CHAPTER 14 Ten Basic Experiments 91
Find the Needle in the Haystack
Now, let’s enrich microorganisms such as ciliates by making a hay infusion. The
bacterial concentration can become very high. You can recognize a high amount
of bacteria when your hay infusion looks somewhat cloudy.
You need:
✔✔Hay
✔✔Pond water
✔✔A petri dish or glass slide with coverslip
✔✔A dropper
✔✔Milk
✔✔A glass bowl or beaker
Cut the hay into smaller pieces, place it in the bowl and add pond
water.
Adding
2 drops of milk to feed the bacteria inside and animate
them to reproduce. The ciliates feed on the bacteria and reproduce,
too. Let this mixture stay for several days or weeks. The infusion will
turn turbid over the next couple of days, which is a sign of microorganism
growth. Drop some liquid from the surface of the water for
microscopic investigation
into your petri dish or onto the glass slide.
Carefully place
the coverslip on the slide to avoid harming any organisms.
Have a look with your microscope using the lowest magnification
first. What you can find is a large variety of protists:
✔✔Flagellates
✔✔Ciliates
✔✔Amoebae
✔✔Heliozoa (»sun animalcules«, due to the arms radiating
from the body)
The bacterial concentration will be very high and you do not know
which bacteria or protists you are growing. Disease-causing organisms
can also proliferate in a hay infusion. It is essential to ensure strict
hygiene when handling the infusion; for example, wash hands thor-
oughly after handling the samples.