146 T. H. BAST 



(J. Multiplication of bone cells 



A detailed account of bone cell division will be taken up 

 in a subsequent paper on amitosis. In the present paper we 

 shall only attempt to establish the fact that bone cell multipli- 

 cation does actually occur. In all preparations, — including nasal 

 bones of dogs, cats, and rabbits; ethmoid and sphenoid of man; 

 parietals of the mouse, rat, rabbit and cat; and the femur of 

 young rats,^ — some stage of either nuclear or cytoplasmic di- 

 vision or both can be seen. The different stages of nuclear 

 divisions are very common and cytoplasmic division is common 

 in young bone. From a previous statement that bone cells 

 form a syncytium it will be clear that cytoplasmic division is 

 not complete in most cases. Since many of the protoplasmic 

 connections break early it is conceivable that all such connections 

 between two sister cells might break. However I am unable 

 to show such a condition. The constriction however is so real 

 that the process of cell division is complete except for a fine 

 connecting process. In all observed cases of nuclear division 

 the method, without exception, was that of amitosis. The con- 

 stricting or dividing nucleus showed no signs of chromatin re- 

 arrangement and the nuclear wall was complete at all stages. 



In the region of newly formed bone, multiplication is rapid 

 and often forms strings of cells (fig. 2). These rows of cells are 

 especially seen along the walls of blood vessels radiating toward 

 the periphery as in the parietal, or lying parallel to the long axis 

 of the bone as in the femur. A number of stages of division are 

 shown in figure 6. In figure 4 several masses of cytoplasm 

 without nuclei are separated from the main cell except for a 

 narrow cytoplasmic connection. The largest of these masses 

 is interesting because it contains a small amount of nuclear 

 material and a faint strand of nucleoplasm extends from the main 

 cell nucleus toward this outlying mass of protoplasm. Most 

 of these masses contain no nuclear material. They seem to be 

 pinched off from the main cell by rapidly forming bone matrix 

 in the region of the constriction. The mass containing the 

 nucleus may have been formed in such a way but carrying with 

 it a portion of the nucleus, or it may be the result of cell division 



