BONES 361 



condition they are called cartilage. As age advances, 

 lime is deposited among the cells, and they become hard 

 and brittle, forming true bone. A layer of cartilage re- 

 mains to cover the ends of most bones. Late in life it 

 may take up lime and so become like bone. 



648. Rickets. Sometimes a child's bones contain too little lime ; 

 then under the influence of continual pressure of standing, the bones of 

 the leg may gradually grow into a bowed shape. This disease is called 

 rickets, and is due to too little nourishment. When fed on a sufficient 

 amount of proper food, the bones soon grow rigid again, and as the 

 child's legs grow longer, their curves become less noticeable. 



649. Broken bones. Bones are often broken. Then 

 the cells are injured, and blood tubes and nerves are torn 

 across. So there will be great pain and tenderness. When 

 a bone is broken, its cells reproduce themselves and fill in 

 the space with new connective tissue. In course of a 

 few weeks, lime is deposited in the new tissue, and the 

 union is complete. When a bone is broken, the surgeon 

 pulls its ends in place and binds them to stiff splints until 

 healing is complete. 



If a bone is broken, the limb should be at once bound to a board or 

 stick with handkerchiefs or strips of cloth. Take care not to tie the 

 bands tightly enough to stop the flow of blood. 



As a person grows older, more lime is deposited in his bones, and 

 they become harder and more brittle. Then they are more likely to be 

 broken and are less able to grow together again. Often a child's bone 

 will bend until it breaks, but its ends still hold together like a broken 

 green stick. In older people it snaps like a dry twig. 



650. Diseases of bones. Bruises or consumption or other 

 causes of disease may produce inflammation and abscesses of the bone 

 as in any other part of the body. Then the bone is very painful and 

 tender and may die. Then the periosteum will form a new bone. If 

 a large piece of bone dies, it wastes away more slowly than new bone 

 is formed. All fourfooted animals have nearly the same bones arranged 



