4. How may the muscles be named?

5. Tell about the muscles of the head, trunk, and limbs.

6. Which muscles are the weakest, and which are the strongest?

7. What is necessary if you would have strong and healthy muscles?

CLa.s.sES AND WORK OF THE MUSCLES.

The muscles are divided into two great cla.s.ses: those which we may move as we choose, called _voluntary_ muscles, and those over which we have no power, called _involuntary_ muscles.

Some muscles support and move the various parts of the body, others have different work to do. The heart, the great involuntary muscle, acts like an engine to drive the blood throughout the body; the lungs draw in and throw out the air in breathing; the stomach helps to churn and change food into blood; the tongue is used in speaking and eating.

QUESTIONS ON THE MUSCLES.

What are the muscles?--"The lean flesh of the body; bands and bundles of fleshy threads which cover the body."

Of what use are the muscles to the body?--"They cover the bones; they support and move the bones and different parts of the body."

Name some parts of the body which are made of muscles.--"The eyeb.a.l.l.s, the eyelids, the tongue, the heart, the lungs."

What color are the muscles?--"Red."

How do the muscles move the bones?--"By shortening or lengthening themselves according to the way the bones are to be moved."

Tell how the muscles move your arm at the elbow.--"The muscles in the front part of the arm shorten themselves, to draw my fore-arm toward the shoulder; when I wish to stretch out the fore-arm these muscles lengthen, while another set of muscles shorten, to draw the fore-arm away from the upper arm."

What do you say about the muscles because they have the power to shorten and lengthen themselves?--"They are elastic."

About how many muscles are there in your whole body?--"About four hundred and fifty."

How may these be divided as you study about them?--"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.

[Ill.u.s.tration: 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 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 pa.s.ses 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.

QUESTIONS FOR THE FORMULA.