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 The reddish muscle found in a piece of beef is a good example of striated muscle. The clear ring surrounding the intestine of a cat (shown by cross section) and the outer portion of the preparation from the cow’s stomach, sold at the butcher shop under the name of _tripe_, are good examples of non-striated muscular tissue. The heart of any animal, of course, shows the heart muscle. *To show the Structure of Striated Muscle.*—Boil a tough piece of beef, as a cut from the neck, until the connective tissue has thoroughly softened. Then with some pointed instrument, separate the main piece into its fiber bundles and these in turn into their smallest divisions. The smallest divisions obtainable are the muscle cells or fibers. *To show Striated Fibers.*—Place a small muscle from the leg of a frog in a fifty-per-cent solution of alcohol and leave it there for half a day or longer. Then cover with water on a glass slide, and with a couple of fine needles tease out the small muscle threads. Protect with a cover glass and examine with a microscope, first with a low and then with a high power. The striations, sarcolemma, and sometimes the nuclei and nerve plates, may be distinguished in such a preparation.