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One very interesting detail in the accompanying text (left) by Dr Collin Dawes was the reference to the Romans and a rock-boring mollusc, the piddock (Pholas dactylus). The piddock is of mixed value: it apparently makes good eating (I'll take that on trust, as I can't stand shellfish) but contributes to coastal erosion due to its mechanically boring into soft rock to make the hole where it lives to filter-feed. However, Pliny the Elder, in his Natural History, mentioned a remarkable property of the piddock:
LXXXVII. Concharum e genere sunt dactyli, ab humanorum unguium similitudine appellati. his natura in tenebris remoto lumine alio fulgere claro, et quanto magis umorem habeant lucere in ore mandentium, lucere in manibus atque etiam in solo ac veste decidentibus guttis, ut procul dubio pateat suci illam naturam esse quam miraremur etiam in corpore.
LXXXVII. The class shellfish includes the piddock. The piddock, named finger-mussel from its resemblance to a human finger-nail. It is the nature of these fish to shine in darkness with a bright light when other light is removed, and in proportion to their amount of moisture to glitter both in the mouth of persons masticating them and in their hands, and even on the floor and on their clothes when drops fall from them, making it clear beyond all doubt that their juice possesses a property that we should marvel at even in a solid object.
- Pliny: Natural History, Volume III, trans. H Rackham, Heinemann / Harvard University Press, Loeb edition (Internet Archive plinynaturalhist017760mbp)
According to this and other accounts, this bioluminescent effect is extremely strong: a number of researchers have studied the effect historically; see, for instance, page 162 of The Edible Mollusks of Great Britain (MS Lovell, 1867. J Beccaria found that a single piddock "rendered seven ounces of milk so luminous that faces might be distinguished by it", and another researcher, Costa, wrote that "if the flesh is chewed and held in the mouth, the breath becomes luminous and looks like a real flame".
The presentation went on to describe the work of Jan and Robert Knight of Knight Scientific, Plymouth, in elucidating the role of the photoprotein involved, pholasin (aka Pholas luciferin), and its use as a diagnostic assay for white blood cells, antioxidants and free radicals. Essentially it enables the detection of inflammation before it becomes symptomatic. (The Knights featured on the BBC's now-defunct QED science documentary series in 1993). Interesting stuff.
Appendix: 12th January 2012. Five years after posting this, I just had an interesting e-mail discussion with Dr Andrew May, a volunteer at Lyme Regis Museum. and the maintainer of the Lyme Regis Museum blog. Andrew asked about a detail in the original version of this post, which said the piddock shells had been found at the site of a Roman villa by the River Lym. Unfortunately my weblog was the only source findable for this detail.
My first suspicion was that I'd misread Dr Dawes' account, so I took a quick detour on the way home today and rechecked (the presentation is still on the wall in the RD&E). Sure enough, it doesn't say what I cited: it says "thousands of shells" were found at the villa site (the Holcombe site where the Holcombe Mirror was found in 1970) and then goes on to discuss piddock without explicitly making the connection. I'd misread, and conflated the details. I took down the blog post and apologised for the wild goose chase I'd started.
However, very good news. Andrew also investigated the story, and checked with the Devon Historic Environment Service (the site, although near Lyme Regis, is just inside the Devon border). They sent him the mollusca report for the Holcombe dig (i.e. what was found in the shell midden near the bath house area of the villa), as published in Devon Archaeological Society, Proceedings, No 32, 1974. Among land snails and other marine species (like Crassus in the movie Spartacus, the Roman occupants liked both snails and oysters), the dig did indeed find shells of the common piddock, Pholas dactylus.
Andrew and I both have our story! I've updated and reinstated the post.
The Devon Historic Environment Record is quite enlightening to read; the Victorian era took rather a different view of archaeological conservation. In the mid-1800s, Roman mosaics were discovered at the Holcombe site. The record says:
Reference to two mosaics, one bought at auction in 1854 and given to Exeter Museum; and one bought on 05/04/1860 and relaid in his house "The Chancel", Sidmouth. ... Hutchinson, P. O. 1848-1894)
This is the Sidmouth historian Peter Orlando Hutchinson. The idea of a local historian buying up archaeological remains and using them for home decoration is quite astonishing to the modern mindset.
Appendix 2: a spot of geeky medical explanation. This piddock topic was, unfortunately, hard-gained. I had more spare time than I wanted, to read the RD&E wall posters over Christmas 2007, due to keeling over with appendicitis late on Christmas Eve and having an appendectomy in the small hours on Christmas Day.
The story, should it interest/edify anyone: I'd been a bit unwell with intermittent stomach pains and bloating for about three months; I was feeling pretty low with it, as the source was unidentifiable, and nothing seemed to help. There seemed to be a vague correlation with heavy meals and fatty foods, and my GP had been working through possibilities such as peptic ulcer, gallstones, whatever. On Christmas Eve, however, the pain become continuous and over the day shifted to lower right. On the evening of Christmas Eve it was bad enough that we took a taxi to the RD&E drop-in centre, where they prodded McBurney's point, and from my reaction instantly diagnosed appendicitis, near-rupture it turned out, and I was in theatre within a couple of hours. So no Christmas festivities, unless you count some of the team that wheeled me in wearing antler hats.
Once I was over the surgery, the pain and bloating stopped, and have never come back. Clearly the appendix was the problem all along. The history's morbidly interesting in hindsight. I don't blame anyone for not spotting it earlier, as early appendicitis is hard to diagnose, especially with the rather vaguer clinical course of the "suppurative" form I had. I'm in the wrong age group anyway (the peak for appendicitis is late teens), and only around 50% of cases manifest in the classic symptoms. Plus the bowel is bad at localising pain; the appendix is served in a general sort of way by a nerve that joins the spinal cord at the T10 vertebra, which gives a generalised mid-belly pain. You only get lower-right pain when the infection worsens and surrounding structures become irritated (hence the classic move of the focus of pain with appendicitis).