150 T. H. BAST 



erating bone. Macewen agrees with Bonome on this point. 

 Macewen beheves also in the multiphcation of osteoblasts but 

 it is difficult to determine whether this proliferation occurs 

 in the osteoblast only or in the bone cell also. According to 

 the following account the actual bone cell does not multiply 

 but has the proliferating potentiality. 



''The osteoblast is the embryonic or free form of the bone 

 cell, and once formed, is capable of great and rapid proliferation, 

 it has also the power of producing matrix which becomes cal- 

 cified .... The bone cell has the function of surrounding 

 itself with a calcareous zone, which it controls, under the agency 

 of the trophic nerves. As long as the bone cell remains embry- 

 onic, it exhibits the power of proliferation; but when it reaches 

 maturity, it assumes the fixed tissue type and becomes station- 

 ary. " Thus according to him adult bone cells do not divide 

 but possess the proliferating potentiality which property is made 

 use of by cells bordering on an injury. 



c. Discussion 



It may be hard to comprehend how bone cells enclosed in a 

 prison wall of bone can multiply. It is still more difficult to 

 interpret the many stages of nuclear and cytoplasmic cleavage 

 as any other thing than cell multiplication. When we consider 

 however that young bone is quite soft and pliable and not so 

 extremely different from other dense tissues, except that some 

 lime salts are deposited in it, it will become apparent that cell 

 division and expansion is not as impossible as it at first seemed. 

 The fact that cell bodies are further apart in the old than in 

 the young bone adds to the evidence that a change or movement, 

 such as occurs in growing tissue, must take place. It might 

 be argued that the tissue which I have described as young 

 bone is not bone at all but only unossified matrix. To this we must 

 reply that these preparations conform to mechanical tests for 

 bone. The staining specificity also supports this view. Gentian 

 violet, which stains most tissues intensely does not stain bone 

 at all or only very slightly. All of the illustrations were taken 

 from parts of the preparations where, according to these methods, 



