.V 



730 THE BONES AND JOINTS. 



symptoms of pyaemia. The Streptococcus and Staphylococcus pyogenes 

 are the most common excitants of suppurative inflammation. 



Fibrous Periostitis. This is a chronic form of inflammation, resulting 

 in the development of new connective tissue in the periosteum, which 

 becomes thickened and dense and unusually adherent to the bone. It 

 may accompany necrosis, chronic arthritis, chronic ulcers of adjacent soft 

 parts, etc., or follow simple acute periostitis. 



L- Ossifying Periostitis results in the formation of new bone from the inner 

 layers of the periosteum. The masses of new-formed bone, called osteo- 

 phytes, are of variable shape. They may form a thin, velvet-like, villous 

 layer (Fig. 483) ; or they are little spicula; or they form larger, rounded 

 masses (see Figs. 481, 482), or a thick, uniform layer extending over a 

 large part of a bone. They may have at first a loose, spongy character, 

 and be loosely connected with the old bone. But layers of compact bone 



FIG. 483. OSSIFYING PERIOSTITIS. 

 An irregular layer of new bone Is forming between the periosteum and the old bone. 



tissue are formed within their medullary spaces, which are thus gradually 

 filled, and they join the old bone so that they may finally become as 

 compact as or even more compact and dense than normal bone to which 

 they are firmly joined. The hyperostoses and exostoses thus formed may 

 remain indefinitely, or they may gradually become smaller and finally 

 disappear by absorption. 



The formation of new bone in osteophytes, or in dense masses beneath 

 and in the periosteum, occurs as a result of the same process by which 

 bone tissue is normally formed. Certain large cells, called osteoUasts, 

 which are developed along the blood-vessels, possess the power of deposit- 

 ing osseous basement substance about themselves and so forming bone. 

 Pathological new formation of bone differs from the normal mainly in 

 the conditions under which it occurs. The blood-vessels around which 

 the pathological bone develops, which grow out of the old vessels, as in the 

 formation of granulation tissue, are irregularly arranged and subject to 

 a variety of abnormal nutritive and mechanical conditions, so that the 

 new bone is usually formed, not in a series of definite systems of lamella, 



