470 LECTURE XVIII. 



whole a pumice-stone like appearance, and here too the 

 subsequent condensation into cortical substance is ac- 

 complished by means of the formation within the 

 individual cavities bounded by the little columns of 

 concentric layers of osseous substance out of the perios- 

 teal marrow. 



These are the normal and pathological processes which 

 we recognize in the formation of bone. From them you 

 may gather, that we have in them to do with a series of 

 permutations or substitutions, which lead in one case to 

 a higher, in another, to a lower form of structure, but 

 are however constantly connected with one another, 

 and, according to the conditions which operate upon the 

 parts, assume sometimes one aspect, sometimes another. 

 It is in our power to incite individual portions of carti- 

 lage to ossify, or to transform themselves into a soft 

 tissue. In this whole series the marrow stands alone as 

 the type of the heterologous forms, inasmuch as it con- 

 tains the smallest and least characteristic cells. The 

 young medullary tissue presents the same structure as 

 the young formations, with which all heterologous 

 tissues begin, and since, as I have already hinted, it at 

 the same time constitutes the real type of all granula- 

 tions, it may be said that, wherever new-formations are 

 about to arise on a large scale, a substitution analogous to 

 the type of young medullary tissue (granulation) also takes 

 place ; and that, no matter how great the solidity pos- 

 sessed by the old tissue, a kind of proliferation neverthe- 

 less always takes place, which produces the germs of the 

 subsequent elements. 



