66 CHEMICAL PHYSIOLOGY. 



strikes a red colour, which is not altered by the addition of 

 caustic soda. 



(/.) Examine microscopically crystals of cholesterin float- 

 ing 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 muci- 

 lage into a reducing sugar, as directed for saliva (Lesson 

 VI, 3). 



(6.) Action on Fats. Mix 10 cc. of bile with 2 cc. of 

 almond oil or oleic acid. Shake them together, 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 almost immediately. 



(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. 



(d.) Favours Filtration and Absorption. Place two small 

 funnels exactly the same size in a filter-stand, and under 

 each a beaker. Into both funnels put a filter-paper ; 

 moisten the one with water (A), and the other with bile 

 (B) ; pour into both an equal volume of almond oil ; cover 

 with a slip of glass to prevent evaporation. Set the whole 

 aside for twelve hours, and note that the oil passes through 

 the filter B, but scarcely any through A. 



(e.) Effect on the Proteid Products of Gastric Digestion. 

 Digest some fibrin in artificial gastric juice, filter, and to the 

 filtrate add drop by drop some ox bile, or a solution of 

 bile-salts. It causes a white precipitate of peptones and 



