DENTINE 251 



interval being perceptible between it and the tube wall, 

 and that acids do not cause contraction or shrinkage of the 

 fibril. He also describes slight enlargements of the fibril at 

 the points where processes are given off to the finer divisions 

 of the tubes. 



The dentinal fibril contributes delicate protoplasmic off- 

 sets to the branches of the dentinal tubes which also 

 contain the finer subdivisions of the neurofibrils. 



FIG. 153. Calcified deposits in pulp, showing incorporation of connective- 

 tissue fibres and cells. Compare with fig. 206 showing calcification within 

 connective tissue of the follicle. ( X 150.) 



Secondary Dentine. Erratic deposits of calcified sub- 

 stance are occasionally found in the pulp, the cells of the 

 pulp taking on a calcifying function. This deposit may 

 appear as detached masses or as an incremental deposit 

 upon the inner surface of the already formed dentine. The 

 latter form, called by Hope well Smith adventitious dentine, 

 is frequently found to be formed as a protection against the 

 approach of caries. 



The detached masses (fig. 153) are round, oval, or irregular 

 in form ; they sometimes appear to be tubular, but the 

 arrangement of the apparent tubes is not uniform as in 



