Monthly Archives: March 2015

Remaking the moist chamber

Having finished the glass microsyringes needed to restore a historical Chambers’ micromanipulator to working condition, the one piece of glassware remaining to be made is the glass chamber. As discussed in the previous post, a glass chamber is a kind of clear cage that sits on the microscope stage. When used with a standard microscope, the sample is contained in a drop of liquid suspended from a large cover slip that forms the roof of the chamber. The observer looks downward through the flat surface of the coverslip into the droplet. The chamber, which can be sealed, creates a microenvironment that slows the evaporation of liquid from the sample. It also provides a space for the tool tips of a micromanipulator to operate upward into the sample contained in the liquid drop.

Glass Chamber

An illustration of the glass chamber along with a view of the photograph of the chamber in place on the microscope stage. [Chambers 1929, 63)

I haven’t discovered what sort of chamber was used with the Chambers’ Micromanipulator that was purchased by the University of Toronto’s School of Hygiene in the late 1920s. Assuming that only one kind was used, it could have been a factory-made version ordered from the Leitz company, or a different design than the one that I made. It’s quite likely, though, that its users would have paid a glassworker to construct a type repeatedly described in the published work of Robert Chambers, inventor of the Chambers’ Micromanipulator, as well as in trade literature related to the instrument and other sources. Instructions for making it can be considered standard—Chambers and his collaborators did much of the early writing about micrurgy. [Chambers (1922a), 340; E. Leitz, Inc. (1926), 10; Chambers and Kopac, (1950), 311]

Chamber 2

A homemade glass chamber. As a recreation it is functional and cosmetically OK.

The glass chamber described in these early sources was relatively straightforward. It consisted of a “fairly thin” glass base of about 50 x 70 mm on which the glass chamber was built. The chamber walls were made from strips of float glass or bakelite, an early plastic. It was roofed over by a large (22 x 40 mm) coverslip.

Remaking the chamber

I followed Chambers’ design as closely as possible using the most affordable material that I could find: thin (1.7 mm) soda-lime float glass cut from the glazing found in cheap picture frames from the dollar store. The entire chamber is made from this glass except for the two top support pieces (A), cut from the slightly thinner glass of a microscope slide, and the coverslip which I purchased online from a laboratory supply site.

Sketchup Chamber

An exploded view of the chamber as I made it, drawn in SketchUp.

I cut the glass using a basic glass cutter from a hardware store. This is a pen-like tool tipped with a small wheel that tapers to a narrow edge. When drawn along a piece of glass, the wheel produces a score line. When pressure is applied to the scored glass, it will tend to split along this line. In practice, this isn’t easy to do reliably when making long, narrow pieces such as those used in the walls of the chamber. A higher quality tool with a tungsten carbide cutting wheel rather than a steel one would probably make this easier.

Glass Tools

A setup for cutting glass in a reasonably precise way. Repeated cuts can be measured using a paper template. Pieces of duct tape provide a bit of friction to keep the glass in place. Using a cork-lined ruler also helps to keep the cut straight. The cutter is lubricated with oil before the score line is made. Pressing the surface opposite the score line against a raised a narrow object like this metal tube helps to start the crack.

The limits of recreation

When I recreated the glass micropipettes that would have been used with this chamber, I felt able to explore some of the “gestural” techniques that the instrument’s operators would have had to master. This wasn’t possible when making the glass chamber. Having spoken to the one remaining scientific glassblower on the U of T campus, whose colleagues know the history of the trade, I learned that in the 1920s or 30s, the parts of the chamber would originaly have been made with a specialized saw used to cold work glass and ceramic.

The glass cutter method is a cheap and rather inefficient compromise. I found it easiest to cut many pieces and select the best. While a diamond saw blade will leave a relatively clean edge, the crack that propagates from the scored line created by a glass cutter leaves an uneven cut surface.  For cosmetic reasons, I tried to even this using a diamond file, though even very rough surfaces would have had no impact on the chamber’s usability.  The best option, of course, would be to commission the pieces from a glass worker with the proper tools.

With any such recreation project, one could get deeply into minutia. Much of the interest comes in setting arbitrary boundaries around what aspects of a historical object to attempt to recreate and what to ignore. It may be worth mentioning, for instance, that the historical directions suggest gluing the pieces together with Canada balsam, a natural material made with the resin of the balsam fir tree. I used modern 2-part epoxy since no glued surface is actually in the optical path.

There are also some potential considerations regarding the height of the chamber. When working with high magnification, this measurement needs to be carefully matched to the focal point of a modified microscope condenser. This is so that high magnification objective lenses receive enough light since they are operating at a greater distance from the microscope stage than if they were used with a standard slide. For my purpose, a chamber within the ballpark range of 8 -10mm is sufficient since I will not be working with especially powerful objectives.

All in all, I’m satisfied with the finished chamber. I expect that it will work well for its intended purpose: the eventual dissection and injection of a living amoeba.  It also looks convincingly like the examples shown in a few surviving photos, especially from the distances at which one would normally observe a reproduction in a museum exhibit.

In the next post on this topic, I’ll discuss the development of microinjection systems used to inject tiny amounts of liquid into living cells or to gather individual microorganisms. The microinjection apparatus is missing from the U of T Chamber’s micromanipulator and I have also attempted to recreate it.