ERUPTION OF THE TEETH. 197 



temporary teeth, cutting them off from the permanent teeth 

 destined to follow them. Absorption, too, may attack the 

 roots of permanent teeth, which is another reason for regard- 

 ing the process as not necessarily dependent upon the approach 

 of a displacing tooth. Closely applied to the excavation 

 produced by absorption is a mass of very vascular soft tissue, 

 the so-called absorbent organ. The surface of this is com- 

 posed of very large peculiar-looking cells, bearing some little 

 resemblance to those known as " myeloid cells," or the 

 " giant cells " of recent authors. Microscopic examination 

 of the excavated surface shows it to be covered with small 

 hemispherical indentations, the "lacunse of Howship," into 

 each of which one of the giant cells fitted, and in which they 

 may sometimes be seen in situ. 



In what manner these giant cells, or " osteoclasts," effect 

 their work is not known, but their presence where absorption 

 of hard tissues is going on is universal. Some suppose that 

 they put forth amoebiform processes, others that they secrete 

 an acid fluid, but nothing very definite is known ; a curious 

 parallel is afforded by the manner in which a fungus can 

 drill and tunnel through and through the dentine, as may be 

 very constantly observed in teeth long buried. 



The process of absorption once commenced does not neces- 

 sarily proceed without intermission, but may give place for 

 a time to actual deposition of osseous tissue on the very sur- 

 face eroded ; probably by the agency of the absorbent cells 

 themselves, which are capable of being calcified in the exca- 

 vations they have individually made. 



These alternations of absorption and deposition, so com- 

 mon a result of inflammations of the pulp, or of the alveolo- 

 dentar periosteum, as to be diagnostic of the former occurrence 

 of these maladies, often occur during the normal process of 

 the removal of the deciduous teeth, and result in the deposi- 

 tion of a tissue not unlike cementum in excavations made 

 in the dentine, or even in the enamel. 



