VOL. XC.] PHILOSOPHICAL TRANSACTIONS. 7*21 



such as cypreae, &c. this substance was proved to be much less in quantity than 

 in those which were afterwards mentioned ; and though of a quality which, like a 

 cement or gluten, served to bind and connect the particles of carbonate Of lime 

 firmly together, so small was the degree of natural inspissation, and so little ad- 

 vanced was the degree of organization, that when the carbonate of lime was dis- 

 solved, even by very feeble acids, little or no vestige of jelly, membrane, or 

 cartilage, could be perceived ; nor indeed could any be detected, but by the small 

 portion of animal coal which was formed, when these shells had been exposed for 

 a short time to a low red heat. 



But, proceeding from shells of this description to others tending to the nature 

 of nacre or mother of pearl, such as some of the patellae, a substance was left 

 untouched by the acids, which had the appearance of a yellowish transparent 

 jelly*. So that the substance which served merely as a gluten in the porcellaneous 

 shells, was not only more abundant in these patellae, but, being more inspissated, 

 was become immediately visible and palpable. In the common oyster, these qua-> 

 lities were more strongly marked ; and in the river muscle, and in the shells com- 

 posed 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 organi- 

 zation 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 prin- 

 ciple, or carbonate of lime, together with a substance varying from a very atte- 

 nuated 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 on 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, eluci- 

 dated and confirmed the observations made on the nature of shell ; for, 1st. The 

 enamel of teeth, in relation to the other bony substances, 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 after the solution of the phosphate of lime, was of a gelatinous 

 consistency, and exhibited but very imperfect traces of organization; by the others 



* The term jelly is here employed only to denote the degree of consistency of this substance, which 

 m its nature is very different from the varieties of animal jelly called gelatin. — Orig. 

 VOL. XVIII. 4 Z 



