Studying protozoa is a hobby that requires a few pieces of equipment, most expensive of which is a microscope. However, if you have access to one in school or university, the rest of the gear is fairly straightforward.
Where to find protists
Good places to look are continuously wet:
- Ponds, fish pools and fountains
- Drains with standing or running water
- Marshy areas
Try sampling from different parts of the same body of water: skim from the surface, from the middle, and scrape up some residue, sediment, or biofilm from the bottom and sides. Only a small quantity (about 50 mL) is necessary to keep you occupied at the microscope for a long time. Having a second look at a sample some days after collecting may also yield different organisms.
Filtering with a plankton net or some fine filter can concentrate planktonic organisms from the water, where otherwise they may be too dilute to find.
Be a safe and responsible collector:
- Take only a small amount of water and/or scum. Don’t uproot plants, kill fish, or damage the water body that you’re sampling from.
- Don’t do anything unsafe, like climbing into storm drains or canals. It’s not worth the risk of injury or death. There are more accessible places to find the same organisms.
- Don’t trespass or violate others’ property.
Using a microscope
Even a cheap microscope can reveal plenty of details about the microscopic world. Here I explain what can be done with a basic student’s microscope.
To be able to see microscopic details, magnification is insufficient, one also needs adequate contrast. Features which absorb light, e.g. opaque or highly colored, can be imaged with bright field microscopy, the default mode of imaging. However transparent features, such as most cells, remain invisible.
One possible way of improving contrast is to fix cells (e.g. with Lugol’s iodine, a mixture of potassium iodide solution and elemental iodine), and then stain them with a staining agent like methylene blue.
For live material, methods such as phase contrast and differential interference contrast have been developed, which use optical principles to reveal transparent objects such as cells by exploiting the difference in refractive index between cytoplasm and the surrounding water. However these usually require much more expensive equipment.
For a basic student’s light microscope, an easy way to improve contrast is to close down the condenser aperture, which is what was used for the pictures on this website. This also darkens the image, but should not be used as a means of adjusting brightness (use the light source controller instead). This increase in contrast comes at the expense of resolution (ability to distinguish closely separated points), but an adequate compromise can usually be found.
Decent images can be obtained by carefully aiming a point-and-shoot digital camera down an eyepiece. Digital photography is cheap and the trick is to take plenty of pictures and then sort out the good ones later. The difficulty lies in having a sufficiently steady hand but this comes with practice.
Higher quality images can be taken by attaching a camera via an adapter to a microscope with a trinocular head. If you can afford these pieces of equipment you probably know how to use them already!
Caring for a microscope
Some reminders for the novice:
- Never attempt to “clean” the lenses with a cloth or tissue. Read this article for more information about why this is a BAD idea and what you can do about dirt.
- Don’t use the coarse focus knob unless you can be sure that it’s not going to crash the objective lens into the coverslip.
- Ramp down the light brightness control before switching it off. When switching it on again, make sure that it’s on the lowest setting. Otherwise you run the risk of blowing out the bulb when you turn it on.
- Cover the microscope with a cover after use, to prevent dust from getting in the works.
Beginners can learn more about microscopy from the short tutorial (and other articles) on Microscopy UK (click on “Intro” on the menu bar on the top of the page).
A more detailed introduction by Davidson and Abramowitz (pdf) explains the principles of microscopy, and demystifies the cryptic markings on different types of lenses.
Nikon’s MicroscopyU website has a wealth of articles on different types of microscopy.