REPAIR OF BONE 77 



The spine and the vertebral extremities of the ribs are com- 

 posed largely of cartilage; it is therefore evident that not only 

 should a young baby's back be supported, but the child should 

 rest in a horizontal position, the spine being so soft that it cannot 

 easily be held upright, even if the little muscles were strong 

 enough to do this without fatigue. 



The pelvis and hip. During the first year or two both the 

 sacrum and the coccyx are still in separate pieces, while the centers 

 in the three portions of the hip-bones are well separated by cartil- 

 age, leaving the acetabulum unossified; the head of the femur is also 

 soft. Consequently, a thought only is needed to explain why the 

 clothing about a, baby's hips should leave them free from pressure. 



Note.' An advantage is derived from the softness of the 

 skeleton during childhood, as the many jarrings and tumbles 

 incident to the child's experience are far less injurious to the jelly- 

 like frame than they would be to a harder one. 



Green-stick fracture.- Up to the age of four years the bones 

 are sufficiently soft to bend rather than break, as an older bone 

 would do under similar circumstances. Usually some of the 

 fibers do break, but not the whole bone; this is called a green- 

 stick fracture, because the bone behaves like a bough of green 

 wood when forcibly bent. 



Rachitis or rickets. In this disease ossification is delayed, 

 and the bones are more soft and yielding than usual until com- 

 pletely ossified. The extremities grow larger and the shafts are 

 often bent. When the mineral salts are finally deposited the bone 

 is permanently misshapen. Rachitis is a disease of malnutrition 

 from deficiency of mineral food. 



Spina bifida. In the formation of the vertebrae, the comple- 

 tion of the arches and spinous processes occurs latest in the lower 

 lumbar and upper sacral region. Sometimes it is not perfect, and 

 the spinal canal is then left open. This condition is known as 

 spina bifida and the membranes and fluid of the spinal cord pro- 

 trude, forming a tumor upon the child's back. Spina bifida 

 occurs rarely in other regions. 



REPAIR OF BONE 



When a bone is broken nature repairs it in her own way. 

 First, more blood flows to the part; then a certain amount of 



