230 THEORY AND PRACTICE 



Chronic periostitis is divided into fibrous and ossifying forms. 

 In fibrous periostitis the characteristic feature is the transforma- 

 tion of the periosteum into a dense fibrous tissue, which closely 

 adheres to the bone and later ossifies. 



Osteitis and osteomyelitis are almost invariably associated. 

 It is almost impossible to find the bone inflamed without the in- 

 volvement of the marrow. This inflammation is infectious and 

 seems to depend upon the bacteria which are disseminated by 

 the blood and lodge in the vessels of the bone. The disease 

 usually begins in the marrow cavities of the long bones, but may 

 occur in the short bones, or even in the flat bones of the skull. 

 The marrow is first found to be deeply congested and of dark- 

 red color. When the bone is sawed through the congested mar- 

 row bulges outward. In the majority of cases there is more or 

 less suppuration and the pus collects in small cavities, forming 

 abscesses in the bone. In severe cases extensive necrosis may 

 result. 



The greater number of cases heal by resolution, some in 

 erosion of the bone, external evacuation of the pus, necrosis and 

 then a chronic inflammation set up by the sequestrum. Some 

 cases are fatal in consequence of pyemia. The extent of the 

 necrosis that may follow osteomyelitis and periostitis is variable 

 according to the severity of the case. In severe cases the entire 

 shaft may die.. The dead bone is known as a sequestrum. 

 Chronic osteomyelitis results from the acute chiefly by the con- 

 tinued irritation by the sequestrum. 



Necrosis of bone is death of the part, due to the nutrition 

 being shut off. This is usually caused by injury to the peri- 

 osteum. We see necrosis sometimes suddenly develop from ex- 

 ternal injuries, such as occur in the bars of the mouth from the 

 bit. The bone dies and large pieces slough off — the sequestra. 

 When the shaft of the large bone dies this way, it usually softens 

 and liquifies and flows out through a fistulous opening. The 

 discharge is ichorous. In the meantime new bone is forming 

 under the periosteum. It is lacking in the characteristics of 

 normal bone but it does very well. 



The treatment for necrosis consists first in using slings un- 

 less the horse shows inclination to lie down. Soon as the pus 



