224 On making Freshrwater MoUuseee 



rme. They did not appear at first much affected, but in eiglit 

 days they were all dead. 



As we do not linow positively, as yet, if the shells which are 

 found in certain beds of saccaroidal limestone of transition, and 

 in certain compact secondary limestones, have lived in the liquid 

 itself, or have formed those soils themselves, or, fmallv, have been 

 brought tliere accidentally : as, on the other liand, it is verv pio- 

 bable that these kinds of chemical deposits have taken phue 

 C-ily by the intermedium of a liquid, the solvent faculty of which 

 was owing to an excess of carbonic acid, — M. Bcudant tried the 

 action of water charjied with this acid on the moUuscas. With tliis 

 view he employed Seltzer water. — The animals [)!uuged into tl it- 

 water were qmekly suffocated. 



Water charged with other mineral acids in very small quan- 

 tities produced nearly the same effect. 



Water charged with 0-()2 of sulphate of iron aff"ccted in the 

 srime w^ay the molhiscT plunged into it ; — in a few seconds all tb.e 

 species submitted to this test, whether univalves or bivalves, 

 died. 



V/ater saturated with sulphuretted hydrogen, and afterwards 

 diluted with its weight of clear water, produced much slower ef- 

 fects : several mollusca; even made various movements in it ; but 

 in a few days they died, the one after the other. 



After these preliminary trials, it was natural to examine if it 

 was not possible gradually to habituate the molluscae of fresh 

 water to live in the waters into which they had been previously 

 plunged so suddenly. In spring 1809, therefore, M. Beudant 

 collected a great number of fresh-water mollu^cie in the environs 

 of Paris: he separated the species, and divided the number of 

 individuals of each of them into two equal portions, putting each 

 itito a vessel by itself: lie thus formed two series of the same 

 species, each including the same number of individuals : he pre- 

 served one as a point of comparison in Seine water, and upon 

 the other he attempted tlie gradual transition which he had in 

 view. 



M. Beudant had at first employed for several days water con- 

 taining only one grain of salt per pound, i. e. about 0-0001 1 : lie 

 afterwards successively increased ihe quantity of salt ; first hv 

 adding a grain every two days, and then every day; and latterly, 

 three grains a day. The experiment lasted si\ months ; at the 

 end of which time the liquid employed contained 0'04 of its 

 weight of salt, comi)rising about 005 of muriate of lime. 



By proceeding in this way, most of our fresh-water molluscac 

 were completely habituated to live in salt water, in which they 

 seemed to be perfectly at case. But in order to make the e.\- 

 perimen't precise, and to draw certain consequences from it, 



M. Beu- 



