60 EXPERIMENTAL PHYSIOLOGY 



Tube 2. After the second tube has been in ice twenty 

 minutes test with Fehling's solution. What is the effect 

 of cold on the action of saliva? 



Tube 3. Keep the third tube in boiling water twenty 

 minutes and test as above. What is the effect of high 

 temperatures on the action of saliva? 



Tube 4. Heat the fourth tube to 36C. for twenty min- 

 utes and then test as above. Does the Fehling's solution 

 give any test for sugar? (Acids prevent the enzyme ac- 

 tion of saliva.) 



Tube 5. Heat the fifth tube to 36 C. for twenty minutes 

 and then test with Fehling's solution. Does saliva convert 

 white of egg to sugar? (Saliva does not affect any 

 proteid.) 



Tube 6. Treat Tube 6 in the same way as Tube 5. Does 

 saliva convert olive oil to sugar? (Saliva does not affect 

 any fats and oils.) 



(The action of saliva is due to the presence of an en- 

 zyme called ptyalin, which converts starch to grape 

 sugar.) 



Tabulate all the functions of saliva. 



XXXVII. DIGESTION OF THE STOMACH GASTRIC JUICE. 



Apparatus. Glycerine solution of pepsin or solid pepsin dis- 

 solved in water, 0.2% hydrochloric acid, concentrated hydrochloric 

 acid, caustic soda, alcohol, minced white of egg, starch, olive oil, 

 milk, rennet dissolved in water, test tubes, dialyzer, constant tem- 

 perature apparatus, distilled water, materials for xanthoproteic and 

 biuret tests. 



Directions. A. Action of the Enzyme Pepsin and Hy- 

 drochloric Acid. Label seven test tubes Tube 1, Tube 2 ; 



