COGSWELL — OX THE HUMAN TEETH. 161 



if tlie projectile force be there spent, the ball will gravitate to the 

 opposite and lower side of the pulp cavity. 



' ' The presence of the foreign body exciting inflammation of the 

 [)ulp, an irregular course of calcification ensues, which results in 

 the deposition around the ball of a certain thickness of osteo- 

 dentine. The pulp then resuming its healthy state and functions, 

 eoats the surface of the osteo-dentine inclosino; the ball, too'ether 

 with the rest of the conical cavity into which the mass projects, with 

 layers of normal ivory. 



' ' The portions of the cement-forming capsule surrounding the 

 base of the tusk, and the part of the pulp which were perforated bv 

 the ball in its passage, are soon replaced by the active reparative 

 power of these highly vascular bodies. 



" The hole formed by the ball in the base of the tusk is then more 

 or less completely filled up by a thick coat of cement from without 

 and of osteo-dentine from within. 



*'By the continued progress of growth, the ball so inclosed is 

 carried forward, in the course indicated toward the middle of the 

 tooth. Should the ball have penetrated the base of the tusk of a 

 young elephant, it may be carried forward by the uninterrupted 

 iXrowth and wear of the tusk, until that base has become the apex, 

 and be finally exposed and discharged by the continual abrasion to 

 which the apex of the tooth is subjected." 



To illustrate this more fully if a molar tooth wdth a superficial 

 cavity, highly sensitive from inflamed tubuli, be carefully filled with 

 a suitable material, preferring that least acted upon by thermal 

 change, and allow the sam.e to remain three months at least, it will 

 be found on removal that the sensibility and pain no longer exists, 

 and in excavating and carefully examining a firm hard layer of 7iew 

 dentuie will be found covering and protecting what was almost too 

 sensitive and painful to bear, this may be considered as i^enewing of 

 tooth structure^ and a supply of v/aste material as well as protec- 

 tion against unnatural abrasion. 



In the composition of the teeth, we have organic and inor- 

 ganic or earthy matter, the density varying chiefly as the earthy 

 matter contained in each. 



