Re: Can't find microbes in lake water
From: Aaron (nghy_at_comcast.net)
Date: 08/06/04
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Date: 6 Aug 2004 04:42:11 -0500
Hi Gregor,
You need to go back to my first response to Bob's question,. where I
pointed out the most likely area to look for concentrations of
organisms. He should include a little plant detritus (decaying
matter) in the slide as the bacteria and the protozoa will tend to
remain in the area.
Now let me expand on why I see Bob's microscope as a problem in this
instance and why it is not as good as the system used by Leeuwenhoek .
I agree that the optics in Bob;s scope are slightly better than
Leeuwenhoek's However, Leeuwenhoek's microscope used a very
effective design to hang the specimen right in front of the magnifying
element of his microscope. He did not have to chase after a target
that could swim quickly out of his field of view. Bob on the other
hand, is working with slides which provide a vast area, relative to
his field of view,, in which the critters can swim.. Further Bob
does not have the basic X-Y stage controls we take for granted on our
scopes. The slide is held by simple clips and he needs to move the
slide with his fingers. Even with X-Y controls it is tough to keep
the protozoans in the field of view at magnificationsnormally used to
see reasonable details. Without the stage controls, Bob is likely to
make vast random jumps across the field instead of being able to
systematically search the area under the coverglass. .
Better subjects for a beginner with this microscope would be mounted
insect parts, printed materials like money and stamps These subjects
are stable and relatively large and would make use of the 4X and 10X
objectives..
Its not that seeing protozoans is impossible with his microscope, it's
just a very difficult task.
Aaron . .
Bob needs to find a sample with enormous concentrations of cells and
he would probably benefit from some gelling agent which slows the
critters down.
To Leeuwenhoek just seeing something swimming was the major
breakthrough. In order to keep Bob's interest and his kids interest I
am sure they want to see some internal details and the cillia
moving.etc. A low magnification image is not going to do the trick.
. .
On Fri, 06 Aug 2004 06:17:51 GMT, "GTO" <gregor_o@NOSPAMyahoo.com>
wrote:
>I agree that this microscope [1] is a toy and your recommendation to
>purchase a used scope is very good. But I still believe that it is better
>than the optics used by Leeuwenhoek [2].
>
>Hence, there is most certainly a possibility for Bob to see single cell
>plants and animals using his scope. I believe his problems are in sample
>prep.
>
>Prof. Werner Nachtigall writes in his beautiful booklet about Microscopy
>[3]:
>
>"Where there is water, there is life. However, a drop of water taken from a
>large, clear lake would contain live organisms only in the rare
>circumstances of a heavy "bloom" of microorganisms."
>
>I recommend to read Werner's chapter about "Aquatic Microorganisms".
>
>Gregor
>
>[1] http://scientificsonline.com/product.asp_Q_pn_E_3112201
>[2] http://www.ucmp.berkeley.edu/history/leeuwenhoek.html
>[3] W. Nachtigall, Exploring with the Microscope, page 111, Sterling
>Publishing Co, Inc., 1995.
>
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