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 appearance presented by Sarsia when 
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 animals 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 short 
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 five minutes’ immersion in fresh water, 
Sarsize 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,” 1850, p. 229. 
