354 COMPOSITION OF BONE. 



liculi, the nourishing materials of the blood reach all parts of 

 the bone. 



The Chemical Composition of Bone 1. Take a tall, 



narrow glass jar, called in the chemical laboratory a "gradu- 

 ate," or a lamp chimney corked at one end answers very well, 

 and nearly fill with water. Add one-sixth as much hydro- 

 chloric acid. Put into this a slender, dry bone, such as a 

 fibula or rib. In twenty-four hours take it out, rinse it 

 thoroughly, and examine it. The acid will probably have dis- 

 solved out the mineral matter and left the animal matter. 



2. Lay a piece of bone on a shovel, or piece of sheet iron, 

 and place in the fire. The animal matter is burned out, 

 leaving the brittle mineral matter. 



Bone is composed of mineral matter, two-thirds, and animal 

 matter, one-third ; in childhood the animal matter is in larger 

 proportion, while in old age the mineral matter is in excess. 



The mineral matter is chiefly calcium phosphate, while 

 the animal matter is largely gelatin. 



Classification of Joints. 1. Immovable, such as the 

 sutures between the bones of the skull ; 



2. Mixed, such as the joints between the vertebrae; 



3. Movable, which allow free motion between the parts ; 



(a) Ball and socket, as in the hip and shoulder ; 



(b) Hinge, as in the knee and elbow ; 



(c) Pivot, as in the forearm, and between the atlas and 

 axis ; 



(d) Gliding, as between the short bones of the wrist and 

 of the ankle. 



Examine these joints in the articulated skeleton, and so 

 far as possible in fresh specimens (of rabbits). Compare 

 the ball and socket joints of the hip and shoulder. Also 

 compare the hinge joints of the knee and elbow. 



Hygiene of the Bones and Joints If a bone is broken, 



