hanical devices found in the skeleton, and
bring about the voluntary, movements. The non-striated muscles surround
the parts on which they act, and produce involuntary movements. Both,
however, are under the control of the nervous system. To bring about the
opposing movements of the body, the striated muscles are arranged in
pairs; and to increase their motion, the bones are used as levers.
Physical exercise is necessary both for the development of the muscles and
for the health and vigor of the entire body.

*Exercises.*--1. Compare the striated and non-striated muscles with
reference to structure, location, and method of work.

2. In what respects is the muscular tissue of the heart like the striated,
and in what respects like the non-striated, muscular tissue?

3. If muscles could push as well as pull, would so many be needed in the
body? Why?

4. Locate muscles that work to some extent against elasticity and gravity.

5. Locate five muscles that act as flexors; five that act as extensors;
two that act as adductors; and two as abductors. Locate sphincter and
radiating muscles.

6. By what means does the nervous system control the muscles?

7. Give proofs of the change of potential into kinetic energy during
muscular contraction.

8. Define the essential properties of muscular tissue and state the
purpose served by each.

9. Describe a lever. For what general purpose are levers used in the body?
What other purpose do they serve outside of the body?

10. Why are levers of the second class not adapted to the work of the
body?

11. Name the class of lever used in bending the elbow; in straightening
the elbow; in raising the knee; in elevating the toes; and in biting. Why
is one able to bite harder with the back teeth than with the front ones
when the same muscles are used in both cases?

12. Measure the distance from the middle of the palm of the hand to the
center of the elbow joint. Find the attachment of the tendon of the biceps
muscle to the radius and measure its distance to the center of the elbow
joint. From these distances calculate the force with which the biceps
contracts in order to support a weight of ten pounds on the palm of the
hand.

13. How does exercise benefit the health? How does a short walk "clear the
brain" and enable one to study to better advantage?

14. When exercisers taken for its effects upon the health, what conditions
should be observed?

PRACTICAL WORK

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