Slowing down fast swimmers

Ciliates and rotifers rarely sit still. A few ways to make them.

• Let the slide stand for a few minutes. As water evaporates at the edges, the space under the coverslip gets thinner and swimmers slow down.
• Add a few teased cotton fibres or plant bits to the drop: organisms get caught between them and stay in view.
• A drop of methyl cellulose solution (sold for microscopy) makes the water thicker. Mix a small amount at the edge of the drop.
• Look for animals that are feeding. A rotifer anchored on debris or a ciliate grazing on a clump of bacteria stays put for a long time.