bioephemera

Pickling a better squid

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Wall of Fishes, Vanderbilt Museum
from Curious Expeditions

Nothing symbolizes the amateur naturalist’s aesthetic as well as a wall of preserved specimens in glass jars, like the jewellike Wall of Fishes in the Vanderbilt Museum (captured here by the wonderful Curious Expeditions, in a fascinating slideshow treasure gallery of the Vanderbilt).

A similar glistening room of glass is found in my revious post about London’s Hunterian Museum.

The problem with historical specimen collections like these is that slowly but surely, they’re falling apart. Storing biological tissue in alcohol or formalin (basically dilute formaldehyde) is a tricky process. Alcohol, which has been used as a preservative since at least the 1600s, dehydrates and bleaches tissues drastically – that’s why so many old specimens look like jaundiced ghosts.

Formalin is less flammable and does a slightly better job of fixing the tissue in a state approximating life – but it’s also smelly, toxic, and distorts the texture of the sample. And both media are fluid, allowing the specimen to be buffeted around over time, resulting in breakage, settling, and distortion.

While visiting the Hunterian and the Wellcome Collection upstairs, I had a long conversation with a curator about how the museum staff patiently maintain the collections by replacing the ethanol and formalin in the older specimens and resealing or replacing the jars. Some of their late 19th and 20th century specimens were suspended in Kaiserling fluid (a glycerin solution) after fixing in formaldehyde; these tend to be in better repair than ethanol specimens.

Unfortunately, the techniques used by curators to preserve vintage specimens have often been lost over the generations – including techniques which once could revitalize the lifelike colors of greyed-out formalin specimens. Collectors have also experimented with a host of solid mounting methods; paraffin can be used, as can acrylic, freeze-drying, mercury injections, corrosion casts using wax or synthetic resin injection, and the plastination procedure made famous by Gunther von Hagens. All have merits and disadvantages. For example, techniques that capture the gross appearance of tissue accurately may destroy cellular structures and DNA (ethanol actually preserves DNA fairly well).

So what about valuable specimens that are already preserved in ethanol or fixed in formalin? How to curate them for the future? The Smithsonian is working on this problem; in fact, they’re experimenting with their male and female giant squid, two centerpieces of the newly remodeled Sant Ocean Hall:


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The Smithsonian’s male giant squid (source)

To create the exhibit, the Smithsonian had to work around post-9/11 rules restricting flammable materials, while maximizing the lifelike appearance of the squid for public display. They turned not to formalin or ethanol, but to a new fluorinated chemical called Novec, developed by 3M:

The fluid differs from both formalin and ethanol in that it’s neither a cross-linking agent nor a preservative, says David A. Hesselroth, a 3M chemist. Instead, Novec is a nonflammable, nontoxic, and ozone-friendly storage medium for already-preserved specimens, he says. Novec products have been in use since the mid-1990s, when they were developed to replace ozone-depleting chlorofluorocarbons in applications such as cleaning electronics.

Novec works by forming a chemical envelope around preserved specimens, explains Joseph Koch, marketing manager for 3M’s electronics materials division. The fluid has very low surface tension, so “it completely spreads around a specimen’s surface, displacing water in all the nooks and crannies,” he says. Novec’s low water solubility keeps the fluid from getting cloudy over time, and it doesn’t leach color from specimens the way alcohol does.

Musteen can vouch for that. “You can still see the squid’s brick-red skin as clearly as on the day it was caught, and the fluid itself is crystal clear,” she says.

Novec doesn’t actually fix specimens – they have to be fixed in formalin first – and it evaporates easily. It’s also denser than water and could force specimens out if they aren’t kept submerged. But it may solve many of the problems with keeping specimens in ethanol or formalin for the long haul.

The Smithsonian won’t be moving its collections over to Novec anytime soon – for now, they’re watching how their squid specimens last. The ideal biological collection can be kept for centuries, as Vanderbilt and Hunter intended – and that’s a lot of observation.

Novec story via A Repository for Bottled Monsters

Comments

  1. #1 llewelly
    November 14, 2008

    The squid doesn’t look ‘brick red’ in the photo.

  2. #2 Jessica Palmer
    November 14, 2008

    I think the “brick red” refers to the female squid. The photo in the post is the male. I had some trouble finding a photo of the female that was well-lit; the photo at the original story is okay, but doesn’t really show “brick red” either.

    I’m looking forward to visiting the Sant Ocean Hall to check it out in person later this winter – right now I’m sick, so I can’t go anywhere.

  3. #3 Laelaps
    November 15, 2008

    Yet another excellent post (in a series of excellent posts, no less!)

    It’s probably better that I read this after I had the fried calamari during dinner last night…

  4. #4 Laurence
    November 18, 2008

    Your comment about ETOH preserving DNA is true, but as you also stated, many specimens are formalin-fixed, then ethanol-stored. While there are techniques that can do it, extracting DNA from formalin-fixed tissues is hit-and-miss and usually yields little high molecular weight DNA.

  5. #5 Jessica Palmer
    November 18, 2008

    Good clarification, Laurence; I should have made that point clearer.

    The irony of historical collections is that many of the bleached, broken, nasty-looking alcohol-preserved specimens which predate formalin have a better shot at yielding usable DNA than their much younger, more aesthetic, but formalin-fixed counterparts.