124 DIGESTION 



18. Importance of Mastication and Insalivation. Each of 

 these processes complements the other, and makes the entire 

 work available; for, by their joint action, they prepare the 

 food in the best possible manner for further digestive changes. 

 The study of these preliminary functions will appear the more 

 important, when we reflect that they are the only ones which 

 we can regulate by the will. Tor, as soon as the act of swallow- 

 ing begins, the food not only passes out of sight, but beyond 

 control; and the subsequent acts of digestion are consequently 

 involuntary and unconsciously performed. 



19. It is generally known that rapid eating interferes with 

 digestion. How does this occur ? In the first place, in rapid 

 eating, the flow of the saliva is insufficient to moisten the solid 

 parts of the food, so that they remain too hard and dry to be 

 easily swallowed. This leads to the free and frequent use of 

 water, or some other beverage, at meals, to " wash down " the 

 food a most pernicious practice. For these fluids not only 



2. Obtain a fresh quantity of saliva, which is best done by revolving 

 a small pebble in the mouth, which causes a copious flow. Collect this 

 in a separate vessel. 



3. Demonstrate that no sugar is present in this starch solution. 

 Obtain from a druggist an ounce or two of "Fehling's solution" (this 

 is a solution of sulphate of copper and of certain alkalies). Sugar has 

 the power of changing the sulphate into an oxide of copper which is red- 

 dish-brown. Of this put half a teaspoonful into a test-tube, add an equal 

 quantity of the starch solution, and let it come to a boil over an alcohol 

 lamp. No change in the blue color will be observed. 



4. Demonstrate that the saliva does not contain sugar by boiling a 

 small quantity with an equal quantity of "Fehling's solution," when no 

 change of the blue color will be observed. 



5. Now in a third test-tube mix a quantity of the starch solution with 

 one-third its volume of fresh saliva, and set aside for five to ten minutes 

 in a warm place, or a glass of warm water of about 100 F. Then take 

 of this again a small quantity and add an equal part of " Fehling's solu- 

 tion," shake the mixture and boil. As soon as the boiling point is 

 approached, it will be seen that the blue color disappears, being replaced 

 by a reddish-brown color. This demonstrates the presence of sugar in 

 the starch solution, produced by the action of the saliva added. 



18. Each of the processes ? Why is a knowledge of the digestive functions important ? 

 How shown ? 



19. Eapid eating ? Describe the process and effects. 



