Cn Shell and Bojie. 3Jj9 



3clly, The animal coal thus formed Is of different incioera- 

 tion. 



4thly, They retain much t)f their original figure, but tlje 

 membranaceous fliells are fubjedl to exfohate *. 



5thly, Thefc fubftances, (pearl, mother-of-pearl, tooth, aisd 

 bone,) when inimerfed in certain acids, part with their liar- 

 dening or offifving fubftances, and then remain in the ilafcc 

 of membrane or cartilage. 



•6thly, When previoufly burned, and afterwards diffolveJ 

 in acids, a quantity of animal coal is feparated, according ta 

 the proportion of the gelatinous, membranaceous, or carti- 

 laginous fubllance, and according to the duration of the red 

 heat. 



And laftly, the acid folutlons of thefe fubftances, by proper 

 precipitants, afford carbonai of lime in the one cafe, and phof- 

 phat of lime principally in the other, in a proportion relative 

 to the membrane or cartilage with which, or on which, the 

 one or the other had been mixed or depofited. 



As porcellaneous fliell principally differs from mother-of- 

 pearl only by a relative proportion between the carbonat of 

 lime an-d the gluten, or membrane; in like manner the ena- 

 mel appears only to be different from tooth or boaie by being 

 deftitute of cartilage, and by being principally formed of phof- 

 phat 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 iame tiuie the like colour is not communicated to the 

 enamel; for it appears probal)le that the cartilages, which 

 form the original ftrufture of the teeth and bones, become 

 the channel by which Lhe tingeing principle is communicated 

 and diffuled. 



Thefe comparative cKpcrlments 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 aiid 

 bone ; and if a (liell ftiould be found compoied of mother- 

 /jf-pcarl, coated by the porcellaneous fubftance, it will rc~ 

 femble a tooth coated by the enamel, with the difference oj 

 carbonat being fubftituted for phofphat of lime. 



"■ Till.-, is u natural confc<iucnce arifing from tluir lua£\ure. 



^ Some 



