7. _A Ganglion_, or what is vulgarly called a "weak" or "weeping" sinew, is the swelling of a bursa. [Footnote: A bursa is a small sack containing a lubricating fluid to prevent friction where tendons play over hard surfaces. There is one shaped like an hourglass on the wrist, just at the edge of the palm. By pressing back the liquid it contains, this bursa may be clearly seen.] It sometimes becomes so distended by fluid as to be mistaken for bone. If on binding something hard upon it for a few days it does not disappear, a physician will remove the liquid by means of a hypodermic syringe, or perhaps cause it to be absorbed by an external application of iodine. PRACTICAL QUESTIONS. 1. What class of lever is the foot when we lift a weight on the toes? 2. Explain the movement of the body backward and forward, when resting upon the thigh bone as a fulcrum. 3. What class of lever do we use when we lift the foot while sitting down? 4. Explain the swing of the arm from the shoulder. 5. What class of lever is used in bending our fingers? 6. What class of lever is our foot when we tap the ground with our toes? 7. What class of lever do we use when we raise ourselves from a stooping position? 8. What class of lever is the foot when we walk? 9. Why can we raise a heavier weight with our hand when lifting from the elbow than from the shoulder? 10. What class of lever do we employ when we are hopping, the thigh bone being bent up toward the body and not used? 11. Describe the motions of the bones when we are using a gimlet. 12. Why do we tire when we stand erect? 13. Why does it rest us to change our work? 14. Why and when is dancing a beneficial exercise? 15. Why can we exert greater force with the back teeth than with the front ones? 16. Why do we lean forward when we wish to rise from a chair? 17. Why does the projection of the heel bone make walking easier? 18. Does a horse travel with less fatigue over a flat than a hilly country? 19. Can you move your upper jaw? 20. Are people naturally right or left-handed? 21. Why can so few persons move their ears by the muscles? 22. Is the blacksmith's right arm healthier than the left? 23. Boys often, though foolishly, thrust a pin into the flesh just above the knee. Why is it not painful? 24. Will ten minutes' practice in a gymnasium answer for a day's exercise? 25. Why would an elastic tendon be unfitted to transmit the motion of a muscle? 26. When one is struck violently on the head, why does he instantly fall? 27. What is the cause of the difference between light and dark meat in a fowl? III. THE SKIN.