OP THE BONES. 387 



The new bone, which is at first very soft and flexible, to 

 such a degree as sometimes to be bent by the action of the 

 muscles, when the old bone, engaged by one extremity in one 

 of the fistulous openings, no longer forms a solid support to 

 it, ultimately acquires and preserves a density and hardness 

 superior to those of the original bones. 



The medullary cavities form in the new bone in proportion 

 as its tissue, which is at first uniformly lax, acquires density 

 at the exterior. 



All these changes take place as if spontaneously in the hu- 

 man species, in circumstances and under the influence of causes 

 which appear to act upon the periosteum to produce inflamma- 

 tion in it, and probably also upon the medullary membrane, 

 that is to say, upon the internal nutritive apparatus, in such a 

 manner as to alter its texture and functions. 



The long bones, in which necrosis occurs most frequently, 

 are the following, being arranged nearly in the order of their 

 frequency: the tibia, femur, the humerus, the mandibular 

 bone, the bones of the fore-arm, the clavicle, the fibula, and 

 the bones of the metatarsus and metacarpus. 



Two theories have been proposed on this subject, the au- 

 thors of which have only erred in making them exclusive, for 

 things sometimes take place in the one way and sometimes in 

 the other. 



Troja, David, Bichat, and many others, have admitted that 

 the sequestrum is formed by the entire body of the original 

 bone rendered more or less thin by absorption and by the sol- 

 vent action of the pus, and that the new bone results from a 

 new formation, of which the external nutritive apparatus, that 

 is to say, the periosteum and its vessels, has furnished the ma- 

 terials, which being deposited in its substance, and especially 

 in its internal surface, have passed through all the states of 

 fluidity and successive hardening which the regular bones 

 present, excepting that the bony hardening commences in 

 many points at once. 



Experiments made on living animals show, that when the 

 periosteum is torn off, it is reproduced along with the bone; 



