THE secrets of a dog鈥檚 extraordinary sense of smell have been unlocked. And
it鈥檚 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鈥檚 best friend. The Defense Advanced Research Projects Agency was
working on landmine detection, says Settles, 鈥渁nd asked if we could understand
how a dog can do what it does so well鈥�.
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.
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They found that a dog鈥檚 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.
鈥淭heir work has helped motivate ours,鈥� 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鈥檚 results are helping them redesign their device, so that
it mimics the way a dog samples air. The machine 鈥渂reathes鈥� 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鈥檚 artificial nose has successfully detected mines in a
test field. Now he is working on improving it鈥攁nd it still has some
catching up to do, as its canine competitor is between 10 and 50 times more
sensitive.