406 ANATOMICAL AND PATHOLOGICAL OBSERVATIONS. 



Wlien a portion of dead or dying bone is about to be 

 separated from the living, the process which occurs is essen- 

 tially the same as that which has now been described. The 

 Haversian canals, which immediately bound the dead or dying 

 bone, are enlarged contemporaneously with the fdling of their 

 caxaties with a cellular growth. As this proceeds, contiguous 

 canals are thrown into one another. At last the dead or 

 dying bone is connected to the living by the cellular mass 

 alone. It is now loose, and has become so in consequence of 

 the cellular layer which surrounds it presenting a free surface 

 and throwing off pus. 



In this process the veins and absorbents act on the osseous 

 texture of the walls of the Haversian canals in no otherwise 

 than in the natural state of the part. They are mediate, not 

 immediate, instruments of absorption. It is the cells of the 

 newly-formed cellular mass, contained in the Haversian canals, 

 which are the immediate cause of the removal of the bone, 

 either by taking it up as nourishment, and substituting them- 

 selves in its stead — the bone being prepared for this absorp- 

 tion in a manner analogous to that which occurs in the 

 digestion of food previously to absorption of it by the cells of 

 the gut ;* or by the active formation of the cells of the new 

 substance monopolising the resources of the part, and so in- 

 ducing the disappearance of the osseous texture by the natural 

 channels of the returning circulation. 



The process by which a slough in the soft parts is separated 

 from the living textu-res is similar to that which occurs in 

 bone. 



In this view of ulceration, there is substituted for the 

 hypothetical active or aggressive power of absorption ascribed 

 to the veins and the lymphatics, a power which is known 



* "Hence, the digestive process, instead of being confined to the stomach 

 and duodenum, is actually carried on -without intermission, in all parts of a 

 living animal body." — Pr out's Bridgewater Treatise, page 534. 



