364 THE TISSUES. 



This proposition is illustrated in caries, where there is merely a 

 loss of bone-substance, and in solutions of continuity, or fractures; 

 the repair in both cases taking place by the formation of true 

 osseous tissue. In the former case, the new bone is formed from a 

 blastema poured out by the periosteum of the bone; but repair 

 after fracture demands a more particular description. 



In most cases of fracture of the long bones of the lower animals, 

 and in those occurring in man which are, for any reason, with diffi- 

 culty kept in apposition during treatment, the formation of the new 

 osseous tissue is preceded by that of cartilage; and in which the 

 osseous tissue is subsequently developed, as are the primary bones 

 at first (pp. 351 8). This cartilage has been incorrectly termed the 

 provisional callus, and has been said by many writers to be always 

 necessary for repair after fracture. Mr. Paget has, however, shown 

 that this is not the fact; and that where the fractured extremities 

 of the bones are kept in accurate apposition, and at rest, it is not 

 formed at all in man ; but the new bone is developed directly from 

 a blastema, in the exudation of which the periosteum doubtless 

 performs the most important part. Indeed, all unbiased observers 

 must have been unable to perceive any trace of provisional callus 

 during recovery from the most favorable cases of fracture of the 

 radius and of the tibia, where it may be felt whenever it actually 

 exists. 



In fracture of the shaft of the long bones, the newly-formed bone 

 at first entirely closes up the medullary canal ; thus forming a plug 

 entering and connecting the fractured extremities. 1 But when this 

 becomes more consolidated and sufficiently strong, the central por- 

 tions are reabsorbed, and the medullary canal again extends through 

 the shaft of the bone as before. It usually requires two years or 

 more to accomplish this object; after which the new bone-tissue at 

 the point of fracture is as perfect as that of any other part of the 

 bone, though some sign of the injury probably always remains. 



In some cases, however, fractures do not unite by the reproduc- 

 tion of bone ; but the fractured extremities are united merely by 

 cartilaginous tissue (or ligament), and then a sort of articulation is 

 found at the point of fracture. This is the case almost invariably 

 in fractures of the neck of the thigh-bone within the capsular liga- 



1 It is this which Dupuytren, who first used the term, designated as the provi- 

 sional callus. 



