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

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[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.

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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 like a net-work of blood-vessels and nerves.  My true skin is covered with a jelly-like substance which gives color to my skin.

5.  My outside skin is not the same thickness over my whole body.  In some parts, as on the palms of my hands and the soles of my feet, it is very thick and tough.

6.  If my outside skin be destroyed, it will grow again; if the jelly-like substance be destroyed, it will re-appear; but if my true skin be destroyed, it will never be perfectly renewed.

7.  More than half of the waste substance of my body passes from it through the pores of the skin, in the form of perspiration.

8.  If I would have a healthy skin,
    I must perspire freely all the time,
    I must keep my body clean,
    I must wear clean clothing,
    I must breathe pure air,
    and live in the sunlight.

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QUESTIONS FOR THE FORMULA.

1.  Where is your skin?

2.  Tell about the skin.

3.  How many skins have you?

4.  Tell about the true skin.

5.  What difference is there in the thickness of your outside skin?

6.  What happens if the different skins be destroyed?

7.  What passes through the pores of the skin?

8.  What is necessary if you would have a healthy skin?

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DIRECTIONS FOR BATHING.

Bathe the whole body at least twice every week.  Do not bathe when tired or after a hearty meal.  After bathing rub well with a coarse towel.

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QUESTIONS ON THE SKIN.

Of what use is the skin?—­“It covers the muscles of the body.”

What can you tell about it?—­“It is flexible, elastic, porous, and absorbent.”

Why do you say it is flexible?—­“Because it is easily bent.”

Why do you say it is porous?—­“Because it is full of little holes, or pores.”

Why do you say it is elastic?—­“Because it will spring back after it is stretched, squeezed, twisted, or bent.”