CONNECTIVE TISSUE. 261 



homogeneous lump into a nucleated plastid, and from this into 

 plastids with nucleoli only, and finally into granular plastids, 

 destitute of nuclei and nucleoli. (See page 55.) 



The interpretation here given does not, however, explain the 

 appearance of such bioplasson bodies in dead bone. Ivory sticks, 

 driven into living bone for surgical or experimental purposes 

 (Billroth), and necrotic bone likewise, exhibit bay-like excava- 

 tions at their surfaces, filled with multinuclear bioplasson masses. 

 Obviously, these masses could not have originated from the dead 

 ivory and the necrotic bone. Their bay-like excavations are ex- 

 plicable, as Virchow has already shown at length, by assuming 

 in them a decalcification and liquefaction of the basis-substance, 

 corresponding with the territories ; and, since Ziegler has demon- 

 strated that even between two thin glass plates, placed into the 

 subcutaneous tissue of animals, migrating plastids accumulate 

 and coalesce into multinuclear masses, a similar process may be 

 admitted for the filling of these bay-like excavations. 



That the multinuclear bodies really arise from the liquefied 

 living bone-tissue itself I have ascertained in provisional teeth, 

 the erosions of which were studied, in the last few years, in my 

 laboratory, by Dr. Frank Abbott; and there can be no doubt 

 that they are a growth of medullary corpuscles from without, 

 whenever the bone is deprived of its life. 



Cartilage with advancing age gradually decreases in amount ; 

 in the aged we find only a thin layer of articular cartilage. In 

 old dogs, the thin layer of the articular cartilage, toward the 

 marrow spaces, is bordered by a well-marked lamellated zone 

 of bone. (See Fig. 108.) 



That the bone-tissue itself does decrease in bulk with advanc- 

 ing age is best illustrated by the toothless jaws of the aged. 

 The cause of this absorption and atrophy of the bone-tissue, 

 invading both the cancellous and compact structure, has not yet 

 been elucidated. 



