. Adventures with animals and plants. Biology. PROBLEM 2. The Digestive System Makes Food Usable 203 Fig. 207 Longitudinal section of an in- cisor. The different kinds of teeth all have the same three regions. What are they? All are alike in structure. Ename. ' Crown Neck Dentine Cement Nerve and blood vessels to dental pulp Root back. Do you note any difference? Now put a grain or two of granulated sugar on your dry tongue. What do you discover.^ Blindfolded, and with nose tightly shut, taste the following substances (someone must put them on your tongue without telling you which is which): s
. Adventures with animals and plants. Biology. PROBLEM 2. The Digestive System Makes Food Usable 203 Fig. 207 Longitudinal section of an in- cisor. The different kinds of teeth all have the same three regions. What are they? All are alike in structure. Ename. ' Crown Neck Dentine Cement Nerve and blood vessels to dental pulp Root back. Do you note any difference? Now put a grain or two of granulated sugar on your dry tongue. What do you discover.^ Blindfolded, and with nose tightly shut, taste the following substances (someone must put them on your tongue without telling you which is which): salt, lemon juice, vinegar, sugar, something bitter, grains of ground coffee, farina, etc. Rinse your mouth after tasting each substance. Which can you recognize? Repeat, with your nose no longer held shut but still blindfolded. What do you conclude? All of your observations must be carefully recorded. Compare them with your classmates'. Why? Can you now name four different ways in which the tongue functions? 7. What can you discover about the number and the arrangement of your teeth? It will help you in your study to know that the teeth in the upper and lower jaws are alike. Use a mirror to discover how you bite off a piece of bread. Which teeth do the work? How are they fitted for it? You have four such teeth at the front, in each jaw. They are called incisors. Which group of mammals has the incisors well developed? Right behind the incisors, you have a single tooth on each side which is some- what more pointed. It is a cuTime, the tooth which is so large in cats, dogs, and their relatives. How do the back teeth differ in shape from incisors and canines? How many back teeth are there in each jaw? How do they function? Bite into a piece of hard chewing gum. What impression does each kind of tooth make on the gum? Can you see that the two teeth directly behind the canine differ from those still farther back? How? Those farthest back are the molars. Between the molars and the can
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