346 THE HUMAN BODY AND ITS FOOD 



Our bodies carry out the functions of digestion and circu- 

 lation without our wills : the muscles of heart and stom- 

 ach do not require our attention. But if you wish to 

 throw a baseball, or to "drive" a golf ball, or to sew or 

 write, your brain must call upon certain muscles to pro- 

 duce the proper motions. The body is held erect, and 

 the joints are prevented from collapsing by the action of a 

 multitude of muscles. 



356. Injuries to Bones and Muscles. When bones are 

 broken, it is not only the mineral matter that breaks, but 

 the connective tissue, and the blood tubes and nerves as 

 well. When the broken pieces are held together by 

 bandages and splints, new cells of connective tissue unite 

 the broken edges, and restore the connections of the 

 nerves and blood vessels. The filling of the connective 

 tissue with minerals is the slowest part of the healing 

 process. When this takes place, the bone is said to 

 "knit" together. As a person grows older, more mineral 

 is deposited in the bones, and they become more brittle. 

 They therefore break more easily than in childhood, and 

 do not unite so readily if broken. 



When the bones of a joint are separated, the bones are 

 said to be dislocated, or "out of joint." In this case the 

 ligaments and muscles at the joint are probably torn. 

 In a bad dislocation the muscles may draw up the bones 

 and prevent them from going back into place for some 

 time. The physician then puts splints on the joint to 

 hold it stiff until the ligament has time to grow together 

 again. The chief difference between a sprain and a dis- 

 location is that in a sprain the bones are not separated. 



