There are almost unlimited things that you can observe with a microscope. If you want to look at an object with a compound microscope, then it has to fulfill three important criteria:
- Small enough: You have to be able to fit it on a microscope slide.
- Thin enough: if it is too thick, then no light will go through and you are only going to see dark blob, or nothing at all.
- Transparent enough: It must allow light to go through. Otherwise you are again not able to see anything.
Let’s say that you want to look at an insect, like a fly. It is way to big, too thick and too dark. You will not be able to see anything when you put it under the microscope.
Luckily there is a solution to the problem! You have to prepare the fly to make it fit on a microscope slide. It means that you have to dissect it. The fly legs and the wings are great things to look at. Take a small scissor and clip the parts off. Of course you want to make sure that the fly is not alive. And do be warned that you do not want to touch decomposing material as there are many bacteria on it. The legs and the wings can then be placed in a drop of water and a cover glass is placed on top. This will make sure that everything is flat and thin. The water is also important for making the image more clear. Look at the specimen with low magnification. Only when it is clear and in focus, increase the magnification.
How to prepare specimens
There is no single way to prepare a specimen. In the example above, we have dissected a fly. But this might not always be the best solution. There are many different ways how microscopists prepare their specimens and in many cases you need some practice and experience. Often you also need to experiment around until you found the best way for the thing that you want to look at. Here are some possible ways:
- Squashing: Objects that are soft can be pressed thin between the slide and the cover glass. A small piece of a soft banana is put on the slide and a cover glass goes on top. Put some tissue paper on the cover glass and then press down vertically. Do not shift horizontally. The banana should be pressed until it becomes a thin and clear film between the slide and cover glass. The tissue paper protects your thumb, should the cover glass break.
- Whole mount: Here the whole specimen is placed on the microscope slide in a drop of water (with cover glass on top – but I don’t have to tell you that anymore, right?). This only works for small insects, tiny mites, animal fur, hair etc.
- Cutting: Thick specimens can be cut into thin sections using a microtome. This is a slightly more advanced topic. If you don’t have a microtome, then you can try to cut it into thin sections using a very sharp knife (such as a razor blade or cutting knife). When you accidentally cut yourself, then you can put your blood under the microscope as well… (just for clarification: this was meant as a warning that cutting specimens without the help of a microtome is difficult and dangerous. The cuts will also not be thin enough). Take a carrot and try it out. Cut it diagonal so that the section becomes thiner and thinner on one side.
- Heating: Material that is too hard to squeeze and too difficult to cut can be made soft by boiling. Take a pumpkin, or a fruit and boil it for a few minutes until it becomes soft. This specimen can then be squeezed between cover glass and slide.
- Scratching: Potato starch grains can be observed by cutting open a potato and then scratching some material off using a knife. This is then suspended it in a drop of water.
- Separation: Some specimens, like algae and other water organisms are already small enough, but they may be clumped together. Just place a small amount of the material on a slide. Then use tweezers or teasing needles to separate the algae, so that it is not in a clump anymore.
- Doing nothing: Some specimens like the skin of an ontion are already thin and transparent enough. All you have to do is place it on a slide with a drop of water. Video:
- How can samples be stored before mounting?
- What are the different kinds of microscope slides?
- Should I make my own microscope slides?
- What characteristics should a specimen have to be suitable for microscopy?
- How can specimens be prepared for observation?
- How do I make a wet mount?
- Which specimens are susceptible to air bubbles?
- How can air bubbles in wet munts be reduced?
- How do you make wet mounts with much water?
- How do you make a permanent slide?
- How difficult is the making of permanent slides?
- Which kinds of mounting medium are there?
- Which mounting medium should I use?
- Why does the mounting medium start to cloud during specimen mounting?