MUTILATION AND REGENERATION 383 



4. Bone. In all animals fractured bones are per- 

 fectly repaired in uncomplicated cases. As, however, 

 the osseous tissue is inelastic, it is essential that the 

 member to which the bone belongs shall be kept abso- 

 lutely quiet, else instead of a bony union, only a fibrous 

 union will take place and a false joint or pseudarthrosis 

 be formed. In the process of repair, the osteoblasts 

 derived from the periosteum or surrounding membrane 

 are the formative cells. They first elaborate a tem- 

 porary or provisional tissue of a nondescript character, 

 known as callus. It much resembles the hyaline carti- 

 lage with centres of ossification seen in embryonal bone 

 formation, and as it calcifies is, like it, without Haver- 

 sian systems and not distinctly laminated. This tissue 

 is the crude material upon which the bone cells subse- 

 quently work as the callus is reconstructed and rear- 

 ranged so as to bring about complete continuity of the 

 injured bone, after which the surplus is removed. The 

 provisional callus surrounds the ends of the broken bone 

 with a spindle-shaped mass of tissue which acts the part 

 of a splint until the true or definitive callus which forms 

 the permanent bond of union is formed, after which it 

 is absorbed. 



The union of the bones and the restoration of function 

 usually requires but a few weeks, but the final removal 

 of the redundant callus and the restoration of the symme- 

 try of the bone is not perfected for years. 



As the bone is a product of the periosteum, the loss of 

 much bony tissue in consequence of disease is not in- 

 compatible with its regeneration if the periosteum is 

 not destroyed or too much injured, and it is not unusual 

 for surgeons to strip off a fairly healthy periosteum from 

 a diseased bone, remove the bone, and subsequently find 

 a fair substitute manufactured by the carefully pre- 

 served membrane. 



5. Cartilage. Damage to cartilage is usually repaired 

 by the intermediation of fibro-connective tissue by 

 which the fragments are held together, no new cartilage 

 being formed. 



