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While sipping on a cocktail, my Uncle Crazy was babbling scores of unproven facts, when out came the claim that our best friend, the dog, as a sense of smell 200,000 times better than humans. I found this number incredibly hard to believe, but he insisted. We phoned several vets, animal clinics, and nose specialists, and while everybody agreed that dogs have a superior sense of smell, nobody could put a number to it. Please help us put this thing to rest.

-- Alex and Uncle Crazy, San Diego

"I'm really glad you called about this." Professor Lawrence (Dr. Dog Nose) Myers apparently has been poised with this hand over the phone, hoping someone would check in with just such an inquiry. Dr. Myers is a recognized expert in canine olfaction. He's a researcher in the Institute for Biological Detection Systems in the School of Veterinary Medicine at Auburn University. They work mostly with bomb- and drug-sniffing dogs, but what he knows would apply to your unemployed pooch as well.

So, we asked. What's the deal? Why do you read that dogs can smell 10, 150, 2000, or 200,000 times better than humans? Where do these numbers come from, and what's the real number? Says Dr. Myers, if you're talking hard science, there is no real answer. No one has ever done a well controlled study comparing a dog's olfactory threshold with a human's. We know something about what humans can smell, and we know something about dogs. But any hard numbers generated by comparing the data are unreliable. The data for humans and for dogs were gathered under different test conditions, so they're not comparable except in a casual, anecdotal kind of way. And until we can teach dogs under test conditions to say, "Yes, now I can smell that," we will probably never have a reliable number. Scent thresholds in dogs is measured by inference from behavior or brainwave readings.

Olfaction in dogs is what vision is to humans. It's their memory system, their primary sense in dealing with the world. As you might expect, then, the physiology of a dog's smeller is much larger and more complex than ours. Dogs have 20 times more scent receptor cells than humans, and the scent-processing section of their brains is larger than ours. Where we might say, "Mmmmm, burgers!" a dog would say, "Mmmmm, fried ground cow muscle, gristle, and fat; soy extender; imitation American cheese made with vegetable oil and dry milk; wheat bun, toasted; a dozen sesame seeds; one leaf day-old lettuce; raw, partly green tomato slice; vinegar and spices in a tomato-based sauce, all touched by the hands of a human that I know and who will give me some if I make a big enough pest of myself!" Dogs smell in minute detail. How do we quantify that?

There's also the problem of reducing the scent stimulus to small enough quantities to get good readings. Dr. Myers doesn't deal in parts per million of odor, he's usually talking about parts per trillion or quintillion. In some cases, the dog's nose is sharper than the technology. Other variables are the type of odor, air temperature and humidity, and the physiological condition of the dog (or human).

Dr. Myers has been quoted as saying dogs can smell a million times better than humans. He says that was a speculative (but possible) number he used in an interview to illustrate a narrow point. The reporter picked up the figure as science and quoted it out of proper context. So where does this leave you and Uncle Crazy? Guess you're both wrong and both right, depending on the dog, the human, the odor, and circumstances. Nobody, not even Dr. Myers, can prove otherwise.

But, hey, Uncle Crazy, a scientist in Michigan has discovered that the best smellers in the world are fish. A thousand times better than dogs, he says. Lay that one on Alex at cocktail time and see what he says.

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maurits May 21, 2013 @ 1:18 p.m.

"Generally" dogs have an olfactory sense approximately 100,000 to 1,000,000 times more acute than a human's. A Bloodhound, (The dog with the highest sense of smell) has a 10,000,000 to 100,000,000 higher ability than a human.


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