[pg 171]To demonstrate the Teeth.—Procure from the dentist a collection of different kinds of teeth, both sound and decayed.
(a) Examine external surfaces of different kinds of teeth, noting general shape, cutting or grinding surfaces, etc. Make a drawing of an incisor and also of a molar.
(b) After soaking some of the teeth for a couple of days in warm water saw one of them in two lengthwise, and another in two crosswise, and smooth the cut surfaces with fine emery or sand paper. Examine both kinds of sections, noting arrangement and extent of dentine, enamel, and pulp. Make drawings.
(c) Examine a decayed tooth. Which substance of the tooth appears to decay most readily? Why is it necessary to cut away a part of the tooth before filling?
(d) Test the effect of acids upon the teeth by leaving a tooth over night in a mixture of one part hydrochloric acid to four parts water, and by leaving a second tooth for a couple of days in strong vinegar. Examine the teeth exposed to the action of acids, noting results.
To show the Importance of Mastication.—Fill two tumblers each half full of water. Into one put a lump of rock salt. Into the other place an equal amount of salt that has been finely pulverized. Which dissolves first and why?
To illustrate Acid and Alkaline Reactions.—To a tumbler half full of water add a teaspoonful of hydrochloric or other acid, as vinegar. To a second tumbler half full of water add an equal amount of cooking soda. Taste each liquid, noting the sour taste of the acid, and the alkaline taste of the soda. Hold a piece of red litmus paper in the soda solution, noting that it is turned blue. Then hold a piece of blue litmus paper in the acid solution, noting that it is turned red. Add acid to the soda solution, and soda to the acid solution, until the conditions are reversed, testing with the red and blue litmus papers.
Hold, for a minute or longer, a narrow strip of red litmus paper in the mouth, noting any change in the color of the paper. Repeat, using blue litmus paper. What effect, if any, has the saliva upon the color of the papers? Has the mouth an acid or an alkaline reaction?
To show the Action of Saliva on Starch.—1 (Optional). Prepare starch paste by mixing half a teaspoonful of starch in half a pint of water and heating the mixture to boiling. Place some of this in a test tube and thin it by adding more water. Then add a small drop of[pg 172] iodine solution (page 136) to the solution of starch. It should turn a deep blue color. This is the test for starch.
Now collect from the mouth, in a clean test tube, two or three teaspoonfuls of saliva. Add portions of this to small amounts of fresh starch solution in two test tubes. Let the tubes stand for five or ten minutes surrounded by water having about the temperature of the body. Test for changes that have occurred as follows: