ORGANS AND PROCESSES OF DIGESTION 59 



flow? What does it do to the salt? Can you taste the salt 

 now? Do you think the effect would be the same if the 

 salt had been dissolved in water? Verify by placing a 

 drop of salt water on the dry tongue. Name two functions 

 of saliva that this experiment shows. 



Again clear the mouth of saliva, wipe the tongue dry, and 

 place on it some powdered cracker. Try to swallow the 

 cracker. Is it easily done? With the tongue moisten the 

 cracker with saliva and try to swallow. Is swallowing easy 

 now? What is another function of saliva? 



Chew some of the cracker slowly and note if any change 

 takes place in its taste. Place on the dry tongue some 

 cracker moistened with water. Is the taste the same? 

 What power has the saliva that is not due to its liquid 

 quality only? (This last power of the saliva is called its 

 chemical power as distinguished from its purely mechani- 

 cal properties.) 



B. Enzyme Action of Saliva. Place in four test tubes a 

 little thin starch paste. Add a cubic centimeter of clear 

 saliva to each, and label Tubes 1, 2, 3, 4. Add a few 

 drops of concentrated hydrochloric acid to the fourth 

 tube. In a fifth tube place 1 c.c. of saliva and a little 

 minced white of egg, and label Tube 5. In a sixth tube 

 place 1 c.c. of saliva and a few drops of olive oil. Label 

 Tube 6. Shake each tube. Pack Tube 2 in ice, and keep 

 Tube 3 in boiling water. 



Tube 1. Test the mixture with litmus paper. Is it acid 

 or alkaline? Now heat gently to a temperature of 36 C. 

 Keep at this temperature for twenty minutes and then 

 test with Fehling's solution. What has the saliva done 

 to the starch? See Ex. XXX. What caused the change 

 in the taste of the cracker in A? 



