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Aim for one cell thickness to a few cells. For a compound microscope, the sample needs to be very thin and as flat as possible. For a low power microscope, such as a dissection scope, the size of the object isn't critical, since its surface will be examined.

Wladimir Bulgar / Science Photo Library / Getty Imagesĭry mount slides can consist of a sample placed on a slide or else a sample covered with a coverslip. Press gently on the coverslip to remove air bubbles and seal the slide. One way to retard evaporation is to use a toothpick to coat the edges of the coverslip with a thin rim of petroleum jelly before dropping the coverslip over the sample. Adding a couple of strands of cotton from tissue or swab or else adding tiny bits of broken coverslip will add space and "corral" the organisms.Īs the liquid evaporates from the edges of the slide, living samples may die. Some organisms (like Paramecium) need more space than what forms between a coverslip and a flat slide. One solution is to add a drop of a commercial preparation called "Proto Slow." A drop of the solution is added to the liquid drop before applying the coverslip. Some living organisms move too quickly to be observed in a wet mount. If the liquid drop is too large, the coverslip will float on the slide, making it hard to focus on the subject using a microscope. Most problems with air bubbles come from not applying the coverslip at an angle, not touching the liquid drop, or from using a viscous (thick) liquid.