38 M. Beudant on Freshwater 



food, probably not very proper for them ; he was sensible 

 that these inconveniencies were the cause of a mortality 

 the results of which ought to be subtracted from the general 

 total, in order to become exactly acquainted with the num- 

 ber of those which perished from the change in the nature 

 of the water. 



In consequence, he always took care to divide the mo- 

 luscx intended for his experiments, into series, identical as 

 to the species and number of the individuals. One of 

 these series was kept in water proper for it, the other was 

 placed in a different water ; thus when he experimented on 

 fresh-water moluscae, he kept half of these animals in fresh- 

 water, frequently renewed, and put the other half into water 

 made salter by degrees. He kept an account of the mor- 

 tality in both cases, and he could consequently judge from 

 the different results, of the number of individuals that per- 

 ished from the saltness of the water. An inverse precaution 

 was taken when he experimented on marine moluscae. 



The following are the principal results obtained from his 

 experiments :, 



1. Fresh-water moluscae perish immediately when 

 plunged suddenly into water as salt as our seas. 



Marine moluscae do the same when suddenly plunged into 

 fresh-water. 



2. Many fresh-water moluscae, could, in a very short 

 time, be made by degrees to live in water which was gra- 

 dually salted to the ordinary saltness of the sea.* 



Many marine moluscae could also, by gradually diminish- 

 ing the saltness of the water, be accustomed to live in frcsh- 

 Tvater.t 



* Among the fresh-water univalves, there are species, of which, in five 

 months and a half, 57 individuals only perished out of 100 with salt 

 water; and 54 out of 100 died in the same time kept in fresh-water; (alj 

 the lymnese, the planorbes, the physa fontinalis, the ancylla fluviatilis, 

 cyclostoma obtusa, paludine porte-plumet). The diiference therefore 

 was nearly nothing ; it was considerable with other univalves, and the 

 bivalves were not able to support the change in water as salt as tlie sea, 

 (see article 3.) 



+ Only 36 to 37 individuals in 100 perished in five months, whilst out 



