*Experiments to show the Composition of Bone.*—1. Examine a slender bone, like that in a chicken’s leg. Note that it resists bending and is difficult to break. Note also that it is elastic—that, when slightly bent, it will spring back. 2. Soak such a bone over night in a mixture of one part hydrochloric acid and four parts water. Then ascertain by bending, stretching, and twisting what properties the bone has lost. The acid has dissolved out the mineral matter. 3. Burn a small piece of bone in a clear gas flame, or on a bed of coals, until it ceases to blaze and turns a white color. Can the bone now be bent or twisted? What properties has it lost and what retained? What substance has been removed from the bone by burning? *Observation on the Gross Structure of Bone.*—1. Procure a long, dry bone. (One that has lain out in the field until it has bleached will answer the purpose excellently.) Test its hardness, strength, and stiffness. Saw it in two a third of the distance from one end, and saw the shorter piece in two lengthwise. Compare the structure at different places. Find rough elevations on the outside for the attachment of muscles, and small openings into the bone for the entrance of blood vessels and nerves. Make drawings to represent the sections. 2. Procure a fresh bone from the butcher shop. Note the difference between it and the dry bone. Examine the materials surrounding the sides and covering the ends of the bone. Saw through the enlarged portion at the end and examine the red marrow. Saw through the middle of the bone and observe the yellow marrow. *To show the Minute Structure of the Bone.*—Prepare a section of bone for microscopic study as follows: With a jeweler’s saw cut as thin a slice as possible. Place this upon a good-sized whetstone, not having too much grit, and keeping it wet rub it under the finger, or a piece of leather, until it is thin enough to let the light shine through. The section may then be washed and examined with the microscope. If the specimen is to be preserved for future study, it may be mounted in the usual way, but with _hard_ balsam. Prepare and study both transverse and longitudinal sections, making drawings. The sections should be prepared from bones that are thoroughly dry but which have not begun to decay. *To show the Structure of a Joint.*—Procure from a butcher the joint of some small animal (hog or sheep). Cut it open and locate the cartilage, synovial membrane, and ligaments. Observe the shape and surface of the rubbing parts and the strength of the ligaments. CHAPTER XV - THE MUSCULAR SYSTEM