336 T. H. BAST 



SUMMARY 



1. Bone cells divide by amitosis. 



2. Division is more rapid in very young than in older bone. 



3. Cell division seems to be a periodic process. In a given 

 area all of the cells are in practically the same stage of division. 



4. Amitosis is the normal method of bone-cell multiplication. 

 That amitosis occurs rather than mitosis may be due to one or 

 all of the following factors, a) High degree of specialization of 

 cells concerned. 6) Disturbance of nutritive equilibrium, c) 

 Insufficient nuclear surface for the proper metaboUc functioning 

 of the cell. 



5. Three types of amitosis are present in bone-cell division, 

 and they are determined by the activity and position of the cen- 

 trosomes. In one type the nucleus is dumb-bell shaped and the 

 centrosomes are placed at the opposite poles of the nucleus. 

 In the second type the centrosomes are placed in the center of 

 the horseshoe-shaped nucleus. The latter type can hardly be 

 considered as amitosis, but should be regarded as cell fragmenta- 

 tion. In this latter case division seems to be entirely due to 

 external pressure. 



6. A correlation of the various accounts of amitosis shows 

 that one other type of amitosis exists. In this type the centro- 

 somes are in no way concerned in the process of division. Cen- 

 trosomes, as such, may or may not be present. A plate-like 

 structure indicates the plane of division. 



