Using the Microscope

This is a continuation of the previous lecture on the parts of the microscope and moving on to using the instrument that will be followed by how to make the various slides. This is a lesson as the one before for a seventh grade Life science class.

Using the microscope demonstrated by the teacher. The teacher who teaches the course will make themselves comfortable, places a prepared slide on the stage, and then shows the students how to use the various objectives to see the image(s) on the slide. The teacher will say there will be a 'click' when the slide is in position.

Using the Coarse adjustment

The teacher and the student while watching the objective lens from the side lower the objective slowly using the coarse adjustment....slowly. Lower the objective till it almost touches the stage, but if it is too low you could break the lens and also crack the slide. Be very careful.

*Some microscopes have an automatic stop that prevents lowering the objective until it hits the slide. Depending on the model always use caution. When you think you know how to use the objective you are ready to place a slide on the stage.

Place a prepared slide on the stage

1. The operator will open the diaphragm until the maximum light comes through as you watch through the eyepiece.

2. The operator will make adjustments using either the coarse or fine adjustments till you see the slide clearly. You should never adjust more than half a turn.

3. The operator will then close the diaphragm and find the position where the amount of light coming through and whatever gives you greater clarity. You may experiment with mirror positions.

If you move the slide very slightly the specimen appears to move in the opposite position. The more practice that you have doing this you will be able to move your slide to view any part of the specimen you wish. The operator should focus first on low power and practice changing the objective then look through the eyepiece and the specimen should be somewhat visible but still a little out of focus. You can correct this by using only the fine adjustment. The operator should always center the specimen and focus first on low power and only on high power if you need to to see the specimen.

Preparing slides

Because of great magnification only the very small and thin materials can be examined with a compound microscope. There are a variety of techniques that are used to prepare slides. (Write these two sentences on the blackboard). You can prepare simple slides with a limited amount of equipment and materials.

There are three general methods of preparing slides

1. First, examining living materials on 'wet mounts' with the specimen is simply placed on a drop of water. This is temporary.

2. Second, there are permanent mounts that can be used for months to years.

3. Third, these are smears that slides of fluids like blood.

Wet Mounts

There are single-celled organisms that take a small amount of pond water or water from a culture of organisms on a clean microscope slide. Take a slip 'cover slip' and gently lower it on to the slide over the specimen. There are also what are called 'tissue mounts' for you can take a leaf or even a lettuce leaf, then tear it forward to the main vein or to the mid-leaf and using tweezers (forceps) pull off a small strip of tissue like the 'epidermis' should have become exposed by tearing a very thin membrane. You will then drop a drop of water on to the slide, cover it and then examine it for stomata and the guard cells surrounding them.

Then you will have 'staining' that will help you see the specimen easier using items like 'Methylene blue'; Lugol's solution; or you could use iodine solution for a very dilution. To use stains you place a drop on a clean slide and let it dry and when you later place a drop of water on to the slide and add your specimen the stain slowly dissolves and stains the specimen.

To be continued: Smears

(I hope anyone reading these articles are remembering learning from these lectures and any hearts or tips that you would like to give will be greatly appreciated.)