464: LECTURE XVIII. 



under the microscope, you remark those excavations, 

 those peculiar holes, which correspond to the liquefying 

 bone-territories. If it be asked therefore in what way 

 bone becomes porous in the early stage of caries, it may 

 be said that the porosity is certainly not due to the for- 

 mation of exudations, seeing that for these there is no 

 room, inasmuch as the vessels within the medullary canals 

 (Figs. 32, 33) are in immediate contact with the osseous 

 tissue. On the contrary, the substance of the bone in 

 the cellular territories liquefies, vacuities form, which are 

 at first filled with a soft substance, composed of a slightly 

 streaky connective tissue with fattily degenerated cells. 

 If round about a medullary canal the territory of one 

 bone-corpuscle after another liquefies, you will after a 

 time find the canal bounded on all sides by a lacunar 

 structure. In the middle of it the vessel conveying the 

 blood still remains, but the substance around about is not 

 bone or exudation, but degenerate tissue. The whole 

 process is a. degenerative ostitis, in which the osseous tissue 

 changes its structure, loses its chemical and morphological 

 characters, and so becomes a soft tissue which no longer 

 contains lime. The tissue, which fills the resulting 

 vacuity in the bone, may vary extremely according to 

 circumstances, consisting in one case of a fattily degene- 

 rating and disintegrating substance (the bone-corpuscles 

 perishing), and in another of a substance rich in cells and 

 containing numerous young cells ; this latter is formed by 

 the division and proliferation of the bone-corpuscles, and 

 the newly produced substance is very analogous to mar- 

 row. Under certain circumstances this substance may 

 grow to such an extent, that if we again borrow our 

 illustration from the surface of the bone, where a vessel 

 sinks in the young medullary matter sprouts out by the 

 side of the vessel, and appears as a little knob, filling one 

 of the pits in the surface. This we call a granulation. 



