They may be divided
into the muscles of my head, the muscles of my trunk, and the muscles of my
limbs."

Of what use are the muscles of your head?--"They cover and move the parts
of my head and face."

Of what use are the muscles of your trunk?--"They move the parts of my neck
and trunk."

Of what use are the muscles of your limbs?--"They move the parts of my arms
and legs."

How can you make your muscles strong?--"By using them."

How can you make your muscles weak?--"By not using them."

What is necessary to make your muscles strong and healthy?--"They must be
used; they must be rested when tired; they must be supplied with pure
blood."

How should the muscles be used?--"They should be exercised in work or
play."

How may they be rested?--"I may rest my muscles by changing position; by
changing my kind of work or play; or by going to sleep."

Explain what you mean by changing your position.--"If I am standing, I must
sit or lie down to rest them; if they are tired, because I have been
sitting too long, I must rest them by standing, walking, or running."

What do you mean by changing the kind of work or play?--"If, in my work or
play, my arms become tired, I must do something in which my arms may rest,
though other parts of my body may be in exercise."

How may you help supply your muscles with good blood?--"By breathing pure
air; by taking wholesome food and drink; and by living in the sunlight."

How does drinking alcoholic liquors hurt the muscles?--"It makes them weak,
and unfit to move the parts of the body."

What wonderful muscle moves without your will?--"The heart."

How does alcohol hurt the heart?--"It makes it beat too fast."

How does "beating too fast" hurt the heart?--"It makes it tired, and
sometimes wears it out." See Appendices on Alcohol and Tobacco.

* * * * *

[Illustration: THE SKIN (very highly magnified).--(From Walker's
_Physiology_, 1884.)]

A, arteries; V, veins; N, nerves; F, fat cells; E, the outer skin; CL, the
color layer; D, the true skin; PT, a perspiratory tube; HF, a hair and hair
sac; EP, muscles; SG, oil glands; TC, tactile corpuscles; CT, connective
tissue.

* * * * *

PART VII.

FORMULA FOR THE LESSON ON THE SKIN.

1. My skin covers my body.

2. It is thin, elastic, flexible, porous, and absorbent.

3. I have two skins; the inner skin is the true skin.

4. My true skin is elastic, and li