174 DISEASES OF THE BONES AND ARTICULATIONS. 



fracture; that in all cases their presence is made manifest by 

 the formation of fistulous abscesses ; and that their removal is 

 imperative. 



In the ox tribe, the digital bones suffer from necrosis, owing 

 to an inflammation of the inter-digital fibrous tissue. 



It was supposed at one time that a sequestrum was reduced in 

 size by the action of the absorbents ; but it is now placed beyond 

 all doubt that dead bone is in every respect a foreign body, and 

 cannot be acted upon by the absorbents more than any other 

 insoluble substance. But at the same time it must be admitted 

 that a sequestrum is much smaller than the original bone ; this 

 can only be accounted for by the fact that its animal basis is 

 dissolved by the purulent discharge, and that it is thus rendered 

 brittle, and liable to be broken into fragments by the movements 

 of the animal. 



Internal necrosis is very rare in the lower animals, one speci- 

 men only in the Museum presenting any appearance of it. The 

 following are its symptoms in the human being, namely, most 

 excruciating pains, supposed to arise from the resistance of the 

 outer sheU to the sw^elling of the inflamed part. The fever is 

 often so high as to prevent the patient obtaining repose. The 

 enlargement, exceedingly hard and diffuse, depends on the swollen 

 condition of the bone, and in time becomes very vascular and 

 softened. The medullary membrane is completely destroyed. 

 The swelling continues for a long time, but abscesses gradually 

 form in the soft parts ; the outer layer of the old bone expands 

 and grows, during the continuance of the suppuration, by the 

 dilation of the Haversian canals; whilst new bone is formed 

 externally, so that the sequestral capsule is partly of old bone 

 and partly of new. "When the sequestrum is removed, and the 

 process of regeneration complete, the bone consists from without 

 inw^ards of the outer shell of new bone, the layer of old bone 

 which is not necrosed, and the central portion of new bone 

 formed by the granulations within, and which for a long time 

 occupies the place of the medullary canal. 



The interior of the bone, at first solid, becomes opened up by 

 the gradual enlargement of the Haversian canals of the new 

 bone, whereby its structure becomes cellular, and in this way it 

 incompletely supplies the place of the medullary canal. 



Many experiments have been made which show that the 



