PHYSIOLOGICAL CHEMISTRY. 



a\strip of starch paste-iodic acid test paper 1 with a little saliva. If 

 thiocyanate be present the test paper will assume a blue color, due 

 to the liberation of iodine and the subsequent formation of the 

 so-called iodide of starch. 



12. Digestion of Starch Paste. To 25 c.c. of starch paste in 

 a small beaker, add 5 drops of saliva and stir thoroughly. At in- 

 tervals of a minute remove a drop of the solution to one of the de- 

 pressions in a test-tablet and test by the iodine test. If the blue 

 color with iodine still forms after 5 minutes, add another 5 drops 

 of saliva. The opalescence of the starch solution should soon dis- 

 appear, indicating the formation of soluble starch which gives a blue 

 color with iodine. This body should soon be transformed into 

 erythro-dextrin which gives a red color with iodine and this in turn 

 should pass into achroo -dextrin which gives no color with iodine. 

 This is called the achromic point. When this point is reached test 

 by Fehling's test to show the production of a reducing body. A 

 positive Fehling's test may be obtained while the solution still 

 reacts red with iodine inasmuch as some iso-maltose is formed 

 from the soluble starch coincidently with the formation of the 

 erythro-dextrin. How long did it take for a complete transforma- 

 tion of the starch? 



13. Digestion of Dry Starch. In a test-tube shake up a small 

 amount of dry starch with a little water. Add a few drops of 

 saliva, mix well and allow to stand. After 10-20 minutes filter and 

 test the filtrate by Fehling's test. What is the result and why ? 



14. Digestion of Inulin. To 5 c.c. of inulin solution in a test- 

 tube add 10 drops of saliva and place the tube in the water-bath at 

 40 C. After one-half hour test the solution by Fehling's test. 2 

 Is any reducing substance present ? What do you conclude regard- 

 ing the salivary digestion of inulin? 



15. Influence of Temperature. In each of four tubes place 

 about 5 c.c. of starch paste. Immerse one tube in cold water from 

 the faucet, keep a second at room temperature and place a third 

 on the water-bath at 40 C. Now add to the contents of each 

 of these three tubes two drops of saliva and shake well; to the 



1 This test paper is prepared as follows : Saturate a good quality of filter paper 

 with 0.5 per cent starch paste to which has been added sufficient iodic acid to 

 make a I per cent solution of iodic acid and allow the paper to dry in the air. 

 Cut it in strips of suitable size and preserve for use. 



2 If the inulin solution gives a reduction before being acted -upon by the saliva 

 it will be necessary to determine the extent of the original reduction by means 

 of a "check" test (see page 47). 



