Making a wet mount

A drop, a coverslip, and how to avoid bubbles and squashed animals.

The basic slide

• Put one drop of sample in the middle of a clean slide.
• Hold a coverslip at an angle, touch one edge to the drop, and lower it slowly so the water spreads without trapping air.
• Touch a piece of tissue to the edge to remove excess water if the coverslip floats around.

Larger animals

Water fleas, copepods and big rotifers get squashed under a flat coverslip. Raise it a little: put a tiny dab of petroleum jelly at each corner of the coverslip, or support it on fragments of a broken coverslip.

Keeping it alive

Under a warm lamp a drop dries out within minutes. Add a little water at the edge with a pipette. A ring of petroleum jelly around the coverslip keeps a slide alive much longer.