Notes on using a Victorian compressorium on a modern microscope.

  by David Walker, UK.



Keeping live microorganisms still for visual study or photography can be a potential challenge for microscopy hobbyists and various approaches have been recommended over the years. These include:

Right: Some typical 'critter immobilising' techniques in the hobbyist's armoury:

1) Dabs of Vaseline at cover slip corners, gently tapping slip to control depth.

2) Filamentous algae or teased fibres in sample.

3) and 4) Supports of various thickness, e.g. aluminium foil or similar thin inert strips for tiniest. 0.4 mm rings (these from NBS) for larger invertebrates.

5) Various solutions to increase viscosity for the critters. Shown is an NBS commercial solution, various homebrews reported.

Like many hobbyists I've tried most of the above and adopt one or more depending on the organism type. One approach I haven't tried is the compressorium which is a mechanical device for accurately controlling the thickness of the water film. A splendid illustrated survey of designs both old and more recent has been presented in a Micscape article 'Compressoria' by Mike Dingley.

Compressoria can be expensive so have never been fortunate to try one. My brother Ian though acquired an example as it was included with his splendid Joseph Casartelli (Manchester) Victorian compound microscope, a stand described in his illustrated Micscape article.

For the finest control of microorganisms especially for the serious worker, a suitable compressorium is probably one of the best approaches but for more casual users like myself it's certainly worth deciding if a given design's advantages outweigh its potential disadvantages coupled with its cost. Especially the older designs which may not always ideally suit the modern microscope. The pros and cons may depend on the exact design but for the Victorian design tried, some observations from the author's experiences are offered below.

A number of organisms studied also tended not to adopt a relaxed pose when compressed to immobilise e.g stentor just contracted. So preferred giving them more space attached to algae etc on a conventional microscope slide with coverslip where they adopted natural feeding poses (and the algae 'set' the film thickness). This observation may reflect my lack of patience waiting for critters to adopt selected poses under a compressorium but found it easier with other methods.

The precise control of film thickness with a compressorium was certainly more convenient compared with the more hit and miss approach with e.g. Vaseline at cover slip corners (sometimes to the organism's demise).

But overall, for my preferred way of looking at critters, flitting from high to low objectives and trying multiple lighting techniques, I found this design more of a hindrance than a bonus. If looking out for a compressorium design, two key features that may have bearing on its ease of use is height of any fittings and if the bottom plate design can accommodate the focus of the condenser to be used.

Comments to the author David Walker are welcomed.


Footnote: 'NBS' mentioned above was Northern Biological Supplies a UK company formerly run by the late and sadly missed Eric Marson. Other commercial reagents are available.

Acknowledgement: Thank you to my brother Ian Walker for the loan of the compressorium and permission to share an image of the Joseph Casartelli microscope.


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Published in the April 2008 edition of Micscape.

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