14. THE REPAIR OF BONE.--Nature's provision for uniting broken bones is very complete. At first, blood is poured out around the ends of the bone, as a result of the injury. This is gradually absorbed, and gives place to a watery fluid, which, thickening from day to day, acquires, at the end of two weeks, the consistency of jelly. This begins to harden, by a deposit of new bone-substance, until, at the expiration of five or six weeks, the broken bone may be said to be united. It is, however, still fragile, and must be used carefully a few weeks longer. The process of hardening continues, and months must pass before the union can be said to be complete. QUESTIONS FOR TOPICAL REVIEW. PAGE 1. What useful purposes do the bones serve? 15, 16 2. State what you can of the composition of the bones. 16 3. Of the usefulness of lime in the bones. 16 4. Of the usefulness of animal substance in the bones. 16 5. State what you can of the structure of the bones. 17 6. Of the strength belonging to the bones. 15, 16, 17 7. What is meant by the human skeleton? 19 8. Give a description of its construction. 19 9. What is meant by a joint in the human frame? 19 10. State what you can of the movable joints. 19, 20 11. What office is performed by the ligaments of the joints? 19, 20 12. What by the cartilage at the joints? 20 13. What movable joints are there? 20, 21 14. Describe the construction of the spinal column. 21 15. What properties and powers does the spinal column possess? 21, 22 16. When is a person taller than at other times? 22 17. Give the reason for this. 22 18. What can you state of the growth of bone? 22 19. Describe the process by which a broken bone is repaired. 23 * * * * * {24} [Illustration: FIG. 7.--THE MUSCLES.] {25} CHAPTER II. THE MUSCLES. _The Muscles--Flexion and Extension--The Tendons--Contraction--Physical Strength--Necessity for Exercise--Its Effects--Forms of Exercise--Walking--Riding--Gymnastics--Open-air Exercise--Sleep--Recreation._ [Sidenote: 1. What are the muscles? Their number? The design of most of them? Of a few?]