THE BONES AND JOINTS. 739 



Necrosis may involve the superficial layers, or the entire thickness of 

 the wall of a long bone, or only the spongy tissue and inner layers, or an 

 entire bone, or a number of different portions of the same bone, but it is 

 most apt to occur in compact bone. 



The death and separation of the bone may be soon followed by the 

 growth of new bone to repair the loss. The periosteum, the medulla, 

 and the surrounding soft tissues may all take part in this new growth. 

 The new bone is usually irregular, rough, and perforated with openings 

 through which pus formed around the sequestrum may be discharged. 

 If the sequestrum be removed, healing may occur by the formation of new 

 bone ; but the bone is usually more or less distorted by the irregular new 

 ossification. 



Phosphorus Necrosis. Under the influence of phosphorus vapor, peri- 

 ostitis and osteitis, particularly of the jaw, are apt to occur, which 



FIG. 488. NECUOrilS OK BOXE. 



Showing sequestrum of dead bone partially surrounded by new-formed subperiosteal bone, with thickening 



of the shaft. 



usually lead to more or less extensive necrosis, generally associated with 

 prolonged and often extensive suppuration. 



Caries of bone is essentially an ulcerative osteitis resulting in progres- 

 sive molecular destruction of the bone tissue. It differs from necrosis in 

 that, in the latter, larger and smaller masses of bone die, while in caries the 

 destruction is molecular and gradual (Fig. 489). It may occur in connec- 

 tion with any form of osteitis, with periostitis and osteomyelitis, or it may 

 be secondary to inflammatory or destructive processes in the joints or ad- 

 jacent soft parts. The depressed surfaces of bones in which caries is pro- 

 gressing are rough and more or less finely jagged, and may be covered 

 with granulations. The minute changes by which ulceration and destruc- 

 tion of the bone are produced in caries are somewhat analogous with those 

 in rarefying osteitis, but there are marked degenerative changes in the 

 bone cells, which may become fatty or converted into a granular ma- 

 terial. Moreover, the basement substance of the bone, instead of being 

 absorbed, may disintegrate, with the formation of larger and smaller 



