2 04 - How a Complex Am?nal Uses Food unit iv 



8. How are the teeth fitted for their work? How does the surface of 

 your tooth differ in appearance and in structure from the surface of a 

 bone? Your tooth is covered with a substance much harder than bone. 

 It is called enamel. Study the diagram of the tooth. Where does the enamel 

 end? Explain. Dentine is a substance much like bone. Like bone it con- 

 tains cells. But enamel is pure mineral matter. What is found in the very 

 inside of the tooth? Which are the living and which the lifeless parts of 

 the tooth? When you have a toothache, you feel pain through the nerve. 

 Where does the nerve lie? What has probably happened to make the 

 tooth ache? What might cause a toothache while you were eating? 



9. What can you do to make sure that your teeth are covered with a 

 good layer of enamel? Write a paragraph on the connection between 

 good teeth and diet. (See Problem i of this unit.) Since enamel is pure 

 mineral matter it is not only hard but brittle. What might tend to crack 

 it? Ask your teacher to do the following: Put into a test tube a small 

 amount of calcium phosphate (the mineral that makes up enamel). Shake 

 it well with a little water. Examine. Add some strong hydrochloric acid. 

 What do you observe? Add weak acid to a very small amount of calcium 

 phosphate and let it stand. What conclusions do you draw? When bac- 

 teria decay food they often form acids. If small particles of food left in 

 your mouth decay, what might happen? 



10. You will find it interesting to make a list of all the rules you can 

 think of which would help to keep your teeth in good condition. Of 

 course, unless you can give a good reason for your rule no one will be 

 interested in it. 



11. How quickly does saliva act in the mouth? Grind up a small piece 

 of soda cracker and moisten it. Lay it on your tongue. Look at the clock. 

 What do you taste? Leave it there several minutes. What do you notice? 

 Explain. Did other members of the class get similar results or is this a 

 peculiarity of your saliva? 



12. What is the effect of gastric (stomach) juice on starch? Ask your 

 teacher to make some artificial gastric juice by adding to a test tube of 

 water a few drops of hydrochloric acid and a little powdered pepsin. 

 Add some of this to starch in a clean test tube. What happens? State 

 clearly what you did to arrive at a conclusion. What was the control? 

 State your conclusion. 



13. What is the effect of gastric juice on protein? Cut some hard boiled 

 white of &^^ into small pieces. Put a quarter of a teaspoonful into a test 

 tube, add two inches of artificial gastric juice, and plug the tube with 

 cotton. (The experiment will be more successful if you boil the \\'ater 

 and take all precautions to exclude bacteria.) Keep the test tube in a warm 

 place. Why? What temperature would you suggest? What would you 

 suggest as a control for this experiment? Examine it alter 10 minutes, 

 several hours, 24 hours, and 48 hours. Make a note of any changes you 

 observe. Explain what you see. 



