Double refraction does not save the day

'A rather nice anisotropic crystal, but I never kicked it!'

I am going to come back to my foot, the weird growing thing, and the very minor operation, later. Don’t forget about it though, I won’t. Promise.

First a brief word about birefringence and polarised light microscopy, as exemplified in the very nice, compact, 50ipol from Nikon, which really illustrates just how fortunate optical microscopists are these days – you can get so much for your money! Five objective lenses, diascopic (transmitted) or eipscopic (reflected) illumination schemes, accessories enabling Differential Interference Contrast (DIC) microscopy and a list of features that would take up the rest of the blog to list.

It was the left foot, on the top, just in case you were wondering, the growing thing.

Polarized light microscopy is a way of increasing the contrast and hence the quality of images from a variety of transparent specimens that exhibit birefringence, that is double refraction of light as it passes through. Intrinsic birefringence occurs naturally in aniostropic crystals, which interact with light in an orientation-dependent manner. Quartz and calcite are examples of anisotropic materials, where as salt with its simple lattice structure is isotropic, it does not matter which direction light impacts the crystal. Polarised light microscopy is, as might be expected, widely used in crystallography and mineralogy.

Just by my little toe – ten days assiduous application of antibiotic cream did nothing and it was getting quite big.

However polarised light microscopy is also an important, and somewhat underused, tool in biology, because many small organelles and similar isolated subcellular particles and macromolecules, usually in solution, exhibit structural birefringence. Structural birefringence is thus important for analysing macromolecular assemblies such as microtubules, muscle fibres and proteins, tropocollagen, some viruses, liquid crystalline DNA and chromosomes as well as larger naturally occurring protein structures such as hair.

My GP thought it was best to cut it off – not my foot, the thing growing on it – and send it away to the path lab for them to figure out; four stitches it took!

Birefringence, especially as utilised with polarised light microscopy, does not just produce qualitative improvements, it also allows quantitative investigations. These are not just the expected crystallographic studies but also in structural biology, allowing investigation of the conformational states of molecules, for example, at different ionic strengths.

So, the results came back from the path lab and it seems I had got something stuck in my foot and then had a rather extreme ‘splinter-like’ reaction. So what was the foreign body? Well, guess what: it was birefringent!

Birefringent, but what? I want to know – it’s my foot! How did it get there? What was it?

They didn’t say! They lead me on like that and then let me down! Should get themselves a 50ipol from Nikon, that’s what I say.