DIGESTION OF FOOD 113 



Describe the tongue; compare its upper and under surface. 



Swallow all the saliva you can, so as to get the mouth as 

 free from it as possible; then raise your tongue, and note 

 how the saliva gathers under it. Where does the saliva come 

 from? 



c. Hold your tongue in the bottom of your mouth, and 

 identify the tonsils at the side of the throat. 



d. Count the total number of teeth in each jaw, and the num- 

 ber of each kind. How do the teeth differ? Why? 



EXERCISE 103 

 DIGESTION OF FOOD 



Apparatus and Materials. Bottles or beakers, pan of water, litmus 

 paper, corn starch, white bread, hard-boiled egg, grater, rennet (or 

 junket tablet), milk, thermometer, pancreatin, pepsin (get the ferments 

 at a drug store), olive oil, Fehling's solution. 



a. Saliva. Put into your mouth a piece of clean, pink 

 litmus paper; what effect has the saliva upon it? Has saliva 

 an acid, or an alkaline, reaction? 



Put on the tongue a pinch of powdered cornstarch; let it 

 soak in the saliva, and note if it becomes sweet. How does 

 saliva affect starch? 



Chew a piece of white bread; does it become sweet? 



b. Gastric Juice. Grate finely a part of the white of a 

 hard-boiled egg ; put a teaspoonf ul of it into a bottle containing 

 about 100 cu. cm. of water, a teaspoonful of dilute hydrochloric 

 acid, and a good-sized pinch of pepsin. Also add a piece of the 

 ungrated white of egg. 



Put the bottle in a warm place for several hours, or over 

 night. What is the result in the case of the grated material? 

 The larger piece? What is the reason for keeping the materials 

 warm? What is the advantage of the chewing of food? 



