MANNER OF THE EEMOVAL OF THE BONE TISSUE. 161 



quickly as arouminous and other soluble substances. 

 But how, precisely, is the wonderful disintegrating 

 action effected ? In the case of adult bone it is pro- 

 bable that the first change that occurs is the soften- 

 ino- of the bone tissue close to the vessel of the Ha- 

 versian canal by imbibition. In this way the passage 

 of nutrient material to the little bioplasts enclosed, 

 or partly enclosed, in the incompletely formed osseous 

 tissue is favoured. Then the little particles of bioplasm 

 themselves grow and multiply in the space in which 

 they lie. The walls of the 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. See Plate VIIL 

 fig. 48. " The structure of the tissues," a course 

 of lectures given at the Royal College of Physicians, 

 1861. The bioplasts of adjacent lacuna3 increase in 

 the same manner, and by degrees lamina after lamina 

 of the osseous tissue of the Haversian rod dissappears, 

 and in place of hard bone, we find soft pnlpy growing 

 bioplasm occupying what is now the '' Haversian 

 space," and filling up the interval between the vessel 

 of the Haversian canal and the boundary formed by 

 the circumferential portion of siirrounding Haversian 

 systems, which will in their turn have to undergo the 

 same process of disintegTation. The bioplasts do not 

 effect the removal of the bone, as might be supposed, 

 by the formation of an acid fluid or by developing 

 some substance that possesses solvent properties. 

 Upon the whole it is more probable that the change 

 is due to a mechanical rubbing away rather than to 

 the action of a chemical solvent. It seems to me most 

 likely that by the incessant movements of the bio- 

 plasm in very close contact with the material to be 

 removed, excessively minute particles are gTadually 

 rubbed off, as it were. The smallest molecules of the 



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