Description
This academic note on Mounting Media provides essential knowledge for tertiary students in Histotechnology, Histopathology, and Laboratory Science. Derived from the authoritative text "Bancroft's Theory & Practice of Histological Techniques" by Dr. S.K. Suvarna et al., the document defines mounting media as the crucial solutions used to embed tissue sections under a cover slip, ensuring specimen protection, permanence, and optical clarity. It outlines the key criteria for an acceptable medium, including a refractive index close to glass (1.5-1.55), transparency, non-reactivity with stains, and proper hardening. The note classifies media into two main types: resinous (hydrophobic) and aqueous. Resinous media, such as Canada Balsam and DPX, require sections to be dehydrated and cleared with solvents like xylene before mounting and are used for creating permanent slides with routine stains. Aqueous media, like glycerol and glycerol jelly, are used for mounting directly from water to preserve stains or specimens that would be damaged by alcohol and xylene, though they often require sealing and are considered more temporary. The guide also covers practical aspects like the ringing of coverslips and proper slide storage to prevent fading. This material is vital for diploma and degree students to understand the selection and application of appropriate mounting media to ensure the longevity and diagnostic quality of histological preparations. Download this resource to master the techniques for finalizing microscope slides in a professional laboratory setting.
What's inside
Mounting Media Objectives At the end of the lecture, you must be able to: • Define mounting media • Describe the reasons for mounting tissues • State the criteria of an acceptable mounting media • Outline the types of mounting media Mounting Media • The mounting medium is the solution in which the specimen is embedded, generally under a cover glass. • Essential to get the best and clearest view of the specimen. • Uses: i. Holds the specimens in place between the cover slip and the slide (protect specimen). ii. For making permanent slides. iii. To maintain a high refractive index. Mounting Media • Most tissues have an RI of between 1.5 and 1.55, so a mounting medium with an RI in this range will give maximum clarity. • There are two major types of mounting media used and the difference is in the solvent. Criteria of Acceptable Mounting Media • RI should be as close as possible to that of glass, i.e., 1.5 • It should be colourless and transparent • Inability to cause stain to diffuse or fade • It should be dried to a non-stick consistency and harden relatively quickly • Inability to shrink back from edge of cover-glass • It should be free flowing and free bubbles Resinous Mounting Media • Commonest types • Are based on hydrophobic organic solvents, usually xylene • Need the section to be dehydrated and cleared before mounting. eg - Canada balsam - Natural resin (R.I. - 1.52) - D.P.X. (R.I. 1.52) - Eukitt -Eupharal -Clear nail polish Canada Balsam • Natural mounting medium obtained from Canadian fir tree • Refractive index 1.54 Advantage Disadvantages Permanent slides can be stored for many years Specimen must be placed into xylene before embedding (because it is hydrophobic) Darkens with age Slowly becomes acidic Fading of many stains Not cheap DPX • A synthetic polystyrene resin that is dissolved in xylene and has some plasticizer added (Distrene 80, plasticizer and xylene). • Colourless, neutral medium in which most standard stains are well preserved (RI 1.52). Advantages Disadvantage Little tendency to fade dyes Not recommended for use with thick sections Hardens in about 24hrs Specimens do not need ringing (sealing the edges of the coverslip) Clear Nail Polish • Can be used to seal the sides of the coverslip when using aqueous mounting media or directly as a mounting medium. • The specimens must first be dehydrated in alcohol and can then be directly mounted (without xylene) in nail polish Advantage Disadvantage Readily available Shrinks a lot when making very thick mounts i.e. whole insects Avoids use of toxic organic solvents to treat specimens Aqueous Mounting Media • Used for mounting sections from distilled water when the stains would be decolorized or removed by alcohol and xylene. • Most are best considered as temporary mounts and need ringing to hold the coverslip in place and prevent drying out. • Tissues do not need any treatment before mounting and can be mounted directly from water or buffer. • Require addition of bacteriostatic agents such as phenol, crystal of thymol or sodium merthiolate to prevent the growth of fungi. Glycerol • A trihydric alcohol with a high RI. • Can be used alone or with the addition of a buffer to control the pH. Advantage Disadvantage Water based avoids use of alcohol dehydration which possibly deforms specimens and toxic organic solvents Difficult to prepare slides which are permanent Does not shrink Glycerol Jelly • Useful for making mounts of water organisms, algae, protozoa etc. • Commonly used to preserve pollen samples. Advantage Disadvantage Avoids use of alcohol dehydration which possibly deforms specimens and toxic organic solvents Difficulty of mounting the sections (bubbles) Does not shrink Need to seal coverslip with nail polish
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