THE GROWTH OF BONE 59 



It was the natural corollary from this belief, that 

 when bone has been destroyed by inflammation or 

 removed by operation, we must look to the periosteum 

 to regenerate new bone ; and as a matter of fact it is 

 well known that if the periosteum is stripped up from 

 the shaft by a purulent collection beneath it, it does 

 in most cases lay down a sheath of bone outside the 

 space in which the pus lay. Again, after fractures 

 we look to the periosteum to produce ensheathing 

 callus to bind the broken ends together again. Some 

 regenerating power, however, must be allowed to 

 osteoblasts derived from the bone itself, to explain 

 the formation of callus between the actual fractured 

 ends and in the medullary cavity. 



Well entrenched as this view has been, it has 

 recently been subjected to most damaging criticism 

 by Sir William Macewen, who goes so far as to state 

 that the function of the periosteum is not to produce 

 bone but to limit the production of bone, and that 

 osseous regeneration takes place from the osteoblasts 

 of the bone itself, not from the periosteum. He 

 supports his thesis by some most interesting experi- 

 ments on animals, and observations on man. 



It has always been admitted that some power of 

 lajdng down bone must be allowed to osteoblasts 

 quite apart from the epiphyseal cartilages or the 

 periosteum, because of course it is their province to 

 fiU in the Haversian canals with concentric rings of 

 new bone, and also to cement the ends of a fracture 

 as intermediary and intramedullary callus. The hard- 

 ness and density of bone rather blind our eyes to the 

 fact that, like every other living tissue, the processes 



