186 ELEMENTABY PHTSIOLOOT. [XVII. 



test-tube so that the acid settles at the bottom. 

 Gently shake the test-tube from side to side, 

 ■when the fluids have nearly mixed a deep purple 

 colour is produced. If too much sugar is added, 

 the fluid will turn brown or black ; if too little 

 sulphuric acid is added the proper temperature 

 (about 70° 0.) for the production of the colour 

 will not be obtained. 



5. Add a few drops of oleic acid to 10 c.c. of bile in 

 a test-tube, shake well, and at once mount a drop 

 and observe in it under the microscope the 

 numerous fatty globules. Place the test-tube 

 with the bile in a warm bath for an hour or so, 

 then shake and mount a drop of the fluid; 

 comparatively few fatty globules will be seen 

 in it under the microscope. The oleic acid has 

 combined with the base of the bile-salts to form 

 a soap (cp. C. § 4). 



G. Place in separate test-tubes 10 c.c. of bile and a 

 couple of drops of oleic acid (a) ; 10 c.c. of bile 

 (b); 10 c.c. of water; to each add 2"5 c.c. of 

 melted fresh butter', shake well, and place in 

 the warm bath. The emulsion will last much 

 longer in (a) than in (&); it will last much longer 

 in (6) than in (c). The emulsifying power of bile 

 is slight; but in the presence of fatty acids it 

 forms soaps (cp. § 6) which have a much greater 

 emulsifying power. 



I If olive oil is used instead of melted butter, it will depend upon 

 tlie amount of fatty acids contained in the olive oil whetbei any 

 difference is observed in (o) and (6). 



