Now we know that dogs really do have a nose for it
THE secrets of a dog's extraordinary sense of smell have been unlocked. And it's good news for Fido, because the discovery could lead to mechanical sniffer dogs replacing the real thing for dangerous tasks such as detecting landmines.
Gary Settles, a mechanical engineer at Penn State University in University Park, says the military asked him and his colleagues to investigate the sniffing powers of man's best friend. The Defense Advanced Research Projects Agency was working on landmine detection, says Settles, "and asked if we could understand how a dog can do what it does so well".
To find out, Settles took pictures of dogs smelling various scents. As dogs breathe, they draw in cooler air, which is then warmed by their bodies and exhaled. Using a technique called Schlieren photography, which records how gases of different temperatures refract light, the researchers obtained images showing the air currents produced by the noses of the sniffing dogs.
They found that a dog's astounding olfactory success comes partly from its ability to divert exhaled air away from a target scent. When a dog exhales, it moves its nose so that the air is deflected through slits on the side. As a result, the exhaled air flows backwards, away from the smell. This prevents the scent being confused with exhaled air, and sets up a current that pulls new air across the target, launching odour molecules into the air. When dogs inhale they shift their noses into an entirely different shape to draw in a large volume of air. Settles is submitting the results to The Journal of Experimental Biology.
"Their work has helped motivate ours," says Joel White, a neuroscientist at Tufts University in Medford, Massachusetts. White is part of a team working with the Penn State researchers to develop an artificial nose that is just as good at detecting landmines as canine sniffers.
White says Settles's results are helping them redesign their device, so that it mimics the way a dog samples air. The machine "breathes" air in and out, instead of drawing it straight through. Because its sensors remove most of the odour molecules from the air it draws in, the machine can use the exhaled air as a baseline. The contrast between this baseline and the inflowing air is what allows the system to detect a particular smell.
White says his group's artificial nose has successfully detected mines in a test field. Now he is working on improving it-and it still has some catching up to do, as its canine competitor is between 10 and 50 times more sensitive.
Author: Mark Schrope
New Scientist issue: 26 August 2000
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