402 APPENDIX. 



of this mixture under the microscope and note that each starch 

 grain has turned blue. 



Prepare another test-tube with water and starch, and boil the 

 mixture in the flame of an alcohol lamp or of a Bunsen burner, 

 keeping the tube agitated all the time in order to prevent the 

 starch from sticking to the inside of the tube. Note that the 

 starch swells up and forms a paste, but does not actually dissolve. 

 Cool the paste by holding the test-tube in "cold water. When 

 sufficiently cool add a drop or two of iodine and note that the 

 starch turns blue. This change of color serves as a test for 

 starch whether uncooked or cooked. Hence we see that undi- 

 gested starch is in the form of granules which do not dissolve 

 in water, but which turn blue when treated with iodine. 



(2) The chemical test for digested starch — i. e., grape-sugar. 



Into a test-tube about one-fourth full of water put a pinch of 

 grape-sugar, shake the tube and note that the grape-sugar dis- 

 solves. Test the solution \jith iodine and note that the blue 

 color does not appear. 



Prepare another solution and to it add about oqe-fifth its vol- 

 ume of a strong solution of sodium hydrate, then to this mixt- 

 ure add a drop or so of a one-per-cent. solution of cnpric sul- 

 phate. Shake the tube to mix the contents thoroughly. Note 

 the light-blue color. Boil the contents of the tube and the 

 color changes, varying from light yellow to orange or brick red. 

 Hence it is seen that digested starch (grape-sugar) dissolves in 

 water, does not turn blue with iodine, but turns yellow or reddish 

 when boiled with a mixture of sodium hydrate and cupric sul- 

 phate. 



(3) The digestion of starch hy saliva. 



Collect about a third of a test-tube full of saliva, the flow of 

 which may be promoted by chewing a piece of rubber or a but- 

 ton. Dip a piece of red litmus paper into the saliva and note 

 that the paper becomes faintly blue, indicating that the saliva is 

 slightly alkaline in its chemical reaction. In another test-tube 

 make a mixture of about equal parts of saliva and water, and to 

 this add a few drops of cool starch paste. Hold the tube con- 

 taining this mixture in the hand for five or ten minutes in order 

 to keep it at the temperature of the body. After a few minutes 

 pour a portion of the mixture in another tube and test with io- 

 dine, which will probably give the blue color indicating the pres- 



