 



So far as can at present be ascertained, the amounts of pigment 

 and of bile salts do not bear a quantitative relationship to one 

 another, so that it is improbable that they are both derived from 

 the same source. 



The Chief Bile Salts are two in number, glycocholate and tauro- 

 cholate of sodium. The two acids are closely related as on hydro- 

 lysis both yield cholalic acid. In the first instance it is combined 

 with aminoacetic acid glycine, in the other with aminoethyl-sul- 

 phonic acid taurine. 



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 small 

 evaporating dish, and move this about so that a thin film of the 

 bile is produced. Now add to the film a very small drop of a con- 

 centrated watery solution of cane sugar, and then a few drops of 

 concentrated sulphuric acid. A purple colour is produced, which 

 can be intensified by warming. Or it may be more simply carried 

 out by shaking a dilute bile solution to which a small quantity of 

 cane sugar solution is added until the test tube is half full of froth. 

 A few drops of concentrated H 2 S0 4 are carefully run down one side 

 of the test tube : froth at place of contact becomes purple. 



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 1,000) instead of cane-sugar. 



EXPERIMENT IV. Hay's Sulphur Test. If a small pinch of 

 powdered 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. For comparison 

 repeat this test with water. 



The Bile Pigments are bilirubin and biliverdin. The former is 

 most abundant in bile of carnivorous, and the latter in that of 

 herbivorous animals. They are detected by Gmelin's test, the play 



