STRUCTURE AND MULTIPLICATION OF BONE CELLS 153 



The structures which I have observed that indicate that bone 

 cells are active in bone production may be enumerated as follows : 



1. Bone cells are much farther apart in old than in young 

 bone. 



2. Bone cells as a rule are somewhat smaller in old than in 

 young bone. 



3. The large protoplasmic masses which lie in the matrix 

 of young bone are almost absent in old bone. This may either 

 indicate that they are used up in bone formation or it may have 

 some bearing on Haour's degeneration theory. 



4. The fact of cell multiplication certainly indicates cell 

 activity, 



SUMMARY 



1. Bone cells are elongated or rounded bodies with proto- 

 plasmic processes radiating in all directions. The cells with their 

 processes completely fill the so-called lacunae and canaliculi. 

 Many of the processes anastomose with similar processes of 

 neighboring cells. 



2. The cell protoplasm is finely granular with highly refractive 

 or deeply stained granules distributed through the more pe- 

 ripheral portion. 



3. The size of the cell depends on the state of proliferation 

 and on the age of the cell. Old cells are usually a little smaller 

 than young cells. 



4. Bone cells are further apart in old than in young bone. 



5. The large protoplasmic masses, lying in the bony matrix 

 of young bone and which are connected to the main cell by narrow 

 strands of protoplasm have almost entirely disappeared in old 

 bone. 



6. The nucleus is rich in chromatin which is grouped in small 

 masses and irregularly distributed. 



7. Bone cells multiply. The multiplication is rapid in young 

 bone and slower in old bone, but division is always by amitosis. 



8. Bone cells are not senile, functionless osteoblasts but ob- 

 servations indicate that they are active cells which are in some 

 way related to bone production. 



THE AMERICAN JOURNAL OF ANATOMY, VOL. 29, NO. 2 



