1C? 



THE USES OF FOODS 



change, or digestion, is caused by the presence in the saliva 

 of a digestive ferment called an enzyme. 



Experiment. To show digestion of starch with saliva. 



Add a few drops of sodium carbonate solution to a test tube a third full 

 of starch paste. Add a tablespoonful of filtered saliva warmed to 

 99 degrees F. Keep it at this temperature on the water bath. At 

 the end of ten minutes test a portion of the solution with Fehl- 

 ing's solution to see if any of the starch has been changed to sugar. 

 Result? 



Enzymes and what they do. We shall find in our later 

 study that enzymes perform an important work in the body 

 of plants and animals. They are the active parts of the 

 digestive fluids and cause the digestion of the nutrients 



in different parts of the food 

 tube. Starches are digested 

 in part by enzymes supplied 

 in the mouth, and in part by 

 other enzymes in the small in- 

 testine. Proteins are digested 

 by enzymes in the stomach 

 and intestines. In the small 

 intestine fats are changed 

 in part by enzyme action 

 into a kind of soft soap, 

 in which form they enter the 

 blood. 



The uses of the teeth. If 

 you study the accompanying 

 diagram of the teeth, or better, your own mouth before a 

 mirror, you will notice that some teeth are broad and 

 rather irregular on the upper surface, and are evidently 

 used for grinding. Others are sharp or pointed, and are 



I. Teeth of the upper jaw, from below. 

 7, 2, incisors; 3, canine; 4, 5, pre- 

 molars; 6, 7, 8, molars. II. Section 

 of a tooth. , enamel; D, dentine; 

 C, cement ; P, pulp cavity into which 

 blood vessels and nerves pass to keep 

 the tooth alive. 



