100 TOMES, ON THE DENTAL TISSUES. 



of the permanent ones, which are then kept within tlie 

 substance of the jaw, or appear in some unusual posi- 

 tion. 



The relations as regards time between the absorption and 

 shedding of temporary teeth and the appearance of the suc- 

 ceeding permanent teeth, are by no means constant. In some 

 cases the temporary teeth are thrown off two years before the 

 corresponding permanent ones come through tlie gums. In 

 others, again, the new will replace tl;e old ones in as many 

 weeks or even days. 



Before the laws which regulate the absorption of the fangs 

 of teeth can be fully recognised, a more perfect knowledge 

 of the condition attending the process must be acquired. 

 Recent examinations have enabled me to add tlie following 

 additional facts bearing upon this subject to t!>ose already 

 known. The process of absorption once commenced, it 

 appears to have been assumed that the same action would 

 be continued, with more or less rapidity, until the tooth falls 

 out ; or if not continual, is suspended only. Such, however, 

 is not constantly the case. Not only is the action of absorp- 

 tion suspended, but one of development takes its place. We 

 find the excavated surface of the dentine cementum and enamel 

 covered with cementum^ tlie latter following all the irre- 

 gularities of the former tissues, and closely united to them. 

 In cases where this development is going on, or being set up 

 is maintained, the teeth afford considerable resistance when 

 their removal is attempted. In those instances where the first 

 teeth have remained, and tend to the displacement of the 

 second set, this deposit of cemeniinn will be found to exist in 

 considerable quantity. 



The development of bone upon the surface which had 

 formerly been tl:e seat of absorption, by no means indicates 

 t'iat the tooth will not again be subject to destructive action. 

 On the contrary, specimens in my collection show that the 

 bone deposited under the above circumstances may itself 

 become the subject of absorption, tljat this process may be 

 again suspended and development be renewed, that the absorp- 

 tion may again take the place of development ; in fact, that 

 wasting and reparation may alternate until by the preponder- 

 ance of the former the tooth is slicd. In sections of teeth 

 showing this peculiar condition of development, we may find 

 upon the growing bcme numerous osteal cells, with here and 

 there a lacunal cell. A bone lacuna, situated within a semi- 

 circular indentation in the dentine, gives the appearance of a 

 lacunal cell, and a lacuna similarly situated in the cementum 

 (a circumstance of common occurrence), has possibly been 



