POISONS. 239 



to the bottom of the glass and remain for ever 

 motionless — killed instantaneously by the mere 

 difference of the density of the two media." * As 

 regards the appeaiance presented by Sarsia Avhcn 

 subjected to " this little experiment," the account 

 just quoted is partly correct; but Professor Agassiz 

 must have been over-hasty in concluding that, be- 

 cause the aTiimals seemed to be thus " killed instan- 

 taneously," such was really the case. Nothing, 

 indeed, could be more natural than his conclusion ; 

 for not only is the contrast between the active 

 swimming motions of the Sarsia in the sea-water 

 and their cessation of all motion in the fresh water 

 very suggestive of instantaneous death ; but a shoi t 

 time after immersion in the latter their contractile 

 tissues, as Professor Agassiz observed, become 

 opalescent and whitish. Nevertheless, if he had 

 taken the precaution of again transferring the 

 Sarsia to sea- water, he would have found that the 

 previous exposure to fresh water had not had the 

 effect which he ascribes to it. After a variable 

 time his specimens would have resumed their swim- 

 ming motions ; and although these might have had 

 their vigour somewhat impaired, the animals would 

 have continued to live for an indefinite time — in 

 fact, quite as long as other specimens which had 

 never been removed from the sea-water. Even 

 after fivQ minutes' immersion in fresh water, 

 Sarsige will revive feebly on being again restored 

 to sea- water, although it may be two or three 

 hours before they do so ; they may then, how- 

 * *' Mem. American Acad. Arts and Sciences," 1800, p. 229. 



