With the advancement of science, discoveries have been made for the progress of this field. One of the oldest discoveries is the development of a laboratory instrument called a Microscope. A microscope is used to see anything invisible to the naked eye. It is used to observe, examine, and study the structures of minute organisms, like shapes of bacteria or viruses, etc. There are many types of microscopes and their use depends on which type of specimen you plan to observe with it. Simple microscopes, compound microscopes, and electron microscopes are the common types of microscopes.
The microscope has many parts which help in its functioning. These include the eyepiece, nosepiece, objective lens, stage, aperture, microscopic light source, condenser, and diaphragm. Apart from these, one important part is the microscope slide. Here in this article, we will talk about this unique and important part of the microscope, different types of slides, and their uses.
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What are Microscope Slides?
A microscope slide is a thin rectangular piece of glass that holds the specimen for observation under the microscope. The size of a typical microscope slide is 75 by 26 mm or 3 by 1 inch and about 1 mm thick. The object to be observed under the microscope is mounted on the slide and then it is placed on the microscope stage for the examination.
The slides are often used with a cover slip or glass slip which is placed over the specimen on the slide. It holds the specimen in place. Once the slide is properly mounted it is held in place on the microscope by the side clamps or slide clips. These keep the mounted slide in place during the examination.
Dimensions of Slides
The most common slides are of the above-mentioned size, 75 by 26 mm or 3 by 1 inch, and about 1 mm thick. But there are other dimensions of slides that are used for different purposes. These are as follows:
- Geological Purpose – 75 x 50 mm
- Petrographic studies – 46 x 27 mm
- For thin sections – 48 x 28 mm
Types of Microscope Slides
Slides are usually made of glass and plastic. The common types of glass used to make slides are borosilicate glass and soda-lime glass. There are many different types of slides depending upon how they are mounted and what is their use. Let us discuss all the types of microscope slides in detail here.
Permanent Microscope Slides
Permanent slides can be stored for a long time if they are made properly. These types of slides mostly contain dead specimens. The evaporation of a solvent locks the specimen in a resin seal. Making permanent slides is easy as it uses a mounting medium that can turn solid. Permanent slides are prepared long before they are to be used and can last up to a century if they are properly mounted. There are different types of permanent slides and they are marked with different abbreviations. These abbreviations are:
- ”wm” stands for the whole amount
- ‘’ls’’ stands for longitudinal section
- ”cs” stands for cross-section
- ‘’sq’’ stands for a squash preparation of a specimen
- ”sm” stands for a smear
- ”st” stands for a stained specimen
Temporary Microscope Slides
Temporary slides are not to be stored for long periods. They are used for short-time observations. Once the observation and examination are done, these slides are discarded. These slides typically use a liquid mounting medium such as water. Wet mount slides are considered to be temporary slides.
Wet Mounted Microscope Slides
Wet-mounted slides are a type of temporary slides that use a liquid mounting medium such as water, glycerin, or immersion oil. It is used to observe liquid specimens or specimens that need to stay in a moist environment. Different mounting liquids have different refractive indices. Water is the most commonly used mounting liquid as it is compatible with most biological specimens. Glycerin is used for its excellent preserving features. While immersion oil is used to mount dry specimens.
These temporary wet-mount slides can be made permanent by covering the cover glass with glue or nail polish. The amount of liquid used to mount the slide is very important. As too little water can dry or crush the specimen and too much water can cause the cover glass to slip, allowing the specimen to swim freely. Make sure to add just the right amount of mounting liquid to the specimen before covering it with the coverslip.
Dry Mounted Microscope Slides
As the name suggests, dry-mounted slides do not use any mounting liquid. The preparation of a dry-mounted slide involves placing the cover slip directly on the dry specimen. In this case, the dry specimen is surrounded by air. Pollen and spores are examined on a dry-mounted slide. These types of slides are useful when there is an incompatibility between the specimen and the mounting liquid. The image quality of dry-mounted slides is comparatively lower than other types of slides. This is because of the difference between the refractive index of the specimen and the surrounding air.
Heat Fixed Slides
In this special type of slide, no coverslip or cover glass is used. A suspension of bacteria is prepared and placed on the microscope slide. The water is evaporated at room temperature and the slide is passed through a gas flame to heat it. The exposure to heat allows the specimen to stick to the slide. Then immersion oil is placed on the specimen on the slide and it is observed by using 100x oil immersion objective.
Graticule Slides
This special type of slide has a grid marked on them. This grid helps the observer to estimate the size of the specimen. Sometimes one square of a grid is subdivided to make a finer grid to identify the size of minute specimens.
Conclusion
The discovery of microscopes has led scientists to develop new insights about the body and diseases. Microscopes help you to view minute objects which are invisible to the naked eye. They have helped to examine and study the minute structures of specimens such as bacteria and viruses in detail. There are many types of microscopes and many parts of microscopes. This article was particularly aimed to help you understand types of microscope slides. Different types of slides include permanent slides, temporary slides, wet mounted, dry mounted, heat fixed, and graticule slides. The differences in these types depend on how they are mounted.
FAQs
How Can You Prepare a Microscope Slide?
The simple steps to prepare a microscope slide involves placing the specimen on the slide, putting a drop of water or oil, or any other mounting liquid on the specimen, and then gently placing the cover slip on the specimen.
What are Prepared Microscope Slides?
These are ready-made slides, meaning that the specimen is preserved and stained already. The preservation is usually done by applying chemicals so that the specimen remains fixed in its position.
What is Microscope Oil?
The microscope oil is called immersion oil. It increases the resolution of the microscope by reducing the light refraction between the immersion objective lens and the cover glass.
What is Cover Slips or Cover Glass?
These are flat thin pieces of glass that are 20mm wide and less than a millimeter thick. It is placed on an object on a slide which is to be observed under the microscope. It keeps the object under observation in its place and provides the physical support it needs.
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