and Observations on the component Parts of Membrane. 373 



substances many days in boiling distilled water, (after having 

 reduced them to a coarse powder, that they might present a 

 larger surface,) but I never could, by any test, discover the 

 slightest vestige of gelatin. The horns therefore which were 

 first mentioned, are very different from the composition of stag's 

 horn, and yield gradually, and with great difficulty, only a 

 small quantity of gelatin. 



Horny scale was next examined ; but I shall first here request 

 permission to make a digression in respect to the scales of fish, 

 which I had not examined when my paper on shell and bone 

 was read. 



As the scales of fish, when viewed by a microscope, and 

 according to the observations of Mr. Leeuwenhoek, appear 

 to be formed of different membranaceous laminae, and as they 

 exhibit the colour and lustre of mother of pearl, it might be 

 expected, that they should prove to be of a similar nature with 

 the substance of stratified shells, or, in other terms, that they 

 should consist of membrane and carbonate of lime. 



But, when scales perfectly clean, and separated from the 

 skin of different fish, (such as the salmon and carp,) had been 

 immersed during four or five hours in diluted nitric acid, till 

 they became transparent, and perfectly membranaceous; the 

 acid liquor, being then saturated with pure ammoniac, afforded 

 a copious precipitate, which was proved to be phosphate of 

 lime. 



The spiculas of the shark's skin, formerly mentioned, were 

 found to be of a similar composition ; and we may therefore re- 

 gard the spiculas and scales of fish as true bony substances, in 

 which the membranaceous part is more predominant than in 

 common bone. 



