Monthly Archives: March 2012

Duhn-nuh duhn-nuh duhn-nuh duhn-nuh Hagman!

Sometimes it seems like it’s only a matter of time before the hagfish comes up for discussion, though at least one person thinks that I may be, and I quote, “vastly over-estimating the market saturation of hagfish blogging.” Perhaps it’s a holdover from that one seminar talk I went to when I was in undergrad given by a professor who researched (among other things) the properties of hagfish slime. While he was talking my friend drew a quick sketch of Hagman, the hagfish superhero, and we all snickered loudly in the back row. Hagman then sporadically came up in conversation for weeks afterward, and still makes me snicker several years later.

Zorro-esque Hagman vs. Niklas Hagman the NHL Left Winger

Hagman fights for truth, justice, and the Stanley Cup.

There’s a good reason that hagfish are one of those creatures that gets a disproportionate amount of cultural presence, and that’s because they’re weird and gross. They’re marine invertebrates, living mostly at great depth in the ocean, burrowing into dead whale carcasses and other rotten corpses and eating their way out. They have no bones or jaws, but intimidating rings of scaly teeth. And when they’re attacked or startled, they produce a cloud of slime, tie themselves in a knot, shimmy out of the slime cloud that’s now engulfed the attacker, and escape.

That’s an impressive trick, disgusting table manners or no.

Hagfish slime is astounding. The mucus the hagfish produces is a milky white goo, and while it doesn’t produce much mucus at any one time, a small amount of mucus quickly turns a large container of water into a large mass of slime.

Hagfish slime contains three things: seawater, slime threads, and mucins. Mucins are proteins found in mucus of all sorts, including saliva and gastric juices, while slime threads are thin protein tendrils that are curled up when excreted by the hagfish and then unfold when in seawater. Both mucins and slime threads are produced by separate glands located all along the body of the hagfish. Given how thick and, er, slimy hagfish slime is, intuition would say that either the slime is made up principally (or at least significantly) of either threads or the mucins, but it seems that this is not the case. It appears that hagfish slime is about 99.996% seawater, 0.0015% slime threads, and 0.002% mucins.

So, given that hagfish slime is so cohesive, those threads and mucins must be pretty remarkable. The threads, when produced, are tightly curled or folded up, and unfold in water; mucin is produced in packets that swell with water, but do not burst. Mucin plays a critical role in the unfolding — threads will not form unless mucins are present in the solution. It’s thought that the mucin packets bind to the the threads somehow, almost like deep conditioner binds to hair, and in doing so make the thread unfold rapidly, but it’s unclear how exactly that works. But given proportion of the threads to mucins, the size of the threads (~15 cm long unstretched, ~3 um thick in the middle), and the mucin packets (~7um long, ~3um thick), there is enough room on the threads for the mucin packets to bind to and give good coverage.

Left:  Slime thread with attached mucins.  Right: schematic of a thread network

Left: The slime thread tapers to the ends, and the ellipsoid mucins bond along its length. Right: The threads curl and tangle around each other, forming a network that traps water.

The threads, when unfolded and covered in water-swollen mucin packets, then form a network throughout the slime mass. The threads are long, and can span the entire slime mass (depending on how much slime the hagfish is producing, ie, how agitated the hagfish is). This means that the threads, which while thin and diffuse, are quite strong, form a mass of channels and chambers in the slime mass. The seawater gets trapped in these channels and chambers, and cannot flow freely anymore. It doesn’t form a chemical gel, that is, the water does not stop flowing, but it slows down sufficiently to form a coherent, slimy mass.

But how does the slime help them evade predators? Sure, it’s startling to suddenly have a mass of slime in your face, but is that enough of a deterrent to justify the energy costs to the hagfish? Slime may not only be startling, but it appears to be thick enough (and cohesive enough) that it clogs the gills of predator fish, which not only startles the attacker, but may suffocate them.

Unfortunately, the hagfish also has gills, and those gills can be clogged by its own slime. To avoid drowning, the hagfish uses its other unique trick: the ability to tie itself in an overhand knot, and wiggle the knot very quickly down the length of its body. This effectively peels the slime off itself, clearing its gills and avoiding suffocation. It’s also useful for escaping from dastardly researchers who’re holding them in midair:

But hagfish also have a nostril, to be able to sniff out dead whale carcasses and other food, and slime can get stuck in it too. To clear it out, hagfish sneeze. Hagfish are the only known type of fish that sneeze, though sadly, “hagfish sneezing” does not turn up any relevant videos.

Here’s some references about hagfish:
Composition, Morphology, and Mechanics of Hagfish Slime. Fudge, D.S. et al, Journal of Experimental Biology 208, 4613-4625, 2005. Journal link, self-hosted link
Kaikoura deep-sea fieldwork: do you love slime?
Hagfish aren’t so horrible after all!

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No Faster-Than-Light Neutrinos Yet

At the end of September, a paper was published with the provocative conclusion that neutrinos had been measured to travel faster than the speed of light. It was big news, and was widely reported in the media as a reasonably established finding (when in reality it had been released on arXiv, an open-access physics portal, but was not yet peer reviewed, and was subject to much eyebrow raising from physicists at large). In the past week, news has come out that there were some systematic sources of error, and the results are not necessarily accurate.

Here’s a quick recap of what the original experiment entailed:

  • a beam of neutrinos was generated at the Large Hadron Collider (LHC), and the beam was aimed through the Alps (ie, underground) to a detector in Italy called OPERA about 730 km away
  • the signal leaving the LHC is timestamped, using a highly accurate (and very carefully calibrated) GPS system
  • as the neutrinos leave the LHC, a light signal is sent to the same location in Italy via a fibre optic cable. This provides a time-of-flight for a light signal to compare to the time-of-flight for the neutrino signal.
  • when the light and neutrino signals are detected in Italy, they are timestamped using the GPS system, and the times of flight cane be compared
  • this repeated over and over again to reduce statistical errors in the measurements
Schematic diagram for the experiment.

The scientists reported that there was a difference in the times-of-flight of about 60 ns, with the neutrino beam reaching the detector before the light signal. Now, the scientists involved have found two sources of error, which, indicentally, mirror my hunch from when this first hit the news. First, the GPS equipment is operating far outside of its normal operating range, and so my not behave exactly as expected; this error is thought to produce a faster neutrino speed. But the second source of error is a loose connection for the fibre optic cable that carries the light signal, introducing a delay that may account for the difference in time elapsed for the two signals (light and neutrino).

I’m not at all surprised at this — when the paper was first put out, I thought it was only a matter of time before a systematic source of error was found. General relativity has held up spectacularly in every experimental test undertaken, and it would take a lot to upend all of that.

I was surprised that the group released their paper as early as they did, and without initial peer review, and I think that speaks to the authority that the scientific community confers on the CERN collaboration. If this exact paper had been written be a group at a small, less renowned institution (assuming they had all the equipment to do the experiment), would it have ever seen the light of day? Would a smaller group release very controversial results which naturally invite a huge amount of attention from popular media, without even subjecting them to peer review first? Would they ask for scrutiny from all and sundry, not just their peers?

I doubt it, because the stakes are too high. For a smaller, less authoritative group, the hit that their reputation could sustain could be devastating. No-one’s going to give CERN side-eye at everything they do from here on, because it’s CERN! They’ve done incredible work and have a very solid reputation. But if a group without that name backing did the same science and presented it that same way, there’s a good chance it’d be either ignored, chalked up to poor science or ineptitude, and probably wouldn’t be given much of a second look.

I bring this up not to cast aspersions at CERN — they do excellent work — but rather to highlight the weight that an authoritative name can carry in the scientific word. We like to think that science is objective and speaks for itself, and that good science will get the recognition it deserves regardless of who does it. This is not true — there’s plenty of excellent scientists who face all sorts of barriers (monetary, linguistic, social, etc) in their attempts to get their science visible. This isn’t to say that crackpots don’t exist — there’s plenty of people with a tenuous grasp of general relativity who insist that “Einstein was WRONG!”, though they are generally easily refuted — but this is a prime example of how having a big name collaboration helps people take a second look at your work, rather than just writing it off as an errant result.

I don’t think that this paper would’ve gotten as much attention from the scientific community (or the popular media, but they’re not the best arbiter of what’s new and important in science) had it not come from such an authoritative group. I think that, like me, most scientists would’ve said “there’s probably an error in the GPS or the cabling” and left it at that. An awful lot of scientists said that this time, but they typically said it after they’d read the paper; I doubt many of them would’ve bothered to read the paper had it not been from an authoritative collboration. It’s a disappointing realization, but it’s always good to have a reminder to check for our unconscious (or conscious) biases.