THE BILE. 



65 



green above, blue, violet, red, and yellow below. It is 

 better to do this reaction after removal of the mucin by 

 acetic acid (Lesson IX., 1, d). Or add the nitric acid, and 

 shake after the addition of every few drops, the successive 

 colours from green to yellow are obtained in great beauty. 



(c.) For a modification applicable to urine, see " Urine." 



7. Cholesterin and Gall Stones. 



(a.) Preparation. Powder a gall-stone and extract it with 

 ether. Heat the test-tube with ether in warm water, and 

 see that no gas is burning near it. 

 Allow a drop of the ethereal solution 

 to evaporate on a glass-slide or watch- 

 glass, and examine the crystals under 

 the microscope. They are flat plates, 

 with an oblong piece cut out of one 

 corner (Fig. 11). 



(b.) Heat a few crystals in a watch- 

 glass with a few drops of moderately 

 strong sulphuric acid, and then add 

 iodine ; a play of colours, passing 

 through violet, blue, green, red, and 

 brown, occurs. (It requires a little 

 practice to get this test always to 

 succeed.) 



Fig. 11. Crystals of 

 Cholesterin. 



(c.) Dissolve some crystals in chloroform, add an equal 

 volume of concentrated sulphuric acid, and shake the mix- 

 ture. When the chloroform solution floats on the top, it 

 becomes blood-red, but changes quickly on exposure to the 

 air, passing through violet and blue to green and yellow. 

 A trace of water decolourises it at once. The layer of sul- 

 phuric acid shows a green fluorescence. [This reaction is not 

 easily performed.] 



(d.) The crystals when acted on by strong sulphuric acid 

 become red. Do this on a slide under the microscope. 



(e.) Place a crystal on a piece of porcelain, add a drop of 

 strong nitric acid, evaporate to dryness at a gentle heat, 

 until a yellow residue is obtained. A drop of ammonia 



5 



