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 with iodine and note that the blue 
color does not appear. 
Prepare another solution and to it add about one-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 cupric 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 by 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- 
