534 Experiments and Obfervations on Shell and Bone. 



5tKly. Thefe fubftances (pearl, mother of pearl, tooth and bone) when Immerfed irt 

 certain acids, part with their hardening or ofilfying fubftances, and then remain in the 

 ftate of membrane or cartilage. 



. 6thly. When previoufly burned, and afterwards diflblved in adds, a quantity of animal 

 coal is feparated, according to the proportion of the gelatinous, membranaceous, or carti- 

 laginous fubftance, and according to the duration of the red heat. 



And laftly, the acid folutions of thefe fubftances by proper precipitants, afford carbo- 

 nate of lime in the one cafe, and phofphate of lime principally in the other, in a propor- 

 tion relative to the membrane or cartilage with which, or on which, the one or the other 

 had been mixed or depofited. 



As porcellaneous (hell principally differs from mother of pearl, only by a relative pro- 

 portion between the carbonate of lime and the gluten, or membrane ; in like manner the 

 enamel appears only to be different from tooth or bone, by being deftitute of cartilage, 

 and by being principally formed of phofphate of lime cemented by gluten. 



The difference in the latter cafe feems to explain, why the bones and teeth of animals fed 

 on madder, become red, when at the fame time the like colour is not communicated to 

 the enamel ; for it appears probable that the cartilages, which form the original ftru£ture 

 of the teeth and bones, become the channel by which the tinging principle is communi- 

 cated and diffufed. 



Thefe comparative experiments prove, that there is a great approximation In the nature 

 of porcellaneous fliell and the enamel of teeth, and alfo in that of mother of pearl and 

 bone ; and if a ftiell fhould be found compofed of mother of pearl, coated by the porcella- 

 neous fuljftance, it will refemble a tooth coated by the enamel, with the difference of car- 

 bonate being fubftituted for phofphate of lime. 



Some experiments on cartilaginous fubftances (which I intended to have Inferted In this 

 paper, but which I am prevented from doing, as they are not as yet fufficiently advanced) 

 have in a great meafure convinced me, that membranes and cartilages (whether deftined to 

 become bones by a natural procefs, as in young animals, or whether they become fuch by 

 morbid offification, as often happens in thofe which are aged) do not contain the offifying 

 fubftance, or phofphate of lime, as a conftltuent principle. I mean by this, that I be- 

 lieve the portion of phofphate of lime found in cartilaginous and horny fubftances, to be 

 fimply mixed as an extraneous matter •, and that when it is abfent, membrane, cartilage, 

 and horn are moft perfeiSt and complete. 



The frequent prefence of phofphate of lime in cartilaginous fubftances, is not a proof of 

 its being one of their conftltuent principles, but only that it has become depofited and 

 mixed with them, in proportion to the tendency they may have to form modifications of 

 bone -, or according to their vicinity with fuch membranes or cartilages, as are liable to 

 fuch a change. If horns are examined, few I believe will be found to contain phofphate 

 of lime in fuch a proportion, as to be confidered an effential ingredient. I would not be 

 underftood to fpeak here of fuch as ftag, or buck horn, for that has every chemical charader 



9f 



