We will start off with one of the small tin frame tanks sold in New York so cheap, or a candy jar, or a small-sized wash-tub—any vessel that will hold water, and is not of iron, tin, or copper, either of which will poison the water.

After washing out the tank carefully, and filling it with clear sea-water, we will place in it twelve silver-shrimps (bait shrimps). At the end of two days they are dead, and you ask why did they die when they had so much water to live in. They died of suffocation, after they had breathed all the air contained in the water. We will take out the dead shrimps, and in the same water place a good handful of ulva (sea-lettuce, sea-salad), one of the most common of all marine plants, and place the aquarium in a strong and direct sunlight, by this means exciting the ulva to work, or, as it is termed, aerify the water. In less than an hour’s time a froth will be seen forming on the surface of the water, and adhering to the sides of the aquarium. Now observe the ulva closely, and from its edges and surface very fine threads of silvery bubbles are pouring out and ascending to the surface. In an hour’s time the water will be thoroughly charged with air. We will again place twelve more shrimps in the aquarium. This time they will live, and we will have established a true aquarium—an aquarium based on the self-sustaining principles of nature, wherein it will not be necessary to change the water.