NATURAL WATER-PURIFIERS.
Mr. Warrington kept for a whole year twelve gallons of water in a state of admirably balanced purity by the following beautiful action:
In the tank, or aquarium, were two gold fish, six water-snails, and two or three specimens of that elegant aquatic plant Valisperia sporalis, which, before the introduction of the water-snails, by its decayed leaves caused a growth of slimy mucus, and made the water turbid and likely to destroy both plants and fish. But under the improved arrangement the slime, as fast as it was engendered, was consumed by the water-snails, which reproduced it in the shape of young snails, which furnished a succulent food to the fish. Meanwhile the Valisperia plants absorbed the carbonic acid exhaled by the respiration of their companions, fixing the carbon in their growing stems and luxuriant blossoms, and refreshing the oxygen (during sunshine in visible little streams) for the respiration of the snails and the fish. The spectacle of perfect equilibrium thus simply maintained between animal, vegetable, and inorganic activity, was strikingly beautiful; and such means might possibly hereafter be made available on a large scale for keeping tanked water sweet and clean.—Quarterly Review, 1850.