Exercise #5: Preparing a Wet Mount
You will be preparing your own slides frequently this semester... This is especially important for viewing fresh cells, tissues, or living organisms. When viewed beneath the microscope, water or other liquid should surround living material. For these observations a wet mount must be made. To prepare a wet mount (shown in the figure to the right), simply place the specimen to be viewed on a clean microscope slide. Place a drop of water onto the specimen while the slide sits on a flat surface. Next, place the edge of a clean coverslip at one edge of the drop and slowly lower the coverslip onto the drop at an angle (in the same manner as lowering the lid of a cedar chest or the hood of a car). Lowering the coverslip at an angle assures that no air bubbles will be trapped beneath the coverslip that may obscure view of the specimen. Air bubbles can be distinguished from other objects by their large, dark, circular outline. If many bubbles are beneath the coverslip, rinse your slide and coverslip and begin again. If water leaks from beneath the coverslip onto the stage, gently wipe the excess water with a paper towel. Coverslips are extremely sharp and must be handled with care to avoid cut fingers or flying broken glass.
Making your crossing threads slide
Keep in mind that you will be making a wet mount in order to have a crossing threads slide. There is a handy advantage to doing this-- you know what threads should look like. You see, often, when students make their first wet mounts, they end up with a lot of air bubbles in their slides. Even if they know that there are air bubbles, they still end up forgetting about them as they start to view their slides. Air bubbles look kind of interesting, so when the student then goes to figure out what they are looking at, they mistake air bubbles for cells.
But not you! That's because when you are done looking at the crossing threads, you can look around your slide and hunt for air bubbles. View some air bubbles to know what they look like. Once you've seen them, you won't be able to mistake air bubbles for cells in the next lab. Congratulations!
Study of Pond Water (optional, see note at bottom)
The purpose of this exercise is to allow the student to practice some of the techniques learned in the above section to see something biological. Only do this after you have completed the other lab exercises, because this is harder to see. Using an eyedropper, add a drop of pond water to a clean slide and place a coverslip on the drop using the wet mount technique outlined above (you do not need any extra regular water to make the wet mount-- the pond water alone is enough).
What to Look For?
The careful observer will find an abundance and diversity of life in a single drop of pond water. Slowly scan the slide using scanning magnification. Your sample will include not only living organisms, but also a variety of non-living objects such as plant debris, sand grains, and mud. Practice following moving organisms using your mechanical stage. Once a particular organism is in focus under scanning magnification, increase your magnification by clicking the low and then high-powered objectives into place. Practice sketching some of the organisms that you view on scrap paper. Most importantly, take your time when making observations!
I will ask about your pond water observations at the end of this lab. The only reason I have made this optional is because I don't want anyone running outside to a frozen pond and putting themselves in danger! If you can stop by a pet store or if you can find an accessible pond, please be sure to view some pond water!
© 2006 STCC Foundation Press, content by Dawn A. Tamarkin, Ph.D.
Last changed: January 21, 2007