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STUDIES IN ADVANCED PHYSIOLOGY. 



and in this way to preclude any material disintegration of 

 bone in any part of the body. As the bone substance is 

 everywhere riddled, even to the smallest bits, with these 

 osteoblasts and their ramifications to such an extent that 



Fig. 43. LAMELLAE TORN FROM A PARIETAL BONE TO SHOW THE FIBRES OF SHARPEY, 

 c, c. (After Sharpey.) 

 b, thick opaque portion of bone, a, holes where fibres had been. 



the point of an ordinary pin would really cover many of 

 them, one can understand under what thorough supervision 

 the repair of normal bone is, and how even in the smallest 

 and most out-of-the-way portions a disintegration or soften- 

 ing in any way is at once remedied. The osteoblasts when 

 once included in these lacunae are never able to leave them, 

 but remain there until death or until the processes of age in 

 later life cause many of them to apparently disintegrate and 

 disappear. This disappearance of the corpuscles from old 

 bones, as well as the continued calcajeous depositions in it, 

 accounts for the brittleness of the bones of old people and 

 the difficulty with which broken portions are healed. 



The Haversian canal with its series of lamellae, lacunae 

 and canaliculi, is called the Haversian system. Where 

 these systems meet, irregular bits of bone frequently fill in 

 the space between. Around the outside of the entire bone 



