STRUCTURE AND MULTIPLICATION OF BONE CELLS 151 



bone was present. Thus in figure 2, as in all other figures, 

 the matrix between the cells and processes was unstained just 

 as in figure 1 which is bone from an adult animal. This point 

 is still further estab ished by the fact that toward the periphery 

 of young parietal bones the cells were close together but the 

 matrix which surrounded them was stained so deeply that they 

 w^ere recognizable only with difficulty. Most of these cells are 

 more rounded and at least partly surrounded by uncalcified 

 matrix. Macewen's observations apparently were much like the 

 above except that he considered the cell an osteoblast as long 

 as it was dividing. If this be the case he failed to recognize 

 that ossification set in before proliferation of cells ceased. 



The above observations of bone cell division are, however, 

 not entirely new. They are only an extended confirmation of 

 the observations of Nowikoff in the bone of the new-born mouse. 

 He states definitely that bone cells completely surrounded by 

 matrix really divide. He gives two figures on page 369 of his 

 article. Figure 'a' is a very good picture of both cytoplasmic 

 structure and nuclear division but figure 'b' shows signs of 

 cytoplasmic coagulation. It corresponds to Retterer's descrip- 

 tion of the cytoplasm. The reason for these two different pic- 

 tures is without doubt due to the fixation. The former was 

 fixed in alcohol while the latter was fixed in sublimate. 



FUNCTIONAL CONSIDERATION 



The foregoing description and discussion of structural details 

 and relationships lead to the question of function. No attempt 

 is made here to answer this important question of bone cell 

 function, however, it is important that certain observations 

 should be reviewed which are suggestive in this connection. 



Among earlier writers nothing is said regarding the function 

 of bone cells, these cells are rather regarded as functionless, 

 senile osteoblasts. This view is held by Gegenbaur, KoUiker and 

 Schaffer. They hold that the osteoblast secretes the matrix. 

 Waldeyer and Retterer describe the matrix as a differentiation 

 of the peripheral protoplasm of the osteoblast. Lewis and Stohr 

 believe that the osteoblast is the active bone former, but they 



