A nose 1,000 times better than ours
Ned Rozell
907-474-7468
Sept. 29, 2023
A dog can tell you a lot about the outdoors. When a Lab vacuums the ground with her
nose and her tail spins like a helicopter blade, you know a grouse is about to fly.
When the dog stops like a dragonfly, then runs off sniffing an invisible path, a snowshoe
hare has crossed your 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. Search-and-rescue groups use
dogs to find lost people, dead people and people buried under earth and snow. Dogs
have also been used to find seals on ice, gas leaks and the presence of gypsy moth
egg sacks.
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 it 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,” each is about
the size of a postage stamp in our noses. 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
the spot 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 trigger strong emotions and memories that may have lain dormant
for years.
With its larger olfactory membranes, a dog’s nose does things ours cannot. 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 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, which 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.
Since the late 1970s, the University of Alaska Fairbanks' Geophysical Institute has
provided this column free in cooperation with the UAF research community. Ned Rozell
is a science writer for the Geophysical Institute. A version of this story appeared
in 1998.