90 ABSORPTION OF BONE. 



In the removal of the temporary bones in the foetus the 

 bioplasts in the central part increase and erode the spicula of 

 temporary bone. The surface is eroded and scooped out into 

 little pits by the bioplasts which consume the bony matter, 

 and at last a cavity is formed which is occupied by multitudes 

 of bioplasts, the descendants of those of the temporary carti- 

 lage. It was discovered by Tomes and De Morgan that, even 

 in the adult, the Haversian systems of the bones were in a 

 continual state of change from absorption of old and deposition 

 of new bone. The process is thus described by Dr. Beale : 

 Around the vessel occupying the Haversian canal, in the slight 

 interval between the vessel and the surface of the bone, are 

 seen a number of little bioplasts. These " little particles of 

 bioplasm grow and multiply in the space in which they lie. 

 The walls of this space (lacuna) are eaten away, and the lacuna 

 becomes enlarged. As the hard material disappears, instead of 

 a lacuna occupied by a single bioplast, we find a greatly- 

 enlarged space, a gigantic lacuna, containing several bioplasts. 

 One of these I figured as early as 1861. The bioplasts of the 

 adjacent lacuna increase in the same manner, and, by degrees, 

 lamina after lamina of the osseous tissue of the Haversian 

 rod disappears, and, in place of hard bone, we find soft, pulpy 

 growing bioplasm occupying what is now [in the dead, dry 

 bone] the ' Haversian space.' . . . The process of disinte- 

 gration 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 gradually becomes infiltrated with calcareous 

 matter, as already described, and a layer or lamina of new bone 

 results " (" Biopl.," p. 157). In this manner, without the de- 

 velopment of any acid or chemically solvent fluid, this soft and 

 pulpy bioplasm erodes and removes the hardest bony matter, 

 such as the fangs of the temporary teeth. Those particles of 

 protoplasm concerned in the absorption of bone can be shown 

 by the carmine process.* 



* In support of this view of absorption being a vital process, per- 

 formed by the plastids or bioplasm masses, we may notice the forma- 

 tion of the so-called giant cells in the absorption of bone. When the 



