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This week's experiment is something that I first noticed as a child.
You may have noticed it yourself. Part of the fun of science is taking
something that you notice yourself and finding out what causes it. For
this experiment, you will need:
a clear, blue sky If you don't
have a blue sky available, you can try using a sheet of blue paper. Other
colors will work, but blue seems to work better. It works best of all
with a blue sky, preferably while you are digging for fossils, bird watching,
or other similar activities.
Stare at the blue sky and let your eyes go a
little out of focus. As you look at the sky, you will notice that you begin
see tiny spots moving around. As you watch them, you should notice that
they seem to be following pathways instead of just moving around randomly. The more you watch them, the easier
it is to see these pathways
and the patterns of their movement.
What are you actually seeing? Are these UFO's? Some strange kind of bird migrations? No, the spots you are seeing are actually inside your eyes. You are seeing white blood cells moving through the blood vessels at the back of your eye. At the back of your eye is your retina. This contains the light sensitive cells that let you see. Tiny blood vessels bring nutrients and oxygen to the cells of the retina. Normally you don't see these vessels, but when you are staring at the blue sky there is nothing else for your eyes to focus on. You don't see the smaller red blood cells, but the white cells are large enough for you to see. The pathways that they are following are the tiny vessels that carry your blood. Some medical researchers are using this as a way to do quick, easy white cell counts for patients with immune system problems. Patients can learn to compare the number of spots that they see with charts, to estimate their white cell count. This helps them avoid taking frequent blood samples. As someone that has a phobia about needles, this sounds like a wonderful idea to me.
This experiment was re-printed with permission from Robert
Krampf
graphics from Microsoft
Clip Gallery
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