EKpiriments atuf Obfervations on Shell and Bone, 531 



I fliall now make a few remarks 00 the enamel of teeth. 



When a tooth, coated with enamel, is immerfed in diluted nitric or muriatic acid, a 

 feeble efFervefcence takes place, and the enamel is completely diflblved ; fo alfo is the 

 bony pait 5 but the cartilage of that part is left, retaining the fliape of the tooth. Or if 

 a tooth, in which the enamel is intermixed with the bony fubftancc, is plunged in the acid, 

 the enamel and the bony part are diflblved in the fame manner as before ; that is to fay, the 

 enamel is completely taken up by the acid, while the tooth, like other bones, remains in a 

 pulpy or cartilaginous ftate, having been deprived of the oflifying fubftance. Confequently, 

 thofe parts which were coated or penetrated by lines of enamel are diminilhed in propor- 

 tion to the thicknefs of the enamel which has been thus diflblved ; but little or no diminu- 

 tion is obferved in the tooth*. 



Mr. Hunter has noticed this ; and fpeaking of enamel fays, " when foaked In a gentle 

 " acid, there appears no gf ifly or flefliy part with which the earthy part had been in- 

 •* corporatedt." 



Now when the difference, which has been lately ftated between porcellaneous ftiell and 

 mother of pearl, is confidered, it is not poffible to avoid the comparing of thefe to enamel 

 and tooth. 



When porcellaneous fliell, whole, or in powder, is expofed to the a£tion of acids, it is 

 compleatly diflblved without leaving anyrefiduum. 



Enamel is alfo completely diflblved in the like manner. 



Porcellaneous fliell and enamel when burned, emit little or no fmoke, nor fcarcely any 

 fmell of burned horn or cartilage. 



Their figure, after having been expofed to fire, is not materially changed, except by 

 cracking in fome parts ; their external glofs partly remains, and their colour at mod be- 

 comes grey, very difl^erent from what happens to mother of pearl, or tooth. In their 

 fradlure they have a fibrous texture ; and in fliort, the only eflential difference between 

 them appears to be, that porcellaneous fliell confifts of carbonate of lime, and enamel of 

 phofphate of lime, each being cemented by a fmall portion of gluten. 



In like manner, if the effeds produced by fire and acid menftrua, on fliells compofed of 

 mother of pearl, and on the fubfliance of teeth and bone, are compared, a great fimilarity 

 will be found ; for when expofed to a red heat, 



ift. They fmoke much, and emit a fmell of burned cartilage or horn. 



andly. They become of a dark grey, or black colour. 



3dly. The animal coal thus formed is of dlfi^rent incineration'. 



4thly. They retain much of their original figure 5 but the membranaceous ftiells are fub- 

 je£l: to exfoliate J. 



• I have alfo obferved, that when rafpings of enamel are put into diluted nitric, or muriatic acid, they 

 are diffolved without any apparent refiduum ; but when rafpings of tooth or bone are thus treated, por- 

 tions of membrane or cartilage remain conefponding to the fize of the rafpings. 



•)• Natural Hiftory of the Human Teeth, p. 35. 



J This is a natural confequencc aiifing from their fttuilure. 



5thly.. 



