292 CHAPTER 35. 



are required in these operations, otherwise a sharp spicula of bone may 

 cause dangerous hemorrhage by perforating one of the larger arteries in 

 the neighbourhood. 



Necrosis, we may add, runs a certain course, and nature endeavours to 

 effect a cure by the formation of new material. Art can only assist by 

 aiding the removal of the old bone at the proper time. If such assist- 

 ance is not given, Nature will in time effect it by setting up a process of 

 caries and sloughing; but it is desirable to avoid the necessity for this 

 further disease. The pus in necrosis, it is to be observed, is healthy, 

 whilst in caries it is unhealthy. 



579. Exfoliation. 



Exfoliation is simply the separation of a dead from a living portion of 

 bone. 



580. Inflammation of Bone and Periosteum. 



Inflammation is readily set up in bone, or in its periosteum, or in both, 

 by concussion or contusion, or by the extension of inflammation from a 

 neighbouring part. 



The processes of inflammation have been already detailed in Chapter 18. 

 They are the same in bone as in the softer tissues. As a result of in- 

 flammation, effusion takes place through the overloaded vessels of the 

 part. The effusion may be wholly taken up again by the veins and 

 absorbents. Very generally, however, some portion of it remains between 

 the bone and its periosteum. This deposit in due time, after parting 

 with the more watery portion of its constituents, solidifies, and becomes 

 bone or something like bone. In fact an Exostosis is formed. It is a 

 rule in Nature, as has been previously stated, that deposits resulting from 

 inflammatory effusions, have a tendency, when they become organised, to 

 partake of the nature of the tissue into which the exudation is effused. 



581. Exostoses. 



Exostoses usually arise, as described in the preceding paragraph, from 

 inflammatory action in the bone or periosteum. They may however 

 arise from ossification of a fibrous or cartilaginous tumour on the peri- 

 osteum. At other times they are formed by abnormal development of 

 any particular part or process of a bone. 



The new bone is always more spongy in its texture than the original 

 tissue; but after a time it consolidates in a great degree. It never, 

 however, becomes equal to the old bone in density and strength. 



Osseous deposits, though they may seem to disappear, are seldom 

 totally removed. They are only lessened. The absorption of that part, 

 which would be removed in time by the operations of Nature, may be 

 hastened by the application of friction, mercury, iodine, or biniodide of 

 mercury, to the part. 



