A Serpentine Tale with a Photo Finish

I confess I rarely spend more than a few seconds a week on Facebook, but the germ — and final chapter — of this essay came from a story link I fortuitously happened to catch by a modern-day wizard of light and glass, Andrew Gordon.

The other day, someone asked me, “what’s the good word?” and usually my response is “penultimate,” as I think it’s a really good word. (It sounds so ominous and demands to be spoken by someone with a deep, sonorous voice like James Earl Jones — and yet it only means “next to last.” You have to admire a word like that.) However, I recently came across another good word that I rather like, although it’s perhaps even less useful in normal conversation: “aposematism.” Coined by British evolutionary biologist Edward Bagnall Poulton in his 1890 book The Colours of Animals: Their Meaning and Use Especially Considered in the Case of Insects, it refers to an animal’s warning coloration. You know all those yellow, red, or other vibrantly colored frogs and newts and other critters? Non-green frogs or other unusually-hued creatures are so colored as a kind of advertising display: it identifies to would-be predators that they’re poisonous. You can see the advantage to this. It doesn’t do a frog much good if the creature that eats it later dies from poisoning.

So the perception of color in the animal world can very often be a matter of life and death. It can be for humans, as well, particularly in our dealings with the natural world.

Reader participation time: quick, name a poisonous snake.

If you said “rattlesnake,” “cobra,” “copperhead,” or something similar — well, sorry, you’re wrong. Those snakes are not poisonous, they’re venomous. It sounds horribly pedantic, but there is a distinction. A poison is a toxin that does its damage by being inhaled or ingested. A venom is a toxin the requires direct injection into the bloodstream, which is what a venomous snake will attempt (fangs for the memories). You could eat a rattlesnake or cobra with no problem (OK, if it’s still alive there will be some problem), and it probably tastes like chicken. You could even conceivably drink snake venom and be fine, as long as you don’t have any cuts in your mouth or any other way for the venom to get into your bloodstream (digestive juices would break down the toxins in the stomach). However, don’t try this at home!

(There is a drink called a snakebite, a mix of lager and cider, that sounds about as appealing as its namesake.)

There are only two known snakes that are actually poisonous: some species in the Rhabdophis genus, such as the red-necked keelback snake indigenous to Thailand, eat poisonous toads, separate out the poison, then secrete it from glands in their necks to ward off predators. (They’re also properly and highly venomous.) There is also a type of garter snake native to Oregon that eats poisonous newts, and while the snake itself is immune to the poison, enough remains in the snake’s liver après dîner that it becomes poisonous to small predators such as birds and rodents.

Alas, aposematism doesn’t help these guys out, although it does come in handy for some kinds of venomous snakes. How can you tell, say, a lethal copperhead from a generally harmless scarlet king snake, both of which, to the relatively untrained eye, look pretty similar? There are little mnemonic rhymes based on these snakes’ color schemes that can offer guidance: “Yellow touching red: You’re dead,” “Red against yellow can kill a fellow,” or, on the happier side, “Red touching black: Safe for Jack.”

Mind you, these are fairly specific to these species, and may not be of much help when you consider all the various kinds of venomous snakes. Generally, it’s a good idea to keep a discrete distance from any unfamiliar snake, especially since venom is only one way they can kill you. (An anaconda, if Hollywood is to be believed, could comfortably swallow Jon Voight whole.)

Venomous or benign, colorful or drab, the snake has been one of humankind’s most potent symbols, and virtually every religion has a snake involved at some point. Indeed, the oldest known example of a religious ritual is serpentine; in 2006, 70,000-year-old spearheads were found near carvings on a snake-shaped rock, providing, said the investigators, the earliest evidence of ritual behavior.

One of western civilization’s most iconic images is that of a snake eating its own tail, called the ouroboros (from the Greek οὐροβόρος ὄφις “tail-devouring snake”), often used as a symbol for self-reflexivity or cyclicality. The oldest known use of the symbol is from a 14th-century B.C. Egyptian funerary text found in the tomb of King Tutankhamen (who was not, as the song goes, “born in Arizona and moved to Babylonia” nor was he “buried with his donkey”). The ouroboros motif is found in many disparate cultures, and is even used in alchemy as, says Wikipedia somewhat poetically, “a symbol of the eternal unity of all things, the cycle of birth and death from which the alchemist sought release and liberation.”

The ouroboros also played a role in decidedly more modern chemistry in a famous story involving German organic chemist Friedrich August Kekulé. (By the way, the family name was originally Kekule, sans accented “e.” His father added the accent after Napoléon invaded Hesse, where they lived, to ensure that the French pronounced their name correctly. The things people worry about.) Anyway, Kekulé was a pioneer in identifying the chemical structure of compounds, and one of his biggest challenges was the hydrocarbon benzene (C6H6). He wrote:

I was sitting, writing at my text-book; but the work did not progress; my thoughts were elsewhere. I turned my chair to the fire and dozed. Again the atoms were gamboling before my eyes. This time the smaller groups kept modestly in the background. My mental eye, rendered more acute by the repeated visions of the kind, could now distinguish larger structures of manifold conformation: long rows, sometimes more closely fitted together; all twining and twisting in snake-like motion. But look! What was that? One of the snakes had seized hold of its own tail, and the form whirled mockingly before my eyes. As if by a flash of lightning I awoke; and this time also I spent the rest of the night in working out the consequences of the hypothesis (via Read, 1957).

And thus had Kekulé ouroborotically divined the ring structure of benzene.

Benzene itself had been known informally as an aromatic resin called gum benzoin since the 15th century, and had been used in medieval medicine and perfumery. It was first chemically isolated in 1825 by Michael Faraday (1791–1867), who, known today for his contributions to electricity and magnetism (he discovered the principles of electromagnetic induction, diamagnetism, and electrolysis), began his career as a chemist. In fact, he invented an early version of what would later be known as the Bunsen burner. From 1821 onward, Faraday was heavily involved with the Royal Institution of Great Britain, and in 1833 he was appointed the Institution’s first Fullerian Professor of Chemistry, which was a lifetime gig. Late in his life, he had frequent conversations with a Scottish physicist named James Clerk Maxwell (1831–1879), who would often attend lectures at the Royal Institution, particularly after being inducted (not electromagnetically) into the Royal Society in 1861.

Maxwell was one of the great polymaths, even dabbling, Vogon-like, in poetry, and the opening line of his “To the Chief Musician upon Nabla: A Tyndallic Ode” — “I come from fields of fractured ice” — perhaps anticipates Led Zeppelin’s “Immigrant Song” by about 100 years. Maxwell is most famous for his equations governing electricity and magnetism, but he also did pioneering work in chemistry, astronomy (he was the first to propose that Saturn’s rings were actually composed of tiny particles), mathematics, and engineering, to name just a few. He is also famous for “Maxwell’s demon,” a thought experiment meant to demonstrate how one might possibly violate the Second Law of Thermodynamics.

In 1860, Maxwell was granted the Chair of Natural Philosophy at King’s College, London, and it was during the five years he spent at King’s College that he would be involved in a wide variety of scientific endeavors — including one that has particular relevance to us.

In 1826 or 1827, Joseph Niepce took what is believed to be the first photograph ever taken. Not a selfie, ​thankfully, but rather the “View from the Window at Le Gras,” it was a black-and-white image, and photography would soon explode into the full gamut of glorious grayscale. But what of color?

In an 1855 paper, Maxwell theorized how the human eye processes color, noting that the eye had separate cones that variously detected red light, green light, and blue light. He then sought a way to demonstrate his color theory, and his intent was not to create a new technology or art form. Working with photographer Thomas Sutton, who had invented the single-lens reflex (SLR) camera, he took three identical photographs of a tartan ribbon (he was Scottish, remember), each one shot through a separate filter — one filter was red, one was green, and one was blue. Sound familiar? Yes, they were basically color separations. (He had also made a fourth separation, yellow, that he ultimately didn’t use.)

In a live lecture on May 17, 1861, he took the three images, developed them as slides, and when he projected each one through the appropriate color filter, the composite image was a full-color photograph. Well, sort of. The problem was that the red and green photographic plates were less sensitive than the blue, so the color balance wasn’t quite true to life. But still. . .

Those conversant in color theory will also note that Maxwell’s demonstration was what we know of as “additive color mixing.” It wasn’t until the advent of a subtractive mixing process, using colorants like inks, that color photography — and color printing — could come to life. But that’s another story for another time.

In the meantime . . . watch out for snakes, whatever color they may be.


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