DISEASES OP BONES 185 



liematogenous origin; that is, the infectious agents are 

 , 'brouglit to tlie marrow by the blood current. 



Which form of osteomyelitis is the more common one ? 

 Purulent osteomyelitis. 



Describe the changes talcing place in osteomyelitis. 



At first the marrow appears dark red, due to hyperemia ; 

 this is followed by absorption of the fat cells of the 

 marrow, thus changing the yellow marrow into the juvenile 

 or red marrow, which either organizes into bone tissue, filling 

 the medullary canal as in callus formation of fractures, or 

 when infected undergoes suppuration. In this case the 

 adjoining bone tissue becomes involved and a rarefying 

 osteitis is the result. As soon as the infectious material 

 .reaches the periosteum it is irritated by the infectious agent 

 and an ossifying periostitis with subsequent exostosis follows, 

 to be destroyed by the rarefying osteitis. As a result of this 

 the ossifying periostitis becomes a purulent periostitis, the 

 neighboring soft parts become infected, an infectious cellulitis 

 ensues, and the pus thus eventually reaches the external 

 world. 



Crive examples of purulent osteomyelitis. 



It is seen in the inderdental spaces of the horse as the- 

 result of pressure from severe bits in pullers ; also in connec- 

 tion with alveolar periostitis in diseases of the teeth. 



Necrosis of Bones. 



What is necrosis of bones f 



Death of the whole bone or part of the bone. 



