THE GROWTH OF BONE 61 



absorbed completely ; once a tiny osseous nodule 

 was found, derived probably from an attached chip 

 of bone, Macewen points out the great practical 

 importance of this in such an operation as sub- 

 periosteal excision of the elbow. If care is not taken 

 to inspect the periosteum, adherent bony flakes may 

 be left which will grow, and lock the joint. If they 

 are all removed, an excellent free joint results. This 

 represents the experience of over two hundred 

 cases. On the other hand, care must be taken 

 not to encroach on the diaphysis of the humerus by 

 removing too much, or it may sprout new bone. 



In other experiments, Macewen removed portions 

 or the whole length of a bone subperiosteally. No 

 regeneration took place to fill the gap, except in a 

 few cases where the animal was young, and the grow- 

 ing epiphyseal ends pushed the extremities together 

 to diminish or obliterate the gap. No new periosteal 

 bone was formed. 



He then repeated Duhamel's silver-ring observa- 

 tion, and found that the burying beneath new osseous 

 tissue occurred just as well if the bone in that neigh- 

 bourhood, or indeed in its whole length, was first 

 deprived of periosteum. The new bone could be 

 seen overflowing the ring from the edges. In this 

 case it is perfectly evident that the osteoblasts 

 providing for growth must have come from the shaft, 

 not from the periosteum. 



A number of important observations are recorded, 

 demonstrating the regenerative powers of bone itself, 

 apart from periosteum, and more particularly in 

 young animals. These may be briefly summarized. 



