Public ledger. [volume] (Memphis, Tenn.) 1865-1893, 1877-05-17
FRESH WATER FISH.
why They CannOt live in salt
Water.
Scientific Americana

Water.
Scientific Americana
It is well known that fresh water fish
cannot live in salt water, and vice versa;
and it has been supposed that the eason
existed in some poisonous effect which
the inappropriate water exerted. NJ.
Paul Bert has recently been investigst.
ing this sSbject, and his conclusion is
that the death of the c~teature is not due
to any toxic action, but is simply a phe-
nomenon of osmosis or transmission of
fluids through the membranes. In order
to prove this. it is only necessary TO
weigh the animal before and after the
experiment. A frog, for example, plusg-
ed in sea water loses one.third its weight.
II only the foot Of the frog be introduced,
the blood globules can be seen to leave
the vessels and distribute themselves un-
der the skin. II an animal be taken, the
skin Of which is not entirely osmotic, the
same phenomena occur in the bronchial
system.
There are certain fish, however, which
exist sometimes in salt, sometimes 10
fresh, water, changing their habitation
in different periods Of life or of the year.
II therefore, in view of the above, be.
comes interesting to see how N. Bert APP
plies his discovery to such apparent ex-
ceptions to the general rule. A fresh
water salmon, for instance, plunged ab.
ruptly in sea water. resists the effects
longer than other fresh water fishes; but
be dies within FIVE or six hours. This
shows, according to N. Bert, that the fish
never proceed suddenly from fresh to
salt water, but enter braekish water,
where the tide GIBBS and flows, and live
there a sufficient time to habituste them
selves to the change. This accounts for
the frequent discovery Of large numbers
Of such migratory fish in the vicinity Of
the mouths Of the rivers which they as.
cend.
A fresh water eel, plunged in salt wa
ter, does not seem Il be affected. But in
investigating the peculiarities " this spe-
cies, NJ. Bert was led into a wrong con.
c%lusion, which may be cited to show how
easy it is, often by pure accident, TO
reach an erroneous determination in la.
boratory experimenting. After having
himself placed several fresh water cells in
salt water, be found, as already stated,
that they remained alive and unharmed.
Wishing to continue the experiments, be
directed his assistant to introduce the
fish, aud report results. To his surprise
the cells then persistently died after a
three or four hours %sojourn 10 salt water,
and long search failed 10 discover the
reason why it was that when NJ. Bert
placed them in the tanks they lived.
while when the assistant did so they per
ished. Finally, NJ. Bert found that biz
assistant, doubtless on account of the
slipperiness Of the cells, lifted them with
a piece OF cloth in his hand. The cloth
rubbed of a little Of the natural slime o.
the animal, which projected it from the
salt water. 0smosis then occurred il
the denqded portion, and the eel eVentu
ally died.
The convers experiment, Of inserting
sea fish in fresh water, produced analo
gous results. The gills we're the seat o
alterations, the same as those noted Il
= fresh water fish placed in salt water. N
5 Bert also observed that the life Of the SCI
fish could be prolonged by adding salt I,
a the fresh water, thus adding further con
: hrmation to his theory.