CEMENT 



301 



solvent agent, probably of an acid nature. The osteoclasts 

 are usually multinucleated or giant cells, and vary very 

 much in size and in the number of their nuclei. It is con- 

 sidered by many that both osteoclasts and osteoblasts are 

 modified connective-tissue cells and are interchangeable, 

 osteoblasts becoming converted into osteoclasts and vice 

 versa. Another view of their origin is that they result from 

 the fusion of leucocytes, but the former is the view more 

 generally held. Hope well Smith states, speaking of the 



FIG. 196. Absorption of a temporary tooth. Ho wahip's lacunae 

 and osteoblasts. Weil process. Stained carmine. ( x 250. ) 



absorption of permanent teeth, that osteoclasts do not exist 

 ' in the innermost zone of the root membrane ' ; he denies 

 the presence of osteoclasts in the absorption of the dentine 

 and cement of permanent teeth, and also considers that 

 true Howship's lacunae are not found on the tooth side of the 

 membrane (4). It is, however, very evident in many 

 instances that Howship's lacunae and osteoclasts are present 

 in both dentine and cement which is undergoing absorption 

 (fig. 197), and they show no recognizable difference to those 

 seen in absorbing bone or temporary teeth. 



Cement being but a modified form of bone, it is reason- 



