THE DIGESTIVE JUICES 79 



of a mucinoid substance is obtained. Filter this off and boil the nitrate ; no 

 protein coagnlable by heat is present. 



3. Add a few drops of bile to (a) acid-albumin prepared as described in 

 Lesson V., and (6) solution of proteoses to which half its volume of 0'2-per- 

 cent. hydrochloric acid has been added. A precipitate occurs in each case. 

 Bile salts precipitate the unpeptonised protein which leaves the stomach. 



4. Pettenkofer's Test for Bile Salts. To a thin film of bile in a capsule 

 add a drop of solution of cane sugar and a drop of concentrated sulphuric 

 acid. A purple colour is produced. This occurs more quickly on the 

 application of heat. The test may also be performed as follows : Shake up 

 some bile and cane sugar solution in a test-tube until a froth is formed. 

 Pour concentrated sulphuric acid gently down the side of the tube : it produces 

 a purple colour in the froth. 



5. Gmelin's Test for Bile Pigments. On to a little fuming nitric acid 

 (i.e. nitric acid containing nitrous acid in solution) in a test-tube pour gently 

 a little bile. Notice the succession of colours green, blue, red, and yellow 

 at the junction of the two liquids. This test may also be performed in a 

 capsule. Place a drop of fuming nitric acid in the middle of a thin film of 

 bile : it becomes surrounded by rings of the above-mentioned colours. 



6. Haifs Test for Bile Salts. Take two beakers full of water ; to 

 one add a few drops of bile, or solution of bile salts. Sprinkle a little 

 flowers of sulphur on the surface of each. It remains floating on the 

 pure water ; but where bile is present the surface tension of the water is 

 reduced, and the sulphur consequently rapidly sinks. This test is very 

 sensitive. 



7. Preparation of Glycockolic Acid. The preparation of the bile acids 

 is usually a task of some difficulty ; the following exercise is a simple one, 

 though unfortunately, for reasons which are not explicable, it does not always 

 succeed. Take a stoppered cylinder, place in it 200 c.c. of ox bile, 10 c.c. of 

 hydrochloric acid, and 25 c.c. of ether, and shake vigorously. Add a crystal 

 of glycocholic acid, and allow the mixture to stand in a cool place. In a time 

 varying from a few minutes to some hours, a mass of crystals of glycocholic 

 acid separates out. This may be filtered off, washed, and dissolved in a little 

 boiling water, and filtered hot. On cooling, needle-like crystals of the acid 

 again separate out. 



8. Cholesterin. (a) Examine crystals of this substance with the micro- 

 scope. Heat these on a slide with a drop of sulphuric acid and water (5:1); 

 the edges of the crystals turn red. 



(6) Salkowski's reaction. Dissolve some cholesterin in chloroform in a 

 dry test-tube, and gently shake with an equal amount of concentrated 

 sulphuric acid ; the solution turns red, and the subjacent acid acquires 

 a green fluorescence. The chloroformic solution of cholesterin is rendered 

 colourless by pouring it into a wet test-tube, and the colour is restored by 

 the addition of sulphuric acid. 



(c) Liebermann's reaction. Two or three drops of acetic anhydride are 

 added to a chloroformic solution of cholesterin and then sulphuric acid drop 

 by drop. A rose-red colour first develops ; this becomes blue and finally 

 bluish-green. 



THE PANCREAS 



The Pancreas is a compound tubulo-racemose gland ; between 

 the secreting acini are situated little masses of epithelial cells without 

 ducts called ' islets of Langerhans.' Examination of the secreting 

 cells in different stages of activity reveals changes comparable to 

 those already described in the case of salivary and gastric cells. 



