This column is provided as a public service by the Geophysical
Institute, University of Alaska Fairbanks, in cooperation with the UAF research
community. Ned Rozell is a science writer at the institute.
A dog can tell you a lot about
the outdoors. When Jane, my Lab, vacuums the ground with her nose and her
tail moves like a helicopter blade, I know a grouse is about to fly. When
Jane stops as abruptly as a dragonfly, then runs off sniffing an invisible
path, I know a snowshoe hare has crossed our trail.
All this entertainment is courtesy of that most sensitive appendage, a dog's
nose. It's an instrument man has not been able to duplicate. A local search-and-rescue
group, PAWS, uses dogs to find lost people, dead people, and people buried
under earth and snow. Dogs have also been used to find gas leaks and the
presence of gypsy moth egg sacks. A researcher here at the University of
Alaska Fairbanks even wants to train a dog to find tiny wood frogs hibernating
in the duff.
Lurking behind those textured, damp nostrils are sensitive membranes that
allow a dog to distinguish smells--molecules of odor that emanate from every
living or once-living thing--at least one thousand times better than humans.
A dog processes odoriferous molecules more readily because a dog has a much
larger set of scent membranes within its nose, explained Robert Burton in
his book, The Language of Smell. While humans have a pair of these "olfactory
receptors" in our noses each about the size of a postage stamp, dogs' receptors
can be as large as a handkerchief, depending on how big the dog is.
Dogs noses work much the way ours do: We inhale molecules of odor, which
then dissolve in mucus. The dissolved odors are picked up by the olfactory
receptors, located behind where sunglasses rest on the nose. An organ called
the olfactory bulb shunts the chemical messages straight to the part of the
brain that deals with stored feelings and memories, bypassing the cerebral
cortex, the main part of the brain. This short-circuit is one reason smells
so rapidly trigger strong emotions and memories that may have lain dormant
for years.
With its larger olfactory membranes, a dog's nose does amazing things. Researchers
at Duke University found that a randomly selected fox terrier could after
three weeks detect the scent of a fingerprint on a glass slide when compared
to four clean slides. When the researchers placed the slides outside in the
rain and dust, the dog was still able to pick out the slide with the fingerprint
after 24 hours of weathering.
Dogs have fantastic tracking ability because humans leave a pretty good scent
trail. Most researchers think the scent trails consists of "rafts," tiny
bits of skin cells that have an odor when mixed with sweat and fed upon by
bacteria. Because the human body sheds about 50 million cells each minute,
rafts fall from the body like a shower of microscopic confetti. Dogs quickly
detect these rafts, as well as other scents that may not be apparent to the
producer, including breath and sweat vapor. Each person's scent trail is
unique, and dogs are remarkably good at separating one person's trail from
another's.
In an experiment performed a century ago, G. J. Romanes lined up 11 men behind
him. He started walking, with each man walking precisely in his footsteps.
After they walked 200 yards, the men dispersed, with five going to the right,
six to the left. All the men hid. Another person released Romanes' dog, who
found Romanes almost instantly after hesitating slightly where the men separated.
Seventy years after Romanes' study, H. Kalmus performed a similar test using
identical twins. The twins must have had quite similar scents, Kalmus reported:
"if the dog was given the scent of one twin, it would happily follow the
other." When both twins were used in the experiment, however, the dog was
able to pick one from the other. What a great tool a dog's nose is--it rarely
malfunctions and the body it's attached to is always happy to see you.
