128 LABORATORY MANUAL 



bone and central canal. The spongy bone contains in 

 its cavities red marrow, while the central canal contains 

 yellow marrow. 



B. Composition. To determine the chemical compo- 

 sition of bone, place a rib in a twenty per cent solu- 

 tion of hydrochloric acid. Leave the bone in the solu- 

 tion for at least four days. At the end of that time 

 examine the bone. Has it changed in shape? Can it 

 be cut ? Is it elastic ? The acid has dissolved from the 

 bone the mineral matter leaving only the animal mat- 

 ter, cartilage. The animal matter may be extracted by 

 burning the bone. Again the shape remains the same 

 but the substance left is hard and brittle. This mineral 

 matter is chiefly lime. 



CHAPTER XXIII 



MUSCULAR SYSTEM. 



Exercise 86. Levers. 



Object: To determine the action and advantages of 

 levers. 



Apparatus 



Yard stick Ring stand 



Weight (500 gms.) Lever holders 



Spring balance 



Directions: A lever is an inflexible bar moving 

 about a fixed point, called a fulcrum, and having two 

 other points, called power and weight. Weight is the 



