©David B. Fankhauser, Ph.D.,
Professor of Biology and Chemistry
             University of Cincinnati Clermont College, 
Batavia OH 45103
10 July 1989, rvsd 2 July 1993, 10 July 1995, 3 July '97, 28 June 01

This page has been accessed Counter times since 19 July 2002. 

    Wet mount preparations are especially valuable for demonstrating motility in microorganisms. Fresh cultures must be used for maximum motility. No stain is employed since most stains kill the organisms (except vital stains). Therefore focusing is more difficult (see step 4 for suggestions). If your microscope has dark field capabilities, this is ideal illumination for this purpose (use the "D" position on the sub-stage condenser dial).   Alternatively, a small disc of dark paper may be placed in the center of teh condensor to approximate dark field optics.

Motility needs to be distinguished from Brownian motion which is due to molecular bombardment.  Brownian motion occurs in all microscopic bodies suspended in water and appears as a random shimmying-shaking. Motility will be in the form of cork-screw spiraling, movement in a given direction, or tumbling in place.

Wet mount preparations are also useful for giving clear images of fresh specimens under the microscope. Features which may be particulate, such as spores of fungi and ferns, and pollen grains may be best observed using this technique.

  1. Place a drop of dH2 O in the center of a slide. [For greater volume of sample, or for hanging drop preparations, use a depression slide for this preparation.]
  2. Sterilely transfer a tiny portion of a single colony to the drop with a loop and suspend (be certain to allow the loop to cool before picking up specimen). Alternatively, place a drop of liquid culture in the center of the slide. For solid specimens or dry spores, transfer a small portion of the specimen with a scalpel.
  3. Lower a clean cover slip over the drop.
  4. Focus on the suspension: Examine under low power, locate a small air bubble on which to focus, since the unstained bacteria will be difficult to see. Work your way up to higher magnification, carefully focusing at each step. View at 1000x oil immersion, again using the bubble to locate the focal point. At 1000x, maximize the depth of field by narrowing the iris diaphragm, and adjust the focus so that most bacteria are in focus. (Because of the depth of the water, not all bacteria will be in focus at a given point.)
  5. Illustrate the types of motility you observe.
  6. Clean up the slide with alcohol first, followed by soap and water. Discard the cover slip.