Saturday, December 27, 2008

Chandler Burr (and I) on the Nature of Scent

(Photo of ChandlerBurr, from I always read Mr. Burr's perfume reviews and articles with keen interest however I had not yet read anything from his book, The Emperor of Scent. But today I stumbled upon some of it and it got me thinking about just how it is that we can smell...

Note: Blogging is new to me so forgive the bumbs... I've been cleaning up some html tags, and edited some content of this piece, to clarify my points and add a few examples.

(photo credit: Robin at words-worth)
BTW: she does NOT let her dog eat chocolate!

For your information: says 100-150 mg/kg of theobromine(related to theophillin and caffine) can cause a lethal toxic reaction in dogs. Milk chocolate contains 44 mg of theobromine per oz. (other types are considerably stronger). Using 100 mg/kg as the toxic dose, if a 2 pound dog ate 2 ounces of pure milk chocolate, that would be the lethal toxic amount; since a Hershey's bar weighs 1.5 ounces, that's a full bar and a half of chocolate, in one sitting... but I'm sure there are dogs who would be able to accomplish this... So take care! I've found there are quite a few human foods that a dog might try eat, that can harm him including onions, avocados, stone fruit pits and lots of other stuff like house plants and out door shrubs. Since most puppies love to chew things, you've got to be quick; I've been 'outfoxed' a few times by my canine friends, too. But I digress.

Mr. Burr goes on to explain the role evolution plays in all this trouble:

"So evolution has by now selected for you a complete, fixed genetic library of enzymes that will bind to and deal with a fixed list of molecules. (It's not an exact one-to-one enzyme-to-foodstuff ratio, but it's precise enough that it's why your dog famously can't digest chocolate, a culinary product his wolf ancestors never ate: evolution never selected for dogs an enzyme that recognized the shape of chocolate's molecules, so if you feed them these molecules, they get sick.) And if just one enzyme is missing, you end up with nasty, sometimes lethal, diseases and disorders" —

He's right. But one of the hallmarks of any living systems is its ability to adapt to changes in its environment. It turns out that we share a considerable amount of DNA material with all other living things. And the wolf (or dog) carries most of what we have, too! It turns out we even have something like 90% (or 75% or some god-awful high percent) of the DNA of corn!! So all living things are really very connected. And under the right conditions it seems to me the dog should be able to adapt to eat many things not intended for his diet. He's a master survivor, after all. In a world marked by upheavals, such as land mass shifts and ice-ages and global warming, it's hard to believe that anything would be able to survive well without the ability to deal with novelty, right?

Blame my background in medical science, but I think immediately of our immune system when I think about novelty; it's specifically designed to deal with all the novel molecules we encounter- even mutated viruses that have never existed anywhere on earth before. This ever vigilant, ever alert army circulates throughall all loactinos of our bodies, on the lookout for any foreign molecules- to them, anything that isn't you is alien, novel and suspect. It nearly instantly detects and decides which molecules are dangerous and which can be tolerated (or welcomed). Every baby begins life dependent but the taste and smell senses are turned on from the first. Every infant must taste and smell new things and begins to discriminate right away. So smell must be adapted especially to detect and deal with novelty: what smells like a nipple, what doesn't, even which breast, left or right; Mothers will tell you, babies know these things.

(oh dear, I lost the credit for this pic when I was editing! But at least I can tell you these dogs have responsible owners and they are eating "Doggy Safe" chocolate pops!)

Going back to dogs: When a dog is exposed to chocolate, he may find he likes it. I would never give chocolate to any dog but my own dogs are inquisitive little bandits (with great noses) and several bags of Pepperidge Farm chocolate chunk cookies have disappeared around our house, thanks to them. Luckily every one of the guilty doggy pack survived (...I've never even seen one of them get sick for their elicit binges!) Apparently doggy treat manufactures are also aware of the canine's forbidden love of chocolate and they now make Dog-Safe chocolate treats (I guess they've removed the offensive, Theobromine).

But back to scent: since it must work with novelty, perhaps it is the same way our immune system does. And how does our immune system do that, by the way? It's helped because ultimately everything within the universe is composed from a relatively small set of elements. When a scientist creates an entirely novel molecule for us to smell, it has been made from these same known building blocks. Organic chemistry is built around predicting how these chemical groups combine, figuring out the rules of how substances form, so we can predict how chemical groups will stick together, break apart and re-combine under different condtions... So, our sense of smell wouldn't try to analyze molecules as entire entities; rather it has to recognize the building blocks, and have a set of rules as to how those materials combine in order to predict (or decode) how any novel combination of building blocks ought to smell (similar to knowing something with such and such a backbone structure can smell like green if it's a straight chain, like sweet citrus if it's branched and minty if it's double bonded. When we read, we apply phonics rules in kcuh that way to translate and pronounce novel words we encounter correctly and fluently the first time we read them from print. In the same way, we can instantly know a unique scent (understanding it as sweet, soft vs sharp, sour etc... by comparing the new compound according to the components and using rules to predict, interpret how they smell).

I can recognize and remember a new face the same way; my visual receptors detect the interaction of light and shape along plane surfaces, noting buldges and recesses, allowing me to view, analyze and react to the novel face aesthetically, emotionally and intellectually, simultaneously and instantly and to memorize it forever. From then on, I should be able to recognize that face, distingush it from any other novel or known face (no matter how similar the faces are...). With practice the majorit yof us even learn to tell identical twin apart, but finer distinctions can require practice. In a similar way we may analyze and categorize smells.

Chandler Burr goes on: "So smell must be incredibly important for us," notes NIH geneticist Dean Hamer, "to devote so much of our DNA to it. The only comparable system—and this was the big surprise to everyone—is the immune system, and we all know why it's important to fight off invaders."

(photo title: Smell001, from

Up to this point I've been blissfully ignorant of the work that's been done in smell, but now I see Luca Turin says anyone can take a crack at this (to figure out how we smell. He says he's got it, and I can't wait to read his book, another Christmas present this year, as my family finally begins to 'get' me perfume related gifts! I agree with the genetists- the immune system is the best model. If the scientists were more generalists, (and Sunday quarterbacks, like me) they might not have been too surprised. Either way, be it via the nose or some other route, you've got to identify all invaders first. That's what the immune system does and that's what smell must do. Afterall, smell is an early detection system, a way to know the world before sight, sound or touch is required. Even from a distance, if you smell smoke, you know there’s fire. Up close, it's a way to tell who has been in the den- even in the dark, or when you weren't there. Interestingly, our sense of smell is unqie in that it is the only spot in the entire body where our CNS (that's our Central Nervous System, the Big Boss) actually comes into physical contact with the outside world without benefit of the 'blood-brain barrier' to protect it. So it is actually designed as a portal where exotic airborne substances mix directly with our nuerons, bathing them in the actual scent chemicals directly. I would not be surprised to learn that immune cells themselves heavily populate that area as well, and help with the process of sequestering and maybe processing the scent chemicals.

So the poets were right in a way, the power of scent is it's magical sillage that can announce, linger behind, travel up our noses into our brains, and even trigger long-lost memories and emotions. Scent remains forever tethered to its source yet it moves through the air as well, ghost like, leaving an indelible trace behind. Hidden from all other senses, it guides us directly to the source like Hansel and Gretel’s trail of breadcrumbs...

I intend to read further into The Emperor of Scent and Lucia Turin's The Secret of Scent. Scent has been something so personal for me for so long, and now I'm finally stepping out into the warm light, of the writers and bloggers who share my passion. It has been fascinating so far and I'm sure every one has a lot more to say! I'll be back later today or tomorrow with my own post (and a double review!) on Dana.

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