242 MOTION AND COORDINATION 



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. i. 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 trans- 

 verse 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 carti- 

 lage, synovial membrane, and ligaments. Observe the shape and surface 

 of the rubbing parts and the strength of the ligaments. 



