RECONSTRUCTION OF BONE. 157 



As more and more bone tissue disappeai's, an in- 

 creasing space between the vessel and the bone tissue 

 results. This space is entirely occupied by bioplasts. 

 Indeed at this time instead of the Haversian rod 

 we should find around its central vessel only a cylin- 

 drical column of soft material, consisting almost 

 entirely of small living bioplasts, each about the size 

 of a white blood corpuscle or somewhat less than 

 this, which have grown and multiplied chiefly at the 

 expense of the bone tissue which had been removed by 

 them. The elements of nutrition required by the bio- 

 plasts, and which are not present in the bone, are no 

 doubt derived from the blood which continues to flow 

 through the vessels while these changes proceed. Thus 

 is formed the "Haversian space" which is seen in a 

 section of dead dry bone. The soft bioplasm contains 

 so much water, that when a section of dry bone is ex- 

 amined, scarcely a trace of the multitude of eroding 

 bioplasts, or of the vessel, can be seen. The bone tissue 

 of the Haversian system having been removed, the 

 process of erosion at the circumference of the space 

 ceases, probably in consequence of the great distance 

 by which the bioplasts near the bone tissue are now 

 separated from the blood, whence certain elements 

 necessary for their growth can alone be derived. 



The process of disintegration gives place to a very 

 different operation. Of the bioplasts in contact with 

 the bone, some no doubt die and disappear. Others are 

 however concerned in the production of soft formed 

 material, which gTadually becomes infilti-ated with 

 calcareous matter, as described in § 208, and a layer 

 or lamina of new bone results. Then immediately 

 within this a second lamina is foiTaed in the same 

 manner. The formation of new layers concentrically 

 one within the other proceeds, imtil a new Haversian 

 system results. The lacuna and canalculi are formed 

 precisely as I have already described in § 208. 



After this new Haversian rod has existed for a certain 



