"
Which jaw is moved in eating?--"The lower jaw."
What work do the teeth perform?--"They cut, tear, and grind the food."
How many teeth has a child in a full set?--"Twenty teeth: ten in each jaw."
How many teeth has a grown person in a full set?--"Thirty-two: sixteen in
each jaw."
What does the tongue do in eating?--"It rolls the food between the teeth,
and helps in swallowing."
What is the saliva?--"A kind of liquid, sometimes called _spit_."
Of what use is it in eating?--"It wets and softens the food."
What do you mean by preserve?--"To keep from injury."
What do you mean by injury?--"Hurt."
How do you preserve your teeth? See Formula.
How do very hot or very cold drinks hurt the teeth?--"They crack the
enamel."
What happens if the enamel is cracked?--"The teeth decay."
Then what must you do to preserve your teeth?--"I must try to keep the
enamel from being cracked or injured in any way."
* * * * *
PART V.
FORMULA FOR DESCRIPTION OF THE BONES.
1. My skull is formed of several bones united, like two saws with their
toothed edges hooked into each other.
2. My spine extends from the base of the skull behind, down the middle of
my back.
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