10 
FRESH-WATER AQUARIUM. 
ments with the Corallina officinalis, Starfish, Confervas, and some small 
plants of the JJlva latissima, and found that they flourished for eight 
weeks without being disturbed; this led him to try some fresli-water 
fishes and larvae, and they succeeded even better than the salt-water 
specimens. Since then Gosse, Hibberd, Warington and others of Eng¬ 
land, and the late Mr. Cotting, of Boston, have done much towards 
forwarding the interests of the aquarium. The whole secret of the 
success of the aquarium lies in the exactness with which we imitate 
nature in arranging and disposing our collections ; but let us understand 
first of all what is meant by the term. An aquarium is a collection of 
water plants and animals, so arranged in suitable ratio that it shall be 
perfectly self-supporting. We do not expect, then, that the water will 
have to be changed until after long periods, if at all; the plants and 
animals should flourish as well as if in their native locality. 
How then is this balance of forces to be attained? This leads us to 
examine the philosophy of the aquarium, which is simply this: The 
element in water on which the fishes live by breathing is free oxygen, 
which, as the water is fanned through the gills or lungs of the fish, comes 
in contact with the walls of its vessels, and arterializes the blood; all 
water contains a certain amount of this oxygen, sufficient to keep a fish 
alive for a short time, but if no means are taken to create a fresh supply, 
it will become exhausted sooner or later, and an escape of carbonic acid 
will render the water poisonous to the fish. In plants, on the other hand, 
we have an agent taking up the carbonic acid in the water, and resolving 
it into carbon and oxygen, the former of which it converts into its sub¬ 
stance, while it expels the latter from every part of its tissue, especially 
from the leaves in the form of minute bubbles, plainly seen in healthy 
plants, and so often compared to drops of quicksilver in appearance. It 
is true that plants absorb oxygen also as fishes do, but they give out so 
much more than they absorb, that this is of slight account. 
Another oxygen-producing agent, as was shown by Liebig, is to be 
found in the almost microscopic forms of animal life which abound in 
water which has stood for sometime exposed to the air. These animal- 
culse seem to form another link in the chain which binds together all kinds 
of animal life of higher or low T er order, however apparently diverse they 
may be. This extra supply of oxygen adds greatly to the support of the 
aquarium, and is no doubt the reason why a large number of fishes can be 
supported with a seemingly small proportion of plants. It would indeed 
be an interesting experiment to try, were we to place a small fish in a 
