«.] 



THE BILE. 



89 



(b.) Place a little impure nitric acid in a test-tube. Slant the tube and 

 pour in bile, a similar play of colours occurs — green above, blue, red, and 

 yellow below. It is better to do this reaction after removal of the mucin by 

 acetic acid (Lesson XL 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. For a modification applicable to urine, see " Urine." 



(c.) To green bile + amm. sulphide and shake = reduction to bilirubin. 



("'.) To yellow bile + KHO and heat, acidulate with HCl = green due to 

 oxidation of bilirubin. 



Fig. 45.— Crystals of 

 Cholesterin. 



7. Cholesterin and Gall-Stones. 



('/.) Preparation. — Powder a gall-stone and extract it with ether 

 or boiling alcoliol. Heat the test-tube in warm water, and see that 

 no gas is burning near it. Drop the solution 

 on a glass-slide, and examine the crystals micro- 

 scopically. They are flat plates, with an oblong 

 piece cut out of one corner (fig. 45). Ethereal 

 solution gives needles, but a hot alcoholic solution 

 gives the typical plates. 



(b.) Heat 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. 



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

 volume of covcenLrated sulphuric acid, and shake the 

 mixture. When the chloroform solution floats on the 

 top, it becomes blood-red, but changes quickly on exposure to the air, passing 

 tlirough violet and blue to green and yellow. A trace of water decolorises 

 it at once. The layer of sulphuric acid shows a green fluorescence. 



{(l.) The crystals when acted on by strong sulphuric acid become red. Do 

 this on a slide under the microscope. 



{c.) Examine microscopically crystals of cholesterin found in hydrocele fluid. 

 The crystals may not be quite perfect, but their characters are quite distinct. 



8. Action of Bile in Digestion, 



{a,) Action on Starch. — Test if bile converts starch mucilage 

 into a reducing sugar, as directed for saliva (Lesson VIII.). 



{!).) Action on Fats. — Mix thoroughly 10 cc. bile with 2 cc. 

 almond-oil, and observe both by the naked eye and the microscope 

 to what extent emulsion occurs, and how long it lasts. Compare 

 a similar mixture of oil and water. In the former case a pretty fair 

 emulsion will be obtained. In the latter the oil and water separate 

 rapidly. 



(c) Mix 10 cc. of bile with 2 cc. of almond-oil, to which some oleic acid is 

 added. Shake well, and keep the tube in a water-bath at 40° C. A very 

 good emulsion is obtained. The bile dissolves the fatty acids, and the 

 latter decompose the salts of the bile-acids ; the bile-acids are liberated, while 

 the fatty acid unites with the alkali of the bile-salts to form a soap. The 

 soap is soluble in the bile, and serves to increase the emulsifying power, as an 

 emulsion once formed lasts much longer in a soapy solution than in water. 



