for list of all Experiments
One of my favorite subjects for the microscope is pond life. Here the word
pond is meant to include all types of freshwater habitat whether lake, reservoir,
pool, ditch or puddle. Dipping an empty jar in the pond will give you plenty
of water to study but the results can be disappointing because the catch
is not concentrated enough bearing in mind that you only use a drop on a
slide. Ideally you need a special specimen net. These can be expensive at
science supply companies but they can be made quite cheaply.
Compound light microscope
Old nylon stocking
Purchase a simple aquarium net at your local pet store. The cheaper the better
and cut off the net leaving only the frame. Take an old nylon or silk stocking
and cut a section of it to form a tube. Attach one end of the tube to the
frame of the aquarium net and to the other end of the tube, attach a clear
plastic jar (approx. 1.5 - 2" in diameter).
When using the specimen net, drag it back and forth through the water for
at least one full minute. This will ensure that as many creatures as possible
settle into the jar at the bottom of the net.
On returning home from the specimen collecting excursion, avoid the temptation
to immediately drop a sample on a slide and pop it on the stage. Doing this
can be quite frustrating because the specimens will be lively and may move
around so fast it's difficult to see them in any detail.
First, let the sit for a couple hours so the contents can stabilize and settle
to the bottom. After this time you should see a "sludge" of material on the
bottom of the jar. This "sludge" is where the critters reside but it may
also contain some other thick material (sand, debris etc) that can make viewing
difficult because it leaves too much room between the slide and coverslip.
There is a way to filter out this material.
Draw a sample into an eyedropper and let it sit in an upright position for
a few minutes. This will cause the heavier material to settle near the tip
of the dropper.
Place a drop of material on a white plate or petri dish. Do this until you
have the contents of the dropper dispersed into a number of individual droplets
scattered on the plate. Each successive drop will have less of the debris.
This can also help you to isolate some of the larger critters like water
fleas and Daphnia.
Select a drop with fine debris that is just barely visible to the eye.
Siphon up the selected drop with an eyedropper and place it on a clean slide.
Put a coverslip onto the drop by resting one side against the slide and then
slowly lower the other end onto the drop. If there is too much water draw
out the excess by touching a piece of tissue to the edge of the coverslip.
The less depth the better, as this will prevent organisms from moving out
The movement caused during slide preparation may cause some of the critters
to go into hiding. If you allow the slide to sit still, they will eventually
show themselves so keep watching.
Finally, you may want to examine larger animals, such as water fleas or Daphnia.
With a tooth pick put three small dabs of Vaseline onto the center of the
slide, leaving enough space at the center for the drop containing the animal.
The Vaseline dabs should be of a height enough to hold the coverslip a millimeter
or so off the slides surface.
Now suck up the drop with the animal and place it in the center of the dabs.
Gently lower the coverslip onto the Vaseline, which it should contact just
before encountering the drop. Use a tooth pick to slowly press the slip down
until the animal is no longer moving about, but is held stationary by the
gentle pressure of the slip. It may take a few tries to learn how much pressure
is needed to stop, but not injure the animal. More water can be added at
the edge of the slip if needed.
Surrey, British Columbia
for list of all Experiments