PROBLEMS OF MODERN SCIENCE 



It can now be realised why the invasion of the 

 cartilage by cells from without as a normal occur- 

 rence in the history of bone-formation is of such 

 peculiar interest, and why its proper understanding 

 is of such predominant importance. It may throw 

 light upon the elucidation of the abnormal invasions 

 occurring in cancer, in the investigation of which 

 so much time, energy, and patient perseverance 

 have been spent, with unfortunately so little 

 tangible result. 



Do the changes in the cartilage whereby it 

 loses its vitality precede the invasion of the cells 

 from without, and does the loss of this vitality 

 imply a diminution of resistance inviting the 

 invasion ? Or, on the other hand, do the invading 

 cells exert an influence resulting in the degenera- 

 tion of the cartilage ? Of the two phenomena, 

 the degeneration of the cartilage apparently takes 

 precedence, and consequently may be the circum- 

 stance which determines the invasion. Concerning 

 the factors which are the influential cause of the 

 degeneration of the cartilage we are absolutely in 

 the dark. 



The cells invading the cartilage seem to be 

 engaged in three main activities. One set, which 

 may be termed ' excavators,' burrow their way 

 into the dying cartilage, in which they eat out 

 relatively large irregular spaces. A second set, 

 ' bone-builders,' deposit bony substance on the 

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