SUGGESTIONS FOR LABORATORY WORK 625 



for starch by adding hot water to a small amount of each (solids) , 

 and then, after cooling, applying the iodine test. 



Dextrin. This is an intermediate product in the conversion of 

 starch into sugar, and during the change different forms of dextrin 

 are produced. 



Test for Dextrin. To a solution of commercial dextrin add a few 

 drops of a solution of iodine. A reddish color is the dextrin test. 



Tests for glycogen, single sugars, and lactose (milk-sugar) are 

 described above (p. 588) . Cane-sugar (sucrose) does not give the 

 Fehling test. It can be split into single sugars (dextrose and 

 levulose) by boiling with a mineral acid, and the sugars thus pro- 

 duced will respond to the Fehling test. Tests for proteins and 

 fats are described above (p. 589). 



STUDY OF DIGESTION 



Salivary Digestion. Add to an inch of dilute starch solution in 

 a test tube a quarter of an inch of saliva. At four minute intervals 

 test a few drops of this mixture with dilute iodine solution. Note 

 the time it takes for the appearance of dextrin, and then for the 

 disappearance of the dextrin. 



The nature of the final product of the salivary digestion of starch 

 may be shown by keeping a test tube of starch solution and saliva, 

 as prepared above, at a temperature of 40 C. for 30 minutes or 

 more. Fehling's test will show the presence of sugar. 



Gastric Digestion of Protein. Gastric digestion proceeds slowly. 

 Allow ample time for the following observation; a good plan is to 

 begin the experiment one day and complete it on the next. 



Fill each of four test tubes about one-third full of water. Add 

 to the first a few drops of commercial pepsin solution; to the 

 second ten drops of a 0.5% solution of hydrochloric acid; to the 

 third and fourth both pepsin and acid. Place in each tube a cube 

 of boiled egg white. The cubes should be approximately the same 

 size. Mark the tubes and place numbers one, two, and three in 

 a thermostat at body temperature, number four in a cool place. 

 Shake each tube at intervals. Several hours later examine all the 

 tubes for evidences of digestion. It will be found that acid pepsin 

 is essential, and warmth desirable for gastric digestion. 



Movements of the Stomach. Expose the stomach of a recently 



