COMPOSITION OF BONE 



27 



strength, yet without moisture the bones could not re- 

 main alive, grow and repair themselves when injured. 

 The collagen represents the part of the bone which has 

 life. The earthy part is simply a deposit of salts of 

 lime made by the living part. 



Changes from infancy to old age. The composi- 

 tion of bone undergoes certain changes with age. In 



FIG. 21. Greenstick fracture 

 of bones of left forearm. 

 (Scudder and Cotton.) 



FIG. 22. Fracture of bones 

 of left forearm. (Scudder 

 and Cotton.) 



childhood, there is more of the animal matter and less 

 of the lime salts than in the adult. The bones of a child 

 are therefore more flexible and less easily broken. Even 

 when a bone is broken, the break usually does not extend 

 across it but makes what is called a greenstick fracture. 

 In adult life, on the contrary, the deposit of earthy 



