Index >> Microscopy Methods in Microbiology >>Bench Microtome Sections

Hard material may be soften with 10% KOH. Some investigators prefer to use dilute ammonia or hypochlorite solutions. Alternatively, the material can be heated, but not boiled. Herbarium materials often contain black precipitates of mercurial preservatives which interefere with the subsequent staining and microscopic examination.

This can be removed by iodine solution-thiosulphate sequence. in this process, the material is first washed in iodine reagent (S8) until no more iodine comes out and then it is transferred to sodium thiosulphate reagent (S9) to remove excess of iodine. The treated material is then soaked in 35% gum Arabic solution having consistency similar to the commercial gum available for sticking paper.

Freeze the block by a series of successive jets of carbon dioxide. If the freezing chamber is provided with a knife cooling device, knife should be moved in such a way that it is in the path of carbon dioxide stream and deflects the gas onto the top of the block for cooling as shown in Figure. The ideal temperature for frozen block varies depending upon the material. Too cold block results into crumbling of sections, while too warm block results into torning or smearing together of sections.

After adjusting the height of stage and desired thickness of section, the blade is lubricated with a drop of water and the material is cut. Better sections are obtained by quick movement of blade. Sections are removed carefully from blade with a fine brush into a watchglass or directly to a drop of aqueous mountant on a slide.