Topics

Ideas for monocular microscopy

Seeing red blood cells
You will need a Petri dish, either a tadpole or several paper tissues (paper towel will do), a small fish like a guppy or a minnow, a monocular microscope, and a good light source. You will also need a net, but a large beaker is often better for catching a fish or tadpole gently. All you have to do is pour water from the large beaker into a smaller beaker until one animal transfers over.

You will need to work quickly. The tail of a tadpole or fish is thin, flat and transparent, which means you can actually see through it, and see the capillary vessels inside the flesh. Get your microscope set up first, and focus it on a small piece of wet paper tissue sitting in the bottom of the Petri dish. If you have an iris diaphragm, close this down as far as possible, and make sure you know how to move the dish so the tissue catches the light.

Both tadpoles and fish breathe through gills, so it is best if you do this with somebody else, who can be given the job of moving the animal so the clear part of its tail is in the light. Scoop your fish or tadpole from the water. If it is a tadpole, just tip it into the dish, and start looking — after a minute, put the dish gently into the tank, let the animal swim away, and if necessary, choose another one.

With a fish, try to lay the fish with its head on the wet tissue, and cover the head with a second layer to stop it flapping around. Try to avoid touching the fish as you will damage its scales — and whether you are using a tadpole or a fish, wash your hands afterwards, before you touch food or drink.

The main thing to remember is that even the thin tail will have a number of layers that the microscope can 'see', but because the flesh is clear, you can focus up and down until the blood vessels are clearly in focus.

This will help you to do this better

Most ponds and still water will develop a collection of life over time, and if you take some green slime, you will normally take a good sample of this life, along with the "slime", which is actually an assortment of algae.

The mistake most beginners make is to put too much 'gunk' onto a slide. Your microscope works when light shines through the stuff on the slide, and your cover slip has to lie down flat. If there is too much gunk, you can't see through it, and the cover slip does not settle down properly.

Take small amounts, and spread even that out with a brush. If you have a fish tank, some of the most interesting gunk comes from the filter. Stir this up a bit, and then take some of the material with an eye dropper and put it in a Petri dish. With a black background and a strong light, you should be able to see if there are any tiny animals in the water. If there are, use an eye dropper to take a sample. If there are no animals, use a flat slide, if there are animals in the gunk, use a well slide.

With any sort of luck, you will strike it lucky when you switch to high power, and you will see some Paramecium or other of the larger wee beasties that often live in water. Keep an eye out also for filamentous algae like Spirogyra, which is easy to spot because it has spiral chloroplasts.

This will help you do this better

The epidermis of a leaf is a single layer of cells. With care, you can peel it off and make a wet mount of it. It is a single layer of cells, so you should be able to see detail in the cells.

This will help you understand

With luck, you will be able to see how the mosquito breathes, and you should be able to see its digestive system, but you should be aware that the wriggler will drown when it cannot get air through its siphon.

This will help you understand

Even though you will probably want the higher magnification of a monocular microscope, you will probably need to use reflected light to see any detail, so think about using a bright reading lamp as your light source.

The most obvious question should be where do the colours come from? Take a close look at the scales and see if they are coloured, then scrape some off and make a wet mount of them.

This will help you understand

If your microscope came with some sort of grid, you may be able to estimate the diameters of the fibres, as well as noting variations in the diameter, any markings or scales on the fibres, and how they terminate or break. Many fibres will take up a variety of dyes, so there is a whole new line of enquiry open there!

See also the entry on animal fur.

This will help you understand

This will help you understand

This might be a little too techo for the kid at home, but did you know that you can identify most Aussie mammals down to species (and certainly to genus) level using a (guard) hair and a microscope? Guard hairs being the longer, thicker (often darker) hairs in the mammal coat, i.e., not the little, soft downy type hairs.

You use 2 diagnostic criteria, the scale pattern on the hair, and the appearance of the hair in cross-section. To get a scale pattern, you paint clear nail varnish onto a microscope slide, lay the the guard hair on the varnish, and quickly peel the hair off when the varnish has dried.

To get a hair cross-section, ecologists have a special metal slide, same size/shape/thickness as a normal glass microscope slide, but with a hole of 1-2mm diameter through it. You take a little bundle of fine frayed nylon cord, and pull this through the hole so as it makes a snug, but not too tight, fit. There should be frizzy bits of nylon sticking out on each slide of the slide in a sort of cloud . then you push a guard hair (or 2 or 3) end-on through the hole.

The nylon fibres hold the hair(s) in place. Get a sharp razor blade, and run this quickly and smoothly at ~30 degrees angle across the slide, trimming away the nylon cloud. Do this on both sides- now you've got a 'slice' of hair in the hole held in place by the nylon threads.

Identifying the beast from whence your hair came is a descriptive/observational exercise, whereby you use a key to different species/genera hairs. The name of the key I used as an ecology undergraduate escapes me, but I'm sure any Aussie zoologist would know [I am still looking, help needed, pm]. It's easy to use, with photos and drawings of patterns to compare to.

This method is a great way to find out what owls, snakes, foxes, cats, etc. have been eating when you go through their droppings, and also a way to work out what spp. are living in an area without trapping them- you make a 'hair trap', a sticky piece of tube or some such that the animals will squeeze through or brush past (if you put the trap in the right place) while going about their daily business. The hairs stick, you simply collect them and identify them.

This will help you understand

This will help you understand

The idea is simple: make a saturated solution of a salt, place a drop on a slide, spread it across the slide, set the slide on the paper towel to clean up any spillage, then place the slide carefully on the microscope stage, and wait for it to dry. The crystals will generally be long and needle-like because of the way the drying proceeds: I leave it as a challenge to find a way of producing larger, more normal slides under these conditions, noting only that a lid for the Petri dish might be a good start.

This will help you understand

A solution of 10 g methyl cellulose in 90 mL water will produce a syrup that will slow most animals down. You can also add 2-3 grams of gelatin to 100 mL of cold water and heat this while stirring. Cool the gelatin solution back to room temperature and add one drop of pond water to one drop of gelatin solution. Alcohol mounts will kill the animals, but a 1% solution of magnesium sulfate will just anaesthetise them. You can also try grinding up a small piece of face tissue and adding the fibres to the pond water to tangle the animals up.

I have never tried this, but I suspect that water-based PVA glues might also be used, but it will probably ruin the slides.

This will help you understand

This could also be interesting

Hints and ideas will go here when I have some

The idea is to take some of the small fragments and see if you can find a way of identifying the different minerals, but it could be interesting to see if heat and mechanical action produce any differences. It might be worth looking at any effects of polarised light here, though this sort of work is best done with thin sections of uniform thickness.

If you have access to high power magnification, why not try a few other rocks. Can you see crystals in basalt, for example?

This will help you understand

Some years ago, I tested two species of flower, Plantago lanceolata, which is a weed, and Kunzea capitata, which happened to be growing in my garden. In each case, pollen grains in a wet mount with a few grains of sugar began to grow, but the Plantago caused violent hay fever, and I have never been back to it. You could try different amounts of sucrose, or compare the effects of fructose or glucose: there is lots to do here.

Here are some hints

You can get to know your own forehead mites the following way: stretch the skin tight with one hand, carefully scrape a spatula or butter knife over the skin in the opposite direction, squeezing out traces of oily material from the sebum glands. (Avoid using too sharp an object, such as a glass edge or sharpened knife.) Next scrape the extracted material off the spatula with a cover slip and lower the slip face down onto a drop of immersion oil previously placed on a glass slide. Then examine the material with an ordinary compound microscope. You will see the creatures that literally make your skin crawl.

- Edward O. Wilson, The Diversity of Life, Belknap 1992, 177.

Comment

You will need a bolt with a wing nut to match, safety goggles, a very sharp blade (a cut-throat razor is best, but these are hard to get and hard to sharpen) and an old cutting board. For small items like leaves, you will need a candle, or some other sort of wax. As an alternative, you will need some scrap polystyrene foam which is probably easier to use.

Put the wing nut on the bolt the "wrong way round", with about one full turn of the nut on the bolt, then fill the empty portion of the nut with whatever you want to section. If you need to section a leaf, prop the bolt upright in an old jar or can, poke the leaf in, and then drip candle wax in, until the leaf is surrounded with wax and leave it to set, or cut some polystyrene foam roughly to size and put a piece of leaf between before you force it down into the threaded hole in the nut.

Put on the safety goggles, get the cutting board, and then trim off any bits that are sticking out of the nut (now you will see why the nut is "wrong way round"). Once that is done, you are ready to start sectioning. Turn the nut slightly, so a tiny amount is pushed out of the threaded hole in the nut, and slice.

This will help you understand

Or you could try taking a closer look at stinging nettles (ouch!). Gardening gloves might be a good idea.

Then how about looking at the fine structures of seeds of different plants, or the detailed structure of a flower, especially the stamens. Cross sections work best under a binocular microscope.

Some comments

This will help you understand

Ideas for binocular microscopy

Moss Animals
You will need a good light source, a Petri dish, a mat of moss and some water and/or alcohol.

There are many animals that live in a moss mat, but they can be hard to flush out. If you slowly add water to a moss mat in a Petri dish, you may be able to persuade the animals to climb up into the dry. Adding alcohol with an eye dropper has the same effect, but you need to watch out for fire, and avoid breathing the fumes. People often use a small amount of formaldehyde (methanal) to flush sea life out of algal mats but this is POISONOUS, and should NEVER be used when you will be hanging over the dish and breathing in the fumes. Ethanol or rubbing alcohol is safer.

This will help you get more out of this

Warning: adult supervision needed

You could examine (under low power) the crystal growth of silver on cast iron chips in a stream of silver containing solution, it's better if the solution is flowing gently. The silver is reduced from solution by metal replacement commonly referred to as diffusion limited aggregation. This process is what we we developed into our 'EFFICAT' System in the mid 1970's and 80s for silver (and other metals) recovery. Students should be able to obtain some silver containing fixer from the local 'friendly' fast photo outlet or photographer. Black and white fixer is best or second best is the Kodak C41 fixer or equivalent.

Note from pm:you could also use silver nitrate solution, but this is corrosive and stains hands etc. Use latex gloves and use a Petri dish on a number of sheets of newspaper to hold everything if you are using silver nitrate solution — and try a bit of fine cleaned copper wire in a well slide with a monocular microscope as well. Now back to Gerald:

Gerald: Steer clear of the blood red bleach fix which is so good at oxidising it will reclaim the silver almost as fast as it deposits and your iron chips will disappear. Spill bleach fix on metals and they CORRODE quick time, one of my acquaintances dropped his new Nikon F100 into it accidentally and even though he retrieved it immediately and cleaned it thoroughly it was a write off - that really hurt!

Gerald: An article appeared in Scientific American, I think in the mid 80s on Diffusion Limited Aggregation which described this process very well I thought and this would be worth reading. I have copy but "it is in a box somewhere" the family motto around these parts. :-))

Gerald: I have been away from this since the late 80s and I am not sure what changes if any which have taken place in the fast photo chemistry that may affect the process. If all else fails a standard pregnant solution could be prepared for the purpose.

This will help you understand the chemistry

This will help you understand

You may find it interesting to see if you can repeat Pasteur's experiment on a sample of tartaric acid: this comes in two forms, "left-handed" and "right-handed", which form mirror-image crystals. Otherwise, examine different types of sugar from castor sugar to coffee crystals and see what you can see.

This will help you understand

This will help you understand

This will help you understand

Ideas for video microscopy

This section was added after Gregg Thorn reminded me that it is possible to attach various cameras to your computer, and record microscopic detail in living colour, write on the screen of your computer, but the ideas can be applied to a variety of cameras

Sundews
Sundews (Drosera sp.) are insect-eating plants, found in swamps and marshes all over Australia. They have sticky hairs with protein-dissolving enzymes, and when an insect is stuck on a leaf, the enzymes break the insect's protein down to amino acids, and this stimulates the leaf to curl over, slowly, bringing more hairs into contact with the insect, and so holding it better. The process generally takes several hours, so this would be a good case for time-lapse studies.

Gentle people can try feeding a sundew on tiny bits of cheese or meat, but if you are growing a sundew in a pot, you need to use very pure sand, and do not add any fertiliser, because these plants are either smart or lazy enough not to produce the dew if they can get enough nitrogen and phosphorus from the soil.

Sounds like a science project? I thought so as well. Congratulations on having such an excellent idea! There are three other genera in the family Droseraceae: the Drosophyllum of the western Mediterranean, Dionaea, from the Carolinas (USA) and Aldrovanda, described as widespread in the Old World.

This will help you understand

This will help you understand

This will help you understand

This will help you understand