3 8o 



FOOD AND DIGESTION 



dextrin has been transformed into reducing sugar, and also that the amount 

 of sugar is greatly increased during the progress of the test. 



6. The Influence of Temperature on Salivary Digestion. Prepare 

 three test-tubes, a, b, c, containing 4 c.c. each of saliva. Boil a, place b in a 

 water-bath at 40 C., and place c in ice water. After c has been cooled down 

 to the temperature of the ice-bath, add to each 2 c.c. of i percent, starch solu- 

 tion and mix. At intervals of 2 to 5 minutes test these three samples for the 

 disappearance of starch and appearance of reducing sugar, as in Experi- 

 ment 5. No change will take place in a; b will be quickly digested, and the 

 digestion in c will be slight or suspended. Upon placing c in a warm bath 

 digestion will quickly occur. 



7. Influence of Acids and Alkalies on Salivary Digestion. To 

 each of 5 test-tubes, a, b, c, d, e, add five c.c. of saliva. Leave a for the normal ; 

 make b strongly alkaline; c exactly neutral; d acid to the extent of o. 2 to 0.3 

 per cent, hydrochloric acid; e strongly acid. Place all in the water-bath at 

 40 C. Add to each 2 c.c. of i per cent, starch paste and mix. Test for 

 starch and for reducing sugar at intervals of 20 minutes and compare, noting 

 the results in the following table: 



After 20 

 minutes. 



After 40 

 minutes. 



The results obtained in the Experiments 5, 6, and 7 show that starch is 

 converted into reducing sugar, and furthermore, that the conditions for its 

 conversion indicate that the change is accomplished by an amylolytic enzyme 

 which in this case is called ptyalin. 



