FAMILIAR TALK CONCERNING THE TEETH. 123 



to the external contour of the tooth will be found. This cavity is prolonged 

 into the root, or roots, if there be more th'an one, and opens by a minute 

 orifice at the extremity of each. This is called the pul]) cavity or chamber, 

 while those portions extending into the roots are distinguished by the name 

 of pulp canals. This pulp cavity is occupied by a highly vascular and 

 nervous tissue, the dental pulp, which is continuous through the opening at 

 the end of the root with the vessels and nerves which supply the teeth and 

 adjacent parts. From this dental pulp, improperly called the nerve, the 

 tooth derives most of its life. The popular idea that the pulp of a tooth is 

 a nerve is not correct; on the contrary, it is composed of much the same 

 elements as any vital tissue. It is from this pulja that the hard tissues of 

 the tooth are developed, it being originally of nearly the size of its indi- 

 vidual tooth, growing smaller as the tooth becomes more fully developed, 

 until at last it occupies only a small portion of the tooth. The exterior of 

 the pulp corresponds in shape with that of the tooth, so that if it be isolated 

 completely from the tooth, its shape will indicate to which kind of tooth it 

 belonged. Its blood-vessels and nerves are numerous, being connected with 

 the general system by passing out through the minute orifice at the end of 

 the root. 



There is, however, another source from which the tooth derives life-, 

 namely, from its peridontium. Covering the roots of teeth is a delicate 

 membrane containing an abundance of blood-vessels and nerves. It is in- 

 timately connected with the gum; also with a corresponding membrane 

 covering the adjacent bone, as well as all bones in the body. For a more 

 familiar term we will call it the root membrane; its correct name is peridon- 

 tium, which signifies, "around a tooth." On bones, however, it is called 

 periosteum. From this r(3ot membrane the tooth derives enough life so that 

 if the pulp die from any cause the tooth will still be retained; which would 

 not be the case if all its nutriment came from the pulp, for in that case, 

 should the pulp die, the tooth would become a foreign substance, and Na- 

 ture would at once set her forces at work to remove it, as she would a thorn 

 or any other alien intruder. Thus we see that though the pulp is dead, 

 there is still life remaining in the tooth, owing to the nourishment it re- 

 ceives from this root membrane; otherwise the tooth would not remain in 

 its bony socket. It is from an inflammation of this root membrane (peri- 

 dontium) that the pain arises when you have a toothache from a tooth in 

 which the pulp has been devitalized; and I will now proceed to explain the 

 causes which excite this irritation. 



"When from any cause the pulp of a tooth "gives up the ghost," what 

 happens? The pulp, being dead, of course decomposes; and if allowed to 

 remain in the tooth, the gasses arising from this decomposition must find a 

 means of exit. If a cavity of decay exists, freely open (for pulps will die 

 sometimes when not exposed by decay, as I will explain hereafter), the 

 gases arising from the dead pulp will escape through the cavity, and no 

 trouble results. But should this cavity be closed, either by the impaction 



