558 PHILOSOPHICAL TRANSACTIONS. [ANNO 1790. 



was received in lime-water, by which it was speedily absorbed, and a proportionate 

 quantity of carbonate of lime was obtained. Though it appears, that the prin- 

 cipal effects during ossification are produced by phosphate of lime, yet we here see, 

 that not only sulphate, but also some carbonate of lime, enters the composition 

 of bones; and it is not a little curious to observe, that as the carbonate of lime 

 exceeds in quantity the phosphate of lime in crustaceous marine animals, and in 

 the egg shells of birds, so in bones it is vice versa. It is possible, when many 

 accurate comparative analyses of bones have been made, that some may be found 

 composed only of phosphate of lime; and that thus, shells containing only car- 

 bonate of lime, and bones containing only phosphate of lime, will form the 2 

 extremities of the chain. 



I shall now make a few remarks on the enamel of teeth. When a tooth coated 

 with enamel is immersed in diluted nitric or muriatic acid, a feeble effervescence 

 takes place, and the enamel is completely dissolved; so also is the bony part, but 

 the cartilage of that part is left, retaining the shape of the tooth. Or, if a tooth 

 in which the enamel is intermixed with the bony substance, is plunged in the acid, 

 the enamel and ihe bony part are dissolved, in the same manner as before; that is 

 to say, the enamel is completely taken up by the acid, while the tooth, like other 

 bones, remains in a pulpy or cartilaginous state, having been deprived of the ossi- 

 fying substance. Consequently, those parts which were coated or penetrated by 

 lines of enamel, are diminished in proportion to the thickness of the enamel 

 which has been thus dissolved; but little or no diminution is observed in the tooth.* 

 Mr. Hunter has noticed this; and, speaking of enamel, says, " when soaked in a 

 gentle acid, there appears no gristly or fleshy part with which the earthy part had 

 been incorporated. "-j~ Now, when the difference which has been lately stated, 

 between porcellaneous shell and mother of pearl, is considered, it is not possible 

 to avoid the comparing of these to enamel and tooth. When porcellaneous shell, 

 whole or in powder, is exposed to the action of acids, it is completely dissolved, 

 without leaving any residuum. 



Enamel is also completely dissolved, in the like manner. Porcellaneous shell 

 and enamel, when burnt, emit little or no smoke, nor scarcely any smell of burnt 

 horn, or cartilage. Their figure, after having been exposed to fire, is not mate- 

 rially changed, except by cracking in some parts: their external gloss partly 

 remains, and their colour at most becomes gray, very different from what happens 

 to mother of pearl, or tooth. In their fracture they have a fibrous texture; and 

 in short the only essential difference between them appears to be, that porcella- 

 neous shell consists of carbonate of lime, and enamel of phosphate of lime, each 

 being cemented by a small portion of gluten. 



* I have also observed, that when raspings of enamel are put into diluted nitric or muriatic acid, they 

 are dissolved without any apparent residuum j but when raspings of tooth or bone are thus treated, 



portions of membrane or cartilage remain, corresponding to the size of the raspings. + Nat. Hist 



of the Human Teeth, p. 35. — Orig. 



