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1858.] the surface than they were wont, and all the animals had lost vigor.

Aëration was resorted to, which was performed by dipping up the water, and pouring it back in a thin stream from a height of several feet, continuing the operation for ten minutes. This was repeated four or five times during the day, and at night more charcoal was added. Some of the pieces were sunk to the bottom, and others were suspended at different depths in the water.

Two or three days passed in this way,—the putrescence kept in check by the means used, but not entirely overcome. Meantime, though none of the stock had died, there was less vitality than at first; especially each morning, after seven or eight hours unaided by aëration.

Tired of what seemed an ineffectual struggle, I determined to leave the Aquarium untouched for a day, and await the result. Accordingly, the charcoal was withdrawn and aëration discontinued. The milky cloud increased in density, and the whole mass of water became turbid. The fishes kept constantly near the surface, swam languidly, and snatched mouthfuls of atmospheric air. The Eel became bloodshot about the gills, and, writhing, gasped for breath. The Soldier-Crabs hung listlessly from their shells, and no longer went about in quest of food. Even the Actiniae shrunk to half their former size; and the Buccina, crawling above the water, ranged themselves in a row upon the dry glass. Disappointed, but not discouraged, I filled several shallow pans with pure seawater, clean sand, and fresh plants, and transferred to them my suffering and wellnigh exhausted animals. A day restored them to their normal condition, and now I was ready to begin my Aquarium anew. But to what purpose should I begin anew? Would there not be the same failure? What had been wrong?

At least two great faults were evident. First, in order to guard against the possibility of a leak, the bottom and posts of the tank had been covered with many coats of an alcoholic varnish. Now it was probable that time enough had not elapsed between the several applications for the thorough evaporation of the alcohol. Might not its gradual infusion in the water have caused the death of the animalcula in such numbers as to taint the whole by their decay?

The second fault was, strewing upon the surface of the sand a handful or two of white powdered quartz, which, from having been pulverized in an iron mortar, was so oxydized as to turn a deep yellow. This might have poisoned the animalcula.

The first fault seemed to me the chief, but I proceeded to remedy both. The whole contents of the tank being removed, it was thoroughly washed on the inside, exposed for several days to the sun and air, and then soaked for twelve hours in clean sea-water. This being thrown away, the stones, scalded and well-washed, were restored, and clean sand replaced the old.

Water was drawn from the dock at high tide; but it was less clear now, on the fourth of June, than that which had been got early in May. This surprised me not a little; for, as I stood upon the wharf and looked down into it just before sunset on the previous evening, I was struck with its beautiful limpidity. Curious to see if its aspect remained unaltered, I went to the same spot where I had stood the night before. The tide was at the same height, but twelve hours had made a marvellous change in the appearance of the water. Its sparkling clearness had given way to greenness and turbidity, and no object could be seen a foot below the surface. No storm had stirred its depths during the night,—why this change? Conjecture was of no practical utility, and I returned home satisfied that my fifteen gallons of water were as clear as any it was then in my power to obtain. Covering the tub from the dust, I left it to settle until sunset. Then the ever-useful siphon drew off two thirds of it tolerably clear, leaving a thick green