and Observations on the component Parts of Membrane. 359 



of the true nacre or mother of pearl, this substance was found 

 not only to constitute a large part of the shell, but even to be 

 more dense, so as no longer to appear gelatinous ; and, in addition 

 to these, strong and visible marks of organization were stamped 

 on every part, and a perfect membranaceous body remained, 

 composed of fibres arranged parallel to each other, according to 

 the configuration of the shells. 



From these facts, proved by the examination of only a very 

 few (comparatively speaking) of the known shells, it appears 

 that the hardening principle, or carbonate of lime, together 

 with a substance varying from a very attenuated gluten to a 

 tough jelly, and from this to a perfectly organized membrane, 

 concur to form the matter of shell ; and, from the result of the 

 experiments, and from all circumstances, there is every reason 

 to believe, that the substance with which, or upon which, the 

 carbonate of lime is mixed or deposited, is of a similar nature, 

 and differs only in relative quantity and density, arising from 

 progressive changes (peculiar to the various species of shells) 

 produced by certain degrees of natural inspissation, and by an. 

 organization more or less perfect. 



The experiments made on teeth, and on the bones of various 

 animals, elucidated and confirmed the observations made on the 

 nature of shell ; for, 



1st. The enamel of teeth (in relation to the other bony sub- 

 stances) was proved to be as the porcellaneous shells are to 

 those formed of mother of pearl ; the cementing substance of 

 the enamel being a gluten, in the same state, and apparently of 

 a similar nature, with that of the porcellaneous shells. And, 



2dly. In certain bones, particularly those of fish, (such as 

 some of the bones of the skate, ) the substance which remained 



mdccc. 3 A 



