454 LECTURE XVIH. 



decisive point, through which the whole subject of bone 

 acquires another aspect, is, I consider, this, that the 

 bone in the formation of marrow is not simply dissolved 

 and its place taken by some exudation or blastema, but 

 that the dissolution of the osseous substance is a trans- 

 formation of the osseous tissue, and that the dissolution 

 results from a transformation of the intercellular sub- 

 stance of the bone into a soft mass of tissue which is no 

 longer in a condition to retain the calcareous salts. If 

 therefore you ask whence the new elements come which 

 arise in the midst of osseous tissue, or how a cancer or 

 collection of pus can form in the middle of the compact 

 cortex of bone, I return you the very simple answer, 

 that they arise in precisely the same manner, that in the 

 course of the natural and normal development of bone 

 the marrow arises. In no part does the osseous tissue 

 first dissolve, then an exudation, and next a new-forma- 

 tion, follow, but the existing tissue is directly converted 

 into the succeeding one. The existing osseous tissue is 

 the matrix of the succeeding cancerous tissue, the cells 

 of the cancer are the immediate descendants of the cells 

 of the bone. 



If now we consider the course of the formation of 

 bone a little more in detail, we find, as we have already 

 in part seen, that the cartilage prepares for ossification 

 in such a way, that its cells in the first instance become 

 larger ; that divisions then take place in them, first in 

 the nuclei and afterwards in the cells themselves ; that 

 these divisions then proceed with great rapidity, so that 

 we obtain larger and larger groups of cells, and in a 

 comparatively short time the place of a single cell is 

 occupied by a relatively very large group of cells (Fig. 

 124). You will remember from my first lecture (p. 33), 

 that a cartilage -cell is distinguished from most other 

 cells by its secreting a special membranous capsule in 



